diff --git a/gcc/d/gdc.texi b/gcc/d/gdc.texi new file mode 100644 index 00000000000..d3bf75ccfa9 --- /dev/null +++ b/gcc/d/gdc.texi @@ -0,0 +1,853 @@ +\input texinfo @c -*-texinfo-*- +@setfilename gdc.info +@settitle The GNU D Compiler + +@c Merge the standard indexes into a single one. +@syncodeindex fn cp +@syncodeindex vr cp +@syncodeindex ky cp +@syncodeindex pg cp +@syncodeindex tp cp + +@include gcc-common.texi + +@c Copyright years for this manual. +@set copyrights-d 2006-2022 + +@copying +@c man begin COPYRIGHT +Copyright @copyright{} @value{copyrights-d} Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. +A copy of the license is included in the +@c man end +section entitled ``GNU Free Documentation License''. +@ignore +@c man begin COPYRIGHT +man page gfdl(7). +@c man end +@end ignore +@end copying + +@ifinfo +@format +@dircategory Software development +@direntry +* gdc: (gdc). A GCC-based compiler for the D language +@end direntry +@end format + +@insertcopying +@end ifinfo + +@titlepage +@title The GNU D Compiler +@versionsubtitle +@author David Friedman, Iain Buclaw + +@page +@vskip 0pt plus 1filll +Published by the Free Software Foundation @* +51 Franklin Street, Fifth Floor@* +Boston, MA 02110-1301, USA@* +@sp 1 +@insertcopying +@end titlepage +@contents +@page + +@node Top +@top Introduction + +This manual describes how to use @command{gdc}, the GNU compiler for +the D programming language. This manual is specifically about +@command{gdc}. For more information about the D programming +language in general, including language specifications and standard +package documentation, see @uref{https://dlang.org/}. + +@menu +* Copying:: The GNU General Public License. +* GNU Free Documentation License:: + How you can share and copy this manual. +* Invoking gdc:: How to run gdc. +* Index:: Index. +@end menu + + +@include gpl_v3.texi + +@include fdl.texi + + +@node Invoking gdc +@chapter Invoking gdc + +@c man title gdc A GCC-based compiler for the D language + +@ignore +@c man begin SYNOPSIS gdc +gdc [@option{-c}|@option{-S}] [@option{-g}] [@option{-pg}] + [@option{-O}@var{level}] [@option{-W}@var{warn}@dots{}] + [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] + [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] + [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} + +Only the most useful options are listed here; see below for the +remainder. +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), gcc(1) +and the Info entries for @file{gdc} and @file{gcc}. +@c man end +@end ignore + +@c man begin DESCRIPTION gdc + +The @command{gdc} command is the GNU compiler for the D language and +supports many of the same options as @command{gcc}. @xref{Option Summary, , +Option Summary, gcc, Using the GNU Compiler Collection (GCC)}. +This manual only documents the options specific to @command{gdc}. + +@c man end + +@menu +* Input and Output files:: Controlling the kind of output: + an executable, object files, assembler files, +* Runtime Options:: Options controlling runtime behavior +* Directory Options:: Where to find module files +* Code Generation:: Options controlling the output of gdc +* Warnings:: Options controlling warnings specific to gdc +* Linking:: Options influencing the linking step +* Developer Options:: Options useful for developers of gdc +@end menu + +@c man begin OPTIONS + +@node Input and Output files +@section Input and Output files +@cindex suffixes for D source +@cindex D source file suffixes + +For any given input file, the file name suffix determines what kind of +compilation is done. The following kinds of input file names are supported: + +@table @gcctabopt +@item @var{file}.d +D source files. +@item @var{file}.dd +Ddoc source files. +@item @var{file}.di +D interface files. +@end table + +You can specify more than one input file on the @command{gdc} command line, +each being compiled separately in the compilation process. If you specify a +@code{-o @var{file}} option, all the input files are compiled together, +producing a single output file, named @var{file}. This is allowed even +when using @code{-S} or @code{-c}. + +@cindex D interface files. +A D interface file contains only what an import of the module needs, +rather than the whole implementation of that module. They can be created +by @command{gdc} from a D source file by using the @code{-H} option. +When the compiler resolves an import declaration, it searches for matching +@file{.di} files first, then for @file{.d}. + +@cindex Ddoc source files. +A Ddoc source file contains code in the D macro processor language. It is +primarily designed for use in producing user documentation from embedded +comments, with a slight affinity towards HTML generation. If a @file{.d} +source file starts with the string @code{Ddoc} then it is treated as general +purpose documentation, not as a D source file. + +@node Runtime Options +@section Runtime Options +@cindex options, runtime + +These options affect the runtime behavior of programs compiled with +@command{gdc}. + +@table @gcctabopt + +@item -fall-instantiations +@cindex @option{-fall-instantiations} +@cindex @option{-fno-all-instantiations} +Generate code for all template instantiations. The default template emission +strategy is to not generate code for declarations that were either +instantiated speculatively, such as from @code{__traits(compiles, ...)}, or +that come from an imported module not being compiled. + +@item -fno-assert +@cindex @option{-fassert} +@cindex @option{-fno-assert} +Turn off code generation for @code{assert} contracts. + +@item -fno-bounds-check +@cindex @option{-fbounds-check} +@cindex @option{-fno-bounds-check} +Turns off array bounds checking for all functions, which can improve +performance for code that uses arrays extensively. Note that this +can result in unpredictable behavior if the code in question actually +does violate array bounds constraints. It is safe to use this option +if you are sure that your code never throws a @code{RangeError}. + +@item -fbounds-check=@var{value} +@cindex @option{-fbounds-check=} +An alternative to @option{-fbounds-check} that allows more control +as to where bounds checking is turned on or off. The following values +are supported: + +@table @samp +@item on +Turns on array bounds checking for all functions. +@item safeonly +Turns on array bounds checking only for @code{@@safe} functions. +@item off +Turns off array bounds checking completely. +@end table + +@item -fno-builtin +@cindex @option{-fbuiltin} +@cindex @option{-fno-builtin} +Don't recognize built-in functions unless they begin with the prefix +@samp{__builtin_}. By default, the compiler will recognize when a +function in the @code{core.stdc} package is a built-in function. + +@item -fcheckaction=@var{value} +@cindex @option{-fcheckaction} +This option controls what code is generated on an assertion, bounds check, or +final switch failure. The following values are supported: + +@table @samp +@item context +Throw an @code{AssertError} with extra context information. +@item halt +Halt the program execution. +@item throw +Throw an @code{AssertError} (the default). +@end table + +@item -fdebug +@item -fdebug=@var{value} +@cindex @option{-fdebug} +@cindex @option{-fno-debug} +Turn on compilation of conditional @code{debug} code into the program. +The @option{-fdebug} option itself sets the debug level to @code{1}, +while @option{-fdebug=} enables @code{debug} code that are identified +by any of the following values: + +@table @samp +@item level +Sets the debug level to @var{level}, any @code{debug} code <= @var{level} +is compiled into the program. +@item ident +Turns on compilation of any @code{debug} code identified by @var{ident}. +@end table + +@item -fno-druntime +@cindex @option{-fdruntime} +@cindex @option{-fno-druntime} +Implements @uref{https://dlang.org/spec/betterc.html}. Assumes that +compilation targets an environment without a D runtime library. + +This is equivalent to compiling with the following options: + +@example +gdc -nophoboslib -fno-exceptions -fno-moduleinfo -fno-rtti +@end example + +@item -fextern-std=@var{standard} +@cindex @option{-fextern-std} +Sets the C++ name mangling compatibility to the version identified by +@var{standard}. The following values are supported: + +@table @samp +@item c++98 +@item c++03 +Sets @code{__traits(getTargetInfo, "cppStd")} to @code{199711}. +@item c++11 +Sets @code{__traits(getTargetInfo, "cppStd")} to @code{201103}. +@item c++14 +Sets @code{__traits(getTargetInfo, "cppStd")} to @code{201402}. +@item c++17 +Sets @code{__traits(getTargetInfo, "cppStd")} to @code{201703}. +This is the default. +@item c++20 +Sets @code{__traits(getTargetInfo, "cppStd")} to @code{202002}. +@end table + +@item -fno-invariants +@cindex @option{-finvariants} +@cindex @option{-fno-invariants} +Turns off code generation for class @code{invariant} contracts. + +@item -fmain +@cindex @option{-fmain} +Generates a default @code{main()} function when compiling. This is useful when +unittesting a library, as it enables running the unittests in a library without +having to manually define an entry-point function. This option does nothing +when @code{main} is already defined in user code. + +@item -fno-moduleinfo +@cindex @option{-fmoduleinfo} +@cindex @option{-fno-moduleinfo} +Turns off generation of the @code{ModuleInfo} and related functions +that would become unreferenced without it, which may allow linking +to programs not written in D. Functions that are not be generated +include module constructors and destructors (@code{static this} and +@code{static ~this}), @code{unittest} code, and @code{DSO} registry +functions for dynamically linked code. + +@item -fonly=@var{filename} +@cindex @option{-fonly} +Tells the compiler to parse and run semantic analysis on all modules +on the command line, but only generate code for the module specified +by @var{filename}. + +@item -fno-postconditions +@cindex @option{-fpostconditions} +@cindex @option{-fno-postconditions} +Turns off code generation for postcondition @code{out} contracts. + +@item -fno-preconditions +@cindex @option{-fpreconditions} +@cindex @option{-fno-preconditions} +Turns off code generation for precondition @code{in} contracts. + +@item -fpreview=@var{id} +@cindex @option{-fpreview} +Turns on an upcoming D language change identified by @var{id}. The following +values are supported: + +@table @samp +@item all +Turns on all upcoming D language features. +@item dip1000 +Implements @uref{https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1000.md} +(Scoped pointers). +@item dip1008 +Implements @uref{https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1008.md} +(Allow exceptions in @code{@@nogc} code). +@item dip1021 +Implements @uref{https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1021.md} +(Mutable function arguments). +@item dip25 +Implements @uref{https://github.com/dlang/DIPs/blob/master/DIPs/archive/DIP25.md} +(Sealed references). +@item dtorfields +Turns on generation for destructing fields of partially constructed objects. +@item fieldwise +Turns on generation of struct equality to use field-wise comparisons. +@item fixaliasthis +Implements new lookup rules that check the current scope for @code{alias this} +before searching in upper scopes. +@item fiximmutableconv +Disallows unsound immutable conversions that were formerly incorrectly +permitted. +@item in +Implements @code{in} parameters to mean @code{scope const [ref]} and accepts +rvalues. +@item inclusiveincontracts +Implements @code{in} contracts of overridden methods to be a superset of parent +contract. +@item intpromote +Implements C-style integral promotion for unary @code{+}, @code{-} and @code{~} +expressions. +@item nosharedaccess +Turns off and disallows all access to shared memory objects. +@item rvaluerefparam +Implements rvalue arguments to @code{ref} parameters. +@item systemvariables +Disables access to variables marked @code{@@system} from @code{@@safe} code. +@end table + +@item -frelease +@cindex @option{-frelease} +@cindex @option{-fno-release} +Turns on compiling in release mode, which means not emitting runtime +checks for contracts and asserts. Array bounds checking is not done +for @code{@@system} and @code{@@trusted} functions, and assertion +failures are undefined behavior. + +This is equivalent to compiling with the following options: + +@example +gdc -fno-assert -fbounds-check=safe -fno-invariants \ + -fno-postconditions -fno-preconditions -fno-switch-errors +@end example + +@item -frevert= +@cindex @option{-frevert} +Turns off a D language feature identified by @var{id}. The following values +are supported: + +@table @samp +@item all +Turns off all revertable D language features. +@item dip25 +Reverts @uref{https://github.com/dlang/DIPs/blob/master/DIPs/archive/DIP25.md} +(Sealed references). +@item dtorfields +Turns off generation for destructing fields of partially constructed objects. +@item markdown +Turns off Markdown replacements in Ddoc comments. +@end table + +@item -fno-rtti +@cindex @option{-frtti} +@cindex @option{-fno-rtti} +Turns off generation of run-time type information for all user defined types. +Any code that uses features of the language that require access to this +information will result in an error. + +@item -fno-switch-errors +@cindex @option{-fswitch-errors} +@cindex @option{-fno-switch-errors} +This option controls what code is generated when no case is matched +in a @code{final switch} statement. The default run time behavior +is to throw a @code{SwitchError}. Turning off @option{-fswitch-errors} +means that instead the execution of the program is immediately halted. + +@item -funittest +@cindex @option{-funittest} +@cindex @option{-fno-unittest} +Turns on compilation of @code{unittest} code, and turns on the +@code{version(unittest)} identifier. This implies @option{-fassert}. + +@item -fversion=@var{value} +@cindex @option{-fversion} +Turns on compilation of conditional @code{version} code into the program +identified by any of the following values: + +@table @samp +@item level +Sets the version level to @var{level}, any @code{version} code >= @var{level} +is compiled into the program. +@item ident +Turns on compilation of @code{version} code identified by @var{ident}. +@end table + +@item -fno-weak-templates +@cindex @option{-fweak-templates} +@cindex @option{-fno-weak-templates} +Turns off emission of declarations that can be defined in multiple objects as +weak symbols. The default is to emit all public symbols as weak, unless the +target lacks support for weak symbols. Disabling this option means that common +symbols are instead put in COMDAT or become private. + +@end table + +@node Directory Options +@section Options for Directory Search +@cindex directory options +@cindex options, directory search +@cindex search path + +These options specify directories to search for files, libraries, and +other parts of the compiler: + +@table @gcctabopt + +@item -I@var{dir} +@cindex @option{-I} +Specify a directory to use when searching for imported modules at +compile time. Multiple @option{-I} options can be used, and the +paths are searched in the same order. + +@item -J@var{dir} +@cindex @option{-J} +Specify a directory to use when searching for files in string imports +at compile time. This switch is required in order to use +@code{import(file)} expressions. Multiple @option{-J} options can be +used, and the paths are searched in the same order. + +@item -L@var{dir} +@cindex @option{-L} +When linking, specify a library search directory, as with @command{gcc}. + +@item -B@var{dir} +@cindex @option{-B} +This option specifies where to find the executables, libraries, +source files, and data files of the compiler itself, as with @command{gcc}. + +@item -fmodule-file=@var{module}=@var{spec} +@cindex @option{-fmodule-file} +This option manipulates file paths of imported modules, such that if an +imported module matches all or the leftmost part of @var{module}, the file +path in @var{spec} is used as the location to search for D sources. +This is used when the source file path and names are not the same as the +package and module hierarchy. Consider the following examples: + +@example +gdc test.d -fmodule-file=A.B=foo.d -fmodule-file=C=bar +@end example + +This will tell the compiler to search in all import paths for the source +file @var{foo.d} when importing @var{A.B}, and the directory @var{bar/} +when importing @var{C}, as annotated in the following D code: + +@example +module test; +import A.B; // Matches A.B, searches for foo.d +import C.D.E; // Matches C, searches for bar/D/E.d +import A.B.C; // No match, searches for A/B/C.d +@end example + +@item -imultilib @var{dir} +@cindex @option{-imultilib} +Use @var{dir} as a subdirectory of the gcc directory containing +target-specific D sources and interfaces. + +@item -iprefix @var{prefix} +@cindex @option{-iprefix} +Specify @var{prefix} as the prefix for the gcc directory containing +target-specific D sources and interfaces. If the @var{prefix} represents +a directory, you should include the final @code{'/'}. + +@item -nostdinc +@cindex @option{-nostdinc} +Do not search the standard system directories for D source and interface +files. Only the directories that have been specified with @option{-I} options +(and the directory of the current file, if appropriate) are searched. + +@end table + +@node Code Generation +@section Code Generation +@cindex options, code generation + +In addition to the many @command{gcc} options controlling code generation, +@command{gdc} has several options specific to itself. + +@table @gcctabopt + +@item -H +@cindex @option{-H} +Generates D interface files for all modules being compiled. The compiler +determines the output file based on the name of the input file, removes +any directory components and suffix, and applies the @file{.di} suffix. + +@item -Hd @var{dir} +@cindex @option{-Hd} +Same as @option{-H}, but writes interface files to directory @var{dir}. +This option can be used with @option{-Hf @var{file}} to independently set the +output file and directory path. + +@item -Hf @var{file} +@cindex @option{-Hf} +Same as @option{-H} but writes interface files to @var{file}. This option can +be used with @option{-Hd @var{dir}} to independently set the output file and +directory path. + +@item -M +@cindex @option{-M} +Output the module dependencies of all source files being compiled in a +format suitable for @command{make}. The compiler outputs one +@command{make} rule containing the object file name for that source file, +a colon, and the names of all imported files. + +@item -MM +@cindex @option{-MM} +Like @option{-M} but does not mention imported modules from the D standard +library package directories. + +@item -MF @var{file} +@cindex @option{-MF} +When used with @option{-M} or @option{-MM}, specifies a @var{file} to write +the dependencies to. When used with the driver options @option{-MD} or +@option{-MMD}, @option{-MF} overrides the default dependency output file. + +@item -MG +@cindex @option{-MG} +This option is for compatibility with @command{gcc}, and is ignored by the +compiler. + +@item -MP +@cindex @option{-MP} +Outputs a phony target for each dependency other than the modules being +compiled, causing each to depend on nothing. + +@item -MT @var{target} +@cindex @option{-MT} +Change the @var{target} of the rule emitted by dependency generation +to be exactly the string you specify. If you want multiple targets, +you can specify them as a single argument to @option{-MT}, or use +multiple @option{-MT} options. + +@item -MQ @var{target} +@cindex @option{-MQ} +Same as @option{-MT}, but it quotes any characters which are special to +@command{make}. + +@item -MD +@cindex @option{-MD} +This option is equivalent to @option{-M -MF @var{file}}. The driver +determines @var{file} by removing any directory components and suffix +from the input file, and then adding a @file{.deps} suffix. + +@item -MMD +@cindex @option{-MMD} +Like @option{-MD} but does not mention imported modules from the D standard +library package directories. + +@item -X +@cindex @option{-X} +Output information describing the contents of all source files being +compiled in JSON format to a file. The driver determines @var{file} by +removing any directory components and suffix from the input file, and then +adding a @file{.json} suffix. + +@item -Xf @var{file} +@cindex @option{-Xf} +Same as @option{-X}, but writes all JSON contents to the specified +@var{file}. + +@item -fdoc +@cindex @option{-fdoc} +Generates @code{Ddoc} documentation and writes it to a file. The compiler +determines @var{file} by removing any directory components and suffix +from the input file, and then adding a @file{.html} suffix. + +@item -fdoc-dir=@var{dir} +@cindex @option{-fdoc-dir} +Same as @option{-fdoc}, but writes documentation to directory @var{dir}. +This option can be used with @option{-fdoc-file=@var{file}} to +independently set the output file and directory path. + +@item -fdoc-file=@var{file} +@cindex @option{-fdoc-file} +Same as @option{-fdoc}, but writes documentation to @var{file}. This +option can be used with @option{-fdoc-dir=@var{dir}} to independently +set the output file and directory path. + +@item -fdoc-inc=@var{file} +@cindex @option{-fdoc-inc} +Specify @var{file} as a @var{Ddoc} macro file to be read. Multiple +@option{-fdoc-inc} options can be used, and files are read and processed +in the same order. + +@item -fdump-c++-spec=@var{file} +For D source files, generate corresponding C++ declarations in @var{file}. + +@item -fdump-c++-spec-verbose +In conjunction with @option{-fdump-c++-spec=} above, add comments for ignored +declarations in the generated C++ header. + +@item -fsave-mixins=@var{file} +@cindex @option{-fsave-mixins} +Generates code expanded from D @code{mixin} statements and writes the +processed sources to @var{file}. This is useful to debug errors in compilation +and provides source for debuggers to show when requested. + +@end table + +@node Warnings +@section Warnings +@cindex options to control warnings +@cindex warning messages +@cindex messages, warning +@cindex suppressing warnings + +Warnings are diagnostic messages that report constructions that +are not inherently erroneous but that are risky or suggest there +is likely to be a bug in the program. Unless @option{-Werror} is +specified, they do not prevent compilation of the program. + +@table @gcctabopt + +@item -Wall +@cindex @option{-Wall} +@cindex @option{-Wno-all} +Turns on all warnings messages. Warnings are not a defined part of +the D language, and all constructs for which this may generate a +warning message are valid code. + +@item -Walloca +@cindex @option{-Walloca} +This option warns on all uses of "alloca" in the source. + +@item -Walloca-larger-than=@var{n} +@cindex @option{-Walloca-larger-than} +@cindex @option{-Wno-alloca-larger-than} +Warn on unbounded uses of alloca, and on bounded uses of alloca +whose bound can be larger than @var{n} bytes. +@option{-Wno-alloca-larger-than} disables +@option{-Walloca-larger-than} warning and is equivalent to +@option{-Walloca-larger-than=@var{SIZE_MAX}} or larger. + +@item -Wcast-result +@cindex @option{-Wcast-result} +@cindex @option{-Wno-cast-result} +Warn about casts that will produce a null or zero result. Currently +this is only done for casting between an imaginary and non-imaginary +data type, or casting between a D and C++ class. + +@item -Wno-deprecated +@cindex @option{-Wdeprecated} +@cindex @option{-Wno-deprecated} +Do not warn about usage of deprecated features and symbols with +@code{deprecated} attributes. + +@item -Werror +@cindex @option{-Werror} +@cindex @option{-Wno-error} +Turns all warnings into errors. + +@item -Wspeculative +@cindex @option{-Wspeculative} +@cindex @option{-Wno-speculative} +List all error messages from speculative compiles, such as +@code{__traits(compiles, ...)}. This option does not report +messages as warnings, and these messages therefore never become +errors when the @option{-Werror} option is also used. + +@item -Wtemplates +@cindex @option{-Wtemplates} +@cindex @option{-Wno-templates} +Warn when a template instantiation is encountered. Some coding +rules disallow templates, and this may be used to enforce that rule. + +@item -Wunknown-pragmas +@cindex @option{-Wunknown-pragmas} +@cindex @option{-Wno-unknown-pragmas} +Warn when a @code{pragma()} is encountered that is not understood by +@command{gdc}. This differs from @option{-fignore-unknown-pragmas} +where a pragma that is part of the D language, but not implemented by +the compiler, won't get reported. + +@item -Wno-varargs +@cindex Wvarargs +@cindex Wno-varargs +Do not warn upon questionable usage of the macros used to handle variable +arguments like @code{va_start}. + +@item -fignore-unknown-pragmas +@cindex @option{-fignore-unknown-pragmas} +@cindex @option{-fno-ignore-unknown-pragmas} +Turns off errors for unsupported pragmas. + +@item -fmax-errors=@var{n} +@cindex @option{-fmax-errors} +Limits the maximum number of error messages to @var{n}, at which point +@command{gdc} bails out rather than attempting to continue processing the +source code. If @var{n} is 0 (the default), there is no limit on the +number of error messages produced. + +@item -fsyntax-only +@cindex @option{-fsyntax-only} +@cindex @option{-fno-syntax-only} +Check the code for syntax errors, but do not actually compile it. This +can be used in conjunction with @option{-fdoc} or @option{-H} to generate +files for each module present on the command-line, but no other output +file. + +@item -ftransition=@var{id} +@cindex @option{-ftransition} +Report additional information about D language changes identified by +@var{id}. The following values are supported: + +@table @samp +@item all +List information on all D language transitions. +@item complex +List all usages of complex or imaginary types. +@item field +List all non-mutable fields which occupy an object instance. +@item in +List all usages of @code{in} on parameter. +@item nogc +List all hidden GC allocations. +@item templates +List statistics on template instantiations. +@item tls +List all variables going into thread local storage. +@item vmarkdown +List instances of Markdown replacements in Ddoc. +@end table + +@end table + +@node Linking +@section Options for Linking +@cindex options, linking +@cindex linking, static + +These options come into play when the compiler links object files into an +executable output file. They are meaningless if the compiler is not doing +a link step. + +@table @gcctabopt + +@item -defaultlib=@var{libname} +@cindex @option{-defaultlib=} +Specify the library to use instead of libphobos when linking. Options +specifying the linkage of libphobos, such as @option{-static-libphobos} +or @option{-shared-libphobos}, are ignored. + +@item -debuglib=@var{libname} +@cindex @option{-debuglib=} +Specify the debug library to use instead of libphobos when linking. +This option has no effect unless the @option{-g} option was also given +on the command line. Options specifying the linkage of libphobos, such +as @option{-static-libphobos} or @option{-shared-libphobos}, are ignored. + +@item -nophoboslib +@cindex @option{-nophoboslib} +Do not use the Phobos or D runtime library when linking. Options specifying +the linkage of libphobos, such as @option{-static-libphobos} or +@option{-shared-libphobos}, are ignored. The standard system libraries are +used normally, unless @option{-nostdlib} or @option{-nodefaultlibs} is used. + +@item -shared-libphobos +@cindex @option{-shared-libphobos} +On systems that provide @file{libgphobos} and @file{libgdruntime} as a +shared and a static library, this option forces the use of the shared +version. If no shared version was built when the compiler was configured, +this option has no effect. + +@item -static-libphobos +@cindex @option{-static-libphobos} +On systems that provide @file{libgphobos} and @file{libgdruntime} as a +shared and a static library, this option forces the use of the static +version. If no static version was built when the compiler was configured, +this option has no effect. + +@end table + +@node Developer Options +@section Developer Options +@cindex developer options +@cindex debug dump options +@cindex dump options + +This section describes command-line options that are primarily of +interest to developers or language tooling. + +@table @gcctabopt + +@item -fdump-d-original +@cindex @option{-fdump-d-original} +Output the internal front-end AST after the @code{semantic3} stage. +This option is only useful for debugging the GNU D compiler itself. + +@item -v +@cindex @option{-v} +Dump information about the compiler language processing stages as the source +program is being compiled. This includes listing all modules that are +processed through the @code{parse}, @code{semantic}, @code{semantic2}, and +@code{semantic3} stages; all @code{import} modules and their file paths; +and all @code{function} bodies that are being compiled. + +@end table + +@c man end + +@node Index +@unnumbered Index + +@printindex cp + +@bye diff --git a/gcc/doc/analyzer.texi b/gcc/doc/analyzer.texi new file mode 100644 index 00000000000..ec49f951435 --- /dev/null +++ b/gcc/doc/analyzer.texi @@ -0,0 +1,569 @@ +@c Copyright (C) 2019-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. +@c Contributed by David Malcolm . + +@node Static Analyzer +@chapter Static Analyzer +@cindex analyzer +@cindex static analysis +@cindex static analyzer + +@menu +* Analyzer Internals:: Analyzer Internals +* Debugging the Analyzer:: Useful debugging tips +@end menu + +@node Analyzer Internals +@section Analyzer Internals +@cindex analyzer, internals +@cindex static analyzer, internals + +@subsection Overview + +The analyzer implementation works on the gimple-SSA representation. +(I chose this in the hopes of making it easy to work with LTO to +do whole-program analysis). + +The implementation is read-only: it doesn't attempt to change anything, +just emit warnings. + +The gimple representation can be seen using @option{-fdump-ipa-analyzer}. +@quotation Tip +If the analyzer ICEs before this is written out, one workaround is to use +@option{--param=analyzer-bb-explosion-factor=0} to force the analyzer +to bail out after analyzing the first basic block. +@end quotation + +First, we build a @code{supergraph} which combines the callgraph and all +of the CFGs into a single directed graph, with both interprocedural and +intraprocedural edges. The nodes and edges in the supergraph are called +``supernodes'' and ``superedges'', and often referred to in code as +@code{snodes} and @code{sedges}. Basic blocks in the CFGs are split at +interprocedural calls, so there can be more than one supernode per +basic block. Most statements will be in just one supernode, but a call +statement can appear in two supernodes: at the end of one for the call, +and again at the start of another for the return. + +The supergraph can be seen using @option{-fdump-analyzer-supergraph}. + +We then build an @code{analysis_plan} which walks the callgraph to +determine which calls might be suitable for being summarized (rather +than fully explored) and thus in what order to explore the functions. + +Next is the heart of the analyzer: we use a worklist to explore state +within the supergraph, building an "exploded graph". +Nodes in the exploded graph correspond to pairs, as in + "Precise Interprocedural Dataflow Analysis via Graph Reachability" + (Thomas Reps, Susan Horwitz and Mooly Sagiv). + +We reuse nodes for pairs we've already seen, and avoid +tracking state too closely, so that (hopefully) we rapidly converge +on a final exploded graph, and terminate the analysis. We also bail +out if the number of exploded nodes gets +larger than a particular multiple of the total number of basic blocks +(to ensure termination in the face of pathological state-explosion +cases, or bugs). We also stop exploring a point once we hit a limit +of states for that point. + +We can identify problems directly when processing a +instance. For example, if we're finding the successors of + +@smallexample + +@end smallexample + +then we can detect a double-free of "ptr". We can then emit a path +to reach the problem by finding the simplest route through the graph. + +Program points in the analysis are much more fine-grained than in the +CFG and supergraph, with points (and thus potentially exploded nodes) +for various events, including before individual statements. +By default the exploded graph merges multiple consecutive statements +in a supernode into one exploded edge to minimize the size of the +exploded graph. This can be suppressed via +@option{-fanalyzer-fine-grained}. +The fine-grained approach seems to make things simpler and more debuggable +that other approaches I tried, in that each point is responsible for one +thing. + +Program points in the analysis also have a "call string" identifying the +stack of callsites below them, so that paths in the exploded graph +correspond to interprocedurally valid paths: we always return to the +correct call site, propagating state information accordingly. +We avoid infinite recursion by stopping the analysis if a callsite +appears more than @code{analyzer-max-recursion-depth} in a callstring +(defaulting to 2). + +@subsection Graphs + +Nodes and edges in the exploded graph are called ``exploded nodes'' and +``exploded edges'' and often referred to in the code as +@code{enodes} and @code{eedges} (especially when distinguishing them +from the @code{snodes} and @code{sedges} in the supergraph). + +Each graph numbers its nodes, giving unique identifiers - supernodes +are referred to throughout dumps in the form @samp{SN': @var{index}} and +exploded nodes in the form @samp{EN: @var{index}} (e.g. @samp{SN: 2} and +@samp{EN:29}). + +The supergraph can be seen using @option{-fdump-analyzer-supergraph-graph}. + +The exploded graph can be seen using @option{-fdump-analyzer-exploded-graph} +and other dump options. Exploded nodes are color-coded in the .dot output +based on state-machine states to make it easier to see state changes at +a glance. + +@subsection State Tracking + +There's a tension between: +@itemize @bullet +@item +precision of analysis in the straight-line case, vs +@item +exponential blow-up in the face of control flow. +@end itemize + +For example, in general, given this CFG: + +@smallexample + A + / \ + B C + \ / + D + / \ + E F + \ / + G +@end smallexample + +we want to avoid differences in state-tracking in B and C from +leading to blow-up. If we don't prevent state blowup, we end up +with exponential growth of the exploded graph like this: + +@smallexample + + 1:A + / \ + / \ + / \ + 2:B 3:C + | | + 4:D 5:D (2 exploded nodes for D) + / \ / \ + 6:E 7:F 8:E 9:F + | | | | + 10:G 11:G 12:G 13:G (4 exploded nodes for G) + +@end smallexample + +Similar issues arise with loops. + +To prevent this, we follow various approaches: + +@enumerate a +@item +state pruning: which tries to discard state that won't be relevant +later on withing the function. +This can be disabled via @option{-fno-analyzer-state-purge}. + +@item +state merging. We can try to find the commonality between two +program_state instances to make a third, simpler program_state. +We have two strategies here: + + @enumerate + @item + the worklist keeps new nodes for the same program_point together, + and tries to merge them before processing, and thus before they have + successors. Hence, in the above, the two nodes for D (4 and 5) reach + the front of the worklist together, and we create a node for D with + the merger of the incoming states. + + @item + try merging with the state of existing enodes for the program_point + (which may have already been explored). There will be duplication, + but only one set of duplication; subsequent duplicates are more likely + to hit the cache. In particular, (hopefully) all merger chains are + finite, and so we guarantee termination. + This is intended to help with loops: we ought to explore the first + iteration, and then have a "subsequent iterations" exploration, + which uses a state merged from that of the first, to be more abstract. + @end enumerate + +We avoid merging pairs of states that have state-machine differences, +as these are the kinds of differences that are likely to be most +interesting. So, for example, given: + +@smallexample + if (condition) + ptr = malloc (size); + else + ptr = local_buf; + + .... do things with 'ptr' + + if (condition) + free (ptr); + + ...etc +@end smallexample + +then we end up with an exploded graph that looks like this: + +@smallexample + + if (condition) + / T \ F + --------- ---------- + / \ + ptr = malloc (size) ptr = local_buf + | | + copy of copy of + "do things with 'ptr'" "do things with 'ptr'" + with ptr: heap-allocated with ptr: stack-allocated + | | + if (condition) if (condition) + | known to be T | known to be F + free (ptr); | + \ / + ----------------------------- + | ('ptr' is pruned, so states can be merged) + etc + +@end smallexample + +where some duplication has occurred, but only for the places where the +the different paths are worth exploringly separately. + +Merging can be disabled via @option{-fno-analyzer-state-merge}. +@end enumerate + +@subsection Region Model + +Part of the state stored at a @code{exploded_node} is a @code{region_model}. +This is an implementation of the region-based ternary model described in +@url{https://www.researchgate.net/publication/221430855_A_Memory_Model_for_Static_Analysis_of_C_Programs, +"A Memory Model for Static Analysis of C Programs"} +(Zhongxing Xu, Ted Kremenek, and Jian Zhang). + +A @code{region_model} encapsulates a representation of the state of +memory, with a @code{store} recording a binding between @code{region} +instances, to @code{svalue} instances. The bindings are organized into +clusters, where regions accessible via well-defined pointer arithmetic +are in the same cluster. The representation is graph-like because values +can be pointers to regions. It also stores a constraint_manager, +capturing relationships between the values. + +Because each node in the @code{exploded_graph} has a @code{region_model}, +and each of the latter is graph-like, the @code{exploded_graph} is in some +ways a graph of graphs. + +Here's an example of printing a @code{program_state}, showing the +@code{region_model} within it, along with state for the @code{malloc} +state machine. + +@smallexample +(gdb) call debug (*this) +rmodel: +stack depth: 1 + frame (index 0): frame: ‘test’@@1 +clusters within frame: ‘test’@@1 + cluster for: ptr_3: &HEAP_ALLOCATED_REGION(12) +m_called_unknown_fn: FALSE +constraint_manager: + equiv classes: + constraints: +malloc: + 0x2e89590: &HEAP_ALLOCATED_REGION(12): unchecked ('ptr_3') +@end smallexample + +This is the state at the point of returning from @code{calls_malloc} back +to @code{test} in the following: + +@smallexample +void * +calls_malloc (void) +@{ + void *result = malloc (1024); + return result; +@} + +void test (void) +@{ + void *ptr = calls_malloc (); + /* etc. */ +@} +@end smallexample + +Within the store, there is the cluster for @code{ptr_3} within the frame +for @code{test}, where the whole cluster is bound to a pointer value, +pointing at @code{HEAP_ALLOCATED_REGION(12)}. Additionally, this pointer +has the @code{unchecked} state for the @code{malloc} state machine +indicating it hasn't yet been checked against NULL since the allocation +call. + +@subsection Analyzer Paths + +We need to explain to the user what the problem is, and to persuade them +that there really is a problem. Hence having a @code{diagnostic_path} +isn't just an incidental detail of the analyzer; it's required. + +Paths ought to be: +@itemize @bullet +@item +interprocedurally-valid +@item +feasible +@end itemize + +Without state-merging, all paths in the exploded graph are feasible +(in terms of constraints being satisfied). +With state-merging, paths in the exploded graph can be infeasible. + +We collate warnings and only emit them for the simplest path +e.g. for a bug in a utility function, with lots of routes to calling it, +we only emit the simplest path (which could be intraprocedural, if +it can be reproduced without a caller). + +We thus want to find the shortest feasible path through the exploded +graph from the origin to the exploded node at which the diagnostic was +saved. Unfortunately, if we simply find the shortest such path and +check if it's feasible we might falsely reject the diagnostic, as there +might be a longer path that is feasible. Examples include the cases +where the diagnostic requires us to go at least once around a loop for a +later condition to be satisfied, or where for a later condition to be +satisfied we need to enter a suite of code that the simpler path skips. + +We attempt to find the shortest feasible path to each diagnostic by +first constructing a ``trimmed graph'' from the exploded graph, +containing only those nodes and edges from which there are paths to +the target node, and using Dijkstra's algorithm to order the trimmed +nodes by minimal distance to the target. + +We then use a worklist to iteratively build a ``feasible graph'' +(actually a tree), capturing the pertinent state along each path, in +which every path to a ``feasible node'' is feasible by construction, +restricting ourselves to the trimmed graph to ensure we stay on target, +and ordering the worklist so that the first feasible path we find to the +target node is the shortest possible path. Hence we start by trying the +shortest possible path, but if that fails, we explore progressively +longer paths, eventually trying iterations through loops. The +exploration is captured in the feasible_graph, which can be dumped as a +.dot file via @option{-fdump-analyzer-feasibility} to visualize the +exploration. The indices of the feasible nodes show the order in which +they were created. We effectively explore the tree of feasible paths in +order of shortest path until we either find a feasible path to the +target node, or hit a limit and give up. + +This is something of a brute-force approach, but the trimmed graph +hopefully keeps the complexity manageable. + +This algorithm can be disabled (for debugging purposes) via +@option{-fno-analyzer-feasibility}, which simply uses the shortest path, +and notes if it is infeasible. + +The above gives us a shortest feasible @code{exploded_path} through the +@code{exploded_graph} (a list of @code{exploded_edge *}). We use this +@code{exploded_path} to build a @code{diagnostic_path} (a list of +@strong{events} for the diagnostic subsystem) - specifically a +@code{checker_path}. + +Having built the @code{checker_path}, we prune it to try to eliminate +events that aren't relevant, to minimize how much the user has to read. + +After pruning, we notify each event in the path of its ID and record the +IDs of interesting events, allowing for events to refer to other events +in their descriptions. The @code{pending_diagnostic} class has various +vfuncs to support emitting more precise descriptions, so that e.g. + +@itemize @bullet +@item +a deref-of-unchecked-malloc diagnostic might use: +@smallexample + returning possibly-NULL pointer to 'make_obj' from 'allocator' +@end smallexample +for a @code{return_event} to make it clearer how the unchecked value moves +from callee back to caller +@item +a double-free diagnostic might use: +@smallexample + second 'free' here; first 'free' was at (3) +@end smallexample +and a use-after-free might use +@smallexample + use after 'free' here; memory was freed at (2) +@end smallexample +@end itemize + +At this point we can emit the diagnostic. + +@subsection Limitations + +@itemize @bullet +@item +Only for C so far +@item +The implementation of call summaries is currently very simplistic. +@item +Lack of function pointer analysis +@item +The constraint-handling code assumes reflexivity in some places +(that values are equal to themselves), which is not the case for NaN. +As a simple workaround, constraints on floating-point values are +currently ignored. +@item +There are various other limitations in the region model (grep for TODO/xfail +in the testsuite). +@item +The constraint_manager's implementation of transitivity is currently too +expensive to enable by default and so must be manually enabled via +@option{-fanalyzer-transitivity}). +@item +The checkers are currently hardcoded and don't allow for user extensibility +(e.g. adding allocate/release pairs). +@item +Although the analyzer's test suite has a proof-of-concept test case for +LTO, LTO support hasn't had extensive testing. There are various +lang-specific things in the analyzer that assume C rather than LTO. +For example, SSA names are printed to the user in ``raw'' form, rather +than printing the underlying variable name. +@end itemize + +Some ideas for other checkers +@itemize @bullet +@item +File-descriptor-based APIs +@item +Linux kernel internal APIs +@item +Signal handling +@end itemize + +@node Debugging the Analyzer +@section Debugging the Analyzer +@cindex analyzer, debugging +@cindex static analyzer, debugging + +@subsection Special Functions for Debugging the Analyzer + +The analyzer recognizes various special functions by name, for use +in debugging the analyzer. Declarations can be seen in the testsuite +in @file{analyzer-decls.h}. None of these functions are actually +implemented. + +Add: +@smallexample + __analyzer_break (); +@end smallexample +to the source being analyzed to trigger a breakpoint in the analyzer when +that source is reached. By putting a series of these in the source, it's +much easier to effectively step through the program state as it's analyzed. + +The analyzer handles: + +@smallexample +__analyzer_describe (0, expr); +@end smallexample + +by emitting a warning describing the 2nd argument (which can be of any +type), at a verbosity level given by the 1st argument. This is for use when +debugging, and may be of use in DejaGnu tests. + +@smallexample +__analyzer_dump (); +@end smallexample + +will dump the copious information about the analyzer's state each time it +reaches the call in its traversal of the source. + +@smallexample +extern void __analyzer_dump_capacity (const void *ptr); +@end smallexample + +will emit a warning describing the capacity of the base region of +the region pointed to by the 1st argument. + +@smallexample +extern void __analyzer_dump_escaped (void); +@end smallexample + +will emit a warning giving the number of decls that have escaped on this +analysis path, followed by a comma-separated list of their names, +in alphabetical order. + +@smallexample +__analyzer_dump_path (); +@end smallexample + +will emit a placeholder ``note'' diagnostic with a path to that call site, +if the analyzer finds a feasible path to it. + +The builtin @code{__analyzer_dump_exploded_nodes} will emit a warning +after analysis containing information on all of the exploded nodes at that +program point: + +@smallexample + __analyzer_dump_exploded_nodes (0); +@end smallexample + +will output the number of ``processed'' nodes, and the IDs of +both ``processed'' and ``merger'' nodes, such as: + +@smallexample +warning: 2 processed enodes: [EN: 56, EN: 58] merger(s): [EN: 54-55, EN: 57, EN: 59] +@end smallexample + +With a non-zero argument + +@smallexample + __analyzer_dump_exploded_nodes (1); +@end smallexample + +it will also dump all of the states within the ``processed'' nodes. + +@smallexample + __analyzer_dump_region_model (); +@end smallexample +will dump the region_model's state to stderr. + +@smallexample +__analyzer_dump_state ("malloc", ptr); +@end smallexample + +will emit a warning describing the state of the 2nd argument +(which can be of any type) with respect to the state machine with +a name matching the 1st argument (which must be a string literal). +This is for use when debugging, and may be of use in DejaGnu tests. + +@smallexample +__analyzer_eval (expr); +@end smallexample +will emit a warning with text "TRUE", FALSE" or "UNKNOWN" based on the +truthfulness of the argument. This is useful for writing DejaGnu tests. + +@smallexample +__analyzer_get_unknown_ptr (); +@end smallexample +will obtain an unknown @code{void *}. + +@subsection Other Debugging Techniques + +The option @option{-fdump-analyzer-json} will dump both the supergraph +and the exploded graph in compressed JSON form. + +One approach when tracking down where a particular bogus state is +introduced into the @code{exploded_graph} is to add custom code to +@code{program_state::validate}. + +The debug function @code{region::is_named_decl_p} can be used when debugging, +such as for assertions and conditional breakpoints. For example, when +tracking down a bug in handling a decl called @code{yy_buffer_stack}, I +temporarily added a: +@smallexample + gcc_assert (!m_base_region->is_named_decl_p ("yy_buffer_stack")); +@end smallexample +to @code{binding_cluster::mark_as_escaped} to trap a point where +@code{yy_buffer_stack} was mistakenly being treated as having escaped. diff --git a/gcc/doc/avr-mmcu.texi b/gcc/doc/avr-mmcu.texi new file mode 100644 index 00000000000..c3e9817928a --- /dev/null +++ b/gcc/doc/avr-mmcu.texi @@ -0,0 +1,83 @@ +@c Copyright (C) 2012-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc/doc/include/fdl.texi. + +@c This file is generated automatically using +@c gcc/config/avr/gen-avr-mmcu-texi.cc from: +@c gcc/config/avr/avr-arch.h +@c gcc/config/avr/avr-devices.cc +@c gcc/config/avr/avr-mcus.def + +@c Please do not edit manually. + +@table @code + +@item avr2 +``Classic'' devices with up to 8@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{attiny22}, @code{attiny26}, @code{at90s2313}, @code{at90s2323}, @code{at90s2333}, @code{at90s2343}, @code{at90s4414}, @code{at90s4433}, @code{at90s4434}, @code{at90c8534}, @code{at90s8515}, @code{at90s8535}. + +@item avr25 +``Classic'' devices with up to 8@tie{}KiB of program memory and with the @code{MOVW} instruction. +@*@var{mcu}@tie{}= @code{attiny13}, @code{attiny13a}, @code{attiny24}, @code{attiny24a}, @code{attiny25}, @code{attiny261}, @code{attiny261a}, @code{attiny2313}, @code{attiny2313a}, @code{attiny43u}, @code{attiny44}, @code{attiny44a}, @code{attiny45}, @code{attiny48}, @code{attiny441}, @code{attiny461}, @code{attiny461a}, @code{attiny4313}, @code{attiny84}, @code{attiny84a}, @code{attiny85}, @code{attiny87}, @code{attiny88}, @code{attiny828}, @code{attiny841}, @code{attiny861}, @code{attiny861a}, @code{ata5272}, @code{ata6616c}, @code{at86rf401}. + +@item avr3 +``Classic'' devices with 16@tie{}KiB up to 64@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{at76c711}, @code{at43usb355}. + +@item avr31 +``Classic'' devices with 128@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{atmega103}, @code{at43usb320}. + +@item avr35 +``Classic'' devices with 16@tie{}KiB up to 64@tie{}KiB of program memory and with the @code{MOVW} instruction. +@*@var{mcu}@tie{}= @code{attiny167}, @code{attiny1634}, @code{atmega8u2}, @code{atmega16u2}, @code{atmega32u2}, @code{ata5505}, @code{ata6617c}, @code{ata664251}, @code{at90usb82}, @code{at90usb162}. + +@item avr4 +``Enhanced'' devices with up to 8@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{atmega48}, @code{atmega48a}, @code{atmega48p}, @code{atmega48pa}, @code{atmega48pb}, @code{atmega8}, @code{atmega8a}, @code{atmega8hva}, @code{atmega88}, @code{atmega88a}, @code{atmega88p}, @code{atmega88pa}, @code{atmega88pb}, @code{atmega8515}, @code{atmega8535}, @code{ata6285}, @code{ata6286}, @code{ata6289}, @code{ata6612c}, @code{at90pwm1}, @code{at90pwm2}, @code{at90pwm2b}, @code{at90pwm3}, @code{at90pwm3b}, @code{at90pwm81}. + +@item avr5 +``Enhanced'' devices with 16@tie{}KiB up to 64@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{atmega16}, @code{atmega16a}, @code{atmega16hva}, @code{atmega16hva2}, @code{atmega16hvb}, @code{atmega16hvbrevb}, @code{atmega16m1}, @code{atmega16u4}, @code{atmega161}, @code{atmega162}, @code{atmega163}, @code{atmega164a}, @code{atmega164p}, @code{atmega164pa}, @code{atmega165}, @code{atmega165a}, @code{atmega165p}, @code{atmega165pa}, @code{atmega168}, @code{atmega168a}, @code{atmega168p}, @code{atmega168pa}, @code{atmega168pb}, @code{atmega169}, @code{atmega169a}, @code{atmega169p}, @code{atmega169pa}, @code{atmega32}, @code{atmega32a}, @code{atmega32c1}, @code{atmega32hvb}, @code{atmega32hvbrevb}, @code{atmega32m1}, @code{atmega32u4}, @code{atmega32u6}, @code{atmega323}, @code{atmega324a}, @code{atmega324p}, @code{atmega324pa}, @code{atmega324pb}, @code{atmega325}, @code{atmega325a}, @code{atmega325p}, @code{atmega325pa}, @code{atmega328}, @code{atmega328p}, @code{atmega328pb}, @code{atmega329}, @code{atmega329a}, @code{atmega329p}, @code{atmega329pa}, @code{atmega3250}, @code{atmega3250a}, @code{atmega3250p}, @code{atmega3250pa}, @code{atmega3290}, @code{atmega3290a}, @code{atmega3290p}, @code{atmega3290pa}, @code{atmega406}, @code{atmega64}, @code{atmega64a}, @code{atmega64c1}, @code{atmega64hve}, @code{atmega64hve2}, @code{atmega64m1}, @code{atmega64rfr2}, @code{atmega640}, @code{atmega644}, @code{atmega644a}, @code{atmega644p}, @code{atmega644pa}, @code{atmega644rfr2}, @code{atmega645}, @code{atmega645a}, @code{atmega645p}, @code{atmega649}, @code{atmega649a}, @code{atmega649p}, @code{atmega6450}, @code{atmega6450a}, @code{atmega6450p}, @code{atmega6490}, @code{atmega6490a}, @code{atmega6490p}, @code{ata5795}, @code{ata5790}, @code{ata5790n}, @code{ata5791}, @code{ata6613c}, @code{ata6614q}, @code{ata5782}, @code{ata5831}, @code{ata8210}, @code{ata8510}, @code{ata5702m322}, @code{at90pwm161}, @code{at90pwm216}, @code{at90pwm316}, @code{at90can32}, @code{at90can64}, @code{at90scr100}, @code{at90usb646}, @code{at90usb647}, @code{at94k}, @code{m3000}. + +@item avr51 +``Enhanced'' devices with 128@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{atmega128}, @code{atmega128a}, @code{atmega128rfa1}, @code{atmega128rfr2}, @code{atmega1280}, @code{atmega1281}, @code{atmega1284}, @code{atmega1284p}, @code{atmega1284rfr2}, @code{at90can128}, @code{at90usb1286}, @code{at90usb1287}. + +@item avr6 +``Enhanced'' devices with 3-byte PC, i.e.@: with more than 128@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{atmega256rfr2}, @code{atmega2560}, @code{atmega2561}, @code{atmega2564rfr2}. + +@item avrxmega2 +``XMEGA'' devices with more than 8@tie{}KiB and up to 64@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{atxmega8e5}, @code{atxmega16a4}, @code{atxmega16a4u}, @code{atxmega16c4}, @code{atxmega16d4}, @code{atxmega16e5}, @code{atxmega32a4}, @code{atxmega32a4u}, @code{atxmega32c3}, @code{atxmega32c4}, @code{atxmega32d3}, @code{atxmega32d4}, @code{atxmega32e5}, @code{avr64da28}, @code{avr64da32}, @code{avr64da48}, @code{avr64da64}, @code{avr64db28}, @code{avr64db32}, @code{avr64db48}, @code{avr64db64}. + +@item avrxmega3 +``XMEGA'' devices with up to 64@tie{}KiB of combined program memory and RAM, and with program memory visible in the RAM address space. +@*@var{mcu}@tie{}= @code{attiny202}, @code{attiny204}, @code{attiny212}, @code{attiny214}, @code{attiny402}, @code{attiny404}, @code{attiny406}, @code{attiny412}, @code{attiny414}, @code{attiny416}, @code{attiny417}, @code{attiny804}, @code{attiny806}, @code{attiny807}, @code{attiny814}, @code{attiny816}, @code{attiny817}, @code{attiny1604}, @code{attiny1606}, @code{attiny1607}, @code{attiny1614}, @code{attiny1616}, @code{attiny1617}, @code{attiny3214}, @code{attiny3216}, @code{attiny3217}, @code{atmega808}, @code{atmega809}, @code{atmega1608}, @code{atmega1609}, @code{atmega3208}, @code{atmega3209}, @code{atmega4808}, @code{atmega4809}, @code{avr32da28}, @code{avr32da32}, @code{avr32da48}, @code{avr32db28}, @code{avr32db32}, @code{avr32db48}. + +@item avrxmega4 +``XMEGA'' devices with more than 64@tie{}KiB and up to 128@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{atxmega64a3}, @code{atxmega64a3u}, @code{atxmega64a4u}, @code{atxmega64b1}, @code{atxmega64b3}, @code{atxmega64c3}, @code{atxmega64d3}, @code{atxmega64d4}, @code{avr128da28}, @code{avr128da32}, @code{avr128da48}, @code{avr128da64}, @code{avr128db28}, @code{avr128db32}, @code{avr128db48}, @code{avr128db64}. + +@item avrxmega5 +``XMEGA'' devices with more than 64@tie{}KiB and up to 128@tie{}KiB of program memory and more than 64@tie{}KiB of RAM. +@*@var{mcu}@tie{}= @code{atxmega64a1}, @code{atxmega64a1u}. + +@item avrxmega6 +``XMEGA'' devices with more than 128@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{atxmega128a3}, @code{atxmega128a3u}, @code{atxmega128b1}, @code{atxmega128b3}, @code{atxmega128c3}, @code{atxmega128d3}, @code{atxmega128d4}, @code{atxmega192a3}, @code{atxmega192a3u}, @code{atxmega192c3}, @code{atxmega192d3}, @code{atxmega256a3}, @code{atxmega256a3b}, @code{atxmega256a3bu}, @code{atxmega256a3u}, @code{atxmega256c3}, @code{atxmega256d3}, @code{atxmega384c3}, @code{atxmega384d3}. + +@item avrxmega7 +``XMEGA'' devices with more than 128@tie{}KiB of program memory and more than 64@tie{}KiB of RAM. +@*@var{mcu}@tie{}= @code{atxmega128a1}, @code{atxmega128a1u}, @code{atxmega128a4u}. + +@item avrtiny +``TINY'' Tiny core devices with 512@tie{}B up to 4@tie{}KiB of program memory. +@*@var{mcu}@tie{}= @code{attiny4}, @code{attiny5}, @code{attiny9}, @code{attiny10}, @code{attiny20}, @code{attiny40}. + +@item avr1 +This ISA is implemented by the minimal AVR core and supported for assembler only. +@*@var{mcu}@tie{}= @code{attiny11}, @code{attiny12}, @code{attiny15}, @code{attiny28}, @code{at90s1200}. + +@end table diff --git a/gcc/doc/bugreport.texi b/gcc/doc/bugreport.texi new file mode 100644 index 00000000000..84246faecee --- /dev/null +++ b/gcc/doc/bugreport.texi @@ -0,0 +1,88 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Bugs +@chapter Reporting Bugs +@cindex bugs +@cindex reporting bugs + +Your bug reports play an essential role in making GCC reliable. + +When you encounter a problem, the first thing to do is to see if it is +already known. @xref{Trouble}. If it isn't known, then you should +report the problem. + +@menu +* Criteria: Bug Criteria. Have you really found a bug? +* Reporting: Bug Reporting. How to report a bug effectively. +@end menu + +@node Bug Criteria +@section Have You Found a Bug? +@cindex bug criteria + +If you are not sure whether you have found a bug, here are some guidelines: + +@itemize @bullet +@cindex fatal signal +@cindex core dump +@item +If the compiler gets a fatal signal, for any input whatever, that is a +compiler bug. Reliable compilers never crash. + +@cindex invalid assembly code +@cindex assembly code, invalid +@item +If the compiler produces invalid assembly code, for any input whatever +(except an @code{asm} statement), that is a compiler bug, unless the +compiler reports errors (not just warnings) which would ordinarily +prevent the assembler from being run. + +@cindex undefined behavior +@cindex undefined function value +@cindex increment operators +@item +If the compiler produces valid assembly code that does not correctly +execute the input source code, that is a compiler bug. + +However, you must double-check to make sure, because you may have a +program whose behavior is undefined, which happened by chance to give +the desired results with another C or C++ compiler. + +For example, in many nonoptimizing compilers, you can write @samp{x;} +at the end of a function instead of @samp{return x;}, with the same +results. But the value of the function is undefined if @code{return} +is omitted; it is not a bug when GCC produces different results. + +Problems often result from expressions with two increment operators, +as in @code{f (*p++, *p++)}. Your previous compiler might have +interpreted that expression the way you intended; GCC might +interpret it another way. Neither compiler is wrong. The bug is +in your code. + +After you have localized the error to a single source line, it should +be easy to check for these things. If your program is correct and +well defined, you have found a compiler bug. + +@item +If the compiler produces an error message for valid input, that is a +compiler bug. + +@cindex invalid input +@item +If the compiler does not produce an error message for invalid input, +that is a compiler bug. However, you should note that your idea of +``invalid input'' might be someone else's idea of ``an extension'' or +``support for traditional practice''. + +@item +If you are an experienced user of one of the languages GCC supports, your +suggestions for improvement of GCC are welcome in any case. +@end itemize + +@node Bug Reporting +@section How and Where to Report Bugs +@cindex compiler bugs, reporting + +Bugs should be reported to the bug database at @value{BUGURL}. diff --git a/gcc/doc/cfg.texi b/gcc/doc/cfg.texi new file mode 100644 index 00000000000..32aacdd0aa8 --- /dev/null +++ b/gcc/doc/cfg.texi @@ -0,0 +1,684 @@ +@c -*-texinfo-*- +@c Copyright (C) 2001-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@c --------------------------------------------------------------------- +@c Control Flow Graph +@c --------------------------------------------------------------------- + +@node Control Flow +@chapter Control Flow Graph +@cindex CFG, Control Flow Graph +@findex basic-block.h + +A control flow graph (CFG) is a data structure built on top of the +intermediate code representation (the RTL or @code{GIMPLE} instruction +stream) abstracting the control flow behavior of a function that is +being compiled. The CFG is a directed graph where the vertices +represent basic blocks and edges represent possible transfer of +control flow from one basic block to another. The data structures +used to represent the control flow graph are defined in +@file{basic-block.h}. + +In GCC, the representation of control flow is maintained throughout +the compilation process, from constructing the CFG early in +@code{pass_build_cfg} to @code{pass_free_cfg} (see @file{passes.def}). +The CFG takes various different modes and may undergo extensive +manipulations, but the graph is always valid between its construction +and its release. This way, transfer of information such as data flow, +a measured profile, or the loop tree, can be propagated through the +passes pipeline, and even from @code{GIMPLE} to @code{RTL}. + +Often the CFG may be better viewed as integral part of instruction +chain, than structure built on the top of it. Updating the compiler's +intermediate representation for instructions cannot be easily done +without proper maintenance of the CFG simultaneously. + +@menu +* Basic Blocks:: The definition and representation of basic blocks. +* Edges:: Types of edges and their representation. +* Profile information:: Representation of frequencies and probabilities. +* Maintaining the CFG:: Keeping the control flow graph and up to date. +* Liveness information:: Using and maintaining liveness information. +@end menu + + +@node Basic Blocks +@section Basic Blocks + +@cindex basic block +@findex basic_block +A basic block is a straight-line sequence of code with only one entry +point and only one exit. In GCC, basic blocks are represented using +the @code{basic_block} data type. + +@findex ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR +Special basic blocks represent possible entry and exit points of a +function. These blocks are called @code{ENTRY_BLOCK_PTR} and +@code{EXIT_BLOCK_PTR}. These blocks do not contain any code. + +@findex BASIC_BLOCK +The @code{BASIC_BLOCK} array contains all basic blocks in an +unspecified order. Each @code{basic_block} structure has a field +that holds a unique integer identifier @code{index} that is the +index of the block in the @code{BASIC_BLOCK} array. +The total number of basic blocks in the function is +@code{n_basic_blocks}. Both the basic block indices and +the total number of basic blocks may vary during the compilation +process, as passes reorder, create, duplicate, and destroy basic +blocks. The index for any block should never be greater than +@code{last_basic_block}. The indices 0 and 1 are special codes +reserved for @code{ENTRY_BLOCK} and @code{EXIT_BLOCK}, the +indices of @code{ENTRY_BLOCK_PTR} and @code{EXIT_BLOCK_PTR}. + +@findex next_bb, prev_bb, FOR_EACH_BB, FOR_ALL_BB +Two pointer members of the @code{basic_block} structure are the +pointers @code{next_bb} and @code{prev_bb}. These are used to keep +doubly linked chain of basic blocks in the same order as the +underlying instruction stream. The chain of basic blocks is updated +transparently by the provided API for manipulating the CFG@. The macro +@code{FOR_EACH_BB} can be used to visit all the basic blocks in +lexicographical order, except @code{ENTRY_BLOCK} and @code{EXIT_BLOCK}. +The macro @code{FOR_ALL_BB} also visits all basic blocks in +lexicographical order, including @code{ENTRY_BLOCK} and @code{EXIT_BLOCK}. + +@findex post_order_compute, inverted_post_order_compute, walk_dominator_tree +The functions @code{post_order_compute} and @code{inverted_post_order_compute} +can be used to compute topological orders of the CFG. The orders are +stored as vectors of basic block indices. The @code{BASIC_BLOCK} array +can be used to iterate each basic block by index. +Dominator traversals are also possible using +@code{walk_dominator_tree}. Given two basic blocks A and B, block A +dominates block B if A is @emph{always} executed before B@. + +Each @code{basic_block} also contains pointers to the first +instruction (the @dfn{head}) and the last instruction (the @dfn{tail}) +or @dfn{end} of the instruction stream contained in a basic block. In +fact, since the @code{basic_block} data type is used to represent +blocks in both major intermediate representations of GCC (@code{GIMPLE} +and RTL), there are pointers to the head and end of a basic block for +both representations, stored in intermediate representation specific +data in the @code{il} field of @code{struct basic_block_def}. + +@findex CODE_LABEL +@findex NOTE_INSN_BASIC_BLOCK +For RTL, these pointers are @code{BB_HEAD} and @code{BB_END}. + +@cindex insn notes, notes +@findex NOTE_INSN_BASIC_BLOCK +In the RTL representation of a function, the instruction stream +contains not only the ``real'' instructions, but also @dfn{notes} +or @dfn{insn notes} (to distinguish them from @dfn{reg notes}). +Any function that moves or duplicates the basic blocks needs +to take care of updating of these notes. Many of these notes expect +that the instruction stream consists of linear regions, so updating +can sometimes be tedious. All types of insn notes are defined +in @file{insn-notes.def}. + +In the RTL function representation, the instructions contained in a +basic block always follow a @code{NOTE_INSN_BASIC_BLOCK}, but zero +or more @code{CODE_LABEL} nodes can precede the block note. +A basic block ends with a control flow instruction or with the last +instruction before the next @code{CODE_LABEL} or +@code{NOTE_INSN_BASIC_BLOCK}. +By definition, a @code{CODE_LABEL} cannot appear in the middle of +the instruction stream of a basic block. + +@findex can_fallthru +@cindex table jump +In addition to notes, the jump table vectors are also represented as +``pseudo-instructions'' inside the insn stream. These vectors never +appear in the basic block and should always be placed just after the +table jump instructions referencing them. After removing the +table-jump it is often difficult to eliminate the code computing the +address and referencing the vector, so cleaning up these vectors is +postponed until after liveness analysis. Thus the jump table vectors +may appear in the insn stream unreferenced and without any purpose. +Before any edge is made @dfn{fall-thru}, the existence of such +construct in the way needs to be checked by calling +@code{can_fallthru} function. + +@cindex GIMPLE statement iterators +For the @code{GIMPLE} representation, the PHI nodes and statements +contained in a basic block are in a @code{gimple_seq} pointed to by +the basic block intermediate language specific pointers. +Abstract containers and iterators are used to access the PHI nodes +and statements in a basic blocks. These iterators are called +@dfn{GIMPLE statement iterators} (GSIs). Grep for @code{^gsi} +in the various @file{gimple-*} and @file{tree-*} files. +There is a @code{gimple_stmt_iterator} type for iterating over +all kinds of statement, and a @code{gphi_iterator} subclass for +iterating over PHI nodes. +The following snippet will pretty-print all PHI nodes the statements +of the current function in the GIMPLE representation. + +@smallexample +basic_block bb; + +FOR_EACH_BB (bb) + @{ + gphi_iterator pi; + gimple_stmt_iterator si; + + for (pi = gsi_start_phis (bb); !gsi_end_p (pi); gsi_next (&pi)) + @{ + gphi *phi = pi.phi (); + print_gimple_stmt (dump_file, phi, 0, TDF_SLIM); + @} + for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si)) + @{ + gimple stmt = gsi_stmt (si); + print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); + @} + @} +@end smallexample + + +@node Edges +@section Edges + +@cindex edge in the flow graph +@findex edge +Edges represent possible control flow transfers from the end of some +basic block A to the head of another basic block B@. We say that A is +a predecessor of B, and B is a successor of A@. Edges are represented +in GCC with the @code{edge} data type. Each @code{edge} acts as a +link between two basic blocks: The @code{src} member of an edge +points to the predecessor basic block of the @code{dest} basic block. +The members @code{preds} and @code{succs} of the @code{basic_block} data +type point to type-safe vectors of edges to the predecessors and +successors of the block. + +@cindex edge iterators +When walking the edges in an edge vector, @dfn{edge iterators} should +be used. Edge iterators are constructed using the +@code{edge_iterator} data structure and several methods are available +to operate on them: + +@ftable @code +@item ei_start +This function initializes an @code{edge_iterator} that points to the +first edge in a vector of edges. + +@item ei_last +This function initializes an @code{edge_iterator} that points to the +last edge in a vector of edges. + +@item ei_end_p +This predicate is @code{true} if an @code{edge_iterator} represents +the last edge in an edge vector. + +@item ei_one_before_end_p +This predicate is @code{true} if an @code{edge_iterator} represents +the second last edge in an edge vector. + +@item ei_next +This function takes a pointer to an @code{edge_iterator} and makes it +point to the next edge in the sequence. + +@item ei_prev +This function takes a pointer to an @code{edge_iterator} and makes it +point to the previous edge in the sequence. + +@item ei_edge +This function returns the @code{edge} currently pointed to by an +@code{edge_iterator}. + +@item ei_safe_edge +This function returns the @code{edge} currently pointed to by an +@code{edge_iterator}, but returns @code{NULL} if the iterator is +pointing at the end of the sequence. This function has been provided +for existing code makes the assumption that a @code{NULL} edge +indicates the end of the sequence. + +@end ftable + +The convenience macro @code{FOR_EACH_EDGE} can be used to visit all of +the edges in a sequence of predecessor or successor edges. It must +not be used when an element might be removed during the traversal, +otherwise elements will be missed. Here is an example of how to use +the macro: + +@smallexample +edge e; +edge_iterator ei; + +FOR_EACH_EDGE (e, ei, bb->succs) + @{ + if (e->flags & EDGE_FALLTHRU) + break; + @} +@end smallexample + +@findex fall-thru +There are various reasons why control flow may transfer from one block +to another. One possibility is that some instruction, for example a +@code{CODE_LABEL}, in a linearized instruction stream just always +starts a new basic block. In this case a @dfn{fall-thru} edge links +the basic block to the first following basic block. But there are +several other reasons why edges may be created. The @code{flags} +field of the @code{edge} data type is used to store information +about the type of edge we are dealing with. Each edge is of one of +the following types: + +@table @emph +@item jump +No type flags are set for edges corresponding to jump instructions. +These edges are used for unconditional or conditional jumps and in +RTL also for table jumps. They are the easiest to manipulate as they +may be freely redirected when the flow graph is not in SSA form. + +@item fall-thru +@findex EDGE_FALLTHRU, force_nonfallthru +Fall-thru edges are present in case where the basic block may continue +execution to the following one without branching. These edges have +the @code{EDGE_FALLTHRU} flag set. Unlike other types of edges, these +edges must come into the basic block immediately following in the +instruction stream. The function @code{force_nonfallthru} is +available to insert an unconditional jump in the case that redirection +is needed. Note that this may require creation of a new basic block. + +@item exception handling +@cindex exception handling +@findex EDGE_ABNORMAL, EDGE_EH +Exception handling edges represent possible control transfers from a +trapping instruction to an exception handler. The definition of +``trapping'' varies. In C++, only function calls can throw, but for +Ada exceptions like division by zero or segmentation fault are +defined and thus each instruction possibly throwing this kind of +exception needs to be handled as control flow instruction. Exception +edges have the @code{EDGE_ABNORMAL} and @code{EDGE_EH} flags set. + +@findex purge_dead_edges +When updating the instruction stream it is easy to change possibly +trapping instruction to non-trapping, by simply removing the exception +edge. The opposite conversion is difficult, but should not happen +anyway. The edges can be eliminated via @code{purge_dead_edges} call. + +@findex REG_EH_REGION, EDGE_ABNORMAL_CALL +In the RTL representation, the destination of an exception edge is +specified by @code{REG_EH_REGION} note attached to the insn. +In case of a trapping call the @code{EDGE_ABNORMAL_CALL} flag is set +too. In the @code{GIMPLE} representation, this extra flag is not set. + +@findex may_trap_p, tree_could_trap_p +In the RTL representation, the predicate @code{may_trap_p} may be used +to check whether instruction still may trap or not. For the tree +representation, the @code{tree_could_trap_p} predicate is available, +but this predicate only checks for possible memory traps, as in +dereferencing an invalid pointer location. + + +@item sibling calls +@cindex sibling call +@findex EDGE_ABNORMAL, EDGE_SIBCALL +Sibling calls or tail calls terminate the function in a non-standard +way and thus an edge to the exit must be present. +@code{EDGE_SIBCALL} and @code{EDGE_ABNORMAL} are set in such case. +These edges only exist in the RTL representation. + +@item computed jumps +@cindex computed jump +@findex EDGE_ABNORMAL +Computed jumps contain edges to all labels in the function referenced +from the code. All those edges have @code{EDGE_ABNORMAL} flag set. +The edges used to represent computed jumps often cause compile time +performance problems, since functions consisting of many taken labels +and many computed jumps may have @emph{very} dense flow graphs, so +these edges need to be handled with special care. During the earlier +stages of the compilation process, GCC tries to avoid such dense flow +graphs by factoring computed jumps. For example, given the following +series of jumps, + +@smallexample + goto *x; + [ @dots{} ] + + goto *x; + [ @dots{} ] + + goto *x; + [ @dots{} ] +@end smallexample + +@noindent +factoring the computed jumps results in the following code sequence +which has a much simpler flow graph: + +@smallexample + goto y; + [ @dots{} ] + + goto y; + [ @dots{} ] + + goto y; + [ @dots{} ] + +y: + goto *x; +@end smallexample + +@findex pass_duplicate_computed_gotos +However, the classic problem with this transformation is that it has a +runtime cost in there resulting code: An extra jump. Therefore, the +computed jumps are un-factored in the later passes of the compiler +(in the pass called @code{pass_duplicate_computed_gotos}). +Be aware of that when you work on passes in that area. There have +been numerous examples already where the compile time for code with +unfactored computed jumps caused some serious headaches. + +@item nonlocal goto handlers +@cindex nonlocal goto handler +@findex EDGE_ABNORMAL, EDGE_ABNORMAL_CALL +GCC allows nested functions to return into caller using a @code{goto} +to a label passed to as an argument to the callee. The labels passed +to nested functions contain special code to cleanup after function +call. Such sections of code are referred to as ``nonlocal goto +receivers''. If a function contains such nonlocal goto receivers, an +edge from the call to the label is created with the +@code{EDGE_ABNORMAL} and @code{EDGE_ABNORMAL_CALL} flags set. + +@item function entry points +@cindex function entry point, alternate function entry point +@findex LABEL_ALTERNATE_NAME +By definition, execution of function starts at basic block 0, so there +is always an edge from the @code{ENTRY_BLOCK_PTR} to basic block 0. +There is no @code{GIMPLE} representation for alternate entry points at +this moment. In RTL, alternate entry points are specified by +@code{CODE_LABEL} with @code{LABEL_ALTERNATE_NAME} defined. This +feature is currently used for multiple entry point prologues and is +limited to post-reload passes only. This can be used by back-ends to +emit alternate prologues for functions called from different contexts. +In future full support for multiple entry functions defined by Fortran +90 needs to be implemented. + +@item function exits +In the pre-reload representation a function terminates after the last +instruction in the insn chain and no explicit return instructions are +used. This corresponds to the fall-thru edge into exit block. After +reload, optimal RTL epilogues are used that use explicit (conditional) +return instructions that are represented by edges with no flags set. + +@end table + + +@node Profile information +@section Profile information + +@cindex profile representation +In many cases a compiler must make a choice whether to trade speed in +one part of code for speed in another, or to trade code size for code +speed. In such cases it is useful to know information about how often +some given block will be executed. That is the purpose for +maintaining profile within the flow graph. +GCC can handle profile information obtained through @dfn{profile +feedback}, but it can also estimate branch probabilities based on +statics and heuristics. + +@cindex profile feedback +The feedback based profile is produced by compiling the program with +instrumentation, executing it on a train run and reading the numbers +of executions of basic blocks and edges back to the compiler while +re-compiling the program to produce the final executable. This method +provides very accurate information about where a program spends most +of its time on the train run. Whether it matches the average run of +course depends on the choice of train data set, but several studies +have shown that the behavior of a program usually changes just +marginally over different data sets. + +@cindex Static profile estimation +@cindex branch prediction +@findex predict.def +When profile feedback is not available, the compiler may be asked to +attempt to predict the behavior of each branch in the program using a +set of heuristics (see @file{predict.def} for details) and compute +estimated frequencies of each basic block by propagating the +probabilities over the graph. + +@findex frequency, count, BB_FREQ_BASE +Each @code{basic_block} contains two integer fields to represent +profile information: @code{frequency} and @code{count}. The +@code{frequency} is an estimation how often is basic block executed +within a function. It is represented as an integer scaled in the +range from 0 to @code{BB_FREQ_BASE}. The most frequently executed +basic block in function is initially set to @code{BB_FREQ_BASE} and +the rest of frequencies are scaled accordingly. During optimization, +the frequency of the most frequent basic block can both decrease (for +instance by loop unrolling) or grow (for instance by cross-jumping +optimization), so scaling sometimes has to be performed multiple +times. + +@findex gcov_type +The @code{count} contains hard-counted numbers of execution measured +during training runs and is nonzero only when profile feedback is +available. This value is represented as the host's widest integer +(typically a 64 bit integer) of the special type @code{gcov_type}. + +Most optimization passes can use only the frequency information of a +basic block, but a few passes may want to know hard execution counts. +The frequencies should always match the counts after scaling, however +during updating of the profile information numerical error may +accumulate into quite large errors. + +@findex REG_BR_PROB_BASE, EDGE_FREQUENCY +Each edge also contains a branch probability field: an integer in the +range from 0 to @code{REG_BR_PROB_BASE}. It represents probability of +passing control from the end of the @code{src} basic block to the +@code{dest} basic block, i.e.@: the probability that control will flow +along this edge. The @code{EDGE_FREQUENCY} macro is available to +compute how frequently a given edge is taken. There is a @code{count} +field for each edge as well, representing same information as for a +basic block. + +The basic block frequencies are not represented in the instruction +stream, but in the RTL representation the edge frequencies are +represented for conditional jumps (via the @code{REG_BR_PROB} +macro) since they are used when instructions are output to the +assembly file and the flow graph is no longer maintained. + +@cindex reverse probability +The probability that control flow arrives via a given edge to its +destination basic block is called @dfn{reverse probability} and is not +directly represented, but it may be easily computed from frequencies +of basic blocks. + +@findex redirect_edge_and_branch +Updating profile information is a delicate task that can unfortunately +not be easily integrated with the CFG manipulation API@. Many of the +functions and hooks to modify the CFG, such as +@code{redirect_edge_and_branch}, do not have enough information to +easily update the profile, so updating it is in the majority of cases +left up to the caller. It is difficult to uncover bugs in the profile +updating code, because they manifest themselves only by producing +worse code, and checking profile consistency is not possible because +of numeric error accumulation. Hence special attention needs to be +given to this issue in each pass that modifies the CFG@. + +@findex REG_BR_PROB_BASE, BB_FREQ_BASE, count +It is important to point out that @code{REG_BR_PROB_BASE} and +@code{BB_FREQ_BASE} are both set low enough to be possible to compute +second power of any frequency or probability in the flow graph, it is +not possible to even square the @code{count} field, as modern CPUs are +fast enough to execute $2^32$ operations quickly. + + +@node Maintaining the CFG +@section Maintaining the CFG +@findex cfghooks.h + +An important task of each compiler pass is to keep both the control +flow graph and all profile information up-to-date. Reconstruction of +the control flow graph after each pass is not an option, since it may be +very expensive and lost profile information cannot be reconstructed at +all. + +GCC has two major intermediate representations, and both use the +@code{basic_block} and @code{edge} data types to represent control +flow. Both representations share as much of the CFG maintenance code +as possible. For each representation, a set of @dfn{hooks} is defined +so that each representation can provide its own implementation of CFG +manipulation routines when necessary. These hooks are defined in +@file{cfghooks.h}. There are hooks for almost all common CFG +manipulations, including block splitting and merging, edge redirection +and creating and deleting basic blocks. These hooks should provide +everything you need to maintain and manipulate the CFG in both the RTL +and @code{GIMPLE} representation. + +At the moment, the basic block boundaries are maintained transparently +when modifying instructions, so there rarely is a need to move them +manually (such as in case someone wants to output instruction outside +basic block explicitly). + +@findex BLOCK_FOR_INSN, gimple_bb +In the RTL representation, each instruction has a +@code{BLOCK_FOR_INSN} value that represents pointer to the basic block +that contains the instruction. In the @code{GIMPLE} representation, the +function @code{gimple_bb} returns a pointer to the basic block +containing the queried statement. + +@cindex GIMPLE statement iterators +When changes need to be applied to a function in its @code{GIMPLE} +representation, @dfn{GIMPLE statement iterators} should be used. These +iterators provide an integrated abstraction of the flow graph and the +instruction stream. Block statement iterators are constructed using +the @code{gimple_stmt_iterator} data structure and several modifiers are +available, including the following: + +@ftable @code +@item gsi_start +This function initializes a @code{gimple_stmt_iterator} that points to +the first non-empty statement in a basic block. + +@item gsi_last +This function initializes a @code{gimple_stmt_iterator} that points to +the last statement in a basic block. + +@item gsi_end_p +This predicate is @code{true} if a @code{gimple_stmt_iterator} +represents the end of a basic block. + +@item gsi_next +This function takes a @code{gimple_stmt_iterator} and makes it point to +its successor. + +@item gsi_prev +This function takes a @code{gimple_stmt_iterator} and makes it point to +its predecessor. + +@item gsi_insert_after +This function inserts a statement after the @code{gimple_stmt_iterator} +passed in. The final parameter determines whether the statement +iterator is updated to point to the newly inserted statement, or left +pointing to the original statement. + +@item gsi_insert_before +This function inserts a statement before the @code{gimple_stmt_iterator} +passed in. The final parameter determines whether the statement +iterator is updated to point to the newly inserted statement, or left +pointing to the original statement. + +@item gsi_remove +This function removes the @code{gimple_stmt_iterator} passed in and +rechains the remaining statements in a basic block, if any. +@end ftable + +@findex BB_HEAD, BB_END +In the RTL representation, the macros @code{BB_HEAD} and @code{BB_END} +may be used to get the head and end @code{rtx} of a basic block. No +abstract iterators are defined for traversing the insn chain, but you +can just use @code{NEXT_INSN} and @code{PREV_INSN} instead. @xref{Insns}. + +@findex purge_dead_edges +Usually a code manipulating pass simplifies the instruction stream and +the flow of control, possibly eliminating some edges. This may for +example happen when a conditional jump is replaced with an +unconditional jump. Updating of edges +is not transparent and each optimization pass is required to do so +manually. However only few cases occur in practice. The pass may +call @code{purge_dead_edges} on a given basic block to remove +superfluous edges, if any. + +@findex redirect_edge_and_branch, redirect_jump +Another common scenario is redirection of branch instructions, but +this is best modeled as redirection of edges in the control flow graph +and thus use of @code{redirect_edge_and_branch} is preferred over more +low level functions, such as @code{redirect_jump} that operate on RTL +chain only. The CFG hooks defined in @file{cfghooks.h} should provide +the complete API required for manipulating and maintaining the CFG@. + +@findex split_block +It is also possible that a pass has to insert control flow instruction +into the middle of a basic block, thus creating an entry point in the +middle of the basic block, which is impossible by definition: The +block must be split to make sure it only has one entry point, i.e.@: the +head of the basic block. The CFG hook @code{split_block} may be used +when an instruction in the middle of a basic block has to become the +target of a jump or branch instruction. + +@findex insert_insn_on_edge +@findex commit_edge_insertions +@findex gsi_insert_on_edge +@findex gsi_commit_edge_inserts +@cindex edge splitting +For a global optimizer, a common operation is to split edges in the +flow graph and insert instructions on them. In the RTL +representation, this can be easily done using the +@code{insert_insn_on_edge} function that emits an instruction +``on the edge'', caching it for a later @code{commit_edge_insertions} +call that will take care of moving the inserted instructions off the +edge into the instruction stream contained in a basic block. This +includes the creation of new basic blocks where needed. In the +@code{GIMPLE} representation, the equivalent functions are +@code{gsi_insert_on_edge} which inserts a block statement +iterator on an edge, and @code{gsi_commit_edge_inserts} which flushes +the instruction to actual instruction stream. + +@findex verify_flow_info +@cindex CFG verification +While debugging the optimization pass, the @code{verify_flow_info} +function may be useful to find bugs in the control flow graph updating +code. + + +@node Liveness information +@section Liveness information +@cindex Liveness representation +Liveness information is useful to determine whether some register is +``live'' at given point of program, i.e.@: that it contains a value that +may be used at a later point in the program. This information is +used, for instance, during register allocation, as the pseudo +registers only need to be assigned to a unique hard register or to a +stack slot if they are live. The hard registers and stack slots may +be freely reused for other values when a register is dead. + +Liveness information is available in the back end starting with +@code{pass_df_initialize} and ending with @code{pass_df_finish}. Three +flavors of live analysis are available: With @code{LR}, it is possible +to determine at any point @code{P} in the function if the register may be +used on some path from @code{P} to the end of the function. With +@code{UR}, it is possible to determine if there is a path from the +beginning of the function to @code{P} that defines the variable. +@code{LIVE} is the intersection of the @code{LR} and @code{UR} and a +variable is live at @code{P} if there is both an assignment that reaches +it from the beginning of the function and a use that can be reached on +some path from @code{P} to the end of the function. + +In general @code{LIVE} is the most useful of the three. The macros +@code{DF_[LR,UR,LIVE]_[IN,OUT]} can be used to access this information. +The macros take a basic block number and return a bitmap that is indexed +by the register number. This information is only guaranteed to be up to +date after calls are made to @code{df_analyze}. See the file +@code{df-core.cc} for details on using the dataflow. + + +@findex REG_DEAD, REG_UNUSED +The liveness information is stored partly in the RTL instruction stream +and partly in the flow graph. Local information is stored in the +instruction stream: Each instruction may contain @code{REG_DEAD} notes +representing that the value of a given register is no longer needed, or +@code{REG_UNUSED} notes representing that the value computed by the +instruction is never used. The second is useful for instructions +computing multiple values at once. + diff --git a/gcc/doc/collect2.texi b/gcc/doc/collect2.texi new file mode 100644 index 00000000000..8155b7906c9 --- /dev/null +++ b/gcc/doc/collect2.texi @@ -0,0 +1,89 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Collect2 +@chapter @code{collect2} + +GCC uses a utility called @code{collect2} on nearly all systems to arrange +to call various initialization functions at start time. + +The program @code{collect2} works by linking the program once and +looking through the linker output file for symbols with particular names +indicating they are constructor functions. If it finds any, it +creates a new temporary @samp{.c} file containing a table of them, +compiles it, and links the program a second time including that file. + +@findex __main +@cindex constructors, automatic calls +The actual calls to the constructors are carried out by a subroutine +called @code{__main}, which is called (automatically) at the beginning +of the body of @code{main} (provided @code{main} was compiled with GNU +CC)@. Calling @code{__main} is necessary, even when compiling C code, to +allow linking C and C++ object code together. (If you use +@option{-nostdlib}, you get an unresolved reference to @code{__main}, +since it's defined in the standard GCC library. Include @option{-lgcc} at +the end of your compiler command line to resolve this reference.) + +The program @code{collect2} is installed as @code{ld} in the directory +where the passes of the compiler are installed. When @code{collect2} +needs to find the @emph{real} @code{ld}, it tries the following file +names: + +@itemize @bullet +@item +a hard coded linker file name, if GCC was configured with the +@option{--with-ld} option. + +@item +@file{real-ld} in the directories listed in the compiler's search +directories. + +@item +@file{real-ld} in the directories listed in the environment variable +@code{PATH}. + +@item +The file specified in the @code{REAL_LD_FILE_NAME} configuration macro, +if specified. + +@item +@file{ld} in the compiler's search directories, except that +@code{collect2} will not execute itself recursively. + +@item +@file{ld} in @code{PATH}. +@end itemize + +``The compiler's search directories'' means all the directories where +@command{gcc} searches for passes of the compiler. This includes +directories that you specify with @option{-B}. + +Cross-compilers search a little differently: + +@itemize @bullet +@item +@file{real-ld} in the compiler's search directories. + +@item +@file{@var{target}-real-ld} in @code{PATH}. + +@item +The file specified in the @code{REAL_LD_FILE_NAME} configuration macro, +if specified. + +@item +@file{ld} in the compiler's search directories. + +@item +@file{@var{target}-ld} in @code{PATH}. +@end itemize + +@code{collect2} explicitly avoids running @code{ld} using the file name +under which @code{collect2} itself was invoked. In fact, it remembers +up a list of such names---in case one copy of @code{collect2} finds +another copy (or version) of @code{collect2} installed as @code{ld} in a +second place in the search path. + +@code{collect2} searches for the utilities @code{nm} and @code{strip} +using the same algorithm as above for @code{ld}. diff --git a/gcc/doc/compat.texi b/gcc/doc/compat.texi new file mode 100644 index 00000000000..ae265fa01de --- /dev/null +++ b/gcc/doc/compat.texi @@ -0,0 +1,156 @@ +@c Copyright (C) 2002-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Compatibility +@chapter Binary Compatibility +@cindex binary compatibility +@cindex ABI +@cindex application binary interface + +Binary compatibility encompasses several related concepts: + +@table @dfn +@item application binary interface (ABI) +The set of runtime conventions followed by all of the tools that deal +with binary representations of a program, including compilers, assemblers, +linkers, and language runtime support. +Some ABIs are formal with a written specification, possibly designed +by multiple interested parties. Others are simply the way things are +actually done by a particular set of tools. + +@item ABI conformance +A compiler conforms to an ABI if it generates code that follows all of +the specifications enumerated by that ABI@. +A library conforms to an ABI if it is implemented according to that ABI@. +An application conforms to an ABI if it is built using tools that conform +to that ABI and does not contain source code that specifically changes +behavior specified by the ABI@. + +@item calling conventions +Calling conventions are a subset of an ABI that specify of how arguments +are passed and function results are returned. + +@item interoperability +Different sets of tools are interoperable if they generate files that +can be used in the same program. The set of tools includes compilers, +assemblers, linkers, libraries, header files, startup files, and debuggers. +Binaries produced by different sets of tools are not interoperable unless +they implement the same ABI@. This applies to different versions of the +same tools as well as tools from different vendors. + +@item intercallability +Whether a function in a binary built by one set of tools can call a +function in a binary built by a different set of tools is a subset +of interoperability. + +@item implementation-defined features +Language standards include lists of implementation-defined features whose +behavior can vary from one implementation to another. Some of these +features are normally covered by a platform's ABI and others are not. +The features that are not covered by an ABI generally affect how a +program behaves, but not intercallability. + +@item compatibility +Conformance to the same ABI and the same behavior of implementation-defined +features are both relevant for compatibility. +@end table + +The application binary interface implemented by a C or C++ compiler +affects code generation and runtime support for: + +@itemize @bullet +@item +size and alignment of data types +@item +layout of structured types +@item +calling conventions +@item +register usage conventions +@item +interfaces for runtime arithmetic support +@item +object file formats +@end itemize + +In addition, the application binary interface implemented by a C++ compiler +affects code generation and runtime support for: +@itemize @bullet +@item +name mangling +@item +exception handling +@item +invoking constructors and destructors +@item +layout, alignment, and padding of classes +@item +layout and alignment of virtual tables +@end itemize + +Some GCC compilation options cause the compiler to generate code that +does not conform to the platform's default ABI@. Other options cause +different program behavior for implementation-defined features that are +not covered by an ABI@. These options are provided for consistency with +other compilers that do not follow the platform's default ABI or the +usual behavior of implementation-defined features for the platform. +Be very careful about using such options. + +Most platforms have a well-defined ABI that covers C code, but ABIs +that cover C++ functionality are not yet common. + +Starting with GCC 3.2, GCC binary conventions for C++ are based on a +written, vendor-neutral C++ ABI that was designed to be specific to +64-bit Itanium but also includes generic specifications that apply to +any platform. +This C++ ABI is also implemented by other compiler vendors on some +platforms, notably GNU/Linux and BSD systems. +We have tried hard to provide a stable ABI that will be compatible with +future GCC releases, but it is possible that we will encounter problems +that make this difficult. Such problems could include different +interpretations of the C++ ABI by different vendors, bugs in the ABI, or +bugs in the implementation of the ABI in different compilers. +GCC's @option{-Wabi} switch warns when G++ generates code that is +probably not compatible with the C++ ABI@. + +The C++ library used with a C++ compiler includes the Standard C++ +Library, with functionality defined in the C++ Standard, plus language +runtime support. The runtime support is included in a C++ ABI, but there +is no formal ABI for the Standard C++ Library. Two implementations +of that library are interoperable if one follows the de-facto ABI of the +other and if they are both built with the same compiler, or with compilers +that conform to the same ABI for C++ compiler and runtime support. + +When G++ and another C++ compiler conform to the same C++ ABI, but the +implementations of the Standard C++ Library that they normally use do not +follow the same ABI for the Standard C++ Library, object files built with +those compilers can be used in the same program only if they use the same +C++ library. This requires specifying the location of the C++ library +header files when invoking the compiler whose usual library is not being +used. The location of GCC's C++ header files depends on how the GCC +build was configured, but can be seen by using the G++ @option{-v} option. +With default configuration options for G++ 3.3 the compile line for a +different C++ compiler needs to include + +@smallexample + -I@var{gcc_install_directory}/include/c++/3.3 +@end smallexample + +Similarly, compiling code with G++ that must use a C++ library other +than the GNU C++ library requires specifying the location of the header +files for that other library. + +The most straightforward way to link a program to use a particular +C++ library is to use a C++ driver that specifies that C++ library by +default. The @command{g++} driver, for example, tells the linker where +to find GCC's C++ library (@file{libstdc++}) plus the other libraries +and startup files it needs, in the proper order. + +If a program must use a different C++ library and it's not possible +to do the final link using a C++ driver that uses that library by default, +it is necessary to tell @command{g++} the location and name of that +library. It might also be necessary to specify different startup files +and other runtime support libraries, and to suppress the use of GCC's +support libraries with one or more of the options @option{-nostdlib}, +@option{-nostartfiles}, and @option{-nodefaultlibs}. diff --git a/gcc/doc/configfiles.texi b/gcc/doc/configfiles.texi new file mode 100644 index 00000000000..76f69559ec3 --- /dev/null +++ b/gcc/doc/configfiles.texi @@ -0,0 +1,69 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Configuration Files +@subsubsection Files Created by @code{configure} + +Here we spell out what files will be set up by @file{configure} in the +@file{gcc} directory. Some other files are created as temporary files +in the configuration process, and are not used in the subsequent +build; these are not documented. + +@itemize @bullet +@item +@file{Makefile} is constructed from @file{Makefile.in}, together with +the host and target fragments (@pxref{Fragments, , Makefile +Fragments}) @file{t-@var{target}} and @file{x-@var{host}} from +@file{config}, if any, and language Makefile fragments +@file{@var{language}/Make-lang.in}. +@item +@file{auto-host.h} contains information about the host machine +determined by @file{configure}. If the host machine is different from +the build machine, then @file{auto-build.h} is also created, +containing such information about the build machine. +@item +@file{config.status} is a script that may be run to recreate the +current configuration. +@item +@file{configargs.h} is a header containing details of the arguments +passed to @file{configure} to configure GCC, and of the thread model +used. +@item +@file{cstamp-h} is used as a timestamp. +@item +If a language @file{config-lang.in} file (@pxref{Front End Config, , +The Front End @file{config-lang.in} File}) sets @code{outputs}, then +the files listed in @code{outputs} there are also generated. +@end itemize + +The following configuration headers are created from the Makefile, +using @file{mkconfig.sh}, rather than directly by @file{configure}. +@file{config.h}, @file{bconfig.h} and @file{tconfig.h} all contain the +@file{xm-@var{machine}.h} header, if any, appropriate to the host, +build and target machines respectively, the configuration headers for +the target, and some definitions; for the host and build machines, +these include the autoconfigured headers generated by +@file{configure}. The other configuration headers are determined by +@file{config.gcc}. They also contain the typedefs for @code{rtx}, +@code{rtvec} and @code{tree}. + +@itemize @bullet +@item +@file{config.h}, for use in programs that run on the host machine. +@item +@file{bconfig.h}, for use in programs that run on the build machine. +@item +@file{tconfig.h}, for use in programs and libraries for the target +machine. +@item +@file{tm_p.h}, which includes the header @file{@var{machine}-protos.h} +that contains prototypes for functions in the target +@file{@var{machine}.c} file. The +@file{@var{machine}-protos.h} header is included after the @file{rtl.h} +and/or @file{tree.h} would have been included. +The @file{tm_p.h} also +includes the header @file{tm-preds.h} which is generated by +@file{genpreds} program during the build to define the declarations +and inline functions for the predicate functions. +@end itemize diff --git a/gcc/doc/configterms.texi b/gcc/doc/configterms.texi new file mode 100644 index 00000000000..b53655b4316 --- /dev/null +++ b/gcc/doc/configterms.texi @@ -0,0 +1,61 @@ +@c Copyright (C) 2001-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Configure Terms +@section Configure Terms and History +@cindex configure terms +@cindex canadian + +The configure and build process has a long and colorful history, and can +be confusing to anyone who doesn't know why things are the way they are. +While there are other documents which describe the configuration process +in detail, here are a few things that everyone working on GCC should +know. + +There are three system names that the build knows about: the machine you +are building on (@dfn{build}), the machine that you are building for +(@dfn{host}), and the machine that GCC will produce code for +(@dfn{target}). When you configure GCC, you specify these with +@option{--build=}, @option{--host=}, and @option{--target=}. + +Specifying the host without specifying the build should be avoided, as +@command{configure} may (and once did) assume that the host you specify +is also the build, which may not be true. + +If build, host, and target are all the same, this is called a +@dfn{native}. If build and host are the same but target is different, +this is called a @dfn{cross}. If build, host, and target are all +different this is called a @dfn{canadian} (for obscure reasons dealing +with Canada's political party and the background of the person working +on the build at that time). If host and target are the same, but build +is different, you are using a cross-compiler to build a native for a +different system. Some people call this a @dfn{host-x-host}, +@dfn{crossed native}, or @dfn{cross-built native}. If build and target +are the same, but host is different, you are using a cross compiler to +build a cross compiler that produces code for the machine you're +building on. This is rare, so there is no common way of describing it. +There is a proposal to call this a @dfn{crossback}. + +If build and host are the same, the GCC you are building will also be +used to build the target libraries (like @code{libstdc++}). If build and host +are different, you must have already built and installed a cross +compiler that will be used to build the target libraries (if you +configured with @option{--target=foo-bar}, this compiler will be called +@command{foo-bar-gcc}). + +In the case of target libraries, the machine you're building for is the +machine you specified with @option{--target}. So, build is the machine +you're building on (no change there), host is the machine you're +building for (the target libraries are built for the target, so host is +the target you specified), and target doesn't apply (because you're not +building a compiler, you're building libraries). The configure/make +process will adjust these variables as needed. It also sets +@code{$with_cross_host} to the original @option{--host} value in case you +need it. + +The @code{libiberty} support library is built up to three times: once +for the host, once for the target (even if they are the same), and once +for the build if build and host are different. This allows it to be +used by all programs which are generated in the course of the build +process. diff --git a/gcc/doc/contrib.texi b/gcc/doc/contrib.texi new file mode 100644 index 00000000000..e14cf5e4751 --- /dev/null +++ b/gcc/doc/contrib.texi @@ -0,0 +1,1776 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Contributors +@unnumbered Contributors to GCC +@cindex contributors + +The GCC project would like to thank its many contributors. Without them the +project would not have been nearly as successful as it has been. Any omissions +in this list are accidental. Feel free to contact +@email{law@@redhat.com} or @email{gerald@@pfeifer.com} if you have been left +out or some of your contributions are not listed. Please keep this list in +alphabetical order. + +@itemize @bullet + +@item +Analog Devices helped implement the support for complex data types +and iterators. + +@item +John David Anglin for threading-related fixes and improvements to +libstdc++-v3, and the HP-UX port. + +@item +James van Artsdalen wrote the code that makes efficient use of +the Intel 80387 register stack. + +@item +Abramo and Roberto Bagnara for the SysV68 Motorola 3300 Delta Series +port. + +@item +Alasdair Baird for various bug fixes. + +@item +Giovanni Bajo for analyzing lots of complicated C++ problem reports. + +@item +Peter Barada for his work to improve code generation for new +ColdFire cores. + +@item +Gerald Baumgartner added the signature extension to the C++ front end. + +@item +Godmar Back for his Java improvements and encouragement. + +@item +Scott Bambrough for help porting the Java compiler. + +@item +Wolfgang Bangerth for processing tons of bug reports. + +@item +Jon Beniston for his Microsoft Windows port of Java and port to Lattice Mico32. + +@item +Daniel Berlin for better DWARF 2 support, faster/better optimizations, +improved alias analysis, plus migrating GCC to Bugzilla. + +@item +Geoff Berry for his Java object serialization work and various patches. + +@item +David Binderman tests weekly snapshots of GCC trunk against Fedora Rawhide +for several architectures. + +@item +Laurynas Biveinis for memory management work and DJGPP port fixes. + +@item +Uros Bizjak for the implementation of x87 math built-in functions and +for various middle end and i386 back end improvements and bug fixes. + +@item +Eric Blake for helping to make GCJ and libgcj conform to the +specifications. + +@item +Janne Blomqvist for contributions to GNU Fortran. + +@item +Hans-J. Boehm for his garbage collector, IA-64 libffi port, and other +Java work. + +@item +Segher Boessenkool for helping maintain the PowerPC port and the +instruction combiner plus various contributions to the middle end. + +@item +Neil Booth for work on cpplib, lang hooks, debug hooks and other +miscellaneous clean-ups. + +@item +Steven Bosscher for integrating the GNU Fortran front end into GCC and for +contributing to the tree-ssa branch. + +@item +Eric Botcazou for fixing middle- and backend bugs left and right. + +@item +Per Bothner for his direction via the steering committee and various +improvements to the infrastructure for supporting new languages. Chill +front end implementation. Initial implementations of +cpplib, fix-header, config.guess, libio, and past C++ library (libg++) +maintainer. Dreaming up, designing and implementing much of GCJ@. + +@item +Devon Bowen helped port GCC to the Tahoe. + +@item +Don Bowman for mips-vxworks contributions. + +@item +James Bowman for the FT32 port. + +@item +Dave Brolley for work on cpplib and Chill. + +@item +Paul Brook for work on the ARM architecture and maintaining GNU Fortran. + +@item +Robert Brown implemented the support for Encore 32000 systems. + +@item +Christian Bruel for improvements to local store elimination. + +@item +Herman A.J. ten Brugge for various fixes. + +@item +Joerg Brunsmann for Java compiler hacking and help with the GCJ FAQ@. + +@item +Joe Buck for his direction via the steering committee from its creation +to 2013. + +@item +Iain Buclaw for the D frontend. + +@item +Craig Burley for leadership of the G77 Fortran effort. + +@item +Tobias Burnus for contributions to GNU Fortran. + +@item +Stephan Buys for contributing Doxygen notes for libstdc++. + +@item +Paolo Carlini for libstdc++ work: lots of efficiency improvements to +the C++ strings, streambufs and formatted I/O, hard detective work on +the frustrating localization issues, and keeping up with the problem reports. + +@item +John Carr for his alias work, SPARC hacking, infrastructure improvements, +previous contributions to the steering committee, loop optimizations, etc. + +@item +Stephane Carrez for 68HC11 and 68HC12 ports. + +@item +Steve Chamberlain for support for the Renesas SH and H8 processors +and the PicoJava processor, and for GCJ config fixes. + +@item +Glenn Chambers for help with the GCJ FAQ@. + +@item +John-Marc Chandonia for various libgcj patches. + +@item +Denis Chertykov for contributing and maintaining the AVR port, the first GCC port +for an 8-bit architecture. + +@item +Kito Cheng for his work on the RISC-V port, including bringing up the test +suite and maintenance. + +@item +Scott Christley for his Objective-C contributions. + +@item +Eric Christopher for his Java porting help and clean-ups. + +@item +Branko Cibej for more warning contributions. + +@item +The @uref{https://www.gnu.org/software/classpath/,,GNU Classpath project} +for all of their merged runtime code. + +@item +Nick Clifton for arm, mcore, fr30, v850, m32r, msp430 rx work, +@option{--help}, and other random hacking. + +@item +Michael Cook for libstdc++ cleanup patches to reduce warnings. + +@item +R. Kelley Cook for making GCC buildable from a read-only directory as +well as other miscellaneous build process and documentation clean-ups. + +@item +Ralf Corsepius for SH testing and minor bug fixing. + +@item +Fran@,{c}ois-Xavier Coudert for contributions to GNU Fortran. + +@item +Stan Cox for care and feeding of the x86 port and lots of behind +the scenes hacking. + +@item +Alex Crain provided changes for the 3b1. + +@item +Ian Dall for major improvements to the NS32k port. + +@item +Paul Dale for his work to add uClinux platform support to the +m68k backend. + +@item +Palmer Dabbelt for his work maintaining the RISC-V port. + +@item +Dario Dariol contributed the four varieties of sample programs +that print a copy of their source. + +@item +Russell Davidson for fstream and stringstream fixes in libstdc++. + +@item +Bud Davis for work on the G77 and GNU Fortran compilers. + +@item +Mo DeJong for GCJ and libgcj bug fixes. + +@item +Jerry DeLisle for contributions to GNU Fortran. + +@item +DJ Delorie for the DJGPP port, build and libiberty maintenance, +various bug fixes, and the M32C, MeP, MSP430, and RL78 ports. + +@item +Arnaud Desitter for helping to debug GNU Fortran. + +@item +Gabriel Dos Reis for contributions to G++, contributions and +maintenance of GCC diagnostics infrastructure, libstdc++-v3, +including @code{valarray<>}, @code{complex<>}, maintaining the numerics library +(including that pesky @code{} :-) and keeping up-to-date anything +to do with numbers. + +@item +Ulrich Drepper for his work on glibc, testing of GCC using glibc, ISO C99 +support, CFG dumping support, etc., plus support of the C++ runtime +libraries including for all kinds of C interface issues, contributing and +maintaining @code{complex<>}, sanity checking and disbursement, configuration +architecture, libio maintenance, and early math work. + +@item +Fran@,{c}ois Dumont for his work on libstdc++-v3, especially maintaining and +improving @code{debug-mode} and associative and unordered containers. + +@item +Zdenek Dvorak for a new loop unroller and various fixes. + +@item +Michael Eager for his work on the Xilinx MicroBlaze port. + +@item +Richard Earnshaw for his ongoing work with the ARM@. + +@item +David Edelsohn for his direction via the steering committee, ongoing work +with the RS6000/PowerPC port, help cleaning up Haifa loop changes, +doing the entire AIX port of libstdc++ with his bare hands, and for +ensuring GCC properly keeps working on AIX@. + +@item +Kevin Ediger for the floating point formatting of num_put::do_put in +libstdc++. + +@item +Phil Edwards for libstdc++ work including configuration hackery, +documentation maintainer, chief breaker of the web pages, the occasional +iostream bug fix, and work on shared library symbol versioning. + +@item +Paul Eggert for random hacking all over GCC@. + +@item +Mark Elbrecht for various DJGPP improvements, and for libstdc++ +configuration support for locales and fstream-related fixes. + +@item +Vadim Egorov for libstdc++ fixes in strings, streambufs, and iostreams. + +@item +Christian Ehrhardt for dealing with bug reports. + +@item +Ben Elliston for his work to move the Objective-C runtime into its +own subdirectory and for his work on autoconf. + +@item +Revital Eres for work on the PowerPC 750CL port. + +@item +Marc Espie for OpenBSD support. + +@item +Doug Evans for much of the global optimization framework, arc, m32r, +and SPARC work. + +@item +Christopher Faylor for his work on the Cygwin port and for caring and +feeding the gcc.gnu.org box and saving its users tons of spam. + +@item +Fred Fish for BeOS support and Ada fixes. + +@item +Ivan Fontes Garcia for the Portuguese translation of the GCJ FAQ@. + +@item +Peter Gerwinski for various bug fixes and the Pascal front end. + +@item +Kaveh R.@: Ghazi for his direction via the steering committee, amazing +work to make @samp{-W -Wall -W* -Werror} useful, and +testing GCC on a plethora of platforms. Kaveh extends his gratitude to +the CAIP Center at Rutgers University for providing him with computing +resources to work on Free Software from the late 1980s to 2010. + +@item +John Gilmore for a donation to the FSF earmarked improving GNU Java. + +@item +Judy Goldberg for c++ contributions. + +@item +Torbjorn Granlund for various fixes and the c-torture testsuite, +multiply- and divide-by-constant optimization, improved long long +support, improved leaf function register allocation, and his direction +via the steering committee. + +@item +Jonny Grant for improvements to @code{collect2's} @option{--help} documentation. + +@item +Anthony Green for his @option{-Os} contributions, the moxie port, and +Java front end work. + +@item +Stu Grossman for gdb hacking, allowing GCJ developers to debug Java code. + +@item +Michael K. Gschwind contributed the port to the PDP-11. + +@item +Richard Biener for his ongoing middle-end contributions and bug fixes +and for release management. + +@item +Ron Guilmette implemented the @command{protoize} and @command{unprotoize} +tools, the support for DWARF 1 symbolic debugging information, and much of +the support for System V Release 4. He has also worked heavily on the +Intel 386 and 860 support. + +@item +Sumanth Gundapaneni for contributing the CR16 port. + +@item +Mostafa Hagog for Swing Modulo Scheduling (SMS) and post reload GCSE@. + +@item +Bruno Haible for improvements in the runtime overhead for EH, new +warnings and assorted bug fixes. + +@item +Andrew Haley for his amazing Java compiler and library efforts. + +@item +Chris Hanson assisted in making GCC work on HP-UX for the 9000 series 300. + +@item +Michael Hayes for various thankless work he's done trying to get +the c30/c40 ports functional. Lots of loop and unroll improvements and +fixes. + +@item +Dara Hazeghi for wading through myriads of target-specific bug reports. + +@item +Kate Hedstrom for staking the G77 folks with an initial testsuite. + +@item +Richard Henderson for his ongoing SPARC, alpha, ia32, and ia64 work, loop +opts, and generally fixing lots of old problems we've ignored for +years, flow rewrite and lots of further stuff, including reviewing +tons of patches. + +@item +Aldy Hernandez for working on the PowerPC port, SIMD support, and +various fixes. + +@item +Nobuyuki Hikichi of Software Research Associates, Tokyo, contributed +the support for the Sony NEWS machine. + +@item +Kazu Hirata for caring and feeding the Renesas H8/300 port and various fixes. + +@item +Katherine Holcomb for work on GNU Fortran. + +@item +Manfred Hollstein for his ongoing work to keep the m88k alive, lots +of testing and bug fixing, particularly of GCC configury code. + +@item +Steve Holmgren for MachTen patches. + +@item +Mat Hostetter for work on the TILE-Gx and TILEPro ports. + +@item +Jan Hubicka for his x86 port improvements. + +@item +Falk Hueffner for working on C and optimization bug reports. + +@item +Bernardo Innocenti for his m68k work, including merging of +ColdFire improvements and uClinux support. + +@item +Christian Iseli for various bug fixes. + +@item +Kamil Iskra for general m68k hacking. + +@item +Lee Iverson for random fixes and MIPS testing. + +@item +Balaji V. Iyer for Cilk+ development and merging. + +@item +Andreas Jaeger for testing and benchmarking of GCC and various bug fixes. + +@item +Martin Jambor for his work on inter-procedural optimizations, the +switch conversion pass, and scalar replacement of aggregates. + +@item +Jakub Jelinek for his SPARC work and sibling call optimizations as well +as lots of bug fixes and test cases, and for improving the Java build +system. + +@item +Janis Johnson for ia64 testing and fixes, her quality improvement +sidetracks, and web page maintenance. + +@item +Kean Johnston for SCO OpenServer support and various fixes. + +@item +Tim Josling for the sample language treelang based originally on Richard +Kenner's ``toy'' language. + +@item +Nicolai Josuttis for additional libstdc++ documentation. + +@item +Klaus Kaempf for his ongoing work to make alpha-vms a viable target. + +@item +Steven G. Kargl for work on GNU Fortran. + +@item +David Kashtan of SRI adapted GCC to VMS@. + +@item +Ryszard Kabatek for many, many libstdc++ bug fixes and optimizations of +strings, especially member functions, and for auto_ptr fixes. + +@item +Geoffrey Keating for his ongoing work to make the PPC work for GNU/Linux +and his automatic regression tester. + +@item +Brendan Kehoe for his ongoing work with G++ and for a lot of early work +in just about every part of libstdc++. + +@item +Oliver M. Kellogg of Deutsche Aerospace contributed the port to the +MIL-STD-1750A@. + +@item +Richard Kenner of the New York University Ultracomputer Research +Laboratory wrote the machine descriptions for the AMD 29000, the DEC +Alpha, the IBM RT PC, and the IBM RS/6000 as well as the support for +instruction attributes. He also made changes to better support RISC +processors including changes to common subexpression elimination, +strength reduction, function calling sequence handling, and condition +code support, in addition to generalizing the code for frame pointer +elimination and delay slot scheduling. Richard Kenner was also the +head maintainer of GCC for several years. + +@item +Mumit Khan for various contributions to the Cygwin and Mingw32 ports and +maintaining binary releases for Microsoft Windows hosts, and for massive libstdc++ +porting work to Cygwin/Mingw32. + +@item +Robin Kirkham for cpu32 support. + +@item +Mark Klein for PA improvements. + +@item +Thomas Koenig for various bug fixes. + +@item +Bruce Korb for the new and improved fixincludes code. + +@item +Benjamin Kosnik for his G++ work and for leading the libstdc++-v3 effort. + +@item +Maxim Kuvyrkov for contributions to the instruction scheduler, the Android +and m68k/Coldfire ports, and optimizations. + +@item +Charles LaBrec contributed the support for the Integrated Solutions +68020 system. + +@item +Asher Langton and Mike Kumbera for contributing Cray pointer support +to GNU Fortran, and for other GNU Fortran improvements. + +@item +Jeff Law for his direction via the steering committee, coordinating the +entire egcs project and GCC 2.95, rolling out snapshots and releases, +handling merges from GCC2, reviewing tons of patches that might have +fallen through the cracks else, and random but extensive hacking. + +@item +Walter Lee for work on the TILE-Gx and TILEPro ports. + +@item +Marc Lehmann for his direction via the steering committee and helping +with analysis and improvements of x86 performance. + +@item +Victor Leikehman for work on GNU Fortran. + +@item +Ted Lemon wrote parts of the RTL reader and printer. + +@item +Kriang Lerdsuwanakij for C++ improvements including template as template +parameter support, and many C++ fixes. + +@item +Warren Levy for tremendous work on libgcj (Java Runtime Library) and +random work on the Java front end. + +@item +Alain Lichnewsky ported GCC to the MIPS CPU@. + +@item +Oskar Liljeblad for hacking on AWT and his many Java bug reports and +patches. + +@item +Robert Lipe for OpenServer support, new testsuites, testing, etc. + +@item +Chen Liqin for various S+core related fixes/improvement, and for +maintaining the S+core port. + +@item +Martin Liska for his work on identical code folding, the sanitizers, +HSA, general bug fixing and for running automated regression testing of GCC +and reporting numerous bugs. + +@item +Weiwen Liu for testing and various bug fixes. + +@item +Manuel L@'opez-Ib@'a@~nez for improving @option{-Wconversion} and +many other diagnostics fixes and improvements. + +@item +Dave Love for his ongoing work with the Fortran front end and +runtime libraries. + +@item +Martin von L@"owis for internal consistency checking infrastructure, +various C++ improvements including namespace support, and tons of +assistance with libstdc++/compiler merges. + +@item +H.J. Lu for his previous contributions to the steering committee, many x86 +bug reports, prototype patches, and keeping the GNU/Linux ports working. + +@item +Greg McGary for random fixes and (someday) bounded pointers. + +@item +Andrew MacLeod for his ongoing work in building a real EH system, +various code generation improvements, work on the global optimizer, etc. + +@item +Vladimir Makarov for hacking some ugly i960 problems, PowerPC hacking +improvements to compile-time performance, overall knowledge and +direction in the area of instruction scheduling, design and +implementation of the automaton based instruction scheduler and +design and implementation of the integrated and local register allocators. + +@item +David Malcolm for his work on improving GCC diagnostics, JIT, self-tests +and unit testing. + +@item +Bob Manson for his behind the scenes work on dejagnu. + +@item +John Marino for contributing the DragonFly BSD port. + +@item +Philip Martin for lots of libstdc++ string and vector iterator fixes and +improvements, and string clean up and testsuites. + +@item +Michael Matz for his work on dominance tree discovery, the x86-64 port, +link-time optimization framework and general optimization improvements. + +@item +All of the Mauve project contributors for Java test code. + +@item +Bryce McKinlay for numerous GCJ and libgcj fixes and improvements. + +@item +Adam Megacz for his work on the Microsoft Windows port of GCJ@. + +@item +Michael Meissner for LRS framework, ia32, m32r, v850, m88k, MIPS, +powerpc, haifa, ECOFF debug support, and other assorted hacking. + +@item +Jason Merrill for his direction via the steering committee and leading +the G++ effort. + +@item +Martin Michlmayr for testing GCC on several architectures using the +entire Debian archive. + +@item +David Miller for his direction via the steering committee, lots of +SPARC work, improvements in jump.cc and interfacing with the Linux kernel +developers. + +@item +Gary Miller ported GCC to Charles River Data Systems machines. + +@item +Alfred Minarik for libstdc++ string and ios bug fixes, and turning the +entire libstdc++ testsuite namespace-compatible. + +@item +Mark Mitchell for his direction via the steering committee, mountains of +C++ work, load/store hoisting out of loops, alias analysis improvements, +ISO C @code{restrict} support, and serving as release manager from 2000 +to 2011. + +@item +Alan Modra for various GNU/Linux bits and testing. + +@item +Toon Moene for his direction via the steering committee, Fortran +maintenance, and his ongoing work to make us make Fortran run fast. + +@item +Jason Molenda for major help in the care and feeding of all the services +on the gcc.gnu.org (formerly egcs.cygnus.com) machine---mail, web +services, ftp services, etc etc. Doing all this work on scrap paper and +the backs of envelopes would have been@dots{} difficult. + +@item +Catherine Moore for fixing various ugly problems we have sent her +way, including the haifa bug which was killing the Alpha & PowerPC +Linux kernels. + +@item +Mike Moreton for his various Java patches. + +@item +David Mosberger-Tang for various Alpha improvements, and for the initial +IA-64 port. + +@item +Stephen Moshier contributed the floating point emulator that assists in +cross-compilation and permits support for floating point numbers wider +than 64 bits and for ISO C99 support. + +@item +Bill Moyer for his behind the scenes work on various issues. + +@item +Philippe De Muyter for his work on the m68k port. + +@item +Joseph S. Myers for his work on the PDP-11 port, format checking and ISO +C99 support, and continuous emphasis on (and contributions to) documentation. + +@item +Nathan Myers for his work on libstdc++-v3: architecture and authorship +through the first three snapshots, including implementation of locale +infrastructure, string, shadow C headers, and the initial project +documentation (DESIGN, CHECKLIST, and so forth). Later, more work on +MT-safe string and shadow headers. + +@item +Felix Natter for documentation on porting libstdc++. + +@item +Nathanael Nerode for cleaning up the configuration/build process. + +@item +NeXT, Inc.@: donated the front end that supports the Objective-C +language. + +@item +Hans-Peter Nilsson for the CRIS and MMIX ports, improvements to the search +engine setup, various documentation fixes and other small fixes. + +@item +Geoff Noer for his work on getting cygwin native builds working. + +@item +Vegard Nossum for running automated regression testing of GCC and reporting +numerous bugs. + +@item +Diego Novillo for his work on Tree SSA, OpenMP, SPEC performance +tracking web pages, GIMPLE tuples, and assorted fixes. + +@item +David O'Brien for the FreeBSD/alpha, FreeBSD/AMD x86-64, FreeBSD/ARM, +FreeBSD/PowerPC, and FreeBSD/SPARC64 ports and related infrastructure +improvements. + +@item +Alexandre Oliva for various build infrastructure improvements, scripts and +amazing testing work, including keeping libtool issues sane and happy. + +@item +Stefan Olsson for work on mt_alloc. + +@item +Melissa O'Neill for various NeXT fixes. + +@item +Rainer Orth for random MIPS work, including improvements to GCC's o32 +ABI support, improvements to dejagnu's MIPS support, Java configuration +clean-ups and porting work, and maintaining the IRIX, Solaris 2, and +Tru64 UNIX ports. + +@item +Steven Pemberton for his contribution of @file{enquire} which allowed GCC to +determine various properties of the floating point unit and generate +@file{float.h} in older versions of GCC. + +@item +Hartmut Penner for work on the s390 port. + +@item +Paul Petersen wrote the machine description for the Alliant FX/8. + +@item +Alexandre Petit-Bianco for implementing much of the Java compiler and +continued Java maintainership. + +@item +Matthias Pfaller for major improvements to the NS32k port. + +@item +Gerald Pfeifer for his direction via the steering committee, pointing +out lots of problems we need to solve, maintenance of the web pages, and +taking care of documentation maintenance in general. + +@item +Marek Polacek for his work on the C front end, the sanitizers and general +bug fixing. + +@item +Andrew Pinski for processing bug reports by the dozen. + +@item +Ovidiu Predescu for his work on the Objective-C front end and runtime +libraries. + +@item +Jerry Quinn for major performance improvements in C++ formatted I/O@. + +@item +Ken Raeburn for various improvements to checker, MIPS ports and various +cleanups in the compiler. + +@item +Rolf W. Rasmussen for hacking on AWT@. + +@item +David Reese of Sun Microsystems contributed to the Solaris on PowerPC +port. + +@item +John Regehr for running automated regression testing of GCC and reporting +numerous bugs. + +@item +Volker Reichelt for running automated regression testing of GCC and reporting +numerous bugs and for keeping up with the problem reports. + +@item +Joern Rennecke for maintaining the sh port, loop, regmove & reload +hacking and developing and maintaining the Epiphany port. + +@item +Loren J. Rittle for improvements to libstdc++-v3 including the FreeBSD +port, threading fixes, thread-related configury changes, critical +threading documentation, and solutions to really tricky I/O problems, +as well as keeping GCC properly working on FreeBSD and continuous testing. + +@item +Craig Rodrigues for processing tons of bug reports. + +@item +Ola R@"onnerup for work on mt_alloc. + +@item +Gavin Romig-Koch for lots of behind the scenes MIPS work. + +@item +David Ronis inspired and encouraged Craig to rewrite the G77 +documentation in texinfo format by contributing a first pass at a +translation of the old @file{g77-0.5.16/f/DOC} file. + +@item +Ken Rose for fixes to GCC's delay slot filling code. + +@item +Ira Rosen for her contributions to the auto-vectorizer. + +@item +Paul Rubin wrote most of the preprocessor. + +@item +P@'etur Run@'olfsson for major performance improvements in C++ formatted I/O and +large file support in C++ filebuf. + +@item +Chip Salzenberg for libstdc++ patches and improvements to locales, traits, +Makefiles, libio, libtool hackery, and ``long long'' support. + +@item +Juha Sarlin for improvements to the H8 code generator. + +@item +Greg Satz assisted in making GCC work on HP-UX for the 9000 series 300. + +@item +Roger Sayle for improvements to constant folding and GCC's RTL optimizers +as well as for fixing numerous bugs. + +@item +Bradley Schatz for his work on the GCJ FAQ@. + +@item +Peter Schauer wrote the code to allow debugging to work on the Alpha. + +@item +William Schelter did most of the work on the Intel 80386 support. + +@item +Tobias Schl@"uter for work on GNU Fortran. + +@item +Bernd Schmidt for various code generation improvements and major +work in the reload pass, serving as release manager for +GCC 2.95.3, and work on the Blackfin and C6X ports. + +@item +Peter Schmid for constant testing of libstdc++---especially application +testing, going above and beyond what was requested for the release +criteria---and libstdc++ header file tweaks. + +@item +Jason Schroeder for jcf-dump patches. + +@item +Andreas Schwab for his work on the m68k port. + +@item +Lars Segerlund for work on GNU Fortran. + +@item +Dodji Seketeli for numerous C++ bug fixes and debug info improvements. + +@item +Tim Shen for major work on @code{}. + +@item +Joel Sherrill for his direction via the steering committee, RTEMS +contributions and RTEMS testing. + +@item +Nathan Sidwell for many C++ fixes/improvements. + +@item +Jeffrey Siegal for helping RMS with the original design of GCC, some +code which handles the parse tree and RTL data structures, constant +folding and help with the original VAX & m68k ports. + +@item +Kenny Simpson for prompting libstdc++ fixes due to defect reports from +the LWG (thereby keeping GCC in line with updates from the ISO)@. + +@item +Franz Sirl for his ongoing work with making the PPC port stable +for GNU/Linux. + +@item +Andrey Slepuhin for assorted AIX hacking. + +@item +Trevor Smigiel for contributing the SPU port. + +@item +Christopher Smith did the port for Convex machines. + +@item +Danny Smith for his major efforts on the Mingw (and Cygwin) ports. +Retired from GCC maintainership August 2010, having mentored two +new maintainers into the role. + +@item +Randy Smith finished the Sun FPA support. + +@item +Ed Smith-Rowland for his continuous work on libstdc++-v3, special functions, +@code{}, and various improvements to C++11 features. + +@item +Scott Snyder for queue, iterator, istream, and string fixes and libstdc++ +testsuite entries. Also for providing the patch to G77 to add +rudimentary support for @code{INTEGER*1}, @code{INTEGER*2}, and +@code{LOGICAL*1}. + +@item +Zdenek Sojka for running automated regression testing of GCC and reporting +numerous bugs. + +@item +Arseny Solokha for running automated regression testing of GCC and reporting +numerous bugs. + +@item +Jayant Sonar for contributing the CR16 port. + +@item +Brad Spencer for contributions to the GLIBCPP_FORCE_NEW technique. + +@item +Richard Stallman, for writing the original GCC and launching the GNU project. + +@item +Jan Stein of the Chalmers Computer Society provided support for +Genix, as well as part of the 32000 machine description. + +@item +Gerhard Steinmetz for running automated regression testing of GCC and reporting +numerous bugs. + +@item +Nigel Stephens for various mips16 related fixes/improvements. + +@item +Jonathan Stone wrote the machine description for the Pyramid computer. + +@item +Graham Stott for various infrastructure improvements. + +@item +John Stracke for his Java HTTP protocol fixes. + +@item +Mike Stump for his Elxsi port, G++ contributions over the years and more +recently his vxworks contributions + +@item +Jeff Sturm for Java porting help, bug fixes, and encouragement. + +@item +Zhendong Su for running automated regression testing of GCC and reporting +numerous bugs. + +@item +Chengnian Sun for running automated regression testing of GCC and reporting +numerous bugs. + +@item +Shigeya Suzuki for this fixes for the bsdi platforms. + +@item +Ian Lance Taylor for the Go frontend, the initial mips16 and mips64 +support, general configury hacking, fixincludes, etc. + +@item +Holger Teutsch provided the support for the Clipper CPU@. + +@item +Gary Thomas for his ongoing work to make the PPC work for GNU/Linux. + +@item +Paul Thomas for contributions to GNU Fortran. + +@item +Philipp Thomas for random bug fixes throughout the compiler + +@item +Jason Thorpe for thread support in libstdc++ on NetBSD@. + +@item +Kresten Krab Thorup wrote the run time support for the Objective-C +language and the fantastic Java bytecode interpreter. + +@item +Michael Tiemann for random bug fixes, the first instruction scheduler, +initial C++ support, function integration, NS32k, SPARC and M88k +machine description work, delay slot scheduling. + +@item +Andreas Tobler for his work porting libgcj to Darwin. + +@item +Teemu Torma for thread safe exception handling support. + +@item +Leonard Tower wrote parts of the parser, RTL generator, and RTL +definitions, and of the VAX machine description. + +@item +Daniel Towner and Hariharan Sandanagobalane contributed and +maintain the picoChip port. + +@item +Tom Tromey for internationalization support and for his many Java +contributions and libgcj maintainership. + +@item +Lassi Tuura for improvements to config.guess to determine HP processor +types. + +@item +Petter Urkedal for libstdc++ CXXFLAGS, math, and algorithms fixes. + +@item +Andy Vaught for the design and initial implementation of the GNU Fortran +front end. + +@item +Brent Verner for work with the libstdc++ cshadow files and their +associated configure steps. + +@item +Todd Vierling for contributions for NetBSD ports. + +@item +Andrew Waterman for contributing the RISC-V port, as well as maintaining it. + +@item +Jonathan Wakely for contributing libstdc++ Doxygen notes and XHTML +guidance and maintaining libstdc++. + +@item +Dean Wakerley for converting the install documentation from HTML to texinfo +in time for GCC 3.0. + +@item +Krister Walfridsson for random bug fixes. + +@item +Feng Wang for contributions to GNU Fortran. + +@item +Stephen M. Webb for time and effort on making libstdc++ shadow files +work with the tricky Solaris 8+ headers, and for pushing the build-time +header tree. Also, for starting and driving the @code{} effort. + +@item +John Wehle for various improvements for the x86 code generator, +related infrastructure improvements to help x86 code generation, +value range propagation and other work, WE32k port. + +@item +Ulrich Weigand for work on the s390 port. + +@item +Janus Weil for contributions to GNU Fortran. + +@item +Zack Weinberg for major work on cpplib and various other bug fixes. + +@item +Matt Welsh for help with Linux Threads support in GCJ@. + +@item +Urban Widmark for help fixing java.io. + +@item +Mark Wielaard for new Java library code and his work integrating with +Classpath. + +@item +Dale Wiles helped port GCC to the Tahoe. + +@item +Bob Wilson from Tensilica, Inc.@: for the Xtensa port. + +@item +Jim Wilson for his direction via the steering committee, tackling hard +problems in various places that nobody else wanted to work on, strength +reduction and other loop optimizations. + +@item +Paul Woegerer and Tal Agmon for the CRX port. + +@item +Carlo Wood for various fixes. + +@item +Tom Wood for work on the m88k port. + +@item +Chung-Ju Wu for his work on the Andes NDS32 port. + +@item +Canqun Yang for work on GNU Fortran. + +@item +Masanobu Yuhara of Fujitsu Laboratories implemented the machine +description for the Tron architecture (specifically, the Gmicro). + +@item +Kevin Zachmann helped port GCC to the Tahoe. + +@item +Ayal Zaks for Swing Modulo Scheduling (SMS). + +@item +Qirun Zhang for running automated regression testing of GCC and reporting +numerous bugs. + +@item +Xiaoqiang Zhang for work on GNU Fortran. + +@item +Gilles Zunino for help porting Java to Irix. + +@end itemize + +The following people are recognized for their contributions to GNAT, +the Ada front end of GCC: +@itemize @bullet +@item +Bernard Banner + +@item +Romain Berrendonner + +@item +Geert Bosch + +@item +Emmanuel Briot + +@item +Joel Brobecker + +@item +Ben Brosgol + +@item +Vincent Celier + +@item +Arnaud Charlet + +@item +Chien Chieng + +@item +Cyrille Comar + +@item +Cyrille Crozes + +@item +Robert Dewar + +@item +Gary Dismukes + +@item +Robert Duff + +@item +Ed Falis + +@item +Ramon Fernandez + +@item +Sam Figueroa + +@item +Vasiliy Fofanov + +@item +Michael Friess + +@item +Franco Gasperoni + +@item +Ted Giering + +@item +Matthew Gingell + +@item +Laurent Guerby + +@item +Jerome Guitton + +@item +Olivier Hainque + +@item +Jerome Hugues + +@item +Hristian Kirtchev + +@item +Jerome Lambourg + +@item +Bruno Leclerc + +@item +Albert Lee + +@item +Sean McNeil + +@item +Javier Miranda + +@item +Laurent Nana + +@item +Pascal Obry + +@item +Dong-Ik Oh + +@item +Laurent Pautet + +@item +Brett Porter + +@item +Thomas Quinot + +@item +Nicolas Roche + +@item +Pat Rogers + +@item +Jose Ruiz + +@item +Douglas Rupp + +@item +Sergey Rybin + +@item +Gail Schenker + +@item +Ed Schonberg + +@item +Nicolas Setton + +@item +Samuel Tardieu + +@end itemize + + +The following people are recognized for their contributions of new +features, bug reports, testing and integration of classpath/libgcj for +GCC version 4.1: +@itemize @bullet +@item +Lillian Angel for @code{JTree} implementation and lots Free Swing +additions and bug fixes. + +@item +Wolfgang Baer for @code{GapContent} bug fixes. + +@item +Anthony Balkissoon for @code{JList}, Free Swing 1.5 updates and mouse event +fixes, lots of Free Swing work including @code{JTable} editing. + +@item +Stuart Ballard for RMI constant fixes. + +@item +Goffredo Baroncelli for @code{HTTPURLConnection} fixes. + +@item +Gary Benson for @code{MessageFormat} fixes. + +@item +Daniel Bonniot for @code{Serialization} fixes. + +@item +Chris Burdess for lots of gnu.xml and http protocol fixes, @code{StAX} +and @code{DOM xml:id} support. + +@item +Ka-Hing Cheung for @code{TreePath} and @code{TreeSelection} fixes. + +@item +Archie Cobbs for build fixes, VM interface updates, +@code{URLClassLoader} updates. + +@item +Kelley Cook for build fixes. + +@item +Martin Cordova for Suggestions for better @code{SocketTimeoutException}. + +@item +David Daney for @code{BitSet} bug fixes, @code{HttpURLConnection} +rewrite and improvements. + +@item +Thomas Fitzsimmons for lots of upgrades to the gtk+ AWT and Cairo 2D +support. Lots of imageio framework additions, lots of AWT and Free +Swing bug fixes. + +@item +Jeroen Frijters for @code{ClassLoader} and nio cleanups, serialization fixes, +better @code{Proxy} support, bug fixes and IKVM integration. + +@item +Santiago Gala for @code{AccessControlContext} fixes. + +@item +Nicolas Geoffray for @code{VMClassLoader} and @code{AccessController} +improvements. + +@item +David Gilbert for @code{basic} and @code{metal} icon and plaf support +and lots of documenting, Lots of Free Swing and metal theme +additions. @code{MetalIconFactory} implementation. + +@item +Anthony Green for @code{MIDI} framework, @code{ALSA} and @code{DSSI} +providers. + +@item +Andrew Haley for @code{Serialization} and @code{URLClassLoader} fixes, +gcj build speedups. + +@item +Kim Ho for @code{JFileChooser} implementation. + +@item +Andrew John Hughes for @code{Locale} and net fixes, URI RFC2986 +updates, @code{Serialization} fixes, @code{Properties} XML support and +generic branch work, VMIntegration guide update. + +@item +Bastiaan Huisman for @code{TimeZone} bug fixing. + +@item +Andreas Jaeger for mprec updates. + +@item +Paul Jenner for better @option{-Werror} support. + +@item +Ito Kazumitsu for @code{NetworkInterface} implementation and updates. + +@item +Roman Kennke for @code{BoxLayout}, @code{GrayFilter} and +@code{SplitPane}, plus bug fixes all over. Lots of Free Swing work +including styled text. + +@item +Simon Kitching for @code{String} cleanups and optimization suggestions. + +@item +Michael Koch for configuration fixes, @code{Locale} updates, bug and +build fixes. + +@item +Guilhem Lavaux for configuration, thread and channel fixes and Kaffe +integration. JCL native @code{Pointer} updates. Logger bug fixes. + +@item +David Lichteblau for JCL support library global/local reference +cleanups. + +@item +Aaron Luchko for JDWP updates and documentation fixes. + +@item +Ziga Mahkovec for @code{Graphics2D} upgraded to Cairo 0.5 and new regex +features. + +@item +Sven de Marothy for BMP imageio support, CSS and @code{TextLayout} +fixes. @code{GtkImage} rewrite, 2D, awt, free swing and date/time fixes and +implementing the Qt4 peers. + +@item +Casey Marshall for crypto algorithm fixes, @code{FileChannel} lock, +@code{SystemLogger} and @code{FileHandler} rotate implementations, NIO +@code{FileChannel.map} support, security and policy updates. + +@item +Bryce McKinlay for RMI work. + +@item +Audrius Meskauskas for lots of Free Corba, RMI and HTML work plus +testing and documenting. + +@item +Kalle Olavi Niemitalo for build fixes. + +@item +Rainer Orth for build fixes. + +@item +Andrew Overholt for @code{File} locking fixes. + +@item +Ingo Proetel for @code{Image}, @code{Logger} and @code{URLClassLoader} +updates. + +@item +Olga Rodimina for @code{MenuSelectionManager} implementation. + +@item +Jan Roehrich for @code{BasicTreeUI} and @code{JTree} fixes. + +@item +Julian Scheid for documentation updates and gjdoc support. + +@item +Christian Schlichtherle for zip fixes and cleanups. + +@item +Robert Schuster for documentation updates and beans fixes, +@code{TreeNode} enumerations and @code{ActionCommand} and various +fixes, XML and URL, AWT and Free Swing bug fixes. + +@item +Keith Seitz for lots of JDWP work. + +@item +Christian Thalinger for 64-bit cleanups, Configuration and VM +interface fixes and @code{CACAO} integration, @code{fdlibm} updates. + +@item +Gael Thomas for @code{VMClassLoader} boot packages support suggestions. + +@item +Andreas Tobler for Darwin and Solaris testing and fixing, @code{Qt4} +support for Darwin/OS X, @code{Graphics2D} support, @code{gtk+} +updates. + +@item +Dalibor Topic for better @code{DEBUG} support, build cleanups and +Kaffe integration. @code{Qt4} build infrastructure, @code{SHA1PRNG} +and @code{GdkPixbugDecoder} updates. + +@item +Tom Tromey for Eclipse integration, generics work, lots of bug fixes +and gcj integration including coordinating The Big Merge. + +@item +Mark Wielaard for bug fixes, packaging and release management, +@code{Clipboard} implementation, system call interrupts and network +timeouts and @code{GdkPixpufDecoder} fixes. + +@end itemize + + +In addition to the above, all of which also contributed time and energy in +testing GCC, we would like to thank the following for their contributions +to testing: + +@itemize @bullet +@item +Michael Abd-El-Malek + +@item +Thomas Arend + +@item +Bonzo Armstrong + +@item +Steven Ashe + +@item +Chris Baldwin + +@item +David Billinghurst + +@item +Jim Blandy + +@item +Stephane Bortzmeyer + +@item +Horst von Brand + +@item +Frank Braun + +@item +Rodney Brown + +@item +Sidney Cadot + +@item +Bradford Castalia + +@item +Robert Clark + +@item +Jonathan Corbet + +@item +Ralph Doncaster + +@item +Richard Emberson + +@item +Levente Farkas + +@item +Graham Fawcett + +@item +Mark Fernyhough + +@item +Robert A. French + +@item +J@"orgen Freyh + +@item +Mark K. Gardner + +@item +Charles-Antoine Gauthier + +@item +Yung Shing Gene + +@item +David Gilbert + +@item +Simon Gornall + +@item +Fred Gray + +@item +John Griffin + +@item +Patrik Hagglund + +@item +Phil Hargett + +@item +Amancio Hasty + +@item +Takafumi Hayashi + +@item +Bryan W. Headley + +@item +Kevin B. Hendricks + +@item +Joep Jansen + +@item +Christian Joensson + +@item +Michel Kern + +@item +David Kidd + +@item +Tobias Kuipers + +@item +Anand Krishnaswamy + +@item +A. O. V. Le Blanc + +@item +llewelly + +@item +Damon Love + +@item +Brad Lucier + +@item +Matthias Klose + +@item +Martin Knoblauch + +@item +Rick Lutowski + +@item +Jesse Macnish + +@item +Stefan Morrell + +@item +Anon A. Mous + +@item +Matthias Mueller + +@item +Pekka Nikander + +@item +Rick Niles + +@item +Jon Olson + +@item +Magnus Persson + +@item +Chris Pollard + +@item +Richard Polton + +@item +Derk Reefman + +@item +David Rees + +@item +Paul Reilly + +@item +Tom Reilly + +@item +Torsten Rueger + +@item +Danny Sadinoff + +@item +Marc Schifer + +@item +Erik Schnetter + +@item +Wayne K. Schroll + +@item +David Schuler + +@item +Vin Shelton + +@item +Tim Souder + +@item +Adam Sulmicki + +@item +Bill Thorson + +@item +George Talbot + +@item +Pedro A. M. Vazquez + +@item +Gregory Warnes + +@item +Ian Watson + +@item +David E. Young + +@item +And many others +@end itemize + +And finally we'd like to thank everyone who uses the compiler, provides +feedback and generally reminds us why we're doing this work in the first +place. diff --git a/gcc/doc/contribute.texi b/gcc/doc/contribute.texi new file mode 100644 index 00000000000..74d8670348b --- /dev/null +++ b/gcc/doc/contribute.texi @@ -0,0 +1,24 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Contributing +@chapter Contributing to GCC Development + +If you would like to help pretest GCC releases to assure they work well, +current development sources are available via Git (see +@uref{https://gcc.gnu.org/git.html}). Source and binary snapshots are +also available for FTP; see @uref{https://gcc.gnu.org/snapshots.html}. + +If you would like to work on improvements to GCC, please read the +advice at these URLs: + +@smallexample +@uref{https://gcc.gnu.org/contribute.html} +@uref{https://gcc.gnu.org/contributewhy.html} +@end smallexample + +@noindent +for information on how to make useful contributions and avoid +duplication of effort. Suggested projects are listed at +@uref{https://gcc.gnu.org/projects/}. diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi new file mode 100644 index 00000000000..90b2767e39a --- /dev/null +++ b/gcc/doc/cpp.texi @@ -0,0 +1,4600 @@ +\input texinfo +@setfilename cpp.info +@settitle The C Preprocessor +@setchapternewpage off +@c @smallbook +@c @cropmarks +@c @finalout + +@include gcc-common.texi + +@copying +@c man begin COPYRIGHT +Copyright @copyright{} 1987-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation. A copy of +the license is included in the +@c man end +section entitled ``GNU Free Documentation License''. +@ignore +@c man begin COPYRIGHT +man page gfdl(7). +@c man end +@end ignore + +@c man begin COPYRIGHT +This manual contains no Invariant Sections. The Front-Cover Texts are +(a) (see below), and the Back-Cover Texts are (b) (see below). + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@end copying + +@c Create a separate index for command line options. +@defcodeindex op +@syncodeindex vr op + +@c Used in cppopts.texi and cppenv.texi. +@set cppmanual + +@ifinfo +@dircategory Software development +@direntry +* Cpp: (cpp). The GNU C preprocessor. +@end direntry +@end ifinfo + +@titlepage +@title The C Preprocessor +@versionsubtitle +@author Richard M. Stallman, Zachary Weinberg +@page +@c There is a fill at the bottom of the page, so we need a filll to +@c override it. +@vskip 0pt plus 1filll +@insertcopying +@end titlepage +@contents +@page + +@ifnottex +@node Top +@top +The C preprocessor implements the macro language used to transform C, +C++, and Objective-C programs before they are compiled. It can also be +useful on its own. + +@menu +* Overview:: +* Header Files:: +* Macros:: +* Conditionals:: +* Diagnostics:: +* Line Control:: +* Pragmas:: +* Other Directives:: +* Preprocessor Output:: +* Traditional Mode:: +* Implementation Details:: +* Invocation:: +* Environment Variables:: +* GNU Free Documentation License:: +* Index of Directives:: +* Option Index:: +* Concept Index:: + +@detailmenu + --- The Detailed Node Listing --- + +Overview + +* Character sets:: +* Initial processing:: +* Tokenization:: +* The preprocessing language:: + +Header Files + +* Include Syntax:: +* Include Operation:: +* Search Path:: +* Once-Only Headers:: +* Alternatives to Wrapper #ifndef:: +* Computed Includes:: +* Wrapper Headers:: +* System Headers:: + +Macros + +* Object-like Macros:: +* Function-like Macros:: +* Macro Arguments:: +* Stringizing:: +* Concatenation:: +* Variadic Macros:: +* Predefined Macros:: +* Undefining and Redefining Macros:: +* Directives Within Macro Arguments:: +* Macro Pitfalls:: + +Predefined Macros + +* Standard Predefined Macros:: +* Common Predefined Macros:: +* System-specific Predefined Macros:: +* C++ Named Operators:: + +Macro Pitfalls + +* Misnesting:: +* Operator Precedence Problems:: +* Swallowing the Semicolon:: +* Duplication of Side Effects:: +* Self-Referential Macros:: +* Argument Prescan:: +* Newlines in Arguments:: + +Conditionals + +* Conditional Uses:: +* Conditional Syntax:: +* Deleted Code:: + +Conditional Syntax + +* Ifdef:: +* If:: +* Defined:: +* Else:: +* Elif:: + +Implementation Details + +* Implementation-defined behavior:: +* Implementation limits:: +* Obsolete Features:: + +Obsolete Features + +* Obsolete Features:: + +@end detailmenu +@end menu + +@insertcopying +@end ifnottex + +@node Overview +@chapter Overview +@c man begin DESCRIPTION +The C preprocessor, often known as @dfn{cpp}, is a @dfn{macro processor} +that is used automatically by the C compiler to transform your program +before compilation. It is called a macro processor because it allows +you to define @dfn{macros}, which are brief abbreviations for longer +constructs. + +The C preprocessor is intended to be used only with C, C++, and +Objective-C source code. In the past, it has been abused as a general +text processor. It will choke on input which does not obey C's lexical +rules. For example, apostrophes will be interpreted as the beginning of +character constants, and cause errors. Also, you cannot rely on it +preserving characteristics of the input which are not significant to +C-family languages. If a Makefile is preprocessed, all the hard tabs +will be removed, and the Makefile will not work. + +Having said that, you can often get away with using cpp on things which +are not C@. Other Algol-ish programming languages are often safe +(Ada, etc.) So is assembly, with caution. @option{-traditional-cpp} +mode preserves more white space, and is otherwise more permissive. Many +of the problems can be avoided by writing C or C++ style comments +instead of native language comments, and keeping macros simple. + +Wherever possible, you should use a preprocessor geared to the language +you are writing in. Modern versions of the GNU assembler have macro +facilities. Most high level programming languages have their own +conditional compilation and inclusion mechanism. If all else fails, +try a true general text processor, such as GNU M4. + +C preprocessors vary in some details. This manual discusses the GNU C +preprocessor, which provides a small superset of the features of ISO +Standard C@. In its default mode, the GNU C preprocessor does not do a +few things required by the standard. These are features which are +rarely, if ever, used, and may cause surprising changes to the meaning +of a program which does not expect them. To get strict ISO Standard C, +you should use the @option{-std=c90}, @option{-std=c99}, +@option{-std=c11} or @option{-std=c17} options, depending +on which version of the standard you want. To get all the mandatory +diagnostics, you must also use @option{-pedantic}. @xref{Invocation}. + +This manual describes the behavior of the ISO preprocessor. To +minimize gratuitous differences, where the ISO preprocessor's +behavior does not conflict with traditional semantics, the +traditional preprocessor should behave the same way. The various +differences that do exist are detailed in the section @ref{Traditional +Mode}. + +For clarity, unless noted otherwise, references to @samp{CPP} in this +manual refer to GNU CPP@. +@c man end + +@menu +* Character sets:: +* Initial processing:: +* Tokenization:: +* The preprocessing language:: +@end menu + +@node Character sets +@section Character sets + +Source code character set processing in C and related languages is +rather complicated. The C standard discusses two character sets, but +there are really at least four. + +The files input to CPP might be in any character set at all. CPP's +very first action, before it even looks for line boundaries, is to +convert the file into the character set it uses for internal +processing. That set is what the C standard calls the @dfn{source} +character set. It must be isomorphic with ISO 10646, also known as +Unicode. CPP uses the UTF-8 encoding of Unicode. + +The character sets of the input files are specified using the +@option{-finput-charset=} option. + +All preprocessing work (the subject of the rest of this manual) is +carried out in the source character set. If you request textual +output from the preprocessor with the @option{-E} option, it will be +in UTF-8. + +After preprocessing is complete, string and character constants are +converted again, into the @dfn{execution} character set. This +character set is under control of the user; the default is UTF-8, +matching the source character set. Wide string and character +constants have their own character set, which is not called out +specifically in the standard. Again, it is under control of the user. +The default is UTF-16 or UTF-32, whichever fits in the target's +@code{wchar_t} type, in the target machine's byte +order.@footnote{UTF-16 does not meet the requirements of the C +standard for a wide character set, but the choice of 16-bit +@code{wchar_t} is enshrined in some system ABIs so we cannot fix +this.} Octal and hexadecimal escape sequences do not undergo +conversion; @t{'\x12'} has the value 0x12 regardless of the currently +selected execution character set. All other escapes are replaced by +the character in the source character set that they represent, then +converted to the execution character set, just like unescaped +characters. + +In identifiers, characters outside the ASCII range can be specified +with the @samp{\u} and @samp{\U} escapes or used directly in the input +encoding. If strict ISO C90 conformance is specified with an option +such as @option{-std=c90}, or @option{-fno-extended-identifiers} is +used, then those constructs are not permitted in identifiers. + +@node Initial processing +@section Initial processing + +The preprocessor performs a series of textual transformations on its +input. These happen before all other processing. Conceptually, they +happen in a rigid order, and the entire file is run through each +transformation before the next one begins. CPP actually does them +all at once, for performance reasons. These transformations correspond +roughly to the first three ``phases of translation'' described in the C +standard. + +@enumerate +@item +@cindex line endings +The input file is read into memory and broken into lines. + +Different systems use different conventions to indicate the end of a +line. GCC accepts the ASCII control sequences @kbd{LF}, @kbd{@w{CR +LF}} and @kbd{CR} as end-of-line markers. These are the canonical +sequences used by Unix, DOS and VMS, and the classic Mac OS (before +OSX) respectively. You may therefore safely copy source code written +on any of those systems to a different one and use it without +conversion. (GCC may lose track of the current line number if a file +doesn't consistently use one convention, as sometimes happens when it +is edited on computers with different conventions that share a network +file system.) + +If the last line of any input file lacks an end-of-line marker, the end +of the file is considered to implicitly supply one. The C standard says +that this condition provokes undefined behavior, so GCC will emit a +warning message. + +@item +@cindex trigraphs +@anchor{trigraphs}If trigraphs are enabled, they are replaced by their +corresponding single characters. By default GCC ignores trigraphs, +but if you request a strictly conforming mode with the @option{-std} +option, or you specify the @option{-trigraphs} option, then it +converts them. + +These are nine three-character sequences, all starting with @samp{??}, +that are defined by ISO C to stand for single characters. They permit +obsolete systems that lack some of C's punctuation to use C@. For +example, @samp{??/} stands for @samp{\}, so @t{'??/n'} is a character +constant for a newline. + +Trigraphs are not popular and many compilers implement them +incorrectly. Portable code should not rely on trigraphs being either +converted or ignored. With @option{-Wtrigraphs} GCC will warn you +when a trigraph may change the meaning of your program if it were +converted. @xref{Wtrigraphs}. + +In a string constant, you can prevent a sequence of question marks +from being confused with a trigraph by inserting a backslash between +the question marks, or by separating the string literal at the +trigraph and making use of string literal concatenation. @t{"(??\?)"} +is the string @samp{(???)}, not @samp{(?]}. Traditional C compilers +do not recognize these idioms. + +The nine trigraphs and their replacements are + +@smallexample +Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- +Replacement: [ ] @{ @} # \ ^ | ~ +@end smallexample + +@item +@cindex continued lines +@cindex backslash-newline +Continued lines are merged into one long line. + +A continued line is a line which ends with a backslash, @samp{\}. The +backslash is removed and the following line is joined with the current +one. No space is inserted, so you may split a line anywhere, even in +the middle of a word. (It is generally more readable to split lines +only at white space.) + +The trailing backslash on a continued line is commonly referred to as a +@dfn{backslash-newline}. + +If there is white space between a backslash and the end of a line, that +is still a continued line. However, as this is usually the result of an +editing mistake, and many compilers will not accept it as a continued +line, GCC will warn you about it. + +@item +@cindex comments +@cindex line comments +@cindex block comments +All comments are replaced with single spaces. + +There are two kinds of comments. @dfn{Block comments} begin with +@samp{/*} and continue until the next @samp{*/}. Block comments do not +nest: + +@smallexample +/* @r{this is} /* @r{one comment} */ @r{text outside comment} +@end smallexample + +@dfn{Line comments} begin with @samp{//} and continue to the end of the +current line. Line comments do not nest either, but it does not matter, +because they would end in the same place anyway. + +@smallexample +// @r{this is} // @r{one comment} +@r{text outside comment} +@end smallexample +@end enumerate + +It is safe to put line comments inside block comments, or vice versa. + +@smallexample +@group +/* @r{block comment} + // @r{contains line comment} + @r{yet more comment} + */ @r{outside comment} + +// @r{line comment} /* @r{contains block comment} */ +@end group +@end smallexample + +But beware of commenting out one end of a block comment with a line +comment. + +@smallexample +@group + // @r{l.c.} /* @r{block comment begins} + @r{oops! this isn't a comment anymore} */ +@end group +@end smallexample + +Comments are not recognized within string literals. +@t{@w{"/* blah */"}} is the string constant @samp{@w{/* blah */}}, not +an empty string. + +Line comments are not in the 1989 edition of the C standard, but they +are recognized by GCC as an extension. In C++ and in the 1999 edition +of the C standard, they are an official part of the language. + +Since these transformations happen before all other processing, you can +split a line mechanically with backslash-newline anywhere. You can +comment out the end of a line. You can continue a line comment onto the +next line with backslash-newline. You can even split @samp{/*}, +@samp{*/}, and @samp{//} onto multiple lines with backslash-newline. +For example: + +@smallexample +@group +/\ +* +*/ # /* +*/ defi\ +ne FO\ +O 10\ +20 +@end group +@end smallexample + +@noindent +is equivalent to @code{@w{#define FOO 1020}}. All these tricks are +extremely confusing and should not be used in code intended to be +readable. + +There is no way to prevent a backslash at the end of a line from being +interpreted as a backslash-newline. This cannot affect any correct +program, however. + +@node Tokenization +@section Tokenization + +@cindex tokens +@cindex preprocessing tokens +After the textual transformations are finished, the input file is +converted into a sequence of @dfn{preprocessing tokens}. These mostly +correspond to the syntactic tokens used by the C compiler, but there are +a few differences. White space separates tokens; it is not itself a +token of any kind. Tokens do not have to be separated by white space, +but it is often necessary to avoid ambiguities. + +When faced with a sequence of characters that has more than one possible +tokenization, the preprocessor is greedy. It always makes each token, +starting from the left, as big as possible before moving on to the next +token. For instance, @code{a+++++b} is interpreted as +@code{@w{a ++ ++ + b}}, not as @code{@w{a ++ + ++ b}}, even though the +latter tokenization could be part of a valid C program and the former +could not. + +Once the input file is broken into tokens, the token boundaries never +change, except when the @samp{##} preprocessing operator is used to paste +tokens together. @xref{Concatenation}. For example, + +@smallexample +@group +#define foo() bar +foo()baz + @expansion{} bar baz +@emph{not} + @expansion{} barbaz +@end group +@end smallexample + +The compiler does not re-tokenize the preprocessor's output. Each +preprocessing token becomes one compiler token. + +@cindex identifiers +Preprocessing tokens fall into five broad classes: identifiers, +preprocessing numbers, string literals, punctuators, and other. An +@dfn{identifier} is the same as an identifier in C: any sequence of +letters, digits, or underscores, which begins with a letter or +underscore. Keywords of C have no significance to the preprocessor; +they are ordinary identifiers. You can define a macro whose name is a +keyword, for instance. The only identifier which can be considered a +preprocessing keyword is @code{defined}. @xref{Defined}. + +This is mostly true of other languages which use the C preprocessor. +However, a few of the keywords of C++ are significant even in the +preprocessor. @xref{C++ Named Operators}. + +In the 1999 C standard, identifiers may contain letters which are not +part of the ``basic source character set'', at the implementation's +discretion (such as accented Latin letters, Greek letters, or Chinese +ideograms). This may be done with an extended character set, or the +@samp{\u} and @samp{\U} escape sequences. + +As an extension, GCC treats @samp{$} as a letter. This is for +compatibility with some systems, such as VMS, where @samp{$} is commonly +used in system-defined function and object names. @samp{$} is not a +letter in strictly conforming mode, or if you specify the @option{-$} +option. @xref{Invocation}. + +@cindex numbers +@cindex preprocessing numbers +A @dfn{preprocessing number} has a rather bizarre definition. The +category includes all the normal integer and floating point constants +one expects of C, but also a number of other things one might not +initially recognize as a number. Formally, preprocessing numbers begin +with an optional period, a required decimal digit, and then continue +with any sequence of letters, digits, underscores, periods, and +exponents. Exponents are the two-character sequences @samp{e+}, +@samp{e-}, @samp{E+}, @samp{E-}, @samp{p+}, @samp{p-}, @samp{P+}, and +@samp{P-}. (The exponents that begin with @samp{p} or @samp{P} are +used for hexadecimal floating-point constants.) + +The purpose of this unusual definition is to isolate the preprocessor +from the full complexity of numeric constants. It does not have to +distinguish between lexically valid and invalid floating-point numbers, +which is complicated. The definition also permits you to split an +identifier at any position and get exactly two tokens, which can then be +pasted back together with the @samp{##} operator. + +It's possible for preprocessing numbers to cause programs to be +misinterpreted. For example, @code{0xE+12} is a preprocessing number +which does not translate to any valid numeric constant, therefore a +syntax error. It does not mean @code{@w{0xE + 12}}, which is what you +might have intended. + +@cindex string literals +@cindex string constants +@cindex character constants +@cindex header file names +@c the @: prevents makeinfo from turning '' into ". +@dfn{String literals} are string constants, character constants, and +header file names (the argument of @samp{#include}).@footnote{The C +standard uses the term @dfn{string literal} to refer only to what we are +calling @dfn{string constants}.} String constants and character +constants are straightforward: @t{"@dots{}"} or @t{'@dots{}'}. In +either case embedded quotes should be escaped with a backslash: +@t{'\'@:'} is the character constant for @samp{'}. There is no limit on +the length of a character constant, but the value of a character +constant that contains more than one character is +implementation-defined. @xref{Implementation Details}. + +Header file names either look like string constants, @t{"@dots{}"}, or are +written with angle brackets instead, @t{<@dots{}>}. In either case, +backslash is an ordinary character. There is no way to escape the +closing quote or angle bracket. The preprocessor looks for the header +file in different places depending on which form you use. @xref{Include +Operation}. + +No string literal may extend past the end of a line. You may use continued +lines instead, or string constant concatenation. + +@cindex punctuators +@cindex digraphs +@cindex alternative tokens +@dfn{Punctuators} are all the usual bits of punctuation which are +meaningful to C and C++. All but three of the punctuation characters in +ASCII are C punctuators. The exceptions are @samp{@@}, @samp{$}, and +@samp{`}. In addition, all the two- and three-character operators are +punctuators. There are also six @dfn{digraphs}, which the C++ standard +calls @dfn{alternative tokens}, which are merely alternate ways to spell +other punctuators. This is a second attempt to work around missing +punctuation in obsolete systems. It has no negative side effects, +unlike trigraphs, but does not cover as much ground. The digraphs and +their corresponding normal punctuators are: + +@smallexample +Digraph: <% %> <: :> %: %:%: +Punctuator: @{ @} [ ] # ## +@end smallexample + +@cindex other tokens +Any other single byte is considered ``other'' and passed on to the +preprocessor's output unchanged. The C compiler will almost certainly +reject source code containing ``other'' tokens. In ASCII, the only +``other'' characters are @samp{@@}, @samp{$}, @samp{`}, and control +characters other than NUL (all bits zero). (Note that @samp{$} is +normally considered a letter.) All bytes with the high bit set +(numeric range 0x7F--0xFF) that were not succesfully interpreted as +part of an extended character in the input encoding are also ``other'' +in the present implementation. + +NUL is a special case because of the high probability that its +appearance is accidental, and because it may be invisible to the user +(many terminals do not display NUL at all). Within comments, NULs are +silently ignored, just as any other character would be. In running +text, NUL is considered white space. For example, these two directives +have the same meaning. + +@smallexample +#define X^@@1 +#define X 1 +@end smallexample + +@noindent +(where @samp{^@@} is ASCII NUL)@. Within string or character constants, +NULs are preserved. In the latter two cases the preprocessor emits a +warning message. + +@node The preprocessing language +@section The preprocessing language +@cindex directives +@cindex preprocessing directives +@cindex directive line +@cindex directive name + +After tokenization, the stream of tokens may simply be passed straight +to the compiler's parser. However, if it contains any operations in the +@dfn{preprocessing language}, it will be transformed first. This stage +corresponds roughly to the standard's ``translation phase 4'' and is +what most people think of as the preprocessor's job. + +The preprocessing language consists of @dfn{directives} to be executed +and @dfn{macros} to be expanded. Its primary capabilities are: + +@itemize @bullet +@item +Inclusion of header files. These are files of declarations that can be +substituted into your program. + +@item +Macro expansion. You can define @dfn{macros}, which are abbreviations +for arbitrary fragments of C code. The preprocessor will replace the +macros with their definitions throughout the program. Some macros are +automatically defined for you. + +@item +Conditional compilation. You can include or exclude parts of the +program according to various conditions. + +@item +Line control. If you use a program to combine or rearrange source files +into an intermediate file which is then compiled, you can use line +control to inform the compiler where each source line originally came +from. + +@item +Diagnostics. You can detect problems at compile time and issue errors +or warnings. +@end itemize + +There are a few more, less useful, features. + +Except for expansion of predefined macros, all these operations are +triggered with @dfn{preprocessing directives}. Preprocessing directives +are lines in your program that start with @samp{#}. Whitespace is +allowed before and after the @samp{#}. The @samp{#} is followed by an +identifier, the @dfn{directive name}. It specifies the operation to +perform. Directives are commonly referred to as @samp{#@var{name}} +where @var{name} is the directive name. For example, @samp{#define} is +the directive that defines a macro. + +The @samp{#} which begins a directive cannot come from a macro +expansion. Also, the directive name is not macro expanded. Thus, if +@code{foo} is defined as a macro expanding to @code{define}, that does +not make @samp{#foo} a valid preprocessing directive. + +The set of valid directive names is fixed. Programs cannot define new +preprocessing directives. + +Some directives require arguments; these make up the rest of the +directive line and must be separated from the directive name by +whitespace. For example, @samp{#define} must be followed by a macro +name and the intended expansion of the macro. + +A preprocessing directive cannot cover more than one line. The line +may, however, be continued with backslash-newline, or by a block comment +which extends past the end of the line. In either case, when the +directive is processed, the continuations have already been merged with +the first line to make one long line. + +@node Header Files +@chapter Header Files + +@cindex header file +A header file is a file containing C declarations and macro definitions +(@pxref{Macros}) to be shared between several source files. You request +the use of a header file in your program by @dfn{including} it, with the +C preprocessing directive @samp{#include}. + +Header files serve two purposes. + +@itemize @bullet +@item +@cindex system header files +System header files declare the interfaces to parts of the operating +system. You include them in your program to supply the definitions and +declarations you need to invoke system calls and libraries. + +@item +Your own header files contain declarations for interfaces between the +source files of your program. Each time you have a group of related +declarations and macro definitions all or most of which are needed in +several different source files, it is a good idea to create a header +file for them. +@end itemize + +Including a header file produces the same results as copying the header +file into each source file that needs it. Such copying would be +time-consuming and error-prone. With a header file, the related +declarations appear in only one place. If they need to be changed, they +can be changed in one place, and programs that include the header file +will automatically use the new version when next recompiled. The header +file eliminates the labor of finding and changing all the copies as well +as the risk that a failure to find one copy will result in +inconsistencies within a program. + +In C, the usual convention is to give header files names that end with +@file{.h}. It is most portable to use only letters, digits, dashes, and +underscores in header file names, and at most one dot. + +@menu +* Include Syntax:: +* Include Operation:: +* Search Path:: +* Once-Only Headers:: +* Alternatives to Wrapper #ifndef:: +* Computed Includes:: +* Wrapper Headers:: +* System Headers:: +@end menu + +@node Include Syntax +@section Include Syntax + +@findex #include +Both user and system header files are included using the preprocessing +directive @samp{#include}. It has two variants: + +@table @code +@item #include <@var{file}> +This variant is used for system header files. It searches for a file +named @var{file} in a standard list of system directories. You can prepend +directories to this list with the @option{-I} option (@pxref{Invocation}). + +@item #include "@var{file}" +This variant is used for header files of your own program. It +searches for a file named @var{file} first in the directory containing +the current file, then in the quote directories and then the same +directories used for @code{<@var{file}>}. You can prepend directories +to the list of quote directories with the @option{-iquote} option. +@end table + +The argument of @samp{#include}, whether delimited with quote marks or +angle brackets, behaves like a string constant in that comments are not +recognized, and macro names are not expanded. Thus, @code{@w{#include +}} specifies inclusion of a system header file named @file{x/*y}. + +However, if backslashes occur within @var{file}, they are considered +ordinary text characters, not escape characters. None of the character +escape sequences appropriate to string constants in C are processed. +Thus, @code{@w{#include "x\n\\y"}} specifies a filename containing three +backslashes. (Some systems interpret @samp{\} as a pathname separator. +All of these also interpret @samp{/} the same way. It is most portable +to use only @samp{/}.) + +It is an error if there is anything (other than comments) on the line +after the file name. + +@node Include Operation +@section Include Operation + +The @samp{#include} directive works by directing the C preprocessor to +scan the specified file as input before continuing with the rest of the +current file. The output from the preprocessor contains the output +already generated, followed by the output resulting from the included +file, followed by the output that comes from the text after the +@samp{#include} directive. For example, if you have a header file +@file{header.h} as follows, + +@smallexample +char *test (void); +@end smallexample + +@noindent +and a main program called @file{program.c} that uses the header file, +like this, + +@smallexample +int x; +#include "header.h" + +int +main (void) +@{ + puts (test ()); +@} +@end smallexample + +@noindent +the compiler will see the same token stream as it would if +@file{program.c} read + +@smallexample +int x; +char *test (void); + +int +main (void) +@{ + puts (test ()); +@} +@end smallexample + +Included files are not limited to declarations and macro definitions; +those are merely the typical uses. Any fragment of a C program can be +included from another file. The include file could even contain the +beginning of a statement that is concluded in the containing file, or +the end of a statement that was started in the including file. However, +an included file must consist of complete tokens. Comments and string +literals which have not been closed by the end of an included file are +invalid. For error recovery, they are considered to end at the end of +the file. + +To avoid confusion, it is best if header files contain only complete +syntactic units---function declarations or definitions, type +declarations, etc. + +The line following the @samp{#include} directive is always treated as a +separate line by the C preprocessor, even if the included file lacks a +final newline. + +@node Search Path +@section Search Path + +By default, the preprocessor looks for header files included by the quote +form of the directive @code{@w{#include "@var{file}"}} first relative to +the directory of the current file, and then in a preconfigured list +of standard system directories. +For example, if @file{/usr/include/sys/stat.h} contains +@code{@w{#include "types.h"}}, GCC looks for @file{types.h} first in +@file{/usr/include/sys}, then in its usual search path. + +For the angle-bracket form @code{@w{#include <@var{file}>}}, the +preprocessor's default behavior is to look only in the standard system +directories. The exact search directory list depends on the target +system, how GCC is configured, and where it is installed. You can +find the default search directory list for your version of CPP by +invoking it with the @option{-v} option. For example, + +@smallexample +cpp -v /dev/null -o /dev/null +@end smallexample + +There are a number of command-line options you can use to add +additional directories to the search path. +The most commonly-used option is @option{-I@var{dir}}, which causes +@var{dir} to be searched after the current directory (for the quote +form of the directive) and ahead of the standard system directories. +You can specify multiple @option{-I} options on the command line, +in which case the directories are searched in left-to-right order. + +If you need separate control over the search paths for the quote and +angle-bracket forms of the @samp{#include} directive, you can use the +@option{-iquote} and/or @option{-isystem} options instead of @option{-I}. +@xref{Invocation}, for a detailed description of these options, as +well as others that are less generally useful. + +If you specify other options on the command line, such as @option{-I}, +that affect where the preprocessor searches for header files, the +directory list printed by the @option{-v} option reflects the actual +search path used by the preprocessor. + +Note that you can also prevent the preprocessor from searching any of +the default system header directories with the @option{-nostdinc} +option. This is useful when you are compiling an operating system +kernel or some other program that does not use the standard C library +facilities, or the standard C library itself. + +@node Once-Only Headers +@section Once-Only Headers +@cindex repeated inclusion +@cindex including just once +@cindex wrapper @code{#ifndef} + +If a header file happens to be included twice, the compiler will process +its contents twice. This is very likely to cause an error, e.g.@: when the +compiler sees the same structure definition twice. Even if it does not, +it will certainly waste time. + +The standard way to prevent this is to enclose the entire real contents +of the file in a conditional, like this: + +@smallexample +@group +/* File foo. */ +#ifndef FILE_FOO_SEEN +#define FILE_FOO_SEEN + +@var{the entire file} + +#endif /* !FILE_FOO_SEEN */ +@end group +@end smallexample + +This construct is commonly known as a @dfn{wrapper #ifndef}. +When the header is included again, the conditional will be false, +because @code{FILE_FOO_SEEN} is defined. The preprocessor will skip +over the entire contents of the file, and the compiler will not see it +twice. + +CPP optimizes even further. It remembers when a header file has a +wrapper @samp{#ifndef}. If a subsequent @samp{#include} specifies that +header, and the macro in the @samp{#ifndef} is still defined, it does +not bother to rescan the file at all. + +You can put comments outside the wrapper. They will not interfere with +this optimization. + +@cindex controlling macro +@cindex guard macro +The macro @code{FILE_FOO_SEEN} is called the @dfn{controlling macro} or +@dfn{guard macro}. In a user header file, the macro name should not +begin with @samp{_}. In a system header file, it should begin with +@samp{__} to avoid conflicts with user programs. In any kind of header +file, the macro name should contain the name of the file and some +additional text, to avoid conflicts with other header files. + +@node Alternatives to Wrapper #ifndef +@section Alternatives to Wrapper #ifndef + +CPP supports two more ways of indicating that a header file should be +read only once. Neither one is as portable as a wrapper @samp{#ifndef} +and we recommend you do not use them in new programs, with the caveat +that @samp{#import} is standard practice in Objective-C. + +@findex #import +CPP supports a variant of @samp{#include} called @samp{#import} which +includes a file, but does so at most once. If you use @samp{#import} +instead of @samp{#include}, then you don't need the conditionals +inside the header file to prevent multiple inclusion of the contents. +@samp{#import} is standard in Objective-C, but is considered a +deprecated extension in C and C++. + +@samp{#import} is not a well designed feature. It requires the users of +a header file to know that it should only be included once. It is much +better for the header file's implementor to write the file so that users +don't need to know this. Using a wrapper @samp{#ifndef} accomplishes +this goal. + +In the present implementation, a single use of @samp{#import} will +prevent the file from ever being read again, by either @samp{#import} or +@samp{#include}. You should not rely on this; do not use both +@samp{#import} and @samp{#include} to refer to the same header file. + +Another way to prevent a header file from being included more than once +is with the @samp{#pragma once} directive (@pxref{Pragmas}). +@samp{#pragma once} does not have the problems that @samp{#import} does, +but it is not recognized by all preprocessors, so you cannot rely on it +in a portable program. + +@node Computed Includes +@section Computed Includes +@cindex computed includes +@cindex macros in include + +Sometimes it is necessary to select one of several different header +files to be included into your program. They might specify +configuration parameters to be used on different sorts of operating +systems, for instance. You could do this with a series of conditionals, + +@smallexample +#if SYSTEM_1 +# include "system_1.h" +#elif SYSTEM_2 +# include "system_2.h" +#elif SYSTEM_3 +@dots{} +#endif +@end smallexample + +That rapidly becomes tedious. Instead, the preprocessor offers the +ability to use a macro for the header name. This is called a +@dfn{computed include}. Instead of writing a header name as the direct +argument of @samp{#include}, you simply put a macro name there instead: + +@smallexample +#define SYSTEM_H "system_1.h" +@dots{} +#include SYSTEM_H +@end smallexample + +@noindent +@code{SYSTEM_H} will be expanded, and the preprocessor will look for +@file{system_1.h} as if the @samp{#include} had been written that way +originally. @code{SYSTEM_H} could be defined by your Makefile with a +@option{-D} option. + +You must be careful when you define the macro. @samp{#define} saves +tokens, not text. The preprocessor has no way of knowing that the macro +will be used as the argument of @samp{#include}, so it generates +ordinary tokens, not a header name. This is unlikely to cause problems +if you use double-quote includes, which are close enough to string +constants. If you use angle brackets, however, you may have trouble. + +The syntax of a computed include is actually a bit more general than the +above. If the first non-whitespace character after @samp{#include} is +not @samp{"} or @samp{<}, then the entire line is macro-expanded +like running text would be. + +If the line expands to a single string constant, the contents of that +string constant are the file to be included. CPP does not re-examine the +string for embedded quotes, but neither does it process backslash +escapes in the string. Therefore + +@smallexample +#define HEADER "a\"b" +#include HEADER +@end smallexample + +@noindent +looks for a file named @file{a\"b}. CPP searches for the file according +to the rules for double-quoted includes. + +If the line expands to a token stream beginning with a @samp{<} token +and including a @samp{>} token, then the tokens between the @samp{<} and +the first @samp{>} are combined to form the filename to be included. +Any whitespace between tokens is reduced to a single space; then any +space after the initial @samp{<} is retained, but a trailing space +before the closing @samp{>} is ignored. CPP searches for the file +according to the rules for angle-bracket includes. + +In either case, if there are any tokens on the line after the file name, +an error occurs and the directive is not processed. It is also an error +if the result of expansion does not match either of the two expected +forms. + +These rules are implementation-defined behavior according to the C +standard. To minimize the risk of different compilers interpreting your +computed includes differently, we recommend you use only a single +object-like macro which expands to a string constant. This will also +minimize confusion for people reading your program. + +@node Wrapper Headers +@section Wrapper Headers +@cindex wrapper headers +@cindex overriding a header file +@findex #include_next + +Sometimes it is necessary to adjust the contents of a system-provided +header file without editing it directly. GCC's @command{fixincludes} +operation does this, for example. One way to do that would be to create +a new header file with the same name and insert it in the search path +before the original header. That works fine as long as you're willing +to replace the old header entirely. But what if you want to refer to +the old header from the new one? + +You cannot simply include the old header with @samp{#include}. That +will start from the beginning, and find your new header again. If your +header is not protected from multiple inclusion (@pxref{Once-Only +Headers}), it will recurse infinitely and cause a fatal error. + +You could include the old header with an absolute pathname: +@smallexample +#include "/usr/include/old-header.h" +@end smallexample +@noindent +This works, but is not clean; should the system headers ever move, you +would have to edit the new headers to match. + +There is no way to solve this problem within the C standard, but you can +use the GNU extension @samp{#include_next}. It means, ``Include the +@emph{next} file with this name''. This directive works like +@samp{#include} except in searching for the specified file: it starts +searching the list of header file directories @emph{after} the directory +in which the current file was found. + +Suppose you specify @option{-I /usr/local/include}, and the list of +directories to search also includes @file{/usr/include}; and suppose +both directories contain @file{signal.h}. Ordinary @code{@w{#include +}} finds the file under @file{/usr/local/include}. If that +file contains @code{@w{#include_next }}, it starts searching +after that directory, and finds the file in @file{/usr/include}. + +@samp{#include_next} does not distinguish between @code{<@var{file}>} +and @code{"@var{file}"} inclusion, nor does it check that the file you +specify has the same name as the current file. It simply looks for the +file named, starting with the directory in the search path after the one +where the current file was found. + +The use of @samp{#include_next} can lead to great confusion. We +recommend it be used only when there is no other alternative. In +particular, it should not be used in the headers belonging to a specific +program; it should be used only to make global corrections along the +lines of @command{fixincludes}. + +@node System Headers +@section System Headers +@cindex system header files + +The header files declaring interfaces to the operating system and +runtime libraries often cannot be written in strictly conforming C@. +Therefore, GCC gives code found in @dfn{system headers} special +treatment. All warnings, other than those generated by @samp{#warning} +(@pxref{Diagnostics}), are suppressed while GCC is processing a system +header. Macros defined in a system header are immune to a few warnings +wherever they are expanded. This immunity is granted on an ad-hoc +basis, when we find that a warning generates lots of false positives +because of code in macros defined in system headers. + +Normally, only the headers found in specific directories are considered +system headers. These directories are determined when GCC is compiled. +There are, however, two ways to make normal headers into system headers: + +@itemize @bullet +@item +Header files found in directories added to the search path with the +@option{-isystem} and @option{-idirafter} command-line options are +treated as system headers for the purposes of diagnostics. + +@item +@findex #pragma GCC system_header +There is also a directive, @code{@w{#pragma GCC system_header}}, which +tells GCC to consider the rest of the current include file a system +header, no matter where it was found. Code that comes before the +@samp{#pragma} in the file is not affected. @code{@w{#pragma GCC +system_header}} has no effect in the primary source file. +@end itemize + +On some targets, such as RS/6000 AIX, GCC implicitly surrounds all +system headers with an @samp{extern "C"} block when compiling as C++. + +@node Macros +@chapter Macros + +A @dfn{macro} is a fragment of code which has been given a name. +Whenever the name is used, it is replaced by the contents of the macro. +There are two kinds of macros. They differ mostly in what they look +like when they are used. @dfn{Object-like} macros resemble data objects +when used, @dfn{function-like} macros resemble function calls. + +You may define any valid identifier as a macro, even if it is a C +keyword. The preprocessor does not know anything about keywords. This +can be useful if you wish to hide a keyword such as @code{const} from an +older compiler that does not understand it. However, the preprocessor +operator @code{defined} (@pxref{Defined}) can never be defined as a +macro, and C++'s named operators (@pxref{C++ Named Operators}) cannot be +macros when you are compiling C++. + +@menu +* Object-like Macros:: +* Function-like Macros:: +* Macro Arguments:: +* Stringizing:: +* Concatenation:: +* Variadic Macros:: +* Predefined Macros:: +* Undefining and Redefining Macros:: +* Directives Within Macro Arguments:: +* Macro Pitfalls:: +@end menu + +@node Object-like Macros +@section Object-like Macros +@cindex object-like macro +@cindex symbolic constants +@cindex manifest constants + +An @dfn{object-like macro} is a simple identifier which will be replaced +by a code fragment. It is called object-like because it looks like a +data object in code that uses it. They are most commonly used to give +symbolic names to numeric constants. + +@findex #define +You create macros with the @samp{#define} directive. @samp{#define} is +followed by the name of the macro and then the token sequence it should +be an abbreviation for, which is variously referred to as the macro's +@dfn{body}, @dfn{expansion} or @dfn{replacement list}. For example, + +@smallexample +#define BUFFER_SIZE 1024 +@end smallexample + +@noindent +defines a macro named @code{BUFFER_SIZE} as an abbreviation for the +token @code{1024}. If somewhere after this @samp{#define} directive +there comes a C statement of the form + +@smallexample +foo = (char *) malloc (BUFFER_SIZE); +@end smallexample + +@noindent +then the C preprocessor will recognize and @dfn{expand} the macro +@code{BUFFER_SIZE}. The C compiler will see the same tokens as it would +if you had written + +@smallexample +foo = (char *) malloc (1024); +@end smallexample + +By convention, macro names are written in uppercase. Programs are +easier to read when it is possible to tell at a glance which names are +macros. + +The macro's body ends at the end of the @samp{#define} line. You may +continue the definition onto multiple lines, if necessary, using +backslash-newline. When the macro is expanded, however, it will all +come out on one line. For example, + +@smallexample +#define NUMBERS 1, \ + 2, \ + 3 +int x[] = @{ NUMBERS @}; + @expansion{} int x[] = @{ 1, 2, 3 @}; +@end smallexample + +@noindent +The most common visible consequence of this is surprising line numbers +in error messages. + +There is no restriction on what can go in a macro body provided it +decomposes into valid preprocessing tokens. Parentheses need not +balance, and the body need not resemble valid C code. (If it does not, +you may get error messages from the C compiler when you use the macro.) + +The C preprocessor scans your program sequentially. Macro definitions +take effect at the place you write them. Therefore, the following input +to the C preprocessor + +@smallexample +foo = X; +#define X 4 +bar = X; +@end smallexample + +@noindent +produces + +@smallexample +foo = X; +bar = 4; +@end smallexample + +When the preprocessor expands a macro name, the macro's expansion +replaces the macro invocation, then the expansion is examined for more +macros to expand. For example, + +@smallexample +@group +#define TABLESIZE BUFSIZE +#define BUFSIZE 1024 +TABLESIZE + @expansion{} BUFSIZE + @expansion{} 1024 +@end group +@end smallexample + +@noindent +@code{TABLESIZE} is expanded first to produce @code{BUFSIZE}, then that +macro is expanded to produce the final result, @code{1024}. + +Notice that @code{BUFSIZE} was not defined when @code{TABLESIZE} was +defined. The @samp{#define} for @code{TABLESIZE} uses exactly the +expansion you specify---in this case, @code{BUFSIZE}---and does not +check to see whether it too contains macro names. Only when you +@emph{use} @code{TABLESIZE} is the result of its expansion scanned for +more macro names. + +This makes a difference if you change the definition of @code{BUFSIZE} +at some point in the source file. @code{TABLESIZE}, defined as shown, +will always expand using the definition of @code{BUFSIZE} that is +currently in effect: + +@smallexample +#define BUFSIZE 1020 +#define TABLESIZE BUFSIZE +#undef BUFSIZE +#define BUFSIZE 37 +@end smallexample + +@noindent +Now @code{TABLESIZE} expands (in two stages) to @code{37}. + +If the expansion of a macro contains its own name, either directly or +via intermediate macros, it is not expanded again when the expansion is +examined for more macros. This prevents infinite recursion. +@xref{Self-Referential Macros}, for the precise details. + +@node Function-like Macros +@section Function-like Macros +@cindex function-like macros + +You can also define macros whose use looks like a function call. These +are called @dfn{function-like macros}. To define a function-like macro, +you use the same @samp{#define} directive, but you put a pair of +parentheses immediately after the macro name. For example, + +@smallexample +#define lang_init() c_init() +lang_init() + @expansion{} c_init() +@end smallexample + +A function-like macro is only expanded if its name appears with a pair +of parentheses after it. If you write just the name, it is left alone. +This can be useful when you have a function and a macro of the same +name, and you wish to use the function sometimes. + +@smallexample +extern void foo(void); +#define foo() /* @r{optimized inline version} */ +@dots{} + foo(); + funcptr = foo; +@end smallexample + +Here the call to @code{foo()} will use the macro, but the function +pointer will get the address of the real function. If the macro were to +be expanded, it would cause a syntax error. + +If you put spaces between the macro name and the parentheses in the +macro definition, that does not define a function-like macro, it defines +an object-like macro whose expansion happens to begin with a pair of +parentheses. + +@smallexample +#define lang_init () c_init() +lang_init() + @expansion{} () c_init()() +@end smallexample + +The first two pairs of parentheses in this expansion come from the +macro. The third is the pair that was originally after the macro +invocation. Since @code{lang_init} is an object-like macro, it does not +consume those parentheses. + +@node Macro Arguments +@section Macro Arguments +@cindex arguments +@cindex macros with arguments +@cindex arguments in macro definitions + +Function-like macros can take @dfn{arguments}, just like true functions. +To define a macro that uses arguments, you insert @dfn{parameters} +between the pair of parentheses in the macro definition that make the +macro function-like. The parameters must be valid C identifiers, +separated by commas and optionally whitespace. + +To invoke a macro that takes arguments, you write the name of the macro +followed by a list of @dfn{actual arguments} in parentheses, separated +by commas. The invocation of the macro need not be restricted to a +single logical line---it can cross as many lines in the source file as +you wish. The number of arguments you give must match the number of +parameters in the macro definition. When the macro is expanded, each +use of a parameter in its body is replaced by the tokens of the +corresponding argument. (You need not use all of the parameters in the +macro body.) + +As an example, here is a macro that computes the minimum of two numeric +values, as it is defined in many C programs, and some uses. + +@smallexample +#define min(X, Y) ((X) < (Y) ? (X) : (Y)) + x = min(a, b); @expansion{} x = ((a) < (b) ? (a) : (b)); + y = min(1, 2); @expansion{} y = ((1) < (2) ? (1) : (2)); + z = min(a + 28, *p); @expansion{} z = ((a + 28) < (*p) ? (a + 28) : (*p)); +@end smallexample + +@noindent +(In this small example you can already see several of the dangers of +macro arguments. @xref{Macro Pitfalls}, for detailed explanations.) + +Leading and trailing whitespace in each argument is dropped, and all +whitespace between the tokens of an argument is reduced to a single +space. Parentheses within each argument must balance; a comma within +such parentheses does not end the argument. However, there is no +requirement for square brackets or braces to balance, and they do not +prevent a comma from separating arguments. Thus, + +@smallexample +macro (array[x = y, x + 1]) +@end smallexample + +@noindent +passes two arguments to @code{macro}: @code{array[x = y} and @code{x + +1]}. If you want to supply @code{array[x = y, x + 1]} as an argument, +you can write it as @code{array[(x = y, x + 1)]}, which is equivalent C +code. + +All arguments to a macro are completely macro-expanded before they are +substituted into the macro body. After substitution, the complete text +is scanned again for macros to expand, including the arguments. This rule +may seem strange, but it is carefully designed so you need not worry +about whether any function call is actually a macro invocation. You can +run into trouble if you try to be too clever, though. @xref{Argument +Prescan}, for detailed discussion. + +For example, @code{min (min (a, b), c)} is first expanded to + +@smallexample + min (((a) < (b) ? (a) : (b)), (c)) +@end smallexample + +@noindent +and then to + +@smallexample +@group +((((a) < (b) ? (a) : (b))) < (c) + ? (((a) < (b) ? (a) : (b))) + : (c)) +@end group +@end smallexample + +@noindent +(Line breaks shown here for clarity would not actually be generated.) + +@cindex empty macro arguments +You can leave macro arguments empty; this is not an error to the +preprocessor (but many macros will then expand to invalid code). +You cannot leave out arguments entirely; if a macro takes two arguments, +there must be exactly one comma at the top level of its argument list. +Here are some silly examples using @code{min}: + +@smallexample +min(, b) @expansion{} (( ) < (b) ? ( ) : (b)) +min(a, ) @expansion{} ((a ) < ( ) ? (a ) : ( )) +min(,) @expansion{} (( ) < ( ) ? ( ) : ( )) +min((,),) @expansion{} (((,)) < ( ) ? ((,)) : ( )) + +min() @error{} macro "min" requires 2 arguments, but only 1 given +min(,,) @error{} macro "min" passed 3 arguments, but takes just 2 +@end smallexample + +Whitespace is not a preprocessing token, so if a macro @code{foo} takes +one argument, @code{@w{foo ()}} and @code{@w{foo ( )}} both supply it an +empty argument. Previous GNU preprocessor implementations and +documentation were incorrect on this point, insisting that a +function-like macro that takes a single argument be passed a space if an +empty argument was required. + +Macro parameters appearing inside string literals are not replaced by +their corresponding actual arguments. + +@smallexample +#define foo(x) x, "x" +foo(bar) @expansion{} bar, "x" +@end smallexample + +@node Stringizing +@section Stringizing +@cindex stringizing +@cindex @samp{#} operator + +Sometimes you may want to convert a macro argument into a string +constant. Parameters are not replaced inside string constants, but you +can use the @samp{#} preprocessing operator instead. When a macro +parameter is used with a leading @samp{#}, the preprocessor replaces it +with the literal text of the actual argument, converted to a string +constant. Unlike normal parameter replacement, the argument is not +macro-expanded first. This is called @dfn{stringizing}. + +There is no way to combine an argument with surrounding text and +stringize it all together. Instead, you can write a series of adjacent +string constants and stringized arguments. The preprocessor +replaces the stringized arguments with string constants. The C +compiler then combines all the adjacent string constants into one +long string. + +Here is an example of a macro definition that uses stringizing: + +@smallexample +@group +#define WARN_IF(EXP) \ +do @{ if (EXP) \ + fprintf (stderr, "Warning: " #EXP "\n"); @} \ +while (0) +WARN_IF (x == 0); + @expansion{} do @{ if (x == 0) + fprintf (stderr, "Warning: " "x == 0" "\n"); @} while (0); +@end group +@end smallexample + +@noindent +The argument for @code{EXP} is substituted once, as-is, into the +@code{if} statement, and once, stringized, into the argument to +@code{fprintf}. If @code{x} were a macro, it would be expanded in the +@code{if} statement, but not in the string. + +The @code{do} and @code{while (0)} are a kludge to make it possible to +write @code{WARN_IF (@var{arg});}, which the resemblance of +@code{WARN_IF} to a function would make C programmers want to do; see +@ref{Swallowing the Semicolon}. + +Stringizing in C involves more than putting double-quote characters +around the fragment. The preprocessor backslash-escapes the quotes +surrounding embedded string constants, and all backslashes within string and +character constants, in order to get a valid C string constant with the +proper contents. Thus, stringizing @code{@w{p = "foo\n";}} results in +@t{@w{"p = \"foo\\n\";"}}. However, backslashes that are not inside string +or character constants are not duplicated: @samp{\n} by itself +stringizes to @t{"\n"}. + +All leading and trailing whitespace in text being stringized is +ignored. Any sequence of whitespace in the middle of the text is +converted to a single space in the stringized result. Comments are +replaced by whitespace long before stringizing happens, so they +never appear in stringized text. + +There is no way to convert a macro argument into a character constant. + +If you want to stringize the result of expansion of a macro argument, +you have to use two levels of macros. + +@smallexample +#define xstr(s) str(s) +#define str(s) #s +#define foo 4 +str (foo) + @expansion{} "foo" +xstr (foo) + @expansion{} xstr (4) + @expansion{} str (4) + @expansion{} "4" +@end smallexample + +@code{s} is stringized when it is used in @code{str}, so it is not +macro-expanded first. But @code{s} is an ordinary argument to +@code{xstr}, so it is completely macro-expanded before @code{xstr} +itself is expanded (@pxref{Argument Prescan}). Therefore, by the time +@code{str} gets to its argument, it has already been macro-expanded. + +@node Concatenation +@section Concatenation +@cindex concatenation +@cindex token pasting +@cindex token concatenation +@cindex @samp{##} operator + +It is often useful to merge two tokens into one while expanding macros. +This is called @dfn{token pasting} or @dfn{token concatenation}. The +@samp{##} preprocessing operator performs token pasting. When a macro +is expanded, the two tokens on either side of each @samp{##} operator +are combined into a single token, which then replaces the @samp{##} and +the two original tokens in the macro expansion. Usually both will be +identifiers, or one will be an identifier and the other a preprocessing +number. When pasted, they make a longer identifier. This isn't the +only valid case. It is also possible to concatenate two numbers (or a +number and a name, such as @code{1.5} and @code{e3}) into a number. +Also, multi-character operators such as @code{+=} can be formed by +token pasting. + +However, two tokens that don't together form a valid token cannot be +pasted together. For example, you cannot concatenate @code{x} with +@code{+} in either order. If you try, the preprocessor issues a warning +and emits the two tokens. Whether it puts white space between the +tokens is undefined. It is common to find unnecessary uses of @samp{##} +in complex macros. If you get this warning, it is likely that you can +simply remove the @samp{##}. + +Both the tokens combined by @samp{##} could come from the macro body, +but you could just as well write them as one token in the first place. +Token pasting is most useful when one or both of the tokens comes from a +macro argument. If either of the tokens next to an @samp{##} is a +parameter name, it is replaced by its actual argument before @samp{##} +executes. As with stringizing, the actual argument is not +macro-expanded first. If the argument is empty, that @samp{##} has no +effect. + +Keep in mind that the C preprocessor converts comments to whitespace +before macros are even considered. Therefore, you cannot create a +comment by concatenating @samp{/} and @samp{*}. You can put as much +whitespace between @samp{##} and its operands as you like, including +comments, and you can put comments in arguments that will be +concatenated. However, it is an error if @samp{##} appears at either +end of a macro body. + +Consider a C program that interprets named commands. There probably +needs to be a table of commands, perhaps an array of structures declared +as follows: + +@smallexample +@group +struct command +@{ + char *name; + void (*function) (void); +@}; +@end group + +@group +struct command commands[] = +@{ + @{ "quit", quit_command @}, + @{ "help", help_command @}, + @dots{} +@}; +@end group +@end smallexample + +It would be cleaner not to have to give each command name twice, once in +the string constant and once in the function name. A macro which takes the +name of a command as an argument can make this unnecessary. The string +constant can be created with stringizing, and the function name by +concatenating the argument with @samp{_command}. Here is how it is done: + +@smallexample +#define COMMAND(NAME) @{ #NAME, NAME ## _command @} + +struct command commands[] = +@{ + COMMAND (quit), + COMMAND (help), + @dots{} +@}; +@end smallexample + +@node Variadic Macros +@section Variadic Macros +@cindex variable number of arguments +@cindex macros with variable arguments +@cindex variadic macros + +A macro can be declared to accept a variable number of arguments much as +a function can. The syntax for defining the macro is similar to that of +a function. Here is an example: + +@smallexample +#define eprintf(...) fprintf (stderr, __VA_ARGS__) +@end smallexample + +This kind of macro is called @dfn{variadic}. When the macro is invoked, +all the tokens in its argument list after the last named argument (this +macro has none), including any commas, become the @dfn{variable +argument}. This sequence of tokens replaces the identifier +@code{@w{__VA_ARGS__}} in the macro body wherever it appears. Thus, we +have this expansion: + +@smallexample +eprintf ("%s:%d: ", input_file, lineno) + @expansion{} fprintf (stderr, "%s:%d: ", input_file, lineno) +@end smallexample + +The variable argument is completely macro-expanded before it is inserted +into the macro expansion, just like an ordinary argument. You may use +the @samp{#} and @samp{##} operators to stringize the variable argument +or to paste its leading or trailing token with another token. (But see +below for an important special case for @samp{##}.) + +If your macro is complicated, you may want a more descriptive name for +the variable argument than @code{@w{__VA_ARGS__}}. CPP permits +this, as an extension. You may write an argument name immediately +before the @samp{...}; that name is used for the variable argument. +The @code{eprintf} macro above could be written + +@smallexample +#define eprintf(args...) fprintf (stderr, args) +@end smallexample + +@noindent +using this extension. You cannot use @code{@w{__VA_ARGS__}} and this +extension in the same macro. + +You can have named arguments as well as variable arguments in a variadic +macro. We could define @code{eprintf} like this, instead: + +@smallexample +#define eprintf(format, ...) fprintf (stderr, format, __VA_ARGS__) +@end smallexample + +@noindent +This formulation looks more descriptive, but historically it was less +flexible: you had to supply at least one argument after the format +string. In standard C, you could not omit the comma separating the +named argument from the variable arguments. (Note that this +restriction has been lifted in C++20, and never existed in GNU C; see +below.) + +Furthermore, if you left the variable argument empty, you would have +gotten a syntax error, because there would have been an extra comma +after the format string. + +@smallexample +eprintf("success!\n", ); + @expansion{} fprintf(stderr, "success!\n", ); +@end smallexample + +This has been fixed in C++20, and GNU CPP also has a pair of +extensions which deal with this problem. + +First, in GNU CPP, and in C++ beginning in C++20, you are allowed to +leave the variable argument out entirely: + +@smallexample +eprintf ("success!\n") + @expansion{} fprintf(stderr, "success!\n", ); +@end smallexample + +@noindent +Second, C++20 introduces the @code{@w{__VA_OPT__}} function macro. +This macro may only appear in the definition of a variadic macro. If +the variable argument has any tokens, then a @code{@w{__VA_OPT__}} +invocation expands to its argument; but if the variable argument does +not have any tokens, the @code{@w{__VA_OPT__}} expands to nothing: + +@smallexample +#define eprintf(format, ...) \ + fprintf (stderr, format __VA_OPT__(,) __VA_ARGS__) +@end smallexample + +@code{@w{__VA_OPT__}} is also available in GNU C and GNU C++. + +Historically, GNU CPP has also had another extension to handle the +trailing comma: the @samp{##} token paste operator has a special +meaning when placed between a comma and a variable argument. Despite +the introduction of @code{@w{__VA_OPT__}}, this extension remains +supported in GNU CPP, for backward compatibility. If you write + +@smallexample +#define eprintf(format, ...) fprintf (stderr, format, ##__VA_ARGS__) +@end smallexample + +@noindent +and the variable argument is left out when the @code{eprintf} macro is +used, then the comma before the @samp{##} will be deleted. This does +@emph{not} happen if you pass an empty argument, nor does it happen if +the token preceding @samp{##} is anything other than a comma. + +@smallexample +eprintf ("success!\n") + @expansion{} fprintf(stderr, "success!\n"); +@end smallexample + +@noindent +The above explanation is ambiguous about the case where the only macro +parameter is a variable arguments parameter, as it is meaningless to +try to distinguish whether no argument at all is an empty argument or +a missing argument. +CPP retains the comma when conforming to a specific C +standard. Otherwise the comma is dropped as an extension to the standard. + +The C standard +mandates that the only place the identifier @code{@w{__VA_ARGS__}} +can appear is in the replacement list of a variadic macro. It may not +be used as a macro name, macro argument name, or within a different type +of macro. It may also be forbidden in open text; the standard is +ambiguous. We recommend you avoid using it except for its defined +purpose. + +Likewise, C++ forbids @code{@w{__VA_OPT__}} anywhere outside the +replacement list of a variadic macro. + +Variadic macros became a standard part of the C language with C99. +GNU CPP previously supported them +with a named variable argument +(@samp{args...}, not @samp{...} and @code{@w{__VA_ARGS__}}), which +is still supported for backward compatibility. + +@node Predefined Macros +@section Predefined Macros + +@cindex predefined macros +Several object-like macros are predefined; you use them without +supplying their definitions. They fall into three classes: standard, +common, and system-specific. + +In C++, there is a fourth category, the named operators. They act like +predefined macros, but you cannot undefine them. + +@menu +* Standard Predefined Macros:: +* Common Predefined Macros:: +* System-specific Predefined Macros:: +* C++ Named Operators:: +@end menu + +@node Standard Predefined Macros +@subsection Standard Predefined Macros +@cindex standard predefined macros. + +The standard predefined macros are specified by the relevant +language standards, so they are available with all compilers that +implement those standards. Older compilers may not provide all of +them. Their names all start with double underscores. + +@table @code +@item __FILE__ +This macro expands to the name of the current input file, in the form of +a C string constant. This is the path by which the preprocessor opened +the file, not the short name specified in @samp{#include} or as the +input file name argument. For example, +@code{"/usr/local/include/myheader.h"} is a possible expansion of this +macro. + +@item __LINE__ +This macro expands to the current input line number, in the form of a +decimal integer constant. While we call it a predefined macro, it's +a pretty strange macro, since its ``definition'' changes with each +new line of source code. +@end table + +@code{__FILE__} and @code{__LINE__} are useful in generating an error +message to report an inconsistency detected by the program; the message +can state the source line at which the inconsistency was detected. For +example, + +@smallexample +fprintf (stderr, "Internal error: " + "negative string length " + "%d at %s, line %d.", + length, __FILE__, __LINE__); +@end smallexample + +An @samp{#include} directive changes the expansions of @code{__FILE__} +and @code{__LINE__} to correspond to the included file. At the end of +that file, when processing resumes on the input file that contained +the @samp{#include} directive, the expansions of @code{__FILE__} and +@code{__LINE__} revert to the values they had before the +@samp{#include} (but @code{__LINE__} is then incremented by one as +processing moves to the line after the @samp{#include}). + +A @samp{#line} directive changes @code{__LINE__}, and may change +@code{__FILE__} as well. @xref{Line Control}. + +C99 introduced @code{__func__}, and GCC has provided @code{__FUNCTION__} +for a long time. Both of these are strings containing the name of the +current function (there are slight semantic differences; see the GCC +manual). Neither of them is a macro; the preprocessor does not know the +name of the current function. They tend to be useful in conjunction +with @code{__FILE__} and @code{__LINE__}, though. + +@table @code + +@item __DATE__ +This macro expands to a string constant that describes the date on which +the preprocessor is being run. The string constant contains eleven +characters and looks like @code{@w{"Feb 12 1996"}}. If the day of the +month is less than 10, it is padded with a space on the left. + +If GCC cannot determine the current date, it will emit a warning message +(once per compilation) and @code{__DATE__} will expand to +@code{@w{"??? ?? ????"}}. + +@item __TIME__ +This macro expands to a string constant that describes the time at +which the preprocessor is being run. The string constant contains +eight characters and looks like @code{"23:59:01"}. + +If GCC cannot determine the current time, it will emit a warning message +(once per compilation) and @code{__TIME__} will expand to +@code{"??:??:??"}. + +@item __STDC__ +In normal operation, this macro expands to the constant 1, to signify +that this compiler conforms to ISO Standard C@. If GNU CPP is used with +a compiler other than GCC, this is not necessarily true; however, the +preprocessor always conforms to the standard unless the +@option{-traditional-cpp} option is used. + +This macro is not defined if the @option{-traditional-cpp} option is used. + +On some hosts, the system compiler uses a different convention, where +@code{__STDC__} is normally 0, but is 1 if the user specifies strict +conformance to the C Standard. CPP follows the host convention when +processing system header files, but when processing user files +@code{__STDC__} is always 1. This has been reported to cause problems; +for instance, some versions of Solaris provide X Windows headers that +expect @code{__STDC__} to be either undefined or 1. @xref{Invocation}. + +@item __STDC_VERSION__ +This macro expands to the C Standard's version number, a long integer +constant of the form @code{@var{yyyy}@var{mm}L} where @var{yyyy} and +@var{mm} are the year and month of the Standard version. This signifies +which version of the C Standard the compiler conforms to. Like +@code{__STDC__}, this is not necessarily accurate for the entire +implementation, unless GNU CPP is being used with GCC@. + +The value @code{199409L} signifies the 1989 C standard as amended in +1994, which is the current default; the value @code{199901L} signifies +the 1999 revision of the C standard; the value @code{201112L} +signifies the 2011 revision of the C standard; the value +@code{201710L} signifies the 2017 revision of the C standard (which is +otherwise identical to the 2011 version apart from correction of +defects). An unspecified value larger than @code{201710L} is used for +the experimental @option{-std=c2x} and @option{-std=gnu2x} modes. + +This macro is not defined if the @option{-traditional-cpp} option is +used, nor when compiling C++ or Objective-C@. + +@item __STDC_HOSTED__ +This macro is defined, with value 1, if the compiler's target is a +@dfn{hosted environment}. A hosted environment has the complete +facilities of the standard C library available. + +@item __cplusplus +This macro is defined when the C++ compiler is in use. You can use +@code{__cplusplus} to test whether a header is compiled by a C compiler +or a C++ compiler. This macro is similar to @code{__STDC_VERSION__}, in +that it expands to a version number. Depending on the language standard +selected, the value of the macro is +@code{199711L} for the 1998 C++ standard, +@code{201103L} for the 2011 C++ standard, +@code{201402L} for the 2014 C++ standard, +@code{201703L} for the 2017 C++ standard, +@code{202002L} for the 2020 C++ standard, +or an unspecified value strictly larger than @code{202002L} for the +experimental languages enabled by @option{-std=c++23} and +@option{-std=gnu++23}. + +@item __OBJC__ +This macro is defined, with value 1, when the Objective-C compiler is in +use. You can use @code{__OBJC__} to test whether a header is compiled +by a C compiler or an Objective-C compiler. + +@item __ASSEMBLER__ +This macro is defined with value 1 when preprocessing assembly +language. + +@end table + +@node Common Predefined Macros +@subsection Common Predefined Macros +@cindex common predefined macros + +The common predefined macros are GNU C extensions. They are available +with the same meanings regardless of the machine or operating system on +which you are using GNU C or GNU Fortran. Their names all start with +double underscores. + +@table @code + +@item __COUNTER__ +This macro expands to sequential integral values starting from 0. In +conjunction with the @code{##} operator, this provides a convenient means to +generate unique identifiers. Care must be taken to ensure that +@code{__COUNTER__} is not expanded prior to inclusion of precompiled headers +which use it. Otherwise, the precompiled headers will not be used. + +@item __GFORTRAN__ +The GNU Fortran compiler defines this. + +@item __GNUC__ +@itemx __GNUC_MINOR__ +@itemx __GNUC_PATCHLEVEL__ +These macros are defined by all GNU compilers that use the C +preprocessor: C, C++, Objective-C and Fortran. Their values are the major +version, minor version, and patch level of the compiler, as integer +constants. For example, GCC version @var{x}.@var{y}.@var{z} +defines @code{__GNUC__} to @var{x}, @code{__GNUC_MINOR__} to @var{y}, +and @code{__GNUC_PATCHLEVEL__} to @var{z}. These +macros are also defined if you invoke the preprocessor directly. + +If all you need to know is whether or not your program is being compiled +by GCC, or a non-GCC compiler that claims to accept the GNU C dialects, +you can simply test @code{__GNUC__}. If you need to write code +which depends on a specific version, you must be more careful. Each +time the minor version is increased, the patch level is reset to zero; +each time the major version is increased, the +minor version and patch level are reset. If you wish to use the +predefined macros directly in the conditional, you will need to write it +like this: + +@smallexample +/* @r{Test for GCC > 3.2.0} */ +#if __GNUC__ > 3 || \ + (__GNUC__ == 3 && (__GNUC_MINOR__ > 2 || \ + (__GNUC_MINOR__ == 2 && \ + __GNUC_PATCHLEVEL__ > 0)) +@end smallexample + +@noindent +Another approach is to use the predefined macros to +calculate a single number, then compare that against a threshold: + +@smallexample +#define GCC_VERSION (__GNUC__ * 10000 \ + + __GNUC_MINOR__ * 100 \ + + __GNUC_PATCHLEVEL__) +@dots{} +/* @r{Test for GCC > 3.2.0} */ +#if GCC_VERSION > 30200 +@end smallexample + +@noindent +Many people find this form easier to understand. + +@item __GNUG__ +The GNU C++ compiler defines this. Testing it is equivalent to +testing @code{@w{(__GNUC__ && __cplusplus)}}. + +@item __STRICT_ANSI__ +GCC defines this macro if and only if the @option{-ansi} switch, or a +@option{-std} switch specifying strict conformance to some version of ISO C +or ISO C++, was specified when GCC was invoked. It is defined to @samp{1}. +This macro exists primarily to direct GNU libc's header files to use only +definitions found in standard C. + +@item __BASE_FILE__ +This macro expands to the name of the main input file, in the form +of a C string constant. This is the source file that was specified +on the command line of the preprocessor or C compiler. + +@item __FILE_NAME__ +This macro expands to the basename of the current input file, in the +form of a C string constant. This is the last path component by which +the preprocessor opened the file. For example, processing +@code{"/usr/local/include/myheader.h"} would set this +macro to @code{"myheader.h"}. + +@item __INCLUDE_LEVEL__ +This macro expands to a decimal integer constant that represents the +depth of nesting in include files. The value of this macro is +incremented on every @samp{#include} directive and decremented at the +end of every included file. It starts out at 0, its value within the +base file specified on the command line. + +@item __ELF__ +This macro is defined if the target uses the ELF object format. + +@item __VERSION__ +This macro expands to a string constant which describes the version of +the compiler in use. You should not rely on its contents having any +particular form, but it can be counted on to contain at least the +release number. + +@item __OPTIMIZE__ +@itemx __OPTIMIZE_SIZE__ +@itemx __NO_INLINE__ +These macros describe the compilation mode. @code{__OPTIMIZE__} is +defined in all optimizing compilations. @code{__OPTIMIZE_SIZE__} is +defined if the compiler is optimizing for size, not speed. +@code{__NO_INLINE__} is defined if no functions will be inlined into +their callers (when not optimizing, or when inlining has been +specifically disabled by @option{-fno-inline}). + +These macros cause certain GNU header files to provide optimized +definitions, using macros or inline functions, of system library +functions. You should not use these macros in any way unless you make +sure that programs will execute with the same effect whether or not they +are defined. If they are defined, their value is 1. + +@item __GNUC_GNU_INLINE__ +GCC defines this macro if functions declared @code{inline} will be +handled in GCC's traditional gnu90 mode. Object files will contain +externally visible definitions of all functions declared @code{inline} +without @code{extern} or @code{static}. They will not contain any +definitions of any functions declared @code{extern inline}. + +@item __GNUC_STDC_INLINE__ +GCC defines this macro if functions declared @code{inline} will be +handled according to the ISO C99 or later standards. Object files will contain +externally visible definitions of all functions declared @code{extern +inline}. They will not contain definitions of any functions declared +@code{inline} without @code{extern}. + +If this macro is defined, GCC supports the @code{gnu_inline} function +attribute as a way to always get the gnu90 behavior. + +@item __CHAR_UNSIGNED__ +GCC defines this macro if and only if the data type @code{char} is +unsigned on the target machine. It exists to cause the standard header +file @file{limits.h} to work correctly. You should not use this macro +yourself; instead, refer to the standard macros defined in @file{limits.h}. + +@item __WCHAR_UNSIGNED__ +Like @code{__CHAR_UNSIGNED__}, this macro is defined if and only if the +data type @code{wchar_t} is unsigned and the front-end is in C++ mode. + +@item __REGISTER_PREFIX__ +This macro expands to a single token (not a string constant) which is +the prefix applied to CPU register names in assembly language for this +target. You can use it to write assembly that is usable in multiple +environments. For example, in the @code{m68k-aout} environment it +expands to nothing, but in the @code{m68k-coff} environment it expands +to a single @samp{%}. + +@item __USER_LABEL_PREFIX__ +This macro expands to a single token which is the prefix applied to +user labels (symbols visible to C code) in assembly. For example, in +the @code{m68k-aout} environment it expands to an @samp{_}, but in the +@code{m68k-coff} environment it expands to nothing. + +This macro will have the correct definition even if +@option{-f(no-)underscores} is in use, but it will not be correct if +target-specific options that adjust this prefix are used (e.g.@: the +OSF/rose @option{-mno-underscores} option). + +@item __SIZE_TYPE__ +@itemx __PTRDIFF_TYPE__ +@itemx __WCHAR_TYPE__ +@itemx __WINT_TYPE__ +@itemx __INTMAX_TYPE__ +@itemx __UINTMAX_TYPE__ +@itemx __SIG_ATOMIC_TYPE__ +@itemx __INT8_TYPE__ +@itemx __INT16_TYPE__ +@itemx __INT32_TYPE__ +@itemx __INT64_TYPE__ +@itemx __UINT8_TYPE__ +@itemx __UINT16_TYPE__ +@itemx __UINT32_TYPE__ +@itemx __UINT64_TYPE__ +@itemx __INT_LEAST8_TYPE__ +@itemx __INT_LEAST16_TYPE__ +@itemx __INT_LEAST32_TYPE__ +@itemx __INT_LEAST64_TYPE__ +@itemx __UINT_LEAST8_TYPE__ +@itemx __UINT_LEAST16_TYPE__ +@itemx __UINT_LEAST32_TYPE__ +@itemx __UINT_LEAST64_TYPE__ +@itemx __INT_FAST8_TYPE__ +@itemx __INT_FAST16_TYPE__ +@itemx __INT_FAST32_TYPE__ +@itemx __INT_FAST64_TYPE__ +@itemx __UINT_FAST8_TYPE__ +@itemx __UINT_FAST16_TYPE__ +@itemx __UINT_FAST32_TYPE__ +@itemx __UINT_FAST64_TYPE__ +@itemx __INTPTR_TYPE__ +@itemx __UINTPTR_TYPE__ +These macros are defined to the correct underlying types for the +@code{size_t}, @code{ptrdiff_t}, @code{wchar_t}, @code{wint_t}, +@code{intmax_t}, @code{uintmax_t}, @code{sig_atomic_t}, @code{int8_t}, +@code{int16_t}, @code{int32_t}, @code{int64_t}, @code{uint8_t}, +@code{uint16_t}, @code{uint32_t}, @code{uint64_t}, +@code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t}, +@code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t}, +@code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t}, +@code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t}, +@code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t}, +@code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t} typedefs, +respectively. They exist to make the standard header files +@file{stddef.h}, @file{stdint.h}, and @file{wchar.h} work correctly. +You should not use these macros directly; instead, include the +appropriate headers and use the typedefs. Some of these macros may +not be defined on particular systems if GCC does not provide a +@file{stdint.h} header on those systems. + +@item __CHAR_BIT__ +Defined to the number of bits used in the representation of the +@code{char} data type. It exists to make the standard header given +numerical limits work correctly. You should not use +this macro directly; instead, include the appropriate headers. + +@item __SCHAR_MAX__ +@itemx __WCHAR_MAX__ +@itemx __SHRT_MAX__ +@itemx __INT_MAX__ +@itemx __LONG_MAX__ +@itemx __LONG_LONG_MAX__ +@itemx __WINT_MAX__ +@itemx __SIZE_MAX__ +@itemx __PTRDIFF_MAX__ +@itemx __INTMAX_MAX__ +@itemx __UINTMAX_MAX__ +@itemx __SIG_ATOMIC_MAX__ +@itemx __INT8_MAX__ +@itemx __INT16_MAX__ +@itemx __INT32_MAX__ +@itemx __INT64_MAX__ +@itemx __UINT8_MAX__ +@itemx __UINT16_MAX__ +@itemx __UINT32_MAX__ +@itemx __UINT64_MAX__ +@itemx __INT_LEAST8_MAX__ +@itemx __INT_LEAST16_MAX__ +@itemx __INT_LEAST32_MAX__ +@itemx __INT_LEAST64_MAX__ +@itemx __UINT_LEAST8_MAX__ +@itemx __UINT_LEAST16_MAX__ +@itemx __UINT_LEAST32_MAX__ +@itemx __UINT_LEAST64_MAX__ +@itemx __INT_FAST8_MAX__ +@itemx __INT_FAST16_MAX__ +@itemx __INT_FAST32_MAX__ +@itemx __INT_FAST64_MAX__ +@itemx __UINT_FAST8_MAX__ +@itemx __UINT_FAST16_MAX__ +@itemx __UINT_FAST32_MAX__ +@itemx __UINT_FAST64_MAX__ +@itemx __INTPTR_MAX__ +@itemx __UINTPTR_MAX__ +@itemx __WCHAR_MIN__ +@itemx __WINT_MIN__ +@itemx __SIG_ATOMIC_MIN__ +Defined to the maximum value of the @code{signed char}, @code{wchar_t}, +@code{signed short}, +@code{signed int}, @code{signed long}, @code{signed long long}, +@code{wint_t}, @code{size_t}, @code{ptrdiff_t}, +@code{intmax_t}, @code{uintmax_t}, @code{sig_atomic_t}, @code{int8_t}, +@code{int16_t}, @code{int32_t}, @code{int64_t}, @code{uint8_t}, +@code{uint16_t}, @code{uint32_t}, @code{uint64_t}, +@code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t}, +@code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t}, +@code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t}, +@code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t}, +@code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t}, +@code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t} types and +to the minimum value of the @code{wchar_t}, @code{wint_t}, and +@code{sig_atomic_t} types respectively. They exist to make the +standard header given numerical limits work correctly. You should not +use these macros directly; instead, include the appropriate headers. +Some of these macros may not be defined on particular systems if GCC +does not provide a @file{stdint.h} header on those systems. + +@item __INT8_C +@itemx __INT16_C +@itemx __INT32_C +@itemx __INT64_C +@itemx __UINT8_C +@itemx __UINT16_C +@itemx __UINT32_C +@itemx __UINT64_C +@itemx __INTMAX_C +@itemx __UINTMAX_C +Defined to implementations of the standard @file{stdint.h} macros with +the same names without the leading @code{__}. They exist the make the +implementation of that header work correctly. You should not use +these macros directly; instead, include the appropriate headers. Some +of these macros may not be defined on particular systems if GCC does +not provide a @file{stdint.h} header on those systems. + +@item __SCHAR_WIDTH__ +@itemx __SHRT_WIDTH__ +@itemx __INT_WIDTH__ +@itemx __LONG_WIDTH__ +@itemx __LONG_LONG_WIDTH__ +@itemx __PTRDIFF_WIDTH__ +@itemx __SIG_ATOMIC_WIDTH__ +@itemx __SIZE_WIDTH__ +@itemx __WCHAR_WIDTH__ +@itemx __WINT_WIDTH__ +@itemx __INT_LEAST8_WIDTH__ +@itemx __INT_LEAST16_WIDTH__ +@itemx __INT_LEAST32_WIDTH__ +@itemx __INT_LEAST64_WIDTH__ +@itemx __INT_FAST8_WIDTH__ +@itemx __INT_FAST16_WIDTH__ +@itemx __INT_FAST32_WIDTH__ +@itemx __INT_FAST64_WIDTH__ +@itemx __INTPTR_WIDTH__ +@itemx __INTMAX_WIDTH__ +Defined to the bit widths of the corresponding types. They exist to +make the implementations of @file{limits.h} and @file{stdint.h} behave +correctly. You should not use these macros directly; instead, include +the appropriate headers. Some of these macros may not be defined on +particular systems if GCC does not provide a @file{stdint.h} header on +those systems. + +@item __SIZEOF_INT__ +@itemx __SIZEOF_LONG__ +@itemx __SIZEOF_LONG_LONG__ +@itemx __SIZEOF_SHORT__ +@itemx __SIZEOF_POINTER__ +@itemx __SIZEOF_FLOAT__ +@itemx __SIZEOF_DOUBLE__ +@itemx __SIZEOF_LONG_DOUBLE__ +@itemx __SIZEOF_SIZE_T__ +@itemx __SIZEOF_WCHAR_T__ +@itemx __SIZEOF_WINT_T__ +@itemx __SIZEOF_PTRDIFF_T__ +Defined to the number of bytes of the C standard data types: @code{int}, +@code{long}, @code{long long}, @code{short}, @code{void *}, @code{float}, +@code{double}, @code{long double}, @code{size_t}, @code{wchar_t}, @code{wint_t} +and @code{ptrdiff_t}. + +@item __BYTE_ORDER__ +@itemx __ORDER_LITTLE_ENDIAN__ +@itemx __ORDER_BIG_ENDIAN__ +@itemx __ORDER_PDP_ENDIAN__ +@code{__BYTE_ORDER__} is defined to one of the values +@code{__ORDER_LITTLE_ENDIAN__}, @code{__ORDER_BIG_ENDIAN__}, or +@code{__ORDER_PDP_ENDIAN__} to reflect the layout of multi-byte and +multi-word quantities in memory. If @code{__BYTE_ORDER__} is equal to +@code{__ORDER_LITTLE_ENDIAN__} or @code{__ORDER_BIG_ENDIAN__}, then +multi-byte and multi-word quantities are laid out identically: the +byte (word) at the lowest address is the least significant or most +significant byte (word) of the quantity, respectively. If +@code{__BYTE_ORDER__} is equal to @code{__ORDER_PDP_ENDIAN__}, then +bytes in 16-bit words are laid out in a little-endian fashion, whereas +the 16-bit subwords of a 32-bit quantity are laid out in big-endian +fashion. + +You should use these macros for testing like this: + +@smallexample +/* @r{Test for a little-endian machine} */ +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__ +@end smallexample + +@item __FLOAT_WORD_ORDER__ +@code{__FLOAT_WORD_ORDER__} is defined to one of the values +@code{__ORDER_LITTLE_ENDIAN__} or @code{__ORDER_BIG_ENDIAN__} to reflect +the layout of the words of multi-word floating-point quantities. + +@item __DEPRECATED +This macro is defined, with value 1, when compiling a C++ source file +with warnings about deprecated constructs enabled. These warnings are +enabled by default, but can be disabled with @option{-Wno-deprecated}. + +@item __EXCEPTIONS +This macro is defined, with value 1, when compiling a C++ source file +with exceptions enabled. If @option{-fno-exceptions} is used when +compiling the file, then this macro is not defined. + +@item __GXX_RTTI +This macro is defined, with value 1, when compiling a C++ source file +with runtime type identification enabled. If @option{-fno-rtti} is +used when compiling the file, then this macro is not defined. + +@item __USING_SJLJ_EXCEPTIONS__ +This macro is defined, with value 1, if the compiler uses the old +mechanism based on @code{setjmp} and @code{longjmp} for exception +handling. + +@item __GXX_EXPERIMENTAL_CXX0X__ +This macro is defined when compiling a C++ source file with C++11 features +enabled, i.e., for all C++ language dialects except @option{-std=c++98} +and @option{-std=gnu++98}. This macro is obsolete, but can be used to +detect experimental C++0x features in very old versions of GCC. Since +GCC 4.7.0 the @code{__cplusplus} macro is defined correctly, so most +code should test @code{__cplusplus >= 201103L} instead of using this +macro. + +@item __GXX_WEAK__ +This macro is defined when compiling a C++ source file. It has the +value 1 if the compiler will use weak symbols, COMDAT sections, or +other similar techniques to collapse symbols with ``vague linkage'' +that are defined in multiple translation units. If the compiler will +not collapse such symbols, this macro is defined with value 0. In +general, user code should not need to make use of this macro; the +purpose of this macro is to ease implementation of the C++ runtime +library provided with G++. + +@item __NEXT_RUNTIME__ +This macro is defined, with value 1, if (and only if) the NeXT runtime +(as in @option{-fnext-runtime}) is in use for Objective-C@. If the GNU +runtime is used, this macro is not defined, so that you can use this +macro to determine which runtime (NeXT or GNU) is being used. + +@item __LP64__ +@itemx _LP64 +These macros are defined, with value 1, if (and only if) the compilation +is for a target where @code{long int} and pointer both use 64-bits and +@code{int} uses 32-bit. + +@item __SSP__ +This macro is defined, with value 1, when @option{-fstack-protector} is in +use. + +@item __SSP_ALL__ +This macro is defined, with value 2, when @option{-fstack-protector-all} is +in use. + +@item __SSP_STRONG__ +This macro is defined, with value 3, when @option{-fstack-protector-strong} is +in use. + +@item __SSP_EXPLICIT__ +This macro is defined, with value 4, when @option{-fstack-protector-explicit} is +in use. + +@item __SANITIZE_ADDRESS__ +This macro is defined, with value 1, when @option{-fsanitize=address} +or @option{-fsanitize=kernel-address} are in use. + +@item __SANITIZE_THREAD__ +This macro is defined, with value 1, when @option{-fsanitize=thread} is in use. + +@item __TIMESTAMP__ +This macro expands to a string constant that describes the date and time +of the last modification of the current source file. The string constant +contains abbreviated day of the week, month, day of the month, time in +hh:mm:ss form, year and looks like @code{@w{"Sun Sep 16 01:03:52 1973"}}. +If the day of the month is less than 10, it is padded with a space on the left. + +If GCC cannot determine the current date, it will emit a warning message +(once per compilation) and @code{__TIMESTAMP__} will expand to +@code{@w{"??? ??? ?? ??:??:?? ????"}}. + +@item __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 +@itemx __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 +@itemx __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 +@itemx __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 +@itemx __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 +These macros are defined when the target processor supports atomic compare +and swap operations on operands 1, 2, 4, 8 or 16 bytes in length, respectively. + +@item __HAVE_SPECULATION_SAFE_VALUE +This macro is defined with the value 1 to show that this version of GCC +supports @code{__builtin_speculation_safe_value}. + +@item __GCC_HAVE_DWARF2_CFI_ASM +This macro is defined when the compiler is emitting DWARF CFI directives +to the assembler. When this is defined, it is possible to emit those same +directives in inline assembly. + +@item __FP_FAST_FMA +@itemx __FP_FAST_FMAF +@itemx __FP_FAST_FMAL +These macros are defined with value 1 if the backend supports the +@code{fma}, @code{fmaf}, and @code{fmal} builtin functions, so that +the include file @file{math.h} can define the macros +@code{FP_FAST_FMA}, @code{FP_FAST_FMAF}, and @code{FP_FAST_FMAL} +for compatibility with the 1999 C standard. + +@item __FP_FAST_FMAF16 +@itemx __FP_FAST_FMAF32 +@itemx __FP_FAST_FMAF64 +@itemx __FP_FAST_FMAF128 +@itemx __FP_FAST_FMAF32X +@itemx __FP_FAST_FMAF64X +@itemx __FP_FAST_FMAF128X +These macros are defined with the value 1 if the backend supports the +@code{fma} functions using the additional @code{_Float@var{n}} and +@code{_Float@var{n}x} types that are defined in ISO/IEC TS +18661-3:2015. The include file @file{math.h} can define the +@code{FP_FAST_FMAF@var{n}} and @code{FP_FAST_FMAF@var{n}x} macros if +the user defined @code{__STDC_WANT_IEC_60559_TYPES_EXT__} before +including @file{math.h}. + +@item __GCC_IEC_559 +This macro is defined to indicate the intended level of support for +IEEE 754 (IEC 60559) floating-point arithmetic. It expands to a +nonnegative integer value. If 0, it indicates that the combination of +the compiler configuration and the command-line options is not +intended to support IEEE 754 arithmetic for @code{float} and +@code{double} as defined in C99 and C11 Annex F (for example, that the +standard rounding modes and exceptions are not supported, or that +optimizations are enabled that conflict with IEEE 754 semantics). If +1, it indicates that IEEE 754 arithmetic is intended to be supported; +this does not mean that all relevant language features are supported +by GCC. If 2 or more, it additionally indicates support for IEEE +754-2008 (in particular, that the binary encodings for quiet and +signaling NaNs are as specified in IEEE 754-2008). + +This macro does not indicate the default state of command-line options +that control optimizations that C99 and C11 permit to be controlled by +standard pragmas, where those standards do not require a particular +default state. It does not indicate whether optimizations respect +signaling NaN semantics (the macro for that is +@code{__SUPPORT_SNAN__}). It does not indicate support for decimal +floating point or the IEEE 754 binary16 and binary128 types. + +@item __GCC_IEC_559_COMPLEX +This macro is defined to indicate the intended level of support for +IEEE 754 (IEC 60559) floating-point arithmetic for complex numbers, as +defined in C99 and C11 Annex G. It expands to a nonnegative integer +value. If 0, it indicates that the combination of the compiler +configuration and the command-line options is not intended to support +Annex G requirements (for example, because @option{-fcx-limited-range} +was used). If 1 or more, it indicates that it is intended to support +those requirements; this does not mean that all relevant language +features are supported by GCC. + +@item __NO_MATH_ERRNO__ +This macro is defined if @option{-fno-math-errno} is used, or enabled +by another option such as @option{-ffast-math} or by default. + +@item __RECIPROCAL_MATH__ +This macro is defined if @option{-freciprocal-math} is used, or enabled +by another option such as @option{-ffast-math} or by default. + +@item __NO_SIGNED_ZEROS__ +This macro is defined if @option{-fno-signed-zeros} is used, or enabled +by another option such as @option{-ffast-math} or by default. + +@item __NO_TRAPPING_MATH__ +This macro is defined if @option{-fno-trapping-math} is used. + +@item __ASSOCIATIVE_MATH__ +This macro is defined if @option{-fassociative-math} is used, or enabled +by another option such as @option{-ffast-math} or by default. + +@item __ROUNDING_MATH__ +This macro is defined if @option{-frounding-math} is used. + +@item __GNUC_EXECUTION_CHARSET_NAME +@itemx __GNUC_WIDE_EXECUTION_CHARSET_NAME +These macros are defined to expand to a narrow string literal of +the name of the narrow and wide compile-time execution character +set used. It directly reflects the name passed to the options +@option{-fexec-charset} and @option{-fwide-exec-charset}, or the defaults +documented for those options (that is, it can expand to something like +@code{"UTF-8"}). @xref{Invocation}. +@end table + +@node System-specific Predefined Macros +@subsection System-specific Predefined Macros + +@cindex system-specific predefined macros +@cindex predefined macros, system-specific +@cindex reserved namespace + +The C preprocessor normally predefines several macros that indicate what +type of system and machine is in use. They are obviously different on +each target supported by GCC@. This manual, being for all systems and +machines, cannot tell you what their names are, but you can use +@command{cpp -dM} to see them all. @xref{Invocation}. All system-specific +predefined macros expand to a constant value, so you can test them with +either @samp{#ifdef} or @samp{#if}. + +The C standard requires that all system-specific macros be part of the +@dfn{reserved namespace}. All names which begin with two underscores, +or an underscore and a capital letter, are reserved for the compiler and +library to use as they wish. However, historically system-specific +macros have had names with no special prefix; for instance, it is common +to find @code{unix} defined on Unix systems. For all such macros, GCC +provides a parallel macro with two underscores added at the beginning +and the end. If @code{unix} is defined, @code{__unix__} will be defined +too. There will never be more than two underscores; the parallel of +@code{_mips} is @code{__mips__}. + +When the @option{-ansi} option, or any @option{-std} option that +requests strict conformance, is given to the compiler, all the +system-specific predefined macros outside the reserved namespace are +suppressed. The parallel macros, inside the reserved namespace, remain +defined. + +We are slowly phasing out all predefined macros which are outside the +reserved namespace. You should never use them in new programs, and we +encourage you to correct older code to use the parallel macros whenever +you find it. We don't recommend you use the system-specific macros that +are in the reserved namespace, either. It is better in the long run to +check specifically for features you need, using a tool such as +@command{autoconf}. + +@node C++ Named Operators +@subsection C++ Named Operators +@cindex named operators +@cindex C++ named operators +@cindex @file{iso646.h} + +In C++, there are eleven keywords which are simply alternate spellings +of operators normally written with punctuation. These keywords are +treated as such even in the preprocessor. They function as operators in +@samp{#if}, and they cannot be defined as macros or poisoned. In C, you +can request that those keywords take their C++ meaning by including +@file{iso646.h}. That header defines each one as a normal object-like +macro expanding to the appropriate punctuator. + +These are the named operators and their corresponding punctuators: + +@multitable {Named Operator} {Punctuator} +@item Named Operator @tab Punctuator +@item @code{and} @tab @code{&&} +@item @code{and_eq} @tab @code{&=} +@item @code{bitand} @tab @code{&} +@item @code{bitor} @tab @code{|} +@item @code{compl} @tab @code{~} +@item @code{not} @tab @code{!} +@item @code{not_eq} @tab @code{!=} +@item @code{or} @tab @code{||} +@item @code{or_eq} @tab @code{|=} +@item @code{xor} @tab @code{^} +@item @code{xor_eq} @tab @code{^=} +@end multitable + +@node Undefining and Redefining Macros +@section Undefining and Redefining Macros +@cindex undefining macros +@cindex redefining macros +@findex #undef + +If a macro ceases to be useful, it may be @dfn{undefined} with the +@samp{#undef} directive. @samp{#undef} takes a single argument, the +name of the macro to undefine. You use the bare macro name, even if the +macro is function-like. It is an error if anything appears on the line +after the macro name. @samp{#undef} has no effect if the name is not a +macro. + +@smallexample +#define FOO 4 +x = FOO; @expansion{} x = 4; +#undef FOO +x = FOO; @expansion{} x = FOO; +@end smallexample + +Once a macro has been undefined, that identifier may be @dfn{redefined} +as a macro by a subsequent @samp{#define} directive. The new definition +need not have any resemblance to the old definition. + +However, if an identifier which is currently a macro is redefined, then +the new definition must be @dfn{effectively the same} as the old one. +Two macro definitions are effectively the same if: +@itemize @bullet +@item Both are the same type of macro (object- or function-like). +@item All the tokens of the replacement list are the same. +@item If there are any parameters, they are the same. +@item Whitespace appears in the same places in both. It need not be +exactly the same amount of whitespace, though. Remember that comments +count as whitespace. +@end itemize + +@noindent +These definitions are effectively the same: +@smallexample +#define FOUR (2 + 2) +#define FOUR (2 + 2) +#define FOUR (2 /* @r{two} */ + 2) +@end smallexample +@noindent +but these are not: +@smallexample +#define FOUR (2 + 2) +#define FOUR ( 2+2 ) +#define FOUR (2 * 2) +#define FOUR(score,and,seven,years,ago) (2 + 2) +@end smallexample + +If a macro is redefined with a definition that is not effectively the +same as the old one, the preprocessor issues a warning and changes the +macro to use the new definition. If the new definition is effectively +the same, the redefinition is silently ignored. This allows, for +instance, two different headers to define a common macro. The +preprocessor will only complain if the definitions do not match. + +@node Directives Within Macro Arguments +@section Directives Within Macro Arguments +@cindex macro arguments and directives + +Occasionally it is convenient to use preprocessor directives within +the arguments of a macro. The C and C++ standards declare that +behavior in these cases is undefined. GNU CPP +processes arbitrary directives within macro arguments in +exactly the same way as it would have processed the directive were the +function-like macro invocation not present. + +If, within a macro invocation, that macro is redefined, then the new +definition takes effect in time for argument pre-expansion, but the +original definition is still used for argument replacement. Here is a +pathological example: + +@smallexample +#define f(x) x x +f (1 +#undef f +#define f 2 +f) +@end smallexample + +@noindent +which expands to + +@smallexample +1 2 1 2 +@end smallexample + +@noindent +with the semantics described above. + +@node Macro Pitfalls +@section Macro Pitfalls +@cindex problems with macros +@cindex pitfalls of macros + +In this section we describe some special rules that apply to macros and +macro expansion, and point out certain cases in which the rules have +counter-intuitive consequences that you must watch out for. + +@menu +* Misnesting:: +* Operator Precedence Problems:: +* Swallowing the Semicolon:: +* Duplication of Side Effects:: +* Self-Referential Macros:: +* Argument Prescan:: +* Newlines in Arguments:: +@end menu + +@node Misnesting +@subsection Misnesting + +When a macro is called with arguments, the arguments are substituted +into the macro body and the result is checked, together with the rest of +the input file, for more macro calls. It is possible to piece together +a macro call coming partially from the macro body and partially from the +arguments. For example, + +@smallexample +#define twice(x) (2*(x)) +#define call_with_1(x) x(1) +call_with_1 (twice) + @expansion{} twice(1) + @expansion{} (2*(1)) +@end smallexample + +Macro definitions do not have to have balanced parentheses. By writing +an unbalanced open parenthesis in a macro body, it is possible to create +a macro call that begins inside the macro body but ends outside of it. +For example, + +@smallexample +#define strange(file) fprintf (file, "%s %d", +@dots{} +strange(stderr) p, 35) + @expansion{} fprintf (stderr, "%s %d", p, 35) +@end smallexample + +The ability to piece together a macro call can be useful, but the use of +unbalanced open parentheses in a macro body is just confusing, and +should be avoided. + +@node Operator Precedence Problems +@subsection Operator Precedence Problems +@cindex parentheses in macro bodies + +You may have noticed that in most of the macro definition examples shown +above, each occurrence of a macro argument name had parentheses around +it. In addition, another pair of parentheses usually surround the +entire macro definition. Here is why it is best to write macros that +way. + +Suppose you define a macro as follows, + +@smallexample +#define ceil_div(x, y) (x + y - 1) / y +@end smallexample + +@noindent +whose purpose is to divide, rounding up. (One use for this operation is +to compute how many @code{int} objects are needed to hold a certain +number of @code{char} objects.) Then suppose it is used as follows: + +@smallexample +a = ceil_div (b & c, sizeof (int)); + @expansion{} a = (b & c + sizeof (int) - 1) / sizeof (int); +@end smallexample + +@noindent +This does not do what is intended. The operator-precedence rules of +C make it equivalent to this: + +@smallexample +a = (b & (c + sizeof (int) - 1)) / sizeof (int); +@end smallexample + +@noindent +What we want is this: + +@smallexample +a = ((b & c) + sizeof (int) - 1)) / sizeof (int); +@end smallexample + +@noindent +Defining the macro as + +@smallexample +#define ceil_div(x, y) ((x) + (y) - 1) / (y) +@end smallexample + +@noindent +provides the desired result. + +Unintended grouping can result in another way. Consider @code{sizeof +ceil_div(1, 2)}. That has the appearance of a C expression that would +compute the size of the type of @code{ceil_div (1, 2)}, but in fact it +means something very different. Here is what it expands to: + +@smallexample +sizeof ((1) + (2) - 1) / (2) +@end smallexample + +@noindent +This would take the size of an integer and divide it by two. The +precedence rules have put the division outside the @code{sizeof} when it +was intended to be inside. + +Parentheses around the entire macro definition prevent such problems. +Here, then, is the recommended way to define @code{ceil_div}: + +@smallexample +#define ceil_div(x, y) (((x) + (y) - 1) / (y)) +@end smallexample + +@node Swallowing the Semicolon +@subsection Swallowing the Semicolon +@cindex semicolons (after macro calls) + +Often it is desirable to define a macro that expands into a compound +statement. Consider, for example, the following macro, that advances a +pointer (the argument @code{p} says where to find it) across whitespace +characters: + +@smallexample +#define SKIP_SPACES(p, limit) \ +@{ char *lim = (limit); \ + while (p < lim) @{ \ + if (*p++ != ' ') @{ \ + p--; break; @}@}@} +@end smallexample + +@noindent +Here backslash-newline is used to split the macro definition, which must +be a single logical line, so that it resembles the way such code would +be laid out if not part of a macro definition. + +A call to this macro might be @code{SKIP_SPACES (p, lim)}. Strictly +speaking, the call expands to a compound statement, which is a complete +statement with no need for a semicolon to end it. However, since it +looks like a function call, it minimizes confusion if you can use it +like a function call, writing a semicolon afterward, as in +@code{SKIP_SPACES (p, lim);} + +This can cause trouble before @code{else} statements, because the +semicolon is actually a null statement. Suppose you write + +@smallexample +if (*p != 0) + SKIP_SPACES (p, lim); +else @dots{} +@end smallexample + +@noindent +The presence of two statements---the compound statement and a null +statement---in between the @code{if} condition and the @code{else} +makes invalid C code. + +The definition of the macro @code{SKIP_SPACES} can be altered to solve +this problem, using a @code{do @dots{} while} statement. Here is how: + +@smallexample +#define SKIP_SPACES(p, limit) \ +do @{ char *lim = (limit); \ + while (p < lim) @{ \ + if (*p++ != ' ') @{ \ + p--; break; @}@}@} \ +while (0) +@end smallexample + +Now @code{SKIP_SPACES (p, lim);} expands into + +@smallexample +do @{@dots{}@} while (0); +@end smallexample + +@noindent +which is one statement. The loop executes exactly once; most compilers +generate no extra code for it. + +@node Duplication of Side Effects +@subsection Duplication of Side Effects + +@cindex side effects (in macro arguments) +@cindex unsafe macros +Many C programs define a macro @code{min}, for ``minimum'', like this: + +@smallexample +#define min(X, Y) ((X) < (Y) ? (X) : (Y)) +@end smallexample + +When you use this macro with an argument containing a side effect, +as shown here, + +@smallexample +next = min (x + y, foo (z)); +@end smallexample + +@noindent +it expands as follows: + +@smallexample +next = ((x + y) < (foo (z)) ? (x + y) : (foo (z))); +@end smallexample + +@noindent +where @code{x + y} has been substituted for @code{X} and @code{foo (z)} +for @code{Y}. + +The function @code{foo} is used only once in the statement as it appears +in the program, but the expression @code{foo (z)} has been substituted +twice into the macro expansion. As a result, @code{foo} might be called +two times when the statement is executed. If it has side effects or if +it takes a long time to compute, the results might not be what you +intended. We say that @code{min} is an @dfn{unsafe} macro. + +The best solution to this problem is to define @code{min} in a way that +computes the value of @code{foo (z)} only once. The C language offers +no standard way to do this, but it can be done with GNU extensions as +follows: + +@smallexample +#define min(X, Y) \ +(@{ typeof (X) x_ = (X); \ + typeof (Y) y_ = (Y); \ + (x_ < y_) ? x_ : y_; @}) +@end smallexample + +The @samp{(@{ @dots{} @})} notation produces a compound statement that +acts as an expression. Its value is the value of its last statement. +This permits us to define local variables and assign each argument to +one. The local variables have underscores after their names to reduce +the risk of conflict with an identifier of wider scope (it is impossible +to avoid this entirely). Now each argument is evaluated exactly once. + +If you do not wish to use GNU C extensions, the only solution is to be +careful when @emph{using} the macro @code{min}. For example, you can +calculate the value of @code{foo (z)}, save it in a variable, and use +that variable in @code{min}: + +@smallexample +@group +#define min(X, Y) ((X) < (Y) ? (X) : (Y)) +@dots{} +@{ + int tem = foo (z); + next = min (x + y, tem); +@} +@end group +@end smallexample + +@noindent +(where we assume that @code{foo} returns type @code{int}). + +@node Self-Referential Macros +@subsection Self-Referential Macros +@cindex self-reference + +A @dfn{self-referential} macro is one whose name appears in its +definition. Recall that all macro definitions are rescanned for more +macros to replace. If the self-reference were considered a use of the +macro, it would produce an infinitely large expansion. To prevent this, +the self-reference is not considered a macro call. It is passed into +the preprocessor output unchanged. Consider an example: + +@smallexample +#define foo (4 + foo) +@end smallexample + +@noindent +where @code{foo} is also a variable in your program. + +Following the ordinary rules, each reference to @code{foo} will expand +into @code{(4 + foo)}; then this will be rescanned and will expand into +@code{(4 + (4 + foo))}; and so on until the computer runs out of memory. + +The self-reference rule cuts this process short after one step, at +@code{(4 + foo)}. Therefore, this macro definition has the possibly +useful effect of causing the program to add 4 to the value of @code{foo} +wherever @code{foo} is referred to. + +In most cases, it is a bad idea to take advantage of this feature. A +person reading the program who sees that @code{foo} is a variable will +not expect that it is a macro as well. The reader will come across the +identifier @code{foo} in the program and think its value should be that +of the variable @code{foo}, whereas in fact the value is four greater. + +One common, useful use of self-reference is to create a macro which +expands to itself. If you write + +@smallexample +#define EPERM EPERM +@end smallexample + +@noindent +then the macro @code{EPERM} expands to @code{EPERM}. Effectively, it is +left alone by the preprocessor whenever it's used in running text. You +can tell that it's a macro with @samp{#ifdef}. You might do this if you +want to define numeric constants with an @code{enum}, but have +@samp{#ifdef} be true for each constant. + +If a macro @code{x} expands to use a macro @code{y}, and the expansion of +@code{y} refers to the macro @code{x}, that is an @dfn{indirect +self-reference} of @code{x}. @code{x} is not expanded in this case +either. Thus, if we have + +@smallexample +#define x (4 + y) +#define y (2 * x) +@end smallexample + +@noindent +then @code{x} and @code{y} expand as follows: + +@smallexample +@group +x @expansion{} (4 + y) + @expansion{} (4 + (2 * x)) + +y @expansion{} (2 * x) + @expansion{} (2 * (4 + y)) +@end group +@end smallexample + +@noindent +Each macro is expanded when it appears in the definition of the other +macro, but not when it indirectly appears in its own definition. + +@node Argument Prescan +@subsection Argument Prescan +@cindex expansion of arguments +@cindex macro argument expansion +@cindex prescan of macro arguments + +Macro arguments are completely macro-expanded before they are +substituted into a macro body, unless they are stringized or pasted +with other tokens. After substitution, the entire macro body, including +the substituted arguments, is scanned again for macros to be expanded. +The result is that the arguments are scanned @emph{twice} to expand +macro calls in them. + +Most of the time, this has no effect. If the argument contained any +macro calls, they are expanded during the first scan. The result +therefore contains no macro calls, so the second scan does not change +it. If the argument were substituted as given, with no prescan, the +single remaining scan would find the same macro calls and produce the +same results. + +You might expect the double scan to change the results when a +self-referential macro is used in an argument of another macro +(@pxref{Self-Referential Macros}): the self-referential macro would be +expanded once in the first scan, and a second time in the second scan. +However, this is not what happens. The self-references that do not +expand in the first scan are marked so that they will not expand in the +second scan either. + +You might wonder, ``Why mention the prescan, if it makes no difference? +And why not skip it and make the preprocessor faster?'' The answer is +that the prescan does make a difference in three special cases: + +@itemize @bullet +@item +Nested calls to a macro. + +We say that @dfn{nested} calls to a macro occur when a macro's argument +contains a call to that very macro. For example, if @code{f} is a macro +that expects one argument, @code{f (f (1))} is a nested pair of calls to +@code{f}. The desired expansion is made by expanding @code{f (1)} and +substituting that into the definition of @code{f}. The prescan causes +the expected result to happen. Without the prescan, @code{f (1)} itself +would be substituted as an argument, and the inner use of @code{f} would +appear during the main scan as an indirect self-reference and would not +be expanded. + +@item +Macros that call other macros that stringize or concatenate. + +If an argument is stringized or concatenated, the prescan does not +occur. If you @emph{want} to expand a macro, then stringize or +concatenate its expansion, you can do that by causing one macro to call +another macro that does the stringizing or concatenation. For +instance, if you have + +@smallexample +#define AFTERX(x) X_ ## x +#define XAFTERX(x) AFTERX(x) +#define TABLESIZE 1024 +#define BUFSIZE TABLESIZE +@end smallexample + +then @code{AFTERX(BUFSIZE)} expands to @code{X_BUFSIZE}, and +@code{XAFTERX(BUFSIZE)} expands to @code{X_1024}. (Not to +@code{X_TABLESIZE}. Prescan always does a complete expansion.) + +@item +Macros used in arguments, whose expansions contain unshielded commas. + +This can cause a macro expanded on the second scan to be called with the +wrong number of arguments. Here is an example: + +@smallexample +#define foo a,b +#define bar(x) lose(x) +#define lose(x) (1 + (x)) +@end smallexample + +We would like @code{bar(foo)} to turn into @code{(1 + (foo))}, which +would then turn into @code{(1 + (a,b))}. Instead, @code{bar(foo)} +expands into @code{lose(a,b)}, and you get an error because @code{lose} +requires a single argument. In this case, the problem is easily solved +by the same parentheses that ought to be used to prevent misnesting of +arithmetic operations: + +@smallexample +#define foo (a,b) +@exdent or +#define bar(x) lose((x)) +@end smallexample + +The extra pair of parentheses prevents the comma in @code{foo}'s +definition from being interpreted as an argument separator. + +@end itemize + +@node Newlines in Arguments +@subsection Newlines in Arguments +@cindex newlines in macro arguments + +The invocation of a function-like macro can extend over many logical +lines. However, in the present implementation, the entire expansion +comes out on one line. Thus line numbers emitted by the compiler or +debugger refer to the line the invocation started on, which might be +different to the line containing the argument causing the problem. + +Here is an example illustrating this: + +@smallexample +#define ignore_second_arg(a,b,c) a; c + +ignore_second_arg (foo (), + ignored (), + syntax error); +@end smallexample + +@noindent +The syntax error triggered by the tokens @code{syntax error} results in +an error message citing line three---the line of ignore_second_arg--- +even though the problematic code comes from line five. + +We consider this a bug, and intend to fix it in the near future. + +@node Conditionals +@chapter Conditionals +@cindex conditionals + +A @dfn{conditional} is a directive that instructs the preprocessor to +select whether or not to include a chunk of code in the final token +stream passed to the compiler. Preprocessor conditionals can test +arithmetic expressions, or whether a name is defined as a macro, or both +simultaneously using the special @code{defined} operator. + +A conditional in the C preprocessor resembles in some ways an @code{if} +statement in C, but it is important to understand the difference between +them. The condition in an @code{if} statement is tested during the +execution of your program. Its purpose is to allow your program to +behave differently from run to run, depending on the data it is +operating on. The condition in a preprocessing conditional directive is +tested when your program is compiled. Its purpose is to allow different +code to be included in the program depending on the situation at the +time of compilation. + +However, the distinction is becoming less clear. Modern compilers often +do test @code{if} statements when a program is compiled, if their +conditions are known not to vary at run time, and eliminate code which +can never be executed. If you can count on your compiler to do this, +you may find that your program is more readable if you use @code{if} +statements with constant conditions (perhaps determined by macros). Of +course, you can only use this to exclude code, not type definitions or +other preprocessing directives, and you can only do it if the code +remains syntactically valid when it is not to be used. + +@menu +* Conditional Uses:: +* Conditional Syntax:: +* Deleted Code:: +@end menu + +@node Conditional Uses +@section Conditional Uses + +There are three general reasons to use a conditional. + +@itemize @bullet +@item +A program may need to use different code depending on the machine or +operating system it is to run on. In some cases the code for one +operating system may be erroneous on another operating system; for +example, it might refer to data types or constants that do not exist on +the other system. When this happens, it is not enough to avoid +executing the invalid code. Its mere presence will cause the compiler +to reject the program. With a preprocessing conditional, the offending +code can be effectively excised from the program when it is not valid. + +@item +You may want to be able to compile the same source file into two +different programs. One version might make frequent time-consuming +consistency checks on its intermediate data, or print the values of +those data for debugging, and the other not. + +@item +A conditional whose condition is always false is one way to exclude code +from the program but keep it as a sort of comment for future reference. +@end itemize + +Simple programs that do not need system-specific logic or complex +debugging hooks generally will not need to use preprocessing +conditionals. + +@node Conditional Syntax +@section Conditional Syntax + +@findex #if +A conditional in the C preprocessor begins with a @dfn{conditional +directive}: @samp{#if}, @samp{#ifdef} or @samp{#ifndef}. + +@menu +* Ifdef:: +* If:: +* Defined:: +* Else:: +* Elif:: +* @code{__has_attribute}:: +* @code{__has_cpp_attribute}:: +* @code{__has_c_attribute}:: +* @code{__has_builtin}:: +* @code{__has_include}:: +@end menu + +@node Ifdef +@subsection Ifdef +@findex #ifdef +@findex #endif + +The simplest sort of conditional is + +@smallexample +@group +#ifdef @var{MACRO} + +@var{controlled text} + +#endif /* @var{MACRO} */ +@end group +@end smallexample + +@cindex conditional group +This block is called a @dfn{conditional group}. @var{controlled text} +will be included in the output of the preprocessor if and only if +@var{MACRO} is defined. We say that the conditional @dfn{succeeds} if +@var{MACRO} is defined, @dfn{fails} if it is not. + +The @var{controlled text} inside of a conditional can include +preprocessing directives. They are executed only if the conditional +succeeds. You can nest conditional groups inside other conditional +groups, but they must be completely nested. In other words, +@samp{#endif} always matches the nearest @samp{#ifdef} (or +@samp{#ifndef}, or @samp{#if}). Also, you cannot start a conditional +group in one file and end it in another. + +Even if a conditional fails, the @var{controlled text} inside it is +still run through initial transformations and tokenization. Therefore, +it must all be lexically valid C@. Normally the only way this matters is +that all comments and string literals inside a failing conditional group +must still be properly ended. + +The comment following the @samp{#endif} is not required, but it is a +good practice if there is a lot of @var{controlled text}, because it +helps people match the @samp{#endif} to the corresponding @samp{#ifdef}. +Older programs sometimes put @var{MACRO} directly after the +@samp{#endif} without enclosing it in a comment. This is invalid code +according to the C standard. CPP accepts it with a warning. It +never affects which @samp{#ifndef} the @samp{#endif} matches. + +@findex #ifndef +Sometimes you wish to use some code if a macro is @emph{not} defined. +You can do this by writing @samp{#ifndef} instead of @samp{#ifdef}. +One common use of @samp{#ifndef} is to include code only the first +time a header file is included. @xref{Once-Only Headers}. + +Macro definitions can vary between compilations for several reasons. +Here are some samples. + +@itemize @bullet +@item +Some macros are predefined on each kind of machine +(@pxref{System-specific Predefined Macros}). This allows you to provide +code specially tuned for a particular machine. + +@item +System header files define more macros, associated with the features +they implement. You can test these macros with conditionals to avoid +using a system feature on a machine where it is not implemented. + +@item +Macros can be defined or undefined with the @option{-D} and @option{-U} +command-line options when you compile the program. You can arrange to +compile the same source file into two different programs by choosing a +macro name to specify which program you want, writing conditionals to +test whether or how this macro is defined, and then controlling the +state of the macro with command-line options, perhaps set in the +Makefile. @xref{Invocation}. + +@item +Your program might have a special header file (often called +@file{config.h}) that is adjusted when the program is compiled. It can +define or not define macros depending on the features of the system and +the desired capabilities of the program. The adjustment can be +automated by a tool such as @command{autoconf}, or done by hand. +@end itemize + +@node If +@subsection If + +The @samp{#if} directive allows you to test the value of an arithmetic +expression, rather than the mere existence of one macro. Its syntax is + +@smallexample +@group +#if @var{expression} + +@var{controlled text} + +#endif /* @var{expression} */ +@end group +@end smallexample + +@var{expression} is a C expression of integer type, subject to stringent +restrictions. It may contain + +@itemize @bullet +@item +Integer constants. + +@item +Character constants, which are interpreted as they would be in normal +code. + +@item +Arithmetic operators for addition, subtraction, multiplication, +division, bitwise operations, shifts, comparisons, and logical +operations (@code{&&} and @code{||}). The latter two obey the usual +short-circuiting rules of standard C@. + +@item +Macros. All macros in the expression are expanded before actual +computation of the expression's value begins. + +@item +Uses of the @code{defined} operator, which lets you check whether macros +are defined in the middle of an @samp{#if}. + +@item +Identifiers that are not macros, which are all considered to be the +number zero. This allows you to write @code{@w{#if MACRO}} instead of +@code{@w{#ifdef MACRO}}, if you know that MACRO, when defined, will +always have a nonzero value. Function-like macros used without their +function call parentheses are also treated as zero. + +In some contexts this shortcut is undesirable. The @option{-Wundef} +option causes GCC to warn whenever it encounters an identifier which is +not a macro in an @samp{#if}. +@end itemize + +The preprocessor does not know anything about types in the language. +Therefore, @code{sizeof} operators are not recognized in @samp{#if}, and +neither are @code{enum} constants. They will be taken as identifiers +which are not macros, and replaced by zero. In the case of +@code{sizeof}, this is likely to cause the expression to be invalid. + +The preprocessor calculates the value of @var{expression}. It carries +out all calculations in the widest integer type known to the compiler; +on most machines supported by GCC this is 64 bits. This is not the same +rule as the compiler uses to calculate the value of a constant +expression, and may give different results in some cases. If the value +comes out to be nonzero, the @samp{#if} succeeds and the @var{controlled +text} is included; otherwise it is skipped. + +@node Defined +@subsection Defined + +@cindex @code{defined} +The special operator @code{defined} is used in @samp{#if} and +@samp{#elif} expressions to test whether a certain name is defined as a +macro. @code{defined @var{name}} and @code{defined (@var{name})} are +both expressions whose value is 1 if @var{name} is defined as a macro at +the current point in the program, and 0 otherwise. Thus, @code{@w{#if +defined MACRO}} is precisely equivalent to @code{@w{#ifdef MACRO}}. + +@code{defined} is useful when you wish to test more than one macro for +existence at once. For example, + +@smallexample +#if defined (__vax__) || defined (__ns16000__) +@end smallexample + +@noindent +would succeed if either of the names @code{__vax__} or +@code{__ns16000__} is defined as a macro. + +Conditionals written like this: + +@smallexample +#if defined BUFSIZE && BUFSIZE >= 1024 +@end smallexample + +@noindent +can generally be simplified to just @code{@w{#if BUFSIZE >= 1024}}, +since if @code{BUFSIZE} is not defined, it will be interpreted as having +the value zero. + +If the @code{defined} operator appears as a result of a macro expansion, +the C standard says the behavior is undefined. GNU cpp treats it as a +genuine @code{defined} operator and evaluates it normally. It will warn +wherever your code uses this feature if you use the command-line option +@option{-Wpedantic}, since other compilers may handle it differently. The +warning is also enabled by @option{-Wextra}, and can also be enabled +individually with @option{-Wexpansion-to-defined}. + +@node Else +@subsection Else + +@findex #else +The @samp{#else} directive can be added to a conditional to provide +alternative text to be used if the condition fails. This is what it +looks like: + +@smallexample +@group +#if @var{expression} +@var{text-if-true} +#else /* Not @var{expression} */ +@var{text-if-false} +#endif /* Not @var{expression} */ +@end group +@end smallexample + +@noindent +If @var{expression} is nonzero, the @var{text-if-true} is included and +the @var{text-if-false} is skipped. If @var{expression} is zero, the +opposite happens. + +You can use @samp{#else} with @samp{#ifdef} and @samp{#ifndef}, too. + +@node Elif +@subsection Elif + +@findex #elif +One common case of nested conditionals is used to check for more than two +possible alternatives. For example, you might have + +@smallexample +#if X == 1 +@dots{} +#else /* X != 1 */ +#if X == 2 +@dots{} +#else /* X != 2 */ +@dots{} +#endif /* X != 2 */ +#endif /* X != 1 */ +@end smallexample + +Another conditional directive, @samp{#elif}, allows this to be +abbreviated as follows: + +@smallexample +#if X == 1 +@dots{} +#elif X == 2 +@dots{} +#else /* X != 2 and X != 1*/ +@dots{} +#endif /* X != 2 and X != 1*/ +@end smallexample + +@samp{#elif} stands for ``else if''. Like @samp{#else}, it goes in the +middle of a conditional group and subdivides it; it does not require a +matching @samp{#endif} of its own. Like @samp{#if}, the @samp{#elif} +directive includes an expression to be tested. The text following the +@samp{#elif} is processed only if the original @samp{#if}-condition +failed and the @samp{#elif} condition succeeds. + +More than one @samp{#elif} can go in the same conditional group. Then +the text after each @samp{#elif} is processed only if the @samp{#elif} +condition succeeds after the original @samp{#if} and all previous +@samp{#elif} directives within it have failed. + +@samp{#else} is allowed after any number of @samp{#elif} directives, but +@samp{#elif} may not follow @samp{#else}. + +@node @code{__has_attribute} +@subsection @code{__has_attribute} +@cindex @code{__has_attribute} + +The special operator @code{__has_attribute (@var{operand})} may be used +in @samp{#if} and @samp{#elif} expressions to test whether the attribute +referenced by its @var{operand} is recognized by GCC. Using the operator +in other contexts is not valid. In C code, if compiling for strict +conformance to standards before C2x, @var{operand} must be +a valid identifier. Otherwise, @var{operand} may be optionally +introduced by the @code{@var{attribute-scope}::} prefix. +The @var{attribute-scope} prefix identifies the ``namespace'' within +which the attribute is recognized. The scope of GCC attributes is +@samp{gnu} or @samp{__gnu__}. The @code{__has_attribute} operator by +itself, without any @var{operand} or parentheses, acts as a predefined +macro so that support for it can be tested in portable code. Thus, +the recommended use of the operator is as follows: + +@smallexample +#if defined __has_attribute +# if __has_attribute (nonnull) +# define ATTR_NONNULL __attribute__ ((nonnull)) +# endif +#endif +@end smallexample + +The first @samp{#if} test succeeds only when the operator is supported +by the version of GCC (or another compiler) being used. Only when that +test succeeds is it valid to use @code{__has_attribute} as a preprocessor +operator. As a result, combining the two tests into a single expression as +shown below would only be valid with a compiler that supports the operator +but not with others that don't. + +@smallexample +#if defined __has_attribute && __has_attribute (nonnull) /* not portable */ +@dots{} +#endif +@end smallexample + +@node @code{__has_cpp_attribute} +@subsection @code{__has_cpp_attribute} +@cindex @code{__has_cpp_attribute} + +The special operator @code{__has_cpp_attribute (@var{operand})} may be used +in @samp{#if} and @samp{#elif} expressions in C++ code to test whether +the attribute referenced by its @var{operand} is recognized by GCC. +@code{__has_cpp_attribute (@var{operand})} is equivalent to +@code{__has_attribute (@var{operand})} except that when @var{operand} +designates a supported standard attribute it evaluates to an integer +constant of the form @code{YYYYMM} indicating the year and month when +the attribute was first introduced into the C++ standard. For additional +information including the dates of the introduction of current standard +attributes, see @w{@uref{https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations/, +SD-6: SG10 Feature Test Recommendations}}. + +@node @code{__has_c_attribute} +@subsection @code{__has_c_attribute} +@cindex @code{__has_c_attribute} + +The special operator @code{__has_c_attribute (@var{operand})} may be +used in @samp{#if} and @samp{#elif} expressions in C code to test +whether the attribute referenced by its @var{operand} is recognized by +GCC in attributes using the @samp{[[]]} syntax. GNU attributes must +be specified with the scope @samp{gnu} or @samp{__gnu__} with +@code{__has_c_attribute}. When @var{operand} designates a supported +standard attribute it evaluates to an integer constant of the form +@code{YYYYMM} indicating the year and month when the attribute was +first introduced into the C standard, or when the syntax of operands +to the attribute was extended in the C standard. + +@node @code{__has_builtin} +@subsection @code{__has_builtin} +@cindex @code{__has_builtin} + +The special operator @code{__has_builtin (@var{operand})} may be used in +constant integer contexts and in preprocessor @samp{#if} and @samp{#elif} +expressions to test whether the symbol named by its @var{operand} is +recognized as a built-in function by GCC in the current language and +conformance mode. It evaluates to a constant integer with a nonzero +value if the argument refers to such a function, and to zero otherwise. +The operator may also be used in preprocessor @samp{#if} and @samp{#elif} +expressions. The @code{__has_builtin} operator by itself, without any +@var{operand} or parentheses, acts as a predefined macro so that support +for it can be tested in portable code. Thus, the recommended use of +the operator is as follows: + +@smallexample +#if defined __has_builtin +# if __has_builtin (__builtin_object_size) +# define builtin_object_size(ptr) __builtin_object_size (ptr, 2) +# endif +#endif +#ifndef builtin_object_size +# define builtin_object_size(ptr) ((size_t)-1) +#endif +@end smallexample + +@node @code{__has_include} +@subsection @code{__has_include} +@cindex @code{__has_include} + +The special operator @code{__has_include (@var{operand})} may be used in +@samp{#if} and @samp{#elif} expressions to test whether the header referenced +by its @var{operand} can be included using the @samp{#include} directive. Using +the operator in other contexts is not valid. The @var{operand} takes +the same form as the file in the @samp{#include} directive (@pxref{Include +Syntax}) and evaluates to a nonzero value if the header can be included and +to zero otherwise. Note that that the ability to include a header doesn't +imply that the header doesn't contain invalid constructs or @samp{#error} +directives that would cause the preprocessor to fail. + +The @code{__has_include} operator by itself, without any @var{operand} or +parentheses, acts as a predefined macro so that support for it can be tested +in portable code. Thus, the recommended use of the operator is as follows: + +@smallexample +#if defined __has_include +# if __has_include () +# include +# endif +#endif +@end smallexample + +The first @samp{#if} test succeeds only when the operator is supported +by the version of GCC (or another compiler) being used. Only when that +test succeeds is it valid to use @code{__has_include} as a preprocessor +operator. As a result, combining the two tests into a single expression +as shown below would only be valid with a compiler that supports the operator +but not with others that don't. + +@smallexample +#if defined __has_include && __has_include ("header.h") /* not portable */ +@dots{} +#endif +@end smallexample + +@node Deleted Code +@section Deleted Code +@cindex commenting out code + +If you replace or delete a part of the program but want to keep the old +code around for future reference, you often cannot simply comment it +out. Block comments do not nest, so the first comment inside the old +code will end the commenting-out. The probable result is a flood of +syntax errors. + +One way to avoid this problem is to use an always-false conditional +instead. For instance, put @code{#if 0} before the deleted code and +@code{#endif} after it. This works even if the code being turned +off contains conditionals, but they must be entire conditionals +(balanced @samp{#if} and @samp{#endif}). + +Some people use @code{#ifdef notdef} instead. This is risky, because +@code{notdef} might be accidentally defined as a macro, and then the +conditional would succeed. @code{#if 0} can be counted on to fail. + +Do not use @code{#if 0} for comments which are not C code. Use a real +comment, instead. The interior of @code{#if 0} must consist of complete +tokens; in particular, single-quote characters must balance. Comments +often contain unbalanced single-quote characters (known in English as +apostrophes). These confuse @code{#if 0}. They don't confuse +@samp{/*}. + +@node Diagnostics +@chapter Diagnostics +@cindex diagnostic +@cindex reporting errors +@cindex reporting warnings + +@findex #error +The directive @samp{#error} causes the preprocessor to report a fatal +error. The tokens forming the rest of the line following @samp{#error} +are used as the error message. + +You would use @samp{#error} inside of a conditional that detects a +combination of parameters which you know the program does not properly +support. For example, if you know that the program will not run +properly on a VAX, you might write + +@smallexample +@group +#ifdef __vax__ +#error "Won't work on VAXen. See comments at get_last_object." +#endif +@end group +@end smallexample + +If you have several configuration parameters that must be set up by +the installation in a consistent way, you can use conditionals to detect +an inconsistency and report it with @samp{#error}. For example, + +@smallexample +#if !defined(FOO) && defined(BAR) +#error "BAR requires FOO." +#endif +@end smallexample + +@findex #warning +The directive @samp{#warning} is like @samp{#error}, but causes the +preprocessor to issue a warning and continue preprocessing. The tokens +following @samp{#warning} are used as the warning message. + +You might use @samp{#warning} in obsolete header files, with a message +directing the user to the header file which should be used instead. + +Neither @samp{#error} nor @samp{#warning} macro-expands its argument. +Internal whitespace sequences are each replaced with a single space. +The line must consist of complete tokens. It is wisest to make the +argument of these directives be a single string constant; this avoids +problems with apostrophes and the like. + +@node Line Control +@chapter Line Control +@cindex line control + +The C preprocessor informs the C compiler of the location in your source +code where each token came from. Presently, this is just the file name +and line number. All the tokens resulting from macro expansion are +reported as having appeared on the line of the source file where the +outermost macro was used. We intend to be more accurate in the future. + +If you write a program which generates source code, such as the +@command{bison} parser generator, you may want to adjust the preprocessor's +notion of the current file name and line number by hand. Parts of the +output from @command{bison} are generated from scratch, other parts come +from a standard parser file. The rest are copied verbatim from +@command{bison}'s input. You would like compiler error messages and +symbolic debuggers to be able to refer to @code{bison}'s input file. + +@findex #line +@command{bison} or any such program can arrange this by writing +@samp{#line} directives into the output file. @samp{#line} is a +directive that specifies the original line number and source file name +for subsequent input in the current preprocessor input file. +@samp{#line} has three variants: + +@table @code +@item #line @var{linenum} +@var{linenum} is a non-negative decimal integer constant. It specifies +the line number which should be reported for the following line of +input. Subsequent lines are counted from @var{linenum}. + +@item #line @var{linenum} @var{filename} +@var{linenum} is the same as for the first form, and has the same +effect. In addition, @var{filename} is a string constant. The +following line and all subsequent lines are reported to come from the +file it specifies, until something else happens to change that. +@var{filename} is interpreted according to the normal rules for a string +constant: backslash escapes are interpreted. This is different from +@samp{#include}. + +@item #line @var{anything else} +@var{anything else} is checked for macro calls, which are expanded. +The result should match one of the above two forms. +@end table + +@samp{#line} directives alter the results of the @code{__FILE__} and +@code{__LINE__} predefined macros from that point on. @xref{Standard +Predefined Macros}. They do not have any effect on @samp{#include}'s +idea of the directory containing the current file. + +@node Pragmas +@chapter Pragmas + +@cindex pragma directive + +The @samp{#pragma} directive is the method specified by the C standard +for providing additional information to the compiler, beyond what is +conveyed in the language itself. The forms of this directive +(commonly known as @dfn{pragmas}) specified by C standard are prefixed with +@code{STDC}. A C compiler is free to attach any meaning it likes to other +pragmas. Most GNU-defined, supported pragmas have been given a +@code{GCC} prefix. + +@cindex @code{_Pragma} +C99 introduced the @code{@w{_Pragma}} operator. This feature addresses a +major problem with @samp{#pragma}: being a directive, it cannot be +produced as the result of macro expansion. @code{@w{_Pragma}} is an +operator, much like @code{sizeof} or @code{defined}, and can be embedded +in a macro. + +Its syntax is @code{@w{_Pragma (@var{string-literal})}}, where +@var{string-literal} can be either a normal or wide-character string +literal. It is destringized, by replacing all @samp{\\} with a single +@samp{\} and all @samp{\"} with a @samp{"}. The result is then +processed as if it had appeared as the right hand side of a +@samp{#pragma} directive. For example, + +@smallexample +_Pragma ("GCC dependency \"parse.y\"") +@end smallexample + +@noindent +has the same effect as @code{#pragma GCC dependency "parse.y"}. The +same effect could be achieved using macros, for example + +@smallexample +#define DO_PRAGMA(x) _Pragma (#x) +DO_PRAGMA (GCC dependency "parse.y") +@end smallexample + +The standard is unclear on where a @code{_Pragma} operator can appear. +The preprocessor does not accept it within a preprocessing conditional +directive like @samp{#if}. To be safe, you are probably best keeping it +out of directives other than @samp{#define}, and putting it on a line of +its own. + +This manual documents the pragmas which are meaningful to the +preprocessor itself. Other pragmas are meaningful to the C or C++ +compilers. They are documented in the GCC manual. + +GCC plugins may provide their own pragmas. + +@ftable @code +@item #pragma GCC dependency +@code{#pragma GCC dependency} allows you to check the relative dates of +the current file and another file. If the other file is more recent than +the current file, a warning is issued. This is useful if the current +file is derived from the other file, and should be regenerated. The +other file is searched for using the normal include search path. +Optional trailing text can be used to give more information in the +warning message. + +@smallexample +#pragma GCC dependency "parse.y" +#pragma GCC dependency "/usr/include/time.h" rerun fixincludes +@end smallexample + +@item #pragma GCC poison +Sometimes, there is an identifier that you want to remove completely +from your program, and make sure that it never creeps back in. To +enforce this, you can @dfn{poison} the identifier with this pragma. +@code{#pragma GCC poison} is followed by a list of identifiers to +poison. If any of those identifiers appears anywhere in the source +after the directive, it is a hard error. For example, + +@smallexample +#pragma GCC poison printf sprintf fprintf +sprintf(some_string, "hello"); +@end smallexample + +@noindent +will produce an error. + +If a poisoned identifier appears as part of the expansion of a macro +which was defined before the identifier was poisoned, it will @emph{not} +cause an error. This lets you poison an identifier without worrying +about system headers defining macros that use it. + +For example, + +@smallexample +#define strrchr rindex +#pragma GCC poison rindex +strrchr(some_string, 'h'); +@end smallexample + +@noindent +will not produce an error. + +@item #pragma GCC system_header +This pragma takes no arguments. It causes the rest of the code in the +current file to be treated as if it came from a system header. +@xref{System Headers}. + +@item #pragma GCC warning +@itemx #pragma GCC error +@code{#pragma GCC warning "message"} causes the preprocessor to issue +a warning diagnostic with the text @samp{message}. The message +contained in the pragma must be a single string literal. Similarly, +@code{#pragma GCC error "message"} issues an error message. Unlike +the @samp{#warning} and @samp{#error} directives, these pragmas can be +embedded in preprocessor macros using @samp{_Pragma}. + +@item #pragma once +If @code{#pragma once} is seen when scanning a header file, that +file will never be read again, no matter what. It is a less-portable +alternative to using @samp{#ifndef} to guard the contents of header files +against multiple inclusions. + +@end ftable + +@node Other Directives +@chapter Other Directives + +@findex #ident +@findex #sccs +The @samp{#ident} directive takes one argument, a string constant. On +some systems, that string constant is copied into a special segment of +the object file. On other systems, the directive is ignored. The +@samp{#sccs} directive is a synonym for @samp{#ident}. + +These directives are not part of the C standard, but they are not +official GNU extensions either. What historical information we have +been able to find, suggests they originated with System V@. + +@cindex null directive +The @dfn{null directive} consists of a @samp{#} followed by a newline, +with only whitespace (including comments) in between. A null directive +is understood as a preprocessing directive but has no effect on the +preprocessor output. The primary significance of the existence of the +null directive is that an input line consisting of just a @samp{#} will +produce no output, rather than a line of output containing just a +@samp{#}. Supposedly some old C programs contain such lines. + +@node Preprocessor Output +@chapter Preprocessor Output + +When the C preprocessor is used with the C, C++, or Objective-C +compilers, it is integrated into the compiler and communicates a stream +of binary tokens directly to the compiler's parser. However, it can +also be used in the more conventional standalone mode, where it produces +textual output. +@c FIXME: Document the library interface. + +@cindex output format +The output from the C preprocessor looks much like the input, except +that all preprocessing directive lines have been replaced with blank +lines and all comments with spaces. Long runs of blank lines are +discarded. + +The ISO standard specifies that it is implementation defined whether a +preprocessor preserves whitespace between tokens, or replaces it with +e.g.@: a single space. In GNU CPP, whitespace between tokens is collapsed +to become a single space, with the exception that the first token on a +non-directive line is preceded with sufficient spaces that it appears in +the same column in the preprocessed output that it appeared in the +original source file. This is so the output is easy to read. +CPP does not insert any +whitespace where there was none in the original source, except where +necessary to prevent an accidental token paste. + +@cindex linemarkers +Source file name and line number information is conveyed by lines +of the form + +@smallexample +# @var{linenum} @var{filename} @var{flags} +@end smallexample + +@noindent +These are called @dfn{linemarkers}. They are inserted as needed into +the output (but never within a string or character constant). They mean +that the following line originated in file @var{filename} at line +@var{linenum}. @var{filename} will never contain any non-printing +characters; they are replaced with octal escape sequences. + +After the file name comes zero or more flags, which are @samp{1}, +@samp{2}, @samp{3}, or @samp{4}. If there are multiple flags, spaces +separate them. Here is what the flags mean: + +@table @samp +@item 1 +This indicates the start of a new file. +@item 2 +This indicates returning to a file (after having included another file). +@item 3 +This indicates that the following text comes from a system header file, +so certain warnings should be suppressed. +@item 4 +This indicates that the following text should be treated as being +wrapped in an implicit @code{extern "C"} block. +@c maybe cross reference SYSTEM_IMPLICIT_EXTERN_C +@end table + +As an extension, the preprocessor accepts linemarkers in non-assembler +input files. They are treated like the corresponding @samp{#line} +directive, (@pxref{Line Control}), except that trailing flags are +permitted, and are interpreted with the meanings described above. If +multiple flags are given, they must be in ascending order. + +Some directives may be duplicated in the output of the preprocessor. +These are @samp{#ident} (always), @samp{#pragma} (only if the +preprocessor does not handle the pragma itself), and @samp{#define} and +@samp{#undef} (with certain debugging options). If this happens, the +@samp{#} of the directive will always be in the first column, and there +will be no space between the @samp{#} and the directive name. If macro +expansion happens to generate tokens which might be mistaken for a +duplicated directive, a space will be inserted between the @samp{#} and +the directive name. + +@node Traditional Mode +@chapter Traditional Mode + +Traditional (pre-standard) C preprocessing is rather different from +the preprocessing specified by the standard. When the preprocessor +is invoked with the +@option{-traditional-cpp} option, it attempts to emulate a traditional +preprocessor. + +This mode is not useful for compiling C code with GCC, +but is intended for use with non-C preprocessing applications. Thus +traditional mode semantics are supported only when invoking +the preprocessor explicitly, and not in the compiler front ends. + +The implementation does not correspond precisely to the behavior of +early pre-standard versions of GCC, nor to any true traditional preprocessor. +After all, inconsistencies among traditional implementations were a +major motivation for C standardization. However, we intend that it +should be compatible with true traditional preprocessors in all ways +that actually matter. + +@menu +* Traditional lexical analysis:: +* Traditional macros:: +* Traditional miscellany:: +* Traditional warnings:: +@end menu + +@node Traditional lexical analysis +@section Traditional lexical analysis + +The traditional preprocessor does not decompose its input into tokens +the same way a standards-conforming preprocessor does. The input is +simply treated as a stream of text with minimal internal form. + +This implementation does not treat trigraphs (@pxref{trigraphs}) +specially since they were an invention of the standards committee. It +handles arbitrarily-positioned escaped newlines properly and splices +the lines as you would expect; many traditional preprocessors did not +do this. + +The form of horizontal whitespace in the input file is preserved in +the output. In particular, hard tabs remain hard tabs. This can be +useful if, for example, you are preprocessing a Makefile. + +Traditional CPP only recognizes C-style block comments, and treats the +@samp{/*} sequence as introducing a comment only if it lies outside +quoted text. Quoted text is introduced by the usual single and double +quotes, and also by an initial @samp{<} in a @code{#include} +directive. + +Traditionally, comments are completely removed and are not replaced +with a space. Since a traditional compiler does its own tokenization +of the output of the preprocessor, this means that comments can +effectively be used as token paste operators. However, comments +behave like separators for text handled by the preprocessor itself, +since it doesn't re-lex its input. For example, in + +@smallexample +#if foo/**/bar +@end smallexample + +@noindent +@samp{foo} and @samp{bar} are distinct identifiers and expanded +separately if they happen to be macros. In other words, this +directive is equivalent to + +@smallexample +#if foo bar +@end smallexample + +@noindent +rather than + +@smallexample +#if foobar +@end smallexample + +Generally speaking, in traditional mode an opening quote need not have +a matching closing quote. In particular, a macro may be defined with +replacement text that contains an unmatched quote. Of course, if you +attempt to compile preprocessed output containing an unmatched quote +you will get a syntax error. + +However, all preprocessing directives other than @code{#define} +require matching quotes. For example: + +@smallexample +#define m This macro's fine and has an unmatched quote +"/* This is not a comment. */ +/* @r{This is a comment. The following #include directive + is ill-formed.} */ +#include }} directives. + +You can specify any number or combination of these options on the +command line to search for header files in several directories. +The lookup order is as follows: + +@enumerate +@item +For the quote form of the include directive, the directory of the current +file is searched first. + +@item +For the quote form of the include directive, the directories specified +by @option{-iquote} options are searched in left-to-right order, +as they appear on the command line. + +@item +Directories specified with @option{-I} options are scanned in +left-to-right order. + +@item +Directories specified with @option{-isystem} options are scanned in +left-to-right order. + +@item +Standard system directories are scanned. + +@item +Directories specified with @option{-idirafter} options are scanned in +left-to-right order. +@end enumerate + +You can use @option{-I} to override a system header +file, substituting your own version, since these directories are +searched before the standard system header file directories. +However, you should +not use this option to add directories that contain vendor-supplied +system header files; use @option{-isystem} for that. + +The @option{-isystem} and @option{-idirafter} options also mark the directory +as a system directory, so that it gets the same special treatment that +is applied to the standard system directories. +@ifset cppmanual +@xref{System Headers}. +@end ifset + +If a standard system include directory, or a directory specified with +@option{-isystem}, is also specified with @option{-I}, the @option{-I} +option is ignored. The directory is still searched but as a +system directory at its normal position in the system include chain. +This is to ensure that GCC's procedure to fix buggy system headers and +the ordering for the @code{#include_next} directive are not inadvertently +changed. +If you really need to change the search order for system directories, +use the @option{-nostdinc} and/or @option{-isystem} options. +@ifset cppmanual +@xref{System Headers}. +@end ifset + +@item -I- +@opindex I- +Split the include path. +This option has been deprecated. Please use @option{-iquote} instead for +@option{-I} directories before the @option{-I-} and remove the @option{-I-} +option. + +Any directories specified with @option{-I} +options before @option{-I-} are searched only for headers requested with +@code{@w{#include "@var{file}"}}; they are not searched for +@code{@w{#include <@var{file}>}}. If additional directories are +specified with @option{-I} options after the @option{-I-}, those +directories are searched for all @samp{#include} directives. + +In addition, @option{-I-} inhibits the use of the directory of the current +file directory as the first search directory for @code{@w{#include +"@var{file}"}}. There is no way to override this effect of @option{-I-}. +@ifset cppmanual +@xref{Search Path}. +@end ifset + +@item -iprefix @var{prefix} +@opindex iprefix +Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} +options. If the prefix represents a directory, you should include the +final @samp{/}. + +@item -iwithprefix @var{dir} +@itemx -iwithprefixbefore @var{dir} +@opindex iwithprefix +@opindex iwithprefixbefore +Append @var{dir} to the prefix specified previously with +@option{-iprefix}, and add the resulting directory to the include search +path. @option{-iwithprefixbefore} puts it in the same place @option{-I} +would; @option{-iwithprefix} puts it where @option{-idirafter} would. + +@item -isysroot @var{dir} +@opindex isysroot +This option is like the @option{--sysroot} option, but applies only to +header files (except for Darwin targets, where it applies to both header +files and libraries). See the @option{--sysroot} option for more +information. + +@item -imultilib @var{dir} +@opindex imultilib +Use @var{dir} as a subdirectory of the directory containing +target-specific C++ headers. + +@item -nostdinc +@opindex nostdinc +Do not search the standard system directories for header files. +Only the directories explicitly specified with @option{-I}, +@option{-iquote}, @option{-isystem}, and/or @option{-idirafter} +options (and the directory of the current file, if appropriate) +are searched. + +@item -nostdinc++ +@opindex nostdinc++ +Do not search for header files in the C++-specific standard directories, +but do still search the other standard directories. (This option is +used when building the C++ library.) + diff --git a/gcc/doc/cppenv.texi b/gcc/doc/cppenv.texi new file mode 100644 index 00000000000..c8125bd34fe --- /dev/null +++ b/gcc/doc/cppenv.texi @@ -0,0 +1,99 @@ +@c Copyright (C) 1999-2022 Free Software Foundation, Inc. +@c This is part of the CPP and GCC manuals. +@c For copying conditions, see the file gcc.texi. + +@c --------------------------------------------------------------------- +@c Environment variables affecting the preprocessor +@c --------------------------------------------------------------------- + +@c If this file is included with the flag ``cppmanual'' set, it is +@c formatted for inclusion in the CPP manual; otherwise the main GCC manual. + +@vtable @env +@item CPATH +@itemx C_INCLUDE_PATH +@itemx CPLUS_INCLUDE_PATH +@itemx OBJC_INCLUDE_PATH +@c Commented out until ObjC++ is part of GCC: +@c @itemx OBJCPLUS_INCLUDE_PATH +Each variable's value is a list of directories separated by a special +character, much like @env{PATH}, in which to look for header files. +The special character, @code{PATH_SEPARATOR}, is target-dependent and +determined at GCC build time. For Microsoft Windows-based targets it is a +semicolon, and for almost all other targets it is a colon. + +@env{CPATH} specifies a list of directories to be searched as if +specified with @option{-I}, but after any paths given with @option{-I} +options on the command line. This environment variable is used +regardless of which language is being preprocessed. + +The remaining environment variables apply only when preprocessing the +particular language indicated. Each specifies a list of directories +to be searched as if specified with @option{-isystem}, but after any +paths given with @option{-isystem} options on the command line. + +In all these variables, an empty element instructs the compiler to +search its current working directory. Empty elements can appear at the +beginning or end of a path. For instance, if the value of +@env{CPATH} is @code{:/special/include}, that has the same +effect as @samp{@w{-I. -I/special/include}}. + +@c man end +@ifset cppmanual +See also @ref{Search Path}. +@end ifset +@c man begin ENVIRONMENT + +@item DEPENDENCIES_OUTPUT +@cindex dependencies for make as output +If this variable is set, its value specifies how to output +dependencies for Make based on the non-system header files processed +by the compiler. System header files are ignored in the dependency +output. + +The value of @env{DEPENDENCIES_OUTPUT} can be just a file name, in +which case the Make rules are written to that file, guessing the target +name from the source file name. Or the value can have the form +@samp{@var{file} @var{target}}, in which case the rules are written to +file @var{file} using @var{target} as the target name. + +In other words, this environment variable is equivalent to combining +the options @option{-MM} and @option{-MF} +@ifset cppmanual +(@pxref{Invocation}), +@end ifset +@ifclear cppmanual +(@pxref{Preprocessor Options}), +@end ifclear +with an optional @option{-MT} switch too. + +@item SUNPRO_DEPENDENCIES +@cindex dependencies for make as output +This variable is the same as @env{DEPENDENCIES_OUTPUT} (see above), +except that system header files are not ignored, so it implies +@option{-M} rather than @option{-MM}. However, the dependence on the +main input file is omitted. +@ifset cppmanual +@xref{Invocation}. +@end ifset +@ifclear cppmanual +@xref{Preprocessor Options}. +@end ifclear + +@item SOURCE_DATE_EPOCH +If this variable is set, its value specifies a UNIX timestamp to be +used in replacement of the current date and time in the @code{__DATE__} +and @code{__TIME__} macros, so that the embedded timestamps become +reproducible. + +The value of @env{SOURCE_DATE_EPOCH} must be a UNIX timestamp, +defined as the number of seconds (excluding leap seconds) since +01 Jan 1970 00:00:00 represented in ASCII; identical to the output of +@code{date +%s} on GNU/Linux and other systems that support the +@code{%s} extension in the @code{date} command. + +The value should be a known timestamp such as the last modification +time of the source or package and it should be set by the build +process. + +@end vtable diff --git a/gcc/doc/cppinternals.texi b/gcc/doc/cppinternals.texi new file mode 100644 index 00000000000..75adbbe7bec --- /dev/null +++ b/gcc/doc/cppinternals.texi @@ -0,0 +1,1066 @@ +\input texinfo +@setfilename cppinternals.info +@settitle The GNU C Preprocessor Internals + +@include gcc-common.texi + +@ifinfo +@dircategory Software development +@direntry +* Cpplib: (cppinternals). Cpplib internals. +@end direntry +@end ifinfo + +@c @smallbook +@c @cropmarks +@c @finalout +@setchapternewpage odd +@ifinfo +This file documents the internals of the GNU C Preprocessor. + +Copyright (C) 2000-2022 Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +@ignore +Permission is granted to process this file through Tex and print the +results, provided the printed document carries copying permission +notice identical to this one except for the removal of this paragraph +(this paragraph not being relevant to the printed manual). + +@end ignore +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that +the entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@end ifinfo + +@titlepage +@title Cpplib Internals +@versionsubtitle +@author Neil Booth +@page +@vskip 0pt plus 1filll +@c man begin COPYRIGHT +Copyright @copyright{} 2000-2022 Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that +the entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@c man end +@end titlepage +@contents +@page + +@ifnottex +@node Top +@top +@chapter Cpplib---the GNU C Preprocessor + +The GNU C preprocessor is +implemented as a library, @dfn{cpplib}, so it can be easily shared between +a stand-alone preprocessor, and a preprocessor integrated with the C, +C++ and Objective-C front ends. It is also available for use by other +programs, though this is not recommended as its exposed interface has +not yet reached a point of reasonable stability. + +The library has been written to be re-entrant, so that it can be used +to preprocess many files simultaneously if necessary. It has also been +written with the preprocessing token as the fundamental unit; the +preprocessor in previous versions of GCC would operate on text strings +as the fundamental unit. + +This brief manual documents the internals of cpplib, and explains some +of the tricky issues. It is intended that, along with the comments in +the source code, a reasonably competent C programmer should be able to +figure out what the code is doing, and why things have been implemented +the way they have. + +@menu +* Conventions:: Conventions used in the code. +* Lexer:: The combined C, C++ and Objective-C Lexer. +* Hash Nodes:: All identifiers are entered into a hash table. +* Macro Expansion:: Macro expansion algorithm. +* Token Spacing:: Spacing and paste avoidance issues. +* Line Numbering:: Tracking location within files. +* Guard Macros:: Optimizing header files with guard macros. +* Files:: File handling. +* Concept Index:: Index. +@end menu +@end ifnottex + +@node Conventions +@unnumbered Conventions +@cindex interface +@cindex header files + +cpplib has two interfaces---one is exposed internally only, and the +other is for both internal and external use. + +The convention is that functions and types that are exposed to multiple +files internally are prefixed with @samp{_cpp_}, and are to be found in +the file @file{internal.h}. Functions and types exposed to external +clients are in @file{cpplib.h}, and prefixed with @samp{cpp_}. For +historical reasons this is no longer quite true, but we should strive to +stick to it. + +We are striving to reduce the information exposed in @file{cpplib.h} to the +bare minimum necessary, and then to keep it there. This makes clear +exactly what external clients are entitled to assume, and allows us to +change internals in the future without worrying whether library clients +are perhaps relying on some kind of undocumented implementation-specific +behavior. + +@node Lexer +@unnumbered The Lexer +@cindex lexer +@cindex newlines +@cindex escaped newlines + +@section Overview +The lexer is contained in the file @file{lex.cc}. It is a hand-coded +lexer, and not implemented as a state machine. It can understand C, C++ +and Objective-C source code, and has been extended to allow reasonably +successful preprocessing of assembly language. The lexer does not make +an initial pass to strip out trigraphs and escaped newlines, but handles +them as they are encountered in a single pass of the input file. It +returns preprocessing tokens individually, not a line at a time. + +It is mostly transparent to users of the library, since the library's +interface for obtaining the next token, @code{cpp_get_token}, takes care +of lexing new tokens, handling directives, and expanding macros as +necessary. However, the lexer does expose some functionality so that +clients of the library can easily spell a given token, such as +@code{cpp_spell_token} and @code{cpp_token_len}. These functions are +useful when generating diagnostics, and for emitting the preprocessed +output. + +@section Lexing a token +Lexing of an individual token is handled by @code{_cpp_lex_direct} and +its subroutines. In its current form the code is quite complicated, +with read ahead characters and such-like, since it strives to not step +back in the character stream in preparation for handling non-ASCII file +encodings. The current plan is to convert any such files to UTF-8 +before processing them. This complexity is therefore unnecessary and +will be removed, so I'll not discuss it further here. + +The job of @code{_cpp_lex_direct} is simply to lex a token. It is not +responsible for issues like directive handling, returning lookahead +tokens directly, multiple-include optimization, or conditional block +skipping. It necessarily has a minor r@^ole to play in memory +management of lexed lines. I discuss these issues in a separate section +(@pxref{Lexing a line}). + +The lexer places the token it lexes into storage pointed to by the +variable @code{cur_token}, and then increments it. This variable is +important for correct diagnostic positioning. Unless a specific line +and column are passed to the diagnostic routines, they will examine the +@code{line} and @code{col} values of the token just before the location +that @code{cur_token} points to, and use that location to report the +diagnostic. + +The lexer does not consider whitespace to be a token in its own right. +If whitespace (other than a new line) precedes a token, it sets the +@code{PREV_WHITE} bit in the token's flags. Each token has its +@code{line} and @code{col} variables set to the line and column of the +first character of the token. This line number is the line number in +the translation unit, and can be converted to a source (file, line) pair +using the line map code. + +The first token on a logical, i.e.@: unescaped, line has the flag +@code{BOL} set for beginning-of-line. This flag is intended for +internal use, both to distinguish a @samp{#} that begins a directive +from one that doesn't, and to generate a call-back to clients that want +to be notified about the start of every non-directive line with tokens +on it. Clients cannot reliably determine this for themselves: the first +token might be a macro, and the tokens of a macro expansion do not have +the @code{BOL} flag set. The macro expansion may even be empty, and the +next token on the line certainly won't have the @code{BOL} flag set. + +New lines are treated specially; exactly how the lexer handles them is +context-dependent. The C standard mandates that directives are +terminated by the first unescaped newline character, even if it appears +in the middle of a macro expansion. Therefore, if the state variable +@code{in_directive} is set, the lexer returns a @code{CPP_EOF} token, +which is normally used to indicate end-of-file, to indicate +end-of-directive. In a directive a @code{CPP_EOF} token never means +end-of-file. Conveniently, if the caller was @code{collect_args}, it +already handles @code{CPP_EOF} as if it were end-of-file, and reports an +error about an unterminated macro argument list. + +The C standard also specifies that a new line in the middle of the +arguments to a macro is treated as whitespace. This white space is +important in case the macro argument is stringized. The state variable +@code{parsing_args} is nonzero when the preprocessor is collecting the +arguments to a macro call. It is set to 1 when looking for the opening +parenthesis to a function-like macro, and 2 when collecting the actual +arguments up to the closing parenthesis, since these two cases need to +be distinguished sometimes. One such time is here: the lexer sets the +@code{PREV_WHITE} flag of a token if it meets a new line when +@code{parsing_args} is set to 2. It doesn't set it if it meets a new +line when @code{parsing_args} is 1, since then code like + +@smallexample +#define foo() bar +foo +baz +@end smallexample + +@noindent would be output with an erroneous space before @samp{baz}: + +@smallexample +foo + baz +@end smallexample + +This is a good example of the subtlety of getting token spacing correct +in the preprocessor; there are plenty of tests in the testsuite for +corner cases like this. + +The lexer is written to treat each of @samp{\r}, @samp{\n}, @samp{\r\n} +and @samp{\n\r} as a single new line indicator. This allows it to +transparently preprocess MS-DOS, Macintosh and Unix files without their +needing to pass through a special filter beforehand. + +We also decided to treat a backslash, either @samp{\} or the trigraph +@samp{??/}, separated from one of the above newline indicators by +non-comment whitespace only, as intending to escape the newline. It +tends to be a typing mistake, and cannot reasonably be mistaken for +anything else in any of the C-family grammars. Since handling it this +way is not strictly conforming to the ISO standard, the library issues a +warning wherever it encounters it. + +Handling newlines like this is made simpler by doing it in one place +only. The function @code{handle_newline} takes care of all newline +characters, and @code{skip_escaped_newlines} takes care of arbitrarily +long sequences of escaped newlines, deferring to @code{handle_newline} +to handle the newlines themselves. + +The most painful aspect of lexing ISO-standard C and C++ is handling +trigraphs and backlash-escaped newlines. Trigraphs are processed before +any interpretation of the meaning of a character is made, and unfortunately +there is a trigraph representation for a backslash, so it is possible for +the trigraph @samp{??/} to introduce an escaped newline. + +Escaped newlines are tedious because theoretically they can occur +anywhere---between the @samp{+} and @samp{=} of the @samp{+=} token, +within the characters of an identifier, and even between the @samp{*} +and @samp{/} that terminates a comment. Moreover, you cannot be sure +there is just one---there might be an arbitrarily long sequence of them. + +So, for example, the routine that lexes a number, @code{parse_number}, +cannot assume that it can scan forwards until the first non-number +character and be done with it, because this could be the @samp{\} +introducing an escaped newline, or the @samp{?} introducing the trigraph +sequence that represents the @samp{\} of an escaped newline. If it +encounters a @samp{?} or @samp{\}, it calls @code{skip_escaped_newlines} +to skip over any potential escaped newlines before checking whether the +number has been finished. + +Similarly code in the main body of @code{_cpp_lex_direct} cannot simply +check for a @samp{=} after a @samp{+} character to determine whether it +has a @samp{+=} token; it needs to be prepared for an escaped newline of +some sort. Such cases use the function @code{get_effective_char}, which +returns the first character after any intervening escaped newlines. + +The lexer needs to keep track of the correct column position, including +counting tabs as specified by the @option{-ftabstop=} option. This +should be done even within C-style comments; they can appear in the +middle of a line, and we want to report diagnostics in the correct +position for text appearing after the end of the comment. + +@anchor{Invalid identifiers} +Some identifiers, such as @code{__VA_ARGS__} and poisoned identifiers, +may be invalid and require a diagnostic. However, if they appear in a +macro expansion we don't want to complain with each use of the macro. +It is therefore best to catch them during the lexing stage, in +@code{parse_identifier}. In both cases, whether a diagnostic is needed +or not is dependent upon the lexer's state. For example, we don't want +to issue a diagnostic for re-poisoning a poisoned identifier, or for +using @code{__VA_ARGS__} in the expansion of a variable-argument macro. +Therefore @code{parse_identifier} makes use of state flags to determine +whether a diagnostic is appropriate. Since we change state on a +per-token basis, and don't lex whole lines at a time, this is not a +problem. + +Another place where state flags are used to change behavior is whilst +lexing header names. Normally, a @samp{<} would be lexed as a single +token. After a @code{#include} directive, though, it should be lexed as +a single token as far as the nearest @samp{>} character. Note that we +don't allow the terminators of header names to be escaped; the first +@samp{"} or @samp{>} terminates the header name. + +Interpretation of some character sequences depends upon whether we are +lexing C, C++ or Objective-C, and on the revision of the standard in +force. For example, @samp{::} is a single token in C++, but in C it is +two separate @samp{:} tokens and almost certainly a syntax error. Such +cases are handled by @code{_cpp_lex_direct} based upon command-line +flags stored in the @code{cpp_options} structure. + +Once a token has been lexed, it leads an independent existence. The +spelling of numbers, identifiers and strings is copied to permanent +storage from the original input buffer, so a token remains valid and +correct even if its source buffer is freed with @code{_cpp_pop_buffer}. +The storage holding the spellings of such tokens remains until the +client program calls cpp_destroy, probably at the end of the translation +unit. + +@anchor{Lexing a line} +@section Lexing a line +@cindex token run + +When the preprocessor was changed to return pointers to tokens, one +feature I wanted was some sort of guarantee regarding how long a +returned pointer remains valid. This is important to the stand-alone +preprocessor, the future direction of the C family front ends, and even +to cpplib itself internally. + +Occasionally the preprocessor wants to be able to peek ahead in the +token stream. For example, after the name of a function-like macro, it +wants to check the next token to see if it is an opening parenthesis. +Another example is that, after reading the first few tokens of a +@code{#pragma} directive and not recognizing it as a registered pragma, +it wants to backtrack and allow the user-defined handler for unknown +pragmas to access the full @code{#pragma} token stream. The stand-alone +preprocessor wants to be able to test the current token with the +previous one to see if a space needs to be inserted to preserve their +separate tokenization upon re-lexing (paste avoidance), so it needs to +be sure the pointer to the previous token is still valid. The +recursive-descent C++ parser wants to be able to perform tentative +parsing arbitrarily far ahead in the token stream, and then to be able +to jump back to a prior position in that stream if necessary. + +The rule I chose, which is fairly natural, is to arrange that the +preprocessor lex all tokens on a line consecutively into a token buffer, +which I call a @dfn{token run}, and when meeting an unescaped new line +(newlines within comments do not count either), to start lexing back at +the beginning of the run. Note that we do @emph{not} lex a line of +tokens at once; if we did that @code{parse_identifier} would not have +state flags available to warn about invalid identifiers (@pxref{Invalid +identifiers}). + +In other words, accessing tokens that appeared earlier in the current +line is valid, but since each logical line overwrites the tokens of the +previous line, tokens from prior lines are unavailable. In particular, +since a directive only occupies a single logical line, this means that +the directive handlers like the @code{#pragma} handler can jump around +in the directive's tokens if necessary. + +Two issues remain: what about tokens that arise from macro expansions, +and what happens when we have a long line that overflows the token run? + +Since we promise clients that we preserve the validity of pointers that +we have already returned for tokens that appeared earlier in the line, +we cannot reallocate the run. Instead, on overflow it is expanded by +chaining a new token run on to the end of the existing one. + +The tokens forming a macro's replacement list are collected by the +@code{#define} handler, and placed in storage that is only freed by +@code{cpp_destroy}. So if a macro is expanded in the line of tokens, +the pointers to the tokens of its expansion that are returned will always +remain valid. However, macros are a little trickier than that, since +they give rise to three sources of fresh tokens. They are the built-in +macros like @code{__LINE__}, and the @samp{#} and @samp{##} operators +for stringizing and token pasting. I handled this by allocating +space for these tokens from the lexer's token run chain. This means +they automatically receive the same lifetime guarantees as lexed tokens, +and we don't need to concern ourselves with freeing them. + +Lexing into a line of tokens solves some of the token memory management +issues, but not all. The opening parenthesis after a function-like +macro name might lie on a different line, and the front ends definitely +want the ability to look ahead past the end of the current line. So +cpplib only moves back to the start of the token run at the end of a +line if the variable @code{keep_tokens} is zero. Line-buffering is +quite natural for the preprocessor, and as a result the only time cpplib +needs to increment this variable is whilst looking for the opening +parenthesis to, and reading the arguments of, a function-like macro. In +the near future cpplib will export an interface to increment and +decrement this variable, so that clients can share full control over the +lifetime of token pointers too. + +The routine @code{_cpp_lex_token} handles moving to new token runs, +calling @code{_cpp_lex_direct} to lex new tokens, or returning +previously-lexed tokens if we stepped back in the token stream. It also +checks each token for the @code{BOL} flag, which might indicate a +directive that needs to be handled, or require a start-of-line call-back +to be made. @code{_cpp_lex_token} also handles skipping over tokens in +failed conditional blocks, and invalidates the control macro of the +multiple-include optimization if a token was successfully lexed outside +a directive. In other words, its callers do not need to concern +themselves with such issues. + +@node Hash Nodes +@unnumbered Hash Nodes +@cindex hash table +@cindex identifiers +@cindex macros +@cindex assertions +@cindex named operators + +When cpplib encounters an ``identifier'', it generates a hash code for +it and stores it in the hash table. By ``identifier'' we mean tokens +with type @code{CPP_NAME}; this includes identifiers in the usual C +sense, as well as keywords, directive names, macro names and so on. For +example, all of @code{pragma}, @code{int}, @code{foo} and +@code{__GNUC__} are identifiers and hashed when lexed. + +Each node in the hash table contain various information about the +identifier it represents. For example, its length and type. At any one +time, each identifier falls into exactly one of three categories: + +@itemize @bullet +@item Macros + +These have been declared to be macros, either on the command line or +with @code{#define}. A few, such as @code{__TIME__} are built-ins +entered in the hash table during initialization. The hash node for a +normal macro points to a structure with more information about the +macro, such as whether it is function-like, how many arguments it takes, +and its expansion. Built-in macros are flagged as special, and instead +contain an enum indicating which of the various built-in macros it is. + +@item Assertions + +Assertions are in a separate namespace to macros. To enforce this, cpp +actually prepends a @code{#} character before hashing and entering it in +the hash table. An assertion's node points to a chain of answers to +that assertion. + +@item Void + +Everything else falls into this category---an identifier that is not +currently a macro, or a macro that has since been undefined with +@code{#undef}. + +When preprocessing C++, this category also includes the named operators, +such as @code{xor}. In expressions these behave like the operators they +represent, but in contexts where the spelling of a token matters they +are spelt differently. This spelling distinction is relevant when they +are operands of the stringizing and pasting macro operators @code{#} and +@code{##}. Named operator hash nodes are flagged, both to catch the +spelling distinction and to prevent them from being defined as macros. +@end itemize + +The same identifiers share the same hash node. Since each identifier +token, after lexing, contains a pointer to its hash node, this is used +to provide rapid lookup of various information. For example, when +parsing a @code{#define} statement, CPP flags each argument's identifier +hash node with the index of that argument. This makes duplicated +argument checking an O(1) operation for each argument. Similarly, for +each identifier in the macro's expansion, lookup to see if it is an +argument, and which argument it is, is also an O(1) operation. Further, +each directive name, such as @code{endif}, has an associated directive +enum stored in its hash node, so that directive lookup is also O(1). + +@node Macro Expansion +@unnumbered Macro Expansion Algorithm +@cindex macro expansion + +Macro expansion is a tricky operation, fraught with nasty corner cases +and situations that render what you thought was a nifty way to +optimize the preprocessor's expansion algorithm wrong in quite subtle +ways. + +I strongly recommend you have a good grasp of how the C and C++ +standards require macros to be expanded before diving into this +section, let alone the code!. If you don't have a clear mental +picture of how things like nested macro expansion, stringizing and +token pasting are supposed to work, damage to your sanity can quickly +result. + +@section Internal representation of macros +@cindex macro representation (internal) + +The preprocessor stores macro expansions in tokenized form. This +saves repeated lexing passes during expansion, at the cost of a small +increase in memory consumption on average. The tokens are stored +contiguously in memory, so a pointer to the first one and a token +count is all you need to get the replacement list of a macro. + +If the macro is a function-like macro the preprocessor also stores its +parameters, in the form of an ordered list of pointers to the hash +table entry of each parameter's identifier. Further, in the macro's +stored expansion each occurrence of a parameter is replaced with a +special token of type @code{CPP_MACRO_ARG}. Each such token holds the +index of the parameter it represents in the parameter list, which +allows rapid replacement of parameters with their arguments during +expansion. Despite this optimization it is still necessary to store +the original parameters to the macro, both for dumping with e.g., +@option{-dD}, and to warn about non-trivial macro redefinitions when +the parameter names have changed. + +@section Macro expansion overview +The preprocessor maintains a @dfn{context stack}, implemented as a +linked list of @code{cpp_context} structures, which together represent +the macro expansion state at any one time. The @code{struct +cpp_reader} member variable @code{context} points to the current top +of this stack. The top normally holds the unexpanded replacement list +of the innermost macro under expansion, except when cpplib is about to +pre-expand an argument, in which case it holds that argument's +unexpanded tokens. + +When there are no macros under expansion, cpplib is in @dfn{base +context}. All contexts other than the base context contain a +contiguous list of tokens delimited by a starting and ending token. +When not in base context, cpplib obtains the next token from the list +of the top context. If there are no tokens left in the list, it pops +that context off the stack, and subsequent ones if necessary, until an +unexhausted context is found or it returns to base context. In base +context, cpplib reads tokens directly from the lexer. + +If it encounters an identifier that is both a macro and enabled for +expansion, cpplib prepares to push a new context for that macro on the +stack by calling the routine @code{enter_macro_context}. When this +routine returns, the new context will contain the unexpanded tokens of +the replacement list of that macro. In the case of function-like +macros, @code{enter_macro_context} also replaces any parameters in the +replacement list, stored as @code{CPP_MACRO_ARG} tokens, with the +appropriate macro argument. If the standard requires that the +parameter be replaced with its expanded argument, the argument will +have been fully macro expanded first. + +@code{enter_macro_context} also handles special macros like +@code{__LINE__}. Although these macros expand to a single token which +cannot contain any further macros, for reasons of token spacing +(@pxref{Token Spacing}) and simplicity of implementation, cpplib +handles these special macros by pushing a context containing just that +one token. + +The final thing that @code{enter_macro_context} does before returning +is to mark the macro disabled for expansion (except for special macros +like @code{__TIME__}). The macro is re-enabled when its context is +later popped from the context stack, as described above. This strict +ordering ensures that a macro is disabled whilst its expansion is +being scanned, but that it is @emph{not} disabled whilst any arguments +to it are being expanded. + +@section Scanning the replacement list for macros to expand +The C standard states that, after any parameters have been replaced +with their possibly-expanded arguments, the replacement list is +scanned for nested macros. Further, any identifiers in the +replacement list that are not expanded during this scan are never +again eligible for expansion in the future, if the reason they were +not expanded is that the macro in question was disabled. + +Clearly this latter condition can only apply to tokens resulting from +argument pre-expansion. Other tokens never have an opportunity to be +re-tested for expansion. It is possible for identifiers that are +function-like macros to not expand initially but to expand during a +later scan. This occurs when the identifier is the last token of an +argument (and therefore originally followed by a comma or a closing +parenthesis in its macro's argument list), and when it replaces its +parameter in the macro's replacement list, the subsequent token +happens to be an opening parenthesis (itself possibly the first token +of an argument). + +It is important to note that when cpplib reads the last token of a +given context, that context still remains on the stack. Only when +looking for the @emph{next} token do we pop it off the stack and drop +to a lower context. This makes backing up by one token easy, but more +importantly ensures that the macro corresponding to the current +context is still disabled when we are considering the last token of +its replacement list for expansion (or indeed expanding it). As an +example, which illustrates many of the points above, consider + +@smallexample +#define foo(x) bar x +foo(foo) (2) +@end smallexample + +@noindent which fully expands to @samp{bar foo (2)}. During pre-expansion +of the argument, @samp{foo} does not expand even though the macro is +enabled, since it has no following parenthesis [pre-expansion of an +argument only uses tokens from that argument; it cannot take tokens +from whatever follows the macro invocation]. This still leaves the +argument token @samp{foo} eligible for future expansion. Then, when +re-scanning after argument replacement, the token @samp{foo} is +rejected for expansion, and marked ineligible for future expansion, +since the macro is now disabled. It is disabled because the +replacement list @samp{bar foo} of the macro is still on the context +stack. + +If instead the algorithm looked for an opening parenthesis first and +then tested whether the macro were disabled it would be subtly wrong. +In the example above, the replacement list of @samp{foo} would be +popped in the process of finding the parenthesis, re-enabling +@samp{foo} and expanding it a second time. + +@section Looking for a function-like macro's opening parenthesis +Function-like macros only expand when immediately followed by a +parenthesis. To do this cpplib needs to temporarily disable macros +and read the next token. Unfortunately, because of spacing issues +(@pxref{Token Spacing}), there can be fake padding tokens in-between, +and if the next real token is not a parenthesis cpplib needs to be +able to back up that one token as well as retain the information in +any intervening padding tokens. + +Backing up more than one token when macros are involved is not +permitted by cpplib, because in general it might involve issues like +restoring popped contexts onto the context stack, which are too hard. +Instead, searching for the parenthesis is handled by a special +function, @code{funlike_invocation_p}, which remembers padding +information as it reads tokens. If the next real token is not an +opening parenthesis, it backs up that one token, and then pushes an +extra context just containing the padding information if necessary. + +@section Marking tokens ineligible for future expansion +As discussed above, cpplib needs a way of marking tokens as +unexpandable. Since the tokens cpplib handles are read-only once they +have been lexed, it instead makes a copy of the token and adds the +flag @code{NO_EXPAND} to the copy. + +For efficiency and to simplify memory management by avoiding having to +remember to free these tokens, they are allocated as temporary tokens +from the lexer's current token run (@pxref{Lexing a line}) using the +function @code{_cpp_temp_token}. The tokens are then re-used once the +current line of tokens has been read in. + +This might sound unsafe. However, tokens runs are not re-used at the +end of a line if it happens to be in the middle of a macro argument +list, and cpplib only wants to back-up more than one lexer token in +situations where no macro expansion is involved, so the optimization +is safe. + +@node Token Spacing +@unnumbered Token Spacing +@cindex paste avoidance +@cindex spacing +@cindex token spacing + +First, consider an issue that only concerns the stand-alone +preprocessor: there needs to be a guarantee that re-reading its preprocessed +output results in an identical token stream. Without taking special +measures, this might not be the case because of macro substitution. +For example: + +@smallexample +#define PLUS + +#define EMPTY +#define f(x) =x= ++PLUS -EMPTY- PLUS+ f(=) + @expansion{} + + - - + + = = = +@emph{not} + @expansion{} ++ -- ++ === +@end smallexample + +One solution would be to simply insert a space between all adjacent +tokens. However, we would like to keep space insertion to a minimum, +both for aesthetic reasons and because it causes problems for people who +still try to abuse the preprocessor for things like Fortran source and +Makefiles. + +For now, just notice that when tokens are added (or removed, as shown by +the @code{EMPTY} example) from the original lexed token stream, we need +to check for accidental token pasting. We call this @dfn{paste +avoidance}. Token addition and removal can only occur because of macro +expansion, but accidental pasting can occur in many places: both before +and after each macro replacement, each argument replacement, and +additionally each token created by the @samp{#} and @samp{##} operators. + +Look at how the preprocessor gets whitespace output correct +normally. The @code{cpp_token} structure contains a flags byte, and one +of those flags is @code{PREV_WHITE}. This is flagged by the lexer, and +indicates that the token was preceded by whitespace of some form other +than a new line. The stand-alone preprocessor can use this flag to +decide whether to insert a space between tokens in the output. + +Now consider the result of the following macro expansion: + +@smallexample +#define add(x, y, z) x + y +z; +sum = add (1,2, 3); + @expansion{} sum = 1 + 2 +3; +@end smallexample + +The interesting thing here is that the tokens @samp{1} and @samp{2} are +output with a preceding space, and @samp{3} is output without a +preceding space, but when lexed none of these tokens had that property. +Careful consideration reveals that @samp{1} gets its preceding +whitespace from the space preceding @samp{add} in the macro invocation, +@emph{not} replacement list. @samp{2} gets its whitespace from the +space preceding the parameter @samp{y} in the macro replacement list, +and @samp{3} has no preceding space because parameter @samp{z} has none +in the replacement list. + +Once lexed, tokens are effectively fixed and cannot be altered, since +pointers to them might be held in many places, in particular by +in-progress macro expansions. So instead of modifying the two tokens +above, the preprocessor inserts a special token, which I call a +@dfn{padding token}, into the token stream to indicate that spacing of +the subsequent token is special. The preprocessor inserts padding +tokens in front of every macro expansion and expanded macro argument. +These point to a @dfn{source token} from which the subsequent real token +should inherit its spacing. In the above example, the source tokens are +@samp{add} in the macro invocation, and @samp{y} and @samp{z} in the +macro replacement list, respectively. + +It is quite easy to get multiple padding tokens in a row, for example if +a macro's first replacement token expands straight into another macro. + +@smallexample +#define foo bar +#define bar baz +[foo] + @expansion{} [baz] +@end smallexample + +Here, two padding tokens are generated with sources the @samp{foo} token +between the brackets, and the @samp{bar} token from foo's replacement +list, respectively. Clearly the first padding token is the one to +use, so the output code should contain a rule that the first +padding token in a sequence is the one that matters. + +But what if a macro expansion is left? Adjusting the above +example slightly: + +@smallexample +#define foo bar +#define bar EMPTY baz +#define EMPTY +[foo] EMPTY; + @expansion{} [ baz] ; +@end smallexample + +As shown, now there should be a space before @samp{baz} and the +semicolon in the output. + +The rules we decided above fail for @samp{baz}: we generate three +padding tokens, one per macro invocation, before the token @samp{baz}. +We would then have it take its spacing from the first of these, which +carries source token @samp{foo} with no leading space. + +It is vital that cpplib get spacing correct in these examples since any +of these macro expansions could be stringized, where spacing matters. + +So, this demonstrates that not just entering macro and argument +expansions, but leaving them requires special handling too. I made +cpplib insert a padding token with a @code{NULL} source token when +leaving macro expansions, as well as after each replaced argument in a +macro's replacement list. It also inserts appropriate padding tokens on +either side of tokens created by the @samp{#} and @samp{##} operators. +I expanded the rule so that, if we see a padding token with a +@code{NULL} source token, @emph{and} that source token has no leading +space, then we behave as if we have seen no padding tokens at all. A +quick check shows this rule will then get the above example correct as +well. + +Now a relationship with paste avoidance is apparent: we have to be +careful about paste avoidance in exactly the same locations we have +padding tokens in order to get white space correct. This makes +implementation of paste avoidance easy: wherever the stand-alone +preprocessor is fixing up spacing because of padding tokens, and it +turns out that no space is needed, it has to take the extra step to +check that a space is not needed after all to avoid an accidental paste. +The function @code{cpp_avoid_paste} advises whether a space is required +between two consecutive tokens. To avoid excessive spacing, it tries +hard to only require a space if one is likely to be necessary, but for +reasons of efficiency it is slightly conservative and might recommend a +space where one is not strictly needed. + +@node Line Numbering +@unnumbered Line numbering +@cindex line numbers + +@section Just which line number anyway? + +There are three reasonable requirements a cpplib client might have for +the line number of a token passed to it: + +@itemize @bullet +@item +The source line it was lexed on. +@item +The line it is output on. This can be different to the line it was +lexed on if, for example, there are intervening escaped newlines or +C-style comments. For example: + +@smallexample +foo /* @r{A long +comment} */ bar \ +baz +@result{} +foo bar baz +@end smallexample + +@item +If the token results from a macro expansion, the line of the macro name, +or possibly the line of the closing parenthesis in the case of +function-like macro expansion. +@end itemize + +The @code{cpp_token} structure contains @code{line} and @code{col} +members. The lexer fills these in with the line and column of the first +character of the token. Consequently, but maybe unexpectedly, a token +from the replacement list of a macro expansion carries the location of +the token within the @code{#define} directive, because cpplib expands a +macro by returning pointers to the tokens in its replacement list. The +current implementation of cpplib assigns tokens created from built-in +macros and the @samp{#} and @samp{##} operators the location of the most +recently lexed token. This is a because they are allocated from the +lexer's token runs, and because of the way the diagnostic routines infer +the appropriate location to report. + +The diagnostic routines in cpplib display the location of the most +recently @emph{lexed} token, unless they are passed a specific line and +column to report. For diagnostics regarding tokens that arise from +macro expansions, it might also be helpful for the user to see the +original location in the macro definition that the token came from. +Since that is exactly the information each token carries, such an +enhancement could be made relatively easily in future. + +The stand-alone preprocessor faces a similar problem when determining +the correct line to output the token on: the position attached to a +token is fairly useless if the token came from a macro expansion. All +tokens on a logical line should be output on its first physical line, so +the token's reported location is also wrong if it is part of a physical +line other than the first. + +To solve these issues, cpplib provides a callback that is generated +whenever it lexes a preprocessing token that starts a new logical line +other than a directive. It passes this token (which may be a +@code{CPP_EOF} token indicating the end of the translation unit) to the +callback routine, which can then use the line and column of this token +to produce correct output. + +@section Representation of line numbers + +As mentioned above, cpplib stores with each token the line number that +it was lexed on. In fact, this number is not the number of the line in +the source file, but instead bears more resemblance to the number of the +line in the translation unit. + +The preprocessor maintains a monotonic increasing line count, which is +incremented at every new line character (and also at the end of any +buffer that does not end in a new line). Since a line number of zero is +useful to indicate certain special states and conditions, this variable +starts counting from one. + +This variable therefore uniquely enumerates each line in the translation +unit. With some simple infrastructure, it is straight forward to map +from this to the original source file and line number pair, saving space +whenever line number information needs to be saved. The code the +implements this mapping lies in the files @file{line-map.cc} and +@file{line-map.h}. + +Command-line macros and assertions are implemented by pushing a buffer +containing the right hand side of an equivalent @code{#define} or +@code{#assert} directive. Some built-in macros are handled similarly. +Since these are all processed before the first line of the main input +file, it will typically have an assigned line closer to twenty than to +one. + +@node Guard Macros +@unnumbered The Multiple-Include Optimization +@cindex guard macros +@cindex controlling macros +@cindex multiple-include optimization + +Header files are often of the form + +@smallexample +#ifndef FOO +#define FOO +@dots{} +#endif +@end smallexample + +@noindent +to prevent the compiler from processing them more than once. The +preprocessor notices such header files, so that if the header file +appears in a subsequent @code{#include} directive and @code{FOO} is +defined, then it is ignored and it doesn't preprocess or even re-open +the file a second time. This is referred to as the @dfn{multiple +include optimization}. + +Under what circumstances is such an optimization valid? If the file +were included a second time, it can only be optimized away if that +inclusion would result in no tokens to return, and no relevant +directives to process. Therefore the current implementation imposes +requirements and makes some allowances as follows: + +@enumerate +@item +There must be no tokens outside the controlling @code{#if}-@code{#endif} +pair, but whitespace and comments are permitted. + +@item +There must be no directives outside the controlling directive pair, but +the @dfn{null directive} (a line containing nothing other than a single +@samp{#} and possibly whitespace) is permitted. + +@item +The opening directive must be of the form + +@smallexample +#ifndef FOO +@end smallexample + +or + +@smallexample +#if !defined FOO [equivalently, #if !defined(FOO)] +@end smallexample + +@item +In the second form above, the tokens forming the @code{#if} expression +must have come directly from the source file---no macro expansion must +have been involved. This is because macro definitions can change, and +tracking whether or not a relevant change has been made is not worth the +implementation cost. + +@item +There can be no @code{#else} or @code{#elif} directives at the outer +conditional block level, because they would probably contain something +of interest to a subsequent pass. +@end enumerate + +First, when pushing a new file on the buffer stack, +@code{_stack_include_file} sets the controlling macro @code{mi_cmacro} to +@code{NULL}, and sets @code{mi_valid} to @code{true}. This indicates +that the preprocessor has not yet encountered anything that would +invalidate the multiple-include optimization. As described in the next +few paragraphs, these two variables having these values effectively +indicates top-of-file. + +When about to return a token that is not part of a directive, +@code{_cpp_lex_token} sets @code{mi_valid} to @code{false}. This +enforces the constraint that tokens outside the controlling conditional +block invalidate the optimization. + +The @code{do_if}, when appropriate, and @code{do_ifndef} directive +handlers pass the controlling macro to the function +@code{push_conditional}. cpplib maintains a stack of nested conditional +blocks, and after processing every opening conditional this function +pushes an @code{if_stack} structure onto the stack. In this structure +it records the controlling macro for the block, provided there is one +and we're at top-of-file (as described above). If an @code{#elif} or +@code{#else} directive is encountered, the controlling macro for that +block is cleared to @code{NULL}. Otherwise, it survives until the +@code{#endif} closing the block, upon which @code{do_endif} sets +@code{mi_valid} to true and stores the controlling macro in +@code{mi_cmacro}. + +@code{_cpp_handle_directive} clears @code{mi_valid} when processing any +directive other than an opening conditional and the null directive. +With this, and requiring top-of-file to record a controlling macro, and +no @code{#else} or @code{#elif} for it to survive and be copied to +@code{mi_cmacro} by @code{do_endif}, we have enforced the absence of +directives outside the main conditional block for the optimization to be +on. + +Note that whilst we are inside the conditional block, @code{mi_valid} is +likely to be reset to @code{false}, but this does not matter since +the closing @code{#endif} restores it to @code{true} if appropriate. + +Finally, since @code{_cpp_lex_direct} pops the file off the buffer stack +at @code{EOF} without returning a token, if the @code{#endif} directive +was not followed by any tokens, @code{mi_valid} is @code{true} and +@code{_cpp_pop_file_buffer} remembers the controlling macro associated +with the file. Subsequent calls to @code{stack_include_file} result in +no buffer being pushed if the controlling macro is defined, effecting +the optimization. + +A quick word on how we handle the + +@smallexample +#if !defined FOO +@end smallexample + +@noindent +case. @code{_cpp_parse_expr} and @code{parse_defined} take steps to see +whether the three stages @samp{!}, @samp{defined-expression} and +@samp{end-of-directive} occur in order in a @code{#if} expression. If +so, they return the guard macro to @code{do_if} in the variable +@code{mi_ind_cmacro}, and otherwise set it to @code{NULL}. +@code{enter_macro_context} sets @code{mi_valid} to false, so if a macro +was expanded whilst parsing any part of the expression, then the +top-of-file test in @code{push_conditional} fails and the optimization +is turned off. + +@node Files +@unnumbered File Handling +@cindex files + +Fairly obviously, the file handling code of cpplib resides in the file +@file{files.cc}. It takes care of the details of file searching, +opening, reading and caching, for both the main source file and all the +headers it recursively includes. + +The basic strategy is to minimize the number of system calls. On many +systems, the basic @code{open ()} and @code{fstat ()} system calls can +be quite expensive. For every @code{#include}-d file, we need to try +all the directories in the search path until we find a match. Some +projects, such as glibc, pass twenty or thirty include paths on the +command line, so this can rapidly become time consuming. + +For a header file we have not encountered before we have little choice +but to do this. However, it is often the case that the same headers are +repeatedly included, and in these cases we try to avoid repeating the +filesystem queries whilst searching for the correct file. + +For each file we try to open, we store the constructed path in a splay +tree. This path first undergoes simplification by the function +@code{_cpp_simplify_pathname}. For example, +@file{/usr/include/bits/../foo.h} is simplified to +@file{/usr/include/foo.h} before we enter it in the splay tree and try +to @code{open ()} the file. CPP will then find subsequent uses of +@file{foo.h}, even as @file{/usr/include/foo.h}, in the splay tree and +save system calls. + +Further, it is likely the file contents have also been cached, saving a +@code{read ()} system call. We don't bother caching the contents of +header files that are re-inclusion protected, and whose re-inclusion +macro is defined when we leave the header file for the first time. If +the host supports it, we try to map suitably large files into memory, +rather than reading them in directly. + +The include paths are internally stored on a null-terminated +singly-linked list, starting with the @code{"header.h"} directory search +chain, which then links into the @code{} directory chain. + +Files included with the @code{} syntax start the lookup directly +in the second half of this chain. However, files included with the +@code{"foo.h"} syntax start at the beginning of the chain, but with one +extra directory prepended. This is the directory of the current file; +the one containing the @code{#include} directive. Prepending this +directory on a per-file basis is handled by the function +@code{search_from}. + +Note that a header included with a directory component, such as +@code{#include "mydir/foo.h"} and opened as +@file{/usr/local/include/mydir/foo.h}, will have the complete path minus +the basename @samp{foo.h} as the current directory. + +Enough information is stored in the splay tree that CPP can immediately +tell whether it can skip the header file because of the multiple include +optimization, whether the file didn't exist or couldn't be opened for +some reason, or whether the header was flagged not to be re-used, as it +is with the obsolete @code{#import} directive. + +For the benefit of MS-DOS filesystems with an 8.3 filename limitation, +CPP offers the ability to treat various include file names as aliases +for the real header files with shorter names. The map from one to the +other is found in a special file called @samp{header.gcc}, stored in the +command line (or system) include directories to which the mapping +applies. This may be higher up the directory tree than the full path to +the file minus the base name. + +@node Concept Index +@unnumbered Concept Index +@printindex cp + +@bye diff --git a/gcc/doc/cppopts.texi b/gcc/doc/cppopts.texi new file mode 100644 index 00000000000..c0a92b37018 --- /dev/null +++ b/gcc/doc/cppopts.texi @@ -0,0 +1,557 @@ +@c Copyright (C) 1999-2022 Free Software Foundation, Inc. +@c This is part of the CPP and GCC manuals. +@c For copying conditions, see the file gcc.texi. + +@c --------------------------------------------------------------------- +@c Options affecting the preprocessor +@c --------------------------------------------------------------------- + +@c If this file is included with the flag ``cppmanual'' set, it is +@c formatted for inclusion in the CPP manual; otherwise the main GCC manual. + +@item -D @var{name} +@opindex D +Predefine @var{name} as a macro, with definition @code{1}. + +@item -D @var{name}=@var{definition} +The contents of @var{definition} are tokenized and processed as if +they appeared during translation phase three in a @samp{#define} +directive. In particular, the definition is truncated by +embedded newline characters. + +If you are invoking the preprocessor from a shell or shell-like +program you may need to use the shell's quoting syntax to protect +characters such as spaces that have a meaning in the shell syntax. + +If you wish to define a function-like macro on the command line, write +its argument list with surrounding parentheses before the equals sign +(if any). Parentheses are meaningful to most shells, so you should +quote the option. With @command{sh} and @command{csh}, +@option{-D'@var{name}(@var{args@dots{}})=@var{definition}'} works. + +@option{-D} and @option{-U} options are processed in the order they +are given on the command line. All @option{-imacros @var{file}} and +@option{-include @var{file}} options are processed after all +@option{-D} and @option{-U} options. + +@item -U @var{name} +@opindex U +Cancel any previous definition of @var{name}, either built in or +provided with a @option{-D} option. + +@item -include @var{file} +@opindex include +Process @var{file} as if @code{#include "file"} appeared as the first +line of the primary source file. However, the first directory searched +for @var{file} is the preprocessor's working directory @emph{instead of} +the directory containing the main source file. If not found there, it +is searched for in the remainder of the @code{#include "@dots{}"} search +chain as normal. + +If multiple @option{-include} options are given, the files are included +in the order they appear on the command line. + +@item -imacros @var{file} +@opindex imacros +Exactly like @option{-include}, except that any output produced by +scanning @var{file} is thrown away. Macros it defines remain defined. +This allows you to acquire all the macros from a header without also +processing its declarations. + +All files specified by @option{-imacros} are processed before all files +specified by @option{-include}. + +@item -undef +@opindex undef +Do not predefine any system-specific or GCC-specific macros. The +standard predefined macros remain defined. +@ifset cppmanual +@xref{Standard Predefined Macros}. +@end ifset + +@item -pthread +@opindex pthread +Define additional macros required for using the POSIX threads library. +You should use this option consistently for both compilation and linking. +This option is supported on GNU/Linux targets, most other Unix derivatives, +and also on x86 Cygwin and MinGW targets. + +@item -M +@opindex M +@cindex @command{make} +@cindex dependencies, @command{make} +Instead of outputting the result of preprocessing, output a rule +suitable for @command{make} describing the dependencies of the main +source file. The preprocessor outputs one @command{make} rule containing +the object file name for that source file, a colon, and the names of all +the included files, including those coming from @option{-include} or +@option{-imacros} command-line options. + +Unless specified explicitly (with @option{-MT} or @option{-MQ}), the +object file name consists of the name of the source file with any +suffix replaced with object file suffix and with any leading directory +parts removed. If there are many included files then the rule is +split into several lines using @samp{\}-newline. The rule has no +commands. + +This option does not suppress the preprocessor's debug output, such as +@option{-dM}. To avoid mixing such debug output with the dependency +rules you should explicitly specify the dependency output file with +@option{-MF}, or use an environment variable like +@env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output +is still sent to the regular output stream as normal. + +Passing @option{-M} to the driver implies @option{-E}, and suppresses +warnings with an implicit @option{-w}. + +@item -MM +@opindex MM +Like @option{-M} but do not mention header files that are found in +system header directories, nor header files that are included, +directly or indirectly, from such a header. + +This implies that the choice of angle brackets or double quotes in an +@samp{#include} directive does not in itself determine whether that +header appears in @option{-MM} dependency output. + +@anchor{dashMF} +@item -MF @var{file} +@opindex MF +When used with @option{-M} or @option{-MM}, specifies a +file to write the dependencies to. If no @option{-MF} switch is given +the preprocessor sends the rules to the same place it would send +preprocessed output. + +When used with the driver options @option{-MD} or @option{-MMD}, +@option{-MF} overrides the default dependency output file. + +If @var{file} is @file{-}, then the dependencies are written to @file{stdout}. + +@item -MG +@opindex MG +In conjunction with an option such as @option{-M} requesting +dependency generation, @option{-MG} assumes missing header files are +generated files and adds them to the dependency list without raising +an error. The dependency filename is taken directly from the +@code{#include} directive without prepending any path. @option{-MG} +also suppresses preprocessed output, as a missing header file renders +this useless. + +This feature is used in automatic updating of makefiles. + +@item -Mno-modules +@opindex Mno-modules +Disable dependency generation for compiled module interfaces. + +@item -MP +@opindex MP +This option instructs CPP to add a phony target for each dependency +other than the main file, causing each to depend on nothing. These +dummy rules work around errors @command{make} gives if you remove header +files without updating the @file{Makefile} to match. + +This is typical output: + +@smallexample +test.o: test.c test.h + +test.h: +@end smallexample + +@item -MT @var{target} +@opindex MT + +Change the target of the rule emitted by dependency generation. By +default CPP takes the name of the main input file, deletes any +directory components and any file suffix such as @samp{.c}, and +appends the platform's usual object suffix. The result is the target. + +An @option{-MT} option sets the target to be exactly the string you +specify. If you want multiple targets, you can specify them as a single +argument to @option{-MT}, or use multiple @option{-MT} options. + +For example, @option{@w{-MT '$(objpfx)foo.o'}} might give + +@smallexample +$(objpfx)foo.o: foo.c +@end smallexample + +@item -MQ @var{target} +@opindex MQ + +Same as @option{-MT}, but it quotes any characters which are special to +Make. @option{@w{-MQ '$(objpfx)foo.o'}} gives + +@smallexample +$$(objpfx)foo.o: foo.c +@end smallexample + +The default target is automatically quoted, as if it were given with +@option{-MQ}. + +@item -MD +@opindex MD +@option{-MD} is equivalent to @option{-M -MF @var{file}}, except that +@option{-E} is not implied. The driver determines @var{file} based on +whether an @option{-o} option is given. If it is, the driver uses its +argument but with a suffix of @file{.d}, otherwise it takes the name +of the input file, removes any directory components and suffix, and +applies a @file{.d} suffix. + +If @option{-MD} is used in conjunction with @option{-E}, any +@option{-o} switch is understood to specify the dependency output file +(@pxref{dashMF,,-MF}), but if used without @option{-E}, each @option{-o} +is understood to specify a target object file. + +Since @option{-E} is not implied, @option{-MD} can be used to generate +a dependency output file as a side effect of the compilation process. + +@item -MMD +@opindex MMD +Like @option{-MD} except mention only user header files, not system +header files. + +@item -fpreprocessed +@opindex fpreprocessed +Indicate to the preprocessor that the input file has already been +preprocessed. This suppresses things like macro expansion, trigraph +conversion, escaped newline splicing, and processing of most directives. +The preprocessor still recognizes and removes comments, so that you can +pass a file preprocessed with @option{-C} to the compiler without +problems. In this mode the integrated preprocessor is little more than +a tokenizer for the front ends. + +@option{-fpreprocessed} is implicit if the input file has one of the +extensions @samp{.i}, @samp{.ii} or @samp{.mi}. These are the +extensions that GCC uses for preprocessed files created by +@option{-save-temps}. + +@item -fdirectives-only +@opindex fdirectives-only +When preprocessing, handle directives, but do not expand macros. + +The option's behavior depends on the @option{-E} and @option{-fpreprocessed} +options. + +With @option{-E}, preprocessing is limited to the handling of directives +such as @code{#define}, @code{#ifdef}, and @code{#error}. Other +preprocessor operations, such as macro expansion and trigraph +conversion are not performed. In addition, the @option{-dD} option is +implicitly enabled. + +With @option{-fpreprocessed}, predefinition of command line and most +builtin macros is disabled. Macros such as @code{__LINE__}, which are +contextually dependent, are handled normally. This enables compilation of +files previously preprocessed with @code{-E -fdirectives-only}. + +With both @option{-E} and @option{-fpreprocessed}, the rules for +@option{-fpreprocessed} take precedence. This enables full preprocessing of +files previously preprocessed with @code{-E -fdirectives-only}. + +@item -fdollars-in-identifiers +@opindex fdollars-in-identifiers +@anchor{fdollars-in-identifiers} +Accept @samp{$} in identifiers. +@ifset cppmanual +@xref{Identifier characters}. +@end ifset + +@item -fextended-identifiers +@opindex fextended-identifiers +Accept universal character names and extended characters in +identifiers. This option is enabled by default for C99 (and later C +standard versions) and C++. + +@item -fno-canonical-system-headers +@opindex fno-canonical-system-headers +When preprocessing, do not shorten system header paths with canonicalization. + +@item -fmax-include-depth=@var{depth} +@opindex fmax-include-depth +Set the maximum depth of the nested #include. The default is 200. + +@item -ftabstop=@var{width} +@opindex ftabstop +Set the distance between tab stops. This helps the preprocessor report +correct column numbers in warnings or errors, even if tabs appear on the +line. If the value is less than 1 or greater than 100, the option is +ignored. The default is 8. + +@item -ftrack-macro-expansion@r{[}=@var{level}@r{]} +@opindex ftrack-macro-expansion +Track locations of tokens across macro expansions. This allows the +compiler to emit diagnostic about the current macro expansion stack +when a compilation error occurs in a macro expansion. Using this +option makes the preprocessor and the compiler consume more +memory. The @var{level} parameter can be used to choose the level of +precision of token location tracking thus decreasing the memory +consumption if necessary. Value @samp{0} of @var{level} de-activates +this option. Value @samp{1} tracks tokens locations in a +degraded mode for the sake of minimal memory overhead. In this mode +all tokens resulting from the expansion of an argument of a +function-like macro have the same location. Value @samp{2} tracks +tokens locations completely. This value is the most memory hungry. +When this option is given no argument, the default parameter value is +@samp{2}. + +Note that @code{-ftrack-macro-expansion=2} is activated by default. + +@item -fmacro-prefix-map=@var{old}=@var{new} +@opindex fmacro-prefix-map +When preprocessing files residing in directory @file{@var{old}}, +expand the @code{__FILE__} and @code{__BASE_FILE__} macros as if the +files resided in directory @file{@var{new}} instead. This can be used +to change an absolute path to a relative path by using @file{.} for +@var{new} which can result in more reproducible builds that are +location independent. This option also affects +@code{__builtin_FILE()} during compilation. See also +@option{-ffile-prefix-map}. + +@item -fexec-charset=@var{charset} +@opindex fexec-charset +@cindex character set, execution +Set the execution character set, used for string and character +constants. The default is UTF-8. @var{charset} can be any encoding +supported by the system's @code{iconv} library routine. + +@item -fwide-exec-charset=@var{charset} +@opindex fwide-exec-charset +@cindex character set, wide execution +Set the wide execution character set, used for wide string and +character constants. The default is one of UTF-32BE, UTF-32LE, UTF-16BE, +or UTF-16LE, whichever corresponds to the width of @code{wchar_t} and the +big-endian or little-endian byte order being used for code generation. As +with @option{-fexec-charset}, @var{charset} can be any encoding supported +by the system's @code{iconv} library routine; however, you will have +problems with encodings that do not fit exactly in @code{wchar_t}. + +@item -finput-charset=@var{charset} +@opindex finput-charset +@cindex character set, input +Set the input character set, used for translation from the character +set of the input file to the source character set used by GCC@. If the +locale does not specify, or GCC cannot get this information from the +locale, the default is UTF-8. This can be overridden by either the locale +or this command-line option. Currently the command-line option takes +precedence if there's a conflict. @var{charset} can be any encoding +supported by the system's @code{iconv} library routine. + +@ifclear cppmanual +@item -fpch-deps +@opindex fpch-deps +When using precompiled headers (@pxref{Precompiled Headers}), this flag +causes the dependency-output flags to also list the files from the +precompiled header's dependencies. If not specified, only the +precompiled header are listed and not the files that were used to +create it, because those files are not consulted when a precompiled +header is used. + +@item -fpch-preprocess +@opindex fpch-preprocess +This option allows use of a precompiled header (@pxref{Precompiled +Headers}) together with @option{-E}. It inserts a special @code{#pragma}, +@code{#pragma GCC pch_preprocess "@var{filename}"} in the output to mark +the place where the precompiled header was found, and its @var{filename}. +When @option{-fpreprocessed} is in use, GCC recognizes this @code{#pragma} +and loads the PCH@. + +This option is off by default, because the resulting preprocessed output +is only really suitable as input to GCC@. It is switched on by +@option{-save-temps}. + +You should not write this @code{#pragma} in your own code, but it is +safe to edit the filename if the PCH file is available in a different +location. The filename may be absolute or it may be relative to GCC's +current directory. +@end ifclear + +@item -fworking-directory +@opindex fworking-directory +@opindex fno-working-directory +Enable generation of linemarkers in the preprocessor output that +let the compiler know the current working directory at the time of +preprocessing. When this option is enabled, the preprocessor +emits, after the initial linemarker, a second linemarker with the +current working directory followed by two slashes. GCC uses this +directory, when it's present in the preprocessed input, as the +directory emitted as the current working directory in some debugging +information formats. This option is implicitly enabled if debugging +information is enabled, but this can be inhibited with the negated +form @option{-fno-working-directory}. If the @option{-P} flag is +present in the command line, this option has no effect, since no +@code{#line} directives are emitted whatsoever. + +@item -A @var{predicate}=@var{answer} +@opindex A +Make an assertion with the predicate @var{predicate} and answer +@var{answer}. This form is preferred to the older form @option{-A +@var{predicate}(@var{answer})}, which is still supported, because +it does not use shell special characters. +@ifset cppmanual +@xref{Obsolete Features}. +@end ifset + +@item -A -@var{predicate}=@var{answer} +Cancel an assertion with the predicate @var{predicate} and answer +@var{answer}. + +@item -C +@opindex C +Do not discard comments. All comments are passed through to the output +file, except for comments in processed directives, which are deleted +along with the directive. + +You should be prepared for side effects when using @option{-C}; it +causes the preprocessor to treat comments as tokens in their own right. +For example, comments appearing at the start of what would be a +directive line have the effect of turning that line into an ordinary +source line, since the first token on the line is no longer a @samp{#}. + +@item -CC +@opindex CC +Do not discard comments, including during macro expansion. This is +like @option{-C}, except that comments contained within macros are +also passed through to the output file where the macro is expanded. + +In addition to the side effects of the @option{-C} option, the +@option{-CC} option causes all C++-style comments inside a macro +to be converted to C-style comments. This is to prevent later use +of that macro from inadvertently commenting out the remainder of +the source line. + +The @option{-CC} option is generally used to support lint comments. + +@item -P +@opindex P +Inhibit generation of linemarkers in the output from the preprocessor. +This might be useful when running the preprocessor on something that is +not C code, and will be sent to a program which might be confused by the +linemarkers. +@ifset cppmanual +@xref{Preprocessor Output}. +@end ifset + +@cindex traditional C language +@cindex C language, traditional +@item -traditional +@itemx -traditional-cpp +@opindex traditional-cpp +@opindex traditional + +Try to imitate the behavior of pre-standard C preprocessors, as +opposed to ISO C preprocessors. +@ifset cppmanual +@xref{Traditional Mode}. +@end ifset +@ifclear cppmanual +See the GNU CPP manual for details. +@end ifclear + +Note that GCC does not otherwise attempt to emulate a pre-standard +C compiler, and these options are only supported with the @option{-E} +switch, or when invoking CPP explicitly. + +@item -trigraphs +@opindex trigraphs +Support ISO C trigraphs. +These are three-character sequences, all starting with @samp{??}, that +are defined by ISO C to stand for single characters. For example, +@samp{??/} stands for @samp{\}, so @samp{'??/n'} is a character +constant for a newline. +@ifset cppmanual +@xref{Initial processing}. +@end ifset + +@ifclear cppmanual +The nine trigraphs and their replacements are + +@smallexample +Trigraph: ??( ??) ??< ??> ??= ??/ ??' ??! ??- +Replacement: [ ] @{ @} # \ ^ | ~ +@end smallexample +@end ifclear + +By default, GCC ignores trigraphs, but in +standard-conforming modes it converts them. See the @option{-std} and +@option{-ansi} options. + +@item -remap +@opindex remap +Enable special code to work around file systems which only permit very +short file names, such as MS-DOS@. + +@item -H +@opindex H +Print the name of each header file used, in addition to other normal +activities. Each name is indented to show how deep in the +@samp{#include} stack it is. Precompiled header files are also +printed, even if they are found to be invalid; an invalid precompiled +header file is printed with @samp{...x} and a valid one with @samp{...!} . + +@item -d@var{letters} +@opindex d +Says to make debugging dumps during compilation as specified by +@var{letters}. The flags documented here are those relevant to the +preprocessor. Other @var{letters} are interpreted +by the compiler proper, or reserved for future versions of GCC, and so +are silently ignored. If you specify @var{letters} whose behavior +conflicts, the result is undefined. +@ifclear cppmanual +@xref{Developer Options}, for more information. +@end ifclear + +@table @gcctabopt +@item -dM +@opindex dM +Instead of the normal output, generate a list of @samp{#define} +directives for all the macros defined during the execution of the +preprocessor, including predefined macros. This gives you a way of +finding out what is predefined in your version of the preprocessor. +Assuming you have no file @file{foo.h}, the command + +@smallexample +touch foo.h; cpp -dM foo.h +@end smallexample + +@noindent +shows all the predefined macros. + +@ifclear cppmanual +If you use @option{-dM} without the @option{-E} option, @option{-dM} is +interpreted as a synonym for @option{-fdump-rtl-mach}. +@xref{Developer Options, , ,gcc}. +@end ifclear + +@item -dD +@opindex dD +Like @option{-dM} except in two respects: it does @emph{not} include the +predefined macros, and it outputs @emph{both} the @samp{#define} +directives and the result of preprocessing. Both kinds of output go to +the standard output file. + +@item -dN +@opindex dN +Like @option{-dD}, but emit only the macro names, not their expansions. + +@item -dI +@opindex dI +Output @samp{#include} directives in addition to the result of +preprocessing. + +@item -dU +@opindex dU +Like @option{-dD} except that only macros that are expanded, or whose +definedness is tested in preprocessor directives, are output; the +output is delayed until the use or test of the macro; and +@samp{#undef} directives are also output for macros tested but +undefined at the time. +@end table + +@item -fdebug-cpp +@opindex fdebug-cpp +This option is only useful for debugging GCC. When used from CPP or with +@option{-E}, it dumps debugging information about location maps. Every +token in the output is preceded by the dump of the map its location +belongs to. + +When used from GCC without @option{-E}, this option has no effect. diff --git a/gcc/doc/cppwarnopts.texi b/gcc/doc/cppwarnopts.texi new file mode 100644 index 00000000000..fa048249369 --- /dev/null +++ b/gcc/doc/cppwarnopts.texi @@ -0,0 +1,82 @@ +@c Copyright (C) 1999-2022 Free Software Foundation, Inc. +@c This is part of the CPP and GCC manuals. +@c For copying conditions, see the file gcc.texi. + +@c --------------------------------------------------------------------- +@c Options affecting preprocessor warnings +@c --------------------------------------------------------------------- + +@c If this file is included with the flag ``cppmanual'' set, it is +@c formatted for inclusion in the CPP manual; otherwise the main GCC manual. + +@item -Wcomment +@itemx -Wcomments +@opindex Wcomment +@opindex Wcomments +Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} +comment, or whenever a backslash-newline appears in a @samp{//} comment. +This warning is enabled by @option{-Wall}. + +@item -Wtrigraphs +@opindex Wtrigraphs +@anchor{Wtrigraphs} +Warn if any trigraphs are encountered that might change the meaning of +the program. Trigraphs within comments are not warned about, +except those that would form escaped newlines. + +This option is implied by @option{-Wall}. If @option{-Wall} is not +given, this option is still enabled unless trigraphs are enabled. To +get trigraph conversion without warnings, but get the other +@option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}. + +@item -Wundef +@opindex Wundef +@opindex Wno-undef +Warn if an undefined identifier is evaluated in an @code{#if} directive. +Such identifiers are replaced with zero. + +@item -Wexpansion-to-defined +@opindex Wexpansion-to-defined +Warn whenever @samp{defined} is encountered in the expansion of a macro +(including the case where the macro is expanded by an @samp{#if} directive). +Such usage is not portable. +This warning is also enabled by @option{-Wpedantic} and @option{-Wextra}. + +@item -Wunused-macros +@opindex Wunused-macros +Warn about macros defined in the main file that are unused. A macro +is @dfn{used} if it is expanded or tested for existence at least once. +The preprocessor also warns if the macro has not been used at the +time it is redefined or undefined. + +Built-in macros, macros defined on the command line, and macros +defined in include files are not warned about. + +@emph{Note:} If a macro is actually used, but only used in skipped +conditional blocks, then the preprocessor reports it as unused. To avoid the +warning in such a case, you might improve the scope of the macro's +definition by, for example, moving it into the first skipped block. +Alternatively, you could provide a dummy use with something like: + +@smallexample +#if defined the_macro_causing_the_warning +#endif +@end smallexample + +@item -Wno-endif-labels +@opindex Wno-endif-labels +@opindex Wendif-labels +Do not warn whenever an @code{#else} or an @code{#endif} are followed by text. +This sometimes happens in older programs with code of the form + +@smallexample +#if FOO +@dots{} +#else FOO +@dots{} +#endif FOO +@end smallexample + +@noindent +The second and third @code{FOO} should be in comments. +This warning is on by default. diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi new file mode 100644 index 00000000000..8da0db9770d --- /dev/null +++ b/gcc/doc/extend.texi @@ -0,0 +1,25550 @@ +c Copyright (C) 1988-2022 Free Software Foundation, Inc. + +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node C Extensions +@chapter Extensions to the C Language Family +@cindex extensions, C language +@cindex C language extensions + +@opindex pedantic +GNU C provides several language features not found in ISO standard C@. +(The @option{-pedantic} option directs GCC to print a warning message if +any of these features is used.) To test for the availability of these +features in conditional compilation, check for a predefined macro +@code{__GNUC__}, which is always defined under GCC@. + +These extensions are available in C and Objective-C@. Most of them are +also available in C++. @xref{C++ Extensions,,Extensions to the +C++ Language}, for extensions that apply @emph{only} to C++. + +Some features that are in ISO C99 but not C90 or C++ are also, as +extensions, accepted by GCC in C90 mode and in C++. + +@menu +* Statement Exprs:: Putting statements and declarations inside expressions. +* Local Labels:: Labels local to a block. +* Labels as Values:: Getting pointers to labels, and computed gotos. +* Nested Functions:: Nested function in GNU C. +* Nonlocal Gotos:: Nonlocal gotos. +* Constructing Calls:: Dispatching a call to another function. +* Typeof:: @code{typeof}: referring to the type of an expression. +* Conditionals:: Omitting the middle operand of a @samp{?:} expression. +* __int128:: 128-bit integers---@code{__int128}. +* Long Long:: Double-word integers---@code{long long int}. +* Complex:: Data types for complex numbers. +* Floating Types:: Additional Floating Types. +* Half-Precision:: Half-Precision Floating Point. +* Decimal Float:: Decimal Floating Types. +* Hex Floats:: Hexadecimal floating-point constants. +* Fixed-Point:: Fixed-Point Types. +* Named Address Spaces::Named address spaces. +* Zero Length:: Zero-length arrays. +* Empty Structures:: Structures with no members. +* Variable Length:: Arrays whose length is computed at run time. +* Variadic Macros:: Macros with a variable number of arguments. +* Escaped Newlines:: Slightly looser rules for escaped newlines. +* Subscripting:: Any array can be subscripted, even if not an lvalue. +* Pointer Arith:: Arithmetic on @code{void}-pointers and function pointers. +* Variadic Pointer Args:: Pointer arguments to variadic functions. +* Pointers to Arrays:: Pointers to arrays with qualifiers work as expected. +* Initializers:: Non-constant initializers. +* Compound Literals:: Compound literals give structures, unions + or arrays as values. +* Designated Inits:: Labeling elements of initializers. +* Case Ranges:: `case 1 ... 9' and such. +* Cast to Union:: Casting to union type from any member of the union. +* Mixed Labels and Declarations:: Mixing declarations, labels and code. +* Function Attributes:: Declaring that functions have no side effects, + or that they can never return. +* Variable Attributes:: Specifying attributes of variables. +* Type Attributes:: Specifying attributes of types. +* Label Attributes:: Specifying attributes on labels. +* Enumerator Attributes:: Specifying attributes on enumerators. +* Statement Attributes:: Specifying attributes on statements. +* Attribute Syntax:: Formal syntax for attributes. +* Function Prototypes:: Prototype declarations and old-style definitions. +* C++ Comments:: C++ comments are recognized. +* Dollar Signs:: Dollar sign is allowed in identifiers. +* Character Escapes:: @samp{\e} stands for the character @key{ESC}. +* Alignment:: Determining the alignment of a function, type or variable. +* Inline:: Defining inline functions (as fast as macros). +* Volatiles:: What constitutes an access to a volatile object. +* Using Assembly Language with C:: Instructions and extensions for interfacing C with assembler. +* Alternate Keywords:: @code{__const__}, @code{__asm__}, etc., for header files. +* Incomplete Enums:: @code{enum foo;}, with details to follow. +* Function Names:: Printable strings which are the name of the current + function. +* Return Address:: Getting the return or frame address of a function. +* Vector Extensions:: Using vector instructions through built-in functions. +* Offsetof:: Special syntax for implementing @code{offsetof}. +* __sync Builtins:: Legacy built-in functions for atomic memory access. +* __atomic Builtins:: Atomic built-in functions with memory model. +* Integer Overflow Builtins:: Built-in functions to perform arithmetics and + arithmetic overflow checking. +* x86 specific memory model extensions for transactional memory:: x86 memory models. +* Object Size Checking:: Built-in functions for limited buffer overflow + checking. +* Other Builtins:: Other built-in functions. +* Target Builtins:: Built-in functions specific to particular targets. +* Target Format Checks:: Format checks specific to particular targets. +* Pragmas:: Pragmas accepted by GCC. +* Unnamed Fields:: Unnamed struct/union fields within structs/unions. +* Thread-Local:: Per-thread variables. +* Binary constants:: Binary constants using the @samp{0b} prefix. +@end menu + +@node Statement Exprs +@section Statements and Declarations in Expressions +@cindex statements inside expressions +@cindex declarations inside expressions +@cindex expressions containing statements +@cindex macros, statements in expressions + +@c the above section title wrapped and causes an underfull hbox.. i +@c changed it from "within" to "in". --mew 4feb93 +A compound statement enclosed in parentheses may appear as an expression +in GNU C@. This allows you to use loops, switches, and local variables +within an expression. + +Recall that a compound statement is a sequence of statements surrounded +by braces; in this construct, parentheses go around the braces. For +example: + +@smallexample +(@{ int y = foo (); int z; + if (y > 0) z = y; + else z = - y; + z; @}) +@end smallexample + +@noindent +is a valid (though slightly more complex than necessary) expression +for the absolute value of @code{foo ()}. + +The last thing in the compound statement should be an expression +followed by a semicolon; the value of this subexpression serves as the +value of the entire construct. (If you use some other kind of statement +last within the braces, the construct has type @code{void}, and thus +effectively no value.) + +This feature is especially useful in making macro definitions ``safe'' (so +that they evaluate each operand exactly once). For example, the +``maximum'' function is commonly defined as a macro in standard C as +follows: + +@smallexample +#define max(a,b) ((a) > (b) ? (a) : (b)) +@end smallexample + +@noindent +@cindex side effects, macro argument +But this definition computes either @var{a} or @var{b} twice, with bad +results if the operand has side effects. In GNU C, if you know the +type of the operands (here taken as @code{int}), you can avoid this +problem by defining the macro as follows: + +@smallexample +#define maxint(a,b) \ + (@{int _a = (a), _b = (b); _a > _b ? _a : _b; @}) +@end smallexample + +Note that introducing variable declarations (as we do in @code{maxint}) can +cause variable shadowing, so while this example using the @code{max} macro +produces correct results: +@smallexample +int _a = 1, _b = 2, c; +c = max (_a, _b); +@end smallexample +@noindent +this example using maxint will not: +@smallexample +int _a = 1, _b = 2, c; +c = maxint (_a, _b); +@end smallexample + +This problem may for instance occur when we use this pattern recursively, like +so: + +@smallexample +#define maxint3(a, b, c) \ + (@{int _a = (a), _b = (b), _c = (c); maxint (maxint (_a, _b), _c); @}) +@end smallexample + +Embedded statements are not allowed in constant expressions, such as +the value of an enumeration constant, the width of a bit-field, or +the initial value of a static variable. + +If you don't know the type of the operand, you can still do this, but you +must use @code{typeof} or @code{__auto_type} (@pxref{Typeof}). + +In G++, the result value of a statement expression undergoes array and +function pointer decay, and is returned by value to the enclosing +expression. For instance, if @code{A} is a class, then + +@smallexample + A a; + + (@{a;@}).Foo () +@end smallexample + +@noindent +constructs a temporary @code{A} object to hold the result of the +statement expression, and that is used to invoke @code{Foo}. +Therefore the @code{this} pointer observed by @code{Foo} is not the +address of @code{a}. + +In a statement expression, any temporaries created within a statement +are destroyed at that statement's end. This makes statement +expressions inside macros slightly different from function calls. In +the latter case temporaries introduced during argument evaluation are +destroyed at the end of the statement that includes the function +call. In the statement expression case they are destroyed during +the statement expression. For instance, + +@smallexample +#define macro(a) (@{__typeof__(a) b = (a); b + 3; @}) +template T function(T a) @{ T b = a; return b + 3; @} + +void foo () +@{ + macro (X ()); + function (X ()); +@} +@end smallexample + +@noindent +has different places where temporaries are destroyed. For the +@code{macro} case, the temporary @code{X} is destroyed just after +the initialization of @code{b}. In the @code{function} case that +temporary is destroyed when the function returns. + +These considerations mean that it is probably a bad idea to use +statement expressions of this form in header files that are designed to +work with C++. (Note that some versions of the GNU C Library contained +header files using statement expressions that lead to precisely this +bug.) + +Jumping into a statement expression with @code{goto} or using a +@code{switch} statement outside the statement expression with a +@code{case} or @code{default} label inside the statement expression is +not permitted. Jumping into a statement expression with a computed +@code{goto} (@pxref{Labels as Values}) has undefined behavior. +Jumping out of a statement expression is permitted, but if the +statement expression is part of a larger expression then it is +unspecified which other subexpressions of that expression have been +evaluated except where the language definition requires certain +subexpressions to be evaluated before or after the statement +expression. A @code{break} or @code{continue} statement inside of +a statement expression used in @code{while}, @code{do} or @code{for} +loop or @code{switch} statement condition +or @code{for} statement init or increment expressions jumps to an +outer loop or @code{switch} statement if any (otherwise it is an error), +rather than to the loop or @code{switch} statement in whose condition +or init or increment expression it appears. +In any case, as with a function call, the evaluation of a +statement expression is not interleaved with the evaluation of other +parts of the containing expression. For example, + +@smallexample + foo (), ((@{ bar1 (); goto a; 0; @}) + bar2 ()), baz(); +@end smallexample + +@noindent +calls @code{foo} and @code{bar1} and does not call @code{baz} but +may or may not call @code{bar2}. If @code{bar2} is called, it is +called after @code{foo} and before @code{bar1}. + +@node Local Labels +@section Locally Declared Labels +@cindex local labels +@cindex macros, local labels + +GCC allows you to declare @dfn{local labels} in any nested block +scope. A local label is just like an ordinary label, but you can +only reference it (with a @code{goto} statement, or by taking its +address) within the block in which it is declared. + +A local label declaration looks like this: + +@smallexample +__label__ @var{label}; +@end smallexample + +@noindent +or + +@smallexample +__label__ @var{label1}, @var{label2}, /* @r{@dots{}} */; +@end smallexample + +Local label declarations must come at the beginning of the block, +before any ordinary declarations or statements. + +The label declaration defines the label @emph{name}, but does not define +the label itself. You must do this in the usual way, with +@code{@var{label}:}, within the statements of the statement expression. + +The local label feature is useful for complex macros. If a macro +contains nested loops, a @code{goto} can be useful for breaking out of +them. However, an ordinary label whose scope is the whole function +cannot be used: if the macro can be expanded several times in one +function, the label is multiply defined in that function. A +local label avoids this problem. For example: + +@smallexample +#define SEARCH(value, array, target) \ +do @{ \ + __label__ found; \ + typeof (target) _SEARCH_target = (target); \ + typeof (*(array)) *_SEARCH_array = (array); \ + int i, j; \ + int value; \ + for (i = 0; i < max; i++) \ + for (j = 0; j < max; j++) \ + if (_SEARCH_array[i][j] == _SEARCH_target) \ + @{ (value) = i; goto found; @} \ + (value) = -1; \ + found:; \ +@} while (0) +@end smallexample + +This could also be written using a statement expression: + +@smallexample +#define SEARCH(array, target) \ +(@{ \ + __label__ found; \ + typeof (target) _SEARCH_target = (target); \ + typeof (*(array)) *_SEARCH_array = (array); \ + int i, j; \ + int value; \ + for (i = 0; i < max; i++) \ + for (j = 0; j < max; j++) \ + if (_SEARCH_array[i][j] == _SEARCH_target) \ + @{ value = i; goto found; @} \ + value = -1; \ + found: \ + value; \ +@}) +@end smallexample + +Local label declarations also make the labels they declare visible to +nested functions, if there are any. @xref{Nested Functions}, for details. + +@node Labels as Values +@section Labels as Values +@cindex labels as values +@cindex computed gotos +@cindex goto with computed label +@cindex address of a label + +You can get the address of a label defined in the current function +(or a containing function) with the unary operator @samp{&&}. The +value has type @code{void *}. This value is a constant and can be used +wherever a constant of that type is valid. For example: + +@smallexample +void *ptr; +/* @r{@dots{}} */ +ptr = &&foo; +@end smallexample + +To use these values, you need to be able to jump to one. This is done +with the computed goto statement@footnote{The analogous feature in +Fortran is called an assigned goto, but that name seems inappropriate in +C, where one can do more than simply store label addresses in label +variables.}, @code{goto *@var{exp};}. For example, + +@smallexample +goto *ptr; +@end smallexample + +@noindent +Any expression of type @code{void *} is allowed. + +One way of using these constants is in initializing a static array that +serves as a jump table: + +@smallexample +static void *array[] = @{ &&foo, &&bar, &&hack @}; +@end smallexample + +@noindent +Then you can select a label with indexing, like this: + +@smallexample +goto *array[i]; +@end smallexample + +@noindent +Note that this does not check whether the subscript is in bounds---array +indexing in C never does that. + +Such an array of label values serves a purpose much like that of the +@code{switch} statement. The @code{switch} statement is cleaner, so +use that rather than an array unless the problem does not fit a +@code{switch} statement very well. + +Another use of label values is in an interpreter for threaded code. +The labels within the interpreter function can be stored in the +threaded code for super-fast dispatching. + +You may not use this mechanism to jump to code in a different function. +If you do that, totally unpredictable things happen. The best way to +avoid this is to store the label address only in automatic variables and +never pass it as an argument. + +An alternate way to write the above example is + +@smallexample +static const int array[] = @{ &&foo - &&foo, &&bar - &&foo, + &&hack - &&foo @}; +goto *(&&foo + array[i]); +@end smallexample + +@noindent +This is more friendly to code living in shared libraries, as it reduces +the number of dynamic relocations that are needed, and by consequence, +allows the data to be read-only. +This alternative with label differences is not supported for the AVR target, +please use the first approach for AVR programs. + +The @code{&&foo} expressions for the same label might have different +values if the containing function is inlined or cloned. If a program +relies on them being always the same, +@code{__attribute__((__noinline__,__noclone__))} should be used to +prevent inlining and cloning. If @code{&&foo} is used in a static +variable initializer, inlining and cloning is forbidden. + +@node Nested Functions +@section Nested Functions +@cindex nested functions +@cindex downward funargs +@cindex thunks + +A @dfn{nested function} is a function defined inside another function. +Nested functions are supported as an extension in GNU C, but are not +supported by GNU C++. + +The nested function's name is local to the block where it is defined. +For example, here we define a nested function named @code{square}, and +call it twice: + +@smallexample +@group +foo (double a, double b) +@{ + double square (double z) @{ return z * z; @} + + return square (a) + square (b); +@} +@end group +@end smallexample + +The nested function can access all the variables of the containing +function that are visible at the point of its definition. This is +called @dfn{lexical scoping}. For example, here we show a nested +function which uses an inherited variable named @code{offset}: + +@smallexample +@group +bar (int *array, int offset, int size) +@{ + int access (int *array, int index) + @{ return array[index + offset]; @} + int i; + /* @r{@dots{}} */ + for (i = 0; i < size; i++) + /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */ +@} +@end group +@end smallexample + +Nested function definitions are permitted within functions in the places +where variable definitions are allowed; that is, in any block, mixed +with the other declarations and statements in the block. + +It is possible to call the nested function from outside the scope of its +name by storing its address or passing the address to another function: + +@smallexample +hack (int *array, int size) +@{ + void store (int index, int value) + @{ array[index] = value; @} + + intermediate (store, size); +@} +@end smallexample + +Here, the function @code{intermediate} receives the address of +@code{store} as an argument. If @code{intermediate} calls @code{store}, +the arguments given to @code{store} are used to store into @code{array}. +But this technique works only so long as the containing function +(@code{hack}, in this example) does not exit. + +If you try to call the nested function through its address after the +containing function exits, all hell breaks loose. If you try +to call it after a containing scope level exits, and if it refers +to some of the variables that are no longer in scope, you may be lucky, +but it's not wise to take the risk. If, however, the nested function +does not refer to anything that has gone out of scope, you should be +safe. + +GCC implements taking the address of a nested function using a technique +called @dfn{trampolines}. This technique was described in +@cite{Lexical Closures for C++} (Thomas M. Breuel, USENIX +C++ Conference Proceedings, October 17-21, 1988). + +A nested function can jump to a label inherited from a containing +function, provided the label is explicitly declared in the containing +function (@pxref{Local Labels}). Such a jump returns instantly to the +containing function, exiting the nested function that did the +@code{goto} and any intermediate functions as well. Here is an example: + +@smallexample +@group +bar (int *array, int offset, int size) +@{ + __label__ failure; + int access (int *array, int index) + @{ + if (index > size) + goto failure; + return array[index + offset]; + @} + int i; + /* @r{@dots{}} */ + for (i = 0; i < size; i++) + /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */ + /* @r{@dots{}} */ + return 0; + + /* @r{Control comes here from @code{access} + if it detects an error.} */ + failure: + return -1; +@} +@end group +@end smallexample + +A nested function always has no linkage. Declaring one with +@code{extern} or @code{static} is erroneous. If you need to declare the nested function +before its definition, use @code{auto} (which is otherwise meaningless +for function declarations). + +@smallexample +bar (int *array, int offset, int size) +@{ + __label__ failure; + auto int access (int *, int); + /* @r{@dots{}} */ + int access (int *array, int index) + @{ + if (index > size) + goto failure; + return array[index + offset]; + @} + /* @r{@dots{}} */ +@} +@end smallexample + +@node Nonlocal Gotos +@section Nonlocal Gotos +@cindex nonlocal gotos + +GCC provides the built-in functions @code{__builtin_setjmp} and +@code{__builtin_longjmp} which are similar to, but not interchangeable +with, the C library functions @code{setjmp} and @code{longjmp}. +The built-in versions are used internally by GCC's libraries +to implement exception handling on some targets. You should use the +standard C library functions declared in @code{} in user code +instead of the builtins. + +The built-in versions of these functions use GCC's normal +mechanisms to save and restore registers using the stack on function +entry and exit. The jump buffer argument @var{buf} holds only the +information needed to restore the stack frame, rather than the entire +set of saved register values. + +An important caveat is that GCC arranges to save and restore only +those registers known to the specific architecture variant being +compiled for. This can make @code{__builtin_setjmp} and +@code{__builtin_longjmp} more efficient than their library +counterparts in some cases, but it can also cause incorrect and +mysterious behavior when mixing with code that uses the full register +set. + +You should declare the jump buffer argument @var{buf} to the +built-in functions as: + +@smallexample +#include +intptr_t @var{buf}[5]; +@end smallexample + +@deftypefn {Built-in Function} {int} __builtin_setjmp (intptr_t *@var{buf}) +This function saves the current stack context in @var{buf}. +@code{__builtin_setjmp} returns 0 when returning directly, +and 1 when returning from @code{__builtin_longjmp} using the same +@var{buf}. +@end deftypefn + +@deftypefn {Built-in Function} {void} __builtin_longjmp (intptr_t *@var{buf}, int @var{val}) +This function restores the stack context in @var{buf}, +saved by a previous call to @code{__builtin_setjmp}. After +@code{__builtin_longjmp} is finished, the program resumes execution as +if the matching @code{__builtin_setjmp} returns the value @var{val}, +which must be 1. + +Because @code{__builtin_longjmp} depends on the function return +mechanism to restore the stack context, it cannot be called +from the same function calling @code{__builtin_setjmp} to +initialize @var{buf}. It can only be called from a function called +(directly or indirectly) from the function calling @code{__builtin_setjmp}. +@end deftypefn + +@node Constructing Calls +@section Constructing Function Calls +@cindex constructing calls +@cindex forwarding calls + +Using the built-in functions described below, you can record +the arguments a function received, and call another function +with the same arguments, without knowing the number or types +of the arguments. + +You can also record the return value of that function call, +and later return that value, without knowing what data type +the function tried to return (as long as your caller expects +that data type). + +However, these built-in functions may interact badly with some +sophisticated features or other extensions of the language. It +is, therefore, not recommended to use them outside very simple +functions acting as mere forwarders for their arguments. + +@deftypefn {Built-in Function} {void *} __builtin_apply_args () +This built-in function returns a pointer to data +describing how to perform a call with the same arguments as are passed +to the current function. + +The function saves the arg pointer register, structure value address, +and all registers that might be used to pass arguments to a function +into a block of memory allocated on the stack. Then it returns the +address of that block. +@end deftypefn + +@deftypefn {Built-in Function} {void *} __builtin_apply (void (*@var{function})(), void *@var{arguments}, size_t @var{size}) +This built-in function invokes @var{function} +with a copy of the parameters described by @var{arguments} +and @var{size}. + +The value of @var{arguments} should be the value returned by +@code{__builtin_apply_args}. The argument @var{size} specifies the size +of the stack argument data, in bytes. + +This function returns a pointer to data describing +how to return whatever value is returned by @var{function}. The data +is saved in a block of memory allocated on the stack. + +It is not always simple to compute the proper value for @var{size}. The +value is used by @code{__builtin_apply} to compute the amount of data +that should be pushed on the stack and copied from the incoming argument +area. +@end deftypefn + +@deftypefn {Built-in Function} {void} __builtin_return (void *@var{result}) +This built-in function returns the value described by @var{result} from +the containing function. You should specify, for @var{result}, a value +returned by @code{__builtin_apply}. +@end deftypefn + +@deftypefn {Built-in Function} {} __builtin_va_arg_pack () +This built-in function represents all anonymous arguments of an inline +function. It can be used only in inline functions that are always +inlined, never compiled as a separate function, such as those using +@code{__attribute__ ((__always_inline__))} or +@code{__attribute__ ((__gnu_inline__))} extern inline functions. +It must be only passed as last argument to some other function +with variable arguments. This is useful for writing small wrapper +inlines for variable argument functions, when using preprocessor +macros is undesirable. For example: +@smallexample +extern int myprintf (FILE *f, const char *format, ...); +extern inline __attribute__ ((__gnu_inline__)) int +myprintf (FILE *f, const char *format, ...) +@{ + int r = fprintf (f, "myprintf: "); + if (r < 0) + return r; + int s = fprintf (f, format, __builtin_va_arg_pack ()); + if (s < 0) + return s; + return r + s; +@} +@end smallexample +@end deftypefn + +@deftypefn {Built-in Function} {size_t} __builtin_va_arg_pack_len () +This built-in function returns the number of anonymous arguments of +an inline function. It can be used only in inline functions that +are always inlined, never compiled as a separate function, such +as those using @code{__attribute__ ((__always_inline__))} or +@code{__attribute__ ((__gnu_inline__))} extern inline functions. +For example following does link- or run-time checking of open +arguments for optimized code: +@smallexample +#ifdef __OPTIMIZE__ +extern inline __attribute__((__gnu_inline__)) int +myopen (const char *path, int oflag, ...) +@{ + if (__builtin_va_arg_pack_len () > 1) + warn_open_too_many_arguments (); + + if (__builtin_constant_p (oflag)) + @{ + if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1) + @{ + warn_open_missing_mode (); + return __open_2 (path, oflag); + @} + return open (path, oflag, __builtin_va_arg_pack ()); + @} + + if (__builtin_va_arg_pack_len () < 1) + return __open_2 (path, oflag); + + return open (path, oflag, __builtin_va_arg_pack ()); +@} +#endif +@end smallexample +@end deftypefn + +@node Typeof +@section Referring to a Type with @code{typeof} +@findex typeof +@findex sizeof +@cindex macros, types of arguments + +Another way to refer to the type of an expression is with @code{typeof}. +The syntax of using of this keyword looks like @code{sizeof}, but the +construct acts semantically like a type name defined with @code{typedef}. + +There are two ways of writing the argument to @code{typeof}: with an +expression or with a type. Here is an example with an expression: + +@smallexample +typeof (x[0](1)) +@end smallexample + +@noindent +This assumes that @code{x} is an array of pointers to functions; +the type described is that of the values of the functions. + +Here is an example with a typename as the argument: + +@smallexample +typeof (int *) +@end smallexample + +@noindent +Here the type described is that of pointers to @code{int}. + +If you are writing a header file that must work when included in ISO C +programs, write @code{__typeof__} instead of @code{typeof}. +@xref{Alternate Keywords}. + +A @code{typeof} construct can be used anywhere a typedef name can be +used. For example, you can use it in a declaration, in a cast, or inside +of @code{sizeof} or @code{typeof}. + +The operand of @code{typeof} is evaluated for its side effects if and +only if it is an expression of variably modified type or the name of +such a type. + +@code{typeof} is often useful in conjunction with +statement expressions (@pxref{Statement Exprs}). +Here is how the two together can +be used to define a safe ``maximum'' macro which operates on any +arithmetic type and evaluates each of its arguments exactly once: + +@smallexample +#define max(a,b) \ + (@{ typeof (a) _a = (a); \ + typeof (b) _b = (b); \ + _a > _b ? _a : _b; @}) +@end smallexample + +@cindex underscores in variables in macros +@cindex @samp{_} in variables in macros +@cindex local variables in macros +@cindex variables, local, in macros +@cindex macros, local variables in + +The reason for using names that start with underscores for the local +variables is to avoid conflicts with variable names that occur within the +expressions that are substituted for @code{a} and @code{b}. Eventually we +hope to design a new form of declaration syntax that allows you to declare +variables whose scopes start only after their initializers; this will be a +more reliable way to prevent such conflicts. + +@noindent +Some more examples of the use of @code{typeof}: + +@itemize @bullet +@item +This declares @code{y} with the type of what @code{x} points to. + +@smallexample +typeof (*x) y; +@end smallexample + +@item +This declares @code{y} as an array of such values. + +@smallexample +typeof (*x) y[4]; +@end smallexample + +@item +This declares @code{y} as an array of pointers to characters: + +@smallexample +typeof (typeof (char *)[4]) y; +@end smallexample + +@noindent +It is equivalent to the following traditional C declaration: + +@smallexample +char *y[4]; +@end smallexample + +To see the meaning of the declaration using @code{typeof}, and why it +might be a useful way to write, rewrite it with these macros: + +@smallexample +#define pointer(T) typeof(T *) +#define array(T, N) typeof(T [N]) +@end smallexample + +@noindent +Now the declaration can be rewritten this way: + +@smallexample +array (pointer (char), 4) y; +@end smallexample + +@noindent +Thus, @code{array (pointer (char), 4)} is the type of arrays of 4 +pointers to @code{char}. +@end itemize + +In GNU C, but not GNU C++, you may also declare the type of a variable +as @code{__auto_type}. In that case, the declaration must declare +only one variable, whose declarator must just be an identifier, the +declaration must be initialized, and the type of the variable is +determined by the initializer; the name of the variable is not in +scope until after the initializer. (In C++, you should use C++11 +@code{auto} for this purpose.) Using @code{__auto_type}, the +``maximum'' macro above could be written as: + +@smallexample +#define max(a,b) \ + (@{ __auto_type _a = (a); \ + __auto_type _b = (b); \ + _a > _b ? _a : _b; @}) +@end smallexample + +Using @code{__auto_type} instead of @code{typeof} has two advantages: + +@itemize @bullet +@item Each argument to the macro appears only once in the expansion of +the macro. This prevents the size of the macro expansion growing +exponentially when calls to such macros are nested inside arguments of +such macros. + +@item If the argument to the macro has variably modified type, it is +evaluated only once when using @code{__auto_type}, but twice if +@code{typeof} is used. +@end itemize + +@node Conditionals +@section Conditionals with Omitted Operands +@cindex conditional expressions, extensions +@cindex omitted middle-operands +@cindex middle-operands, omitted +@cindex extensions, @code{?:} +@cindex @code{?:} extensions + +The middle operand in a conditional expression may be omitted. Then +if the first operand is nonzero, its value is the value of the conditional +expression. + +Therefore, the expression + +@smallexample +x ? : y +@end smallexample + +@noindent +has the value of @code{x} if that is nonzero; otherwise, the value of +@code{y}. + +This example is perfectly equivalent to + +@smallexample +x ? x : y +@end smallexample + +@cindex side effect in @code{?:} +@cindex @code{?:} side effect +@noindent +In this simple case, the ability to omit the middle operand is not +especially useful. When it becomes useful is when the first operand does, +or may (if it is a macro argument), contain a side effect. Then repeating +the operand in the middle would perform the side effect twice. Omitting +the middle operand uses the value already computed without the undesirable +effects of recomputing it. + +@node __int128 +@section 128-bit Integers +@cindex @code{__int128} data types + +As an extension the integer scalar type @code{__int128} is supported for +targets which have an integer mode wide enough to hold 128 bits. +Simply write @code{__int128} for a signed 128-bit integer, or +@code{unsigned __int128} for an unsigned 128-bit integer. There is no +support in GCC for expressing an integer constant of type @code{__int128} +for targets with @code{long long} integer less than 128 bits wide. + +@node Long Long +@section Double-Word Integers +@cindex @code{long long} data types +@cindex double-word arithmetic +@cindex multiprecision arithmetic +@cindex @code{LL} integer suffix +@cindex @code{ULL} integer suffix + +ISO C99 and ISO C++11 support data types for integers that are at least +64 bits wide, and as an extension GCC supports them in C90 and C++98 modes. +Simply write @code{long long int} for a signed integer, or +@code{unsigned long long int} for an unsigned integer. To make an +integer constant of type @code{long long int}, add the suffix @samp{LL} +to the integer. To make an integer constant of type @code{unsigned long +long int}, add the suffix @samp{ULL} to the integer. + +You can use these types in arithmetic like any other integer types. +Addition, subtraction, and bitwise boolean operations on these types +are open-coded on all types of machines. Multiplication is open-coded +if the machine supports a fullword-to-doubleword widening multiply +instruction. Division and shifts are open-coded only on machines that +provide special support. The operations that are not open-coded use +special library routines that come with GCC@. + +There may be pitfalls when you use @code{long long} types for function +arguments without function prototypes. If a function +expects type @code{int} for its argument, and you pass a value of type +@code{long long int}, confusion results because the caller and the +subroutine disagree about the number of bytes for the argument. +Likewise, if the function expects @code{long long int} and you pass +@code{int}. The best way to avoid such problems is to use prototypes. + +@node Complex +@section Complex Numbers +@cindex complex numbers +@cindex @code{_Complex} keyword +@cindex @code{__complex__} keyword + +ISO C99 supports complex floating data types, and as an extension GCC +supports them in C90 mode and in C++. GCC also supports complex integer data +types which are not part of ISO C99. You can declare complex types +using the keyword @code{_Complex}. As an extension, the older GNU +keyword @code{__complex__} is also supported. + +For example, @samp{_Complex double x;} declares @code{x} as a +variable whose real part and imaginary part are both of type +@code{double}. @samp{_Complex short int y;} declares @code{y} to +have real and imaginary parts of type @code{short int}; this is not +likely to be useful, but it shows that the set of complex types is +complete. + +To write a constant with a complex data type, use the suffix @samp{i} or +@samp{j} (either one; they are equivalent). For example, @code{2.5fi} +has type @code{_Complex float} and @code{3i} has type +@code{_Complex int}. Such a constant always has a pure imaginary +value, but you can form any complex value you like by adding one to a +real constant. This is a GNU extension; if you have an ISO C99 +conforming C library (such as the GNU C Library), and want to construct complex +constants of floating type, you should include @code{} and +use the macros @code{I} or @code{_Complex_I} instead. + +The ISO C++14 library also defines the @samp{i} suffix, so C++14 code +that includes the @samp{} header cannot use @samp{i} for the +GNU extension. The @samp{j} suffix still has the GNU meaning. + +GCC can handle both implicit and explicit casts between the @code{_Complex} +types and other @code{_Complex} types as casting both the real and imaginary +parts to the scalar type. +GCC can handle implicit and explicit casts from a scalar type to a @code{_Complex} +type and where the imaginary part will be considered zero. +The C front-end can handle implicit and explicit casts from a @code{_Complex} type +to a scalar type where the imaginary part will be ignored. In C++ code, this cast +is considered illformed and G++ will error out. + +GCC provides a built-in function @code{__builtin_complex} will can be used to +construct a complex value. + +@cindex @code{__real__} keyword +@cindex @code{__imag__} keyword + +GCC has a few extensions which can be used to extract the real +and the imaginary part of the complex-valued expression. Note +these expressions are lvalues if the @var{exp} is an lvalue. +These expressions operands have the type of a complex type +which might get prompoted to a complex type from a scalar type. +E.g. @code{__real__ (int)@var{x}} is the same as casting to +@code{_Complex int} before @code{__real__} is done. + +@multitable @columnfractions .4 .6 +@headitem Expression @tab Description +@item @code{__real__ @var{exp}} +@tab Extract the real part of @var{exp}. +@item @code{__imag__ @var{exp}} +@tab Extract the imaginary part of @var{exp}. +@end multitable + +For values of floating point, you should use the ISO C99 +functions, declared in @code{} and also provided as +built-in functions by GCC@. + +@multitable @columnfractions .4 .2 .2 .2 +@headitem Expression @tab float @tab double @tab long double +@item @code{__real__ @var{exp}} +@tab @code{crealf} @tab @code{creal} @tab @code{creall} +@item @code{__imag__ @var{exp}} +@tab @code{cimagf} @tab @code{cimag} @tab @code{cimagl} +@end multitable + +@cindex complex conjugation +The operator @samp{~} performs complex conjugation when used on a value +with a complex type. This is a GNU extension; for values of +floating type, you should use the ISO C99 functions @code{conjf}, +@code{conj} and @code{conjl}, declared in @code{} and also +provided as built-in functions by GCC@. Note unlike the @code{__real__} +and @code{__imag__} operators, this operator will not do an implicit cast +to the complex type because the @samp{~} is already a normal operator. + +GCC can allocate complex automatic variables in a noncontiguous +fashion; it's even possible for the real part to be in a register while +the imaginary part is on the stack (or vice versa). Only the DWARF +debug info format can represent this, so use of DWARF is recommended. +If you are using the stabs debug info format, GCC describes a noncontiguous +complex variable as if it were two separate variables of noncomplex type. +If the variable's actual name is @code{foo}, the two fictitious +variables are named @code{foo$real} and @code{foo$imag}. You can +examine and set these two fictitious variables with your debugger. + +@deftypefn {Built-in Function} @var{type} __builtin_complex (@var{real}, @var{imag}) + +The built-in function @code{__builtin_complex} is provided for use in +implementing the ISO C11 macros @code{CMPLXF}, @code{CMPLX} and +@code{CMPLXL}. @var{real} and @var{imag} must have the same type, a +real binary floating-point type, and the result has the corresponding +complex type with real and imaginary parts @var{real} and @var{imag}. +Unlike @samp{@var{real} + I * @var{imag}}, this works even when +infinities, NaNs and negative zeros are involved. + +@end deftypefn + +@node Floating Types +@section Additional Floating Types +@cindex additional floating types +@cindex @code{_Float@var{n}} data types +@cindex @code{_Float@var{n}x} data types +@cindex @code{__float80} data type +@cindex @code{__float128} data type +@cindex @code{__ibm128} data type +@cindex @code{w} floating point suffix +@cindex @code{q} floating point suffix +@cindex @code{W} floating point suffix +@cindex @code{Q} floating point suffix + +ISO/IEC TS 18661-3:2015 defines C support for additional floating +types @code{_Float@var{n}} and @code{_Float@var{n}x}, and GCC supports +these type names; the set of types supported depends on the target +architecture. These types are not supported when compiling C++. +Constants with these types use suffixes @code{f@var{n}} or +@code{F@var{n}} and @code{f@var{n}x} or @code{F@var{n}x}. These type +names can be used together with @code{_Complex} to declare complex +types. + +As an extension, GNU C and GNU C++ support additional floating +types, which are not supported by all targets. +@itemize @bullet +@item @code{__float128} is available on i386, x86_64, IA-64, and +hppa HP-UX, as well as on PowerPC GNU/Linux targets that enable +the vector scalar (VSX) instruction set. @code{__float128} supports +the 128-bit floating type. On i386, x86_64, PowerPC, and IA-64 +other than HP-UX, @code{__float128} is an alias for @code{_Float128}. +On hppa and IA-64 HP-UX, @code{__float128} is an alias for @code{long +double}. + +@item @code{__float80} is available on the i386, x86_64, and IA-64 +targets, and supports the 80-bit (@code{XFmode}) floating type. It is +an alias for the type name @code{_Float64x} on these targets. + +@item @code{__ibm128} is available on PowerPC targets, and provides +access to the IBM extended double format which is the current format +used for @code{long double}. When @code{long double} transitions to +@code{__float128} on PowerPC in the future, @code{__ibm128} will remain +for use in conversions between the two types. +@end itemize + +Support for these additional types includes the arithmetic operators: +add, subtract, multiply, divide; unary arithmetic operators; +relational operators; equality operators; and conversions to and from +integer and other floating types. Use a suffix @samp{w} or @samp{W} +in a literal constant of type @code{__float80} or type +@code{__ibm128}. Use a suffix @samp{q} or @samp{Q} for @code{__float128}. + +In order to use @code{_Float128}, @code{__float128}, and @code{__ibm128} +on PowerPC Linux systems, you must use the @option{-mfloat128} option. It is +expected in future versions of GCC that @code{_Float128} and @code{__float128} +will be enabled automatically. + +The @code{_Float128} type is supported on all systems where +@code{__float128} is supported or where @code{long double} has the +IEEE binary128 format. The @code{_Float64x} type is supported on all +systems where @code{__float128} is supported. The @code{_Float32} +type is supported on all systems supporting IEEE binary32; the +@code{_Float64} and @code{_Float32x} types are supported on all systems +supporting IEEE binary64. The @code{_Float16} type is supported on AArch64 +systems by default, on ARM systems when the IEEE format for 16-bit +floating-point types is selected with @option{-mfp16-format=ieee} and, +for both C and C++, on x86 systems with SSE2 enabled. GCC does not currently +support @code{_Float128x} on any systems. + +On the i386, x86_64, IA-64, and HP-UX targets, you can declare complex +types using the corresponding internal complex type, @code{XCmode} for +@code{__float80} type and @code{TCmode} for @code{__float128} type: + +@smallexample +typedef _Complex float __attribute__((mode(TC))) _Complex128; +typedef _Complex float __attribute__((mode(XC))) _Complex80; +@end smallexample + +On the PowerPC Linux VSX targets, you can declare complex types using +the corresponding internal complex type, @code{KCmode} for +@code{__float128} type and @code{ICmode} for @code{__ibm128} type: + +@smallexample +typedef _Complex float __attribute__((mode(KC))) _Complex_float128; +typedef _Complex float __attribute__((mode(IC))) _Complex_ibm128; +@end smallexample + +@node Half-Precision +@section Half-Precision Floating Point +@cindex half-precision floating point +@cindex @code{__fp16} data type +@cindex @code{__Float16} data type + +On ARM and AArch64 targets, GCC supports half-precision (16-bit) floating +point via the @code{__fp16} type defined in the ARM C Language Extensions. +On ARM systems, you must enable this type explicitly with the +@option{-mfp16-format} command-line option in order to use it. +On x86 targets with SSE2 enabled, GCC supports half-precision (16-bit) +floating point via the @code{_Float16} type. For C++, x86 provides a builtin +type named @code{_Float16} which contains same data format as C. + +ARM targets support two incompatible representations for half-precision +floating-point values. You must choose one of the representations and +use it consistently in your program. + +Specifying @option{-mfp16-format=ieee} selects the IEEE 754-2008 format. +This format can represent normalized values in the range of @math{2^{-14}} to 65504. +There are 11 bits of significand precision, approximately 3 +decimal digits. + +Specifying @option{-mfp16-format=alternative} selects the ARM +alternative format. This representation is similar to the IEEE +format, but does not support infinities or NaNs. Instead, the range +of exponents is extended, so that this format can represent normalized +values in the range of @math{2^{-14}} to 131008. + +The GCC port for AArch64 only supports the IEEE 754-2008 format, and does +not require use of the @option{-mfp16-format} command-line option. + +The @code{__fp16} type may only be used as an argument to intrinsics defined +in @code{}, or as a storage format. For purposes of +arithmetic and other operations, @code{__fp16} values in C or C++ +expressions are automatically promoted to @code{float}. + +The ARM target provides hardware support for conversions between +@code{__fp16} and @code{float} values +as an extension to VFP and NEON (Advanced SIMD), and from ARMv8-A provides +hardware support for conversions between @code{__fp16} and @code{double} +values. GCC generates code using these hardware instructions if you +compile with options to select an FPU that provides them; +for example, @option{-mfpu=neon-fp16 -mfloat-abi=softfp}, +in addition to the @option{-mfp16-format} option to select +a half-precision format. + +Language-level support for the @code{__fp16} data type is +independent of whether GCC generates code using hardware floating-point +instructions. In cases where hardware support is not specified, GCC +implements conversions between @code{__fp16} and other types as library +calls. + +It is recommended that portable code use the @code{_Float16} type defined +by ISO/IEC TS 18661-3:2015. @xref{Floating Types}. + +On x86 targets with SSE2 enabled, without @option{-mavx512fp16}, +all operations will be emulated by software emulation and the @code{float} +instructions. The default behavior for @code{FLT_EVAL_METHOD} is to keep the +intermediate result of the operation as 32-bit precision. This may lead to +inconsistent behavior between software emulation and AVX512-FP16 instructions. +Using @option{-fexcess-precision=16} will force round back after each operation. + +Using @option{-mavx512fp16} will generate AVX512-FP16 instructions instead of +software emulation. The default behavior of @code{FLT_EVAL_METHOD} is to round +after each operation. The same is true with @option{-fexcess-precision=standard} +and @option{-mfpmath=sse}. If there is no @option{-mfpmath=sse}, +@option{-fexcess-precision=standard} alone does the same thing as before, +It is useful for code that does not have @code{_Float16} and runs on the x87 +FPU. + +@node Decimal Float +@section Decimal Floating Types +@cindex decimal floating types +@cindex @code{_Decimal32} data type +@cindex @code{_Decimal64} data type +@cindex @code{_Decimal128} data type +@cindex @code{df} integer suffix +@cindex @code{dd} integer suffix +@cindex @code{dl} integer suffix +@cindex @code{DF} integer suffix +@cindex @code{DD} integer suffix +@cindex @code{DL} integer suffix + +As an extension, GNU C supports decimal floating types as +defined in the N1312 draft of ISO/IEC WDTR24732. Support for decimal +floating types in GCC will evolve as the draft technical report changes. +Calling conventions for any target might also change. Not all targets +support decimal floating types. + +The decimal floating types are @code{_Decimal32}, @code{_Decimal64}, and +@code{_Decimal128}. They use a radix of ten, unlike the floating types +@code{float}, @code{double}, and @code{long double} whose radix is not +specified by the C standard but is usually two. + +Support for decimal floating types includes the arithmetic operators +add, subtract, multiply, divide; unary arithmetic operators; +relational operators; equality operators; and conversions to and from +integer and other floating types. Use a suffix @samp{df} or +@samp{DF} in a literal constant of type @code{_Decimal32}, @samp{dd} +or @samp{DD} for @code{_Decimal64}, and @samp{dl} or @samp{DL} for +@code{_Decimal128}. + +GCC support of decimal float as specified by the draft technical report +is incomplete: + +@itemize @bullet +@item +When the value of a decimal floating type cannot be represented in the +integer type to which it is being converted, the result is undefined +rather than the result value specified by the draft technical report. + +@item +GCC does not provide the C library functionality associated with +@file{math.h}, @file{fenv.h}, @file{stdio.h}, @file{stdlib.h}, and +@file{wchar.h}, which must come from a separate C library implementation. +Because of this the GNU C compiler does not define macro +@code{__STDC_DEC_FP__} to indicate that the implementation conforms to +the technical report. +@end itemize + +Types @code{_Decimal32}, @code{_Decimal64}, and @code{_Decimal128} +are supported by the DWARF debug information format. + +@node Hex Floats +@section Hex Floats +@cindex hex floats + +ISO C99 and ISO C++17 support floating-point numbers written not only in +the usual decimal notation, such as @code{1.55e1}, but also numbers such as +@code{0x1.fp3} written in hexadecimal format. As a GNU extension, GCC +supports this in C90 mode (except in some cases when strictly +conforming) and in C++98, C++11 and C++14 modes. In that format the +@samp{0x} hex introducer and the @samp{p} or @samp{P} exponent field are +mandatory. The exponent is a decimal number that indicates the power of +2 by which the significant part is multiplied. Thus @samp{0x1.f} is +@tex +$1 {15\over16}$, +@end tex +@ifnottex +1 15/16, +@end ifnottex +@samp{p3} multiplies it by 8, and the value of @code{0x1.fp3} +is the same as @code{1.55e1}. + +Unlike for floating-point numbers in the decimal notation the exponent +is always required in the hexadecimal notation. Otherwise the compiler +would not be able to resolve the ambiguity of, e.g., @code{0x1.f}. This +could mean @code{1.0f} or @code{1.9375} since @samp{f} is also the +extension for floating-point constants of type @code{float}. + +@node Fixed-Point +@section Fixed-Point Types +@cindex fixed-point types +@cindex @code{_Fract} data type +@cindex @code{_Accum} data type +@cindex @code{_Sat} data type +@cindex @code{hr} fixed-suffix +@cindex @code{r} fixed-suffix +@cindex @code{lr} fixed-suffix +@cindex @code{llr} fixed-suffix +@cindex @code{uhr} fixed-suffix +@cindex @code{ur} fixed-suffix +@cindex @code{ulr} fixed-suffix +@cindex @code{ullr} fixed-suffix +@cindex @code{hk} fixed-suffix +@cindex @code{k} fixed-suffix +@cindex @code{lk} fixed-suffix +@cindex @code{llk} fixed-suffix +@cindex @code{uhk} fixed-suffix +@cindex @code{uk} fixed-suffix +@cindex @code{ulk} fixed-suffix +@cindex @code{ullk} fixed-suffix +@cindex @code{HR} fixed-suffix +@cindex @code{R} fixed-suffix +@cindex @code{LR} fixed-suffix +@cindex @code{LLR} fixed-suffix +@cindex @code{UHR} fixed-suffix +@cindex @code{UR} fixed-suffix +@cindex @code{ULR} fixed-suffix +@cindex @code{ULLR} fixed-suffix +@cindex @code{HK} fixed-suffix +@cindex @code{K} fixed-suffix +@cindex @code{LK} fixed-suffix +@cindex @code{LLK} fixed-suffix +@cindex @code{UHK} fixed-suffix +@cindex @code{UK} fixed-suffix +@cindex @code{ULK} fixed-suffix +@cindex @code{ULLK} fixed-suffix + +As an extension, GNU C supports fixed-point types as +defined in the N1169 draft of ISO/IEC DTR 18037. Support for fixed-point +types in GCC will evolve as the draft technical report changes. +Calling conventions for any target might also change. Not all targets +support fixed-point types. + +The fixed-point types are +@code{short _Fract}, +@code{_Fract}, +@code{long _Fract}, +@code{long long _Fract}, +@code{unsigned short _Fract}, +@code{unsigned _Fract}, +@code{unsigned long _Fract}, +@code{unsigned long long _Fract}, +@code{_Sat short _Fract}, +@code{_Sat _Fract}, +@code{_Sat long _Fract}, +@code{_Sat long long _Fract}, +@code{_Sat unsigned short _Fract}, +@code{_Sat unsigned _Fract}, +@code{_Sat unsigned long _Fract}, +@code{_Sat unsigned long long _Fract}, +@code{short _Accum}, +@code{_Accum}, +@code{long _Accum}, +@code{long long _Accum}, +@code{unsigned short _Accum}, +@code{unsigned _Accum}, +@code{unsigned long _Accum}, +@code{unsigned long long _Accum}, +@code{_Sat short _Accum}, +@code{_Sat _Accum}, +@code{_Sat long _Accum}, +@code{_Sat long long _Accum}, +@code{_Sat unsigned short _Accum}, +@code{_Sat unsigned _Accum}, +@code{_Sat unsigned long _Accum}, +@code{_Sat unsigned long long _Accum}. + +Fixed-point data values contain fractional and optional integral parts. +The format of fixed-point data varies and depends on the target machine. + +Support for fixed-point types includes: +@itemize @bullet +@item +prefix and postfix increment and decrement operators (@code{++}, @code{--}) +@item +unary arithmetic operators (@code{+}, @code{-}, @code{!}) +@item +binary arithmetic operators (@code{+}, @code{-}, @code{*}, @code{/}) +@item +binary shift operators (@code{<<}, @code{>>}) +@item +relational operators (@code{<}, @code{<=}, @code{>=}, @code{>}) +@item +equality operators (@code{==}, @code{!=}) +@item +assignment operators (@code{+=}, @code{-=}, @code{*=}, @code{/=}, +@code{<<=}, @code{>>=}) +@item +conversions to and from integer, floating-point, or fixed-point types +@end itemize + +Use a suffix in a fixed-point literal constant: +@itemize +@item @samp{hr} or @samp{HR} for @code{short _Fract} and +@code{_Sat short _Fract} +@item @samp{r} or @samp{R} for @code{_Fract} and @code{_Sat _Fract} +@item @samp{lr} or @samp{LR} for @code{long _Fract} and +@code{_Sat long _Fract} +@item @samp{llr} or @samp{LLR} for @code{long long _Fract} and +@code{_Sat long long _Fract} +@item @samp{uhr} or @samp{UHR} for @code{unsigned short _Fract} and +@code{_Sat unsigned short _Fract} +@item @samp{ur} or @samp{UR} for @code{unsigned _Fract} and +@code{_Sat unsigned _Fract} +@item @samp{ulr} or @samp{ULR} for @code{unsigned long _Fract} and +@code{_Sat unsigned long _Fract} +@item @samp{ullr} or @samp{ULLR} for @code{unsigned long long _Fract} +and @code{_Sat unsigned long long _Fract} +@item @samp{hk} or @samp{HK} for @code{short _Accum} and +@code{_Sat short _Accum} +@item @samp{k} or @samp{K} for @code{_Accum} and @code{_Sat _Accum} +@item @samp{lk} or @samp{LK} for @code{long _Accum} and +@code{_Sat long _Accum} +@item @samp{llk} or @samp{LLK} for @code{long long _Accum} and +@code{_Sat long long _Accum} +@item @samp{uhk} or @samp{UHK} for @code{unsigned short _Accum} and +@code{_Sat unsigned short _Accum} +@item @samp{uk} or @samp{UK} for @code{unsigned _Accum} and +@code{_Sat unsigned _Accum} +@item @samp{ulk} or @samp{ULK} for @code{unsigned long _Accum} and +@code{_Sat unsigned long _Accum} +@item @samp{ullk} or @samp{ULLK} for @code{unsigned long long _Accum} +and @code{_Sat unsigned long long _Accum} +@end itemize + +GCC support of fixed-point types as specified by the draft technical report +is incomplete: + +@itemize @bullet +@item +Pragmas to control overflow and rounding behaviors are not implemented. +@end itemize + +Fixed-point types are supported by the DWARF debug information format. + +@node Named Address Spaces +@section Named Address Spaces +@cindex Named Address Spaces + +As an extension, GNU C supports named address spaces as +defined in the N1275 draft of ISO/IEC DTR 18037. Support for named +address spaces in GCC will evolve as the draft technical report +changes. Calling conventions for any target might also change. At +present, only the AVR, M32C, PRU, RL78, and x86 targets support +address spaces other than the generic address space. + +Address space identifiers may be used exactly like any other C type +qualifier (e.g., @code{const} or @code{volatile}). See the N1275 +document for more details. + +@anchor{AVR Named Address Spaces} +@subsection AVR Named Address Spaces + +On the AVR target, there are several address spaces that can be used +in order to put read-only data into the flash memory and access that +data by means of the special instructions @code{LPM} or @code{ELPM} +needed to read from flash. + +Devices belonging to @code{avrtiny} and @code{avrxmega3} can access +flash memory by means of @code{LD*} instructions because the flash +memory is mapped into the RAM address space. There is @emph{no need} +for language extensions like @code{__flash} or attribute +@ref{AVR Variable Attributes,,@code{progmem}}. +The default linker description files for these devices cater for that +feature and @code{.rodata} stays in flash: The compiler just generates +@code{LD*} instructions, and the linker script adds core specific +offsets to all @code{.rodata} symbols: @code{0x4000} in the case of +@code{avrtiny} and @code{0x8000} in the case of @code{avrxmega3}. +See @ref{AVR Options} for a list of respective devices. + +For devices not in @code{avrtiny} or @code{avrxmega3}, +any data including read-only data is located in RAM (the generic +address space) because flash memory is not visible in the RAM address +space. In order to locate read-only data in flash memory @emph{and} +to generate the right instructions to access this data without +using (inline) assembler code, special address spaces are needed. + +@table @code +@item __flash +@cindex @code{__flash} AVR Named Address Spaces +The @code{__flash} qualifier locates data in the +@code{.progmem.data} section. Data is read using the @code{LPM} +instruction. Pointers to this address space are 16 bits wide. + +@item __flash1 +@itemx __flash2 +@itemx __flash3 +@itemx __flash4 +@itemx __flash5 +@cindex @code{__flash1} AVR Named Address Spaces +@cindex @code{__flash2} AVR Named Address Spaces +@cindex @code{__flash3} AVR Named Address Spaces +@cindex @code{__flash4} AVR Named Address Spaces +@cindex @code{__flash5} AVR Named Address Spaces +These are 16-bit address spaces locating data in section +@code{.progmem@var{N}.data} where @var{N} refers to +address space @code{__flash@var{N}}. +The compiler sets the @code{RAMPZ} segment register appropriately +before reading data by means of the @code{ELPM} instruction. + +@item __memx +@cindex @code{__memx} AVR Named Address Spaces +This is a 24-bit address space that linearizes flash and RAM: +If the high bit of the address is set, data is read from +RAM using the lower two bytes as RAM address. +If the high bit of the address is clear, data is read from flash +with @code{RAMPZ} set according to the high byte of the address. +@xref{AVR Built-in Functions,,@code{__builtin_avr_flash_segment}}. + +Objects in this address space are located in @code{.progmemx.data}. +@end table + +@b{Example} + +@smallexample +char my_read (const __flash char ** p) +@{ + /* p is a pointer to RAM that points to a pointer to flash. + The first indirection of p reads that flash pointer + from RAM and the second indirection reads a char from this + flash address. */ + + return **p; +@} + +/* Locate array[] in flash memory */ +const __flash int array[] = @{ 3, 5, 7, 11, 13, 17, 19 @}; + +int i = 1; + +int main (void) +@{ + /* Return 17 by reading from flash memory */ + return array[array[i]]; +@} +@end smallexample + +@noindent +For each named address space supported by avr-gcc there is an equally +named but uppercase built-in macro defined. +The purpose is to facilitate testing if respective address space +support is available or not: + +@smallexample +#ifdef __FLASH +const __flash int var = 1; + +int read_var (void) +@{ + return var; +@} +#else +#include /* From AVR-LibC */ + +const int var PROGMEM = 1; + +int read_var (void) +@{ + return (int) pgm_read_word (&var); +@} +#endif /* __FLASH */ +@end smallexample + +@noindent +Notice that attribute @ref{AVR Variable Attributes,,@code{progmem}} +locates data in flash but +accesses to these data read from generic address space, i.e.@: +from RAM, +so that you need special accessors like @code{pgm_read_byte} +from @w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC}} +together with attribute @code{progmem}. + +@noindent +@b{Limitations and caveats} + +@itemize +@item +Reading across the 64@tie{}KiB section boundary of +the @code{__flash} or @code{__flash@var{N}} address spaces +shows undefined behavior. The only address space that +supports reading across the 64@tie{}KiB flash segment boundaries is +@code{__memx}. + +@item +If you use one of the @code{__flash@var{N}} address spaces +you must arrange your linker script to locate the +@code{.progmem@var{N}.data} sections according to your needs. + +@item +Any data or pointers to the non-generic address spaces must +be qualified as @code{const}, i.e.@: as read-only data. +This still applies if the data in one of these address +spaces like software version number or calibration lookup table are intended to +be changed after load time by, say, a boot loader. In this case +the right qualification is @code{const} @code{volatile} so that the compiler +must not optimize away known values or insert them +as immediates into operands of instructions. + +@item +The following code initializes a variable @code{pfoo} +located in static storage with a 24-bit address: +@smallexample +extern const __memx char foo; +const __memx void *pfoo = &foo; +@end smallexample + +@item +On the reduced Tiny devices like ATtiny40, no address spaces are supported. +Just use vanilla C / C++ code without overhead as outlined above. +Attribute @code{progmem} is supported but works differently, +see @ref{AVR Variable Attributes}. + +@end itemize + +@subsection M32C Named Address Spaces +@cindex @code{__far} M32C Named Address Spaces + +On the M32C target, with the R8C and M16C CPU variants, variables +qualified with @code{__far} are accessed using 32-bit addresses in +order to access memory beyond the first 64@tie{}Ki bytes. If +@code{__far} is used with the M32CM or M32C CPU variants, it has no +effect. + +@subsection PRU Named Address Spaces +@cindex @code{__regio_symbol} PRU Named Address Spaces + +On the PRU target, variables qualified with @code{__regio_symbol} are +aliases used to access the special I/O CPU registers. They must be +declared as @code{extern} because such variables will not be allocated in +any data memory. They must also be marked as @code{volatile}, and can +only be 32-bit integer types. The only names those variables can have +are @code{__R30} and @code{__R31}, representing respectively the +@code{R30} and @code{R31} special I/O CPU registers. Hence the following +example is the only valid usage of @code{__regio_symbol}: + +@smallexample +extern volatile __regio_symbol uint32_t __R30; +extern volatile __regio_symbol uint32_t __R31; +@end smallexample + +@subsection RL78 Named Address Spaces +@cindex @code{__far} RL78 Named Address Spaces + +On the RL78 target, variables qualified with @code{__far} are accessed +with 32-bit pointers (20-bit addresses) rather than the default 16-bit +addresses. Non-far variables are assumed to appear in the topmost +64@tie{}KiB of the address space. + +@subsection x86 Named Address Spaces +@cindex x86 named address spaces + +On the x86 target, variables may be declared as being relative +to the @code{%fs} or @code{%gs} segments. + +@table @code +@item __seg_fs +@itemx __seg_gs +@cindex @code{__seg_fs} x86 named address space +@cindex @code{__seg_gs} x86 named address space +The object is accessed with the respective segment override prefix. + +The respective segment base must be set via some method specific to +the operating system. Rather than require an expensive system call +to retrieve the segment base, these address spaces are not considered +to be subspaces of the generic (flat) address space. This means that +explicit casts are required to convert pointers between these address +spaces and the generic address space. In practice the application +should cast to @code{uintptr_t} and apply the segment base offset +that it installed previously. + +The preprocessor symbols @code{__SEG_FS} and @code{__SEG_GS} are +defined when these address spaces are supported. +@end table + +@node Zero Length +@section Arrays of Length Zero +@cindex arrays of length zero +@cindex zero-length arrays +@cindex length-zero arrays +@cindex flexible array members + +Declaring zero-length arrays is allowed in GNU C as an extension. +A zero-length array can be useful as the last element of a structure +that is really a header for a variable-length object: + +@smallexample +struct line @{ + int length; + char contents[0]; +@}; + +struct line *thisline = (struct line *) + malloc (sizeof (struct line) + this_length); +thisline->length = this_length; +@end smallexample + +Although the size of a zero-length array is zero, an array member of +this kind may increase the size of the enclosing type as a result of tail +padding. The offset of a zero-length array member from the beginning +of the enclosing structure is the same as the offset of an array with +one or more elements of the same type. The alignment of a zero-length +array is the same as the alignment of its elements. + +Declaring zero-length arrays in other contexts, including as interior +members of structure objects or as non-member objects, is discouraged. +Accessing elements of zero-length arrays declared in such contexts is +undefined and may be diagnosed. + +In the absence of the zero-length array extension, in ISO C90 +the @code{contents} array in the example above would typically be declared +to have a single element. Unlike a zero-length array which only contributes +to the size of the enclosing structure for the purposes of alignment, +a one-element array always occupies at least as much space as a single +object of the type. Although using one-element arrays this way is +discouraged, GCC handles accesses to trailing one-element array members +analogously to zero-length arrays. + +The preferred mechanism to declare variable-length types like +@code{struct line} above is the ISO C99 @dfn{flexible array member}, +with slightly different syntax and semantics: + +@itemize @bullet +@item +Flexible array members are written as @code{contents[]} without +the @code{0}. + +@item +Flexible array members have incomplete type, and so the @code{sizeof} +operator may not be applied. As a quirk of the original implementation +of zero-length arrays, @code{sizeof} evaluates to zero. + +@item +Flexible array members may only appear as the last member of a +@code{struct} that is otherwise non-empty. + +@item +A structure containing a flexible array member, or a union containing +such a structure (possibly recursively), may not be a member of a +structure or an element of an array. (However, these uses are +permitted by GCC as extensions.) +@end itemize + +Non-empty initialization of zero-length +arrays is treated like any case where there are more initializer +elements than the array holds, in that a suitable warning about ``excess +elements in array'' is given, and the excess elements (all of them, in +this case) are ignored. + +GCC allows static initialization of flexible array members. +This is equivalent to defining a new structure containing the original +structure followed by an array of sufficient size to contain the data. +E.g.@: in the following, @code{f1} is constructed as if it were declared +like @code{f2}. + +@smallexample +struct f1 @{ + int x; int y[]; +@} f1 = @{ 1, @{ 2, 3, 4 @} @}; + +struct f2 @{ + struct f1 f1; int data[3]; +@} f2 = @{ @{ 1 @}, @{ 2, 3, 4 @} @}; +@end smallexample + +@noindent +The convenience of this extension is that @code{f1} has the desired +type, eliminating the need to consistently refer to @code{f2.f1}. + +This has symmetry with normal static arrays, in that an array of +unknown size is also written with @code{[]}. + +Of course, this extension only makes sense if the extra data comes at +the end of a top-level object, as otherwise we would be overwriting +data at subsequent offsets. To avoid undue complication and confusion +with initialization of deeply nested arrays, we simply disallow any +non-empty initialization except when the structure is the top-level +object. For example: + +@smallexample +struct foo @{ int x; int y[]; @}; +struct bar @{ struct foo z; @}; + +struct foo a = @{ 1, @{ 2, 3, 4 @} @}; // @r{Valid.} +struct bar b = @{ @{ 1, @{ 2, 3, 4 @} @} @}; // @r{Invalid.} +struct bar c = @{ @{ 1, @{ @} @} @}; // @r{Valid.} +struct foo d[1] = @{ @{ 1, @{ 2, 3, 4 @} @} @}; // @r{Invalid.} +@end smallexample + +@node Empty Structures +@section Structures with No Members +@cindex empty structures +@cindex zero-size structures + +GCC permits a C structure to have no members: + +@smallexample +struct empty @{ +@}; +@end smallexample + +The structure has size zero. In C++, empty structures are part +of the language. G++ treats empty structures as if they had a single +member of type @code{char}. + +@node Variable Length +@section Arrays of Variable Length +@cindex variable-length arrays +@cindex arrays of variable length +@cindex VLAs + +Variable-length automatic arrays are allowed in ISO C99, and as an +extension GCC accepts them in C90 mode and in C++. These arrays are +declared like any other automatic arrays, but with a length that is not +a constant expression. The storage is allocated at the point of +declaration and deallocated when the block scope containing the declaration +exits. For +example: + +@smallexample +FILE * +concat_fopen (char *s1, char *s2, char *mode) +@{ + char str[strlen (s1) + strlen (s2) + 1]; + strcpy (str, s1); + strcat (str, s2); + return fopen (str, mode); +@} +@end smallexample + +@cindex scope of a variable length array +@cindex variable-length array scope +@cindex deallocating variable length arrays +Jumping or breaking out of the scope of the array name deallocates the +storage. Jumping into the scope is not allowed; you get an error +message for it. + +@cindex variable-length array in a structure +As an extension, GCC accepts variable-length arrays as a member of +a structure or a union. For example: + +@smallexample +void +foo (int n) +@{ + struct S @{ int x[n]; @}; +@} +@end smallexample + +@cindex @code{alloca} vs variable-length arrays +You can use the function @code{alloca} to get an effect much like +variable-length arrays. The function @code{alloca} is available in +many other C implementations (but not in all). On the other hand, +variable-length arrays are more elegant. + +There are other differences between these two methods. Space allocated +with @code{alloca} exists until the containing @emph{function} returns. +The space for a variable-length array is deallocated as soon as the array +name's scope ends, unless you also use @code{alloca} in this scope. + +You can also use variable-length arrays as arguments to functions: + +@smallexample +struct entry +tester (int len, char data[len][len]) +@{ + /* @r{@dots{}} */ +@} +@end smallexample + +The length of an array is computed once when the storage is allocated +and is remembered for the scope of the array in case you access it with +@code{sizeof}. + +If you want to pass the array first and the length afterward, you can +use a forward declaration in the parameter list---another GNU extension. + +@smallexample +struct entry +tester (int len; char data[len][len], int len) +@{ + /* @r{@dots{}} */ +@} +@end smallexample + +@cindex parameter forward declaration +The @samp{int len} before the semicolon is a @dfn{parameter forward +declaration}, and it serves the purpose of making the name @code{len} +known when the declaration of @code{data} is parsed. + +You can write any number of such parameter forward declarations in the +parameter list. They can be separated by commas or semicolons, but the +last one must end with a semicolon, which is followed by the ``real'' +parameter declarations. Each forward declaration must match a ``real'' +declaration in parameter name and data type. ISO C99 does not support +parameter forward declarations. + +@node Variadic Macros +@section Macros with a Variable Number of Arguments. +@cindex variable number of arguments +@cindex macro with variable arguments +@cindex rest argument (in macro) +@cindex variadic macros + +In the ISO C standard of 1999, a macro can be declared to accept a +variable number of arguments much as a function can. The syntax for +defining the macro is similar to that of a function. Here is an +example: + +@smallexample +#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__) +@end smallexample + +@noindent +Here @samp{@dots{}} is a @dfn{variable argument}. In the invocation of +such a macro, it represents the zero or more tokens until the closing +parenthesis that ends the invocation, including any commas. This set of +tokens replaces the identifier @code{__VA_ARGS__} in the macro body +wherever it appears. See the CPP manual for more information. + +GCC has long supported variadic macros, and used a different syntax that +allowed you to give a name to the variable arguments just like any other +argument. Here is an example: + +@smallexample +#define debug(format, args...) fprintf (stderr, format, args) +@end smallexample + +@noindent +This is in all ways equivalent to the ISO C example above, but arguably +more readable and descriptive. + +GNU CPP has two further variadic macro extensions, and permits them to +be used with either of the above forms of macro definition. + +In standard C, you are not allowed to leave the variable argument out +entirely; but you are allowed to pass an empty argument. For example, +this invocation is invalid in ISO C, because there is no comma after +the string: + +@smallexample +debug ("A message") +@end smallexample + +GNU CPP permits you to completely omit the variable arguments in this +way. In the above examples, the compiler would complain, though since +the expansion of the macro still has the extra comma after the format +string. + +To help solve this problem, CPP behaves specially for variable arguments +used with the token paste operator, @samp{##}. If instead you write + +@smallexample +#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__) +@end smallexample + +@noindent +and if the variable arguments are omitted or empty, the @samp{##} +operator causes the preprocessor to remove the comma before it. If you +do provide some variable arguments in your macro invocation, GNU CPP +does not complain about the paste operation and instead places the +variable arguments after the comma. Just like any other pasted macro +argument, these arguments are not macro expanded. + +@node Escaped Newlines +@section Slightly Looser Rules for Escaped Newlines +@cindex escaped newlines +@cindex newlines (escaped) + +The preprocessor treatment of escaped newlines is more relaxed +than that specified by the C90 standard, which requires the newline +to immediately follow a backslash. +GCC's implementation allows whitespace in the form +of spaces, horizontal and vertical tabs, and form feeds between the +backslash and the subsequent newline. The preprocessor issues a +warning, but treats it as a valid escaped newline and combines the two +lines to form a single logical line. This works within comments and +tokens, as well as between tokens. Comments are @emph{not} treated as +whitespace for the purposes of this relaxation, since they have not +yet been replaced with spaces. + +@node Subscripting +@section Non-Lvalue Arrays May Have Subscripts +@cindex subscripting +@cindex arrays, non-lvalue + +@cindex subscripting and function values +In ISO C99, arrays that are not lvalues still decay to pointers, and +may be subscripted, although they may not be modified or used after +the next sequence point and the unary @samp{&} operator may not be +applied to them. As an extension, GNU C allows such arrays to be +subscripted in C90 mode, though otherwise they do not decay to +pointers outside C99 mode. For example, +this is valid in GNU C though not valid in C90: + +@smallexample +@group +struct foo @{int a[4];@}; + +struct foo f(); + +bar (int index) +@{ + return f().a[index]; +@} +@end group +@end smallexample + +@node Pointer Arith +@section Arithmetic on @code{void}- and Function-Pointers +@cindex void pointers, arithmetic +@cindex void, size of pointer to +@cindex function pointers, arithmetic +@cindex function, size of pointer to + +In GNU C, addition and subtraction operations are supported on pointers to +@code{void} and on pointers to functions. This is done by treating the +size of a @code{void} or of a function as 1. + +A consequence of this is that @code{sizeof} is also allowed on @code{void} +and on function types, and returns 1. + +@opindex Wpointer-arith +The option @option{-Wpointer-arith} requests a warning if these extensions +are used. + +@node Variadic Pointer Args +@section Pointer Arguments in Variadic Functions +@cindex pointer arguments in variadic functions +@cindex variadic functions, pointer arguments + +Standard C requires that pointer types used with @code{va_arg} in +functions with variable argument lists either must be compatible with +that of the actual argument, or that one type must be a pointer to +@code{void} and the other a pointer to a character type. GNU C +implements the POSIX XSI extension that additionally permits the use +of @code{va_arg} with a pointer type to receive arguments of any other +pointer type. + +In particular, in GNU C @samp{va_arg (ap, void *)} can safely be used +to consume an argument of any pointer type. + +@node Pointers to Arrays +@section Pointers to Arrays with Qualifiers Work as Expected +@cindex pointers to arrays +@cindex const qualifier + +In GNU C, pointers to arrays with qualifiers work similar to pointers +to other qualified types. For example, a value of type @code{int (*)[5]} +can be used to initialize a variable of type @code{const int (*)[5]}. +These types are incompatible in ISO C because the @code{const} qualifier +is formally attached to the element type of the array and not the +array itself. + +@smallexample +extern void +transpose (int N, int M, double out[M][N], const double in[N][M]); +double x[3][2]; +double y[2][3]; +@r{@dots{}} +transpose(3, 2, y, x); +@end smallexample + +@node Initializers +@section Non-Constant Initializers +@cindex initializers, non-constant +@cindex non-constant initializers + +As in standard C++ and ISO C99, the elements of an aggregate initializer for an +automatic variable are not required to be constant expressions in GNU C@. +Here is an example of an initializer with run-time varying elements: + +@smallexample +foo (float f, float g) +@{ + float beat_freqs[2] = @{ f-g, f+g @}; + /* @r{@dots{}} */ +@} +@end smallexample + +@node Compound Literals +@section Compound Literals +@cindex constructor expressions +@cindex initializations in expressions +@cindex structures, constructor expression +@cindex expressions, constructor +@cindex compound literals +@c The GNU C name for what C99 calls compound literals was "constructor expressions". + +A compound literal looks like a cast of a brace-enclosed aggregate +initializer list. Its value is an object of the type specified in +the cast, containing the elements specified in the initializer. +Unlike the result of a cast, a compound literal is an lvalue. ISO +C99 and later support compound literals. As an extension, GCC +supports compound literals also in C90 mode and in C++, although +as explained below, the C++ semantics are somewhat different. + +Usually, the specified type of a compound literal is a structure. Assume +that @code{struct foo} and @code{structure} are declared as shown: + +@smallexample +struct foo @{int a; char b[2];@} structure; +@end smallexample + +@noindent +Here is an example of constructing a @code{struct foo} with a compound literal: + +@smallexample +structure = ((struct foo) @{x + y, 'a', 0@}); +@end smallexample + +@noindent +This is equivalent to writing the following: + +@smallexample +@{ + struct foo temp = @{x + y, 'a', 0@}; + structure = temp; +@} +@end smallexample + +You can also construct an array, though this is dangerous in C++, as +explained below. If all the elements of the compound literal are +(made up of) simple constant expressions suitable for use in +initializers of objects of static storage duration, then the compound +literal can be coerced to a pointer to its first element and used in +such an initializer, as shown here: + +@smallexample +char **foo = (char *[]) @{ "x", "y", "z" @}; +@end smallexample + +Compound literals for scalar types and union types are also allowed. In +the following example the variable @code{i} is initialized to the value +@code{2}, the result of incrementing the unnamed object created by +the compound literal. + +@smallexample +int i = ++(int) @{ 1 @}; +@end smallexample + +As a GNU extension, GCC allows initialization of objects with static storage +duration by compound literals (which is not possible in ISO C99 because +the initializer is not a constant). +It is handled as if the object were initialized only with the brace-enclosed +list if the types of the compound literal and the object match. +The elements of the compound literal must be constant. +If the object being initialized has array type of unknown size, the size is +determined by the size of the compound literal. + +@smallexample +static struct foo x = (struct foo) @{1, 'a', 'b'@}; +static int y[] = (int []) @{1, 2, 3@}; +static int z[] = (int [3]) @{1@}; +@end smallexample + +@noindent +The above lines are equivalent to the following: +@smallexample +static struct foo x = @{1, 'a', 'b'@}; +static int y[] = @{1, 2, 3@}; +static int z[] = @{1, 0, 0@}; +@end smallexample + +In C, a compound literal designates an unnamed object with static or +automatic storage duration. In C++, a compound literal designates a +temporary object that only lives until the end of its full-expression. +As a result, well-defined C code that takes the address of a subobject +of a compound literal can be undefined in C++, so G++ rejects +the conversion of a temporary array to a pointer. For instance, if +the array compound literal example above appeared inside a function, +any subsequent use of @code{foo} in C++ would have undefined behavior +because the lifetime of the array ends after the declaration of @code{foo}. + +As an optimization, G++ sometimes gives array compound literals longer +lifetimes: when the array either appears outside a function or has +a @code{const}-qualified type. If @code{foo} and its initializer had +elements of type @code{char *const} rather than @code{char *}, or if +@code{foo} were a global variable, the array would have static storage +duration. But it is probably safest just to avoid the use of array +compound literals in C++ code. + +@node Designated Inits +@section Designated Initializers +@cindex initializers with labeled elements +@cindex labeled elements in initializers +@cindex case labels in initializers +@cindex designated initializers + +Standard C90 requires the elements of an initializer to appear in a fixed +order, the same as the order of the elements in the array or structure +being initialized. + +In ISO C99 you can give the elements in any order, specifying the array +indices or structure field names they apply to, and GNU C allows this as +an extension in C90 mode as well. This extension is not +implemented in GNU C++. + +To specify an array index, write +@samp{[@var{index}] =} before the element value. For example, + +@smallexample +int a[6] = @{ [4] = 29, [2] = 15 @}; +@end smallexample + +@noindent +is equivalent to + +@smallexample +int a[6] = @{ 0, 0, 15, 0, 29, 0 @}; +@end smallexample + +@noindent +The index values must be constant expressions, even if the array being +initialized is automatic. + +An alternative syntax for this that has been obsolete since GCC 2.5 but +GCC still accepts is to write @samp{[@var{index}]} before the element +value, with no @samp{=}. + +To initialize a range of elements to the same value, write +@samp{[@var{first} ... @var{last}] = @var{value}}. This is a GNU +extension. For example, + +@smallexample +int widths[] = @{ [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 @}; +@end smallexample + +@noindent +If the value in it has side effects, the side effects happen only once, +not for each initialized field by the range initializer. + +@noindent +Note that the length of the array is the highest value specified +plus one. + +In a structure initializer, specify the name of a field to initialize +with @samp{.@var{fieldname} =} before the element value. For example, +given the following structure, + +@smallexample +struct point @{ int x, y; @}; +@end smallexample + +@noindent +the following initialization + +@smallexample +struct point p = @{ .y = yvalue, .x = xvalue @}; +@end smallexample + +@noindent +is equivalent to + +@smallexample +struct point p = @{ xvalue, yvalue @}; +@end smallexample + +Another syntax that has the same meaning, obsolete since GCC 2.5, is +@samp{@var{fieldname}:}, as shown here: + +@smallexample +struct point p = @{ y: yvalue, x: xvalue @}; +@end smallexample + +Omitted fields are implicitly initialized the same as for objects +that have static storage duration. + +@cindex designators +The @samp{[@var{index}]} or @samp{.@var{fieldname}} is known as a +@dfn{designator}. You can also use a designator (or the obsolete colon +syntax) when initializing a union, to specify which element of the union +should be used. For example, + +@smallexample +union foo @{ int i; double d; @}; + +union foo f = @{ .d = 4 @}; +@end smallexample + +@noindent +converts 4 to a @code{double} to store it in the union using +the second element. By contrast, casting 4 to type @code{union foo} +stores it into the union as the integer @code{i}, since it is +an integer. @xref{Cast to Union}. + +You can combine this technique of naming elements with ordinary C +initialization of successive elements. Each initializer element that +does not have a designator applies to the next consecutive element of the +array or structure. For example, + +@smallexample +int a[6] = @{ [1] = v1, v2, [4] = v4 @}; +@end smallexample + +@noindent +is equivalent to + +@smallexample +int a[6] = @{ 0, v1, v2, 0, v4, 0 @}; +@end smallexample + +Labeling the elements of an array initializer is especially useful +when the indices are characters or belong to an @code{enum} type. +For example: + +@smallexample +int whitespace[256] + = @{ [' '] = 1, ['\t'] = 1, ['\h'] = 1, + ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 @}; +@end smallexample + +@cindex designator lists +You can also write a series of @samp{.@var{fieldname}} and +@samp{[@var{index}]} designators before an @samp{=} to specify a +nested subobject to initialize; the list is taken relative to the +subobject corresponding to the closest surrounding brace pair. For +example, with the @samp{struct point} declaration above: + +@smallexample +struct point ptarray[10] = @{ [2].y = yv2, [2].x = xv2, [0].x = xv0 @}; +@end smallexample + +If the same field is initialized multiple times, or overlapping +fields of a union are initialized, the value from the last +initialization is used. When a field of a union is itself a structure, +the entire structure from the last field initialized is used. If any previous +initializer has side effect, it is unspecified whether the side effect +happens or not. Currently, GCC discards the side-effecting +initializer expressions and issues a warning. + +@node Case Ranges +@section Case Ranges +@cindex case ranges +@cindex ranges in case statements + +You can specify a range of consecutive values in a single @code{case} label, +like this: + +@smallexample +case @var{low} ... @var{high}: +@end smallexample + +@noindent +This has the same effect as the proper number of individual @code{case} +labels, one for each integer value from @var{low} to @var{high}, inclusive. + +This feature is especially useful for ranges of ASCII character codes: + +@smallexample +case 'A' ... 'Z': +@end smallexample + +@strong{Be careful:} Write spaces around the @code{...}, for otherwise +it may be parsed wrong when you use it with integer values. For example, +write this: + +@smallexample +case 1 ... 5: +@end smallexample + +@noindent +rather than this: + +@smallexample +case 1...5: +@end smallexample + +@node Cast to Union +@section Cast to a Union Type +@cindex cast to a union +@cindex union, casting to a + +A cast to a union type is a C extension not available in C++. It looks +just like ordinary casts with the constraint that the type specified is +a union type. You can specify the type either with the @code{union} +keyword or with a @code{typedef} name that refers to a union. The result +of a cast to a union is a temporary rvalue of the union type with a member +whose type matches that of the operand initialized to the value of +the operand. The effect of a cast to a union is similar to a compound +literal except that it yields an rvalue like standard casts do. +@xref{Compound Literals}. + +Expressions that may be cast to the union type are those whose type matches +at least one of the members of the union. Thus, given the following union +and variables: + +@smallexample +union foo @{ int i; double d; @}; +int x; +double y; +union foo z; +@end smallexample + +@noindent +both @code{x} and @code{y} can be cast to type @code{union foo} and +the following assignments +@smallexample + z = (union foo) x; + z = (union foo) y; +@end smallexample +are shorthand equivalents of these +@smallexample + z = (union foo) @{ .i = x @}; + z = (union foo) @{ .d = y @}; +@end smallexample + +However, @code{(union foo) FLT_MAX;} is not a valid cast because the union +has no member of type @code{float}. + +Using the cast as the right-hand side of an assignment to a variable of +union type is equivalent to storing in a member of the union with +the same type + +@smallexample +union foo u; +/* @r{@dots{}} */ +u = (union foo) x @equiv{} u.i = x +u = (union foo) y @equiv{} u.d = y +@end smallexample + +You can also use the union cast as a function argument: + +@smallexample +void hack (union foo); +/* @r{@dots{}} */ +hack ((union foo) x); +@end smallexample + +@node Mixed Labels and Declarations +@section Mixed Declarations, Labels and Code +@cindex mixed declarations and code +@cindex declarations, mixed with code +@cindex code, mixed with declarations + +ISO C99 and ISO C++ allow declarations and code to be freely mixed +within compound statements. ISO C2X allows labels to be +placed before declarations and at the end of a compound statement. +As an extension, GNU C also allows all this in C90 mode. For example, +you could do: + +@smallexample +int i; +/* @r{@dots{}} */ +i++; +int j = i + 2; +@end smallexample + +Each identifier is visible from where it is declared until the end of +the enclosing block. + +@node Function Attributes +@section Declaring Attributes of Functions +@cindex function attributes +@cindex declaring attributes of functions +@cindex @code{volatile} applied to function +@cindex @code{const} applied to function + +In GNU C and C++, you can use function attributes to specify certain +function properties that may help the compiler optimize calls or +check code more carefully for correctness. For example, you +can use attributes to specify that a function never returns +(@code{noreturn}), returns a value depending only on the values of +its arguments (@code{const}), or has @code{printf}-style arguments +(@code{format}). + +You can also use attributes to control memory placement, code +generation options or call/return conventions within the function +being annotated. Many of these attributes are target-specific. For +example, many targets support attributes for defining interrupt +handler functions, which typically must follow special register usage +and return conventions. Such attributes are described in the subsection +for each target. However, a considerable number of attributes are +supported by most, if not all targets. Those are described in +the @ref{Common Function Attributes} section. + +Function attributes are introduced by the @code{__attribute__} keyword +in the declaration of a function, followed by an attribute specification +enclosed in double parentheses. You can specify multiple attributes in +a declaration by separating them by commas within the double parentheses +or by immediately following one attribute specification with another. +@xref{Attribute Syntax}, for the exact rules on attribute syntax and +placement. Compatible attribute specifications on distinct declarations +of the same function are merged. An attribute specification that is not +compatible with attributes already applied to a declaration of the same +function is ignored with a warning. + +Some function attributes take one or more arguments that refer to +the function's parameters by their positions within the function parameter +list. Such attribute arguments are referred to as @dfn{positional arguments}. +Unless specified otherwise, positional arguments that specify properties +of parameters with pointer types can also specify the same properties of +the implicit C++ @code{this} argument in non-static member functions, and +of parameters of reference to a pointer type. For ordinary functions, +position one refers to the first parameter on the list. In C++ non-static +member functions, position one refers to the implicit @code{this} pointer. +The same restrictions and effects apply to function attributes used with +ordinary functions or C++ member functions. + +GCC also supports attributes on +variable declarations (@pxref{Variable Attributes}), +labels (@pxref{Label Attributes}), +enumerators (@pxref{Enumerator Attributes}), +statements (@pxref{Statement Attributes}), +types (@pxref{Type Attributes}), +and on field declarations (for @code{tainted_args}). + +There is some overlap between the purposes of attributes and pragmas +(@pxref{Pragmas,,Pragmas Accepted by GCC}). It has been +found convenient to use @code{__attribute__} to achieve a natural +attachment of attributes to their corresponding declarations, whereas +@code{#pragma} is of use for compatibility with other compilers +or constructs that do not naturally form part of the grammar. + +In addition to the attributes documented here, +GCC plugins may provide their own attributes. + +@menu +* Common Function Attributes:: +* AArch64 Function Attributes:: +* AMD GCN Function Attributes:: +* ARC Function Attributes:: +* ARM Function Attributes:: +* AVR Function Attributes:: +* Blackfin Function Attributes:: +* BPF Function Attributes:: +* C-SKY Function Attributes:: +* Epiphany Function Attributes:: +* H8/300 Function Attributes:: +* IA-64 Function Attributes:: +* M32C Function Attributes:: +* M32R/D Function Attributes:: +* m68k Function Attributes:: +* MCORE Function Attributes:: +* MeP Function Attributes:: +* MicroBlaze Function Attributes:: +* Microsoft Windows Function Attributes:: +* MIPS Function Attributes:: +* MSP430 Function Attributes:: +* NDS32 Function Attributes:: +* Nios II Function Attributes:: +* Nvidia PTX Function Attributes:: +* PowerPC Function Attributes:: +* RISC-V Function Attributes:: +* RL78 Function Attributes:: +* RX Function Attributes:: +* S/390 Function Attributes:: +* SH Function Attributes:: +* Symbian OS Function Attributes:: +* V850 Function Attributes:: +* Visium Function Attributes:: +* x86 Function Attributes:: +* Xstormy16 Function Attributes:: +@end menu + +@node Common Function Attributes +@subsection Common Function Attributes + +The following attributes are supported on most targets. + +@table @code +@c Keep this table alphabetized by attribute name. Treat _ as space. + +@item access (@var{access-mode}, @var{ref-index}) +@itemx access (@var{access-mode}, @var{ref-index}, @var{size-index}) + +The @code{access} attribute enables the detection of invalid or unsafe +accesses by functions to which they apply or their callers, as well as +write-only accesses to objects that are never read from. Such accesses +may be diagnosed by warnings such as @option{-Wstringop-overflow}, +@option{-Wuninitialized}, @option{-Wunused}, and others. + +The @code{access} attribute specifies that a function to whose by-reference +arguments the attribute applies accesses the referenced object according to +@var{access-mode}. The @var{access-mode} argument is required and must be +one of four names: @code{read_only}, @code{read_write}, @code{write_only}, +or @code{none}. The remaining two are positional arguments. + +The required @var{ref-index} positional argument denotes a function +argument of pointer (or in C++, reference) type that is subject to +the access. The same pointer argument can be referenced by at most one +distinct @code{access} attribute. + +The optional @var{size-index} positional argument denotes a function +argument of integer type that specifies the maximum size of the access. +The size is the number of elements of the type referenced by @var{ref-index}, +or the number of bytes when the pointer type is @code{void*}. When no +@var{size-index} argument is specified, the pointer argument must be either +null or point to a space that is suitably aligned and large for at least one +object of the referenced type (this implies that a past-the-end pointer is +not a valid argument). The actual size of the access may be less but it +must not be more. + +The @code{read_only} access mode specifies that the pointer to which it +applies is used to read the referenced object but not write to it. Unless +the argument specifying the size of the access denoted by @var{size-index} +is zero, the referenced object must be initialized. The mode implies +a stronger guarantee than the @code{const} qualifier which, when cast away +from a pointer, does not prevent the pointed-to object from being modified. +Examples of the use of the @code{read_only} access mode is the argument to +the @code{puts} function, or the second and third arguments to +the @code{memcpy} function. + +@smallexample +__attribute__ ((access (read_only, 1))) int puts (const char*); +__attribute__ ((access (read_only, 2, 3))) void* memcpy (void*, const void*, size_t); +@end smallexample + +The @code{read_write} access mode applies to arguments of pointer types +without the @code{const} qualifier. It specifies that the pointer to which +it applies is used to both read and write the referenced object. Unless +the argument specifying the size of the access denoted by @var{size-index} +is zero, the object referenced by the pointer must be initialized. An example +of the use of the @code{read_write} access mode is the first argument to +the @code{strcat} function. + +@smallexample +__attribute__ ((access (read_write, 1), access (read_only, 2))) char* strcat (char*, const char*); +@end smallexample + +The @code{write_only} access mode applies to arguments of pointer types +without the @code{const} qualifier. It specifies that the pointer to which +it applies is used to write to the referenced object but not read from it. +The object referenced by the pointer need not be initialized. An example +of the use of the @code{write_only} access mode is the first argument to +the @code{strcpy} function, or the first two arguments to the @code{fgets} +function. + +@smallexample +__attribute__ ((access (write_only, 1), access (read_only, 2))) char* strcpy (char*, const char*); +__attribute__ ((access (write_only, 1, 2), access (read_write, 3))) int fgets (char*, int, FILE*); +@end smallexample + +The access mode @code{none} specifies that the pointer to which it applies +is not used to access the referenced object at all. Unless the pointer is +null the pointed-to object must exist and have at least the size as denoted +by the @var{size-index} argument. When the optional @var{size-index} +argument is omitted for an argument of @code{void*} type the actual pointer +agument is ignored. The referenced object need not be initialized. +The mode is intended to be used as a means to help validate the expected +object size, for example in functions that call @code{__builtin_object_size}. +@xref{Object Size Checking}. + +Note that the @code{access} attribute merely specifies how an object +referenced by the pointer argument can be accessed; it does not imply that +an access @strong{will} happen. Also, the @code{access} attribute does not +imply the attribute @code{nonnull}; it may be appropriate to add both attributes +at the declaration of a function that unconditionally manipulates a buffer via +a pointer argument. See the @code{nonnull} attribute for more information and +caveats. + +@item alias ("@var{target}") +@cindex @code{alias} function attribute +The @code{alias} attribute causes the declaration to be emitted as an alias +for another symbol, which must have been previously declared with the same +type, and for variables, also the same size and alignment. Declaring an alias +with a different type than the target is undefined and may be diagnosed. As +an example, the following declarations: + +@smallexample +void __f () @{ /* @r{Do something.} */; @} +void f () __attribute__ ((weak, alias ("__f"))); +@end smallexample + +@noindent +define @samp{f} to be a weak alias for @samp{__f}. In C++, the mangled name +for the target must be used. It is an error if @samp{__f} is not defined in +the same translation unit. + +This attribute requires assembler and object file support, +and may not be available on all targets. + +@item aligned +@itemx aligned (@var{alignment}) +@cindex @code{aligned} function attribute +The @code{aligned} attribute specifies a minimum alignment for +the first instruction of the function, measured in bytes. When specified, +@var{alignment} must be an integer constant power of 2. Specifying no +@var{alignment} argument implies the ideal alignment for the target. +The @code{__alignof__} operator can be used to determine what that is +(@pxref{Alignment}). The attribute has no effect when a definition for +the function is not provided in the same translation unit. + +The attribute cannot be used to decrease the alignment of a function +previously declared with a more restrictive alignment; only to increase +it. Attempts to do otherwise are diagnosed. Some targets specify +a minimum default alignment for functions that is greater than 1. On +such targets, specifying a less restrictive alignment is silently ignored. +Using the attribute overrides the effect of the @option{-falign-functions} +(@pxref{Optimize Options}) option for this function. + +Note that the effectiveness of @code{aligned} attributes may be +limited by inherent limitations in the system linker +and/or object file format. On some systems, the +linker is only able to arrange for functions to be aligned up to a +certain maximum alignment. (For some linkers, the maximum supported +alignment may be very very small.) See your linker documentation for +further information. + +The @code{aligned} attribute can also be used for variables and fields +(@pxref{Variable Attributes}.) + +@item alloc_align (@var{position}) +@cindex @code{alloc_align} function attribute +The @code{alloc_align} attribute may be applied to a function that +returns a pointer and takes at least one argument of an integer or +enumerated type. +It indicates that the returned pointer is aligned on a boundary given +by the function argument at @var{position}. Meaningful alignments are +powers of 2 greater than one. GCC uses this information to improve +pointer alignment analysis. + +The function parameter denoting the allocated alignment is specified by +one constant integer argument whose number is the argument of the attribute. +Argument numbering starts at one. + +For instance, + +@smallexample +void* my_memalign (size_t, size_t) __attribute__ ((alloc_align (1))); +@end smallexample + +@noindent +declares that @code{my_memalign} returns memory with minimum alignment +given by parameter 1. + +@item alloc_size (@var{position}) +@itemx alloc_size (@var{position-1}, @var{position-2}) +@cindex @code{alloc_size} function attribute +The @code{alloc_size} attribute may be applied to a function that +returns a pointer and takes at least one argument of an integer or +enumerated type. +It indicates that the returned pointer points to memory whose size is +given by the function argument at @var{position-1}, or by the product +of the arguments at @var{position-1} and @var{position-2}. Meaningful +sizes are positive values less than @code{PTRDIFF_MAX}. GCC uses this +information to improve the results of @code{__builtin_object_size}. + +The function parameter(s) denoting the allocated size are specified by +one or two integer arguments supplied to the attribute. The allocated size +is either the value of the single function argument specified or the product +of the two function arguments specified. Argument numbering starts at +one for ordinary functions, and at two for C++ non-static member functions. + +For instance, + +@smallexample +void* my_calloc (size_t, size_t) __attribute__ ((alloc_size (1, 2))); +void* my_realloc (void*, size_t) __attribute__ ((alloc_size (2))); +@end smallexample + +@noindent +declares that @code{my_calloc} returns memory of the size given by +the product of parameter 1 and 2 and that @code{my_realloc} returns memory +of the size given by parameter 2. + +@item always_inline +@cindex @code{always_inline} function attribute +Generally, functions are not inlined unless optimization is specified. +For functions declared inline, this attribute inlines the function +independent of any restrictions that otherwise apply to inlining. +Failure to inline such a function is diagnosed as an error. +Note that if such a function is called indirectly the compiler may +or may not inline it depending on optimization level and a failure +to inline an indirect call may or may not be diagnosed. + +@item artificial +@cindex @code{artificial} function attribute +This attribute is useful for small inline wrappers that if possible +should appear during debugging as a unit. Depending on the debug +info format it either means marking the function as artificial +or using the caller location for all instructions within the inlined +body. + +@item assume_aligned (@var{alignment}) +@itemx assume_aligned (@var{alignment}, @var{offset}) +@cindex @code{assume_aligned} function attribute +The @code{assume_aligned} attribute may be applied to a function that +returns a pointer. It indicates that the returned pointer is aligned +on a boundary given by @var{alignment}. If the attribute has two +arguments, the second argument is misalignment @var{offset}. Meaningful +values of @var{alignment} are powers of 2 greater than one. Meaningful +values of @var{offset} are greater than zero and less than @var{alignment}. + +For instance + +@smallexample +void* my_alloc1 (size_t) __attribute__((assume_aligned (16))); +void* my_alloc2 (size_t) __attribute__((assume_aligned (32, 8))); +@end smallexample + +@noindent +declares that @code{my_alloc1} returns 16-byte aligned pointers and +that @code{my_alloc2} returns a pointer whose value modulo 32 is equal +to 8. + +@item cold +@cindex @code{cold} function attribute +The @code{cold} attribute on functions is used to inform the compiler that +the function is unlikely to be executed. The function is optimized for +size rather than speed and on many targets it is placed into a special +subsection of the text section so all cold functions appear close together, +improving code locality of non-cold parts of program. The paths leading +to calls of cold functions within code are marked as unlikely by the branch +prediction mechanism. It is thus useful to mark functions used to handle +unlikely conditions, such as @code{perror}, as cold to improve optimization +of hot functions that do call marked functions in rare occasions. + +When profile feedback is available, via @option{-fprofile-use}, cold functions +are automatically detected and this attribute is ignored. + +@item const +@cindex @code{const} function attribute +@cindex functions that have no side effects +Calls to functions whose return value is not affected by changes to +the observable state of the program and that have no observable effects +on such state other than to return a value may lend themselves to +optimizations such as common subexpression elimination. Declaring such +functions with the @code{const} attribute allows GCC to avoid emitting +some calls in repeated invocations of the function with the same argument +values. + +For example, + +@smallexample +int square (int) __attribute__ ((const)); +@end smallexample + +@noindent +tells GCC that subsequent calls to function @code{square} with the same +argument value can be replaced by the result of the first call regardless +of the statements in between. + +The @code{const} attribute prohibits a function from reading objects +that affect its return value between successive invocations. However, +functions declared with the attribute can safely read objects that do +not change their return value, such as non-volatile constants. + +The @code{const} attribute imposes greater restrictions on a function's +definition than the similar @code{pure} attribute. Declaring the same +function with both the @code{const} and the @code{pure} attribute is +diagnosed. Because a const function cannot have any observable side +effects it does not make sense for it to return @code{void}. Declaring +such a function is diagnosed. + +@cindex pointer arguments +Note that a function that has pointer arguments and examines the data +pointed to must @emph{not} be declared @code{const} if the pointed-to +data might change between successive invocations of the function. In +general, since a function cannot distinguish data that might change +from data that cannot, const functions should never take pointer or, +in C++, reference arguments. Likewise, a function that calls a non-const +function usually must not be const itself. + +@item constructor +@itemx destructor +@itemx constructor (@var{priority}) +@itemx destructor (@var{priority}) +@cindex @code{constructor} function attribute +@cindex @code{destructor} function attribute +The @code{constructor} attribute causes the function to be called +automatically before execution enters @code{main ()}. Similarly, the +@code{destructor} attribute causes the function to be called +automatically after @code{main ()} completes or @code{exit ()} is +called. Functions with these attributes are useful for +initializing data that is used implicitly during the execution of +the program. + +On some targets the attributes also accept an integer argument to +specify a priority to control the order in which constructor and +destructor functions are run. A constructor +with a smaller priority number runs before a constructor with a larger +priority number; the opposite relationship holds for destructors. Note +that priorities 0-100 are reserved. So, if you have a constructor that +allocates a resource and a destructor that deallocates the same +resource, both functions typically have the same priority. The +priorities for constructor and destructor functions are the same as +those specified for namespace-scope C++ objects (@pxref{C++ Attributes}). +However, at present, the order in which constructors for C++ objects +with static storage duration and functions decorated with attribute +@code{constructor} are invoked is unspecified. In mixed declarations, +attribute @code{init_priority} can be used to impose a specific ordering. + +Using the argument forms of the @code{constructor} and @code{destructor} +attributes on targets where the feature is not supported is rejected with +an error. + +@item copy +@itemx copy (@var{function}) +@cindex @code{copy} function attribute +The @code{copy} attribute applies the set of attributes with which +@var{function} has been declared to the declaration of the function +to which the attribute is applied. The attribute is designed for +libraries that define aliases or function resolvers that are expected +to specify the same set of attributes as their targets. The @code{copy} +attribute can be used with functions, variables, or types. However, +the kind of symbol to which the attribute is applied (either function +or variable) must match the kind of symbol to which the argument refers. +The @code{copy} attribute copies only syntactic and semantic attributes +but not attributes that affect a symbol's linkage or visibility such as +@code{alias}, @code{visibility}, or @code{weak}. The @code{deprecated} +and @code{target_clones} attribute are also not copied. +@xref{Common Type Attributes}. +@xref{Common Variable Attributes}. + +For example, the @var{StrongAlias} macro below makes use of the @code{alias} +and @code{copy} attributes to define an alias named @var{alloc} for function +@var{allocate} declared with attributes @var{alloc_size}, @var{malloc}, and +@var{nothrow}. Thanks to the @code{__typeof__} operator the alias has +the same type as the target function. As a result of the @code{copy} +attribute the alias also shares the same attributes as the target. + +@smallexample +#define StrongAlias(TargetFunc, AliasDecl) \ + extern __typeof__ (TargetFunc) AliasDecl \ + __attribute__ ((alias (#TargetFunc), copy (TargetFunc))); + +extern __attribute__ ((alloc_size (1), malloc, nothrow)) + void* allocate (size_t); +StrongAlias (allocate, alloc); +@end smallexample + +@item deprecated +@itemx deprecated (@var{msg}) +@cindex @code{deprecated} function attribute +The @code{deprecated} attribute results in a warning if the function +is used anywhere in the source file. This is useful when identifying +functions that are expected to be removed in a future version of a +program. The warning also includes the location of the declaration +of the deprecated function, to enable users to easily find further +information about why the function is deprecated, or what they should +do instead. Note that the warnings only occurs for uses: + +@smallexample +int old_fn () __attribute__ ((deprecated)); +int old_fn (); +int (*fn_ptr)() = old_fn; +@end smallexample + +@noindent +results in a warning on line 3 but not line 2. The optional @var{msg} +argument, which must be a string, is printed in the warning if +present. + +The @code{deprecated} attribute can also be used for variables and +types (@pxref{Variable Attributes}, @pxref{Type Attributes}.) + +The message attached to the attribute is affected by the setting of +the @option{-fmessage-length} option. + +@item unavailable +@itemx unavailable (@var{msg}) +@cindex @code{unavailable} function attribute +The @code{unavailable} attribute results in an error if the function +is used anywhere in the source file. This is useful when identifying +functions that have been removed from a particular variation of an +interface. Other than emitting an error rather than a warning, the +@code{unavailable} attribute behaves in the same manner as +@code{deprecated}. + +The @code{unavailable} attribute can also be used for variables and +types (@pxref{Variable Attributes}, @pxref{Type Attributes}.) + +@item error ("@var{message}") +@itemx warning ("@var{message}") +@cindex @code{error} function attribute +@cindex @code{warning} function attribute +If the @code{error} or @code{warning} attribute +is used on a function declaration and a call to such a function +is not eliminated through dead code elimination or other optimizations, +an error or warning (respectively) that includes @var{message} is diagnosed. +This is useful +for compile-time checking, especially together with @code{__builtin_constant_p} +and inline functions where checking the inline function arguments is not +possible through @code{extern char [(condition) ? 1 : -1];} tricks. + +While it is possible to leave the function undefined and thus invoke +a link failure (to define the function with +a message in @code{.gnu.warning*} section), +when using these attributes the problem is diagnosed +earlier and with exact location of the call even in presence of inline +functions or when not emitting debugging information. + +@item externally_visible +@cindex @code{externally_visible} function attribute +This attribute, attached to a global variable or function, nullifies +the effect of the @option{-fwhole-program} command-line option, so the +object remains visible outside the current compilation unit. + +If @option{-fwhole-program} is used together with @option{-flto} and +@command{gold} is used as the linker plugin, +@code{externally_visible} attributes are automatically added to functions +(not variable yet due to a current @command{gold} issue) +that are accessed outside of LTO objects according to resolution file +produced by @command{gold}. +For other linkers that cannot generate resolution file, +explicit @code{externally_visible} attributes are still necessary. + +@item fd_arg +@itemx fd_arg (@var{N}) +@cindex @code{fd_arg} function attribute +The @code{fd_arg} attribute may be applied to a function that takes an open +file descriptor at referenced argument @var{N}. + +It indicates that the passed filedescriptor must not have been closed. +Therefore, when the analyzer is enabled with @option{-fanalyzer}, the +analyzer may emit a @option{-Wanalyzer-fd-use-after-close} diagnostic +if it detects a code path in which a function with this attribute is +called with a closed file descriptor. + +The attribute also indicates that the file descriptor must have been checked for +validity before usage. Therefore, analyzer may emit +@option{-Wanalyzer-fd-use-without-check} diagnostic if it detects a code path in +which a function with this attribute is called with a file descriptor that has +not been checked for validity. + +@item fd_arg_read +@itemx fd_arg_read (@var{N}) +@cindex @code{fd_arg_read} function attribute +The @code{fd_arg_read} is identical to @code{fd_arg}, but with the additional +requirement that it might read from the file descriptor, and thus, the file +descriptor must not have been opened as write-only. + +The analyzer may emit a @option{-Wanalyzer-access-mode-mismatch} +diagnostic if it detects a code path in which a function with this +attribute is called on a file descriptor opened with @code{O_WRONLY}. + +@item fd_arg_write +@itemx fd_arg_write (@var{N}) +@cindex @code{fd_arg_write} function attribute +The @code{fd_arg_write} is identical to @code{fd_arg_read} except that the +analyzer may emit a @option{-Wanalyzer-access-mode-mismatch} diagnostic if +it detects a code path in which a function with this attribute is called on a +file descriptor opened with @code{O_RDONLY}. + +@item flatten +@cindex @code{flatten} function attribute +Generally, inlining into a function is limited. For a function marked with +this attribute, every call inside this function is inlined, if possible. +Functions declared with attribute @code{noinline} and similar are not +inlined. Whether the function itself is considered for inlining depends +on its size and the current inlining parameters. + +@item format (@var{archetype}, @var{string-index}, @var{first-to-check}) +@cindex @code{format} function attribute +@cindex functions with @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style arguments +@opindex Wformat +The @code{format} attribute specifies that a function takes @code{printf}, +@code{scanf}, @code{strftime} or @code{strfmon} style arguments that +should be type-checked against a format string. For example, the +declaration: + +@smallexample +extern int +my_printf (void *my_object, const char *my_format, ...) + __attribute__ ((format (printf, 2, 3))); +@end smallexample + +@noindent +causes the compiler to check the arguments in calls to @code{my_printf} +for consistency with the @code{printf} style format string argument +@code{my_format}. + +The parameter @var{archetype} determines how the format string is +interpreted, and should be @code{printf}, @code{scanf}, @code{strftime}, +@code{gnu_printf}, @code{gnu_scanf}, @code{gnu_strftime} or +@code{strfmon}. (You can also use @code{__printf__}, +@code{__scanf__}, @code{__strftime__} or @code{__strfmon__}.) On +MinGW targets, @code{ms_printf}, @code{ms_scanf}, and +@code{ms_strftime} are also present. +@var{archetype} values such as @code{printf} refer to the formats accepted +by the system's C runtime library, +while values prefixed with @samp{gnu_} always refer +to the formats accepted by the GNU C Library. On Microsoft Windows +targets, values prefixed with @samp{ms_} refer to the formats accepted by the +@file{msvcrt.dll} library. +The parameter @var{string-index} +specifies which argument is the format string argument (starting +from 1), while @var{first-to-check} is the number of the first +argument to check against the format string. For functions +where the arguments are not available to be checked (such as +@code{vprintf}), specify the third parameter as zero. In this case the +compiler only checks the format string for consistency. For +@code{strftime} formats, the third parameter is required to be zero. +Since non-static C++ methods have an implicit @code{this} argument, the +arguments of such methods should be counted from two, not one, when +giving values for @var{string-index} and @var{first-to-check}. + +In the example above, the format string (@code{my_format}) is the second +argument of the function @code{my_print}, and the arguments to check +start with the third argument, so the correct parameters for the format +attribute are 2 and 3. + +@opindex ffreestanding +@opindex fno-builtin +The @code{format} attribute allows you to identify your own functions +that take format strings as arguments, so that GCC can check the +calls to these functions for errors. The compiler always (unless +@option{-ffreestanding} or @option{-fno-builtin} is used) checks formats +for the standard library functions @code{printf}, @code{fprintf}, +@code{sprintf}, @code{scanf}, @code{fscanf}, @code{sscanf}, @code{strftime}, +@code{vprintf}, @code{vfprintf} and @code{vsprintf} whenever such +warnings are requested (using @option{-Wformat}), so there is no need to +modify the header file @file{stdio.h}. In C99 mode, the functions +@code{snprintf}, @code{vsnprintf}, @code{vscanf}, @code{vfscanf} and +@code{vsscanf} are also checked. Except in strictly conforming C +standard modes, the X/Open function @code{strfmon} is also checked as +are @code{printf_unlocked} and @code{fprintf_unlocked}. +@xref{C Dialect Options,,Options Controlling C Dialect}. + +For Objective-C dialects, @code{NSString} (or @code{__NSString__}) is +recognized in the same context. Declarations including these format attributes +are parsed for correct syntax, however the result of checking of such format +strings is not yet defined, and is not carried out by this version of the +compiler. + +The target may also provide additional types of format checks. +@xref{Target Format Checks,,Format Checks Specific to Particular +Target Machines}. + +@item format_arg (@var{string-index}) +@cindex @code{format_arg} function attribute +@opindex Wformat-nonliteral +The @code{format_arg} attribute specifies that a function takes one or +more format strings for a @code{printf}, @code{scanf}, @code{strftime} or +@code{strfmon} style function and modifies it (for example, to translate +it into another language), so the result can be passed to a +@code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style +function (with the remaining arguments to the format function the same +as they would have been for the unmodified string). Multiple +@code{format_arg} attributes may be applied to the same function, each +designating a distinct parameter as a format string. For example, the +declaration: + +@smallexample +extern char * +my_dgettext (char *my_domain, const char *my_format) + __attribute__ ((format_arg (2))); +@end smallexample + +@noindent +causes the compiler to check the arguments in calls to a @code{printf}, +@code{scanf}, @code{strftime} or @code{strfmon} type function, whose +format string argument is a call to the @code{my_dgettext} function, for +consistency with the format string argument @code{my_format}. If the +@code{format_arg} attribute had not been specified, all the compiler +could tell in such calls to format functions would be that the format +string argument is not constant; this would generate a warning when +@option{-Wformat-nonliteral} is used, but the calls could not be checked +without the attribute. + +In calls to a function declared with more than one @code{format_arg} +attribute, each with a distinct argument value, the corresponding +actual function arguments are checked against all format strings +designated by the attributes. This capability is designed to support +the GNU @code{ngettext} family of functions. + +The parameter @var{string-index} specifies which argument is the format +string argument (starting from one). Since non-static C++ methods have +an implicit @code{this} argument, the arguments of such methods should +be counted from two. + +The @code{format_arg} attribute allows you to identify your own +functions that modify format strings, so that GCC can check the +calls to @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} +type function whose operands are a call to one of your own function. +The compiler always treats @code{gettext}, @code{dgettext}, and +@code{dcgettext} in this manner except when strict ISO C support is +requested by @option{-ansi} or an appropriate @option{-std} option, or +@option{-ffreestanding} or @option{-fno-builtin} +is used. @xref{C Dialect Options,,Options +Controlling C Dialect}. + +For Objective-C dialects, the @code{format-arg} attribute may refer to an +@code{NSString} reference for compatibility with the @code{format} attribute +above. + +The target may also allow additional types in @code{format-arg} attributes. +@xref{Target Format Checks,,Format Checks Specific to Particular +Target Machines}. + +@item gnu_inline +@cindex @code{gnu_inline} function attribute +This attribute should be used with a function that is also declared +with the @code{inline} keyword. It directs GCC to treat the function +as if it were defined in gnu90 mode even when compiling in C99 or +gnu99 mode. + +If the function is declared @code{extern}, then this definition of the +function is used only for inlining. In no case is the function +compiled as a standalone function, not even if you take its address +explicitly. Such an address becomes an external reference, as if you +had only declared the function, and had not defined it. This has +almost the effect of a macro. The way to use this is to put a +function definition in a header file with this attribute, and put +another copy of the function, without @code{extern}, in a library +file. The definition in the header file causes most calls to the +function to be inlined. If any uses of the function remain, they +refer to the single copy in the library. Note that the two +definitions of the functions need not be precisely the same, although +if they do not have the same effect your program may behave oddly. + +In C, if the function is neither @code{extern} nor @code{static}, then +the function is compiled as a standalone function, as well as being +inlined where possible. + +This is how GCC traditionally handled functions declared +@code{inline}. Since ISO C99 specifies a different semantics for +@code{inline}, this function attribute is provided as a transition +measure and as a useful feature in its own right. This attribute is +available in GCC 4.1.3 and later. It is available if either of the +preprocessor macros @code{__GNUC_GNU_INLINE__} or +@code{__GNUC_STDC_INLINE__} are defined. @xref{Inline,,An Inline +Function is As Fast As a Macro}. + +In C++, this attribute does not depend on @code{extern} in any way, +but it still requires the @code{inline} keyword to enable its special +behavior. + +@item hot +@cindex @code{hot} function attribute +The @code{hot} attribute on a function is used to inform the compiler that +the function is a hot spot of the compiled program. The function is +optimized more aggressively and on many targets it is placed into a special +subsection of the text section so all hot functions appear close together, +improving locality. + +When profile feedback is available, via @option{-fprofile-use}, hot functions +are automatically detected and this attribute is ignored. + +@item ifunc ("@var{resolver}") +@cindex @code{ifunc} function attribute +@cindex indirect functions +@cindex functions that are dynamically resolved +The @code{ifunc} attribute is used to mark a function as an indirect +function using the STT_GNU_IFUNC symbol type extension to the ELF +standard. This allows the resolution of the symbol value to be +determined dynamically at load time, and an optimized version of the +routine to be selected for the particular processor or other system +characteristics determined then. To use this attribute, first define +the implementation functions available, and a resolver function that +returns a pointer to the selected implementation function. The +implementation functions' declarations must match the API of the +function being implemented. The resolver should be declared to +be a function taking no arguments and returning a pointer to +a function of the same type as the implementation. For example: + +@smallexample +void *my_memcpy (void *dst, const void *src, size_t len) +@{ + @dots{} + return dst; +@} + +static void * (*resolve_memcpy (void))(void *, const void *, size_t) +@{ + return my_memcpy; // we will just always select this routine +@} +@end smallexample + +@noindent +The exported header file declaring the function the user calls would +contain: + +@smallexample +extern void *memcpy (void *, const void *, size_t); +@end smallexample + +@noindent +allowing the user to call @code{memcpy} as a regular function, unaware of +the actual implementation. Finally, the indirect function needs to be +defined in the same translation unit as the resolver function: + +@smallexample +void *memcpy (void *, const void *, size_t) + __attribute__ ((ifunc ("resolve_memcpy"))); +@end smallexample + +In C++, the @code{ifunc} attribute takes a string that is the mangled name +of the resolver function. A C++ resolver for a non-static member function +of class @code{C} should be declared to return a pointer to a non-member +function taking pointer to @code{C} as the first argument, followed by +the same arguments as of the implementation function. G++ checks +the signatures of the two functions and issues +a @option{-Wattribute-alias} warning for mismatches. To suppress a warning +for the necessary cast from a pointer to the implementation member function +to the type of the corresponding non-member function use +the @option{-Wno-pmf-conversions} option. For example: + +@smallexample +class S +@{ +private: + int debug_impl (int); + int optimized_impl (int); + + typedef int Func (S*, int); + + static Func* resolver (); +public: + + int interface (int); +@}; + +int S::debug_impl (int) @{ /* @r{@dots{}} */ @} +int S::optimized_impl (int) @{ /* @r{@dots{}} */ @} + +S::Func* S::resolver () +@{ + int (S::*pimpl) (int) + = getenv ("DEBUG") ? &S::debug_impl : &S::optimized_impl; + + // Cast triggers -Wno-pmf-conversions. + return reinterpret_cast(pimpl); +@} + +int S::interface (int) __attribute__ ((ifunc ("_ZN1S8resolverEv"))); +@end smallexample + +Indirect functions cannot be weak. Binutils version 2.20.1 or higher +and GNU C Library version 2.11.1 are required to use this feature. + +@item interrupt +@itemx interrupt_handler +Many GCC back ends support attributes to indicate that a function is +an interrupt handler, which tells the compiler to generate function +entry and exit sequences that differ from those from regular +functions. The exact syntax and behavior are target-specific; +refer to the following subsections for details. + +@item leaf +@cindex @code{leaf} function attribute +Calls to external functions with this attribute must return to the +current compilation unit only by return or by exception handling. In +particular, a leaf function is not allowed to invoke callback functions +passed to it from the current compilation unit, directly call functions +exported by the unit, or @code{longjmp} into the unit. Leaf functions +might still call functions from other compilation units and thus they +are not necessarily leaf in the sense that they contain no function +calls at all. + +The attribute is intended for library functions to improve dataflow +analysis. The compiler takes the hint that any data not escaping the +current compilation unit cannot be used or modified by the leaf +function. For example, the @code{sin} function is a leaf function, but +@code{qsort} is not. + +Note that leaf functions might indirectly run a signal handler defined +in the current compilation unit that uses static variables. Similarly, +when lazy symbol resolution is in effect, leaf functions might invoke +indirect functions whose resolver function or implementation function is +defined in the current compilation unit and uses static variables. There +is no standard-compliant way to write such a signal handler, resolver +function, or implementation function, and the best that you can do is to +remove the @code{leaf} attribute or mark all such static variables +@code{volatile}. Lastly, for ELF-based systems that support symbol +interposition, care should be taken that functions defined in the +current compilation unit do not unexpectedly interpose other symbols +based on the defined standards mode and defined feature test macros; +otherwise an inadvertent callback would be added. + +The attribute has no effect on functions defined within the current +compilation unit. This is to allow easy merging of multiple compilation +units into one, for example, by using the link-time optimization. For +this reason the attribute is not allowed on types to annotate indirect +calls. + +@item malloc +@item malloc (@var{deallocator}) +@item malloc (@var{deallocator}, @var{ptr-index}) +@cindex @code{malloc} function attribute +@cindex functions that behave like malloc +Attribute @code{malloc} indicates that a function is @code{malloc}-like, +i.e., that the pointer @var{P} returned by the function cannot alias any +other pointer valid when the function returns, and moreover no +pointers to valid objects occur in any storage addressed by @var{P}. In +addition, the GCC predicts that a function with the attribute returns +non-null in most cases. + +Independently, the form of the attribute with one or two arguments +associates @code{deallocator} as a suitable deallocation function for +pointers returned from the @code{malloc}-like function. @var{ptr-index} +denotes the positional argument to which when the pointer is passed in +calls to @code{deallocator} has the effect of deallocating it. + +Using the attribute with no arguments is designed to improve optimization +by relying on the aliasing property it implies. Functions like @code{malloc} +and @code{calloc} have this property because they return a pointer to +uninitialized or zeroed-out, newly obtained storage. However, functions +like @code{realloc} do not have this property, as they may return pointers +to storage containing pointers to existing objects. Additionally, since +all such functions are assumed to return null only infrequently, callers +can be optimized based on that assumption. + +Associating a function with a @var{deallocator} helps detect calls to +mismatched allocation and deallocation functions and diagnose them under +the control of options such as @option{-Wmismatched-dealloc}. It also +makes it possible to diagnose attempts to deallocate objects that were not +allocated dynamically, by @option{-Wfree-nonheap-object}. To indicate +that an allocation function both satisifies the nonaliasing property and +has a deallocator associated with it, both the plain form of the attribute +and the one with the @var{deallocator} argument must be used. The same +function can be both an allocator and a deallocator. Since inlining one +of the associated functions but not the other could result in apparent +mismatches, this form of attribute @code{malloc} is not accepted on inline +functions. For the same reason, using the attribute prevents both +the allocation and deallocation functions from being expanded inline. + +For example, besides stating that the functions return pointers that do +not alias any others, the following declarations make @code{fclose} +a suitable deallocator for pointers returned from all functions except +@code{popen}, and @code{pclose} as the only suitable deallocator for +pointers returned from @code{popen}. The deallocator functions must +be declared before they can be referenced in the attribute. + +@smallexample +int fclose (FILE*); +int pclose (FILE*); + +__attribute__ ((malloc, malloc (fclose, 1))) + FILE* fdopen (int, const char*); +__attribute__ ((malloc, malloc (fclose, 1))) + FILE* fopen (const char*, const char*); +__attribute__ ((malloc, malloc (fclose, 1))) + FILE* fmemopen(void *, size_t, const char *); +__attribute__ ((malloc, malloc (pclose, 1))) + FILE* popen (const char*, const char*); +__attribute__ ((malloc, malloc (fclose, 1))) + FILE* tmpfile (void); +@end smallexample + +The warnings guarded by @option{-fanalyzer} respect allocation and +deallocation pairs marked with the @code{malloc}. In particular: + +@itemize @bullet + +@item +The analyzer will emit a @option{-Wanalyzer-mismatching-deallocation} +diagnostic if there is an execution path in which the result of an +allocation call is passed to a different deallocator. + +@item +The analyzer will emit a @option{-Wanalyzer-double-free} +diagnostic if there is an execution path in which a value is passed +more than once to a deallocation call. + +@item +The analyzer will consider the possibility that an allocation function +could fail and return NULL. It will emit +@option{-Wanalyzer-possible-null-dereference} and +@option{-Wanalyzer-possible-null-argument} diagnostics if there are +execution paths in which an unchecked result of an allocation call is +dereferenced or passed to a function requiring a non-null argument. +If the allocator always returns non-null, use +@code{__attribute__ ((returns_nonnull))} to suppress these warnings. +For example: +@smallexample +char *xstrdup (const char *) + __attribute__((malloc (free), returns_nonnull)); +@end smallexample + +@item +The analyzer will emit a @option{-Wanalyzer-use-after-free} +diagnostic if there is an execution path in which the memory passed +by pointer to a deallocation call is used after the deallocation. + +@item +The analyzer will emit a @option{-Wanalyzer-malloc-leak} diagnostic if +there is an execution path in which the result of an allocation call +is leaked (without being passed to the deallocation function). + +@item +The analyzer will emit a @option{-Wanalyzer-free-of-non-heap} diagnostic +if a deallocation function is used on a global or on-stack variable. + +@end itemize + +The analyzer assumes that deallocators can gracefully handle the @code{NULL} +pointer. If this is not the case, the deallocator can be marked with +@code{__attribute__((nonnull))} so that @option{-fanalyzer} can emit +a @option{-Wanalyzer-possible-null-argument} diagnostic for code paths +in which the deallocator is called with NULL. + +@item no_icf +@cindex @code{no_icf} function attribute +This function attribute prevents a functions from being merged with another +semantically equivalent function. + +@item no_instrument_function +@cindex @code{no_instrument_function} function attribute +@opindex finstrument-functions +@opindex p +@opindex pg +If any of @option{-finstrument-functions}, @option{-p}, or @option{-pg} are +given, profiling function calls are +generated at entry and exit of most user-compiled functions. +Functions with this attribute are not so instrumented. + +@item no_profile_instrument_function +@cindex @code{no_profile_instrument_function} function attribute +The @code{no_profile_instrument_function} attribute on functions is used +to inform the compiler that it should not process any profile feedback based +optimization code instrumentation. + +@item no_reorder +@cindex @code{no_reorder} function attribute +Do not reorder functions or variables marked @code{no_reorder} +against each other or top level assembler statements the executable. +The actual order in the program will depend on the linker command +line. Static variables marked like this are also not removed. +This has a similar effect +as the @option{-fno-toplevel-reorder} option, but only applies to the +marked symbols. + +@item no_sanitize ("@var{sanitize_option}") +@cindex @code{no_sanitize} function attribute +The @code{no_sanitize} attribute on functions is used +to inform the compiler that it should not do sanitization of any option +mentioned in @var{sanitize_option}. A list of values acceptable by +the @option{-fsanitize} option can be provided. + +@smallexample +void __attribute__ ((no_sanitize ("alignment", "object-size"))) +f () @{ /* @r{Do something.} */; @} +void __attribute__ ((no_sanitize ("alignment,object-size"))) +g () @{ /* @r{Do something.} */; @} +@end smallexample + +@item no_sanitize_address +@itemx no_address_safety_analysis +@cindex @code{no_sanitize_address} function attribute +The @code{no_sanitize_address} attribute on functions is used +to inform the compiler that it should not instrument memory accesses +in the function when compiling with the @option{-fsanitize=address} option. +The @code{no_address_safety_analysis} is a deprecated alias of the +@code{no_sanitize_address} attribute, new code should use +@code{no_sanitize_address}. + +@item no_sanitize_thread +@cindex @code{no_sanitize_thread} function attribute +The @code{no_sanitize_thread} attribute on functions is used +to inform the compiler that it should not instrument memory accesses +in the function when compiling with the @option{-fsanitize=thread} option. + +@item no_sanitize_undefined +@cindex @code{no_sanitize_undefined} function attribute +The @code{no_sanitize_undefined} attribute on functions is used +to inform the compiler that it should not check for undefined behavior +in the function when compiling with the @option{-fsanitize=undefined} option. + +@item no_sanitize_coverage +@cindex @code{no_sanitize_coverage} function attribute +The @code{no_sanitize_coverage} attribute on functions is used +to inform the compiler that it should not do coverage-guided +fuzzing code instrumentation (@option{-fsanitize-coverage}). + +@item no_split_stack +@cindex @code{no_split_stack} function attribute +@opindex fsplit-stack +If @option{-fsplit-stack} is given, functions have a small +prologue which decides whether to split the stack. Functions with the +@code{no_split_stack} attribute do not have that prologue, and thus +may run with only a small amount of stack space available. + +@item no_stack_limit +@cindex @code{no_stack_limit} function attribute +This attribute locally overrides the @option{-fstack-limit-register} +and @option{-fstack-limit-symbol} command-line options; it has the effect +of disabling stack limit checking in the function it applies to. + +@item noclone +@cindex @code{noclone} function attribute +This function attribute prevents a function from being considered for +cloning---a mechanism that produces specialized copies of functions +and which is (currently) performed by interprocedural constant +propagation. + +@item noinline +@cindex @code{noinline} function attribute +This function attribute prevents a function from being considered for +inlining. +@c Don't enumerate the optimizations by name here; we try to be +@c future-compatible with this mechanism. +If the function does not have side effects, there are optimizations +other than inlining that cause function calls to be optimized away, +although the function call is live. To keep such calls from being +optimized away, put +@smallexample +asm (""); +@end smallexample + +@noindent +(@pxref{Extended Asm}) in the called function, to serve as a special +side effect. + +@item noipa +@cindex @code{noipa} function attribute +Disable interprocedural optimizations between the function with this +attribute and its callers, as if the body of the function is not available +when optimizing callers and the callers are unavailable when optimizing +the body. This attribute implies @code{noinline}, @code{noclone} and +@code{no_icf} attributes. However, this attribute is not equivalent +to a combination of other attributes, because its purpose is to suppress +existing and future optimizations employing interprocedural analysis, +including those that do not have an attribute suitable for disabling +them individually. This attribute is supported mainly for the purpose +of testing the compiler. + +@item nonnull +@itemx nonnull (@var{arg-index}, @dots{}) +@cindex @code{nonnull} function attribute +@cindex functions with non-null pointer arguments +The @code{nonnull} attribute may be applied to a function that takes at +least one argument of a pointer type. It indicates that the referenced +arguments must be non-null pointers. For instance, the declaration: + +@smallexample +extern void * +my_memcpy (void *dest, const void *src, size_t len) + __attribute__((nonnull (1, 2))); +@end smallexample + +@noindent +informs the compiler that, in calls to @code{my_memcpy}, arguments +@var{dest} and @var{src} must be non-null. + +The attribute has an effect both on functions calls and function definitions. + +For function calls: +@itemize @bullet +@item If the compiler determines that a null pointer is +passed in an argument slot marked as non-null, and the +@option{-Wnonnull} option is enabled, a warning is issued. +@xref{Warning Options}. +@item The @option{-fisolate-erroneous-paths-attribute} option can be +specified to have GCC transform calls with null arguments to non-null +functions into traps. @xref{Optimize Options}. +@item The compiler may also perform optimizations based on the +knowledge that certain function arguments cannot be null. These +optimizations can be disabled by the +@option{-fno-delete-null-pointer-checks} option. @xref{Optimize Options}. +@end itemize + +For function definitions: +@itemize @bullet +@item If the compiler determines that a function parameter that is +marked with nonnull is compared with null, and +@option{-Wnonnull-compare} option is enabled, a warning is issued. +@xref{Warning Options}. +@item The compiler may also perform optimizations based on the +knowledge that @code{nonnul} parameters cannot be null. This can +currently not be disabled other than by removing the nonnull +attribute. +@end itemize + +If no @var{arg-index} is given to the @code{nonnull} attribute, +all pointer arguments are marked as non-null. To illustrate, the +following declaration is equivalent to the previous example: + +@smallexample +extern void * +my_memcpy (void *dest, const void *src, size_t len) + __attribute__((nonnull)); +@end smallexample + +@item noplt +@cindex @code{noplt} function attribute +The @code{noplt} attribute is the counterpart to option @option{-fno-plt}. +Calls to functions marked with this attribute in position-independent code +do not use the PLT. + +@smallexample +@group +/* Externally defined function foo. */ +int foo () __attribute__ ((noplt)); + +int +main (/* @r{@dots{}} */) +@{ + /* @r{@dots{}} */ + foo (); + /* @r{@dots{}} */ +@} +@end group +@end smallexample + +The @code{noplt} attribute on function @code{foo} +tells the compiler to assume that +the function @code{foo} is externally defined and that the call to +@code{foo} must avoid the PLT +in position-independent code. + +In position-dependent code, a few targets also convert calls to +functions that are marked to not use the PLT to use the GOT instead. + +@item noreturn +@cindex @code{noreturn} function attribute +@cindex functions that never return +A few standard library functions, such as @code{abort} and @code{exit}, +cannot return. GCC knows this automatically. Some programs define +their own functions that never return. You can declare them +@code{noreturn} to tell the compiler this fact. For example, + +@smallexample +@group +void fatal () __attribute__ ((noreturn)); + +void +fatal (/* @r{@dots{}} */) +@{ + /* @r{@dots{}} */ /* @r{Print error message.} */ /* @r{@dots{}} */ + exit (1); +@} +@end group +@end smallexample + +The @code{noreturn} keyword tells the compiler to assume that +@code{fatal} cannot return. It can then optimize without regard to what +would happen if @code{fatal} ever did return. This makes slightly +better code. More importantly, it helps avoid spurious warnings of +uninitialized variables. + +The @code{noreturn} keyword does not affect the exceptional path when that +applies: a @code{noreturn}-marked function may still return to the caller +by throwing an exception or calling @code{longjmp}. + +In order to preserve backtraces, GCC will never turn calls to +@code{noreturn} functions into tail calls. + +Do not assume that registers saved by the calling function are +restored before calling the @code{noreturn} function. + +It does not make sense for a @code{noreturn} function to have a return +type other than @code{void}. + +@item nothrow +@cindex @code{nothrow} function attribute +The @code{nothrow} attribute is used to inform the compiler that a +function cannot throw an exception. For example, most functions in +the standard C library can be guaranteed not to throw an exception +with the notable exceptions of @code{qsort} and @code{bsearch} that +take function pointer arguments. + +@item optimize (@var{level}, @dots{}) +@item optimize (@var{string}, @dots{}) +@cindex @code{optimize} function attribute +The @code{optimize} attribute is used to specify that a function is to +be compiled with different optimization options than specified on the +command line. The optimize attribute arguments of a function behave +behave as if appended to the command-line. + +Valid arguments are constant non-negative integers and +strings. Each numeric argument specifies an optimization @var{level}. +Each @var{string} argument consists of one or more comma-separated +substrings. Each substring that begins with the letter @code{O} refers +to an optimization option such as @option{-O0} or @option{-Os}. Other +substrings are taken as suffixes to the @code{-f} prefix jointly +forming the name of an optimization option. @xref{Optimize Options}. + +@samp{#pragma GCC optimize} can be used to set optimization options +for more than one function. @xref{Function Specific Option Pragmas}, +for details about the pragma. + +Providing multiple strings as arguments separated by commas to specify +multiple options is equivalent to separating the option suffixes with +a comma (@samp{,}) within a single string. Spaces are not permitted +within the strings. + +Not every optimization option that starts with the @var{-f} prefix +specified by the attribute necessarily has an effect on the function. +The @code{optimize} attribute should be used for debugging purposes only. +It is not suitable in production code. + +@item patchable_function_entry +@cindex @code{patchable_function_entry} function attribute +@cindex extra NOP instructions at the function entry point +In case the target's text segment can be made writable at run time by +any means, padding the function entry with a number of NOPs can be +used to provide a universal tool for instrumentation. + +The @code{patchable_function_entry} function attribute can be used to +change the number of NOPs to any desired value. The two-value syntax +is the same as for the command-line switch +@option{-fpatchable-function-entry=N,M}, generating @var{N} NOPs, with +the function entry point before the @var{M}th NOP instruction. +@var{M} defaults to 0 if omitted e.g.@: function entry point is before +the first NOP. + +If patchable function entries are enabled globally using the command-line +option @option{-fpatchable-function-entry=N,M}, then you must disable +instrumentation on all functions that are part of the instrumentation +framework with the attribute @code{patchable_function_entry (0)} +to prevent recursion. + +@item pure +@cindex @code{pure} function attribute +@cindex functions that have no side effects + +Calls to functions that have no observable effects on the state of +the program other than to return a value may lend themselves to optimizations +such as common subexpression elimination. Declaring such functions with +the @code{pure} attribute allows GCC to avoid emitting some calls in repeated +invocations of the function with the same argument values. + +The @code{pure} attribute prohibits a function from modifying the state +of the program that is observable by means other than inspecting +the function's return value. However, functions declared with the @code{pure} +attribute can safely read any non-volatile objects, and modify the value of +objects in a way that does not affect their return value or the observable +state of the program. + +For example, + +@smallexample +int hash (char *) __attribute__ ((pure)); +@end smallexample + +@noindent +tells GCC that subsequent calls to the function @code{hash} with the same +string can be replaced by the result of the first call provided the state +of the program observable by @code{hash}, including the contents of the array +itself, does not change in between. Even though @code{hash} takes a non-const +pointer argument it must not modify the array it points to, or any other object +whose value the rest of the program may depend on. However, the caller may +safely change the contents of the array between successive calls to +the function (doing so disables the optimization). The restriction also +applies to member objects referenced by the @code{this} pointer in C++ +non-static member functions. + +Some common examples of pure functions are @code{strlen} or @code{memcmp}. +Interesting non-pure functions are functions with infinite loops or those +depending on volatile memory or other system resource, that may change between +consecutive calls (such as the standard C @code{feof} function in +a multithreading environment). + +The @code{pure} attribute imposes similar but looser restrictions on +a function's definition than the @code{const} attribute: @code{pure} +allows the function to read any non-volatile memory, even if it changes +in between successive invocations of the function. Declaring the same +function with both the @code{pure} and the @code{const} attribute is +diagnosed. Because a pure function cannot have any observable side +effects it does not make sense for such a function to return @code{void}. +Declaring such a function is diagnosed. + +@item returns_nonnull +@cindex @code{returns_nonnull} function attribute +The @code{returns_nonnull} attribute specifies that the function +return value should be a non-null pointer. For instance, the declaration: + +@smallexample +extern void * +mymalloc (size_t len) __attribute__((returns_nonnull)); +@end smallexample + +@noindent +lets the compiler optimize callers based on the knowledge +that the return value will never be null. + +@item returns_twice +@cindex @code{returns_twice} function attribute +@cindex functions that return more than once +The @code{returns_twice} attribute tells the compiler that a function may +return more than one time. The compiler ensures that all registers +are dead before calling such a function and emits a warning about +the variables that may be clobbered after the second return from the +function. Examples of such functions are @code{setjmp} and @code{vfork}. +The @code{longjmp}-like counterpart of such function, if any, might need +to be marked with the @code{noreturn} attribute. + +@item section ("@var{section-name}") +@cindex @code{section} function attribute +@cindex functions in arbitrary sections +Normally, the compiler places the code it generates in the @code{text} section. +Sometimes, however, you need additional sections, or you need certain +particular functions to appear in special sections. The @code{section} +attribute specifies that a function lives in a particular section. +For example, the declaration: + +@smallexample +extern void foobar (void) __attribute__ ((section ("bar"))); +@end smallexample + +@noindent +puts the function @code{foobar} in the @code{bar} section. + +Some file formats do not support arbitrary sections so the @code{section} +attribute is not available on all platforms. +If you need to map the entire contents of a module to a particular +section, consider using the facilities of the linker instead. + +@item sentinel +@itemx sentinel (@var{position}) +@cindex @code{sentinel} function attribute +This function attribute indicates that an argument in a call to the function +is expected to be an explicit @code{NULL}. The attribute is only valid on +variadic functions. By default, the sentinel is expected to be the last +argument of the function call. If the optional @var{position} argument +is specified to the attribute, the sentinel must be located at +@var{position} counting backwards from the end of the argument list. + +@smallexample +__attribute__ ((sentinel)) +is equivalent to +__attribute__ ((sentinel(0))) +@end smallexample + +The attribute is automatically set with a position of 0 for the built-in +functions @code{execl} and @code{execlp}. The built-in function +@code{execle} has the attribute set with a position of 1. + +A valid @code{NULL} in this context is defined as zero with any object +pointer type. If your system defines the @code{NULL} macro with +an integer type then you need to add an explicit cast. During +installation GCC replaces the system @code{} header with +a copy that redefines NULL appropriately. + +The warnings for missing or incorrect sentinels are enabled with +@option{-Wformat}. + +@item simd +@itemx simd("@var{mask}") +@cindex @code{simd} function attribute +This attribute enables creation of one or more function versions that +can process multiple arguments using SIMD instructions from a +single invocation. Specifying this attribute allows compiler to +assume that such versions are available at link time (provided +in the same or another translation unit). Generated versions are +target-dependent and described in the corresponding Vector ABI document. For +x86_64 target this document can be found +@w{@uref{https://sourceware.org/glibc/wiki/libmvec?action=AttachFile&do=view&target=VectorABI.txt,here}}. + +The optional argument @var{mask} may have the value +@code{notinbranch} or @code{inbranch}, +and instructs the compiler to generate non-masked or masked +clones correspondingly. By default, all clones are generated. + +If the attribute is specified and @code{#pragma omp declare simd} is +present on a declaration and the @option{-fopenmp} or @option{-fopenmp-simd} +switch is specified, then the attribute is ignored. + +@item stack_protect +@cindex @code{stack_protect} function attribute +This attribute adds stack protection code to the function if +flags @option{-fstack-protector}, @option{-fstack-protector-strong} +or @option{-fstack-protector-explicit} are set. + +@item no_stack_protector +@cindex @code{no_stack_protector} function attribute +This attribute prevents stack protection code for the function. + +@item target (@var{string}, @dots{}) +@cindex @code{target} function attribute +Multiple target back ends implement the @code{target} attribute +to specify that a function is to +be compiled with different target options than specified on the +command line. The original target command-line options are ignored. +One or more strings can be provided as arguments. +Each string consists of one or more comma-separated suffixes to +the @code{-m} prefix jointly forming the name of a machine-dependent +option. @xref{Submodel Options,,Machine-Dependent Options}. + +The @code{target} attribute can be used for instance to have a function +compiled with a different ISA (instruction set architecture) than the +default. @samp{#pragma GCC target} can be used to specify target-specific +options for more than one function. @xref{Function Specific Option Pragmas}, +for details about the pragma. + +For instance, on an x86, you could declare one function with the +@code{target("sse4.1,arch=core2")} attribute and another with +@code{target("sse4a,arch=amdfam10")}. This is equivalent to +compiling the first function with @option{-msse4.1} and +@option{-march=core2} options, and the second function with +@option{-msse4a} and @option{-march=amdfam10} options. It is up to you +to make sure that a function is only invoked on a machine that +supports the particular ISA it is compiled for (for example by using +@code{cpuid} on x86 to determine what feature bits and architecture +family are used). + +@smallexample +int core2_func (void) __attribute__ ((__target__ ("arch=core2"))); +int sse3_func (void) __attribute__ ((__target__ ("sse3"))); +@end smallexample + +Providing multiple strings as arguments separated by commas to specify +multiple options is equivalent to separating the option suffixes with +a comma (@samp{,}) within a single string. Spaces are not permitted +within the strings. + +The options supported are specific to each target; refer to @ref{x86 +Function Attributes}, @ref{PowerPC Function Attributes}, +@ref{ARM Function Attributes}, @ref{AArch64 Function Attributes}, +@ref{Nios II Function Attributes}, and @ref{S/390 Function Attributes} +for details. + +@item symver ("@var{name2}@@@var{nodename}") +@cindex @code{symver} function attribute +On ELF targets this attribute creates a symbol version. The @var{name2} part +of the parameter is the actual name of the symbol by which it will be +externally referenced. The @code{nodename} portion should be the name of a +node specified in the version script supplied to the linker when building a +shared library. Versioned symbol must be defined and must be exported with +default visibility. + +@smallexample +__attribute__ ((__symver__ ("foo@@VERS_1"))) int +foo_v1 (void) +@{ +@} +@end smallexample + +Will produce a @code{.symver foo_v1, foo@@VERS_1} directive in the assembler +output. + +One can also define multiple version for a given symbol +(starting from binutils 2.35). + +@smallexample +__attribute__ ((__symver__ ("foo@@VERS_2"), __symver__ ("foo@@VERS_3"))) +int symver_foo_v1 (void) +@{ +@} +@end smallexample + +This example creates a symbol name @code{symver_foo_v1} +which will be version @code{VERS_2} and @code{VERS_3} of @code{foo}. + +If you have an older release of binutils, then symbol alias needs to +be used: + +@smallexample +__attribute__ ((__symver__ ("foo@@VERS_2"))) +int foo_v1 (void) +@{ + return 0; +@} + +__attribute__ ((__symver__ ("foo@@VERS_3"))) +__attribute__ ((alias ("foo_v1"))) +int symver_foo_v1 (void); +@end smallexample + +Finally if the parameter is @code{"@var{name2}@@@@@var{nodename}"} then in +addition to creating a symbol version (as if +@code{"@var{name2}@@@var{nodename}"} was used) the version will be also used +to resolve @var{name2} by the linker. + +@item tainted_args +@cindex @code{tainted_args} function attribute +The @code{tainted_args} attribute is used to specify that a function is called +in a way that requires sanitization of its arguments, such as a system +call in an operating system kernel. Such a function can be considered part +of the ``attack surface'' of the program. The attribute can be used both +on function declarations, and on field declarations containing function +pointers. In the latter case, any function used as an initializer of +such a callback field will be treated as being called with tainted +arguments. + +The analyzer will pay particular attention to such functions when both +@option{-fanalyzer} and @option{-fanalyzer-checker=taint} are supplied, +potentially issuing warnings guarded by +@option{-Wanalyzer-tainted-allocation-size}, +@option{-Wanalyzer-tainted-array-index}, +@option{-Wanalyzer-tainted-divisor}, +@option{-Wanalyzer-tainted-offset}, +and @option{-Wanalyzer-tainted-size}. + +@item target_clones (@var{options}) +@cindex @code{target_clones} function attribute +The @code{target_clones} attribute is used to specify that a function +be cloned into multiple versions compiled with different target options +than specified on the command line. The supported options and restrictions +are the same as for @code{target} attribute. + +For instance, on an x86, you could compile a function with +@code{target_clones("sse4.1,avx")}. GCC creates two function clones, +one compiled with @option{-msse4.1} and another with @option{-mavx}. + +On a PowerPC, you can compile a function with +@code{target_clones("cpu=power9,default")}. GCC will create two +function clones, one compiled with @option{-mcpu=power9} and another +with the default options. GCC must be configured to use GLIBC 2.23 or +newer in order to use the @code{target_clones} attribute. + +It also creates a resolver function (see +the @code{ifunc} attribute above) that dynamically selects a clone +suitable for current architecture. The resolver is created only if there +is a usage of a function with @code{target_clones} attribute. + +Note that any subsequent call of a function without @code{target_clone} +from a @code{target_clone} caller will not lead to copying +(target clone) of the called function. +If you want to enforce such behaviour, +we recommend declaring the calling function with the @code{flatten} attribute? + +@item unused +@cindex @code{unused} function attribute +This attribute, attached to a function, means that the function is meant +to be possibly unused. GCC does not produce a warning for this +function. + +@item used +@cindex @code{used} function attribute +This attribute, attached to a function, means that code must be emitted +for the function even if it appears that the function is not referenced. +This is useful, for example, when the function is referenced only in +inline assembly. + +When applied to a member function of a C++ class template, the +attribute also means that the function is instantiated if the +class itself is instantiated. + +@item retain +@cindex @code{retain} function attribute +For ELF targets that support the GNU or FreeBSD OSABIs, this attribute +will save the function from linker garbage collection. To support +this behavior, functions that have not been placed in specific sections +(e.g. by the @code{section} attribute, or the @code{-ffunction-sections} +option), will be placed in new, unique sections. + +This additional functionality requires Binutils version 2.36 or later. + +@item visibility ("@var{visibility_type}") +@cindex @code{visibility} function attribute +This attribute affects the linkage of the declaration to which it is attached. +It can be applied to variables (@pxref{Common Variable Attributes}) and types +(@pxref{Common Type Attributes}) as well as functions. + +There are four supported @var{visibility_type} values: default, +hidden, protected or internal visibility. + +@smallexample +void __attribute__ ((visibility ("protected"))) +f () @{ /* @r{Do something.} */; @} +int i __attribute__ ((visibility ("hidden"))); +@end smallexample + +The possible values of @var{visibility_type} correspond to the +visibility settings in the ELF gABI. + +@table @code +@c keep this list of visibilities in alphabetical order. + +@item default +Default visibility is the normal case for the object file format. +This value is available for the visibility attribute to override other +options that may change the assumed visibility of entities. + +On ELF, default visibility means that the declaration is visible to other +modules and, in shared libraries, means that the declared entity may be +overridden. + +On Darwin, default visibility means that the declaration is visible to +other modules. + +Default visibility corresponds to ``external linkage'' in the language. + +@item hidden +Hidden visibility indicates that the entity declared has a new +form of linkage, which we call ``hidden linkage''. Two +declarations of an object with hidden linkage refer to the same object +if they are in the same shared object. + +@item internal +Internal visibility is like hidden visibility, but with additional +processor specific semantics. Unless otherwise specified by the +psABI, GCC defines internal visibility to mean that a function is +@emph{never} called from another module. Compare this with hidden +functions which, while they cannot be referenced directly by other +modules, can be referenced indirectly via function pointers. By +indicating that a function cannot be called from outside the module, +GCC may for instance omit the load of a PIC register since it is known +that the calling function loaded the correct value. + +@item protected +Protected visibility is like default visibility except that it +indicates that references within the defining module bind to the +definition in that module. That is, the declared entity cannot be +overridden by another module. + +@end table + +All visibilities are supported on many, but not all, ELF targets +(supported when the assembler supports the @samp{.visibility} +pseudo-op). Default visibility is supported everywhere. Hidden +visibility is supported on Darwin targets. + +The visibility attribute should be applied only to declarations that +would otherwise have external linkage. The attribute should be applied +consistently, so that the same entity should not be declared with +different settings of the attribute. + +In C++, the visibility attribute applies to types as well as functions +and objects, because in C++ types have linkage. A class must not have +greater visibility than its non-static data member types and bases, +and class members default to the visibility of their class. Also, a +declaration without explicit visibility is limited to the visibility +of its type. + +In C++, you can mark member functions and static member variables of a +class with the visibility attribute. This is useful if you know a +particular method or static member variable should only be used from +one shared object; then you can mark it hidden while the rest of the +class has default visibility. Care must be taken to avoid breaking +the One Definition Rule; for example, it is usually not useful to mark +an inline method as hidden without marking the whole class as hidden. + +A C++ namespace declaration can also have the visibility attribute. + +@smallexample +namespace nspace1 __attribute__ ((visibility ("protected"))) +@{ /* @r{Do something.} */; @} +@end smallexample + +This attribute applies only to the particular namespace body, not to +other definitions of the same namespace; it is equivalent to using +@samp{#pragma GCC visibility} before and after the namespace +definition (@pxref{Visibility Pragmas}). + +In C++, if a template argument has limited visibility, this +restriction is implicitly propagated to the template instantiation. +Otherwise, template instantiations and specializations default to the +visibility of their template. + +If both the template and enclosing class have explicit visibility, the +visibility from the template is used. + +@item warn_unused_result +@cindex @code{warn_unused_result} function attribute +The @code{warn_unused_result} attribute causes a warning to be emitted +if a caller of the function with this attribute does not use its +return value. This is useful for functions where not checking +the result is either a security problem or always a bug, such as +@code{realloc}. + +@smallexample +int fn () __attribute__ ((warn_unused_result)); +int foo () +@{ + if (fn () < 0) return -1; + fn (); + return 0; +@} +@end smallexample + +@noindent +results in warning on line 5. + +@item weak +@cindex @code{weak} function attribute +The @code{weak} attribute causes a declaration of an external symbol +to be emitted as a weak symbol rather than a global. This is primarily +useful in defining library functions that can be overridden in user code, +though it can also be used with non-function declarations. The overriding +symbol must have the same type as the weak symbol. In addition, if it +designates a variable it must also have the same size and alignment as +the weak symbol. Weak symbols are supported for ELF targets, and also +for a.out targets when using the GNU assembler and linker. + +@item weakref +@itemx weakref ("@var{target}") +@cindex @code{weakref} function attribute +The @code{weakref} attribute marks a declaration as a weak reference. +Without arguments, it should be accompanied by an @code{alias} attribute +naming the target symbol. Alternatively, @var{target} may be given as +an argument to @code{weakref} itself, naming the target definition of +the alias. The @var{target} must have the same type as the declaration. +In addition, if it designates a variable it must also have the same size +and alignment as the declaration. In either form of the declaration +@code{weakref} implicitly marks the declared symbol as @code{weak}. Without +a @var{target} given as an argument to @code{weakref} or to @code{alias}, +@code{weakref} is equivalent to @code{weak} (in that case the declaration +may be @code{extern}). + +@smallexample +/* Given the declaration: */ +extern int y (void); + +/* the following... */ +static int x (void) __attribute__ ((weakref ("y"))); + +/* is equivalent to... */ +static int x (void) __attribute__ ((weakref, alias ("y"))); + +/* or, alternatively, to... */ +static int x (void) __attribute__ ((weakref)); +static int x (void) __attribute__ ((alias ("y"))); +@end smallexample + +A weak reference is an alias that does not by itself require a +definition to be given for the target symbol. If the target symbol is +only referenced through weak references, then it becomes a @code{weak} +undefined symbol. If it is directly referenced, however, then such +strong references prevail, and a definition is required for the +symbol, not necessarily in the same translation unit. + +The effect is equivalent to moving all references to the alias to a +separate translation unit, renaming the alias to the aliased symbol, +declaring it as weak, compiling the two separate translation units and +performing a link with relocatable output (i.e.@: @code{ld -r}) on them. + +A declaration to which @code{weakref} is attached and that is associated +with a named @code{target} must be @code{static}. + +@item zero_call_used_regs ("@var{choice}") +@cindex @code{zero_call_used_regs} function attribute + +The @code{zero_call_used_regs} attribute causes the compiler to zero +a subset of all call-used registers@footnote{A ``call-used'' register +is a register whose contents can be changed by a function call; +therefore, a caller cannot assume that the register has the same contents +on return from the function as it had before calling the function. Such +registers are also called ``call-clobbered'', ``caller-saved'', or +``volatile''.} at function return. +This is used to increase program security by either mitigating +Return-Oriented Programming (ROP) attacks or preventing information leakage +through registers. + +In order to satisfy users with different security needs and control the +run-time overhead at the same time, the @var{choice} parameter provides a +flexible way to choose the subset of the call-used registers to be zeroed. +The three basic values of @var{choice} are: + +@itemize @bullet +@item +@samp{skip} doesn't zero any call-used registers. + +@item +@samp{used} only zeros call-used registers that are used in the function. +A ``used'' register is one whose content has been set or referenced in +the function. + +@item +@samp{all} zeros all call-used registers. +@end itemize + +In addition to these three basic choices, it is possible to modify +@samp{used} or @samp{all} as follows: + +@itemize @bullet +@item +Adding @samp{-gpr} restricts the zeroing to general-purpose registers. + +@item +Adding @samp{-arg} restricts the zeroing to registers that can sometimes +be used to pass function arguments. This includes all argument registers +defined by the platform's calling conversion, regardless of whether the +function uses those registers for function arguments or not. +@end itemize + +The modifiers can be used individually or together. If they are used +together, they must appear in the order above. + +The full list of @var{choice}s is therefore: + +@table @code +@item skip +doesn't zero any call-used register. + +@item used +only zeros call-used registers that are used in the function. + +@item used-gpr +only zeros call-used general purpose registers that are used in the function. + +@item used-arg +only zeros call-used registers that are used in the function and pass arguments. + +@item used-gpr-arg +only zeros call-used general purpose registers that are used in the function +and pass arguments. + +@item all +zeros all call-used registers. + +@item all-gpr +zeros all call-used general purpose registers. + +@item all-arg +zeros all call-used registers that pass arguments. + +@item all-gpr-arg +zeros all call-used general purpose registers that pass +arguments. +@end table + +Of this list, @samp{used-arg}, @samp{used-gpr-arg}, @samp{all-arg}, +and @samp{all-gpr-arg} are mainly used for ROP mitigation. + +The default for the attribute is controlled by @option{-fzero-call-used-regs}. +@end table + +@c This is the end of the target-independent attribute table + +@node AArch64 Function Attributes +@subsection AArch64 Function Attributes + +The following target-specific function attributes are available for the +AArch64 target. For the most part, these options mirror the behavior of +similar command-line options (@pxref{AArch64 Options}), but on a +per-function basis. + +@table @code +@item general-regs-only +@cindex @code{general-regs-only} function attribute, AArch64 +Indicates that no floating-point or Advanced SIMD registers should be +used when generating code for this function. If the function explicitly +uses floating-point code, then the compiler gives an error. This is +the same behavior as that of the command-line option +@option{-mgeneral-regs-only}. + +@item fix-cortex-a53-835769 +@cindex @code{fix-cortex-a53-835769} function attribute, AArch64 +Indicates that the workaround for the Cortex-A53 erratum 835769 should be +applied to this function. To explicitly disable the workaround for this +function specify the negated form: @code{no-fix-cortex-a53-835769}. +This corresponds to the behavior of the command line options +@option{-mfix-cortex-a53-835769} and @option{-mno-fix-cortex-a53-835769}. + +@item cmodel= +@cindex @code{cmodel=} function attribute, AArch64 +Indicates that code should be generated for a particular code model for +this function. The behavior and permissible arguments are the same as +for the command line option @option{-mcmodel=}. + +@item strict-align +@itemx no-strict-align +@cindex @code{strict-align} function attribute, AArch64 +@code{strict-align} indicates that the compiler should not assume that unaligned +memory references are handled by the system. To allow the compiler to assume +that aligned memory references are handled by the system, the inverse attribute +@code{no-strict-align} can be specified. The behavior is same as for the +command-line option @option{-mstrict-align} and @option{-mno-strict-align}. + +@item omit-leaf-frame-pointer +@cindex @code{omit-leaf-frame-pointer} function attribute, AArch64 +Indicates that the frame pointer should be omitted for a leaf function call. +To keep the frame pointer, the inverse attribute +@code{no-omit-leaf-frame-pointer} can be specified. These attributes have +the same behavior as the command-line options @option{-momit-leaf-frame-pointer} +and @option{-mno-omit-leaf-frame-pointer}. + +@item tls-dialect= +@cindex @code{tls-dialect=} function attribute, AArch64 +Specifies the TLS dialect to use for this function. The behavior and +permissible arguments are the same as for the command-line option +@option{-mtls-dialect=}. + +@item arch= +@cindex @code{arch=} function attribute, AArch64 +Specifies the architecture version and architectural extensions to use +for this function. The behavior and permissible arguments are the same as +for the @option{-march=} command-line option. + +@item tune= +@cindex @code{tune=} function attribute, AArch64 +Specifies the core for which to tune the performance of this function. +The behavior and permissible arguments are the same as for the @option{-mtune=} +command-line option. + +@item cpu= +@cindex @code{cpu=} function attribute, AArch64 +Specifies the core for which to tune the performance of this function and also +whose architectural features to use. The behavior and valid arguments are the +same as for the @option{-mcpu=} command-line option. + +@item sign-return-address +@cindex @code{sign-return-address} function attribute, AArch64 +Select the function scope on which return address signing will be applied. The +behavior and permissible arguments are the same as for the command-line option +@option{-msign-return-address=}. The default value is @code{none}. This +attribute is deprecated. The @code{branch-protection} attribute should +be used instead. + +@item branch-protection +@cindex @code{branch-protection} function attribute, AArch64 +Select the function scope on which branch protection will be applied. The +behavior and permissible arguments are the same as for the command-line option +@option{-mbranch-protection=}. The default value is @code{none}. + +@item outline-atomics +@cindex @code{outline-atomics} function attribute, AArch64 +Enable or disable calls to out-of-line helpers to implement atomic operations. +This corresponds to the behavior of the command line options +@option{-moutline-atomics} and @option{-mno-outline-atomics}. + +@end table + +The above target attributes can be specified as follows: + +@smallexample +__attribute__((target("@var{attr-string}"))) +int +f (int a) +@{ + return a + 5; +@} +@end smallexample + +where @code{@var{attr-string}} is one of the attribute strings specified above. + +Additionally, the architectural extension string may be specified on its +own. This can be used to turn on and off particular architectural extensions +without having to specify a particular architecture version or core. Example: + +@smallexample +__attribute__((target("+crc+nocrypto"))) +int +foo (int a) +@{ + return a + 5; +@} +@end smallexample + +In this example @code{target("+crc+nocrypto")} enables the @code{crc} +extension and disables the @code{crypto} extension for the function @code{foo} +without modifying an existing @option{-march=} or @option{-mcpu} option. + +Multiple target function attributes can be specified by separating them with +a comma. For example: +@smallexample +__attribute__((target("arch=armv8-a+crc+crypto,tune=cortex-a53"))) +int +foo (int a) +@{ + return a + 5; +@} +@end smallexample + +is valid and compiles function @code{foo} for ARMv8-A with @code{crc} +and @code{crypto} extensions and tunes it for @code{cortex-a53}. + +@subsubsection Inlining rules +Specifying target attributes on individual functions or performing link-time +optimization across translation units compiled with different target options +can affect function inlining rules: + +In particular, a caller function can inline a callee function only if the +architectural features available to the callee are a subset of the features +available to the caller. +For example: A function @code{foo} compiled with @option{-march=armv8-a+crc}, +or tagged with the equivalent @code{arch=armv8-a+crc} attribute, +can inline a function @code{bar} compiled with @option{-march=armv8-a+nocrc} +because the all the architectural features that function @code{bar} requires +are available to function @code{foo}. Conversely, function @code{bar} cannot +inline function @code{foo}. + +Additionally inlining a function compiled with @option{-mstrict-align} into a +function compiled without @code{-mstrict-align} is not allowed. +However, inlining a function compiled without @option{-mstrict-align} into a +function compiled with @option{-mstrict-align} is allowed. + +Note that CPU tuning options and attributes such as the @option{-mcpu=}, +@option{-mtune=} do not inhibit inlining unless the CPU specified by the +@option{-mcpu=} option or the @code{cpu=} attribute conflicts with the +architectural feature rules specified above. + +@node AMD GCN Function Attributes +@subsection AMD GCN Function Attributes + +These function attributes are supported by the AMD GCN back end: + +@table @code +@item amdgpu_hsa_kernel +@cindex @code{amdgpu_hsa_kernel} function attribute, AMD GCN +This attribute indicates that the corresponding function should be compiled as +a kernel function, that is an entry point that can be invoked from the host +via the HSA runtime library. By default functions are only callable only from +other GCN functions. + +This attribute is implicitly applied to any function named @code{main}, using +default parameters. + +Kernel functions may return an integer value, which will be written to a +conventional place within the HSA "kernargs" region. + +The attribute parameters configure what values are passed into the kernel +function by the GPU drivers, via the initial register state. Some values are +used by the compiler, and therefore forced on. Enabling other options may +break assumptions in the compiler and/or run-time libraries. + +@table @code +@item private_segment_buffer +Set @code{enable_sgpr_private_segment_buffer} flag. Always on (required to +locate the stack). + +@item dispatch_ptr +Set @code{enable_sgpr_dispatch_ptr} flag. Always on (required to locate the +launch dimensions). + +@item queue_ptr +Set @code{enable_sgpr_queue_ptr} flag. Always on (required to convert address +spaces). + +@item kernarg_segment_ptr +Set @code{enable_sgpr_kernarg_segment_ptr} flag. Always on (required to +locate the kernel arguments, "kernargs"). + +@item dispatch_id +Set @code{enable_sgpr_dispatch_id} flag. + +@item flat_scratch_init +Set @code{enable_sgpr_flat_scratch_init} flag. + +@item private_segment_size +Set @code{enable_sgpr_private_segment_size} flag. + +@item grid_workgroup_count_X +Set @code{enable_sgpr_grid_workgroup_count_x} flag. Always on (required to +use OpenACC/OpenMP). + +@item grid_workgroup_count_Y +Set @code{enable_sgpr_grid_workgroup_count_y} flag. + +@item grid_workgroup_count_Z +Set @code{enable_sgpr_grid_workgroup_count_z} flag. + +@item workgroup_id_X +Set @code{enable_sgpr_workgroup_id_x} flag. + +@item workgroup_id_Y +Set @code{enable_sgpr_workgroup_id_y} flag. + +@item workgroup_id_Z +Set @code{enable_sgpr_workgroup_id_z} flag. + +@item workgroup_info +Set @code{enable_sgpr_workgroup_info} flag. + +@item private_segment_wave_offset +Set @code{enable_sgpr_private_segment_wave_byte_offset} flag. Always on +(required to locate the stack). + +@item work_item_id_X +Set @code{enable_vgpr_workitem_id} parameter. Always on (can't be disabled). + +@item work_item_id_Y +Set @code{enable_vgpr_workitem_id} parameter. Always on (required to enable +vectorization.) + +@item work_item_id_Z +Set @code{enable_vgpr_workitem_id} parameter. Always on (required to use +OpenACC/OpenMP). + +@end table +@end table + +@node ARC Function Attributes +@subsection ARC Function Attributes + +These function attributes are supported by the ARC back end: + +@table @code +@item interrupt +@cindex @code{interrupt} function attribute, ARC +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. + +On the ARC, you must specify the kind of interrupt to be handled +in a parameter to the interrupt attribute like this: + +@smallexample +void f () __attribute__ ((interrupt ("ilink1"))); +@end smallexample + +Permissible values for this parameter are: @w{@code{ilink1}} and +@w{@code{ilink2}} for ARCv1 architecture, and @w{@code{ilink}} and +@w{@code{firq}} for ARCv2 architecture. + +@item long_call +@itemx medium_call +@itemx short_call +@cindex @code{long_call} function attribute, ARC +@cindex @code{medium_call} function attribute, ARC +@cindex @code{short_call} function attribute, ARC +@cindex indirect calls, ARC +These attributes specify how a particular function is called. +These attributes override the +@option{-mlong-calls} and @option{-mmedium-calls} (@pxref{ARC Options}) +command-line switches and @code{#pragma long_calls} settings. + +For ARC, a function marked with the @code{long_call} attribute is +always called using register-indirect jump-and-link instructions, +thereby enabling the called function to be placed anywhere within the +32-bit address space. A function marked with the @code{medium_call} +attribute will always be close enough to be called with an unconditional +branch-and-link instruction, which has a 25-bit offset from +the call site. A function marked with the @code{short_call} +attribute will always be close enough to be called with a conditional +branch-and-link instruction, which has a 21-bit offset from +the call site. + +@item jli_always +@cindex @code{jli_always} function attribute, ARC +Forces a particular function to be called using @code{jli} +instruction. The @code{jli} instruction makes use of a table stored +into @code{.jlitab} section, which holds the location of the functions +which are addressed using this instruction. + +@item jli_fixed +@cindex @code{jli_fixed} function attribute, ARC +Identical like the above one, but the location of the function in the +@code{jli} table is known and given as an attribute parameter. + +@item secure_call +@cindex @code{secure_call} function attribute, ARC +This attribute allows one to mark secure-code functions that are +callable from normal mode. The location of the secure call function +into the @code{sjli} table needs to be passed as argument. + +@item naked +@cindex @code{naked} function attribute, ARC +This attribute allows the compiler to construct the requisite function +declaration, while allowing the body of the function to be assembly +code. The specified function will not have prologue/epilogue +sequences generated by the compiler. Only basic @code{asm} statements +can safely be included in naked functions (@pxref{Basic Asm}). While +using extended @code{asm} or a mixture of basic @code{asm} and C code +may appear to work, they cannot be depended upon to work reliably and +are not supported. + +@end table + +@node ARM Function Attributes +@subsection ARM Function Attributes + +These function attributes are supported for ARM targets: + +@table @code + +@item general-regs-only +@cindex @code{general-regs-only} function attribute, ARM +Indicates that no floating-point or Advanced SIMD registers should be +used when generating code for this function. If the function explicitly +uses floating-point code, then the compiler gives an error. This is +the same behavior as that of the command-line option +@option{-mgeneral-regs-only}. + +@item interrupt +@cindex @code{interrupt} function attribute, ARM +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. + +You can specify the kind of interrupt to be handled by +adding an optional parameter to the interrupt attribute like this: + +@smallexample +void f () __attribute__ ((interrupt ("IRQ"))); +@end smallexample + +@noindent +Permissible values for this parameter are: @code{IRQ}, @code{FIQ}, +@code{SWI}, @code{ABORT} and @code{UNDEF}. + +On ARMv7-M the interrupt type is ignored, and the attribute means the function +may be called with a word-aligned stack pointer. + +@item isr +@cindex @code{isr} function attribute, ARM +Use this attribute on ARM to write Interrupt Service Routines. This is an +alias to the @code{interrupt} attribute above. + +@item long_call +@itemx short_call +@cindex @code{long_call} function attribute, ARM +@cindex @code{short_call} function attribute, ARM +@cindex indirect calls, ARM +These attributes specify how a particular function is called. +These attributes override the +@option{-mlong-calls} (@pxref{ARM Options}) +command-line switch and @code{#pragma long_calls} settings. For ARM, the +@code{long_call} attribute indicates that the function might be far +away from the call site and require a different (more expensive) +calling sequence. The @code{short_call} attribute always places +the offset to the function from the call site into the @samp{BL} +instruction directly. + +@item naked +@cindex @code{naked} function attribute, ARM +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. + +@item pcs +@cindex @code{pcs} function attribute, ARM + +The @code{pcs} attribute can be used to control the calling convention +used for a function on ARM. The attribute takes an argument that specifies +the calling convention to use. + +When compiling using the AAPCS ABI (or a variant of it) then valid +values for the argument are @code{"aapcs"} and @code{"aapcs-vfp"}. In +order to use a variant other than @code{"aapcs"} then the compiler must +be permitted to use the appropriate co-processor registers (i.e., the +VFP registers must be available in order to use @code{"aapcs-vfp"}). +For example, + +@smallexample +/* Argument passed in r0, and result returned in r0+r1. */ +double f2d (float) __attribute__((pcs("aapcs"))); +@end smallexample + +Variadic functions always use the @code{"aapcs"} calling convention and +the compiler rejects attempts to specify an alternative. + +@item target (@var{options}) +@cindex @code{target} function attribute +As discussed in @ref{Common Function Attributes}, this attribute +allows specification of target-specific compilation options. + +On ARM, the following options are allowed: + +@table @samp +@item thumb +@cindex @code{target("thumb")} function attribute, ARM +Force code generation in the Thumb (T16/T32) ISA, depending on the +architecture level. + +@item arm +@cindex @code{target("arm")} function attribute, ARM +Force code generation in the ARM (A32) ISA. + +Functions from different modes can be inlined in the caller's mode. + +@item fpu= +@cindex @code{target("fpu=")} function attribute, ARM +Specifies the fpu for which to tune the performance of this function. +The behavior and permissible arguments are the same as for the @option{-mfpu=} +command-line option. + +@item arch= +@cindex @code{arch=} function attribute, ARM +Specifies the architecture version and architectural extensions to use +for this function. The behavior and permissible arguments are the same as +for the @option{-march=} command-line option. + +The above target attributes can be specified as follows: + +@smallexample +__attribute__((target("arch=armv8-a+crc"))) +int +f (int a) +@{ + return a + 5; +@} +@end smallexample + +Additionally, the architectural extension string may be specified on its +own. This can be used to turn on and off particular architectural extensions +without having to specify a particular architecture version or core. Example: + +@smallexample +__attribute__((target("+crc+nocrypto"))) +int +foo (int a) +@{ + return a + 5; +@} +@end smallexample + +In this example @code{target("+crc+nocrypto")} enables the @code{crc} +extension and disables the @code{crypto} extension for the function @code{foo} +without modifying an existing @option{-march=} or @option{-mcpu} option. + +@end table + +@end table + +@node AVR Function Attributes +@subsection AVR Function Attributes + +These function attributes are supported by the AVR back end: + +@table @code +@item interrupt +@cindex @code{interrupt} function attribute, AVR +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. + +On the AVR, the hardware globally disables interrupts when an +interrupt is executed. The first instruction of an interrupt handler +declared with this attribute is a @code{SEI} instruction to +re-enable interrupts. See also the @code{signal} function attribute +that does not insert a @code{SEI} instruction. If both @code{signal} and +@code{interrupt} are specified for the same function, @code{signal} +is silently ignored. + +@item naked +@cindex @code{naked} function attribute, AVR +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. + +@item no_gccisr +@cindex @code{no_gccisr} function attribute, AVR +Do not use @code{__gcc_isr} pseudo instructions in a function with +the @code{interrupt} or @code{signal} attribute aka. interrupt +service routine (ISR). +Use this attribute if the preamble of the ISR prologue should always read +@example +push __zero_reg__ +push __tmp_reg__ +in __tmp_reg__, __SREG__ +push __tmp_reg__ +clr __zero_reg__ +@end example +and accordingly for the postamble of the epilogue --- no matter whether +the mentioned registers are actually used in the ISR or not. +Situations where you might want to use this attribute include: +@itemize @bullet +@item +Code that (effectively) clobbers bits of @code{SREG} other than the +@code{I}-flag by writing to the memory location of @code{SREG}. +@item +Code that uses inline assembler to jump to a different function which +expects (parts of) the prologue code as outlined above to be present. +@end itemize +To disable @code{__gcc_isr} generation for the whole compilation unit, +there is option @option{-mno-gas-isr-prologues}, @pxref{AVR Options}. + +@item OS_main +@itemx OS_task +@cindex @code{OS_main} function attribute, AVR +@cindex @code{OS_task} function attribute, AVR +On AVR, functions with the @code{OS_main} or @code{OS_task} attribute +do not save/restore any call-saved register in their prologue/epilogue. + +The @code{OS_main} attribute can be used when there @emph{is +guarantee} that interrupts are disabled at the time when the function +is entered. This saves resources when the stack pointer has to be +changed to set up a frame for local variables. + +The @code{OS_task} attribute can be used when there is @emph{no +guarantee} that interrupts are disabled at that time when the function +is entered like for, e@.g@. task functions in a multi-threading operating +system. In that case, changing the stack pointer register is +guarded by save/clear/restore of the global interrupt enable flag. + +The differences to the @code{naked} function attribute are: +@itemize @bullet +@item @code{naked} functions do not have a return instruction whereas +@code{OS_main} and @code{OS_task} functions have a @code{RET} or +@code{RETI} return instruction. +@item @code{naked} functions do not set up a frame for local variables +or a frame pointer whereas @code{OS_main} and @code{OS_task} do this +as needed. +@end itemize + +@item signal +@cindex @code{signal} function attribute, AVR +Use this attribute on the AVR to indicate that the specified +function is an interrupt handler. The compiler generates function +entry and exit sequences suitable for use in an interrupt handler when this +attribute is present. + +See also the @code{interrupt} function attribute. + +The AVR hardware globally disables interrupts when an interrupt is executed. +Interrupt handler functions defined with the @code{signal} attribute +do not re-enable interrupts. It is save to enable interrupts in a +@code{signal} handler. This ``save'' only applies to the code +generated by the compiler and not to the IRQ layout of the +application which is responsibility of the application. + +If both @code{signal} and @code{interrupt} are specified for the same +function, @code{signal} is silently ignored. +@end table + +@node Blackfin Function Attributes +@subsection Blackfin Function Attributes + +These function attributes are supported by the Blackfin back end: + +@table @code + +@item exception_handler +@cindex @code{exception_handler} function attribute +@cindex exception handler functions, Blackfin +Use this attribute on the Blackfin to indicate that the specified function +is an exception handler. The compiler generates function entry and +exit sequences suitable for use in an exception handler when this +attribute is present. + +@item interrupt_handler +@cindex @code{interrupt_handler} function attribute, Blackfin +Use this attribute to +indicate that the specified function is an interrupt handler. The compiler +generates function entry and exit sequences suitable for use in an +interrupt handler when this attribute is present. + +@item kspisusp +@cindex @code{kspisusp} function attribute, Blackfin +@cindex User stack pointer in interrupts on the Blackfin +When used together with @code{interrupt_handler}, @code{exception_handler} +or @code{nmi_handler}, code is generated to load the stack pointer +from the USP register in the function prologue. + +@item l1_text +@cindex @code{l1_text} function attribute, Blackfin +This attribute specifies a function to be placed into L1 Instruction +SRAM@. The function is put into a specific section named @code{.l1.text}. +With @option{-mfdpic}, function calls with a such function as the callee +or caller uses inlined PLT. + +@item l2 +@cindex @code{l2} function attribute, Blackfin +This attribute specifies a function to be placed into L2 +SRAM. The function is put into a specific section named +@code{.l2.text}. With @option{-mfdpic}, callers of such functions use +an inlined PLT. + +@item longcall +@itemx shortcall +@cindex indirect calls, Blackfin +@cindex @code{longcall} function attribute, Blackfin +@cindex @code{shortcall} function attribute, Blackfin +The @code{longcall} attribute +indicates that the function might be far away from the call site and +require a different (more expensive) calling sequence. The +@code{shortcall} attribute indicates that the function is always close +enough for the shorter calling sequence to be used. These attributes +override the @option{-mlongcall} switch. + +@item nesting +@cindex @code{nesting} function attribute, Blackfin +@cindex Allow nesting in an interrupt handler on the Blackfin processor +Use this attribute together with @code{interrupt_handler}, +@code{exception_handler} or @code{nmi_handler} to indicate that the function +entry code should enable nested interrupts or exceptions. + +@item nmi_handler +@cindex @code{nmi_handler} function attribute, Blackfin +@cindex NMI handler functions on the Blackfin processor +Use this attribute on the Blackfin to indicate that the specified function +is an NMI handler. The compiler generates function entry and +exit sequences suitable for use in an NMI handler when this +attribute is present. + +@item saveall +@cindex @code{saveall} function attribute, Blackfin +@cindex save all registers on the Blackfin +Use this attribute to indicate that +all registers except the stack pointer should be saved in the prologue +regardless of whether they are used or not. +@end table + +@node BPF Function Attributes +@subsection BPF Function Attributes + +These function attributes are supported by the BPF back end: + +@table @code +@item kernel_helper +@cindex @code{kernel helper}, function attribute, BPF +use this attribute to indicate the specified function declaration is a +kernel helper. The helper function is passed as an argument to the +attribute. Example: + +@smallexample +int bpf_probe_read (void *dst, int size, const void *unsafe_ptr) + __attribute__ ((kernel_helper (4))); +@end smallexample +@end table + +@node C-SKY Function Attributes +@subsection C-SKY Function Attributes + +These function attributes are supported by the C-SKY back end: + +@table @code +@item interrupt +@itemx isr +@cindex @code{interrupt} function attribute, C-SKY +@cindex @code{isr} function attribute, C-SKY +Use these attributes to indicate that the specified function +is an interrupt handler. +The compiler generates function entry and exit sequences suitable for +use in an interrupt handler when either of these attributes are present. + +Use of these options requires the @option{-mistack} command-line option +to enable support for the necessary interrupt stack instructions. They +are ignored with a warning otherwise. @xref{C-SKY Options}. + +@item naked +@cindex @code{naked} function attribute, C-SKY +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. +@end table + + +@node Epiphany Function Attributes +@subsection Epiphany Function Attributes + +These function attributes are supported by the Epiphany back end: + +@table @code +@item disinterrupt +@cindex @code{disinterrupt} function attribute, Epiphany +This attribute causes the compiler to emit +instructions to disable interrupts for the duration of the given +function. + +@item forwarder_section +@cindex @code{forwarder_section} function attribute, Epiphany +This attribute modifies the behavior of an interrupt handler. +The interrupt handler may be in external memory which cannot be +reached by a branch instruction, so generate a local memory trampoline +to transfer control. The single parameter identifies the section where +the trampoline is placed. + +@item interrupt +@cindex @code{interrupt} function attribute, Epiphany +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. It may also generate +a special section with code to initialize the interrupt vector table. + +On Epiphany targets one or more optional parameters can be added like this: + +@smallexample +void __attribute__ ((interrupt ("dma0, dma1"))) universal_dma_handler (); +@end smallexample + +Permissible values for these parameters are: @w{@code{reset}}, +@w{@code{software_exception}}, @w{@code{page_miss}}, +@w{@code{timer0}}, @w{@code{timer1}}, @w{@code{message}}, +@w{@code{dma0}}, @w{@code{dma1}}, @w{@code{wand}} and @w{@code{swi}}. +Multiple parameters indicate that multiple entries in the interrupt +vector table should be initialized for this function, i.e.@: for each +parameter @w{@var{name}}, a jump to the function is emitted in +the section @w{ivt_entry_@var{name}}. The parameter(s) may be omitted +entirely, in which case no interrupt vector table entry is provided. + +Note that interrupts are enabled inside the function +unless the @code{disinterrupt} attribute is also specified. + +The following examples are all valid uses of these attributes on +Epiphany targets: +@smallexample +void __attribute__ ((interrupt)) universal_handler (); +void __attribute__ ((interrupt ("dma1"))) dma1_handler (); +void __attribute__ ((interrupt ("dma0, dma1"))) + universal_dma_handler (); +void __attribute__ ((interrupt ("timer0"), disinterrupt)) + fast_timer_handler (); +void __attribute__ ((interrupt ("dma0, dma1"), + forwarder_section ("tramp"))) + external_dma_handler (); +@end smallexample + +@item long_call +@itemx short_call +@cindex @code{long_call} function attribute, Epiphany +@cindex @code{short_call} function attribute, Epiphany +@cindex indirect calls, Epiphany +These attributes specify how a particular function is called. +These attributes override the +@option{-mlong-calls} (@pxref{Adapteva Epiphany Options}) +command-line switch and @code{#pragma long_calls} settings. +@end table + + +@node H8/300 Function Attributes +@subsection H8/300 Function Attributes + +These function attributes are available for H8/300 targets: + +@table @code +@item function_vector +@cindex @code{function_vector} function attribute, H8/300 +Use this attribute on the H8/300, H8/300H, and H8S to indicate +that the specified function should be called through the function vector. +Calling a function through the function vector reduces code size; however, +the function vector has a limited size (maximum 128 entries on the H8/300 +and 64 entries on the H8/300H and H8S) +and shares space with the interrupt vector. + +@item interrupt_handler +@cindex @code{interrupt_handler} function attribute, H8/300 +Use this attribute on the H8/300, H8/300H, and H8S to +indicate that the specified function is an interrupt handler. The compiler +generates function entry and exit sequences suitable for use in an +interrupt handler when this attribute is present. + +@item saveall +@cindex @code{saveall} function attribute, H8/300 +@cindex save all registers on the H8/300, H8/300H, and H8S +Use this attribute on the H8/300, H8/300H, and H8S to indicate that +all registers except the stack pointer should be saved in the prologue +regardless of whether they are used or not. +@end table + +@node IA-64 Function Attributes +@subsection IA-64 Function Attributes + +These function attributes are supported on IA-64 targets: + +@table @code +@item syscall_linkage +@cindex @code{syscall_linkage} function attribute, IA-64 +This attribute is used to modify the IA-64 calling convention by marking +all input registers as live at all function exits. This makes it possible +to restart a system call after an interrupt without having to save/restore +the input registers. This also prevents kernel data from leaking into +application code. + +@item version_id +@cindex @code{version_id} function attribute, IA-64 +This IA-64 HP-UX attribute, attached to a global variable or function, renames a +symbol to contain a version string, thus allowing for function level +versioning. HP-UX system header files may use function level versioning +for some system calls. + +@smallexample +extern int foo () __attribute__((version_id ("20040821"))); +@end smallexample + +@noindent +Calls to @code{foo} are mapped to calls to @code{foo@{20040821@}}. +@end table + +@node M32C Function Attributes +@subsection M32C Function Attributes + +These function attributes are supported by the M32C back end: + +@table @code +@item bank_switch +@cindex @code{bank_switch} function attribute, M32C +When added to an interrupt handler with the M32C port, causes the +prologue and epilogue to use bank switching to preserve the registers +rather than saving them on the stack. + +@item fast_interrupt +@cindex @code{fast_interrupt} function attribute, M32C +Use this attribute on the M32C port to indicate that the specified +function is a fast interrupt handler. This is just like the +@code{interrupt} attribute, except that @code{freit} is used to return +instead of @code{reit}. + +@item function_vector +@cindex @code{function_vector} function attribute, M16C/M32C +On M16C/M32C targets, the @code{function_vector} attribute declares a +special page subroutine call function. Use of this attribute reduces +the code size by 2 bytes for each call generated to the +subroutine. The argument to the attribute is the vector number entry +from the special page vector table which contains the 16 low-order +bits of the subroutine's entry address. Each vector table has special +page number (18 to 255) that is used in @code{jsrs} instructions. +Jump addresses of the routines are generated by adding 0x0F0000 (in +case of M16C targets) or 0xFF0000 (in case of M32C targets), to the +2-byte addresses set in the vector table. Therefore you need to ensure +that all the special page vector routines should get mapped within the +address range 0x0F0000 to 0x0FFFFF (for M16C) and 0xFF0000 to 0xFFFFFF +(for M32C). + +In the following example 2 bytes are saved for each call to +function @code{foo}. + +@smallexample +void foo (void) __attribute__((function_vector(0x18))); +void foo (void) +@{ +@} + +void bar (void) +@{ + foo(); +@} +@end smallexample + +If functions are defined in one file and are called in another file, +then be sure to write this declaration in both files. + +This attribute is ignored for R8C target. + +@item interrupt +@cindex @code{interrupt} function attribute, M32C +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. +@end table + +@node M32R/D Function Attributes +@subsection M32R/D Function Attributes + +These function attributes are supported by the M32R/D back end: + +@table @code +@item interrupt +@cindex @code{interrupt} function attribute, M32R/D +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. + +@item model (@var{model-name}) +@cindex @code{model} function attribute, M32R/D +@cindex function addressability on the M32R/D + +On the M32R/D, use this attribute to set the addressability of an +object, and of the code generated for a function. The identifier +@var{model-name} is one of @code{small}, @code{medium}, or +@code{large}, representing each of the code models. + +Small model objects live in the lower 16MB of memory (so that their +addresses can be loaded with the @code{ld24} instruction), and are +callable with the @code{bl} instruction. + +Medium model objects may live anywhere in the 32-bit address space (the +compiler generates @code{seth/add3} instructions to load their addresses), +and are callable with the @code{bl} instruction. + +Large model objects may live anywhere in the 32-bit address space (the +compiler generates @code{seth/add3} instructions to load their addresses), +and may not be reachable with the @code{bl} instruction (the compiler +generates the much slower @code{seth/add3/jl} instruction sequence). +@end table + +@node m68k Function Attributes +@subsection m68k Function Attributes + +These function attributes are supported by the m68k back end: + +@table @code +@item interrupt +@itemx interrupt_handler +@cindex @code{interrupt} function attribute, m68k +@cindex @code{interrupt_handler} function attribute, m68k +Use this attribute to +indicate that the specified function is an interrupt handler. The compiler +generates function entry and exit sequences suitable for use in an +interrupt handler when this attribute is present. Either name may be used. + +@item interrupt_thread +@cindex @code{interrupt_thread} function attribute, fido +Use this attribute on fido, a subarchitecture of the m68k, to indicate +that the specified function is an interrupt handler that is designed +to run as a thread. The compiler omits generate prologue/epilogue +sequences and replaces the return instruction with a @code{sleep} +instruction. This attribute is available only on fido. +@end table + +@node MCORE Function Attributes +@subsection MCORE Function Attributes + +These function attributes are supported by the MCORE back end: + +@table @code +@item naked +@cindex @code{naked} function attribute, MCORE +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. +@end table + +@node MeP Function Attributes +@subsection MeP Function Attributes + +These function attributes are supported by the MeP back end: + +@table @code +@item disinterrupt +@cindex @code{disinterrupt} function attribute, MeP +On MeP targets, this attribute causes the compiler to emit +instructions to disable interrupts for the duration of the given +function. + +@item interrupt +@cindex @code{interrupt} function attribute, MeP +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. + +@item near +@cindex @code{near} function attribute, MeP +This attribute causes the compiler to assume the called +function is close enough to use the normal calling convention, +overriding the @option{-mtf} command-line option. + +@item far +@cindex @code{far} function attribute, MeP +On MeP targets this causes the compiler to use a calling convention +that assumes the called function is too far away for the built-in +addressing modes. + +@item vliw +@cindex @code{vliw} function attribute, MeP +The @code{vliw} attribute tells the compiler to emit +instructions in VLIW mode instead of core mode. Note that this +attribute is not allowed unless a VLIW coprocessor has been configured +and enabled through command-line options. +@end table + +@node MicroBlaze Function Attributes +@subsection MicroBlaze Function Attributes + +These function attributes are supported on MicroBlaze targets: + +@table @code +@item save_volatiles +@cindex @code{save_volatiles} function attribute, MicroBlaze +Use this attribute to indicate that the function is +an interrupt handler. All volatile registers (in addition to non-volatile +registers) are saved in the function prologue. If the function is a leaf +function, only volatiles used by the function are saved. A normal function +return is generated instead of a return from interrupt. + +@item break_handler +@cindex @code{break_handler} function attribute, MicroBlaze +@cindex break handler functions +Use this attribute to indicate that +the specified function is a break handler. The compiler generates function +entry and exit sequences suitable for use in an break handler when this +attribute is present. The return from @code{break_handler} is done through +the @code{rtbd} instead of @code{rtsd}. + +@smallexample +void f () __attribute__ ((break_handler)); +@end smallexample + +@item interrupt_handler +@itemx fast_interrupt +@cindex @code{interrupt_handler} function attribute, MicroBlaze +@cindex @code{fast_interrupt} function attribute, MicroBlaze +These attributes indicate that the specified function is an interrupt +handler. Use the @code{fast_interrupt} attribute to indicate handlers +used in low-latency interrupt mode, and @code{interrupt_handler} for +interrupts that do not use low-latency handlers. In both cases, GCC +emits appropriate prologue code and generates a return from the handler +using @code{rtid} instead of @code{rtsd}. +@end table + +@node Microsoft Windows Function Attributes +@subsection Microsoft Windows Function Attributes + +The following attributes are available on Microsoft Windows and Symbian OS +targets. + +@table @code +@item dllexport +@cindex @code{dllexport} function attribute +@cindex @code{__declspec(dllexport)} +On Microsoft Windows targets and Symbian OS targets the +@code{dllexport} attribute causes the compiler to provide a global +pointer to a pointer in a DLL, so that it can be referenced with the +@code{dllimport} attribute. On Microsoft Windows targets, the pointer +name is formed by combining @code{_imp__} and the function or variable +name. + +You can use @code{__declspec(dllexport)} as a synonym for +@code{__attribute__ ((dllexport))} for compatibility with other +compilers. + +On systems that support the @code{visibility} attribute, this +attribute also implies ``default'' visibility. It is an error to +explicitly specify any other visibility. + +GCC's default behavior is to emit all inline functions with the +@code{dllexport} attribute. Since this can cause object file-size bloat, +you can use @option{-fno-keep-inline-dllexport}, which tells GCC to +ignore the attribute for inlined functions unless the +@option{-fkeep-inline-functions} flag is used instead. + +The attribute is ignored for undefined symbols. + +When applied to C++ classes, the attribute marks defined non-inlined +member functions and static data members as exports. Static consts +initialized in-class are not marked unless they are also defined +out-of-class. + +For Microsoft Windows targets there are alternative methods for +including the symbol in the DLL's export table such as using a +@file{.def} file with an @code{EXPORTS} section or, with GNU ld, using +the @option{--export-all} linker flag. + +@item dllimport +@cindex @code{dllimport} function attribute +@cindex @code{__declspec(dllimport)} +On Microsoft Windows and Symbian OS targets, the @code{dllimport} +attribute causes the compiler to reference a function or variable via +a global pointer to a pointer that is set up by the DLL exporting the +symbol. The attribute implies @code{extern}. On Microsoft Windows +targets, the pointer name is formed by combining @code{_imp__} and the +function or variable name. + +You can use @code{__declspec(dllimport)} as a synonym for +@code{__attribute__ ((dllimport))} for compatibility with other +compilers. + +On systems that support the @code{visibility} attribute, this +attribute also implies ``default'' visibility. It is an error to +explicitly specify any other visibility. + +Currently, the attribute is ignored for inlined functions. If the +attribute is applied to a symbol @emph{definition}, an error is reported. +If a symbol previously declared @code{dllimport} is later defined, the +attribute is ignored in subsequent references, and a warning is emitted. +The attribute is also overridden by a subsequent declaration as +@code{dllexport}. + +When applied to C++ classes, the attribute marks non-inlined +member functions and static data members as imports. However, the +attribute is ignored for virtual methods to allow creation of vtables +using thunks. + +On the SH Symbian OS target the @code{dllimport} attribute also has +another affect---it can cause the vtable and run-time type information +for a class to be exported. This happens when the class has a +dllimported constructor or a non-inline, non-pure virtual function +and, for either of those two conditions, the class also has an inline +constructor or destructor and has a key function that is defined in +the current translation unit. + +For Microsoft Windows targets the use of the @code{dllimport} +attribute on functions is not necessary, but provides a small +performance benefit by eliminating a thunk in the DLL@. The use of the +@code{dllimport} attribute on imported variables can be avoided by passing the +@option{--enable-auto-import} switch to the GNU linker. As with +functions, using the attribute for a variable eliminates a thunk in +the DLL@. + +One drawback to using this attribute is that a pointer to a +@emph{variable} marked as @code{dllimport} cannot be used as a constant +address. However, a pointer to a @emph{function} with the +@code{dllimport} attribute can be used as a constant initializer; in +this case, the address of a stub function in the import lib is +referenced. On Microsoft Windows targets, the attribute can be disabled +for functions by setting the @option{-mnop-fun-dllimport} flag. +@end table + +@node MIPS Function Attributes +@subsection MIPS Function Attributes + +These function attributes are supported by the MIPS back end: + +@table @code +@item interrupt +@cindex @code{interrupt} function attribute, MIPS +Use this attribute to indicate that the specified function is an interrupt +handler. The compiler generates function entry and exit sequences suitable +for use in an interrupt handler when this attribute is present. +An optional argument is supported for the interrupt attribute which allows +the interrupt mode to be described. By default GCC assumes the external +interrupt controller (EIC) mode is in use, this can be explicitly set using +@code{eic}. When interrupts are non-masked then the requested Interrupt +Priority Level (IPL) is copied to the current IPL which has the effect of only +enabling higher priority interrupts. To use vectored interrupt mode use +the argument @code{vector=[sw0|sw1|hw0|hw1|hw2|hw3|hw4|hw5]}, this will change +the behavior of the non-masked interrupt support and GCC will arrange to mask +all interrupts from sw0 up to and including the specified interrupt vector. + +You can use the following attributes to modify the behavior +of an interrupt handler: +@table @code +@item use_shadow_register_set +@cindex @code{use_shadow_register_set} function attribute, MIPS +Assume that the handler uses a shadow register set, instead of +the main general-purpose registers. An optional argument @code{intstack} is +supported to indicate that the shadow register set contains a valid stack +pointer. + +@item keep_interrupts_masked +@cindex @code{keep_interrupts_masked} function attribute, MIPS +Keep interrupts masked for the whole function. Without this attribute, +GCC tries to reenable interrupts for as much of the function as it can. + +@item use_debug_exception_return +@cindex @code{use_debug_exception_return} function attribute, MIPS +Return using the @code{deret} instruction. Interrupt handlers that don't +have this attribute return using @code{eret} instead. +@end table + +You can use any combination of these attributes, as shown below: +@smallexample +void __attribute__ ((interrupt)) v0 (); +void __attribute__ ((interrupt, use_shadow_register_set)) v1 (); +void __attribute__ ((interrupt, keep_interrupts_masked)) v2 (); +void __attribute__ ((interrupt, use_debug_exception_return)) v3 (); +void __attribute__ ((interrupt, use_shadow_register_set, + keep_interrupts_masked)) v4 (); +void __attribute__ ((interrupt, use_shadow_register_set, + use_debug_exception_return)) v5 (); +void __attribute__ ((interrupt, keep_interrupts_masked, + use_debug_exception_return)) v6 (); +void __attribute__ ((interrupt, use_shadow_register_set, + keep_interrupts_masked, + use_debug_exception_return)) v7 (); +void __attribute__ ((interrupt("eic"))) v8 (); +void __attribute__ ((interrupt("vector=hw3"))) v9 (); +@end smallexample + +@item long_call +@itemx short_call +@itemx near +@itemx far +@cindex indirect calls, MIPS +@cindex @code{long_call} function attribute, MIPS +@cindex @code{short_call} function attribute, MIPS +@cindex @code{near} function attribute, MIPS +@cindex @code{far} function attribute, MIPS +These attributes specify how a particular function is called on MIPS@. +The attributes override the @option{-mlong-calls} (@pxref{MIPS Options}) +command-line switch. The @code{long_call} and @code{far} attributes are +synonyms, and cause the compiler to always call +the function by first loading its address into a register, and then using +the contents of that register. The @code{short_call} and @code{near} +attributes are synonyms, and have the opposite +effect; they specify that non-PIC calls should be made using the more +efficient @code{jal} instruction. + +@item mips16 +@itemx nomips16 +@cindex @code{mips16} function attribute, MIPS +@cindex @code{nomips16} function attribute, MIPS + +On MIPS targets, you can use the @code{mips16} and @code{nomips16} +function attributes to locally select or turn off MIPS16 code generation. +A function with the @code{mips16} attribute is emitted as MIPS16 code, +while MIPS16 code generation is disabled for functions with the +@code{nomips16} attribute. These attributes override the +@option{-mips16} and @option{-mno-mips16} options on the command line +(@pxref{MIPS Options}). + +When compiling files containing mixed MIPS16 and non-MIPS16 code, the +preprocessor symbol @code{__mips16} reflects the setting on the command line, +not that within individual functions. Mixed MIPS16 and non-MIPS16 code +may interact badly with some GCC extensions such as @code{__builtin_apply} +(@pxref{Constructing Calls}). + +@item micromips, MIPS +@itemx nomicromips, MIPS +@cindex @code{micromips} function attribute +@cindex @code{nomicromips} function attribute + +On MIPS targets, you can use the @code{micromips} and @code{nomicromips} +function attributes to locally select or turn off microMIPS code generation. +A function with the @code{micromips} attribute is emitted as microMIPS code, +while microMIPS code generation is disabled for functions with the +@code{nomicromips} attribute. These attributes override the +@option{-mmicromips} and @option{-mno-micromips} options on the command line +(@pxref{MIPS Options}). + +When compiling files containing mixed microMIPS and non-microMIPS code, the +preprocessor symbol @code{__mips_micromips} reflects the setting on the +command line, +not that within individual functions. Mixed microMIPS and non-microMIPS code +may interact badly with some GCC extensions such as @code{__builtin_apply} +(@pxref{Constructing Calls}). + +@item nocompression +@cindex @code{nocompression} function attribute, MIPS +On MIPS targets, you can use the @code{nocompression} function attribute +to locally turn off MIPS16 and microMIPS code generation. This attribute +overrides the @option{-mips16} and @option{-mmicromips} options on the +command line (@pxref{MIPS Options}). +@end table + +@node MSP430 Function Attributes +@subsection MSP430 Function Attributes + +These function attributes are supported by the MSP430 back end: + +@table @code +@item critical +@cindex @code{critical} function attribute, MSP430 +Critical functions disable interrupts upon entry and restore the +previous interrupt state upon exit. Critical functions cannot also +have the @code{naked}, @code{reentrant} or @code{interrupt} attributes. + +The MSP430 hardware ensures that interrupts are disabled on entry to +@code{interrupt} functions, and restores the previous interrupt state +on exit. The @code{critical} attribute is therefore redundant on +@code{interrupt} functions. + +@item interrupt +@cindex @code{interrupt} function attribute, MSP430 +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. + +You can provide an argument to the interrupt +attribute which specifies a name or number. If the argument is a +number it indicates the slot in the interrupt vector table (0 - 31) to +which this handler should be assigned. If the argument is a name it +is treated as a symbolic name for the vector slot. These names should +match up with appropriate entries in the linker script. By default +the names @code{watchdog} for vector 26, @code{nmi} for vector 30 and +@code{reset} for vector 31 are recognized. + +@item naked +@cindex @code{naked} function attribute, MSP430 +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. + +@item reentrant +@cindex @code{reentrant} function attribute, MSP430 +Reentrant functions disable interrupts upon entry and enable them +upon exit. Reentrant functions cannot also have the @code{naked} +or @code{critical} attributes. They can have the @code{interrupt} +attribute. + +@item wakeup +@cindex @code{wakeup} function attribute, MSP430 +This attribute only applies to interrupt functions. It is silently +ignored if applied to a non-interrupt function. A wakeup interrupt +function will rouse the processor from any low-power state that it +might be in when the function exits. + +@item lower +@itemx upper +@itemx either +@cindex @code{lower} function attribute, MSP430 +@cindex @code{upper} function attribute, MSP430 +@cindex @code{either} function attribute, MSP430 +On the MSP430 target these attributes can be used to specify whether +the function or variable should be placed into low memory, high +memory, or the placement should be left to the linker to decide. The +attributes are only significant if compiling for the MSP430X +architecture in the large memory model. + +The attributes work in conjunction with a linker script that has been +augmented to specify where to place sections with a @code{.lower} and +a @code{.upper} prefix. So, for example, as well as placing the +@code{.data} section, the script also specifies the placement of a +@code{.lower.data} and a @code{.upper.data} section. The intention +is that @code{lower} sections are placed into a small but easier to +access memory region and the upper sections are placed into a larger, but +slower to access, region. + +The @code{either} attribute is special. It tells the linker to place +the object into the corresponding @code{lower} section if there is +room for it. If there is insufficient room then the object is placed +into the corresponding @code{upper} section instead. Note that the +placement algorithm is not very sophisticated. It does not attempt to +find an optimal packing of the @code{lower} sections. It just makes +one pass over the objects and does the best that it can. Using the +@option{-ffunction-sections} and @option{-fdata-sections} command-line +options can help the packing, however, since they produce smaller, +easier to pack regions. +@end table + +@node NDS32 Function Attributes +@subsection NDS32 Function Attributes + +These function attributes are supported by the NDS32 back end: + +@table @code +@item exception +@cindex @code{exception} function attribute +@cindex exception handler functions, NDS32 +Use this attribute on the NDS32 target to indicate that the specified function +is an exception handler. The compiler will generate corresponding sections +for use in an exception handler. + +@item interrupt +@cindex @code{interrupt} function attribute, NDS32 +On NDS32 target, this attribute indicates that the specified function +is an interrupt handler. The compiler generates corresponding sections +for use in an interrupt handler. You can use the following attributes +to modify the behavior: +@table @code +@item nested +@cindex @code{nested} function attribute, NDS32 +This interrupt service routine is interruptible. +@item not_nested +@cindex @code{not_nested} function attribute, NDS32 +This interrupt service routine is not interruptible. +@item nested_ready +@cindex @code{nested_ready} function attribute, NDS32 +This interrupt service routine is interruptible after @code{PSW.GIE} +(global interrupt enable) is set. This allows interrupt service routine to +finish some short critical code before enabling interrupts. +@item save_all +@cindex @code{save_all} function attribute, NDS32 +The system will help save all registers into stack before entering +interrupt handler. +@item partial_save +@cindex @code{partial_save} function attribute, NDS32 +The system will help save caller registers into stack before entering +interrupt handler. +@end table + +@item naked +@cindex @code{naked} function attribute, NDS32 +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. + +@item reset +@cindex @code{reset} function attribute, NDS32 +@cindex reset handler functions +Use this attribute on the NDS32 target to indicate that the specified function +is a reset handler. The compiler will generate corresponding sections +for use in a reset handler. You can use the following attributes +to provide extra exception handling: +@table @code +@item nmi +@cindex @code{nmi} function attribute, NDS32 +Provide a user-defined function to handle NMI exception. +@item warm +@cindex @code{warm} function attribute, NDS32 +Provide a user-defined function to handle warm reset exception. +@end table +@end table + +@node Nios II Function Attributes +@subsection Nios II Function Attributes + +These function attributes are supported by the Nios II back end: + +@table @code +@item target (@var{options}) +@cindex @code{target} function attribute +As discussed in @ref{Common Function Attributes}, this attribute +allows specification of target-specific compilation options. + +When compiling for Nios II, the following options are allowed: + +@table @samp +@item custom-@var{insn}=@var{N} +@itemx no-custom-@var{insn} +@cindex @code{target("custom-@var{insn}=@var{N}")} function attribute, Nios II +@cindex @code{target("no-custom-@var{insn}")} function attribute, Nios II +Each @samp{custom-@var{insn}=@var{N}} attribute locally enables use of a +custom instruction with encoding @var{N} when generating code that uses +@var{insn}. Similarly, @samp{no-custom-@var{insn}} locally inhibits use of +the custom instruction @var{insn}. +These target attributes correspond to the +@option{-mcustom-@var{insn}=@var{N}} and @option{-mno-custom-@var{insn}} +command-line options, and support the same set of @var{insn} keywords. +@xref{Nios II Options}, for more information. + +@item custom-fpu-cfg=@var{name} +@cindex @code{target("custom-fpu-cfg=@var{name}")} function attribute, Nios II +This attribute corresponds to the @option{-mcustom-fpu-cfg=@var{name}} +command-line option, to select a predefined set of custom instructions +named @var{name}. +@xref{Nios II Options}, for more information. +@end table +@end table + +@node Nvidia PTX Function Attributes +@subsection Nvidia PTX Function Attributes + +These function attributes are supported by the Nvidia PTX back end: + +@table @code +@item kernel +@cindex @code{kernel} attribute, Nvidia PTX +This attribute indicates that the corresponding function should be compiled +as a kernel function, which can be invoked from the host via the CUDA RT +library. +By default functions are only callable only from other PTX functions. + +Kernel functions must have @code{void} return type. +@end table + +@node PowerPC Function Attributes +@subsection PowerPC Function Attributes + +These function attributes are supported by the PowerPC back end: + +@table @code +@item longcall +@itemx shortcall +@cindex indirect calls, PowerPC +@cindex @code{longcall} function attribute, PowerPC +@cindex @code{shortcall} function attribute, PowerPC +The @code{longcall} attribute +indicates that the function might be far away from the call site and +require a different (more expensive) calling sequence. The +@code{shortcall} attribute indicates that the function is always close +enough for the shorter calling sequence to be used. These attributes +override both the @option{-mlongcall} switch and +the @code{#pragma longcall} setting. + +@xref{RS/6000 and PowerPC Options}, for more information on whether long +calls are necessary. + +@item target (@var{options}) +@cindex @code{target} function attribute +As discussed in @ref{Common Function Attributes}, this attribute +allows specification of target-specific compilation options. + +On the PowerPC, the following options are allowed: + +@table @samp +@item altivec +@itemx no-altivec +@cindex @code{target("altivec")} function attribute, PowerPC +Generate code that uses (does not use) AltiVec instructions. In +32-bit code, you cannot enable AltiVec instructions unless +@option{-mabi=altivec} is used on the command line. + +@item cmpb +@itemx no-cmpb +@cindex @code{target("cmpb")} function attribute, PowerPC +Generate code that uses (does not use) the compare bytes instruction +implemented on the POWER6 processor and other processors that support +the PowerPC V2.05 architecture. + +@item dlmzb +@itemx no-dlmzb +@cindex @code{target("dlmzb")} function attribute, PowerPC +Generate code that uses (does not use) the string-search @samp{dlmzb} +instruction on the IBM 405, 440, 464 and 476 processors. This instruction is +generated by default when targeting those processors. + +@item fprnd +@itemx no-fprnd +@cindex @code{target("fprnd")} function attribute, PowerPC +Generate code that uses (does not use) the FP round to integer +instructions implemented on the POWER5+ processor and other processors +that support the PowerPC V2.03 architecture. + +@item hard-dfp +@itemx no-hard-dfp +@cindex @code{target("hard-dfp")} function attribute, PowerPC +Generate code that uses (does not use) the decimal floating-point +instructions implemented on some POWER processors. + +@item isel +@itemx no-isel +@cindex @code{target("isel")} function attribute, PowerPC +Generate code that uses (does not use) ISEL instruction. + +@item mfcrf +@itemx no-mfcrf +@cindex @code{target("mfcrf")} function attribute, PowerPC +Generate code that uses (does not use) the move from condition +register field instruction implemented on the POWER4 processor and +other processors that support the PowerPC V2.01 architecture. + +@item mulhw +@itemx no-mulhw +@cindex @code{target("mulhw")} function attribute, PowerPC +Generate code that uses (does not use) the half-word multiply and +multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. +These instructions are generated by default when targeting those +processors. + +@item multiple +@itemx no-multiple +@cindex @code{target("multiple")} function attribute, PowerPC +Generate code that uses (does not use) the load multiple word +instructions and the store multiple word instructions. + +@item update +@itemx no-update +@cindex @code{target("update")} function attribute, PowerPC +Generate code that uses (does not use) the load or store instructions +that update the base register to the address of the calculated memory +location. + +@item popcntb +@itemx no-popcntb +@cindex @code{target("popcntb")} function attribute, PowerPC +Generate code that uses (does not use) the popcount and double-precision +FP reciprocal estimate instruction implemented on the POWER5 +processor and other processors that support the PowerPC V2.02 +architecture. + +@item popcntd +@itemx no-popcntd +@cindex @code{target("popcntd")} function attribute, PowerPC +Generate code that uses (does not use) the popcount instruction +implemented on the POWER7 processor and other processors that support +the PowerPC V2.06 architecture. + +@item powerpc-gfxopt +@itemx no-powerpc-gfxopt +@cindex @code{target("powerpc-gfxopt")} function attribute, PowerPC +Generate code that uses (does not use) the optional PowerPC +architecture instructions in the Graphics group, including +floating-point select. + +@item powerpc-gpopt +@itemx no-powerpc-gpopt +@cindex @code{target("powerpc-gpopt")} function attribute, PowerPC +Generate code that uses (does not use) the optional PowerPC +architecture instructions in the General Purpose group, including +floating-point square root. + +@item recip-precision +@itemx no-recip-precision +@cindex @code{target("recip-precision")} function attribute, PowerPC +Assume (do not assume) that the reciprocal estimate instructions +provide higher-precision estimates than is mandated by the PowerPC +ABI. + +@item string +@itemx no-string +@cindex @code{target("string")} function attribute, PowerPC +Generate code that uses (does not use) the load string instructions +and the store string word instructions to save multiple registers and +do small block moves. + +@item vsx +@itemx no-vsx +@cindex @code{target("vsx")} function attribute, PowerPC +Generate code that uses (does not use) vector/scalar (VSX) +instructions, and also enable the use of built-in functions that allow +more direct access to the VSX instruction set. In 32-bit code, you +cannot enable VSX or AltiVec instructions unless +@option{-mabi=altivec} is used on the command line. + +@item friz +@itemx no-friz +@cindex @code{target("friz")} function attribute, PowerPC +Generate (do not generate) the @code{friz} instruction when the +@option{-funsafe-math-optimizations} option is used to optimize +rounding a floating-point value to 64-bit integer and back to floating +point. The @code{friz} instruction does not return the same value if +the floating-point number is too large to fit in an integer. + +@item avoid-indexed-addresses +@itemx no-avoid-indexed-addresses +@cindex @code{target("avoid-indexed-addresses")} function attribute, PowerPC +Generate code that tries to avoid (not avoid) the use of indexed load +or store instructions. + +@item paired +@itemx no-paired +@cindex @code{target("paired")} function attribute, PowerPC +Generate code that uses (does not use) the generation of PAIRED simd +instructions. + +@item longcall +@itemx no-longcall +@cindex @code{target("longcall")} function attribute, PowerPC +Generate code that assumes (does not assume) that all calls are far +away so that a longer more expensive calling sequence is required. + +@item cpu=@var{CPU} +@cindex @code{target("cpu=@var{CPU}")} function attribute, PowerPC +Specify the architecture to generate code for when compiling the +function. If you select the @code{target("cpu=power7")} attribute when +generating 32-bit code, VSX and AltiVec instructions are not generated +unless you use the @option{-mabi=altivec} option on the command line. + +@item tune=@var{TUNE} +@cindex @code{target("tune=@var{TUNE}")} function attribute, PowerPC +Specify the architecture to tune for when compiling the function. If +you do not specify the @code{target("tune=@var{TUNE}")} attribute and +you do specify the @code{target("cpu=@var{CPU}")} attribute, +compilation tunes for the @var{CPU} architecture, and not the +default tuning specified on the command line. +@end table + +On the PowerPC, the inliner does not inline a +function that has different target options than the caller, unless the +callee has a subset of the target options of the caller. +@end table + +@node RISC-V Function Attributes +@subsection RISC-V Function Attributes + +These function attributes are supported by the RISC-V back end: + +@table @code +@item naked +@cindex @code{naked} function attribute, RISC-V +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. + +@item interrupt +@cindex @code{interrupt} function attribute, RISC-V +Use this attribute to indicate that the specified function is an interrupt +handler. The compiler generates function entry and exit sequences suitable +for use in an interrupt handler when this attribute is present. + +You can specify the kind of interrupt to be handled by adding an optional +parameter to the interrupt attribute like this: + +@smallexample +void f (void) __attribute__ ((interrupt ("user"))); +@end smallexample + +Permissible values for this parameter are @code{user}, @code{supervisor}, +and @code{machine}. If there is no parameter, then it defaults to +@code{machine}. +@end table + +@node RL78 Function Attributes +@subsection RL78 Function Attributes + +These function attributes are supported by the RL78 back end: + +@table @code +@item interrupt +@itemx brk_interrupt +@cindex @code{interrupt} function attribute, RL78 +@cindex @code{brk_interrupt} function attribute, RL78 +These attributes indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. + +Use @code{brk_interrupt} instead of @code{interrupt} for +handlers intended to be used with the @code{BRK} opcode (i.e.@: those +that must end with @code{RETB} instead of @code{RETI}). + +@item naked +@cindex @code{naked} function attribute, RL78 +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. +@end table + +@node RX Function Attributes +@subsection RX Function Attributes + +These function attributes are supported by the RX back end: + +@table @code +@item fast_interrupt +@cindex @code{fast_interrupt} function attribute, RX +Use this attribute on the RX port to indicate that the specified +function is a fast interrupt handler. This is just like the +@code{interrupt} attribute, except that @code{freit} is used to return +instead of @code{reit}. + +@item interrupt +@cindex @code{interrupt} function attribute, RX +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. + +On RX and RL78 targets, you may specify one or more vector numbers as arguments +to the attribute, as well as naming an alternate table name. +Parameters are handled sequentially, so one handler can be assigned to +multiple entries in multiple tables. One may also pass the magic +string @code{"$default"} which causes the function to be used for any +unfilled slots in the current table. + +This example shows a simple assignment of a function to one vector in +the default table (note that preprocessor macros may be used for +chip-specific symbolic vector names): +@smallexample +void __attribute__ ((interrupt (5))) txd1_handler (); +@end smallexample + +This example assigns a function to two slots in the default table +(using preprocessor macros defined elsewhere) and makes it the default +for the @code{dct} table: +@smallexample +void __attribute__ ((interrupt (RXD1_VECT,RXD2_VECT,"dct","$default"))) + txd1_handler (); +@end smallexample + +@item naked +@cindex @code{naked} function attribute, RX +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. + +@item vector +@cindex @code{vector} function attribute, RX +This RX attribute is similar to the @code{interrupt} attribute, including its +parameters, but does not make the function an interrupt-handler type +function (i.e.@: it retains the normal C function calling ABI). See the +@code{interrupt} attribute for a description of its arguments. +@end table + +@node S/390 Function Attributes +@subsection S/390 Function Attributes + +These function attributes are supported on the S/390: + +@table @code +@item hotpatch (@var{halfwords-before-function-label},@var{halfwords-after-function-label}) +@cindex @code{hotpatch} function attribute, S/390 + +On S/390 System z targets, you can use this function attribute to +make GCC generate a ``hot-patching'' function prologue. If the +@option{-mhotpatch=} command-line option is used at the same time, +the @code{hotpatch} attribute takes precedence. The first of the +two arguments specifies the number of halfwords to be added before +the function label. A second argument can be used to specify the +number of halfwords to be added after the function label. For +both arguments the maximum allowed value is 1000000. + +If both arguments are zero, hotpatching is disabled. + +@item target (@var{options}) +@cindex @code{target} function attribute +As discussed in @ref{Common Function Attributes}, this attribute +allows specification of target-specific compilation options. + +On S/390, the following options are supported: + +@table @samp +@item arch= +@item tune= +@item stack-guard= +@item stack-size= +@item branch-cost= +@item warn-framesize= +@item backchain +@itemx no-backchain +@item hard-dfp +@itemx no-hard-dfp +@item hard-float +@itemx soft-float +@item htm +@itemx no-htm +@item vx +@itemx no-vx +@item packed-stack +@itemx no-packed-stack +@item small-exec +@itemx no-small-exec +@item mvcle +@itemx no-mvcle +@item warn-dynamicstack +@itemx no-warn-dynamicstack +@end table + +The options work exactly like the S/390 specific command line +options (without the prefix @option{-m}) except that they do not +change any feature macros. For example, + +@smallexample +@code{target("no-vx")} +@end smallexample + +does not undefine the @code{__VEC__} macro. +@end table + +@node SH Function Attributes +@subsection SH Function Attributes + +These function attributes are supported on the SH family of processors: + +@table @code +@item function_vector +@cindex @code{function_vector} function attribute, SH +@cindex calling functions through the function vector on SH2A +On SH2A targets, this attribute declares a function to be called using the +TBR relative addressing mode. The argument to this attribute is the entry +number of the same function in a vector table containing all the TBR +relative addressable functions. For correct operation the TBR must be setup +accordingly to point to the start of the vector table before any functions with +this attribute are invoked. Usually a good place to do the initialization is +the startup routine. The TBR relative vector table can have at max 256 function +entries. The jumps to these functions are generated using a SH2A specific, +non delayed branch instruction JSR/N @@(disp8,TBR). You must use GAS and GLD +from GNU binutils version 2.7 or later for this attribute to work correctly. + +In an application, for a function being called once, this attribute +saves at least 8 bytes of code; and if other successive calls are being +made to the same function, it saves 2 bytes of code per each of these +calls. + +@item interrupt_handler +@cindex @code{interrupt_handler} function attribute, SH +Use this attribute to +indicate that the specified function is an interrupt handler. The compiler +generates function entry and exit sequences suitable for use in an +interrupt handler when this attribute is present. + +@item nosave_low_regs +@cindex @code{nosave_low_regs} function attribute, SH +Use this attribute on SH targets to indicate that an @code{interrupt_handler} +function should not save and restore registers R0..R7. This can be used on SH3* +and SH4* targets that have a second R0..R7 register bank for non-reentrant +interrupt handlers. + +@item renesas +@cindex @code{renesas} function attribute, SH +On SH targets this attribute specifies that the function or struct follows the +Renesas ABI. + +@item resbank +@cindex @code{resbank} function attribute, SH +On the SH2A target, this attribute enables the high-speed register +saving and restoration using a register bank for @code{interrupt_handler} +routines. Saving to the bank is performed automatically after the CPU +accepts an interrupt that uses a register bank. + +The nineteen 32-bit registers comprising general register R0 to R14, +control register GBR, and system registers MACH, MACL, and PR and the +vector table address offset are saved into a register bank. Register +banks are stacked in first-in last-out (FILO) sequence. Restoration +from the bank is executed by issuing a RESBANK instruction. + +@item sp_switch +@cindex @code{sp_switch} function attribute, SH +Use this attribute on the SH to indicate an @code{interrupt_handler} +function should switch to an alternate stack. It expects a string +argument that names a global variable holding the address of the +alternate stack. + +@smallexample +void *alt_stack; +void f () __attribute__ ((interrupt_handler, + sp_switch ("alt_stack"))); +@end smallexample + +@item trap_exit +@cindex @code{trap_exit} function attribute, SH +Use this attribute on the SH for an @code{interrupt_handler} to return using +@code{trapa} instead of @code{rte}. This attribute expects an integer +argument specifying the trap number to be used. + +@item trapa_handler +@cindex @code{trapa_handler} function attribute, SH +On SH targets this function attribute is similar to @code{interrupt_handler} +but it does not save and restore all registers. +@end table + +@node Symbian OS Function Attributes +@subsection Symbian OS Function Attributes + +@xref{Microsoft Windows Function Attributes}, for discussion of the +@code{dllexport} and @code{dllimport} attributes. + +@node V850 Function Attributes +@subsection V850 Function Attributes + +The V850 back end supports these function attributes: + +@table @code +@item interrupt +@itemx interrupt_handler +@cindex @code{interrupt} function attribute, V850 +@cindex @code{interrupt_handler} function attribute, V850 +Use these attributes to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when either attribute is present. +@end table + +@node Visium Function Attributes +@subsection Visium Function Attributes + +These function attributes are supported by the Visium back end: + +@table @code +@item interrupt +@cindex @code{interrupt} function attribute, Visium +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. +@end table + +@node x86 Function Attributes +@subsection x86 Function Attributes + +These function attributes are supported by the x86 back end: + +@table @code +@item cdecl +@cindex @code{cdecl} function attribute, x86-32 +@cindex functions that pop the argument stack on x86-32 +@opindex mrtd +On the x86-32 targets, the @code{cdecl} attribute causes the compiler to +assume that the calling function pops off the stack space used to +pass arguments. This is +useful to override the effects of the @option{-mrtd} switch. + +@item fastcall +@cindex @code{fastcall} function attribute, x86-32 +@cindex functions that pop the argument stack on x86-32 +On x86-32 targets, the @code{fastcall} attribute causes the compiler to +pass the first argument (if of integral type) in the register ECX and +the second argument (if of integral type) in the register EDX@. Subsequent +and other typed arguments are passed on the stack. The called function +pops the arguments off the stack. If the number of arguments is variable all +arguments are pushed on the stack. + +@item thiscall +@cindex @code{thiscall} function attribute, x86-32 +@cindex functions that pop the argument stack on x86-32 +On x86-32 targets, the @code{thiscall} attribute causes the compiler to +pass the first argument (if of integral type) in the register ECX. +Subsequent and other typed arguments are passed on the stack. The called +function pops the arguments off the stack. +If the number of arguments is variable all arguments are pushed on the +stack. +The @code{thiscall} attribute is intended for C++ non-static member functions. +As a GCC extension, this calling convention can be used for C functions +and for static member methods. + +@item ms_abi +@itemx sysv_abi +@cindex @code{ms_abi} function attribute, x86 +@cindex @code{sysv_abi} function attribute, x86 + +On 32-bit and 64-bit x86 targets, you can use an ABI attribute +to indicate which calling convention should be used for a function. The +@code{ms_abi} attribute tells the compiler to use the Microsoft ABI, +while the @code{sysv_abi} attribute tells the compiler to use the System V +ELF ABI, which is used on GNU/Linux and other systems. The default is to use +the Microsoft ABI when targeting Windows. On all other systems, the default +is the System V ELF ABI. + +Note, the @code{ms_abi} attribute for Microsoft Windows 64-bit targets currently +requires the @option{-maccumulate-outgoing-args} option. + +@item callee_pop_aggregate_return (@var{number}) +@cindex @code{callee_pop_aggregate_return} function attribute, x86 + +On x86-32 targets, you can use this attribute to control how +aggregates are returned in memory. If the caller is responsible for +popping the hidden pointer together with the rest of the arguments, specify +@var{number} equal to zero. If callee is responsible for popping the +hidden pointer, specify @var{number} equal to one. + +The default x86-32 ABI assumes that the callee pops the +stack for hidden pointer. However, on x86-32 Microsoft Windows targets, +the compiler assumes that the +caller pops the stack for hidden pointer. + +@item ms_hook_prologue +@cindex @code{ms_hook_prologue} function attribute, x86 + +On 32-bit and 64-bit x86 targets, you can use +this function attribute to make GCC generate the ``hot-patching'' function +prologue used in Win32 API functions in Microsoft Windows XP Service Pack 2 +and newer. + +@item naked +@cindex @code{naked} function attribute, x86 +This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +@code{asm} statements can safely be included in naked functions +(@pxref{Basic Asm}). While using extended @code{asm} or a mixture of +basic @code{asm} and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. + +@item regparm (@var{number}) +@cindex @code{regparm} function attribute, x86 +@cindex functions that are passed arguments in registers on x86-32 +On x86-32 targets, the @code{regparm} attribute causes the compiler to +pass arguments number one to @var{number} if they are of integral type +in registers EAX, EDX, and ECX instead of on the stack. Functions that +take a variable number of arguments continue to be passed all of their +arguments on the stack. + +Beware that on some ELF systems this attribute is unsuitable for +global functions in shared libraries with lazy binding (which is the +default). Lazy binding sends the first call via resolving code in +the loader, which might assume EAX, EDX and ECX can be clobbered, as +per the standard calling conventions. Solaris 8 is affected by this. +Systems with the GNU C Library version 2.1 or higher +and FreeBSD are believed to be +safe since the loaders there save EAX, EDX and ECX. (Lazy binding can be +disabled with the linker or the loader if desired, to avoid the +problem.) + +@item sseregparm +@cindex @code{sseregparm} function attribute, x86 +On x86-32 targets with SSE support, the @code{sseregparm} attribute +causes the compiler to pass up to 3 floating-point arguments in +SSE registers instead of on the stack. Functions that take a +variable number of arguments continue to pass all of their +floating-point arguments on the stack. + +@item force_align_arg_pointer +@cindex @code{force_align_arg_pointer} function attribute, x86 +On x86 targets, the @code{force_align_arg_pointer} attribute may be +applied to individual function definitions, generating an alternate +prologue and epilogue that realigns the run-time stack if necessary. +This supports mixing legacy codes that run with a 4-byte aligned stack +with modern codes that keep a 16-byte stack for SSE compatibility. + +@item stdcall +@cindex @code{stdcall} function attribute, x86-32 +@cindex functions that pop the argument stack on x86-32 +On x86-32 targets, the @code{stdcall} attribute causes the compiler to +assume that the called function pops off the stack space used to +pass arguments, unless it takes a variable number of arguments. + +@item no_caller_saved_registers +@cindex @code{no_caller_saved_registers} function attribute, x86 +Use this attribute to indicate that the specified function has no +caller-saved registers. That is, all registers are callee-saved. For +example, this attribute can be used for a function called from an +interrupt handler. The compiler generates proper function entry and +exit sequences to save and restore any modified registers, except for +the EFLAGS register. Since GCC doesn't preserve SSE, MMX nor x87 +states, the GCC option @option{-mgeneral-regs-only} should be used to +compile functions with @code{no_caller_saved_registers} attribute. + +@item interrupt +@cindex @code{interrupt} function attribute, x86 +Use this attribute to indicate that the specified function is an +interrupt handler or an exception handler (depending on parameters passed +to the function, explained further). The compiler generates function +entry and exit sequences suitable for use in an interrupt handler when +this attribute is present. The @code{IRET} instruction, instead of the +@code{RET} instruction, is used to return from interrupt handlers. All +registers, except for the EFLAGS register which is restored by the +@code{IRET} instruction, are preserved by the compiler. Since GCC +doesn't preserve SSE, MMX nor x87 states, the GCC option +@option{-mgeneral-regs-only} should be used to compile interrupt and +exception handlers. + +Any interruptible-without-stack-switch code must be compiled with +@option{-mno-red-zone} since interrupt handlers can and will, because +of the hardware design, touch the red zone. + +An interrupt handler must be declared with a mandatory pointer +argument: + +@smallexample +struct interrupt_frame; + +__attribute__ ((interrupt)) +void +f (struct interrupt_frame *frame) +@{ +@} +@end smallexample + +@noindent +and you must define @code{struct interrupt_frame} as described in the +processor's manual. + +Exception handlers differ from interrupt handlers because the system +pushes an error code on the stack. An exception handler declaration is +similar to that for an interrupt handler, but with a different mandatory +function signature. The compiler arranges to pop the error code off the +stack before the @code{IRET} instruction. + +@smallexample +#ifdef __x86_64__ +typedef unsigned long long int uword_t; +#else +typedef unsigned int uword_t; +#endif + +struct interrupt_frame; + +__attribute__ ((interrupt)) +void +f (struct interrupt_frame *frame, uword_t error_code) +@{ + ... +@} +@end smallexample + +Exception handlers should only be used for exceptions that push an error +code; you should use an interrupt handler in other cases. The system +will crash if the wrong kind of handler is used. + +@item target (@var{options}) +@cindex @code{target} function attribute +As discussed in @ref{Common Function Attributes}, this attribute +allows specification of target-specific compilation options. + +On the x86, the following options are allowed: +@table @samp +@item 3dnow +@itemx no-3dnow +@cindex @code{target("3dnow")} function attribute, x86 +Enable/disable the generation of the 3DNow!@: instructions. + +@item 3dnowa +@itemx no-3dnowa +@cindex @code{target("3dnowa")} function attribute, x86 +Enable/disable the generation of the enhanced 3DNow!@: instructions. + +@item abm +@itemx no-abm +@cindex @code{target("abm")} function attribute, x86 +Enable/disable the generation of the advanced bit instructions. + +@item adx +@itemx no-adx +@cindex @code{target("adx")} function attribute, x86 +Enable/disable the generation of the ADX instructions. + +@item aes +@itemx no-aes +@cindex @code{target("aes")} function attribute, x86 +Enable/disable the generation of the AES instructions. + +@item avx +@itemx no-avx +@cindex @code{target("avx")} function attribute, x86 +Enable/disable the generation of the AVX instructions. + +@item avx2 +@itemx no-avx2 +@cindex @code{target("avx2")} function attribute, x86 +Enable/disable the generation of the AVX2 instructions. + +@item avx5124fmaps +@itemx no-avx5124fmaps +@cindex @code{target("avx5124fmaps")} function attribute, x86 +Enable/disable the generation of the AVX5124FMAPS instructions. + +@item avx5124vnniw +@itemx no-avx5124vnniw +@cindex @code{target("avx5124vnniw")} function attribute, x86 +Enable/disable the generation of the AVX5124VNNIW instructions. + +@item avx512bitalg +@itemx no-avx512bitalg +@cindex @code{target("avx512bitalg")} function attribute, x86 +Enable/disable the generation of the AVX512BITALG instructions. + +@item avx512bw +@itemx no-avx512bw +@cindex @code{target("avx512bw")} function attribute, x86 +Enable/disable the generation of the AVX512BW instructions. + +@item avx512cd +@itemx no-avx512cd +@cindex @code{target("avx512cd")} function attribute, x86 +Enable/disable the generation of the AVX512CD instructions. + +@item avx512dq +@itemx no-avx512dq +@cindex @code{target("avx512dq")} function attribute, x86 +Enable/disable the generation of the AVX512DQ instructions. + +@item avx512er +@itemx no-avx512er +@cindex @code{target("avx512er")} function attribute, x86 +Enable/disable the generation of the AVX512ER instructions. + +@item avx512f +@itemx no-avx512f +@cindex @code{target("avx512f")} function attribute, x86 +Enable/disable the generation of the AVX512F instructions. + +@item avx512ifma +@itemx no-avx512ifma +@cindex @code{target("avx512ifma")} function attribute, x86 +Enable/disable the generation of the AVX512IFMA instructions. + +@item avx512pf +@itemx no-avx512pf +@cindex @code{target("avx512pf")} function attribute, x86 +Enable/disable the generation of the AVX512PF instructions. + +@item avx512vbmi +@itemx no-avx512vbmi +@cindex @code{target("avx512vbmi")} function attribute, x86 +Enable/disable the generation of the AVX512VBMI instructions. + +@item avx512vbmi2 +@itemx no-avx512vbmi2 +@cindex @code{target("avx512vbmi2")} function attribute, x86 +Enable/disable the generation of the AVX512VBMI2 instructions. + +@item avx512vl +@itemx no-avx512vl +@cindex @code{target("avx512vl")} function attribute, x86 +Enable/disable the generation of the AVX512VL instructions. + +@item avx512vnni +@itemx no-avx512vnni +@cindex @code{target("avx512vnni")} function attribute, x86 +Enable/disable the generation of the AVX512VNNI instructions. + +@item avx512vpopcntdq +@itemx no-avx512vpopcntdq +@cindex @code{target("avx512vpopcntdq")} function attribute, x86 +Enable/disable the generation of the AVX512VPOPCNTDQ instructions. + +@item bmi +@itemx no-bmi +@cindex @code{target("bmi")} function attribute, x86 +Enable/disable the generation of the BMI instructions. + +@item bmi2 +@itemx no-bmi2 +@cindex @code{target("bmi2")} function attribute, x86 +Enable/disable the generation of the BMI2 instructions. + +@item cldemote +@itemx no-cldemote +@cindex @code{target("cldemote")} function attribute, x86 +Enable/disable the generation of the CLDEMOTE instructions. + +@item clflushopt +@itemx no-clflushopt +@cindex @code{target("clflushopt")} function attribute, x86 +Enable/disable the generation of the CLFLUSHOPT instructions. + +@item clwb +@itemx no-clwb +@cindex @code{target("clwb")} function attribute, x86 +Enable/disable the generation of the CLWB instructions. + +@item clzero +@itemx no-clzero +@cindex @code{target("clzero")} function attribute, x86 +Enable/disable the generation of the CLZERO instructions. + +@item crc32 +@itemx no-crc32 +@cindex @code{target("crc32")} function attribute, x86 +Enable/disable the generation of the CRC32 instructions. + +@item cx16 +@itemx no-cx16 +@cindex @code{target("cx16")} function attribute, x86 +Enable/disable the generation of the CMPXCHG16B instructions. + +@item default +@cindex @code{target("default")} function attribute, x86 +@xref{Function Multiversioning}, where it is used to specify the +default function version. + +@item f16c +@itemx no-f16c +@cindex @code{target("f16c")} function attribute, x86 +Enable/disable the generation of the F16C instructions. + +@item fma +@itemx no-fma +@cindex @code{target("fma")} function attribute, x86 +Enable/disable the generation of the FMA instructions. + +@item fma4 +@itemx no-fma4 +@cindex @code{target("fma4")} function attribute, x86 +Enable/disable the generation of the FMA4 instructions. + +@item fsgsbase +@itemx no-fsgsbase +@cindex @code{target("fsgsbase")} function attribute, x86 +Enable/disable the generation of the FSGSBASE instructions. + +@item fxsr +@itemx no-fxsr +@cindex @code{target("fxsr")} function attribute, x86 +Enable/disable the generation of the FXSR instructions. + +@item gfni +@itemx no-gfni +@cindex @code{target("gfni")} function attribute, x86 +Enable/disable the generation of the GFNI instructions. + +@item hle +@itemx no-hle +@cindex @code{target("hle")} function attribute, x86 +Enable/disable the generation of the HLE instruction prefixes. + +@item lwp +@itemx no-lwp +@cindex @code{target("lwp")} function attribute, x86 +Enable/disable the generation of the LWP instructions. + +@item lzcnt +@itemx no-lzcnt +@cindex @code{target("lzcnt")} function attribute, x86 +Enable/disable the generation of the LZCNT instructions. + +@item mmx +@itemx no-mmx +@cindex @code{target("mmx")} function attribute, x86 +Enable/disable the generation of the MMX instructions. + +@item movbe +@itemx no-movbe +@cindex @code{target("movbe")} function attribute, x86 +Enable/disable the generation of the MOVBE instructions. + +@item movdir64b +@itemx no-movdir64b +@cindex @code{target("movdir64b")} function attribute, x86 +Enable/disable the generation of the MOVDIR64B instructions. + +@item movdiri +@itemx no-movdiri +@cindex @code{target("movdiri")} function attribute, x86 +Enable/disable the generation of the MOVDIRI instructions. + +@item mwait +@itemx no-mwait +@cindex @code{target("mwait")} function attribute, x86 +Enable/disable the generation of the MWAIT and MONITOR instructions. + +@item mwaitx +@itemx no-mwaitx +@cindex @code{target("mwaitx")} function attribute, x86 +Enable/disable the generation of the MWAITX instructions. + +@item pclmul +@itemx no-pclmul +@cindex @code{target("pclmul")} function attribute, x86 +Enable/disable the generation of the PCLMUL instructions. + +@item pconfig +@itemx no-pconfig +@cindex @code{target("pconfig")} function attribute, x86 +Enable/disable the generation of the PCONFIG instructions. + +@item pku +@itemx no-pku +@cindex @code{target("pku")} function attribute, x86 +Enable/disable the generation of the PKU instructions. + +@item popcnt +@itemx no-popcnt +@cindex @code{target("popcnt")} function attribute, x86 +Enable/disable the generation of the POPCNT instruction. + +@item prefetchwt1 +@itemx no-prefetchwt1 +@cindex @code{target("prefetchwt1")} function attribute, x86 +Enable/disable the generation of the PREFETCHWT1 instructions. + +@item prfchw +@itemx no-prfchw +@cindex @code{target("prfchw")} function attribute, x86 +Enable/disable the generation of the PREFETCHW instruction. + +@item ptwrite +@itemx no-ptwrite +@cindex @code{target("ptwrite")} function attribute, x86 +Enable/disable the generation of the PTWRITE instructions. + +@item rdpid +@itemx no-rdpid +@cindex @code{target("rdpid")} function attribute, x86 +Enable/disable the generation of the RDPID instructions. + +@item rdrnd +@itemx no-rdrnd +@cindex @code{target("rdrnd")} function attribute, x86 +Enable/disable the generation of the RDRND instructions. + +@item rdseed +@itemx no-rdseed +@cindex @code{target("rdseed")} function attribute, x86 +Enable/disable the generation of the RDSEED instructions. + +@item rtm +@itemx no-rtm +@cindex @code{target("rtm")} function attribute, x86 +Enable/disable the generation of the RTM instructions. + +@item sahf +@itemx no-sahf +@cindex @code{target("sahf")} function attribute, x86 +Enable/disable the generation of the SAHF instructions. + +@item sgx +@itemx no-sgx +@cindex @code{target("sgx")} function attribute, x86 +Enable/disable the generation of the SGX instructions. + +@item sha +@itemx no-sha +@cindex @code{target("sha")} function attribute, x86 +Enable/disable the generation of the SHA instructions. + +@item shstk +@itemx no-shstk +@cindex @code{target("shstk")} function attribute, x86 +Enable/disable the shadow stack built-in functions from CET. + +@item sse +@itemx no-sse +@cindex @code{target("sse")} function attribute, x86 +Enable/disable the generation of the SSE instructions. + +@item sse2 +@itemx no-sse2 +@cindex @code{target("sse2")} function attribute, x86 +Enable/disable the generation of the SSE2 instructions. + +@item sse3 +@itemx no-sse3 +@cindex @code{target("sse3")} function attribute, x86 +Enable/disable the generation of the SSE3 instructions. + +@item sse4 +@itemx no-sse4 +@cindex @code{target("sse4")} function attribute, x86 +Enable/disable the generation of the SSE4 instructions (both SSE4.1 +and SSE4.2). + +@item sse4.1 +@itemx no-sse4.1 +@cindex @code{target("sse4.1")} function attribute, x86 +Enable/disable the generation of the SSE4.1 instructions. + +@item sse4.2 +@itemx no-sse4.2 +@cindex @code{target("sse4.2")} function attribute, x86 +Enable/disable the generation of the SSE4.2 instructions. + +@item sse4a +@itemx no-sse4a +@cindex @code{target("sse4a")} function attribute, x86 +Enable/disable the generation of the SSE4A instructions. + +@item ssse3 +@itemx no-ssse3 +@cindex @code{target("ssse3")} function attribute, x86 +Enable/disable the generation of the SSSE3 instructions. + +@item tbm +@itemx no-tbm +@cindex @code{target("tbm")} function attribute, x86 +Enable/disable the generation of the TBM instructions. + +@item vaes +@itemx no-vaes +@cindex @code{target("vaes")} function attribute, x86 +Enable/disable the generation of the VAES instructions. + +@item vpclmulqdq +@itemx no-vpclmulqdq +@cindex @code{target("vpclmulqdq")} function attribute, x86 +Enable/disable the generation of the VPCLMULQDQ instructions. + +@item waitpkg +@itemx no-waitpkg +@cindex @code{target("waitpkg")} function attribute, x86 +Enable/disable the generation of the WAITPKG instructions. + +@item wbnoinvd +@itemx no-wbnoinvd +@cindex @code{target("wbnoinvd")} function attribute, x86 +Enable/disable the generation of the WBNOINVD instructions. + +@item xop +@itemx no-xop +@cindex @code{target("xop")} function attribute, x86 +Enable/disable the generation of the XOP instructions. + +@item xsave +@itemx no-xsave +@cindex @code{target("xsave")} function attribute, x86 +Enable/disable the generation of the XSAVE instructions. + +@item xsavec +@itemx no-xsavec +@cindex @code{target("xsavec")} function attribute, x86 +Enable/disable the generation of the XSAVEC instructions. + +@item xsaveopt +@itemx no-xsaveopt +@cindex @code{target("xsaveopt")} function attribute, x86 +Enable/disable the generation of the XSAVEOPT instructions. + +@item xsaves +@itemx no-xsaves +@cindex @code{target("xsaves")} function attribute, x86 +Enable/disable the generation of the XSAVES instructions. + +@item amx-tile +@itemx no-amx-tile +@cindex @code{target("amx-tile")} function attribute, x86 +Enable/disable the generation of the AMX-TILE instructions. + +@item amx-int8 +@itemx no-amx-int8 +@cindex @code{target("amx-int8")} function attribute, x86 +Enable/disable the generation of the AMX-INT8 instructions. + +@item amx-bf16 +@itemx no-amx-bf16 +@cindex @code{target("amx-bf16")} function attribute, x86 +Enable/disable the generation of the AMX-BF16 instructions. + +@item uintr +@itemx no-uintr +@cindex @code{target("uintr")} function attribute, x86 +Enable/disable the generation of the UINTR instructions. + +@item hreset +@itemx no-hreset +@cindex @code{target("hreset")} function attribute, x86 +Enable/disable the generation of the HRESET instruction. + +@item kl +@itemx no-kl +@cindex @code{target("kl")} function attribute, x86 +Enable/disable the generation of the KEYLOCKER instructions. + +@item widekl +@itemx no-widekl +@cindex @code{target("widekl")} function attribute, x86 +Enable/disable the generation of the WIDEKL instructions. + +@item avxvnni +@itemx no-avxvnni +@cindex @code{target("avxvnni")} function attribute, x86 +Enable/disable the generation of the AVXVNNI instructions. + +@item avxifma +@itemx no-avxifma +@cindex @code{target("avxifma")} function attribute, x86 +Enable/disable the generation of the AVXIFMA instructions. + +@item avxvnniint8 +@itemx no-avxvnniint8 +@cindex @code{target("avxvnniint8")} function attribute, x86 +Enable/disable the generation of the AVXVNNIINT8 instructions. + +@item avxneconvert +@itemx no-avxneconvert +@cindex @code{target("avxneconvert")} function attribute, x86 +Enable/disable the generation of the AVXNECONVERT instructions. + +@item cmpccxadd +@itemx no-cmpccxadd +@cindex @code{target("cmpccxadd")} function attribute, x86 +Enable/disable the generation of the CMPccXADD instructions. + +@item amx-fp16 +@itemx no-amx-fp16 +@cindex @code{target("amx-fp16")} function attribute, x86 +Enable/disable the generation of the AMX-FP16 instructions. + +@item prefetchi +@itemx no-prefetchi +@cindex @code{target("prefetchi")} function attribute, x86 +Enable/disable the generation of the PREFETCHI instructions. + +@item raoint +@itemx no-raoint +@cindex @code{target("raoint")} function attribute, x86 +Enable/disable the generation of the RAOINT instructions. + +@item cld +@itemx no-cld +@cindex @code{target("cld")} function attribute, x86 +Enable/disable the generation of the CLD before string moves. + +@item fancy-math-387 +@itemx no-fancy-math-387 +@cindex @code{target("fancy-math-387")} function attribute, x86 +Enable/disable the generation of the @code{sin}, @code{cos}, and +@code{sqrt} instructions on the 387 floating-point unit. + +@item ieee-fp +@itemx no-ieee-fp +@cindex @code{target("ieee-fp")} function attribute, x86 +Enable/disable the generation of floating point that depends on IEEE arithmetic. + +@item inline-all-stringops +@itemx no-inline-all-stringops +@cindex @code{target("inline-all-stringops")} function attribute, x86 +Enable/disable inlining of string operations. + +@item inline-stringops-dynamically +@itemx no-inline-stringops-dynamically +@cindex @code{target("inline-stringops-dynamically")} function attribute, x86 +Enable/disable the generation of the inline code to do small string +operations and calling the library routines for large operations. + +@item align-stringops +@itemx no-align-stringops +@cindex @code{target("align-stringops")} function attribute, x86 +Do/do not align destination of inlined string operations. + +@item recip +@itemx no-recip +@cindex @code{target("recip")} function attribute, x86 +Enable/disable the generation of RCPSS, RCPPS, RSQRTSS and RSQRTPS +instructions followed an additional Newton-Raphson step instead of +doing a floating-point division. + +@item general-regs-only +@cindex @code{target("general-regs-only")} function attribute, x86 +Generate code which uses only the general registers. + +@item arch=@var{ARCH} +@cindex @code{target("arch=@var{ARCH}")} function attribute, x86 +Specify the architecture to generate code for in compiling the function. + +@item tune=@var{TUNE} +@cindex @code{target("tune=@var{TUNE}")} function attribute, x86 +Specify the architecture to tune for in compiling the function. + +@item fpmath=@var{FPMATH} +@cindex @code{target("fpmath=@var{FPMATH}")} function attribute, x86 +Specify which floating-point unit to use. You must specify the +@code{target("fpmath=sse,387")} option as +@code{target("fpmath=sse+387")} because the comma would separate +different options. + +@item prefer-vector-width=@var{OPT} +@cindex @code{prefer-vector-width} function attribute, x86 +On x86 targets, the @code{prefer-vector-width} attribute informs the +compiler to use @var{OPT}-bit vector width in instructions +instead of the default on the selected platform. + +Valid @var{OPT} values are: + +@table @samp +@item none +No extra limitations applied to GCC other than defined by the selected platform. + +@item 128 +Prefer 128-bit vector width for instructions. + +@item 256 +Prefer 256-bit vector width for instructions. + +@item 512 +Prefer 512-bit vector width for instructions. +@end table + +On the x86, the inliner does not inline a +function that has different target options than the caller, unless the +callee has a subset of the target options of the caller. For example +a function declared with @code{target("sse3")} can inline a function +with @code{target("sse2")}, since @code{-msse3} implies @code{-msse2}. +@end table + +@item indirect_branch("@var{choice}") +@cindex @code{indirect_branch} function attribute, x86 +On x86 targets, the @code{indirect_branch} attribute causes the compiler +to convert indirect call and jump with @var{choice}. @samp{keep} +keeps indirect call and jump unmodified. @samp{thunk} converts indirect +call and jump to call and return thunk. @samp{thunk-inline} converts +indirect call and jump to inlined call and return thunk. +@samp{thunk-extern} converts indirect call and jump to external call +and return thunk provided in a separate object file. + +@item function_return("@var{choice}") +@cindex @code{function_return} function attribute, x86 +On x86 targets, the @code{function_return} attribute causes the compiler +to convert function return with @var{choice}. @samp{keep} keeps function +return unmodified. @samp{thunk} converts function return to call and +return thunk. @samp{thunk-inline} converts function return to inlined +call and return thunk. @samp{thunk-extern} converts function return to +external call and return thunk provided in a separate object file. + +@item nocf_check +@cindex @code{nocf_check} function attribute +The @code{nocf_check} attribute on a function is used to inform the +compiler that the function's prologue should not be instrumented when +compiled with the @option{-fcf-protection=branch} option. The +compiler assumes that the function's address is a valid target for a +control-flow transfer. + +The @code{nocf_check} attribute on a type of pointer to function is +used to inform the compiler that a call through the pointer should +not be instrumented when compiled with the +@option{-fcf-protection=branch} option. The compiler assumes +that the function's address from the pointer is a valid target for +a control-flow transfer. A direct function call through a function +name is assumed to be a safe call thus direct calls are not +instrumented by the compiler. + +The @code{nocf_check} attribute is applied to an object's type. +In case of assignment of a function address or a function pointer to +another pointer, the attribute is not carried over from the right-hand +object's type; the type of left-hand object stays unchanged. The +compiler checks for @code{nocf_check} attribute mismatch and reports +a warning in case of mismatch. + +@smallexample +@{ +int foo (void) __attribute__(nocf_check); +void (*foo1)(void) __attribute__(nocf_check); +void (*foo2)(void); + +/* foo's address is assumed to be valid. */ +int +foo (void) + + /* This call site is not checked for control-flow + validity. */ + (*foo1)(); + + /* A warning is issued about attribute mismatch. */ + foo1 = foo2; + + /* This call site is still not checked. */ + (*foo1)(); + + /* This call site is checked. */ + (*foo2)(); + + /* A warning is issued about attribute mismatch. */ + foo2 = foo1; + + /* This call site is still checked. */ + (*foo2)(); + + return 0; +@} +@end smallexample + +@item cf_check +@cindex @code{cf_check} function attribute, x86 + +The @code{cf_check} attribute on a function is used to inform the +compiler that ENDBR instruction should be placed at the function +entry when @option{-fcf-protection=branch} is enabled. + +@item indirect_return +@cindex @code{indirect_return} function attribute, x86 + +The @code{indirect_return} attribute can be applied to a function, +as well as variable or type of function pointer to inform the +compiler that the function may return via indirect branch. + +@item fentry_name("@var{name}") +@cindex @code{fentry_name} function attribute, x86 +On x86 targets, the @code{fentry_name} attribute sets the function to +call on function entry when function instrumentation is enabled +with @option{-pg -mfentry}. When @var{name} is nop then a 5 byte +nop sequence is generated. + +@item fentry_section("@var{name}") +@cindex @code{fentry_section} function attribute, x86 +On x86 targets, the @code{fentry_section} attribute sets the name +of the section to record function entry instrumentation calls in when +enabled with @option{-pg -mrecord-mcount} + +@item nodirect_extern_access +@cindex @code{nodirect_extern_access} function attribute +@opindex mno-direct-extern-access +This attribute, attached to a global variable or function, is the +counterpart to option @option{-mno-direct-extern-access}. + +@end table + +@node Xstormy16 Function Attributes +@subsection Xstormy16 Function Attributes + +These function attributes are supported by the Xstormy16 back end: + +@table @code +@item interrupt +@cindex @code{interrupt} function attribute, Xstormy16 +Use this attribute to indicate +that the specified function is an interrupt handler. The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. +@end table + +@node Variable Attributes +@section Specifying Attributes of Variables +@cindex attribute of variables +@cindex variable attributes + +The keyword @code{__attribute__} allows you to specify special properties +of variables, function parameters, or structure, union, and, in C++, class +members. This @code{__attribute__} keyword is followed by an attribute +specification enclosed in double parentheses. Some attributes are currently +defined generically for variables. Other attributes are defined for +variables on particular target systems. Other attributes are available +for functions (@pxref{Function Attributes}), labels (@pxref{Label Attributes}), +enumerators (@pxref{Enumerator Attributes}), statements +(@pxref{Statement Attributes}), and for types (@pxref{Type Attributes}). +Other front ends might define more attributes +(@pxref{C++ Extensions,,Extensions to the C++ Language}). + +@xref{Attribute Syntax}, for details of the exact syntax for using +attributes. + +@menu +* Common Variable Attributes:: +* ARC Variable Attributes:: +* AVR Variable Attributes:: +* Blackfin Variable Attributes:: +* H8/300 Variable Attributes:: +* IA-64 Variable Attributes:: +* LoongArch Variable Attributes:: +* M32R/D Variable Attributes:: +* MeP Variable Attributes:: +* Microsoft Windows Variable Attributes:: +* MSP430 Variable Attributes:: +* Nvidia PTX Variable Attributes:: +* PowerPC Variable Attributes:: +* RL78 Variable Attributes:: +* V850 Variable Attributes:: +* x86 Variable Attributes:: +* Xstormy16 Variable Attributes:: +@end menu + +@node Common Variable Attributes +@subsection Common Variable Attributes + +The following attributes are supported on most targets. + +@table @code + +@item alias ("@var{target}") +@cindex @code{alias} variable attribute +The @code{alias} variable attribute causes the declaration to be emitted +as an alias for another symbol known as an @dfn{alias target}. Except +for top-level qualifiers the alias target must have the same type as +the alias. For instance, the following + +@smallexample +int var_target; +extern int __attribute__ ((alias ("var_target"))) var_alias; +@end smallexample + +@noindent +defines @code{var_alias} to be an alias for the @code{var_target} variable. + +It is an error if the alias target is not defined in the same translation +unit as the alias. + +Note that in the absence of the attribute GCC assumes that distinct +declarations with external linkage denote distinct objects. Using both +the alias and the alias target to access the same object is undefined +in a translation unit without a declaration of the alias with the attribute. + +This attribute requires assembler and object file support, and may not be +available on all targets. + +@cindex @code{aligned} variable attribute +@item aligned +@itemx aligned (@var{alignment}) +The @code{aligned} attribute specifies a minimum alignment for the variable +or structure field, measured in bytes. When specified, @var{alignment} must +be an integer constant power of 2. Specifying no @var{alignment} argument +implies the maximum alignment for the target, which is often, but by no +means always, 8 or 16 bytes. + +For example, the declaration: + +@smallexample +int x __attribute__ ((aligned (16))) = 0; +@end smallexample + +@noindent +causes the compiler to allocate the global variable @code{x} on a +16-byte boundary. On a 68040, this could be used in conjunction with +an @code{asm} expression to access the @code{move16} instruction which +requires 16-byte aligned operands. + +You can also specify the alignment of structure fields. For example, to +create a double-word aligned @code{int} pair, you could write: + +@smallexample +struct foo @{ int x[2] __attribute__ ((aligned (8))); @}; +@end smallexample + +@noindent +This is an alternative to creating a union with a @code{double} member, +which forces the union to be double-word aligned. + +As in the preceding examples, you can explicitly specify the alignment +(in bytes) that you wish the compiler to use for a given variable or +structure field. Alternatively, you can leave out the alignment factor +and just ask the compiler to align a variable or field to the +default alignment for the target architecture you are compiling for. +The default alignment is sufficient for all scalar types, but may not be +enough for all vector types on a target that supports vector operations. +The default alignment is fixed for a particular target ABI. + +GCC also provides a target specific macro @code{__BIGGEST_ALIGNMENT__}, +which is the largest alignment ever used for any data type on the +target machine you are compiling for. For example, you could write: + +@smallexample +short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__))); +@end smallexample + +The compiler automatically sets the alignment for the declared +variable or field to @code{__BIGGEST_ALIGNMENT__}. Doing this can +often make copy operations more efficient, because the compiler can +use whatever instructions copy the biggest chunks of memory when +performing copies to or from the variables or fields that you have +aligned this way. Note that the value of @code{__BIGGEST_ALIGNMENT__} +may change depending on command-line options. + +When used on a struct, or struct member, the @code{aligned} attribute can +only increase the alignment; in order to decrease it, the @code{packed} +attribute must be specified as well. When used as part of a typedef, the +@code{aligned} attribute can both increase and decrease alignment, and +specifying the @code{packed} attribute generates a warning. + +Note that the effectiveness of @code{aligned} attributes for static +variables may be limited by inherent limitations in the system linker +and/or object file format. On some systems, the linker is +only able to arrange for variables to be aligned up to a certain maximum +alignment. (For some linkers, the maximum supported alignment may +be very very small.) If your linker is only able to align variables +up to a maximum of 8-byte alignment, then specifying @code{aligned(16)} +in an @code{__attribute__} still only provides you with 8-byte +alignment. See your linker documentation for further information. + +Stack variables are not affected by linker restrictions; GCC can properly +align them on any target. + +The @code{aligned} attribute can also be used for functions +(@pxref{Common Function Attributes}.) + +@cindex @code{warn_if_not_aligned} variable attribute +@item warn_if_not_aligned (@var{alignment}) +This attribute specifies a threshold for the structure field, measured +in bytes. If the structure field is aligned below the threshold, a +warning will be issued. For example, the declaration: + +@smallexample +struct foo +@{ + int i1; + int i2; + unsigned long long x __attribute__ ((warn_if_not_aligned (16))); +@}; +@end smallexample + +@noindent +causes the compiler to issue an warning on @code{struct foo}, like +@samp{warning: alignment 8 of 'struct foo' is less than 16}. +The compiler also issues a warning, like @samp{warning: 'x' offset +8 in 'struct foo' isn't aligned to 16}, when the structure field has +the misaligned offset: + +@smallexample +struct __attribute__ ((aligned (16))) foo +@{ + int i1; + int i2; + unsigned long long x __attribute__ ((warn_if_not_aligned (16))); +@}; +@end smallexample + +This warning can be disabled by @option{-Wno-if-not-aligned}. +The @code{warn_if_not_aligned} attribute can also be used for types +(@pxref{Common Type Attributes}.) + +@cindex @code{strict_flex_array} variable attribute +@item strict_flex_array (@var{level}) +The @code{strict_flex_array} attribute should be attached to the trailing +array field of a structure. It controls when to treat the trailing array +field of a structure as a flexible array member for the purposes of accessing +the elements of such an array. +@var{level} must be an integer betwen 0 to 3. + +@var{level}=0 is the least strict level, all trailing arrays of structures +are treated as flexible array members. @var{level}=3 is the strictest level, +only when the trailing array is declared as a flexible array member per C99 +standard onwards (@samp{[]}), it is treated as a flexible array member. + +There are two more levels in between 0 and 3, which are provided to support +older codes that use GCC zero-length array extension (@samp{[0]}) or one-element +array as flexible array members (@samp{[1]}): +When @var{level} is 1, the trailing array is treated as a flexible array member +when it is declared as either @samp{[]}, @samp{[0]}, or @samp{[1]}; +When @var{level} is 2, the trailing array is treated as a flexible array member +when it is declared as either @samp{[]}, or @samp{[0]}. + +This attribute can be used with or without the @option{-fstrict-flex-arrays}. +When both the attribute and the option present at the same time, the level of +the strictness for the specific trailing array field is determined by the +attribute. + +@item alloc_size (@var{position}) +@itemx alloc_size (@var{position-1}, @var{position-2}) +@cindex @code{alloc_size} variable attribute +The @code{alloc_size} variable attribute may be applied to the declaration +of a pointer to a function that returns a pointer and takes at least one +argument of an integer type. It indicates that the returned pointer points +to an object whose size is given by the function argument at @var{position}, +or by the product of the arguments at @var{position-1} and @var{position-2}. +Meaningful sizes are positive values less than @code{PTRDIFF_MAX}. Other +sizes are diagnosed when detected. GCC uses this information to improve +the results of @code{__builtin_object_size}. + +For instance, the following declarations + +@smallexample +typedef __attribute__ ((alloc_size (1, 2))) void* + (*calloc_ptr) (size_t, size_t); +typedef __attribute__ ((alloc_size (1))) void* + (*malloc_ptr) (size_t); +@end smallexample + +@noindent +specify that @code{calloc_ptr} is a pointer of a function that, like +the standard C function @code{calloc}, returns an object whose size +is given by the product of arguments 1 and 2, and similarly, that +@code{malloc_ptr}, like the standard C function @code{malloc}, +returns an object whose size is given by argument 1 to the function. + +@item cleanup (@var{cleanup_function}) +@cindex @code{cleanup} variable attribute +The @code{cleanup} attribute runs a function when the variable goes +out of scope. This attribute can only be applied to auto function +scope variables; it may not be applied to parameters or variables +with static storage duration. The function must take one parameter, +a pointer to a type compatible with the variable. The return value +of the function (if any) is ignored. + +If @option{-fexceptions} is enabled, then @var{cleanup_function} +is run during the stack unwinding that happens during the +processing of the exception. Note that the @code{cleanup} attribute +does not allow the exception to be caught, only to perform an action. +It is undefined what happens if @var{cleanup_function} does not +return normally. + +@item common +@itemx nocommon +@cindex @code{common} variable attribute +@cindex @code{nocommon} variable attribute +@opindex fcommon +@opindex fno-common +The @code{common} attribute requests GCC to place a variable in +``common'' storage. The @code{nocommon} attribute requests the +opposite---to allocate space for it directly. + +These attributes override the default chosen by the +@option{-fno-common} and @option{-fcommon} flags respectively. + +@item copy +@itemx copy (@var{variable}) +@cindex @code{copy} variable attribute +The @code{copy} attribute applies the set of attributes with which +@var{variable} has been declared to the declaration of the variable +to which the attribute is applied. The attribute is designed for +libraries that define aliases that are expected to specify the same +set of attributes as the aliased symbols. The @code{copy} attribute +can be used with variables, functions or types. However, the kind +of symbol to which the attribute is applied (either varible or +function) must match the kind of symbol to which the argument refers. +The @code{copy} attribute copies only syntactic and semantic attributes +but not attributes that affect a symbol's linkage or visibility such as +@code{alias}, @code{visibility}, or @code{weak}. The @code{deprecated} +attribute is also not copied. @xref{Common Function Attributes}. +@xref{Common Type Attributes}. + +@item deprecated +@itemx deprecated (@var{msg}) +@cindex @code{deprecated} variable attribute +The @code{deprecated} attribute results in a warning if the variable +is used anywhere in the source file. This is useful when identifying +variables that are expected to be removed in a future version of a +program. The warning also includes the location of the declaration +of the deprecated variable, to enable users to easily find further +information about why the variable is deprecated, or what they should +do instead. Note that the warning only occurs for uses: + +@smallexample +extern int old_var __attribute__ ((deprecated)); +extern int old_var; +int new_fn () @{ return old_var; @} +@end smallexample + +@noindent +results in a warning on line 3 but not line 2. The optional @var{msg} +argument, which must be a string, is printed in the warning if +present. + +The @code{deprecated} attribute can also be used for functions and +types (@pxref{Common Function Attributes}, +@pxref{Common Type Attributes}). + +The message attached to the attribute is affected by the setting of +the @option{-fmessage-length} option. + +@item unavailable +@itemx unavailable (@var{msg}) +@cindex @code{unavailable} variable attribute +The @code{unavailable} attribute indicates that the variable so marked +is not available, if it is used anywhere in the source file. It behaves +in the same manner as the @code{deprecated} attribute except that the +compiler will emit an error rather than a warning. + +It is expected that items marked as @code{deprecated} will eventually be +withdrawn from interfaces, and then become unavailable. This attribute +allows for marking them appropriately. + +The @code{unavailable} attribute can also be used for functions and +types (@pxref{Common Function Attributes}, +@pxref{Common Type Attributes}). + +@item mode (@var{mode}) +@cindex @code{mode} variable attribute +This attribute specifies the data type for the declaration---whichever +type corresponds to the mode @var{mode}. This in effect lets you +request an integer or floating-point type according to its width. + +@xref{Machine Modes,,, gccint, GNU Compiler Collection (GCC) Internals}, +for a list of the possible keywords for @var{mode}. +You may also specify a mode of @code{byte} or @code{__byte__} to +indicate the mode corresponding to a one-byte integer, @code{word} or +@code{__word__} for the mode of a one-word integer, and @code{pointer} +or @code{__pointer__} for the mode used to represent pointers. + +@item nonstring +@cindex @code{nonstring} variable attribute +The @code{nonstring} variable attribute specifies that an object or member +declaration with type array of @code{char}, @code{signed char}, or +@code{unsigned char}, or pointer to such a type is intended to store +character arrays that do not necessarily contain a terminating @code{NUL}. +This is useful in detecting uses of such arrays or pointers with functions +that expect @code{NUL}-terminated strings, and to avoid warnings when such +an array or pointer is used as an argument to a bounded string manipulation +function such as @code{strncpy}. For example, without the attribute, GCC +will issue a warning for the @code{strncpy} call below because it may +truncate the copy without appending the terminating @code{NUL} character. +Using the attribute makes it possible to suppress the warning. However, +when the array is declared with the attribute the call to @code{strlen} is +diagnosed because when the array doesn't contain a @code{NUL}-terminated +string the call is undefined. To copy, compare, of search non-string +character arrays use the @code{memcpy}, @code{memcmp}, @code{memchr}, +and other functions that operate on arrays of bytes. In addition, +calling @code{strnlen} and @code{strndup} with such arrays is safe +provided a suitable bound is specified, and not diagnosed. + +@smallexample +struct Data +@{ + char name [32] __attribute__ ((nonstring)); +@}; + +int f (struct Data *pd, const char *s) +@{ + strncpy (pd->name, s, sizeof pd->name); + @dots{} + return strlen (pd->name); // unsafe, gets a warning +@} +@end smallexample + +@item packed +@cindex @code{packed} variable attribute +The @code{packed} attribute specifies that a structure member should have +the smallest possible alignment---one bit for a bit-field and one byte +otherwise, unless a larger value is specified with the @code{aligned} +attribute. The attribute does not apply to non-member objects. + +For example in the structure below, the member array @code{x} is packed +so that it immediately follows @code{a} with no intervening padding: + +@smallexample +struct foo +@{ + char a; + int x[2] __attribute__ ((packed)); +@}; +@end smallexample + +@emph{Note:} The 4.1, 4.2 and 4.3 series of GCC ignore the +@code{packed} attribute on bit-fields of type @code{char}. This has +been fixed in GCC 4.4 but the change can lead to differences in the +structure layout. See the documentation of +@option{-Wpacked-bitfield-compat} for more information. + +@item section ("@var{section-name}") +@cindex @code{section} variable attribute +Normally, the compiler places the objects it generates in sections like +@code{data} and @code{bss}. Sometimes, however, you need additional sections, +or you need certain particular variables to appear in special sections, +for example to map to special hardware. The @code{section} +attribute specifies that a variable (or function) lives in a particular +section. For example, this small program uses several specific section names: + +@smallexample +struct duart a __attribute__ ((section ("DUART_A"))) = @{ 0 @}; +struct duart b __attribute__ ((section ("DUART_B"))) = @{ 0 @}; +char stack[10000] __attribute__ ((section ("STACK"))) = @{ 0 @}; +int init_data __attribute__ ((section ("INITDATA"))); + +main() +@{ + /* @r{Initialize stack pointer} */ + init_sp (stack + sizeof (stack)); + + /* @r{Initialize initialized data} */ + memcpy (&init_data, &data, &edata - &data); + + /* @r{Turn on the serial ports} */ + init_duart (&a); + init_duart (&b); +@} +@end smallexample + +@noindent +Use the @code{section} attribute with +@emph{global} variables and not @emph{local} variables, +as shown in the example. + +You may use the @code{section} attribute with initialized or +uninitialized global variables but the linker requires +each object be defined once, with the exception that uninitialized +variables tentatively go in the @code{common} (or @code{bss}) section +and can be multiply ``defined''. Using the @code{section} attribute +changes what section the variable goes into and may cause the +linker to issue an error if an uninitialized variable has multiple +definitions. You can force a variable to be initialized with the +@option{-fno-common} flag or the @code{nocommon} attribute. + +Some file formats do not support arbitrary sections so the @code{section} +attribute is not available on all platforms. +If you need to map the entire contents of a module to a particular +section, consider using the facilities of the linker instead. + +@item tls_model ("@var{tls_model}") +@cindex @code{tls_model} variable attribute +The @code{tls_model} attribute sets thread-local storage model +(@pxref{Thread-Local}) of a particular @code{__thread} variable, +overriding @option{-ftls-model=} command-line switch on a per-variable +basis. +The @var{tls_model} argument should be one of @code{global-dynamic}, +@code{local-dynamic}, @code{initial-exec} or @code{local-exec}. + +Not all targets support this attribute. + +@item unused +@cindex @code{unused} variable attribute +This attribute, attached to a variable or structure field, means that +the variable or field is meant to be possibly unused. GCC does not +produce a warning for this variable or field. + +@item used +@cindex @code{used} variable attribute +This attribute, attached to a variable with static storage, means that +the variable must be emitted even if it appears that the variable is not +referenced. + +When applied to a static data member of a C++ class template, the +attribute also means that the member is instantiated if the +class itself is instantiated. + +@item retain +@cindex @code{retain} variable attribute +For ELF targets that support the GNU or FreeBSD OSABIs, this attribute +will save the variable from linker garbage collection. To support +this behavior, variables that have not been placed in specific sections +(e.g. by the @code{section} attribute, or the @code{-fdata-sections} option), +will be placed in new, unique sections. + +This additional functionality requires Binutils version 2.36 or later. + +@item uninitialized +@cindex @code{uninitialized} variable attribute +This attribute, attached to a variable with automatic storage, means that +the variable should not be automatically initialized by the compiler when +the option @code{-ftrivial-auto-var-init} presents. + +With the option @code{-ftrivial-auto-var-init}, all the automatic variables +that do not have explicit initializers will be initialized by the compiler. +These additional compiler initializations might incur run-time overhead, +sometimes dramatically. This attribute can be used to mark some variables +to be excluded from such automatical initialization in order to reduce runtime +overhead. + +This attribute has no effect when the option @code{-ftrivial-auto-var-init} +does not present. + +@item vector_size (@var{bytes}) +@cindex @code{vector_size} variable attribute +This attribute specifies the vector size for the type of the declared +variable, measured in bytes. The type to which it applies is known as +the @dfn{base type}. The @var{bytes} argument must be a positive +power-of-two multiple of the base type size. For example, the declaration: + +@smallexample +int foo __attribute__ ((vector_size (16))); +@end smallexample + +@noindent +causes the compiler to set the mode for @code{foo}, to be 16 bytes, +divided into @code{int} sized units. Assuming a 32-bit @code{int}, +@code{foo}'s type is a vector of four units of four bytes each, and +the corresponding mode of @code{foo} is @code{V4SI}. +@xref{Vector Extensions}, for details of manipulating vector variables. + +This attribute is only applicable to integral and floating scalars, +although arrays, pointers, and function return values are allowed in +conjunction with this construct. + +Aggregates with this attribute are invalid, even if they are of the same +size as a corresponding scalar. For example, the declaration: + +@smallexample +struct S @{ int a; @}; +struct S __attribute__ ((vector_size (16))) foo; +@end smallexample + +@noindent +is invalid even if the size of the structure is the same as the size of +the @code{int}. + +@item visibility ("@var{visibility_type}") +@cindex @code{visibility} variable attribute +This attribute affects the linkage of the declaration to which it is attached. +The @code{visibility} attribute is described in +@ref{Common Function Attributes}. + +@item weak +@cindex @code{weak} variable attribute +The @code{weak} attribute is described in +@ref{Common Function Attributes}. + +@item noinit +@cindex @code{noinit} variable attribute +Any data with the @code{noinit} attribute will not be initialized by +the C runtime startup code, or the program loader. Not initializing +data in this way can reduce program startup times. + +This attribute is specific to ELF targets and relies on the linker +script to place sections with the @code{.noinit} prefix in the right +location. + +@item persistent +@cindex @code{persistent} variable attribute +Any data with the @code{persistent} attribute will not be initialized by +the C runtime startup code, but will be initialized by the program +loader. This enables the value of the variable to @samp{persist} +between processor resets. + +This attribute is specific to ELF targets and relies on the linker +script to place the sections with the @code{.persistent} prefix in the +right location. Specifically, some type of non-volatile, writeable +memory is required. + +@item objc_nullability (@var{nullability kind}) @r{(Objective-C and Objective-C++ only)} +@cindex @code{objc_nullability} variable attribute +This attribute applies to pointer variables only. It allows marking the +pointer with one of four possible values describing the conditions under +which the pointer might have a @code{nil} value. In most cases, the +attribute is intended to be an internal representation for property and +method nullability (specified by language keywords); it is not recommended +to use it directly. + +When @var{nullability kind} is @code{"unspecified"} or @code{0}, nothing is +known about the conditions in which the pointer might be @code{nil}. Making +this state specific serves to avoid false positives in diagnostics. + +When @var{nullability kind} is @code{"nonnull"} or @code{1}, the pointer has +no meaning if it is @code{nil} and thus the compiler is free to emit +diagnostics if it can be determined that the value will be @code{nil}. + +When @var{nullability kind} is @code{"nullable"} or @code{2}, the pointer might +be @code{nil} and carry meaning as such. + +When @var{nullability kind} is @code{"resettable"} or @code{3} (used only in +the context of property attribute lists) this describes the case in which a +property setter may take the value @code{nil} (which perhaps causes the +property to be reset in some manner to a default) but for which the property +getter will never validly return @code{nil}. + +@end table + +@node ARC Variable Attributes +@subsection ARC Variable Attributes + +@table @code +@item aux +@cindex @code{aux} variable attribute, ARC +The @code{aux} attribute is used to directly access the ARC's +auxiliary register space from C. The auxilirary register number is +given via attribute argument. + +@end table + +@node AVR Variable Attributes +@subsection AVR Variable Attributes + +@table @code +@item progmem +@cindex @code{progmem} variable attribute, AVR +The @code{progmem} attribute is used on the AVR to place read-only +data in the non-volatile program memory (flash). The @code{progmem} +attribute accomplishes this by putting respective variables into a +section whose name starts with @code{.progmem}. + +This attribute works similar to the @code{section} attribute +but adds additional checking. + +@table @asis +@item @bullet{} Ordinary AVR cores with 32 general purpose registers: +@code{progmem} affects the location +of the data but not how this data is accessed. +In order to read data located with the @code{progmem} attribute +(inline) assembler must be used. +@smallexample +/* Use custom macros from @w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC}} */ +#include + +/* Locate var in flash memory */ +const int var[2] PROGMEM = @{ 1, 2 @}; + +int read_var (int i) +@{ + /* Access var[] by accessor macro from avr/pgmspace.h */ + return (int) pgm_read_word (& var[i]); +@} +@end smallexample + +AVR is a Harvard architecture processor and data and read-only data +normally resides in the data memory (RAM). + +See also the @ref{AVR Named Address Spaces} section for +an alternate way to locate and access data in flash memory. + +@item @bullet{} AVR cores with flash memory visible in the RAM address range: +On such devices, there is no need for attribute @code{progmem} or +@ref{AVR Named Address Spaces,,@code{__flash}} qualifier at all. +Just use standard C / C++. The compiler will generate @code{LD*} +instructions. As flash memory is visible in the RAM address range, +and the default linker script does @emph{not} locate @code{.rodata} in +RAM, no special features are needed in order not to waste RAM for +read-only data or to read from flash. You might even get slightly better +performance by +avoiding @code{progmem} and @code{__flash}. This applies to devices from +families @code{avrtiny} and @code{avrxmega3}, see @ref{AVR Options} for +an overview. + +@item @bullet{} Reduced AVR Tiny cores like ATtiny40: +The compiler adds @code{0x4000} +to the addresses of objects and declarations in @code{progmem} and locates +the objects in flash memory, namely in section @code{.progmem.data}. +The offset is needed because the flash memory is visible in the RAM +address space starting at address @code{0x4000}. + +Data in @code{progmem} can be accessed by means of ordinary C@tie{}code, +no special functions or macros are needed. + +@smallexample +/* var is located in flash memory */ +extern const int var[2] __attribute__((progmem)); + +int read_var (int i) +@{ + return var[i]; +@} +@end smallexample + +Please notice that on these devices, there is no need for @code{progmem} +at all. + +@end table + +@item io +@itemx io (@var{addr}) +@cindex @code{io} variable attribute, AVR +Variables with the @code{io} attribute are used to address +memory-mapped peripherals in the io address range. +If an address is specified, the variable +is assigned that address, and the value is interpreted as an +address in the data address space. +Example: + +@smallexample +volatile int porta __attribute__((io (0x22))); +@end smallexample + +The address specified in the address in the data address range. + +Otherwise, the variable it is not assigned an address, but the +compiler will still use in/out instructions where applicable, +assuming some other module assigns an address in the io address range. +Example: + +@smallexample +extern volatile int porta __attribute__((io)); +@end smallexample + +@item io_low +@itemx io_low (@var{addr}) +@cindex @code{io_low} variable attribute, AVR +This is like the @code{io} attribute, but additionally it informs the +compiler that the object lies in the lower half of the I/O area, +allowing the use of @code{cbi}, @code{sbi}, @code{sbic} and @code{sbis} +instructions. + +@item address +@itemx address (@var{addr}) +@cindex @code{address} variable attribute, AVR +Variables with the @code{address} attribute are used to address +memory-mapped peripherals that may lie outside the io address range. + +@smallexample +volatile int porta __attribute__((address (0x600))); +@end smallexample + +@item absdata +@cindex @code{absdata} variable attribute, AVR +Variables in static storage and with the @code{absdata} attribute can +be accessed by the @code{LDS} and @code{STS} instructions which take +absolute addresses. + +@itemize @bullet +@item +This attribute is only supported for the reduced AVR Tiny core +like ATtiny40. + +@item +You must make sure that respective data is located in the +address range @code{0x40}@dots{}@code{0xbf} accessible by +@code{LDS} and @code{STS}. One way to achieve this as an +appropriate linker description file. + +@item +If the location does not fit the address range of @code{LDS} +and @code{STS}, there is currently (Binutils 2.26) just an unspecific +warning like +@quotation +@code{module.cc:(.text+0x1c): warning: internal error: out of range error} +@end quotation + +@end itemize + +See also the @option{-mabsdata} @ref{AVR Options,command-line option}. + +@end table + +@node Blackfin Variable Attributes +@subsection Blackfin Variable Attributes + +Three attributes are currently defined for the Blackfin. + +@table @code +@item l1_data +@itemx l1_data_A +@itemx l1_data_B +@cindex @code{l1_data} variable attribute, Blackfin +@cindex @code{l1_data_A} variable attribute, Blackfin +@cindex @code{l1_data_B} variable attribute, Blackfin +Use these attributes on the Blackfin to place the variable into L1 Data SRAM. +Variables with @code{l1_data} attribute are put into the specific section +named @code{.l1.data}. Those with @code{l1_data_A} attribute are put into +the specific section named @code{.l1.data.A}. Those with @code{l1_data_B} +attribute are put into the specific section named @code{.l1.data.B}. + +@item l2 +@cindex @code{l2} variable attribute, Blackfin +Use this attribute on the Blackfin to place the variable into L2 SRAM. +Variables with @code{l2} attribute are put into the specific section +named @code{.l2.data}. +@end table + +@node H8/300 Variable Attributes +@subsection H8/300 Variable Attributes + +These variable attributes are available for H8/300 targets: + +@table @code +@item eightbit_data +@cindex @code{eightbit_data} variable attribute, H8/300 +@cindex eight-bit data on the H8/300, H8/300H, and H8S +Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified +variable should be placed into the eight-bit data section. +The compiler generates more efficient code for certain operations +on data in the eight-bit data area. Note the eight-bit data area is limited to +256 bytes of data. + +You must use GAS and GLD from GNU binutils version 2.7 or later for +this attribute to work correctly. + +@item tiny_data +@cindex @code{tiny_data} variable attribute, H8/300 +@cindex tiny data section on the H8/300H and H8S +Use this attribute on the H8/300H and H8S to indicate that the specified +variable should be placed into the tiny data section. +The compiler generates more efficient code for loads and stores +on data in the tiny data section. Note the tiny data area is limited to +slightly under 32KB of data. + +@end table + +@node IA-64 Variable Attributes +@subsection IA-64 Variable Attributes + +The IA-64 back end supports the following variable attribute: + +@table @code +@item model (@var{model-name}) +@cindex @code{model} variable attribute, IA-64 + +On IA-64, use this attribute to set the addressability of an object. +At present, the only supported identifier for @var{model-name} is +@code{small}, indicating addressability via ``small'' (22-bit) +addresses (so that their addresses can be loaded with the @code{addl} +instruction). Caveat: such addressing is by definition not position +independent and hence this attribute must not be used for objects +defined by shared libraries. + +@end table + +@node LoongArch Variable Attributes +@subsection LoongArch Variable Attributes + +One attribute is currently defined for the LoongArch. + +@table @code +@item model("@var{name}") +@cindex @code{model} variable attribute, LoongArch +Use this attribute on the LoongArch to use a different code model for +addressing this variable, than the code model specified by the global +@option{-mcmodel} option. This attribute is mostly useful if a +@code{section} attribute and/or a linker script will locate this object +specially. Currently the only supported values of @var{name} are +@code{normal} and @code{extreme}. +@end table + +@node M32R/D Variable Attributes +@subsection M32R/D Variable Attributes + +One attribute is currently defined for the M32R/D@. + +@table @code +@item model (@var{model-name}) +@cindex @code{model-name} variable attribute, M32R/D +@cindex variable addressability on the M32R/D +Use this attribute on the M32R/D to set the addressability of an object. +The identifier @var{model-name} is one of @code{small}, @code{medium}, +or @code{large}, representing each of the code models. + +Small model objects live in the lower 16MB of memory (so that their +addresses can be loaded with the @code{ld24} instruction). + +Medium and large model objects may live anywhere in the 32-bit address space +(the compiler generates @code{seth/add3} instructions to load their +addresses). +@end table + +@node MeP Variable Attributes +@subsection MeP Variable Attributes + +The MeP target has a number of addressing modes and busses. The +@code{near} space spans the standard memory space's first 16 megabytes +(24 bits). The @code{far} space spans the entire 32-bit memory space. +The @code{based} space is a 128-byte region in the memory space that +is addressed relative to the @code{$tp} register. The @code{tiny} +space is a 65536-byte region relative to the @code{$gp} register. In +addition to these memory regions, the MeP target has a separate 16-bit +control bus which is specified with @code{cb} attributes. + +@table @code + +@item based +@cindex @code{based} variable attribute, MeP +Any variable with the @code{based} attribute is assigned to the +@code{.based} section, and is accessed with relative to the +@code{$tp} register. + +@item tiny +@cindex @code{tiny} variable attribute, MeP +Likewise, the @code{tiny} attribute assigned variables to the +@code{.tiny} section, relative to the @code{$gp} register. + +@item near +@cindex @code{near} variable attribute, MeP +Variables with the @code{near} attribute are assumed to have addresses +that fit in a 24-bit addressing mode. This is the default for large +variables (@code{-mtiny=4} is the default) but this attribute can +override @code{-mtiny=} for small variables, or override @code{-ml}. + +@item far +@cindex @code{far} variable attribute, MeP +Variables with the @code{far} attribute are addressed using a full +32-bit address. Since this covers the entire memory space, this +allows modules to make no assumptions about where variables might be +stored. + +@item io +@cindex @code{io} variable attribute, MeP +@itemx io (@var{addr}) +Variables with the @code{io} attribute are used to address +memory-mapped peripherals. If an address is specified, the variable +is assigned that address, else it is not assigned an address (it is +assumed some other module assigns an address). Example: + +@smallexample +int timer_count __attribute__((io(0x123))); +@end smallexample + +@item cb +@itemx cb (@var{addr}) +@cindex @code{cb} variable attribute, MeP +Variables with the @code{cb} attribute are used to access the control +bus, using special instructions. @code{addr} indicates the control bus +address. Example: + +@smallexample +int cpu_clock __attribute__((cb(0x123))); +@end smallexample + +@end table + +@node Microsoft Windows Variable Attributes +@subsection Microsoft Windows Variable Attributes + +You can use these attributes on Microsoft Windows targets. +@ref{x86 Variable Attributes} for additional Windows compatibility +attributes available on all x86 targets. + +@table @code +@item dllimport +@itemx dllexport +@cindex @code{dllimport} variable attribute +@cindex @code{dllexport} variable attribute +The @code{dllimport} and @code{dllexport} attributes are described in +@ref{Microsoft Windows Function Attributes}. + +@item selectany +@cindex @code{selectany} variable attribute +The @code{selectany} attribute causes an initialized global variable to +have link-once semantics. When multiple definitions of the variable are +encountered by the linker, the first is selected and the remainder are +discarded. Following usage by the Microsoft compiler, the linker is told +@emph{not} to warn about size or content differences of the multiple +definitions. + +Although the primary usage of this attribute is for POD types, the +attribute can also be applied to global C++ objects that are initialized +by a constructor. In this case, the static initialization and destruction +code for the object is emitted in each translation defining the object, +but the calls to the constructor and destructor are protected by a +link-once guard variable. + +The @code{selectany} attribute is only available on Microsoft Windows +targets. You can use @code{__declspec (selectany)} as a synonym for +@code{__attribute__ ((selectany))} for compatibility with other +compilers. + +@item shared +@cindex @code{shared} variable attribute +On Microsoft Windows, in addition to putting variable definitions in a named +section, the section can also be shared among all running copies of an +executable or DLL@. For example, this small program defines shared data +by putting it in a named section @code{shared} and marking the section +shareable: + +@smallexample +int foo __attribute__((section ("shared"), shared)) = 0; + +int +main() +@{ + /* @r{Read and write foo. All running + copies see the same value.} */ + return 0; +@} +@end smallexample + +@noindent +You may only use the @code{shared} attribute along with @code{section} +attribute with a fully-initialized global definition because of the way +linkers work. See @code{section} attribute for more information. + +The @code{shared} attribute is only available on Microsoft Windows@. + +@end table + +@node MSP430 Variable Attributes +@subsection MSP430 Variable Attributes + +@table @code +@item upper +@itemx either +@cindex @code{upper} variable attribute, MSP430 +@cindex @code{either} variable attribute, MSP430 +These attributes are the same as the MSP430 function attributes of the +same name (@pxref{MSP430 Function Attributes}). + +@item lower +@cindex @code{lower} variable attribute, MSP430 +This option behaves mostly the same as the MSP430 function attribute of the +same name (@pxref{MSP430 Function Attributes}), but it has some additional +functionality. + +If @option{-mdata-region=}@{@code{upper,either,none}@} has been passed, or +the @code{section} attribute is applied to a variable, the compiler will +generate 430X instructions to handle it. This is because the compiler has +to assume that the variable could get placed in the upper memory region +(above address 0xFFFF). Marking the variable with the @code{lower} attribute +informs the compiler that the variable will be placed in lower memory so it +is safe to use 430 instructions to handle it. + +In the case of the @code{section} attribute, the section name given +will be used, and the @code{.lower} prefix will not be added. + +@end table + +@node Nvidia PTX Variable Attributes +@subsection Nvidia PTX Variable Attributes + +These variable attributes are supported by the Nvidia PTX back end: + +@table @code +@item shared +@cindex @code{shared} attribute, Nvidia PTX +Use this attribute to place a variable in the @code{.shared} memory space. +This memory space is private to each cooperative thread array; only threads +within one thread block refer to the same instance of the variable. +The runtime does not initialize variables in this memory space. +@end table + +@node PowerPC Variable Attributes +@subsection PowerPC Variable Attributes + +Three attributes currently are defined for PowerPC configurations: +@code{altivec}, @code{ms_struct} and @code{gcc_struct}. + +@cindex @code{ms_struct} variable attribute, PowerPC +@cindex @code{gcc_struct} variable attribute, PowerPC +For full documentation of the struct attributes please see the +documentation in @ref{x86 Variable Attributes}. + +@cindex @code{altivec} variable attribute, PowerPC +For documentation of @code{altivec} attribute please see the +documentation in @ref{PowerPC Type Attributes}. + +@node RL78 Variable Attributes +@subsection RL78 Variable Attributes + +@cindex @code{saddr} variable attribute, RL78 +The RL78 back end supports the @code{saddr} variable attribute. This +specifies placement of the corresponding variable in the SADDR area, +which can be accessed more efficiently than the default memory region. + +@node V850 Variable Attributes +@subsection V850 Variable Attributes + +These variable attributes are supported by the V850 back end: + +@table @code + +@item sda +@cindex @code{sda} variable attribute, V850 +Use this attribute to explicitly place a variable in the small data area, +which can hold up to 64 kilobytes. + +@item tda +@cindex @code{tda} variable attribute, V850 +Use this attribute to explicitly place a variable in the tiny data area, +which can hold up to 256 bytes in total. + +@item zda +@cindex @code{zda} variable attribute, V850 +Use this attribute to explicitly place a variable in the first 32 kilobytes +of memory. +@end table + +@node x86 Variable Attributes +@subsection x86 Variable Attributes + +Two attributes are currently defined for x86 configurations: +@code{ms_struct} and @code{gcc_struct}. + +@table @code +@item ms_struct +@itemx gcc_struct +@cindex @code{ms_struct} variable attribute, x86 +@cindex @code{gcc_struct} variable attribute, x86 + +If @code{packed} is used on a structure, or if bit-fields are used, +it may be that the Microsoft ABI lays out the structure differently +than the way GCC normally does. Particularly when moving packed +data between functions compiled with GCC and the native Microsoft compiler +(either via function call or as data in a file), it may be necessary to access +either format. + +The @code{ms_struct} and @code{gcc_struct} attributes correspond +to the @option{-mms-bitfields} and @option{-mno-ms-bitfields} +command-line options, respectively; +see @ref{x86 Options}, for details of how structure layout is affected. +@xref{x86 Type Attributes}, for information about the corresponding +attributes on types. + +@end table + +@node Xstormy16 Variable Attributes +@subsection Xstormy16 Variable Attributes + +One attribute is currently defined for xstormy16 configurations: +@code{below100}. + +@table @code +@item below100 +@cindex @code{below100} variable attribute, Xstormy16 + +If a variable has the @code{below100} attribute (@code{BELOW100} is +allowed also), GCC places the variable in the first 0x100 bytes of +memory and use special opcodes to access it. Such variables are +placed in either the @code{.bss_below100} section or the +@code{.data_below100} section. + +@end table + +@node Type Attributes +@section Specifying Attributes of Types +@cindex attribute of types +@cindex type attributes + +The keyword @code{__attribute__} allows you to specify various special +properties of types. Some type attributes apply only to structure and +union types, and in C++, also class types, while others can apply to +any type defined via a @code{typedef} declaration. Unless otherwise +specified, the same restrictions and effects apply to attributes regardless +of whether a type is a trivial structure or a C++ class with user-defined +constructors, destructors, or a copy assignment. + +Other attributes are defined for functions (@pxref{Function Attributes}), +labels (@pxref{Label Attributes}), enumerators (@pxref{Enumerator +Attributes}), statements (@pxref{Statement Attributes}), and for variables +(@pxref{Variable Attributes}). + +The @code{__attribute__} keyword is followed by an attribute specification +enclosed in double parentheses. + +You may specify type attributes in an enum, struct or union type +declaration or definition by placing them immediately after the +@code{struct}, @code{union} or @code{enum} keyword. You can also place +them just past the closing curly brace of the definition, but this is less +preferred because logically the type should be fully defined at +the closing brace. + +You can also include type attributes in a @code{typedef} declaration. +@xref{Attribute Syntax}, for details of the exact syntax for using +attributes. + +@menu +* Common Type Attributes:: +* ARC Type Attributes:: +* ARM Type Attributes:: +* BPF Type Attributes:: +* MeP Type Attributes:: +* PowerPC Type Attributes:: +* x86 Type Attributes:: +@end menu + +@node Common Type Attributes +@subsection Common Type Attributes + +The following type attributes are supported on most targets. + +@table @code +@cindex @code{aligned} type attribute +@item aligned +@itemx aligned (@var{alignment}) +The @code{aligned} attribute specifies a minimum alignment (in bytes) for +variables of the specified type. When specified, @var{alignment} must be +a power of 2. Specifying no @var{alignment} argument implies the maximum +alignment for the target, which is often, but by no means always, 8 or 16 +bytes. For example, the declarations: + +@smallexample +struct __attribute__ ((aligned (8))) S @{ short f[3]; @}; +typedef int more_aligned_int __attribute__ ((aligned (8))); +@end smallexample + +@noindent +force the compiler to ensure (as far as it can) that each variable whose +type is @code{struct S} or @code{more_aligned_int} is allocated and +aligned @emph{at least} on a 8-byte boundary. On a SPARC, having all +variables of type @code{struct S} aligned to 8-byte boundaries allows +the compiler to use the @code{ldd} and @code{std} (doubleword load and +store) instructions when copying one variable of type @code{struct S} to +another, thus improving run-time efficiency. + +Note that the alignment of any given @code{struct} or @code{union} type +is required by the ISO C standard to be at least a perfect multiple of +the lowest common multiple of the alignments of all of the members of +the @code{struct} or @code{union} in question. This means that you @emph{can} +effectively adjust the alignment of a @code{struct} or @code{union} +type by attaching an @code{aligned} attribute to any one of the members +of such a type, but the notation illustrated in the example above is a +more obvious, intuitive, and readable way to request the compiler to +adjust the alignment of an entire @code{struct} or @code{union} type. + +As in the preceding example, you can explicitly specify the alignment +(in bytes) that you wish the compiler to use for a given @code{struct} +or @code{union} type. Alternatively, you can leave out the alignment factor +and just ask the compiler to align a type to the maximum +useful alignment for the target machine you are compiling for. For +example, you could write: + +@smallexample +struct __attribute__ ((aligned)) S @{ short f[3]; @}; +@end smallexample + +Whenever you leave out the alignment factor in an @code{aligned} +attribute specification, the compiler automatically sets the alignment +for the type to the largest alignment that is ever used for any data +type on the target machine you are compiling for. Doing this can often +make copy operations more efficient, because the compiler can use +whatever instructions copy the biggest chunks of memory when performing +copies to or from the variables that have types that you have aligned +this way. + +In the example above, if the size of each @code{short} is 2 bytes, then +the size of the entire @code{struct S} type is 6 bytes. The smallest +power of two that is greater than or equal to that is 8, so the +compiler sets the alignment for the entire @code{struct S} type to 8 +bytes. + +Note that although you can ask the compiler to select a time-efficient +alignment for a given type and then declare only individual stand-alone +objects of that type, the compiler's ability to select a time-efficient +alignment is primarily useful only when you plan to create arrays of +variables having the relevant (efficiently aligned) type. If you +declare or use arrays of variables of an efficiently-aligned type, then +it is likely that your program also does pointer arithmetic (or +subscripting, which amounts to the same thing) on pointers to the +relevant type, and the code that the compiler generates for these +pointer arithmetic operations is often more efficient for +efficiently-aligned types than for other types. + +Note that the effectiveness of @code{aligned} attributes may be limited +by inherent limitations in your linker. On many systems, the linker is +only able to arrange for variables to be aligned up to a certain maximum +alignment. (For some linkers, the maximum supported alignment may +be very very small.) If your linker is only able to align variables +up to a maximum of 8-byte alignment, then specifying @code{aligned (16)} +in an @code{__attribute__} still only provides you with 8-byte +alignment. See your linker documentation for further information. + +When used on a struct, or struct member, the @code{aligned} attribute can +only increase the alignment; in order to decrease it, the @code{packed} +attribute must be specified as well. When used as part of a typedef, the +@code{aligned} attribute can both increase and decrease alignment, and +specifying the @code{packed} attribute generates a warning. + +@cindex @code{warn_if_not_aligned} type attribute +@item warn_if_not_aligned (@var{alignment}) +This attribute specifies a threshold for the structure field, measured +in bytes. If the structure field is aligned below the threshold, a +warning will be issued. For example, the declaration: + +@smallexample +typedef unsigned long long __u64 + __attribute__((aligned (4), warn_if_not_aligned (8))); + +struct foo +@{ + int i1; + int i2; + __u64 x; +@}; +@end smallexample + +@noindent +causes the compiler to issue an warning on @code{struct foo}, like +@samp{warning: alignment 4 of 'struct foo' is less than 8}. +It is used to define @code{struct foo} in such a way that +@code{struct foo} has the same layout and the structure field @code{x} +has the same alignment when @code{__u64} is aligned at either 4 or +8 bytes. Align @code{struct foo} to 8 bytes: + +@smallexample +struct __attribute__ ((aligned (8))) foo +@{ + int i1; + int i2; + __u64 x; +@}; +@end smallexample + +@noindent +silences the warning. The compiler also issues a warning, like +@samp{warning: 'x' offset 12 in 'struct foo' isn't aligned to 8}, +when the structure field has the misaligned offset: + +@smallexample +struct __attribute__ ((aligned (8))) foo +@{ + int i1; + int i2; + int i3; + __u64 x; +@}; +@end smallexample + +This warning can be disabled by @option{-Wno-if-not-aligned}. + +@item alloc_size (@var{position}) +@itemx alloc_size (@var{position-1}, @var{position-2}) +@cindex @code{alloc_size} type attribute +The @code{alloc_size} type attribute may be applied to the definition +of a type of a function that returns a pointer and takes at least one +argument of an integer type. It indicates that the returned pointer +points to an object whose size is given by the function argument at +@var{position-1}, or by the product of the arguments at @var{position-1} +and @var{position-2}. Meaningful sizes are positive values less than +@code{PTRDIFF_MAX}. Other sizes are disagnosed when detected. GCC uses +this information to improve the results of @code{__builtin_object_size}. + +For instance, the following declarations + +@smallexample +typedef __attribute__ ((alloc_size (1, 2))) void* + calloc_type (size_t, size_t); +typedef __attribute__ ((alloc_size (1))) void* + malloc_type (size_t); +@end smallexample + +@noindent +specify that @code{calloc_type} is a type of a function that, like +the standard C function @code{calloc}, returns an object whose size +is given by the product of arguments 1 and 2, and that +@code{malloc_type}, like the standard C function @code{malloc}, +returns an object whose size is given by argument 1 to the function. + +@item copy +@itemx copy (@var{expression}) +@cindex @code{copy} type attribute +The @code{copy} attribute applies the set of attributes with which +the type of the @var{expression} has been declared to the declaration +of the type to which the attribute is applied. The attribute is +designed for libraries that define aliases that are expected to +specify the same set of attributes as the aliased symbols. +The @code{copy} attribute can be used with types, variables, or +functions. However, the kind of symbol to which the attribute is +applied (either varible or function) must match the kind of symbol +to which the argument refers. +The @code{copy} attribute copies only syntactic and semantic attributes +but not attributes that affect a symbol's linkage or visibility such as +@code{alias}, @code{visibility}, or @code{weak}. The @code{deprecated} +attribute is also not copied. @xref{Common Function Attributes}. +@xref{Common Variable Attributes}. + +For example, suppose @code{struct A} below is defined in some third +party library header to have the alignment requirement @code{N} and +to force a warning whenever a variable of the type is not so aligned +due to attribute @code{packed}. Specifying the @code{copy} attribute +on the definition on the unrelated @code{struct B} has the effect of +copying all relevant attributes from the type referenced by the pointer +expression to @code{struct B}. + +@smallexample +struct __attribute__ ((aligned (N), warn_if_not_aligned (N))) +A @{ /* @r{@dots{}} */ @}; +struct __attribute__ ((copy ( (struct A *)0)) B @{ /* @r{@dots{}} */ @}; +@end smallexample + +@item deprecated +@itemx deprecated (@var{msg}) +@cindex @code{deprecated} type attribute +The @code{deprecated} attribute results in a warning if the type +is used anywhere in the source file. This is useful when identifying +types that are expected to be removed in a future version of a program. +If possible, the warning also includes the location of the declaration +of the deprecated type, to enable users to easily find further +information about why the type is deprecated, or what they should do +instead. Note that the warnings only occur for uses and then only +if the type is being applied to an identifier that itself is not being +declared as deprecated. + +@smallexample +typedef int T1 __attribute__ ((deprecated)); +T1 x; +typedef T1 T2; +T2 y; +typedef T1 T3 __attribute__ ((deprecated)); +T3 z __attribute__ ((deprecated)); +@end smallexample + +@noindent +results in a warning on line 2 and 3 but not lines 4, 5, or 6. No +warning is issued for line 4 because T2 is not explicitly +deprecated. Line 5 has no warning because T3 is explicitly +deprecated. Similarly for line 6. The optional @var{msg} +argument, which must be a string, is printed in the warning if +present. Control characters in the string will be replaced with +escape sequences, and if the @option{-fmessage-length} option is set +to 0 (its default value) then any newline characters will be ignored. + +The @code{deprecated} attribute can also be used for functions and +variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.) + +The message attached to the attribute is affected by the setting of +the @option{-fmessage-length} option. + +@item unavailable +@itemx unavailable (@var{msg}) +@cindex @code{unavailable} type attribute +The @code{unavailable} attribute behaves in the same manner as the +@code{deprecated} one, but emits an error rather than a warning. It is +used to indicate that a (perhaps previously @code{deprecated}) type is +no longer usable. + +The @code{unavailable} attribute can also be used for functions and +variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.) + +@item designated_init +@cindex @code{designated_init} type attribute +This attribute may only be applied to structure types. It indicates +that any initialization of an object of this type must use designated +initializers rather than positional initializers. The intent of this +attribute is to allow the programmer to indicate that a structure's +layout may change, and that therefore relying on positional +initialization will result in future breakage. + +GCC emits warnings based on this attribute by default; use +@option{-Wno-designated-init} to suppress them. + +@item may_alias +@cindex @code{may_alias} type attribute +Accesses through pointers to types with this attribute are not subject +to type-based alias analysis, but are instead assumed to be able to alias +any other type of objects. +In the context of section 6.5 paragraph 7 of the C99 standard, +an lvalue expression +dereferencing such a pointer is treated like having a character type. +See @option{-fstrict-aliasing} for more information on aliasing issues. +This extension exists to support some vector APIs, in which pointers to +one vector type are permitted to alias pointers to a different vector type. + +Note that an object of a type with this attribute does not have any +special semantics. + +Example of use: + +@smallexample +typedef short __attribute__ ((__may_alias__)) short_a; + +int +main (void) +@{ + int a = 0x12345678; + short_a *b = (short_a *) &a; + + b[1] = 0; + + if (a == 0x12345678) + abort(); + + exit(0); +@} +@end smallexample + +@noindent +If you replaced @code{short_a} with @code{short} in the variable +declaration, the above program would abort when compiled with +@option{-fstrict-aliasing}, which is on by default at @option{-O2} or +above. + +@item mode (@var{mode}) +@cindex @code{mode} type attribute +This attribute specifies the data type for the declaration---whichever +type corresponds to the mode @var{mode}. This in effect lets you +request an integer or floating-point type according to its width. + +@xref{Machine Modes,,, gccint, GNU Compiler Collection (GCC) Internals}, +for a list of the possible keywords for @var{mode}. +You may also specify a mode of @code{byte} or @code{__byte__} to +indicate the mode corresponding to a one-byte integer, @code{word} or +@code{__word__} for the mode of a one-word integer, and @code{pointer} +or @code{__pointer__} for the mode used to represent pointers. + +@item packed +@cindex @code{packed} type attribute +This attribute, attached to a @code{struct}, @code{union}, or C++ @code{class} +type definition, specifies that each of its members (other than zero-width +bit-fields) is placed to minimize the memory required. This is equivalent +to specifying the @code{packed} attribute on each of the members. + +@opindex fshort-enums +When attached to an @code{enum} definition, the @code{packed} attribute +indicates that the smallest integral type should be used. +Specifying the @option{-fshort-enums} flag on the command line +is equivalent to specifying the @code{packed} +attribute on all @code{enum} definitions. + +In the following example @code{struct my_packed_struct}'s members are +packed closely together, but the internal layout of its @code{s} member +is not packed---to do that, @code{struct my_unpacked_struct} needs to +be packed too. + +@smallexample +struct my_unpacked_struct + @{ + char c; + int i; + @}; + +struct __attribute__ ((__packed__)) my_packed_struct + @{ + char c; + int i; + struct my_unpacked_struct s; + @}; +@end smallexample + +You may only specify the @code{packed} attribute on the definition +of an @code{enum}, @code{struct}, @code{union}, or @code{class}, +not on a @code{typedef} that does not also define the enumerated type, +structure, union, or class. + +@item scalar_storage_order ("@var{endianness}") +@cindex @code{scalar_storage_order} type attribute +When attached to a @code{union} or a @code{struct}, this attribute sets +the storage order, aka endianness, of the scalar fields of the type, as +well as the array fields whose component is scalar. The supported +endiannesses are @code{big-endian} and @code{little-endian}. The attribute +has no effects on fields which are themselves a @code{union}, a @code{struct} +or an array whose component is a @code{union} or a @code{struct}, and it is +possible for these fields to have a different scalar storage order than the +enclosing type. + +Note that neither pointer nor vector fields are considered scalar fields in +this context, so the attribute has no effects on these fields. + +This attribute is supported only for targets that use a uniform default +scalar storage order (fortunately, most of them), i.e.@: targets that store +the scalars either all in big-endian or all in little-endian. + +Additional restrictions are enforced for types with the reverse scalar +storage order with regard to the scalar storage order of the target: + +@itemize +@item Taking the address of a scalar field of a @code{union} or a +@code{struct} with reverse scalar storage order is not permitted and yields +an error. +@item Taking the address of an array field, whose component is scalar, of +a @code{union} or a @code{struct} with reverse scalar storage order is +permitted but yields a warning, unless @option{-Wno-scalar-storage-order} +is specified. +@item Taking the address of a @code{union} or a @code{struct} with reverse +scalar storage order is permitted. +@end itemize + +These restrictions exist because the storage order attribute is lost when +the address of a scalar or the address of an array with scalar component is +taken, so storing indirectly through this address generally does not work. +The second case is nevertheless allowed to be able to perform a block copy +from or to the array. + +Moreover, the use of type punning or aliasing to toggle the storage order +is not supported; that is to say, if a given scalar object can be accessed +through distinct types that assign a different storage order to it, then the +behavior is undefined. + +@item transparent_union +@cindex @code{transparent_union} type attribute + +This attribute, attached to a @code{union} type definition, indicates +that any function parameter having that union type causes calls to that +function to be treated in a special way. + +First, the argument corresponding to a transparent union type can be of +any type in the union; no cast is required. Also, if the union contains +a pointer type, the corresponding argument can be a null pointer +constant or a void pointer expression; and if the union contains a void +pointer type, the corresponding argument can be any pointer expression. +If the union member type is a pointer, qualifiers like @code{const} on +the referenced type must be respected, just as with normal pointer +conversions. + +Second, the argument is passed to the function using the calling +conventions of the first member of the transparent union, not the calling +conventions of the union itself. All members of the union must have the +same machine representation; this is necessary for this argument passing +to work properly. + +Transparent unions are designed for library functions that have multiple +interfaces for compatibility reasons. For example, suppose the +@code{wait} function must accept either a value of type @code{int *} to +comply with POSIX, or a value of type @code{union wait *} to comply with +the 4.1BSD interface. If @code{wait}'s parameter were @code{void *}, +@code{wait} would accept both kinds of arguments, but it would also +accept any other pointer type and this would make argument type checking +less useful. Instead, @code{} might define the interface +as follows: + +@smallexample +typedef union __attribute__ ((__transparent_union__)) + @{ + int *__ip; + union wait *__up; + @} wait_status_ptr_t; + +pid_t wait (wait_status_ptr_t); +@end smallexample + +@noindent +This interface allows either @code{int *} or @code{union wait *} +arguments to be passed, using the @code{int *} calling convention. +The program can call @code{wait} with arguments of either type: + +@smallexample +int w1 () @{ int w; return wait (&w); @} +int w2 () @{ union wait w; return wait (&w); @} +@end smallexample + +@noindent +With this interface, @code{wait}'s implementation might look like this: + +@smallexample +pid_t wait (wait_status_ptr_t p) +@{ + return waitpid (-1, p.__ip, 0); +@} +@end smallexample + +@item unused +@cindex @code{unused} type attribute +When attached to a type (including a @code{union} or a @code{struct}), +this attribute means that variables of that type are meant to appear +possibly unused. GCC does not produce a warning for any variables of +that type, even if the variable appears to do nothing. This is often +the case with lock or thread classes, which are usually defined and then +not referenced, but contain constructors and destructors that have +nontrivial bookkeeping functions. + +@item vector_size (@var{bytes}) +@cindex @code{vector_size} type attribute +This attribute specifies the vector size for the type, measured in bytes. +The type to which it applies is known as the @dfn{base type}. The @var{bytes} +argument must be a positive power-of-two multiple of the base type size. For +example, the following declarations: + +@smallexample +typedef __attribute__ ((vector_size (32))) int int_vec32_t ; +typedef __attribute__ ((vector_size (32))) int* int_vec32_ptr_t; +typedef __attribute__ ((vector_size (32))) int int_vec32_arr3_t[3]; +@end smallexample + +@noindent +define @code{int_vec32_t} to be a 32-byte vector type composed of @code{int} +sized units. With @code{int} having a size of 4 bytes, the type defines +a vector of eight units, four bytes each. The mode of variables of type +@code{int_vec32_t} is @code{V8SI}. @code{int_vec32_ptr_t} is then defined +to be a pointer to such a vector type, and @code{int_vec32_arr3_t} to be +an array of three such vectors. @xref{Vector Extensions}, for details of +manipulating objects of vector types. + +This attribute is only applicable to integral and floating scalar types. +In function declarations the attribute applies to the function return +type. + +For example, the following: +@smallexample +__attribute__ ((vector_size (16))) float get_flt_vec16 (void); +@end smallexample +declares @code{get_flt_vec16} to be a function returning a 16-byte vector +with the base type @code{float}. + +@item visibility +@cindex @code{visibility} type attribute +In C++, attribute visibility (@pxref{Function Attributes}) can also be +applied to class, struct, union and enum types. Unlike other type +attributes, the attribute must appear between the initial keyword and +the name of the type; it cannot appear after the body of the type. + +Note that the type visibility is applied to vague linkage entities +associated with the class (vtable, typeinfo node, etc.). In +particular, if a class is thrown as an exception in one shared object +and caught in another, the class must have default visibility. +Otherwise the two shared objects are unable to use the same +typeinfo node and exception handling will break. + +@item objc_root_class @r{(Objective-C and Objective-C++ only)} +@cindex @code{objc_root_class} type attribute +This attribute marks a class as being a root class, and thus allows +the compiler to elide any warnings about a missing superclass and to +make additional checks for mandatory methods as needed. + +@end table + +To specify multiple attributes, separate them by commas within the +double parentheses: for example, @samp{__attribute__ ((aligned (16), +packed))}. + +@node ARC Type Attributes +@subsection ARC Type Attributes + +@cindex @code{uncached} type attribute, ARC +Declaring objects with @code{uncached} allows you to exclude +data-cache participation in load and store operations on those objects +without involving the additional semantic implications of +@code{volatile}. The @code{.di} instruction suffix is used for all +loads and stores of data declared @code{uncached}. + +@node ARM Type Attributes +@subsection ARM Type Attributes + +@cindex @code{notshared} type attribute, ARM +On those ARM targets that support @code{dllimport} (such as Symbian +OS), you can use the @code{notshared} attribute to indicate that the +virtual table and other similar data for a class should not be +exported from a DLL@. For example: + +@smallexample +class __declspec(notshared) C @{ +public: + __declspec(dllimport) C(); + virtual void f(); +@} + +__declspec(dllexport) +C::C() @{@} +@end smallexample + +@noindent +In this code, @code{C::C} is exported from the current DLL, but the +virtual table for @code{C} is not exported. (You can use +@code{__attribute__} instead of @code{__declspec} if you prefer, but +most Symbian OS code uses @code{__declspec}.) + +@node BPF Type Attributes +@subsection BPF Type Attributes + +@cindex @code{preserve_access_index} type attribute, BPF +BPF Compile Once - Run Everywhere (CO-RE) support. When attached to a +@code{struct} or @code{union} type definition, indicates that CO-RE +relocation information should be generated for any access to a variable +of that type. The behavior is equivalent to the programmer manually +wrapping every such access with @code{__builtin_preserve_access_index}. + + +@node MeP Type Attributes +@subsection MeP Type Attributes + +@cindex @code{based} type attribute, MeP +@cindex @code{tiny} type attribute, MeP +@cindex @code{near} type attribute, MeP +@cindex @code{far} type attribute, MeP +Many of the MeP variable attributes may be applied to types as well. +Specifically, the @code{based}, @code{tiny}, @code{near}, and +@code{far} attributes may be applied to either. The @code{io} and +@code{cb} attributes may not be applied to types. + +@node PowerPC Type Attributes +@subsection PowerPC Type Attributes + +Three attributes currently are defined for PowerPC configurations: +@code{altivec}, @code{ms_struct} and @code{gcc_struct}. + +@cindex @code{ms_struct} type attribute, PowerPC +@cindex @code{gcc_struct} type attribute, PowerPC +For full documentation of the @code{ms_struct} and @code{gcc_struct} +attributes please see the documentation in @ref{x86 Type Attributes}. + +@cindex @code{altivec} type attribute, PowerPC +The @code{altivec} attribute allows one to declare AltiVec vector data +types supported by the AltiVec Programming Interface Manual. The +attribute requires an argument to specify one of three vector types: +@code{vector__}, @code{pixel__} (always followed by unsigned short), +and @code{bool__} (always followed by unsigned). + +@smallexample +__attribute__((altivec(vector__))) +__attribute__((altivec(pixel__))) unsigned short +__attribute__((altivec(bool__))) unsigned +@end smallexample + +These attributes mainly are intended to support the @code{__vector}, +@code{__pixel}, and @code{__bool} AltiVec keywords. + +@node x86 Type Attributes +@subsection x86 Type Attributes + +Two attributes are currently defined for x86 configurations: +@code{ms_struct} and @code{gcc_struct}. + +@table @code + +@item ms_struct +@itemx gcc_struct +@cindex @code{ms_struct} type attribute, x86 +@cindex @code{gcc_struct} type attribute, x86 + +If @code{packed} is used on a structure, or if bit-fields are used +it may be that the Microsoft ABI packs them differently +than GCC normally packs them. Particularly when moving packed +data between functions compiled with GCC and the native Microsoft compiler +(either via function call or as data in a file), it may be necessary to access +either format. + +The @code{ms_struct} and @code{gcc_struct} attributes correspond +to the @option{-mms-bitfields} and @option{-mno-ms-bitfields} +command-line options, respectively; +see @ref{x86 Options}, for details of how structure layout is affected. +@xref{x86 Variable Attributes}, for information about the corresponding +attributes on variables. + +@end table + +@node Label Attributes +@section Label Attributes +@cindex Label Attributes + +GCC allows attributes to be set on C labels. @xref{Attribute Syntax}, for +details of the exact syntax for using attributes. Other attributes are +available for functions (@pxref{Function Attributes}), variables +(@pxref{Variable Attributes}), enumerators (@pxref{Enumerator Attributes}), +statements (@pxref{Statement Attributes}), and for types +(@pxref{Type Attributes}). A label attribute followed +by a declaration appertains to the label and not the declaration. + +This example uses the @code{cold} label attribute to indicate the +@code{ErrorHandling} branch is unlikely to be taken and that the +@code{ErrorHandling} label is unused: + +@smallexample + + asm goto ("some asm" : : : : NoError); + +/* This branch (the fall-through from the asm) is less commonly used */ +ErrorHandling: + __attribute__((cold, unused)); /* Semi-colon is required here */ + printf("error\n"); + return 0; + +NoError: + printf("no error\n"); + return 1; +@end smallexample + +@table @code +@item unused +@cindex @code{unused} label attribute +This feature is intended for program-generated code that may contain +unused labels, but which is compiled with @option{-Wall}. It is +not normally appropriate to use in it human-written code, though it +could be useful in cases where the code that jumps to the label is +contained within an @code{#ifdef} conditional. + +@item hot +@cindex @code{hot} label attribute +The @code{hot} attribute on a label is used to inform the compiler that +the path following the label is more likely than paths that are not so +annotated. This attribute is used in cases where @code{__builtin_expect} +cannot be used, for instance with computed goto or @code{asm goto}. + +@item cold +@cindex @code{cold} label attribute +The @code{cold} attribute on labels is used to inform the compiler that +the path following the label is unlikely to be executed. This attribute +is used in cases where @code{__builtin_expect} cannot be used, for instance +with computed goto or @code{asm goto}. + +@end table + +@node Enumerator Attributes +@section Enumerator Attributes +@cindex Enumerator Attributes + +GCC allows attributes to be set on enumerators. @xref{Attribute Syntax}, for +details of the exact syntax for using attributes. Other attributes are +available for functions (@pxref{Function Attributes}), variables +(@pxref{Variable Attributes}), labels (@pxref{Label Attributes}), statements +(@pxref{Statement Attributes}), and for types (@pxref{Type Attributes}). + +This example uses the @code{deprecated} enumerator attribute to indicate the +@code{oldval} enumerator is deprecated: + +@smallexample +enum E @{ + oldval __attribute__((deprecated)), + newval +@}; + +int +fn (void) +@{ + return oldval; +@} +@end smallexample + +@table @code +@item deprecated +@cindex @code{deprecated} enumerator attribute +The @code{deprecated} attribute results in a warning if the enumerator +is used anywhere in the source file. This is useful when identifying +enumerators that are expected to be removed in a future version of a +program. The warning also includes the location of the declaration +of the deprecated enumerator, to enable users to easily find further +information about why the enumerator is deprecated, or what they should +do instead. Note that the warnings only occurs for uses. + +@item unavailable +@cindex @code{unavailable} enumerator attribute +The @code{unavailable} attribute results in an error if the enumerator +is used anywhere in the source file. In other respects it behaves in the +same manner as the @code{deprecated} attribute. + +@end table + +@node Statement Attributes +@section Statement Attributes +@cindex Statement Attributes + +GCC allows attributes to be set on null statements. @xref{Attribute Syntax}, +for details of the exact syntax for using attributes. Other attributes are +available for functions (@pxref{Function Attributes}), variables +(@pxref{Variable Attributes}), labels (@pxref{Label Attributes}), enumerators +(@pxref{Enumerator Attributes}), and for types (@pxref{Type Attributes}). + +@table @code +@item fallthrough +@cindex @code{fallthrough} statement attribute +The @code{fallthrough} attribute with a null statement serves as a +fallthrough statement. It hints to the compiler that a statement +that falls through to another case label, or user-defined label +in a switch statement is intentional and thus the +@option{-Wimplicit-fallthrough} warning must not trigger. The +fallthrough attribute may appear at most once in each attribute +list, and may not be mixed with other attributes. It can only +be used in a switch statement (the compiler will issue an error +otherwise), after a preceding statement and before a logically +succeeding case label, or user-defined label. + +This example uses the @code{fallthrough} statement attribute to indicate that +the @option{-Wimplicit-fallthrough} warning should not be emitted: + +@smallexample +switch (cond) + @{ + case 1: + bar (1); + __attribute__((fallthrough)); + case 2: + @dots{} + @} +@end smallexample + +@item assume +@cindex @code{assume} statement attribute +The @code{assume} attribute with a null statement serves as portable +assumption. It should have a single argument, a conditional expression, +which is not evaluated. If the argument would evaluate to true +at the point where it appears, it has no effect, otherwise there +is undefined behavior. This is a GNU variant of the ISO C++23 +standard @code{assume} attribute, but it can be used in any version of +both C and C++. + +@smallexample +int +foo (int x, int y) +@{ + __attribute__((assume(x == 42))); + __attribute__((assume(++y == 43))); + return x + y; +@} +@end smallexample + +@code{y} is not actually incremented and the compiler can but does not +have to optimize it to just @code{return 42 + 42;}. + +@end table + +@node Attribute Syntax +@section Attribute Syntax +@cindex attribute syntax + +This section describes the syntax with which @code{__attribute__} may be +used, and the constructs to which attribute specifiers bind, for the C +language. Some details may vary for C++ and Objective-C@. Because of +infelicities in the grammar for attributes, some forms described here +may not be successfully parsed in all cases. + +There are some problems with the semantics of attributes in C++. For +example, there are no manglings for attributes, although they may affect +code generation, so problems may arise when attributed types are used in +conjunction with templates or overloading. Similarly, @code{typeid} +does not distinguish between types with different attributes. Support +for attributes in C++ may be restricted in future to attributes on +declarations only, but not on nested declarators. + +@xref{Function Attributes}, for details of the semantics of attributes +applying to functions. @xref{Variable Attributes}, for details of the +semantics of attributes applying to variables. @xref{Type Attributes}, +for details of the semantics of attributes applying to structure, union +and enumerated types. +@xref{Label Attributes}, for details of the semantics of attributes +applying to labels. +@xref{Enumerator Attributes}, for details of the semantics of attributes +applying to enumerators. +@xref{Statement Attributes}, for details of the semantics of attributes +applying to statements. + +An @dfn{attribute specifier} is of the form +@code{__attribute__ ((@var{attribute-list}))}. An @dfn{attribute list} +is a possibly empty comma-separated sequence of @dfn{attributes}, where +each attribute is one of the following: + +@itemize @bullet +@item +Empty. Empty attributes are ignored. + +@item +An attribute name +(which may be an identifier such as @code{unused}, or a reserved +word such as @code{const}). + +@item +An attribute name followed by a parenthesized list of +parameters for the attribute. +These parameters take one of the following forms: + +@itemize @bullet +@item +An identifier. For example, @code{mode} attributes use this form. + +@item +An identifier followed by a comma and a non-empty comma-separated list +of expressions. For example, @code{format} attributes use this form. + +@item +A possibly empty comma-separated list of expressions. For example, +@code{format_arg} attributes use this form with the list being a single +integer constant expression, and @code{alias} attributes use this form +with the list being a single string constant. +@end itemize +@end itemize + +An @dfn{attribute specifier list} is a sequence of one or more attribute +specifiers, not separated by any other tokens. + +You may optionally specify attribute names with @samp{__} +preceding and following the name. +This allows you to use them in header files without +being concerned about a possible macro of the same name. For example, +you may use the attribute name @code{__noreturn__} instead of @code{noreturn}. + + +@subsubheading Label Attributes + +In GNU C, an attribute specifier list may appear after the colon following a +label, other than a @code{case} or @code{default} label. GNU C++ only permits +attributes on labels if the attribute specifier is immediately +followed by a semicolon (i.e., the label applies to an empty +statement). If the semicolon is missing, C++ label attributes are +ambiguous, as it is permissible for a declaration, which could begin +with an attribute list, to be labelled in C++. Declarations cannot be +labelled in C90 or C99, so the ambiguity does not arise there. + +@subsubheading Enumerator Attributes + +In GNU C, an attribute specifier list may appear as part of an enumerator. +The attribute goes after the enumeration constant, before @code{=}, if +present. The optional attribute in the enumerator appertains to the +enumeration constant. It is not possible to place the attribute after +the constant expression, if present. + +@subsubheading Statement Attributes +In GNU C, an attribute specifier list may appear as part of a null +statement. The attribute goes before the semicolon. + +@subsubheading Type Attributes + +An attribute specifier list may appear as part of a @code{struct}, +@code{union} or @code{enum} specifier. It may go either immediately +after the @code{struct}, @code{union} or @code{enum} keyword, or after +the closing brace. The former syntax is preferred. +Where attribute specifiers follow the closing brace, they are considered +to relate to the structure, union or enumerated type defined, not to any +enclosing declaration the type specifier appears in, and the type +defined is not complete until after the attribute specifiers. +@c Otherwise, there would be the following problems: a shift/reduce +@c conflict between attributes binding the struct/union/enum and +@c binding to the list of specifiers/qualifiers; and "aligned" +@c attributes could use sizeof for the structure, but the size could be +@c changed later by "packed" attributes. + + +@subsubheading All other attributes + +Otherwise, an attribute specifier appears as part of a declaration, +counting declarations of unnamed parameters and type names, and relates +to that declaration (which may be nested in another declaration, for +example in the case of a parameter declaration), or to a particular declarator +within a declaration. Where an +attribute specifier is applied to a parameter declared as a function or +an array, it should apply to the function or array rather than the +pointer to which the parameter is implicitly converted, but this is not +yet correctly implemented. + +Any list of specifiers and qualifiers at the start of a declaration may +contain attribute specifiers, whether or not such a list may in that +context contain storage class specifiers. (Some attributes, however, +are essentially in the nature of storage class specifiers, and only make +sense where storage class specifiers may be used; for example, +@code{section}.) There is one necessary limitation to this syntax: the +first old-style parameter declaration in a function definition cannot +begin with an attribute specifier, because such an attribute applies to +the function instead by syntax described below (which, however, is not +yet implemented in this case). In some other cases, attribute +specifiers are permitted by this grammar but not yet supported by the +compiler. All attribute specifiers in this place relate to the +declaration as a whole. In the obsolescent usage where a type of +@code{int} is implied by the absence of type specifiers, such a list of +specifiers and qualifiers may be an attribute specifier list with no +other specifiers or qualifiers. + +At present, the first parameter in a function prototype must have some +type specifier that is not an attribute specifier; this resolves an +ambiguity in the interpretation of @code{void f(int +(__attribute__((foo)) x))}, but is subject to change. At present, if +the parentheses of a function declarator contain only attributes then +those attributes are ignored, rather than yielding an error or warning +or implying a single parameter of type int, but this is subject to +change. + +An attribute specifier list may appear immediately before a declarator +(other than the first) in a comma-separated list of declarators in a +declaration of more than one identifier using a single list of +specifiers and qualifiers. Such attribute specifiers apply +only to the identifier before whose declarator they appear. For +example, in + +@smallexample +__attribute__((noreturn)) void d0 (void), + __attribute__((format(printf, 1, 2))) d1 (const char *, ...), + d2 (void); +@end smallexample + +@noindent +the @code{noreturn} attribute applies to all the functions +declared; the @code{format} attribute only applies to @code{d1}. + +An attribute specifier list may appear immediately before the comma, +@code{=} or semicolon terminating the declaration of an identifier other +than a function definition. Such attribute specifiers apply +to the declared object or function. Where an +assembler name for an object or function is specified (@pxref{Asm +Labels}), the attribute must follow the @code{asm} +specification. + +An attribute specifier list may, in future, be permitted to appear after +the declarator in a function definition (before any old-style parameter +declarations or the function body). + +Attribute specifiers may be mixed with type qualifiers appearing inside +the @code{[]} of a parameter array declarator, in the C99 construct by +which such qualifiers are applied to the pointer to which the array is +implicitly converted. Such attribute specifiers apply to the pointer, +not to the array, but at present this is not implemented and they are +ignored. + +An attribute specifier list may appear at the start of a nested +declarator. At present, there are some limitations in this usage: the +attributes correctly apply to the declarator, but for most individual +attributes the semantics this implies are not implemented. +When attribute specifiers follow the @code{*} of a pointer +declarator, they may be mixed with any type qualifiers present. +The following describes the formal semantics of this syntax. It makes the +most sense if you are familiar with the formal specification of +declarators in the ISO C standard. + +Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration @code{T +D1}, where @code{T} contains declaration specifiers that specify a type +@var{Type} (such as @code{int}) and @code{D1} is a declarator that +contains an identifier @var{ident}. The type specified for @var{ident} +for derived declarators whose type does not include an attribute +specifier is as in the ISO C standard. + +If @code{D1} has the form @code{( @var{attribute-specifier-list} D )}, +and the declaration @code{T D} specifies the type +``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then +@code{T D1} specifies the type ``@var{derived-declarator-type-list} +@var{attribute-specifier-list} @var{Type}'' for @var{ident}. + +If @code{D1} has the form @code{* +@var{type-qualifier-and-attribute-specifier-list} D}, and the +declaration @code{T D} specifies the type +``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then +@code{T D1} specifies the type ``@var{derived-declarator-type-list} +@var{type-qualifier-and-attribute-specifier-list} pointer to @var{Type}'' for +@var{ident}. + +For example, + +@smallexample +void (__attribute__((noreturn)) ****f) (void); +@end smallexample + +@noindent +specifies the type ``pointer to pointer to pointer to pointer to +non-returning function returning @code{void}''. As another example, + +@smallexample +char *__attribute__((aligned(8))) *f; +@end smallexample + +@noindent +specifies the type ``pointer to 8-byte-aligned pointer to @code{char}''. +Note again that this does not work with most attributes; for example, +the usage of @samp{aligned} and @samp{noreturn} attributes given above +is not yet supported. + +For compatibility with existing code written for compiler versions that +did not implement attributes on nested declarators, some laxity is +allowed in the placing of attributes. If an attribute that only applies +to types is applied to a declaration, it is treated as applying to +the type of that declaration. If an attribute that only applies to +declarations is applied to the type of a declaration, it is treated +as applying to that declaration; and, for compatibility with code +placing the attributes immediately before the identifier declared, such +an attribute applied to a function return type is treated as +applying to the function type, and such an attribute applied to an array +element type is treated as applying to the array type. If an +attribute that only applies to function types is applied to a +pointer-to-function type, it is treated as applying to the pointer +target type; if such an attribute is applied to a function return type +that is not a pointer-to-function type, it is treated as applying +to the function type. + +@node Function Prototypes +@section Prototypes and Old-Style Function Definitions +@cindex function prototype declarations +@cindex old-style function definitions +@cindex promotion of formal parameters + +GNU C extends ISO C to allow a function prototype to override a later +old-style non-prototype definition. Consider the following example: + +@smallexample +/* @r{Use prototypes unless the compiler is old-fashioned.} */ +#ifdef __STDC__ +#define P(x) x +#else +#define P(x) () +#endif + +/* @r{Prototype function declaration.} */ +int isroot P((uid_t)); + +/* @r{Old-style function definition.} */ +int +isroot (x) /* @r{??? lossage here ???} */ + uid_t x; +@{ + return x == 0; +@} +@end smallexample + +Suppose the type @code{uid_t} happens to be @code{short}. ISO C does +not allow this example, because subword arguments in old-style +non-prototype definitions are promoted. Therefore in this example the +function definition's argument is really an @code{int}, which does not +match the prototype argument type of @code{short}. + +This restriction of ISO C makes it hard to write code that is portable +to traditional C compilers, because the programmer does not know +whether the @code{uid_t} type is @code{short}, @code{int}, or +@code{long}. Therefore, in cases like these GNU C allows a prototype +to override a later old-style definition. More precisely, in GNU C, a +function prototype argument type overrides the argument type specified +by a later old-style definition if the former type is the same as the +latter type before promotion. Thus in GNU C the above example is +equivalent to the following: + +@smallexample +int isroot (uid_t); + +int +isroot (uid_t x) +@{ + return x == 0; +@} +@end smallexample + +@noindent +GNU C++ does not support old-style function definitions, so this +extension is irrelevant. + +@node C++ Comments +@section C++ Style Comments +@cindex @code{//} +@cindex C++ comments +@cindex comments, C++ style + +In GNU C, you may use C++ style comments, which start with @samp{//} and +continue until the end of the line. Many other C implementations allow +such comments, and they are included in the 1999 C standard. However, +C++ style comments are not recognized if you specify an @option{-std} +option specifying a version of ISO C before C99, or @option{-ansi} +(equivalent to @option{-std=c90}). + +@node Dollar Signs +@section Dollar Signs in Identifier Names +@cindex $ +@cindex dollar signs in identifier names +@cindex identifier names, dollar signs in + +In GNU C, you may normally use dollar signs in identifier names. +This is because many traditional C implementations allow such identifiers. +However, dollar signs in identifiers are not supported on a few target +machines, typically because the target assembler does not allow them. + +@node Character Escapes +@section The Character @key{ESC} in Constants + +You can use the sequence @samp{\e} in a string or character constant to +stand for the ASCII character @key{ESC}. + +@node Alignment +@section Determining the Alignment of Functions, Types or Variables +@cindex alignment +@cindex type alignment +@cindex variable alignment + +The keyword @code{__alignof__} determines the alignment requirement of +a function, object, or a type, or the minimum alignment usually required +by a type. Its syntax is just like @code{sizeof} and C11 @code{_Alignof}. + +For example, if the target machine requires a @code{double} value to be +aligned on an 8-byte boundary, then @code{__alignof__ (double)} is 8. +This is true on many RISC machines. On more traditional machine +designs, @code{__alignof__ (double)} is 4 or even 2. + +Some machines never actually require alignment; they allow references to any +data type even at an odd address. For these machines, @code{__alignof__} +reports the smallest alignment that GCC gives the data type, usually as +mandated by the target ABI. + +If the operand of @code{__alignof__} is an lvalue rather than a type, +its value is the required alignment for its type, taking into account +any minimum alignment specified by attribute @code{aligned} +(@pxref{Common Variable Attributes}). For example, after this +declaration: + +@smallexample +struct foo @{ int x; char y; @} foo1; +@end smallexample + +@noindent +the value of @code{__alignof__ (foo1.y)} is 1, even though its actual +alignment is probably 2 or 4, the same as @code{__alignof__ (int)}. +It is an error to ask for the alignment of an incomplete type other +than @code{void}. + +If the operand of the @code{__alignof__} expression is a function, +the expression evaluates to the alignment of the function which may +be specified by attribute @code{aligned} (@pxref{Common Function Attributes}). + +@node Inline +@section An Inline Function is As Fast As a Macro +@cindex inline functions +@cindex integrating function code +@cindex open coding +@cindex macros, inline alternative + +By declaring a function inline, you can direct GCC to make +calls to that function faster. One way GCC can achieve this is to +integrate that function's code into the code for its callers. This +makes execution faster by eliminating the function-call overhead; in +addition, if any of the actual argument values are constant, their +known values may permit simplifications at compile time so that not +all of the inline function's code needs to be included. The effect on +code size is less predictable; object code may be larger or smaller +with function inlining, depending on the particular case. You can +also direct GCC to try to integrate all ``simple enough'' functions +into their callers with the option @option{-finline-functions}. + +GCC implements three different semantics of declaring a function +inline. One is available with @option{-std=gnu89} or +@option{-fgnu89-inline} or when @code{gnu_inline} attribute is present +on all inline declarations, another when +@option{-std=c99}, +@option{-std=gnu99} or an option for a later C version is used +(without @option{-fgnu89-inline}), and the third +is used when compiling C++. + +To declare a function inline, use the @code{inline} keyword in its +declaration, like this: + +@smallexample +static inline int +inc (int *a) +@{ + return (*a)++; +@} +@end smallexample + +If you are writing a header file to be included in ISO C90 programs, write +@code{__inline__} instead of @code{inline}. @xref{Alternate Keywords}. + +The three types of inlining behave similarly in two important cases: +when the @code{inline} keyword is used on a @code{static} function, +like the example above, and when a function is first declared without +using the @code{inline} keyword and then is defined with +@code{inline}, like this: + +@smallexample +extern int inc (int *a); +inline int +inc (int *a) +@{ + return (*a)++; +@} +@end smallexample + +In both of these common cases, the program behaves the same as if you +had not used the @code{inline} keyword, except for its speed. + +@cindex inline functions, omission of +@opindex fkeep-inline-functions +When a function is both inline and @code{static}, if all calls to the +function are integrated into the caller, and the function's address is +never used, then the function's own assembler code is never referenced. +In this case, GCC does not actually output assembler code for the +function, unless you specify the option @option{-fkeep-inline-functions}. +If there is a nonintegrated call, then the function is compiled to +assembler code as usual. The function must also be compiled as usual if +the program refers to its address, because that cannot be inlined. + +@opindex Winline +Note that certain usages in a function definition can make it unsuitable +for inline substitution. Among these usages are: variadic functions, +use of @code{alloca}, use of computed goto (@pxref{Labels as Values}), +use of nonlocal goto, use of nested functions, use of @code{setjmp}, use +of @code{__builtin_longjmp} and use of @code{__builtin_return} or +@code{__builtin_apply_args}. Using @option{-Winline} warns when a +function marked @code{inline} could not be substituted, and gives the +reason for the failure. + +@cindex automatic @code{inline} for C++ member fns +@cindex @code{inline} automatic for C++ member fns +@cindex member fns, automatically @code{inline} +@cindex C++ member fns, automatically @code{inline} +@opindex fno-default-inline +As required by ISO C++, GCC considers member functions defined within +the body of a class to be marked inline even if they are +not explicitly declared with the @code{inline} keyword. You can +override this with @option{-fno-default-inline}; @pxref{C++ Dialect +Options,,Options Controlling C++ Dialect}. + +GCC does not inline any functions when not optimizing unless you specify +the @samp{always_inline} attribute for the function, like this: + +@smallexample +/* @r{Prototype.} */ +inline void foo (const char) __attribute__((always_inline)); +@end smallexample + +The remainder of this section is specific to GNU C90 inlining. + +@cindex non-static inline function +When an inline function is not @code{static}, then the compiler must assume +that there may be calls from other source files; since a global symbol can +be defined only once in any program, the function must not be defined in +the other source files, so the calls therein cannot be integrated. +Therefore, a non-@code{static} inline function is always compiled on its +own in the usual fashion. + +If you specify both @code{inline} and @code{extern} in the function +definition, then the definition is used only for inlining. In no case +is the function compiled on its own, not even if you refer to its +address explicitly. Such an address becomes an external reference, as +if you had only declared the function, and had not defined it. + +This combination of @code{inline} and @code{extern} has almost the +effect of a macro. The way to use it is to put a function definition in +a header file with these keywords, and put another copy of the +definition (lacking @code{inline} and @code{extern}) in a library file. +The definition in the header file causes most calls to the function +to be inlined. If any uses of the function remain, they refer to +the single copy in the library. + +@node Volatiles +@section When is a Volatile Object Accessed? +@cindex accessing volatiles +@cindex volatile read +@cindex volatile write +@cindex volatile access + +C has the concept of volatile objects. These are normally accessed by +pointers and used for accessing hardware or inter-thread +communication. The standard encourages compilers to refrain from +optimizations concerning accesses to volatile objects, but leaves it +implementation defined as to what constitutes a volatile access. The +minimum requirement is that at a sequence point all previous accesses +to volatile objects have stabilized and no subsequent accesses have +occurred. Thus an implementation is free to reorder and combine +volatile accesses that occur between sequence points, but cannot do +so for accesses across a sequence point. The use of volatile does +not allow you to violate the restriction on updating objects multiple +times between two sequence points. + +Accesses to non-volatile objects are not ordered with respect to +volatile accesses. You cannot use a volatile object as a memory +barrier to order a sequence of writes to non-volatile memory. For +instance: + +@smallexample +int *ptr = @var{something}; +volatile int vobj; +*ptr = @var{something}; +vobj = 1; +@end smallexample + +@noindent +Unless @var{*ptr} and @var{vobj} can be aliased, it is not guaranteed +that the write to @var{*ptr} occurs by the time the update +of @var{vobj} happens. If you need this guarantee, you must use +a stronger memory barrier such as: + +@smallexample +int *ptr = @var{something}; +volatile int vobj; +*ptr = @var{something}; +asm volatile ("" : : : "memory"); +vobj = 1; +@end smallexample + +A scalar volatile object is read when it is accessed in a void context: + +@smallexample +volatile int *src = @var{somevalue}; +*src; +@end smallexample + +Such expressions are rvalues, and GCC implements this as a +read of the volatile object being pointed to. + +Assignments are also expressions and have an rvalue. However when +assigning to a scalar volatile, the volatile object is not reread, +regardless of whether the assignment expression's rvalue is used or +not. If the assignment's rvalue is used, the value is that assigned +to the volatile object. For instance, there is no read of @var{vobj} +in all the following cases: + +@smallexample +int obj; +volatile int vobj; +vobj = @var{something}; +obj = vobj = @var{something}; +obj ? vobj = @var{onething} : vobj = @var{anotherthing}; +obj = (@var{something}, vobj = @var{anotherthing}); +@end smallexample + +If you need to read the volatile object after an assignment has +occurred, you must use a separate expression with an intervening +sequence point. + +As bit-fields are not individually addressable, volatile bit-fields may +be implicitly read when written to, or when adjacent bit-fields are +accessed. Bit-field operations may be optimized such that adjacent +bit-fields are only partially accessed, if they straddle a storage unit +boundary. For these reasons it is unwise to use volatile bit-fields to +access hardware. + +@node Using Assembly Language with C +@section How to Use Inline Assembly Language in C Code +@cindex @code{asm} keyword +@cindex assembly language in C +@cindex inline assembly language +@cindex mixing assembly language and C + +The @code{asm} keyword allows you to embed assembler instructions +within C code. GCC provides two forms of inline @code{asm} +statements. A @dfn{basic @code{asm}} statement is one with no +operands (@pxref{Basic Asm}), while an @dfn{extended @code{asm}} +statement (@pxref{Extended Asm}) includes one or more operands. +The extended form is preferred for mixing C and assembly language +within a function, but to include assembly language at +top level you must use basic @code{asm}. + +You can also use the @code{asm} keyword to override the assembler name +for a C symbol, or to place a C variable in a specific register. + +@menu +* Basic Asm:: Inline assembler without operands. +* Extended Asm:: Inline assembler with operands. +* Constraints:: Constraints for @code{asm} operands +* Asm Labels:: Specifying the assembler name to use for a C symbol. +* Explicit Register Variables:: Defining variables residing in specified + registers. +* Size of an asm:: How GCC calculates the size of an @code{asm} block. +@end menu + +@node Basic Asm +@subsection Basic Asm --- Assembler Instructions Without Operands +@cindex basic @code{asm} +@cindex assembly language in C, basic + +A basic @code{asm} statement has the following syntax: + +@example +asm @var{asm-qualifiers} ( @var{AssemblerInstructions} ) +@end example + +For the C language, the @code{asm} keyword is a GNU extension. +When writing C code that can be compiled with @option{-ansi} and the +@option{-std} options that select C dialects without GNU extensions, use +@code{__asm__} instead of @code{asm} (@pxref{Alternate Keywords}). For +the C++ language, @code{asm} is a standard keyword, but @code{__asm__} +can be used for code compiled with @option{-fno-asm}. + +@subsubheading Qualifiers +@table @code +@item volatile +The optional @code{volatile} qualifier has no effect. +All basic @code{asm} blocks are implicitly volatile. + +@item inline +If you use the @code{inline} qualifier, then for inlining purposes the size +of the @code{asm} statement is taken as the smallest size possible (@pxref{Size +of an asm}). +@end table + +@subsubheading Parameters +@table @var + +@item AssemblerInstructions +This is a literal string that specifies the assembler code. The string can +contain any instructions recognized by the assembler, including directives. +GCC does not parse the assembler instructions themselves and +does not know what they mean or even whether they are valid assembler input. + +You may place multiple assembler instructions together in a single @code{asm} +string, separated by the characters normally used in assembly code for the +system. A combination that works in most places is a newline to break the +line, plus a tab character (written as @samp{\n\t}). +Some assemblers allow semicolons as a line separator. However, +note that some assembler dialects use semicolons to start a comment. +@end table + +@subsubheading Remarks +Using extended @code{asm} (@pxref{Extended Asm}) typically produces +smaller, safer, and more efficient code, and in most cases it is a +better solution than basic @code{asm}. However, there are two +situations where only basic @code{asm} can be used: + +@itemize @bullet +@item +Extended @code{asm} statements have to be inside a C +function, so to write inline assembly language at file scope (``top-level''), +outside of C functions, you must use basic @code{asm}. +You can use this technique to emit assembler directives, +define assembly language macros that can be invoked elsewhere in the file, +or write entire functions in assembly language. +Basic @code{asm} statements outside of functions may not use any +qualifiers. + +@item +Functions declared +with the @code{naked} attribute also require basic @code{asm} +(@pxref{Function Attributes}). +@end itemize + +Safely accessing C data and calling functions from basic @code{asm} is more +complex than it may appear. To access C data, it is better to use extended +@code{asm}. + +Do not expect a sequence of @code{asm} statements to remain perfectly +consecutive after compilation. If certain instructions need to remain +consecutive in the output, put them in a single multi-instruction @code{asm} +statement. Note that GCC's optimizers can move @code{asm} statements +relative to other code, including across jumps. + +@code{asm} statements may not perform jumps into other @code{asm} statements. +GCC does not know about these jumps, and therefore cannot take +account of them when deciding how to optimize. Jumps from @code{asm} to C +labels are only supported in extended @code{asm}. + +Under certain circumstances, GCC may duplicate (or remove duplicates of) your +assembly code when optimizing. This can lead to unexpected duplicate +symbol errors during compilation if your assembly code defines symbols or +labels. + +@strong{Warning:} The C standards do not specify semantics for @code{asm}, +making it a potential source of incompatibilities between compilers. These +incompatibilities may not produce compiler warnings/errors. + +GCC does not parse basic @code{asm}'s @var{AssemblerInstructions}, which +means there is no way to communicate to the compiler what is happening +inside them. GCC has no visibility of symbols in the @code{asm} and may +discard them as unreferenced. It also does not know about side effects of +the assembler code, such as modifications to memory or registers. Unlike +some compilers, GCC assumes that no changes to general purpose registers +occur. This assumption may change in a future release. + +To avoid complications from future changes to the semantics and the +compatibility issues between compilers, consider replacing basic @code{asm} +with extended @code{asm}. See +@uref{https://gcc.gnu.org/wiki/ConvertBasicAsmToExtended, How to convert +from basic asm to extended asm} for information about how to perform this +conversion. + +The compiler copies the assembler instructions in a basic @code{asm} +verbatim to the assembly language output file, without +processing dialects or any of the @samp{%} operators that are available with +extended @code{asm}. This results in minor differences between basic +@code{asm} strings and extended @code{asm} templates. For example, to refer to +registers you might use @samp{%eax} in basic @code{asm} and +@samp{%%eax} in extended @code{asm}. + +On targets such as x86 that support multiple assembler dialects, +all basic @code{asm} blocks use the assembler dialect specified by the +@option{-masm} command-line option (@pxref{x86 Options}). +Basic @code{asm} provides no +mechanism to provide different assembler strings for different dialects. + +For basic @code{asm} with non-empty assembler string GCC assumes +the assembler block does not change any general purpose registers, +but it may read or write any globally accessible variable. + +Here is an example of basic @code{asm} for i386: + +@example +/* Note that this code will not compile with -masm=intel */ +#define DebugBreak() asm("int $3") +@end example + +@node Extended Asm +@subsection Extended Asm - Assembler Instructions with C Expression Operands +@cindex extended @code{asm} +@cindex assembly language in C, extended + +With extended @code{asm} you can read and write C variables from +assembler and perform jumps from assembler code to C labels. +Extended @code{asm} syntax uses colons (@samp{:}) to delimit +the operand parameters after the assembler template: + +@example +asm @var{asm-qualifiers} ( @var{AssemblerTemplate} + : @var{OutputOperands} + @r{[} : @var{InputOperands} + @r{[} : @var{Clobbers} @r{]} @r{]}) + +asm @var{asm-qualifiers} ( @var{AssemblerTemplate} + : @var{OutputOperands} + : @var{InputOperands} + : @var{Clobbers} + : @var{GotoLabels}) +@end example +where in the last form, @var{asm-qualifiers} contains @code{goto} (and in the +first form, not). + +The @code{asm} keyword is a GNU extension. +When writing code that can be compiled with @option{-ansi} and the +various @option{-std} options, use @code{__asm__} instead of +@code{asm} (@pxref{Alternate Keywords}). + +@subsubheading Qualifiers +@table @code + +@item volatile +The typical use of extended @code{asm} statements is to manipulate input +values to produce output values. However, your @code{asm} statements may +also produce side effects. If so, you may need to use the @code{volatile} +qualifier to disable certain optimizations. @xref{Volatile}. + +@item inline +If you use the @code{inline} qualifier, then for inlining purposes the size +of the @code{asm} statement is taken as the smallest size possible +(@pxref{Size of an asm}). + +@item goto +This qualifier informs the compiler that the @code{asm} statement may +perform a jump to one of the labels listed in the @var{GotoLabels}. +@xref{GotoLabels}. +@end table + +@subsubheading Parameters +@table @var +@item AssemblerTemplate +This is a literal string that is the template for the assembler code. It is a +combination of fixed text and tokens that refer to the input, output, +and goto parameters. @xref{AssemblerTemplate}. + +@item OutputOperands +A comma-separated list of the C variables modified by the instructions in the +@var{AssemblerTemplate}. An empty list is permitted. @xref{OutputOperands}. + +@item InputOperands +A comma-separated list of C expressions read by the instructions in the +@var{AssemblerTemplate}. An empty list is permitted. @xref{InputOperands}. + +@item Clobbers +A comma-separated list of registers or other values changed by the +@var{AssemblerTemplate}, beyond those listed as outputs. +An empty list is permitted. @xref{Clobbers and Scratch Registers}. + +@item GotoLabels +When you are using the @code{goto} form of @code{asm}, this section contains +the list of all C labels to which the code in the +@var{AssemblerTemplate} may jump. +@xref{GotoLabels}. + +@code{asm} statements may not perform jumps into other @code{asm} statements, +only to the listed @var{GotoLabels}. +GCC's optimizers do not know about other jumps; therefore they cannot take +account of them when deciding how to optimize. +@end table + +The total number of input + output + goto operands is limited to 30. + +@subsubheading Remarks +The @code{asm} statement allows you to include assembly instructions directly +within C code. This may help you to maximize performance in time-sensitive +code or to access assembly instructions that are not readily available to C +programs. + +Note that extended @code{asm} statements must be inside a function. Only +basic @code{asm} may be outside functions (@pxref{Basic Asm}). +Functions declared with the @code{naked} attribute also require basic +@code{asm} (@pxref{Function Attributes}). + +While the uses of @code{asm} are many and varied, it may help to think of an +@code{asm} statement as a series of low-level instructions that convert input +parameters to output parameters. So a simple (if not particularly useful) +example for i386 using @code{asm} might look like this: + +@example +int src = 1; +int dst; + +asm ("mov %1, %0\n\t" + "add $1, %0" + : "=r" (dst) + : "r" (src)); + +printf("%d\n", dst); +@end example + +This code copies @code{src} to @code{dst} and add 1 to @code{dst}. + +@anchor{Volatile} +@subsubsection Volatile +@cindex volatile @code{asm} +@cindex @code{asm} volatile + +GCC's optimizers sometimes discard @code{asm} statements if they determine +there is no need for the output variables. Also, the optimizers may move +code out of loops if they believe that the code will always return the same +result (i.e.@: none of its input values change between calls). Using the +@code{volatile} qualifier disables these optimizations. @code{asm} statements +that have no output operands and @code{asm goto} statements, +are implicitly volatile. + +This i386 code demonstrates a case that does not use (or require) the +@code{volatile} qualifier. If it is performing assertion checking, this code +uses @code{asm} to perform the validation. Otherwise, @code{dwRes} is +unreferenced by any code. As a result, the optimizers can discard the +@code{asm} statement, which in turn removes the need for the entire +@code{DoCheck} routine. By omitting the @code{volatile} qualifier when it +isn't needed you allow the optimizers to produce the most efficient code +possible. + +@example +void DoCheck(uint32_t dwSomeValue) +@{ + uint32_t dwRes; + + // Assumes dwSomeValue is not zero. + asm ("bsfl %1,%0" + : "=r" (dwRes) + : "r" (dwSomeValue) + : "cc"); + + assert(dwRes > 3); +@} +@end example + +The next example shows a case where the optimizers can recognize that the input +(@code{dwSomeValue}) never changes during the execution of the function and can +therefore move the @code{asm} outside the loop to produce more efficient code. +Again, using the @code{volatile} qualifier disables this type of optimization. + +@example +void do_print(uint32_t dwSomeValue) +@{ + uint32_t dwRes; + + for (uint32_t x=0; x < 5; x++) + @{ + // Assumes dwSomeValue is not zero. + asm ("bsfl %1,%0" + : "=r" (dwRes) + : "r" (dwSomeValue) + : "cc"); + + printf("%u: %u %u\n", x, dwSomeValue, dwRes); + @} +@} +@end example + +The following example demonstrates a case where you need to use the +@code{volatile} qualifier. +It uses the x86 @code{rdtsc} instruction, which reads +the computer's time-stamp counter. Without the @code{volatile} qualifier, +the optimizers might assume that the @code{asm} block will always return the +same value and therefore optimize away the second call. + +@example +uint64_t msr; + +asm volatile ( "rdtsc\n\t" // Returns the time in EDX:EAX. + "shl $32, %%rdx\n\t" // Shift the upper bits left. + "or %%rdx, %0" // 'Or' in the lower bits. + : "=a" (msr) + : + : "rdx"); + +printf("msr: %llx\n", msr); + +// Do other work... + +// Reprint the timestamp +asm volatile ( "rdtsc\n\t" // Returns the time in EDX:EAX. + "shl $32, %%rdx\n\t" // Shift the upper bits left. + "or %%rdx, %0" // 'Or' in the lower bits. + : "=a" (msr) + : + : "rdx"); + +printf("msr: %llx\n", msr); +@end example + +GCC's optimizers do not treat this code like the non-volatile code in the +earlier examples. They do not move it out of loops or omit it on the +assumption that the result from a previous call is still valid. + +Note that the compiler can move even @code{volatile asm} instructions relative +to other code, including across jump instructions. For example, on many +targets there is a system register that controls the rounding mode of +floating-point operations. Setting it with a @code{volatile asm} statement, +as in the following PowerPC example, does not work reliably. + +@example +asm volatile("mtfsf 255, %0" : : "f" (fpenv)); +sum = x + y; +@end example + +The compiler may move the addition back before the @code{volatile asm} +statement. To make it work as expected, add an artificial dependency to +the @code{asm} by referencing a variable in the subsequent code, for +example: + +@example +asm volatile ("mtfsf 255,%1" : "=X" (sum) : "f" (fpenv)); +sum = x + y; +@end example + +Under certain circumstances, GCC may duplicate (or remove duplicates of) your +assembly code when optimizing. This can lead to unexpected duplicate symbol +errors during compilation if your @code{asm} code defines symbols or labels. +Using @samp{%=} +(@pxref{AssemblerTemplate}) may help resolve this problem. + +@anchor{AssemblerTemplate} +@subsubsection Assembler Template +@cindex @code{asm} assembler template + +An assembler template is a literal string containing assembler instructions. +The compiler replaces tokens in the template that refer +to inputs, outputs, and goto labels, +and then outputs the resulting string to the assembler. The +string can contain any instructions recognized by the assembler, including +directives. GCC does not parse the assembler instructions +themselves and does not know what they mean or even whether they are valid +assembler input. However, it does count the statements +(@pxref{Size of an asm}). + +You may place multiple assembler instructions together in a single @code{asm} +string, separated by the characters normally used in assembly code for the +system. A combination that works in most places is a newline to break the +line, plus a tab character to move to the instruction field (written as +@samp{\n\t}). +Some assemblers allow semicolons as a line separator. However, note +that some assembler dialects use semicolons to start a comment. + +Do not expect a sequence of @code{asm} statements to remain perfectly +consecutive after compilation, even when you are using the @code{volatile} +qualifier. If certain instructions need to remain consecutive in the output, +put them in a single multi-instruction @code{asm} statement. + +Accessing data from C programs without using input/output operands (such as +by using global symbols directly from the assembler template) may not work as +expected. Similarly, calling functions directly from an assembler template +requires a detailed understanding of the target assembler and ABI. + +Since GCC does not parse the assembler template, +it has no visibility of any +symbols it references. This may result in GCC discarding those symbols as +unreferenced unless they are also listed as input, output, or goto operands. + +@subsubheading Special format strings + +In addition to the tokens described by the input, output, and goto operands, +these tokens have special meanings in the assembler template: + +@table @samp +@item %% +Outputs a single @samp{%} into the assembler code. + +@item %= +Outputs a number that is unique to each instance of the @code{asm} +statement in the entire compilation. This option is useful when creating local +labels and referring to them multiple times in a single template that +generates multiple assembler instructions. + +@item %@{ +@itemx %| +@itemx %@} +Outputs @samp{@{}, @samp{|}, and @samp{@}} characters (respectively) +into the assembler code. When unescaped, these characters have special +meaning to indicate multiple assembler dialects, as described below. +@end table + +@subsubheading Multiple assembler dialects in @code{asm} templates + +On targets such as x86, GCC supports multiple assembler dialects. +The @option{-masm} option controls which dialect GCC uses as its +default for inline assembler. The target-specific documentation for the +@option{-masm} option contains the list of supported dialects, as well as the +default dialect if the option is not specified. This information may be +important to understand, since assembler code that works correctly when +compiled using one dialect will likely fail if compiled using another. +@xref{x86 Options}. + +If your code needs to support multiple assembler dialects (for example, if +you are writing public headers that need to support a variety of compilation +options), use constructs of this form: + +@example +@{ dialect0 | dialect1 | dialect2... @} +@end example + +This construct outputs @code{dialect0} +when using dialect #0 to compile the code, +@code{dialect1} for dialect #1, etc. If there are fewer alternatives within the +braces than the number of dialects the compiler supports, the construct +outputs nothing. + +For example, if an x86 compiler supports two dialects +(@samp{att}, @samp{intel}), an +assembler template such as this: + +@example +"bt@{l %[Offset],%[Base] | %[Base],%[Offset]@}; jc %l2" +@end example + +@noindent +is equivalent to one of + +@example +"btl %[Offset],%[Base] ; jc %l2" @r{/* att dialect */} +"bt %[Base],%[Offset]; jc %l2" @r{/* intel dialect */} +@end example + +Using that same compiler, this code: + +@example +"xchg@{l@}\t@{%%@}ebx, %1" +@end example + +@noindent +corresponds to either + +@example +"xchgl\t%%ebx, %1" @r{/* att dialect */} +"xchg\tebx, %1" @r{/* intel dialect */} +@end example + +There is no support for nesting dialect alternatives. + +@anchor{OutputOperands} +@subsubsection Output Operands +@cindex @code{asm} output operands + +An @code{asm} statement has zero or more output operands indicating the names +of C variables modified by the assembler code. + +In this i386 example, @code{old} (referred to in the template string as +@code{%0}) and @code{*Base} (as @code{%1}) are outputs and @code{Offset} +(@code{%2}) is an input: + +@example +bool old; + +__asm__ ("btsl %2,%1\n\t" // Turn on zero-based bit #Offset in Base. + "sbb %0,%0" // Use the CF to calculate old. + : "=r" (old), "+rm" (*Base) + : "Ir" (Offset) + : "cc"); + +return old; +@end example + +Operands are separated by commas. Each operand has this format: + +@example +@r{[} [@var{asmSymbolicName}] @r{]} @var{constraint} (@var{cvariablename}) +@end example + +@table @var +@item asmSymbolicName +Specifies a symbolic name for the operand. +Reference the name in the assembler template +by enclosing it in square brackets +(i.e.@: @samp{%[Value]}). The scope of the name is the @code{asm} statement +that contains the definition. Any valid C variable name is acceptable, +including names already defined in the surrounding code. No two operands +within the same @code{asm} statement can use the same symbolic name. + +When not using an @var{asmSymbolicName}, use the (zero-based) position +of the operand +in the list of operands in the assembler template. For example if there are +three output operands, use @samp{%0} in the template to refer to the first, +@samp{%1} for the second, and @samp{%2} for the third. + +@item constraint +A string constant specifying constraints on the placement of the operand; +@xref{Constraints}, for details. + +Output constraints must begin with either @samp{=} (a variable overwriting an +existing value) or @samp{+} (when reading and writing). When using +@samp{=}, do not assume the location contains the existing value +on entry to the @code{asm}, except +when the operand is tied to an input; @pxref{InputOperands,,Input Operands}. + +After the prefix, there must be one or more additional constraints +(@pxref{Constraints}) that describe where the value resides. Common +constraints include @samp{r} for register and @samp{m} for memory. +When you list more than one possible location (for example, @code{"=rm"}), +the compiler chooses the most efficient one based on the current context. +If you list as many alternates as the @code{asm} statement allows, you permit +the optimizers to produce the best possible code. +If you must use a specific register, but your Machine Constraints do not +provide sufficient control to select the specific register you want, +local register variables may provide a solution (@pxref{Local Register +Variables}). + +@item cvariablename +Specifies a C lvalue expression to hold the output, typically a variable name. +The enclosing parentheses are a required part of the syntax. + +@end table + +When the compiler selects the registers to use to +represent the output operands, it does not use any of the clobbered registers +(@pxref{Clobbers and Scratch Registers}). + +Output operand expressions must be lvalues. The compiler cannot check whether +the operands have data types that are reasonable for the instruction being +executed. For output expressions that are not directly addressable (for +example a bit-field), the constraint must allow a register. In that case, GCC +uses the register as the output of the @code{asm}, and then stores that +register into the output. + +Operands using the @samp{+} constraint modifier count as two operands +(that is, both as input and output) towards the total maximum of 30 operands +per @code{asm} statement. + +Use the @samp{&} constraint modifier (@pxref{Modifiers}) on all output +operands that must not overlap an input. Otherwise, +GCC may allocate the output operand in the same register as an unrelated +input operand, on the assumption that the assembler code consumes its +inputs before producing outputs. This assumption may be false if the assembler +code actually consists of more than one instruction. + +The same problem can occur if one output parameter (@var{a}) allows a register +constraint and another output parameter (@var{b}) allows a memory constraint. +The code generated by GCC to access the memory address in @var{b} can contain +registers which @emph{might} be shared by @var{a}, and GCC considers those +registers to be inputs to the asm. As above, GCC assumes that such input +registers are consumed before any outputs are written. This assumption may +result in incorrect behavior if the @code{asm} statement writes to @var{a} +before using +@var{b}. Combining the @samp{&} modifier with the register constraint on @var{a} +ensures that modifying @var{a} does not affect the address referenced by +@var{b}. Otherwise, the location of @var{b} +is undefined if @var{a} is modified before using @var{b}. + +@code{asm} supports operand modifiers on operands (for example @samp{%k2} +instead of simply @samp{%2}). Typically these qualifiers are hardware +dependent. The list of supported modifiers for x86 is found at +@ref{x86Operandmodifiers,x86 Operand modifiers}. + +If the C code that follows the @code{asm} makes no use of any of the output +operands, use @code{volatile} for the @code{asm} statement to prevent the +optimizers from discarding the @code{asm} statement as unneeded +(see @ref{Volatile}). + +This code makes no use of the optional @var{asmSymbolicName}. Therefore it +references the first output operand as @code{%0} (were there a second, it +would be @code{%1}, etc). The number of the first input operand is one greater +than that of the last output operand. In this i386 example, that makes +@code{Mask} referenced as @code{%1}: + +@example +uint32_t Mask = 1234; +uint32_t Index; + + asm ("bsfl %1, %0" + : "=r" (Index) + : "r" (Mask) + : "cc"); +@end example + +That code overwrites the variable @code{Index} (@samp{=}), +placing the value in a register (@samp{r}). +Using the generic @samp{r} constraint instead of a constraint for a specific +register allows the compiler to pick the register to use, which can result +in more efficient code. This may not be possible if an assembler instruction +requires a specific register. + +The following i386 example uses the @var{asmSymbolicName} syntax. +It produces the +same result as the code above, but some may consider it more readable or more +maintainable since reordering index numbers is not necessary when adding or +removing operands. The names @code{aIndex} and @code{aMask} +are only used in this example to emphasize which +names get used where. +It is acceptable to reuse the names @code{Index} and @code{Mask}. + +@example +uint32_t Mask = 1234; +uint32_t Index; + + asm ("bsfl %[aMask], %[aIndex]" + : [aIndex] "=r" (Index) + : [aMask] "r" (Mask) + : "cc"); +@end example + +Here are some more examples of output operands. + +@example +uint32_t c = 1; +uint32_t d; +uint32_t *e = &c; + +asm ("mov %[e], %[d]" + : [d] "=rm" (d) + : [e] "rm" (*e)); +@end example + +Here, @code{d} may either be in a register or in memory. Since the compiler +might already have the current value of the @code{uint32_t} location +pointed to by @code{e} +in a register, you can enable it to choose the best location +for @code{d} by specifying both constraints. + +@anchor{FlagOutputOperands} +@subsubsection Flag Output Operands +@cindex @code{asm} flag output operands + +Some targets have a special register that holds the ``flags'' for the +result of an operation or comparison. Normally, the contents of that +register are either unmodifed by the asm, or the @code{asm} statement is +considered to clobber the contents. + +On some targets, a special form of output operand exists by which +conditions in the flags register may be outputs of the asm. The set of +conditions supported are target specific, but the general rule is that +the output variable must be a scalar integer, and the value is boolean. +When supported, the target defines the preprocessor symbol +@code{__GCC_ASM_FLAG_OUTPUTS__}. + +Because of the special nature of the flag output operands, the constraint +may not include alternatives. + +Most often, the target has only one flags register, and thus is an implied +operand of many instructions. In this case, the operand should not be +referenced within the assembler template via @code{%0} etc, as there's +no corresponding text in the assembly language. + +@table @asis +@item ARM +@itemx AArch64 +The flag output constraints for the ARM family are of the form +@samp{=@@cc@var{cond}} where @var{cond} is one of the standard +conditions defined in the ARM ARM for @code{ConditionHolds}. + +@table @code +@item eq +Z flag set, or equal +@item ne +Z flag clear or not equal +@item cs +@itemx hs +C flag set or unsigned greater than equal +@item cc +@itemx lo +C flag clear or unsigned less than +@item mi +N flag set or ``minus'' +@item pl +N flag clear or ``plus'' +@item vs +V flag set or signed overflow +@item vc +V flag clear +@item hi +unsigned greater than +@item ls +unsigned less than equal +@item ge +signed greater than equal +@item lt +signed less than +@item gt +signed greater than +@item le +signed less than equal +@end table + +The flag output constraints are not supported in thumb1 mode. + +@item x86 family +The flag output constraints for the x86 family are of the form +@samp{=@@cc@var{cond}} where @var{cond} is one of the standard +conditions defined in the ISA manual for @code{j@var{cc}} or +@code{set@var{cc}}. + +@table @code +@item a +``above'' or unsigned greater than +@item ae +``above or equal'' or unsigned greater than or equal +@item b +``below'' or unsigned less than +@item be +``below or equal'' or unsigned less than or equal +@item c +carry flag set +@item e +@itemx z +``equal'' or zero flag set +@item g +signed greater than +@item ge +signed greater than or equal +@item l +signed less than +@item le +signed less than or equal +@item o +overflow flag set +@item p +parity flag set +@item s +sign flag set +@item na +@itemx nae +@itemx nb +@itemx nbe +@itemx nc +@itemx ne +@itemx ng +@itemx nge +@itemx nl +@itemx nle +@itemx no +@itemx np +@itemx ns +@itemx nz +``not'' @var{flag}, or inverted versions of those above +@end table + +@end table + +@anchor{InputOperands} +@subsubsection Input Operands +@cindex @code{asm} input operands +@cindex @code{asm} expressions + +Input operands make values from C variables and expressions available to the +assembly code. + +Operands are separated by commas. Each operand has this format: + +@example +@r{[} [@var{asmSymbolicName}] @r{]} @var{constraint} (@var{cexpression}) +@end example + +@table @var +@item asmSymbolicName +Specifies a symbolic name for the operand. +Reference the name in the assembler template +by enclosing it in square brackets +(i.e.@: @samp{%[Value]}). The scope of the name is the @code{asm} statement +that contains the definition. Any valid C variable name is acceptable, +including names already defined in the surrounding code. No two operands +within the same @code{asm} statement can use the same symbolic name. + +When not using an @var{asmSymbolicName}, use the (zero-based) position +of the operand +in the list of operands in the assembler template. For example if there are +two output operands and three inputs, +use @samp{%2} in the template to refer to the first input operand, +@samp{%3} for the second, and @samp{%4} for the third. + +@item constraint +A string constant specifying constraints on the placement of the operand; +@xref{Constraints}, for details. + +Input constraint strings may not begin with either @samp{=} or @samp{+}. +When you list more than one possible location (for example, @samp{"irm"}), +the compiler chooses the most efficient one based on the current context. +If you must use a specific register, but your Machine Constraints do not +provide sufficient control to select the specific register you want, +local register variables may provide a solution (@pxref{Local Register +Variables}). + +Input constraints can also be digits (for example, @code{"0"}). This indicates +that the specified input must be in the same place as the output constraint +at the (zero-based) index in the output constraint list. +When using @var{asmSymbolicName} syntax for the output operands, +you may use these names (enclosed in brackets @samp{[]}) instead of digits. + +@item cexpression +This is the C variable or expression being passed to the @code{asm} statement +as input. The enclosing parentheses are a required part of the syntax. + +@end table + +When the compiler selects the registers to use to represent the input +operands, it does not use any of the clobbered registers +(@pxref{Clobbers and Scratch Registers}). + +If there are no output operands but there are input operands, place two +consecutive colons where the output operands would go: + +@example +__asm__ ("some instructions" + : /* No outputs. */ + : "r" (Offset / 8)); +@end example + +@strong{Warning:} Do @emph{not} modify the contents of input-only operands +(except for inputs tied to outputs). The compiler assumes that on exit from +the @code{asm} statement these operands contain the same values as they +had before executing the statement. +It is @emph{not} possible to use clobbers +to inform the compiler that the values in these inputs are changing. One +common work-around is to tie the changing input variable to an output variable +that never gets used. Note, however, that if the code that follows the +@code{asm} statement makes no use of any of the output operands, the GCC +optimizers may discard the @code{asm} statement as unneeded +(see @ref{Volatile}). + +@code{asm} supports operand modifiers on operands (for example @samp{%k2} +instead of simply @samp{%2}). Typically these qualifiers are hardware +dependent. The list of supported modifiers for x86 is found at +@ref{x86Operandmodifiers,x86 Operand modifiers}. + +In this example using the fictitious @code{combine} instruction, the +constraint @code{"0"} for input operand 1 says that it must occupy the same +location as output operand 0. Only input operands may use numbers in +constraints, and they must each refer to an output operand. Only a number (or +the symbolic assembler name) in the constraint can guarantee that one operand +is in the same place as another. The mere fact that @code{foo} is the value of +both operands is not enough to guarantee that they are in the same place in +the generated assembler code. + +@example +asm ("combine %2, %0" + : "=r" (foo) + : "0" (foo), "g" (bar)); +@end example + +Here is an example using symbolic names. + +@example +asm ("cmoveq %1, %2, %[result]" + : [result] "=r"(result) + : "r" (test), "r" (new), "[result]" (old)); +@end example + +@anchor{Clobbers and Scratch Registers} +@subsubsection Clobbers and Scratch Registers +@cindex @code{asm} clobbers +@cindex @code{asm} scratch registers + +While the compiler is aware of changes to entries listed in the output +operands, the inline @code{asm} code may modify more than just the outputs. For +example, calculations may require additional registers, or the processor may +overwrite a register as a side effect of a particular assembler instruction. +In order to inform the compiler of these changes, list them in the clobber +list. Clobber list items are either register names or the special clobbers +(listed below). Each clobber list item is a string constant +enclosed in double quotes and separated by commas. + +Clobber descriptions may not in any way overlap with an input or output +operand. For example, you may not have an operand describing a register class +with one member when listing that register in the clobber list. Variables +declared to live in specific registers (@pxref{Explicit Register +Variables}) and used +as @code{asm} input or output operands must have no part mentioned in the +clobber description. In particular, there is no way to specify that input +operands get modified without also specifying them as output operands. + +When the compiler selects which registers to use to represent input and output +operands, it does not use any of the clobbered registers. As a result, +clobbered registers are available for any use in the assembler code. + +Another restriction is that the clobber list should not contain the +stack pointer register. This is because the compiler requires the +value of the stack pointer to be the same after an @code{asm} +statement as it was on entry to the statement. However, previous +versions of GCC did not enforce this rule and allowed the stack +pointer to appear in the list, with unclear semantics. This behavior +is deprecated and listing the stack pointer may become an error in +future versions of GCC@. + +Here is a realistic example for the VAX showing the use of clobbered +registers: + +@example +asm volatile ("movc3 %0, %1, %2" + : /* No outputs. */ + : "g" (from), "g" (to), "g" (count) + : "r0", "r1", "r2", "r3", "r4", "r5", "memory"); +@end example + +Also, there are two special clobber arguments: + +@table @code +@item "cc" +The @code{"cc"} clobber indicates that the assembler code modifies the flags +register. On some machines, GCC represents the condition codes as a specific +hardware register; @code{"cc"} serves to name this register. +On other machines, condition code handling is different, +and specifying @code{"cc"} has no effect. But +it is valid no matter what the target. + +@item "memory" +The @code{"memory"} clobber tells the compiler that the assembly code +performs memory +reads or writes to items other than those listed in the input and output +operands (for example, accessing the memory pointed to by one of the input +parameters). To ensure memory contains correct values, GCC may need to flush +specific register values to memory before executing the @code{asm}. Further, +the compiler does not assume that any values read from memory before an +@code{asm} remain unchanged after that @code{asm}; it reloads them as +needed. +Using the @code{"memory"} clobber effectively forms a read/write +memory barrier for the compiler. + +Note that this clobber does not prevent the @emph{processor} from doing +speculative reads past the @code{asm} statement. To prevent that, you need +processor-specific fence instructions. + +@end table + +Flushing registers to memory has performance implications and may be +an issue for time-sensitive code. You can provide better information +to GCC to avoid this, as shown in the following examples. At a +minimum, aliasing rules allow GCC to know what memory @emph{doesn't} +need to be flushed. + +Here is a fictitious sum of squares instruction, that takes two +pointers to floating point values in memory and produces a floating +point register output. +Notice that @code{x}, and @code{y} both appear twice in the @code{asm} +parameters, once to specify memory accessed, and once to specify a +base register used by the @code{asm}. You won't normally be wasting a +register by doing this as GCC can use the same register for both +purposes. However, it would be foolish to use both @code{%1} and +@code{%3} for @code{x} in this @code{asm} and expect them to be the +same. In fact, @code{%3} may well not be a register. It might be a +symbolic memory reference to the object pointed to by @code{x}. + +@smallexample +asm ("sumsq %0, %1, %2" + : "+f" (result) + : "r" (x), "r" (y), "m" (*x), "m" (*y)); +@end smallexample + +Here is a fictitious @code{*z++ = *x++ * *y++} instruction. +Notice that the @code{x}, @code{y} and @code{z} pointer registers +must be specified as input/output because the @code{asm} modifies +them. + +@smallexample +asm ("vecmul %0, %1, %2" + : "+r" (z), "+r" (x), "+r" (y), "=m" (*z) + : "m" (*x), "m" (*y)); +@end smallexample + +An x86 example where the string memory argument is of unknown length. + +@smallexample +asm("repne scasb" + : "=c" (count), "+D" (p) + : "m" (*(const char (*)[]) p), "0" (-1), "a" (0)); +@end smallexample + +If you know the above will only be reading a ten byte array then you +could instead use a memory input like: +@code{"m" (*(const char (*)[10]) p)}. + +Here is an example of a PowerPC vector scale implemented in assembly, +complete with vector and condition code clobbers, and some initialized +offset registers that are unchanged by the @code{asm}. + +@smallexample +void +dscal (size_t n, double *x, double alpha) +@{ + asm ("/* lots of asm here */" + : "+m" (*(double (*)[n]) x), "+&r" (n), "+b" (x) + : "d" (alpha), "b" (32), "b" (48), "b" (64), + "b" (80), "b" (96), "b" (112) + : "cr0", + "vs32","vs33","vs34","vs35","vs36","vs37","vs38","vs39", + "vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47"); +@} +@end smallexample + +Rather than allocating fixed registers via clobbers to provide scratch +registers for an @code{asm} statement, an alternative is to define a +variable and make it an early-clobber output as with @code{a2} and +@code{a3} in the example below. This gives the compiler register +allocator more freedom. You can also define a variable and make it an +output tied to an input as with @code{a0} and @code{a1}, tied +respectively to @code{ap} and @code{lda}. Of course, with tied +outputs your @code{asm} can't use the input value after modifying the +output register since they are one and the same register. What's +more, if you omit the early-clobber on the output, it is possible that +GCC might allocate the same register to another of the inputs if GCC +could prove they had the same value on entry to the @code{asm}. This +is why @code{a1} has an early-clobber. Its tied input, @code{lda} +might conceivably be known to have the value 16 and without an +early-clobber share the same register as @code{%11}. On the other +hand, @code{ap} can't be the same as any of the other inputs, so an +early-clobber on @code{a0} is not needed. It is also not desirable in +this case. An early-clobber on @code{a0} would cause GCC to allocate +a separate register for the @code{"m" (*(const double (*)[]) ap)} +input. Note that tying an input to an output is the way to set up an +initialized temporary register modified by an @code{asm} statement. +An input not tied to an output is assumed by GCC to be unchanged, for +example @code{"b" (16)} below sets up @code{%11} to 16, and GCC might +use that register in following code if the value 16 happened to be +needed. You can even use a normal @code{asm} output for a scratch if +all inputs that might share the same register are consumed before the +scratch is used. The VSX registers clobbered by the @code{asm} +statement could have used this technique except for GCC's limit on the +number of @code{asm} parameters. + +@smallexample +static void +dgemv_kernel_4x4 (long n, const double *ap, long lda, + const double *x, double *y, double alpha) +@{ + double *a0; + double *a1; + double *a2; + double *a3; + + __asm__ + ( + /* lots of asm here */ + "#n=%1 ap=%8=%12 lda=%13 x=%7=%10 y=%0=%2 alpha=%9 o16=%11\n" + "#a0=%3 a1=%4 a2=%5 a3=%6" + : + "+m" (*(double (*)[n]) y), + "+&r" (n), // 1 + "+b" (y), // 2 + "=b" (a0), // 3 + "=&b" (a1), // 4 + "=&b" (a2), // 5 + "=&b" (a3) // 6 + : + "m" (*(const double (*)[n]) x), + "m" (*(const double (*)[]) ap), + "d" (alpha), // 9 + "r" (x), // 10 + "b" (16), // 11 + "3" (ap), // 12 + "4" (lda) // 13 + : + "cr0", + "vs32","vs33","vs34","vs35","vs36","vs37", + "vs40","vs41","vs42","vs43","vs44","vs45","vs46","vs47" + ); +@} +@end smallexample + +@anchor{GotoLabels} +@subsubsection Goto Labels +@cindex @code{asm} goto labels + +@code{asm goto} allows assembly code to jump to one or more C labels. The +@var{GotoLabels} section in an @code{asm goto} statement contains +a comma-separated +list of all C labels to which the assembler code may jump. GCC assumes that +@code{asm} execution falls through to the next statement (if this is not the +case, consider using the @code{__builtin_unreachable} intrinsic after the +@code{asm} statement). Optimization of @code{asm goto} may be improved by +using the @code{hot} and @code{cold} label attributes (@pxref{Label +Attributes}). + +If the assembler code does modify anything, use the @code{"memory"} clobber +to force the +optimizers to flush all register values to memory and reload them if +necessary after the @code{asm} statement. + +Also note that an @code{asm goto} statement is always implicitly +considered volatile. + +Be careful when you set output operands inside @code{asm goto} only on +some possible control flow paths. If you don't set up the output on +given path and never use it on this path, it is okay. Otherwise, you +should use @samp{+} constraint modifier meaning that the operand is +input and output one. With this modifier you will have the correct +values on all possible paths from the @code{asm goto}. + +To reference a label in the assembler template, prefix it with +@samp{%l} (lowercase @samp{L}) followed by its (zero-based) position +in @var{GotoLabels} plus the number of input and output operands. +Output operand with constraint modifier @samp{+} is counted as two +operands because it is considered as one output and one input operand. +For example, if the @code{asm} has three inputs, one output operand +with constraint modifier @samp{+} and one output operand with +constraint modifier @samp{=} and references two labels, refer to the +first label as @samp{%l6} and the second as @samp{%l7}). + +Alternately, you can reference labels using the actual C label name +enclosed in brackets. For example, to reference a label named +@code{carry}, you can use @samp{%l[carry]}. The label must still be +listed in the @var{GotoLabels} section when using this approach. It +is better to use the named references for labels as in this case you +can avoid counting input and output operands and special treatment of +output operands with constraint modifier @samp{+}. + +Here is an example of @code{asm goto} for i386: + +@example +asm goto ( + "btl %1, %0\n\t" + "jc %l2" + : /* No outputs. */ + : "r" (p1), "r" (p2) + : "cc" + : carry); + +return 0; + +carry: +return 1; +@end example + +The following example shows an @code{asm goto} that uses a memory clobber. + +@example +int frob(int x) +@{ + int y; + asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5" + : /* No outputs. */ + : "r"(x), "r"(&y) + : "r5", "memory" + : error); + return y; +error: + return -1; +@} +@end example + +The following example shows an @code{asm goto} that uses an output. + +@example +int foo(int count) +@{ + asm goto ("dec %0; jb %l[stop]" + : "+r" (count) + : + : + : stop); + return count; +stop: + return 0; +@} +@end example + +The following artificial example shows an @code{asm goto} that sets +up an output only on one path inside the @code{asm goto}. Usage of +constraint modifier @code{=} instead of @code{+} would be wrong as +@code{factor} is used on all paths from the @code{asm goto}. + +@example +int foo(int inp) +@{ + int factor = 0; + asm goto ("cmp %1, 10; jb %l[lab]; mov 2, %0" + : "+r" (factor) + : "r" (inp) + : + : lab); +lab: + return inp * factor; /* return 2 * inp or 0 if inp < 10 */ +@} +@end example + +@anchor{x86Operandmodifiers} +@subsubsection x86 Operand Modifiers + +References to input, output, and goto operands in the assembler template +of extended @code{asm} statements can use +modifiers to affect the way the operands are formatted in +the code output to the assembler. For example, the +following code uses the @samp{h} and @samp{b} modifiers for x86: + +@example +uint16_t num; +asm volatile ("xchg %h0, %b0" : "+a" (num) ); +@end example + +@noindent +These modifiers generate this assembler code: + +@example +xchg %ah, %al +@end example + +The rest of this discussion uses the following code for illustrative purposes. + +@example +int main() +@{ + int iInt = 1; + +top: + + asm volatile goto ("some assembler instructions here" + : /* No outputs. */ + : "q" (iInt), "X" (sizeof(unsigned char) + 1), "i" (42) + : /* No clobbers. */ + : top); +@} +@end example + +With no modifiers, this is what the output from the operands would be +for the @samp{att} and @samp{intel} dialects of assembler: + +@multitable {Operand} {$.L2} {OFFSET FLAT:.L2} +@headitem Operand @tab @samp{att} @tab @samp{intel} +@item @code{%0} +@tab @code{%eax} +@tab @code{eax} +@item @code{%1} +@tab @code{$2} +@tab @code{2} +@item @code{%3} +@tab @code{$.L3} +@tab @code{OFFSET FLAT:.L3} +@item @code{%4} +@tab @code{$8} +@tab @code{8} +@item @code{%5} +@tab @code{%xmm0} +@tab @code{xmm0} +@item @code{%7} +@tab @code{$0} +@tab @code{0} +@end multitable + +The table below shows the list of supported modifiers and their effects. + +@multitable {Modifier} {Print the opcode suffix for the size of th} {Operand} {@samp{att}} {@samp{intel}} +@headitem Modifier @tab Description @tab Operand @tab @samp{att} @tab @samp{intel} +@item @code{A} +@tab Print an absolute memory reference. +@tab @code{%A0} +@tab @code{*%rax} +@tab @code{rax} +@item @code{b} +@tab Print the QImode name of the register. +@tab @code{%b0} +@tab @code{%al} +@tab @code{al} +@item @code{B} +@tab print the opcode suffix of b. +@tab @code{%B0} +@tab @code{b} +@tab +@item @code{c} +@tab Require a constant operand and print the constant expression with no punctuation. +@tab @code{%c1} +@tab @code{2} +@tab @code{2} +@item @code{d} +@tab print duplicated register operand for AVX instruction. +@tab @code{%d5} +@tab @code{%xmm0, %xmm0} +@tab @code{xmm0, xmm0} +@item @code{E} +@tab Print the address in Double Integer (DImode) mode (8 bytes) when the target is 64-bit. +Otherwise mode is unspecified (VOIDmode). +@tab @code{%E1} +@tab @code{%(rax)} +@tab @code{[rax]} +@item @code{g} +@tab Print the V16SFmode name of the register. +@tab @code{%g0} +@tab @code{%zmm0} +@tab @code{zmm0} +@item @code{h} +@tab Print the QImode name for a ``high'' register. +@tab @code{%h0} +@tab @code{%ah} +@tab @code{ah} +@item @code{H} +@tab Add 8 bytes to an offsettable memory reference. Useful when accessing the +high 8 bytes of SSE values. For a memref in (%rax), it generates +@tab @code{%H0} +@tab @code{8(%rax)} +@tab @code{8[rax]} +@item @code{k} +@tab Print the SImode name of the register. +@tab @code{%k0} +@tab @code{%eax} +@tab @code{eax} +@item @code{l} +@tab Print the label name with no punctuation. +@tab @code{%l3} +@tab @code{.L3} +@tab @code{.L3} +@item @code{L} +@tab print the opcode suffix of l. +@tab @code{%L0} +@tab @code{l} +@tab +@item @code{N} +@tab print maskz. +@tab @code{%N7} +@tab @code{@{z@}} +@tab @code{@{z@}} +@item @code{p} +@tab Print raw symbol name (without syntax-specific prefixes). +@tab @code{%p2} +@tab @code{42} +@tab @code{42} +@item @code{P} +@tab If used for a function, print the PLT suffix and generate PIC code. +For example, emit @code{foo@@PLT} instead of 'foo' for the function +foo(). If used for a constant, drop all syntax-specific prefixes and +issue the bare constant. See @code{p} above. +@item @code{q} +@tab Print the DImode name of the register. +@tab @code{%q0} +@tab @code{%rax} +@tab @code{rax} +@item @code{Q} +@tab print the opcode suffix of q. +@tab @code{%Q0} +@tab @code{q} +@tab +@item @code{R} +@tab print embedded rounding and sae. +@tab @code{%R4} +@tab @code{@{rn-sae@}, } +@tab @code{, @{rn-sae@}} +@item @code{r} +@tab print only sae. +@tab @code{%r4} +@tab @code{@{sae@}, } +@tab @code{, @{sae@}} +@item @code{s} +@tab print a shift double count, followed by the assemblers argument +delimiterprint the opcode suffix of s. +@tab @code{%s1} +@tab @code{$2, } +@tab @code{2, } +@item @code{S} +@tab print the opcode suffix of s. +@tab @code{%S0} +@tab @code{s} +@tab +@item @code{t} +@tab print the V8SFmode name of the register. +@tab @code{%t5} +@tab @code{%ymm0} +@tab @code{ymm0} +@item @code{T} +@tab print the opcode suffix of t. +@tab @code{%T0} +@tab @code{t} +@tab +@item @code{V} +@tab print naked full integer register name without %. +@tab @code{%V0} +@tab @code{eax} +@tab @code{eax} +@item @code{w} +@tab Print the HImode name of the register. +@tab @code{%w0} +@tab @code{%ax} +@tab @code{ax} +@item @code{W} +@tab print the opcode suffix of w. +@tab @code{%W0} +@tab @code{w} +@tab +@item @code{x} +@tab print the V4SFmode name of the register. +@tab @code{%x5} +@tab @code{%xmm0} +@tab @code{xmm0} +@item @code{y} +@tab print "st(0)" instead of "st" as a register. +@tab @code{%y6} +@tab @code{%st(0)} +@tab @code{st(0)} +@item @code{z} +@tab Print the opcode suffix for the size of the current integer operand (one of @code{b}/@code{w}/@code{l}/@code{q}). +@tab @code{%z0} +@tab @code{l} +@tab +@item @code{Z} +@tab Like @code{z}, with special suffixes for x87 instructions. +@end multitable + + +@anchor{x86floatingpointasmoperands} +@subsubsection x86 Floating-Point @code{asm} Operands + +On x86 targets, there are several rules on the usage of stack-like registers +in the operands of an @code{asm}. These rules apply only to the operands +that are stack-like registers: + +@enumerate +@item +Given a set of input registers that die in an @code{asm}, it is +necessary to know which are implicitly popped by the @code{asm}, and +which must be explicitly popped by GCC@. + +An input register that is implicitly popped by the @code{asm} must be +explicitly clobbered, unless it is constrained to match an +output operand. + +@item +For any input register that is implicitly popped by an @code{asm}, it is +necessary to know how to adjust the stack to compensate for the pop. +If any non-popped input is closer to the top of the reg-stack than +the implicitly popped register, it would not be possible to know what the +stack looked like---it's not clear how the rest of the stack ``slides +up''. + +All implicitly popped input registers must be closer to the top of +the reg-stack than any input that is not implicitly popped. + +It is possible that if an input dies in an @code{asm}, the compiler might +use the input register for an output reload. Consider this example: + +@smallexample +asm ("foo" : "=t" (a) : "f" (b)); +@end smallexample + +@noindent +This code says that input @code{b} is not popped by the @code{asm}, and that +the @code{asm} pushes a result onto the reg-stack, i.e., the stack is one +deeper after the @code{asm} than it was before. But, it is possible that +reload may think that it can use the same register for both the input and +the output. + +To prevent this from happening, +if any input operand uses the @samp{f} constraint, all output register +constraints must use the @samp{&} early-clobber modifier. + +The example above is correctly written as: + +@smallexample +asm ("foo" : "=&t" (a) : "f" (b)); +@end smallexample + +@item +Some operands need to be in particular places on the stack. All +output operands fall in this category---GCC has no other way to +know which registers the outputs appear in unless you indicate +this in the constraints. + +Output operands must specifically indicate which register an output +appears in after an @code{asm}. @samp{=f} is not allowed: the operand +constraints must select a class with a single register. + +@item +Output operands may not be ``inserted'' between existing stack registers. +Since no 387 opcode uses a read/write operand, all output operands +are dead before the @code{asm}, and are pushed by the @code{asm}. +It makes no sense to push anywhere but the top of the reg-stack. + +Output operands must start at the top of the reg-stack: output +operands may not ``skip'' a register. + +@item +Some @code{asm} statements may need extra stack space for internal +calculations. This can be guaranteed by clobbering stack registers +unrelated to the inputs and outputs. + +@end enumerate + +This @code{asm} +takes one input, which is internally popped, and produces two outputs. + +@smallexample +asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp)); +@end smallexample + +@noindent +This @code{asm} takes two inputs, which are popped by the @code{fyl2xp1} opcode, +and replaces them with one output. The @code{st(1)} clobber is necessary +for the compiler to know that @code{fyl2xp1} pops both inputs. + +@smallexample +asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)"); +@end smallexample + +@anchor{msp430Operandmodifiers} +@subsubsection MSP430 Operand Modifiers + +The list below describes the supported modifiers and their effects for MSP430. + +@multitable @columnfractions .10 .90 +@headitem Modifier @tab Description +@item @code{A} @tab Select low 16-bits of the constant/register/memory operand. +@item @code{B} @tab Select high 16-bits of the constant/register/memory +operand. +@item @code{C} @tab Select bits 32-47 of the constant/register/memory operand. +@item @code{D} @tab Select bits 48-63 of the constant/register/memory operand. +@item @code{H} @tab Equivalent to @code{B} (for backwards compatibility). +@item @code{I} @tab Print the inverse (logical @code{NOT}) of the constant +value. +@item @code{J} @tab Print an integer without a @code{#} prefix. +@item @code{L} @tab Equivalent to @code{A} (for backwards compatibility). +@item @code{O} @tab Offset of the current frame from the top of the stack. +@item @code{Q} @tab Use the @code{A} instruction postfix. +@item @code{R} @tab Inverse of condition code, for unsigned comparisons. +@item @code{W} @tab Subtract 16 from the constant value. +@item @code{X} @tab Use the @code{X} instruction postfix. +@item @code{Y} @tab Subtract 4 from the constant value. +@item @code{Z} @tab Subtract 1 from the constant value. +@item @code{b} @tab Append @code{.B}, @code{.W} or @code{.A} to the +instruction, depending on the mode. +@item @code{d} @tab Offset 1 byte of a memory reference or constant value. +@item @code{e} @tab Offset 3 bytes of a memory reference or constant value. +@item @code{f} @tab Offset 5 bytes of a memory reference or constant value. +@item @code{g} @tab Offset 7 bytes of a memory reference or constant value. +@item @code{p} @tab Print the value of 2, raised to the power of the given +constant. Used to select the specified bit position. +@item @code{r} @tab Inverse of condition code, for signed comparisons. +@item @code{x} @tab Equivialent to @code{X}, but only for pointers. +@end multitable + +@lowersections +@include md.texi +@raisesections + +@node Asm Labels +@subsection Controlling Names Used in Assembler Code +@cindex assembler names for identifiers +@cindex names used in assembler code +@cindex identifiers, names in assembler code + +You can specify the name to be used in the assembler code for a C +function or variable by writing the @code{asm} (or @code{__asm__}) +keyword after the declarator. +It is up to you to make sure that the assembler names you choose do not +conflict with any other assembler symbols, or reference registers. + +@subsubheading Assembler names for data + +This sample shows how to specify the assembler name for data: + +@smallexample +int foo asm ("myfoo") = 2; +@end smallexample + +@noindent +This specifies that the name to be used for the variable @code{foo} in +the assembler code should be @samp{myfoo} rather than the usual +@samp{_foo}. + +On systems where an underscore is normally prepended to the name of a C +variable, this feature allows you to define names for the +linker that do not start with an underscore. + +GCC does not support using this feature with a non-static local variable +since such variables do not have assembler names. If you are +trying to put the variable in a particular register, see +@ref{Explicit Register Variables}. + +@subsubheading Assembler names for functions + +To specify the assembler name for functions, write a declaration for the +function before its definition and put @code{asm} there, like this: + +@smallexample +int func (int x, int y) asm ("MYFUNC"); + +int func (int x, int y) +@{ + /* @r{@dots{}} */ +@end smallexample + +@noindent +This specifies that the name to be used for the function @code{func} in +the assembler code should be @code{MYFUNC}. + +@node Explicit Register Variables +@subsection Variables in Specified Registers +@anchor{Explicit Reg Vars} +@cindex explicit register variables +@cindex variables in specified registers +@cindex specified registers + +GNU C allows you to associate specific hardware registers with C +variables. In almost all cases, allowing the compiler to assign +registers produces the best code. However under certain unusual +circumstances, more precise control over the variable storage is +required. + +Both global and local variables can be associated with a register. The +consequences of performing this association are very different between +the two, as explained in the sections below. + +@menu +* Global Register Variables:: Variables declared at global scope. +* Local Register Variables:: Variables declared within a function. +@end menu + +@node Global Register Variables +@subsubsection Defining Global Register Variables +@anchor{Global Reg Vars} +@cindex global register variables +@cindex registers, global variables in +@cindex registers, global allocation + +You can define a global register variable and associate it with a specified +register like this: + +@smallexample +register int *foo asm ("r12"); +@end smallexample + +@noindent +Here @code{r12} is the name of the register that should be used. Note that +this is the same syntax used for defining local register variables, but for +a global variable the declaration appears outside a function. The +@code{register} keyword is required, and cannot be combined with +@code{static}. The register name must be a valid register name for the +target platform. + +Do not use type qualifiers such as @code{const} and @code{volatile}, as +the outcome may be contrary to expectations. In particular, using the +@code{volatile} qualifier does not fully prevent the compiler from +optimizing accesses to the register. + +Registers are a scarce resource on most systems and allowing the +compiler to manage their usage usually results in the best code. However, +under special circumstances it can make sense to reserve some globally. +For example this may be useful in programs such as programming language +interpreters that have a couple of global variables that are accessed +very often. + +After defining a global register variable, for the current compilation +unit: + +@itemize @bullet +@item If the register is a call-saved register, call ABI is affected: +the register will not be restored in function epilogue sequences after +the variable has been assigned. Therefore, functions cannot safely +return to callers that assume standard ABI. +@item Conversely, if the register is a call-clobbered register, making +calls to functions that use standard ABI may lose contents of the variable. +Such calls may be created by the compiler even if none are evident in +the original program, for example when libgcc functions are used to +make up for unavailable instructions. +@item Accesses to the variable may be optimized as usual and the register +remains available for allocation and use in any computations, provided that +observable values of the variable are not affected. +@item If the variable is referenced in inline assembly, the type of access +must be provided to the compiler via constraints (@pxref{Constraints}). +Accesses from basic asms are not supported. +@end itemize + +Note that these points @emph{only} apply to code that is compiled with the +definition. The behavior of code that is merely linked in (for example +code from libraries) is not affected. + +If you want to recompile source files that do not actually use your global +register variable so they do not use the specified register for any other +purpose, you need not actually add the global register declaration to +their source code. It suffices to specify the compiler option +@option{-ffixed-@var{reg}} (@pxref{Code Gen Options}) to reserve the +register. + +@subsubheading Declaring the variable + +Global register variables cannot have initial values, because an +executable file has no means to supply initial contents for a register. + +When selecting a register, choose one that is normally saved and +restored by function calls on your machine. This ensures that code +which is unaware of this reservation (such as library routines) will +restore it before returning. + +On machines with register windows, be sure to choose a global +register that is not affected magically by the function call mechanism. + +@subsubheading Using the variable + +@cindex @code{qsort}, and global register variables +When calling routines that are not aware of the reservation, be +cautious if those routines call back into code which uses them. As an +example, if you call the system library version of @code{qsort}, it may +clobber your registers during execution, but (if you have selected +appropriate registers) it will restore them before returning. However +it will @emph{not} restore them before calling @code{qsort}'s comparison +function. As a result, global values will not reliably be available to +the comparison function unless the @code{qsort} function itself is rebuilt. + +Similarly, it is not safe to access the global register variables from signal +handlers or from more than one thread of control. Unless you recompile +them specially for the task at hand, the system library routines may +temporarily use the register for other things. Furthermore, since the register +is not reserved exclusively for the variable, accessing it from handlers of +asynchronous signals may observe unrelated temporary values residing in the +register. + +@cindex register variable after @code{longjmp} +@cindex global register after @code{longjmp} +@cindex value after @code{longjmp} +@findex longjmp +@findex setjmp +On most machines, @code{longjmp} restores to each global register +variable the value it had at the time of the @code{setjmp}. On some +machines, however, @code{longjmp} does not change the value of global +register variables. To be portable, the function that called @code{setjmp} +should make other arrangements to save the values of the global register +variables, and to restore them in a @code{longjmp}. This way, the same +thing happens regardless of what @code{longjmp} does. + +@node Local Register Variables +@subsubsection Specifying Registers for Local Variables +@anchor{Local Reg Vars} +@cindex local variables, specifying registers +@cindex specifying registers for local variables +@cindex registers for local variables + +You can define a local register variable and associate it with a specified +register like this: + +@smallexample +register int *foo asm ("r12"); +@end smallexample + +@noindent +Here @code{r12} is the name of the register that should be used. Note +that this is the same syntax used for defining global register variables, +but for a local variable the declaration appears within a function. The +@code{register} keyword is required, and cannot be combined with +@code{static}. The register name must be a valid register name for the +target platform. + +Do not use type qualifiers such as @code{const} and @code{volatile}, as +the outcome may be contrary to expectations. In particular, when the +@code{const} qualifier is used, the compiler may substitute the +variable with its initializer in @code{asm} statements, which may cause +the corresponding operand to appear in a different register. + +As with global register variables, it is recommended that you choose +a register that is normally saved and restored by function calls on your +machine, so that calls to library routines will not clobber it. + +The only supported use for this feature is to specify registers +for input and output operands when calling Extended @code{asm} +(@pxref{Extended Asm}). This may be necessary if the constraints for a +particular machine don't provide sufficient control to select the desired +register. To force an operand into a register, create a local variable +and specify the register name after the variable's declaration. Then use +the local variable for the @code{asm} operand and specify any constraint +letter that matches the register: + +@smallexample +register int *p1 asm ("r0") = @dots{}; +register int *p2 asm ("r1") = @dots{}; +register int *result asm ("r0"); +asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2)); +@end smallexample + +@emph{Warning:} In the above example, be aware that a register (for example +@code{r0}) can be call-clobbered by subsequent code, including function +calls and library calls for arithmetic operators on other variables (for +example the initialization of @code{p2}). In this case, use temporary +variables for expressions between the register assignments: + +@smallexample +int t1 = @dots{}; +register int *p1 asm ("r0") = @dots{}; +register int *p2 asm ("r1") = t1; +register int *result asm ("r0"); +asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2)); +@end smallexample + +Defining a register variable does not reserve the register. Other than +when invoking the Extended @code{asm}, the contents of the specified +register are not guaranteed. For this reason, the following uses +are explicitly @emph{not} supported. If they appear to work, it is only +happenstance, and may stop working as intended due to (seemingly) +unrelated changes in surrounding code, or even minor changes in the +optimization of a future version of gcc: + +@itemize @bullet +@item Passing parameters to or from Basic @code{asm} +@item Passing parameters to or from Extended @code{asm} without using input +or output operands. +@item Passing parameters to or from routines written in assembler (or +other languages) using non-standard calling conventions. +@end itemize + +Some developers use Local Register Variables in an attempt to improve +gcc's allocation of registers, especially in large functions. In this +case the register name is essentially a hint to the register allocator. +While in some instances this can generate better code, improvements are +subject to the whims of the allocator/optimizers. Since there are no +guarantees that your improvements won't be lost, this usage of Local +Register Variables is discouraged. + +On the MIPS platform, there is related use for local register variables +with slightly different characteristics (@pxref{MIPS Coprocessors,, +Defining coprocessor specifics for MIPS targets, gccint, +GNU Compiler Collection (GCC) Internals}). + +@node Size of an asm +@subsection Size of an @code{asm} + +Some targets require that GCC track the size of each instruction used +in order to generate correct code. Because the final length of the +code produced by an @code{asm} statement is only known by the +assembler, GCC must make an estimate as to how big it will be. It +does this by counting the number of instructions in the pattern of the +@code{asm} and multiplying that by the length of the longest +instruction supported by that processor. (When working out the number +of instructions, it assumes that any occurrence of a newline or of +whatever statement separator character is supported by the assembler --- +typically @samp{;} --- indicates the end of an instruction.) + +Normally, GCC's estimate is adequate to ensure that correct +code is generated, but it is possible to confuse the compiler if you use +pseudo instructions or assembler macros that expand into multiple real +instructions, or if you use assembler directives that expand to more +space in the object file than is needed for a single instruction. +If this happens then the assembler may produce a diagnostic saying that +a label is unreachable. + +@cindex @code{asm inline} +This size is also used for inlining decisions. If you use @code{asm inline} +instead of just @code{asm}, then for inlining purposes the size of the asm +is taken as the minimum size, ignoring how many instructions GCC thinks it is. + +@node Alternate Keywords +@section Alternate Keywords +@cindex alternate keywords +@cindex keywords, alternate + +@option{-ansi} and the various @option{-std} options disable certain +keywords. This causes trouble when you want to use GNU C extensions, or +a general-purpose header file that should be usable by all programs, +including ISO C programs. The keywords @code{asm}, @code{typeof} and +@code{inline} are not available in programs compiled with +@option{-ansi} or @option{-std} (although @code{inline} can be used in a +program compiled with @option{-std=c99} or a later standard). The +ISO C99 keyword +@code{restrict} is only available when @option{-std=gnu99} (which will +eventually be the default) or @option{-std=c99} (or the equivalent +@option{-std=iso9899:1999}), or an option for a later standard +version, is used. + +The way to solve these problems is to put @samp{__} at the beginning and +end of each problematical keyword. For example, use @code{__asm__} +instead of @code{asm}, and @code{__inline__} instead of @code{inline}. + +Other C compilers won't accept these alternative keywords; if you want to +compile with another compiler, you can define the alternate keywords as +macros to replace them with the customary keywords. It looks like this: + +@smallexample +#ifndef __GNUC__ +#define __asm__ asm +#endif +@end smallexample + +@findex __extension__ +@opindex pedantic +@option{-pedantic} and other options cause warnings for many GNU C extensions. +You can +prevent such warnings within one expression by writing +@code{__extension__} before the expression. @code{__extension__} has no +effect aside from this. + +@node Incomplete Enums +@section Incomplete @code{enum} Types + +You can define an @code{enum} tag without specifying its possible values. +This results in an incomplete type, much like what you get if you write +@code{struct foo} without describing the elements. A later declaration +that does specify the possible values completes the type. + +You cannot allocate variables or storage using the type while it is +incomplete. However, you can work with pointers to that type. + +This extension may not be very useful, but it makes the handling of +@code{enum} more consistent with the way @code{struct} and @code{union} +are handled. + +This extension is not supported by GNU C++. + +@node Function Names +@section Function Names as Strings +@cindex @code{__func__} identifier +@cindex @code{__FUNCTION__} identifier +@cindex @code{__PRETTY_FUNCTION__} identifier + +GCC provides three magic constants that hold the name of the current +function as a string. In C++11 and later modes, all three are treated +as constant expressions and can be used in @code{constexpr} constexts. +The first of these constants is @code{__func__}, which is part of +the C99 standard: + +The identifier @code{__func__} is implicitly declared by the translator +as if, immediately following the opening brace of each function +definition, the declaration + +@smallexample +static const char __func__[] = "function-name"; +@end smallexample + +@noindent +appeared, where function-name is the name of the lexically-enclosing +function. This name is the unadorned name of the function. As an +extension, at file (or, in C++, namespace scope), @code{__func__} +evaluates to the empty string. + +@code{__FUNCTION__} is another name for @code{__func__}, provided for +backward compatibility with old versions of GCC. + +In C, @code{__PRETTY_FUNCTION__} is yet another name for +@code{__func__}, except that at file scope (or, in C++, namespace scope), +it evaluates to the string @code{"top level"}. In addition, in C++, +@code{__PRETTY_FUNCTION__} contains the signature of the function as +well as its bare name. For example, this program: + +@smallexample +extern "C" int printf (const char *, ...); + +class a @{ + public: + void sub (int i) + @{ + printf ("__FUNCTION__ = %s\n", __FUNCTION__); + printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__); + @} +@}; + +int +main (void) +@{ + a ax; + ax.sub (0); + return 0; +@} +@end smallexample + +@noindent +gives this output: + +@smallexample +__FUNCTION__ = sub +__PRETTY_FUNCTION__ = void a::sub(int) +@end smallexample + +These identifiers are variables, not preprocessor macros, and may not +be used to initialize @code{char} arrays or be concatenated with string +literals. + +@node Return Address +@section Getting the Return or Frame Address of a Function + +These functions may be used to get information about the callers of a +function. + +@deftypefn {Built-in Function} {void *} __builtin_return_address (unsigned int @var{level}) +This function returns the return address of the current function, or of +one of its callers. The @var{level} argument is number of frames to +scan up the call stack. A value of @code{0} yields the return address +of the current function, a value of @code{1} yields the return address +of the caller of the current function, and so forth. When inlining +the expected behavior is that the function returns the address of +the function that is returned to. To work around this behavior use +the @code{noinline} function attribute. + +The @var{level} argument must be a constant integer. + +On some machines it may be impossible to determine the return address of +any function other than the current one; in such cases, or when the top +of the stack has been reached, this function returns an unspecified +value. In addition, @code{__builtin_frame_address} may be used +to determine if the top of the stack has been reached. + +Additional post-processing of the returned value may be needed, see +@code{__builtin_extract_return_addr}. + +The stored representation of the return address in memory may be different +from the address returned by @code{__builtin_return_address}. For example, +on AArch64 the stored address may be mangled with return address signing +whereas the address returned by @code{__builtin_return_address} is not. + +Calling this function with a nonzero argument can have unpredictable +effects, including crashing the calling program. As a result, calls +that are considered unsafe are diagnosed when the @option{-Wframe-address} +option is in effect. Such calls should only be made in debugging +situations. + +On targets where code addresses are representable as @code{void *}, +@smallexample +void *addr = __builtin_extract_return_addr (__builtin_return_address (0)); +@end smallexample +gives the code address where the current function would return. For example, +such an address may be used with @code{dladdr} or other interfaces that work +with code addresses. +@end deftypefn + +@deftypefn {Built-in Function} {void *} __builtin_extract_return_addr (void *@var{addr}) +The address as returned by @code{__builtin_return_address} may have to be fed +through this function to get the actual encoded address. For example, on the +31-bit S/390 platform the highest bit has to be masked out, or on SPARC +platforms an offset has to be added for the true next instruction to be +executed. + +If no fixup is needed, this function simply passes through @var{addr}. +@end deftypefn + +@deftypefn {Built-in Function} {void *} __builtin_frob_return_addr (void *@var{addr}) +This function does the reverse of @code{__builtin_extract_return_addr}. +@end deftypefn + +@deftypefn {Built-in Function} {void *} __builtin_frame_address (unsigned int @var{level}) +This function is similar to @code{__builtin_return_address}, but it +returns the address of the function frame rather than the return address +of the function. Calling @code{__builtin_frame_address} with a value of +@code{0} yields the frame address of the current function, a value of +@code{1} yields the frame address of the caller of the current function, +and so forth. + +The frame is the area on the stack that holds local variables and saved +registers. The frame address is normally the address of the first word +pushed on to the stack by the function. However, the exact definition +depends upon the processor and the calling convention. If the processor +has a dedicated frame pointer register, and the function has a frame, +then @code{__builtin_frame_address} returns the value of the frame +pointer register. + +On some machines it may be impossible to determine the frame address of +any function other than the current one; in such cases, or when the top +of the stack has been reached, this function returns @code{0} if +the first frame pointer is properly initialized by the startup code. + +Calling this function with a nonzero argument can have unpredictable +effects, including crashing the calling program. As a result, calls +that are considered unsafe are diagnosed when the @option{-Wframe-address} +option is in effect. Such calls should only be made in debugging +situations. +@end deftypefn + +@node Vector Extensions +@section Using Vector Instructions through Built-in Functions + +On some targets, the instruction set contains SIMD vector instructions which +operate on multiple values contained in one large register at the same time. +For example, on the x86 the MMX, 3DNow!@: and SSE extensions can be used +this way. + +The first step in using these extensions is to provide the necessary data +types. This should be done using an appropriate @code{typedef}: + +@smallexample +typedef int v4si __attribute__ ((vector_size (16))); +@end smallexample + +@noindent +The @code{int} type specifies the @dfn{base type}, while the attribute specifies +the vector size for the variable, measured in bytes. For example, the +declaration above causes the compiler to set the mode for the @code{v4si} +type to be 16 bytes wide and divided into @code{int} sized units. For +a 32-bit @code{int} this means a vector of 4 units of 4 bytes, and the +corresponding mode of @code{foo} is @acronym{V4SI}. + +The @code{vector_size} attribute is only applicable to integral and +floating scalars, although arrays, pointers, and function return values +are allowed in conjunction with this construct. Only sizes that are +positive power-of-two multiples of the base type size are currently allowed. + +All the basic integer types can be used as base types, both as signed +and as unsigned: @code{char}, @code{short}, @code{int}, @code{long}, +@code{long long}. In addition, @code{float} and @code{double} can be +used to build floating-point vector types. + +Specifying a combination that is not valid for the current architecture +causes GCC to synthesize the instructions using a narrower mode. +For example, if you specify a variable of type @code{V4SI} and your +architecture does not allow for this specific SIMD type, GCC +produces code that uses 4 @code{SIs}. + +The types defined in this manner can be used with a subset of normal C +operations. Currently, GCC allows using the following operators +on these types: @code{+, -, *, /, unary minus, ^, |, &, ~, %}@. + +The operations behave like C++ @code{valarrays}. Addition is defined as +the addition of the corresponding elements of the operands. For +example, in the code below, each of the 4 elements in @var{a} is +added to the corresponding 4 elements in @var{b} and the resulting +vector is stored in @var{c}. + +@smallexample +typedef int v4si __attribute__ ((vector_size (16))); + +v4si a, b, c; + +c = a + b; +@end smallexample + +Subtraction, multiplication, division, and the logical operations +operate in a similar manner. Likewise, the result of using the unary +minus or complement operators on a vector type is a vector whose +elements are the negative or complemented values of the corresponding +elements in the operand. + +It is possible to use shifting operators @code{<<}, @code{>>} on +integer-type vectors. The operation is defined as following: @code{@{a0, +a1, @dots{}, an@} >> @{b0, b1, @dots{}, bn@} == @{a0 >> b0, a1 >> b1, +@dots{}, an >> bn@}}@. Vector operands must have the same number of +elements. + +For convenience, it is allowed to use a binary vector operation +where one operand is a scalar. In that case the compiler transforms +the scalar operand into a vector where each element is the scalar from +the operation. The transformation happens only if the scalar could be +safely converted to the vector-element type. +Consider the following code. + +@smallexample +typedef int v4si __attribute__ ((vector_size (16))); + +v4si a, b, c; +long l; + +a = b + 1; /* a = b + @{1,1,1,1@}; */ +a = 2 * b; /* a = @{2,2,2,2@} * b; */ + +a = l + a; /* Error, cannot convert long to int. */ +@end smallexample + +Vectors can be subscripted as if the vector were an array with +the same number of elements and base type. Out of bound accesses +invoke undefined behavior at run time. Warnings for out of bound +accesses for vector subscription can be enabled with +@option{-Warray-bounds}. + +Vector comparison is supported with standard comparison +operators: @code{==, !=, <, <=, >, >=}. Comparison operands can be +vector expressions of integer-type or real-type. Comparison between +integer-type vectors and real-type vectors are not supported. The +result of the comparison is a vector of the same width and number of +elements as the comparison operands with a signed integral element +type. + +Vectors are compared element-wise producing 0 when comparison is false +and -1 (constant of the appropriate type where all bits are set) +otherwise. Consider the following example. + +@smallexample +typedef int v4si __attribute__ ((vector_size (16))); + +v4si a = @{1,2,3,4@}; +v4si b = @{3,2,1,4@}; +v4si c; + +c = a > b; /* The result would be @{0, 0,-1, 0@} */ +c = a == b; /* The result would be @{0,-1, 0,-1@} */ +@end smallexample + +In C++, the ternary operator @code{?:} is available. @code{a?b:c}, where +@code{b} and @code{c} are vectors of the same type and @code{a} is an +integer vector with the same number of elements of the same size as @code{b} +and @code{c}, computes all three arguments and creates a vector +@code{@{a[0]?b[0]:c[0], a[1]?b[1]:c[1], @dots{}@}}. Note that unlike in +OpenCL, @code{a} is thus interpreted as @code{a != 0} and not @code{a < 0}. +As in the case of binary operations, this syntax is also accepted when +one of @code{b} or @code{c} is a scalar that is then transformed into a +vector. If both @code{b} and @code{c} are scalars and the type of +@code{true?b:c} has the same size as the element type of @code{a}, then +@code{b} and @code{c} are converted to a vector type whose elements have +this type and with the same number of elements as @code{a}. + +In C++, the logic operators @code{!, &&, ||} are available for vectors. +@code{!v} is equivalent to @code{v == 0}, @code{a && b} is equivalent to +@code{a!=0 & b!=0} and @code{a || b} is equivalent to @code{a!=0 | b!=0}. +For mixed operations between a scalar @code{s} and a vector @code{v}, +@code{s && v} is equivalent to @code{s?v!=0:0} (the evaluation is +short-circuit) and @code{v && s} is equivalent to @code{v!=0 & (s?-1:0)}. + +@findex __builtin_shuffle +Vector shuffling is available using functions +@code{__builtin_shuffle (vec, mask)} and +@code{__builtin_shuffle (vec0, vec1, mask)}. +Both functions construct a permutation of elements from one or two +vectors and return a vector of the same type as the input vector(s). +The @var{mask} is an integral vector with the same width (@var{W}) +and element count (@var{N}) as the output vector. + +The elements of the input vectors are numbered in memory ordering of +@var{vec0} beginning at 0 and @var{vec1} beginning at @var{N}. The +elements of @var{mask} are considered modulo @var{N} in the single-operand +case and modulo @math{2*@var{N}} in the two-operand case. + +Consider the following example, + +@smallexample +typedef int v4si __attribute__ ((vector_size (16))); + +v4si a = @{1,2,3,4@}; +v4si b = @{5,6,7,8@}; +v4si mask1 = @{0,1,1,3@}; +v4si mask2 = @{0,4,2,5@}; +v4si res; + +res = __builtin_shuffle (a, mask1); /* res is @{1,2,2,4@} */ +res = __builtin_shuffle (a, b, mask2); /* res is @{1,5,3,6@} */ +@end smallexample + +Note that @code{__builtin_shuffle} is intentionally semantically +compatible with the OpenCL @code{shuffle} and @code{shuffle2} functions. + +You can declare variables and use them in function calls and returns, as +well as in assignments and some casts. You can specify a vector type as +a return type for a function. Vector types can also be used as function +arguments. It is possible to cast from one vector type to another, +provided they are of the same size (in fact, you can also cast vectors +to and from other datatypes of the same size). + +You cannot operate between vectors of different lengths or different +signedness without a cast. + +@findex __builtin_shufflevector +Vector shuffling is available using the +@code{__builtin_shufflevector (vec1, vec2, index...)} +function. @var{vec1} and @var{vec2} must be expressions with +vector type with a compatible element type. The result of +@code{__builtin_shufflevector} is a vector with the same element type +as @var{vec1} and @var{vec2} but that has an element count equal to +the number of indices specified. + +The @var{index} arguments are a list of integers that specify the +elements indices of the first two vectors that should be extracted and +returned in a new vector. These element indices are numbered sequentially +starting with the first vector, continuing into the second vector. +An index of -1 can be used to indicate that the corresponding element in +the returned vector is a don't care and can be freely chosen to optimized +the generated code sequence performing the shuffle operation. + +Consider the following example, +@smallexample +typedef int v4si __attribute__ ((vector_size (16))); +typedef int v8si __attribute__ ((vector_size (32))); + +v8si a = @{1,-2,3,-4,5,-6,7,-8@}; +v4si b = __builtin_shufflevector (a, a, 0, 2, 4, 6); /* b is @{1,3,5,7@} */ +v4si c = @{-2,-4,-6,-8@}; +v8si d = __builtin_shufflevector (c, b, 4, 0, 5, 1, 6, 2, 7, 3); /* d is a */ +@end smallexample + +@findex __builtin_convertvector +Vector conversion is available using the +@code{__builtin_convertvector (vec, vectype)} +function. @var{vec} must be an expression with integral or floating +vector type and @var{vectype} an integral or floating vector type with the +same number of elements. The result has @var{vectype} type and value of +a C cast of every element of @var{vec} to the element type of @var{vectype}. + +Consider the following example, +@smallexample +typedef int v4si __attribute__ ((vector_size (16))); +typedef float v4sf __attribute__ ((vector_size (16))); +typedef double v4df __attribute__ ((vector_size (32))); +typedef unsigned long long v4di __attribute__ ((vector_size (32))); + +v4si a = @{1,-2,3,-4@}; +v4sf b = @{1.5f,-2.5f,3.f,7.f@}; +v4di c = @{1ULL,5ULL,0ULL,10ULL@}; +v4sf d = __builtin_convertvector (a, v4sf); /* d is @{1.f,-2.f,3.f,-4.f@} */ +/* Equivalent of: + v4sf d = @{ (float)a[0], (float)a[1], (float)a[2], (float)a[3] @}; */ +v4df e = __builtin_convertvector (a, v4df); /* e is @{1.,-2.,3.,-4.@} */ +v4df f = __builtin_convertvector (b, v4df); /* f is @{1.5,-2.5,3.,7.@} */ +v4si g = __builtin_convertvector (f, v4si); /* g is @{1,-2,3,7@} */ +v4si h = __builtin_convertvector (c, v4si); /* h is @{1,5,0,10@} */ +@end smallexample + +@cindex vector types, using with x86 intrinsics +Sometimes it is desirable to write code using a mix of generic vector +operations (for clarity) and machine-specific vector intrinsics (to +access vector instructions that are not exposed via generic built-ins). +On x86, intrinsic functions for integer vectors typically use the same +vector type @code{__m128i} irrespective of how they interpret the vector, +making it necessary to cast their arguments and return values from/to +other vector types. In C, you can make use of a @code{union} type: +@c In C++ such type punning via a union is not allowed by the language +@smallexample +#include + +typedef unsigned char u8x16 __attribute__ ((vector_size (16))); +typedef unsigned int u32x4 __attribute__ ((vector_size (16))); + +typedef union @{ + __m128i mm; + u8x16 u8; + u32x4 u32; +@} v128; +@end smallexample + +@noindent +for variables that can be used with both built-in operators and x86 +intrinsics: + +@smallexample +v128 x, y = @{ 0 @}; +memcpy (&x, ptr, sizeof x); +y.u8 += 0x80; +x.mm = _mm_adds_epu8 (x.mm, y.mm); +x.u32 &= 0xffffff; + +/* Instead of a variable, a compound literal may be used to pass the + return value of an intrinsic call to a function expecting the union: */ +v128 foo (v128); +x = foo ((v128) @{_mm_adds_epu8 (x.mm, y.mm)@}); +@c This could be done implicitly with __attribute__((transparent_union)), +@c but GCC does not accept it for unions of vector types (PR 88955). +@end smallexample + +@node Offsetof +@section Support for @code{offsetof} +@findex __builtin_offsetof + +GCC implements for both C and C++ a syntactic extension to implement +the @code{offsetof} macro. + +@smallexample +primary: + "__builtin_offsetof" "(" @code{typename} "," offsetof_member_designator ")" + +offsetof_member_designator: + @code{identifier} + | offsetof_member_designator "." @code{identifier} + | offsetof_member_designator "[" @code{expr} "]" +@end smallexample + +This extension is sufficient such that + +@smallexample +#define offsetof(@var{type}, @var{member}) __builtin_offsetof (@var{type}, @var{member}) +@end smallexample + +@noindent +is a suitable definition of the @code{offsetof} macro. In C++, @var{type} +may be dependent. In either case, @var{member} may consist of a single +identifier, or a sequence of member accesses and array references. + +@node __sync Builtins +@section Legacy @code{__sync} Built-in Functions for Atomic Memory Access + +The following built-in functions +are intended to be compatible with those described +in the @cite{Intel Itanium Processor-specific Application Binary Interface}, +section 7.4. As such, they depart from normal GCC practice by not using +the @samp{__builtin_} prefix and also by being overloaded so that they +work on multiple types. + +The definition given in the Intel documentation allows only for the use of +the types @code{int}, @code{long}, @code{long long} or their unsigned +counterparts. GCC allows any scalar type that is 1, 2, 4 or 8 bytes in +size other than the C type @code{_Bool} or the C++ type @code{bool}. +Operations on pointer arguments are performed as if the operands were +of the @code{uintptr_t} type. That is, they are not scaled by the size +of the type to which the pointer points. + +These functions are implemented in terms of the @samp{__atomic} +builtins (@pxref{__atomic Builtins}). They should not be used for new +code which should use the @samp{__atomic} builtins instead. + +Not all operations are supported by all target processors. If a particular +operation cannot be implemented on the target processor, a warning is +generated and a call to an external function is generated. The external +function carries the same name as the built-in version, +with an additional suffix +@samp{_@var{n}} where @var{n} is the size of the data type. + +@c ??? Should we have a mechanism to suppress this warning? This is almost +@c useful for implementing the operation under the control of an external +@c mutex. + +In most cases, these built-in functions are considered a @dfn{full barrier}. +That is, +no memory operand is moved across the operation, either forward or +backward. Further, instructions are issued as necessary to prevent the +processor from speculating loads across the operation and from queuing stores +after the operation. + +All of the routines are described in the Intel documentation to take +``an optional list of variables protected by the memory barrier''. It's +not clear what is meant by that; it could mean that @emph{only} the +listed variables are protected, or it could mean a list of additional +variables to be protected. The list is ignored by GCC which treats it as +empty. GCC interprets an empty list as meaning that all globally +accessible variables should be protected. + +@table @code +@item @var{type} __sync_fetch_and_add (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_fetch_and_sub (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_fetch_and_or (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_fetch_and_and (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_fetch_and_xor (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_fetch_and_nand (@var{type} *ptr, @var{type} value, ...) +@findex __sync_fetch_and_add +@findex __sync_fetch_and_sub +@findex __sync_fetch_and_or +@findex __sync_fetch_and_and +@findex __sync_fetch_and_xor +@findex __sync_fetch_and_nand +These built-in functions perform the operation suggested by the name, and +returns the value that had previously been in memory. That is, operations +on integer operands have the following semantics. Operations on pointer +arguments are performed as if the operands were of the @code{uintptr_t} +type. That is, they are not scaled by the size of the type to which +the pointer points. + +@smallexample +@{ tmp = *ptr; *ptr @var{op}= value; return tmp; @} +@{ tmp = *ptr; *ptr = ~(tmp & value); return tmp; @} // nand +@end smallexample + +The object pointed to by the first argument must be of integer or pointer +type. It must not be a boolean type. + +@emph{Note:} GCC 4.4 and later implement @code{__sync_fetch_and_nand} +as @code{*ptr = ~(tmp & value)} instead of @code{*ptr = ~tmp & value}. + +@item @var{type} __sync_add_and_fetch (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_sub_and_fetch (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_or_and_fetch (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_and_and_fetch (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_xor_and_fetch (@var{type} *ptr, @var{type} value, ...) +@itemx @var{type} __sync_nand_and_fetch (@var{type} *ptr, @var{type} value, ...) +@findex __sync_add_and_fetch +@findex __sync_sub_and_fetch +@findex __sync_or_and_fetch +@findex __sync_and_and_fetch +@findex __sync_xor_and_fetch +@findex __sync_nand_and_fetch +These built-in functions perform the operation suggested by the name, and +return the new value. That is, operations on integer operands have +the following semantics. Operations on pointer operands are performed as +if the operand's type were @code{uintptr_t}. + +@smallexample +@{ *ptr @var{op}= value; return *ptr; @} +@{ *ptr = ~(*ptr & value); return *ptr; @} // nand +@end smallexample + +The same constraints on arguments apply as for the corresponding +@code{__sync_op_and_fetch} built-in functions. + +@emph{Note:} GCC 4.4 and later implement @code{__sync_nand_and_fetch} +as @code{*ptr = ~(*ptr & value)} instead of +@code{*ptr = ~*ptr & value}. + +@item bool __sync_bool_compare_and_swap (@var{type} *ptr, @var{type} oldval, @var{type} newval, ...) +@itemx @var{type} __sync_val_compare_and_swap (@var{type} *ptr, @var{type} oldval, @var{type} newval, ...) +@findex __sync_bool_compare_and_swap +@findex __sync_val_compare_and_swap +These built-in functions perform an atomic compare and swap. +That is, if the current +value of @code{*@var{ptr}} is @var{oldval}, then write @var{newval} into +@code{*@var{ptr}}. + +The ``bool'' version returns @code{true} if the comparison is successful and +@var{newval} is written. The ``val'' version returns the contents +of @code{*@var{ptr}} before the operation. + +@item __sync_synchronize (...) +@findex __sync_synchronize +This built-in function issues a full memory barrier. + +@item @var{type} __sync_lock_test_and_set (@var{type} *ptr, @var{type} value, ...) +@findex __sync_lock_test_and_set +This built-in function, as described by Intel, is not a traditional test-and-set +operation, but rather an atomic exchange operation. It writes @var{value} +into @code{*@var{ptr}}, and returns the previous contents of +@code{*@var{ptr}}. + +Many targets have only minimal support for such locks, and do not support +a full exchange operation. In this case, a target may support reduced +functionality here by which the @emph{only} valid value to store is the +immediate constant 1. The exact value actually stored in @code{*@var{ptr}} +is implementation defined. + +This built-in function is not a full barrier, +but rather an @dfn{acquire barrier}. +This means that references after the operation cannot move to (or be +speculated to) before the operation, but previous memory stores may not +be globally visible yet, and previous memory loads may not yet be +satisfied. + +@item void __sync_lock_release (@var{type} *ptr, ...) +@findex __sync_lock_release +This built-in function releases the lock acquired by +@code{__sync_lock_test_and_set}. +Normally this means writing the constant 0 to @code{*@var{ptr}}. + +This built-in function is not a full barrier, +but rather a @dfn{release barrier}. +This means that all previous memory stores are globally visible, and all +previous memory loads have been satisfied, but following memory reads +are not prevented from being speculated to before the barrier. +@end table + +@node __atomic Builtins +@section Built-in Functions for Memory Model Aware Atomic Operations + +The following built-in functions approximately match the requirements +for the C++11 memory model. They are all +identified by being prefixed with @samp{__atomic} and most are +overloaded so that they work with multiple types. + +These functions are intended to replace the legacy @samp{__sync} +builtins. The main difference is that the memory order that is requested +is a parameter to the functions. New code should always use the +@samp{__atomic} builtins rather than the @samp{__sync} builtins. + +Note that the @samp{__atomic} builtins assume that programs will +conform to the C++11 memory model. In particular, they assume +that programs are free of data races. See the C++11 standard for +detailed requirements. + +The @samp{__atomic} builtins can be used with any integral scalar or +pointer type that is 1, 2, 4, or 8 bytes in length. 16-byte integral +types are also allowed if @samp{__int128} (@pxref{__int128}) is +supported by the architecture. + +The four non-arithmetic functions (load, store, exchange, and +compare_exchange) all have a generic version as well. This generic +version works on any data type. It uses the lock-free built-in function +if the specific data type size makes that possible; otherwise, an +external call is left to be resolved at run time. This external call is +the same format with the addition of a @samp{size_t} parameter inserted +as the first parameter indicating the size of the object being pointed to. +All objects must be the same size. + +There are 6 different memory orders that can be specified. These map +to the C++11 memory orders with the same names, see the C++11 standard +or the @uref{https://gcc.gnu.org/wiki/Atomic/GCCMM/AtomicSync,GCC wiki +on atomic synchronization} for detailed definitions. Individual +targets may also support additional memory orders for use on specific +architectures. Refer to the target documentation for details of +these. + +An atomic operation can both constrain code motion and +be mapped to hardware instructions for synchronization between threads +(e.g., a fence). To which extent this happens is controlled by the +memory orders, which are listed here in approximately ascending order of +strength. The description of each memory order is only meant to roughly +illustrate the effects and is not a specification; see the C++11 +memory model for precise semantics. + +@table @code +@item __ATOMIC_RELAXED +Implies no inter-thread ordering constraints. +@item __ATOMIC_CONSUME +This is currently implemented using the stronger @code{__ATOMIC_ACQUIRE} +memory order because of a deficiency in C++11's semantics for +@code{memory_order_consume}. +@item __ATOMIC_ACQUIRE +Creates an inter-thread happens-before constraint from the release (or +stronger) semantic store to this acquire load. Can prevent hoisting +of code to before the operation. +@item __ATOMIC_RELEASE +Creates an inter-thread happens-before constraint to acquire (or stronger) +semantic loads that read from this release store. Can prevent sinking +of code to after the operation. +@item __ATOMIC_ACQ_REL +Combines the effects of both @code{__ATOMIC_ACQUIRE} and +@code{__ATOMIC_RELEASE}. +@item __ATOMIC_SEQ_CST +Enforces total ordering with all other @code{__ATOMIC_SEQ_CST} operations. +@end table + +Note that in the C++11 memory model, @emph{fences} (e.g., +@samp{__atomic_thread_fence}) take effect in combination with other +atomic operations on specific memory locations (e.g., atomic loads); +operations on specific memory locations do not necessarily affect other +operations in the same way. + +Target architectures are encouraged to provide their own patterns for +each of the atomic built-in functions. If no target is provided, the original +non-memory model set of @samp{__sync} atomic built-in functions are +used, along with any required synchronization fences surrounding it in +order to achieve the proper behavior. Execution in this case is subject +to the same restrictions as those built-in functions. + +If there is no pattern or mechanism to provide a lock-free instruction +sequence, a call is made to an external routine with the same parameters +to be resolved at run time. + +When implementing patterns for these built-in functions, the memory order +parameter can be ignored as long as the pattern implements the most +restrictive @code{__ATOMIC_SEQ_CST} memory order. Any of the other memory +orders execute correctly with this memory order but they may not execute as +efficiently as they could with a more appropriate implementation of the +relaxed requirements. + +Note that the C++11 standard allows for the memory order parameter to be +determined at run time rather than at compile time. These built-in +functions map any run-time value to @code{__ATOMIC_SEQ_CST} rather +than invoke a runtime library call or inline a switch statement. This is +standard compliant, safe, and the simplest approach for now. + +The memory order parameter is a signed int, but only the lower 16 bits are +reserved for the memory order. The remainder of the signed int is reserved +for target use and should be 0. Use of the predefined atomic values +ensures proper usage. + +@deftypefn {Built-in Function} @var{type} __atomic_load_n (@var{type} *ptr, int memorder) +This built-in function implements an atomic load operation. It returns the +contents of @code{*@var{ptr}}. + +The valid memory order variants are +@code{__ATOMIC_RELAXED}, @code{__ATOMIC_SEQ_CST}, @code{__ATOMIC_ACQUIRE}, +and @code{__ATOMIC_CONSUME}. + +@end deftypefn + +@deftypefn {Built-in Function} void __atomic_load (@var{type} *ptr, @var{type} *ret, int memorder) +This is the generic version of an atomic load. It returns the +contents of @code{*@var{ptr}} in @code{*@var{ret}}. + +@end deftypefn + +@deftypefn {Built-in Function} void __atomic_store_n (@var{type} *ptr, @var{type} val, int memorder) +This built-in function implements an atomic store operation. It writes +@code{@var{val}} into @code{*@var{ptr}}. + +The valid memory order variants are +@code{__ATOMIC_RELAXED}, @code{__ATOMIC_SEQ_CST}, and @code{__ATOMIC_RELEASE}. + +@end deftypefn + +@deftypefn {Built-in Function} void __atomic_store (@var{type} *ptr, @var{type} *val, int memorder) +This is the generic version of an atomic store. It stores the value +of @code{*@var{val}} into @code{*@var{ptr}}. + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __atomic_exchange_n (@var{type} *ptr, @var{type} val, int memorder) +This built-in function implements an atomic exchange operation. It writes +@var{val} into @code{*@var{ptr}}, and returns the previous contents of +@code{*@var{ptr}}. + +All memory order variants are valid. + +@end deftypefn + +@deftypefn {Built-in Function} void __atomic_exchange (@var{type} *ptr, @var{type} *val, @var{type} *ret, int memorder) +This is the generic version of an atomic exchange. It stores the +contents of @code{*@var{val}} into @code{*@var{ptr}}. The original value +of @code{*@var{ptr}} is copied into @code{*@var{ret}}. + +@end deftypefn + +@deftypefn {Built-in Function} bool __atomic_compare_exchange_n (@var{type} *ptr, @var{type} *expected, @var{type} desired, bool weak, int success_memorder, int failure_memorder) +This built-in function implements an atomic compare and exchange operation. +This compares the contents of @code{*@var{ptr}} with the contents of +@code{*@var{expected}}. If equal, the operation is a @emph{read-modify-write} +operation that writes @var{desired} into @code{*@var{ptr}}. If they are not +equal, the operation is a @emph{read} and the current contents of +@code{*@var{ptr}} are written into @code{*@var{expected}}. @var{weak} is @code{true} +for weak compare_exchange, which may fail spuriously, and @code{false} for +the strong variation, which never fails spuriously. Many targets +only offer the strong variation and ignore the parameter. When in doubt, use +the strong variation. + +If @var{desired} is written into @code{*@var{ptr}} then @code{true} is returned +and memory is affected according to the +memory order specified by @var{success_memorder}. There are no +restrictions on what memory order can be used here. + +Otherwise, @code{false} is returned and memory is affected according +to @var{failure_memorder}. This memory order cannot be +@code{__ATOMIC_RELEASE} nor @code{__ATOMIC_ACQ_REL}. It also cannot be a +stronger order than that specified by @var{success_memorder}. + +@end deftypefn + +@deftypefn {Built-in Function} bool __atomic_compare_exchange (@var{type} *ptr, @var{type} *expected, @var{type} *desired, bool weak, int success_memorder, int failure_memorder) +This built-in function implements the generic version of +@code{__atomic_compare_exchange}. The function is virtually identical to +@code{__atomic_compare_exchange_n}, except the desired value is also a +pointer. + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __atomic_add_fetch (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_sub_fetch (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_and_fetch (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_xor_fetch (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_or_fetch (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_nand_fetch (@var{type} *ptr, @var{type} val, int memorder) +These built-in functions perform the operation suggested by the name, and +return the result of the operation. Operations on pointer arguments are +performed as if the operands were of the @code{uintptr_t} type. That is, +they are not scaled by the size of the type to which the pointer points. + +@smallexample +@{ *ptr @var{op}= val; return *ptr; @} +@{ *ptr = ~(*ptr & val); return *ptr; @} // nand +@end smallexample + +The object pointed to by the first argument must be of integer or pointer +type. It must not be a boolean type. All memory orders are valid. + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __atomic_fetch_add (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_fetch_sub (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_fetch_and (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_fetch_xor (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_fetch_or (@var{type} *ptr, @var{type} val, int memorder) +@deftypefnx {Built-in Function} @var{type} __atomic_fetch_nand (@var{type} *ptr, @var{type} val, int memorder) +These built-in functions perform the operation suggested by the name, and +return the value that had previously been in @code{*@var{ptr}}. Operations +on pointer arguments are performed as if the operands were of +the @code{uintptr_t} type. That is, they are not scaled by the size of +the type to which the pointer points. + +@smallexample +@{ tmp = *ptr; *ptr @var{op}= val; return tmp; @} +@{ tmp = *ptr; *ptr = ~(*ptr & val); return tmp; @} // nand +@end smallexample + +The same constraints on arguments apply as for the corresponding +@code{__atomic_op_fetch} built-in functions. All memory orders are valid. + +@end deftypefn + +@deftypefn {Built-in Function} bool __atomic_test_and_set (void *ptr, int memorder) + +This built-in function performs an atomic test-and-set operation on +the byte at @code{*@var{ptr}}. The byte is set to some implementation +defined nonzero ``set'' value and the return value is @code{true} if and only +if the previous contents were ``set''. +It should be only used for operands of type @code{bool} or @code{char}. For +other types only part of the value may be set. + +All memory orders are valid. + +@end deftypefn + +@deftypefn {Built-in Function} void __atomic_clear (bool *ptr, int memorder) + +This built-in function performs an atomic clear operation on +@code{*@var{ptr}}. After the operation, @code{*@var{ptr}} contains 0. +It should be only used for operands of type @code{bool} or @code{char} and +in conjunction with @code{__atomic_test_and_set}. +For other types it may only clear partially. If the type is not @code{bool} +prefer using @code{__atomic_store}. + +The valid memory order variants are +@code{__ATOMIC_RELAXED}, @code{__ATOMIC_SEQ_CST}, and +@code{__ATOMIC_RELEASE}. + +@end deftypefn + +@deftypefn {Built-in Function} void __atomic_thread_fence (int memorder) + +This built-in function acts as a synchronization fence between threads +based on the specified memory order. + +All memory orders are valid. + +@end deftypefn + +@deftypefn {Built-in Function} void __atomic_signal_fence (int memorder) + +This built-in function acts as a synchronization fence between a thread +and signal handlers based in the same thread. + +All memory orders are valid. + +@end deftypefn + +@deftypefn {Built-in Function} bool __atomic_always_lock_free (size_t size, void *ptr) + +This built-in function returns @code{true} if objects of @var{size} bytes always +generate lock-free atomic instructions for the target architecture. +@var{size} must resolve to a compile-time constant and the result also +resolves to a compile-time constant. + +@var{ptr} is an optional pointer to the object that may be used to determine +alignment. A value of 0 indicates typical alignment should be used. The +compiler may also ignore this parameter. + +@smallexample +if (__atomic_always_lock_free (sizeof (long long), 0)) +@end smallexample + +@end deftypefn + +@deftypefn {Built-in Function} bool __atomic_is_lock_free (size_t size, void *ptr) + +This built-in function returns @code{true} if objects of @var{size} bytes always +generate lock-free atomic instructions for the target architecture. If +the built-in function is not known to be lock-free, a call is made to a +runtime routine named @code{__atomic_is_lock_free}. + +@var{ptr} is an optional pointer to the object that may be used to determine +alignment. A value of 0 indicates typical alignment should be used. The +compiler may also ignore this parameter. +@end deftypefn + +@node Integer Overflow Builtins +@section Built-in Functions to Perform Arithmetic with Overflow Checking + +The following built-in functions allow performing simple arithmetic operations +together with checking whether the operations overflowed. + +@deftypefn {Built-in Function} bool __builtin_add_overflow (@var{type1} a, @var{type2} b, @var{type3} *res) +@deftypefnx {Built-in Function} bool __builtin_sadd_overflow (int a, int b, int *res) +@deftypefnx {Built-in Function} bool __builtin_saddl_overflow (long int a, long int b, long int *res) +@deftypefnx {Built-in Function} bool __builtin_saddll_overflow (long long int a, long long int b, long long int *res) +@deftypefnx {Built-in Function} bool __builtin_uadd_overflow (unsigned int a, unsigned int b, unsigned int *res) +@deftypefnx {Built-in Function} bool __builtin_uaddl_overflow (unsigned long int a, unsigned long int b, unsigned long int *res) +@deftypefnx {Built-in Function} bool __builtin_uaddll_overflow (unsigned long long int a, unsigned long long int b, unsigned long long int *res) + +These built-in functions promote the first two operands into infinite precision signed +type and perform addition on those promoted operands. The result is then +cast to the type the third pointer argument points to and stored there. +If the stored result is equal to the infinite precision result, the built-in +functions return @code{false}, otherwise they return @code{true}. As the addition is +performed in infinite signed precision, these built-in functions have fully defined +behavior for all argument values. + +The first built-in function allows arbitrary integral types for operands and +the result type must be pointer to some integral type other than enumerated or +boolean type, the rest of the built-in functions have explicit integer types. + +The compiler will attempt to use hardware instructions to implement +these built-in functions where possible, like conditional jump on overflow +after addition, conditional jump on carry etc. + +@end deftypefn + +@deftypefn {Built-in Function} bool __builtin_sub_overflow (@var{type1} a, @var{type2} b, @var{type3} *res) +@deftypefnx {Built-in Function} bool __builtin_ssub_overflow (int a, int b, int *res) +@deftypefnx {Built-in Function} bool __builtin_ssubl_overflow (long int a, long int b, long int *res) +@deftypefnx {Built-in Function} bool __builtin_ssubll_overflow (long long int a, long long int b, long long int *res) +@deftypefnx {Built-in Function} bool __builtin_usub_overflow (unsigned int a, unsigned int b, unsigned int *res) +@deftypefnx {Built-in Function} bool __builtin_usubl_overflow (unsigned long int a, unsigned long int b, unsigned long int *res) +@deftypefnx {Built-in Function} bool __builtin_usubll_overflow (unsigned long long int a, unsigned long long int b, unsigned long long int *res) + +These built-in functions are similar to the add overflow checking built-in +functions above, except they perform subtraction, subtract the second argument +from the first one, instead of addition. + +@end deftypefn + +@deftypefn {Built-in Function} bool __builtin_mul_overflow (@var{type1} a, @var{type2} b, @var{type3} *res) +@deftypefnx {Built-in Function} bool __builtin_smul_overflow (int a, int b, int *res) +@deftypefnx {Built-in Function} bool __builtin_smull_overflow (long int a, long int b, long int *res) +@deftypefnx {Built-in Function} bool __builtin_smulll_overflow (long long int a, long long int b, long long int *res) +@deftypefnx {Built-in Function} bool __builtin_umul_overflow (unsigned int a, unsigned int b, unsigned int *res) +@deftypefnx {Built-in Function} bool __builtin_umull_overflow (unsigned long int a, unsigned long int b, unsigned long int *res) +@deftypefnx {Built-in Function} bool __builtin_umulll_overflow (unsigned long long int a, unsigned long long int b, unsigned long long int *res) + +These built-in functions are similar to the add overflow checking built-in +functions above, except they perform multiplication, instead of addition. + +@end deftypefn + +The following built-in functions allow checking if simple arithmetic operation +would overflow. + +@deftypefn {Built-in Function} bool __builtin_add_overflow_p (@var{type1} a, @var{type2} b, @var{type3} c) +@deftypefnx {Built-in Function} bool __builtin_sub_overflow_p (@var{type1} a, @var{type2} b, @var{type3} c) +@deftypefnx {Built-in Function} bool __builtin_mul_overflow_p (@var{type1} a, @var{type2} b, @var{type3} c) + +These built-in functions are similar to @code{__builtin_add_overflow}, +@code{__builtin_sub_overflow}, or @code{__builtin_mul_overflow}, except that +they don't store the result of the arithmetic operation anywhere and the +last argument is not a pointer, but some expression with integral type other +than enumerated or boolean type. + +The built-in functions promote the first two operands into infinite precision signed type +and perform addition on those promoted operands. The result is then +cast to the type of the third argument. If the cast result is equal to the infinite +precision result, the built-in functions return @code{false}, otherwise they return @code{true}. +The value of the third argument is ignored, just the side effects in the third argument +are evaluated, and no integral argument promotions are performed on the last argument. +If the third argument is a bit-field, the type used for the result cast has the +precision and signedness of the given bit-field, rather than precision and signedness +of the underlying type. + +For example, the following macro can be used to portably check, at +compile-time, whether or not adding two constant integers will overflow, +and perform the addition only when it is known to be safe and not to trigger +a @option{-Woverflow} warning. + +@smallexample +#define INT_ADD_OVERFLOW_P(a, b) \ + __builtin_add_overflow_p (a, b, (__typeof__ ((a) + (b))) 0) + +enum @{ + A = INT_MAX, B = 3, + C = INT_ADD_OVERFLOW_P (A, B) ? 0 : A + B, + D = __builtin_add_overflow_p (1, SCHAR_MAX, (signed char) 0) +@}; +@end smallexample + +The compiler will attempt to use hardware instructions to implement +these built-in functions where possible, like conditional jump on overflow +after addition, conditional jump on carry etc. + +@end deftypefn + +@node x86 specific memory model extensions for transactional memory +@section x86-Specific Memory Model Extensions for Transactional Memory + +The x86 architecture supports additional memory ordering flags +to mark critical sections for hardware lock elision. +These must be specified in addition to an existing memory order to +atomic intrinsics. + +@table @code +@item __ATOMIC_HLE_ACQUIRE +Start lock elision on a lock variable. +Memory order must be @code{__ATOMIC_ACQUIRE} or stronger. +@item __ATOMIC_HLE_RELEASE +End lock elision on a lock variable. +Memory order must be @code{__ATOMIC_RELEASE} or stronger. +@end table + +When a lock acquire fails, it is required for good performance to abort +the transaction quickly. This can be done with a @code{_mm_pause}. + +@smallexample +#include // For _mm_pause + +int lockvar; + +/* Acquire lock with lock elision */ +while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE)) + _mm_pause(); /* Abort failed transaction */ +... +/* Free lock with lock elision */ +__atomic_store_n(&lockvar, 0, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE); +@end smallexample + +@node Object Size Checking +@section Object Size Checking Built-in Functions +@findex __builtin_object_size +@findex __builtin_dynamic_object_size +@findex __builtin___memcpy_chk +@findex __builtin___mempcpy_chk +@findex __builtin___memmove_chk +@findex __builtin___memset_chk +@findex __builtin___strcpy_chk +@findex __builtin___stpcpy_chk +@findex __builtin___strncpy_chk +@findex __builtin___strcat_chk +@findex __builtin___strncat_chk +@findex __builtin___sprintf_chk +@findex __builtin___snprintf_chk +@findex __builtin___vsprintf_chk +@findex __builtin___vsnprintf_chk +@findex __builtin___printf_chk +@findex __builtin___vprintf_chk +@findex __builtin___fprintf_chk +@findex __builtin___vfprintf_chk + +GCC implements a limited buffer overflow protection mechanism that can +prevent some buffer overflow attacks by determining the sizes of objects +into which data is about to be written and preventing the writes when +the size isn't sufficient. The built-in functions described below yield +the best results when used together and when optimization is enabled. +For example, to detect object sizes across function boundaries or to +follow pointer assignments through non-trivial control flow they rely +on various optimization passes enabled with @option{-O2}. However, to +a limited extent, they can be used without optimization as well. + +@deftypefn {Built-in Function} {size_t} __builtin_object_size (const void * @var{ptr}, int @var{type}) +is a built-in construct that returns a constant number of bytes from +@var{ptr} to the end of the object @var{ptr} pointer points to +(if known at compile time). To determine the sizes of dynamically allocated +objects the function relies on the allocation functions called to obtain +the storage to be declared with the @code{alloc_size} attribute (@pxref{Common +Function Attributes}). @code{__builtin_object_size} never evaluates +its arguments for side effects. If there are any side effects in them, it +returns @code{(size_t) -1} for @var{type} 0 or 1 and @code{(size_t) 0} +for @var{type} 2 or 3. If there are multiple objects @var{ptr} can +point to and all of them are known at compile time, the returned number +is the maximum of remaining byte counts in those objects if @var{type} & 2 is +0 and minimum if nonzero. If it is not possible to determine which objects +@var{ptr} points to at compile time, @code{__builtin_object_size} should +return @code{(size_t) -1} for @var{type} 0 or 1 and @code{(size_t) 0} +for @var{type} 2 or 3. + +@var{type} is an integer constant from 0 to 3. If the least significant +bit is clear, objects are whole variables, if it is set, a closest +surrounding subobject is considered the object a pointer points to. +The second bit determines if maximum or minimum of remaining bytes +is computed. + +@smallexample +struct V @{ char buf1[10]; int b; char buf2[10]; @} var; +char *p = &var.buf1[1], *q = &var.b; + +/* Here the object p points to is var. */ +assert (__builtin_object_size (p, 0) == sizeof (var) - 1); +/* The subobject p points to is var.buf1. */ +assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1); +/* The object q points to is var. */ +assert (__builtin_object_size (q, 0) + == (char *) (&var + 1) - (char *) &var.b); +/* The subobject q points to is var.b. */ +assert (__builtin_object_size (q, 1) == sizeof (var.b)); +@end smallexample +@end deftypefn + +@deftypefn {Built-in Function} {size_t} __builtin_dynamic_object_size (const void * @var{ptr}, int @var{type}) +is similar to @code{__builtin_object_size} in that it returns a number of bytes +from @var{ptr} to the end of the object @var{ptr} pointer points to, except +that the size returned may not be a constant. This results in successful +evaluation of object size estimates in a wider range of use cases and can be +more precise than @code{__builtin_object_size}, but it incurs a performance +penalty since it may add a runtime overhead on size computation. Semantics of +@var{type} as well as return values in case it is not possible to determine +which objects @var{ptr} points to at compile time are the same as in the case +of @code{__builtin_object_size}. +@end deftypefn + +There are built-in functions added for many common string operation +functions, e.g., for @code{memcpy} @code{__builtin___memcpy_chk} +built-in is provided. This built-in has an additional last argument, +which is the number of bytes remaining in the object the @var{dest} +argument points to or @code{(size_t) -1} if the size is not known. + +The built-in functions are optimized into the normal string functions +like @code{memcpy} if the last argument is @code{(size_t) -1} or if +it is known at compile time that the destination object will not +be overflowed. If the compiler can determine at compile time that the +object will always be overflowed, it issues a warning. + +The intended use can be e.g.@: + +@smallexample +#undef memcpy +#define bos0(dest) __builtin_object_size (dest, 0) +#define memcpy(dest, src, n) \ + __builtin___memcpy_chk (dest, src, n, bos0 (dest)) + +char *volatile p; +char buf[10]; +/* It is unknown what object p points to, so this is optimized + into plain memcpy - no checking is possible. */ +memcpy (p, "abcde", n); +/* Destination is known and length too. It is known at compile + time there will be no overflow. */ +memcpy (&buf[5], "abcde", 5); +/* Destination is known, but the length is not known at compile time. + This will result in __memcpy_chk call that can check for overflow + at run time. */ +memcpy (&buf[5], "abcde", n); +/* Destination is known and it is known at compile time there will + be overflow. There will be a warning and __memcpy_chk call that + will abort the program at run time. */ +memcpy (&buf[6], "abcde", 5); +@end smallexample + +Such built-in functions are provided for @code{memcpy}, @code{mempcpy}, +@code{memmove}, @code{memset}, @code{strcpy}, @code{stpcpy}, @code{strncpy}, +@code{strcat} and @code{strncat}. + +There are also checking built-in functions for formatted output functions. +@smallexample +int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...); +int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os, + const char *fmt, ...); +int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt, + va_list ap); +int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os, + const char *fmt, va_list ap); +@end smallexample + +The added @var{flag} argument is passed unchanged to @code{__sprintf_chk} +etc.@: functions and can contain implementation specific flags on what +additional security measures the checking function might take, such as +handling @code{%n} differently. + +The @var{os} argument is the object size @var{s} points to, like in the +other built-in functions. There is a small difference in the behavior +though, if @var{os} is @code{(size_t) -1}, the built-in functions are +optimized into the non-checking functions only if @var{flag} is 0, otherwise +the checking function is called with @var{os} argument set to +@code{(size_t) -1}. + +In addition to this, there are checking built-in functions +@code{__builtin___printf_chk}, @code{__builtin___vprintf_chk}, +@code{__builtin___fprintf_chk} and @code{__builtin___vfprintf_chk}. +These have just one additional argument, @var{flag}, right before +format string @var{fmt}. If the compiler is able to optimize them to +@code{fputc} etc.@: functions, it does, otherwise the checking function +is called and the @var{flag} argument passed to it. + +@node Other Builtins +@section Other Built-in Functions Provided by GCC +@cindex built-in functions +@findex __builtin_alloca +@findex __builtin_alloca_with_align +@findex __builtin_alloca_with_align_and_max +@findex __builtin_call_with_static_chain +@findex __builtin_extend_pointer +@findex __builtin_fpclassify +@findex __builtin_has_attribute +@findex __builtin_isfinite +@findex __builtin_isnormal +@findex __builtin_isgreater +@findex __builtin_isgreaterequal +@findex __builtin_isinf_sign +@findex __builtin_isless +@findex __builtin_islessequal +@findex __builtin_islessgreater +@findex __builtin_issignaling +@findex __builtin_isunordered +@findex __builtin_object_size +@findex __builtin_powi +@findex __builtin_powif +@findex __builtin_powil +@findex __builtin_speculation_safe_value +@findex _Exit +@findex _exit +@findex abort +@findex abs +@findex acos +@findex acosf +@findex acosh +@findex acoshf +@findex acoshl +@findex acosl +@findex alloca +@findex asin +@findex asinf +@findex asinh +@findex asinhf +@findex asinhl +@findex asinl +@findex atan +@findex atan2 +@findex atan2f +@findex atan2l +@findex atanf +@findex atanh +@findex atanhf +@findex atanhl +@findex atanl +@findex bcmp +@findex bzero +@findex cabs +@findex cabsf +@findex cabsl +@findex cacos +@findex cacosf +@findex cacosh +@findex cacoshf +@findex cacoshl +@findex cacosl +@findex calloc +@findex carg +@findex cargf +@findex cargl +@findex casin +@findex casinf +@findex casinh +@findex casinhf +@findex casinhl +@findex casinl +@findex catan +@findex catanf +@findex catanh +@findex catanhf +@findex catanhl +@findex catanl +@findex cbrt +@findex cbrtf +@findex cbrtl +@findex ccos +@findex ccosf +@findex ccosh +@findex ccoshf +@findex ccoshl +@findex ccosl +@findex ceil +@findex ceilf +@findex ceill +@findex cexp +@findex cexpf +@findex cexpl +@findex cimag +@findex cimagf +@findex cimagl +@findex clog +@findex clogf +@findex clogl +@findex clog10 +@findex clog10f +@findex clog10l +@findex conj +@findex conjf +@findex conjl +@findex copysign +@findex copysignf +@findex copysignl +@findex cos +@findex cosf +@findex cosh +@findex coshf +@findex coshl +@findex cosl +@findex cpow +@findex cpowf +@findex cpowl +@findex cproj +@findex cprojf +@findex cprojl +@findex creal +@findex crealf +@findex creall +@findex csin +@findex csinf +@findex csinh +@findex csinhf +@findex csinhl +@findex csinl +@findex csqrt +@findex csqrtf +@findex csqrtl +@findex ctan +@findex ctanf +@findex ctanh +@findex ctanhf +@findex ctanhl +@findex ctanl +@findex dcgettext +@findex dgettext +@findex drem +@findex dremf +@findex dreml +@findex erf +@findex erfc +@findex erfcf +@findex erfcl +@findex erff +@findex erfl +@findex exit +@findex exp +@findex exp10 +@findex exp10f +@findex exp10l +@findex exp2 +@findex exp2f +@findex exp2l +@findex expf +@findex expl +@findex expm1 +@findex expm1f +@findex expm1l +@findex fabs +@findex fabsf +@findex fabsl +@findex fdim +@findex fdimf +@findex fdiml +@findex ffs +@findex floor +@findex floorf +@findex floorl +@findex fma +@findex fmaf +@findex fmal +@findex fmax +@findex fmaxf +@findex fmaxl +@findex fmin +@findex fminf +@findex fminl +@findex fmod +@findex fmodf +@findex fmodl +@findex fprintf +@findex fprintf_unlocked +@findex fputs +@findex fputs_unlocked +@findex free +@findex frexp +@findex frexpf +@findex frexpl +@findex fscanf +@findex gamma +@findex gammaf +@findex gammal +@findex gamma_r +@findex gammaf_r +@findex gammal_r +@findex gettext +@findex hypot +@findex hypotf +@findex hypotl +@findex ilogb +@findex ilogbf +@findex ilogbl +@findex imaxabs +@findex index +@findex isalnum +@findex isalpha +@findex isascii +@findex isblank +@findex iscntrl +@findex isdigit +@findex isgraph +@findex islower +@findex isprint +@findex ispunct +@findex isspace +@findex isupper +@findex iswalnum +@findex iswalpha +@findex iswblank +@findex iswcntrl +@findex iswdigit +@findex iswgraph +@findex iswlower +@findex iswprint +@findex iswpunct +@findex iswspace +@findex iswupper +@findex iswxdigit +@findex isxdigit +@findex j0 +@findex j0f +@findex j0l +@findex j1 +@findex j1f +@findex j1l +@findex jn +@findex jnf +@findex jnl +@findex labs +@findex ldexp +@findex ldexpf +@findex ldexpl +@findex lgamma +@findex lgammaf +@findex lgammal +@findex lgamma_r +@findex lgammaf_r +@findex lgammal_r +@findex llabs +@findex llrint +@findex llrintf +@findex llrintl +@findex llround +@findex llroundf +@findex llroundl +@findex log +@findex log10 +@findex log10f +@findex log10l +@findex log1p +@findex log1pf +@findex log1pl +@findex log2 +@findex log2f +@findex log2l +@findex logb +@findex logbf +@findex logbl +@findex logf +@findex logl +@findex lrint +@findex lrintf +@findex lrintl +@findex lround +@findex lroundf +@findex lroundl +@findex malloc +@findex memchr +@findex memcmp +@findex memcpy +@findex mempcpy +@findex memset +@findex modf +@findex modff +@findex modfl +@findex nearbyint +@findex nearbyintf +@findex nearbyintl +@findex nextafter +@findex nextafterf +@findex nextafterl +@findex nexttoward +@findex nexttowardf +@findex nexttowardl +@findex pow +@findex pow10 +@findex pow10f +@findex pow10l +@findex powf +@findex powl +@findex printf +@findex printf_unlocked +@findex putchar +@findex puts +@findex realloc +@findex remainder +@findex remainderf +@findex remainderl +@findex remquo +@findex remquof +@findex remquol +@findex rindex +@findex rint +@findex rintf +@findex rintl +@findex round +@findex roundf +@findex roundl +@findex scalb +@findex scalbf +@findex scalbl +@findex scalbln +@findex scalblnf +@findex scalblnf +@findex scalbn +@findex scalbnf +@findex scanfnl +@findex signbit +@findex signbitf +@findex signbitl +@findex signbitd32 +@findex signbitd64 +@findex signbitd128 +@findex significand +@findex significandf +@findex significandl +@findex sin +@findex sincos +@findex sincosf +@findex sincosl +@findex sinf +@findex sinh +@findex sinhf +@findex sinhl +@findex sinl +@findex snprintf +@findex sprintf +@findex sqrt +@findex sqrtf +@findex sqrtl +@findex sscanf +@findex stpcpy +@findex stpncpy +@findex strcasecmp +@findex strcat +@findex strchr +@findex strcmp +@findex strcpy +@findex strcspn +@findex strdup +@findex strfmon +@findex strftime +@findex strlen +@findex strncasecmp +@findex strncat +@findex strncmp +@findex strncpy +@findex strndup +@findex strnlen +@findex strpbrk +@findex strrchr +@findex strspn +@findex strstr +@findex tan +@findex tanf +@findex tanh +@findex tanhf +@findex tanhl +@findex tanl +@findex tgamma +@findex tgammaf +@findex tgammal +@findex toascii +@findex tolower +@findex toupper +@findex towlower +@findex towupper +@findex trunc +@findex truncf +@findex truncl +@findex vfprintf +@findex vfscanf +@findex vprintf +@findex vscanf +@findex vsnprintf +@findex vsprintf +@findex vsscanf +@findex y0 +@findex y0f +@findex y0l +@findex y1 +@findex y1f +@findex y1l +@findex yn +@findex ynf +@findex ynl + +GCC provides a large number of built-in functions other than the ones +mentioned above. Some of these are for internal use in the processing +of exceptions or variable-length argument lists and are not +documented here because they may change from time to time; we do not +recommend general use of these functions. + +The remaining functions are provided for optimization purposes. + +With the exception of built-ins that have library equivalents such as +the standard C library functions discussed below, or that expand to +library calls, GCC built-in functions are always expanded inline and +thus do not have corresponding entry points and their address cannot +be obtained. Attempting to use them in an expression other than +a function call results in a compile-time error. + +@opindex fno-builtin +GCC includes built-in versions of many of the functions in the standard +C library. These functions come in two forms: one whose names start with +the @code{__builtin_} prefix, and the other without. Both forms have the +same type (including prototype), the same address (when their address is +taken), and the same meaning as the C library functions even if you specify +the @option{-fno-builtin} option @pxref{C Dialect Options}). Many of these +functions are only optimized in certain cases; if they are not optimized in +a particular case, a call to the library function is emitted. + +@opindex ansi +@opindex std +Outside strict ISO C mode (@option{-ansi}, @option{-std=c90}, +@option{-std=c99} or @option{-std=c11}), the functions +@code{_exit}, @code{alloca}, @code{bcmp}, @code{bzero}, +@code{dcgettext}, @code{dgettext}, @code{dremf}, @code{dreml}, +@code{drem}, @code{exp10f}, @code{exp10l}, @code{exp10}, @code{ffsll}, +@code{ffsl}, @code{ffs}, @code{fprintf_unlocked}, +@code{fputs_unlocked}, @code{gammaf}, @code{gammal}, @code{gamma}, +@code{gammaf_r}, @code{gammal_r}, @code{gamma_r}, @code{gettext}, +@code{index}, @code{isascii}, @code{j0f}, @code{j0l}, @code{j0}, +@code{j1f}, @code{j1l}, @code{j1}, @code{jnf}, @code{jnl}, @code{jn}, +@code{lgammaf_r}, @code{lgammal_r}, @code{lgamma_r}, @code{mempcpy}, +@code{pow10f}, @code{pow10l}, @code{pow10}, @code{printf_unlocked}, +@code{rindex}, @code{roundeven}, @code{roundevenf}, @code{roundevenl}, +@code{scalbf}, @code{scalbl}, @code{scalb}, +@code{signbit}, @code{signbitf}, @code{signbitl}, @code{signbitd32}, +@code{signbitd64}, @code{signbitd128}, @code{significandf}, +@code{significandl}, @code{significand}, @code{sincosf}, +@code{sincosl}, @code{sincos}, @code{stpcpy}, @code{stpncpy}, +@code{strcasecmp}, @code{strdup}, @code{strfmon}, @code{strncasecmp}, +@code{strndup}, @code{strnlen}, @code{toascii}, @code{y0f}, @code{y0l}, +@code{y0}, @code{y1f}, @code{y1l}, @code{y1}, @code{ynf}, @code{ynl} and +@code{yn} +may be handled as built-in functions. +All these functions have corresponding versions +prefixed with @code{__builtin_}, which may be used even in strict C90 +mode. + +The ISO C99 functions +@code{_Exit}, @code{acoshf}, @code{acoshl}, @code{acosh}, @code{asinhf}, +@code{asinhl}, @code{asinh}, @code{atanhf}, @code{atanhl}, @code{atanh}, +@code{cabsf}, @code{cabsl}, @code{cabs}, @code{cacosf}, @code{cacoshf}, +@code{cacoshl}, @code{cacosh}, @code{cacosl}, @code{cacos}, +@code{cargf}, @code{cargl}, @code{carg}, @code{casinf}, @code{casinhf}, +@code{casinhl}, @code{casinh}, @code{casinl}, @code{casin}, +@code{catanf}, @code{catanhf}, @code{catanhl}, @code{catanh}, +@code{catanl}, @code{catan}, @code{cbrtf}, @code{cbrtl}, @code{cbrt}, +@code{ccosf}, @code{ccoshf}, @code{ccoshl}, @code{ccosh}, @code{ccosl}, +@code{ccos}, @code{cexpf}, @code{cexpl}, @code{cexp}, @code{cimagf}, +@code{cimagl}, @code{cimag}, @code{clogf}, @code{clogl}, @code{clog}, +@code{conjf}, @code{conjl}, @code{conj}, @code{copysignf}, @code{copysignl}, +@code{copysign}, @code{cpowf}, @code{cpowl}, @code{cpow}, @code{cprojf}, +@code{cprojl}, @code{cproj}, @code{crealf}, @code{creall}, @code{creal}, +@code{csinf}, @code{csinhf}, @code{csinhl}, @code{csinh}, @code{csinl}, +@code{csin}, @code{csqrtf}, @code{csqrtl}, @code{csqrt}, @code{ctanf}, +@code{ctanhf}, @code{ctanhl}, @code{ctanh}, @code{ctanl}, @code{ctan}, +@code{erfcf}, @code{erfcl}, @code{erfc}, @code{erff}, @code{erfl}, +@code{erf}, @code{exp2f}, @code{exp2l}, @code{exp2}, @code{expm1f}, +@code{expm1l}, @code{expm1}, @code{fdimf}, @code{fdiml}, @code{fdim}, +@code{fmaf}, @code{fmal}, @code{fmaxf}, @code{fmaxl}, @code{fmax}, +@code{fma}, @code{fminf}, @code{fminl}, @code{fmin}, @code{hypotf}, +@code{hypotl}, @code{hypot}, @code{ilogbf}, @code{ilogbl}, @code{ilogb}, +@code{imaxabs}, @code{isblank}, @code{iswblank}, @code{lgammaf}, +@code{lgammal}, @code{lgamma}, @code{llabs}, @code{llrintf}, @code{llrintl}, +@code{llrint}, @code{llroundf}, @code{llroundl}, @code{llround}, +@code{log1pf}, @code{log1pl}, @code{log1p}, @code{log2f}, @code{log2l}, +@code{log2}, @code{logbf}, @code{logbl}, @code{logb}, @code{lrintf}, +@code{lrintl}, @code{lrint}, @code{lroundf}, @code{lroundl}, +@code{lround}, @code{nearbyintf}, @code{nearbyintl}, @code{nearbyint}, +@code{nextafterf}, @code{nextafterl}, @code{nextafter}, +@code{nexttowardf}, @code{nexttowardl}, @code{nexttoward}, +@code{remainderf}, @code{remainderl}, @code{remainder}, @code{remquof}, +@code{remquol}, @code{remquo}, @code{rintf}, @code{rintl}, @code{rint}, +@code{roundf}, @code{roundl}, @code{round}, @code{scalblnf}, +@code{scalblnl}, @code{scalbln}, @code{scalbnf}, @code{scalbnl}, +@code{scalbn}, @code{snprintf}, @code{tgammaf}, @code{tgammal}, +@code{tgamma}, @code{truncf}, @code{truncl}, @code{trunc}, +@code{vfscanf}, @code{vscanf}, @code{vsnprintf} and @code{vsscanf} +are handled as built-in functions +except in strict ISO C90 mode (@option{-ansi} or @option{-std=c90}). + +There are also built-in versions of the ISO C99 functions +@code{acosf}, @code{acosl}, @code{asinf}, @code{asinl}, @code{atan2f}, +@code{atan2l}, @code{atanf}, @code{atanl}, @code{ceilf}, @code{ceill}, +@code{cosf}, @code{coshf}, @code{coshl}, @code{cosl}, @code{expf}, +@code{expl}, @code{fabsf}, @code{fabsl}, @code{floorf}, @code{floorl}, +@code{fmodf}, @code{fmodl}, @code{frexpf}, @code{frexpl}, @code{ldexpf}, +@code{ldexpl}, @code{log10f}, @code{log10l}, @code{logf}, @code{logl}, +@code{modfl}, @code{modff}, @code{powf}, @code{powl}, @code{sinf}, +@code{sinhf}, @code{sinhl}, @code{sinl}, @code{sqrtf}, @code{sqrtl}, +@code{tanf}, @code{tanhf}, @code{tanhl} and @code{tanl} +that are recognized in any mode since ISO C90 reserves these names for +the purpose to which ISO C99 puts them. All these functions have +corresponding versions prefixed with @code{__builtin_}. + +There are also built-in functions @code{__builtin_fabsf@var{n}}, +@code{__builtin_fabsf@var{n}x}, @code{__builtin_copysignf@var{n}} and +@code{__builtin_copysignf@var{n}x}, corresponding to the TS 18661-3 +functions @code{fabsf@var{n}}, @code{fabsf@var{n}x}, +@code{copysignf@var{n}} and @code{copysignf@var{n}x}, for supported +types @code{_Float@var{n}} and @code{_Float@var{n}x}. + +There are also GNU extension functions @code{clog10}, @code{clog10f} and +@code{clog10l} which names are reserved by ISO C99 for future use. +All these functions have versions prefixed with @code{__builtin_}. + +The ISO C94 functions +@code{iswalnum}, @code{iswalpha}, @code{iswcntrl}, @code{iswdigit}, +@code{iswgraph}, @code{iswlower}, @code{iswprint}, @code{iswpunct}, +@code{iswspace}, @code{iswupper}, @code{iswxdigit}, @code{towlower} and +@code{towupper} +are handled as built-in functions +except in strict ISO C90 mode (@option{-ansi} or @option{-std=c90}). + +The ISO C90 functions +@code{abort}, @code{abs}, @code{acos}, @code{asin}, @code{atan2}, +@code{atan}, @code{calloc}, @code{ceil}, @code{cosh}, @code{cos}, +@code{exit}, @code{exp}, @code{fabs}, @code{floor}, @code{fmod}, +@code{fprintf}, @code{fputs}, @code{free}, @code{frexp}, @code{fscanf}, +@code{isalnum}, @code{isalpha}, @code{iscntrl}, @code{isdigit}, +@code{isgraph}, @code{islower}, @code{isprint}, @code{ispunct}, +@code{isspace}, @code{isupper}, @code{isxdigit}, @code{tolower}, +@code{toupper}, @code{labs}, @code{ldexp}, @code{log10}, @code{log}, +@code{malloc}, @code{memchr}, @code{memcmp}, @code{memcpy}, +@code{memset}, @code{modf}, @code{pow}, @code{printf}, @code{putchar}, +@code{puts}, @code{realloc}, @code{scanf}, @code{sinh}, @code{sin}, +@code{snprintf}, @code{sprintf}, @code{sqrt}, @code{sscanf}, @code{strcat}, +@code{strchr}, @code{strcmp}, @code{strcpy}, @code{strcspn}, +@code{strlen}, @code{strncat}, @code{strncmp}, @code{strncpy}, +@code{strpbrk}, @code{strrchr}, @code{strspn}, @code{strstr}, +@code{tanh}, @code{tan}, @code{vfprintf}, @code{vprintf} and @code{vsprintf} +are all recognized as built-in functions unless +@option{-fno-builtin} is specified (or @option{-fno-builtin-@var{function}} +is specified for an individual function). All of these functions have +corresponding versions prefixed with @code{__builtin_}. + +GCC provides built-in versions of the ISO C99 floating-point comparison +macros that avoid raising exceptions for unordered operands. They have +the same names as the standard macros ( @code{isgreater}, +@code{isgreaterequal}, @code{isless}, @code{islessequal}, +@code{islessgreater}, and @code{isunordered}) , with @code{__builtin_} +prefixed. We intend for a library implementor to be able to simply +@code{#define} each standard macro to its built-in equivalent. +In the same fashion, GCC provides @code{fpclassify}, @code{isfinite}, +@code{isinf_sign}, @code{isnormal} and @code{signbit} built-ins used with +@code{__builtin_} prefixed. The @code{isinf} and @code{isnan} +built-in functions appear both with and without the @code{__builtin_} prefix. +With @code{-ffinite-math-only} option the @code{isinf} and @code{isnan} +built-in functions will always return 0. + +GCC provides built-in versions of the ISO C99 floating-point rounding and +exceptions handling functions @code{fegetround}, @code{feclearexcept} and +@code{feraiseexcept}. They may not be available for all targets, and because +they need close interaction with libc internal values, they may not be available +for all target libcs, but in all cases they will gracefully fallback to libc +calls. These built-in functions appear both with and without the +@code{__builtin_} prefix. + +@deftypefn {Built-in Function} void *__builtin_alloca (size_t size) +The @code{__builtin_alloca} function must be called at block scope. +The function allocates an object @var{size} bytes large on the stack +of the calling function. The object is aligned on the default stack +alignment boundary for the target determined by the +@code{__BIGGEST_ALIGNMENT__} macro. The @code{__builtin_alloca} +function returns a pointer to the first byte of the allocated object. +The lifetime of the allocated object ends just before the calling +function returns to its caller. This is so even when +@code{__builtin_alloca} is called within a nested block. + +For example, the following function allocates eight objects of @code{n} +bytes each on the stack, storing a pointer to each in consecutive elements +of the array @code{a}. It then passes the array to function @code{g} +which can safely use the storage pointed to by each of the array elements. + +@smallexample +void f (unsigned n) +@{ + void *a [8]; + for (int i = 0; i != 8; ++i) + a [i] = __builtin_alloca (n); + + g (a, n); // @r{safe} +@} +@end smallexample + +Since the @code{__builtin_alloca} function doesn't validate its argument +it is the responsibility of its caller to make sure the argument doesn't +cause it to exceed the stack size limit. +The @code{__builtin_alloca} function is provided to make it possible to +allocate on the stack arrays of bytes with an upper bound that may be +computed at run time. Since C99 Variable Length Arrays offer +similar functionality under a portable, more convenient, and safer +interface they are recommended instead, in both C99 and C++ programs +where GCC provides them as an extension. +@xref{Variable Length}, for details. + +@end deftypefn + +@deftypefn {Built-in Function} void *__builtin_alloca_with_align (size_t size, size_t alignment) +The @code{__builtin_alloca_with_align} function must be called at block +scope. The function allocates an object @var{size} bytes large on +the stack of the calling function. The allocated object is aligned on +the boundary specified by the argument @var{alignment} whose unit is given +in bits (not bytes). The @var{size} argument must be positive and not +exceed the stack size limit. The @var{alignment} argument must be a constant +integer expression that evaluates to a power of 2 greater than or equal to +@code{CHAR_BIT} and less than some unspecified maximum. Invocations +with other values are rejected with an error indicating the valid bounds. +The function returns a pointer to the first byte of the allocated object. +The lifetime of the allocated object ends at the end of the block in which +the function was called. The allocated storage is released no later than +just before the calling function returns to its caller, but may be released +at the end of the block in which the function was called. + +For example, in the following function the call to @code{g} is unsafe +because when @code{overalign} is non-zero, the space allocated by +@code{__builtin_alloca_with_align} may have been released at the end +of the @code{if} statement in which it was called. + +@smallexample +void f (unsigned n, bool overalign) +@{ + void *p; + if (overalign) + p = __builtin_alloca_with_align (n, 64 /* bits */); + else + p = __builtin_alloc (n); + + g (p, n); // @r{unsafe} +@} +@end smallexample + +Since the @code{__builtin_alloca_with_align} function doesn't validate its +@var{size} argument it is the responsibility of its caller to make sure +the argument doesn't cause it to exceed the stack size limit. +The @code{__builtin_alloca_with_align} function is provided to make +it possible to allocate on the stack overaligned arrays of bytes with +an upper bound that may be computed at run time. Since C99 +Variable Length Arrays offer the same functionality under +a portable, more convenient, and safer interface they are recommended +instead, in both C99 and C++ programs where GCC provides them as +an extension. @xref{Variable Length}, for details. + +@end deftypefn + +@deftypefn {Built-in Function} void *__builtin_alloca_with_align_and_max (size_t size, size_t alignment, size_t max_size) +Similar to @code{__builtin_alloca_with_align} but takes an extra argument +specifying an upper bound for @var{size} in case its value cannot be computed +at compile time, for use by @option{-fstack-usage}, @option{-Wstack-usage} +and @option{-Walloca-larger-than}. @var{max_size} must be a constant integer +expression, it has no effect on code generation and no attempt is made to +check its compatibility with @var{size}. + +@end deftypefn + +@deftypefn {Built-in Function} bool __builtin_has_attribute (@var{type-or-expression}, @var{attribute}) +The @code{__builtin_has_attribute} function evaluates to an integer constant +expression equal to @code{true} if the symbol or type referenced by +the @var{type-or-expression} argument has been declared with +the @var{attribute} referenced by the second argument. For +an @var{type-or-expression} argument that does not reference a symbol, +since attributes do not apply to expressions the built-in consider +the type of the argument. Neither argument is evaluated. +The @var{type-or-expression} argument is subject to the same +restrictions as the argument to @code{typeof} (@pxref{Typeof}). The +@var{attribute} argument is an attribute name optionally followed by +a comma-separated list of arguments enclosed in parentheses. Both forms +of attribute names---with and without double leading and trailing +underscores---are recognized. @xref{Attribute Syntax}, for details. +When no attribute arguments are specified for an attribute that expects +one or more arguments the function returns @code{true} if +@var{type-or-expression} has been declared with the attribute regardless +of the attribute argument values. Arguments provided for an attribute +that expects some are validated and matched up to the provided number. +The function returns @code{true} if all provided arguments match. For +example, the first call to the function below evaluates to @code{true} +because @code{x} is declared with the @code{aligned} attribute but +the second call evaluates to @code{false} because @code{x} is declared +@code{aligned (8)} and not @code{aligned (4)}. + +@smallexample +__attribute__ ((aligned (8))) int x; +_Static_assert (__builtin_has_attribute (x, aligned), "aligned"); +_Static_assert (!__builtin_has_attribute (x, aligned (4)), "aligned (4)"); +@end smallexample + +Due to a limitation the @code{__builtin_has_attribute} function returns +@code{false} for the @code{mode} attribute even if the type or variable +referenced by the @var{type-or-expression} argument was declared with one. +The function is also not supported with labels, and in C with enumerators. + +Note that unlike the @code{__has_attribute} preprocessor operator which +is suitable for use in @code{#if} preprocessing directives +@code{__builtin_has_attribute} is an intrinsic function that is not +recognized in such contexts. + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __builtin_speculation_safe_value (@var{type} val, @var{type} failval) + +This built-in function can be used to help mitigate against unsafe +speculative execution. @var{type} may be any integral type or any +pointer type. + +@enumerate +@item +If the CPU is not speculatively executing the code, then @var{val} +is returned. +@item +If the CPU is executing speculatively then either: +@itemize +@item +The function may cause execution to pause until it is known that the +code is no-longer being executed speculatively (in which case +@var{val} can be returned, as above); or +@item +The function may use target-dependent speculation tracking state to cause +@var{failval} to be returned when it is known that speculative +execution has incorrectly predicted a conditional branch operation. +@end itemize +@end enumerate + +The second argument, @var{failval}, is optional and defaults to zero +if omitted. + +GCC defines the preprocessor macro +@code{__HAVE_BUILTIN_SPECULATION_SAFE_VALUE} for targets that have been +updated to support this builtin. + +The built-in function can be used where a variable appears to be used in a +safe way, but the CPU, due to speculative execution may temporarily ignore +the bounds checks. Consider, for example, the following function: + +@smallexample +int array[500]; +int f (unsigned untrusted_index) +@{ + if (untrusted_index < 500) + return array[untrusted_index]; + return 0; +@} +@end smallexample + +If the function is called repeatedly with @code{untrusted_index} less +than the limit of 500, then a branch predictor will learn that the +block of code that returns a value stored in @code{array} will be +executed. If the function is subsequently called with an +out-of-range value it will still try to execute that block of code +first until the CPU determines that the prediction was incorrect +(the CPU will unwind any incorrect operations at that point). +However, depending on how the result of the function is used, it might be +possible to leave traces in the cache that can reveal what was stored +at the out-of-bounds location. The built-in function can be used to +provide some protection against leaking data in this way by changing +the code to: + +@smallexample +int array[500]; +int f (unsigned untrusted_index) +@{ + if (untrusted_index < 500) + return array[__builtin_speculation_safe_value (untrusted_index)]; + return 0; +@} +@end smallexample + +The built-in function will either cause execution to stall until the +conditional branch has been fully resolved, or it may permit +speculative execution to continue, but using 0 instead of +@code{untrusted_value} if that exceeds the limit. + +If accessing any memory location is potentially unsafe when speculative +execution is incorrect, then the code can be rewritten as + +@smallexample +int array[500]; +int f (unsigned untrusted_index) +@{ + if (untrusted_index < 500) + return *__builtin_speculation_safe_value (&array[untrusted_index], NULL); + return 0; +@} +@end smallexample + +which will cause a @code{NULL} pointer to be used for the unsafe case. + +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_types_compatible_p (@var{type1}, @var{type2}) + +You can use the built-in function @code{__builtin_types_compatible_p} to +determine whether two types are the same. + +This built-in function returns 1 if the unqualified versions of the +types @var{type1} and @var{type2} (which are types, not expressions) are +compatible, 0 otherwise. The result of this built-in function can be +used in integer constant expressions. + +This built-in function ignores top level qualifiers (e.g., @code{const}, +@code{volatile}). For example, @code{int} is equivalent to @code{const +int}. + +The type @code{int[]} and @code{int[5]} are compatible. On the other +hand, @code{int} and @code{char *} are not compatible, even if the size +of their types, on the particular architecture are the same. Also, the +amount of pointer indirection is taken into account when determining +similarity. Consequently, @code{short *} is not similar to +@code{short **}. Furthermore, two types that are typedefed are +considered compatible if their underlying types are compatible. + +An @code{enum} type is not considered to be compatible with another +@code{enum} type even if both are compatible with the same integer +type; this is what the C standard specifies. +For example, @code{enum @{foo, bar@}} is not similar to +@code{enum @{hot, dog@}}. + +You typically use this function in code whose execution varies +depending on the arguments' types. For example: + +@smallexample +#define foo(x) \ + (@{ \ + typeof (x) tmp = (x); \ + if (__builtin_types_compatible_p (typeof (x), long double)) \ + tmp = foo_long_double (tmp); \ + else if (__builtin_types_compatible_p (typeof (x), double)) \ + tmp = foo_double (tmp); \ + else if (__builtin_types_compatible_p (typeof (x), float)) \ + tmp = foo_float (tmp); \ + else \ + abort (); \ + tmp; \ + @}) +@end smallexample + +@emph{Note:} This construct is only available for C@. + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __builtin_call_with_static_chain (@var{call_exp}, @var{pointer_exp}) + +The @var{call_exp} expression must be a function call, and the +@var{pointer_exp} expression must be a pointer. The @var{pointer_exp} +is passed to the function call in the target's static chain location. +The result of builtin is the result of the function call. + +@emph{Note:} This builtin is only available for C@. +This builtin can be used to call Go closures from C. + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __builtin_choose_expr (@var{const_exp}, @var{exp1}, @var{exp2}) + +You can use the built-in function @code{__builtin_choose_expr} to +evaluate code depending on the value of a constant expression. This +built-in function returns @var{exp1} if @var{const_exp}, which is an +integer constant expression, is nonzero. Otherwise it returns @var{exp2}. + +This built-in function is analogous to the @samp{? :} operator in C, +except that the expression returned has its type unaltered by promotion +rules. Also, the built-in function does not evaluate the expression +that is not chosen. For example, if @var{const_exp} evaluates to @code{true}, +@var{exp2} is not evaluated even if it has side effects. + +This built-in function can return an lvalue if the chosen argument is an +lvalue. + +If @var{exp1} is returned, the return type is the same as @var{exp1}'s +type. Similarly, if @var{exp2} is returned, its return type is the same +as @var{exp2}. + +Example: + +@smallexample +#define foo(x) \ + __builtin_choose_expr ( \ + __builtin_types_compatible_p (typeof (x), double), \ + foo_double (x), \ + __builtin_choose_expr ( \ + __builtin_types_compatible_p (typeof (x), float), \ + foo_float (x), \ + /* @r{The void expression results in a compile-time error} \ + @r{when assigning the result to something.} */ \ + (void)0)) +@end smallexample + +@emph{Note:} This construct is only available for C@. Furthermore, the +unused expression (@var{exp1} or @var{exp2} depending on the value of +@var{const_exp}) may still generate syntax errors. This may change in +future revisions. + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __builtin_tgmath (@var{functions}, @var{arguments}) + +The built-in function @code{__builtin_tgmath}, available only for C +and Objective-C, calls a function determined according to the rules of +@code{} macros. It is intended to be used in +implementations of that header, so that expansions of macros from that +header only expand each of their arguments once, to avoid problems +when calls to such macros are nested inside the arguments of other +calls to such macros; in addition, it results in better diagnostics +for invalid calls to @code{} macros than implementations +using other GNU C language features. For example, the @code{pow} +type-generic macro might be defined as: + +@smallexample +#define pow(a, b) __builtin_tgmath (powf, pow, powl, \ + cpowf, cpow, cpowl, a, b) +@end smallexample + +The arguments to @code{__builtin_tgmath} are at least two pointers to +functions, followed by the arguments to the type-generic macro (which +will be passed as arguments to the selected function). All the +pointers to functions must be pointers to prototyped functions, none +of which may have variable arguments, and all of which must have the +same number of parameters; the number of parameters of the first +function determines how many arguments to @code{__builtin_tgmath} are +interpreted as function pointers, and how many as the arguments to the +called function. + +The types of the specified functions must all be different, but +related to each other in the same way as a set of functions that may +be selected between by a macro in @code{}. This means that +the functions are parameterized by a floating-point type @var{t}, +different for each such function. The function return types may all +be the same type, or they may be @var{t} for each function, or they +may be the real type corresponding to @var{t} for each function (if +some of the types @var{t} are complex). Likewise, for each parameter +position, the type of the parameter in that position may always be the +same type, or may be @var{t} for each function (this case must apply +for at least one parameter position), or may be the real type +corresponding to @var{t} for each function. + +The standard rules for @code{} macros are used to find a +common type @var{u} from the types of the arguments for parameters +whose types vary between the functions; complex integer types (a GNU +extension) are treated like @code{_Complex double} for this purpose +(or @code{_Complex _Float64} if all the function return types are the +same @code{_Float@var{n}} or @code{_Float@var{n}x} type). +If the function return types vary, or are all the same integer type, +the function called is the one for which @var{t} is @var{u}, and it is +an error if there is no such function. If the function return types +are all the same floating-point type, the type-generic macro is taken +to be one of those from TS 18661 that rounds the result to a narrower +type; if there is a function for which @var{t} is @var{u}, it is +called, and otherwise the first function, if any, for which @var{t} +has at least the range and precision of @var{u} is called, and it is +an error if there is no such function. + +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_constant_p (@var{exp}) +You can use the built-in function @code{__builtin_constant_p} to +determine if a value is known to be constant at compile time and hence +that GCC can perform constant-folding on expressions involving that +value. The argument of the function is the value to test. The function +returns the integer 1 if the argument is known to be a compile-time +constant and 0 if it is not known to be a compile-time constant. A +return of 0 does not indicate that the value is @emph{not} a constant, +but merely that GCC cannot prove it is a constant with the specified +value of the @option{-O} option. + +You typically use this function in an embedded application where +memory is a critical resource. If you have some complex calculation, +you may want it to be folded if it involves constants, but need to call +a function if it does not. For example: + +@smallexample +#define Scale_Value(X) \ + (__builtin_constant_p (X) \ + ? ((X) * SCALE + OFFSET) : Scale (X)) +@end smallexample + +You may use this built-in function in either a macro or an inline +function. However, if you use it in an inlined function and pass an +argument of the function as the argument to the built-in, GCC +never returns 1 when you call the inline function with a string constant +or compound literal (@pxref{Compound Literals}) and does not return 1 +when you pass a constant numeric value to the inline function unless you +specify the @option{-O} option. + +You may also use @code{__builtin_constant_p} in initializers for static +data. For instance, you can write + +@smallexample +static const int table[] = @{ + __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1, + /* @r{@dots{}} */ +@}; +@end smallexample + +@noindent +This is an acceptable initializer even if @var{EXPRESSION} is not a +constant expression, including the case where +@code{__builtin_constant_p} returns 1 because @var{EXPRESSION} can be +folded to a constant but @var{EXPRESSION} contains operands that are +not otherwise permitted in a static initializer (for example, +@code{0 && foo ()}). GCC must be more conservative about evaluating the +built-in in this case, because it has no opportunity to perform +optimization. +@end deftypefn + +@deftypefn {Built-in Function} bool __builtin_is_constant_evaluated (void) +The @code{__builtin_is_constant_evaluated} function is available only +in C++. The built-in is intended to be used by implementations of +the @code{std::is_constant_evaluated} C++ function. Programs should make +use of the latter function rather than invoking the built-in directly. + +The main use case of the built-in is to determine whether a @code{constexpr} +function is being called in a @code{constexpr} context. A call to +the function evaluates to a core constant expression with the value +@code{true} if and only if it occurs within the evaluation of an expression +or conversion that is manifestly constant-evaluated as defined in the C++ +standard. Manifestly constant-evaluated contexts include constant-expressions, +the conditions of @code{constexpr if} statements, constraint-expressions, and +initializers of variables usable in constant expressions. For more details +refer to the latest revision of the C++ standard. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_clear_padding (@var{ptr}) +The built-in function @code{__builtin_clear_padding} function clears +padding bits inside of the object representation of object pointed by +@var{ptr}, which has to be a pointer. The value representation of the +object is not affected. The type of the object is assumed to be the type +the pointer points to. Inside of a union, the only cleared bits are +bits that are padding bits for all the union members. + +This built-in-function is useful if the padding bits of an object might +have intederminate values and the object representation needs to be +bitwise compared to some other object, for example for atomic operations. + +For C++, @var{ptr} argument type should be pointer to trivially-copyable +type, unless the argument is address of a variable or parameter, because +otherwise it isn't known if the type isn't just a base class whose padding +bits are reused or laid out differently in a derived class. +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __builtin_bit_cast (@var{type}, @var{arg}) +The @code{__builtin_bit_cast} function is available only +in C++. The built-in is intended to be used by implementations of +the @code{std::bit_cast} C++ template function. Programs should make +use of the latter function rather than invoking the built-in directly. + +This built-in function allows reinterpreting the bits of the @var{arg} +argument as if it had type @var{type}. @var{type} and the type of the +@var{arg} argument need to be trivially copyable types with the same size. +When manifestly constant-evaluated, it performs extra diagnostics required +for @code{std::bit_cast} and returns a constant expression if @var{arg} +is a constant expression. For more details +refer to the latest revision of the C++ standard. +@end deftypefn + +@deftypefn {Built-in Function} long __builtin_expect (long @var{exp}, long @var{c}) +@opindex fprofile-arcs +You may use @code{__builtin_expect} to provide the compiler with +branch prediction information. In general, you should prefer to +use actual profile feedback for this (@option{-fprofile-arcs}), as +programmers are notoriously bad at predicting how their programs +actually perform. However, there are applications in which this +data is hard to collect. + +The return value is the value of @var{exp}, which should be an integral +expression. The semantics of the built-in are that it is expected that +@var{exp} == @var{c}. For example: + +@smallexample +if (__builtin_expect (x, 0)) + foo (); +@end smallexample + +@noindent +indicates that we do not expect to call @code{foo}, since +we expect @code{x} to be zero. Since you are limited to integral +expressions for @var{exp}, you should use constructions such as + +@smallexample +if (__builtin_expect (ptr != NULL, 1)) + foo (*ptr); +@end smallexample + +@noindent +when testing pointer or floating-point values. + +For the purposes of branch prediction optimizations, the probability that +a @code{__builtin_expect} expression is @code{true} is controlled by GCC's +@code{builtin-expect-probability} parameter, which defaults to 90%. + +You can also use @code{__builtin_expect_with_probability} to explicitly +assign a probability value to individual expressions. If the built-in +is used in a loop construct, the provided probability will influence +the expected number of iterations made by loop optimizations. +@end deftypefn + +@deftypefn {Built-in Function} long __builtin_expect_with_probability +(long @var{exp}, long @var{c}, double @var{probability}) + +This function has the same semantics as @code{__builtin_expect}, +but the caller provides the expected probability that @var{exp} == @var{c}. +The last argument, @var{probability}, is a floating-point value in the +range 0.0 to 1.0, inclusive. The @var{probability} argument must be +constant floating-point expression. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_trap (void) +This function causes the program to exit abnormally. GCC implements +this function by using a target-dependent mechanism (such as +intentionally executing an illegal instruction) or by calling +@code{abort}. The mechanism used may vary from release to release so +you should not rely on any particular implementation. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_unreachable (void) +If control flow reaches the point of the @code{__builtin_unreachable}, +the program is undefined. It is useful in situations where the +compiler cannot deduce the unreachability of the code. + +One such case is immediately following an @code{asm} statement that +either never terminates, or one that transfers control elsewhere +and never returns. In this example, without the +@code{__builtin_unreachable}, GCC issues a warning that control +reaches the end of a non-void function. It also generates code +to return after the @code{asm}. + +@smallexample +int f (int c, int v) +@{ + if (c) + @{ + return v; + @} + else + @{ + asm("jmp error_handler"); + __builtin_unreachable (); + @} +@} +@end smallexample + +@noindent +Because the @code{asm} statement unconditionally transfers control out +of the function, control never reaches the end of the function +body. The @code{__builtin_unreachable} is in fact unreachable and +communicates this fact to the compiler. + +Another use for @code{__builtin_unreachable} is following a call a +function that never returns but that is not declared +@code{__attribute__((noreturn))}, as in this example: + +@smallexample +void function_that_never_returns (void); + +int g (int c) +@{ + if (c) + @{ + return 1; + @} + else + @{ + function_that_never_returns (); + __builtin_unreachable (); + @} +@} +@end smallexample + +@end deftypefn + +@deftypefn {Built-in Function} @var{type} __builtin_assoc_barrier (@var{type} @var{expr}) +This built-in inhibits re-association of the floating-point expression +@var{expr} with expressions consuming the return value of the built-in. The +expression @var{expr} itself can be reordered, and the whole expression +@var{expr} can be reordered with operands after the barrier. The barrier is +only relevant when @code{-fassociative-math} is active, since otherwise +floating-point is not treated as associative. + +@smallexample +float x0 = a + b - b; +float x1 = __builtin_assoc_barrier(a + b) - b; +@end smallexample + +@noindent +means that, with @code{-fassociative-math}, @code{x0} can be optimized to +@code{x0 = a} but @code{x1} cannot. +@end deftypefn + +@deftypefn {Built-in Function} {void *} __builtin_assume_aligned (const void *@var{exp}, size_t @var{align}, ...) +This function returns its first argument, and allows the compiler +to assume that the returned pointer is at least @var{align} bytes +aligned. This built-in can have either two or three arguments, +if it has three, the third argument should have integer type, and +if it is nonzero means misalignment offset. For example: + +@smallexample +void *x = __builtin_assume_aligned (arg, 16); +@end smallexample + +@noindent +means that the compiler can assume @code{x}, set to @code{arg}, is at least +16-byte aligned, while: + +@smallexample +void *x = __builtin_assume_aligned (arg, 32, 8); +@end smallexample + +@noindent +means that the compiler can assume for @code{x}, set to @code{arg}, that +@code{(char *) x - 8} is 32-byte aligned. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_LINE () +This function is the equivalent of the preprocessor @code{__LINE__} +macro and returns a constant integer expression that evaluates to +the line number of the invocation of the built-in. When used as a C++ +default argument for a function @var{F}, it returns the line number +of the call to @var{F}. +@end deftypefn + +@deftypefn {Built-in Function} {const char *} __builtin_FUNCTION () +This function is the equivalent of the @code{__FUNCTION__} symbol +and returns an address constant pointing to the name of the function +from which the built-in was invoked, or the empty string if +the invocation is not at function scope. When used as a C++ default +argument for a function @var{F}, it returns the name of @var{F}'s +caller or the empty string if the call was not made at function +scope. +@end deftypefn + +@deftypefn {Built-in Function} {const char *} __builtin_FILE () +This function is the equivalent of the preprocessor @code{__FILE__} +macro and returns an address constant pointing to the file name +containing the invocation of the built-in, or the empty string if +the invocation is not at function scope. When used as a C++ default +argument for a function @var{F}, it returns the file name of the call +to @var{F} or the empty string if the call was not made at function +scope. + +For example, in the following, each call to function @code{foo} will +print a line similar to @code{"file.c:123: foo: message"} with the name +of the file and the line number of the @code{printf} call, the name of +the function @code{foo}, followed by the word @code{message}. + +@smallexample +const char* +function (const char *func = __builtin_FUNCTION ()) +@{ + return func; +@} + +void foo (void) +@{ + printf ("%s:%i: %s: message\n", file (), line (), function ()); +@} +@end smallexample + +@end deftypefn + +@deftypefn {Built-in Function} void __builtin___clear_cache (void *@var{begin}, void *@var{end}) +This function is used to flush the processor's instruction cache for +the region of memory between @var{begin} inclusive and @var{end} +exclusive. Some targets require that the instruction cache be +flushed, after modifying memory containing code, in order to obtain +deterministic behavior. + +If the target does not require instruction cache flushes, +@code{__builtin___clear_cache} has no effect. Otherwise either +instructions are emitted in-line to clear the instruction cache or a +call to the @code{__clear_cache} function in libgcc is made. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_prefetch (const void *@var{addr}, ...) +This function is used to minimize cache-miss latency by moving data into +a cache before it is accessed. +You can insert calls to @code{__builtin_prefetch} into code for which +you know addresses of data in memory that is likely to be accessed soon. +If the target supports them, data prefetch instructions are generated. +If the prefetch is done early enough before the access then the data will +be in the cache by the time it is accessed. + +The value of @var{addr} is the address of the memory to prefetch. +There are two optional arguments, @var{rw} and @var{locality}. +The value of @var{rw} is a compile-time constant one or zero; one +means that the prefetch is preparing for a write to the memory address +and zero, the default, means that the prefetch is preparing for a read. +The value @var{locality} must be a compile-time constant integer between +zero and three. A value of zero means that the data has no temporal +locality, so it need not be left in the cache after the access. A value +of three means that the data has a high degree of temporal locality and +should be left in all levels of cache possible. Values of one and two +mean, respectively, a low or moderate degree of temporal locality. The +default is three. + +@smallexample +for (i = 0; i < n; i++) + @{ + a[i] = a[i] + b[i]; + __builtin_prefetch (&a[i+j], 1, 1); + __builtin_prefetch (&b[i+j], 0, 1); + /* @r{@dots{}} */ + @} +@end smallexample + +Data prefetch does not generate faults if @var{addr} is invalid, but +the address expression itself must be valid. For example, a prefetch +of @code{p->next} does not fault if @code{p->next} is not a valid +address, but evaluation faults if @code{p} is not a valid address. + +If the target does not support data prefetch, the address expression +is evaluated if it includes side effects but no other code is generated +and GCC does not issue a warning. +@end deftypefn + +@deftypefn {Built-in Function}{size_t} __builtin_object_size (const void * @var{ptr}, int @var{type}) +Returns the size of an object pointed to by @var{ptr}. @xref{Object Size +Checking}, for a detailed description of the function. +@end deftypefn + +@deftypefn {Built-in Function} double __builtin_huge_val (void) +Returns a positive infinity, if supported by the floating-point format, +else @code{DBL_MAX}. This function is suitable for implementing the +ISO C macro @code{HUGE_VAL}. +@end deftypefn + +@deftypefn {Built-in Function} float __builtin_huge_valf (void) +Similar to @code{__builtin_huge_val}, except the return type is @code{float}. +@end deftypefn + +@deftypefn {Built-in Function} {long double} __builtin_huge_vall (void) +Similar to @code{__builtin_huge_val}, except the return +type is @code{long double}. +@end deftypefn + +@deftypefn {Built-in Function} _Float@var{n} __builtin_huge_valf@var{n} (void) +Similar to @code{__builtin_huge_val}, except the return type is +@code{_Float@var{n}}. +@end deftypefn + +@deftypefn {Built-in Function} _Float@var{n}x __builtin_huge_valf@var{n}x (void) +Similar to @code{__builtin_huge_val}, except the return type is +@code{_Float@var{n}x}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_fpclassify (int, int, int, int, int, ...) +This built-in implements the C99 fpclassify functionality. The first +five int arguments should be the target library's notion of the +possible FP classes and are used for return values. They must be +constant values and they must appear in this order: @code{FP_NAN}, +@code{FP_INFINITE}, @code{FP_NORMAL}, @code{FP_SUBNORMAL} and +@code{FP_ZERO}. The ellipsis is for exactly one floating-point value +to classify. GCC treats the last argument as type-generic, which +means it does not do default promotion from float to double. +@end deftypefn + +@deftypefn {Built-in Function} double __builtin_inf (void) +Similar to @code{__builtin_huge_val}, except a warning is generated +if the target floating-point format does not support infinities. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal32 __builtin_infd32 (void) +Similar to @code{__builtin_inf}, except the return type is @code{_Decimal32}. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal64 __builtin_infd64 (void) +Similar to @code{__builtin_inf}, except the return type is @code{_Decimal64}. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal128 __builtin_infd128 (void) +Similar to @code{__builtin_inf}, except the return type is @code{_Decimal128}. +@end deftypefn + +@deftypefn {Built-in Function} float __builtin_inff (void) +Similar to @code{__builtin_inf}, except the return type is @code{float}. +This function is suitable for implementing the ISO C99 macro @code{INFINITY}. +@end deftypefn + +@deftypefn {Built-in Function} {long double} __builtin_infl (void) +Similar to @code{__builtin_inf}, except the return +type is @code{long double}. +@end deftypefn + +@deftypefn {Built-in Function} _Float@var{n} __builtin_inff@var{n} (void) +Similar to @code{__builtin_inf}, except the return +type is @code{_Float@var{n}}. +@end deftypefn + +@deftypefn {Built-in Function} _Float@var{n} __builtin_inff@var{n}x (void) +Similar to @code{__builtin_inf}, except the return +type is @code{_Float@var{n}x}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_isinf_sign (...) +Similar to @code{isinf}, except the return value is -1 for +an argument of @code{-Inf} and 1 for an argument of @code{+Inf}. +Note while the parameter list is an +ellipsis, this function only accepts exactly one floating-point +argument. GCC treats this parameter as type-generic, which means it +does not do default promotion from float to double. +@end deftypefn + +@deftypefn {Built-in Function} double __builtin_nan (const char *str) +This is an implementation of the ISO C99 function @code{nan}. + +Since ISO C99 defines this function in terms of @code{strtod}, which we +do not implement, a description of the parsing is in order. The string +is parsed as by @code{strtol}; that is, the base is recognized by +leading @samp{0} or @samp{0x} prefixes. The number parsed is placed +in the significand such that the least significant bit of the number +is at the least significant bit of the significand. The number is +truncated to fit the significand field provided. The significand is +forced to be a quiet NaN@. + +This function, if given a string literal all of which would have been +consumed by @code{strtol}, is evaluated early enough that it is considered a +compile-time constant. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal32 __builtin_nand32 (const char *str) +Similar to @code{__builtin_nan}, except the return type is @code{_Decimal32}. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal64 __builtin_nand64 (const char *str) +Similar to @code{__builtin_nan}, except the return type is @code{_Decimal64}. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal128 __builtin_nand128 (const char *str) +Similar to @code{__builtin_nan}, except the return type is @code{_Decimal128}. +@end deftypefn + +@deftypefn {Built-in Function} float __builtin_nanf (const char *str) +Similar to @code{__builtin_nan}, except the return type is @code{float}. +@end deftypefn + +@deftypefn {Built-in Function} {long double} __builtin_nanl (const char *str) +Similar to @code{__builtin_nan}, except the return type is @code{long double}. +@end deftypefn + +@deftypefn {Built-in Function} _Float@var{n} __builtin_nanf@var{n} (const char *str) +Similar to @code{__builtin_nan}, except the return type is +@code{_Float@var{n}}. +@end deftypefn + +@deftypefn {Built-in Function} _Float@var{n}x __builtin_nanf@var{n}x (const char *str) +Similar to @code{__builtin_nan}, except the return type is +@code{_Float@var{n}x}. +@end deftypefn + +@deftypefn {Built-in Function} double __builtin_nans (const char *str) +Similar to @code{__builtin_nan}, except the significand is forced +to be a signaling NaN@. The @code{nans} function is proposed by +@uref{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htm,,WG14 N965}. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal32 __builtin_nansd32 (const char *str) +Similar to @code{__builtin_nans}, except the return type is @code{_Decimal32}. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal64 __builtin_nansd64 (const char *str) +Similar to @code{__builtin_nans}, except the return type is @code{_Decimal64}. +@end deftypefn + +@deftypefn {Built-in Function} _Decimal128 __builtin_nansd128 (const char *str) +Similar to @code{__builtin_nans}, except the return type is @code{_Decimal128}. +@end deftypefn + +@deftypefn {Built-in Function} float __builtin_nansf (const char *str) +Similar to @code{__builtin_nans}, except the return type is @code{float}. +@end deftypefn + +@deftypefn {Built-in Function} {long double} __builtin_nansl (const char *str) +Similar to @code{__builtin_nans}, except the return type is @code{long double}. +@end deftypefn + +@deftypefn {Built-in Function} _Float@var{n} __builtin_nansf@var{n} (const char *str) +Similar to @code{__builtin_nans}, except the return type is +@code{_Float@var{n}}. +@end deftypefn + +@deftypefn {Built-in Function} _Float@var{n}x __builtin_nansf@var{n}x (const char *str) +Similar to @code{__builtin_nans}, except the return type is +@code{_Float@var{n}x}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_issignaling (...) +Return non-zero if the argument is a signaling NaN and zero otherwise. +Note while the parameter list is an +ellipsis, this function only accepts exactly one floating-point +argument. GCC treats this parameter as type-generic, which means it +does not do default promotion from float to double. +This built-in function can work even without the non-default +@code{-fsignaling-nans} option, although if a signaling NaN is computed, +stored or passed as argument to some function other than this built-in +in the current translation unit, it is safer to use @code{-fsignaling-nans}. +With @code{-ffinite-math-only} option this built-in function will always +return 0. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_ffs (int x) +Returns one plus the index of the least significant 1-bit of @var{x}, or +if @var{x} is zero, returns zero. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_clz (unsigned int x) +Returns the number of leading 0-bits in @var{x}, starting at the most +significant bit position. If @var{x} is 0, the result is undefined. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_ctz (unsigned int x) +Returns the number of trailing 0-bits in @var{x}, starting at the least +significant bit position. If @var{x} is 0, the result is undefined. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_clrsb (int x) +Returns the number of leading redundant sign bits in @var{x}, i.e.@: the +number of bits following the most significant bit that are identical +to it. There are no special cases for 0 or other values. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_popcount (unsigned int x) +Returns the number of 1-bits in @var{x}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_parity (unsigned int x) +Returns the parity of @var{x}, i.e.@: the number of 1-bits in @var{x} +modulo 2. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_ffsl (long) +Similar to @code{__builtin_ffs}, except the argument type is +@code{long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_clzl (unsigned long) +Similar to @code{__builtin_clz}, except the argument type is +@code{unsigned long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_ctzl (unsigned long) +Similar to @code{__builtin_ctz}, except the argument type is +@code{unsigned long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_clrsbl (long) +Similar to @code{__builtin_clrsb}, except the argument type is +@code{long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_popcountl (unsigned long) +Similar to @code{__builtin_popcount}, except the argument type is +@code{unsigned long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_parityl (unsigned long) +Similar to @code{__builtin_parity}, except the argument type is +@code{unsigned long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_ffsll (long long) +Similar to @code{__builtin_ffs}, except the argument type is +@code{long long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_clzll (unsigned long long) +Similar to @code{__builtin_clz}, except the argument type is +@code{unsigned long long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_ctzll (unsigned long long) +Similar to @code{__builtin_ctz}, except the argument type is +@code{unsigned long long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_clrsbll (long long) +Similar to @code{__builtin_clrsb}, except the argument type is +@code{long long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_popcountll (unsigned long long) +Similar to @code{__builtin_popcount}, except the argument type is +@code{unsigned long long}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_parityll (unsigned long long) +Similar to @code{__builtin_parity}, except the argument type is +@code{unsigned long long}. +@end deftypefn + +@deftypefn {Built-in Function} double __builtin_powi (double, int) +Returns the first argument raised to the power of the second. Unlike the +@code{pow} function no guarantees about precision and rounding are made. +@end deftypefn + +@deftypefn {Built-in Function} float __builtin_powif (float, int) +Similar to @code{__builtin_powi}, except the argument and return types +are @code{float}. +@end deftypefn + +@deftypefn {Built-in Function} {long double} __builtin_powil (long double, int) +Similar to @code{__builtin_powi}, except the argument and return types +are @code{long double}. +@end deftypefn + +@deftypefn {Built-in Function} uint16_t __builtin_bswap16 (uint16_t x) +Returns @var{x} with the order of the bytes reversed; for example, +@code{0xaabb} becomes @code{0xbbaa}. Byte here always means +exactly 8 bits. +@end deftypefn + +@deftypefn {Built-in Function} uint32_t __builtin_bswap32 (uint32_t x) +Similar to @code{__builtin_bswap16}, except the argument and return types +are 32-bit. +@end deftypefn + +@deftypefn {Built-in Function} uint64_t __builtin_bswap64 (uint64_t x) +Similar to @code{__builtin_bswap32}, except the argument and return types +are 64-bit. +@end deftypefn + +@deftypefn {Built-in Function} uint128_t __builtin_bswap128 (uint128_t x) +Similar to @code{__builtin_bswap64}, except the argument and return types +are 128-bit. Only supported on targets when 128-bit types are supported. +@end deftypefn + + +@deftypefn {Built-in Function} Pmode __builtin_extend_pointer (void * x) +On targets where the user visible pointer size is smaller than the size +of an actual hardware address this function returns the extended user +pointer. Targets where this is true included ILP32 mode on x86_64 or +Aarch64. This function is mainly useful when writing inline assembly +code. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_goacc_parlevel_id (int x) +Returns the openacc gang, worker or vector id depending on whether @var{x} is +0, 1 or 2. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_goacc_parlevel_size (int x) +Returns the openacc gang, worker or vector size depending on whether @var{x} is +0, 1 or 2. +@end deftypefn + +@node Target Builtins +@section Built-in Functions Specific to Particular Target Machines + +On some target machines, GCC supports many built-in functions specific +to those machines. Generally these generate calls to specific machine +instructions, but allow the compiler to schedule those calls. + +@menu +* AArch64 Built-in Functions:: +* Alpha Built-in Functions:: +* Altera Nios II Built-in Functions:: +* ARC Built-in Functions:: +* ARC SIMD Built-in Functions:: +* ARM iWMMXt Built-in Functions:: +* ARM C Language Extensions (ACLE):: +* ARM Floating Point Status and Control Intrinsics:: +* ARM ARMv8-M Security Extensions:: +* AVR Built-in Functions:: +* Blackfin Built-in Functions:: +* BPF Built-in Functions:: +* FR-V Built-in Functions:: +* MIPS DSP Built-in Functions:: +* MIPS Paired-Single Support:: +* MIPS Loongson Built-in Functions:: +* MIPS SIMD Architecture (MSA) Support:: +* Other MIPS Built-in Functions:: +* MSP430 Built-in Functions:: +* NDS32 Built-in Functions:: +* picoChip Built-in Functions:: +* Basic PowerPC Built-in Functions:: +* PowerPC AltiVec/VSX Built-in Functions:: +* PowerPC Hardware Transactional Memory Built-in Functions:: +* PowerPC Atomic Memory Operation Functions:: +* PowerPC Matrix-Multiply Assist Built-in Functions:: +* PRU Built-in Functions:: +* RISC-V Built-in Functions:: +* RX Built-in Functions:: +* S/390 System z Built-in Functions:: +* SH Built-in Functions:: +* SPARC VIS Built-in Functions:: +* TI C6X Built-in Functions:: +* x86 Built-in Functions:: +* x86 transactional memory intrinsics:: +* x86 control-flow protection intrinsics:: +@end menu + +@node AArch64 Built-in Functions +@subsection AArch64 Built-in Functions + +These built-in functions are available for the AArch64 family of +processors. +@smallexample +unsigned int __builtin_aarch64_get_fpcr (); +void __builtin_aarch64_set_fpcr (unsigned int); +unsigned int __builtin_aarch64_get_fpsr (); +void __builtin_aarch64_set_fpsr (unsigned int); + +unsigned long long __builtin_aarch64_get_fpcr64 (); +void __builtin_aarch64_set_fpcr64 (unsigned long long); +unsigned long long __builtin_aarch64_get_fpsr64 (); +void __builtin_aarch64_set_fpsr64 (unsigned long long); +@end smallexample + +@node Alpha Built-in Functions +@subsection Alpha Built-in Functions + +These built-in functions are available for the Alpha family of +processors, depending on the command-line switches used. + +The following built-in functions are always available. They +all generate the machine instruction that is part of the name. + +@smallexample +long __builtin_alpha_implver (void); +long __builtin_alpha_rpcc (void); +long __builtin_alpha_amask (long); +long __builtin_alpha_cmpbge (long, long); +long __builtin_alpha_extbl (long, long); +long __builtin_alpha_extwl (long, long); +long __builtin_alpha_extll (long, long); +long __builtin_alpha_extql (long, long); +long __builtin_alpha_extwh (long, long); +long __builtin_alpha_extlh (long, long); +long __builtin_alpha_extqh (long, long); +long __builtin_alpha_insbl (long, long); +long __builtin_alpha_inswl (long, long); +long __builtin_alpha_insll (long, long); +long __builtin_alpha_insql (long, long); +long __builtin_alpha_inswh (long, long); +long __builtin_alpha_inslh (long, long); +long __builtin_alpha_insqh (long, long); +long __builtin_alpha_mskbl (long, long); +long __builtin_alpha_mskwl (long, long); +long __builtin_alpha_mskll (long, long); +long __builtin_alpha_mskql (long, long); +long __builtin_alpha_mskwh (long, long); +long __builtin_alpha_msklh (long, long); +long __builtin_alpha_mskqh (long, long); +long __builtin_alpha_umulh (long, long); +long __builtin_alpha_zap (long, long); +long __builtin_alpha_zapnot (long, long); +@end smallexample + +The following built-in functions are always with @option{-mmax} +or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{pca56} or +later. They all generate the machine instruction that is part +of the name. + +@smallexample +long __builtin_alpha_pklb (long); +long __builtin_alpha_pkwb (long); +long __builtin_alpha_unpkbl (long); +long __builtin_alpha_unpkbw (long); +long __builtin_alpha_minub8 (long, long); +long __builtin_alpha_minsb8 (long, long); +long __builtin_alpha_minuw4 (long, long); +long __builtin_alpha_minsw4 (long, long); +long __builtin_alpha_maxub8 (long, long); +long __builtin_alpha_maxsb8 (long, long); +long __builtin_alpha_maxuw4 (long, long); +long __builtin_alpha_maxsw4 (long, long); +long __builtin_alpha_perr (long, long); +@end smallexample + +The following built-in functions are always with @option{-mcix} +or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{ev67} or +later. They all generate the machine instruction that is part +of the name. + +@smallexample +long __builtin_alpha_cttz (long); +long __builtin_alpha_ctlz (long); +long __builtin_alpha_ctpop (long); +@end smallexample + +The following built-in functions are available on systems that use the OSF/1 +PALcode. Normally they invoke the @code{rduniq} and @code{wruniq} +PAL calls, but when invoked with @option{-mtls-kernel}, they invoke +@code{rdval} and @code{wrval}. + +@smallexample +void *__builtin_thread_pointer (void); +void __builtin_set_thread_pointer (void *); +@end smallexample + +@node Altera Nios II Built-in Functions +@subsection Altera Nios II Built-in Functions + +These built-in functions are available for the Altera Nios II +family of processors. + +The following built-in functions are always available. They +all generate the machine instruction that is part of the name. + +@example +int __builtin_ldbio (volatile const void *); +int __builtin_ldbuio (volatile const void *); +int __builtin_ldhio (volatile const void *); +int __builtin_ldhuio (volatile const void *); +int __builtin_ldwio (volatile const void *); +void __builtin_stbio (volatile void *, int); +void __builtin_sthio (volatile void *, int); +void __builtin_stwio (volatile void *, int); +void __builtin_sync (void); +int __builtin_rdctl (int); +int __builtin_rdprs (int, int); +void __builtin_wrctl (int, int); +void __builtin_flushd (volatile void *); +void __builtin_flushda (volatile void *); +int __builtin_wrpie (int); +void __builtin_eni (int); +int __builtin_ldex (volatile const void *); +int __builtin_stex (volatile void *, int); +int __builtin_ldsex (volatile const void *); +int __builtin_stsex (volatile void *, int); +@end example + +The following built-in functions are always available. They +all generate a Nios II Custom Instruction. The name of the +function represents the types that the function takes and +returns. The letter before the @code{n} is the return type +or void if absent. The @code{n} represents the first parameter +to all the custom instructions, the custom instruction number. +The two letters after the @code{n} represent the up to two +parameters to the function. + +The letters represent the following data types: +@table @code +@item +@code{void} for return type and no parameter for parameter types. + +@item i +@code{int} for return type and parameter type + +@item f +@code{float} for return type and parameter type + +@item p +@code{void *} for return type and parameter type + +@end table + +And the function names are: +@example +void __builtin_custom_n (void); +void __builtin_custom_ni (int); +void __builtin_custom_nf (float); +void __builtin_custom_np (void *); +void __builtin_custom_nii (int, int); +void __builtin_custom_nif (int, float); +void __builtin_custom_nip (int, void *); +void __builtin_custom_nfi (float, int); +void __builtin_custom_nff (float, float); +void __builtin_custom_nfp (float, void *); +void __builtin_custom_npi (void *, int); +void __builtin_custom_npf (void *, float); +void __builtin_custom_npp (void *, void *); +int __builtin_custom_in (void); +int __builtin_custom_ini (int); +int __builtin_custom_inf (float); +int __builtin_custom_inp (void *); +int __builtin_custom_inii (int, int); +int __builtin_custom_inif (int, float); +int __builtin_custom_inip (int, void *); +int __builtin_custom_infi (float, int); +int __builtin_custom_inff (float, float); +int __builtin_custom_infp (float, void *); +int __builtin_custom_inpi (void *, int); +int __builtin_custom_inpf (void *, float); +int __builtin_custom_inpp (void *, void *); +float __builtin_custom_fn (void); +float __builtin_custom_fni (int); +float __builtin_custom_fnf (float); +float __builtin_custom_fnp (void *); +float __builtin_custom_fnii (int, int); +float __builtin_custom_fnif (int, float); +float __builtin_custom_fnip (int, void *); +float __builtin_custom_fnfi (float, int); +float __builtin_custom_fnff (float, float); +float __builtin_custom_fnfp (float, void *); +float __builtin_custom_fnpi (void *, int); +float __builtin_custom_fnpf (void *, float); +float __builtin_custom_fnpp (void *, void *); +void * __builtin_custom_pn (void); +void * __builtin_custom_pni (int); +void * __builtin_custom_pnf (float); +void * __builtin_custom_pnp (void *); +void * __builtin_custom_pnii (int, int); +void * __builtin_custom_pnif (int, float); +void * __builtin_custom_pnip (int, void *); +void * __builtin_custom_pnfi (float, int); +void * __builtin_custom_pnff (float, float); +void * __builtin_custom_pnfp (float, void *); +void * __builtin_custom_pnpi (void *, int); +void * __builtin_custom_pnpf (void *, float); +void * __builtin_custom_pnpp (void *, void *); +@end example + +@node ARC Built-in Functions +@subsection ARC Built-in Functions + +The following built-in functions are provided for ARC targets. The +built-ins generate the corresponding assembly instructions. In the +examples given below, the generated code often requires an operand or +result to be in a register. Where necessary further code will be +generated to ensure this is true, but for brevity this is not +described in each case. + +@emph{Note:} Using a built-in to generate an instruction not supported +by a target may cause problems. At present the compiler is not +guaranteed to detect such misuse, and as a result an internal compiler +error may be generated. + +@deftypefn {Built-in Function} int __builtin_arc_aligned (void *@var{val}, int @var{alignval}) +Return 1 if @var{val} is known to have the byte alignment given +by @var{alignval}, otherwise return 0. +Note that this is different from +@smallexample +__alignof__(*(char *)@var{val}) >= alignval +@end smallexample +because __alignof__ sees only the type of the dereference, whereas +__builtin_arc_align uses alignment information from the pointer +as well as from the pointed-to type. +The information available will depend on optimization level. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_brk (void) +Generates +@example +brk +@end example +@end deftypefn + +@deftypefn {Built-in Function} {unsigned int} __builtin_arc_core_read (unsigned int @var{regno}) +The operand is the number of a register to be read. Generates: +@example +mov @var{dest}, r@var{regno} +@end example +where the value in @var{dest} will be the result returned from the +built-in. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_core_write (unsigned int @var{regno}, unsigned int @var{val}) +The first operand is the number of a register to be written, the +second operand is a compile time constant to write into that +register. Generates: +@example +mov r@var{regno}, @var{val} +@end example +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_arc_divaw (int @var{a}, int @var{b}) +Only available if either @option{-mcpu=ARC700} or @option{-meA} is set. +Generates: +@example +divaw @var{dest}, @var{a}, @var{b} +@end example +where the value in @var{dest} will be the result returned from the +built-in. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_flag (unsigned int @var{a}) +Generates +@example +flag @var{a} +@end example +@end deftypefn + +@deftypefn {Built-in Function} {unsigned int} __builtin_arc_lr (unsigned int @var{auxr}) +The operand, @var{auxv}, is the address of an auxiliary register and +must be a compile time constant. Generates: +@example +lr @var{dest}, [@var{auxr}] +@end example +Where the value in @var{dest} will be the result returned from the +built-in. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_mul64 (int @var{a}, int @var{b}) +Only available with @option{-mmul64}. Generates: +@example +mul64 @var{a}, @var{b} +@end example +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_mulu64 (unsigned int @var{a}, unsigned int @var{b}) +Only available with @option{-mmul64}. Generates: +@example +mulu64 @var{a}, @var{b} +@end example +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_nop (void) +Generates: +@example +nop +@end example +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_arc_norm (int @var{src}) +Only valid if the @samp{norm} instruction is available through the +@option{-mnorm} option or by default with @option{-mcpu=ARC700}. +Generates: +@example +norm @var{dest}, @var{src} +@end example +Where the value in @var{dest} will be the result returned from the +built-in. +@end deftypefn + +@deftypefn {Built-in Function} {short int} __builtin_arc_normw (short int @var{src}) +Only valid if the @samp{normw} instruction is available through the +@option{-mnorm} option or by default with @option{-mcpu=ARC700}. +Generates: +@example +normw @var{dest}, @var{src} +@end example +Where the value in @var{dest} will be the result returned from the +built-in. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_rtie (void) +Generates: +@example +rtie +@end example +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_sleep (int @var{a} +Generates: +@example +sleep @var{a} +@end example +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_sr (unsigned int @var{val}, unsigned int @var{auxr}) +The first argument, @var{val}, is a compile time constant to be +written to the register, the second argument, @var{auxr}, is the +address of an auxiliary register. Generates: +@example +sr @var{val}, [@var{auxr}] +@end example +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_arc_swap (int @var{src}) +Only valid with @option{-mswap}. Generates: +@example +swap @var{dest}, @var{src} +@end example +Where the value in @var{dest} will be the result returned from the +built-in. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_swi (void) +Generates: +@example +swi +@end example +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_sync (void) +Only available with @option{-mcpu=ARC700}. Generates: +@example +sync +@end example +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_trap_s (unsigned int @var{c}) +Only available with @option{-mcpu=ARC700}. Generates: +@example +trap_s @var{c} +@end example +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_arc_unimp_s (void) +Only available with @option{-mcpu=ARC700}. Generates: +@example +unimp_s +@end example +@end deftypefn + +The instructions generated by the following builtins are not +considered as candidates for scheduling. They are not moved around by +the compiler during scheduling, and thus can be expected to appear +where they are put in the C code: +@example +__builtin_arc_brk() +__builtin_arc_core_read() +__builtin_arc_core_write() +__builtin_arc_flag() +__builtin_arc_lr() +__builtin_arc_sleep() +__builtin_arc_sr() +__builtin_arc_swi() +@end example + +@node ARC SIMD Built-in Functions +@subsection ARC SIMD Built-in Functions + +SIMD builtins provided by the compiler can be used to generate the +vector instructions. This section describes the available builtins +and their usage in programs. With the @option{-msimd} option, the +compiler provides 128-bit vector types, which can be specified using +the @code{vector_size} attribute. The header file @file{arc-simd.h} +can be included to use the following predefined types: +@example +typedef int __v4si __attribute__((vector_size(16))); +typedef short __v8hi __attribute__((vector_size(16))); +@end example + +These types can be used to define 128-bit variables. The built-in +functions listed in the following section can be used on these +variables to generate the vector operations. + +For all builtins, @code{__builtin_arc_@var{someinsn}}, the header file +@file{arc-simd.h} also provides equivalent macros called +@code{_@var{someinsn}} that can be used for programming ease and +improved readability. The following macros for DMA control are also +provided: +@example +#define _setup_dma_in_channel_reg _vdiwr +#define _setup_dma_out_channel_reg _vdowr +@end example + +The following is a complete list of all the SIMD built-ins provided +for ARC, grouped by calling signature. + +The following take two @code{__v8hi} arguments and return a +@code{__v8hi} result: +@example +__v8hi __builtin_arc_vaddaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vaddw (__v8hi, __v8hi); +__v8hi __builtin_arc_vand (__v8hi, __v8hi); +__v8hi __builtin_arc_vandaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vavb (__v8hi, __v8hi); +__v8hi __builtin_arc_vavrb (__v8hi, __v8hi); +__v8hi __builtin_arc_vbic (__v8hi, __v8hi); +__v8hi __builtin_arc_vbicaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vdifaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vdifw (__v8hi, __v8hi); +__v8hi __builtin_arc_veqw (__v8hi, __v8hi); +__v8hi __builtin_arc_vh264f (__v8hi, __v8hi); +__v8hi __builtin_arc_vh264ft (__v8hi, __v8hi); +__v8hi __builtin_arc_vh264fw (__v8hi, __v8hi); +__v8hi __builtin_arc_vlew (__v8hi, __v8hi); +__v8hi __builtin_arc_vltw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmaxaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmaxw (__v8hi, __v8hi); +__v8hi __builtin_arc_vminaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vminw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr1aw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr1w (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr2aw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr2w (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr3aw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr3w (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr4aw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr4w (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr5aw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr5w (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr6aw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr6w (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr7aw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmr7w (__v8hi, __v8hi); +__v8hi __builtin_arc_vmrb (__v8hi, __v8hi); +__v8hi __builtin_arc_vmulaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmulfaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmulfw (__v8hi, __v8hi); +__v8hi __builtin_arc_vmulw (__v8hi, __v8hi); +__v8hi __builtin_arc_vnew (__v8hi, __v8hi); +__v8hi __builtin_arc_vor (__v8hi, __v8hi); +__v8hi __builtin_arc_vsubaw (__v8hi, __v8hi); +__v8hi __builtin_arc_vsubw (__v8hi, __v8hi); +__v8hi __builtin_arc_vsummw (__v8hi, __v8hi); +__v8hi __builtin_arc_vvc1f (__v8hi, __v8hi); +__v8hi __builtin_arc_vvc1ft (__v8hi, __v8hi); +__v8hi __builtin_arc_vxor (__v8hi, __v8hi); +__v8hi __builtin_arc_vxoraw (__v8hi, __v8hi); +@end example + +The following take one @code{__v8hi} and one @code{int} argument and return a +@code{__v8hi} result: + +@example +__v8hi __builtin_arc_vbaddw (__v8hi, int); +__v8hi __builtin_arc_vbmaxw (__v8hi, int); +__v8hi __builtin_arc_vbminw (__v8hi, int); +__v8hi __builtin_arc_vbmulaw (__v8hi, int); +__v8hi __builtin_arc_vbmulfw (__v8hi, int); +__v8hi __builtin_arc_vbmulw (__v8hi, int); +__v8hi __builtin_arc_vbrsubw (__v8hi, int); +__v8hi __builtin_arc_vbsubw (__v8hi, int); +@end example + +The following take one @code{__v8hi} argument and one @code{int} argument which +must be a 3-bit compile time constant indicating a register number +I0-I7. They return a @code{__v8hi} result. +@example +__v8hi __builtin_arc_vasrw (__v8hi, const int); +__v8hi __builtin_arc_vsr8 (__v8hi, const int); +__v8hi __builtin_arc_vsr8aw (__v8hi, const int); +@end example + +The following take one @code{__v8hi} argument and one @code{int} +argument which must be a 6-bit compile time constant. They return a +@code{__v8hi} result. +@example +__v8hi __builtin_arc_vasrpwbi (__v8hi, const int); +__v8hi __builtin_arc_vasrrpwbi (__v8hi, const int); +__v8hi __builtin_arc_vasrrwi (__v8hi, const int); +__v8hi __builtin_arc_vasrsrwi (__v8hi, const int); +__v8hi __builtin_arc_vasrwi (__v8hi, const int); +__v8hi __builtin_arc_vsr8awi (__v8hi, const int); +__v8hi __builtin_arc_vsr8i (__v8hi, const int); +@end example + +The following take one @code{__v8hi} argument and one @code{int} argument which +must be a 8-bit compile time constant. They return a @code{__v8hi} +result. +@example +__v8hi __builtin_arc_vd6tapf (__v8hi, const int); +__v8hi __builtin_arc_vmvaw (__v8hi, const int); +__v8hi __builtin_arc_vmvw (__v8hi, const int); +__v8hi __builtin_arc_vmvzw (__v8hi, const int); +@end example + +The following take two @code{int} arguments, the second of which which +must be a 8-bit compile time constant. They return a @code{__v8hi} +result: +@example +__v8hi __builtin_arc_vmovaw (int, const int); +__v8hi __builtin_arc_vmovw (int, const int); +__v8hi __builtin_arc_vmovzw (int, const int); +@end example + +The following take a single @code{__v8hi} argument and return a +@code{__v8hi} result: +@example +__v8hi __builtin_arc_vabsaw (__v8hi); +__v8hi __builtin_arc_vabsw (__v8hi); +__v8hi __builtin_arc_vaddsuw (__v8hi); +__v8hi __builtin_arc_vexch1 (__v8hi); +__v8hi __builtin_arc_vexch2 (__v8hi); +__v8hi __builtin_arc_vexch4 (__v8hi); +__v8hi __builtin_arc_vsignw (__v8hi); +__v8hi __builtin_arc_vupbaw (__v8hi); +__v8hi __builtin_arc_vupbw (__v8hi); +__v8hi __builtin_arc_vupsbaw (__v8hi); +__v8hi __builtin_arc_vupsbw (__v8hi); +@end example + +The following take two @code{int} arguments and return no result: +@example +void __builtin_arc_vdirun (int, int); +void __builtin_arc_vdorun (int, int); +@end example + +The following take two @code{int} arguments and return no result. The +first argument must a 3-bit compile time constant indicating one of +the DR0-DR7 DMA setup channels: +@example +void __builtin_arc_vdiwr (const int, int); +void __builtin_arc_vdowr (const int, int); +@end example + +The following take an @code{int} argument and return no result: +@example +void __builtin_arc_vendrec (int); +void __builtin_arc_vrec (int); +void __builtin_arc_vrecrun (int); +void __builtin_arc_vrun (int); +@end example + +The following take a @code{__v8hi} argument and two @code{int} +arguments and return a @code{__v8hi} result. The second argument must +be a 3-bit compile time constants, indicating one the registers I0-I7, +and the third argument must be an 8-bit compile time constant. + +@emph{Note:} Although the equivalent hardware instructions do not take +an SIMD register as an operand, these builtins overwrite the relevant +bits of the @code{__v8hi} register provided as the first argument with +the value loaded from the @code{[Ib, u8]} location in the SDM. + +@example +__v8hi __builtin_arc_vld32 (__v8hi, const int, const int); +__v8hi __builtin_arc_vld32wh (__v8hi, const int, const int); +__v8hi __builtin_arc_vld32wl (__v8hi, const int, const int); +__v8hi __builtin_arc_vld64 (__v8hi, const int, const int); +@end example + +The following take two @code{int} arguments and return a @code{__v8hi} +result. The first argument must be a 3-bit compile time constants, +indicating one the registers I0-I7, and the second argument must be an +8-bit compile time constant. + +@example +__v8hi __builtin_arc_vld128 (const int, const int); +__v8hi __builtin_arc_vld64w (const int, const int); +@end example + +The following take a @code{__v8hi} argument and two @code{int} +arguments and return no result. The second argument must be a 3-bit +compile time constants, indicating one the registers I0-I7, and the +third argument must be an 8-bit compile time constant. + +@example +void __builtin_arc_vst128 (__v8hi, const int, const int); +void __builtin_arc_vst64 (__v8hi, const int, const int); +@end example + +The following take a @code{__v8hi} argument and three @code{int} +arguments and return no result. The second argument must be a 3-bit +compile-time constant, identifying the 16-bit sub-register to be +stored, the third argument must be a 3-bit compile time constants, +indicating one the registers I0-I7, and the fourth argument must be an +8-bit compile time constant. + +@example +void __builtin_arc_vst16_n (__v8hi, const int, const int, const int); +void __builtin_arc_vst32_n (__v8hi, const int, const int, const int); +@end example + +@node ARM iWMMXt Built-in Functions +@subsection ARM iWMMXt Built-in Functions + +These built-in functions are available for the ARM family of +processors when the @option{-mcpu=iwmmxt} switch is used: + +@smallexample +typedef int v2si __attribute__ ((vector_size (8))); +typedef short v4hi __attribute__ ((vector_size (8))); +typedef char v8qi __attribute__ ((vector_size (8))); + +int __builtin_arm_getwcgr0 (void); +void __builtin_arm_setwcgr0 (int); +int __builtin_arm_getwcgr1 (void); +void __builtin_arm_setwcgr1 (int); +int __builtin_arm_getwcgr2 (void); +void __builtin_arm_setwcgr2 (int); +int __builtin_arm_getwcgr3 (void); +void __builtin_arm_setwcgr3 (int); +int __builtin_arm_textrmsb (v8qi, int); +int __builtin_arm_textrmsh (v4hi, int); +int __builtin_arm_textrmsw (v2si, int); +int __builtin_arm_textrmub (v8qi, int); +int __builtin_arm_textrmuh (v4hi, int); +int __builtin_arm_textrmuw (v2si, int); +v8qi __builtin_arm_tinsrb (v8qi, int, int); +v4hi __builtin_arm_tinsrh (v4hi, int, int); +v2si __builtin_arm_tinsrw (v2si, int, int); +long long __builtin_arm_tmia (long long, int, int); +long long __builtin_arm_tmiabb (long long, int, int); +long long __builtin_arm_tmiabt (long long, int, int); +long long __builtin_arm_tmiaph (long long, int, int); +long long __builtin_arm_tmiatb (long long, int, int); +long long __builtin_arm_tmiatt (long long, int, int); +int __builtin_arm_tmovmskb (v8qi); +int __builtin_arm_tmovmskh (v4hi); +int __builtin_arm_tmovmskw (v2si); +long long __builtin_arm_waccb (v8qi); +long long __builtin_arm_wacch (v4hi); +long long __builtin_arm_waccw (v2si); +v8qi __builtin_arm_waddb (v8qi, v8qi); +v8qi __builtin_arm_waddbss (v8qi, v8qi); +v8qi __builtin_arm_waddbus (v8qi, v8qi); +v4hi __builtin_arm_waddh (v4hi, v4hi); +v4hi __builtin_arm_waddhss (v4hi, v4hi); +v4hi __builtin_arm_waddhus (v4hi, v4hi); +v2si __builtin_arm_waddw (v2si, v2si); +v2si __builtin_arm_waddwss (v2si, v2si); +v2si __builtin_arm_waddwus (v2si, v2si); +v8qi __builtin_arm_walign (v8qi, v8qi, int); +long long __builtin_arm_wand(long long, long long); +long long __builtin_arm_wandn (long long, long long); +v8qi __builtin_arm_wavg2b (v8qi, v8qi); +v8qi __builtin_arm_wavg2br (v8qi, v8qi); +v4hi __builtin_arm_wavg2h (v4hi, v4hi); +v4hi __builtin_arm_wavg2hr (v4hi, v4hi); +v8qi __builtin_arm_wcmpeqb (v8qi, v8qi); +v4hi __builtin_arm_wcmpeqh (v4hi, v4hi); +v2si __builtin_arm_wcmpeqw (v2si, v2si); +v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi); +v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi); +v2si __builtin_arm_wcmpgtsw (v2si, v2si); +v8qi __builtin_arm_wcmpgtub (v8qi, v8qi); +v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi); +v2si __builtin_arm_wcmpgtuw (v2si, v2si); +long long __builtin_arm_wmacs (long long, v4hi, v4hi); +long long __builtin_arm_wmacsz (v4hi, v4hi); +long long __builtin_arm_wmacu (long long, v4hi, v4hi); +long long __builtin_arm_wmacuz (v4hi, v4hi); +v4hi __builtin_arm_wmadds (v4hi, v4hi); +v4hi __builtin_arm_wmaddu (v4hi, v4hi); +v8qi __builtin_arm_wmaxsb (v8qi, v8qi); +v4hi __builtin_arm_wmaxsh (v4hi, v4hi); +v2si __builtin_arm_wmaxsw (v2si, v2si); +v8qi __builtin_arm_wmaxub (v8qi, v8qi); +v4hi __builtin_arm_wmaxuh (v4hi, v4hi); +v2si __builtin_arm_wmaxuw (v2si, v2si); +v8qi __builtin_arm_wminsb (v8qi, v8qi); +v4hi __builtin_arm_wminsh (v4hi, v4hi); +v2si __builtin_arm_wminsw (v2si, v2si); +v8qi __builtin_arm_wminub (v8qi, v8qi); +v4hi __builtin_arm_wminuh (v4hi, v4hi); +v2si __builtin_arm_wminuw (v2si, v2si); +v4hi __builtin_arm_wmulsm (v4hi, v4hi); +v4hi __builtin_arm_wmulul (v4hi, v4hi); +v4hi __builtin_arm_wmulum (v4hi, v4hi); +long long __builtin_arm_wor (long long, long long); +v2si __builtin_arm_wpackdss (long long, long long); +v2si __builtin_arm_wpackdus (long long, long long); +v8qi __builtin_arm_wpackhss (v4hi, v4hi); +v8qi __builtin_arm_wpackhus (v4hi, v4hi); +v4hi __builtin_arm_wpackwss (v2si, v2si); +v4hi __builtin_arm_wpackwus (v2si, v2si); +long long __builtin_arm_wrord (long long, long long); +long long __builtin_arm_wrordi (long long, int); +v4hi __builtin_arm_wrorh (v4hi, long long); +v4hi __builtin_arm_wrorhi (v4hi, int); +v2si __builtin_arm_wrorw (v2si, long long); +v2si __builtin_arm_wrorwi (v2si, int); +v2si __builtin_arm_wsadb (v2si, v8qi, v8qi); +v2si __builtin_arm_wsadbz (v8qi, v8qi); +v2si __builtin_arm_wsadh (v2si, v4hi, v4hi); +v2si __builtin_arm_wsadhz (v4hi, v4hi); +v4hi __builtin_arm_wshufh (v4hi, int); +long long __builtin_arm_wslld (long long, long long); +long long __builtin_arm_wslldi (long long, int); +v4hi __builtin_arm_wsllh (v4hi, long long); +v4hi __builtin_arm_wsllhi (v4hi, int); +v2si __builtin_arm_wsllw (v2si, long long); +v2si __builtin_arm_wsllwi (v2si, int); +long long __builtin_arm_wsrad (long long, long long); +long long __builtin_arm_wsradi (long long, int); +v4hi __builtin_arm_wsrah (v4hi, long long); +v4hi __builtin_arm_wsrahi (v4hi, int); +v2si __builtin_arm_wsraw (v2si, long long); +v2si __builtin_arm_wsrawi (v2si, int); +long long __builtin_arm_wsrld (long long, long long); +long long __builtin_arm_wsrldi (long long, int); +v4hi __builtin_arm_wsrlh (v4hi, long long); +v4hi __builtin_arm_wsrlhi (v4hi, int); +v2si __builtin_arm_wsrlw (v2si, long long); +v2si __builtin_arm_wsrlwi (v2si, int); +v8qi __builtin_arm_wsubb (v8qi, v8qi); +v8qi __builtin_arm_wsubbss (v8qi, v8qi); +v8qi __builtin_arm_wsubbus (v8qi, v8qi); +v4hi __builtin_arm_wsubh (v4hi, v4hi); +v4hi __builtin_arm_wsubhss (v4hi, v4hi); +v4hi __builtin_arm_wsubhus (v4hi, v4hi); +v2si __builtin_arm_wsubw (v2si, v2si); +v2si __builtin_arm_wsubwss (v2si, v2si); +v2si __builtin_arm_wsubwus (v2si, v2si); +v4hi __builtin_arm_wunpckehsb (v8qi); +v2si __builtin_arm_wunpckehsh (v4hi); +long long __builtin_arm_wunpckehsw (v2si); +v4hi __builtin_arm_wunpckehub (v8qi); +v2si __builtin_arm_wunpckehuh (v4hi); +long long __builtin_arm_wunpckehuw (v2si); +v4hi __builtin_arm_wunpckelsb (v8qi); +v2si __builtin_arm_wunpckelsh (v4hi); +long long __builtin_arm_wunpckelsw (v2si); +v4hi __builtin_arm_wunpckelub (v8qi); +v2si __builtin_arm_wunpckeluh (v4hi); +long long __builtin_arm_wunpckeluw (v2si); +v8qi __builtin_arm_wunpckihb (v8qi, v8qi); +v4hi __builtin_arm_wunpckihh (v4hi, v4hi); +v2si __builtin_arm_wunpckihw (v2si, v2si); +v8qi __builtin_arm_wunpckilb (v8qi, v8qi); +v4hi __builtin_arm_wunpckilh (v4hi, v4hi); +v2si __builtin_arm_wunpckilw (v2si, v2si); +long long __builtin_arm_wxor (long long, long long); +long long __builtin_arm_wzero (); +@end smallexample + + +@node ARM C Language Extensions (ACLE) +@subsection ARM C Language Extensions (ACLE) + +GCC implements extensions for C as described in the ARM C Language +Extensions (ACLE) specification, which can be found at +@uref{https://developer.arm.com/documentation/ihi0053/latest/}. + +As a part of ACLE, GCC implements extensions for Advanced SIMD as described in +the ARM C Language Extensions Specification. The complete list of Advanced SIMD +intrinsics can be found at +@uref{https://developer.arm.com/documentation/ihi0073/latest/}. +The built-in intrinsics for the Advanced SIMD extension are available when +NEON is enabled. + +Currently, ARM and AArch64 back ends do not support ACLE 2.0 fully. Both +back ends support CRC32 intrinsics and the ARM back end supports the +Coprocessor intrinsics, all from @file{arm_acle.h}. The ARM back end's 16-bit +floating-point Advanced SIMD intrinsics currently comply to ACLE v1.1. +AArch64's back end does not have support for 16-bit floating point Advanced SIMD +intrinsics yet. + +See @ref{ARM Options} and @ref{AArch64 Options} for more information on the +availability of extensions. + +@node ARM Floating Point Status and Control Intrinsics +@subsection ARM Floating Point Status and Control Intrinsics + +These built-in functions are available for the ARM family of +processors with floating-point unit. + +@smallexample +unsigned int __builtin_arm_get_fpscr (); +void __builtin_arm_set_fpscr (unsigned int); +@end smallexample + +@node ARM ARMv8-M Security Extensions +@subsection ARM ARMv8-M Security Extensions + +GCC implements the ARMv8-M Security Extensions as described in the ARMv8-M +Security Extensions: Requirements on Development Tools Engineering +Specification, which can be found at +@uref{https://developer.arm.com/documentation/ecm0359818/latest/}. + +As part of the Security Extensions GCC implements two new function attributes: +@code{cmse_nonsecure_entry} and @code{cmse_nonsecure_call}. + +As part of the Security Extensions GCC implements the intrinsics below. FPTR +is used here to mean any function pointer type. + +@smallexample +cmse_address_info_t cmse_TT (void *); +cmse_address_info_t cmse_TT_fptr (FPTR); +cmse_address_info_t cmse_TTT (void *); +cmse_address_info_t cmse_TTT_fptr (FPTR); +cmse_address_info_t cmse_TTA (void *); +cmse_address_info_t cmse_TTA_fptr (FPTR); +cmse_address_info_t cmse_TTAT (void *); +cmse_address_info_t cmse_TTAT_fptr (FPTR); +void * cmse_check_address_range (void *, size_t, int); +typeof(p) cmse_nsfptr_create (FPTR p); +intptr_t cmse_is_nsfptr (FPTR); +int cmse_nonsecure_caller (void); +@end smallexample + +@node AVR Built-in Functions +@subsection AVR Built-in Functions + +For each built-in function for AVR, there is an equally named, +uppercase built-in macro defined. That way users can easily query if +or if not a specific built-in is implemented or not. For example, if +@code{__builtin_avr_nop} is available the macro +@code{__BUILTIN_AVR_NOP} is defined to @code{1} and undefined otherwise. + +@table @code + +@item void __builtin_avr_nop (void) +@itemx void __builtin_avr_sei (void) +@itemx void __builtin_avr_cli (void) +@itemx void __builtin_avr_sleep (void) +@itemx void __builtin_avr_wdr (void) +@itemx unsigned char __builtin_avr_swap (unsigned char) +@itemx unsigned int __builtin_avr_fmul (unsigned char, unsigned char) +@itemx int __builtin_avr_fmuls (char, char) +@itemx int __builtin_avr_fmulsu (char, unsigned char) +These built-in functions map to the respective machine +instruction, i.e.@: @code{nop}, @code{sei}, @code{cli}, @code{sleep}, +@code{wdr}, @code{swap}, @code{fmul}, @code{fmuls} +resp. @code{fmulsu}. The three @code{fmul*} built-ins are implemented +as library call if no hardware multiplier is available. + +@item void __builtin_avr_delay_cycles (unsigned long ticks) +Delay execution for @var{ticks} cycles. Note that this +built-in does not take into account the effect of interrupts that +might increase delay time. @var{ticks} must be a compile-time +integer constant; delays with a variable number of cycles are not supported. + +@item char __builtin_avr_flash_segment (const __memx void*) +This built-in takes a byte address to the 24-bit +@ref{AVR Named Address Spaces,address space} @code{__memx} and returns +the number of the flash segment (the 64 KiB chunk) where the address +points to. Counting starts at @code{0}. +If the address does not point to flash memory, return @code{-1}. + +@item uint8_t __builtin_avr_insert_bits (uint32_t map, uint8_t bits, uint8_t val) +Insert bits from @var{bits} into @var{val} and return the resulting +value. The nibbles of @var{map} determine how the insertion is +performed: Let @var{X} be the @var{n}-th nibble of @var{map} +@enumerate +@item If @var{X} is @code{0xf}, +then the @var{n}-th bit of @var{val} is returned unaltered. + +@item If X is in the range 0@dots{}7, +then the @var{n}-th result bit is set to the @var{X}-th bit of @var{bits} + +@item If X is in the range 8@dots{}@code{0xe}, +then the @var{n}-th result bit is undefined. +@end enumerate + +@noindent +One typical use case for this built-in is adjusting input and +output values to non-contiguous port layouts. Some examples: + +@smallexample +// same as val, bits is unused +__builtin_avr_insert_bits (0xffffffff, bits, val); +@end smallexample + +@smallexample +// same as bits, val is unused +__builtin_avr_insert_bits (0x76543210, bits, val); +@end smallexample + +@smallexample +// same as rotating bits by 4 +__builtin_avr_insert_bits (0x32107654, bits, 0); +@end smallexample + +@smallexample +// high nibble of result is the high nibble of val +// low nibble of result is the low nibble of bits +__builtin_avr_insert_bits (0xffff3210, bits, val); +@end smallexample + +@smallexample +// reverse the bit order of bits +__builtin_avr_insert_bits (0x01234567, bits, 0); +@end smallexample + +@item void __builtin_avr_nops (unsigned count) +Insert @var{count} @code{NOP} instructions. +The number of instructions must be a compile-time integer constant. + +@end table + +@noindent +There are many more AVR-specific built-in functions that are used to +implement the ISO/IEC TR 18037 ``Embedded C'' fixed-point functions of +section 7.18a.6. You don't need to use these built-ins directly. +Instead, use the declarations as supplied by the @code{stdfix.h} header +with GNU-C99: + +@smallexample +#include + +// Re-interpret the bit representation of unsigned 16-bit +// integer @var{uval} as Q-format 0.16 value. +unsigned fract get_bits (uint_ur_t uval) +@{ + return urbits (uval); +@} +@end smallexample + +@node Blackfin Built-in Functions +@subsection Blackfin Built-in Functions + +Currently, there are two Blackfin-specific built-in functions. These are +used for generating @code{CSYNC} and @code{SSYNC} machine insns without +using inline assembly; by using these built-in functions the compiler can +automatically add workarounds for hardware errata involving these +instructions. These functions are named as follows: + +@smallexample +void __builtin_bfin_csync (void); +void __builtin_bfin_ssync (void); +@end smallexample + +@node BPF Built-in Functions +@subsection BPF Built-in Functions + +The following built-in functions are available for eBPF targets. + +@deftypefn {Built-in Function} unsigned long long __builtin_bpf_load_byte (unsigned long long @var{offset}) +Load a byte from the @code{struct sk_buff} packet data pointed by the register @code{%r6} and return it. +@end deftypefn + +@deftypefn {Built-in Function} unsigned long long __builtin_bpf_load_half (unsigned long long @var{offset}) +Load 16-bits from the @code{struct sk_buff} packet data pointed by the register @code{%r6} and return it. +@end deftypefn + +@deftypefn {Built-in Function} unsigned long long __builtin_bpf_load_word (unsigned long long @var{offset}) +Load 32-bits from the @code{struct sk_buff} packet data pointed by the register @code{%r6} and return it. +@end deftypefn + +@deftypefn {Built-in Function} void * __builtin_preserve_access_index (@var{expr}) +BPF Compile Once-Run Everywhere (CO-RE) support. Instruct GCC to generate CO-RE relocation records for any accesses to aggregate data structures (struct, union, array types) in @var{expr}. This builtin is otherwise transparent, the return value is whatever @var{expr} evaluates to. It is also overloaded: @var{expr} may be of any type (not necessarily a pointer), the return type is the same. Has no effect if @code{-mco-re} is not in effect (either specified or implied). +@end deftypefn + +@deftypefn {Built-in Function} unsigned int __builtin_preserve_field_info (@var{expr}, unsigned int @var{kind}) +BPF Compile Once-Run Everywhere (CO-RE) support. This builtin is used to +extract information to aid in struct/union relocations. @var{expr} is +an access to a field of a struct or union. Depending on @var{kind}, different +information is returned to the program. A CO-RE relocation for the access in +@var{expr} with kind @var{kind} is recorded if @code{-mco-re} is in effect. + +The following values are supported for @var{kind}: +@table @var +@item FIELD_BYTE_OFFSET = 0 +The returned value is the offset, in bytes, of the field from the +beginning of the containing structure. For bitfields, the byte offset +of the containing word. + +@item FIELD_BYTE_SIZE = 1 +The returned value is the size, in bytes, of the field. For bitfields, +the size in bytes of the containing word. + +@item FIELD_EXISTENCE = 2 +The returned value is 1 if the field exists, 0 otherwise. Always 1 at +compile time. + +@item FIELD_SIGNEDNESS = 3 +The returned value is 1 if the field is signed, 0 otherwise. + +@item FIELD_LSHIFT_U64 = 4 +@itemx FIELD_RSHIFT_U64 = 5 +The returned value is the number of bits of left- or right-shifting +respectively needed in order to recover the original value of the field, +after it has been loaded by a read of FIELD_BYTE_SIZE bytes into an +unsigned 64-bit value. Primarily useful for reading bitfield values +from structures which may change between kernel versions. + +@end table + +Note that the return value is a constant which is known at +compile-time. If the field has a variable offset then +FIELD_BYTE_OFFSET, FIELD_LSHIFT_U64 and FIELD_RSHIFT_U64 are not +supported. Similarly, if the field has a variable size then +FIELD_BYTE_SIZE, FIELD_LSHIFT_U64 and FIELD_RSHIFT_U64 are not +supported. + +For example, __builtin_preserve_field_info can be used to reliably +extract bitfield values from a structure which may change between +kernel versions: + +@example +struct S +@{ + short a; + int x:7; + int y:5; +@}; + +int +read_y (struct S *arg) +@{ + unsigned long long val; + unsigned int offset = __builtin_preserve_field_info (arg->y, FIELD_BYTE_OFFSET); + unsigned int size = __builtin_presrve_field_info (arg->y, FIELD_BYTE_SIZE); + + /* Read size bytes from arg + offset into val. */ + bpf_probe_read (&val, size, arg + offset); + + val <<= __builtin_preserve_field_info (arg->y, FIELD_LSHIFT_U64); + + if (__builtin_preserve_field_info (arg->y, FIELD_SIGNEDNESS)) + val = ((long long) val >> __builtin_preserve_field_info (arg->y, FIELD_RSHIFT_U64)); + else + val >>= __builtin_preserve_field_info (arg->y, FIELD_RSHIFT_U64); + + return val; +@} + +@end example +@end deftypefn + +@node FR-V Built-in Functions +@subsection FR-V Built-in Functions + +GCC provides many FR-V-specific built-in functions. In general, +these functions are intended to be compatible with those described +by @cite{FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu +Semiconductor}. The two exceptions are @code{__MDUNPACKH} and +@code{__MBTOHE}, the GCC forms of which pass 128-bit values by +pointer rather than by value. + +Most of the functions are named after specific FR-V instructions. +Such functions are said to be ``directly mapped'' and are summarized +here in tabular form. + +@menu +* Argument Types:: +* Directly-mapped Integer Functions:: +* Directly-mapped Media Functions:: +* Raw read/write Functions:: +* Other Built-in Functions:: +@end menu + +@node Argument Types +@subsubsection Argument Types + +The arguments to the built-in functions can be divided into three groups: +register numbers, compile-time constants and run-time values. In order +to make this classification clear at a glance, the arguments and return +values are given the following pseudo types: + +@multitable @columnfractions .20 .30 .15 .35 +@headitem Pseudo type @tab Real C type @tab Constant? @tab Description +@item @code{uh} @tab @code{unsigned short} @tab No @tab an unsigned halfword +@item @code{uw1} @tab @code{unsigned int} @tab No @tab an unsigned word +@item @code{sw1} @tab @code{int} @tab No @tab a signed word +@item @code{uw2} @tab @code{unsigned long long} @tab No +@tab an unsigned doubleword +@item @code{sw2} @tab @code{long long} @tab No @tab a signed doubleword +@item @code{const} @tab @code{int} @tab Yes @tab an integer constant +@item @code{acc} @tab @code{int} @tab Yes @tab an ACC register number +@item @code{iacc} @tab @code{int} @tab Yes @tab an IACC register number +@end multitable + +These pseudo types are not defined by GCC, they are simply a notational +convenience used in this manual. + +Arguments of type @code{uh}, @code{uw1}, @code{sw1}, @code{uw2} +and @code{sw2} are evaluated at run time. They correspond to +register operands in the underlying FR-V instructions. + +@code{const} arguments represent immediate operands in the underlying +FR-V instructions. They must be compile-time constants. + +@code{acc} arguments are evaluated at compile time and specify the number +of an accumulator register. For example, an @code{acc} argument of 2 +selects the ACC2 register. + +@code{iacc} arguments are similar to @code{acc} arguments but specify the +number of an IACC register. See @pxref{Other Built-in Functions} +for more details. + +@node Directly-mapped Integer Functions +@subsubsection Directly-Mapped Integer Functions + +The functions listed below map directly to FR-V I-type instructions. + +@multitable @columnfractions .45 .32 .23 +@headitem Function prototype @tab Example usage @tab Assembly output +@item @code{sw1 __ADDSS (sw1, sw1)} +@tab @code{@var{c} = __ADDSS (@var{a}, @var{b})} +@tab @code{ADDSS @var{a},@var{b},@var{c}} +@item @code{sw1 __SCAN (sw1, sw1)} +@tab @code{@var{c} = __SCAN (@var{a}, @var{b})} +@tab @code{SCAN @var{a},@var{b},@var{c}} +@item @code{sw1 __SCUTSS (sw1)} +@tab @code{@var{b} = __SCUTSS (@var{a})} +@tab @code{SCUTSS @var{a},@var{b}} +@item @code{sw1 __SLASS (sw1, sw1)} +@tab @code{@var{c} = __SLASS (@var{a}, @var{b})} +@tab @code{SLASS @var{a},@var{b},@var{c}} +@item @code{void __SMASS (sw1, sw1)} +@tab @code{__SMASS (@var{a}, @var{b})} +@tab @code{SMASS @var{a},@var{b}} +@item @code{void __SMSSS (sw1, sw1)} +@tab @code{__SMSSS (@var{a}, @var{b})} +@tab @code{SMSSS @var{a},@var{b}} +@item @code{void __SMU (sw1, sw1)} +@tab @code{__SMU (@var{a}, @var{b})} +@tab @code{SMU @var{a},@var{b}} +@item @code{sw2 __SMUL (sw1, sw1)} +@tab @code{@var{c} = __SMUL (@var{a}, @var{b})} +@tab @code{SMUL @var{a},@var{b},@var{c}} +@item @code{sw1 __SUBSS (sw1, sw1)} +@tab @code{@var{c} = __SUBSS (@var{a}, @var{b})} +@tab @code{SUBSS @var{a},@var{b},@var{c}} +@item @code{uw2 __UMUL (uw1, uw1)} +@tab @code{@var{c} = __UMUL (@var{a}, @var{b})} +@tab @code{UMUL @var{a},@var{b},@var{c}} +@end multitable + +@node Directly-mapped Media Functions +@subsubsection Directly-Mapped Media Functions + +The functions listed below map directly to FR-V M-type instructions. + +@multitable @columnfractions .45 .32 .23 +@headitem Function prototype @tab Example usage @tab Assembly output +@item @code{uw1 __MABSHS (sw1)} +@tab @code{@var{b} = __MABSHS (@var{a})} +@tab @code{MABSHS @var{a},@var{b}} +@item @code{void __MADDACCS (acc, acc)} +@tab @code{__MADDACCS (@var{b}, @var{a})} +@tab @code{MADDACCS @var{a},@var{b}} +@item @code{sw1 __MADDHSS (sw1, sw1)} +@tab @code{@var{c} = __MADDHSS (@var{a}, @var{b})} +@tab @code{MADDHSS @var{a},@var{b},@var{c}} +@item @code{uw1 __MADDHUS (uw1, uw1)} +@tab @code{@var{c} = __MADDHUS (@var{a}, @var{b})} +@tab @code{MADDHUS @var{a},@var{b},@var{c}} +@item @code{uw1 __MAND (uw1, uw1)} +@tab @code{@var{c} = __MAND (@var{a}, @var{b})} +@tab @code{MAND @var{a},@var{b},@var{c}} +@item @code{void __MASACCS (acc, acc)} +@tab @code{__MASACCS (@var{b}, @var{a})} +@tab @code{MASACCS @var{a},@var{b}} +@item @code{uw1 __MAVEH (uw1, uw1)} +@tab @code{@var{c} = __MAVEH (@var{a}, @var{b})} +@tab @code{MAVEH @var{a},@var{b},@var{c}} +@item @code{uw2 __MBTOH (uw1)} +@tab @code{@var{b} = __MBTOH (@var{a})} +@tab @code{MBTOH @var{a},@var{b}} +@item @code{void __MBTOHE (uw1 *, uw1)} +@tab @code{__MBTOHE (&@var{b}, @var{a})} +@tab @code{MBTOHE @var{a},@var{b}} +@item @code{void __MCLRACC (acc)} +@tab @code{__MCLRACC (@var{a})} +@tab @code{MCLRACC @var{a}} +@item @code{void __MCLRACCA (void)} +@tab @code{__MCLRACCA ()} +@tab @code{MCLRACCA} +@item @code{uw1 __Mcop1 (uw1, uw1)} +@tab @code{@var{c} = __Mcop1 (@var{a}, @var{b})} +@tab @code{Mcop1 @var{a},@var{b},@var{c}} +@item @code{uw1 __Mcop2 (uw1, uw1)} +@tab @code{@var{c} = __Mcop2 (@var{a}, @var{b})} +@tab @code{Mcop2 @var{a},@var{b},@var{c}} +@item @code{uw1 __MCPLHI (uw2, const)} +@tab @code{@var{c} = __MCPLHI (@var{a}, @var{b})} +@tab @code{MCPLHI @var{a},#@var{b},@var{c}} +@item @code{uw1 __MCPLI (uw2, const)} +@tab @code{@var{c} = __MCPLI (@var{a}, @var{b})} +@tab @code{MCPLI @var{a},#@var{b},@var{c}} +@item @code{void __MCPXIS (acc, sw1, sw1)} +@tab @code{__MCPXIS (@var{c}, @var{a}, @var{b})} +@tab @code{MCPXIS @var{a},@var{b},@var{c}} +@item @code{void __MCPXIU (acc, uw1, uw1)} +@tab @code{__MCPXIU (@var{c}, @var{a}, @var{b})} +@tab @code{MCPXIU @var{a},@var{b},@var{c}} +@item @code{void __MCPXRS (acc, sw1, sw1)} +@tab @code{__MCPXRS (@var{c}, @var{a}, @var{b})} +@tab @code{MCPXRS @var{a},@var{b},@var{c}} +@item @code{void __MCPXRU (acc, uw1, uw1)} +@tab @code{__MCPXRU (@var{c}, @var{a}, @var{b})} +@tab @code{MCPXRU @var{a},@var{b},@var{c}} +@item @code{uw1 __MCUT (acc, uw1)} +@tab @code{@var{c} = __MCUT (@var{a}, @var{b})} +@tab @code{MCUT @var{a},@var{b},@var{c}} +@item @code{uw1 __MCUTSS (acc, sw1)} +@tab @code{@var{c} = __MCUTSS (@var{a}, @var{b})} +@tab @code{MCUTSS @var{a},@var{b},@var{c}} +@item @code{void __MDADDACCS (acc, acc)} +@tab @code{__MDADDACCS (@var{b}, @var{a})} +@tab @code{MDADDACCS @var{a},@var{b}} +@item @code{void __MDASACCS (acc, acc)} +@tab @code{__MDASACCS (@var{b}, @var{a})} +@tab @code{MDASACCS @var{a},@var{b}} +@item @code{uw2 __MDCUTSSI (acc, const)} +@tab @code{@var{c} = __MDCUTSSI (@var{a}, @var{b})} +@tab @code{MDCUTSSI @var{a},#@var{b},@var{c}} +@item @code{uw2 __MDPACKH (uw2, uw2)} +@tab @code{@var{c} = __MDPACKH (@var{a}, @var{b})} +@tab @code{MDPACKH @var{a},@var{b},@var{c}} +@item @code{uw2 __MDROTLI (uw2, const)} +@tab @code{@var{c} = __MDROTLI (@var{a}, @var{b})} +@tab @code{MDROTLI @var{a},#@var{b},@var{c}} +@item @code{void __MDSUBACCS (acc, acc)} +@tab @code{__MDSUBACCS (@var{b}, @var{a})} +@tab @code{MDSUBACCS @var{a},@var{b}} +@item @code{void __MDUNPACKH (uw1 *, uw2)} +@tab @code{__MDUNPACKH (&@var{b}, @var{a})} +@tab @code{MDUNPACKH @var{a},@var{b}} +@item @code{uw2 __MEXPDHD (uw1, const)} +@tab @code{@var{c} = __MEXPDHD (@var{a}, @var{b})} +@tab @code{MEXPDHD @var{a},#@var{b},@var{c}} +@item @code{uw1 __MEXPDHW (uw1, const)} +@tab @code{@var{c} = __MEXPDHW (@var{a}, @var{b})} +@tab @code{MEXPDHW @var{a},#@var{b},@var{c}} +@item @code{uw1 __MHDSETH (uw1, const)} +@tab @code{@var{c} = __MHDSETH (@var{a}, @var{b})} +@tab @code{MHDSETH @var{a},#@var{b},@var{c}} +@item @code{sw1 __MHDSETS (const)} +@tab @code{@var{b} = __MHDSETS (@var{a})} +@tab @code{MHDSETS #@var{a},@var{b}} +@item @code{uw1 __MHSETHIH (uw1, const)} +@tab @code{@var{b} = __MHSETHIH (@var{b}, @var{a})} +@tab @code{MHSETHIH #@var{a},@var{b}} +@item @code{sw1 __MHSETHIS (sw1, const)} +@tab @code{@var{b} = __MHSETHIS (@var{b}, @var{a})} +@tab @code{MHSETHIS #@var{a},@var{b}} +@item @code{uw1 __MHSETLOH (uw1, const)} +@tab @code{@var{b} = __MHSETLOH (@var{b}, @var{a})} +@tab @code{MHSETLOH #@var{a},@var{b}} +@item @code{sw1 __MHSETLOS (sw1, const)} +@tab @code{@var{b} = __MHSETLOS (@var{b}, @var{a})} +@tab @code{MHSETLOS #@var{a},@var{b}} +@item @code{uw1 __MHTOB (uw2)} +@tab @code{@var{b} = __MHTOB (@var{a})} +@tab @code{MHTOB @var{a},@var{b}} +@item @code{void __MMACHS (acc, sw1, sw1)} +@tab @code{__MMACHS (@var{c}, @var{a}, @var{b})} +@tab @code{MMACHS @var{a},@var{b},@var{c}} +@item @code{void __MMACHU (acc, uw1, uw1)} +@tab @code{__MMACHU (@var{c}, @var{a}, @var{b})} +@tab @code{MMACHU @var{a},@var{b},@var{c}} +@item @code{void __MMRDHS (acc, sw1, sw1)} +@tab @code{__MMRDHS (@var{c}, @var{a}, @var{b})} +@tab @code{MMRDHS @var{a},@var{b},@var{c}} +@item @code{void __MMRDHU (acc, uw1, uw1)} +@tab @code{__MMRDHU (@var{c}, @var{a}, @var{b})} +@tab @code{MMRDHU @var{a},@var{b},@var{c}} +@item @code{void __MMULHS (acc, sw1, sw1)} +@tab @code{__MMULHS (@var{c}, @var{a}, @var{b})} +@tab @code{MMULHS @var{a},@var{b},@var{c}} +@item @code{void __MMULHU (acc, uw1, uw1)} +@tab @code{__MMULHU (@var{c}, @var{a}, @var{b})} +@tab @code{MMULHU @var{a},@var{b},@var{c}} +@item @code{void __MMULXHS (acc, sw1, sw1)} +@tab @code{__MMULXHS (@var{c}, @var{a}, @var{b})} +@tab @code{MMULXHS @var{a},@var{b},@var{c}} +@item @code{void __MMULXHU (acc, uw1, uw1)} +@tab @code{__MMULXHU (@var{c}, @var{a}, @var{b})} +@tab @code{MMULXHU @var{a},@var{b},@var{c}} +@item @code{uw1 __MNOT (uw1)} +@tab @code{@var{b} = __MNOT (@var{a})} +@tab @code{MNOT @var{a},@var{b}} +@item @code{uw1 __MOR (uw1, uw1)} +@tab @code{@var{c} = __MOR (@var{a}, @var{b})} +@tab @code{MOR @var{a},@var{b},@var{c}} +@item @code{uw1 __MPACKH (uh, uh)} +@tab @code{@var{c} = __MPACKH (@var{a}, @var{b})} +@tab @code{MPACKH @var{a},@var{b},@var{c}} +@item @code{sw2 __MQADDHSS (sw2, sw2)} +@tab @code{@var{c} = __MQADDHSS (@var{a}, @var{b})} +@tab @code{MQADDHSS @var{a},@var{b},@var{c}} +@item @code{uw2 __MQADDHUS (uw2, uw2)} +@tab @code{@var{c} = __MQADDHUS (@var{a}, @var{b})} +@tab @code{MQADDHUS @var{a},@var{b},@var{c}} +@item @code{void __MQCPXIS (acc, sw2, sw2)} +@tab @code{__MQCPXIS (@var{c}, @var{a}, @var{b})} +@tab @code{MQCPXIS @var{a},@var{b},@var{c}} +@item @code{void __MQCPXIU (acc, uw2, uw2)} +@tab @code{__MQCPXIU (@var{c}, @var{a}, @var{b})} +@tab @code{MQCPXIU @var{a},@var{b},@var{c}} +@item @code{void __MQCPXRS (acc, sw2, sw2)} +@tab @code{__MQCPXRS (@var{c}, @var{a}, @var{b})} +@tab @code{MQCPXRS @var{a},@var{b},@var{c}} +@item @code{void __MQCPXRU (acc, uw2, uw2)} +@tab @code{__MQCPXRU (@var{c}, @var{a}, @var{b})} +@tab @code{MQCPXRU @var{a},@var{b},@var{c}} +@item @code{sw2 __MQLCLRHS (sw2, sw2)} +@tab @code{@var{c} = __MQLCLRHS (@var{a}, @var{b})} +@tab @code{MQLCLRHS @var{a},@var{b},@var{c}} +@item @code{sw2 __MQLMTHS (sw2, sw2)} +@tab @code{@var{c} = __MQLMTHS (@var{a}, @var{b})} +@tab @code{MQLMTHS @var{a},@var{b},@var{c}} +@item @code{void __MQMACHS (acc, sw2, sw2)} +@tab @code{__MQMACHS (@var{c}, @var{a}, @var{b})} +@tab @code{MQMACHS @var{a},@var{b},@var{c}} +@item @code{void __MQMACHU (acc, uw2, uw2)} +@tab @code{__MQMACHU (@var{c}, @var{a}, @var{b})} +@tab @code{MQMACHU @var{a},@var{b},@var{c}} +@item @code{void __MQMACXHS (acc, sw2, sw2)} +@tab @code{__MQMACXHS (@var{c}, @var{a}, @var{b})} +@tab @code{MQMACXHS @var{a},@var{b},@var{c}} +@item @code{void __MQMULHS (acc, sw2, sw2)} +@tab @code{__MQMULHS (@var{c}, @var{a}, @var{b})} +@tab @code{MQMULHS @var{a},@var{b},@var{c}} +@item @code{void __MQMULHU (acc, uw2, uw2)} +@tab @code{__MQMULHU (@var{c}, @var{a}, @var{b})} +@tab @code{MQMULHU @var{a},@var{b},@var{c}} +@item @code{void __MQMULXHS (acc, sw2, sw2)} +@tab @code{__MQMULXHS (@var{c}, @var{a}, @var{b})} +@tab @code{MQMULXHS @var{a},@var{b},@var{c}} +@item @code{void __MQMULXHU (acc, uw2, uw2)} +@tab @code{__MQMULXHU (@var{c}, @var{a}, @var{b})} +@tab @code{MQMULXHU @var{a},@var{b},@var{c}} +@item @code{sw2 __MQSATHS (sw2, sw2)} +@tab @code{@var{c} = __MQSATHS (@var{a}, @var{b})} +@tab @code{MQSATHS @var{a},@var{b},@var{c}} +@item @code{uw2 __MQSLLHI (uw2, int)} +@tab @code{@var{c} = __MQSLLHI (@var{a}, @var{b})} +@tab @code{MQSLLHI @var{a},@var{b},@var{c}} +@item @code{sw2 __MQSRAHI (sw2, int)} +@tab @code{@var{c} = __MQSRAHI (@var{a}, @var{b})} +@tab @code{MQSRAHI @var{a},@var{b},@var{c}} +@item @code{sw2 __MQSUBHSS (sw2, sw2)} +@tab @code{@var{c} = __MQSUBHSS (@var{a}, @var{b})} +@tab @code{MQSUBHSS @var{a},@var{b},@var{c}} +@item @code{uw2 __MQSUBHUS (uw2, uw2)} +@tab @code{@var{c} = __MQSUBHUS (@var{a}, @var{b})} +@tab @code{MQSUBHUS @var{a},@var{b},@var{c}} +@item @code{void __MQXMACHS (acc, sw2, sw2)} +@tab @code{__MQXMACHS (@var{c}, @var{a}, @var{b})} +@tab @code{MQXMACHS @var{a},@var{b},@var{c}} +@item @code{void __MQXMACXHS (acc, sw2, sw2)} +@tab @code{__MQXMACXHS (@var{c}, @var{a}, @var{b})} +@tab @code{MQXMACXHS @var{a},@var{b},@var{c}} +@item @code{uw1 __MRDACC (acc)} +@tab @code{@var{b} = __MRDACC (@var{a})} +@tab @code{MRDACC @var{a},@var{b}} +@item @code{uw1 __MRDACCG (acc)} +@tab @code{@var{b} = __MRDACCG (@var{a})} +@tab @code{MRDACCG @var{a},@var{b}} +@item @code{uw1 __MROTLI (uw1, const)} +@tab @code{@var{c} = __MROTLI (@var{a}, @var{b})} +@tab @code{MROTLI @var{a},#@var{b},@var{c}} +@item @code{uw1 __MROTRI (uw1, const)} +@tab @code{@var{c} = __MROTRI (@var{a}, @var{b})} +@tab @code{MROTRI @var{a},#@var{b},@var{c}} +@item @code{sw1 __MSATHS (sw1, sw1)} +@tab @code{@var{c} = __MSATHS (@var{a}, @var{b})} +@tab @code{MSATHS @var{a},@var{b},@var{c}} +@item @code{uw1 __MSATHU (uw1, uw1)} +@tab @code{@var{c} = __MSATHU (@var{a}, @var{b})} +@tab @code{MSATHU @var{a},@var{b},@var{c}} +@item @code{uw1 __MSLLHI (uw1, const)} +@tab @code{@var{c} = __MSLLHI (@var{a}, @var{b})} +@tab @code{MSLLHI @var{a},#@var{b},@var{c}} +@item @code{sw1 __MSRAHI (sw1, const)} +@tab @code{@var{c} = __MSRAHI (@var{a}, @var{b})} +@tab @code{MSRAHI @var{a},#@var{b},@var{c}} +@item @code{uw1 __MSRLHI (uw1, const)} +@tab @code{@var{c} = __MSRLHI (@var{a}, @var{b})} +@tab @code{MSRLHI @var{a},#@var{b},@var{c}} +@item @code{void __MSUBACCS (acc, acc)} +@tab @code{__MSUBACCS (@var{b}, @var{a})} +@tab @code{MSUBACCS @var{a},@var{b}} +@item @code{sw1 __MSUBHSS (sw1, sw1)} +@tab @code{@var{c} = __MSUBHSS (@var{a}, @var{b})} +@tab @code{MSUBHSS @var{a},@var{b},@var{c}} +@item @code{uw1 __MSUBHUS (uw1, uw1)} +@tab @code{@var{c} = __MSUBHUS (@var{a}, @var{b})} +@tab @code{MSUBHUS @var{a},@var{b},@var{c}} +@item @code{void __MTRAP (void)} +@tab @code{__MTRAP ()} +@tab @code{MTRAP} +@item @code{uw2 __MUNPACKH (uw1)} +@tab @code{@var{b} = __MUNPACKH (@var{a})} +@tab @code{MUNPACKH @var{a},@var{b}} +@item @code{uw1 __MWCUT (uw2, uw1)} +@tab @code{@var{c} = __MWCUT (@var{a}, @var{b})} +@tab @code{MWCUT @var{a},@var{b},@var{c}} +@item @code{void __MWTACC (acc, uw1)} +@tab @code{__MWTACC (@var{b}, @var{a})} +@tab @code{MWTACC @var{a},@var{b}} +@item @code{void __MWTACCG (acc, uw1)} +@tab @code{__MWTACCG (@var{b}, @var{a})} +@tab @code{MWTACCG @var{a},@var{b}} +@item @code{uw1 __MXOR (uw1, uw1)} +@tab @code{@var{c} = __MXOR (@var{a}, @var{b})} +@tab @code{MXOR @var{a},@var{b},@var{c}} +@end multitable + +@node Raw read/write Functions +@subsubsection Raw Read/Write Functions + +This sections describes built-in functions related to read and write +instructions to access memory. These functions generate +@code{membar} instructions to flush the I/O load and stores where +appropriate, as described in Fujitsu's manual described above. + +@table @code + +@item unsigned char __builtin_read8 (void *@var{data}) +@item unsigned short __builtin_read16 (void *@var{data}) +@item unsigned long __builtin_read32 (void *@var{data}) +@item unsigned long long __builtin_read64 (void *@var{data}) + +@item void __builtin_write8 (void *@var{data}, unsigned char @var{datum}) +@item void __builtin_write16 (void *@var{data}, unsigned short @var{datum}) +@item void __builtin_write32 (void *@var{data}, unsigned long @var{datum}) +@item void __builtin_write64 (void *@var{data}, unsigned long long @var{datum}) +@end table + +@node Other Built-in Functions +@subsubsection Other Built-in Functions + +This section describes built-in functions that are not named after +a specific FR-V instruction. + +@table @code +@item sw2 __IACCreadll (iacc @var{reg}) +Return the full 64-bit value of IACC0@. The @var{reg} argument is reserved +for future expansion and must be 0. + +@item sw1 __IACCreadl (iacc @var{reg}) +Return the value of IACC0H if @var{reg} is 0 and IACC0L if @var{reg} is 1. +Other values of @var{reg} are rejected as invalid. + +@item void __IACCsetll (iacc @var{reg}, sw2 @var{x}) +Set the full 64-bit value of IACC0 to @var{x}. The @var{reg} argument +is reserved for future expansion and must be 0. + +@item void __IACCsetl (iacc @var{reg}, sw1 @var{x}) +Set IACC0H to @var{x} if @var{reg} is 0 and IACC0L to @var{x} if @var{reg} +is 1. Other values of @var{reg} are rejected as invalid. + +@item void __data_prefetch0 (const void *@var{x}) +Use the @code{dcpl} instruction to load the contents of address @var{x} +into the data cache. + +@item void __data_prefetch (const void *@var{x}) +Use the @code{nldub} instruction to load the contents of address @var{x} +into the data cache. The instruction is issued in slot I1@. +@end table + +@node MIPS DSP Built-in Functions +@subsection MIPS DSP Built-in Functions + +The MIPS DSP Application-Specific Extension (ASE) includes new +instructions that are designed to improve the performance of DSP and +media applications. It provides instructions that operate on packed +8-bit/16-bit integer data, Q7, Q15 and Q31 fractional data. + +GCC supports MIPS DSP operations using both the generic +vector extensions (@pxref{Vector Extensions}) and a collection of +MIPS-specific built-in functions. Both kinds of support are +enabled by the @option{-mdsp} command-line option. + +Revision 2 of the ASE was introduced in the second half of 2006. +This revision adds extra instructions to the original ASE, but is +otherwise backwards-compatible with it. You can select revision 2 +using the command-line option @option{-mdspr2}; this option implies +@option{-mdsp}. + +The SCOUNT and POS bits of the DSP control register are global. The +WRDSP, EXTPDP, EXTPDPV and MTHLIP instructions modify the SCOUNT and +POS bits. During optimization, the compiler does not delete these +instructions and it does not delete calls to functions containing +these instructions. + +At present, GCC only provides support for operations on 32-bit +vectors. The vector type associated with 8-bit integer data is +usually called @code{v4i8}, the vector type associated with Q7 +is usually called @code{v4q7}, the vector type associated with 16-bit +integer data is usually called @code{v2i16}, and the vector type +associated with Q15 is usually called @code{v2q15}. They can be +defined in C as follows: + +@smallexample +typedef signed char v4i8 __attribute__ ((vector_size(4))); +typedef signed char v4q7 __attribute__ ((vector_size(4))); +typedef short v2i16 __attribute__ ((vector_size(4))); +typedef short v2q15 __attribute__ ((vector_size(4))); +@end smallexample + +@code{v4i8}, @code{v4q7}, @code{v2i16} and @code{v2q15} values are +initialized in the same way as aggregates. For example: + +@smallexample +v4i8 a = @{1, 2, 3, 4@}; +v4i8 b; +b = (v4i8) @{5, 6, 7, 8@}; + +v2q15 c = @{0x0fcb, 0x3a75@}; +v2q15 d; +d = (v2q15) @{0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15@}; +@end smallexample + +@emph{Note:} The CPU's endianness determines the order in which values +are packed. On little-endian targets, the first value is the least +significant and the last value is the most significant. The opposite +order applies to big-endian targets. For example, the code above +sets the lowest byte of @code{a} to @code{1} on little-endian targets +and @code{4} on big-endian targets. + +@emph{Note:} Q7, Q15 and Q31 values must be initialized with their integer +representation. As shown in this example, the integer representation +of a Q7 value can be obtained by multiplying the fractional value by +@code{0x1.0p7}. The equivalent for Q15 values is to multiply by +@code{0x1.0p15}. The equivalent for Q31 values is to multiply by +@code{0x1.0p31}. + +The table below lists the @code{v4i8} and @code{v2q15} operations for which +hardware support exists. @code{a} and @code{b} are @code{v4i8} values, +and @code{c} and @code{d} are @code{v2q15} values. + +@multitable @columnfractions .50 .50 +@headitem C code @tab MIPS instruction +@item @code{a + b} @tab @code{addu.qb} +@item @code{c + d} @tab @code{addq.ph} +@item @code{a - b} @tab @code{subu.qb} +@item @code{c - d} @tab @code{subq.ph} +@end multitable + +The table below lists the @code{v2i16} operation for which +hardware support exists for the DSP ASE REV 2. @code{e} and @code{f} are +@code{v2i16} values. + +@multitable @columnfractions .50 .50 +@headitem C code @tab MIPS instruction +@item @code{e * f} @tab @code{mul.ph} +@end multitable + +It is easier to describe the DSP built-in functions if we first define +the following types: + +@smallexample +typedef int q31; +typedef int i32; +typedef unsigned int ui32; +typedef long long a64; +@end smallexample + +@code{q31} and @code{i32} are actually the same as @code{int}, but we +use @code{q31} to indicate a Q31 fractional value and @code{i32} to +indicate a 32-bit integer value. Similarly, @code{a64} is the same as +@code{long long}, but we use @code{a64} to indicate values that are +placed in one of the four DSP accumulators (@code{$ac0}, +@code{$ac1}, @code{$ac2} or @code{$ac3}). + +Also, some built-in functions prefer or require immediate numbers as +parameters, because the corresponding DSP instructions accept both immediate +numbers and register operands, or accept immediate numbers only. The +immediate parameters are listed as follows. + +@smallexample +imm0_3: 0 to 3. +imm0_7: 0 to 7. +imm0_15: 0 to 15. +imm0_31: 0 to 31. +imm0_63: 0 to 63. +imm0_255: 0 to 255. +imm_n32_31: -32 to 31. +imm_n512_511: -512 to 511. +@end smallexample + +The following built-in functions map directly to a particular MIPS DSP +instruction. Please refer to the architecture specification +for details on what each instruction does. + +@smallexample +v2q15 __builtin_mips_addq_ph (v2q15, v2q15); +v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15); +q31 __builtin_mips_addq_s_w (q31, q31); +v4i8 __builtin_mips_addu_qb (v4i8, v4i8); +v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8); +v2q15 __builtin_mips_subq_ph (v2q15, v2q15); +v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15); +q31 __builtin_mips_subq_s_w (q31, q31); +v4i8 __builtin_mips_subu_qb (v4i8, v4i8); +v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8); +i32 __builtin_mips_addsc (i32, i32); +i32 __builtin_mips_addwc (i32, i32); +i32 __builtin_mips_modsub (i32, i32); +i32 __builtin_mips_raddu_w_qb (v4i8); +v2q15 __builtin_mips_absq_s_ph (v2q15); +q31 __builtin_mips_absq_s_w (q31); +v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15); +v2q15 __builtin_mips_precrq_ph_w (q31, q31); +v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31); +v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15); +q31 __builtin_mips_preceq_w_phl (v2q15); +q31 __builtin_mips_preceq_w_phr (v2q15); +v2q15 __builtin_mips_precequ_ph_qbl (v4i8); +v2q15 __builtin_mips_precequ_ph_qbr (v4i8); +v2q15 __builtin_mips_precequ_ph_qbla (v4i8); +v2q15 __builtin_mips_precequ_ph_qbra (v4i8); +v2q15 __builtin_mips_preceu_ph_qbl (v4i8); +v2q15 __builtin_mips_preceu_ph_qbr (v4i8); +v2q15 __builtin_mips_preceu_ph_qbla (v4i8); +v2q15 __builtin_mips_preceu_ph_qbra (v4i8); +v4i8 __builtin_mips_shll_qb (v4i8, imm0_7); +v4i8 __builtin_mips_shll_qb (v4i8, i32); +v2q15 __builtin_mips_shll_ph (v2q15, imm0_15); +v2q15 __builtin_mips_shll_ph (v2q15, i32); +v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15); +v2q15 __builtin_mips_shll_s_ph (v2q15, i32); +q31 __builtin_mips_shll_s_w (q31, imm0_31); +q31 __builtin_mips_shll_s_w (q31, i32); +v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7); +v4i8 __builtin_mips_shrl_qb (v4i8, i32); +v2q15 __builtin_mips_shra_ph (v2q15, imm0_15); +v2q15 __builtin_mips_shra_ph (v2q15, i32); +v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15); +v2q15 __builtin_mips_shra_r_ph (v2q15, i32); +q31 __builtin_mips_shra_r_w (q31, imm0_31); +q31 __builtin_mips_shra_r_w (q31, i32); +v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15); +v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15); +v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15); +q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15); +q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15); +a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8); +a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8); +a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8); +a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8); +a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15); +a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31); +a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15); +a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31); +a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15); +a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15); +a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15); +a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15); +a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15); +i32 __builtin_mips_bitrev (i32); +i32 __builtin_mips_insv (i32, i32); +v4i8 __builtin_mips_repl_qb (imm0_255); +v4i8 __builtin_mips_repl_qb (i32); +v2q15 __builtin_mips_repl_ph (imm_n512_511); +v2q15 __builtin_mips_repl_ph (i32); +void __builtin_mips_cmpu_eq_qb (v4i8, v4i8); +void __builtin_mips_cmpu_lt_qb (v4i8, v4i8); +void __builtin_mips_cmpu_le_qb (v4i8, v4i8); +i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8); +i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8); +i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8); +void __builtin_mips_cmp_eq_ph (v2q15, v2q15); +void __builtin_mips_cmp_lt_ph (v2q15, v2q15); +void __builtin_mips_cmp_le_ph (v2q15, v2q15); +v4i8 __builtin_mips_pick_qb (v4i8, v4i8); +v2q15 __builtin_mips_pick_ph (v2q15, v2q15); +v2q15 __builtin_mips_packrl_ph (v2q15, v2q15); +i32 __builtin_mips_extr_w (a64, imm0_31); +i32 __builtin_mips_extr_w (a64, i32); +i32 __builtin_mips_extr_r_w (a64, imm0_31); +i32 __builtin_mips_extr_s_h (a64, i32); +i32 __builtin_mips_extr_rs_w (a64, imm0_31); +i32 __builtin_mips_extr_rs_w (a64, i32); +i32 __builtin_mips_extr_s_h (a64, imm0_31); +i32 __builtin_mips_extr_r_w (a64, i32); +i32 __builtin_mips_extp (a64, imm0_31); +i32 __builtin_mips_extp (a64, i32); +i32 __builtin_mips_extpdp (a64, imm0_31); +i32 __builtin_mips_extpdp (a64, i32); +a64 __builtin_mips_shilo (a64, imm_n32_31); +a64 __builtin_mips_shilo (a64, i32); +a64 __builtin_mips_mthlip (a64, i32); +void __builtin_mips_wrdsp (i32, imm0_63); +i32 __builtin_mips_rddsp (imm0_63); +i32 __builtin_mips_lbux (void *, i32); +i32 __builtin_mips_lhx (void *, i32); +i32 __builtin_mips_lwx (void *, i32); +a64 __builtin_mips_ldx (void *, i32); /* MIPS64 only */ +i32 __builtin_mips_bposge32 (void); +a64 __builtin_mips_madd (a64, i32, i32); +a64 __builtin_mips_maddu (a64, ui32, ui32); +a64 __builtin_mips_msub (a64, i32, i32); +a64 __builtin_mips_msubu (a64, ui32, ui32); +a64 __builtin_mips_mult (i32, i32); +a64 __builtin_mips_multu (ui32, ui32); +@end smallexample + +The following built-in functions map directly to a particular MIPS DSP REV 2 +instruction. Please refer to the architecture specification +for details on what each instruction does. + +@smallexample +v4q7 __builtin_mips_absq_s_qb (v4q7); +v2i16 __builtin_mips_addu_ph (v2i16, v2i16); +v2i16 __builtin_mips_addu_s_ph (v2i16, v2i16); +v4i8 __builtin_mips_adduh_qb (v4i8, v4i8); +v4i8 __builtin_mips_adduh_r_qb (v4i8, v4i8); +i32 __builtin_mips_append (i32, i32, imm0_31); +i32 __builtin_mips_balign (i32, i32, imm0_3); +i32 __builtin_mips_cmpgdu_eq_qb (v4i8, v4i8); +i32 __builtin_mips_cmpgdu_lt_qb (v4i8, v4i8); +i32 __builtin_mips_cmpgdu_le_qb (v4i8, v4i8); +a64 __builtin_mips_dpa_w_ph (a64, v2i16, v2i16); +a64 __builtin_mips_dps_w_ph (a64, v2i16, v2i16); +v2i16 __builtin_mips_mul_ph (v2i16, v2i16); +v2i16 __builtin_mips_mul_s_ph (v2i16, v2i16); +q31 __builtin_mips_mulq_rs_w (q31, q31); +v2q15 __builtin_mips_mulq_s_ph (v2q15, v2q15); +q31 __builtin_mips_mulq_s_w (q31, q31); +a64 __builtin_mips_mulsa_w_ph (a64, v2i16, v2i16); +v4i8 __builtin_mips_precr_qb_ph (v2i16, v2i16); +v2i16 __builtin_mips_precr_sra_ph_w (i32, i32, imm0_31); +v2i16 __builtin_mips_precr_sra_r_ph_w (i32, i32, imm0_31); +i32 __builtin_mips_prepend (i32, i32, imm0_31); +v4i8 __builtin_mips_shra_qb (v4i8, imm0_7); +v4i8 __builtin_mips_shra_r_qb (v4i8, imm0_7); +v4i8 __builtin_mips_shra_qb (v4i8, i32); +v4i8 __builtin_mips_shra_r_qb (v4i8, i32); +v2i16 __builtin_mips_shrl_ph (v2i16, imm0_15); +v2i16 __builtin_mips_shrl_ph (v2i16, i32); +v2i16 __builtin_mips_subu_ph (v2i16, v2i16); +v2i16 __builtin_mips_subu_s_ph (v2i16, v2i16); +v4i8 __builtin_mips_subuh_qb (v4i8, v4i8); +v4i8 __builtin_mips_subuh_r_qb (v4i8, v4i8); +v2q15 __builtin_mips_addqh_ph (v2q15, v2q15); +v2q15 __builtin_mips_addqh_r_ph (v2q15, v2q15); +q31 __builtin_mips_addqh_w (q31, q31); +q31 __builtin_mips_addqh_r_w (q31, q31); +v2q15 __builtin_mips_subqh_ph (v2q15, v2q15); +v2q15 __builtin_mips_subqh_r_ph (v2q15, v2q15); +q31 __builtin_mips_subqh_w (q31, q31); +q31 __builtin_mips_subqh_r_w (q31, q31); +a64 __builtin_mips_dpax_w_ph (a64, v2i16, v2i16); +a64 __builtin_mips_dpsx_w_ph (a64, v2i16, v2i16); +a64 __builtin_mips_dpaqx_s_w_ph (a64, v2q15, v2q15); +a64 __builtin_mips_dpaqx_sa_w_ph (a64, v2q15, v2q15); +a64 __builtin_mips_dpsqx_s_w_ph (a64, v2q15, v2q15); +a64 __builtin_mips_dpsqx_sa_w_ph (a64, v2q15, v2q15); +@end smallexample + + +@node MIPS Paired-Single Support +@subsection MIPS Paired-Single Support + +The MIPS64 architecture includes a number of instructions that +operate on pairs of single-precision floating-point values. +Each pair is packed into a 64-bit floating-point register, +with one element being designated the ``upper half'' and +the other being designated the ``lower half''. + +GCC supports paired-single operations using both the generic +vector extensions (@pxref{Vector Extensions}) and a collection of +MIPS-specific built-in functions. Both kinds of support are +enabled by the @option{-mpaired-single} command-line option. + +The vector type associated with paired-single values is usually +called @code{v2sf}. It can be defined in C as follows: + +@smallexample +typedef float v2sf __attribute__ ((vector_size (8))); +@end smallexample + +@code{v2sf} values are initialized in the same way as aggregates. +For example: + +@smallexample +v2sf a = @{1.5, 9.1@}; +v2sf b; +float e, f; +b = (v2sf) @{e, f@}; +@end smallexample + +@emph{Note:} The CPU's endianness determines which value is stored in +the upper half of a register and which value is stored in the lower half. +On little-endian targets, the first value is the lower one and the second +value is the upper one. The opposite order applies to big-endian targets. +For example, the code above sets the lower half of @code{a} to +@code{1.5} on little-endian targets and @code{9.1} on big-endian targets. + +@node MIPS Loongson Built-in Functions +@subsection MIPS Loongson Built-in Functions + +GCC provides intrinsics to access the SIMD instructions provided by the +ST Microelectronics Loongson-2E and -2F processors. These intrinsics, +available after inclusion of the @code{loongson.h} header file, +operate on the following 64-bit vector types: + +@itemize +@item @code{uint8x8_t}, a vector of eight unsigned 8-bit integers; +@item @code{uint16x4_t}, a vector of four unsigned 16-bit integers; +@item @code{uint32x2_t}, a vector of two unsigned 32-bit integers; +@item @code{int8x8_t}, a vector of eight signed 8-bit integers; +@item @code{int16x4_t}, a vector of four signed 16-bit integers; +@item @code{int32x2_t}, a vector of two signed 32-bit integers. +@end itemize + +The intrinsics provided are listed below; each is named after the +machine instruction to which it corresponds, with suffixes added as +appropriate to distinguish intrinsics that expand to the same machine +instruction yet have different argument types. Refer to the architecture +documentation for a description of the functionality of each +instruction. + +@smallexample +int16x4_t packsswh (int32x2_t s, int32x2_t t); +int8x8_t packsshb (int16x4_t s, int16x4_t t); +uint8x8_t packushb (uint16x4_t s, uint16x4_t t); +uint32x2_t paddw_u (uint32x2_t s, uint32x2_t t); +uint16x4_t paddh_u (uint16x4_t s, uint16x4_t t); +uint8x8_t paddb_u (uint8x8_t s, uint8x8_t t); +int32x2_t paddw_s (int32x2_t s, int32x2_t t); +int16x4_t paddh_s (int16x4_t s, int16x4_t t); +int8x8_t paddb_s (int8x8_t s, int8x8_t t); +uint64_t paddd_u (uint64_t s, uint64_t t); +int64_t paddd_s (int64_t s, int64_t t); +int16x4_t paddsh (int16x4_t s, int16x4_t t); +int8x8_t paddsb (int8x8_t s, int8x8_t t); +uint16x4_t paddush (uint16x4_t s, uint16x4_t t); +uint8x8_t paddusb (uint8x8_t s, uint8x8_t t); +uint64_t pandn_ud (uint64_t s, uint64_t t); +uint32x2_t pandn_uw (uint32x2_t s, uint32x2_t t); +uint16x4_t pandn_uh (uint16x4_t s, uint16x4_t t); +uint8x8_t pandn_ub (uint8x8_t s, uint8x8_t t); +int64_t pandn_sd (int64_t s, int64_t t); +int32x2_t pandn_sw (int32x2_t s, int32x2_t t); +int16x4_t pandn_sh (int16x4_t s, int16x4_t t); +int8x8_t pandn_sb (int8x8_t s, int8x8_t t); +uint16x4_t pavgh (uint16x4_t s, uint16x4_t t); +uint8x8_t pavgb (uint8x8_t s, uint8x8_t t); +uint32x2_t pcmpeqw_u (uint32x2_t s, uint32x2_t t); +uint16x4_t pcmpeqh_u (uint16x4_t s, uint16x4_t t); +uint8x8_t pcmpeqb_u (uint8x8_t s, uint8x8_t t); +int32x2_t pcmpeqw_s (int32x2_t s, int32x2_t t); +int16x4_t pcmpeqh_s (int16x4_t s, int16x4_t t); +int8x8_t pcmpeqb_s (int8x8_t s, int8x8_t t); +uint32x2_t pcmpgtw_u (uint32x2_t s, uint32x2_t t); +uint16x4_t pcmpgth_u (uint16x4_t s, uint16x4_t t); +uint8x8_t pcmpgtb_u (uint8x8_t s, uint8x8_t t); +int32x2_t pcmpgtw_s (int32x2_t s, int32x2_t t); +int16x4_t pcmpgth_s (int16x4_t s, int16x4_t t); +int8x8_t pcmpgtb_s (int8x8_t s, int8x8_t t); +uint16x4_t pextrh_u (uint16x4_t s, int field); +int16x4_t pextrh_s (int16x4_t s, int field); +uint16x4_t pinsrh_0_u (uint16x4_t s, uint16x4_t t); +uint16x4_t pinsrh_1_u (uint16x4_t s, uint16x4_t t); +uint16x4_t pinsrh_2_u (uint16x4_t s, uint16x4_t t); +uint16x4_t pinsrh_3_u (uint16x4_t s, uint16x4_t t); +int16x4_t pinsrh_0_s (int16x4_t s, int16x4_t t); +int16x4_t pinsrh_1_s (int16x4_t s, int16x4_t t); +int16x4_t pinsrh_2_s (int16x4_t s, int16x4_t t); +int16x4_t pinsrh_3_s (int16x4_t s, int16x4_t t); +int32x2_t pmaddhw (int16x4_t s, int16x4_t t); +int16x4_t pmaxsh (int16x4_t s, int16x4_t t); +uint8x8_t pmaxub (uint8x8_t s, uint8x8_t t); +int16x4_t pminsh (int16x4_t s, int16x4_t t); +uint8x8_t pminub (uint8x8_t s, uint8x8_t t); +uint8x8_t pmovmskb_u (uint8x8_t s); +int8x8_t pmovmskb_s (int8x8_t s); +uint16x4_t pmulhuh (uint16x4_t s, uint16x4_t t); +int16x4_t pmulhh (int16x4_t s, int16x4_t t); +int16x4_t pmullh (int16x4_t s, int16x4_t t); +int64_t pmuluw (uint32x2_t s, uint32x2_t t); +uint8x8_t pasubub (uint8x8_t s, uint8x8_t t); +uint16x4_t biadd (uint8x8_t s); +uint16x4_t psadbh (uint8x8_t s, uint8x8_t t); +uint16x4_t pshufh_u (uint16x4_t dest, uint16x4_t s, uint8_t order); +int16x4_t pshufh_s (int16x4_t dest, int16x4_t s, uint8_t order); +uint16x4_t psllh_u (uint16x4_t s, uint8_t amount); +int16x4_t psllh_s (int16x4_t s, uint8_t amount); +uint32x2_t psllw_u (uint32x2_t s, uint8_t amount); +int32x2_t psllw_s (int32x2_t s, uint8_t amount); +uint16x4_t psrlh_u (uint16x4_t s, uint8_t amount); +int16x4_t psrlh_s (int16x4_t s, uint8_t amount); +uint32x2_t psrlw_u (uint32x2_t s, uint8_t amount); +int32x2_t psrlw_s (int32x2_t s, uint8_t amount); +uint16x4_t psrah_u (uint16x4_t s, uint8_t amount); +int16x4_t psrah_s (int16x4_t s, uint8_t amount); +uint32x2_t psraw_u (uint32x2_t s, uint8_t amount); +int32x2_t psraw_s (int32x2_t s, uint8_t amount); +uint32x2_t psubw_u (uint32x2_t s, uint32x2_t t); +uint16x4_t psubh_u (uint16x4_t s, uint16x4_t t); +uint8x8_t psubb_u (uint8x8_t s, uint8x8_t t); +int32x2_t psubw_s (int32x2_t s, int32x2_t t); +int16x4_t psubh_s (int16x4_t s, int16x4_t t); +int8x8_t psubb_s (int8x8_t s, int8x8_t t); +uint64_t psubd_u (uint64_t s, uint64_t t); +int64_t psubd_s (int64_t s, int64_t t); +int16x4_t psubsh (int16x4_t s, int16x4_t t); +int8x8_t psubsb (int8x8_t s, int8x8_t t); +uint16x4_t psubush (uint16x4_t s, uint16x4_t t); +uint8x8_t psubusb (uint8x8_t s, uint8x8_t t); +uint32x2_t punpckhwd_u (uint32x2_t s, uint32x2_t t); +uint16x4_t punpckhhw_u (uint16x4_t s, uint16x4_t t); +uint8x8_t punpckhbh_u (uint8x8_t s, uint8x8_t t); +int32x2_t punpckhwd_s (int32x2_t s, int32x2_t t); +int16x4_t punpckhhw_s (int16x4_t s, int16x4_t t); +int8x8_t punpckhbh_s (int8x8_t s, int8x8_t t); +uint32x2_t punpcklwd_u (uint32x2_t s, uint32x2_t t); +uint16x4_t punpcklhw_u (uint16x4_t s, uint16x4_t t); +uint8x8_t punpcklbh_u (uint8x8_t s, uint8x8_t t); +int32x2_t punpcklwd_s (int32x2_t s, int32x2_t t); +int16x4_t punpcklhw_s (int16x4_t s, int16x4_t t); +int8x8_t punpcklbh_s (int8x8_t s, int8x8_t t); +@end smallexample + +@menu +* Paired-Single Arithmetic:: +* Paired-Single Built-in Functions:: +* MIPS-3D Built-in Functions:: +@end menu + +@node Paired-Single Arithmetic +@subsubsection Paired-Single Arithmetic + +The table below lists the @code{v2sf} operations for which hardware +support exists. @code{a}, @code{b} and @code{c} are @code{v2sf} +values and @code{x} is an integral value. + +@multitable @columnfractions .50 .50 +@headitem C code @tab MIPS instruction +@item @code{a + b} @tab @code{add.ps} +@item @code{a - b} @tab @code{sub.ps} +@item @code{-a} @tab @code{neg.ps} +@item @code{a * b} @tab @code{mul.ps} +@item @code{a * b + c} @tab @code{madd.ps} +@item @code{a * b - c} @tab @code{msub.ps} +@item @code{-(a * b + c)} @tab @code{nmadd.ps} +@item @code{-(a * b - c)} @tab @code{nmsub.ps} +@item @code{x ? a : b} @tab @code{movn.ps}/@code{movz.ps} +@end multitable + +Note that the multiply-accumulate instructions can be disabled +using the command-line option @code{-mno-fused-madd}. + +@node Paired-Single Built-in Functions +@subsubsection Paired-Single Built-in Functions + +The following paired-single functions map directly to a particular +MIPS instruction. Please refer to the architecture specification +for details on what each instruction does. + +@table @code +@item v2sf __builtin_mips_pll_ps (v2sf, v2sf) +Pair lower lower (@code{pll.ps}). + +@item v2sf __builtin_mips_pul_ps (v2sf, v2sf) +Pair upper lower (@code{pul.ps}). + +@item v2sf __builtin_mips_plu_ps (v2sf, v2sf) +Pair lower upper (@code{plu.ps}). + +@item v2sf __builtin_mips_puu_ps (v2sf, v2sf) +Pair upper upper (@code{puu.ps}). + +@item v2sf __builtin_mips_cvt_ps_s (float, float) +Convert pair to paired single (@code{cvt.ps.s}). + +@item float __builtin_mips_cvt_s_pl (v2sf) +Convert pair lower to single (@code{cvt.s.pl}). + +@item float __builtin_mips_cvt_s_pu (v2sf) +Convert pair upper to single (@code{cvt.s.pu}). + +@item v2sf __builtin_mips_abs_ps (v2sf) +Absolute value (@code{abs.ps}). + +@item v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int) +Align variable (@code{alnv.ps}). + +@emph{Note:} The value of the third parameter must be 0 or 4 +modulo 8, otherwise the result is unpredictable. Please read the +instruction description for details. +@end table + +The following multi-instruction functions are also available. +In each case, @var{cond} can be any of the 16 floating-point conditions: +@code{f}, @code{un}, @code{eq}, @code{ueq}, @code{olt}, @code{ult}, +@code{ole}, @code{ule}, @code{sf}, @code{ngle}, @code{seq}, @code{ngl}, +@code{lt}, @code{nge}, @code{le} or @code{ngt}. + +@table @code +@item v2sf __builtin_mips_movt_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d}) +@itemx v2sf __builtin_mips_movf_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d}) +Conditional move based on floating-point comparison (@code{c.@var{cond}.ps}, +@code{movt.ps}/@code{movf.ps}). + +The @code{movt} functions return the value @var{x} computed by: + +@smallexample +c.@var{cond}.ps @var{cc},@var{a},@var{b} +mov.ps @var{x},@var{c} +movt.ps @var{x},@var{d},@var{cc} +@end smallexample + +The @code{movf} functions are similar but use @code{movf.ps} instead +of @code{movt.ps}. + +@item int __builtin_mips_upper_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}) +@itemx int __builtin_mips_lower_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}) +Comparison of two paired-single values (@code{c.@var{cond}.ps}, +@code{bc1t}/@code{bc1f}). + +These functions compare @var{a} and @var{b} using @code{c.@var{cond}.ps} +and return either the upper or lower half of the result. For example: + +@smallexample +v2sf a, b; +if (__builtin_mips_upper_c_eq_ps (a, b)) + upper_halves_are_equal (); +else + upper_halves_are_unequal (); + +if (__builtin_mips_lower_c_eq_ps (a, b)) + lower_halves_are_equal (); +else + lower_halves_are_unequal (); +@end smallexample +@end table + +@node MIPS-3D Built-in Functions +@subsubsection MIPS-3D Built-in Functions + +The MIPS-3D Application-Specific Extension (ASE) includes additional +paired-single instructions that are designed to improve the performance +of 3D graphics operations. Support for these instructions is controlled +by the @option{-mips3d} command-line option. + +The functions listed below map directly to a particular MIPS-3D +instruction. Please refer to the architecture specification for +more details on what each instruction does. + +@table @code +@item v2sf __builtin_mips_addr_ps (v2sf, v2sf) +Reduction add (@code{addr.ps}). + +@item v2sf __builtin_mips_mulr_ps (v2sf, v2sf) +Reduction multiply (@code{mulr.ps}). + +@item v2sf __builtin_mips_cvt_pw_ps (v2sf) +Convert paired single to paired word (@code{cvt.pw.ps}). + +@item v2sf __builtin_mips_cvt_ps_pw (v2sf) +Convert paired word to paired single (@code{cvt.ps.pw}). + +@item float __builtin_mips_recip1_s (float) +@itemx double __builtin_mips_recip1_d (double) +@itemx v2sf __builtin_mips_recip1_ps (v2sf) +Reduced-precision reciprocal (sequence step 1) (@code{recip1.@var{fmt}}). + +@item float __builtin_mips_recip2_s (float, float) +@itemx double __builtin_mips_recip2_d (double, double) +@itemx v2sf __builtin_mips_recip2_ps (v2sf, v2sf) +Reduced-precision reciprocal (sequence step 2) (@code{recip2.@var{fmt}}). + +@item float __builtin_mips_rsqrt1_s (float) +@itemx double __builtin_mips_rsqrt1_d (double) +@itemx v2sf __builtin_mips_rsqrt1_ps (v2sf) +Reduced-precision reciprocal square root (sequence step 1) +(@code{rsqrt1.@var{fmt}}). + +@item float __builtin_mips_rsqrt2_s (float, float) +@itemx double __builtin_mips_rsqrt2_d (double, double) +@itemx v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf) +Reduced-precision reciprocal square root (sequence step 2) +(@code{rsqrt2.@var{fmt}}). +@end table + +The following multi-instruction functions are also available. +In each case, @var{cond} can be any of the 16 floating-point conditions: +@code{f}, @code{un}, @code{eq}, @code{ueq}, @code{olt}, @code{ult}, +@code{ole}, @code{ule}, @code{sf}, @code{ngle}, @code{seq}, +@code{ngl}, @code{lt}, @code{nge}, @code{le} or @code{ngt}. + +@table @code +@item int __builtin_mips_cabs_@var{cond}_s (float @var{a}, float @var{b}) +@itemx int __builtin_mips_cabs_@var{cond}_d (double @var{a}, double @var{b}) +Absolute comparison of two scalar values (@code{cabs.@var{cond}.@var{fmt}}, +@code{bc1t}/@code{bc1f}). + +These functions compare @var{a} and @var{b} using @code{cabs.@var{cond}.s} +or @code{cabs.@var{cond}.d} and return the result as a boolean value. +For example: + +@smallexample +float a, b; +if (__builtin_mips_cabs_eq_s (a, b)) + true (); +else + false (); +@end smallexample + +@item int __builtin_mips_upper_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}) +@itemx int __builtin_mips_lower_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}) +Absolute comparison of two paired-single values (@code{cabs.@var{cond}.ps}, +@code{bc1t}/@code{bc1f}). + +These functions compare @var{a} and @var{b} using @code{cabs.@var{cond}.ps} +and return either the upper or lower half of the result. For example: + +@smallexample +v2sf a, b; +if (__builtin_mips_upper_cabs_eq_ps (a, b)) + upper_halves_are_equal (); +else + upper_halves_are_unequal (); + +if (__builtin_mips_lower_cabs_eq_ps (a, b)) + lower_halves_are_equal (); +else + lower_halves_are_unequal (); +@end smallexample + +@item v2sf __builtin_mips_movt_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d}) +@itemx v2sf __builtin_mips_movf_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d}) +Conditional move based on absolute comparison (@code{cabs.@var{cond}.ps}, +@code{movt.ps}/@code{movf.ps}). + +The @code{movt} functions return the value @var{x} computed by: + +@smallexample +cabs.@var{cond}.ps @var{cc},@var{a},@var{b} +mov.ps @var{x},@var{c} +movt.ps @var{x},@var{d},@var{cc} +@end smallexample + +The @code{movf} functions are similar but use @code{movf.ps} instead +of @code{movt.ps}. + +@item int __builtin_mips_any_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}) +@itemx int __builtin_mips_all_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}) +@itemx int __builtin_mips_any_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}) +@itemx int __builtin_mips_all_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}) +Comparison of two paired-single values +(@code{c.@var{cond}.ps}/@code{cabs.@var{cond}.ps}, +@code{bc1any2t}/@code{bc1any2f}). + +These functions compare @var{a} and @var{b} using @code{c.@var{cond}.ps} +or @code{cabs.@var{cond}.ps}. The @code{any} forms return @code{true} if either +result is @code{true} and the @code{all} forms return @code{true} if both results are @code{true}. +For example: + +@smallexample +v2sf a, b; +if (__builtin_mips_any_c_eq_ps (a, b)) + one_is_true (); +else + both_are_false (); + +if (__builtin_mips_all_c_eq_ps (a, b)) + both_are_true (); +else + one_is_false (); +@end smallexample + +@item int __builtin_mips_any_c_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d}) +@itemx int __builtin_mips_all_c_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d}) +@itemx int __builtin_mips_any_cabs_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d}) +@itemx int __builtin_mips_all_cabs_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d}) +Comparison of four paired-single values +(@code{c.@var{cond}.ps}/@code{cabs.@var{cond}.ps}, +@code{bc1any4t}/@code{bc1any4f}). + +These functions use @code{c.@var{cond}.ps} or @code{cabs.@var{cond}.ps} +to compare @var{a} with @var{b} and to compare @var{c} with @var{d}. +The @code{any} forms return @code{true} if any of the four results are @code{true} +and the @code{all} forms return @code{true} if all four results are @code{true}. +For example: + +@smallexample +v2sf a, b, c, d; +if (__builtin_mips_any_c_eq_4s (a, b, c, d)) + some_are_true (); +else + all_are_false (); + +if (__builtin_mips_all_c_eq_4s (a, b, c, d)) + all_are_true (); +else + some_are_false (); +@end smallexample +@end table + +@node MIPS SIMD Architecture (MSA) Support +@subsection MIPS SIMD Architecture (MSA) Support + +@menu +* MIPS SIMD Architecture Built-in Functions:: +@end menu + +GCC provides intrinsics to access the SIMD instructions provided by the +MSA MIPS SIMD Architecture. The interface is made available by including +@code{} and using @option{-mmsa -mhard-float -mfp64 -mnan=2008}. +For each @code{__builtin_msa_*}, there is a shortened name of the intrinsic, +@code{__msa_*}. + +MSA implements 128-bit wide vector registers, operating on 8-, 16-, 32- and +64-bit integer, 16- and 32-bit fixed-point, or 32- and 64-bit floating point +data elements. The following vectors typedefs are included in @code{msa.h}: +@itemize +@item @code{v16i8}, a vector of sixteen signed 8-bit integers; +@item @code{v16u8}, a vector of sixteen unsigned 8-bit integers; +@item @code{v8i16}, a vector of eight signed 16-bit integers; +@item @code{v8u16}, a vector of eight unsigned 16-bit integers; +@item @code{v4i32}, a vector of four signed 32-bit integers; +@item @code{v4u32}, a vector of four unsigned 32-bit integers; +@item @code{v2i64}, a vector of two signed 64-bit integers; +@item @code{v2u64}, a vector of two unsigned 64-bit integers; +@item @code{v4f32}, a vector of four 32-bit floats; +@item @code{v2f64}, a vector of two 64-bit doubles. +@end itemize + +Instructions and corresponding built-ins may have additional restrictions and/or +input/output values manipulated: +@itemize +@item @code{imm0_1}, an integer literal in range 0 to 1; +@item @code{imm0_3}, an integer literal in range 0 to 3; +@item @code{imm0_7}, an integer literal in range 0 to 7; +@item @code{imm0_15}, an integer literal in range 0 to 15; +@item @code{imm0_31}, an integer literal in range 0 to 31; +@item @code{imm0_63}, an integer literal in range 0 to 63; +@item @code{imm0_255}, an integer literal in range 0 to 255; +@item @code{imm_n16_15}, an integer literal in range -16 to 15; +@item @code{imm_n512_511}, an integer literal in range -512 to 511; +@item @code{imm_n1024_1022}, an integer literal in range -512 to 511 left +shifted by 1 bit, i.e., -1024, -1022, @dots{}, 1020, 1022; +@item @code{imm_n2048_2044}, an integer literal in range -512 to 511 left +shifted by 2 bits, i.e., -2048, -2044, @dots{}, 2040, 2044; +@item @code{imm_n4096_4088}, an integer literal in range -512 to 511 left +shifted by 3 bits, i.e., -4096, -4088, @dots{}, 4080, 4088; +@item @code{imm1_4}, an integer literal in range 1 to 4; +@item @code{i32, i64, u32, u64, f32, f64}, defined as follows: +@end itemize + +@smallexample +@{ +typedef int i32; +#if __LONG_MAX__ == __LONG_LONG_MAX__ +typedef long i64; +#else +typedef long long i64; +#endif + +typedef unsigned int u32; +#if __LONG_MAX__ == __LONG_LONG_MAX__ +typedef unsigned long u64; +#else +typedef unsigned long long u64; +#endif + +typedef double f64; +typedef float f32; +@} +@end smallexample + +@node MIPS SIMD Architecture Built-in Functions +@subsubsection MIPS SIMD Architecture Built-in Functions + +The intrinsics provided are listed below; each is named after the +machine instruction. + +@smallexample +v16i8 __builtin_msa_add_a_b (v16i8, v16i8); +v8i16 __builtin_msa_add_a_h (v8i16, v8i16); +v4i32 __builtin_msa_add_a_w (v4i32, v4i32); +v2i64 __builtin_msa_add_a_d (v2i64, v2i64); + +v16i8 __builtin_msa_adds_a_b (v16i8, v16i8); +v8i16 __builtin_msa_adds_a_h (v8i16, v8i16); +v4i32 __builtin_msa_adds_a_w (v4i32, v4i32); +v2i64 __builtin_msa_adds_a_d (v2i64, v2i64); + +v16i8 __builtin_msa_adds_s_b (v16i8, v16i8); +v8i16 __builtin_msa_adds_s_h (v8i16, v8i16); +v4i32 __builtin_msa_adds_s_w (v4i32, v4i32); +v2i64 __builtin_msa_adds_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_adds_u_b (v16u8, v16u8); +v8u16 __builtin_msa_adds_u_h (v8u16, v8u16); +v4u32 __builtin_msa_adds_u_w (v4u32, v4u32); +v2u64 __builtin_msa_adds_u_d (v2u64, v2u64); + +v16i8 __builtin_msa_addv_b (v16i8, v16i8); +v8i16 __builtin_msa_addv_h (v8i16, v8i16); +v4i32 __builtin_msa_addv_w (v4i32, v4i32); +v2i64 __builtin_msa_addv_d (v2i64, v2i64); + +v16i8 __builtin_msa_addvi_b (v16i8, imm0_31); +v8i16 __builtin_msa_addvi_h (v8i16, imm0_31); +v4i32 __builtin_msa_addvi_w (v4i32, imm0_31); +v2i64 __builtin_msa_addvi_d (v2i64, imm0_31); + +v16u8 __builtin_msa_and_v (v16u8, v16u8); + +v16u8 __builtin_msa_andi_b (v16u8, imm0_255); + +v16i8 __builtin_msa_asub_s_b (v16i8, v16i8); +v8i16 __builtin_msa_asub_s_h (v8i16, v8i16); +v4i32 __builtin_msa_asub_s_w (v4i32, v4i32); +v2i64 __builtin_msa_asub_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_asub_u_b (v16u8, v16u8); +v8u16 __builtin_msa_asub_u_h (v8u16, v8u16); +v4u32 __builtin_msa_asub_u_w (v4u32, v4u32); +v2u64 __builtin_msa_asub_u_d (v2u64, v2u64); + +v16i8 __builtin_msa_ave_s_b (v16i8, v16i8); +v8i16 __builtin_msa_ave_s_h (v8i16, v8i16); +v4i32 __builtin_msa_ave_s_w (v4i32, v4i32); +v2i64 __builtin_msa_ave_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_ave_u_b (v16u8, v16u8); +v8u16 __builtin_msa_ave_u_h (v8u16, v8u16); +v4u32 __builtin_msa_ave_u_w (v4u32, v4u32); +v2u64 __builtin_msa_ave_u_d (v2u64, v2u64); + +v16i8 __builtin_msa_aver_s_b (v16i8, v16i8); +v8i16 __builtin_msa_aver_s_h (v8i16, v8i16); +v4i32 __builtin_msa_aver_s_w (v4i32, v4i32); +v2i64 __builtin_msa_aver_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_aver_u_b (v16u8, v16u8); +v8u16 __builtin_msa_aver_u_h (v8u16, v8u16); +v4u32 __builtin_msa_aver_u_w (v4u32, v4u32); +v2u64 __builtin_msa_aver_u_d (v2u64, v2u64); + +v16u8 __builtin_msa_bclr_b (v16u8, v16u8); +v8u16 __builtin_msa_bclr_h (v8u16, v8u16); +v4u32 __builtin_msa_bclr_w (v4u32, v4u32); +v2u64 __builtin_msa_bclr_d (v2u64, v2u64); + +v16u8 __builtin_msa_bclri_b (v16u8, imm0_7); +v8u16 __builtin_msa_bclri_h (v8u16, imm0_15); +v4u32 __builtin_msa_bclri_w (v4u32, imm0_31); +v2u64 __builtin_msa_bclri_d (v2u64, imm0_63); + +v16u8 __builtin_msa_binsl_b (v16u8, v16u8, v16u8); +v8u16 __builtin_msa_binsl_h (v8u16, v8u16, v8u16); +v4u32 __builtin_msa_binsl_w (v4u32, v4u32, v4u32); +v2u64 __builtin_msa_binsl_d (v2u64, v2u64, v2u64); + +v16u8 __builtin_msa_binsli_b (v16u8, v16u8, imm0_7); +v8u16 __builtin_msa_binsli_h (v8u16, v8u16, imm0_15); +v4u32 __builtin_msa_binsli_w (v4u32, v4u32, imm0_31); +v2u64 __builtin_msa_binsli_d (v2u64, v2u64, imm0_63); + +v16u8 __builtin_msa_binsr_b (v16u8, v16u8, v16u8); +v8u16 __builtin_msa_binsr_h (v8u16, v8u16, v8u16); +v4u32 __builtin_msa_binsr_w (v4u32, v4u32, v4u32); +v2u64 __builtin_msa_binsr_d (v2u64, v2u64, v2u64); + +v16u8 __builtin_msa_binsri_b (v16u8, v16u8, imm0_7); +v8u16 __builtin_msa_binsri_h (v8u16, v8u16, imm0_15); +v4u32 __builtin_msa_binsri_w (v4u32, v4u32, imm0_31); +v2u64 __builtin_msa_binsri_d (v2u64, v2u64, imm0_63); + +v16u8 __builtin_msa_bmnz_v (v16u8, v16u8, v16u8); + +v16u8 __builtin_msa_bmnzi_b (v16u8, v16u8, imm0_255); + +v16u8 __builtin_msa_bmz_v (v16u8, v16u8, v16u8); + +v16u8 __builtin_msa_bmzi_b (v16u8, v16u8, imm0_255); + +v16u8 __builtin_msa_bneg_b (v16u8, v16u8); +v8u16 __builtin_msa_bneg_h (v8u16, v8u16); +v4u32 __builtin_msa_bneg_w (v4u32, v4u32); +v2u64 __builtin_msa_bneg_d (v2u64, v2u64); + +v16u8 __builtin_msa_bnegi_b (v16u8, imm0_7); +v8u16 __builtin_msa_bnegi_h (v8u16, imm0_15); +v4u32 __builtin_msa_bnegi_w (v4u32, imm0_31); +v2u64 __builtin_msa_bnegi_d (v2u64, imm0_63); + +i32 __builtin_msa_bnz_b (v16u8); +i32 __builtin_msa_bnz_h (v8u16); +i32 __builtin_msa_bnz_w (v4u32); +i32 __builtin_msa_bnz_d (v2u64); + +i32 __builtin_msa_bnz_v (v16u8); + +v16u8 __builtin_msa_bsel_v (v16u8, v16u8, v16u8); + +v16u8 __builtin_msa_bseli_b (v16u8, v16u8, imm0_255); + +v16u8 __builtin_msa_bset_b (v16u8, v16u8); +v8u16 __builtin_msa_bset_h (v8u16, v8u16); +v4u32 __builtin_msa_bset_w (v4u32, v4u32); +v2u64 __builtin_msa_bset_d (v2u64, v2u64); + +v16u8 __builtin_msa_bseti_b (v16u8, imm0_7); +v8u16 __builtin_msa_bseti_h (v8u16, imm0_15); +v4u32 __builtin_msa_bseti_w (v4u32, imm0_31); +v2u64 __builtin_msa_bseti_d (v2u64, imm0_63); + +i32 __builtin_msa_bz_b (v16u8); +i32 __builtin_msa_bz_h (v8u16); +i32 __builtin_msa_bz_w (v4u32); +i32 __builtin_msa_bz_d (v2u64); + +i32 __builtin_msa_bz_v (v16u8); + +v16i8 __builtin_msa_ceq_b (v16i8, v16i8); +v8i16 __builtin_msa_ceq_h (v8i16, v8i16); +v4i32 __builtin_msa_ceq_w (v4i32, v4i32); +v2i64 __builtin_msa_ceq_d (v2i64, v2i64); + +v16i8 __builtin_msa_ceqi_b (v16i8, imm_n16_15); +v8i16 __builtin_msa_ceqi_h (v8i16, imm_n16_15); +v4i32 __builtin_msa_ceqi_w (v4i32, imm_n16_15); +v2i64 __builtin_msa_ceqi_d (v2i64, imm_n16_15); + +i32 __builtin_msa_cfcmsa (imm0_31); + +v16i8 __builtin_msa_cle_s_b (v16i8, v16i8); +v8i16 __builtin_msa_cle_s_h (v8i16, v8i16); +v4i32 __builtin_msa_cle_s_w (v4i32, v4i32); +v2i64 __builtin_msa_cle_s_d (v2i64, v2i64); + +v16i8 __builtin_msa_cle_u_b (v16u8, v16u8); +v8i16 __builtin_msa_cle_u_h (v8u16, v8u16); +v4i32 __builtin_msa_cle_u_w (v4u32, v4u32); +v2i64 __builtin_msa_cle_u_d (v2u64, v2u64); + +v16i8 __builtin_msa_clei_s_b (v16i8, imm_n16_15); +v8i16 __builtin_msa_clei_s_h (v8i16, imm_n16_15); +v4i32 __builtin_msa_clei_s_w (v4i32, imm_n16_15); +v2i64 __builtin_msa_clei_s_d (v2i64, imm_n16_15); + +v16i8 __builtin_msa_clei_u_b (v16u8, imm0_31); +v8i16 __builtin_msa_clei_u_h (v8u16, imm0_31); +v4i32 __builtin_msa_clei_u_w (v4u32, imm0_31); +v2i64 __builtin_msa_clei_u_d (v2u64, imm0_31); + +v16i8 __builtin_msa_clt_s_b (v16i8, v16i8); +v8i16 __builtin_msa_clt_s_h (v8i16, v8i16); +v4i32 __builtin_msa_clt_s_w (v4i32, v4i32); +v2i64 __builtin_msa_clt_s_d (v2i64, v2i64); + +v16i8 __builtin_msa_clt_u_b (v16u8, v16u8); +v8i16 __builtin_msa_clt_u_h (v8u16, v8u16); +v4i32 __builtin_msa_clt_u_w (v4u32, v4u32); +v2i64 __builtin_msa_clt_u_d (v2u64, v2u64); + +v16i8 __builtin_msa_clti_s_b (v16i8, imm_n16_15); +v8i16 __builtin_msa_clti_s_h (v8i16, imm_n16_15); +v4i32 __builtin_msa_clti_s_w (v4i32, imm_n16_15); +v2i64 __builtin_msa_clti_s_d (v2i64, imm_n16_15); + +v16i8 __builtin_msa_clti_u_b (v16u8, imm0_31); +v8i16 __builtin_msa_clti_u_h (v8u16, imm0_31); +v4i32 __builtin_msa_clti_u_w (v4u32, imm0_31); +v2i64 __builtin_msa_clti_u_d (v2u64, imm0_31); + +i32 __builtin_msa_copy_s_b (v16i8, imm0_15); +i32 __builtin_msa_copy_s_h (v8i16, imm0_7); +i32 __builtin_msa_copy_s_w (v4i32, imm0_3); +i64 __builtin_msa_copy_s_d (v2i64, imm0_1); + +u32 __builtin_msa_copy_u_b (v16i8, imm0_15); +u32 __builtin_msa_copy_u_h (v8i16, imm0_7); +u32 __builtin_msa_copy_u_w (v4i32, imm0_3); +u64 __builtin_msa_copy_u_d (v2i64, imm0_1); + +void __builtin_msa_ctcmsa (imm0_31, i32); + +v16i8 __builtin_msa_div_s_b (v16i8, v16i8); +v8i16 __builtin_msa_div_s_h (v8i16, v8i16); +v4i32 __builtin_msa_div_s_w (v4i32, v4i32); +v2i64 __builtin_msa_div_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_div_u_b (v16u8, v16u8); +v8u16 __builtin_msa_div_u_h (v8u16, v8u16); +v4u32 __builtin_msa_div_u_w (v4u32, v4u32); +v2u64 __builtin_msa_div_u_d (v2u64, v2u64); + +v8i16 __builtin_msa_dotp_s_h (v16i8, v16i8); +v4i32 __builtin_msa_dotp_s_w (v8i16, v8i16); +v2i64 __builtin_msa_dotp_s_d (v4i32, v4i32); + +v8u16 __builtin_msa_dotp_u_h (v16u8, v16u8); +v4u32 __builtin_msa_dotp_u_w (v8u16, v8u16); +v2u64 __builtin_msa_dotp_u_d (v4u32, v4u32); + +v8i16 __builtin_msa_dpadd_s_h (v8i16, v16i8, v16i8); +v4i32 __builtin_msa_dpadd_s_w (v4i32, v8i16, v8i16); +v2i64 __builtin_msa_dpadd_s_d (v2i64, v4i32, v4i32); + +v8u16 __builtin_msa_dpadd_u_h (v8u16, v16u8, v16u8); +v4u32 __builtin_msa_dpadd_u_w (v4u32, v8u16, v8u16); +v2u64 __builtin_msa_dpadd_u_d (v2u64, v4u32, v4u32); + +v8i16 __builtin_msa_dpsub_s_h (v8i16, v16i8, v16i8); +v4i32 __builtin_msa_dpsub_s_w (v4i32, v8i16, v8i16); +v2i64 __builtin_msa_dpsub_s_d (v2i64, v4i32, v4i32); + +v8i16 __builtin_msa_dpsub_u_h (v8i16, v16u8, v16u8); +v4i32 __builtin_msa_dpsub_u_w (v4i32, v8u16, v8u16); +v2i64 __builtin_msa_dpsub_u_d (v2i64, v4u32, v4u32); + +v4f32 __builtin_msa_fadd_w (v4f32, v4f32); +v2f64 __builtin_msa_fadd_d (v2f64, v2f64); + +v4i32 __builtin_msa_fcaf_w (v4f32, v4f32); +v2i64 __builtin_msa_fcaf_d (v2f64, v2f64); + +v4i32 __builtin_msa_fceq_w (v4f32, v4f32); +v2i64 __builtin_msa_fceq_d (v2f64, v2f64); + +v4i32 __builtin_msa_fclass_w (v4f32); +v2i64 __builtin_msa_fclass_d (v2f64); + +v4i32 __builtin_msa_fcle_w (v4f32, v4f32); +v2i64 __builtin_msa_fcle_d (v2f64, v2f64); + +v4i32 __builtin_msa_fclt_w (v4f32, v4f32); +v2i64 __builtin_msa_fclt_d (v2f64, v2f64); + +v4i32 __builtin_msa_fcne_w (v4f32, v4f32); +v2i64 __builtin_msa_fcne_d (v2f64, v2f64); + +v4i32 __builtin_msa_fcor_w (v4f32, v4f32); +v2i64 __builtin_msa_fcor_d (v2f64, v2f64); + +v4i32 __builtin_msa_fcueq_w (v4f32, v4f32); +v2i64 __builtin_msa_fcueq_d (v2f64, v2f64); + +v4i32 __builtin_msa_fcule_w (v4f32, v4f32); +v2i64 __builtin_msa_fcule_d (v2f64, v2f64); + +v4i32 __builtin_msa_fcult_w (v4f32, v4f32); +v2i64 __builtin_msa_fcult_d (v2f64, v2f64); + +v4i32 __builtin_msa_fcun_w (v4f32, v4f32); +v2i64 __builtin_msa_fcun_d (v2f64, v2f64); + +v4i32 __builtin_msa_fcune_w (v4f32, v4f32); +v2i64 __builtin_msa_fcune_d (v2f64, v2f64); + +v4f32 __builtin_msa_fdiv_w (v4f32, v4f32); +v2f64 __builtin_msa_fdiv_d (v2f64, v2f64); + +v8i16 __builtin_msa_fexdo_h (v4f32, v4f32); +v4f32 __builtin_msa_fexdo_w (v2f64, v2f64); + +v4f32 __builtin_msa_fexp2_w (v4f32, v4i32); +v2f64 __builtin_msa_fexp2_d (v2f64, v2i64); + +v4f32 __builtin_msa_fexupl_w (v8i16); +v2f64 __builtin_msa_fexupl_d (v4f32); + +v4f32 __builtin_msa_fexupr_w (v8i16); +v2f64 __builtin_msa_fexupr_d (v4f32); + +v4f32 __builtin_msa_ffint_s_w (v4i32); +v2f64 __builtin_msa_ffint_s_d (v2i64); + +v4f32 __builtin_msa_ffint_u_w (v4u32); +v2f64 __builtin_msa_ffint_u_d (v2u64); + +v4f32 __builtin_msa_ffql_w (v8i16); +v2f64 __builtin_msa_ffql_d (v4i32); + +v4f32 __builtin_msa_ffqr_w (v8i16); +v2f64 __builtin_msa_ffqr_d (v4i32); + +v16i8 __builtin_msa_fill_b (i32); +v8i16 __builtin_msa_fill_h (i32); +v4i32 __builtin_msa_fill_w (i32); +v2i64 __builtin_msa_fill_d (i64); + +v4f32 __builtin_msa_flog2_w (v4f32); +v2f64 __builtin_msa_flog2_d (v2f64); + +v4f32 __builtin_msa_fmadd_w (v4f32, v4f32, v4f32); +v2f64 __builtin_msa_fmadd_d (v2f64, v2f64, v2f64); + +v4f32 __builtin_msa_fmax_w (v4f32, v4f32); +v2f64 __builtin_msa_fmax_d (v2f64, v2f64); + +v4f32 __builtin_msa_fmax_a_w (v4f32, v4f32); +v2f64 __builtin_msa_fmax_a_d (v2f64, v2f64); + +v4f32 __builtin_msa_fmin_w (v4f32, v4f32); +v2f64 __builtin_msa_fmin_d (v2f64, v2f64); + +v4f32 __builtin_msa_fmin_a_w (v4f32, v4f32); +v2f64 __builtin_msa_fmin_a_d (v2f64, v2f64); + +v4f32 __builtin_msa_fmsub_w (v4f32, v4f32, v4f32); +v2f64 __builtin_msa_fmsub_d (v2f64, v2f64, v2f64); + +v4f32 __builtin_msa_fmul_w (v4f32, v4f32); +v2f64 __builtin_msa_fmul_d (v2f64, v2f64); + +v4f32 __builtin_msa_frint_w (v4f32); +v2f64 __builtin_msa_frint_d (v2f64); + +v4f32 __builtin_msa_frcp_w (v4f32); +v2f64 __builtin_msa_frcp_d (v2f64); + +v4f32 __builtin_msa_frsqrt_w (v4f32); +v2f64 __builtin_msa_frsqrt_d (v2f64); + +v4i32 __builtin_msa_fsaf_w (v4f32, v4f32); +v2i64 __builtin_msa_fsaf_d (v2f64, v2f64); + +v4i32 __builtin_msa_fseq_w (v4f32, v4f32); +v2i64 __builtin_msa_fseq_d (v2f64, v2f64); + +v4i32 __builtin_msa_fsle_w (v4f32, v4f32); +v2i64 __builtin_msa_fsle_d (v2f64, v2f64); + +v4i32 __builtin_msa_fslt_w (v4f32, v4f32); +v2i64 __builtin_msa_fslt_d (v2f64, v2f64); + +v4i32 __builtin_msa_fsne_w (v4f32, v4f32); +v2i64 __builtin_msa_fsne_d (v2f64, v2f64); + +v4i32 __builtin_msa_fsor_w (v4f32, v4f32); +v2i64 __builtin_msa_fsor_d (v2f64, v2f64); + +v4f32 __builtin_msa_fsqrt_w (v4f32); +v2f64 __builtin_msa_fsqrt_d (v2f64); + +v4f32 __builtin_msa_fsub_w (v4f32, v4f32); +v2f64 __builtin_msa_fsub_d (v2f64, v2f64); + +v4i32 __builtin_msa_fsueq_w (v4f32, v4f32); +v2i64 __builtin_msa_fsueq_d (v2f64, v2f64); + +v4i32 __builtin_msa_fsule_w (v4f32, v4f32); +v2i64 __builtin_msa_fsule_d (v2f64, v2f64); + +v4i32 __builtin_msa_fsult_w (v4f32, v4f32); +v2i64 __builtin_msa_fsult_d (v2f64, v2f64); + +v4i32 __builtin_msa_fsun_w (v4f32, v4f32); +v2i64 __builtin_msa_fsun_d (v2f64, v2f64); + +v4i32 __builtin_msa_fsune_w (v4f32, v4f32); +v2i64 __builtin_msa_fsune_d (v2f64, v2f64); + +v4i32 __builtin_msa_ftint_s_w (v4f32); +v2i64 __builtin_msa_ftint_s_d (v2f64); + +v4u32 __builtin_msa_ftint_u_w (v4f32); +v2u64 __builtin_msa_ftint_u_d (v2f64); + +v8i16 __builtin_msa_ftq_h (v4f32, v4f32); +v4i32 __builtin_msa_ftq_w (v2f64, v2f64); + +v4i32 __builtin_msa_ftrunc_s_w (v4f32); +v2i64 __builtin_msa_ftrunc_s_d (v2f64); + +v4u32 __builtin_msa_ftrunc_u_w (v4f32); +v2u64 __builtin_msa_ftrunc_u_d (v2f64); + +v8i16 __builtin_msa_hadd_s_h (v16i8, v16i8); +v4i32 __builtin_msa_hadd_s_w (v8i16, v8i16); +v2i64 __builtin_msa_hadd_s_d (v4i32, v4i32); + +v8u16 __builtin_msa_hadd_u_h (v16u8, v16u8); +v4u32 __builtin_msa_hadd_u_w (v8u16, v8u16); +v2u64 __builtin_msa_hadd_u_d (v4u32, v4u32); + +v8i16 __builtin_msa_hsub_s_h (v16i8, v16i8); +v4i32 __builtin_msa_hsub_s_w (v8i16, v8i16); +v2i64 __builtin_msa_hsub_s_d (v4i32, v4i32); + +v8i16 __builtin_msa_hsub_u_h (v16u8, v16u8); +v4i32 __builtin_msa_hsub_u_w (v8u16, v8u16); +v2i64 __builtin_msa_hsub_u_d (v4u32, v4u32); + +v16i8 __builtin_msa_ilvev_b (v16i8, v16i8); +v8i16 __builtin_msa_ilvev_h (v8i16, v8i16); +v4i32 __builtin_msa_ilvev_w (v4i32, v4i32); +v2i64 __builtin_msa_ilvev_d (v2i64, v2i64); + +v16i8 __builtin_msa_ilvl_b (v16i8, v16i8); +v8i16 __builtin_msa_ilvl_h (v8i16, v8i16); +v4i32 __builtin_msa_ilvl_w (v4i32, v4i32); +v2i64 __builtin_msa_ilvl_d (v2i64, v2i64); + +v16i8 __builtin_msa_ilvod_b (v16i8, v16i8); +v8i16 __builtin_msa_ilvod_h (v8i16, v8i16); +v4i32 __builtin_msa_ilvod_w (v4i32, v4i32); +v2i64 __builtin_msa_ilvod_d (v2i64, v2i64); + +v16i8 __builtin_msa_ilvr_b (v16i8, v16i8); +v8i16 __builtin_msa_ilvr_h (v8i16, v8i16); +v4i32 __builtin_msa_ilvr_w (v4i32, v4i32); +v2i64 __builtin_msa_ilvr_d (v2i64, v2i64); + +v16i8 __builtin_msa_insert_b (v16i8, imm0_15, i32); +v8i16 __builtin_msa_insert_h (v8i16, imm0_7, i32); +v4i32 __builtin_msa_insert_w (v4i32, imm0_3, i32); +v2i64 __builtin_msa_insert_d (v2i64, imm0_1, i64); + +v16i8 __builtin_msa_insve_b (v16i8, imm0_15, v16i8); +v8i16 __builtin_msa_insve_h (v8i16, imm0_7, v8i16); +v4i32 __builtin_msa_insve_w (v4i32, imm0_3, v4i32); +v2i64 __builtin_msa_insve_d (v2i64, imm0_1, v2i64); + +v16i8 __builtin_msa_ld_b (const void *, imm_n512_511); +v8i16 __builtin_msa_ld_h (const void *, imm_n1024_1022); +v4i32 __builtin_msa_ld_w (const void *, imm_n2048_2044); +v2i64 __builtin_msa_ld_d (const void *, imm_n4096_4088); + +v16i8 __builtin_msa_ldi_b (imm_n512_511); +v8i16 __builtin_msa_ldi_h (imm_n512_511); +v4i32 __builtin_msa_ldi_w (imm_n512_511); +v2i64 __builtin_msa_ldi_d (imm_n512_511); + +v8i16 __builtin_msa_madd_q_h (v8i16, v8i16, v8i16); +v4i32 __builtin_msa_madd_q_w (v4i32, v4i32, v4i32); + +v8i16 __builtin_msa_maddr_q_h (v8i16, v8i16, v8i16); +v4i32 __builtin_msa_maddr_q_w (v4i32, v4i32, v4i32); + +v16i8 __builtin_msa_maddv_b (v16i8, v16i8, v16i8); +v8i16 __builtin_msa_maddv_h (v8i16, v8i16, v8i16); +v4i32 __builtin_msa_maddv_w (v4i32, v4i32, v4i32); +v2i64 __builtin_msa_maddv_d (v2i64, v2i64, v2i64); + +v16i8 __builtin_msa_max_a_b (v16i8, v16i8); +v8i16 __builtin_msa_max_a_h (v8i16, v8i16); +v4i32 __builtin_msa_max_a_w (v4i32, v4i32); +v2i64 __builtin_msa_max_a_d (v2i64, v2i64); + +v16i8 __builtin_msa_max_s_b (v16i8, v16i8); +v8i16 __builtin_msa_max_s_h (v8i16, v8i16); +v4i32 __builtin_msa_max_s_w (v4i32, v4i32); +v2i64 __builtin_msa_max_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_max_u_b (v16u8, v16u8); +v8u16 __builtin_msa_max_u_h (v8u16, v8u16); +v4u32 __builtin_msa_max_u_w (v4u32, v4u32); +v2u64 __builtin_msa_max_u_d (v2u64, v2u64); + +v16i8 __builtin_msa_maxi_s_b (v16i8, imm_n16_15); +v8i16 __builtin_msa_maxi_s_h (v8i16, imm_n16_15); +v4i32 __builtin_msa_maxi_s_w (v4i32, imm_n16_15); +v2i64 __builtin_msa_maxi_s_d (v2i64, imm_n16_15); + +v16u8 __builtin_msa_maxi_u_b (v16u8, imm0_31); +v8u16 __builtin_msa_maxi_u_h (v8u16, imm0_31); +v4u32 __builtin_msa_maxi_u_w (v4u32, imm0_31); +v2u64 __builtin_msa_maxi_u_d (v2u64, imm0_31); + +v16i8 __builtin_msa_min_a_b (v16i8, v16i8); +v8i16 __builtin_msa_min_a_h (v8i16, v8i16); +v4i32 __builtin_msa_min_a_w (v4i32, v4i32); +v2i64 __builtin_msa_min_a_d (v2i64, v2i64); + +v16i8 __builtin_msa_min_s_b (v16i8, v16i8); +v8i16 __builtin_msa_min_s_h (v8i16, v8i16); +v4i32 __builtin_msa_min_s_w (v4i32, v4i32); +v2i64 __builtin_msa_min_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_min_u_b (v16u8, v16u8); +v8u16 __builtin_msa_min_u_h (v8u16, v8u16); +v4u32 __builtin_msa_min_u_w (v4u32, v4u32); +v2u64 __builtin_msa_min_u_d (v2u64, v2u64); + +v16i8 __builtin_msa_mini_s_b (v16i8, imm_n16_15); +v8i16 __builtin_msa_mini_s_h (v8i16, imm_n16_15); +v4i32 __builtin_msa_mini_s_w (v4i32, imm_n16_15); +v2i64 __builtin_msa_mini_s_d (v2i64, imm_n16_15); + +v16u8 __builtin_msa_mini_u_b (v16u8, imm0_31); +v8u16 __builtin_msa_mini_u_h (v8u16, imm0_31); +v4u32 __builtin_msa_mini_u_w (v4u32, imm0_31); +v2u64 __builtin_msa_mini_u_d (v2u64, imm0_31); + +v16i8 __builtin_msa_mod_s_b (v16i8, v16i8); +v8i16 __builtin_msa_mod_s_h (v8i16, v8i16); +v4i32 __builtin_msa_mod_s_w (v4i32, v4i32); +v2i64 __builtin_msa_mod_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_mod_u_b (v16u8, v16u8); +v8u16 __builtin_msa_mod_u_h (v8u16, v8u16); +v4u32 __builtin_msa_mod_u_w (v4u32, v4u32); +v2u64 __builtin_msa_mod_u_d (v2u64, v2u64); + +v16i8 __builtin_msa_move_v (v16i8); + +v8i16 __builtin_msa_msub_q_h (v8i16, v8i16, v8i16); +v4i32 __builtin_msa_msub_q_w (v4i32, v4i32, v4i32); + +v8i16 __builtin_msa_msubr_q_h (v8i16, v8i16, v8i16); +v4i32 __builtin_msa_msubr_q_w (v4i32, v4i32, v4i32); + +v16i8 __builtin_msa_msubv_b (v16i8, v16i8, v16i8); +v8i16 __builtin_msa_msubv_h (v8i16, v8i16, v8i16); +v4i32 __builtin_msa_msubv_w (v4i32, v4i32, v4i32); +v2i64 __builtin_msa_msubv_d (v2i64, v2i64, v2i64); + +v8i16 __builtin_msa_mul_q_h (v8i16, v8i16); +v4i32 __builtin_msa_mul_q_w (v4i32, v4i32); + +v8i16 __builtin_msa_mulr_q_h (v8i16, v8i16); +v4i32 __builtin_msa_mulr_q_w (v4i32, v4i32); + +v16i8 __builtin_msa_mulv_b (v16i8, v16i8); +v8i16 __builtin_msa_mulv_h (v8i16, v8i16); +v4i32 __builtin_msa_mulv_w (v4i32, v4i32); +v2i64 __builtin_msa_mulv_d (v2i64, v2i64); + +v16i8 __builtin_msa_nloc_b (v16i8); +v8i16 __builtin_msa_nloc_h (v8i16); +v4i32 __builtin_msa_nloc_w (v4i32); +v2i64 __builtin_msa_nloc_d (v2i64); + +v16i8 __builtin_msa_nlzc_b (v16i8); +v8i16 __builtin_msa_nlzc_h (v8i16); +v4i32 __builtin_msa_nlzc_w (v4i32); +v2i64 __builtin_msa_nlzc_d (v2i64); + +v16u8 __builtin_msa_nor_v (v16u8, v16u8); + +v16u8 __builtin_msa_nori_b (v16u8, imm0_255); + +v16u8 __builtin_msa_or_v (v16u8, v16u8); + +v16u8 __builtin_msa_ori_b (v16u8, imm0_255); + +v16i8 __builtin_msa_pckev_b (v16i8, v16i8); +v8i16 __builtin_msa_pckev_h (v8i16, v8i16); +v4i32 __builtin_msa_pckev_w (v4i32, v4i32); +v2i64 __builtin_msa_pckev_d (v2i64, v2i64); + +v16i8 __builtin_msa_pckod_b (v16i8, v16i8); +v8i16 __builtin_msa_pckod_h (v8i16, v8i16); +v4i32 __builtin_msa_pckod_w (v4i32, v4i32); +v2i64 __builtin_msa_pckod_d (v2i64, v2i64); + +v16i8 __builtin_msa_pcnt_b (v16i8); +v8i16 __builtin_msa_pcnt_h (v8i16); +v4i32 __builtin_msa_pcnt_w (v4i32); +v2i64 __builtin_msa_pcnt_d (v2i64); + +v16i8 __builtin_msa_sat_s_b (v16i8, imm0_7); +v8i16 __builtin_msa_sat_s_h (v8i16, imm0_15); +v4i32 __builtin_msa_sat_s_w (v4i32, imm0_31); +v2i64 __builtin_msa_sat_s_d (v2i64, imm0_63); + +v16u8 __builtin_msa_sat_u_b (v16u8, imm0_7); +v8u16 __builtin_msa_sat_u_h (v8u16, imm0_15); +v4u32 __builtin_msa_sat_u_w (v4u32, imm0_31); +v2u64 __builtin_msa_sat_u_d (v2u64, imm0_63); + +v16i8 __builtin_msa_shf_b (v16i8, imm0_255); +v8i16 __builtin_msa_shf_h (v8i16, imm0_255); +v4i32 __builtin_msa_shf_w (v4i32, imm0_255); + +v16i8 __builtin_msa_sld_b (v16i8, v16i8, i32); +v8i16 __builtin_msa_sld_h (v8i16, v8i16, i32); +v4i32 __builtin_msa_sld_w (v4i32, v4i32, i32); +v2i64 __builtin_msa_sld_d (v2i64, v2i64, i32); + +v16i8 __builtin_msa_sldi_b (v16i8, v16i8, imm0_15); +v8i16 __builtin_msa_sldi_h (v8i16, v8i16, imm0_7); +v4i32 __builtin_msa_sldi_w (v4i32, v4i32, imm0_3); +v2i64 __builtin_msa_sldi_d (v2i64, v2i64, imm0_1); + +v16i8 __builtin_msa_sll_b (v16i8, v16i8); +v8i16 __builtin_msa_sll_h (v8i16, v8i16); +v4i32 __builtin_msa_sll_w (v4i32, v4i32); +v2i64 __builtin_msa_sll_d (v2i64, v2i64); + +v16i8 __builtin_msa_slli_b (v16i8, imm0_7); +v8i16 __builtin_msa_slli_h (v8i16, imm0_15); +v4i32 __builtin_msa_slli_w (v4i32, imm0_31); +v2i64 __builtin_msa_slli_d (v2i64, imm0_63); + +v16i8 __builtin_msa_splat_b (v16i8, i32); +v8i16 __builtin_msa_splat_h (v8i16, i32); +v4i32 __builtin_msa_splat_w (v4i32, i32); +v2i64 __builtin_msa_splat_d (v2i64, i32); + +v16i8 __builtin_msa_splati_b (v16i8, imm0_15); +v8i16 __builtin_msa_splati_h (v8i16, imm0_7); +v4i32 __builtin_msa_splati_w (v4i32, imm0_3); +v2i64 __builtin_msa_splati_d (v2i64, imm0_1); + +v16i8 __builtin_msa_sra_b (v16i8, v16i8); +v8i16 __builtin_msa_sra_h (v8i16, v8i16); +v4i32 __builtin_msa_sra_w (v4i32, v4i32); +v2i64 __builtin_msa_sra_d (v2i64, v2i64); + +v16i8 __builtin_msa_srai_b (v16i8, imm0_7); +v8i16 __builtin_msa_srai_h (v8i16, imm0_15); +v4i32 __builtin_msa_srai_w (v4i32, imm0_31); +v2i64 __builtin_msa_srai_d (v2i64, imm0_63); + +v16i8 __builtin_msa_srar_b (v16i8, v16i8); +v8i16 __builtin_msa_srar_h (v8i16, v8i16); +v4i32 __builtin_msa_srar_w (v4i32, v4i32); +v2i64 __builtin_msa_srar_d (v2i64, v2i64); + +v16i8 __builtin_msa_srari_b (v16i8, imm0_7); +v8i16 __builtin_msa_srari_h (v8i16, imm0_15); +v4i32 __builtin_msa_srari_w (v4i32, imm0_31); +v2i64 __builtin_msa_srari_d (v2i64, imm0_63); + +v16i8 __builtin_msa_srl_b (v16i8, v16i8); +v8i16 __builtin_msa_srl_h (v8i16, v8i16); +v4i32 __builtin_msa_srl_w (v4i32, v4i32); +v2i64 __builtin_msa_srl_d (v2i64, v2i64); + +v16i8 __builtin_msa_srli_b (v16i8, imm0_7); +v8i16 __builtin_msa_srli_h (v8i16, imm0_15); +v4i32 __builtin_msa_srli_w (v4i32, imm0_31); +v2i64 __builtin_msa_srli_d (v2i64, imm0_63); + +v16i8 __builtin_msa_srlr_b (v16i8, v16i8); +v8i16 __builtin_msa_srlr_h (v8i16, v8i16); +v4i32 __builtin_msa_srlr_w (v4i32, v4i32); +v2i64 __builtin_msa_srlr_d (v2i64, v2i64); + +v16i8 __builtin_msa_srlri_b (v16i8, imm0_7); +v8i16 __builtin_msa_srlri_h (v8i16, imm0_15); +v4i32 __builtin_msa_srlri_w (v4i32, imm0_31); +v2i64 __builtin_msa_srlri_d (v2i64, imm0_63); + +void __builtin_msa_st_b (v16i8, void *, imm_n512_511); +void __builtin_msa_st_h (v8i16, void *, imm_n1024_1022); +void __builtin_msa_st_w (v4i32, void *, imm_n2048_2044); +void __builtin_msa_st_d (v2i64, void *, imm_n4096_4088); + +v16i8 __builtin_msa_subs_s_b (v16i8, v16i8); +v8i16 __builtin_msa_subs_s_h (v8i16, v8i16); +v4i32 __builtin_msa_subs_s_w (v4i32, v4i32); +v2i64 __builtin_msa_subs_s_d (v2i64, v2i64); + +v16u8 __builtin_msa_subs_u_b (v16u8, v16u8); +v8u16 __builtin_msa_subs_u_h (v8u16, v8u16); +v4u32 __builtin_msa_subs_u_w (v4u32, v4u32); +v2u64 __builtin_msa_subs_u_d (v2u64, v2u64); + +v16u8 __builtin_msa_subsus_u_b (v16u8, v16i8); +v8u16 __builtin_msa_subsus_u_h (v8u16, v8i16); +v4u32 __builtin_msa_subsus_u_w (v4u32, v4i32); +v2u64 __builtin_msa_subsus_u_d (v2u64, v2i64); + +v16i8 __builtin_msa_subsuu_s_b (v16u8, v16u8); +v8i16 __builtin_msa_subsuu_s_h (v8u16, v8u16); +v4i32 __builtin_msa_subsuu_s_w (v4u32, v4u32); +v2i64 __builtin_msa_subsuu_s_d (v2u64, v2u64); + +v16i8 __builtin_msa_subv_b (v16i8, v16i8); +v8i16 __builtin_msa_subv_h (v8i16, v8i16); +v4i32 __builtin_msa_subv_w (v4i32, v4i32); +v2i64 __builtin_msa_subv_d (v2i64, v2i64); + +v16i8 __builtin_msa_subvi_b (v16i8, imm0_31); +v8i16 __builtin_msa_subvi_h (v8i16, imm0_31); +v4i32 __builtin_msa_subvi_w (v4i32, imm0_31); +v2i64 __builtin_msa_subvi_d (v2i64, imm0_31); + +v16i8 __builtin_msa_vshf_b (v16i8, v16i8, v16i8); +v8i16 __builtin_msa_vshf_h (v8i16, v8i16, v8i16); +v4i32 __builtin_msa_vshf_w (v4i32, v4i32, v4i32); +v2i64 __builtin_msa_vshf_d (v2i64, v2i64, v2i64); + +v16u8 __builtin_msa_xor_v (v16u8, v16u8); + +v16u8 __builtin_msa_xori_b (v16u8, imm0_255); +@end smallexample + +@node Other MIPS Built-in Functions +@subsection Other MIPS Built-in Functions + +GCC provides other MIPS-specific built-in functions: + +@table @code +@item void __builtin_mips_cache (int @var{op}, const volatile void *@var{addr}) +Insert a @samp{cache} instruction with operands @var{op} and @var{addr}. +GCC defines the preprocessor macro @code{___GCC_HAVE_BUILTIN_MIPS_CACHE} +when this function is available. + +@item unsigned int __builtin_mips_get_fcsr (void) +@itemx void __builtin_mips_set_fcsr (unsigned int @var{value}) +Get and set the contents of the floating-point control and status register +(FPU control register 31). These functions are only available in hard-float +code but can be called in both MIPS16 and non-MIPS16 contexts. + +@code{__builtin_mips_set_fcsr} can be used to change any bit of the +register except the condition codes, which GCC assumes are preserved. +@end table + +@node MSP430 Built-in Functions +@subsection MSP430 Built-in Functions + +GCC provides a couple of special builtin functions to aid in the +writing of interrupt handlers in C. + +@table @code +@item __bic_SR_register_on_exit (int @var{mask}) +This clears the indicated bits in the saved copy of the status register +currently residing on the stack. This only works inside interrupt +handlers and the changes to the status register will only take affect +once the handler returns. + +@item __bis_SR_register_on_exit (int @var{mask}) +This sets the indicated bits in the saved copy of the status register +currently residing on the stack. This only works inside interrupt +handlers and the changes to the status register will only take affect +once the handler returns. + +@item __delay_cycles (long long @var{cycles}) +This inserts an instruction sequence that takes exactly @var{cycles} +cycles (between 0 and about 17E9) to complete. The inserted sequence +may use jumps, loops, or no-ops, and does not interfere with any other +instructions. Note that @var{cycles} must be a compile-time constant +integer - that is, you must pass a number, not a variable that may be +optimized to a constant later. The number of cycles delayed by this +builtin is exact. +@end table + +@node NDS32 Built-in Functions +@subsection NDS32 Built-in Functions + +These built-in functions are available for the NDS32 target: + +@deftypefn {Built-in Function} void __builtin_nds32_isync (int *@var{addr}) +Insert an ISYNC instruction into the instruction stream where +@var{addr} is an instruction address for serialization. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_nds32_isb (void) +Insert an ISB instruction into the instruction stream. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_nds32_mfsr (int @var{sr}) +Return the content of a system register which is mapped by @var{sr}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_nds32_mfusr (int @var{usr}) +Return the content of a user space register which is mapped by @var{usr}. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_nds32_mtsr (int @var{value}, int @var{sr}) +Move the @var{value} to a system register which is mapped by @var{sr}. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_nds32_mtusr (int @var{value}, int @var{usr}) +Move the @var{value} to a user space register which is mapped by @var{usr}. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_nds32_setgie_en (void) +Enable global interrupt. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_nds32_setgie_dis (void) +Disable global interrupt. +@end deftypefn + +@node picoChip Built-in Functions +@subsection picoChip Built-in Functions + +GCC provides an interface to selected machine instructions from the +picoChip instruction set. + +@table @code +@item int __builtin_sbc (int @var{value}) +Sign bit count. Return the number of consecutive bits in @var{value} +that have the same value as the sign bit. The result is the number of +leading sign bits minus one, giving the number of redundant sign bits in +@var{value}. + +@item int __builtin_byteswap (int @var{value}) +Byte swap. Return the result of swapping the upper and lower bytes of +@var{value}. + +@item int __builtin_brev (int @var{value}) +Bit reversal. Return the result of reversing the bits in +@var{value}. Bit 15 is swapped with bit 0, bit 14 is swapped with bit 1, +and so on. + +@item int __builtin_adds (int @var{x}, int @var{y}) +Saturating addition. Return the result of adding @var{x} and @var{y}, +storing the value 32767 if the result overflows. + +@item int __builtin_subs (int @var{x}, int @var{y}) +Saturating subtraction. Return the result of subtracting @var{y} from +@var{x}, storing the value @minus{}32768 if the result overflows. + +@item void __builtin_halt (void) +Halt. The processor stops execution. This built-in is useful for +implementing assertions. + +@end table + +@node Basic PowerPC Built-in Functions +@subsection Basic PowerPC Built-in Functions + +@menu +* Basic PowerPC Built-in Functions Available on all Configurations:: +* Basic PowerPC Built-in Functions Available on ISA 2.05:: +* Basic PowerPC Built-in Functions Available on ISA 2.06:: +* Basic PowerPC Built-in Functions Available on ISA 2.07:: +* Basic PowerPC Built-in Functions Available on ISA 3.0:: +* Basic PowerPC Built-in Functions Available on ISA 3.1:: +@end menu + +This section describes PowerPC built-in functions that do not require +the inclusion of any special header files to declare prototypes or +provide macro definitions. The sections that follow describe +additional PowerPC built-in functions. + +@node Basic PowerPC Built-in Functions Available on all Configurations +@subsubsection Basic PowerPC Built-in Functions Available on all Configurations + +@deftypefn {Built-in Function} void __builtin_cpu_init (void) +This function is a @code{nop} on the PowerPC platform and is included solely +to maintain API compatibility with the x86 builtins. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_cpu_is (const char *@var{cpuname}) +This function returns a value of @code{1} if the run-time CPU is of type +@var{cpuname} and returns @code{0} otherwise + +The @code{__builtin_cpu_is} function requires GLIBC 2.23 or newer +which exports the hardware capability bits. GCC defines the macro +@code{__BUILTIN_CPU_SUPPORTS__} if the @code{__builtin_cpu_supports} +built-in function is fully supported. + +If GCC was configured to use a GLIBC before 2.23, the built-in +function @code{__builtin_cpu_is} always returns a 0 and the compiler +issues a warning. + +The following CPU names can be detected: + +@table @samp +@item power10 +IBM POWER10 Server CPU. +@item power9 +IBM POWER9 Server CPU. +@item power8 +IBM POWER8 Server CPU. +@item power7 +IBM POWER7 Server CPU. +@item power6x +IBM POWER6 Server CPU (RAW mode). +@item power6 +IBM POWER6 Server CPU (Architected mode). +@item power5+ +IBM POWER5+ Server CPU. +@item power5 +IBM POWER5 Server CPU. +@item ppc970 +IBM 970 Server CPU (ie, Apple G5). +@item power4 +IBM POWER4 Server CPU. +@item ppca2 +IBM A2 64-bit Embedded CPU +@item ppc476 +IBM PowerPC 476FP 32-bit Embedded CPU. +@item ppc464 +IBM PowerPC 464 32-bit Embedded CPU. +@item ppc440 +PowerPC 440 32-bit Embedded CPU. +@item ppc405 +PowerPC 405 32-bit Embedded CPU. +@item ppc-cell-be +IBM PowerPC Cell Broadband Engine Architecture CPU. +@end table + +Here is an example: +@smallexample +#ifdef __BUILTIN_CPU_SUPPORTS__ + if (__builtin_cpu_is ("power8")) + @{ + do_power8 (); // POWER8 specific implementation. + @} + else +#endif + @{ + do_generic (); // Generic implementation. + @} +@end smallexample +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_cpu_supports (const char *@var{feature}) +This function returns a value of @code{1} if the run-time CPU supports the HWCAP +feature @var{feature} and returns @code{0} otherwise. + +The @code{__builtin_cpu_supports} function requires GLIBC 2.23 or +newer which exports the hardware capability bits. GCC defines the +macro @code{__BUILTIN_CPU_SUPPORTS__} if the +@code{__builtin_cpu_supports} built-in function is fully supported. + +If GCC was configured to use a GLIBC before 2.23, the built-in +function @code{__builtin_cpu_supports} always returns a 0 and the +compiler issues a warning. + +The following features can be +detected: + +@table @samp +@item 4xxmac +4xx CPU has a Multiply Accumulator. +@item altivec +CPU has a SIMD/Vector Unit. +@item arch_2_05 +CPU supports ISA 2.05 (eg, POWER6) +@item arch_2_06 +CPU supports ISA 2.06 (eg, POWER7) +@item arch_2_07 +CPU supports ISA 2.07 (eg, POWER8) +@item arch_3_00 +CPU supports ISA 3.0 (eg, POWER9) +@item arch_3_1 +CPU supports ISA 3.1 (eg, POWER10) +@item archpmu +CPU supports the set of compatible performance monitoring events. +@item booke +CPU supports the Embedded ISA category. +@item cellbe +CPU has a CELL broadband engine. +@item darn +CPU supports the @code{darn} (deliver a random number) instruction. +@item dfp +CPU has a decimal floating point unit. +@item dscr +CPU supports the data stream control register. +@item ebb +CPU supports event base branching. +@item efpdouble +CPU has a SPE double precision floating point unit. +@item efpsingle +CPU has a SPE single precision floating point unit. +@item fpu +CPU has a floating point unit. +@item htm +CPU has hardware transaction memory instructions. +@item htm-nosc +Kernel aborts hardware transactions when a syscall is made. +@item htm-no-suspend +CPU supports hardware transaction memory but does not support the +@code{tsuspend.} instruction. +@item ic_snoop +CPU supports icache snooping capabilities. +@item ieee128 +CPU supports 128-bit IEEE binary floating point instructions. +@item isel +CPU supports the integer select instruction. +@item mma +CPU supports the matrix-multiply assist instructions. +@item mmu +CPU has a memory management unit. +@item notb +CPU does not have a timebase (eg, 601 and 403gx). +@item pa6t +CPU supports the PA Semi 6T CORE ISA. +@item power4 +CPU supports ISA 2.00 (eg, POWER4) +@item power5 +CPU supports ISA 2.02 (eg, POWER5) +@item power5+ +CPU supports ISA 2.03 (eg, POWER5+) +@item power6x +CPU supports ISA 2.05 (eg, POWER6) extended opcodes mffgpr and mftgpr. +@item ppc32 +CPU supports 32-bit mode execution. +@item ppc601 +CPU supports the old POWER ISA (eg, 601) +@item ppc64 +CPU supports 64-bit mode execution. +@item ppcle +CPU supports a little-endian mode that uses address swizzling. +@item scv +Kernel supports system call vectored. +@item smt +CPU support simultaneous multi-threading. +@item spe +CPU has a signal processing extension unit. +@item tar +CPU supports the target address register. +@item true_le +CPU supports true little-endian mode. +@item ucache +CPU has unified I/D cache. +@item vcrypto +CPU supports the vector cryptography instructions. +@item vsx +CPU supports the vector-scalar extension. +@end table + +Here is an example: +@smallexample +#ifdef __BUILTIN_CPU_SUPPORTS__ + if (__builtin_cpu_supports ("fpu")) + @{ + asm("fadd %0,%1,%2" : "=d"(dst) : "d"(src1), "d"(src2)); + @} + else +#endif + @{ + dst = __fadd (src1, src2); // Software FP addition function. + @} +@end smallexample +@end deftypefn + +The following built-in functions are also available on all PowerPC +processors: +@smallexample +uint64_t __builtin_ppc_get_timebase (); +unsigned long __builtin_ppc_mftb (); +double __builtin_unpack_ibm128 (__ibm128, int); +__ibm128 __builtin_pack_ibm128 (double, double); +double __builtin_mffs (void); +void __builtin_mtfsf (const int, double); +void __builtin_mtfsb0 (const int); +void __builtin_mtfsb1 (const int); +void __builtin_set_fpscr_rn (int); +@end smallexample + +The @code{__builtin_ppc_get_timebase} and @code{__builtin_ppc_mftb} +functions generate instructions to read the Time Base Register. The +@code{__builtin_ppc_get_timebase} function may generate multiple +instructions and always returns the 64 bits of the Time Base Register. +The @code{__builtin_ppc_mftb} function always generates one instruction and +returns the Time Base Register value as an unsigned long, throwing away +the most significant word on 32-bit environments. The @code{__builtin_mffs} +return the value of the FPSCR register. Note, ISA 3.0 supports the +@code{__builtin_mffsl()} which permits software to read the control and +non-sticky status bits in the FSPCR without the higher latency associated with +accessing the sticky status bits. The @code{__builtin_mtfsf} takes a constant +8-bit integer field mask and a double precision floating point argument +and generates the @code{mtfsf} (extended mnemonic) instruction to write new +values to selected fields of the FPSCR. The +@code{__builtin_mtfsb0} and @code{__builtin_mtfsb1} take the bit to change +as an argument. The valid bit range is between 0 and 31. The builtins map to +the @code{mtfsb0} and @code{mtfsb1} instructions which take the argument and +add 32. Hence these instructions only modify the FPSCR[32:63] bits by +changing the specified bit to a zero or one respectively. The +@code{__builtin_set_fpscr_rn} builtin allows changing both of the floating +point rounding mode bits. The argument is a 2-bit value. The argument can +either be a @code{const int} or stored in a variable. The builtin uses +the ISA 3.0 +instruction @code{mffscrn} if available, otherwise it reads the FPSCR, masks +the current rounding mode bits out and OR's in the new value. + +@node Basic PowerPC Built-in Functions Available on ISA 2.05 +@subsubsection Basic PowerPC Built-in Functions Available on ISA 2.05 + +The basic built-in functions described in this section are +available on the PowerPC family of processors starting with ISA 2.05 +or later. Unless specific options are explicitly disabled on the +command line, specifying option @option{-mcpu=power6} has the effect of +enabling the @option{-mpowerpc64}, @option{-mpowerpc-gpopt}, +@option{-mpowerpc-gfxopt}, @option{-mmfcrf}, @option{-mpopcntb}, +@option{-mfprnd}, @option{-mcmpb}, @option{-mhard-dfp}, and +@option{-mrecip-precision} options. Specify the +@option{-maltivec} option explicitly in +combination with the above options if desired. + +The following functions require option @option{-mcmpb}. +@smallexample +unsigned long long __builtin_cmpb (unsigned long long int, unsigned long long int); +unsigned int __builtin_cmpb (unsigned int, unsigned int); +@end smallexample + +The @code{__builtin_cmpb} function +performs a byte-wise compare on the contents of its two arguments, +returning the result of the byte-wise comparison as the returned +value. For each byte comparison, the corresponding byte of the return +value holds 0xff if the input bytes are equal and 0 if the input bytes +are not equal. If either of the arguments to this built-in function +is wider than 32 bits, the function call expands into the form that +expects @code{unsigned long long int} arguments +which is only available on 64-bit targets. + +The following built-in functions are available +when hardware decimal floating point +(@option{-mhard-dfp}) is available: +@smallexample +void __builtin_set_fpscr_drn(int); +_Decimal64 __builtin_ddedpd (int, _Decimal64); +_Decimal128 __builtin_ddedpdq (int, _Decimal128); +_Decimal64 __builtin_denbcd (int, _Decimal64); +_Decimal128 __builtin_denbcdq (int, _Decimal128); +_Decimal64 __builtin_diex (long long, _Decimal64); +_Decimal128 _builtin_diexq (long long, _Decimal128); +_Decimal64 __builtin_dscli (_Decimal64, int); +_Decimal128 __builtin_dscliq (_Decimal128, int); +_Decimal64 __builtin_dscri (_Decimal64, int); +_Decimal128 __builtin_dscriq (_Decimal128, int); +long long __builtin_dxex (_Decimal64); +long long __builtin_dxexq (_Decimal128); +_Decimal128 __builtin_pack_dec128 (unsigned long long, unsigned long long); +unsigned long long __builtin_unpack_dec128 (_Decimal128, int); + +The @code{__builtin_set_fpscr_drn} builtin allows changing the three decimal +floating point rounding mode bits. The argument is a 3-bit value. The +argument can either be a @code{const int} or the value can be stored in +a variable. +The builtin uses the ISA 3.0 instruction @code{mffscdrn} if available. +Otherwise the builtin reads the FPSCR, masks the current decimal rounding +mode bits out and OR's in the new value. + +@end smallexample + +The following functions require @option{-mhard-float}, +@option{-mpowerpc-gfxopt}, and @option{-mpopcntb} options. + +@smallexample +double __builtin_recipdiv (double, double); +float __builtin_recipdivf (float, float); +double __builtin_rsqrt (double); +float __builtin_rsqrtf (float); +@end smallexample + +The @code{vec_rsqrt}, @code{__builtin_rsqrt}, and +@code{__builtin_rsqrtf} functions generate multiple instructions to +implement the reciprocal sqrt functionality using reciprocal sqrt +estimate instructions. + +The @code{__builtin_recipdiv}, and @code{__builtin_recipdivf} +functions generate multiple instructions to implement division using +the reciprocal estimate instructions. + +The following functions require @option{-mhard-float} and +@option{-mmultiple} options. + +The @code{__builtin_unpack_longdouble} function takes a +@code{long double} argument and a compile time constant of 0 or 1. If +the constant is 0, the first @code{double} within the +@code{long double} is returned, otherwise the second @code{double} +is returned. The @code{__builtin_unpack_longdouble} function is only +available if @code{long double} uses the IBM extended double +representation. + +The @code{__builtin_pack_longdouble} function takes two @code{double} +arguments and returns a @code{long double} value that combines the two +arguments. The @code{__builtin_pack_longdouble} function is only +available if @code{long double} uses the IBM extended double +representation. + +The @code{__builtin_unpack_ibm128} function takes a @code{__ibm128} +argument and a compile time constant of 0 or 1. If the constant is 0, +the first @code{double} within the @code{__ibm128} is returned, +otherwise the second @code{double} is returned. + +The @code{__builtin_pack_ibm128} function takes two @code{double} +arguments and returns a @code{__ibm128} value that combines the two +arguments. + +Additional built-in functions are available for the 64-bit PowerPC +family of processors, for efficient use of 128-bit floating point +(@code{__float128}) values. + +@node Basic PowerPC Built-in Functions Available on ISA 2.06 +@subsubsection Basic PowerPC Built-in Functions Available on ISA 2.06 + +The basic built-in functions described in this section are +available on the PowerPC family of processors starting with ISA 2.05 +or later. Unless specific options are explicitly disabled on the +command line, specifying option @option{-mcpu=power7} has the effect of +enabling all the same options as for @option{-mcpu=power6} in +addition to the @option{-maltivec}, @option{-mpopcntd}, and +@option{-mvsx} options. + +The following basic built-in functions require @option{-mpopcntd}: +@smallexample +unsigned int __builtin_addg6s (unsigned int, unsigned int); +long long __builtin_bpermd (long long, long long); +unsigned int __builtin_cbcdtd (unsigned int); +unsigned int __builtin_cdtbcd (unsigned int); +long long __builtin_divde (long long, long long); +unsigned long long __builtin_divdeu (unsigned long long, unsigned long long); +int __builtin_divwe (int, int); +unsigned int __builtin_divweu (unsigned int, unsigned int); +vector __int128 __builtin_pack_vector_int128 (long long, long long); +void __builtin_rs6000_speculation_barrier (void); +long long __builtin_unpack_vector_int128 (vector __int128, signed char); +@end smallexample + +Of these, the @code{__builtin_divde} and @code{__builtin_divdeu} functions +require a 64-bit environment. + +The following basic built-in functions, which are also supported on +x86 targets, require @option{-mfloat128}. +@smallexample +__float128 __builtin_fabsq (__float128); +__float128 __builtin_copysignq (__float128, __float128); +__float128 __builtin_infq (void); +__float128 __builtin_huge_valq (void); +__float128 __builtin_nanq (void); +__float128 __builtin_nansq (void); + +__float128 __builtin_sqrtf128 (__float128); +__float128 __builtin_fmaf128 (__float128, __float128, __float128); +@end smallexample + +@node Basic PowerPC Built-in Functions Available on ISA 2.07 +@subsubsection Basic PowerPC Built-in Functions Available on ISA 2.07 + +The basic built-in functions described in this section are +available on the PowerPC family of processors starting with ISA 2.07 +or later. Unless specific options are explicitly disabled on the +command line, specifying option @option{-mcpu=power8} has the effect of +enabling all the same options as for @option{-mcpu=power7} in +addition to the @option{-mpower8-fusion}, @option{-mpower8-vector}, +@option{-mcrypto}, @option{-mhtm}, @option{-mquad-memory}, and +@option{-mquad-memory-atomic} options. + +This section intentionally empty. + +@node Basic PowerPC Built-in Functions Available on ISA 3.0 +@subsubsection Basic PowerPC Built-in Functions Available on ISA 3.0 + +The basic built-in functions described in this section are +available on the PowerPC family of processors starting with ISA 3.0 +or later. Unless specific options are explicitly disabled on the +command line, specifying option @option{-mcpu=power9} has the effect of +enabling all the same options as for @option{-mcpu=power8} in +addition to the @option{-misel} option. + +The following built-in functions are available on Linux 64-bit systems +that use the ISA 3.0 instruction set (@option{-mcpu=power9}): + +@table @code +@item __float128 __builtin_addf128_round_to_odd (__float128, __float128) +Perform a 128-bit IEEE floating point add using round to odd as the +rounding mode. +@findex __builtin_addf128_round_to_odd + +@item __float128 __builtin_subf128_round_to_odd (__float128, __float128) +Perform a 128-bit IEEE floating point subtract using round to odd as +the rounding mode. +@findex __builtin_subf128_round_to_odd + +@item __float128 __builtin_mulf128_round_to_odd (__float128, __float128) +Perform a 128-bit IEEE floating point multiply using round to odd as +the rounding mode. +@findex __builtin_mulf128_round_to_odd + +@item __float128 __builtin_divf128_round_to_odd (__float128, __float128) +Perform a 128-bit IEEE floating point divide using round to odd as +the rounding mode. +@findex __builtin_divf128_round_to_odd + +@item __float128 __builtin_sqrtf128_round_to_odd (__float128) +Perform a 128-bit IEEE floating point square root using round to odd +as the rounding mode. +@findex __builtin_sqrtf128_round_to_odd + +@item __float128 __builtin_fmaf128_round_to_odd (__float128, __float128, __float128) +Perform a 128-bit IEEE floating point fused multiply and add operation +using round to odd as the rounding mode. +@findex __builtin_fmaf128_round_to_odd + +@item double __builtin_truncf128_round_to_odd (__float128) +Convert a 128-bit IEEE floating point value to @code{double} using +round to odd as the rounding mode. +@findex __builtin_truncf128_round_to_odd +@end table + +The following additional built-in functions are also available for the +PowerPC family of processors, starting with ISA 3.0 or later: +@smallexample +long long __builtin_darn (void); +long long __builtin_darn_raw (void); +int __builtin_darn_32 (void); +@end smallexample + +The @code{__builtin_darn} and @code{__builtin_darn_raw} +functions require a +64-bit environment supporting ISA 3.0 or later. +The @code{__builtin_darn} function provides a 64-bit conditioned +random number. The @code{__builtin_darn_raw} function provides a +64-bit raw random number. The @code{__builtin_darn_32} function +provides a 32-bit conditioned random number. + +The following additional built-in functions are also available for the +PowerPC family of processors, starting with ISA 3.0 or later: + +@smallexample +int __builtin_byte_in_set (unsigned char u, unsigned long long set); +int __builtin_byte_in_range (unsigned char u, unsigned int range); +int __builtin_byte_in_either_range (unsigned char u, unsigned int ranges); + +int __builtin_dfp_dtstsfi_lt (unsigned int comparison, _Decimal64 value); +int __builtin_dfp_dtstsfi_lt (unsigned int comparison, _Decimal128 value); +int __builtin_dfp_dtstsfi_lt_dd (unsigned int comparison, _Decimal64 value); +int __builtin_dfp_dtstsfi_lt_td (unsigned int comparison, _Decimal128 value); + +int __builtin_dfp_dtstsfi_gt (unsigned int comparison, _Decimal64 value); +int __builtin_dfp_dtstsfi_gt (unsigned int comparison, _Decimal128 value); +int __builtin_dfp_dtstsfi_gt_dd (unsigned int comparison, _Decimal64 value); +int __builtin_dfp_dtstsfi_gt_td (unsigned int comparison, _Decimal128 value); + +int __builtin_dfp_dtstsfi_eq (unsigned int comparison, _Decimal64 value); +int __builtin_dfp_dtstsfi_eq (unsigned int comparison, _Decimal128 value); +int __builtin_dfp_dtstsfi_eq_dd (unsigned int comparison, _Decimal64 value); +int __builtin_dfp_dtstsfi_eq_td (unsigned int comparison, _Decimal128 value); + +int __builtin_dfp_dtstsfi_ov (unsigned int comparison, _Decimal64 value); +int __builtin_dfp_dtstsfi_ov (unsigned int comparison, _Decimal128 value); +int __builtin_dfp_dtstsfi_ov_dd (unsigned int comparison, _Decimal64 value); +int __builtin_dfp_dtstsfi_ov_td (unsigned int comparison, _Decimal128 value); + +double __builtin_mffsl(void); + +@end smallexample +The @code{__builtin_byte_in_set} function requires a +64-bit environment supporting ISA 3.0 or later. This function returns +a non-zero value if and only if its @code{u} argument exactly equals one of +the eight bytes contained within its 64-bit @code{set} argument. + +The @code{__builtin_byte_in_range} and +@code{__builtin_byte_in_either_range} require an environment +supporting ISA 3.0 or later. For these two functions, the +@code{range} argument is encoded as 4 bytes, organized as +@code{hi_1:lo_1:hi_2:lo_2}. +The @code{__builtin_byte_in_range} function returns a +non-zero value if and only if its @code{u} argument is within the +range bounded between @code{lo_2} and @code{hi_2} inclusive. +The @code{__builtin_byte_in_either_range} function returns non-zero if +and only if its @code{u} argument is within either the range bounded +between @code{lo_1} and @code{hi_1} inclusive or the range bounded +between @code{lo_2} and @code{hi_2} inclusive. + +The @code{__builtin_dfp_dtstsfi_lt} function returns a non-zero value +if and only if the number of signficant digits of its @code{value} argument +is less than its @code{comparison} argument. The +@code{__builtin_dfp_dtstsfi_lt_dd} and +@code{__builtin_dfp_dtstsfi_lt_td} functions behave similarly, but +require that the type of the @code{value} argument be +@code{__Decimal64} and @code{__Decimal128} respectively. + +The @code{__builtin_dfp_dtstsfi_gt} function returns a non-zero value +if and only if the number of signficant digits of its @code{value} argument +is greater than its @code{comparison} argument. The +@code{__builtin_dfp_dtstsfi_gt_dd} and +@code{__builtin_dfp_dtstsfi_gt_td} functions behave similarly, but +require that the type of the @code{value} argument be +@code{__Decimal64} and @code{__Decimal128} respectively. + +The @code{__builtin_dfp_dtstsfi_eq} function returns a non-zero value +if and only if the number of signficant digits of its @code{value} argument +equals its @code{comparison} argument. The +@code{__builtin_dfp_dtstsfi_eq_dd} and +@code{__builtin_dfp_dtstsfi_eq_td} functions behave similarly, but +require that the type of the @code{value} argument be +@code{__Decimal64} and @code{__Decimal128} respectively. + +The @code{__builtin_dfp_dtstsfi_ov} function returns a non-zero value +if and only if its @code{value} argument has an undefined number of +significant digits, such as when @code{value} is an encoding of @code{NaN}. +The @code{__builtin_dfp_dtstsfi_ov_dd} and +@code{__builtin_dfp_dtstsfi_ov_td} functions behave similarly, but +require that the type of the @code{value} argument be +@code{__Decimal64} and @code{__Decimal128} respectively. + +The @code{__builtin_mffsl} uses the ISA 3.0 @code{mffsl} instruction to read +the FPSCR. The instruction is a lower latency version of the @code{mffs} +instruction. If the @code{mffsl} instruction is not available, then the +builtin uses the older @code{mffs} instruction to read the FPSCR. + +@node Basic PowerPC Built-in Functions Available on ISA 3.1 +@subsubsection Basic PowerPC Built-in Functions Available on ISA 3.1 + +The basic built-in functions described in this section are +available on the PowerPC family of processors starting with ISA 3.1. +Unless specific options are explicitly disabled on the +command line, specifying option @option{-mcpu=power10} has the effect of +enabling all the same options as for @option{-mcpu=power9}. + +The following built-in functions are available on Linux 64-bit systems +that use a future architecture instruction set (@option{-mcpu=power10}): + +@smallexample +@exdent unsigned long long +@exdent __builtin_cfuged (unsigned long long, unsigned long long) +@end smallexample +Perform a 64-bit centrifuge operation, as if implemented by the +@code{cfuged} instruction. +@findex __builtin_cfuged + +@smallexample +@exdent unsigned long long +@exdent __builtin_cntlzdm (unsigned long long, unsigned long long) +@end smallexample +Perform a 64-bit count leading zeros operation under mask, as if +implemented by the @code{cntlzdm} instruction. +@findex __builtin_cntlzdm + +@smallexample +@exdent unsigned long long +@exdent __builtin_cnttzdm (unsigned long long, unsigned long long) +@end smallexample +Perform a 64-bit count trailing zeros operation under mask, as if +implemented by the @code{cnttzdm} instruction. +@findex __builtin_cnttzdm + +@smallexample +@exdent unsigned long long +@exdent __builtin_pdepd (unsigned long long, unsigned long long) +@end smallexample +Perform a 64-bit parallel bits deposit operation, as if implemented by the +@code{pdepd} instruction. +@findex __builtin_pdepd + +@smallexample +@exdent unsigned long long +@exdent __builtin_pextd (unsigned long long, unsigned long long) +@end smallexample +Perform a 64-bit parallel bits extract operation, as if implemented by the +@code{pextd} instruction. +@findex __builtin_pextd + +@smallexample +@exdent vector signed __int128 vsx_xl_sext (signed long long, signed char *) + +@exdent vector signed __int128 vsx_xl_sext (signed long long, signed short *) + +@exdent vector signed __int128 vsx_xl_sext (signed long long, signed int *) + +@exdent vector signed __int128 vsx_xl_sext (signed long long, signed long long *) + +@exdent vector unsigned __int128 vsx_xl_zext (signed long long, unsigned char *) + +@exdent vector unsigned __int128 vsx_xl_zext (signed long long, unsigned short *) + +@exdent vector unsigned __int128 vsx_xl_zext (signed long long, unsigned int *) + +@exdent vector unsigned __int128 vsx_xl_zext (signed long long, unsigned long long *) +@end smallexample + +Load (and sign extend) to an __int128 vector, as if implemented by the ISA 3.1 +@code{lxvrbx}, @code{lxvrhx}, @code{lxvrwx}, and @code{lxvrdx} instructions. +@findex vsx_xl_sext +@findex vsx_xl_zext + +@smallexample +@exdent void vec_xst_trunc (vector signed __int128, signed long long, signed char *) + +@exdent void vec_xst_trunc (vector signed __int128, signed long long, signed short *) + +@exdent void vec_xst_trunc (vector signed __int128, signed long long, signed int *) + +@exdent void vec_xst_trunc (vector signed __int128, signed long long, signed long long *) + +@exdent void vec_xst_trunc (vector unsigned __int128, signed long long, unsigned char *) + +@exdent void vec_xst_trunc (vector unsigned __int128, signed long long, unsigned short *) + +@exdent void vec_xst_trunc (vector unsigned __int128, signed long long, unsigned int *) + +@exdent void vec_xst_trunc (vector unsigned __int128, signed long long, unsigned long long *) +@end smallexample + +Truncate and store the rightmost element of a vector, as if implemented by the +ISA 3.1 @code{stxvrbx}, @code{stxvrhx}, @code{stxvrwx}, and @code{stxvrdx} +instructions. +@findex vec_xst_trunc + +@node PowerPC AltiVec/VSX Built-in Functions +@subsection PowerPC AltiVec/VSX Built-in Functions + +GCC provides an interface for the PowerPC family of processors to access +the AltiVec operations described in Motorola's AltiVec Programming +Interface Manual. The interface is made available by including +@code{} and using @option{-maltivec} and +@option{-mabi=altivec}. The interface supports the following vector +types. + +@smallexample +vector unsigned char +vector signed char +vector bool char + +vector unsigned short +vector signed short +vector bool short +vector pixel + +vector unsigned int +vector signed int +vector bool int +vector float +@end smallexample + +GCC's implementation of the high-level language interface available from +C and C++ code differs from Motorola's documentation in several ways. + +@itemize @bullet + +@item +A vector constant is a list of constant expressions within curly braces. + +@item +A vector initializer requires no cast if the vector constant is of the +same type as the variable it is initializing. + +@item +If @code{signed} or @code{unsigned} is omitted, the signedness of the +vector type is the default signedness of the base type. The default +varies depending on the operating system, so a portable program should +always specify the signedness. + +@item +Compiling with @option{-maltivec} adds keywords @code{__vector}, +@code{vector}, @code{__pixel}, @code{pixel}, @code{__bool} and +@code{bool}. When compiling ISO C, the context-sensitive substitution +of the keywords @code{vector}, @code{pixel} and @code{bool} is +disabled. To use them, you must include @code{} instead. + +@item +GCC allows using a @code{typedef} name as the type specifier for a +vector type, but only under the following circumstances: + +@itemize @bullet + +@item +When using @code{__vector} instead of @code{vector}; for example, + +@smallexample +typedef signed short int16; +__vector int16 data; +@end smallexample + +@item +When using @code{vector} in keyword-and-predefine mode; for example, + +@smallexample +typedef signed short int16; +vector int16 data; +@end smallexample + +Note that keyword-and-predefine mode is enabled by disabling GNU +extensions (e.g., by using @code{-std=c11}) and including +@code{}. +@end itemize + +@item +For C, overloaded functions are implemented with macros so the following +does not work: + +@smallexample + vec_add ((vector signed int)@{1, 2, 3, 4@}, foo); +@end smallexample + +@noindent +Since @code{vec_add} is a macro, the vector constant in the example +is treated as four separate arguments. Wrap the entire argument in +parentheses for this to work. +@end itemize + +@emph{Note:} Only the @code{} interface is supported. +Internally, GCC uses built-in functions to achieve the functionality in +the aforementioned header file, but they are not supported and are +subject to change without notice. + +GCC complies with the Power Vector Intrinsic Programming Reference (PVIPR), +which may be found at +@uref{https://openpowerfoundation.org/?resource_lib=power-vector-intrinsic-programming-reference}. +Chapter 4 of this document fully documents the vector API interfaces +that must be +provided by compliant compilers. Programmers should preferentially use +the interfaces described therein. However, historically GCC has provided +additional interfaces for access to vector instructions. These are +briefly described below. Where the PVIPR provides a portable interface, +other functions in GCC that provide the same capabilities should be +considered deprecated. + +The PVIPR documents the following overloaded functions: + +@multitable @columnfractions 0.33 0.33 0.33 + +@item @code{vec_abs} +@tab @code{vec_absd} +@tab @code{vec_abss} +@item @code{vec_add} +@tab @code{vec_addc} +@tab @code{vec_adde} +@item @code{vec_addec} +@tab @code{vec_adds} +@tab @code{vec_all_eq} +@item @code{vec_all_ge} +@tab @code{vec_all_gt} +@tab @code{vec_all_in} +@item @code{vec_all_le} +@tab @code{vec_all_lt} +@tab @code{vec_all_nan} +@item @code{vec_all_ne} +@tab @code{vec_all_nge} +@tab @code{vec_all_ngt} +@item @code{vec_all_nle} +@tab @code{vec_all_nlt} +@tab @code{vec_all_numeric} +@item @code{vec_and} +@tab @code{vec_andc} +@tab @code{vec_any_eq} +@item @code{vec_any_ge} +@tab @code{vec_any_gt} +@tab @code{vec_any_le} +@item @code{vec_any_lt} +@tab @code{vec_any_nan} +@tab @code{vec_any_ne} +@item @code{vec_any_nge} +@tab @code{vec_any_ngt} +@tab @code{vec_any_nle} +@item @code{vec_any_nlt} +@tab @code{vec_any_numeric} +@tab @code{vec_any_out} +@item @code{vec_avg} +@tab @code{vec_bperm} +@tab @code{vec_ceil} +@item @code{vec_cipher_be} +@tab @code{vec_cipherlast_be} +@tab @code{vec_cmpb} +@item @code{vec_cmpeq} +@tab @code{vec_cmpge} +@tab @code{vec_cmpgt} +@item @code{vec_cmple} +@tab @code{vec_cmplt} +@tab @code{vec_cmpne} +@item @code{vec_cmpnez} +@tab @code{vec_cntlz} +@tab @code{vec_cntlz_lsbb} +@item @code{vec_cnttz} +@tab @code{vec_cnttz_lsbb} +@tab @code{vec_cpsgn} +@item @code{vec_ctf} +@tab @code{vec_cts} +@tab @code{vec_ctu} +@item @code{vec_div} +@tab @code{vec_double} +@tab @code{vec_doublee} +@item @code{vec_doubleh} +@tab @code{vec_doublel} +@tab @code{vec_doubleo} +@item @code{vec_eqv} +@tab @code{vec_expte} +@tab @code{vec_extract} +@item @code{vec_extract_exp} +@tab @code{vec_extract_fp32_from_shorth} +@tab @code{vec_extract_fp32_from_shortl} +@item @code{vec_extract_sig} +@tab @code{vec_extract_4b} +@tab @code{vec_first_match_index} +@item @code{vec_first_match_or_eos_index} +@tab @code{vec_first_mismatch_index} +@tab @code{vec_first_mismatch_or_eos_index} +@item @code{vec_float} +@tab @code{vec_float2} +@tab @code{vec_floate} +@item @code{vec_floato} +@tab @code{vec_floor} +@tab @code{vec_gb} +@item @code{vec_insert} +@tab @code{vec_insert_exp} +@tab @code{vec_insert4b} +@item @code{vec_ld} +@tab @code{vec_lde} +@tab @code{vec_ldl} +@item @code{vec_loge} +@tab @code{vec_madd} +@tab @code{vec_madds} +@item @code{vec_max} +@tab @code{vec_mergee} +@tab @code{vec_mergeh} +@item @code{vec_mergel} +@tab @code{vec_mergeo} +@tab @code{vec_mfvscr} +@item @code{vec_min} +@tab @code{vec_mradds} +@tab @code{vec_msub} +@item @code{vec_msum} +@tab @code{vec_msums} +@tab @code{vec_mtvscr} +@item @code{vec_mul} +@tab @code{vec_mule} +@tab @code{vec_mulo} +@item @code{vec_nabs} +@tab @code{vec_nand} +@tab @code{vec_ncipher_be} +@item @code{vec_ncipherlast_be} +@tab @code{vec_nearbyint} +@tab @code{vec_neg} +@item @code{vec_nmadd} +@tab @code{vec_nmsub} +@tab @code{vec_nor} +@item @code{vec_or} +@tab @code{vec_orc} +@tab @code{vec_pack} +@item @code{vec_pack_to_short_fp32} +@tab @code{vec_packpx} +@tab @code{vec_packs} +@item @code{vec_packsu} +@tab @code{vec_parity_lsbb} +@tab @code{vec_perm} +@item @code{vec_permxor} +@tab @code{vec_pmsum_be} +@tab @code{vec_popcnt} +@item @code{vec_re} +@tab @code{vec_recipdiv} +@tab @code{vec_revb} +@item @code{vec_reve} +@tab @code{vec_rint} +@tab @code{vec_rl} +@item @code{vec_rlmi} +@tab @code{vec_rlnm} +@tab @code{vec_round} +@item @code{vec_rsqrt} +@tab @code{vec_rsqrte} +@tab @code{vec_sbox_be} +@item @code{vec_sel} +@tab @code{vec_shasigma_be} +@tab @code{vec_signed} +@item @code{vec_signed2} +@tab @code{vec_signede} +@tab @code{vec_signedo} +@item @code{vec_sl} +@tab @code{vec_sld} +@tab @code{vec_sldw} +@item @code{vec_sll} +@tab @code{vec_slo} +@tab @code{vec_slv} +@item @code{vec_splat} +@tab @code{vec_splat_s8} +@tab @code{vec_splat_s16} +@item @code{vec_splat_s32} +@tab @code{vec_splat_u8} +@tab @code{vec_splat_u16} +@item @code{vec_splat_u32} +@tab @code{vec_splats} +@tab @code{vec_sqrt} +@item @code{vec_sr} +@tab @code{vec_sra} +@tab @code{vec_srl} +@item @code{vec_sro} +@tab @code{vec_srv} +@tab @code{vec_st} +@item @code{vec_ste} +@tab @code{vec_stl} +@tab @code{vec_sub} +@item @code{vec_subc} +@tab @code{vec_sube} +@tab @code{vec_subec} +@item @code{vec_subs} +@tab @code{vec_sum2s} +@tab @code{vec_sum4s} +@item @code{vec_sums} +@tab @code{vec_test_data_class} +@tab @code{vec_trunc} +@item @code{vec_unpackh} +@tab @code{vec_unpackl} +@tab @code{vec_unsigned} +@item @code{vec_unsigned2} +@tab @code{vec_unsignede} +@tab @code{vec_unsignedo} +@item @code{vec_xl} +@tab @code{vec_xl_be} +@tab @code{vec_xl_len} +@item @code{vec_xl_len_r} +@tab @code{vec_xor} +@tab @code{vec_xst} +@item @code{vec_xst_be} +@tab @code{vec_xst_len} +@tab @code{vec_xst_len_r} + +@end multitable + +@menu +* PowerPC AltiVec Built-in Functions on ISA 2.05:: +* PowerPC AltiVec Built-in Functions Available on ISA 2.06:: +* PowerPC AltiVec Built-in Functions Available on ISA 2.07:: +* PowerPC AltiVec Built-in Functions Available on ISA 3.0:: +* PowerPC AltiVec Built-in Functions Available on ISA 3.1:: +@end menu + +@node PowerPC AltiVec Built-in Functions on ISA 2.05 +@subsubsection PowerPC AltiVec Built-in Functions on ISA 2.05 + +The following interfaces are supported for the generic and specific +AltiVec operations and the AltiVec predicates. In cases where there +is a direct mapping between generic and specific operations, only the +generic names are shown here, although the specific operations can also +be used. + +Arguments that are documented as @code{const int} require literal +integral values within the range required for that operation. + +Only functions excluded from the PVIPR are listed here. + +@smallexample +void vec_dss (const int); + +void vec_dssall (void); + +void vec_dst (const vector unsigned char *, int, const int); +void vec_dst (const vector signed char *, int, const int); +void vec_dst (const vector bool char *, int, const int); +void vec_dst (const vector unsigned short *, int, const int); +void vec_dst (const vector signed short *, int, const int); +void vec_dst (const vector bool short *, int, const int); +void vec_dst (const vector pixel *, int, const int); +void vec_dst (const vector unsigned int *, int, const int); +void vec_dst (const vector signed int *, int, const int); +void vec_dst (const vector bool int *, int, const int); +void vec_dst (const vector float *, int, const int); +void vec_dst (const unsigned char *, int, const int); +void vec_dst (const signed char *, int, const int); +void vec_dst (const unsigned short *, int, const int); +void vec_dst (const short *, int, const int); +void vec_dst (const unsigned int *, int, const int); +void vec_dst (const int *, int, const int); +void vec_dst (const float *, int, const int); + +void vec_dstst (const vector unsigned char *, int, const int); +void vec_dstst (const vector signed char *, int, const int); +void vec_dstst (const vector bool char *, int, const int); +void vec_dstst (const vector unsigned short *, int, const int); +void vec_dstst (const vector signed short *, int, const int); +void vec_dstst (const vector bool short *, int, const int); +void vec_dstst (const vector pixel *, int, const int); +void vec_dstst (const vector unsigned int *, int, const int); +void vec_dstst (const vector signed int *, int, const int); +void vec_dstst (const vector bool int *, int, const int); +void vec_dstst (const vector float *, int, const int); +void vec_dstst (const unsigned char *, int, const int); +void vec_dstst (const signed char *, int, const int); +void vec_dstst (const unsigned short *, int, const int); +void vec_dstst (const short *, int, const int); +void vec_dstst (const unsigned int *, int, const int); +void vec_dstst (const int *, int, const int); +void vec_dstst (const unsigned long *, int, const int); +void vec_dstst (const long *, int, const int); +void vec_dstst (const float *, int, const int); + +void vec_dststt (const vector unsigned char *, int, const int); +void vec_dststt (const vector signed char *, int, const int); +void vec_dststt (const vector bool char *, int, const int); +void vec_dststt (const vector unsigned short *, int, const int); +void vec_dststt (const vector signed short *, int, const int); +void vec_dststt (const vector bool short *, int, const int); +void vec_dststt (const vector pixel *, int, const int); +void vec_dststt (const vector unsigned int *, int, const int); +void vec_dststt (const vector signed int *, int, const int); +void vec_dststt (const vector bool int *, int, const int); +void vec_dststt (const vector float *, int, const int); +void vec_dststt (const unsigned char *, int, const int); +void vec_dststt (const signed char *, int, const int); +void vec_dststt (const unsigned short *, int, const int); +void vec_dststt (const short *, int, const int); +void vec_dststt (const unsigned int *, int, const int); +void vec_dststt (const int *, int, const int); +void vec_dststt (const float *, int, const int); + +void vec_dstt (const vector unsigned char *, int, const int); +void vec_dstt (const vector signed char *, int, const int); +void vec_dstt (const vector bool char *, int, const int); +void vec_dstt (const vector unsigned short *, int, const int); +void vec_dstt (const vector signed short *, int, const int); +void vec_dstt (const vector bool short *, int, const int); +void vec_dstt (const vector pixel *, int, const int); +void vec_dstt (const vector unsigned int *, int, const int); +void vec_dstt (const vector signed int *, int, const int); +void vec_dstt (const vector bool int *, int, const int); +void vec_dstt (const vector float *, int, const int); +void vec_dstt (const unsigned char *, int, const int); +void vec_dstt (const signed char *, int, const int); +void vec_dstt (const unsigned short *, int, const int); +void vec_dstt (const short *, int, const int); +void vec_dstt (const unsigned int *, int, const int); +void vec_dstt (const int *, int, const int); +void vec_dstt (const float *, int, const int); + +vector signed char vec_lvebx (int, char *); +vector unsigned char vec_lvebx (int, unsigned char *); + +vector signed short vec_lvehx (int, short *); +vector unsigned short vec_lvehx (int, unsigned short *); + +vector float vec_lvewx (int, float *); +vector signed int vec_lvewx (int, int *); +vector unsigned int vec_lvewx (int, unsigned int *); + +vector unsigned char vec_lvsl (int, const unsigned char *); +vector unsigned char vec_lvsl (int, const signed char *); +vector unsigned char vec_lvsl (int, const unsigned short *); +vector unsigned char vec_lvsl (int, const short *); +vector unsigned char vec_lvsl (int, const unsigned int *); +vector unsigned char vec_lvsl (int, const int *); +vector unsigned char vec_lvsl (int, const float *); + +vector unsigned char vec_lvsr (int, const unsigned char *); +vector unsigned char vec_lvsr (int, const signed char *); +vector unsigned char vec_lvsr (int, const unsigned short *); +vector unsigned char vec_lvsr (int, const short *); +vector unsigned char vec_lvsr (int, const unsigned int *); +vector unsigned char vec_lvsr (int, const int *); +vector unsigned char vec_lvsr (int, const float *); + +void vec_stvebx (vector signed char, int, signed char *); +void vec_stvebx (vector unsigned char, int, unsigned char *); +void vec_stvebx (vector bool char, int, signed char *); +void vec_stvebx (vector bool char, int, unsigned char *); + +void vec_stvehx (vector signed short, int, short *); +void vec_stvehx (vector unsigned short, int, unsigned short *); +void vec_stvehx (vector bool short, int, short *); +void vec_stvehx (vector bool short, int, unsigned short *); + +void vec_stvewx (vector float, int, float *); +void vec_stvewx (vector signed int, int, int *); +void vec_stvewx (vector unsigned int, int, unsigned int *); +void vec_stvewx (vector bool int, int, int *); +void vec_stvewx (vector bool int, int, unsigned int *); + +vector float vec_vaddfp (vector float, vector float); + +vector signed char vec_vaddsbs (vector bool char, vector signed char); +vector signed char vec_vaddsbs (vector signed char, vector bool char); +vector signed char vec_vaddsbs (vector signed char, vector signed char); + +vector signed short vec_vaddshs (vector bool short, vector signed short); +vector signed short vec_vaddshs (vector signed short, vector bool short); +vector signed short vec_vaddshs (vector signed short, vector signed short); + +vector signed int vec_vaddsws (vector bool int, vector signed int); +vector signed int vec_vaddsws (vector signed int, vector bool int); +vector signed int vec_vaddsws (vector signed int, vector signed int); + +vector signed char vec_vaddubm (vector bool char, vector signed char); +vector signed char vec_vaddubm (vector signed char, vector bool char); +vector signed char vec_vaddubm (vector signed char, vector signed char); +vector unsigned char vec_vaddubm (vector bool char, vector unsigned char); +vector unsigned char vec_vaddubm (vector unsigned char, vector bool char); +vector unsigned char vec_vaddubm (vector unsigned char, vector unsigned char); + +vector unsigned char vec_vaddubs (vector bool char, vector unsigned char); +vector unsigned char vec_vaddubs (vector unsigned char, vector bool char); +vector unsigned char vec_vaddubs (vector unsigned char, vector unsigned char); + +vector signed short vec_vadduhm (vector bool short, vector signed short); +vector signed short vec_vadduhm (vector signed short, vector bool short); +vector signed short vec_vadduhm (vector signed short, vector signed short); +vector unsigned short vec_vadduhm (vector bool short, vector unsigned short); +vector unsigned short vec_vadduhm (vector unsigned short, vector bool short); +vector unsigned short vec_vadduhm (vector unsigned short, vector unsigned short); + +vector unsigned short vec_vadduhs (vector bool short, vector unsigned short); +vector unsigned short vec_vadduhs (vector unsigned short, vector bool short); +vector unsigned short vec_vadduhs (vector unsigned short, vector unsigned short); + +vector signed int vec_vadduwm (vector bool int, vector signed int); +vector signed int vec_vadduwm (vector signed int, vector bool int); +vector signed int vec_vadduwm (vector signed int, vector signed int); +vector unsigned int vec_vadduwm (vector bool int, vector unsigned int); +vector unsigned int vec_vadduwm (vector unsigned int, vector bool int); +vector unsigned int vec_vadduwm (vector unsigned int, vector unsigned int); + +vector unsigned int vec_vadduws (vector bool int, vector unsigned int); +vector unsigned int vec_vadduws (vector unsigned int, vector bool int); +vector unsigned int vec_vadduws (vector unsigned int, vector unsigned int); + +vector signed char vec_vavgsb (vector signed char, vector signed char); + +vector signed short vec_vavgsh (vector signed short, vector signed short); + +vector signed int vec_vavgsw (vector signed int, vector signed int); + +vector unsigned char vec_vavgub (vector unsigned char, vector unsigned char); + +vector unsigned short vec_vavguh (vector unsigned short, vector unsigned short); + +vector unsigned int vec_vavguw (vector unsigned int, vector unsigned int); + +vector float vec_vcfsx (vector signed int, const int); + +vector float vec_vcfux (vector unsigned int, const int); + +vector bool int vec_vcmpeqfp (vector float, vector float); + +vector bool char vec_vcmpequb (vector signed char, vector signed char); +vector bool char vec_vcmpequb (vector unsigned char, vector unsigned char); + +vector bool short vec_vcmpequh (vector signed short, vector signed short); +vector bool short vec_vcmpequh (vector unsigned short, vector unsigned short); + +vector bool int vec_vcmpequw (vector signed int, vector signed int); +vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int); + +vector bool int vec_vcmpgtfp (vector float, vector float); + +vector bool char vec_vcmpgtsb (vector signed char, vector signed char); + +vector bool short vec_vcmpgtsh (vector signed short, vector signed short); + +vector bool int vec_vcmpgtsw (vector signed int, vector signed int); + +vector bool char vec_vcmpgtub (vector unsigned char, vector unsigned char); + +vector bool short vec_vcmpgtuh (vector unsigned short, vector unsigned short); + +vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int); + +vector float vec_vmaxfp (vector float, vector float); + +vector signed char vec_vmaxsb (vector bool char, vector signed char); +vector signed char vec_vmaxsb (vector signed char, vector bool char); +vector signed char vec_vmaxsb (vector signed char, vector signed char); + +vector signed short vec_vmaxsh (vector bool short, vector signed short); +vector signed short vec_vmaxsh (vector signed short, vector bool short); +vector signed short vec_vmaxsh (vector signed short, vector signed short); + +vector signed int vec_vmaxsw (vector bool int, vector signed int); +vector signed int vec_vmaxsw (vector signed int, vector bool int); +vector signed int vec_vmaxsw (vector signed int, vector signed int); + +vector unsigned char vec_vmaxub (vector bool char, vector unsigned char); +vector unsigned char vec_vmaxub (vector unsigned char, vector bool char); +vector unsigned char vec_vmaxub (vector unsigned char, vector unsigned char); + +vector unsigned short vec_vmaxuh (vector bool short, vector unsigned short); +vector unsigned short vec_vmaxuh (vector unsigned short, vector bool short); +vector unsigned short vec_vmaxuh (vector unsigned short, vector unsigned short); + +vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int); +vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int); +vector unsigned int vec_vmaxuw (vector unsigned int, vector unsigned int); + +vector float vec_vminfp (vector float, vector float); + +vector signed char vec_vminsb (vector bool char, vector signed char); +vector signed char vec_vminsb (vector signed char, vector bool char); +vector signed char vec_vminsb (vector signed char, vector signed char); + +vector signed short vec_vminsh (vector bool short, vector signed short); +vector signed short vec_vminsh (vector signed short, vector bool short); +vector signed short vec_vminsh (vector signed short, vector signed short); + +vector signed int vec_vminsw (vector bool int, vector signed int); +vector signed int vec_vminsw (vector signed int, vector bool int); +vector signed int vec_vminsw (vector signed int, vector signed int); + +vector unsigned char vec_vminub (vector bool char, vector unsigned char); +vector unsigned char vec_vminub (vector unsigned char, vector bool char); +vector unsigned char vec_vminub (vector unsigned char, vector unsigned char); + +vector unsigned short vec_vminuh (vector bool short, vector unsigned short); +vector unsigned short vec_vminuh (vector unsigned short, vector bool short); +vector unsigned short vec_vminuh (vector unsigned short, vector unsigned short); + +vector unsigned int vec_vminuw (vector bool int, vector unsigned int); +vector unsigned int vec_vminuw (vector unsigned int, vector bool int); +vector unsigned int vec_vminuw (vector unsigned int, vector unsigned int); + +vector bool char vec_vmrghb (vector bool char, vector bool char); +vector signed char vec_vmrghb (vector signed char, vector signed char); +vector unsigned char vec_vmrghb (vector unsigned char, vector unsigned char); + +vector bool short vec_vmrghh (vector bool short, vector bool short); +vector signed short vec_vmrghh (vector signed short, vector signed short); +vector unsigned short vec_vmrghh (vector unsigned short, vector unsigned short); +vector pixel vec_vmrghh (vector pixel, vector pixel); + +vector float vec_vmrghw (vector float, vector float); +vector bool int vec_vmrghw (vector bool int, vector bool int); +vector signed int vec_vmrghw (vector signed int, vector signed int); +vector unsigned int vec_vmrghw (vector unsigned int, vector unsigned int); + +vector bool char vec_vmrglb (vector bool char, vector bool char); +vector signed char vec_vmrglb (vector signed char, vector signed char); +vector unsigned char vec_vmrglb (vector unsigned char, vector unsigned char); + +vector bool short vec_vmrglh (vector bool short, vector bool short); +vector signed short vec_vmrglh (vector signed short, vector signed short); +vector unsigned short vec_vmrglh (vector unsigned short, vector unsigned short); +vector pixel vec_vmrglh (vector pixel, vector pixel); + +vector float vec_vmrglw (vector float, vector float); +vector signed int vec_vmrglw (vector signed int, vector signed int); +vector unsigned int vec_vmrglw (vector unsigned int, vector unsigned int); +vector bool int vec_vmrglw (vector bool int, vector bool int); + +vector signed int vec_vmsummbm (vector signed char, vector unsigned char, + vector signed int); + +vector signed int vec_vmsumshm (vector signed short, vector signed short, + vector signed int); + +vector signed int vec_vmsumshs (vector signed short, vector signed short, + vector signed int); + +vector unsigned int vec_vmsumubm (vector unsigned char, vector unsigned char, + vector unsigned int); + +vector unsigned int vec_vmsumuhm (vector unsigned short, vector unsigned short, + vector unsigned int); + +vector unsigned int vec_vmsumuhs (vector unsigned short, vector unsigned short, + vector unsigned int); + +vector signed short vec_vmulesb (vector signed char, vector signed char); + +vector signed int vec_vmulesh (vector signed short, vector signed short); + +vector unsigned short vec_vmuleub (vector unsigned char, vector unsigned char); + +vector unsigned int vec_vmuleuh (vector unsigned short, vector unsigned short); + +vector signed short vec_vmulosb (vector signed char, vector signed char); + +vector signed int vec_vmulosh (vector signed short, vector signed short); + +vector unsigned short vec_vmuloub (vector unsigned char, vector unsigned char); + +vector unsigned int vec_vmulouh (vector unsigned short, vector unsigned short); + +vector signed char vec_vpkshss (vector signed short, vector signed short); + +vector unsigned char vec_vpkshus (vector signed short, vector signed short); + +vector signed short vec_vpkswss (vector signed int, vector signed int); + +vector unsigned short vec_vpkswus (vector signed int, vector signed int); + +vector bool char vec_vpkuhum (vector bool short, vector bool short); +vector signed char vec_vpkuhum (vector signed short, vector signed short); +vector unsigned char vec_vpkuhum (vector unsigned short, vector unsigned short); + +vector unsigned char vec_vpkuhus (vector unsigned short, vector unsigned short); + +vector bool short vec_vpkuwum (vector bool int, vector bool int); +vector signed short vec_vpkuwum (vector signed int, vector signed int); +vector unsigned short vec_vpkuwum (vector unsigned int, vector unsigned int); + +vector unsigned short vec_vpkuwus (vector unsigned int, vector unsigned int); + +vector signed char vec_vrlb (vector signed char, vector unsigned char); +vector unsigned char vec_vrlb (vector unsigned char, vector unsigned char); + +vector signed short vec_vrlh (vector signed short, vector unsigned short); +vector unsigned short vec_vrlh (vector unsigned short, vector unsigned short); + +vector signed int vec_vrlw (vector signed int, vector unsigned int); +vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int); + +vector signed char vec_vslb (vector signed char, vector unsigned char); +vector unsigned char vec_vslb (vector unsigned char, vector unsigned char); + +vector signed short vec_vslh (vector signed short, vector unsigned short); +vector unsigned short vec_vslh (vector unsigned short, vector unsigned short); + +vector signed int vec_vslw (vector signed int, vector unsigned int); +vector unsigned int vec_vslw (vector unsigned int, vector unsigned int); + +vector signed char vec_vspltb (vector signed char, const int); +vector unsigned char vec_vspltb (vector unsigned char, const int); +vector bool char vec_vspltb (vector bool char, const int); + +vector bool short vec_vsplth (vector bool short, const int); +vector signed short vec_vsplth (vector signed short, const int); +vector unsigned short vec_vsplth (vector unsigned short, const int); +vector pixel vec_vsplth (vector pixel, const int); + +vector float vec_vspltw (vector float, const int); +vector signed int vec_vspltw (vector signed int, const int); +vector unsigned int vec_vspltw (vector unsigned int, const int); +vector bool int vec_vspltw (vector bool int, const int); + +vector signed char vec_vsrab (vector signed char, vector unsigned char); +vector unsigned char vec_vsrab (vector unsigned char, vector unsigned char); + +vector signed short vec_vsrah (vector signed short, vector unsigned short); +vector unsigned short vec_vsrah (vector unsigned short, vector unsigned short); + +vector signed int vec_vsraw (vector signed int, vector unsigned int); +vector unsigned int vec_vsraw (vector unsigned int, vector unsigned int); + +vector signed char vec_vsrb (vector signed char, vector unsigned char); +vector unsigned char vec_vsrb (vector unsigned char, vector unsigned char); + +vector signed short vec_vsrh (vector signed short, vector unsigned short); +vector unsigned short vec_vsrh (vector unsigned short, vector unsigned short); + +vector signed int vec_vsrw (vector signed int, vector unsigned int); +vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int); + +vector float vec_vsubfp (vector float, vector float); + +vector signed char vec_vsubsbs (vector bool char, vector signed char); +vector signed char vec_vsubsbs (vector signed char, vector bool char); +vector signed char vec_vsubsbs (vector signed char, vector signed char); + +vector signed short vec_vsubshs (vector bool short, vector signed short); +vector signed short vec_vsubshs (vector signed short, vector bool short); +vector signed short vec_vsubshs (vector signed short, vector signed short); + +vector signed int vec_vsubsws (vector bool int, vector signed int); +vector signed int vec_vsubsws (vector signed int, vector bool int); +vector signed int vec_vsubsws (vector signed int, vector signed int); + +vector signed char vec_vsububm (vector bool char, vector signed char); +vector signed char vec_vsububm (vector signed char, vector bool char); +vector signed char vec_vsububm (vector signed char, vector signed char); +vector unsigned char vec_vsububm (vector bool char, vector unsigned char); +vector unsigned char vec_vsububm (vector unsigned char, vector bool char); +vector unsigned char vec_vsububm (vector unsigned char, vector unsigned char); + +vector unsigned char vec_vsububs (vector bool char, vector unsigned char); +vector unsigned char vec_vsububs (vector unsigned char, vector bool char); +vector unsigned char vec_vsububs (vector unsigned char, vector unsigned char); + +vector signed short vec_vsubuhm (vector bool short, vector signed short); +vector signed short vec_vsubuhm (vector signed short, vector bool short); +vector signed short vec_vsubuhm (vector signed short, vector signed short); +vector unsigned short vec_vsubuhm (vector bool short, vector unsigned short); +vector unsigned short vec_vsubuhm (vector unsigned short, vector bool short); +vector unsigned short vec_vsubuhm (vector unsigned short, vector unsigned short); + +vector unsigned short vec_vsubuhs (vector bool short, vector unsigned short); +vector unsigned short vec_vsubuhs (vector unsigned short, vector bool short); +vector unsigned short vec_vsubuhs (vector unsigned short, vector unsigned short); + +vector signed int vec_vsubuwm (vector bool int, vector signed int); +vector signed int vec_vsubuwm (vector signed int, vector bool int); +vector signed int vec_vsubuwm (vector signed int, vector signed int); +vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int); +vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int); +vector unsigned int vec_vsubuwm (vector unsigned int, vector unsigned int); + +vector unsigned int vec_vsubuws (vector bool int, vector unsigned int); +vector unsigned int vec_vsubuws (vector unsigned int, vector bool int); +vector unsigned int vec_vsubuws (vector unsigned int, vector unsigned int); + +vector signed int vec_vsum4sbs (vector signed char, vector signed int); + +vector signed int vec_vsum4shs (vector signed short, vector signed int); + +vector unsigned int vec_vsum4ubs (vector unsigned char, vector unsigned int); + +vector unsigned int vec_vupkhpx (vector pixel); + +vector bool short vec_vupkhsb (vector bool char); +vector signed short vec_vupkhsb (vector signed char); + +vector bool int vec_vupkhsh (vector bool short); +vector signed int vec_vupkhsh (vector signed short); + +vector unsigned int vec_vupklpx (vector pixel); + +vector bool short vec_vupklsb (vector bool char); +vector signed short vec_vupklsb (vector signed char); + +vector bool int vec_vupklsh (vector bool short); +vector signed int vec_vupklsh (vector signed short); +@end smallexample + +@node PowerPC AltiVec Built-in Functions Available on ISA 2.06 +@subsubsection PowerPC AltiVec Built-in Functions Available on ISA 2.06 + +The AltiVec built-in functions described in this section are +available on the PowerPC family of processors starting with ISA 2.06 +or later. These are normally enabled by adding @option{-mvsx} to the +command line. + +When @option{-mvsx} is used, the following additional vector types are +implemented. + +@smallexample +vector unsigned __int128 +vector signed __int128 +vector unsigned long long int +vector signed long long int +vector double +@end smallexample + +The long long types are only implemented for 64-bit code generation. + +Only functions excluded from the PVIPR are listed here. + +@smallexample +void vec_dst (const unsigned long *, int, const int); +void vec_dst (const long *, int, const int); + +void vec_dststt (const unsigned long *, int, const int); +void vec_dststt (const long *, int, const int); + +void vec_dstt (const unsigned long *, int, const int); +void vec_dstt (const long *, int, const int); + +vector unsigned char vec_lvsl (int, const unsigned long *); +vector unsigned char vec_lvsl (int, const long *); + +vector unsigned char vec_lvsr (int, const unsigned long *); +vector unsigned char vec_lvsr (int, const long *); + +vector unsigned char vec_lvsl (int, const double *); +vector unsigned char vec_lvsr (int, const double *); + +vector double vec_vsx_ld (int, const vector double *); +vector double vec_vsx_ld (int, const double *); +vector float vec_vsx_ld (int, const vector float *); +vector float vec_vsx_ld (int, const float *); +vector bool int vec_vsx_ld (int, const vector bool int *); +vector signed int vec_vsx_ld (int, const vector signed int *); +vector signed int vec_vsx_ld (int, const int *); +vector signed int vec_vsx_ld (int, const long *); +vector unsigned int vec_vsx_ld (int, const vector unsigned int *); +vector unsigned int vec_vsx_ld (int, const unsigned int *); +vector unsigned int vec_vsx_ld (int, const unsigned long *); +vector bool short vec_vsx_ld (int, const vector bool short *); +vector pixel vec_vsx_ld (int, const vector pixel *); +vector signed short vec_vsx_ld (int, const vector signed short *); +vector signed short vec_vsx_ld (int, const short *); +vector unsigned short vec_vsx_ld (int, const vector unsigned short *); +vector unsigned short vec_vsx_ld (int, const unsigned short *); +vector bool char vec_vsx_ld (int, const vector bool char *); +vector signed char vec_vsx_ld (int, const vector signed char *); +vector signed char vec_vsx_ld (int, const signed char *); +vector unsigned char vec_vsx_ld (int, const vector unsigned char *); +vector unsigned char vec_vsx_ld (int, const unsigned char *); + +void vec_vsx_st (vector double, int, vector double *); +void vec_vsx_st (vector double, int, double *); +void vec_vsx_st (vector float, int, vector float *); +void vec_vsx_st (vector float, int, float *); +void vec_vsx_st (vector signed int, int, vector signed int *); +void vec_vsx_st (vector signed int, int, int *); +void vec_vsx_st (vector unsigned int, int, vector unsigned int *); +void vec_vsx_st (vector unsigned int, int, unsigned int *); +void vec_vsx_st (vector bool int, int, vector bool int *); +void vec_vsx_st (vector bool int, int, unsigned int *); +void vec_vsx_st (vector bool int, int, int *); +void vec_vsx_st (vector signed short, int, vector signed short *); +void vec_vsx_st (vector signed short, int, short *); +void vec_vsx_st (vector unsigned short, int, vector unsigned short *); +void vec_vsx_st (vector unsigned short, int, unsigned short *); +void vec_vsx_st (vector bool short, int, vector bool short *); +void vec_vsx_st (vector bool short, int, unsigned short *); +void vec_vsx_st (vector pixel, int, vector pixel *); +void vec_vsx_st (vector pixel, int, unsigned short *); +void vec_vsx_st (vector pixel, int, short *); +void vec_vsx_st (vector bool short, int, short *); +void vec_vsx_st (vector signed char, int, vector signed char *); +void vec_vsx_st (vector signed char, int, signed char *); +void vec_vsx_st (vector unsigned char, int, vector unsigned char *); +void vec_vsx_st (vector unsigned char, int, unsigned char *); +void vec_vsx_st (vector bool char, int, vector bool char *); +void vec_vsx_st (vector bool char, int, unsigned char *); +void vec_vsx_st (vector bool char, int, signed char *); + +vector double vec_xxpermdi (vector double, vector double, const int); +vector float vec_xxpermdi (vector float, vector float, const int); +vector long long vec_xxpermdi (vector long long, vector long long, const int); +vector unsigned long long vec_xxpermdi (vector unsigned long long, + vector unsigned long long, const int); +vector int vec_xxpermdi (vector int, vector int, const int); +vector unsigned int vec_xxpermdi (vector unsigned int, + vector unsigned int, const int); +vector short vec_xxpermdi (vector short, vector short, const int); +vector unsigned short vec_xxpermdi (vector unsigned short, + vector unsigned short, const int); +vector signed char vec_xxpermdi (vector signed char, vector signed char, + const int); +vector unsigned char vec_xxpermdi (vector unsigned char, + vector unsigned char, const int); + +vector double vec_xxsldi (vector double, vector double, int); +vector float vec_xxsldi (vector float, vector float, int); +vector long long vec_xxsldi (vector long long, vector long long, int); +vector unsigned long long vec_xxsldi (vector unsigned long long, + vector unsigned long long, int); +vector int vec_xxsldi (vector int, vector int, int); +vector unsigned int vec_xxsldi (vector unsigned int, vector unsigned int, int); +vector short vec_xxsldi (vector short, vector short, int); +vector unsigned short vec_xxsldi (vector unsigned short, + vector unsigned short, int); +vector signed char vec_xxsldi (vector signed char, vector signed char, int); +vector unsigned char vec_xxsldi (vector unsigned char, + vector unsigned char, int); +@end smallexample + +Note that the @samp{vec_ld} and @samp{vec_st} built-in functions always +generate the AltiVec @samp{LVX} and @samp{STVX} instructions even +if the VSX instruction set is available. The @samp{vec_vsx_ld} and +@samp{vec_vsx_st} built-in functions always generate the VSX @samp{LXVD2X}, +@samp{LXVW4X}, @samp{STXVD2X}, and @samp{STXVW4X} instructions. + +@node PowerPC AltiVec Built-in Functions Available on ISA 2.07 +@subsubsection PowerPC AltiVec Built-in Functions Available on ISA 2.07 + +If the ISA 2.07 additions to the vector/scalar (power8-vector) +instruction set are available, the following additional functions are +available for both 32-bit and 64-bit targets. For 64-bit targets, you +can use @var{vector long} instead of @var{vector long long}, +@var{vector bool long} instead of @var{vector bool long long}, and +@var{vector unsigned long} instead of @var{vector unsigned long long}. + +Only functions excluded from the PVIPR are listed here. + +@smallexample +vector long long vec_vaddudm (vector long long, vector long long); +vector long long vec_vaddudm (vector bool long long, vector long long); +vector long long vec_vaddudm (vector long long, vector bool long long); +vector unsigned long long vec_vaddudm (vector unsigned long long, + vector unsigned long long); +vector unsigned long long vec_vaddudm (vector bool unsigned long long, + vector unsigned long long); +vector unsigned long long vec_vaddudm (vector unsigned long long, + vector bool unsigned long long); + +vector long long vec_vclz (vector long long); +vector unsigned long long vec_vclz (vector unsigned long long); +vector int vec_vclz (vector int); +vector unsigned int vec_vclz (vector int); +vector short vec_vclz (vector short); +vector unsigned short vec_vclz (vector unsigned short); +vector signed char vec_vclz (vector signed char); +vector unsigned char vec_vclz (vector unsigned char); + +vector signed char vec_vclzb (vector signed char); +vector unsigned char vec_vclzb (vector unsigned char); + +vector long long vec_vclzd (vector long long); +vector unsigned long long vec_vclzd (vector unsigned long long); + +vector short vec_vclzh (vector short); +vector unsigned short vec_vclzh (vector unsigned short); + +vector int vec_vclzw (vector int); +vector unsigned int vec_vclzw (vector int); + +vector signed char vec_vgbbd (vector signed char); +vector unsigned char vec_vgbbd (vector unsigned char); + +vector long long vec_vmaxsd (vector long long, vector long long); + +vector unsigned long long vec_vmaxud (vector unsigned long long, + unsigned vector long long); + +vector long long vec_vminsd (vector long long, vector long long); + +vector unsigned long long vec_vminud (vector long long, vector long long); + +vector int vec_vpksdss (vector long long, vector long long); +vector unsigned int vec_vpksdss (vector long long, vector long long); + +vector unsigned int vec_vpkudus (vector unsigned long long, + vector unsigned long long); + +vector int vec_vpkudum (vector long long, vector long long); +vector unsigned int vec_vpkudum (vector unsigned long long, + vector unsigned long long); +vector bool int vec_vpkudum (vector bool long long, vector bool long long); + +vector long long vec_vpopcnt (vector long long); +vector unsigned long long vec_vpopcnt (vector unsigned long long); +vector int vec_vpopcnt (vector int); +vector unsigned int vec_vpopcnt (vector int); +vector short vec_vpopcnt (vector short); +vector unsigned short vec_vpopcnt (vector unsigned short); +vector signed char vec_vpopcnt (vector signed char); +vector unsigned char vec_vpopcnt (vector unsigned char); + +vector signed char vec_vpopcntb (vector signed char); +vector unsigned char vec_vpopcntb (vector unsigned char); + +vector long long vec_vpopcntd (vector long long); +vector unsigned long long vec_vpopcntd (vector unsigned long long); + +vector short vec_vpopcnth (vector short); +vector unsigned short vec_vpopcnth (vector unsigned short); + +vector int vec_vpopcntw (vector int); +vector unsigned int vec_vpopcntw (vector int); + +vector long long vec_vrld (vector long long, vector unsigned long long); +vector unsigned long long vec_vrld (vector unsigned long long, + vector unsigned long long); + +vector long long vec_vsld (vector long long, vector unsigned long long); +vector long long vec_vsld (vector unsigned long long, + vector unsigned long long); + +vector long long vec_vsrad (vector long long, vector unsigned long long); +vector unsigned long long vec_vsrad (vector unsigned long long, + vector unsigned long long); + +vector long long vec_vsrd (vector long long, vector unsigned long long); +vector unsigned long long char vec_vsrd (vector unsigned long long, + vector unsigned long long); + +vector long long vec_vsubudm (vector long long, vector long long); +vector long long vec_vsubudm (vector bool long long, vector long long); +vector long long vec_vsubudm (vector long long, vector bool long long); +vector unsigned long long vec_vsubudm (vector unsigned long long, + vector unsigned long long); +vector unsigned long long vec_vsubudm (vector bool long long, + vector unsigned long long); +vector unsigned long long vec_vsubudm (vector unsigned long long, + vector bool long long); + +vector long long vec_vupkhsw (vector int); +vector unsigned long long vec_vupkhsw (vector unsigned int); + +vector long long vec_vupklsw (vector int); +vector unsigned long long vec_vupklsw (vector int); +@end smallexample + +If the ISA 2.07 additions to the vector/scalar (power8-vector) +instruction set are available, the following additional functions are +available for 64-bit targets. New vector types +(@var{vector __int128} and @var{vector __uint128}) are available +to hold the @var{__int128} and @var{__uint128} types to use these +builtins. + +The normal vector extract, and set operations work on +@var{vector __int128} and @var{vector __uint128} types, +but the index value must be 0. + +Only functions excluded from the PVIPR are listed here. + +@smallexample +vector __int128 vec_vaddcuq (vector __int128, vector __int128); +vector __uint128 vec_vaddcuq (vector __uint128, vector __uint128); + +vector __int128 vec_vadduqm (vector __int128, vector __int128); +vector __uint128 vec_vadduqm (vector __uint128, vector __uint128); + +vector __int128 vec_vaddecuq (vector __int128, vector __int128, + vector __int128); +vector __uint128 vec_vaddecuq (vector __uint128, vector __uint128, + vector __uint128); + +vector __int128 vec_vaddeuqm (vector __int128, vector __int128, + vector __int128); +vector __uint128 vec_vaddeuqm (vector __uint128, vector __uint128, + vector __uint128); + +vector __int128 vec_vsubecuq (vector __int128, vector __int128, + vector __int128); +vector __uint128 vec_vsubecuq (vector __uint128, vector __uint128, + vector __uint128); + +vector __int128 vec_vsubeuqm (vector __int128, vector __int128, + vector __int128); +vector __uint128 vec_vsubeuqm (vector __uint128, vector __uint128, + vector __uint128); + +vector __int128 vec_vsubcuq (vector __int128, vector __int128); +vector __uint128 vec_vsubcuq (vector __uint128, vector __uint128); + +__int128 vec_vsubuqm (__int128, __int128); +__uint128 vec_vsubuqm (__uint128, __uint128); + +vector __int128 __builtin_bcdadd (vector __int128, vector __int128, const int); +vector unsigned char __builtin_bcdadd (vector unsigned char, vector unsigned char, + const int); +int __builtin_bcdadd_lt (vector __int128, vector __int128, const int); +int __builtin_bcdadd_lt (vector unsigned char, vector unsigned char, const int); +int __builtin_bcdadd_eq (vector __int128, vector __int128, const int); +int __builtin_bcdadd_eq (vector unsigned char, vector unsigned char, const int); +int __builtin_bcdadd_gt (vector __int128, vector __int128, const int); +int __builtin_bcdadd_gt (vector unsigned char, vector unsigned char, const int); +int __builtin_bcdadd_ov (vector __int128, vector __int128, const int); +int __builtin_bcdadd_ov (vector unsigned char, vector unsigned char, const int); + +vector __int128 __builtin_bcdsub (vector __int128, vector __int128, const int); +vector unsigned char __builtin_bcdsub (vector unsigned char, vector unsigned char, + const int); +int __builtin_bcdsub_lt (vector __int128, vector __int128, const int); +int __builtin_bcdsub_lt (vector unsigned char, vector unsigned char, const int); +int __builtin_bcdsub_eq (vector __int128, vector __int128, const int); +int __builtin_bcdsub_eq (vector unsigned char, vector unsigned char, const int); +int __builtin_bcdsub_gt (vector __int128, vector __int128, const int); +int __builtin_bcdsub_gt (vector unsigned char, vector unsigned char, const int); +int __builtin_bcdsub_ov (vector __int128, vector __int128, const int); +int __builtin_bcdsub_ov (vector unsigned char, vector unsigned char, const int); +@end smallexample + +@node PowerPC AltiVec Built-in Functions Available on ISA 3.0 +@subsubsection PowerPC AltiVec Built-in Functions Available on ISA 3.0 + +The following additional built-in functions are also available for the +PowerPC family of processors, starting with ISA 3.0 +(@option{-mcpu=power9}) or later. + +Only instructions excluded from the PVIPR are listed here. + +@smallexample +unsigned int scalar_extract_exp (double source); +unsigned long long int scalar_extract_exp (__ieee128 source); + +unsigned long long int scalar_extract_sig (double source); +unsigned __int128 scalar_extract_sig (__ieee128 source); + +double scalar_insert_exp (unsigned long long int significand, + unsigned long long int exponent); +double scalar_insert_exp (double significand, unsigned long long int exponent); + +ieee_128 scalar_insert_exp (unsigned __int128 significand, + unsigned long long int exponent); +ieee_128 scalar_insert_exp (ieee_128 significand, unsigned long long int exponent); + +int scalar_cmp_exp_gt (double arg1, double arg2); +int scalar_cmp_exp_lt (double arg1, double arg2); +int scalar_cmp_exp_eq (double arg1, double arg2); +int scalar_cmp_exp_unordered (double arg1, double arg2); + +bool scalar_test_data_class (float source, const int condition); +bool scalar_test_data_class (double source, const int condition); +bool scalar_test_data_class (__ieee128 source, const int condition); + +bool scalar_test_neg (float source); +bool scalar_test_neg (double source); +bool scalar_test_neg (__ieee128 source); +@end smallexample + +The @code{scalar_extract_exp} and @code{scalar_extract_sig} +functions require a 64-bit environment supporting ISA 3.0 or later. +The @code{scalar_extract_exp} and @code{scalar_extract_sig} built-in +functions return the significand and the biased exponent value +respectively of their @code{source} arguments. +When supplied with a 64-bit @code{source} argument, the +result returned by @code{scalar_extract_sig} has +the @code{0x0010000000000000} bit set if the +function's @code{source} argument is in normalized form. +Otherwise, this bit is set to 0. +When supplied with a 128-bit @code{source} argument, the +@code{0x00010000000000000000000000000000} bit of the result is +treated similarly. +Note that the sign of the significand is not represented in the result +returned from the @code{scalar_extract_sig} function. Use the +@code{scalar_test_neg} function to test the sign of its @code{double} +argument. + +The @code{scalar_insert_exp} +functions require a 64-bit environment supporting ISA 3.0 or later. +When supplied with a 64-bit first argument, the +@code{scalar_insert_exp} built-in function returns a double-precision +floating point value that is constructed by assembling the values of its +@code{significand} and @code{exponent} arguments. The sign of the +result is copied from the most significant bit of the +@code{significand} argument. The significand and exponent components +of the result are composed of the least significant 11 bits of the +@code{exponent} argument and the least significant 52 bits of the +@code{significand} argument respectively. + +When supplied with a 128-bit first argument, the +@code{scalar_insert_exp} built-in function returns a quad-precision +ieee floating point value. The sign bit of the result is copied from +the most significant bit of the @code{significand} argument. +The significand and exponent components of the result are composed of +the least significant 15 bits of the @code{exponent} argument and the +least significant 112 bits of the @code{significand} argument respectively. + +The @code{scalar_cmp_exp_gt}, @code{scalar_cmp_exp_lt}, +@code{scalar_cmp_exp_eq}, and @code{scalar_cmp_exp_unordered} built-in +functions return a non-zero value if @code{arg1} is greater than, less +than, equal to, or not comparable to @code{arg2} respectively. The +arguments are not comparable if one or the other equals NaN (not a +number). + +The @code{scalar_test_data_class} built-in function returns 1 +if any of the condition tests enabled by the value of the +@code{condition} variable are true, and 0 otherwise. The +@code{condition} argument must be a compile-time constant integer with +value not exceeding 127. The +@code{condition} argument is encoded as a bitmask with each bit +enabling the testing of a different condition, as characterized by the +following: +@smallexample +0x40 Test for NaN +0x20 Test for +Infinity +0x10 Test for -Infinity +0x08 Test for +Zero +0x04 Test for -Zero +0x02 Test for +Denormal +0x01 Test for -Denormal +@end smallexample + +The @code{scalar_test_neg} built-in function returns 1 if its +@code{source} argument holds a negative value, 0 otherwise. + +The following built-in functions are also available for the PowerPC family +of processors, starting with ISA 3.0 or later +(@option{-mcpu=power9}). These string functions are described +separately in order to group the descriptions closer to the function +prototypes. + +Only functions excluded from the PVIPR are listed here. + +@smallexample +int vec_all_nez (vector signed char, vector signed char); +int vec_all_nez (vector unsigned char, vector unsigned char); +int vec_all_nez (vector signed short, vector signed short); +int vec_all_nez (vector unsigned short, vector unsigned short); +int vec_all_nez (vector signed int, vector signed int); +int vec_all_nez (vector unsigned int, vector unsigned int); + +int vec_any_eqz (vector signed char, vector signed char); +int vec_any_eqz (vector unsigned char, vector unsigned char); +int vec_any_eqz (vector signed short, vector signed short); +int vec_any_eqz (vector unsigned short, vector unsigned short); +int vec_any_eqz (vector signed int, vector signed int); +int vec_any_eqz (vector unsigned int, vector unsigned int); + +signed char vec_xlx (unsigned int index, vector signed char data); +unsigned char vec_xlx (unsigned int index, vector unsigned char data); +signed short vec_xlx (unsigned int index, vector signed short data); +unsigned short vec_xlx (unsigned int index, vector unsigned short data); +signed int vec_xlx (unsigned int index, vector signed int data); +unsigned int vec_xlx (unsigned int index, vector unsigned int data); +float vec_xlx (unsigned int index, vector float data); + +signed char vec_xrx (unsigned int index, vector signed char data); +unsigned char vec_xrx (unsigned int index, vector unsigned char data); +signed short vec_xrx (unsigned int index, vector signed short data); +unsigned short vec_xrx (unsigned int index, vector unsigned short data); +signed int vec_xrx (unsigned int index, vector signed int data); +unsigned int vec_xrx (unsigned int index, vector unsigned int data); +float vec_xrx (unsigned int index, vector float data); +@end smallexample + +The @code{vec_all_nez}, @code{vec_any_eqz}, and @code{vec_cmpnez} +perform pairwise comparisons between the elements at the same +positions within their two vector arguments. +The @code{vec_all_nez} function returns a +non-zero value if and only if all pairwise comparisons are not +equal and no element of either vector argument contains a zero. +The @code{vec_any_eqz} function returns a +non-zero value if and only if at least one pairwise comparison is equal +or if at least one element of either vector argument contains a zero. +The @code{vec_cmpnez} function returns a vector of the same type as +its two arguments, within which each element consists of all ones to +denote that either the corresponding elements of the incoming arguments are +not equal or that at least one of the corresponding elements contains +zero. Otherwise, the element of the returned vector contains all zeros. + +The @code{vec_xlx} and @code{vec_xrx} functions extract the single +element selected by the @code{index} argument from the vector +represented by the @code{data} argument. The @code{index} argument +always specifies a byte offset, regardless of the size of the vector +element. With @code{vec_xlx}, @code{index} is the offset of the first +byte of the element to be extracted. With @code{vec_xrx}, @code{index} +represents the last byte of the element to be extracted, measured +from the right end of the vector. In other words, the last byte of +the element to be extracted is found at position @code{(15 - index)}. +There is no requirement that @code{index} be a multiple of the vector +element size. However, if the size of the vector element added to +@code{index} is greater than 15, the content of the returned value is +undefined. + +The following functions are also available if the ISA 3.0 instruction +set additions (@option{-mcpu=power9}) are available. + +Only functions excluded from the PVIPR are listed here. + +@smallexample +vector long long vec_vctz (vector long long); +vector unsigned long long vec_vctz (vector unsigned long long); +vector int vec_vctz (vector int); +vector unsigned int vec_vctz (vector int); +vector short vec_vctz (vector short); +vector unsigned short vec_vctz (vector unsigned short); +vector signed char vec_vctz (vector signed char); +vector unsigned char vec_vctz (vector unsigned char); + +vector signed char vec_vctzb (vector signed char); +vector unsigned char vec_vctzb (vector unsigned char); + +vector long long vec_vctzd (vector long long); +vector unsigned long long vec_vctzd (vector unsigned long long); + +vector short vec_vctzh (vector short); +vector unsigned short vec_vctzh (vector unsigned short); + +vector int vec_vctzw (vector int); +vector unsigned int vec_vctzw (vector int); + +vector int vec_vprtyb (vector int); +vector unsigned int vec_vprtyb (vector unsigned int); +vector long long vec_vprtyb (vector long long); +vector unsigned long long vec_vprtyb (vector unsigned long long); + +vector int vec_vprtybw (vector int); +vector unsigned int vec_vprtybw (vector unsigned int); + +vector long long vec_vprtybd (vector long long); +vector unsigned long long vec_vprtybd (vector unsigned long long); +@end smallexample + +On 64-bit targets, if the ISA 3.0 additions (@option{-mcpu=power9}) +are available: + +@smallexample +vector long vec_vprtyb (vector long); +vector unsigned long vec_vprtyb (vector unsigned long); +vector __int128 vec_vprtyb (vector __int128); +vector __uint128 vec_vprtyb (vector __uint128); + +vector long vec_vprtybd (vector long); +vector unsigned long vec_vprtybd (vector unsigned long); + +vector __int128 vec_vprtybq (vector __int128); +vector __uint128 vec_vprtybd (vector __uint128); +@end smallexample + +The following built-in functions are available for the PowerPC family +of processors, starting with ISA 3.0 or later (@option{-mcpu=power9}). + +Only functions excluded from the PVIPR are listed here. + +@smallexample +__vector unsigned char +vec_absdb (__vector unsigned char arg1, __vector unsigned char arg2); +__vector unsigned short +vec_absdh (__vector unsigned short arg1, __vector unsigned short arg2); +__vector unsigned int +vec_absdw (__vector unsigned int arg1, __vector unsigned int arg2); +@end smallexample + +The @code{vec_absd}, @code{vec_absdb}, @code{vec_absdh}, and +@code{vec_absdw} built-in functions each computes the absolute +differences of the pairs of vector elements supplied in its two vector +arguments, placing the absolute differences into the corresponding +elements of the vector result. + +The following built-in functions are available for the PowerPC family +of processors, starting with ISA 3.0 or later (@option{-mcpu=power9}): +@smallexample +vector unsigned int vec_vrlnm (vector unsigned int, vector unsigned int); +vector unsigned long long vec_vrlnm (vector unsigned long long, + vector unsigned long long); +@end smallexample + +The result of @code{vec_vrlnm} is obtained by rotating each element +of the first argument vector left and ANDing it with a mask. The +second argument vector contains the mask beginning in bits 11:15, +the mask end in bits 19:23, and the shift count in bits 27:31, +of each element. + +If the cryptographic instructions are enabled (@option{-mcrypto} or +@option{-mcpu=power8}), the following builtins are enabled. + +Only functions excluded from the PVIPR are listed here. + +@smallexample +vector unsigned long long __builtin_crypto_vsbox (vector unsigned long long); + +vector unsigned long long __builtin_crypto_vcipher (vector unsigned long long, + vector unsigned long long); + +vector unsigned long long __builtin_crypto_vcipherlast + (vector unsigned long long, + vector unsigned long long); + +vector unsigned long long __builtin_crypto_vncipher (vector unsigned long long, + vector unsigned long long); + +vector unsigned long long __builtin_crypto_vncipherlast (vector unsigned long long, + vector unsigned long long); + +vector unsigned char __builtin_crypto_vpermxor (vector unsigned char, + vector unsigned char, + vector unsigned char); + +vector unsigned short __builtin_crypto_vpermxor (vector unsigned short, + vector unsigned short, + vector unsigned short); + +vector unsigned int __builtin_crypto_vpermxor (vector unsigned int, + vector unsigned int, + vector unsigned int); + +vector unsigned long long __builtin_crypto_vpermxor (vector unsigned long long, + vector unsigned long long, + vector unsigned long long); + +vector unsigned char __builtin_crypto_vpmsumb (vector unsigned char, + vector unsigned char); + +vector unsigned short __builtin_crypto_vpmsumh (vector unsigned short, + vector unsigned short); + +vector unsigned int __builtin_crypto_vpmsumw (vector unsigned int, + vector unsigned int); + +vector unsigned long long __builtin_crypto_vpmsumd (vector unsigned long long, + vector unsigned long long); + +vector unsigned long long __builtin_crypto_vshasigmad (vector unsigned long long, + int, int); + +vector unsigned int __builtin_crypto_vshasigmaw (vector unsigned int, int, int); +@end smallexample + +The second argument to @var{__builtin_crypto_vshasigmad} and +@var{__builtin_crypto_vshasigmaw} must be a constant +integer that is 0 or 1. The third argument to these built-in functions +must be a constant integer in the range of 0 to 15. + +The following sign extension builtins are provided: + +@smallexample +vector signed int vec_signexti (vector signed char a); +vector signed long long vec_signextll (vector signed char a); +vector signed int vec_signexti (vector signed short a); +vector signed long long vec_signextll (vector signed short a); +vector signed long long vec_signextll (vector signed int a); +vector signed long long vec_signextq (vector signed long long a); +@end smallexample + +Each element of the result is produced by sign-extending the element of the +input vector that would fall in the least significant portion of the result +element. For example, a sign-extension of a vector signed char to a vector +signed long long will sign extend the rightmost byte of each doubleword. + +@node PowerPC AltiVec Built-in Functions Available on ISA 3.1 +@subsubsection PowerPC AltiVec Built-in Functions Available on ISA 3.1 + +The following additional built-in functions are also available for the +PowerPC family of processors, starting with ISA 3.1 (@option{-mcpu=power10}): + + +@smallexample +@exdent vector unsigned long long int +@exdent vec_cfuge (vector unsigned long long int, vector unsigned long long int); +@end smallexample +Perform a vector centrifuge operation, as if implemented by the +@code{vcfuged} instruction. +@findex vec_cfuge + +@smallexample +@exdent vector unsigned long long int +@exdent vec_cntlzm (vector unsigned long long int, vector unsigned long long int); +@end smallexample +Perform a vector count leading zeros under bit mask operation, as if +implemented by the @code{vclzdm} instruction. +@findex vec_cntlzm + +@smallexample +@exdent vector unsigned long long int +@exdent vec_cnttzm (vector unsigned long long int, vector unsigned long long int); +@end smallexample +Perform a vector count trailing zeros under bit mask operation, as if +implemented by the @code{vctzdm} instruction. +@findex vec_cnttzm + +@smallexample +@exdent vector signed char +@exdent vec_clrl (vector signed char a, unsigned int n); +@exdent vector unsigned char +@exdent vec_clrl (vector unsigned char a, unsigned int n); +@end smallexample +Clear the left-most @code{(16 - n)} bytes of vector argument @code{a}, as if +implemented by the @code{vclrlb} instruction on a big-endian target +and by the @code{vclrrb} instruction on a little-endian target. A +value of @code{n} that is greater than 16 is treated as if it equaled 16. +@findex vec_clrl + +@smallexample +@exdent vector signed char +@exdent vec_clrr (vector signed char a, unsigned int n); +@exdent vector unsigned char +@exdent vec_clrr (vector unsigned char a, unsigned int n); +@end smallexample +Clear the right-most @code{(16 - n)} bytes of vector argument @code{a}, as if +implemented by the @code{vclrrb} instruction on a big-endian target +and by the @code{vclrlb} instruction on a little-endian target. A +value of @code{n} that is greater than 16 is treated as if it equaled 16. +@findex vec_clrr + +@smallexample +@exdent vector unsigned long long int +@exdent vec_gnb (vector unsigned __int128, const unsigned char); +@end smallexample +Perform a 128-bit vector gather operation, as if implemented by the +@code{vgnb} instruction. The second argument must be a literal +integer value between 2 and 7 inclusive. +@findex vec_gnb + + +Vector Extract + +@smallexample +@exdent vector unsigned long long int +@exdent vec_extractl (vector unsigned char, vector unsigned char, unsigned int); +@exdent vector unsigned long long int +@exdent vec_extractl (vector unsigned short, vector unsigned short, unsigned int); +@exdent vector unsigned long long int +@exdent vec_extractl (vector unsigned int, vector unsigned int, unsigned int); +@exdent vector unsigned long long int +@exdent vec_extractl (vector unsigned long long, vector unsigned long long, unsigned int); +@end smallexample +Extract an element from two concatenated vectors starting at the given byte index +in natural-endian order, and place it zero-extended in doubleword 1 of the result +according to natural element order. If the byte index is out of range for the +data type, the intrinsic will be rejected. +For little-endian, this output will match the placement by the hardware +instruction, i.e., dword[0] in RTL notation. For big-endian, an additional +instruction is needed to move it from the "left" doubleword to the "right" one. +For little-endian, semantics matching the @code{vextdubvrx}, +@code{vextduhvrx}, @code{vextduwvrx} instruction will be generated, while for +big-endian, semantics matching the @code{vextdubvlx}, @code{vextduhvlx}, +@code{vextduwvlx} instructions +will be generated. Note that some fairly anomalous results can be generated if +the byte index is not aligned on an element boundary for the element being +extracted. This is a limitation of the bi-endian vector programming model is +consistent with the limitation on @code{vec_perm}. +@findex vec_extractl + +@smallexample +@exdent vector unsigned long long int +@exdent vec_extracth (vector unsigned char, vector unsigned char, unsigned int); +@exdent vector unsigned long long int +@exdent vec_extracth (vector unsigned short, vector unsigned short, +unsigned int); +@exdent vector unsigned long long int +@exdent vec_extracth (vector unsigned int, vector unsigned int, unsigned int); +@exdent vector unsigned long long int +@exdent vec_extracth (vector unsigned long long, vector unsigned long long, +unsigned int); +@end smallexample +Extract an element from two concatenated vectors starting at the given byte +index. The index is based on big endian order for a little endian system. +Similarly, the index is based on little endian order for a big endian system. +The extraced elements are zero-extended and put in doubleword 1 +according to natural element order. If the byte index is out of range for the +data type, the intrinsic will be rejected. For little-endian, this output +will match the placement by the hardware instruction (vextdubvrx, vextduhvrx, +vextduwvrx, vextddvrx) i.e., dword[0] in RTL +notation. For big-endian, an additional instruction is needed to move it +from the "left" doubleword to the "right" one. For little-endian, semantics +matching the @code{vextdubvlx}, @code{vextduhvlx}, @code{vextduwvlx} +instructions will be generated, while for big-endian, semantics matching the +@code{vextdubvrx}, @code{vextduhvrx}, @code{vextduwvrx} instructions will +be generated. Note that some fairly anomalous +results can be generated if the byte index is not aligned on the +element boundary for the element being extracted. This is a +limitation of the bi-endian vector programming model consistent with the +limitation on @code{vec_perm}. +@findex vec_extracth +@smallexample +@exdent vector unsigned long long int +@exdent vec_pdep (vector unsigned long long int, vector unsigned long long int); +@end smallexample +Perform a vector parallel bits deposit operation, as if implemented by +the @code{vpdepd} instruction. +@findex vec_pdep + +Vector Insert + +@smallexample +@exdent vector unsigned char +@exdent vec_insertl (unsigned char, vector unsigned char, unsigned int); +@exdent vector unsigned short +@exdent vec_insertl (unsigned short, vector unsigned short, unsigned int); +@exdent vector unsigned int +@exdent vec_insertl (unsigned int, vector unsigned int, unsigned int); +@exdent vector unsigned long long +@exdent vec_insertl (unsigned long long, vector unsigned long long, +unsigned int); +@exdent vector unsigned char +@exdent vec_insertl (vector unsigned char, vector unsigned char, unsigned int; +@exdent vector unsigned short +@exdent vec_insertl (vector unsigned short, vector unsigned short, +unsigned int); +@exdent vector unsigned int +@exdent vec_insertl (vector unsigned int, vector unsigned int, unsigned int); +@end smallexample + +Let src be the first argument, when the first argument is a scalar, or the +rightmost element of the left doubleword of the first argument, when the first +argument is a vector. Insert the source into the destination at the position +given by the third argument, using natural element order in the second +argument. The rest of the second argument is unchanged. If the byte +index is greater than 14 for halfwords, greater than 12 for words, or +greater than 8 for doublewords the result is undefined. For little-endian, +the generated code will be semantically equivalent to @code{vins[bhwd]rx} +instructions. Similarly for big-endian it will be semantically equivalent +to @code{vins[bhwd]lx}. Note that some fairly anomalous results can be +generated if the byte index is not aligned on an element boundary for the +type of element being inserted. +@findex vec_insertl + +@smallexample +@exdent vector unsigned char +@exdent vec_inserth (unsigned char, vector unsigned char, unsigned int); +@exdent vector unsigned short +@exdent vec_inserth (unsigned short, vector unsigned short, unsigned int); +@exdent vector unsigned int +@exdent vec_inserth (unsigned int, vector unsigned int, unsigned int); +@exdent vector unsigned long long +@exdent vec_inserth (unsigned long long, vector unsigned long long, +unsigned int); +@exdent vector unsigned char +@exdent vec_inserth (vector unsigned char, vector unsigned char, unsigned int); +@exdent vector unsigned short +@exdent vec_inserth (vector unsigned short, vector unsigned short, +unsigned int); +@exdent vector unsigned int +@exdent vec_inserth (vector unsigned int, vector unsigned int, unsigned int); +@end smallexample + +Let src be the first argument, when the first argument is a scalar, or the +rightmost element of the first argument, when the first argument is a vector. +Insert src into the second argument at the position identified by the third +argument, using opposite element order in the second argument, and leaving the +rest of the second argument unchanged. If the byte index is greater than 14 +for halfwords, 12 for words, or 8 for doublewords, the intrinsic will be +rejected. Note that the underlying hardware instruction uses the same register +for the second argument and the result. +For little-endian, the code generation will be semantically equivalent to +@code{vins[bhwd]lx}, while for big-endian it will be semantically equivalent to +@code{vins[bhwd]rx}. +Note that some fairly anomalous results can be generated if the byte index is +not aligned on an element boundary for the sort of element being inserted. +@findex vec_inserth + +Vector Replace Element +@smallexample +@exdent vector signed int vec_replace_elt (vector signed int, signed int, +const int); +@exdent vector unsigned int vec_replace_elt (vector unsigned int, +unsigned int, const int); +@exdent vector float vec_replace_elt (vector float, float, const int); +@exdent vector signed long long vec_replace_elt (vector signed long long, +signed long long, const int); +@exdent vector unsigned long long vec_replace_elt (vector unsigned long long, +unsigned long long, const int); +@exdent vector double rec_replace_elt (vector double, double, const int); +@end smallexample +The third argument (constrained to [0,3]) identifies the natural-endian +element number of the first argument that will be replaced by the second +argument to produce the result. The other elements of the first argument will +remain unchanged in the result. + +If it's desirable to insert a word at an unaligned position, use +vec_replace_unaligned instead. + +@findex vec_replace_element + +Vector Replace Unaligned +@smallexample +@exdent vector unsigned char vec_replace_unaligned (vector unsigned char, +signed int, const int); +@exdent vector unsigned char vec_replace_unaligned (vector unsigned char, +unsigned int, const int); +@exdent vector unsigned char vec_replace_unaligned (vector unsigned char, +float, const int); +@exdent vector unsigned char vec_replace_unaligned (vector unsigned char, +signed long long, const int); +@exdent vector unsigned char vec_replace_unaligned (vector unsigned char, +unsigned long long, const int); +@exdent vector unsigned char vec_replace_unaligned (vector unsigned char, +double, const int); +@end smallexample + +The second argument replaces a portion of the first argument to produce the +result, with the rest of the first argument unchanged in the result. The +third argument identifies the byte index (using left-to-right, or big-endian +order) where the high-order byte of the second argument will be placed, with +the remaining bytes of the second argument placed naturally "to the right" +of the high-order byte. + +The programmer is responsible for understanding the endianness issues involved +with the first argument and the result. +@findex vec_replace_unaligned + +Vector Shift Left Double Bit Immediate +@smallexample +@exdent vector signed char vec_sldb (vector signed char, vector signed char, +const unsigned int); +@exdent vector unsigned char vec_sldb (vector unsigned char, +vector unsigned char, const unsigned int); +@exdent vector signed short vec_sldb (vector signed short, vector signed short, +const unsigned int); +@exdent vector unsigned short vec_sldb (vector unsigned short, +vector unsigned short, const unsigned int); +@exdent vector signed int vec_sldb (vector signed int, vector signed int, +const unsigned int); +@exdent vector unsigned int vec_sldb (vector unsigned int, vector unsigned int, +const unsigned int); +@exdent vector signed long long vec_sldb (vector signed long long, +vector signed long long, const unsigned int); +@exdent vector unsigned long long vec_sldb (vector unsigned long long, +vector unsigned long long, const unsigned int); +@end smallexample + +Shift the combined input vectors left by the amount specified by the low-order +three bits of the third argument, and return the leftmost remaining 128 bits. +Code using this instruction must be endian-aware. + +@findex vec_sldb + +Vector Shift Right Double Bit Immediate + +@smallexample +@exdent vector signed char vec_srdb (vector signed char, vector signed char, +const unsigned int); +@exdent vector unsigned char vec_srdb (vector unsigned char, vector unsigned char, +const unsigned int); +@exdent vector signed short vec_srdb (vector signed short, vector signed short, +const unsigned int); +@exdent vector unsigned short vec_srdb (vector unsigned short, vector unsigned short, +const unsigned int); +@exdent vector signed int vec_srdb (vector signed int, vector signed int, +const unsigned int); +@exdent vector unsigned int vec_srdb (vector unsigned int, vector unsigned int, +const unsigned int); +@exdent vector signed long long vec_srdb (vector signed long long, +vector signed long long, const unsigned int); +@exdent vector unsigned long long vec_srdb (vector unsigned long long, +vector unsigned long long, const unsigned int); +@end smallexample + +Shift the combined input vectors right by the amount specified by the low-order +three bits of the third argument, and return the remaining 128 bits. Code +using this built-in must be endian-aware. + +@findex vec_srdb + +Vector Splat + +@smallexample +@exdent vector signed int vec_splati (const signed int); +@exdent vector float vec_splati (const float); +@end smallexample + +Splat a 32-bit immediate into a vector of words. + +@findex vec_splati + +@smallexample +@exdent vector double vec_splatid (const float); +@end smallexample + +Convert a single precision floating-point value to double-precision and splat +the result to a vector of double-precision floats. + +@findex vec_splatid + +@smallexample +@exdent vector signed int vec_splati_ins (vector signed int, +const unsigned int, const signed int); +@exdent vector unsigned int vec_splati_ins (vector unsigned int, +const unsigned int, const unsigned int); +@exdent vector float vec_splati_ins (vector float, const unsigned int, +const float); +@end smallexample + +Argument 2 must be either 0 or 1. Splat the value of argument 3 into the word +identified by argument 2 of each doubleword of argument 1 and return the +result. The other words of argument 1 are unchanged. + +@findex vec_splati_ins + +Vector Blend Variable + +@smallexample +@exdent vector signed char vec_blendv (vector signed char, vector signed char, +vector unsigned char); +@exdent vector unsigned char vec_blendv (vector unsigned char, +vector unsigned char, vector unsigned char); +@exdent vector signed short vec_blendv (vector signed short, +vector signed short, vector unsigned short); +@exdent vector unsigned short vec_blendv (vector unsigned short, +vector unsigned short, vector unsigned short); +@exdent vector signed int vec_blendv (vector signed int, vector signed int, +vector unsigned int); +@exdent vector unsigned int vec_blendv (vector unsigned int, +vector unsigned int, vector unsigned int); +@exdent vector signed long long vec_blendv (vector signed long long, +vector signed long long, vector unsigned long long); +@exdent vector unsigned long long vec_blendv (vector unsigned long long, +vector unsigned long long, vector unsigned long long); +@exdent vector float vec_blendv (vector float, vector float, +vector unsigned int); +@exdent vector double vec_blendv (vector double, vector double, +vector unsigned long long); +@end smallexample + +Blend the first and second argument vectors according to the sign bits of the +corresponding elements of the third argument vector. This is similar to the +@code{vsel} and @code{xxsel} instructions but for bigger elements. + +@findex vec_blendv + +Vector Permute Extended + +@smallexample +@exdent vector signed char vec_permx (vector signed char, vector signed char, +vector unsigned char, const int); +@exdent vector unsigned char vec_permx (vector unsigned char, +vector unsigned char, vector unsigned char, const int); +@exdent vector signed short vec_permx (vector signed short, +vector signed short, vector unsigned char, const int); +@exdent vector unsigned short vec_permx (vector unsigned short, +vector unsigned short, vector unsigned char, const int); +@exdent vector signed int vec_permx (vector signed int, vector signed int, +vector unsigned char, const int); +@exdent vector unsigned int vec_permx (vector unsigned int, +vector unsigned int, vector unsigned char, const int); +@exdent vector signed long long vec_permx (vector signed long long, +vector signed long long, vector unsigned char, const int); +@exdent vector unsigned long long vec_permx (vector unsigned long long, +vector unsigned long long, vector unsigned char, const int); +@exdent vector float (vector float, vector float, vector unsigned char, +const int); +@exdent vector double (vector double, vector double, vector unsigned char, +const int); +@end smallexample + +Perform a partial permute of the first two arguments, which form a 32-byte +section of an emulated vector up to 256 bytes wide, using the partial permute +control vector in the third argument. The fourth argument (constrained to +values of 0-7) identifies which 32-byte section of the emulated vector is +contained in the first two arguments. +@findex vec_permx + +@smallexample +@exdent vector unsigned long long int +@exdent vec_pext (vector unsigned long long int, vector unsigned long long int); +@end smallexample +Perform a vector parallel bit extract operation, as if implemented by +the @code{vpextd} instruction. +@findex vec_pext + +@smallexample +@exdent vector unsigned char vec_stril (vector unsigned char); +@exdent vector signed char vec_stril (vector signed char); +@exdent vector unsigned short vec_stril (vector unsigned short); +@exdent vector signed short vec_stril (vector signed short); +@end smallexample +Isolate the left-most non-zero elements of the incoming vector argument, +replacing all elements to the right of the left-most zero element +found within the argument with zero. The typical implementation uses +the @code{vstribl} or @code{vstrihl} instruction on big-endian targets +and uses the @code{vstribr} or @code{vstrihr} instruction on +little-endian targets. +@findex vec_stril + +@smallexample +@exdent int vec_stril_p (vector unsigned char); +@exdent int vec_stril_p (vector signed char); +@exdent int short vec_stril_p (vector unsigned short); +@exdent int vec_stril_p (vector signed short); +@end smallexample +Return a non-zero value if and only if the argument contains a zero +element. The typical implementation uses +the @code{vstribl.} or @code{vstrihl.} instruction on big-endian targets +and uses the @code{vstribr.} or @code{vstrihr.} instruction on +little-endian targets. Choose this built-in to check for presence of +zero element if the same argument is also passed to @code{vec_stril}. +@findex vec_stril_p + +@smallexample +@exdent vector unsigned char vec_strir (vector unsigned char); +@exdent vector signed char vec_strir (vector signed char); +@exdent vector unsigned short vec_strir (vector unsigned short); +@exdent vector signed short vec_strir (vector signed short); +@end smallexample +Isolate the right-most non-zero elements of the incoming vector argument, +replacing all elements to the left of the right-most zero element +found within the argument with zero. The typical implementation uses +the @code{vstribr} or @code{vstrihr} instruction on big-endian targets +and uses the @code{vstribl} or @code{vstrihl} instruction on +little-endian targets. +@findex vec_strir + +@smallexample +@exdent int vec_strir_p (vector unsigned char); +@exdent int vec_strir_p (vector signed char); +@exdent int short vec_strir_p (vector unsigned short); +@exdent int vec_strir_p (vector signed short); +@end smallexample +Return a non-zero value if and only if the argument contains a zero +element. The typical implementation uses +the @code{vstribr.} or @code{vstrihr.} instruction on big-endian targets +and uses the @code{vstribl.} or @code{vstrihl.} instruction on +little-endian targets. Choose this built-in to check for presence of +zero element if the same argument is also passed to @code{vec_strir}. +@findex vec_strir_p + +@smallexample +@exdent vector unsigned char +@exdent vec_ternarylogic (vector unsigned char, vector unsigned char, + vector unsigned char, const unsigned int); +@exdent vector unsigned short +@exdent vec_ternarylogic (vector unsigned short, vector unsigned short, + vector unsigned short, const unsigned int); +@exdent vector unsigned int +@exdent vec_ternarylogic (vector unsigned int, vector unsigned int, + vector unsigned int, const unsigned int); +@exdent vector unsigned long long int +@exdent vec_ternarylogic (vector unsigned long long int, vector unsigned long long int, + vector unsigned long long int, const unsigned int); +@exdent vector unsigned __int128 +@exdent vec_ternarylogic (vector unsigned __int128, vector unsigned __int128, + vector unsigned __int128, const unsigned int); +@end smallexample +Perform a 128-bit vector evaluate operation, as if implemented by the +@code{xxeval} instruction. The fourth argument must be a literal +integer value between 0 and 255 inclusive. +@findex vec_ternarylogic + +@smallexample +@exdent vector unsigned char vec_genpcvm (vector unsigned char, const int); +@exdent vector unsigned short vec_genpcvm (vector unsigned short, const int); +@exdent vector unsigned int vec_genpcvm (vector unsigned int, const int); +@exdent vector unsigned int vec_genpcvm (vector unsigned long long int, + const int); +@end smallexample + +Vector Integer Multiply/Divide/Modulo + +@smallexample +@exdent vector signed int +@exdent vec_mulh (vector signed int a, vector signed int b); +@exdent vector unsigned int +@exdent vec_mulh (vector unsigned int a, vector unsigned int b); +@end smallexample + +For each integer value @code{i} from 0 to 3, do the following. The integer +value in word element @code{i} of a is multiplied by the integer value in word +element @code{i} of b. The high-order 32 bits of the 64-bit product are placed +into word element @code{i} of the vector returned. + +@smallexample +@exdent vector signed long long +@exdent vec_mulh (vector signed long long a, vector signed long long b); +@exdent vector unsigned long long +@exdent vec_mulh (vector unsigned long long a, vector unsigned long long b); +@end smallexample + +For each integer value @code{i} from 0 to 1, do the following. The integer +value in doubleword element @code{i} of a is multiplied by the integer value in +doubleword element @code{i} of b. The high-order 64 bits of the 128-bit product +are placed into doubleword element @code{i} of the vector returned. + +@smallexample +@exdent vector unsigned long long +@exdent vec_mul (vector unsigned long long a, vector unsigned long long b); +@exdent vector signed long long +@exdent vec_mul (vector signed long long a, vector signed long long b); +@end smallexample + +For each integer value @code{i} from 0 to 1, do the following. The integer +value in doubleword element @code{i} of a is multiplied by the integer value in +doubleword element @code{i} of b. The low-order 64 bits of the 128-bit product +are placed into doubleword element @code{i} of the vector returned. + +@smallexample +@exdent vector signed int +@exdent vec_div (vector signed int a, vector signed int b); +@exdent vector unsigned int +@exdent vec_div (vector unsigned int a, vector unsigned int b); +@end smallexample + +For each integer value @code{i} from 0 to 3, do the following. The integer in +word element @code{i} of a is divided by the integer in word element @code{i} +of b. The unique integer quotient is placed into the word element @code{i} of +the vector returned. If an attempt is made to perform any of the divisions + ÷ 0 then the quotient is undefined. + +@smallexample +@exdent vector signed long long +@exdent vec_div (vector signed long long a, vector signed long long b); +@exdent vector unsigned long long +@exdent vec_div (vector unsigned long long a, vector unsigned long long b); +@end smallexample + +For each integer value @code{i} from 0 to 1, do the following. The integer in +doubleword element @code{i} of a is divided by the integer in doubleword +element @code{i} of b. The unique integer quotient is placed into the +doubleword element @code{i} of the vector returned. If an attempt is made to +perform any of the divisions 0x8000_0000_0000_0000 ÷ -1 or ÷ 0 then +the quotient is undefined. + +@smallexample +@exdent vector signed int +@exdent vec_dive (vector signed int a, vector signed int b); +@exdent vector unsigned int +@exdent vec_dive (vector unsigned int a, vector unsigned int b); +@end smallexample + +For each integer value @code{i} from 0 to 3, do the following. The integer in +word element @code{i} of a is shifted left by 32 bits, then divided by the +integer in word element @code{i} of b. The unique integer quotient is placed +into the word element @code{i} of the vector returned. If the quotient cannot +be represented in 32 bits, or if an attempt is made to perform any of the +divisions ÷ 0 then the quotient is undefined. + +@smallexample +@exdent vector signed long long +@exdent vec_dive (vector signed long long a, vector signed long long b); +@exdent vector unsigned long long +@exdent vec_dive (vector unsigned long long a, vector unsigned long long b); +@end smallexample + +For each integer value @code{i} from 0 to 1, do the following. The integer in +doubleword element @code{i} of a is shifted left by 64 bits, then divided by +the integer in doubleword element @code{i} of b. The unique integer quotient is +placed into the doubleword element @code{i} of the vector returned. If the +quotient cannot be represented in 64 bits, or if an attempt is made to perform + ÷ 0 then the quotient is undefined. + +@smallexample +@exdent vector signed int +@exdent vec_mod (vector signed int a, vector signed int b); +@exdent vector unsigned int +@exdent vec_mod (vector unsigned int a, vector unsigned int b); +@end smallexample + +For each integer value @code{i} from 0 to 3, do the following. The integer in +word element @code{i} of a is divided by the integer in word element @code{i} +of b. The unique integer remainder is placed into the word element @code{i} of +the vector returned. If an attempt is made to perform any of the divisions +0x8000_0000 ÷ -1 or ÷ 0 then the remainder is undefined. + +@smallexample +@exdent vector signed long long +@exdent vec_mod (vector signed long long a, vector signed long long b); +@exdent vector unsigned long long +@exdent vec_mod (vector unsigned long long a, vector unsigned long long b); +@end smallexample + +For each integer value @code{i} from 0 to 1, do the following. The integer in +doubleword element @code{i} of a is divided by the integer in doubleword +element @code{i} of b. The unique integer remainder is placed into the +doubleword element @code{i} of the vector returned. If an attempt is made to +perform ÷ 0 then the remainder is undefined. + +Generate PCV from specified Mask size, as if implemented by the +@code{xxgenpcvbm}, @code{xxgenpcvhm}, @code{xxgenpcvwm} instructions, where +immediate value is either 0, 1, 2 or 3. +@findex vec_genpcvm + +@smallexample +@exdent vector unsigned __int128 vec_rl (vector unsigned __int128 A, + vector unsigned __int128 B); +@exdent vector signed __int128 vec_rl (vector signed __int128 A, + vector unsigned __int128 B); +@end smallexample + +Result value: Each element of R is obtained by rotating the corresponding element +of A left by the number of bits specified by the corresponding element of B. + + +@smallexample +@exdent vector unsigned __int128 vec_rlmi (vector unsigned __int128, + vector unsigned __int128, + vector unsigned __int128); +@exdent vector signed __int128 vec_rlmi (vector signed __int128, + vector signed __int128, + vector unsigned __int128); +@end smallexample + +Returns the result of rotating the first input and inserting it under mask +into the second input. The first bit in the mask, the last bit in the mask are +obtained from the two 7-bit fields bits [108:115] and bits [117:123] +respectively of the second input. The shift is obtained from the third input +in the 7-bit field [125:131] where all bits counted from zero at the left. + +@smallexample +@exdent vector unsigned __int128 vec_rlnm (vector unsigned __int128, + vector unsigned __int128, + vector unsigned __int128); +@exdent vector signed __int128 vec_rlnm (vector signed __int128, + vector unsigned __int128, + vector unsigned __int128); +@end smallexample + +Returns the result of rotating the first input and ANDing it with a mask. The +first bit in the mask and the last bit in the mask are obtained from the two +7-bit fields bits [117:123] and bits [125:131] respectively of the second +input. The shift is obtained from the third input in the 7-bit field bits +[125:131] where all bits counted from zero at the left. + +@smallexample +@exdent vector unsigned __int128 vec_sl(vector unsigned __int128 A, vector unsigned __int128 B); +@exdent vector signed __int128 vec_sl(vector signed __int128 A, vector unsigned __int128 B); +@end smallexample + +Result value: Each element of R is obtained by shifting the corresponding element of +A left by the number of bits specified by the corresponding element of B. + +@smallexample +@exdent vector unsigned __int128 vec_sr(vector unsigned __int128 A, vector unsigned __int128 B); +@exdent vector signed __int128 vec_sr(vector signed __int128 A, vector unsigned __int128 B); +@end smallexample + +Result value: Each element of R is obtained by shifting the corresponding element of +A right by the number of bits specified by the corresponding element of B. + +@smallexample +@exdent vector unsigned __int128 vec_sra(vector unsigned __int128 A, vector unsigned __int128 B); +@exdent vector signed __int128 vec_sra(vector signed __int128 A, vector unsigned __int128 B); +@end smallexample + +Result value: Each element of R is obtained by arithmetic shifting the corresponding +element of A right by the number of bits specified by the corresponding element of B. + +@smallexample +@exdent vector unsigned __int128 vec_mule (vector unsigned long long, + vector unsigned long long); +@exdent vector signed __int128 vec_mule (vector signed long long, + vector signed long long); +@end smallexample + +Returns a vector containing a 128-bit integer result of multiplying the even +doubleword elements of the two inputs. + +@smallexample +@exdent vector unsigned __int128 vec_mulo (vector unsigned long long, + vector unsigned long long); +@exdent vector signed __int128 vec_mulo (vector signed long long, + vector signed long long); +@end smallexample + +Returns a vector containing a 128-bit integer result of multiplying the odd +doubleword elements of the two inputs. + +@smallexample +@exdent vector unsigned __int128 vec_div (vector unsigned __int128, + vector unsigned __int128); +@exdent vector signed __int128 vec_div (vector signed __int128, + vector signed __int128); +@end smallexample + +Returns the result of dividing the first operand by the second operand. An +attempt to divide any value by zero or to divide the most negative signed +128-bit integer by negative one results in an undefined value. + +@smallexample +@exdent vector unsigned __int128 vec_dive (vector unsigned __int128, + vector unsigned __int128); +@exdent vector signed __int128 vec_dive (vector signed __int128, + vector signed __int128); +@end smallexample + +The result is produced by shifting the first input left by 128 bits and +dividing by the second. If an attempt is made to divide by zero or the result +is larger than 128 bits, the result is undefined. + +@smallexample +@exdent vector unsigned __int128 vec_mod (vector unsigned __int128, + vector unsigned __int128); +@exdent vector signed __int128 vec_mod (vector signed __int128, + vector signed __int128); +@end smallexample + +The result is the modulo result of dividing the first input by the second +input. + +The following builtins perform 128-bit vector comparisons. The +@code{vec_all_xx}, @code{vec_any_xx}, and @code{vec_cmpxx}, where @code{xx} is +one of the operations @code{eq, ne, gt, lt, ge, le} perform pairwise +comparisons between the elements at the same positions within their two vector +arguments. The @code{vec_all_xx}function returns a non-zero value if and only +if all pairwise comparisons are true. The @code{vec_any_xx} function returns +a non-zero value if and only if at least one pairwise comparison is true. The +@code{vec_cmpxx}function returns a vector of the same type as its two +arguments, within which each element consists of all ones to denote that +specified logical comparison of the corresponding elements was true. +Otherwise, the element of the returned vector contains all zeros. + +@smallexample +vector bool __int128 vec_cmpeq (vector signed __int128, vector signed __int128); +vector bool __int128 vec_cmpeq (vector unsigned __int128, vector unsigned __int128); +vector bool __int128 vec_cmpne (vector signed __int128, vector signed __int128); +vector bool __int128 vec_cmpne (vector unsigned __int128, vector unsigned __int128); +vector bool __int128 vec_cmpgt (vector signed __int128, vector signed __int128); +vector bool __int128 vec_cmpgt (vector unsigned __int128, vector unsigned __int128); +vector bool __int128 vec_cmplt (vector signed __int128, vector signed __int128); +vector bool __int128 vec_cmplt (vector unsigned __int128, vector unsigned __int128); +vector bool __int128 vec_cmpge (vector signed __int128, vector signed __int128); +vector bool __int128 vec_cmpge (vector unsigned __int128, vector unsigned __int128); +vector bool __int128 vec_cmple (vector signed __int128, vector signed __int128); +vector bool __int128 vec_cmple (vector unsigned __int128, vector unsigned __int128); + +int vec_all_eq (vector signed __int128, vector signed __int128); +int vec_all_eq (vector unsigned __int128, vector unsigned __int128); +int vec_all_ne (vector signed __int128, vector signed __int128); +int vec_all_ne (vector unsigned __int128, vector unsigned __int128); +int vec_all_gt (vector signed __int128, vector signed __int128); +int vec_all_gt (vector unsigned __int128, vector unsigned __int128); +int vec_all_lt (vector signed __int128, vector signed __int128); +int vec_all_lt (vector unsigned __int128, vector unsigned __int128); +int vec_all_ge (vector signed __int128, vector signed __int128); +int vec_all_ge (vector unsigned __int128, vector unsigned __int128); +int vec_all_le (vector signed __int128, vector signed __int128); +int vec_all_le (vector unsigned __int128, vector unsigned __int128); + +int vec_any_eq (vector signed __int128, vector signed __int128); +int vec_any_eq (vector unsigned __int128, vector unsigned __int128); +int vec_any_ne (vector signed __int128, vector signed __int128); +int vec_any_ne (vector unsigned __int128, vector unsigned __int128); +int vec_any_gt (vector signed __int128, vector signed __int128); +int vec_any_gt (vector unsigned __int128, vector unsigned __int128); +int vec_any_lt (vector signed __int128, vector signed __int128); +int vec_any_lt (vector unsigned __int128, vector unsigned __int128); +int vec_any_ge (vector signed __int128, vector signed __int128); +int vec_any_ge (vector unsigned __int128, vector unsigned __int128); +int vec_any_le (vector signed __int128, vector signed __int128); +int vec_any_le (vector unsigned __int128, vector unsigned __int128); +@end smallexample + + +@node PowerPC Hardware Transactional Memory Built-in Functions +@subsection PowerPC Hardware Transactional Memory Built-in Functions +GCC provides two interfaces for accessing the Hardware Transactional +Memory (HTM) instructions available on some of the PowerPC family +of processors (eg, POWER8). The two interfaces come in a low level +interface, consisting of built-in functions specific to PowerPC and a +higher level interface consisting of inline functions that are common +between PowerPC and S/390. + +@subsubsection PowerPC HTM Low Level Built-in Functions + +The following low level built-in functions are available with +@option{-mhtm} or @option{-mcpu=CPU} where CPU is `power8' or later. +They all generate the machine instruction that is part of the name. + +The HTM builtins (with the exception of @code{__builtin_tbegin}) return +the full 4-bit condition register value set by their associated hardware +instruction. The header file @code{htmintrin.h} defines some macros that can +be used to decipher the return value. The @code{__builtin_tbegin} builtin +returns a simple @code{true} or @code{false} value depending on whether a transaction was +successfully started or not. The arguments of the builtins match exactly the +type and order of the associated hardware instruction's operands, except for +the @code{__builtin_tcheck} builtin, which does not take any input arguments. +Refer to the ISA manual for a description of each instruction's operands. + +@smallexample +unsigned int __builtin_tbegin (unsigned int); +unsigned int __builtin_tend (unsigned int); + +unsigned int __builtin_tabort (unsigned int); +unsigned int __builtin_tabortdc (unsigned int, unsigned int, unsigned int); +unsigned int __builtin_tabortdci (unsigned int, unsigned int, int); +unsigned int __builtin_tabortwc (unsigned int, unsigned int, unsigned int); +unsigned int __builtin_tabortwci (unsigned int, unsigned int, int); + +unsigned int __builtin_tcheck (void); +unsigned int __builtin_treclaim (unsigned int); +unsigned int __builtin_trechkpt (void); +unsigned int __builtin_tsr (unsigned int); +@end smallexample + +In addition to the above HTM built-ins, we have added built-ins for +some common extended mnemonics of the HTM instructions: + +@smallexample +unsigned int __builtin_tendall (void); +unsigned int __builtin_tresume (void); +unsigned int __builtin_tsuspend (void); +@end smallexample + +Note that the semantics of the above HTM builtins are required to mimic +the locking semantics used for critical sections. Builtins that are used +to create a new transaction or restart a suspended transaction must have +lock acquisition like semantics while those builtins that end or suspend a +transaction must have lock release like semantics. Specifically, this must +mimic lock semantics as specified by C++11, for example: Lock acquisition is +as-if an execution of __atomic_exchange_n(&globallock,1,__ATOMIC_ACQUIRE) +that returns 0, and lock release is as-if an execution of +__atomic_store(&globallock,0,__ATOMIC_RELEASE), with globallock being an +implicit implementation-defined lock used for all transactions. The HTM +instructions associated with with the builtins inherently provide the +correct acquisition and release hardware barriers required. However, +the compiler must also be prohibited from moving loads and stores across +the builtins in a way that would violate their semantics. This has been +accomplished by adding memory barriers to the associated HTM instructions +(which is a conservative approach to provide acquire and release semantics). +Earlier versions of the compiler did not treat the HTM instructions as +memory barriers. A @code{__TM_FENCE__} macro has been added, which can +be used to determine whether the current compiler treats HTM instructions +as memory barriers or not. This allows the user to explicitly add memory +barriers to their code when using an older version of the compiler. + +The following set of built-in functions are available to gain access +to the HTM specific special purpose registers. + +@smallexample +unsigned long __builtin_get_texasr (void); +unsigned long __builtin_get_texasru (void); +unsigned long __builtin_get_tfhar (void); +unsigned long __builtin_get_tfiar (void); + +void __builtin_set_texasr (unsigned long); +void __builtin_set_texasru (unsigned long); +void __builtin_set_tfhar (unsigned long); +void __builtin_set_tfiar (unsigned long); +@end smallexample + +Example usage of these low level built-in functions may look like: + +@smallexample +#include + +int num_retries = 10; + +while (1) + @{ + if (__builtin_tbegin (0)) + @{ + /* Transaction State Initiated. */ + if (is_locked (lock)) + __builtin_tabort (0); + ... transaction code... + __builtin_tend (0); + break; + @} + else + @{ + /* Transaction State Failed. Use locks if the transaction + failure is "persistent" or we've tried too many times. */ + if (num_retries-- <= 0 + || _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ())) + @{ + acquire_lock (lock); + ... non transactional fallback path... + release_lock (lock); + break; + @} + @} + @} +@end smallexample + +One final built-in function has been added that returns the value of +the 2-bit Transaction State field of the Machine Status Register (MSR) +as stored in @code{CR0}. + +@smallexample +unsigned long __builtin_ttest (void) +@end smallexample + +This built-in can be used to determine the current transaction state +using the following code example: + +@smallexample +#include + +unsigned char tx_state = _HTM_STATE (__builtin_ttest ()); + +if (tx_state == _HTM_TRANSACTIONAL) + @{ + /* Code to use in transactional state. */ + @} +else if (tx_state == _HTM_NONTRANSACTIONAL) + @{ + /* Code to use in non-transactional state. */ + @} +else if (tx_state == _HTM_SUSPENDED) + @{ + /* Code to use in transaction suspended state. */ + @} +@end smallexample + +@subsubsection PowerPC HTM High Level Inline Functions + +The following high level HTM interface is made available by including +@code{} and using @option{-mhtm} or @option{-mcpu=CPU} +where CPU is `power8' or later. This interface is common between PowerPC +and S/390, allowing users to write one HTM source implementation that +can be compiled and executed on either system. + +@smallexample +long __TM_simple_begin (void); +long __TM_begin (void* const TM_buff); +long __TM_end (void); +void __TM_abort (void); +void __TM_named_abort (unsigned char const code); +void __TM_resume (void); +void __TM_suspend (void); + +long __TM_is_user_abort (void* const TM_buff); +long __TM_is_named_user_abort (void* const TM_buff, unsigned char *code); +long __TM_is_illegal (void* const TM_buff); +long __TM_is_footprint_exceeded (void* const TM_buff); +long __TM_nesting_depth (void* const TM_buff); +long __TM_is_nested_too_deep(void* const TM_buff); +long __TM_is_conflict(void* const TM_buff); +long __TM_is_failure_persistent(void* const TM_buff); +long __TM_failure_address(void* const TM_buff); +long long __TM_failure_code(void* const TM_buff); +@end smallexample + +Using these common set of HTM inline functions, we can create +a more portable version of the HTM example in the previous +section that will work on either PowerPC or S/390: + +@smallexample +#include + +int num_retries = 10; +TM_buff_type TM_buff; + +while (1) + @{ + if (__TM_begin (TM_buff) == _HTM_TBEGIN_STARTED) + @{ + /* Transaction State Initiated. */ + if (is_locked (lock)) + __TM_abort (); + ... transaction code... + __TM_end (); + break; + @} + else + @{ + /* Transaction State Failed. Use locks if the transaction + failure is "persistent" or we've tried too many times. */ + if (num_retries-- <= 0 + || __TM_is_failure_persistent (TM_buff)) + @{ + acquire_lock (lock); + ... non transactional fallback path... + release_lock (lock); + break; + @} + @} + @} +@end smallexample + +@node PowerPC Atomic Memory Operation Functions +@subsection PowerPC Atomic Memory Operation Functions +ISA 3.0 of the PowerPC added new atomic memory operation (amo) +instructions. GCC provides support for these instructions in 64-bit +environments. All of the functions are declared in the include file +@code{amo.h}. + +The functions supported are: + +@smallexample +#include + +uint32_t amo_lwat_add (uint32_t *, uint32_t); +uint32_t amo_lwat_xor (uint32_t *, uint32_t); +uint32_t amo_lwat_ior (uint32_t *, uint32_t); +uint32_t amo_lwat_and (uint32_t *, uint32_t); +uint32_t amo_lwat_umax (uint32_t *, uint32_t); +uint32_t amo_lwat_umin (uint32_t *, uint32_t); +uint32_t amo_lwat_swap (uint32_t *, uint32_t); + +int32_t amo_lwat_sadd (int32_t *, int32_t); +int32_t amo_lwat_smax (int32_t *, int32_t); +int32_t amo_lwat_smin (int32_t *, int32_t); +int32_t amo_lwat_sswap (int32_t *, int32_t); + +uint64_t amo_ldat_add (uint64_t *, uint64_t); +uint64_t amo_ldat_xor (uint64_t *, uint64_t); +uint64_t amo_ldat_ior (uint64_t *, uint64_t); +uint64_t amo_ldat_and (uint64_t *, uint64_t); +uint64_t amo_ldat_umax (uint64_t *, uint64_t); +uint64_t amo_ldat_umin (uint64_t *, uint64_t); +uint64_t amo_ldat_swap (uint64_t *, uint64_t); + +int64_t amo_ldat_sadd (int64_t *, int64_t); +int64_t amo_ldat_smax (int64_t *, int64_t); +int64_t amo_ldat_smin (int64_t *, int64_t); +int64_t amo_ldat_sswap (int64_t *, int64_t); + +void amo_stwat_add (uint32_t *, uint32_t); +void amo_stwat_xor (uint32_t *, uint32_t); +void amo_stwat_ior (uint32_t *, uint32_t); +void amo_stwat_and (uint32_t *, uint32_t); +void amo_stwat_umax (uint32_t *, uint32_t); +void amo_stwat_umin (uint32_t *, uint32_t); + +void amo_stwat_sadd (int32_t *, int32_t); +void amo_stwat_smax (int32_t *, int32_t); +void amo_stwat_smin (int32_t *, int32_t); + +void amo_stdat_add (uint64_t *, uint64_t); +void amo_stdat_xor (uint64_t *, uint64_t); +void amo_stdat_ior (uint64_t *, uint64_t); +void amo_stdat_and (uint64_t *, uint64_t); +void amo_stdat_umax (uint64_t *, uint64_t); +void amo_stdat_umin (uint64_t *, uint64_t); + +void amo_stdat_sadd (int64_t *, int64_t); +void amo_stdat_smax (int64_t *, int64_t); +void amo_stdat_smin (int64_t *, int64_t); +@end smallexample + +@node PowerPC Matrix-Multiply Assist Built-in Functions +@subsection PowerPC Matrix-Multiply Assist Built-in Functions +ISA 3.1 of the PowerPC added new Matrix-Multiply Assist (MMA) instructions. +GCC provides support for these instructions through the following built-in +functions which are enabled with the @code{-mmma} option. The vec_t type +below is defined to be a normal vector unsigned char type. The uint2, uint4 +and uint8 parameters are 2-bit, 4-bit and 8-bit unsigned integer constants +respectively. The compiler will verify that they are constants and that +their values are within range. + +The built-in functions supported are: + +@smallexample +void __builtin_mma_xvi4ger8 (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvi8ger4 (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvi16ger2 (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvi16ger2s (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf16ger2 (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvbf16ger2 (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf32ger (__vector_quad *, vec_t, vec_t); + +void __builtin_mma_xvi4ger8pp (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvi8ger4pp (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvi8ger4spp(__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvi16ger2pp (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvi16ger2spp (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf16ger2pp (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf16ger2pn (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf16ger2np (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf16ger2nn (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvbf16ger2pp (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvbf16ger2pn (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvbf16ger2np (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvbf16ger2nn (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf32gerpp (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf32gerpn (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf32gernp (__vector_quad *, vec_t, vec_t); +void __builtin_mma_xvf32gernn (__vector_quad *, vec_t, vec_t); + +void __builtin_mma_pmxvi4ger8 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint8); +void __builtin_mma_pmxvi4ger8pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint8); + +void __builtin_mma_pmxvi8ger4 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint4); +void __builtin_mma_pmxvi8ger4pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint4); +void __builtin_mma_pmxvi8ger4spp(__vector_quad *, vec_t, vec_t, uint4, uint4, uint4); + +void __builtin_mma_pmxvi16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvi16ger2s (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvf16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvbf16ger2 (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); + +void __builtin_mma_pmxvi16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvi16ger2spp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvf16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvf16ger2pn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvf16ger2np (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvf16ger2nn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvbf16ger2pp (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvbf16ger2pn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvbf16ger2np (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); +void __builtin_mma_pmxvbf16ger2nn (__vector_quad *, vec_t, vec_t, uint4, uint4, uint2); + +void __builtin_mma_pmxvf32ger (__vector_quad *, vec_t, vec_t, uint4, uint4); +void __builtin_mma_pmxvf32gerpp (__vector_quad *, vec_t, vec_t, uint4, uint4); +void __builtin_mma_pmxvf32gerpn (__vector_quad *, vec_t, vec_t, uint4, uint4); +void __builtin_mma_pmxvf32gernp (__vector_quad *, vec_t, vec_t, uint4, uint4); +void __builtin_mma_pmxvf32gernn (__vector_quad *, vec_t, vec_t, uint4, uint4); + +void __builtin_mma_xvf64ger (__vector_quad *, __vector_pair, vec_t); +void __builtin_mma_xvf64gerpp (__vector_quad *, __vector_pair, vec_t); +void __builtin_mma_xvf64gerpn (__vector_quad *, __vector_pair, vec_t); +void __builtin_mma_xvf64gernp (__vector_quad *, __vector_pair, vec_t); +void __builtin_mma_xvf64gernn (__vector_quad *, __vector_pair, vec_t); + +void __builtin_mma_pmxvf64ger (__vector_quad *, __vector_pair, vec_t, uint4, uint2); +void __builtin_mma_pmxvf64gerpp (__vector_quad *, __vector_pair, vec_t, uint4, uint2); +void __builtin_mma_pmxvf64gerpn (__vector_quad *, __vector_pair, vec_t, uint4, uint2); +void __builtin_mma_pmxvf64gernp (__vector_quad *, __vector_pair, vec_t, uint4, uint2); +void __builtin_mma_pmxvf64gernn (__vector_quad *, __vector_pair, vec_t, uint4, uint2); + +void __builtin_mma_xxmtacc (__vector_quad *); +void __builtin_mma_xxmfacc (__vector_quad *); +void __builtin_mma_xxsetaccz (__vector_quad *); + +void __builtin_mma_build_acc (__vector_quad *, vec_t, vec_t, vec_t, vec_t); +void __builtin_mma_disassemble_acc (void *, __vector_quad *); + +void __builtin_vsx_build_pair (__vector_pair *, vec_t, vec_t); +void __builtin_vsx_disassemble_pair (void *, __vector_pair *); + +vec_t __builtin_vsx_xvcvspbf16 (vec_t); +vec_t __builtin_vsx_xvcvbf16spn (vec_t); + +__vector_pair __builtin_vsx_lxvp (size_t, __vector_pair *); +void __builtin_vsx_stxvp (__vector_pair, size_t, __vector_pair *); +@end smallexample + +@node PRU Built-in Functions +@subsection PRU Built-in Functions + +GCC provides a couple of special builtin functions to aid in utilizing +special PRU instructions. + +The built-in functions supported are: + +@table @code +@item __delay_cycles (long long @var{cycles}) +This inserts an instruction sequence that takes exactly @var{cycles} +cycles (between 0 and 0xffffffff) to complete. The inserted sequence +may use jumps, loops, or no-ops, and does not interfere with any other +instructions. Note that @var{cycles} must be a compile-time constant +integer - that is, you must pass a number, not a variable that may be +optimized to a constant later. The number of cycles delayed by this +builtin is exact. + +@item __halt (void) +This inserts a HALT instruction to stop processor execution. + +@item unsigned int __lmbd (unsigned int @var{wordval}, unsigned int @var{bitval}) +This inserts LMBD instruction to calculate the left-most bit with value +@var{bitval} in value @var{wordval}. Only the least significant bit +of @var{bitval} is taken into account. +@end table + +@node RISC-V Built-in Functions +@subsection RISC-V Built-in Functions + +These built-in functions are available for the RISC-V family of +processors. + +@deftypefn {Built-in Function} {void *} __builtin_thread_pointer (void) +Returns the value that is currently set in the @samp{tp} register. +@end deftypefn + +@node RX Built-in Functions +@subsection RX Built-in Functions +GCC supports some of the RX instructions which cannot be expressed in +the C programming language via the use of built-in functions. The +following functions are supported: + +@deftypefn {Built-in Function} void __builtin_rx_brk (void) +Generates the @code{brk} machine instruction. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_clrpsw (int) +Generates the @code{clrpsw} machine instruction to clear the specified +bit in the processor status word. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_int (int) +Generates the @code{int} machine instruction to generate an interrupt +with the specified value. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_machi (int, int) +Generates the @code{machi} machine instruction to add the result of +multiplying the top 16 bits of the two arguments into the +accumulator. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_maclo (int, int) +Generates the @code{maclo} machine instruction to add the result of +multiplying the bottom 16 bits of the two arguments into the +accumulator. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_mulhi (int, int) +Generates the @code{mulhi} machine instruction to place the result of +multiplying the top 16 bits of the two arguments into the +accumulator. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_mullo (int, int) +Generates the @code{mullo} machine instruction to place the result of +multiplying the bottom 16 bits of the two arguments into the +accumulator. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_rx_mvfachi (void) +Generates the @code{mvfachi} machine instruction to read the top +32 bits of the accumulator. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_rx_mvfacmi (void) +Generates the @code{mvfacmi} machine instruction to read the middle +32 bits of the accumulator. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_rx_mvfc (int) +Generates the @code{mvfc} machine instruction which reads the control +register specified in its argument and returns its value. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_mvtachi (int) +Generates the @code{mvtachi} machine instruction to set the top +32 bits of the accumulator. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_mvtaclo (int) +Generates the @code{mvtaclo} machine instruction to set the bottom +32 bits of the accumulator. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_mvtc (int reg, int val) +Generates the @code{mvtc} machine instruction which sets control +register number @code{reg} to @code{val}. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_mvtipl (int) +Generates the @code{mvtipl} machine instruction set the interrupt +priority level. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_racw (int) +Generates the @code{racw} machine instruction to round the accumulator +according to the specified mode. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_rx_revw (int) +Generates the @code{revw} machine instruction which swaps the bytes in +the argument so that bits 0--7 now occupy bits 8--15 and vice versa, +and also bits 16--23 occupy bits 24--31 and vice versa. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_rmpa (void) +Generates the @code{rmpa} machine instruction which initiates a +repeated multiply and accumulate sequence. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_round (float) +Generates the @code{round} machine instruction which returns the +floating-point argument rounded according to the current rounding mode +set in the floating-point status word register. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_rx_sat (int) +Generates the @code{sat} machine instruction which returns the +saturated value of the argument. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_setpsw (int) +Generates the @code{setpsw} machine instruction to set the specified +bit in the processor status word. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_rx_wait (void) +Generates the @code{wait} machine instruction. +@end deftypefn + +@node S/390 System z Built-in Functions +@subsection S/390 System z Built-in Functions +@deftypefn {Built-in Function} int __builtin_tbegin (void*) +Generates the @code{tbegin} machine instruction starting a +non-constrained hardware transaction. If the parameter is non-NULL the +memory area is used to store the transaction diagnostic buffer and +will be passed as first operand to @code{tbegin}. This buffer can be +defined using the @code{struct __htm_tdb} C struct defined in +@code{htmintrin.h} and must reside on a double-word boundary. The +second tbegin operand is set to @code{0xff0c}. This enables +save/restore of all GPRs and disables aborts for FPR and AR +manipulations inside the transaction body. The condition code set by +the tbegin instruction is returned as integer value. The tbegin +instruction by definition overwrites the content of all FPRs. The +compiler will generate code which saves and restores the FPRs. For +soft-float code it is recommended to used the @code{*_nofloat} +variant. In order to prevent a TDB from being written it is required +to pass a constant zero value as parameter. Passing a zero value +through a variable is not sufficient. Although modifications of +access registers inside the transaction will not trigger an +transaction abort it is not supported to actually modify them. Access +registers do not get saved when entering a transaction. They will have +undefined state when reaching the abort code. +@end deftypefn + +Macros for the possible return codes of tbegin are defined in the +@code{htmintrin.h} header file: + +@table @code +@item _HTM_TBEGIN_STARTED +@code{tbegin} has been executed as part of normal processing. The +transaction body is supposed to be executed. +@item _HTM_TBEGIN_INDETERMINATE +The transaction was aborted due to an indeterminate condition which +might be persistent. +@item _HTM_TBEGIN_TRANSIENT +The transaction aborted due to a transient failure. The transaction +should be re-executed in that case. +@item _HTM_TBEGIN_PERSISTENT +The transaction aborted due to a persistent failure. Re-execution +under same circumstances will not be productive. +@end table + +@defmac _HTM_FIRST_USER_ABORT_CODE +The @code{_HTM_FIRST_USER_ABORT_CODE} defined in @code{htmintrin.h} +specifies the first abort code which can be used for +@code{__builtin_tabort}. Values below this threshold are reserved for +machine use. +@end defmac + +@deftp {Data type} {struct __htm_tdb} +The @code{struct __htm_tdb} defined in @code{htmintrin.h} describes +the structure of the transaction diagnostic block as specified in the +Principles of Operation manual chapter 5-91. +@end deftp + +@deftypefn {Built-in Function} int __builtin_tbegin_nofloat (void*) +Same as @code{__builtin_tbegin} but without FPR saves and restores. +Using this variant in code making use of FPRs will leave the FPRs in +undefined state when entering the transaction abort handler code. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_tbegin_retry (void*, int) +In addition to @code{__builtin_tbegin} a loop for transient failures +is generated. If tbegin returns a condition code of 2 the transaction +will be retried as often as specified in the second argument. The +perform processor assist instruction is used to tell the CPU about the +number of fails so far. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_tbegin_retry_nofloat (void*, int) +Same as @code{__builtin_tbegin_retry} but without FPR saves and +restores. Using this variant in code making use of FPRs will leave +the FPRs in undefined state when entering the transaction abort +handler code. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_tbeginc (void) +Generates the @code{tbeginc} machine instruction starting a constrained +hardware transaction. The second operand is set to @code{0xff08}. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_tend (void) +Generates the @code{tend} machine instruction finishing a transaction +and making the changes visible to other threads. The condition code +generated by tend is returned as integer value. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_tabort (int) +Generates the @code{tabort} machine instruction with the specified +abort code. Abort codes from 0 through 255 are reserved and will +result in an error message. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_tx_assist (int) +Generates the @code{ppa rX,rY,1} machine instruction. Where the +integer parameter is loaded into rX and a value of zero is loaded into +rY. The integer parameter specifies the number of times the +transaction repeatedly aborted. +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_tx_nesting_depth (void) +Generates the @code{etnd} machine instruction. The current nesting +depth is returned as integer value. For a nesting depth of 0 the code +is not executed as part of an transaction. +@end deftypefn + +@deftypefn {Built-in Function} void __builtin_non_tx_store (uint64_t *, uint64_t) + +Generates the @code{ntstg} machine instruction. The second argument +is written to the first arguments location. The store operation will +not be rolled-back in case of an transaction abort. +@end deftypefn + +@node SH Built-in Functions +@subsection SH Built-in Functions +The following built-in functions are supported on the SH1, SH2, SH3 and SH4 +families of processors: + +@deftypefn {Built-in Function} {void} __builtin_set_thread_pointer (void *@var{ptr}) +Sets the @samp{GBR} register to the specified value @var{ptr}. This is usually +used by system code that manages threads and execution contexts. The compiler +normally does not generate code that modifies the contents of @samp{GBR} and +thus the value is preserved across function calls. Changing the @samp{GBR} +value in user code must be done with caution, since the compiler might use +@samp{GBR} in order to access thread local variables. + +@end deftypefn + +@deftypefn {Built-in Function} {void *} __builtin_thread_pointer (void) +Returns the value that is currently set in the @samp{GBR} register. +Memory loads and stores that use the thread pointer as a base address are +turned into @samp{GBR} based displacement loads and stores, if possible. +For example: +@smallexample +struct my_tcb +@{ + int a, b, c, d, e; +@}; + +int get_tcb_value (void) +@{ + // Generate @samp{mov.l @@(8,gbr),r0} instruction + return ((my_tcb*)__builtin_thread_pointer ())->c; +@} + +@end smallexample +@end deftypefn + +@deftypefn {Built-in Function} {unsigned int} __builtin_sh_get_fpscr (void) +Returns the value that is currently set in the @samp{FPSCR} register. +@end deftypefn + +@deftypefn {Built-in Function} {void} __builtin_sh_set_fpscr (unsigned int @var{val}) +Sets the @samp{FPSCR} register to the specified value @var{val}, while +preserving the current values of the FR, SZ and PR bits. +@end deftypefn + +@node SPARC VIS Built-in Functions +@subsection SPARC VIS Built-in Functions + +GCC supports SIMD operations on the SPARC using both the generic vector +extensions (@pxref{Vector Extensions}) as well as built-in functions for +the SPARC Visual Instruction Set (VIS). When you use the @option{-mvis} +switch, the VIS extension is exposed as the following built-in functions: + +@smallexample +typedef int v1si __attribute__ ((vector_size (4))); +typedef int v2si __attribute__ ((vector_size (8))); +typedef short v4hi __attribute__ ((vector_size (8))); +typedef short v2hi __attribute__ ((vector_size (4))); +typedef unsigned char v8qi __attribute__ ((vector_size (8))); +typedef unsigned char v4qi __attribute__ ((vector_size (4))); + +void __builtin_vis_write_gsr (int64_t); +int64_t __builtin_vis_read_gsr (void); + +void * __builtin_vis_alignaddr (void *, long); +void * __builtin_vis_alignaddrl (void *, long); +int64_t __builtin_vis_faligndatadi (int64_t, int64_t); +v2si __builtin_vis_faligndatav2si (v2si, v2si); +v4hi __builtin_vis_faligndatav4hi (v4si, v4si); +v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi); + +v4hi __builtin_vis_fexpand (v4qi); + +v4hi __builtin_vis_fmul8x16 (v4qi, v4hi); +v4hi __builtin_vis_fmul8x16au (v4qi, v2hi); +v4hi __builtin_vis_fmul8x16al (v4qi, v2hi); +v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi); +v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi); +v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi); +v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi); + +v4qi __builtin_vis_fpack16 (v4hi); +v8qi __builtin_vis_fpack32 (v2si, v8qi); +v2hi __builtin_vis_fpackfix (v2si); +v8qi __builtin_vis_fpmerge (v4qi, v4qi); + +int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t); + +long __builtin_vis_edge8 (void *, void *); +long __builtin_vis_edge8l (void *, void *); +long __builtin_vis_edge16 (void *, void *); +long __builtin_vis_edge16l (void *, void *); +long __builtin_vis_edge32 (void *, void *); +long __builtin_vis_edge32l (void *, void *); + +long __builtin_vis_fcmple16 (v4hi, v4hi); +long __builtin_vis_fcmple32 (v2si, v2si); +long __builtin_vis_fcmpne16 (v4hi, v4hi); +long __builtin_vis_fcmpne32 (v2si, v2si); +long __builtin_vis_fcmpgt16 (v4hi, v4hi); +long __builtin_vis_fcmpgt32 (v2si, v2si); +long __builtin_vis_fcmpeq16 (v4hi, v4hi); +long __builtin_vis_fcmpeq32 (v2si, v2si); + +v4hi __builtin_vis_fpadd16 (v4hi, v4hi); +v2hi __builtin_vis_fpadd16s (v2hi, v2hi); +v2si __builtin_vis_fpadd32 (v2si, v2si); +v1si __builtin_vis_fpadd32s (v1si, v1si); +v4hi __builtin_vis_fpsub16 (v4hi, v4hi); +v2hi __builtin_vis_fpsub16s (v2hi, v2hi); +v2si __builtin_vis_fpsub32 (v2si, v2si); +v1si __builtin_vis_fpsub32s (v1si, v1si); + +long __builtin_vis_array8 (long, long); +long __builtin_vis_array16 (long, long); +long __builtin_vis_array32 (long, long); +@end smallexample + +When you use the @option{-mvis2} switch, the VIS version 2.0 built-in +functions also become available: + +@smallexample +long __builtin_vis_bmask (long, long); +int64_t __builtin_vis_bshuffledi (int64_t, int64_t); +v2si __builtin_vis_bshufflev2si (v2si, v2si); +v4hi __builtin_vis_bshufflev2si (v4hi, v4hi); +v8qi __builtin_vis_bshufflev2si (v8qi, v8qi); + +long __builtin_vis_edge8n (void *, void *); +long __builtin_vis_edge8ln (void *, void *); +long __builtin_vis_edge16n (void *, void *); +long __builtin_vis_edge16ln (void *, void *); +long __builtin_vis_edge32n (void *, void *); +long __builtin_vis_edge32ln (void *, void *); +@end smallexample + +When you use the @option{-mvis3} switch, the VIS version 3.0 built-in +functions also become available: + +@smallexample +void __builtin_vis_cmask8 (long); +void __builtin_vis_cmask16 (long); +void __builtin_vis_cmask32 (long); + +v4hi __builtin_vis_fchksm16 (v4hi, v4hi); + +v4hi __builtin_vis_fsll16 (v4hi, v4hi); +v4hi __builtin_vis_fslas16 (v4hi, v4hi); +v4hi __builtin_vis_fsrl16 (v4hi, v4hi); +v4hi __builtin_vis_fsra16 (v4hi, v4hi); +v2si __builtin_vis_fsll16 (v2si, v2si); +v2si __builtin_vis_fslas16 (v2si, v2si); +v2si __builtin_vis_fsrl16 (v2si, v2si); +v2si __builtin_vis_fsra16 (v2si, v2si); + +long __builtin_vis_pdistn (v8qi, v8qi); + +v4hi __builtin_vis_fmean16 (v4hi, v4hi); + +int64_t __builtin_vis_fpadd64 (int64_t, int64_t); +int64_t __builtin_vis_fpsub64 (int64_t, int64_t); + +v4hi __builtin_vis_fpadds16 (v4hi, v4hi); +v2hi __builtin_vis_fpadds16s (v2hi, v2hi); +v4hi __builtin_vis_fpsubs16 (v4hi, v4hi); +v2hi __builtin_vis_fpsubs16s (v2hi, v2hi); +v2si __builtin_vis_fpadds32 (v2si, v2si); +v1si __builtin_vis_fpadds32s (v1si, v1si); +v2si __builtin_vis_fpsubs32 (v2si, v2si); +v1si __builtin_vis_fpsubs32s (v1si, v1si); + +long __builtin_vis_fucmple8 (v8qi, v8qi); +long __builtin_vis_fucmpne8 (v8qi, v8qi); +long __builtin_vis_fucmpgt8 (v8qi, v8qi); +long __builtin_vis_fucmpeq8 (v8qi, v8qi); + +float __builtin_vis_fhadds (float, float); +double __builtin_vis_fhaddd (double, double); +float __builtin_vis_fhsubs (float, float); +double __builtin_vis_fhsubd (double, double); +float __builtin_vis_fnhadds (float, float); +double __builtin_vis_fnhaddd (double, double); + +int64_t __builtin_vis_umulxhi (int64_t, int64_t); +int64_t __builtin_vis_xmulx (int64_t, int64_t); +int64_t __builtin_vis_xmulxhi (int64_t, int64_t); +@end smallexample + +When you use the @option{-mvis4} switch, the VIS version 4.0 built-in +functions also become available: + +@smallexample +v8qi __builtin_vis_fpadd8 (v8qi, v8qi); +v8qi __builtin_vis_fpadds8 (v8qi, v8qi); +v8qi __builtin_vis_fpaddus8 (v8qi, v8qi); +v4hi __builtin_vis_fpaddus16 (v4hi, v4hi); + +v8qi __builtin_vis_fpsub8 (v8qi, v8qi); +v8qi __builtin_vis_fpsubs8 (v8qi, v8qi); +v8qi __builtin_vis_fpsubus8 (v8qi, v8qi); +v4hi __builtin_vis_fpsubus16 (v4hi, v4hi); + +long __builtin_vis_fpcmple8 (v8qi, v8qi); +long __builtin_vis_fpcmpgt8 (v8qi, v8qi); +long __builtin_vis_fpcmpule16 (v4hi, v4hi); +long __builtin_vis_fpcmpugt16 (v4hi, v4hi); +long __builtin_vis_fpcmpule32 (v2si, v2si); +long __builtin_vis_fpcmpugt32 (v2si, v2si); + +v8qi __builtin_vis_fpmax8 (v8qi, v8qi); +v4hi __builtin_vis_fpmax16 (v4hi, v4hi); +v2si __builtin_vis_fpmax32 (v2si, v2si); + +v8qi __builtin_vis_fpmaxu8 (v8qi, v8qi); +v4hi __builtin_vis_fpmaxu16 (v4hi, v4hi); +v2si __builtin_vis_fpmaxu32 (v2si, v2si); + +v8qi __builtin_vis_fpmin8 (v8qi, v8qi); +v4hi __builtin_vis_fpmin16 (v4hi, v4hi); +v2si __builtin_vis_fpmin32 (v2si, v2si); + +v8qi __builtin_vis_fpminu8 (v8qi, v8qi); +v4hi __builtin_vis_fpminu16 (v4hi, v4hi); +v2si __builtin_vis_fpminu32 (v2si, v2si); +@end smallexample + +When you use the @option{-mvis4b} switch, the VIS version 4.0B +built-in functions also become available: + +@smallexample +v8qi __builtin_vis_dictunpack8 (double, int); +v4hi __builtin_vis_dictunpack16 (double, int); +v2si __builtin_vis_dictunpack32 (double, int); + +long __builtin_vis_fpcmple8shl (v8qi, v8qi, int); +long __builtin_vis_fpcmpgt8shl (v8qi, v8qi, int); +long __builtin_vis_fpcmpeq8shl (v8qi, v8qi, int); +long __builtin_vis_fpcmpne8shl (v8qi, v8qi, int); + +long __builtin_vis_fpcmple16shl (v4hi, v4hi, int); +long __builtin_vis_fpcmpgt16shl (v4hi, v4hi, int); +long __builtin_vis_fpcmpeq16shl (v4hi, v4hi, int); +long __builtin_vis_fpcmpne16shl (v4hi, v4hi, int); + +long __builtin_vis_fpcmple32shl (v2si, v2si, int); +long __builtin_vis_fpcmpgt32shl (v2si, v2si, int); +long __builtin_vis_fpcmpeq32shl (v2si, v2si, int); +long __builtin_vis_fpcmpne32shl (v2si, v2si, int); + +long __builtin_vis_fpcmpule8shl (v8qi, v8qi, int); +long __builtin_vis_fpcmpugt8shl (v8qi, v8qi, int); +long __builtin_vis_fpcmpule16shl (v4hi, v4hi, int); +long __builtin_vis_fpcmpugt16shl (v4hi, v4hi, int); +long __builtin_vis_fpcmpule32shl (v2si, v2si, int); +long __builtin_vis_fpcmpugt32shl (v2si, v2si, int); + +long __builtin_vis_fpcmpde8shl (v8qi, v8qi, int); +long __builtin_vis_fpcmpde16shl (v4hi, v4hi, int); +long __builtin_vis_fpcmpde32shl (v2si, v2si, int); + +long __builtin_vis_fpcmpur8shl (v8qi, v8qi, int); +long __builtin_vis_fpcmpur16shl (v4hi, v4hi, int); +long __builtin_vis_fpcmpur32shl (v2si, v2si, int); +@end smallexample + +@node TI C6X Built-in Functions +@subsection TI C6X Built-in Functions + +GCC provides intrinsics to access certain instructions of the TI C6X +processors. These intrinsics, listed below, are available after +inclusion of the @code{c6x_intrinsics.h} header file. They map directly +to C6X instructions. + +@smallexample +int _sadd (int, int); +int _ssub (int, int); +int _sadd2 (int, int); +int _ssub2 (int, int); +long long _mpy2 (int, int); +long long _smpy2 (int, int); +int _add4 (int, int); +int _sub4 (int, int); +int _saddu4 (int, int); + +int _smpy (int, int); +int _smpyh (int, int); +int _smpyhl (int, int); +int _smpylh (int, int); + +int _sshl (int, int); +int _subc (int, int); + +int _avg2 (int, int); +int _avgu4 (int, int); + +int _clrr (int, int); +int _extr (int, int); +int _extru (int, int); +int _abs (int); +int _abs2 (int); +@end smallexample + +@node x86 Built-in Functions +@subsection x86 Built-in Functions + +These built-in functions are available for the x86-32 and x86-64 family +of computers, depending on the command-line switches used. + +If you specify command-line switches such as @option{-msse}, +the compiler could use the extended instruction sets even if the built-ins +are not used explicitly in the program. For this reason, applications +that perform run-time CPU detection must compile separate files for each +supported architecture, using the appropriate flags. In particular, +the file containing the CPU detection code should be compiled without +these options. + +The following machine modes are available for use with MMX built-in functions +(@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32-bit integers, +@code{V4HI} for a vector of four 16-bit integers, and @code{V8QI} for a +vector of eight 8-bit integers. Some of the built-in functions operate on +MMX registers as a whole 64-bit entity, these use @code{V1DI} as their mode. + +If 3DNow!@: extensions are enabled, @code{V2SF} is used as a mode for a vector +of two 32-bit floating-point values. + +If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32-bit +floating-point values. Some instructions use a vector of four 32-bit +integers, these use @code{V4SI}. Finally, some instructions operate on an +entire vector register, interpreting it as a 128-bit integer, these use mode +@code{TI}. + +The x86-32 and x86-64 family of processors use additional built-in +functions for efficient use of @code{TF} (@code{__float128}) 128-bit +floating point and @code{TC} 128-bit complex floating-point values. + +The following floating-point built-in functions are always available. All +of them implement the function that is part of the name. + +@smallexample +__float128 __builtin_fabsq (__float128) +__float128 __builtin_copysignq (__float128, __float128) +@end smallexample + +The following built-in functions are always available. + +@table @code +@item __float128 __builtin_infq (void) +Similar to @code{__builtin_inf}, except the return type is @code{__float128}. +@findex __builtin_infq + +@item __float128 __builtin_huge_valq (void) +Similar to @code{__builtin_huge_val}, except the return type is @code{__float128}. +@findex __builtin_huge_valq + +@item __float128 __builtin_nanq (void) +Similar to @code{__builtin_nan}, except the return type is @code{__float128}. +@findex __builtin_nanq + +@item __float128 __builtin_nansq (void) +Similar to @code{__builtin_nans}, except the return type is @code{__float128}. +@findex __builtin_nansq +@end table + +The following built-in function is always available. + +@table @code +@item void __builtin_ia32_pause (void) +Generates the @code{pause} machine instruction with a compiler memory +barrier. +@end table + +The following built-in functions are always available and can be used to +check the target platform type. + +@deftypefn {Built-in Function} void __builtin_cpu_init (void) +This function runs the CPU detection code to check the type of CPU and the +features supported. This built-in function needs to be invoked along with the built-in functions +to check CPU type and features, @code{__builtin_cpu_is} and +@code{__builtin_cpu_supports}, only when used in a function that is +executed before any constructors are called. The CPU detection code is +automatically executed in a very high priority constructor. + +For example, this function has to be used in @code{ifunc} resolvers that +check for CPU type using the built-in functions @code{__builtin_cpu_is} +and @code{__builtin_cpu_supports}, or in constructors on targets that +don't support constructor priority. +@smallexample + +static void (*resolve_memcpy (void)) (void) +@{ + // ifunc resolvers fire before constructors, explicitly call the init + // function. + __builtin_cpu_init (); + if (__builtin_cpu_supports ("ssse3")) + return ssse3_memcpy; // super fast memcpy with ssse3 instructions. + else + return default_memcpy; +@} + +void *memcpy (void *, const void *, size_t) + __attribute__ ((ifunc ("resolve_memcpy"))); +@end smallexample + +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_cpu_is (const char *@var{cpuname}) +This function returns a positive integer if the run-time CPU +is of type @var{cpuname} +and returns @code{0} otherwise. The following CPU names can be detected: + +@table @samp +@item amd +AMD CPU. + +@item intel +Intel CPU. + +@item atom +Intel Atom CPU. + +@item slm +Intel Silvermont CPU. + +@item core2 +Intel Core 2 CPU. + +@item corei7 +Intel Core i7 CPU. + +@item nehalem +Intel Core i7 Nehalem CPU. + +@item westmere +Intel Core i7 Westmere CPU. + +@item sandybridge +Intel Core i7 Sandy Bridge CPU. + +@item ivybridge +Intel Core i7 Ivy Bridge CPU. + +@item haswell +Intel Core i7 Haswell CPU. + +@item broadwell +Intel Core i7 Broadwell CPU. + +@item skylake +Intel Core i7 Skylake CPU. + +@item skylake-avx512 +Intel Core i7 Skylake AVX512 CPU. + +@item cannonlake +Intel Core i7 Cannon Lake CPU. + +@item icelake-client +Intel Core i7 Ice Lake Client CPU. + +@item icelake-server +Intel Core i7 Ice Lake Server CPU. + +@item cascadelake +Intel Core i7 Cascadelake CPU. + +@item tigerlake +Intel Core i7 Tigerlake CPU. + +@item cooperlake +Intel Core i7 Cooperlake CPU. + +@item sapphirerapids +Intel Core i7 sapphirerapids CPU. + +@item alderlake +Intel Core i7 Alderlake CPU. + +@item rocketlake +Intel Core i7 Rocketlake CPU. + +@item graniterapids +Intel Core i7 graniterapids CPU. + +@item bonnell +Intel Atom Bonnell CPU. + +@item silvermont +Intel Atom Silvermont CPU. + +@item goldmont +Intel Atom Goldmont CPU. + +@item goldmont-plus +Intel Atom Goldmont Plus CPU. + +@item tremont +Intel Atom Tremont CPU. + +@item sierraforest +Intel Atom Sierra Forest CPU. + +@item grandridge +Intel Atom Grand Ridge CPU. + +@item knl +Intel Knights Landing CPU. + +@item knm +Intel Knights Mill CPU. + +@item lujiazui +ZHAOXIN lujiazui CPU. + +@item amdfam10h +AMD Family 10h CPU. + +@item barcelona +AMD Family 10h Barcelona CPU. + +@item shanghai +AMD Family 10h Shanghai CPU. + +@item istanbul +AMD Family 10h Istanbul CPU. + +@item btver1 +AMD Family 14h CPU. + +@item amdfam15h +AMD Family 15h CPU. + +@item bdver1 +AMD Family 15h Bulldozer version 1. + +@item bdver2 +AMD Family 15h Bulldozer version 2. + +@item bdver3 +AMD Family 15h Bulldozer version 3. + +@item bdver4 +AMD Family 15h Bulldozer version 4. + +@item btver2 +AMD Family 16h CPU. + +@item amdfam17h +AMD Family 17h CPU. + +@item znver1 +AMD Family 17h Zen version 1. + +@item znver2 +AMD Family 17h Zen version 2. + +@item amdfam19h +AMD Family 19h CPU. + +@item znver3 +AMD Family 19h Zen version 3. + +@item znver4 +AMD Family 19h Zen version 4. + +@item x86-64 +Baseline x86-64 microarchitecture level (as defined in x86-64 psABI). + +@item x86-64-v2 +x86-64-v2 microarchitecture level. + +@item x86-64-v3 +x86-64-v3 microarchitecture level. + +@item x86-64-v4 +x86-64-v4 microarchitecture level. +@end table + +Here is an example: +@smallexample +if (__builtin_cpu_is ("corei7")) + @{ + do_corei7 (); // Core i7 specific implementation. + @} +else + @{ + do_generic (); // Generic implementation. + @} +@end smallexample +@end deftypefn + +@deftypefn {Built-in Function} int __builtin_cpu_supports (const char *@var{feature}) +This function returns a positive integer if the run-time CPU +supports @var{feature} +and returns @code{0} otherwise. The following features can be detected: + +@table @samp +@item cmov +CMOV instruction. +@item mmx +MMX instructions. +@item popcnt +POPCNT instruction. +@item sse +SSE instructions. +@item sse2 +SSE2 instructions. +@item sse3 +SSE3 instructions. +@item ssse3 +SSSE3 instructions. +@item sse4.1 +SSE4.1 instructions. +@item sse4.2 +SSE4.2 instructions. +@item avx +AVX instructions. +@item avx2 +AVX2 instructions. +@item sse4a +SSE4A instructions. +@item fma4 +FMA4 instructions. +@item xop +XOP instructions. +@item fma +FMA instructions. +@item avx512f +AVX512F instructions. +@item bmi +BMI instructions. +@item bmi2 +BMI2 instructions. +@item aes +AES instructions. +@item pclmul +PCLMUL instructions. +@item avx512vl +AVX512VL instructions. +@item avx512bw +AVX512BW instructions. +@item avx512dq +AVX512DQ instructions. +@item avx512cd +AVX512CD instructions. +@item avx512er +AVX512ER instructions. +@item avx512pf +AVX512PF instructions. +@item avx512vbmi +AVX512VBMI instructions. +@item avx512ifma +AVX512IFMA instructions. +@item avx5124vnniw +AVX5124VNNIW instructions. +@item avx5124fmaps +AVX5124FMAPS instructions. +@item avx512vpopcntdq +AVX512VPOPCNTDQ instructions. +@item avx512vbmi2 +AVX512VBMI2 instructions. +@item gfni +GFNI instructions. +@item vpclmulqdq +VPCLMULQDQ instructions. +@item avx512vnni +AVX512VNNI instructions. +@item avx512bitalg +AVX512BITALG instructions. +@end table + +Here is an example: +@smallexample +if (__builtin_cpu_supports ("popcnt")) + @{ + asm("popcnt %1,%0" : "=r"(count) : "rm"(n) : "cc"); + @} +else + @{ + count = generic_countbits (n); //generic implementation. + @} +@end smallexample +@end deftypefn + +The following built-in functions are made available by @option{-mmmx}. +All of them generate the machine instruction that is part of the name. + +@smallexample +v8qi __builtin_ia32_paddb (v8qi, v8qi); +v4hi __builtin_ia32_paddw (v4hi, v4hi); +v2si __builtin_ia32_paddd (v2si, v2si); +v8qi __builtin_ia32_psubb (v8qi, v8qi); +v4hi __builtin_ia32_psubw (v4hi, v4hi); +v2si __builtin_ia32_psubd (v2si, v2si); +v8qi __builtin_ia32_paddsb (v8qi, v8qi); +v4hi __builtin_ia32_paddsw (v4hi, v4hi); +v8qi __builtin_ia32_psubsb (v8qi, v8qi); +v4hi __builtin_ia32_psubsw (v4hi, v4hi); +v8qi __builtin_ia32_paddusb (v8qi, v8qi); +v4hi __builtin_ia32_paddusw (v4hi, v4hi); +v8qi __builtin_ia32_psubusb (v8qi, v8qi); +v4hi __builtin_ia32_psubusw (v4hi, v4hi); +v4hi __builtin_ia32_pmullw (v4hi, v4hi); +v4hi __builtin_ia32_pmulhw (v4hi, v4hi); +di __builtin_ia32_pand (di, di); +di __builtin_ia32_pandn (di,di); +di __builtin_ia32_por (di, di); +di __builtin_ia32_pxor (di, di); +v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi); +v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi); +v2si __builtin_ia32_pcmpeqd (v2si, v2si); +v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi); +v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi); +v2si __builtin_ia32_pcmpgtd (v2si, v2si); +v8qi __builtin_ia32_punpckhbw (v8qi, v8qi); +v4hi __builtin_ia32_punpckhwd (v4hi, v4hi); +v2si __builtin_ia32_punpckhdq (v2si, v2si); +v8qi __builtin_ia32_punpcklbw (v8qi, v8qi); +v4hi __builtin_ia32_punpcklwd (v4hi, v4hi); +v2si __builtin_ia32_punpckldq (v2si, v2si); +v8qi __builtin_ia32_packsswb (v4hi, v4hi); +v4hi __builtin_ia32_packssdw (v2si, v2si); +v8qi __builtin_ia32_packuswb (v4hi, v4hi); + +v4hi __builtin_ia32_psllw (v4hi, v4hi); +v2si __builtin_ia32_pslld (v2si, v2si); +v1di __builtin_ia32_psllq (v1di, v1di); +v4hi __builtin_ia32_psrlw (v4hi, v4hi); +v2si __builtin_ia32_psrld (v2si, v2si); +v1di __builtin_ia32_psrlq (v1di, v1di); +v4hi __builtin_ia32_psraw (v4hi, v4hi); +v2si __builtin_ia32_psrad (v2si, v2si); +v4hi __builtin_ia32_psllwi (v4hi, int); +v2si __builtin_ia32_pslldi (v2si, int); +v1di __builtin_ia32_psllqi (v1di, int); +v4hi __builtin_ia32_psrlwi (v4hi, int); +v2si __builtin_ia32_psrldi (v2si, int); +v1di __builtin_ia32_psrlqi (v1di, int); +v4hi __builtin_ia32_psrawi (v4hi, int); +v2si __builtin_ia32_psradi (v2si, int); +@end smallexample + +The following built-in functions are made available either with +@option{-msse}, or with @option{-m3dnowa}. All of them generate +the machine instruction that is part of the name. + +@smallexample +v4hi __builtin_ia32_pmulhuw (v4hi, v4hi); +v8qi __builtin_ia32_pavgb (v8qi, v8qi); +v4hi __builtin_ia32_pavgw (v4hi, v4hi); +v1di __builtin_ia32_psadbw (v8qi, v8qi); +v8qi __builtin_ia32_pmaxub (v8qi, v8qi); +v4hi __builtin_ia32_pmaxsw (v4hi, v4hi); +v8qi __builtin_ia32_pminub (v8qi, v8qi); +v4hi __builtin_ia32_pminsw (v4hi, v4hi); +int __builtin_ia32_pmovmskb (v8qi); +void __builtin_ia32_maskmovq (v8qi, v8qi, char *); +void __builtin_ia32_movntq (di *, di); +void __builtin_ia32_sfence (void); +@end smallexample + +The following built-in functions are available when @option{-msse} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +int __builtin_ia32_comieq (v4sf, v4sf); +int __builtin_ia32_comineq (v4sf, v4sf); +int __builtin_ia32_comilt (v4sf, v4sf); +int __builtin_ia32_comile (v4sf, v4sf); +int __builtin_ia32_comigt (v4sf, v4sf); +int __builtin_ia32_comige (v4sf, v4sf); +int __builtin_ia32_ucomieq (v4sf, v4sf); +int __builtin_ia32_ucomineq (v4sf, v4sf); +int __builtin_ia32_ucomilt (v4sf, v4sf); +int __builtin_ia32_ucomile (v4sf, v4sf); +int __builtin_ia32_ucomigt (v4sf, v4sf); +int __builtin_ia32_ucomige (v4sf, v4sf); +v4sf __builtin_ia32_addps (v4sf, v4sf); +v4sf __builtin_ia32_subps (v4sf, v4sf); +v4sf __builtin_ia32_mulps (v4sf, v4sf); +v4sf __builtin_ia32_divps (v4sf, v4sf); +v4sf __builtin_ia32_addss (v4sf, v4sf); +v4sf __builtin_ia32_subss (v4sf, v4sf); +v4sf __builtin_ia32_mulss (v4sf, v4sf); +v4sf __builtin_ia32_divss (v4sf, v4sf); +v4sf __builtin_ia32_cmpeqps (v4sf, v4sf); +v4sf __builtin_ia32_cmpltps (v4sf, v4sf); +v4sf __builtin_ia32_cmpleps (v4sf, v4sf); +v4sf __builtin_ia32_cmpgtps (v4sf, v4sf); +v4sf __builtin_ia32_cmpgeps (v4sf, v4sf); +v4sf __builtin_ia32_cmpunordps (v4sf, v4sf); +v4sf __builtin_ia32_cmpneqps (v4sf, v4sf); +v4sf __builtin_ia32_cmpnltps (v4sf, v4sf); +v4sf __builtin_ia32_cmpnleps (v4sf, v4sf); +v4sf __builtin_ia32_cmpngtps (v4sf, v4sf); +v4sf __builtin_ia32_cmpngeps (v4sf, v4sf); +v4sf __builtin_ia32_cmpordps (v4sf, v4sf); +v4sf __builtin_ia32_cmpeqss (v4sf, v4sf); +v4sf __builtin_ia32_cmpltss (v4sf, v4sf); +v4sf __builtin_ia32_cmpless (v4sf, v4sf); +v4sf __builtin_ia32_cmpunordss (v4sf, v4sf); +v4sf __builtin_ia32_cmpneqss (v4sf, v4sf); +v4sf __builtin_ia32_cmpnltss (v4sf, v4sf); +v4sf __builtin_ia32_cmpnless (v4sf, v4sf); +v4sf __builtin_ia32_cmpordss (v4sf, v4sf); +v4sf __builtin_ia32_maxps (v4sf, v4sf); +v4sf __builtin_ia32_maxss (v4sf, v4sf); +v4sf __builtin_ia32_minps (v4sf, v4sf); +v4sf __builtin_ia32_minss (v4sf, v4sf); +v4sf __builtin_ia32_andps (v4sf, v4sf); +v4sf __builtin_ia32_andnps (v4sf, v4sf); +v4sf __builtin_ia32_orps (v4sf, v4sf); +v4sf __builtin_ia32_xorps (v4sf, v4sf); +v4sf __builtin_ia32_movss (v4sf, v4sf); +v4sf __builtin_ia32_movhlps (v4sf, v4sf); +v4sf __builtin_ia32_movlhps (v4sf, v4sf); +v4sf __builtin_ia32_unpckhps (v4sf, v4sf); +v4sf __builtin_ia32_unpcklps (v4sf, v4sf); +v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si); +v4sf __builtin_ia32_cvtsi2ss (v4sf, int); +v2si __builtin_ia32_cvtps2pi (v4sf); +int __builtin_ia32_cvtss2si (v4sf); +v2si __builtin_ia32_cvttps2pi (v4sf); +int __builtin_ia32_cvttss2si (v4sf); +v4sf __builtin_ia32_rcpps (v4sf); +v4sf __builtin_ia32_rsqrtps (v4sf); +v4sf __builtin_ia32_sqrtps (v4sf); +v4sf __builtin_ia32_rcpss (v4sf); +v4sf __builtin_ia32_rsqrtss (v4sf); +v4sf __builtin_ia32_sqrtss (v4sf); +v4sf __builtin_ia32_shufps (v4sf, v4sf, int); +void __builtin_ia32_movntps (float *, v4sf); +int __builtin_ia32_movmskps (v4sf); +@end smallexample + +The following built-in functions are available when @option{-msse} is used. + +@table @code +@item v4sf __builtin_ia32_loadups (float *) +Generates the @code{movups} machine instruction as a load from memory. +@item void __builtin_ia32_storeups (float *, v4sf) +Generates the @code{movups} machine instruction as a store to memory. +@item v4sf __builtin_ia32_loadss (float *) +Generates the @code{movss} machine instruction as a load from memory. +@item v4sf __builtin_ia32_loadhps (v4sf, const v2sf *) +Generates the @code{movhps} machine instruction as a load from memory. +@item v4sf __builtin_ia32_loadlps (v4sf, const v2sf *) +Generates the @code{movlps} machine instruction as a load from memory +@item void __builtin_ia32_storehps (v2sf *, v4sf) +Generates the @code{movhps} machine instruction as a store to memory. +@item void __builtin_ia32_storelps (v2sf *, v4sf) +Generates the @code{movlps} machine instruction as a store to memory. +@end table + +The following built-in functions are available when @option{-msse2} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +int __builtin_ia32_comisdeq (v2df, v2df); +int __builtin_ia32_comisdlt (v2df, v2df); +int __builtin_ia32_comisdle (v2df, v2df); +int __builtin_ia32_comisdgt (v2df, v2df); +int __builtin_ia32_comisdge (v2df, v2df); +int __builtin_ia32_comisdneq (v2df, v2df); +int __builtin_ia32_ucomisdeq (v2df, v2df); +int __builtin_ia32_ucomisdlt (v2df, v2df); +int __builtin_ia32_ucomisdle (v2df, v2df); +int __builtin_ia32_ucomisdgt (v2df, v2df); +int __builtin_ia32_ucomisdge (v2df, v2df); +int __builtin_ia32_ucomisdneq (v2df, v2df); +v2df __builtin_ia32_cmpeqpd (v2df, v2df); +v2df __builtin_ia32_cmpltpd (v2df, v2df); +v2df __builtin_ia32_cmplepd (v2df, v2df); +v2df __builtin_ia32_cmpgtpd (v2df, v2df); +v2df __builtin_ia32_cmpgepd (v2df, v2df); +v2df __builtin_ia32_cmpunordpd (v2df, v2df); +v2df __builtin_ia32_cmpneqpd (v2df, v2df); +v2df __builtin_ia32_cmpnltpd (v2df, v2df); +v2df __builtin_ia32_cmpnlepd (v2df, v2df); +v2df __builtin_ia32_cmpngtpd (v2df, v2df); +v2df __builtin_ia32_cmpngepd (v2df, v2df); +v2df __builtin_ia32_cmpordpd (v2df, v2df); +v2df __builtin_ia32_cmpeqsd (v2df, v2df); +v2df __builtin_ia32_cmpltsd (v2df, v2df); +v2df __builtin_ia32_cmplesd (v2df, v2df); +v2df __builtin_ia32_cmpunordsd (v2df, v2df); +v2df __builtin_ia32_cmpneqsd (v2df, v2df); +v2df __builtin_ia32_cmpnltsd (v2df, v2df); +v2df __builtin_ia32_cmpnlesd (v2df, v2df); +v2df __builtin_ia32_cmpordsd (v2df, v2df); +v2di __builtin_ia32_paddq (v2di, v2di); +v2di __builtin_ia32_psubq (v2di, v2di); +v2df __builtin_ia32_addpd (v2df, v2df); +v2df __builtin_ia32_subpd (v2df, v2df); +v2df __builtin_ia32_mulpd (v2df, v2df); +v2df __builtin_ia32_divpd (v2df, v2df); +v2df __builtin_ia32_addsd (v2df, v2df); +v2df __builtin_ia32_subsd (v2df, v2df); +v2df __builtin_ia32_mulsd (v2df, v2df); +v2df __builtin_ia32_divsd (v2df, v2df); +v2df __builtin_ia32_minpd (v2df, v2df); +v2df __builtin_ia32_maxpd (v2df, v2df); +v2df __builtin_ia32_minsd (v2df, v2df); +v2df __builtin_ia32_maxsd (v2df, v2df); +v2df __builtin_ia32_andpd (v2df, v2df); +v2df __builtin_ia32_andnpd (v2df, v2df); +v2df __builtin_ia32_orpd (v2df, v2df); +v2df __builtin_ia32_xorpd (v2df, v2df); +v2df __builtin_ia32_movsd (v2df, v2df); +v2df __builtin_ia32_unpckhpd (v2df, v2df); +v2df __builtin_ia32_unpcklpd (v2df, v2df); +v16qi __builtin_ia32_paddb128 (v16qi, v16qi); +v8hi __builtin_ia32_paddw128 (v8hi, v8hi); +v4si __builtin_ia32_paddd128 (v4si, v4si); +v2di __builtin_ia32_paddq128 (v2di, v2di); +v16qi __builtin_ia32_psubb128 (v16qi, v16qi); +v8hi __builtin_ia32_psubw128 (v8hi, v8hi); +v4si __builtin_ia32_psubd128 (v4si, v4si); +v2di __builtin_ia32_psubq128 (v2di, v2di); +v8hi __builtin_ia32_pmullw128 (v8hi, v8hi); +v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi); +v2di __builtin_ia32_pand128 (v2di, v2di); +v2di __builtin_ia32_pandn128 (v2di, v2di); +v2di __builtin_ia32_por128 (v2di, v2di); +v2di __builtin_ia32_pxor128 (v2di, v2di); +v16qi __builtin_ia32_pavgb128 (v16qi, v16qi); +v8hi __builtin_ia32_pavgw128 (v8hi, v8hi); +v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi); +v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi); +v4si __builtin_ia32_pcmpeqd128 (v4si, v4si); +v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi); +v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi); +v4si __builtin_ia32_pcmpgtd128 (v4si, v4si); +v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi); +v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi); +v16qi __builtin_ia32_pminub128 (v16qi, v16qi); +v8hi __builtin_ia32_pminsw128 (v8hi, v8hi); +v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi); +v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi); +v4si __builtin_ia32_punpckhdq128 (v4si, v4si); +v2di __builtin_ia32_punpckhqdq128 (v2di, v2di); +v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi); +v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi); +v4si __builtin_ia32_punpckldq128 (v4si, v4si); +v2di __builtin_ia32_punpcklqdq128 (v2di, v2di); +v16qi __builtin_ia32_packsswb128 (v8hi, v8hi); +v8hi __builtin_ia32_packssdw128 (v4si, v4si); +v16qi __builtin_ia32_packuswb128 (v8hi, v8hi); +v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi); +void __builtin_ia32_maskmovdqu (v16qi, v16qi); +v2df __builtin_ia32_loadupd (double *); +void __builtin_ia32_storeupd (double *, v2df); +v2df __builtin_ia32_loadhpd (v2df, double const *); +v2df __builtin_ia32_loadlpd (v2df, double const *); +int __builtin_ia32_movmskpd (v2df); +int __builtin_ia32_pmovmskb128 (v16qi); +void __builtin_ia32_movnti (int *, int); +void __builtin_ia32_movnti64 (long long int *, long long int); +void __builtin_ia32_movntpd (double *, v2df); +void __builtin_ia32_movntdq (v2df *, v2df); +v4si __builtin_ia32_pshufd (v4si, int); +v8hi __builtin_ia32_pshuflw (v8hi, int); +v8hi __builtin_ia32_pshufhw (v8hi, int); +v2di __builtin_ia32_psadbw128 (v16qi, v16qi); +v2df __builtin_ia32_sqrtpd (v2df); +v2df __builtin_ia32_sqrtsd (v2df); +v2df __builtin_ia32_shufpd (v2df, v2df, int); +v2df __builtin_ia32_cvtdq2pd (v4si); +v4sf __builtin_ia32_cvtdq2ps (v4si); +v4si __builtin_ia32_cvtpd2dq (v2df); +v2si __builtin_ia32_cvtpd2pi (v2df); +v4sf __builtin_ia32_cvtpd2ps (v2df); +v4si __builtin_ia32_cvttpd2dq (v2df); +v2si __builtin_ia32_cvttpd2pi (v2df); +v2df __builtin_ia32_cvtpi2pd (v2si); +int __builtin_ia32_cvtsd2si (v2df); +int __builtin_ia32_cvttsd2si (v2df); +long long __builtin_ia32_cvtsd2si64 (v2df); +long long __builtin_ia32_cvttsd2si64 (v2df); +v4si __builtin_ia32_cvtps2dq (v4sf); +v2df __builtin_ia32_cvtps2pd (v4sf); +v4si __builtin_ia32_cvttps2dq (v4sf); +v2df __builtin_ia32_cvtsi2sd (v2df, int); +v2df __builtin_ia32_cvtsi642sd (v2df, long long); +v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df); +v2df __builtin_ia32_cvtss2sd (v2df, v4sf); +void __builtin_ia32_clflush (const void *); +void __builtin_ia32_lfence (void); +void __builtin_ia32_mfence (void); +v16qi __builtin_ia32_loaddqu (const char *); +void __builtin_ia32_storedqu (char *, v16qi); +v1di __builtin_ia32_pmuludq (v2si, v2si); +v2di __builtin_ia32_pmuludq128 (v4si, v4si); +v8hi __builtin_ia32_psllw128 (v8hi, v8hi); +v4si __builtin_ia32_pslld128 (v4si, v4si); +v2di __builtin_ia32_psllq128 (v2di, v2di); +v8hi __builtin_ia32_psrlw128 (v8hi, v8hi); +v4si __builtin_ia32_psrld128 (v4si, v4si); +v2di __builtin_ia32_psrlq128 (v2di, v2di); +v8hi __builtin_ia32_psraw128 (v8hi, v8hi); +v4si __builtin_ia32_psrad128 (v4si, v4si); +v2di __builtin_ia32_pslldqi128 (v2di, int); +v8hi __builtin_ia32_psllwi128 (v8hi, int); +v4si __builtin_ia32_pslldi128 (v4si, int); +v2di __builtin_ia32_psllqi128 (v2di, int); +v2di __builtin_ia32_psrldqi128 (v2di, int); +v8hi __builtin_ia32_psrlwi128 (v8hi, int); +v4si __builtin_ia32_psrldi128 (v4si, int); +v2di __builtin_ia32_psrlqi128 (v2di, int); +v8hi __builtin_ia32_psrawi128 (v8hi, int); +v4si __builtin_ia32_psradi128 (v4si, int); +v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi); +v2di __builtin_ia32_movq128 (v2di); +@end smallexample + +The following built-in functions are available when @option{-msse3} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +v2df __builtin_ia32_addsubpd (v2df, v2df); +v4sf __builtin_ia32_addsubps (v4sf, v4sf); +v2df __builtin_ia32_haddpd (v2df, v2df); +v4sf __builtin_ia32_haddps (v4sf, v4sf); +v2df __builtin_ia32_hsubpd (v2df, v2df); +v4sf __builtin_ia32_hsubps (v4sf, v4sf); +v16qi __builtin_ia32_lddqu (char const *); +void __builtin_ia32_monitor (void *, unsigned int, unsigned int); +v4sf __builtin_ia32_movshdup (v4sf); +v4sf __builtin_ia32_movsldup (v4sf); +void __builtin_ia32_mwait (unsigned int, unsigned int); +@end smallexample + +The following built-in functions are available when @option{-mssse3} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +v2si __builtin_ia32_phaddd (v2si, v2si); +v4hi __builtin_ia32_phaddw (v4hi, v4hi); +v4hi __builtin_ia32_phaddsw (v4hi, v4hi); +v2si __builtin_ia32_phsubd (v2si, v2si); +v4hi __builtin_ia32_phsubw (v4hi, v4hi); +v4hi __builtin_ia32_phsubsw (v4hi, v4hi); +v4hi __builtin_ia32_pmaddubsw (v8qi, v8qi); +v4hi __builtin_ia32_pmulhrsw (v4hi, v4hi); +v8qi __builtin_ia32_pshufb (v8qi, v8qi); +v8qi __builtin_ia32_psignb (v8qi, v8qi); +v2si __builtin_ia32_psignd (v2si, v2si); +v4hi __builtin_ia32_psignw (v4hi, v4hi); +v1di __builtin_ia32_palignr (v1di, v1di, int); +v8qi __builtin_ia32_pabsb (v8qi); +v2si __builtin_ia32_pabsd (v2si); +v4hi __builtin_ia32_pabsw (v4hi); +@end smallexample + +The following built-in functions are available when @option{-mssse3} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +v4si __builtin_ia32_phaddd128 (v4si, v4si); +v8hi __builtin_ia32_phaddw128 (v8hi, v8hi); +v8hi __builtin_ia32_phaddsw128 (v8hi, v8hi); +v4si __builtin_ia32_phsubd128 (v4si, v4si); +v8hi __builtin_ia32_phsubw128 (v8hi, v8hi); +v8hi __builtin_ia32_phsubsw128 (v8hi, v8hi); +v8hi __builtin_ia32_pmaddubsw128 (v16qi, v16qi); +v8hi __builtin_ia32_pmulhrsw128 (v8hi, v8hi); +v16qi __builtin_ia32_pshufb128 (v16qi, v16qi); +v16qi __builtin_ia32_psignb128 (v16qi, v16qi); +v4si __builtin_ia32_psignd128 (v4si, v4si); +v8hi __builtin_ia32_psignw128 (v8hi, v8hi); +v2di __builtin_ia32_palignr128 (v2di, v2di, int); +v16qi __builtin_ia32_pabsb128 (v16qi); +v4si __builtin_ia32_pabsd128 (v4si); +v8hi __builtin_ia32_pabsw128 (v8hi); +@end smallexample + +The following built-in functions are available when @option{-msse4.1} is +used. All of them generate the machine instruction that is part of the +name. + +@smallexample +v2df __builtin_ia32_blendpd (v2df, v2df, const int); +v4sf __builtin_ia32_blendps (v4sf, v4sf, const int); +v2df __builtin_ia32_blendvpd (v2df, v2df, v2df); +v4sf __builtin_ia32_blendvps (v4sf, v4sf, v4sf); +v2df __builtin_ia32_dppd (v2df, v2df, const int); +v4sf __builtin_ia32_dpps (v4sf, v4sf, const int); +v4sf __builtin_ia32_insertps128 (v4sf, v4sf, const int); +v2di __builtin_ia32_movntdqa (v2di *); +v16qi __builtin_ia32_mpsadbw128 (v16qi, v16qi, const int); +v8hi __builtin_ia32_packusdw128 (v4si, v4si); +v16qi __builtin_ia32_pblendvb128 (v16qi, v16qi, v16qi); +v8hi __builtin_ia32_pblendw128 (v8hi, v8hi, const int); +v2di __builtin_ia32_pcmpeqq (v2di, v2di); +v8hi __builtin_ia32_phminposuw128 (v8hi); +v16qi __builtin_ia32_pmaxsb128 (v16qi, v16qi); +v4si __builtin_ia32_pmaxsd128 (v4si, v4si); +v4si __builtin_ia32_pmaxud128 (v4si, v4si); +v8hi __builtin_ia32_pmaxuw128 (v8hi, v8hi); +v16qi __builtin_ia32_pminsb128 (v16qi, v16qi); +v4si __builtin_ia32_pminsd128 (v4si, v4si); +v4si __builtin_ia32_pminud128 (v4si, v4si); +v8hi __builtin_ia32_pminuw128 (v8hi, v8hi); +v4si __builtin_ia32_pmovsxbd128 (v16qi); +v2di __builtin_ia32_pmovsxbq128 (v16qi); +v8hi __builtin_ia32_pmovsxbw128 (v16qi); +v2di __builtin_ia32_pmovsxdq128 (v4si); +v4si __builtin_ia32_pmovsxwd128 (v8hi); +v2di __builtin_ia32_pmovsxwq128 (v8hi); +v4si __builtin_ia32_pmovzxbd128 (v16qi); +v2di __builtin_ia32_pmovzxbq128 (v16qi); +v8hi __builtin_ia32_pmovzxbw128 (v16qi); +v2di __builtin_ia32_pmovzxdq128 (v4si); +v4si __builtin_ia32_pmovzxwd128 (v8hi); +v2di __builtin_ia32_pmovzxwq128 (v8hi); +v2di __builtin_ia32_pmuldq128 (v4si, v4si); +v4si __builtin_ia32_pmulld128 (v4si, v4si); +int __builtin_ia32_ptestc128 (v2di, v2di); +int __builtin_ia32_ptestnzc128 (v2di, v2di); +int __builtin_ia32_ptestz128 (v2di, v2di); +v2df __builtin_ia32_roundpd (v2df, const int); +v4sf __builtin_ia32_roundps (v4sf, const int); +v2df __builtin_ia32_roundsd (v2df, v2df, const int); +v4sf __builtin_ia32_roundss (v4sf, v4sf, const int); +@end smallexample + +The following built-in functions are available when @option{-msse4.1} is +used. + +@table @code +@item v4sf __builtin_ia32_vec_set_v4sf (v4sf, float, const int) +Generates the @code{insertps} machine instruction. +@item int __builtin_ia32_vec_ext_v16qi (v16qi, const int) +Generates the @code{pextrb} machine instruction. +@item v16qi __builtin_ia32_vec_set_v16qi (v16qi, int, const int) +Generates the @code{pinsrb} machine instruction. +@item v4si __builtin_ia32_vec_set_v4si (v4si, int, const int) +Generates the @code{pinsrd} machine instruction. +@item v2di __builtin_ia32_vec_set_v2di (v2di, long long, const int) +Generates the @code{pinsrq} machine instruction in 64bit mode. +@end table + +The following built-in functions are changed to generate new SSE4.1 +instructions when @option{-msse4.1} is used. + +@table @code +@item float __builtin_ia32_vec_ext_v4sf (v4sf, const int) +Generates the @code{extractps} machine instruction. +@item int __builtin_ia32_vec_ext_v4si (v4si, const int) +Generates the @code{pextrd} machine instruction. +@item long long __builtin_ia32_vec_ext_v2di (v2di, const int) +Generates the @code{pextrq} machine instruction in 64bit mode. +@end table + +The following built-in functions are available when @option{-msse4.2} is +used. All of them generate the machine instruction that is part of the +name. + +@smallexample +v16qi __builtin_ia32_pcmpestrm128 (v16qi, int, v16qi, int, const int); +int __builtin_ia32_pcmpestri128 (v16qi, int, v16qi, int, const int); +int __builtin_ia32_pcmpestria128 (v16qi, int, v16qi, int, const int); +int __builtin_ia32_pcmpestric128 (v16qi, int, v16qi, int, const int); +int __builtin_ia32_pcmpestrio128 (v16qi, int, v16qi, int, const int); +int __builtin_ia32_pcmpestris128 (v16qi, int, v16qi, int, const int); +int __builtin_ia32_pcmpestriz128 (v16qi, int, v16qi, int, const int); +v16qi __builtin_ia32_pcmpistrm128 (v16qi, v16qi, const int); +int __builtin_ia32_pcmpistri128 (v16qi, v16qi, const int); +int __builtin_ia32_pcmpistria128 (v16qi, v16qi, const int); +int __builtin_ia32_pcmpistric128 (v16qi, v16qi, const int); +int __builtin_ia32_pcmpistrio128 (v16qi, v16qi, const int); +int __builtin_ia32_pcmpistris128 (v16qi, v16qi, const int); +int __builtin_ia32_pcmpistriz128 (v16qi, v16qi, const int); +v2di __builtin_ia32_pcmpgtq (v2di, v2di); +@end smallexample + +The following built-in functions are available when @option{-msse4.2} is +used. + +@table @code +@item unsigned int __builtin_ia32_crc32qi (unsigned int, unsigned char) +Generates the @code{crc32b} machine instruction. +@item unsigned int __builtin_ia32_crc32hi (unsigned int, unsigned short) +Generates the @code{crc32w} machine instruction. +@item unsigned int __builtin_ia32_crc32si (unsigned int, unsigned int) +Generates the @code{crc32l} machine instruction. +@item unsigned long long __builtin_ia32_crc32di (unsigned long long, unsigned long long) +Generates the @code{crc32q} machine instruction. +@end table + +The following built-in functions are changed to generate new SSE4.2 +instructions when @option{-msse4.2} is used. + +@table @code +@item int __builtin_popcount (unsigned int) +Generates the @code{popcntl} machine instruction. +@item int __builtin_popcountl (unsigned long) +Generates the @code{popcntl} or @code{popcntq} machine instruction, +depending on the size of @code{unsigned long}. +@item int __builtin_popcountll (unsigned long long) +Generates the @code{popcntq} machine instruction. +@end table + +The following built-in functions are available when @option{-mavx} is +used. All of them generate the machine instruction that is part of the +name. + +@smallexample +v4df __builtin_ia32_addpd256 (v4df,v4df); +v8sf __builtin_ia32_addps256 (v8sf,v8sf); +v4df __builtin_ia32_addsubpd256 (v4df,v4df); +v8sf __builtin_ia32_addsubps256 (v8sf,v8sf); +v4df __builtin_ia32_andnpd256 (v4df,v4df); +v8sf __builtin_ia32_andnps256 (v8sf,v8sf); +v4df __builtin_ia32_andpd256 (v4df,v4df); +v8sf __builtin_ia32_andps256 (v8sf,v8sf); +v4df __builtin_ia32_blendpd256 (v4df,v4df,int); +v8sf __builtin_ia32_blendps256 (v8sf,v8sf,int); +v4df __builtin_ia32_blendvpd256 (v4df,v4df,v4df); +v8sf __builtin_ia32_blendvps256 (v8sf,v8sf,v8sf); +v2df __builtin_ia32_cmppd (v2df,v2df,int); +v4df __builtin_ia32_cmppd256 (v4df,v4df,int); +v4sf __builtin_ia32_cmpps (v4sf,v4sf,int); +v8sf __builtin_ia32_cmpps256 (v8sf,v8sf,int); +v2df __builtin_ia32_cmpsd (v2df,v2df,int); +v4sf __builtin_ia32_cmpss (v4sf,v4sf,int); +v4df __builtin_ia32_cvtdq2pd256 (v4si); +v8sf __builtin_ia32_cvtdq2ps256 (v8si); +v4si __builtin_ia32_cvtpd2dq256 (v4df); +v4sf __builtin_ia32_cvtpd2ps256 (v4df); +v8si __builtin_ia32_cvtps2dq256 (v8sf); +v4df __builtin_ia32_cvtps2pd256 (v4sf); +v4si __builtin_ia32_cvttpd2dq256 (v4df); +v8si __builtin_ia32_cvttps2dq256 (v8sf); +v4df __builtin_ia32_divpd256 (v4df,v4df); +v8sf __builtin_ia32_divps256 (v8sf,v8sf); +v8sf __builtin_ia32_dpps256 (v8sf,v8sf,int); +v4df __builtin_ia32_haddpd256 (v4df,v4df); +v8sf __builtin_ia32_haddps256 (v8sf,v8sf); +v4df __builtin_ia32_hsubpd256 (v4df,v4df); +v8sf __builtin_ia32_hsubps256 (v8sf,v8sf); +v32qi __builtin_ia32_lddqu256 (pcchar); +v32qi __builtin_ia32_loaddqu256 (pcchar); +v4df __builtin_ia32_loadupd256 (pcdouble); +v8sf __builtin_ia32_loadups256 (pcfloat); +v2df __builtin_ia32_maskloadpd (pcv2df,v2df); +v4df __builtin_ia32_maskloadpd256 (pcv4df,v4df); +v4sf __builtin_ia32_maskloadps (pcv4sf,v4sf); +v8sf __builtin_ia32_maskloadps256 (pcv8sf,v8sf); +void __builtin_ia32_maskstorepd (pv2df,v2df,v2df); +void __builtin_ia32_maskstorepd256 (pv4df,v4df,v4df); +void __builtin_ia32_maskstoreps (pv4sf,v4sf,v4sf); +void __builtin_ia32_maskstoreps256 (pv8sf,v8sf,v8sf); +v4df __builtin_ia32_maxpd256 (v4df,v4df); +v8sf __builtin_ia32_maxps256 (v8sf,v8sf); +v4df __builtin_ia32_minpd256 (v4df,v4df); +v8sf __builtin_ia32_minps256 (v8sf,v8sf); +v4df __builtin_ia32_movddup256 (v4df); +int __builtin_ia32_movmskpd256 (v4df); +int __builtin_ia32_movmskps256 (v8sf); +v8sf __builtin_ia32_movshdup256 (v8sf); +v8sf __builtin_ia32_movsldup256 (v8sf); +v4df __builtin_ia32_mulpd256 (v4df,v4df); +v8sf __builtin_ia32_mulps256 (v8sf,v8sf); +v4df __builtin_ia32_orpd256 (v4df,v4df); +v8sf __builtin_ia32_orps256 (v8sf,v8sf); +v2df __builtin_ia32_pd_pd256 (v4df); +v4df __builtin_ia32_pd256_pd (v2df); +v4sf __builtin_ia32_ps_ps256 (v8sf); +v8sf __builtin_ia32_ps256_ps (v4sf); +int __builtin_ia32_ptestc256 (v4di,v4di,ptest); +int __builtin_ia32_ptestnzc256 (v4di,v4di,ptest); +int __builtin_ia32_ptestz256 (v4di,v4di,ptest); +v8sf __builtin_ia32_rcpps256 (v8sf); +v4df __builtin_ia32_roundpd256 (v4df,int); +v8sf __builtin_ia32_roundps256 (v8sf,int); +v8sf __builtin_ia32_rsqrtps_nr256 (v8sf); +v8sf __builtin_ia32_rsqrtps256 (v8sf); +v4df __builtin_ia32_shufpd256 (v4df,v4df,int); +v8sf __builtin_ia32_shufps256 (v8sf,v8sf,int); +v4si __builtin_ia32_si_si256 (v8si); +v8si __builtin_ia32_si256_si (v4si); +v4df __builtin_ia32_sqrtpd256 (v4df); +v8sf __builtin_ia32_sqrtps_nr256 (v8sf); +v8sf __builtin_ia32_sqrtps256 (v8sf); +void __builtin_ia32_storedqu256 (pchar,v32qi); +void __builtin_ia32_storeupd256 (pdouble,v4df); +void __builtin_ia32_storeups256 (pfloat,v8sf); +v4df __builtin_ia32_subpd256 (v4df,v4df); +v8sf __builtin_ia32_subps256 (v8sf,v8sf); +v4df __builtin_ia32_unpckhpd256 (v4df,v4df); +v8sf __builtin_ia32_unpckhps256 (v8sf,v8sf); +v4df __builtin_ia32_unpcklpd256 (v4df,v4df); +v8sf __builtin_ia32_unpcklps256 (v8sf,v8sf); +v4df __builtin_ia32_vbroadcastf128_pd256 (pcv2df); +v8sf __builtin_ia32_vbroadcastf128_ps256 (pcv4sf); +v4df __builtin_ia32_vbroadcastsd256 (pcdouble); +v4sf __builtin_ia32_vbroadcastss (pcfloat); +v8sf __builtin_ia32_vbroadcastss256 (pcfloat); +v2df __builtin_ia32_vextractf128_pd256 (v4df,int); +v4sf __builtin_ia32_vextractf128_ps256 (v8sf,int); +v4si __builtin_ia32_vextractf128_si256 (v8si,int); +v4df __builtin_ia32_vinsertf128_pd256 (v4df,v2df,int); +v8sf __builtin_ia32_vinsertf128_ps256 (v8sf,v4sf,int); +v8si __builtin_ia32_vinsertf128_si256 (v8si,v4si,int); +v4df __builtin_ia32_vperm2f128_pd256 (v4df,v4df,int); +v8sf __builtin_ia32_vperm2f128_ps256 (v8sf,v8sf,int); +v8si __builtin_ia32_vperm2f128_si256 (v8si,v8si,int); +v2df __builtin_ia32_vpermil2pd (v2df,v2df,v2di,int); +v4df __builtin_ia32_vpermil2pd256 (v4df,v4df,v4di,int); +v4sf __builtin_ia32_vpermil2ps (v4sf,v4sf,v4si,int); +v8sf __builtin_ia32_vpermil2ps256 (v8sf,v8sf,v8si,int); +v2df __builtin_ia32_vpermilpd (v2df,int); +v4df __builtin_ia32_vpermilpd256 (v4df,int); +v4sf __builtin_ia32_vpermilps (v4sf,int); +v8sf __builtin_ia32_vpermilps256 (v8sf,int); +v2df __builtin_ia32_vpermilvarpd (v2df,v2di); +v4df __builtin_ia32_vpermilvarpd256 (v4df,v4di); +v4sf __builtin_ia32_vpermilvarps (v4sf,v4si); +v8sf __builtin_ia32_vpermilvarps256 (v8sf,v8si); +int __builtin_ia32_vtestcpd (v2df,v2df,ptest); +int __builtin_ia32_vtestcpd256 (v4df,v4df,ptest); +int __builtin_ia32_vtestcps (v4sf,v4sf,ptest); +int __builtin_ia32_vtestcps256 (v8sf,v8sf,ptest); +int __builtin_ia32_vtestnzcpd (v2df,v2df,ptest); +int __builtin_ia32_vtestnzcpd256 (v4df,v4df,ptest); +int __builtin_ia32_vtestnzcps (v4sf,v4sf,ptest); +int __builtin_ia32_vtestnzcps256 (v8sf,v8sf,ptest); +int __builtin_ia32_vtestzpd (v2df,v2df,ptest); +int __builtin_ia32_vtestzpd256 (v4df,v4df,ptest); +int __builtin_ia32_vtestzps (v4sf,v4sf,ptest); +int __builtin_ia32_vtestzps256 (v8sf,v8sf,ptest); +void __builtin_ia32_vzeroall (void); +void __builtin_ia32_vzeroupper (void); +v4df __builtin_ia32_xorpd256 (v4df,v4df); +v8sf __builtin_ia32_xorps256 (v8sf,v8sf); +@end smallexample + +The following built-in functions are available when @option{-mavx2} is +used. All of them generate the machine instruction that is part of the +name. + +@smallexample +v32qi __builtin_ia32_mpsadbw256 (v32qi,v32qi,int); +v32qi __builtin_ia32_pabsb256 (v32qi); +v16hi __builtin_ia32_pabsw256 (v16hi); +v8si __builtin_ia32_pabsd256 (v8si); +v16hi __builtin_ia32_packssdw256 (v8si,v8si); +v32qi __builtin_ia32_packsswb256 (v16hi,v16hi); +v16hi __builtin_ia32_packusdw256 (v8si,v8si); +v32qi __builtin_ia32_packuswb256 (v16hi,v16hi); +v32qi __builtin_ia32_paddb256 (v32qi,v32qi); +v16hi __builtin_ia32_paddw256 (v16hi,v16hi); +v8si __builtin_ia32_paddd256 (v8si,v8si); +v4di __builtin_ia32_paddq256 (v4di,v4di); +v32qi __builtin_ia32_paddsb256 (v32qi,v32qi); +v16hi __builtin_ia32_paddsw256 (v16hi,v16hi); +v32qi __builtin_ia32_paddusb256 (v32qi,v32qi); +v16hi __builtin_ia32_paddusw256 (v16hi,v16hi); +v4di __builtin_ia32_palignr256 (v4di,v4di,int); +v4di __builtin_ia32_andsi256 (v4di,v4di); +v4di __builtin_ia32_andnotsi256 (v4di,v4di); +v32qi __builtin_ia32_pavgb256 (v32qi,v32qi); +v16hi __builtin_ia32_pavgw256 (v16hi,v16hi); +v32qi __builtin_ia32_pblendvb256 (v32qi,v32qi,v32qi); +v16hi __builtin_ia32_pblendw256 (v16hi,v16hi,int); +v32qi __builtin_ia32_pcmpeqb256 (v32qi,v32qi); +v16hi __builtin_ia32_pcmpeqw256 (v16hi,v16hi); +v8si __builtin_ia32_pcmpeqd256 (c8si,v8si); +v4di __builtin_ia32_pcmpeqq256 (v4di,v4di); +v32qi __builtin_ia32_pcmpgtb256 (v32qi,v32qi); +v16hi __builtin_ia32_pcmpgtw256 (16hi,v16hi); +v8si __builtin_ia32_pcmpgtd256 (v8si,v8si); +v4di __builtin_ia32_pcmpgtq256 (v4di,v4di); +v16hi __builtin_ia32_phaddw256 (v16hi,v16hi); +v8si __builtin_ia32_phaddd256 (v8si,v8si); +v16hi __builtin_ia32_phaddsw256 (v16hi,v16hi); +v16hi __builtin_ia32_phsubw256 (v16hi,v16hi); +v8si __builtin_ia32_phsubd256 (v8si,v8si); +v16hi __builtin_ia32_phsubsw256 (v16hi,v16hi); +v32qi __builtin_ia32_pmaddubsw256 (v32qi,v32qi); +v16hi __builtin_ia32_pmaddwd256 (v16hi,v16hi); +v32qi __builtin_ia32_pmaxsb256 (v32qi,v32qi); +v16hi __builtin_ia32_pmaxsw256 (v16hi,v16hi); +v8si __builtin_ia32_pmaxsd256 (v8si,v8si); +v32qi __builtin_ia32_pmaxub256 (v32qi,v32qi); +v16hi __builtin_ia32_pmaxuw256 (v16hi,v16hi); +v8si __builtin_ia32_pmaxud256 (v8si,v8si); +v32qi __builtin_ia32_pminsb256 (v32qi,v32qi); +v16hi __builtin_ia32_pminsw256 (v16hi,v16hi); +v8si __builtin_ia32_pminsd256 (v8si,v8si); +v32qi __builtin_ia32_pminub256 (v32qi,v32qi); +v16hi __builtin_ia32_pminuw256 (v16hi,v16hi); +v8si __builtin_ia32_pminud256 (v8si,v8si); +int __builtin_ia32_pmovmskb256 (v32qi); +v16hi __builtin_ia32_pmovsxbw256 (v16qi); +v8si __builtin_ia32_pmovsxbd256 (v16qi); +v4di __builtin_ia32_pmovsxbq256 (v16qi); +v8si __builtin_ia32_pmovsxwd256 (v8hi); +v4di __builtin_ia32_pmovsxwq256 (v8hi); +v4di __builtin_ia32_pmovsxdq256 (v4si); +v16hi __builtin_ia32_pmovzxbw256 (v16qi); +v8si __builtin_ia32_pmovzxbd256 (v16qi); +v4di __builtin_ia32_pmovzxbq256 (v16qi); +v8si __builtin_ia32_pmovzxwd256 (v8hi); +v4di __builtin_ia32_pmovzxwq256 (v8hi); +v4di __builtin_ia32_pmovzxdq256 (v4si); +v4di __builtin_ia32_pmuldq256 (v8si,v8si); +v16hi __builtin_ia32_pmulhrsw256 (v16hi, v16hi); +v16hi __builtin_ia32_pmulhuw256 (v16hi,v16hi); +v16hi __builtin_ia32_pmulhw256 (v16hi,v16hi); +v16hi __builtin_ia32_pmullw256 (v16hi,v16hi); +v8si __builtin_ia32_pmulld256 (v8si,v8si); +v4di __builtin_ia32_pmuludq256 (v8si,v8si); +v4di __builtin_ia32_por256 (v4di,v4di); +v16hi __builtin_ia32_psadbw256 (v32qi,v32qi); +v32qi __builtin_ia32_pshufb256 (v32qi,v32qi); +v8si __builtin_ia32_pshufd256 (v8si,int); +v16hi __builtin_ia32_pshufhw256 (v16hi,int); +v16hi __builtin_ia32_pshuflw256 (v16hi,int); +v32qi __builtin_ia32_psignb256 (v32qi,v32qi); +v16hi __builtin_ia32_psignw256 (v16hi,v16hi); +v8si __builtin_ia32_psignd256 (v8si,v8si); +v4di __builtin_ia32_pslldqi256 (v4di,int); +v16hi __builtin_ia32_psllwi256 (16hi,int); +v16hi __builtin_ia32_psllw256(v16hi,v8hi); +v8si __builtin_ia32_pslldi256 (v8si,int); +v8si __builtin_ia32_pslld256(v8si,v4si); +v4di __builtin_ia32_psllqi256 (v4di,int); +v4di __builtin_ia32_psllq256(v4di,v2di); +v16hi __builtin_ia32_psrawi256 (v16hi,int); +v16hi __builtin_ia32_psraw256 (v16hi,v8hi); +v8si __builtin_ia32_psradi256 (v8si,int); +v8si __builtin_ia32_psrad256 (v8si,v4si); +v4di __builtin_ia32_psrldqi256 (v4di, int); +v16hi __builtin_ia32_psrlwi256 (v16hi,int); +v16hi __builtin_ia32_psrlw256 (v16hi,v8hi); +v8si __builtin_ia32_psrldi256 (v8si,int); +v8si __builtin_ia32_psrld256 (v8si,v4si); +v4di __builtin_ia32_psrlqi256 (v4di,int); +v4di __builtin_ia32_psrlq256(v4di,v2di); +v32qi __builtin_ia32_psubb256 (v32qi,v32qi); +v32hi __builtin_ia32_psubw256 (v16hi,v16hi); +v8si __builtin_ia32_psubd256 (v8si,v8si); +v4di __builtin_ia32_psubq256 (v4di,v4di); +v32qi __builtin_ia32_psubsb256 (v32qi,v32qi); +v16hi __builtin_ia32_psubsw256 (v16hi,v16hi); +v32qi __builtin_ia32_psubusb256 (v32qi,v32qi); +v16hi __builtin_ia32_psubusw256 (v16hi,v16hi); +v32qi __builtin_ia32_punpckhbw256 (v32qi,v32qi); +v16hi __builtin_ia32_punpckhwd256 (v16hi,v16hi); +v8si __builtin_ia32_punpckhdq256 (v8si,v8si); +v4di __builtin_ia32_punpckhqdq256 (v4di,v4di); +v32qi __builtin_ia32_punpcklbw256 (v32qi,v32qi); +v16hi __builtin_ia32_punpcklwd256 (v16hi,v16hi); +v8si __builtin_ia32_punpckldq256 (v8si,v8si); +v4di __builtin_ia32_punpcklqdq256 (v4di,v4di); +v4di __builtin_ia32_pxor256 (v4di,v4di); +v4di __builtin_ia32_movntdqa256 (pv4di); +v4sf __builtin_ia32_vbroadcastss_ps (v4sf); +v8sf __builtin_ia32_vbroadcastss_ps256 (v4sf); +v4df __builtin_ia32_vbroadcastsd_pd256 (v2df); +v4di __builtin_ia32_vbroadcastsi256 (v2di); +v4si __builtin_ia32_pblendd128 (v4si,v4si); +v8si __builtin_ia32_pblendd256 (v8si,v8si); +v32qi __builtin_ia32_pbroadcastb256 (v16qi); +v16hi __builtin_ia32_pbroadcastw256 (v8hi); +v8si __builtin_ia32_pbroadcastd256 (v4si); +v4di __builtin_ia32_pbroadcastq256 (v2di); +v16qi __builtin_ia32_pbroadcastb128 (v16qi); +v8hi __builtin_ia32_pbroadcastw128 (v8hi); +v4si __builtin_ia32_pbroadcastd128 (v4si); +v2di __builtin_ia32_pbroadcastq128 (v2di); +v8si __builtin_ia32_permvarsi256 (v8si,v8si); +v4df __builtin_ia32_permdf256 (v4df,int); +v8sf __builtin_ia32_permvarsf256 (v8sf,v8sf); +v4di __builtin_ia32_permdi256 (v4di,int); +v4di __builtin_ia32_permti256 (v4di,v4di,int); +v4di __builtin_ia32_extract128i256 (v4di,int); +v4di __builtin_ia32_insert128i256 (v4di,v2di,int); +v8si __builtin_ia32_maskloadd256 (pcv8si,v8si); +v4di __builtin_ia32_maskloadq256 (pcv4di,v4di); +v4si __builtin_ia32_maskloadd (pcv4si,v4si); +v2di __builtin_ia32_maskloadq (pcv2di,v2di); +void __builtin_ia32_maskstored256 (pv8si,v8si,v8si); +void __builtin_ia32_maskstoreq256 (pv4di,v4di,v4di); +void __builtin_ia32_maskstored (pv4si,v4si,v4si); +void __builtin_ia32_maskstoreq (pv2di,v2di,v2di); +v8si __builtin_ia32_psllv8si (v8si,v8si); +v4si __builtin_ia32_psllv4si (v4si,v4si); +v4di __builtin_ia32_psllv4di (v4di,v4di); +v2di __builtin_ia32_psllv2di (v2di,v2di); +v8si __builtin_ia32_psrav8si (v8si,v8si); +v4si __builtin_ia32_psrav4si (v4si,v4si); +v8si __builtin_ia32_psrlv8si (v8si,v8si); +v4si __builtin_ia32_psrlv4si (v4si,v4si); +v4di __builtin_ia32_psrlv4di (v4di,v4di); +v2di __builtin_ia32_psrlv2di (v2di,v2di); +v2df __builtin_ia32_gathersiv2df (v2df, pcdouble,v4si,v2df,int); +v4df __builtin_ia32_gathersiv4df (v4df, pcdouble,v4si,v4df,int); +v2df __builtin_ia32_gatherdiv2df (v2df, pcdouble,v2di,v2df,int); +v4df __builtin_ia32_gatherdiv4df (v4df, pcdouble,v4di,v4df,int); +v4sf __builtin_ia32_gathersiv4sf (v4sf, pcfloat,v4si,v4sf,int); +v8sf __builtin_ia32_gathersiv8sf (v8sf, pcfloat,v8si,v8sf,int); +v4sf __builtin_ia32_gatherdiv4sf (v4sf, pcfloat,v2di,v4sf,int); +v4sf __builtin_ia32_gatherdiv4sf256 (v4sf, pcfloat,v4di,v4sf,int); +v2di __builtin_ia32_gathersiv2di (v2di, pcint64,v4si,v2di,int); +v4di __builtin_ia32_gathersiv4di (v4di, pcint64,v4si,v4di,int); +v2di __builtin_ia32_gatherdiv2di (v2di, pcint64,v2di,v2di,int); +v4di __builtin_ia32_gatherdiv4di (v4di, pcint64,v4di,v4di,int); +v4si __builtin_ia32_gathersiv4si (v4si, pcint,v4si,v4si,int); +v8si __builtin_ia32_gathersiv8si (v8si, pcint,v8si,v8si,int); +v4si __builtin_ia32_gatherdiv4si (v4si, pcint,v2di,v4si,int); +v4si __builtin_ia32_gatherdiv4si256 (v4si, pcint,v4di,v4si,int); +@end smallexample + +The following built-in functions are available when @option{-maes} is +used. All of them generate the machine instruction that is part of the +name. + +@smallexample +v2di __builtin_ia32_aesenc128 (v2di, v2di); +v2di __builtin_ia32_aesenclast128 (v2di, v2di); +v2di __builtin_ia32_aesdec128 (v2di, v2di); +v2di __builtin_ia32_aesdeclast128 (v2di, v2di); +v2di __builtin_ia32_aeskeygenassist128 (v2di, const int); +v2di __builtin_ia32_aesimc128 (v2di); +@end smallexample + +The following built-in function is available when @option{-mpclmul} is +used. + +@table @code +@item v2di __builtin_ia32_pclmulqdq128 (v2di, v2di, const int) +Generates the @code{pclmulqdq} machine instruction. +@end table + +The following built-in function is available when @option{-mfsgsbase} is +used. All of them generate the machine instruction that is part of the +name. + +@smallexample +unsigned int __builtin_ia32_rdfsbase32 (void); +unsigned long long __builtin_ia32_rdfsbase64 (void); +unsigned int __builtin_ia32_rdgsbase32 (void); +unsigned long long __builtin_ia32_rdgsbase64 (void); +void _writefsbase_u32 (unsigned int); +void _writefsbase_u64 (unsigned long long); +void _writegsbase_u32 (unsigned int); +void _writegsbase_u64 (unsigned long long); +@end smallexample + +The following built-in function is available when @option{-mrdrnd} is +used. All of them generate the machine instruction that is part of the +name. + +@smallexample +unsigned int __builtin_ia32_rdrand16_step (unsigned short *); +unsigned int __builtin_ia32_rdrand32_step (unsigned int *); +unsigned int __builtin_ia32_rdrand64_step (unsigned long long *); +@end smallexample + +The following built-in function is available when @option{-mptwrite} is +used. All of them generate the machine instruction that is part of the +name. + +@smallexample +void __builtin_ia32_ptwrite32 (unsigned); +void __builtin_ia32_ptwrite64 (unsigned long long); +@end smallexample + +The following built-in functions are available when @option{-msse4a} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +void __builtin_ia32_movntsd (double *, v2df); +void __builtin_ia32_movntss (float *, v4sf); +v2di __builtin_ia32_extrq (v2di, v16qi); +v2di __builtin_ia32_extrqi (v2di, const unsigned int, const unsigned int); +v2di __builtin_ia32_insertq (v2di, v2di); +v2di __builtin_ia32_insertqi (v2di, v2di, const unsigned int, const unsigned int); +@end smallexample + +The following built-in functions are available when @option{-mxop} is used. +@smallexample +v2df __builtin_ia32_vfrczpd (v2df); +v4sf __builtin_ia32_vfrczps (v4sf); +v2df __builtin_ia32_vfrczsd (v2df); +v4sf __builtin_ia32_vfrczss (v4sf); +v4df __builtin_ia32_vfrczpd256 (v4df); +v8sf __builtin_ia32_vfrczps256 (v8sf); +v2di __builtin_ia32_vpcmov (v2di, v2di, v2di); +v2di __builtin_ia32_vpcmov_v2di (v2di, v2di, v2di); +v4si __builtin_ia32_vpcmov_v4si (v4si, v4si, v4si); +v8hi __builtin_ia32_vpcmov_v8hi (v8hi, v8hi, v8hi); +v16qi __builtin_ia32_vpcmov_v16qi (v16qi, v16qi, v16qi); +v2df __builtin_ia32_vpcmov_v2df (v2df, v2df, v2df); +v4sf __builtin_ia32_vpcmov_v4sf (v4sf, v4sf, v4sf); +v4di __builtin_ia32_vpcmov_v4di256 (v4di, v4di, v4di); +v8si __builtin_ia32_vpcmov_v8si256 (v8si, v8si, v8si); +v16hi __builtin_ia32_vpcmov_v16hi256 (v16hi, v16hi, v16hi); +v32qi __builtin_ia32_vpcmov_v32qi256 (v32qi, v32qi, v32qi); +v4df __builtin_ia32_vpcmov_v4df256 (v4df, v4df, v4df); +v8sf __builtin_ia32_vpcmov_v8sf256 (v8sf, v8sf, v8sf); +v16qi __builtin_ia32_vpcomeqb (v16qi, v16qi); +v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi); +v4si __builtin_ia32_vpcomeqd (v4si, v4si); +v2di __builtin_ia32_vpcomeqq (v2di, v2di); +v16qi __builtin_ia32_vpcomequb (v16qi, v16qi); +v4si __builtin_ia32_vpcomequd (v4si, v4si); +v2di __builtin_ia32_vpcomequq (v2di, v2di); +v8hi __builtin_ia32_vpcomequw (v8hi, v8hi); +v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi); +v16qi __builtin_ia32_vpcomfalseb (v16qi, v16qi); +v4si __builtin_ia32_vpcomfalsed (v4si, v4si); +v2di __builtin_ia32_vpcomfalseq (v2di, v2di); +v16qi __builtin_ia32_vpcomfalseub (v16qi, v16qi); +v4si __builtin_ia32_vpcomfalseud (v4si, v4si); +v2di __builtin_ia32_vpcomfalseuq (v2di, v2di); +v8hi __builtin_ia32_vpcomfalseuw (v8hi, v8hi); +v8hi __builtin_ia32_vpcomfalsew (v8hi, v8hi); +v16qi __builtin_ia32_vpcomgeb (v16qi, v16qi); +v4si __builtin_ia32_vpcomged (v4si, v4si); +v2di __builtin_ia32_vpcomgeq (v2di, v2di); +v16qi __builtin_ia32_vpcomgeub (v16qi, v16qi); +v4si __builtin_ia32_vpcomgeud (v4si, v4si); +v2di __builtin_ia32_vpcomgeuq (v2di, v2di); +v8hi __builtin_ia32_vpcomgeuw (v8hi, v8hi); +v8hi __builtin_ia32_vpcomgew (v8hi, v8hi); +v16qi __builtin_ia32_vpcomgtb (v16qi, v16qi); +v4si __builtin_ia32_vpcomgtd (v4si, v4si); +v2di __builtin_ia32_vpcomgtq (v2di, v2di); +v16qi __builtin_ia32_vpcomgtub (v16qi, v16qi); +v4si __builtin_ia32_vpcomgtud (v4si, v4si); +v2di __builtin_ia32_vpcomgtuq (v2di, v2di); +v8hi __builtin_ia32_vpcomgtuw (v8hi, v8hi); +v8hi __builtin_ia32_vpcomgtw (v8hi, v8hi); +v16qi __builtin_ia32_vpcomleb (v16qi, v16qi); +v4si __builtin_ia32_vpcomled (v4si, v4si); +v2di __builtin_ia32_vpcomleq (v2di, v2di); +v16qi __builtin_ia32_vpcomleub (v16qi, v16qi); +v4si __builtin_ia32_vpcomleud (v4si, v4si); +v2di __builtin_ia32_vpcomleuq (v2di, v2di); +v8hi __builtin_ia32_vpcomleuw (v8hi, v8hi); +v8hi __builtin_ia32_vpcomlew (v8hi, v8hi); +v16qi __builtin_ia32_vpcomltb (v16qi, v16qi); +v4si __builtin_ia32_vpcomltd (v4si, v4si); +v2di __builtin_ia32_vpcomltq (v2di, v2di); +v16qi __builtin_ia32_vpcomltub (v16qi, v16qi); +v4si __builtin_ia32_vpcomltud (v4si, v4si); +v2di __builtin_ia32_vpcomltuq (v2di, v2di); +v8hi __builtin_ia32_vpcomltuw (v8hi, v8hi); +v8hi __builtin_ia32_vpcomltw (v8hi, v8hi); +v16qi __builtin_ia32_vpcomneb (v16qi, v16qi); +v4si __builtin_ia32_vpcomned (v4si, v4si); +v2di __builtin_ia32_vpcomneq (v2di, v2di); +v16qi __builtin_ia32_vpcomneub (v16qi, v16qi); +v4si __builtin_ia32_vpcomneud (v4si, v4si); +v2di __builtin_ia32_vpcomneuq (v2di, v2di); +v8hi __builtin_ia32_vpcomneuw (v8hi, v8hi); +v8hi __builtin_ia32_vpcomnew (v8hi, v8hi); +v16qi __builtin_ia32_vpcomtrueb (v16qi, v16qi); +v4si __builtin_ia32_vpcomtrued (v4si, v4si); +v2di __builtin_ia32_vpcomtrueq (v2di, v2di); +v16qi __builtin_ia32_vpcomtrueub (v16qi, v16qi); +v4si __builtin_ia32_vpcomtrueud (v4si, v4si); +v2di __builtin_ia32_vpcomtrueuq (v2di, v2di); +v8hi __builtin_ia32_vpcomtrueuw (v8hi, v8hi); +v8hi __builtin_ia32_vpcomtruew (v8hi, v8hi); +v4si __builtin_ia32_vphaddbd (v16qi); +v2di __builtin_ia32_vphaddbq (v16qi); +v8hi __builtin_ia32_vphaddbw (v16qi); +v2di __builtin_ia32_vphadddq (v4si); +v4si __builtin_ia32_vphaddubd (v16qi); +v2di __builtin_ia32_vphaddubq (v16qi); +v8hi __builtin_ia32_vphaddubw (v16qi); +v2di __builtin_ia32_vphaddudq (v4si); +v4si __builtin_ia32_vphadduwd (v8hi); +v2di __builtin_ia32_vphadduwq (v8hi); +v4si __builtin_ia32_vphaddwd (v8hi); +v2di __builtin_ia32_vphaddwq (v8hi); +v8hi __builtin_ia32_vphsubbw (v16qi); +v2di __builtin_ia32_vphsubdq (v4si); +v4si __builtin_ia32_vphsubwd (v8hi); +v4si __builtin_ia32_vpmacsdd (v4si, v4si, v4si); +v2di __builtin_ia32_vpmacsdqh (v4si, v4si, v2di); +v2di __builtin_ia32_vpmacsdql (v4si, v4si, v2di); +v4si __builtin_ia32_vpmacssdd (v4si, v4si, v4si); +v2di __builtin_ia32_vpmacssdqh (v4si, v4si, v2di); +v2di __builtin_ia32_vpmacssdql (v4si, v4si, v2di); +v4si __builtin_ia32_vpmacsswd (v8hi, v8hi, v4si); +v8hi __builtin_ia32_vpmacssww (v8hi, v8hi, v8hi); +v4si __builtin_ia32_vpmacswd (v8hi, v8hi, v4si); +v8hi __builtin_ia32_vpmacsww (v8hi, v8hi, v8hi); +v4si __builtin_ia32_vpmadcsswd (v8hi, v8hi, v4si); +v4si __builtin_ia32_vpmadcswd (v8hi, v8hi, v4si); +v16qi __builtin_ia32_vpperm (v16qi, v16qi, v16qi); +v16qi __builtin_ia32_vprotb (v16qi, v16qi); +v4si __builtin_ia32_vprotd (v4si, v4si); +v2di __builtin_ia32_vprotq (v2di, v2di); +v8hi __builtin_ia32_vprotw (v8hi, v8hi); +v16qi __builtin_ia32_vpshab (v16qi, v16qi); +v4si __builtin_ia32_vpshad (v4si, v4si); +v2di __builtin_ia32_vpshaq (v2di, v2di); +v8hi __builtin_ia32_vpshaw (v8hi, v8hi); +v16qi __builtin_ia32_vpshlb (v16qi, v16qi); +v4si __builtin_ia32_vpshld (v4si, v4si); +v2di __builtin_ia32_vpshlq (v2di, v2di); +v8hi __builtin_ia32_vpshlw (v8hi, v8hi); +@end smallexample + +The following built-in functions are available when @option{-mfma4} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +v2df __builtin_ia32_vfmaddpd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfmaddps (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfmaddsd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfmaddss (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfmsubpd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfmsubps (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfmsubsd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfmsubss (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfnmaddpd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfnmaddps (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfnmaddsd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfnmaddss (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfnmsubpd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfnmsubps (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfnmsubsd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfnmsubss (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfmaddsubpd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfmaddsubps (v4sf, v4sf, v4sf); +v2df __builtin_ia32_vfmsubaddpd (v2df, v2df, v2df); +v4sf __builtin_ia32_vfmsubaddps (v4sf, v4sf, v4sf); +v4df __builtin_ia32_vfmaddpd256 (v4df, v4df, v4df); +v8sf __builtin_ia32_vfmaddps256 (v8sf, v8sf, v8sf); +v4df __builtin_ia32_vfmsubpd256 (v4df, v4df, v4df); +v8sf __builtin_ia32_vfmsubps256 (v8sf, v8sf, v8sf); +v4df __builtin_ia32_vfnmaddpd256 (v4df, v4df, v4df); +v8sf __builtin_ia32_vfnmaddps256 (v8sf, v8sf, v8sf); +v4df __builtin_ia32_vfnmsubpd256 (v4df, v4df, v4df); +v8sf __builtin_ia32_vfnmsubps256 (v8sf, v8sf, v8sf); +v4df __builtin_ia32_vfmaddsubpd256 (v4df, v4df, v4df); +v8sf __builtin_ia32_vfmaddsubps256 (v8sf, v8sf, v8sf); +v4df __builtin_ia32_vfmsubaddpd256 (v4df, v4df, v4df); +v8sf __builtin_ia32_vfmsubaddps256 (v8sf, v8sf, v8sf); + +@end smallexample + +The following built-in functions are available when @option{-mlwp} is used. + +@smallexample +void __builtin_ia32_llwpcb16 (void *); +void __builtin_ia32_llwpcb32 (void *); +void __builtin_ia32_llwpcb64 (void *); +void * __builtin_ia32_llwpcb16 (void); +void * __builtin_ia32_llwpcb32 (void); +void * __builtin_ia32_llwpcb64 (void); +void __builtin_ia32_lwpval16 (unsigned short, unsigned int, unsigned short); +void __builtin_ia32_lwpval32 (unsigned int, unsigned int, unsigned int); +void __builtin_ia32_lwpval64 (unsigned __int64, unsigned int, unsigned int); +unsigned char __builtin_ia32_lwpins16 (unsigned short, unsigned int, unsigned short); +unsigned char __builtin_ia32_lwpins32 (unsigned int, unsigned int, unsigned int); +unsigned char __builtin_ia32_lwpins64 (unsigned __int64, unsigned int, unsigned int); +@end smallexample + +The following built-in functions are available when @option{-mbmi} is used. +All of them generate the machine instruction that is part of the name. +@smallexample +unsigned int __builtin_ia32_bextr_u32(unsigned int, unsigned int); +unsigned long long __builtin_ia32_bextr_u64 (unsigned long long, unsigned long long); +@end smallexample + +The following built-in functions are available when @option{-mbmi2} is used. +All of them generate the machine instruction that is part of the name. +@smallexample +unsigned int _bzhi_u32 (unsigned int, unsigned int); +unsigned int _pdep_u32 (unsigned int, unsigned int); +unsigned int _pext_u32 (unsigned int, unsigned int); +unsigned long long _bzhi_u64 (unsigned long long, unsigned long long); +unsigned long long _pdep_u64 (unsigned long long, unsigned long long); +unsigned long long _pext_u64 (unsigned long long, unsigned long long); +@end smallexample + +The following built-in functions are available when @option{-mlzcnt} is used. +All of them generate the machine instruction that is part of the name. +@smallexample +unsigned short __builtin_ia32_lzcnt_u16(unsigned short); +unsigned int __builtin_ia32_lzcnt_u32(unsigned int); +unsigned long long __builtin_ia32_lzcnt_u64 (unsigned long long); +@end smallexample + +The following built-in functions are available when @option{-mfxsr} is used. +All of them generate the machine instruction that is part of the name. +@smallexample +void __builtin_ia32_fxsave (void *); +void __builtin_ia32_fxrstor (void *); +void __builtin_ia32_fxsave64 (void *); +void __builtin_ia32_fxrstor64 (void *); +@end smallexample + +The following built-in functions are available when @option{-mxsave} is used. +All of them generate the machine instruction that is part of the name. +@smallexample +void __builtin_ia32_xsave (void *, long long); +void __builtin_ia32_xrstor (void *, long long); +void __builtin_ia32_xsave64 (void *, long long); +void __builtin_ia32_xrstor64 (void *, long long); +@end smallexample + +The following built-in functions are available when @option{-mxsaveopt} is used. +All of them generate the machine instruction that is part of the name. +@smallexample +void __builtin_ia32_xsaveopt (void *, long long); +void __builtin_ia32_xsaveopt64 (void *, long long); +@end smallexample + +The following built-in functions are available when @option{-mtbm} is used. +Both of them generate the immediate form of the bextr machine instruction. +@smallexample +unsigned int __builtin_ia32_bextri_u32 (unsigned int, + const unsigned int); +unsigned long long __builtin_ia32_bextri_u64 (unsigned long long, + const unsigned long long); +@end smallexample + + +The following built-in functions are available when @option{-m3dnow} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +void __builtin_ia32_femms (void); +v8qi __builtin_ia32_pavgusb (v8qi, v8qi); +v2si __builtin_ia32_pf2id (v2sf); +v2sf __builtin_ia32_pfacc (v2sf, v2sf); +v2sf __builtin_ia32_pfadd (v2sf, v2sf); +v2si __builtin_ia32_pfcmpeq (v2sf, v2sf); +v2si __builtin_ia32_pfcmpge (v2sf, v2sf); +v2si __builtin_ia32_pfcmpgt (v2sf, v2sf); +v2sf __builtin_ia32_pfmax (v2sf, v2sf); +v2sf __builtin_ia32_pfmin (v2sf, v2sf); +v2sf __builtin_ia32_pfmul (v2sf, v2sf); +v2sf __builtin_ia32_pfrcp (v2sf); +v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf); +v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf); +v2sf __builtin_ia32_pfrsqrt (v2sf); +v2sf __builtin_ia32_pfsub (v2sf, v2sf); +v2sf __builtin_ia32_pfsubr (v2sf, v2sf); +v2sf __builtin_ia32_pi2fd (v2si); +v4hi __builtin_ia32_pmulhrw (v4hi, v4hi); +@end smallexample + +The following built-in functions are available when @option{-m3dnowa} is used. +All of them generate the machine instruction that is part of the name. + +@smallexample +v2si __builtin_ia32_pf2iw (v2sf); +v2sf __builtin_ia32_pfnacc (v2sf, v2sf); +v2sf __builtin_ia32_pfpnacc (v2sf, v2sf); +v2sf __builtin_ia32_pi2fw (v2si); +v2sf __builtin_ia32_pswapdsf (v2sf); +v2si __builtin_ia32_pswapdsi (v2si); +@end smallexample + +The following built-in functions are available when @option{-mrtm} is used +They are used for restricted transactional memory. These are the internal +low level functions. Normally the functions in +@ref{x86 transactional memory intrinsics} should be used instead. + +@smallexample +int __builtin_ia32_xbegin (); +void __builtin_ia32_xend (); +void __builtin_ia32_xabort (status); +int __builtin_ia32_xtest (); +@end smallexample + +The following built-in functions are available when @option{-mmwaitx} is used. +All of them generate the machine instruction that is part of the name. +@smallexample +void __builtin_ia32_monitorx (void *, unsigned int, unsigned int); +void __builtin_ia32_mwaitx (unsigned int, unsigned int, unsigned int); +@end smallexample + +The following built-in functions are available when @option{-mclzero} is used. +All of them generate the machine instruction that is part of the name. +@smallexample +void __builtin_i32_clzero (void *); +@end smallexample + +The following built-in functions are available when @option{-mpku} is used. +They generate reads and writes to PKRU. +@smallexample +void __builtin_ia32_wrpkru (unsigned int); +unsigned int __builtin_ia32_rdpkru (); +@end smallexample + +The following built-in functions are available when +@option{-mshstk} option is used. They support shadow stack +machine instructions from Intel Control-flow Enforcement Technology (CET). +Each built-in function generates the machine instruction that is part +of the function's name. These are the internal low-level functions. +Normally the functions in @ref{x86 control-flow protection intrinsics} +should be used instead. + +@smallexample +unsigned int __builtin_ia32_rdsspd (void); +unsigned long long __builtin_ia32_rdsspq (void); +void __builtin_ia32_incsspd (unsigned int); +void __builtin_ia32_incsspq (unsigned long long); +void __builtin_ia32_saveprevssp(void); +void __builtin_ia32_rstorssp(void *); +void __builtin_ia32_wrssd(unsigned int, void *); +void __builtin_ia32_wrssq(unsigned long long, void *); +void __builtin_ia32_wrussd(unsigned int, void *); +void __builtin_ia32_wrussq(unsigned long long, void *); +void __builtin_ia32_setssbsy(void); +void __builtin_ia32_clrssbsy(void *); +@end smallexample + +@node x86 transactional memory intrinsics +@subsection x86 Transactional Memory Intrinsics + +These hardware transactional memory intrinsics for x86 allow you to use +memory transactions with RTM (Restricted Transactional Memory). +This support is enabled with the @option{-mrtm} option. +For using HLE (Hardware Lock Elision) see +@ref{x86 specific memory model extensions for transactional memory} instead. + +A memory transaction commits all changes to memory in an atomic way, +as visible to other threads. If the transaction fails it is rolled back +and all side effects discarded. + +Generally there is no guarantee that a memory transaction ever succeeds +and suitable fallback code always needs to be supplied. + +@deftypefn {RTM Function} {unsigned} _xbegin () +Start a RTM (Restricted Transactional Memory) transaction. +Returns @code{_XBEGIN_STARTED} when the transaction +started successfully (note this is not 0, so the constant has to be +explicitly tested). + +If the transaction aborts, all side effects +are undone and an abort code encoded as a bit mask is returned. +The following macros are defined: + +@table @code +@item _XABORT_EXPLICIT +Transaction was explicitly aborted with @code{_xabort}. The parameter passed +to @code{_xabort} is available with @code{_XABORT_CODE(status)}. +@item _XABORT_RETRY +Transaction retry is possible. +@item _XABORT_CONFLICT +Transaction abort due to a memory conflict with another thread. +@item _XABORT_CAPACITY +Transaction abort due to the transaction using too much memory. +@item _XABORT_DEBUG +Transaction abort due to a debug trap. +@item _XABORT_NESTED +Transaction abort in an inner nested transaction. +@end table + +There is no guarantee +any transaction ever succeeds, so there always needs to be a valid +fallback path. +@end deftypefn + +@deftypefn {RTM Function} {void} _xend () +Commit the current transaction. When no transaction is active this faults. +All memory side effects of the transaction become visible +to other threads in an atomic manner. +@end deftypefn + +@deftypefn {RTM Function} {int} _xtest () +Return a nonzero value if a transaction is currently active, otherwise 0. +@end deftypefn + +@deftypefn {RTM Function} {void} _xabort (status) +Abort the current transaction. When no transaction is active this is a no-op. +The @var{status} is an 8-bit constant; its value is encoded in the return +value from @code{_xbegin}. +@end deftypefn + +Here is an example showing handling for @code{_XABORT_RETRY} +and a fallback path for other failures: + +@smallexample +#include + +int n_tries, max_tries; +unsigned status = _XABORT_EXPLICIT; +... + +for (n_tries = 0; n_tries < max_tries; n_tries++) + @{ + status = _xbegin (); + if (status == _XBEGIN_STARTED || !(status & _XABORT_RETRY)) + break; + @} +if (status == _XBEGIN_STARTED) + @{ + ... transaction code... + _xend (); + @} +else + @{ + ... non-transactional fallback path... + @} +@end smallexample + +@noindent +Note that, in most cases, the transactional and non-transactional code +must synchronize together to ensure consistency. + +@node x86 control-flow protection intrinsics +@subsection x86 Control-Flow Protection Intrinsics + +@deftypefn {CET Function} {ret_type} _get_ssp (void) +Get the current value of shadow stack pointer if shadow stack support +from Intel CET is enabled in the hardware or @code{0} otherwise. +The @code{ret_type} is @code{unsigned long long} for 64-bit targets +and @code{unsigned int} for 32-bit targets. +@end deftypefn + +@deftypefn {CET Function} void _inc_ssp (unsigned int) +Increment the current shadow stack pointer by the size specified by the +function argument. The argument is masked to a byte value for security +reasons, so to increment by more than 255 bytes you must call the function +multiple times. +@end deftypefn + +The shadow stack unwind code looks like: + +@smallexample +#include + +/* Unwind the shadow stack for EH. */ +#define _Unwind_Frames_Extra(x) \ + do \ + @{ \ + _Unwind_Word ssp = _get_ssp (); \ + if (ssp != 0) \ + @{ \ + _Unwind_Word tmp = (x); \ + while (tmp > 255) \ + @{ \ + _inc_ssp (tmp); \ + tmp -= 255; \ + @} \ + _inc_ssp (tmp); \ + @} \ + @} \ + while (0) +@end smallexample + +@noindent +This code runs unconditionally on all 64-bit processors. For 32-bit +processors the code runs on those that support multi-byte NOP instructions. + +@node Target Format Checks +@section Format Checks Specific to Particular Target Machines + +For some target machines, GCC supports additional options to the +format attribute +(@pxref{Function Attributes,,Declaring Attributes of Functions}). + +@menu +* Solaris Format Checks:: +* Darwin Format Checks:: +@end menu + +@node Solaris Format Checks +@subsection Solaris Format Checks + +Solaris targets support the @code{cmn_err} (or @code{__cmn_err__}) format +check. @code{cmn_err} accepts a subset of the standard @code{printf} +conversions, and the two-argument @code{%b} conversion for displaying +bit-fields. See the Solaris man page for @code{cmn_err} for more information. + +@node Darwin Format Checks +@subsection Darwin Format Checks + +In addition to the full set of format archetypes (attribute format style +arguments such as @code{printf}, @code{scanf}, @code{strftime}, and +@code{strfmon}), Darwin targets also support the @code{CFString} (or +@code{__CFString__}) archetype in the @code{format} attribute. +Declarations with this archetype are parsed for correct syntax +and argument types. However, parsing of the format string itself and +validating arguments against it in calls to such functions is currently +not performed. + +Additionally, @code{CFStringRefs} (defined by the @code{CoreFoundation} headers) may +also be used as format arguments. Note that the relevant headers are only likely to be +available on Darwin (OSX) installations. On such installations, the XCode and system +documentation provide descriptions of @code{CFString}, @code{CFStringRefs} and +associated functions. + +@node Pragmas +@section Pragmas Accepted by GCC +@cindex pragmas +@cindex @code{#pragma} + +GCC supports several types of pragmas, primarily in order to compile +code originally written for other compilers. Note that in general +we do not recommend the use of pragmas; @xref{Function Attributes}, +for further explanation. + +The GNU C preprocessor recognizes several pragmas in addition to the +compiler pragmas documented here. Refer to the CPP manual for more +information. + +@menu +* AArch64 Pragmas:: +* ARM Pragmas:: +* M32C Pragmas:: +* MeP Pragmas:: +* PRU Pragmas:: +* RS/6000 and PowerPC Pragmas:: +* S/390 Pragmas:: +* Darwin Pragmas:: +* Solaris Pragmas:: +* Symbol-Renaming Pragmas:: +* Structure-Layout Pragmas:: +* Weak Pragmas:: +* Diagnostic Pragmas:: +* Visibility Pragmas:: +* Push/Pop Macro Pragmas:: +* Function Specific Option Pragmas:: +* Loop-Specific Pragmas:: +@end menu + +@node AArch64 Pragmas +@subsection AArch64 Pragmas + +The pragmas defined by the AArch64 target correspond to the AArch64 +target function attributes. They can be specified as below: +@smallexample +#pragma GCC target("string") +@end smallexample + +where @code{@var{string}} can be any string accepted as an AArch64 target +attribute. @xref{AArch64 Function Attributes}, for more details +on the permissible values of @code{string}. + +@node ARM Pragmas +@subsection ARM Pragmas + +The ARM target defines pragmas for controlling the default addition of +@code{long_call} and @code{short_call} attributes to functions. +@xref{Function Attributes}, for information about the effects of these +attributes. + +@table @code +@item long_calls +@cindex pragma, long_calls +Set all subsequent functions to have the @code{long_call} attribute. + +@item no_long_calls +@cindex pragma, no_long_calls +Set all subsequent functions to have the @code{short_call} attribute. + +@item long_calls_off +@cindex pragma, long_calls_off +Do not affect the @code{long_call} or @code{short_call} attributes of +subsequent functions. +@end table + +@node M32C Pragmas +@subsection M32C Pragmas + +@table @code +@item GCC memregs @var{number} +@cindex pragma, memregs +Overrides the command-line option @code{-memregs=} for the current +file. Use with care! This pragma must be before any function in the +file, and mixing different memregs values in different objects may +make them incompatible. This pragma is useful when a +performance-critical function uses a memreg for temporary values, +as it may allow you to reduce the number of memregs used. + +@item ADDRESS @var{name} @var{address} +@cindex pragma, address +For any declared symbols matching @var{name}, this does three things +to that symbol: it forces the symbol to be located at the given +address (a number), it forces the symbol to be volatile, and it +changes the symbol's scope to be static. This pragma exists for +compatibility with other compilers, but note that the common +@code{1234H} numeric syntax is not supported (use @code{0x1234} +instead). Example: + +@smallexample +#pragma ADDRESS port3 0x103 +char port3; +@end smallexample + +@end table + +@node MeP Pragmas +@subsection MeP Pragmas + +@table @code + +@item custom io_volatile (on|off) +@cindex pragma, custom io_volatile +Overrides the command-line option @code{-mio-volatile} for the current +file. Note that for compatibility with future GCC releases, this +option should only be used once before any @code{io} variables in each +file. + +@item GCC coprocessor available @var{registers} +@cindex pragma, coprocessor available +Specifies which coprocessor registers are available to the register +allocator. @var{registers} may be a single register, register range +separated by ellipses, or comma-separated list of those. Example: + +@smallexample +#pragma GCC coprocessor available $c0...$c10, $c28 +@end smallexample + +@item GCC coprocessor call_saved @var{registers} +@cindex pragma, coprocessor call_saved +Specifies which coprocessor registers are to be saved and restored by +any function using them. @var{registers} may be a single register, +register range separated by ellipses, or comma-separated list of +those. Example: + +@smallexample +#pragma GCC coprocessor call_saved $c4...$c6, $c31 +@end smallexample + +@item GCC coprocessor subclass '(A|B|C|D)' = @var{registers} +@cindex pragma, coprocessor subclass +Creates and defines a register class. These register classes can be +used by inline @code{asm} constructs. @var{registers} may be a single +register, register range separated by ellipses, or comma-separated +list of those. Example: + +@smallexample +#pragma GCC coprocessor subclass 'B' = $c2, $c4, $c6 + +asm ("cpfoo %0" : "=B" (x)); +@end smallexample + +@item GCC disinterrupt @var{name} , @var{name} @dots{} +@cindex pragma, disinterrupt +For the named functions, the compiler adds code to disable interrupts +for the duration of those functions. If any functions so named +are not encountered in the source, a warning is emitted that the pragma is +not used. Examples: + +@smallexample +#pragma disinterrupt foo +#pragma disinterrupt bar, grill +int foo () @{ @dots{} @} +@end smallexample + +@item GCC call @var{name} , @var{name} @dots{} +@cindex pragma, call +For the named functions, the compiler always uses a register-indirect +call model when calling the named functions. Examples: + +@smallexample +extern int foo (); +#pragma call foo +@end smallexample + +@end table + +@node PRU Pragmas +@subsection PRU Pragmas + +@table @code + +@item ctable_entry @var{index} @var{constant_address} +@cindex pragma, ctable_entry +Specifies that the PRU CTABLE entry given by @var{index} has the value +@var{constant_address}. This enables GCC to emit LBCO/SBCO instructions +when the load/store address is known and can be addressed with some CTABLE +entry. For example: + +@smallexample +/* will compile to "sbco Rx, 2, 0x10, 4" */ +#pragma ctable_entry 2 0x4802a000 +*(unsigned int *)0x4802a010 = val; +@end smallexample + +@end table + +@node RS/6000 and PowerPC Pragmas +@subsection RS/6000 and PowerPC Pragmas + +The RS/6000 and PowerPC targets define one pragma for controlling +whether or not the @code{longcall} attribute is added to function +declarations by default. This pragma overrides the @option{-mlongcall} +option, but not the @code{longcall} and @code{shortcall} attributes. +@xref{RS/6000 and PowerPC Options}, for more information about when long +calls are and are not necessary. + +@table @code +@item longcall (1) +@cindex pragma, longcall +Apply the @code{longcall} attribute to all subsequent function +declarations. + +@item longcall (0) +Do not apply the @code{longcall} attribute to subsequent function +declarations. +@end table + +@c Describe h8300 pragmas here. +@c Describe sh pragmas here. +@c Describe v850 pragmas here. + +@node S/390 Pragmas +@subsection S/390 Pragmas + +The pragmas defined by the S/390 target correspond to the S/390 +target function attributes and some the additional options: + +@table @samp +@item zvector +@itemx no-zvector +@end table + +Note that options of the pragma, unlike options of the target +attribute, do change the value of preprocessor macros like +@code{__VEC__}. They can be specified as below: + +@smallexample +#pragma GCC target("string[,string]...") +#pragma GCC target("string"[,"string"]...) +@end smallexample + +@node Darwin Pragmas +@subsection Darwin Pragmas + +The following pragmas are available for all architectures running the +Darwin operating system. These are useful for compatibility with other +Mac OS compilers. + +@table @code +@item mark @var{tokens}@dots{} +@cindex pragma, mark +This pragma is accepted, but has no effect. + +@item options align=@var{alignment} +@cindex pragma, options align +This pragma sets the alignment of fields in structures. The values of +@var{alignment} may be @code{mac68k}, to emulate m68k alignment, or +@code{power}, to emulate PowerPC alignment. Uses of this pragma nest +properly; to restore the previous setting, use @code{reset} for the +@var{alignment}. + +@item segment @var{tokens}@dots{} +@cindex pragma, segment +This pragma is accepted, but has no effect. + +@item unused (@var{var} [, @var{var}]@dots{}) +@cindex pragma, unused +This pragma declares variables to be possibly unused. GCC does not +produce warnings for the listed variables. The effect is similar to +that of the @code{unused} attribute, except that this pragma may appear +anywhere within the variables' scopes. +@end table + +@node Solaris Pragmas +@subsection Solaris Pragmas + +The Solaris target supports @code{#pragma redefine_extname} +(@pxref{Symbol-Renaming Pragmas}). It also supports additional +@code{#pragma} directives for compatibility with the system compiler. + +@table @code +@item align @var{alignment} (@var{variable} [, @var{variable}]...) +@cindex pragma, align + +Increase the minimum alignment of each @var{variable} to @var{alignment}. +This is the same as GCC's @code{aligned} attribute @pxref{Variable +Attributes}). Macro expansion occurs on the arguments to this pragma +when compiling C and Objective-C@. It does not currently occur when +compiling C++, but this is a bug which may be fixed in a future +release. + +@item fini (@var{function} [, @var{function}]...) +@cindex pragma, fini + +This pragma causes each listed @var{function} to be called after +main, or during shared module unloading, by adding a call to the +@code{.fini} section. + +@item init (@var{function} [, @var{function}]...) +@cindex pragma, init + +This pragma causes each listed @var{function} to be called during +initialization (before @code{main}) or during shared module loading, by +adding a call to the @code{.init} section. + +@end table + +@node Symbol-Renaming Pragmas +@subsection Symbol-Renaming Pragmas + +GCC supports a @code{#pragma} directive that changes the name used in +assembly for a given declaration. While this pragma is supported on all +platforms, it is intended primarily to provide compatibility with the +Solaris system headers. This effect can also be achieved using the asm +labels extension (@pxref{Asm Labels}). + +@table @code +@item redefine_extname @var{oldname} @var{newname} +@cindex pragma, redefine_extname + +This pragma gives the C function @var{oldname} the assembly symbol +@var{newname}. The preprocessor macro @code{__PRAGMA_REDEFINE_EXTNAME} +is defined if this pragma is available (currently on all platforms). +@end table + +This pragma and the @code{asm} labels extension interact in a complicated +manner. Here are some corner cases you may want to be aware of: + +@enumerate +@item This pragma silently applies only to declarations with external +linkage. The @code{asm} label feature does not have this restriction. + +@item In C++, this pragma silently applies only to declarations with +``C'' linkage. Again, @code{asm} labels do not have this restriction. + +@item If either of the ways of changing the assembly name of a +declaration are applied to a declaration whose assembly name has +already been determined (either by a previous use of one of these +features, or because the compiler needed the assembly name in order to +generate code), and the new name is different, a warning issues and +the name does not change. + +@item The @var{oldname} used by @code{#pragma redefine_extname} is +always the C-language name. +@end enumerate + +@node Structure-Layout Pragmas +@subsection Structure-Layout Pragmas + +For compatibility with Microsoft Windows compilers, GCC supports a +set of @code{#pragma} directives that change the maximum alignment of +members of structures (other than zero-width bit-fields), unions, and +classes subsequently defined. The @var{n} value below always is required +to be a small power of two and specifies the new alignment in bytes. + +@enumerate +@item @code{#pragma pack(@var{n})} simply sets the new alignment. +@item @code{#pragma pack()} sets the alignment to the one that was in +effect when compilation started (see also command-line option +@option{-fpack-struct[=@var{n}]} @pxref{Code Gen Options}). +@item @code{#pragma pack(push[,@var{n}])} pushes the current alignment +setting on an internal stack and then optionally sets the new alignment. +@item @code{#pragma pack(pop)} restores the alignment setting to the one +saved at the top of the internal stack (and removes that stack entry). +Note that @code{#pragma pack([@var{n}])} does not influence this internal +stack; thus it is possible to have @code{#pragma pack(push)} followed by +multiple @code{#pragma pack(@var{n})} instances and finalized by a single +@code{#pragma pack(pop)}. +@end enumerate + +Some targets, e.g.@: x86 and PowerPC, support the @code{#pragma ms_struct} +directive which lays out structures and unions subsequently defined as the +documented @code{__attribute__ ((ms_struct))}. + +@enumerate +@item @code{#pragma ms_struct on} turns on the Microsoft layout. +@item @code{#pragma ms_struct off} turns off the Microsoft layout. +@item @code{#pragma ms_struct reset} goes back to the default layout. +@end enumerate + +Most targets also support the @code{#pragma scalar_storage_order} directive +which lays out structures and unions subsequently defined as the documented +@code{__attribute__ ((scalar_storage_order))}. + +@enumerate +@item @code{#pragma scalar_storage_order big-endian} sets the storage order +of the scalar fields to big-endian. +@item @code{#pragma scalar_storage_order little-endian} sets the storage order +of the scalar fields to little-endian. +@item @code{#pragma scalar_storage_order default} goes back to the endianness +that was in effect when compilation started (see also command-line option +@option{-fsso-struct=@var{endianness}} @pxref{C Dialect Options}). +@end enumerate + +@node Weak Pragmas +@subsection Weak Pragmas + +For compatibility with SVR4, GCC supports a set of @code{#pragma} +directives for declaring symbols to be weak, and defining weak +aliases. + +@table @code +@item #pragma weak @var{symbol} +@cindex pragma, weak +This pragma declares @var{symbol} to be weak, as if the declaration +had the attribute of the same name. The pragma may appear before +or after the declaration of @var{symbol}. It is not an error for +@var{symbol} to never be defined at all. + +@item #pragma weak @var{symbol1} = @var{symbol2} +This pragma declares @var{symbol1} to be a weak alias of @var{symbol2}. +It is an error if @var{symbol2} is not defined in the current +translation unit. +@end table + +@node Diagnostic Pragmas +@subsection Diagnostic Pragmas + +GCC allows the user to selectively enable or disable certain types of +diagnostics, and change the kind of the diagnostic. For example, a +project's policy might require that all sources compile with +@option{-Werror} but certain files might have exceptions allowing +specific types of warnings. Or, a project might selectively enable +diagnostics and treat them as errors depending on which preprocessor +macros are defined. + +@table @code +@item #pragma GCC diagnostic @var{kind} @var{option} +@cindex pragma, diagnostic + +Modifies the disposition of a diagnostic. Note that not all +diagnostics are modifiable; at the moment only warnings (normally +controlled by @samp{-W@dots{}}) can be controlled, and not all of them. +Use @option{-fdiagnostics-show-option} to determine which diagnostics +are controllable and which option controls them. + +@var{kind} is @samp{error} to treat this diagnostic as an error, +@samp{warning} to treat it like a warning (even if @option{-Werror} is +in effect), or @samp{ignored} if the diagnostic is to be ignored. +@var{option} is a double quoted string that matches the command-line +option. + +@smallexample +#pragma GCC diagnostic warning "-Wformat" +#pragma GCC diagnostic error "-Wformat" +#pragma GCC diagnostic ignored "-Wformat" +@end smallexample + +Note that these pragmas override any command-line options. GCC keeps +track of the location of each pragma, and issues diagnostics according +to the state as of that point in the source file. Thus, pragmas occurring +after a line do not affect diagnostics caused by that line. + +@item #pragma GCC diagnostic push +@itemx #pragma GCC diagnostic pop + +Causes GCC to remember the state of the diagnostics as of each +@code{push}, and restore to that point at each @code{pop}. If a +@code{pop} has no matching @code{push}, the command-line options are +restored. + +@smallexample +#pragma GCC diagnostic error "-Wuninitialized" + foo(a); /* error is given for this one */ +#pragma GCC diagnostic push +#pragma GCC diagnostic ignored "-Wuninitialized" + foo(b); /* no diagnostic for this one */ +#pragma GCC diagnostic pop + foo(c); /* error is given for this one */ +#pragma GCC diagnostic pop + foo(d); /* depends on command-line options */ +@end smallexample + +@item #pragma GCC diagnostic ignored_attributes + +Similarly to @option{-Wno-attributes=}, this pragma allows users to suppress +warnings about unknown scoped attributes (in C++11 and C2X). For example, +@code{#pragma GCC diagnostic ignored_attributes "vendor::attr"} disables +warning about the following declaration: + +@smallexample +[[vendor::attr]] void f(); +@end smallexample + +whereas @code{#pragma GCC diagnostic ignored_attributes "vendor::"} prevents +warning about both of these declarations: + +@smallexample +[[vendor::safe]] void f(); +[[vendor::unsafe]] void f2(); +@end smallexample + +@end table + +GCC also offers a simple mechanism for printing messages during +compilation. + +@table @code +@item #pragma message @var{string} +@cindex pragma, diagnostic + +Prints @var{string} as a compiler message on compilation. The message +is informational only, and is neither a compilation warning nor an +error. Newlines can be included in the string by using the @samp{\n} +escape sequence. + +@smallexample +#pragma message "Compiling " __FILE__ "..." +@end smallexample + +@var{string} may be parenthesized, and is printed with location +information. For example, + +@smallexample +#define DO_PRAGMA(x) _Pragma (#x) +#define TODO(x) DO_PRAGMA(message ("TODO - " #x)) + +TODO(Remember to fix this) +@end smallexample + +@noindent +prints @samp{/tmp/file.c:4: note: #pragma message: +TODO - Remember to fix this}. + +@item #pragma GCC error @var{message} +@cindex pragma, diagnostic +Generates an error message. This pragma @emph{is} considered to +indicate an error in the compilation, and it will be treated as such. + +Newlines can be included in the string by using the @samp{\n} +escape sequence. They will be displayed as newlines even if the +@option{-fmessage-length} option is set to zero. + +The error is only generated if the pragma is present in the code after +pre-processing has been completed. It does not matter however if the +code containing the pragma is unreachable: + +@smallexample +#if 0 +#pragma GCC error "this error is not seen" +#endif +void foo (void) +@{ + return; +#pragma GCC error "this error is seen" +@} +@end smallexample + +@item #pragma GCC warning @var{message} +@cindex pragma, diagnostic +This is just like @samp{pragma GCC error} except that a warning +message is issued instead of an error message. Unless +@option{-Werror} is in effect, in which case this pragma will generate +an error as well. + +@end table + +@node Visibility Pragmas +@subsection Visibility Pragmas + +@table @code +@item #pragma GCC visibility push(@var{visibility}) +@itemx #pragma GCC visibility pop +@cindex pragma, visibility + +This pragma allows the user to set the visibility for multiple +declarations without having to give each a visibility attribute +(@pxref{Function Attributes}). + +In C++, @samp{#pragma GCC visibility} affects only namespace-scope +declarations. Class members and template specializations are not +affected; if you want to override the visibility for a particular +member or instantiation, you must use an attribute. + +@end table + + +@node Push/Pop Macro Pragmas +@subsection Push/Pop Macro Pragmas + +For compatibility with Microsoft Windows compilers, GCC supports +@samp{#pragma push_macro(@var{"macro_name"})} +and @samp{#pragma pop_macro(@var{"macro_name"})}. + +@table @code +@item #pragma push_macro(@var{"macro_name"}) +@cindex pragma, push_macro +This pragma saves the value of the macro named as @var{macro_name} to +the top of the stack for this macro. + +@item #pragma pop_macro(@var{"macro_name"}) +@cindex pragma, pop_macro +This pragma sets the value of the macro named as @var{macro_name} to +the value on top of the stack for this macro. If the stack for +@var{macro_name} is empty, the value of the macro remains unchanged. +@end table + +For example: + +@smallexample +#define X 1 +#pragma push_macro("X") +#undef X +#define X -1 +#pragma pop_macro("X") +int x [X]; +@end smallexample + +@noindent +In this example, the definition of X as 1 is saved by @code{#pragma +push_macro} and restored by @code{#pragma pop_macro}. + +@node Function Specific Option Pragmas +@subsection Function Specific Option Pragmas + +@table @code +@item #pragma GCC target (@var{string}, @dots{}) +@cindex pragma GCC target + +This pragma allows you to set target-specific options for functions +defined later in the source file. One or more strings can be +specified. Each function that is defined after this point is treated +as if it had been declared with one @code{target(}@var{string}@code{)} +attribute for each @var{string} argument. The parentheses around +the strings in the pragma are optional. @xref{Function Attributes}, +for more information about the @code{target} attribute and the attribute +syntax. + +The @code{#pragma GCC target} pragma is presently implemented for +x86, ARM, AArch64, PowerPC, S/390, and Nios II targets only. + +@item #pragma GCC optimize (@var{string}, @dots{}) +@cindex pragma GCC optimize + +This pragma allows you to set global optimization options for functions +defined later in the source file. One or more strings can be +specified. Each function that is defined after this point is treated +as if it had been declared with one @code{optimize(}@var{string}@code{)} +attribute for each @var{string} argument. The parentheses around +the strings in the pragma are optional. @xref{Function Attributes}, +for more information about the @code{optimize} attribute and the attribute +syntax. + +@item #pragma GCC push_options +@itemx #pragma GCC pop_options +@cindex pragma GCC push_options +@cindex pragma GCC pop_options + +These pragmas maintain a stack of the current target and optimization +options. It is intended for include files where you temporarily want +to switch to using a different @samp{#pragma GCC target} or +@samp{#pragma GCC optimize} and then to pop back to the previous +options. + +@item #pragma GCC reset_options +@cindex pragma GCC reset_options + +This pragma clears the current @code{#pragma GCC target} and +@code{#pragma GCC optimize} to use the default switches as specified +on the command line. + +@end table + +@node Loop-Specific Pragmas +@subsection Loop-Specific Pragmas + +@table @code +@item #pragma GCC ivdep +@cindex pragma GCC ivdep + +With this pragma, the programmer asserts that there are no loop-carried +dependencies which would prevent consecutive iterations of +the following loop from executing concurrently with SIMD +(single instruction multiple data) instructions. + +For example, the compiler can only unconditionally vectorize the following +loop with the pragma: + +@smallexample +void foo (int n, int *a, int *b, int *c) +@{ + int i, j; +#pragma GCC ivdep + for (i = 0; i < n; ++i) + a[i] = b[i] + c[i]; +@} +@end smallexample + +@noindent +In this example, using the @code{restrict} qualifier had the same +effect. In the following example, that would not be possible. Assume +@math{k < -m} or @math{k >= m}. Only with the pragma, the compiler knows +that it can unconditionally vectorize the following loop: + +@smallexample +void ignore_vec_dep (int *a, int k, int c, int m) +@{ +#pragma GCC ivdep + for (int i = 0; i < m; i++) + a[i] = a[i + k] * c; +@} +@end smallexample + +@item #pragma GCC unroll @var{n} +@cindex pragma GCC unroll @var{n} + +You can use this pragma to control how many times a loop should be unrolled. +It must be placed immediately before a @code{for}, @code{while} or @code{do} +loop or a @code{#pragma GCC ivdep}, and applies only to the loop that follows. +@var{n} is an integer constant expression specifying the unrolling factor. +The values of @math{0} and @math{1} block any unrolling of the loop. + +@end table + +@node Unnamed Fields +@section Unnamed Structure and Union Fields +@cindex @code{struct} +@cindex @code{union} + +As permitted by ISO C11 and for compatibility with other compilers, +GCC allows you to define +a structure or union that contains, as fields, structures and unions +without names. For example: + +@smallexample +struct @{ + int a; + union @{ + int b; + float c; + @}; + int d; +@} foo; +@end smallexample + +@noindent +In this example, you are able to access members of the unnamed +union with code like @samp{foo.b}. Note that only unnamed structs and +unions are allowed, you may not have, for example, an unnamed +@code{int}. + +You must never create such structures that cause ambiguous field definitions. +For example, in this structure: + +@smallexample +struct @{ + int a; + struct @{ + int a; + @}; +@} foo; +@end smallexample + +@noindent +it is ambiguous which @code{a} is being referred to with @samp{foo.a}. +The compiler gives errors for such constructs. + +@opindex fms-extensions +Unless @option{-fms-extensions} is used, the unnamed field must be a +structure or union definition without a tag (for example, @samp{struct +@{ int a; @};}). If @option{-fms-extensions} is used, the field may +also be a definition with a tag such as @samp{struct foo @{ int a; +@};}, a reference to a previously defined structure or union such as +@samp{struct foo;}, or a reference to a @code{typedef} name for a +previously defined structure or union type. + +@opindex fplan9-extensions +The option @option{-fplan9-extensions} enables +@option{-fms-extensions} as well as two other extensions. First, a +pointer to a structure is automatically converted to a pointer to an +anonymous field for assignments and function calls. For example: + +@smallexample +struct s1 @{ int a; @}; +struct s2 @{ struct s1; @}; +extern void f1 (struct s1 *); +void f2 (struct s2 *p) @{ f1 (p); @} +@end smallexample + +@noindent +In the call to @code{f1} inside @code{f2}, the pointer @code{p} is +converted into a pointer to the anonymous field. + +Second, when the type of an anonymous field is a @code{typedef} for a +@code{struct} or @code{union}, code may refer to the field using the +name of the @code{typedef}. + +@smallexample +typedef struct @{ int a; @} s1; +struct s2 @{ s1; @}; +s1 f1 (struct s2 *p) @{ return p->s1; @} +@end smallexample + +These usages are only permitted when they are not ambiguous. + +@node Thread-Local +@section Thread-Local Storage +@cindex Thread-Local Storage +@cindex @acronym{TLS} +@cindex @code{__thread} + +Thread-local storage (@acronym{TLS}) is a mechanism by which variables +are allocated such that there is one instance of the variable per extant +thread. The runtime model GCC uses to implement this originates +in the IA-64 processor-specific ABI, but has since been migrated +to other processors as well. It requires significant support from +the linker (@command{ld}), dynamic linker (@command{ld.so}), and +system libraries (@file{libc.so} and @file{libpthread.so}), so it +is not available everywhere. + +At the user level, the extension is visible with a new storage +class keyword: @code{__thread}. For example: + +@smallexample +__thread int i; +extern __thread struct state s; +static __thread char *p; +@end smallexample + +The @code{__thread} specifier may be used alone, with the @code{extern} +or @code{static} specifiers, but with no other storage class specifier. +When used with @code{extern} or @code{static}, @code{__thread} must appear +immediately after the other storage class specifier. + +The @code{__thread} specifier may be applied to any global, file-scoped +static, function-scoped static, or static data member of a class. It may +not be applied to block-scoped automatic or non-static data member. + +When the address-of operator is applied to a thread-local variable, it is +evaluated at run time and returns the address of the current thread's +instance of that variable. An address so obtained may be used by any +thread. When a thread terminates, any pointers to thread-local variables +in that thread become invalid. + +No static initialization may refer to the address of a thread-local variable. + +In C++, if an initializer is present for a thread-local variable, it must +be a @var{constant-expression}, as defined in 5.19.2 of the ANSI/ISO C++ +standard. + +See @uref{https://www.akkadia.org/drepper/tls.pdf, +ELF Handling For Thread-Local Storage} for a detailed explanation of +the four thread-local storage addressing models, and how the runtime +is expected to function. + +@menu +* C99 Thread-Local Edits:: +* C++98 Thread-Local Edits:: +@end menu + +@node C99 Thread-Local Edits +@subsection ISO/IEC 9899:1999 Edits for Thread-Local Storage + +The following are a set of changes to ISO/IEC 9899:1999 (aka C99) +that document the exact semantics of the language extension. + +@itemize @bullet +@item +@cite{5.1.2 Execution environments} + +Add new text after paragraph 1 + +@quotation +Within either execution environment, a @dfn{thread} is a flow of +control within a program. It is implementation defined whether +or not there may be more than one thread associated with a program. +It is implementation defined how threads beyond the first are +created, the name and type of the function called at thread +startup, and how threads may be terminated. However, objects +with thread storage duration shall be initialized before thread +startup. +@end quotation + +@item +@cite{6.2.4 Storage durations of objects} + +Add new text before paragraph 3 + +@quotation +An object whose identifier is declared with the storage-class +specifier @w{@code{__thread}} has @dfn{thread storage duration}. +Its lifetime is the entire execution of the thread, and its +stored value is initialized only once, prior to thread startup. +@end quotation + +@item +@cite{6.4.1 Keywords} + +Add @code{__thread}. + +@item +@cite{6.7.1 Storage-class specifiers} + +Add @code{__thread} to the list of storage class specifiers in +paragraph 1. + +Change paragraph 2 to + +@quotation +With the exception of @code{__thread}, at most one storage-class +specifier may be given [@dots{}]. The @code{__thread} specifier may +be used alone, or immediately following @code{extern} or +@code{static}. +@end quotation + +Add new text after paragraph 6 + +@quotation +The declaration of an identifier for a variable that has +block scope that specifies @code{__thread} shall also +specify either @code{extern} or @code{static}. + +The @code{__thread} specifier shall be used only with +variables. +@end quotation +@end itemize + +@node C++98 Thread-Local Edits +@subsection ISO/IEC 14882:1998 Edits for Thread-Local Storage + +The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) +that document the exact semantics of the language extension. + +@itemize @bullet +@item +@b{[intro.execution]} + +New text after paragraph 4 + +@quotation +A @dfn{thread} is a flow of control within the abstract machine. +It is implementation defined whether or not there may be more than +one thread. +@end quotation + +New text after paragraph 7 + +@quotation +It is unspecified whether additional action must be taken to +ensure when and whether side effects are visible to other threads. +@end quotation + +@item +@b{[lex.key]} + +Add @code{__thread}. + +@item +@b{[basic.start.main]} + +Add after paragraph 5 + +@quotation +The thread that begins execution at the @code{main} function is called +the @dfn{main thread}. It is implementation defined how functions +beginning threads other than the main thread are designated or typed. +A function so designated, as well as the @code{main} function, is called +a @dfn{thread startup function}. It is implementation defined what +happens if a thread startup function returns. It is implementation +defined what happens to other threads when any thread calls @code{exit}. +@end quotation + +@item +@b{[basic.start.init]} + +Add after paragraph 4 + +@quotation +The storage for an object of thread storage duration shall be +statically initialized before the first statement of the thread startup +function. An object of thread storage duration shall not require +dynamic initialization. +@end quotation + +@item +@b{[basic.start.term]} + +Add after paragraph 3 + +@quotation +The type of an object with thread storage duration shall not have a +non-trivial destructor, nor shall it be an array type whose elements +(directly or indirectly) have non-trivial destructors. +@end quotation + +@item +@b{[basic.stc]} + +Add ``thread storage duration'' to the list in paragraph 1. + +Change paragraph 2 + +@quotation +Thread, static, and automatic storage durations are associated with +objects introduced by declarations [@dots{}]. +@end quotation + +Add @code{__thread} to the list of specifiers in paragraph 3. + +@item +@b{[basic.stc.thread]} + +New section before @b{[basic.stc.static]} + +@quotation +The keyword @code{__thread} applied to a non-local object gives the +object thread storage duration. + +A local variable or class data member declared both @code{static} +and @code{__thread} gives the variable or member thread storage +duration. +@end quotation + +@item +@b{[basic.stc.static]} + +Change paragraph 1 + +@quotation +All objects that have neither thread storage duration, dynamic +storage duration nor are local [@dots{}]. +@end quotation + +@item +@b{[dcl.stc]} + +Add @code{__thread} to the list in paragraph 1. + +Change paragraph 1 + +@quotation +With the exception of @code{__thread}, at most one +@var{storage-class-specifier} shall appear in a given +@var{decl-specifier-seq}. The @code{__thread} specifier may +be used alone, or immediately following the @code{extern} or +@code{static} specifiers. [@dots{}] +@end quotation + +Add after paragraph 5 + +@quotation +The @code{__thread} specifier can be applied only to the names of objects +and to anonymous unions. +@end quotation + +@item +@b{[class.mem]} + +Add after paragraph 6 + +@quotation +Non-@code{static} members shall not be @code{__thread}. +@end quotation +@end itemize + +@node Binary constants +@section Binary Constants using the @samp{0b} Prefix +@cindex Binary constants using the @samp{0b} prefix + +Integer constants can be written as binary constants, consisting of a +sequence of @samp{0} and @samp{1} digits, prefixed by @samp{0b} or +@samp{0B}. This is particularly useful in environments that operate a +lot on the bit level (like microcontrollers). + +The following statements are identical: + +@smallexample +i = 42; +i = 0x2a; +i = 052; +i = 0b101010; +@end smallexample + +The type of these constants follows the same rules as for octal or +hexadecimal integer constants, so suffixes like @samp{L} or @samp{UL} +can be applied. + +@node C++ Extensions +@chapter Extensions to the C++ Language +@cindex extensions, C++ language +@cindex C++ language extensions + +The GNU compiler provides these extensions to the C++ language (and you +can also use most of the C language extensions in your C++ programs). If you +want to write code that checks whether these features are available, you can +test for the GNU compiler the same way as for C programs: check for a +predefined macro @code{__GNUC__}. You can also use @code{__GNUG__} to +test specifically for GNU C++ (@pxref{Common Predefined Macros,, +Predefined Macros,cpp,The GNU C Preprocessor}). + +@menu +* C++ Volatiles:: What constitutes an access to a volatile object. +* Restricted Pointers:: C99 restricted pointers and references. +* Vague Linkage:: Where G++ puts inlines, vtables and such. +* C++ Interface:: You can use a single C++ header file for both + declarations and definitions. +* Template Instantiation:: Methods for ensuring that exactly one copy of + each needed template instantiation is emitted. +* Bound member functions:: You can extract a function pointer to the + method denoted by a @samp{->*} or @samp{.*} expression. +* C++ Attributes:: Variable, function, and type attributes for C++ only. +* Function Multiversioning:: Declaring multiple function versions. +* Type Traits:: Compiler support for type traits. +* C++ Concepts:: Improved support for generic programming. +* Deprecated Features:: Things will disappear from G++. +* Backwards Compatibility:: Compatibilities with earlier definitions of C++. +@end menu + +@node C++ Volatiles +@section When is a Volatile C++ Object Accessed? +@cindex accessing volatiles +@cindex volatile read +@cindex volatile write +@cindex volatile access + +The C++ standard differs from the C standard in its treatment of +volatile objects. It fails to specify what constitutes a volatile +access, except to say that C++ should behave in a similar manner to C +with respect to volatiles, where possible. However, the different +lvalueness of expressions between C and C++ complicate the behavior. +G++ behaves the same as GCC for volatile access, @xref{C +Extensions,,Volatiles}, for a description of GCC's behavior. + +The C and C++ language specifications differ when an object is +accessed in a void context: + +@smallexample +volatile int *src = @var{somevalue}; +*src; +@end smallexample + +The C++ standard specifies that such expressions do not undergo lvalue +to rvalue conversion, and that the type of the dereferenced object may +be incomplete. The C++ standard does not specify explicitly that it +is lvalue to rvalue conversion that is responsible for causing an +access. There is reason to believe that it is, because otherwise +certain simple expressions become undefined. However, because it +would surprise most programmers, G++ treats dereferencing a pointer to +volatile object of complete type as GCC would do for an equivalent +type in C@. When the object has incomplete type, G++ issues a +warning; if you wish to force an error, you must force a conversion to +rvalue with, for instance, a static cast. + +When using a reference to volatile, G++ does not treat equivalent +expressions as accesses to volatiles, but instead issues a warning that +no volatile is accessed. The rationale for this is that otherwise it +becomes difficult to determine where volatile access occur, and not +possible to ignore the return value from functions returning volatile +references. Again, if you wish to force a read, cast the reference to +an rvalue. + +G++ implements the same behavior as GCC does when assigning to a +volatile object---there is no reread of the assigned-to object, the +assigned rvalue is reused. Note that in C++ assignment expressions +are lvalues, and if used as an lvalue, the volatile object is +referred to. For instance, @var{vref} refers to @var{vobj}, as +expected, in the following example: + +@smallexample +volatile int vobj; +volatile int &vref = vobj = @var{something}; +@end smallexample + +@node Restricted Pointers +@section Restricting Pointer Aliasing +@cindex restricted pointers +@cindex restricted references +@cindex restricted this pointer + +As with the C front end, G++ understands the C99 feature of restricted pointers, +specified with the @code{__restrict__}, or @code{__restrict} type +qualifier. Because you cannot compile C++ by specifying the @option{-std=c99} +language flag, @code{restrict} is not a keyword in C++. + +In addition to allowing restricted pointers, you can specify restricted +references, which indicate that the reference is not aliased in the local +context. + +@smallexample +void fn (int *__restrict__ rptr, int &__restrict__ rref) +@{ + /* @r{@dots{}} */ +@} +@end smallexample + +@noindent +In the body of @code{fn}, @var{rptr} points to an unaliased integer and +@var{rref} refers to a (different) unaliased integer. + +You may also specify whether a member function's @var{this} pointer is +unaliased by using @code{__restrict__} as a member function qualifier. + +@smallexample +void T::fn () __restrict__ +@{ + /* @r{@dots{}} */ +@} +@end smallexample + +@noindent +Within the body of @code{T::fn}, @var{this} has the effective +definition @code{T *__restrict__ const this}. Notice that the +interpretation of a @code{__restrict__} member function qualifier is +different to that of @code{const} or @code{volatile} qualifier, in that it +is applied to the pointer rather than the object. This is consistent with +other compilers that implement restricted pointers. + +As with all outermost parameter qualifiers, @code{__restrict__} is +ignored in function definition matching. This means you only need to +specify @code{__restrict__} in a function definition, rather than +in a function prototype as well. + +@node Vague Linkage +@section Vague Linkage +@cindex vague linkage + +There are several constructs in C++ that require space in the object +file but are not clearly tied to a single translation unit. We say that +these constructs have ``vague linkage''. Typically such constructs are +emitted wherever they are needed, though sometimes we can be more +clever. + +@table @asis +@item Inline Functions +Inline functions are typically defined in a header file which can be +included in many different compilations. Hopefully they can usually be +inlined, but sometimes an out-of-line copy is necessary, if the address +of the function is taken or if inlining fails. In general, we emit an +out-of-line copy in all translation units where one is needed. As an +exception, we only emit inline virtual functions with the vtable, since +it always requires a copy. + +Local static variables and string constants used in an inline function +are also considered to have vague linkage, since they must be shared +between all inlined and out-of-line instances of the function. + +@item VTables +@cindex vtable +C++ virtual functions are implemented in most compilers using a lookup +table, known as a vtable. The vtable contains pointers to the virtual +functions provided by a class, and each object of the class contains a +pointer to its vtable (or vtables, in some multiple-inheritance +situations). If the class declares any non-inline, non-pure virtual +functions, the first one is chosen as the ``key method'' for the class, +and the vtable is only emitted in the translation unit where the key +method is defined. + +@emph{Note:} If the chosen key method is later defined as inline, the +vtable is still emitted in every translation unit that defines it. +Make sure that any inline virtuals are declared inline in the class +body, even if they are not defined there. + +@item @code{type_info} objects +@cindex @code{type_info} +@cindex RTTI +C++ requires information about types to be written out in order to +implement @samp{dynamic_cast}, @samp{typeid} and exception handling. +For polymorphic classes (classes with virtual functions), the @samp{type_info} +object is written out along with the vtable so that @samp{dynamic_cast} +can determine the dynamic type of a class object at run time. For all +other types, we write out the @samp{type_info} object when it is used: when +applying @samp{typeid} to an expression, throwing an object, or +referring to a type in a catch clause or exception specification. + +@item Template Instantiations +Most everything in this section also applies to template instantiations, +but there are other options as well. +@xref{Template Instantiation,,Where's the Template?}. + +@end table + +When used with GNU ld version 2.8 or later on an ELF system such as +GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of +these constructs will be discarded at link time. This is known as +COMDAT support. + +On targets that don't support COMDAT, but do support weak symbols, GCC +uses them. This way one copy overrides all the others, but +the unused copies still take up space in the executable. + +For targets that do not support either COMDAT or weak symbols, +most entities with vague linkage are emitted as local symbols to +avoid duplicate definition errors from the linker. This does not happen +for local statics in inlines, however, as having multiple copies +almost certainly breaks things. + +@xref{C++ Interface,,Declarations and Definitions in One Header}, for +another way to control placement of these constructs. + +@node C++ Interface +@section C++ Interface and Implementation Pragmas + +@cindex interface and implementation headers, C++ +@cindex C++ interface and implementation headers +@cindex pragmas, interface and implementation + +@code{#pragma interface} and @code{#pragma implementation} provide the +user with a way of explicitly directing the compiler to emit entities +with vague linkage (and debugging information) in a particular +translation unit. + +@emph{Note:} These @code{#pragma}s have been superceded as of GCC 2.7.2 +by COMDAT support and the ``key method'' heuristic +mentioned in @ref{Vague Linkage}. Using them can actually cause your +program to grow due to unnecessary out-of-line copies of inline +functions. + +@table @code +@item #pragma interface +@itemx #pragma interface "@var{subdir}/@var{objects}.h" +@kindex #pragma interface +Use this directive in @emph{header files} that define object classes, to save +space in most of the object files that use those classes. Normally, +local copies of certain information (backup copies of inline member +functions, debugging information, and the internal tables that implement +virtual functions) must be kept in each object file that includes class +definitions. You can use this pragma to avoid such duplication. When a +header file containing @samp{#pragma interface} is included in a +compilation, this auxiliary information is not generated (unless +the main input source file itself uses @samp{#pragma implementation}). +Instead, the object files contain references to be resolved at link +time. + +The second form of this directive is useful for the case where you have +multiple headers with the same name in different directories. If you +use this form, you must specify the same string to @samp{#pragma +implementation}. + +@item #pragma implementation +@itemx #pragma implementation "@var{objects}.h" +@kindex #pragma implementation +Use this pragma in a @emph{main input file}, when you want full output from +included header files to be generated (and made globally visible). The +included header file, in turn, should use @samp{#pragma interface}. +Backup copies of inline member functions, debugging information, and the +internal tables used to implement virtual functions are all generated in +implementation files. + +@cindex implied @code{#pragma implementation} +@cindex @code{#pragma implementation}, implied +@cindex naming convention, implementation headers +If you use @samp{#pragma implementation} with no argument, it applies to +an include file with the same basename@footnote{A file's @dfn{basename} +is the name stripped of all leading path information and of trailing +suffixes, such as @samp{.h} or @samp{.C} or @samp{.cc}.} as your source +file. For example, in @file{allclass.cc}, giving just +@samp{#pragma implementation} +by itself is equivalent to @samp{#pragma implementation "allclass.h"}. + +Use the string argument if you want a single implementation file to +include code from multiple header files. (You must also use +@samp{#include} to include the header file; @samp{#pragma +implementation} only specifies how to use the file---it doesn't actually +include it.) + +There is no way to split up the contents of a single header file into +multiple implementation files. +@end table + +@cindex inlining and C++ pragmas +@cindex C++ pragmas, effect on inlining +@cindex pragmas in C++, effect on inlining +@samp{#pragma implementation} and @samp{#pragma interface} also have an +effect on function inlining. + +If you define a class in a header file marked with @samp{#pragma +interface}, the effect on an inline function defined in that class is +similar to an explicit @code{extern} declaration---the compiler emits +no code at all to define an independent version of the function. Its +definition is used only for inlining with its callers. + +@opindex fno-implement-inlines +Conversely, when you include the same header file in a main source file +that declares it as @samp{#pragma implementation}, the compiler emits +code for the function itself; this defines a version of the function +that can be found via pointers (or by callers compiled without +inlining). If all calls to the function can be inlined, you can avoid +emitting the function by compiling with @option{-fno-implement-inlines}. +If any calls are not inlined, you will get linker errors. + +@node Template Instantiation +@section Where's the Template? +@cindex template instantiation + +C++ templates were the first language feature to require more +intelligence from the environment than was traditionally found on a UNIX +system. Somehow the compiler and linker have to make sure that each +template instance occurs exactly once in the executable if it is needed, +and not at all otherwise. There are two basic approaches to this +problem, which are referred to as the Borland model and the Cfront model. + +@table @asis +@item Borland model +Borland C++ solved the template instantiation problem by adding the code +equivalent of common blocks to their linker; the compiler emits template +instances in each translation unit that uses them, and the linker +collapses them together. The advantage of this model is that the linker +only has to consider the object files themselves; there is no external +complexity to worry about. The disadvantage is that compilation time +is increased because the template code is being compiled repeatedly. +Code written for this model tends to include definitions of all +templates in the header file, since they must be seen to be +instantiated. + +@item Cfront model +The AT&T C++ translator, Cfront, solved the template instantiation +problem by creating the notion of a template repository, an +automatically maintained place where template instances are stored. A +more modern version of the repository works as follows: As individual +object files are built, the compiler places any template definitions and +instantiations encountered in the repository. At link time, the link +wrapper adds in the objects in the repository and compiles any needed +instances that were not previously emitted. The advantages of this +model are more optimal compilation speed and the ability to use the +system linker; to implement the Borland model a compiler vendor also +needs to replace the linker. The disadvantages are vastly increased +complexity, and thus potential for error; for some code this can be +just as transparent, but in practice it can been very difficult to build +multiple programs in one directory and one program in multiple +directories. Code written for this model tends to separate definitions +of non-inline member templates into a separate file, which should be +compiled separately. +@end table + +G++ implements the Borland model on targets where the linker supports it, +including ELF targets (such as GNU/Linux), Mac OS X and Microsoft Windows. +Otherwise G++ implements neither automatic model. + +You have the following options for dealing with template instantiations: + +@enumerate +@item +Do nothing. Code written for the Borland model works fine, but +each translation unit contains instances of each of the templates it +uses. The duplicate instances will be discarded by the linker, but in +a large program, this can lead to an unacceptable amount of code +duplication in object files or shared libraries. + +Duplicate instances of a template can be avoided by defining an explicit +instantiation in one object file, and preventing the compiler from doing +implicit instantiations in any other object files by using an explicit +instantiation declaration, using the @code{extern template} syntax: + +@smallexample +extern template int max (int, int); +@end smallexample + +This syntax is defined in the C++ 2011 standard, but has been supported by +G++ and other compilers since well before 2011. + +Explicit instantiations can be used for the largest or most frequently +duplicated instances, without having to know exactly which other instances +are used in the rest of the program. You can scatter the explicit +instantiations throughout your program, perhaps putting them in the +translation units where the instances are used or the translation units +that define the templates themselves; you can put all of the explicit +instantiations you need into one big file; or you can create small files +like + +@smallexample +#include "Foo.h" +#include "Foo.cc" + +template class Foo; +template ostream& operator << + (ostream&, const Foo&); +@end smallexample + +@noindent +for each of the instances you need, and create a template instantiation +library from those. + +This is the simplest option, but also offers flexibility and +fine-grained control when necessary. It is also the most portable +alternative and programs using this approach will work with most modern +compilers. + +@item +@opindex fno-implicit-templates +Compile your code with @option{-fno-implicit-templates} to disable the +implicit generation of template instances, and explicitly instantiate +all the ones you use. This approach requires more knowledge of exactly +which instances you need than do the others, but it's less +mysterious and allows greater control if you want to ensure that only +the intended instances are used. + +If you are using Cfront-model code, you can probably get away with not +using @option{-fno-implicit-templates} when compiling files that don't +@samp{#include} the member template definitions. + +If you use one big file to do the instantiations, you may want to +compile it without @option{-fno-implicit-templates} so you get all of the +instances required by your explicit instantiations (but not by any +other files) without having to specify them as well. + +In addition to forward declaration of explicit instantiations +(with @code{extern}), G++ has extended the template instantiation +syntax to support instantiation of the compiler support data for a +template class (i.e.@: the vtable) without instantiating any of its +members (with @code{inline}), and instantiation of only the static data +members of a template class, without the support data or member +functions (with @code{static}): + +@smallexample +inline template class Foo; +static template class Foo; +@end smallexample +@end enumerate + +@node Bound member functions +@section Extracting the Function Pointer from a Bound Pointer to Member Function +@cindex pmf +@cindex pointer to member function +@cindex bound pointer to member function + +In C++, pointer to member functions (PMFs) are implemented using a wide +pointer of sorts to handle all the possible call mechanisms; the PMF +needs to store information about how to adjust the @samp{this} pointer, +and if the function pointed to is virtual, where to find the vtable, and +where in the vtable to look for the member function. If you are using +PMFs in an inner loop, you should really reconsider that decision. If +that is not an option, you can extract the pointer to the function that +would be called for a given object/PMF pair and call it directly inside +the inner loop, to save a bit of time. + +Note that you still pay the penalty for the call through a +function pointer; on most modern architectures, such a call defeats the +branch prediction features of the CPU@. This is also true of normal +virtual function calls. + +The syntax for this extension is + +@smallexample +extern A a; +extern int (A::*fp)(); +typedef int (*fptr)(A *); + +fptr p = (fptr)(a.*fp); +@end smallexample + +For PMF constants (i.e.@: expressions of the form @samp{&Klasse::Member}), +no object is needed to obtain the address of the function. They can be +converted to function pointers directly: + +@smallexample +fptr p1 = (fptr)(&A::foo); +@end smallexample + +@opindex Wno-pmf-conversions +You must specify @option{-Wno-pmf-conversions} to use this extension. + +@node C++ Attributes +@section C++-Specific Variable, Function, and Type Attributes + +Some attributes only make sense for C++ programs. + +@table @code +@item abi_tag ("@var{tag}", ...) +@cindex @code{abi_tag} function attribute +@cindex @code{abi_tag} variable attribute +@cindex @code{abi_tag} type attribute +The @code{abi_tag} attribute can be applied to a function, variable, or class +declaration. It modifies the mangled name of the entity to +incorporate the tag name, in order to distinguish the function or +class from an earlier version with a different ABI; perhaps the class +has changed size, or the function has a different return type that is +not encoded in the mangled name. + +The attribute can also be applied to an inline namespace, but does not +affect the mangled name of the namespace; in this case it is only used +for @option{-Wabi-tag} warnings and automatic tagging of functions and +variables. Tagging inline namespaces is generally preferable to +tagging individual declarations, but the latter is sometimes +necessary, such as when only certain members of a class need to be +tagged. + +The argument can be a list of strings of arbitrary length. The +strings are sorted on output, so the order of the list is +unimportant. + +A redeclaration of an entity must not add new ABI tags, +since doing so would change the mangled name. + +The ABI tags apply to a name, so all instantiations and +specializations of a template have the same tags. The attribute will +be ignored if applied to an explicit specialization or instantiation. + +The @option{-Wabi-tag} flag enables a warning about a class which does +not have all the ABI tags used by its subobjects and virtual functions; for users with code +that needs to coexist with an earlier ABI, using this option can help +to find all affected types that need to be tagged. + +When a type involving an ABI tag is used as the type of a variable or +return type of a function where that tag is not already present in the +signature of the function, the tag is automatically applied to the +variable or function. @option{-Wabi-tag} also warns about this +situation; this warning can be avoided by explicitly tagging the +variable or function or moving it into a tagged inline namespace. + +@item init_priority (@var{priority}) +@cindex @code{init_priority} variable attribute + +In Standard C++, objects defined at namespace scope are guaranteed to be +initialized in an order in strict accordance with that of their definitions +@emph{in a given translation unit}. No guarantee is made for initializations +across translation units. However, GNU C++ allows users to control the +order of initialization of objects defined at namespace scope with the +@code{init_priority} attribute by specifying a relative @var{priority}, +a constant integral expression currently bounded between 101 and 65535 +inclusive. Lower numbers indicate a higher priority. + +In the following example, @code{A} would normally be created before +@code{B}, but the @code{init_priority} attribute reverses that order: + +@smallexample +Some_Class A __attribute__ ((init_priority (2000))); +Some_Class B __attribute__ ((init_priority (543))); +@end smallexample + +@noindent +Note that the particular values of @var{priority} do not matter; only their +relative ordering. + +@item warn_unused +@cindex @code{warn_unused} type attribute + +For C++ types with non-trivial constructors and/or destructors it is +impossible for the compiler to determine whether a variable of this +type is truly unused if it is not referenced. This type attribute +informs the compiler that variables of this type should be warned +about if they appear to be unused, just like variables of fundamental +types. + +This attribute is appropriate for types which just represent a value, +such as @code{std::string}; it is not appropriate for types which +control a resource, such as @code{std::lock_guard}. + +This attribute is also accepted in C, but it is unnecessary because C +does not have constructors or destructors. + +@end table + +@node Function Multiversioning +@section Function Multiversioning +@cindex function versions + +With the GNU C++ front end, for x86 targets, you may specify multiple +versions of a function, where each function is specialized for a +specific target feature. At runtime, the appropriate version of the +function is automatically executed depending on the characteristics of +the execution platform. Here is an example. + +@smallexample +__attribute__ ((target ("default"))) +int foo () +@{ + // The default version of foo. + return 0; +@} + +__attribute__ ((target ("sse4.2"))) +int foo () +@{ + // foo version for SSE4.2 + return 1; +@} + +__attribute__ ((target ("arch=atom"))) +int foo () +@{ + // foo version for the Intel ATOM processor + return 2; +@} + +__attribute__ ((target ("arch=amdfam10"))) +int foo () +@{ + // foo version for the AMD Family 0x10 processors. + return 3; +@} + +int main () +@{ + int (*p)() = &foo; + assert ((*p) () == foo ()); + return 0; +@} +@end smallexample + +In the above example, four versions of function foo are created. The +first version of foo with the target attribute "default" is the default +version. This version gets executed when no other target specific +version qualifies for execution on a particular platform. A new version +of foo is created by using the same function signature but with a +different target string. Function foo is called or a pointer to it is +taken just like a regular function. GCC takes care of doing the +dispatching to call the right version at runtime. Refer to the +@uref{https://gcc.gnu.org/wiki/FunctionMultiVersioning, GCC wiki on +Function Multiversioning} for more details. + +@node Type Traits +@section Type Traits + +The C++ front end implements syntactic extensions that allow +compile-time determination of +various characteristics of a type (or of a +pair of types). + +@table @code +@item __has_nothrow_assign (type) +If @code{type} is @code{const}-qualified or is a reference type then +the trait is @code{false}. Otherwise if @code{__has_trivial_assign (type)} +is @code{true} then the trait is @code{true}, else if @code{type} is +a cv-qualified class or union type with copy assignment operators that are +known not to throw an exception then the trait is @code{true}, else it is +@code{false}. +Requires: @code{type} shall be a complete type, (possibly cv-qualified) +@code{void}, or an array of unknown bound. + +@item __has_nothrow_copy (type) +If @code{__has_trivial_copy (type)} is @code{true} then the trait is +@code{true}, else if @code{type} is a cv-qualified class or union type +with copy constructors that are known not to throw an exception then +the trait is @code{true}, else it is @code{false}. +Requires: @code{type} shall be a complete type, (possibly cv-qualified) +@code{void}, or an array of unknown bound. + +@item __has_nothrow_constructor (type) +If @code{__has_trivial_constructor (type)} is @code{true} then the trait +is @code{true}, else if @code{type} is a cv class or union type (or array +thereof) with a default constructor that is known not to throw an +exception then the trait is @code{true}, else it is @code{false}. +Requires: @code{type} shall be a complete type, (possibly cv-qualified) +@code{void}, or an array of unknown bound. + +@item __has_trivial_assign (type) +If @code{type} is @code{const}- qualified or is a reference type then +the trait is @code{false}. Otherwise if @code{__is_trivial (type)} is +@code{true} then the trait is @code{true}, else if @code{type} is +a cv-qualified class or union type with a trivial copy assignment +([class.copy]) then the trait is @code{true}, else it is @code{false}. +Requires: @code{type} shall be a complete type, (possibly cv-qualified) +@code{void}, or an array of unknown bound. + +@item __has_trivial_copy (type) +If @code{__is_trivial (type)} is @code{true} or @code{type} is a reference +type then the trait is @code{true}, else if @code{type} is a cv class +or union type with a trivial copy constructor ([class.copy]) then the trait +is @code{true}, else it is @code{false}. Requires: @code{type} shall be +a complete type, (possibly cv-qualified) @code{void}, or an array of unknown +bound. + +@item __has_trivial_constructor (type) +If @code{__is_trivial (type)} is @code{true} then the trait is @code{true}, +else if @code{type} is a cv-qualified class or union type (or array thereof) +with a trivial default constructor ([class.ctor]) then the trait is @code{true}, +else it is @code{false}. +Requires: @code{type} shall be a complete type, (possibly cv-qualified) +@code{void}, or an array of unknown bound. + +@item __has_trivial_destructor (type) +If @code{__is_trivial (type)} is @code{true} or @code{type} is a reference type +then the trait is @code{true}, else if @code{type} is a cv class or union +type (or array thereof) with a trivial destructor ([class.dtor]) then +the trait is @code{true}, else it is @code{false}. +Requires: @code{type} shall be a complete type, (possibly cv-qualified) +@code{void}, or an array of unknown bound. + +@item __has_virtual_destructor (type) +If @code{type} is a class type with a virtual destructor +([class.dtor]) then the trait is @code{true}, else it is @code{false}. +Requires: If @code{type} is a non-union class type, it shall be a complete type. + +@item __is_abstract (type) +If @code{type} is an abstract class ([class.abstract]) then the trait +is @code{true}, else it is @code{false}. +Requires: If @code{type} is a non-union class type, it shall be a complete type. + +@item __is_aggregate (type) +If @code{type} is an aggregate type ([dcl.init.aggr]) the trait is +@code{true}, else it is @code{false}. +Requires: If @code{type} is a class type, it shall be a complete type. + +@item __is_base_of (base_type, derived_type) +If @code{base_type} is a base class of @code{derived_type} +([class.derived]) then the trait is @code{true}, otherwise it is @code{false}. +Top-level cv-qualifications of @code{base_type} and +@code{derived_type} are ignored. For the purposes of this trait, a +class type is considered is own base. +Requires: if @code{__is_class (base_type)} and @code{__is_class (derived_type)} +are @code{true} and @code{base_type} and @code{derived_type} are not the same +type (disregarding cv-qualifiers), @code{derived_type} shall be a complete +type. A diagnostic is produced if this requirement is not met. + +@item __is_class (type) +If @code{type} is a cv-qualified class type, and not a union type +([basic.compound]) the trait is @code{true}, else it is @code{false}. + +@item __is_empty (type) +If @code{__is_class (type)} is @code{false} then the trait is @code{false}. +Otherwise @code{type} is considered empty if and only if: @code{type} +has no non-static data members, or all non-static data members, if +any, are bit-fields of length 0, and @code{type} has no virtual +members, and @code{type} has no virtual base classes, and @code{type} +has no base classes @code{base_type} for which +@code{__is_empty (base_type)} is @code{false}. +Requires: If @code{type} is a non-union class type, it shall be a complete type. + +@item __is_enum (type) +If @code{type} is a cv enumeration type ([basic.compound]) the trait is +@code{true}, else it is @code{false}. + +@item __is_final (type) +If @code{type} is a class or union type marked @code{final}, then the trait +is @code{true}, else it is @code{false}. +Requires: If @code{type} is a class type, it shall be a complete type. + +@item __is_literal_type (type) +If @code{type} is a literal type ([basic.types]) the trait is +@code{true}, else it is @code{false}. +Requires: @code{type} shall be a complete type, (possibly cv-qualified) +@code{void}, or an array of unknown bound. + +@item __is_pod (type) +If @code{type} is a cv POD type ([basic.types]) then the trait is @code{true}, +else it is @code{false}. +Requires: @code{type} shall be a complete type, (possibly cv-qualified) +@code{void}, or an array of unknown bound. + +@item __is_polymorphic (type) +If @code{type} is a polymorphic class ([class.virtual]) then the trait +is @code{true}, else it is @code{false}. +Requires: If @code{type} is a non-union class type, it shall be a complete type. + +@item __is_standard_layout (type) +If @code{type} is a standard-layout type ([basic.types]) the trait is +@code{true}, else it is @code{false}. +Requires: @code{type} shall be a complete type, an array of complete types, +or (possibly cv-qualified) @code{void}. + +@item __is_trivial (type) +If @code{type} is a trivial type ([basic.types]) the trait is +@code{true}, else it is @code{false}. +Requires: @code{type} shall be a complete type, an array of complete types, +or (possibly cv-qualified) @code{void}. + +@item __is_union (type) +If @code{type} is a cv union type ([basic.compound]) the trait is +@code{true}, else it is @code{false}. + +@item __underlying_type (type) +The underlying type of @code{type}. +Requires: @code{type} shall be an enumeration type ([dcl.enum]). + +@item __integer_pack (length) +When used as the pattern of a pack expansion within a template +definition, expands to a template argument pack containing integers +from @code{0} to @code{length-1}. This is provided for efficient +implementation of @code{std::make_integer_sequence}. + +@end table + + +@node C++ Concepts +@section C++ Concepts + +C++ concepts provide much-improved support for generic programming. In +particular, they allow the specification of constraints on template arguments. +The constraints are used to extend the usual overloading and partial +specialization capabilities of the language, allowing generic data structures +and algorithms to be ``refined'' based on their properties rather than their +type names. + +The following keywords are reserved for concepts. + +@table @code +@item assumes +States an expression as an assumption, and if possible, verifies that the +assumption is valid. For example, @code{assume(n > 0)}. + +@item axiom +Introduces an axiom definition. Axioms introduce requirements on values. + +@item forall +Introduces a universally quantified object in an axiom. For example, +@code{forall (int n) n + 0 == n}). + +@item concept +Introduces a concept definition. Concepts are sets of syntactic and semantic +requirements on types and their values. + +@item requires +Introduces constraints on template arguments or requirements for a member +function of a class template. + +@end table + +The front end also exposes a number of internal mechanism that can be used +to simplify the writing of type traits. Note that some of these traits are +likely to be removed in the future. + +@table @code +@item __is_same (type1, type2) +A binary type trait: @code{true} whenever the type arguments are the same. + +@end table + + +@node Deprecated Features +@section Deprecated Features + +In the past, the GNU C++ compiler was extended to experiment with new +features, at a time when the C++ language was still evolving. Now that +the C++ standard is complete, some of those features are superseded by +superior alternatives. Using the old features might cause a warning in +some cases that the feature will be dropped in the future. In other +cases, the feature might be gone already. + +G++ allows a virtual function returning @samp{void *} to be overridden +by one returning a different pointer type. This extension to the +covariant return type rules is now deprecated and will be removed from a +future version. + +The use of default arguments in function pointers, function typedefs +and other places where they are not permitted by the standard is +deprecated and will be removed from a future version of G++. + +G++ allows floating-point literals to appear in integral constant expressions, +e.g.@: @samp{ enum E @{ e = int(2.2 * 3.7) @} } +This extension is deprecated and will be removed from a future version. + +G++ allows static data members of const floating-point type to be declared +with an initializer in a class definition. The standard only allows +initializers for static members of const integral types and const +enumeration types so this extension has been deprecated and will be removed +from a future version. + +G++ allows attributes to follow a parenthesized direct initializer, +e.g.@: @samp{ int f (0) __attribute__ ((something)); } This extension +has been ignored since G++ 3.3 and is deprecated. + +G++ allows anonymous structs and unions to have members that are not +public non-static data members (i.e.@: fields). These extensions are +deprecated. + +@node Backwards Compatibility +@section Backwards Compatibility +@cindex Backwards Compatibility +@cindex ARM [Annotated C++ Reference Manual] + +Now that there is a definitive ISO standard C++, G++ has a specification +to adhere to. The C++ language evolved over time, and features that +used to be acceptable in previous drafts of the standard, such as the ARM +[Annotated C++ Reference Manual], are no longer accepted. In order to allow +compilation of C++ written to such drafts, G++ contains some backwards +compatibilities. @emph{All such backwards compatibility features are +liable to disappear in future versions of G++.} They should be considered +deprecated. @xref{Deprecated Features}. + +@table @code + +@item Implicit C language +Old C system header files did not contain an @code{extern "C" @{@dots{}@}} +scope to set the language. On such systems, all system header files are +implicitly scoped inside a C language scope. Such headers must +correctly prototype function argument types, there is no leeway for +@code{()} to indicate an unspecified set of arguments. + +@end table + +@c LocalWords: emph deftypefn builtin ARCv2EM SIMD builtins msimd +@c LocalWords: typedef v4si v8hi DMA dma vdiwr vdowr diff --git a/gcc/doc/fragments.texi b/gcc/doc/fragments.texi new file mode 100644 index 00000000000..d2d98c794de --- /dev/null +++ b/gcc/doc/fragments.texi @@ -0,0 +1,273 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Fragments +@chapter Makefile Fragments +@cindex makefile fragment + +When you configure GCC using the @file{configure} script, it will +construct the file @file{Makefile} from the template file +@file{Makefile.in}. When it does this, it can incorporate makefile +fragments from the @file{config} directory. These are used to set +Makefile parameters that are not amenable to being calculated by +autoconf. The list of fragments to incorporate is set by +@file{config.gcc} (and occasionally @file{config.build} +and @file{config.host}); @xref{System Config}. + +Fragments are named either @file{t-@var{target}} or @file{x-@var{host}}, +depending on whether they are relevant to configuring GCC to produce +code for a particular target, or to configuring GCC to run on a +particular host. Here @var{target} and @var{host} are mnemonics +which usually have some relationship to the canonical system name, but +no formal connection. + +If these files do not exist, it means nothing needs to be added for a +given target or host. Most targets need a few @file{t-@var{target}} +fragments, but needing @file{x-@var{host}} fragments is rare. + +@menu +* Target Fragment:: Writing @file{t-@var{target}} files. +* Host Fragment:: Writing @file{x-@var{host}} files. +@end menu + +@node Target Fragment +@section Target Makefile Fragments +@cindex target makefile fragment +@cindex @file{t-@var{target}} + +Target makefile fragments can set these Makefile variables. + +@table @code +@findex LIBGCC2_CFLAGS +@item LIBGCC2_CFLAGS +Compiler flags to use when compiling @file{libgcc2.c}. + +@findex LIB2FUNCS_EXTRA +@item LIB2FUNCS_EXTRA +A list of source file names to be compiled or assembled and inserted +into @file{libgcc.a}. + +@findex CRTSTUFF_T_CFLAGS +@item CRTSTUFF_T_CFLAGS +Special flags used when compiling @file{crtstuff.c}. +@xref{Initialization}. + +@findex CRTSTUFF_T_CFLAGS_S +@item CRTSTUFF_T_CFLAGS_S +Special flags used when compiling @file{crtstuff.c} for shared +linking. Used if you use @file{crtbeginS.o} and @file{crtendS.o} +in @code{EXTRA-PARTS}. +@xref{Initialization}. + +@findex MULTILIB_OPTIONS +@item MULTILIB_OPTIONS +For some targets, invoking GCC in different ways produces objects +that cannot be linked together. For example, for some targets GCC +produces both big and little endian code. For these targets, you must +arrange for multiple versions of @file{libgcc.a} to be compiled, one for +each set of incompatible options. When GCC invokes the linker, it +arranges to link in the right version of @file{libgcc.a}, based on +the command line options used. + +The @code{MULTILIB_OPTIONS} macro lists the set of options for which +special versions of @file{libgcc.a} must be built. Write options that +are mutually incompatible side by side, separated by a slash. Write +options that may be used together separated by a space. The build +procedure will build all combinations of compatible options. + +For example, if you set @code{MULTILIB_OPTIONS} to @samp{m68000/m68020 +msoft-float}, @file{Makefile} will build special versions of +@file{libgcc.a} using the following sets of options: @option{-m68000}, +@option{-m68020}, @option{-msoft-float}, @samp{-m68000 -msoft-float}, and +@samp{-m68020 -msoft-float}. + +@findex MULTILIB_DIRNAMES +@item MULTILIB_DIRNAMES +If @code{MULTILIB_OPTIONS} is used, this variable specifies the +directory names that should be used to hold the various libraries. +Write one element in @code{MULTILIB_DIRNAMES} for each element in +@code{MULTILIB_OPTIONS}. If @code{MULTILIB_DIRNAMES} is not used, the +default value will be @code{MULTILIB_OPTIONS}, with all slashes treated +as spaces. + +@code{MULTILIB_DIRNAMES} describes the multilib directories using GCC +conventions and is applied to directories that are part of the GCC +installation. When multilib-enabled, the compiler will add a +subdirectory of the form @var{prefix}/@var{multilib} before each +directory in the search path for libraries and crt files. + +For example, if @code{MULTILIB_OPTIONS} is set to @samp{m68000/m68020 +msoft-float}, then the default value of @code{MULTILIB_DIRNAMES} is +@samp{m68000 m68020 msoft-float}. You may specify a different value if +you desire a different set of directory names. + +@findex MULTILIB_MATCHES +@item MULTILIB_MATCHES +Sometimes the same option may be written in two different ways. If an +option is listed in @code{MULTILIB_OPTIONS}, GCC needs to know about +any synonyms. In that case, set @code{MULTILIB_MATCHES} to a list of +items of the form @samp{option=option} to describe all relevant +synonyms. For example, @samp{m68000=mc68000 m68020=mc68020}. + +@findex MULTILIB_EXCEPTIONS +@item MULTILIB_EXCEPTIONS +Sometimes when there are multiple sets of @code{MULTILIB_OPTIONS} being +specified, there are combinations that should not be built. In that +case, set @code{MULTILIB_EXCEPTIONS} to be all of the switch exceptions +in shell case syntax that should not be built. + +For example the ARM processor cannot execute both hardware floating +point instructions and the reduced size THUMB instructions at the same +time, so there is no need to build libraries with both of these +options enabled. Therefore @code{MULTILIB_EXCEPTIONS} is set to: +@smallexample +*mthumb/*mhard-float* +@end smallexample + +@findex MULTILIB_REQUIRED +@item MULTILIB_REQUIRED +Sometimes when there are only a few combinations are required, it would +be a big effort to come up with a @code{MULTILIB_EXCEPTIONS} list to +cover all undesired ones. In such a case, just listing all the required +combinations in @code{MULTILIB_REQUIRED} would be more straightforward. + +The way to specify the entries in @code{MULTILIB_REQUIRED} is same with +the way used for @code{MULTILIB_EXCEPTIONS}, only this time what are +required will be specified. Suppose there are multiple sets of +@code{MULTILIB_OPTIONS} and only two combinations are required, one +for ARMv7-M and one for ARMv7-R with hard floating-point ABI and FPU, the +@code{MULTILIB_REQUIRED} can be set to: +@smallexample +@code{MULTILIB_REQUIRED} = mthumb/march=armv7-m +@code{MULTILIB_REQUIRED} += march=armv7-r/mfloat-abi=hard/mfpu=vfpv3-d16 +@end smallexample + +The @code{MULTILIB_REQUIRED} can be used together with +@code{MULTILIB_EXCEPTIONS}. The option combinations generated from +@code{MULTILIB_OPTIONS} will be filtered by @code{MULTILIB_EXCEPTIONS} +and then by @code{MULTILIB_REQUIRED}. + +@findex MULTILIB_REUSE +@item MULTILIB_REUSE +Sometimes it is desirable to reuse one existing multilib for different +sets of options. Such kind of reuse can minimize the number of multilib +variants. And for some targets it is better to reuse an existing multilib +than to fall back to default multilib when there is no corresponding multilib. +This can be done by adding reuse rules to @code{MULTILIB_REUSE}. + +A reuse rule is comprised of two parts connected by equality sign. The left +part is the option set used to build multilib and the right part is the option +set that will reuse this multilib. Both parts should only use options +specified in @code{MULTILIB_OPTIONS} and the equality signs found in options +name should be replaced with periods. An explicit period in the rule can be +escaped by preceding it with a backslash. The order of options in the left +part matters and should be same with those specified in +@code{MULTILIB_REQUIRED} or aligned with the order in @code{MULTILIB_OPTIONS}. +There is no such limitation for options in the right part as we don't build +multilib from them. + +@code{MULTILIB_REUSE} is different from @code{MULTILIB_MATCHES} in that it +sets up relations between two option sets rather than two options. Here is an +example to demo how we reuse libraries built in Thumb mode for applications built +in ARM mode: +@smallexample +@code{MULTILIB_REUSE} = mthumb/march.armv7-r=marm/march.armv7-r +@end smallexample + +Before the advent of @code{MULTILIB_REUSE}, GCC select multilib by comparing command +line options with options used to build multilib. The @code{MULTILIB_REUSE} is +complementary to that way. Only when the original comparison matches nothing it will +work to see if it is OK to reuse some existing multilib. + +@findex MULTILIB_EXTRA_OPTS +@item MULTILIB_EXTRA_OPTS +Sometimes it is desirable that when building multiple versions of +@file{libgcc.a} certain options should always be passed on to the +compiler. In that case, set @code{MULTILIB_EXTRA_OPTS} to be the list +of options to be used for all builds. If you set this, you should +probably set @code{CRTSTUFF_T_CFLAGS} to a dash followed by it. + +@findex MULTILIB_OSDIRNAMES +@item MULTILIB_OSDIRNAMES +If @code{MULTILIB_OPTIONS} is used, this variable specifies +a list of subdirectory names, that are used to modify the search +path depending on the chosen multilib. Unlike @code{MULTILIB_DIRNAMES}, +@code{MULTILIB_OSDIRNAMES} describes the multilib directories using +operating systems conventions, and is applied to the directories such as +@code{lib} or those in the @env{LIBRARY_PATH} environment variable. +The format is either the same as of +@code{MULTILIB_DIRNAMES}, or a set of mappings. When it is the same +as @code{MULTILIB_DIRNAMES}, it describes the multilib directories +using operating system conventions, rather than GCC conventions. When it is a set +of mappings of the form @var{gccdir}=@var{osdir}, the left side gives +the GCC convention and the right gives the equivalent OS defined +location. If the @var{osdir} part begins with a @samp{!}, +GCC will not search in the non-multilib directory and use +exclusively the multilib directory. Otherwise, the compiler will +examine the search path for libraries and crt files twice; the first +time it will add @var{multilib} to each directory in the search path, +the second it will not. + +For configurations that support both multilib and multiarch, +@code{MULTILIB_OSDIRNAMES} also encodes the multiarch name, thus +subsuming @code{MULTIARCH_DIRNAME}. The multiarch name is appended to +each directory name, separated by a colon (e.g.@: +@samp{../lib32:i386-linux-gnu}). + +Each multiarch subdirectory will be searched before the corresponding OS +multilib directory, for example @samp{/lib/i386-linux-gnu} before +@samp{/lib/../lib32}. The multiarch name will also be used to modify the +system header search path, as explained for @code{MULTIARCH_DIRNAME}. + +@findex MULTIARCH_DIRNAME +@item MULTIARCH_DIRNAME +This variable specifies the multiarch name for configurations that are +multiarch-enabled but not multilibbed configurations. + +The multiarch name is used to augment the search path for libraries, crt +files and system header files with additional locations. The compiler +will add a multiarch subdirectory of the form +@var{prefix}/@var{multiarch} before each directory in the library and +crt search path. It will also add two directories +@code{LOCAL_INCLUDE_DIR}/@var{multiarch} and +@code{NATIVE_SYSTEM_HEADER_DIR}/@var{multiarch}) to the system header +search path, respectively before @code{LOCAL_INCLUDE_DIR} and +@code{NATIVE_SYSTEM_HEADER_DIR}. + +@code{MULTIARCH_DIRNAME} is not used for configurations that support +both multilib and multiarch. In that case, multiarch names are encoded +in @code{MULTILIB_OSDIRNAMES} instead. + +More documentation about multiarch can be found at +@uref{https://wiki.debian.org/Multiarch}. + +@findex SPECS +@item SPECS +Unfortunately, setting @code{MULTILIB_EXTRA_OPTS} is not enough, since +it does not affect the build of target libraries, at least not the +build of the default multilib. One possible work-around is to use +@code{DRIVER_SELF_SPECS} to bring options from the @file{specs} file +as if they had been passed in the compiler driver command line. +However, you don't want to be adding these options after the toolchain +is installed, so you can instead tweak the @file{specs} file that will +be used during the toolchain build, while you still install the +original, built-in @file{specs}. The trick is to set @code{SPECS} to +some other filename (say @file{specs.install}), that will then be +created out of the built-in specs, and introduce a @file{Makefile} +rule to generate the @file{specs} file that's going to be used at +build time out of your @file{specs.install}. + +@item T_CFLAGS +These are extra flags to pass to the C compiler. They are used both +when building GCC, and when compiling things with the just-built GCC@. +This variable is deprecated and should not be used. +@end table + +@node Host Fragment +@section Host Makefile Fragments +@cindex host makefile fragment +@cindex @file{x-@var{host}} + +The use of @file{x-@var{host}} fragments is discouraged. You should only +use it for makefile dependencies. diff --git a/gcc/doc/frontends.texi b/gcc/doc/frontends.texi new file mode 100644 index 00000000000..e1b5b6153fc --- /dev/null +++ b/gcc/doc/frontends.texi @@ -0,0 +1,61 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node G++ and GCC +@chapter Programming Languages Supported by GCC + +@cindex GCC +@cindex GNU Compiler Collection +@cindex GNU C Compiler +@cindex Ada +@cindex D +@cindex Fortran +@cindex Go +@cindex Objective-C +@cindex Objective-C++ +GCC stands for ``GNU Compiler Collection''. GCC is an integrated +distribution of compilers for several major programming languages. These +languages currently include C, C++, Objective-C, Objective-C++, +Fortran, Ada, D, and Go. + +The abbreviation @dfn{GCC} has multiple meanings in common use. The +current official meaning is ``GNU Compiler Collection'', which refers +generically to the complete suite of tools. The name historically stood +for ``GNU C Compiler'', and this usage is still common when the emphasis +is on compiling C programs. Finally, the name is also used when speaking +of the @dfn{language-independent} component of GCC: code shared among the +compilers for all supported languages. + +The language-independent component of GCC includes the majority of the +optimizers, as well as the ``back ends'' that generate machine code for +various processors. + +@cindex COBOL +@cindex Mercury +The part of a compiler that is specific to a particular language is +called the ``front end''. In addition to the front ends that are +integrated components of GCC, there are several other front ends that +are maintained separately. These support languages such as +Mercury, and COBOL@. To use these, they must be built together with +GCC proper. + +@cindex C++ +@cindex G++ +@cindex Ada +@cindex GNAT +Most of the compilers for languages other than C have their own names. +The C++ compiler is G++, the Ada compiler is GNAT, and so on. When we +talk about compiling one of those languages, we might refer to that +compiler by its own name, or as GCC@. Either is correct. + +@cindex compiler compared to C++ preprocessor +@cindex intermediate C version, nonexistent +@cindex C intermediate output, nonexistent +Historically, compilers for many languages, including C++ and Fortran, +have been implemented as ``preprocessors'' which emit another high +level language such as C@. None of the compilers included in GCC are +implemented this way; they all generate machine code directly. This +sort of preprocessor should not be confused with the @dfn{C +preprocessor}, which is an integral feature of the C, C++, Objective-C +and Objective-C++ languages. diff --git a/gcc/doc/gcc.texi b/gcc/doc/gcc.texi new file mode 100644 index 00000000000..21bea70e2d8 --- /dev/null +++ b/gcc/doc/gcc.texi @@ -0,0 +1,219 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename gcc.info +@c INTERNALS is used by md.texi to determine whether to include the +@c whole of that file, in the internals manual, or only the part +@c dealing with constraints, in the user manual. +@clear INTERNALS + +@c NOTE: checks/things to do: +@c +@c -have bob do a search in all seven files for "mew" (ideally --mew, +@c but i may have forgotten the occasional "--"..). +@c Just checked... all have `--'! Bob 22Jul96 +@c Use this to search: grep -n '\-\-mew' *.texi +@c -item/itemx, text after all (sub/sub)section titles, etc.. +@c -consider putting the lists of options on pp 17--> etc in columns or +@c some such. +@c -overfulls. do a search for "mew" in the files, and you will see +@c overfulls that i noted but could not deal with. +@c -have to add text: beginning of chapter 8 + +@c +@c anything else? --mew 10feb93 + +@include gcc-common.texi + +@settitle Using the GNU Compiler Collection (GCC) + +@c Create a separate index for command line options. +@defcodeindex op +@c Merge the standard indexes into a single one. +@syncodeindex fn cp +@syncodeindex vr cp +@syncodeindex ky cp +@syncodeindex pg cp +@syncodeindex tp cp + +@paragraphindent 1 + +@c %**end of header + +@copying +Copyright @copyright{} 1988-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``Funding Free Software'', the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end copying +@ifnottex +@dircategory Software development +@direntry +* gcc: (gcc). The GNU Compiler Collection. +* g++: (gcc). The GNU C++ compiler. +* gcov: (gcc) Gcov. @command{gcov}---a test coverage program. +* gcov-tool: (gcc) Gcov-tool. @command{gcov-tool}---an offline gcda profile processing program. +* gcov-dump: (gcc) Gcov-dump. @command{gcov-dump}---an offline gcda and gcno profile dump tool. +* lto-dump: (gcc) lto-dump. @command{lto-dump}---Tool for +dumping LTO object files. +@end direntry +This file documents the use of the GNU compilers. +@sp 1 +@insertcopying +@sp 1 +@end ifnottex + +@setchapternewpage odd +@titlepage +@title Using the GNU Compiler Collection +@versionsubtitle +@author Richard M. Stallman and the @sc{GCC} Developer Community +@page +@vskip 0pt plus 1filll +Published by: +@multitable @columnfractions 0.5 0.5 +@item GNU Press +@tab Website: @uref{http://www.gnupress.org} +@item a division of the +@tab General: @email{press@@gnu.org} +@item Free Software Foundation +@tab Orders: @email{sales@@gnu.org} +@item 51 Franklin Street, Fifth Floor +@tab Tel 617-542-5942 +@item Boston, MA 02110-1301 USA +@tab Fax 617-542-2652 +@end multitable +@sp 2 +@ifset FSFPRINT +@c Update this ISBN when printing a new edition. +@acronym{ISBN} 1-882114-39-6 + +Cover art by Gary M. Torrisi. Cover design by Jonathan Richard. +@end ifset +@ifclear FSFPRINT +Last printed October 2003 for GCC 3.3.1.@* +Printed copies are available for $45 each. +@end ifclear +@sp 1 +@insertcopying +@end titlepage +@summarycontents +@contents +@page + +@node Top, G++ and GCC +@top Introduction +@cindex introduction + +This manual documents how to use the GNU compilers, +as well as their features and incompatibilities, and how to report +bugs. It corresponds to the compilers +@ifset VERSION_PACKAGE +@value{VERSION_PACKAGE} +@end ifset +version @value{version-GCC}. +The internals of the GNU compilers, including how to port them to new +targets and some information about how to write front ends for new +languages, are documented in a separate manual. @xref{Top,, +Introduction, gccint, GNU Compiler Collection (GCC) Internals}. + +@menu +* G++ and GCC:: You can compile C or C++ programs. +* Standards:: Language standards supported by GCC. +* Invoking GCC:: Command options supported by @samp{gcc}. +* C Implementation:: How GCC implements the ISO C specification. +* C++ Implementation:: How GCC implements the ISO C++ specification. +* C Extensions:: GNU extensions to the C language family. +* C++ Extensions:: GNU extensions to the C++ language. +* Objective-C:: GNU Objective-C runtime features. +* Compatibility:: Binary Compatibility +* Gcov:: @command{gcov}---a test coverage program. +* Gcov-tool:: @command{gcov-tool}---an offline gcda profile processing program. +* Gcov-dump:: @command{gcov-dump}---an offline gcda and gcno profile dump tool. +* lto-dump:: @command{lto-dump}---Tool for dumping LTO +object files. +* Trouble:: If you have trouble using GCC. +* Bugs:: How, why and where to report bugs. +* Service:: How To Get Help with GCC +* Contributing:: How to contribute to testing and developing GCC. + +* Funding:: How to help assure funding for free software. +* GNU Project:: The GNU Project and GNU/Linux. + +* Copying:: GNU General Public License says + how you can copy and share GCC. +* GNU Free Documentation License:: How you can copy and share this manual. +* Contributors:: People who have contributed to GCC. + +* Option Index:: Index to command line options. +* Keyword Index:: Index of concepts and symbol names. +@end menu + +@include frontends.texi +@include standards.texi +@include invoke.texi +@include implement-c.texi +@include implement-cxx.texi +@include extend.texi +@include objc.texi +@include compat.texi +@include gcov.texi +@include gcov-tool.texi +@include gcov-dump.texi +@include lto-dump.texi +@include trouble.texi +@include bugreport.texi +@include service.texi +@include contribute.texi + +@include funding.texi +@include gnu.texi +@include gpl_v3.texi + +@c --------------------------------------------------------------------- +@c GFDL +@c --------------------------------------------------------------------- + +@include fdl.texi + +@include contrib.texi + +@c --------------------------------------------------------------------- +@c Indexes +@c --------------------------------------------------------------------- + +@node Option Index +@unnumbered Option Index + +GCC's command line options are indexed here without any initial @samp{-} +or @samp{--}. Where an option has both positive and negative forms +(such as @option{-f@var{option}} and @option{-fno-@var{option}}), +relevant entries in the manual are indexed under the most appropriate +form; it may sometimes be useful to look up both forms. + +@printindex op + +@node Keyword Index +@unnumbered Keyword Index + +@printindex cp + +@c --------------------------------------------------------------------- +@c Epilogue +@c --------------------------------------------------------------------- + +@bye diff --git a/gcc/doc/gccint.texi b/gcc/doc/gccint.texi new file mode 100644 index 00000000000..f6aa065e0a1 --- /dev/null +++ b/gcc/doc/gccint.texi @@ -0,0 +1,206 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename gccint.info +@c INTERNALS is used by md.texi to determine whether to include the +@c whole of that file, in the internals manual, or only the part +@c dealing with constraints, in the user manual. +@set INTERNALS + +@c See miscellaneous notes in gcc.texi on checks/things to do. + +@include gcc-common.texi + +@settitle GNU Compiler Collection (GCC) Internals + +@c Create a separate index for command line options. +@defcodeindex op +@c Merge the standard indexes into a single one. +@syncodeindex fn cp +@syncodeindex vr cp +@syncodeindex ky cp +@syncodeindex pg cp +@syncodeindex tp cp + +@paragraphindent 1 + +@c %**end of header + +@copying +Copyright @copyright{} 1988-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``Funding Free Software'', the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end copying +@ifnottex +@dircategory Software development +@direntry +* gccint: (gccint). Internals of the GNU Compiler Collection. +@end direntry +This file documents the internals of the GNU compilers. +@sp 1 +@insertcopying +@sp 1 +@end ifnottex + +@setchapternewpage odd +@titlepage +@title GNU Compiler Collection Internals +@versionsubtitle +@author Richard M. Stallman and the @sc{GCC} Developer Community +@page +@vskip 0pt plus 1filll +@insertcopying +@end titlepage +@summarycontents +@contents +@page + +@node Top, Contributing +@top Introduction +@cindex introduction + +This manual documents the internals of the GNU compilers, including +how to port them to new targets and some information about how to +write front ends for new languages. It corresponds to the compilers +@ifset VERSION_PACKAGE +@value{VERSION_PACKAGE} +@end ifset +version @value{version-GCC}. The use of the GNU compilers is documented in a +separate manual. @xref{Top,, Introduction, gcc, Using the GNU +Compiler Collection (GCC)}. + +This manual is mainly a reference manual rather than a tutorial. It +discusses how to contribute to GCC (@pxref{Contributing}), the +characteristics of the machines supported by GCC as hosts and targets +(@pxref{Portability}), how GCC relates to the ABIs on such systems +(@pxref{Interface}), and the characteristics of the languages for +which GCC front ends are written (@pxref{Languages}). It then +describes the GCC source tree structure and build system, some of the +interfaces to GCC front ends, and how support for a target system is +implemented in GCC@. + +Additional tutorial information is linked to from +@uref{https://gcc.gnu.org/readings.html}. + +@menu +* Contributing:: How to contribute to testing and developing GCC. +* Portability:: Goals of GCC's portability features. +* Interface:: Function-call interface of GCC output. +* Libgcc:: Low-level runtime library used by GCC. +* Languages:: Languages for which GCC front ends are written. +* Source Tree:: GCC source tree structure and build system. +* Testsuites:: GCC testsuites. +* Options:: Option specification files. +* Passes:: Order of passes, what they do, and what each file is for. +* poly_int:: Representation of runtime sizes and offsets. +* GENERIC:: Language-independent representation generated by Front Ends +* GIMPLE:: Tuple representation used by Tree SSA optimizers +* Tree SSA:: Analysis and optimization of GIMPLE +* RTL:: Machine-dependent low-level intermediate representation. +* Control Flow:: Maintaining and manipulating the control flow graph. +* Loop Analysis and Representation:: Analysis and representation of loops +* Machine Desc:: How to write machine description instruction patterns. +* Target Macros:: How to write the machine description C macros and functions. +* Host Config:: Writing the @file{xm-@var{machine}.h} file. +* Fragments:: Writing the @file{t-@var{target}} and @file{x-@var{host}} files. +* Collect2:: How @code{collect2} works; how it finds @code{ld}. +* Header Dirs:: Understanding the standard header file directories. +* Type Information:: GCC's memory management; generating type information. +* Plugins:: Extending the compiler with plugins. +* LTO:: Using Link-Time Optimization. + +* Match and Simplify:: How to write expression simplification patterns for GIMPLE and GENERIC +* Static Analyzer:: Working with the static analyzer. +* User Experience Guidelines:: Guidelines for implementing diagnostics and options. +* Funding:: How to help assure funding for free software. +* GNU Project:: The GNU Project and GNU/Linux. + +* Copying:: GNU General Public License says + how you can copy and share GCC. +* GNU Free Documentation License:: How you can copy and share this manual. +* Contributors:: People who have contributed to GCC. + +* Option Index:: Index to command line options. +* Concept Index:: Index of concepts and symbol names. +@end menu + +@include contribute.texi +@include portability.texi +@include interface.texi +@include libgcc.texi +@include languages.texi +@include sourcebuild.texi +@include options.texi +@include passes.texi +@include poly-int.texi +@include generic.texi +@include gimple.texi +@include tree-ssa.texi +@include rtl.texi +@include cfg.texi +@include loop.texi +@include md.texi +@include tm.texi +@include hostconfig.texi +@include fragments.texi +@include collect2.texi +@include headerdirs.texi +@include gty.texi +@include plugins.texi +@include lto.texi +@include match-and-simplify.texi +@include analyzer.texi +@include ux.texi + +@include funding.texi +@include gnu.texi +@include gpl_v3.texi + +@c --------------------------------------------------------------------- +@c GFDL +@c --------------------------------------------------------------------- + +@include fdl.texi + +@include contrib.texi + +@c --------------------------------------------------------------------- +@c Indexes +@c --------------------------------------------------------------------- + +@node Option Index +@unnumbered Option Index + +GCC's command line options are indexed here without any initial @samp{-} +or @samp{--}. Where an option has both positive and negative forms +(such as @option{-f@var{option}} and @option{-fno-@var{option}}), +relevant entries in the manual are indexed under the most appropriate +form; it may sometimes be useful to look up both forms. + +@printindex op + +@node Concept Index +@unnumbered Concept Index + +@printindex cp + +@c --------------------------------------------------------------------- +@c Epilogue +@c --------------------------------------------------------------------- + +@bye diff --git a/gcc/doc/gcov-dump.texi b/gcc/doc/gcov-dump.texi new file mode 100644 index 00000000000..0491ab17bc1 --- /dev/null +++ b/gcc/doc/gcov-dump.texi @@ -0,0 +1,99 @@ +@c Copyright (C) 2017-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ignore +@c man begin COPYRIGHT +Copyright @copyright{} 2017-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename gcov-dump +@settitle offline gcda and gcno profile dump tool +@end ignore + +@node Gcov-dump +@chapter @command{gcov-dump}---an Offline Gcda and Gcno Profile Dump Tool + +@menu +* Gcov-dump Intro:: Introduction to gcov-dump. +* Invoking Gcov-dump:: How to use gcov-dump. +@end menu + +@node Gcov-dump Intro +@section Introduction to @command{gcov-dump} +@c man begin DESCRIPTION + +@command{gcov-dump} is a tool you can use in conjunction with GCC to +dump content of gcda and gcno profile files offline. + +@c man end + +@node Invoking Gcov-dump +@section Invoking @command{gcov-dump} + +@smallexample +Usage: gcov-dump @r{[}@var{OPTION}@r{]} ... @var{gcovfiles} +@end smallexample + +@command{gcov-dump} accepts the following options: + +@ignore +@c man begin SYNOPSIS +gcov-dump [@option{-v}|@option{--version}] + [@option{-h}|@option{--help}] + [@option{-l}|@option{--long}] + [@option{-p}|@option{--positions}] + [@option{-r}|@option{--raw}] + [@option{-s}|@option{--stable}] + @var{gcovfiles} +@c man end +@end ignore + +@c man begin OPTIONS +@table @gcctabopt +@item -h +@itemx --help +Display help about using @command{gcov-dump} (on the standard output), and +exit without doing any further processing. + +@item -l +@itemx --long +Dump content of records. + +@item -p +@itemx --positions +Dump positions of records. + +@item -r +@itemx --raw +Print content records in raw format. + +@item -s +@itemx --stable +Print content in stable format usable for comparison. + +@item -v +@itemx --version +Display the @command{gcov-dump} version number (on the standard output), +and exit without doing any further processing. +@end table + +@c man end diff --git a/gcc/doc/gcov-tool.texi b/gcc/doc/gcov-tool.texi new file mode 100644 index 00000000000..77150836acc --- /dev/null +++ b/gcc/doc/gcov-tool.texi @@ -0,0 +1,267 @@ +@c Copyright (C) 2014-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ignore +@c man begin COPYRIGHT +Copyright @copyright{} 2014-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename gcov-tool +@settitle offline gcda profile processing tool +@end ignore + +@node Gcov-tool +@chapter @command{gcov-tool}---an Offline Gcda Profile Processing Tool + +@command{gcov-tool} is a tool you can use in conjunction with GCC to +manipulate or process gcda profile files offline. + +@menu +* Gcov-tool Intro:: Introduction to gcov-tool. +* Invoking Gcov-tool:: How to use gcov-tool. +@end menu + +@node Gcov-tool Intro +@section Introduction to @command{gcov-tool} +@c man begin DESCRIPTION + +@command{gcov-tool} is an offline tool to process gcc's gcda profile files. + +Current gcov-tool supports the following functionalities: + +@itemize @bullet +@item +merge two sets of profiles with weights. + +@item +read a stream of profiles with associated filenames and merge it with a set of +profiles with weights. + +@item +read one set of profile and rewrite profile contents. One can scale or +normalize the count values. +@end itemize + +Examples of the use cases for this tool are: +@itemize @bullet +@item +Collect the profiles for different set of inputs, and use this tool to merge +them. One can specify the weight to factor in the relative importance of +each input. + +@item +Collect profiles from target systems without a filesystem (freestanding +environments). Merge the collected profiles with associated profiles +present on the host system. One can specify the weight to factor in the +relative importance of each input. + +@item +Rewrite the profile after removing a subset of the gcda files, while maintaining +the consistency of the summary and the histogram. + +@item +It can also be used to debug or libgcov code as the tools shares the majority +code as the runtime library. +@end itemize + +Note that for the merging operation, this profile generated offline may +contain slight different values from the online merged profile. Here are +a list of typical differences: + +@itemize @bullet +@item +histogram difference: This offline tool recomputes the histogram after merging +the counters. The resulting histogram, therefore, is precise. The online +merging does not have this capability -- the histogram is merged from two +histograms and the result is an approximation. + +@item +summary checksum difference: Summary checksum uses a CRC32 operation. The value +depends on the link list order of gcov-info objects. This order is different in +gcov-tool from that in the online merge. It's expected to have different +summary checksums. It does not really matter as the compiler does not use this +checksum anywhere. + +@item +value profile counter values difference: Some counter values for value profile +are runtime dependent, like heap addresses. It's normal to see some difference +in these kind of counters. +@end itemize + +@c man end + +@node Invoking Gcov-tool +@section Invoking @command{gcov-tool} + +@smallexample +gcov-tool @r{[}@var{global-options}@r{]} SUB_COMMAND @r{[}@var{sub_command-options}@r{]} @var{profile_dir} +@end smallexample + +@command{gcov-tool} accepts the following options: + +@ignore +@c man begin SYNOPSIS +gcov-tool [@option{-v}|@option{--version}] [@option{-h}|@option{--help}] + +gcov-tool merge [merge-options] @var{directory1} @var{directory2} + [@option{-o}|@option{--output} @var{directory}] + [@option{-v}|@option{--verbose}] + [@option{-w}|@option{--weight} @var{w1,w2}] + +gcov-tool merge-stream [merge-stream-options] [@var{file}] + [@option{-v}|@option{--verbose}] + [@option{-w}|@option{--weight} @var{w1,w2}] + +gcov-tool rewrite [rewrite-options] @var{directory} + [@option{-n}|@option{--normalize} @var{long_long_value}] + [@option{-o}|@option{--output} @var{directory}] + [@option{-s}|@option{--scale} @var{float_or_simple-frac_value}] + [@option{-v}|@option{--verbose}] + +gcov-tool overlap [overlap-options] @var{directory1} @var{directory2} + [@option{-f}|@option{--function}] + [@option{-F}|@option{--fullname}] + [@option{-h}|@option{--hotonly}] + [@option{-o}|@option{--object}] + [@option{-t}|@option{--hot_threshold}] @var{float} + [@option{-v}|@option{--verbose}] + +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), gcc(1), gcov(1) and the Info entry for +@file{gcc}. +@c man end +@end ignore + +@c man begin OPTIONS +@table @gcctabopt +@item -h +@itemx --help +Display help about using @command{gcov-tool} (on the standard output), and +exit without doing any further processing. + +@item -v +@itemx --version +Display the @command{gcov-tool} version number (on the standard output), +and exit without doing any further processing. + +@item merge +Merge two profile directories. +@table @gcctabopt + +@item -o @var{directory} +@itemx --output @var{directory} +Set the output profile directory. Default output directory name is +@var{merged_profile}. + +@item -v +@itemx --verbose +Set the verbose mode. + +@item -w @var{w1},@var{w2} +@itemx --weight @var{w1},@var{w2} +Set the merge weights of the @var{directory1} and @var{directory2}, +respectively. The default weights are 1 for both. +@end table + +@item merge-stream +Collect profiles with associated filenames from a @emph{gcfn} and @emph{gcda} +data stream. Read the stream from the file specified by @var{file} or from +@file{stdin}. Merge the profiles with associated profiles in the host +filesystem. Apply the optional weights while merging profiles. + +For the generation of a @emph{gcfn} and @emph{gcda} data stream on the target +system, please have a look at the @code{__gcov_filename_to_gcfn()} and +@code{__gcov_info_to_gcda()} functions declared in @code{#include }. +@table @gcctabopt + +@item -v +@itemx --verbose +Set the verbose mode. + +@item -w @var{w1},@var{w2} +@itemx --weight @var{w1},@var{w2} +Set the merge weights of the profiles from the @emph{gcfn} and @emph{gcda} data +stream and the associated profiles in the host filesystem, respectively. The +default weights are 1 for both. +@end table + +@item rewrite +Read the specified profile directory and rewrite to a new directory. +@table @gcctabopt + +@item -n @var{long_long_value} +@itemx --normalize +Normalize the profile. The specified value is the max counter value +in the new profile. + +@item -o @var{directory} +@itemx --output @var{directory} +Set the output profile directory. Default output name is @var{rewrite_profile}. + +@item -s @var{float_or_simple-frac_value} +@itemx --scale @var{float_or_simple-frac_value} +Scale the profile counters. The specified value can be in floating point value, +or simple fraction value form, such 1, 2, 2/3, and 5/3. + +@item -v +@itemx --verbose +Set the verbose mode. +@end table + +@item overlap +Compute the overlap score between the two specified profile directories. +The overlap score is computed based on the arc profiles. It is defined as +the sum of min (p1_counter[i] / p1_sum_all, p2_counter[i] / p2_sum_all), +for all arc counter i, where p1_counter[i] and p2_counter[i] are two +matched counters and p1_sum_all and p2_sum_all are the sum of counter +values in profile 1 and profile 2, respectively. + +@table @gcctabopt +@item -f +@itemx --function +Print function level overlap score. + +@item -F +@itemx --fullname +Print full gcda filename. + +@item -h +@itemx --hotonly +Only print info for hot objects/functions. + +@item -o +@itemx --object +Print object level overlap score. + +@item -t @var{float} +@itemx --hot_threshold +Set the threshold for hot counter value. + +@item -v +@itemx --verbose +Set the verbose mode. +@end table + +@end table + +@c man end diff --git a/gcc/doc/gcov.texi b/gcc/doc/gcov.texi new file mode 100644 index 00000000000..a1f7d26e610 --- /dev/null +++ b/gcc/doc/gcov.texi @@ -0,0 +1,1362 @@ +@c Copyright (C) 1996-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ignore +@c man begin COPYRIGHT +Copyright @copyright{} 1996-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename gcov +@settitle coverage testing tool +@end ignore + +@node Gcov +@chapter @command{gcov}---a Test Coverage Program + +@command{gcov} is a tool you can use in conjunction with GCC to +test code coverage in your programs. + +@menu +* Gcov Intro:: Introduction to gcov. +* Invoking Gcov:: How to use gcov. +* Gcov and Optimization:: Using gcov with GCC optimization. +* Gcov Data Files:: The files used by gcov. +* Cross-profiling:: Data file relocation. +* Freestanding Environments:: How to use profiling and test + coverage in freestanding environments. +@end menu + +@node Gcov Intro +@section Introduction to @command{gcov} +@c man begin DESCRIPTION + +@command{gcov} is a test coverage program. Use it in concert with GCC +to analyze your programs to help create more efficient, faster running +code and to discover untested parts of your program. You can use +@command{gcov} as a profiling tool to help discover where your +optimization efforts will best affect your code. You can also use +@command{gcov} along with the other profiling tool, @command{gprof}, to +assess which parts of your code use the greatest amount of computing +time. + +Profiling tools help you analyze your code's performance. Using a +profiler such as @command{gcov} or @command{gprof}, you can find out some +basic performance statistics, such as: + +@itemize @bullet +@item +how often each line of code executes + +@item +what lines of code are actually executed + +@item +how much computing time each section of code uses +@end itemize + +Once you know these things about how your code works when compiled, you +can look at each module to see which modules should be optimized. +@command{gcov} helps you determine where to work on optimization. + +Software developers also use coverage testing in concert with +testsuites, to make sure software is actually good enough for a release. +Testsuites can verify that a program works as expected; a coverage +program tests to see how much of the program is exercised by the +testsuite. Developers can then determine what kinds of test cases need +to be added to the testsuites to create both better testing and a better +final product. + +You should compile your code without optimization if you plan to use +@command{gcov} because the optimization, by combining some lines of code +into one function, may not give you as much information as you need to +look for `hot spots' where the code is using a great deal of computer +time. Likewise, because @command{gcov} accumulates statistics by line (at +the lowest resolution), it works best with a programming style that +places only one statement on each line. If you use complicated macros +that expand to loops or to other control structures, the statistics are +less helpful---they only report on the line where the macro call +appears. If your complex macros behave like functions, you can replace +them with inline functions to solve this problem. + +@command{gcov} creates a logfile called @file{@var{sourcefile}.gcov} which +indicates how many times each line of a source file @file{@var{sourcefile}.c} +has executed. You can use these logfiles along with @command{gprof} to aid +in fine-tuning the performance of your programs. @command{gprof} gives +timing information you can use along with the information you get from +@command{gcov}. + +@command{gcov} works only on code compiled with GCC@. It is not +compatible with any other profiling or test coverage mechanism. + +@c man end + +@node Invoking Gcov +@section Invoking @command{gcov} + +@smallexample +gcov @r{[}@var{options}@r{]} @var{files} +@end smallexample + +@command{gcov} accepts the following options: + +@ignore +@c man begin SYNOPSIS +gcov [@option{-v}|@option{--version}] [@option{-h}|@option{--help}] + [@option{-a}|@option{--all-blocks}] + [@option{-b}|@option{--branch-probabilities}] + [@option{-c}|@option{--branch-counts}] + [@option{-d}|@option{--display-progress}] + [@option{-f}|@option{--function-summaries}] + [@option{-j}|@option{--json-format}] + [@option{-H}|@option{--human-readable}] + [@option{-k}|@option{--use-colors}] + [@option{-l}|@option{--long-file-names}] + [@option{-m}|@option{--demangled-names}] + [@option{-n}|@option{--no-output}] + [@option{-o}|@option{--object-directory} @var{directory|file}] + [@option{-p}|@option{--preserve-paths}] + [@option{-q}|@option{--use-hotness-colors}] + [@option{-r}|@option{--relative-only}] + [@option{-s}|@option{--source-prefix} @var{directory}] + [@option{-t}|@option{--stdout}] + [@option{-u}|@option{--unconditional-branches}] + [@option{-x}|@option{--hash-filenames}] + @var{files} +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for @file{gcc}. +@c man end +@end ignore + +@c man begin OPTIONS +@table @gcctabopt + +@item -a +@itemx --all-blocks +Write individual execution counts for every basic block. Normally gcov +outputs execution counts only for the main blocks of a line. With this +option you can determine if blocks within a single line are not being +executed. + +@item -b +@itemx --branch-probabilities +Write branch frequencies to the output file, and write branch summary +info to the standard output. This option allows you to see how often +each branch in your program was taken. Unconditional branches will not +be shown, unless the @option{-u} option is given. + +@item -c +@itemx --branch-counts +Write branch frequencies as the number of branches taken, rather than +the percentage of branches taken. + +@item -d +@itemx --display-progress +Display the progress on the standard output. + +@item -f +@itemx --function-summaries +Output summaries for each function in addition to the file level summary. + +@item -h +@itemx --help +Display help about using @command{gcov} (on the standard output), and +exit without doing any further processing. + +@item -j +@itemx --json-format +Output gcov file in an easy-to-parse JSON intermediate format +which does not require source code for generation. The JSON +file is compressed with gzip compression algorithm +and the files have @file{.gcov.json.gz} extension. + +Structure of the JSON is following: + +@smallexample +@{ + "current_working_directory": "foo/bar", + "data_file": "a.out", + "format_version": "1", + "gcc_version": "11.1.1 20210510" + "files": ["$file"] +@} +@end smallexample + +Fields of the root element have following semantics: + +@itemize @bullet +@item +@var{current_working_directory}: working directory where +a compilation unit was compiled + +@item +@var{data_file}: name of the data file (GCDA) + +@item +@var{format_version}: semantic version of the format + +@item +@var{gcc_version}: version of the GCC compiler +@end itemize + +Each @var{file} has the following form: + +@smallexample +@{ + "file": "a.c", + "functions": ["$function"], + "lines": ["$line"] +@} +@end smallexample + +Fields of the @var{file} element have following semantics: + +@itemize @bullet +@item +@var{file_name}: name of the source file +@end itemize + +Each @var{function} has the following form: + +@smallexample +@{ + "blocks": 2, + "blocks_executed": 2, + "demangled_name": "foo", + "end_column": 1, + "end_line": 4, + "execution_count": 1, + "name": "foo", + "start_column": 5, + "start_line": 1 +@} +@end smallexample + +Fields of the @var{function} element have following semantics: + +@itemize @bullet +@item +@var{blocks}: number of blocks that are in the function + +@item +@var{blocks_executed}: number of executed blocks of the function + +@item +@var{demangled_name}: demangled name of the function + +@item +@var{end_column}: column in the source file where the function ends + +@item +@var{end_line}: line in the source file where the function ends + +@item +@var{execution_count}: number of executions of the function + +@item +@var{name}: name of the function + +@item +@var{start_column}: column in the source file where the function begins + +@item +@var{start_line}: line in the source file where the function begins +@end itemize + +Note that line numbers and column numbers number from 1. In the current +implementation, @var{start_line} and @var{start_column} do not include +any template parameters and the leading return type but that +this is likely to be fixed in the future. + +Each @var{line} has the following form: + +@smallexample +@{ + "branches": ["$branch"], + "count": 2, + "line_number": 15, + "unexecuted_block": false, + "function_name": "foo", +@} +@end smallexample + +Branches are present only with @var{-b} option. +Fields of the @var{line} element have following semantics: + +@itemize @bullet +@item +@var{count}: number of executions of the line + +@item +@var{line_number}: line number + +@item +@var{unexecuted_block}: flag whether the line contains an unexecuted block +(not all statements on the line are executed) + +@item +@var{function_name}: a name of a function this @var{line} belongs to +(for a line with an inlined statements can be not set) +@end itemize + +Each @var{branch} has the following form: + +@smallexample +@{ + "count": 11, + "fallthrough": true, + "throw": false +@} +@end smallexample + +Fields of the @var{branch} element have following semantics: + +@itemize @bullet +@item +@var{count}: number of executions of the branch + +@item +@var{fallthrough}: true when the branch is a fall through branch + +@item +@var{throw}: true when the branch is an exceptional branch +@end itemize + +@item -H +@itemx --human-readable +Write counts in human readable format (like 24.6k). + +@item -k +@itemx --use-colors + +Use colors for lines of code that have zero coverage. We use red color for +non-exceptional lines and cyan for exceptional. Same colors are used for +basic blocks with @option{-a} option. + +@item -l +@itemx --long-file-names +Create long file names for included source files. For example, if the +header file @file{x.h} contains code, and was included in the file +@file{a.c}, then running @command{gcov} on the file @file{a.c} will +produce an output file called @file{a.c##x.h.gcov} instead of +@file{x.h.gcov}. This can be useful if @file{x.h} is included in +multiple source files and you want to see the individual +contributions. If you use the @samp{-p} option, both the including +and included file names will be complete path names. + +@item -m +@itemx --demangled-names +Display demangled function names in output. The default is to show +mangled function names. + +@item -n +@itemx --no-output +Do not create the @command{gcov} output file. + +@item -o @var{directory|file} +@itemx --object-directory @var{directory} +@itemx --object-file @var{file} +Specify either the directory containing the gcov data files, or the +object path name. The @file{.gcno}, and +@file{.gcda} data files are searched for using this option. If a directory +is specified, the data files are in that directory and named after the +input file name, without its extension. If a file is specified here, +the data files are named after that file, without its extension. + +@item -p +@itemx --preserve-paths +Preserve complete path information in the names of generated +@file{.gcov} files. Without this option, just the filename component is +used. With this option, all directories are used, with @samp{/} characters +translated to @samp{#} characters, @file{.} directory components +removed and unremoveable @file{..} +components renamed to @samp{^}. This is useful if sourcefiles are in several +different directories. + +@item -q +@itemx --use-hotness-colors + +Emit perf-like colored output for hot lines. Legend of the color scale +is printed at the very beginning of the output file. + +@item -r +@itemx --relative-only +Only output information about source files with a relative pathname +(after source prefix elision). Absolute paths are usually system +header files and coverage of any inline functions therein is normally +uninteresting. + +@item -s @var{directory} +@itemx --source-prefix @var{directory} +A prefix for source file names to remove when generating the output +coverage files. This option is useful when building in a separate +directory, and the pathname to the source directory is not wanted when +determining the output file names. Note that this prefix detection is +applied before determining whether the source file is absolute. + +@item -t +@itemx --stdout +Output to standard output instead of output files. + +@item -u +@itemx --unconditional-branches +When branch probabilities are given, include those of unconditional branches. +Unconditional branches are normally not interesting. + +@item -v +@itemx --version +Display the @command{gcov} version number (on the standard output), +and exit without doing any further processing. + +@item -w +@itemx --verbose +Print verbose informations related to basic blocks and arcs. + +@item -x +@itemx --hash-filenames +When using @var{--preserve-paths}, +gcov uses the full pathname of the source files to create +an output filename. This can lead to long filenames that can overflow +filesystem limits. This option creates names of the form +@file{@var{source-file}##@var{md5}.gcov}, +where the @var{source-file} component is the final filename part and +the @var{md5} component is calculated from the full mangled name that +would have been used otherwise. The option is an alternative +to the @var{--preserve-paths} on systems which have a filesystem limit. + +@end table + +@command{gcov} should be run with the current directory the same as that +when you invoked the compiler. Otherwise it will not be able to locate +the source files. @command{gcov} produces files called +@file{@var{mangledname}.gcov} in the current directory. These contain +the coverage information of the source file they correspond to. +One @file{.gcov} file is produced for each source (or header) file +containing code, +which was compiled to produce the data files. The @var{mangledname} part +of the output file name is usually simply the source file name, but can +be something more complicated if the @samp{-l} or @samp{-p} options are +given. Refer to those options for details. + +If you invoke @command{gcov} with multiple input files, the +contributions from each input file are summed. Typically you would +invoke it with the same list of files as the final link of your executable. + +The @file{.gcov} files contain the @samp{:} separated fields along with +program source code. The format is + +@smallexample +@var{execution_count}:@var{line_number}:@var{source line text} +@end smallexample + +Additional block information may succeed each line, when requested by +command line option. The @var{execution_count} is @samp{-} for lines +containing no code. Unexecuted lines are marked @samp{#####} or +@samp{=====}, depending on whether they are reachable by +non-exceptional paths or only exceptional paths such as C++ exception +handlers, respectively. Given the @samp{-a} option, unexecuted blocks are +marked @samp{$$$$$} or @samp{%%%%%}, depending on whether a basic block +is reachable via non-exceptional or exceptional paths. +Executed basic blocks having a statement with zero @var{execution_count} +end with @samp{*} character and are colored with magenta color with +the @option{-k} option. This functionality is not supported in Ada. + +Note that GCC can completely remove the bodies of functions that are +not needed -- for instance if they are inlined everywhere. Such functions +are marked with @samp{-}, which can be confusing. +Use the @option{-fkeep-inline-functions} and @option{-fkeep-static-functions} +options to retain these functions and +allow gcov to properly show their @var{execution_count}. + +Some lines of information at the start have @var{line_number} of zero. +These preamble lines are of the form + +@smallexample +-:0:@var{tag}:@var{value} +@end smallexample + +The ordering and number of these preamble lines will be augmented as +@command{gcov} development progresses --- do not rely on them remaining +unchanged. Use @var{tag} to locate a particular preamble line. + +The additional block information is of the form + +@smallexample +@var{tag} @var{information} +@end smallexample + +The @var{information} is human readable, but designed to be simple +enough for machine parsing too. + +When printing percentages, 0% and 100% are only printed when the values +are @emph{exactly} 0% and 100% respectively. Other values which would +conventionally be rounded to 0% or 100% are instead printed as the +nearest non-boundary value. + +When using @command{gcov}, you must first compile your program +with a special GCC option @samp{--coverage}. +This tells the compiler to generate additional information needed by +gcov (basically a flow graph of the program) and also includes +additional code in the object files for generating the extra profiling +information needed by gcov. These additional files are placed in the +directory where the object file is located. + +Running the program will cause profile output to be generated. For each +source file compiled with @option{-fprofile-arcs}, an accompanying +@file{.gcda} file will be placed in the object file directory. + +Running @command{gcov} with your program's source file names as arguments +will now produce a listing of the code along with frequency of execution +for each line. For example, if your program is called @file{tmp.cpp}, this +is what you see when you use the basic @command{gcov} facility: + +@smallexample +$ g++ --coverage tmp.cpp -c +$ g++ --coverage tmp.o +$ a.out +$ gcov tmp.cpp -m +File 'tmp.cpp' +Lines executed:92.86% of 14 +Creating 'tmp.cpp.gcov' +@end smallexample + +The file @file{tmp.cpp.gcov} contains output from @command{gcov}. +Here is a sample: + +@smallexample + -: 0:Source:tmp.cpp + -: 0:Working directory:/home/gcc/testcase + -: 0:Graph:tmp.gcno + -: 0:Data:tmp.gcda + -: 0:Runs:1 + -: 0:Programs:1 + -: 1:#include + -: 2: + -: 3:template + -: 4:class Foo + -: 5:@{ + -: 6: public: + 1*: 7: Foo(): b (1000) @{@} +------------------ +Foo::Foo(): + #####: 7: Foo(): b (1000) @{@} +------------------ +Foo::Foo(): + 1: 7: Foo(): b (1000) @{@} +------------------ + 2*: 8: void inc () @{ b++; @} +------------------ +Foo::inc(): + #####: 8: void inc () @{ b++; @} +------------------ +Foo::inc(): + 2: 8: void inc () @{ b++; @} +------------------ + -: 9: + -: 10: private: + -: 11: int b; + -: 12:@}; + -: 13: + -: 14:template class Foo; + -: 15:template class Foo; + -: 16: + -: 17:int + 1: 18:main (void) + -: 19:@{ + -: 20: int i, total; + 1: 21: Foo counter; + -: 22: + 1: 23: counter.inc(); + 1: 24: counter.inc(); + 1: 25: total = 0; + -: 26: + 11: 27: for (i = 0; i < 10; i++) + 10: 28: total += i; + -: 29: + 1*: 30: int v = total > 100 ? 1 : 2; + -: 31: + 1: 32: if (total != 45) + #####: 33: printf ("Failure\n"); + -: 34: else + 1: 35: printf ("Success\n"); + 1: 36: return 0; + -: 37:@} +@end smallexample + +Note that line 7 is shown in the report multiple times. First occurrence +presents total number of execution of the line and the next two belong +to instances of class Foo constructors. As you can also see, line 30 contains +some unexecuted basic blocks and thus execution count has asterisk symbol. + +When you use the @option{-a} option, you will get individual block +counts, and the output looks like this: + +@smallexample + -: 0:Source:tmp.cpp + -: 0:Working directory:/home/gcc/testcase + -: 0:Graph:tmp.gcno + -: 0:Data:tmp.gcda + -: 0:Runs:1 + -: 0:Programs:1 + -: 1:#include + -: 2: + -: 3:template + -: 4:class Foo + -: 5:@{ + -: 6: public: + 1*: 7: Foo(): b (1000) @{@} +------------------ +Foo::Foo(): + #####: 7: Foo(): b (1000) @{@} +------------------ +Foo::Foo(): + 1: 7: Foo(): b (1000) @{@} +------------------ + 2*: 8: void inc () @{ b++; @} +------------------ +Foo::inc(): + #####: 8: void inc () @{ b++; @} +------------------ +Foo::inc(): + 2: 8: void inc () @{ b++; @} +------------------ + -: 9: + -: 10: private: + -: 11: int b; + -: 12:@}; + -: 13: + -: 14:template class Foo; + -: 15:template class Foo; + -: 16: + -: 17:int + 1: 18:main (void) + -: 19:@{ + -: 20: int i, total; + 1: 21: Foo counter; + 1: 21-block 0 + -: 22: + 1: 23: counter.inc(); + 1: 23-block 0 + 1: 24: counter.inc(); + 1: 24-block 0 + 1: 25: total = 0; + -: 26: + 11: 27: for (i = 0; i < 10; i++) + 1: 27-block 0 + 11: 27-block 1 + 10: 28: total += i; + 10: 28-block 0 + -: 29: + 1*: 30: int v = total > 100 ? 1 : 2; + 1: 30-block 0 + %%%%%: 30-block 1 + 1: 30-block 2 + -: 31: + 1: 32: if (total != 45) + 1: 32-block 0 + #####: 33: printf ("Failure\n"); + %%%%%: 33-block 0 + -: 34: else + 1: 35: printf ("Success\n"); + 1: 35-block 0 + 1: 36: return 0; + 1: 36-block 0 + -: 37:@} +@end smallexample + +In this mode, each basic block is only shown on one line -- the last +line of the block. A multi-line block will only contribute to the +execution count of that last line, and other lines will not be shown +to contain code, unless previous blocks end on those lines. +The total execution count of a line is shown and subsequent lines show +the execution counts for individual blocks that end on that line. After each +block, the branch and call counts of the block will be shown, if the +@option{-b} option is given. + +Because of the way GCC instruments calls, a call count can be shown +after a line with no individual blocks. +As you can see, line 33 contains a basic block that was not executed. + +@need 450 +When you use the @option{-b} option, your output looks like this: + +@smallexample + -: 0:Source:tmp.cpp + -: 0:Working directory:/home/gcc/testcase + -: 0:Graph:tmp.gcno + -: 0:Data:tmp.gcda + -: 0:Runs:1 + -: 0:Programs:1 + -: 1:#include + -: 2: + -: 3:template + -: 4:class Foo + -: 5:@{ + -: 6: public: + 1*: 7: Foo(): b (1000) @{@} +------------------ +Foo::Foo(): +function Foo::Foo() called 0 returned 0% blocks executed 0% + #####: 7: Foo(): b (1000) @{@} +------------------ +Foo::Foo(): +function Foo::Foo() called 1 returned 100% blocks executed 100% + 1: 7: Foo(): b (1000) @{@} +------------------ + 2*: 8: void inc () @{ b++; @} +------------------ +Foo::inc(): +function Foo::inc() called 0 returned 0% blocks executed 0% + #####: 8: void inc () @{ b++; @} +------------------ +Foo::inc(): +function Foo::inc() called 2 returned 100% blocks executed 100% + 2: 8: void inc () @{ b++; @} +------------------ + -: 9: + -: 10: private: + -: 11: int b; + -: 12:@}; + -: 13: + -: 14:template class Foo; + -: 15:template class Foo; + -: 16: + -: 17:int +function main called 1 returned 100% blocks executed 81% + 1: 18:main (void) + -: 19:@{ + -: 20: int i, total; + 1: 21: Foo counter; +call 0 returned 100% +branch 1 taken 100% (fallthrough) +branch 2 taken 0% (throw) + -: 22: + 1: 23: counter.inc(); +call 0 returned 100% +branch 1 taken 100% (fallthrough) +branch 2 taken 0% (throw) + 1: 24: counter.inc(); +call 0 returned 100% +branch 1 taken 100% (fallthrough) +branch 2 taken 0% (throw) + 1: 25: total = 0; + -: 26: + 11: 27: for (i = 0; i < 10; i++) +branch 0 taken 91% (fallthrough) +branch 1 taken 9% + 10: 28: total += i; + -: 29: + 1*: 30: int v = total > 100 ? 1 : 2; +branch 0 taken 0% (fallthrough) +branch 1 taken 100% + -: 31: + 1: 32: if (total != 45) +branch 0 taken 0% (fallthrough) +branch 1 taken 100% + #####: 33: printf ("Failure\n"); +call 0 never executed +branch 1 never executed +branch 2 never executed + -: 34: else + 1: 35: printf ("Success\n"); +call 0 returned 100% +branch 1 taken 100% (fallthrough) +branch 2 taken 0% (throw) + 1: 36: return 0; + -: 37:@} +@end smallexample + +For each function, a line is printed showing how many times the function +is called, how many times it returns and what percentage of the +function's blocks were executed. + +For each basic block, a line is printed after the last line of the basic +block describing the branch or call that ends the basic block. There can +be multiple branches and calls listed for a single source line if there +are multiple basic blocks that end on that line. In this case, the +branches and calls are each given a number. There is no simple way to map +these branches and calls back to source constructs. In general, though, +the lowest numbered branch or call will correspond to the leftmost construct +on the source line. + +For a branch, if it was executed at least once, then a percentage +indicating the number of times the branch was taken divided by the +number of times the branch was executed will be printed. Otherwise, the +message ``never executed'' is printed. + +For a call, if it was executed at least once, then a percentage +indicating the number of times the call returned divided by the number +of times the call was executed will be printed. This will usually be +100%, but may be less for functions that call @code{exit} or @code{longjmp}, +and thus may not return every time they are called. + +The execution counts are cumulative. If the example program were +executed again without removing the @file{.gcda} file, the count for the +number of times each line in the source was executed would be added to +the results of the previous run(s). This is potentially useful in +several ways. For example, it could be used to accumulate data over a +number of program runs as part of a test verification suite, or to +provide more accurate long-term information over a large number of +program runs. + +The data in the @file{.gcda} files is saved immediately before the program +exits. For each source file compiled with @option{-fprofile-arcs}, the +profiling code first attempts to read in an existing @file{.gcda} file; if +the file doesn't match the executable (differing number of basic block +counts) it will ignore the contents of the file. It then adds in the +new execution counts and finally writes the data to the file. + +@node Gcov and Optimization +@section Using @command{gcov} with GCC Optimization + +If you plan to use @command{gcov} to help optimize your code, you must +first compile your program with a special GCC option +@samp{--coverage}. Aside from that, you can use any +other GCC options; but if you want to prove that every single line +in your program was executed, you should not compile with optimization +at the same time. On some machines the optimizer can eliminate some +simple code lines by combining them with other lines. For example, code +like this: + +@smallexample +if (a != b) + c = 1; +else + c = 0; +@end smallexample + +@noindent +can be compiled into one instruction on some machines. In this case, +there is no way for @command{gcov} to calculate separate execution counts +for each line because there isn't separate code for each line. Hence +the @command{gcov} output looks like this if you compiled the program with +optimization: + +@smallexample + 100: 12:if (a != b) + 100: 13: c = 1; + 100: 14:else + 100: 15: c = 0; +@end smallexample + +The output shows that this block of code, combined by optimization, +executed 100 times. In one sense this result is correct, because there +was only one instruction representing all four of these lines. However, +the output does not indicate how many times the result was 0 and how +many times the result was 1. + +Inlineable functions can create unexpected line counts. Line counts are +shown for the source code of the inlineable function, but what is shown +depends on where the function is inlined, or if it is not inlined at all. + +If the function is not inlined, the compiler must emit an out of line +copy of the function, in any object file that needs it. If +@file{fileA.o} and @file{fileB.o} both contain out of line bodies of a +particular inlineable function, they will also both contain coverage +counts for that function. When @file{fileA.o} and @file{fileB.o} are +linked together, the linker will, on many systems, select one of those +out of line bodies for all calls to that function, and remove or ignore +the other. Unfortunately, it will not remove the coverage counters for +the unused function body. Hence when instrumented, all but one use of +that function will show zero counts. + +If the function is inlined in several places, the block structure in +each location might not be the same. For instance, a condition might +now be calculable at compile time in some instances. Because the +coverage of all the uses of the inline function will be shown for the +same source lines, the line counts themselves might seem inconsistent. + +Long-running applications can use the @code{__gcov_reset} and @code{__gcov_dump} +facilities to restrict profile collection to the program region of +interest. Calling @code{__gcov_reset(void)} will clear all run-time profile +counters to zero, and calling @code{__gcov_dump(void)} will cause the profile +information collected at that point to be dumped to @file{.gcda} output files. +Instrumented applications use a static destructor with priority 99 +to invoke the @code{__gcov_dump} function. Thus @code{__gcov_dump} +is executed after all user defined static destructors, +as well as handlers registered with @code{atexit}. + +If an executable loads a dynamic shared object via dlopen functionality, +@option{-Wl,--dynamic-list-data} is needed to dump all profile data. + +Profiling run-time library reports various errors related to profile +manipulation and profile saving. Errors are printed into standard error output +or @samp{GCOV_ERROR_FILE} file, if environment variable is used. +In order to terminate immediately after an errors occurs +set @samp{GCOV_EXIT_AT_ERROR} environment variable. +That can help users to find profile clashing which leads +to a misleading profile. + +@c man end + +@node Gcov Data Files +@section Brief Description of @command{gcov} Data Files + +@command{gcov} uses two files for profiling. The names of these files +are derived from the original @emph{object} file by substituting the +file suffix with either @file{.gcno}, or @file{.gcda}. The files +contain coverage and profile data stored in a platform-independent format. +The @file{.gcno} files are placed in the same directory as the object +file. By default, the @file{.gcda} files are also stored in the same +directory as the object file, but the GCC @option{-fprofile-dir} option +may be used to store the @file{.gcda} files in a separate directory. + +The @file{.gcno} notes file is generated when the source file is compiled +with the GCC @option{-ftest-coverage} option. It contains information to +reconstruct the basic block graphs and assign source line numbers to +blocks. + +The @file{.gcda} count data file is generated when a program containing +object files built with the GCC @option{-fprofile-arcs} option is executed. +A separate @file{.gcda} file is created for each object file compiled with +this option. It contains arc transition counts, value profile counts, and +some summary information. + +It is not recommended to access the coverage files directly. +Consumers should use the intermediate format that is provided +by @command{gcov} tool via @option{--json-format} option. + +@node Cross-profiling +@section Data File Relocation to Support Cross-Profiling + +Running the program will cause profile output to be generated. For each +source file compiled with @option{-fprofile-arcs}, an accompanying @file{.gcda} +file will be placed in the object file directory. That implicitly requires +running the program on the same system as it was built or having the same +absolute directory structure on the target system. The program will try +to create the needed directory structure, if it is not already present. + +To support cross-profiling, a program compiled with @option{-fprofile-arcs} +can relocate the data files based on two environment variables: + +@itemize @bullet +@item +GCOV_PREFIX contains the prefix to add to the absolute paths +in the object file. Prefix can be absolute, or relative. The +default is no prefix. + +@item +GCOV_PREFIX_STRIP indicates the how many initial directory names to strip off +the hardwired absolute paths. Default value is 0. + +@emph{Note:} If GCOV_PREFIX_STRIP is set without GCOV_PREFIX is undefined, + then a relative path is made out of the hardwired absolute paths. +@end itemize + +For example, if the object file @file{/user/build/foo.o} was built with +@option{-fprofile-arcs}, the final executable will try to create the data file +@file{/user/build/foo.gcda} when running on the target system. This will +fail if the corresponding directory does not exist and it is unable to create +it. This can be overcome by, for example, setting the environment as +@samp{GCOV_PREFIX=/target/run} and @samp{GCOV_PREFIX_STRIP=1}. Such a +setting will name the data file @file{/target/run/build/foo.gcda}. + +You must move the data files to the expected directory tree in order to +use them for profile directed optimizations (@option{-fprofile-use}), or to +use the @command{gcov} tool. + +@node Freestanding Environments +@section Profiling and Test Coverage in Freestanding Environments + +In case your application runs in a hosted environment such as GNU/Linux, then +this section is likely not relevant to you. This section is intended for +application developers targeting freestanding environments (for example +embedded systems) with limited resources. In particular, systems or test cases +which do not support constructors/destructors or the C library file I/O. In +this section, the @dfn{target system} runs your application instrumented for +profiling or test coverage. You develop and analyze your application on the +@dfn{host system}. We now provide an overview how profiling and test coverage +can be obtained in this scenario followed by a tutorial which can be exercised +on the host system. Finally, some system initialization caveats are listed. + +@subsection Overview + +For an application instrumented for profiling or test coverage, the compiler +generates some global data structures which are updated by instrumentation code +while the application runs. These data structures are called the @dfn{gcov +information}. Normally, when the application exits, the gcov information is +stored to @file{.gcda} files. There is one file per translation unit +instrumented for profiling or test coverage. The function +@code{__gcov_exit()}, which stores the gcov information to a file, is called by +a global destructor function for each translation unit instrumented for +profiling or test coverage. It runs at process exit. In a global constructor +function, the @code{__gcov_init()} function is called to register the gcov +information of a translation unit in a global list. In some situations, this +procedure does not work. Firstly, if you want to profile the global +constructor or exit processing of an operating system, the compiler generated +functions may conflict with the test objectives. Secondly, you may want to +test early parts of the system initialization or abnormal program behaviour +which do not allow a global constructor or exit processing. Thirdly, you need +a filesystem to store the files. + +The @option{-fprofile-info-section} GCC option enables you to use profiling and +test coverage in freestanding environments. This option disables the use of +global constructors and destructors for the gcov information. Instead, a +pointer to the gcov information is stored in a special linker input section for +each translation unit which is compiled with this option. By default, the +section name is @code{.gcov_info}. The gcov information is statically +initialized. The pointers to the gcov information from all translation units +of an executable can be collected by the linker in a contiguous memory block. +For the GNU linker, the below linker script output section definition can be +used to achieve this: + +@smallexample + .gcov_info : + @{ + PROVIDE (__gcov_info_start = .); + KEEP (*(.gcov_info)) + PROVIDE (__gcov_info_end = .); + @} +@end smallexample + +The linker will provide two global symbols, @code{__gcov_info_start} and +@code{__gcov_info_end}, which define the start and end of the array of pointers +to gcov information blocks, respectively. The @code{KEEP ()} directive is +required to prevent a garbage collection of the pointers. They are not +directly referenced by anything in the executable. The section may be placed +in a read-only memory area. + +In order to transfer the profiling and test coverage data from the target to +the host system, the application has to provide a function to produce a +reliable in order byte stream from the target to the host. The byte stream may +be compressed and encoded using error detection and correction codes to meet +application-specific requirements. The GCC provided @file{libgcov} target +library provides two functions, @code{__gcov_info_to_gcda()} and +@code{__gcov_filename_to_gcfn()}, to generate a byte stream from a gcov +information bock. The functions are declared in @code{#include }. The +byte stream can be deserialized by the @command{merge-stream} subcommand of the +@command{gcov-tool} to create or update @file{.gcda} files in the host +filesystem for the instrumented application. + +@subsection Tutorial + +This tutorial should be exercised on the host system. We will build a program +instrumented for test coverage. The program runs an application and dumps the +gcov information to @file{stderr} encoded as a printable character stream. The +application simply decodes such character streams from @file{stdin} and writes +the decoded character stream to @file{stdout} (warning: this is binary data). +The decoded character stream is consumed by the @command{merge-stream} +subcommand of the @command{gcov-tool} to create or update the @file{.gcda} +files. + +To get started, create an empty directory. Change into the new directory. +Then you will create the following three files in this directory + +@enumerate +@item +@file{app.h} - a header file included by @file{app.c} and @file{main.c}, + +@item +@file{app.c} - a source file which contains an example application, and + +@item +@file{main.c} - a source file which contains the program main function and code +to dump the gcov information. +@end enumerate + +Firstly, create the header file @file{app.h} with the following content: + +@smallexample +static const unsigned char a = 'a'; + +static inline unsigned char * +encode (unsigned char c, unsigned char buf[2]) +@{ + buf[0] = c % 16 + a; + buf[1] = (c / 16) % 16 + a; + return buf; +@} + +extern void application (void); +@end smallexample + +Secondly, create the source file @file{app.c} with the following content: + +@smallexample +#include "app.h" + +#include + +/* The application reads a character stream encoded by encode() from stdin, + decodes it, and writes the decoded characters to stdout. Characters other + than the 16 characters 'a' to 'p' are ignored. */ + +static int can_decode (unsigned char c) +@{ + return (unsigned char)(c - a) < 16; +@} + +void +application (void) +@{ + int first = 1; + int i; + unsigned char c; + + while ((i = fgetc (stdin)) != EOF) + @{ + unsigned char x = (unsigned char)i; + + if (can_decode (x)) + @{ + if (first) + c = x - a; + else + fputc (c + 16 * (x - a), stdout); + first = !first; + @} + else + first = 1; + @} +@} +@end smallexample + +Thirdly, create the source file @file{main.c} with the following content: + +@smallexample +#include "app.h" + +#include +#include +#include + +/* The start and end symbols are provided by the linker script. We use the + array notation to avoid issues with a potential small-data area. */ + +extern const struct gcov_info *const __gcov_info_start[]; +extern const struct gcov_info *const __gcov_info_end[]; + +/* This function shall produce a reliable in order byte stream to transfer the + gcov information from the target to the host system. */ + +static void +dump (const void *d, unsigned n, void *arg) +@{ + (void)arg; + const unsigned char *c = d; + unsigned char buf[2]; + + for (unsigned i = 0; i < n; ++i) + fwrite (encode (c[i], buf), sizeof (buf), 1, stderr); +@} + +/* The filename is serialized to a gcfn data stream by the + __gcov_filename_to_gcfn() function. The gcfn data is used by the + "merge-stream" subcommand of the "gcov-tool" to figure out the filename + associated with the gcov information. */ + +static void +filename (const char *f, void *arg) +@{ + __gcov_filename_to_gcfn (f, dump, arg); +@} + +/* The __gcov_info_to_gcda() function may have to allocate memory under + certain conditions. Simply try it out if it is needed for your application + or not. */ + +static void * +allocate (unsigned length, void *arg) +@{ + (void)arg; + return malloc (length); +@} + +/* Dump the gcov information of all translation units. */ + +static void +dump_gcov_info (void) +@{ + const struct gcov_info *const *info = __gcov_info_start; + const struct gcov_info *const *end = __gcov_info_end; + + /* Obfuscate variable to prevent compiler optimizations. */ + __asm__ ("" : "+r" (info)); + + while (info != end) + @{ + void *arg = NULL; + __gcov_info_to_gcda (*info, filename, dump, allocate, arg); + fputc ('\n', stderr); + ++info; + @} +@} + +/* The main() function just runs the application and then dumps the gcov + information to stderr. */ + +int +main (void) +@{ + application (); + dump_gcov_info (); + return 0; +@} +@end smallexample + +If we compile @file{app.c} with test coverage and no extra profiling options, +then a global constructor (@code{_sub_I_00100_0} here, it may have a different +name in your environment) and destructor (@code{_sub_D_00100_1}) is used to +register and dump the gcov information, respectively. We also see undefined +references to @code{__gcov_init} and @code{__gcov_exit}: + +@smallexample +$ gcc --coverage -c app.c +$ nm app.o +0000000000000000 r a +0000000000000030 T application +0000000000000000 t can_decode + U fgetc + U fputc +0000000000000000 b __gcov0.application +0000000000000038 b __gcov0.can_decode +0000000000000000 d __gcov_.application +00000000000000c0 d __gcov_.can_decode + U __gcov_exit + U __gcov_init + U __gcov_merge_add + U stdin + U stdout +0000000000000161 t _sub_D_00100_1 +0000000000000151 t _sub_I_00100_0 +@end smallexample + +Compile @file{app.c} and @file{main.c} with test coverage and +@option{-fprofile-info-section}. Now, a read-only pointer size object is +present in the @code{.gcov_info} section and there are no undefined references +to @code{__gcov_init} and @code{__gcov_exit}: + +@smallexample +$ gcc --coverage -fprofile-info-section -c main.c +$ gcc --coverage -fprofile-info-section -c app.c +$ objdump -h app.o + +app.o: file format elf64-x86-64 + +Sections: +Idx Name Size VMA LMA File off Algn + 0 .text 00000151 0000000000000000 0000000000000000 00000040 2**0 + CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE + 1 .data 00000100 0000000000000000 0000000000000000 000001a0 2**5 + CONTENTS, ALLOC, LOAD, RELOC, DATA + 2 .bss 00000040 0000000000000000 0000000000000000 000002a0 2**5 + ALLOC + 3 .rodata 0000003c 0000000000000000 0000000000000000 000002a0 2**3 + CONTENTS, ALLOC, LOAD, READONLY, DATA + 4 .gcov_info 00000008 0000000000000000 0000000000000000 000002e0 2**3 + CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA + 5 .comment 0000004e 0000000000000000 0000000000000000 000002e8 2**0 + CONTENTS, READONLY + 6 .note.GNU-stack 00000000 0000000000000000 0000000000000000 00000336 2**0 + CONTENTS, READONLY + 7 .eh_frame 00000058 0000000000000000 0000000000000000 00000338 2**3 + CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA +@end smallexample + +We have to customize the program link procedure so that all the +@code{.gcov_info} linker input sections are placed in a contiguous memory block +with a begin and end symbol. Firstly, get the default linker script using the +following commands (we assume a GNU linker): + +@smallexample +$ ld --verbose | sed '1,/^===/d' | sed '/^===/d' > linkcmds +@end smallexample + +Secondly, open the file @file{linkcmds} with a text editor and place the linker +output section definition from the overview after the @code{.rodata} section +definition. Link the program executable using the customized linker script: + +@smallexample +$ gcc --coverage main.o app.o -T linkcmds -Wl,-Map,app.map +@end smallexample + +In the linker map file @file{app.map}, we see that the linker placed the +read-only pointer size objects of our objects files @file{main.o} and +@file{app.o} into a contiguous memory block and provided the symbols +@code{__gcov_info_start} and @code{__gcov_info_end}: + +@smallexample +$ grep -C 1 "\.gcov_info" app.map + +.gcov_info 0x0000000000403ac0 0x10 + 0x0000000000403ac0 PROVIDE (__gcov_info_start = .) + *(.gcov_info) + .gcov_info 0x0000000000403ac0 0x8 main.o + .gcov_info 0x0000000000403ac8 0x8 app.o + 0x0000000000403ad0 PROVIDE (__gcov_info_end = .) +@end smallexample + +Make sure no @file{.gcda} files are present. Run the program with nothing to +decode and dump @file{stderr} to the file @file{gcda-0.txt} (first run). Run +the program to decode @file{gcda-0.txt} and send it to the @command{gcov-tool} +using the @command{merge-stream} subcommand to create the @file{.gcda} files +(second run). Run @command{gcov} to produce a report for @file{app.c}. We see +that the first run with nothing to decode results in a partially covered +application: + +@smallexample +$ rm -f app.gcda main.gcda +$ echo "" | ./a.out 2>gcda-0.txt +$ ./a.out gcda-1.txt | gcov-tool merge-stream +$ gcov -bc app.c +File 'app.c' +Lines executed:69.23% of 13 +Branches executed:66.67% of 6 +Taken at least once:50.00% of 6 +Calls executed:66.67% of 3 +Creating 'app.c.gcov' + +Lines executed:69.23% of 13 +@end smallexample + +Run the program to decode @file{gcda-1.txt} and send it to the +@command{gcov-tool} using the @command{merge-stream} subcommand to update the +@file{.gcda} files. Run @command{gcov} to produce a report for @file{app.c}. +Since the second run decoded the gcov information of the first run, we have now +a fully covered application: + +@smallexample +$ ./a.out gcda-2.txt | gcov-tool merge-stream +$ gcov -bc app.c +File 'app.c' +Lines executed:100.00% of 13 +Branches executed:100.00% of 6 +Taken at least once:100.00% of 6 +Calls executed:100.00% of 3 +Creating 'app.c.gcov' + +Lines executed:100.00% of 13 +@end smallexample + +@subsection System Initialization Caveats + +The gcov information of a translation unit consists of several global data +structures. For example, the instrumented code may update program flow graph +edge counters in a zero-initialized data structure. It is safe to run +instrumented code before the zero-initialized data is cleared to zero. The +coverage information obtained before the zero-initialized data is cleared to +zero is unusable. Dumping the gcov information using +@code{__gcov_info_to_gcda()} before the zero-initialized data is cleared to +zero or the initialized data is loaded, is undefined behaviour. Clearing the +zero-initialized data to zero through a function instrumented for profiling or +test coverage is undefined behaviour, since it may produce inconsistent program +flow graph edge counters for example. diff --git a/gcc/doc/generic.texi b/gcc/doc/generic.texi new file mode 100644 index 00000000000..e5f9d1be8ea --- /dev/null +++ b/gcc/doc/generic.texi @@ -0,0 +1,3619 @@ +@c Copyright (C) 2004-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@c --------------------------------------------------------------------- +@c GENERIC +@c --------------------------------------------------------------------- + +@node GENERIC +@chapter GENERIC +@cindex GENERIC + +The purpose of GENERIC is simply to provide a +language-independent way of representing an entire function in +trees. To this end, it was necessary to add a few new tree codes +to the back end, but almost everything was already there. If you +can express it with the codes in @code{gcc/tree.def}, it's +GENERIC@. + +Early on, there was a great deal of debate about how to think +about statements in a tree IL@. In GENERIC, a statement is +defined as any expression whose value, if any, is ignored. A +statement will always have @code{TREE_SIDE_EFFECTS} set (or it +will be discarded), but a non-statement expression may also have +side effects. A @code{CALL_EXPR}, for instance. + +It would be possible for some local optimizations to work on the +GENERIC form of a function; indeed, the adapted tree inliner +works fine on GENERIC, but the current compiler performs inlining +after lowering to GIMPLE (a restricted form described in the next +section). Indeed, currently the frontends perform this lowering +before handing off to @code{tree_rest_of_compilation}, but this +seems inelegant. + +@menu +* Deficiencies:: Topics not yet covered in this document. +* Tree overview:: All about @code{tree}s. +* Types:: Fundamental and aggregate types. +* Declarations:: Type declarations and variables. +* Attributes:: Declaration and type attributes. +* Expressions: Expression trees. Operating on data. +* Statements:: Control flow and related trees. +* Functions:: Function bodies, linkage, and other aspects. +* Language-dependent trees:: Topics and trees specific to language front ends. +* C and C++ Trees:: Trees specific to C and C++. +@end menu + +@c --------------------------------------------------------------------- +@c Deficiencies +@c --------------------------------------------------------------------- + +@node Deficiencies +@section Deficiencies + +@c The spelling of "incomplet" and "incorrekt" below is intentional. +There are many places in which this document is incomplet and incorrekt. +It is, as of yet, only @emph{preliminary} documentation. + +@c --------------------------------------------------------------------- +@c Overview +@c --------------------------------------------------------------------- + +@node Tree overview +@section Overview +@cindex tree +@findex TREE_CODE + +The central data structure used by the internal representation is the +@code{tree}. These nodes, while all of the C type @code{tree}, are of +many varieties. A @code{tree} is a pointer type, but the object to +which it points may be of a variety of types. From this point forward, +we will refer to trees in ordinary type, rather than in @code{this +font}, except when talking about the actual C type @code{tree}. + +You can tell what kind of node a particular tree is by using the +@code{TREE_CODE} macro. Many, many macros take trees as input and +return trees as output. However, most macros require a certain kind of +tree node as input. In other words, there is a type-system for trees, +but it is not reflected in the C type-system. + +For safety, it is useful to configure GCC with @option{--enable-checking}. +Although this results in a significant performance penalty (since all +tree types are checked at run-time), and is therefore inappropriate in a +release version, it is extremely helpful during the development process. + +Many macros behave as predicates. Many, although not all, of these +predicates end in @samp{_P}. Do not rely on the result type of these +macros being of any particular type. You may, however, rely on the fact +that the type can be compared to @code{0}, so that statements like +@smallexample +if (TEST_P (t) && !TEST_P (y)) + x = 1; +@end smallexample +@noindent +and +@smallexample +int i = (TEST_P (t) != 0); +@end smallexample +@noindent +are legal. Macros that return @code{int} values now may be changed to +return @code{tree} values, or other pointers in the future. Even those +that continue to return @code{int} may return multiple nonzero codes +where previously they returned only zero and one. Therefore, you should +not write code like +@smallexample +if (TEST_P (t) == 1) +@end smallexample +@noindent +as this code is not guaranteed to work correctly in the future. + +You should not take the address of values returned by the macros or +functions described here. In particular, no guarantee is given that the +values are lvalues. + +In general, the names of macros are all in uppercase, while the names of +functions are entirely in lowercase. There are rare exceptions to this +rule. You should assume that any macro or function whose name is made +up entirely of uppercase letters may evaluate its arguments more than +once. You may assume that a macro or function whose name is made up +entirely of lowercase letters will evaluate its arguments only once. + +The @code{error_mark_node} is a special tree. Its tree code is +@code{ERROR_MARK}, but since there is only ever one node with that code, +the usual practice is to compare the tree against +@code{error_mark_node}. (This test is just a test for pointer +equality.) If an error has occurred during front-end processing the +flag @code{errorcount} will be set. If the front end has encountered +code it cannot handle, it will issue a message to the user and set +@code{sorrycount}. When these flags are set, any macro or function +which normally returns a tree of a particular kind may instead return +the @code{error_mark_node}. Thus, if you intend to do any processing of +erroneous code, you must be prepared to deal with the +@code{error_mark_node}. + +Occasionally, a particular tree slot (like an operand to an expression, +or a particular field in a declaration) will be referred to as +``reserved for the back end''. These slots are used to store RTL when +the tree is converted to RTL for use by the GCC back end. However, if +that process is not taking place (e.g., if the front end is being hooked +up to an intelligent editor), then those slots may be used by the +back end presently in use. + +If you encounter situations that do not match this documentation, such +as tree nodes of types not mentioned here, or macros documented to +return entities of a particular kind that instead return entities of +some different kind, you have found a bug, either in the front end or in +the documentation. Please report these bugs as you would any other +bug. + +@menu +* Macros and Functions::Macros and functions that can be used with all trees. +* Identifiers:: The names of things. +* Containers:: Lists and vectors. +@end menu + +@c --------------------------------------------------------------------- +@c Trees +@c --------------------------------------------------------------------- + +@node Macros and Functions +@subsection Trees +@cindex tree +@findex TREE_CHAIN +@findex TREE_TYPE + +All GENERIC trees have two fields in common. First, @code{TREE_CHAIN} +is a pointer that can be used as a singly-linked list to other trees. +The other is @code{TREE_TYPE}. Many trees store the type of an +expression or declaration in this field. + +These are some other functions for handling trees: + +@ftable @code + +@item tree_size +Return the number of bytes a tree takes. + +@item build0 +@itemx build1 +@itemx build2 +@itemx build3 +@itemx build4 +@itemx build5 +@itemx build6 + +These functions build a tree and supply values to put in each +parameter. The basic signature is @samp{@w{code, type, [operands]}}. +@code{code} is the @code{TREE_CODE}, and @code{type} is a tree +representing the @code{TREE_TYPE}. These are followed by the +operands, each of which is also a tree. + +@end ftable + + +@c --------------------------------------------------------------------- +@c Identifiers +@c --------------------------------------------------------------------- + +@node Identifiers +@subsection Identifiers +@cindex identifier +@cindex name +@tindex IDENTIFIER_NODE + +An @code{IDENTIFIER_NODE} represents a slightly more general concept +than the standard C or C++ concept of identifier. In particular, an +@code{IDENTIFIER_NODE} may contain a @samp{$}, or other extraordinary +characters. + +There are never two distinct @code{IDENTIFIER_NODE}s representing the +same identifier. Therefore, you may use pointer equality to compare +@code{IDENTIFIER_NODE}s, rather than using a routine like +@code{strcmp}. Use @code{get_identifier} to obtain the unique +@code{IDENTIFIER_NODE} for a supplied string. + +You can use the following macros to access identifiers: +@ftable @code +@item IDENTIFIER_POINTER +The string represented by the identifier, represented as a +@code{char*}. This string is always @code{NUL}-terminated, and contains +no embedded @code{NUL} characters. + +@item IDENTIFIER_LENGTH +The length of the string returned by @code{IDENTIFIER_POINTER}, not +including the trailing @code{NUL}. This value of +@code{IDENTIFIER_LENGTH (x)} is always the same as @code{strlen +(IDENTIFIER_POINTER (x))}. + +@item IDENTIFIER_OPNAME_P +This predicate holds if the identifier represents the name of an +overloaded operator. In this case, you should not depend on the +contents of either the @code{IDENTIFIER_POINTER} or the +@code{IDENTIFIER_LENGTH}. + +@item IDENTIFIER_TYPENAME_P +This predicate holds if the identifier represents the name of a +user-defined conversion operator. In this case, the @code{TREE_TYPE} of +the @code{IDENTIFIER_NODE} holds the type to which the conversion +operator converts. + +@end ftable + +@c --------------------------------------------------------------------- +@c Containers +@c --------------------------------------------------------------------- + +@node Containers +@subsection Containers +@cindex container +@cindex list +@cindex vector +@tindex TREE_LIST +@tindex TREE_VEC +@findex TREE_PURPOSE +@findex TREE_VALUE +@findex TREE_VEC_LENGTH +@findex TREE_VEC_ELT + +Two common container data structures can be represented directly with +tree nodes. A @code{TREE_LIST} is a singly linked list containing two +trees per node. These are the @code{TREE_PURPOSE} and @code{TREE_VALUE} +of each node. (Often, the @code{TREE_PURPOSE} contains some kind of +tag, or additional information, while the @code{TREE_VALUE} contains the +majority of the payload. In other cases, the @code{TREE_PURPOSE} is +simply @code{NULL_TREE}, while in still others both the +@code{TREE_PURPOSE} and @code{TREE_VALUE} are of equal stature.) Given +one @code{TREE_LIST} node, the next node is found by following the +@code{TREE_CHAIN}. If the @code{TREE_CHAIN} is @code{NULL_TREE}, then +you have reached the end of the list. + +A @code{TREE_VEC} is a simple vector. The @code{TREE_VEC_LENGTH} is an +integer (not a tree) giving the number of nodes in the vector. The +nodes themselves are accessed using the @code{TREE_VEC_ELT} macro, which +takes two arguments. The first is the @code{TREE_VEC} in question; the +second is an integer indicating which element in the vector is desired. +The elements are indexed from zero. + +@c --------------------------------------------------------------------- +@c Types +@c --------------------------------------------------------------------- + +@node Types +@section Types +@cindex type +@cindex pointer +@cindex reference +@cindex fundamental type +@cindex array +@tindex VOID_TYPE +@tindex INTEGER_TYPE +@tindex TYPE_MIN_VALUE +@tindex TYPE_MAX_VALUE +@tindex REAL_TYPE +@tindex FIXED_POINT_TYPE +@tindex COMPLEX_TYPE +@tindex ENUMERAL_TYPE +@tindex BOOLEAN_TYPE +@tindex POINTER_TYPE +@tindex REFERENCE_TYPE +@tindex FUNCTION_TYPE +@tindex METHOD_TYPE +@tindex ARRAY_TYPE +@tindex RECORD_TYPE +@tindex UNION_TYPE +@tindex OPAQUE_TYPE +@tindex UNKNOWN_TYPE +@tindex OFFSET_TYPE +@findex TYPE_UNQUALIFIED +@findex TYPE_QUAL_CONST +@findex TYPE_QUAL_VOLATILE +@findex TYPE_QUAL_RESTRICT +@findex TYPE_MAIN_VARIANT +@cindex qualified type +@findex TYPE_SIZE +@findex TYPE_ALIGN +@findex TYPE_PRECISION +@findex TYPE_ARG_TYPES +@findex TYPE_METHOD_BASETYPE +@findex TYPE_OFFSET_BASETYPE +@findex TREE_TYPE +@findex TYPE_CONTEXT +@findex TYPE_NAME +@findex TYPENAME_TYPE_FULLNAME +@findex TYPE_FIELDS +@findex TYPE_CANONICAL +@findex TYPE_STRUCTURAL_EQUALITY_P +@findex SET_TYPE_STRUCTURAL_EQUALITY + +All types have corresponding tree nodes. However, you should not assume +that there is exactly one tree node corresponding to each type. There +are often multiple nodes corresponding to the same type. + +For the most part, different kinds of types have different tree codes. +(For example, pointer types use a @code{POINTER_TYPE} code while arrays +use an @code{ARRAY_TYPE} code.) However, pointers to member functions +use the @code{RECORD_TYPE} code. Therefore, when writing a +@code{switch} statement that depends on the code associated with a +particular type, you should take care to handle pointers to member +functions under the @code{RECORD_TYPE} case label. + +The following functions and macros deal with cv-qualification of types: +@ftable @code +@item TYPE_MAIN_VARIANT +This macro returns the unqualified version of a type. It may be applied +to an unqualified type, but it is not always the identity function in +that case. +@end ftable + +A few other macros and functions are usable with all types: +@ftable @code +@item TYPE_SIZE +The number of bits required to represent the type, represented as an +@code{INTEGER_CST}. For an incomplete type, @code{TYPE_SIZE} will be +@code{NULL_TREE}. + +@item TYPE_ALIGN +The alignment of the type, in bits, represented as an @code{int}. + +@item TYPE_NAME +This macro returns a declaration (in the form of a @code{TYPE_DECL}) for +the type. (Note this macro does @emph{not} return an +@code{IDENTIFIER_NODE}, as you might expect, given its name!) You can +look at the @code{DECL_NAME} of the @code{TYPE_DECL} to obtain the +actual name of the type. The @code{TYPE_NAME} will be @code{NULL_TREE} +for a type that is not a built-in type, the result of a typedef, or a +named class type. + +@item TYPE_CANONICAL +This macro returns the ``canonical'' type for the given type +node. Canonical types are used to improve performance in the C++ and +Objective-C++ front ends by allowing efficient comparison between two +type nodes in @code{same_type_p}: if the @code{TYPE_CANONICAL} values +of the types are equal, the types are equivalent; otherwise, the types +are not equivalent. The notion of equivalence for canonical types is +the same as the notion of type equivalence in the language itself. For +instance, + +When @code{TYPE_CANONICAL} is @code{NULL_TREE}, there is no canonical +type for the given type node. In this case, comparison between this +type and any other type requires the compiler to perform a deep, +``structural'' comparison to see if the two type nodes have the same +form and properties. + +The canonical type for a node is always the most fundamental type in +the equivalence class of types. For instance, @code{int} is its own +canonical type. A typedef @code{I} of @code{int} will have @code{int} +as its canonical type. Similarly, @code{I*}@ and a typedef @code{IP}@ +(defined to @code{I*}) will has @code{int*} as their canonical +type. When building a new type node, be sure to set +@code{TYPE_CANONICAL} to the appropriate canonical type. If the new +type is a compound type (built from other types), and any of those +other types require structural equality, use +@code{SET_TYPE_STRUCTURAL_EQUALITY} to ensure that the new type also +requires structural equality. Finally, if for some reason you cannot +guarantee that @code{TYPE_CANONICAL} will point to the canonical type, +use @code{SET_TYPE_STRUCTURAL_EQUALITY} to make sure that the new +type--and any type constructed based on it--requires structural +equality. If you suspect that the canonical type system is +miscomparing types, pass @code{--param verify-canonical-types=1} to +the compiler or configure with @code{--enable-checking} to force the +compiler to verify its canonical-type comparisons against the +structural comparisons; the compiler will then print any warnings if +the canonical types miscompare. + +@item TYPE_STRUCTURAL_EQUALITY_P +This predicate holds when the node requires structural equality +checks, e.g., when @code{TYPE_CANONICAL} is @code{NULL_TREE}. + +@item SET_TYPE_STRUCTURAL_EQUALITY +This macro states that the type node it is given requires structural +equality checks, e.g., it sets @code{TYPE_CANONICAL} to +@code{NULL_TREE}. + +@item same_type_p +This predicate takes two types as input, and holds if they are the same +type. For example, if one type is a @code{typedef} for the other, or +both are @code{typedef}s for the same type. This predicate also holds if +the two trees given as input are simply copies of one another; i.e., +there is no difference between them at the source level, but, for +whatever reason, a duplicate has been made in the representation. You +should never use @code{==} (pointer equality) to compare types; always +use @code{same_type_p} instead. +@end ftable + +Detailed below are the various kinds of types, and the macros that can +be used to access them. Although other kinds of types are used +elsewhere in G++, the types described here are the only ones that you +will encounter while examining the intermediate representation. + +@table @code +@item VOID_TYPE +Used to represent the @code{void} type. + +@item INTEGER_TYPE +Used to represent the various integral types, including @code{char}, +@code{short}, @code{int}, @code{long}, and @code{long long}. This code +is not used for enumeration types, nor for the @code{bool} type. +The @code{TYPE_PRECISION} is the number of bits used in +the representation, represented as an @code{unsigned int}. (Note that +in the general case this is not the same value as @code{TYPE_SIZE}; +suppose that there were a 24-bit integer type, but that alignment +requirements for the ABI required 32-bit alignment. Then, +@code{TYPE_SIZE} would be an @code{INTEGER_CST} for 32, while +@code{TYPE_PRECISION} would be 24.) The integer type is unsigned if +@code{TYPE_UNSIGNED} holds; otherwise, it is signed. + +The @code{TYPE_MIN_VALUE} is an @code{INTEGER_CST} for the smallest +integer that may be represented by this type. Similarly, the +@code{TYPE_MAX_VALUE} is an @code{INTEGER_CST} for the largest integer +that may be represented by this type. + +@item REAL_TYPE +Used to represent the @code{float}, @code{double}, and @code{long +double} types. The number of bits in the floating-point representation +is given by @code{TYPE_PRECISION}, as in the @code{INTEGER_TYPE} case. + +@item FIXED_POINT_TYPE +Used to represent the @code{short _Fract}, @code{_Fract}, @code{long +_Fract}, @code{long long _Fract}, @code{short _Accum}, @code{_Accum}, +@code{long _Accum}, and @code{long long _Accum} types. The number of bits +in the fixed-point representation is given by @code{TYPE_PRECISION}, +as in the @code{INTEGER_TYPE} case. There may be padding bits, fractional +bits and integral bits. The number of fractional bits is given by +@code{TYPE_FBIT}, and the number of integral bits is given by @code{TYPE_IBIT}. +The fixed-point type is unsigned if @code{TYPE_UNSIGNED} holds; otherwise, +it is signed. +The fixed-point type is saturating if @code{TYPE_SATURATING} holds; otherwise, +it is not saturating. + +@item COMPLEX_TYPE +Used to represent GCC built-in @code{__complex__} data types. The +@code{TREE_TYPE} is the type of the real and imaginary parts. + +@item ENUMERAL_TYPE +Used to represent an enumeration type. The @code{TYPE_PRECISION} gives +(as an @code{int}), the number of bits used to represent the type. If +there are no negative enumeration constants, @code{TYPE_UNSIGNED} will +hold. The minimum and maximum enumeration constants may be obtained +with @code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE}, respectively; each +of these macros returns an @code{INTEGER_CST}. + +The actual enumeration constants themselves may be obtained by looking +at the @code{TYPE_VALUES}. This macro will return a @code{TREE_LIST}, +containing the constants. The @code{TREE_PURPOSE} of each node will be +an @code{IDENTIFIER_NODE} giving the name of the constant; the +@code{TREE_VALUE} will be an @code{INTEGER_CST} giving the value +assigned to that constant. These constants will appear in the order in +which they were declared. The @code{TREE_TYPE} of each of these +constants will be the type of enumeration type itself. + +@item OPAQUE_TYPE +Used for things that have a @code{MODE_OPAQUE} mode class in the +backend. Opaque types have a size and precision, and can be held in +memory or registers. They are used when we do not want the compiler to +make assumptions about the availability of other operations as would +happen with integer types. + +@item BOOLEAN_TYPE +Used to represent the @code{bool} type. + +@item POINTER_TYPE +Used to represent pointer types, and pointer to data member types. The +@code{TREE_TYPE} gives the type to which this type points. + +@item REFERENCE_TYPE +Used to represent reference types. The @code{TREE_TYPE} gives the type +to which this type refers. + +@item FUNCTION_TYPE +Used to represent the type of non-member functions and of static member +functions. The @code{TREE_TYPE} gives the return type of the function. +The @code{TYPE_ARG_TYPES} are a @code{TREE_LIST} of the argument types. +The @code{TREE_VALUE} of each node in this list is the type of the +corresponding argument; the @code{TREE_PURPOSE} is an expression for the +default argument value, if any. If the last node in the list is +@code{void_list_node} (a @code{TREE_LIST} node whose @code{TREE_VALUE} +is the @code{void_type_node}), then functions of this type do not take +variable arguments. Otherwise, they do take a variable number of +arguments. + +Note that in C (but not in C++) a function declared like @code{void f()} +is an unprototyped function taking a variable number of arguments; the +@code{TYPE_ARG_TYPES} of such a function will be @code{NULL}. + +@item METHOD_TYPE +Used to represent the type of a non-static member function. Like a +@code{FUNCTION_TYPE}, the return type is given by the @code{TREE_TYPE}. +The type of @code{*this}, i.e., the class of which functions of this +type are a member, is given by the @code{TYPE_METHOD_BASETYPE}. The +@code{TYPE_ARG_TYPES} is the parameter list, as for a +@code{FUNCTION_TYPE}, and includes the @code{this} argument. + +@item ARRAY_TYPE +Used to represent array types. The @code{TREE_TYPE} gives the type of +the elements in the array. If the array-bound is present in the type, +the @code{TYPE_DOMAIN} is an @code{INTEGER_TYPE} whose +@code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE} will be the lower and +upper bounds of the array, respectively. The @code{TYPE_MIN_VALUE} will +always be an @code{INTEGER_CST} for zero, while the +@code{TYPE_MAX_VALUE} will be one less than the number of elements in +the array, i.e., the highest value which may be used to index an element +in the array. + +@item RECORD_TYPE +Used to represent @code{struct} and @code{class} types, as well as +pointers to member functions and similar constructs in other languages. +@code{TYPE_FIELDS} contains the items contained in this type, each of +which can be a @code{FIELD_DECL}, @code{VAR_DECL}, @code{CONST_DECL}, or +@code{TYPE_DECL}. You may not make any assumptions about the ordering +of the fields in the type or whether one or more of them overlap. + +@item UNION_TYPE +Used to represent @code{union} types. Similar to @code{RECORD_TYPE} +except that all @code{FIELD_DECL} nodes in @code{TYPE_FIELD} start at +bit position zero. + +@item QUAL_UNION_TYPE +Used to represent part of a variant record in Ada. Similar to +@code{UNION_TYPE} except that each @code{FIELD_DECL} has a +@code{DECL_QUALIFIER} field, which contains a boolean expression that +indicates whether the field is present in the object. The type will only +have one field, so each field's @code{DECL_QUALIFIER} is only evaluated +if none of the expressions in the previous fields in @code{TYPE_FIELDS} +are nonzero. Normally these expressions will reference a field in the +outer object using a @code{PLACEHOLDER_EXPR}. + +@item LANG_TYPE +This node is used to represent a language-specific type. The front +end must handle it. + +@item OFFSET_TYPE +This node is used to represent a pointer-to-data member. For a data +member @code{X::m} the @code{TYPE_OFFSET_BASETYPE} is @code{X} and the +@code{TREE_TYPE} is the type of @code{m}. + +@end table + +There are variables whose values represent some of the basic types. +These include: +@table @code +@item void_type_node +A node for @code{void}. + +@item integer_type_node +A node for @code{int}. + +@item unsigned_type_node. +A node for @code{unsigned int}. + +@item char_type_node. +A node for @code{char}. +@end table +@noindent +It may sometimes be useful to compare one of these variables with a type +in hand, using @code{same_type_p}. + +@c --------------------------------------------------------------------- +@c Declarations +@c --------------------------------------------------------------------- + +@node Declarations +@section Declarations +@cindex declaration +@cindex variable +@cindex type declaration +@tindex LABEL_DECL +@tindex CONST_DECL +@tindex TYPE_DECL +@tindex VAR_DECL +@tindex PARM_DECL +@tindex DEBUG_EXPR_DECL +@tindex FIELD_DECL +@tindex NAMESPACE_DECL +@tindex RESULT_DECL +@tindex TEMPLATE_DECL +@tindex THUNK_DECL +@findex THUNK_DELTA +@findex DECL_INITIAL +@findex DECL_SIZE +@findex DECL_ALIGN +@findex DECL_EXTERNAL + +This section covers the various kinds of declarations that appear in the +internal representation, except for declarations of functions +(represented by @code{FUNCTION_DECL} nodes), which are described in +@ref{Functions}. + +@menu +* Working with declarations:: Macros and functions that work on +declarations. +* Internal structure:: How declaration nodes are represented. +@end menu + +@node Working with declarations +@subsection Working with declarations + +Some macros can be used with any kind of declaration. These include: +@ftable @code +@item DECL_NAME +This macro returns an @code{IDENTIFIER_NODE} giving the name of the +entity. + +@item TREE_TYPE +This macro returns the type of the entity declared. + +@item EXPR_FILENAME +This macro returns the name of the file in which the entity was +declared, as a @code{char*}. For an entity declared implicitly by the +compiler (like @code{__builtin_memcpy}), this will be the string +@code{""}. + +@item EXPR_LINENO +This macro returns the line number at which the entity was declared, as +an @code{int}. + +@item DECL_ARTIFICIAL +This predicate holds if the declaration was implicitly generated by the +compiler. For example, this predicate will hold of an implicitly +declared member function, or of the @code{TYPE_DECL} implicitly +generated for a class type. Recall that in C++ code like: +@smallexample +struct S @{@}; +@end smallexample +@noindent +is roughly equivalent to C code like: +@smallexample +struct S @{@}; +typedef struct S S; +@end smallexample +The implicitly generated @code{typedef} declaration is represented by a +@code{TYPE_DECL} for which @code{DECL_ARTIFICIAL} holds. + +@end ftable + +The various kinds of declarations include: +@table @code +@item LABEL_DECL +These nodes are used to represent labels in function bodies. For more +information, see @ref{Functions}. These nodes only appear in block +scopes. + +@item CONST_DECL +These nodes are used to represent enumeration constants. The value of +the constant is given by @code{DECL_INITIAL} which will be an +@code{INTEGER_CST} with the same type as the @code{TREE_TYPE} of the +@code{CONST_DECL}, i.e., an @code{ENUMERAL_TYPE}. + +@item RESULT_DECL +These nodes represent the value returned by a function. When a value is +assigned to a @code{RESULT_DECL}, that indicates that the value should +be returned, via bitwise copy, by the function. You can use +@code{DECL_SIZE} and @code{DECL_ALIGN} on a @code{RESULT_DECL}, just as +with a @code{VAR_DECL}. + +@item TYPE_DECL +These nodes represent @code{typedef} declarations. The @code{TREE_TYPE} +is the type declared to have the name given by @code{DECL_NAME}. In +some cases, there is no associated name. + +@item VAR_DECL +These nodes represent variables with namespace or block scope, as well +as static data members. The @code{DECL_SIZE} and @code{DECL_ALIGN} are +analogous to @code{TYPE_SIZE} and @code{TYPE_ALIGN}. For a declaration, +you should always use the @code{DECL_SIZE} and @code{DECL_ALIGN} rather +than the @code{TYPE_SIZE} and @code{TYPE_ALIGN} given by the +@code{TREE_TYPE}, since special attributes may have been applied to the +variable to give it a particular size and alignment. You may use the +predicates @code{DECL_THIS_STATIC} or @code{DECL_THIS_EXTERN} to test +whether the storage class specifiers @code{static} or @code{extern} were +used to declare a variable. + +If this variable is initialized (but does not require a constructor), +the @code{DECL_INITIAL} will be an expression for the initializer. The +initializer should be evaluated, and a bitwise copy into the variable +performed. If the @code{DECL_INITIAL} is the @code{error_mark_node}, +there is an initializer, but it is given by an explicit statement later +in the code; no bitwise copy is required. + +GCC provides an extension that allows either automatic variables, or +global variables, to be placed in particular registers. This extension +is being used for a particular @code{VAR_DECL} if @code{DECL_REGISTER} +holds for the @code{VAR_DECL}, and if @code{DECL_ASSEMBLER_NAME} is not +equal to @code{DECL_NAME}. In that case, @code{DECL_ASSEMBLER_NAME} is +the name of the register into which the variable will be placed. + +@item PARM_DECL +Used to represent a parameter to a function. Treat these nodes +similarly to @code{VAR_DECL} nodes. These nodes only appear in the +@code{DECL_ARGUMENTS} for a @code{FUNCTION_DECL}. + +The @code{DECL_ARG_TYPE} for a @code{PARM_DECL} is the type that will +actually be used when a value is passed to this function. It may be a +wider type than the @code{TREE_TYPE} of the parameter; for example, the +ordinary type might be @code{short} while the @code{DECL_ARG_TYPE} is +@code{int}. + +@item DEBUG_EXPR_DECL +Used to represent an anonymous debug-information temporary created to +hold an expression as it is optimized away, so that its value can be +referenced in debug bind statements. + +@item FIELD_DECL +These nodes represent non-static data members. The @code{DECL_SIZE} and +@code{DECL_ALIGN} behave as for @code{VAR_DECL} nodes. +The position of the field within the parent record is specified by a +combination of three attributes. @code{DECL_FIELD_OFFSET} is the position, +counting in bytes, of the @code{DECL_OFFSET_ALIGN}-bit sized word containing +the bit of the field closest to the beginning of the structure. +@code{DECL_FIELD_BIT_OFFSET} is the bit offset of the first bit of the field +within this word; this may be nonzero even for fields that are not bit-fields, +since @code{DECL_OFFSET_ALIGN} may be greater than the natural alignment +of the field's type. + +If @code{DECL_C_BIT_FIELD} holds, this field is a bit-field. In a bit-field, +@code{DECL_BIT_FIELD_TYPE} also contains the type that was originally +specified for it, while DECL_TYPE may be a modified type with lesser precision, +according to the size of the bit field. + +@item NAMESPACE_DECL +Namespaces provide a name hierarchy for other declarations. They +appear in the @code{DECL_CONTEXT} of other @code{_DECL} nodes. + +@end table + +@node Internal structure +@subsection Internal structure + +@code{DECL} nodes are represented internally as a hierarchy of +structures. + +@menu +* Current structure hierarchy:: The current DECL node structure +hierarchy. +* Adding new DECL node types:: How to add a new DECL node to a +frontend. +@end menu + +@node Current structure hierarchy +@subsubsection Current structure hierarchy + +@table @code + +@item struct tree_decl_minimal +This is the minimal structure to inherit from in order for common +@code{DECL} macros to work. The fields it contains are a unique ID, +source location, context, and name. + +@item struct tree_decl_common +This structure inherits from @code{struct tree_decl_minimal}. It +contains fields that most @code{DECL} nodes need, such as a field to +store alignment, machine mode, size, and attributes. + +@item struct tree_field_decl +This structure inherits from @code{struct tree_decl_common}. It is +used to represent @code{FIELD_DECL}. + +@item struct tree_label_decl +This structure inherits from @code{struct tree_decl_common}. It is +used to represent @code{LABEL_DECL}. + +@item struct tree_translation_unit_decl +This structure inherits from @code{struct tree_decl_common}. It is +used to represent @code{TRANSLATION_UNIT_DECL}. + +@item struct tree_decl_with_rtl +This structure inherits from @code{struct tree_decl_common}. It +contains a field to store the low-level RTL associated with a +@code{DECL} node. + +@item struct tree_result_decl +This structure inherits from @code{struct tree_decl_with_rtl}. It is +used to represent @code{RESULT_DECL}. + +@item struct tree_const_decl +This structure inherits from @code{struct tree_decl_with_rtl}. It is +used to represent @code{CONST_DECL}. + +@item struct tree_parm_decl +This structure inherits from @code{struct tree_decl_with_rtl}. It is +used to represent @code{PARM_DECL}. + +@item struct tree_decl_with_vis +This structure inherits from @code{struct tree_decl_with_rtl}. It +contains fields necessary to store visibility information, as well as +a section name and assembler name. + +@item struct tree_var_decl +This structure inherits from @code{struct tree_decl_with_vis}. It is +used to represent @code{VAR_DECL}. + +@item struct tree_function_decl +This structure inherits from @code{struct tree_decl_with_vis}. It is +used to represent @code{FUNCTION_DECL}. + +@end table +@node Adding new DECL node types +@subsubsection Adding new DECL node types + +Adding a new @code{DECL} tree consists of the following steps + +@table @asis + +@item Add a new tree code for the @code{DECL} node +For language specific @code{DECL} nodes, there is a @file{.def} file +in each frontend directory where the tree code should be added. +For @code{DECL} nodes that are part of the middle-end, the code should +be added to @file{tree.def}. + +@item Create a new structure type for the @code{DECL} node +These structures should inherit from one of the existing structures in +the language hierarchy by using that structure as the first member. + +@smallexample +struct tree_foo_decl +@{ + struct tree_decl_with_vis common; +@} +@end smallexample + +Would create a structure name @code{tree_foo_decl} that inherits from +@code{struct tree_decl_with_vis}. + +For language specific @code{DECL} nodes, this new structure type +should go in the appropriate @file{.h} file. +For @code{DECL} nodes that are part of the middle-end, the structure +type should go in @file{tree.h}. + +@item Add a member to the tree structure enumerator for the node +For garbage collection and dynamic checking purposes, each @code{DECL} +node structure type is required to have a unique enumerator value +specified with it. +For language specific @code{DECL} nodes, this new enumerator value +should go in the appropriate @file{.def} file. +For @code{DECL} nodes that are part of the middle-end, the enumerator +values are specified in @file{treestruct.def}. + +@item Update @code{union tree_node} +In order to make your new structure type usable, it must be added to +@code{union tree_node}. +For language specific @code{DECL} nodes, a new entry should be added +to the appropriate @file{.h} file of the form +@smallexample + struct tree_foo_decl GTY ((tag ("TS_VAR_DECL"))) foo_decl; +@end smallexample +For @code{DECL} nodes that are part of the middle-end, the additional +member goes directly into @code{union tree_node} in @file{tree.h}. + +@item Update dynamic checking info +In order to be able to check whether accessing a named portion of +@code{union tree_node} is legal, and whether a certain @code{DECL} node +contains one of the enumerated @code{DECL} node structures in the +hierarchy, a simple lookup table is used. +This lookup table needs to be kept up to date with the tree structure +hierarchy, or else checking and containment macros will fail +inappropriately. + +For language specific @code{DECL} nodes, there is an @code{init_ts} +function in an appropriate @file{.c} file, which initializes the lookup +table. +Code setting up the table for new @code{DECL} nodes should be added +there. +For each @code{DECL} tree code and enumerator value representing a +member of the inheritance hierarchy, the table should contain 1 if +that tree code inherits (directly or indirectly) from that member. +Thus, a @code{FOO_DECL} node derived from @code{struct decl_with_rtl}, +and enumerator value @code{TS_FOO_DECL}, would be set up as follows +@smallexample +tree_contains_struct[FOO_DECL][TS_FOO_DECL] = 1; +tree_contains_struct[FOO_DECL][TS_DECL_WRTL] = 1; +tree_contains_struct[FOO_DECL][TS_DECL_COMMON] = 1; +tree_contains_struct[FOO_DECL][TS_DECL_MINIMAL] = 1; +@end smallexample + +For @code{DECL} nodes that are part of the middle-end, the setup code +goes into @file{tree.cc}. + +@item Add macros to access any new fields and flags + +Each added field or flag should have a macro that is used to access +it, that performs appropriate checking to ensure only the right type of +@code{DECL} nodes access the field. + +These macros generally take the following form +@smallexample +#define FOO_DECL_FIELDNAME(NODE) FOO_DECL_CHECK(NODE)->foo_decl.fieldname +@end smallexample +However, if the structure is simply a base class for further +structures, something like the following should be used +@smallexample +#define BASE_STRUCT_CHECK(T) CONTAINS_STRUCT_CHECK(T, TS_BASE_STRUCT) +#define BASE_STRUCT_FIELDNAME(NODE) \ + (BASE_STRUCT_CHECK(NODE)->base_struct.fieldname +@end smallexample + +Reading them from the generated @file{all-tree.def} file (which in +turn includes all the @file{tree.def} files), @file{gencheck.cc} is +used during GCC's build to generate the @code{*_CHECK} macros for all +tree codes. + +@end table + + +@c --------------------------------------------------------------------- +@c Attributes +@c --------------------------------------------------------------------- +@node Attributes +@section Attributes in trees +@cindex attributes + +Attributes, as specified using the @code{__attribute__} keyword, are +represented internally as a @code{TREE_LIST}. The @code{TREE_PURPOSE} +is the name of the attribute, as an @code{IDENTIFIER_NODE}. The +@code{TREE_VALUE} is a @code{TREE_LIST} of the arguments of the +attribute, if any, or @code{NULL_TREE} if there are no arguments; the +arguments are stored as the @code{TREE_VALUE} of successive entries in +the list, and may be identifiers or expressions. The @code{TREE_CHAIN} +of the attribute is the next attribute in a list of attributes applying +to the same declaration or type, or @code{NULL_TREE} if there are no +further attributes in the list. + +Attributes may be attached to declarations and to types; these +attributes may be accessed with the following macros. All attributes +are stored in this way, and many also cause other changes to the +declaration or type or to other internal compiler data structures. + +@deftypefn {Tree Macro} tree DECL_ATTRIBUTES (tree @var{decl}) +This macro returns the attributes on the declaration @var{decl}. +@end deftypefn + +@deftypefn {Tree Macro} tree TYPE_ATTRIBUTES (tree @var{type}) +This macro returns the attributes on the type @var{type}. +@end deftypefn + + +@c --------------------------------------------------------------------- +@c Expressions +@c --------------------------------------------------------------------- + +@node Expression trees +@section Expressions +@cindex expression +@findex TREE_TYPE +@findex TREE_OPERAND + +The internal representation for expressions is for the most part quite +straightforward. However, there are a few facts that one must bear in +mind. In particular, the expression ``tree'' is actually a directed +acyclic graph. (For example there may be many references to the integer +constant zero throughout the source program; many of these will be +represented by the same expression node.) You should not rely on +certain kinds of node being shared, nor should you rely on certain kinds of +nodes being unshared. + +The following macros can be used with all expression nodes: + +@ftable @code +@item TREE_TYPE +Returns the type of the expression. This value may not be precisely the +same type that would be given the expression in the original program. +@end ftable + +In what follows, some nodes that one might expect to always have type +@code{bool} are documented to have either integral or boolean type. At +some point in the future, the C front end may also make use of this same +intermediate representation, and at this point these nodes will +certainly have integral type. The previous sentence is not meant to +imply that the C++ front end does not or will not give these nodes +integral type. + +Below, we list the various kinds of expression nodes. Except where +noted otherwise, the operands to an expression are accessed using the +@code{TREE_OPERAND} macro. For example, to access the first operand to +a binary plus expression @code{expr}, use: + +@smallexample +TREE_OPERAND (expr, 0) +@end smallexample +@noindent + +As this example indicates, the operands are zero-indexed. + + +@menu +* Constants: Constant expressions. +* Storage References:: +* Unary and Binary Expressions:: +* Vectors:: +@end menu + +@node Constant expressions +@subsection Constant expressions +@tindex INTEGER_CST +@findex tree_int_cst_lt +@findex tree_int_cst_equal +@tindex tree_fits_uhwi_p +@tindex tree_fits_shwi_p +@tindex tree_to_uhwi +@tindex tree_to_shwi +@tindex TREE_INT_CST_NUNITS +@tindex TREE_INT_CST_ELT +@tindex TREE_INT_CST_LOW +@tindex REAL_CST +@tindex FIXED_CST +@tindex COMPLEX_CST +@tindex VECTOR_CST +@tindex STRING_CST +@tindex POLY_INT_CST +@findex TREE_STRING_LENGTH +@findex TREE_STRING_POINTER + +The table below begins with constants, moves on to unary expressions, +then proceeds to binary expressions, and concludes with various other +kinds of expressions: + +@table @code +@item INTEGER_CST +These nodes represent integer constants. Note that the type of these +constants is obtained with @code{TREE_TYPE}; they are not always of type +@code{int}. In particular, @code{char} constants are represented with +@code{INTEGER_CST} nodes. The value of the integer constant @code{e} is +represented in an array of HOST_WIDE_INT. There are enough elements +in the array to represent the value without taking extra elements for +redundant 0s or -1. The number of elements used to represent @code{e} +is available via @code{TREE_INT_CST_NUNITS}. Element @code{i} can be +extracted by using @code{TREE_INT_CST_ELT (e, i)}. +@code{TREE_INT_CST_LOW} is a shorthand for @code{TREE_INT_CST_ELT (e, 0)}. + +The functions @code{tree_fits_shwi_p} and @code{tree_fits_uhwi_p} +can be used to tell if the value is small enough to fit in a +signed HOST_WIDE_INT or an unsigned HOST_WIDE_INT respectively. +The value can then be extracted using @code{tree_to_shwi} and +@code{tree_to_uhwi}. + +@item REAL_CST + +FIXME: Talk about how to obtain representations of this constant, do +comparisons, and so forth. + +@item FIXED_CST + +These nodes represent fixed-point constants. The type of these constants +is obtained with @code{TREE_TYPE}. @code{TREE_FIXED_CST_PTR} points to +a @code{struct fixed_value}; @code{TREE_FIXED_CST} returns the structure +itself. @code{struct fixed_value} contains @code{data} with the size of two +@code{HOST_BITS_PER_WIDE_INT} and @code{mode} as the associated fixed-point +machine mode for @code{data}. + +@item COMPLEX_CST +These nodes are used to represent complex number constants, that is a +@code{__complex__} whose parts are constant nodes. The +@code{TREE_REALPART} and @code{TREE_IMAGPART} return the real and the +imaginary parts respectively. + +@item VECTOR_CST +These nodes are used to represent vector constants. Each vector +constant @var{v} is treated as a specific instance of an arbitrary-length +sequence that itself contains @samp{VECTOR_CST_NPATTERNS (@var{v})} +interleaved patterns. Each pattern has the form: + +@smallexample +@{ @var{base0}, @var{base1}, @var{base1} + @var{step}, @var{base1} + @var{step} * 2, @dots{} @} +@end smallexample + +The first three elements in each pattern are enough to determine the +values of the other elements. However, if all @var{step}s are zero, +only the first two elements are needed. If in addition each @var{base1} +is equal to the corresponding @var{base0}, only the first element in +each pattern is needed. The number of encoded elements per pattern +is given by @samp{VECTOR_CST_NELTS_PER_PATTERN (@var{v})}. + +For example, the constant: + +@smallexample +@{ 0, 1, 2, 6, 3, 8, 4, 10, 5, 12, 6, 14, 7, 16, 8, 18 @} +@end smallexample + +is interpreted as an interleaving of the sequences: + +@smallexample +@{ 0, 2, 3, 4, 5, 6, 7, 8 @} +@{ 1, 6, 8, 10, 12, 14, 16, 18 @} +@end smallexample + +where the sequences are represented by the following patterns: + +@smallexample +@var{base0} == 0, @var{base1} == 2, @var{step} == 1 +@var{base0} == 1, @var{base1} == 6, @var{step} == 2 +@end smallexample + +In this case: + +@smallexample +VECTOR_CST_NPATTERNS (@var{v}) == 2 +VECTOR_CST_NELTS_PER_PATTERN (@var{v}) == 3 +@end smallexample + +The vector is therefore encoded using the first 6 elements +(@samp{@{ 0, 1, 2, 6, 3, 8 @}}), with the remaining 10 elements +being implicit extensions of them. + +Sometimes this scheme can create two possible encodings of the same +vector. For example @{ 0, 1 @} could be seen as two patterns with +one element each or one pattern with two elements (@var{base0} and +@var{base1}). The canonical encoding is always the one with the +fewest patterns or (if both encodings have the same number of +petterns) the one with the fewest encoded elements. + +@samp{vector_cst_encoding_nelts (@var{v})} gives the total number of +encoded elements in @var{v}, which is 6 in the example above. +@code{VECTOR_CST_ENCODED_ELTS (@var{v})} gives a pointer to the elements +encoded in @var{v} and @code{VECTOR_CST_ENCODED_ELT (@var{v}, @var{i})} +accesses the value of encoded element @var{i}. + +@samp{VECTOR_CST_DUPLICATE_P (@var{v})} is true if @var{v} simply contains +repeated instances of @samp{VECTOR_CST_NPATTERNS (@var{v})} values. This is +a shorthand for testing @samp{VECTOR_CST_NELTS_PER_PATTERN (@var{v}) == 1}. + +@samp{VECTOR_CST_STEPPED_P (@var{v})} is true if at least one +pattern in @var{v} has a nonzero step. This is a shorthand for +testing @samp{VECTOR_CST_NELTS_PER_PATTERN (@var{v}) == 3}. + +The utility function @code{vector_cst_elt} gives the value of an +arbitrary index as a @code{tree}. @code{vector_cst_int_elt} gives +the same value as a @code{wide_int}. + +@item STRING_CST +These nodes represent string-constants. The @code{TREE_STRING_LENGTH} +returns the length of the string, as an @code{int}. The +@code{TREE_STRING_POINTER} is a @code{char*} containing the string +itself. The string may not be @code{NUL}-terminated, and it may contain +embedded @code{NUL} characters. Therefore, the +@code{TREE_STRING_LENGTH} includes the trailing @code{NUL} if it is +present. + +For wide string constants, the @code{TREE_STRING_LENGTH} is the number +of bytes in the string, and the @code{TREE_STRING_POINTER} +points to an array of the bytes of the string, as represented on the +target system (that is, as integers in the target endianness). Wide and +non-wide string constants are distinguished only by the @code{TREE_TYPE} +of the @code{STRING_CST}. + +FIXME: The formats of string constants are not well-defined when the +target system bytes are not the same width as host system bytes. + +@item POLY_INT_CST +These nodes represent invariants that depend on some target-specific +runtime parameters. They consist of @code{NUM_POLY_INT_COEFFS} +coefficients, with the first coefficient being the constant term and +the others being multipliers that are applied to the runtime parameters. + +@code{POLY_INT_CST_ELT (@var{x}, @var{i})} references coefficient number +@var{i} of @code{POLY_INT_CST} node @var{x}. Each coefficient is an +@code{INTEGER_CST}. + +@end table + +@node Storage References +@subsection References to storage +@tindex ADDR_EXPR +@tindex INDIRECT_REF +@tindex MEM_REF +@tindex ARRAY_REF +@tindex ARRAY_RANGE_REF +@tindex TARGET_MEM_REF +@tindex COMPONENT_REF + +@table @code +@item ARRAY_REF +These nodes represent array accesses. The first operand is the array; +the second is the index. To calculate the address of the memory +accessed, you must scale the index by the size of the type of the array +elements. The type of these expressions must be the type of a component of +the array. The third and fourth operands are used after gimplification +to represent the lower bound and component size but should not be used +directly; call @code{array_ref_low_bound} and @code{array_ref_element_size} +instead. + +@item ARRAY_RANGE_REF +These nodes represent access to a range (or ``slice'') of an array. The +operands are the same as that for @code{ARRAY_REF} and have the same +meanings. The type of these expressions must be an array whose component +type is the same as that of the first operand. The range of that array +type determines the amount of data these expressions access. + +@item COMPONENT_REF +These nodes represent non-static data member accesses. The first +operand is the object (rather than a pointer to it); the second operand +is the @code{FIELD_DECL} for the data member. The third operand represents +the byte offset of the field, but should not be used directly; call +@code{component_ref_field_offset} instead. + +@item ADDR_EXPR +These nodes are used to represent the address of an object. (These +expressions will always have pointer or reference type.) The operand may +be another expression, or it may be a declaration. + +As an extension, GCC allows users to take the address of a label. In +this case, the operand of the @code{ADDR_EXPR} will be a +@code{LABEL_DECL}. The type of such an expression is @code{void*}. + +If the object addressed is not an lvalue, a temporary is created, and +the address of the temporary is used. + +@item INDIRECT_REF +These nodes are used to represent the object pointed to by a pointer. +The operand is the pointer being dereferenced; it will always have +pointer or reference type. + +@item MEM_REF +These nodes are used to represent the object pointed to by a pointer +offset by a constant. +The first operand is the pointer being dereferenced; it will always have +pointer or reference type. The second operand is a pointer constant +serving as constant offset applied to the pointer being dereferenced +with its type specifying the type to be used for type-based alias analysis. +The type of the node specifies the alignment of the access. + +@item TARGET_MEM_REF +These nodes represent memory accesses whose address directly map to +an addressing mode of the target architecture. The first argument +is @code{TMR_BASE} and is a pointer to the object being accessed. +The second argument is @code{TMR_OFFSET} which is a pointer constant +with dual purpose serving both as constant offset and holder of +the type used for type-based alias analysis. The first two operands +have exactly the same semantics as @code{MEM_REF}. The third +and fourth operand are @code{TMR_INDEX} and @code{TMR_STEP} where +the former is an integer and the latter an integer constant. The +fifth and last operand is @code{TMR_INDEX2} which is an alternate +non-constant offset. Any of the third to last operands may be +@code{NULL} if the corresponding component does not appear in +the address, but @code{TMR_INDEX} and @code{TMR_STEP} shall be +always supplied in pair. The Address of the @code{TARGET_MEM_REF} +is determined in the following way. + +@smallexample +TMR_BASE + TMR_OFFSET + TMR_INDEX * TMR_STEP + TMR_INDEX2 +@end smallexample + +The type of the node specifies the alignment of the access. + +@end table + +@node Unary and Binary Expressions +@subsection Unary and Binary Expressions +@tindex NEGATE_EXPR +@tindex ABS_EXPR +@tindex ABSU_EXPR +@tindex BIT_NOT_EXPR +@tindex TRUTH_NOT_EXPR +@tindex PREDECREMENT_EXPR +@tindex PREINCREMENT_EXPR +@tindex POSTDECREMENT_EXPR +@tindex POSTINCREMENT_EXPR +@tindex FIX_TRUNC_EXPR +@tindex FLOAT_EXPR +@tindex COMPLEX_EXPR +@tindex CONJ_EXPR +@tindex REALPART_EXPR +@tindex IMAGPART_EXPR +@tindex NON_LVALUE_EXPR +@tindex NOP_EXPR +@tindex CONVERT_EXPR +@tindex FIXED_CONVERT_EXPR +@tindex THROW_EXPR +@tindex LSHIFT_EXPR +@tindex RSHIFT_EXPR +@tindex BIT_IOR_EXPR +@tindex BIT_XOR_EXPR +@tindex BIT_AND_EXPR +@tindex TRUTH_ANDIF_EXPR +@tindex TRUTH_ORIF_EXPR +@tindex TRUTH_AND_EXPR +@tindex TRUTH_OR_EXPR +@tindex TRUTH_XOR_EXPR +@tindex POINTER_PLUS_EXPR +@tindex POINTER_DIFF_EXPR +@tindex PLUS_EXPR +@tindex MINUS_EXPR +@tindex MULT_EXPR +@tindex WIDEN_MULT_EXPR +@tindex MULT_HIGHPART_EXPR +@tindex RDIV_EXPR +@tindex TRUNC_DIV_EXPR +@tindex FLOOR_DIV_EXPR +@tindex CEIL_DIV_EXPR +@tindex ROUND_DIV_EXPR +@tindex TRUNC_MOD_EXPR +@tindex FLOOR_MOD_EXPR +@tindex CEIL_MOD_EXPR +@tindex ROUND_MOD_EXPR +@tindex EXACT_DIV_EXPR +@tindex LT_EXPR +@tindex LE_EXPR +@tindex GT_EXPR +@tindex GE_EXPR +@tindex EQ_EXPR +@tindex NE_EXPR +@tindex ORDERED_EXPR +@tindex UNORDERED_EXPR +@tindex UNLT_EXPR +@tindex UNLE_EXPR +@tindex UNGT_EXPR +@tindex UNGE_EXPR +@tindex UNEQ_EXPR +@tindex LTGT_EXPR +@tindex MODIFY_EXPR +@tindex INIT_EXPR +@tindex COMPOUND_EXPR +@tindex COND_EXPR +@tindex CALL_EXPR +@tindex STMT_EXPR +@tindex BIND_EXPR +@tindex LOOP_EXPR +@tindex EXIT_EXPR +@tindex CLEANUP_POINT_EXPR +@tindex CONSTRUCTOR +@tindex COMPOUND_LITERAL_EXPR +@tindex SAVE_EXPR +@tindex TARGET_EXPR +@tindex VA_ARG_EXPR +@tindex ANNOTATE_EXPR + +@table @code +@item NEGATE_EXPR +These nodes represent unary negation of the single operand, for both +integer and floating-point types. The type of negation can be +determined by looking at the type of the expression. + +The behavior of this operation on signed arithmetic overflow is +controlled by the @code{flag_wrapv} and @code{flag_trapv} variables. + +@item ABS_EXPR +These nodes represent the absolute value of the single operand, for +both integer and floating-point types. This is typically used to +implement the @code{abs}, @code{labs} and @code{llabs} builtins for +integer types, and the @code{fabs}, @code{fabsf} and @code{fabsl} +builtins for floating point types. The type of abs operation can +be determined by looking at the type of the expression. + +This node is not used for complex types. To represent the modulus +or complex abs of a complex value, use the @code{BUILT_IN_CABS}, +@code{BUILT_IN_CABSF} or @code{BUILT_IN_CABSL} builtins, as used +to implement the C99 @code{cabs}, @code{cabsf} and @code{cabsl} +built-in functions. + +@item ABSU_EXPR +These nodes represent the absolute value of the single operand in +equivalent unsigned type such that @code{ABSU_EXPR} of @code{TYPE_MIN} +is well defined. + +@item BIT_NOT_EXPR +These nodes represent bitwise complement, and will always have integral +type. The only operand is the value to be complemented. + +@item TRUTH_NOT_EXPR +These nodes represent logical negation, and will always have integral +(or boolean) type. The operand is the value being negated. The type +of the operand and that of the result are always of @code{BOOLEAN_TYPE} +or @code{INTEGER_TYPE}. + +@item PREDECREMENT_EXPR +@itemx PREINCREMENT_EXPR +@itemx POSTDECREMENT_EXPR +@itemx POSTINCREMENT_EXPR +These nodes represent increment and decrement expressions. The value of +the single operand is computed, and the operand incremented or +decremented. In the case of @code{PREDECREMENT_EXPR} and +@code{PREINCREMENT_EXPR}, the value of the expression is the value +resulting after the increment or decrement; in the case of +@code{POSTDECREMENT_EXPR} and @code{POSTINCREMENT_EXPR} is the value +before the increment or decrement occurs. The type of the operand, like +that of the result, will be either integral, boolean, or floating-point. + +@item FIX_TRUNC_EXPR +These nodes represent conversion of a floating-point value to an +integer. The single operand will have a floating-point type, while +the complete expression will have an integral (or boolean) type. The +operand is rounded towards zero. + +@item FLOAT_EXPR +These nodes represent conversion of an integral (or boolean) value to a +floating-point value. The single operand will have integral type, while +the complete expression will have a floating-point type. + +FIXME: How is the operand supposed to be rounded? Is this dependent on +@option{-mieee}? + +@item COMPLEX_EXPR +These nodes are used to represent complex numbers constructed from two +expressions of the same (integer or real) type. The first operand is the +real part and the second operand is the imaginary part. + +@item CONJ_EXPR +These nodes represent the conjugate of their operand. + +@item REALPART_EXPR +@itemx IMAGPART_EXPR +These nodes represent respectively the real and the imaginary parts +of complex numbers (their sole argument). + +@item NON_LVALUE_EXPR +These nodes indicate that their one and only operand is not an lvalue. +A back end can treat these identically to the single operand. + +@item NOP_EXPR +These nodes are used to represent conversions that do not require any +code-generation. For example, conversion of a @code{char*} to an +@code{int*} does not require any code be generated; such a conversion is +represented by a @code{NOP_EXPR}. The single operand is the expression +to be converted. The conversion from a pointer to a reference is also +represented with a @code{NOP_EXPR}. + +@item CONVERT_EXPR +These nodes are similar to @code{NOP_EXPR}s, but are used in those +situations where code may need to be generated. For example, if an +@code{int*} is converted to an @code{int} code may need to be generated +on some platforms. These nodes are never used for C++-specific +conversions, like conversions between pointers to different classes in +an inheritance hierarchy. Any adjustments that need to be made in such +cases are always indicated explicitly. Similarly, a user-defined +conversion is never represented by a @code{CONVERT_EXPR}; instead, the +function calls are made explicit. + +@item FIXED_CONVERT_EXPR +These nodes are used to represent conversions that involve fixed-point +values. For example, from a fixed-point value to another fixed-point value, +from an integer to a fixed-point value, from a fixed-point value to an +integer, from a floating-point value to a fixed-point value, or from +a fixed-point value to a floating-point value. + +@item LSHIFT_EXPR +@itemx RSHIFT_EXPR +These nodes represent left and right shifts, respectively. The first +operand is the value to shift; it will always be of integral type. The +second operand is an expression for the number of bits by which to +shift. Right shift should be treated as arithmetic, i.e., the +high-order bits should be zero-filled when the expression has unsigned +type and filled with the sign bit when the expression has signed type. +Note that the result is undefined if the second operand is larger +than or equal to the first operand's type size. Unlike most nodes, these +can have a vector as first operand and a scalar as second operand. + + +@item BIT_IOR_EXPR +@itemx BIT_XOR_EXPR +@itemx BIT_AND_EXPR +These nodes represent bitwise inclusive or, bitwise exclusive or, and +bitwise and, respectively. Both operands will always have integral +type. + +@item TRUTH_ANDIF_EXPR +@itemx TRUTH_ORIF_EXPR +These nodes represent logical ``and'' and logical ``or'', respectively. +These operators are not strict; i.e., the second operand is evaluated +only if the value of the expression is not determined by evaluation of +the first operand. The type of the operands and that of the result are +always of @code{BOOLEAN_TYPE} or @code{INTEGER_TYPE}. + +@item TRUTH_AND_EXPR +@itemx TRUTH_OR_EXPR +@itemx TRUTH_XOR_EXPR +These nodes represent logical and, logical or, and logical exclusive or. +They are strict; both arguments are always evaluated. There are no +corresponding operators in C or C++, but the front end will sometimes +generate these expressions anyhow, if it can tell that strictness does +not matter. The type of the operands and that of the result are +always of @code{BOOLEAN_TYPE} or @code{INTEGER_TYPE}. + +@item POINTER_PLUS_EXPR +This node represents pointer arithmetic. The first operand is always +a pointer/reference type. The second operand is always an unsigned +integer type compatible with sizetype. This and POINTER_DIFF_EXPR are +the only binary arithmetic operators that can operate on pointer types. + +@item POINTER_DIFF_EXPR +This node represents pointer subtraction. The two operands always +have pointer/reference type. It returns a signed integer of the same +precision as the pointers. The behavior is undefined if the difference +of the two pointers, seen as infinite precision non-negative integers, +does not fit in the result type. The result does not depend on the +pointer type, it is not divided by the size of the pointed-to type. + +@item PLUS_EXPR +@itemx MINUS_EXPR +@itemx MULT_EXPR +These nodes represent various binary arithmetic operations. +Respectively, these operations are addition, subtraction (of the second +operand from the first) and multiplication. Their operands may have +either integral or floating type, but there will never be case in which +one operand is of floating type and the other is of integral type. + +The behavior of these operations on signed arithmetic overflow is +controlled by the @code{flag_wrapv} and @code{flag_trapv} variables. + +@item WIDEN_MULT_EXPR +This node represents a widening multiplication. The operands have +integral types with same @var{b} bits of precision, producing an +integral type result with at least @math{2@var{b}} bits of precision. +The behaviour is equivalent to extending both operands, possibly of +different signedness, to the result type, then multiplying them. + +@item MULT_HIGHPART_EXPR +This node represents the ``high-part'' of a widening multiplication. +For an integral type with @var{b} bits of precision, the result is +the most significant @var{b} bits of the full @math{2@var{b}} product. +Both operands must have the same precision and same signedness. + +@item RDIV_EXPR +This node represents a floating point division operation. + +@item TRUNC_DIV_EXPR +@itemx FLOOR_DIV_EXPR +@itemx CEIL_DIV_EXPR +@itemx ROUND_DIV_EXPR +These nodes represent integer division operations that return an integer +result. @code{TRUNC_DIV_EXPR} rounds towards zero, @code{FLOOR_DIV_EXPR} +rounds towards negative infinity, @code{CEIL_DIV_EXPR} rounds towards +positive infinity and @code{ROUND_DIV_EXPR} rounds to the closest integer. +Integer division in C and C++ is truncating, i.e.@: @code{TRUNC_DIV_EXPR}. + +The behavior of these operations on signed arithmetic overflow, when +dividing the minimum signed integer by minus one, is controlled by the +@code{flag_wrapv} and @code{flag_trapv} variables. + +@item TRUNC_MOD_EXPR +@itemx FLOOR_MOD_EXPR +@itemx CEIL_MOD_EXPR +@itemx ROUND_MOD_EXPR +These nodes represent the integer remainder or modulus operation. +The integer modulus of two operands @code{a} and @code{b} is +defined as @code{a - (a/b)*b} where the division calculated using +the corresponding division operator. Hence for @code{TRUNC_MOD_EXPR} +this definition assumes division using truncation towards zero, i.e.@: +@code{TRUNC_DIV_EXPR}. Integer remainder in C and C++ uses truncating +division, i.e.@: @code{TRUNC_MOD_EXPR}. + +@item EXACT_DIV_EXPR +The @code{EXACT_DIV_EXPR} code is used to represent integer divisions where +the numerator is known to be an exact multiple of the denominator. This +allows the backend to choose between the faster of @code{TRUNC_DIV_EXPR}, +@code{CEIL_DIV_EXPR} and @code{FLOOR_DIV_EXPR} for the current target. + +@item LT_EXPR +@itemx LE_EXPR +@itemx GT_EXPR +@itemx GE_EXPR +@itemx LTGT_EXPR +@itemx EQ_EXPR +@itemx NE_EXPR +These nodes represent the less than, less than or equal to, greater than, +greater than or equal to, less or greater than, equal, and not equal +comparison operators. The first and second operands will either be both +of integral type, both of floating type or both of vector type, except for +LTGT_EXPR where they will only be both of floating type. The result type +of these expressions will always be of integral, boolean or signed integral +vector type. These operations return the result type's zero value for false, +the result type's one value for true, and a vector whose elements are zero +(false) or minus one (true) for vectors. + +For floating point comparisons, if we honor IEEE NaNs and either operand +is NaN, then @code{NE_EXPR} always returns true and the remaining operators +always return false. On some targets, comparisons against an IEEE NaN, +other than equality and inequality, may generate a floating-point exception. + +@item ORDERED_EXPR +@itemx UNORDERED_EXPR +These nodes represent non-trapping ordered and unordered comparison +operators. These operations take two floating point operands and +determine whether they are ordered or unordered relative to each other. +If either operand is an IEEE NaN, their comparison is defined to be +unordered, otherwise the comparison is defined to be ordered. The +result type of these expressions will always be of integral or boolean +type. These operations return the result type's zero value for false, +and the result type's one value for true. + +@item UNLT_EXPR +@itemx UNLE_EXPR +@itemx UNGT_EXPR +@itemx UNGE_EXPR +@itemx UNEQ_EXPR +These nodes represent the unordered comparison operators. +These operations take two floating point operands and determine whether +the operands are unordered or are less than, less than or equal to, +greater than, greater than or equal to, or equal respectively. For +example, @code{UNLT_EXPR} returns true if either operand is an IEEE +NaN or the first operand is less than the second. All these operations +are guaranteed not to generate a floating point exception. The result +type of these expressions will always be of integral or boolean type. +These operations return the result type's zero value for false, +and the result type's one value for true. + +@item MODIFY_EXPR +These nodes represent assignment. The left-hand side is the first +operand; the right-hand side is the second operand. The left-hand side +will be a @code{VAR_DECL}, @code{INDIRECT_REF}, @code{COMPONENT_REF}, or +other lvalue. + +These nodes are used to represent not only assignment with @samp{=} but +also compound assignments (like @samp{+=}), by reduction to @samp{=} +assignment. In other words, the representation for @samp{i += 3} looks +just like that for @samp{i = i + 3}. + +@item INIT_EXPR +These nodes are just like @code{MODIFY_EXPR}, but are used only when a +variable is initialized, rather than assigned to subsequently. This +means that we can assume that the target of the initialization is not +used in computing its own value; any reference to the lhs in computing +the rhs is undefined. + +@item COMPOUND_EXPR +These nodes represent comma-expressions. The first operand is an +expression whose value is computed and thrown away prior to the +evaluation of the second operand. The value of the entire expression is +the value of the second operand. + +@item COND_EXPR +These nodes represent @code{?:} expressions. The first operand +is of boolean or integral type. If it evaluates to a nonzero value, +the second operand should be evaluated, and returned as the value of the +expression. Otherwise, the third operand is evaluated, and returned as +the value of the expression. + +The second operand must have the same type as the entire expression, +unless it unconditionally throws an exception or calls a noreturn +function, in which case it should have void type. The same constraints +apply to the third operand. This allows array bounds checks to be +represented conveniently as @code{(i >= 0 && i < 10) ? i : abort()}. + +As a GNU extension, the C language front-ends allow the second +operand of the @code{?:} operator may be omitted in the source. +For example, @code{x ? : 3} is equivalent to @code{x ? x : 3}, +assuming that @code{x} is an expression without side effects. +In the tree representation, however, the second operand is always +present, possibly protected by @code{SAVE_EXPR} if the first +argument does cause side effects. + +@item CALL_EXPR +These nodes are used to represent calls to functions, including +non-static member functions. @code{CALL_EXPR}s are implemented as +expression nodes with a variable number of operands. Rather than using +@code{TREE_OPERAND} to extract them, it is preferable to use the +specialized accessor macros and functions that operate specifically on +@code{CALL_EXPR} nodes. + +@code{CALL_EXPR_FN} returns a pointer to the +function to call; it is always an expression whose type is a +@code{POINTER_TYPE}. + +The number of arguments to the call is returned by @code{call_expr_nargs}, +while the arguments themselves can be accessed with the @code{CALL_EXPR_ARG} +macro. The arguments are zero-indexed and numbered left-to-right. +You can iterate over the arguments using @code{FOR_EACH_CALL_EXPR_ARG}, as in: + +@smallexample +tree call, arg; +call_expr_arg_iterator iter; +FOR_EACH_CALL_EXPR_ARG (arg, iter, call) + /* arg is bound to successive arguments of call. */ + @dots{}; +@end smallexample + +For non-static +member functions, there will be an operand corresponding to the +@code{this} pointer. There will always be expressions corresponding to +all of the arguments, even if the function is declared with default +arguments and some arguments are not explicitly provided at the call +sites. + +@code{CALL_EXPR}s also have a @code{CALL_EXPR_STATIC_CHAIN} operand that +is used to implement nested functions. This operand is otherwise null. + +@item CLEANUP_POINT_EXPR +These nodes represent full-expressions. The single operand is an +expression to evaluate. Any destructor calls engendered by the creation +of temporaries during the evaluation of that expression should be +performed immediately after the expression is evaluated. + +@item CONSTRUCTOR +These nodes represent the brace-enclosed initializers for a structure or an +array. They contain a sequence of component values made out of a vector of +constructor_elt, which is a (@code{INDEX}, @code{VALUE}) pair. + +If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is a @code{RECORD_TYPE}, +@code{UNION_TYPE} or @code{QUAL_UNION_TYPE} then the @code{INDEX} of each +node in the sequence will be a @code{FIELD_DECL} and the @code{VALUE} will +be the expression used to initialize that field. + +If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is an @code{ARRAY_TYPE}, +then the @code{INDEX} of each node in the sequence will be an +@code{INTEGER_CST} or a @code{RANGE_EXPR} of two @code{INTEGER_CST}s. +A single @code{INTEGER_CST} indicates which element of the array is being +assigned to. A @code{RANGE_EXPR} indicates an inclusive range of elements +to initialize. In both cases the @code{VALUE} is the corresponding +initializer. It is re-evaluated for each element of a +@code{RANGE_EXPR}. If the @code{INDEX} is @code{NULL_TREE}, then +the initializer is for the next available array element. + +In the front end, you should not depend on the fields appearing in any +particular order. However, in the middle end, fields must appear in +declaration order. You should not assume that all fields will be +represented. Unrepresented fields will be cleared (zeroed), unless the +CONSTRUCTOR_NO_CLEARING flag is set, in which case their value becomes +undefined. + +@item COMPOUND_LITERAL_EXPR +@findex COMPOUND_LITERAL_EXPR_DECL_EXPR +@findex COMPOUND_LITERAL_EXPR_DECL +These nodes represent ISO C99 compound literals. The +@code{COMPOUND_LITERAL_EXPR_DECL_EXPR} is a @code{DECL_EXPR} +containing an anonymous @code{VAR_DECL} for +the unnamed object represented by the compound literal; the +@code{DECL_INITIAL} of that @code{VAR_DECL} is a @code{CONSTRUCTOR} +representing the brace-enclosed list of initializers in the compound +literal. That anonymous @code{VAR_DECL} can also be accessed directly +by the @code{COMPOUND_LITERAL_EXPR_DECL} macro. + +@item SAVE_EXPR + +A @code{SAVE_EXPR} represents an expression (possibly involving +side effects) that is used more than once. The side effects should +occur only the first time the expression is evaluated. Subsequent uses +should just reuse the computed value. The first operand to the +@code{SAVE_EXPR} is the expression to evaluate. The side effects should +be executed where the @code{SAVE_EXPR} is first encountered in a +depth-first preorder traversal of the expression tree. + +@item TARGET_EXPR +A @code{TARGET_EXPR} represents a temporary object. The first operand +is a @code{VAR_DECL} for the temporary variable. The second operand is +the initializer for the temporary. The initializer is evaluated and, +if non-void, copied (bitwise) into the temporary. If the initializer +is void, that means that it will perform the initialization itself. + +Often, a @code{TARGET_EXPR} occurs on the right-hand side of an +assignment, or as the second operand to a comma-expression which is +itself the right-hand side of an assignment, etc. In this case, we say +that the @code{TARGET_EXPR} is ``normal''; otherwise, we say it is +``orphaned''. For a normal @code{TARGET_EXPR} the temporary variable +should be treated as an alias for the left-hand side of the assignment, +rather than as a new temporary variable. + +The third operand to the @code{TARGET_EXPR}, if present, is a +cleanup-expression (i.e., destructor call) for the temporary. If this +expression is orphaned, then this expression must be executed when the +statement containing this expression is complete. These cleanups must +always be executed in the order opposite to that in which they were +encountered. Note that if a temporary is created on one branch of a +conditional operator (i.e., in the second or third operand to a +@code{COND_EXPR}), the cleanup must be run only if that branch is +actually executed. + +@item VA_ARG_EXPR +This node is used to implement support for the C/C++ variable argument-list +mechanism. It represents expressions like @code{va_arg (ap, type)}. +Its @code{TREE_TYPE} yields the tree representation for @code{type} and +its sole argument yields the representation for @code{ap}. + +@item ANNOTATE_EXPR +This node is used to attach markers to an expression. The first operand +is the annotated expression, the second is an @code{INTEGER_CST} with +a value from @code{enum annot_expr_kind}, the third is an @code{INTEGER_CST}. +@end table + + +@node Vectors +@subsection Vectors +@tindex VEC_DUPLICATE_EXPR +@tindex VEC_SERIES_EXPR +@tindex VEC_LSHIFT_EXPR +@tindex VEC_RSHIFT_EXPR +@tindex VEC_WIDEN_MULT_HI_EXPR +@tindex VEC_WIDEN_MULT_LO_EXPR +@tindex VEC_WIDEN_PLUS_HI_EXPR +@tindex VEC_WIDEN_PLUS_LO_EXPR +@tindex VEC_WIDEN_MINUS_HI_EXPR +@tindex VEC_WIDEN_MINUS_LO_EXPR +@tindex VEC_UNPACK_HI_EXPR +@tindex VEC_UNPACK_LO_EXPR +@tindex VEC_UNPACK_FLOAT_HI_EXPR +@tindex VEC_UNPACK_FLOAT_LO_EXPR +@tindex VEC_UNPACK_FIX_TRUNC_HI_EXPR +@tindex VEC_UNPACK_FIX_TRUNC_LO_EXPR +@tindex VEC_PACK_TRUNC_EXPR +@tindex VEC_PACK_SAT_EXPR +@tindex VEC_PACK_FIX_TRUNC_EXPR +@tindex VEC_PACK_FLOAT_EXPR +@tindex VEC_COND_EXPR +@tindex SAD_EXPR + +@table @code +@item VEC_DUPLICATE_EXPR +This node has a single operand and represents a vector in which every +element is equal to that operand. + +@item VEC_SERIES_EXPR +This node represents a vector formed from a scalar base and step, +given as the first and second operands respectively. Element @var{i} +of the result is equal to @samp{@var{base} + @var{i}*@var{step}}. + +This node is restricted to integral types, in order to avoid +specifying the rounding behavior for floating-point types. + +@item VEC_LSHIFT_EXPR +@itemx VEC_RSHIFT_EXPR +These nodes represent whole vector left and right shifts, respectively. +The first operand is the vector to shift; it will always be of vector type. +The second operand is an expression for the number of bits by which to +shift. Note that the result is undefined if the second operand is larger +than or equal to the first operand's type size. + +@item VEC_WIDEN_MULT_HI_EXPR +@itemx VEC_WIDEN_MULT_LO_EXPR +These nodes represent widening vector multiplication of the high and low +parts of the two input vectors, respectively. Their operands are vectors +that contain the same number of elements (@code{N}) of the same integral type. +The result is a vector that contains half as many elements, of an integral type +whose size is twice as wide. In the case of @code{VEC_WIDEN_MULT_HI_EXPR} the +high @code{N/2} elements of the two vector are multiplied to produce the +vector of @code{N/2} products. In the case of @code{VEC_WIDEN_MULT_LO_EXPR} the +low @code{N/2} elements of the two vector are multiplied to produce the +vector of @code{N/2} products. + +@item VEC_WIDEN_PLUS_HI_EXPR +@itemx VEC_WIDEN_PLUS_LO_EXPR +These nodes represent widening vector addition of the high and low parts of +the two input vectors, respectively. Their operands are vectors that contain +the same number of elements (@code{N}) of the same integral type. The result +is a vector that contains half as many elements, of an integral type whose size +is twice as wide. In the case of @code{VEC_WIDEN_PLUS_HI_EXPR} the high +@code{N/2} elements of the two vectors are added to produce the vector of +@code{N/2} products. In the case of @code{VEC_WIDEN_PLUS_LO_EXPR} the low +@code{N/2} elements of the two vectors are added to produce the vector of +@code{N/2} products. + +@item VEC_WIDEN_MINUS_HI_EXPR +@itemx VEC_WIDEN_MINUS_LO_EXPR +These nodes represent widening vector subtraction of the high and low parts of +the two input vectors, respectively. Their operands are vectors that contain +the same number of elements (@code{N}) of the same integral type. The high/low +elements of the second vector are subtracted from the high/low elements of the +first. The result is a vector that contains half as many elements, of an +integral type whose size is twice as wide. In the case of +@code{VEC_WIDEN_MINUS_HI_EXPR} the high @code{N/2} elements of the second +vector are subtracted from the high @code{N/2} of the first to produce the +vector of @code{N/2} products. In the case of +@code{VEC_WIDEN_MINUS_LO_EXPR} the low @code{N/2} elements of the second +vector are subtracted from the low @code{N/2} of the first to produce the +vector of @code{N/2} products. + +@item VEC_UNPACK_HI_EXPR +@itemx VEC_UNPACK_LO_EXPR +These nodes represent unpacking of the high and low parts of the input vector, +respectively. The single operand is a vector that contains @code{N} elements +of the same integral or floating point type. The result is a vector +that contains half as many elements, of an integral or floating point type +whose size is twice as wide. In the case of @code{VEC_UNPACK_HI_EXPR} the +high @code{N/2} elements of the vector are extracted and widened (promoted). +In the case of @code{VEC_UNPACK_LO_EXPR} the low @code{N/2} elements of the +vector are extracted and widened (promoted). + +@item VEC_UNPACK_FLOAT_HI_EXPR +@itemx VEC_UNPACK_FLOAT_LO_EXPR +These nodes represent unpacking of the high and low parts of the input vector, +where the values are converted from fixed point to floating point. The +single operand is a vector that contains @code{N} elements of the same +integral type. The result is a vector that contains half as many elements +of a floating point type whose size is twice as wide. In the case of +@code{VEC_UNPACK_FLOAT_HI_EXPR} the high @code{N/2} elements of the vector are +extracted, converted and widened. In the case of @code{VEC_UNPACK_FLOAT_LO_EXPR} +the low @code{N/2} elements of the vector are extracted, converted and widened. + +@item VEC_UNPACK_FIX_TRUNC_HI_EXPR +@itemx VEC_UNPACK_FIX_TRUNC_LO_EXPR +These nodes represent unpacking of the high and low parts of the input vector, +where the values are truncated from floating point to fixed point. The +single operand is a vector that contains @code{N} elements of the same +floating point type. The result is a vector that contains half as many +elements of an integral type whose size is twice as wide. In the case of +@code{VEC_UNPACK_FIX_TRUNC_HI_EXPR} the high @code{N/2} elements of the +vector are extracted and converted with truncation. In the case of +@code{VEC_UNPACK_FIX_TRUNC_LO_EXPR} the low @code{N/2} elements of the +vector are extracted and converted with truncation. + +@item VEC_PACK_TRUNC_EXPR +This node represents packing of truncated elements of the two input vectors +into the output vector. Input operands are vectors that contain the same +number of elements of the same integral or floating point type. The result +is a vector that contains twice as many elements of an integral or floating +point type whose size is half as wide. The elements of the two vectors are +demoted and merged (concatenated) to form the output vector. + +@item VEC_PACK_SAT_EXPR +This node represents packing of elements of the two input vectors into the +output vector using saturation. Input operands are vectors that contain +the same number of elements of the same integral type. The result is a +vector that contains twice as many elements of an integral type whose size +is half as wide. The elements of the two vectors are demoted and merged +(concatenated) to form the output vector. + +@item VEC_PACK_FIX_TRUNC_EXPR +This node represents packing of elements of the two input vectors into the +output vector, where the values are converted from floating point +to fixed point. Input operands are vectors that contain the same number +of elements of a floating point type. The result is a vector that contains +twice as many elements of an integral type whose size is half as wide. The +elements of the two vectors are merged (concatenated) to form the output +vector. + +@item VEC_PACK_FLOAT_EXPR +This node represents packing of elements of the two input vectors into the +output vector, where the values are converted from fixed point to floating +point. Input operands are vectors that contain the same number of elements +of an integral type. The result is a vector that contains twice as many +elements of floating point type whose size is half as wide. The elements of +the two vectors are merged (concatenated) to form the output vector. + +@item VEC_COND_EXPR +These nodes represent @code{?:} expressions. The three operands must be +vectors of the same size and number of elements. The second and third +operands must have the same type as the entire expression. The first +operand is of signed integral vector type. If an element of the first +operand evaluates to a zero value, the corresponding element of the +result is taken from the third operand. If it evaluates to a minus one +value, it is taken from the second operand. It should never evaluate to +any other value currently, but optimizations should not rely on that +property. In contrast with a @code{COND_EXPR}, all operands are always +evaluated. + +@item SAD_EXPR +This node represents the Sum of Absolute Differences operation. The three +operands must be vectors of integral types. The first and second operand +must have the same type. The size of the vector element of the third +operand must be at lease twice of the size of the vector element of the +first and second one. The SAD is calculated between the first and second +operands, added to the third operand, and returned. + +@end table + + +@c --------------------------------------------------------------------- +@c Statements +@c --------------------------------------------------------------------- + +@node Statements +@section Statements +@cindex Statements + +Most statements in GIMPLE are assignment statements, represented by +@code{GIMPLE_ASSIGN}. No other C expressions can appear at statement level; +a reference to a volatile object is converted into a +@code{GIMPLE_ASSIGN}. + +There are also several varieties of complex statements. + +@menu +* Basic Statements:: +* Blocks:: +* Statement Sequences:: +* Empty Statements:: +* Jumps:: +* Cleanups:: +* OpenMP:: +* OpenACC:: +@end menu + +@node Basic Statements +@subsection Basic Statements +@cindex Basic Statements + +@table @code +@item ASM_EXPR + +Used to represent an inline assembly statement. For an inline assembly +statement like: +@smallexample +asm ("mov x, y"); +@end smallexample +The @code{ASM_STRING} macro will return a @code{STRING_CST} node for +@code{"mov x, y"}. If the original statement made use of the +extended-assembly syntax, then @code{ASM_OUTPUTS}, +@code{ASM_INPUTS}, and @code{ASM_CLOBBERS} will be the outputs, inputs, +and clobbers for the statement, represented as @code{STRING_CST} nodes. +The extended-assembly syntax looks like: +@smallexample +asm ("fsinx %1,%0" : "=f" (result) : "f" (angle)); +@end smallexample +The first string is the @code{ASM_STRING}, containing the instruction +template. The next two strings are the output and inputs, respectively; +this statement has no clobbers. As this example indicates, ``plain'' +assembly statements are merely a special case of extended assembly +statements; they have no cv-qualifiers, outputs, inputs, or clobbers. +All of the strings will be @code{NUL}-terminated, and will contain no +embedded @code{NUL}-characters. + +If the assembly statement is declared @code{volatile}, or if the +statement was not an extended assembly statement, and is therefore +implicitly volatile, then the predicate @code{ASM_VOLATILE_P} will hold +of the @code{ASM_EXPR}. + +@item DECL_EXPR + +Used to represent a local declaration. The @code{DECL_EXPR_DECL} macro +can be used to obtain the entity declared. This declaration may be a +@code{LABEL_DECL}, indicating that the label declared is a local label. +(As an extension, GCC allows the declaration of labels with scope.) In +C, this declaration may be a @code{FUNCTION_DECL}, indicating the +use of the GCC nested function extension. For more information, +@pxref{Functions}. + +@item LABEL_EXPR + +Used to represent a label. The @code{LABEL_DECL} declared by this +statement can be obtained with the @code{LABEL_EXPR_LABEL} macro. The +@code{IDENTIFIER_NODE} giving the name of the label can be obtained from +the @code{LABEL_DECL} with @code{DECL_NAME}. + +@item GOTO_EXPR + +Used to represent a @code{goto} statement. The @code{GOTO_DESTINATION} will +usually be a @code{LABEL_DECL}. However, if the ``computed goto'' extension +has been used, the @code{GOTO_DESTINATION} will be an arbitrary expression +indicating the destination. This expression will always have pointer type. + +@item RETURN_EXPR + +Used to represent a @code{return} statement. Operand 0 represents the +value to return. It should either be the @code{RESULT_DECL} for the +containing function, or a @code{MODIFY_EXPR} or @code{INIT_EXPR} +setting the function's @code{RESULT_DECL}. It will be +@code{NULL_TREE} if the statement was just +@smallexample +return; +@end smallexample + +@item LOOP_EXPR +These nodes represent ``infinite'' loops. The @code{LOOP_EXPR_BODY} +represents the body of the loop. It should be executed forever, unless +an @code{EXIT_EXPR} is encountered. + +@item EXIT_EXPR +These nodes represent conditional exits from the nearest enclosing +@code{LOOP_EXPR}. The single operand is the condition; if it is +nonzero, then the loop should be exited. An @code{EXIT_EXPR} will only +appear within a @code{LOOP_EXPR}. + +@item SWITCH_EXPR + +Used to represent a @code{switch} statement. The @code{SWITCH_COND} +is the expression on which the switch is occurring. The +@code{SWITCH_BODY} is the body of the switch statement. +@code{SWITCH_ALL_CASES_P} is true if the switch includes a default +label or the case label ranges cover all possible values of the +condition expression. + +Note that @code{TREE_TYPE} for a @code{SWITCH_EXPR} represents the +original type of switch expression as given in the source, before any +compiler conversions, instead of the type of the switch expression +itself (which is not meaningful). + +@item CASE_LABEL_EXPR + +Use to represent a @code{case} label, range of @code{case} labels, or a +@code{default} label. If @code{CASE_LOW} is @code{NULL_TREE}, then this is a +@code{default} label. Otherwise, if @code{CASE_HIGH} is @code{NULL_TREE}, then +this is an ordinary @code{case} label. In this case, @code{CASE_LOW} is +an expression giving the value of the label. Both @code{CASE_LOW} and +@code{CASE_HIGH} are @code{INTEGER_CST} nodes. These values will have +the same type as the condition expression in the switch statement. + +Otherwise, if both @code{CASE_LOW} and @code{CASE_HIGH} are defined, the +statement is a range of case labels. Such statements originate with the +extension that allows users to write things of the form: +@smallexample +case 2 ... 5: +@end smallexample +The first value will be @code{CASE_LOW}, while the second will be +@code{CASE_HIGH}. + +@item DEBUG_BEGIN_STMT + +Marks the beginning of a source statement, for purposes of debug +information generation. + +@end table + + +@node Blocks +@subsection Blocks +@cindex Blocks + +Block scopes and the variables they declare in GENERIC are +expressed using the @code{BIND_EXPR} code, which in previous +versions of GCC was primarily used for the C statement-expression +extension. + +Variables in a block are collected into @code{BIND_EXPR_VARS} in +declaration order through their @code{TREE_CHAIN} field. Any runtime +initialization is moved out of @code{DECL_INITIAL} and into a +statement in the controlled block. When gimplifying from C or C++, +this initialization replaces the @code{DECL_STMT}. These variables +will never require cleanups. The scope of these variables is just the +body + +Variable-length arrays (VLAs) complicate this process, as their size +often refers to variables initialized earlier in the block and their +initialization involves an explicit stack allocation. To handle this, +we add an indirection and replace them with a pointer to stack space +allocated by means of @code{alloca}. In most cases, we also arrange +for this space to be reclaimed when the enclosing @code{BIND_EXPR} is +exited, the exception to this being when there is an explicit call to +@code{alloca} in the source code, in which case the stack is left +depressed on exit of the @code{BIND_EXPR}. + +A C++ program will usually contain more @code{BIND_EXPR}s than +there are syntactic blocks in the source code, since several C++ +constructs have implicit scopes associated with them. On the +other hand, although the C++ front end uses pseudo-scopes to +handle cleanups for objects with destructors, these don't +translate into the GIMPLE form; multiple declarations at the same +level use the same @code{BIND_EXPR}. + +@node Statement Sequences +@subsection Statement Sequences +@cindex Statement Sequences + +Multiple statements at the same nesting level are collected into +a @code{STATEMENT_LIST}. Statement lists are modified and +traversed using the interface in @samp{tree-iterator.h}. + +@node Empty Statements +@subsection Empty Statements +@cindex Empty Statements + +Whenever possible, statements with no effect are discarded. But +if they are nested within another construct which cannot be +discarded for some reason, they are instead replaced with an +empty statement, generated by @code{build_empty_stmt}. +Initially, all empty statements were shared, after the pattern of +the Java front end, but this caused a lot of trouble in practice. + +An empty statement is represented as @code{(void)0}. + +@node Jumps +@subsection Jumps +@cindex Jumps + +Other jumps are expressed by either @code{GOTO_EXPR} or +@code{RETURN_EXPR}. + +The operand of a @code{GOTO_EXPR} must be either a label or a +variable containing the address to jump to. + +The operand of a @code{RETURN_EXPR} is either @code{NULL_TREE}, +@code{RESULT_DECL}, or a @code{MODIFY_EXPR} which sets the return +value. It would be nice to move the @code{MODIFY_EXPR} into a +separate statement, but the special return semantics in +@code{expand_return} make that difficult. It may still happen in +the future, perhaps by moving most of that logic into +@code{expand_assignment}. + +@node Cleanups +@subsection Cleanups +@cindex Cleanups + +Destructors for local C++ objects and similar dynamic cleanups are +represented in GIMPLE by a @code{TRY_FINALLY_EXPR}. +@code{TRY_FINALLY_EXPR} has two operands, both of which are a sequence +of statements to execute. The first sequence is executed. When it +completes the second sequence is executed. + +The first sequence may complete in the following ways: + +@enumerate + +@item Execute the last statement in the sequence and fall off the +end. + +@item Execute a goto statement (@code{GOTO_EXPR}) to an ordinary +label outside the sequence. + +@item Execute a return statement (@code{RETURN_EXPR}). + +@item Throw an exception. This is currently not explicitly represented in +GIMPLE. + +@end enumerate + +The second sequence is not executed if the first sequence completes by +calling @code{setjmp} or @code{exit} or any other function that does +not return. The second sequence is also not executed if the first +sequence completes via a non-local goto or a computed goto (in general +the compiler does not know whether such a goto statement exits the +first sequence or not, so we assume that it doesn't). + +After the second sequence is executed, if it completes normally by +falling off the end, execution continues wherever the first sequence +would have continued, by falling off the end, or doing a goto, etc. + +If the second sequence is an @code{EH_ELSE_EXPR} selector, then the +sequence in its first operand is used when the first sequence completes +normally, and that in its second operand is used for exceptional +cleanups, i.e., when an exception propagates out of the first sequence. + +@code{TRY_FINALLY_EXPR} complicates the flow graph, since the cleanup +needs to appear on every edge out of the controlled block; this +reduces the freedom to move code across these edges. Therefore, the +EH lowering pass which runs before most of the optimization passes +eliminates these expressions by explicitly adding the cleanup to each +edge. Rethrowing the exception is represented using @code{RESX_EXPR}. + +@node OpenMP +@subsection OpenMP +@tindex OMP_PARALLEL +@tindex OMP_FOR +@tindex OMP_SECTIONS +@tindex OMP_SINGLE +@tindex OMP_SECTION +@tindex OMP_MASTER +@tindex OMP_ORDERED +@tindex OMP_CRITICAL +@tindex OMP_RETURN +@tindex OMP_CONTINUE +@tindex OMP_ATOMIC +@tindex OMP_CLAUSE + +All the statements starting with @code{OMP_} represent directives and +clauses used by the OpenMP API @w{@uref{https://www.openmp.org}}. + +@table @code +@item OMP_PARALLEL + +Represents @code{#pragma omp parallel [clause1 @dots{} clauseN]}. It +has four operands: + +Operand @code{OMP_PARALLEL_BODY} is valid while in GENERIC and +High GIMPLE forms. It contains the body of code to be executed +by all the threads. During GIMPLE lowering, this operand becomes +@code{NULL} and the body is emitted linearly after +@code{OMP_PARALLEL}. + +Operand @code{OMP_PARALLEL_CLAUSES} is the list of clauses +associated with the directive. + +Operand @code{OMP_PARALLEL_FN} is created by +@code{pass_lower_omp}, it contains the @code{FUNCTION_DECL} +for the function that will contain the body of the parallel +region. + +Operand @code{OMP_PARALLEL_DATA_ARG} is also created by +@code{pass_lower_omp}. If there are shared variables to be +communicated to the children threads, this operand will contain +the @code{VAR_DECL} that contains all the shared values and +variables. + +@item OMP_FOR + +Represents @code{#pragma omp for [clause1 @dots{} clauseN]}. It has +six operands: + +Operand @code{OMP_FOR_BODY} contains the loop body. + +Operand @code{OMP_FOR_CLAUSES} is the list of clauses +associated with the directive. + +Operand @code{OMP_FOR_INIT} is the loop initialization code of +the form @code{VAR = N1}. + +Operand @code{OMP_FOR_COND} is the loop conditional expression +of the form @code{VAR @{<,>,<=,>=@} N2}. + +Operand @code{OMP_FOR_INCR} is the loop index increment of the +form @code{VAR @{+=,-=@} INCR}. + +Operand @code{OMP_FOR_PRE_BODY} contains side effect code from +operands @code{OMP_FOR_INIT}, @code{OMP_FOR_COND} and +@code{OMP_FOR_INC}. These side effects are part of the +@code{OMP_FOR} block but must be evaluated before the start of +loop body. + +The loop index variable @code{VAR} must be a signed integer variable, +which is implicitly private to each thread. Bounds +@code{N1} and @code{N2} and the increment expression +@code{INCR} are required to be loop invariant integer +expressions that are evaluated without any synchronization. The +evaluation order, frequency of evaluation and side effects are +unspecified by the standard. + +@item OMP_SECTIONS + +Represents @code{#pragma omp sections [clause1 @dots{} clauseN]}. + +Operand @code{OMP_SECTIONS_BODY} contains the sections body, +which in turn contains a set of @code{OMP_SECTION} nodes for +each of the concurrent sections delimited by @code{#pragma omp +section}. + +Operand @code{OMP_SECTIONS_CLAUSES} is the list of clauses +associated with the directive. + +@item OMP_SECTION + +Section delimiter for @code{OMP_SECTIONS}. + +@item OMP_SINGLE + +Represents @code{#pragma omp single}. + +Operand @code{OMP_SINGLE_BODY} contains the body of code to be +executed by a single thread. + +Operand @code{OMP_SINGLE_CLAUSES} is the list of clauses +associated with the directive. + +@item OMP_MASTER + +Represents @code{#pragma omp master}. + +Operand @code{OMP_MASTER_BODY} contains the body of code to be +executed by the master thread. + +@item OMP_ORDERED + +Represents @code{#pragma omp ordered}. + +Operand @code{OMP_ORDERED_BODY} contains the body of code to be +executed in the sequential order dictated by the loop index +variable. + +@item OMP_CRITICAL + +Represents @code{#pragma omp critical [name]}. + +Operand @code{OMP_CRITICAL_BODY} is the critical section. + +Operand @code{OMP_CRITICAL_NAME} is an optional identifier to +label the critical section. + +@item OMP_RETURN + +This does not represent any OpenMP directive, it is an artificial +marker to indicate the end of the body of an OpenMP@. It is used +by the flow graph (@code{tree-cfg.cc}) and OpenMP region +building code (@code{omp-low.cc}). + +@item OMP_CONTINUE + +Similarly, this instruction does not represent an OpenMP +directive, it is used by @code{OMP_FOR} (and similar codes) as well as +@code{OMP_SECTIONS} to mark the place where the code needs to +loop to the next iteration, or the next section, respectively. + +In some cases, @code{OMP_CONTINUE} is placed right before +@code{OMP_RETURN}. But if there are cleanups that need to +occur right after the looping body, it will be emitted between +@code{OMP_CONTINUE} and @code{OMP_RETURN}. + +@item OMP_ATOMIC + +Represents @code{#pragma omp atomic}. + +Operand 0 is the address at which the atomic operation is to be +performed. + +Operand 1 is the expression to evaluate. The gimplifier tries +three alternative code generation strategies. Whenever possible, +an atomic update built-in is used. If that fails, a +compare-and-swap loop is attempted. If that also fails, a +regular critical section around the expression is used. + +@item OMP_CLAUSE + +Represents clauses associated with one of the @code{OMP_} directives. +Clauses are represented by separate subcodes defined in +@file{tree.h}. Clauses codes can be one of: +@code{OMP_CLAUSE_PRIVATE}, @code{OMP_CLAUSE_SHARED}, +@code{OMP_CLAUSE_FIRSTPRIVATE}, +@code{OMP_CLAUSE_LASTPRIVATE}, @code{OMP_CLAUSE_COPYIN}, +@code{OMP_CLAUSE_COPYPRIVATE}, @code{OMP_CLAUSE_IF}, +@code{OMP_CLAUSE_NUM_THREADS}, @code{OMP_CLAUSE_SCHEDULE}, +@code{OMP_CLAUSE_NOWAIT}, @code{OMP_CLAUSE_ORDERED}, +@code{OMP_CLAUSE_DEFAULT}, @code{OMP_CLAUSE_REDUCTION}, +@code{OMP_CLAUSE_COLLAPSE}, @code{OMP_CLAUSE_UNTIED}, +@code{OMP_CLAUSE_FINAL}, and @code{OMP_CLAUSE_MERGEABLE}. Each code +represents the corresponding OpenMP clause. + +Clauses associated with the same directive are chained together +via @code{OMP_CLAUSE_CHAIN}. Those clauses that accept a list +of variables are restricted to exactly one, accessed with +@code{OMP_CLAUSE_VAR}. Therefore, multiple variables under the +same clause @code{C} need to be represented as multiple @code{C} clauses +chained together. This facilitates adding new clauses during +compilation. + +@end table + +@node OpenACC +@subsection OpenACC +@tindex OACC_CACHE +@tindex OACC_DATA +@tindex OACC_DECLARE +@tindex OACC_ENTER_DATA +@tindex OACC_EXIT_DATA +@tindex OACC_HOST_DATA +@tindex OACC_KERNELS +@tindex OACC_LOOP +@tindex OACC_PARALLEL +@tindex OACC_SERIAL +@tindex OACC_UPDATE + +All the statements starting with @code{OACC_} represent directives and +clauses used by the OpenACC API @w{@uref{https://www.openacc.org}}. + +@table @code +@item OACC_CACHE + +Represents @code{#pragma acc cache (var @dots{})}. + +@item OACC_DATA + +Represents @code{#pragma acc data [clause1 @dots{} clauseN]}. + +@item OACC_DECLARE + +Represents @code{#pragma acc declare [clause1 @dots{} clauseN]}. + +@item OACC_ENTER_DATA + +Represents @code{#pragma acc enter data [clause1 @dots{} clauseN]}. + +@item OACC_EXIT_DATA + +Represents @code{#pragma acc exit data [clause1 @dots{} clauseN]}. + +@item OACC_HOST_DATA + +Represents @code{#pragma acc host_data [clause1 @dots{} clauseN]}. + +@item OACC_KERNELS + +Represents @code{#pragma acc kernels [clause1 @dots{} clauseN]}. + +@item OACC_LOOP + +Represents @code{#pragma acc loop [clause1 @dots{} clauseN]}. + +See the description of the @code{OMP_FOR} code. + +@item OACC_PARALLEL + +Represents @code{#pragma acc parallel [clause1 @dots{} clauseN]}. + +@item OACC_SERIAL + +Represents @code{#pragma acc serial [clause1 @dots{} clauseN]}. + +@item OACC_UPDATE + +Represents @code{#pragma acc update [clause1 @dots{} clauseN]}. + +@end table + +@c --------------------------------------------------------------------- +@c Functions +@c --------------------------------------------------------------------- + +@node Functions +@section Functions +@cindex function +@tindex FUNCTION_DECL + +A function is represented by a @code{FUNCTION_DECL} node. It stores +the basic pieces of the function such as body, parameters, and return +type as well as information on the surrounding context, visibility, +and linkage. + +@menu +* Function Basics:: Function names, body, and parameters. +* Function Properties:: Context, linkage, etc. +@end menu + +@c --------------------------------------------------------------------- +@c Function Basics +@c --------------------------------------------------------------------- + +@node Function Basics +@subsection Function Basics +@findex DECL_NAME +@findex DECL_ASSEMBLER_NAME +@findex TREE_PUBLIC +@findex DECL_ARTIFICIAL +@findex DECL_FUNCTION_SPECIFIC_TARGET +@findex DECL_FUNCTION_SPECIFIC_OPTIMIZATION + +A function has four core parts: the name, the parameters, the result, +and the body. The following macros and functions access these parts +of a @code{FUNCTION_DECL} as well as other basic features: +@ftable @code +@item DECL_NAME +This macro returns the unqualified name of the function, as an +@code{IDENTIFIER_NODE}. For an instantiation of a function template, +the @code{DECL_NAME} is the unqualified name of the template, not +something like @code{f}. The value of @code{DECL_NAME} is +undefined when used on a constructor, destructor, overloaded operator, +or type-conversion operator, or any function that is implicitly +generated by the compiler. See below for macros that can be used to +distinguish these cases. + +@item DECL_ASSEMBLER_NAME +This macro returns the mangled name of the function, also an +@code{IDENTIFIER_NODE}. This name does not contain leading underscores +on systems that prefix all identifiers with underscores. The mangled +name is computed in the same way on all platforms; if special processing +is required to deal with the object file format used on a particular +platform, it is the responsibility of the back end to perform those +modifications. (Of course, the back end should not modify +@code{DECL_ASSEMBLER_NAME} itself.) + +Using @code{DECL_ASSEMBLER_NAME} will cause additional memory to be +allocated (for the mangled name of the entity) so it should be used +only when emitting assembly code. It should not be used within the +optimizers to determine whether or not two declarations are the same, +even though some of the existing optimizers do use it in that way. +These uses will be removed over time. + +@item DECL_ARGUMENTS +This macro returns the @code{PARM_DECL} for the first argument to the +function. Subsequent @code{PARM_DECL} nodes can be obtained by +following the @code{TREE_CHAIN} links. + +@item DECL_RESULT +This macro returns the @code{RESULT_DECL} for the function. + +@item DECL_SAVED_TREE +This macro returns the complete body of the function. + +@item TREE_TYPE +This macro returns the @code{FUNCTION_TYPE} or @code{METHOD_TYPE} for +the function. + +@item DECL_INITIAL +A function that has a definition in the current translation unit will +have a non-@code{NULL} @code{DECL_INITIAL}. However, back ends should not make +use of the particular value given by @code{DECL_INITIAL}. + +It should contain a tree of @code{BLOCK} nodes that mirrors the scopes +that variables are bound in the function. Each block contains a list +of decls declared in a basic block, a pointer to a chain of blocks at +the next lower scope level, then a pointer to the next block at the +same level and a backpointer to the parent @code{BLOCK} or +@code{FUNCTION_DECL}. So given a function as follows: + +@smallexample +void foo() +@{ + int a; + @{ + int b; + @} + int c; +@} +@end smallexample + +you would get the following: + +@smallexample +tree foo = FUNCTION_DECL; +tree decl_a = VAR_DECL; +tree decl_b = VAR_DECL; +tree decl_c = VAR_DECL; +tree block_a = BLOCK; +tree block_b = BLOCK; +tree block_c = BLOCK; +BLOCK_VARS(block_a) = decl_a; +BLOCK_SUBBLOCKS(block_a) = block_b; +BLOCK_CHAIN(block_a) = block_c; +BLOCK_SUPERCONTEXT(block_a) = foo; +BLOCK_VARS(block_b) = decl_b; +BLOCK_SUPERCONTEXT(block_b) = block_a; +BLOCK_VARS(block_c) = decl_c; +BLOCK_SUPERCONTEXT(block_c) = foo; +DECL_INITIAL(foo) = block_a; +@end smallexample + +@end ftable + +@c --------------------------------------------------------------------- +@c Function Properties +@c --------------------------------------------------------------------- + +@node Function Properties +@subsection Function Properties +@cindex function properties +@cindex statements + +To determine the scope of a function, you can use the +@code{DECL_CONTEXT} macro. This macro will return the class +(either a @code{RECORD_TYPE} or a @code{UNION_TYPE}) or namespace (a +@code{NAMESPACE_DECL}) of which the function is a member. For a virtual +function, this macro returns the class in which the function was +actually defined, not the base class in which the virtual declaration +occurred. + +In C, the @code{DECL_CONTEXT} for a function maybe another function. +This representation indicates that the GNU nested function extension +is in use. For details on the semantics of nested functions, see the +GCC Manual. The nested function can refer to local variables in its +containing function. Such references are not explicitly marked in the +tree structure; back ends must look at the @code{DECL_CONTEXT} for the +referenced @code{VAR_DECL}. If the @code{DECL_CONTEXT} for the +referenced @code{VAR_DECL} is not the same as the function currently +being processed, and neither @code{DECL_EXTERNAL} nor +@code{TREE_STATIC} hold, then the reference is to a local variable in +a containing function, and the back end must take appropriate action. + +@ftable @code +@item DECL_EXTERNAL +This predicate holds if the function is undefined. + +@item TREE_PUBLIC +This predicate holds if the function has external linkage. + +@item TREE_STATIC +This predicate holds if the function has been defined. + +@item TREE_THIS_VOLATILE +This predicate holds if the function does not return normally. + +@item TREE_READONLY +This predicate holds if the function can only read its arguments. + +@item DECL_PURE_P +This predicate holds if the function can only read its arguments, but +may also read global memory. + +@item DECL_VIRTUAL_P +This predicate holds if the function is virtual. + +@item DECL_ARTIFICIAL +This macro holds if the function was implicitly generated by the +compiler, rather than explicitly declared. In addition to implicitly +generated class member functions, this macro holds for the special +functions created to implement static initialization and destruction, to +compute run-time type information, and so forth. + +@item DECL_FUNCTION_SPECIFIC_TARGET +This macro returns a tree node that holds the target options that are +to be used to compile this particular function or @code{NULL_TREE} if +the function is to be compiled with the target options specified on +the command line. + +@item DECL_FUNCTION_SPECIFIC_OPTIMIZATION +This macro returns a tree node that holds the optimization options +that are to be used to compile this particular function or +@code{NULL_TREE} if the function is to be compiled with the +optimization options specified on the command line. + +@end ftable + +@c --------------------------------------------------------------------- +@c Language-dependent trees +@c --------------------------------------------------------------------- + +@node Language-dependent trees +@section Language-dependent trees +@cindex language-dependent trees + +Front ends may wish to keep some state associated with various GENERIC +trees while parsing. To support this, trees provide a set of flags +that may be used by the front end. They are accessed using +@code{TREE_LANG_FLAG_n} where @samp{n} is currently 0 through 6. + +If necessary, a front end can use some language-dependent tree +codes in its GENERIC representation, so long as it provides a +hook for converting them to GIMPLE and doesn't expect them to +work with any (hypothetical) optimizers that run before the +conversion to GIMPLE@. The intermediate representation used while +parsing C and C++ looks very little like GENERIC, but the C and +C++ gimplifier hooks are perfectly happy to take it as input and +spit out GIMPLE@. + + + +@node C and C++ Trees +@section C and C++ Trees + +This section documents the internal representation used by GCC to +represent C and C++ source programs. When presented with a C or C++ +source program, GCC parses the program, performs semantic analysis +(including the generation of error messages), and then produces the +internal representation described here. This representation contains a +complete representation for the entire translation unit provided as +input to the front end. This representation is then typically processed +by a code-generator in order to produce machine code, but could also be +used in the creation of source browsers, intelligent editors, automatic +documentation generators, interpreters, and any other programs needing +the ability to process C or C++ code. + +This section explains the internal representation. In particular, it +documents the internal representation for C and C++ source +constructs, and the macros, functions, and variables that can be used to +access these constructs. The C++ representation is largely a superset +of the representation used in the C front end. There is only one +construct used in C that does not appear in the C++ front end and that +is the GNU ``nested function'' extension. Many of the macros documented +here do not apply in C because the corresponding language constructs do +not appear in C@. + +The C and C++ front ends generate a mix of GENERIC trees and ones +specific to C and C++. These language-specific trees are higher-level +constructs than the ones in GENERIC to make the parser's job easier. +This section describes those trees that aren't part of GENERIC as well +as aspects of GENERIC trees that are treated in a language-specific +manner. + +If you are developing a ``back end'', be it is a code-generator or some +other tool, that uses this representation, you may occasionally find +that you need to ask questions not easily answered by the functions and +macros available here. If that situation occurs, it is quite likely +that GCC already supports the functionality you desire, but that the +interface is simply not documented here. In that case, you should ask +the GCC maintainers (via mail to @email{gcc@@gcc.gnu.org}) about +documenting the functionality you require. Similarly, if you find +yourself writing functions that do not deal directly with your back end, +but instead might be useful to other people using the GCC front end, you +should submit your patches for inclusion in GCC@. + +@menu +* Types for C++:: Fundamental and aggregate types. +* Namespaces:: Namespaces. +* Classes:: Classes. +* Functions for C++:: Overloading and accessors for C++. +* Statements for C and C++:: Statements specific to C and C++. +* C++ Expressions:: From @code{typeid} to @code{throw}. +@end menu + +@node Types for C++ +@subsection Types for C++ +@tindex UNKNOWN_TYPE +@tindex TYPENAME_TYPE +@tindex TYPEOF_TYPE +@findex cp_type_quals +@findex TYPE_UNQUALIFIED +@findex TYPE_QUAL_CONST +@findex TYPE_QUAL_VOLATILE +@findex TYPE_QUAL_RESTRICT +@findex TYPE_MAIN_VARIANT +@cindex qualified type +@findex TYPE_SIZE +@findex TYPE_ALIGN +@findex TYPE_PRECISION +@findex TYPE_ARG_TYPES +@findex TYPE_METHOD_BASETYPE +@findex TYPE_PTRDATAMEM_P +@findex TYPE_OFFSET_BASETYPE +@findex TREE_TYPE +@findex TYPE_CONTEXT +@findex TYPE_NAME +@findex TYPENAME_TYPE_FULLNAME +@findex TYPE_FIELDS +@findex TYPE_PTROBV_P + +In C++, an array type is not qualified; rather the type of the array +elements is qualified. This situation is reflected in the intermediate +representation. The macros described here will always examine the +qualification of the underlying element type when applied to an array +type. (If the element type is itself an array, then the recursion +continues until a non-array type is found, and the qualification of this +type is examined.) So, for example, @code{CP_TYPE_CONST_P} will hold of +the type @code{const int ()[7]}, denoting an array of seven @code{int}s. + +The following functions and macros deal with cv-qualification of types: +@ftable @code +@item cp_type_quals +This function returns the set of type qualifiers applied to this type. +This value is @code{TYPE_UNQUALIFIED} if no qualifiers have been +applied. The @code{TYPE_QUAL_CONST} bit is set if the type is +@code{const}-qualified. The @code{TYPE_QUAL_VOLATILE} bit is set if the +type is @code{volatile}-qualified. The @code{TYPE_QUAL_RESTRICT} bit is +set if the type is @code{restrict}-qualified. + +@item CP_TYPE_CONST_P +This macro holds if the type is @code{const}-qualified. + +@item CP_TYPE_VOLATILE_P +This macro holds if the type is @code{volatile}-qualified. + +@item CP_TYPE_RESTRICT_P +This macro holds if the type is @code{restrict}-qualified. + +@item CP_TYPE_CONST_NON_VOLATILE_P +This predicate holds for a type that is @code{const}-qualified, but +@emph{not} @code{volatile}-qualified; other cv-qualifiers are ignored as +well: only the @code{const}-ness is tested. + +@end ftable + +A few other macros and functions are usable with all types: +@ftable @code +@item TYPE_SIZE +The number of bits required to represent the type, represented as an +@code{INTEGER_CST}. For an incomplete type, @code{TYPE_SIZE} will be +@code{NULL_TREE}. + +@item TYPE_ALIGN +The alignment of the type, in bits, represented as an @code{int}. + +@item TYPE_NAME +This macro returns a declaration (in the form of a @code{TYPE_DECL}) for +the type. (Note this macro does @emph{not} return an +@code{IDENTIFIER_NODE}, as you might expect, given its name!) You can +look at the @code{DECL_NAME} of the @code{TYPE_DECL} to obtain the +actual name of the type. The @code{TYPE_NAME} will be @code{NULL_TREE} +for a type that is not a built-in type, the result of a typedef, or a +named class type. + +@item CP_INTEGRAL_TYPE +This predicate holds if the type is an integral type. Notice that in +C++, enumerations are @emph{not} integral types. + +@item ARITHMETIC_TYPE_P +This predicate holds if the type is an integral type (in the C++ sense) +or a floating point type. + +@item CLASS_TYPE_P +This predicate holds for a class-type. + +@item TYPE_BUILT_IN +This predicate holds for a built-in type. + +@item TYPE_PTRDATAMEM_P +This predicate holds if the type is a pointer to data member. + +@item TYPE_PTR_P +This predicate holds if the type is a pointer type, and the pointee is +not a data member. + +@item TYPE_PTRFN_P +This predicate holds for a pointer to function type. + +@item TYPE_PTROB_P +This predicate holds for a pointer to object type. Note however that it +does not hold for the generic pointer to object type @code{void *}. You +may use @code{TYPE_PTROBV_P} to test for a pointer to object type as +well as @code{void *}. + +@end ftable + +The table below describes types specific to C and C++ as well as +language-dependent info about GENERIC types. + +@table @code + +@item POINTER_TYPE +Used to represent pointer types, and pointer to data member types. If +@code{TREE_TYPE} +is a pointer to data member type, then @code{TYPE_PTRDATAMEM_P} will hold. +For a pointer to data member type of the form @samp{T X::*}, +@code{TYPE_PTRMEM_CLASS_TYPE} will be the type @code{X}, while +@code{TYPE_PTRMEM_POINTED_TO_TYPE} will be the type @code{T}. + +@item RECORD_TYPE +Used to represent @code{struct} and @code{class} types in C and C++. If +@code{TYPE_PTRMEMFUNC_P} holds, then this type is a pointer-to-member +type. In that case, the @code{TYPE_PTRMEMFUNC_FN_TYPE} is a +@code{POINTER_TYPE} pointing to a @code{METHOD_TYPE}. The +@code{METHOD_TYPE} is the type of a function pointed to by the +pointer-to-member function. If @code{TYPE_PTRMEMFUNC_P} does not hold, +this type is a class type. For more information, @pxref{Classes}. + +@item UNKNOWN_TYPE +This node is used to represent a type the knowledge of which is +insufficient for a sound processing. + +@item TYPENAME_TYPE +Used to represent a construct of the form @code{typename T::A}. The +@code{TYPE_CONTEXT} is @code{T}; the @code{TYPE_NAME} is an +@code{IDENTIFIER_NODE} for @code{A}. If the type is specified via a +template-id, then @code{TYPENAME_TYPE_FULLNAME} yields a +@code{TEMPLATE_ID_EXPR}. The @code{TREE_TYPE} is non-@code{NULL} if the +node is implicitly generated in support for the implicit typename +extension; in which case the @code{TREE_TYPE} is a type node for the +base-class. + +@item TYPEOF_TYPE +Used to represent the @code{__typeof__} extension. The +@code{TYPE_FIELDS} is the expression the type of which is being +represented. + +@end table + + +@c --------------------------------------------------------------------- +@c Namespaces +@c --------------------------------------------------------------------- + +@node Namespaces +@subsection Namespaces +@cindex namespace, scope +@tindex NAMESPACE_DECL + +The root of the entire intermediate representation is the variable +@code{global_namespace}. This is the namespace specified with @code{::} +in C++ source code. All other namespaces, types, variables, functions, +and so forth can be found starting with this namespace. + +However, except for the fact that it is distinguished as the root of the +representation, the global namespace is no different from any other +namespace. Thus, in what follows, we describe namespaces generally, +rather than the global namespace in particular. + +A namespace is represented by a @code{NAMESPACE_DECL} node. + +The following macros and functions can be used on a @code{NAMESPACE_DECL}: + +@ftable @code +@item DECL_NAME +This macro is used to obtain the @code{IDENTIFIER_NODE} corresponding to +the unqualified name of the name of the namespace (@pxref{Identifiers}). +The name of the global namespace is @samp{::}, even though in C++ the +global namespace is unnamed. However, you should use comparison with +@code{global_namespace}, rather than @code{DECL_NAME} to determine +whether or not a namespace is the global one. An unnamed namespace +will have a @code{DECL_NAME} equal to @code{anonymous_namespace_name}. +Within a single translation unit, all unnamed namespaces will have the +same name. + +@item DECL_CONTEXT +This macro returns the enclosing namespace. The @code{DECL_CONTEXT} for +the @code{global_namespace} is @code{NULL_TREE}. + +@item DECL_NAMESPACE_ALIAS +If this declaration is for a namespace alias, then +@code{DECL_NAMESPACE_ALIAS} is the namespace for which this one is an +alias. + +Do not attempt to use @code{cp_namespace_decls} for a namespace which is +an alias. Instead, follow @code{DECL_NAMESPACE_ALIAS} links until you +reach an ordinary, non-alias, namespace, and call +@code{cp_namespace_decls} there. + +@item DECL_NAMESPACE_STD_P +This predicate holds if the namespace is the special @code{::std} +namespace. + +@item cp_namespace_decls +This function will return the declarations contained in the namespace, +including types, overloaded functions, other namespaces, and so forth. +If there are no declarations, this function will return +@code{NULL_TREE}. The declarations are connected through their +@code{TREE_CHAIN} fields. + +Although most entries on this list will be declarations, +@code{TREE_LIST} nodes may also appear. In this case, the +@code{TREE_VALUE} will be an @code{OVERLOAD}. The value of the +@code{TREE_PURPOSE} is unspecified; back ends should ignore this value. +As with the other kinds of declarations returned by +@code{cp_namespace_decls}, the @code{TREE_CHAIN} will point to the next +declaration in this list. + +For more information on the kinds of declarations that can occur on this +list, @xref{Declarations}. Some declarations will not appear on this +list. In particular, no @code{FIELD_DECL}, @code{LABEL_DECL}, or +@code{PARM_DECL} nodes will appear here. + +This function cannot be used with namespaces that have +@code{DECL_NAMESPACE_ALIAS} set. + +@end ftable + +@c --------------------------------------------------------------------- +@c Classes +@c --------------------------------------------------------------------- + +@node Classes +@subsection Classes +@cindex class, scope +@tindex RECORD_TYPE +@tindex UNION_TYPE +@findex CLASSTYPE_DECLARED_CLASS +@findex TYPE_BINFO +@findex BINFO_TYPE +@findex TYPE_FIELDS +@findex TYPE_VFIELD + +Besides namespaces, the other high-level scoping construct in C++ is the +class. (Throughout this manual the term @dfn{class} is used to mean the +types referred to in the ANSI/ISO C++ Standard as classes; these include +types defined with the @code{class}, @code{struct}, and @code{union} +keywords.) + +A class type is represented by either a @code{RECORD_TYPE} or a +@code{UNION_TYPE}. A class declared with the @code{union} tag is +represented by a @code{UNION_TYPE}, while classes declared with either +the @code{struct} or the @code{class} tag are represented by +@code{RECORD_TYPE}s. You can use the @code{CLASSTYPE_DECLARED_CLASS} +macro to discern whether or not a particular type is a @code{class} as +opposed to a @code{struct}. This macro will be true only for classes +declared with the @code{class} tag. + +Almost all members are available on the @code{TYPE_FIELDS} +list. Given one member, the next can be found by following the +@code{TREE_CHAIN}. You should not depend in any way on the order in +which fields appear on this list. All nodes on this list will be +@samp{DECL} nodes. A @code{FIELD_DECL} is used to represent a non-static +data member, a @code{VAR_DECL} is used to represent a static data +member, and a @code{TYPE_DECL} is used to represent a type. Note that +the @code{CONST_DECL} for an enumeration constant will appear on this +list, if the enumeration type was declared in the class. (Of course, +the @code{TYPE_DECL} for the enumeration type will appear here as well.) +There are no entries for base classes on this list. In particular, +there is no @code{FIELD_DECL} for the ``base-class portion'' of an +object. If a function member is overloaded, each of the overloaded +functions appears; no @code{OVERLOAD} nodes appear on the @code{TYPE_FIELDS} +list. Implicitly declared functions (including default constructors, +copy constructors, assignment operators, and destructors) will appear on +this list as well. + +The @code{TYPE_VFIELD} is a compiler-generated field used to point to +virtual function tables. It may or may not appear on the +@code{TYPE_FIELDS} list. However, back ends should handle the +@code{TYPE_VFIELD} just like all the entries on the @code{TYPE_FIELDS} +list. + +Every class has an associated @dfn{binfo}, which can be obtained with +@code{TYPE_BINFO}. Binfos are used to represent base-classes. The +binfo given by @code{TYPE_BINFO} is the degenerate case, whereby every +class is considered to be its own base-class. The base binfos for a +particular binfo are held in a vector, whose length is obtained with +@code{BINFO_N_BASE_BINFOS}. The base binfos themselves are obtained +with @code{BINFO_BASE_BINFO} and @code{BINFO_BASE_ITERATE}. To add a +new binfo, use @code{BINFO_BASE_APPEND}. The vector of base binfos can +be obtained with @code{BINFO_BASE_BINFOS}, but normally you do not need +to use that. The class type associated with a binfo is given by +@code{BINFO_TYPE}. It is not always the case that @code{BINFO_TYPE +(TYPE_BINFO (x))}, because of typedefs and qualified types. Neither is +it the case that @code{TYPE_BINFO (BINFO_TYPE (y))} is the same binfo as +@code{y}. The reason is that if @code{y} is a binfo representing a +base-class @code{B} of a derived class @code{D}, then @code{BINFO_TYPE +(y)} will be @code{B}, and @code{TYPE_BINFO (BINFO_TYPE (y))} will be +@code{B} as its own base-class, rather than as a base-class of @code{D}. + +The access to a base type can be found with @code{BINFO_BASE_ACCESS}. +This will produce @code{access_public_node}, @code{access_private_node} +or @code{access_protected_node}. If bases are always public, +@code{BINFO_BASE_ACCESSES} may be @code{NULL}. + +@code{BINFO_VIRTUAL_P} is used to specify whether the binfo is inherited +virtually or not. The other flags, @code{BINFO_FLAG_0} to +@code{BINFO_FLAG_6}, can be used for language specific use. + +The following macros can be used on a tree node representing a class-type. + +@ftable @code +@item LOCAL_CLASS_P +This predicate holds if the class is local class @emph{i.e.}@: declared +inside a function body. + +@item TYPE_POLYMORPHIC_P +This predicate holds if the class has at least one virtual function +(declared or inherited). + +@item TYPE_HAS_DEFAULT_CONSTRUCTOR +This predicate holds whenever its argument represents a class-type with +default constructor. + +@item CLASSTYPE_HAS_MUTABLE +@itemx TYPE_HAS_MUTABLE_P +These predicates hold for a class-type having a mutable data member. + +@item CLASSTYPE_NON_POD_P +This predicate holds only for class-types that are not PODs. + +@item TYPE_HAS_NEW_OPERATOR +This predicate holds for a class-type that defines +@code{operator new}. + +@item TYPE_HAS_ARRAY_NEW_OPERATOR +This predicate holds for a class-type for which +@code{operator new[]} is defined. + +@item TYPE_OVERLOADS_CALL_EXPR +This predicate holds for class-type for which the function call +@code{operator()} is overloaded. + +@item TYPE_OVERLOADS_ARRAY_REF +This predicate holds for a class-type that overloads +@code{operator[]} + +@item TYPE_OVERLOADS_ARROW +This predicate holds for a class-type for which @code{operator->} is +overloaded. + +@end ftable + +@node Functions for C++ +@subsection Functions for C++ +@cindex function +@tindex FUNCTION_DECL +@tindex OVERLOAD +@findex OVL_CURRENT +@findex OVL_NEXT + +A function is represented by a @code{FUNCTION_DECL} node. A set of +overloaded functions is sometimes represented by an @code{OVERLOAD} node. + +An @code{OVERLOAD} node is not a declaration, so none of the +@samp{DECL_} macros should be used on an @code{OVERLOAD}. An +@code{OVERLOAD} node is similar to a @code{TREE_LIST}. Use +@code{OVL_CURRENT} to get the function associated with an +@code{OVERLOAD} node; use @code{OVL_NEXT} to get the next +@code{OVERLOAD} node in the list of overloaded functions. The macros +@code{OVL_CURRENT} and @code{OVL_NEXT} are actually polymorphic; you can +use them to work with @code{FUNCTION_DECL} nodes as well as with +overloads. In the case of a @code{FUNCTION_DECL}, @code{OVL_CURRENT} +will always return the function itself, and @code{OVL_NEXT} will always +be @code{NULL_TREE}. + +To determine the scope of a function, you can use the +@code{DECL_CONTEXT} macro. This macro will return the class +(either a @code{RECORD_TYPE} or a @code{UNION_TYPE}) or namespace (a +@code{NAMESPACE_DECL}) of which the function is a member. For a virtual +function, this macro returns the class in which the function was +actually defined, not the base class in which the virtual declaration +occurred. + +If a friend function is defined in a class scope, the +@code{DECL_FRIEND_CONTEXT} macro can be used to determine the class in +which it was defined. For example, in +@smallexample +class C @{ friend void f() @{@} @}; +@end smallexample +@noindent +the @code{DECL_CONTEXT} for @code{f} will be the +@code{global_namespace}, but the @code{DECL_FRIEND_CONTEXT} will be the +@code{RECORD_TYPE} for @code{C}. + + +The following macros and functions can be used on a @code{FUNCTION_DECL}: +@ftable @code +@item DECL_MAIN_P +This predicate holds for a function that is the program entry point +@code{::code}. + +@item DECL_LOCAL_FUNCTION_P +This predicate holds if the function was declared at block scope, even +though it has a global scope. + +@item DECL_ANTICIPATED +This predicate holds if the function is a built-in function but its +prototype is not yet explicitly declared. + +@item DECL_EXTERN_C_FUNCTION_P +This predicate holds if the function is declared as an +`@code{extern "C"}' function. + +@item DECL_LINKONCE_P +This macro holds if multiple copies of this function may be emitted in +various translation units. It is the responsibility of the linker to +merge the various copies. Template instantiations are the most common +example of functions for which @code{DECL_LINKONCE_P} holds; G++ +instantiates needed templates in all translation units which require them, +and then relies on the linker to remove duplicate instantiations. + +FIXME: This macro is not yet implemented. + +@item DECL_FUNCTION_MEMBER_P +This macro holds if the function is a member of a class, rather than a +member of a namespace. + +@item DECL_STATIC_FUNCTION_P +This predicate holds if the function a static member function. + +@item DECL_NONSTATIC_MEMBER_FUNCTION_P +This macro holds for a non-static member function. + +@item DECL_CONST_MEMFUNC_P +This predicate holds for a @code{const}-member function. + +@item DECL_VOLATILE_MEMFUNC_P +This predicate holds for a @code{volatile}-member function. + +@item DECL_CONSTRUCTOR_P +This macro holds if the function is a constructor. + +@item DECL_NONCONVERTING_P +This predicate holds if the constructor is a non-converting constructor. + +@item DECL_COMPLETE_CONSTRUCTOR_P +This predicate holds for a function which is a constructor for an object +of a complete type. + +@item DECL_BASE_CONSTRUCTOR_P +This predicate holds for a function which is a constructor for a base +class sub-object. + +@item DECL_COPY_CONSTRUCTOR_P +This predicate holds for a function which is a copy-constructor. + +@item DECL_DESTRUCTOR_P +This macro holds if the function is a destructor. + +@item DECL_COMPLETE_DESTRUCTOR_P +This predicate holds if the function is the destructor for an object a +complete type. + +@item DECL_OVERLOADED_OPERATOR_P +This macro holds if the function is an overloaded operator. + +@item DECL_CONV_FN_P +This macro holds if the function is a type-conversion operator. + +@item DECL_GLOBAL_CTOR_P +This predicate holds if the function is a file-scope initialization +function. + +@item DECL_GLOBAL_DTOR_P +This predicate holds if the function is a file-scope finalization +function. + +@item DECL_THUNK_P +This predicate holds if the function is a thunk. + +These functions represent stub code that adjusts the @code{this} pointer +and then jumps to another function. When the jumped-to function +returns, control is transferred directly to the caller, without +returning to the thunk. The first parameter to the thunk is always the +@code{this} pointer; the thunk should add @code{THUNK_DELTA} to this +value. (The @code{THUNK_DELTA} is an @code{int}, not an +@code{INTEGER_CST}.) + +Then, if @code{THUNK_VCALL_OFFSET} (an @code{INTEGER_CST}) is nonzero +the adjusted @code{this} pointer must be adjusted again. The complete +calculation is given by the following pseudo-code: + +@smallexample +this += THUNK_DELTA +if (THUNK_VCALL_OFFSET) + this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET] +@end smallexample + +Finally, the thunk should jump to the location given +by @code{DECL_INITIAL}; this will always be an expression for the +address of a function. + +@item DECL_NON_THUNK_FUNCTION_P +This predicate holds if the function is @emph{not} a thunk function. + +@item GLOBAL_INIT_PRIORITY +If either @code{DECL_GLOBAL_CTOR_P} or @code{DECL_GLOBAL_DTOR_P} holds, +then this gives the initialization priority for the function. The +linker will arrange that all functions for which +@code{DECL_GLOBAL_CTOR_P} holds are run in increasing order of priority +before @code{main} is called. When the program exits, all functions for +which @code{DECL_GLOBAL_DTOR_P} holds are run in the reverse order. + +@item TYPE_RAISES_EXCEPTIONS +This macro returns the list of exceptions that a (member-)function can +raise. The returned list, if non @code{NULL}, is comprised of nodes +whose @code{TREE_VALUE} represents a type. + +@item TYPE_NOTHROW_P +This predicate holds when the exception-specification of its arguments +is of the form `@code{()}'. + +@item DECL_ARRAY_DELETE_OPERATOR_P +This predicate holds if the function an overloaded +@code{operator delete[]}. + +@end ftable + +@c --------------------------------------------------------------------- +@c Function Bodies +@c --------------------------------------------------------------------- + +@node Statements for C and C++ +@subsection Statements for C and C++ +@cindex statements +@tindex BREAK_STMT +@tindex CLEANUP_STMT +@findex CLEANUP_DECL +@findex CLEANUP_EXPR +@tindex CONTINUE_STMT +@tindex DECL_STMT +@findex DECL_STMT_DECL +@tindex DO_STMT +@findex DO_BODY +@findex DO_COND +@tindex EMPTY_CLASS_EXPR +@tindex EXPR_STMT +@findex EXPR_STMT_EXPR +@tindex FOR_STMT +@findex FOR_INIT_STMT +@findex FOR_COND +@findex FOR_EXPR +@findex FOR_BODY +@tindex HANDLER +@tindex IF_STMT +@findex IF_COND +@findex THEN_CLAUSE +@findex ELSE_CLAUSE +@tindex RETURN_STMT +@findex RETURN_EXPR +@tindex SUBOBJECT +@findex SUBOBJECT_CLEANUP +@tindex SWITCH_STMT +@findex SWITCH_COND +@findex SWITCH_BODY +@tindex TRY_BLOCK +@findex TRY_STMTS +@findex TRY_HANDLERS +@findex HANDLER_PARMS +@findex HANDLER_BODY +@findex USING_STMT +@tindex WHILE_STMT +@findex WHILE_BODY +@findex WHILE_COND + +A function that has a definition in the current translation unit has +a non-@code{NULL} @code{DECL_INITIAL}. However, back ends should not make +use of the particular value given by @code{DECL_INITIAL}. + +The @code{DECL_SAVED_TREE} gives the complete body of the +function. + +There are tree nodes corresponding to all of the source-level +statement constructs, used within the C and C++ frontends. These are +enumerated here, together with a list of the various macros that can +be used to obtain information about them. There are a few macros that +can be used with all statements: + +@ftable @code +@item STMT_IS_FULL_EXPR_P +In C++, statements normally constitute ``full expressions''; temporaries +created during a statement are destroyed when the statement is complete. +However, G++ sometimes represents expressions by statements; these +statements will not have @code{STMT_IS_FULL_EXPR_P} set. Temporaries +created during such statements should be destroyed when the innermost +enclosing statement with @code{STMT_IS_FULL_EXPR_P} set is exited. + +@end ftable + +Here is the list of the various statement nodes, and the macros used to +access them. This documentation describes the use of these nodes in +non-template functions (including instantiations of template functions). +In template functions, the same nodes are used, but sometimes in +slightly different ways. + +Many of the statements have substatements. For example, a @code{while} +loop has a body, which is itself a statement. If the substatement +is @code{NULL_TREE}, it is considered equivalent to a statement +consisting of a single @code{;}, i.e., an expression statement in which +the expression has been omitted. A substatement may in fact be a list +of statements, connected via their @code{TREE_CHAIN}s. So, you should +always process the statement tree by looping over substatements, like +this: +@smallexample +void process_stmt (stmt) + tree stmt; +@{ + while (stmt) + @{ + switch (TREE_CODE (stmt)) + @{ + case IF_STMT: + process_stmt (THEN_CLAUSE (stmt)); + /* @r{More processing here.} */ + break; + + @dots{} + @} + + stmt = TREE_CHAIN (stmt); + @} +@} +@end smallexample +In other words, while the @code{then} clause of an @code{if} statement +in C++ can be only one statement (although that one statement may be a +compound statement), the intermediate representation sometimes uses +several statements chained together. + +@table @code +@item BREAK_STMT + +Used to represent a @code{break} statement. There are no additional +fields. + +@item CLEANUP_STMT + +Used to represent an action that should take place upon exit from the +enclosing scope. Typically, these actions are calls to destructors for +local objects, but back ends cannot rely on this fact. If these nodes +are in fact representing such destructors, @code{CLEANUP_DECL} will be +the @code{VAR_DECL} destroyed. Otherwise, @code{CLEANUP_DECL} will be +@code{NULL_TREE}. In any case, the @code{CLEANUP_EXPR} is the +expression to execute. The cleanups executed on exit from a scope +should be run in the reverse order of the order in which the associated +@code{CLEANUP_STMT}s were encountered. + +@item CONTINUE_STMT + +Used to represent a @code{continue} statement. There are no additional +fields. + +@item CTOR_STMT + +Used to mark the beginning (if @code{CTOR_BEGIN_P} holds) or end (if +@code{CTOR_END_P} holds of the main body of a constructor. See also +@code{SUBOBJECT} for more information on how to use these nodes. + +@item DO_STMT + +Used to represent a @code{do} loop. The body of the loop is given by +@code{DO_BODY} while the termination condition for the loop is given by +@code{DO_COND}. The condition for a @code{do}-statement is always an +expression. + +@item EMPTY_CLASS_EXPR + +Used to represent a temporary object of a class with no data whose +address is never taken. (All such objects are interchangeable.) The +@code{TREE_TYPE} represents the type of the object. + +@item EXPR_STMT + +Used to represent an expression statement. Use @code{EXPR_STMT_EXPR} to +obtain the expression. + +@item FOR_STMT + +Used to represent a @code{for} statement. The @code{FOR_INIT_STMT} is +the initialization statement for the loop. The @code{FOR_COND} is the +termination condition. The @code{FOR_EXPR} is the expression executed +right before the @code{FOR_COND} on each loop iteration; often, this +expression increments a counter. The body of the loop is given by +@code{FOR_BODY}. @code{FOR_SCOPE} holds the scope of the @code{for} +statement (used in the C++ front end only). Note that +@code{FOR_INIT_STMT} and @code{FOR_BODY} return statements, while +@code{FOR_COND} and @code{FOR_EXPR} return expressions. + +@item HANDLER + +Used to represent a C++ @code{catch} block. The @code{HANDLER_TYPE} +is the type of exception that will be caught by this handler; it is +equal (by pointer equality) to @code{NULL} if this handler is for all +types. @code{HANDLER_PARMS} is the @code{DECL_STMT} for the catch +parameter, and @code{HANDLER_BODY} is the code for the block itself. + +@item IF_STMT + +Used to represent an @code{if} statement. The @code{IF_COND} is the +expression. + +If the condition is a @code{TREE_LIST}, then the @code{TREE_PURPOSE} is +a statement (usually a @code{DECL_STMT}). Each time the condition is +evaluated, the statement should be executed. Then, the +@code{TREE_VALUE} should be used as the conditional expression itself. +This representation is used to handle C++ code like this: + +@smallexample +if (int i = 7) @dots{} +@end smallexample + +where there is a new local variable (or variables) declared within the +condition. + +The @code{THEN_CLAUSE} represents the statement given by the @code{then} +condition, while the @code{ELSE_CLAUSE} represents the statement given +by the @code{else} condition. + +C++ distinguishes between this and @code{COND_EXPR} for handling templates. + +@item SUBOBJECT + +In a constructor, these nodes are used to mark the point at which a +subobject of @code{this} is fully constructed. If, after this point, an +exception is thrown before a @code{CTOR_STMT} with @code{CTOR_END_P} set +is encountered, the @code{SUBOBJECT_CLEANUP} must be executed. The +cleanups must be executed in the reverse order in which they appear. + +@item SWITCH_STMT + +Used to represent a @code{switch} statement. The @code{SWITCH_STMT_COND} +is the expression on which the switch is occurring. See the documentation +for an @code{IF_STMT} for more information on the representation used +for the condition. The @code{SWITCH_STMT_BODY} is the body of the switch +statement. The @code{SWITCH_STMT_TYPE} is the original type of switch +expression as given in the source, before any compiler conversions. +The @code{SWITCH_STMT_SCOPE} is the statement scope (used in the +C++ front end only). + +There are also two boolean flags used with @code{SWITCH_STMT}. +@code{SWITCH_STMT_ALL_CASES_P} is true if the switch includes a default label +or the case label ranges cover all possible values of the condition +expression. @code{SWITCH_STMT_NO_BREAK_P} is true if there are no +@code{break} statements in the switch. + +@item TRY_BLOCK +Used to represent a @code{try} block. The body of the try block is +given by @code{TRY_STMTS}. Each of the catch blocks is a @code{HANDLER} +node. The first handler is given by @code{TRY_HANDLERS}. Subsequent +handlers are obtained by following the @code{TREE_CHAIN} link from one +handler to the next. The body of the handler is given by +@code{HANDLER_BODY}. + +If @code{CLEANUP_P} holds of the @code{TRY_BLOCK}, then the +@code{TRY_HANDLERS} will not be a @code{HANDLER} node. Instead, it will +be an expression that should be executed if an exception is thrown in +the try block. It must rethrow the exception after executing that code. +And, if an exception is thrown while the expression is executing, +@code{terminate} must be called. + +@item USING_STMT +Used to represent a @code{using} directive. The namespace is given by +@code{USING_STMT_NAMESPACE}, which will be a NAMESPACE_DECL@. This node +is needed inside template functions, to implement using directives +during instantiation. + +@item WHILE_STMT + +Used to represent a @code{while} loop. The @code{WHILE_COND} is the +termination condition for the loop. See the documentation for an +@code{IF_STMT} for more information on the representation used for the +condition. + +The @code{WHILE_BODY} is the body of the loop. + +@end table + +@node C++ Expressions +@subsection C++ Expressions + +This section describes expressions specific to the C and C++ front +ends. + +@table @code +@item TYPEID_EXPR + +Used to represent a @code{typeid} expression. + +@item NEW_EXPR +@itemx VEC_NEW_EXPR + +Used to represent a call to @code{new} and @code{new[]} respectively. + +@item DELETE_EXPR +@itemx VEC_DELETE_EXPR + +Used to represent a call to @code{delete} and @code{delete[]} respectively. + +@item MEMBER_REF + +Represents a reference to a member of a class. + +@item THROW_EXPR + +Represents an instance of @code{throw} in the program. Operand 0, +which is the expression to throw, may be @code{NULL_TREE}. + + +@item AGGR_INIT_EXPR +An @code{AGGR_INIT_EXPR} represents the initialization as the return +value of a function call, or as the result of a constructor. An +@code{AGGR_INIT_EXPR} will only appear as a full-expression, or as the +second operand of a @code{TARGET_EXPR}. @code{AGGR_INIT_EXPR}s have +a representation similar to that of @code{CALL_EXPR}s. You can use +the @code{AGGR_INIT_EXPR_FN} and @code{AGGR_INIT_EXPR_ARG} macros to access +the function to call and the arguments to pass. + +If @code{AGGR_INIT_VIA_CTOR_P} holds of the @code{AGGR_INIT_EXPR}, then +the initialization is via a constructor call. The address of the +@code{AGGR_INIT_EXPR_SLOT} operand, which is always a @code{VAR_DECL}, +is taken, and this value replaces the first argument in the argument +list. + +In either case, the expression is void. + + +@end table diff --git a/gcc/doc/gimple.texi b/gcc/doc/gimple.texi new file mode 100644 index 00000000000..7832fa6ff90 --- /dev/null +++ b/gcc/doc/gimple.texi @@ -0,0 +1,2772 @@ +@c Copyright (C) 2008-2022 Free Software Foundation, Inc. +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node GIMPLE +@chapter GIMPLE +@cindex GIMPLE + +GIMPLE is a three-address representation derived from GENERIC by +breaking down GENERIC expressions into tuples of no more than 3 +operands (with some exceptions like function calls). GIMPLE was +heavily influenced by the SIMPLE IL used by the McCAT compiler +project at McGill University, though we have made some different +choices. For one thing, SIMPLE doesn't support @code{goto}. + +Temporaries are introduced to hold intermediate values needed to +compute complex expressions. Additionally, all the control +structures used in GENERIC are lowered into conditional jumps, +lexical scopes are removed and exception regions are converted +into an on the side exception region tree. + +The compiler pass which converts GENERIC into GIMPLE is referred to as +the @samp{gimplifier}. The gimplifier works recursively, generating +GIMPLE tuples out of the original GENERIC expressions. + +One of the early implementation strategies used for the GIMPLE +representation was to use the same internal data structures used +by front ends to represent parse trees. This simplified +implementation because we could leverage existing functionality +and interfaces. However, GIMPLE is a much more restrictive +representation than abstract syntax trees (AST), therefore it +does not require the full structural complexity provided by the +main tree data structure. + +The GENERIC representation of a function is stored in the +@code{DECL_SAVED_TREE} field of the associated @code{FUNCTION_DECL} +tree node. It is converted to GIMPLE by a call to +@code{gimplify_function_tree}. + +If a front end wants to include language-specific tree codes in the tree +representation which it provides to the back end, it must provide a +definition of @code{LANG_HOOKS_GIMPLIFY_EXPR} which knows how to +convert the front end trees to GIMPLE@. Usually such a hook will involve +much of the same code for expanding front end trees to RTL@. This function +can return fully lowered GIMPLE, or it can return GENERIC trees and let the +main gimplifier lower them the rest of the way; this is often simpler. +GIMPLE that is not fully lowered is known as ``High GIMPLE'' and +consists of the IL before the pass @code{pass_lower_cf}. High GIMPLE +contains some container statements like lexical scopes +(represented by @code{GIMPLE_BIND}) and nested expressions (e.g., +@code{GIMPLE_TRY}), while ``Low GIMPLE'' exposes all of the +implicit jumps for control and exception expressions directly in +the IL and EH region trees. + +The C and C++ front ends currently convert directly from front end +trees to GIMPLE, and hand that off to the back end rather than first +converting to GENERIC@. Their gimplifier hooks know about all the +@code{_STMT} nodes and how to convert them to GENERIC forms. There +was some work done on a genericization pass which would run first, but +the existence of @code{STMT_EXPR} meant that in order to convert all +of the C statements into GENERIC equivalents would involve walking the +entire tree anyway, so it was simpler to lower all the way. This +might change in the future if someone writes an optimization pass +which would work better with higher-level trees, but currently the +optimizers all expect GIMPLE@. + +You can request to dump a C-like representation of the GIMPLE form +with the flag @option{-fdump-tree-gimple}. + +@menu +* Tuple representation:: +* Class hierarchy of GIMPLE statements:: +* GIMPLE instruction set:: +* GIMPLE Exception Handling:: +* Temporaries:: +* Operands:: +* Manipulating GIMPLE statements:: +* Tuple specific accessors:: +* GIMPLE sequences:: +* Sequence iterators:: +* Adding a new GIMPLE statement code:: +* Statement and operand traversals:: +@end menu + +@node Tuple representation +@section Tuple representation +@cindex tuples + +GIMPLE instructions are tuples of variable size divided in two +groups: a header describing the instruction and its locations, +and a variable length body with all the operands. Tuples are +organized into a hierarchy with 3 main classes of tuples. + +@subsection @code{gimple} (gsbase) +@cindex gimple + +This is the root of the hierarchy, it holds basic information +needed by most GIMPLE statements. There are some fields that +may not be relevant to every GIMPLE statement, but those were +moved into the base structure to take advantage of holes left by +other fields (thus making the structure more compact). The +structure takes 4 words (32 bytes) on 64 bit hosts: + +@multitable {@code{references_memory_p}} {Size (bits)} +@item Field @tab Size (bits) +@item @code{code} @tab 8 +@item @code{subcode} @tab 16 +@item @code{no_warning} @tab 1 +@item @code{visited} @tab 1 +@item @code{nontemporal_move} @tab 1 +@item @code{plf} @tab 2 +@item @code{modified} @tab 1 +@item @code{has_volatile_ops} @tab 1 +@item @code{references_memory_p} @tab 1 +@item @code{uid} @tab 32 +@item @code{location} @tab 32 +@item @code{num_ops} @tab 32 +@item @code{bb} @tab 64 +@item @code{block} @tab 63 +@item Total size @tab 32 bytes +@end multitable + +@itemize @bullet +@item @code{code} +Main identifier for a GIMPLE instruction. + +@item @code{subcode} +Used to distinguish different variants of the same basic +instruction or provide flags applicable to a given code. The +@code{subcode} flags field has different uses depending on the code of +the instruction, but mostly it distinguishes instructions of the +same family. The most prominent use of this field is in +assignments, where subcode indicates the operation done on the +RHS of the assignment. For example, a = b + c is encoded as +@code{GIMPLE_ASSIGN }. + +@item @code{no_warning} +Bitflag to indicate whether a warning has already been issued on +this statement. + +@item @code{visited} +General purpose ``visited'' marker. Set and cleared by each pass +when needed. + +@item @code{nontemporal_move} +Bitflag used in assignments that represent non-temporal moves. +Although this bitflag is only used in assignments, it was moved +into the base to take advantage of the bit holes left by the +previous fields. + +@item @code{plf} +Pass Local Flags. This 2-bit mask can be used as general purpose +markers by any pass. Passes are responsible for clearing and +setting these two flags accordingly. + +@item @code{modified} +Bitflag to indicate whether the statement has been modified. +Used mainly by the operand scanner to determine when to re-scan a +statement for operands. + +@item @code{has_volatile_ops} +Bitflag to indicate whether this statement contains operands that +have been marked volatile. + +@item @code{references_memory_p} +Bitflag to indicate whether this statement contains memory +references (i.e., its operands are either global variables, or +pointer dereferences or anything that must reside in memory). + +@item @code{uid} +This is an unsigned integer used by passes that want to assign +IDs to every statement. These IDs must be assigned and used by +each pass. + +@item @code{location} +This is a @code{location_t} identifier to specify source code +location for this statement. It is inherited from the front +end. + +@item @code{num_ops} +Number of operands that this statement has. This specifies the +size of the operand vector embedded in the tuple. Only used in +some tuples, but it is declared in the base tuple to take +advantage of the 32-bit hole left by the previous fields. + +@item @code{bb} +Basic block holding the instruction. + +@item @code{block} +Lexical block holding this statement. Also used for debug +information generation. +@end itemize + +@subsection @code{gimple_statement_with_ops} +@cindex gimple_statement_with_ops + +This tuple is actually split in two: +@code{gimple_statement_with_ops_base} and +@code{gimple_statement_with_ops}. This is needed to accommodate the +way the operand vector is allocated. The operand vector is +defined to be an array of 1 element. So, to allocate a dynamic +number of operands, the memory allocator (@code{gimple_alloc}) simply +allocates enough memory to hold the structure itself plus @code{N +- 1} operands which run ``off the end'' of the structure. For +example, to allocate space for a tuple with 3 operands, +@code{gimple_alloc} reserves @code{sizeof (struct +gimple_statement_with_ops) + 2 * sizeof (tree)} bytes. + +On the other hand, several fields in this tuple need to be shared +with the @code{gimple_statement_with_memory_ops} tuple. So, these +common fields are placed in @code{gimple_statement_with_ops_base} which +is then inherited from the other two tuples. + + +@multitable {@code{def_ops}} {48 + 8 * @code{num_ops} bytes} +@item @code{gsbase} @tab 256 +@item @code{def_ops} @tab 64 +@item @code{use_ops} @tab 64 +@item @code{op} @tab @code{num_ops} * 64 +@item Total size @tab 48 + 8 * @code{num_ops} bytes +@end multitable + +@itemize @bullet +@item @code{gsbase} +Inherited from @code{struct gimple}. + +@item @code{def_ops} +Array of pointers into the operand array indicating all the slots that +contain a variable written-to by the statement. This array is +also used for immediate use chaining. Note that it would be +possible to not rely on this array, but the changes required to +implement this are pretty invasive. + +@item @code{use_ops} +Similar to @code{def_ops} but for variables read by the statement. + +@item @code{op} +Array of trees with @code{num_ops} slots. +@end itemize + +@subsection @code{gimple_statement_with_memory_ops} + +This tuple is essentially identical to @code{gimple_statement_with_ops}, +except that it contains 4 additional fields to hold vectors +related memory stores and loads. Similar to the previous case, +the structure is split in two to accommodate for the operand +vector (@code{gimple_statement_with_memory_ops_base} and +@code{gimple_statement_with_memory_ops}). + + +@multitable {@code{vdef_ops}} {80 + 8 * @code{num_ops} bytes} +@item Field @tab Size (bits) +@item @code{gsbase} @tab 256 +@item @code{def_ops} @tab 64 +@item @code{use_ops} @tab 64 +@item @code{vdef_ops} @tab 64 +@item @code{vuse_ops} @tab 64 +@item @code{stores} @tab 64 +@item @code{loads} @tab 64 +@item @code{op} @tab @code{num_ops} * 64 +@item Total size @tab 80 + 8 * @code{num_ops} bytes +@end multitable + +@itemize @bullet +@item @code{vdef_ops} +Similar to @code{def_ops} but for @code{VDEF} operators. There is +one entry per memory symbol written by this statement. This is +used to maintain the memory SSA use-def and def-def chains. + +@item @code{vuse_ops} +Similar to @code{use_ops} but for @code{VUSE} operators. There is +one entry per memory symbol loaded by this statement. This is +used to maintain the memory SSA use-def chains. + +@item @code{stores} +Bitset with all the UIDs for the symbols written-to by the +statement. This is different than @code{vdef_ops} in that all the +affected symbols are mentioned in this set. If memory +partitioning is enabled, the @code{vdef_ops} vector will refer to memory +partitions. Furthermore, no SSA information is stored in this +set. + +@item @code{loads} +Similar to @code{stores}, but for memory loads. (Note that there +is some amount of redundancy here, it should be possible to +reduce memory utilization further by removing these sets). +@end itemize + +All the other tuples are defined in terms of these three basic +ones. Each tuple will add some fields. + + +@node Class hierarchy of GIMPLE statements +@section Class hierarchy of GIMPLE statements +@cindex GIMPLE class hierarchy + +The following diagram shows the C++ inheritance hierarchy of statement +kinds, along with their relationships to @code{GSS_} values (layouts) and +@code{GIMPLE_} values (codes): + +@smallexample + gimple + | layout: GSS_BASE + | used for 4 codes: GIMPLE_ERROR_MARK + | GIMPLE_NOP + | GIMPLE_OMP_SECTIONS_SWITCH + | GIMPLE_PREDICT + | + + gimple_statement_with_ops_base + | | (no GSS layout) + | | + | + gimple_statement_with_ops + | | | layout: GSS_WITH_OPS + | | | + | | + gcond + | | | code: GIMPLE_COND + | | | + | | + gdebug + | | | code: GIMPLE_DEBUG + | | | + | | + ggoto + | | | code: GIMPLE_GOTO + | | | + | | + glabel + | | | code: GIMPLE_LABEL + | | | + | | + gswitch + | | code: GIMPLE_SWITCH + | | + | + gimple_statement_with_memory_ops_base + | | layout: GSS_WITH_MEM_OPS_BASE + | | + | + gimple_statement_with_memory_ops + | | | layout: GSS_WITH_MEM_OPS + | | | + | | + gassign + | | | code GIMPLE_ASSIGN + | | | + | | + greturn + | | code GIMPLE_RETURN + | | + | + gcall + | | layout: GSS_CALL, code: GIMPLE_CALL + | | + | + gasm + | | layout: GSS_ASM, code: GIMPLE_ASM + | | + | + gtransaction + | layout: GSS_TRANSACTION, code: GIMPLE_TRANSACTION + | + + gimple_statement_omp + | | layout: GSS_OMP. Used for code GIMPLE_OMP_SECTION + | | + | + gomp_critical + | | layout: GSS_OMP_CRITICAL, code: GIMPLE_OMP_CRITICAL + | | + | + gomp_for + | | layout: GSS_OMP_FOR, code: GIMPLE_OMP_FOR + | | + | + gomp_parallel_layout + | | | layout: GSS_OMP_PARALLEL_LAYOUT + | | | + | | + gimple_statement_omp_taskreg + | | | | + | | | + gomp_parallel + | | | | code: GIMPLE_OMP_PARALLEL + | | | | + | | | + gomp_task + | | | code: GIMPLE_OMP_TASK + | | | + | | + gimple_statement_omp_target + | | code: GIMPLE_OMP_TARGET + | | + | + gomp_sections + | | layout: GSS_OMP_SECTIONS, code: GIMPLE_OMP_SECTIONS + | | + | + gimple_statement_omp_single_layout + | | layout: GSS_OMP_SINGLE_LAYOUT + | | + | + gomp_single + | | code: GIMPLE_OMP_SINGLE + | | + | + gomp_teams + | code: GIMPLE_OMP_TEAMS + | + + gbind + | layout: GSS_BIND, code: GIMPLE_BIND + | + + gcatch + | layout: GSS_CATCH, code: GIMPLE_CATCH + | + + geh_filter + | layout: GSS_EH_FILTER, code: GIMPLE_EH_FILTER + | + + geh_else + | layout: GSS_EH_ELSE, code: GIMPLE_EH_ELSE + | + + geh_mnt + | layout: GSS_EH_MNT, code: GIMPLE_EH_MUST_NOT_THROW + | + + gphi + | layout: GSS_PHI, code: GIMPLE_PHI + | + + gimple_statement_eh_ctrl + | | layout: GSS_EH_CTRL + | | + | + gresx + | | code: GIMPLE_RESX + | | + | + geh_dispatch + | code: GIMPLE_EH_DISPATCH + | + + gtry + | layout: GSS_TRY, code: GIMPLE_TRY + | + + gimple_statement_wce + | layout: GSS_WCE, code: GIMPLE_WITH_CLEANUP_EXPR + | + + gomp_continue + | layout: GSS_OMP_CONTINUE, code: GIMPLE_OMP_CONTINUE + | + + gomp_atomic_load + | layout: GSS_OMP_ATOMIC_LOAD, code: GIMPLE_OMP_ATOMIC_LOAD + | + + gimple_statement_omp_atomic_store_layout + | layout: GSS_OMP_ATOMIC_STORE_LAYOUT, + | code: GIMPLE_OMP_ATOMIC_STORE + | + + gomp_atomic_store + | code: GIMPLE_OMP_ATOMIC_STORE + | + + gomp_return + code: GIMPLE_OMP_RETURN +@end smallexample + + +@node GIMPLE instruction set +@section GIMPLE instruction set +@cindex GIMPLE instruction set + +The following table briefly describes the GIMPLE instruction set. + +@multitable {@code{GIMPLE_OMP_SECTIONS_SWITCH}} {High GIMPLE} {Low GIMPLE} +@item Instruction @tab High GIMPLE @tab Low GIMPLE +@item @code{GIMPLE_ASM} @tab x @tab x +@item @code{GIMPLE_ASSIGN} @tab x @tab x +@item @code{GIMPLE_BIND} @tab x @tab +@item @code{GIMPLE_CALL} @tab x @tab x +@item @code{GIMPLE_CATCH} @tab x @tab +@item @code{GIMPLE_COND} @tab x @tab x +@item @code{GIMPLE_DEBUG} @tab x @tab x +@item @code{GIMPLE_EH_FILTER} @tab x @tab +@item @code{GIMPLE_GOTO} @tab x @tab x +@item @code{GIMPLE_LABEL} @tab x @tab x +@item @code{GIMPLE_NOP} @tab x @tab x +@item @code{GIMPLE_OMP_ATOMIC_LOAD} @tab x @tab x +@item @code{GIMPLE_OMP_ATOMIC_STORE} @tab x @tab x +@item @code{GIMPLE_OMP_CONTINUE} @tab x @tab x +@item @code{GIMPLE_OMP_CRITICAL} @tab x @tab x +@item @code{GIMPLE_OMP_FOR} @tab x @tab x +@item @code{GIMPLE_OMP_MASTER} @tab x @tab x +@item @code{GIMPLE_OMP_ORDERED} @tab x @tab x +@item @code{GIMPLE_OMP_PARALLEL} @tab x @tab x +@item @code{GIMPLE_OMP_RETURN} @tab x @tab x +@item @code{GIMPLE_OMP_SECTION} @tab x @tab x +@item @code{GIMPLE_OMP_SECTIONS} @tab x @tab x +@item @code{GIMPLE_OMP_SECTIONS_SWITCH} @tab x @tab x +@item @code{GIMPLE_OMP_SINGLE} @tab x @tab x +@item @code{GIMPLE_PHI} @tab @tab x +@item @code{GIMPLE_RESX} @tab @tab x +@item @code{GIMPLE_RETURN} @tab x @tab x +@item @code{GIMPLE_SWITCH} @tab x @tab x +@item @code{GIMPLE_TRY} @tab x @tab +@end multitable + +@node GIMPLE Exception Handling +@section Exception Handling +@cindex GIMPLE Exception Handling + +Other exception handling constructs are represented using +@code{GIMPLE_TRY_CATCH}. @code{GIMPLE_TRY_CATCH} has two operands. The +first operand is a sequence of statements to execute. If executing +these statements does not throw an exception, then the second operand +is ignored. Otherwise, if an exception is thrown, then the second +operand of the @code{GIMPLE_TRY_CATCH} is checked. The second +operand may have the following forms: + +@enumerate + +@item A sequence of statements to execute. When an exception occurs, +these statements are executed, and then the exception is rethrown. + +@item A sequence of @code{GIMPLE_CATCH} statements. Each +@code{GIMPLE_CATCH} has a list of applicable exception types and +handler code. If the thrown exception matches one of the caught +types, the associated handler code is executed. If the handler +code falls off the bottom, execution continues after the original +@code{GIMPLE_TRY_CATCH}. + +@item A @code{GIMPLE_EH_FILTER} statement. This has a list of +permitted exception types, and code to handle a match failure. If the +thrown exception does not match one of the allowed types, the +associated match failure code is executed. If the thrown exception +does match, it continues unwinding the stack looking for the next +handler. + +@end enumerate + +Currently throwing an exception is not directly represented in +GIMPLE, since it is implemented by calling a function. At some +point in the future we will want to add some way to express that +the call will throw an exception of a known type. + +Just before running the optimizers, the compiler lowers the +high-level EH constructs above into a set of @samp{goto}s, magic +labels, and EH regions. Continuing to unwind at the end of a +cleanup is represented with a @code{GIMPLE_RESX}. + + +@node Temporaries +@section Temporaries +@cindex Temporaries + +When gimplification encounters a subexpression that is too +complex, it creates a new temporary variable to hold the value of +the subexpression, and adds a new statement to initialize it +before the current statement. These special temporaries are known +as @samp{expression temporaries}, and are allocated using +@code{get_formal_tmp_var}. The compiler tries to always evaluate +identical expressions into the same temporary, to simplify +elimination of redundant calculations. + +We can only use expression temporaries when we know that it will +not be reevaluated before its value is used, and that it will not +be otherwise modified@footnote{These restrictions are derived +from those in Morgan 4.8.}. Other temporaries can be allocated +using @code{get_initialized_tmp_var} or @code{create_tmp_var}. + +Currently, an expression like @code{a = b + 5} is not reduced any +further. We tried converting it to something like +@smallexample +T1 = b + 5; +a = T1; +@end smallexample +but this bloated the representation for minimal benefit. However, a +variable which must live in memory cannot appear in an expression; its +value is explicitly loaded into a temporary first. Similarly, storing +the value of an expression to a memory variable goes through a +temporary. + +@node Operands +@section Operands +@cindex Operands + +In general, expressions in GIMPLE consist of an operation and the +appropriate number of simple operands; these operands must either be a +GIMPLE rvalue (@code{is_gimple_val}), i.e.@: a constant or a register +variable. More complex operands are factored out into temporaries, so +that +@smallexample +a = b + c + d +@end smallexample +becomes +@smallexample +T1 = b + c; +a = T1 + d; +@end smallexample + +The same rule holds for arguments to a @code{GIMPLE_CALL}. + +The target of an assignment is usually a variable, but can also be a +@code{MEM_REF} or a compound lvalue as described below. + +@menu +* Compound Expressions:: +* Compound Lvalues:: +* Conditional Expressions:: +* Logical Operators:: +@end menu + +@node Compound Expressions +@subsection Compound Expressions +@cindex Compound Expressions + +The left-hand side of a C comma expression is simply moved into a separate +statement. + +@node Compound Lvalues +@subsection Compound Lvalues +@cindex Compound Lvalues + +Currently compound lvalues involving array and structure field references +are not broken down; an expression like @code{a.b[2] = 42} is not reduced +any further (though complex array subscripts are). This restriction is a +workaround for limitations in later optimizers; if we were to convert this +to + +@smallexample +T1 = &a.b; +T1[2] = 42; +@end smallexample + +alias analysis would not remember that the reference to @code{T1[2]} came +by way of @code{a.b}, so it would think that the assignment could alias +another member of @code{a}; this broke @code{struct-alias-1.c}. Future +optimizer improvements may make this limitation unnecessary. + +@node Conditional Expressions +@subsection Conditional Expressions +@cindex Conditional Expressions + +A C @code{?:} expression is converted into an @code{if} statement with +each branch assigning to the same temporary. So, + +@smallexample +a = b ? c : d; +@end smallexample +becomes +@smallexample +if (b == 1) + T1 = c; +else + T1 = d; +a = T1; +@end smallexample + +The GIMPLE level if-conversion pass re-introduces @code{?:} +expression, if appropriate. It is used to vectorize loops with +conditions using vector conditional operations. + +Note that in GIMPLE, @code{if} statements are represented using +@code{GIMPLE_COND}, as described below. + +@node Logical Operators +@subsection Logical Operators +@cindex Logical Operators + +Except when they appear in the condition operand of a +@code{GIMPLE_COND}, logical `and' and `or' operators are simplified +as follows: @code{a = b && c} becomes + +@smallexample +T1 = (bool)b; +if (T1 == true) + T1 = (bool)c; +a = T1; +@end smallexample + +Note that @code{T1} in this example cannot be an expression temporary, +because it has two different assignments. + +@subsection Manipulating operands + +All gimple operands are of type @code{tree}. But only certain +types of trees are allowed to be used as operand tuples. Basic +validation is controlled by the function +@code{get_gimple_rhs_class}, which given a tree code, returns an +@code{enum} with the following values of type @code{enum +gimple_rhs_class} + +@itemize @bullet +@item @code{GIMPLE_INVALID_RHS} +The tree cannot be used as a GIMPLE operand. + +@item @code{GIMPLE_TERNARY_RHS} +The tree is a valid GIMPLE ternary operation. + +@item @code{GIMPLE_BINARY_RHS} +The tree is a valid GIMPLE binary operation. + +@item @code{GIMPLE_UNARY_RHS} +The tree is a valid GIMPLE unary operation. + +@item @code{GIMPLE_SINGLE_RHS} +The tree is a single object, that cannot be split into simpler +operands (for instance, @code{SSA_NAME}, @code{VAR_DECL}, @code{COMPONENT_REF}, etc). + +This operand class also acts as an escape hatch for tree nodes +that may be flattened out into the operand vector, but would need +more than two slots on the RHS. For instance, a @code{COND_EXPR} +expression of the form @code{(a op b) ? x : y} could be flattened +out on the operand vector using 4 slots, but it would also +require additional processing to distinguish @code{c = a op b} +from @code{c = a op b ? x : y}. Something similar occurs with +@code{ASSERT_EXPR}. In time, these special case tree +expressions should be flattened into the operand vector. +@end itemize + +For tree nodes in the categories @code{GIMPLE_TERNARY_RHS}, +@code{GIMPLE_BINARY_RHS} and @code{GIMPLE_UNARY_RHS}, they cannot be +stored inside tuples directly. They first need to be flattened and +separated into individual components. For instance, given the GENERIC +expression + +@smallexample +a = b + c +@end smallexample + +its tree representation is: + +@smallexample +MODIFY_EXPR , PLUS_EXPR , VAR_DECL >> +@end smallexample + +In this case, the GIMPLE form for this statement is logically +identical to its GENERIC form but in GIMPLE, the @code{PLUS_EXPR} +on the RHS of the assignment is not represented as a tree, +instead the two operands are taken out of the @code{PLUS_EXPR} sub-tree +and flattened into the GIMPLE tuple as follows: + +@smallexample +GIMPLE_ASSIGN , VAR_DECL , VAR_DECL > +@end smallexample + +@subsection Operand vector allocation + +The operand vector is stored at the bottom of the three tuple +structures that accept operands. This means, that depending on +the code of a given statement, its operand vector will be at +different offsets from the base of the structure. To access +tuple operands use the following accessors + +@deftypefn {GIMPLE function} unsigned gimple_num_ops (gimple g) +Returns the number of operands in statement G. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_op (gimple g, unsigned i) +Returns operand @code{I} from statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_ops (gimple g) +Returns a pointer into the operand vector for statement @code{G}. This +is computed using an internal table called @code{gimple_ops_offset_}[]. +This table is indexed by the gimple code of @code{G}. + +When the compiler is built, this table is filled-in using the +sizes of the structures used by each statement code defined in +gimple.def. Since the operand vector is at the bottom of the +structure, for a gimple code @code{C} the offset is computed as sizeof +(struct-of @code{C}) - sizeof (tree). + +This mechanism adds one memory indirection to every access when +using @code{gimple_op}(), if this becomes a bottleneck, a pass can +choose to memoize the result from @code{gimple_ops}() and use that to +access the operands. +@end deftypefn + +@subsection Operand validation + +When adding a new operand to a gimple statement, the operand will +be validated according to what each tuple accepts in its operand +vector. These predicates are called by the +@code{gimple_@var{name}_set_...()}. Each tuple will use one of the +following predicates (Note, this list is not exhaustive): + +@deftypefn {GIMPLE function} bool is_gimple_val (tree t) +Returns true if t is a "GIMPLE value", which are all the +non-addressable stack variables (variables for which +@code{is_gimple_reg} returns true) and constants (expressions for which +@code{is_gimple_min_invariant} returns true). +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_addressable (tree t) +Returns true if t is a symbol or memory reference whose address +can be taken. +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_asm_val (tree t) +Similar to @code{is_gimple_val} but it also accepts hard registers. +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_call_addr (tree t) +Return true if t is a valid expression to use as the function +called by a @code{GIMPLE_CALL}. +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_mem_ref_addr (tree t) +Return true if t is a valid expression to use as first operand +of a @code{MEM_REF} expression. +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_constant (tree t) +Return true if t is a valid gimple constant. +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_min_invariant (tree t) +Return true if t is a valid minimal invariant. This is different +from constants, in that the specific value of t may not be known +at compile time, but it is known that it doesn't change (e.g., +the address of a function local variable). +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_ip_invariant (tree t) +Return true if t is an interprocedural invariant. This means that t +is a valid invariant in all functions (e.g.@: it can be an address of a +global variable but not of a local one). +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_ip_invariant_address (tree t) +Return true if t is an @code{ADDR_EXPR} that does not change once the +program is running (and which is valid in all functions). +@end deftypefn + + +@subsection Statement validation + +@deftypefn {GIMPLE function} bool is_gimple_assign (gimple g) +Return true if the code of g is @code{GIMPLE_ASSIGN}. +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_call (gimple g) +Return true if the code of g is @code{GIMPLE_CALL}. +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_debug (gimple g) +Return true if the code of g is @code{GIMPLE_DEBUG}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_assign_cast_p (const_gimple g) +Return true if g is a @code{GIMPLE_ASSIGN} that performs a type cast +operation. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_debug_bind_p (gimple g) +Return true if g is a @code{GIMPLE_DEBUG} that binds the value of an +expression to a variable. +@end deftypefn + +@deftypefn {GIMPLE function} bool is_gimple_omp (gimple g) +Return true if g is any of the OpenMP codes. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_debug_begin_stmt_p (gimple g) +Return true if g is a @code{GIMPLE_DEBUG} that marks the beginning of +a source statement. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_debug_inline_entry_p (gimple g) +Return true if g is a @code{GIMPLE_DEBUG} that marks the entry +point of an inlined function. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_debug_nonbind_marker_p (gimple g) +Return true if g is a @code{GIMPLE_DEBUG} that marks a program location, +without any variable binding. +@end deftypefn + +@node Manipulating GIMPLE statements +@section Manipulating GIMPLE statements +@cindex Manipulating GIMPLE statements + +This section documents all the functions available to handle each +of the GIMPLE instructions. + +@subsection Common accessors +The following are common accessors for gimple statements. + +@deftypefn {GIMPLE function} {enum gimple_code} gimple_code (gimple g) +Return the code for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} basic_block gimple_bb (gimple g) +Return the basic block to which statement @code{G} belongs to. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_block (gimple g) +Return the lexical scope block holding statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {enum tree_code} gimple_expr_code (gimple stmt) +Return the tree code for the expression computed by @code{STMT}. This +is only meaningful for @code{GIMPLE_CALL}, @code{GIMPLE_ASSIGN} and +@code{GIMPLE_COND}. If @code{STMT} is @code{GIMPLE_CALL}, it will return @code{CALL_EXPR}. +For @code{GIMPLE_COND}, it returns the code of the comparison predicate. +For @code{GIMPLE_ASSIGN} it returns the code of the operation performed +by the @code{RHS} of the assignment. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_block (gimple g, tree block) +Set the lexical scope block of @code{G} to @code{BLOCK}. +@end deftypefn + +@deftypefn {GIMPLE function} location_t gimple_locus (gimple g) +Return locus information for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_locus (gimple g, location_t locus) +Set locus information for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_locus_empty_p (gimple g) +Return true if @code{G} does not have locus information. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_no_warning_p (gimple stmt) +Return true if no warnings should be emitted for statement @code{STMT}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_visited (gimple stmt, bool visited_p) +Set the visited status on statement @code{STMT} to @code{VISITED_P}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_visited_p (gimple stmt) +Return the visited status on statement @code{STMT}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_plf (gimple stmt, enum plf_mask plf, bool val_p) +Set pass local flag @code{PLF} on statement @code{STMT} to @code{VAL_P}. +@end deftypefn + +@deftypefn {GIMPLE function} {unsigned int} gimple_plf (gimple stmt, enum plf_mask plf) +Return the value of pass local flag @code{PLF} on statement @code{STMT}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_has_ops (gimple g) +Return true if statement @code{G} has register or memory operands. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_has_mem_ops (gimple g) +Return true if statement @code{G} has memory operands. +@end deftypefn + +@deftypefn {GIMPLE function} unsigned gimple_num_ops (gimple g) +Return the number of operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_ops (gimple g) +Return the array of operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_op (gimple g, unsigned i) +Return operand @code{I} for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_op_ptr (gimple g, unsigned i) +Return a pointer to operand @code{I} for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_op (gimple g, unsigned i, tree op) +Set operand @code{I} of statement @code{G} to @code{OP}. +@end deftypefn + +@deftypefn {GIMPLE function} bitmap gimple_addresses_taken (gimple stmt) +Return the set of symbols that have had their address taken by +@code{STMT}. +@end deftypefn + +@deftypefn {GIMPLE function} {struct def_optype_d *} gimple_def_ops (gimple g) +Return the set of @code{DEF} operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_def_ops (gimple g, struct def_optype_d *def) +Set @code{DEF} to be the set of @code{DEF} operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {struct use_optype_d *} gimple_use_ops (gimple g) +Return the set of @code{USE} operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_use_ops (gimple g, struct use_optype_d *use) +Set @code{USE} to be the set of @code{USE} operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {struct voptype_d *} gimple_vuse_ops (gimple g) +Return the set of @code{VUSE} operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_vuse_ops (gimple g, struct voptype_d *ops) +Set @code{OPS} to be the set of @code{VUSE} operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {struct voptype_d *} gimple_vdef_ops (gimple g) +Return the set of @code{VDEF} operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_vdef_ops (gimple g, struct voptype_d *ops) +Set @code{OPS} to be the set of @code{VDEF} operands for statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} bitmap gimple_loaded_syms (gimple g) +Return the set of symbols loaded by statement @code{G}. Each element of +the set is the @code{DECL_UID} of the corresponding symbol. +@end deftypefn + +@deftypefn {GIMPLE function} bitmap gimple_stored_syms (gimple g) +Return the set of symbols stored by statement @code{G}. Each element of +the set is the @code{DECL_UID} of the corresponding symbol. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_modified_p (gimple g) +Return true if statement @code{G} has operands and the modified field +has been set. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_has_volatile_ops (gimple stmt) +Return true if statement @code{STMT} contains volatile operands. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_set_has_volatile_ops (gimple stmt, bool volatilep) +Return true if statement @code{STMT} contains volatile operands. +@end deftypefn + +@deftypefn {GIMPLE function} void update_stmt (gimple s) +Mark statement @code{S} as modified, and update it. +@end deftypefn + +@deftypefn {GIMPLE function} void update_stmt_if_modified (gimple s) +Update statement @code{S} if it has been marked modified. +@end deftypefn + +@deftypefn {GIMPLE function} gimple gimple_copy (gimple stmt) +Return a deep copy of statement @code{STMT}. +@end deftypefn + +@node Tuple specific accessors +@section Tuple specific accessors +@cindex Tuple specific accessors + +@menu +* @code{GIMPLE_ASM}:: +* @code{GIMPLE_ASSIGN}:: +* @code{GIMPLE_BIND}:: +* @code{GIMPLE_CALL}:: +* @code{GIMPLE_CATCH}:: +* @code{GIMPLE_COND}:: +* @code{GIMPLE_DEBUG}:: +* @code{GIMPLE_EH_FILTER}:: +* @code{GIMPLE_LABEL}:: +* @code{GIMPLE_GOTO}:: +* @code{GIMPLE_NOP}:: +* @code{GIMPLE_OMP_ATOMIC_LOAD}:: +* @code{GIMPLE_OMP_ATOMIC_STORE}:: +* @code{GIMPLE_OMP_CONTINUE}:: +* @code{GIMPLE_OMP_CRITICAL}:: +* @code{GIMPLE_OMP_FOR}:: +* @code{GIMPLE_OMP_MASTER}:: +* @code{GIMPLE_OMP_ORDERED}:: +* @code{GIMPLE_OMP_PARALLEL}:: +* @code{GIMPLE_OMP_RETURN}:: +* @code{GIMPLE_OMP_SECTION}:: +* @code{GIMPLE_OMP_SECTIONS}:: +* @code{GIMPLE_OMP_SINGLE}:: +* @code{GIMPLE_PHI}:: +* @code{GIMPLE_RESX}:: +* @code{GIMPLE_RETURN}:: +* @code{GIMPLE_SWITCH}:: +* @code{GIMPLE_TRY}:: +* @code{GIMPLE_WITH_CLEANUP_EXPR}:: +@end menu + + +@node @code{GIMPLE_ASM} +@subsection @code{GIMPLE_ASM} +@cindex @code{GIMPLE_ASM} + +@deftypefn {GIMPLE function} gasm *gimple_build_asm_vec ( @ +const char *string, vec *inputs, @ +vec *outputs, vec *clobbers, @ +vec *labels) +Build a @code{GIMPLE_ASM} statement. This statement is used for +building in-line assembly constructs. @code{STRING} is the assembly +code. @code{INPUTS}, @code{OUTPUTS}, @code{CLOBBERS} and @code{LABELS} +are the inputs, outputs, clobbered registers and labels. +@end deftypefn + +@deftypefn {GIMPLE function} unsigned gimple_asm_ninputs (const gasm *g) +Return the number of input operands for @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} unsigned gimple_asm_noutputs (const gasm *g) +Return the number of output operands for @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} unsigned gimple_asm_nclobbers (const gasm *g) +Return the number of clobber operands for @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_asm_input_op (const gasm *g, @ +unsigned index) +Return input operand @code{INDEX} of @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_asm_set_input_op (gasm *g, @ +unsigned index, tree in_op) +Set @code{IN_OP} to be input operand @code{INDEX} in @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_asm_output_op (const gasm *g, @ +unsigned index) +Return output operand @code{INDEX} of @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_asm_set_output_op (gasm *g, @ +unsigned index, tree out_op) +Set @code{OUT_OP} to be output operand @code{INDEX} in @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_asm_clobber_op (const gasm *g, @ +unsigned index) +Return clobber operand @code{INDEX} of @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_asm_set_clobber_op (gasm *g, @ +unsigned index, tree clobber_op) +Set @code{CLOBBER_OP} to be clobber operand @code{INDEX} in @code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {const char *} gimple_asm_string (const gasm *g) +Return the string representing the assembly instruction in +@code{GIMPLE_ASM} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_asm_volatile_p (const gasm *g) +Return true if @code{G} is an asm statement marked volatile. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_asm_set_volatile (gasm *g, @ +bool volatile_p) +Mark asm statement @code{G} as volatile or non-volatile based on +@code{VOLATILE_P}. +@end deftypefn + +@node @code{GIMPLE_ASSIGN} +@subsection @code{GIMPLE_ASSIGN} +@cindex @code{GIMPLE_ASSIGN} + +@deftypefn {GIMPLE function} gassign *gimple_build_assign (tree lhs, tree rhs) +Build a @code{GIMPLE_ASSIGN} statement. The left-hand side is an lvalue +passed in lhs. The right-hand side can be either a unary or +binary tree expression. The expression tree rhs will be +flattened and its operands assigned to the corresponding operand +slots in the new statement. This function is useful when you +already have a tree expression that you want to convert into a +tuple. However, try to avoid building expression trees for the +sole purpose of calling this function. If you already have the +operands in separate trees, it is better to use +@code{gimple_build_assign} with @code{enum tree_code} argument and separate +arguments for each operand. +@end deftypefn + +@deftypefn {GIMPLE function} gassign *gimple_build_assign @ +(tree lhs, enum tree_code subcode, tree op1, tree op2, tree op3) +This function is similar to two operand @code{gimple_build_assign}, +but is used to build a @code{GIMPLE_ASSIGN} statement when the operands of the +right-hand side of the assignment are already split into +different operands. + +The left-hand side is an lvalue passed in lhs. Subcode is the +@code{tree_code} for the right-hand side of the assignment. Op1, op2 and op3 +are the operands. +@end deftypefn + +@deftypefn {GIMPLE function} gassign *gimple_build_assign @ +(tree lhs, enum tree_code subcode, tree op1, tree op2) +Like the above 5 operand @code{gimple_build_assign}, but with the last +argument @code{NULL} - this overload should not be used for +@code{GIMPLE_TERNARY_RHS} assignments. +@end deftypefn + +@deftypefn {GIMPLE function} gassign *gimple_build_assign @ +(tree lhs, enum tree_code subcode, tree op1) +Like the above 4 operand @code{gimple_build_assign}, but with the last +argument @code{NULL} - this overload should be used only for +@code{GIMPLE_UNARY_RHS} and @code{GIMPLE_SINGLE_RHS} assignments. +@end deftypefn + +@deftypefn {GIMPLE function} gimple gimplify_assign (tree dst, tree src, gimple_seq *seq_p) +Build a new @code{GIMPLE_ASSIGN} tuple and append it to the end of +@code{*SEQ_P}. +@end deftypefn + +@code{DST}/@code{SRC} are the destination and source respectively. You can +pass ungimplified trees in @code{DST} or @code{SRC}, in which +case they will be converted to a gimple operand if necessary. + +This function returns the newly created @code{GIMPLE_ASSIGN} tuple. + +@deftypefn {GIMPLE function} {enum tree_code} gimple_assign_rhs_code (gimple g) +Return the code of the expression computed on the @code{RHS} of +assignment statement @code{G}. +@end deftypefn + + +@deftypefn {GIMPLE function} {enum gimple_rhs_class} gimple_assign_rhs_class (gimple g) +Return the gimple rhs class of the code for the expression +computed on the rhs of assignment statement @code{G}. This will never +return @code{GIMPLE_INVALID_RHS}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_assign_lhs (gimple g) +Return the @code{LHS} of assignment statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_assign_lhs_ptr (gimple g) +Return a pointer to the @code{LHS} of assignment statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_assign_rhs1 (gimple g) +Return the first operand on the @code{RHS} of assignment statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_assign_rhs1_ptr (gimple g) +Return the address of the first operand on the @code{RHS} of assignment +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_assign_rhs2 (gimple g) +Return the second operand on the @code{RHS} of assignment statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_assign_rhs2_ptr (gimple g) +Return the address of the second operand on the @code{RHS} of assignment +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_assign_rhs3 (gimple g) +Return the third operand on the @code{RHS} of assignment statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_assign_rhs3_ptr (gimple g) +Return the address of the third operand on the @code{RHS} of assignment +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_assign_set_lhs (gimple g, tree lhs) +Set @code{LHS} to be the @code{LHS} operand of assignment statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_assign_set_rhs1 (gimple g, tree rhs) +Set @code{RHS} to be the first operand on the @code{RHS} of assignment +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_assign_set_rhs2 (gimple g, tree rhs) +Set @code{RHS} to be the second operand on the @code{RHS} of assignment +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_assign_set_rhs3 (gimple g, tree rhs) +Set @code{RHS} to be the third operand on the @code{RHS} of assignment +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_assign_cast_p (const_gimple s) +Return true if @code{S} is a type-cast assignment. +@end deftypefn + + +@node @code{GIMPLE_BIND} +@subsection @code{GIMPLE_BIND} +@cindex @code{GIMPLE_BIND} + +@deftypefn {GIMPLE function} gbind *gimple_build_bind (tree vars, @ +gimple_seq body) +Build a @code{GIMPLE_BIND} statement with a list of variables in @code{VARS} +and a body of statements in sequence @code{BODY}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_bind_vars (const gbind *g) +Return the variables declared in the @code{GIMPLE_BIND} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_bind_set_vars (gbind *g, tree vars) +Set @code{VARS} to be the set of variables declared in the @code{GIMPLE_BIND} +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_bind_append_vars (gbind *g, tree vars) +Append @code{VARS} to the set of variables declared in the @code{GIMPLE_BIND} +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_bind_body (gbind *g) +Return the GIMPLE sequence contained in the @code{GIMPLE_BIND} statement +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_bind_set_body (gbind *g, @ +gimple_seq seq) +Set @code{SEQ} to be sequence contained in the @code{GIMPLE_BIND} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_bind_add_stmt (gbind *gs, gimple stmt) +Append a statement to the end of a @code{GIMPLE_BIND}'s body. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_bind_add_seq (gbind *gs, @ +gimple_seq seq) +Append a sequence of statements to the end of a @code{GIMPLE_BIND}'s +body. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_bind_block (const gbind *g) +Return the @code{TREE_BLOCK} node associated with @code{GIMPLE_BIND} statement +@code{G}. This is analogous to the @code{BIND_EXPR_BLOCK} field in trees. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_bind_set_block (gbind *g, tree block) +Set @code{BLOCK} to be the @code{TREE_BLOCK} node associated with @code{GIMPLE_BIND} +statement @code{G}. +@end deftypefn + + +@node @code{GIMPLE_CALL} +@subsection @code{GIMPLE_CALL} +@cindex @code{GIMPLE_CALL} + +@deftypefn {GIMPLE function} gcall *gimple_build_call (tree fn, @ +unsigned nargs, ...) +Build a @code{GIMPLE_CALL} statement to function @code{FN}. The argument @code{FN} +must be either a @code{FUNCTION_DECL} or a gimple call address as +determined by @code{is_gimple_call_addr}. @code{NARGS} are the number of +arguments. The rest of the arguments follow the argument @code{NARGS}, +and must be trees that are valid as rvalues in gimple (i.e., each +operand is validated with @code{is_gimple_operand}). +@end deftypefn + + +@deftypefn {GIMPLE function} gcall *gimple_build_call_from_tree (tree call_expr, @ +tree fnptrtype) +Build a @code{GIMPLE_CALL} from a @code{CALL_EXPR} node. The arguments +and the function are taken from the expression directly. The type of the +@code{GIMPLE_CALL} is set from the second parameter passed by a caller. +This routine assumes that @code{call_expr} is already in GIMPLE form. +That is, its operands are GIMPLE values and the function call needs no further +simplification. All the call flags in @code{call_expr} are copied over +to the new @code{GIMPLE_CALL}. +@end deftypefn + +@deftypefn {GIMPLE function} gcall *gimple_build_call_vec (tree fn, @ +@code{vec} args) +Identical to @code{gimple_build_call} but the arguments are stored in a +@code{vec}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_call_lhs (gimple g) +Return the @code{LHS} of call statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_call_lhs_ptr (gimple g) +Return a pointer to the @code{LHS} of call statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_call_set_lhs (gimple g, tree lhs) +Set @code{LHS} to be the @code{LHS} operand of call statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_call_fn (gimple g) +Return the tree node representing the function called by call +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_call_set_fn (gcall *g, tree fn) +Set @code{FN} to be the function called by call statement @code{G}. This has +to be a gimple value specifying the address of the called +function. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_call_fndecl (gimple g) +If a given @code{GIMPLE_CALL}'s callee is a @code{FUNCTION_DECL}, return it. +Otherwise return @code{NULL}. This function is analogous to +@code{get_callee_fndecl} in @code{GENERIC}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_call_set_fndecl (gimple g, tree fndecl) +Set the called function to @code{FNDECL}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_call_return_type (const gcall *g) +Return the type returned by call statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_call_chain (gimple g) +Return the static chain for call statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_call_set_chain (gcall *g, tree chain) +Set @code{CHAIN} to be the static chain for call statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} unsigned gimple_call_num_args (gimple g) +Return the number of arguments used by call statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_call_arg (gimple g, unsigned index) +Return the argument at position @code{INDEX} for call statement @code{G}. The +first argument is 0. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_call_arg_ptr (gimple g, unsigned index) +Return a pointer to the argument at position @code{INDEX} for call +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_call_set_arg (gimple g, unsigned index, tree arg) +Set @code{ARG} to be the argument at position @code{INDEX} for call statement +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_call_set_tail (gcall *s) +Mark call statement @code{S} as being a tail call (i.e., a call just +before the exit of a function). These calls are candidate for +tail call optimization. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_call_tail_p (gcall *s) +Return true if @code{GIMPLE_CALL} @code{S} is marked as a tail call. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_call_noreturn_p (gimple s) +Return true if @code{S} is a noreturn call. +@end deftypefn + +@deftypefn {GIMPLE function} gimple gimple_call_copy_skip_args (gcall *stmt, @ +bitmap args_to_skip) +Build a @code{GIMPLE_CALL} identical to @code{STMT} but skipping the arguments +in the positions marked by the set @code{ARGS_TO_SKIP}. +@end deftypefn + + +@node @code{GIMPLE_CATCH} +@subsection @code{GIMPLE_CATCH} +@cindex @code{GIMPLE_CATCH} + +@deftypefn {GIMPLE function} gcatch *gimple_build_catch (tree types, @ +gimple_seq handler) +Build a @code{GIMPLE_CATCH} statement. @code{TYPES} are the tree types this +catch handles. @code{HANDLER} is a sequence of statements with the code +for the handler. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_catch_types (const gcatch *g) +Return the types handled by @code{GIMPLE_CATCH} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_catch_types_ptr (gcatch *g) +Return a pointer to the types handled by @code{GIMPLE_CATCH} statement +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_catch_handler (gcatch *g) +Return the GIMPLE sequence representing the body of the handler +of @code{GIMPLE_CATCH} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_catch_set_types (gcatch *g, tree t) +Set @code{T} to be the set of types handled by @code{GIMPLE_CATCH} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_catch_set_handler (gcatch *g, @ +gimple_seq handler) +Set @code{HANDLER} to be the body of @code{GIMPLE_CATCH} @code{G}. +@end deftypefn + + +@node @code{GIMPLE_COND} +@subsection @code{GIMPLE_COND} +@cindex @code{GIMPLE_COND} + +@deftypefn {GIMPLE function} gcond *gimple_build_cond ( @ +enum tree_code pred_code, tree lhs, tree rhs, tree t_label, tree f_label) +Build a @code{GIMPLE_COND} statement. @code{A} @code{GIMPLE_COND} statement compares +@code{LHS} and @code{RHS} and if the condition in @code{PRED_CODE} is true, jump to +the label in @code{t_label}, otherwise jump to the label in @code{f_label}. +@code{PRED_CODE} are relational operator tree codes like @code{EQ_EXPR}, +@code{LT_EXPR}, @code{LE_EXPR}, @code{NE_EXPR}, etc. +@end deftypefn + + +@deftypefn {GIMPLE function} gcond *gimple_build_cond_from_tree (tree cond, @ +tree t_label, tree f_label) +Build a @code{GIMPLE_COND} statement from the conditional expression +tree @code{COND}. @code{T_LABEL} and @code{F_LABEL} are as in @code{gimple_build_cond}. +@end deftypefn + +@deftypefn {GIMPLE function} {enum tree_code} gimple_cond_code (gimple g) +Return the code of the predicate computed by conditional +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_cond_set_code (gcond *g, @ +enum tree_code code) +Set @code{CODE} to be the predicate code for the conditional statement +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_cond_lhs (gimple g) +Return the @code{LHS} of the predicate computed by conditional statement +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_cond_set_lhs (gcond *g, tree lhs) +Set @code{LHS} to be the @code{LHS} operand of the predicate computed by +conditional statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_cond_rhs (gimple g) +Return the @code{RHS} operand of the predicate computed by conditional +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_cond_set_rhs (gcond *g, tree rhs) +Set @code{RHS} to be the @code{RHS} operand of the predicate computed by +conditional statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_cond_true_label (const gcond *g) +Return the label used by conditional statement @code{G} when its +predicate evaluates to true. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_cond_set_true_label (gcond *g, tree label) +Set @code{LABEL} to be the label used by conditional statement @code{G} when +its predicate evaluates to true. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_cond_set_false_label (gcond *g, tree label) +Set @code{LABEL} to be the label used by conditional statement @code{G} when +its predicate evaluates to false. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_cond_false_label (const gcond *g) +Return the label used by conditional statement @code{G} when its +predicate evaluates to false. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_cond_make_false (gcond *g) +Set the conditional @code{COND_STMT} to be of the form 'if (1 == 0)'. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_cond_make_true (gcond *g) +Set the conditional @code{COND_STMT} to be of the form 'if (1 == 1)'. +@end deftypefn + +@node @code{GIMPLE_DEBUG} +@subsection @code{GIMPLE_DEBUG} +@cindex @code{GIMPLE_DEBUG} +@cindex @code{GIMPLE_DEBUG_BIND} +@cindex @code{GIMPLE_DEBUG_BEGIN_STMT} +@cindex @code{GIMPLE_DEBUG_INLINE_ENTRY} + +@deftypefn {GIMPLE function} gdebug *gimple_build_debug_bind (tree var, @ +tree value, gimple stmt) +Build a @code{GIMPLE_DEBUG} statement with @code{GIMPLE_DEBUG_BIND} +@code{subcode}. The effect of this statement is to tell debug +information generation machinery that the value of user variable +@code{var} is given by @code{value} at that point, and to remain with +that value until @code{var} runs out of scope, a +dynamically-subsequent debug bind statement overrides the binding, or +conflicting values reach a control flow merge point. Even if +components of the @code{value} expression change afterwards, the +variable is supposed to retain the same value, though not necessarily +the same location. + +It is expected that @code{var} be most often a tree for automatic user +variables (@code{VAR_DECL} or @code{PARM_DECL}) that satisfy the +requirements for gimple registers, but it may also be a tree for a +scalarized component of a user variable (@code{ARRAY_REF}, +@code{COMPONENT_REF}), or a debug temporary (@code{DEBUG_EXPR_DECL}). + +As for @code{value}, it can be an arbitrary tree expression, but it is +recommended that it be in a suitable form for a gimple assignment +@code{RHS}. It is not expected that user variables that could appear +as @code{var} ever appear in @code{value}, because in the latter we'd +have their @code{SSA_NAME}s instead, but even if they were not in SSA +form, user variables appearing in @code{value} are to be regarded as +part of the executable code space, whereas those in @code{var} are to +be regarded as part of the source code space. There is no way to +refer to the value bound to a user variable within a @code{value} +expression. + +If @code{value} is @code{GIMPLE_DEBUG_BIND_NOVALUE}, debug information +generation machinery is informed that the variable @code{var} is +unbound, i.e., that its value is indeterminate, which sometimes means +it is really unavailable, and other times that the compiler could not +keep track of it. + +Block and location information for the newly-created stmt are +taken from @code{stmt}, if given. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_debug_bind_get_var (gimple stmt) +Return the user variable @var{var} that is bound at @code{stmt}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_debug_bind_get_value (gimple stmt) +Return the value expression that is bound to a user variable at +@code{stmt}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_debug_bind_get_value_ptr (gimple stmt) +Return a pointer to the value expression that is bound to a user +variable at @code{stmt}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_debug_bind_set_var (gimple stmt, tree var) +Modify the user variable bound at @code{stmt} to @var{var}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_debug_bind_set_value (gimple stmt, tree var) +Modify the value bound to the user variable bound at @code{stmt} to +@var{value}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_debug_bind_reset_value (gimple stmt) +Modify the value bound to the user variable bound at @code{stmt} so +that the variable becomes unbound. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_debug_bind_has_value_p (gimple stmt) +Return @code{TRUE} if @code{stmt} binds a user variable to a value, +and @code{FALSE} if it unbinds the variable. +@end deftypefn + +@deftypefn {GIMPLE function} gimple gimple_build_debug_begin_stmt (tree block, location_t location) +Build a @code{GIMPLE_DEBUG} statement with +@code{GIMPLE_DEBUG_BEGIN_STMT} @code{subcode}. The effect of this +statement is to tell debug information generation machinery that the +user statement at the given @code{location} and @code{block} starts at +the point at which the statement is inserted. The intent is that side +effects (e.g.@: variable bindings) of all prior user statements are +observable, and that none of the side effects of subsequent user +statements are. +@end deftypefn + +@deftypefn {GIMPLE function} gimple gimple_build_debug_inline_entry (tree block, location_t location) +Build a @code{GIMPLE_DEBUG} statement with +@code{GIMPLE_DEBUG_INLINE_ENTRY} @code{subcode}. The effect of this +statement is to tell debug information generation machinery that a +function call at @code{location} underwent inline substitution, that +@code{block} is the enclosing lexical block created for the +substitution, and that at the point of the program in which the stmt is +inserted, all parameters for the inlined function are bound to the +respective arguments, and none of the side effects of its stmts are +observable. +@end deftypefn + +@node @code{GIMPLE_EH_FILTER} +@subsection @code{GIMPLE_EH_FILTER} +@cindex @code{GIMPLE_EH_FILTER} + +@deftypefn {GIMPLE function} geh_filter *gimple_build_eh_filter (tree types, @ +gimple_seq failure) +Build a @code{GIMPLE_EH_FILTER} statement. @code{TYPES} are the filter's +types. @code{FAILURE} is a sequence with the filter's failure action. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_eh_filter_types (gimple g) +Return the types handled by @code{GIMPLE_EH_FILTER} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_eh_filter_types_ptr (gimple g) +Return a pointer to the types handled by @code{GIMPLE_EH_FILTER} +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_eh_filter_failure (gimple g) +Return the sequence of statement to execute when @code{GIMPLE_EH_FILTER} +statement fails. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_eh_filter_set_types (geh_filter *g, @ +tree types) +Set @code{TYPES} to be the set of types handled by @code{GIMPLE_EH_FILTER} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_eh_filter_set_failure (geh_filter *g, @ +gimple_seq failure) +Set @code{FAILURE} to be the sequence of statements to execute on +failure for @code{GIMPLE_EH_FILTER} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_eh_must_not_throw_fndecl ( @ +geh_mnt *eh_mnt_stmt) +Get the function decl to be called by the MUST_NOT_THROW region. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_eh_must_not_throw_set_fndecl ( @ +geh_mnt *eh_mnt_stmt, tree decl) +Set the function decl to be called by GS to DECL. +@end deftypefn + + +@node @code{GIMPLE_LABEL} +@subsection @code{GIMPLE_LABEL} +@cindex @code{GIMPLE_LABEL} + +@deftypefn {GIMPLE function} glabel *gimple_build_label (tree label) +Build a @code{GIMPLE_LABEL} statement with corresponding to the tree +label, @code{LABEL}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_label_label (const glabel *g) +Return the @code{LABEL_DECL} node used by @code{GIMPLE_LABEL} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_label_set_label (glabel *g, tree label) +Set @code{LABEL} to be the @code{LABEL_DECL} node used by @code{GIMPLE_LABEL} +statement @code{G}. +@end deftypefn + +@node @code{GIMPLE_GOTO} +@subsection @code{GIMPLE_GOTO} +@cindex @code{GIMPLE_GOTO} + +@deftypefn {GIMPLE function} ggoto *gimple_build_goto (tree dest) +Build a @code{GIMPLE_GOTO} statement to label @code{DEST}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_goto_dest (gimple g) +Return the destination of the unconditional jump @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_goto_set_dest (ggoto *g, tree dest) +Set @code{DEST} to be the destination of the unconditional jump @code{G}. +@end deftypefn + + +@node @code{GIMPLE_NOP} +@subsection @code{GIMPLE_NOP} +@cindex @code{GIMPLE_NOP} + +@deftypefn {GIMPLE function} gimple gimple_build_nop (void) +Build a @code{GIMPLE_NOP} statement. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_nop_p (gimple g) +Returns @code{TRUE} if statement @code{G} is a @code{GIMPLE_NOP}. +@end deftypefn + +@node @code{GIMPLE_OMP_ATOMIC_LOAD} +@subsection @code{GIMPLE_OMP_ATOMIC_LOAD} +@cindex @code{GIMPLE_OMP_ATOMIC_LOAD} + +@deftypefn {GIMPLE function} gomp_atomic_load *gimple_build_omp_atomic_load ( @ +tree lhs, tree rhs) +Build a @code{GIMPLE_OMP_ATOMIC_LOAD} statement. @code{LHS} is the left-hand +side of the assignment. @code{RHS} is the right-hand side of the +assignment. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_atomic_load_set_lhs ( @ +gomp_atomic_load *g, tree lhs) +Set the @code{LHS} of an atomic load. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_atomic_load_lhs ( @ +const gomp_atomic_load *g) +Get the @code{LHS} of an atomic load. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_atomic_load_set_rhs ( @ +gomp_atomic_load *g, tree rhs) +Set the @code{RHS} of an atomic set. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_atomic_load_rhs ( @ +const gomp_atomic_load *g) +Get the @code{RHS} of an atomic set. +@end deftypefn + + +@node @code{GIMPLE_OMP_ATOMIC_STORE} +@subsection @code{GIMPLE_OMP_ATOMIC_STORE} +@cindex @code{GIMPLE_OMP_ATOMIC_STORE} + +@deftypefn {GIMPLE function} gomp_atomic_store *gimple_build_omp_atomic_store ( @ +tree val) +Build a @code{GIMPLE_OMP_ATOMIC_STORE} statement. @code{VAL} is the value to be +stored. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_atomic_store_set_val ( @ +gomp_atomic_store *g, tree val) +Set the value being stored in an atomic store. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_atomic_store_val ( @ +const gomp_atomic_store *g) +Return the value being stored in an atomic store. +@end deftypefn + +@node @code{GIMPLE_OMP_CONTINUE} +@subsection @code{GIMPLE_OMP_CONTINUE} +@cindex @code{GIMPLE_OMP_CONTINUE} + +@deftypefn {GIMPLE function} gomp_continue *gimple_build_omp_continue ( @ +tree control_def, tree control_use) +Build a @code{GIMPLE_OMP_CONTINUE} statement. @code{CONTROL_DEF} is the +definition of the control variable. @code{CONTROL_USE} is the use of +the control variable. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_continue_control_def ( @ +const gomp_continue *s) +Return the definition of the control variable on a +@code{GIMPLE_OMP_CONTINUE} in @code{S}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_continue_control_def_ptr ( @ +gomp_continue *s) +Same as above, but return the pointer. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_continue_set_control_def ( @ +gomp_continue *s) +Set the control variable definition for a @code{GIMPLE_OMP_CONTINUE} +statement in @code{S}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_continue_control_use ( @ +const gomp_continue *s) +Return the use of the control variable on a @code{GIMPLE_OMP_CONTINUE} +in @code{S}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_continue_control_use_ptr ( @ +gomp_continue *s) +Same as above, but return the pointer. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_continue_set_control_use ( @ +gomp_continue *s) +Set the control variable use for a @code{GIMPLE_OMP_CONTINUE} statement +in @code{S}. +@end deftypefn + + +@node @code{GIMPLE_OMP_CRITICAL} +@subsection @code{GIMPLE_OMP_CRITICAL} +@cindex @code{GIMPLE_OMP_CRITICAL} + +@deftypefn {GIMPLE function} gomp_critical *gimple_build_omp_critical ( @ +gimple_seq body, tree name) +Build a @code{GIMPLE_OMP_CRITICAL} statement. @code{BODY} is the sequence of +statements for which only one thread can execute. @code{NAME} is an +optional identifier for this critical block. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_critical_name ( @ +const gomp_critical *g) +Return the name associated with @code{OMP_CRITICAL} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_critical_name_ptr ( @ +gomp_critical *g) +Return a pointer to the name associated with @code{OMP} critical +statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_critical_set_name ( @ +gomp_critical *g, tree name) +Set @code{NAME} to be the name associated with @code{OMP} critical statement @code{G}. +@end deftypefn + +@node @code{GIMPLE_OMP_FOR} +@subsection @code{GIMPLE_OMP_FOR} +@cindex @code{GIMPLE_OMP_FOR} + +@deftypefn {GIMPLE function} gomp_for *gimple_build_omp_for (gimple_seq body, @ +tree clauses, tree index, tree initial, tree final, tree incr, @ +gimple_seq pre_body, enum tree_code omp_for_cond) +Build a @code{GIMPLE_OMP_FOR} statement. @code{BODY} is sequence of statements +inside the for loop. @code{CLAUSES}, are any of the loop +construct's clauses. @code{PRE_BODY} is the +sequence of statements that are loop invariant. @code{INDEX} is the +index variable. @code{INITIAL} is the initial value of @code{INDEX}. @code{FINAL} is +final value of @code{INDEX}. OMP_FOR_COND is the predicate used to +compare @code{INDEX} and @code{FINAL}. @code{INCR} is the increment expression. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_for_clauses (gimple g) +Return the clauses associated with @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_for_clauses_ptr (gimple g) +Return a pointer to the @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_for_set_clauses (gimple g, tree clauses) +Set @code{CLAUSES} to be the list of clauses associated with @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_for_index (gimple g) +Return the index variable for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_for_index_ptr (gimple g) +Return a pointer to the index variable for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_for_set_index (gimple g, tree index) +Set @code{INDEX} to be the index variable for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_for_initial (gimple g) +Return the initial value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_for_initial_ptr (gimple g) +Return a pointer to the initial value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_for_set_initial (gimple g, tree initial) +Set @code{INITIAL} to be the initial value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_for_final (gimple g) +Return the final value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_for_final_ptr (gimple g) +turn a pointer to the final value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_for_set_final (gimple g, tree final) +Set @code{FINAL} to be the final value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_for_incr (gimple g) +Return the increment value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_for_incr_ptr (gimple g) +Return a pointer to the increment value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_for_set_incr (gimple g, tree incr) +Set @code{INCR} to be the increment value for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_omp_for_pre_body (gimple g) +Return the sequence of statements to execute before the @code{OMP_FOR} +statement @code{G} starts. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_for_set_pre_body (gimple g, gimple_seq pre_body) +Set @code{PRE_BODY} to be the sequence of statements to execute before +the @code{OMP_FOR} statement @code{G} starts. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_for_set_cond (gimple g, enum tree_code cond) +Set @code{COND} to be the condition code for @code{OMP_FOR} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {enum tree_code} gimple_omp_for_cond (gimple g) +Return the condition code associated with @code{OMP_FOR} @code{G}. +@end deftypefn + + +@node @code{GIMPLE_OMP_MASTER} +@subsection @code{GIMPLE_OMP_MASTER} +@cindex @code{GIMPLE_OMP_MASTER} + +@deftypefn {GIMPLE function} gimple gimple_build_omp_master (gimple_seq body) +Build a @code{GIMPLE_OMP_MASTER} statement. @code{BODY} is the sequence of +statements to be executed by just the master. +@end deftypefn + + +@node @code{GIMPLE_OMP_ORDERED} +@subsection @code{GIMPLE_OMP_ORDERED} +@cindex @code{GIMPLE_OMP_ORDERED} + +@deftypefn {GIMPLE function} gimple gimple_build_omp_ordered (gimple_seq body) +Build a @code{GIMPLE_OMP_ORDERED} statement. + +@code{BODY} is the sequence of statements inside a loop that will +executed in sequence. +@end deftypefn + +@node @code{GIMPLE_OMP_PARALLEL} +@subsection @code{GIMPLE_OMP_PARALLEL} +@cindex @code{GIMPLE_OMP_PARALLEL} + +@deftypefn {GIMPLE function} gomp_parallel *gimple_build_omp_parallel (@ +gimple_seq body, tree clauses, tree child_fn, tree data_arg) +Build a @code{GIMPLE_OMP_PARALLEL} statement. + +@code{BODY} is sequence of statements which are executed in parallel. +@code{CLAUSES}, are the @code{OMP} parallel construct's clauses. @code{CHILD_FN} is +the function created for the parallel threads to execute. +@code{DATA_ARG} are the shared data argument(s). +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_omp_parallel_combined_p (gimple g) +Return true if @code{OMP} parallel statement @code{G} has the +@code{GF_OMP_PARALLEL_COMBINED} flag set. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_parallel_set_combined_p (gimple g) +Set the @code{GF_OMP_PARALLEL_COMBINED} field in @code{OMP} parallel statement +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_omp_body (gimple g) +Return the body for the @code{OMP} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_set_body (gimple g, gimple_seq body) +Set @code{BODY} to be the body for the @code{OMP} statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_parallel_clauses (gimple g) +Return the clauses associated with @code{OMP_PARALLEL} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_parallel_clauses_ptr ( @ +gomp_parallel *g) +Return a pointer to the clauses associated with @code{OMP_PARALLEL} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_parallel_set_clauses ( @ +gomp_parallel *g, tree clauses) +Set @code{CLAUSES} to be the list of clauses associated with +@code{OMP_PARALLEL} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_parallel_child_fn ( @ +const gomp_parallel *g) +Return the child function used to hold the body of @code{OMP_PARALLEL} +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_parallel_child_fn_ptr ( @ +gomp_parallel *g) +Return a pointer to the child function used to hold the body of +@code{OMP_PARALLEL} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_parallel_set_child_fn ( @ +gomp_parallel *g, tree child_fn) +Set @code{CHILD_FN} to be the child function for @code{OMP_PARALLEL} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_parallel_data_arg ( @ +const gomp_parallel *g) +Return the artificial argument used to send variables and values +from the parent to the children threads in @code{OMP_PARALLEL} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_parallel_data_arg_ptr ( @ +gomp_parallel *g) +Return a pointer to the data argument for @code{OMP_PARALLEL} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_parallel_set_data_arg ( @ +gomp_parallel *g, tree data_arg) +Set @code{DATA_ARG} to be the data argument for @code{OMP_PARALLEL} @code{G}. +@end deftypefn + + +@node @code{GIMPLE_OMP_RETURN} +@subsection @code{GIMPLE_OMP_RETURN} +@cindex @code{GIMPLE_OMP_RETURN} + +@deftypefn {GIMPLE function} gimple gimple_build_omp_return (bool wait_p) +Build a @code{GIMPLE_OMP_RETURN} statement. @code{WAIT_P} is true if this is a +non-waiting return. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_return_set_nowait (gimple s) +Set the nowait flag on @code{GIMPLE_OMP_RETURN} statement @code{S}. +@end deftypefn + + +@deftypefn {GIMPLE function} bool gimple_omp_return_nowait_p (gimple g) +Return true if @code{OMP} return statement @code{G} has the +@code{GF_OMP_RETURN_NOWAIT} flag set. +@end deftypefn + +@node @code{GIMPLE_OMP_SECTION} +@subsection @code{GIMPLE_OMP_SECTION} +@cindex @code{GIMPLE_OMP_SECTION} + +@deftypefn {GIMPLE function} gimple gimple_build_omp_section (gimple_seq body) +Build a @code{GIMPLE_OMP_SECTION} statement for a sections statement. + +@code{BODY} is the sequence of statements in the section. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_omp_section_last_p (gimple g) +Return true if @code{OMP} section statement @code{G} has the +@code{GF_OMP_SECTION_LAST} flag set. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_section_set_last (gimple g) +Set the @code{GF_OMP_SECTION_LAST} flag on @code{G}. +@end deftypefn + +@node @code{GIMPLE_OMP_SECTIONS} +@subsection @code{GIMPLE_OMP_SECTIONS} +@cindex @code{GIMPLE_OMP_SECTIONS} + +@deftypefn {GIMPLE function} gomp_sections *gimple_build_omp_sections ( @ +gimple_seq body, tree clauses) +Build a @code{GIMPLE_OMP_SECTIONS} statement. @code{BODY} is a sequence of +section statements. @code{CLAUSES} are any of the @code{OMP} sections +construct's clauses: private, firstprivate, lastprivate, +reduction, and nowait. +@end deftypefn + + +@deftypefn {GIMPLE function} gimple gimple_build_omp_sections_switch (void) +Build a @code{GIMPLE_OMP_SECTIONS_SWITCH} statement. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_sections_control (gimple g) +Return the control variable associated with the +@code{GIMPLE_OMP_SECTIONS} in @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_sections_control_ptr (gimple g) +Return a pointer to the clauses associated with the +@code{GIMPLE_OMP_SECTIONS} in @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_sections_set_control (gimple g, tree control) +Set @code{CONTROL} to be the set of clauses associated with the +@code{GIMPLE_OMP_SECTIONS} in @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_sections_clauses (gimple g) +Return the clauses associated with @code{OMP_SECTIONS} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_sections_clauses_ptr (gimple g) +Return a pointer to the clauses associated with @code{OMP_SECTIONS} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_sections_set_clauses (gimple g, tree clauses) +Set @code{CLAUSES} to be the set of clauses associated with @code{OMP_SECTIONS} +@code{G}. +@end deftypefn + + +@node @code{GIMPLE_OMP_SINGLE} +@subsection @code{GIMPLE_OMP_SINGLE} +@cindex @code{GIMPLE_OMP_SINGLE} + +@deftypefn {GIMPLE function} gomp_single *gimple_build_omp_single ( @ +gimple_seq body, tree clauses) +Build a @code{GIMPLE_OMP_SINGLE} statement. @code{BODY} is the sequence of +statements that will be executed once. @code{CLAUSES} are any of the +@code{OMP} single construct's clauses: private, firstprivate, +copyprivate, nowait. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_omp_single_clauses (gimple g) +Return the clauses associated with @code{OMP_SINGLE} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_omp_single_clauses_ptr (gimple g) +Return a pointer to the clauses associated with @code{OMP_SINGLE} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_omp_single_set_clauses ( @ +gomp_single *g, tree clauses) +Set @code{CLAUSES} to be the clauses associated with @code{OMP_SINGLE} @code{G}. +@end deftypefn + + +@node @code{GIMPLE_PHI} +@subsection @code{GIMPLE_PHI} +@cindex @code{GIMPLE_PHI} + +@deftypefn {GIMPLE function} unsigned gimple_phi_capacity (gimple g) +Return the maximum number of arguments supported by @code{GIMPLE_PHI} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} unsigned gimple_phi_num_args (gimple g) +Return the number of arguments in @code{GIMPLE_PHI} @code{G}. This must always +be exactly the number of incoming edges for the basic block +holding @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_phi_result (gimple g) +Return the @code{SSA} name created by @code{GIMPLE_PHI} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {tree *} gimple_phi_result_ptr (gimple g) +Return a pointer to the @code{SSA} name created by @code{GIMPLE_PHI} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_phi_set_result (gphi *g, tree result) +Set @code{RESULT} to be the @code{SSA} name created by @code{GIMPLE_PHI} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} {struct phi_arg_d *} gimple_phi_arg (gimple g, index) +Return the @code{PHI} argument corresponding to incoming edge @code{INDEX} for +@code{GIMPLE_PHI} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_phi_set_arg (gphi *g, index, @ +struct phi_arg_d * phiarg) +Set @code{PHIARG} to be the argument corresponding to incoming edge +@code{INDEX} for @code{GIMPLE_PHI} @code{G}. +@end deftypefn + +@node @code{GIMPLE_RESX} +@subsection @code{GIMPLE_RESX} +@cindex @code{GIMPLE_RESX} + +@deftypefn {GIMPLE function} gresx *gimple_build_resx (int region) +Build a @code{GIMPLE_RESX} statement which is a statement. This +statement is a placeholder for _Unwind_Resume before we know if a +function call or a branch is needed. @code{REGION} is the exception +region from which control is flowing. +@end deftypefn + +@deftypefn {GIMPLE function} int gimple_resx_region (const gresx *g) +Return the region number for @code{GIMPLE_RESX} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_resx_set_region (gresx *g, int region) +Set @code{REGION} to be the region number for @code{GIMPLE_RESX} @code{G}. +@end deftypefn + +@node @code{GIMPLE_RETURN} +@subsection @code{GIMPLE_RETURN} +@cindex @code{GIMPLE_RETURN} + +@deftypefn {GIMPLE function} greturn *gimple_build_return (tree retval) +Build a @code{GIMPLE_RETURN} statement whose return value is retval. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_return_retval (const greturn *g) +Return the return value for @code{GIMPLE_RETURN} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_return_set_retval (greturn *g, @ +tree retval) +Set @code{RETVAL} to be the return value for @code{GIMPLE_RETURN} @code{G}. +@end deftypefn + +@node @code{GIMPLE_SWITCH} +@subsection @code{GIMPLE_SWITCH} +@cindex @code{GIMPLE_SWITCH} + +@deftypefn {GIMPLE function} gswitch *gimple_build_switch (tree index, @ +tree default_label, @code{vec} *args) +Build a @code{GIMPLE_SWITCH} statement. @code{INDEX} is the index variable +to switch on, and @code{DEFAULT_LABEL} represents the default label. +@code{ARGS} is a vector of @code{CASE_LABEL_EXPR} trees that contain the +non-default case labels. Each label is a tree of code @code{CASE_LABEL_EXPR}. +@end deftypefn + +@deftypefn {GIMPLE function} unsigned gimple_switch_num_labels ( @ +const gswitch *g) +Return the number of labels associated with the switch statement +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_switch_set_num_labels (gswitch *g, @ +unsigned nlabels) +Set @code{NLABELS} to be the number of labels for the switch statement +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_switch_index (const gswitch *g) +Return the index variable used by the switch statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_switch_set_index (gswitch *g, @ +tree index) +Set @code{INDEX} to be the index variable for switch statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_switch_label (const gswitch *g, @ +unsigned index) +Return the label numbered @code{INDEX}. The default label is 0, followed +by any labels in a switch statement. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_switch_set_label (gswitch *g, @ +unsigned index, tree label) +Set the label number @code{INDEX} to @code{LABEL}. 0 is always the default +label. +@end deftypefn + +@deftypefn {GIMPLE function} tree gimple_switch_default_label ( @ +const gswitch *g) +Return the default label for a switch statement. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_switch_set_default_label (gswitch *g, @ +tree label) +Set the default label for a switch statement. +@end deftypefn + + +@node @code{GIMPLE_TRY} +@subsection @code{GIMPLE_TRY} +@cindex @code{GIMPLE_TRY} + +@deftypefn {GIMPLE function} gtry *gimple_build_try (gimple_seq eval, @ +gimple_seq cleanup, unsigned int kind) +Build a @code{GIMPLE_TRY} statement. @code{EVAL} is a sequence with the +expression to evaluate. @code{CLEANUP} is a sequence of statements to +run at clean-up time. @code{KIND} is the enumeration value +@code{GIMPLE_TRY_CATCH} if this statement denotes a try/catch construct +or @code{GIMPLE_TRY_FINALLY} if this statement denotes a try/finally +construct. +@end deftypefn + +@deftypefn {GIMPLE function} {enum gimple_try_flags} gimple_try_kind (gimple g) +Return the kind of try block represented by @code{GIMPLE_TRY} @code{G}. This is +either @code{GIMPLE_TRY_CATCH} or @code{GIMPLE_TRY_FINALLY}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_try_catch_is_cleanup (gimple g) +Return the @code{GIMPLE_TRY_CATCH_IS_CLEANUP} flag. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_try_eval (gimple g) +Return the sequence of statements used as the body for @code{GIMPLE_TRY} +@code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_try_cleanup (gimple g) +Return the sequence of statements used as the cleanup body for +@code{GIMPLE_TRY} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_try_set_catch_is_cleanup (gimple g, @ +bool catch_is_cleanup) +Set the @code{GIMPLE_TRY_CATCH_IS_CLEANUP} flag. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_try_set_eval (gtry *g, gimple_seq eval) +Set @code{EVAL} to be the sequence of statements to use as the body for +@code{GIMPLE_TRY} @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_try_set_cleanup (gtry *g, @ +gimple_seq cleanup) +Set @code{CLEANUP} to be the sequence of statements to use as the +cleanup body for @code{GIMPLE_TRY} @code{G}. +@end deftypefn + +@node @code{GIMPLE_WITH_CLEANUP_EXPR} +@subsection @code{GIMPLE_WITH_CLEANUP_EXPR} +@cindex @code{GIMPLE_WITH_CLEANUP_EXPR} + +@deftypefn {GIMPLE function} gimple gimple_build_wce (gimple_seq cleanup) +Build a @code{GIMPLE_WITH_CLEANUP_EXPR} statement. @code{CLEANUP} is the +clean-up expression. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_wce_cleanup (gimple g) +Return the cleanup sequence for cleanup statement @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_wce_set_cleanup (gimple g, gimple_seq cleanup) +Set @code{CLEANUP} to be the cleanup sequence for @code{G}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_wce_cleanup_eh_only (gimple g) +Return the @code{CLEANUP_EH_ONLY} flag for a @code{WCE} tuple. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_wce_set_cleanup_eh_only (gimple g, bool eh_only_p) +Set the @code{CLEANUP_EH_ONLY} flag for a @code{WCE} tuple. +@end deftypefn + + +@node GIMPLE sequences +@section GIMPLE sequences +@cindex GIMPLE sequences + +GIMPLE sequences are the tuple equivalent of @code{STATEMENT_LIST}'s +used in @code{GENERIC}. They are used to chain statements together, and +when used in conjunction with sequence iterators, provide a +framework for iterating through statements. + +GIMPLE sequences are of type struct @code{gimple_sequence}, but are more +commonly passed by reference to functions dealing with sequences. +The type for a sequence pointer is @code{gimple_seq} which is the same +as struct @code{gimple_sequence} *. When declaring a local sequence, +you can define a local variable of type struct @code{gimple_sequence}. +When declaring a sequence allocated on the garbage collected +heap, use the function @code{gimple_seq_alloc} documented below. + +There are convenience functions for iterating through sequences +in the section entitled Sequence Iterators. + +Below is a list of functions to manipulate and query sequences. + +@deftypefn {GIMPLE function} void gimple_seq_add_stmt (gimple_seq *seq, gimple g) +Link a gimple statement to the end of the sequence *@code{SEQ} if @code{G} is +not @code{NULL}. If *@code{SEQ} is @code{NULL}, allocate a sequence before linking. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_seq_add_seq (gimple_seq *dest, gimple_seq src) +Append sequence @code{SRC} to the end of sequence *@code{DEST} if @code{SRC} is not +@code{NULL}. If *@code{DEST} is @code{NULL}, allocate a new sequence before +appending. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_seq_deep_copy (gimple_seq src) +Perform a deep copy of sequence @code{SRC} and return the result. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_seq_reverse (gimple_seq seq) +Reverse the order of the statements in the sequence @code{SEQ}. Return +@code{SEQ}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple gimple_seq_first (gimple_seq s) +Return the first statement in sequence @code{S}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple gimple_seq_last (gimple_seq s) +Return the last statement in sequence @code{S}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_seq_set_last (gimple_seq s, gimple last) +Set the last statement in sequence @code{S} to the statement in @code{LAST}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_seq_set_first (gimple_seq s, gimple first) +Set the first statement in sequence @code{S} to the statement in @code{FIRST}. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_seq_init (gimple_seq s) +Initialize sequence @code{S} to an empty sequence. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gimple_seq_alloc (void) +Allocate a new sequence in the garbage collected store and return +it. +@end deftypefn + +@deftypefn {GIMPLE function} void gimple_seq_copy (gimple_seq dest, gimple_seq src) +Copy the sequence @code{SRC} into the sequence @code{DEST}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_seq_empty_p (gimple_seq s) +Return true if the sequence @code{S} is empty. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq bb_seq (basic_block bb) +Returns the sequence of statements in @code{BB}. +@end deftypefn + +@deftypefn {GIMPLE function} void set_bb_seq (basic_block bb, gimple_seq seq) +Sets the sequence of statements in @code{BB} to @code{SEQ}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gimple_seq_singleton_p (gimple_seq seq) +Determine whether @code{SEQ} contains exactly one statement. +@end deftypefn + +@node Sequence iterators +@section Sequence iterators +@cindex Sequence iterators + +Sequence iterators are convenience constructs for iterating +through statements in a sequence. Given a sequence @code{SEQ}, here is +a typical use of gimple sequence iterators: + +@smallexample +gimple_stmt_iterator gsi; + +for (gsi = gsi_start (seq); !gsi_end_p (gsi); gsi_next (&gsi)) + @{ + gimple g = gsi_stmt (gsi); + /* Do something with gimple statement @code{G}. */ + @} +@end smallexample + +Backward iterations are possible: + +@smallexample + for (gsi = gsi_last (seq); !gsi_end_p (gsi); gsi_prev (&gsi)) +@end smallexample + +Forward and backward iterations on basic blocks are possible with +@code{gsi_start_bb} and @code{gsi_last_bb}. + +In the documentation below we sometimes refer to enum +@code{gsi_iterator_update}. The valid options for this enumeration are: + +@itemize @bullet +@item @code{GSI_NEW_STMT} +Only valid when a single statement is added. Move the iterator to it. + +@item @code{GSI_SAME_STMT} +Leave the iterator at the same statement. + +@item @code{GSI_CONTINUE_LINKING} +Move iterator to whatever position is suitable for linking other +statements in the same direction. +@end itemize + +Below is a list of the functions used to manipulate and use +statement iterators. + +@deftypefn {GIMPLE function} gimple_stmt_iterator gsi_start (gimple_seq seq) +Return a new iterator pointing to the sequence @code{SEQ}'s first +statement. If @code{SEQ} is empty, the iterator's basic block is @code{NULL}. +Use @code{gsi_start_bb} instead when the iterator needs to always have +the correct basic block set. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_stmt_iterator gsi_start_bb (basic_block bb) +Return a new iterator pointing to the first statement in basic +block @code{BB}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_stmt_iterator gsi_last (gimple_seq seq) +Return a new iterator initially pointing to the last statement of +sequence @code{SEQ}. If @code{SEQ} is empty, the iterator's basic block is +@code{NULL}. Use @code{gsi_last_bb} instead when the iterator needs to always +have the correct basic block set. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_stmt_iterator gsi_last_bb (basic_block bb) +Return a new iterator pointing to the last statement in basic +block @code{BB}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gsi_end_p (gimple_stmt_iterator i) +Return @code{TRUE} if at the end of @code{I}. +@end deftypefn + +@deftypefn {GIMPLE function} bool gsi_one_before_end_p (gimple_stmt_iterator i) +Return @code{TRUE} if we're one statement before the end of @code{I}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_next (gimple_stmt_iterator *i) +Advance the iterator to the next gimple statement. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_prev (gimple_stmt_iterator *i) +Advance the iterator to the previous gimple statement. +@end deftypefn + +@deftypefn {GIMPLE function} gimple gsi_stmt (gimple_stmt_iterator i) +Return the current stmt. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_stmt_iterator gsi_after_labels (basic_block bb) +Return a block statement iterator that points to the first +non-label statement in block @code{BB}. +@end deftypefn + +@deftypefn {GIMPLE function} {gimple *} gsi_stmt_ptr (gimple_stmt_iterator *i) +Return a pointer to the current stmt. +@end deftypefn + +@deftypefn {GIMPLE function} basic_block gsi_bb (gimple_stmt_iterator i) +Return the basic block associated with this iterator. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gsi_seq (gimple_stmt_iterator i) +Return the sequence associated with this iterator. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_remove (gimple_stmt_iterator *i, bool remove_eh_info) +Remove the current stmt from the sequence. The iterator is +updated to point to the next statement. When @code{REMOVE_EH_INFO} is +true we remove the statement pointed to by iterator @code{I} from the @code{EH} +tables. Otherwise we do not modify the @code{EH} tables. Generally, +@code{REMOVE_EH_INFO} should be true when the statement is going to be +removed from the @code{IL} and not reinserted elsewhere. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_link_seq_before (gimple_stmt_iterator *i, gimple_seq seq, enum gsi_iterator_update mode) +Links the sequence of statements @code{SEQ} before the statement pointed +by iterator @code{I}. @code{MODE} indicates what to do with the iterator +after insertion (see @code{enum gsi_iterator_update} above). +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_link_before (gimple_stmt_iterator *i, gimple g, enum gsi_iterator_update mode) +Links statement @code{G} before the statement pointed-to by iterator @code{I}. +Updates iterator @code{I} according to @code{MODE}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_link_seq_after (gimple_stmt_iterator *i, @ +gimple_seq seq, enum gsi_iterator_update mode) +Links sequence @code{SEQ} after the statement pointed-to by iterator @code{I}. +@code{MODE} is as in @code{gsi_insert_after}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_link_after (gimple_stmt_iterator *i, @ +gimple g, enum gsi_iterator_update mode) +Links statement @code{G} after the statement pointed-to by iterator @code{I}. +@code{MODE} is as in @code{gsi_insert_after}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gsi_split_seq_after (gimple_stmt_iterator i) +Move all statements in the sequence after @code{I} to a new sequence. +Return this new sequence. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_seq gsi_split_seq_before (gimple_stmt_iterator *i) +Move all statements in the sequence before @code{I} to a new sequence. +Return this new sequence. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_replace (gimple_stmt_iterator *i, @ +gimple stmt, bool update_eh_info) +Replace the statement pointed-to by @code{I} to @code{STMT}. If @code{UPDATE_EH_INFO} +is true, the exception handling information of the original +statement is moved to the new statement. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_insert_before (gimple_stmt_iterator *i, @ +gimple stmt, enum gsi_iterator_update mode) +Insert statement @code{STMT} before the statement pointed-to by iterator +@code{I}, update @code{STMT}'s basic block and scan it for new operands. @code{MODE} +specifies how to update iterator @code{I} after insertion (see enum +@code{gsi_iterator_update}). +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_insert_seq_before (gimple_stmt_iterator *i, @ +gimple_seq seq, enum gsi_iterator_update mode) +Like @code{gsi_insert_before}, but for all the statements in @code{SEQ}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_insert_after (gimple_stmt_iterator *i, @ +gimple stmt, enum gsi_iterator_update mode) +Insert statement @code{STMT} after the statement pointed-to by iterator +@code{I}, update @code{STMT}'s basic block and scan it for new operands. @code{MODE} +specifies how to update iterator @code{I} after insertion (see enum +@code{gsi_iterator_update}). +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_insert_seq_after (gimple_stmt_iterator *i, @ +gimple_seq seq, enum gsi_iterator_update mode) +Like @code{gsi_insert_after}, but for all the statements in @code{SEQ}. +@end deftypefn + +@deftypefn {GIMPLE function} gimple_stmt_iterator gsi_for_stmt (gimple stmt) +Finds iterator for @code{STMT}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_move_after (gimple_stmt_iterator *from, @ +gimple_stmt_iterator *to) +Move the statement at @code{FROM} so it comes right after the statement +at @code{TO}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_move_before (gimple_stmt_iterator *from, @ +gimple_stmt_iterator *to) +Move the statement at @code{FROM} so it comes right before the statement +at @code{TO}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_move_to_bb_end (gimple_stmt_iterator *from, @ +basic_block bb) +Move the statement at @code{FROM} to the end of basic block @code{BB}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_insert_on_edge (edge e, gimple stmt) +Add @code{STMT} to the pending list of edge @code{E}. No actual insertion is +made until a call to @code{gsi_commit_edge_inserts}() is made. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_insert_seq_on_edge (edge e, gimple_seq seq) +Add the sequence of statements in @code{SEQ} to the pending list of edge +@code{E}. No actual insertion is made until a call to +@code{gsi_commit_edge_inserts}() is made. +@end deftypefn + +@deftypefn {GIMPLE function} basic_block gsi_insert_on_edge_immediate (edge e, gimple stmt) +Similar to @code{gsi_insert_on_edge}+@code{gsi_commit_edge_inserts}. If a new +block has to be created, it is returned. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_commit_one_edge_insert (edge e, basic_block *new_bb) +Commit insertions pending at edge @code{E}. If a new block is created, +set @code{NEW_BB} to this block, otherwise set it to @code{NULL}. +@end deftypefn + +@deftypefn {GIMPLE function} void gsi_commit_edge_inserts (void) +This routine will commit all pending edge insertions, creating +any new basic blocks which are necessary. +@end deftypefn + + +@node Adding a new GIMPLE statement code +@section Adding a new GIMPLE statement code +@cindex Adding a new GIMPLE statement code + +The first step in adding a new GIMPLE statement code, is +modifying the file @code{gimple.def}, which contains all the GIMPLE +codes. Then you must add a corresponding gimple subclass +located in @code{gimple.h}. This in turn, will require you to add a +corresponding @code{GTY} tag in @code{gsstruct.def}, and code to handle +this tag in @code{gss_for_code} which is located in @code{gimple.cc}. + +In order for the garbage collector to know the size of the +structure you created in @code{gimple.h}, you need to add a case to +handle your new GIMPLE statement in @code{gimple_size} which is located +in @code{gimple.cc}. + +You will probably want to create a function to build the new +gimple statement in @code{gimple.cc}. The function should be called +@code{gimple_build_@var{new-tuple-name}}, and should return the new tuple +as a pointer to the appropriate gimple subclass. + +If your new statement requires accessors for any members or +operands it may have, put simple inline accessors in +@code{gimple.h} and any non-trivial accessors in @code{gimple.cc} with a +corresponding prototype in @code{gimple.h}. + +You should add the new statement subclass to the class hierarchy diagram +in @code{gimple.texi}. + + +@node Statement and operand traversals +@section Statement and operand traversals +@cindex Statement and operand traversals + +There are two functions available for walking statements and +sequences: @code{walk_gimple_stmt} and @code{walk_gimple_seq}, +accordingly, and a third function for walking the operands in a +statement: @code{walk_gimple_op}. + +@deftypefn {GIMPLE function} tree walk_gimple_stmt (gimple_stmt_iterator *gsi, @ + walk_stmt_fn callback_stmt, walk_tree_fn callback_op, struct walk_stmt_info *wi) +This function is used to walk the current statement in @code{GSI}, +optionally using traversal state stored in @code{WI}. If @code{WI} is @code{NULL}, no +state is kept during the traversal. + +The callback @code{CALLBACK_STMT} is called. If @code{CALLBACK_STMT} returns +true, it means that the callback function has handled all the +operands of the statement and it is not necessary to walk its +operands. + +If @code{CALLBACK_STMT} is @code{NULL} or it returns false, @code{CALLBACK_OP} is +called on each operand of the statement via @code{walk_gimple_op}. If +@code{walk_gimple_op} returns non-@code{NULL} for any operand, the remaining +operands are not scanned. + +The return value is that returned by the last call to +@code{walk_gimple_op}, or @code{NULL_TREE} if no @code{CALLBACK_OP} is specified. +@end deftypefn + + +@deftypefn {GIMPLE function} tree walk_gimple_op (gimple stmt, @ + walk_tree_fn callback_op, struct walk_stmt_info *wi) +Use this function to walk the operands of statement @code{STMT}. Every +operand is walked via @code{walk_tree} with optional state information +in @code{WI}. + +@code{CALLBACK_OP} is called on each operand of @code{STMT} via @code{walk_tree}. +Additional parameters to @code{walk_tree} must be stored in @code{WI}. For +each operand @code{OP}, @code{walk_tree} is called as: + +@smallexample +walk_tree (&@code{OP}, @code{CALLBACK_OP}, @code{WI}, @code{PSET}) +@end smallexample + +If @code{CALLBACK_OP} returns non-@code{NULL} for an operand, the remaining +operands are not scanned. The return value is that returned by +the last call to @code{walk_tree}, or @code{NULL_TREE} if no @code{CALLBACK_OP} is +specified. +@end deftypefn + + +@deftypefn {GIMPLE function} tree walk_gimple_seq (gimple_seq seq, @ + walk_stmt_fn callback_stmt, walk_tree_fn callback_op, struct walk_stmt_info *wi) +This function walks all the statements in the sequence @code{SEQ} +calling @code{walk_gimple_stmt} on each one. @code{WI} is as in +@code{walk_gimple_stmt}. If @code{walk_gimple_stmt} returns non-@code{NULL}, the walk +is stopped and the value returned. Otherwise, all the statements +are walked and @code{NULL_TREE} returned. +@end deftypefn diff --git a/gcc/doc/gnu.texi b/gcc/doc/gnu.texi new file mode 100644 index 00000000000..8ff116aedf5 --- /dev/null +++ b/gcc/doc/gnu.texi @@ -0,0 +1,20 @@ +@c Copyright (C) 2001 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node GNU Project +@unnumbered The GNU Project and GNU/Linux + +The GNU Project was launched in 1984 to develop a complete Unix-like +operating system which is free software: the GNU system. (GNU is a +recursive acronym for ``GNU's Not Unix''; it is pronounced +``guh-NEW''@.) Variants of the GNU operating system, which use the +kernel Linux, are now widely used; though these systems are often +referred to as ``Linux'', they are more accurately called GNU/Linux +systems. + +For more information, see: +@smallexample +@uref{https://www.gnu.org/} +@uref{https://www.gnu.org/gnu/linux-and-gnu.html} +@end smallexample diff --git a/gcc/doc/gty.texi b/gcc/doc/gty.texi new file mode 100644 index 00000000000..4f791b300ba --- /dev/null +++ b/gcc/doc/gty.texi @@ -0,0 +1,735 @@ +@c Copyright (C) 2002-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Type Information +@chapter Memory Management and Type Information +@cindex GGC +@findex GTY + +GCC uses some fairly sophisticated memory management techniques, which +involve determining information about GCC's data structures from GCC's +source code and using this information to perform garbage collection and +implement precompiled headers. + +A full C++ parser would be too complicated for this task, so a limited +subset of C++ is interpreted and special markers are used to determine +what parts of the source to look at. All @code{struct}, @code{union} +and @code{template} structure declarations that define data structures +that are allocated under control of the garbage collector must be +marked. All global variables that hold pointers to garbage-collected +memory must also be marked. Finally, all global variables that need +to be saved and restored by a precompiled header must be marked. (The +precompiled header mechanism can only save static variables if they're +scalar. Complex data structures must be allocated in garbage-collected +memory to be saved in a precompiled header.) + +The full format of a marker is +@smallexample +GTY (([@var{option}] [(@var{param})], [@var{option}] [(@var{param})] @dots{})) +@end smallexample +@noindent +but in most cases no options are needed. The outer double parentheses +are still necessary, though: @code{GTY(())}. Markers can appear: + +@itemize @bullet +@item +In a structure definition, before the open brace; +@item +In a global variable declaration, after the keyword @code{static} or +@code{extern}; and +@item +In a structure field definition, before the name of the field. +@end itemize + +Here are some examples of marking simple data structures and globals. + +@smallexample +struct GTY(()) @var{tag} +@{ + @var{fields}@dots{} +@}; + +typedef struct GTY(()) @var{tag} +@{ + @var{fields}@dots{} +@} *@var{typename}; + +static GTY(()) struct @var{tag} *@var{list}; /* @r{points to GC memory} */ +static GTY(()) int @var{counter}; /* @r{save counter in a PCH} */ +@end smallexample + +The parser understands simple typedefs such as +@code{typedef struct @var{tag} *@var{name};} and +@code{typedef int @var{name};}. +These don't need to be marked. + +However, in combination with GTY, avoid using typedefs such as +@code{typedef int_hash<@dots{}> @var{name};} +for these generate infinite-recursion code. +See @uref{https://gcc.gnu.org/PR103157,PR103157}. +Instead, you may use +@code{struct @var{name} : int_hash<@dots{}> @{@};}, +for example. + +Since @code{gengtype}'s understanding of C++ is limited, there are +several constructs and declarations that are not supported inside +classes/structures marked for automatic GC code generation. The +following C++ constructs produce a @code{gengtype} error on +structures/classes marked for automatic GC code generation: + +@itemize @bullet +@item +Type definitions inside classes/structures are not supported. +@item +Enumerations inside classes/structures are not supported. +@end itemize + +If you have a class or structure using any of the above constructs, +you need to mark that class as @code{GTY ((user))} and provide your +own marking routines (see section @ref{User GC} for details). + +It is always valid to include function definitions inside classes. +Those are always ignored by @code{gengtype}, as it only cares about +data members. + +@menu +* GTY Options:: What goes inside a @code{GTY(())}. +* Inheritance and GTY:: Adding GTY to a class hierarchy. +* User GC:: Adding user-provided GC marking routines. +* GGC Roots:: Making global variables GGC roots. +* Files:: How the generated files work. +* Invoking the garbage collector:: How to invoke the garbage collector. +* Troubleshooting:: When something does not work as expected. +@end menu + +@node GTY Options +@section The Inside of a @code{GTY(())} + +Sometimes the C code is not enough to fully describe the type +structure. Extra information can be provided with @code{GTY} options +and additional markers. Some options take a parameter, which may be +either a string or a type name, depending on the parameter. If an +option takes no parameter, it is acceptable either to omit the +parameter entirely, or to provide an empty string as a parameter. For +example, @code{@w{GTY ((skip))}} and @code{@w{GTY ((skip ("")))}} are +equivalent. + +When the parameter is a string, often it is a fragment of C code. Four +special escapes may be used in these strings, to refer to pieces of +the data structure being marked: + +@cindex % in GTY option +@table @code +@item %h +The current structure. +@item %1 +The structure that immediately contains the current structure. +@item %0 +The outermost structure that contains the current structure. +@item %a +A partial expression of the form @code{[i1][i2]@dots{}} that indexes +the array item currently being marked. +@end table + +For instance, suppose that you have a structure of the form +@smallexample +struct A @{ + @dots{} +@}; +struct B @{ + struct A foo[12]; +@}; +@end smallexample +@noindent +and @code{b} is a variable of type @code{struct B}. When marking +@samp{b.foo[11]}, @code{%h} would expand to @samp{b.foo[11]}, +@code{%0} and @code{%1} would both expand to @samp{b}, and @code{%a} +would expand to @samp{[11]}. + +As in ordinary C, adjacent strings will be concatenated; this is +helpful when you have a complicated expression. +@smallexample +@group +GTY ((chain_next ("TREE_CODE (&%h.generic) == INTEGER_TYPE" + " ? TYPE_NEXT_VARIANT (&%h.generic)" + " : TREE_CHAIN (&%h.generic)"))) +@end group +@end smallexample + +The available options are: + +@table @code +@findex length +@item length ("@var{expression}") + +There are two places the type machinery will need to be explicitly told +the length of an array of non-atomic objects. The first case is when a +structure ends in a variable-length array, like this: +@smallexample +struct GTY(()) rtvec_def @{ + int num_elem; /* @r{number of elements} */ + rtx GTY ((length ("%h.num_elem"))) elem[1]; +@}; +@end smallexample + +In this case, the @code{length} option is used to override the specified +array length (which should usually be @code{1}). The parameter of the +option is a fragment of C code that calculates the length. + +The second case is when a structure or a global variable contains a +pointer to an array, like this: +@smallexample +struct gimple_omp_for_iter * GTY((length ("%h.collapse"))) iter; +@end smallexample +In this case, @code{iter} has been allocated by writing something like +@smallexample + x->iter = ggc_alloc_cleared_vec_gimple_omp_for_iter (collapse); +@end smallexample +and the @code{collapse} provides the length of the field. + +This second use of @code{length} also works on global variables, like: +@verbatim +static GTY((length("reg_known_value_size"))) rtx *reg_known_value; +@end verbatim + +Note that the @code{length} option is only meant for use with arrays of +non-atomic objects, that is, objects that contain pointers pointing to +other GTY-managed objects. For other GC-allocated arrays and strings +you should use @code{atomic} or @code{string_length}. + +@findex string_length +@item string_length ("@var{expression}") + +In order to simplify production of PCH, a structure member that is a plain +array of bytes (an optionally @code{const} and/or @code{unsigned} @code{char +*}) is treated specially by the infrastructure. Even if such an array has not +been allocated in GC-controlled memory, it will still be written properly into +a PCH. The machinery responsible for this needs to know the length of the +data; by default, the length is determined by calling @code{strlen} on the +pointer. The @code{string_length} option specifies an alternate way to +determine the length, such as by inspecting another struct member: + +@smallexample +struct GTY(()) non_terminated_string @{ + size_t sz; + const char * GTY((string_length ("%h.sz"))) data; +@}; +@end smallexample + +@findex skip +@item skip + +If @code{skip} is applied to a field, the type machinery will ignore it. +This is somewhat dangerous; the only safe use is in a union when one +field really isn't ever used. + +@findex callback +@item callback + +@code{callback} should be applied to fields with pointer to function type +and causes the field to be ignored similarly to @code{skip}, except when +writing PCH and the field is non-NULL it will remember the field's address +for relocation purposes if the process writing PCH has different load base +from a process reading PCH. + +@findex for_user +@item for_user + +Use this to mark types that need to be marked by user gc routines, but are not +refered to in a template argument. So if you have some user gc type T1 and a +non user gc type T2 you can give T2 the for_user option so that the marking +functions for T1 can call non mangled functions to mark T2. + +@findex desc +@findex tag +@findex default +@item desc ("@var{expression}") +@itemx tag ("@var{constant}") +@itemx default + +The type machinery needs to be told which field of a @code{union} is +currently active. This is done by giving each field a constant +@code{tag} value, and then specifying a discriminator using @code{desc}. +The value of the expression given by @code{desc} is compared against +each @code{tag} value, each of which should be different. If no +@code{tag} is matched, the field marked with @code{default} is used if +there is one, otherwise no field in the union will be marked. + +In the @code{desc} option, the ``current structure'' is the union that +it discriminates. Use @code{%1} to mean the structure containing it. +There are no escapes available to the @code{tag} option, since it is a +constant. + +For example, +@smallexample +struct GTY(()) tree_binding +@{ + struct tree_common common; + union tree_binding_u @{ + tree GTY ((tag ("0"))) scope; + struct cp_binding_level * GTY ((tag ("1"))) level; + @} GTY ((desc ("BINDING_HAS_LEVEL_P ((tree)&%0)"))) xscope; + tree value; +@}; +@end smallexample + +In this example, the value of BINDING_HAS_LEVEL_P when applied to a +@code{struct tree_binding *} is presumed to be 0 or 1. If 1, the type +mechanism will treat the field @code{level} as being present and if 0, +will treat the field @code{scope} as being present. + +The @code{desc} and @code{tag} options can also be used for inheritance +to denote which subclass an instance is. See @ref{Inheritance and GTY} +for more information. + +@findex cache +@item cache + +When the @code{cache} option is applied to a global variable gt_cleare_cache is +called on that variable between the mark and sweep phases of garbage +collection. The gt_clear_cache function is free to mark blocks as used, or to +clear pointers in the variable. + +@findex deletable +@item deletable + +@code{deletable}, when applied to a global variable, indicates that when +garbage collection runs, there's no need to mark anything pointed to +by this variable, it can just be set to @code{NULL} instead. This is used +to keep a list of free structures around for re-use. + +@findex maybe_undef +@item maybe_undef + +When applied to a field, @code{maybe_undef} indicates that it's OK if +the structure that this fields points to is never defined, so long as +this field is always @code{NULL}. This is used to avoid requiring +backends to define certain optional structures. It doesn't work with +language frontends. + +@findex nested_ptr +@item nested_ptr (@var{type}, "@var{to expression}", "@var{from expression}") + +The type machinery expects all pointers to point to the start of an +object. Sometimes for abstraction purposes it's convenient to have +a pointer which points inside an object. So long as it's possible to +convert the original object to and from the pointer, such pointers +can still be used. @var{type} is the type of the original object, +the @var{to expression} returns the pointer given the original object, +and the @var{from expression} returns the original object given +the pointer. The pointer will be available using the @code{%h} +escape. + +@findex chain_next +@findex chain_prev +@findex chain_circular +@item chain_next ("@var{expression}") +@itemx chain_prev ("@var{expression}") +@itemx chain_circular ("@var{expression}") + +It's helpful for the type machinery to know if objects are often +chained together in long lists; this lets it generate code that uses +less stack space by iterating along the list instead of recursing down +it. @code{chain_next} is an expression for the next item in the list, +@code{chain_prev} is an expression for the previous item. For singly +linked lists, use only @code{chain_next}; for doubly linked lists, use +both. The machinery requires that taking the next item of the +previous item gives the original item. @code{chain_circular} is similar +to @code{chain_next}, but can be used for circular single linked lists. + +@findex reorder +@item reorder ("@var{function name}") + +Some data structures depend on the relative ordering of pointers. If +the precompiled header machinery needs to change that ordering, it +will call the function referenced by the @code{reorder} option, before +changing the pointers in the object that's pointed to by the field the +option applies to. The function must take four arguments, with the +signature @samp{@w{void *, void *, gt_pointer_operator, void *}}. +The first parameter is a pointer to the structure that contains the +object being updated, or the object itself if there is no containing +structure. The second parameter is a cookie that should be ignored. +The third parameter is a routine that, given a pointer, will update it +to its correct new value. The fourth parameter is a cookie that must +be passed to the second parameter. + +PCH cannot handle data structures that depend on the absolute values +of pointers. @code{reorder} functions can be expensive. When +possible, it is better to depend on properties of the data, like an ID +number or the hash of a string instead. + +@findex atomic +@item atomic + +The @code{atomic} option can only be used with pointers. It informs +the GC machinery that the memory that the pointer points to does not +contain any pointers, and hence it should be treated by the GC and PCH +machinery as an ``atomic'' block of memory that does not need to be +examined when scanning memory for pointers. In particular, the +machinery will not scan that memory for pointers to mark them as +reachable (when marking pointers for GC) or to relocate them (when +writing a PCH file). + +The @code{atomic} option differs from the @code{skip} option. +@code{atomic} keeps the memory under Garbage Collection, but makes the +GC ignore the contents of the memory. @code{skip} is more drastic in +that it causes the pointer and the memory to be completely ignored by +the Garbage Collector. So, memory marked as @code{atomic} is +automatically freed when no longer reachable, while memory marked as +@code{skip} is not. + +The @code{atomic} option must be used with great care, because all +sorts of problem can occur if used incorrectly, that is, if the memory +the pointer points to does actually contain a pointer. + +Here is an example of how to use it: +@smallexample +struct GTY(()) my_struct @{ + int number_of_elements; + unsigned int * GTY ((atomic)) elements; +@}; +@end smallexample +In this case, @code{elements} is a pointer under GC, and the memory it +points to needs to be allocated using the Garbage Collector, and will +be freed automatically by the Garbage Collector when it is no longer +referenced. But the memory that the pointer points to is an array of +@code{unsigned int} elements, and the GC must not try to scan it to +find pointers to mark or relocate, which is why it is marked with the +@code{atomic} option. + +Note that, currently, global variables cannot be marked with +@code{atomic}; only fields of a struct can. This is a known +limitation. It would be useful to be able to mark global pointers +with @code{atomic} to make the PCH machinery aware of them so that +they are saved and restored correctly to PCH files. + +@findex special +@item special ("@var{name}") + +The @code{special} option is used to mark types that have to be dealt +with by special case machinery. The parameter is the name of the +special case. See @file{gengtype.cc} for further details. Avoid +adding new special cases unless there is no other alternative. + +@findex user +@item user + +The @code{user} option indicates that the code to mark structure +fields is completely handled by user-provided routines. See section +@ref{User GC} for details on what functions need to be provided. +@end table + +@node Inheritance and GTY +@section Support for inheritance +gengtype has some support for simple class hierarchies. You can use +this to have gengtype autogenerate marking routines, provided: + +@itemize @bullet +@item +There must be a concrete base class, with a discriminator expression +that can be used to identify which subclass an instance is. +@item +Only single inheritance is used. +@item +None of the classes within the hierarchy are templates. +@end itemize + +If your class hierarchy does not fit in this pattern, you must use +@ref{User GC} instead. + +The base class and its discriminator must be identified using the ``desc'' +option. Each concrete subclass must use the ``tag'' option to identify +which value of the discriminator it corresponds to. + +Every class in the hierarchy must have a @code{GTY(())} marker, as +gengtype will only attempt to parse classes that have such a marker +@footnote{Classes lacking such a marker will not be identified as being +part of the hierarchy, and so the marking routines will not handle them, +leading to a assertion failure within the marking routines due to an +unknown tag value (assuming that assertions are enabled).}. + +@smallexample +class GTY((desc("%h.kind"), tag("0"))) example_base +@{ +public: + int kind; + tree a; +@}; + +class GTY((tag("1"))) some_subclass : public example_base +@{ +public: + tree b; +@}; + +class GTY((tag("2"))) some_other_subclass : public example_base +@{ +public: + tree c; +@}; +@end smallexample + +The generated marking routines for the above will contain a ``switch'' +on ``kind'', visiting all appropriate fields. For example, if kind is +2, it will cast to ``some_other_subclass'' and visit fields a, b, and c. + +@node User GC +@section Support for user-provided GC marking routines +@cindex user gc +The garbage collector supports types for which no automatic marking +code is generated. For these types, the user is required to provide +three functions: one to act as a marker for garbage collection, and +two functions to act as marker and pointer walker for pre-compiled +headers. + +Given a structure @code{struct GTY((user)) my_struct}, the following functions +should be defined to mark @code{my_struct}: + +@smallexample +void gt_ggc_mx (my_struct *p) +@{ + /* This marks field 'fld'. */ + gt_ggc_mx (p->fld); +@} + +void gt_pch_nx (my_struct *p) +@{ + /* This marks field 'fld'. */ + gt_pch_nx (tp->fld); +@} + +void gt_pch_nx (my_struct *p, gt_pointer_operator op, void *cookie) +@{ + /* For every field 'fld', call the given pointer operator. */ + op (&(tp->fld), NULL, cookie); +@} +@end smallexample + +In general, each marker @code{M} should call @code{M} for every +pointer field in the structure. Fields that are not allocated in GC +or are not pointers must be ignored. + +For embedded lists (e.g., structures with a @code{next} or @code{prev} +pointer), the marker must follow the chain and mark every element in +it. + +Note that the rules for the pointer walker @code{gt_pch_nx (my_struct +*, gt_pointer_operator, void *)} are slightly different. In this +case, the operation @code{op} must be applied to the @emph{address} of +every pointer field. + +@subsection User-provided marking routines for template types +When a template type @code{TP} is marked with @code{GTY}, all +instances of that type are considered user-provided types. This means +that the individual instances of @code{TP} do not need to be marked +with @code{GTY}. The user needs to provide template functions to mark +all the fields of the type. + +The following code snippets represent all the functions that need to +be provided. Note that type @code{TP} may reference to more than one +type. In these snippets, there is only one type @code{T}, but there +could be more. + +@smallexample +template +void gt_ggc_mx (TP *tp) +@{ + extern void gt_ggc_mx (T&); + + /* This marks field 'fld' of type 'T'. */ + gt_ggc_mx (tp->fld); +@} + +template +void gt_pch_nx (TP *tp) +@{ + extern void gt_pch_nx (T&); + + /* This marks field 'fld' of type 'T'. */ + gt_pch_nx (tp->fld); +@} + +template +void gt_pch_nx (TP *tp, gt_pointer_operator op, void *cookie) +@{ + /* For every field 'fld' of 'tp' with type 'T *', call the given + pointer operator. */ + op (&(tp->fld), NULL, cookie); +@} + +template +void gt_pch_nx (TP *tp, gt_pointer_operator, void *cookie) +@{ + extern void gt_pch_nx (T *, gt_pointer_operator, void *); + + /* For every field 'fld' of 'tp' with type 'T', call the pointer + walker for all the fields of T. */ + gt_pch_nx (&(tp->fld), op, cookie); +@} +@end smallexample + +Support for user-defined types is currently limited. The following +restrictions apply: + +@enumerate +@item Type @code{TP} and all the argument types @code{T} must be +marked with @code{GTY}. + +@item Type @code{TP} can only have type names in its argument list. + +@item The pointer walker functions are different for @code{TP} and +@code{TP}. In the case of @code{TP}, references to +@code{T} must be handled by calling @code{gt_pch_nx} (which +will, in turn, walk all the pointers inside fields of @code{T}). +In the case of @code{TP}, references to @code{T *} must be +handled by calling the @code{op} function on the address of the +pointer (see the code snippets above). +@end enumerate + +@node GGC Roots +@section Marking Roots for the Garbage Collector +@cindex roots, marking +@cindex marking roots + +In addition to keeping track of types, the type machinery also locates +the global variables (@dfn{roots}) that the garbage collector starts +at. Roots must be declared using one of the following syntaxes: + +@itemize @bullet +@item +@code{extern GTY(([@var{options}])) @var{type} @var{name};} +@item +@code{static GTY(([@var{options}])) @var{type} @var{name};} +@end itemize +@noindent +The syntax +@itemize @bullet +@item +@code{GTY(([@var{options}])) @var{type} @var{name};} +@end itemize +@noindent +is @emph{not} accepted. There should be an @code{extern} declaration +of such a variable in a header somewhere---mark that, not the +definition. Or, if the variable is only used in one file, make it +@code{static}. + +@node Files +@section Source Files Containing Type Information +@cindex generated files +@cindex files, generated + +Whenever you add @code{GTY} markers to a source file that previously +had none, or create a new source file containing @code{GTY} markers, +there are three things you need to do: + +@enumerate +@item +You need to add the file to the list of source files the type +machinery scans. There are four cases: + +@enumerate a +@item +For a back-end file, this is usually done +automatically; if not, you should add it to @code{target_gtfiles} in +the appropriate port's entries in @file{config.gcc}. + +@item +For files shared by all front ends, add the filename to the +@code{GTFILES} variable in @file{Makefile.in}. + +@item +For files that are part of one front end, add the filename to the +@code{gtfiles} variable defined in the appropriate +@file{config-lang.in}. +Headers should appear before non-headers in this list. + +@item +For files that are part of some but not all front ends, add the +filename to the @code{gtfiles} variable of @emph{all} the front ends +that use it. +@end enumerate + +@item +If the file was a header file, you'll need to check that it's included +in the right place to be visible to the generated files. For a back-end +header file, this should be done automatically. For a front-end header +file, it needs to be included by the same file that includes +@file{gtype-@var{lang}.h}. For other header files, it needs to be +included in @file{gtype-desc.cc}, which is a generated file, so add it to +@code{ifiles} in @code{open_base_file} in @file{gengtype.cc}. + +For source files that aren't header files, the machinery will generate a +header file that should be included in the source file you just changed. +The file will be called @file{gt-@var{path}.h} where @var{path} is the +pathname relative to the @file{gcc} directory with slashes replaced by +@verb{|-|}, so for example the header file to be included in +@file{cp/parser.cc} is called @file{gt-cp-parser.h}. The +generated header file should be included after everything else in the +source file. + +@end enumerate + +For language frontends, there is another file that needs to be included +somewhere. It will be called @file{gtype-@var{lang}.h}, where +@var{lang} is the name of the subdirectory the language is contained in. + +Plugins can add additional root tables. Run the @code{gengtype} +utility in plugin mode as @code{gengtype -P pluginout.h @var{source-dir} +@var{file-list} @var{plugin*.c}} with your plugin files +@var{plugin*.c} using @code{GTY} to generate the @var{pluginout.h} file. +The GCC build tree is needed to be present in that mode. + + +@node Invoking the garbage collector +@section How to invoke the garbage collector +@cindex garbage collector, invocation +@findex ggc_collect + +The GCC garbage collector GGC is only invoked explicitly. In contrast +with many other garbage collectors, it is not implicitly invoked by +allocation routines when a lot of memory has been consumed. So the +only way to have GGC reclaim storage is to call the @code{ggc_collect} +function explicitly. +With @var{mode} @code{GGC_COLLECT_FORCE} or otherwise (default +@code{GGC_COLLECT_HEURISTIC}) when the internal heuristic decides to +collect, this call is potentially an expensive operation, as it may +have to scan the entire heap. Beware that local variables (on the GCC +call stack) are not followed by such an invocation (as many other +garbage collectors do): you should reference all your data from static +or external @code{GTY}-ed variables, and it is advised to call +@code{ggc_collect} with a shallow call stack. The GGC is an exact mark +and sweep garbage collector (so it does not scan the call stack for +pointers). In practice GCC passes don't often call @code{ggc_collect} +themselves, because it is called by the pass manager between passes. + +At the time of the @code{ggc_collect} call all pointers in the GC-marked +structures must be valid or @code{NULL}. In practice this means that +there should not be uninitialized pointer fields in the structures even +if your code never reads or writes those fields at a particular +instance. One way to ensure this is to use cleared versions of +allocators unless all the fields are initialized manually immediately +after allocation. + +@node Troubleshooting +@section Troubleshooting the garbage collector +@cindex garbage collector, troubleshooting + +With the current garbage collector implementation, most issues should +show up as GCC compilation errors. Some of the most commonly +encountered issues are described below. + +@itemize @bullet +@item Gengtype does not produce allocators for a @code{GTY}-marked type. +Gengtype checks if there is at least one possible path from GC roots to +at least one instance of each type before outputting allocators. If +there is no such path, the @code{GTY} markers will be ignored and no +allocators will be output. Solve this by making sure that there exists +at least one such path. If creating it is unfeasible or raises a ``code +smell'', consider if you really must use GC for allocating such type. + +@item Link-time errors about undefined @code{gt_ggc_r_foo_bar} and +similarly-named symbols. Check if your @file{foo_bar} source file has +@code{#include "gt-foo_bar.h"} as its very last line. + +@end itemize diff --git a/gcc/doc/headerdirs.texi b/gcc/doc/headerdirs.texi new file mode 100644 index 00000000000..82269342a0d --- /dev/null +++ b/gcc/doc/headerdirs.texi @@ -0,0 +1,32 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Header Dirs +@chapter Standard Header File Directories + +@code{GCC_INCLUDE_DIR} means the same thing for native and cross. It is +where GCC stores its private include files, and also where GCC +stores the fixed include files. A cross compiled GCC runs +@code{fixincludes} on the header files in @file{$(tooldir)/include}. +(If the cross compilation header files need to be fixed, they must be +installed before GCC is built. If the cross compilation header files +are already suitable for GCC, nothing special need be done). + +@code{GPLUSPLUS_INCLUDE_DIR} means the same thing for native and cross. It +is where @command{g++} looks first for header files. The C++ library +installs only target independent header files in that directory. + +@code{LOCAL_INCLUDE_DIR} is used only by native compilers. GCC +doesn't install anything there. It is normally +@file{/usr/local/include}. This is where local additions to a packaged +system should place header files. + +@code{CROSS_INCLUDE_DIR} is used only by cross compilers. GCC +doesn't install anything there. + +@code{TOOL_INCLUDE_DIR} is used for both native and cross compilers. It +is the place for other packages to install header files that GCC will +use. For a cross-compiler, this is the equivalent of +@file{/usr/include}. When you build a cross-compiler, +@code{fixincludes} processes any header files in this directory. diff --git a/gcc/doc/hostconfig.texi b/gcc/doc/hostconfig.texi new file mode 100644 index 00000000000..4b6ca464cf5 --- /dev/null +++ b/gcc/doc/hostconfig.texi @@ -0,0 +1,229 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gccint.texi. + +@node Host Config +@chapter Host Configuration +@cindex host configuration + +Most details about the machine and system on which the compiler is +actually running are detected by the @command{configure} script. Some +things are impossible for @command{configure} to detect; these are +described in two ways, either by macros defined in a file named +@file{xm-@var{machine}.h} or by hook functions in the file specified +by the @var{out_host_hook_obj} variable in @file{config.gcc}. (The +intention is that very few hosts will need a header file but nearly +every fully supported host will need to override some hooks.) + +If you need to define only a few macros, and they have simple +definitions, consider using the @code{xm_defines} variable in your +@file{config.gcc} entry instead of creating a host configuration +header. @xref{System Config}. + +@menu +* Host Common:: Things every host probably needs implemented. +* Filesystem:: Your host cannot have the letter `a' in filenames? +* Host Misc:: Rare configuration options for hosts. +@end menu + +@node Host Common +@section Host Common +@cindex host hooks +@cindex host functions + +Some things are just not portable, even between similar operating systems, +and are too difficult for autoconf to detect. They get implemented using +hook functions in the file specified by the @var{host_hook_obj} +variable in @file{config.gcc}. + +@deftypefn {Host Hook} void HOST_HOOKS_EXTRA_SIGNALS (void) +This host hook is used to set up handling for extra signals. The most +common thing to do in this hook is to detect stack overflow. +@end deftypefn + +@deftypefn {Host Hook} {void *} HOST_HOOKS_GT_PCH_GET_ADDRESS (size_t @ + @var{size}, int @var{fd}) +This host hook returns the address of some space that is likely to be +free in some subsequent invocation of the compiler. We intend to load +the PCH data at this address such that the data need not be relocated. +The area should be able to hold @var{size} bytes. If the host uses +@code{mmap}, @var{fd} is an open file descriptor that can be used for +probing. +@end deftypefn + +@deftypefn {Host Hook} int HOST_HOOKS_GT_PCH_USE_ADDRESS (void * @var{address}, @ + size_t @var{size}, int @var{fd}, size_t @var{offset}) +This host hook is called when a PCH file is about to be loaded. +We want to load @var{size} bytes from @var{fd} at @var{offset} +into memory at @var{address}. The given address will be the result of +a previous invocation of @code{HOST_HOOKS_GT_PCH_GET_ADDRESS}. +Return @minus{}1 if we couldn't allocate @var{size} bytes at @var{address}. +Return 0 if the memory is allocated but the data is not loaded. Return 1 +if the hook has performed everything. + +If the implementation uses reserved address space, free any reserved +space beyond @var{size}, regardless of the return value. If no PCH will +be loaded, this hook may be called with @var{size} zero, in which case +all reserved address space should be freed. + +Do not try to handle values of @var{address} that could not have been +returned by this executable; just return @minus{}1. Such values usually +indicate an out-of-date PCH file (built by some other GCC executable), +and such a PCH file won't work. +@end deftypefn + +@deftypefn {Host Hook} size_t HOST_HOOKS_GT_PCH_ALLOC_GRANULARITY (void); +This host hook returns the alignment required for allocating virtual +memory. Usually this is the same as getpagesize, but on some hosts the +alignment for reserving memory differs from the pagesize for committing +memory. +@end deftypefn + +@node Filesystem +@section Host Filesystem +@cindex configuration file +@cindex @file{xm-@var{machine}.h} + +GCC needs to know a number of things about the semantics of the host +machine's filesystem. Filesystems with Unix and MS-DOS semantics are +automatically detected. For other systems, you can define the +following macros in @file{xm-@var{machine}.h}. + +@ftable @code +@item HAVE_DOS_BASED_FILE_SYSTEM +This macro is automatically defined by @file{system.h} if the host +file system obeys the semantics defined by MS-DOS instead of Unix. +DOS file systems are case insensitive, file specifications may begin +with a drive letter, and both forward slash and backslash (@samp{/} +and @samp{\}) are directory separators. + +@item DIR_SEPARATOR +@itemx DIR_SEPARATOR_2 +If defined, these macros expand to character constants specifying +separators for directory names within a file specification. +@file{system.h} will automatically give them appropriate values on +Unix and MS-DOS file systems. If your file system is neither of +these, define one or both appropriately in @file{xm-@var{machine}.h}. + +However, operating systems like VMS, where constructing a pathname is +more complicated than just stringing together directory names +separated by a special character, should not define either of these +macros. + +@item PATH_SEPARATOR +If defined, this macro should expand to a character constant +specifying the separator for elements of search paths. The default +value is a colon (@samp{:}). DOS-based systems usually, but not +always, use semicolon (@samp{;}). + +@item VMS +Define this macro if the host system is VMS@. + +@item HOST_OBJECT_SUFFIX +Define this macro to be a C string representing the suffix for object +files on your host machine. If you do not define this macro, GCC will +use @samp{.o} as the suffix for object files. + +@item HOST_EXECUTABLE_SUFFIX +Define this macro to be a C string representing the suffix for +executable files on your host machine. If you do not define this macro, +GCC will use the null string as the suffix for executable files. + +@item HOST_BIT_BUCKET +A pathname defined by the host operating system, which can be opened as +a file and written to, but all the information written is discarded. +This is commonly known as a @dfn{bit bucket} or @dfn{null device}. If +you do not define this macro, GCC will use @samp{/dev/null} as the bit +bucket. If the host does not support a bit bucket, define this macro to +an invalid filename. + +@item UPDATE_PATH_HOST_CANONICALIZE (@var{path}) +If defined, a C statement (sans semicolon) that performs host-dependent +canonicalization when a path used in a compilation driver or +preprocessor is canonicalized. @var{path} is a malloc-ed path to be +canonicalized. If the C statement does canonicalize @var{path} into a +different buffer, the old path should be freed and the new buffer should +have been allocated with malloc. + +@item DUMPFILE_FORMAT +Define this macro to be a C string representing the format to use for +constructing the index part of debugging dump file names. The resultant +string must fit in fifteen bytes. The full filename will be the +concatenation of: the prefix of the assembler file name, the string +resulting from applying this format to an index number, and a string +unique to each dump file kind, e.g.@: @samp{rtl}. + +If you do not define this macro, GCC will use @samp{.%02d.}. You should +define this macro if using the default will create an invalid file name. + +@item DELETE_IF_ORDINARY +Define this macro to be a C statement (sans semicolon) that performs +host-dependent removal of ordinary temp files in the compilation driver. + +If you do not define this macro, GCC will use the default version. You +should define this macro if the default version does not reliably remove +the temp file as, for example, on VMS which allows multiple versions +of a file. + +@item HOST_LACKS_INODE_NUMBERS +Define this macro if the host filesystem does not report meaningful inode +numbers in struct stat. +@end ftable + +@node Host Misc +@section Host Misc +@cindex configuration file +@cindex @file{xm-@var{machine}.h} + +@ftable @code +@item FATAL_EXIT_CODE +A C expression for the status code to be returned when the compiler +exits after serious errors. The default is the system-provided macro +@samp{EXIT_FAILURE}, or @samp{1} if the system doesn't define that +macro. Define this macro only if these defaults are incorrect. + +@item SUCCESS_EXIT_CODE +A C expression for the status code to be returned when the compiler +exits without serious errors. (Warnings are not serious errors.) The +default is the system-provided macro @samp{EXIT_SUCCESS}, or @samp{0} if +the system doesn't define that macro. Define this macro only if these +defaults are incorrect. + +@item USE_C_ALLOCA +Define this macro if GCC should use the C implementation of @code{alloca} +provided by @file{libiberty.a}. This only affects how some parts of the +compiler itself allocate memory. It does not change code generation. + +When GCC is built with a compiler other than itself, the C @code{alloca} +is always used. This is because most other implementations have serious +bugs. You should define this macro only on a system where no +stack-based @code{alloca} can possibly work. For instance, if a system +has a small limit on the size of the stack, GCC's builtin @code{alloca} +will not work reliably. + +@item COLLECT2_HOST_INITIALIZATION +If defined, a C statement (sans semicolon) that performs host-dependent +initialization when @code{collect2} is being initialized. + +@item GCC_DRIVER_HOST_INITIALIZATION +If defined, a C statement (sans semicolon) that performs host-dependent +initialization when a compilation driver is being initialized. + +@item HOST_LONG_LONG_FORMAT +If defined, the string used to indicate an argument of type @code{long +long} to functions like @code{printf}. The default value is +@code{"ll"}. + +@item HOST_LONG_FORMAT +If defined, the string used to indicate an argument of type @code{long} +to functions like @code{printf}. The default value is @code{"l"}. + +@item HOST_PTR_PRINTF +If defined, the string used to indicate an argument of type @code{void *} +to functions like @code{printf}. The default value is @code{"%p"}. +@end ftable + +In addition, if @command{configure} generates an incorrect definition of +any of the macros in @file{auto-host.h}, you can override that +definition in a host configuration header. If you need to do this, +first see if it is possible to fix @command{configure}. diff --git a/gcc/doc/implement-c.texi b/gcc/doc/implement-c.texi new file mode 100644 index 00000000000..c2088ffa777 --- /dev/null +++ b/gcc/doc/implement-c.texi @@ -0,0 +1,746 @@ +@c Copyright (C) 2001-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node C Implementation +@chapter C Implementation-Defined Behavior +@cindex implementation-defined behavior, C language + +A conforming implementation of ISO C is required to document its +choice of behavior in each of the areas that are designated +``implementation defined''. The following lists all such areas, +along with the section numbers from the ISO/IEC 9899:1990, ISO/IEC +9899:1999 and ISO/IEC 9899:2011 standards. Some areas are only +implementation-defined in one version of the standard. + +Some choices depend on the externally determined ABI for the platform +(including standard character encodings) which GCC follows; these are +listed as ``determined by ABI'' below. @xref{Compatibility, , Binary +Compatibility}, and @uref{https://gcc.gnu.org/readings.html}. Some +choices are documented in the preprocessor manual. +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. Some choices are made by the +library and operating system (or other environment when compiling for +a freestanding environment); refer to their documentation for details. + +@menu +* Translation implementation:: +* Environment implementation:: +* Identifiers implementation:: +* Characters implementation:: +* Integers implementation:: +* Floating point implementation:: +* Arrays and pointers implementation:: +* Hints implementation:: +* Structures unions enumerations and bit-fields implementation:: +* Qualifiers implementation:: +* Declarators implementation:: +* Statements implementation:: +* Preprocessing directives implementation:: +* Library functions implementation:: +* Architecture implementation:: +* Locale-specific behavior implementation:: +@end menu + +@node Translation implementation +@section Translation + +@itemize @bullet +@item +@cite{How a diagnostic is identified (C90 3.7, C99 and C11 3.10, C90, +C99 and C11 5.1.1.3).} + +Diagnostics consist of all the output sent to stderr by GCC@. + +@item +@cite{Whether each nonempty sequence of white-space characters other than +new-line is retained or replaced by one space character in translation +phase 3 (C90, C99 and C11 5.1.1.2).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. + +@end itemize + +@node Environment implementation +@section Environment + +The behavior of most of these points are dependent on the implementation +of the C library, and are not defined by GCC itself. + +@itemize @bullet +@item +@cite{The mapping between physical source file multibyte characters +and the source character set in translation phase 1 (C90, C99 and C11 +5.1.1.2).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. + +@end itemize + +@node Identifiers implementation +@section Identifiers + +@itemize @bullet +@item +@cite{Which additional multibyte characters may appear in identifiers +and their correspondence to universal character names (C99 and C11 6.4.2).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. + +@item +@cite{The number of significant initial characters in an identifier +(C90 6.1.2, C90, C99 and C11 5.2.4.1, C99 and C11 6.4.2).} + +For internal names, all characters are significant. For external names, +the number of significant characters are defined by the linker; for +almost all targets, all characters are significant. + +@item +@cite{Whether case distinctions are significant in an identifier with +external linkage (C90 6.1.2).} + +This is a property of the linker. C99 and C11 require that case distinctions +are always significant in identifiers with external linkage and +systems without this property are not supported by GCC@. + +@end itemize + +@node Characters implementation +@section Characters + +@itemize @bullet +@item +@cite{The number of bits in a byte (C90 3.4, C99 and C11 3.6).} + +Determined by ABI@. + +@item +@cite{The values of the members of the execution character set (C90, +C99 and C11 5.2.1).} + +Determined by ABI@. + +@item +@cite{The unique value of the member of the execution character set produced +for each of the standard alphabetic escape sequences (C90, C99 and C11 +5.2.2).} + +Determined by ABI@. + +@item +@cite{The value of a @code{char} object into which has been stored any +character other than a member of the basic execution character set +(C90 6.1.2.5, C99 and C11 6.2.5).} + +Determined by ABI@. + +@item +@cite{Which of @code{signed char} or @code{unsigned char} has the same +range, representation, and behavior as ``plain'' @code{char} (C90 +6.1.2.5, C90 6.2.1.1, C99 and C11 6.2.5, C99 and C11 6.3.1.1).} + +@opindex fsigned-char +@opindex funsigned-char +Determined by ABI@. The options @option{-funsigned-char} and +@option{-fsigned-char} change the default. @xref{C Dialect Options, , +Options Controlling C Dialect}. + +@item +@cite{The mapping of members of the source character set (in character +constants and string literals) to members of the execution character +set (C90 6.1.3.4, C99 and C11 6.4.4.4, C90, C99 and C11 5.1.1.2).} + +Determined by ABI@. + +@item +@cite{The value of an integer character constant containing more than one +character or containing a character or escape sequence that does not map +to a single-byte execution character (C90 6.1.3.4, C99 and C11 6.4.4.4).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. + +@item +@cite{The value of a wide character constant containing more than one +multibyte character or a single multibyte character that maps to +multiple members of the extended execution character set, or +containing a multibyte character or escape sequence not represented in +the extended execution character set (C90 6.1.3.4, C99 and C11 +6.4.4.4).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. + +@item +@cite{The current locale used to convert a wide character constant consisting +of a single multibyte character that maps to a member of the extended +execution character set into a corresponding wide character code (C90 +6.1.3.4, C99 and C11 6.4.4.4).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. + +@item +@cite{Whether differently-prefixed wide string literal tokens can be +concatenated and, if so, the treatment of the resulting multibyte +character sequence (C11 6.4.5).} + +Such tokens may not be concatenated. + +@item +@cite{The current locale used to convert a wide string literal into +corresponding wide character codes (C90 6.1.4, C99 and C11 6.4.5).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. + +@item +@cite{The value of a string literal containing a multibyte character or escape +sequence not represented in the execution character set (C90 6.1.4, +C99 and C11 6.4.5).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. + +@item +@cite{The encoding of any of @code{wchar_t}, @code{char16_t}, and +@code{char32_t} where the corresponding standard encoding macro +(@code{__STDC_ISO_10646__}, @code{__STDC_UTF_16__}, or +@code{__STDC_UTF_32__}) is not defined (C11 6.10.8.2).} + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. @code{char16_t} and +@code{char32_t} literals are always encoded in UTF-16 and UTF-32 +respectively. + +@end itemize + +@node Integers implementation +@section Integers + +@itemize @bullet +@item +@cite{Any extended integer types that exist in the implementation (C99 +and C11 6.2.5).} + +GCC does not support any extended integer types. +@c The __mode__ attribute might create types of precisions not +@c otherwise supported, but the syntax isn't right for use everywhere +@c the standard type names might be used. Predefined typedefs should +@c be used if any extended integer types are to be defined. The +@c __int128_t and __uint128_t typedefs are not extended integer types +@c as they are generally longer than the ABI-specified intmax_t. + +@item +@cite{Whether signed integer types are represented using sign and magnitude, +two's complement, or one's complement, and whether the extraordinary value +is a trap representation or an ordinary value (C99 and C11 6.2.6.2).} + +GCC supports only two's complement integer types, and all bit patterns +are ordinary values. + +@item +@cite{The rank of any extended integer type relative to another extended +integer type with the same precision (C99 and C11 6.3.1.1).} + +GCC does not support any extended integer types. +@c If it did, there would only be one of each precision and signedness. + +@item +@cite{The result of, or the signal raised by, converting an integer to a +signed integer type when the value cannot be represented in an object of +that type (C90 6.2.1.2, C99 and C11 6.3.1.3).} + +For conversion to a type of width @math{N}, the value is reduced +modulo @math{2^N} to be within range of the type; no signal is raised. + +@item +@cite{The results of some bitwise operations on signed integers (C90 +6.3, C99 and C11 6.5).} + +Bitwise operators act on the representation of the value including +both the sign and value bits, where the sign bit is considered +immediately above the highest-value value bit. Signed @samp{>>} acts +on negative numbers by sign extension. + +As an extension to the C language, GCC does not use the latitude given in +C99 and C11 only to treat certain aspects of signed @samp{<<} as undefined. +However, @option{-fsanitize=shift} (and @option{-fsanitize=undefined}) will +diagnose such cases. They are also diagnosed where constant +expressions are required. + +@item +@cite{The sign of the remainder on integer division (C90 6.3.5).} + +GCC always follows the C99 and C11 requirement that the result of division is +truncated towards zero. + +@end itemize + +@node Floating point implementation +@section Floating Point + +@itemize @bullet +@item +@cite{The accuracy of the floating-point operations and of the library +functions in @code{} and @code{} that return floating-point +results (C90, C99 and C11 5.2.4.2.2).} + +The accuracy is unknown. + +@item +@cite{The rounding behaviors characterized by non-standard values +of @code{FLT_ROUNDS} @gol +(C90, C99 and C11 5.2.4.2.2).} + +GCC does not use such values. + +@item +@cite{The evaluation methods characterized by non-standard negative +values of @code{FLT_EVAL_METHOD} (C99 and C11 5.2.4.2.2).} + +GCC does not use such values. + +@item +@cite{The direction of rounding when an integer is converted to a +floating-point number that cannot exactly represent the original +value (C90 6.2.1.3, C99 and C11 6.3.1.4).} + +C99 Annex F is followed. + +@item +@cite{The direction of rounding when a floating-point number is +converted to a narrower floating-point number (C90 6.2.1.4, C99 and C11 +6.3.1.5).} + +C99 Annex F is followed. + +@item +@cite{How the nearest representable value or the larger or smaller +representable value immediately adjacent to the nearest representable +value is chosen for certain floating constants (C90 6.1.3.1, C99 and C11 +6.4.4.2).} + +C99 Annex F is followed. + +@item +@cite{Whether and how floating expressions are contracted when not +disallowed by the @code{FP_CONTRACT} pragma (C99 and C11 6.5).} + +Expressions are currently only contracted if @option{-ffp-contract=fast}, +@option{-funsafe-math-optimizations} or @option{-ffast-math} are used. +This is subject to change. + +@item +@cite{The default state for the @code{FENV_ACCESS} pragma (C99 and C11 +7.6.1).} + +This pragma is not implemented, but the default is to ``off'' unless +@option{-frounding-math} is used and @option{-fno-trapping-math} is not +in which case it is ``on''. + +@item +@cite{Additional floating-point exceptions, rounding modes, environments, +and classifications, and their macro names (C99 and C11 7.6, C99 and +C11 7.12).} + +This is dependent on the implementation of the C library, and is not +defined by GCC itself. + +@item +@cite{The default state for the @code{FP_CONTRACT} pragma (C99 and C11 +7.12.2).} + +This pragma is not implemented. Expressions are currently only +contracted if @option{-ffp-contract=fast}, +@option{-funsafe-math-optimizations} or @option{-ffast-math} are used. +This is subject to change. + +@item +@cite{Whether the ``inexact'' floating-point exception can be raised +when the rounded result actually does equal the mathematical result +in an IEC 60559 conformant implementation (C99 F.9).} + +This is dependent on the implementation of the C library, and is not +defined by GCC itself. + +@item +@cite{Whether the ``underflow'' (and ``inexact'') floating-point +exception can be raised when a result is tiny but not inexact in an +IEC 60559 conformant implementation (C99 F.9).} + +This is dependent on the implementation of the C library, and is not +defined by GCC itself. + +@end itemize + +@node Arrays and pointers implementation +@section Arrays and Pointers + +@itemize @bullet +@item +@cite{The result of converting a pointer to an integer or +vice versa (C90 6.3.4, C99 and C11 6.3.2.3).} + +A cast from pointer to integer discards most-significant bits if the +pointer representation is larger than the integer type, +sign-extends@footnote{Future versions of GCC may zero-extend, or use +a target-defined @code{ptr_extend} pattern. Do not rely on sign extension.} +if the pointer representation is smaller than the integer type, otherwise +the bits are unchanged. +@c ??? We've always claimed that pointers were unsigned entities. +@c Shouldn't we therefore be doing zero-extension? If so, the bug +@c is in convert_to_integer, where we call type_for_size and request +@c a signed integral type. On the other hand, it might be most useful +@c for the target if we extend according to POINTERS_EXTEND_UNSIGNED. + +A cast from integer to pointer discards most-significant bits if the +pointer representation is smaller than the integer type, extends according +to the signedness of the integer type if the pointer representation +is larger than the integer type, otherwise the bits are unchanged. + +When casting from pointer to integer and back again, the resulting +pointer must reference the same object as the original pointer, otherwise +the behavior is undefined. That is, one may not use integer arithmetic to +avoid the undefined behavior of pointer arithmetic as proscribed in +C99 and C11 6.5.6/8. + +@item +@cite{The size of the result of subtracting two pointers to elements +of the same array (C90 6.3.6, C99 and C11 6.5.6).} + +The value is as specified in the standard and the type is determined +by the ABI@. + +@end itemize + +@node Hints implementation +@section Hints + +@itemize @bullet +@item +@cite{The extent to which suggestions made by using the @code{register} +storage-class specifier are effective (C90 6.5.1, C99 and C11 6.7.1).} + +The @code{register} specifier affects code generation only in these ways: + +@itemize @bullet +@item +When used as part of the register variable extension, see +@ref{Explicit Register Variables}. + +@item +When @option{-O0} is in use, the compiler allocates distinct stack +memory for all variables that do not have the @code{register} +storage-class specifier; if @code{register} is specified, the variable +may have a shorter lifespan than the code would indicate and may never +be placed in memory. + +@item +On some rare x86 targets, @code{setjmp} doesn't save the registers in +all circumstances. In those cases, GCC doesn't allocate any variables +in registers unless they are marked @code{register}. + +@end itemize + +@item +@cite{The extent to which suggestions made by using the inline function +specifier are effective (C99 and C11 6.7.4).} + +GCC will not inline any functions if the @option{-fno-inline} option is +used or if @option{-O0} is used. Otherwise, GCC may still be unable to +inline a function for many reasons; the @option{-Winline} option may be +used to determine if a function has not been inlined and why not. + +@end itemize + +@node Structures unions enumerations and bit-fields implementation +@section Structures, Unions, Enumerations, and Bit-Fields + +@itemize @bullet +@item +@cite{A member of a union object is accessed using a member of a +different type (C90 6.3.2.3).} + +The relevant bytes of the representation of the object are treated as +an object of the type used for the access. @xref{Type-punning}. This +may be a trap representation. + +@item +@cite{Whether a ``plain'' @code{int} bit-field is treated as a +@code{signed int} bit-field or as an @code{unsigned int} bit-field +(C90 6.5.2, C90 6.5.2.1, C99 and C11 6.7.2, C99 and C11 6.7.2.1).} + +@opindex funsigned-bitfields +By default it is treated as @code{signed int} but this may be changed +by the @option{-funsigned-bitfields} option. + +@item +@cite{Allowable bit-field types other than @code{_Bool}, @code{signed int}, +and @code{unsigned int} (C99 and C11 6.7.2.1).} + +Other integer types, such as @code{long int}, and enumerated types are +permitted even in strictly conforming mode. + +@item +@cite{Whether atomic types are permitted for bit-fields (C11 6.7.2.1).} + +Atomic types are not permitted for bit-fields. + +@item +@cite{Whether a bit-field can straddle a storage-unit boundary (C90 +6.5.2.1, C99 and C11 6.7.2.1).} + +Determined by ABI@. + +@item +@cite{The order of allocation of bit-fields within a unit (C90 +6.5.2.1, C99 and C11 6.7.2.1).} + +Determined by ABI@. + +@item +@cite{The alignment of non-bit-field members of structures (C90 +6.5.2.1, C99 and C11 6.7.2.1).} + +Determined by ABI@. + +@item +@cite{The integer type compatible with each enumerated type (C90 +6.5.2.2, C99 and C11 6.7.2.2).} + +@opindex fshort-enums +Normally, the type is @code{unsigned int} if there are no negative +values in the enumeration, otherwise @code{int}. If +@option{-fshort-enums} is specified, then if there are negative values +it is the first of @code{signed char}, @code{short} and @code{int} +that can represent all the values, otherwise it is the first of +@code{unsigned char}, @code{unsigned short} and @code{unsigned int} +that can represent all the values. +@c On a few unusual targets with 64-bit int, this doesn't agree with +@c the code and one of the types accessed via mode attributes (which +@c are not currently considered extended integer types) may be used. +@c If these types are made extended integer types, it would still be +@c the case that -fshort-enums stops the implementation from +@c conforming to C90 on those targets. + +On some targets, @option{-fshort-enums} is the default; this is +determined by the ABI@. + +@end itemize + +@node Qualifiers implementation +@section Qualifiers + +@itemize @bullet +@item +@cite{What constitutes an access to an object that has volatile-qualified +type (C90 6.5.3, C99 and C11 6.7.3).} + +Such an object is normally accessed by pointers and used for accessing +hardware. In most expressions, it is intuitively obvious what is a read +and what is a write. For example + +@smallexample +volatile int *dst = @var{somevalue}; +volatile int *src = @var{someothervalue}; +*dst = *src; +@end smallexample + +@noindent +will cause a read of the volatile object pointed to by @var{src} and store the +value into the volatile object pointed to by @var{dst}. There is no +guarantee that these reads and writes are atomic, especially for objects +larger than @code{int}. + +However, if the volatile storage is not being modified, and the value of +the volatile storage is not used, then the situation is less obvious. +For example + +@smallexample +volatile int *src = @var{somevalue}; +*src; +@end smallexample + +According to the C standard, such an expression is an rvalue whose type +is the unqualified version of its original type, i.e.@: @code{int}. Whether +GCC interprets this as a read of the volatile object being pointed to or +only as a request to evaluate the expression for its side effects depends +on this type. + +If it is a scalar type, or on most targets an aggregate type whose only +member object is of a scalar type, or a union type whose member objects +are of scalar types, the expression is interpreted by GCC as a read of +the volatile object; in the other cases, the expression is only evaluated +for its side effects. + +When an object of an aggregate type, with the same size and alignment as a +scalar type @code{S}, is the subject of a volatile access by an assignment +expression or an atomic function, the access to it is performed as if the +object's declared type were @code{volatile S}. + +@end itemize + +@node Declarators implementation +@section Declarators + +@itemize @bullet +@item +@cite{The maximum number of declarators that may modify an arithmetic, +structure or union type (C90 6.5.4).} + +GCC is only limited by available memory. + +@end itemize + +@node Statements implementation +@section Statements + +@itemize @bullet +@item +@cite{The maximum number of @code{case} values in a @code{switch} +statement (C90 6.6.4.2).} + +GCC is only limited by available memory. + +@end itemize + +@node Preprocessing directives implementation +@section Preprocessing Directives + +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}, for details of these aspects of +implementation-defined behavior. + +@itemize @bullet +@item +@cite{The locations within @code{#pragma} directives where header name +preprocessing tokens are recognized (C11 6.4, C11 6.4.7).} + +@item +@cite{How sequences in both forms of header names are mapped to headers +or external source file names (C90 6.1.7, C99 and C11 6.4.7).} + +@item +@cite{Whether the value of a character constant in a constant expression +that controls conditional inclusion matches the value of the same character +constant in the execution character set (C90 6.8.1, C99 and C11 6.10.1).} + +@item +@cite{Whether the value of a single-character character constant in a +constant expression that controls conditional inclusion may have a +negative value (C90 6.8.1, C99 and C11 6.10.1).} + +@item +@cite{The places that are searched for an included @samp{<>} delimited +header, and how the places are specified or the header is +identified (C90 6.8.2, C99 and C11 6.10.2).} + +@item +@cite{How the named source file is searched for in an included @samp{""} +delimited header (C90 6.8.2, C99 and C11 6.10.2).} + +@item +@cite{The method by which preprocessing tokens (possibly resulting from +macro expansion) in a @code{#include} directive are combined into a header +name (C90 6.8.2, C99 and C11 6.10.2).} + +@item +@cite{The nesting limit for @code{#include} processing (C90 6.8.2, C99 +and C11 6.10.2).} + +@item +@cite{Whether the @samp{#} operator inserts a @samp{\} character before +the @samp{\} character that begins a universal character name in a +character constant or string literal (C99 and C11 6.10.3.2).} + +@item +@cite{The behavior on each recognized non-@code{STDC #pragma} +directive (C90 6.8.6, C99 and C11 6.10.6).} + +@xref{Pragmas, , Pragmas, cpp, The C Preprocessor}, for details of +pragmas accepted by GCC on all targets. @xref{Pragmas, , Pragmas +Accepted by GCC}, for details of target-specific pragmas. + +@item +@cite{The definitions for @code{__DATE__} and @code{__TIME__} when +respectively, the date and time of translation are not available (C90 +6.8.8, C99 6.10.8, C11 6.10.8.1).} + +@end itemize + +@node Library functions implementation +@section Library Functions + +The behavior of most of these points are dependent on the implementation +of the C library, and are not defined by GCC itself. + +@itemize @bullet +@item +@cite{The null pointer constant to which the macro @code{NULL} expands +(C90 7.1.6, C99 7.17, C11 7.19).} + +In @code{}, @code{NULL} expands to @code{((void *)0)}. GCC +does not provide the other headers which define @code{NULL} and some +library implementations may use other definitions in those headers. + +@end itemize + +@node Architecture implementation +@section Architecture + +@itemize @bullet +@item +@cite{The values or expressions assigned to the macros specified in the +headers @code{}, @code{}, and @code{} +(C90, C99 and C11 5.2.4.2, C99 7.18.2, C99 7.18.3, C11 7.20.2, C11 7.20.3).} + +Determined by ABI@. + +@item +@cite{The result of attempting to indirectly access an object with +automatic or thread storage duration from a thread other than the one +with which it is associated (C11 6.2.4).} + +Such accesses are supported, subject to the same requirements for +synchronization for concurrent accesses as for concurrent accesses to +any object. + +@item +@cite{The number, order, and encoding of bytes in any object +(when not explicitly specified in this International Standard) (C99 +and C11 6.2.6.1).} + +Determined by ABI@. + +@item +@cite{Whether any extended alignments are supported and the contexts +in which they are supported (C11 6.2.8).} + +Extended alignments up to @math{2^{28}} (bytes) are supported for +objects of automatic storage duration. Alignments supported for +objects of static and thread storage duration are determined by the +ABI. + +@item +@cite{Valid alignment values other than those returned by an _Alignof +expression for fundamental types, if any (C11 6.2.8).} + +Valid alignments are powers of 2 up to and including @math{2^{28}}. + +@item +@cite{The value of the result of the @code{sizeof} and @code{_Alignof} +operators (C90 6.3.3.4, C99 and C11 6.5.3.4).} + +Determined by ABI@. + +@end itemize + +@node Locale-specific behavior implementation +@section Locale-Specific Behavior + +The behavior of these points are dependent on the implementation +of the C library, and are not defined by GCC itself. diff --git a/gcc/doc/implement-cxx.texi b/gcc/doc/implement-cxx.texi new file mode 100644 index 00000000000..1eee18c0b09 --- /dev/null +++ b/gcc/doc/implement-cxx.texi @@ -0,0 +1,62 @@ +@c Copyright (C) 2009-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node C++ Implementation +@chapter C++ Implementation-Defined Behavior +@cindex implementation-defined behavior, C++ language + +A conforming implementation of ISO C++ is required to document its +choice of behavior in each of the areas that are designated +``implementation defined''. The following lists all such areas, +along with the section numbers from the ISO/IEC 14882:1998 and ISO/IEC +14882:2003 standards. Some areas are only implementation-defined in +one version of the standard. + +Some choices depend on the externally determined ABI for the platform +(including standard character encodings) which GCC follows; these are +listed as ``determined by ABI'' below. @xref{Compatibility, , Binary +Compatibility}, and @uref{https://gcc.gnu.org/readings.html}. Some +choices are documented in the preprocessor manual. +@xref{Implementation-defined behavior, , Implementation-defined +behavior, cpp, The C Preprocessor}. Some choices are documented in +the corresponding document for the C language. @xref{C +Implementation}. Some choices are made by the library and operating +system (or other environment when compiling for a freestanding +environment); refer to their documentation for details. + +@menu +* Conditionally-supported behavior:: +* Exception handling:: +@end menu + +@node Conditionally-supported behavior +@section Conditionally-Supported Behavior + +@cite{Each implementation shall include documentation that identifies +all conditionally-supported constructs that it does not support (C++0x +1.4).} + +@itemize @bullet +@item +@cite{Whether an argument of class type with a non-trivial copy +constructor or destructor can be passed to ... (C++0x 5.2.2).} + +Such argument passing is supported, using the same +pass-by-invisible-reference approach used for normal function +arguments of such types. + +@end itemize + +@node Exception handling +@section Exception Handling + +@itemize @bullet +@item +@cite{In the situation where no matching handler is found, it is +implementation-defined whether or not the stack is unwound before +std::terminate() is called (C++98 15.5.1).} + +The stack is not unwound before std::terminate is called. + +@end itemize diff --git a/gcc/doc/include/fdl.texi b/gcc/doc/include/fdl.texi new file mode 100644 index 00000000000..e2bcdfd579b --- /dev/null +++ b/gcc/doc/include/fdl.texi @@ -0,0 +1,547 @@ +@ignore +@c Set file name and title for man page. +@setfilename gfdl +@settitle GNU Free Documentation License +@c man begin SEEALSO +gpl(7), fsf-funding(7). +@c man end +@c man begin COPYRIGHT +Copyright @copyright{} 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. +@uref{https://fsf.org/} + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@c This file is intended to be included within another document, +@c hence no sectioning command or @node. +@c man end +@end ignore +@c Special handling for inclusion in the install manual. +@ifset gfdlhtml +@ifnothtml +@comment node-name, next, previous, up +@node GNU Free Documentation License, Concept Index, Specific, Top +@end ifnothtml +@html +

Installing GCC: GNU Free Documentation License

+@end html +@ifnothtml +@unnumbered GNU Free Documentation License +@end ifnothtml +@end ifset +@c man begin DESCRIPTION +@ifclear gfdlhtml +@comment For some cases, this default @node/@unnumbered is not applicable and +@comment causes warnings. In those cases, the including file can set +@comment nodefaultgnufreedocumentationlicensenode and provide it's own version. +@comment F.i., when this file is included in an @raisesections context, the +@comment including file can use an @unnumberedsec. +@ifclear nodefaultgnufreedocumentationlicensenode +@node GNU Free Documentation License +@unnumbered GNU Free Documentation License +@end ifclear +@end ifclear + +@cindex FDL, GNU Free Documentation License +@center Version 1.3, 3 November 2008 + +@display +Copyright @copyright{} 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. +@uref{https://fsf.org/} + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display + +@enumerate 0 +@item +PREAMBLE + +The purpose of this License is to make a manual, textbook, or other +functional and useful document @dfn{free} in the sense of freedom: to +assure everyone the effective freedom to copy and redistribute it, +with or without modifying it, either commercially or noncommercially. +Secondarily, this License preserves for the author and publisher a way +to get credit for their work, while not being considered responsible +for modifications made by others. + +This License is a kind of ``copyleft'', which means that derivative +works of the document must themselves be free in the same sense. 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Any attempt +otherwise to copy, modify, sublicense, or distribute it is void, and +will automatically terminate your rights under this License. + +However, if you cease all violation of this License, then your license +from a particular copyright holder is reinstated (a) provisionally, +unless and until the copyright holder explicitly and finally +terminates your license, and (b) permanently, if the copyright holder +fails to notify you of the violation by some reasonable means prior to +60 days after the cessation. + +Moreover, your license from a particular copyright holder is +reinstated permanently if the copyright holder notifies you of the +violation by some reasonable means, this is the first time you have +received notice of violation of this License (for any work) from that +copyright holder, and you cure the violation prior to 30 days after +your receipt of the notice. + +Termination of your rights under this section does not terminate the +licenses of parties who have received copies or rights from you under +this License. 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A copy of the license is included in the section entitled ``GNU + Free Documentation License''. +@end group +@end smallexample + +If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, +replace the ``with...Texts.'' line with this: + +@smallexample +@group + with the Invariant Sections being @var{list their titles}, with + the Front-Cover Texts being @var{list}, and with the Back-Cover Texts + being @var{list}. +@end group +@end smallexample + +If you have Invariant Sections without Cover Texts, or some other +combination of the three, merge those two alternatives to suit the +situation. + +If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, +to permit their use in free software. + +@c Local Variables: +@c ispell-local-pdict: "ispell-dict" +@c End: + +@c man end diff --git a/gcc/doc/include/funding.texi b/gcc/doc/include/funding.texi new file mode 100644 index 00000000000..d1583fabc0d --- /dev/null +++ b/gcc/doc/include/funding.texi @@ -0,0 +1,60 @@ +@ignore +@c Set file name and title for man page. +@setfilename fsf-funding +@settitle Funding Free Software +@c man begin SEEALSO +gpl(7), gfdl(7). +@c man end +@end ignore +@node Funding +@c man begin DESCRIPTION +@unnumbered Funding Free Software + +If you want to have more free software a few years from now, it makes +sense for you to help encourage people to contribute funds for its +development. The most effective approach known is to encourage +commercial redistributors to donate. + +Users of free software systems can boost the pace of development by +encouraging for-a-fee distributors to donate part of their selling price +to free software developers---the Free Software Foundation, and others. + +The way to convince distributors to do this is to demand it and expect +it from them. So when you compare distributors, judge them partly by +how much they give to free software development. Show distributors +they must compete to be the one who gives the most. + +To make this approach work, you must insist on numbers that you can +compare, such as, ``We will donate ten dollars to the Frobnitz project +for each disk sold.'' Don't be satisfied with a vague promise, such as +``A portion of the profits are donated,'' since it doesn't give a basis +for comparison. + +Even a precise fraction ``of the profits from this disk'' is not very +meaningful, since creative accounting and unrelated business decisions +can greatly alter what fraction of the sales price counts as profit. +If the price you pay is $50, ten percent of the profit is probably +less than a dollar; it might be a few cents, or nothing at all. + +Some redistributors do development work themselves. This is useful too; +but to keep everyone honest, you need to inquire how much they do, and +what kind. Some kinds of development make much more long-term +difference than others. For example, maintaining a separate version of +a program contributes very little; maintaining the standard version of a +program for the whole community contributes much. Easy new ports +contribute little, since someone else would surely do them; difficult +ports such as adding a new CPU to the GNU Compiler Collection contribute more; +major new features or packages contribute the most. + +By establishing the idea that supporting further development is ``the +proper thing to do'' when distributing free software for a fee, we can +assure a steady flow of resources into making more free software. +@c man end + +@display +@c man begin COPYRIGHT +Copyright @copyright{} 1994 Free Software Foundation, Inc. +Verbatim copying and redistribution of this section is permitted +without royalty; alteration is not permitted. +@c man end +@end display diff --git a/gcc/doc/include/gcc-common.texi b/gcc/doc/include/gcc-common.texi new file mode 100644 index 00000000000..4365e4fe1d8 --- /dev/null +++ b/gcc/doc/include/gcc-common.texi @@ -0,0 +1,73 @@ +@c Copyright (C) 2001-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@c Version number and development mode. +@c version-GCC is @set to the base GCC version number. +@c DEVELOPMENT is @set for an in-development version, @clear for a +@c release version (corresponding to ``experimental''/anything else +@c in gcc/DEV-PHASE). + +@include gcc-vers.texi + +@c Common macros to support generating man pages: + +@macro gcctabopt{body} +@code{\body\} +@end macro +@macro gccoptlist{body} +@smallexample +\body\ +@end smallexample +@end macro +@c Makeinfo handles the above macro OK, TeX needs manual line breaks; +@c they get lost at some point in handling the macro. But if @macro is +@c used here rather than @alias, it produces double line breaks. +@iftex +@alias gol = * +@end iftex +@ifnottex +@macro gol +@end macro +@end ifnottex + +@c For FSF printing, define FSFPRINT. Also update the ISBN and last +@c printing date for the manual being printed. +@c @set FSFPRINT +@ifset FSFPRINT +@smallbook +@finalout +@c Cause even numbered pages to be printed on the left hand side of +@c the page and odd numbered pages to be printed on the right hand +@c side of the page. Using this, you can print on both sides of a +@c sheet of paper and have the text on the same part of the sheet. + +@c The text on right hand pages is pushed towards the right hand +@c margin and the text on left hand pages is pushed toward the left +@c hand margin. +@c (To provide the reverse effect, set bindingoffset to -0.75in.) +@tex +\global\bindingoffset=0.75in +\global\normaloffset =0.75in +@end tex +@end ifset + +@c Macro to generate a "For the N.N.N version" subtitle on the title +@c page of TeX documentation. This macro should be used in the +@c titlepage environment after the title and any other subtitles have +@c been placed, and before any authors are placed. +@macro versionsubtitle +@ifclear DEVELOPMENT +@subtitle For @sc{gcc} version @value{version-GCC} +@end ifclear +@ifset DEVELOPMENT +@subtitle For @sc{gcc} version @value{version-GCC} (pre-release) +@end ifset +@ifset VERSION_PACKAGE +@sp 1 +@subtitle @value{VERSION_PACKAGE} +@end ifset +@c Even if there are no authors, the second titlepage line should be +@c forced to the bottom of the page. +@vskip 0pt plus 1filll +@end macro diff --git a/gcc/doc/include/gpl_v3.texi b/gcc/doc/include/gpl_v3.texi new file mode 100644 index 00000000000..c978f2154d2 --- /dev/null +++ b/gcc/doc/include/gpl_v3.texi @@ -0,0 +1,733 @@ +@ignore +@c Set file name and title for man page. +@setfilename gpl +@settitle GNU General Public License +@c man begin SEEALSO +gfdl(7), fsf-funding(7). +@c man end +@c man begin COPYRIGHT +Copyright @copyright{} 2007 Free Software Foundation, Inc. + +Everyone is permitted to copy and distribute verbatim copies of this +license document, but changing it is not allowed. +@c man end +@end ignore +@node Copying +@c man begin DESCRIPTION +@unnumbered GNU General Public License +@center Version 3, 29 June 2007 + +@c This file is intended to be included in another file. + +@display +Copyright @copyright{} 2007 Free Software Foundation, Inc. @url{https://fsf.org/} + +Everyone is permitted to copy and distribute verbatim copies of this +license document, but changing it is not allowed. +@end display + +@heading Preamble + +The GNU General Public License is a free, copyleft license for +software and other kinds of works. + +The licenses for most software and other practical works are designed +to take away your freedom to share and change the works. By contrast, +the GNU General Public License is intended to guarantee your freedom +to share and change all versions of a program--to make sure it remains +free software for all its users. We, the Free Software Foundation, +use the GNU General Public License for most of our software; it +applies also to any other work released this way by its authors. You +can apply it to your programs, too. + +When we speak of free software, we are referring to freedom, not +price. Our General Public Licenses are designed to make sure that you +have the freedom to distribute copies of free software (and charge for +them if you wish), that you receive source code or can get it if you +want it, that you can change the software or use pieces of it in new +free programs, and that you know you can do these things. + +To protect your rights, we need to prevent others from denying you +these rights or asking you to surrender the rights. Therefore, you +have certain responsibilities if you distribute copies of the +software, or if you modify it: responsibilities to respect the freedom +of others. + +For example, if you distribute copies of such a program, whether +gratis or for a fee, you must pass on to the recipients the same +freedoms that you received. You must make sure that they, too, +receive or can get the source code. And you must show them these +terms so they know their rights. + +Developers that use the GNU GPL protect your rights with two steps: +(1) assert copyright on the software, and (2) offer you this License +giving you legal permission to copy, distribute and/or modify it. + +For the developers' and authors' protection, the GPL clearly explains +that there is no warranty for this free software. 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If such problems arise substantially in +other domains, we stand ready to extend this provision to those +domains in future versions of the GPL, as needed to protect the +freedom of users. + +Finally, every program is threatened constantly by software patents. +States should not allow patents to restrict development and use of +software on general-purpose computers, but in those that do, we wish +to avoid the special danger that patents applied to a free program +could make it effectively proprietary. To prevent this, the GPL +assures that patents cannot be used to render the program non-free. + +The precise terms and conditions for copying, distribution and +modification follow. + +@heading TERMS AND CONDITIONS + +@enumerate 0 +@item Definitions. + +``This License'' refers to version 3 of the GNU General Public License. + +``Copyright'' also means copyright-like laws that apply to other kinds +of works, such as semiconductor masks. + +``The Program'' refers to any copyrightable work licensed under this +License. Each licensee is addressed as ``you''. ``Licensees'' and +``recipients'' may be individuals or organizations. + +To ``modify'' a work means to copy from or adapt all or part of the work +in a fashion requiring copyright permission, other than the making of +an exact copy. 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Mere interaction with a user +through a computer network, with no transfer of a copy, is not +conveying. + +An interactive user interface displays ``Appropriate Legal Notices'' to +the extent that it includes a convenient and prominently visible +feature that (1) displays an appropriate copyright notice, and (2) +tells the user that there is no warranty for the work (except to the +extent that warranties are provided), that licensees may convey the +work under this License, and how to view a copy of this License. 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This +requirement modifies the requirement in section 4 to ``keep intact all +notices''. + +@item +You must license the entire work, as a whole, under this License to +anyone who comes into possession of a copy. This License will +therefore apply, along with any applicable section 7 additional terms, +to the whole of the work, and all its parts, regardless of how they +are packaged. 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But this requirement does not apply +if neither you nor any third party retains the ability to install +modified object code on the User Product (for example, the work has +been installed in ROM). + +The requirement to provide Installation Information does not include a +requirement to continue to provide support service, warranty, or +updates for a work that has been modified or installed by the +recipient, or for the User Product in which it has been modified or +installed. Access to a network may be denied when the modification +itself materially and adversely affects the operation of the network +or violates the rules and protocols for communication across the +network. + +Corresponding Source conveyed, and Installation Information provided, +in accord with this section must be in a format that is publicly +documented (and with an implementation available to the public in +source code form), and must require no special password or key for +unpacking, reading or copying. + +@item Additional Terms. + +``Additional permissions'' are terms that supplement the terms of this +License by making exceptions from one or more of its conditions. +Additional permissions that are applicable to the entire Program shall +be treated as though they were included in this License, to the extent +that they are valid under applicable law. If additional permissions +apply only to part of the Program, that part may be used separately +under those permissions, but the entire Program remains governed by +this License without regard to the additional permissions. + +When you convey a copy of a covered work, you may at your option +remove any additional permissions from that copy, or from any part of +it. (Additional permissions may be written to require their own +removal in certain cases when you modify the work.) You may place +additional permissions on material, added by you to a covered work, +for which you have or can give appropriate copyright permission. + +Notwithstanding any other provision of this License, for material you +add to a covered work, you may (if authorized by the copyright holders +of that material) supplement the terms of this License with terms: + +@enumerate a +@item +Disclaiming warranty or limiting liability differently from the terms +of sections 15 and 16 of this License; or + +@item +Requiring preservation of specified reasonable legal notices or author +attributions in that material or in the Appropriate Legal Notices +displayed by works containing it; or + +@item +Prohibiting misrepresentation of the origin of that material, or +requiring that modified versions of such material be marked in +reasonable ways as different from the original version; or + +@item +Limiting the use for publicity purposes of names of licensors or +authors of the material; or + +@item +Declining to grant rights under trademark law for use of some trade +names, trademarks, or service marks; or + +@item +Requiring indemnification of licensors and authors of that material by +anyone who conveys the material (or modified versions of it) with +contractual assumptions of liability to the recipient, for any +liability that these contractual assumptions directly impose on those +licensors and authors. +@end enumerate + +All other non-permissive additional terms are considered ``further +restrictions'' within the meaning of section 10. If the Program as you +received it, or any part of it, contains a notice stating that it is +governed by this License along with a term that is a further +restriction, you may remove that term. If a license document contains +a further restriction but permits relicensing or conveying under this +License, you may add to a covered work material governed by the terms +of that license document, provided that the further restriction does +not survive such relicensing or conveying. + +If you add terms to a covered work in accord with this section, you +must place, in the relevant source files, a statement of the +additional terms that apply to those files, or a notice indicating +where to find the applicable terms. + +Additional terms, permissive or non-permissive, may be stated in the +form of a separately written license, or stated as exceptions; the +above requirements apply either way. + +@item Termination. + +You may not propagate or modify a covered work except as expressly +provided under this License. Any attempt otherwise to propagate or +modify it is void, and will automatically terminate your rights under +this License (including any patent licenses granted under the third +paragraph of section 11). + +However, if you cease all violation of this License, then your license +from a particular copyright holder is reinstated (a) provisionally, +unless and until the copyright holder explicitly and finally +terminates your license, and (b) permanently, if the copyright holder +fails to notify you of the violation by some reasonable means prior to +60 days after the cessation. + +Moreover, your license from a particular copyright holder is +reinstated permanently if the copyright holder notifies you of the +violation by some reasonable means, this is the first time you have +received notice of violation of this License (for any work) from that +copyright holder, and you cure the violation prior to 30 days after +your receipt of the notice. + +Termination of your rights under this section does not terminate the +licenses of parties who have received copies or rights from you under +this License. If your rights have been terminated and not permanently +reinstated, you do not qualify to receive new licenses for the same +material under section 10. + +@item Acceptance Not Required for Having Copies. + +You are not required to accept this License in order to receive or run +a copy of the Program. Ancillary propagation of a covered work +occurring solely as a consequence of using peer-to-peer transmission +to receive a copy likewise does not require acceptance. However, +nothing other than this License grants you permission to propagate or +modify any covered work. These actions infringe copyright if you do +not accept this License. Therefore, by modifying or propagating a +covered work, you indicate your acceptance of this License to do so. + +@item Automatic Licensing of Downstream Recipients. + +Each time you convey a covered work, the recipient automatically +receives a license from the original licensors, to run, modify and +propagate that work, subject to this License. You are not responsible +for enforcing compliance by third parties with this License. + +An ``entity transaction'' is a transaction transferring control of an +organization, or substantially all assets of one, or subdividing an +organization, or merging organizations. If propagation of a covered +work results from an entity transaction, each party to that +transaction who receives a copy of the work also receives whatever +licenses to the work the party's predecessor in interest had or could +give under the previous paragraph, plus a right to possession of the +Corresponding Source of the work from the predecessor in interest, if +the predecessor has it or can get it with reasonable efforts. + +You may not impose any further restrictions on the exercise of the +rights granted or affirmed under this License. For example, you may +not impose a license fee, royalty, or other charge for exercise of +rights granted under this License, and you may not initiate litigation +(including a cross-claim or counterclaim in a lawsuit) alleging that +any patent claim is infringed by making, using, selling, offering for +sale, or importing the Program or any portion of it. + +@item Patents. + +A ``contributor'' is a copyright holder who authorizes use under this +License of the Program or a work on which the Program is based. The +work thus licensed is called the contributor's ``contributor version''. + +A contributor's ``essential patent claims'' are all patent claims owned +or controlled by the contributor, whether already acquired or +hereafter acquired, that would be infringed by some manner, permitted +by this License, of making, using, or selling its contributor version, +but do not include claims that would be infringed only as a +consequence of further modification of the contributor version. For +purposes of this definition, ``control'' includes the right to grant +patent sublicenses in a manner consistent with the requirements of +this License. + +Each contributor grants you a non-exclusive, worldwide, royalty-free +patent license under the contributor's essential patent claims, to +make, use, sell, offer for sale, import and otherwise run, modify and +propagate the contents of its contributor version. + +In the following three paragraphs, a ``patent license'' is any express +agreement or commitment, however denominated, not to enforce a patent +(such as an express permission to practice a patent or covenant not to +sue for patent infringement). To ``grant'' such a patent license to a +party means to make such an agreement or commitment not to enforce a +patent against the party. + +If you convey a covered work, knowingly relying on a patent license, +and the Corresponding Source of the work is not available for anyone +to copy, free of charge and under the terms of this License, through a +publicly available network server or other readily accessible means, +then you must either (1) cause the Corresponding Source to be so +available, or (2) arrange to deprive yourself of the benefit of the +patent license for this particular work, or (3) arrange, in a manner +consistent with the requirements of this License, to extend the patent +license to downstream recipients. ``Knowingly relying'' means you have +actual knowledge that, but for the patent license, your conveying the +covered work in a country, or your recipient's use of the covered work +in a country, would infringe one or more identifiable patents in that +country that you have reason to believe are valid. + +If, pursuant to or in connection with a single transaction or +arrangement, you convey, or propagate by procuring conveyance of, a +covered work, and grant a patent license to some of the parties +receiving the covered work authorizing them to use, propagate, modify +or convey a specific copy of the covered work, then the patent license +you grant is automatically extended to all recipients of the covered +work and works based on it. + +A patent license is ``discriminatory'' if it does not include within the +scope of its coverage, prohibits the exercise of, or is conditioned on +the non-exercise of one or more of the rights that are specifically +granted under this License. You may not convey a covered work if you +are a party to an arrangement with a third party that is in the +business of distributing software, under which you make payment to the +third party based on the extent of your activity of conveying the +work, and under which the third party grants, to any of the parties +who would receive the covered work from you, a discriminatory patent +license (a) in connection with copies of the covered work conveyed by +you (or copies made from those copies), or (b) primarily for and in +connection with specific products or compilations that contain the +covered work, unless you entered into that arrangement, or that patent +license was granted, prior to 28 March 2007. + +Nothing in this License shall be construed as excluding or limiting +any implied license or other defenses to infringement that may +otherwise be available to you under applicable patent law. + +@item No Surrender of Others' Freedom. + +If conditions are imposed on you (whether by court order, agreement or +otherwise) that contradict the conditions of this License, they do not +excuse you from the conditions of this License. If you cannot convey +a covered work so as to satisfy simultaneously your obligations under +this License and any other pertinent obligations, then as a +consequence you may not convey it at all. For example, if you agree +to terms that obligate you to collect a royalty for further conveying +from those to whom you convey the Program, the only way you could +satisfy both those terms and this License would be to refrain entirely +from conveying the Program. + +@item Use with the GNU Affero General Public License. + +Notwithstanding any other provision of this License, you have +permission to link or combine any covered work with a work licensed +under version 3 of the GNU Affero General Public License into a single +combined work, and to convey the resulting work. The terms of this +License will continue to apply to the part which is the covered work, +but the special requirements of the GNU Affero General Public License, +section 13, concerning interaction through a network will apply to the +combination as such. + +@item Revised Versions of this License. + +The Free Software Foundation may publish revised and/or new versions +of the GNU General Public License from time to time. Such new +versions will be similar in spirit to the present version, but may +differ in detail to address new problems or concerns. + +Each version is given a distinguishing version number. If the Program +specifies that a certain numbered version of the GNU General Public +License ``or any later version'' applies to it, you have the option of +following the terms and conditions either of that numbered version or +of any later version published by the Free Software Foundation. If +the Program does not specify a version number of the GNU General +Public License, you may choose any version ever published by the Free +Software Foundation. + +If the Program specifies that a proxy can decide which future versions +of the GNU General Public License can be used, that proxy's public +statement of acceptance of a version permanently authorizes you to +choose that version for the Program. + +Later license versions may give you additional or different +permissions. However, no additional obligations are imposed on any +author or copyright holder as a result of your choosing to follow a +later version. + +@item Disclaimer of Warranty. + +THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY +APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT +HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT +WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT +LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND +PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE +DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR +CORRECTION. + +@item Limitation of Liability. + +IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING +WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR +CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, +INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES +ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT +NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR +LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM +TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER +PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. + +@item Interpretation of Sections 15 and 16. + +If the disclaimer of warranty and limitation of liability provided +above cannot be given local legal effect according to their terms, +reviewing courts shall apply local law that most closely approximates +an absolute waiver of all civil liability in connection with the +Program, unless a warranty or assumption of liability accompanies a +copy of the Program in return for a fee. + +@end enumerate + +@heading END OF TERMS AND CONDITIONS + +@heading How to Apply These Terms to Your New Programs + +If you develop a new program, and you want it to be of the greatest +possible use to the public, the best way to achieve this is to make it +free software which everyone can redistribute and change under these +terms. + +To do so, attach the following notices to the program. It is safest +to attach them to the start of each source file to most effectively +state the exclusion of warranty; and each file should have at least +the ``copyright'' line and a pointer to where the full notice is found. + +@smallexample +@var{one line to give the program's name and a brief idea of what it does.} +Copyright (C) @var{year} @var{name of author} + +This program is free software: you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation, either version 3 of the License, or (at +your option) any later version. + +This program is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program. If not, see @url{https://www.gnu.org/licenses/}. +@end smallexample + +Also add information on how to contact you by electronic and paper mail. + +If the program does terminal interaction, make it output a short +notice like this when it starts in an interactive mode: + +@smallexample +@var{program} Copyright (C) @var{year} @var{name of author} +This program comes with ABSOLUTELY NO WARRANTY; for details type @samp{show w}. +This is free software, and you are welcome to redistribute it +under certain conditions; type @samp{show c} for details. +@end smallexample + +The hypothetical commands @samp{show w} and @samp{show c} should show +the appropriate parts of the General Public License. Of course, your +program's commands might be different; for a GUI interface, you would +use an ``about box''. + +You should also get your employer (if you work as a programmer) or school, +if any, to sign a ``copyright disclaimer'' for the program, if necessary. +For more information on this, and how to apply and follow the GNU GPL, see +@url{https://www.gnu.org/licenses/}. + +The GNU General Public License does not permit incorporating your +program into proprietary programs. If your program is a subroutine +library, you may consider it more useful to permit linking proprietary +applications with the library. If this is what you want to do, use +the GNU Lesser General Public License instead of this License. But +first, please read @url{https://www.gnu.org/licenses/why-not-lgpl.html}. +@c man end diff --git a/gcc/doc/install.texi b/gcc/doc/install.texi new file mode 100644 index 00000000000..a01b8053afe --- /dev/null +++ b/gcc/doc/install.texi @@ -0,0 +1,5268 @@ +\input texinfo.tex @c -*-texinfo-*- +@c @ifnothtml +@c %**start of header +@setfilename gccinstall.info +@setchapternewpage odd +@c %**end of header +@c @end ifnothtml + +@include gcc-common.texi + +@c Specify title for specific html page +@ifset indexhtml +@settitle Installing GCC +@end ifset +@ifset specifichtml +@settitle Host/Target specific installation notes for GCC +@end ifset +@ifset prerequisiteshtml +@settitle Prerequisites for GCC +@end ifset +@ifset downloadhtml +@settitle Downloading GCC +@end ifset +@ifset configurehtml +@settitle Installing GCC: Configuration +@end ifset +@ifset buildhtml +@settitle Installing GCC: Building +@end ifset +@ifset testhtml +@settitle Installing GCC: Testing +@end ifset +@ifset finalinstallhtml +@settitle Installing GCC: Final installation +@end ifset +@ifset binarieshtml +@settitle Installing GCC: Binaries +@end ifset +@ifset gfdlhtml +@settitle Installing GCC: GNU Free Documentation License +@end ifset + +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c *** Converted to texinfo by Dean Wakerley, dean@wakerley.com + +@c IMPORTANT: whenever you modify this file, run `install.texi2html' to +@c test the generation of HTML documents for the gcc.gnu.org web pages. +@c +@c Do not use @footnote{} in this file as it breaks install.texi2html! + +@c Include everything if we're not making html +@ifnothtml +@set indexhtml +@set specifichtml +@set prerequisiteshtml +@set downloadhtml +@set configurehtml +@set buildhtml +@set testhtml +@set finalinstallhtml +@set binarieshtml +@set gfdlhtml +@end ifnothtml + +@c Part 2 Summary Description and Copyright +@copying +Copyright @copyright{} 1988-2022 Free Software Foundation, Inc. +@sp 1 +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, the Front-Cover texts being (a) (see below), and +with the Back-Cover Texts being (b) (see below). A copy of the +license is included in the section entitled ``@uref{./gfdl.html,,GNU +Free Documentation License}''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end copying +@ifinfo +@insertcopying +@end ifinfo +@dircategory Software development +@direntry +* gccinstall: (gccinstall). Installing the GNU Compiler Collection. +@end direntry + +@c Part 3 Titlepage and Copyright +@titlepage +@title Installing GCC +@versionsubtitle + +@c The following two commands start the copyright page. +@page +@vskip 0pt plus 1filll +@insertcopying +@end titlepage + +@c Part 4 Top node, Master Menu, and/or Table of Contents +@ifinfo +@node Top, , , (dir) +@comment node-name, next, Previous, up + +@menu +* Installing GCC:: This document describes the generic installation + procedure for GCC as well as detailing some target + specific installation instructions. + +* Specific:: Host/target specific installation notes for GCC. +* Binaries:: Where to get pre-compiled binaries. + +* GNU Free Documentation License:: How you can copy and share this manual. +* Concept Index:: This index has two entries. +@end menu +@end ifinfo + +@iftex +@contents +@end iftex + +@c Part 5 The Body of the Document +@c ***Installing GCC********************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Installing GCC, Binaries, , Top +@end ifnothtml +@ifset indexhtml +@ifnothtml +@chapter Installing GCC +@end ifnothtml + +The latest version of this document is always available at +@uref{https://gcc.gnu.org/install/,,https://gcc.gnu.org/install/}. +It refers to the current development sources, instructions for +specific released versions are included with the sources. + +This document describes the generic installation procedure for GCC as well +as detailing some target specific installation instructions. + +GCC includes several components that previously were separate distributions +with their own installation instructions. This document supersedes all +package-specific installation instructions. + +@emph{Before} starting the build/install procedure please check the +@ifnothtml +@ref{Specific, host/target specific installation notes}. +@end ifnothtml +@ifhtml +@uref{specific.html,,host/target specific installation notes}. +@end ifhtml +We recommend you browse the entire generic installation instructions before +you proceed. + +Lists of successful builds for released versions of GCC are +available at @uref{https://gcc.gnu.org/buildstat.html}. +These lists are updated as new information becomes available. + +The installation procedure itself is broken into five steps. + +@ifinfo +@menu +* Prerequisites:: +* Downloading the source:: +* Configuration:: +* Building:: +* Testing:: (optional) +* Final install:: +@end menu +@end ifinfo +@ifhtml +@enumerate +@item +@uref{prerequisites.html,,Prerequisites} +@item +@uref{download.html,,Downloading the source} +@item +@uref{configure.html,,Configuration} +@item +@uref{build.html,,Building} +@item +@uref{test.html,,Testing} (optional) +@item +@uref{finalinstall.html,,Final install} +@end enumerate +@end ifhtml + +Please note that GCC does not support @samp{make uninstall} and probably +won't do so in the near future as this would open a can of worms. Instead, +we suggest that you install GCC into a directory of its own and simply +remove that directory when you do not need that specific version of GCC +any longer, and, if shared libraries are installed there as well, no +more binaries exist that use them. + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} + +@insertcopying +@end ifhtml +@end ifset + +@c ***Prerequisites************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Prerequisites, Downloading the source, , Installing GCC +@end ifnothtml +@ifset prerequisiteshtml +@ifnothtml +@chapter Prerequisites +@end ifnothtml +@cindex Prerequisites + +GCC requires that various tools and packages be available for use in the +build procedure. Modifying GCC sources requires additional tools +described below. + +@heading Tools/packages necessary for building GCC +@table @asis +@item ISO C++11 compiler +Necessary to bootstrap GCC. + +Versions of GCC prior to 11 also allow bootstrapping with an ISO C++98 +compiler, versions of GCC prior to 4.8 also allow bootstrapping with a +ISO C89 compiler, and versions of GCC prior to 3.4 also allow +bootstrapping with a traditional (K&R) C compiler. + +To build all languages in a cross-compiler or other configuration where +3-stage bootstrap is not performed, you need to start with an existing +GCC binary (version 4.8 or later) because source code for language +frontends other than C might use GCC extensions. + +@item C standard library and headers + +In order to build GCC, the C standard library and headers must be present +for all target variants for which target libraries will be built (and not +only the variant of the host C++ compiler). + +This affects the popular @samp{x86_64-pc-linux-gnu} platform (among +other multilib targets), for which 64-bit (@samp{x86_64}) and 32-bit +(@samp{i386}) libc headers are usually packaged separately. If you do a +build of a native compiler on @samp{x86_64-pc-linux-gnu}, make sure you +either have the 32-bit libc developer package properly installed (the exact +name of the package depends on your distro) or you must build GCC as a +64-bit only compiler by configuring with the option +@option{--disable-multilib}. Otherwise, you may encounter an error such as +@samp{fatal error: gnu/stubs-32.h: No such file} + +@item @anchor{GNAT-prerequisite}GNAT + +In order to build GNAT, the Ada compiler, you need a working GNAT +compiler (GCC version 5.1 or later). + +This includes GNAT tools such as @command{gnatmake} and +@command{gnatlink}, since the Ada front end is written in Ada and +uses some GNAT-specific extensions. + +In order to build a cross compiler, it is strongly recommended to install +the new compiler as native first, and then use it to build the cross +compiler. Other native compiler versions may work but this is not guaranteed and +will typically fail with hard to understand compilation errors during the +build. + +Similarly, it is strongly recommended to use an older version of GNAT to build +GNAT. More recent versions of GNAT than the version built are not guaranteed +to work and will often fail during the build with compilation errors. + +Note that @command{configure} does not test whether the GNAT installation works +and has a sufficiently recent version; if too old a GNAT version is +installed and @option{--enable-languages=ada} is used, the build will fail. + +@env{ADA_INCLUDE_PATH} and @env{ADA_OBJECT_PATH} environment variables +must not be set when building the Ada compiler, the Ada tools, or the +Ada runtime libraries. You can check that your build environment is clean +by verifying that @samp{gnatls -v} lists only one explicit path in each +section. + +@item @anchor{GDC-prerequisite}GDC + +In order to build GDC, the D compiler, you need a working GDC +compiler (GCC version 9.1 or later) and D runtime library, +@samp{libphobos}, as the D front end is written in D. + +Versions of GDC prior to 12 can be built with an ISO C++11 compiler, which can +then be installed and used to bootstrap newer versions of the D front end. + +It is strongly recommended to use an older version of GDC to build GDC. More +recent versions of GDC than the version built are not guaranteed to work and +will often fail during the build with compilation errors relating to +deprecations or removed features. + +Note that @command{configure} does not test whether the GDC installation works +and has a sufficiently recent version. Though the implementation of the D +front end does not make use of any GDC-specific extensions, or novel features +of the D language, if too old a GDC version is installed and +@option{--enable-languages=d} is used, the build will fail. + +On some targets, @samp{libphobos} isn't enabled by default, but compiles +and works if @option{--enable-libphobos} is used. Specifics are +documented for affected targets. + +@item A ``working'' POSIX compatible shell, or GNU bash + +Necessary when running @command{configure} because some +@command{/bin/sh} shells have bugs and may crash when configuring the +target libraries. In other cases, @command{/bin/sh} or @command{ksh} +have disastrous corner-case performance problems. This +can cause target @command{configure} runs to literally take days to +complete in some cases. + +So on some platforms @command{/bin/ksh} is sufficient, on others it +isn't. See the host/target specific instructions for your platform, or +use @command{bash} to be sure. Then set @env{CONFIG_SHELL} in your +environment to your ``good'' shell prior to running +@command{configure}/@command{make}. + +@command{zsh} is not a fully compliant POSIX shell and will not +work when configuring GCC@. + +@item A POSIX or SVR4 awk + +Necessary for creating some of the generated source files for GCC@. +If in doubt, use a recent GNU awk version, as some of the older ones +are broken. GNU awk version 3.1.5 is known to work. + +@item GNU binutils + +Necessary in some circumstances, optional in others. See the +host/target specific instructions for your platform for the exact +requirements. + +Note binutils 2.35 or newer is required for LTO to work correctly +with GNU libtool that includes doing a bootstrap with LTO enabled. + +@item gzip version 1.2.4 (or later) or +@itemx bzip2 version 1.0.2 (or later) + +Necessary to uncompress GCC @command{tar} files when source code is +obtained via HTTPS mirror sites. + +@item GNU make version 3.80 (or later) + +You must have GNU make installed to build GCC@. + +@item GNU tar version 1.14 (or later) + +Necessary (only on some platforms) to untar the source code. Many +systems' @command{tar} programs will also work, only try GNU +@command{tar} if you have problems. + +@item Perl version between 5.6.1 and 5.6.24 + +Necessary when targeting Darwin, building @samp{libstdc++}, +and not using @option{--disable-symvers}. +Necessary when targeting Solaris 2 with Solaris @command{ld} and not using +@option{--disable-symvers}. + +Necessary when regenerating @file{Makefile} dependencies in libiberty. +Necessary when regenerating @file{libiberty/functions.texi}. +Necessary when generating manpages from Texinfo manuals. +Used by various scripts to generate some files included in the source +repository (mainly Unicode-related and rarely changing) from source +tables. + +Used by @command{automake}. + +@end table + +Several support libraries are necessary to build GCC, some are required, +others optional. While any sufficiently new version of required tools +usually work, library requirements are generally stricter. Newer +versions may work in some cases, but it's safer to use the exact +versions documented. We appreciate bug reports about problems with +newer versions, though. If your OS vendor provides packages for the +support libraries then using those packages may be the simplest way to +install the libraries. + +@table @asis +@item GNU Multiple Precision Library (GMP) version 4.3.2 (or later) + +Necessary to build GCC@. If a GMP source distribution is found in a +subdirectory of your GCC sources named @file{gmp}, it will be built +together with GCC. Alternatively, if GMP is already installed but it +is not in your library search path, you will have to configure with the +@option{--with-gmp} configure option. See also @option{--with-gmp-lib} +and @option{--with-gmp-include}. +The in-tree build is only supported with the GMP version that +download_prerequisites installs. + +@item MPFR Library version 3.1.0 (or later) + +Necessary to build GCC@. It can be downloaded from +@uref{https://www.mpfr.org}. If an MPFR source distribution is found +in a subdirectory of your GCC sources named @file{mpfr}, it will be +built together with GCC. Alternatively, if MPFR is already installed +but it is not in your default library search path, the +@option{--with-mpfr} configure option should be used. See also +@option{--with-mpfr-lib} and @option{--with-mpfr-include}. +The in-tree build is only supported with the MPFR version that +download_prerequisites installs. + +@item MPC Library version 1.0.1 (or later) + +Necessary to build GCC@. It can be downloaded from +@uref{https://www.multiprecision.org/mpc/}. If an MPC source distribution +is found in a subdirectory of your GCC sources named @file{mpc}, it +will be built together with GCC. Alternatively, if MPC is already +installed but it is not in your default library search path, the +@option{--with-mpc} configure option should be used. See also +@option{--with-mpc-lib} and @option{--with-mpc-include}. +The in-tree build is only supported with the MPC version that +download_prerequisites installs. + +@item isl Library version 0.15 or later. + +Necessary to build GCC with the Graphite loop optimizations. +It can be downloaded from @uref{https://gcc.gnu.org/pub/gcc/infrastructure/}. +If an isl source distribution is found +in a subdirectory of your GCC sources named @file{isl}, it will be +built together with GCC. Alternatively, the @option{--with-isl} configure +option should be used if isl is not installed in your default library +search path. + +@item zstd Library. + +Necessary to build GCC with zstd compression used for LTO bytecode. +The library is searched in your default library patch search. +Alternatively, the @option{--with-zstd} configure option should be used. + +@end table + +@heading Tools/packages necessary for modifying GCC +@table @asis +@item autoconf version 2.69 +@itemx GNU m4 version 1.4.6 (or later) + +Necessary when modifying @file{configure.ac}, @file{aclocal.m4}, etc.@: +to regenerate @file{configure} and @file{config.in} files. + +@item automake version 1.15.1 + +Necessary when modifying a @file{Makefile.am} file to regenerate its +associated @file{Makefile.in}. + +Much of GCC does not use automake, so directly edit the @file{Makefile.in} +file. Specifically this applies to the @file{gcc}, @file{intl}, +@file{libcpp}, @file{libiberty}, @file{libobjc} directories as well +as any of their subdirectories. + +For directories that use automake, GCC requires the latest release in +the 1.15 series, which is currently 1.15.1. When regenerating a directory +to a newer version, please update all the directories using an older 1.15 +to the latest released version. + +@item gettext version 0.14.5 (or later) + +Needed to regenerate @file{gcc.pot}. + +@item gperf version 2.7.2 (or later) + +Necessary when modifying @command{gperf} input files, e.g.@: +@file{gcc/cp/cfns.gperf} to regenerate its associated header file, e.g.@: +@file{gcc/cp/cfns.h}. + +@item DejaGnu version 1.5.3 (or later) +@itemx Expect +@itemx Tcl +@c Once Tcl 8.5 or higher is required, remove any obsolete +@c compatibility workarounds: +@c git grep 'compatibility with earlier Tcl releases' + +Necessary to run the GCC testsuite; see the section on testing for +details. + +@item autogen version 5.5.4 (or later) and +@itemx guile version 1.4.1 (or later) + +Necessary to regenerate @file{fixinc/fixincl.x} from +@file{fixinc/inclhack.def} and @file{fixinc/*.tpl}. + +Necessary to run @samp{make check} for @file{fixinc}. + +Necessary to regenerate the top level @file{Makefile.in} file from +@file{Makefile.tpl} and @file{Makefile.def}. + +@item Flex version 2.5.4 (or later) + +Necessary when modifying @file{*.l} files. + +Necessary to build GCC during development because the generated output +files are not included in the version-controlled source repository. +They are included in releases. + +@item Texinfo version 4.7 (or later) + +Necessary for running @command{makeinfo} when modifying @file{*.texi} +files to test your changes. + +Necessary for running @command{make dvi} or @command{make pdf} to +create printable documentation in DVI or PDF format. Texinfo version +4.8 or later is required for @command{make pdf}. + +Necessary to build GCC documentation during development because the +generated output files are not included in the repository. They are +included in releases. + +@item @TeX{} (any working version) + +Necessary for running @command{texi2dvi} and @command{texi2pdf}, which +are used when running @command{make dvi} or @command{make pdf} to create +DVI or PDF files, respectively. + +@item Sphinx version 1.0 (or later) + +Necessary to regenerate @file{jit/docs/_build/texinfo} from the @file{.rst} +files in the directories below @file{jit/docs}. + +@item git (any version) +@itemx SSH (any version) + +Necessary to access the source repository. Public releases and weekly +snapshots of the development sources are also available via HTTPS@. + +@item GNU diffutils version 2.7 (or later) + +Useful when submitting patches for the GCC source code. + +@item patch version 2.5.4 (or later) + +Necessary when applying patches, created with @command{diff}, to one's +own sources. + +@end table + +@html +

+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Downloading the source************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Downloading the source, Configuration, Prerequisites, Installing GCC +@end ifnothtml +@ifset downloadhtml +@ifnothtml +@chapter Downloading GCC +@end ifnothtml +@cindex Downloading GCC +@cindex Downloading the Source + +GCC is distributed via @uref{https://gcc.gnu.org/git.html,,git} and via +HTTPS as tarballs compressed with @command{gzip} or @command{bzip2}. + +Please refer to the @uref{https://gcc.gnu.org/releases.html,,releases web page} +for information on how to obtain GCC@. + +The source distribution includes the C, C++, Objective-C, Fortran, +and Ada (in the case of GCC 3.1 and later) compilers, as well as +runtime libraries for C++, Objective-C, and Fortran. +For previous versions these were downloadable as separate components such +as the core GCC distribution, which included the C language front end and +shared components, and language-specific distributions including the +language front end and the language runtime (where appropriate). + +If you also intend to build binutils (either to upgrade an existing +installation or for use in place of the corresponding tools of your +OS), unpack the binutils distribution either in the same directory or +a separate one. In the latter case, add symbolic links to any +components of the binutils you intend to build alongside the compiler +(@file{bfd}, @file{binutils}, @file{gas}, @file{gprof}, @file{ld}, +@file{opcodes}, @dots{}) to the directory containing the GCC sources. + +Likewise the GMP, MPFR and MPC libraries can be automatically built +together with GCC. You may simply run the +@command{contrib/download_prerequisites} script in the GCC source directory +to set up everything. +Otherwise unpack the GMP, MPFR and/or MPC source +distributions in the directory containing the GCC sources and rename +their directories to @file{gmp}, @file{mpfr} and @file{mpc}, +respectively (or use symbolic links with the same name). + +@html +

+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Configuration*********************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Configuration, Building, Downloading the source, Installing GCC +@end ifnothtml +@ifset configurehtml +@ifnothtml +@chapter Installing GCC: Configuration +@end ifnothtml +@cindex Configuration +@cindex Installing GCC: Configuration + +Like most GNU software, GCC must be configured before it can be built. +This document describes the recommended configuration procedure +for both native and cross targets. + +We use @var{srcdir} to refer to the toplevel source directory for +GCC; we use @var{objdir} to refer to the toplevel build/object directory. + +If you obtained the sources by cloning the repository, @var{srcdir} +must refer to the top @file{gcc} directory, the one where the +@file{MAINTAINERS} file can be found, and not its @file{gcc} +subdirectory, otherwise the build will fail. + +If either @var{srcdir} or @var{objdir} is located on an automounted NFS +file system, the shell's built-in @command{pwd} command will return +temporary pathnames. Using these can lead to various sorts of build +problems. To avoid this issue, set the @env{PWDCMD} environment +variable to an automounter-aware @command{pwd} command, e.g., +@command{pawd} or @samp{amq -w}, during the configuration and build +phases. + +First, we @strong{highly} recommend that GCC be built into a +separate directory from the sources which does @strong{not} reside +within the source tree. This is how we generally build GCC; building +where @var{srcdir} == @var{objdir} should still work, but doesn't +get extensive testing; building where @var{objdir} is a subdirectory +of @var{srcdir} is unsupported. + +If you have previously built GCC in the same directory for a +different target machine, do @samp{make distclean} to delete all files +that might be invalid. One of the files this deletes is @file{Makefile}; +if @samp{make distclean} complains that @file{Makefile} does not exist +or issues a message like ``don't know how to make distclean'' it probably +means that the directory is already suitably clean. However, with the +recommended method of building in a separate @var{objdir}, you should +simply use a different @var{objdir} for each target. + +Second, when configuring a native system, either @command{cc} or +@command{gcc} must be in your path or you must set @env{CC} in +your environment before running configure. Otherwise the configuration +scripts may fail. + +@ignore +Note that the bootstrap compiler and the resulting GCC must be link +compatible, else the bootstrap will fail with linker errors about +incompatible object file formats. Several multilibed targets are +affected by this requirement, see +@ifnothtml +@ref{Specific, host/target specific installation notes}. +@end ifnothtml +@ifhtml +@uref{specific.html,,host/target specific installation notes}. +@end ifhtml +@end ignore + +To configure GCC: + +@smallexample +% mkdir @var{objdir} +% cd @var{objdir} +% @var{srcdir}/configure [@var{options}] [@var{target}] +@end smallexample + +@heading Distributor options + +If you will be distributing binary versions of GCC, with modifications +to the source code, you should use the options described in this +section to make clear that your version contains modifications. + +@table @code +@item --with-pkgversion=@var{version} +Specify a string that identifies your package. You may wish +to include a build number or build date. This version string will be +included in the output of @command{gcc --version}. This suffix does +not replace the default version string, only the @samp{GCC} part. + +The default value is @samp{GCC}. + +@item --with-bugurl=@var{url} +Specify the URL that users should visit if they wish to report a bug. +You are of course welcome to forward bugs reported to you to the FSF, +if you determine that they are not bugs in your modifications. + +The default value refers to the FSF's GCC bug tracker. + +@item --with-documentation-root-url=@var{url} +Specify the URL root that contains GCC option documentation. The @var{url} +should end with a @code{/} character. + +The default value is @uref{https://gcc.gnu.org/onlinedocs/,,https://gcc.gnu.org/onlinedocs/}. + +@item --with-changes-root-url=@var{url} +Specify the URL root that contains information about changes in GCC +releases like @code{gcc-@var{version}/changes.html}. +The @var{url} should end with a @code{/} character. + +The default value is @uref{https://gcc.gnu.org/,,https://gcc.gnu.org/}. + +@end table + +@heading Host, Build and Target specification + +Specify the host, build and target machine configurations. You do this +when you run the @file{configure} script. + +The @dfn{build} machine is the system which you are using, the +@dfn{host} machine is the system where you want to run the resulting +compiler (normally the build machine), and the @dfn{target} machine is +the system for which you want the compiler to generate code. + +If you are building a compiler to produce code for the machine it runs +on (a native compiler), you normally do not need to specify any operands +to @file{configure}; it will try to guess the type of machine you are on +and use that as the build, host and target machines. So you don't need +to specify a configuration when building a native compiler unless +@file{configure} cannot figure out what your configuration is or guesses +wrong. + +In those cases, specify the build machine's @dfn{configuration name} +with the @option{--host} option; the host and target will default to be +the same as the host machine. + +Here is an example: + +@smallexample +./configure --host=x86_64-pc-linux-gnu +@end smallexample + +A configuration name may be canonical or it may be more or less +abbreviated (@file{config.sub} script produces canonical versions). + +A canonical configuration name has three parts, separated by dashes. +It looks like this: @samp{@var{cpu}-@var{company}-@var{system}}. + +Here are the possible CPU types: + +@quotation +aarch64, aarch64_be, alpha, alpha64, amdgcn, arc, arceb, arm, armeb, avr, bfin, +bpf, cris, csky, epiphany, fido, fr30, frv, ft32, h8300, hppa, hppa2.0, +hppa64, i486, i686, ia64, iq2000, lm32, loongarch64, m32c, m32r, m32rle, m68k, +mcore, microblaze, microblazeel, mips, mips64, mips64el, mips64octeon, +mips64orion, mips64vr, mipsel, mipsisa32, mipsisa32r2, mipsisa64, mipsisa64r2, +mipsisa64r2el, mipsisa64sb1, mipsisa64sr71k, mipstx39, mmix, mn10300, moxie, +msp430, nds32be, nds32le, nios2, nvptx, or1k, pdp11, powerpc, powerpc64, +powerpc64le, powerpcle, pru, riscv32, riscv32be, riscv64, riscv64be, rl78, rx, +s390, s390x, sh, shle, sparc, sparc64, tic6x, v850, +v850e, v850e1, vax, visium, x86_64, xstormy16, xtensa +@end quotation + +Here is a list of system types: + +@quotation +aix@var{version}, amdhsa, aout, cygwin, darwin@var{version}, +eabi, eabialtivec, eabisim, eabisimaltivec, elf, elf32, +elfbare, elfoabi, freebsd@var{version}, gnu, hpux, hpux@var{version}, +kfreebsd-gnu, kopensolaris-gnu, linux-androideabi, linux-gnu, +linux-gnu_altivec, linux-musl, linux-uclibc, lynxos, mingw32, mingw32crt, +mmixware, msdosdjgpp, netbsd, netbsdelf@var{version}, nto-qnx, openbsd, +rtems, solaris@var{version}, symbianelf, tpf, uclinux, uclinux_eabi, vms, +vxworks, vxworksae, vxworksmils +@end quotation + +@heading Options specification + +Use @var{options} to override several configure time options for +GCC@. A list of supported @var{options} follows; @samp{configure +--help} may list other options, but those not listed below may not +work and should not normally be used. + +Note that each @option{--enable} option has a corresponding +@option{--disable} option and that each @option{--with} option has a +corresponding @option{--without} option. + +@table @code +@item --prefix=@var{dirname} +Specify the toplevel installation +directory. This is the recommended way to install the tools into a directory +other than the default. The toplevel installation directory defaults to +@file{/usr/local}. + +We @strong{highly} recommend against @var{dirname} being the same or a +subdirectory of @var{objdir} or vice versa. If specifying a directory +beneath a user's home directory tree, some shells will not expand +@var{dirname} correctly if it contains the @samp{~} metacharacter; use +@env{$HOME} instead. + +The following standard @command{autoconf} options are supported. Normally you +should not need to use these options. +@table @code +@item --exec-prefix=@var{dirname} +Specify the toplevel installation directory for architecture-dependent +files. The default is @file{@var{prefix}}. + +@item --bindir=@var{dirname} +Specify the installation directory for the executables called by users +(such as @command{gcc} and @command{g++}). The default is +@file{@var{exec-prefix}/bin}. + +@item --libdir=@var{dirname} +Specify the installation directory for object code libraries and +internal data files of GCC@. The default is @file{@var{exec-prefix}/lib}. + +@item --libexecdir=@var{dirname} +Specify the installation directory for internal executables of GCC@. +The default is @file{@var{exec-prefix}/libexec}. + +@item --with-slibdir=@var{dirname} +Specify the installation directory for the shared libgcc library. The +default is @file{@var{libdir}}. + +@item --datarootdir=@var{dirname} +Specify the root of the directory tree for read-only architecture-independent +data files referenced by GCC@. The default is @file{@var{prefix}/share}. + +@item --infodir=@var{dirname} +Specify the installation directory for documentation in info format. +The default is @file{@var{datarootdir}/info}. + +@item --datadir=@var{dirname} +Specify the installation directory for some architecture-independent +data files referenced by GCC@. The default is @file{@var{datarootdir}}. + +@item --docdir=@var{dirname} +Specify the installation directory for documentation files (other +than Info) for GCC@. The default is @file{@var{datarootdir}/doc}. + +@item --htmldir=@var{dirname} +Specify the installation directory for HTML documentation files. +The default is @file{@var{docdir}}. + +@item --pdfdir=@var{dirname} +Specify the installation directory for PDF documentation files. +The default is @file{@var{docdir}}. + +@item --mandir=@var{dirname} +Specify the installation directory for manual pages. The default is +@file{@var{datarootdir}/man}. (Note that the manual pages are only extracts +from the full GCC manuals, which are provided in Texinfo format. The manpages +are derived by an automatic conversion process from parts of the full +manual.) + +@item --with-gxx-include-dir=@var{dirname} +Specify +the installation directory for G++ header files. The default depends +on other configuration options, and differs between cross and native +configurations. + +@item --with-specs=@var{specs} +Specify additional command line driver SPECS. +This can be useful if you need to turn on a non-standard feature by +default without modifying the compiler's source code, for instance +@option{--with-specs=%@{!fcommon:%@{!fno-common:-fno-common@}@}}. +@ifnothtml +@xref{Spec Files,, Specifying subprocesses and the switches to pass to them, +gcc, Using the GNU Compiler Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``Spec Files'' in the main manual +@end ifhtml + +@end table + +@item --program-prefix=@var{prefix} +GCC supports some transformations of the names of its programs when +installing them. This option prepends @var{prefix} to the names of +programs to install in @var{bindir} (see above). For example, specifying +@option{--program-prefix=foo-} would result in @samp{gcc} +being installed as @file{/usr/local/bin/foo-gcc}. + +@item --program-suffix=@var{suffix} +Appends @var{suffix} to the names of programs to install in @var{bindir} +(see above). For example, specifying @option{--program-suffix=-3.1} +would result in @samp{gcc} being installed as +@file{/usr/local/bin/gcc-3.1}. + +@item --program-transform-name=@var{pattern} +Applies the @samp{sed} script @var{pattern} to be applied to the names +of programs to install in @var{bindir} (see above). @var{pattern} has to +consist of one or more basic @samp{sed} editing commands, separated by +semicolons. For example, if you want the @samp{gcc} program name to be +transformed to the installed program @file{/usr/local/bin/myowngcc} and +the @samp{g++} program name to be transformed to +@file{/usr/local/bin/gspecial++} without changing other program names, +you could use the pattern +@option{--program-transform-name='s/^gcc$/myowngcc/; s/^g++$/gspecial++/'} +to achieve this effect. + +All three options can be combined and used together, resulting in more +complex conversion patterns. As a basic rule, @var{prefix} (and +@var{suffix}) are prepended (appended) before further transformations +can happen with a special transformation script @var{pattern}. + +As currently implemented, this option only takes effect for native +builds; cross compiler binaries' names are not transformed even when a +transformation is explicitly asked for by one of these options. + +For native builds, some of the installed programs are also installed +with the target alias in front of their name, as in +@samp{i686-pc-linux-gnu-gcc}. All of the above transformations happen +before the target alias is prepended to the name---so, specifying +@option{--program-prefix=foo-} and @option{program-suffix=-3.1}, the +resulting binary would be installed as +@file{/usr/local/bin/i686-pc-linux-gnu-foo-gcc-3.1}. + +As a last shortcoming, none of the installed Ada programs are +transformed yet, which will be fixed in some time. + +@item --with-local-prefix=@var{dirname} +Specify the +installation directory for local include files. The default is +@file{/usr/local}. Specify this option if you want the compiler to +search directory @file{@var{dirname}/include} for locally installed +header files @emph{instead} of @file{/usr/local/include}. + +You should specify @option{--with-local-prefix} @strong{only} if your +site has a different convention (not @file{/usr/local}) for where to put +site-specific files. + +The default value for @option{--with-local-prefix} is @file{/usr/local} +regardless of the value of @option{--prefix}. Specifying +@option{--prefix} has no effect on which directory GCC searches for +local header files. This may seem counterintuitive, but actually it is +logical. + +The purpose of @option{--prefix} is to specify where to @emph{install +GCC}. The local header files in @file{/usr/local/include}---if you put +any in that directory---are not part of GCC@. They are part of other +programs---perhaps many others. (GCC installs its own header files in +another directory which is based on the @option{--prefix} value.) + +Both the local-prefix include directory and the GCC-prefix include +directory are part of GCC's ``system include'' directories. Although these +two directories are not fixed, they need to be searched in the proper +order for the correct processing of the include_next directive. The +local-prefix include directory is searched before the GCC-prefix +include directory. Another characteristic of system include directories +is that pedantic warnings are turned off for headers in these directories. + +Some autoconf macros add @option{-I @var{directory}} options to the +compiler command line, to ensure that directories containing installed +packages' headers are searched. When @var{directory} is one of GCC's +system include directories, GCC will ignore the option so that system +directories continue to be processed in the correct order. This +may result in a search order different from what was specified but the +directory will still be searched. + +GCC automatically searches for ordinary libraries using +@env{GCC_EXEC_PREFIX}. Thus, when the same installation prefix is +used for both GCC and packages, GCC will automatically search for +both headers and libraries. This provides a configuration that is +easy to use. GCC behaves in a manner similar to that when it is +installed as a system compiler in @file{/usr}. + +Sites that need to install multiple versions of GCC may not want to +use the above simple configuration. It is possible to use the +@option{--program-prefix}, @option{--program-suffix} and +@option{--program-transform-name} options to install multiple versions +into a single directory, but it may be simpler to use different prefixes +and the @option{--with-local-prefix} option to specify the location of the +site-specific files for each version. It will then be necessary for +users to specify explicitly the location of local site libraries +(e.g., with @env{LIBRARY_PATH}). + +The same value can be used for both @option{--with-local-prefix} and +@option{--prefix} provided it is not @file{/usr}. This can be used +to avoid the default search of @file{/usr/local/include}. + +@strong{Do not} specify @file{/usr} as the @option{--with-local-prefix}! +The directory you use for @option{--with-local-prefix} @strong{must not} +contain any of the system's standard header files. If it did contain +them, certain programs would be miscompiled (including GNU Emacs, on +certain targets), because this would override and nullify the header +file corrections made by the @command{fixincludes} script. + +Indications are that people who use this option use it based on mistaken +ideas of what it is for. People use it as if it specified where to +install part of GCC@. Perhaps they make this assumption because +installing GCC creates the directory. + +@item --with-gcc-major-version-only +Specifies that GCC should use only the major number rather than +@var{major}.@var{minor}.@var{patchlevel} in filesystem paths. + +@item --with-native-system-header-dir=@var{dirname} +Specifies that @var{dirname} is the directory that contains native system +header files, rather than @file{/usr/include}. This option is most useful +if you are creating a compiler that should be isolated from the system +as much as possible. It is most commonly used with the +@option{--with-sysroot} option and will cause GCC to search +@var{dirname} inside the system root specified by that option. + +@item --enable-shared[=@var{package}[,@dots{}]] +Build shared versions of libraries, if shared libraries are supported on +the target platform. Unlike GCC 2.95.x and earlier, shared libraries +are enabled by default on all platforms that support shared libraries. + +If a list of packages is given as an argument, build shared libraries +only for the listed packages. For other packages, only static libraries +will be built. Package names currently recognized in the GCC tree are +@samp{libgcc} (also known as @samp{gcc}), @samp{libstdc++} (not +@samp{libstdc++-v3}), @samp{libffi}, @samp{zlib}, @samp{boehm-gc}, +@samp{ada}, @samp{libada}, @samp{libgo}, @samp{libobjc}, and @samp{libphobos}. +Note @samp{libiberty} does not support shared libraries at all. + +Use @option{--disable-shared} to build only static libraries. Note that +@option{--disable-shared} does not accept a list of package names as +argument, only @option{--enable-shared} does. + +Contrast with @option{--enable-host-shared}, which affects @emph{host} +code. + +@item --enable-host-shared +Specify that the @emph{host} code should be built into position-independent +machine code (with -fPIC), allowing it to be used within shared libraries, +but yielding a slightly slower compiler. + +This option is required when building the libgccjit.so library. + +Contrast with @option{--enable-shared}, which affects @emph{target} +libraries. + +@item @anchor{with-gnu-as}--with-gnu-as +Specify that the compiler should assume that the +assembler it finds is the GNU assembler. However, this does not modify +the rules to find an assembler and will result in confusion if the +assembler found is not actually the GNU assembler. (Confusion may also +result if the compiler finds the GNU assembler but has not been +configured with @option{--with-gnu-as}.) If you have more than one +assembler installed on your system, you may want to use this option in +connection with @option{--with-as=@var{pathname}} or +@option{--with-build-time-tools=@var{pathname}}. + +The following systems are the only ones where it makes a difference +whether you use the GNU assembler. On any other system, +@option{--with-gnu-as} has no effect. + +@itemize @bullet +@item @samp{hppa1.0-@var{any}-@var{any}} +@item @samp{hppa1.1-@var{any}-@var{any}} +@item @samp{sparc-sun-solaris2.@var{any}} +@item @samp{sparc64-@var{any}-solaris2.@var{any}} +@end itemize + +@item @anchor{with-as}--with-as=@var{pathname} +Specify that the compiler should use the assembler pointed to by +@var{pathname}, rather than the one found by the standard rules to find +an assembler, which are: +@itemize @bullet +@item +Unless GCC is being built with a cross compiler, check the +@file{@var{libexec}/gcc/@var{target}/@var{version}} directory. +@var{libexec} defaults to @file{@var{exec-prefix}/libexec}; +@var{exec-prefix} defaults to @var{prefix}, which +defaults to @file{/usr/local} unless overridden by the +@option{--prefix=@var{pathname}} switch described above. @var{target} +is the target system triple, such as @samp{sparc-sun-solaris2.7}, and +@var{version} denotes the GCC version, such as 3.0. + +@item +If the target system is the same that you are building on, check +operating system specific directories (e.g.@: @file{/usr/ccs/bin} on +Solaris 2). + +@item +Check in the @env{PATH} for a tool whose name is prefixed by the +target system triple. + +@item +Check in the @env{PATH} for a tool whose name is not prefixed by the +target system triple, if the host and target system triple are +the same (in other words, we use a host tool if it can be used for +the target as well). +@end itemize + +You may want to use @option{--with-as} if no assembler +is installed in the directories listed above, or if you have multiple +assemblers installed and want to choose one that is not found by the +above rules. + +@item @anchor{with-gnu-ld}--with-gnu-ld +Same as @uref{#with-gnu-as,,@option{--with-gnu-as}} +but for the linker. + +@item --with-ld=@var{pathname} +Same as @uref{#with-as,,@option{--with-as}} +but for the linker. + +@item --with-dsymutil=@var{pathname} +Same as @uref{#with-as,,@option{--with-as}} +but for the debug linker (only used on Darwin platforms so far). + +@item --with-tls=@var{dialect} +Specify the default TLS dialect, for systems were there is a choice. +For ARM targets, possible values for @var{dialect} are @code{gnu} or +@code{gnu2}, which select between the original GNU dialect and the GNU TLS +descriptor-based dialect. + +@item --enable-multiarch +Specify whether to enable or disable multiarch support. The default is +to check for glibc start files in a multiarch location, and enable it +if the files are found. The auto detection is enabled for native builds, +and for cross builds configured with @option{--with-sysroot}, and without +@option{--with-native-system-header-dir}. +More documentation about multiarch can be found at +@uref{https://wiki.debian.org/Multiarch}. + +@item --enable-sjlj-exceptions +Force use of the @code{setjmp}/@code{longjmp}-based scheme for exceptions. +@samp{configure} ordinarily picks the correct value based on the platform. +Only use this option if you are sure you need a different setting. + +@item --enable-vtable-verify +Specify whether to enable or disable the vtable verification feature. +Enabling this feature causes libstdc++ to be built with its virtual calls +in verifiable mode. This means that, when linked with libvtv, every +virtual call in libstdc++ will verify the vtable pointer through which the +call will be made before actually making the call. If not linked with libvtv, +the verifier will call stub functions (in libstdc++ itself) and do nothing. +If vtable verification is disabled, then libstdc++ is not built with its +virtual calls in verifiable mode at all. However the libvtv library will +still be built (see @option{--disable-libvtv} to turn off building libvtv). +@option{--disable-vtable-verify} is the default. + +@item --disable-gcov +Specify that the run-time library used for coverage analysis +and associated host tools should not be built. + +@item --disable-multilib +Specify that multiple target +libraries to support different target variants, calling +conventions, etc.@: should not be built. The default is to build a +predefined set of them. + +Some targets provide finer-grained control over which multilibs are built +(e.g., @option{--disable-softfloat}): +@table @code +@item arm-*-* +fpu, 26bit, underscore, interwork, biendian, nofmult. + +@item m68*-*-* +softfloat, m68881, m68000, m68020. + +@item mips*-*-* +single-float, biendian, softfloat. + +@item msp430-*-* +no-exceptions + +@item powerpc*-*-*, rs6000*-*-* +aix64, pthread, softfloat, powercpu, powerpccpu, powerpcos, biendian, +sysv, aix. + +@end table + +@item --with-multilib-list=@var{list} +@itemx --without-multilib-list +Specify what multilibs to build. @var{list} is a comma separated list of +values, possibly consisting of a single value. Currently only implemented +for aarch64*-*-*, arm*-*-*, loongarch64-*-*, riscv*-*-*, sh*-*-* and +x86-64-*-linux*. The accepted values and meaning for each target is given +below. + +@table @code +@item aarch64*-*-* +@var{list} is a comma separated list of @code{ilp32}, and @code{lp64} +to enable ILP32 and LP64 run-time libraries, respectively. If +@var{list} is empty, then there will be no multilibs and only the +default run-time library will be built. If @var{list} is +@code{default} or --with-multilib-list= is not specified, then the +default set of libraries is selected based on the value of +@option{--target}. + +@item arm*-*-* +@var{list} is a comma separated list of @code{aprofile} and +@code{rmprofile} to build multilibs for A or R and M architecture +profiles respectively. Note that, due to some limitation of the current +multilib framework, using the combined @code{aprofile,rmprofile} +multilibs selects in some cases a less optimal multilib than when using +the multilib profile for the architecture targetted. The special value +@code{default} is also accepted and is equivalent to omitting the +option, i.e., only the default run-time library will be enabled. + +@var{list} may instead contain @code{@@name}, to use the multilib +configuration Makefile fragment @file{name} in @file{gcc/config/arm} in +the source tree (it is part of the corresponding sources, after all). +It is recommended, but not required, that files used for this purpose to +be named starting with @file{t-ml-}, to make their intended purpose +self-evident, in line with GCC conventions. Such files enable custom, +user-chosen multilib lists to be configured. Whether multiple such +files can be used together depends on the contents of the supplied +files. See @file{gcc/config/arm/t-multilib} and its supplementary +@file{gcc/config/arm/t-*profile} files for an example of what such +Makefile fragments might look like for this version of GCC. The macros +expected to be defined in these fragments are not stable across GCC +releases, so make sure they define the @code{MULTILIB}-related macros +expected by the version of GCC you are building. +@ifnothtml +@xref{Target Fragment,, Target Makefile Fragments, gccint, GNU Compiler +Collection (GCC) Internals}. +@end ifnothtml +@ifhtml +See ``Target Makefile Fragments'' in the internals manual. +@end ifhtml + +The table below gives the combination of ISAs, architectures, FPUs and +floating-point ABIs for which multilibs are built for each predefined +profile. The union of these options is considered when specifying both +@code{aprofile} and @code{rmprofile}. + +@multitable @columnfractions .15 .28 .30 +@item Option @tab aprofile @tab rmprofile +@item ISAs +@tab @code{-marm} and @code{-mthumb} +@tab @code{-mthumb} +@item Architectures@*@*@*@*@*@* +@tab default architecture@* +@code{-march=armv7-a}@* +@code{-march=armv7ve}@* +@code{-march=armv8-a}@*@*@* +@tab default architecture@* +@code{-march=armv6s-m}@* +@code{-march=armv7-m}@* +@code{-march=armv7e-m}@* +@code{-march=armv8-m.base}@* +@code{-march=armv8-m.main}@* +@code{-march=armv7} +@item FPUs@*@*@*@*@* +@tab none@* +@code{-mfpu=vfpv3-d16}@* +@code{-mfpu=neon}@* +@code{-mfpu=vfpv4-d16}@* +@code{-mfpu=neon-vfpv4}@* +@code{-mfpu=neon-fp-armv8} +@tab none@* +@code{-mfpu=vfpv3-d16}@* +@code{-mfpu=fpv4-sp-d16}@* +@code{-mfpu=fpv5-sp-d16}@* +@code{-mfpu=fpv5-d16}@* +@item floating-point@/ ABIs@*@* +@tab @code{-mfloat-abi=soft}@* +@code{-mfloat-abi=softfp}@* +@code{-mfloat-abi=hard} +@tab @code{-mfloat-abi=soft}@* +@code{-mfloat-abi=softfp}@* +@code{-mfloat-abi=hard} +@end multitable + +@item loongarch*-*-* +@var{list} is a comma-separated list of the following ABI identifiers: +@code{lp64d[/base]} @code{lp64f[/base]} @code{lp64d[/base]}, where the +@code{/base} suffix may be omitted, to enable their respective run-time +libraries. If @var{list} is empty or @code{default}, +or if @option{--with-multilib-list} is not specified, then the default ABI +as specified by @option{--with-abi} or implied by @option{--target} is selected. + +@item riscv*-*-* +@var{list} is a single ABI name. The target architecture must be either +@code{rv32gc} or @code{rv64gc}. This will build a single multilib for the +specified architecture and ABI pair. If @code{--with-multilib-list} is not +given, then a default set of multilibs is selected based on the value of +@option{--target}. This is usually a large set of multilibs. + +@item sh*-*-* +@var{list} is a comma separated list of CPU names. These must be of the +form @code{sh*} or @code{m*} (in which case they match the compiler option +for that processor). The list should not contain any endian options - +these are handled by @option{--with-endian}. + +If @var{list} is empty, then there will be no multilibs for extra +processors. The multilib for the secondary endian remains enabled. + +As a special case, if an entry in the list starts with a @code{!} +(exclamation point), then it is added to the list of excluded multilibs. +Entries of this sort should be compatible with @samp{MULTILIB_EXCLUDES} +(once the leading @code{!} has been stripped). + +If @option{--with-multilib-list} is not given, then a default set of +multilibs is selected based on the value of @option{--target}. This is +usually the complete set of libraries, but some targets imply a more +specialized subset. + +Example 1: to configure a compiler for SH4A only, but supporting both +endians, with little endian being the default: +@smallexample +--with-cpu=sh4a --with-endian=little,big --with-multilib-list= +@end smallexample + +Example 2: to configure a compiler for both SH4A and SH4AL-DSP, but with +only little endian SH4AL: +@smallexample +--with-cpu=sh4a --with-endian=little,big \ +--with-multilib-list=sh4al,!mb/m4al +@end smallexample + +@item x86-64-*-linux* +@var{list} is a comma separated list of @code{m32}, @code{m64} and +@code{mx32} to enable 32-bit, 64-bit and x32 run-time libraries, +respectively. If @var{list} is empty, then there will be no multilibs +and only the default run-time library will be enabled. + +If @option{--with-multilib-list} is not given, then only 32-bit and +64-bit run-time libraries will be enabled. +@end table + +@item --with-multilib-generator=@var{config} +Specify what multilibs to build. @var{config} is a semicolon separated list of +values, possibly consisting of a single value. Currently only implemented +for riscv*-*-elf*. The accepted values and meanings are given below. + + +Every config is constructed with four components: architecture string, ABI, +reuse rule with architecture string and reuse rule with sub-extension. + +Example 1: Add multi-lib suppport for rv32i with ilp32. +@smallexample +rv32i-ilp32-- +@end smallexample + +Example 2: Add multi-lib suppport for rv32i with ilp32 and rv32imafd with ilp32. +@smallexample +rv32i-ilp32--;rv32imafd-ilp32-- +@end smallexample + +Example 3: Add multi-lib suppport for rv32i with ilp32; rv32im with ilp32 and +rv32ic with ilp32 will reuse this multi-lib set. +@smallexample +rv32i-ilp32-rv32im-c +@end smallexample + +Example 4: Add multi-lib suppport for rv64ima with lp64; rv64imaf with lp64, +rv64imac with lp64 and rv64imafc with lp64 will reuse this multi-lib set. +@smallexample +rv64ima-lp64--f,c,fc +@end smallexample + +@option{--with-multilib-generator} have an optional configuration argument +@option{--cmodel=val} for code model, this option will expand with other +config options, @var{val} is a comma separated list of possible code model, +currently we support medlow and medany. + +Example 5: Add multi-lib suppport for rv64ima with lp64; rv64ima with lp64 and +medlow code model +@smallexample +rv64ima-lp64--;--cmodel=medlow +@end smallexample + +Example 6: Add multi-lib suppport for rv64ima with lp64; rv64ima with lp64 and +medlow code model; rv64ima with lp64 and medany code model +@smallexample +rv64ima-lp64--;--cmodel=medlow,medany +@end smallexample + +@item --with-endian=@var{endians} +Specify what endians to use. +Currently only implemented for sh*-*-*. + +@var{endians} may be one of the following: +@table @code +@item big +Use big endian exclusively. +@item little +Use little endian exclusively. +@item big,little +Use big endian by default. Provide a multilib for little endian. +@item little,big +Use little endian by default. Provide a multilib for big endian. +@end table + +@item --enable-threads +Specify that the target +supports threads. This affects the Objective-C compiler and runtime +library, and exception handling for other languages like C++. +On some systems, this is the default. + +In general, the best (and, in many cases, the only known) threading +model available will be configured for use. Beware that on some +systems, GCC has not been taught what threading models are generally +available for the system. In this case, @option{--enable-threads} is an +alias for @option{--enable-threads=single}. + +@item --disable-threads +Specify that threading support should be disabled for the system. +This is an alias for @option{--enable-threads=single}. + +@item --enable-threads=@var{lib} +Specify that +@var{lib} is the thread support library. This affects the Objective-C +compiler and runtime library, and exception handling for other languages +like C++. The possibilities for @var{lib} are: + +@table @code +@item aix +AIX thread support. +@item dce +DCE thread support. +@item lynx +LynxOS thread support. +@item mipssde +MIPS SDE thread support. +@item no +This is an alias for @samp{single}. +@item posix +Generic POSIX/Unix98 thread support. +@item rtems +RTEMS thread support. +@item single +Disable thread support, should work for all platforms. +@item tpf +TPF thread support. +@item vxworks +VxWorks thread support. +@item win32 +Microsoft Win32 API thread support. +@end table + +@item --enable-tls +Specify that the target supports TLS (Thread Local Storage). Usually +configure can correctly determine if TLS is supported. In cases where +it guesses incorrectly, TLS can be explicitly enabled or disabled with +@option{--enable-tls} or @option{--disable-tls}. This can happen if +the assembler supports TLS but the C library does not, or if the +assumptions made by the configure test are incorrect. + +@item --disable-tls +Specify that the target does not support TLS. +This is an alias for @option{--enable-tls=no}. + +@item --disable-tm-clone-registry +Disable TM clone registry in libgcc. It is enabled in libgcc by default. +This option helps to reduce code size for embedded targets which do +not use transactional memory. + +@item --with-cpu=@var{cpu} +@itemx --with-cpu-32=@var{cpu} +@itemx --with-cpu-64=@var{cpu} +Specify which cpu variant the compiler should generate code for by default. +@var{cpu} will be used as the default value of the @option{-mcpu=} switch. +This option is only supported on some targets, including ARC, ARM, i386, M68k, +PowerPC, and SPARC@. It is mandatory for ARC@. The @option{--with-cpu-32} and +@option{--with-cpu-64} options specify separate default CPUs for +32-bit and 64-bit modes; these options are only supported for aarch64, i386, +x86-64, PowerPC, and SPARC@. + +@item --with-schedule=@var{cpu} +@itemx --with-arch=@var{cpu} +@itemx --with-arch-32=@var{cpu} +@itemx --with-arch-64=@var{cpu} +@itemx --with-tune=@var{cpu} +@itemx --with-tune-32=@var{cpu} +@itemx --with-tune-64=@var{cpu} +@itemx --with-abi=@var{abi} +@itemx --with-fpu=@var{type} +@itemx --with-float=@var{type} +These configure options provide default values for the @option{-mschedule=}, +@option{-march=}, @option{-mtune=}, @option{-mabi=}, and @option{-mfpu=} +options and for @option{-mhard-float} or @option{-msoft-float}. As with +@option{--with-cpu}, which switches will be accepted and acceptable values +of the arguments depend on the target. + +@item --with-mode=@var{mode} +Specify if the compiler should default to @option{-marm} or @option{-mthumb}. +This option is only supported on ARM targets. + +@item --with-stack-offset=@var{num} +This option sets the default for the -mstack-offset=@var{num} option, +and will thus generally also control the setting of this option for +libraries. This option is only supported on Epiphany targets. + +@item --with-fpmath=@var{isa} +This options sets @option{-mfpmath=sse} by default and specifies the default +ISA for floating-point arithmetics. You can select either @samp{sse} which +enables @option{-msse2} or @samp{avx} which enables @option{-mavx} by default. +This option is only supported on i386 and x86-64 targets. + +@item --with-fp-32=@var{mode} +On MIPS targets, set the default value for the @option{-mfp} option when using +the o32 ABI. The possibilities for @var{mode} are: +@table @code +@item 32 +Use the o32 FP32 ABI extension, as with the @option{-mfp32} command-line +option. +@item xx +Use the o32 FPXX ABI extension, as with the @option{-mfpxx} command-line +option. +@item 64 +Use the o32 FP64 ABI extension, as with the @option{-mfp64} command-line +option. +@end table +In the absence of this configuration option the default is to use the o32 +FP32 ABI extension. + +@item --with-odd-spreg-32 +On MIPS targets, set the @option{-modd-spreg} option by default when using +the o32 ABI. + +@item --without-odd-spreg-32 +On MIPS targets, set the @option{-mno-odd-spreg} option by default when using +the o32 ABI. This is normally used in conjunction with +@option{--with-fp-32=64} in order to target the o32 FP64A ABI extension. + +@item --with-nan=@var{encoding} +On MIPS targets, set the default encoding convention to use for the +special not-a-number (NaN) IEEE 754 floating-point data. The +possibilities for @var{encoding} are: +@table @code +@item legacy +Use the legacy encoding, as with the @option{-mnan=legacy} command-line +option. +@item 2008 +Use the 754-2008 encoding, as with the @option{-mnan=2008} command-line +option. +@end table +To use this configuration option you must have an assembler version +installed that supports the @option{-mnan=} command-line option too. +In the absence of this configuration option the default convention is +the legacy encoding, as when neither of the @option{-mnan=2008} and +@option{-mnan=legacy} command-line options has been used. + +@item --with-divide=@var{type} +Specify how the compiler should generate code for checking for +division by zero. This option is only supported on the MIPS target. +The possibilities for @var{type} are: +@table @code +@item traps +Division by zero checks use conditional traps (this is the default on +systems that support conditional traps). +@item breaks +Division by zero checks use the break instruction. +@end table + +@item --with-compact-branches=@var{policy} +Specify how the compiler should generate branch instructions. +This option is only supported on the MIPS target. +The possibilities for @var{type} are: +@table @code +@item optimal +Cause a delay slot branch to be used if one is available in the +current ISA and the delay slot is successfully filled. If the delay slot +is not filled, a compact branch will be chosen if one is available. +@item never +Ensures that compact branch instructions will never be generated. +@item always +Ensures that a compact branch instruction will be generated if available. +If a compact branch instruction is not available, +a delay slot form of the branch will be used instead. +This option is supported from MIPS Release 6 onwards. +For pre-R6/microMIPS/MIPS16, this option is just same as never/optimal. +@end table + +@c If you make --with-llsc the default for additional targets, +@c update the --with-llsc description in the MIPS section below. + +@item --with-llsc +On MIPS targets, make @option{-mllsc} the default when no +@option{-mno-llsc} option is passed. This is the default for +Linux-based targets, as the kernel will emulate them if the ISA does +not provide them. + +@item --without-llsc +On MIPS targets, make @option{-mno-llsc} the default when no +@option{-mllsc} option is passed. + +@item --with-synci +On MIPS targets, make @option{-msynci} the default when no +@option{-mno-synci} option is passed. + +@item --without-synci +On MIPS targets, make @option{-mno-synci} the default when no +@option{-msynci} option is passed. This is the default. + +@item --with-lxc1-sxc1 +On MIPS targets, make @option{-mlxc1-sxc1} the default when no +@option{-mno-lxc1-sxc1} option is passed. This is the default. + +@item --without-lxc1-sxc1 +On MIPS targets, make @option{-mno-lxc1-sxc1} the default when no +@option{-mlxc1-sxc1} option is passed. The indexed load/store +instructions are not directly a problem but can lead to unexpected +behaviour when deployed in an application intended for a 32-bit address +space but run on a 64-bit processor. The issue is seen because all +known MIPS 64-bit Linux kernels execute o32 and n32 applications +with 64-bit addressing enabled which affects the overflow behaviour +of the indexed addressing mode. GCC will assume that ordinary +32-bit arithmetic overflow behaviour is the same whether performed +as an @code{addu} instruction or as part of the address calculation +in @code{lwxc1} type instructions. This assumption holds true in a +pure 32-bit environment and can hold true in a 64-bit environment if +the address space is accurately set to be 32-bit for o32 and n32. + +@item --with-madd4 +On MIPS targets, make @option{-mmadd4} the default when no +@option{-mno-madd4} option is passed. This is the default. + +@item --without-madd4 +On MIPS targets, make @option{-mno-madd4} the default when no +@option{-mmadd4} option is passed. The @code{madd4} instruction +family can be problematic when targeting a combination of cores that +implement these instructions differently. There are two known cores +that implement these as fused operations instead of unfused (where +unfused is normally expected). Disabling these instructions is the +only way to ensure compatible code is generated; this will incur +a performance penalty. + +@item --with-mips-plt +On MIPS targets, make use of copy relocations and PLTs. +These features are extensions to the traditional +SVR4-based MIPS ABIs and require support from GNU binutils +and the runtime C library. + +@item --with-stack-clash-protection-guard-size=@var{size} +On certain targets this option sets the default stack clash protection guard +size as a power of two in bytes. On AArch64 @var{size} is required to be either +12 (4KB) or 16 (64KB). + +@item --with-isa-spec=@var{ISA-spec-string} +On RISC-V targets specify the default version of the RISC-V Unprivileged +(formerly User-Level) ISA specification to produce code conforming to. +The possibilities for @var{ISA-spec-string} are: +@table @code +@item 2.2 +Produce code conforming to version 2.2. +@item 20190608 +Produce code conforming to version 20190608. +@item 20191213 +Produce code conforming to version 20191213. +@end table +In the absence of this configuration option the default version is 20191213. + +@item --enable-__cxa_atexit +Define if you want to use __cxa_atexit, rather than atexit, to +register C++ destructors for local statics and global objects. +This is essential for fully standards-compliant handling of +destructors, but requires __cxa_atexit in libc. This option is currently +only available on systems with GNU libc. When enabled, this will cause +@option{-fuse-cxa-atexit} to be passed by default. + +@item --enable-gnu-indirect-function +Define if you want to enable the @code{ifunc} attribute. This option is +currently only available on systems with GNU libc on certain targets. + +@item --enable-target-optspace +Specify that target +libraries should be optimized for code space instead of code speed. +This is the default for the m32r platform. + +@item --with-cpp-install-dir=@var{dirname} +Specify that the user visible @command{cpp} program should be installed +in @file{@var{prefix}/@var{dirname}/cpp}, in addition to @var{bindir}. + +@item --enable-comdat +Enable COMDAT group support. This is primarily used to override the +automatically detected value. + +@item --enable-initfini-array +Force the use of sections @code{.init_array} and @code{.fini_array} +(instead of @code{.init} and @code{.fini}) for constructors and +destructors. Option @option{--disable-initfini-array} has the +opposite effect. If neither option is specified, the configure script +will try to guess whether the @code{.init_array} and +@code{.fini_array} sections are supported and, if they are, use them. + +@item --enable-link-mutex +When building GCC, use a mutex to avoid linking the compilers for +multiple languages at the same time, to avoid thrashing on build +systems with limited free memory. The default is not to use such a mutex. + +@item --enable-link-serialization +When building GCC, use make dependencies to serialize linking the compilers for +multiple languages, to avoid thrashing on build +systems with limited free memory. The default is not to add such +dependencies and thus with parallel make potentially link different +compilers concurrently. If the argument is a positive integer, allow +that number of concurrent link processes for the large binaries. + +@item --enable-maintainer-mode +The build rules that regenerate the Autoconf and Automake output files as +well as the GCC master message catalog @file{gcc.pot} are normally +disabled. This is because it can only be rebuilt if the complete source +tree is present. If you have changed the sources and want to rebuild the +catalog, configuring with @option{--enable-maintainer-mode} will enable +this. Note that you need a recent version of the @code{gettext} tools +to do so. + +@item --disable-bootstrap +For a native build, the default configuration is to perform +a 3-stage bootstrap of the compiler when @samp{make} is invoked, +testing that GCC can compile itself correctly. If you want to disable +this process, you can configure with @option{--disable-bootstrap}. + +@item --enable-bootstrap +In special cases, you may want to perform a 3-stage build +even if the target and host triplets are different. +This is possible when the host can run code compiled for +the target (e.g.@: host is i686-linux, target is i486-linux). +Starting from GCC 4.2, to do this you have to configure explicitly +with @option{--enable-bootstrap}. + +@item --enable-generated-files-in-srcdir +Neither the .c and .h files that are generated from Bison and flex nor the +info manuals and man pages that are built from the .texi files are present +in the repository development tree. When building GCC from that development tree, +or from one of our snapshots, those generated files are placed in your +build directory, which allows for the source to be in a readonly +directory. + +If you configure with @option{--enable-generated-files-in-srcdir} then those +generated files will go into the source directory. This is mainly intended +for generating release or prerelease tarballs of the GCC sources, since it +is not a requirement that the users of source releases to have flex, Bison, +or makeinfo. + +@item --enable-version-specific-runtime-libs +Specify +that runtime libraries should be installed in the compiler specific +subdirectory (@file{@var{libdir}/gcc}) rather than the usual places. In +addition, @samp{libstdc++}'s include files will be installed into +@file{@var{libdir}} unless you overruled it by using +@option{--with-gxx-include-dir=@var{dirname}}. Using this option is +particularly useful if you intend to use several versions of GCC in +parallel. The default is @samp{yes} for @samp{libada}, and @samp{no} for +the remaining libraries. + +@item @anchor{WithAixSoname}--with-aix-soname=@samp{aix}, @samp{svr4} or @samp{both} +Traditional AIX shared library versioning (versioned @code{Shared Object} +files as members of unversioned @code{Archive Library} files named +@samp{lib.a}) causes numerous headaches for package managers. However, +@code{Import Files} as members of @code{Archive Library} files allow for +@strong{filename-based versioning} of shared libraries as seen on Linux/SVR4, +where this is called the "SONAME". But as they prevent static linking, +@code{Import Files} may be used with @code{Runtime Linking} only, where the +linker does search for @samp{libNAME.so} before @samp{libNAME.a} library +filenames with the @samp{-lNAME} linker flag. + +@anchor{AixLdCommand}For detailed information please refer to the AIX +@uref{https://www.ibm.com/support/knowledgecenter/search/%22the%20ld%20command%2C%20also%20called%20the%20linkage%20editor%20or%20binder%22,,ld +Command} reference. + +As long as shared library creation is enabled, upon: +@table @code +@item --with-aix-soname=aix +@item --with-aix-soname=both + A (traditional AIX) @code{Shared Archive Library} file is created: + @itemize @bullet + @item using the @samp{libNAME.a} filename scheme + @item with the @code{Shared Object} file as archive member named + @samp{libNAME.so.V} (except for @samp{libgcc_s}, where the @code{Shared + Object} file is named @samp{shr.o} for backwards compatibility), which + @itemize @minus + @item is used for runtime loading from inside the @samp{libNAME.a} file + @item is used for dynamic loading via + @code{dlopen("libNAME.a(libNAME.so.V)", RTLD_MEMBER)} + @item is used for shared linking + @item is used for static linking, so no separate @code{Static Archive + Library} file is needed + @end itemize + @end itemize +@item --with-aix-soname=both +@item --with-aix-soname=svr4 + A (second) @code{Shared Archive Library} file is created: + @itemize @bullet + @item using the @samp{libNAME.so.V} filename scheme + @item with the @code{Shared Object} file as archive member named + @samp{shr.o}, which + @itemize @minus + @item is created with the @code{-G linker flag} + @item has the @code{F_LOADONLY} flag set + @item is used for runtime loading from inside the @samp{libNAME.so.V} file + @item is used for dynamic loading via @code{dlopen("libNAME.so.V(shr.o)", + RTLD_MEMBER)} + @end itemize + @item with the @code{Import File} as archive member named @samp{shr.imp}, + which + @itemize @minus + @item refers to @samp{libNAME.so.V(shr.o)} as the "SONAME", to be recorded + in the @code{Loader Section} of subsequent binaries + @item indicates whether @samp{libNAME.so.V(shr.o)} is 32 or 64 bit + @item lists all the public symbols exported by @samp{lib.so.V(shr.o)}, + eventually decorated with the @code{@samp{weak} Keyword} + @item is necessary for shared linking against @samp{lib.so.V(shr.o)} + @end itemize + @end itemize + A symbolic link using the @samp{libNAME.so} filename scheme is created: + @itemize @bullet + @item pointing to the @samp{libNAME.so.V} @code{Shared Archive Library} file + @item to permit the @code{ld Command} to find @samp{lib.so.V(shr.imp)} via + the @samp{-lNAME} argument (requires @code{Runtime Linking} to be enabled) + @item to permit dynamic loading of @samp{lib.so.V(shr.o)} without the need + to specify the version number via @code{dlopen("libNAME.so(shr.o)", + RTLD_MEMBER)} + @end itemize +@end table + +As long as static library creation is enabled, upon: +@table @code +@item --with-aix-soname=svr4 + A @code{Static Archive Library} is created: + @itemize @bullet + @item using the @samp{libNAME.a} filename scheme + @item with all the @code{Static Object} files as archive members, which + @itemize @minus + @item are used for static linking + @end itemize + @end itemize +@end table + +While the aix-soname=@samp{svr4} option does not create @code{Shared Object} +files as members of unversioned @code{Archive Library} files any more, package +managers still are responsible to +@uref{./specific.html#TransferAixShobj,,transfer} @code{Shared Object} files +found as member of a previously installed unversioned @code{Archive Library} +file into the newly installed @code{Archive Library} file with the same +filename. + +@emph{WARNING:} Creating @code{Shared Object} files with @code{Runtime Linking} +enabled may bloat the TOC, eventually leading to @code{TOC overflow} errors, +requiring the use of either the @option{-Wl,-bbigtoc} linker flag (seen to +break with the @code{GDB} debugger) or some of the TOC-related compiler flags, +@ifnothtml +@xref{RS/6000 and PowerPC Options,, RS/6000 and PowerPC Options, gcc, +Using the GNU Compiler Collection (GCC)}. +@end ifnothtml +@ifhtml +see ``RS/6000 and PowerPC Options'' in the main manual. +@end ifhtml + +@option{--with-aix-soname} is currently supported by @samp{libgcc_s} only, so +this option is still experimental and not for normal use yet. + +Default is the traditional behavior @option{--with-aix-soname=@samp{aix}}. + +@item --enable-languages=@var{lang1},@var{lang2},@dots{} +Specify that only a particular subset of compilers and +their runtime libraries should be built. For a list of valid values for +@var{langN} you can issue the following command in the +@file{gcc} directory of your GCC source tree:@* +@smallexample +grep ^language= */config-lang.in +@end smallexample +Currently, you can use any of the following: +@code{all}, @code{default}, @code{ada}, @code{c}, @code{c++}, @code{d}, +@code{fortran}, @code{go}, @code{jit}, @code{lto}, @code{objc}, @code{obj-c++}. +Building the Ada compiler has special requirements, see below. +If you do not pass this flag, or specify the option @code{default}, then the +default languages available in the @file{gcc} sub-tree will be configured. +Ada, D, Go, Jit, and Objective-C++ are not default languages. LTO is not a +default language, but is built by default because @option{--enable-lto} is +enabled by default. The other languages are default languages. If +@code{all} is specified, then all available languages are built. An +exception is @code{jit} language, which requires +@option{--enable-host-shared} to be included with @code{all}. + +@item --enable-stage1-languages=@var{lang1},@var{lang2},@dots{} +Specify that a particular subset of compilers and their runtime +libraries should be built with the system C compiler during stage 1 of +the bootstrap process, rather than only in later stages with the +bootstrapped C compiler. The list of valid values is the same as for +@option{--enable-languages}, and the option @code{all} will select all +of the languages enabled by @option{--enable-languages}. This option is +primarily useful for GCC development; for instance, when a development +version of the compiler cannot bootstrap due to compiler bugs, or when +one is debugging front ends other than the C front end. When this +option is used, one can then build the target libraries for the +specified languages with the stage-1 compiler by using @command{make +stage1-bubble all-target}, or run the testsuite on the stage-1 compiler +for the specified languages using @command{make stage1-start check-gcc}. + +@item --disable-libada +Specify that the run-time libraries and tools used by GNAT should not +be built. This can be useful for debugging, or for compatibility with +previous Ada build procedures, when it was required to explicitly +do a @samp{make -C gcc gnatlib_and_tools}. + +@item --disable-libsanitizer +Specify that the run-time libraries for the various sanitizers should +not be built. + +@item --disable-libssp +Specify that the run-time libraries for stack smashing protection +should not be built or linked against. On many targets library support +is provided by the C library instead. + +@item --disable-libquadmath +Specify that the GCC quad-precision math library should not be built. +On some systems, the library is required to be linkable when building +the Fortran front end, unless @option{--disable-libquadmath-support} +is used. + +@item --disable-libquadmath-support +Specify that the Fortran front end and @code{libgfortran} do not add +support for @code{libquadmath} on systems supporting it. + +@item --disable-libgomp +Specify that the GNU Offloading and Multi Processing Runtime Library +should not be built. + +@item --disable-libvtv +Specify that the run-time libraries used by vtable verification +should not be built. + +@item --with-dwarf2 +Specify that the compiler should +use DWARF 2 debugging information as the default. + +@item --with-advance-toolchain=@var{at} +On 64-bit PowerPC Linux systems, configure the compiler to use the +header files, library files, and the dynamic linker from the Advance +Toolchain release @var{at} instead of the default versions that are +provided by the Linux distribution. In general, this option is +intended for the developers of GCC, and it is not intended for general +use. + +@item --enable-targets=all +@itemx --enable-targets=@var{target_list} +Some GCC targets, e.g.@: powerpc64-linux, build bi-arch compilers. +These are compilers that are able to generate either 64-bit or 32-bit +code. Typically, the corresponding 32-bit target, e.g.@: +powerpc-linux for powerpc64-linux, only generates 32-bit code. This +option enables the 32-bit target to be a bi-arch compiler, which is +useful when you want a bi-arch compiler that defaults to 32-bit, and +you are building a bi-arch or multi-arch binutils in a combined tree. +On mips-linux, this will build a tri-arch compiler (ABI o32/n32/64), +defaulted to o32. +Currently, this option only affects sparc-linux, powerpc-linux, x86-linux, +mips-linux and s390-linux. + +@item --enable-default-pie +Turn on @option{-fPIE} and @option{-pie} by default. + +@item --enable-secureplt +This option enables @option{-msecure-plt} by default for powerpc-linux. +@ifnothtml +@xref{RS/6000 and PowerPC Options,, RS/6000 and PowerPC Options, gcc, +Using the GNU Compiler Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``RS/6000 and PowerPC Options'' in the main manual +@end ifhtml + +@item --enable-default-ssp +Turn on @option{-fstack-protector-strong} by default. + +@item --enable-cld +This option enables @option{-mcld} by default for 32-bit x86 targets. +@ifnothtml +@xref{i386 and x86-64 Options,, i386 and x86-64 Options, gcc, +Using the GNU Compiler Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``i386 and x86-64 Options'' in the main manual +@end ifhtml + +@item --enable-large-address-aware +The @option{--enable-large-address-aware} option arranges for MinGW +executables to be linked using the @option{--large-address-aware} +option, that enables the use of more than 2GB of memory. If GCC is +configured with this option, its effects can be reversed by passing the +@option{-Wl,--disable-large-address-aware} option to the so-configured +compiler driver. + +@item --enable-win32-registry +@itemx --enable-win32-registry=@var{key} +@itemx --disable-win32-registry +The @option{--enable-win32-registry} option enables Microsoft Windows-hosted GCC +to look up installations paths in the registry using the following key: + +@smallexample +@code{HKEY_LOCAL_MACHINE\SOFTWARE\Free Software Foundation\@var{key}} +@end smallexample + +@var{key} defaults to GCC version number, and can be overridden by the +@option{--enable-win32-registry=@var{key}} option. Vendors and distributors +who use custom installers are encouraged to provide a different key, +perhaps one comprised of vendor name and GCC version number, to +avoid conflict with existing installations. This feature is enabled +by default, and can be disabled by @option{--disable-win32-registry} +option. This option has no effect on the other hosts. + +@item --nfp +Specify that the machine does not have a floating point unit. This +option only applies to @samp{m68k-sun-sunos@var{n}}. On any other +system, @option{--nfp} has no effect. + +@item --enable-werror +@itemx --disable-werror +@itemx --enable-werror=yes +@itemx --enable-werror=no +When you specify this option, it controls whether certain files in the +compiler are built with @option{-Werror} in bootstrap stage2 and later. +If you don't specify it, @option{-Werror} is turned on for the main +development trunk. However it defaults to off for release branches and +final releases. The specific files which get @option{-Werror} are +controlled by the Makefiles. + +@item --enable-checking +@itemx --disable-checking +@itemx --enable-checking=@var{list} +This option controls performing internal consistency checks in the compiler. +It does not change the generated code, but adds error checking of the +requested complexity. This slows down the compiler and may only work +properly if you are building the compiler with GCC@. + +When the option is not specified, the active set of checks depends on context. +Namely, bootstrap stage 1 defaults to @samp{--enable-checking=yes}, builds +from release branches or release archives default to +@samp{--enable-checking=release}, and otherwise +@samp{--enable-checking=yes,extra} is used. When the option is +specified without a @var{list}, the result is the same as +@samp{--enable-checking=yes}. Likewise, @samp{--disable-checking} is +equivalent to @samp{--enable-checking=no}. + +The categories of checks available in @var{list} are @samp{yes} (most common +checks @samp{assert,misc,gc,gimple,rtlflag,runtime,tree,types}), @samp{no} +(no checks at all), @samp{all} (all but @samp{valgrind}), @samp{release} +(cheapest checks @samp{assert,runtime}) or @samp{none} (same as @samp{no}). +@samp{release} checks are always on and to disable them +@samp{--disable-checking} or @samp{--enable-checking=no[,]} +must be explicitly requested. Disabling assertions makes the compiler and +runtime slightly faster but increases the risk of undetected internal errors +causing wrong code to be generated. + +Individual checks can be enabled with these flags: @samp{assert}, @samp{df}, +@samp{extra}, @samp{fold}, @samp{gc}, @samp{gcac}, @samp{gimple}, +@samp{misc}, @samp{rtl}, @samp{rtlflag}, @samp{runtime}, @samp{tree}, +@samp{types} and @samp{valgrind}. @samp{extra} extends @samp{misc} +checking with extra checks that might affect code generation and should +therefore not differ between stage1 and later stages in bootstrap. + +The @samp{valgrind} check requires the external @command{valgrind} simulator, +available from @uref{https://valgrind.org}. The @samp{rtl} checks are +expensive and the @samp{df}, @samp{gcac} and @samp{valgrind} checks are very +expensive. + +@item --disable-stage1-checking +@itemx --enable-stage1-checking +@itemx --enable-stage1-checking=@var{list} +This option affects only bootstrap build. If no @option{--enable-checking} +option is specified the stage1 compiler is built with @samp{yes} checking +enabled, otherwise the stage1 checking flags are the same as specified by +@option{--enable-checking}. To build the stage1 compiler with +different checking options use @option{--enable-stage1-checking}. +The list of checking options is the same as for @option{--enable-checking}. +If your system is too slow or too small to bootstrap a released compiler +with checking for stage1 enabled, you can use @samp{--disable-stage1-checking} +to disable checking for the stage1 compiler. + +@item --enable-coverage +@itemx --enable-coverage=@var{level} +With this option, the compiler is built to collect self coverage +information, every time it is run. This is for internal development +purposes, and only works when the compiler is being built with gcc. The +@var{level} argument controls whether the compiler is built optimized or +not, values are @samp{opt} and @samp{noopt}. For coverage analysis you +want to disable optimization, for performance analysis you want to +enable optimization. When coverage is enabled, the default level is +without optimization. + +@item --enable-gather-detailed-mem-stats +When this option is specified more detailed information on memory +allocation is gathered. This information is printed when using +@option{-fmem-report}. + +@item --enable-valgrind-annotations +Mark selected memory related operations in the compiler when run under +valgrind to suppress false positives. + +@item --enable-nls +@itemx --disable-nls +The @option{--enable-nls} option enables Native Language Support (NLS), +which lets GCC output diagnostics in languages other than American +English. Native Language Support is enabled by default if not doing a +canadian cross build. The @option{--disable-nls} option disables NLS@. + +@item --with-included-gettext +If NLS is enabled, the @option{--with-included-gettext} option causes the build +procedure to prefer its copy of GNU @command{gettext}. + +@item --with-catgets +If NLS is enabled, and if the host lacks @code{gettext} but has the +inferior @code{catgets} interface, the GCC build procedure normally +ignores @code{catgets} and instead uses GCC's copy of the GNU +@code{gettext} library. The @option{--with-catgets} option causes the +build procedure to use the host's @code{catgets} in this situation. + +@item --with-libiconv-prefix=@var{dir} +Search for libiconv header files in @file{@var{dir}/include} and +libiconv library files in @file{@var{dir}/lib}. + +@item --enable-obsolete +Enable configuration for an obsoleted system. If you attempt to +configure GCC for a system (build, host, or target) which has been +obsoleted, and you do not specify this flag, configure will halt with an +error message. + +All support for systems which have been obsoleted in one release of GCC +is removed entirely in the next major release, unless someone steps +forward to maintain the port. + +@item --enable-decimal-float +@itemx --enable-decimal-float=yes +@itemx --enable-decimal-float=no +@itemx --enable-decimal-float=bid +@itemx --enable-decimal-float=dpd +@itemx --disable-decimal-float +Enable (or disable) support for the C decimal floating point extension +that is in the IEEE 754-2008 standard. This is enabled by default only +on PowerPC, i386, and x86_64 GNU/Linux systems. Other systems may also +support it, but require the user to specifically enable it. You can +optionally control which decimal floating point format is used (either +@samp{bid} or @samp{dpd}). The @samp{bid} (binary integer decimal) +format is default on i386 and x86_64 systems, and the @samp{dpd} +(densely packed decimal) format is default on PowerPC systems. + +@item --enable-fixed-point +@itemx --disable-fixed-point +Enable (or disable) support for C fixed-point arithmetic. +This option is enabled by default for some targets (such as MIPS) which +have hardware-support for fixed-point operations. On other targets, you +may enable this option manually. + +@item --with-long-double-128 +Specify if @code{long double} type should be 128-bit by default on selected +GNU/Linux architectures. If using @code{--without-long-double-128}, +@code{long double} will be by default 64-bit, the same as @code{double} type. +When neither of these configure options are used, the default will be +128-bit @code{long double} when built against GNU C Library 2.4 and later, +64-bit @code{long double} otherwise. + +@item --with-long-double-format=ibm +@itemx --with-long-double-format=ieee +Specify whether @code{long double} uses the IBM extended double format +or the IEEE 128-bit floating point format on PowerPC Linux systems. +This configuration switch will only work on little endian PowerPC +Linux systems and on big endian 64-bit systems where the default cpu +is at least power7 (i.e.@: @option{--with-cpu=power7}, +@option{--with-cpu=power8}, or @option{--with-cpu=power9} is used). + +If you use the @option{--with-long-double-64} configuration option, +the @option{--with-long-double-format=ibm} and +@option{--with-long-double-format=ieee} options are ignored. + +The default @code{long double} format is to use IBM extended double. +Until all of the libraries are converted to use IEEE 128-bit floating +point, it is not recommended to use +@option{--with-long-double-format=ieee}. + +@item --enable-fdpic +On SH Linux systems, generate ELF FDPIC code. + +@item --with-gmp=@var{pathname} +@itemx --with-gmp-include=@var{pathname} +@itemx --with-gmp-lib=@var{pathname} +@itemx --with-mpfr=@var{pathname} +@itemx --with-mpfr-include=@var{pathname} +@itemx --with-mpfr-lib=@var{pathname} +@itemx --with-mpc=@var{pathname} +@itemx --with-mpc-include=@var{pathname} +@itemx --with-mpc-lib=@var{pathname} +If you want to build GCC but do not have the GMP library, the MPFR +library and/or the MPC library installed in a standard location and +do not have their sources present in the GCC source tree then you +can explicitly specify the directory where they are installed +(@samp{--with-gmp=@var{gmpinstalldir}}, +@samp{--with-mpfr=@/@var{mpfrinstalldir}}, +@samp{--with-mpc=@/@var{mpcinstalldir}}). The +@option{--with-gmp=@/@var{gmpinstalldir}} option is shorthand for +@option{--with-gmp-lib=@/@var{gmpinstalldir}/lib} and +@option{--with-gmp-include=@/@var{gmpinstalldir}/include}. Likewise the +@option{--with-mpfr=@/@var{mpfrinstalldir}} option is shorthand for +@option{--with-mpfr-lib=@/@var{mpfrinstalldir}/lib} and +@option{--with-mpfr-include=@/@var{mpfrinstalldir}/include}, also the +@option{--with-mpc=@/@var{mpcinstalldir}} option is shorthand for +@option{--with-mpc-lib=@/@var{mpcinstalldir}/lib} and +@option{--with-mpc-include=@/@var{mpcinstalldir}/include}. If these +shorthand assumptions are not correct, you can use the explicit +include and lib options directly. You might also need to ensure the +shared libraries can be found by the dynamic linker when building and +using GCC, for example by setting the runtime shared library path +variable (@env{LD_LIBRARY_PATH} on GNU/Linux and Solaris systems). + +These flags are applicable to the host platform only. When building +a cross compiler, they will not be used to configure target libraries. + +@item --with-isl=@var{pathname} +@itemx --with-isl-include=@var{pathname} +@itemx --with-isl-lib=@var{pathname} +If you do not have the isl library installed in a standard location and you +want to build GCC, you can explicitly specify the directory where it is +installed (@samp{--with-isl=@/@var{islinstalldir}}). The +@option{--with-isl=@/@var{islinstalldir}} option is shorthand for +@option{--with-isl-lib=@/@var{islinstalldir}/lib} and +@option{--with-isl-include=@/@var{islinstalldir}/include}. If this +shorthand assumption is not correct, you can use the explicit +include and lib options directly. + +These flags are applicable to the host platform only. When building +a cross compiler, they will not be used to configure target libraries. + +@item --with-stage1-ldflags=@var{flags} +This option may be used to set linker flags to be used when linking +stage 1 of GCC. These are also used when linking GCC if configured with +@option{--disable-bootstrap}. If @option{--with-stage1-libs} is not set to a +value, then the default is @samp{-static-libstdc++ -static-libgcc}, if +supported. + +@item --with-stage1-libs=@var{libs} +This option may be used to set libraries to be used when linking stage 1 +of GCC. These are also used when linking GCC if configured with +@option{--disable-bootstrap}. + +@item --with-boot-ldflags=@var{flags} +This option may be used to set linker flags to be used when linking +stage 2 and later when bootstrapping GCC. If --with-boot-libs +is not is set to a value, then the default is +@samp{-static-libstdc++ -static-libgcc}. + +@item --with-boot-libs=@var{libs} +This option may be used to set libraries to be used when linking stage 2 +and later when bootstrapping GCC. + +@item --with-debug-prefix-map=@var{map} +Convert source directory names using @option{-fdebug-prefix-map} when +building runtime libraries. @samp{@var{map}} is a space-separated +list of maps of the form @samp{@var{old}=@var{new}}. + +@item --enable-linker-build-id +Tells GCC to pass @option{--build-id} option to the linker for all final +links (links performed without the @option{-r} or @option{--relocatable} +option), if the linker supports it. If you specify +@option{--enable-linker-build-id}, but your linker does not +support @option{--build-id} option, a warning is issued and the +@option{--enable-linker-build-id} option is ignored. The default is off. + +@item --with-linker-hash-style=@var{choice} +Tells GCC to pass @option{--hash-style=@var{choice}} option to the +linker for all final links. @var{choice} can be one of +@samp{sysv}, @samp{gnu}, and @samp{both} where @samp{sysv} is the default. + +@item --enable-gnu-unique-object +@itemx --disable-gnu-unique-object +Tells GCC to use the gnu_unique_object relocation for C++ template +static data members and inline function local statics. Enabled by +default for a toolchain with an assembler that accepts it and +GLIBC 2.11 or above, otherwise disabled. + +@item --with-diagnostics-color=@var{choice} +Tells GCC to use @var{choice} as the default for @option{-fdiagnostics-color=} +option (if not used explicitly on the command line). @var{choice} +can be one of @samp{never}, @samp{auto}, @samp{always}, and @samp{auto-if-env} +where @samp{auto} is the default. @samp{auto-if-env} makes +@option{-fdiagnostics-color=auto} the default if @env{GCC_COLORS} +is present and non-empty in the environment of the compiler, and +@option{-fdiagnostics-color=never} otherwise. + +@item --with-diagnostics-urls=@var{choice} +Tells GCC to use @var{choice} as the default for @option{-fdiagnostics-urls=} +option (if not used explicitly on the command line). @var{choice} +can be one of @samp{never}, @samp{auto}, @samp{always}, and @samp{auto-if-env} +where @samp{auto} is the default. @samp{auto-if-env} makes +@option{-fdiagnostics-urls=auto} the default if @env{GCC_URLS} +or @env{TERM_URLS} is present and non-empty in the environment of the +compiler, and @option{-fdiagnostics-urls=never} otherwise. + +@item --enable-lto +@itemx --disable-lto +Enable support for link-time optimization (LTO). This is enabled by +default, and may be disabled using @option{--disable-lto}. + +@item --enable-linker-plugin-configure-flags=FLAGS +@itemx --enable-linker-plugin-flags=FLAGS +By default, linker plugins (such as the LTO plugin) are built for the +host system architecture. For the case that the linker has a +different (but run-time compatible) architecture, these flags can be +specified to build plugins that are compatible to the linker. For +example, if you are building GCC for a 64-bit x86_64 +(@samp{x86_64-pc-linux-gnu}) host system, but have a 32-bit x86 +GNU/Linux (@samp{i686-pc-linux-gnu}) linker executable (which is +executable on the former system), you can configure GCC as follows for +getting compatible linker plugins: + +@smallexample +% @var{srcdir}/configure \ + --host=x86_64-pc-linux-gnu \ + --enable-linker-plugin-configure-flags=--host=i686-pc-linux-gnu \ + --enable-linker-plugin-flags='CC=gcc\ -m32\ -Wl,-rpath,[...]/i686-pc-linux-gnu/lib' +@end smallexample + +@item --with-plugin-ld=@var{pathname} +Enable an alternate linker to be used at link-time optimization (LTO) +link time when @option{-fuse-linker-plugin} is enabled. +This linker should have plugin support such as gold starting with +version 2.20 or GNU ld starting with version 2.21. +See @option{-fuse-linker-plugin} for details. + +@item --enable-canonical-system-headers +@itemx --disable-canonical-system-headers +Enable system header path canonicalization for @file{libcpp}. This can +produce shorter header file paths in diagnostics and dependency output +files, but these changed header paths may conflict with some compilation +environments. Enabled by default, and may be disabled using +@option{--disable-canonical-system-headers}. + +@item --with-glibc-version=@var{major}.@var{minor} +Tell GCC that when the GNU C Library (glibc) is used on the target it +will be version @var{major}.@var{minor} or later. Normally this can +be detected from the C library's header files, but this option may be +needed when bootstrapping a cross toolchain without the header files +available for building the initial bootstrap compiler. + +If GCC is configured with some multilibs that use glibc and some that +do not, this option applies only to the multilibs that use glibc. +However, such configurations may not work well as not all the relevant +configuration in GCC is on a per-multilib basis. + +@item --enable-as-accelerator-for=@var{target} +Build as offload target compiler. Specify offload host triple by @var{target}. + +@item --enable-offload-targets=@var{target1}[=@var{path1}],@dots{},@var{targetN}[=@var{pathN}] +Enable offloading to targets @var{target1}, @dots{}, @var{targetN}. +Offload compilers are expected to be already installed. Default search +path for them is @file{@var{exec-prefix}}, but it can be changed by +specifying paths @var{path1}, @dots{}, @var{pathN}. + +@smallexample +% @var{srcdir}/configure \ + --enable-offload-targets=amdgcn-amdhsa,nvptx-none +@end smallexample + +@item --enable-offload-defaulted + +Tell GCC that configured but not installed offload compilers and libgomp +plugins are silently ignored. Useful for distribution compilers where +those are in separate optional packages and where the presence or absence +of those optional packages should determine the actual supported offloading +target set rather than the GCC configure-time selection. + +@item --enable-cet +@itemx --disable-cet +Enable building target run-time libraries with control-flow +instrumentation, see @option{-fcf-protection} option. When +@code{--enable-cet} is specified target libraries are configured +to add @option{-fcf-protection} and, if needed, other target +specific options to a set of building options. + +@code{--enable-cet=auto} is default. CET is enabled on Linux/x86 if +target binutils supports @code{Intel CET} instructions and disabled +otherwise. In this case, the target libraries are configured to get +additional @option{-fcf-protection} option. + +@item --with-riscv-attribute=@samp{yes}, @samp{no} or @samp{default} +Generate RISC-V attribute by default, in order to record extra build +information in object. + +The option is disabled by default. It is enabled on RISC-V/ELF (bare-metal) +target if target binutils supported. + +@item --enable-s390-excess-float-precision +@itemx --disable-s390-excess-float-precision +On s390(x) targets, enable treatment of float expressions with double precision +when in standards-compliant mode (e.g., when @code{--std=c99} or +@code{-fexcess-precision=standard} are given). + +For a native build and cross compiles that have target headers, the option's +default is derived from glibc's behavior. When glibc clamps float_t to double, +GCC follows and enables the option. For other cross compiles, the default is +disabled. + +@item --with-zstd=@var{pathname} +@itemx --with-zstd-include=@var{pathname} +@itemx --with-zstd-lib=@var{pathname} +If you do not have the @code{zstd} library installed in a standard +location and you want to build GCC, you can explicitly specify the +directory where it is installed (@samp{--with-zstd=@/@var{zstdinstalldir}}). +The @option{--with-zstd=@/@var{zstdinstalldir}} option is shorthand for +@option{--with-zstd-lib=@/@var{zstdinstalldir}/lib} and +@option{--with-zstd-include=@/@var{zstdinstalldir}/include}. If this +shorthand assumption is not correct, you can use the explicit +include and lib options directly. + +These flags are applicable to the host platform only. When building +a cross compiler, they will not be used to configure target libraries. +@end table + +@subheading Cross-Compiler-Specific Options +The following options only apply to building cross compilers. + +@table @code +@item --with-toolexeclibdir=@var{dir} +Specify the installation directory for libraries built with a cross compiler. +The default is @option{$@{gcc_tooldir@}/lib}. + +@item --with-sysroot +@itemx --with-sysroot=@var{dir} +Tells GCC to consider @var{dir} as the root of a tree that contains +(a subset of) the root filesystem of the target operating system. +Target system headers, libraries and run-time object files will be +searched for in there. More specifically, this acts as if +@option{--sysroot=@var{dir}} was added to the default options of the built +compiler. The specified directory is not copied into the +install tree, unlike the options @option{--with-headers} and +@option{--with-libs} that this option obsoletes. The default value, +in case @option{--with-sysroot} is not given an argument, is +@option{$@{gcc_tooldir@}/sys-root}. If the specified directory is a +subdirectory of @option{$@{exec_prefix@}}, then it will be found relative to +the GCC binaries if the installation tree is moved. + +This option affects the system root for the compiler used to build +target libraries (which runs on the build system) and the compiler newly +installed with @code{make install}; it does not affect the compiler which is +used to build GCC itself. + +If you specify the @option{--with-native-system-header-dir=@var{dirname}} +option then the compiler will search that directory within @var{dirname} for +native system headers rather than the default @file{/usr/include}. + +@item --with-build-sysroot +@itemx --with-build-sysroot=@var{dir} +Tells GCC to consider @var{dir} as the system root (see +@option{--with-sysroot}) while building target libraries, instead of +the directory specified with @option{--with-sysroot}. This option is +only useful when you are already using @option{--with-sysroot}. You +can use @option{--with-build-sysroot} when you are configuring with +@option{--prefix} set to a directory that is different from the one in +which you are installing GCC and your target libraries. + +This option affects the system root for the compiler used to build +target libraries (which runs on the build system); it does not affect +the compiler which is used to build GCC itself. + +If you specify the @option{--with-native-system-header-dir=@var{dirname}} +option then the compiler will search that directory within @var{dirname} for +native system headers rather than the default @file{/usr/include}. + +@item --with-headers +@itemx --with-headers=@var{dir} +Deprecated in favor of @option{--with-sysroot}. +Specifies that target headers are available when building a cross compiler. +The @var{dir} argument specifies a directory which has the target include +files. These include files will be copied into the @file{gcc} install +directory. @emph{This option with the @var{dir} argument is required} when +building a cross compiler, if @file{@var{prefix}/@var{target}/sys-include} +doesn't pre-exist. If @file{@var{prefix}/@var{target}/sys-include} does +pre-exist, the @var{dir} argument may be omitted. @command{fixincludes} +will be run on these files to make them compatible with GCC@. + +@item --without-headers +Tells GCC not use any target headers from a libc when building a cross +compiler. When crossing to GNU/Linux, you need the headers so GCC +can build the exception handling for libgcc. + +@item --with-libs +@itemx --with-libs="@var{dir1} @var{dir2} @dots{} @var{dirN}" +Deprecated in favor of @option{--with-sysroot}. +Specifies a list of directories which contain the target runtime +libraries. These libraries will be copied into the @file{gcc} install +directory. If the directory list is omitted, this option has no +effect. + +@item --with-newlib +Specifies that @samp{newlib} is +being used as the target C library. This causes @code{__eprintf} to be +omitted from @file{libgcc.a} on the assumption that it will be provided by +@samp{newlib}. + +@html + +@end html +@item --with-avrlibc +Only supported for the AVR target. Specifies that @samp{AVR-Libc} is +being used as the target C@tie{} library. This causes float support +functions like @code{__addsf3} to be omitted from @file{libgcc.a} on +the assumption that it will be provided by @file{libm.a}. For more +technical details, cf. @uref{https://gcc.gnu.org/PR54461,,PR54461}. +It is not supported for +RTEMS configurations, which currently use newlib. The option is +supported since version 4.7.2 and is the default in 4.8.0 and newer. + +@item --with-double=@{32|64|32,64|64,32@} +@itemx --with-long-double=@{32|64|32,64|64,32|double@} +Only supported for the AVR target since version@tie{}10. +Specify the default layout available for the C/C++ @samp{double} +and @samp{long double} type, respectively. The following rules apply: +@itemize +@item +The first value after the @samp{=} specifies the default layout (in bits) +of the type and also the default for the @option{-mdouble=} resp. +@option{-mlong-double=} compiler option. +@item +If more than one value is specified, respective multilib variants are +available, and @option{-mdouble=} resp. @option{-mlong-double=} acts +as a multilib option. +@item +If @option{--with-long-double=double} is specified, @samp{double} and +@samp{long double} will have the same layout. +@item +The defaults are @option{--with-long-double=64,32} and +@option{--with-double=32,64}. The default @samp{double} layout imposed by +the latter is compatible with older versions of the compiler that implement +@samp{double} as a 32-bit type, which does not comply to the language standard. +@end itemize +Not all combinations of @option{--with-double=} and +@option{--with-long-double=} are valid. For example, the combination +@option{--with-double=32,64} @option{--with-long-double=32} will be +rejected because the first option specifies the availability of +multilibs for @samp{double}, whereas the second option implies +that @samp{long double} --- and hence also @samp{double} --- is always +32@tie{}bits wide. + +@item --with-double-comparison=@{tristate|bool|libf7@} +Only supported for the AVR target since version@tie{}10. +Specify what result format is returned by library functions that +compare 64-bit floating point values (@code{DFmode}). +The GCC default is @samp{tristate}. If the floating point +implementation returns a boolean instead, set it to @samp{bool}. + +@item --with-libf7=@{libgcc|math|math-symbols|no@} +Only supported for the AVR target since version@tie{}10. +Specify to which degree code from LibF7 is included in libgcc. +LibF7 is an ad-hoc, AVR-specific, 64-bit floating point emulation +written in C and (inline) assembly. @samp{libgcc} adds support +for functions that one would usually expect in libgcc like double addition, +double comparisons and double conversions. @samp{math} also adds routines +that one would expect in @file{libm.a}, but with @code{__} (two underscores) +prepended to the symbol names as specified by @file{math.h}. +@samp{math-symbols} also defines weak aliases for the functions +declared in @file{math.h}. However, @code{--with-libf7} won't +install no @file{math.h} header file whatsoever, this file must come +from elsewhere. This option sets @option{--with-double-comparison} +to @samp{bool}. + +@item --with-nds32-lib=@var{library} +Specifies that @var{library} setting is used for building @file{libgcc.a}. +Currently, the valid @var{library} is @samp{newlib} or @samp{mculib}. +This option is only supported for the NDS32 target. + +@item --with-build-time-tools=@var{dir} +Specifies where to find the set of target tools (assembler, linker, etc.) +that will be used while building GCC itself. This option can be useful +if the directory layouts are different between the system you are building +GCC on, and the system where you will deploy it. + +For example, on an @samp{ia64-hp-hpux} system, you may have the GNU +assembler and linker in @file{/usr/bin}, and the native tools in a +different path, and build a toolchain that expects to find the +native tools in @file{/usr/bin}. + +When you use this option, you should ensure that @var{dir} includes +@command{ar}, @command{as}, @command{ld}, @command{nm}, +@command{ranlib} and @command{strip} if necessary, and possibly +@command{objdump}. Otherwise, GCC may use an inconsistent set of +tools. +@end table + +@subsubheading Overriding @command{configure} test results + +Sometimes, it might be necessary to override the result of some +@command{configure} test, for example in order to ease porting to a new +system or work around a bug in a test. The toplevel @command{configure} +script provides three variables for this: + +@table @code + +@item build_configargs +@cindex @code{build_configargs} +The contents of this variable is passed to all build @command{configure} +scripts. + +@item host_configargs +@cindex @code{host_configargs} +The contents of this variable is passed to all host @command{configure} +scripts. + +@item target_configargs +@cindex @code{target_configargs} +The contents of this variable is passed to all target @command{configure} +scripts. + +@end table + +In order to avoid shell and @command{make} quoting issues for complex +overrides, you can pass a setting for @env{CONFIG_SITE} and set +variables in the site file. + +@subheading Objective-C-Specific Options + +The following options apply to the build of the Objective-C runtime library. + +@table @code +@item --enable-objc-gc +Specify that an additional variant of the GNU Objective-C runtime library +is built, using an external build of the Boehm-Demers-Weiser garbage +collector (@uref{https://www.hboehm.info/gc/}). This library needs to be +available for each multilib variant, unless configured with +@option{--enable-objc-gc=@samp{auto}} in which case the build of the +additional runtime library is skipped when not available and the build +continues. + +@item --with-target-bdw-gc=@var{list} +@itemx --with-target-bdw-gc-include=@var{list} +@itemx --with-target-bdw-gc-lib=@var{list} +Specify search directories for the garbage collector header files and +libraries. @var{list} is a comma separated list of key value pairs of the +form @samp{@var{multilibdir}=@var{path}}, where the default multilib key +is named as @samp{.} (dot), or is omitted (e.g.@: +@samp{--with-target-bdw-gc=/opt/bdw-gc,32=/opt-bdw-gc32}). + +The options @option{--with-target-bdw-gc-include} and +@option{--with-target-bdw-gc-lib} must always be specified together +for each multilib variant and they take precedence over +@option{--with-target-bdw-gc}. If @option{--with-target-bdw-gc-include} +is missing values for a multilib, then the value for the default +multilib is used (e.g.@: @samp{--with-target-bdw-gc-include=/opt/bdw-gc/include} +@samp{--with-target-bdw-gc-lib=/opt/bdw-gc/lib64,32=/opt-bdw-gc/lib32}). +If none of these options are specified, the library is assumed in +default locations. +@end table + +@subheading D-Specific Options + +The following options apply to the build of the D runtime library. + +@table @code +@item --enable-libphobos-checking +@itemx --disable-libphobos-checking +@itemx --enable-libphobos-checking=@var{list} +This option controls whether run-time checks and contracts are compiled into +the D runtime library. When the option is not specified, the library is built +with @samp{release} checking. When the option is specified without a +@var{list}, the result is the same as @samp{--enable-libphobos-checking=yes}. +Likewise, @samp{--disable-libphobos-checking} is equivalent to +@samp{--enable-libphobos-checking=no}. + +The categories of checks available in @var{list} are @samp{yes} (compiles +libphobos with @option{-fno-release}), @samp{no} (compiles libphobos with +@option{-frelease}), @samp{all} (same as @samp{yes}), @samp{none} or +@samp{release} (same as @samp{no}). + +Individual checks available in @var{list} are @samp{assert} (compiles libphobos +with an extra option @option{-fassert}). + +@item --with-libphobos-druntime-only +@itemx --with-libphobos-druntime-only=@var{choice} +Specify whether to build only the core D runtime library (druntime), or both +the core and standard library (phobos) into libphobos. This is useful for +targets that have full support in druntime, but no or incomplete support +in phobos. @var{choice} can be one of @samp{auto}, @samp{yes}, and @samp{no} +where @samp{auto} is the default. + +When the option is not specified, the default choice @samp{auto} means that it +is inferred whether the target has support for the phobos standard library. +When the option is specified without a @var{choice}, the result is the same as +@samp{--with-libphobos-druntime-only=yes}. + +@item --with-target-system-zlib +Use installed @samp{zlib} rather than that included with GCC@. This needs +to be available for each multilib variant, unless configured with +@option{--with-target-system-zlib=@samp{auto}} in which case the GCC@ included +@samp{zlib} is only used when the system installed library is not available. +@end table + +@html +

+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Building**************************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Building, Testing, Configuration, Installing GCC +@end ifnothtml +@ifset buildhtml +@ifnothtml +@chapter Building +@end ifnothtml +@cindex Installing GCC: Building + +Now that GCC is configured, you are ready to build the compiler and +runtime libraries. + +Some commands executed when making the compiler may fail (return a +nonzero status) and be ignored by @command{make}. These failures, which +are often due to files that were not found, are expected, and can safely +be ignored. + +It is normal to have compiler warnings when compiling certain files. +Unless you are a GCC developer, you can generally ignore these warnings +unless they cause compilation to fail. Developers should attempt to fix +any warnings encountered, however they can temporarily continue past +warnings-as-errors by specifying the configure flag +@option{--disable-werror}. + +On certain old systems, defining certain environment variables such as +@env{CC} can interfere with the functioning of @command{make}. + +If you encounter seemingly strange errors when trying to build the +compiler in a directory other than the source directory, it could be +because you have previously configured the compiler in the source +directory. Make sure you have done all the necessary preparations. + +If you build GCC on a BSD system using a directory stored in an old System +V file system, problems may occur in running @command{fixincludes} if the +System V file system doesn't support symbolic links. These problems +result in a failure to fix the declaration of @code{size_t} in +@file{sys/types.h}. If you find that @code{size_t} is a signed type and +that type mismatches occur, this could be the cause. + +The solution is not to use such a directory for building GCC@. + +Similarly, when building from the source repository or snapshots, or if you modify +@file{*.l} files, you need the Flex lexical analyzer generator +installed. If you do not modify @file{*.l} files, releases contain +the Flex-generated files and you do not need Flex installed to build +them. There is still one Flex-based lexical analyzer (part of the +build machinery, not of GCC itself) that is used even if you only +build the C front end. + +When building from the source repository or snapshots, or if you modify Texinfo +documentation, you need version 4.7 or later of Texinfo installed if you +want Info documentation to be regenerated. Releases contain Info +documentation pre-built for the unmodified documentation in the release. + +@section Building a native compiler + +For a native build, the default configuration is to perform +a 3-stage bootstrap of the compiler when @samp{make} is invoked. +This will build the entire GCC system and ensure that it compiles +itself correctly. It can be disabled with the @option{--disable-bootstrap} +parameter to @samp{configure}, but bootstrapping is suggested because +the compiler will be tested more completely and could also have +better performance. + +The bootstrapping process will complete the following steps: + +@itemize @bullet +@item +Build tools necessary to build the compiler. + +@item +Perform a 3-stage bootstrap of the compiler. This includes building +three times the target tools for use by the compiler such as binutils +(bfd, binutils, gas, gprof, ld, and opcodes) if they have been +individually linked or moved into the top level GCC source tree before +configuring. + +@item +Perform a comparison test of the stage2 and stage3 compilers. + +@item +Build runtime libraries using the stage3 compiler from the previous step. + +@end itemize + +If you are short on disk space you might consider @samp{make +bootstrap-lean} instead. The sequence of compilation is the +same described above, but object files from the stage1 and +stage2 of the 3-stage bootstrap of the compiler are deleted as +soon as they are no longer needed. + +If you wish to use non-default GCC flags when compiling the stage2 +and stage3 compilers, set @code{BOOT_CFLAGS} on the command line when +doing @samp{make}. For example, if you want to save additional space +during the bootstrap and in the final installation as well, you can +build the compiler binaries without debugging information as in the +following example. This will save roughly 40% of disk space both for +the bootstrap and the final installation. (Libraries will still contain +debugging information.) + +@smallexample +make BOOT_CFLAGS='-O' bootstrap +@end smallexample + +You can place non-default optimization flags into @code{BOOT_CFLAGS}; they +are less well tested here than the default of @samp{-g -O2}, but should +still work. In a few cases, you may find that you need to specify special +flags such as @option{-msoft-float} here to complete the bootstrap; or, +if the native compiler miscompiles the stage1 compiler, you may need +to work around this, by choosing @code{BOOT_CFLAGS} to avoid the parts +of the stage1 compiler that were miscompiled, or by using @samp{make +bootstrap4} to increase the number of stages of bootstrap. + +@code{BOOT_CFLAGS} does not apply to bootstrapped target libraries. +Since these are always compiled with the compiler currently being +bootstrapped, you can use @code{CFLAGS_FOR_TARGET} to modify their +compilation flags, as for non-bootstrapped target libraries. +Again, if the native compiler miscompiles the stage1 compiler, you may +need to work around this by avoiding non-working parts of the stage1 +compiler. Use @code{STAGE1_TFLAGS} to this end. + +If you used the flag @option{--enable-languages=@dots{}} to restrict +the compilers to be built, only those you've actually enabled will be +built. This will of course only build those runtime libraries, for +which the particular compiler has been built. Please note, +that re-defining @env{LANGUAGES} when calling @samp{make} +@strong{does not} work anymore! + +If the comparison of stage2 and stage3 fails, this normally indicates +that the stage2 compiler has compiled GCC incorrectly, and is therefore +a potentially serious bug which you should investigate and report. (On +a few systems, meaningful comparison of object files is impossible; they +always appear ``different''. If you encounter this problem, you will +need to disable comparison in the @file{Makefile}.) + +If you do not want to bootstrap your compiler, you can configure with +@option{--disable-bootstrap}. In particular cases, you may want to +bootstrap your compiler even if the target system is not the same as +the one you are building on: for example, you could build a +@code{powerpc-unknown-linux-gnu} toolchain on a +@code{powerpc64-unknown-linux-gnu} host. In this case, pass +@option{--enable-bootstrap} to the configure script. + +@code{BUILD_CONFIG} can be used to bring in additional customization +to the build. It can be set to a whitespace-separated list of names. +For each such @code{NAME}, top-level @file{config/@code{NAME}.mk} will +be included by the top-level @file{Makefile}, bringing in any settings +it contains. The default @code{BUILD_CONFIG} can be set using the +configure option @option{--with-build-config=@code{NAME}...}. Some +examples of supported build configurations are: + +@table @asis +@item @samp{bootstrap-O1} +Removes any @option{-O}-started option from @code{BOOT_CFLAGS}, and adds +@option{-O1} to it. @samp{BUILD_CONFIG=bootstrap-O1} is equivalent to +@samp{BOOT_CFLAGS='-g -O1'}. + +@item @samp{bootstrap-O3} +@itemx @samp{bootstrap-Og} +Analogous to @code{bootstrap-O1}. + +@item @samp{bootstrap-lto} +Enables Link-Time Optimization for host tools during bootstrapping. +@samp{BUILD_CONFIG=bootstrap-lto} is equivalent to adding +@option{-flto} to @samp{BOOT_CFLAGS}. This option assumes that the host +supports the linker plugin (e.g.@: GNU ld version 2.21 or later or GNU gold +version 2.21 or later). + +@item @samp{bootstrap-lto-noplugin} +This option is similar to @code{bootstrap-lto}, but is intended for +hosts that do not support the linker plugin. Without the linker plugin +static libraries are not compiled with link-time optimizations. Since +the GCC middle end and back end are in @file{libbackend.a} this means +that only the front end is actually LTO optimized. + +@item @samp{bootstrap-lto-lean} +This option is similar to @code{bootstrap-lto}, but is intended for +faster build by only using LTO in the final bootstrap stage. +With @samp{make profiledbootstrap} the LTO frontend +is trained only on generator files. + +@item @samp{bootstrap-debug} +Verifies that the compiler generates the same executable code, whether +or not it is asked to emit debug information. To this end, this +option builds stage2 host programs without debug information, and uses +@file{contrib/compare-debug} to compare them with the stripped stage3 +object files. If @code{BOOT_CFLAGS} is overridden so as to not enable +debug information, stage2 will have it, and stage3 won't. This option +is enabled by default when GCC bootstrapping is enabled, if +@code{strip} can turn object files compiled with and without debug +info into identical object files. In addition to better test +coverage, this option makes default bootstraps faster and leaner. + +@item @samp{bootstrap-debug-big} +Rather than comparing stripped object files, as in +@code{bootstrap-debug}, this option saves internal compiler dumps +during stage2 and stage3 and compares them as well, which helps catch +additional potential problems, but at a great cost in terms of disk +space. It can be specified in addition to @samp{bootstrap-debug}. + +@item @samp{bootstrap-debug-lean} +This option saves disk space compared with @code{bootstrap-debug-big}, +but at the expense of some recompilation. Instead of saving the dumps +of stage2 and stage3 until the final compare, it uses +@option{-fcompare-debug} to generate, compare and remove the dumps +during stage3, repeating the compilation that already took place in +stage2, whose dumps were not saved. + +@item @samp{bootstrap-debug-lib} +This option tests executable code invariance over debug information +generation on target libraries, just like @code{bootstrap-debug-lean} +tests it on host programs. It builds stage3 libraries with +@option{-fcompare-debug}, and it can be used along with any of the +@code{bootstrap-debug} options above. + +There aren't @code{-lean} or @code{-big} counterparts to this option +because most libraries are only build in stage3, so bootstrap compares +would not get significant coverage. Moreover, the few libraries built +in stage2 are used in stage3 host programs, so we wouldn't want to +compile stage2 libraries with different options for comparison purposes. + +@item @samp{bootstrap-debug-ckovw} +Arranges for error messages to be issued if the compiler built on any +stage is run without the option @option{-fcompare-debug}. This is +useful to verify the full @option{-fcompare-debug} testing coverage. It +must be used along with @code{bootstrap-debug-lean} and +@code{bootstrap-debug-lib}. + +@item @samp{bootstrap-cet} +This option enables Intel CET for host tools during bootstrapping. +@samp{BUILD_CONFIG=bootstrap-cet} is equivalent to adding +@option{-fcf-protection} to @samp{BOOT_CFLAGS}. This option +assumes that the host supports Intel CET (e.g.@: GNU assembler version +2.30 or later). + +@item @samp{bootstrap-time} +Arranges for the run time of each program started by the GCC driver, +built in any stage, to be logged to @file{time.log}, in the top level of +the build tree. + +@item @samp{bootstrap-asan} +Compiles GCC itself using Address Sanitization in order to catch invalid memory +accesses within the GCC code. + +@item @samp{bootstrap-hwasan} +Compiles GCC itself using HWAddress Sanitization in order to catch invalid +memory accesses within the GCC code. This option is only available on AArch64 +systems that are running Linux kernel version 5.4 or later. + +@end table + +@section Building a cross compiler + +When building a cross compiler, it is not generally possible to do a +3-stage bootstrap of the compiler. This makes for an interesting problem +as parts of GCC can only be built with GCC@. + +To build a cross compiler, we recommend first building and installing a +native compiler. You can then use the native GCC compiler to build the +cross compiler. The installed native compiler needs to be GCC version +2.95 or later. + +Assuming you have already installed a native copy of GCC and configured +your cross compiler, issue the command @command{make}, which performs the +following steps: + +@itemize @bullet +@item +Build host tools necessary to build the compiler. + +@item +Build target tools for use by the compiler such as binutils (bfd, +binutils, gas, gprof, ld, and opcodes) +if they have been individually linked or moved into the top level GCC source +tree before configuring. + +@item +Build the compiler (single stage only). + +@item +Build runtime libraries using the compiler from the previous step. +@end itemize + +Note that if an error occurs in any step the make process will exit. + +If you are not building GNU binutils in the same source tree as GCC, +you will need a cross-assembler and cross-linker installed before +configuring GCC@. Put them in the directory +@file{@var{prefix}/@var{target}/bin}. Here is a table of the tools +you should put in this directory: + +@table @file +@item as +This should be the cross-assembler. + +@item ld +This should be the cross-linker. + +@item ar +This should be the cross-archiver: a program which can manipulate +archive files (linker libraries) in the target machine's format. + +@item ranlib +This should be a program to construct a symbol table in an archive file. +@end table + +The installation of GCC will find these programs in that directory, +and copy or link them to the proper place to for the cross-compiler to +find them when run later. + +The easiest way to provide these files is to build the Binutils package. +Configure it with the same @option{--host} and @option{--target} +options that you use for configuring GCC, then build and install +them. They install their executables automatically into the proper +directory. Alas, they do not support all the targets that GCC +supports. + +If you are not building a C library in the same source tree as GCC, +you should also provide the target libraries and headers before +configuring GCC, specifying the directories with +@option{--with-sysroot} or @option{--with-headers} and +@option{--with-libs}. Many targets also require ``start files'' such +as @file{crt0.o} and +@file{crtn.o} which are linked into each executable. There may be several +alternatives for @file{crt0.o}, for use with profiling or other +compilation options. Check your target's definition of +@code{STARTFILE_SPEC} to find out what start files it uses. + +@section Building in parallel + +GNU Make 3.80 and above, which is necessary to build GCC, support +building in parallel. To activate this, you can use @samp{make -j 2} +instead of @samp{make}. You can also specify a bigger number, and +in most cases using a value greater than the number of processors in +your machine will result in fewer and shorter I/O latency hits, thus +improving overall throughput; this is especially true for slow drives +and network filesystems. + +@section Building the Ada compiler + +@ifnothtml +@ref{GNAT-prerequisite}. +@end ifnothtml +@ifhtml +@uref{prerequisites.html#GNAT-prerequisite,,GNAT prerequisites}. +@end ifhtml + +@section Building the D compiler + +@ifnothtml +@ref{GDC-prerequisite}. +@end ifnothtml +@ifhtml +@uref{prerequisites.html#GDC-prerequisite,,GDC prerequisites}. +@end ifhtml + +@section Building with profile feedback + +It is possible to use profile feedback to optimize the compiler itself. This +should result in a faster compiler binary. Experiments done on x86 using gcc +3.3 showed approximately 7 percent speedup on compiling C programs. To +bootstrap the compiler with profile feedback, use @code{make profiledbootstrap}. + +When @samp{make profiledbootstrap} is run, it will first build a @code{stage1} +compiler. This compiler is used to build a @code{stageprofile} compiler +instrumented to collect execution counts of instruction and branch +probabilities. Training run is done by building @code{stagetrain} +compiler. Finally a @code{stagefeedback} compiler is built +using the information collected. + +Unlike standard bootstrap, several additional restrictions apply. The +compiler used to build @code{stage1} needs to support a 64-bit integral type. +It is recommended to only use GCC for this. + +On Linux/x86_64 hosts with some restrictions (no virtualization) it is +also possible to do autofdo build with @samp{make +autoprofiledback}. This uses Linux perf to sample branches in the +binary and then rebuild it with feedback derived from the profile. +Linux perf and the @code{autofdo} toolkit needs to be installed for +this. + +Only the profile from the current build is used, so when an error +occurs it is recommended to clean before restarting. Otherwise +the code quality may be much worse. + +@html +

+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Testing***************************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Testing, Final install, Building, Installing GCC +@end ifnothtml +@ifset testhtml +@ifnothtml +@chapter Installing GCC: Testing +@end ifnothtml +@cindex Testing +@cindex Installing GCC: Testing +@cindex Testsuite + +Before you install GCC, we encourage you to run the testsuites and to +compare your results with results from a similar configuration that have +been submitted to the +@uref{https://gcc.gnu.org/ml/gcc-testresults/,,gcc-testresults mailing list}. +Some of these archived results are linked from the build status lists +at @uref{https://gcc.gnu.org/buildstat.html}, although not everyone who +reports a successful build runs the testsuites and submits the results. +This step is optional and may require you to download additional software, +but it can give you confidence in your new GCC installation or point out +problems before you install and start using your new GCC@. + +First, you must have @uref{download.html,,downloaded the testsuites}. +These are part of the full distribution, but if you downloaded the +``core'' compiler plus any front ends, you must download the testsuites +separately. + +Second, you must have the testing tools installed. This includes +@uref{https://www.gnu.org/software/dejagnu/,,DejaGnu}, Tcl, and Expect; +the DejaGnu site has links to these. +Some optional tests also require Python3 and pytest module. + +If the directories where @command{runtest} and @command{expect} were +installed are not in the @env{PATH}, you may need to set the following +environment variables appropriately, as in the following example (which +assumes that DejaGnu has been installed under @file{/usr/local}): + +@smallexample +TCL_LIBRARY = /usr/local/share/tcl8.0 +DEJAGNULIBS = /usr/local/share/dejagnu +@end smallexample + +(On systems such as Cygwin, these paths are required to be actual +paths, not mounts or links; presumably this is due to some lack of +portability in the DejaGnu code.) + + +Finally, you can run the testsuite (which may take a long time): +@smallexample +cd @var{objdir}; make -k check +@end smallexample + +This will test various components of GCC, such as compiler +front ends and runtime libraries. While running the testsuite, DejaGnu +might emit some harmless messages resembling +@samp{WARNING: Couldn't find the global config file.} or +@samp{WARNING: Couldn't find tool init file} that can be ignored. + +If you are testing a cross-compiler, you may want to run the testsuite +on a simulator as described at @uref{https://gcc.gnu.org/simtest-howto.html}. + +@section How can you run the testsuite on selected tests? + +In order to run sets of tests selectively, there are targets +@samp{make check-gcc} and language specific @samp{make check-c}, +@samp{make check-c++}, @samp{make check-d} @samp{make check-fortran}, +@samp{make check-ada}, @samp{make check-objc}, @samp{make check-obj-c++}, +@samp{make check-lto} +in the @file{gcc} subdirectory of the object directory. You can also +just run @samp{make check} in a subdirectory of the object directory. + + +A more selective way to just run all @command{gcc} execute tests in the +testsuite is to use + +@smallexample +make check-gcc RUNTESTFLAGS="execute.exp @var{other-options}" +@end smallexample + +Likewise, in order to run only the @command{g++} ``old-deja'' tests in +the testsuite with filenames matching @samp{9805*}, you would use + +@smallexample +make check-g++ RUNTESTFLAGS="old-deja.exp=9805* @var{other-options}" +@end smallexample + +The file-matching expression following @var{filename}@command{.exp=} is treated +as a series of whitespace-delimited glob expressions so that multiple patterns +may be passed, although any whitespace must either be escaped or surrounded by +single quotes if multiple expressions are desired. For example, + +@smallexample +make check-g++ RUNTESTFLAGS="old-deja.exp=9805*\ virtual2.c @var{other-options}" +make check-g++ RUNTESTFLAGS="'old-deja.exp=9805* virtual2.c' @var{other-options}" +@end smallexample + +The @file{*.exp} files are located in the testsuite directories of the GCC +source, the most important ones being @file{compile.exp}, +@file{execute.exp}, @file{dg.exp} and @file{old-deja.exp}. +To get a list of the possible @file{*.exp} files, pipe the +output of @samp{make check} into a file and look at the +@samp{Running @dots{} .exp} lines. + +@section Passing options and running multiple testsuites + +You can pass multiple options to the testsuite using the +@samp{--target_board} option of DejaGNU, either passed as part of +@samp{RUNTESTFLAGS}, or directly to @command{runtest} if you prefer to +work outside the makefiles. For example, + +@smallexample +make check-g++ RUNTESTFLAGS="--target_board=unix/-O3/-fmerge-constants" +@end smallexample + +will run the standard @command{g++} testsuites (``unix'' is the target name +for a standard native testsuite situation), passing +@samp{-O3 -fmerge-constants} to the compiler on every test, i.e., +slashes separate options. + +You can run the testsuites multiple times using combinations of options +with a syntax similar to the brace expansion of popular shells: + +@smallexample +@dots{}"--target_board=arm-sim\@{-mhard-float,-msoft-float\@}\@{-O1,-O2,-O3,\@}" +@end smallexample + +(Note the empty option caused by the trailing comma in the final group.) +The following will run each testsuite eight times using the @samp{arm-sim} +target, as if you had specified all possible combinations yourself: + +@smallexample +--target_board='arm-sim/-mhard-float/-O1 \ + arm-sim/-mhard-float/-O2 \ + arm-sim/-mhard-float/-O3 \ + arm-sim/-mhard-float \ + arm-sim/-msoft-float/-O1 \ + arm-sim/-msoft-float/-O2 \ + arm-sim/-msoft-float/-O3 \ + arm-sim/-msoft-float' +@end smallexample + +They can be combined as many times as you wish, in arbitrary ways. This +list: + +@smallexample +@dots{}"--target_board=unix/-Wextra\@{-O3,-fno-strength\@}\@{-fomit-frame,\@}" +@end smallexample + +will generate four combinations, all involving @samp{-Wextra}. + +The disadvantage to this method is that the testsuites are run in serial, +which is a waste on multiprocessor systems. For users with GNU Make and +a shell which performs brace expansion, you can run the testsuites in +parallel by having the shell perform the combinations and @command{make} +do the parallel runs. Instead of using @samp{--target_board}, use a +special makefile target: + +@smallexample +make -j@var{N} check-@var{testsuite}//@var{test-target}/@var{option1}/@var{option2}/@dots{} +@end smallexample + +For example, + +@smallexample +make -j3 check-gcc//sh-hms-sim/@{-m1,-m2,-m3,-m3e,-m4@}/@{,-nofpu@} +@end smallexample + +will run three concurrent ``make-gcc'' testsuites, eventually testing all +ten combinations as described above. Note that this is currently only +supported in the @file{gcc} subdirectory. (To see how this works, try +typing @command{echo} before the example given here.) + + +@section How to interpret test results + +The result of running the testsuite are various @file{*.sum} and @file{*.log} +files in the testsuite subdirectories. The @file{*.log} files contain a +detailed log of the compiler invocations and the corresponding +results, the @file{*.sum} files summarize the results. These summaries +contain status codes for all tests: + +@itemize @bullet +@item +PASS: the test passed as expected +@item +XPASS: the test unexpectedly passed +@item +FAIL: the test unexpectedly failed +@item +XFAIL: the test failed as expected +@item +UNSUPPORTED: the test is not supported on this platform +@item +ERROR: the testsuite detected an error +@item +WARNING: the testsuite detected a possible problem +@end itemize + +It is normal for some tests to report unexpected failures. At the +current time the testing harness does not allow fine grained control +over whether or not a test is expected to fail. This problem should +be fixed in future releases. + + +@section Submitting test results + +If you want to report the results to the GCC project, use the +@file{contrib/test_summary} shell script. Start it in the @var{objdir} with + +@smallexample +@var{srcdir}/contrib/test_summary -p your_commentary.txt \ + -m gcc-testresults@@gcc.gnu.org |sh +@end smallexample + +This script uses the @command{Mail} program to send the results, so +make sure it is in your @env{PATH}. The file @file{your_commentary.txt} is +prepended to the testsuite summary and should contain any special +remarks you have on your results or your build environment. Please +do not edit the testsuite result block or the subject line, as these +messages may be automatically processed. + +@html +

+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Final install*********************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Final install, , Testing, Installing GCC +@end ifnothtml +@ifset finalinstallhtml +@ifnothtml +@chapter Installing GCC: Final installation +@end ifnothtml + +Now that GCC has been built (and optionally tested), you can install it with +@smallexample +cd @var{objdir} && make install +@end smallexample + +We strongly recommend to install into a target directory where there is +no previous version of GCC present. Also, the GNAT runtime should not +be stripped, as this would break certain features of the debugger that +depend on this debugging information (catching Ada exceptions for +instance). + +That step completes the installation of GCC; user level binaries can +be found in @file{@var{prefix}/bin} where @var{prefix} is the value +you specified with the @option{--prefix} to configure (or +@file{/usr/local} by default). (If you specified @option{--bindir}, +that directory will be used instead; otherwise, if you specified +@option{--exec-prefix}, @file{@var{exec-prefix}/bin} will be used.) +Headers for the C++ library are installed in +@file{@var{prefix}/include}; libraries in @file{@var{libdir}} +(normally @file{@var{prefix}/lib}); internal parts of the compiler in +@file{@var{libdir}/gcc} and @file{@var{libexecdir}/gcc}; documentation +in info format in @file{@var{infodir}} (normally +@file{@var{prefix}/info}). + +When installing cross-compilers, GCC's executables +are not only installed into @file{@var{bindir}}, that +is, @file{@var{exec-prefix}/bin}, but additionally into +@file{@var{exec-prefix}/@var{target-alias}/bin}, if that directory +exists. Typically, such @dfn{tooldirs} hold target-specific +binutils, including assembler and linker. + +Installation into a temporary staging area or into a @command{chroot} +jail can be achieved with the command + +@smallexample +make DESTDIR=@var{path-to-rootdir} install +@end smallexample + +@noindent +where @var{path-to-rootdir} is the absolute path of +a directory relative to which all installation paths will be +interpreted. Note that the directory specified by @code{DESTDIR} +need not exist yet; it will be created if necessary. + +There is a subtle point with tooldirs and @code{DESTDIR}: +If you relocate a cross-compiler installation with +e.g.@: @samp{DESTDIR=@var{rootdir}}, then the directory +@file{@var{rootdir}/@var{exec-prefix}/@var{target-alias}/bin} will +be filled with duplicated GCC executables only if it already exists, +it will not be created otherwise. This is regarded as a feature, +not as a bug, because it gives slightly more control to the packagers +using the @code{DESTDIR} feature. + +You can install stripped programs and libraries with + +@smallexample +make install-strip +@end smallexample + +If you are bootstrapping a released version of GCC then please +quickly review the build status page for your release, available from +@uref{https://gcc.gnu.org/buildstat.html}. +If your system is not listed for the version of GCC that you built, +send a note to +@email{gcc@@gcc.gnu.org} indicating +that you successfully built and installed GCC@. +Include the following information: + +@itemize @bullet +@item +Output from running @file{@var{srcdir}/config.guess}. Do not send +that file itself, just the one-line output from running it. + +@item +The output of @samp{gcc -v} for your newly installed @command{gcc}. +This tells us which version of GCC you built and the options you passed to +configure. + +@item +Whether you enabled all languages or a subset of them. If you used a +full distribution then this information is part of the configure +options in the output of @samp{gcc -v}, but if you downloaded the +``core'' compiler plus additional front ends then it isn't apparent +which ones you built unless you tell us about it. + +@item +If the build was for GNU/Linux, also include: +@itemize @bullet +@item +The distribution name and version (e.g., Red Hat 7.1 or Debian 2.2.3); +this information should be available from @file{/etc/issue}. + +@item +The version of the Linux kernel, available from @samp{uname --version} +or @samp{uname -a}. + +@item +The version of glibc you used; for RPM-based systems like Red Hat, +Mandrake, and SuSE type @samp{rpm -q glibc} to get the glibc version, +and on systems like Debian and Progeny use @samp{dpkg -l libc6}. +@end itemize +For other systems, you can include similar information if you think it is +relevant. + +@item +Any other information that you think would be useful to people building +GCC on the same configuration. The new entry in the build status list +will include a link to the archived copy of your message. +@end itemize + +We'd also like to know if the +@ifnothtml +@ref{Specific, host/target specific installation notes} +@end ifnothtml +@ifhtml +@uref{specific.html,,host/target specific installation notes} +@end ifhtml +didn't include your host/target information or if that information is +incomplete or out of date. Send a note to +@email{gcc@@gcc.gnu.org} detailing how the information should be changed. + +If you find a bug, please report it following the +@uref{../bugs/,,bug reporting guidelines}. + +If you want to print the GCC manuals, do @samp{cd @var{objdir}; make +dvi}. You will need to have @command{texi2dvi} (version at least 4.7) +and @TeX{} installed. This creates a number of @file{.dvi} files in +subdirectories of @file{@var{objdir}}; these may be converted for +printing with programs such as @command{dvips}. Alternately, by using +@samp{make pdf} in place of @samp{make dvi}, you can create documentation +in the form of @file{.pdf} files; this requires @command{texi2pdf}, which +is included with Texinfo version 4.8 and later. You can also +@uref{https://shop.fsf.org/,,buy printed manuals from the +Free Software Foundation}, though such manuals may not be for the most +recent version of GCC@. + +If you would like to generate online HTML documentation, do @samp{cd +@var{objdir}; make html} and HTML will be generated for the gcc manuals in +@file{@var{objdir}/gcc/HTML}. + +@html +

+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Binaries**************************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Binaries, Specific, Installing GCC, Top +@end ifnothtml +@ifset binarieshtml +@ifnothtml +@chapter Installing GCC: Binaries +@end ifnothtml +@cindex Binaries +@cindex Installing GCC: Binaries + +We are often asked about pre-compiled versions of GCC@. While we cannot +provide these for all platforms, below you'll find links to binaries for +various platforms where creating them by yourself is not easy due to various +reasons. + +Please note that we did not create these binaries, nor do we +support them. If you have any problems installing them, please +contact their makers. + +@itemize +@item +AIX: +@itemize +@item +@uref{http://www.perzl.org/aix/,,AIX Open Source Packages (AIX5L AIX 6.1 +AIX 7.1)}. +@end itemize + +@item +DOS---@uref{http://www.delorie.com/djgpp/,,DJGPP}. + +@item +HP-UX: +@itemize +@item +@uref{http://hpux.connect.org.uk/,,HP-UX Porting Center}; +@end itemize + +@item +Solaris 2 (SPARC, Intel): +@itemize +@item +@uref{https://www.opencsw.org/,,OpenCSW} +@end itemize + +@item +macOS: +@itemize +@item +The @uref{https://brew.sh,,Homebrew} package manager; +@item +@uref{https://www.macports.org,,MacPorts}. +@end itemize + +@item +Microsoft Windows: +@itemize +@item +The @uref{https://sourceware.org/cygwin/,,Cygwin} project; +@item +The @uref{https://osdn.net/projects/mingw/,,MinGW} and +@uref{https://www.mingw-w64.org/,,mingw-w64} projects. +@end itemize + +@item +@uref{http://www.openpkg.org/,,OpenPKG} offers binaries for quite a +number of platforms. + +@item +The @uref{https://gcc.gnu.org/wiki/GFortranBinaries,,GFortran Wiki} has +links to GNU Fortran binaries for several platforms. +@end itemize + +@html +

+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***Specific**************************************************************** +@ifnothtml +@comment node-name, next, previous, up +@node Specific, GNU Free Documentation License, Binaries, Top +@end ifnothtml +@ifset specifichtml +@ifnothtml +@chapter Host/target specific installation notes for GCC +@end ifnothtml +@cindex Specific +@cindex Specific installation notes +@cindex Target specific installation +@cindex Host specific installation +@cindex Target specific installation notes + +Please read this document carefully @emph{before} installing the +GNU Compiler Collection on your machine. + +Note that this list of install notes is @emph{not} a list of supported +hosts or targets. Not all supported hosts and targets are listed +here, only the ones that require host-specific or target-specific +information have to. + +@ifhtml +@itemize +@item +@uref{#aarch64-x-x,,aarch64*-*-*} +@item +@uref{#alpha-x-x,,alpha*-*-*} +@item +@uref{#amdgcn-x-amdhsa,,amdgcn-*-amdhsa} +@item +@uref{#amd64-x-solaris2,,amd64-*-solaris2*} +@item +@uref{#arc-x-elf32,,arc-*-elf32} +@item +@uref{#arc-linux-uclibc,,arc-linux-uclibc} +@item +@uref{#arm-x-eabi,,arm-*-eabi} +@item +@uref{#avr,,avr} +@item +@uref{#bfin,,Blackfin} +@item +@uref{#cris,,cris} +@item +@uref{#dos,,DOS} +@item +@uref{#epiphany-x-elf,,epiphany-*-elf} +@item +@uref{#ft32-x-elf,,ft32-*-elf} +@item +@uref{#x-x-freebsd,,*-*-freebsd*} +@item +@uref{#h8300-hms,,h8300-hms} +@item +@uref{#hppa-hp-hpux,,hppa*-hp-hpux*} +@item +@uref{#hppa-hp-hpux10,,hppa*-hp-hpux10} +@item +@uref{#hppa-hp-hpux11,,hppa*-hp-hpux11} +@item +@uref{#x-x-linux-gnu,,*-*-linux-gnu} +@item +@uref{#ix86-x-linux,,i?86-*-linux*} +@item +@uref{#ix86-x-solaris2,,i?86-*-solaris2*} +@item +@uref{#ia64-x-linux,,ia64-*-linux} +@item +@uref{#ia64-x-hpux,,ia64-*-hpux*} +@item +@uref{#x-ibm-aix,,*-ibm-aix*} +@item +@uref{#iq2000-x-elf,,iq2000-*-elf} +@item +@uref{#loongarch,,loongarch} +@item +@uref{#lm32-x-elf,,lm32-*-elf} +@item +@uref{#lm32-x-uclinux,,lm32-*-uclinux} +@item +@uref{#m32c-x-elf,,m32c-*-elf} +@item +@uref{#m32r-x-elf,,m32r-*-elf} +@item +@uref{#m68k-x-x,,m68k-*-*} +@item +@uref{#m68k-x-uclinux,,m68k-*-uclinux} +@item +@uref{#microblaze-x-elf,,microblaze-*-elf} +@item +@uref{#mips-x-x,,mips-*-*} +@item +@uref{#moxie-x-elf,,moxie-*-elf} +@item +@uref{#msp430-x-elf,,msp430-*-elf} +@item +@uref{#nds32le-x-elf,,nds32le-*-elf} +@item +@uref{#nds32be-x-elf,,nds32be-*-elf} +@item +@uref{#nvptx-x-none,,nvptx-*-none} +@item +@uref{#or1k-x-elf,,or1k-*-elf} +@item +@uref{#or1k-x-linux,,or1k-*-linux} +@item +@uref{#powerpc-x-x,,powerpc*-*-*} +@item +@uref{#powerpc-x-darwin,,powerpc-*-darwin*} +@item +@uref{#powerpc-x-elf,,powerpc-*-elf} +@item +@uref{#powerpc-x-linux-gnu,,powerpc*-*-linux-gnu*} +@item +@uref{#powerpc-x-netbsd,,powerpc-*-netbsd*} +@item +@uref{#powerpc-x-eabisim,,powerpc-*-eabisim} +@item +@uref{#powerpc-x-eabi,,powerpc-*-eabi} +@item +@uref{#powerpcle-x-elf,,powerpcle-*-elf} +@item +@uref{#powerpcle-x-eabisim,,powerpcle-*-eabisim} +@item +@uref{#powerpcle-x-eabi,,powerpcle-*-eabi} +@item +@uref{#riscv32-x-elf,,riscv32-*-elf} +@item +@uref{#riscv32-x-linux,,riscv32-*-linux} +@item +@uref{#riscv64-x-elf,,riscv64-*-elf} +@item +@uref{#riscv64-x-linux,,riscv64-*-linux} +@item +@uref{#rl78-x-elf,,rl78-*-elf} +@item +@uref{#rx-x-elf,,rx-*-elf} +@item +@uref{#s390-x-linux,,s390-*-linux*} +@item +@uref{#s390x-x-linux,,s390x-*-linux*} +@item +@uref{#s390x-ibm-tpf,,s390x-ibm-tpf*} +@item +@uref{#x-x-solaris2,,*-*-solaris2*} +@item +@uref{#sparc-x-x,,sparc*-*-*} +@item +@uref{#sparc-sun-solaris2,,sparc-sun-solaris2*} +@item +@uref{#sparc-x-linux,,sparc-*-linux*} +@item +@uref{#sparc64-x-solaris2,,sparc64-*-solaris2*} +@item +@uref{#sparcv9-x-solaris2,,sparcv9-*-solaris2*} +@item +@uref{#c6x-x-x,,c6x-*-*} +@item +@uref{#visium-x-elf, visium-*-elf} +@item +@uref{#x-x-vxworks,,*-*-vxworks*} +@item +@uref{#x86-64-x-x,,x86_64-*-*, amd64-*-*} +@item +@uref{#x86-64-x-solaris2,,x86_64-*-solaris2*} +@item +@uref{#xtensa-x-elf,,xtensa*-*-elf} +@item +@uref{#xtensa-x-linux,,xtensa*-*-linux*} +@item +@uref{#windows,,Microsoft Windows} +@item +@uref{#x-x-cygwin,,*-*-cygwin} +@item +@uref{#x-x-mingw32,,*-*-mingw32} +@item +@uref{#os2,,OS/2} +@item +@uref{#older,,Older systems} +@end itemize + +@itemize +@item +@uref{#elf,,all ELF targets} (SVR4, Solaris 2, etc.) +@end itemize +@end ifhtml + + +@html + +

+@end html +@anchor{aarch64-x-x} +@heading aarch64*-*-* +Binutils pre 2.24 does not have support for selecting @option{-mabi} and +does not support ILP32. If it is used to build GCC 4.9 or later, GCC will +not support option @option{-mabi=ilp32}. + +To enable a workaround for the Cortex-A53 erratum number 835769 by default +(for all CPUs regardless of -mcpu option given) at configure time use the +@option{--enable-fix-cortex-a53-835769} option. This will enable the fix by +default and can be explicitly disabled during compilation by passing the +@option{-mno-fix-cortex-a53-835769} option. Conversely, +@option{--disable-fix-cortex-a53-835769} will disable the workaround by +default. The workaround is disabled by default if neither of +@option{--enable-fix-cortex-a53-835769} or +@option{--disable-fix-cortex-a53-835769} is given at configure time. + +To enable a workaround for the Cortex-A53 erratum number 843419 by default +(for all CPUs regardless of -mcpu option given) at configure time use the +@option{--enable-fix-cortex-a53-843419} option. This workaround is applied at +link time. Enabling the workaround will cause GCC to pass the relevant option +to the linker. It can be explicitly disabled during compilation by passing the +@option{-mno-fix-cortex-a53-843419} option. Conversely, +@option{--disable-fix-cortex-a53-843419} will disable the workaround by default. +The workaround is disabled by default if neither of +@option{--enable-fix-cortex-a53-843419} or +@option{--disable-fix-cortex-a53-843419} is given at configure time. + +To enable Branch Target Identification Mechanism and Return Address Signing by +default at configure time use the @option{--enable-standard-branch-protection} +option. This is equivalent to having @option{-mbranch-protection=standard} +during compilation. This can be explicitly disabled during compilation by +passing the @option{-mbranch-protection=none} option which turns off all +types of branch protections. Conversely, +@option{--disable-standard-branch-protection} will disable both the +protections by default. This mechanism is turned off by default if neither +of the options are given at configure time. + +@html +
+@end html +@anchor{alpha-x-x} +@heading alpha*-*-* +This section contains general configuration information for all +Alpha-based platforms using ELF@. In addition to reading this +section, please read all other sections that match your target. + +@html +
+@end html +@anchor{amd64-x-solaris2} +@heading amd64-*-solaris2* +This is a synonym for @samp{x86_64-*-solaris2*}. + +@html +
+@end html +@anchor{amdgcn-x-amdhsa} +@heading amdgcn-*-amdhsa +AMD GCN GPU target. + +Instead of GNU Binutils, you will need to install LLVM 13.0.1, or later, and copy +@file{bin/llvm-mc} to @file{amdgcn-amdhsa/bin/as}, +@file{bin/lld} to @file{amdgcn-amdhsa/bin/ld}, +@file{bin/llvm-nm} to @file{amdgcn-amdhsa/bin/nm}, and +@file{bin/llvm-ar} to both @file{bin/amdgcn-amdhsa-ar} and +@file{bin/amdgcn-amdhsa-ranlib}. + +Use Newlib (3.2.0, or newer). + +To run the binaries, install the HSA Runtime from the +@uref{https://rocm.github.io,,ROCm Platform}, and use +@file{libexec/gcc/amdhsa-amdhsa/@var{version}/gcn-run} to launch them +on the GPU. + +@html +
+@end html +@anchor{arc-x-elf32} +@heading arc-*-elf32 + +Use @samp{configure --target=arc-elf32 --with-cpu=@var{cpu} --enable-languages="c,c++"} +to configure GCC, with @var{cpu} being one of @samp{arc600}, @samp{arc601}, +or @samp{arc700}@. + +@html +
+@end html +@anchor{arc-linux-uclibc} +@heading arc-linux-uclibc + +Use @samp{configure --target=arc-linux-uclibc --with-cpu=arc700 --enable-languages="c,c++"} to configure GCC@. + +@html +
+@end html +@anchor{arm-x-eabi} +@heading arm-*-eabi +ARM-family processors. + +Building the Ada frontend commonly fails (an infinite loop executing +@code{xsinfo}) if the host compiler is GNAT 4.8. Host compilers built from the +GNAT 4.6, 4.9 or 5 release branches are known to succeed. + +@html +
+@end html +@anchor{avr} +@heading avr +ATMEL AVR-family micro controllers. These are used in embedded +applications. There are no standard Unix configurations. +@ifnothtml +@xref{AVR Options,, AVR Options, gcc, Using the GNU Compiler +Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``AVR Options'' in the main manual +@end ifhtml +for the list of supported MCU types. + +Use @samp{configure --target=avr --enable-languages="c"} to configure GCC@. + +Further installation notes and other useful information about AVR tools +can also be obtained from: + +@itemize @bullet +@item +@uref{http://www.nongnu.org/avr/,,http://www.nongnu.org/avr/} +@item +@uref{http://www.amelek.gda.pl/avr/,,http://www.amelek.gda.pl/avr/} +@end itemize + +The following error: +@smallexample +Error: register required +@end smallexample + +indicates that you should upgrade to a newer version of the binutils. + +@html +
+@end html +@anchor{bfin} +@heading Blackfin +The Blackfin processor, an Analog Devices DSP. +@ifnothtml +@xref{Blackfin Options,, Blackfin Options, gcc, Using the GNU Compiler +Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``Blackfin Options'' in the main manual +@end ifhtml + +More information, and a version of binutils with support for this processor, +are available at @uref{https://sourceforge.net/projects/adi-toolchain/}. + +@html +
+@end html +@anchor{cris} +@heading CRIS +CRIS is a CPU architecture in Axis Communications systems-on-a-chip, for +example the ETRAX series. These are used in embedded applications. + +@ifnothtml +@xref{CRIS Options,, CRIS Options, gcc, Using the GNU Compiler +Collection (GCC)}, +@end ifnothtml +@ifhtml +See ``CRIS Options'' in the main manual +@end ifhtml +for a list of CRIS-specific options. + +Use @samp{configure --target=cris-elf} to configure GCC@ for building +a cross-compiler for CRIS. +@html +
+@end html +@anchor{dos} +@heading DOS +Please have a look at the @uref{binaries.html,,binaries page}. + +You cannot install GCC by itself on MSDOS; it will not compile under +any MSDOS compiler except itself. You need to get the complete +compilation package DJGPP, which includes binaries as well as sources, +and includes all the necessary compilation tools and libraries. + +@html +
+@end html +@anchor{epiphany-x-elf} +@heading epiphany-*-elf +Adapteva Epiphany. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{x-x-freebsd} +@heading *-*-freebsd* +In order to better utilize FreeBSD base system functionality and match +the configuration of the system compiler, GCC 4.5 and above as well as +GCC 4.4 past 2010-06-20 leverage SSP support in libc (which is present +on FreeBSD 7 or later) and the use of @code{__cxa_atexit} by default +(on FreeBSD 6 or later). The use of @code{dl_iterate_phdr} inside +@file{libgcc_s.so.1} and boehm-gc (on FreeBSD 7 or later) is enabled +by GCC 4.5 and above. + +We support FreeBSD using the ELF file format with DWARF 2 debugging +for all CPU architectures. There are +no known issues with mixing object files and libraries with different +debugging formats. Otherwise, this release of GCC should now match +more of the configuration used in the stock FreeBSD configuration of +GCC@. In particular, @option{--enable-threads} is now configured by +default. However, as a general user, do not attempt to replace the +system compiler with this release. Known to bootstrap and check with +good results on FreeBSD 7.2-STABLE@. In the past, known to bootstrap +and check with good results on FreeBSD 3.0, 3.4, 4.0, 4.2, 4.3, 4.4, +4.5, 4.8, 4.9 and 5-CURRENT@. + +The version of binutils installed in @file{/usr/bin} probably works +with this release of GCC@. Bootstrapping against the latest GNU +binutils and/or the version found in @file{/usr/ports/devel/binutils} has +been known to enable additional features and improve overall testsuite +results. However, it is currently known that boehm-gc may not configure +properly on FreeBSD prior to the FreeBSD 7.0 release with GNU binutils +after 2.16.1. + +@html +
+@end html +@anchor{ft32-x-elf} +@heading ft32-*-elf +The FT32 processor. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{h8300-hms} +@heading h8300-hms +Renesas H8/300 series of processors. + +Please have a look at the @uref{binaries.html,,binaries page}. + +The calling convention and structure layout has changed in release 2.6. +All code must be recompiled. The calling convention now passes the +first three arguments in function calls in registers. Structures are no +longer a multiple of 2 bytes. + +@html +
+@end html +@anchor{hppa-hp-hpux} +@heading hppa*-hp-hpux* +Support for HP-UX version 9 and older was discontinued in GCC 3.4. + +We require using gas/binutils on all hppa platforms. Version 2.19 or +later is recommended. + +It may be helpful to configure GCC with the +@uref{./configure.html#with-gnu-as,,@option{--with-gnu-as}} and +@option{--with-as=@dots{}} options to ensure that GCC can find GAS@. + +The HP assembler should not be used with GCC. It is rarely tested and may +not work. It shouldn't be used with any languages other than C due to its +many limitations. + +Specifically, @option{-g} does not work (HP-UX uses a peculiar debugging +format which GCC does not know about). It also inserts timestamps +into each object file it creates, causing the 3-stage comparison test to +fail during a bootstrap. You should be able to continue by saying +@samp{make all-host all-target} after getting the failure from @samp{make}. + +Various GCC features are not supported. For example, it does not support weak +symbols or alias definitions. As a result, explicit template instantiations +are required when using C++. This makes it difficult if not impossible to +build many C++ applications. + +There are two default scheduling models for instructions. These are +PROCESSOR_7100LC and PROCESSOR_8000. They are selected from the pa-risc +architecture specified for the target machine when configuring. +PROCESSOR_8000 is the default. PROCESSOR_7100LC is selected when +the target is a @samp{hppa1*} machine. + +The PROCESSOR_8000 model is not well suited to older processors. Thus, +it is important to completely specify the machine architecture when +configuring if you want a model other than PROCESSOR_8000. The macro +TARGET_SCHED_DEFAULT can be defined in BOOT_CFLAGS if a different +default scheduling model is desired. + +As of GCC 4.0, GCC uses the UNIX 95 namespace for HP-UX 10.10 +through 11.00, and the UNIX 98 namespace for HP-UX 11.11 and later. +This namespace change might cause problems when bootstrapping with +an earlier version of GCC or the HP compiler as essentially the same +namespace is required for an entire build. This problem can be avoided +in a number of ways. With HP cc, @env{UNIX_STD} can be set to @samp{95} +or @samp{98}. Another way is to add an appropriate set of predefines +to @env{CC}. The description for the @option{munix=} option contains +a list of the predefines used with each standard. + +More specific information to @samp{hppa*-hp-hpux*} targets follows. + +@html +
+@end html +@anchor{hppa-hp-hpux10} +@heading hppa*-hp-hpux10 +For hpux10.20, we @emph{highly} recommend you pick up the latest sed patch +@code{PHCO_19798} from HP@. + +The C++ ABI has changed incompatibly in GCC 4.0. COMDAT subspaces are +used for one-only code and data. This resolves many of the previous +problems in using C++ on this target. However, the ABI is not compatible +with the one implemented under HP-UX 11 using secondary definitions. + +@html +
+@end html +@anchor{hppa-hp-hpux11} +@heading hppa*-hp-hpux11 +GCC 3.0 and up support HP-UX 11. GCC 2.95.x is not supported and cannot +be used to compile GCC 3.0 and up. + +The libffi library haven't been ported to 64-bit HP-UX@ and doesn't build. + +Refer to @uref{binaries.html,,binaries} for information about obtaining +precompiled GCC binaries for HP-UX@. Precompiled binaries must be obtained +to build the Ada language as it cannot be bootstrapped using C@. Ada is +only available for the 32-bit PA-RISC runtime. + +Starting with GCC 3.4 an ISO C compiler is required to bootstrap. The +bundled compiler supports only traditional C; you will need either HP's +unbundled compiler, or a binary distribution of GCC@. + +It is possible to build GCC 3.3 starting with the bundled HP compiler, +but the process requires several steps. GCC 3.3 can then be used to +build later versions. + +There are several possible approaches to building the distribution. +Binutils can be built first using the HP tools. Then, the GCC +distribution can be built. The second approach is to build GCC +first using the HP tools, then build binutils, then rebuild GCC@. +There have been problems with various binary distributions, so it +is best not to start from a binary distribution. + +On 64-bit capable systems, there are two distinct targets. Different +installation prefixes must be used if both are to be installed on +the same system. The @samp{hppa[1-2]*-hp-hpux11*} target generates code +for the 32-bit PA-RISC runtime architecture and uses the HP linker. +The @samp{hppa64-hp-hpux11*} target generates 64-bit code for the +PA-RISC 2.0 architecture. + +The script config.guess now selects the target type based on the compiler +detected during configuration. You must define @env{PATH} or @env{CC} so +that configure finds an appropriate compiler for the initial bootstrap. +When @env{CC} is used, the definition should contain the options that are +needed whenever @env{CC} is used. + +Specifically, options that determine the runtime architecture must be +in @env{CC} to correctly select the target for the build. It is also +convenient to place many other compiler options in @env{CC}. For example, +@env{CC="cc -Ac +DA2.0W -Wp,-H16376 -D_CLASSIC_TYPES -D_HPUX_SOURCE"} +can be used to bootstrap the GCC 3.3 branch with the HP compiler in +64-bit K&R/bundled mode. The @option{+DA2.0W} option will result in +the automatic selection of the @samp{hppa64-hp-hpux11*} target. The +macro definition table of cpp needs to be increased for a successful +build with the HP compiler. _CLASSIC_TYPES and _HPUX_SOURCE need to +be defined when building with the bundled compiler, or when using the +@option{-Ac} option. These defines aren't necessary with @option{-Ae}. + +It is best to explicitly configure the @samp{hppa64-hp-hpux11*} target +with the @option{--with-ld=@dots{}} option. This overrides the standard +search for ld. The two linkers supported on this target require different +commands. The default linker is determined during configuration. As a +result, it's not possible to switch linkers in the middle of a GCC build. +This has been reported to sometimes occur in unified builds of binutils +and GCC@. + +A recent linker patch must be installed for the correct operation of +GCC 3.3 and later. @code{PHSS_26559} and @code{PHSS_24304} are the +oldest linker patches that are known to work. They are for HP-UX +11.00 and 11.11, respectively. @code{PHSS_24303}, the companion to +@code{PHSS_24304}, might be usable but it hasn't been tested. These +patches have been superseded. Consult the HP patch database to obtain +the currently recommended linker patch for your system. + +The patches are necessary for the support of weak symbols on the +32-bit port, and for the running of initializers and finalizers. Weak +symbols are implemented using SOM secondary definition symbols. Prior +to HP-UX 11, there are bugs in the linker support for secondary symbols. +The patches correct a problem of linker core dumps creating shared +libraries containing secondary symbols, as well as various other +linking issues involving secondary symbols. + +GCC 3.3 uses the ELF DT_INIT_ARRAY and DT_FINI_ARRAY capabilities to +run initializers and finalizers on the 64-bit port. The 32-bit port +uses the linker @option{+init} and @option{+fini} options for the same +purpose. The patches correct various problems with the +init/+fini +options, including program core dumps. Binutils 2.14 corrects a +problem on the 64-bit port resulting from HP's non-standard use of +the .init and .fini sections for array initializers and finalizers. + +Although the HP and GNU linkers are both supported for the +@samp{hppa64-hp-hpux11*} target, it is strongly recommended that the +HP linker be used for link editing on this target. + +At this time, the GNU linker does not support the creation of long +branch stubs. As a result, it cannot successfully link binaries +containing branch offsets larger than 8 megabytes. In addition, +there are problems linking shared libraries, linking executables +with @option{-static}, and with dwarf2 unwind and exception support. +It also doesn't provide stubs for internal calls to global functions +in shared libraries, so these calls cannot be overloaded. + +The HP dynamic loader does not support GNU symbol versioning, so symbol +versioning is not supported. It may be necessary to disable symbol +versioning with @option{--disable-symvers} when using GNU ld. + +POSIX threads are the default. The optional DCE thread library is not +supported, so @option{--enable-threads=dce} does not work. + +@html +
+@end html +@anchor{x-x-linux-gnu} +@heading *-*-linux-gnu +The @code{.init_array} and @code{.fini_array} sections are enabled +unconditionally which requires at least glibc 2.1 and binutils 2.12. + +Versions of libstdc++-v3 starting with 3.2.1 require bug fixes present +in glibc 2.2.5 and later. More information is available in the +libstdc++-v3 documentation. + +@html +
+@end html +@anchor{ix86-x-linux} +@heading i?86-*-linux* +As of GCC 3.3, binutils 2.13.1 or later is required for this platform. +See @uref{https://gcc.gnu.org/PR10877,,bug 10877} for more information. + +If you receive Signal 11 errors when building on GNU/Linux, then it is +possible you have a hardware problem. Further information on this can be +found on @uref{https://www.bitwizard.nl/sig11/,,www.bitwizard.nl}. + +@html +
+@end html +@anchor{ix86-x-solaris2} +@heading i?86-*-solaris2* +Use this for Solaris 11.3 or later on x86 and x86-64 systems. Starting +with GCC 4.7, there is also a 64-bit @samp{amd64-*-solaris2*} or +@samp{x86_64-*-solaris2*} configuration that corresponds to +@samp{sparcv9-sun-solaris2*}. + +It is recommended that you configure GCC to use the GNU assembler. The +versions included in Solaris 11.3, from GNU binutils 2.23.1 or +newer (available as @file{/usr/bin/gas} and +@file{/usr/gnu/bin/as}), work fine. The current version, from GNU +binutils 2.34, is known to work. Recent versions of the Solaris assembler in +@file{/usr/bin/as} work almost as well, though. + +For linking, the Solaris linker is preferred. If you want to use the GNU +linker instead, the version in Solaris 11.3, from GNU binutils 2.23.1 or +newer (in @file{/usr/gnu/bin/ld} and @file{/usr/bin/gld}), works, +as does the latest version, from GNU binutils 2.34. + +To use GNU @command{as}, configure with the options +@option{--with-gnu-as --with-as=@//usr/@/gnu/@/bin/@/as}. It may be necessary +to configure with @option{--without-gnu-ld --with-ld=@//usr/@/ccs/@/bin/@/ld} to +guarantee use of Solaris @command{ld}. +@c FIXME: why --without-gnu-ld --with-ld? + +@html +
+@end html +@anchor{ia64-x-linux} +@heading ia64-*-linux +IA-64 processor (also known as IPF, or Itanium Processor Family) +running GNU/Linux. + +If you are using the installed system libunwind library with +@option{--with-system-libunwind}, then you must use libunwind 0.98 or +later. + +@html +
+@end html +@anchor{ia64-x-hpux} +@heading ia64-*-hpux* +Building GCC on this target requires the GNU Assembler. The bundled HP +assembler will not work. To prevent GCC from using the wrong assembler, +the option @option{--with-gnu-as} may be necessary. + +The GCC libunwind library has not been ported to HPUX@. This means that for +GCC versions 3.2.3 and earlier, @option{--enable-libunwind-exceptions} +is required to build GCC@. For GCC 3.3 and later, this is the default. +For gcc 3.4.3 and later, @option{--enable-libunwind-exceptions} is +removed and the system libunwind library will always be used. + +@html +
+ +@end html +@anchor{x-ibm-aix} +@heading *-ibm-aix* +Support for AIX version 3 and older was discontinued in GCC 3.4. +Support for AIX version 4.2 and older was discontinued in GCC 4.5. + +``out of memory'' bootstrap failures may indicate a problem with +process resource limits (ulimit). Hard limits are configured in the +@file{/etc/security/limits} system configuration file. + +GCC 4.9 and above require a C++ compiler for bootstrap. IBM VAC++ / xlC +cannot bootstrap GCC. xlc can bootstrap an older version of GCC and +G++ can bootstrap recent releases of GCC. + +GCC can bootstrap with recent versions of IBM XLC, but bootstrapping +with an earlier release of GCC is recommended. Bootstrapping with XLC +requires a larger data segment, which can be enabled through the +@var{LDR_CNTRL} environment variable, e.g., + +@smallexample +% LDR_CNTRL=MAXDATA=0x50000000 +% export LDR_CNTRL +@end smallexample + +One can start with a pre-compiled version of GCC to build from +sources. One may delete GCC's ``fixed'' header files when starting +with a version of GCC built for an earlier release of AIX. + +To speed up the configuration phases of bootstrapping and installing GCC, +one may use GNU Bash instead of AIX @command{/bin/sh}, e.g., + +@smallexample +% CONFIG_SHELL=/opt/freeware/bin/bash +% export CONFIG_SHELL +@end smallexample + +and then proceed as described in @uref{build.html,,the build +instructions}, where we strongly recommend specifying an absolute path +to invoke @var{srcdir}/configure. + +Because GCC on AIX is built as a 32-bit executable by default, +(although it can generate 64-bit programs) the GMP and MPFR libraries +required by gfortran must be 32-bit libraries. Building GMP and MPFR +as static archive libraries works better than shared libraries. + +Errors involving @code{alloca} when building GCC generally are due +to an incorrect definition of @code{CC} in the Makefile or mixing files +compiled with the native C compiler and GCC@. During the stage1 phase of +the build, the native AIX compiler @strong{must} be invoked as @command{cc} +(not @command{xlc}). Once @command{configure} has been informed of +@command{xlc}, one needs to use @samp{make distclean} to remove the +configure cache files and ensure that @env{CC} environment variable +does not provide a definition that will confuse @command{configure}. +If this error occurs during stage2 or later, then the problem most likely +is the version of Make (see above). + +The native @command{as} and @command{ld} are recommended for +bootstrapping on AIX@. The GNU Assembler, GNU Linker, and GNU +Binutils version 2.20 is the minimum level that supports bootstrap on +AIX 5@. The GNU Assembler has not been updated to support AIX 6@ or +AIX 7. The native AIX tools do interoperate with GCC@. + +AIX 7.1 added partial support for DWARF debugging, but full support +requires AIX 7.1 TL03 SP7 that supports additional DWARF sections and +fixes a bug in the assembler. AIX 7.1 TL03 SP5 distributed a version +of libm.a missing important symbols; a fix for IV77796 will be +included in SP6. + +AIX 5.3 TL10, AIX 6.1 TL05 and AIX 7.1 TL00 introduced an AIX +assembler change that sometimes produces corrupt assembly files +causing AIX linker errors. The bug breaks GCC bootstrap on AIX and +can cause compilation failures with existing GCC installations. An +AIX iFix for AIX 5.3 is available (APAR IZ98385 for AIX 5.3 TL10, APAR +IZ98477 for AIX 5.3 TL11 and IZ98134 for AIX 5.3 TL12). AIX 5.3 TL11 SP8, +AIX 5.3 TL12 SP5, AIX 6.1 TL04 SP11, AIX 6.1 TL05 SP7, AIX 6.1 TL06 SP6, +AIX 6.1 TL07 and AIX 7.1 TL01 should include the fix. + +Building @file{libstdc++.a} requires a fix for an AIX Assembler bug +APAR IY26685 (AIX 4.3) or APAR IY25528 (AIX 5.1). It also requires a +fix for another AIX Assembler bug and a co-dependent AIX Archiver fix +referenced as APAR IY53606 (AIX 5.2) or as APAR IY54774 (AIX 5.1) + +@anchor{TransferAixShobj} +@samp{libstdc++} in GCC 3.4 increments the major version number of the +shared object and GCC installation places the @file{libstdc++.a} +shared library in a common location which will overwrite the and GCC +3.3 version of the shared library. Applications either need to be +re-linked against the new shared library or the GCC 3.1 and GCC 3.3 +versions of the @samp{libstdc++} shared object needs to be available +to the AIX runtime loader. The GCC 3.1 @samp{libstdc++.so.4}, if +present, and GCC 3.3 @samp{libstdc++.so.5} shared objects can be +installed for runtime dynamic loading using the following steps to set +the @samp{F_LOADONLY} flag in the shared object for @emph{each} +multilib @file{libstdc++.a} installed: + +Extract the shared objects from the currently installed +@file{libstdc++.a} archive: +@smallexample +% ar -x libstdc++.a libstdc++.so.4 libstdc++.so.5 +@end smallexample + +Enable the @samp{F_LOADONLY} flag so that the shared object will be +available for runtime dynamic loading, but not linking: +@smallexample +% strip -e libstdc++.so.4 libstdc++.so.5 +@end smallexample + +Archive the runtime-only shared object in the GCC 3.4 +@file{libstdc++.a} archive: +@smallexample +% ar -q libstdc++.a libstdc++.so.4 libstdc++.so.5 +@end smallexample + +Eventually, the +@uref{./configure.html#WithAixSoname,,@option{--with-aix-soname=svr4}} +configure option may drop the need for this procedure for libraries that +support it. + +Linking executables and shared libraries may produce warnings of +duplicate symbols. The assembly files generated by GCC for AIX always +have included multiple symbol definitions for certain global variable +and function declarations in the original program. The warnings should +not prevent the linker from producing a correct library or runnable +executable. + +AIX 4.3 utilizes a ``large format'' archive to support both 32-bit and +64-bit object modules. The routines provided in AIX 4.3.0 and AIX 4.3.1 +to parse archive libraries did not handle the new format correctly. +These routines are used by GCC and result in error messages during +linking such as ``not a COFF file''. The version of the routines shipped +with AIX 4.3.1 should work for a 32-bit environment. The @option{-g} +option of the archive command may be used to create archives of 32-bit +objects using the original ``small format''. A correct version of the +routines is shipped with AIX 4.3.2 and above. + +Some versions of the AIX binder (linker) can fail with a relocation +overflow severe error when the @option{-bbigtoc} option is used to link +GCC-produced object files into an executable that overflows the TOC@. A fix +for APAR IX75823 (OVERFLOW DURING LINK WHEN USING GCC AND -BBIGTOC) is +available from IBM Customer Support and from its +@uref{https://techsupport.services.ibm.com/,,techsupport.services.ibm.com} +website as PTF U455193. + +The AIX 4.3.2.1 linker (bos.rte.bind_cmds Level 4.3.2.1) will dump core +with a segmentation fault when invoked by any version of GCC@. A fix for +APAR IX87327 is available from IBM Customer Support and from its +@uref{https://techsupport.services.ibm.com/,,techsupport.services.ibm.com} +website as PTF U461879. This fix is incorporated in AIX 4.3.3 and above. + +The initial assembler shipped with AIX 4.3.0 generates incorrect object +files. A fix for APAR IX74254 (64BIT DISASSEMBLED OUTPUT FROM COMPILER FAILS +TO ASSEMBLE/BIND) is available from IBM Customer Support and from its +@uref{https://techsupport.services.ibm.com/,,techsupport.services.ibm.com} +website as PTF U453956. This fix is incorporated in AIX 4.3.1 and above. + +AIX provides National Language Support (NLS)@. Compilers and assemblers +use NLS to support locale-specific representations of various data +formats including floating-point numbers (e.g., @samp{.} vs @samp{,} for +separating decimal fractions). There have been problems reported where +GCC does not produce the same floating-point formats that the assembler +expects. If one encounters this problem, set the @env{LANG} +environment variable to @samp{C} or @samp{En_US}. + +A default can be specified with the @option{-mcpu=@var{cpu_type}} +switch and using the configure option @option{--with-cpu-@var{cpu_type}}. + +@html +
+@end html +@anchor{iq2000-x-elf} +@heading iq2000-*-elf +Vitesse IQ2000 processors. These are used in embedded +applications. There are no standard Unix configurations. + +@html +
+@end html +@anchor{lm32-x-elf} +@heading lm32-*-elf +Lattice Mico32 processor. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{lm32-x-uclinux} +@heading lm32-*-uclinux +Lattice Mico32 processor. +This configuration is intended for embedded systems running uClinux. + +@html +
+@end html +@anchor{loongarch} +@heading LoongArch +LoongArch processor. +The following LoongArch targets are available: +@table @code +@item loongarch64-linux-gnu* +LoongArch processor running GNU/Linux. This target triplet may be coupled +with a small set of possible suffixes to identify their default ABI type: +@table @code +@item f64 +Uses @code{lp64d/base} ABI by default. +@item f32 +Uses @code{lp64f/base} ABI by default. +@item sf +Uses @code{lp64s/base} ABI by default. +@end table + +@item loongarch64-linux-gnu +Same as @code{loongarch64-linux-gnuf64}, but may be used with +@option{--with-abi=*} to configure the default ABI type. +@end table + +More information about LoongArch can be found at +@uref{https://github.com/loongson/LoongArch-Documentation}. + +@html +
+@end html +@anchor{m32c-x-elf} +@heading m32c-*-elf +Renesas M32C processor. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{m32r-x-elf} +@heading m32r-*-elf +Renesas M32R processor. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{m68k-x-x} +@heading m68k-*-* +By default, +@samp{m68k-*-elf*}, @samp{m68k-*-rtems}, @samp{m68k-*-uclinux} and +@samp{m68k-*-linux} +build libraries for both M680x0 and ColdFire processors. If you only +need the M680x0 libraries, you can omit the ColdFire ones by passing +@option{--with-arch=m68k} to @command{configure}. Alternatively, you +can omit the M680x0 libraries by passing @option{--with-arch=cf} to +@command{configure}. These targets default to 5206 or 5475 code as +appropriate for the target system when +configured with @option{--with-arch=cf} and 68020 code otherwise. + +The @samp{m68k-*-netbsd} and +@samp{m68k-*-openbsd} targets also support the @option{--with-arch} +option. They will generate ColdFire CFV4e code when configured with +@option{--with-arch=cf} and 68020 code otherwise. + +You can override the default processors listed above by configuring +with @option{--with-cpu=@var{target}}. This @var{target} can either +be a @option{-mcpu} argument or one of the following values: +@samp{m68000}, @samp{m68010}, @samp{m68020}, @samp{m68030}, +@samp{m68040}, @samp{m68060}, @samp{m68020-40} and @samp{m68020-60}. + +GCC requires at least binutils version 2.17 on these targets. + +@html +
+@end html +@anchor{m68k-x-uclinux} +@heading m68k-*-uclinux +GCC 4.3 changed the uClinux configuration so that it uses the +@samp{m68k-linux-gnu} ABI rather than the @samp{m68k-elf} ABI. +It also added improved support for C++ and flat shared libraries, +both of which were ABI changes. + +@html +
+@end html +@anchor{microblaze-x-elf} +@heading microblaze-*-elf +Xilinx MicroBlaze processor. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{mips-x-x} +@heading mips-*-* +If on a MIPS system you get an error message saying ``does not have gp +sections for all it's [sic] sectons [sic]'', don't worry about it. This +happens whenever you use GAS with the MIPS linker, but there is not +really anything wrong, and it is okay to use the output file. You can +stop such warnings by installing the GNU linker. + +It would be nice to extend GAS to produce the gp tables, but they are +optional, and there should not be a warning about their absence. + +The libstdc++ atomic locking routines for MIPS targets requires MIPS II +and later. A patch went in just after the GCC 3.3 release to +make @samp{mips*-*-*} use the generic implementation instead. You can also +configure for @samp{mipsel-elf} as a workaround. The +@samp{mips*-*-linux*} target continues to use the MIPS II routines. More +work on this is expected in future releases. + +@c If you make --with-llsc the default for another target, please also +@c update the description of the --with-llsc option. + +The built-in @code{__sync_*} functions are available on MIPS II and +later systems and others that support the @samp{ll}, @samp{sc} and +@samp{sync} instructions. This can be overridden by passing +@option{--with-llsc} or @option{--without-llsc} when configuring GCC. +Since the Linux kernel emulates these instructions if they are +missing, the default for @samp{mips*-*-linux*} targets is +@option{--with-llsc}. The @option{--with-llsc} and +@option{--without-llsc} configure options may be overridden at compile +time by passing the @option{-mllsc} or @option{-mno-llsc} options to +the compiler. + +MIPS systems check for division by zero (unless +@option{-mno-check-zero-division} is passed to the compiler) by +generating either a conditional trap or a break instruction. Using +trap results in smaller code, but is only supported on MIPS II and +later. Also, some versions of the Linux kernel have a bug that +prevents trap from generating the proper signal (@code{SIGFPE}). To enable +the use of break, use the @option{--with-divide=breaks} +@command{configure} option when configuring GCC@. The default is to +use traps on systems that support them. + +@html +
+@end html +@anchor{moxie-x-elf} +@heading moxie-*-elf +The moxie processor. + +@html +
+@end html +@anchor{msp430-x-elf} +@heading msp430-*-elf* +TI MSP430 processor. +This configuration is intended for embedded systems. + +@samp{msp430-*-elf} is the standard configuration with most GCC +features enabled by default. + +@samp{msp430-*-elfbare} is tuned for a bare-metal environment, and disables +features related to shared libraries and other functionality not used for +this device. This reduces code and data usage of the GCC libraries, resulting +in a minimal run-time environment by default. + +Features disabled by default include: +@itemize +@item transactional memory +@item __cxa_atexit +@end itemize + +@html +
+@end html +@anchor{nds32le-x-elf} +@heading nds32le-*-elf +Andes NDS32 target in little endian mode. + +@html +
+@end html +@anchor{nds32be-x-elf} +@heading nds32be-*-elf +Andes NDS32 target in big endian mode. + +@html +
+@end html +@anchor{nvptx-x-none} +@heading nvptx-*-none +Nvidia PTX target. + +Instead of GNU binutils, you will need to install +@uref{https://github.com/MentorEmbedded/nvptx-tools/,,nvptx-tools}. +Tell GCC where to find it: +@option{--with-build-time-tools=[install-nvptx-tools]/nvptx-none/bin}. + +You will need newlib 3.1.0 or later. It can be +automatically built together with GCC@. For this, add a symbolic link +to nvptx-newlib's @file{newlib} directory to the directory containing +the GCC sources. + +Use the @option{--disable-sjlj-exceptions} and +@option{--enable-newlib-io-long-long} options when configuring. + +The @option{--with-arch} option may be specified to override the +default value for the @option{-march} option, and to also build +corresponding target libraries. +The default is @option{--with-arch=sm_30}. + +For example, if @option{--with-arch=sm_70} is specified, +@option{-march=sm_30} and @option{-march=sm_70} target libraries are +built, and code generation defaults to @option{-march=sm_70}. + +@html +
+@end html +@anchor{or1k-x-elf} +@heading or1k-*-elf +The OpenRISC 1000 32-bit processor with delay slots. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{or1k-x-linux} +@heading or1k-*-linux +The OpenRISC 1000 32-bit processor with delay slots. + +@html +
+@end html +@anchor{powerpc-x-x} +@heading powerpc-*-* +You can specify a default version for the @option{-mcpu=@var{cpu_type}} +switch by using the configure option @option{--with-cpu-@var{cpu_type}}. + +You will need GNU binutils 2.20 or newer. + +@html +
+@end html +@anchor{powerpc-x-darwin} +@heading powerpc-*-darwin* +PowerPC running Darwin (Mac OS X kernel). + +Pre-installed versions of Mac OS X may not include any developer tools, +meaning that you will not be able to build GCC from source. Tool +binaries are available at +@uref{https://opensource.apple.com}. + +This version of GCC requires at least cctools-590.36. The +cctools-590.36 package referenced from +@uref{https://gcc.gnu.org/ml/gcc/2006-03/msg00507.html} will not work +on systems older than 10.3.9 (aka darwin7.9.0). + +@html +
+@end html +@anchor{powerpc-x-elf} +@heading powerpc-*-elf +PowerPC system in big endian mode, running System V.4. + +@html +
+@end html +@anchor{powerpc-x-linux-gnu} +@heading powerpc*-*-linux-gnu* +PowerPC system in big endian mode running Linux. + +@html +
+@end html +@anchor{powerpc-x-netbsd} +@heading powerpc-*-netbsd* +PowerPC system in big endian mode running NetBSD@. + +@html +
+@end html +@anchor{powerpc-x-eabisim} +@heading powerpc-*-eabisim +Embedded PowerPC system in big endian mode for use in running under the +PSIM simulator. + +@html +
+@end html +@anchor{powerpc-x-eabi} +@heading powerpc-*-eabi +Embedded PowerPC system in big endian mode. + +@html +
+@end html +@anchor{powerpcle-x-elf} +@heading powerpcle-*-elf +PowerPC system in little endian mode, running System V.4. + +@html +
+@end html +@anchor{powerpcle-x-eabisim} +@heading powerpcle-*-eabisim +Embedded PowerPC system in little endian mode for use in running under +the PSIM simulator. + +@html +
+@end html +@anchor{powerpcle-x-eabi} +@heading powerpcle-*-eabi +Embedded PowerPC system in little endian mode. + +@html +
+@end html +@anchor{rl78-x-elf} +@heading rl78-*-elf +The Renesas RL78 processor. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{riscv32-x-elf} +@heading riscv32-*-elf +The RISC-V RV32 instruction set. +This configuration is intended for embedded systems. +This (and all other RISC-V) targets require the binutils 2.30 release. + +@html +
+@end html +@anchor{riscv32-x-linux} +@heading riscv32-*-linux +The RISC-V RV32 instruction set running GNU/Linux. +This (and all other RISC-V) targets require the binutils 2.30 release. + +@html +
+@end html +@anchor{riscv64-x-elf} +@heading riscv64-*-elf +The RISC-V RV64 instruction set. +This configuration is intended for embedded systems. +This (and all other RISC-V) targets require the binutils 2.30 release. + +@html +
+@end html +@anchor{riscv64-x-linux} +@heading riscv64-*-linux +The RISC-V RV64 instruction set running GNU/Linux. +This (and all other RISC-V) targets require the binutils 2.30 release. + +@html +
+@end html +@anchor{rx-x-elf} +@heading rx-*-elf +The Renesas RX processor. + +@html +
+@end html +@anchor{s390-x-linux} +@heading s390-*-linux* +S/390 system running GNU/Linux for S/390@. + +@html +
+@end html +@anchor{s390x-x-linux} +@heading s390x-*-linux* +zSeries system (64-bit) running GNU/Linux for zSeries@. + +@html +
+@end html +@anchor{s390x-ibm-tpf} +@heading s390x-ibm-tpf* +zSeries system (64-bit) running TPF@. This platform is +supported as cross-compilation target only. + +@html +
+@end html +@c Please use Solaris 2 to refer to all release of Solaris, starting +@c with 2.0 until 2.6, 7, 8, etc. Solaris 1 was a marketing name for +@c SunOS 4 releases which we don't use to avoid confusion. Solaris +@c alone is too unspecific and must be avoided. +@anchor{x-x-solaris2} +@heading *-*-solaris2* +Support for Solaris 10 has been removed in GCC 10. Support for Solaris +9 has been removed in GCC 5. Support for Solaris 8 has been removed in +GCC 4.8. Support for Solaris 7 has been removed in GCC 4.6. + +Solaris 11.3 provides GCC 4.5.2, 4.7.3, and 4.8.2 as +@command{/usr/gcc/4.5/bin/gcc} or similar. Newer Solaris versions +provide one or more of GCC 5, 7, and 9. Alternatively, +you can install a pre-built GCC to bootstrap and install GCC. See the +@uref{binaries.html,,binaries page} for details. + +The Solaris 2 @command{/bin/sh} will often fail to configure +@samp{libstdc++-v3}. We therefore recommend using the +following initial sequence of commands + +@smallexample +% CONFIG_SHELL=/bin/ksh +% export CONFIG_SHELL +@end smallexample + +@noindent +and proceed as described in @uref{configure.html,,the configure instructions}. +In addition we strongly recommend specifying an absolute path to invoke +@command{@var{srcdir}/configure}. + +In Solaris 11, you need to check for @code{system/header}, +@code{system/linker}, and @code{developer/assembler} packages. + +Trying to use the linker and other tools in +@file{/usr/ucb} to install GCC has been observed to cause trouble. +For example, the linker may hang indefinitely. The fix is to remove +@file{/usr/ucb} from your @env{PATH}. + +The build process works more smoothly with the legacy Solaris tools so, if you +have @file{/usr/xpg4/bin} in your @env{PATH}, we recommend that you place +@file{/usr/bin} before @file{/usr/xpg4/bin} for the duration of the build. + +We recommend the use of the Solaris assembler or the GNU assembler, in +conjunction with the Solaris linker. The GNU @command{as} +versions included in Solaris 11.3, +from GNU binutils 2.23.1 or newer (in @file{/usr/bin/gas} and +@file{/usr/gnu/bin/as}), are known to work. +The current version, from GNU binutils 2.34, +is known to work as well. Note that your mileage may vary +if you use a combination of the GNU tools and the Solaris tools: while the +combination GNU @command{as} + Solaris @command{ld} should reasonably work, +the reverse combination Solaris @command{as} + GNU @command{ld} may fail to +build or cause memory corruption at runtime in some cases for C++ programs. +@c FIXME: still? +GNU @command{ld} usually works as well. Again, the current +version (2.34) is known to work, but generally lacks platform specific +features, so better stay with Solaris @command{ld}. To use the LTO linker +plugin (@option{-fuse-linker-plugin}) with GNU @command{ld}, GNU +binutils @emph{must} be configured with @option{--enable-largefile}. + +To enable symbol versioning in @samp{libstdc++} with the Solaris linker, +you need to have any version of GNU @command{c++filt}, which is part of +GNU binutils. @samp{libstdc++} symbol versioning will be disabled if no +appropriate version is found. Solaris @command{c++filt} from the Solaris +Studio compilers does @emph{not} work. + +In order to build the GNU D compiler, GDC, a working @samp{libphobos} is +needed. That library wasn't built by default in GCC 9--11 on SPARC, or +on x86 when the Solaris assembler is used, but can be enabled by +configuring with @option{--enable-libphobos}. Also, GDC 9.4.0 is +required on x86, while GDC 9.3.0 is known to work on SPARC. + +The versions of the GNU Multiple Precision Library (GMP), the MPFR +library and the MPC library bundled with Solaris 11.3 and later are +usually recent enough to match GCC's requirements. There are two +caveats: + +@itemize @bullet +@item +While the version of the GMP library in Solaris 11.3 works with GCC, you +need to configure with @option{--with-gmp-include=/usr/include/gmp}. + +@item +The version of the MPFR libary included in Solaris 11.3 is too old; you +need to provide a more recent one. + +@end itemize + +@html +
+@end html +@anchor{sparc-x-x} +@heading sparc*-*-* +This section contains general configuration information for all +SPARC-based platforms. In addition to reading this section, please +read all other sections that match your target. + +Newer versions of the GNU Multiple Precision Library (GMP), the MPFR +library and the MPC library are known to be miscompiled by earlier +versions of GCC on these platforms. We therefore recommend the use +of the exact versions of these libraries listed as minimal versions +in @uref{prerequisites.html,,the prerequisites}. + +@html +
+@end html +@anchor{sparc-sun-solaris2} +@heading sparc-sun-solaris2* +When GCC is configured to use GNU binutils 2.14 or later, the binaries +produced are smaller than the ones produced using Solaris native tools; +this difference is quite significant for binaries containing debugging +information. + +Starting with Solaris 7, the operating system is capable of executing +64-bit SPARC V9 binaries. GCC 3.1 and later properly supports +this; the @option{-m64} option enables 64-bit code generation. +However, if all you want is code tuned for the UltraSPARC CPU, you +should try the @option{-mtune=ultrasparc} option instead, which produces +code that, unlike full 64-bit code, can still run on non-UltraSPARC +machines. + +When configuring the GNU Multiple Precision Library (GMP), the MPFR +library or the MPC library on a Solaris 7 or later system, the canonical +target triplet must be specified as the @command{build} parameter on the +configure line. This target triplet can be obtained by invoking @command{./config.guess} in the toplevel source directory of GCC (and +not that of GMP or MPFR or MPC). For example on a Solaris 11 system: + +@smallexample +% ./configure --build=sparc-sun-solaris2.11 --prefix=xxx +@end smallexample + +@html +
+@end html +@anchor{sparc-x-linux} +@heading sparc-*-linux* + +@html +
+@end html +@anchor{sparc64-x-solaris2} +@heading sparc64-*-solaris2* +When configuring a 64-bit-default GCC on Solaris/SPARC, you must use a +build compiler that generates 64-bit code, either by default or by +specifying @samp{CC='gcc -m64' CXX='gcc-m64'} to @command{configure}. +Additionally, you @emph{must} pass @option{--build=sparc64-sun-solaris2.11} +or @option{--build=sparcv9-sun-solaris2.11} because @file{config.guess} +misdetects this situation, which can cause build failures. + +When configuring the GNU Multiple Precision Library (GMP), the MPFR +library or the MPC library, the canonical target triplet must be specified +as the @command{build} parameter on the configure line. For example +on a Solaris 11 system: + +@smallexample +% ./configure --build=sparc64-sun-solaris2.11 --prefix=xxx +@end smallexample + +@html +
+@end html +@anchor{sparcv9-x-solaris2} +@heading sparcv9-*-solaris2* +This is a synonym for @samp{sparc64-*-solaris2*}. + +@html +
+@end html +@anchor{c6x-x-x} +@heading c6x-*-* +The C6X family of processors. This port requires binutils-2.22 or newer. + +@html +
+@end html +@anchor{visium-x-elf} +@heading visium-*-elf +CDS VISIUMcore processor. +This configuration is intended for embedded systems. + +@html +
+@end html +@anchor{x-x-vxworks} +@heading *-*-vxworks* +Support for VxWorks is in flux. At present GCC supports @emph{only} the +very recent VxWorks 5.5 (aka Tornado 2.2) release, and only on PowerPC@. +We welcome patches for other architectures supported by VxWorks 5.5. +Support for VxWorks AE would also be welcome; we believe this is merely +a matter of writing an appropriate ``configlette'' (see below). We are +not interested in supporting older, a.out or COFF-based, versions of +VxWorks in GCC 3. + +VxWorks comes with an older version of GCC installed in +@file{@var{$WIND_BASE}/host}; we recommend you do not overwrite it. +Choose an installation @var{prefix} entirely outside @var{$WIND_BASE}. +Before running @command{configure}, create the directories @file{@var{prefix}} +and @file{@var{prefix}/bin}. Link or copy the appropriate assembler, +linker, etc.@: into @file{@var{prefix}/bin}, and set your @var{PATH} to +include that directory while running both @command{configure} and +@command{make}. + +You must give @command{configure} the +@option{--with-headers=@var{$WIND_BASE}/target/h} switch so that it can +find the VxWorks system headers. Since VxWorks is a cross compilation +target only, you must also specify @option{--target=@var{target}}. +@command{configure} will attempt to create the directory +@file{@var{prefix}/@var{target}/sys-include} and copy files into it; +make sure the user running @command{configure} has sufficient privilege +to do so. + +GCC's exception handling runtime requires a special ``configlette'' +module, @file{contrib/gthr_supp_vxw_5x.c}. Follow the instructions in +that file to add the module to your kernel build. (Future versions of +VxWorks will incorporate this module.) + +@html +
+@end html +@anchor{x86-64-x-x} +@heading x86_64-*-*, amd64-*-* +GCC supports the x86-64 architecture implemented by the AMD64 processor +(amd64-*-* is an alias for x86_64-*-*) on GNU/Linux, FreeBSD and NetBSD@. +On GNU/Linux the default is a bi-arch compiler which is able to generate +both 64-bit x86-64 and 32-bit x86 code (via the @option{-m32} switch). + +@html +
+@end html +@anchor{x86-64-x-solaris2} +@heading x86_64-*-solaris2* +GCC also supports the x86-64 architecture implemented by the AMD64 +processor (@samp{amd64-*-*} is an alias for @samp{x86_64-*-*}) on +Solaris 10 or later. Unlike other systems, without special options a +bi-arch compiler is built which generates 32-bit code by default, but +can generate 64-bit x86-64 code with the @option{-m64} switch. Since +GCC 4.7, there is also a configuration that defaults to 64-bit code, but +can generate 32-bit code with @option{-m32}. To configure and build +this way, you have to provide all support libraries like @file{libgmp} +as 64-bit code, configure with @option{--target=x86_64-pc-solaris2.11} +and @samp{CC=gcc -m64}. + +@html +
+@end html +@anchor{xtensa-x-elf} +@heading xtensa*-*-elf +This target is intended for embedded Xtensa systems using the +@samp{newlib} C library. It uses ELF but does not support shared +objects. Designed-defined instructions specified via the +Tensilica Instruction Extension (TIE) language are only supported +through inline assembly. + +The Xtensa configuration information must be specified prior to +building GCC@. The @file{include/xtensa-config.h} header +file contains the configuration information. If you created your +own Xtensa configuration with the Xtensa Processor Generator, the +downloaded files include a customized copy of this header file, +which you can use to replace the default header file. + +@html +
+@end html +@anchor{xtensa-x-linux} +@heading xtensa*-*-linux* +This target is for Xtensa systems running GNU/Linux. It supports ELF +shared objects and the GNU C library (glibc). It also generates +position-independent code (PIC) regardless of whether the +@option{-fpic} or @option{-fPIC} options are used. In other +respects, this target is the same as the +@uref{#xtensa*-*-elf,,@samp{xtensa*-*-elf}} target. + +@html +
+@end html +@anchor{windows} +@heading Microsoft Windows + +@subheading Intel 16-bit versions +The 16-bit versions of Microsoft Windows, such as Windows 3.1, are not +supported. + +However, the 32-bit port has limited support for Microsoft +Windows 3.11 in the Win32s environment, as a target only. See below. + +@subheading Intel 32-bit versions +The 32-bit versions of Windows, including Windows 95, Windows NT, Windows +XP, and Windows Vista, are supported by several different target +platforms. These targets differ in which Windows subsystem they target +and which C libraries are used. + +@itemize +@item Cygwin @uref{#x-x-cygwin,,*-*-cygwin}: Cygwin provides a user-space +Linux API emulation layer in the Win32 subsystem. +@item MinGW @uref{#x-x-mingw32,,*-*-mingw32}: MinGW is a native GCC port for +the Win32 subsystem that provides a subset of POSIX. +@item MKS i386-pc-mks: NuTCracker from MKS. See +@uref{https://www.mkssoftware.com} for more information. +@end itemize + +@subheading Intel 64-bit versions +GCC contains support for x86-64 using the mingw-w64 +runtime library, available from @uref{https://www.mingw-w64.org/downloads/}. +This library should be used with the target triple x86_64-pc-mingw32. + +@subheading Windows CE +Windows CE is supported as a target only on Hitachi +SuperH (sh-wince-pe), and MIPS (mips-wince-pe). + +@subheading Other Windows Platforms +GCC no longer supports Windows NT on the Alpha or PowerPC. + +GCC no longer supports the Windows POSIX subsystem. However, it does +support the Interix subsystem. See above. + +Old target names including *-*-winnt and *-*-windowsnt are no longer used. + +PW32 (i386-pc-pw32) support was never completed, and the project seems to +be inactive. See @uref{http://pw32.sourceforge.net/} for more information. + +UWIN support has been removed due to a lack of maintenance. + +@html +
+@end html +@anchor{x-x-cygwin} +@heading *-*-cygwin +Ports of GCC are included with the +@uref{http://www.cygwin.com/,,Cygwin environment}. + +GCC will build under Cygwin without modification; it does not build +with Microsoft's C++ compiler and there are no plans to make it do so. + +The Cygwin native compiler can be configured to target any 32-bit x86 +cpu architecture desired; the default is i686-pc-cygwin. It should be +used with as up-to-date a version of binutils as possible; use either +the latest official GNU binutils release in the Cygwin distribution, +or version 2.20 or above if building your own. + +@html +
+@end html +@anchor{x-x-mingw32} +@heading *-*-mingw32 +GCC will build with and support only MinGW runtime 3.12 and later. +Earlier versions of headers are incompatible with the new default semantics +of @code{extern inline} in @code{-std=c99} and @code{-std=gnu99} modes. + +To support emitting DWARF debugging info you need to use GNU binutils +version 2.16 or above containing support for the @code{.secrel32} +assembler pseudo-op. + +@html +
+@end html +@anchor{older} +@heading Older systems +GCC contains support files for many older (1980s and early +1990s) Unix variants. For the most part, support for these systems +has not been deliberately removed, but it has not been maintained for +several years and may suffer from bitrot. + +Starting with GCC 3.1, each release has a list of ``obsoleted'' systems. +Support for these systems is still present in that release, but +@command{configure} will fail unless the @option{--enable-obsolete} +option is given. Unless a maintainer steps forward, support for these +systems will be removed from the next release of GCC@. + +Support for old systems as hosts for GCC can cause problems if the +workarounds for compiler, library and operating system bugs affect the +cleanliness or maintainability of the rest of GCC@. In some cases, to +bring GCC up on such a system, if still possible with current GCC, may +require first installing an old version of GCC which did work on that +system, and using it to compile a more recent GCC, to avoid bugs in the +vendor compiler. Old releases of GCC 1 and GCC 2 are available in the +@file{old-releases} directory on the @uref{../mirrors.html,,GCC mirror +sites}. Header bugs may generally be avoided using +@command{fixincludes}, but bugs or deficiencies in libraries and the +operating system may still cause problems. + +Support for older systems as targets for cross-compilation is less +problematic than support for them as hosts for GCC; if an enthusiast +wishes to make such a target work again (including resurrecting any of +the targets that never worked with GCC 2, starting from the last +version before they were removed), patches +@uref{../contribute.html,,following the usual requirements} would be +likely to be accepted, since they should not affect the support for more +modern targets. + +For some systems, old versions of GNU binutils may also be useful, +and are available from @file{pub/binutils/old-releases} on +@uref{https://sourceware.org/mirrors.html,,sourceware.org mirror sites}. + +Some of the information on specific systems above relates to +such older systems, but much of the information +about GCC on such systems (which may no longer be applicable to +current GCC) is to be found in the GCC texinfo manual. + +@html +
+@end html +@anchor{elf} +@heading all ELF targets (SVR4, Solaris 2, etc.) +C++ support is significantly better on ELF targets if you use the +@uref{./configure.html#with-gnu-ld,,GNU linker}; duplicate copies of +inlines, vtables and template instantiations will be discarded +automatically. + + +@html +
+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c ***GFDL******************************************************************** +@ifset gfdlhtml +@include fdl.texi +@html +

+

+@end html +@ifhtml +@uref{./index.html,,Return to the GCC Installation page} +@end ifhtml +@end ifset + +@c *************************************************************************** +@c Part 6 The End of the Document +@ifinfo +@comment node-name, next, previous, up +@node Concept Index, , GNU Free Documentation License, Top +@end ifinfo + +@ifinfo +@unnumbered Concept Index + +@printindex cp + +@contents +@end ifinfo +@bye diff --git a/gcc/doc/interface.texi b/gcc/doc/interface.texi new file mode 100644 index 00000000000..e1dfc927aa7 --- /dev/null +++ b/gcc/doc/interface.texi @@ -0,0 +1,70 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Interface +@chapter Interfacing to GCC Output +@cindex interfacing to GCC output +@cindex run-time conventions +@cindex function call conventions +@cindex conventions, run-time + +GCC is normally configured to use the same function calling convention +normally in use on the target system. This is done with the +machine-description macros described (@pxref{Target Macros}). + +@cindex unions, returning +@cindex structures, returning +@cindex returning structures and unions +However, returning of structure and union values is done differently on +some target machines. As a result, functions compiled with PCC +returning such types cannot be called from code compiled with GCC, +and vice versa. This does not cause trouble often because few Unix +library routines return structures or unions. + +GCC code returns structures and unions that are 1, 2, 4 or 8 bytes +long in the same registers used for @code{int} or @code{double} return +values. (GCC typically allocates variables of such types in +registers also.) Structures and unions of other sizes are returned by +storing them into an address passed by the caller (usually in a +register). The target hook @code{TARGET_STRUCT_VALUE_RTX} +tells GCC where to pass this address. + +By contrast, PCC on most target machines returns structures and unions +of any size by copying the data into an area of static storage, and then +returning the address of that storage as if it were a pointer value. +The caller must copy the data from that memory area to the place where +the value is wanted. This is slower than the method used by GCC, and +fails to be reentrant. + +On some target machines, such as RISC machines and the 80386, the +standard system convention is to pass to the subroutine the address of +where to return the value. On these machines, GCC has been +configured to be compatible with the standard compiler, when this method +is used. It may not be compatible for structures of 1, 2, 4 or 8 bytes. + +@cindex argument passing +@cindex passing arguments +GCC uses the system's standard convention for passing arguments. On +some machines, the first few arguments are passed in registers; in +others, all are passed on the stack. It would be possible to use +registers for argument passing on any machine, and this would probably +result in a significant speedup. But the result would be complete +incompatibility with code that follows the standard convention. So this +change is practical only if you are switching to GCC as the sole C +compiler for the system. We may implement register argument passing on +certain machines once we have a complete GNU system so that we can +compile the libraries with GCC@. + +On some machines (particularly the SPARC), certain types of arguments +are passed ``by invisible reference''. This means that the value is +stored in memory, and the address of the memory location is passed to +the subroutine. + +@cindex @code{longjmp} and automatic variables +If you use @code{longjmp}, beware of automatic variables. ISO C says that +automatic variables that are not declared @code{volatile} have undefined +values after a @code{longjmp}. And this is all GCC promises to do, +because it is very difficult to restore register variables correctly, and +one of GCC's features is that it can put variables in registers without +your asking it to. diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi new file mode 100644 index 00000000000..975ee64103f --- /dev/null +++ b/gcc/doc/invoke.texi @@ -0,0 +1,35442 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ignore +@c man begin INCLUDE +@include gcc-vers.texi +@c man end + +@c man begin COPYRIGHT +Copyright @copyright{} 1988-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename gcc +@settitle GNU project C and C++ compiler +@c man begin SYNOPSIS +gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] + [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] + [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] + [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] + [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] + [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] + [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} + +Only the most useful options are listed here; see below for the +remainder. @command{g++} accepts mostly the same options as @command{gcc}. +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), +cpp(1), gcov(1), as(1), ld(1), gdb(1) +and the Info entries for @file{gcc}, @file{cpp}, @file{as}, +@file{ld}, @file{binutils} and @file{gdb}. +@c man end +@c man begin BUGS +For instructions on reporting bugs, see +@w{@value{BUGURL}}. +@c man end +@c man begin AUTHOR +See the Info entry for @command{gcc}, or +@w{@uref{https://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, +for contributors to GCC@. +@c man end +@end ignore + +@node Invoking GCC +@chapter GCC Command Options +@cindex GCC command options +@cindex command options +@cindex options, GCC command + +@c man begin DESCRIPTION +When you invoke GCC, it normally does preprocessing, compilation, +assembly and linking. The ``overall options'' allow you to stop this +process at an intermediate stage. For example, the @option{-c} option +says not to run the linker. Then the output consists of object files +output by the assembler. +@xref{Overall Options,,Options Controlling the Kind of Output}. + +Other options are passed on to one or more stages of processing. Some options +control the preprocessor and others the compiler itself. Yet other +options control the assembler and linker; most of these are not +documented here, since you rarely need to use any of them. + +@cindex C compilation options +Most of the command-line options that you can use with GCC are useful +for C programs; when an option is only useful with another language +(usually C++), the explanation says so explicitly. If the description +for a particular option does not mention a source language, you can use +that option with all supported languages. + +@cindex cross compiling +@cindex specifying machine version +@cindex specifying compiler version and target machine +@cindex compiler version, specifying +@cindex target machine, specifying +The usual way to run GCC is to run the executable called @command{gcc}, or +@command{@var{machine}-gcc} when cross-compiling, or +@command{@var{machine}-gcc-@var{version}} to run a specific version of GCC. +When you compile C++ programs, you should invoke GCC as @command{g++} +instead. @xref{Invoking G++,,Compiling C++ Programs}, +for information about the differences in behavior between @command{gcc} +and @command{g++} when compiling C++ programs. + +@cindex grouping options +@cindex options, grouping +The @command{gcc} program accepts options and file names as operands. Many +options have multi-letter names; therefore multiple single-letter options +may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d +-v}}. + +@cindex order of options +@cindex options, order +You can mix options and other arguments. For the most part, the order +you use doesn't matter. Order does matter when you use several +options of the same kind; for example, if you specify @option{-L} more +than once, the directories are searched in the order specified. Also, +the placement of the @option{-l} option is significant. + +Many options have long names starting with @samp{-f} or with +@samp{-W}---for example, +@option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of +these have both positive and negative forms; the negative form of +@option{-ffoo} is @option{-fno-foo}. This manual documents +only one of these two forms, whichever one is not the default. + +Some options take one or more arguments typically separated either +by a space or by the equals sign (@samp{=}) from the option name. +Unless documented otherwise, an argument can be either numeric or +a string. Numeric arguments must typically be small unsigned decimal +or hexadecimal integers. Hexadecimal arguments must begin with +the @samp{0x} prefix. Arguments to options that specify a size +threshold of some sort may be arbitrarily large decimal or hexadecimal +integers followed by a byte size suffix designating a multiple of bytes +such as @code{kB} and @code{KiB} for kilobyte and kibibyte, respectively, +@code{MB} and @code{MiB} for megabyte and mebibyte, @code{GB} and +@code{GiB} for gigabyte and gigibyte, and so on. Such arguments are +designated by @var{byte-size} in the following text. Refer to the NIST, +IEC, and other relevant national and international standards for the full +listing and explanation of the binary and decimal byte size prefixes. + +@c man end + +@xref{Option Index}, for an index to GCC's options. + +@menu +* Option Summary:: Brief list of all options, without explanations. +* Overall Options:: Controlling the kind of output: + an executable, object files, assembler files, + or preprocessed source. +* Invoking G++:: Compiling C++ programs. +* C Dialect Options:: Controlling the variant of C language compiled. +* C++ Dialect Options:: Variations on C++. +* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C + and Objective-C++. +* Diagnostic Message Formatting Options:: Controlling how diagnostics should + be formatted. +* Warning Options:: How picky should the compiler be? +* Static Analyzer Options:: More expensive warnings. +* Debugging Options:: Producing debuggable code. +* Optimize Options:: How much optimization? +* Instrumentation Options:: Enabling profiling and extra run-time error checking. +* Preprocessor Options:: Controlling header files and macro definitions. + Also, getting dependency information for Make. +* Assembler Options:: Passing options to the assembler. +* Link Options:: Specifying libraries and so on. +* Directory Options:: Where to find header files and libraries. + Where to find the compiler executable files. +* Code Gen Options:: Specifying conventions for function calls, data layout + and register usage. +* Developer Options:: Printing GCC configuration info, statistics, and + debugging dumps. +* Submodel Options:: Target-specific options, such as compiling for a + specific processor variant. +* Spec Files:: How to pass switches to sub-processes. +* Environment Variables:: Env vars that affect GCC. +* Precompiled Headers:: Compiling a header once, and using it many times. +* C++ Modules:: Experimental C++20 module system. +@end menu + +@c man begin OPTIONS + +@node Option Summary +@section Option Summary + +Here is a summary of all the options, grouped by type. Explanations are +in the following sections. + +@table @emph +@item Overall Options +@xref{Overall Options,,Options Controlling the Kind of Output}. +@gccoptlist{-c -S -E -o @var{file} @gol +-dumpbase @var{dumpbase} -dumpbase-ext @var{auxdropsuf} @gol +-dumpdir @var{dumppfx} -x @var{language} @gol +-v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help --version @gol +-pass-exit-codes -pipe -specs=@var{file} -wrapper @gol +@@@var{file} -ffile-prefix-map=@var{old}=@var{new} @gol +-fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol +-fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{unit} -fdump-go-spec=@var{file}} + +@item C Language Options +@xref{C Dialect Options,,Options Controlling C Dialect}. +@gccoptlist{-ansi -std=@var{standard} -aux-info @var{filename} @gol +-fno-asm @gol +-fno-builtin -fno-builtin-@var{function} -fcond-mismatch @gol +-ffreestanding -fgimple -fgnu-tm -fgnu89-inline -fhosted @gol +-flax-vector-conversions -fms-extensions @gol +-foffload=@var{arg} -foffload-options=@var{arg} @gol +-fopenacc -fopenacc-dim=@var{geom} @gol +-fopenmp -fopenmp-simd @gol +-fpermitted-flt-eval-methods=@var{standard} @gol +-fplan9-extensions -fsigned-bitfields -funsigned-bitfields @gol +-fsigned-char -funsigned-char -fstrict-flex-arrays[=@var{n}] @gol +-fsso-struct=@var{endianness}} + +@item C++ Language Options +@xref{C++ Dialect Options,,Options Controlling C++ Dialect}. +@gccoptlist{-fabi-version=@var{n} -fno-access-control @gol +-faligned-new=@var{n} -fargs-in-order=@var{n} -fchar8_t -fcheck-new @gol +-fconstexpr-depth=@var{n} -fconstexpr-cache-depth=@var{n} @gol +-fconstexpr-loop-limit=@var{n} -fconstexpr-ops-limit=@var{n} @gol +-fno-elide-constructors @gol +-fno-enforce-eh-specs @gol +-fno-gnu-keywords @gol +-fno-implicit-templates @gol +-fno-implicit-inline-templates @gol +-fno-implement-inlines @gol +-fmodule-header@r{[}=@var{kind}@r{]} -fmodule-only -fmodules-ts @gol +-fmodule-implicit-inline @gol +-fno-module-lazy @gol +-fmodule-mapper=@var{specification} @gol +-fmodule-version-ignore @gol +-fms-extensions @gol +-fnew-inheriting-ctors @gol +-fnew-ttp-matching @gol +-fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol +-fno-optional-diags -fpermissive @gol +-fno-pretty-templates @gol +-fno-rtti -fsized-deallocation @gol +-ftemplate-backtrace-limit=@var{n} @gol +-ftemplate-depth=@var{n} @gol +-fno-threadsafe-statics -fuse-cxa-atexit @gol +-fno-weak -nostdinc++ @gol +-fvisibility-inlines-hidden @gol +-fvisibility-ms-compat @gol +-fext-numeric-literals @gol +-flang-info-include-translate@r{[}=@var{header}@r{]} @gol +-flang-info-include-translate-not @gol +-flang-info-module-cmi@r{[}=@var{module}@r{]} @gol +-stdlib=@var{libstdc++,libc++} @gol +-Wabi-tag -Wcatch-value -Wcatch-value=@var{n} @gol +-Wno-class-conversion -Wclass-memaccess @gol +-Wcomma-subscript -Wconditionally-supported @gol +-Wno-conversion-null -Wctad-maybe-unsupported @gol +-Wctor-dtor-privacy -Wdangling-reference @gol +-Wno-delete-incomplete @gol +-Wdelete-non-virtual-dtor -Wno-deprecated-array-compare @gol +-Wdeprecated-copy -Wdeprecated-copy-dtor @gol +-Wno-deprecated-enum-enum-conversion -Wno-deprecated-enum-float-conversion @gol +-Weffc++ -Wno-exceptions -Wextra-semi -Wno-inaccessible-base @gol +-Wno-inherited-variadic-ctor -Wno-init-list-lifetime @gol +-Winvalid-imported-macros @gol +-Wno-invalid-offsetof -Wno-literal-suffix @gol +-Wmismatched-new-delete -Wmismatched-tags @gol +-Wmultiple-inheritance -Wnamespaces -Wnarrowing @gol +-Wnoexcept -Wnoexcept-type -Wnon-virtual-dtor @gol +-Wpessimizing-move -Wno-placement-new -Wplacement-new=@var{n} @gol +-Wrange-loop-construct -Wredundant-move -Wredundant-tags @gol +-Wreorder -Wregister @gol +-Wstrict-null-sentinel -Wno-subobject-linkage -Wtemplates @gol +-Wno-non-template-friend -Wold-style-cast @gol +-Woverloaded-virtual -Wno-pmf-conversions -Wself-move -Wsign-promo @gol +-Wsized-deallocation -Wsuggest-final-methods @gol +-Wsuggest-final-types -Wsuggest-override @gol +-Wno-terminate -Wuseless-cast -Wno-vexing-parse @gol +-Wvirtual-inheritance @gol +-Wno-virtual-move-assign -Wvolatile -Wzero-as-null-pointer-constant} + +@item Objective-C and Objective-C++ Language Options +@xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling +Objective-C and Objective-C++ Dialects}. +@gccoptlist{-fconstant-string-class=@var{class-name} @gol +-fgnu-runtime -fnext-runtime @gol +-fno-nil-receivers @gol +-fobjc-abi-version=@var{n} @gol +-fobjc-call-cxx-cdtors @gol +-fobjc-direct-dispatch @gol +-fobjc-exceptions @gol +-fobjc-gc @gol +-fobjc-nilcheck @gol +-fobjc-std=objc1 @gol +-fno-local-ivars @gol +-fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} @gol +-freplace-objc-classes @gol +-fzero-link @gol +-gen-decls @gol +-Wassign-intercept -Wno-property-assign-default @gol +-Wno-protocol -Wobjc-root-class -Wselector @gol +-Wstrict-selector-match @gol +-Wundeclared-selector} + +@item Diagnostic Message Formatting Options +@xref{Diagnostic Message Formatting Options,,Options to Control Diagnostic Messages Formatting}. +@gccoptlist{-fmessage-length=@var{n} @gol +-fdiagnostics-plain-output @gol +-fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol +-fdiagnostics-color=@r{[}auto@r{|}never@r{|}always@r{]} @gol +-fdiagnostics-urls=@r{[}auto@r{|}never@r{|}always@r{]} @gol +-fdiagnostics-format=@r{[}text@r{|}sarif-stderr@r{|}sarif-file@r{|}json@r{|}json-stderr@r{|}json-file@r{]} @gol +-fno-diagnostics-show-option -fno-diagnostics-show-caret @gol +-fno-diagnostics-show-labels -fno-diagnostics-show-line-numbers @gol +-fno-diagnostics-show-cwe @gol +-fno-diagnostics-show-rule @gol +-fdiagnostics-minimum-margin-width=@var{width} @gol +-fdiagnostics-parseable-fixits -fdiagnostics-generate-patch @gol +-fdiagnostics-show-template-tree -fno-elide-type @gol +-fdiagnostics-path-format=@r{[}none@r{|}separate-events@r{|}inline-events@r{]} @gol +-fdiagnostics-show-path-depths @gol +-fno-show-column @gol +-fdiagnostics-column-unit=@r{[}display@r{|}byte@r{]} @gol +-fdiagnostics-column-origin=@var{origin} @gol +-fdiagnostics-escape-format=@r{[}unicode@r{|}bytes@r{]}} + +@item Warning Options +@xref{Warning Options,,Options to Request or Suppress Warnings}. +@gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol +-pedantic-errors @gol +-w -Wextra -Wall -Wabi=@var{n} @gol +-Waddress -Wno-address-of-packed-member -Waggregate-return @gol +-Walloc-size-larger-than=@var{byte-size} -Walloc-zero @gol +-Walloca -Walloca-larger-than=@var{byte-size} @gol +-Wno-aggressive-loop-optimizations @gol +-Warith-conversion @gol +-Warray-bounds -Warray-bounds=@var{n} -Warray-compare @gol +-Wno-attributes -Wattribute-alias=@var{n} -Wno-attribute-alias @gol +-Wno-attribute-warning @gol +-Wbidi-chars=@r{[}none@r{|}unpaired@r{|}any@r{|}ucn@r{]} @gol +-Wbool-compare -Wbool-operation @gol +-Wno-builtin-declaration-mismatch @gol +-Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat @gol +-Wc11-c2x-compat @gol +-Wc++-compat -Wc++11-compat -Wc++14-compat -Wc++17-compat @gol +-Wc++20-compat @gol +-Wno-c++11-extensions -Wno-c++14-extensions -Wno-c++17-extensions @gol +-Wno-c++20-extensions -Wno-c++23-extensions @gol +-Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual @gol +-Wchar-subscripts @gol +-Wclobbered -Wcomment @gol +-Wconversion -Wno-coverage-mismatch -Wno-cpp @gol +-Wdangling-else -Wdangling-pointer -Wdangling-pointer=@var{n} @gol +-Wdate-time @gol +-Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init @gol +-Wdisabled-optimization @gol +-Wno-discarded-array-qualifiers -Wno-discarded-qualifiers @gol +-Wno-div-by-zero -Wdouble-promotion @gol +-Wduplicated-branches -Wduplicated-cond @gol +-Wempty-body -Wno-endif-labels -Wenum-compare -Wenum-conversion @gol +-Wenum-int-mismatch @gol +-Werror -Werror=* -Wexpansion-to-defined -Wfatal-errors @gol +-Wfloat-conversion -Wfloat-equal -Wformat -Wformat=2 @gol +-Wno-format-contains-nul -Wno-format-extra-args @gol +-Wformat-nonliteral -Wformat-overflow=@var{n} @gol +-Wformat-security -Wformat-signedness -Wformat-truncation=@var{n} @gol +-Wformat-y2k -Wframe-address @gol +-Wframe-larger-than=@var{byte-size} -Wno-free-nonheap-object @gol +-Wno-if-not-aligned -Wno-ignored-attributes @gol +-Wignored-qualifiers -Wno-incompatible-pointer-types @gol +-Wimplicit -Wimplicit-fallthrough -Wimplicit-fallthrough=@var{n} @gol +-Wno-implicit-function-declaration -Wno-implicit-int @gol +-Winfinite-recursion @gol +-Winit-self -Winline -Wno-int-conversion -Wint-in-bool-context @gol +-Wno-int-to-pointer-cast -Wno-invalid-memory-model @gol +-Winvalid-pch -Winvalid-utf8 -Wno-unicode -Wjump-misses-init @gol +-Wlarger-than=@var{byte-size} -Wlogical-not-parentheses -Wlogical-op @gol +-Wlong-long -Wno-lto-type-mismatch -Wmain -Wmaybe-uninitialized @gol +-Wmemset-elt-size -Wmemset-transposed-args @gol +-Wmisleading-indentation -Wmissing-attributes -Wmissing-braces @gol +-Wmissing-field-initializers -Wmissing-format-attribute @gol +-Wmissing-include-dirs -Wmissing-noreturn -Wno-missing-profile @gol +-Wno-multichar -Wmultistatement-macros -Wnonnull -Wnonnull-compare @gol +-Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} @gol +-Wnull-dereference -Wno-odr @gol +-Wopenacc-parallelism @gol +-Wopenmp-simd @gol +-Wno-overflow -Woverlength-strings -Wno-override-init-side-effects @gol +-Wpacked -Wno-packed-bitfield-compat -Wpacked-not-aligned -Wpadded @gol +-Wparentheses -Wno-pedantic-ms-format @gol +-Wpointer-arith -Wno-pointer-compare -Wno-pointer-to-int-cast @gol +-Wno-pragmas -Wno-prio-ctor-dtor -Wredundant-decls @gol +-Wrestrict -Wno-return-local-addr -Wreturn-type @gol +-Wno-scalar-storage-order -Wsequence-point @gol +-Wshadow -Wshadow=global -Wshadow=local -Wshadow=compatible-local @gol +-Wno-shadow-ivar @gol +-Wno-shift-count-negative -Wno-shift-count-overflow -Wshift-negative-value @gol +-Wno-shift-overflow -Wshift-overflow=@var{n} @gol +-Wsign-compare -Wsign-conversion @gol +-Wno-sizeof-array-argument @gol +-Wsizeof-array-div @gol +-Wsizeof-pointer-div -Wsizeof-pointer-memaccess @gol +-Wstack-protector -Wstack-usage=@var{byte-size} -Wstrict-aliasing @gol +-Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=@var{n} @gol +-Wstring-compare @gol +-Wno-stringop-overflow -Wno-stringop-overread @gol +-Wno-stringop-truncation @gol +-Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}malloc@r{]} @gol +-Wswitch -Wno-switch-bool -Wswitch-default -Wswitch-enum @gol +-Wno-switch-outside-range -Wno-switch-unreachable -Wsync-nand @gol +-Wsystem-headers -Wtautological-compare -Wtrampolines -Wtrigraphs @gol +-Wtrivial-auto-var-init -Wtsan -Wtype-limits -Wundef @gol +-Wuninitialized -Wunknown-pragmas @gol +-Wunsuffixed-float-constants -Wunused @gol +-Wunused-but-set-parameter -Wunused-but-set-variable @gol +-Wunused-const-variable -Wunused-const-variable=@var{n} @gol +-Wunused-function -Wunused-label -Wunused-local-typedefs @gol +-Wunused-macros @gol +-Wunused-parameter -Wno-unused-result @gol +-Wunused-value -Wunused-variable @gol +-Wno-varargs -Wvariadic-macros @gol +-Wvector-operation-performance @gol +-Wvla -Wvla-larger-than=@var{byte-size} -Wno-vla-larger-than @gol +-Wvolatile-register-var -Wwrite-strings @gol +-Wxor-used-as-pow @gol +-Wzero-length-bounds} + +@item Static Analyzer Options +@gccoptlist{ +-fanalyzer @gol +-fanalyzer-call-summaries @gol +-fanalyzer-checker=@var{name} @gol +-fno-analyzer-feasibility @gol +-fanalyzer-fine-grained @gol +-fno-analyzer-state-merge @gol +-fno-analyzer-state-purge @gol +-fanalyzer-transitivity @gol +-fno-analyzer-undo-inlining @gol +-fanalyzer-verbose-edges @gol +-fanalyzer-verbose-state-changes @gol +-fanalyzer-verbosity=@var{level} @gol +-fdump-analyzer @gol +-fdump-analyzer-callgraph @gol +-fdump-analyzer-exploded-graph @gol +-fdump-analyzer-exploded-nodes @gol +-fdump-analyzer-exploded-nodes-2 @gol +-fdump-analyzer-exploded-nodes-3 @gol +-fdump-analyzer-exploded-paths @gol +-fdump-analyzer-feasibility @gol +-fdump-analyzer-json @gol +-fdump-analyzer-state-purge @gol +-fdump-analyzer-stderr @gol +-fdump-analyzer-supergraph @gol +-fdump-analyzer-untracked @gol +-Wno-analyzer-double-fclose @gol +-Wno-analyzer-double-free @gol +-Wno-analyzer-exposure-through-output-file @gol +-Wno-analyzer-exposure-through-uninit-copy @gol +-Wno-analyzer-fd-access-mode-mismatch @gol +-Wno-analyzer-fd-double-close @gol +-Wno-analyzer-fd-leak @gol +-Wno-analyzer-fd-use-after-close @gol +-Wno-analyzer-fd-use-without-check @gol +-Wno-analyzer-file-leak @gol +-Wno-analyzer-free-of-non-heap @gol +-Wno-analyzer-imprecise-fp-arithmetic @gol +-Wno-analyzer-jump-through-null @gol +-Wno-analyzer-malloc-leak @gol +-Wno-analyzer-mismatching-deallocation @gol +-Wno-analyzer-null-argument @gol +-Wno-analyzer-null-dereference @gol +-Wno-analyzer-out-of-bounds @gol +-Wno-analyzer-possible-null-argument @gol +-Wno-analyzer-possible-null-dereference @gol +-Wno-analyzer-putenv-of-auto-var @gol +-Wno-analyzer-shift-count-negative @gol +-Wno-analyzer-shift-count-overflow @gol +-Wno-analyzer-stale-setjmp-buffer @gol +-Wno-analyzer-tainted-allocation-size @gol +-Wno-analyzer-tainted-array-index @gol +-Wno-analyzer-tainted-divisor @gol +-Wno-analyzer-tainted-offset @gol +-Wno-analyzer-tainted-size @gol +-Wanalyzer-too-complex @gol +-Wno-analyzer-unsafe-call-within-signal-handler @gol +-Wno-analyzer-use-after-free @gol +-Wno-analyzer-use-of-pointer-in-stale-stack-frame @gol +-Wno-analyzer-use-of-uninitialized-value @gol +-Wno-analyzer-va-arg-type-mismatch @gol +-Wno-analyzer-va-list-exhausted @gol +-Wno-analyzer-va-list-leak @gol +-Wno-analyzer-va-list-use-after-va-end @gol +-Wno-analyzer-write-to-const @gol +-Wno-analyzer-write-to-string-literal @gol +} + +@item C and Objective-C-only Warning Options +@gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol +-Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol +-Wold-style-declaration -Wold-style-definition @gol +-Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol +-Wdeclaration-after-statement -Wpointer-sign} + +@item Debugging Options +@xref{Debugging Options,,Options for Debugging Your Program}. +@gccoptlist{-g -g@var{level} -gdwarf -gdwarf-@var{version} @gol +-gbtf -gctf -gctf@var{level} @gol +-ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol +-gstrict-dwarf -gno-strict-dwarf @gol +-gas-loc-support -gno-as-loc-support @gol +-gas-locview-support -gno-as-locview-support @gol +-gcolumn-info -gno-column-info -gdwarf32 -gdwarf64 @gol +-gstatement-frontiers -gno-statement-frontiers @gol +-gvariable-location-views -gno-variable-location-views @gol +-ginternal-reset-location-views -gno-internal-reset-location-views @gol +-ginline-points -gno-inline-points @gol +-gvms -gz@r{[}=@var{type}@r{]} @gol +-gsplit-dwarf -gdescribe-dies -gno-describe-dies @gol +-fdebug-prefix-map=@var{old}=@var{new} -fdebug-types-section @gol +-fno-eliminate-unused-debug-types @gol +-femit-struct-debug-baseonly -femit-struct-debug-reduced @gol +-femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol +-fno-eliminate-unused-debug-symbols -femit-class-debug-always @gol +-fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol +-fvar-tracking -fvar-tracking-assignments} + +@item Optimization Options +@xref{Optimize Options,,Options that Control Optimization}. +@gccoptlist{-faggressive-loop-optimizations @gol +-falign-functions[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol +-falign-jumps[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol +-falign-labels[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol +-falign-loops[=@var{n}[:@var{m}:[@var{n2}[:@var{m2}]]]] @gol +-fno-allocation-dce -fallow-store-data-races @gol +-fassociative-math -fauto-profile -fauto-profile[=@var{path}] @gol +-fauto-inc-dec -fbranch-probabilities @gol +-fcaller-saves @gol +-fcombine-stack-adjustments -fconserve-stack @gol +-fcompare-elim -fcprop-registers -fcrossjumping @gol +-fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol +-fcx-limited-range @gol +-fdata-sections -fdce -fdelayed-branch @gol +-fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively @gol +-fdevirtualize-at-ltrans -fdse @gol +-fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol +-ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol +-ffinite-loops @gol +-fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol +-fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol +-fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol +-fif-conversion2 -findirect-inlining @gol +-finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol +-finline-small-functions -fipa-modref -fipa-cp -fipa-cp-clone @gol +-fipa-bit-cp -fipa-vrp -fipa-pta -fipa-profile -fipa-pure-const @gol +-fipa-reference -fipa-reference-addressable @gol +-fipa-stack-alignment -fipa-icf -fira-algorithm=@var{algorithm} @gol +-flive-patching=@var{level} @gol +-fira-region=@var{region} -fira-hoist-pressure @gol +-fira-loop-pressure -fno-ira-share-save-slots @gol +-fno-ira-share-spill-slots @gol +-fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute @gol +-fivopts -fkeep-inline-functions -fkeep-static-functions @gol +-fkeep-static-consts -flimit-function-alignment -flive-range-shrinkage @gol +-floop-block -floop-interchange -floop-strip-mine @gol +-floop-unroll-and-jam -floop-nest-optimize @gol +-floop-parallelize-all -flra-remat -flto -flto-compression-level @gol +-flto-partition=@var{alg} -fmerge-all-constants @gol +-fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol +-fmove-loop-invariants -fmove-loop-stores -fno-branch-count-reg @gol +-fno-defer-pop -fno-fp-int-builtin-inexact -fno-function-cse @gol +-fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole @gol +-fno-peephole2 -fno-printf-return-value -fno-sched-interblock @gol +-fno-sched-spec -fno-signed-zeros @gol +-fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol +-fomit-frame-pointer -foptimize-sibling-calls @gol +-fpartial-inlining -fpeel-loops -fpredictive-commoning @gol +-fprefetch-loop-arrays @gol +-fprofile-correction @gol +-fprofile-use -fprofile-use=@var{path} -fprofile-partial-training @gol +-fprofile-values -fprofile-reorder-functions @gol +-freciprocal-math -free -frename-registers -freorder-blocks @gol +-freorder-blocks-algorithm=@var{algorithm} @gol +-freorder-blocks-and-partition -freorder-functions @gol +-frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol +-frounding-math -fsave-optimization-record @gol +-fsched2-use-superblocks -fsched-pressure @gol +-fsched-spec-load -fsched-spec-load-dangerous @gol +-fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol +-fsched-group-heuristic -fsched-critical-path-heuristic @gol +-fsched-spec-insn-heuristic -fsched-rank-heuristic @gol +-fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol +-fschedule-fusion @gol +-fschedule-insns -fschedule-insns2 -fsection-anchors @gol +-fselective-scheduling -fselective-scheduling2 @gol +-fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol +-fsemantic-interposition -fshrink-wrap -fshrink-wrap-separate @gol +-fsignaling-nans @gol +-fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-loops@gol +-fsplit-paths @gol +-fsplit-wide-types -fsplit-wide-types-early -fssa-backprop -fssa-phiopt @gol +-fstdarg-opt -fstore-merging -fstrict-aliasing -fipa-strict-aliasing @gol +-fthread-jumps -ftracer -ftree-bit-ccp @gol +-ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol +-ftree-coalesce-vars -ftree-copy-prop -ftree-dce -ftree-dominator-opts @gol +-ftree-dse -ftree-forwprop -ftree-fre -fcode-hoisting @gol +-ftree-loop-if-convert -ftree-loop-im @gol +-ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol +-ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol +-ftree-loop-vectorize @gol +-ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol +-ftree-reassoc -ftree-scev-cprop -ftree-sink -ftree-slsr -ftree-sra @gol +-ftree-switch-conversion -ftree-tail-merge @gol +-ftree-ter -ftree-vectorize -ftree-vrp -ftrivial-auto-var-init @gol +-funconstrained-commons -funit-at-a-time -funroll-all-loops @gol +-funroll-loops -funsafe-math-optimizations -funswitch-loops @gol +-fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt @gol +-fweb -fwhole-program -fwpa -fuse-linker-plugin -fzero-call-used-regs @gol +--param @var{name}=@var{value} +-O -O0 -O1 -O2 -O3 -Os -Ofast -Og -Oz} + +@item Program Instrumentation Options +@xref{Instrumentation Options,,Program Instrumentation Options}. +@gccoptlist{-p -pg -fprofile-arcs --coverage -ftest-coverage @gol +-fprofile-abs-path @gol +-fprofile-dir=@var{path} -fprofile-generate -fprofile-generate=@var{path} @gol +-fprofile-info-section -fprofile-info-section=@var{name} @gol +-fprofile-note=@var{path} -fprofile-prefix-path=@var{path} @gol +-fprofile-update=@var{method} -fprofile-filter-files=@var{regex} @gol +-fprofile-exclude-files=@var{regex} @gol +-fprofile-reproducible=@r{[}multithreaded@r{|}parallel-runs@r{|}serial@r{]} @gol +-fsanitize=@var{style} -fsanitize-recover -fsanitize-recover=@var{style} @gol +-fsanitize-trap -fsanitize-trap=@var{style} @gol +-fasan-shadow-offset=@var{number} -fsanitize-sections=@var{s1},@var{s2},... @gol +-fsanitize-undefined-trap-on-error -fbounds-check @gol +-fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{|}check@r{]} @gol +-fharden-compares -fharden-conditional-branches @gol +-fstack-protector -fstack-protector-all -fstack-protector-strong @gol +-fstack-protector-explicit -fstack-check @gol +-fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol +-fno-stack-limit -fsplit-stack @gol +-fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} @gol +-fvtv-counts -fvtv-debug @gol +-finstrument-functions -finstrument-functions-once @gol +-finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol +-finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{}} @gol +-fprofile-prefix-map=@var{old}=@var{new} + +@item Preprocessor Options +@xref{Preprocessor Options,,Options Controlling the Preprocessor}. +@gccoptlist{-A@var{question}=@var{answer} @gol +-A-@var{question}@r{[}=@var{answer}@r{]} @gol +-C -CC -D@var{macro}@r{[}=@var{defn}@r{]} @gol +-dD -dI -dM -dN -dU @gol +-fdebug-cpp -fdirectives-only -fdollars-in-identifiers @gol +-fexec-charset=@var{charset} -fextended-identifiers @gol +-finput-charset=@var{charset} -flarge-source-files @gol +-fmacro-prefix-map=@var{old}=@var{new} -fmax-include-depth=@var{depth} @gol +-fno-canonical-system-headers -fpch-deps -fpch-preprocess @gol +-fpreprocessed -ftabstop=@var{width} -ftrack-macro-expansion @gol +-fwide-exec-charset=@var{charset} -fworking-directory @gol +-H -imacros @var{file} -include @var{file} @gol +-M -MD -MF -MG -MM -MMD -MP -MQ -MT -Mno-modules @gol +-no-integrated-cpp -P -pthread -remap @gol +-traditional -traditional-cpp -trigraphs @gol +-U@var{macro} -undef @gol +-Wp,@var{option} -Xpreprocessor @var{option}} + +@item Assembler Options +@xref{Assembler Options,,Passing Options to the Assembler}. +@gccoptlist{-Wa,@var{option} -Xassembler @var{option}} + +@item Linker Options +@xref{Link Options,,Options for Linking}. +@gccoptlist{@var{object-file-name} -fuse-ld=@var{linker} -l@var{library} @gol +-nostartfiles -nodefaultlibs -nolibc -nostdlib -nostdlib++ @gol +-e @var{entry} --entry=@var{entry} @gol +-pie -pthread -r -rdynamic @gol +-s -static -static-pie -static-libgcc -static-libstdc++ @gol +-static-libasan -static-libtsan -static-liblsan -static-libubsan @gol +-shared -shared-libgcc -symbolic @gol +-T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol +-u @var{symbol} -z @var{keyword}} + +@item Directory Options +@xref{Directory Options,,Options for Directory Search}. +@gccoptlist{-B@var{prefix} -I@var{dir} -I- @gol +-idirafter @var{dir} @gol +-imacros @var{file} -imultilib @var{dir} @gol +-iplugindir=@var{dir} -iprefix @var{file} @gol +-iquote @var{dir} -isysroot @var{dir} -isystem @var{dir} @gol +-iwithprefix @var{dir} -iwithprefixbefore @var{dir} @gol +-L@var{dir} -no-canonical-prefixes --no-sysroot-suffix @gol +-nostdinc -nostdinc++ --sysroot=@var{dir}} + +@item Code Generation Options +@xref{Code Gen Options,,Options for Code Generation Conventions}. +@gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol +-ffixed-@var{reg} -fexceptions @gol +-fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol +-fasynchronous-unwind-tables @gol +-fno-gnu-unique @gol +-finhibit-size-directive -fcommon -fno-ident @gol +-fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt @gol +-fno-jump-tables -fno-bit-tests @gol +-frecord-gcc-switches @gol +-freg-struct-return -fshort-enums -fshort-wchar @gol +-fverbose-asm -fpack-struct[=@var{n}] @gol +-fleading-underscore -ftls-model=@var{model} @gol +-fstack-reuse=@var{reuse_level} @gol +-ftrampolines -ftrapv -fwrapv @gol +-fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} @gol +-fstrict-volatile-bitfields -fsync-libcalls} + +@item Developer Options +@xref{Developer Options,,GCC Developer Options}. +@gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol +-dumpfullversion -fcallgraph-info@r{[}=su,da@r{]} +-fchecking -fchecking=@var{n} +-fdbg-cnt-list @gol -fdbg-cnt=@var{counter-value-list} @gol +-fdisable-ipa-@var{pass_name} @gol +-fdisable-rtl-@var{pass_name} @gol +-fdisable-rtl-@var{pass-name}=@var{range-list} @gol +-fdisable-tree-@var{pass_name} @gol +-fdisable-tree-@var{pass-name}=@var{range-list} @gol +-fdump-debug -fdump-earlydebug @gol +-fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol +-fdump-final-insns@r{[}=@var{file}@r{]} @gol +-fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol +-fdump-lang-all @gol +-fdump-lang-@var{switch} @gol +-fdump-lang-@var{switch}-@var{options} @gol +-fdump-lang-@var{switch}-@var{options}=@var{filename} @gol +-fdump-passes @gol +-fdump-rtl-@var{pass} -fdump-rtl-@var{pass}=@var{filename} @gol +-fdump-statistics @gol +-fdump-tree-all @gol +-fdump-tree-@var{switch} @gol +-fdump-tree-@var{switch}-@var{options} @gol +-fdump-tree-@var{switch}-@var{options}=@var{filename} @gol +-fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol +-fenable-@var{kind}-@var{pass} @gol +-fenable-@var{kind}-@var{pass}=@var{range-list} @gol +-fira-verbose=@var{n} @gol +-flto-report -flto-report-wpa -fmem-report-wpa @gol +-fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report @gol +-fopt-info -fopt-info-@var{options}@r{[}=@var{file}@r{]} @gol +-fmultiflags -fprofile-report @gol +-frandom-seed=@var{string} -fsched-verbose=@var{n} @gol +-fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol +-fstats -fstack-usage -ftime-report -ftime-report-details @gol +-fvar-tracking-assignments-toggle -gtoggle @gol +-print-file-name=@var{library} -print-libgcc-file-name @gol +-print-multi-directory -print-multi-lib -print-multi-os-directory @gol +-print-prog-name=@var{program} -print-search-dirs -Q @gol +-print-sysroot -print-sysroot-headers-suffix @gol +-save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}} + +@item Machine-Dependent Options +@xref{Submodel Options,,Machine-Dependent Options}. +@c This list is ordered alphanumerically by subsection name. +@c Try and put the significant identifier (CPU or system) first, +@c so users have a clue at guessing where the ones they want will be. + +@emph{AArch64 Options} +@gccoptlist{-mabi=@var{name} -mbig-endian -mlittle-endian @gol +-mgeneral-regs-only @gol +-mcmodel=tiny -mcmodel=small -mcmodel=large @gol +-mstrict-align -mno-strict-align @gol +-momit-leaf-frame-pointer @gol +-mtls-dialect=desc -mtls-dialect=traditional @gol +-mtls-size=@var{size} @gol +-mfix-cortex-a53-835769 -mfix-cortex-a53-843419 @gol +-mlow-precision-recip-sqrt -mlow-precision-sqrt -mlow-precision-div @gol +-mpc-relative-literal-loads @gol +-msign-return-address=@var{scope} @gol +-mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf} ++@var{b-key}]|@var{bti} @gol +-mharden-sls=@var{opts} @gol +-march=@var{name} -mcpu=@var{name} -mtune=@var{name} @gol +-moverride=@var{string} -mverbose-cost-dump @gol +-mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{sysreg} @gol +-mstack-protector-guard-offset=@var{offset} -mtrack-speculation @gol +-moutline-atomics } + +@emph{Adapteva Epiphany Options} +@gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol +-mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol +-msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol +-mround-nearest -mlong-calls -mshort-calls -msmall16 @gol +-mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol +-msplit-vecmove-early -m1reg-@var{reg}} + +@emph{AMD GCN Options} +@gccoptlist{-march=@var{gpu} -mtune=@var{gpu} -mstack-size=@var{bytes}} + +@emph{ARC Options} +@gccoptlist{-mbarrel-shifter -mjli-always @gol +-mcpu=@var{cpu} -mA6 -mARC600 -mA7 -mARC700 @gol +-mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr @gol +-mea -mno-mpy -mmul32x16 -mmul64 -matomic @gol +-mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap @gol +-mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape @gol +-mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof @gol +-mlong-calls -mmedium-calls -msdata -mirq-ctrl-saved @gol +-mrgf-banked-regs -mlpc-width=@var{width} -G @var{num} @gol +-mvolatile-cache -mtp-regno=@var{regno} @gol +-malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc @gol +-mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi @gol +-mexpand-adddi -mindexed-loads -mlra -mlra-priority-none @gol +-mlra-priority-compact -mlra-priority-noncompact -mmillicode @gol +-mmixed-code -mq-class -mRcq -mRcw -msize-level=@var{level} @gol +-mtune=@var{cpu} -mmultcost=@var{num} -mcode-density-frame @gol +-munalign-prob-threshold=@var{probability} -mmpy-option=@var{multo} @gol +-mdiv-rem -mcode-density -mll64 -mfpu=@var{fpu} -mrf16 -mbranch-index} + +@emph{ARM Options} +@gccoptlist{-mapcs-frame -mno-apcs-frame @gol +-mabi=@var{name} @gol +-mapcs-stack-check -mno-apcs-stack-check @gol +-mapcs-reentrant -mno-apcs-reentrant @gol +-mgeneral-regs-only @gol +-msched-prolog -mno-sched-prolog @gol +-mlittle-endian -mbig-endian @gol +-mbe8 -mbe32 @gol +-mfloat-abi=@var{name} @gol +-mfp16-format=@var{name} +-mthumb-interwork -mno-thumb-interwork @gol +-mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol +-mtune=@var{name} -mprint-tune-info @gol +-mstructure-size-boundary=@var{n} @gol +-mabort-on-noreturn @gol +-mlong-calls -mno-long-calls @gol +-msingle-pic-base -mno-single-pic-base @gol +-mpic-register=@var{reg} @gol +-mnop-fun-dllimport @gol +-mpoke-function-name @gol +-mthumb -marm -mflip-thumb @gol +-mtpcs-frame -mtpcs-leaf-frame @gol +-mcaller-super-interworking -mcallee-super-interworking @gol +-mtp=@var{name} -mtls-dialect=@var{dialect} @gol +-mword-relocations @gol +-mfix-cortex-m3-ldrd @gol +-mfix-cortex-a57-aes-1742098 @gol +-mfix-cortex-a72-aes-1655431 @gol +-munaligned-access @gol +-mneon-for-64bits @gol +-mslow-flash-data @gol +-masm-syntax-unified @gol +-mrestrict-it @gol +-mverbose-cost-dump @gol +-mpure-code @gol +-mcmse @gol +-mfix-cmse-cve-2021-35465 @gol +-mstack-protector-guard=@var{guard} -mstack-protector-guard-offset=@var{offset} @gol +-mfdpic} + +@emph{AVR Options} +@gccoptlist{-mmcu=@var{mcu} -mabsdata -maccumulate-args @gol +-mbranch-cost=@var{cost} @gol +-mcall-prologues -mgas-isr-prologues -mint8 @gol +-mdouble=@var{bits} -mlong-double=@var{bits} @gol +-mn_flash=@var{size} -mno-interrupts @gol +-mmain-is-OS_task -mrelax -mrmw -mstrict-X -mtiny-stack @gol +-mfract-convert-truncate @gol +-mshort-calls -nodevicelib -nodevicespecs @gol +-Waddr-space-convert -Wmisspelled-isr} + +@emph{Blackfin Options} +@gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol +-msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol +-mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol +-mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol +-mno-id-shared-library -mshared-library-id=@var{n} @gol +-mleaf-id-shared-library -mno-leaf-id-shared-library @gol +-msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol +-mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol +-micplb} + +@emph{C6X Options} +@gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol +-msim -msdata=@var{sdata-type}} + +@emph{CRIS Options} +@gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} +-mtune=@var{cpu} -mmax-stack-frame=@var{n} @gol +-metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol +-mstack-align -mdata-align -mconst-align @gol +-m32-bit -m16-bit -m8-bit -mno-prologue-epilogue @gol +-melf -maout -sim -sim2 @gol +-mmul-bug-workaround -mno-mul-bug-workaround} + +@emph{C-SKY Options} +@gccoptlist{-march=@var{arch} -mcpu=@var{cpu} @gol +-mbig-endian -EB -mlittle-endian -EL @gol +-mhard-float -msoft-float -mfpu=@var{fpu} -mdouble-float -mfdivdu @gol +-mfloat-abi=@var{name} @gol +-melrw -mistack -mmp -mcp -mcache -msecurity -mtrust @gol +-mdsp -medsp -mvdsp @gol +-mdiv -msmart -mhigh-registers -manchor @gol +-mpushpop -mmultiple-stld -mconstpool -mstack-size -mccrt @gol +-mbranch-cost=@var{n} -mcse-cc -msched-prolog -msim} + +@emph{Darwin Options} +@gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol +-arch_only -bind_at_load -bundle -bundle_loader @gol +-client_name -compatibility_version -current_version @gol +-dead_strip @gol +-dependency-file -dylib_file -dylinker_install_name @gol +-dynamic -dynamiclib -exported_symbols_list @gol +-filelist -flat_namespace -force_cpusubtype_ALL @gol +-force_flat_namespace -headerpad_max_install_names @gol +-iframework @gol +-image_base -init -install_name -keep_private_externs @gol +-multi_module -multiply_defined -multiply_defined_unused @gol +-noall_load -no_dead_strip_inits_and_terms @gol +-nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol +-pagezero_size -prebind -prebind_all_twolevel_modules @gol +-private_bundle -read_only_relocs -sectalign @gol +-sectobjectsymbols -whyload -seg1addr @gol +-sectcreate -sectobjectsymbols -sectorder @gol +-segaddr -segs_read_only_addr -segs_read_write_addr @gol +-seg_addr_table -seg_addr_table_filename -seglinkedit @gol +-segprot -segs_read_only_addr -segs_read_write_addr @gol +-single_module -static -sub_library -sub_umbrella @gol +-twolevel_namespace -umbrella -undefined @gol +-unexported_symbols_list -weak_reference_mismatches @gol +-whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol +-mkernel -mone-byte-bool} + +@emph{DEC Alpha Options} +@gccoptlist{-mno-fp-regs -msoft-float @gol +-mieee -mieee-with-inexact -mieee-conformant @gol +-mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol +-mtrap-precision=@var{mode} -mbuild-constants @gol +-mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol +-mbwx -mmax -mfix -mcix @gol +-mfloat-vax -mfloat-ieee @gol +-mexplicit-relocs -msmall-data -mlarge-data @gol +-msmall-text -mlarge-text @gol +-mmemory-latency=@var{time}} + +@emph{eBPF Options} +@gccoptlist{-mbig-endian -mlittle-endian -mkernel=@var{version} +-mframe-limit=@var{bytes} -mxbpf -mco-re -mno-co-re +-mjmpext -mjmp32 -malu32 -mcpu=@var{version}} + +@emph{FR30 Options} +@gccoptlist{-msmall-model -mno-lsim} + +@emph{FT32 Options} +@gccoptlist{-msim -mlra -mnodiv -mft32b -mcompress -mnopm} + +@emph{FRV Options} +@gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol +-mhard-float -msoft-float @gol +-malloc-cc -mfixed-cc -mdword -mno-dword @gol +-mdouble -mno-double @gol +-mmedia -mno-media -mmuladd -mno-muladd @gol +-mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol +-mlinked-fp -mlong-calls -malign-labels @gol +-mlibrary-pic -macc-4 -macc-8 @gol +-mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol +-moptimize-membar -mno-optimize-membar @gol +-mscc -mno-scc -mcond-exec -mno-cond-exec @gol +-mvliw-branch -mno-vliw-branch @gol +-mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol +-mno-nested-cond-exec -mtomcat-stats @gol +-mTLS -mtls @gol +-mcpu=@var{cpu}} + +@emph{GNU/Linux Options} +@gccoptlist{-mglibc -muclibc -mmusl -mbionic -mandroid @gol +-tno-android-cc -tno-android-ld} + +@emph{H8/300 Options} +@gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300} + +@emph{HPPA Options} +@gccoptlist{-march=@var{architecture-type} @gol +-mcaller-copies -mdisable-fpregs -mdisable-indexing @gol +-mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol +-mfixed-range=@var{register-range} @gol +-mjump-in-delay -mlinker-opt -mlong-calls @gol +-mlong-load-store -mno-disable-fpregs @gol +-mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol +-mno-jump-in-delay -mno-long-load-store @gol +-mno-portable-runtime -mno-soft-float @gol +-mno-space-regs -msoft-float -mpa-risc-1-0 @gol +-mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol +-mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol +-munix=@var{unix-std} -nolibdld -static -threads} + +@emph{IA-64 Options} +@gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol +-mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol +-mconstant-gp -mauto-pic -mfused-madd @gol +-minline-float-divide-min-latency @gol +-minline-float-divide-max-throughput @gol +-mno-inline-float-divide @gol +-minline-int-divide-min-latency @gol +-minline-int-divide-max-throughput @gol +-mno-inline-int-divide @gol +-minline-sqrt-min-latency -minline-sqrt-max-throughput @gol +-mno-inline-sqrt @gol +-mdwarf2-asm -mearly-stop-bits @gol +-mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol +-mtune=@var{cpu-type} -milp32 -mlp64 @gol +-msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol +-msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol +-msched-spec-ldc -msched-spec-control-ldc @gol +-msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol +-msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol +-msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol +-msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}} + +@emph{LM32 Options} +@gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol +-msign-extend-enabled -muser-enabled} + +@emph{LoongArch Options} +@gccoptlist{-march=@var{cpu-type} -mtune=@var{cpu-type} -mabi=@var{base-abi-type} @gol +-mfpu=@var{fpu-type} -msoft-float -msingle-float -mdouble-float @gol +-mbranch-cost=@var{n} -mcheck-zero-division -mno-check-zero-division @gol +-mcond-move-int -mno-cond-move-int @gol +-mcond-move-float -mno-cond-move-float @gol +-memcpy -mno-memcpy -mstrict-align -mno-strict-align @gol +-mmax-inline-memcpy-size=@var{n} @gol +-mexplicit-relocs -mno-explicit-relocs @gol +-mdirect-extern-access -mno-direct-extern-access @gol +-mcmodel=@var{code-model}} + +@emph{M32R/D Options} +@gccoptlist{-m32r2 -m32rx -m32r @gol +-mdebug @gol +-malign-loops -mno-align-loops @gol +-missue-rate=@var{number} @gol +-mbranch-cost=@var{number} @gol +-mmodel=@var{code-size-model-type} @gol +-msdata=@var{sdata-type} @gol +-mno-flush-func -mflush-func=@var{name} @gol +-mno-flush-trap -mflush-trap=@var{number} @gol +-G @var{num}} + +@emph{M32C Options} +@gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} + +@emph{M680x0 Options} +@gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} @gol +-m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol +-m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol +-mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol +-mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol +-mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol +-malign-int -mstrict-align -msep-data -mno-sep-data @gol +-mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol +-mxgot -mno-xgot -mlong-jump-table-offsets} + +@emph{MCore Options} +@gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol +-mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol +-m4byte-functions -mno-4byte-functions -mcallgraph-data @gol +-mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol +-mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} + +@emph{MeP Options} +@gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol +-mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol +-mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol +-mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol +-mtiny=@var{n}} + +@emph{MicroBlaze Options} +@gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol +-mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol +-mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol +-mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol +-mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-@var{app-model} @gol +-mpic-data-is-text-relative} + +@emph{MIPS Options} +@gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol +-mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 @gol +-mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 @gol +-mips16 -mno-mips16 -mflip-mips16 @gol +-minterlink-compressed -mno-interlink-compressed @gol +-minterlink-mips16 -mno-interlink-mips16 @gol +-mabi=@var{abi} -mabicalls -mno-abicalls @gol +-mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol +-mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float @gol +-mno-float -msingle-float -mdouble-float @gol +-modd-spreg -mno-odd-spreg @gol +-mabs=@var{mode} -mnan=@var{encoding} @gol +-mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol +-mmcu -mmno-mcu @gol +-meva -mno-eva @gol +-mvirt -mno-virt @gol +-mxpa -mno-xpa @gol +-mcrc -mno-crc @gol +-mginv -mno-ginv @gol +-mmicromips -mno-micromips @gol +-mmsa -mno-msa @gol +-mloongson-mmi -mno-loongson-mmi @gol +-mloongson-ext -mno-loongson-ext @gol +-mloongson-ext2 -mno-loongson-ext2 @gol +-mfpu=@var{fpu-type} @gol +-msmartmips -mno-smartmips @gol +-mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol +-mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol +-mlong64 -mlong32 -msym32 -mno-sym32 @gol +-G@var{num} -mlocal-sdata -mno-local-sdata @gol +-mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol +-membedded-data -mno-embedded-data @gol +-muninit-const-in-rodata -mno-uninit-const-in-rodata @gol +-mcode-readable=@var{setting} @gol +-msplit-addresses -mno-split-addresses @gol +-mexplicit-relocs -mno-explicit-relocs @gol +-mcheck-zero-division -mno-check-zero-division @gol +-mdivide-traps -mdivide-breaks @gol +-mload-store-pairs -mno-load-store-pairs @gol +-munaligned-access -mno-unaligned-access @gol +-mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol +-mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp @gol +-mfix-24k -mno-fix-24k @gol +-mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol +-mfix-r5900 -mno-fix-r5900 @gol +-mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 @gol +-mfix-vr4120 -mno-fix-vr4120 @gol +-mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol +-mflush-func=@var{func} -mno-flush-func @gol +-mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol +-mcompact-branches=@var{policy} @gol +-mfp-exceptions -mno-fp-exceptions @gol +-mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol +-mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4 @gol +-mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address @gol +-mframe-header-opt -mno-frame-header-opt} + +@emph{MMIX Options} +@gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol +-mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol +-melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol +-mno-base-addresses -msingle-exit -mno-single-exit} + +@emph{MN10300 Options} +@gccoptlist{-mmult-bug -mno-mult-bug @gol +-mno-am33 -mam33 -mam33-2 -mam34 @gol +-mtune=@var{cpu-type} @gol +-mreturn-pointer-on-d0 @gol +-mno-crt0 -mrelax -mliw -msetlb} + +@emph{Moxie Options} +@gccoptlist{-meb -mel -mmul.x -mno-crt0} + +@emph{MSP430 Options} +@gccoptlist{-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax @gol +-mwarn-mcu @gol +-mcode-region= -mdata-region= @gol +-msilicon-errata= -msilicon-errata-warn= @gol +-mhwmult= -minrt -mtiny-printf -mmax-inline-shift=} + +@emph{NDS32 Options} +@gccoptlist{-mbig-endian -mlittle-endian @gol +-mreduced-regs -mfull-regs @gol +-mcmov -mno-cmov @gol +-mext-perf -mno-ext-perf @gol +-mext-perf2 -mno-ext-perf2 @gol +-mext-string -mno-ext-string @gol +-mv3push -mno-v3push @gol +-m16bit -mno-16bit @gol +-misr-vector-size=@var{num} @gol +-mcache-block-size=@var{num} @gol +-march=@var{arch} @gol +-mcmodel=@var{code-model} @gol +-mctor-dtor -mrelax} + +@emph{Nios II Options} +@gccoptlist{-G @var{num} -mgpopt=@var{option} -mgpopt -mno-gpopt @gol +-mgprel-sec=@var{regexp} -mr0rel-sec=@var{regexp} @gol +-mel -meb @gol +-mno-bypass-cache -mbypass-cache @gol +-mno-cache-volatile -mcache-volatile @gol +-mno-fast-sw-div -mfast-sw-div @gol +-mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div @gol +-mcustom-@var{insn}=@var{N} -mno-custom-@var{insn} @gol +-mcustom-fpu-cfg=@var{name} @gol +-mhal -msmallc -msys-crt0=@var{name} -msys-lib=@var{name} @gol +-march=@var{arch} -mbmx -mno-bmx -mcdx -mno-cdx} + +@emph{Nvidia PTX Options} +@gccoptlist{-m64 -mmainkernel -moptimize} + +@emph{OpenRISC Options} +@gccoptlist{-mboard=@var{name} -mnewlib -mhard-mul -mhard-div @gol +-msoft-mul -msoft-div @gol +-msoft-float -mhard-float -mdouble-float -munordered-float @gol +-mcmov -mror -mrori -msext -msfimm -mshftimm @gol +-mcmodel=@var{code-model}} + +@emph{PDP-11 Options} +@gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol +-mint32 -mno-int16 -mint16 -mno-int32 @gol +-msplit -munix-asm -mdec-asm -mgnu-asm -mlra} + +@emph{picoChip Options} +@gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol +-msymbol-as-address -mno-inefficient-warnings} + +@emph{PowerPC Options} +See RS/6000 and PowerPC Options. + +@emph{PRU Options} +@gccoptlist{-mmcu=@var{mcu} -minrt -mno-relax -mloop @gol +-mabi=@var{variant} @gol} + +@emph{RISC-V Options} +@gccoptlist{-mbranch-cost=@var{N-instruction} @gol +-mplt -mno-plt @gol +-mabi=@var{ABI-string} @gol +-mfdiv -mno-fdiv @gol +-mdiv -mno-div @gol +-misa-spec=@var{ISA-spec-string} @gol +-march=@var{ISA-string} @gol +-mtune=@var{processor-string} @gol +-mpreferred-stack-boundary=@var{num} @gol +-msmall-data-limit=@var{N-bytes} @gol +-msave-restore -mno-save-restore @gol +-mshorten-memrefs -mno-shorten-memrefs @gol +-mstrict-align -mno-strict-align @gol +-mcmodel=medlow -mcmodel=medany @gol +-mexplicit-relocs -mno-explicit-relocs @gol +-mrelax -mno-relax @gol +-mriscv-attribute -mno-riscv-attribute @gol +-malign-data=@var{type} @gol +-mbig-endian -mlittle-endian @gol +-mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol +-mstack-protector-guard-offset=@var{offset}} +-mcsr-check -mno-csr-check @gol + +@emph{RL78 Options} +@gccoptlist{-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs @gol +-mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 @gol +-m64bit-doubles -m32bit-doubles -msave-mduc-in-interrupts} + +@emph{RS/6000 and PowerPC Options} +@gccoptlist{-mcpu=@var{cpu-type} @gol +-mtune=@var{cpu-type} @gol +-mcmodel=@var{code-model} @gol +-mpowerpc64 @gol +-maltivec -mno-altivec @gol +-mpowerpc-gpopt -mno-powerpc-gpopt @gol +-mpowerpc-gfxopt -mno-powerpc-gfxopt @gol +-mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol +-mfprnd -mno-fprnd @gol +-mcmpb -mno-cmpb -mhard-dfp -mno-hard-dfp @gol +-mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol +-m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol +-malign-power -malign-natural @gol +-msoft-float -mhard-float -mmultiple -mno-multiple @gol +-mupdate -mno-update @gol +-mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol +-mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol +-mstrict-align -mno-strict-align -mrelocatable @gol +-mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol +-mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol +-mdynamic-no-pic -mswdiv -msingle-pic-base @gol +-mprioritize-restricted-insns=@var{priority} @gol +-msched-costly-dep=@var{dependence_type} @gol +-minsert-sched-nops=@var{scheme} @gol +-mcall-aixdesc -mcall-eabi -mcall-freebsd @gol +-mcall-linux -mcall-netbsd -mcall-openbsd @gol +-mcall-sysv -mcall-sysv-eabi -mcall-sysv-noeabi @gol +-mtraceback=@var{traceback_type} @gol +-maix-struct-return -msvr4-struct-return @gol +-mabi=@var{abi-type} -msecure-plt -mbss-plt @gol +-mlongcall -mno-longcall -mpltseq -mno-pltseq @gol +-mblock-move-inline-limit=@var{num} @gol +-mblock-compare-inline-limit=@var{num} @gol +-mblock-compare-inline-loop-limit=@var{num} @gol +-mno-block-ops-unaligned-vsx @gol +-mstring-compare-inline-limit=@var{num} @gol +-misel -mno-isel @gol +-mvrsave -mno-vrsave @gol +-mmulhw -mno-mulhw @gol +-mdlmzb -mno-dlmzb @gol +-mprototype -mno-prototype @gol +-msim -mmvme -mads -myellowknife -memb -msdata @gol +-msdata=@var{opt} -mreadonly-in-sdata -mvxworks -G @var{num} @gol +-mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol +-mno-recip-precision @gol +-mveclibabi=@var{type} -mfriz -mno-friz @gol +-mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol +-msave-toc-indirect -mno-save-toc-indirect @gol +-mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector @gol +-mcrypto -mno-crypto -mhtm -mno-htm @gol +-mquad-memory -mno-quad-memory @gol +-mquad-memory-atomic -mno-quad-memory-atomic @gol +-mcompat-align-parm -mno-compat-align-parm @gol +-mfloat128 -mno-float128 -mfloat128-hardware -mno-float128-hardware @gol +-mgnu-attribute -mno-gnu-attribute @gol +-mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{reg} @gol +-mstack-protector-guard-offset=@var{offset} -mprefixed -mno-prefixed @gol +-mpcrel -mno-pcrel -mmma -mno-mmma -mrop-protect -mno-rop-protect @gol +-mprivileged -mno-privileged} + +@emph{RX Options} +@gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol +-mcpu=@gol +-mbig-endian-data -mlittle-endian-data @gol +-msmall-data @gol +-msim -mno-sim@gol +-mas100-syntax -mno-as100-syntax@gol +-mrelax@gol +-mmax-constant-size=@gol +-mint-register=@gol +-mpid@gol +-mallow-string-insns -mno-allow-string-insns@gol +-mjsr@gol +-mno-warn-multiple-fast-interrupts@gol +-msave-acc-in-interrupts} + +@emph{S/390 and zSeries Options} +@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol +-mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol +-mlong-double-64 -mlong-double-128 @gol +-mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol +-msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol +-m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol +-mhtm -mvx -mzvector @gol +-mtpf-trace -mno-tpf-trace -mtpf-trace-skip -mno-tpf-trace-skip @gol +-mfused-madd -mno-fused-madd @gol +-mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard @gol +-mhotpatch=@var{halfwords},@var{halfwords}} + +@emph{Score Options} +@gccoptlist{-meb -mel @gol +-mnhwloop @gol +-muls @gol +-mmac @gol +-mscore5 -mscore5u -mscore7 -mscore7d} + +@emph{SH Options} +@gccoptlist{-m1 -m2 -m2e @gol +-m2a-nofpu -m2a-single-only -m2a-single -m2a @gol +-m3 -m3e @gol +-m4-nofpu -m4-single-only -m4-single -m4 @gol +-m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol +-mb -ml -mdalign -mrelax @gol +-mbigtable -mfmovd -mrenesas -mno-renesas -mnomacsave @gol +-mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol +-mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol +-mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol +-maccumulate-outgoing-args @gol +-matomic-model=@var{atomic-model} @gol +-mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch @gol +-mcbranch-force-delay-slot @gol +-mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol +-mpretend-cmove -mtas} + +@emph{Solaris 2 Options} +@gccoptlist{-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text @gol +-pthreads} + +@emph{SPARC Options} +@gccoptlist{-mcpu=@var{cpu-type} @gol +-mtune=@var{cpu-type} @gol +-mcmodel=@var{code-model} @gol +-mmemory-model=@var{mem-model} @gol +-m32 -m64 -mapp-regs -mno-app-regs @gol +-mfaster-structs -mno-faster-structs -mflat -mno-flat @gol +-mfpu -mno-fpu -mhard-float -msoft-float @gol +-mhard-quad-float -msoft-quad-float @gol +-mstack-bias -mno-stack-bias @gol +-mstd-struct-return -mno-std-struct-return @gol +-munaligned-doubles -mno-unaligned-doubles @gol +-muser-mode -mno-user-mode @gol +-mv8plus -mno-v8plus -mvis -mno-vis @gol +-mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol +-mvis4 -mno-vis4 -mvis4b -mno-vis4b @gol +-mcbcond -mno-cbcond -mfmaf -mno-fmaf -mfsmuld -mno-fsmuld @gol +-mpopc -mno-popc -msubxc -mno-subxc @gol +-mfix-at697f -mfix-ut699 -mfix-ut700 -mfix-gr712rc @gol +-mlra -mno-lra} + +@emph{System V Options} +@gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} + +@emph{V850 Options} +@gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol +-mprolog-function -mno-prolog-function -mspace @gol +-mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol +-mapp-regs -mno-app-regs @gol +-mdisable-callt -mno-disable-callt @gol +-mv850e2v3 -mv850e2 -mv850e1 -mv850es @gol +-mv850e -mv850 -mv850e3v5 @gol +-mloop @gol +-mrelax @gol +-mlong-jumps @gol +-msoft-float @gol +-mhard-float @gol +-mgcc-abi @gol +-mrh850-abi @gol +-mbig-switch} + +@emph{VAX Options} +@gccoptlist{-mg -mgnu -munix -mlra} + +@emph{Visium Options} +@gccoptlist{-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float @gol +-mcpu=@var{cpu-type} -mtune=@var{cpu-type} -msv-mode -muser-mode} + +@emph{VMS Options} +@gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol +-mpointer-size=@var{size}} + +@emph{VxWorks Options} +@gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol +-Xbind-lazy -Xbind-now} + +@emph{x86 Options} +@gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol +-mtune-ctrl=@var{feature-list} -mdump-tune-features -mno-default @gol +-mfpmath=@var{unit} @gol +-masm=@var{dialect} -mno-fancy-math-387 @gol +-mno-fp-ret-in-387 -m80387 -mhard-float -msoft-float @gol +-mno-wide-multiply -mrtd -malign-double @gol +-mpreferred-stack-boundary=@var{num} @gol +-mincoming-stack-boundary=@var{num} @gol +-mcld -mcx16 -msahf -mmovbe -mcrc32 -mmwait @gol +-mrecip -mrecip=@var{opt} @gol +-mvzeroupper -mprefer-avx128 -mprefer-vector-width=@var{opt} @gol +-mmove-max=@var{bits} -mstore-max=@var{bits} @gol +-mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol +-mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -mavx512vl @gol +-mavx512bw -mavx512dq -mavx512ifma -mavx512vbmi -msha -maes @gol +-mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mpconfig -mwbnoinvd @gol +-mptwrite -mprefetchwt1 -mclflushopt -mclwb -mxsavec -mxsaves @gol +-msse4a -m3dnow -m3dnowa -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop @gol +-madx -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mhle -mlwp @gol +-mmwaitx -mclzero -mpku -mthreads -mgfni -mvaes -mwaitpkg @gol +-mshstk -mmanual-endbr -mcet-switch -mforce-indirect-call @gol +-mavx512vbmi2 -mavx512bf16 -menqcmd @gol +-mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq @gol +-mavx5124fmaps -mavx512vnni -mavx5124vnniw -mprfchw -mrdpid @gol +-mrdseed -msgx -mavx512vp2intersect -mserialize -mtsxldtrk@gol +-mamx-tile -mamx-int8 -mamx-bf16 -muintr -mhreset -mavxvnni@gol +-mavx512fp16 -mavxifma -mavxvnniint8 -mavxneconvert -mcmpccxadd -mamx-fp16 @gol +-mprefetchi -mraoint @gol +-mcldemote -mms-bitfields -mno-align-stringops -minline-all-stringops @gol +-minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol +-mkl -mwidekl @gol +-mmemcpy-strategy=@var{strategy} -mmemset-strategy=@var{strategy} @gol +-mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol +-m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 @gol +-mregparm=@var{num} -msseregparm @gol +-mveclibabi=@var{type} -mvect8-ret-in-mem @gol +-mpc32 -mpc64 -mpc80 -mstackrealign @gol +-momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol +-mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol +-m32 -m64 -mx32 -m16 -miamcu -mlarge-data-threshold=@var{num} @gol +-msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv @gol +-minstrument-return=@var{type} -mfentry-name=@var{name} -mfentry-section=@var{name} @gol +-mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol +-malign-data=@var{type} -mstack-protector-guard=@var{guard} @gol +-mstack-protector-guard-reg=@var{reg} @gol +-mstack-protector-guard-offset=@var{offset} @gol +-mstack-protector-guard-symbol=@var{symbol} @gol +-mgeneral-regs-only -mcall-ms2sysv-xlogues -mrelax-cmpxchg-loop @gol +-mindirect-branch=@var{choice} -mfunction-return=@var{choice} @gol +-mindirect-branch-register -mharden-sls=@var{choice} @gol +-mindirect-branch-cs-prefix -mneeded -mno-direct-extern-access} + +@emph{x86 Windows Options} +@gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol +-mnop-fun-dllimport -mthread @gol +-municode -mwin32 -mwindows -fno-set-stack-executable} + +@emph{Xstormy16 Options} +@gccoptlist{-msim} + +@emph{Xtensa Options} +@gccoptlist{-mconst16 -mno-const16 @gol +-mfused-madd -mno-fused-madd @gol +-mforce-no-pic @gol +-mserialize-volatile -mno-serialize-volatile @gol +-mtext-section-literals -mno-text-section-literals @gol +-mauto-litpools -mno-auto-litpools @gol +-mtarget-align -mno-target-align @gol +-mlongcalls -mno-longcalls @gol +-mabi=@var{abi-type} @gol +-mextra-l32r-costs=@var{cycles}} + +@emph{zSeries Options} +See S/390 and zSeries Options. +@end table + + +@node Overall Options +@section Options Controlling the Kind of Output + +Compilation can involve up to four stages: preprocessing, compilation +proper, assembly and linking, always in that order. GCC is capable of +preprocessing and compiling several files either into several +assembler input files, or into one assembler input file; then each +assembler input file produces an object file, and linking combines all +the object files (those newly compiled, and those specified as input) +into an executable file. + +@cindex file name suffix +For any given input file, the file name suffix determines what kind of +compilation is done: + +@table @gcctabopt +@item @var{file}.c +C source code that must be preprocessed. + +@item @var{file}.i +C source code that should not be preprocessed. + +@item @var{file}.ii +C++ source code that should not be preprocessed. + +@item @var{file}.m +Objective-C source code. Note that you must link with the @file{libobjc} +library to make an Objective-C program work. + +@item @var{file}.mi +Objective-C source code that should not be preprocessed. + +@item @var{file}.mm +@itemx @var{file}.M +Objective-C++ source code. Note that you must link with the @file{libobjc} +library to make an Objective-C++ program work. Note that @samp{.M} refers +to a literal capital M@. + +@item @var{file}.mii +Objective-C++ source code that should not be preprocessed. + +@item @var{file}.h +C, C++, Objective-C or Objective-C++ header file to be turned into a +precompiled header (default), or C, C++ header file to be turned into an +Ada spec (via the @option{-fdump-ada-spec} switch). + +@item @var{file}.cc +@itemx @var{file}.cp +@itemx @var{file}.cxx +@itemx @var{file}.cpp +@itemx @var{file}.CPP +@itemx @var{file}.c++ +@itemx @var{file}.C +C++ source code that must be preprocessed. Note that in @samp{.cxx}, +the last two letters must both be literally @samp{x}. Likewise, +@samp{.C} refers to a literal capital C@. + +@item @var{file}.mm +@itemx @var{file}.M +Objective-C++ source code that must be preprocessed. + +@item @var{file}.mii +Objective-C++ source code that should not be preprocessed. + +@item @var{file}.hh +@itemx @var{file}.H +@itemx @var{file}.hp +@itemx @var{file}.hxx +@itemx @var{file}.hpp +@itemx @var{file}.HPP +@itemx @var{file}.h++ +@itemx @var{file}.tcc +C++ header file to be turned into a precompiled header or Ada spec. + +@item @var{file}.f +@itemx @var{file}.for +@itemx @var{file}.ftn +Fixed form Fortran source code that should not be preprocessed. + +@item @var{file}.F +@itemx @var{file}.FOR +@itemx @var{file}.fpp +@itemx @var{file}.FPP +@itemx @var{file}.FTN +Fixed form Fortran source code that must be preprocessed (with the traditional +preprocessor). + +@item @var{file}.f90 +@itemx @var{file}.f95 +@itemx @var{file}.f03 +@itemx @var{file}.f08 +Free form Fortran source code that should not be preprocessed. + +@item @var{file}.F90 +@itemx @var{file}.F95 +@itemx @var{file}.F03 +@itemx @var{file}.F08 +Free form Fortran source code that must be preprocessed (with the +traditional preprocessor). + +@item @var{file}.go +Go source code. + +@item @var{file}.d +D source code. + +@item @var{file}.di +D interface file. + +@item @var{file}.dd +D documentation code (Ddoc). + +@item @var{file}.ads +Ada source code file that contains a library unit declaration (a +declaration of a package, subprogram, or generic, or a generic +instantiation), or a library unit renaming declaration (a package, +generic, or subprogram renaming declaration). Such files are also +called @dfn{specs}. + +@item @var{file}.adb +Ada source code file containing a library unit body (a subprogram or +package body). Such files are also called @dfn{bodies}. + +@c GCC also knows about some suffixes for languages not yet included: +@c Ratfor: +@c @var{file}.r + +@item @var{file}.s +Assembler code. + +@item @var{file}.S +@itemx @var{file}.sx +Assembler code that must be preprocessed. + +@item @var{other} +An object file to be fed straight into linking. +Any file name with no recognized suffix is treated this way. +@end table + +@opindex x +You can specify the input language explicitly with the @option{-x} option: + +@table @gcctabopt +@item -x @var{language} +Specify explicitly the @var{language} for the following input files +(rather than letting the compiler choose a default based on the file +name suffix). This option applies to all following input files until +the next @option{-x} option. Possible values for @var{language} are: +@smallexample +c c-header cpp-output +c++ c++-header c++-system-header c++-user-header c++-cpp-output +objective-c objective-c-header objective-c-cpp-output +objective-c++ objective-c++-header objective-c++-cpp-output +assembler assembler-with-cpp +ada +d +f77 f77-cpp-input f95 f95-cpp-input +go +@end smallexample + +@item -x none +Turn off any specification of a language, so that subsequent files are +handled according to their file name suffixes (as they are if @option{-x} +has not been used at all). +@end table + +If you only want some of the stages of compilation, you can use +@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and +one of the options @option{-c}, @option{-S}, or @option{-E} to say where +@command{gcc} is to stop. Note that some combinations (for example, +@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. + +@table @gcctabopt +@item -c +@opindex c +Compile or assemble the source files, but do not link. The linking +stage simply is not done. The ultimate output is in the form of an +object file for each source file. + +By default, the object file name for a source file is made by replacing +the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. + +Unrecognized input files, not requiring compilation or assembly, are +ignored. + +@item -S +@opindex S +Stop after the stage of compilation proper; do not assemble. The output +is in the form of an assembler code file for each non-assembler input +file specified. + +By default, the assembler file name for a source file is made by +replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. + +Input files that don't require compilation are ignored. + +@item -E +@opindex E +Stop after the preprocessing stage; do not run the compiler proper. The +output is in the form of preprocessed source code, which is sent to the +standard output. + +Input files that don't require preprocessing are ignored. + +@cindex output file option +@item -o @var{file} +@opindex o +Place the primary output in file @var{file}. This applies to whatever +sort of output is being produced, whether it be an executable file, an +object file, an assembler file or preprocessed C code. + +If @option{-o} is not specified, the default is to put an executable +file in @file{a.out}, the object file for +@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its +assembler file in @file{@var{source}.s}, a precompiled header file in +@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on +standard output. + +Though @option{-o} names only the primary output, it also affects the +naming of auxiliary and dump outputs. See the examples below. Unless +overridden, both auxiliary outputs and dump outputs are placed in the +same directory as the primary output. In auxiliary outputs, the suffix +of the input file is replaced with that of the auxiliary output file +type; in dump outputs, the suffix of the dump file is appended to the +input file suffix. In compilation commands, the base name of both +auxiliary and dump outputs is that of the primary output; in compile and +link commands, the primary output name, minus the executable suffix, is +combined with the input file name. If both share the same base name, +disregarding the suffix, the result of the combination is that base +name, otherwise, they are concatenated, separated by a dash. + +@smallexample +gcc -c foo.c ... +@end smallexample + +will use @file{foo.o} as the primary output, and place aux outputs and +dumps next to it, e.g., aux file @file{foo.dwo} for +@option{-gsplit-dwarf}, and dump file @file{foo.c.???r.final} for +@option{-fdump-rtl-final}. + +If a non-linker output file is explicitly specified, aux and dump files +by default take the same base name: + +@smallexample +gcc -c foo.c -o dir/foobar.o ... +@end smallexample + +will name aux outputs @file{dir/foobar.*} and dump outputs +@file{dir/foobar.c.*}. + +A linker output will instead prefix aux and dump outputs: + +@smallexample +gcc foo.c bar.c -o dir/foobar ... +@end smallexample + +will generally name aux outputs @file{dir/foobar-foo.*} and +@file{dir/foobar-bar.*}, and dump outputs @file{dir/foobar-foo.c.*} and +@file{dir/foobar-bar.c.*}. + +The one exception to the above is when the executable shares the base +name with the single input: + +@smallexample +gcc foo.c -o dir/foo ... +@end smallexample + +in which case aux outputs are named @file{dir/foo.*} and dump outputs +named @file{dir/foo.c.*}. + +The location and the names of auxiliary and dump outputs can be adjusted +by the options @option{-dumpbase}, @option{-dumpbase-ext}, +@option{-dumpdir}, @option{-save-temps=cwd}, and +@option{-save-temps=obj}. + + +@item -dumpbase @var{dumpbase} +@opindex dumpbase +This option sets the base name for auxiliary and dump output files. It +does not affect the name of the primary output file. Intermediate +outputs, when preserved, are not regarded as primary outputs, but as +auxiliary outputs: + +@smallexample +gcc -save-temps -S foo.c +@end smallexample + +saves the (no longer) temporary preprocessed file in @file{foo.i}, and +then compiles to the (implied) output file @file{foo.s}, whereas: + +@smallexample +gcc -save-temps -dumpbase save-foo -c foo.c +@end smallexample + +preprocesses to in @file{save-foo.i}, compiles to @file{save-foo.s} (now +an intermediate, thus auxiliary output), and then assembles to the +(implied) output file @file{foo.o}. + +Absent this option, dump and aux files take their names from the input +file, or from the (non-linker) output file, if one is explicitly +specified: dump output files (e.g. those requested by @option{-fdump-*} +options) with the input name suffix, and aux output files (those +requested by other non-dump options, e.g. @code{-save-temps}, +@code{-gsplit-dwarf}, @code{-fcallgraph-info}) without it. + +Similar suffix differentiation of dump and aux outputs can be attained +for explicitly-given @option{-dumpbase basename.suf} by also specifying +@option{-dumpbase-ext .suf}. + +If @var{dumpbase} is explicitly specified with any directory component, +any @var{dumppfx} specification (e.g. @option{-dumpdir} or +@option{-save-temps=*}) is ignored, and instead of appending to it, +@var{dumpbase} fully overrides it: + +@smallexample +gcc foo.c -c -o dir/foo.o -dumpbase alt/foo \ + -dumpdir pfx- -save-temps=cwd ... +@end smallexample + +creates auxiliary and dump outputs named @file{alt/foo.*}, disregarding +@file{dir/} in @option{-o}, the @file{./} prefix implied by +@option{-save-temps=cwd}, and @file{pfx-} in @option{-dumpdir}. + +When @option{-dumpbase} is specified in a command that compiles multiple +inputs, or that compiles and then links, it may be combined with +@var{dumppfx}, as specified under @option{-dumpdir}. Then, each input +file is compiled using the combined @var{dumppfx}, and default values +for @var{dumpbase} and @var{auxdropsuf} are computed for each input +file: + +@smallexample +gcc foo.c bar.c -c -dumpbase main ... +@end smallexample + +creates @file{foo.o} and @file{bar.o} as primary outputs, and avoids +overwriting the auxiliary and dump outputs by using the @var{dumpbase} +as a prefix, creating auxiliary and dump outputs named @file{main-foo.*} +and @file{main-bar.*}. + +An empty string specified as @var{dumpbase} avoids the influence of the +output basename in the naming of auxiliary and dump outputs during +compilation, computing default values : + +@smallexample +gcc -c foo.c -o dir/foobar.o -dumpbase '' ... +@end smallexample + +will name aux outputs @file{dir/foo.*} and dump outputs +@file{dir/foo.c.*}. Note how their basenames are taken from the input +name, but the directory still defaults to that of the output. + +The empty-string dumpbase does not prevent the use of the output +basename for outputs during linking: + +@smallexample +gcc foo.c bar.c -o dir/foobar -dumpbase '' -flto ... +@end smallexample + +The compilation of the source files will name auxiliary outputs +@file{dir/foo.*} and @file{dir/bar.*}, and dump outputs +@file{dir/foo.c.*} and @file{dir/bar.c.*}. LTO recompilation during +linking will use @file{dir/foobar.} as the prefix for dumps and +auxiliary files. + + +@item -dumpbase-ext @var{auxdropsuf} +@opindex dumpbase-ext +When forming the name of an auxiliary (but not a dump) output file, drop +trailing @var{auxdropsuf} from @var{dumpbase} before appending any +suffixes. If not specified, this option defaults to the suffix of a +default @var{dumpbase}, i.e., the suffix of the input file when +@option{-dumpbase} is not present in the command line, or @var{dumpbase} +is combined with @var{dumppfx}. + +@smallexample +gcc foo.c -c -o dir/foo.o -dumpbase x-foo.c -dumpbase-ext .c ... +@end smallexample + +creates @file{dir/foo.o} as the main output, and generates auxiliary +outputs in @file{dir/x-foo.*}, taking the location of the primary +output, and dropping the @file{.c} suffix from the @var{dumpbase}. Dump +outputs retain the suffix: @file{dir/x-foo.c.*}. + +This option is disregarded if it does not match the suffix of a +specified @var{dumpbase}, except as an alternative to the executable +suffix when appending the linker output base name to @var{dumppfx}, as +specified below: + +@smallexample +gcc foo.c bar.c -o main.out -dumpbase-ext .out ... +@end smallexample + +creates @file{main.out} as the primary output, and avoids overwriting +the auxiliary and dump outputs by using the executable name minus +@var{auxdropsuf} as a prefix, creating auxiliary outputs named +@file{main-foo.*} and @file{main-bar.*} and dump outputs named +@file{main-foo.c.*} and @file{main-bar.c.*}. + + +@item -dumpdir @var{dumppfx} +@opindex dumpdir +When forming the name of an auxiliary or dump output file, use +@var{dumppfx} as a prefix: + +@smallexample +gcc -dumpdir pfx- -c foo.c ... +@end smallexample + +creates @file{foo.o} as the primary output, and auxiliary outputs named +@file{pfx-foo.*}, combining the given @var{dumppfx} with the default +@var{dumpbase} derived from the default primary output, derived in turn +from the input name. Dump outputs also take the input name suffix: +@file{pfx-foo.c.*}. + +If @var{dumppfx} is to be used as a directory name, it must end with a +directory separator: + +@smallexample +gcc -dumpdir dir/ -c foo.c -o obj/bar.o ... +@end smallexample + +creates @file{obj/bar.o} as the primary output, and auxiliary outputs +named @file{dir/bar.*}, combining the given @var{dumppfx} with the +default @var{dumpbase} derived from the primary output name. Dump +outputs also take the input name suffix: @file{dir/bar.c.*}. + +It defaults to the location of the output file, unless the output +file is a special file like @code{/dev/null}. Options +@option{-save-temps=cwd} and @option{-save-temps=obj} override this +default, just like an explicit @option{-dumpdir} option. In case +multiple such options are given, the last one prevails: + +@smallexample +gcc -dumpdir pfx- -c foo.c -save-temps=obj ... +@end smallexample + +outputs @file{foo.o}, with auxiliary outputs named @file{foo.*} because +@option{-save-temps=*} overrides the @var{dumppfx} given by the earlier +@option{-dumpdir} option. It does not matter that @option{=obj} is the +default for @option{-save-temps}, nor that the output directory is +implicitly the current directory. Dump outputs are named +@file{foo.c.*}. + +When compiling from multiple input files, if @option{-dumpbase} is +specified, @var{dumpbase}, minus a @var{auxdropsuf} suffix, and a dash +are appended to (or override, if containing any directory components) an +explicit or defaulted @var{dumppfx}, so that each of the multiple +compilations gets differently-named aux and dump outputs. + +@smallexample +gcc foo.c bar.c -c -dumpdir dir/pfx- -dumpbase main ... +@end smallexample + +outputs auxiliary dumps to @file{dir/pfx-main-foo.*} and +@file{dir/pfx-main-bar.*}, appending @var{dumpbase}- to @var{dumppfx}. +Dump outputs retain the input file suffix: @file{dir/pfx-main-foo.c.*} +and @file{dir/pfx-main-bar.c.*}, respectively. Contrast with the +single-input compilation: + +@smallexample +gcc foo.c -c -dumpdir dir/pfx- -dumpbase main ... +@end smallexample + +that, applying @option{-dumpbase} to a single source, does not compute +and append a separate @var{dumpbase} per input file. Its auxiliary and +dump outputs go in @file{dir/pfx-main.*}. + +When compiling and then linking from multiple input files, a defaulted +or explicitly specified @var{dumppfx} also undergoes the @var{dumpbase}- +transformation above (e.g. the compilation of @file{foo.c} and +@file{bar.c} above, but without @option{-c}). If neither +@option{-dumpdir} nor @option{-dumpbase} are given, the linker output +base name, minus @var{auxdropsuf}, if specified, or the executable +suffix otherwise, plus a dash is appended to the default @var{dumppfx} +instead. Note, however, that unlike earlier cases of linking: + +@smallexample +gcc foo.c bar.c -dumpdir dir/pfx- -o main ... +@end smallexample + +does not append the output name @file{main} to @var{dumppfx}, because +@option{-dumpdir} is explicitly specified. The goal is that the +explicitly-specified @var{dumppfx} may contain the specified output name +as part of the prefix, if desired; only an explicitly-specified +@option{-dumpbase} would be combined with it, in order to avoid simply +discarding a meaningful option. + +When compiling and then linking from a single input file, the linker +output base name will only be appended to the default @var{dumppfx} as +above if it does not share the base name with the single input file +name. This has been covered in single-input linking cases above, but +not with an explicit @option{-dumpdir} that inhibits the combination, +even if overridden by @option{-save-temps=*}: + +@smallexample +gcc foo.c -dumpdir alt/pfx- -o dir/main.exe -save-temps=cwd ... +@end smallexample + +Auxiliary outputs are named @file{foo.*}, and dump outputs +@file{foo.c.*}, in the current working directory as ultimately requested +by @option{-save-temps=cwd}. + +Summing it all up for an intuitive though slightly imprecise data flow: +the primary output name is broken into a directory part and a basename +part; @var{dumppfx} is set to the former, unless overridden by +@option{-dumpdir} or @option{-save-temps=*}, and @var{dumpbase} is set +to the latter, unless overriden by @option{-dumpbase}. If there are +multiple inputs or linking, this @var{dumpbase} may be combined with +@var{dumppfx} and taken from each input file. Auxiliary output names +for each input are formed by combining @var{dumppfx}, @var{dumpbase} +minus suffix, and the auxiliary output suffix; dump output names are +only different in that the suffix from @var{dumpbase} is retained. + +When it comes to auxiliary and dump outputs created during LTO +recompilation, a combination of @var{dumppfx} and @var{dumpbase}, as +given or as derived from the linker output name but not from inputs, +even in cases in which this combination would not otherwise be used as +such, is passed down with a trailing period replacing the compiler-added +dash, if any, as a @option{-dumpdir} option to @command{lto-wrapper}; +being involved in linking, this program does not normally get any +@option{-dumpbase} and @option{-dumpbase-ext}, and it ignores them. + +When running sub-compilers, @command{lto-wrapper} appends LTO stage +names to the received @var{dumppfx}, ensures it contains a directory +component so that it overrides any @option{-dumpdir}, and passes that as +@option{-dumpbase} to sub-compilers. + +@item -v +@opindex v +Print (on standard error output) the commands executed to run the stages +of compilation. Also print the version number of the compiler driver +program and of the preprocessor and the compiler proper. + +@item -### +@opindex ### +Like @option{-v} except the commands are not executed and arguments +are quoted unless they contain only alphanumeric characters or @code{./-_}. +This is useful for shell scripts to capture the driver-generated command lines. + +@item --help +@opindex help +Print (on the standard output) a description of the command-line options +understood by @command{gcc}. If the @option{-v} option is also specified +then @option{--help} is also passed on to the various processes +invoked by @command{gcc}, so that they can display the command-line options +they accept. If the @option{-Wextra} option has also been specified +(prior to the @option{--help} option), then command-line options that +have no documentation associated with them are also displayed. + +@item --target-help +@opindex target-help +Print (on the standard output) a description of target-specific command-line +options for each tool. For some targets extra target-specific +information may also be printed. + +@item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]} +Print (on the standard output) a description of the command-line +options understood by the compiler that fit into all specified classes +and qualifiers. These are the supported classes: + +@table @asis +@item @samp{optimizers} +Display all of the optimization options supported by the +compiler. + +@item @samp{warnings} +Display all of the options controlling warning messages +produced by the compiler. + +@item @samp{target} +Display target-specific options. Unlike the +@option{--target-help} option however, target-specific options of the +linker and assembler are not displayed. This is because those +tools do not currently support the extended @option{--help=} syntax. + +@item @samp{params} +Display the values recognized by the @option{--param} +option. + +@item @var{language} +Display the options supported for @var{language}, where +@var{language} is the name of one of the languages supported in this +version of GCC@. If an option is supported by all languages, one needs +to select @samp{common} class. + +@item @samp{common} +Display the options that are common to all languages. +@end table + +These are the supported qualifiers: + +@table @asis +@item @samp{undocumented} +Display only those options that are undocumented. + +@item @samp{joined} +Display options taking an argument that appears after an equal +sign in the same continuous piece of text, such as: +@samp{--help=target}. + +@item @samp{separate} +Display options taking an argument that appears as a separate word +following the original option, such as: @samp{-o output-file}. +@end table + +Thus for example to display all the undocumented target-specific +switches supported by the compiler, use: + +@smallexample +--help=target,undocumented +@end smallexample + +The sense of a qualifier can be inverted by prefixing it with the +@samp{^} character, so for example to display all binary warning +options (i.e., ones that are either on or off and that do not take an +argument) that have a description, use: + +@smallexample +--help=warnings,^joined,^undocumented +@end smallexample + +The argument to @option{--help=} should not consist solely of inverted +qualifiers. + +Combining several classes is possible, although this usually +restricts the output so much that there is nothing to display. One +case where it does work, however, is when one of the classes is +@var{target}. For example, to display all the target-specific +optimization options, use: + +@smallexample +--help=target,optimizers +@end smallexample + +The @option{--help=} option can be repeated on the command line. Each +successive use displays its requested class of options, skipping +those that have already been displayed. If @option{--help} is also +specified anywhere on the command line then this takes precedence +over any @option{--help=} option. + +If the @option{-Q} option appears on the command line before the +@option{--help=} option, then the descriptive text displayed by +@option{--help=} is changed. Instead of describing the displayed +options, an indication is given as to whether the option is enabled, +disabled or set to a specific value (assuming that the compiler +knows this at the point where the @option{--help=} option is used). + +Here is a truncated example from the ARM port of @command{gcc}: + +@smallexample + % gcc -Q -mabi=2 --help=target -c + The following options are target specific: + -mabi= 2 + -mabort-on-noreturn [disabled] + -mapcs [disabled] +@end smallexample + +The output is sensitive to the effects of previous command-line +options, so for example it is possible to find out which optimizations +are enabled at @option{-O2} by using: + +@smallexample +-Q -O2 --help=optimizers +@end smallexample + +Alternatively you can discover which binary optimizations are enabled +by @option{-O3} by using: + +@smallexample +gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts +gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts +diff /tmp/O2-opts /tmp/O3-opts | grep enabled +@end smallexample + +@item --version +@opindex version +Display the version number and copyrights of the invoked GCC@. + +@item -pass-exit-codes +@opindex pass-exit-codes +Normally the @command{gcc} program exits with the code of 1 if any +phase of the compiler returns a non-success return code. If you specify +@option{-pass-exit-codes}, the @command{gcc} program instead returns with +the numerically highest error produced by any phase returning an error +indication. The C, C++, and Fortran front ends return 4 if an internal +compiler error is encountered. + +@item -pipe +@opindex pipe +Use pipes rather than temporary files for communication between the +various stages of compilation. This fails to work on some systems where +the assembler is unable to read from a pipe; but the GNU assembler has +no trouble. + +@item -specs=@var{file} +@opindex specs +Process @var{file} after the compiler reads in the standard @file{specs} +file, in order to override the defaults which the @command{gcc} driver +program uses when determining what switches to pass to @command{cc1}, +@command{cc1plus}, @command{as}, @command{ld}, etc. More than one +@option{-specs=@var{file}} can be specified on the command line, and they +are processed in order, from left to right. @xref{Spec Files}, for +information about the format of the @var{file}. + +@item -wrapper +@opindex wrapper +Invoke all subcommands under a wrapper program. The name of the +wrapper program and its parameters are passed as a comma separated +list. + +@smallexample +gcc -c t.c -wrapper gdb,--args +@end smallexample + +@noindent +This invokes all subprograms of @command{gcc} under +@samp{gdb --args}, thus the invocation of @command{cc1} is +@samp{gdb --args cc1 @dots{}}. + +@item -ffile-prefix-map=@var{old}=@var{new} +@opindex ffile-prefix-map +When compiling files residing in directory @file{@var{old}}, record +any references to them in the result of the compilation as if the +files resided in directory @file{@var{new}} instead. Specifying this +option is equivalent to specifying all the individual +@option{-f*-prefix-map} options. This can be used to make reproducible +builds that are location independent. See also +@option{-fmacro-prefix-map}, @option{-fdebug-prefix-map} and +@option{-fprofile-prefix-map}. + +@item -fplugin=@var{name}.so +@opindex fplugin +Load the plugin code in file @var{name}.so, assumed to be a +shared object to be dlopen'd by the compiler. The base name of +the shared object file is used to identify the plugin for the +purposes of argument parsing (See +@option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below). +Each plugin should define the callback functions specified in the +Plugins API. + +@item -fplugin-arg-@var{name}-@var{key}=@var{value} +@opindex fplugin-arg +Define an argument called @var{key} with a value of @var{value} +for the plugin called @var{name}. + +@item -fdump-ada-spec@r{[}-slim@r{]} +@opindex fdump-ada-spec +For C and C++ source and include files, generate corresponding Ada specs. +@xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn, +GNAT User's Guide}, which provides detailed documentation on this feature. + +@item -fada-spec-parent=@var{unit} +@opindex fada-spec-parent +In conjunction with @option{-fdump-ada-spec@r{[}-slim@r{]}} above, generate +Ada specs as child units of parent @var{unit}. + +@item -fdump-go-spec=@var{file} +@opindex fdump-go-spec +For input files in any language, generate corresponding Go +declarations in @var{file}. This generates Go @code{const}, +@code{type}, @code{var}, and @code{func} declarations which may be a +useful way to start writing a Go interface to code written in some +other language. + +@include @value{srcdir}/../libiberty/at-file.texi +@end table + +@node Invoking G++ +@section Compiling C++ Programs + +@cindex suffixes for C++ source +@cindex C++ source file suffixes +C++ source files conventionally use one of the suffixes @samp{.C}, +@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or +@samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp}, +@samp{.H}, or (for shared template code) @samp{.tcc}; and +preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes +files with these names and compiles them as C++ programs even if you +call the compiler the same way as for compiling C programs (usually +with the name @command{gcc}). + +@findex g++ +@findex c++ +However, the use of @command{gcc} does not add the C++ library. +@command{g++} is a program that calls GCC and automatically specifies linking +against the C++ library. It treats @samp{.c}, +@samp{.h} and @samp{.i} files as C++ source files instead of C source +files unless @option{-x} is used. This program is also useful when +precompiling a C header file with a @samp{.h} extension for use in C++ +compilations. On many systems, @command{g++} is also installed with +the name @command{c++}. + +@cindex invoking @command{g++} +When you compile C++ programs, you may specify many of the same +command-line options that you use for compiling programs in any +language; or command-line options meaningful for C and related +languages; or options that are meaningful only for C++ programs. +@xref{C Dialect Options,,Options Controlling C Dialect}, for +explanations of options for languages related to C@. +@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for +explanations of options that are meaningful only for C++ programs. + +@node C Dialect Options +@section Options Controlling C Dialect +@cindex dialect options +@cindex language dialect options +@cindex options, dialect + +The following options control the dialect of C (or languages derived +from C, such as C++, Objective-C and Objective-C++) that the compiler +accepts: + +@table @gcctabopt +@cindex ANSI support +@cindex ISO support +@item -ansi +@opindex ansi +In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is +equivalent to @option{-std=c++98}. + +This turns off certain features of GCC that are incompatible with ISO +C90 (when compiling C code), or of standard C++ (when compiling C++ code), +such as the @code{asm} and @code{typeof} keywords, and +predefined macros such as @code{unix} and @code{vax} that identify the +type of system you are using. It also enables the undesirable and +rarely used ISO trigraph feature. For the C compiler, +it disables recognition of C++ style @samp{//} comments as well as +the @code{inline} keyword. + +The alternate keywords @code{__asm__}, @code{__extension__}, +@code{__inline__} and @code{__typeof__} continue to work despite +@option{-ansi}. You would not want to use them in an ISO C program, of +course, but it is useful to put them in header files that might be included +in compilations done with @option{-ansi}. Alternate predefined macros +such as @code{__unix__} and @code{__vax__} are also available, with or +without @option{-ansi}. + +The @option{-ansi} option does not cause non-ISO programs to be +rejected gratuitously. For that, @option{-Wpedantic} is required in +addition to @option{-ansi}. @xref{Warning Options}. + +The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} +option is used. Some header files may notice this macro and refrain +from declaring certain functions or defining certain macros that the +ISO standard doesn't call for; this is to avoid interfering with any +programs that might use these names for other things. + +Functions that are normally built in but do not have semantics +defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in +functions when @option{-ansi} is used. @xref{Other Builtins,,Other +built-in functions provided by GCC}, for details of the functions +affected. + +@item -std= +@opindex std +Determine the language standard. @xref{Standards,,Language Standards +Supported by GCC}, for details of these standard versions. This option +is currently only supported when compiling C or C++. + +The compiler can accept several base standards, such as @samp{c90} or +@samp{c++98}, and GNU dialects of those standards, such as +@samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the +compiler accepts all programs following that standard plus those +using GNU extensions that do not contradict it. For example, +@option{-std=c90} turns off certain features of GCC that are +incompatible with ISO C90, such as the @code{asm} and @code{typeof} +keywords, but not other GNU extensions that do not have a meaning in +ISO C90, such as omitting the middle term of a @code{?:} +expression. On the other hand, when a GNU dialect of a standard is +specified, all features supported by the compiler are enabled, even when +those features change the meaning of the base standard. As a result, some +strict-conforming programs may be rejected. The particular standard +is used by @option{-Wpedantic} to identify which features are GNU +extensions given that version of the standard. For example +@option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//} +comments, while @option{-std=gnu99 -Wpedantic} does not. + +A value for this option must be provided; possible values are + +@table @samp +@item c90 +@itemx c89 +@itemx iso9899:1990 +Support all ISO C90 programs (certain GNU extensions that conflict +with ISO C90 are disabled). Same as @option{-ansi} for C code. + +@item iso9899:199409 +ISO C90 as modified in amendment 1. + +@item c99 +@itemx c9x +@itemx iso9899:1999 +@itemx iso9899:199x +ISO C99. This standard is substantially completely supported, modulo +bugs and floating-point issues +(mainly but not entirely relating to optional C99 features from +Annexes F and G). See +@w{@uref{https://gcc.gnu.org/c99status.html}} for more information. The +names @samp{c9x} and @samp{iso9899:199x} are deprecated. + +@item c11 +@itemx c1x +@itemx iso9899:2011 +ISO C11, the 2011 revision of the ISO C standard. This standard is +substantially completely supported, modulo bugs, floating-point issues +(mainly but not entirely relating to optional C11 features from +Annexes F and G) and the optional Annexes K (Bounds-checking +interfaces) and L (Analyzability). The name @samp{c1x} is deprecated. + +@item c17 +@itemx c18 +@itemx iso9899:2017 +@itemx iso9899:2018 +ISO C17, the 2017 revision of the ISO C standard +(published in 2018). This standard is +same as C11 except for corrections of defects (all of which are also +applied with @option{-std=c11}) and a new value of +@code{__STDC_VERSION__}, and so is supported to the same extent as C11. + +@item c2x +The next version of the ISO C standard, still under development. The +support for this version is experimental and incomplete. + +@item gnu90 +@itemx gnu89 +GNU dialect of ISO C90 (including some C99 features). + +@item gnu99 +@itemx gnu9x +GNU dialect of ISO C99. The name @samp{gnu9x} is deprecated. + +@item gnu11 +@itemx gnu1x +GNU dialect of ISO C11. +The name @samp{gnu1x} is deprecated. + +@item gnu17 +@itemx gnu18 +GNU dialect of ISO C17. This is the default for C code. + +@item gnu2x +The next version of the ISO C standard, still under development, plus +GNU extensions. The support for this version is experimental and +incomplete. + +@item c++98 +@itemx c++03 +The 1998 ISO C++ standard plus the 2003 technical corrigendum and some +additional defect reports. Same as @option{-ansi} for C++ code. + +@item gnu++98 +@itemx gnu++03 +GNU dialect of @option{-std=c++98}. + +@item c++11 +@itemx c++0x +The 2011 ISO C++ standard plus amendments. +The name @samp{c++0x} is deprecated. + +@item gnu++11 +@itemx gnu++0x +GNU dialect of @option{-std=c++11}. +The name @samp{gnu++0x} is deprecated. + +@item c++14 +@itemx c++1y +The 2014 ISO C++ standard plus amendments. +The name @samp{c++1y} is deprecated. + +@item gnu++14 +@itemx gnu++1y +GNU dialect of @option{-std=c++14}. +The name @samp{gnu++1y} is deprecated. + +@item c++17 +@itemx c++1z +The 2017 ISO C++ standard plus amendments. +The name @samp{c++1z} is deprecated. + +@item gnu++17 +@itemx gnu++1z +GNU dialect of @option{-std=c++17}. +This is the default for C++ code. +The name @samp{gnu++1z} is deprecated. + +@item c++20 +@itemx c++2a +The 2020 ISO C++ standard plus amendments. +Support is experimental, and could change in incompatible ways in +future releases. +The name @samp{c++2a} is deprecated. + +@item gnu++20 +@itemx gnu++2a +GNU dialect of @option{-std=c++20}. +Support is experimental, and could change in incompatible ways in +future releases. +The name @samp{gnu++2a} is deprecated. + +@item c++2b +@itemx c++23 +The next revision of the ISO C++ standard, planned for +2023. Support is highly experimental, and will almost certainly +change in incompatible ways in future releases. + +@item gnu++2b +@itemx gnu++23 +GNU dialect of @option{-std=c++2b}. Support is highly experimental, +and will almost certainly change in incompatible ways in future +releases. +@end table + +@item -aux-info @var{filename} +@opindex aux-info +Output to the given filename prototyped declarations for all functions +declared and/or defined in a translation unit, including those in header +files. This option is silently ignored in any language other than C@. + +Besides declarations, the file indicates, in comments, the origin of +each declaration (source file and line), whether the declaration was +implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or +@samp{O} for old, respectively, in the first character after the line +number and the colon), and whether it came from a declaration or a +definition (@samp{C} or @samp{F}, respectively, in the following +character). In the case of function definitions, a K&R-style list of +arguments followed by their declarations is also provided, inside +comments, after the declaration. + +@item -fno-asm +@opindex fno-asm +@opindex fasm +Do not recognize @code{asm}, @code{inline} or @code{typeof} as a +keyword, so that code can use these words as identifiers. You can use +the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} +instead. In C, @option{-ansi} implies @option{-fno-asm}. + +In C++, @code{inline} is a standard keyword and is not affected by +this switch. You may want to use the @option{-fno-gnu-keywords} flag +instead, which disables @code{typeof} but not @code{asm} and +@code{inline}. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), +this switch only affects the @code{asm} and @code{typeof} keywords, +since @code{inline} is a standard keyword in ISO C99. In C2X mode +(@option{-std=c2x} or @option{-std=gnu2x}), this switch only affects +the @code{asm} keyword, since @code{typeof} is a standard keyword in +ISO C2X. + +@item -fno-builtin +@itemx -fno-builtin-@var{function} +@opindex fno-builtin +@opindex fbuiltin +@cindex built-in functions +Don't recognize built-in functions that do not begin with +@samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in +functions provided by GCC}, for details of the functions affected, +including those which are not built-in functions when @option{-ansi} or +@option{-std} options for strict ISO C conformance are used because they +do not have an ISO standard meaning. + +GCC normally generates special code to handle certain built-in functions +more efficiently; for instance, calls to @code{alloca} may become single +instructions which adjust the stack directly, and calls to @code{memcpy} +may become inline copy loops. The resulting code is often both smaller +and faster, but since the function calls no longer appear as such, you +cannot set a breakpoint on those calls, nor can you change the behavior +of the functions by linking with a different library. In addition, +when a function is recognized as a built-in function, GCC may use +information about that function to warn about problems with calls to +that function, or to generate more efficient code, even if the +resulting code still contains calls to that function. For example, +warnings are given with @option{-Wformat} for bad calls to +@code{printf} when @code{printf} is built in and @code{strlen} is +known not to modify global memory. + +With the @option{-fno-builtin-@var{function}} option +only the built-in function @var{function} is +disabled. @var{function} must not begin with @samp{__builtin_}. If a +function is named that is not built-in in this version of GCC, this +option is ignored. There is no corresponding +@option{-fbuiltin-@var{function}} option; if you wish to enable +built-in functions selectively when using @option{-fno-builtin} or +@option{-ffreestanding}, you may define macros such as: + +@smallexample +#define abs(n) __builtin_abs ((n)) +#define strcpy(d, s) __builtin_strcpy ((d), (s)) +@end smallexample + +@item -fcond-mismatch +@opindex fcond-mismatch +Allow conditional expressions with mismatched types in the second and +third arguments. The value of such an expression is void. This option +is not supported for C++. + +@item -ffreestanding +@opindex ffreestanding +@cindex hosted environment + +Assert that compilation targets a freestanding environment. This +implies @option{-fno-builtin}. A freestanding environment +is one in which the standard library may not exist, and program startup may +not necessarily be at @code{main}. The most obvious example is an OS kernel. +This is equivalent to @option{-fno-hosted}. + +@xref{Standards,,Language Standards Supported by GCC}, for details of +freestanding and hosted environments. + +@item -fgimple +@opindex fgimple + +Enable parsing of function definitions marked with @code{__GIMPLE}. +This is an experimental feature that allows unit testing of GIMPLE +passes. + +@item -fgnu-tm +@opindex fgnu-tm +When the option @option{-fgnu-tm} is specified, the compiler +generates code for the Linux variant of Intel's current Transactional +Memory ABI specification document (Revision 1.1, May 6 2009). This is +an experimental feature whose interface may change in future versions +of GCC, as the official specification changes. Please note that not +all architectures are supported for this feature. + +For more information on GCC's support for transactional memory, +@xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU +Transactional Memory Library}. + +Note that the transactional memory feature is not supported with +non-call exceptions (@option{-fnon-call-exceptions}). + +@item -fgnu89-inline +@opindex fgnu89-inline +The option @option{-fgnu89-inline} tells GCC to use the traditional +GNU semantics for @code{inline} functions when in C99 mode. +@xref{Inline,,An Inline Function is As Fast As a Macro}. +Using this option is roughly equivalent to adding the +@code{gnu_inline} function attribute to all inline functions +(@pxref{Function Attributes}). + +The option @option{-fno-gnu89-inline} explicitly tells GCC to use the +C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it +specifies the default behavior). +This option is not supported in @option{-std=c90} or +@option{-std=gnu90} mode. + +The preprocessor macros @code{__GNUC_GNU_INLINE__} and +@code{__GNUC_STDC_INLINE__} may be used to check which semantics are +in effect for @code{inline} functions. @xref{Common Predefined +Macros,,,cpp,The C Preprocessor}. + +@item -fhosted +@opindex fhosted +@cindex hosted environment + +Assert that compilation targets a hosted environment. This implies +@option{-fbuiltin}. A hosted environment is one in which the +entire standard library is available, and in which @code{main} has a return +type of @code{int}. Examples are nearly everything except a kernel. +This is equivalent to @option{-fno-freestanding}. + +@item -flax-vector-conversions +@opindex flax-vector-conversions +Allow implicit conversions between vectors with differing numbers of +elements and/or incompatible element types. This option should not be +used for new code. + +@item -fms-extensions +@opindex fms-extensions +Accept some non-standard constructs used in Microsoft header files. + +In C++ code, this allows member names in structures to be similar +to previous types declarations. + +@smallexample +typedef int UOW; +struct ABC @{ + UOW UOW; +@}; +@end smallexample + +Some cases of unnamed fields in structures and unions are only +accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union +fields within structs/unions}, for details. + +Note that this option is off for all targets except for x86 +targets using ms-abi. + +@item -foffload=disable +@itemx -foffload=default +@itemx -foffload=@var{target-list} +@opindex foffload +@cindex Offloading targets +@cindex OpenACC offloading targets +@cindex OpenMP offloading targets +Specify for which OpenMP and OpenACC offload targets code should be generated. +The default behavior, equivalent to @option{-foffload=default}, is to generate +code for all supported offload targets. The @option{-foffload=disable} form +generates code only for the host fallback, while +@option{-foffload=@var{target-list}} generates code only for the specified +comma-separated list of offload targets. + +Offload targets are specified in GCC's internal target-triplet format. You can +run the compiler with @option{-v} to show the list of configured offload targets +under @code{OFFLOAD_TARGET_NAMES}. + +@item -foffload-options=@var{options} +@itemx -foffload-options=@var{target-triplet-list}=@var{options} +@opindex foffload-options +@cindex Offloading options +@cindex OpenACC offloading options +@cindex OpenMP offloading options + +With @option{-foffload-options=@var{options}}, GCC passes the specified +@var{options} to the compilers for all enabled offloading targets. You can +specify options that apply only to a specific target or targets by using +the @option{-foffload-options=@var{target-list}=@var{options}} form. The +@var{target-list} is a comma-separated list in the same format as for the +@option{-foffload=} option. + +Typical command lines are + +@smallexample +-foffload-options=-lgfortran -foffload-options=-lm +-foffload-options="-lgfortran -lm" -foffload-options=nvptx-none=-latomic +-foffload-options=amdgcn-amdhsa=-march=gfx906 -foffload-options=-lm +@end smallexample + +@item -fopenacc +@opindex fopenacc +@cindex OpenACC accelerator programming +Enable handling of OpenACC directives @code{#pragma acc} in C/C++ and +@code{!$acc} in Fortran. When @option{-fopenacc} is specified, the +compiler generates accelerated code according to the OpenACC Application +Programming Interface v2.6 @w{@uref{https://www.openacc.org}}. This option +implies @option{-pthread}, and thus is only supported on targets that +have support for @option{-pthread}. + +@item -fopenacc-dim=@var{geom} +@opindex fopenacc-dim +@cindex OpenACC accelerator programming +Specify default compute dimensions for parallel offload regions that do +not explicitly specify. The @var{geom} value is a triple of +':'-separated sizes, in order 'gang', 'worker' and, 'vector'. A size +can be omitted, to use a target-specific default value. + +@item -fopenmp +@opindex fopenmp +@cindex OpenMP parallel +Enable handling of OpenMP directives @code{#pragma omp} in C/C++, +@code{[[omp::directive(...)]]} and @code{[[omp::sequence(...)]]} in C++ and +@code{!$omp} in Fortran. When @option{-fopenmp} is specified, the +compiler generates parallel code according to the OpenMP Application +Program Interface v4.5 @w{@uref{https://www.openmp.org}}. This option +implies @option{-pthread}, and thus is only supported on targets that +have support for @option{-pthread}. @option{-fopenmp} implies +@option{-fopenmp-simd}. + +@item -fopenmp-simd +@opindex fopenmp-simd +@cindex OpenMP SIMD +@cindex SIMD +Enable handling of OpenMP's @code{simd}, @code{declare simd}, +@code{declare reduction}, @code{assume}, @code{ordered}, @code{scan}, +@code{loop} directives and combined or composite directives with +@code{simd} as constituent with @code{#pragma omp} in C/C++, +@code{[[omp::directive(...)]]} and @code{[[omp::sequence(...)]]} in C++ +and @code{!$omp} in Fortran. Other OpenMP directives are ignored. + +@item -fpermitted-flt-eval-methods=@var{style} +@opindex fpermitted-flt-eval-methods +@opindex fpermitted-flt-eval-methods=c11 +@opindex fpermitted-flt-eval-methods=ts-18661-3 +ISO/IEC TS 18661-3 defines new permissible values for +@code{FLT_EVAL_METHOD} that indicate that operations and constants with +a semantic type that is an interchange or extended format should be +evaluated to the precision and range of that type. These new values are +a superset of those permitted under C99/C11, which does not specify the +meaning of other positive values of @code{FLT_EVAL_METHOD}. As such, code +conforming to C11 may not have been written expecting the possibility of +the new values. + +@option{-fpermitted-flt-eval-methods} specifies whether the compiler +should allow only the values of @code{FLT_EVAL_METHOD} specified in C99/C11, +or the extended set of values specified in ISO/IEC TS 18661-3. + +@var{style} is either @code{c11} or @code{ts-18661-3} as appropriate. + +The default when in a standards compliant mode (@option{-std=c11} or similar) +is @option{-fpermitted-flt-eval-methods=c11}. The default when in a GNU +dialect (@option{-std=gnu11} or similar) is +@option{-fpermitted-flt-eval-methods=ts-18661-3}. + +@item -fplan9-extensions +@opindex fplan9-extensions +Accept some non-standard constructs used in Plan 9 code. + +This enables @option{-fms-extensions}, permits passing pointers to +structures with anonymous fields to functions that expect pointers to +elements of the type of the field, and permits referring to anonymous +fields declared using a typedef. @xref{Unnamed Fields,,Unnamed +struct/union fields within structs/unions}, for details. This is only +supported for C, not C++. + +@item -fsigned-bitfields +@itemx -funsigned-bitfields +@itemx -fno-signed-bitfields +@itemx -fno-unsigned-bitfields +@opindex fsigned-bitfields +@opindex funsigned-bitfields +@opindex fno-signed-bitfields +@opindex fno-unsigned-bitfields +These options control whether a bit-field is signed or unsigned, when the +declaration does not use either @code{signed} or @code{unsigned}. By +default, such a bit-field is signed, because this is consistent: the +basic integer types such as @code{int} are signed types. + +@item -fsigned-char +@opindex fsigned-char +Let the type @code{char} be signed, like @code{signed char}. + +Note that this is equivalent to @option{-fno-unsigned-char}, which is +the negative form of @option{-funsigned-char}. Likewise, the option +@option{-fno-signed-char} is equivalent to @option{-funsigned-char}. + +@item -funsigned-char +@opindex funsigned-char +Let the type @code{char} be unsigned, like @code{unsigned char}. + +Each kind of machine has a default for what @code{char} should +be. It is either like @code{unsigned char} by default or like +@code{signed char} by default. + +Ideally, a portable program should always use @code{signed char} or +@code{unsigned char} when it depends on the signedness of an object. +But many programs have been written to use plain @code{char} and +expect it to be signed, or expect it to be unsigned, depending on the +machines they were written for. This option, and its inverse, let you +make such a program work with the opposite default. + +The type @code{char} is always a distinct type from each of +@code{signed char} or @code{unsigned char}, even though its behavior +is always just like one of those two. + +@item -fstrict-flex-arrays +@opindex fstrict-flex-arrays +@opindex fno-strict-flex-arrays +Control when to treat the trailing array of a structure as a flexible array +member for the purpose of accessing the elements of such an array. +The positive form is equivalent to @option{-fstrict-flex-arrays=3}, which is the +strictest. A trailing array is treated as a flexible array member only when it +is declared as a flexible array member per C99 standard onwards. +The negative form is equivalent to @option{-fstrict-flex-arrays=0}, which is the +least strict. All trailing arrays of structures are treated as flexible array +members. + +@item -fstrict-flex-arrays=@var{level} +@opindex fstrict-flex-arrays=@var{level} +Control when to treat the trailing array of a structure as a flexible array +member for the purpose of accessing the elements of such an array. The value +of @var{level} controls the level of strictness. + +The possible values of @var{level} are the same as for the +@code{strict_flex_array} attribute (@pxref{Variable Attributes}). + +You can control this behavior for a specific trailing array field of a +structure by using the variable attribute @code{strict_flex_array} attribute +(@pxref{Variable Attributes}). + +@item -fsso-struct=@var{endianness} +@opindex fsso-struct +Set the default scalar storage order of structures and unions to the +specified endianness. The accepted values are @samp{big-endian}, +@samp{little-endian} and @samp{native} for the native endianness of +the target (the default). This option is not supported for C++. + +@strong{Warning:} the @option{-fsso-struct} switch causes GCC to generate +code that is not binary compatible with code generated without it if the +specified endianness is not the native endianness of the target. +@end table + +@node C++ Dialect Options +@section Options Controlling C++ Dialect + +@cindex compiler options, C++ +@cindex C++ options, command-line +@cindex options, C++ +This section describes the command-line options that are only meaningful +for C++ programs. You can also use most of the GNU compiler options +regardless of what language your program is in. For example, you +might compile a file @file{firstClass.C} like this: + +@smallexample +g++ -g -fstrict-enums -O -c firstClass.C +@end smallexample + +@noindent +In this example, only @option{-fstrict-enums} is an option meant +only for C++ programs; you can use the other options with any +language supported by GCC@. + +Some options for compiling C programs, such as @option{-std}, are also +relevant for C++ programs. +@xref{C Dialect Options,,Options Controlling C Dialect}. + +Here is a list of options that are @emph{only} for compiling C++ programs: + +@table @gcctabopt + +@item -fabi-version=@var{n} +@opindex fabi-version +Use version @var{n} of the C++ ABI@. The default is version 0. + +Version 0 refers to the version conforming most closely to +the C++ ABI specification. Therefore, the ABI obtained using version 0 +will change in different versions of G++ as ABI bugs are fixed. + +Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. + +Version 2 is the version of the C++ ABI that first appeared in G++ +3.4, and was the default through G++ 4.9. + +Version 3 corrects an error in mangling a constant address as a +template argument. + +Version 4, which first appeared in G++ 4.5, implements a standard +mangling for vector types. + +Version 5, which first appeared in G++ 4.6, corrects the mangling of +attribute const/volatile on function pointer types, decltype of a +plain decl, and use of a function parameter in the declaration of +another parameter. + +Version 6, which first appeared in G++ 4.7, corrects the promotion +behavior of C++11 scoped enums and the mangling of template argument +packs, const/static_cast, prefix ++ and --, and a class scope function +used as a template argument. + +Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a +builtin type and corrects the mangling of lambdas in default argument +scope. + +Version 8, which first appeared in G++ 4.9, corrects the substitution +behavior of function types with function-cv-qualifiers. + +Version 9, which first appeared in G++ 5.2, corrects the alignment of +@code{nullptr_t}. + +Version 10, which first appeared in G++ 6.1, adds mangling of +attributes that affect type identity, such as ia32 calling convention +attributes (e.g.@: @samp{stdcall}). + +Version 11, which first appeared in G++ 7, corrects the mangling of +sizeof... expressions and operator names. For multiple entities with +the same name within a function, that are declared in different scopes, +the mangling now changes starting with the twelfth occurrence. It also +implies @option{-fnew-inheriting-ctors}. + +Version 12, which first appeared in G++ 8, corrects the calling +conventions for empty classes on the x86_64 target and for classes +with only deleted copy/move constructors. It accidentally changes the +calling convention for classes with a deleted copy constructor and a +trivial move constructor. + +Version 13, which first appeared in G++ 8.2, fixes the accidental +change in version 12. + +Version 14, which first appeared in G++ 10, corrects the mangling of +the nullptr expression. + +Version 15, which first appeared in G++ 10.3, corrects G++ 10 ABI +tag regression. + +Version 16, which first appeared in G++ 11, changes the mangling of +@code{__alignof__} to be distinct from that of @code{alignof}, and +dependent operator names. + +Version 17, which first appeared in G++ 12, fixes layout of classes +that inherit from aggregate classes with default member initializers +in C++14 and up. + +Version 18, which first appeard in G++ 13, fixes manglings of lambdas +that have additional context. + +See also @option{-Wabi}. + +@item -fabi-compat-version=@var{n} +@opindex fabi-compat-version +On targets that support strong aliases, G++ +works around mangling changes by creating an alias with the correct +mangled name when defining a symbol with an incorrect mangled name. +This switch specifies which ABI version to use for the alias. + +With @option{-fabi-version=0} (the default), this defaults to 13 (GCC 8.2 +compatibility). If another ABI version is explicitly selected, this +defaults to 0. For compatibility with GCC versions 3.2 through 4.9, +use @option{-fabi-compat-version=2}. + +If this option is not provided but @option{-Wabi=@var{n}} is, that +version is used for compatibility aliases. If this option is provided +along with @option{-Wabi} (without the version), the version from this +option is used for the warning. + +@item -fno-access-control +@opindex fno-access-control +@opindex faccess-control +Turn off all access checking. This switch is mainly useful for working +around bugs in the access control code. + +@item -faligned-new +@opindex faligned-new +Enable support for C++17 @code{new} of types that require more +alignment than @code{void* ::operator new(std::size_t)} provides. A +numeric argument such as @code{-faligned-new=32} can be used to +specify how much alignment (in bytes) is provided by that function, +but few users will need to override the default of +@code{alignof(std::max_align_t)}. + +This flag is enabled by default for @option{-std=c++17}. + +@item -fchar8_t +@itemx -fno-char8_t +@opindex fchar8_t +@opindex fno-char8_t +Enable support for @code{char8_t} as adopted for C++20. This includes +the addition of a new @code{char8_t} fundamental type, changes to the +types of UTF-8 string and character literals, new signatures for +user-defined literals, associated standard library updates, and new +@code{__cpp_char8_t} and @code{__cpp_lib_char8_t} feature test macros. + +This option enables functions to be overloaded for ordinary and UTF-8 +strings: + +@smallexample +int f(const char *); // #1 +int f(const char8_t *); // #2 +int v1 = f("text"); // Calls #1 +int v2 = f(u8"text"); // Calls #2 +@end smallexample + +@noindent +and introduces new signatures for user-defined literals: + +@smallexample +int operator""_udl1(char8_t); +int v3 = u8'x'_udl1; +int operator""_udl2(const char8_t*, std::size_t); +int v4 = u8"text"_udl2; +template int operator""_udl3(); +int v5 = u8"text"_udl3; +@end smallexample + +@noindent +The change to the types of UTF-8 string and character literals introduces +incompatibilities with ISO C++11 and later standards. For example, the +following code is well-formed under ISO C++11, but is ill-formed when +@option{-fchar8_t} is specified. + +@smallexample +char ca[] = u8"xx"; // error: char-array initialized from wide + // string +const char *cp = u8"xx";// error: invalid conversion from + // `const char8_t*' to `const char*' +int f(const char*); +auto v = f(u8"xx"); // error: invalid conversion from + // `const char8_t*' to `const char*' +std::string s@{u8"xx"@}; // error: no matching function for call to + // `std::basic_string::basic_string()' +using namespace std::literals; +s = u8"xx"s; // error: conversion from + // `basic_string' to non-scalar + // type `basic_string' requested +@end smallexample + +@item -fcheck-new +@opindex fcheck-new +Check that the pointer returned by @code{operator new} is non-null +before attempting to modify the storage allocated. This check is +normally unnecessary because the C++ standard specifies that +@code{operator new} only returns @code{0} if it is declared +@code{throw()}, in which case the compiler always checks the +return value even without this option. In all other cases, when +@code{operator new} has a non-empty exception specification, memory +exhaustion is signalled by throwing @code{std::bad_alloc}. See also +@samp{new (nothrow)}. + +@item -fconcepts +@itemx -fconcepts-ts +@opindex fconcepts +@opindex fconcepts-ts +Enable support for the C++ Concepts feature for constraining template +arguments. With @option{-std=c++20} and above, Concepts are part of +the language standard, so @option{-fconcepts} defaults to on. + +Some constructs that were allowed by the earlier C++ Extensions for +Concepts Technical Specification, ISO 19217 (2015), but didn't make it +into the standard, can additionally be enabled by +@option{-fconcepts-ts}. + +@item -fconstexpr-depth=@var{n} +@opindex fconstexpr-depth +Set the maximum nested evaluation depth for C++11 constexpr functions +to @var{n}. A limit is needed to detect endless recursion during +constant expression evaluation. The minimum specified by the standard +is 512. + +@item -fconstexpr-cache-depth=@var{n} +@opindex fconstexpr-cache-depth +Set the maximum level of nested evaluation depth for C++11 constexpr +functions that will be cached to @var{n}. This is a heuristic that +trades off compilation speed (when the cache avoids repeated +calculations) against memory consumption (when the cache grows very +large from highly recursive evaluations). The default is 8. Very few +users are likely to want to adjust it, but if your code does heavy +constexpr calculations you might want to experiment to find which +value works best for you. + +@item -fconstexpr-fp-except +@opindex fconstexpr-fp-except +Annex F of the C standard specifies that IEC559 floating point +exceptions encountered at compile time should not stop compilation. +C++ compilers have historically not followed this guidance, instead +treating floating point division by zero as non-constant even though +it has a well defined value. This flag tells the compiler to give +Annex F priority over other rules saying that a particular operation +is undefined. + +@smallexample +constexpr float inf = 1./0.; // OK with -fconstexpr-fp-except +@end smallexample + +@item -fconstexpr-loop-limit=@var{n} +@opindex fconstexpr-loop-limit +Set the maximum number of iterations for a loop in C++14 constexpr functions +to @var{n}. A limit is needed to detect infinite loops during +constant expression evaluation. The default is 262144 (1<<18). + +@item -fconstexpr-ops-limit=@var{n} +@opindex fconstexpr-ops-limit +Set the maximum number of operations during a single constexpr evaluation. +Even when number of iterations of a single loop is limited with the above limit, +if there are several nested loops and each of them has many iterations but still +smaller than the above limit, or if in a body of some loop or even outside +of a loop too many expressions need to be evaluated, the resulting constexpr +evaluation might take too long. +The default is 33554432 (1<<25). + +@item -fcoroutines +@opindex fcoroutines +Enable support for the C++ coroutines extension (experimental). + +@item -fno-elide-constructors +@opindex fno-elide-constructors +@opindex felide-constructors +The C++ standard allows an implementation to omit creating a temporary +that is only used to initialize another object of the same type. +Specifying this option disables that optimization, and forces G++ to +call the copy constructor in all cases. This option also causes G++ +to call trivial member functions which otherwise would be expanded inline. + +In C++17, the compiler is required to omit these temporaries, but this +option still affects trivial member functions. + +@item -fno-enforce-eh-specs +@opindex fno-enforce-eh-specs +@opindex fenforce-eh-specs +Don't generate code to check for violation of exception specifications +at run time. This option violates the C++ standard, but may be useful +for reducing code size in production builds, much like defining +@code{NDEBUG}. This does not give user code permission to throw +exceptions in violation of the exception specifications; the compiler +still optimizes based on the specifications, so throwing an +unexpected exception results in undefined behavior at run time. + +@item -fextern-tls-init +@itemx -fno-extern-tls-init +@opindex fextern-tls-init +@opindex fno-extern-tls-init +The C++11 and OpenMP standards allow @code{thread_local} and +@code{threadprivate} variables to have dynamic (runtime) +initialization. To support this, any use of such a variable goes +through a wrapper function that performs any necessary initialization. +When the use and definition of the variable are in the same +translation unit, this overhead can be optimized away, but when the +use is in a different translation unit there is significant overhead +even if the variable doesn't actually need dynamic initialization. If +the programmer can be sure that no use of the variable in a +non-defining TU needs to trigger dynamic initialization (either +because the variable is statically initialized, or a use of the +variable in the defining TU will be executed before any uses in +another TU), they can avoid this overhead with the +@option{-fno-extern-tls-init} option. + +On targets that support symbol aliases, the default is +@option{-fextern-tls-init}. On targets that do not support symbol +aliases, the default is @option{-fno-extern-tls-init}. + +@item -ffold-simple-inlines +@itemx -fno-fold-simple-inlines +@opindex ffold-simple-inlines +@opindex fno-fold-simple-inlines +Permit the C++ frontend to fold calls to @code{std::move}, @code{std::forward}, +@code{std::addressof} and @code{std::as_const}. In contrast to inlining, this +means no debug information will be generated for such calls. Since these +functions are rarely interesting to debug, this flag is enabled by default +unless @option{-fno-inline} is active. + +@item -fno-gnu-keywords +@opindex fno-gnu-keywords +@opindex fgnu-keywords +Do not recognize @code{typeof} as a keyword, so that code can use this +word as an identifier. You can use the keyword @code{__typeof__} instead. +This option is implied by the strict ISO C++ dialects: @option{-ansi}, +@option{-std=c++98}, @option{-std=c++11}, etc. + +@item -fimplicit-constexpr +@opindex fimplicit-constexpr +Make inline functions implicitly constexpr, if they satisfy the +requirements for a constexpr function. This option can be used in +C++14 mode or later. This can result in initialization changing from +dynamic to static and other optimizations. + +@item -fno-implicit-templates +@opindex fno-implicit-templates +@opindex fimplicit-templates +Never emit code for non-inline templates that are instantiated +implicitly (i.e.@: by use); only emit code for explicit instantiations. +If you use this option, you must take care to structure your code to +include all the necessary explicit instantiations to avoid getting +undefined symbols at link time. +@xref{Template Instantiation}, for more information. + +@item -fno-implicit-inline-templates +@opindex fno-implicit-inline-templates +@opindex fimplicit-inline-templates +Don't emit code for implicit instantiations of inline templates, either. +The default is to handle inlines differently so that compiles with and +without optimization need the same set of explicit instantiations. + +@item -fno-implement-inlines +@opindex fno-implement-inlines +@opindex fimplement-inlines +To save space, do not emit out-of-line copies of inline functions +controlled by @code{#pragma implementation}. This causes linker +errors if these functions are not inlined everywhere they are called. + +@item -fmodules-ts +@itemx -fno-modules-ts +@opindex fmodules-ts +@opindex fno-modules-ts +Enable support for C++20 modules (@pxref{C++ Modules}). The +@option{-fno-modules-ts} is usually not needed, as that is the +default. Even though this is a C++20 feature, it is not currently +implicitly enabled by selecting that standard version. + +@item -fmodule-header +@itemx -fmodule-header=user +@itemx -fmodule-header=system +@opindex fmodule-header +Compile a header file to create an importable header unit. + +@item -fmodule-implicit-inline +@opindex fmodule-implicit-inline +Member functions defined in their class definitions are not implicitly +inline for modular code. This is different to traditional C++ +behavior, for good reasons. However, it may result in a difficulty +during code porting. This option makes such function definitions +implicitly inline. It does however generate an ABI incompatibility, +so you must use it everywhere or nowhere. (Such definitions outside +of a named module remain implicitly inline, regardless.) + +@item -fno-module-lazy +@opindex fno-module-lazy +@opindex fmodule-lazy +Disable lazy module importing and module mapper creation. + +@item -fmodule-mapper=@r{[}@var{hostname}@r{]}:@var{port}@r{[}?@var{ident}@r{]} +@itemx -fmodule-mapper=|@var{program}@r{[}?@var{ident}@r{]} @var{args...} +@itemx -fmodule-mapper==@var{socket}@r{[}?@var{ident}@r{]} +@itemx -fmodule-mapper=<>@r{[}@var{inout}@r{]}@r{[}?@var{ident}@r{]} +@itemx -fmodule-mapper=<@var{in}>@var{out}@r{[}?@var{ident}@r{]} +@itemx -fmodule-mapper=@var{file}@r{[}?@var{ident}@r{]} +@vindex CXX_MODULE_MAPPER @r{environment variable} +@opindex fmodule-mapper +An oracle to query for module name to filename mappings. If +unspecified the @env{CXX_MODULE_MAPPER} environment variable is used, +and if that is unset, an in-process default is provided. + +@item -fmodule-only +@opindex fmodule-only +Only emit the Compiled Module Interface, inhibiting any object file. + +@item -fms-extensions +@opindex fms-extensions +Disable Wpedantic warnings about constructs used in MFC, such as implicit +int and getting a pointer to member function via non-standard syntax. + +@item -fnew-inheriting-ctors +@opindex fnew-inheriting-ctors +Enable the P0136 adjustment to the semantics of C++11 constructor +inheritance. This is part of C++17 but also considered to be a Defect +Report against C++11 and C++14. This flag is enabled by default +unless @option{-fabi-version=10} or lower is specified. + +@item -fnew-ttp-matching +@opindex fnew-ttp-matching +Enable the P0522 resolution to Core issue 150, template template +parameters and default arguments: this allows a template with default +template arguments as an argument for a template template parameter +with fewer template parameters. This flag is enabled by default for +@option{-std=c++17}. + +@item -fno-nonansi-builtins +@opindex fno-nonansi-builtins +@opindex fnonansi-builtins +Disable built-in declarations of functions that are not mandated by +ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, +@code{index}, @code{bzero}, @code{conjf}, and other related functions. + +@item -fnothrow-opt +@opindex fnothrow-opt +Treat a @code{throw()} exception specification as if it were a +@code{noexcept} specification to reduce or eliminate the text size +overhead relative to a function with no exception specification. If +the function has local variables of types with non-trivial +destructors, the exception specification actually makes the +function smaller because the EH cleanups for those variables can be +optimized away. The semantic effect is that an exception thrown out of +a function with such an exception specification results in a call +to @code{terminate} rather than @code{unexpected}. + +@item -fno-operator-names +@opindex fno-operator-names +@opindex foperator-names +Do not treat the operator name keywords @code{and}, @code{bitand}, +@code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as +synonyms as keywords. + +@item -fno-optional-diags +@opindex fno-optional-diags +@opindex foptional-diags +Disable diagnostics that the standard says a compiler does not need to +issue. Currently, the only such diagnostic issued by G++ is the one for +a name having multiple meanings within a class. + +@item -fpermissive +@opindex fpermissive +Downgrade some diagnostics about nonconformant code from errors to +warnings. Thus, using @option{-fpermissive} allows some +nonconforming code to compile. + +@item -fno-pretty-templates +@opindex fno-pretty-templates +@opindex fpretty-templates +When an error message refers to a specialization of a function +template, the compiler normally prints the signature of the +template followed by the template arguments and any typedefs or +typenames in the signature (e.g.@: @code{void f(T) [with T = int]} +rather than @code{void f(int)}) so that it's clear which template is +involved. When an error message refers to a specialization of a class +template, the compiler omits any template arguments that match +the default template arguments for that template. If either of these +behaviors make it harder to understand the error message rather than +easier, you can use @option{-fno-pretty-templates} to disable them. + +@item -fno-rtti +@opindex fno-rtti +@opindex frtti +Disable generation of information about every class with virtual +functions for use by the C++ run-time type identification features +(@code{dynamic_cast} and @code{typeid}). If you don't use those parts +of the language, you can save some space by using this flag. Note that +exception handling uses the same information, but G++ generates it as +needed. The @code{dynamic_cast} operator can still be used for casts that +do not require run-time type information, i.e.@: casts to @code{void *} or to +unambiguous base classes. + +Mixing code compiled with @option{-frtti} with that compiled with +@option{-fno-rtti} may not work. For example, programs may +fail to link if a class compiled with @option{-fno-rtti} is used as a base +for a class compiled with @option{-frtti}. + +@item -fsized-deallocation +@opindex fsized-deallocation +Enable the built-in global declarations +@smallexample +void operator delete (void *, std::size_t) noexcept; +void operator delete[] (void *, std::size_t) noexcept; +@end smallexample +as introduced in C++14. This is useful for user-defined replacement +deallocation functions that, for example, use the size of the object +to make deallocation faster. Enabled by default under +@option{-std=c++14} and above. The flag @option{-Wsized-deallocation} +warns about places that might want to add a definition. + +@item -fstrict-enums +@opindex fstrict-enums +Allow the compiler to optimize using the assumption that a value of +enumerated type can only be one of the values of the enumeration (as +defined in the C++ standard; basically, a value that can be +represented in the minimum number of bits needed to represent all the +enumerators). This assumption may not be valid if the program uses a +cast to convert an arbitrary integer value to the enumerated type. + +@item -fstrong-eval-order +@opindex fstrong-eval-order +Evaluate member access, array subscripting, and shift expressions in +left-to-right order, and evaluate assignment in right-to-left order, +as adopted for C++17. Enabled by default with @option{-std=c++17}. +@option{-fstrong-eval-order=some} enables just the ordering of member +access and shift expressions, and is the default without +@option{-std=c++17}. + +@item -ftemplate-backtrace-limit=@var{n} +@opindex ftemplate-backtrace-limit +Set the maximum number of template instantiation notes for a single +warning or error to @var{n}. The default value is 10. + +@item -ftemplate-depth=@var{n} +@opindex ftemplate-depth +Set the maximum instantiation depth for template classes to @var{n}. +A limit on the template instantiation depth is needed to detect +endless recursions during template class instantiation. ANSI/ISO C++ +conforming programs must not rely on a maximum depth greater than 17 +(changed to 1024 in C++11). The default value is 900, as the compiler +can run out of stack space before hitting 1024 in some situations. + +@item -fno-threadsafe-statics +@opindex fno-threadsafe-statics +@opindex fthreadsafe-statics +Do not emit the extra code to use the routines specified in the C++ +ABI for thread-safe initialization of local statics. You can use this +option to reduce code size slightly in code that doesn't need to be +thread-safe. + +@item -fuse-cxa-atexit +@opindex fuse-cxa-atexit +Register destructors for objects with static storage duration with the +@code{__cxa_atexit} function rather than the @code{atexit} function. +This option is required for fully standards-compliant handling of static +destructors, but only works if your C library supports +@code{__cxa_atexit}. + +@item -fno-use-cxa-get-exception-ptr +@opindex fno-use-cxa-get-exception-ptr +@opindex fuse-cxa-get-exception-ptr +Don't use the @code{__cxa_get_exception_ptr} runtime routine. This +causes @code{std::uncaught_exception} to be incorrect, but is necessary +if the runtime routine is not available. + +@item -fvisibility-inlines-hidden +@opindex fvisibility-inlines-hidden +This switch declares that the user does not attempt to compare +pointers to inline functions or methods where the addresses of the two functions +are taken in different shared objects. + +The effect of this is that GCC may, effectively, mark inline methods with +@code{__attribute__ ((visibility ("hidden")))} so that they do not +appear in the export table of a DSO and do not require a PLT indirection +when used within the DSO@. Enabling this option can have a dramatic effect +on load and link times of a DSO as it massively reduces the size of the +dynamic export table when the library makes heavy use of templates. + +The behavior of this switch is not quite the same as marking the +methods as hidden directly, because it does not affect static variables +local to the function or cause the compiler to deduce that +the function is defined in only one shared object. + +You may mark a method as having a visibility explicitly to negate the +effect of the switch for that method. For example, if you do want to +compare pointers to a particular inline method, you might mark it as +having default visibility. Marking the enclosing class with explicit +visibility has no effect. + +Explicitly instantiated inline methods are unaffected by this option +as their linkage might otherwise cross a shared library boundary. +@xref{Template Instantiation}. + +@item -fvisibility-ms-compat +@opindex fvisibility-ms-compat +This flag attempts to use visibility settings to make GCC's C++ +linkage model compatible with that of Microsoft Visual Studio. + +The flag makes these changes to GCC's linkage model: + +@enumerate +@item +It sets the default visibility to @code{hidden}, like +@option{-fvisibility=hidden}. + +@item +Types, but not their members, are not hidden by default. + +@item +The One Definition Rule is relaxed for types without explicit +visibility specifications that are defined in more than one +shared object: those declarations are permitted if they are +permitted when this option is not used. +@end enumerate + +In new code it is better to use @option{-fvisibility=hidden} and +export those classes that are intended to be externally visible. +Unfortunately it is possible for code to rely, perhaps accidentally, +on the Visual Studio behavior. + +Among the consequences of these changes are that static data members +of the same type with the same name but defined in different shared +objects are different, so changing one does not change the other; +and that pointers to function members defined in different shared +objects may not compare equal. When this flag is given, it is a +violation of the ODR to define types with the same name differently. + +@item -fno-weak +@opindex fno-weak +@opindex fweak +Do not use weak symbol support, even if it is provided by the linker. +By default, G++ uses weak symbols if they are available. This +option exists only for testing, and should not be used by end-users; +it results in inferior code and has no benefits. This option may +be removed in a future release of G++. + +@item -fext-numeric-literals @r{(C++ and Objective-C++ only)} +@opindex fext-numeric-literals +@opindex fno-ext-numeric-literals +Accept imaginary, fixed-point, or machine-defined +literal number suffixes as GNU extensions. +When this option is turned off these suffixes are treated +as C++11 user-defined literal numeric suffixes. +This is on by default for all pre-C++11 dialects and all GNU dialects: +@option{-std=c++98}, @option{-std=gnu++98}, @option{-std=gnu++11}, +@option{-std=gnu++14}. +This option is off by default +for ISO C++11 onwards (@option{-std=c++11}, ...). + +@item -nostdinc++ +@opindex nostdinc++ +Do not search for header files in the standard directories specific to +C++, but do still search the other standard directories. (This option +is used when building the C++ library.) + +@item -flang-info-include-translate +@itemx -flang-info-include-translate-not +@itemx -flang-info-include-translate=@var{header} +@opindex flang-info-include-translate +@opindex flang-info-include-translate-not +Inform of include translation events. The first will note accepted +include translations, the second will note declined include +translations. The @var{header} form will inform of include +translations relating to that specific header. If @var{header} is of +the form @code{"user"} or @code{} it will be resolved to a +specific user or system header using the include path. + +@item -flang-info-module-cmi +@itemx -flang-info-module-cmi=@var{module} +@opindex flang-info-module-cmi +Inform of Compiled Module Interface pathnames. The first will note +all read CMI pathnames. The @var{module} form will not reading a +specific module's CMI. @var{module} may be a named module or a +header-unit (the latter indicated by either being a pathname containing +directory separators or enclosed in @code{<>} or @code{""}). + +@item -stdlib=@var{libstdc++,libc++} +@opindex stdlib +When G++ is configured to support this option, it allows specification of +alternate C++ runtime libraries. Two options are available: @var{libstdc++} +(the default, native C++ runtime for G++) and @var{libc++} which is the +C++ runtime installed on some operating systems (e.g. Darwin versions from +Darwin11 onwards). The option switches G++ to use the headers from the +specified library and to emit @code{-lstdc++} or @code{-lc++} respectively, +when a C++ runtime is required for linking. +@end table + +In addition, these warning options have meanings only for C++ programs: + +@table @gcctabopt +@item -Wabi-tag @r{(C++ and Objective-C++ only)} +@opindex Wabi-tag +Warn when a type with an ABI tag is used in a context that does not +have that ABI tag. See @ref{C++ Attributes} for more information +about ABI tags. + +@item -Wcomma-subscript @r{(C++ and Objective-C++ only)} +@opindex Wcomma-subscript +@opindex Wno-comma-subscript +Warn about uses of a comma expression within a subscripting expression. +This usage was deprecated in C++20 and is going to be removed in C++23. +However, a comma expression wrapped in @code{( )} is not deprecated. Example: + +@smallexample +@group +void f(int *a, int b, int c) @{ + a[b,c]; // deprecated in C++20, invalid in C++23 + a[(b,c)]; // OK +@} +@end group +@end smallexample + +In C++23 it is valid to have comma separated expressions in a subscript +when an overloaded subscript operator is found and supports the right +number and types of arguments. G++ will accept the formerly valid syntax +for code that is not valid in C++23 but used to be valid but deprecated +in C++20 with a pedantic warning that can be disabled with +@option{-Wno-comma-subscript}. + +Enabled by default with @option{-std=c++20} unless @option{-Wno-deprecated}, +and with @option{-std=c++23} regardless of @option{-Wno-deprecated}. + +@item -Wctad-maybe-unsupported @r{(C++ and Objective-C++ only)} +@opindex Wctad-maybe-unsupported +@opindex Wno-ctad-maybe-unsupported +Warn when performing class template argument deduction (CTAD) on a type with +no explicitly written deduction guides. This warning will point out cases +where CTAD succeeded only because the compiler synthesized the implicit +deduction guides, which might not be what the programmer intended. Certain +style guides allow CTAD only on types that specifically "opt-in"; i.e., on +types that are designed to support CTAD. This warning can be suppressed with +the following pattern: + +@smallexample +struct allow_ctad_t; // any name works +template struct S @{ + S(T) @{ @} +@}; +S(allow_ctad_t) -> S; // guide with incomplete parameter type will never be considered +@end smallexample + +@item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)} +@opindex Wctor-dtor-privacy +@opindex Wno-ctor-dtor-privacy +Warn when a class seems unusable because all the constructors or +destructors in that class are private, and it has neither friends nor +public static member functions. Also warn if there are no non-private +methods, and there's at least one private member function that isn't +a constructor or destructor. + +@item -Wdangling-reference @r{(C++ and Objective-C++ only)} +@opindex Wdangling-reference +@opindex Wno-dangling-reference +Warn when a reference is bound to a temporary whose lifetime has ended. +For example: + +@smallexample +int n = 1; +const int& r = std::max(n - 1, n + 1); // r is dangling +@end smallexample + +In the example above, two temporaries are created, one for each +argument, and a reference to one of the temporaries is returned. +However, both temporaries are destroyed at the end of the full +expression, so the reference @code{r} is dangling. This warning +also detects dangling references in member initializer lists: + +@smallexample +const int& f(const int& i) @{ return i; @} +struct S @{ + const int &r; // r is dangling + S() : r(f(10)) @{ @} +@}; +@end smallexample + +Member functions are checked as well, but only their object argument: + +@smallexample +struct S @{ + const S& self () @{ return *this; @} +@}; +const S& s = S().self(); // s is dangling +@end smallexample + +Certain functions are safe in this respect, for example @code{std::use_facet}: +they take and return a reference, but they don't return one of its arguments, +which can fool the warning. Such functions can be excluded from the warning +by wrapping them in a @code{#pragma}: + +@smallexample +#pragma GCC diagnostic push +#pragma GCC diagnostic ignored "-Wdangling-reference" +const T& foo (const T&) @{ @dots{} @} +#pragma GCC diagnostic pop +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)} +@opindex Wdelete-non-virtual-dtor +@opindex Wno-delete-non-virtual-dtor +Warn when @code{delete} is used to destroy an instance of a class that +has virtual functions and non-virtual destructor. It is unsafe to delete +an instance of a derived class through a pointer to a base class if the +base class does not have a virtual destructor. This warning is enabled +by @option{-Wall}. + +@item -Wdeprecated-copy @r{(C++ and Objective-C++ only)} +@opindex Wdeprecated-copy +@opindex Wno-deprecated-copy +Warn that the implicit declaration of a copy constructor or copy +assignment operator is deprecated if the class has a user-provided +copy constructor or copy assignment operator, in C++11 and up. This +warning is enabled by @option{-Wextra}. With +@option{-Wdeprecated-copy-dtor}, also deprecate if the class has a +user-provided destructor. + +@item -Wno-deprecated-enum-enum-conversion @r{(C++ and Objective-C++ only)} +@opindex Wdeprecated-enum-enum-conversion +@opindex Wno-deprecated-enum-enum-conversion +Disable the warning about the case when the usual arithmetic conversions +are applied on operands where one is of enumeration type and the other is +of a different enumeration type. This conversion was deprecated in C++20. +For example: + +@smallexample +enum E1 @{ e @}; +enum E2 @{ f @}; +int k = f - e; +@end smallexample + +@option{-Wdeprecated-enum-enum-conversion} is enabled by default with +@option{-std=c++20}. In pre-C++20 dialects, this warning can be enabled +by @option{-Wenum-conversion}. + +@item -Wno-deprecated-enum-float-conversion @r{(C++ and Objective-C++ only)} +@opindex Wdeprecated-enum-float-conversion +@opindex Wno-deprecated-enum-float-conversion +Disable the warning about the case when the usual arithmetic conversions +are applied on operands where one is of enumeration type and the other is +of a floating-point type. This conversion was deprecated in C++20. For +example: + +@smallexample +enum E1 @{ e @}; +enum E2 @{ f @}; +bool b = e <= 3.7; +@end smallexample + +@option{-Wdeprecated-enum-float-conversion} is enabled by default with +@option{-std=c++20}. In pre-C++20 dialects, this warning can be enabled +by @option{-Wenum-conversion}. + +@item -Wno-init-list-lifetime @r{(C++ and Objective-C++ only)} +@opindex Winit-list-lifetime +@opindex Wno-init-list-lifetime +Do not warn about uses of @code{std::initializer_list} that are likely +to result in dangling pointers. Since the underlying array for an +@code{initializer_list} is handled like a normal C++ temporary object, +it is easy to inadvertently keep a pointer to the array past the end +of the array's lifetime. For example: + +@itemize @bullet +@item +If a function returns a temporary @code{initializer_list}, or a local +@code{initializer_list} variable, the array's lifetime ends at the end +of the return statement, so the value returned has a dangling pointer. + +@item +If a new-expression creates an @code{initializer_list}, the array only +lives until the end of the enclosing full-expression, so the +@code{initializer_list} in the heap has a dangling pointer. + +@item +When an @code{initializer_list} variable is assigned from a +brace-enclosed initializer list, the temporary array created for the +right side of the assignment only lives until the end of the +full-expression, so at the next statement the @code{initializer_list} +variable has a dangling pointer. + +@smallexample +// li's initial underlying array lives as long as li +std::initializer_list li = @{ 1,2,3 @}; +// assignment changes li to point to a temporary array +li = @{ 4, 5 @}; +// now the temporary is gone and li has a dangling pointer +int i = li.begin()[0] // undefined behavior +@end smallexample + +@item +When a list constructor stores the @code{begin} pointer from the +@code{initializer_list} argument, this doesn't extend the lifetime of +the array, so if a class variable is constructed from a temporary +@code{initializer_list}, the pointer is left dangling by the end of +the variable declaration statement. + +@end itemize + +@item -Winvalid-imported-macros +@opindex Winvalid-imported-macros +@opindex Wno-invalid-imported-macros +Verify all imported macro definitions are valid at the end of +compilation. This is not enabled by default, as it requires +additional processing to determine. It may be useful when preparing +sets of header-units to ensure consistent macros. + +@item -Wno-literal-suffix @r{(C++ and Objective-C++ only)} +@opindex Wliteral-suffix +@opindex Wno-literal-suffix +Do not warn when a string or character literal is followed by a +ud-suffix which does not begin with an underscore. As a conforming +extension, GCC treats such suffixes as separate preprocessing tokens +in order to maintain backwards compatibility with code that uses +formatting macros from @code{}. For example: + +@smallexample +#define __STDC_FORMAT_MACROS +#include +#include + +int main() @{ + int64_t i64 = 123; + printf("My int64: %" PRId64"\n", i64); +@} +@end smallexample + +In this case, @code{PRId64} is treated as a separate preprocessing token. + +This option also controls warnings when a user-defined literal +operator is declared with a literal suffix identifier that doesn't +begin with an underscore. Literal suffix identifiers that don't begin +with an underscore are reserved for future standardization. + +These warnings are enabled by default. + +@item -Wno-narrowing @r{(C++ and Objective-C++ only)} +@opindex Wnarrowing +@opindex Wno-narrowing +For C++11 and later standards, narrowing conversions are diagnosed by default, +as required by the standard. A narrowing conversion from a constant produces +an error, and a narrowing conversion from a non-constant produces a warning, +but @option{-Wno-narrowing} suppresses the diagnostic. +Note that this does not affect the meaning of well-formed code; +narrowing conversions are still considered ill-formed in SFINAE contexts. + +With @option{-Wnarrowing} in C++98, warn when a narrowing +conversion prohibited by C++11 occurs within +@samp{@{ @}}, e.g. + +@smallexample +int i = @{ 2.2 @}; // error: narrowing from double to int +@end smallexample + +This flag is included in @option{-Wall} and @option{-Wc++11-compat}. + +@item -Wnoexcept @r{(C++ and Objective-C++ only)} +@opindex Wnoexcept +@opindex Wno-noexcept +Warn when a noexcept-expression evaluates to false because of a call +to a function that does not have a non-throwing exception +specification (i.e. @code{throw()} or @code{noexcept}) but is known by +the compiler to never throw an exception. + +@item -Wnoexcept-type @r{(C++ and Objective-C++ only)} +@opindex Wnoexcept-type +@opindex Wno-noexcept-type +Warn if the C++17 feature making @code{noexcept} part of a function +type changes the mangled name of a symbol relative to C++14. Enabled +by @option{-Wabi} and @option{-Wc++17-compat}. + +As an example: + +@smallexample +template void f(T t) @{ t(); @}; +void g() noexcept; +void h() @{ f(g); @} +@end smallexample + +@noindent +In C++14, @code{f} calls @code{f}, but in +C++17 it calls @code{f}. + +@item -Wclass-memaccess @r{(C++ and Objective-C++ only)} +@opindex Wclass-memaccess +@opindex Wno-class-memaccess +Warn when the destination of a call to a raw memory function such as +@code{memset} or @code{memcpy} is an object of class type, and when writing +into such an object might bypass the class non-trivial or deleted constructor +or copy assignment, violate const-correctness or encapsulation, or corrupt +virtual table pointers. Modifying the representation of such objects may +violate invariants maintained by member functions of the class. For example, +the call to @code{memset} below is undefined because it modifies a non-trivial +class object and is, therefore, diagnosed. The safe way to either initialize +or clear the storage of objects of such types is by using the appropriate +constructor or assignment operator, if one is available. +@smallexample +std::string str = "abc"; +memset (&str, 0, sizeof str); +@end smallexample +The @option{-Wclass-memaccess} option is enabled by @option{-Wall}. +Explicitly casting the pointer to the class object to @code{void *} or +to a type that can be safely accessed by the raw memory function suppresses +the warning. + +@item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)} +@opindex Wnon-virtual-dtor +@opindex Wno-non-virtual-dtor +Warn when a class has virtual functions and an accessible non-virtual +destructor itself or in an accessible polymorphic base class, in which +case it is possible but unsafe to delete an instance of a derived +class through a pointer to the class itself or base class. This +warning is automatically enabled if @option{-Weffc++} is specified. + +@item -Wregister @r{(C++ and Objective-C++ only)} +@opindex Wregister +@opindex Wno-register +Warn on uses of the @code{register} storage class specifier, except +when it is part of the GNU @ref{Explicit Register Variables} extension. +The use of the @code{register} keyword as storage class specifier has +been deprecated in C++11 and removed in C++17. +Enabled by default with @option{-std=c++17}. + +@item -Wreorder @r{(C++ and Objective-C++ only)} +@opindex Wreorder +@opindex Wno-reorder +@cindex reordering, warning +@cindex warning for reordering of member initializers +Warn when the order of member initializers given in the code does not +match the order in which they must be executed. For instance: + +@smallexample +struct A @{ + int i; + int j; + A(): j (0), i (1) @{ @} +@}; +@end smallexample + +@noindent +The compiler rearranges the member initializers for @code{i} +and @code{j} to match the declaration order of the members, emitting +a warning to that effect. This warning is enabled by @option{-Wall}. + +@item -Wno-pessimizing-move @r{(C++ and Objective-C++ only)} +@opindex Wpessimizing-move +@opindex Wno-pessimizing-move +This warning warns when a call to @code{std::move} prevents copy +elision. A typical scenario when copy elision can occur is when returning in +a function with a class return type, when the expression being returned is the +name of a non-volatile automatic object, and is not a function parameter, and +has the same type as the function return type. + +@smallexample +struct T @{ +@dots{} +@}; +T fn() +@{ + T t; + @dots{} + return std::move (t); +@} +@end smallexample + +But in this example, the @code{std::move} call prevents copy elision. + +This warning is enabled by @option{-Wall}. + +@item -Wno-redundant-move @r{(C++ and Objective-C++ only)} +@opindex Wredundant-move +@opindex Wno-redundant-move +This warning warns about redundant calls to @code{std::move}; that is, when +a move operation would have been performed even without the @code{std::move} +call. This happens because the compiler is forced to treat the object as if +it were an rvalue in certain situations such as returning a local variable, +where copy elision isn't applicable. Consider: + +@smallexample +struct T @{ +@dots{} +@}; +T fn(T t) +@{ + @dots{} + return std::move (t); +@} +@end smallexample + +Here, the @code{std::move} call is redundant. Because G++ implements Core +Issue 1579, another example is: + +@smallexample +struct T @{ // convertible to U +@dots{} +@}; +struct U @{ +@dots{} +@}; +U fn() +@{ + T t; + @dots{} + return std::move (t); +@} +@end smallexample +In this example, copy elision isn't applicable because the type of the +expression being returned and the function return type differ, yet G++ +treats the return value as if it were designated by an rvalue. + +This warning is enabled by @option{-Wextra}. + +@item -Wrange-loop-construct @r{(C++ and Objective-C++ only)} +@opindex Wrange-loop-construct +@opindex Wno-range-loop-construct +This warning warns when a C++ range-based for-loop is creating an unnecessary +copy. This can happen when the range declaration is not a reference, but +probably should be. For example: + +@smallexample +struct S @{ char arr[128]; @}; +void fn () @{ + S arr[5]; + for (const auto x : arr) @{ @dots{} @} +@} +@end smallexample + +It does not warn when the type being copied is a trivially-copyable type whose +size is less than 64 bytes. + +This warning also warns when a loop variable in a range-based for-loop is +initialized with a value of a different type resulting in a copy. For example: + +@smallexample +void fn() @{ + int arr[10]; + for (const double &x : arr) @{ @dots{} @} +@} +@end smallexample + +In the example above, in every iteration of the loop a temporary value of +type @code{double} is created and destroyed, to which the reference +@code{const double &} is bound. + +This warning is enabled by @option{-Wall}. + +@item -Wredundant-tags @r{(C++ and Objective-C++ only)} +@opindex Wredundant-tags +@opindex Wno-redundant-tags +Warn about redundant class-key and enum-key in references to class types +and enumerated types in contexts where the key can be eliminated without +causing an ambiguity. For example: + +@smallexample +struct foo; +struct foo *p; // warn that keyword struct can be eliminated +@end smallexample + +@noindent +On the other hand, in this example there is no warning: + +@smallexample +struct foo; +void foo (); // "hides" struct foo +void bar (struct foo&); // no warning, keyword struct is necessary +@end smallexample + +@item -Wno-subobject-linkage @r{(C++ and Objective-C++ only)} +@opindex Wsubobject-linkage +@opindex Wno-subobject-linkage +Do not warn +if a class type has a base or a field whose type uses the anonymous +namespace or depends on a type with no linkage. If a type A depends on +a type B with no or internal linkage, defining it in multiple +translation units would be an ODR violation because the meaning of B +is different in each translation unit. If A only appears in a single +translation unit, the best way to silence the warning is to give it +internal linkage by putting it in an anonymous namespace as well. The +compiler doesn't give this warning for types defined in the main .C +file, as those are unlikely to have multiple definitions. +@option{-Wsubobject-linkage} is enabled by default. + +@item -Weffc++ @r{(C++ and Objective-C++ only)} +@opindex Weffc++ +@opindex Wno-effc++ +Warn about violations of the following style guidelines from Scott Meyers' +@cite{Effective C++} series of books: + +@itemize @bullet +@item +Define a copy constructor and an assignment operator for classes +with dynamically-allocated memory. + +@item +Prefer initialization to assignment in constructors. + +@item +Have @code{operator=} return a reference to @code{*this}. + +@item +Don't try to return a reference when you must return an object. + +@item +Distinguish between prefix and postfix forms of increment and +decrement operators. + +@item +Never overload @code{&&}, @code{||}, or @code{,}. + +@end itemize + +This option also enables @option{-Wnon-virtual-dtor}, which is also +one of the effective C++ recommendations. However, the check is +extended to warn about the lack of virtual destructor in accessible +non-polymorphic bases classes too. + +When selecting this option, be aware that the standard library +headers do not obey all of these guidelines; use @samp{grep -v} +to filter out those warnings. + +@item -Wno-exceptions @r{(C++ and Objective-C++ only)} +@opindex Wexceptions +@opindex Wno-exceptions +Disable the warning about the case when an exception handler is shadowed by +another handler, which can point out a wrong ordering of exception handlers. + +@item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)} +@opindex Wstrict-null-sentinel +@opindex Wno-strict-null-sentinel +Warn about the use of an uncasted @code{NULL} as sentinel. When +compiling only with GCC this is a valid sentinel, as @code{NULL} is defined +to @code{__null}. Although it is a null pointer constant rather than a +null pointer, it is guaranteed to be of the same size as a pointer. +But this use is not portable across different compilers. + +@item -Wno-non-template-friend @r{(C++ and Objective-C++ only)} +@opindex Wno-non-template-friend +@opindex Wnon-template-friend +Disable warnings when non-template friend functions are declared +within a template. In very old versions of GCC that predate implementation +of the ISO standard, declarations such as +@samp{friend int foo(int)}, where the name of the friend is an unqualified-id, +could be interpreted as a particular specialization of a template +function; the warning exists to diagnose compatibility problems, +and is enabled by default. + +@item -Wold-style-cast @r{(C++ and Objective-C++ only)} +@opindex Wold-style-cast +@opindex Wno-old-style-cast +Warn if an old-style (C-style) cast to a non-void type is used within +a C++ program. The new-style casts (@code{dynamic_cast}, +@code{static_cast}, @code{reinterpret_cast}, and @code{const_cast}) are +less vulnerable to unintended effects and much easier to search for. + +@item -Woverloaded-virtual @r{(C++ and Objective-C++ only)} +@itemx -Woverloaded-virtual=@var{n} +@opindex Woverloaded-virtual +@opindex Wno-overloaded-virtual +@cindex overloaded virtual function, warning +@cindex warning for overloaded virtual function +Warn when a function declaration hides virtual functions from a +base class. For example, in: + +@smallexample +struct A @{ + virtual void f(); +@}; + +struct B: public A @{ + void f(int); // does not override +@}; +@end smallexample + +the @code{A} class version of @code{f} is hidden in @code{B}, and code +like: + +@smallexample +B* b; +b->f(); +@end smallexample + +@noindent +fails to compile. + +The optional level suffix controls the behavior when all the +declarations in the derived class override virtual functions in the +base class, even if not all of the base functions are overridden: + +@smallexample +struct C @{ + virtual void f(); + virtual void f(int); +@}; + +struct D: public C @{ + void f(int); // does override +@} +@end smallexample + +This pattern is less likely to be a mistake; if D is only used +virtually, the user might have decided that the base class semantics +for some of the overloads are fine. + +At level 1, this case does not warn; at level 2, it does. +@option{-Woverloaded-virtual} by itself selects level 2. Level 1 is +included in @option{-Wall}. + +@item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)} +@opindex Wno-pmf-conversions +@opindex Wpmf-conversions +Disable the diagnostic for converting a bound pointer to member function +to a plain pointer. + +@item -Wsign-promo @r{(C++ and Objective-C++ only)} +@opindex Wsign-promo +@opindex Wno-sign-promo +Warn when overload resolution chooses a promotion from unsigned or +enumerated type to a signed type, over a conversion to an unsigned type of +the same size. Previous versions of G++ tried to preserve +unsignedness, but the standard mandates the current behavior. + +@item -Wtemplates @r{(C++ and Objective-C++ only)} +@opindex Wtemplates +@opindex Wno-templates +Warn when a primary template declaration is encountered. Some coding +rules disallow templates, and this may be used to enforce that rule. +The warning is inactive inside a system header file, such as the STL, so +one can still use the STL. One may also instantiate or specialize +templates. + +@item -Wmismatched-new-delete @r{(C++ and Objective-C++ only)} +@opindex Wmismatched-new-delete +@opindex Wno-mismatched-new-delete +Warn for mismatches between calls to @code{operator new} or @code{operator +delete} and the corresponding call to the allocation or deallocation function. +This includes invocations of C++ @code{operator delete} with pointers +returned from either mismatched forms of @code{operator new}, or from other +functions that allocate objects for which the @code{operator delete} isn't +a suitable deallocator, as well as calls to other deallocation functions +with pointers returned from @code{operator new} for which the deallocation +function isn't suitable. + +For example, the @code{delete} expression in the function below is diagnosed +because it doesn't match the array form of the @code{new} expression +the pointer argument was returned from. Similarly, the call to @code{free} +is also diagnosed. + +@smallexample +void f () +@{ + int *a = new int[n]; + delete a; // warning: mismatch in array forms of expressions + + char *p = new char[n]; + free (p); // warning: mismatch between new and free +@} +@end smallexample + +The related option @option{-Wmismatched-dealloc} diagnoses mismatches +involving allocation and deallocation functions other than @code{operator +new} and @code{operator delete}. + +@option{-Wmismatched-new-delete} is included in @option{-Wall}. + +@item -Wmismatched-tags @r{(C++ and Objective-C++ only)} +@opindex Wmismatched-tags +@opindex Wno-mismatched-tags +Warn for declarations of structs, classes, and class templates and their +specializations with a class-key that does not match either the definition +or the first declaration if no definition is provided. + +For example, the declaration of @code{struct Object} in the argument list +of @code{draw} triggers the warning. To avoid it, either remove the redundant +class-key @code{struct} or replace it with @code{class} to match its definition. +@smallexample +class Object @{ +public: + virtual ~Object () = 0; +@}; +void draw (struct Object*); +@end smallexample + +It is not wrong to declare a class with the class-key @code{struct} as +the example above shows. The @option{-Wmismatched-tags} option is intended +to help achieve a consistent style of class declarations. In code that is +intended to be portable to Windows-based compilers the warning helps prevent +unresolved references due to the difference in the mangling of symbols +declared with different class-keys. The option can be used either on its +own or in conjunction with @option{-Wredundant-tags}. + +@item -Wmultiple-inheritance @r{(C++ and Objective-C++ only)} +@opindex Wmultiple-inheritance +@opindex Wno-multiple-inheritance +Warn when a class is defined with multiple direct base classes. Some +coding rules disallow multiple inheritance, and this may be used to +enforce that rule. The warning is inactive inside a system header file, +such as the STL, so one can still use the STL. One may also define +classes that indirectly use multiple inheritance. + +@item -Wvirtual-inheritance +@opindex Wvirtual-inheritance +@opindex Wno-virtual-inheritance +Warn when a class is defined with a virtual direct base class. Some +coding rules disallow multiple inheritance, and this may be used to +enforce that rule. The warning is inactive inside a system header file, +such as the STL, so one can still use the STL. One may also define +classes that indirectly use virtual inheritance. + +@item -Wno-virtual-move-assign +@opindex Wvirtual-move-assign +@opindex Wno-virtual-move-assign +Suppress warnings about inheriting from a virtual base with a +non-trivial C++11 move assignment operator. This is dangerous because +if the virtual base is reachable along more than one path, it is +moved multiple times, which can mean both objects end up in the +moved-from state. If the move assignment operator is written to avoid +moving from a moved-from object, this warning can be disabled. + +@item -Wnamespaces +@opindex Wnamespaces +@opindex Wno-namespaces +Warn when a namespace definition is opened. Some coding rules disallow +namespaces, and this may be used to enforce that rule. The warning is +inactive inside a system header file, such as the STL, so one can still +use the STL. One may also use using directives and qualified names. + +@item -Wno-terminate @r{(C++ and Objective-C++ only)} +@opindex Wterminate +@opindex Wno-terminate +Disable the warning about a throw-expression that will immediately +result in a call to @code{terminate}. + +@item -Wno-vexing-parse @r{(C++ and Objective-C++ only)} +@opindex Wvexing-parse +@opindex Wno-vexing-parse +Warn about the most vexing parse syntactic ambiguity. This warns about +the cases when a declaration looks like a variable definition, but the +C++ language requires it to be interpreted as a function declaration. +For instance: + +@smallexample +void f(double a) @{ + int i(); // extern int i (void); + int n(int(a)); // extern int n (int); +@} +@end smallexample + +Another example: + +@smallexample +struct S @{ S(int); @}; +void f(double a) @{ + S x(int(a)); // extern struct S x (int); + S y(int()); // extern struct S y (int (*) (void)); + S z(); // extern struct S z (void); +@} +@end smallexample + +The warning will suggest options how to deal with such an ambiguity; e.g., +it can suggest removing the parentheses or using braces instead. + +This warning is enabled by default. + +@item -Wno-class-conversion @r{(C++ and Objective-C++ only)} +@opindex Wno-class-conversion +@opindex Wclass-conversion +Do not warn when a conversion function converts an +object to the same type, to a base class of that type, or to void; such +a conversion function will never be called. + +@item -Wvolatile @r{(C++ and Objective-C++ only)} +@opindex Wvolatile +@opindex Wno-volatile +Warn about deprecated uses of the @code{volatile} qualifier. This includes +postfix and prefix @code{++} and @code{--} expressions of +@code{volatile}-qualified types, using simple assignments where the left +operand is a @code{volatile}-qualified non-class type for their value, +compound assignments where the left operand is a @code{volatile}-qualified +non-class type, @code{volatile}-qualified function return type, +@code{volatile}-qualified parameter type, and structured bindings of a +@code{volatile}-qualified type. This usage was deprecated in C++20. + +Enabled by default with @option{-std=c++20}. + +@item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)} +@opindex Wzero-as-null-pointer-constant +@opindex Wno-zero-as-null-pointer-constant +Warn when a literal @samp{0} is used as null pointer constant. This can +be useful to facilitate the conversion to @code{nullptr} in C++11. + +@item -Waligned-new +@opindex Waligned-new +@opindex Wno-aligned-new +Warn about a new-expression of a type that requires greater alignment +than the @code{alignof(std::max_align_t)} but uses an allocation +function without an explicit alignment parameter. This option is +enabled by @option{-Wall}. + +Normally this only warns about global allocation functions, but +@option{-Waligned-new=all} also warns about class member allocation +functions. + +@item -Wno-placement-new +@itemx -Wplacement-new=@var{n} +@opindex Wplacement-new +@opindex Wno-placement-new +Warn about placement new expressions with undefined behavior, such as +constructing an object in a buffer that is smaller than the type of +the object. For example, the placement new expression below is diagnosed +because it attempts to construct an array of 64 integers in a buffer only +64 bytes large. +@smallexample +char buf [64]; +new (buf) int[64]; +@end smallexample +This warning is enabled by default. + +@table @gcctabopt +@item -Wplacement-new=1 +This is the default warning level of @option{-Wplacement-new}. At this +level the warning is not issued for some strictly undefined constructs that +GCC allows as extensions for compatibility with legacy code. For example, +the following @code{new} expression is not diagnosed at this level even +though it has undefined behavior according to the C++ standard because +it writes past the end of the one-element array. +@smallexample +struct S @{ int n, a[1]; @}; +S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]); +new (s->a)int [32](); +@end smallexample + +@item -Wplacement-new=2 +At this level, in addition to diagnosing all the same constructs as at level +1, a diagnostic is also issued for placement new expressions that construct +an object in the last member of structure whose type is an array of a single +element and whose size is less than the size of the object being constructed. +While the previous example would be diagnosed, the following construct makes +use of the flexible member array extension to avoid the warning at level 2. +@smallexample +struct S @{ int n, a[]; @}; +S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]); +new (s->a)int [32](); +@end smallexample + +@end table + +@item -Wcatch-value +@itemx -Wcatch-value=@var{n} @r{(C++ and Objective-C++ only)} +@opindex Wcatch-value +@opindex Wno-catch-value +Warn about catch handlers that do not catch via reference. +With @option{-Wcatch-value=1} (or @option{-Wcatch-value} for short) +warn about polymorphic class types that are caught by value. +With @option{-Wcatch-value=2} warn about all class types that are caught +by value. With @option{-Wcatch-value=3} warn about all types that are +not caught by reference. @option{-Wcatch-value} is enabled by @option{-Wall}. + +@item -Wconditionally-supported @r{(C++ and Objective-C++ only)} +@opindex Wconditionally-supported +@opindex Wno-conditionally-supported +Warn for conditionally-supported (C++11 [intro.defs]) constructs. + +@item -Wno-delete-incomplete @r{(C++ and Objective-C++ only)} +@opindex Wdelete-incomplete +@opindex Wno-delete-incomplete +Do not warn when deleting a pointer to incomplete type, which may cause +undefined behavior at runtime. This warning is enabled by default. + +@item -Wextra-semi @r{(C++, Objective-C++ only)} +@opindex Wextra-semi +@opindex Wno-extra-semi +Warn about redundant semicolons after in-class function definitions. + +@item -Wno-inaccessible-base @r{(C++, Objective-C++ only)} +@opindex Winaccessible-base +@opindex Wno-inaccessible-base +This option controls warnings +when a base class is inaccessible in a class derived from it due to +ambiguity. The warning is enabled by default. +Note that the warning for ambiguous virtual +bases is enabled by the @option{-Wextra} option. +@smallexample +@group +struct A @{ int a; @}; + +struct B : A @{ @}; + +struct C : B, A @{ @}; +@end group +@end smallexample + +@item -Wno-inherited-variadic-ctor +@opindex Winherited-variadic-ctor +@opindex Wno-inherited-variadic-ctor +Suppress warnings about use of C++11 inheriting constructors when the +base class inherited from has a C variadic constructor; the warning is +on by default because the ellipsis is not inherited. + +@item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)} +@opindex Wno-invalid-offsetof +@opindex Winvalid-offsetof +Suppress warnings from applying the @code{offsetof} macro to a non-POD +type. According to the 2014 ISO C++ standard, applying @code{offsetof} +to a non-standard-layout type is undefined. In existing C++ implementations, +however, @code{offsetof} typically gives meaningful results. +This flag is for users who are aware that they are +writing nonportable code and who have deliberately chosen to ignore the +warning about it. + +The restrictions on @code{offsetof} may be relaxed in a future version +of the C++ standard. + +@item -Wsized-deallocation @r{(C++ and Objective-C++ only)} +@opindex Wsized-deallocation +@opindex Wno-sized-deallocation +Warn about a definition of an unsized deallocation function +@smallexample +void operator delete (void *) noexcept; +void operator delete[] (void *) noexcept; +@end smallexample +without a definition of the corresponding sized deallocation function +@smallexample +void operator delete (void *, std::size_t) noexcept; +void operator delete[] (void *, std::size_t) noexcept; +@end smallexample +or vice versa. Enabled by @option{-Wextra} along with +@option{-fsized-deallocation}. + +@item -Wsuggest-final-types +@opindex Wno-suggest-final-types +@opindex Wsuggest-final-types +Warn about types with virtual methods where code quality would be improved +if the type were declared with the C++11 @code{final} specifier, +or, if possible, +declared in an anonymous namespace. This allows GCC to more aggressively +devirtualize the polymorphic calls. This warning is more effective with +link-time optimization, +where the information about the class hierarchy graph is +more complete. + +@item -Wsuggest-final-methods +@opindex Wno-suggest-final-methods +@opindex Wsuggest-final-methods +Warn about virtual methods where code quality would be improved if the method +were declared with the C++11 @code{final} specifier, +or, if possible, its type were +declared in an anonymous namespace or with the @code{final} specifier. +This warning is +more effective with link-time optimization, where the information about the +class hierarchy graph is more complete. It is recommended to first consider +suggestions of @option{-Wsuggest-final-types} and then rebuild with new +annotations. + +@item -Wsuggest-override +@opindex Wsuggest-override +@opindex Wno-suggest-override +Warn about overriding virtual functions that are not marked with the +@code{override} keyword. + +@item -Wuse-after-free +@itemx -Wuse-after-free=@var{n} +@opindex Wuse-after-free +@opindex Wno-use-after-free +Warn about uses of pointers to dynamically allocated objects that have +been rendered indeterminate by a call to a deallocation function. +The warning is enabled at all optimization levels but may yield different +results with optimization than without. + +@table @gcctabopt +@item -Wuse-after-free=1 +At level 1 the warning attempts to diagnose only unconditional uses +of pointers made indeterminate by a deallocation call or a successful +call to @code{realloc}, regardless of whether or not the call resulted +in an actual reallocatio of memory. This includes double-@code{free} +calls as well as uses in arithmetic and relational expressions. Although +undefined, uses of indeterminate pointers in equality (or inequality) +expressions are not diagnosed at this level. +@item -Wuse-after-free=2 +At level 2, in addition to unconditional uses, the warning also diagnoses +conditional uses of pointers made indeterminate by a deallocation call. +As at level 2, uses in equality (or inequality) expressions are not +diagnosed. For example, the second call to @code{free} in the following +function is diagnosed at this level: +@smallexample +struct A @{ int refcount; void *data; @}; + +void release (struct A *p) +@{ + int refcount = --p->refcount; + free (p); + if (refcount == 0) + free (p->data); // warning: p may be used after free +@} +@end smallexample +@item -Wuse-after-free=3 +At level 3, the warning also diagnoses uses of indeterminate pointers in +equality expressions. All uses of indeterminate pointers are undefined +but equality tests sometimes appear after calls to @code{realloc} as +an attempt to determine whether the call resulted in relocating the object +to a different address. They are diagnosed at a separate level to aid +legacy code gradually transition to safe alternatives. For example, +the equality test in the function below is diagnosed at this level: +@smallexample +void adjust_pointers (int**, int); + +void grow (int **p, int n) +@{ + int **q = (int**)realloc (p, n *= 2); + if (q == p) + return; + adjust_pointers ((int**)q, n); +@} +@end smallexample +To avoid the warning at this level, store offsets into allocated memory +instead of pointers. This approach obviates needing to adjust the stored +pointers after reallocation. +@end table + +@option{-Wuse-after-free=2} is included in @option{-Wall}. + +@item -Wuseless-cast @r{(C++ and Objective-C++ only)} +@opindex Wuseless-cast +@opindex Wno-useless-cast +Warn when an expression is cast to its own type. This warning does not +occur when a class object is converted to a non-reference type as that +is a way to create a temporary: + +@smallexample +struct S @{ @}; +void g (S&&); +void f (S&& arg) +@{ + g (S(arg)); // make arg prvalue so that it can bind to S&& +@} +@end smallexample + +@item -Wno-conversion-null @r{(C++ and Objective-C++ only)} +@opindex Wconversion-null +@opindex Wno-conversion-null +Do not warn for conversions between @code{NULL} and non-pointer +types. @option{-Wconversion-null} is enabled by default. + +@end table + +@node Objective-C and Objective-C++ Dialect Options +@section Options Controlling Objective-C and Objective-C++ Dialects + +@cindex compiler options, Objective-C and Objective-C++ +@cindex Objective-C and Objective-C++ options, command-line +@cindex options, Objective-C and Objective-C++ +(NOTE: This manual does not describe the Objective-C and Objective-C++ +languages themselves. @xref{Standards,,Language Standards +Supported by GCC}, for references.) + +This section describes the command-line options that are only meaningful +for Objective-C and Objective-C++ programs. You can also use most of +the language-independent GNU compiler options. +For example, you might compile a file @file{some_class.m} like this: + +@smallexample +gcc -g -fgnu-runtime -O -c some_class.m +@end smallexample + +@noindent +In this example, @option{-fgnu-runtime} is an option meant only for +Objective-C and Objective-C++ programs; you can use the other options with +any language supported by GCC@. + +Note that since Objective-C is an extension of the C language, Objective-C +compilations may also use options specific to the C front-end (e.g., +@option{-Wtraditional}). Similarly, Objective-C++ compilations may use +C++-specific options (e.g., @option{-Wabi}). + +Here is a list of options that are @emph{only} for compiling Objective-C +and Objective-C++ programs: + +@table @gcctabopt +@item -fconstant-string-class=@var{class-name} +@opindex fconstant-string-class +Use @var{class-name} as the name of the class to instantiate for each +literal string specified with the syntax @code{@@"@dots{}"}. The default +class name is @code{NXConstantString} if the GNU runtime is being used, and +@code{NSConstantString} if the NeXT runtime is being used (see below). The +@option{-fconstant-cfstrings} option, if also present, overrides the +@option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals +to be laid out as constant CoreFoundation strings. + +@item -fgnu-runtime +@opindex fgnu-runtime +Generate object code compatible with the standard GNU Objective-C +runtime. This is the default for most types of systems. + +@item -fnext-runtime +@opindex fnext-runtime +Generate output compatible with the NeXT runtime. This is the default +for NeXT-based systems, including Darwin and Mac OS X@. The macro +@code{__NEXT_RUNTIME__} is predefined if (and only if) this option is +used. + +@item -fno-nil-receivers +@opindex fno-nil-receivers +@opindex fnil-receivers +Assume that all Objective-C message dispatches (@code{[receiver +message:arg]}) in this translation unit ensure that the receiver is +not @code{nil}. This allows for more efficient entry points in the +runtime to be used. This option is only available in conjunction with +the NeXT runtime and ABI version 0 or 1. + +@item -fobjc-abi-version=@var{n} +@opindex fobjc-abi-version +Use version @var{n} of the Objective-C ABI for the selected runtime. +This option is currently supported only for the NeXT runtime. In that +case, Version 0 is the traditional (32-bit) ABI without support for +properties and other Objective-C 2.0 additions. Version 1 is the +traditional (32-bit) ABI with support for properties and other +Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If +nothing is specified, the default is Version 0 on 32-bit target +machines, and Version 2 on 64-bit target machines. + +@item -fobjc-call-cxx-cdtors +@opindex fobjc-call-cxx-cdtors +For each Objective-C class, check if any of its instance variables is a +C++ object with a non-trivial default constructor. If so, synthesize a +special @code{- (id) .cxx_construct} instance method which runs +non-trivial default constructors on any such instance variables, in order, +and then return @code{self}. Similarly, check if any instance variable +is a C++ object with a non-trivial destructor, and if so, synthesize a +special @code{- (void) .cxx_destruct} method which runs +all such default destructors, in reverse order. + +The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} +methods thusly generated only operate on instance variables +declared in the current Objective-C class, and not those inherited +from superclasses. It is the responsibility of the Objective-C +runtime to invoke all such methods in an object's inheritance +hierarchy. The @code{- (id) .cxx_construct} methods are invoked +by the runtime immediately after a new object instance is allocated; +the @code{- (void) .cxx_destruct} methods are invoked immediately +before the runtime deallocates an object instance. + +As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has +support for invoking the @code{- (id) .cxx_construct} and +@code{- (void) .cxx_destruct} methods. + +@item -fobjc-direct-dispatch +@opindex fobjc-direct-dispatch +Allow fast jumps to the message dispatcher. On Darwin this is +accomplished via the comm page. + +@item -fobjc-exceptions +@opindex fobjc-exceptions +Enable syntactic support for structured exception handling in +Objective-C, similar to what is offered by C++. This option +is required to use the Objective-C keywords @code{@@try}, +@code{@@throw}, @code{@@catch}, @code{@@finally} and +@code{@@synchronized}. This option is available with both the GNU +runtime and the NeXT runtime (but not available in conjunction with +the NeXT runtime on Mac OS X 10.2 and earlier). + +@item -fobjc-gc +@opindex fobjc-gc +Enable garbage collection (GC) in Objective-C and Objective-C++ +programs. This option is only available with the NeXT runtime; the +GNU runtime has a different garbage collection implementation that +does not require special compiler flags. + +@item -fobjc-nilcheck +@opindex fobjc-nilcheck +For the NeXT runtime with version 2 of the ABI, check for a nil +receiver in method invocations before doing the actual method call. +This is the default and can be disabled using +@option{-fno-objc-nilcheck}. Class methods and super calls are never +checked for nil in this way no matter what this flag is set to. +Currently this flag does nothing when the GNU runtime, or an older +version of the NeXT runtime ABI, is used. + +@item -fobjc-std=objc1 +@opindex fobjc-std +Conform to the language syntax of Objective-C 1.0, the language +recognized by GCC 4.0. This only affects the Objective-C additions to +the C/C++ language; it does not affect conformance to C/C++ standards, +which is controlled by the separate C/C++ dialect option flags. When +this option is used with the Objective-C or Objective-C++ compiler, +any Objective-C syntax that is not recognized by GCC 4.0 is rejected. +This is useful if you need to make sure that your Objective-C code can +be compiled with older versions of GCC@. + +@item -freplace-objc-classes +@opindex freplace-objc-classes +Emit a special marker instructing @command{ld(1)} not to statically link in +the resulting object file, and allow @command{dyld(1)} to load it in at +run time instead. This is used in conjunction with the Fix-and-Continue +debugging mode, where the object file in question may be recompiled and +dynamically reloaded in the course of program execution, without the need +to restart the program itself. Currently, Fix-and-Continue functionality +is only available in conjunction with the NeXT runtime on Mac OS X 10.3 +and later. + +@item -fzero-link +@opindex fzero-link +When compiling for the NeXT runtime, the compiler ordinarily replaces calls +to @code{objc_getClass("@dots{}")} (when the name of the class is known at +compile time) with static class references that get initialized at load time, +which improves run-time performance. Specifying the @option{-fzero-link} flag +suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} +to be retained. This is useful in Zero-Link debugging mode, since it allows +for individual class implementations to be modified during program execution. +The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")} +regardless of command-line options. + +@item -fno-local-ivars +@opindex fno-local-ivars +@opindex flocal-ivars +By default instance variables in Objective-C can be accessed as if +they were local variables from within the methods of the class they're +declared in. This can lead to shadowing between instance variables +and other variables declared either locally inside a class method or +globally with the same name. Specifying the @option{-fno-local-ivars} +flag disables this behavior thus avoiding variable shadowing issues. + +@item -fivar-visibility=@r{[}public@r{|}protected@r{|}private@r{|}package@r{]} +@opindex fivar-visibility +Set the default instance variable visibility to the specified option +so that instance variables declared outside the scope of any access +modifier directives default to the specified visibility. + +@item -gen-decls +@opindex gen-decls +Dump interface declarations for all classes seen in the source file to a +file named @file{@var{sourcename}.decl}. + +@item -Wassign-intercept @r{(Objective-C and Objective-C++ only)} +@opindex Wassign-intercept +@opindex Wno-assign-intercept +Warn whenever an Objective-C assignment is being intercepted by the +garbage collector. + +@item -Wno-property-assign-default @r{(Objective-C and Objective-C++ only)} +@opindex Wproperty-assign-default +@opindex Wno-property-assign-default +Do not warn if a property for an Objective-C object has no assign +semantics specified. + +@item -Wno-protocol @r{(Objective-C and Objective-C++ only)} +@opindex Wno-protocol +@opindex Wprotocol +If a class is declared to implement a protocol, a warning is issued for +every method in the protocol that is not implemented by the class. The +default behavior is to issue a warning for every method not explicitly +implemented in the class, even if a method implementation is inherited +from the superclass. If you use the @option{-Wno-protocol} option, then +methods inherited from the superclass are considered to be implemented, +and no warning is issued for them. + +@item -Wobjc-root-class @r{(Objective-C and Objective-C++ only)} +@opindex Wobjc-root-class +Warn if a class interface lacks a superclass. Most classes will inherit +from @code{NSObject} (or @code{Object}) for example. When declaring +classes intended to be root classes, the warning can be suppressed by +marking their interfaces with @code{__attribute__((objc_root_class))}. + +@item -Wselector @r{(Objective-C and Objective-C++ only)} +@opindex Wselector +@opindex Wno-selector +Warn if multiple methods of different types for the same selector are +found during compilation. The check is performed on the list of methods +in the final stage of compilation. Additionally, a check is performed +for each selector appearing in a @code{@@selector(@dots{})} +expression, and a corresponding method for that selector has been found +during compilation. Because these checks scan the method table only at +the end of compilation, these warnings are not produced if the final +stage of compilation is not reached, for example because an error is +found during compilation, or because the @option{-fsyntax-only} option is +being used. + +@item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)} +@opindex Wstrict-selector-match +@opindex Wno-strict-selector-match +Warn if multiple methods with differing argument and/or return types are +found for a given selector when attempting to send a message using this +selector to a receiver of type @code{id} or @code{Class}. When this flag +is off (which is the default behavior), the compiler omits such warnings +if any differences found are confined to types that share the same size +and alignment. + +@item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)} +@opindex Wundeclared-selector +@opindex Wno-undeclared-selector +Warn if a @code{@@selector(@dots{})} expression referring to an +undeclared selector is found. A selector is considered undeclared if no +method with that name has been declared before the +@code{@@selector(@dots{})} expression, either explicitly in an +@code{@@interface} or @code{@@protocol} declaration, or implicitly in +an @code{@@implementation} section. This option always performs its +checks as soon as a @code{@@selector(@dots{})} expression is found, +while @option{-Wselector} only performs its checks in the final stage of +compilation. This also enforces the coding style convention +that methods and selectors must be declared before being used. + +@item -print-objc-runtime-info +@opindex print-objc-runtime-info +Generate C header describing the largest structure that is passed by +value, if any. + +@end table + +@node Diagnostic Message Formatting Options +@section Options to Control Diagnostic Messages Formatting +@cindex options to control diagnostics formatting +@cindex diagnostic messages +@cindex message formatting + +Traditionally, diagnostic messages have been formatted irrespective of +the output device's aspect (e.g.@: its width, @dots{}). You can use the +options described below +to control the formatting algorithm for diagnostic messages, +e.g.@: how many characters per line, how often source location +information should be reported. Note that some language front ends may not +honor these options. + +@table @gcctabopt +@item -fmessage-length=@var{n} +@opindex fmessage-length +Try to format error messages so that they fit on lines of about +@var{n} characters. If @var{n} is zero, then no line-wrapping is +done; each error message appears on a single line. This is the +default for all front ends. + +Note - this option also affects the display of the @samp{#error} and +@samp{#warning} pre-processor directives, and the @samp{deprecated} +function/type/variable attribute. It does not however affect the +@samp{pragma GCC warning} and @samp{pragma GCC error} pragmas. + +@item -fdiagnostics-plain-output +This option requests that diagnostic output look as plain as possible, which +may be useful when running @command{dejagnu} or other utilities that need to +parse diagnostics output and prefer that it remain more stable over time. +@option{-fdiagnostics-plain-output} is currently equivalent to the following +options: +@gccoptlist{-fno-diagnostics-show-caret @gol +-fno-diagnostics-show-line-numbers @gol +-fdiagnostics-color=never @gol +-fdiagnostics-urls=never @gol +-fdiagnostics-path-format=separate-events} +In the future, if GCC changes the default appearance of its diagnostics, the +corresponding option to disable the new behavior will be added to this list. + +@item -fdiagnostics-show-location=once +@opindex fdiagnostics-show-location +Only meaningful in line-wrapping mode. Instructs the diagnostic messages +reporter to emit source location information @emph{once}; that is, in +case the message is too long to fit on a single physical line and has to +be wrapped, the source location won't be emitted (as prefix) again, +over and over, in subsequent continuation lines. This is the default +behavior. + +@item -fdiagnostics-show-location=every-line +Only meaningful in line-wrapping mode. Instructs the diagnostic +messages reporter to emit the same source location information (as +prefix) for physical lines that result from the process of breaking +a message which is too long to fit on a single line. + +@item -fdiagnostics-color[=@var{WHEN}] +@itemx -fno-diagnostics-color +@opindex fdiagnostics-color +@cindex highlight, color +@vindex GCC_COLORS @r{environment variable} +Use color in diagnostics. @var{WHEN} is @samp{never}, @samp{always}, +or @samp{auto}. The default depends on how the compiler has been configured, +it can be any of the above @var{WHEN} options or also @samp{never} +if @env{GCC_COLORS} environment variable isn't present in the environment, +and @samp{auto} otherwise. +@samp{auto} makes GCC use color only when the standard error is a terminal, +and when not executing in an emacs shell. +The forms @option{-fdiagnostics-color} and @option{-fno-diagnostics-color} are +aliases for @option{-fdiagnostics-color=always} and +@option{-fdiagnostics-color=never}, respectively. + +The colors are defined by the environment variable @env{GCC_COLORS}. +Its value is a colon-separated list of capabilities and Select Graphic +Rendition (SGR) substrings. SGR commands are interpreted by the +terminal or terminal emulator. (See the section in the documentation +of your text terminal for permitted values and their meanings as +character attributes.) These substring values are integers in decimal +representation and can be concatenated with semicolons. +Common values to concatenate include +@samp{1} for bold, +@samp{4} for underline, +@samp{5} for blink, +@samp{7} for inverse, +@samp{39} for default foreground color, +@samp{30} to @samp{37} for foreground colors, +@samp{90} to @samp{97} for 16-color mode foreground colors, +@samp{38;5;0} to @samp{38;5;255} +for 88-color and 256-color modes foreground colors, +@samp{49} for default background color, +@samp{40} to @samp{47} for background colors, +@samp{100} to @samp{107} for 16-color mode background colors, +and @samp{48;5;0} to @samp{48;5;255} +for 88-color and 256-color modes background colors. + +The default @env{GCC_COLORS} is +@smallexample +error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\ +quote=01:path=01;36:fixit-insert=32:fixit-delete=31:\ +diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\ +type-diff=01;32:fnname=01;32:targs=35 +@end smallexample +@noindent +where @samp{01;31} is bold red, @samp{01;35} is bold magenta, +@samp{01;36} is bold cyan, @samp{32} is green, @samp{34} is blue, +@samp{01} is bold, and @samp{31} is red. +Setting @env{GCC_COLORS} to the empty string disables colors. +Supported capabilities are as follows. + +@table @code +@item error= +@vindex error GCC_COLORS @r{capability} +SGR substring for error: markers. + +@item warning= +@vindex warning GCC_COLORS @r{capability} +SGR substring for warning: markers. + +@item note= +@vindex note GCC_COLORS @r{capability} +SGR substring for note: markers. + +@item path= +@vindex path GCC_COLORS @r{capability} +SGR substring for colorizing paths of control-flow events as printed +via @option{-fdiagnostics-path-format=}, such as the identifiers of +individual events and lines indicating interprocedural calls and returns. + +@item range1= +@vindex range1 GCC_COLORS @r{capability} +SGR substring for first additional range. + +@item range2= +@vindex range2 GCC_COLORS @r{capability} +SGR substring for second additional range. + +@item locus= +@vindex locus GCC_COLORS @r{capability} +SGR substring for location information, @samp{file:line} or +@samp{file:line:column} etc. + +@item quote= +@vindex quote GCC_COLORS @r{capability} +SGR substring for information printed within quotes. + +@item fnname= +@vindex fnname GCC_COLORS @r{capability} +SGR substring for names of C++ functions. + +@item targs= +@vindex targs GCC_COLORS @r{capability} +SGR substring for C++ function template parameter bindings. + +@item fixit-insert= +@vindex fixit-insert GCC_COLORS @r{capability} +SGR substring for fix-it hints suggesting text to +be inserted or replaced. + +@item fixit-delete= +@vindex fixit-delete GCC_COLORS @r{capability} +SGR substring for fix-it hints suggesting text to +be deleted. + +@item diff-filename= +@vindex diff-filename GCC_COLORS @r{capability} +SGR substring for filename headers within generated patches. + +@item diff-hunk= +@vindex diff-hunk GCC_COLORS @r{capability} +SGR substring for the starts of hunks within generated patches. + +@item diff-delete= +@vindex diff-delete GCC_COLORS @r{capability} +SGR substring for deleted lines within generated patches. + +@item diff-insert= +@vindex diff-insert GCC_COLORS @r{capability} +SGR substring for inserted lines within generated patches. + +@item type-diff= +@vindex type-diff GCC_COLORS @r{capability} +SGR substring for highlighting mismatching types within template +arguments in the C++ frontend. +@end table + +@item -fdiagnostics-urls[=@var{WHEN}] +@opindex fdiagnostics-urls +@cindex urls +@vindex GCC_URLS @r{environment variable} +@vindex TERM_URLS @r{environment variable} +Use escape sequences to embed URLs in diagnostics. For example, when +@option{-fdiagnostics-show-option} emits text showing the command-line +option controlling a diagnostic, embed a URL for documentation of that +option. + +@var{WHEN} is @samp{never}, @samp{always}, or @samp{auto}. +@samp{auto} makes GCC use URL escape sequences only when the standard error +is a terminal, and when not executing in an emacs shell or any graphical +terminal which is known to be incompatible with this feature, see below. + +The default depends on how the compiler has been configured. +It can be any of the above @var{WHEN} options. + +GCC can also be configured (via the +@option{--with-diagnostics-urls=auto-if-env} configure-time option) +so that the default is affected by environment variables. +Under such a configuration, GCC defaults to using @samp{auto} +if either @env{GCC_URLS} or @env{TERM_URLS} environment variables are +present and non-empty in the environment of the compiler, or @samp{never} +if neither are. + +However, even with @option{-fdiagnostics-urls=always} the behavior is +dependent on those environment variables: +If @env{GCC_URLS} is set to empty or @samp{no}, do not embed URLs in +diagnostics. If set to @samp{st}, URLs use ST escape sequences. +If set to @samp{bel}, the default, URLs use BEL escape sequences. +Any other non-empty value enables the feature. +If @env{GCC_URLS} is not set, use @env{TERM_URLS} as a fallback. +Note: ST is an ANSI escape sequence, string terminator @samp{ESC \}, +BEL is an ASCII character, CTRL-G that usually sounds like a beep. + +At this time GCC tries to detect also a few terminals that are known to +not implement the URL feature, and have bugs or at least had bugs in +some versions that are still in use, where the URL escapes are likely +to misbehave, i.e. print garbage on the screen. +That list is currently xfce4-terminal, certain known to be buggy +gnome-terminal versions, the linux console, and mingw. +This check can be skipped with the @option{-fdiagnostics-urls=always}. + +@item -fno-diagnostics-show-option +@opindex fno-diagnostics-show-option +@opindex fdiagnostics-show-option +By default, each diagnostic emitted includes text indicating the +command-line option that directly controls the diagnostic (if such an +option is known to the diagnostic machinery). Specifying the +@option{-fno-diagnostics-show-option} flag suppresses that behavior. + +@item -fno-diagnostics-show-caret +@opindex fno-diagnostics-show-caret +@opindex fdiagnostics-show-caret +By default, each diagnostic emitted includes the original source line +and a caret @samp{^} indicating the column. This option suppresses this +information. The source line is truncated to @var{n} characters, if +the @option{-fmessage-length=n} option is given. When the output is done +to the terminal, the width is limited to the width given by the +@env{COLUMNS} environment variable or, if not set, to the terminal width. + +@item -fno-diagnostics-show-labels +@opindex fno-diagnostics-show-labels +@opindex fdiagnostics-show-labels +By default, when printing source code (via @option{-fdiagnostics-show-caret}), +diagnostics can label ranges of source code with pertinent information, such +as the types of expressions: + +@smallexample + printf ("foo %s bar", long_i + long_j); + ~^ ~~~~~~~~~~~~~~~ + | | + char * long int +@end smallexample + +This option suppresses the printing of these labels (in the example above, +the vertical bars and the ``char *'' and ``long int'' text). + +@item -fno-diagnostics-show-cwe +@opindex fno-diagnostics-show-cwe +@opindex fdiagnostics-show-cwe +Diagnostic messages can optionally have an associated +@uref{https://cwe.mitre.org/index.html, CWE} identifier. +GCC itself only provides such metadata for some of the @option{-fanalyzer} +diagnostics. GCC plugins may also provide diagnostics with such metadata. +By default, if this information is present, it will be printed with +the diagnostic. This option suppresses the printing of this metadata. + +@item -fno-diagnostics-show-rules +@opindex fno-diagnostics-show-rules +@opindex fdiagnostics-show-rules +Diagnostic messages can optionally have rules associated with them, such +as from a coding standard, or a specification. +GCC itself does not do this for any of its diagnostics, but plugins may do so. +By default, if this information is present, it will be printed with +the diagnostic. This option suppresses the printing of this metadata. + +@item -fno-diagnostics-show-line-numbers +@opindex fno-diagnostics-show-line-numbers +@opindex fdiagnostics-show-line-numbers +By default, when printing source code (via @option{-fdiagnostics-show-caret}), +a left margin is printed, showing line numbers. This option suppresses this +left margin. + +@item -fdiagnostics-minimum-margin-width=@var{width} +@opindex fdiagnostics-minimum-margin-width +This option controls the minimum width of the left margin printed by +@option{-fdiagnostics-show-line-numbers}. It defaults to 6. + +@item -fdiagnostics-parseable-fixits +@opindex fdiagnostics-parseable-fixits +Emit fix-it hints in a machine-parseable format, suitable for consumption +by IDEs. For each fix-it, a line will be printed after the relevant +diagnostic, starting with the string ``fix-it:''. For example: + +@smallexample +fix-it:"test.c":@{45:3-45:21@}:"gtk_widget_show_all" +@end smallexample + +The location is expressed as a half-open range, expressed as a count of +bytes, starting at byte 1 for the initial column. In the above example, +bytes 3 through 20 of line 45 of ``test.c'' are to be replaced with the +given string: + +@smallexample +00000000011111111112222222222 +12345678901234567890123456789 + gtk_widget_showall (dlg); + ^^^^^^^^^^^^^^^^^^ + gtk_widget_show_all +@end smallexample + +The filename and replacement string escape backslash as ``\\", tab as ``\t'', +newline as ``\n'', double quotes as ``\"'', non-printable characters as octal +(e.g. vertical tab as ``\013''). + +An empty replacement string indicates that the given range is to be removed. +An empty range (e.g. ``45:3-45:3'') indicates that the string is to +be inserted at the given position. + +@item -fdiagnostics-generate-patch +@opindex fdiagnostics-generate-patch +Print fix-it hints to stderr in unified diff format, after any diagnostics +are printed. For example: + +@smallexample +--- test.c ++++ test.c +@@ -42,5 +42,5 @@ + + void show_cb(GtkDialog *dlg) + @{ +- gtk_widget_showall(dlg); ++ gtk_widget_show_all(dlg); + @} + +@end smallexample + +The diff may or may not be colorized, following the same rules +as for diagnostics (see @option{-fdiagnostics-color}). + +@item -fdiagnostics-show-template-tree +@opindex fdiagnostics-show-template-tree + +In the C++ frontend, when printing diagnostics showing mismatching +template types, such as: + +@smallexample + could not convert 'std::map >()' + from 'map<[...],vector>' to 'map<[...],vector> +@end smallexample + +the @option{-fdiagnostics-show-template-tree} flag enables printing a +tree-like structure showing the common and differing parts of the types, +such as: + +@smallexample + map< + [...], + vector< + [double != float]>> +@end smallexample + +The parts that differ are highlighted with color (``double'' and +``float'' in this case). + +@item -fno-elide-type +@opindex fno-elide-type +@opindex felide-type +By default when the C++ frontend prints diagnostics showing mismatching +template types, common parts of the types are printed as ``[...]'' to +simplify the error message. For example: + +@smallexample + could not convert 'std::map >()' + from 'map<[...],vector>' to 'map<[...],vector> +@end smallexample + +Specifying the @option{-fno-elide-type} flag suppresses that behavior. +This flag also affects the output of the +@option{-fdiagnostics-show-template-tree} flag. + +@item -fdiagnostics-path-format=@var{KIND} +@opindex fdiagnostics-path-format +Specify how to print paths of control-flow events for diagnostics that +have such a path associated with them. + +@var{KIND} is @samp{none}, @samp{separate-events}, or @samp{inline-events}, +the default. + +@samp{none} means to not print diagnostic paths. + +@samp{separate-events} means to print a separate ``note'' diagnostic for +each event within the diagnostic. For example: + +@smallexample +test.c:29:5: error: passing NULL as argument 1 to 'PyList_Append' which requires a non-NULL parameter +test.c:25:10: note: (1) when 'PyList_New' fails, returning NULL +test.c:27:3: note: (2) when 'i < count' +test.c:29:5: note: (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 +@end smallexample + +@samp{inline-events} means to print the events ``inline'' within the source +code. This view attempts to consolidate the events into runs of +sufficiently-close events, printing them as labelled ranges within the source. + +For example, the same events as above might be printed as: + +@smallexample + 'test': events 1-3 + | + | 25 | list = PyList_New(0); + | | ^~~~~~~~~~~~~ + | | | + | | (1) when 'PyList_New' fails, returning NULL + | 26 | + | 27 | for (i = 0; i < count; i++) @{ + | | ~~~ + | | | + | | (2) when 'i < count' + | 28 | item = PyLong_FromLong(random()); + | 29 | PyList_Append(list, item); + | | ~~~~~~~~~~~~~~~~~~~~~~~~~ + | | | + | | (3) when calling 'PyList_Append', passing NULL from (1) as argument 1 + | +@end smallexample + +Interprocedural control flow is shown by grouping the events by stack frame, +and using indentation to show how stack frames are nested, pushed, and popped. + +For example: + +@smallexample + 'test': events 1-2 + | + | 133 | @{ + | | ^ + | | | + | | (1) entering 'test' + | 134 | boxed_int *obj = make_boxed_int (i); + | | ~~~~~~~~~~~~~~~~~~ + | | | + | | (2) calling 'make_boxed_int' + | + +--> 'make_boxed_int': events 3-4 + | + | 120 | @{ + | | ^ + | | | + | | (3) entering 'make_boxed_int' + | 121 | boxed_int *result = (boxed_int *)wrapped_malloc (sizeof (boxed_int)); + | | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + | | | + | | (4) calling 'wrapped_malloc' + | + +--> 'wrapped_malloc': events 5-6 + | + | 7 | @{ + | | ^ + | | | + | | (5) entering 'wrapped_malloc' + | 8 | return malloc (size); + | | ~~~~~~~~~~~~~ + | | | + | | (6) calling 'malloc' + | + <-------------+ + | + 'test': event 7 + | + | 138 | free_boxed_int (obj); + | | ^~~~~~~~~~~~~~~~~~~~ + | | | + | | (7) calling 'free_boxed_int' + | +(etc) +@end smallexample + +@item -fdiagnostics-show-path-depths +@opindex fdiagnostics-show-path-depths +This option provides additional information when printing control-flow paths +associated with a diagnostic. + +If this is option is provided then the stack depth will be printed for +each run of events within @option{-fdiagnostics-path-format=inline-events}. +If provided with @option{-fdiagnostics-path-format=separate-events}, then +the stack depth and function declaration will be appended when printing +each event. + +This is intended for use by GCC developers and plugin developers when +debugging diagnostics that report interprocedural control flow. + +@item -fno-show-column +@opindex fno-show-column +@opindex fshow-column +Do not print column numbers in diagnostics. This may be necessary if +diagnostics are being scanned by a program that does not understand the +column numbers, such as @command{dejagnu}. + +@item -fdiagnostics-column-unit=@var{UNIT} +@opindex fdiagnostics-column-unit +Select the units for the column number. This affects traditional diagnostics +(in the absence of @option{-fno-show-column}), as well as JSON format +diagnostics if requested. + +The default @var{UNIT}, @samp{display}, considers the number of display +columns occupied by each character. This may be larger than the number +of bytes required to encode the character, in the case of tab +characters, or it may be smaller, in the case of multibyte characters. +For example, the character ``GREEK SMALL LETTER PI (U+03C0)'' occupies one +display column, and its UTF-8 encoding requires two bytes; the character +``SLIGHTLY SMILING FACE (U+1F642)'' occupies two display columns, and +its UTF-8 encoding requires four bytes. + +Setting @var{UNIT} to @samp{byte} changes the column number to the raw byte +count in all cases, as was traditionally output by GCC prior to version 11.1.0. + +@item -fdiagnostics-column-origin=@var{ORIGIN} +@opindex fdiagnostics-column-origin +Select the origin for column numbers, i.e. the column number assigned to the +first column. The default value of 1 corresponds to traditional GCC +behavior and to the GNU style guide. Some utilities may perform better with an +origin of 0; any non-negative value may be specified. + +@item -fdiagnostics-escape-format=@var{FORMAT} +@opindex fdiagnostics-escape-format +When GCC prints pertinent source lines for a diagnostic it normally attempts +to print the source bytes directly. However, some diagnostics relate to encoding +issues in the source file, such as malformed UTF-8, or issues with Unicode +normalization. These diagnostics are flagged so that GCC will escape bytes +that are not printable ASCII when printing their pertinent source lines. + +This option controls how such bytes should be escaped. + +The default @var{FORMAT}, @samp{unicode} displays Unicode characters that +are not printable ASCII in the form @samp{}, and bytes that do not +correspond to a Unicode character validly-encoded in UTF-8-encoded will be +displayed as hexadecimal in the form @samp{}. + +For example, a source line containing the string @samp{before} followed by the +Unicode character U+03C0 (``GREEK SMALL LETTER PI'', with UTF-8 encoding +0xCF 0x80) followed by the byte 0xBF (a stray UTF-8 trailing byte), followed by +the string @samp{after} will be printed for such a diagnostic as: + +@smallexample + beforeafter +@end smallexample + +Setting @var{FORMAT} to @samp{bytes} will display all non-printable-ASCII bytes +in the form @samp{}, thus showing the underlying encoding of non-ASCII +Unicode characters. For the example above, the following will be printed: + +@smallexample + before<80>after +@end smallexample + +@item -fdiagnostics-format=@var{FORMAT} +@opindex fdiagnostics-format +Select a different format for printing diagnostics. +@var{FORMAT} is @samp{text}, @samp{sarif-stderr}, @samp{sarif-file}, +@samp{json}, @samp{json-stderr}, or @samp{json-file}. + +The default is @samp{text}. + +The @samp{sarif-stderr} and @samp{sarif-file} formats both emit +diagnostics in SARIF Version 2.1.0 format, either to stderr, or to a file +named @file{@var{source}.sarif}, respectively. + +The @samp{json} format is a synonym for @samp{json-stderr}. +The @samp{json-stderr} and @samp{json-file} formats are identical, apart from +where the JSON is emitted to - with the former, the JSON is emitted to stderr, +whereas with @samp{json-file} it is written to @file{@var{source}.gcc.json}. + +The emitted JSON consists of a top-level JSON array containing JSON objects +representing the diagnostics. The JSON is emitted as one line, without +formatting; the examples below have been formatted for clarity. + +Diagnostics can have child diagnostics. For example, this error and note: + +@smallexample +misleading-indentation.c:15:3: warning: this 'if' clause does not + guard... [-Wmisleading-indentation] + 15 | if (flag) + | ^~ +misleading-indentation.c:17:5: note: ...this statement, but the latter + is misleadingly indented as if it were guarded by the 'if' + 17 | y = 2; + | ^ +@end smallexample + +@noindent +might be printed in JSON form (after formatting) like this: + +@smallexample +[ + @{ + "kind": "warning", + "locations": [ + @{ + "caret": @{ + "display-column": 3, + "byte-column": 3, + "column": 3, + "file": "misleading-indentation.c", + "line": 15 + @}, + "finish": @{ + "display-column": 4, + "byte-column": 4, + "column": 4, + "file": "misleading-indentation.c", + "line": 15 + @} + @} + ], + "message": "this \u2018if\u2019 clause does not guard...", + "option": "-Wmisleading-indentation", + "option_url": "https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wmisleading-indentation", + "children": [ + @{ + "kind": "note", + "locations": [ + @{ + "caret": @{ + "display-column": 5, + "byte-column": 5, + "column": 5, + "file": "misleading-indentation.c", + "line": 17 + @} + @} + ], + "escape-source": false, + "message": "...this statement, but the latter is @dots{}" + @} + ] + "escape-source": false, + "column-origin": 1, + @} +] +@end smallexample + +@noindent +where the @code{note} is a child of the @code{warning}. + +A diagnostic has a @code{kind}. If this is @code{warning}, then there is +an @code{option} key describing the command-line option controlling the +warning. + +A diagnostic can contain zero or more locations. Each location has an +optional @code{label} string and up to three positions within it: a +@code{caret} position and optional @code{start} and @code{finish} positions. +A position is described by a @code{file} name, a @code{line} number, and +three numbers indicating a column position: +@itemize @bullet + +@item +@code{display-column} counts display columns, accounting for tabs and +multibyte characters. + +@item +@code{byte-column} counts raw bytes. + +@item +@code{column} is equal to one of +the previous two, as dictated by the @option{-fdiagnostics-column-unit} +option. + +@end itemize +All three columns are relative to the origin specified by +@option{-fdiagnostics-column-origin}, which is typically equal to 1 but may +be set, for instance, to 0 for compatibility with other utilities that +number columns from 0. The column origin is recorded in the JSON output in +the @code{column-origin} tag. In the remaining examples below, the extra +column number outputs have been omitted for brevity. + +For example, this error: + +@smallexample +bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' @{aka + 'struct s'@} and 'T' @{aka 'struct t'@}) + 64 | return callee_4a () + callee_4b (); + | ~~~~~~~~~~~~ ^ ~~~~~~~~~~~~ + | | | + | | T @{aka struct t@} + | S @{aka struct s@} +@end smallexample + +@noindent +has three locations. Its primary location is at the ``+'' token at column +23. It has two secondary locations, describing the left and right-hand sides +of the expression, which have labels. It might be printed in JSON form as: + +@smallexample + @{ + "children": [], + "kind": "error", + "locations": [ + @{ + "caret": @{ + "column": 23, "file": "bad-binary-ops.c", "line": 64 + @} + @}, + @{ + "caret": @{ + "column": 10, "file": "bad-binary-ops.c", "line": 64 + @}, + "finish": @{ + "column": 21, "file": "bad-binary-ops.c", "line": 64 + @}, + "label": "S @{aka struct s@}" + @}, + @{ + "caret": @{ + "column": 25, "file": "bad-binary-ops.c", "line": 64 + @}, + "finish": @{ + "column": 36, "file": "bad-binary-ops.c", "line": 64 + @}, + "label": "T @{aka struct t@}" + @} + ], + "escape-source": false, + "message": "invalid operands to binary + @dots{}" + @} +@end smallexample + +If a diagnostic contains fix-it hints, it has a @code{fixits} array, +consisting of half-open intervals, similar to the output of +@option{-fdiagnostics-parseable-fixits}. For example, this diagnostic +with a replacement fix-it hint: + +@smallexample +demo.c:8:15: error: 'struct s' has no member named 'colour'; did you + mean 'color'? + 8 | return ptr->colour; + | ^~~~~~ + | color +@end smallexample + +@noindent +might be printed in JSON form as: + +@smallexample + @{ + "children": [], + "fixits": [ + @{ + "next": @{ + "column": 21, + "file": "demo.c", + "line": 8 + @}, + "start": @{ + "column": 15, + "file": "demo.c", + "line": 8 + @}, + "string": "color" + @} + ], + "kind": "error", + "locations": [ + @{ + "caret": @{ + "column": 15, + "file": "demo.c", + "line": 8 + @}, + "finish": @{ + "column": 20, + "file": "demo.c", + "line": 8 + @} + @} + ], + "escape-source": false, + "message": "\u2018struct s\u2019 has no member named @dots{}" + @} +@end smallexample + +@noindent +where the fix-it hint suggests replacing the text from @code{start} up +to but not including @code{next} with @code{string}'s value. Deletions +are expressed via an empty value for @code{string}, insertions by +having @code{start} equal @code{next}. + +If the diagnostic has a path of control-flow events associated with it, +it has a @code{path} array of objects representing the events. Each +event object has a @code{description} string, a @code{location} object, +along with a @code{function} string and a @code{depth} number for +representing interprocedural paths. The @code{function} represents the +current function at that event, and the @code{depth} represents the +stack depth relative to some baseline: the higher, the more frames are +within the stack. + +For example, the intraprocedural example shown for +@option{-fdiagnostics-path-format=} might have this JSON for its path: + +@smallexample + "path": [ + @{ + "depth": 0, + "description": "when 'PyList_New' fails, returning NULL", + "function": "test", + "location": @{ + "column": 10, + "file": "test.c", + "line": 25 + @} + @}, + @{ + "depth": 0, + "description": "when 'i < count'", + "function": "test", + "location": @{ + "column": 3, + "file": "test.c", + "line": 27 + @} + @}, + @{ + "depth": 0, + "description": "when calling 'PyList_Append', passing NULL from (1) as argument 1", + "function": "test", + "location": @{ + "column": 5, + "file": "test.c", + "line": 29 + @} + @} + ] +@end smallexample + +Diagnostics have a boolean attribute @code{escape-source}, hinting whether +non-ASCII bytes should be escaped when printing the pertinent lines of +source code (@code{true} for diagnostics involving source encoding issues). + +@end table + +@node Warning Options +@section Options to Request or Suppress Warnings +@cindex options to control warnings +@cindex warning messages +@cindex messages, warning +@cindex suppressing warnings + +Warnings are diagnostic messages that report constructions that +are not inherently erroneous but that are risky or suggest there +may have been an error. + +The following language-independent options do not enable specific +warnings but control the kinds of diagnostics produced by GCC@. + +@table @gcctabopt +@cindex syntax checking +@item -fsyntax-only +@opindex fsyntax-only +Check the code for syntax errors, but don't do anything beyond that. + +@item -fmax-errors=@var{n} +@opindex fmax-errors +Limits the maximum number of error messages to @var{n}, at which point +GCC bails out rather than attempting to continue processing the source +code. If @var{n} is 0 (the default), there is no limit on the number +of error messages produced. If @option{-Wfatal-errors} is also +specified, then @option{-Wfatal-errors} takes precedence over this +option. + +@item -w +@opindex w +Inhibit all warning messages. + +@item -Werror +@opindex Werror +@opindex Wno-error +Make all warnings into errors. + +@item -Werror= +@opindex Werror= +@opindex Wno-error= +Make the specified warning into an error. The specifier for a warning +is appended; for example @option{-Werror=switch} turns the warnings +controlled by @option{-Wswitch} into errors. This switch takes a +negative form, to be used to negate @option{-Werror} for specific +warnings; for example @option{-Wno-error=switch} makes +@option{-Wswitch} warnings not be errors, even when @option{-Werror} +is in effect. + +The warning message for each controllable warning includes the +option that controls the warning. That option can then be used with +@option{-Werror=} and @option{-Wno-error=} as described above. +(Printing of the option in the warning message can be disabled using the +@option{-fno-diagnostics-show-option} flag.) + +Note that specifying @option{-Werror=}@var{foo} automatically implies +@option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not +imply anything. + +@item -Wfatal-errors +@opindex Wfatal-errors +@opindex Wno-fatal-errors +This option causes the compiler to abort compilation on the first error +occurred rather than trying to keep going and printing further error +messages. + +@end table + +You can request many specific warnings with options beginning with +@samp{-W}, for example @option{-Wimplicit} to request warnings on +implicit declarations. Each of these specific warning options also +has a negative form beginning @samp{-Wno-} to turn off warnings; for +example, @option{-Wno-implicit}. This manual lists only one of the +two forms, whichever is not the default. For further +language-specific options also refer to @ref{C++ Dialect Options} and +@ref{Objective-C and Objective-C++ Dialect Options}. +Additional warnings can be produced by enabling the static analyzer; +@xref{Static Analyzer Options}. + +Some options, such as @option{-Wall} and @option{-Wextra}, turn on other +options, such as @option{-Wunused}, which may turn on further options, +such as @option{-Wunused-value}. The combined effect of positive and +negative forms is that more specific options have priority over less +specific ones, independently of their position in the command-line. For +options of the same specificity, the last one takes effect. Options +enabled or disabled via pragmas (@pxref{Diagnostic Pragmas}) take effect +as if they appeared at the end of the command-line. + +When an unrecognized warning option is requested (e.g., +@option{-Wunknown-warning}), GCC emits a diagnostic stating +that the option is not recognized. However, if the @option{-Wno-} form +is used, the behavior is slightly different: no diagnostic is +produced for @option{-Wno-unknown-warning} unless other diagnostics +are being produced. This allows the use of new @option{-Wno-} options +with old compilers, but if something goes wrong, the compiler +warns that an unrecognized option is present. + +The effectiveness of some warnings depends on optimizations also being +enabled. For example @option{-Wsuggest-final-types} is more effective +with link-time optimization and some instances of other warnings may +not be issued at all unless optimization is enabled. While optimization +in general improves the efficacy of control and data flow sensitive +warnings, in some cases it may also cause false positives. + +@table @gcctabopt +@item -Wpedantic +@itemx -pedantic +@opindex pedantic +@opindex Wpedantic +@opindex Wno-pedantic +Issue all the warnings demanded by strict ISO C and ISO C++; +reject all programs that use forbidden extensions, and some other +programs that do not follow ISO C and ISO C++. For ISO C, follows the +version of the ISO C standard specified by any @option{-std} option used. + +Valid ISO C and ISO C++ programs should compile properly with or without +this option (though a rare few require @option{-ansi} or a +@option{-std} option specifying the required version of ISO C)@. However, +without this option, certain GNU extensions and traditional C and C++ +features are supported as well. With this option, they are rejected. + +@option{-Wpedantic} does not cause warning messages for use of the +alternate keywords whose names begin and end with @samp{__}. This alternate +format can also be used to disable warnings for non-ISO @samp{__intN} types, +i.e. @samp{__intN__}. +Pedantic warnings are also disabled in the expression that follows +@code{__extension__}. However, only system header files should use +these escape routes; application programs should avoid them. +@xref{Alternate Keywords}. + +Some users try to use @option{-Wpedantic} to check programs for strict ISO +C conformance. They soon find that it does not do quite what they want: +it finds some non-ISO practices, but not all---only those for which +ISO C @emph{requires} a diagnostic, and some others for which +diagnostics have been added. + +A feature to report any failure to conform to ISO C might be useful in +some instances, but would require considerable additional work and would +be quite different from @option{-Wpedantic}. We don't have plans to +support such a feature in the near future. + +Where the standard specified with @option{-std} represents a GNU +extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a +corresponding @dfn{base standard}, the version of ISO C on which the GNU +extended dialect is based. Warnings from @option{-Wpedantic} are given +where they are required by the base standard. (It does not make sense +for such warnings to be given only for features not in the specified GNU +C dialect, since by definition the GNU dialects of C include all +features the compiler supports with the given option, and there would be +nothing to warn about.) + +@item -pedantic-errors +@opindex pedantic-errors +Give an error whenever the @dfn{base standard} (see @option{-Wpedantic}) +requires a diagnostic, in some cases where there is undefined behavior +at compile-time and in some other cases that do not prevent compilation +of programs that are valid according to the standard. This is not +equivalent to @option{-Werror=pedantic}, since there are errors enabled +by this option and not enabled by the latter and vice versa. + +@item -Wall +@opindex Wall +@opindex Wno-all +This enables all the warnings about constructions that some users +consider questionable, and that are easy to avoid (or modify to +prevent the warning), even in conjunction with macros. This also +enables some language-specific warnings described in @ref{C++ Dialect +Options} and @ref{Objective-C and Objective-C++ Dialect Options}. + +@option{-Wall} turns on the following warning flags: + +@gccoptlist{-Waddress @gol +-Warray-bounds=1 @r{(only with} @option{-O2}@r{)} @gol +-Warray-compare @gol +-Warray-parameter=2 @r{(C and Objective-C only)} @gol +-Wbool-compare @gol +-Wbool-operation @gol +-Wc++11-compat -Wc++14-compat @gol +-Wcatch-value @r{(C++ and Objective-C++ only)} @gol +-Wchar-subscripts @gol +-Wcomment @gol +-Wdangling-pointer=2 @gol +-Wduplicate-decl-specifier @r{(C and Objective-C only)} @gol +-Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol +-Wenum-int-mismatch @r{(C and Objective-C only)} @gol +-Wformat @gol +-Wformat-overflow @gol +-Wformat-truncation @gol +-Wint-in-bool-context @gol +-Wimplicit @r{(C and Objective-C only)} @gol +-Wimplicit-int @r{(C and Objective-C only)} @gol +-Wimplicit-function-declaration @r{(C and Objective-C only)} @gol +-Winit-self @r{(only for C++)} @gol +-Wlogical-not-parentheses @gol +-Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol +-Wmaybe-uninitialized @gol +-Wmemset-elt-size @gol +-Wmemset-transposed-args @gol +-Wmisleading-indentation @r{(only for C/C++)} @gol +-Wmismatched-dealloc @gol +-Wmismatched-new-delete @r{(only for C/C++)} @gol +-Wmissing-attributes @gol +-Wmissing-braces @r{(only for C/ObjC)} @gol +-Wmultistatement-macros @gol +-Wnarrowing @r{(only for C++)} @gol +-Wnonnull @gol +-Wnonnull-compare @gol +-Wopenmp-simd @gol +-Wparentheses @gol +-Wpessimizing-move @r{(only for C++)} @gol +-Wpointer-sign @gol +-Wrange-loop-construct @r{(only for C++)} @gol +-Wreorder @gol +-Wrestrict @gol +-Wreturn-type @gol +-Wself-move @r{(only for C++)} @gol +-Wsequence-point @gol +-Wsign-compare @r{(only in C++)} @gol +-Wsizeof-array-div @gol +-Wsizeof-pointer-div @gol +-Wsizeof-pointer-memaccess @gol +-Wstrict-aliasing @gol +-Wstrict-overflow=1 @gol +-Wswitch @gol +-Wtautological-compare @gol +-Wtrigraphs @gol +-Wuninitialized @gol +-Wunknown-pragmas @gol +-Wunused-function @gol +-Wunused-label @gol +-Wunused-value @gol +-Wunused-variable @gol +-Wuse-after-free=3 @gol +-Wvla-parameter @r{(C and Objective-C only)} @gol +-Wvolatile-register-var @gol +-Wzero-length-bounds} + +Note that some warning flags are not implied by @option{-Wall}. Some of +them warn about constructions that users generally do not consider +questionable, but which occasionally you might wish to check for; +others warn about constructions that are necessary or hard to avoid in +some cases, and there is no simple way to modify the code to suppress +the warning. Some of them are enabled by @option{-Wextra} but many of +them must be enabled individually. + +@item -Wextra +@opindex W +@opindex Wextra +@opindex Wno-extra +This enables some extra warning flags that are not enabled by +@option{-Wall}. (This option used to be called @option{-W}. The older +name is still supported, but the newer name is more descriptive.) + +@gccoptlist{-Wclobbered @gol +-Wcast-function-type @gol +-Wdeprecated-copy @r{(C++ only)} @gol +-Wempty-body @gol +-Wenum-conversion @r{(C only)} @gol +-Wignored-qualifiers @gol +-Wimplicit-fallthrough=3 @gol +-Wmissing-field-initializers @gol +-Wmissing-parameter-type @r{(C only)} @gol +-Wold-style-declaration @r{(C only)} @gol +-Woverride-init @gol +-Wsign-compare @r{(C only)} @gol +-Wstring-compare @gol +-Wredundant-move @r{(only for C++)} @gol +-Wtype-limits @gol +-Wuninitialized @gol +-Wshift-negative-value @r{(in C++11 to C++17 and in C99 and newer)} @gol +-Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol +-Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)}} + + +The option @option{-Wextra} also prints warning messages for the +following cases: + +@itemize @bullet + +@item +A pointer is compared against integer zero with @code{<}, @code{<=}, +@code{>}, or @code{>=}. + +@item +(C++ only) An enumerator and a non-enumerator both appear in a +conditional expression. + +@item +(C++ only) Ambiguous virtual bases. + +@item +(C++ only) Subscripting an array that has been declared @code{register}. + +@item +(C++ only) Taking the address of a variable that has been declared +@code{register}. + +@item +(C++ only) A base class is not initialized in the copy constructor +of a derived class. + +@end itemize + +@item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)} +@opindex Wabi +@opindex Wno-abi + +Warn about code affected by ABI changes. This includes code that may +not be compatible with the vendor-neutral C++ ABI as well as the psABI +for the particular target. + +Since G++ now defaults to updating the ABI with each major release, +normally @option{-Wabi} warns only about C++ ABI compatibility +problems if there is a check added later in a release series for an +ABI issue discovered since the initial release. @option{-Wabi} warns +about more things if an older ABI version is selected (with +@option{-fabi-version=@var{n}}). + +@option{-Wabi} can also be used with an explicit version number to +warn about C++ ABI compatibility with a particular @option{-fabi-version} +level, e.g.@: @option{-Wabi=2} to warn about changes relative to +@option{-fabi-version=2}. + +If an explicit version number is provided and +@option{-fabi-compat-version} is not specified, the version number +from this option is used for compatibility aliases. If no explicit +version number is provided with this option, but +@option{-fabi-compat-version} is specified, that version number is +used for C++ ABI warnings. + +Although an effort has been made to warn about +all such cases, there are probably some cases that are not warned about, +even though G++ is generating incompatible code. There may also be +cases where warnings are emitted even though the code that is generated +is compatible. + +You should rewrite your code to avoid these warnings if you are +concerned about the fact that code generated by G++ may not be binary +compatible with code generated by other compilers. + +Known incompatibilities in @option{-fabi-version=2} (which was the +default from GCC 3.4 to 4.9) include: + +@itemize @bullet + +@item +A template with a non-type template parameter of reference type was +mangled incorrectly: +@smallexample +extern int N; +template struct S @{@}; +void n (S) @{2@} +@end smallexample + +This was fixed in @option{-fabi-version=3}. + +@item +SIMD vector types declared using @code{__attribute ((vector_size))} were +mangled in a non-standard way that does not allow for overloading of +functions taking vectors of different sizes. + +The mangling was changed in @option{-fabi-version=4}. + +@item +@code{__attribute ((const))} and @code{noreturn} were mangled as type +qualifiers, and @code{decltype} of a plain declaration was folded away. + +These mangling issues were fixed in @option{-fabi-version=5}. + +@item +Scoped enumerators passed as arguments to a variadic function are +promoted like unscoped enumerators, causing @code{va_arg} to complain. +On most targets this does not actually affect the parameter passing +ABI, as there is no way to pass an argument smaller than @code{int}. + +Also, the ABI changed the mangling of template argument packs, +@code{const_cast}, @code{static_cast}, prefix increment/decrement, and +a class scope function used as a template argument. + +These issues were corrected in @option{-fabi-version=6}. + +@item +Lambdas in default argument scope were mangled incorrectly, and the +ABI changed the mangling of @code{nullptr_t}. + +These issues were corrected in @option{-fabi-version=7}. + +@item +When mangling a function type with function-cv-qualifiers, the +un-qualified function type was incorrectly treated as a substitution +candidate. + +This was fixed in @option{-fabi-version=8}, the default for GCC 5.1. + +@item +@code{decltype(nullptr)} incorrectly had an alignment of 1, leading to +unaligned accesses. Note that this did not affect the ABI of a +function with a @code{nullptr_t} parameter, as parameters have a +minimum alignment. + +This was fixed in @option{-fabi-version=9}, the default for GCC 5.2. + +@item +Target-specific attributes that affect the identity of a type, such as +ia32 calling conventions on a function type (stdcall, regparm, etc.), +did not affect the mangled name, leading to name collisions when +function pointers were used as template arguments. + +This was fixed in @option{-fabi-version=10}, the default for GCC 6.1. + +@end itemize + +This option also enables warnings about psABI-related changes. +The known psABI changes at this point include: + +@itemize @bullet + +@item +For SysV/x86-64, unions with @code{long double} members are +passed in memory as specified in psABI. Prior to GCC 4.4, this was not +the case. For example: + +@smallexample +union U @{ + long double ld; + int i; +@}; +@end smallexample + +@noindent +@code{union U} is now always passed in memory. + +@end itemize + +@item -Wchar-subscripts +@opindex Wchar-subscripts +@opindex Wno-char-subscripts +Warn if an array subscript has type @code{char}. This is a common cause +of error, as programmers often forget that this type is signed on some +machines. +This warning is enabled by @option{-Wall}. + +@item -Wno-coverage-mismatch +@opindex Wno-coverage-mismatch +@opindex Wcoverage-mismatch +Warn if feedback profiles do not match when using the +@option{-fprofile-use} option. +If a source file is changed between compiling with @option{-fprofile-generate} +and with @option{-fprofile-use}, the files with the profile feedback can fail +to match the source file and GCC cannot use the profile feedback +information. By default, this warning is enabled and is treated as an +error. @option{-Wno-coverage-mismatch} can be used to disable the +warning or @option{-Wno-error=coverage-mismatch} can be used to +disable the error. Disabling the error for this warning can result in +poorly optimized code and is useful only in the +case of very minor changes such as bug fixes to an existing code-base. +Completely disabling the warning is not recommended. + +@item -Wno-coverage-invalid-line-number +@opindex Wno-coverage-invalid-line-number +@opindex Wcoverage-invalid-line-number +Warn in case a function ends earlier than it begins due +to an invalid linenum macros. The warning is emitted only +with @option{--coverage} enabled. + +By default, this warning is enabled and is treated as an +error. @option{-Wno-coverage-invalid-line-number} can be used to disable the +warning or @option{-Wno-error=coverage-invalid-line-number} can be used to +disable the error. + +@item -Wno-cpp @r{(C, Objective-C, C++, Objective-C++ and Fortran only)} +@opindex Wno-cpp +@opindex Wcpp +Suppress warning messages emitted by @code{#warning} directives. + +@item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)} +@opindex Wdouble-promotion +@opindex Wno-double-promotion +Give a warning when a value of type @code{float} is implicitly +promoted to @code{double}. CPUs with a 32-bit ``single-precision'' +floating-point unit implement @code{float} in hardware, but emulate +@code{double} in software. On such a machine, doing computations +using @code{double} values is much more expensive because of the +overhead required for software emulation. + +It is easy to accidentally do computations with @code{double} because +floating-point literals are implicitly of type @code{double}. For +example, in: +@smallexample +@group +float area(float radius) +@{ + return 3.14159 * radius * radius; +@} +@end group +@end smallexample +the compiler performs the entire computation with @code{double} +because the floating-point literal is a @code{double}. + +@item -Wduplicate-decl-specifier @r{(C and Objective-C only)} +@opindex Wduplicate-decl-specifier +@opindex Wno-duplicate-decl-specifier +Warn if a declaration has duplicate @code{const}, @code{volatile}, +@code{restrict} or @code{_Atomic} specifier. This warning is enabled by +@option{-Wall}. + +@item -Wformat +@itemx -Wformat=@var{n} +@opindex Wformat +@opindex Wno-format +@opindex ffreestanding +@opindex fno-builtin +@opindex Wformat= +Check calls to @code{printf} and @code{scanf}, etc., to make sure that +the arguments supplied have types appropriate to the format string +specified, and that the conversions specified in the format string make +sense. This includes standard functions, and others specified by format +attributes (@pxref{Function Attributes}), in the @code{printf}, +@code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, +not in the C standard) families (or other target-specific families). +Which functions are checked without format attributes having been +specified depends on the standard version selected, and such checks of +functions without the attribute specified are disabled by +@option{-ffreestanding} or @option{-fno-builtin}. + +The formats are checked against the format features supported by GNU +libc version 2.2. These include all ISO C90 and C99 features, as well +as features from the Single Unix Specification and some BSD and GNU +extensions. Other library implementations may not support all these +features; GCC does not support warning about features that go beyond a +particular library's limitations. However, if @option{-Wpedantic} is used +with @option{-Wformat}, warnings are given about format features not +in the selected standard version (but not for @code{strfmon} formats, +since those are not in any version of the C standard). @xref{C Dialect +Options,,Options Controlling C Dialect}. + +@table @gcctabopt +@item -Wformat=1 +@itemx -Wformat +@opindex Wformat +@opindex Wformat=1 +Option @option{-Wformat} is equivalent to @option{-Wformat=1}, and +@option{-Wno-format} is equivalent to @option{-Wformat=0}. Since +@option{-Wformat} also checks for null format arguments for several +functions, @option{-Wformat} also implies @option{-Wnonnull}. Some +aspects of this level of format checking can be disabled by the +options: @option{-Wno-format-contains-nul}, +@option{-Wno-format-extra-args}, and @option{-Wno-format-zero-length}. +@option{-Wformat} is enabled by @option{-Wall}. + +@item -Wformat=2 +@opindex Wformat=2 +Enable @option{-Wformat} plus additional format checks. Currently +equivalent to @option{-Wformat -Wformat-nonliteral -Wformat-security +-Wformat-y2k}. +@end table + +@item -Wno-format-contains-nul +@opindex Wno-format-contains-nul +@opindex Wformat-contains-nul +If @option{-Wformat} is specified, do not warn about format strings that +contain NUL bytes. + +@item -Wno-format-extra-args +@opindex Wno-format-extra-args +@opindex Wformat-extra-args +If @option{-Wformat} is specified, do not warn about excess arguments to a +@code{printf} or @code{scanf} format function. The C standard specifies +that such arguments are ignored. + +Where the unused arguments lie between used arguments that are +specified with @samp{$} operand number specifications, normally +warnings are still given, since the implementation could not know what +type to pass to @code{va_arg} to skip the unused arguments. However, +in the case of @code{scanf} formats, this option suppresses the +warning if the unused arguments are all pointers, since the Single +Unix Specification says that such unused arguments are allowed. + +@item -Wformat-overflow +@itemx -Wformat-overflow=@var{level} +@opindex Wformat-overflow +@opindex Wno-format-overflow +Warn about calls to formatted input/output functions such as @code{sprintf} +and @code{vsprintf} that might overflow the destination buffer. When the +exact number of bytes written by a format directive cannot be determined +at compile-time it is estimated based on heuristics that depend on the +@var{level} argument and on optimization. While enabling optimization +will in most cases improve the accuracy of the warning, it may also +result in false positives. + +@table @gcctabopt +@item -Wformat-overflow +@itemx -Wformat-overflow=1 +@opindex Wformat-overflow +@opindex Wno-format-overflow +Level @var{1} of @option{-Wformat-overflow} enabled by @option{-Wformat} +employs a conservative approach that warns only about calls that most +likely overflow the buffer. At this level, numeric arguments to format +directives with unknown values are assumed to have the value of one, and +strings of unknown length to be empty. Numeric arguments that are known +to be bounded to a subrange of their type, or string arguments whose output +is bounded either by their directive's precision or by a finite set of +string literals, are assumed to take on the value within the range that +results in the most bytes on output. For example, the call to @code{sprintf} +below is diagnosed because even with both @var{a} and @var{b} equal to zero, +the terminating NUL character (@code{'\0'}) appended by the function +to the destination buffer will be written past its end. Increasing +the size of the buffer by a single byte is sufficient to avoid the +warning, though it may not be sufficient to avoid the overflow. + +@smallexample +void f (int a, int b) +@{ + char buf [13]; + sprintf (buf, "a = %i, b = %i\n", a, b); +@} +@end smallexample + +@item -Wformat-overflow=2 +Level @var{2} warns also about calls that might overflow the destination +buffer given an argument of sufficient length or magnitude. At level +@var{2}, unknown numeric arguments are assumed to have the minimum +representable value for signed types with a precision greater than 1, and +the maximum representable value otherwise. Unknown string arguments whose +length cannot be assumed to be bounded either by the directive's precision, +or by a finite set of string literals they may evaluate to, or the character +array they may point to, are assumed to be 1 character long. + +At level @var{2}, the call in the example above is again diagnosed, but +this time because with @var{a} equal to a 32-bit @code{INT_MIN} the first +@code{%i} directive will write some of its digits beyond the end of +the destination buffer. To make the call safe regardless of the values +of the two variables, the size of the destination buffer must be increased +to at least 34 bytes. GCC includes the minimum size of the buffer in +an informational note following the warning. + +An alternative to increasing the size of the destination buffer is to +constrain the range of formatted values. The maximum length of string +arguments can be bounded by specifying the precision in the format +directive. When numeric arguments of format directives can be assumed +to be bounded by less than the precision of their type, choosing +an appropriate length modifier to the format specifier will reduce +the required buffer size. For example, if @var{a} and @var{b} in the +example above can be assumed to be within the precision of +the @code{short int} type then using either the @code{%hi} format +directive or casting the argument to @code{short} reduces the maximum +required size of the buffer to 24 bytes. + +@smallexample +void f (int a, int b) +@{ + char buf [23]; + sprintf (buf, "a = %hi, b = %i\n", a, (short)b); +@} +@end smallexample +@end table + +@item -Wno-format-zero-length +@opindex Wno-format-zero-length +@opindex Wformat-zero-length +If @option{-Wformat} is specified, do not warn about zero-length formats. +The C standard specifies that zero-length formats are allowed. + +@item -Wformat-nonliteral +@opindex Wformat-nonliteral +@opindex Wno-format-nonliteral +If @option{-Wformat} is specified, also warn if the format string is not a +string literal and so cannot be checked, unless the format function +takes its format arguments as a @code{va_list}. + +@item -Wformat-security +@opindex Wformat-security +@opindex Wno-format-security +If @option{-Wformat} is specified, also warn about uses of format +functions that represent possible security problems. At present, this +warns about calls to @code{printf} and @code{scanf} functions where the +format string is not a string literal and there are no format arguments, +as in @code{printf (foo);}. This may be a security hole if the format +string came from untrusted input and contains @samp{%n}. (This is +currently a subset of what @option{-Wformat-nonliteral} warns about, but +in future warnings may be added to @option{-Wformat-security} that are not +included in @option{-Wformat-nonliteral}.) + +@item -Wformat-signedness +@opindex Wformat-signedness +@opindex Wno-format-signedness +If @option{-Wformat} is specified, also warn if the format string +requires an unsigned argument and the argument is signed and vice versa. + +@item -Wformat-truncation +@itemx -Wformat-truncation=@var{level} +@opindex Wformat-truncation +@opindex Wno-format-truncation +Warn about calls to formatted input/output functions such as @code{snprintf} +and @code{vsnprintf} that might result in output truncation. When the exact +number of bytes written by a format directive cannot be determined at +compile-time it is estimated based on heuristics that depend on +the @var{level} argument and on optimization. While enabling optimization +will in most cases improve the accuracy of the warning, it may also result +in false positives. Except as noted otherwise, the option uses the same +logic @option{-Wformat-overflow}. + +@table @gcctabopt +@item -Wformat-truncation +@itemx -Wformat-truncation=1 +@opindex Wformat-truncation +@opindex Wno-format-truncation +Level @var{1} of @option{-Wformat-truncation} enabled by @option{-Wformat} +employs a conservative approach that warns only about calls to bounded +functions whose return value is unused and that will most likely result +in output truncation. + +@item -Wformat-truncation=2 +Level @var{2} warns also about calls to bounded functions whose return +value is used and that might result in truncation given an argument of +sufficient length or magnitude. +@end table + +@item -Wformat-y2k +@opindex Wformat-y2k +@opindex Wno-format-y2k +If @option{-Wformat} is specified, also warn about @code{strftime} +formats that may yield only a two-digit year. + +@item -Wnonnull +@opindex Wnonnull +@opindex Wno-nonnull +Warn about passing a null pointer for arguments marked as +requiring a non-null value by the @code{nonnull} function attribute. + +@option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It +can be disabled with the @option{-Wno-nonnull} option. + +@item -Wnonnull-compare +@opindex Wnonnull-compare +@opindex Wno-nonnull-compare +Warn when comparing an argument marked with the @code{nonnull} +function attribute against null inside the function. + +@option{-Wnonnull-compare} is included in @option{-Wall}. It +can be disabled with the @option{-Wno-nonnull-compare} option. + +@item -Wnull-dereference +@opindex Wnull-dereference +@opindex Wno-null-dereference +Warn if the compiler detects paths that trigger erroneous or +undefined behavior due to dereferencing a null pointer. This option +is only active when @option{-fdelete-null-pointer-checks} is active, +which is enabled by optimizations in most targets. The precision of +the warnings depends on the optimization options used. + +@item -Winfinite-recursion +@opindex Winfinite-recursion +@opindex Wno-infinite-recursion +Warn about infinitely recursive calls. The warning is effective at all +optimization levels but requires optimization in order to detect infinite +recursion in calls between two or more functions. +@option{-Winfinite-recursion} is included in @option{-Wall}. + +@item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)} +@opindex Winit-self +@opindex Wno-init-self +Warn about uninitialized variables that are initialized with themselves. +Note this option can only be used with the @option{-Wuninitialized} option. + +For example, GCC warns about @code{i} being uninitialized in the +following snippet only when @option{-Winit-self} has been specified: +@smallexample +@group +int f() +@{ + int i = i; + return i; +@} +@end group +@end smallexample + +This warning is enabled by @option{-Wall} in C++. + +@item -Wno-implicit-int @r{(C and Objective-C only)} +@opindex Wimplicit-int +@opindex Wno-implicit-int +This option controls warnings when a declaration does not specify a type. +This warning is enabled by default in C99 and later dialects of C, +and also by @option{-Wall}. + +@item -Wno-implicit-function-declaration @r{(C and Objective-C only)} +@opindex Wimplicit-function-declaration +@opindex Wno-implicit-function-declaration +This option controls warnings when a function is used before being declared. +This warning is enabled by default in C99 and later dialects of C, +and also by @option{-Wall}. +The warning is made into an error by @option{-pedantic-errors}. + +@item -Wimplicit @r{(C and Objective-C only)} +@opindex Wimplicit +@opindex Wno-implicit +Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. +This warning is enabled by @option{-Wall}. + +@item -Wimplicit-fallthrough +@opindex Wimplicit-fallthrough +@opindex Wno-implicit-fallthrough +@option{-Wimplicit-fallthrough} is the same as @option{-Wimplicit-fallthrough=3} +and @option{-Wno-implicit-fallthrough} is the same as +@option{-Wimplicit-fallthrough=0}. + +@item -Wimplicit-fallthrough=@var{n} +@opindex Wimplicit-fallthrough= +Warn when a switch case falls through. For example: + +@smallexample +@group +switch (cond) + @{ + case 1: + a = 1; + break; + case 2: + a = 2; + case 3: + a = 3; + break; + @} +@end group +@end smallexample + +This warning does not warn when the last statement of a case cannot +fall through, e.g. when there is a return statement or a call to function +declared with the noreturn attribute. @option{-Wimplicit-fallthrough=} +also takes into account control flow statements, such as ifs, and only +warns when appropriate. E.g.@: + +@smallexample +@group +switch (cond) + @{ + case 1: + if (i > 3) @{ + bar (5); + break; + @} else if (i < 1) @{ + bar (0); + @} else + return; + default: + @dots{} + @} +@end group +@end smallexample + +Since there are occasions where a switch case fall through is desirable, +GCC provides an attribute, @code{__attribute__ ((fallthrough))}, that is +to be used along with a null statement to suppress this warning that +would normally occur: + +@smallexample +@group +switch (cond) + @{ + case 1: + bar (0); + __attribute__ ((fallthrough)); + default: + @dots{} + @} +@end group +@end smallexample + +C++17 provides a standard way to suppress the @option{-Wimplicit-fallthrough} +warning using @code{[[fallthrough]];} instead of the GNU attribute. In C++11 +or C++14 users can use @code{[[gnu::fallthrough]];}, which is a GNU extension. +Instead of these attributes, it is also possible to add a fallthrough comment +to silence the warning. The whole body of the C or C++ style comment should +match the given regular expressions listed below. The option argument @var{n} +specifies what kind of comments are accepted: + +@itemize @bullet + +@item @option{-Wimplicit-fallthrough=0} disables the warning altogether. + +@item @option{-Wimplicit-fallthrough=1} matches @code{.*} regular +expression, any comment is used as fallthrough comment. + +@item @option{-Wimplicit-fallthrough=2} case insensitively matches +@code{.*falls?[ \t-]*thr(ough|u).*} regular expression. + +@item @option{-Wimplicit-fallthrough=3} case sensitively matches one of the +following regular expressions: + +@itemize @bullet + +@item @code{-fallthrough} + +@item @code{@@fallthrough@@} + +@item @code{lint -fallthrough[ \t]*} + +@item @code{[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?@*FALL(S | |-)?THR(OUGH|U)[ \t.!]*(-[^\n\r]*)?} + +@item @code{[ \t.!]*(Else,? |Intentional(ly)? )?@*Fall((s | |-)[Tt]|t)hr(ough|u)[ \t.!]*(-[^\n\r]*)?} + +@item @code{[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?@*fall(s | |-)?thr(ough|u)[ \t.!]*(-[^\n\r]*)?} + +@end itemize + +@item @option{-Wimplicit-fallthrough=4} case sensitively matches one of the +following regular expressions: + +@itemize @bullet + +@item @code{-fallthrough} + +@item @code{@@fallthrough@@} + +@item @code{lint -fallthrough[ \t]*} + +@item @code{[ \t]*FALLTHR(OUGH|U)[ \t]*} + +@end itemize + +@item @option{-Wimplicit-fallthrough=5} doesn't recognize any comments as +fallthrough comments, only attributes disable the warning. + +@end itemize + +The comment needs to be followed after optional whitespace and other comments +by @code{case} or @code{default} keywords or by a user label that precedes some +@code{case} or @code{default} label. + +@smallexample +@group +switch (cond) + @{ + case 1: + bar (0); + /* FALLTHRU */ + default: + @dots{} + @} +@end group +@end smallexample + +The @option{-Wimplicit-fallthrough=3} warning is enabled by @option{-Wextra}. + +@item -Wno-if-not-aligned @r{(C, C++, Objective-C and Objective-C++ only)} +@opindex Wif-not-aligned +@opindex Wno-if-not-aligned +Control if warnings triggered by the @code{warn_if_not_aligned} attribute +should be issued. These warnings are enabled by default. + +@item -Wignored-qualifiers @r{(C and C++ only)} +@opindex Wignored-qualifiers +@opindex Wno-ignored-qualifiers +Warn if the return type of a function has a type qualifier +such as @code{const}. For ISO C such a type qualifier has no effect, +since the value returned by a function is not an lvalue. +For C++, the warning is only emitted for scalar types or @code{void}. +ISO C prohibits qualified @code{void} return types on function +definitions, so such return types always receive a warning +even without this option. + +This warning is also enabled by @option{-Wextra}. + +@item -Wno-ignored-attributes @r{(C and C++ only)} +@opindex Wignored-attributes +@opindex Wno-ignored-attributes +This option controls warnings when an attribute is ignored. +This is different from the +@option{-Wattributes} option in that it warns whenever the compiler decides +to drop an attribute, not that the attribute is either unknown, used in a +wrong place, etc. This warning is enabled by default. + +@item -Wmain +@opindex Wmain +@opindex Wno-main +Warn if the type of @code{main} is suspicious. @code{main} should be +a function with external linkage, returning int, taking either zero +arguments, two, or three arguments of appropriate types. This warning +is enabled by default in C++ and is enabled by either @option{-Wall} +or @option{-Wpedantic}. + +@item -Wmisleading-indentation @r{(C and C++ only)} +@opindex Wmisleading-indentation +@opindex Wno-misleading-indentation +Warn when the indentation of the code does not reflect the block structure. +Specifically, a warning is issued for @code{if}, @code{else}, @code{while}, and +@code{for} clauses with a guarded statement that does not use braces, +followed by an unguarded statement with the same indentation. + +In the following example, the call to ``bar'' is misleadingly indented as +if it were guarded by the ``if'' conditional. + +@smallexample + if (some_condition ()) + foo (); + bar (); /* Gotcha: this is not guarded by the "if". */ +@end smallexample + +In the case of mixed tabs and spaces, the warning uses the +@option{-ftabstop=} option to determine if the statements line up +(defaulting to 8). + +The warning is not issued for code involving multiline preprocessor logic +such as the following example. + +@smallexample + if (flagA) + foo (0); +#if SOME_CONDITION_THAT_DOES_NOT_HOLD + if (flagB) +#endif + foo (1); +@end smallexample + +The warning is not issued after a @code{#line} directive, since this +typically indicates autogenerated code, and no assumptions can be made +about the layout of the file that the directive references. + +This warning is enabled by @option{-Wall} in C and C++. + +@item -Wmissing-attributes +@opindex Wmissing-attributes +@opindex Wno-missing-attributes +Warn when a declaration of a function is missing one or more attributes +that a related function is declared with and whose absence may adversely +affect the correctness or efficiency of generated code. For example, +the warning is issued for declarations of aliases that use attributes +to specify less restrictive requirements than those of their targets. +This typically represents a potential optimization opportunity. +By contrast, the @option{-Wattribute-alias=2} option controls warnings +issued when the alias is more restrictive than the target, which could +lead to incorrect code generation. +Attributes considered include @code{alloc_align}, @code{alloc_size}, +@code{cold}, @code{const}, @code{hot}, @code{leaf}, @code{malloc}, +@code{nonnull}, @code{noreturn}, @code{nothrow}, @code{pure}, +@code{returns_nonnull}, and @code{returns_twice}. + +In C++, the warning is issued when an explicit specialization of a primary +template declared with attribute @code{alloc_align}, @code{alloc_size}, +@code{assume_aligned}, @code{format}, @code{format_arg}, @code{malloc}, +or @code{nonnull} is declared without it. Attributes @code{deprecated}, +@code{error}, and @code{warning} suppress the warning. +(@pxref{Function Attributes}). + +You can use the @code{copy} attribute to apply the same +set of attributes to a declaration as that on another declaration without +explicitly enumerating the attributes. This attribute can be applied +to declarations of functions (@pxref{Common Function Attributes}), +variables (@pxref{Common Variable Attributes}), or types +(@pxref{Common Type Attributes}). + +@option{-Wmissing-attributes} is enabled by @option{-Wall}. + +For example, since the declaration of the primary function template +below makes use of both attribute @code{malloc} and @code{alloc_size} +the declaration of the explicit specialization of the template is +diagnosed because it is missing one of the attributes. + +@smallexample +template +T* __attribute__ ((malloc, alloc_size (1))) +allocate (size_t); + +template <> +void* __attribute__ ((malloc)) // missing alloc_size +allocate (size_t); +@end smallexample + +@item -Wmissing-braces +@opindex Wmissing-braces +@opindex Wno-missing-braces +Warn if an aggregate or union initializer is not fully bracketed. In +the following example, the initializer for @code{a} is not fully +bracketed, but that for @code{b} is fully bracketed. + +@smallexample +int a[2][2] = @{ 0, 1, 2, 3 @}; +int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Wmissing-include-dirs @r{(C, C++, Objective-C, Objective-C++ and Fortran only)} +@opindex Wmissing-include-dirs +@opindex Wno-missing-include-dirs +Warn if a user-supplied include directory does not exist. This opions is disabled +by default for C, C++, Objective-C and Objective-C++. For Fortran, it is partially +enabled by default by warning for -I and -J, only. + +@item -Wno-missing-profile +@opindex Wmissing-profile +@opindex Wno-missing-profile +This option controls warnings if feedback profiles are missing when using the +@option{-fprofile-use} option. +This option diagnoses those cases where a new function or a new file is added +between compiling with @option{-fprofile-generate} and with +@option{-fprofile-use}, without regenerating the profiles. +In these cases, the profile feedback data files do not contain any +profile feedback information for +the newly added function or file respectively. Also, in the case when profile +count data (.gcda) files are removed, GCC cannot use any profile feedback +information. In all these cases, warnings are issued to inform you that a +profile generation step is due. +Ignoring the warning can result in poorly optimized code. +@option{-Wno-missing-profile} can be used to +disable the warning, but this is not recommended and should be done only +when non-existent profile data is justified. + +@item -Wmismatched-dealloc +@opindex Wmismatched-dealloc +@opindex Wno-mismatched-dealloc + +Warn for calls to deallocation functions with pointer arguments returned +from from allocations functions for which the former isn't a suitable +deallocator. A pair of functions can be associated as matching allocators +and deallocators by use of attribute @code{malloc}. Unless disabled by +the @option{-fno-builtin} option the standard functions @code{calloc}, +@code{malloc}, @code{realloc}, and @code{free}, as well as the corresponding +forms of C++ @code{operator new} and @code{operator delete} are implicitly +associated as matching allocators and deallocators. In the following +example @code{mydealloc} is the deallocator for pointers returned from +@code{myalloc}. + +@smallexample +void mydealloc (void*); + +__attribute__ ((malloc (mydealloc, 1))) void* +myalloc (size_t); + +void f (void) +@{ + void *p = myalloc (32); + // @dots{}use p@dots{} + free (p); // warning: not a matching deallocator for myalloc + mydealloc (p); // ok +@} +@end smallexample + +In C++, the related option @option{-Wmismatched-new-delete} diagnoses +mismatches involving either @code{operator new} or @code{operator delete}. + +Option @option{-Wmismatched-dealloc} is included in @option{-Wall}. + +@item -Wmultistatement-macros +@opindex Wmultistatement-macros +@opindex Wno-multistatement-macros +Warn about unsafe multiple statement macros that appear to be guarded +by a clause such as @code{if}, @code{else}, @code{for}, @code{switch}, or +@code{while}, in which only the first statement is actually guarded after +the macro is expanded. + +For example: + +@smallexample +#define DOIT x++; y++ +if (c) + DOIT; +@end smallexample + +will increment @code{y} unconditionally, not just when @code{c} holds. +The can usually be fixed by wrapping the macro in a do-while loop: +@smallexample +#define DOIT do @{ x++; y++; @} while (0) +if (c) + DOIT; +@end smallexample + +This warning is enabled by @option{-Wall} in C and C++. + +@item -Wparentheses +@opindex Wparentheses +@opindex Wno-parentheses +Warn if parentheses are omitted in certain contexts, such +as when there is an assignment in a context where a truth value +is expected, or when operators are nested whose precedence people +often get confused about. + +Also warn if a comparison like @code{x<=y<=z} appears; this is +equivalent to @code{(x<=y ? 1 : 0) <= z}, which is a different +interpretation from that of ordinary mathematical notation. + +Also warn for dangerous uses of the GNU extension to +@code{?:} with omitted middle operand. When the condition +in the @code{?}: operator is a boolean expression, the omitted value is +always 1. Often programmers expect it to be a value computed +inside the conditional expression instead. + +For C++ this also warns for some cases of unnecessary parentheses in +declarations, which can indicate an attempt at a function call instead +of a declaration: +@smallexample +@{ + // Declares a local variable called mymutex. + std::unique_lock (mymutex); + // User meant std::unique_lock lock (mymutex); +@} +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Wno-self-move @r{(C++ and Objective-C++ only)} +@opindex Wself-move +@opindex Wno-self-move +This warning warns when a value is moved to itself with @code{std::move}. +Such a @code{std::move} typically has no effect. + +@smallexample +struct T @{ +@dots{} +@}; +void fn() +@{ + T t; + @dots{} + t = std::move (t); +@} +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Wsequence-point +@opindex Wsequence-point +@opindex Wno-sequence-point +Warn about code that may have undefined semantics because of violations +of sequence point rules in the C and C++ standards. + +The C and C++ standards define the order in which expressions in a C/C++ +program are evaluated in terms of @dfn{sequence points}, which represent +a partial ordering between the execution of parts of the program: those +executed before the sequence point, and those executed after it. These +occur after the evaluation of a full expression (one which is not part +of a larger expression), after the evaluation of the first operand of a +@code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a +function is called (but after the evaluation of its arguments and the +expression denoting the called function), and in certain other places. +Other than as expressed by the sequence point rules, the order of +evaluation of subexpressions of an expression is not specified. All +these rules describe only a partial order rather than a total order, +since, for example, if two functions are called within one expression +with no sequence point between them, the order in which the functions +are called is not specified. However, the standards committee have +ruled that function calls do not overlap. + +It is not specified when between sequence points modifications to the +values of objects take effect. Programs whose behavior depends on this +have undefined behavior; the C and C++ standards specify that ``Between +the previous and next sequence point an object shall have its stored +value modified at most once by the evaluation of an expression. +Furthermore, the prior value shall be read only to determine the value +to be stored.''. If a program breaks these rules, the results on any +particular implementation are entirely unpredictable. + +Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] += b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not +diagnosed by this option, and it may give an occasional false positive +result, but in general it has been found fairly effective at detecting +this sort of problem in programs. + +The C++17 standard will define the order of evaluation of operands in +more cases: in particular it requires that the right-hand side of an +assignment be evaluated before the left-hand side, so the above +examples are no longer undefined. But this option will still warn +about them, to help people avoid writing code that is undefined in C +and earlier revisions of C++. + +The standard is worded confusingly, therefore there is some debate +over the precise meaning of the sequence point rules in subtle cases. +Links to discussions of the problem, including proposed formal +definitions, may be found on the GCC readings page, at +@uref{https://gcc.gnu.org/@/readings.html}. + +This warning is enabled by @option{-Wall} for C and C++. + +@item -Wno-return-local-addr +@opindex Wno-return-local-addr +@opindex Wreturn-local-addr +Do not warn about returning a pointer (or in C++, a reference) to a +variable that goes out of scope after the function returns. + +@item -Wreturn-type +@opindex Wreturn-type +@opindex Wno-return-type +Warn whenever a function is defined with a return type that defaults +to @code{int}. Also warn about any @code{return} statement with no +return value in a function whose return type is not @code{void} +(falling off the end of the function body is considered returning +without a value). + +For C only, warn about a @code{return} statement with an expression in a +function whose return type is @code{void}, unless the expression type is +also @code{void}. As a GNU extension, the latter case is accepted +without a warning unless @option{-Wpedantic} is used. Attempting +to use the return value of a non-@code{void} function other than @code{main} +that flows off the end by reaching the closing curly brace that terminates +the function is undefined. + +Unlike in C, in C++, flowing off the end of a non-@code{void} function other +than @code{main} results in undefined behavior even when the value of +the function is not used. + +This warning is enabled by default in C++ and by @option{-Wall} otherwise. + +@item -Wno-shift-count-negative +@opindex Wshift-count-negative +@opindex Wno-shift-count-negative +Controls warnings if a shift count is negative. +This warning is enabled by default. + +@item -Wno-shift-count-overflow +@opindex Wshift-count-overflow +@opindex Wno-shift-count-overflow +Controls warnings if a shift count is greater than or equal to the bit width +of the type. This warning is enabled by default. + +@item -Wshift-negative-value +@opindex Wshift-negative-value +@opindex Wno-shift-negative-value +Warn if left shifting a negative value. This warning is enabled by +@option{-Wextra} in C99 (and newer) and C++11 to C++17 modes. + +@item -Wno-shift-overflow +@itemx -Wshift-overflow=@var{n} +@opindex Wshift-overflow +@opindex Wno-shift-overflow +These options control warnings about left shift overflows. + +@table @gcctabopt +@item -Wshift-overflow=1 +This is the warning level of @option{-Wshift-overflow} and is enabled +by default in C99 and C++11 modes (and newer). This warning level does +not warn about left-shifting 1 into the sign bit. (However, in C, such +an overflow is still rejected in contexts where an integer constant expression +is required.) No warning is emitted in C++20 mode (and newer), as signed left +shifts always wrap. + +@item -Wshift-overflow=2 +This warning level also warns about left-shifting 1 into the sign bit, +unless C++14 mode (or newer) is active. +@end table + +@item -Wswitch +@opindex Wswitch +@opindex Wno-switch +Warn whenever a @code{switch} statement has an index of enumerated type +and lacks a @code{case} for one or more of the named codes of that +enumeration. (The presence of a @code{default} label prevents this +warning.) @code{case} labels outside the enumeration range also +provoke warnings when this option is used (even if there is a +@code{default} label). +This warning is enabled by @option{-Wall}. + +@item -Wswitch-default +@opindex Wswitch-default +@opindex Wno-switch-default +Warn whenever a @code{switch} statement does not have a @code{default} +case. + +@item -Wswitch-enum +@opindex Wswitch-enum +@opindex Wno-switch-enum +Warn whenever a @code{switch} statement has an index of enumerated type +and lacks a @code{case} for one or more of the named codes of that +enumeration. @code{case} labels outside the enumeration range also +provoke warnings when this option is used. The only difference +between @option{-Wswitch} and this option is that this option gives a +warning about an omitted enumeration code even if there is a +@code{default} label. + +@item -Wno-switch-bool +@opindex Wswitch-bool +@opindex Wno-switch-bool +Do not warn when a @code{switch} statement has an index of boolean type +and the case values are outside the range of a boolean type. +It is possible to suppress this warning by casting the controlling +expression to a type other than @code{bool}. For example: +@smallexample +@group +switch ((int) (a == 4)) + @{ + @dots{} + @} +@end group +@end smallexample +This warning is enabled by default for C and C++ programs. + +@item -Wno-switch-outside-range +@opindex Wswitch-outside-range +@opindex Wno-switch-outside-range +This option controls warnings when a @code{switch} case has a value +that is outside of its +respective type range. This warning is enabled by default for +C and C++ programs. + +@item -Wno-switch-unreachable +@opindex Wswitch-unreachable +@opindex Wno-switch-unreachable +Do not warn when a @code{switch} statement contains statements between the +controlling expression and the first case label, which will never be +executed. For example: +@smallexample +@group +switch (cond) + @{ + i = 15; + @dots{} + case 5: + @dots{} + @} +@end group +@end smallexample +@option{-Wswitch-unreachable} does not warn if the statement between the +controlling expression and the first case label is just a declaration: +@smallexample +@group +switch (cond) + @{ + int i; + @dots{} + case 5: + i = 5; + @dots{} + @} +@end group +@end smallexample +This warning is enabled by default for C and C++ programs. + +@item -Wsync-nand @r{(C and C++ only)} +@opindex Wsync-nand +@opindex Wno-sync-nand +Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch} +built-in functions are used. These functions changed semantics in GCC 4.4. + +@item -Wtrivial-auto-var-init +@opindex Wtrivial-auto-var-init +@opindex Wno-trivial-auto-var-init +Warn when @code{-ftrivial-auto-var-init} cannot initialize the automatic +variable. A common situation is an automatic variable that is declared +between the controlling expression and the first case label of a @code{switch} +statement. + +@item -Wunused-but-set-parameter +@opindex Wunused-but-set-parameter +@opindex Wno-unused-but-set-parameter +Warn whenever a function parameter is assigned to, but otherwise unused +(aside from its declaration). + +To suppress this warning use the @code{unused} attribute +(@pxref{Variable Attributes}). + +This warning is also enabled by @option{-Wunused} together with +@option{-Wextra}. + +@item -Wunused-but-set-variable +@opindex Wunused-but-set-variable +@opindex Wno-unused-but-set-variable +Warn whenever a local variable is assigned to, but otherwise unused +(aside from its declaration). +This warning is enabled by @option{-Wall}. + +To suppress this warning use the @code{unused} attribute +(@pxref{Variable Attributes}). + +This warning is also enabled by @option{-Wunused}, which is enabled +by @option{-Wall}. + +@item -Wunused-function +@opindex Wunused-function +@opindex Wno-unused-function +Warn whenever a static function is declared but not defined or a +non-inline static function is unused. +This warning is enabled by @option{-Wall}. + +@item -Wunused-label +@opindex Wunused-label +@opindex Wno-unused-label +Warn whenever a label is declared but not used. +This warning is enabled by @option{-Wall}. + +To suppress this warning use the @code{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)} +@opindex Wunused-local-typedefs +@opindex Wno-unused-local-typedefs +Warn when a typedef locally defined in a function is not used. +This warning is enabled by @option{-Wall}. + +@item -Wunused-parameter +@opindex Wunused-parameter +@opindex Wno-unused-parameter +Warn whenever a function parameter is unused aside from its declaration. + +To suppress this warning use the @code{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wno-unused-result +@opindex Wunused-result +@opindex Wno-unused-result +Do not warn if a caller of a function marked with attribute +@code{warn_unused_result} (@pxref{Function Attributes}) does not use +its return value. The default is @option{-Wunused-result}. + +@item -Wunused-variable +@opindex Wunused-variable +@opindex Wno-unused-variable +Warn whenever a local or static variable is unused aside from its +declaration. This option implies @option{-Wunused-const-variable=1} for C, +but not for C++. This warning is enabled by @option{-Wall}. + +To suppress this warning use the @code{unused} attribute +(@pxref{Variable Attributes}). + +@item -Wunused-const-variable +@itemx -Wunused-const-variable=@var{n} +@opindex Wunused-const-variable +@opindex Wno-unused-const-variable +Warn whenever a constant static variable is unused aside from its declaration. +@option{-Wunused-const-variable=1} is enabled by @option{-Wunused-variable} +for C, but not for C++. In C this declares variable storage, but in C++ this +is not an error since const variables take the place of @code{#define}s. + +To suppress this warning use the @code{unused} attribute +(@pxref{Variable Attributes}). + +@table @gcctabopt +@item -Wunused-const-variable=1 +This is the warning level that is enabled by @option{-Wunused-variable} for +C. It warns only about unused static const variables defined in the main +compilation unit, but not about static const variables declared in any +header included. + +@item -Wunused-const-variable=2 +This warning level also warns for unused constant static variables in +headers (excluding system headers). This is the warning level of +@option{-Wunused-const-variable} and must be explicitly requested since +in C++ this isn't an error and in C it might be harder to clean up all +headers included. +@end table + +@item -Wunused-value +@opindex Wunused-value +@opindex Wno-unused-value +Warn whenever a statement computes a result that is explicitly not +used. To suppress this warning cast the unused expression to +@code{void}. This includes an expression-statement or the left-hand +side of a comma expression that contains no side effects. For example, +an expression such as @code{x[i,j]} causes a warning, while +@code{x[(void)i,j]} does not. + +This warning is enabled by @option{-Wall}. + +@item -Wunused +@opindex Wunused +@opindex Wno-unused +All the above @option{-Wunused} options combined. + +In order to get a warning about an unused function parameter, you must +either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies +@option{-Wunused}), or separately specify @option{-Wunused-parameter}. + +@item -Wuninitialized +@opindex Wuninitialized +@opindex Wno-uninitialized +Warn if an object with automatic or allocated storage duration is used +without having been initialized. In C++, also warn if a non-static +reference or non-static @code{const} member appears in a class without +constructors. + +In addition, passing a pointer (or in C++, a reference) to an uninitialized +object to a @code{const}-qualified argument of a built-in function known to +read the object is also diagnosed by this warning. +(@option{-Wmaybe-uninitialized} is issued for ordinary functions.) + +If you want to warn about code that uses the uninitialized value of the +variable in its own initializer, use the @option{-Winit-self} option. + +These warnings occur for individual uninitialized elements of +structure, union or array variables as well as for variables that are +uninitialized as a whole. They do not occur for variables or elements +declared @code{volatile}. Because these warnings depend on +optimization, the exact variables or elements for which there are +warnings depend on the precise optimization options and version of GCC +used. + +Note that there may be no warning about a variable that is used only +to compute a value that itself is never used, because such +computations may be deleted by data flow analysis before the warnings +are printed. + +In C++, this warning also warns about using uninitialized objects in +member-initializer-lists. For example, GCC warns about @code{b} being +uninitialized in the following snippet: + +@smallexample +struct A @{ + int a; + int b; + A() : a(b) @{ @} +@}; +@end smallexample + +@item -Wno-invalid-memory-model +@opindex Winvalid-memory-model +@opindex Wno-invalid-memory-model +This option controls warnings +for invocations of @ref{__atomic Builtins}, @ref{__sync Builtins}, +and the C11 atomic generic functions with a memory consistency argument +that is either invalid for the operation or outside the range of values +of the @code{memory_order} enumeration. For example, since the +@code{__atomic_store} and @code{__atomic_store_n} built-ins are only +defined for the relaxed, release, and sequentially consistent memory +orders the following code is diagnosed: + +@smallexample +void store (int *i) +@{ + __atomic_store_n (i, 0, memory_order_consume); +@} +@end smallexample + +@option{-Winvalid-memory-model} is enabled by default. + +@item -Wmaybe-uninitialized +@opindex Wmaybe-uninitialized +@opindex Wno-maybe-uninitialized +For an object with automatic or allocated storage duration, if there exists +a path from the function entry to a use of the object that is initialized, +but there exist some other paths for which the object is not initialized, +the compiler emits a warning if it cannot prove the uninitialized paths +are not executed at run time. + +In addition, passing a pointer (or in C++, a reference) to an uninitialized +object to a @code{const}-qualified function argument is also diagnosed by +this warning. (@option{-Wuninitialized} is issued for built-in functions +known to read the object.) Annotating the function with attribute +@code{access (none)} indicates that the argument isn't used to access +the object and avoids the warning (@pxref{Common Function Attributes}). + +These warnings are only possible in optimizing compilation, because otherwise +GCC does not keep track of the state of variables. + +These warnings are made optional because GCC may not be able to determine when +the code is correct in spite of appearing to have an error. Here is one +example of how this can happen: + +@smallexample +@group +@{ + int x; + switch (y) + @{ + case 1: x = 1; + break; + case 2: x = 4; + break; + case 3: x = 5; + @} + foo (x); +@} +@end group +@end smallexample + +@noindent +If the value of @code{y} is always 1, 2 or 3, then @code{x} is +always initialized, but GCC doesn't know this. To suppress the +warning, you need to provide a default case with assert(0) or +similar code. + +@cindex @code{longjmp} warnings +This option also warns when a non-volatile automatic variable might be +changed by a call to @code{longjmp}. +The compiler sees only the calls to @code{setjmp}. It cannot know +where @code{longjmp} will be called; in fact, a signal handler could +call it at any point in the code. As a result, you may get a warning +even when there is in fact no problem because @code{longjmp} cannot +in fact be called at the place that would cause a problem. + +Some spurious warnings can be avoided if you declare all the functions +you use that never return as @code{noreturn}. @xref{Function +Attributes}. + +This warning is enabled by @option{-Wall} or @option{-Wextra}. + +@item -Wunknown-pragmas +@opindex Wunknown-pragmas +@opindex Wno-unknown-pragmas +@cindex warning for unknown pragmas +@cindex unknown pragmas, warning +@cindex pragmas, warning of unknown +Warn when a @code{#pragma} directive is encountered that is not understood by +GCC@. If this command-line option is used, warnings are even issued +for unknown pragmas in system header files. This is not the case if +the warnings are only enabled by the @option{-Wall} command-line option. + +@item -Wno-pragmas +@opindex Wno-pragmas +@opindex Wpragmas +Do not warn about misuses of pragmas, such as incorrect parameters, +invalid syntax, or conflicts between pragmas. See also +@option{-Wunknown-pragmas}. + +@item -Wno-prio-ctor-dtor +@opindex Wno-prio-ctor-dtor +@opindex Wprio-ctor-dtor +Do not warn if a priority from 0 to 100 is used for constructor or destructor. +The use of constructor and destructor attributes allow you to assign a +priority to the constructor/destructor to control its order of execution +before @code{main} is called or after it returns. The priority values must be +greater than 100 as the compiler reserves priority values between 0--100 for +the implementation. + +@item -Wstrict-aliasing +@opindex Wstrict-aliasing +@opindex Wno-strict-aliasing +This option is only active when @option{-fstrict-aliasing} is active. +It warns about code that might break the strict aliasing rules that the +compiler is using for optimization. The warning does not catch all +cases, but does attempt to catch the more common pitfalls. It is +included in @option{-Wall}. +It is equivalent to @option{-Wstrict-aliasing=3} + +@item -Wstrict-aliasing=n +@opindex Wstrict-aliasing=n +This option is only active when @option{-fstrict-aliasing} is active. +It warns about code that might break the strict aliasing rules that the +compiler is using for optimization. +Higher levels correspond to higher accuracy (fewer false positives). +Higher levels also correspond to more effort, similar to the way @option{-O} +works. +@option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}. + +Level 1: Most aggressive, quick, least accurate. +Possibly useful when higher levels +do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few +false negatives. However, it has many false positives. +Warns for all pointer conversions between possibly incompatible types, +even if never dereferenced. Runs in the front end only. + +Level 2: Aggressive, quick, not too precise. +May still have many false positives (not as many as level 1 though), +and few false negatives (but possibly more than level 1). +Unlike level 1, it only warns when an address is taken. Warns about +incomplete types. Runs in the front end only. + +Level 3 (default for @option{-Wstrict-aliasing}): +Should have very few false positives and few false +negatives. Slightly slower than levels 1 or 2 when optimization is enabled. +Takes care of the common pun+dereference pattern in the front end: +@code{*(int*)&some_float}. +If optimization is enabled, it also runs in the back end, where it deals +with multiple statement cases using flow-sensitive points-to information. +Only warns when the converted pointer is dereferenced. +Does not warn about incomplete types. + +@item -Wstrict-overflow +@itemx -Wstrict-overflow=@var{n} +@opindex Wstrict-overflow +@opindex Wno-strict-overflow +This option is only active when signed overflow is undefined. +It warns about cases where the compiler optimizes based on the +assumption that signed overflow does not occur. Note that it does not +warn about all cases where the code might overflow: it only warns +about cases where the compiler implements some optimization. Thus +this warning depends on the optimization level. + +An optimization that assumes that signed overflow does not occur is +perfectly safe if the values of the variables involved are such that +overflow never does, in fact, occur. Therefore this warning can +easily give a false positive: a warning about code that is not +actually a problem. To help focus on important issues, several +warning levels are defined. No warnings are issued for the use of +undefined signed overflow when estimating how many iterations a loop +requires, in particular when determining whether a loop will be +executed at all. + +@table @gcctabopt +@item -Wstrict-overflow=1 +Warn about cases that are both questionable and easy to avoid. For +example the compiler simplifies +@code{x + 1 > x} to @code{1}. This level of +@option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels +are not, and must be explicitly requested. + +@item -Wstrict-overflow=2 +Also warn about other cases where a comparison is simplified to a +constant. For example: @code{abs (x) >= 0}. This can only be +simplified when signed integer overflow is undefined, because +@code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than +zero. @option{-Wstrict-overflow} (with no level) is the same as +@option{-Wstrict-overflow=2}. + +@item -Wstrict-overflow=3 +Also warn about other cases where a comparison is simplified. For +example: @code{x + 1 > 1} is simplified to @code{x > 0}. + +@item -Wstrict-overflow=4 +Also warn about other simplifications not covered by the above cases. +For example: @code{(x * 10) / 5} is simplified to @code{x * 2}. + +@item -Wstrict-overflow=5 +Also warn about cases where the compiler reduces the magnitude of a +constant involved in a comparison. For example: @code{x + 2 > y} is +simplified to @code{x + 1 >= y}. This is reported only at the +highest warning level because this simplification applies to many +comparisons, so this warning level gives a very large number of +false positives. +@end table + +@item -Wstring-compare +@opindex Wstring-compare +@opindex Wno-string-compare +Warn for calls to @code{strcmp} and @code{strncmp} whose result is +determined to be either zero or non-zero in tests for such equality +owing to the length of one argument being greater than the size of +the array the other argument is stored in (or the bound in the case +of @code{strncmp}). Such calls could be mistakes. For example, +the call to @code{strcmp} below is diagnosed because its result is +necessarily non-zero irrespective of the contents of the array @code{a}. + +@smallexample +extern char a[4]; +void f (char *d) +@{ + strcpy (d, "string"); + @dots{} + if (0 == strcmp (a, d)) // cannot be true + puts ("a and d are the same"); +@} +@end smallexample + +@option{-Wstring-compare} is enabled by @option{-Wextra}. + +@item -Wno-stringop-overflow +@item -Wstringop-overflow +@itemx -Wstringop-overflow=@var{type} +@opindex Wstringop-overflow +@opindex Wno-stringop-overflow +Warn for calls to string manipulation functions such as @code{memcpy} and +@code{strcpy} that are determined to overflow the destination buffer. The +optional argument is one greater than the type of Object Size Checking to +perform to determine the size of the destination. @xref{Object Size Checking}. +The argument is meaningful only for functions that operate on character arrays +but not for raw memory functions like @code{memcpy} which always make use +of Object Size type-0. The option also warns for calls that specify a size +in excess of the largest possible object or at most @code{SIZE_MAX / 2} bytes. +The option produces the best results with optimization enabled but can detect +a small subset of simple buffer overflows even without optimization in +calls to the GCC built-in functions like @code{__builtin_memcpy} that +correspond to the standard functions. In any case, the option warns about +just a subset of buffer overflows detected by the corresponding overflow +checking built-ins. For example, the option issues a warning for +the @code{strcpy} call below because it copies at least 5 characters +(the string @code{"blue"} including the terminating NUL) into the buffer +of size 4. + +@smallexample +enum Color @{ blue, purple, yellow @}; +const char* f (enum Color clr) +@{ + static char buf [4]; + const char *str; + switch (clr) + @{ + case blue: str = "blue"; break; + case purple: str = "purple"; break; + case yellow: str = "yellow"; break; + @} + + return strcpy (buf, str); // warning here +@} +@end smallexample + +Option @option{-Wstringop-overflow=2} is enabled by default. + +@table @gcctabopt +@item -Wstringop-overflow +@itemx -Wstringop-overflow=1 +@opindex Wstringop-overflow +@opindex Wno-stringop-overflow +The @option{-Wstringop-overflow=1} option uses type-zero Object Size Checking +to determine the sizes of destination objects. At this setting the option +does not warn for writes past the end of subobjects of larger objects accessed +by pointers unless the size of the largest surrounding object is known. When +the destination may be one of several objects it is assumed to be the largest +one of them. On Linux systems, when optimization is enabled at this setting +the option warns for the same code as when the @code{_FORTIFY_SOURCE} macro +is defined to a non-zero value. + +@item -Wstringop-overflow=2 +The @option{-Wstringop-overflow=2} option uses type-one Object Size Checking +to determine the sizes of destination objects. At this setting the option +warns about overflows when writing to members of the largest complete +objects whose exact size is known. However, it does not warn for excessive +writes to the same members of unknown objects referenced by pointers since +they may point to arrays containing unknown numbers of elements. This is +the default setting of the option. + +@item -Wstringop-overflow=3 +The @option{-Wstringop-overflow=3} option uses type-two Object Size Checking +to determine the sizes of destination objects. At this setting the option +warns about overflowing the smallest object or data member. This is the +most restrictive setting of the option that may result in warnings for safe +code. + +@item -Wstringop-overflow=4 +The @option{-Wstringop-overflow=4} option uses type-three Object Size Checking +to determine the sizes of destination objects. At this setting the option +warns about overflowing any data members, and when the destination is +one of several objects it uses the size of the largest of them to decide +whether to issue a warning. Similarly to @option{-Wstringop-overflow=3} this +setting of the option may result in warnings for benign code. +@end table + +@item -Wno-stringop-overread +@opindex Wstringop-overread +@opindex Wno-stringop-overread +Warn for calls to string manipulation functions such as @code{memchr}, or +@code{strcpy} that are determined to read past the end of the source +sequence. + +Option @option{-Wstringop-overread} is enabled by default. + +@item -Wno-stringop-truncation +@opindex Wstringop-truncation +@opindex Wno-stringop-truncation +Do not warn for calls to bounded string manipulation functions +such as @code{strncat}, +@code{strncpy}, and @code{stpncpy} that may either truncate the copied string +or leave the destination unchanged. + +In the following example, the call to @code{strncat} specifies a bound that +is less than the length of the source string. As a result, the copy of +the source will be truncated and so the call is diagnosed. To avoid the +warning use @code{bufsize - strlen (buf) - 1)} as the bound. + +@smallexample +void append (char *buf, size_t bufsize) +@{ + strncat (buf, ".txt", 3); +@} +@end smallexample + +As another example, the following call to @code{strncpy} results in copying +to @code{d} just the characters preceding the terminating NUL, without +appending the NUL to the end. Assuming the result of @code{strncpy} is +necessarily a NUL-terminated string is a common mistake, and so the call +is diagnosed. To avoid the warning when the result is not expected to be +NUL-terminated, call @code{memcpy} instead. + +@smallexample +void copy (char *d, const char *s) +@{ + strncpy (d, s, strlen (s)); +@} +@end smallexample + +In the following example, the call to @code{strncpy} specifies the size +of the destination buffer as the bound. If the length of the source +string is equal to or greater than this size the result of the copy will +not be NUL-terminated. Therefore, the call is also diagnosed. To avoid +the warning, specify @code{sizeof buf - 1} as the bound and set the last +element of the buffer to @code{NUL}. + +@smallexample +void copy (const char *s) +@{ + char buf[80]; + strncpy (buf, s, sizeof buf); + @dots{} +@} +@end smallexample + +In situations where a character array is intended to store a sequence +of bytes with no terminating @code{NUL} such an array may be annotated +with attribute @code{nonstring} to avoid this warning. Such arrays, +however, are not suitable arguments to functions that expect +@code{NUL}-terminated strings. To help detect accidental misuses of +such arrays GCC issues warnings unless it can prove that the use is +safe. @xref{Common Variable Attributes}. + +@item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{|}cold@r{|}malloc@r{]} +@opindex Wsuggest-attribute= +@opindex Wno-suggest-attribute= +Warn for cases where adding an attribute may be beneficial. The +attributes currently supported are listed below. + +@table @gcctabopt +@item -Wsuggest-attribute=pure +@itemx -Wsuggest-attribute=const +@itemx -Wsuggest-attribute=noreturn +@itemx -Wmissing-noreturn +@itemx -Wsuggest-attribute=malloc +@opindex Wsuggest-attribute=pure +@opindex Wno-suggest-attribute=pure +@opindex Wsuggest-attribute=const +@opindex Wno-suggest-attribute=const +@opindex Wsuggest-attribute=noreturn +@opindex Wno-suggest-attribute=noreturn +@opindex Wmissing-noreturn +@opindex Wno-missing-noreturn +@opindex Wsuggest-attribute=malloc +@opindex Wno-suggest-attribute=malloc + +Warn about functions that might be candidates for attributes +@code{pure}, @code{const} or @code{noreturn} or @code{malloc}. The compiler +only warns for functions visible in other compilation units or (in the case of +@code{pure} and @code{const}) if it cannot prove that the function returns +normally. A function returns normally if it doesn't contain an infinite loop or +return abnormally by throwing, calling @code{abort} or trapping. This analysis +requires option @option{-fipa-pure-const}, which is enabled by default at +@option{-O} and higher. Higher optimization levels improve the accuracy +of the analysis. + +@item -Wsuggest-attribute=format +@itemx -Wmissing-format-attribute +@opindex Wsuggest-attribute=format +@opindex Wmissing-format-attribute +@opindex Wno-suggest-attribute=format +@opindex Wno-missing-format-attribute +@opindex Wformat +@opindex Wno-format + +Warn about function pointers that might be candidates for @code{format} +attributes. Note these are only possible candidates, not absolute ones. +GCC guesses that function pointers with @code{format} attributes that +are used in assignment, initialization, parameter passing or return +statements should have a corresponding @code{format} attribute in the +resulting type. I.e.@: the left-hand side of the assignment or +initialization, the type of the parameter variable, or the return type +of the containing function respectively should also have a @code{format} +attribute to avoid the warning. + +GCC also warns about function definitions that might be +candidates for @code{format} attributes. Again, these are only +possible candidates. GCC guesses that @code{format} attributes +might be appropriate for any function that calls a function like +@code{vprintf} or @code{vscanf}, but this might not always be the +case, and some functions for which @code{format} attributes are +appropriate may not be detected. + +@item -Wsuggest-attribute=cold +@opindex Wsuggest-attribute=cold +@opindex Wno-suggest-attribute=cold + +Warn about functions that might be candidates for @code{cold} attribute. This +is based on static detection and generally only warns about functions which +always leads to a call to another @code{cold} function such as wrappers of +C++ @code{throw} or fatal error reporting functions leading to @code{abort}. +@end table + +@item -Walloc-zero +@opindex Wno-alloc-zero +@opindex Walloc-zero +Warn about calls to allocation functions decorated with attribute +@code{alloc_size} that specify zero bytes, including those to the built-in +forms of the functions @code{aligned_alloc}, @code{alloca}, @code{calloc}, +@code{malloc}, and @code{realloc}. Because the behavior of these functions +when called with a zero size differs among implementations (and in the case +of @code{realloc} has been deprecated) relying on it may result in subtle +portability bugs and should be avoided. + +@item -Walloc-size-larger-than=@var{byte-size} +@opindex Walloc-size-larger-than= +@opindex Wno-alloc-size-larger-than +Warn about calls to functions decorated with attribute @code{alloc_size} +that attempt to allocate objects larger than the specified number of bytes, +or where the result of the size computation in an integer type with infinite +precision would exceed the value of @samp{PTRDIFF_MAX} on the target. +@option{-Walloc-size-larger-than=}@samp{PTRDIFF_MAX} is enabled by default. +Warnings controlled by the option can be disabled either by specifying +@var{byte-size} of @samp{SIZE_MAX} or more or by +@option{-Wno-alloc-size-larger-than}. +@xref{Function Attributes}. + +@item -Wno-alloc-size-larger-than +@opindex Wno-alloc-size-larger-than +Disable @option{-Walloc-size-larger-than=} warnings. The option is +equivalent to @option{-Walloc-size-larger-than=}@samp{SIZE_MAX} or +larger. + +@item -Walloca +@opindex Wno-alloca +@opindex Walloca +This option warns on all uses of @code{alloca} in the source. + +@item -Walloca-larger-than=@var{byte-size} +@opindex Walloca-larger-than= +@opindex Wno-alloca-larger-than +This option warns on calls to @code{alloca} with an integer argument whose +value is either zero, or that is not bounded by a controlling predicate +that limits its value to at most @var{byte-size}. It also warns for calls +to @code{alloca} where the bound value is unknown. Arguments of non-integer +types are considered unbounded even if they appear to be constrained to +the expected range. + +For example, a bounded case of @code{alloca} could be: + +@smallexample +void func (size_t n) +@{ + void *p; + if (n <= 1000) + p = alloca (n); + else + p = malloc (n); + f (p); +@} +@end smallexample + +In the above example, passing @code{-Walloca-larger-than=1000} would not +issue a warning because the call to @code{alloca} is known to be at most +1000 bytes. However, if @code{-Walloca-larger-than=500} were passed, +the compiler would emit a warning. + +Unbounded uses, on the other hand, are uses of @code{alloca} with no +controlling predicate constraining its integer argument. For example: + +@smallexample +void func () +@{ + void *p = alloca (n); + f (p); +@} +@end smallexample + +If @code{-Walloca-larger-than=500} were passed, the above would trigger +a warning, but this time because of the lack of bounds checking. + +Note, that even seemingly correct code involving signed integers could +cause a warning: + +@smallexample +void func (signed int n) +@{ + if (n < 500) + @{ + p = alloca (n); + f (p); + @} +@} +@end smallexample + +In the above example, @var{n} could be negative, causing a larger than +expected argument to be implicitly cast into the @code{alloca} call. + +This option also warns when @code{alloca} is used in a loop. + +@option{-Walloca-larger-than=}@samp{PTRDIFF_MAX} is enabled by default +but is usually only effective when @option{-ftree-vrp} is active (default +for @option{-O2} and above). + +See also @option{-Wvla-larger-than=}@samp{byte-size}. + +@item -Wno-alloca-larger-than +@opindex Wno-alloca-larger-than +Disable @option{-Walloca-larger-than=} warnings. The option is +equivalent to @option{-Walloca-larger-than=}@samp{SIZE_MAX} or larger. + +@item -Warith-conversion +@opindex Warith-conversion +@opindex Wno-arith-conversion +Do warn about implicit conversions from arithmetic operations even +when conversion of the operands to the same type cannot change their +values. This affects warnings from @option{-Wconversion}, +@option{-Wfloat-conversion}, and @option{-Wsign-conversion}. + +@smallexample +@group +void f (char c, int i) +@{ + c = c + i; // warns with @option{-Wconversion} + c = c + 1; // only warns with @option{-Warith-conversion} +@} +@end group +@end smallexample + +@item -Warray-bounds +@itemx -Warray-bounds=@var{n} +@opindex Wno-array-bounds +@opindex Warray-bounds +Warn about out of bounds subscripts or offsets into arrays. This warning +is enabled by @option{-Wall}. It is more effective when @option{-ftree-vrp} +is active (the default for @option{-O2} and above) but a subset of instances +are issued even without optimization. + +@table @gcctabopt +@item -Warray-bounds=1 +This is the default warning level of @option{-Warray-bounds} and is enabled +by @option{-Wall}; higher levels are not, and must be explicitly requested. + +@item -Warray-bounds=2 +This warning level also warns about out of bounds accesses to trailing +struct members of one-element array types (@pxref{Zero Length}) and about +the intermediate results of pointer arithmetic that may yield out of bounds +values. This warning level may give a larger number of false positives and +is deactivated by default. +@end table + +@item -Warray-compare +@opindex Warray-compare +@opindex Wno-array-compare +Warn about equality and relational comparisons between two operands of array +type. This comparison was deprecated in C++20. For example: + +@smallexample +int arr1[5]; +int arr2[5]; +bool same = arr1 == arr2; +@end smallexample + +@option{-Warray-compare} is enabled by @option{-Wall}. + +@item -Warray-parameter +@itemx -Warray-parameter=@var{n} +@opindex Wno-array-parameter +Warn about redeclarations of functions involving arguments of array or +pointer types of inconsistent kinds or forms, and enable the detection +of out-of-bounds accesses to such parameters by warnings such as +@option{-Warray-bounds}. + +If the first function declaration uses the array form the bound specified +in the array is assumed to be the minimum number of elements expected to +be provided in calls to the function and the maximum number of elements +accessed by it. Failing to provide arguments of sufficient size or accessing +more than the maximum number of elements may be diagnosed by warnings such +as @option{-Warray-bounds}. At level 1 the warning diagnoses inconsistencies +involving array parameters declared using the @code{T[static N]} form. + +For example, the warning triggers for the following redeclarations because +the first one allows an array of any size to be passed to @code{f} while +the second one with the keyword @code{static} specifies that the array +argument must have at least four elements. + +@smallexample +void f (int[static 4]); +void f (int[]); // warning (inconsistent array form) + +void g (void) +@{ + int *p = (int *)malloc (4); + f (p); // warning (array too small) + @dots{} +@} +@end smallexample + +At level 2 the warning also triggers for redeclarations involving any other +inconsistency in array or pointer argument forms denoting array sizes. +Pointers and arrays of unspecified bound are considered equivalent and do +not trigger a warning. + +@smallexample +void g (int*); +void g (int[]); // no warning +void g (int[8]); // warning (inconsistent array bound) +@end smallexample + +@option{-Warray-parameter=2} is included in @option{-Wall}. The +@option{-Wvla-parameter} option triggers warnings for similar inconsistencies +involving Variable Length Array arguments. + +@item -Wattribute-alias=@var{n} +@itemx -Wno-attribute-alias +@opindex Wattribute-alias +@opindex Wno-attribute-alias +Warn about declarations using the @code{alias} and similar attributes whose +target is incompatible with the type of the alias. +@xref{Function Attributes,,Declaring Attributes of Functions}. + +@table @gcctabopt +@item -Wattribute-alias=1 +The default warning level of the @option{-Wattribute-alias} option diagnoses +incompatibilities between the type of the alias declaration and that of its +target. Such incompatibilities are typically indicative of bugs. + +@item -Wattribute-alias=2 + +At this level @option{-Wattribute-alias} also diagnoses cases where +the attributes of the alias declaration are more restrictive than the +attributes applied to its target. These mismatches can potentially +result in incorrect code generation. In other cases they may be +benign and could be resolved simply by adding the missing attribute to +the target. For comparison, see the @option{-Wmissing-attributes} +option, which controls diagnostics when the alias declaration is less +restrictive than the target, rather than more restrictive. + +Attributes considered include @code{alloc_align}, @code{alloc_size}, +@code{cold}, @code{const}, @code{hot}, @code{leaf}, @code{malloc}, +@code{nonnull}, @code{noreturn}, @code{nothrow}, @code{pure}, +@code{returns_nonnull}, and @code{returns_twice}. +@end table + +@option{-Wattribute-alias} is equivalent to @option{-Wattribute-alias=1}. +This is the default. You can disable these warnings with either +@option{-Wno-attribute-alias} or @option{-Wattribute-alias=0}. + +@item -Wbidi-chars=@r{[}none@r{|}unpaired@r{|}any@r{|}ucn@r{]} +@opindex Wbidi-chars= +@opindex Wbidi-chars +@opindex Wno-bidi-chars +Warn about possibly misleading UTF-8 bidirectional control characters in +comments, string literals, character constants, and identifiers. Such +characters can change left-to-right writing direction into right-to-left +(and vice versa), which can cause confusion between the logical order and +visual order. This may be dangerous; for instance, it may seem that a piece +of code is not commented out, whereas it in fact is. + +There are three levels of warning supported by GCC@. The default is +@option{-Wbidi-chars=unpaired}, which warns about improperly terminated +bidi contexts. @option{-Wbidi-chars=none} turns the warning off. +@option{-Wbidi-chars=any} warns about any use of bidirectional control +characters. + +By default, this warning does not warn about UCNs. It is, however, possible +to turn on such checking by using @option{-Wbidi-chars=unpaired,ucn} or +@option{-Wbidi-chars=any,ucn}. Using @option{-Wbidi-chars=ucn} is valid, +and is equivalent to @option{-Wbidi-chars=unpaired,ucn}, if no previous +@option{-Wbidi-chars=any} was specified. + +@item -Wbool-compare +@opindex Wno-bool-compare +@opindex Wbool-compare +Warn about boolean expression compared with an integer value different from +@code{true}/@code{false}. For instance, the following comparison is +always false: +@smallexample +int n = 5; +@dots{} +if ((n > 1) == 2) @{ @dots{} @} +@end smallexample +This warning is enabled by @option{-Wall}. + +@item -Wbool-operation +@opindex Wno-bool-operation +@opindex Wbool-operation +Warn about suspicious operations on expressions of a boolean type. For +instance, bitwise negation of a boolean is very likely a bug in the program. +For C, this warning also warns about incrementing or decrementing a boolean, +which rarely makes sense. (In C++, decrementing a boolean is always invalid. +Incrementing a boolean is invalid in C++17, and deprecated otherwise.) + +This warning is enabled by @option{-Wall}. + +@item -Wduplicated-branches +@opindex Wno-duplicated-branches +@opindex Wduplicated-branches +Warn when an if-else has identical branches. This warning detects cases like +@smallexample +if (p != NULL) + return 0; +else + return 0; +@end smallexample +It doesn't warn when both branches contain just a null statement. This warning +also warn for conditional operators: +@smallexample + int i = x ? *p : *p; +@end smallexample + +@item -Wduplicated-cond +@opindex Wno-duplicated-cond +@opindex Wduplicated-cond +Warn about duplicated conditions in an if-else-if chain. For instance, +warn for the following code: +@smallexample +if (p->q != NULL) @{ @dots{} @} +else if (p->q != NULL) @{ @dots{} @} +@end smallexample + +@item -Wframe-address +@opindex Wno-frame-address +@opindex Wframe-address +Warn when the @samp{__builtin_frame_address} or @samp{__builtin_return_address} +is called with an argument greater than 0. Such calls may return indeterminate +values or crash the program. The warning is included in @option{-Wall}. + +@item -Wno-discarded-qualifiers @r{(C and Objective-C only)} +@opindex Wno-discarded-qualifiers +@opindex Wdiscarded-qualifiers +Do not warn if type qualifiers on pointers are being discarded. +Typically, the compiler warns if a @code{const char *} variable is +passed to a function that takes a @code{char *} parameter. This option +can be used to suppress such a warning. + +@item -Wno-discarded-array-qualifiers @r{(C and Objective-C only)} +@opindex Wno-discarded-array-qualifiers +@opindex Wdiscarded-array-qualifiers +Do not warn if type qualifiers on arrays which are pointer targets +are being discarded. Typically, the compiler warns if a +@code{const int (*)[]} variable is passed to a function that +takes a @code{int (*)[]} parameter. This option can be used to +suppress such a warning. + +@item -Wno-incompatible-pointer-types @r{(C and Objective-C only)} +@opindex Wno-incompatible-pointer-types +@opindex Wincompatible-pointer-types +Do not warn when there is a conversion between pointers that have incompatible +types. This warning is for cases not covered by @option{-Wno-pointer-sign}, +which warns for pointer argument passing or assignment with different +signedness. + +@item -Wno-int-conversion @r{(C and Objective-C only)} +@opindex Wno-int-conversion +@opindex Wint-conversion +Do not warn about incompatible integer to pointer and pointer to integer +conversions. This warning is about implicit conversions; for explicit +conversions the warnings @option{-Wno-int-to-pointer-cast} and +@option{-Wno-pointer-to-int-cast} may be used. + +@item -Wzero-length-bounds +@opindex Wzero-length-bounds +@opindex Wzero-length-bounds +Warn about accesses to elements of zero-length array members that might +overlap other members of the same object. Declaring interior zero-length +arrays is discouraged because accesses to them are undefined. See +@xref{Zero Length}. + +For example, the first two stores in function @code{bad} are diagnosed +because the array elements overlap the subsequent members @code{b} and +@code{c}. The third store is diagnosed by @option{-Warray-bounds} +because it is beyond the bounds of the enclosing object. + +@smallexample +struct X @{ int a[0]; int b, c; @}; +struct X x; + +void bad (void) +@{ + x.a[0] = 0; // -Wzero-length-bounds + x.a[1] = 1; // -Wzero-length-bounds + x.a[2] = 2; // -Warray-bounds +@} +@end smallexample + +Option @option{-Wzero-length-bounds} is enabled by @option{-Warray-bounds}. + +@item -Wno-div-by-zero +@opindex Wno-div-by-zero +@opindex Wdiv-by-zero +Do not warn about compile-time integer division by zero. Floating-point +division by zero is not warned about, as it can be a legitimate way of +obtaining infinities and NaNs. + +@item -Wsystem-headers +@opindex Wsystem-headers +@opindex Wno-system-headers +@cindex warnings from system headers +@cindex system headers, warnings from +Print warning messages for constructs found in system header files. +Warnings from system headers are normally suppressed, on the assumption +that they usually do not indicate real problems and would only make the +compiler output harder to read. Using this command-line option tells +GCC to emit warnings from system headers as if they occurred in user +code. However, note that using @option{-Wall} in conjunction with this +option does @emph{not} warn about unknown pragmas in system +headers---for that, @option{-Wunknown-pragmas} must also be used. + +@item -Wtautological-compare +@opindex Wtautological-compare +@opindex Wno-tautological-compare +Warn if a self-comparison always evaluates to true or false. This +warning detects various mistakes such as: +@smallexample +int i = 1; +@dots{} +if (i > i) @{ @dots{} @} +@end smallexample + +This warning also warns about bitwise comparisons that always evaluate +to true or false, for instance: +@smallexample +if ((a & 16) == 10) @{ @dots{} @} +@end smallexample +will always be false. + +This warning is enabled by @option{-Wall}. + +@item -Wtrampolines +@opindex Wtrampolines +@opindex Wno-trampolines +Warn about trampolines generated for pointers to nested functions. +A trampoline is a small piece of data or code that is created at run +time on the stack when the address of a nested function is taken, and is +used to call the nested function indirectly. For some targets, it is +made up of data only and thus requires no special treatment. But, for +most targets, it is made up of code and thus requires the stack to be +made executable in order for the program to work properly. + +@item -Wfloat-equal +@opindex Wfloat-equal +@opindex Wno-float-equal +Warn if floating-point values are used in equality comparisons. + +The idea behind this is that sometimes it is convenient (for the +programmer) to consider floating-point values as approximations to +infinitely precise real numbers. If you are doing this, then you need +to compute (by analyzing the code, or in some other way) the maximum or +likely maximum error that the computation introduces, and allow for it +when performing comparisons (and when producing output, but that's a +different problem). In particular, instead of testing for equality, you +should check to see whether the two values have ranges that overlap; and +this is done with the relational operators, so equality comparisons are +probably mistaken. + +@item -Wtraditional @r{(C and Objective-C only)} +@opindex Wtraditional +@opindex Wno-traditional +Warn about certain constructs that behave differently in traditional and +ISO C@. Also warn about ISO C constructs that have no traditional C +equivalent, and/or problematic constructs that should be avoided. + +@itemize @bullet +@item +Macro parameters that appear within string literals in the macro body. +In traditional C macro replacement takes place within string literals, +but in ISO C it does not. + +@item +In traditional C, some preprocessor directives did not exist. +Traditional preprocessors only considered a line to be a directive +if the @samp{#} appeared in column 1 on the line. Therefore +@option{-Wtraditional} warns about directives that traditional C +understands but ignores because the @samp{#} does not appear as the +first character on the line. It also suggests you hide directives like +@code{#pragma} not understood by traditional C by indenting them. Some +traditional implementations do not recognize @code{#elif}, so this option +suggests avoiding it altogether. + +@item +A function-like macro that appears without arguments. + +@item +The unary plus operator. + +@item +The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point +constant suffixes. (Traditional C does support the @samp{L} suffix on integer +constants.) Note, these suffixes appear in macros defined in the system +headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{}. +Use of these macros in user code might normally lead to spurious +warnings, however GCC's integrated preprocessor has enough context to +avoid warning in these cases. + +@item +A function declared external in one block and then used after the end of +the block. + +@item +A @code{switch} statement has an operand of type @code{long}. + +@item +A non-@code{static} function declaration follows a @code{static} one. +This construct is not accepted by some traditional C compilers. + +@item +The ISO type of an integer constant has a different width or +signedness from its traditional type. This warning is only issued if +the base of the constant is ten. I.e.@: hexadecimal or octal values, which +typically represent bit patterns, are not warned about. + +@item +Usage of ISO string concatenation is detected. + +@item +Initialization of automatic aggregates. + +@item +Identifier conflicts with labels. Traditional C lacks a separate +namespace for labels. + +@item +Initialization of unions. If the initializer is zero, the warning is +omitted. This is done under the assumption that the zero initializer in +user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing +initializer warnings and relies on default initialization to zero in the +traditional C case. + +@item +Conversions by prototypes between fixed/floating-point values and vice +versa. The absence of these prototypes when compiling with traditional +C causes serious problems. This is a subset of the possible +conversion warnings; for the full set use @option{-Wtraditional-conversion}. + +@item +Use of ISO C style function definitions. This warning intentionally is +@emph{not} issued for prototype declarations or variadic functions +because these ISO C features appear in your code when using +libiberty's traditional C compatibility macros, @code{PARAMS} and +@code{VPARAMS}. This warning is also bypassed for nested functions +because that feature is already a GCC extension and thus not relevant to +traditional C compatibility. +@end itemize + +@item -Wtraditional-conversion @r{(C and Objective-C only)} +@opindex Wtraditional-conversion +@opindex Wno-traditional-conversion +Warn if a prototype causes a type conversion that is different from what +would happen to the same argument in the absence of a prototype. This +includes conversions of fixed point to floating and vice versa, and +conversions changing the width or signedness of a fixed-point argument +except when the same as the default promotion. + +@item -Wdeclaration-after-statement @r{(C and Objective-C only)} +@opindex Wdeclaration-after-statement +@opindex Wno-declaration-after-statement +Warn when a declaration is found after a statement in a block. This +construct, known from C++, was introduced with ISO C99 and is by default +allowed in GCC@. It is not supported by ISO C90. @xref{Mixed Labels and Declarations}. + +@item -Wshadow +@opindex Wshadow +@opindex Wno-shadow +Warn whenever a local variable or type declaration shadows another +variable, parameter, type, class member (in C++), or instance variable +(in Objective-C) or whenever a built-in function is shadowed. Note +that in C++, the compiler warns if a local variable shadows an +explicit typedef, but not if it shadows a struct/class/enum. +If this warning is enabled, it includes also all instances of +local shadowing. This means that @option{-Wno-shadow=local} +and @option{-Wno-shadow=compatible-local} are ignored when +@option{-Wshadow} is used. +Same as @option{-Wshadow=global}. + +@item -Wno-shadow-ivar @r{(Objective-C only)} +@opindex Wno-shadow-ivar +@opindex Wshadow-ivar +Do not warn whenever a local variable shadows an instance variable in an +Objective-C method. + +@item -Wshadow=global +@opindex Wshadow=global +Warn for any shadowing. +Same as @option{-Wshadow}. + +@item -Wshadow=local +@opindex Wshadow=local +Warn when a local variable shadows another local variable or parameter. + +@item -Wshadow=compatible-local +@opindex Wshadow=compatible-local +Warn when a local variable shadows another local variable or parameter +whose type is compatible with that of the shadowing variable. In C++, +type compatibility here means the type of the shadowing variable can be +converted to that of the shadowed variable. The creation of this flag +(in addition to @option{-Wshadow=local}) is based on the idea that when +a local variable shadows another one of incompatible type, it is most +likely intentional, not a bug or typo, as shown in the following example: + +@smallexample +@group +for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i) +@{ + for (int i = 0; i < N; ++i) + @{ + ... + @} + ... +@} +@end group +@end smallexample + +Since the two variable @code{i} in the example above have incompatible types, +enabling only @option{-Wshadow=compatible-local} does not emit a warning. +Because their types are incompatible, if a programmer accidentally uses one +in place of the other, type checking is expected to catch that and emit an +error or warning. Use of this flag instead of @option{-Wshadow=local} can +possibly reduce the number of warnings triggered by intentional shadowing. +Note that this also means that shadowing @code{const char *i} by +@code{char *i} does not emit a warning. + +This warning is also enabled by @option{-Wshadow=local}. + +@item -Wlarger-than=@var{byte-size} +@opindex Wlarger-than= +@opindex Wlarger-than-@var{byte-size} +Warn whenever an object is defined whose size exceeds @var{byte-size}. +@option{-Wlarger-than=}@samp{PTRDIFF_MAX} is enabled by default. +Warnings controlled by the option can be disabled either by specifying +@var{byte-size} of @samp{SIZE_MAX} or more or by @option{-Wno-larger-than}. + +Also warn for calls to bounded functions such as @code{memchr} or +@code{strnlen} that specify a bound greater than the largest possible +object, which is @samp{PTRDIFF_MAX} bytes by default. These warnings +can only be disabled by @option{-Wno-larger-than}. + +@item -Wno-larger-than +@opindex Wno-larger-than +Disable @option{-Wlarger-than=} warnings. The option is equivalent +to @option{-Wlarger-than=}@samp{SIZE_MAX} or larger. + +@item -Wframe-larger-than=@var{byte-size} +@opindex Wframe-larger-than= +@opindex Wno-frame-larger-than +Warn if the size of a function frame exceeds @var{byte-size}. +The computation done to determine the stack frame size is approximate +and not conservative. +The actual requirements may be somewhat greater than @var{byte-size} +even if you do not get a warning. In addition, any space allocated +via @code{alloca}, variable-length arrays, or related constructs +is not included by the compiler when determining +whether or not to issue a warning. +@option{-Wframe-larger-than=}@samp{PTRDIFF_MAX} is enabled by default. +Warnings controlled by the option can be disabled either by specifying +@var{byte-size} of @samp{SIZE_MAX} or more or by +@option{-Wno-frame-larger-than}. + +@item -Wno-frame-larger-than +@opindex Wno-frame-larger-than +Disable @option{-Wframe-larger-than=} warnings. The option is equivalent +to @option{-Wframe-larger-than=}@samp{SIZE_MAX} or larger. + +@item -Wfree-nonheap-object +@opindex Wfree-nonheap-object +@opindex Wno-free-nonheap-object +Warn when attempting to deallocate an object that was either not allocated +on the heap, or by using a pointer that was not returned from a prior call +to the corresponding allocation function. For example, because the call +to @code{stpcpy} returns a pointer to the terminating nul character and +not to the beginning of the object, the call to @code{free} below is +diagnosed. + +@smallexample +void f (char *p) +@{ + p = stpcpy (p, "abc"); + // ... + free (p); // warning +@} +@end smallexample + +@option{-Wfree-nonheap-object} is included in @option{-Wall}. + +@item -Wstack-usage=@var{byte-size} +@opindex Wstack-usage +@opindex Wno-stack-usage +Warn if the stack usage of a function might exceed @var{byte-size}. +The computation done to determine the stack usage is conservative. +Any space allocated via @code{alloca}, variable-length arrays, or related +constructs is included by the compiler when determining whether or not to +issue a warning. + +The message is in keeping with the output of @option{-fstack-usage}. + +@itemize +@item +If the stack usage is fully static but exceeds the specified amount, it's: + +@smallexample + warning: stack usage is 1120 bytes +@end smallexample +@item +If the stack usage is (partly) dynamic but bounded, it's: + +@smallexample + warning: stack usage might be 1648 bytes +@end smallexample +@item +If the stack usage is (partly) dynamic and not bounded, it's: + +@smallexample + warning: stack usage might be unbounded +@end smallexample +@end itemize + +@option{-Wstack-usage=}@samp{PTRDIFF_MAX} is enabled by default. +Warnings controlled by the option can be disabled either by specifying +@var{byte-size} of @samp{SIZE_MAX} or more or by +@option{-Wno-stack-usage}. + +@item -Wno-stack-usage +@opindex Wno-stack-usage +Disable @option{-Wstack-usage=} warnings. The option is equivalent +to @option{-Wstack-usage=}@samp{SIZE_MAX} or larger. + +@item -Wunsafe-loop-optimizations +@opindex Wunsafe-loop-optimizations +@opindex Wno-unsafe-loop-optimizations +Warn if the loop cannot be optimized because the compiler cannot +assume anything on the bounds of the loop indices. With +@option{-funsafe-loop-optimizations} warn if the compiler makes +such assumptions. + +@item -Wno-pedantic-ms-format @r{(MinGW targets only)} +@opindex Wno-pedantic-ms-format +@opindex Wpedantic-ms-format +When used in combination with @option{-Wformat} +and @option{-pedantic} without GNU extensions, this option +disables the warnings about non-ISO @code{printf} / @code{scanf} format +width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets, +which depend on the MS runtime. + +@item -Wpointer-arith +@opindex Wpointer-arith +@opindex Wno-pointer-arith +Warn about anything that depends on the ``size of'' a function type or +of @code{void}. GNU C assigns these types a size of 1, for +convenience in calculations with @code{void *} pointers and pointers +to functions. In C++, warn also when an arithmetic operation involves +@code{NULL}. This warning is also enabled by @option{-Wpedantic}. + +@item -Wno-pointer-compare +@opindex Wpointer-compare +@opindex Wno-pointer-compare +Do not warn if a pointer is compared with a zero character constant. +This usually +means that the pointer was meant to be dereferenced. For example: + +@smallexample +const char *p = foo (); +if (p == '\0') + return 42; +@end smallexample + +Note that the code above is invalid in C++11. + +This warning is enabled by default. + +@item -Wtsan +@opindex Wtsan +@opindex Wno-tsan +Warn about unsupported features in ThreadSanitizer. + +ThreadSanitizer does not support @code{std::atomic_thread_fence} and +can report false positives. + +This warning is enabled by default. + +@item -Wtype-limits +@opindex Wtype-limits +@opindex Wno-type-limits +Warn if a comparison is always true or always false due to the limited +range of the data type, but do not warn for constant expressions. For +example, warn if an unsigned variable is compared against zero with +@code{<} or @code{>=}. This warning is also enabled by +@option{-Wextra}. + +@item -Wabsolute-value @r{(C and Objective-C only)} +@opindex Wabsolute-value +@opindex Wno-absolute-value +Warn for calls to standard functions that compute the absolute value +of an argument when a more appropriate standard function is available. +For example, calling @code{abs(3.14)} triggers the warning because the +appropriate function to call to compute the absolute value of a double +argument is @code{fabs}. The option also triggers warnings when the +argument in a call to such a function has an unsigned type. This +warning can be suppressed with an explicit type cast and it is also +enabled by @option{-Wextra}. + +@include cppwarnopts.texi + +@item -Wbad-function-cast @r{(C and Objective-C only)} +@opindex Wbad-function-cast +@opindex Wno-bad-function-cast +Warn when a function call is cast to a non-matching type. +For example, warn if a call to a function returning an integer type +is cast to a pointer type. + +@item -Wc90-c99-compat @r{(C and Objective-C only)} +@opindex Wc90-c99-compat +@opindex Wno-c90-c99-compat +Warn about features not present in ISO C90, but present in ISO C99. +For instance, warn about use of variable length arrays, @code{long long} +type, @code{bool} type, compound literals, designated initializers, and so +on. This option is independent of the standards mode. Warnings are disabled +in the expression that follows @code{__extension__}. + +@item -Wc99-c11-compat @r{(C and Objective-C only)} +@opindex Wc99-c11-compat +@opindex Wno-c99-c11-compat +Warn about features not present in ISO C99, but present in ISO C11. +For instance, warn about use of anonymous structures and unions, +@code{_Atomic} type qualifier, @code{_Thread_local} storage-class specifier, +@code{_Alignas} specifier, @code{Alignof} operator, @code{_Generic} keyword, +and so on. This option is independent of the standards mode. Warnings are +disabled in the expression that follows @code{__extension__}. + +@item -Wc11-c2x-compat @r{(C and Objective-C only)} +@opindex Wc11-c2x-compat +@opindex Wno-c11-c2x-compat +Warn about features not present in ISO C11, but present in ISO C2X. +For instance, warn about omitting the string in @code{_Static_assert}, +use of @samp{[[]]} syntax for attributes, use of decimal +floating-point types, and so on. This option is independent of the +standards mode. Warnings are disabled in the expression that follows +@code{__extension__}. + +@item -Wc++-compat @r{(C and Objective-C only)} +@opindex Wc++-compat +@opindex Wno-c++-compat +Warn about ISO C constructs that are outside of the common subset of +ISO C and ISO C++, e.g.@: request for implicit conversion from +@code{void *} to a pointer to non-@code{void} type. + +@item -Wc++11-compat @r{(C++ and Objective-C++ only)} +@opindex Wc++11-compat +@opindex Wno-c++11-compat +Warn about C++ constructs whose meaning differs between ISO C++ 1998 +and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords +in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is +enabled by @option{-Wall}. + +@item -Wc++14-compat @r{(C++ and Objective-C++ only)} +@opindex Wc++14-compat +@opindex Wno-c++14-compat +Warn about C++ constructs whose meaning differs between ISO C++ 2011 +and ISO C++ 2014. This warning is enabled by @option{-Wall}. + +@item -Wc++17-compat @r{(C++ and Objective-C++ only)} +@opindex Wc++17-compat +@opindex Wno-c++17-compat +Warn about C++ constructs whose meaning differs between ISO C++ 2014 +and ISO C++ 2017. This warning is enabled by @option{-Wall}. + +@item -Wc++20-compat @r{(C++ and Objective-C++ only)} +@opindex Wc++20-compat +@opindex Wno-c++20-compat +Warn about C++ constructs whose meaning differs between ISO C++ 2017 +and ISO C++ 2020. This warning is enabled by @option{-Wall}. + +@item -Wno-c++11-extensions @r{(C++ and Objective-C++ only)} +@opindex Wc++11-extensions +@opindex Wno-c++11-extensions +Do not warn about C++11 constructs in code being compiled using +an older C++ standard. Even without this option, some C++11 constructs +will only be diagnosed if @option{-Wpedantic} is used. + +@item -Wno-c++14-extensions @r{(C++ and Objective-C++ only)} +@opindex Wc++14-extensions +@opindex Wno-c++14-extensions +Do not warn about C++14 constructs in code being compiled using +an older C++ standard. Even without this option, some C++14 constructs +will only be diagnosed if @option{-Wpedantic} is used. + +@item -Wno-c++17-extensions @r{(C++ and Objective-C++ only)} +@opindex Wc++17-extensions +@opindex Wno-c++17-extensions +Do not warn about C++17 constructs in code being compiled using +an older C++ standard. Even without this option, some C++17 constructs +will only be diagnosed if @option{-Wpedantic} is used. + +@item -Wno-c++20-extensions @r{(C++ and Objective-C++ only)} +@opindex Wc++20-extensions +@opindex Wno-c++20-extensions +Do not warn about C++20 constructs in code being compiled using +an older C++ standard. Even without this option, some C++20 constructs +will only be diagnosed if @option{-Wpedantic} is used. + +@item -Wno-c++23-extensions @r{(C++ and Objective-C++ only)} +@opindex Wc++23-extensions +@opindex Wno-c++23-extensions +Do not warn about C++23 constructs in code being compiled using +an older C++ standard. Even without this option, some C++23 constructs +will only be diagnosed if @option{-Wpedantic} is used. + +@item -Wcast-qual +@opindex Wcast-qual +@opindex Wno-cast-qual +Warn whenever a pointer is cast so as to remove a type qualifier from +the target type. For example, warn if a @code{const char *} is cast +to an ordinary @code{char *}. + +Also warn when making a cast that introduces a type qualifier in an +unsafe way. For example, casting @code{char **} to @code{const char **} +is unsafe, as in this example: + +@smallexample + /* p is char ** value. */ + const char **q = (const char **) p; + /* Assignment of readonly string to const char * is OK. */ + *q = "string"; + /* Now char** pointer points to read-only memory. */ + **p = 'b'; +@end smallexample + +@item -Wcast-align +@opindex Wcast-align +@opindex Wno-cast-align +Warn whenever a pointer is cast such that the required alignment of the +target is increased. For example, warn if a @code{char *} is cast to +an @code{int *} on machines where integers can only be accessed at +two- or four-byte boundaries. + +@item -Wcast-align=strict +@opindex Wcast-align=strict +Warn whenever a pointer is cast such that the required alignment of the +target is increased. For example, warn if a @code{char *} is cast to +an @code{int *} regardless of the target machine. + +@item -Wcast-function-type +@opindex Wcast-function-type +@opindex Wno-cast-function-type +Warn when a function pointer is cast to an incompatible function pointer. +In a cast involving function types with a variable argument list only +the types of initial arguments that are provided are considered. +Any parameter of pointer-type matches any other pointer-type. Any benign +differences in integral types are ignored, like @code{int} vs.@: @code{long} +on ILP32 targets. Likewise type qualifiers are ignored. The function +type @code{void (*) (void)} is special and matches everything, which can +be used to suppress this warning. +In a cast involving pointer to member types this warning warns whenever +the type cast is changing the pointer to member type. +This warning is enabled by @option{-Wextra}. + +@item -Wwrite-strings +@opindex Wwrite-strings +@opindex Wno-write-strings +When compiling C, give string constants the type @code{const +char[@var{length}]} so that copying the address of one into a +non-@code{const} @code{char *} pointer produces a warning. These +warnings help you find at compile time code that can try to write +into a string constant, but only if you have been very careful about +using @code{const} in declarations and prototypes. Otherwise, it is +just a nuisance. This is why we did not make @option{-Wall} request +these warnings. + +When compiling C++, warn about the deprecated conversion from string +literals to @code{char *}. This warning is enabled by default for C++ +programs. + +@item -Wclobbered +@opindex Wclobbered +@opindex Wno-clobbered +Warn for variables that might be changed by @code{longjmp} or +@code{vfork}. This warning is also enabled by @option{-Wextra}. + +@item -Wconversion +@opindex Wconversion +@opindex Wno-conversion +Warn for implicit conversions that may alter a value. This includes +conversions between real and integer, like @code{abs (x)} when +@code{x} is @code{double}; conversions between signed and unsigned, +like @code{unsigned ui = -1}; and conversions to smaller types, like +@code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs +((int) x)} and @code{ui = (unsigned) -1}, or if the value is not +changed by the conversion like in @code{abs (2.0)}. Warnings about +conversions between signed and unsigned integers can be disabled by +using @option{-Wno-sign-conversion}. + +For C++, also warn for confusing overload resolution for user-defined +conversions; and conversions that never use a type conversion +operator: conversions to @code{void}, the same type, a base class or a +reference to them. Warnings about conversions between signed and +unsigned integers are disabled by default in C++ unless +@option{-Wsign-conversion} is explicitly enabled. + +Warnings about conversion from arithmetic on a small type back to that +type are only given with @option{-Warith-conversion}. + +@item -Wdangling-else +@opindex Wdangling-else +@opindex Wno-dangling-else +Warn about constructions where there may be confusion to which +@code{if} statement an @code{else} branch belongs. Here is an example of +such a case: + +@smallexample +@group +@{ + if (a) + if (b) + foo (); + else + bar (); +@} +@end group +@end smallexample + +In C/C++, every @code{else} branch belongs to the innermost possible +@code{if} statement, which in this example is @code{if (b)}. This is +often not what the programmer expected, as illustrated in the above +example by indentation the programmer chose. When there is the +potential for this confusion, GCC issues a warning when this flag +is specified. To eliminate the warning, add explicit braces around +the innermost @code{if} statement so there is no way the @code{else} +can belong to the enclosing @code{if}. The resulting code +looks like this: + +@smallexample +@group +@{ + if (a) + @{ + if (b) + foo (); + else + bar (); + @} +@} +@end group +@end smallexample + +This warning is enabled by @option{-Wparentheses}. + +@item -Wdangling-pointer +@itemx -Wdangling-pointer=@var{n} +@opindex Wdangling-pointer +@opindex Wno-dangling-pointer +Warn about uses of pointers (or C++ references) to objects with automatic +storage duration after their lifetime has ended. This includes local +variables declared in nested blocks, compound literals and other unnamed +temporary objects. In addition, warn about storing the address of such +objects in escaped pointers. The warning is enabled at all optimization +levels but may yield different results with optimization than without. + +@table @gcctabopt +@item -Wdangling-pointer=1 +At level 1 the warning diagnoses only unconditional uses of dangling pointers. +For example +@smallexample +int f (int c1, int c2, x) +@{ + char *p = strchr ((char[])@{ c1, c2 @}, c3); + return p ? *p : 'x'; // warning: dangling pointer to a compound literal +@} +@end smallexample +In the following function the store of the address of the local variable +@code{x} in the escaped pointer @code{*p} also triggers the warning. +@smallexample +void g (int **p) +@{ + int x = 7; + *p = &x; // warning: storing the address of a local variable in *p +@} +@end smallexample + +@item -Wdangling-pointer=2 +At level 2, in addition to unconditional uses the warning also diagnoses +conditional uses of dangling pointers. + +For example, because the array @var{a} in the following function is out of +scope when the pointer @var{s} that was set to point is used, the warning +triggers at this level. + +@smallexample +void f (char *s) +@{ + if (!s) + @{ + char a[12] = "tmpname"; + s = a; + @} + strcat (s, ".tmp"); // warning: dangling pointer to a may be used + ... +@} +@end smallexample +@end table + +@option{-Wdangling-pointer=2} is included in @option{-Wall}. + +@item -Wdate-time +@opindex Wdate-time +@opindex Wno-date-time +Warn when macros @code{__TIME__}, @code{__DATE__} or @code{__TIMESTAMP__} +are encountered as they might prevent bit-wise-identical reproducible +compilations. + +@item -Wempty-body +@opindex Wempty-body +@opindex Wno-empty-body +Warn if an empty body occurs in an @code{if}, @code{else} or @code{do +while} statement. This warning is also enabled by @option{-Wextra}. + +@item -Wno-endif-labels +@opindex Wendif-labels +@opindex Wno-endif-labels +Do not warn about stray tokens after @code{#else} and @code{#endif}. + +@item -Wenum-compare +@opindex Wenum-compare +@opindex Wno-enum-compare +Warn about a comparison between values of different enumerated types. +In C++ enumerated type mismatches in conditional expressions are also +diagnosed and the warning is enabled by default. In C this warning is +enabled by @option{-Wall}. + +@item -Wenum-conversion +@opindex Wenum-conversion +@opindex Wno-enum-conversion +Warn when a value of enumerated type is implicitly converted to a +different enumerated type. This warning is enabled by @option{-Wextra} +in C@. + +@item -Wenum-int-mismatch @r{(C and Objective-C only)} +@opindex Wenum-int-mismatch +@opindex Wno-enum-int-mismatch +Warn about mismatches between an enumerated type and an integer type in +declarations. For example: + +@smallexample +enum E @{ l = -1, z = 0, g = 1 @}; +int foo(void); +enum E foo(void); +@end smallexample + +In C, an enumerated type is compatible with @code{char}, a signed +integer type, or an unsigned integer type. However, since the choice +of the underlying type of an enumerated type is implementation-defined, +such mismatches may cause portability issues. In C++, such mismatches +are an error. In C, this warning is enabled by @option{-Wall} and +@option{-Wc++-compat}. + +@item -Wjump-misses-init @r{(C, Objective-C only)} +@opindex Wjump-misses-init +@opindex Wno-jump-misses-init +Warn if a @code{goto} statement or a @code{switch} statement jumps +forward across the initialization of a variable, or jumps backward to a +label after the variable has been initialized. This only warns about +variables that are initialized when they are declared. This warning is +only supported for C and Objective-C; in C++ this sort of branch is an +error in any case. + +@option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It +can be disabled with the @option{-Wno-jump-misses-init} option. + +@item -Wsign-compare +@opindex Wsign-compare +@opindex Wno-sign-compare +@cindex warning for comparison of signed and unsigned values +@cindex comparison of signed and unsigned values, warning +@cindex signed and unsigned values, comparison warning +Warn when a comparison between signed and unsigned values could produce +an incorrect result when the signed value is converted to unsigned. +In C++, this warning is also enabled by @option{-Wall}. In C, it is +also enabled by @option{-Wextra}. + +@item -Wsign-conversion +@opindex Wsign-conversion +@opindex Wno-sign-conversion +Warn for implicit conversions that may change the sign of an integer +value, like assigning a signed integer expression to an unsigned +integer variable. An explicit cast silences the warning. In C, this +option is enabled also by @option{-Wconversion}. + +@item -Wfloat-conversion +@opindex Wfloat-conversion +@opindex Wno-float-conversion +Warn for implicit conversions that reduce the precision of a real value. +This includes conversions from real to integer, and from higher precision +real to lower precision real values. This option is also enabled by +@option{-Wconversion}. + +@item -Wno-scalar-storage-order +@opindex Wno-scalar-storage-order +@opindex Wscalar-storage-order +Do not warn on suspicious constructs involving reverse scalar storage order. + +@item -Wsizeof-array-div +@opindex Wsizeof-array-div +@opindex Wno-sizeof-array-div +Warn about divisions of two sizeof operators when the first one is applied +to an array and the divisor does not equal the size of the array element. +In such a case, the computation will not yield the number of elements in the +array, which is likely what the user intended. This warning warns e.g. about +@smallexample +int fn () +@{ + int arr[10]; + return sizeof (arr) / sizeof (short); +@} +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Wsizeof-pointer-div +@opindex Wsizeof-pointer-div +@opindex Wno-sizeof-pointer-div +Warn for suspicious divisions of two sizeof expressions that divide +the pointer size by the element size, which is the usual way to compute +the array size but won't work out correctly with pointers. This warning +warns e.g.@: about @code{sizeof (ptr) / sizeof (ptr[0])} if @code{ptr} is +not an array, but a pointer. This warning is enabled by @option{-Wall}. + +@item -Wsizeof-pointer-memaccess +@opindex Wsizeof-pointer-memaccess +@opindex Wno-sizeof-pointer-memaccess +Warn for suspicious length parameters to certain string and memory built-in +functions if the argument uses @code{sizeof}. This warning triggers for +example for @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not +an array, but a pointer, and suggests a possible fix, or about +@code{memcpy (&foo, ptr, sizeof (&foo));}. @option{-Wsizeof-pointer-memaccess} +also warns about calls to bounded string copy functions like @code{strncat} +or @code{strncpy} that specify as the bound a @code{sizeof} expression of +the source array. For example, in the following function the call to +@code{strncat} specifies the size of the source string as the bound. That +is almost certainly a mistake and so the call is diagnosed. +@smallexample +void make_file (const char *name) +@{ + char path[PATH_MAX]; + strncpy (path, name, sizeof path - 1); + strncat (path, ".text", sizeof ".text"); + @dots{} +@} +@end smallexample + +The @option{-Wsizeof-pointer-memaccess} option is enabled by @option{-Wall}. + +@item -Wno-sizeof-array-argument +@opindex Wsizeof-array-argument +@opindex Wno-sizeof-array-argument +Do not warn when the @code{sizeof} operator is applied to a parameter that is +declared as an array in a function definition. This warning is enabled by +default for C and C++ programs. + +@item -Wmemset-elt-size +@opindex Wmemset-elt-size +@opindex Wno-memset-elt-size +Warn for suspicious calls to the @code{memset} built-in function, if the +first argument references an array, and the third argument is a number +equal to the number of elements, but not equal to the size of the array +in memory. This indicates that the user has omitted a multiplication by +the element size. This warning is enabled by @option{-Wall}. + +@item -Wmemset-transposed-args +@opindex Wmemset-transposed-args +@opindex Wno-memset-transposed-args +Warn for suspicious calls to the @code{memset} built-in function where +the second argument is not zero and the third argument is zero. For +example, the call @code{memset (buf, sizeof buf, 0)} is diagnosed because +@code{memset (buf, 0, sizeof buf)} was meant instead. The diagnostic +is only emitted if the third argument is a literal zero. Otherwise, if +it is an expression that is folded to zero, or a cast of zero to some +type, it is far less likely that the arguments have been mistakenly +transposed and no warning is emitted. This warning is enabled +by @option{-Wall}. + +@item -Waddress +@opindex Waddress +@opindex Wno-address +Warn about suspicious uses of address expressions. These include comparing +the address of a function or a declared object to the null pointer constant +such as in +@smallexample +void f (void); +void g (void) +@{ + if (!f) // warning: expression evaluates to false + abort (); +@} +@end smallexample +comparisons of a pointer to a string literal, such as in +@smallexample +void f (const char *x) +@{ + if (x == "abc") // warning: expression evaluates to false + puts ("equal"); +@} +@end smallexample +and tests of the results of pointer addition or subtraction for equality +to null, such as in +@smallexample +void f (const int *p, int i) +@{ + return p + i == NULL; +@} +@end smallexample +Such uses typically indicate a programmer error: the address of most +functions and objects necessarily evaluates to true (the exception are +weak symbols), so their use in a conditional might indicate missing +parentheses in a function call or a missing dereference in an array +expression. The subset of the warning for object pointers can be +suppressed by casting the pointer operand to an integer type such +as @code{intptr_t} or @code{uintptr_t}. +Comparisons against string literals result in unspecified behavior +and are not portable, and suggest the intent was to call @code{strcmp}. +The warning is suppressed if the suspicious expression is the result +of macro expansion. +@option{-Waddress} warning is enabled by @option{-Wall}. + +@item -Wno-address-of-packed-member +@opindex Waddress-of-packed-member +@opindex Wno-address-of-packed-member +Do not warn when the address of packed member of struct or union is taken, +which usually results in an unaligned pointer value. This is +enabled by default. + +@item -Wlogical-op +@opindex Wlogical-op +@opindex Wno-logical-op +Warn about suspicious uses of logical operators in expressions. +This includes using logical operators in contexts where a +bit-wise operator is likely to be expected. Also warns when +the operands of a logical operator are the same: +@smallexample +extern int a; +if (a < 0 && a < 0) @{ @dots{} @} +@end smallexample + +@item -Wlogical-not-parentheses +@opindex Wlogical-not-parentheses +@opindex Wno-logical-not-parentheses +Warn about logical not used on the left hand side operand of a comparison. +This option does not warn if the right operand is considered to be a boolean +expression. Its purpose is to detect suspicious code like the following: +@smallexample +int a; +@dots{} +if (!a > 1) @{ @dots{} @} +@end smallexample + +It is possible to suppress the warning by wrapping the LHS into +parentheses: +@smallexample +if ((!a) > 1) @{ @dots{} @} +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Waggregate-return +@opindex Waggregate-return +@opindex Wno-aggregate-return +Warn if any functions that return structures or unions are defined or +called. (In languages where you can return an array, this also elicits +a warning.) + +@item -Wno-aggressive-loop-optimizations +@opindex Wno-aggressive-loop-optimizations +@opindex Waggressive-loop-optimizations +Warn if in a loop with constant number of iterations the compiler detects +undefined behavior in some statement during one or more of the iterations. + +@item -Wno-attributes +@opindex Wno-attributes +@opindex Wattributes +Do not warn if an unexpected @code{__attribute__} is used, such as +unrecognized attributes, function attributes applied to variables, +etc. This does not stop errors for incorrect use of supported +attributes. + +Additionally, using @option{-Wno-attributes=}, it is possible to suppress +warnings about unknown scoped attributes (in C++11 and C2X). For example, +@option{-Wno-attributes=vendor::attr} disables warning about the following +declaration: + +@smallexample +[[vendor::attr]] void f(); +@end smallexample + +It is also possible to disable warning about all attributes in a namespace +using @option{-Wno-attributes=vendor::} which prevents warning about both +of these declarations: + +@smallexample +[[vendor::safe]] void f(); +[[vendor::unsafe]] void f2(); +@end smallexample + +Note that @option{-Wno-attributes=} does not imply @option{-Wno-attributes}. + +@item -Wno-builtin-declaration-mismatch +@opindex Wno-builtin-declaration-mismatch +@opindex Wbuiltin-declaration-mismatch +Warn if a built-in function is declared with an incompatible signature +or as a non-function, or when a built-in function declared with a type +that does not include a prototype is called with arguments whose promoted +types do not match those expected by the function. When @option{-Wextra} +is specified, also warn when a built-in function that takes arguments is +declared without a prototype. The @option{-Wbuiltin-declaration-mismatch} +warning is enabled by default. To avoid the warning include the appropriate +header to bring the prototypes of built-in functions into scope. + +For example, the call to @code{memset} below is diagnosed by the warning +because the function expects a value of type @code{size_t} as its argument +but the type of @code{32} is @code{int}. With @option{-Wextra}, +the declaration of the function is diagnosed as well. +@smallexample +extern void* memset (); +void f (void *d) +@{ + memset (d, '\0', 32); +@} +@end smallexample + +@item -Wno-builtin-macro-redefined +@opindex Wno-builtin-macro-redefined +@opindex Wbuiltin-macro-redefined +Do not warn if certain built-in macros are redefined. This suppresses +warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__}, +@code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}. + +@item -Wstrict-prototypes @r{(C and Objective-C only)} +@opindex Wstrict-prototypes +@opindex Wno-strict-prototypes +Warn if a function is declared or defined without specifying the +argument types. (An old-style function definition is permitted without +a warning if preceded by a declaration that specifies the argument +types.) + +@item -Wold-style-declaration @r{(C and Objective-C only)} +@opindex Wold-style-declaration +@opindex Wno-old-style-declaration +Warn for obsolescent usages, according to the C Standard, in a +declaration. For example, warn if storage-class specifiers like +@code{static} are not the first things in a declaration. This warning +is also enabled by @option{-Wextra}. + +@item -Wold-style-definition @r{(C and Objective-C only)} +@opindex Wold-style-definition +@opindex Wno-old-style-definition +Warn if an old-style function definition is used. A warning is given +even if there is a previous prototype. A definition using @samp{()} +is not considered an old-style definition in C2X mode, because it is +equivalent to @samp{(void)} in that case, but is considered an +old-style definition for older standards. + +@item -Wmissing-parameter-type @r{(C and Objective-C only)} +@opindex Wmissing-parameter-type +@opindex Wno-missing-parameter-type +A function parameter is declared without a type specifier in K&R-style +functions: + +@smallexample +void foo(bar) @{ @} +@end smallexample + +This warning is also enabled by @option{-Wextra}. + +@item -Wmissing-prototypes @r{(C and Objective-C only)} +@opindex Wmissing-prototypes +@opindex Wno-missing-prototypes +Warn if a global function is defined without a previous prototype +declaration. This warning is issued even if the definition itself +provides a prototype. Use this option to detect global functions +that do not have a matching prototype declaration in a header file. +This option is not valid for C++ because all function declarations +provide prototypes and a non-matching declaration declares an +overload rather than conflict with an earlier declaration. +Use @option{-Wmissing-declarations} to detect missing declarations in C++. + +@item -Wmissing-declarations +@opindex Wmissing-declarations +@opindex Wno-missing-declarations +Warn if a global function is defined without a previous declaration. +Do so even if the definition itself provides a prototype. +Use this option to detect global functions that are not declared in +header files. In C, no warnings are issued for functions with previous +non-prototype declarations; use @option{-Wmissing-prototypes} to detect +missing prototypes. In C++, no warnings are issued for function templates, +or for inline functions, or for functions in anonymous namespaces. + +@item -Wmissing-field-initializers +@opindex Wmissing-field-initializers +@opindex Wno-missing-field-initializers +@opindex W +@opindex Wextra +@opindex Wno-extra +Warn if a structure's initializer has some fields missing. For +example, the following code causes such a warning, because +@code{x.h} is implicitly zero: + +@smallexample +struct s @{ int f, g, h; @}; +struct s x = @{ 3, 4 @}; +@end smallexample + +This option does not warn about designated initializers, so the following +modification does not trigger a warning: + +@smallexample +struct s @{ int f, g, h; @}; +struct s x = @{ .f = 3, .g = 4 @}; +@end smallexample + +In C this option does not warn about the universal zero initializer +@samp{@{ 0 @}}: + +@smallexample +struct s @{ int f, g, h; @}; +struct s x = @{ 0 @}; +@end smallexample + +Likewise, in C++ this option does not warn about the empty @{ @} +initializer, for example: + +@smallexample +struct s @{ int f, g, h; @}; +s x = @{ @}; +@end smallexample + +This warning is included in @option{-Wextra}. To get other @option{-Wextra} +warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}. + +@item -Wno-missing-requires +@opindex Wmissing-requires +@opindex Wno-missing-requires + +By default, the compiler warns about a concept-id appearing as a C++20 simple-requirement: + +@smallexample +bool satisfied = requires @{ C @}; +@end smallexample + +Here @samp{satisfied} will be true if @samp{C} is a valid +expression, which it is for all T. Presumably the user meant to write + +@smallexample +bool satisfied = requires @{ requires C @}; +@end smallexample + +so @samp{satisfied} is only true if concept @samp{C} is satisfied for +type @samp{T}. + +This warning can be disabled with @option{-Wno-missing-requires}. + +@item -Wno-missing-template-keyword +@opindex Wmissing-template-keyword +@opindex Wno-missing-template-keyword + +The member access tokens ., -> and :: must be followed by the @code{template} +keyword if the parent object is dependent and the member being named is a +template. + +@smallexample +template +void DoStuff (X x) +@{ + x.template DoSomeOtherStuff(); // Good. + x.DoMoreStuff(); // Warning, x is dependent. +@} +@end smallexample + +In rare cases it is possible to get false positives. To silence this, wrap +the expression in parentheses. For example, the following is treated as a +template, even where m and N are integers: + +@smallexample +void NotATemplate (my_class t) +@{ + int N = 5; + + bool test = t.m < N > (0); // Treated as a template. + test = (t.m < N) > (0); // Same meaning, but not treated as a template. +@} +@end smallexample + +This warning can be disabled with @option{-Wno-missing-template-keyword}. + +@item -Wno-multichar +@opindex Wno-multichar +@opindex Wmultichar +Do not warn if a multicharacter constant (@samp{'FOOF'}) is used. +Usually they indicate a typo in the user's code, as they have +implementation-defined values, and should not be used in portable code. + +@item -Wnormalized=@r{[}none@r{|}id@r{|}nfc@r{|}nfkc@r{]} +@opindex Wnormalized= +@opindex Wnormalized +@opindex Wno-normalized +@cindex NFC +@cindex NFKC +@cindex character set, input normalization +In ISO C and ISO C++, two identifiers are different if they are +different sequences of characters. However, sometimes when characters +outside the basic ASCII character set are used, you can have two +different character sequences that look the same. To avoid confusion, +the ISO 10646 standard sets out some @dfn{normalization rules} which +when applied ensure that two sequences that look the same are turned into +the same sequence. GCC can warn you if you are using identifiers that +have not been normalized; this option controls that warning. + +There are four levels of warning supported by GCC@. The default is +@option{-Wnormalized=nfc}, which warns about any identifier that is +not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the +recommended form for most uses. It is equivalent to +@option{-Wnormalized}. + +Unfortunately, there are some characters allowed in identifiers by +ISO C and ISO C++ that, when turned into NFC, are not allowed in +identifiers. That is, there's no way to use these symbols in portable +ISO C or C++ and have all your identifiers in NFC@. +@option{-Wnormalized=id} suppresses the warning for these characters. +It is hoped that future versions of the standards involved will correct +this, which is why this option is not the default. + +You can switch the warning off for all characters by writing +@option{-Wnormalized=none} or @option{-Wno-normalized}. You should +only do this if you are using some other normalization scheme (like +``D''), because otherwise you can easily create bugs that are +literally impossible to see. + +Some characters in ISO 10646 have distinct meanings but look identical +in some fonts or display methodologies, especially once formatting has +been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL +LETTER N'', displays just like a regular @code{n} that has been +placed in a superscript. ISO 10646 defines the @dfn{NFKC} +normalization scheme to convert all these into a standard form as +well, and GCC warns if your code is not in NFKC if you use +@option{-Wnormalized=nfkc}. This warning is comparable to warning +about every identifier that contains the letter O because it might be +confused with the digit 0, and so is not the default, but may be +useful as a local coding convention if the programming environment +cannot be fixed to display these characters distinctly. + +@item -Wno-attribute-warning +@opindex Wno-attribute-warning +@opindex Wattribute-warning +Do not warn about usage of functions (@pxref{Function Attributes}) +declared with @code{warning} attribute. By default, this warning is +enabled. @option{-Wno-attribute-warning} can be used to disable the +warning or @option{-Wno-error=attribute-warning} can be used to +disable the error when compiled with @option{-Werror} flag. + +@item -Wno-deprecated +@opindex Wno-deprecated +@opindex Wdeprecated +Do not warn about usage of deprecated features. @xref{Deprecated Features}. + +@item -Wno-deprecated-declarations +@opindex Wno-deprecated-declarations +@opindex Wdeprecated-declarations +Do not warn about uses of functions (@pxref{Function Attributes}), +variables (@pxref{Variable Attributes}), and types (@pxref{Type +Attributes}) marked as deprecated by using the @code{deprecated} +attribute. + +@item -Wno-overflow +@opindex Wno-overflow +@opindex Woverflow +Do not warn about compile-time overflow in constant expressions. + +@item -Wno-odr +@opindex Wno-odr +@opindex Wodr +Warn about One Definition Rule violations during link-time optimization. +Enabled by default. + +@item -Wopenacc-parallelism +@opindex Wopenacc-parallelism +@opindex Wno-openacc-parallelism +@cindex OpenACC accelerator programming +Warn about potentially suboptimal choices related to OpenACC parallelism. + +@item -Wopenmp-simd +@opindex Wopenmp-simd +@opindex Wno-openmp-simd +Warn if the vectorizer cost model overrides the OpenMP +simd directive set by user. The @option{-fsimd-cost-model=unlimited} +option can be used to relax the cost model. + +@item -Woverride-init @r{(C and Objective-C only)} +@opindex Woverride-init +@opindex Wno-override-init +@opindex W +@opindex Wextra +@opindex Wno-extra +Warn if an initialized field without side effects is overridden when +using designated initializers (@pxref{Designated Inits, , Designated +Initializers}). + +This warning is included in @option{-Wextra}. To get other +@option{-Wextra} warnings without this one, use @option{-Wextra +-Wno-override-init}. + +@item -Wno-override-init-side-effects @r{(C and Objective-C only)} +@opindex Woverride-init-side-effects +@opindex Wno-override-init-side-effects +Do not warn if an initialized field with side effects is overridden when +using designated initializers (@pxref{Designated Inits, , Designated +Initializers}). This warning is enabled by default. + +@item -Wpacked +@opindex Wpacked +@opindex Wno-packed +Warn if a structure is given the packed attribute, but the packed +attribute has no effect on the layout or size of the structure. +Such structures may be mis-aligned for little benefit. For +instance, in this code, the variable @code{f.x} in @code{struct bar} +is misaligned even though @code{struct bar} does not itself +have the packed attribute: + +@smallexample +@group +struct foo @{ + int x; + char a, b, c, d; +@} __attribute__((packed)); +struct bar @{ + char z; + struct foo f; +@}; +@end group +@end smallexample + +@item -Wnopacked-bitfield-compat +@opindex Wpacked-bitfield-compat +@opindex Wno-packed-bitfield-compat +The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute +on bit-fields of type @code{char}. This was fixed in GCC 4.4 but +the change can lead to differences in the structure layout. GCC +informs you when the offset of such a field has changed in GCC 4.4. +For example there is no longer a 4-bit padding between field @code{a} +and @code{b} in this structure: + +@smallexample +struct foo +@{ + char a:4; + char b:8; +@} __attribute__ ((packed)); +@end smallexample + +This warning is enabled by default. Use +@option{-Wno-packed-bitfield-compat} to disable this warning. + +@item -Wpacked-not-aligned @r{(C, C++, Objective-C and Objective-C++ only)} +@opindex Wpacked-not-aligned +@opindex Wno-packed-not-aligned +Warn if a structure field with explicitly specified alignment in a +packed struct or union is misaligned. For example, a warning will +be issued on @code{struct S}, like, @code{warning: alignment 1 of +'struct S' is less than 8}, in this code: + +@smallexample +@group +struct __attribute__ ((aligned (8))) S8 @{ char a[8]; @}; +struct __attribute__ ((packed)) S @{ + struct S8 s8; +@}; +@end group +@end smallexample + +This warning is enabled by @option{-Wall}. + +@item -Wpadded +@opindex Wpadded +@opindex Wno-padded +Warn if padding is included in a structure, either to align an element +of the structure or to align the whole structure. Sometimes when this +happens it is possible to rearrange the fields of the structure to +reduce the padding and so make the structure smaller. + +@item -Wredundant-decls +@opindex Wredundant-decls +@opindex Wno-redundant-decls +Warn if anything is declared more than once in the same scope, even in +cases where multiple declaration is valid and changes nothing. + +@item -Wrestrict +@opindex Wrestrict +@opindex Wno-restrict +Warn when an object referenced by a @code{restrict}-qualified parameter +(or, in C++, a @code{__restrict}-qualified parameter) is aliased by another +argument, or when copies between such objects overlap. For example, +the call to the @code{strcpy} function below attempts to truncate the string +by replacing its initial characters with the last four. However, because +the call writes the terminating NUL into @code{a[4]}, the copies overlap and +the call is diagnosed. + +@smallexample +void foo (void) +@{ + char a[] = "abcd1234"; + strcpy (a, a + 4); + @dots{} +@} +@end smallexample +The @option{-Wrestrict} option detects some instances of simple overlap +even without optimization but works best at @option{-O2} and above. It +is included in @option{-Wall}. + +@item -Wnested-externs @r{(C and Objective-C only)} +@opindex Wnested-externs +@opindex Wno-nested-externs +Warn if an @code{extern} declaration is encountered within a function. + +@item -Winline +@opindex Winline +@opindex Wno-inline +Warn if a function that is declared as inline cannot be inlined. +Even with this option, the compiler does not warn about failures to +inline functions declared in system headers. + +The compiler uses a variety of heuristics to determine whether or not +to inline a function. For example, the compiler takes into account +the size of the function being inlined and the amount of inlining +that has already been done in the current function. Therefore, +seemingly insignificant changes in the source program can cause the +warnings produced by @option{-Winline} to appear or disappear. + +@item -Winterference-size +@opindex Winterference-size +Warn about use of C++17 @code{std::hardware_destructive_interference_size} +without specifying its value with @option{--param destructive-interference-size}. +Also warn about questionable values for that option. + +This variable is intended to be used for controlling class layout, to +avoid false sharing in concurrent code: + +@smallexample +struct independent_fields @{ + alignas(std::hardware_destructive_interference_size) std::atomic one; + alignas(std::hardware_destructive_interference_size) std::atomic two; +@}; +@end smallexample + +Here @samp{one} and @samp{two} are intended to be far enough apart +that stores to one won't require accesses to the other to reload the +cache line. + +By default, @option{--param destructive-interference-size} and +@option{--param constructive-interference-size} are set based on the +current @option{-mtune} option, typically to the L1 cache line size +for the particular target CPU, sometimes to a range if tuning for a +generic target. So all translation units that depend on ABI +compatibility for the use of these variables must be compiled with +the same @option{-mtune} (or @option{-mcpu}). + +If ABI stability is important, such as if the use is in a header for a +library, you should probably not use the hardware interference size +variables at all. Alternatively, you can force a particular value +with @option{--param}. + +If you are confident that your use of the variable does not affect ABI +outside a single build of your project, you can turn off the warning +with @option{-Wno-interference-size}. + +@item -Wint-in-bool-context +@opindex Wint-in-bool-context +@opindex Wno-int-in-bool-context +Warn for suspicious use of integer values where boolean values are expected, +such as conditional expressions (?:) using non-boolean integer constants in +boolean context, like @code{if (a <= b ? 2 : 3)}. Or left shifting of signed +integers in boolean context, like @code{for (a = 0; 1 << a; a++);}. Likewise +for all kinds of multiplications regardless of the data type. +This warning is enabled by @option{-Wall}. + +@item -Wno-int-to-pointer-cast +@opindex Wno-int-to-pointer-cast +@opindex Wint-to-pointer-cast +Suppress warnings from casts to pointer type of an integer of a +different size. In C++, casting to a pointer type of smaller size is +an error. @option{Wint-to-pointer-cast} is enabled by default. + + +@item -Wno-pointer-to-int-cast @r{(C and Objective-C only)} +@opindex Wno-pointer-to-int-cast +@opindex Wpointer-to-int-cast +Suppress warnings from casts from a pointer to an integer type of a +different size. + +@item -Winvalid-pch +@opindex Winvalid-pch +@opindex Wno-invalid-pch +Warn if a precompiled header (@pxref{Precompiled Headers}) is found in +the search path but cannot be used. + +@item -Winvalid-utf8 +@opindex Winvalid-utf8 +@opindex Wno-invalid-utf8 +Warn if an invalid UTF-8 character is found. +This warning is on by default for C++23 if @option{-finput-charset=UTF-8} +is used and turned into error with @option{-pedantic-errors}. + +@item -Wno-unicode +@opindex Wunicode +@opindex Wno-unicode +Don't diagnose invalid forms of delimited or named escape sequences which are +treated as separate tokens. @option{Wunicode} is enabled by default. + +@item -Wlong-long +@opindex Wlong-long +@opindex Wno-long-long +Warn if @code{long long} type is used. This is enabled by either +@option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98 +modes. To inhibit the warning messages, use @option{-Wno-long-long}. + +@item -Wvariadic-macros +@opindex Wvariadic-macros +@opindex Wno-variadic-macros +Warn if variadic macros are used in ISO C90 mode, or if the GNU +alternate syntax is used in ISO C99 mode. This is enabled by either +@option{-Wpedantic} or @option{-Wtraditional}. To inhibit the warning +messages, use @option{-Wno-variadic-macros}. + +@item -Wno-varargs +@opindex Wvarargs +@opindex Wno-varargs +Do not warn upon questionable usage of the macros used to handle variable +arguments like @code{va_start}. These warnings are enabled by default. + +@item -Wvector-operation-performance +@opindex Wvector-operation-performance +@opindex Wno-vector-operation-performance +Warn if vector operation is not implemented via SIMD capabilities of the +architecture. Mainly useful for the performance tuning. +Vector operation can be implemented @code{piecewise}, which means that the +scalar operation is performed on every vector element; +@code{in parallel}, which means that the vector operation is implemented +using scalars of wider type, which normally is more performance efficient; +and @code{as a single scalar}, which means that vector fits into a +scalar type. + +@item -Wvla +@opindex Wvla +@opindex Wno-vla +Warn if a variable-length array is used in the code. +@option{-Wno-vla} prevents the @option{-Wpedantic} warning of +the variable-length array. + +@item -Wvla-larger-than=@var{byte-size} +@opindex Wvla-larger-than= +@opindex Wno-vla-larger-than +If this option is used, the compiler warns for declarations of +variable-length arrays whose size is either unbounded, or bounded +by an argument that allows the array size to exceed @var{byte-size} +bytes. This is similar to how @option{-Walloca-larger-than=}@var{byte-size} +works, but with variable-length arrays. + +Note that GCC may optimize small variable-length arrays of a known +value into plain arrays, so this warning may not get triggered for +such arrays. + +@option{-Wvla-larger-than=}@samp{PTRDIFF_MAX} is enabled by default but +is typically only effective when @option{-ftree-vrp} is active (default +for @option{-O2} and above). + +See also @option{-Walloca-larger-than=@var{byte-size}}. + +@item -Wno-vla-larger-than +@opindex Wno-vla-larger-than +Disable @option{-Wvla-larger-than=} warnings. The option is equivalent +to @option{-Wvla-larger-than=}@samp{SIZE_MAX} or larger. + +@item -Wvla-parameter +@opindex Wno-vla-parameter +Warn about redeclarations of functions involving arguments of Variable +Length Array types of inconsistent kinds or forms, and enable the detection +of out-of-bounds accesses to such parameters by warnings such as +@option{-Warray-bounds}. + +If the first function declaration uses the VLA form the bound specified +in the array is assumed to be the minimum number of elements expected to +be provided in calls to the function and the maximum number of elements +accessed by it. Failing to provide arguments of sufficient size or +accessing more than the maximum number of elements may be diagnosed. + +For example, the warning triggers for the following redeclarations because +the first one allows an array of any size to be passed to @code{f} while +the second one specifies that the array argument must have at least @code{n} +elements. In addition, calling @code{f} with the associated VLA bound +parameter in excess of the actual VLA bound triggers a warning as well. + +@smallexample +void f (int n, int[n]); +void f (int, int[]); // warning: argument 2 previously declared as a VLA + +void g (int n) +@{ + if (n > 4) + return; + int a[n]; + f (sizeof a, a); // warning: access to a by f may be out of bounds + @dots{} +@} + +@end smallexample + +@option{-Wvla-parameter} is included in @option{-Wall}. The +@option{-Warray-parameter} option triggers warnings for similar problems +involving ordinary array arguments. + +@item -Wvolatile-register-var +@opindex Wvolatile-register-var +@opindex Wno-volatile-register-var +Warn if a register variable is declared volatile. The volatile +modifier does not inhibit all optimizations that may eliminate reads +and/or writes to register variables. This warning is enabled by +@option{-Wall}. + +@item -Wxor-used-as-pow @r{(C, C++, Objective-C and Objective-C++ only)} +@opindex Wxor-used-as-pow +@opindex Wno-xor-used-as-pow +Warn about uses of @code{^}, the exclusive or operator, where it appears +the user meant exponentiation. Specifically, the warning occurs when the +left-hand side is the decimal constant 2 or 10 and the right-hand side +is also a decimal constant. + +In C and C++, @code{^} means exclusive or, whereas in some other languages +(e.g. TeX and some versions of BASIC) it means exponentiation. + +This warning is enabled by default. It can be silenced by converting one +of the operands to hexadecimal. + +@item -Wdisabled-optimization +@opindex Wdisabled-optimization +@opindex Wno-disabled-optimization +Warn if a requested optimization pass is disabled. This warning does +not generally indicate that there is anything wrong with your code; it +merely indicates that GCC's optimizers are unable to handle the code +effectively. Often, the problem is that your code is too big or too +complex; GCC refuses to optimize programs when the optimization +itself is likely to take inordinate amounts of time. + +@item -Wpointer-sign @r{(C and Objective-C only)} +@opindex Wpointer-sign +@opindex Wno-pointer-sign +Warn for pointer argument passing or assignment with different signedness. +This option is only supported for C and Objective-C@. It is implied by +@option{-Wall} and by @option{-Wpedantic}, which can be disabled with +@option{-Wno-pointer-sign}. + +@item -Wstack-protector +@opindex Wstack-protector +@opindex Wno-stack-protector +This option is only active when @option{-fstack-protector} is active. It +warns about functions that are not protected against stack smashing. + +@item -Woverlength-strings +@opindex Woverlength-strings +@opindex Wno-overlength-strings +Warn about string constants that are longer than the ``minimum +maximum'' length specified in the C standard. Modern compilers +generally allow string constants that are much longer than the +standard's minimum limit, but very portable programs should avoid +using longer strings. + +The limit applies @emph{after} string constant concatenation, and does +not count the trailing NUL@. In C90, the limit was 509 characters; in +C99, it was raised to 4095. C++98 does not specify a normative +minimum maximum, so we do not diagnose overlength strings in C++@. + +This option is implied by @option{-Wpedantic}, and can be disabled with +@option{-Wno-overlength-strings}. + +@item -Wunsuffixed-float-constants @r{(C and Objective-C only)} +@opindex Wunsuffixed-float-constants +@opindex Wno-unsuffixed-float-constants + +Issue a warning for any floating constant that does not have +a suffix. When used together with @option{-Wsystem-headers} it +warns about such constants in system header files. This can be useful +when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma +from the decimal floating-point extension to C99. + +@item -Wno-lto-type-mismatch +@opindex Wlto-type-mismatch +@opindex Wno-lto-type-mismatch + +During the link-time optimization, do not warn about type mismatches in +global declarations from different compilation units. +Requires @option{-flto} to be enabled. Enabled by default. + +@item -Wno-designated-init @r{(C and Objective-C only)} +@opindex Wdesignated-init +@opindex Wno-designated-init +Suppress warnings when a positional initializer is used to initialize +a structure that has been marked with the @code{designated_init} +attribute. + +@end table + +@node Static Analyzer Options +@section Options That Control Static Analysis + +@table @gcctabopt +@item -fanalyzer +@opindex analyzer +@opindex fanalyzer +@opindex fno-analyzer +This option enables an static analysis of program flow which looks +for ``interesting'' interprocedural paths through the +code, and issues warnings for problems found on them. + +This analysis is much more expensive than other GCC warnings. + +Enabling this option effectively enables the following warnings: + +@gccoptlist{ @gol +-Wanalyzer-allocation-size @gol +-Wanalyzer-double-fclose @gol +-Wanalyzer-double-free @gol +-Wanalyzer-exposure-through-output-file @gol +-Wanalyzer-exposure-through-uninit-copy @gol +-Wanalyzer-fd-access-mode-mismatch @gol +-Wanalyzer-fd-double-close @gol +-Wanalyzer-fd-leak @gol +-Wanalyzer-fd-use-after-close @gol +-Wanalyzer-fd-use-without-check @gol +-Wanalyzer-file-leak @gol +-Wanalyzer-free-of-non-heap @gol +-Wanalyzer-imprecise-fp-arithmetic @gol +-Wanalyzer-jump-through-null @gol +-Wanalyzer-malloc-leak @gol +-Wanalyzer-mismatching-deallocation @gol +-Wanalyzer-null-argument @gol +-Wanalyzer-null-dereference @gol +-Wanalyzer-out-of-bounds @gol +-Wanalyzer-possible-null-argument @gol +-Wanalyzer-possible-null-dereference @gol +-Wanalyzer-putenv-of-auto-var @gol +-Wanalyzer-shift-count-negative @gol +-Wanalyzer-shift-count-overflow @gol +-Wanalyzer-stale-setjmp-buffer @gol +-Wanalyzer-unsafe-call-within-signal-handler @gol +-Wanalyzer-use-after-free @gol +-Wanalyzer-use-of-pointer-in-stale-stack-frame @gol +-Wanalyzer-use-of-uninitialized-value @gol +-Wanalyzer-va-arg-type-mismatch @gol +-Wanalyzer-va-list-exhausted @gol +-Wanalyzer-va-list-leak @gol +-Wanalyzer-va-list-use-after-va-end @gol +-Wanalyzer-write-to-const @gol +-Wanalyzer-write-to-string-literal @gol +} +@ignore +-Wanalyzer-tainted-allocation-size @gol +-Wanalyzer-tainted-array-index @gol +-Wanalyzer-tainted-divisor @gol +-Wanalyzer-tainted-offset @gol +-Wanalyzer-tainted-size @gol +@end ignore + +This option is only available if GCC was configured with analyzer +support enabled. + +@item -Wanalyzer-too-complex +@opindex Wanalyzer-too-complex +@opindex Wno-analyzer-too-complex +If @option{-fanalyzer} is enabled, the analyzer uses various heuristics +to attempt to explore the control flow and data flow in the program, +but these can be defeated by sufficiently complicated code. + +By default, the analysis silently stops if the code is too +complicated for the analyzer to fully explore and it reaches an internal +limit. The @option{-Wanalyzer-too-complex} option warns if this occurs. + +@item -Wno-analyzer-allocation-size +@opindex Wanalyzer-allocation-size +@opindex Wno-analyzer-allocation-size +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-allocation-size} +to disable it. + +This diagnostic warns for paths through the code in which a pointer to +a buffer is assigned to point at a buffer with a size that is not a +multiple of @code{sizeof (*pointer)}. + +See @uref{https://cwe.mitre.org/data/definitions/131.html, CWE-131: Incorrect Calculation of Buffer Size}. + +@item -Wno-analyzer-double-fclose +@opindex Wanalyzer-double-fclose +@opindex Wno-analyzer-double-fclose +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-double-fclose} to disable it. + +This diagnostic warns for paths through the code in which a @code{FILE *} +can have @code{fclose} called on it more than once. + +See @uref{https://cwe.mitre.org/data/definitions/1341.html, CWE-1341: Multiple Releases of Same Resource or Handle}. + +@item -Wno-analyzer-double-free +@opindex Wanalyzer-double-free +@opindex Wno-analyzer-double-free +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-double-free} to disable it. + +This diagnostic warns for paths through the code in which a pointer +can have a deallocator called on it more than once, either @code{free}, +or a deallocator referenced by attribute @code{malloc}. + +See @uref{https://cwe.mitre.org/data/definitions/415.html, CWE-415: Double Free}. + +@item -Wno-analyzer-exposure-through-output-file +@opindex Wanalyzer-exposure-through-output-file +@opindex Wno-analyzer-exposure-through-output-file +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-exposure-through-output-file} +to disable it. + +This diagnostic warns for paths through the code in which a +security-sensitive value is written to an output file +(such as writing a password to a log file). + +See @uref{https://cwe.mitre.org/data/definitions/532.html, CWE-532: Information Exposure Through Log Files}. + +@item -Wanalyzer-exposure-through-uninit-copy +@opindex Wanalyzer-exposure-through-uninit-copy +@opindex Wno-analyzer-exposure-through-uninit-copy +This warning requires both @option{-fanalyzer} and the use of a plugin +to specify a function that copies across a ``trust boundary''. Use +@option{-Wno-analyzer-exposure-through-uninit-copy} to disable it. + +This diagnostic warns for ``infoleaks'' - paths through the code in which +uninitialized values are copied across a security boundary +(such as code within an OS kernel that copies a partially-initialized +struct on the stack to user space). + +See @uref{https://cwe.mitre.org/data/definitions/200.html, CWE-200: Exposure of Sensitive Information to an Unauthorized Actor}. + +@item -Wno-analyzer-fd-access-mode-mismatch +@opindex Wanalyzer-fd-access-mode-mismatch +@opindex Wno-analyzer-fd-access-mode-mismatch +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-fd-access-mode-mismatch} +to disable it. + +This diagnostic warns for paths through code in which a +@code{read} on a write-only file descriptor is attempted, or vice versa. + +This diagnostic also warns for code paths in a which a function with attribute +@code{fd_arg_read (N)} is called with a file descriptor opened with +@code{O_WRONLY} at referenced argument @code{N} or a function with attribute +@code{fd_arg_write (N)} is called with a file descriptor opened with +@code{O_RDONLY} at referenced argument @var{N}. + +@item -Wno-analyzer-fd-double-close +@opindex Wanalyzer-fd-double-close +@opindex Wno-analyzer-fd-double-close +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-fd-double-close} +to disable it. + +This diagnostic warns for paths through code in which a +file descriptor can be closed more than once. + +See @uref{https://cwe.mitre.org/data/definitions/1341.html, CWE-1341: Multiple Releases of Same Resource or Handle}. + +@item -Wno-analyzer-fd-leak +@opindex Wanalyzer-fd-leak +@opindex Wno-analyzer-fd-leak +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-fd-leak} +to disable it. + +This diagnostic warns for paths through code in which an +open file descriptor is leaked. + +See @uref{https://cwe.mitre.org/data/definitions/775.html, CWE-775: Missing Release of File Descriptor or Handle after Effective Lifetime}. + +@item -Wno-analyzer-fd-use-after-close +@opindex Wanalyzer-fd-use-after-close +@opindex Wno-analyzer-fd-use-after-close +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-fd-use-after-close} +to disable it. + +This diagnostic warns for paths through code in which a +read or write is called on a closed file descriptor. + +This diagnostic also warns for paths through code in which +a function with attribute @code{fd_arg (N)} or @code{fd_arg_read (N)} +or @code{fd_arg_write (N)} is called with a closed file descriptor at +referenced argument @code{N}. + +@item -Wno-analyzer-fd-use-without-check +@opindex Wanalyzer-fd-use-without-check +@opindex Wno-analyzer-fd-use-without-check +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-fd-use-without-check} +to disable it. + +This diagnostic warns for paths through code in which a +file descriptor is used without being checked for validity. + +This diagnostic also warns for paths through code in which +a function with attribute @code{fd_arg (N)} or @code{fd_arg_read (N)} +or @code{fd_arg_write (N)} is called with a file descriptor, at referenced +argument @code{N}, without being checked for validity. + +@item -Wno-analyzer-file-leak +@opindex Wanalyzer-file-leak +@opindex Wno-analyzer-file-leak +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-file-leak} +to disable it. + +This diagnostic warns for paths through the code in which a +@code{} @code{FILE *} stream object is leaked. + +See @uref{https://cwe.mitre.org/data/definitions/775.html, CWE-775: Missing Release of File Descriptor or Handle after Effective Lifetime}. + +@item -Wno-analyzer-free-of-non-heap +@opindex Wanalyzer-free-of-non-heap +@opindex Wno-analyzer-free-of-non-heap +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-free-of-non-heap} +to disable it. + +This diagnostic warns for paths through the code in which @code{free} +is called on a non-heap pointer (e.g. an on-stack buffer, or a global). + +See @uref{https://cwe.mitre.org/data/definitions/590.html, CWE-590: Free of Memory not on the Heap}. + +@item -Wno-analyzer-imprecise-fp-arithmetic +@opindex Wanalyzer-imprecise-fp-arithmetic +@opindex Wno-analyzer-imprecise-fp-arithmetic +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-imprecise-fp-arithmetic} +to disable it. + +This diagnostic warns for paths through the code in which floating-point +arithmetic is used in locations where precise computation is needed. This +diagnostic only warns on use of floating-point operands inside the +calculation of an allocation size at the moment. + +@item -Wno-analyzer-jump-through-null +@opindex Wanalyzer-jump-through-null +@opindex Wno-analyzer-jump-through-null +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-jump-through-null} +to disable it. + +This diagnostic warns for paths through the code in which a @code{NULL} +function pointer is called. + +@item -Wno-analyzer-malloc-leak +@opindex Wanalyzer-malloc-leak +@opindex Wno-analyzer-malloc-leak +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-malloc-leak} +to disable it. + +This diagnostic warns for paths through the code in which a +pointer allocated via an allocator is leaked: either @code{malloc}, +or a function marked with attribute @code{malloc}. + +See @uref{https://cwe.mitre.org/data/definitions/401.html, CWE-401: Missing Release of Memory after Effective Lifetime}. + +@item -Wno-analyzer-mismatching-deallocation +@opindex Wanalyzer-mismatching-deallocation +@opindex Wno-analyzer-mismatching-deallocation +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-mismatching-deallocation} +to disable it. + +This diagnostic warns for paths through the code in which the +wrong deallocation function is called on a pointer value, based on +which function was used to allocate the pointer value. The diagnostic +will warn about mismatches between @code{free}, scalar @code{delete} +and vector @code{delete[]}, and those marked as allocator/deallocator +pairs using attribute @code{malloc}. + +See @uref{https://cwe.mitre.org/data/definitions/762.html, CWE-762: Mismatched Memory Management Routines}. + +@item -Wno-analyzer-out-of-bounds +@opindex Wanalyzer-out-of-bounds +@opindex Wno-analyzer-out-of-bounds +This warning requires @option{-fanalyzer} to enable it; use +@option{-Wno-analyzer-out-of-bounds} to disable it. + +This diagnostic warns for path through the code in which a buffer is +definitely read or written out-of-bounds. The diagnostic applies for +cases where the analyzer is able to determine a constant offset and for +accesses past the end of a buffer, also a constant capacity. Further, +the diagnostic does limited checking for accesses past the end when the +offset as well as the capacity is symbolic. + +See @uref{https://cwe.mitre.org/data/definitions/119.html, CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer}. + +@item -Wno-analyzer-possible-null-argument +@opindex Wanalyzer-possible-null-argument +@opindex Wno-analyzer-possible-null-argument +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-possible-null-argument} to disable it. + +This diagnostic warns for paths through the code in which a +possibly-NULL value is passed to a function argument marked +with @code{__attribute__((nonnull))} as requiring a non-NULL +value. + +See @uref{https://cwe.mitre.org/data/definitions/690.html, CWE-690: Unchecked Return Value to NULL Pointer Dereference}. + +@item -Wno-analyzer-possible-null-dereference +@opindex Wanalyzer-possible-null-dereference +@opindex Wno-analyzer-possible-null-dereference +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-possible-null-dereference} to disable it. + +This diagnostic warns for paths through the code in which a +possibly-NULL value is dereferenced. + +See @uref{https://cwe.mitre.org/data/definitions/690.html, CWE-690: Unchecked Return Value to NULL Pointer Dereference}. + +@item -Wno-analyzer-null-argument +@opindex Wanalyzer-null-argument +@opindex Wno-analyzer-null-argument +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-null-argument} to disable it. + +This diagnostic warns for paths through the code in which a +value known to be NULL is passed to a function argument marked +with @code{__attribute__((nonnull))} as requiring a non-NULL +value. + +See @uref{https://cwe.mitre.org/data/definitions/476.html, CWE-476: NULL Pointer Dereference}. + +@item -Wno-analyzer-null-dereference +@opindex Wanalyzer-null-dereference +@opindex Wno-analyzer-null-dereference +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-null-dereference} to disable it. + +This diagnostic warns for paths through the code in which a +value known to be NULL is dereferenced. + +See @uref{https://cwe.mitre.org/data/definitions/476.html, CWE-476: NULL Pointer Dereference}. + +@item -Wno-analyzer-putenv-of-auto-var +@opindex Wanalyzer-putenv-of-auto-var +@opindex Wno-analyzer-putenv-of-auto-var +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-putenv-of-auto-var} to disable it. + +This diagnostic warns for paths through the code in which a +call to @code{putenv} is passed a pointer to an automatic variable +or an on-stack buffer. + +See @uref{https://wiki.sei.cmu.edu/confluence/x/6NYxBQ, POS34-C. Do not call putenv() with a pointer to an automatic variable as the argument}. + +@item -Wno-analyzer-shift-count-negative +@opindex Wanalyzer-shift-count-negative +@opindex Wno-analyzer-shift-count-negative +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-shift-count-negative} to disable it. + +This diagnostic warns for paths through the code in which a +shift is attempted with a negative count. It is analogous to +the @option{-Wshift-count-negative} diagnostic implemented in +the C/C++ front ends, but is implemented based on analyzing +interprocedural paths, rather than merely parsing the syntax tree. +However, the analyzer does not prioritize detection of such paths, so +false negatives are more likely relative to other warnings. + +@item -Wno-analyzer-shift-count-overflow +@opindex Wanalyzer-shift-count-overflow +@opindex Wno-analyzer-shift-count-overflow +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-shift-count-overflow} to disable it. + +This diagnostic warns for paths through the code in which a +shift is attempted with a count greater than or equal to the +precision of the operand's type. It is analogous to +the @option{-Wshift-count-overflow} diagnostic implemented in +the C/C++ front ends, but is implemented based on analyzing +interprocedural paths, rather than merely parsing the syntax tree. +However, the analyzer does not prioritize detection of such paths, so +false negatives are more likely relative to other warnings. + +@item -Wno-analyzer-stale-setjmp-buffer +@opindex Wanalyzer-stale-setjmp-buffer +@opindex Wno-analyzer-stale-setjmp-buffer +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-stale-setjmp-buffer} to disable it. + +This diagnostic warns for paths through the code in which +@code{longjmp} is called to rewind to a @code{jmp_buf} relating +to a @code{setjmp} call in a function that has returned. + +When @code{setjmp} is called on a @code{jmp_buf} to record a rewind +location, it records the stack frame. The stack frame becomes invalid +when the function containing the @code{setjmp} call returns. Attempting +to rewind to it via @code{longjmp} would reference a stack frame that +no longer exists, and likely lead to a crash (or worse). + +@item -Wno-analyzer-tainted-allocation-size +@opindex Wanalyzer-tainted-allocation-size +@opindex Wno-analyzer-tainted-allocation-size +This warning requires both @option{-fanalyzer} and +@option{-fanalyzer-checker=taint} to enable it; +use @option{-Wno-analyzer-tainted-allocation-size} to disable it. + +This diagnostic warns for paths through the code in which a value +that could be under an attacker's control is used as the size +of an allocation without being sanitized, so that an attacker could +inject an excessively large allocation and potentially cause a denial +of service attack. + +See @uref{https://cwe.mitre.org/data/definitions/789.html, CWE-789: Memory Allocation with Excessive Size Value}. + +@item -Wno-analyzer-tainted-array-index +@opindex Wanalyzer-tainted-array-index +@opindex Wno-analyzer-tainted-array-index +This warning requires both @option{-fanalyzer} and +@option{-fanalyzer-checker=taint} to enable it; +use @option{-Wno-analyzer-tainted-array-index} to disable it. + +This diagnostic warns for paths through the code in which a value +that could be under an attacker's control is used as the index +of an array access without being sanitized, so that an attacker +could inject an out-of-bounds access. + +See @uref{https://cwe.mitre.org/data/definitions/129.html, CWE-129: Improper Validation of Array Index}. + +@item -Wno-analyzer-tainted-divisor +@opindex Wanalyzer-tainted-divisor +@opindex Wno-analyzer-tainted-divisor +This warning requires both @option{-fanalyzer} and +@option{-fanalyzer-checker=taint} to enable it; +use @option{-Wno-analyzer-tainted-divisor} to disable it. + +This diagnostic warns for paths through the code in which a value +that could be under an attacker's control is used as the divisor +in a division or modulus operation without being sanitized, so that +an attacker could inject a division-by-zero. + +See @uref{https://cwe.mitre.org/data/definitions/369.html, CWE-369: Divide By Zero}. + +@item -Wno-analyzer-tainted-offset +@opindex Wanalyzer-tainted-offset +@opindex Wno-analyzer-tainted-offset +This warning requires both @option{-fanalyzer} and +@option{-fanalyzer-checker=taint} to enable it; +use @option{-Wno-analyzer-tainted-offset} to disable it. + +This diagnostic warns for paths through the code in which a value +that could be under an attacker's control is used as a pointer offset +without being sanitized, so that an attacker could inject an out-of-bounds +access. + +See @uref{https://cwe.mitre.org/data/definitions/823.html, CWE-823: Use of Out-of-range Pointer Offset}. + +@item -Wno-analyzer-tainted-size +@opindex Wanalyzer-tainted-size +@opindex Wno-analyzer-tainted-size +This warning requires both @option{-fanalyzer} and +@option{-fanalyzer-checker=taint} to enable it; +use @option{-Wno-analyzer-tainted-size} to disable it. + +This diagnostic warns for paths through the code in which a value +that could be under an attacker's control is used as the size of +an operation such as @code{memset} without being sanitized, so that an +attacker could inject an out-of-bounds access. + +See @uref{https://cwe.mitre.org/data/definitions/129.html, CWE-129: Improper Validation of Array Index}. + +@item -Wno-analyzer-unsafe-call-within-signal-handler +@opindex Wanalyzer-unsafe-call-within-signal-handler +@opindex Wno-analyzer-unsafe-call-within-signal-handler +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-unsafe-call-within-signal-handler} to disable it. + +This diagnostic warns for paths through the code in which a +function known to be async-signal-unsafe (such as @code{fprintf}) is +called from a signal handler. + +See @uref{https://cwe.mitre.org/data/definitions/479.html, CWE-479: Signal Handler Use of a Non-reentrant Function}. + +@item -Wno-analyzer-use-after-free +@opindex Wanalyzer-use-after-free +@opindex Wno-analyzer-use-after-free +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-use-after-free} to disable it. + +This diagnostic warns for paths through the code in which a +pointer is used after a deallocator is called on it: either @code{free}, +or a deallocator referenced by attribute @code{malloc}. + +See @uref{https://cwe.mitre.org/data/definitions/416.html, CWE-416: Use After Free}. + +@item -Wno-analyzer-use-of-pointer-in-stale-stack-frame +@opindex Wanalyzer-use-of-pointer-in-stale-stack-frame +@opindex Wno-analyzer-use-of-pointer-in-stale-stack-frame +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-use-of-pointer-in-stale-stack-frame} +to disable it. + +This diagnostic warns for paths through the code in which a pointer +is dereferenced that points to a variable in a stale stack frame. + +@item -Wno-analyzer-va-arg-type-mismatch +@opindex Wanalyzer-va-arg-type-mismatch +@opindex Wno-analyzer-va-arg-type-mismatch +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-va-arg-type-mismatch} +to disable it. + +This diagnostic warns for interprocedural paths through the code for which +the analyzer detects an attempt to use @code{va_arg} to extract a value +passed to a variadic call, but uses a type that does not match that of +the expression passed to the call. + +See @uref{https://cwe.mitre.org/data/definitions/686.html, CWE-686: Function Call With Incorrect Argument Type}. + +@item -Wno-analyzer-va-list-exhausted +@opindex Wanalyzer-va-list-exhausted +@opindex Wno-analyzer-va-list-exhausted +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-va-list-exhausted} +to disable it. + +This diagnostic warns for interprocedural paths through the code for which +the analyzer detects an attempt to use @code{va_arg} to access the next +value passed to a variadic call, but all of the values in the +@code{va_list} have already been consumed. + +See @uref{https://cwe.mitre.org/data/definitions/685.html, CWE-685: Function Call With Incorrect Number of Arguments}. + +@item -Wno-analyzer-va-list-leak +@opindex Wanalyzer-va-list-leak +@opindex Wno-analyzer-va-list-leak +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-va-list-leak} +to disable it. + +This diagnostic warns for interprocedural paths through the code for which +the analyzer detects that @code{va_start} or @code{va_copy} has been called +on a @code{va_list} without a corresponding call to @code{va_end}. + +@item -Wno-analyzer-va-list-use-after-va-end +@opindex Wanalyzer-va-list-use-after-va-end +@opindex Wno-analyzer-va-list-use-after-va-end +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-va-list-use-after-va-end} +to disable it. + +This diagnostic warns for interprocedural paths through the code for which +the analyzer detects an attempt to use a @code{va_list} after +@code{va_end} has been called on it. +@code{va_list}. + +@item -Wno-analyzer-write-to-const +@opindex Wanalyzer-write-to-const +@opindex Wno-analyzer-write-to-const +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-write-to-const} +to disable it. + +This diagnostic warns for paths through the code in which the analyzer +detects an attempt to write through a pointer to a @code{const} object. +However, the analyzer does not prioritize detection of such paths, so +false negatives are more likely relative to other warnings. + +@item -Wno-analyzer-write-to-string-literal +@opindex Wanalyzer-write-to-string-literal +@opindex Wno-analyzer-write-to-string-literal +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-write-to-string-literal} +to disable it. + +This diagnostic warns for paths through the code in which the analyzer +detects an attempt to write through a pointer to a string literal. +However, the analyzer does not prioritize detection of such paths, so +false negatives are more likely relative to other warnings. + +@item -Wno-analyzer-use-of-uninitialized-value +@opindex Wanalyzer-use-of-uninitialized-value +@opindex Wno-analyzer-use-of-uninitialized-value +This warning requires @option{-fanalyzer}, which enables it; use +@option{-Wno-analyzer-use-of-uninitialized-value} to disable it. + +This diagnostic warns for paths through the code in which an uninitialized +value is used. + +See @uref{https://cwe.mitre.org/data/definitions/457.html, CWE-457: Use of Uninitialized Variable}. + +@end table + +The analyzer has hardcoded knowledge about the behavior of the following +memory-management functions: + +@itemize @bullet +@item @code{alloca} +@item The built-in functions @code{__builtin_alloc}, +@code{__builtin_alloc_with_align}, @item @code{__builtin_calloc}, +@code{__builtin_free}, @code{__builtin_malloc}, @code{__builtin_memcpy}, +@code{__builtin_memcpy_chk}, @code{__builtin_memset}, +@code{__builtin_memset_chk}, @code{__builtin_realloc}, +@code{__builtin_stack_restore}, and @code{__builtin_stack_save} +@item @code{calloc} +@item @code{free} +@item @code{malloc} +@item @code{memset} +@item @code{operator delete} +@item @code{operator delete []} +@item @code{operator new} +@item @code{operator new []} +@item @code{realloc} +@item @code{strdup} +@item @code{strndup} +@end itemize + +of the following functions for working with file descriptors: + +@itemize @bullet +@item @code{open} +@item @code{close} +@item @code{creat} +@item @code{dup}, @code{dup2} and @code{dup3} +@item @code{pipe}, and @code{pipe2} +@item @code{read} +@item @code{write} +@end itemize + +of the following functions for working with @code{} streams: +@itemize @bullet +@item The built-in functions @code{__builtin_fprintf}, +@code{__builtin_fprintf_unlocked}, @code{__builtin_fputc}, +@code{__builtin_fputc_unlocked}, @code{__builtin_fputs}, +@code{__builtin_fputs_unlocked}, @code{__builtin_fwrite}, +@code{__builtin_fwrite_unlocked}, @code{__builtin_printf}, +@code{__builtin_printf_unlocked}, @code{__builtin_putc}, +@code{__builtin_putchar}, @code{__builtin_putchar_unlocked}, +@code{__builtin_putc_unlocked}, @code{__builtin_puts}, +@code{__builtin_puts_unlocked}, @code{__builtin_vfprintf}, and +@code{__builtin_vprintf} +@item @code{fopen} +@item @code{fclose} +@item @code{fgets} +@item @code{fgets_unlocked} +@item @code{fread} +@item @code{getchar} +@item @code{fprintf} +@item @code{printf} +@item @code{fwrite} +@end itemize + +and of the following functions: + +@itemize @bullet +@item The built-in functions @code{__builtin_expect}, +@code{__builtin_expect_with_probability}, @code{__builtin_strchr}, +@code{__builtin_strcpy}, @code{__builtin_strcpy_chk}, +@code{__builtin_strlen}, @code{__builtin_va_copy}, and +@code{__builtin_va_start} +@item The GNU extensions @code{error} and @code{error_at_line} +@item @code{getpass} +@item @code{longjmp} +@item @code{putenv} +@item @code{setjmp} +@item @code{siglongjmp} +@item @code{signal} +@item @code{sigsetjmp} +@item @code{strchr} +@item @code{strlen} +@end itemize + +In addition, various functions with an @code{__analyzer_} prefix have +special meaning to the analyzer, described in the GCC Internals manual. + +Pertinent parameters for controlling the exploration are: +@option{--param analyzer-bb-explosion-factor=@var{value}}, +@option{--param analyzer-max-enodes-per-program-point=@var{value}}, +@option{--param analyzer-max-recursion-depth=@var{value}}, and +@option{--param analyzer-min-snodes-for-call-summary=@var{value}}. + +The following options control the analyzer. + +@table @gcctabopt + +@item -fanalyzer-call-summaries +@opindex fanalyzer-call-summaries +@opindex fno-analyzer-call-summaries +Simplify interprocedural analysis by computing the effect of certain calls, +rather than exploring all paths through the function from callsite to each +possible return. + +If enabled, call summaries are only used for functions with more than one +call site, and that are sufficiently complicated (as per +@option{--param analyzer-min-snodes-for-call-summary=@var{value}}). + +@item -fanalyzer-checker=@var{name} +@opindex fanalyzer-checker +Restrict the analyzer to run just the named checker, and enable it. + +Some checkers are disabled by default (even with @option{-fanalyzer}), +such as the @code{taint} checker that implements +@option{-Wanalyzer-tainted-array-index}, and this option is required +to enable them. + +@emph{Note:} currently, @option{-fanalyzer-checker=taint} disables the +following warnings from @option{-fanalyzer}: + +@gccoptlist{ @gol +-Wanalyzer-double-fclose @gol +-Wanalyzer-double-free @gol +-Wanalyzer-exposure-through-output-file @gol +-Wanalyzer-fd-access-mode-mismatch @gol +-Wanalyzer-fd-double-close @gol +-Wanalyzer-fd-leak @gol +-Wanalyzer-fd-use-after-close @gol +-Wanalyzer-fd-use-without-check @gol +-Wanalyzer-file-leak @gol +-Wanalyzer-free-of-non-heap @gol +-Wanalyzer-malloc-leak @gol +-Wanalyzer-mismatching-deallocation @gol +-Wanalyzer-null-argument @gol +-Wanalyzer-null-dereference @gol +-Wanalyzer-possible-null-argument @gol +-Wanalyzer-possible-null-dereference @gol +-Wanalyzer-unsafe-call-within-signal-handler @gol +-Wanalyzer-use-after-free @gol +-Wanalyzer-va-list-leak @gol +-Wanalyzer-va-list-use-after-va-end @gol +} + +@item -fno-analyzer-feasibility +@opindex fanalyzer-feasibility +@opindex fno-analyzer-feasibility +This option is intended for analyzer developers. + +By default the analyzer verifies that there is a feasible control flow path +for each diagnostic it emits: that the conditions that hold are not mutually +exclusive. Diagnostics for which no feasible path can be found are rejected. +This filtering can be suppressed with @option{-fno-analyzer-feasibility}, for +debugging issues in this code. + +@item -fanalyzer-fine-grained +@opindex fanalyzer-fine-grained +@opindex fno-analyzer-fine-grained +This option is intended for analyzer developers. + +Internally the analyzer builds an ``exploded graph'' that combines +control flow graphs with data flow information. + +By default, an edge in this graph can contain the effects of a run +of multiple statements within a basic block. With +@option{-fanalyzer-fine-grained}, each statement gets its own edge. + +@item -fanalyzer-show-duplicate-count +@opindex fanalyzer-show-duplicate-count +@opindex fno-analyzer-show-duplicate-count +This option is intended for analyzer developers: if multiple diagnostics +have been detected as being duplicates of each other, it emits a note when +reporting the best diagnostic, giving the number of additional diagnostics +that were suppressed by the deduplication logic. + +@item -fno-analyzer-state-merge +@opindex fanalyzer-state-merge +@opindex fno-analyzer-state-merge +This option is intended for analyzer developers. + +By default the analyzer attempts to simplify analysis by merging +sufficiently similar states at each program point as it builds its +``exploded graph''. With @option{-fno-analyzer-state-merge} this +merging can be suppressed, for debugging state-handling issues. + +@item -fno-analyzer-state-purge +@opindex fanalyzer-state-purge +@opindex fno-analyzer-state-purge +This option is intended for analyzer developers. + +By default the analyzer attempts to simplify analysis by purging +aspects of state at a program point that appear to no longer be relevant +e.g. the values of locals that aren't accessed later in the function +and which aren't relevant to leak analysis. + +With @option{-fno-analyzer-state-purge} this purging of state can +be suppressed, for debugging state-handling issues. + +@item -fanalyzer-transitivity +@opindex fanalyzer-transitivity +@opindex fno-analyzer-transitivity +This option enables transitivity of constraints within the analyzer. + +@item -fno-analyzer-undo-inlining +@opindex fanalyzer-undo-inlining +@opindex fno-analyzer-undo-inlining +This option is intended for analyzer developers. + +@option{-fanalyzer} runs relatively late compared to other code analysis +tools, and some optimizations have already been applied to the code. In +particular function inlining may have occurred, leading to the +interprocedural execution paths emitted by the analyzer containing +function frames that don't correspond to those in the original source +code. + +By default the analyzer attempts to reconstruct the original function +frames, and to emit events showing the inlined calls. + +With @option{-fno-analyzer-undo-inlining} this attempt to reconstruct +the original frame information can be be disabled, which may be of help +when debugging issues in the analyzer. + +@item -fanalyzer-verbose-edges +This option is intended for analyzer developers. It enables more +verbose, lower-level detail in the descriptions of control flow +within diagnostic paths. + +@item -fanalyzer-verbose-state-changes +This option is intended for analyzer developers. It enables more +verbose, lower-level detail in the descriptions of events relating +to state machines within diagnostic paths. + +@item -fanalyzer-verbosity=@var{level} +This option controls the complexity of the control flow paths that are +emitted for analyzer diagnostics. + +The @var{level} can be one of: + +@table @samp +@item 0 +At this level, interprocedural call and return events are displayed, +along with the most pertinent state-change events relating to +a diagnostic. For example, for a double-@code{free} diagnostic, +both calls to @code{free} will be shown. + +@item 1 +As per the previous level, but also show events for the entry +to each function. + +@item 2 +As per the previous level, but also show events relating to +control flow that are significant to triggering the issue +(e.g. ``true path taken'' at a conditional). + +This level is the default. + +@item 3 +As per the previous level, but show all control flow events, not +just significant ones. + +@item 4 +This level is intended for analyzer developers; it adds various +other events intended for debugging the analyzer. + +@end table + +@item -fdump-analyzer +@opindex fdump-analyzer +Dump internal details about what the analyzer is doing to +@file{@var{file}.analyzer.txt}. +This option is overridden by @option{-fdump-analyzer-stderr}. + +@item -fdump-analyzer-stderr +@opindex fdump-analyzer-stderr +Dump internal details about what the analyzer is doing to stderr. +This option overrides @option{-fdump-analyzer}. + +@item -fdump-analyzer-callgraph +@opindex fdump-analyzer-callgraph +Dump a representation of the call graph suitable for viewing with +GraphViz to @file{@var{file}.callgraph.dot}. + +@item -fdump-analyzer-exploded-graph +@opindex fdump-analyzer-exploded-graph +Dump a representation of the ``exploded graph'' suitable for viewing with +GraphViz to @file{@var{file}.eg.dot}. +Nodes are color-coded based on state-machine states to emphasize +state changes. + +@item -fdump-analyzer-exploded-nodes +@opindex dump-analyzer-exploded-nodes +Emit diagnostics showing where nodes in the ``exploded graph'' are +in relation to the program source. + +@item -fdump-analyzer-exploded-nodes-2 +@opindex dump-analyzer-exploded-nodes-2 +Dump a textual representation of the ``exploded graph'' to +@file{@var{file}.eg.txt}. + +@item -fdump-analyzer-exploded-nodes-3 +@opindex dump-analyzer-exploded-nodes-3 +Dump a textual representation of the ``exploded graph'' to +one dump file per node, to @file{@var{file}.eg-@var{id}.txt}. +This is typically a large number of dump files. + +@item -fdump-analyzer-exploded-paths +@opindex fdump-analyzer-exploded-paths +Dump a textual representation of the ``exploded path'' for each +diagnostic to @file{@var{file}.@var{idx}.@var{kind}.epath.txt}. + +@item -fdump-analyzer-feasibility +@opindex dump-analyzer-feasibility +Dump internal details about the analyzer's search for feasible paths. +The details are written in a form suitable for viewing with GraphViz +to filenames of the form @file{@var{file}.*.fg.dot}, +@file{@var{file}.*.tg.dot}, and @file{@var{file}.*.fpath.txt}. + +@item -fdump-analyzer-json +@opindex fdump-analyzer-json +Dump a compressed JSON representation of analyzer internals to +@file{@var{file}.analyzer.json.gz}. The precise format is subject +to change. + +@item -fdump-analyzer-state-purge +@opindex fdump-analyzer-state-purge +As per @option{-fdump-analyzer-supergraph}, dump a representation of the +``supergraph'' suitable for viewing with GraphViz, but annotate the +graph with information on what state will be purged at each node. +The graph is written to @file{@var{file}.state-purge.dot}. + +@item -fdump-analyzer-supergraph +@opindex fdump-analyzer-supergraph +Dump representations of the ``supergraph'' suitable for viewing with +GraphViz to @file{@var{file}.supergraph.dot} and to +@file{@var{file}.supergraph-eg.dot}. These show all of the +control flow graphs in the program, with interprocedural edges for +calls and returns. The second dump contains annotations showing nodes +in the ``exploded graph'' and diagnostics associated with them. + +@item -fdump-analyzer-untracked +@opindex fdump-analyzer-untracked +Emit custom warnings with internal details intended for analyzer developers. + +@end table + +@node Debugging Options +@section Options for Debugging Your Program +@cindex options, debugging +@cindex debugging information options + +To tell GCC to emit extra information for use by a debugger, in almost +all cases you need only to add @option{-g} to your other options. Some debug +formats can co-exist (like DWARF with CTF) when each of them is enabled +explicitly by adding the respective command line option to your other options. + +GCC allows you to use @option{-g} with +@option{-O}. The shortcuts taken by optimized code may occasionally +be surprising: some variables you declared may not exist +at all; flow of control may briefly move where you did not expect it; +some statements may not be executed because they compute constant +results or their values are already at hand; some statements may +execute in different places because they have been moved out of loops. +Nevertheless it is possible to debug optimized output. This makes +it reasonable to use the optimizer for programs that might have bugs. + +If you are not using some other optimization option, consider +using @option{-Og} (@pxref{Optimize Options}) with @option{-g}. +With no @option{-O} option at all, some compiler passes that collect +information useful for debugging do not run at all, so that +@option{-Og} may result in a better debugging experience. + +@table @gcctabopt +@item -g +@opindex g +Produce debugging information in the operating system's native format +(stabs, COFF, XCOFF, or DWARF)@. GDB can work with this debugging +information. + +On most systems that use stabs format, @option{-g} enables use of extra +debugging information that only GDB can use; this extra information +makes debugging work better in GDB but probably makes other debuggers +crash or refuse to read the program. If you want to control for certain whether +to generate the extra information, use @option{-gvms} (see below). + +@item -ggdb +@opindex ggdb +Produce debugging information for use by GDB@. This means to use the +most expressive format available (DWARF, stabs, or the native format +if neither of those are supported), including GDB extensions if at all +possible. + +@item -gdwarf +@itemx -gdwarf-@var{version} +@opindex gdwarf +Produce debugging information in DWARF format (if that is supported). +The value of @var{version} may be either 2, 3, 4 or 5; the default +version for most targets is 5 (with the exception of VxWorks, TPF and +Darwin/Mac OS X, which default to version 2, and AIX, which defaults +to version 4). + +Note that with DWARF Version 2, some ports require and always +use some non-conflicting DWARF 3 extensions in the unwind tables. + +Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments} +for maximum benefit. Version 5 requires GDB 8.0 or higher. + +GCC no longer supports DWARF Version 1, which is substantially +different than Version 2 and later. For historical reasons, some +other DWARF-related options such as +@option{-fno-dwarf2-cfi-asm}) retain a reference to DWARF Version 2 +in their names, but apply to all currently-supported versions of DWARF. + +@item -gbtf +@opindex gbtf +Request BTF debug information. BTF is the default debugging format for the +eBPF target. On other targets, like x86, BTF debug information can be +generated along with DWARF debug information when both of the debug formats are +enabled explicitly via their respective command line options. + +@item -gctf +@itemx -gctf@var{level} +@opindex gctf +Request CTF debug information and use level to specify how much CTF debug +information should be produced. If @option{-gctf} is specified +without a value for level, the default level of CTF debug information is 2. + +CTF debug information can be generated along with DWARF debug information when +both of the debug formats are enabled explicitly via their respective command +line options. + +Level 0 produces no CTF debug information at all. Thus, @option{-gctf0} +negates @option{-gctf}. + +Level 1 produces CTF information for tracebacks only. This includes callsite +information, but does not include type information. + +Level 2 produces type information for entities (functions, data objects etc.) +at file-scope or global-scope only. + +@item -gvms +@opindex gvms +Produce debugging information in Alpha/VMS debug format (if that is +supported). This is the format used by DEBUG on Alpha/VMS systems. + +@item -g@var{level} +@itemx -ggdb@var{level} +@itemx -gvms@var{level} +Request debugging information and also use @var{level} to specify how +much information. The default level is 2. + +Level 0 produces no debug information at all. Thus, @option{-g0} negates +@option{-g}. + +Level 1 produces minimal information, enough for making backtraces in +parts of the program that you don't plan to debug. This includes +descriptions of functions and external variables, and line number +tables, but no information about local variables. + +Level 3 includes extra information, such as all the macro definitions +present in the program. Some debuggers support macro expansion when +you use @option{-g3}. + +If you use multiple @option{-g} options, with or without level numbers, +the last such option is the one that is effective. + +@option{-gdwarf} does not accept a concatenated debug level, to avoid +confusion with @option{-gdwarf-@var{level}}. +Instead use an additional @option{-g@var{level}} option to change the +debug level for DWARF. + +@item -fno-eliminate-unused-debug-symbols +@opindex feliminate-unused-debug-symbols +@opindex fno-eliminate-unused-debug-symbols +By default, no debug information is produced for symbols that are not actually +used. Use this option if you want debug information for all symbols. + +@item -femit-class-debug-always +@opindex femit-class-debug-always +Instead of emitting debugging information for a C++ class in only one +object file, emit it in all object files using the class. This option +should be used only with debuggers that are unable to handle the way GCC +normally emits debugging information for classes because using this +option increases the size of debugging information by as much as a +factor of two. + +@item -fno-merge-debug-strings +@opindex fmerge-debug-strings +@opindex fno-merge-debug-strings +Direct the linker to not merge together strings in the debugging +information that are identical in different object files. Merging is +not supported by all assemblers or linkers. Merging decreases the size +of the debug information in the output file at the cost of increasing +link processing time. Merging is enabled by default. + +@item -fdebug-prefix-map=@var{old}=@var{new} +@opindex fdebug-prefix-map +When compiling files residing in directory @file{@var{old}}, record +debugging information describing them as if the files resided in +directory @file{@var{new}} instead. This can be used to replace a +build-time path with an install-time path in the debug info. It can +also be used to change an absolute path to a relative path by using +@file{.} for @var{new}. This can give more reproducible builds, which +are location independent, but may require an extra command to tell GDB +where to find the source files. See also @option{-ffile-prefix-map}. + +@item -fvar-tracking +@opindex fvar-tracking +Run variable tracking pass. It computes where variables are stored at each +position in code. Better debugging information is then generated +(if the debugging information format supports this information). + +It is enabled by default when compiling with optimization (@option{-Os}, +@option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and +the debug info format supports it. + +@item -fvar-tracking-assignments +@opindex fvar-tracking-assignments +@opindex fno-var-tracking-assignments +Annotate assignments to user variables early in the compilation and +attempt to carry the annotations over throughout the compilation all the +way to the end, in an attempt to improve debug information while +optimizing. Use of @option{-gdwarf-4} is recommended along with it. + +It can be enabled even if var-tracking is disabled, in which case +annotations are created and maintained, but discarded at the end. +By default, this flag is enabled together with @option{-fvar-tracking}, +except when selective scheduling is enabled. + +@item -gsplit-dwarf +@opindex gsplit-dwarf +If DWARF debugging information is enabled, separate as much debugging +information as possible into a separate output file with the extension +@file{.dwo}. This option allows the build system to avoid linking files with +debug information. To be useful, this option requires a debugger capable of +reading @file{.dwo} files. + +@item -gdwarf32 +@itemx -gdwarf64 +@opindex gdwarf32 +@opindex gdwarf64 +If DWARF debugging information is enabled, the @option{-gdwarf32} selects +the 32-bit DWARF format and the @option{-gdwarf64} selects the 64-bit +DWARF format. The default is target specific, on most targets it is +@option{-gdwarf32} though. The 32-bit DWARF format is smaller, but +can't support more than 2GiB of debug information in any of the DWARF +debug information sections. The 64-bit DWARF format allows larger debug +information and might not be well supported by all consumers yet. + +@item -gdescribe-dies +@opindex gdescribe-dies +Add description attributes to some DWARF DIEs that have no name attribute, +such as artificial variables, external references and call site +parameter DIEs. + +@item -gpubnames +@opindex gpubnames +Generate DWARF @code{.debug_pubnames} and @code{.debug_pubtypes} sections. + +@item -ggnu-pubnames +@opindex ggnu-pubnames +Generate @code{.debug_pubnames} and @code{.debug_pubtypes} sections in a format +suitable for conversion into a GDB@ index. This option is only useful +with a linker that can produce GDB@ index version 7. + +@item -fdebug-types-section +@opindex fdebug-types-section +@opindex fno-debug-types-section +When using DWARF Version 4 or higher, type DIEs can be put into +their own @code{.debug_types} section instead of making them part of the +@code{.debug_info} section. It is more efficient to put them in a separate +comdat section since the linker can then remove duplicates. +But not all DWARF consumers support @code{.debug_types} sections yet +and on some objects @code{.debug_types} produces larger instead of smaller +debugging information. + +@item -grecord-gcc-switches +@itemx -gno-record-gcc-switches +@opindex grecord-gcc-switches +@opindex gno-record-gcc-switches +This switch causes the command-line options used to invoke the +compiler that may affect code generation to be appended to the +DW_AT_producer attribute in DWARF debugging information. The options +are concatenated with spaces separating them from each other and from +the compiler version. +It is enabled by default. +See also @option{-frecord-gcc-switches} for another +way of storing compiler options into the object file. + +@item -gstrict-dwarf +@opindex gstrict-dwarf +Disallow using extensions of later DWARF standard version than selected +with @option{-gdwarf-@var{version}}. On most targets using non-conflicting +DWARF extensions from later standard versions is allowed. + +@item -gno-strict-dwarf +@opindex gno-strict-dwarf +Allow using extensions of later DWARF standard version than selected with +@option{-gdwarf-@var{version}}. + +@item -gas-loc-support +@opindex gas-loc-support +Inform the compiler that the assembler supports @code{.loc} directives. +It may then use them for the assembler to generate DWARF2+ line number +tables. + +This is generally desirable, because assembler-generated line-number +tables are a lot more compact than those the compiler can generate +itself. + +This option will be enabled by default if, at GCC configure time, the +assembler was found to support such directives. + +@item -gno-as-loc-support +@opindex gno-as-loc-support +Force GCC to generate DWARF2+ line number tables internally, if DWARF2+ +line number tables are to be generated. + +@item -gas-locview-support +@opindex gas-locview-support +Inform the compiler that the assembler supports @code{view} assignment +and reset assertion checking in @code{.loc} directives. + +This option will be enabled by default if, at GCC configure time, the +assembler was found to support them. + +@item -gno-as-locview-support +Force GCC to assign view numbers internally, if +@option{-gvariable-location-views} are explicitly requested. + +@item -gcolumn-info +@itemx -gno-column-info +@opindex gcolumn-info +@opindex gno-column-info +Emit location column information into DWARF debugging information, rather +than just file and line. +This option is enabled by default. + +@item -gstatement-frontiers +@itemx -gno-statement-frontiers +@opindex gstatement-frontiers +@opindex gno-statement-frontiers +This option causes GCC to create markers in the internal representation +at the beginning of statements, and to keep them roughly in place +throughout compilation, using them to guide the output of @code{is_stmt} +markers in the line number table. This is enabled by default when +compiling with optimization (@option{-Os}, @option{-O1}, @option{-O2}, +@dots{}), and outputting DWARF 2 debug information at the normal level. + +@item -gvariable-location-views +@itemx -gvariable-location-views=incompat5 +@itemx -gno-variable-location-views +@opindex gvariable-location-views +@opindex gvariable-location-views=incompat5 +@opindex gno-variable-location-views +Augment variable location lists with progressive view numbers implied +from the line number table. This enables debug information consumers to +inspect state at certain points of the program, even if no instructions +associated with the corresponding source locations are present at that +point. If the assembler lacks support for view numbers in line number +tables, this will cause the compiler to emit the line number table, +which generally makes them somewhat less compact. The augmented line +number tables and location lists are fully backward-compatible, so they +can be consumed by debug information consumers that are not aware of +these augmentations, but they won't derive any benefit from them either. + +This is enabled by default when outputting DWARF 2 debug information at +the normal level, as long as there is assembler support, +@option{-fvar-tracking-assignments} is enabled and +@option{-gstrict-dwarf} is not. When assembler support is not +available, this may still be enabled, but it will force GCC to output +internal line number tables, and if +@option{-ginternal-reset-location-views} is not enabled, that will most +certainly lead to silently mismatching location views. + +There is a proposed representation for view numbers that is not backward +compatible with the location list format introduced in DWARF 5, that can +be enabled with @option{-gvariable-location-views=incompat5}. This +option may be removed in the future, is only provided as a reference +implementation of the proposed representation. Debug information +consumers are not expected to support this extended format, and they +would be rendered unable to decode location lists using it. + +@item -ginternal-reset-location-views +@itemx -gno-internal-reset-location-views +@opindex ginternal-reset-location-views +@opindex gno-internal-reset-location-views +Attempt to determine location views that can be omitted from location +view lists. This requires the compiler to have very accurate insn +length estimates, which isn't always the case, and it may cause +incorrect view lists to be generated silently when using an assembler +that does not support location view lists. The GNU assembler will flag +any such error as a @code{view number mismatch}. This is only enabled +on ports that define a reliable estimation function. + +@item -ginline-points +@itemx -gno-inline-points +@opindex ginline-points +@opindex gno-inline-points +Generate extended debug information for inlined functions. Location +view tracking markers are inserted at inlined entry points, so that +address and view numbers can be computed and output in debug +information. This can be enabled independently of location views, in +which case the view numbers won't be output, but it can only be enabled +along with statement frontiers, and it is only enabled by default if +location views are enabled. + +@item -gz@r{[}=@var{type}@r{]} +@opindex gz +Produce compressed debug sections in DWARF format, if that is supported. +If @var{type} is not given, the default type depends on the capabilities +of the assembler and linker used. @var{type} may be one of +@samp{none} (don't compress debug sections), or @samp{zlib} (use zlib +compression in ELF gABI format). If the linker doesn't support writing +compressed debug sections, the option is rejected. Otherwise, if the +assembler does not support them, @option{-gz} is silently ignored when +producing object files. + +@item -femit-struct-debug-baseonly +@opindex femit-struct-debug-baseonly +Emit debug information for struct-like types +only when the base name of the compilation source file +matches the base name of file in which the struct is defined. + +This option substantially reduces the size of debugging information, +but at significant potential loss in type information to the debugger. +See @option{-femit-struct-debug-reduced} for a less aggressive option. +See @option{-femit-struct-debug-detailed} for more detailed control. + +This option works only with DWARF debug output. + +@item -femit-struct-debug-reduced +@opindex femit-struct-debug-reduced +Emit debug information for struct-like types +only when the base name of the compilation source file +matches the base name of file in which the type is defined, +unless the struct is a template or defined in a system header. + +This option significantly reduces the size of debugging information, +with some potential loss in type information to the debugger. +See @option{-femit-struct-debug-baseonly} for a more aggressive option. +See @option{-femit-struct-debug-detailed} for more detailed control. + +This option works only with DWARF debug output. + +@item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} +@opindex femit-struct-debug-detailed +Specify the struct-like types +for which the compiler generates debug information. +The intent is to reduce duplicate struct debug information +between different object files within the same program. + +This option is a detailed version of +@option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly}, +which serves for most needs. + +A specification has the syntax@* +[@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none}) + +The optional first word limits the specification to +structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}). +A struct type is used directly when it is the type of a variable, member. +Indirect uses arise through pointers to structs. +That is, when use of an incomplete struct is valid, the use is indirect. +An example is +@samp{struct one direct; struct two * indirect;}. + +The optional second word limits the specification to +ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}). +Generic structs are a bit complicated to explain. +For C++, these are non-explicit specializations of template classes, +or non-template classes within the above. +Other programming languages have generics, +but @option{-femit-struct-debug-detailed} does not yet implement them. + +The third word specifies the source files for those +structs for which the compiler should emit debug information. +The values @samp{none} and @samp{any} have the normal meaning. +The value @samp{base} means that +the base of name of the file in which the type declaration appears +must match the base of the name of the main compilation file. +In practice, this means that when compiling @file{foo.c}, debug information +is generated for types declared in that file and @file{foo.h}, +but not other header files. +The value @samp{sys} means those types satisfying @samp{base} +or declared in system or compiler headers. + +You may need to experiment to determine the best settings for your application. + +The default is @option{-femit-struct-debug-detailed=all}. + +This option works only with DWARF debug output. + +@item -fno-dwarf2-cfi-asm +@opindex fdwarf2-cfi-asm +@opindex fno-dwarf2-cfi-asm +Emit DWARF unwind info as compiler generated @code{.eh_frame} section +instead of using GAS @code{.cfi_*} directives. + +@item -fno-eliminate-unused-debug-types +@opindex feliminate-unused-debug-types +@opindex fno-eliminate-unused-debug-types +Normally, when producing DWARF output, GCC avoids producing debug symbol +output for types that are nowhere used in the source file being compiled. +Sometimes it is useful to have GCC emit debugging +information for all types declared in a compilation +unit, regardless of whether or not they are actually used +in that compilation unit, for example +if, in the debugger, you want to cast a value to a type that is +not actually used in your program (but is declared). More often, +however, this results in a significant amount of wasted space. +@end table + +@node Optimize Options +@section Options That Control Optimization +@cindex optimize options +@cindex options, optimization + +These options control various sorts of optimizations. + +Without any optimization option, the compiler's goal is to reduce the +cost of compilation and to make debugging produce the expected +results. Statements are independent: if you stop the program with a +breakpoint between statements, you can then assign a new value to any +variable or change the program counter to any other statement in the +function and get exactly the results you expect from the source +code. + +Turning on optimization flags makes the compiler attempt to improve +the performance and/or code size at the expense of compilation time +and possibly the ability to debug the program. + +The compiler performs optimization based on the knowledge it has of the +program. Compiling multiple files at once to a single output file mode allows +the compiler to use information gained from all of the files when compiling +each of them. + +Not all optimizations are controlled directly by a flag. Only +optimizations that have a flag are listed in this section. + +Most optimizations are completely disabled at @option{-O0} or if an +@option{-O} level is not set on the command line, even if individual +optimization flags are specified. Similarly, @option{-Og} suppresses +many optimization passes. + +Depending on the target and how GCC was configured, a slightly different +set of optimizations may be enabled at each @option{-O} level than +those listed here. You can invoke GCC with @option{-Q --help=optimizers} +to find out the exact set of optimizations that are enabled at each level. +@xref{Overall Options}, for examples. + +@table @gcctabopt +@item -O +@itemx -O1 +@opindex O +@opindex O1 +Optimize. Optimizing compilation takes somewhat more time, and a lot +more memory for a large function. + +With @option{-O}, the compiler tries to reduce code size and execution +time, without performing any optimizations that take a great deal of +compilation time. + +@c Note that in addition to the default_options_table list in opts.cc, +@c several optimization flags default to true but control optimization +@c passes that are explicitly disabled at -O0. + +@option{-O} turns on the following optimization flags: + +@c Please keep the following list alphabetized. +@gccoptlist{-fauto-inc-dec @gol +-fbranch-count-reg @gol +-fcombine-stack-adjustments @gol +-fcompare-elim @gol +-fcprop-registers @gol +-fdce @gol +-fdefer-pop @gol +-fdelayed-branch @gol +-fdse @gol +-fforward-propagate @gol +-fguess-branch-probability @gol +-fif-conversion @gol +-fif-conversion2 @gol +-finline-functions-called-once @gol +-fipa-modref @gol +-fipa-profile @gol +-fipa-pure-const @gol +-fipa-reference @gol +-fipa-reference-addressable @gol +-fmerge-constants @gol +-fmove-loop-invariants @gol +-fmove-loop-stores@gol +-fomit-frame-pointer @gol +-freorder-blocks @gol +-fshrink-wrap @gol +-fshrink-wrap-separate @gol +-fsplit-wide-types @gol +-fssa-backprop @gol +-fssa-phiopt @gol +-ftree-bit-ccp @gol +-ftree-ccp @gol +-ftree-ch @gol +-ftree-coalesce-vars @gol +-ftree-copy-prop @gol +-ftree-dce @gol +-ftree-dominator-opts @gol +-ftree-dse @gol +-ftree-forwprop @gol +-ftree-fre @gol +-ftree-phiprop @gol +-ftree-pta @gol +-ftree-scev-cprop @gol +-ftree-sink @gol +-ftree-slsr @gol +-ftree-sra @gol +-ftree-ter @gol +-funit-at-a-time} + +@item -O2 +@opindex O2 +Optimize even more. GCC performs nearly all supported optimizations +that do not involve a space-speed tradeoff. +As compared to @option{-O}, this option increases both compilation time +and the performance of the generated code. + +@option{-O2} turns on all optimization flags specified by @option{-O1}. It +also turns on the following optimization flags: + +@c Please keep the following list alphabetized! +@gccoptlist{-falign-functions -falign-jumps @gol +-falign-labels -falign-loops @gol +-fcaller-saves @gol +-fcode-hoisting @gol +-fcrossjumping @gol +-fcse-follow-jumps -fcse-skip-blocks @gol +-fdelete-null-pointer-checks @gol +-fdevirtualize -fdevirtualize-speculatively @gol +-fexpensive-optimizations @gol +-ffinite-loops @gol +-fgcse -fgcse-lm @gol +-fhoist-adjacent-loads @gol +-finline-functions @gol +-finline-small-functions @gol +-findirect-inlining @gol +-fipa-bit-cp -fipa-cp -fipa-icf @gol +-fipa-ra -fipa-sra -fipa-vrp @gol +-fisolate-erroneous-paths-dereference @gol +-flra-remat @gol +-foptimize-sibling-calls @gol +-foptimize-strlen @gol +-fpartial-inlining @gol +-fpeephole2 @gol +-freorder-blocks-algorithm=stc @gol +-freorder-blocks-and-partition -freorder-functions @gol +-frerun-cse-after-loop @gol +-fschedule-insns -fschedule-insns2 @gol +-fsched-interblock -fsched-spec @gol +-fstore-merging @gol +-fstrict-aliasing @gol +-fthread-jumps @gol +-ftree-builtin-call-dce @gol +-ftree-loop-vectorize @gol +-ftree-pre @gol +-ftree-slp-vectorize @gol +-ftree-switch-conversion -ftree-tail-merge @gol +-ftree-vrp @gol +-fvect-cost-model=very-cheap} + +Please note the warning under @option{-fgcse} about +invoking @option{-O2} on programs that use computed gotos. + +@item -O3 +@opindex O3 +Optimize yet more. @option{-O3} turns on all optimizations specified +by @option{-O2} and also turns on the following optimization flags: + +@c Please keep the following list alphabetized! +@gccoptlist{-fgcse-after-reload @gol +-fipa-cp-clone +-floop-interchange @gol +-floop-unroll-and-jam @gol +-fpeel-loops @gol +-fpredictive-commoning @gol +-fsplit-loops @gol +-fsplit-paths @gol +-ftree-loop-distribution @gol +-ftree-partial-pre @gol +-funswitch-loops @gol +-fvect-cost-model=dynamic @gol +-fversion-loops-for-strides} + +@item -O0 +@opindex O0 +Reduce compilation time and make debugging produce the expected +results. This is the default. + +@item -Os +@opindex Os +Optimize for size. @option{-Os} enables all @option{-O2} optimizations +except those that often increase code size: + +@gccoptlist{-falign-functions -falign-jumps @gol +-falign-labels -falign-loops @gol +-fprefetch-loop-arrays -freorder-blocks-algorithm=stc} + +It also enables @option{-finline-functions}, causes the compiler to tune for +code size rather than execution speed, and performs further optimizations +designed to reduce code size. + +@item -Ofast +@opindex Ofast +Disregard strict standards compliance. @option{-Ofast} enables all +@option{-O3} optimizations. It also enables optimizations that are not +valid for all standard-compliant programs. +It turns on @option{-ffast-math}, @option{-fallow-store-data-races} +and the Fortran-specific @option{-fstack-arrays}, unless +@option{-fmax-stack-var-size} is specified, and @option{-fno-protect-parens}. +It turns off @option{-fsemantic-interposition}. + +@item -Og +@opindex Og +Optimize debugging experience. @option{-Og} should be the optimization +level of choice for the standard edit-compile-debug cycle, offering +a reasonable level of optimization while maintaining fast compilation +and a good debugging experience. It is a better choice than @option{-O0} +for producing debuggable code because some compiler passes +that collect debug information are disabled at @option{-O0}. + +Like @option{-O0}, @option{-Og} completely disables a number of +optimization passes so that individual options controlling them have +no effect. Otherwise @option{-Og} enables all @option{-O1} +optimization flags except for those that may interfere with debugging: + +@gccoptlist{-fbranch-count-reg -fdelayed-branch @gol +-fdse -fif-conversion -fif-conversion2 @gol +-finline-functions-called-once @gol +-fmove-loop-invariants -fmove-loop-stores -fssa-phiopt @gol +-ftree-bit-ccp -ftree-dse -ftree-pta -ftree-sra} + +@item -Oz +@opindex Oz +Optimize aggressively for size rather than speed. This may increase +the number of instructions executed if those instructions require +fewer bytes to encode. @option{-Oz} behaves similarly to @option{-Os} +including enabling most @option{-O2} optimizations. + +@end table + +If you use multiple @option{-O} options, with or without level numbers, +the last such option is the one that is effective. + +Options of the form @option{-f@var{flag}} specify machine-independent +flags. Most flags have both positive and negative forms; the negative +form of @option{-ffoo} is @option{-fno-foo}. In the table +below, only one of the forms is listed---the one you typically +use. You can figure out the other form by either removing @samp{no-} +or adding it. + +The following options control specific optimizations. They are either +activated by @option{-O} options or are related to ones that are. You +can use the following flags in the rare cases when ``fine-tuning'' of +optimizations to be performed is desired. + +@table @gcctabopt +@item -fno-defer-pop +@opindex fno-defer-pop +@opindex fdefer-pop +For machines that must pop arguments after a function call, always pop +the arguments as soon as each function returns. +At levels @option{-O1} and higher, @option{-fdefer-pop} is the default; +this allows the compiler to let arguments accumulate on the stack for several +function calls and pop them all at once. + +@item -fforward-propagate +@opindex fforward-propagate +Perform a forward propagation pass on RTL@. The pass tries to combine two +instructions and checks if the result can be simplified. If loop unrolling +is active, two passes are performed and the second is scheduled after +loop unrolling. + +This option is enabled by default at optimization levels @option{-O1}, +@option{-O2}, @option{-O3}, @option{-Os}. + +@item -ffp-contract=@var{style} +@opindex ffp-contract +@option{-ffp-contract=off} disables floating-point expression contraction. +@option{-ffp-contract=fast} enables floating-point expression contraction +such as forming of fused multiply-add operations if the target has +native support for them. +@option{-ffp-contract=on} enables floating-point expression contraction +if allowed by the language standard. This is currently not implemented +and treated equal to @option{-ffp-contract=off}. + +The default is @option{-ffp-contract=fast}. + +@item -fomit-frame-pointer +@opindex fomit-frame-pointer +Omit the frame pointer in functions that don't need one. This avoids the +instructions to save, set up and restore the frame pointer; on many targets +it also makes an extra register available. + +On some targets this flag has no effect because the standard calling sequence +always uses a frame pointer, so it cannot be omitted. + +Note that @option{-fno-omit-frame-pointer} doesn't guarantee the frame pointer +is used in all functions. Several targets always omit the frame pointer in +leaf functions. + +Enabled by default at @option{-O1} and higher. + +@item -foptimize-sibling-calls +@opindex foptimize-sibling-calls +Optimize sibling and tail recursive calls. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -foptimize-strlen +@opindex foptimize-strlen +Optimize various standard C string functions (e.g.@: @code{strlen}, +@code{strchr} or @code{strcpy}) and +their @code{_FORTIFY_SOURCE} counterparts into faster alternatives. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -fno-inline +@opindex fno-inline +@opindex finline +Do not expand any functions inline apart from those marked with +the @code{always_inline} attribute. This is the default when not +optimizing. + +Single functions can be exempted from inlining by marking them +with the @code{noinline} attribute. + +@item -finline-small-functions +@opindex finline-small-functions +Integrate functions into their callers when their body is smaller than expected +function call code (so overall size of program gets smaller). The compiler +heuristically decides which functions are simple enough to be worth integrating +in this way. This inlining applies to all functions, even those not declared +inline. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -findirect-inlining +@opindex findirect-inlining +Inline also indirect calls that are discovered to be known at compile +time thanks to previous inlining. This option has any effect only +when inlining itself is turned on by the @option{-finline-functions} +or @option{-finline-small-functions} options. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -finline-functions +@opindex finline-functions +Consider all functions for inlining, even if they are not declared inline. +The compiler heuristically decides which functions are worth integrating +in this way. + +If all calls to a given function are integrated, and the function is +declared @code{static}, then the function is normally not output as +assembler code in its own right. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. Also enabled +by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -finline-functions-called-once +@opindex finline-functions-called-once +Consider all @code{static} functions called once for inlining into their +caller even if they are not marked @code{inline}. If a call to a given +function is integrated, then the function is not output as assembler code +in its own right. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}, +but not @option{-Og}. + +@item -fearly-inlining +@opindex fearly-inlining +Inline functions marked by @code{always_inline} and functions whose body seems +smaller than the function call overhead early before doing +@option{-fprofile-generate} instrumentation and real inlining pass. Doing so +makes profiling significantly cheaper and usually inlining faster on programs +having large chains of nested wrapper functions. + +Enabled by default. + +@item -fipa-sra +@opindex fipa-sra +Perform interprocedural scalar replacement of aggregates, removal of +unused parameters and replacement of parameters passed by reference +by parameters passed by value. + +Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}. + +@item -finline-limit=@var{n} +@opindex finline-limit +By default, GCC limits the size of functions that can be inlined. This flag +allows coarse control of this limit. @var{n} is the size of functions that +can be inlined in number of pseudo instructions. + +Inlining is actually controlled by a number of parameters, which may be +specified individually by using @option{--param @var{name}=@var{value}}. +The @option{-finline-limit=@var{n}} option sets some of these parameters +as follows: + +@table @gcctabopt +@item max-inline-insns-single +is set to @var{n}/2. +@item max-inline-insns-auto +is set to @var{n}/2. +@end table + +See below for a documentation of the individual +parameters controlling inlining and for the defaults of these parameters. + +@emph{Note:} there may be no value to @option{-finline-limit} that results +in default behavior. + +@emph{Note:} pseudo instruction represents, in this particular context, an +abstract measurement of function's size. In no way does it represent a count +of assembly instructions and as such its exact meaning might change from one +release to an another. + +@item -fno-keep-inline-dllexport +@opindex fno-keep-inline-dllexport +@opindex fkeep-inline-dllexport +This is a more fine-grained version of @option{-fkeep-inline-functions}, +which applies only to functions that are declared using the @code{dllexport} +attribute or declspec. @xref{Function Attributes,,Declaring Attributes of +Functions}. + +@item -fkeep-inline-functions +@opindex fkeep-inline-functions +In C, emit @code{static} functions that are declared @code{inline} +into the object file, even if the function has been inlined into all +of its callers. This switch does not affect functions using the +@code{extern inline} extension in GNU C90@. In C++, emit any and all +inline functions into the object file. + +@item -fkeep-static-functions +@opindex fkeep-static-functions +Emit @code{static} functions into the object file, even if the function +is never used. + +@item -fkeep-static-consts +@opindex fkeep-static-consts +Emit variables declared @code{static const} when optimization isn't turned +on, even if the variables aren't referenced. + +GCC enables this option by default. If you want to force the compiler to +check if a variable is referenced, regardless of whether or not +optimization is turned on, use the @option{-fno-keep-static-consts} option. + +@item -fmerge-constants +@opindex fmerge-constants +Attempt to merge identical constants (string constants and floating-point +constants) across compilation units. + +This option is the default for optimized compilation if the assembler and +linker support it. Use @option{-fno-merge-constants} to inhibit this +behavior. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fmerge-all-constants +@opindex fmerge-all-constants +Attempt to merge identical constants and identical variables. + +This option implies @option{-fmerge-constants}. In addition to +@option{-fmerge-constants} this considers e.g.@: even constant initialized +arrays or initialized constant variables with integral or floating-point +types. Languages like C or C++ require each variable, including multiple +instances of the same variable in recursive calls, to have distinct locations, +so using this option results in non-conforming +behavior. + +@item -fmodulo-sched +@opindex fmodulo-sched +Perform swing modulo scheduling immediately before the first scheduling +pass. This pass looks at innermost loops and reorders their +instructions by overlapping different iterations. + +@item -fmodulo-sched-allow-regmoves +@opindex fmodulo-sched-allow-regmoves +Perform more aggressive SMS-based modulo scheduling with register moves +allowed. By setting this flag certain anti-dependences edges are +deleted, which triggers the generation of reg-moves based on the +life-range analysis. This option is effective only with +@option{-fmodulo-sched} enabled. + +@item -fno-branch-count-reg +@opindex fno-branch-count-reg +@opindex fbranch-count-reg +Disable the optimization pass that scans for opportunities to use +``decrement and branch'' instructions on a count register instead of +instruction sequences that decrement a register, compare it against zero, and +then branch based upon the result. This option is only meaningful on +architectures that support such instructions, which include x86, PowerPC, +IA-64 and S/390. Note that the @option{-fno-branch-count-reg} option +doesn't remove the decrement and branch instructions from the generated +instruction stream introduced by other optimization passes. + +The default is @option{-fbranch-count-reg} at @option{-O1} and higher, +except for @option{-Og}. + +@item -fno-function-cse +@opindex fno-function-cse +@opindex ffunction-cse +Do not put function addresses in registers; make each instruction that +calls a constant function contain the function's address explicitly. + +This option results in less efficient code, but some strange hacks +that alter the assembler output may be confused by the optimizations +performed when this option is not used. + +The default is @option{-ffunction-cse} + +@item -fno-zero-initialized-in-bss +@opindex fno-zero-initialized-in-bss +@opindex fzero-initialized-in-bss +If the target supports a BSS section, GCC by default puts variables that +are initialized to zero into BSS@. This can save space in the resulting +code. + +This option turns off this behavior because some programs explicitly +rely on variables going to the data section---e.g., so that the +resulting executable can find the beginning of that section and/or make +assumptions based on that. + +The default is @option{-fzero-initialized-in-bss}. + +@item -fthread-jumps +@opindex fthread-jumps +Perform optimizations that check to see if a jump branches to a +location where another comparison subsumed by the first is found. If +so, the first branch is redirected to either the destination of the +second branch or a point immediately following it, depending on whether +the condition is known to be true or false. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fsplit-wide-types +@opindex fsplit-wide-types +When using a type that occupies multiple registers, such as @code{long +long} on a 32-bit system, split the registers apart and allocate them +independently. This normally generates better code for those types, +but may make debugging more difficult. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, +@option{-Os}. + +@item -fsplit-wide-types-early +@opindex fsplit-wide-types-early +Fully split wide types early, instead of very late. +This option has no effect unless @option{-fsplit-wide-types} is turned on. + +This is the default on some targets. + +@item -fcse-follow-jumps +@opindex fcse-follow-jumps +In common subexpression elimination (CSE), scan through jump instructions +when the target of the jump is not reached by any other path. For +example, when CSE encounters an @code{if} statement with an +@code{else} clause, CSE follows the jump when the condition +tested is false. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fcse-skip-blocks +@opindex fcse-skip-blocks +This is similar to @option{-fcse-follow-jumps}, but causes CSE to +follow jumps that conditionally skip over blocks. When CSE +encounters a simple @code{if} statement with no else clause, +@option{-fcse-skip-blocks} causes CSE to follow the jump around the +body of the @code{if}. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -frerun-cse-after-loop +@opindex frerun-cse-after-loop +Re-run common subexpression elimination after loop optimizations are +performed. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fgcse +@opindex fgcse +Perform a global common subexpression elimination pass. +This pass also performs global constant and copy propagation. + +@emph{Note:} When compiling a program using computed gotos, a GCC +extension, you may get better run-time performance if you disable +the global common subexpression elimination pass by adding +@option{-fno-gcse} to the command line. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fgcse-lm +@opindex fgcse-lm +When @option{-fgcse-lm} is enabled, global common subexpression elimination +attempts to move loads that are only killed by stores into themselves. This +allows a loop containing a load/store sequence to be changed to a load outside +the loop, and a copy/store within the loop. + +Enabled by default when @option{-fgcse} is enabled. + +@item -fgcse-sm +@opindex fgcse-sm +When @option{-fgcse-sm} is enabled, a store motion pass is run after +global common subexpression elimination. This pass attempts to move +stores out of loops. When used in conjunction with @option{-fgcse-lm}, +loops containing a load/store sequence can be changed to a load before +the loop and a store after the loop. + +Not enabled at any optimization level. + +@item -fgcse-las +@opindex fgcse-las +When @option{-fgcse-las} is enabled, the global common subexpression +elimination pass eliminates redundant loads that come after stores to the +same memory location (both partial and full redundancies). + +Not enabled at any optimization level. + +@item -fgcse-after-reload +@opindex fgcse-after-reload +When @option{-fgcse-after-reload} is enabled, a redundant load elimination +pass is performed after reload. The purpose of this pass is to clean up +redundant spilling. + +Enabled by @option{-O3}, @option{-fprofile-use} and @option{-fauto-profile}. + +@item -faggressive-loop-optimizations +@opindex faggressive-loop-optimizations +This option tells the loop optimizer to use language constraints to +derive bounds for the number of iterations of a loop. This assumes that +loop code does not invoke undefined behavior by for example causing signed +integer overflows or out-of-bound array accesses. The bounds for the +number of iterations of a loop are used to guide loop unrolling and peeling +and loop exit test optimizations. +This option is enabled by default. + +@item -funconstrained-commons +@opindex funconstrained-commons +This option tells the compiler that variables declared in common blocks +(e.g.@: Fortran) may later be overridden with longer trailing arrays. This +prevents certain optimizations that depend on knowing the array bounds. + +@item -fcrossjumping +@opindex fcrossjumping +Perform cross-jumping transformation. +This transformation unifies equivalent code and saves code size. The +resulting code may or may not perform better than without cross-jumping. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fauto-inc-dec +@opindex fauto-inc-dec +Combine increments or decrements of addresses with memory accesses. +This pass is always skipped on architectures that do not have +instructions to support this. Enabled by default at @option{-O1} and +higher on architectures that support this. + +@item -fdce +@opindex fdce +Perform dead code elimination (DCE) on RTL@. +Enabled by default at @option{-O1} and higher. + +@item -fdse +@opindex fdse +Perform dead store elimination (DSE) on RTL@. +Enabled by default at @option{-O1} and higher. + +@item -fif-conversion +@opindex fif-conversion +Attempt to transform conditional jumps into branch-less equivalents. This +includes use of conditional moves, min, max, set flags and abs instructions, and +some tricks doable by standard arithmetics. The use of conditional execution +on chips where it is available is controlled by @option{-fif-conversion2}. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, but +not with @option{-Og}. + +@item -fif-conversion2 +@opindex fif-conversion2 +Use conditional execution (where available) to transform conditional jumps into +branch-less equivalents. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, but +not with @option{-Og}. + +@item -fdeclone-ctor-dtor +@opindex fdeclone-ctor-dtor +The C++ ABI requires multiple entry points for constructors and +destructors: one for a base subobject, one for a complete object, and +one for a virtual destructor that calls operator delete afterwards. +For a hierarchy with virtual bases, the base and complete variants are +clones, which means two copies of the function. With this option, the +base and complete variants are changed to be thunks that call a common +implementation. + +Enabled by @option{-Os}. + +@item -fdelete-null-pointer-checks +@opindex fdelete-null-pointer-checks +Assume that programs cannot safely dereference null pointers, and that +no code or data element resides at address zero. +This option enables simple constant +folding optimizations at all optimization levels. In addition, other +optimization passes in GCC use this flag to control global dataflow +analyses that eliminate useless checks for null pointers; these assume +that a memory access to address zero always results in a trap, so +that if a pointer is checked after it has already been dereferenced, +it cannot be null. + +Note however that in some environments this assumption is not true. +Use @option{-fno-delete-null-pointer-checks} to disable this optimization +for programs that depend on that behavior. + +This option is enabled by default on most targets. On Nios II ELF, it +defaults to off. On AVR and MSP430, this option is completely disabled. + +Passes that use the dataflow information +are enabled independently at different optimization levels. + +@item -fdevirtualize +@opindex fdevirtualize +Attempt to convert calls to virtual functions to direct calls. This +is done both within a procedure and interprocedurally as part of +indirect inlining (@option{-findirect-inlining}) and interprocedural constant +propagation (@option{-fipa-cp}). +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fdevirtualize-speculatively +@opindex fdevirtualize-speculatively +Attempt to convert calls to virtual functions to speculative direct calls. +Based on the analysis of the type inheritance graph, determine for a given call +the set of likely targets. If the set is small, preferably of size 1, change +the call into a conditional deciding between direct and indirect calls. The +speculative calls enable more optimizations, such as inlining. When they seem +useless after further optimization, they are converted back into original form. + +@item -fdevirtualize-at-ltrans +@opindex fdevirtualize-at-ltrans +Stream extra information needed for aggressive devirtualization when running +the link-time optimizer in local transformation mode. +This option enables more devirtualization but +significantly increases the size of streamed data. For this reason it is +disabled by default. + +@item -fexpensive-optimizations +@opindex fexpensive-optimizations +Perform a number of minor optimizations that are relatively expensive. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -free +@opindex free +Attempt to remove redundant extension instructions. This is especially +helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit +registers after writing to their lower 32-bit half. + +Enabled for Alpha, AArch64 and x86 at levels @option{-O2}, +@option{-O3}, @option{-Os}. + +@item -fno-lifetime-dse +@opindex fno-lifetime-dse +@opindex flifetime-dse +In C++ the value of an object is only affected by changes within its +lifetime: when the constructor begins, the object has an indeterminate +value, and any changes during the lifetime of the object are dead when +the object is destroyed. Normally dead store elimination will take +advantage of this; if your code relies on the value of the object +storage persisting beyond the lifetime of the object, you can use this +flag to disable this optimization. To preserve stores before the +constructor starts (e.g.@: because your operator new clears the object +storage) but still treat the object as dead after the destructor, you +can use @option{-flifetime-dse=1}. The default behavior can be +explicitly selected with @option{-flifetime-dse=2}. +@option{-flifetime-dse=0} is equivalent to @option{-fno-lifetime-dse}. + +@item -flive-range-shrinkage +@opindex flive-range-shrinkage +Attempt to decrease register pressure through register live range +shrinkage. This is helpful for fast processors with small or moderate +size register sets. + +@item -fira-algorithm=@var{algorithm} +@opindex fira-algorithm +Use the specified coloring algorithm for the integrated register +allocator. The @var{algorithm} argument can be @samp{priority}, which +specifies Chow's priority coloring, or @samp{CB}, which specifies +Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented +for all architectures, but for those targets that do support it, it is +the default because it generates better code. + +@item -fira-region=@var{region} +@opindex fira-region +Use specified regions for the integrated register allocator. The +@var{region} argument should be one of the following: + +@table @samp + +@item all +Use all loops as register allocation regions. +This can give the best results for machines with a small and/or +irregular register set. + +@item mixed +Use all loops except for loops with small register pressure +as the regions. This value usually gives +the best results in most cases and for most architectures, +and is enabled by default when compiling with optimization for speed +(@option{-O}, @option{-O2}, @dots{}). + +@item one +Use all functions as a single region. +This typically results in the smallest code size, and is enabled by default for +@option{-Os} or @option{-O0}. + +@end table + +@item -fira-hoist-pressure +@opindex fira-hoist-pressure +Use IRA to evaluate register pressure in the code hoisting pass for +decisions to hoist expressions. This option usually results in smaller +code, but it can slow the compiler down. + +This option is enabled at level @option{-Os} for all targets. + +@item -fira-loop-pressure +@opindex fira-loop-pressure +Use IRA to evaluate register pressure in loops for decisions to move +loop invariants. This option usually results in generation +of faster and smaller code on machines with large register files (>= 32 +registers), but it can slow the compiler down. + +This option is enabled at level @option{-O3} for some targets. + +@item -fno-ira-share-save-slots +@opindex fno-ira-share-save-slots +@opindex fira-share-save-slots +Disable sharing of stack slots used for saving call-used hard +registers living through a call. Each hard register gets a +separate stack slot, and as a result function stack frames are +larger. + +@item -fno-ira-share-spill-slots +@opindex fno-ira-share-spill-slots +@opindex fira-share-spill-slots +Disable sharing of stack slots allocated for pseudo-registers. Each +pseudo-register that does not get a hard register gets a separate +stack slot, and as a result function stack frames are larger. + +@item -flra-remat +@opindex flra-remat +Enable CFG-sensitive rematerialization in LRA. Instead of loading +values of spilled pseudos, LRA tries to rematerialize (recalculate) +values if it is profitable. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fdelayed-branch +@opindex fdelayed-branch +If supported for the target machine, attempt to reorder instructions +to exploit instruction slots available after delayed branch +instructions. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}, +but not at @option{-Og}. + +@item -fschedule-insns +@opindex fschedule-insns +If supported for the target machine, attempt to reorder instructions to +eliminate execution stalls due to required data being unavailable. This +helps machines that have slow floating point or memory load instructions +by allowing other instructions to be issued until the result of the load +or floating-point instruction is required. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -fschedule-insns2 +@opindex fschedule-insns2 +Similar to @option{-fschedule-insns}, but requests an additional pass of +instruction scheduling after register allocation has been done. This is +especially useful on machines with a relatively small number of +registers and where memory load instructions take more than one cycle. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fno-sched-interblock +@opindex fno-sched-interblock +@opindex fsched-interblock +Disable instruction scheduling across basic blocks, which +is normally enabled when scheduling before register allocation, i.e.@: +with @option{-fschedule-insns} or at @option{-O2} or higher. + +@item -fno-sched-spec +@opindex fno-sched-spec +@opindex fsched-spec +Disable speculative motion of non-load instructions, which +is normally enabled when scheduling before register allocation, i.e.@: +with @option{-fschedule-insns} or at @option{-O2} or higher. + +@item -fsched-pressure +@opindex fsched-pressure +Enable register pressure sensitive insn scheduling before register +allocation. This only makes sense when scheduling before register +allocation is enabled, i.e.@: with @option{-fschedule-insns} or at +@option{-O2} or higher. Usage of this option can improve the +generated code and decrease its size by preventing register pressure +increase above the number of available hard registers and subsequent +spills in register allocation. + +@item -fsched-spec-load +@opindex fsched-spec-load +Allow speculative motion of some load instructions. This only makes +sense when scheduling before register allocation, i.e.@: with +@option{-fschedule-insns} or at @option{-O2} or higher. + +@item -fsched-spec-load-dangerous +@opindex fsched-spec-load-dangerous +Allow speculative motion of more load instructions. This only makes +sense when scheduling before register allocation, i.e.@: with +@option{-fschedule-insns} or at @option{-O2} or higher. + +@item -fsched-stalled-insns +@itemx -fsched-stalled-insns=@var{n} +@opindex fsched-stalled-insns +Define how many insns (if any) can be moved prematurely from the queue +of stalled insns into the ready list during the second scheduling pass. +@option{-fno-sched-stalled-insns} means that no insns are moved +prematurely, @option{-fsched-stalled-insns=0} means there is no limit +on how many queued insns can be moved prematurely. +@option{-fsched-stalled-insns} without a value is equivalent to +@option{-fsched-stalled-insns=1}. + +@item -fsched-stalled-insns-dep +@itemx -fsched-stalled-insns-dep=@var{n} +@opindex fsched-stalled-insns-dep +Define how many insn groups (cycles) are examined for a dependency +on a stalled insn that is a candidate for premature removal from the queue +of stalled insns. This has an effect only during the second scheduling pass, +and only if @option{-fsched-stalled-insns} is used. +@option{-fno-sched-stalled-insns-dep} is equivalent to +@option{-fsched-stalled-insns-dep=0}. +@option{-fsched-stalled-insns-dep} without a value is equivalent to +@option{-fsched-stalled-insns-dep=1}. + +@item -fsched2-use-superblocks +@opindex fsched2-use-superblocks +When scheduling after register allocation, use superblock scheduling. +This allows motion across basic block boundaries, +resulting in faster schedules. This option is experimental, as not all machine +descriptions used by GCC model the CPU closely enough to avoid unreliable +results from the algorithm. + +This only makes sense when scheduling after register allocation, i.e.@: with +@option{-fschedule-insns2} or at @option{-O2} or higher. + +@item -fsched-group-heuristic +@opindex fsched-group-heuristic +Enable the group heuristic in the scheduler. This heuristic favors +the instruction that belongs to a schedule group. This is enabled +by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} +or @option{-fschedule-insns2} or at @option{-O2} or higher. + +@item -fsched-critical-path-heuristic +@opindex fsched-critical-path-heuristic +Enable the critical-path heuristic in the scheduler. This heuristic favors +instructions on the critical path. This is enabled by default when +scheduling is enabled, i.e.@: with @option{-fschedule-insns} +or @option{-fschedule-insns2} or at @option{-O2} or higher. + +@item -fsched-spec-insn-heuristic +@opindex fsched-spec-insn-heuristic +Enable the speculative instruction heuristic in the scheduler. This +heuristic favors speculative instructions with greater dependency weakness. +This is enabled by default when scheduling is enabled, i.e.@: +with @option{-fschedule-insns} or @option{-fschedule-insns2} +or at @option{-O2} or higher. + +@item -fsched-rank-heuristic +@opindex fsched-rank-heuristic +Enable the rank heuristic in the scheduler. This heuristic favors +the instruction belonging to a basic block with greater size or frequency. +This is enabled by default when scheduling is enabled, i.e.@: +with @option{-fschedule-insns} or @option{-fschedule-insns2} or +at @option{-O2} or higher. + +@item -fsched-last-insn-heuristic +@opindex fsched-last-insn-heuristic +Enable the last-instruction heuristic in the scheduler. This heuristic +favors the instruction that is less dependent on the last instruction +scheduled. This is enabled by default when scheduling is enabled, +i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or +at @option{-O2} or higher. + +@item -fsched-dep-count-heuristic +@opindex fsched-dep-count-heuristic +Enable the dependent-count heuristic in the scheduler. This heuristic +favors the instruction that has more instructions depending on it. +This is enabled by default when scheduling is enabled, i.e.@: +with @option{-fschedule-insns} or @option{-fschedule-insns2} or +at @option{-O2} or higher. + +@item -freschedule-modulo-scheduled-loops +@opindex freschedule-modulo-scheduled-loops +Modulo scheduling is performed before traditional scheduling. If a loop +is modulo scheduled, later scheduling passes may change its schedule. +Use this option to control that behavior. + +@item -fselective-scheduling +@opindex fselective-scheduling +Schedule instructions using selective scheduling algorithm. Selective +scheduling runs instead of the first scheduler pass. + +@item -fselective-scheduling2 +@opindex fselective-scheduling2 +Schedule instructions using selective scheduling algorithm. Selective +scheduling runs instead of the second scheduler pass. + +@item -fsel-sched-pipelining +@opindex fsel-sched-pipelining +Enable software pipelining of innermost loops during selective scheduling. +This option has no effect unless one of @option{-fselective-scheduling} or +@option{-fselective-scheduling2} is turned on. + +@item -fsel-sched-pipelining-outer-loops +@opindex fsel-sched-pipelining-outer-loops +When pipelining loops during selective scheduling, also pipeline outer loops. +This option has no effect unless @option{-fsel-sched-pipelining} is turned on. + +@item -fsemantic-interposition +@opindex fsemantic-interposition +Some object formats, like ELF, allow interposing of symbols by the +dynamic linker. +This means that for symbols exported from the DSO, the compiler cannot perform +interprocedural propagation, inlining and other optimizations in anticipation +that the function or variable in question may change. While this feature is +useful, for example, to rewrite memory allocation functions by a debugging +implementation, it is expensive in the terms of code quality. +With @option{-fno-semantic-interposition} the compiler assumes that +if interposition happens for functions the overwriting function will have +precisely the same semantics (and side effects). +Similarly if interposition happens +for variables, the constructor of the variable will be the same. The flag +has no effect for functions explicitly declared inline +(where it is never allowed for interposition to change semantics) +and for symbols explicitly declared weak. + +@item -fshrink-wrap +@opindex fshrink-wrap +Emit function prologues only before parts of the function that need it, +rather than at the top of the function. This flag is enabled by default at +@option{-O} and higher. + +@item -fshrink-wrap-separate +@opindex fshrink-wrap-separate +Shrink-wrap separate parts of the prologue and epilogue separately, so that +those parts are only executed when needed. +This option is on by default, but has no effect unless @option{-fshrink-wrap} +is also turned on and the target supports this. + +@item -fcaller-saves +@opindex fcaller-saves +Enable allocation of values to registers that are clobbered by +function calls, by emitting extra instructions to save and restore the +registers around such calls. Such allocation is done only when it +seems to result in better code. + +This option is always enabled by default on certain machines, usually +those which have no call-preserved registers to use instead. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fcombine-stack-adjustments +@opindex fcombine-stack-adjustments +Tracks stack adjustments (pushes and pops) and stack memory references +and then tries to find ways to combine them. + +Enabled by default at @option{-O1} and higher. + +@item -fipa-ra +@opindex fipa-ra +Use caller save registers for allocation if those registers are not used by +any called function. In that case it is not necessary to save and restore +them around calls. This is only possible if called functions are part of +same compilation unit as current function and they are compiled before it. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}, however the option +is disabled if generated code will be instrumented for profiling +(@option{-p}, or @option{-pg}) or if callee's register usage cannot be known +exactly (this happens on targets that do not expose prologues +and epilogues in RTL). + +@item -fconserve-stack +@opindex fconserve-stack +Attempt to minimize stack usage. The compiler attempts to use less +stack space, even if that makes the program slower. This option +implies setting the @option{large-stack-frame} parameter to 100 +and the @option{large-stack-frame-growth} parameter to 400. + +@item -ftree-reassoc +@opindex ftree-reassoc +Perform reassociation on trees. This flag is enabled by default +at @option{-O1} and higher. + +@item -fcode-hoisting +@opindex fcode-hoisting +Perform code hoisting. Code hoisting tries to move the +evaluation of expressions executed on all paths to the function exit +as early as possible. This is especially useful as a code size +optimization, but it often helps for code speed as well. +This flag is enabled by default at @option{-O2} and higher. + +@item -ftree-pre +@opindex ftree-pre +Perform partial redundancy elimination (PRE) on trees. This flag is +enabled by default at @option{-O2} and @option{-O3}. + +@item -ftree-partial-pre +@opindex ftree-partial-pre +Make partial redundancy elimination (PRE) more aggressive. This flag is +enabled by default at @option{-O3}. + +@item -ftree-forwprop +@opindex ftree-forwprop +Perform forward propagation on trees. This flag is enabled by default +at @option{-O1} and higher. + +@item -ftree-fre +@opindex ftree-fre +Perform full redundancy elimination (FRE) on trees. The difference +between FRE and PRE is that FRE only considers expressions +that are computed on all paths leading to the redundant computation. +This analysis is faster than PRE, though it exposes fewer redundancies. +This flag is enabled by default at @option{-O1} and higher. + +@item -ftree-phiprop +@opindex ftree-phiprop +Perform hoisting of loads from conditional pointers on trees. This +pass is enabled by default at @option{-O1} and higher. + +@item -fhoist-adjacent-loads +@opindex fhoist-adjacent-loads +Speculatively hoist loads from both branches of an if-then-else if the +loads are from adjacent locations in the same structure and the target +architecture has a conditional move instruction. This flag is enabled +by default at @option{-O2} and higher. + +@item -ftree-copy-prop +@opindex ftree-copy-prop +Perform copy propagation on trees. This pass eliminates unnecessary +copy operations. This flag is enabled by default at @option{-O1} and +higher. + +@item -fipa-pure-const +@opindex fipa-pure-const +Discover which functions are pure or constant. +Enabled by default at @option{-O1} and higher. + +@item -fipa-reference +@opindex fipa-reference +Discover which static variables do not escape the +compilation unit. +Enabled by default at @option{-O1} and higher. + +@item -fipa-reference-addressable +@opindex fipa-reference-addressable +Discover read-only, write-only and non-addressable static variables. +Enabled by default at @option{-O1} and higher. + +@item -fipa-stack-alignment +@opindex fipa-stack-alignment +Reduce stack alignment on call sites if possible. +Enabled by default. + +@item -fipa-pta +@opindex fipa-pta +Perform interprocedural pointer analysis and interprocedural modification +and reference analysis. This option can cause excessive memory and +compile-time usage on large compilation units. It is not enabled by +default at any optimization level. + +@item -fipa-profile +@opindex fipa-profile +Perform interprocedural profile propagation. The functions called only from +cold functions are marked as cold. Also functions executed once (such as +@code{cold}, @code{noreturn}, static constructors or destructors) are +identified. Cold functions and loop less parts of functions executed once are +then optimized for size. +Enabled by default at @option{-O1} and higher. + +@item -fipa-modref +@opindex fipa-modref +Perform interprocedural mod/ref analysis. This optimization analyzes the side +effects of functions (memory locations that are modified or referenced) and +enables better optimization across the function call boundary. This flag is +enabled by default at @option{-O1} and higher. + +@item -fipa-cp +@opindex fipa-cp +Perform interprocedural constant propagation. +This optimization analyzes the program to determine when values passed +to functions are constants and then optimizes accordingly. +This optimization can substantially increase performance +if the application has constants passed to functions. +This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}. +It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -fipa-cp-clone +@opindex fipa-cp-clone +Perform function cloning to make interprocedural constant propagation stronger. +When enabled, interprocedural constant propagation performs function cloning +when externally visible function can be called with constant arguments. +Because this optimization can create multiple copies of functions, +it may significantly increase code size +(see @option{--param ipa-cp-unit-growth=@var{value}}). +This flag is enabled by default at @option{-O3}. +It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -fipa-bit-cp +@opindex fipa-bit-cp +When enabled, perform interprocedural bitwise constant +propagation. This flag is enabled by default at @option{-O2} and +by @option{-fprofile-use} and @option{-fauto-profile}. +It requires that @option{-fipa-cp} is enabled. + +@item -fipa-vrp +@opindex fipa-vrp +When enabled, perform interprocedural propagation of value +ranges. This flag is enabled by default at @option{-O2}. It requires +that @option{-fipa-cp} is enabled. + +@item -fipa-icf +@opindex fipa-icf +Perform Identical Code Folding for functions and read-only variables. +The optimization reduces code size and may disturb unwind stacks by replacing +a function by equivalent one with a different name. The optimization works +more effectively with link-time optimization enabled. + +Although the behavior is similar to the Gold Linker's ICF optimization, GCC ICF +works on different levels and thus the optimizations are not same - there are +equivalences that are found only by GCC and equivalences found only by Gold. + +This flag is enabled by default at @option{-O2} and @option{-Os}. + +@item -flive-patching=@var{level} +@opindex flive-patching +Control GCC's optimizations to produce output suitable for live-patching. + +If the compiler's optimization uses a function's body or information extracted +from its body to optimize/change another function, the latter is called an +impacted function of the former. If a function is patched, its impacted +functions should be patched too. + +The impacted functions are determined by the compiler's interprocedural +optimizations. For example, a caller is impacted when inlining a function +into its caller, +cloning a function and changing its caller to call this new clone, +or extracting a function's pureness/constness information to optimize +its direct or indirect callers, etc. + +Usually, the more IPA optimizations enabled, the larger the number of +impacted functions for each function. In order to control the number of +impacted functions and more easily compute the list of impacted function, +IPA optimizations can be partially enabled at two different levels. + +The @var{level} argument should be one of the following: + +@table @samp + +@item inline-clone + +Only enable inlining and cloning optimizations, which includes inlining, +cloning, interprocedural scalar replacement of aggregates and partial inlining. +As a result, when patching a function, all its callers and its clones' +callers are impacted, therefore need to be patched as well. + +@option{-flive-patching=inline-clone} disables the following optimization flags: +@gccoptlist{-fwhole-program -fipa-pta -fipa-reference -fipa-ra @gol +-fipa-icf -fipa-icf-functions -fipa-icf-variables @gol +-fipa-bit-cp -fipa-vrp -fipa-pure-const -fipa-reference-addressable @gol +-fipa-stack-alignment -fipa-modref} + +@item inline-only-static + +Only enable inlining of static functions. +As a result, when patching a static function, all its callers are impacted +and so need to be patched as well. + +In addition to all the flags that @option{-flive-patching=inline-clone} +disables, +@option{-flive-patching=inline-only-static} disables the following additional +optimization flags: +@gccoptlist{-fipa-cp-clone -fipa-sra -fpartial-inlining -fipa-cp} + +@end table + +When @option{-flive-patching} is specified without any value, the default value +is @var{inline-clone}. + +This flag is disabled by default. + +Note that @option{-flive-patching} is not supported with link-time optimization +(@option{-flto}). + +@item -fisolate-erroneous-paths-dereference +@opindex fisolate-erroneous-paths-dereference +Detect paths that trigger erroneous or undefined behavior due to +dereferencing a null pointer. Isolate those paths from the main control +flow and turn the statement with erroneous or undefined behavior into a trap. +This flag is enabled by default at @option{-O2} and higher and depends on +@option{-fdelete-null-pointer-checks} also being enabled. + +@item -fisolate-erroneous-paths-attribute +@opindex fisolate-erroneous-paths-attribute +Detect paths that trigger erroneous or undefined behavior due to a null value +being used in a way forbidden by a @code{returns_nonnull} or @code{nonnull} +attribute. Isolate those paths from the main control flow and turn the +statement with erroneous or undefined behavior into a trap. This is not +currently enabled, but may be enabled by @option{-O2} in the future. + +@item -ftree-sink +@opindex ftree-sink +Perform forward store motion on trees. This flag is +enabled by default at @option{-O1} and higher. + +@item -ftree-bit-ccp +@opindex ftree-bit-ccp +Perform sparse conditional bit constant propagation on trees and propagate +pointer alignment information. +This pass only operates on local scalar variables and is enabled by default +at @option{-O1} and higher, except for @option{-Og}. +It requires that @option{-ftree-ccp} is enabled. + +@item -ftree-ccp +@opindex ftree-ccp +Perform sparse conditional constant propagation (CCP) on trees. This +pass only operates on local scalar variables and is enabled by default +at @option{-O1} and higher. + +@item -fssa-backprop +@opindex fssa-backprop +Propagate information about uses of a value up the definition chain +in order to simplify the definitions. For example, this pass strips +sign operations if the sign of a value never matters. The flag is +enabled by default at @option{-O1} and higher. + +@item -fssa-phiopt +@opindex fssa-phiopt +Perform pattern matching on SSA PHI nodes to optimize conditional +code. This pass is enabled by default at @option{-O1} and higher, +except for @option{-Og}. + +@item -ftree-switch-conversion +@opindex ftree-switch-conversion +Perform conversion of simple initializations in a switch to +initializations from a scalar array. This flag is enabled by default +at @option{-O2} and higher. + +@item -ftree-tail-merge +@opindex ftree-tail-merge +Look for identical code sequences. When found, replace one with a jump to the +other. This optimization is known as tail merging or cross jumping. This flag +is enabled by default at @option{-O2} and higher. The compilation time +in this pass can +be limited using @option{max-tail-merge-comparisons} parameter and +@option{max-tail-merge-iterations} parameter. + +@item -ftree-dce +@opindex ftree-dce +Perform dead code elimination (DCE) on trees. This flag is enabled by +default at @option{-O1} and higher. + +@item -ftree-builtin-call-dce +@opindex ftree-builtin-call-dce +Perform conditional dead code elimination (DCE) for calls to built-in functions +that may set @code{errno} but are otherwise free of side effects. This flag is +enabled by default at @option{-O2} and higher if @option{-Os} is not also +specified. + +@item -ffinite-loops +@opindex ffinite-loops +@opindex fno-finite-loops +Assume that a loop with an exit will eventually take the exit and not loop +indefinitely. This allows the compiler to remove loops that otherwise have +no side-effects, not considering eventual endless looping as such. + +This option is enabled by default at @option{-O2} for C++ with -std=c++11 +or higher. + +@item -ftree-dominator-opts +@opindex ftree-dominator-opts +Perform a variety of simple scalar cleanups (constant/copy +propagation, redundancy elimination, range propagation and expression +simplification) based on a dominator tree traversal. This also +performs jump threading (to reduce jumps to jumps). This flag is +enabled by default at @option{-O1} and higher. + +@item -ftree-dse +@opindex ftree-dse +Perform dead store elimination (DSE) on trees. A dead store is a store into +a memory location that is later overwritten by another store without +any intervening loads. In this case the earlier store can be deleted. This +flag is enabled by default at @option{-O1} and higher. + +@item -ftree-ch +@opindex ftree-ch +Perform loop header copying on trees. This is beneficial since it increases +effectiveness of code motion optimizations. It also saves one jump. This flag +is enabled by default at @option{-O1} and higher. It is not enabled +for @option{-Os}, since it usually increases code size. + +@item -ftree-loop-optimize +@opindex ftree-loop-optimize +Perform loop optimizations on trees. This flag is enabled by default +at @option{-O1} and higher. + +@item -ftree-loop-linear +@itemx -floop-strip-mine +@itemx -floop-block +@opindex ftree-loop-linear +@opindex floop-strip-mine +@opindex floop-block +Perform loop nest optimizations. Same as +@option{-floop-nest-optimize}. To use this code transformation, GCC has +to be configured with @option{--with-isl} to enable the Graphite loop +transformation infrastructure. + +@item -fgraphite-identity +@opindex fgraphite-identity +Enable the identity transformation for graphite. For every SCoP we generate +the polyhedral representation and transform it back to gimple. Using +@option{-fgraphite-identity} we can check the costs or benefits of the +GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations +are also performed by the code generator isl, like index splitting and +dead code elimination in loops. + +@item -floop-nest-optimize +@opindex floop-nest-optimize +Enable the isl based loop nest optimizer. This is a generic loop nest +optimizer based on the Pluto optimization algorithms. It calculates a loop +structure optimized for data-locality and parallelism. This option +is experimental. + +@item -floop-parallelize-all +@opindex floop-parallelize-all +Use the Graphite data dependence analysis to identify loops that can +be parallelized. Parallelize all the loops that can be analyzed to +not contain loop carried dependences without checking that it is +profitable to parallelize the loops. + +@item -ftree-coalesce-vars +@opindex ftree-coalesce-vars +While transforming the program out of the SSA representation, attempt to +reduce copying by coalescing versions of different user-defined +variables, instead of just compiler temporaries. This may severely +limit the ability to debug an optimized program compiled with +@option{-fno-var-tracking-assignments}. In the negated form, this flag +prevents SSA coalescing of user variables. This option is enabled by +default if optimization is enabled, and it does very little otherwise. + +@item -ftree-loop-if-convert +@opindex ftree-loop-if-convert +Attempt to transform conditional jumps in the innermost loops to +branch-less equivalents. The intent is to remove control-flow from +the innermost loops in order to improve the ability of the +vectorization pass to handle these loops. This is enabled by default +if vectorization is enabled. + +@item -ftree-loop-distribution +@opindex ftree-loop-distribution +Perform loop distribution. This flag can improve cache performance on +big loop bodies and allow further loop optimizations, like +parallelization or vectorization, to take place. For example, the loop +@smallexample +DO I = 1, N + A(I) = B(I) + C + D(I) = E(I) * F +ENDDO +@end smallexample +is transformed to +@smallexample +DO I = 1, N + A(I) = B(I) + C +ENDDO +DO I = 1, N + D(I) = E(I) * F +ENDDO +@end smallexample +This flag is enabled by default at @option{-O3}. +It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -ftree-loop-distribute-patterns +@opindex ftree-loop-distribute-patterns +Perform loop distribution of patterns that can be code generated with +calls to a library. This flag is enabled by default at @option{-O2} and +higher, and by @option{-fprofile-use} and @option{-fauto-profile}. + +This pass distributes the initialization loops and generates a call to +memset zero. For example, the loop +@smallexample +DO I = 1, N + A(I) = 0 + B(I) = A(I) + I +ENDDO +@end smallexample +is transformed to +@smallexample +DO I = 1, N + A(I) = 0 +ENDDO +DO I = 1, N + B(I) = A(I) + I +ENDDO +@end smallexample +and the initialization loop is transformed into a call to memset zero. +This flag is enabled by default at @option{-O3}. +It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -floop-interchange +@opindex floop-interchange +Perform loop interchange outside of graphite. This flag can improve cache +performance on loop nest and allow further loop optimizations, like +vectorization, to take place. For example, the loop +@smallexample +for (int i = 0; i < N; i++) + for (int j = 0; j < N; j++) + for (int k = 0; k < N; k++) + c[i][j] = c[i][j] + a[i][k]*b[k][j]; +@end smallexample +is transformed to +@smallexample +for (int i = 0; i < N; i++) + for (int k = 0; k < N; k++) + for (int j = 0; j < N; j++) + c[i][j] = c[i][j] + a[i][k]*b[k][j]; +@end smallexample +This flag is enabled by default at @option{-O3}. +It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -floop-unroll-and-jam +@opindex floop-unroll-and-jam +Apply unroll and jam transformations on feasible loops. In a loop +nest this unrolls the outer loop by some factor and fuses the resulting +multiple inner loops. This flag is enabled by default at @option{-O3}. +It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -ftree-loop-im +@opindex ftree-loop-im +Perform loop invariant motion on trees. This pass moves only invariants that +are hard to handle at RTL level (function calls, operations that expand to +nontrivial sequences of insns). With @option{-funswitch-loops} it also moves +operands of conditions that are invariant out of the loop, so that we can use +just trivial invariantness analysis in loop unswitching. The pass also includes +store motion. + +@item -ftree-loop-ivcanon +@opindex ftree-loop-ivcanon +Create a canonical counter for number of iterations in loops for which +determining number of iterations requires complicated analysis. Later +optimizations then may determine the number easily. Useful especially +in connection with unrolling. + +@item -ftree-scev-cprop +@opindex ftree-scev-cprop +Perform final value replacement. If a variable is modified in a loop +in such a way that its value when exiting the loop can be determined using +only its initial value and the number of loop iterations, replace uses of +the final value by such a computation, provided it is sufficiently cheap. +This reduces data dependencies and may allow further simplifications. +Enabled by default at @option{-O1} and higher. + +@item -fivopts +@opindex fivopts +Perform induction variable optimizations (strength reduction, induction +variable merging and induction variable elimination) on trees. + +@item -ftree-parallelize-loops=n +@opindex ftree-parallelize-loops +Parallelize loops, i.e., split their iteration space to run in n threads. +This is only possible for loops whose iterations are independent +and can be arbitrarily reordered. The optimization is only +profitable on multiprocessor machines, for loops that are CPU-intensive, +rather than constrained e.g.@: by memory bandwidth. This option +implies @option{-pthread}, and thus is only supported on targets +that have support for @option{-pthread}. + +@item -ftree-pta +@opindex ftree-pta +Perform function-local points-to analysis on trees. This flag is +enabled by default at @option{-O1} and higher, except for @option{-Og}. + +@item -ftree-sra +@opindex ftree-sra +Perform scalar replacement of aggregates. This pass replaces structure +references with scalars to prevent committing structures to memory too +early. This flag is enabled by default at @option{-O1} and higher, +except for @option{-Og}. + +@item -fstore-merging +@opindex fstore-merging +Perform merging of narrow stores to consecutive memory addresses. This pass +merges contiguous stores of immediate values narrower than a word into fewer +wider stores to reduce the number of instructions. This is enabled by default +at @option{-O2} and higher as well as @option{-Os}. + +@item -ftree-ter +@opindex ftree-ter +Perform temporary expression replacement during the SSA->normal phase. Single +use/single def temporaries are replaced at their use location with their +defining expression. This results in non-GIMPLE code, but gives the expanders +much more complex trees to work on resulting in better RTL generation. This is +enabled by default at @option{-O1} and higher. + +@item -ftree-slsr +@opindex ftree-slsr +Perform straight-line strength reduction on trees. This recognizes related +expressions involving multiplications and replaces them by less expensive +calculations when possible. This is enabled by default at @option{-O1} and +higher. + +@item -ftree-vectorize +@opindex ftree-vectorize +Perform vectorization on trees. This flag enables @option{-ftree-loop-vectorize} +and @option{-ftree-slp-vectorize} if not explicitly specified. + +@item -ftree-loop-vectorize +@opindex ftree-loop-vectorize +Perform loop vectorization on trees. This flag is enabled by default at +@option{-O2} and by @option{-ftree-vectorize}, @option{-fprofile-use}, +and @option{-fauto-profile}. + +@item -ftree-slp-vectorize +@opindex ftree-slp-vectorize +Perform basic block vectorization on trees. This flag is enabled by default at +@option{-O2} and by @option{-ftree-vectorize}, @option{-fprofile-use}, +and @option{-fauto-profile}. + +@item -ftrivial-auto-var-init=@var{choice} +@opindex ftrivial-auto-var-init +Initialize automatic variables with either a pattern or with zeroes to increase +the security and predictability of a program by preventing uninitialized memory +disclosure and use. +GCC still considers an automatic variable that doesn't have an explicit +initializer as uninitialized, @option{-Wuninitialized} and +@option{-Wanalyzer-use-of-uninitialized-value} will still report +warning messages on such automatic variables. +With this option, GCC will also initialize any padding of automatic variables +that have structure or union types to zeroes. +However, the current implementation cannot initialize automatic variables that +are declared between the controlling expression and the first case of a +@code{switch} statement. Using @option{-Wtrivial-auto-var-init} to report all +such cases. + +The three values of @var{choice} are: + +@itemize @bullet +@item +@samp{uninitialized} doesn't initialize any automatic variables. +This is C and C++'s default. + +@item +@samp{pattern} Initialize automatic variables with values which will likely +transform logic bugs into crashes down the line, are easily recognized in a +crash dump and without being values that programmers can rely on for useful +program semantics. +The current value is byte-repeatable pattern with byte "0xFE". +The values used for pattern initialization might be changed in the future. + +@item +@samp{zero} Initialize automatic variables with zeroes. +@end itemize + +The default is @samp{uninitialized}. + +You can control this behavior for a specific variable by using the variable +attribute @code{uninitialized} (@pxref{Variable Attributes}). + +@item -fvect-cost-model=@var{model} +@opindex fvect-cost-model +Alter the cost model used for vectorization. The @var{model} argument +should be one of @samp{unlimited}, @samp{dynamic}, @samp{cheap} or +@samp{very-cheap}. +With the @samp{unlimited} model the vectorized code-path is assumed +to be profitable while with the @samp{dynamic} model a runtime check +guards the vectorized code-path to enable it only for iteration +counts that will likely execute faster than when executing the original +scalar loop. The @samp{cheap} model disables vectorization of +loops where doing so would be cost prohibitive for example due to +required runtime checks for data dependence or alignment but otherwise +is equal to the @samp{dynamic} model. The @samp{very-cheap} model only +allows vectorization if the vector code would entirely replace the +scalar code that is being vectorized. For example, if each iteration +of a vectorized loop would only be able to handle exactly four iterations +of the scalar loop, the @samp{very-cheap} model would only allow +vectorization if the scalar iteration count is known to be a multiple +of four. + +The default cost model depends on other optimization flags and is +either @samp{dynamic} or @samp{cheap}. + +@item -fsimd-cost-model=@var{model} +@opindex fsimd-cost-model +Alter the cost model used for vectorization of loops marked with the OpenMP +simd directive. The @var{model} argument should be one of +@samp{unlimited}, @samp{dynamic}, @samp{cheap}. All values of @var{model} +have the same meaning as described in @option{-fvect-cost-model} and by +default a cost model defined with @option{-fvect-cost-model} is used. + +@item -ftree-vrp +@opindex ftree-vrp +Perform Value Range Propagation on trees. This is similar to the +constant propagation pass, but instead of values, ranges of values are +propagated. This allows the optimizers to remove unnecessary range +checks like array bound checks and null pointer checks. This is +enabled by default at @option{-O2} and higher. Null pointer check +elimination is only done if @option{-fdelete-null-pointer-checks} is +enabled. + +@item -fsplit-paths +@opindex fsplit-paths +Split paths leading to loop backedges. This can improve dead code +elimination and common subexpression elimination. This is enabled by +default at @option{-O3} and above. + +@item -fsplit-ivs-in-unroller +@opindex fsplit-ivs-in-unroller +Enables expression of values of induction variables in later iterations +of the unrolled loop using the value in the first iteration. This breaks +long dependency chains, thus improving efficiency of the scheduling passes. + +A combination of @option{-fweb} and CSE is often sufficient to obtain the +same effect. However, that is not reliable in cases where the loop body +is more complicated than a single basic block. It also does not work at all +on some architectures due to restrictions in the CSE pass. + +This optimization is enabled by default. + +@item -fvariable-expansion-in-unroller +@opindex fvariable-expansion-in-unroller +With this option, the compiler creates multiple copies of some +local variables when unrolling a loop, which can result in superior code. + +This optimization is enabled by default for PowerPC targets, but disabled +by default otherwise. + +@item -fpartial-inlining +@opindex fpartial-inlining +Inline parts of functions. This option has any effect only +when inlining itself is turned on by the @option{-finline-functions} +or @option{-finline-small-functions} options. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fpredictive-commoning +@opindex fpredictive-commoning +Perform predictive commoning optimization, i.e., reusing computations +(especially memory loads and stores) performed in previous +iterations of loops. + +This option is enabled at level @option{-O3}. +It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -fprefetch-loop-arrays +@opindex fprefetch-loop-arrays +If supported by the target machine, generate instructions to prefetch +memory to improve the performance of loops that access large arrays. + +This option may generate better or worse code; results are highly +dependent on the structure of loops within the source code. + +Disabled at level @option{-Os}. + +@item -fno-printf-return-value +@opindex fno-printf-return-value +@opindex fprintf-return-value +Do not substitute constants for known return value of formatted output +functions such as @code{sprintf}, @code{snprintf}, @code{vsprintf}, and +@code{vsnprintf} (but not @code{printf} of @code{fprintf}). This +transformation allows GCC to optimize or even eliminate branches based +on the known return value of these functions called with arguments that +are either constant, or whose values are known to be in a range that +makes determining the exact return value possible. For example, when +@option{-fprintf-return-value} is in effect, both the branch and the +body of the @code{if} statement (but not the call to @code{snprint}) +can be optimized away when @code{i} is a 32-bit or smaller integer +because the return value is guaranteed to be at most 8. + +@smallexample +char buf[9]; +if (snprintf (buf, "%08x", i) >= sizeof buf) + @dots{} +@end smallexample + +The @option{-fprintf-return-value} option relies on other optimizations +and yields best results with @option{-O2} and above. It works in tandem +with the @option{-Wformat-overflow} and @option{-Wformat-truncation} +options. The @option{-fprintf-return-value} option is enabled by default. + +@item -fno-peephole +@itemx -fno-peephole2 +@opindex fno-peephole +@opindex fpeephole +@opindex fno-peephole2 +@opindex fpeephole2 +Disable any machine-specific peephole optimizations. The difference +between @option{-fno-peephole} and @option{-fno-peephole2} is in how they +are implemented in the compiler; some targets use one, some use the +other, a few use both. + +@option{-fpeephole} is enabled by default. +@option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fno-guess-branch-probability +@opindex fno-guess-branch-probability +@opindex fguess-branch-probability +Do not guess branch probabilities using heuristics. + +GCC uses heuristics to guess branch probabilities if they are +not provided by profiling feedback (@option{-fprofile-arcs}). These +heuristics are based on the control flow graph. If some branch probabilities +are specified by @code{__builtin_expect}, then the heuristics are +used to guess branch probabilities for the rest of the control flow graph, +taking the @code{__builtin_expect} info into account. The interactions +between the heuristics and @code{__builtin_expect} can be complex, and in +some cases, it may be useful to disable the heuristics so that the effects +of @code{__builtin_expect} are easier to understand. + +It is also possible to specify expected probability of the expression +with @code{__builtin_expect_with_probability} built-in function. + +The default is @option{-fguess-branch-probability} at levels +@option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. + +@item -freorder-blocks +@opindex freorder-blocks +Reorder basic blocks in the compiled function in order to reduce number of +taken branches and improve code locality. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. + +@item -freorder-blocks-algorithm=@var{algorithm} +@opindex freorder-blocks-algorithm +Use the specified algorithm for basic block reordering. The +@var{algorithm} argument can be @samp{simple}, which does not increase +code size (except sometimes due to secondary effects like alignment), +or @samp{stc}, the ``software trace cache'' algorithm, which tries to +put all often executed code together, minimizing the number of branches +executed by making extra copies of code. + +The default is @samp{simple} at levels @option{-O1}, @option{-Os}, and +@samp{stc} at levels @option{-O2}, @option{-O3}. + +@item -freorder-blocks-and-partition +@opindex freorder-blocks-and-partition +In addition to reordering basic blocks in the compiled function, in order +to reduce number of taken branches, partitions hot and cold basic blocks +into separate sections of the assembly and @file{.o} files, to improve +paging and cache locality performance. + +This optimization is automatically turned off in the presence of +exception handling or unwind tables (on targets using setjump/longjump or target specific scheme), for linkonce sections, for functions with a user-defined +section attribute and on any architecture that does not support named +sections. When @option{-fsplit-stack} is used this option is not +enabled by default (to avoid linker errors), but may be enabled +explicitly (if using a working linker). + +Enabled for x86 at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -freorder-functions +@opindex freorder-functions +Reorder functions in the object file in order to +improve code locality. This is implemented by using special +subsections @code{.text.hot} for most frequently executed functions and +@code{.text.unlikely} for unlikely executed functions. Reordering is done by +the linker so object file format must support named sections and linker must +place them in a reasonable way. + +This option isn't effective unless you either provide profile feedback +(see @option{-fprofile-arcs} for details) or manually annotate functions with +@code{hot} or @code{cold} attributes (@pxref{Common Function Attributes}). + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fstrict-aliasing +@opindex fstrict-aliasing +Allow the compiler to assume the strictest aliasing rules applicable to +the language being compiled. For C (and C++), this activates +optimizations based on the type of expressions. In particular, an +object of one type is assumed never to reside at the same address as an +object of a different type, unless the types are almost the same. For +example, an @code{unsigned int} can alias an @code{int}, but not a +@code{void*} or a @code{double}. A character type may alias any other +type. + +@anchor{Type-punning}Pay special attention to code like this: +@smallexample +union a_union @{ + int i; + double d; +@}; + +int f() @{ + union a_union t; + t.d = 3.0; + return t.i; +@} +@end smallexample +The practice of reading from a different union member than the one most +recently written to (called ``type-punning'') is common. Even with +@option{-fstrict-aliasing}, type-punning is allowed, provided the memory +is accessed through the union type. So, the code above works as +expected. @xref{Structures unions enumerations and bit-fields +implementation}. However, this code might not: +@smallexample +int f() @{ + union a_union t; + int* ip; + t.d = 3.0; + ip = &t.i; + return *ip; +@} +@end smallexample + +Similarly, access by taking the address, casting the resulting pointer +and dereferencing the result has undefined behavior, even if the cast +uses a union type, e.g.: +@smallexample +int f() @{ + double d = 3.0; + return ((union a_union *) &d)->i; +@} +@end smallexample + +The @option{-fstrict-aliasing} option is enabled at levels +@option{-O2}, @option{-O3}, @option{-Os}. + +@item -fipa-strict-aliasing +@opindex fipa-strict-aliasing +Controls whether rules of @option{-fstrict-aliasing} are applied across +function boundaries. Note that if multiple functions gets inlined into a +single function the memory accesses are no longer considered to be crossing a +function boundary. + +The @option{-fipa-strict-aliasing} option is enabled by default and is +effective only in combination with @option{-fstrict-aliasing}. + +@item -falign-functions +@itemx -falign-functions=@var{n} +@itemx -falign-functions=@var{n}:@var{m} +@itemx -falign-functions=@var{n}:@var{m}:@var{n2} +@itemx -falign-functions=@var{n}:@var{m}:@var{n2}:@var{m2} +@opindex falign-functions +Align the start of functions to the next power-of-two greater than or +equal to @var{n}, skipping up to @var{m}-1 bytes. This ensures that at +least the first @var{m} bytes of the function can be fetched by the CPU +without crossing an @var{n}-byte alignment boundary. + +If @var{m} is not specified, it defaults to @var{n}. + +Examples: @option{-falign-functions=32} aligns functions to the next +32-byte boundary, @option{-falign-functions=24} aligns to the next +32-byte boundary only if this can be done by skipping 23 bytes or less, +@option{-falign-functions=32:7} aligns to the next +32-byte boundary only if this can be done by skipping 6 bytes or less. + +The second pair of @var{n2}:@var{m2} values allows you to specify +a secondary alignment: @option{-falign-functions=64:7:32:3} aligns to +the next 64-byte boundary if this can be done by skipping 6 bytes or less, +otherwise aligns to the next 32-byte boundary if this can be done +by skipping 2 bytes or less. +If @var{m2} is not specified, it defaults to @var{n2}. + +Some assemblers only support this flag when @var{n} is a power of two; +in that case, it is rounded up. + +@option{-fno-align-functions} and @option{-falign-functions=1} are +equivalent and mean that functions are not aligned. + +If @var{n} is not specified or is zero, use a machine-dependent default. +The maximum allowed @var{n} option value is 65536. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -flimit-function-alignment +If this option is enabled, the compiler tries to avoid unnecessarily +overaligning functions. It attempts to instruct the assembler to align +by the amount specified by @option{-falign-functions}, but not to +skip more bytes than the size of the function. + +@item -falign-labels +@itemx -falign-labels=@var{n} +@itemx -falign-labels=@var{n}:@var{m} +@itemx -falign-labels=@var{n}:@var{m}:@var{n2} +@itemx -falign-labels=@var{n}:@var{m}:@var{n2}:@var{m2} +@opindex falign-labels +Align all branch targets to a power-of-two boundary. + +Parameters of this option are analogous to the @option{-falign-functions} option. +@option{-fno-align-labels} and @option{-falign-labels=1} are +equivalent and mean that labels are not aligned. + +If @option{-falign-loops} or @option{-falign-jumps} are applicable and +are greater than this value, then their values are used instead. + +If @var{n} is not specified or is zero, use a machine-dependent default +which is very likely to be @samp{1}, meaning no alignment. +The maximum allowed @var{n} option value is 65536. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -falign-loops +@itemx -falign-loops=@var{n} +@itemx -falign-loops=@var{n}:@var{m} +@itemx -falign-loops=@var{n}:@var{m}:@var{n2} +@itemx -falign-loops=@var{n}:@var{m}:@var{n2}:@var{m2} +@opindex falign-loops +Align loops to a power-of-two boundary. If the loops are executed +many times, this makes up for any execution of the dummy padding +instructions. + +If @option{-falign-labels} is greater than this value, then its value +is used instead. + +Parameters of this option are analogous to the @option{-falign-functions} option. +@option{-fno-align-loops} and @option{-falign-loops=1} are +equivalent and mean that loops are not aligned. +The maximum allowed @var{n} option value is 65536. + +If @var{n} is not specified or is zero, use a machine-dependent default. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -falign-jumps +@itemx -falign-jumps=@var{n} +@itemx -falign-jumps=@var{n}:@var{m} +@itemx -falign-jumps=@var{n}:@var{m}:@var{n2} +@itemx -falign-jumps=@var{n}:@var{m}:@var{n2}:@var{m2} +@opindex falign-jumps +Align branch targets to a power-of-two boundary, for branch targets +where the targets can only be reached by jumping. In this case, +no dummy operations need be executed. + +If @option{-falign-labels} is greater than this value, then its value +is used instead. + +Parameters of this option are analogous to the @option{-falign-functions} option. +@option{-fno-align-jumps} and @option{-falign-jumps=1} are +equivalent and mean that loops are not aligned. + +If @var{n} is not specified or is zero, use a machine-dependent default. +The maximum allowed @var{n} option value is 65536. + +Enabled at levels @option{-O2}, @option{-O3}. + +@item -fno-allocation-dce +@opindex fno-allocation-dce +Do not remove unused C++ allocations in dead code elimination. + +@item -fallow-store-data-races +@opindex fallow-store-data-races +Allow the compiler to perform optimizations that may introduce new data races +on stores, without proving that the variable cannot be concurrently accessed +by other threads. Does not affect optimization of local data. It is safe to +use this option if it is known that global data will not be accessed by +multiple threads. + +Examples of optimizations enabled by @option{-fallow-store-data-races} include +hoisting or if-conversions that may cause a value that was already in memory +to be re-written with that same value. Such re-writing is safe in a single +threaded context but may be unsafe in a multi-threaded context. Note that on +some processors, if-conversions may be required in order to enable +vectorization. + +Enabled at level @option{-Ofast}. + +@item -funit-at-a-time +@opindex funit-at-a-time +This option is left for compatibility reasons. @option{-funit-at-a-time} +has no effect, while @option{-fno-unit-at-a-time} implies +@option{-fno-toplevel-reorder} and @option{-fno-section-anchors}. + +Enabled by default. + +@item -fno-toplevel-reorder +@opindex fno-toplevel-reorder +@opindex ftoplevel-reorder +Do not reorder top-level functions, variables, and @code{asm} +statements. Output them in the same order that they appear in the +input file. When this option is used, unreferenced static variables +are not removed. This option is intended to support existing code +that relies on a particular ordering. For new code, it is better to +use attributes when possible. + +@option{-ftoplevel-reorder} is the default at @option{-O1} and higher, and +also at @option{-O0} if @option{-fsection-anchors} is explicitly requested. +Additionally @option{-fno-toplevel-reorder} implies +@option{-fno-section-anchors}. + +@item -funreachable-traps +@opindex funreachable-traps +With this option, the compiler turns calls to +@code{__builtin_unreachable} into traps, instead of using them for +optimization. This also affects any such calls implicitly generated +by the compiler. + +This option has the same effect as @option{-fsanitize=unreachable +-fsanitize-trap=unreachable}, but does not affect the values of those +options. If @option{-fsanitize=unreachable} is enabled, that option +takes priority over this one. + +This option is enabled by default at @option{-O0} and @option{-Og}. + +@item -fweb +@opindex fweb +Constructs webs as commonly used for register allocation purposes and assign +each web individual pseudo register. This allows the register allocation pass +to operate on pseudos directly, but also strengthens several other optimization +passes, such as CSE, loop optimizer and trivial dead code remover. It can, +however, make debugging impossible, since variables no longer stay in a +``home register''. + +Enabled by default with @option{-funroll-loops}. + +@item -fwhole-program +@opindex fwhole-program +Assume that the current compilation unit represents the whole program being +compiled. All public functions and variables with the exception of @code{main} +and those merged by attribute @code{externally_visible} become static functions +and in effect are optimized more aggressively by interprocedural optimizers. + +This option should not be used in combination with @option{-flto}. +Instead relying on a linker plugin should provide safer and more precise +information. + +@item -flto[=@var{n}] +@opindex flto +This option runs the standard link-time optimizer. When invoked +with source code, it generates GIMPLE (one of GCC's internal +representations) and writes it to special ELF sections in the object +file. When the object files are linked together, all the function +bodies are read from these ELF sections and instantiated as if they +had been part of the same translation unit. + +To use the link-time optimizer, @option{-flto} and optimization +options should be specified at compile time and during the final link. +It is recommended that you compile all the files participating in the +same link with the same options and also specify those options at +link time. +For example: + +@smallexample +gcc -c -O2 -flto foo.c +gcc -c -O2 -flto bar.c +gcc -o myprog -flto -O2 foo.o bar.o +@end smallexample + +The first two invocations to GCC save a bytecode representation +of GIMPLE into special ELF sections inside @file{foo.o} and +@file{bar.o}. The final invocation reads the GIMPLE bytecode from +@file{foo.o} and @file{bar.o}, merges the two files into a single +internal image, and compiles the result as usual. Since both +@file{foo.o} and @file{bar.o} are merged into a single image, this +causes all the interprocedural analyses and optimizations in GCC to +work across the two files as if they were a single one. This means, +for example, that the inliner is able to inline functions in +@file{bar.o} into functions in @file{foo.o} and vice-versa. + +Another (simpler) way to enable link-time optimization is: + +@smallexample +gcc -o myprog -flto -O2 foo.c bar.c +@end smallexample + +The above generates bytecode for @file{foo.c} and @file{bar.c}, +merges them together into a single GIMPLE representation and optimizes +them as usual to produce @file{myprog}. + +The important thing to keep in mind is that to enable link-time +optimizations you need to use the GCC driver to perform the link step. +GCC automatically performs link-time optimization if any of the +objects involved were compiled with the @option{-flto} command-line option. +You can always override +the automatic decision to do link-time optimization +by passing @option{-fno-lto} to the link command. + +To make whole program optimization effective, it is necessary to make +certain whole program assumptions. The compiler needs to know +what functions and variables can be accessed by libraries and runtime +outside of the link-time optimized unit. When supported by the linker, +the linker plugin (see @option{-fuse-linker-plugin}) passes information +to the compiler about used and externally visible symbols. When +the linker plugin is not available, @option{-fwhole-program} should be +used to allow the compiler to make these assumptions, which leads +to more aggressive optimization decisions. + +When a file is compiled with @option{-flto} without +@option{-fuse-linker-plugin}, the generated object file is larger than +a regular object file because it contains GIMPLE bytecodes and the usual +final code (see @option{-ffat-lto-objects}). This means that +object files with LTO information can be linked as normal object +files; if @option{-fno-lto} is passed to the linker, no +interprocedural optimizations are applied. Note that when +@option{-fno-fat-lto-objects} is enabled the compile stage is faster +but you cannot perform a regular, non-LTO link on them. + +When producing the final binary, GCC only +applies link-time optimizations to those files that contain bytecode. +Therefore, you can mix and match object files and libraries with +GIMPLE bytecodes and final object code. GCC automatically selects +which files to optimize in LTO mode and which files to link without +further processing. + +Generally, options specified at link time override those +specified at compile time, although in some cases GCC attempts to infer +link-time options from the settings used to compile the input files. + +If you do not specify an optimization level option @option{-O} at +link time, then GCC uses the highest optimization level +used when compiling the object files. Note that it is generally +ineffective to specify an optimization level option only at link time and +not at compile time, for two reasons. First, compiling without +optimization suppresses compiler passes that gather information +needed for effective optimization at link time. Second, some early +optimization passes can be performed only at compile time and +not at link time. + +There are some code generation flags preserved by GCC when +generating bytecodes, as they need to be used during the final link. +Currently, the following options and their settings are taken from +the first object file that explicitly specifies them: +@option{-fcommon}, @option{-fexceptions}, @option{-fnon-call-exceptions}, +@option{-fgnu-tm} and all the @option{-m} target flags. + +The following options @option{-fPIC}, @option{-fpic}, @option{-fpie} and +@option{-fPIE} are combined based on the following scheme: + +@smallexample +@option{-fPIC} + @option{-fpic} = @option{-fpic} +@option{-fPIC} + @option{-fno-pic} = @option{-fno-pic} +@option{-fpic/-fPIC} + (no option) = (no option) +@option{-fPIC} + @option{-fPIE} = @option{-fPIE} +@option{-fpic} + @option{-fPIE} = @option{-fpie} +@option{-fPIC/-fpic} + @option{-fpie} = @option{-fpie} +@end smallexample + +Certain ABI-changing flags are required to match in all compilation units, +and trying to override this at link time with a conflicting value +is ignored. This includes options such as @option{-freg-struct-return} +and @option{-fpcc-struct-return}. + +Other options such as @option{-ffp-contract}, @option{-fno-strict-overflow}, +@option{-fwrapv}, @option{-fno-trapv} or @option{-fno-strict-aliasing} +are passed through to the link stage and merged conservatively for +conflicting translation units. Specifically +@option{-fno-strict-overflow}, @option{-fwrapv} and @option{-fno-trapv} take +precedence; and for example @option{-ffp-contract=off} takes precedence +over @option{-ffp-contract=fast}. You can override them at link time. + +Diagnostic options such as @option{-Wstringop-overflow} are passed +through to the link stage and their setting matches that of the +compile-step at function granularity. Note that this matters only +for diagnostics emitted during optimization. Note that code +transforms such as inlining can lead to warnings being enabled +or disabled for regions if code not consistent with the setting +at compile time. + +When you need to pass options to the assembler via @option{-Wa} or +@option{-Xassembler} make sure to either compile such translation +units with @option{-fno-lto} or consistently use the same assembler +options on all translation units. You can alternatively also +specify assembler options at LTO link time. + +To enable debug info generation you need to supply @option{-g} at +compile time. If any of the input files at link time were built +with debug info generation enabled the link will enable debug info +generation as well. Any elaborate debug info settings +like the dwarf level @option{-gdwarf-5} need to be explicitly repeated +at the linker command line and mixing different settings in different +translation units is discouraged. + +If LTO encounters objects with C linkage declared with incompatible +types in separate translation units to be linked together (undefined +behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be +issued. The behavior is still undefined at run time. Similar +diagnostics may be raised for other languages. + +Another feature of LTO is that it is possible to apply interprocedural +optimizations on files written in different languages: + +@smallexample +gcc -c -flto foo.c +g++ -c -flto bar.cc +gfortran -c -flto baz.f90 +g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran +@end smallexample + +Notice that the final link is done with @command{g++} to get the C++ +runtime libraries and @option{-lgfortran} is added to get the Fortran +runtime libraries. In general, when mixing languages in LTO mode, you +should use the same link command options as when mixing languages in a +regular (non-LTO) compilation. + +If object files containing GIMPLE bytecode are stored in a library archive, say +@file{libfoo.a}, it is possible to extract and use them in an LTO link if you +are using a linker with plugin support. To create static libraries suitable +for LTO, use @command{gcc-ar} and @command{gcc-ranlib} instead of @command{ar} +and @command{ranlib}; +to show the symbols of object files with GIMPLE bytecode, use +@command{gcc-nm}. Those commands require that @command{ar}, @command{ranlib} +and @command{nm} have been compiled with plugin support. At link time, use the +flag @option{-fuse-linker-plugin} to ensure that the library participates in +the LTO optimization process: + +@smallexample +gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo +@end smallexample + +With the linker plugin enabled, the linker extracts the needed +GIMPLE files from @file{libfoo.a} and passes them on to the running GCC +to make them part of the aggregated GIMPLE image to be optimized. + +If you are not using a linker with plugin support and/or do not +enable the linker plugin, then the objects inside @file{libfoo.a} +are extracted and linked as usual, but they do not participate +in the LTO optimization process. In order to make a static library suitable +for both LTO optimization and usual linkage, compile its object files with +@option{-flto} @option{-ffat-lto-objects}. + +Link-time optimizations do not require the presence of the whole program to +operate. If the program does not require any symbols to be exported, it is +possible to combine @option{-flto} and @option{-fwhole-program} to allow +the interprocedural optimizers to use more aggressive assumptions which may +lead to improved optimization opportunities. +Use of @option{-fwhole-program} is not needed when linker plugin is +active (see @option{-fuse-linker-plugin}). + +The current implementation of LTO makes no +attempt to generate bytecode that is portable between different +types of hosts. The bytecode files are versioned and there is a +strict version check, so bytecode files generated in one version of +GCC do not work with an older or newer version of GCC. + +Link-time optimization does not work well with generation of debugging +information on systems other than those using a combination of ELF and +DWARF. + +If you specify the optional @var{n}, the optimization and code +generation done at link time is executed in parallel using @var{n} +parallel jobs by utilizing an installed @command{make} program. The +environment variable @env{MAKE} may be used to override the program +used. + +You can also specify @option{-flto=jobserver} to use GNU make's +job server mode to determine the number of parallel jobs. This +is useful when the Makefile calling GCC is already executing in parallel. +You must prepend a @samp{+} to the command recipe in the parent Makefile +for this to work. This option likely only works if @env{MAKE} is +GNU make. Even without the option value, GCC tries to automatically +detect a running GNU make's job server. + +Use @option{-flto=auto} to use GNU make's job server, if available, +or otherwise fall back to autodetection of the number of CPU threads +present in your system. + +@item -flto-partition=@var{alg} +@opindex flto-partition +Specify the partitioning algorithm used by the link-time optimizer. +The value is either @samp{1to1} to specify a partitioning mirroring +the original source files or @samp{balanced} to specify partitioning +into equally sized chunks (whenever possible) or @samp{max} to create +new partition for every symbol where possible. Specifying @samp{none} +as an algorithm disables partitioning and streaming completely. +The default value is @samp{balanced}. While @samp{1to1} can be used +as an workaround for various code ordering issues, the @samp{max} +partitioning is intended for internal testing only. +The value @samp{one} specifies that exactly one partition should be +used while the value @samp{none} bypasses partitioning and executes +the link-time optimization step directly from the WPA phase. + +@item -flto-compression-level=@var{n} +@opindex flto-compression-level +This option specifies the level of compression used for intermediate +language written to LTO object files, and is only meaningful in +conjunction with LTO mode (@option{-flto}). GCC currently supports two +LTO compression algorithms. For zstd, valid values are 0 (no compression) +to 19 (maximum compression), while zlib supports values from 0 to 9. +Values outside this range are clamped to either minimum or maximum +of the supported values. If the option is not given, +a default balanced compression setting is used. + +@item -fuse-linker-plugin +@opindex fuse-linker-plugin +Enables the use of a linker plugin during link-time optimization. This +option relies on plugin support in the linker, which is available in gold +or in GNU ld 2.21 or newer. + +This option enables the extraction of object files with GIMPLE bytecode out +of library archives. This improves the quality of optimization by exposing +more code to the link-time optimizer. This information specifies what +symbols can be accessed externally (by non-LTO object or during dynamic +linking). Resulting code quality improvements on binaries (and shared +libraries that use hidden visibility) are similar to @option{-fwhole-program}. +See @option{-flto} for a description of the effect of this flag and how to +use it. + +This option is enabled by default when LTO support in GCC is enabled +and GCC was configured for use with +a linker supporting plugins (GNU ld 2.21 or newer or gold). + +@item -ffat-lto-objects +@opindex ffat-lto-objects +Fat LTO objects are object files that contain both the intermediate language +and the object code. This makes them usable for both LTO linking and normal +linking. This option is effective only when compiling with @option{-flto} +and is ignored at link time. + +@option{-fno-fat-lto-objects} improves compilation time over plain LTO, but +requires the complete toolchain to be aware of LTO. It requires a linker with +linker plugin support for basic functionality. Additionally, +@command{nm}, @command{ar} and @command{ranlib} +need to support linker plugins to allow a full-featured build environment +(capable of building static libraries etc). GCC provides the @command{gcc-ar}, +@command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options +to these tools. With non fat LTO makefiles need to be modified to use them. + +Note that modern binutils provide plugin auto-load mechanism. +Installing the linker plugin into @file{$libdir/bfd-plugins} has the same +effect as usage of the command wrappers (@command{gcc-ar}, @command{gcc-nm} and +@command{gcc-ranlib}). + +The default is @option{-fno-fat-lto-objects} on targets with linker plugin +support. + +@item -fcompare-elim +@opindex fcompare-elim +After register allocation and post-register allocation instruction splitting, +identify arithmetic instructions that compute processor flags similar to a +comparison operation based on that arithmetic. If possible, eliminate the +explicit comparison operation. + +This pass only applies to certain targets that cannot explicitly represent +the comparison operation before register allocation is complete. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fcprop-registers +@opindex fcprop-registers +After register allocation and post-register allocation instruction splitting, +perform a copy-propagation pass to try to reduce scheduling dependencies +and occasionally eliminate the copy. + +Enabled at levels @option{-O1}, @option{-O2}, @option{-O3}, @option{-Os}. + +@item -fprofile-correction +@opindex fprofile-correction +Profiles collected using an instrumented binary for multi-threaded programs may +be inconsistent due to missed counter updates. When this option is specified, +GCC uses heuristics to correct or smooth out such inconsistencies. By +default, GCC emits an error message when an inconsistent profile is detected. + +This option is enabled by @option{-fauto-profile}. + +@item -fprofile-partial-training +@opindex fprofile-partial-training +With @code{-fprofile-use} all portions of programs not executed during train +run are optimized agressively for size rather than speed. In some cases it is +not practical to train all possible hot paths in the program. (For +example, program may contain functions specific for a given hardware and +trianing may not cover all hardware configurations program is run on.) With +@code{-fprofile-partial-training} profile feedback will be ignored for all +functions not executed during the train run leading them to be optimized as if +they were compiled without profile feedback. This leads to better performance +when train run is not representative but also leads to significantly bigger +code. + +@item -fprofile-use +@itemx -fprofile-use=@var{path} +@opindex fprofile-use +Enable profile feedback-directed optimizations, +and the following optimizations, many of which +are generally profitable only with profile feedback available: + +@gccoptlist{-fbranch-probabilities -fprofile-values @gol +-funroll-loops -fpeel-loops -ftracer -fvpt @gol +-finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp @gol +-fpredictive-commoning -fsplit-loops -funswitch-loops @gol +-fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize @gol +-fvect-cost-model=dynamic -ftree-loop-distribute-patterns @gol +-fprofile-reorder-functions} + +Before you can use this option, you must first generate profiling information. +@xref{Instrumentation Options}, for information about the +@option{-fprofile-generate} option. + +By default, GCC emits an error message if the feedback profiles do not +match the source code. This error can be turned into a warning by using +@option{-Wno-error=coverage-mismatch}. Note this may result in poorly +optimized code. Additionally, by default, GCC also emits a warning message if +the feedback profiles do not exist (see @option{-Wmissing-profile}). + +If @var{path} is specified, GCC looks at the @var{path} to find +the profile feedback data files. See @option{-fprofile-dir}. + +@item -fauto-profile +@itemx -fauto-profile=@var{path} +@opindex fauto-profile +Enable sampling-based feedback-directed optimizations, +and the following optimizations, +many of which are generally profitable only with profile feedback available: + +@gccoptlist{-fbranch-probabilities -fprofile-values @gol +-funroll-loops -fpeel-loops -ftracer -fvpt @gol +-finline-functions -fipa-cp -fipa-cp-clone -fipa-bit-cp @gol +-fpredictive-commoning -fsplit-loops -funswitch-loops @gol +-fgcse-after-reload -ftree-loop-vectorize -ftree-slp-vectorize @gol +-fvect-cost-model=dynamic -ftree-loop-distribute-patterns @gol +-fprofile-correction} + +@var{path} is the name of a file containing AutoFDO profile information. +If omitted, it defaults to @file{fbdata.afdo} in the current directory. + +Producing an AutoFDO profile data file requires running your program +with the @command{perf} utility on a supported GNU/Linux target system. +For more information, see @uref{https://perf.wiki.kernel.org/}. + +E.g. +@smallexample +perf record -e br_inst_retired:near_taken -b -o perf.data \ + -- your_program +@end smallexample + +Then use the @command{create_gcov} tool to convert the raw profile data +to a format that can be used by GCC.@ You must also supply the +unstripped binary for your program to this tool. +See @uref{https://github.com/google/autofdo}. + +E.g. +@smallexample +create_gcov --binary=your_program.unstripped --profile=perf.data \ + --gcov=profile.afdo +@end smallexample +@end table + +The following options control compiler behavior regarding floating-point +arithmetic. These options trade off between speed and +correctness. All must be specifically enabled. + +@table @gcctabopt +@item -ffloat-store +@opindex ffloat-store +Do not store floating-point variables in registers, and inhibit other +options that might change whether a floating-point value is taken from a +register or memory. + +@cindex floating-point precision +This option prevents undesirable excess precision on machines such as +the 68000 where the floating registers (of the 68881) keep more +precision than a @code{double} is supposed to have. Similarly for the +x86 architecture. For most programs, the excess precision does only +good, but a few programs rely on the precise definition of IEEE floating +point. Use @option{-ffloat-store} for such programs, after modifying +them to store all pertinent intermediate computations into variables. + +@item -fexcess-precision=@var{style} +@opindex fexcess-precision +This option allows further control over excess precision on machines +where floating-point operations occur in a format with more precision or +range than the IEEE standard and interchange floating-point types. By +default, @option{-fexcess-precision=fast} is in effect; this means that +operations may be carried out in a wider precision than the types specified +in the source if that would result in faster code, and it is unpredictable +when rounding to the types specified in the source code takes place. +When compiling C or C++, if @option{-fexcess-precision=standard} is specified +then excess precision follows the rules specified in ISO C99 or C++; in particular, +both casts and assignments cause values to be rounded to their +semantic types (whereas @option{-ffloat-store} only affects +assignments). This option is enabled by default for C or C++ if a strict +conformance option such as @option{-std=c99} or @option{-std=c++17} is used. +@option{-ffast-math} enables @option{-fexcess-precision=fast} by default +regardless of whether a strict conformance option is used. + +@opindex mfpmath +@option{-fexcess-precision=standard} is not implemented for languages +other than C or C++. On the x86, it has no effect if @option{-mfpmath=sse} +or @option{-mfpmath=sse+387} is specified; in the former case, IEEE +semantics apply without excess precision, and in the latter, rounding +is unpredictable. + +@item -ffast-math +@opindex ffast-math +Sets the options @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, +@option{-ffinite-math-only}, @option{-fno-rounding-math}, +@option{-fno-signaling-nans}, @option{-fcx-limited-range} and +@option{-fexcess-precision=fast}. + +This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. + +This option is not turned on by any @option{-O} option besides +@option{-Ofast} since it can result in incorrect output for programs +that depend on an exact implementation of IEEE or ISO rules/specifications +for math functions. It may, however, yield faster code for programs +that do not require the guarantees of these specifications. + +@item -fno-math-errno +@opindex fno-math-errno +@opindex fmath-errno +Do not set @code{errno} after calling math functions that are executed +with a single instruction, e.g., @code{sqrt}. A program that relies on +IEEE exceptions for math error handling may want to use this flag +for speed while maintaining IEEE arithmetic compatibility. + +This option is not turned on by any @option{-O} option since +it can result in incorrect output for programs that depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. It may, however, yield faster code for programs +that do not require the guarantees of these specifications. + +The default is @option{-fmath-errno}. + +On Darwin systems, the math library never sets @code{errno}. There is +therefore no reason for the compiler to consider the possibility that +it might, and @option{-fno-math-errno} is the default. + +@item -funsafe-math-optimizations +@opindex funsafe-math-optimizations + +Allow optimizations for floating-point arithmetic that (a) assume +that arguments and results are valid and (b) may violate IEEE or +ANSI standards. When used at link time, it may include libraries +or startup files that change the default FPU control word or other +similar optimizations. + +This option is not turned on by any @option{-O} option since +it can result in incorrect output for programs that depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. It may, however, yield faster code for programs +that do not require the guarantees of these specifications. +Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math}, +@option{-fassociative-math} and @option{-freciprocal-math}. + +The default is @option{-fno-unsafe-math-optimizations}. + +@item -fassociative-math +@opindex fassociative-math + +Allow re-association of operands in series of floating-point operations. +This violates the ISO C and C++ language standard by possibly changing +computation result. NOTE: re-ordering may change the sign of zero as +well as ignore NaNs and inhibit or create underflow or overflow (and +thus cannot be used on code that relies on rounding behavior like +@code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons +and thus may not be used when ordered comparisons are required. +This option requires that both @option{-fno-signed-zeros} and +@option{-fno-trapping-math} be in effect. Moreover, it doesn't make +much sense with @option{-frounding-math}. For Fortran the option +is automatically enabled when both @option{-fno-signed-zeros} and +@option{-fno-trapping-math} are in effect. + +The default is @option{-fno-associative-math}. + +@item -freciprocal-math +@opindex freciprocal-math + +Allow the reciprocal of a value to be used instead of dividing by +the value if this enables optimizations. For example @code{x / y} +can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)} +is subject to common subexpression elimination. Note that this loses +precision and increases the number of flops operating on the value. + +The default is @option{-fno-reciprocal-math}. + +@item -ffinite-math-only +@opindex ffinite-math-only +Allow optimizations for floating-point arithmetic that assume +that arguments and results are not NaNs or +-Infs. + +This option is not turned on by any @option{-O} option since +it can result in incorrect output for programs that depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. It may, however, yield faster code for programs +that do not require the guarantees of these specifications. + +The default is @option{-fno-finite-math-only}. + +@item -fno-signed-zeros +@opindex fno-signed-zeros +@opindex fsigned-zeros +Allow optimizations for floating-point arithmetic that ignore the +signedness of zero. IEEE arithmetic specifies the behavior of +distinct +0.0 and @minus{}0.0 values, which then prohibits simplification +of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}). +This option implies that the sign of a zero result isn't significant. + +The default is @option{-fsigned-zeros}. + +@item -fno-trapping-math +@opindex fno-trapping-math +@opindex ftrapping-math +Compile code assuming that floating-point operations cannot generate +user-visible traps. These traps include division by zero, overflow, +underflow, inexact result and invalid operation. This option requires +that @option{-fno-signaling-nans} be in effect. Setting this option may +allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example. + +This option should never be turned on by any @option{-O} option since +it can result in incorrect output for programs that depend on +an exact implementation of IEEE or ISO rules/specifications for +math functions. + +The default is @option{-ftrapping-math}. + +Future versions of GCC may provide finer control of this setting +using C99's @code{FENV_ACCESS} pragma. This command-line option +will be used along with @option{-frounding-math} to specify the +default state for @code{FENV_ACCESS}. + +@item -frounding-math +@opindex frounding-math +Disable transformations and optimizations that assume default floating-point +rounding behavior. This is round-to-zero for all floating point +to integer conversions, and round-to-nearest for all other arithmetic +truncations. This option should be specified for programs that change +the FP rounding mode dynamically, or that may be executed with a +non-default rounding mode. This option disables constant folding of +floating-point expressions at compile time (which may be affected by +rounding mode) and arithmetic transformations that are unsafe in the +presence of sign-dependent rounding modes. + +The default is @option{-fno-rounding-math}. + +This option is experimental and does not currently guarantee to +disable all GCC optimizations that are affected by rounding mode. +Future versions of GCC may provide finer control of this setting +using C99's @code{FENV_ACCESS} pragma. This command-line option +will be used along with @option{-ftrapping-math} to specify the +default state for @code{FENV_ACCESS}. + +@item -fsignaling-nans +@opindex fsignaling-nans +Compile code assuming that IEEE signaling NaNs may generate user-visible +traps during floating-point operations. Setting this option disables +optimizations that may change the number of exceptions visible with +signaling NaNs. This option implies @option{-ftrapping-math}. + +This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to +be defined. + +The default is @option{-fno-signaling-nans}. + +This option is experimental and does not currently guarantee to +disable all GCC optimizations that affect signaling NaN behavior. + +@item -fno-fp-int-builtin-inexact +@opindex fno-fp-int-builtin-inexact +@opindex ffp-int-builtin-inexact +Do not allow the built-in functions @code{ceil}, @code{floor}, +@code{round} and @code{trunc}, and their @code{float} and @code{long +double} variants, to generate code that raises the ``inexact'' +floating-point exception for noninteger arguments. ISO C99 and C11 +allow these functions to raise the ``inexact'' exception, but ISO/IEC +TS 18661-1:2014, the C bindings to IEEE 754-2008, as integrated into +ISO C2X, does not allow these functions to do so. + +The default is @option{-ffp-int-builtin-inexact}, allowing the +exception to be raised, unless C2X or a later C standard is selected. +This option does nothing unless @option{-ftrapping-math} is in effect. + +Even if @option{-fno-fp-int-builtin-inexact} is used, if the functions +generate a call to a library function then the ``inexact'' exception +may be raised if the library implementation does not follow TS 18661. + +@item -fsingle-precision-constant +@opindex fsingle-precision-constant +Treat floating-point constants as single precision instead of +implicitly converting them to double-precision constants. + +@item -fcx-limited-range +@opindex fcx-limited-range +When enabled, this option states that a range reduction step is not +needed when performing complex division. Also, there is no checking +whether the result of a complex multiplication or division is @code{NaN ++ I*NaN}, with an attempt to rescue the situation in that case. The +default is @option{-fno-cx-limited-range}, but is enabled by +@option{-ffast-math}. + +This option controls the default setting of the ISO C99 +@code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to +all languages. + +@item -fcx-fortran-rules +@opindex fcx-fortran-rules +Complex multiplication and division follow Fortran rules. Range +reduction is done as part of complex division, but there is no checking +whether the result of a complex multiplication or division is @code{NaN ++ I*NaN}, with an attempt to rescue the situation in that case. + +The default is @option{-fno-cx-fortran-rules}. + +@end table + +The following options control optimizations that may improve +performance, but are not enabled by any @option{-O} options. This +section includes experimental options that may produce broken code. + +@table @gcctabopt +@item -fbranch-probabilities +@opindex fbranch-probabilities +After running a program compiled with @option{-fprofile-arcs} +(@pxref{Instrumentation Options}), +you can compile it a second time using +@option{-fbranch-probabilities}, to improve optimizations based on +the number of times each branch was taken. When a program +compiled with @option{-fprofile-arcs} exits, it saves arc execution +counts to a file called @file{@var{sourcename}.gcda} for each source +file. The information in this data file is very dependent on the +structure of the generated code, so you must use the same source code +and the same optimization options for both compilations. +See details about the file naming in @option{-fprofile-arcs}. + +With @option{-fbranch-probabilities}, GCC puts a +@samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. +These can be used to improve optimization. Currently, they are only +used in one place: in @file{reorg.cc}, instead of guessing which path a +branch is most likely to take, the @samp{REG_BR_PROB} values are used to +exactly determine which path is taken more often. + +Enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -fprofile-values +@opindex fprofile-values +If combined with @option{-fprofile-arcs}, it adds code so that some +data about values of expressions in the program is gathered. + +With @option{-fbranch-probabilities}, it reads back the data gathered +from profiling values of expressions for usage in optimizations. + +Enabled by @option{-fprofile-generate}, @option{-fprofile-use}, and +@option{-fauto-profile}. + +@item -fprofile-reorder-functions +@opindex fprofile-reorder-functions +Function reordering based on profile instrumentation collects +first time of execution of a function and orders these functions +in ascending order. + +Enabled with @option{-fprofile-use}. + +@item -fvpt +@opindex fvpt +If combined with @option{-fprofile-arcs}, this option instructs the compiler +to add code to gather information about values of expressions. + +With @option{-fbranch-probabilities}, it reads back the data gathered +and actually performs the optimizations based on them. +Currently the optimizations include specialization of division operations +using the knowledge about the value of the denominator. + +Enabled with @option{-fprofile-use} and @option{-fauto-profile}. + +@item -frename-registers +@opindex frename-registers +Attempt to avoid false dependencies in scheduled code by making use +of registers left over after register allocation. This optimization +most benefits processors with lots of registers. Depending on the +debug information format adopted by the target, however, it can +make debugging impossible, since variables no longer stay in +a ``home register''. + +Enabled by default with @option{-funroll-loops}. + +@item -fschedule-fusion +@opindex fschedule-fusion +Performs a target dependent pass over the instruction stream to schedule +instructions of same type together because target machine can execute them +more efficiently if they are adjacent to each other in the instruction flow. + +Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. + +@item -ftracer +@opindex ftracer +Perform tail duplication to enlarge superblock size. This transformation +simplifies the control flow of the function allowing other optimizations to do +a better job. + +Enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -funroll-loops +@opindex funroll-loops +Unroll loops whose number of iterations can be determined at compile time or +upon entry to the loop. @option{-funroll-loops} implies +@option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}. +It also turns on complete loop peeling (i.e.@: complete removal of loops with +a small constant number of iterations). This option makes code larger, and may +or may not make it run faster. + +Enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -funroll-all-loops +@opindex funroll-all-loops +Unroll all loops, even if their number of iterations is uncertain when +the loop is entered. This usually makes programs run more slowly. +@option{-funroll-all-loops} implies the same options as +@option{-funroll-loops}. + +@item -fpeel-loops +@opindex fpeel-loops +Peels loops for which there is enough information that they do not +roll much (from profile feedback or static analysis). It also turns on +complete loop peeling (i.e.@: complete removal of loops with small constant +number of iterations). + +Enabled by @option{-O3}, @option{-fprofile-use}, and @option{-fauto-profile}. + +@item -fmove-loop-invariants +@opindex fmove-loop-invariants +Enables the loop invariant motion pass in the RTL loop optimizer. Enabled +at level @option{-O1} and higher, except for @option{-Og}. + +@item -fmove-loop-stores +@opindex fmove-loop-stores +Enables the loop store motion pass in the GIMPLE loop optimizer. This +moves invariant stores to after the end of the loop in exchange for +carrying the stored value in a register across the iteration. +Note for this option to have an effect @option{-ftree-loop-im} has to +be enabled as well. Enabled at level @option{-O1} and higher, except +for @option{-Og}. + +@item -fsplit-loops +@opindex fsplit-loops +Split a loop into two if it contains a condition that's always true +for one side of the iteration space and false for the other. + +Enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -funswitch-loops +@opindex funswitch-loops +Move branches with loop invariant conditions out of the loop, with duplicates +of the loop on both branches (modified according to result of the condition). + +Enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -fversion-loops-for-strides +@opindex fversion-loops-for-strides +If a loop iterates over an array with a variable stride, create another +version of the loop that assumes the stride is always one. For example: + +@smallexample +for (int i = 0; i < n; ++i) + x[i * stride] = @dots{}; +@end smallexample + +becomes: + +@smallexample +if (stride == 1) + for (int i = 0; i < n; ++i) + x[i] = @dots{}; +else + for (int i = 0; i < n; ++i) + x[i * stride] = @dots{}; +@end smallexample + +This is particularly useful for assumed-shape arrays in Fortran where +(for example) it allows better vectorization assuming contiguous accesses. +This flag is enabled by default at @option{-O3}. +It is also enabled by @option{-fprofile-use} and @option{-fauto-profile}. + +@item -ffunction-sections +@itemx -fdata-sections +@opindex ffunction-sections +@opindex fdata-sections +Place each function or data item into its own section in the output +file if the target supports arbitrary sections. The name of the +function or the name of the data item determines the section's name +in the output file. + +Use these options on systems where the linker can perform optimizations to +improve locality of reference in the instruction space. Most systems using the +ELF object format have linkers with such optimizations. On AIX, the linker +rearranges sections (CSECTs) based on the call graph. The performance impact +varies. + +Together with a linker garbage collection (linker @option{--gc-sections} +option) these options may lead to smaller statically-linked executables (after +stripping). + +On ELF/DWARF systems these options do not degenerate the quality of the debug +information. There could be issues with other object files/debug info formats. + +Only use these options when there are significant benefits from doing so. When +you specify these options, the assembler and linker create larger object and +executable files and are also slower. These options affect code generation. +They prevent optimizations by the compiler and assembler using relative +locations inside a translation unit since the locations are unknown until +link time. An example of such an optimization is relaxing calls to short call +instructions. + +@item -fstdarg-opt +@opindex fstdarg-opt +Optimize the prologue of variadic argument functions with respect to usage of +those arguments. + +@item -fsection-anchors +@opindex fsection-anchors +Try to reduce the number of symbolic address calculations by using +shared ``anchor'' symbols to address nearby objects. This transformation +can help to reduce the number of GOT entries and GOT accesses on some +targets. + +For example, the implementation of the following function @code{foo}: + +@smallexample +static int a, b, c; +int foo (void) @{ return a + b + c; @} +@end smallexample + +@noindent +usually calculates the addresses of all three variables, but if you +compile it with @option{-fsection-anchors}, it accesses the variables +from a common anchor point instead. The effect is similar to the +following pseudocode (which isn't valid C): + +@smallexample +int foo (void) +@{ + register int *xr = &x; + return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; +@} +@end smallexample + +Not all targets support this option. + +@item -fzero-call-used-regs=@var{choice} +@opindex fzero-call-used-regs +Zero call-used registers at function return to increase program +security by either mitigating Return-Oriented Programming (ROP) +attacks or preventing information leakage through registers. + +The possible values of @var{choice} are the same as for the +@code{zero_call_used_regs} attribute (@pxref{Function Attributes}). +The default is @samp{skip}. + +You can control this behavior for a specific function by using the function +attribute @code{zero_call_used_regs} (@pxref{Function Attributes}). + +@item --param @var{name}=@var{value} +@opindex param +In some places, GCC uses various constants to control the amount of +optimization that is done. For example, GCC does not inline functions +that contain more than a certain number of instructions. You can +control some of these constants on the command line using the +@option{--param} option. + +The names of specific parameters, and the meaning of the values, are +tied to the internals of the compiler, and are subject to change +without notice in future releases. + +In order to get minimal, maximal and default value of a parameter, +one can use @option{--help=param -Q} options. + +In each case, the @var{value} is an integer. The following choices +of @var{name} are recognized for all targets: + +@table @gcctabopt +@item predictable-branch-outcome +When branch is predicted to be taken with probability lower than this threshold +(in percent), then it is considered well predictable. + +@item max-rtl-if-conversion-insns +RTL if-conversion tries to remove conditional branches around a block and +replace them with conditionally executed instructions. This parameter +gives the maximum number of instructions in a block which should be +considered for if-conversion. The compiler will +also use other heuristics to decide whether if-conversion is likely to be +profitable. + +@item max-rtl-if-conversion-predictable-cost +RTL if-conversion will try to remove conditional branches around a block +and replace them with conditionally executed instructions. These parameters +give the maximum permissible cost for the sequence that would be generated +by if-conversion depending on whether the branch is statically determined +to be predictable or not. The units for this parameter are the same as +those for the GCC internal seq_cost metric. The compiler will try to +provide a reasonable default for this parameter using the BRANCH_COST +target macro. + +@item max-crossjump-edges +The maximum number of incoming edges to consider for cross-jumping. +The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in +the number of edges incoming to each block. Increasing values mean +more aggressive optimization, making the compilation time increase with +probably small improvement in executable size. + +@item min-crossjump-insns +The minimum number of instructions that must be matched at the end +of two blocks before cross-jumping is performed on them. This +value is ignored in the case where all instructions in the block being +cross-jumped from are matched. + +@item max-grow-copy-bb-insns +The maximum code size expansion factor when copying basic blocks +instead of jumping. The expansion is relative to a jump instruction. + +@item max-goto-duplication-insns +The maximum number of instructions to duplicate to a block that jumps +to a computed goto. To avoid @math{O(N^2)} behavior in a number of +passes, GCC factors computed gotos early in the compilation process, +and unfactors them as late as possible. Only computed jumps at the +end of a basic blocks with no more than max-goto-duplication-insns are +unfactored. + +@item max-delay-slot-insn-search +The maximum number of instructions to consider when looking for an +instruction to fill a delay slot. If more than this arbitrary number of +instructions are searched, the time savings from filling the delay slot +are minimal, so stop searching. Increasing values mean more +aggressive optimization, making the compilation time increase with probably +small improvement in execution time. + +@item max-delay-slot-live-search +When trying to fill delay slots, the maximum number of instructions to +consider when searching for a block with valid live register +information. Increasing this arbitrarily chosen value means more +aggressive optimization, increasing the compilation time. This parameter +should be removed when the delay slot code is rewritten to maintain the +control-flow graph. + +@item max-gcse-memory +The approximate maximum amount of memory in @code{kB} that can be allocated in +order to perform the global common subexpression elimination +optimization. If more memory than specified is required, the +optimization is not done. + +@item max-gcse-insertion-ratio +If the ratio of expression insertions to deletions is larger than this value +for any expression, then RTL PRE inserts or removes the expression and thus +leaves partially redundant computations in the instruction stream. + +@item max-pending-list-length +The maximum number of pending dependencies scheduling allows +before flushing the current state and starting over. Large functions +with few branches or calls can create excessively large lists which +needlessly consume memory and resources. + +@item max-modulo-backtrack-attempts +The maximum number of backtrack attempts the scheduler should make +when modulo scheduling a loop. Larger values can exponentially increase +compilation time. + +@item max-inline-functions-called-once-loop-depth +Maximal loop depth of a call considered by inline heuristics that tries to +inline all functions called once. + +@item max-inline-functions-called-once-insns +Maximal estimated size of functions produced while inlining functions called +once. + +@item max-inline-insns-single +Several parameters control the tree inliner used in GCC@. This number sets the +maximum number of instructions (counted in GCC's internal representation) in a +single function that the tree inliner considers for inlining. This only +affects functions declared inline and methods implemented in a class +declaration (C++). + + +@item max-inline-insns-auto +When you use @option{-finline-functions} (included in @option{-O3}), +a lot of functions that would otherwise not be considered for inlining +by the compiler are investigated. To those functions, a different +(more restrictive) limit compared to functions declared inline can +be applied (@option{--param max-inline-insns-auto}). + +@item max-inline-insns-small +This is bound applied to calls which are considered relevant with +@option{-finline-small-functions}. + +@item max-inline-insns-size +This is bound applied to calls which are optimized for size. Small growth +may be desirable to anticipate optimization oppurtunities exposed by inlining. + +@item uninlined-function-insns +Number of instructions accounted by inliner for function overhead such as +function prologue and epilogue. + +@item uninlined-function-time +Extra time accounted by inliner for function overhead such as time needed to +execute function prologue and epilogue. + +@item inline-heuristics-hint-percent +The scale (in percents) applied to @option{inline-insns-single}, +@option{inline-insns-single-O2}, @option{inline-insns-auto} +when inline heuristics hints that inlining is +very profitable (will enable later optimizations). + +@item uninlined-thunk-insns +@item uninlined-thunk-time +Same as @option{--param uninlined-function-insns} and +@option{--param uninlined-function-time} but applied to function thunks. + +@item inline-min-speedup +When estimated performance improvement of caller + callee runtime exceeds this +threshold (in percent), the function can be inlined regardless of the limit on +@option{--param max-inline-insns-single} and @option{--param +max-inline-insns-auto}. + +@item large-function-insns +The limit specifying really large functions. For functions larger than this +limit after inlining, inlining is constrained by +@option{--param large-function-growth}. This parameter is useful primarily +to avoid extreme compilation time caused by non-linear algorithms used by the +back end. + +@item large-function-growth +Specifies maximal growth of large function caused by inlining in percents. +For example, parameter value 100 limits large function growth to 2.0 times +the original size. + +@item large-unit-insns +The limit specifying large translation unit. Growth caused by inlining of +units larger than this limit is limited by @option{--param inline-unit-growth}. +For small units this might be too tight. +For example, consider a unit consisting of function A +that is inline and B that just calls A three times. If B is small relative to +A, the growth of unit is 300\% and yet such inlining is very sane. For very +large units consisting of small inlineable functions, however, the overall unit +growth limit is needed to avoid exponential explosion of code size. Thus for +smaller units, the size is increased to @option{--param large-unit-insns} +before applying @option{--param inline-unit-growth}. + +@item lazy-modules +Maximum number of concurrently open C++ module files when lazy loading. + +@item inline-unit-growth +Specifies maximal overall growth of the compilation unit caused by inlining. +For example, parameter value 20 limits unit growth to 1.2 times the original +size. Cold functions (either marked cold via an attribute or by profile +feedback) are not accounted into the unit size. + +@item ipa-cp-unit-growth +Specifies maximal overall growth of the compilation unit caused by +interprocedural constant propagation. For example, parameter value 10 limits +unit growth to 1.1 times the original size. + +@item ipa-cp-large-unit-insns +The size of translation unit that IPA-CP pass considers large. + +@item large-stack-frame +The limit specifying large stack frames. While inlining the algorithm is trying +to not grow past this limit too much. + +@item large-stack-frame-growth +Specifies maximal growth of large stack frames caused by inlining in percents. +For example, parameter value 1000 limits large stack frame growth to 11 times +the original size. + +@item max-inline-insns-recursive +@itemx max-inline-insns-recursive-auto +Specifies the maximum number of instructions an out-of-line copy of a +self-recursive inline +function can grow into by performing recursive inlining. + +@option{--param max-inline-insns-recursive} applies to functions +declared inline. +For functions not declared inline, recursive inlining +happens only when @option{-finline-functions} (included in @option{-O3}) is +enabled; @option{--param max-inline-insns-recursive-auto} applies instead. + +@item max-inline-recursive-depth +@itemx max-inline-recursive-depth-auto +Specifies the maximum recursion depth used for recursive inlining. + +@option{--param max-inline-recursive-depth} applies to functions +declared inline. For functions not declared inline, recursive inlining +happens only when @option{-finline-functions} (included in @option{-O3}) is +enabled; @option{--param max-inline-recursive-depth-auto} applies instead. + +@item min-inline-recursive-probability +Recursive inlining is profitable only for function having deep recursion +in average and can hurt for function having little recursion depth by +increasing the prologue size or complexity of function body to other +optimizers. + +When profile feedback is available (see @option{-fprofile-generate}) the actual +recursion depth can be guessed from the probability that function recurses +via a given call expression. This parameter limits inlining only to call +expressions whose probability exceeds the given threshold (in percents). + +@item early-inlining-insns +Specify growth that the early inliner can make. In effect it increases +the amount of inlining for code having a large abstraction penalty. + +@item max-early-inliner-iterations +Limit of iterations of the early inliner. This basically bounds +the number of nested indirect calls the early inliner can resolve. +Deeper chains are still handled by late inlining. + +@item comdat-sharing-probability +Probability (in percent) that C++ inline function with comdat visibility +are shared across multiple compilation units. + +@item modref-max-bases +@item modref-max-refs +@item modref-max-accesses +Specifies the maximal number of base pointers, references and accesses stored +for a single function by mod/ref analysis. + +@item modref-max-tests +Specifies the maxmal number of tests alias oracle can perform to disambiguate +memory locations using the mod/ref information. This parameter ought to be +bigger than @option{--param modref-max-bases} and @option{--param +modref-max-refs}. + +@item modref-max-depth +Specifies the maximum depth of DFS walk used by modref escape analysis. +Setting to 0 disables the analysis completely. + +@item modref-max-escape-points +Specifies the maximum number of escape points tracked by modref per SSA-name. + +@item modref-max-adjustments +Specifies the maximum number the access range is enlarged during modref dataflow +analysis. + +@item profile-func-internal-id +A parameter to control whether to use function internal id in profile +database lookup. If the value is 0, the compiler uses an id that +is based on function assembler name and filename, which makes old profile +data more tolerant to source changes such as function reordering etc. + +@item min-vect-loop-bound +The minimum number of iterations under which loops are not vectorized +when @option{-ftree-vectorize} is used. The number of iterations after +vectorization needs to be greater than the value specified by this option +to allow vectorization. + +@item gcse-cost-distance-ratio +Scaling factor in calculation of maximum distance an expression +can be moved by GCSE optimizations. This is currently supported only in the +code hoisting pass. The bigger the ratio, the more aggressive code hoisting +is with simple expressions, i.e., the expressions that have cost +less than @option{gcse-unrestricted-cost}. Specifying 0 disables +hoisting of simple expressions. + +@item gcse-unrestricted-cost +Cost, roughly measured as the cost of a single typical machine +instruction, at which GCSE optimizations do not constrain +the distance an expression can travel. This is currently +supported only in the code hoisting pass. The lesser the cost, +the more aggressive code hoisting is. Specifying 0 +allows all expressions to travel unrestricted distances. + +@item max-hoist-depth +The depth of search in the dominator tree for expressions to hoist. +This is used to avoid quadratic behavior in hoisting algorithm. +The value of 0 does not limit on the search, but may slow down compilation +of huge functions. + +@item max-tail-merge-comparisons +The maximum amount of similar bbs to compare a bb with. This is used to +avoid quadratic behavior in tree tail merging. + +@item max-tail-merge-iterations +The maximum amount of iterations of the pass over the function. This is used to +limit compilation time in tree tail merging. + +@item store-merging-allow-unaligned +Allow the store merging pass to introduce unaligned stores if it is legal to +do so. + +@item max-stores-to-merge +The maximum number of stores to attempt to merge into wider stores in the store +merging pass. + +@item max-store-chains-to-track +The maximum number of store chains to track at the same time in the attempt +to merge them into wider stores in the store merging pass. + +@item max-stores-to-track +The maximum number of stores to track at the same time in the attemt to +to merge them into wider stores in the store merging pass. + +@item max-unrolled-insns +The maximum number of instructions that a loop may have to be unrolled. +If a loop is unrolled, this parameter also determines how many times +the loop code is unrolled. + +@item max-average-unrolled-insns +The maximum number of instructions biased by probabilities of their execution +that a loop may have to be unrolled. If a loop is unrolled, +this parameter also determines how many times the loop code is unrolled. + +@item max-unroll-times +The maximum number of unrollings of a single loop. + +@item max-peeled-insns +The maximum number of instructions that a loop may have to be peeled. +If a loop is peeled, this parameter also determines how many times +the loop code is peeled. + +@item max-peel-times +The maximum number of peelings of a single loop. + +@item max-peel-branches +The maximum number of branches on the hot path through the peeled sequence. + +@item max-completely-peeled-insns +The maximum number of insns of a completely peeled loop. + +@item max-completely-peel-times +The maximum number of iterations of a loop to be suitable for complete peeling. + +@item max-completely-peel-loop-nest-depth +The maximum depth of a loop nest suitable for complete peeling. + +@item max-unswitch-insns +The maximum number of insns of an unswitched loop. + +@item lim-expensive +The minimum cost of an expensive expression in the loop invariant motion. + +@item min-loop-cond-split-prob +When FDO profile information is available, @option{min-loop-cond-split-prob} +specifies minimum threshold for probability of semi-invariant condition +statement to trigger loop split. + +@item iv-consider-all-candidates-bound +Bound on number of candidates for induction variables, below which +all candidates are considered for each use in induction variable +optimizations. If there are more candidates than this, +only the most relevant ones are considered to avoid quadratic time complexity. + +@item iv-max-considered-uses +The induction variable optimizations give up on loops that contain more +induction variable uses. + +@item iv-always-prune-cand-set-bound +If the number of candidates in the set is smaller than this value, +always try to remove unnecessary ivs from the set +when adding a new one. + +@item avg-loop-niter +Average number of iterations of a loop. + +@item dse-max-object-size +Maximum size (in bytes) of objects tracked bytewise by dead store elimination. +Larger values may result in larger compilation times. + +@item dse-max-alias-queries-per-store +Maximum number of queries into the alias oracle per store. +Larger values result in larger compilation times and may result in more +removed dead stores. + +@item scev-max-expr-size +Bound on size of expressions used in the scalar evolutions analyzer. +Large expressions slow the analyzer. + +@item scev-max-expr-complexity +Bound on the complexity of the expressions in the scalar evolutions analyzer. +Complex expressions slow the analyzer. + +@item max-tree-if-conversion-phi-args +Maximum number of arguments in a PHI supported by TREE if conversion +unless the loop is marked with simd pragma. + +@item vect-max-layout-candidates +The maximum number of possible vector layouts (such as permutations) +to consider when optimizing to-be-vectorized code. + +@item vect-max-version-for-alignment-checks +The maximum number of run-time checks that can be performed when +doing loop versioning for alignment in the vectorizer. + +@item vect-max-version-for-alias-checks +The maximum number of run-time checks that can be performed when +doing loop versioning for alias in the vectorizer. + +@item vect-max-peeling-for-alignment +The maximum number of loop peels to enhance access alignment +for vectorizer. Value -1 means no limit. + +@item max-iterations-to-track +The maximum number of iterations of a loop the brute-force algorithm +for analysis of the number of iterations of the loop tries to evaluate. + +@item hot-bb-count-fraction +The denominator n of fraction 1/n of the maximal execution count of a +basic block in the entire program that a basic block needs to at least +have in order to be considered hot. The default is 10000, which means +that a basic block is considered hot if its execution count is greater +than 1/10000 of the maximal execution count. 0 means that it is never +considered hot. Used in non-LTO mode. + +@item hot-bb-count-ws-permille +The number of most executed permilles, ranging from 0 to 1000, of the +profiled execution of the entire program to which the execution count +of a basic block must be part of in order to be considered hot. The +default is 990, which means that a basic block is considered hot if +its execution count contributes to the upper 990 permilles, or 99.0%, +of the profiled execution of the entire program. 0 means that it is +never considered hot. Used in LTO mode. + +@item hot-bb-frequency-fraction +The denominator n of fraction 1/n of the execution frequency of the +entry block of a function that a basic block of this function needs +to at least have in order to be considered hot. The default is 1000, +which means that a basic block is considered hot in a function if it +is executed more frequently than 1/1000 of the frequency of the entry +block of the function. 0 means that it is never considered hot. + +@item unlikely-bb-count-fraction +The denominator n of fraction 1/n of the number of profiled runs of +the entire program below which the execution count of a basic block +must be in order for the basic block to be considered unlikely executed. +The default is 20, which means that a basic block is considered unlikely +executed if it is executed in fewer than 1/20, or 5%, of the runs of +the program. 0 means that it is always considered unlikely executed. + +@item max-predicted-iterations +The maximum number of loop iterations we predict statically. This is useful +in cases where a function contains a single loop with known bound and +another loop with unknown bound. +The known number of iterations is predicted correctly, while +the unknown number of iterations average to roughly 10. This means that the +loop without bounds appears artificially cold relative to the other one. + +@item builtin-expect-probability +Control the probability of the expression having the specified value. This +parameter takes a percentage (i.e.@: 0 ... 100) as input. + +@item builtin-string-cmp-inline-length +The maximum length of a constant string for a builtin string cmp call +eligible for inlining. + +@item align-threshold + +Select fraction of the maximal frequency of executions of a basic block in +a function to align the basic block. + +@item align-loop-iterations + +A loop expected to iterate at least the selected number of iterations is +aligned. + +@item tracer-dynamic-coverage +@itemx tracer-dynamic-coverage-feedback + +This value is used to limit superblock formation once the given percentage of +executed instructions is covered. This limits unnecessary code size +expansion. + +The @option{tracer-dynamic-coverage-feedback} parameter +is used only when profile +feedback is available. The real profiles (as opposed to statically estimated +ones) are much less balanced allowing the threshold to be larger value. + +@item tracer-max-code-growth +Stop tail duplication once code growth has reached given percentage. This is +a rather artificial limit, as most of the duplicates are eliminated later in +cross jumping, so it may be set to much higher values than is the desired code +growth. + +@item tracer-min-branch-ratio + +Stop reverse growth when the reverse probability of best edge is less than this +threshold (in percent). + +@item tracer-min-branch-probability +@itemx tracer-min-branch-probability-feedback + +Stop forward growth if the best edge has probability lower than this +threshold. + +Similarly to @option{tracer-dynamic-coverage} two parameters are +provided. @option{tracer-min-branch-probability-feedback} is used for +compilation with profile feedback and @option{tracer-min-branch-probability} +compilation without. The value for compilation with profile feedback +needs to be more conservative (higher) in order to make tracer +effective. + +@item stack-clash-protection-guard-size +Specify the size of the operating system provided stack guard as +2 raised to @var{num} bytes. Higher values may reduce the +number of explicit probes, but a value larger than the operating system +provided guard will leave code vulnerable to stack clash style attacks. + +@item stack-clash-protection-probe-interval +Stack clash protection involves probing stack space as it is allocated. This +param controls the maximum distance between probes into the stack as 2 raised +to @var{num} bytes. Higher values may reduce the number of explicit probes, but a value +larger than the operating system provided guard will leave code vulnerable to +stack clash style attacks. + +@item max-cse-path-length + +The maximum number of basic blocks on path that CSE considers. + +@item max-cse-insns +The maximum number of instructions CSE processes before flushing. + +@item ggc-min-expand + +GCC uses a garbage collector to manage its own memory allocation. This +parameter specifies the minimum percentage by which the garbage +collector's heap should be allowed to expand between collections. +Tuning this may improve compilation speed; it has no effect on code +generation. + +The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when +RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is +the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If +GCC is not able to calculate RAM on a particular platform, the lower +bound of 30% is used. Setting this parameter and +@option{ggc-min-heapsize} to zero causes a full collection to occur at +every opportunity. This is extremely slow, but can be useful for +debugging. + +@item ggc-min-heapsize + +Minimum size of the garbage collector's heap before it begins bothering +to collect garbage. The first collection occurs after the heap expands +by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again, +tuning this may improve compilation speed, and has no effect on code +generation. + +The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that +tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but +with a lower bound of 4096 (four megabytes) and an upper bound of +131072 (128 megabytes). If GCC is not able to calculate RAM on a +particular platform, the lower bound is used. Setting this parameter +very large effectively disables garbage collection. Setting this +parameter and @option{ggc-min-expand} to zero causes a full collection +to occur at every opportunity. + +@item max-reload-search-insns +The maximum number of instruction reload should look backward for equivalent +register. Increasing values mean more aggressive optimization, making the +compilation time increase with probably slightly better performance. + +@item max-cselib-memory-locations +The maximum number of memory locations cselib should take into account. +Increasing values mean more aggressive optimization, making the compilation time +increase with probably slightly better performance. + +@item max-sched-ready-insns +The maximum number of instructions ready to be issued the scheduler should +consider at any given time during the first scheduling pass. Increasing +values mean more thorough searches, making the compilation time increase +with probably little benefit. + +@item max-sched-region-blocks +The maximum number of blocks in a region to be considered for +interblock scheduling. + +@item max-pipeline-region-blocks +The maximum number of blocks in a region to be considered for +pipelining in the selective scheduler. + +@item max-sched-region-insns +The maximum number of insns in a region to be considered for +interblock scheduling. + +@item max-pipeline-region-insns +The maximum number of insns in a region to be considered for +pipelining in the selective scheduler. + +@item min-spec-prob +The minimum probability (in percents) of reaching a source block +for interblock speculative scheduling. + +@item max-sched-extend-regions-iters +The maximum number of iterations through CFG to extend regions. +A value of 0 disables region extensions. + +@item max-sched-insn-conflict-delay +The maximum conflict delay for an insn to be considered for speculative motion. + +@item sched-spec-prob-cutoff +The minimal probability of speculation success (in percents), so that +speculative insns are scheduled. + +@item sched-state-edge-prob-cutoff +The minimum probability an edge must have for the scheduler to save its +state across it. + +@item sched-mem-true-dep-cost +Minimal distance (in CPU cycles) between store and load targeting same +memory locations. + +@item selsched-max-lookahead +The maximum size of the lookahead window of selective scheduling. It is a +depth of search for available instructions. + +@item selsched-max-sched-times +The maximum number of times that an instruction is scheduled during +selective scheduling. This is the limit on the number of iterations +through which the instruction may be pipelined. + +@item selsched-insns-to-rename +The maximum number of best instructions in the ready list that are considered +for renaming in the selective scheduler. + +@item sms-min-sc +The minimum value of stage count that swing modulo scheduler +generates. + +@item max-last-value-rtl +The maximum size measured as number of RTLs that can be recorded in an expression +in combiner for a pseudo register as last known value of that register. + +@item max-combine-insns +The maximum number of instructions the RTL combiner tries to combine. + +@item integer-share-limit +Small integer constants can use a shared data structure, reducing the +compiler's memory usage and increasing its speed. This sets the maximum +value of a shared integer constant. + +@item ssp-buffer-size +The minimum size of buffers (i.e.@: arrays) that receive stack smashing +protection when @option{-fstack-protector} is used. + +@item min-size-for-stack-sharing +The minimum size of variables taking part in stack slot sharing when not +optimizing. + +@item max-jump-thread-duplication-stmts +Maximum number of statements allowed in a block that needs to be +duplicated when threading jumps. + +@item max-jump-thread-paths +The maximum number of paths to consider when searching for jump threading +opportunities. When arriving at a block, incoming edges are only considered +if the number of paths to be searched so far multiplied by the number of +incoming edges does not exhaust the specified maximum number of paths to +consider. + +@item max-fields-for-field-sensitive +Maximum number of fields in a structure treated in +a field sensitive manner during pointer analysis. + +@item prefetch-latency +Estimate on average number of instructions that are executed before +prefetch finishes. The distance prefetched ahead is proportional +to this constant. Increasing this number may also lead to less +streams being prefetched (see @option{simultaneous-prefetches}). + +@item simultaneous-prefetches +Maximum number of prefetches that can run at the same time. + +@item l1-cache-line-size +The size of cache line in L1 data cache, in bytes. + +@item l1-cache-size +The size of L1 data cache, in kilobytes. + +@item l2-cache-size +The size of L2 data cache, in kilobytes. + +@item prefetch-dynamic-strides +Whether the loop array prefetch pass should issue software prefetch hints +for strides that are non-constant. In some cases this may be +beneficial, though the fact the stride is non-constant may make it +hard to predict when there is clear benefit to issuing these hints. + +Set to 1 if the prefetch hints should be issued for non-constant +strides. Set to 0 if prefetch hints should be issued only for strides that +are known to be constant and below @option{prefetch-minimum-stride}. + +@item prefetch-minimum-stride +Minimum constant stride, in bytes, to start using prefetch hints for. If +the stride is less than this threshold, prefetch hints will not be issued. + +This setting is useful for processors that have hardware prefetchers, in +which case there may be conflicts between the hardware prefetchers and +the software prefetchers. If the hardware prefetchers have a maximum +stride they can handle, it should be used here to improve the use of +software prefetchers. + +A value of -1 means we don't have a threshold and therefore +prefetch hints can be issued for any constant stride. + +This setting is only useful for strides that are known and constant. + +@item destructive-interference-size +@item constructive-interference-size +The values for the C++17 variables +@code{std::hardware_destructive_interference_size} and +@code{std::hardware_constructive_interference_size}. The destructive +interference size is the minimum recommended offset between two +independent concurrently-accessed objects; the constructive +interference size is the maximum recommended size of contiguous memory +accessed together. Typically both will be the size of an L1 cache +line for the target, in bytes. For a generic target covering a range of L1 +cache line sizes, typically the constructive interference size will be +the small end of the range and the destructive size will be the large +end. + +The destructive interference size is intended to be used for layout, +and thus has ABI impact. The default value is not expected to be +stable, and on some targets varies with @option{-mtune}, so use of +this variable in a context where ABI stability is important, such as +the public interface of a library, is strongly discouraged; if it is +used in that context, users can stabilize the value using this +option. + +The constructive interference size is less sensitive, as it is +typically only used in a @samp{static_assert} to make sure that a type +fits within a cache line. + +See also @option{-Winterference-size}. + +@item loop-interchange-max-num-stmts +The maximum number of stmts in a loop to be interchanged. + +@item loop-interchange-stride-ratio +The minimum ratio between stride of two loops for interchange to be profitable. + +@item min-insn-to-prefetch-ratio +The minimum ratio between the number of instructions and the +number of prefetches to enable prefetching in a loop. + +@item prefetch-min-insn-to-mem-ratio +The minimum ratio between the number of instructions and the +number of memory references to enable prefetching in a loop. + +@item use-canonical-types +Whether the compiler should use the ``canonical'' type system. +Should always be 1, which uses a more efficient internal +mechanism for comparing types in C++ and Objective-C++. However, if +bugs in the canonical type system are causing compilation failures, +set this value to 0 to disable canonical types. + +@item switch-conversion-max-branch-ratio +Switch initialization conversion refuses to create arrays that are +bigger than @option{switch-conversion-max-branch-ratio} times the number of +branches in the switch. + +@item max-partial-antic-length +Maximum length of the partial antic set computed during the tree +partial redundancy elimination optimization (@option{-ftree-pre}) when +optimizing at @option{-O3} and above. For some sorts of source code +the enhanced partial redundancy elimination optimization can run away, +consuming all of the memory available on the host machine. This +parameter sets a limit on the length of the sets that are computed, +which prevents the runaway behavior. Setting a value of 0 for +this parameter allows an unlimited set length. + +@item rpo-vn-max-loop-depth +Maximum loop depth that is value-numbered optimistically. +When the limit hits the innermost +@var{rpo-vn-max-loop-depth} loops and the outermost loop in the +loop nest are value-numbered optimistically and the remaining ones not. + +@item sccvn-max-alias-queries-per-access +Maximum number of alias-oracle queries we perform when looking for +redundancies for loads and stores. If this limit is hit the search +is aborted and the load or store is not considered redundant. The +number of queries is algorithmically limited to the number of +stores on all paths from the load to the function entry. + +@item ira-max-loops-num +IRA uses regional register allocation by default. If a function +contains more loops than the number given by this parameter, only at most +the given number of the most frequently-executed loops form regions +for regional register allocation. + +@item ira-max-conflict-table-size +Although IRA uses a sophisticated algorithm to compress the conflict +table, the table can still require excessive amounts of memory for +huge functions. If the conflict table for a function could be more +than the size in MB given by this parameter, the register allocator +instead uses a faster, simpler, and lower-quality +algorithm that does not require building a pseudo-register conflict table. + +@item ira-loop-reserved-regs +IRA can be used to evaluate more accurate register pressure in loops +for decisions to move loop invariants (see @option{-O3}). The number +of available registers reserved for some other purposes is given +by this parameter. Default of the parameter +is the best found from numerous experiments. + +@item ira-consider-dup-in-all-alts +Make IRA to consider matching constraint (duplicated operand number) +heavily in all available alternatives for preferred register class. +If it is set as zero, it means IRA only respects the matching +constraint when it's in the only available alternative with an +appropriate register class. Otherwise, it means IRA will check all +available alternatives for preferred register class even if it has +found some choice with an appropriate register class and respect the +found qualified matching constraint. + +@item lra-inheritance-ebb-probability-cutoff +LRA tries to reuse values reloaded in registers in subsequent insns. +This optimization is called inheritance. EBB is used as a region to +do this optimization. The parameter defines a minimal fall-through +edge probability in percentage used to add BB to inheritance EBB in +LRA. The default value was chosen +from numerous runs of SPEC2000 on x86-64. + +@item loop-invariant-max-bbs-in-loop +Loop invariant motion can be very expensive, both in compilation time and +in amount of needed compile-time memory, with very large loops. Loops +with more basic blocks than this parameter won't have loop invariant +motion optimization performed on them. + +@item loop-max-datarefs-for-datadeps +Building data dependencies is expensive for very large loops. This +parameter limits the number of data references in loops that are +considered for data dependence analysis. These large loops are no +handled by the optimizations using loop data dependencies. + +@item max-vartrack-size +Sets a maximum number of hash table slots to use during variable +tracking dataflow analysis of any function. If this limit is exceeded +with variable tracking at assignments enabled, analysis for that +function is retried without it, after removing all debug insns from +the function. If the limit is exceeded even without debug insns, var +tracking analysis is completely disabled for the function. Setting +the parameter to zero makes it unlimited. + +@item max-vartrack-expr-depth +Sets a maximum number of recursion levels when attempting to map +variable names or debug temporaries to value expressions. This trades +compilation time for more complete debug information. If this is set too +low, value expressions that are available and could be represented in +debug information may end up not being used; setting this higher may +enable the compiler to find more complex debug expressions, but compile +time and memory use may grow. + +@item max-debug-marker-count +Sets a threshold on the number of debug markers (e.g.@: begin stmt +markers) to avoid complexity explosion at inlining or expanding to RTL. +If a function has more such gimple stmts than the set limit, such stmts +will be dropped from the inlined copy of a function, and from its RTL +expansion. + +@item min-nondebug-insn-uid +Use uids starting at this parameter for nondebug insns. The range below +the parameter is reserved exclusively for debug insns created by +@option{-fvar-tracking-assignments}, but debug insns may get +(non-overlapping) uids above it if the reserved range is exhausted. + +@item ipa-sra-ptr-growth-factor +IPA-SRA replaces a pointer to an aggregate with one or more new +parameters only when their cumulative size is less or equal to +@option{ipa-sra-ptr-growth-factor} times the size of the original +pointer parameter. + +@item ipa-sra-max-replacements +Maximum pieces of an aggregate that IPA-SRA tracks. As a +consequence, it is also the maximum number of replacements of a formal +parameter. + +@item sra-max-scalarization-size-Ospeed +@itemx sra-max-scalarization-size-Osize +The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to +replace scalar parts of aggregates with uses of independent scalar +variables. These parameters control the maximum size, in storage units, +of aggregate which is considered for replacement when compiling for +speed +(@option{sra-max-scalarization-size-Ospeed}) or size +(@option{sra-max-scalarization-size-Osize}) respectively. + +@item sra-max-propagations +The maximum number of artificial accesses that Scalar Replacement of +Aggregates (SRA) will track, per one local variable, in order to +facilitate copy propagation. + +@item tm-max-aggregate-size +When making copies of thread-local variables in a transaction, this +parameter specifies the size in bytes after which variables are +saved with the logging functions as opposed to save/restore code +sequence pairs. This option only applies when using +@option{-fgnu-tm}. + +@item graphite-max-nb-scop-params +To avoid exponential effects in the Graphite loop transforms, the +number of parameters in a Static Control Part (SCoP) is bounded. +A value of zero can be used to lift +the bound. A variable whose value is unknown at compilation time and +defined outside a SCoP is a parameter of the SCoP. + +@item loop-block-tile-size +Loop blocking or strip mining transforms, enabled with +@option{-floop-block} or @option{-floop-strip-mine}, strip mine each +loop in the loop nest by a given number of iterations. The strip +length can be changed using the @option{loop-block-tile-size} +parameter. + +@item ipa-jump-function-lookups +Specifies number of statements visited during jump function offset discovery. + +@item ipa-cp-value-list-size +IPA-CP attempts to track all possible values and types passed to a function's +parameter in order to propagate them and perform devirtualization. +@option{ipa-cp-value-list-size} is the maximum number of values and types it +stores per one formal parameter of a function. + +@item ipa-cp-eval-threshold +IPA-CP calculates its own score of cloning profitability heuristics +and performs those cloning opportunities with scores that exceed +@option{ipa-cp-eval-threshold}. + +@item ipa-cp-max-recursive-depth +Maximum depth of recursive cloning for self-recursive function. + +@item ipa-cp-min-recursive-probability +Recursive cloning only when the probability of call being executed exceeds +the parameter. + +@item ipa-cp-profile-count-base +When using @option{-fprofile-use} option, IPA-CP will consider the measured +execution count of a call graph edge at this percentage position in their +histogram as the basis for its heuristics calculation. + +@item ipa-cp-recursive-freq-factor +The number of times interprocedural copy propagation expects recursive +functions to call themselves. + +@item ipa-cp-recursion-penalty +Percentage penalty the recursive functions will receive when they +are evaluated for cloning. + +@item ipa-cp-single-call-penalty +Percentage penalty functions containing a single call to another +function will receive when they are evaluated for cloning. + +@item ipa-max-agg-items +IPA-CP is also capable to propagate a number of scalar values passed +in an aggregate. @option{ipa-max-agg-items} controls the maximum +number of such values per one parameter. + +@item ipa-cp-loop-hint-bonus +When IPA-CP determines that a cloning candidate would make the number +of iterations of a loop known, it adds a bonus of +@option{ipa-cp-loop-hint-bonus} to the profitability score of +the candidate. + +@item ipa-max-loop-predicates +The maximum number of different predicates IPA will use to describe when +loops in a function have known properties. + +@item ipa-max-aa-steps +During its analysis of function bodies, IPA-CP employs alias analysis +in order to track values pointed to by function parameters. In order +not spend too much time analyzing huge functions, it gives up and +consider all memory clobbered after examining +@option{ipa-max-aa-steps} statements modifying memory. + +@item ipa-max-switch-predicate-bounds +Maximal number of boundary endpoints of case ranges of switch statement. +For switch exceeding this limit, IPA-CP will not construct cloning cost +predicate, which is used to estimate cloning benefit, for default case +of the switch statement. + +@item ipa-max-param-expr-ops +IPA-CP will analyze conditional statement that references some function +parameter to estimate benefit for cloning upon certain constant value. +But if number of operations in a parameter expression exceeds +@option{ipa-max-param-expr-ops}, the expression is treated as complicated +one, and is not handled by IPA analysis. + +@item lto-partitions +Specify desired number of partitions produced during WHOPR compilation. +The number of partitions should exceed the number of CPUs used for compilation. + +@item lto-min-partition +Size of minimal partition for WHOPR (in estimated instructions). +This prevents expenses of splitting very small programs into too many +partitions. + +@item lto-max-partition +Size of max partition for WHOPR (in estimated instructions). +to provide an upper bound for individual size of partition. +Meant to be used only with balanced partitioning. + +@item lto-max-streaming-parallelism +Maximal number of parallel processes used for LTO streaming. + +@item cxx-max-namespaces-for-diagnostic-help +The maximum number of namespaces to consult for suggestions when C++ +name lookup fails for an identifier. + +@item sink-frequency-threshold +The maximum relative execution frequency (in percents) of the target block +relative to a statement's original block to allow statement sinking of a +statement. Larger numbers result in more aggressive statement sinking. +A small positive adjustment is applied for +statements with memory operands as those are even more profitable so sink. + +@item max-stores-to-sink +The maximum number of conditional store pairs that can be sunk. Set to 0 +if either vectorization (@option{-ftree-vectorize}) or if-conversion +(@option{-ftree-loop-if-convert}) is disabled. + +@item case-values-threshold +The smallest number of different values for which it is best to use a +jump-table instead of a tree of conditional branches. If the value is +0, use the default for the machine. + +@item jump-table-max-growth-ratio-for-size +The maximum code size growth ratio when expanding +into a jump table (in percent). The parameter is used when +optimizing for size. + +@item jump-table-max-growth-ratio-for-speed +The maximum code size growth ratio when expanding +into a jump table (in percent). The parameter is used when +optimizing for speed. + +@item tree-reassoc-width +Set the maximum number of instructions executed in parallel in +reassociated tree. This parameter overrides target dependent +heuristics used by default if has non zero value. + +@item sched-pressure-algorithm +Choose between the two available implementations of +@option{-fsched-pressure}. Algorithm 1 is the original implementation +and is the more likely to prevent instructions from being reordered. +Algorithm 2 was designed to be a compromise between the relatively +conservative approach taken by algorithm 1 and the rather aggressive +approach taken by the default scheduler. It relies more heavily on +having a regular register file and accurate register pressure classes. +See @file{haifa-sched.cc} in the GCC sources for more details. + +The default choice depends on the target. + +@item max-slsr-cand-scan +Set the maximum number of existing candidates that are considered when +seeking a basis for a new straight-line strength reduction candidate. + +@item asan-globals +Enable buffer overflow detection for global objects. This kind +of protection is enabled by default if you are using +@option{-fsanitize=address} option. +To disable global objects protection use @option{--param asan-globals=0}. + +@item asan-stack +Enable buffer overflow detection for stack objects. This kind of +protection is enabled by default when using @option{-fsanitize=address}. +To disable stack protection use @option{--param asan-stack=0} option. + +@item asan-instrument-reads +Enable buffer overflow detection for memory reads. This kind of +protection is enabled by default when using @option{-fsanitize=address}. +To disable memory reads protection use +@option{--param asan-instrument-reads=0}. + +@item asan-instrument-writes +Enable buffer overflow detection for memory writes. This kind of +protection is enabled by default when using @option{-fsanitize=address}. +To disable memory writes protection use +@option{--param asan-instrument-writes=0} option. + +@item asan-memintrin +Enable detection for built-in functions. This kind of protection +is enabled by default when using @option{-fsanitize=address}. +To disable built-in functions protection use +@option{--param asan-memintrin=0}. + +@item asan-use-after-return +Enable detection of use-after-return. This kind of protection +is enabled by default when using the @option{-fsanitize=address} option. +To disable it use @option{--param asan-use-after-return=0}. + +Note: By default the check is disabled at run time. To enable it, +add @code{detect_stack_use_after_return=1} to the environment variable +@env{ASAN_OPTIONS}. + +@item asan-instrumentation-with-call-threshold +If number of memory accesses in function being instrumented +is greater or equal to this number, use callbacks instead of inline checks. +E.g. to disable inline code use +@option{--param asan-instrumentation-with-call-threshold=0}. + +@item hwasan-instrument-stack +Enable hwasan instrumentation of statically sized stack-allocated variables. +This kind of instrumentation is enabled by default when using +@option{-fsanitize=hwaddress} and disabled by default when using +@option{-fsanitize=kernel-hwaddress}. +To disable stack instrumentation use +@option{--param hwasan-instrument-stack=0}, and to enable it use +@option{--param hwasan-instrument-stack=1}. + +@item hwasan-random-frame-tag +When using stack instrumentation, decide tags for stack variables using a +deterministic sequence beginning at a random tag for each frame. With this +parameter unset tags are chosen using the same sequence but beginning from 1. +This is enabled by default for @option{-fsanitize=hwaddress} and unavailable +for @option{-fsanitize=kernel-hwaddress}. +To disable it use @option{--param hwasan-random-frame-tag=0}. + +@item hwasan-instrument-allocas +Enable hwasan instrumentation of dynamically sized stack-allocated variables. +This kind of instrumentation is enabled by default when using +@option{-fsanitize=hwaddress} and disabled by default when using +@option{-fsanitize=kernel-hwaddress}. +To disable instrumentation of such variables use +@option{--param hwasan-instrument-allocas=0}, and to enable it use +@option{--param hwasan-instrument-allocas=1}. + +@item hwasan-instrument-reads +Enable hwasan checks on memory reads. Instrumentation of reads is enabled by +default for both @option{-fsanitize=hwaddress} and +@option{-fsanitize=kernel-hwaddress}. +To disable checking memory reads use +@option{--param hwasan-instrument-reads=0}. + +@item hwasan-instrument-writes +Enable hwasan checks on memory writes. Instrumentation of writes is enabled by +default for both @option{-fsanitize=hwaddress} and +@option{-fsanitize=kernel-hwaddress}. +To disable checking memory writes use +@option{--param hwasan-instrument-writes=0}. + +@item hwasan-instrument-mem-intrinsics +Enable hwasan instrumentation of builtin functions. Instrumentation of these +builtin functions is enabled by default for both @option{-fsanitize=hwaddress} +and @option{-fsanitize=kernel-hwaddress}. +To disable instrumentation of builtin functions use +@option{--param hwasan-instrument-mem-intrinsics=0}. + +@item use-after-scope-direct-emission-threshold +If the size of a local variable in bytes is smaller or equal to this +number, directly poison (or unpoison) shadow memory instead of using +run-time callbacks. + +@item tsan-distinguish-volatile +Emit special instrumentation for accesses to volatiles. + +@item tsan-instrument-func-entry-exit +Emit instrumentation calls to __tsan_func_entry() and __tsan_func_exit(). + +@item max-fsm-thread-path-insns +Maximum number of instructions to copy when duplicating blocks on a +finite state automaton jump thread path. + +@item threader-debug +threader-debug=[none|all] Enables verbose dumping of the threader solver. + +@item parloops-chunk-size +Chunk size of omp schedule for loops parallelized by parloops. + +@item parloops-schedule +Schedule type of omp schedule for loops parallelized by parloops (static, +dynamic, guided, auto, runtime). + +@item parloops-min-per-thread +The minimum number of iterations per thread of an innermost parallelized +loop for which the parallelized variant is preferred over the single threaded +one. Note that for a parallelized loop nest the +minimum number of iterations of the outermost loop per thread is two. + +@item max-ssa-name-query-depth +Maximum depth of recursion when querying properties of SSA names in things +like fold routines. One level of recursion corresponds to following a +use-def chain. + +@item max-speculative-devirt-maydefs +The maximum number of may-defs we analyze when looking for a must-def +specifying the dynamic type of an object that invokes a virtual call +we may be able to devirtualize speculatively. + +@item max-vrp-switch-assertions +The maximum number of assertions to add along the default edge of a switch +statement during VRP. + +@item evrp-sparse-threshold +Maximum number of basic blocks before EVRP uses a sparse cache. + +@item vrp1-mode +Specifies the mode VRP pass 1 should operate in. + +@item vrp2-mode +Specifies the mode VRP pass 2 should operate in. + +@item ranger-debug +Specifies the type of debug output to be issued for ranges. + +@item evrp-switch-limit +Specifies the maximum number of switch cases before EVRP ignores a switch. + +@item unroll-jam-min-percent +The minimum percentage of memory references that must be optimized +away for the unroll-and-jam transformation to be considered profitable. + +@item unroll-jam-max-unroll +The maximum number of times the outer loop should be unrolled by +the unroll-and-jam transformation. + +@item max-rtl-if-conversion-unpredictable-cost +Maximum permissible cost for the sequence that would be generated +by the RTL if-conversion pass for a branch that is considered unpredictable. + +@item max-variable-expansions-in-unroller +If @option{-fvariable-expansion-in-unroller} is used, the maximum number +of times that an individual variable will be expanded during loop unrolling. + +@item partial-inlining-entry-probability +Maximum probability of the entry BB of split region +(in percent relative to entry BB of the function) +to make partial inlining happen. + +@item max-tracked-strlens +Maximum number of strings for which strlen optimization pass will +track string lengths. + +@item gcse-after-reload-partial-fraction +The threshold ratio for performing partial redundancy +elimination after reload. + +@item gcse-after-reload-critical-fraction +The threshold ratio of critical edges execution count that +permit performing redundancy elimination after reload. + +@item max-loop-header-insns +The maximum number of insns in loop header duplicated +by the copy loop headers pass. + +@item vect-epilogues-nomask +Enable loop epilogue vectorization using smaller vector size. + +@item vect-partial-vector-usage +Controls when the loop vectorizer considers using partial vector loads +and stores as an alternative to falling back to scalar code. 0 stops +the vectorizer from ever using partial vector loads and stores. 1 allows +partial vector loads and stores if vectorization removes the need for the +code to iterate. 2 allows partial vector loads and stores in all loops. +The parameter only has an effect on targets that support partial +vector loads and stores. + +@item vect-inner-loop-cost-factor +The maximum factor which the loop vectorizer applies to the cost of statements +in an inner loop relative to the loop being vectorized. The factor applied +is the maximum of the estimated number of iterations of the inner loop and +this parameter. The default value of this parameter is 50. + +@item vect-induction-float +Enable loop vectorization of floating point inductions. + +@item avoid-fma-max-bits +Maximum number of bits for which we avoid creating FMAs. + +@item sms-loop-average-count-threshold +A threshold on the average loop count considered by the swing modulo scheduler. + +@item sms-dfa-history +The number of cycles the swing modulo scheduler considers when checking +conflicts using DFA. + +@item graphite-allow-codegen-errors +Whether codegen errors should be ICEs when @option{-fchecking}. + +@item sms-max-ii-factor +A factor for tuning the upper bound that swing modulo scheduler +uses for scheduling a loop. + +@item lra-max-considered-reload-pseudos +The max number of reload pseudos which are considered during +spilling a non-reload pseudo. + +@item max-pow-sqrt-depth +Maximum depth of sqrt chains to use when synthesizing exponentiation +by a real constant. + +@item max-dse-active-local-stores +Maximum number of active local stores in RTL dead store elimination. + +@item asan-instrument-allocas +Enable asan allocas/VLAs protection. + +@item max-iterations-computation-cost +Bound on the cost of an expression to compute the number of iterations. + +@item max-isl-operations +Maximum number of isl operations, 0 means unlimited. + +@item graphite-max-arrays-per-scop +Maximum number of arrays per scop. + +@item max-vartrack-reverse-op-size +Max. size of loc list for which reverse ops should be added. + +@item fsm-scale-path-stmts +Scale factor to apply to the number of statements in a threading path +when comparing to the number of (scaled) blocks. + +@item uninit-control-dep-attempts +Maximum number of nested calls to search for control dependencies +during uninitialized variable analysis. + +@item fsm-scale-path-blocks +Scale factor to apply to the number of blocks in a threading path +when comparing to the number of (scaled) statements. + +@item sched-autopref-queue-depth +Hardware autoprefetcher scheduler model control flag. +Number of lookahead cycles the model looks into; at ' +' only enable instruction sorting heuristic. + +@item loop-versioning-max-inner-insns +The maximum number of instructions that an inner loop can have +before the loop versioning pass considers it too big to copy. + +@item loop-versioning-max-outer-insns +The maximum number of instructions that an outer loop can have +before the loop versioning pass considers it too big to copy, +discounting any instructions in inner loops that directly benefit +from versioning. + +@item ssa-name-def-chain-limit +The maximum number of SSA_NAME assignments to follow in determining +a property of a variable such as its value. This limits the number +of iterations or recursive calls GCC performs when optimizing certain +statements or when determining their validity prior to issuing +diagnostics. + +@item store-merging-max-size +Maximum size of a single store merging region in bytes. + +@item hash-table-verification-limit +The number of elements for which hash table verification is done +for each searched element. + +@item max-find-base-term-values +Maximum number of VALUEs handled during a single find_base_term call. + +@item analyzer-max-enodes-per-program-point +The maximum number of exploded nodes per program point within +the analyzer, before terminating analysis of that point. + +@item analyzer-max-constraints +The maximum number of constraints per state. + +@item analyzer-min-snodes-for-call-summary +The minimum number of supernodes within a function for the +analyzer to consider summarizing its effects at call sites. + +@item analyzer-max-enodes-for-full-dump +The maximum depth of exploded nodes that should appear in a dot dump +before switching to a less verbose format. + +@item analyzer-max-recursion-depth +The maximum number of times a callsite can appear in a call stack +within the analyzer, before terminating analysis of a call that would +recurse deeper. + +@item analyzer-max-svalue-depth +The maximum depth of a symbolic value, before approximating +the value as unknown. + +@item analyzer-max-infeasible-edges +The maximum number of infeasible edges to reject before declaring +a diagnostic as infeasible. + +@item gimple-fe-computed-hot-bb-threshold +The number of executions of a basic block which is considered hot. +The parameter is used only in GIMPLE FE. + +@item analyzer-bb-explosion-factor +The maximum number of 'after supernode' exploded nodes within the analyzer +per supernode, before terminating analysis. + +@item ranger-logical-depth +Maximum depth of logical expression evaluation ranger will look through +when evaluating outgoing edge ranges. + +@item relation-block-limit +Maximum number of relations the oracle will register in a basic block. + +@item min-pagesize +Minimum page size for warning purposes. + +@item openacc-kernels +Specify mode of OpenACC `kernels' constructs handling. +With @option{--param=openacc-kernels=decompose}, OpenACC `kernels' +constructs are decomposed into parts, a sequence of compute +constructs, each then handled individually. +This is work in progress. +With @option{--param=openacc-kernels=parloops}, OpenACC `kernels' +constructs are handled by the @samp{parloops} pass, en bloc. +This is the current default. + +@item openacc-privatization +Specify mode of OpenACC privatization diagnostics for +@option{-fopt-info-omp-note} and applicable +@option{-fdump-tree-*-details}. +With @option{--param=openacc-privatization=quiet}, don't diagnose. +This is the current default. +With @option{--param=openacc-privatization=noisy}, do diagnose. + +@end table + +The following choices of @var{name} are available on AArch64 targets: + +@table @gcctabopt +@item aarch64-sve-compare-costs +When vectorizing for SVE, consider using ``unpacked'' vectors for +smaller elements and use the cost model to pick the cheapest approach. +Also use the cost model to choose between SVE and Advanced SIMD vectorization. + +Using unpacked vectors includes storing smaller elements in larger +containers and accessing elements with extending loads and truncating +stores. + +@item aarch64-float-recp-precision +The number of Newton iterations for calculating the reciprocal for float type. +The precision of division is proportional to this param when division +approximation is enabled. The default value is 1. + +@item aarch64-double-recp-precision +The number of Newton iterations for calculating the reciprocal for double type. +The precision of division is propotional to this param when division +approximation is enabled. The default value is 2. + +@item aarch64-autovec-preference +Force an ISA selection strategy for auto-vectorization. Accepts values from +0 to 4, inclusive. +@table @samp +@item 0 +Use the default heuristics. +@item 1 +Use only Advanced SIMD for auto-vectorization. +@item 2 +Use only SVE for auto-vectorization. +@item 3 +Use both Advanced SIMD and SVE. Prefer Advanced SIMD when the costs are +deemed equal. +@item 4 +Use both Advanced SIMD and SVE. Prefer SVE when the costs are deemed equal. +@end table +The default value is 0. + +@item aarch64-loop-vect-issue-rate-niters +The tuning for some AArch64 CPUs tries to take both latencies and issue +rates into account when deciding whether a loop should be vectorized +using SVE, vectorized using Advanced SIMD, or not vectorized at all. +If this parameter is set to @var{n}, GCC will not use this heuristic +for loops that are known to execute in fewer than @var{n} Advanced +SIMD iterations. + +@item aarch64-vect-unroll-limit +The vectorizer will use available tuning information to determine whether it +would be beneficial to unroll the main vectorized loop and by how much. This +parameter set's the upper bound of how much the vectorizer will unroll the main +loop. The default value is four. + +@end table + +The following choices of @var{name} are available on i386 and x86_64 targets: + +@table @gcctabopt +@item x86-stlf-window-ninsns +Instructions number above which STFL stall penalty can be compensated. + +@end table + +@end table + +@node Instrumentation Options +@section Program Instrumentation Options +@cindex instrumentation options +@cindex program instrumentation options +@cindex run-time error checking options +@cindex profiling options +@cindex options, program instrumentation +@cindex options, run-time error checking +@cindex options, profiling + +GCC supports a number of command-line options that control adding +run-time instrumentation to the code it normally generates. +For example, one purpose of instrumentation is collect profiling +statistics for use in finding program hot spots, code coverage +analysis, or profile-guided optimizations. +Another class of program instrumentation is adding run-time checking +to detect programming errors like invalid pointer +dereferences or out-of-bounds array accesses, as well as deliberately +hostile attacks such as stack smashing or C++ vtable hijacking. +There is also a general hook which can be used to implement other +forms of tracing or function-level instrumentation for debug or +program analysis purposes. + +@table @gcctabopt +@cindex @command{prof} +@cindex @command{gprof} +@item -p +@itemx -pg +@opindex p +@opindex pg +Generate extra code to write profile information suitable for the +analysis program @command{prof} (for @option{-p}) or @command{gprof} +(for @option{-pg}). You must use this option when compiling +the source files you want data about, and you must also use it when +linking. + +You can use the function attribute @code{no_instrument_function} to +suppress profiling of individual functions when compiling with these options. +@xref{Common Function Attributes}. + +@item -fprofile-arcs +@opindex fprofile-arcs +Add code so that program flow @dfn{arcs} are instrumented. During +execution the program records how many times each branch and call is +executed and how many times it is taken or returns. On targets that support +constructors with priority support, profiling properly handles constructors, +destructors and C++ constructors (and destructors) of classes which are used +as a type of a global variable. + +When the compiled +program exits it saves this data to a file called +@file{@var{auxname}.gcda} for each source file. The data may be used for +profile-directed optimizations (@option{-fbranch-probabilities}), or for +test coverage analysis (@option{-ftest-coverage}). Each object file's +@var{auxname} is generated from the name of the output file, if +explicitly specified and it is not the final executable, otherwise it is +the basename of the source file. In both cases any suffix is removed +(e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or +@file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}). + +Note that if a command line directly links source files, the corresponding +@var{.gcda} files will be prefixed with the unsuffixed name of the output file. +E.g. @code{gcc a.c b.c -o binary} would generate @file{binary-a.gcda} and +@file{binary-b.gcda} files. + +@xref{Cross-profiling}. + +@cindex @command{gcov} +@item --coverage +@opindex coverage + +This option is used to compile and link code instrumented for coverage +analysis. The option is a synonym for @option{-fprofile-arcs} +@option{-ftest-coverage} (when compiling) and @option{-lgcov} (when +linking). See the documentation for those options for more details. + +@itemize + +@item +Compile the source files with @option{-fprofile-arcs} plus optimization +and code generation options. For test coverage analysis, use the +additional @option{-ftest-coverage} option. You do not need to profile +every source file in a program. + +@item +Compile the source files additionally with @option{-fprofile-abs-path} +to create absolute path names in the @file{.gcno} files. This allows +@command{gcov} to find the correct sources in projects where compilations +occur with different working directories. + +@item +Link your object files with @option{-lgcov} or @option{-fprofile-arcs} +(the latter implies the former). + +@item +Run the program on a representative workload to generate the arc profile +information. This may be repeated any number of times. You can run +concurrent instances of your program, and provided that the file system +supports locking, the data files will be correctly updated. Unless +a strict ISO C dialect option is in effect, @code{fork} calls are +detected and correctly handled without double counting. + +Moreover, an object file can be recompiled multiple times +and the corresponding @file{.gcda} file merges as long as +the source file and the compiler options are unchanged. + +@item +For profile-directed optimizations, compile the source files again with +the same optimization and code generation options plus +@option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that +Control Optimization}). + +@item +For test coverage analysis, use @command{gcov} to produce human readable +information from the @file{.gcno} and @file{.gcda} files. Refer to the +@command{gcov} documentation for further information. + +@end itemize + +With @option{-fprofile-arcs}, for each function of your program GCC +creates a program flow graph, then finds a spanning tree for the graph. +Only arcs that are not on the spanning tree have to be instrumented: the +compiler adds code to count the number of times that these arcs are +executed. When an arc is the only exit or only entrance to a block, the +instrumentation code can be added to the block; otherwise, a new basic +block must be created to hold the instrumentation code. + +@need 2000 +@item -ftest-coverage +@opindex ftest-coverage +Produce a notes file that the @command{gcov} code-coverage utility +(@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to +show program coverage. Each source file's note file is called +@file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option +above for a description of @var{auxname} and instructions on how to +generate test coverage data. Coverage data matches the source files +more closely if you do not optimize. + +@item -fprofile-abs-path +@opindex fprofile-abs-path +Automatically convert relative source file names to absolute path names +in the @file{.gcno} files. This allows @command{gcov} to find the correct +sources in projects where compilations occur with different working +directories. + +@item -fprofile-dir=@var{path} +@opindex fprofile-dir + +Set the directory to search for the profile data files in to @var{path}. +This option affects only the profile data generated by +@option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs} +and used by @option{-fprofile-use} and @option{-fbranch-probabilities} +and its related options. Both absolute and relative paths can be used. +By default, GCC uses the current directory as @var{path}, thus the +profile data file appears in the same directory as the object file. +In order to prevent the file name clashing, if the object file name is +not an absolute path, we mangle the absolute path of the +@file{@var{sourcename}.gcda} file and use it as the file name of a +@file{.gcda} file. See details about the file naming in @option{-fprofile-arcs}. +See similar option @option{-fprofile-note}. + +When an executable is run in a massive parallel environment, it is recommended +to save profile to different folders. That can be done with variables +in @var{path} that are exported during run-time: + +@table @gcctabopt + +@item %p +process ID. + +@item %q@{VAR@} +value of environment variable @var{VAR} + +@end table + +@item -fprofile-generate +@itemx -fprofile-generate=@var{path} +@opindex fprofile-generate + +Enable options usually used for instrumenting application to produce +profile useful for later recompilation with profile feedback based +optimization. You must use @option{-fprofile-generate} both when +compiling and when linking your program. + +The following options are enabled: +@option{-fprofile-arcs}, @option{-fprofile-values}, +@option{-finline-functions}, and @option{-fipa-bit-cp}. + +If @var{path} is specified, GCC looks at the @var{path} to find +the profile feedback data files. See @option{-fprofile-dir}. + +To optimize the program based on the collected profile information, use +@option{-fprofile-use}. @xref{Optimize Options}, for more information. + +@item -fprofile-info-section +@itemx -fprofile-info-section=@var{name} +@opindex fprofile-info-section + +Register the profile information in the specified section instead of using a +constructor/destructor. The section name is @var{name} if it is specified, +otherwise the section name defaults to @code{.gcov_info}. A pointer to the +profile information generated by @option{-fprofile-arcs} is placed in the +specified section for each translation unit. This option disables the profile +information registration through a constructor and it disables the profile +information processing through a destructor. This option is not intended to be +used in hosted environments such as GNU/Linux. It targets freestanding +environments (for example embedded systems) with limited resources which do not +support constructors/destructors or the C library file I/O. + +The linker could collect the input sections in a continuous memory block and +define start and end symbols. A GNU linker script example which defines a +linker output section follows: + +@smallexample + .gcov_info : + @{ + PROVIDE (__gcov_info_start = .); + KEEP (*(.gcov_info)) + PROVIDE (__gcov_info_end = .); + @} +@end smallexample + +The program could dump the profiling information registered in this linker set +for example like this: + +@smallexample +#include +#include +#include + +extern const struct gcov_info *const __gcov_info_start[]; +extern const struct gcov_info *const __gcov_info_end[]; + +static void +dump (const void *d, unsigned n, void *arg) +@{ + const unsigned char *c = d; + + for (unsigned i = 0; i < n; ++i) + printf ("%02x", c[i]); +@} + +static void +filename (const char *f, void *arg) +@{ + __gcov_filename_to_gcfn (f, dump, arg ); +@} + +static void * +allocate (unsigned length, void *arg) +@{ + return malloc (length); +@} + +static void +dump_gcov_info (void) +@{ + const struct gcov_info *const *info = __gcov_info_start; + const struct gcov_info *const *end = __gcov_info_end; + + /* Obfuscate variable to prevent compiler optimizations. */ + __asm__ ("" : "+r" (info)); + + while (info != end) + @{ + void *arg = NULL; + __gcov_info_to_gcda (*info, filename, dump, allocate, arg); + putchar ('\n'); + ++info; + @} +@} + +int +main (void) +@{ + dump_gcov_info (); + return 0; +@} +@end smallexample + +The @command{merge-stream} subcommand of @command{gcov-tool} may be used to +deserialize the data stream generated by the @code{__gcov_filename_to_gcfn} and +@code{__gcov_info_to_gcda} functions and merge the profile information into +@file{.gcda} files on the host filesystem. + +@item -fprofile-note=@var{path} +@opindex fprofile-note + +If @var{path} is specified, GCC saves @file{.gcno} file into @var{path} +location. If you combine the option with multiple source files, +the @file{.gcno} file will be overwritten. + +@item -fprofile-prefix-path=@var{path} +@opindex fprofile-prefix-path + +This option can be used in combination with +@option{profile-generate=}@var{profile_dir} and +@option{profile-use=}@var{profile_dir} to inform GCC where is the base +directory of built source tree. By default @var{profile_dir} will contain +files with mangled absolute paths of all object files in the built project. +This is not desirable when directory used to build the instrumented binary +differs from the directory used to build the binary optimized with profile +feedback because the profile data will not be found during the optimized build. +In such setups @option{-fprofile-prefix-path=}@var{path} with @var{path} +pointing to the base directory of the build can be used to strip the irrelevant +part of the path and keep all file names relative to the main build directory. + +@item -fprofile-prefix-map=@var{old}=@var{new} +@opindex fprofile-prefix-map +When compiling files residing in directory @file{@var{old}}, record +profiling information (with @option{--coverage}) +describing them as if the files resided in +directory @file{@var{new}} instead. +See also @option{-ffile-prefix-map}. + +@item -fprofile-update=@var{method} +@opindex fprofile-update + +Alter the update method for an application instrumented for profile +feedback based optimization. The @var{method} argument should be one of +@samp{single}, @samp{atomic} or @samp{prefer-atomic}. +The first one is useful for single-threaded applications, +while the second one prevents profile corruption by emitting thread-safe code. + +@strong{Warning:} When an application does not properly join all threads +(or creates an detached thread), a profile file can be still corrupted. + +Using @samp{prefer-atomic} would be transformed either to @samp{atomic}, +when supported by a target, or to @samp{single} otherwise. The GCC driver +automatically selects @samp{prefer-atomic} when @option{-pthread} +is present in the command line. + +@item -fprofile-filter-files=@var{regex} +@opindex fprofile-filter-files + +Instrument only functions from files whose name matches +any of the regular expressions (separated by semi-colons). + +For example, @option{-fprofile-filter-files=main\.c;module.*\.c} will instrument +only @file{main.c} and all C files starting with 'module'. + +@item -fprofile-exclude-files=@var{regex} +@opindex fprofile-exclude-files + +Instrument only functions from files whose name does not match +any of the regular expressions (separated by semi-colons). + +For example, @option{-fprofile-exclude-files=/usr/.*} will prevent instrumentation +of all files that are located in the @file{/usr/} folder. + +@item -fprofile-reproducible=@r{[}multithreaded@r{|}parallel-runs@r{|}serial@r{]} +@opindex fprofile-reproducible +Control level of reproducibility of profile gathered by +@code{-fprofile-generate}. This makes it possible to rebuild program +with same outcome which is useful, for example, for distribution +packages. + +With @option{-fprofile-reproducible=serial} the profile gathered by +@option{-fprofile-generate} is reproducible provided the trained program +behaves the same at each invocation of the train run, it is not +multi-threaded and profile data streaming is always done in the same +order. Note that profile streaming happens at the end of program run but +also before @code{fork} function is invoked. + +Note that it is quite common that execution counts of some part of +programs depends, for example, on length of temporary file names or +memory space randomization (that may affect hash-table collision rate). +Such non-reproducible part of programs may be annotated by +@code{no_instrument_function} function attribute. @command{gcov-dump} with +@option{-l} can be used to dump gathered data and verify that they are +indeed reproducible. + +With @option{-fprofile-reproducible=parallel-runs} collected profile +stays reproducible regardless the order of streaming of the data into +gcda files. This setting makes it possible to run multiple instances of +instrumented program in parallel (such as with @code{make -j}). This +reduces quality of gathered data, in particular of indirect call +profiling. + +@item -fsanitize=address +@opindex fsanitize=address +Enable AddressSanitizer, a fast memory error detector. +Memory access instructions are instrumented to detect +out-of-bounds and use-after-free bugs. +The option enables @option{-fsanitize-address-use-after-scope}. +See @uref{https://github.com/google/sanitizers/wiki/AddressSanitizer} for +more details. The run-time behavior can be influenced using the +@env{ASAN_OPTIONS} environment variable. When set to @code{help=1}, +the available options are shown at startup of the instrumented program. See +@url{https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags} +for a list of supported options. +The option cannot be combined with @option{-fsanitize=thread} or +@option{-fsanitize=hwaddress}. Note that the only target +@option{-fsanitize=hwaddress} is currently supported on is AArch64. + +@item -fsanitize=kernel-address +@opindex fsanitize=kernel-address +Enable AddressSanitizer for Linux kernel. +See @uref{https://github.com/google/kasan} for more details. + +@item -fsanitize=hwaddress +@opindex fsanitize=hwaddress +Enable Hardware-assisted AddressSanitizer, which uses a hardware ability to +ignore the top byte of a pointer to allow the detection of memory errors with +a low memory overhead. +Memory access instructions are instrumented to detect out-of-bounds and +use-after-free bugs. +The option enables @option{-fsanitize-address-use-after-scope}. +See +@uref{https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html} +for more details. The run-time behavior can be influenced using the +@env{HWASAN_OPTIONS} environment variable. When set to @code{help=1}, +the available options are shown at startup of the instrumented program. +The option cannot be combined with @option{-fsanitize=thread} or +@option{-fsanitize=address}, and is currently only available on AArch64. + +@item -fsanitize=kernel-hwaddress +@opindex fsanitize=kernel-hwaddress +Enable Hardware-assisted AddressSanitizer for compilation of the Linux kernel. +Similar to @option{-fsanitize=kernel-address} but using an alternate +instrumentation method, and similar to @option{-fsanitize=hwaddress} but with +instrumentation differences necessary for compiling the Linux kernel. +These differences are to avoid hwasan library initialization calls and to +account for the stack pointer having a different value in its top byte. + +@emph{Note:} This option has different defaults to the @option{-fsanitize=hwaddress}. +Instrumenting the stack and alloca calls are not on by default but are still +possible by specifying the command-line options +@option{--param hwasan-instrument-stack=1} and +@option{--param hwasan-instrument-allocas=1} respectively. Using a random frame +tag is not implemented for kernel instrumentation. + +@item -fsanitize=pointer-compare +@opindex fsanitize=pointer-compare +Instrument comparison operation (<, <=, >, >=) with pointer operands. +The option must be combined with either @option{-fsanitize=kernel-address} or +@option{-fsanitize=address} +The option cannot be combined with @option{-fsanitize=thread}. +Note: By default the check is disabled at run time. To enable it, +add @code{detect_invalid_pointer_pairs=2} to the environment variable +@env{ASAN_OPTIONS}. Using @code{detect_invalid_pointer_pairs=1} detects +invalid operation only when both pointers are non-null. + +@item -fsanitize=pointer-subtract +@opindex fsanitize=pointer-subtract +Instrument subtraction with pointer operands. +The option must be combined with either @option{-fsanitize=kernel-address} or +@option{-fsanitize=address} +The option cannot be combined with @option{-fsanitize=thread}. +Note: By default the check is disabled at run time. To enable it, +add @code{detect_invalid_pointer_pairs=2} to the environment variable +@env{ASAN_OPTIONS}. Using @code{detect_invalid_pointer_pairs=1} detects +invalid operation only when both pointers are non-null. + +@item -fsanitize=shadow-call-stack +@opindex fsanitize=shadow-call-stack +Enable ShadowCallStack, a security enhancement mechanism used to protect +programs against return address overwrites (e.g. stack buffer overflows.) +It works by saving a function's return address to a separately allocated +shadow call stack in the function prologue and restoring the return address +from the shadow call stack in the function epilogue. Instrumentation only +occurs in functions that need to save the return address to the stack. + +Currently it only supports the aarch64 platform. It is specifically +designed for linux kernels that enable the CONFIG_SHADOW_CALL_STACK option. +For the user space programs, runtime support is not currently provided +in libc and libgcc. Users who want to use this feature in user space need +to provide their own support for the runtime. It should be noted that +this may cause the ABI rules to be broken. + +On aarch64, the instrumentation makes use of the platform register @code{x18}. +This generally means that any code that may run on the same thread as code +compiled with ShadowCallStack must be compiled with the flag +@option{-ffixed-x18}, otherwise functions compiled without +@option{-ffixed-x18} might clobber @code{x18} and so corrupt the shadow +stack pointer. + +Also, because there is no userspace runtime support, code compiled with +ShadowCallStack cannot use exception handling. Use @option{-fno-exceptions} +to turn off exceptions. + +See @uref{https://clang.llvm.org/docs/ShadowCallStack.html} for more +details. + +@item -fsanitize=thread +@opindex fsanitize=thread +Enable ThreadSanitizer, a fast data race detector. +Memory access instructions are instrumented to detect +data race bugs. See @uref{https://github.com/google/sanitizers/wiki#threadsanitizer} for more +details. The run-time behavior can be influenced using the @env{TSAN_OPTIONS} +environment variable; see +@url{https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags} for a list of +supported options. +The option cannot be combined with @option{-fsanitize=address}, +@option{-fsanitize=leak}. + +Note that sanitized atomic builtins cannot throw exceptions when +operating on invalid memory addresses with non-call exceptions +(@option{-fnon-call-exceptions}). + +@item -fsanitize=leak +@opindex fsanitize=leak +Enable LeakSanitizer, a memory leak detector. +This option only matters for linking of executables and +the executable is linked against a library that overrides @code{malloc} +and other allocator functions. See +@uref{https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer} for more +details. The run-time behavior can be influenced using the +@env{LSAN_OPTIONS} environment variable. +The option cannot be combined with @option{-fsanitize=thread}. + +@item -fsanitize=undefined +@opindex fsanitize=undefined +Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. +Various computations are instrumented to detect undefined behavior +at runtime. See @uref{https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html} for more details. The run-time behavior can be influenced using the +@env{UBSAN_OPTIONS} environment variable. Current suboptions are: + +@table @gcctabopt + +@item -fsanitize=shift +@opindex fsanitize=shift +This option enables checking that the result of a shift operation is +not undefined. Note that what exactly is considered undefined differs +slightly between C and C++, as well as between ISO C90 and C99, etc. +This option has two suboptions, @option{-fsanitize=shift-base} and +@option{-fsanitize=shift-exponent}. + +@item -fsanitize=shift-exponent +@opindex fsanitize=shift-exponent +This option enables checking that the second argument of a shift operation +is not negative and is smaller than the precision of the promoted first +argument. + +@item -fsanitize=shift-base +@opindex fsanitize=shift-base +If the second argument of a shift operation is within range, check that the +result of a shift operation is not undefined. Note that what exactly is +considered undefined differs slightly between C and C++, as well as between +ISO C90 and C99, etc. + +@item -fsanitize=integer-divide-by-zero +@opindex fsanitize=integer-divide-by-zero +Detect integer division by zero. + +@item -fsanitize=unreachable +@opindex fsanitize=unreachable +With this option, the compiler turns the @code{__builtin_unreachable} +call into a diagnostics message call instead. When reaching the +@code{__builtin_unreachable} call, the behavior is undefined. + +@item -fsanitize=vla-bound +@opindex fsanitize=vla-bound +This option instructs the compiler to check that the size of a variable +length array is positive. + +@item -fsanitize=null +@opindex fsanitize=null +This option enables pointer checking. Particularly, the application +built with this option turned on will issue an error message when it +tries to dereference a NULL pointer, or if a reference (possibly an +rvalue reference) is bound to a NULL pointer, or if a method is invoked +on an object pointed by a NULL pointer. + +@item -fsanitize=return +@opindex fsanitize=return +This option enables return statement checking. Programs +built with this option turned on will issue an error message +when the end of a non-void function is reached without actually +returning a value. This option works in C++ only. + +@item -fsanitize=signed-integer-overflow +@opindex fsanitize=signed-integer-overflow +This option enables signed integer overflow checking. We check that +the result of @code{+}, @code{*}, and both unary and binary @code{-} +does not overflow in the signed arithmetics. This also detects +@code{INT_MIN / -1} signed division. Note, integer promotion +rules must be taken into account. That is, the following is not an +overflow: +@smallexample +signed char a = SCHAR_MAX; +a++; +@end smallexample + +@item -fsanitize=bounds +@opindex fsanitize=bounds +This option enables instrumentation of array bounds. Various out of bounds +accesses are detected. Flexible array members, flexible array member-like +arrays, and initializers of variables with static storage are not instrumented. + +@item -fsanitize=bounds-strict +@opindex fsanitize=bounds-strict +This option enables strict instrumentation of array bounds. Most out of bounds +accesses are detected, including flexible array members and flexible array +member-like arrays. Initializers of variables with static storage are not +instrumented. + +@item -fsanitize=alignment +@opindex fsanitize=alignment + +This option enables checking of alignment of pointers when they are +dereferenced, or when a reference is bound to insufficiently aligned target, +or when a method or constructor is invoked on insufficiently aligned object. + +@item -fsanitize=object-size +@opindex fsanitize=object-size +This option enables instrumentation of memory references using the +@code{__builtin_object_size} function. Various out of bounds pointer +accesses are detected. + +@item -fsanitize=float-divide-by-zero +@opindex fsanitize=float-divide-by-zero +Detect floating-point division by zero. Unlike other similar options, +@option{-fsanitize=float-divide-by-zero} is not enabled by +@option{-fsanitize=undefined}, since floating-point division by zero can +be a legitimate way of obtaining infinities and NaNs. + +@item -fsanitize=float-cast-overflow +@opindex fsanitize=float-cast-overflow +This option enables floating-point type to integer conversion checking. +We check that the result of the conversion does not overflow. +Unlike other similar options, @option{-fsanitize=float-cast-overflow} is +not enabled by @option{-fsanitize=undefined}. +This option does not work well with @code{FE_INVALID} exceptions enabled. + +@item -fsanitize=nonnull-attribute +@opindex fsanitize=nonnull-attribute + +This option enables instrumentation of calls, checking whether null values +are not passed to arguments marked as requiring a non-null value by the +@code{nonnull} function attribute. + +@item -fsanitize=returns-nonnull-attribute +@opindex fsanitize=returns-nonnull-attribute + +This option enables instrumentation of return statements in functions +marked with @code{returns_nonnull} function attribute, to detect returning +of null values from such functions. + +@item -fsanitize=bool +@opindex fsanitize=bool + +This option enables instrumentation of loads from bool. If a value other +than 0/1 is loaded, a run-time error is issued. + +@item -fsanitize=enum +@opindex fsanitize=enum + +This option enables instrumentation of loads from an enum type. If +a value outside the range of values for the enum type is loaded, +a run-time error is issued. + +@item -fsanitize=vptr +@opindex fsanitize=vptr + +This option enables instrumentation of C++ member function calls, member +accesses and some conversions between pointers to base and derived classes, +to verify the referenced object has the correct dynamic type. + +@item -fsanitize=pointer-overflow +@opindex fsanitize=pointer-overflow + +This option enables instrumentation of pointer arithmetics. If the pointer +arithmetics overflows, a run-time error is issued. + +@item -fsanitize=builtin +@opindex fsanitize=builtin + +This option enables instrumentation of arguments to selected builtin +functions. If an invalid value is passed to such arguments, a run-time +error is issued. E.g.@ passing 0 as the argument to @code{__builtin_ctz} +or @code{__builtin_clz} invokes undefined behavior and is diagnosed +by this option. + +@end table + +Note that sanitizers tend to increase the rate of false positive +warnings, most notably those around @option{-Wmaybe-uninitialized}. +We recommend against combining @option{-Werror} and [the use of] +sanitizers. + +While @option{-ftrapv} causes traps for signed overflows to be emitted, +@option{-fsanitize=undefined} gives a diagnostic message. +This currently works only for the C family of languages. + +@item -fno-sanitize=all +@opindex fno-sanitize=all + +This option disables all previously enabled sanitizers. +@option{-fsanitize=all} is not allowed, as some sanitizers cannot be used +together. + +@item -fasan-shadow-offset=@var{number} +@opindex fasan-shadow-offset +This option forces GCC to use custom shadow offset in AddressSanitizer checks. +It is useful for experimenting with different shadow memory layouts in +Kernel AddressSanitizer. + +@item -fsanitize-sections=@var{s1},@var{s2},... +@opindex fsanitize-sections +Sanitize global variables in selected user-defined sections. @var{si} may +contain wildcards. + +@item -fsanitize-recover@r{[}=@var{opts}@r{]} +@opindex fsanitize-recover +@opindex fno-sanitize-recover +@option{-fsanitize-recover=} controls error recovery mode for sanitizers +mentioned in comma-separated list of @var{opts}. Enabling this option +for a sanitizer component causes it to attempt to continue +running the program as if no error happened. This means multiple +runtime errors can be reported in a single program run, and the exit +code of the program may indicate success even when errors +have been reported. The @option{-fno-sanitize-recover=} option +can be used to alter +this behavior: only the first detected error is reported +and program then exits with a non-zero exit code. + +Currently this feature only works for @option{-fsanitize=undefined} (and its suboptions +except for @option{-fsanitize=unreachable} and @option{-fsanitize=return}), +@option{-fsanitize=float-cast-overflow}, @option{-fsanitize=float-divide-by-zero}, +@option{-fsanitize=bounds-strict}, +@option{-fsanitize=kernel-address} and @option{-fsanitize=address}. +For these sanitizers error recovery is turned on by default, +except @option{-fsanitize=address}, for which this feature is experimental. +@option{-fsanitize-recover=all} and @option{-fno-sanitize-recover=all} is also +accepted, the former enables recovery for all sanitizers that support it, +the latter disables recovery for all sanitizers that support it. + +Even if a recovery mode is turned on the compiler side, it needs to be also +enabled on the runtime library side, otherwise the failures are still fatal. +The runtime library defaults to @code{halt_on_error=0} for +ThreadSanitizer and UndefinedBehaviorSanitizer, while default value for +AddressSanitizer is @code{halt_on_error=1}. This can be overridden through +setting the @code{halt_on_error} flag in the corresponding environment variable. + +Syntax without an explicit @var{opts} parameter is deprecated. It is +equivalent to specifying an @var{opts} list of: + +@smallexample +undefined,float-cast-overflow,float-divide-by-zero,bounds-strict +@end smallexample + +@item -fsanitize-address-use-after-scope +@opindex fsanitize-address-use-after-scope +Enable sanitization of local variables to detect use-after-scope bugs. +The option sets @option{-fstack-reuse} to @samp{none}. + +@item -fsanitize-trap@r{[}=@var{opts}@r{]} +@opindex fsanitize-trap +@opindex fno-sanitize-trap +The @option{-fsanitize-trap=} option instructs the compiler to +report for sanitizers mentioned in comma-separated list of @var{opts} +undefined behavior using @code{__builtin_trap} rather than a @code{libubsan} +library routine. If this option is enabled for certain sanitizer, +it takes precedence over the @option{-fsanitizer-recover=} for that +sanitizer, @code{__builtin_trap} will be emitted and be fatal regardless +of whether recovery is enabled or disabled using @option{-fsanitize-recover=}. + +The advantage of this is that the @code{libubsan} library is not needed +and is not linked in, so this is usable even in freestanding environments. + +Currently this feature works with @option{-fsanitize=undefined} (and its suboptions +except for @option{-fsanitize=vptr}), @option{-fsanitize=float-cast-overflow}, +@option{-fsanitize=float-divide-by-zero} and +@option{-fsanitize=bounds-strict}. @code{-fsanitize-trap=all} can be also +specified, which enables it for @code{undefined} suboptions, +@option{-fsanitize=float-cast-overflow}, +@option{-fsanitize=float-divide-by-zero} and +@option{-fsanitize=bounds-strict}. +If @code{-fsanitize-trap=undefined} or @code{-fsanitize-trap=all} is used +and @code{-fsanitize=vptr} is enabled on the command line, the +instrumentation is silently ignored as the instrumentation always needs +@code{libubsan} support, @option{-fsanitize-trap=vptr} is not allowed. + +@item -fsanitize-undefined-trap-on-error +@opindex fsanitize-undefined-trap-on-error +The @option{-fsanitize-undefined-trap-on-error} option is deprecated +equivalent of @option{-fsanitize-trap=all}. + +@item -fsanitize-coverage=trace-pc +@opindex fsanitize-coverage=trace-pc +Enable coverage-guided fuzzing code instrumentation. +Inserts a call to @code{__sanitizer_cov_trace_pc} into every basic block. + +@item -fsanitize-coverage=trace-cmp +@opindex fsanitize-coverage=trace-cmp +Enable dataflow guided fuzzing code instrumentation. +Inserts a call to @code{__sanitizer_cov_trace_cmp1}, +@code{__sanitizer_cov_trace_cmp2}, @code{__sanitizer_cov_trace_cmp4} or +@code{__sanitizer_cov_trace_cmp8} for integral comparison with both operands +variable or @code{__sanitizer_cov_trace_const_cmp1}, +@code{__sanitizer_cov_trace_const_cmp2}, +@code{__sanitizer_cov_trace_const_cmp4} or +@code{__sanitizer_cov_trace_const_cmp8} for integral comparison with one +operand constant, @code{__sanitizer_cov_trace_cmpf} or +@code{__sanitizer_cov_trace_cmpd} for float or double comparisons and +@code{__sanitizer_cov_trace_switch} for switch statements. + +@item -fcf-protection=@r{[}full@r{|}branch@r{|}return@r{|}none@r{|}check@r{]} +@opindex fcf-protection +Enable code instrumentation of control-flow transfers to increase +program security by checking that target addresses of control-flow +transfer instructions (such as indirect function call, function return, +indirect jump) are valid. This prevents diverting the flow of control +to an unexpected target. This is intended to protect against such +threats as Return-oriented Programming (ROP), and similarly +call/jmp-oriented programming (COP/JOP). + +The value @code{branch} tells the compiler to implement checking of +validity of control-flow transfer at the point of indirect branch +instructions, i.e.@: call/jmp instructions. The value @code{return} +implements checking of validity at the point of returning from a +function. The value @code{full} is an alias for specifying both +@code{branch} and @code{return}. The value @code{none} turns off +instrumentation. + +The value @code{check} is used for the final link with link-time +optimization (LTO). An error is issued if LTO object files are +compiled with different @option{-fcf-protection} values. The +value @code{check} is ignored at the compile time. + +The macro @code{__CET__} is defined when @option{-fcf-protection} is +used. The first bit of @code{__CET__} is set to 1 for the value +@code{branch} and the second bit of @code{__CET__} is set to 1 for +the @code{return}. + +You can also use the @code{nocf_check} attribute to identify +which functions and calls should be skipped from instrumentation +(@pxref{Function Attributes}). + +Currently the x86 GNU/Linux target provides an implementation based +on Intel Control-flow Enforcement Technology (CET) which works for +i686 processor or newer. + +@item -fharden-compares +@opindex fharden-compares +For every logical test that survives gimple optimizations and is +@emph{not} the condition in a conditional branch (for example, +conditions tested for conditional moves, or to store in boolean +variables), emit extra code to compute and verify the reversed +condition, and to call @code{__builtin_trap} if the results do not +match. Use with @samp{-fharden-conditional-branches} to cover all +conditionals. + +@item -fharden-conditional-branches +@opindex fharden-conditional-branches +For every non-vectorized conditional branch that survives gimple +optimizations, emit extra code to compute and verify the reversed +condition, and to call @code{__builtin_trap} if the result is +unexpected. Use with @samp{-fharden-compares} to cover all +conditionals. + +@item -fstack-protector +@opindex fstack-protector +Emit extra code to check for buffer overflows, such as stack smashing +attacks. This is done by adding a guard variable to functions with +vulnerable objects. This includes functions that call @code{alloca}, and +functions with buffers larger than or equal to 8 bytes. The guards are +initialized when a function is entered and then checked when the function +exits. If a guard check fails, an error message is printed and the program +exits. Only variables that are actually allocated on the stack are +considered, optimized away variables or variables allocated in registers +don't count. + +@item -fstack-protector-all +@opindex fstack-protector-all +Like @option{-fstack-protector} except that all functions are protected. + +@item -fstack-protector-strong +@opindex fstack-protector-strong +Like @option{-fstack-protector} but includes additional functions to +be protected --- those that have local array definitions, or have +references to local frame addresses. Only variables that are actually +allocated on the stack are considered, optimized away variables or variables +allocated in registers don't count. + +@item -fstack-protector-explicit +@opindex fstack-protector-explicit +Like @option{-fstack-protector} but only protects those functions which +have the @code{stack_protect} attribute. + +@item -fstack-check +@opindex fstack-check +Generate code to verify that you do not go beyond the boundary of the +stack. You should specify this flag if you are running in an +environment with multiple threads, but you only rarely need to specify it in +a single-threaded environment since stack overflow is automatically +detected on nearly all systems if there is only one stack. + +Note that this switch does not actually cause checking to be done; the +operating system or the language runtime must do that. The switch causes +generation of code to ensure that they see the stack being extended. + +You can additionally specify a string parameter: @samp{no} means no +checking, @samp{generic} means force the use of old-style checking, +@samp{specific} means use the best checking method and is equivalent +to bare @option{-fstack-check}. + +Old-style checking is a generic mechanism that requires no specific +target support in the compiler but comes with the following drawbacks: + +@enumerate +@item +Modified allocation strategy for large objects: they are always +allocated dynamically if their size exceeds a fixed threshold. Note this +may change the semantics of some code. + +@item +Fixed limit on the size of the static frame of functions: when it is +topped by a particular function, stack checking is not reliable and +a warning is issued by the compiler. + +@item +Inefficiency: because of both the modified allocation strategy and the +generic implementation, code performance is hampered. +@end enumerate + +Note that old-style stack checking is also the fallback method for +@samp{specific} if no target support has been added in the compiler. + +@samp{-fstack-check=} is designed for Ada's needs to detect infinite recursion +and stack overflows. @samp{specific} is an excellent choice when compiling +Ada code. It is not generally sufficient to protect against stack-clash +attacks. To protect against those you want @samp{-fstack-clash-protection}. + +@item -fstack-clash-protection +@opindex fstack-clash-protection +Generate code to prevent stack clash style attacks. When this option is +enabled, the compiler will only allocate one page of stack space at a time +and each page is accessed immediately after allocation. Thus, it prevents +allocations from jumping over any stack guard page provided by the +operating system. + +Most targets do not fully support stack clash protection. However, on +those targets @option{-fstack-clash-protection} will protect dynamic stack +allocations. @option{-fstack-clash-protection} may also provide limited +protection for static stack allocations if the target supports +@option{-fstack-check=specific}. + +@item -fstack-limit-register=@var{reg} +@itemx -fstack-limit-symbol=@var{sym} +@itemx -fno-stack-limit +@opindex fstack-limit-register +@opindex fstack-limit-symbol +@opindex fno-stack-limit +Generate code to ensure that the stack does not grow beyond a certain value, +either the value of a register or the address of a symbol. If a larger +stack is required, a signal is raised at run time. For most targets, +the signal is raised before the stack overruns the boundary, so +it is possible to catch the signal without taking special precautions. + +For instance, if the stack starts at absolute address @samp{0x80000000} +and grows downwards, you can use the flags +@option{-fstack-limit-symbol=__stack_limit} and +@option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit +of 128KB@. Note that this may only work with the GNU linker. + +You can locally override stack limit checking by using the +@code{no_stack_limit} function attribute (@pxref{Function Attributes}). + +@item -fsplit-stack +@opindex fsplit-stack +Generate code to automatically split the stack before it overflows. +The resulting program has a discontiguous stack which can only +overflow if the program is unable to allocate any more memory. This +is most useful when running threaded programs, as it is no longer +necessary to calculate a good stack size to use for each thread. This +is currently only implemented for the x86 targets running +GNU/Linux. + +When code compiled with @option{-fsplit-stack} calls code compiled +without @option{-fsplit-stack}, there may not be much stack space +available for the latter code to run. If compiling all code, +including library code, with @option{-fsplit-stack} is not an option, +then the linker can fix up these calls so that the code compiled +without @option{-fsplit-stack} always has a large stack. Support for +this is implemented in the gold linker in GNU binutils release 2.21 +and later. + +@item -fvtable-verify=@r{[}std@r{|}preinit@r{|}none@r{]} +@opindex fvtable-verify +This option is only available when compiling C++ code. +It turns on (or off, if using @option{-fvtable-verify=none}) the security +feature that verifies at run time, for every virtual call, that +the vtable pointer through which the call is made is valid for the type of +the object, and has not been corrupted or overwritten. If an invalid vtable +pointer is detected at run time, an error is reported and execution of the +program is immediately halted. + +This option causes run-time data structures to be built at program startup, +which are used for verifying the vtable pointers. +The options @samp{std} and @samp{preinit} +control the timing of when these data structures are built. In both cases the +data structures are built before execution reaches @code{main}. Using +@option{-fvtable-verify=std} causes the data structures to be built after +shared libraries have been loaded and initialized. +@option{-fvtable-verify=preinit} causes them to be built before shared +libraries have been loaded and initialized. + +If this option appears multiple times in the command line with different +values specified, @samp{none} takes highest priority over both @samp{std} and +@samp{preinit}; @samp{preinit} takes priority over @samp{std}. + +@item -fvtv-debug +@opindex fvtv-debug +When used in conjunction with @option{-fvtable-verify=std} or +@option{-fvtable-verify=preinit}, causes debug versions of the +runtime functions for the vtable verification feature to be called. +This flag also causes the compiler to log information about which +vtable pointers it finds for each class. +This information is written to a file named @file{vtv_set_ptr_data.log} +in the directory named by the environment variable @env{VTV_LOGS_DIR} +if that is defined or the current working directory otherwise. + +Note: This feature @emph{appends} data to the log file. If you want a fresh log +file, be sure to delete any existing one. + +@item -fvtv-counts +@opindex fvtv-counts +This is a debugging flag. When used in conjunction with +@option{-fvtable-verify=std} or @option{-fvtable-verify=preinit}, this +causes the compiler to keep track of the total number of virtual calls +it encounters and the number of verifications it inserts. It also +counts the number of calls to certain run-time library functions +that it inserts and logs this information for each compilation unit. +The compiler writes this information to a file named +@file{vtv_count_data.log} in the directory named by the environment +variable @env{VTV_LOGS_DIR} if that is defined or the current working +directory otherwise. It also counts the size of the vtable pointer sets +for each class, and writes this information to @file{vtv_class_set_sizes.log} +in the same directory. + +Note: This feature @emph{appends} data to the log files. To get fresh log +files, be sure to delete any existing ones. + +@item -finstrument-functions +@opindex finstrument-functions +Generate instrumentation calls for entry and exit to functions. Just +after function entry and just before function exit, the following +profiling functions are called with the address of the current +function and its call site. (On some platforms, +@code{__builtin_return_address} does not work beyond the current +function, so the call site information may not be available to the +profiling functions otherwise.) + +@smallexample +void __cyg_profile_func_enter (void *this_fn, + void *call_site); +void __cyg_profile_func_exit (void *this_fn, + void *call_site); +@end smallexample + +The first argument is the address of the start of the current function, +which may be looked up exactly in the symbol table. + +This instrumentation is also done for functions expanded inline in other +functions. The profiling calls indicate where, conceptually, the +inline function is entered and exited. This means that addressable +versions of such functions must be available. If all your uses of a +function are expanded inline, this may mean an additional expansion of +code size. If you use @code{extern inline} in your C code, an +addressable version of such functions must be provided. (This is +normally the case anyway, but if you get lucky and the optimizer always +expands the functions inline, you might have gotten away without +providing static copies.) + +A function may be given the attribute @code{no_instrument_function}, in +which case this instrumentation is not done. This can be used, for +example, for the profiling functions listed above, high-priority +interrupt routines, and any functions from which the profiling functions +cannot safely be called (perhaps signal handlers, if the profiling +routines generate output or allocate memory). +@xref{Common Function Attributes}. + +@item -finstrument-functions-once +@opindex -finstrument-functions-once +This is similar to @option{-finstrument-functions}, but the profiling +functions are called only once per instrumented function, i.e. the first +profiling function is called after the first entry into the instrumented +function and the second profiling function is called before the exit +corresponding to this first entry. + +The definition of @code{once} for the purpose of this option is a little +vague because the implementation is not protected against data races. +As a result, the implementation only guarantees that the profiling +functions are called at @emph{least} once per process and at @emph{most} +once per thread, but the calls are always paired, that is to say, if a +thread calls the first function, then it will call the second function, +unless it never reaches the exit of the instrumented function. + +@item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} +@opindex finstrument-functions-exclude-file-list + +Set the list of functions that are excluded from instrumentation (see +the description of @option{-finstrument-functions}). If the file that +contains a function definition matches with one of @var{file}, then +that function is not instrumented. The match is done on substrings: +if the @var{file} parameter is a substring of the file name, it is +considered to be a match. + +For example: + +@smallexample +-finstrument-functions-exclude-file-list=/bits/stl,include/sys +@end smallexample + +@noindent +excludes any inline function defined in files whose pathnames +contain @file{/bits/stl} or @file{include/sys}. + +If, for some reason, you want to include letter @samp{,} in one of +@var{sym}, write @samp{\,}. For example, +@option{-finstrument-functions-exclude-file-list='\,\,tmp'} +(note the single quote surrounding the option). + +@item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} +@opindex finstrument-functions-exclude-function-list + +This is similar to @option{-finstrument-functions-exclude-file-list}, +but this option sets the list of function names to be excluded from +instrumentation. The function name to be matched is its user-visible +name, such as @code{vector blah(const vector &)}, not the +internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The +match is done on substrings: if the @var{sym} parameter is a substring +of the function name, it is considered to be a match. For C99 and C++ +extended identifiers, the function name must be given in UTF-8, not +using universal character names. + +@item -fpatchable-function-entry=@var{N}[,@var{M}] +@opindex fpatchable-function-entry +Generate @var{N} NOPs right at the beginning +of each function, with the function entry point before the @var{M}th NOP. +If @var{M} is omitted, it defaults to @code{0} so the +function entry points to the address just at the first NOP. +The NOP instructions reserve extra space which can be used to patch in +any desired instrumentation at run time, provided that the code segment +is writable. The amount of space is controllable indirectly via +the number of NOPs; the NOP instruction used corresponds to the instruction +emitted by the internal GCC back-end interface @code{gen_nop}. This behavior +is target-specific and may also depend on the architecture variant and/or +other compilation options. + +For run-time identification, the starting addresses of these areas, +which correspond to their respective function entries minus @var{M}, +are additionally collected in the @code{__patchable_function_entries} +section of the resulting binary. + +Note that the value of @code{__attribute__ ((patchable_function_entry +(N,M)))} takes precedence over command-line option +@option{-fpatchable-function-entry=N,M}. This can be used to increase +the area size or to remove it completely on a single function. +If @code{N=0}, no pad location is recorded. + +The NOP instructions are inserted at---and maybe before, depending on +@var{M}---the function entry address, even before the prologue. On +PowerPC with the ELFv2 ABI, for a function with dual entry points, +the local entry point is this function entry address. + +The maximum value of @var{N} and @var{M} is 65535. On PowerPC with the +ELFv2 ABI, for a function with dual entry points, the supported values +for @var{M} are 0, 2, 6 and 14. +@end table + + +@node Preprocessor Options +@section Options Controlling the Preprocessor +@cindex preprocessor options +@cindex options, preprocessor + +These options control the C preprocessor, which is run on each C source +file before actual compilation. + +If you use the @option{-E} option, nothing is done except preprocessing. +Some of these options make sense only together with @option{-E} because +they cause the preprocessor output to be unsuitable for actual +compilation. + +In addition to the options listed here, there are a number of options +to control search paths for include files documented in +@ref{Directory Options}. +Options to control preprocessor diagnostics are listed in +@ref{Warning Options}. + +@table @gcctabopt +@include cppopts.texi + +@item -Wp,@var{option} +@opindex Wp +You can use @option{-Wp,@var{option}} to bypass the compiler driver +and pass @var{option} directly through to the preprocessor. If +@var{option} contains commas, it is split into multiple options at the +commas. However, many options are modified, translated or interpreted +by the compiler driver before being passed to the preprocessor, and +@option{-Wp} forcibly bypasses this phase. The preprocessor's direct +interface is undocumented and subject to change, so whenever possible +you should avoid using @option{-Wp} and let the driver handle the +options instead. + +@item -Xpreprocessor @var{option} +@opindex Xpreprocessor +Pass @var{option} as an option to the preprocessor. You can use this to +supply system-specific preprocessor options that GCC does not +recognize. + +If you want to pass an option that takes an argument, you must use +@option{-Xpreprocessor} twice, once for the option and once for the argument. + +@item -no-integrated-cpp +@opindex no-integrated-cpp +Perform preprocessing as a separate pass before compilation. +By default, GCC performs preprocessing as an integrated part of +input tokenization and parsing. +If this option is provided, the appropriate language front end +(@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++, +and Objective-C, respectively) is instead invoked twice, +once for preprocessing only and once for actual compilation +of the preprocessed input. +This option may be useful in conjunction with the @option{-B} or +@option{-wrapper} options to specify an alternate preprocessor or +perform additional processing of the program source between +normal preprocessing and compilation. + +@item -flarge-source-files +@opindex flarge-source-files +Adjust GCC to expect large source files, at the expense of slower +compilation and higher memory usage. + +Specifically, GCC normally tracks both column numbers and line numbers +within source files and it normally prints both of these numbers in +diagnostics. However, once it has processed a certain number of source +lines, it stops tracking column numbers and only tracks line numbers. +This means that diagnostics for later lines do not include column numbers. +It also means that options like @option{-Wmisleading-indentation} cease to work +at that point, although the compiler prints a note if this happens. +Passing @option{-flarge-source-files} significantly increases the number +of source lines that GCC can process before it stops tracking columns. + +@end table + +@node Assembler Options +@section Passing Options to the Assembler + +@c prevent bad page break with this line +You can pass options to the assembler. + +@table @gcctabopt +@item -Wa,@var{option} +@opindex Wa +Pass @var{option} as an option to the assembler. If @var{option} +contains commas, it is split into multiple options at the commas. + +@item -Xassembler @var{option} +@opindex Xassembler +Pass @var{option} as an option to the assembler. You can use this to +supply system-specific assembler options that GCC does not +recognize. + +If you want to pass an option that takes an argument, you must use +@option{-Xassembler} twice, once for the option and once for the argument. + +@end table + +@node Link Options +@section Options for Linking +@cindex link options +@cindex options, linking + +These options come into play when the compiler links object files into +an executable output file. They are meaningless if the compiler is +not doing a link step. + +@table @gcctabopt +@cindex file names +@item @var{object-file-name} +A file name that does not end in a special recognized suffix is +considered to name an object file or library. (Object files are +distinguished from libraries by the linker according to the file +contents.) If linking is done, these object files are used as input +to the linker. + +@item -c +@itemx -S +@itemx -E +@opindex c +@opindex S +@opindex E +If any of these options is used, then the linker is not run, and +object file names should not be used as arguments. @xref{Overall +Options}. + +@item -flinker-output=@var{type} +@opindex flinker-output +This option controls code generation of the link-time optimizer. By +default the linker output is automatically determined by the linker +plugin. For debugging the compiler and if incremental linking with a +non-LTO object file is desired, it may be useful to control the type +manually. + +If @var{type} is @samp{exec}, code generation produces a static +binary. In this case @option{-fpic} and @option{-fpie} are both +disabled. + +If @var{type} is @samp{dyn}, code generation produces a shared +library. In this case @option{-fpic} or @option{-fPIC} is preserved, +but not enabled automatically. This allows to build shared libraries +without position-independent code on architectures where this is +possible, i.e.@: on x86. + +If @var{type} is @samp{pie}, code generation produces an @option{-fpie} +executable. This results in similar optimizations as @samp{exec} +except that @option{-fpie} is not disabled if specified at compilation +time. + +If @var{type} is @samp{rel}, the compiler assumes that incremental linking is +done. The sections containing intermediate code for link-time optimization are +merged, pre-optimized, and output to the resulting object file. In addition, if +@option{-ffat-lto-objects} is specified, binary code is produced for future +non-LTO linking. The object file produced by incremental linking is smaller +than a static library produced from the same object files. At link time the +result of incremental linking also loads faster than a static +library assuming that the majority of objects in the library are used. + +Finally @samp{nolto-rel} configures the compiler for incremental linking where +code generation is forced, a final binary is produced, and the intermediate +code for later link-time optimization is stripped. When multiple object files +are linked together the resulting code is better optimized than with +link-time optimizations disabled (for example, cross-module inlining +happens), but most of benefits of whole program optimizations are lost. + +During the incremental link (by @option{-r}) the linker plugin defaults to +@option{rel}. With current interfaces to GNU Binutils it is however not +possible to incrementally link LTO objects and non-LTO objects into a single +mixed object file. If any of object files in incremental link cannot +be used for link-time optimization, the linker plugin issues a warning and +uses @samp{nolto-rel}. To maintain whole program optimization, it is +recommended to link such objects into static library instead. Alternatively it +is possible to use H.J. Lu's binutils with support for mixed objects. + +@item -fuse-ld=bfd +@opindex fuse-ld=bfd +Use the @command{bfd} linker instead of the default linker. + +@item -fuse-ld=gold +@opindex fuse-ld=gold +Use the @command{gold} linker instead of the default linker. + +@item -fuse-ld=lld +@opindex fuse-ld=lld +Use the LLVM @command{lld} linker instead of the default linker. + +@item -fuse-ld=mold +@opindex fuse-ld=mold +Use the Modern Linker (@command{mold}) instead of the default linker. + +@cindex Libraries +@item -l@var{library} +@itemx -l @var{library} +@opindex l +Search the library named @var{library} when linking. (The second +alternative with the library as a separate argument is only for +POSIX compliance and is not recommended.) + +The @option{-l} option is passed directly to the linker by GCC. Refer +to your linker documentation for exact details. The general +description below applies to the GNU linker. + +The linker searches a standard list of directories for the library. +The directories searched include several standard system directories +plus any that you specify with @option{-L}. + +Static libraries are archives of object files, and have file names +like @file{lib@var{library}.a}. Some targets also support shared +libraries, which typically have names like @file{lib@var{library}.so}. +If both static and shared libraries are found, the linker gives +preference to linking with the shared library unless the +@option{-static} option is used. + +It makes a difference where in the command you write this option; the +linker searches and processes libraries and object files in the order they +are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} +after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers +to functions in @samp{z}, those functions may not be loaded. + +@item -lobjc +@opindex lobjc +You need this special case of the @option{-l} option in order to +link an Objective-C or Objective-C++ program. + +@item -nostartfiles +@opindex nostartfiles +Do not use the standard system startup files when linking. +The standard system libraries are used normally, unless @option{-nostdlib}, +@option{-nolibc}, or @option{-nodefaultlibs} is used. + +@item -nodefaultlibs +@opindex nodefaultlibs +Do not use the standard system libraries when linking. +Only the libraries you specify are passed to the linker, and options +specifying linkage of the system libraries, such as @option{-static-libgcc} +or @option{-shared-libgcc}, are ignored. +The standard startup files are used normally, unless @option{-nostartfiles} +is used. + +The compiler may generate calls to @code{memcmp}, +@code{memset}, @code{memcpy} and @code{memmove}. +These entries are usually resolved by entries in +libc. These entry points should be supplied through some other +mechanism when this option is specified. + +@item -nolibc +@opindex nolibc +Do not use the C library or system libraries tightly coupled with it when +linking. Still link with the startup files, @file{libgcc} or toolchain +provided language support libraries such as @file{libgnat}, @file{libgfortran} +or @file{libstdc++} unless options preventing their inclusion are used as +well. This typically removes @option{-lc} from the link command line, as well +as system libraries that normally go with it and become meaningless when +absence of a C library is assumed, for example @option{-lpthread} or +@option{-lm} in some configurations. This is intended for bare-board +targets when there is indeed no C library available. + +@item -nostdlib +@opindex nostdlib +Do not use the standard system startup files or libraries when linking. +No startup files and only the libraries you specify are passed to +the linker, and options specifying linkage of the system libraries, such as +@option{-static-libgcc} or @option{-shared-libgcc}, are ignored. + +The compiler may generate calls to @code{memcmp}, @code{memset}, +@code{memcpy} and @code{memmove}. +These entries are usually resolved by entries in +libc. These entry points should be supplied through some other +mechanism when this option is specified. + +@cindex @option{-lgcc}, use with @option{-nostdlib} +@cindex @option{-nostdlib} and unresolved references +@cindex unresolved references and @option{-nostdlib} +@cindex @option{-lgcc}, use with @option{-nodefaultlibs} +@cindex @option{-nodefaultlibs} and unresolved references +@cindex unresolved references and @option{-nodefaultlibs} +One of the standard libraries bypassed by @option{-nostdlib} and +@option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines +which GCC uses to overcome shortcomings of particular machines, or special +needs for some languages. +(@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler +Collection (GCC) Internals}, +for more discussion of @file{libgcc.a}.) +In most cases, you need @file{libgcc.a} even when you want to avoid +other standard libraries. In other words, when you specify @option{-nostdlib} +or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. +This ensures that you have no unresolved references to internal GCC +library subroutines. +(An example of such an internal subroutine is @code{__main}, used to ensure C++ +constructors are called; @pxref{Collect2,,@code{collect2}, gccint, +GNU Compiler Collection (GCC) Internals}.) + +@item -nostdlib++ +@opindex nostdlib++ +Do not implicitly link with standard C++ libraries. + +@item -e @var{entry} +@itemx --entry=@var{entry} +@opindex e +@opindex entry + +Specify that the program entry point is @var{entry}. The argument is +interpreted by the linker; the GNU linker accepts either a symbol name +or an address. + +@item -pie +@opindex pie +Produce a dynamically linked position independent executable on targets +that support it. For predictable results, you must also specify the same +set of options used for compilation (@option{-fpie}, @option{-fPIE}, +or model suboptions) when you specify this linker option. + +@item -no-pie +@opindex no-pie +Don't produce a dynamically linked position independent executable. + +@item -static-pie +@opindex static-pie +Produce a static position independent executable on targets that support +it. A static position independent executable is similar to a static +executable, but can be loaded at any address without a dynamic linker. +For predictable results, you must also specify the same set of options +used for compilation (@option{-fpie}, @option{-fPIE}, or model +suboptions) when you specify this linker option. + +@item -pthread +@opindex pthread +Link with the POSIX threads library. This option is supported on +GNU/Linux targets, most other Unix derivatives, and also on +x86 Cygwin and MinGW targets. On some targets this option also sets +flags for the preprocessor, so it should be used consistently for both +compilation and linking. + +@item -r +@opindex r +Produce a relocatable object as output. This is also known as partial +linking. + +@item -rdynamic +@opindex rdynamic +Pass the flag @option{-export-dynamic} to the ELF linker, on targets +that support it. This instructs the linker to add all symbols, not +only used ones, to the dynamic symbol table. This option is needed +for some uses of @code{dlopen} or to allow obtaining backtraces +from within a program. + +@item -s +@opindex s +Remove all symbol table and relocation information from the executable. + +@item -static +@opindex static +On systems that support dynamic linking, this overrides @option{-pie} +and prevents linking with the shared libraries. On other systems, this +option has no effect. + +@item -shared +@opindex shared +Produce a shared object which can then be linked with other objects to +form an executable. Not all systems support this option. For predictable +results, you must also specify the same set of options used for compilation +(@option{-fpic}, @option{-fPIC}, or model suboptions) when +you specify this linker option.@footnote{On some systems, @samp{gcc -shared} +needs to build supplementary stub code for constructors to work. On +multi-libbed systems, @samp{gcc -shared} must select the correct support +libraries to link against. Failing to supply the correct flags may lead +to subtle defects. Supplying them in cases where they are not necessary +is innocuous.} + +@item -shared-libgcc +@itemx -static-libgcc +@opindex shared-libgcc +@opindex static-libgcc +On systems that provide @file{libgcc} as a shared library, these options +force the use of either the shared or static version, respectively. +If no shared version of @file{libgcc} was built when the compiler was +configured, these options have no effect. + +There are several situations in which an application should use the +shared @file{libgcc} instead of the static version. The most common +of these is when the application wishes to throw and catch exceptions +across different shared libraries. In that case, each of the libraries +as well as the application itself should use the shared @file{libgcc}. + +Therefore, the G++ driver automatically adds @option{-shared-libgcc} +whenever you build a shared library or a main executable, because C++ +programs typically use exceptions, so this is the right thing to do. + +If, instead, you use the GCC driver to create shared libraries, you may +find that they are not always linked with the shared @file{libgcc}. +If GCC finds, at its configuration time, that you have a non-GNU linker +or a GNU linker that does not support option @option{--eh-frame-hdr}, +it links the shared version of @file{libgcc} into shared libraries +by default. Otherwise, it takes advantage of the linker and optimizes +away the linking with the shared version of @file{libgcc}, linking with +the static version of libgcc by default. This allows exceptions to +propagate through such shared libraries, without incurring relocation +costs at library load time. + +However, if a library or main executable is supposed to throw or catch +exceptions, you must link it using the G++ driver, or using the option +@option{-shared-libgcc}, such that it is linked with the shared +@file{libgcc}. + +@item -static-libasan +@opindex static-libasan +When the @option{-fsanitize=address} option is used to link a program, +the GCC driver automatically links against @option{libasan}. If +@file{libasan} is available as a shared library, and the @option{-static} +option is not used, then this links against the shared version of +@file{libasan}. The @option{-static-libasan} option directs the GCC +driver to link @file{libasan} statically, without necessarily linking +other libraries statically. + +@item -static-libtsan +@opindex static-libtsan +When the @option{-fsanitize=thread} option is used to link a program, +the GCC driver automatically links against @option{libtsan}. If +@file{libtsan} is available as a shared library, and the @option{-static} +option is not used, then this links against the shared version of +@file{libtsan}. The @option{-static-libtsan} option directs the GCC +driver to link @file{libtsan} statically, without necessarily linking +other libraries statically. + +@item -static-liblsan +@opindex static-liblsan +When the @option{-fsanitize=leak} option is used to link a program, +the GCC driver automatically links against @option{liblsan}. If +@file{liblsan} is available as a shared library, and the @option{-static} +option is not used, then this links against the shared version of +@file{liblsan}. The @option{-static-liblsan} option directs the GCC +driver to link @file{liblsan} statically, without necessarily linking +other libraries statically. + +@item -static-libubsan +@opindex static-libubsan +When the @option{-fsanitize=undefined} option is used to link a program, +the GCC driver automatically links against @option{libubsan}. If +@file{libubsan} is available as a shared library, and the @option{-static} +option is not used, then this links against the shared version of +@file{libubsan}. The @option{-static-libubsan} option directs the GCC +driver to link @file{libubsan} statically, without necessarily linking +other libraries statically. + +@item -static-libstdc++ +@opindex static-libstdc++ +When the @command{g++} program is used to link a C++ program, it +normally automatically links against @option{libstdc++}. If +@file{libstdc++} is available as a shared library, and the +@option{-static} option is not used, then this links against the +shared version of @file{libstdc++}. That is normally fine. However, it +is sometimes useful to freeze the version of @file{libstdc++} used by +the program without going all the way to a fully static link. The +@option{-static-libstdc++} option directs the @command{g++} driver to +link @file{libstdc++} statically, without necessarily linking other +libraries statically. + +@item -symbolic +@opindex symbolic +Bind references to global symbols when building a shared object. Warn +about any unresolved references (unless overridden by the link editor +option @option{-Xlinker -z -Xlinker defs}). Only a few systems support +this option. + +@item -T @var{script} +@opindex T +@cindex linker script +Use @var{script} as the linker script. This option is supported by most +systems using the GNU linker. On some targets, such as bare-board +targets without an operating system, the @option{-T} option may be required +when linking to avoid references to undefined symbols. + +@item -Xlinker @var{option} +@opindex Xlinker +Pass @var{option} as an option to the linker. You can use this to +supply system-specific linker options that GCC does not recognize. + +If you want to pass an option that takes a separate argument, you must use +@option{-Xlinker} twice, once for the option and once for the argument. +For example, to pass @option{-assert definitions}, you must write +@option{-Xlinker -assert -Xlinker definitions}. It does not work to write +@option{-Xlinker "-assert definitions"}, because this passes the entire +string as a single argument, which is not what the linker expects. + +When using the GNU linker, it is usually more convenient to pass +arguments to linker options using the @option{@var{option}=@var{value}} +syntax than as separate arguments. For example, you can specify +@option{-Xlinker -Map=output.map} rather than +@option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support +this syntax for command-line options. + +@item -Wl,@var{option} +@opindex Wl +Pass @var{option} as an option to the linker. If @var{option} contains +commas, it is split into multiple options at the commas. You can use this +syntax to pass an argument to the option. +For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the +linker. When using the GNU linker, you can also get the same effect with +@option{-Wl,-Map=output.map}. + +@item -u @var{symbol} +@opindex u +Pretend the symbol @var{symbol} is undefined, to force linking of +library modules to define it. You can use @option{-u} multiple times with +different symbols to force loading of additional library modules. + +@item -z @var{keyword} +@opindex z +@option{-z} is passed directly on to the linker along with the keyword +@var{keyword}. See the section in the documentation of your linker for +permitted values and their meanings. +@end table + +@node Directory Options +@section Options for Directory Search +@cindex directory options +@cindex options, directory search +@cindex search path + +These options specify directories to search for header files, for +libraries and for parts of the compiler: + +@table @gcctabopt +@include cppdiropts.texi + +@item -iplugindir=@var{dir} +@opindex iplugindir= +Set the directory to search for plugins that are passed +by @option{-fplugin=@var{name}} instead of +@option{-fplugin=@var{path}/@var{name}.so}. This option is not meant +to be used by the user, but only passed by the driver. + +@item -L@var{dir} +@opindex L +Add directory @var{dir} to the list of directories to be searched +for @option{-l}. + +@item -B@var{prefix} +@opindex B +This option specifies where to find the executables, libraries, +include files, and data files of the compiler itself. + +The compiler driver program runs one or more of the subprograms +@command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries +@var{prefix} as a prefix for each program it tries to run, both with and +without @samp{@var{machine}/@var{version}/} for the corresponding target +machine and compiler version. + +For each subprogram to be run, the compiler driver first tries the +@option{-B} prefix, if any. If that name is not found, or if @option{-B} +is not specified, the driver tries two standard prefixes, +@file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of +those results in a file name that is found, the unmodified program +name is searched for using the directories specified in your +@env{PATH} environment variable. + +The compiler checks to see if the path provided by @option{-B} +refers to a directory, and if necessary it adds a directory +separator character at the end of the path. + +@option{-B} prefixes that effectively specify directory names also apply +to libraries in the linker, because the compiler translates these +options into @option{-L} options for the linker. They also apply to +include files in the preprocessor, because the compiler translates these +options into @option{-isystem} options for the preprocessor. In this case, +the compiler appends @samp{include} to the prefix. + +The runtime support file @file{libgcc.a} can also be searched for using +the @option{-B} prefix, if needed. If it is not found there, the two +standard prefixes above are tried, and that is all. The file is left +out of the link if it is not found by those means. + +Another way to specify a prefix much like the @option{-B} prefix is to use +the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment +Variables}. + +As a special kludge, if the path provided by @option{-B} is +@file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to +9, then it is replaced by @file{[dir/]include}. This is to help +with boot-strapping the compiler. + +@item -no-canonical-prefixes +@opindex no-canonical-prefixes +Do not expand any symbolic links, resolve references to @samp{/../} +or @samp{/./}, or make the path absolute when generating a relative +prefix. + +@item --sysroot=@var{dir} +@opindex sysroot +Use @var{dir} as the logical root directory for headers and libraries. +For example, if the compiler normally searches for headers in +@file{/usr/include} and libraries in @file{/usr/lib}, it instead +searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}. + +If you use both this option and the @option{-isysroot} option, then +the @option{--sysroot} option applies to libraries, but the +@option{-isysroot} option applies to header files. + +The GNU linker (beginning with version 2.16) has the necessary support +for this option. If your linker does not support this option, the +header file aspect of @option{--sysroot} still works, but the +library aspect does not. + +@item --no-sysroot-suffix +@opindex no-sysroot-suffix +For some targets, a suffix is added to the root directory specified +with @option{--sysroot}, depending on the other options used, so that +headers may for example be found in +@file{@var{dir}/@var{suffix}/usr/include} instead of +@file{@var{dir}/usr/include}. This option disables the addition of +such a suffix. + +@end table + +@node Code Gen Options +@section Options for Code Generation Conventions +@cindex code generation conventions +@cindex options, code generation +@cindex run-time options + +These machine-independent options control the interface conventions +used in code generation. + +Most of them have both positive and negative forms; the negative form +of @option{-ffoo} is @option{-fno-foo}. In the table below, only +one of the forms is listed---the one that is not the default. You +can figure out the other form by either removing @samp{no-} or adding +it. + +@table @gcctabopt +@item -fstack-reuse=@var{reuse-level} +@opindex fstack_reuse +This option controls stack space reuse for user declared local/auto variables +and compiler generated temporaries. @var{reuse_level} can be @samp{all}, +@samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all +local variables and temporaries, @samp{named_vars} enables the reuse only for +user defined local variables with names, and @samp{none} disables stack reuse +completely. The default value is @samp{all}. The option is needed when the +program extends the lifetime of a scoped local variable or a compiler generated +temporary beyond the end point defined by the language. When a lifetime of +a variable ends, and if the variable lives in memory, the optimizing compiler +has the freedom to reuse its stack space with other temporaries or scoped +local variables whose live range does not overlap with it. Legacy code extending +local lifetime is likely to break with the stack reuse optimization. + +For example, + +@smallexample + int *p; + @{ + int local1; + + p = &local1; + local1 = 10; + .... + @} + @{ + int local2; + local2 = 20; + ... + @} + + if (*p == 10) // out of scope use of local1 + @{ + + @} +@end smallexample + +Another example: +@smallexample + + struct A + @{ + A(int k) : i(k), j(k) @{ @} + int i; + int j; + @}; + + A *ap; + + void foo(const A& ar) + @{ + ap = &ar; + @} + + void bar() + @{ + foo(A(10)); // temp object's lifetime ends when foo returns + + @{ + A a(20); + .... + @} + ap->i+= 10; // ap references out of scope temp whose space + // is reused with a. What is the value of ap->i? + @} + +@end smallexample + +The lifetime of a compiler generated temporary is well defined by the C++ +standard. When a lifetime of a temporary ends, and if the temporary lives +in memory, the optimizing compiler has the freedom to reuse its stack +space with other temporaries or scoped local variables whose live range +does not overlap with it. However some of the legacy code relies on +the behavior of older compilers in which temporaries' stack space is +not reused, the aggressive stack reuse can lead to runtime errors. This +option is used to control the temporary stack reuse optimization. + +@item -ftrapv +@opindex ftrapv +This option generates traps for signed overflow on addition, subtraction, +multiplication operations. +The options @option{-ftrapv} and @option{-fwrapv} override each other, so using +@option{-ftrapv} @option{-fwrapv} on the command-line results in +@option{-fwrapv} being effective. Note that only active options override, so +using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line +results in @option{-ftrapv} being effective. + +@item -fwrapv +@opindex fwrapv +This option instructs the compiler to assume that signed arithmetic +overflow of addition, subtraction and multiplication wraps around +using twos-complement representation. This flag enables some optimizations +and disables others. +The options @option{-ftrapv} and @option{-fwrapv} override each other, so using +@option{-ftrapv} @option{-fwrapv} on the command-line results in +@option{-fwrapv} being effective. Note that only active options override, so +using @option{-ftrapv} @option{-fwrapv} @option{-fno-wrapv} on the command-line +results in @option{-ftrapv} being effective. + +@item -fwrapv-pointer +@opindex fwrapv-pointer +This option instructs the compiler to assume that pointer arithmetic +overflow on addition and subtraction wraps around using twos-complement +representation. This flag disables some optimizations which assume +pointer overflow is invalid. + +@item -fstrict-overflow +@opindex fstrict-overflow +This option implies @option{-fno-wrapv} @option{-fno-wrapv-pointer} and when +negated implies @option{-fwrapv} @option{-fwrapv-pointer}. + +@item -fexceptions +@opindex fexceptions +Enable exception handling. Generates extra code needed to propagate +exceptions. For some targets, this implies GCC generates frame +unwind information for all functions, which can produce significant data +size overhead, although it does not affect execution. If you do not +specify this option, GCC enables it by default for languages like +C++ that normally require exception handling, and disables it for +languages like C that do not normally require it. However, you may need +to enable this option when compiling C code that needs to interoperate +properly with exception handlers written in C++. You may also wish to +disable this option if you are compiling older C++ programs that don't +use exception handling. + +@item -fnon-call-exceptions +@opindex fnon-call-exceptions +Generate code that allows trapping instructions to throw exceptions. +Note that this requires platform-specific runtime support that does +not exist everywhere. Moreover, it only allows @emph{trapping} +instructions to throw exceptions, i.e.@: memory references or floating-point +instructions. It does not allow exceptions to be thrown from +arbitrary signal handlers such as @code{SIGALRM}. This enables +@option{-fexceptions}. + +@item -fdelete-dead-exceptions +@opindex fdelete-dead-exceptions +Consider that instructions that may throw exceptions but don't otherwise +contribute to the execution of the program can be optimized away. +This does not affect calls to functions except those with the +@code{pure} or @code{const} attributes. +This option is enabled by default for the Ada and C++ compilers, as permitted by +the language specifications. +Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. + +@item -funwind-tables +@opindex funwind-tables +Similar to @option{-fexceptions}, except that it just generates any needed +static data, but does not affect the generated code in any other way. +You normally do not need to enable this option; instead, a language processor +that needs this handling enables it on your behalf. + +@item -fasynchronous-unwind-tables +@opindex fasynchronous-unwind-tables +Generate unwind table in DWARF format, if supported by target machine. The +table is exact at each instruction boundary, so it can be used for stack +unwinding from asynchronous events (such as debugger or garbage collector). + +@item -fno-gnu-unique +@opindex fno-gnu-unique +@opindex fgnu-unique +On systems with recent GNU assembler and C library, the C++ compiler +uses the @code{STB_GNU_UNIQUE} binding to make sure that definitions +of template static data members and static local variables in inline +functions are unique even in the presence of @code{RTLD_LOCAL}; this +is necessary to avoid problems with a library used by two different +@code{RTLD_LOCAL} plugins depending on a definition in one of them and +therefore disagreeing with the other one about the binding of the +symbol. But this causes @code{dlclose} to be ignored for affected +DSOs; if your program relies on reinitialization of a DSO via +@code{dlclose} and @code{dlopen}, you can use +@option{-fno-gnu-unique}. + +@item -fpcc-struct-return +@opindex fpcc-struct-return +Return ``short'' @code{struct} and @code{union} values in memory like +longer ones, rather than in registers. This convention is less +efficient, but it has the advantage of allowing intercallability between +GCC-compiled files and files compiled with other compilers, particularly +the Portable C Compiler (pcc). + +The precise convention for returning structures in memory depends +on the target configuration macros. + +Short structures and unions are those whose size and alignment match +that of some integer type. + +@strong{Warning:} code compiled with the @option{-fpcc-struct-return} +switch is not binary compatible with code compiled with the +@option{-freg-struct-return} switch. +Use it to conform to a non-default application binary interface. + +@item -freg-struct-return +@opindex freg-struct-return +Return @code{struct} and @code{union} values in registers when possible. +This is more efficient for small structures than +@option{-fpcc-struct-return}. + +If you specify neither @option{-fpcc-struct-return} nor +@option{-freg-struct-return}, GCC defaults to whichever convention is +standard for the target. If there is no standard convention, GCC +defaults to @option{-fpcc-struct-return}, except on targets where GCC is +the principal compiler. In those cases, we can choose the standard, and +we chose the more efficient register return alternative. + +@strong{Warning:} code compiled with the @option{-freg-struct-return} +switch is not binary compatible with code compiled with the +@option{-fpcc-struct-return} switch. +Use it to conform to a non-default application binary interface. + +@item -fshort-enums +@opindex fshort-enums +Allocate to an @code{enum} type only as many bytes as it needs for the +declared range of possible values. Specifically, the @code{enum} type +is equivalent to the smallest integer type that has enough room. + +@strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate +code that is not binary compatible with code generated without that switch. +Use it to conform to a non-default application binary interface. + +@item -fshort-wchar +@opindex fshort-wchar +Override the underlying type for @code{wchar_t} to be @code{short +unsigned int} instead of the default for the target. This option is +useful for building programs to run under WINE@. + +@strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate +code that is not binary compatible with code generated without that switch. +Use it to conform to a non-default application binary interface. + +@item -fcommon +@opindex fcommon +@opindex fno-common +@cindex tentative definitions +In C code, this option controls the placement of global variables +defined without an initializer, known as @dfn{tentative definitions} +in the C standard. Tentative definitions are distinct from declarations +of a variable with the @code{extern} keyword, which do not allocate storage. + +The default is @option{-fno-common}, which specifies that the compiler places +uninitialized global variables in the BSS section of the object file. +This inhibits the merging of tentative definitions by the linker so you get a +multiple-definition error if the same variable is accidentally defined in more +than one compilation unit. + +The @option{-fcommon} places uninitialized global variables in a common block. +This allows the linker to resolve all tentative definitions of the same variable +in different compilation units to the same object, or to a non-tentative +definition. This behavior is inconsistent with C++, and on many targets implies +a speed and code size penalty on global variable references. It is mainly +useful to enable legacy code to link without errors. + +@item -fno-ident +@opindex fno-ident +@opindex fident +Ignore the @code{#ident} directive. + +@item -finhibit-size-directive +@opindex finhibit-size-directive +Don't output a @code{.size} assembler directive, or anything else that +would cause trouble if the function is split in the middle, and the +two halves are placed at locations far apart in memory. This option is +used when compiling @file{crtstuff.c}; you should not need to use it +for anything else. + +@item -fverbose-asm +@opindex fverbose-asm +Put extra commentary information in the generated assembly code to +make it more readable. This option is generally only of use to those +who actually need to read the generated assembly code (perhaps while +debugging the compiler itself). + +@option{-fno-verbose-asm}, the default, causes the +extra information to be omitted and is useful when comparing two assembler +files. + +The added comments include: + +@itemize @bullet + +@item +information on the compiler version and command-line options, + +@item +the source code lines associated with the assembly instructions, +in the form FILENAME:LINENUMBER:CONTENT OF LINE, + +@item +hints on which high-level expressions correspond to +the various assembly instruction operands. + +@end itemize + +For example, given this C source file: + +@smallexample +int test (int n) +@{ + int i; + int total = 0; + + for (i = 0; i < n; i++) + total += i * i; + + return total; +@} +@end smallexample + +compiling to (x86_64) assembly via @option{-S} and emitting the result +direct to stdout via @option{-o} @option{-} + +@smallexample +gcc -S test.c -fverbose-asm -Os -o - +@end smallexample + +gives output similar to this: + +@smallexample + .file "test.c" +# GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu) + [...snip...] +# options passed: + [...snip...] + + .text + .globl test + .type test, @@function +test: +.LFB0: + .cfi_startproc +# test.c:4: int total = 0; + xorl %eax, %eax # +# test.c:6: for (i = 0; i < n; i++) + xorl %edx, %edx # i +.L2: +# test.c:6: for (i = 0; i < n; i++) + cmpl %edi, %edx # n, i + jge .L5 #, +# test.c:7: total += i * i; + movl %edx, %ecx # i, tmp92 + imull %edx, %ecx # i, tmp92 +# test.c:6: for (i = 0; i < n; i++) + incl %edx # i +# test.c:7: total += i * i; + addl %ecx, %eax # tmp92, + jmp .L2 # +.L5: +# test.c:10: @} + ret + .cfi_endproc +.LFE0: + .size test, .-test + .ident "GCC: (GNU) 7.0.0 20160809 (experimental)" + .section .note.GNU-stack,"",@@progbits +@end smallexample + +The comments are intended for humans rather than machines and hence the +precise format of the comments is subject to change. + +@item -frecord-gcc-switches +@opindex frecord-gcc-switches +This switch causes the command line used to invoke the +compiler to be recorded into the object file that is being created. +This switch is only implemented on some targets and the exact format +of the recording is target and binary file format dependent, but it +usually takes the form of a section containing ASCII text. This +switch is related to the @option{-fverbose-asm} switch, but that +switch only records information in the assembler output file as +comments, so it never reaches the object file. +See also @option{-grecord-gcc-switches} for another +way of storing compiler options into the object file. + +@item -fpic +@opindex fpic +@cindex global offset table +@cindex PIC +Generate position-independent code (PIC) suitable for use in a shared +library, if supported for the target machine. Such code accesses all +constant addresses through a global offset table (GOT)@. The dynamic +loader resolves the GOT entries when the program starts (the dynamic +loader is not part of GCC; it is part of the operating system). If +the GOT size for the linked executable exceeds a machine-specific +maximum size, you get an error message from the linker indicating that +@option{-fpic} does not work; in that case, recompile with @option{-fPIC} +instead. (These maximums are 8k on the SPARC, 28k on AArch64 and 32k +on the m68k and RS/6000. The x86 has no such limit.) + +Position-independent code requires special support, and therefore works +only on certain machines. For the x86, GCC supports PIC for System V +but not for the Sun 386i. Code generated for the IBM RS/6000 is always +position-independent. + +When this flag is set, the macros @code{__pic__} and @code{__PIC__} +are defined to 1. + +@item -fPIC +@opindex fPIC +If supported for the target machine, emit position-independent code, +suitable for dynamic linking and avoiding any limit on the size of the +global offset table. This option makes a difference on AArch64, m68k, +PowerPC and SPARC@. + +Position-independent code requires special support, and therefore works +only on certain machines. + +When this flag is set, the macros @code{__pic__} and @code{__PIC__} +are defined to 2. + +@item -fpie +@itemx -fPIE +@opindex fpie +@opindex fPIE +These options are similar to @option{-fpic} and @option{-fPIC}, but the +generated position-independent code can be only linked into executables. +Usually these options are used to compile code that will be linked using +the @option{-pie} GCC option. + +@option{-fpie} and @option{-fPIE} both define the macros +@code{__pie__} and @code{__PIE__}. The macros have the value 1 +for @option{-fpie} and 2 for @option{-fPIE}. + +@item -fno-plt +@opindex fno-plt +@opindex fplt +Do not use the PLT for external function calls in position-independent code. +Instead, load the callee address at call sites from the GOT and branch to it. +This leads to more efficient code by eliminating PLT stubs and exposing +GOT loads to optimizations. On architectures such as 32-bit x86 where +PLT stubs expect the GOT pointer in a specific register, this gives more +register allocation freedom to the compiler. +Lazy binding requires use of the PLT; +with @option{-fno-plt} all external symbols are resolved at load time. + +Alternatively, the function attribute @code{noplt} can be used to avoid calls +through the PLT for specific external functions. + +In position-dependent code, a few targets also convert calls to +functions that are marked to not use the PLT to use the GOT instead. + +@item -fno-jump-tables +@opindex fno-jump-tables +@opindex fjump-tables +Do not use jump tables for switch statements even where it would be +more efficient than other code generation strategies. This option is +of use in conjunction with @option{-fpic} or @option{-fPIC} for +building code that forms part of a dynamic linker and cannot +reference the address of a jump table. On some targets, jump tables +do not require a GOT and this option is not needed. + +@item -fno-bit-tests +@opindex fno-bit-tests +@opindex fbit-tests +Do not use bit tests for switch statements even where it would be +more efficient than other code generation strategies. + +@item -ffixed-@var{reg} +@opindex ffixed +Treat the register named @var{reg} as a fixed register; generated code +should never refer to it (except perhaps as a stack pointer, frame +pointer or in some other fixed role). + +@var{reg} must be the name of a register. The register names accepted +are machine-specific and are defined in the @code{REGISTER_NAMES} +macro in the machine description macro file. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fcall-used-@var{reg} +@opindex fcall-used +Treat the register named @var{reg} as an allocable register that is +clobbered by function calls. It may be allocated for temporaries or +variables that do not live across a call. Functions compiled this way +do not save and restore the register @var{reg}. + +It is an error to use this flag with the frame pointer or stack pointer. +Use of this flag for other registers that have fixed pervasive roles in +the machine's execution model produces disastrous results. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fcall-saved-@var{reg} +@opindex fcall-saved +Treat the register named @var{reg} as an allocable register saved by +functions. It may be allocated even for temporaries or variables that +live across a call. Functions compiled this way save and restore +the register @var{reg} if they use it. + +It is an error to use this flag with the frame pointer or stack pointer. +Use of this flag for other registers that have fixed pervasive roles in +the machine's execution model produces disastrous results. + +A different sort of disaster results from the use of this flag for +a register in which function values may be returned. + +This flag does not have a negative form, because it specifies a +three-way choice. + +@item -fpack-struct[=@var{n}] +@opindex fpack-struct +Without a value specified, pack all structure members together without +holes. When a value is specified (which must be a small power of two), pack +structure members according to this value, representing the maximum +alignment (that is, objects with default alignment requirements larger than +this are output potentially unaligned at the next fitting location. + +@strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate +code that is not binary compatible with code generated without that switch. +Additionally, it makes the code suboptimal. +Use it to conform to a non-default application binary interface. + +@item -fleading-underscore +@opindex fleading-underscore +This option and its counterpart, @option{-fno-leading-underscore}, forcibly +change the way C symbols are represented in the object file. One use +is to help link with legacy assembly code. + +@strong{Warning:} the @option{-fleading-underscore} switch causes GCC to +generate code that is not binary compatible with code generated without that +switch. Use it to conform to a non-default application binary interface. +Not all targets provide complete support for this switch. + +@item -ftls-model=@var{model} +@opindex ftls-model +Alter the thread-local storage model to be used (@pxref{Thread-Local}). +The @var{model} argument should be one of @samp{global-dynamic}, +@samp{local-dynamic}, @samp{initial-exec} or @samp{local-exec}. +Note that the choice is subject to optimization: the compiler may use +a more efficient model for symbols not visible outside of the translation +unit, or if @option{-fpic} is not given on the command line. + +The default without @option{-fpic} is @samp{initial-exec}; with +@option{-fpic} the default is @samp{global-dynamic}. + +@item -ftrampolines +@opindex ftrampolines +For targets that normally need trampolines for nested functions, always +generate them instead of using descriptors. Otherwise, for targets that +do not need them, like for example HP-PA or IA-64, do nothing. + +A trampoline is a small piece of code that is created at run time on the +stack when the address of a nested function is taken, and is used to call +the nested function indirectly. Therefore, it requires the stack to be +made executable in order for the program to work properly. + +@option{-fno-trampolines} is enabled by default on a language by language +basis to let the compiler avoid generating them, if it computes that this +is safe, and replace them with descriptors. Descriptors are made up of data +only, but the generated code must be prepared to deal with them. As of this +writing, @option{-fno-trampolines} is enabled by default only for Ada. + +Moreover, code compiled with @option{-ftrampolines} and code compiled with +@option{-fno-trampolines} are not binary compatible if nested functions are +present. This option must therefore be used on a program-wide basis and be +manipulated with extreme care. + +For languages other than Ada, the @code{-ftrampolines} and +@code{-fno-trampolines} options currently have no effect, and +trampolines are always generated on platforms that need them +for nested functions. + +@item -fvisibility=@r{[}default@r{|}internal@r{|}hidden@r{|}protected@r{]} +@opindex fvisibility +Set the default ELF image symbol visibility to the specified option---all +symbols are marked with this unless overridden within the code. +Using this feature can very substantially improve linking and +load times of shared object libraries, produce more optimized +code, provide near-perfect API export and prevent symbol clashes. +It is @strong{strongly} recommended that you use this in any shared objects +you distribute. + +Despite the nomenclature, @samp{default} always means public; i.e., +available to be linked against from outside the shared object. +@samp{protected} and @samp{internal} are pretty useless in real-world +usage so the only other commonly used option is @samp{hidden}. +The default if @option{-fvisibility} isn't specified is +@samp{default}, i.e., make every symbol public. + +A good explanation of the benefits offered by ensuring ELF +symbols have the correct visibility is given by ``How To Write +Shared Libraries'' by Ulrich Drepper (which can be found at +@w{@uref{https://www.akkadia.org/drepper/}})---however a superior +solution made possible by this option to marking things hidden when +the default is public is to make the default hidden and mark things +public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden} +and @code{__attribute__ ((visibility("default")))} instead of +@code{__declspec(dllexport)} you get almost identical semantics with +identical syntax. This is a great boon to those working with +cross-platform projects. + +For those adding visibility support to existing code, you may find +@code{#pragma GCC visibility} of use. This works by you enclosing +the declarations you wish to set visibility for with (for example) +@code{#pragma GCC visibility push(hidden)} and +@code{#pragma GCC visibility pop}. +Bear in mind that symbol visibility should be viewed @strong{as +part of the API interface contract} and thus all new code should +always specify visibility when it is not the default; i.e., declarations +only for use within the local DSO should @strong{always} be marked explicitly +as hidden as so to avoid PLT indirection overheads---making this +abundantly clear also aids readability and self-documentation of the code. +Note that due to ISO C++ specification requirements, @code{operator new} and +@code{operator delete} must always be of default visibility. + +Be aware that headers from outside your project, in particular system +headers and headers from any other library you use, may not be +expecting to be compiled with visibility other than the default. You +may need to explicitly say @code{#pragma GCC visibility push(default)} +before including any such headers. + +@code{extern} declarations are not affected by @option{-fvisibility}, so +a lot of code can be recompiled with @option{-fvisibility=hidden} with +no modifications. However, this means that calls to @code{extern} +functions with no explicit visibility use the PLT, so it is more +effective to use @code{__attribute ((visibility))} and/or +@code{#pragma GCC visibility} to tell the compiler which @code{extern} +declarations should be treated as hidden. + +Note that @option{-fvisibility} does affect C++ vague linkage +entities. This means that, for instance, an exception class that is +be thrown between DSOs must be explicitly marked with default +visibility so that the @samp{type_info} nodes are unified between +the DSOs. + +An overview of these techniques, their benefits and how to use them +is at @uref{https://gcc.gnu.org/@/wiki/@/Visibility}. + +@item -fstrict-volatile-bitfields +@opindex fstrict-volatile-bitfields +This option should be used if accesses to volatile bit-fields (or other +structure fields, although the compiler usually honors those types +anyway) should use a single access of the width of the +field's type, aligned to a natural alignment if possible. For +example, targets with memory-mapped peripheral registers might require +all such accesses to be 16 bits wide; with this flag you can +declare all peripheral bit-fields as @code{unsigned short} (assuming short +is 16 bits on these targets) to force GCC to use 16-bit accesses +instead of, perhaps, a more efficient 32-bit access. + +If this option is disabled, the compiler uses the most efficient +instruction. In the previous example, that might be a 32-bit load +instruction, even though that accesses bytes that do not contain +any portion of the bit-field, or memory-mapped registers unrelated to +the one being updated. + +In some cases, such as when the @code{packed} attribute is applied to a +structure field, it may not be possible to access the field with a single +read or write that is correctly aligned for the target machine. In this +case GCC falls back to generating multiple accesses rather than code that +will fault or truncate the result at run time. + +Note: Due to restrictions of the C/C++11 memory model, write accesses are +not allowed to touch non bit-field members. It is therefore recommended +to define all bits of the field's type as bit-field members. + +The default value of this option is determined by the application binary +interface for the target processor. + +@item -fsync-libcalls +@opindex fsync-libcalls +This option controls whether any out-of-line instance of the @code{__sync} +family of functions may be used to implement the C++11 @code{__atomic} +family of functions. + +The default value of this option is enabled, thus the only useful form +of the option is @option{-fno-sync-libcalls}. This option is used in +the implementation of the @file{libatomic} runtime library. + +@end table + +@node Developer Options +@section GCC Developer Options +@cindex developer options +@cindex debugging GCC +@cindex debug dump options +@cindex dump options +@cindex compilation statistics + +This section describes command-line options that are primarily of +interest to GCC developers, including options to support compiler +testing and investigation of compiler bugs and compile-time +performance problems. This includes options that produce debug dumps +at various points in the compilation; that print statistics such as +memory use and execution time; and that print information about GCC's +configuration, such as where it searches for libraries. You should +rarely need to use any of these options for ordinary compilation and +linking tasks. + +Many developer options that cause GCC to dump output to a file take an +optional @samp{=@var{filename}} suffix. You can specify @samp{stdout} +or @samp{-} to dump to standard output, and @samp{stderr} for standard +error. + +If @samp{=@var{filename}} is omitted, a default dump file name is +constructed by concatenating the base dump file name, a pass number, +phase letter, and pass name. The base dump file name is the name of +output file produced by the compiler if explicitly specified and not +an executable; otherwise it is the source file name. +The pass number is determined by the order passes are registered with +the compiler's pass manager. +This is generally the same as the order of execution, but passes +registered by plugins, target-specific passes, or passes that are +otherwise registered late are numbered higher than the pass named +@samp{final}, even if they are executed earlier. The phase letter is +one of @samp{i} (inter-procedural analysis), @samp{l} +(language-specific), @samp{r} (RTL), or @samp{t} (tree). +The files are created in the directory of the output file. + +@table @gcctabopt + +@item -fcallgraph-info +@itemx -fcallgraph-info=@var{MARKERS} +@opindex fcallgraph-info +Makes the compiler output callgraph information for the program, on a +per-object-file basis. The information is generated in the common VCG +format. It can be decorated with additional, per-node and/or per-edge +information, if a list of comma-separated markers is additionally +specified. When the @code{su} marker is specified, the callgraph is +decorated with stack usage information; it is equivalent to +@option{-fstack-usage}. When the @code{da} marker is specified, the +callgraph is decorated with information about dynamically allocated +objects. + +When compiling with @option{-flto}, no callgraph information is output +along with the object file. At LTO link time, @option{-fcallgraph-info} +may generate multiple callgraph information files next to intermediate +LTO output files. + +@item -d@var{letters} +@itemx -fdump-rtl-@var{pass} +@itemx -fdump-rtl-@var{pass}=@var{filename} +@opindex d +@opindex fdump-rtl-@var{pass} +Says to make debugging dumps during compilation at times specified by +@var{letters}. This is used for debugging the RTL-based passes of the +compiler. + +Some @option{-d@var{letters}} switches have different meaning when +@option{-E} is used for preprocessing. @xref{Preprocessor Options}, +for information about preprocessor-specific dump options. + +Debug dumps can be enabled with a @option{-fdump-rtl} switch or some +@option{-d} option @var{letters}. Here are the possible +letters for use in @var{pass} and @var{letters}, and their meanings: + +@table @gcctabopt + +@item -fdump-rtl-alignments +@opindex fdump-rtl-alignments +Dump after branch alignments have been computed. + +@item -fdump-rtl-asmcons +@opindex fdump-rtl-asmcons +Dump after fixing rtl statements that have unsatisfied in/out constraints. + +@item -fdump-rtl-auto_inc_dec +@opindex fdump-rtl-auto_inc_dec +Dump after auto-inc-dec discovery. This pass is only run on +architectures that have auto inc or auto dec instructions. + +@item -fdump-rtl-barriers +@opindex fdump-rtl-barriers +Dump after cleaning up the barrier instructions. + +@item -fdump-rtl-bbpart +@opindex fdump-rtl-bbpart +Dump after partitioning hot and cold basic blocks. + +@item -fdump-rtl-bbro +@opindex fdump-rtl-bbro +Dump after block reordering. + +@item -fdump-rtl-btl1 +@itemx -fdump-rtl-btl2 +@opindex fdump-rtl-btl2 +@opindex fdump-rtl-btl2 +@option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping +after the two branch +target load optimization passes. + +@item -fdump-rtl-bypass +@opindex fdump-rtl-bypass +Dump after jump bypassing and control flow optimizations. + +@item -fdump-rtl-combine +@opindex fdump-rtl-combine +Dump after the RTL instruction combination pass. + +@item -fdump-rtl-compgotos +@opindex fdump-rtl-compgotos +Dump after duplicating the computed gotos. + +@item -fdump-rtl-ce1 +@itemx -fdump-rtl-ce2 +@itemx -fdump-rtl-ce3 +@opindex fdump-rtl-ce1 +@opindex fdump-rtl-ce2 +@opindex fdump-rtl-ce3 +@option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and +@option{-fdump-rtl-ce3} enable dumping after the three +if conversion passes. + +@item -fdump-rtl-cprop_hardreg +@opindex fdump-rtl-cprop_hardreg +Dump after hard register copy propagation. + +@item -fdump-rtl-csa +@opindex fdump-rtl-csa +Dump after combining stack adjustments. + +@item -fdump-rtl-cse1 +@itemx -fdump-rtl-cse2 +@opindex fdump-rtl-cse1 +@opindex fdump-rtl-cse2 +@option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after +the two common subexpression elimination passes. + +@item -fdump-rtl-dce +@opindex fdump-rtl-dce +Dump after the standalone dead code elimination passes. + +@item -fdump-rtl-dbr +@opindex fdump-rtl-dbr +Dump after delayed branch scheduling. + +@item -fdump-rtl-dce1 +@itemx -fdump-rtl-dce2 +@opindex fdump-rtl-dce1 +@opindex fdump-rtl-dce2 +@option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after +the two dead store elimination passes. + +@item -fdump-rtl-eh +@opindex fdump-rtl-eh +Dump after finalization of EH handling code. + +@item -fdump-rtl-eh_ranges +@opindex fdump-rtl-eh_ranges +Dump after conversion of EH handling range regions. + +@item -fdump-rtl-expand +@opindex fdump-rtl-expand +Dump after RTL generation. + +@item -fdump-rtl-fwprop1 +@itemx -fdump-rtl-fwprop2 +@opindex fdump-rtl-fwprop1 +@opindex fdump-rtl-fwprop2 +@option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable +dumping after the two forward propagation passes. + +@item -fdump-rtl-gcse1 +@itemx -fdump-rtl-gcse2 +@opindex fdump-rtl-gcse1 +@opindex fdump-rtl-gcse2 +@option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping +after global common subexpression elimination. + +@item -fdump-rtl-init-regs +@opindex fdump-rtl-init-regs +Dump after the initialization of the registers. + +@item -fdump-rtl-initvals +@opindex fdump-rtl-initvals +Dump after the computation of the initial value sets. + +@item -fdump-rtl-into_cfglayout +@opindex fdump-rtl-into_cfglayout +Dump after converting to cfglayout mode. + +@item -fdump-rtl-ira +@opindex fdump-rtl-ira +Dump after iterated register allocation. + +@item -fdump-rtl-jump +@opindex fdump-rtl-jump +Dump after the second jump optimization. + +@item -fdump-rtl-loop2 +@opindex fdump-rtl-loop2 +@option{-fdump-rtl-loop2} enables dumping after the rtl +loop optimization passes. + +@item -fdump-rtl-mach +@opindex fdump-rtl-mach +Dump after performing the machine dependent reorganization pass, if that +pass exists. + +@item -fdump-rtl-mode_sw +@opindex fdump-rtl-mode_sw +Dump after removing redundant mode switches. + +@item -fdump-rtl-rnreg +@opindex fdump-rtl-rnreg +Dump after register renumbering. + +@item -fdump-rtl-outof_cfglayout +@opindex fdump-rtl-outof_cfglayout +Dump after converting from cfglayout mode. + +@item -fdump-rtl-peephole2 +@opindex fdump-rtl-peephole2 +Dump after the peephole pass. + +@item -fdump-rtl-postreload +@opindex fdump-rtl-postreload +Dump after post-reload optimizations. + +@item -fdump-rtl-pro_and_epilogue +@opindex fdump-rtl-pro_and_epilogue +Dump after generating the function prologues and epilogues. + +@item -fdump-rtl-sched1 +@itemx -fdump-rtl-sched2 +@opindex fdump-rtl-sched1 +@opindex fdump-rtl-sched2 +@option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping +after the basic block scheduling passes. + +@item -fdump-rtl-ree +@opindex fdump-rtl-ree +Dump after sign/zero extension elimination. + +@item -fdump-rtl-seqabstr +@opindex fdump-rtl-seqabstr +Dump after common sequence discovery. + +@item -fdump-rtl-shorten +@opindex fdump-rtl-shorten +Dump after shortening branches. + +@item -fdump-rtl-sibling +@opindex fdump-rtl-sibling +Dump after sibling call optimizations. + +@item -fdump-rtl-split1 +@itemx -fdump-rtl-split2 +@itemx -fdump-rtl-split3 +@itemx -fdump-rtl-split4 +@itemx -fdump-rtl-split5 +@opindex fdump-rtl-split1 +@opindex fdump-rtl-split2 +@opindex fdump-rtl-split3 +@opindex fdump-rtl-split4 +@opindex fdump-rtl-split5 +These options enable dumping after five rounds of +instruction splitting. + +@item -fdump-rtl-sms +@opindex fdump-rtl-sms +Dump after modulo scheduling. This pass is only run on some +architectures. + +@item -fdump-rtl-stack +@opindex fdump-rtl-stack +Dump after conversion from GCC's ``flat register file'' registers to the +x87's stack-like registers. This pass is only run on x86 variants. + +@item -fdump-rtl-subreg1 +@itemx -fdump-rtl-subreg2 +@opindex fdump-rtl-subreg1 +@opindex fdump-rtl-subreg2 +@option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after +the two subreg expansion passes. + +@item -fdump-rtl-unshare +@opindex fdump-rtl-unshare +Dump after all rtl has been unshared. + +@item -fdump-rtl-vartrack +@opindex fdump-rtl-vartrack +Dump after variable tracking. + +@item -fdump-rtl-vregs +@opindex fdump-rtl-vregs +Dump after converting virtual registers to hard registers. + +@item -fdump-rtl-web +@opindex fdump-rtl-web +Dump after live range splitting. + +@item -fdump-rtl-regclass +@itemx -fdump-rtl-subregs_of_mode_init +@itemx -fdump-rtl-subregs_of_mode_finish +@itemx -fdump-rtl-dfinit +@itemx -fdump-rtl-dfinish +@opindex fdump-rtl-regclass +@opindex fdump-rtl-subregs_of_mode_init +@opindex fdump-rtl-subregs_of_mode_finish +@opindex fdump-rtl-dfinit +@opindex fdump-rtl-dfinish +These dumps are defined but always produce empty files. + +@item -da +@itemx -fdump-rtl-all +@opindex da +@opindex fdump-rtl-all +Produce all the dumps listed above. + +@item -dA +@opindex dA +Annotate the assembler output with miscellaneous debugging information. + +@item -dD +@opindex dD +Dump all macro definitions, at the end of preprocessing, in addition to +normal output. + +@item -dH +@opindex dH +Produce a core dump whenever an error occurs. + +@item -dp +@opindex dp +Annotate the assembler output with a comment indicating which +pattern and alternative is used. The length and cost of each instruction are +also printed. + +@item -dP +@opindex dP +Dump the RTL in the assembler output as a comment before each instruction. +Also turns on @option{-dp} annotation. + +@item -dx +@opindex dx +Just generate RTL for a function instead of compiling it. Usually used +with @option{-fdump-rtl-expand}. +@end table + +@item -fdump-debug +@opindex fdump-debug +Dump debugging information generated during the debug +generation phase. + +@item -fdump-earlydebug +@opindex fdump-earlydebug +Dump debugging information generated during the early debug +generation phase. + +@item -fdump-noaddr +@opindex fdump-noaddr +When doing debugging dumps, suppress address output. This makes it more +feasible to use diff on debugging dumps for compiler invocations with +different compiler binaries and/or different +text / bss / data / heap / stack / dso start locations. + +@item -freport-bug +@opindex freport-bug +Collect and dump debug information into a temporary file if an +internal compiler error (ICE) occurs. + +@item -fdump-unnumbered +@opindex fdump-unnumbered +When doing debugging dumps, suppress instruction numbers and address output. +This makes it more feasible to use diff on debugging dumps for compiler +invocations with different options, in particular with and without +@option{-g}. + +@item -fdump-unnumbered-links +@opindex fdump-unnumbered-links +When doing debugging dumps (see @option{-d} option above), suppress +instruction numbers for the links to the previous and next instructions +in a sequence. + +@item -fdump-ipa-@var{switch} +@itemx -fdump-ipa-@var{switch}-@var{options} +@opindex fdump-ipa +Control the dumping at various stages of inter-procedural analysis +language tree to a file. The file name is generated by appending a +switch specific suffix to the source file name, and the file is created +in the same directory as the output file. The following dumps are +possible: + +@table @samp +@item all +Enables all inter-procedural analysis dumps. + +@item cgraph +Dumps information about call-graph optimization, unused function removal, +and inlining decisions. + +@item inline +Dump after function inlining. + +@end table + +Additionally, the options @option{-optimized}, @option{-missed}, +@option{-note}, and @option{-all} can be provided, with the same meaning +as for @option{-fopt-info}, defaulting to @option{-optimized}. + +For example, @option{-fdump-ipa-inline-optimized-missed} will emit +information on callsites that were inlined, along with callsites +that were not inlined. + +By default, the dump will contain messages about successful +optimizations (equivalent to @option{-optimized}) together with +low-level details about the analysis. + +@item -fdump-lang +@opindex fdump-lang +Dump language-specific information. The file name is made by appending +@file{.lang} to the source file name. + +@item -fdump-lang-all +@itemx -fdump-lang-@var{switch} +@itemx -fdump-lang-@var{switch}-@var{options} +@itemx -fdump-lang-@var{switch}-@var{options}=@var{filename} +@opindex fdump-lang-all +@opindex fdump-lang +Control the dumping of language-specific information. The @var{options} +and @var{filename} portions behave as described in the +@option{-fdump-tree} option. The following @var{switch} values are +accepted: + +@table @samp +@item all + +Enable all language-specific dumps. + +@item class +Dump class hierarchy information. Virtual table information is emitted +unless '@option{slim}' is specified. This option is applicable to C++ only. + +@item module +Dump module information. Options @option{lineno} (locations), +@option{graph} (reachability), @option{blocks} (clusters), +@option{uid} (serialization), @option{alias} (mergeable), +@option{asmname} (Elrond), @option{eh} (mapper) & @option{vops} +(macros) may provide additional information. This option is +applicable to C++ only. + +@item raw +Dump the raw internal tree data. This option is applicable to C++ only. + +@end table + +@item -fdump-passes +@opindex fdump-passes +Print on @file{stderr} the list of optimization passes that are turned +on and off by the current command-line options. + +@item -fdump-statistics-@var{option} +@opindex fdump-statistics +Enable and control dumping of pass statistics in a separate file. The +file name is generated by appending a suffix ending in +@samp{.statistics} to the source file name, and the file is created in +the same directory as the output file. If the @samp{-@var{option}} +form is used, @samp{-stats} causes counters to be summed over the +whole compilation unit while @samp{-details} dumps every event as +the passes generate them. The default with no option is to sum +counters for each function compiled. + +@item -fdump-tree-all +@itemx -fdump-tree-@var{switch} +@itemx -fdump-tree-@var{switch}-@var{options} +@itemx -fdump-tree-@var{switch}-@var{options}=@var{filename} +@opindex fdump-tree-all +@opindex fdump-tree +Control the dumping at various stages of processing the intermediate +language tree to a file. If the @samp{-@var{options}} +form is used, @var{options} is a list of @samp{-} separated options +which control the details of the dump. Not all options are applicable +to all dumps; those that are not meaningful are ignored. The +following options are available + +@table @samp +@item address +Print the address of each node. Usually this is not meaningful as it +changes according to the environment and source file. Its primary use +is for tying up a dump file with a debug environment. +@item asmname +If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that +in the dump instead of @code{DECL_NAME}. Its primary use is ease of +use working backward from mangled names in the assembly file. +@item slim +When dumping front-end intermediate representations, inhibit dumping +of members of a scope or body of a function merely because that scope +has been reached. Only dump such items when they are directly reachable +by some other path. + +When dumping pretty-printed trees, this option inhibits dumping the +bodies of control structures. + +When dumping RTL, print the RTL in slim (condensed) form instead of +the default LISP-like representation. +@item raw +Print a raw representation of the tree. By default, trees are +pretty-printed into a C-like representation. +@item details +Enable more detailed dumps (not honored by every dump option). Also +include information from the optimization passes. +@item stats +Enable dumping various statistics about the pass (not honored by every dump +option). +@item blocks +Enable showing basic block boundaries (disabled in raw dumps). +@item graph +For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}), +dump a representation of the control flow graph suitable for viewing with +GraphViz to @file{@var{file}.@var{passid}.@var{pass}.dot}. Each function in +the file is pretty-printed as a subgraph, so that GraphViz can render them +all in a single plot. + +This option currently only works for RTL dumps, and the RTL is always +dumped in slim form. +@item vops +Enable showing virtual operands for every statement. +@item lineno +Enable showing line numbers for statements. +@item uid +Enable showing the unique ID (@code{DECL_UID}) for each variable. +@item verbose +Enable showing the tree dump for each statement. +@item eh +Enable showing the EH region number holding each statement. +@item scev +Enable showing scalar evolution analysis details. +@item optimized +Enable showing optimization information (only available in certain +passes). +@item missed +Enable showing missed optimization information (only available in certain +passes). +@item note +Enable other detailed optimization information (only available in +certain passes). +@item all +Turn on all options, except @option{raw}, @option{slim}, @option{verbose} +and @option{lineno}. +@item optall +Turn on all optimization options, i.e., @option{optimized}, +@option{missed}, and @option{note}. +@end table + +To determine what tree dumps are available or find the dump for a pass +of interest follow the steps below. + +@enumerate +@item +Invoke GCC with @option{-fdump-passes} and in the @file{stderr} output +look for a code that corresponds to the pass you are interested in. +For example, the codes @code{tree-evrp}, @code{tree-vrp1}, and +@code{tree-vrp2} correspond to the three Value Range Propagation passes. +The number at the end distinguishes distinct invocations of the same pass. +@item +To enable the creation of the dump file, append the pass code to +the @option{-fdump-} option prefix and invoke GCC with it. For example, +to enable the dump from the Early Value Range Propagation pass, invoke +GCC with the @option{-fdump-tree-evrp} option. Optionally, you may +specify the name of the dump file. If you don't specify one, GCC +creates as described below. +@item +Find the pass dump in a file whose name is composed of three components +separated by a period: the name of the source file GCC was invoked to +compile, a numeric suffix indicating the pass number followed by the +letter @samp{t} for tree passes (and the letter @samp{r} for RTL passes), +and finally the pass code. For example, the Early VRP pass dump might +be in a file named @file{myfile.c.038t.evrp} in the current working +directory. Note that the numeric codes are not stable and may change +from one version of GCC to another. +@end enumerate + +@item -fopt-info +@itemx -fopt-info-@var{options} +@itemx -fopt-info-@var{options}=@var{filename} +@opindex fopt-info +Controls optimization dumps from various optimization passes. If the +@samp{-@var{options}} form is used, @var{options} is a list of +@samp{-} separated option keywords to select the dump details and +optimizations. + +The @var{options} can be divided into three groups: +@enumerate +@item +options describing what kinds of messages should be emitted, +@item +options describing the verbosity of the dump, and +@item +options describing which optimizations should be included. +@end enumerate +The options from each group can be freely mixed as they are +non-overlapping. However, in case of any conflicts, +the later options override the earlier options on the command +line. + +The following options control which kinds of messages should be emitted: + +@table @samp +@item optimized +Print information when an optimization is successfully applied. It is +up to a pass to decide which information is relevant. For example, the +vectorizer passes print the source location of loops which are +successfully vectorized. +@item missed +Print information about missed optimizations. Individual passes +control which information to include in the output. +@item note +Print verbose information about optimizations, such as certain +transformations, more detailed messages about decisions etc. +@item all +Print detailed optimization information. This includes +@samp{optimized}, @samp{missed}, and @samp{note}. +@end table + +The following option controls the dump verbosity: + +@table @samp +@item internals +By default, only ``high-level'' messages are emitted. This option enables +additional, more detailed, messages, which are likely to only be of interest +to GCC developers. +@end table + +One or more of the following option keywords can be used to describe a +group of optimizations: + +@table @samp +@item ipa +Enable dumps from all interprocedural optimizations. +@item loop +Enable dumps from all loop optimizations. +@item inline +Enable dumps from all inlining optimizations. +@item omp +Enable dumps from all OMP (Offloading and Multi Processing) optimizations. +@item vec +Enable dumps from all vectorization optimizations. +@item optall +Enable dumps from all optimizations. This is a superset of +the optimization groups listed above. +@end table + +If @var{options} is +omitted, it defaults to @samp{optimized-optall}, which means to dump messages +about successful optimizations from all the passes, omitting messages +that are treated as ``internals''. + +If the @var{filename} is provided, then the dumps from all the +applicable optimizations are concatenated into the @var{filename}. +Otherwise the dump is output onto @file{stderr}. Though multiple +@option{-fopt-info} options are accepted, only one of them can include +a @var{filename}. If other filenames are provided then all but the +first such option are ignored. + +Note that the output @var{filename} is overwritten +in case of multiple translation units. If a combined output from +multiple translation units is desired, @file{stderr} should be used +instead. + +In the following example, the optimization info is output to +@file{stderr}: + +@smallexample +gcc -O3 -fopt-info +@end smallexample + +This example: +@smallexample +gcc -O3 -fopt-info-missed=missed.all +@end smallexample + +@noindent +outputs missed optimization report from all the passes into +@file{missed.all}, and this one: + +@smallexample +gcc -O2 -ftree-vectorize -fopt-info-vec-missed +@end smallexample + +@noindent +prints information about missed optimization opportunities from +vectorization passes on @file{stderr}. +Note that @option{-fopt-info-vec-missed} is equivalent to +@option{-fopt-info-missed-vec}. The order of the optimization group +names and message types listed after @option{-fopt-info} does not matter. + +As another example, +@smallexample +gcc -O3 -fopt-info-inline-optimized-missed=inline.txt +@end smallexample + +@noindent +outputs information about missed optimizations as well as +optimized locations from all the inlining passes into +@file{inline.txt}. + +Finally, consider: + +@smallexample +gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt +@end smallexample + +@noindent +Here the two output filenames @file{vec.miss} and @file{loop.opt} are +in conflict since only one output file is allowed. In this case, only +the first option takes effect and the subsequent options are +ignored. Thus only @file{vec.miss} is produced which contains +dumps from the vectorizer about missed opportunities. + +@item -fsave-optimization-record +@opindex fsave-optimization-record +Write a SRCFILE.opt-record.json.gz file detailing what optimizations +were performed, for those optimizations that support @option{-fopt-info}. + +This option is experimental and the format of the data within the +compressed JSON file is subject to change. + +It is roughly equivalent to a machine-readable version of +@option{-fopt-info-all}, as a collection of messages with source file, +line number and column number, with the following additional data for +each message: + +@itemize @bullet + +@item +the execution count of the code being optimized, along with metadata about +whether this was from actual profile data, or just an estimate, allowing +consumers to prioritize messages by code hotness, + +@item +the function name of the code being optimized, where applicable, + +@item +the ``inlining chain'' for the code being optimized, so that when +a function is inlined into several different places (which might +themselves be inlined), the reader can distinguish between the copies, + +@item +objects identifying those parts of the message that refer to expressions, +statements or symbol-table nodes, which of these categories they are, and, +when available, their source code location, + +@item +the GCC pass that emitted the message, and + +@item +the location in GCC's own code from which the message was emitted + +@end itemize + +Additionally, some messages are logically nested within other +messages, reflecting implementation details of the optimization +passes. + +@item -fsched-verbose=@var{n} +@opindex fsched-verbose +On targets that use instruction scheduling, this option controls the +amount of debugging output the scheduler prints to the dump files. + +For @var{n} greater than zero, @option{-fsched-verbose} outputs the +same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}. +For @var{n} greater than one, it also output basic block probabilities, +detailed ready list information and unit/insn info. For @var{n} greater +than two, it includes RTL at abort point, control-flow and regions info. +And for @var{n} over four, @option{-fsched-verbose} also includes +dependence info. + + + +@item -fenable-@var{kind}-@var{pass} +@itemx -fdisable-@var{kind}-@var{pass}=@var{range-list} +@opindex fdisable- +@opindex fenable- + +This is a set of options that are used to explicitly disable/enable +optimization passes. These options are intended for use for debugging GCC. +Compiler users should use regular options for enabling/disabling +passes instead. + +@table @gcctabopt + +@item -fdisable-ipa-@var{pass} +Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is +statically invoked in the compiler multiple times, the pass name should be +appended with a sequential number starting from 1. + +@item -fdisable-rtl-@var{pass} +@itemx -fdisable-rtl-@var{pass}=@var{range-list} +Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is +statically invoked in the compiler multiple times, the pass name should be +appended with a sequential number starting from 1. @var{range-list} is a +comma-separated list of function ranges or assembler names. Each range is a number +pair separated by a colon. The range is inclusive in both ends. If the range +is trivial, the number pair can be simplified as a single number. If the +function's call graph node's @var{uid} falls within one of the specified ranges, +the @var{pass} is disabled for that function. The @var{uid} is shown in the +function header of a dump file, and the pass names can be dumped by using +option @option{-fdump-passes}. + +@item -fdisable-tree-@var{pass} +@itemx -fdisable-tree-@var{pass}=@var{range-list} +Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of +option arguments. + +@item -fenable-ipa-@var{pass} +Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is +statically invoked in the compiler multiple times, the pass name should be +appended with a sequential number starting from 1. + +@item -fenable-rtl-@var{pass} +@itemx -fenable-rtl-@var{pass}=@var{range-list} +Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument +description and examples. + +@item -fenable-tree-@var{pass} +@itemx -fenable-tree-@var{pass}=@var{range-list} +Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description +of option arguments. + +@end table + +Here are some examples showing uses of these options. + +@smallexample + +# disable ccp1 for all functions + -fdisable-tree-ccp1 +# disable complete unroll for function whose cgraph node uid is 1 + -fenable-tree-cunroll=1 +# disable gcse2 for functions at the following ranges [1,1], +# [300,400], and [400,1000] +# disable gcse2 for functions foo and foo2 + -fdisable-rtl-gcse2=foo,foo2 +# disable early inlining + -fdisable-tree-einline +# disable ipa inlining + -fdisable-ipa-inline +# enable tree full unroll + -fenable-tree-unroll + +@end smallexample + +@item -fchecking +@itemx -fchecking=@var{n} +@opindex fchecking +@opindex fno-checking +Enable internal consistency checking. The default depends on +the compiler configuration. @option{-fchecking=2} enables further +internal consistency checking that might affect code generation. + +@item -frandom-seed=@var{string} +@opindex frandom-seed +This option provides a seed that GCC uses in place of +random numbers in generating certain symbol names +that have to be different in every compiled file. It is also used to +place unique stamps in coverage data files and the object files that +produce them. You can use the @option{-frandom-seed} option to produce +reproducibly identical object files. + +The @var{string} can either be a number (decimal, octal or hex) or an +arbitrary string (in which case it's converted to a number by +computing CRC32). + +The @var{string} should be different for every file you compile. + +@item -save-temps +@opindex save-temps +Store the usual ``temporary'' intermediate files permanently; name them +as auxiliary output files, as specified described under +@option{-dumpbase} and @option{-dumpdir}. + +When used in combination with the @option{-x} command-line option, +@option{-save-temps} is sensible enough to avoid overwriting an +input source file with the same extension as an intermediate file. +The corresponding intermediate file may be obtained by renaming the +source file before using @option{-save-temps}. + +@item -save-temps=cwd +@opindex save-temps=cwd +Equivalent to @option{-save-temps -dumpdir ./}. + +@item -save-temps=obj +@opindex save-temps=obj +Equivalent to @option{-save-temps -dumpdir @file{outdir/}}, where +@file{outdir/} is the directory of the output file specified after the +@option{-o} option, including any directory separators. If the +@option{-o} option is not used, the @option{-save-temps=obj} switch +behaves like @option{-save-temps=cwd}. + +@item -time@r{[}=@var{file}@r{]} +@opindex time +Report the CPU time taken by each subprocess in the compilation +sequence. For C source files, this is the compiler proper and assembler +(plus the linker if linking is done). + +Without the specification of an output file, the output looks like this: + +@smallexample +# cc1 0.12 0.01 +# as 0.00 0.01 +@end smallexample + +The first number on each line is the ``user time'', that is time spent +executing the program itself. The second number is ``system time'', +time spent executing operating system routines on behalf of the program. +Both numbers are in seconds. + +With the specification of an output file, the output is appended to the +named file, and it looks like this: + +@smallexample +0.12 0.01 cc1 @var{options} +0.00 0.01 as @var{options} +@end smallexample + +The ``user time'' and the ``system time'' are moved before the program +name, and the options passed to the program are displayed, so that one +can later tell what file was being compiled, and with which options. + +@item -fdump-final-insns@r{[}=@var{file}@r{]} +@opindex fdump-final-insns +Dump the final internal representation (RTL) to @var{file}. If the +optional argument is omitted (or if @var{file} is @code{.}), the name +of the dump file is determined by appending @code{.gkd} to the +dump base name, see @option{-dumpbase}. + +@item -fcompare-debug@r{[}=@var{opts}@r{]} +@opindex fcompare-debug +@opindex fno-compare-debug +If no error occurs during compilation, run the compiler a second time, +adding @var{opts} and @option{-fcompare-debug-second} to the arguments +passed to the second compilation. Dump the final internal +representation in both compilations, and print an error if they differ. + +If the equal sign is omitted, the default @option{-gtoggle} is used. + +The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty +and nonzero, implicitly enables @option{-fcompare-debug}. If +@env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash, +then it is used for @var{opts}, otherwise the default @option{-gtoggle} +is used. + +@option{-fcompare-debug=}, with the equal sign but without @var{opts}, +is equivalent to @option{-fno-compare-debug}, which disables the dumping +of the final representation and the second compilation, preventing even +@env{GCC_COMPARE_DEBUG} from taking effect. + +To verify full coverage during @option{-fcompare-debug} testing, set +@env{GCC_COMPARE_DEBUG} to say @option{-fcompare-debug-not-overridden}, +which GCC rejects as an invalid option in any actual compilation +(rather than preprocessing, assembly or linking). To get just a +warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug +not overridden} will do. + +@item -fcompare-debug-second +@opindex fcompare-debug-second +This option is implicitly passed to the compiler for the second +compilation requested by @option{-fcompare-debug}, along with options to +silence warnings, and omitting other options that would cause the compiler +to produce output to files or to standard output as a side effect. Dump +files and preserved temporary files are renamed so as to contain the +@code{.gk} additional extension during the second compilation, to avoid +overwriting those generated by the first. + +When this option is passed to the compiler driver, it causes the +@emph{first} compilation to be skipped, which makes it useful for little +other than debugging the compiler proper. + +@item -gtoggle +@opindex gtoggle +Turn off generation of debug info, if leaving out this option +generates it, or turn it on at level 2 otherwise. The position of this +argument in the command line does not matter; it takes effect after all +other options are processed, and it does so only once, no matter how +many times it is given. This is mainly intended to be used with +@option{-fcompare-debug}. + +@item -fvar-tracking-assignments-toggle +@opindex fvar-tracking-assignments-toggle +@opindex fno-var-tracking-assignments-toggle +Toggle @option{-fvar-tracking-assignments}, in the same way that +@option{-gtoggle} toggles @option{-g}. + +@item -Q +@opindex Q +Makes the compiler print out each function name as it is compiled, and +print some statistics about each pass when it finishes. + +@item -ftime-report +@opindex ftime-report +Makes the compiler print some statistics about the time consumed by each +pass when it finishes. + +@item -ftime-report-details +@opindex ftime-report-details +Record the time consumed by infrastructure parts separately for each pass. + +@item -fira-verbose=@var{n} +@opindex fira-verbose +Control the verbosity of the dump file for the integrated register allocator. +The default value is 5. If the value @var{n} is greater or equal to 10, +the dump output is sent to stderr using the same format as @var{n} minus 10. + +@item -flto-report +@opindex flto-report +Prints a report with internal details on the workings of the link-time +optimizer. The contents of this report vary from version to version. +It is meant to be useful to GCC developers when processing object +files in LTO mode (via @option{-flto}). + +Disabled by default. + +@item -flto-report-wpa +@opindex flto-report-wpa +Like @option{-flto-report}, but only print for the WPA phase of link-time +optimization. + +@item -fmem-report +@opindex fmem-report +Makes the compiler print some statistics about permanent memory +allocation when it finishes. + +@item -fmem-report-wpa +@opindex fmem-report-wpa +Makes the compiler print some statistics about permanent memory +allocation for the WPA phase only. + +@item -fpre-ipa-mem-report +@opindex fpre-ipa-mem-report +@item -fpost-ipa-mem-report +@opindex fpost-ipa-mem-report +Makes the compiler print some statistics about permanent memory +allocation before or after interprocedural optimization. + +@item -fmultiflags +@opindex fmultiflags +This option enables multilib-aware @code{TFLAGS} to be used to build +target libraries with options different from those the compiler is +configured to use by default, through the use of specs (@xref{Spec +Files}) set up by compiler internals, by the target, or by builders at +configure time. + +Like @code{TFLAGS}, this allows the target libraries to be built for +portable baseline environments, while the compiler defaults to more +demanding ones. That's useful because users can easily override the +defaults the compiler is configured to use to build their own programs, +if the defaults are not ideal for their target environment, whereas +rebuilding the runtime libraries is usually not as easy or desirable. + +Unlike @code{TFLAGS}, the use of specs enables different flags to be +selected for different multilibs. The way to accomplish that is to +build with @samp{make TFLAGS=-fmultiflags}, after configuring +@samp{--with-specs=%@{fmultiflags:...@}}. + +This option is discarded by the driver once it's done processing driver +self spec. + +It is also useful to check that @code{TFLAGS} are being used to build +all target libraries, by configuring a non-bootstrap compiler +@samp{--with-specs='%@{!fmultiflags:%emissing TFLAGS@}'} and building +the compiler and target libraries. + +@item -fprofile-report +@opindex fprofile-report +Makes the compiler print some statistics about consistency of the +(estimated) profile and effect of individual passes. + +@item -fstack-usage +@opindex fstack-usage +Makes the compiler output stack usage information for the program, on a +per-function basis. The filename for the dump is made by appending +@file{.su} to the @var{auxname}. @var{auxname} is generated from the name of +the output file, if explicitly specified and it is not an executable, +otherwise it is the basename of the source file. An entry is made up +of three fields: + +@itemize +@item +The name of the function. +@item +A number of bytes. +@item +One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}. +@end itemize + +The qualifier @code{static} means that the function manipulates the stack +statically: a fixed number of bytes are allocated for the frame on function +entry and released on function exit; no stack adjustments are otherwise made +in the function. The second field is this fixed number of bytes. + +The qualifier @code{dynamic} means that the function manipulates the stack +dynamically: in addition to the static allocation described above, stack +adjustments are made in the body of the function, for example to push/pop +arguments around function calls. If the qualifier @code{bounded} is also +present, the amount of these adjustments is bounded at compile time and +the second field is an upper bound of the total amount of stack used by +the function. If it is not present, the amount of these adjustments is +not bounded at compile time and the second field only represents the +bounded part. + +@item -fstats +@opindex fstats +Emit statistics about front-end processing at the end of the compilation. +This option is supported only by the C++ front end, and +the information is generally only useful to the G++ development team. + +@item -fdbg-cnt-list +@opindex fdbg-cnt-list +Print the name and the counter upper bound for all debug counters. + + +@item -fdbg-cnt=@var{counter-value-list} +@opindex fdbg-cnt +Set the internal debug counter lower and upper bound. @var{counter-value-list} +is a comma-separated list of @var{name}:@var{lower_bound1}-@var{upper_bound1} +[:@var{lower_bound2}-@var{upper_bound2}...] tuples which sets +the name of the counter and list of closed intervals. +The @var{lower_bound} is optional and is zero +initialized if not set. +For example, with @option{-fdbg-cnt=dce:2-4:10-11,tail_call:10}, +@code{dbg_cnt(dce)} returns true only for second, third, fourth, tenth and +eleventh invocation. +For @code{dbg_cnt(tail_call)} true is returned for first 10 invocations. + +@item -print-file-name=@var{library} +@opindex print-file-name +Print the full absolute name of the library file @var{library} that +would be used when linking---and don't do anything else. With this +option, GCC does not compile or link anything; it just prints the +file name. + +@item -print-multi-directory +@opindex print-multi-directory +Print the directory name corresponding to the multilib selected by any +other switches present in the command line. This directory is supposed +to exist in @env{GCC_EXEC_PREFIX}. + +@item -print-multi-lib +@opindex print-multi-lib +Print the mapping from multilib directory names to compiler switches +that enable them. The directory name is separated from the switches by +@samp{;}, and each switch starts with an @samp{@@} instead of the +@samp{-}, without spaces between multiple switches. This is supposed to +ease shell processing. + +@item -print-multi-os-directory +@opindex print-multi-os-directory +Print the path to OS libraries for the selected +multilib, relative to some @file{lib} subdirectory. If OS libraries are +present in the @file{lib} subdirectory and no multilibs are used, this is +usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}} +sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or +@file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}} +subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}. + +@item -print-multiarch +@opindex print-multiarch +Print the path to OS libraries for the selected multiarch, +relative to some @file{lib} subdirectory. + +@item -print-prog-name=@var{program} +@opindex print-prog-name +Like @option{-print-file-name}, but searches for a program such as @command{cpp}. + +@item -print-libgcc-file-name +@opindex print-libgcc-file-name +Same as @option{-print-file-name=libgcc.a}. + +This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} +but you do want to link with @file{libgcc.a}. You can do: + +@smallexample +gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` +@end smallexample + +@item -print-search-dirs +@opindex print-search-dirs +Print the name of the configured installation directory and a list of +program and library directories @command{gcc} searches---and don't do anything else. + +This is useful when @command{gcc} prints the error message +@samp{installation problem, cannot exec cpp0: No such file or directory}. +To resolve this you either need to put @file{cpp0} and the other compiler +components where @command{gcc} expects to find them, or you can set the environment +variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. +Don't forget the trailing @samp{/}. +@xref{Environment Variables}. + +@item -print-sysroot +@opindex print-sysroot +Print the target sysroot directory that is used during +compilation. This is the target sysroot specified either at configure +time or using the @option{--sysroot} option, possibly with an extra +suffix that depends on compilation options. If no target sysroot is +specified, the option prints nothing. + +@item -print-sysroot-headers-suffix +@opindex print-sysroot-headers-suffix +Print the suffix added to the target sysroot when searching for +headers, or give an error if the compiler is not configured with such +a suffix---and don't do anything else. + +@item -dumpmachine +@opindex dumpmachine +Print the compiler's target machine (for example, +@samp{i686-pc-linux-gnu})---and don't do anything else. + +@item -dumpversion +@opindex dumpversion +Print the compiler version (for example, @code{3.0}, @code{6.3.0} or @code{7})---and don't do +anything else. This is the compiler version used in filesystem paths and +specs. Depending on how the compiler has been configured it can be just +a single number (major version), two numbers separated by a dot (major and +minor version) or three numbers separated by dots (major, minor and patchlevel +version). + +@item -dumpfullversion +@opindex dumpfullversion +Print the full compiler version---and don't do anything else. The output is +always three numbers separated by dots, major, minor and patchlevel version. + +@item -dumpspecs +@opindex dumpspecs +Print the compiler's built-in specs---and don't do anything else. (This +is used when GCC itself is being built.) @xref{Spec Files}. +@end table + +@node Submodel Options +@section Machine-Dependent Options +@cindex submodel options +@cindex specifying hardware config +@cindex hardware models and configurations, specifying +@cindex target-dependent options +@cindex machine-dependent options + +Each target machine supported by GCC can have its own options---for +example, to allow you to compile for a particular processor variant or +ABI, or to control optimizations specific to that machine. By +convention, the names of machine-specific options start with +@samp{-m}. + +Some configurations of the compiler also support additional target-specific +options, usually for compatibility with other compilers on the same +platform. + +@c This list is ordered alphanumerically by subsection name. +@c It should be the same order and spelling as these options are listed +@c in Machine Dependent Options + +@menu +* AArch64 Options:: +* Adapteva Epiphany Options:: +* AMD GCN Options:: +* ARC Options:: +* ARM Options:: +* AVR Options:: +* Blackfin Options:: +* C6X Options:: +* CRIS Options:: +* C-SKY Options:: +* Darwin Options:: +* DEC Alpha Options:: +* eBPF Options:: +* FR30 Options:: +* FT32 Options:: +* FRV Options:: +* GNU/Linux Options:: +* H8/300 Options:: +* HPPA Options:: +* IA-64 Options:: +* LM32 Options:: +* LoongArch Options:: +* M32C Options:: +* M32R/D Options:: +* M680x0 Options:: +* MCore Options:: +* MeP Options:: +* MicroBlaze Options:: +* MIPS Options:: +* MMIX Options:: +* MN10300 Options:: +* Moxie Options:: +* MSP430 Options:: +* NDS32 Options:: +* Nios II Options:: +* Nvidia PTX Options:: +* OpenRISC Options:: +* PDP-11 Options:: +* picoChip Options:: +* PowerPC Options:: +* PRU Options:: +* RISC-V Options:: +* RL78 Options:: +* RS/6000 and PowerPC Options:: +* RX Options:: +* S/390 and zSeries Options:: +* Score Options:: +* SH Options:: +* Solaris 2 Options:: +* SPARC Options:: +* System V Options:: +* V850 Options:: +* VAX Options:: +* Visium Options:: +* VMS Options:: +* VxWorks Options:: +* x86 Options:: +* x86 Windows Options:: +* Xstormy16 Options:: +* Xtensa Options:: +* zSeries Options:: +@end menu + +@node AArch64 Options +@subsection AArch64 Options +@cindex AArch64 Options + +These options are defined for AArch64 implementations: + +@table @gcctabopt + +@item -mabi=@var{name} +@opindex mabi +Generate code for the specified data model. Permissible values +are @samp{ilp32} for SysV-like data model where int, long int and pointers +are 32 bits, and @samp{lp64} for SysV-like data model where int is 32 bits, +but long int and pointers are 64 bits. + +The default depends on the specific target configuration. Note that +the LP64 and ILP32 ABIs are not link-compatible; you must compile your +entire program with the same ABI, and link with a compatible set of libraries. + +@item -mbig-endian +@opindex mbig-endian +Generate big-endian code. This is the default when GCC is configured for an +@samp{aarch64_be-*-*} target. + +@item -mgeneral-regs-only +@opindex mgeneral-regs-only +Generate code which uses only the general-purpose registers. This will prevent +the compiler from using floating-point and Advanced SIMD registers but will not +impose any restrictions on the assembler. + +@item -mlittle-endian +@opindex mlittle-endian +Generate little-endian code. This is the default when GCC is configured for an +@samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target. + +@item -mcmodel=tiny +@opindex mcmodel=tiny +Generate code for the tiny code model. The program and its statically defined +symbols must be within 1MB of each other. Programs can be statically or +dynamically linked. + +@item -mcmodel=small +@opindex mcmodel=small +Generate code for the small code model. The program and its statically defined +symbols must be within 4GB of each other. Programs can be statically or +dynamically linked. This is the default code model. + +@item -mcmodel=large +@opindex mcmodel=large +Generate code for the large code model. This makes no assumptions about +addresses and sizes of sections. Programs can be statically linked only. The +@option{-mcmodel=large} option is incompatible with @option{-mabi=ilp32}, +@option{-fpic} and @option{-fPIC}. + +@item -mstrict-align +@itemx -mno-strict-align +@opindex mstrict-align +@opindex mno-strict-align +Avoid or allow generating memory accesses that may not be aligned on a natural +object boundary as described in the architecture specification. + +@item -momit-leaf-frame-pointer +@itemx -mno-omit-leaf-frame-pointer +@opindex momit-leaf-frame-pointer +@opindex mno-omit-leaf-frame-pointer +Omit or keep the frame pointer in leaf functions. The former behavior is the +default. + +@item -mstack-protector-guard=@var{guard} +@itemx -mstack-protector-guard-reg=@var{reg} +@itemx -mstack-protector-guard-offset=@var{offset} +@opindex mstack-protector-guard +@opindex mstack-protector-guard-reg +@opindex mstack-protector-guard-offset +Generate stack protection code using canary at @var{guard}. Supported +locations are @samp{global} for a global canary or @samp{sysreg} for a +canary in an appropriate system register. + +With the latter choice the options +@option{-mstack-protector-guard-reg=@var{reg}} and +@option{-mstack-protector-guard-offset=@var{offset}} furthermore specify +which system register to use as base register for reading the canary, +and from what offset from that base register. There is no default +register or offset as this is entirely for use within the Linux +kernel. + +@item -mtls-dialect=desc +@opindex mtls-dialect=desc +Use TLS descriptors as the thread-local storage mechanism for dynamic accesses +of TLS variables. This is the default. + +@item -mtls-dialect=traditional +@opindex mtls-dialect=traditional +Use traditional TLS as the thread-local storage mechanism for dynamic accesses +of TLS variables. + +@item -mtls-size=@var{size} +@opindex mtls-size +Specify bit size of immediate TLS offsets. Valid values are 12, 24, 32, 48. +This option requires binutils 2.26 or newer. + +@item -mfix-cortex-a53-835769 +@itemx -mno-fix-cortex-a53-835769 +@opindex mfix-cortex-a53-835769 +@opindex mno-fix-cortex-a53-835769 +Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769. +This involves inserting a NOP instruction between memory instructions and +64-bit integer multiply-accumulate instructions. + +@item -mfix-cortex-a53-843419 +@itemx -mno-fix-cortex-a53-843419 +@opindex mfix-cortex-a53-843419 +@opindex mno-fix-cortex-a53-843419 +Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419. +This erratum workaround is made at link time and this will only pass the +corresponding flag to the linker. + +@item -mlow-precision-recip-sqrt +@itemx -mno-low-precision-recip-sqrt +@opindex mlow-precision-recip-sqrt +@opindex mno-low-precision-recip-sqrt +Enable or disable the reciprocal square root approximation. +This option only has an effect if @option{-ffast-math} or +@option{-funsafe-math-optimizations} is used as well. Enabling this reduces +precision of reciprocal square root results to about 16 bits for +single precision and to 32 bits for double precision. + +@item -mlow-precision-sqrt +@itemx -mno-low-precision-sqrt +@opindex mlow-precision-sqrt +@opindex mno-low-precision-sqrt +Enable or disable the square root approximation. +This option only has an effect if @option{-ffast-math} or +@option{-funsafe-math-optimizations} is used as well. Enabling this reduces +precision of square root results to about 16 bits for +single precision and to 32 bits for double precision. +If enabled, it implies @option{-mlow-precision-recip-sqrt}. + +@item -mlow-precision-div +@itemx -mno-low-precision-div +@opindex mlow-precision-div +@opindex mno-low-precision-div +Enable or disable the division approximation. +This option only has an effect if @option{-ffast-math} or +@option{-funsafe-math-optimizations} is used as well. Enabling this reduces +precision of division results to about 16 bits for +single precision and to 32 bits for double precision. + +@item -mtrack-speculation +@itemx -mno-track-speculation +Enable or disable generation of additional code to track speculative +execution through conditional branches. The tracking state can then +be used by the compiler when expanding calls to +@code{__builtin_speculation_safe_copy} to permit a more efficient code +sequence to be generated. + +@item -moutline-atomics +@itemx -mno-outline-atomics +Enable or disable calls to out-of-line helpers to implement atomic operations. +These helpers will, at runtime, determine if the LSE instructions from +ARMv8.1-A can be used; if not, they will use the load/store-exclusive +instructions that are present in the base ARMv8.0 ISA. + +This option is only applicable when compiling for the base ARMv8.0 +instruction set. If using a later revision, e.g. @option{-march=armv8.1-a} +or @option{-march=armv8-a+lse}, the ARMv8.1-Atomics instructions will be +used directly. The same applies when using @option{-mcpu=} when the +selected cpu supports the @samp{lse} feature. +This option is on by default. + +@item -march=@var{name} +@opindex march +Specify the name of the target architecture and, optionally, one or +more feature modifiers. This option has the form +@option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}. + +The table below summarizes the permissible values for @var{arch} +and the features that they enable by default: + +@multitable @columnfractions 0.20 0.20 0.60 +@headitem @var{arch} value @tab Architecture @tab Includes by default +@item @samp{armv8-a} @tab Armv8-A @tab @samp{+fp}, @samp{+simd} +@item @samp{armv8.1-a} @tab Armv8.1-A @tab @samp{armv8-a}, @samp{+crc}, @samp{+lse}, @samp{+rdma} +@item @samp{armv8.2-a} @tab Armv8.2-A @tab @samp{armv8.1-a} +@item @samp{armv8.3-a} @tab Armv8.3-A @tab @samp{armv8.2-a}, @samp{+pauth} +@item @samp{armv8.4-a} @tab Armv8.4-A @tab @samp{armv8.3-a}, @samp{+flagm}, @samp{+fp16fml}, @samp{+dotprod} +@item @samp{armv8.5-a} @tab Armv8.5-A @tab @samp{armv8.4-a}, @samp{+sb}, @samp{+ssbs}, @samp{+predres} +@item @samp{armv8.6-a} @tab Armv8.6-A @tab @samp{armv8.5-a}, @samp{+bf16}, @samp{+i8mm} +@item @samp{armv8.7-a} @tab Armv8.7-A @tab @samp{armv8.6-a}, @samp{+ls64} +@item @samp{armv8.8-a} @tab Armv8.8-a @tab @samp{armv8.7-a}, @samp{+mops} +@item @samp{armv9-a} @tab Armv9-A @tab @samp{armv8.5-a}, @samp{+sve}, @samp{+sve2} +@item @samp{armv9.1-a} @tab Armv9.1-A @tab @samp{armv9-a}, @samp{+bf16}, @samp{+i8mm} +@item @samp{armv9.2-a} @tab Armv9.2-A @tab @samp{armv9.1-a}, @samp{+ls64} +@item @samp{armv9.3-a} @tab Armv9.3-A @tab @samp{armv9.2-a}, @samp{+mops} +@item @samp{armv8-r} @tab Armv8-R @tab @samp{armv8-r} +@end multitable + +The value @samp{native} is available on native AArch64 GNU/Linux and +causes the compiler to pick the architecture of the host system. This +option has no effect if the compiler is unable to recognize the +architecture of the host system, + +The permissible values for @var{feature} are listed in the sub-section +on @ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu} +Feature Modifiers}. Where conflicting feature modifiers are +specified, the right-most feature is used. + +GCC uses @var{name} to determine what kind of instructions it can emit +when generating assembly code. If @option{-march} is specified +without either of @option{-mtune} or @option{-mcpu} also being +specified, the code is tuned to perform well across a range of target +processors implementing the target architecture. + +@item -mtune=@var{name} +@opindex mtune +Specify the name of the target processor for which GCC should tune the +performance of the code. Permissible values for this option are: +@samp{generic}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55}, +@samp{cortex-a57}, @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75}, +@samp{cortex-a76}, @samp{cortex-a76ae}, @samp{cortex-a77}, +@samp{cortex-a65}, @samp{cortex-a65ae}, @samp{cortex-a34}, +@samp{cortex-a78}, @samp{cortex-a78ae}, @samp{cortex-a78c}, +@samp{ares}, @samp{exynos-m1}, @samp{emag}, @samp{falkor}, +@samp{neoverse-512tvb}, @samp{neoverse-e1}, @samp{neoverse-n1}, +@samp{neoverse-n2}, @samp{neoverse-v1}, @samp{neoverse-v2}, @samp{qdf24xx}, +@samp{saphira}, @samp{phecda}, @samp{xgene1}, @samp{vulcan}, +@samp{octeontx}, @samp{octeontx81}, @samp{octeontx83}, +@samp{octeontx2}, @samp{octeontx2t98}, @samp{octeontx2t96} +@samp{octeontx2t93}, @samp{octeontx2f95}, @samp{octeontx2f95n}, +@samp{octeontx2f95mm}, +@samp{a64fx}, +@samp{thunderx}, @samp{thunderxt88}, +@samp{thunderxt88p1}, @samp{thunderxt81}, @samp{tsv110}, +@samp{thunderxt83}, @samp{thunderx2t99}, @samp{thunderx3t110}, @samp{zeus}, +@samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, +@samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53}, +@samp{cortex-a75.cortex-a55}, @samp{cortex-a76.cortex-a55}, +@samp{cortex-r82}, @samp{cortex-x1}, @samp{cortex-x2}, +@samp{cortex-a510}, @samp{cortex-a710}, @samp{ampere1}, @samp{native}. + +The values @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, +@samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53}, +@samp{cortex-a75.cortex-a55}, @samp{cortex-a76.cortex-a55} specify that GCC +should tune for a big.LITTLE system. + +The value @samp{neoverse-512tvb} specifies that GCC should tune +for Neoverse cores that (a) implement SVE and (b) have a total vector +bandwidth of 512 bits per cycle. In other words, the option tells GCC to +tune for Neoverse cores that can execute 4 128-bit Advanced SIMD arithmetic +instructions a cycle and that can execute an equivalent number of SVE +arithmetic instructions per cycle (2 for 256-bit SVE, 4 for 128-bit SVE). +This is more general than tuning for a specific core like Neoverse V1 +but is more specific than the default tuning described below. + +Additionally on native AArch64 GNU/Linux systems the value +@samp{native} tunes performance to the host system. This option has no effect +if the compiler is unable to recognize the processor of the host system. + +Where none of @option{-mtune=}, @option{-mcpu=} or @option{-march=} +are specified, the code is tuned to perform well across a range +of target processors. + +This option cannot be suffixed by feature modifiers. + +@item -mcpu=@var{name} +@opindex mcpu +Specify the name of the target processor, optionally suffixed by one +or more feature modifiers. This option has the form +@option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where +the permissible values for @var{cpu} are the same as those available +for @option{-mtune}. The permissible values for @var{feature} are +documented in the sub-section on +@ref{aarch64-feature-modifiers,,@option{-march} and @option{-mcpu} +Feature Modifiers}. Where conflicting feature modifiers are +specified, the right-most feature is used. + +GCC uses @var{name} to determine what kind of instructions it can emit when +generating assembly code (as if by @option{-march}) and to determine +the target processor for which to tune for performance (as if +by @option{-mtune}). Where this option is used in conjunction +with @option{-march} or @option{-mtune}, those options take precedence +over the appropriate part of this option. + +@option{-mcpu=neoverse-512tvb} is special in that it does not refer +to a specific core, but instead refers to all Neoverse cores that +(a) implement SVE and (b) have a total vector bandwidth of 512 bits +a cycle. Unless overridden by @option{-march}, +@option{-mcpu=neoverse-512tvb} generates code that can run on a +Neoverse V1 core, since Neoverse V1 is the first Neoverse core with +these properties. Unless overridden by @option{-mtune}, +@option{-mcpu=neoverse-512tvb} tunes code in the same way as for +@option{-mtune=neoverse-512tvb}. + +@item -moverride=@var{string} +@opindex moverride +Override tuning decisions made by the back-end in response to a +@option{-mtune=} switch. The syntax, semantics, and accepted values +for @var{string} in this option are not guaranteed to be consistent +across releases. + +This option is only intended to be useful when developing GCC. + +@item -mverbose-cost-dump +@opindex mverbose-cost-dump +Enable verbose cost model dumping in the debug dump files. This option is +provided for use in debugging the compiler. + +@item -mpc-relative-literal-loads +@itemx -mno-pc-relative-literal-loads +@opindex mpc-relative-literal-loads +@opindex mno-pc-relative-literal-loads +Enable or disable PC-relative literal loads. With this option literal pools are +accessed using a single instruction and emitted after each function. This +limits the maximum size of functions to 1MB. This is enabled by default for +@option{-mcmodel=tiny}. + +@item -msign-return-address=@var{scope} +@opindex msign-return-address +Select the function scope on which return address signing will be applied. +Permissible values are @samp{none}, which disables return address signing, +@samp{non-leaf}, which enables pointer signing for functions which are not leaf +functions, and @samp{all}, which enables pointer signing for all functions. The +default value is @samp{none}. This option has been deprecated by +-mbranch-protection. + +@item -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}+@var{b-key}]|@var{bti} +@opindex mbranch-protection +Select the branch protection features to use. +@samp{none} is the default and turns off all types of branch protection. +@samp{standard} turns on all types of branch protection features. If a feature +has additional tuning options, then @samp{standard} sets it to its standard +level. +@samp{pac-ret[+@var{leaf}]} turns on return address signing to its standard +level: signing functions that save the return address to memory (non-leaf +functions will practically always do this) using the a-key. The optional +argument @samp{leaf} can be used to extend the signing to include leaf +functions. The optional argument @samp{b-key} can be used to sign the functions +with the B-key instead of the A-key. +@samp{bti} turns on branch target identification mechanism. + +@item -mharden-sls=@var{opts} +@opindex mharden-sls +Enable compiler hardening against straight line speculation (SLS). +@var{opts} is a comma-separated list of the following options: +@table @samp +@item retbr +@item blr +@end table +In addition, @samp{-mharden-sls=all} enables all SLS hardening while +@samp{-mharden-sls=none} disables all SLS hardening. + +@item -msve-vector-bits=@var{bits} +@opindex msve-vector-bits +Specify the number of bits in an SVE vector register. This option only has +an effect when SVE is enabled. + +GCC supports two forms of SVE code generation: ``vector-length +agnostic'' output that works with any size of vector register and +``vector-length specific'' output that allows GCC to make assumptions +about the vector length when it is useful for optimization reasons. +The possible values of @samp{bits} are: @samp{scalable}, @samp{128}, +@samp{256}, @samp{512}, @samp{1024} and @samp{2048}. +Specifying @samp{scalable} selects vector-length agnostic +output. At present @samp{-msve-vector-bits=128} also generates vector-length +agnostic output for big-endian targets. All other values generate +vector-length specific code. The behavior of these values may change +in future releases and no value except @samp{scalable} should be +relied on for producing code that is portable across different +hardware SVE vector lengths. + +The default is @samp{-msve-vector-bits=scalable}, which produces +vector-length agnostic code. +@end table + +@subsubsection @option{-march} and @option{-mcpu} Feature Modifiers +@anchor{aarch64-feature-modifiers} +@cindex @option{-march} feature modifiers +@cindex @option{-mcpu} feature modifiers +Feature modifiers used with @option{-march} and @option{-mcpu} can be any of +the following and their inverses @option{no@var{feature}}: + +@table @samp +@item crc +Enable CRC extension. This is on by default for +@option{-march=armv8.1-a}. +@item crypto +Enable Crypto extension. This also enables Advanced SIMD and floating-point +instructions. +@item fp +Enable floating-point instructions. This is on by default for all possible +values for options @option{-march} and @option{-mcpu}. +@item simd +Enable Advanced SIMD instructions. This also enables floating-point +instructions. This is on by default for all possible values for options +@option{-march} and @option{-mcpu}. +@item sve +Enable Scalable Vector Extension instructions. This also enables Advanced +SIMD and floating-point instructions. +@item lse +Enable Large System Extension instructions. This is on by default for +@option{-march=armv8.1-a}. +@item rdma +Enable Round Double Multiply Accumulate instructions. This is on by default +for @option{-march=armv8.1-a}. +@item fp16 +Enable FP16 extension. This also enables floating-point instructions. +@item fp16fml +Enable FP16 fmla extension. This also enables FP16 extensions and +floating-point instructions. This option is enabled by default for @option{-march=armv8.4-a}. Use of this option with architectures prior to Armv8.2-A is not supported. + +@item rcpc +Enable the RcPc extension. This does not change code generation from GCC, +but is passed on to the assembler, enabling inline asm statements to use +instructions from the RcPc extension. +@item dotprod +Enable the Dot Product extension. This also enables Advanced SIMD instructions. +@item aes +Enable the Armv8-a aes and pmull crypto extension. This also enables Advanced +SIMD instructions. +@item sha2 +Enable the Armv8-a sha2 crypto extension. This also enables Advanced SIMD instructions. +@item sha3 +Enable the sha512 and sha3 crypto extension. This also enables Advanced SIMD +instructions. Use of this option with architectures prior to Armv8.2-A is not supported. +@item sm4 +Enable the sm3 and sm4 crypto extension. This also enables Advanced SIMD instructions. +Use of this option with architectures prior to Armv8.2-A is not supported. +@item profile +Enable the Statistical Profiling extension. This option is only to enable the +extension at the assembler level and does not affect code generation. +@item rng +Enable the Armv8.5-a Random Number instructions. This option is only to +enable the extension at the assembler level and does not affect code +generation. +@item memtag +Enable the Armv8.5-a Memory Tagging Extensions. +Use of this option with architectures prior to Armv8.5-A is not supported. +@item sb +Enable the Armv8-a Speculation Barrier instruction. This option is only to +enable the extension at the assembler level and does not affect code +generation. This option is enabled by default for @option{-march=armv8.5-a}. +@item ssbs +Enable the Armv8-a Speculative Store Bypass Safe instruction. This option +is only to enable the extension at the assembler level and does not affect code +generation. This option is enabled by default for @option{-march=armv8.5-a}. +@item predres +Enable the Armv8-a Execution and Data Prediction Restriction instructions. +This option is only to enable the extension at the assembler level and does +not affect code generation. This option is enabled by default for +@option{-march=armv8.5-a}. +@item sve2 +Enable the Armv8-a Scalable Vector Extension 2. This also enables SVE +instructions. +@item sve2-bitperm +Enable SVE2 bitperm instructions. This also enables SVE2 instructions. +@item sve2-sm4 +Enable SVE2 sm4 instructions. This also enables SVE2 instructions. +@item sve2-aes +Enable SVE2 aes instructions. This also enables SVE2 instructions. +@item sve2-sha3 +Enable SVE2 sha3 instructions. This also enables SVE2 instructions. +@item tme +Enable the Transactional Memory Extension. +@item i8mm +Enable 8-bit Integer Matrix Multiply instructions. This also enables +Advanced SIMD and floating-point instructions. This option is enabled by +default for @option{-march=armv8.6-a}. Use of this option with architectures +prior to Armv8.2-A is not supported. +@item f32mm +Enable 32-bit Floating point Matrix Multiply instructions. This also enables +SVE instructions. Use of this option with architectures prior to Armv8.2-A is +not supported. +@item f64mm +Enable 64-bit Floating point Matrix Multiply instructions. This also enables +SVE instructions. Use of this option with architectures prior to Armv8.2-A is +not supported. +@item bf16 +Enable brain half-precision floating-point instructions. This also enables +Advanced SIMD and floating-point instructions. This option is enabled by +default for @option{-march=armv8.6-a}. Use of this option with architectures +prior to Armv8.2-A is not supported. +@item ls64 +Enable the 64-byte atomic load and store instructions for accelerators. +This option is enabled by default for @option{-march=armv8.7-a}. +@item mops +Enable the instructions to accelerate memory operations like @code{memcpy}, +@code{memmove}, @code{memset}. This option is enabled by default for +@option{-march=armv8.8-a} +@item flagm +Enable the Flag Manipulation instructions Extension. +@item pauth +Enable the Pointer Authentication Extension. + +@end table + +Feature @option{crypto} implies @option{aes}, @option{sha2}, and @option{simd}, +which implies @option{fp}. +Conversely, @option{nofp} implies @option{nosimd}, which implies +@option{nocrypto}, @option{noaes} and @option{nosha2}. + +@node Adapteva Epiphany Options +@subsection Adapteva Epiphany Options + +These @samp{-m} options are defined for Adapteva Epiphany: + +@table @gcctabopt +@item -mhalf-reg-file +@opindex mhalf-reg-file +Don't allocate any register in the range @code{r32}@dots{}@code{r63}. +That allows code to run on hardware variants that lack these registers. + +@item -mprefer-short-insn-regs +@opindex mprefer-short-insn-regs +Preferentially allocate registers that allow short instruction generation. +This can result in increased instruction count, so this may either reduce or +increase overall code size. + +@item -mbranch-cost=@var{num} +@opindex mbranch-cost +Set the cost of branches to roughly @var{num} ``simple'' instructions. +This cost is only a heuristic and is not guaranteed to produce +consistent results across releases. + +@item -mcmove +@opindex mcmove +Enable the generation of conditional moves. + +@item -mnops=@var{num} +@opindex mnops +Emit @var{num} NOPs before every other generated instruction. + +@item -mno-soft-cmpsf +@opindex mno-soft-cmpsf +@opindex msoft-cmpsf +For single-precision floating-point comparisons, emit an @code{fsub} instruction +and test the flags. This is faster than a software comparison, but can +get incorrect results in the presence of NaNs, or when two different small +numbers are compared such that their difference is calculated as zero. +The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant, +software comparisons. + +@item -mstack-offset=@var{num} +@opindex mstack-offset +Set the offset between the top of the stack and the stack pointer. +E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7} +can be used by leaf functions without stack allocation. +Values other than @samp{8} or @samp{16} are untested and unlikely to work. +Note also that this option changes the ABI; compiling a program with a +different stack offset than the libraries have been compiled with +generally does not work. +This option can be useful if you want to evaluate if a different stack +offset would give you better code, but to actually use a different stack +offset to build working programs, it is recommended to configure the +toolchain with the appropriate @option{--with-stack-offset=@var{num}} option. + +@item -mno-round-nearest +@opindex mno-round-nearest +@opindex mround-nearest +Make the scheduler assume that the rounding mode has been set to +truncating. The default is @option{-mround-nearest}. + +@item -mlong-calls +@opindex mlong-calls +If not otherwise specified by an attribute, assume all calls might be beyond +the offset range of the @code{b} / @code{bl} instructions, and therefore load the +function address into a register before performing a (otherwise direct) call. +This is the default. + +@item -mshort-calls +@opindex short-calls +If not otherwise specified by an attribute, assume all direct calls are +in the range of the @code{b} / @code{bl} instructions, so use these instructions +for direct calls. The default is @option{-mlong-calls}. + +@item -msmall16 +@opindex msmall16 +Assume addresses can be loaded as 16-bit unsigned values. This does not +apply to function addresses for which @option{-mlong-calls} semantics +are in effect. + +@item -mfp-mode=@var{mode} +@opindex mfp-mode +Set the prevailing mode of the floating-point unit. +This determines the floating-point mode that is provided and expected +at function call and return time. Making this mode match the mode you +predominantly need at function start can make your programs smaller and +faster by avoiding unnecessary mode switches. + +@var{mode} can be set to one the following values: + +@table @samp +@item caller +Any mode at function entry is valid, and retained or restored when +the function returns, and when it calls other functions. +This mode is useful for compiling libraries or other compilation units +you might want to incorporate into different programs with different +prevailing FPU modes, and the convenience of being able to use a single +object file outweighs the size and speed overhead for any extra +mode switching that might be needed, compared with what would be needed +with a more specific choice of prevailing FPU mode. + +@item truncate +This is the mode used for floating-point calculations with +truncating (i.e.@: round towards zero) rounding mode. That includes +conversion from floating point to integer. + +@item round-nearest +This is the mode used for floating-point calculations with +round-to-nearest-or-even rounding mode. + +@item int +This is the mode used to perform integer calculations in the FPU, e.g.@: +integer multiply, or integer multiply-and-accumulate. +@end table + +The default is @option{-mfp-mode=caller} + +@item -mno-split-lohi +@itemx -mno-postinc +@itemx -mno-postmodify +@opindex mno-split-lohi +@opindex msplit-lohi +@opindex mno-postinc +@opindex mpostinc +@opindex mno-postmodify +@opindex mpostmodify +Code generation tweaks that disable, respectively, splitting of 32-bit +loads, generation of post-increment addresses, and generation of +post-modify addresses. The defaults are @option{msplit-lohi}, +@option{-mpost-inc}, and @option{-mpost-modify}. + +@item -mnovect-double +@opindex mno-vect-double +@opindex mvect-double +Change the preferred SIMD mode to SImode. The default is +@option{-mvect-double}, which uses DImode as preferred SIMD mode. + +@item -max-vect-align=@var{num} +@opindex max-vect-align +The maximum alignment for SIMD vector mode types. +@var{num} may be 4 or 8. The default is 8. +Note that this is an ABI change, even though many library function +interfaces are unaffected if they don't use SIMD vector modes +in places that affect size and/or alignment of relevant types. + +@item -msplit-vecmove-early +@opindex msplit-vecmove-early +Split vector moves into single word moves before reload. In theory this +can give better register allocation, but so far the reverse seems to be +generally the case. + +@item -m1reg-@var{reg} +@opindex m1reg- +Specify a register to hold the constant @minus{}1, which makes loading small negative +constants and certain bitmasks faster. +Allowable values for @var{reg} are @samp{r43} and @samp{r63}, +which specify use of that register as a fixed register, +and @samp{none}, which means that no register is used for this +purpose. The default is @option{-m1reg-none}. + +@end table + +@node AMD GCN Options +@subsection AMD GCN Options +@cindex AMD GCN Options + +These options are defined specifically for the AMD GCN port. + +@table @gcctabopt + +@item -march=@var{gpu} +@opindex march +@itemx -mtune=@var{gpu} +@opindex mtune +Set architecture type or tuning for @var{gpu}. Supported values for @var{gpu} +are + +@table @samp +@item fiji +Compile for GCN3 Fiji devices (gfx803). + +@item gfx900 +Compile for GCN5 Vega 10 devices (gfx900). + +@item gfx906 +Compile for GCN5 Vega 20 devices (gfx906). + +@item gfx908 +Compile for CDNA1 Instinct MI100 series devices (gfx908). + +@item gfx90a +Compile for CDNA2 Instinct MI200 series devices (gfx90a). + +@end table + +@item -msram-ecc=on +@itemx -msram-ecc=off +@itemx -msram-ecc=any +@opindex msram-ecc +Compile binaries suitable for devices with the SRAM-ECC feature enabled, +disabled, or either mode. This feature can be enabled per-process on some +devices. The compiled code must match the device mode. The default is +@samp{any}, for devices that support it. + +@item -mstack-size=@var{bytes} +@opindex mstack-size +Specify how many @var{bytes} of stack space will be requested for each GPU +thread (wave-front). Beware that there may be many threads and limited memory +available. The size of the stack allocation may also have an impact on +run-time performance. The default is 32KB when using OpenACC or OpenMP, and +1MB otherwise. + +@item -mxnack +@opindex mxnack +Compile binaries suitable for devices with the XNACK feature enabled. Some +devices always require XNACK and some allow the user to configure XNACK. The +compiled code must match the device mode. The default is @samp{-mno-xnack}. +At present this option is a placeholder for support that is not yet +implemented. + +@end table + +@node ARC Options +@subsection ARC Options +@cindex ARC options + +The following options control the architecture variant for which code +is being compiled: + +@c architecture variants +@table @gcctabopt + +@item -mbarrel-shifter +@opindex mbarrel-shifter +Generate instructions supported by barrel shifter. This is the default +unless @option{-mcpu=ARC601} or @samp{-mcpu=ARCEM} is in effect. + +@item -mjli-always +@opindex mjli-always +Force to call a function using jli_s instruction. This option is +valid only for ARCv2 architecture. + +@item -mcpu=@var{cpu} +@opindex mcpu +Set architecture type, register usage, and instruction scheduling +parameters for @var{cpu}. There are also shortcut alias options +available for backward compatibility and convenience. Supported +values for @var{cpu} are + +@table @samp +@opindex mA6 +@opindex mARC600 +@item arc600 +Compile for ARC600. Aliases: @option{-mA6}, @option{-mARC600}. + +@item arc601 +@opindex mARC601 +Compile for ARC601. Alias: @option{-mARC601}. + +@item arc700 +@opindex mA7 +@opindex mARC700 +Compile for ARC700. Aliases: @option{-mA7}, @option{-mARC700}. +This is the default when configured with @option{--with-cpu=arc700}@. + +@item arcem +Compile for ARC EM. + +@item archs +Compile for ARC HS. + +@item em +Compile for ARC EM CPU with no hardware extensions. + +@item em4 +Compile for ARC EM4 CPU. + +@item em4_dmips +Compile for ARC EM4 DMIPS CPU. + +@item em4_fpus +Compile for ARC EM4 DMIPS CPU with the single-precision floating-point +extension. + +@item em4_fpuda +Compile for ARC EM4 DMIPS CPU with single-precision floating-point and +double assist instructions. + +@item hs +Compile for ARC HS CPU with no hardware extensions except the atomic +instructions. + +@item hs34 +Compile for ARC HS34 CPU. + +@item hs38 +Compile for ARC HS38 CPU. + +@item hs38_linux +Compile for ARC HS38 CPU with all hardware extensions on. + +@item hs4x +Compile for ARC HS4x CPU. + +@item hs4xd +Compile for ARC HS4xD CPU. + +@item hs4x_rel31 +Compile for ARC HS4x CPU release 3.10a. + +@item arc600_norm +Compile for ARC 600 CPU with @code{norm} instructions enabled. + +@item arc600_mul32x16 +Compile for ARC 600 CPU with @code{norm} and 32x16-bit multiply +instructions enabled. + +@item arc600_mul64 +Compile for ARC 600 CPU with @code{norm} and @code{mul64}-family +instructions enabled. + +@item arc601_norm +Compile for ARC 601 CPU with @code{norm} instructions enabled. + +@item arc601_mul32x16 +Compile for ARC 601 CPU with @code{norm} and 32x16-bit multiply +instructions enabled. + +@item arc601_mul64 +Compile for ARC 601 CPU with @code{norm} and @code{mul64}-family +instructions enabled. + +@item nps400 +Compile for ARC 700 on NPS400 chip. + +@item em_mini +Compile for ARC EM minimalist configuration featuring reduced register +set. + +@end table + +@item -mdpfp +@opindex mdpfp +@itemx -mdpfp-compact +@opindex mdpfp-compact +Generate double-precision FPX instructions, tuned for the compact +implementation. + +@item -mdpfp-fast +@opindex mdpfp-fast +Generate double-precision FPX instructions, tuned for the fast +implementation. + +@item -mno-dpfp-lrsr +@opindex mno-dpfp-lrsr +Disable @code{lr} and @code{sr} instructions from using FPX extension +aux registers. + +@item -mea +@opindex mea +Generate extended arithmetic instructions. Currently only +@code{divaw}, @code{adds}, @code{subs}, and @code{sat16} are +supported. Only valid for @option{-mcpu=ARC700}. + +@item -mno-mpy +@opindex mno-mpy +@opindex mmpy +Do not generate @code{mpy}-family instructions for ARC700. This option is +deprecated. + +@item -mmul32x16 +@opindex mmul32x16 +Generate 32x16-bit multiply and multiply-accumulate instructions. + +@item -mmul64 +@opindex mmul64 +Generate @code{mul64} and @code{mulu64} instructions. +Only valid for @option{-mcpu=ARC600}. + +@item -mnorm +@opindex mnorm +Generate @code{norm} instructions. This is the default if @option{-mcpu=ARC700} +is in effect. + +@item -mspfp +@opindex mspfp +@itemx -mspfp-compact +@opindex mspfp-compact +Generate single-precision FPX instructions, tuned for the compact +implementation. + +@item -mspfp-fast +@opindex mspfp-fast +Generate single-precision FPX instructions, tuned for the fast +implementation. + +@item -msimd +@opindex msimd +Enable generation of ARC SIMD instructions via target-specific +builtins. Only valid for @option{-mcpu=ARC700}. + +@item -msoft-float +@opindex msoft-float +This option ignored; it is provided for compatibility purposes only. +Software floating-point code is emitted by default, and this default +can overridden by FPX options; @option{-mspfp}, @option{-mspfp-compact}, or +@option{-mspfp-fast} for single precision, and @option{-mdpfp}, +@option{-mdpfp-compact}, or @option{-mdpfp-fast} for double precision. + +@item -mswap +@opindex mswap +Generate @code{swap} instructions. + +@item -matomic +@opindex matomic +This enables use of the locked load/store conditional extension to implement +atomic memory built-in functions. Not available for ARC 6xx or ARC +EM cores. + +@item -mdiv-rem +@opindex mdiv-rem +Enable @code{div} and @code{rem} instructions for ARCv2 cores. + +@item -mcode-density +@opindex mcode-density +Enable code density instructions for ARC EM. +This option is on by default for ARC HS. + +@item -mll64 +@opindex mll64 +Enable double load/store operations for ARC HS cores. + +@item -mtp-regno=@var{regno} +@opindex mtp-regno +Specify thread pointer register number. + +@item -mmpy-option=@var{multo} +@opindex mmpy-option +Compile ARCv2 code with a multiplier design option. You can specify +the option using either a string or numeric value for @var{multo}. +@samp{wlh1} is the default value. The recognized values are: + +@table @samp +@item 0 +@itemx none +No multiplier available. + +@item 1 +@itemx w +16x16 multiplier, fully pipelined. +The following instructions are enabled: @code{mpyw} and @code{mpyuw}. + +@item 2 +@itemx wlh1 +32x32 multiplier, fully +pipelined (1 stage). The following instructions are additionally +enabled: @code{mpy}, @code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. + +@item 3 +@itemx wlh2 +32x32 multiplier, fully pipelined +(2 stages). The following instructions are additionally enabled: @code{mpy}, +@code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. + +@item 4 +@itemx wlh3 +Two 16x16 multipliers, blocking, +sequential. The following instructions are additionally enabled: @code{mpy}, +@code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. + +@item 5 +@itemx wlh4 +One 16x16 multiplier, blocking, +sequential. The following instructions are additionally enabled: @code{mpy}, +@code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. + +@item 6 +@itemx wlh5 +One 32x4 multiplier, blocking, +sequential. The following instructions are additionally enabled: @code{mpy}, +@code{mpyu}, @code{mpym}, @code{mpymu}, and @code{mpy_s}. + +@item 7 +@itemx plus_dmpy +ARC HS SIMD support. + +@item 8 +@itemx plus_macd +ARC HS SIMD support. + +@item 9 +@itemx plus_qmacw +ARC HS SIMD support. + +@end table + +This option is only available for ARCv2 cores@. + +@item -mfpu=@var{fpu} +@opindex mfpu +Enables support for specific floating-point hardware extensions for ARCv2 +cores. Supported values for @var{fpu} are: + +@table @samp + +@item fpus +Enables support for single-precision floating-point hardware +extensions@. + +@item fpud +Enables support for double-precision floating-point hardware +extensions. The single-precision floating-point extension is also +enabled. Not available for ARC EM@. + +@item fpuda +Enables support for double-precision floating-point hardware +extensions using double-precision assist instructions. The single-precision +floating-point extension is also enabled. This option is +only available for ARC EM@. + +@item fpuda_div +Enables support for double-precision floating-point hardware +extensions using double-precision assist instructions. +The single-precision floating-point, square-root, and divide +extensions are also enabled. This option is +only available for ARC EM@. + +@item fpuda_fma +Enables support for double-precision floating-point hardware +extensions using double-precision assist instructions. +The single-precision floating-point and fused multiply and add +hardware extensions are also enabled. This option is +only available for ARC EM@. + +@item fpuda_all +Enables support for double-precision floating-point hardware +extensions using double-precision assist instructions. +All single-precision floating-point hardware extensions are also +enabled. This option is only available for ARC EM@. + +@item fpus_div +Enables support for single-precision floating-point, square-root and divide +hardware extensions@. + +@item fpud_div +Enables support for double-precision floating-point, square-root and divide +hardware extensions. This option +includes option @samp{fpus_div}. Not available for ARC EM@. + +@item fpus_fma +Enables support for single-precision floating-point and +fused multiply and add hardware extensions@. + +@item fpud_fma +Enables support for double-precision floating-point and +fused multiply and add hardware extensions. This option +includes option @samp{fpus_fma}. Not available for ARC EM@. + +@item fpus_all +Enables support for all single-precision floating-point hardware +extensions@. + +@item fpud_all +Enables support for all single- and double-precision floating-point +hardware extensions. Not available for ARC EM@. + +@end table + +@item -mirq-ctrl-saved=@var{register-range}, @var{blink}, @var{lp_count} +@opindex mirq-ctrl-saved +Specifies general-purposes registers that the processor automatically +saves/restores on interrupt entry and exit. @var{register-range} is +specified as two registers separated by a dash. The register range +always starts with @code{r0}, the upper limit is @code{fp} register. +@var{blink} and @var{lp_count} are optional. This option is only +valid for ARC EM and ARC HS cores. + +@item -mrgf-banked-regs=@var{number} +@opindex mrgf-banked-regs +Specifies the number of registers replicated in second register bank +on entry to fast interrupt. Fast interrupts are interrupts with the +highest priority level P0. These interrupts save only PC and STATUS32 +registers to avoid memory transactions during interrupt entry and exit +sequences. Use this option when you are using fast interrupts in an +ARC V2 family processor. Permitted values are 4, 8, 16, and 32. + +@item -mlpc-width=@var{width} +@opindex mlpc-width +Specify the width of the @code{lp_count} register. Valid values for +@var{width} are 8, 16, 20, 24, 28 and 32 bits. The default width is +fixed to 32 bits. If the width is less than 32, the compiler does not +attempt to transform loops in your program to use the zero-delay loop +mechanism unless it is known that the @code{lp_count} register can +hold the required loop-counter value. Depending on the width +specified, the compiler and run-time library might continue to use the +loop mechanism for various needs. This option defines macro +@code{__ARC_LPC_WIDTH__} with the value of @var{width}. + +@item -mrf16 +@opindex mrf16 +This option instructs the compiler to generate code for a 16-entry +register file. This option defines the @code{__ARC_RF16__} +preprocessor macro. + +@item -mbranch-index +@opindex mbranch-index +Enable use of @code{bi} or @code{bih} instructions to implement jump +tables. + +@end table + +The following options are passed through to the assembler, and also +define preprocessor macro symbols. + +@c Flags used by the assembler, but for which we define preprocessor +@c macro symbols as well. +@table @gcctabopt +@item -mdsp-packa +@opindex mdsp-packa +Passed down to the assembler to enable the DSP Pack A extensions. +Also sets the preprocessor symbol @code{__Xdsp_packa}. This option is +deprecated. + +@item -mdvbf +@opindex mdvbf +Passed down to the assembler to enable the dual Viterbi butterfly +extension. Also sets the preprocessor symbol @code{__Xdvbf}. This +option is deprecated. + +@c ARC700 4.10 extension instruction +@item -mlock +@opindex mlock +Passed down to the assembler to enable the locked load/store +conditional extension. Also sets the preprocessor symbol +@code{__Xlock}. + +@item -mmac-d16 +@opindex mmac-d16 +Passed down to the assembler. Also sets the preprocessor symbol +@code{__Xxmac_d16}. This option is deprecated. + +@item -mmac-24 +@opindex mmac-24 +Passed down to the assembler. Also sets the preprocessor symbol +@code{__Xxmac_24}. This option is deprecated. + +@c ARC700 4.10 extension instruction +@item -mrtsc +@opindex mrtsc +Passed down to the assembler to enable the 64-bit time-stamp counter +extension instruction. Also sets the preprocessor symbol +@code{__Xrtsc}. This option is deprecated. + +@c ARC700 4.10 extension instruction +@item -mswape +@opindex mswape +Passed down to the assembler to enable the swap byte ordering +extension instruction. Also sets the preprocessor symbol +@code{__Xswape}. + +@item -mtelephony +@opindex mtelephony +Passed down to the assembler to enable dual- and single-operand +instructions for telephony. Also sets the preprocessor symbol +@code{__Xtelephony}. This option is deprecated. + +@item -mxy +@opindex mxy +Passed down to the assembler to enable the XY memory extension. Also +sets the preprocessor symbol @code{__Xxy}. + +@end table + +The following options control how the assembly code is annotated: + +@c Assembly annotation options +@table @gcctabopt +@item -misize +@opindex misize +Annotate assembler instructions with estimated addresses. + +@item -mannotate-align +@opindex mannotate-align +Explain what alignment considerations lead to the decision to make an +instruction short or long. + +@end table + +The following options are passed through to the linker: + +@c options passed through to the linker +@table @gcctabopt +@item -marclinux +@opindex marclinux +Passed through to the linker, to specify use of the @code{arclinux} emulation. +This option is enabled by default in tool chains built for +@w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets +when profiling is not requested. + +@item -marclinux_prof +@opindex marclinux_prof +Passed through to the linker, to specify use of the +@code{arclinux_prof} emulation. This option is enabled by default in +tool chains built for @w{@code{arc-linux-uclibc}} and +@w{@code{arceb-linux-uclibc}} targets when profiling is requested. + +@end table + +The following options control the semantics of generated code: + +@c semantically relevant code generation options +@table @gcctabopt +@item -mlong-calls +@opindex mlong-calls +Generate calls as register indirect calls, thus providing access +to the full 32-bit address range. + +@item -mmedium-calls +@opindex mmedium-calls +Don't use less than 25-bit addressing range for calls, which is the +offset available for an unconditional branch-and-link +instruction. Conditional execution of function calls is suppressed, to +allow use of the 25-bit range, rather than the 21-bit range with +conditional branch-and-link. This is the default for tool chains built +for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} targets. + +@item -G @var{num} +@opindex G +Put definitions of externally-visible data in a small data section if +that data is no bigger than @var{num} bytes. The default value of +@var{num} is 4 for any ARC configuration, or 8 when we have double +load/store operations. + +@item -mno-sdata +@opindex mno-sdata +@opindex msdata +Do not generate sdata references. This is the default for tool chains +built for @w{@code{arc-linux-uclibc}} and @w{@code{arceb-linux-uclibc}} +targets. + +@item -mvolatile-cache +@opindex mvolatile-cache +Use ordinarily cached memory accesses for volatile references. This is the +default. + +@item -mno-volatile-cache +@opindex mno-volatile-cache +@opindex mvolatile-cache +Enable cache bypass for volatile references. + +@end table + +The following options fine tune code generation: +@c code generation tuning options +@table @gcctabopt +@item -malign-call +@opindex malign-call +Does nothing. Preserved for backward compatibility. + +@item -mauto-modify-reg +@opindex mauto-modify-reg +Enable the use of pre/post modify with register displacement. + +@item -mbbit-peephole +@opindex mbbit-peephole +Enable bbit peephole2. + +@item -mno-brcc +@opindex mno-brcc +This option disables a target-specific pass in @file{arc_reorg} to +generate compare-and-branch (@code{br@var{cc}}) instructions. +It has no effect on +generation of these instructions driven by the combiner pass. + +@item -mcase-vector-pcrel +@opindex mcase-vector-pcrel +Use PC-relative switch case tables to enable case table shortening. +This is the default for @option{-Os}. + +@item -mcompact-casesi +@opindex mcompact-casesi +Enable compact @code{casesi} pattern. This is the default for @option{-Os}, +and only available for ARCv1 cores. This option is deprecated. + +@item -mno-cond-exec +@opindex mno-cond-exec +Disable the ARCompact-specific pass to generate conditional +execution instructions. + +Due to delay slot scheduling and interactions between operand numbers, +literal sizes, instruction lengths, and the support for conditional execution, +the target-independent pass to generate conditional execution is often lacking, +so the ARC port has kept a special pass around that tries to find more +conditional execution generation opportunities after register allocation, +branch shortening, and delay slot scheduling have been done. This pass +generally, but not always, improves performance and code size, at the cost of +extra compilation time, which is why there is an option to switch it off. +If you have a problem with call instructions exceeding their allowable +offset range because they are conditionalized, you should consider using +@option{-mmedium-calls} instead. + +@item -mearly-cbranchsi +@opindex mearly-cbranchsi +Enable pre-reload use of the @code{cbranchsi} pattern. + +@item -mexpand-adddi +@opindex mexpand-adddi +Expand @code{adddi3} and @code{subdi3} at RTL generation time into +@code{add.f}, @code{adc} etc. This option is deprecated. + +@item -mindexed-loads +@opindex mindexed-loads +Enable the use of indexed loads. This can be problematic because some +optimizers then assume that indexed stores exist, which is not +the case. + +@item -mlra +@opindex mlra +Enable Local Register Allocation. This is still experimental for ARC, +so by default the compiler uses standard reload +(i.e.@: @option{-mno-lra}). + +@item -mlra-priority-none +@opindex mlra-priority-none +Don't indicate any priority for target registers. + +@item -mlra-priority-compact +@opindex mlra-priority-compact +Indicate target register priority for r0..r3 / r12..r15. + +@item -mlra-priority-noncompact +@opindex mlra-priority-noncompact +Reduce target register priority for r0..r3 / r12..r15. + +@item -mmillicode +@opindex mmillicode +When optimizing for size (using @option{-Os}), prologues and epilogues +that have to save or restore a large number of registers are often +shortened by using call to a special function in libgcc; this is +referred to as a @emph{millicode} call. As these calls can pose +performance issues, and/or cause linking issues when linking in a +nonstandard way, this option is provided to turn on or off millicode +call generation. + +@item -mcode-density-frame +@opindex mcode-density-frame +This option enable the compiler to emit @code{enter} and @code{leave} +instructions. These instructions are only valid for CPUs with +code-density feature. + +@item -mmixed-code +@opindex mmixed-code +Does nothing. Preserved for backward compatibility. + +@item -mq-class +@opindex mq-class +Ths option is deprecated. Enable @samp{q} instruction alternatives. +This is the default for @option{-Os}. + +@item -mRcq +@opindex mRcq +Does nothing. Preserved for backward compatibility. + +@item -mRcw +@opindex mRcw +Does nothing. Preserved for backward compatibility. + +@item -msize-level=@var{level} +@opindex msize-level +Fine-tune size optimization with regards to instruction lengths and alignment. +The recognized values for @var{level} are: +@table @samp +@item 0 +No size optimization. This level is deprecated and treated like @samp{1}. + +@item 1 +Short instructions are used opportunistically. + +@item 2 +In addition, alignment of loops and of code after barriers are dropped. + +@item 3 +In addition, optional data alignment is dropped, and the option @option{Os} is enabled. + +@end table + +This defaults to @samp{3} when @option{-Os} is in effect. Otherwise, +the behavior when this is not set is equivalent to level @samp{1}. + +@item -mtune=@var{cpu} +@opindex mtune +Set instruction scheduling parameters for @var{cpu}, overriding any implied +by @option{-mcpu=}. + +Supported values for @var{cpu} are + +@table @samp +@item ARC600 +Tune for ARC600 CPU. + +@item ARC601 +Tune for ARC601 CPU. + +@item ARC700 +Tune for ARC700 CPU with standard multiplier block. + +@item ARC700-xmac +Tune for ARC700 CPU with XMAC block. + +@item ARC725D +Tune for ARC725D CPU. + +@item ARC750D +Tune for ARC750D CPU. + +@item core3 +Tune for ARCv2 core3 type CPU. This option enable usage of +@code{dbnz} instruction. + +@item release31a +Tune for ARC4x release 3.10a. + +@end table + +@item -mmultcost=@var{num} +@opindex mmultcost +Cost to assume for a multiply instruction, with @samp{4} being equal to a +normal instruction. + +@item -munalign-prob-threshold=@var{probability} +@opindex munalign-prob-threshold +Does nothing. Preserved for backward compatibility. + +@end table + +The following options are maintained for backward compatibility, but +are now deprecated and will be removed in a future release: + +@c Deprecated options +@table @gcctabopt + +@item -margonaut +@opindex margonaut +Obsolete FPX. + +@item -mbig-endian +@opindex mbig-endian +@itemx -EB +@opindex EB +Compile code for big-endian targets. Use of these options is now +deprecated. Big-endian code is supported by configuring GCC to build +@w{@code{arceb-elf32}} and @w{@code{arceb-linux-uclibc}} targets, +for which big endian is the default. + +@item -mlittle-endian +@opindex mlittle-endian +@itemx -EL +@opindex EL +Compile code for little-endian targets. Use of these options is now +deprecated. Little-endian code is supported by configuring GCC to build +@w{@code{arc-elf32}} and @w{@code{arc-linux-uclibc}} targets, +for which little endian is the default. + +@item -mbarrel_shifter +@opindex mbarrel_shifter +Replaced by @option{-mbarrel-shifter}. + +@item -mdpfp_compact +@opindex mdpfp_compact +Replaced by @option{-mdpfp-compact}. + +@item -mdpfp_fast +@opindex mdpfp_fast +Replaced by @option{-mdpfp-fast}. + +@item -mdsp_packa +@opindex mdsp_packa +Replaced by @option{-mdsp-packa}. + +@item -mEA +@opindex mEA +Replaced by @option{-mea}. + +@item -mmac_24 +@opindex mmac_24 +Replaced by @option{-mmac-24}. + +@item -mmac_d16 +@opindex mmac_d16 +Replaced by @option{-mmac-d16}. + +@item -mspfp_compact +@opindex mspfp_compact +Replaced by @option{-mspfp-compact}. + +@item -mspfp_fast +@opindex mspfp_fast +Replaced by @option{-mspfp-fast}. + +@item -mtune=@var{cpu} +@opindex mtune +Values @samp{arc600}, @samp{arc601}, @samp{arc700} and +@samp{arc700-xmac} for @var{cpu} are replaced by @samp{ARC600}, +@samp{ARC601}, @samp{ARC700} and @samp{ARC700-xmac} respectively. + +@item -multcost=@var{num} +@opindex multcost +Replaced by @option{-mmultcost}. + +@end table + +@node ARM Options +@subsection ARM Options +@cindex ARM options + +These @samp{-m} options are defined for the ARM port: + +@table @gcctabopt +@item -mabi=@var{name} +@opindex mabi +Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu}, +@samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}. + +@item -mapcs-frame +@opindex mapcs-frame +Generate a stack frame that is compliant with the ARM Procedure Call +Standard for all functions, even if this is not strictly necessary for +correct execution of the code. Specifying @option{-fomit-frame-pointer} +with this option causes the stack frames not to be generated for +leaf functions. The default is @option{-mno-apcs-frame}. +This option is deprecated. + +@item -mapcs +@opindex mapcs +This is a synonym for @option{-mapcs-frame} and is deprecated. + +@ignore +@c not currently implemented +@item -mapcs-stack-check +@opindex mapcs-stack-check +Generate code to check the amount of stack space available upon entry to +every function (that actually uses some stack space). If there is +insufficient space available then either the function +@code{__rt_stkovf_split_small} or @code{__rt_stkovf_split_big} is +called, depending upon the amount of stack space required. The runtime +system is required to provide these functions. The default is +@option{-mno-apcs-stack-check}, since this produces smaller code. + +@c not currently implemented +@item -mapcs-reentrant +@opindex mapcs-reentrant +Generate reentrant, position-independent code. The default is +@option{-mno-apcs-reentrant}. +@end ignore + +@item -mthumb-interwork +@opindex mthumb-interwork +Generate code that supports calling between the ARM and Thumb +instruction sets. Without this option, on pre-v5 architectures, the +two instruction sets cannot be reliably used inside one program. The +default is @option{-mno-thumb-interwork}, since slightly larger code +is generated when @option{-mthumb-interwork} is specified. In AAPCS +configurations this option is meaningless. + +@item -mno-sched-prolog +@opindex mno-sched-prolog +@opindex msched-prolog +Prevent the reordering of instructions in the function prologue, or the +merging of those instruction with the instructions in the function's +body. This means that all functions start with a recognizable set +of instructions (or in fact one of a choice from a small set of +different function prologues), and this information can be used to +locate the start of functions inside an executable piece of code. The +default is @option{-msched-prolog}. + +@item -mfloat-abi=@var{name} +@opindex mfloat-abi +Specifies which floating-point ABI to use. Permissible values +are: @samp{soft}, @samp{softfp} and @samp{hard}. + +Specifying @samp{soft} causes GCC to generate output containing +library calls for floating-point operations. +@samp{softfp} allows the generation of code using hardware floating-point +instructions, but still uses the soft-float calling conventions. +@samp{hard} allows generation of floating-point instructions +and uses FPU-specific calling conventions. + +The default depends on the specific target configuration. Note that +the hard-float and soft-float ABIs are not link-compatible; you must +compile your entire program with the same ABI, and link with a +compatible set of libraries. + +@item -mgeneral-regs-only +@opindex mgeneral-regs-only +Generate code which uses only the general-purpose registers. This will prevent +the compiler from using floating-point and Advanced SIMD registers but will not +impose any restrictions on the assembler. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a processor running in little-endian mode. This is +the default for all standard configurations. + +@item -mbig-endian +@opindex mbig-endian +Generate code for a processor running in big-endian mode; the default is +to compile code for a little-endian processor. + +@item -mbe8 +@itemx -mbe32 +@opindex mbe8 +When linking a big-endian image select between BE8 and BE32 formats. +The option has no effect for little-endian images and is ignored. The +default is dependent on the selected target architecture. For ARMv6 +and later architectures the default is BE8, for older architectures +the default is BE32. BE32 format has been deprecated by ARM. + +@item -march=@var{name}@r{[}+extension@dots{}@r{]} +@opindex march +This specifies the name of the target ARM architecture. GCC uses this +name to determine what kind of instructions it can emit when generating +assembly code. This option can be used in conjunction with or instead +of the @option{-mcpu=} option. + +Permissible names are: +@samp{armv4t}, +@samp{armv5t}, @samp{armv5te}, +@samp{armv6}, @samp{armv6j}, @samp{armv6k}, @samp{armv6kz}, @samp{armv6t2}, +@samp{armv6z}, @samp{armv6zk}, +@samp{armv7}, @samp{armv7-a}, @samp{armv7ve}, +@samp{armv8-a}, @samp{armv8.1-a}, @samp{armv8.2-a}, @samp{armv8.3-a}, +@samp{armv8.4-a}, +@samp{armv8.5-a}, +@samp{armv8.6-a}, +@samp{armv9-a}, +@samp{armv7-r}, +@samp{armv8-r}, +@samp{armv6-m}, @samp{armv6s-m}, +@samp{armv7-m}, @samp{armv7e-m}, +@samp{armv8-m.base}, @samp{armv8-m.main}, +@samp{armv8.1-m.main}, +@samp{armv9-a}, +@samp{iwmmxt} and @samp{iwmmxt2}. + +Additionally, the following architectures, which lack support for the +Thumb execution state, are recognized but support is deprecated: @samp{armv4}. + +Many of the architectures support extensions. These can be added by +appending @samp{+@var{extension}} to the architecture name. Extension +options are processed in order and capabilities accumulate. An extension +will also enable any necessary base extensions +upon which it depends. For example, the @samp{+crypto} extension +will always enable the @samp{+simd} extension. The exception to the +additive construction is for extensions that are prefixed with +@samp{+no@dots{}}: these extensions disable the specified option and +any other extensions that may depend on the presence of that +extension. + +For example, @samp{-march=armv7-a+simd+nofp+vfpv4} is equivalent to +writing @samp{-march=armv7-a+vfpv4} since the @samp{+simd} option is +entirely disabled by the @samp{+nofp} option that follows it. + +Most extension names are generically named, but have an effect that is +dependent upon the architecture to which it is applied. For example, +the @samp{+simd} option can be applied to both @samp{armv7-a} and +@samp{armv8-a} architectures, but will enable the original ARMv7-A +Advanced SIMD (Neon) extensions for @samp{armv7-a} and the ARMv8-A +variant for @samp{armv8-a}. + +The table below lists the supported extensions for each architecture. +Architectures not mentioned do not support any extensions. + +@table @samp +@item armv5te +@itemx armv6 +@itemx armv6j +@itemx armv6k +@itemx armv6kz +@itemx armv6t2 +@itemx armv6z +@itemx armv6zk +@table @samp +@item +fp +The VFPv2 floating-point instructions. The extension @samp{+vfpv2} can be +used as an alias for this extension. + +@item +nofp +Disable the floating-point instructions. +@end table + +@item armv7 +The common subset of the ARMv7-A, ARMv7-R and ARMv7-M architectures. +@table @samp +@item +fp +The VFPv3 floating-point instructions, with 16 double-precision +registers. The extension @samp{+vfpv3-d16} can be used as an alias +for this extension. Note that floating-point is not supported by the +base ARMv7-M architecture, but is compatible with both the ARMv7-A and +ARMv7-R architectures. + +@item +nofp +Disable the floating-point instructions. +@end table + +@item armv7-a +@table @samp +@item +mp +The multiprocessing extension. + +@item +sec +The security extension. + +@item +fp +The VFPv3 floating-point instructions, with 16 double-precision +registers. The extension @samp{+vfpv3-d16} can be used as an alias +for this extension. + +@item +simd +The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions. +The extensions @samp{+neon} and @samp{+neon-vfpv3} can be used as aliases +for this extension. + +@item +vfpv3 +The VFPv3 floating-point instructions, with 32 double-precision +registers. + +@item +vfpv3-d16-fp16 +The VFPv3 floating-point instructions, with 16 double-precision +registers and the half-precision floating-point conversion operations. + +@item +vfpv3-fp16 +The VFPv3 floating-point instructions, with 32 double-precision +registers and the half-precision floating-point conversion operations. + +@item +vfpv4-d16 +The VFPv4 floating-point instructions, with 16 double-precision +registers. + +@item +vfpv4 +The VFPv4 floating-point instructions, with 32 double-precision +registers. + +@item +neon-fp16 +The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with +the half-precision floating-point conversion operations. + +@item +neon-vfpv4 +The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. + +@item +nosimd +Disable the Advanced SIMD instructions (does not disable floating point). + +@item +nofp +Disable the floating-point and Advanced SIMD instructions. +@end table + +@item armv7ve +The extended version of the ARMv7-A architecture with support for +virtualization. +@table @samp +@item +fp +The VFPv4 floating-point instructions, with 16 double-precision registers. +The extension @samp{+vfpv4-d16} can be used as an alias for this extension. + +@item +simd +The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions. The +extension @samp{+neon-vfpv4} can be used as an alias for this extension. + +@item +vfpv3-d16 +The VFPv3 floating-point instructions, with 16 double-precision +registers. + +@item +vfpv3 +The VFPv3 floating-point instructions, with 32 double-precision +registers. + +@item +vfpv3-d16-fp16 +The VFPv3 floating-point instructions, with 16 double-precision +registers and the half-precision floating-point conversion operations. + +@item +vfpv3-fp16 +The VFPv3 floating-point instructions, with 32 double-precision +registers and the half-precision floating-point conversion operations. + +@item +vfpv4-d16 +The VFPv4 floating-point instructions, with 16 double-precision +registers. + +@item +vfpv4 +The VFPv4 floating-point instructions, with 32 double-precision +registers. + +@item +neon +The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions. +The extension @samp{+neon-vfpv3} can be used as an alias for this extension. + +@item +neon-fp16 +The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with +the half-precision floating-point conversion operations. + +@item +nosimd +Disable the Advanced SIMD instructions (does not disable floating point). + +@item +nofp +Disable the floating-point and Advanced SIMD instructions. +@end table + +@item armv8-a +@table @samp +@item +crc +The Cyclic Redundancy Check (CRC) instructions. +@item +simd +The ARMv8-A Advanced SIMD and floating-point instructions. +@item +crypto +The cryptographic instructions. +@item +nocrypto +Disable the cryptographic instructions. +@item +nofp +Disable the floating-point, Advanced SIMD and cryptographic instructions. +@item +sb +Speculation Barrier Instruction. +@item +predres +Execution and Data Prediction Restriction Instructions. +@end table + +@item armv8.1-a +@table @samp +@item +simd +The ARMv8.1-A Advanced SIMD and floating-point instructions. + +@item +crypto +The cryptographic instructions. This also enables the Advanced SIMD and +floating-point instructions. + +@item +nocrypto +Disable the cryptographic instructions. + +@item +nofp +Disable the floating-point, Advanced SIMD and cryptographic instructions. + +@item +sb +Speculation Barrier Instruction. + +@item +predres +Execution and Data Prediction Restriction Instructions. +@end table + +@item armv8.2-a +@itemx armv8.3-a +@table @samp +@item +fp16 +The half-precision floating-point data processing instructions. +This also enables the Advanced SIMD and floating-point instructions. + +@item +fp16fml +The half-precision floating-point fmla extension. This also enables +the half-precision floating-point extension and Advanced SIMD and +floating-point instructions. + +@item +simd +The ARMv8.1-A Advanced SIMD and floating-point instructions. + +@item +crypto +The cryptographic instructions. This also enables the Advanced SIMD and +floating-point instructions. + +@item +dotprod +Enable the Dot Product extension. This also enables Advanced SIMD instructions. + +@item +nocrypto +Disable the cryptographic extension. + +@item +nofp +Disable the floating-point, Advanced SIMD and cryptographic instructions. + +@item +sb +Speculation Barrier Instruction. + +@item +predres +Execution and Data Prediction Restriction Instructions. + +@item +i8mm +8-bit Integer Matrix Multiply instructions. +This also enables Advanced SIMD and floating-point instructions. + +@item +bf16 +Brain half-precision floating-point instructions. +This also enables Advanced SIMD and floating-point instructions. +@end table + +@item armv8.4-a +@table @samp +@item +fp16 +The half-precision floating-point data processing instructions. +This also enables the Advanced SIMD and floating-point instructions as well +as the Dot Product extension and the half-precision floating-point fmla +extension. + +@item +simd +The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the +Dot Product extension. + +@item +crypto +The cryptographic instructions. This also enables the Advanced SIMD and +floating-point instructions as well as the Dot Product extension. + +@item +nocrypto +Disable the cryptographic extension. + +@item +nofp +Disable the floating-point, Advanced SIMD and cryptographic instructions. + +@item +sb +Speculation Barrier Instruction. + +@item +predres +Execution and Data Prediction Restriction Instructions. + +@item +i8mm +8-bit Integer Matrix Multiply instructions. +This also enables Advanced SIMD and floating-point instructions. + +@item +bf16 +Brain half-precision floating-point instructions. +This also enables Advanced SIMD and floating-point instructions. +@end table + +@item armv8.5-a +@table @samp +@item +fp16 +The half-precision floating-point data processing instructions. +This also enables the Advanced SIMD and floating-point instructions as well +as the Dot Product extension and the half-precision floating-point fmla +extension. + +@item +simd +The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the +Dot Product extension. + +@item +crypto +The cryptographic instructions. This also enables the Advanced SIMD and +floating-point instructions as well as the Dot Product extension. + +@item +nocrypto +Disable the cryptographic extension. + +@item +nofp +Disable the floating-point, Advanced SIMD and cryptographic instructions. + +@item +i8mm +8-bit Integer Matrix Multiply instructions. +This also enables Advanced SIMD and floating-point instructions. + +@item +bf16 +Brain half-precision floating-point instructions. +This also enables Advanced SIMD and floating-point instructions. +@end table + +@item armv8.6-a +@table @samp +@item +fp16 +The half-precision floating-point data processing instructions. +This also enables the Advanced SIMD and floating-point instructions as well +as the Dot Product extension and the half-precision floating-point fmla +extension. + +@item +simd +The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the +Dot Product extension. + +@item +crypto +The cryptographic instructions. This also enables the Advanced SIMD and +floating-point instructions as well as the Dot Product extension. + +@item +nocrypto +Disable the cryptographic extension. + +@item +nofp +Disable the floating-point, Advanced SIMD and cryptographic instructions. + +@item +i8mm +8-bit Integer Matrix Multiply instructions. +This also enables Advanced SIMD and floating-point instructions. + +@item +bf16 +Brain half-precision floating-point instructions. +This also enables Advanced SIMD and floating-point instructions. +@end table + +@item armv7-r +@table @samp +@item +fp.sp +The single-precision VFPv3 floating-point instructions. The extension +@samp{+vfpv3xd} can be used as an alias for this extension. + +@item +fp +The VFPv3 floating-point instructions with 16 double-precision registers. +The extension +vfpv3-d16 can be used as an alias for this extension. + +@item +vfpv3xd-d16-fp16 +The single-precision VFPv3 floating-point instructions with 16 double-precision +registers and the half-precision floating-point conversion operations. + +@item +vfpv3-d16-fp16 +The VFPv3 floating-point instructions with 16 double-precision +registers and the half-precision floating-point conversion operations. + +@item +nofp +Disable the floating-point extension. + +@item +idiv +The ARM-state integer division instructions. + +@item +noidiv +Disable the ARM-state integer division extension. +@end table + +@item armv7e-m +@table @samp +@item +fp +The single-precision VFPv4 floating-point instructions. + +@item +fpv5 +The single-precision FPv5 floating-point instructions. + +@item +fp.dp +The single- and double-precision FPv5 floating-point instructions. + +@item +nofp +Disable the floating-point extensions. +@end table + +@item armv8.1-m.main +@table @samp + +@item +dsp +The DSP instructions. + +@item +mve +The M-Profile Vector Extension (MVE) integer instructions. + +@item +mve.fp +The M-Profile Vector Extension (MVE) integer and single precision +floating-point instructions. + +@item +fp +The single-precision floating-point instructions. + +@item +fp.dp +The single- and double-precision floating-point instructions. + +@item +nofp +Disable the floating-point extension. + +@item +cdecp0, +cdecp1, ... , +cdecp7 +Enable the Custom Datapath Extension (CDE) on selected coprocessors according +to the numbers given in the options in the range 0 to 7. +@end table + +@item armv8-m.main +@table @samp +@item +dsp +The DSP instructions. + +@item +nodsp +Disable the DSP extension. + +@item +fp +The single-precision floating-point instructions. + +@item +fp.dp +The single- and double-precision floating-point instructions. + +@item +nofp +Disable the floating-point extension. + +@item +cdecp0, +cdecp1, ... , +cdecp7 +Enable the Custom Datapath Extension (CDE) on selected coprocessors according +to the numbers given in the options in the range 0 to 7. +@end table + +@item armv8-r +@table @samp +@item +crc +The Cyclic Redundancy Check (CRC) instructions. +@item +fp.sp +The single-precision FPv5 floating-point instructions. +@item +simd +The ARMv8-A Advanced SIMD and floating-point instructions. +@item +crypto +The cryptographic instructions. +@item +nocrypto +Disable the cryptographic instructions. +@item +nofp +Disable the floating-point, Advanced SIMD and cryptographic instructions. +@end table + +@end table + +@option{-march=native} causes the compiler to auto-detect the architecture +of the build computer. At present, this feature is only supported on +GNU/Linux, and not all architectures are recognized. If the auto-detect +is unsuccessful the option has no effect. + +@item -mtune=@var{name} +@opindex mtune +This option specifies the name of the target ARM processor for +which GCC should tune the performance of the code. +For some ARM implementations better performance can be obtained by using +this option. +Permissible names are: @samp{arm7tdmi}, @samp{arm7tdmi-s}, @samp{arm710t}, +@samp{arm720t}, @samp{arm740t}, @samp{strongarm}, @samp{strongarm110}, +@samp{strongarm1100}, @samp{strongarm1110}, @samp{arm8}, @samp{arm810}, +@samp{arm9}, @samp{arm9e}, @samp{arm920}, @samp{arm920t}, @samp{arm922t}, +@samp{arm946e-s}, @samp{arm966e-s}, @samp{arm968e-s}, @samp{arm926ej-s}, +@samp{arm940t}, @samp{arm9tdmi}, @samp{arm10tdmi}, @samp{arm1020t}, +@samp{arm1026ej-s}, @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e}, +@samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp}, +@samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s}, +@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8}, +@samp{cortex-a9}, @samp{cortex-a12}, @samp{cortex-a15}, @samp{cortex-a17}, +@samp{cortex-a32}, @samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55}, +@samp{cortex-a57}, @samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75}, +@samp{cortex-a76}, @samp{cortex-a76ae}, @samp{cortex-a77}, +@samp{cortex-a78}, @samp{cortex-a78ae}, @samp{cortex-a78c}, @samp{cortex-a710}, +@samp{ares}, @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-r5}, +@samp{cortex-r7}, @samp{cortex-r8}, @samp{cortex-r52}, @samp{cortex-r52plus}, +@samp{cortex-m0}, @samp{cortex-m0plus}, @samp{cortex-m1}, @samp{cortex-m3}, +@samp{cortex-m4}, @samp{cortex-m7}, @samp{cortex-m23}, @samp{cortex-m33}, +@samp{cortex-m35p}, @samp{cortex-m55}, @samp{cortex-x1}, +@samp{cortex-m1.small-multiply}, @samp{cortex-m0.small-multiply}, +@samp{cortex-m0plus.small-multiply}, @samp{exynos-m1}, @samp{marvell-pj4}, +@samp{neoverse-n1}, @samp{neoverse-n2}, @samp{neoverse-v1}, @samp{xscale}, +@samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}, @samp{fa526}, @samp{fa626}, +@samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te}, @samp{star-mc1}, +@samp{xgene1}. + +Additionally, this option can specify that GCC should tune the performance +of the code for a big.LITTLE system. Permissible names are: +@samp{cortex-a15.cortex-a7}, @samp{cortex-a17.cortex-a7}, +@samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, +@samp{cortex-a72.cortex-a35}, @samp{cortex-a73.cortex-a53}, +@samp{cortex-a75.cortex-a55}, @samp{cortex-a76.cortex-a55}. + +@option{-mtune=generic-@var{arch}} specifies that GCC should tune the +performance for a blend of processors within architecture @var{arch}. +The aim is to generate code that run well on the current most popular +processors, balancing between optimizations that benefit some CPUs in the +range, and avoiding performance pitfalls of other CPUs. The effects of +this option may change in future GCC versions as CPU models come and go. + +@option{-mtune} permits the same extension options as @option{-mcpu}, but +the extension options do not affect the tuning of the generated code. + +@option{-mtune=native} causes the compiler to auto-detect the CPU +of the build computer. At present, this feature is only supported on +GNU/Linux, and not all architectures are recognized. If the auto-detect is +unsuccessful the option has no effect. + +@item -mcpu=@var{name}@r{[}+extension@dots{}@r{]} +@opindex mcpu +This specifies the name of the target ARM processor. GCC uses this name +to derive the name of the target ARM architecture (as if specified +by @option{-march}) and the ARM processor type for which to tune for +performance (as if specified by @option{-mtune}). Where this option +is used in conjunction with @option{-march} or @option{-mtune}, +those options take precedence over the appropriate part of this option. + +Many of the supported CPUs implement optional architectural +extensions. Where this is so the architectural extensions are +normally enabled by default. If implementations that lack the +extension exist, then the extension syntax can be used to disable +those extensions that have been omitted. For floating-point and +Advanced SIMD (Neon) instructions, the settings of the options +@option{-mfloat-abi} and @option{-mfpu} must also be considered: +floating-point and Advanced SIMD instructions will only be used if +@option{-mfloat-abi} is not set to @samp{soft}; and any setting of +@option{-mfpu} other than @samp{auto} will override the available +floating-point and SIMD extension instructions. + +For example, @samp{cortex-a9} can be found in three major +configurations: integer only, with just a floating-point unit or with +floating-point and Advanced SIMD. The default is to enable all the +instructions, but the extensions @samp{+nosimd} and @samp{+nofp} can +be used to disable just the SIMD or both the SIMD and floating-point +instructions respectively. + +Permissible names for this option are the same as those for +@option{-mtune}. + +The following extension options are common to the listed CPUs: + +@table @samp +@item +nodsp +Disable the DSP instructions on @samp{cortex-m33}, @samp{cortex-m35p} +and @samp{cortex-m55}. Also disable the M-Profile Vector Extension (MVE) +integer and single precision floating-point instructions on @samp{cortex-m55}. + +@item +nomve +Disable the M-Profile Vector Extension (MVE) integer and single precision +floating-point instructions on @samp{cortex-m55}. + +@item +nomve.fp +Disable the M-Profile Vector Extension (MVE) single precision floating-point +instructions on @samp{cortex-m55}. + +@item +nofp +Disables the floating-point instructions on @samp{arm9e}, +@samp{arm946e-s}, @samp{arm966e-s}, @samp{arm968e-s}, @samp{arm10e}, +@samp{arm1020e}, @samp{arm1022e}, @samp{arm926ej-s}, +@samp{arm1026ej-s}, @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-r8}, +@samp{cortex-m4}, @samp{cortex-m7}, @samp{cortex-m33}, @samp{cortex-m35p} +and @samp{cortex-m55}. +Disables the floating-point and SIMD instructions on +@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7}, +@samp{cortex-a8}, @samp{cortex-a9}, @samp{cortex-a12}, +@samp{cortex-a15}, @samp{cortex-a17}, @samp{cortex-a15.cortex-a7}, +@samp{cortex-a17.cortex-a7}, @samp{cortex-a32}, @samp{cortex-a35}, +@samp{cortex-a53} and @samp{cortex-a55}. + +@item +nofp.dp +Disables the double-precision component of the floating-point instructions +on @samp{cortex-r5}, @samp{cortex-r7}, @samp{cortex-r8}, @samp{cortex-r52}, +@samp{cortex-r52plus} and @samp{cortex-m7}. + +@item +nosimd +Disables the SIMD (but not floating-point) instructions on +@samp{generic-armv7-a}, @samp{cortex-a5}, @samp{cortex-a7} +and @samp{cortex-a9}. + +@item +crypto +Enables the cryptographic instructions on @samp{cortex-a32}, +@samp{cortex-a35}, @samp{cortex-a53}, @samp{cortex-a55}, @samp{cortex-a57}, +@samp{cortex-a72}, @samp{cortex-a73}, @samp{cortex-a75}, @samp{exynos-m1}, +@samp{xgene1}, @samp{cortex-a57.cortex-a53}, @samp{cortex-a72.cortex-a53}, +@samp{cortex-a73.cortex-a35}, @samp{cortex-a73.cortex-a53} and +@samp{cortex-a75.cortex-a55}. +@end table + +Additionally the @samp{generic-armv7-a} pseudo target defaults to +VFPv3 with 16 double-precision registers. It supports the following +extension options: @samp{mp}, @samp{sec}, @samp{vfpv3-d16}, +@samp{vfpv3}, @samp{vfpv3-d16-fp16}, @samp{vfpv3-fp16}, +@samp{vfpv4-d16}, @samp{vfpv4}, @samp{neon}, @samp{neon-vfpv3}, +@samp{neon-fp16}, @samp{neon-vfpv4}. The meanings are the same as for +the extensions to @option{-march=armv7-a}. + +@option{-mcpu=generic-@var{arch}} is also permissible, and is +equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}. +See @option{-mtune} for more information. + +@option{-mcpu=native} causes the compiler to auto-detect the CPU +of the build computer. At present, this feature is only supported on +GNU/Linux, and not all architectures are recognized. If the auto-detect +is unsuccessful the option has no effect. + +@item -mfpu=@var{name} +@opindex mfpu +This specifies what floating-point hardware (or hardware emulation) is +available on the target. Permissible names are: @samp{auto}, @samp{vfpv2}, +@samp{vfpv3}, +@samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, +@samp{vfpv3xd-fp16}, @samp{neon-vfpv3}, @samp{neon-fp16}, @samp{vfpv4}, +@samp{vfpv4-d16}, @samp{fpv4-sp-d16}, @samp{neon-vfpv4}, +@samp{fpv5-d16}, @samp{fpv5-sp-d16}, +@samp{fp-armv8}, @samp{neon-fp-armv8} and @samp{crypto-neon-fp-armv8}. +Note that @samp{neon} is an alias for @samp{neon-vfpv3} and @samp{vfp} +is an alias for @samp{vfpv2}. + +The setting @samp{auto} is the default and is special. It causes the +compiler to select the floating-point and Advanced SIMD instructions +based on the settings of @option{-mcpu} and @option{-march}. + +If the selected floating-point hardware includes the NEON extension +(e.g.@: @option{-mfpu=neon}), note that floating-point +operations are not generated by GCC's auto-vectorization pass unless +@option{-funsafe-math-optimizations} is also specified. This is +because NEON hardware does not fully implement the IEEE 754 standard for +floating-point arithmetic (in particular denormal values are treated as +zero), so the use of NEON instructions may lead to a loss of precision. + +You can also set the fpu name at function level by using the @code{target("fpu=")} function attributes (@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}). + +@item -mfp16-format=@var{name} +@opindex mfp16-format +Specify the format of the @code{__fp16} half-precision floating-point type. +Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative}; +the default is @samp{none}, in which case the @code{__fp16} type is not +defined. @xref{Half-Precision}, for more information. + +@item -mstructure-size-boundary=@var{n} +@opindex mstructure-size-boundary +The sizes of all structures and unions are rounded up to a multiple +of the number of bits set by this option. Permissible values are 8, 32 +and 64. The default value varies for different toolchains. For the COFF +targeted toolchain the default value is 8. A value of 64 is only allowed +if the underlying ABI supports it. + +Specifying a larger number can produce faster, more efficient code, but +can also increase the size of the program. Different values are potentially +incompatible. Code compiled with one value cannot necessarily expect to +work with code or libraries compiled with another value, if they exchange +information using structures or unions. + +This option is deprecated. + +@item -mabort-on-noreturn +@opindex mabort-on-noreturn +Generate a call to the function @code{abort} at the end of a +@code{noreturn} function. It is executed if the function tries to +return. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Tells the compiler to perform function calls by first loading the +address of the function into a register and then performing a subroutine +call on this register. This switch is needed if the target function +lies outside of the 64-megabyte addressing range of the offset-based +version of subroutine call instruction. + +Even if this switch is enabled, not all function calls are turned +into long calls. The heuristic is that static functions, functions +that have the @code{short_call} attribute, functions that are inside +the scope of a @code{#pragma no_long_calls} directive, and functions whose +definitions have already been compiled within the current compilation +unit are not turned into long calls. The exceptions to this rule are +that weak function definitions, functions with the @code{long_call} +attribute or the @code{section} attribute, and functions that are within +the scope of a @code{#pragma long_calls} directive are always +turned into long calls. + +This feature is not enabled by default. Specifying +@option{-mno-long-calls} restores the default behavior, as does +placing the function calls within the scope of a @code{#pragma +long_calls_off} directive. Note these switches have no effect on how +the compiler generates code to handle function calls via function +pointers. + +@item -msingle-pic-base +@opindex msingle-pic-base +Treat the register used for PIC addressing as read-only, rather than +loading it in the prologue for each function. The runtime system is +responsible for initializing this register with an appropriate value +before execution begins. + +@item -mpic-register=@var{reg} +@opindex mpic-register +Specify the register to be used for PIC addressing. +For standard PIC base case, the default is any suitable register +determined by compiler. For single PIC base case, the default is +@samp{R9} if target is EABI based or stack-checking is enabled, +otherwise the default is @samp{R10}. + +@item -mpic-data-is-text-relative +@opindex mpic-data-is-text-relative +Assume that the displacement between the text and data segments is fixed +at static link time. This permits using PC-relative addressing +operations to access data known to be in the data segment. For +non-VxWorks RTP targets, this option is enabled by default. When +disabled on such targets, it will enable @option{-msingle-pic-base} by +default. + +@item -mpoke-function-name +@opindex mpoke-function-name +Write the name of each function into the text section, directly +preceding the function prologue. The generated code is similar to this: + +@smallexample + t0 + .ascii "arm_poke_function_name", 0 + .align + t1 + .word 0xff000000 + (t1 - t0) + arm_poke_function_name + mov ip, sp + stmfd sp!, @{fp, ip, lr, pc@} + sub fp, ip, #4 +@end smallexample + +When performing a stack backtrace, code can inspect the value of +@code{pc} stored at @code{fp + 0}. If the trace function then looks at +location @code{pc - 12} and the top 8 bits are set, then we know that +there is a function name embedded immediately preceding this location +and has length @code{((pc[-3]) & 0xff000000)}. + +@item -mthumb +@itemx -marm +@opindex marm +@opindex mthumb + +Select between generating code that executes in ARM and Thumb +states. The default for most configurations is to generate code +that executes in ARM state, but the default can be changed by +configuring GCC with the @option{--with-mode=}@var{state} +configure option. + +You can also override the ARM and Thumb mode for each function +by using the @code{target("thumb")} and @code{target("arm")} function attributes +(@pxref{ARM Function Attributes}) or pragmas (@pxref{Function Specific Option Pragmas}). + +@item -mflip-thumb +@opindex mflip-thumb +Switch ARM/Thumb modes on alternating functions. +This option is provided for regression testing of mixed Thumb/ARM code +generation, and is not intended for ordinary use in compiling code. + +@item -mtpcs-frame +@opindex mtpcs-frame +Generate a stack frame that is compliant with the Thumb Procedure Call +Standard for all non-leaf functions. (A leaf function is one that does +not call any other functions.) The default is @option{-mno-tpcs-frame}. + +@item -mtpcs-leaf-frame +@opindex mtpcs-leaf-frame +Generate a stack frame that is compliant with the Thumb Procedure Call +Standard for all leaf functions. (A leaf function is one that does +not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. + +@item -mcallee-super-interworking +@opindex mcallee-super-interworking +Gives all externally visible functions in the file being compiled an ARM +instruction set header which switches to Thumb mode before executing the +rest of the function. This allows these functions to be called from +non-interworking code. This option is not valid in AAPCS configurations +because interworking is enabled by default. + +@item -mcaller-super-interworking +@opindex mcaller-super-interworking +Allows calls via function pointers (including virtual functions) to +execute correctly regardless of whether the target code has been +compiled for interworking or not. There is a small overhead in the cost +of executing a function pointer if this option is enabled. This option +is not valid in AAPCS configurations because interworking is enabled +by default. + +@item -mtp=@var{name} +@opindex mtp +Specify the access model for the thread local storage pointer. The valid +models are @samp{soft}, which generates calls to @code{__aeabi_read_tp}, +@samp{cp15}, which fetches the thread pointer from @code{cp15} directly +(supported in the arm6k architecture), and @samp{auto}, which uses the +best available method for the selected processor. The default setting is +@samp{auto}. + +@item -mtls-dialect=@var{dialect} +@opindex mtls-dialect +Specify the dialect to use for accessing thread local storage. Two +@var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The +@samp{gnu} dialect selects the original GNU scheme for supporting +local and global dynamic TLS models. The @samp{gnu2} dialect +selects the GNU descriptor scheme, which provides better performance +for shared libraries. The GNU descriptor scheme is compatible with +the original scheme, but does require new assembler, linker and +library support. Initial and local exec TLS models are unaffected by +this option and always use the original scheme. + +@item -mword-relocations +@opindex mword-relocations +Only generate absolute relocations on word-sized values (i.e.@: R_ARM_ABS32). +This is enabled by default on targets (uClinux, SymbianOS) where the runtime +loader imposes this restriction, and when @option{-fpic} or @option{-fPIC} +is specified. This option conflicts with @option{-mslow-flash-data}. + +@item -mfix-cortex-m3-ldrd +@opindex mfix-cortex-m3-ldrd +Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions +with overlapping destination and base registers are used. This option avoids +generating these instructions. This option is enabled by default when +@option{-mcpu=cortex-m3} is specified. + +@item -mfix-cortex-a57-aes-1742098 +@itemx -mno-fix-cortex-a57-aes-1742098 +@itemx -mfix-cortex-a72-aes-1655431 +@itemx -mno-fix-cortex-a72-aes-1655431 +Enable (disable) mitigation for an erratum on Cortex-A57 and +Cortex-A72 that affects the AES cryptographic instructions. This +option is enabled by default when either @option{-mcpu=cortex-a57} or +@option{-mcpu=cortex-a72} is specified. + +@item -munaligned-access +@itemx -mno-unaligned-access +@opindex munaligned-access +@opindex mno-unaligned-access +Enables (or disables) reading and writing of 16- and 32- bit values +from addresses that are not 16- or 32- bit aligned. By default +unaligned access is disabled for all pre-ARMv6, all ARMv6-M and for +ARMv8-M Baseline architectures, and enabled for all other +architectures. If unaligned access is not enabled then words in packed +data structures are accessed a byte at a time. + +The ARM attribute @code{Tag_CPU_unaligned_access} is set in the +generated object file to either true or false, depending upon the +setting of this option. If unaligned access is enabled then the +preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} is also +defined. + +@item -mneon-for-64bits +@opindex mneon-for-64bits +This option is deprecated and has no effect. + +@item -mslow-flash-data +@opindex mslow-flash-data +Assume loading data from flash is slower than fetching instruction. +Therefore literal load is minimized for better performance. +This option is only supported when compiling for ARMv7 M-profile and +off by default. It conflicts with @option{-mword-relocations}. + +@item -masm-syntax-unified +@opindex masm-syntax-unified +Assume inline assembler is using unified asm syntax. The default is +currently off which implies divided syntax. This option has no impact +on Thumb2. However, this may change in future releases of GCC. +Divided syntax should be considered deprecated. + +@item -mrestrict-it +@opindex mrestrict-it +Restricts generation of IT blocks to conform to the rules of ARMv8-A. +IT blocks can only contain a single 16-bit instruction from a select +set of instructions. This option is on by default for ARMv8-A Thumb mode. + +@item -mprint-tune-info +@opindex mprint-tune-info +Print CPU tuning information as comment in assembler file. This is +an option used only for regression testing of the compiler and not +intended for ordinary use in compiling code. This option is disabled +by default. + +@item -mverbose-cost-dump +@opindex mverbose-cost-dump +Enable verbose cost model dumping in the debug dump files. This option is +provided for use in debugging the compiler. + +@item -mpure-code +@opindex mpure-code +Do not allow constant data to be placed in code sections. +Additionally, when compiling for ELF object format give all text sections the +ELF processor-specific section attribute @code{SHF_ARM_PURECODE}. This option +is only available when generating non-pic code for M-profile targets. + +@item -mcmse +@opindex mcmse +Generate secure code as per the "ARMv8-M Security Extensions: Requirements on +Development Tools Engineering Specification", which can be found on +@url{https://developer.arm.com/documentation/ecm0359818/latest/}. + +@item -mfix-cmse-cve-2021-35465 +@opindex mfix-cmse-cve-2021-35465 +Mitigate against a potential security issue with the @code{VLLDM} instruction +in some M-profile devices when using CMSE (CVE-2021-365465). This option is +enabled by default when the option @option{-mcpu=} is used with +@code{cortex-m33}, @code{cortex-m35p}, @code{cortex-m55} or @code{star-mc1}. +The option @option{-mno-fix-cmse-cve-2021-35465} can be used to disable +the mitigation. + +@item -mstack-protector-guard=@var{guard} +@itemx -mstack-protector-guard-offset=@var{offset} +@opindex mstack-protector-guard +@opindex mstack-protector-guard-offset +Generate stack protection code using canary at @var{guard}. Supported +locations are @samp{global} for a global canary or @samp{tls} for a +canary accessible via the TLS register. The option +@option{-mstack-protector-guard-offset=} is for use with +@option{-fstack-protector-guard=tls} and not for use in user-land code. + +@item -mfdpic +@itemx -mno-fdpic +@opindex mfdpic +@opindex mno-fdpic +Select the FDPIC ABI, which uses 64-bit function descriptors to +represent pointers to functions. When the compiler is configured for +@code{arm-*-uclinuxfdpiceabi} targets, this option is on by default +and implies @option{-fPIE} if none of the PIC/PIE-related options is +provided. On other targets, it only enables the FDPIC-specific code +generation features, and the user should explicitly provide the +PIC/PIE-related options as needed. + +Note that static linking is not supported because it would still +involve the dynamic linker when the program self-relocates. If such +behavior is acceptable, use -static and -Wl,-dynamic-linker options. + +The opposite @option{-mno-fdpic} option is useful (and required) to +build the Linux kernel using the same (@code{arm-*-uclinuxfdpiceabi}) +toolchain as the one used to build the userland programs. + +@end table + +@node AVR Options +@subsection AVR Options +@cindex AVR Options + +These options are defined for AVR implementations: + +@table @gcctabopt +@item -mmcu=@var{mcu} +@opindex mmcu +Specify Atmel AVR instruction set architectures (ISA) or MCU type. + +The default for this option is@tie{}@samp{avr2}. + +GCC supports the following AVR devices and ISAs: + +@include avr-mmcu.texi + +@item -mabsdata +@opindex mabsdata + +Assume that all data in static storage can be accessed by LDS / STS +instructions. This option has only an effect on reduced Tiny devices like +ATtiny40. See also the @code{absdata} +@ref{AVR Variable Attributes,variable attribute}. + +@item -maccumulate-args +@opindex maccumulate-args +Accumulate outgoing function arguments and acquire/release the needed +stack space for outgoing function arguments once in function +prologue/epilogue. Without this option, outgoing arguments are pushed +before calling a function and popped afterwards. + +Popping the arguments after the function call can be expensive on +AVR so that accumulating the stack space might lead to smaller +executables because arguments need not be removed from the +stack after such a function call. + +This option can lead to reduced code size for functions that perform +several calls to functions that get their arguments on the stack like +calls to printf-like functions. + +@item -mbranch-cost=@var{cost} +@opindex mbranch-cost +Set the branch costs for conditional branch instructions to +@var{cost}. Reasonable values for @var{cost} are small, non-negative +integers. The default branch cost is 0. + +@item -mcall-prologues +@opindex mcall-prologues +Functions prologues/epilogues are expanded as calls to appropriate +subroutines. Code size is smaller. + +@item -mdouble=@var{bits} +@itemx -mlong-double=@var{bits} +@opindex mdouble +@opindex mlong-double +Set the size (in bits) of the @code{double} or @code{long double} type, +respectively. Possible values for @var{bits} are 32 and 64. +Whether or not a specific value for @var{bits} is allowed depends on +the @code{--with-double=} and @code{--with-long-double=} +@w{@uref{https://gcc.gnu.org/install/configure.html#avr,configure options}}, +and the same applies for the default values of the options. + +@item -mgas-isr-prologues +@opindex mgas-isr-prologues +Interrupt service routines (ISRs) may use the @code{__gcc_isr} pseudo +instruction supported by GNU Binutils. +If this option is on, the feature can still be disabled for individual +ISRs by means of the @ref{AVR Function Attributes,,@code{no_gccisr}} +function attribute. This feature is activated per default +if optimization is on (but not with @option{-Og}, @pxref{Optimize Options}), +and if GNU Binutils support @w{@uref{https://sourceware.org/PR21683,PR21683}}. + +@item -mint8 +@opindex mint8 +Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a +@code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes, +and @code{long long} is 4 bytes. Please note that this option does not +conform to the C standards, but it results in smaller code +size. + +@item -mmain-is-OS_task +@opindex mmain-is-OS_task +Do not save registers in @code{main}. The effect is the same like +attaching attribute @ref{AVR Function Attributes,,@code{OS_task}} +to @code{main}. It is activated per default if optimization is on. + +@item -mn-flash=@var{num} +@opindex mn-flash +Assume that the flash memory has a size of +@var{num} times 64@tie{}KiB. + +@item -mno-interrupts +@opindex mno-interrupts +Generated code is not compatible with hardware interrupts. +Code size is smaller. + +@item -mrelax +@opindex mrelax +Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter +@code{RCALL} resp.@: @code{RJMP} instruction if applicable. +Setting @option{-mrelax} just adds the @option{--mlink-relax} option to +the assembler's command line and the @option{--relax} option to the +linker's command line. + +Jump relaxing is performed by the linker because jump offsets are not +known before code is located. Therefore, the assembler code generated by the +compiler is the same, but the instructions in the executable may +differ from instructions in the assembler code. + +Relaxing must be turned on if linker stubs are needed, see the +section on @code{EIND} and linker stubs below. + +@item -mrmw +@opindex mrmw +Assume that the device supports the Read-Modify-Write +instructions @code{XCH}, @code{LAC}, @code{LAS} and @code{LAT}. + +@item -mshort-calls +@opindex mshort-calls + +Assume that @code{RJMP} and @code{RCALL} can target the whole +program memory. + +This option is used internally for multilib selection. It is +not an optimization option, and you don't need to set it by hand. + +@item -msp8 +@opindex msp8 +Treat the stack pointer register as an 8-bit register, +i.e.@: assume the high byte of the stack pointer is zero. +In general, you don't need to set this option by hand. + +This option is used internally by the compiler to select and +build multilibs for architectures @code{avr2} and @code{avr25}. +These architectures mix devices with and without @code{SPH}. +For any setting other than @option{-mmcu=avr2} or @option{-mmcu=avr25} +the compiler driver adds or removes this option from the compiler +proper's command line, because the compiler then knows if the device +or architecture has an 8-bit stack pointer and thus no @code{SPH} +register or not. + +@item -mstrict-X +@opindex mstrict-X +Use address register @code{X} in a way proposed by the hardware. This means +that @code{X} is only used in indirect, post-increment or +pre-decrement addressing. + +Without this option, the @code{X} register may be used in the same way +as @code{Y} or @code{Z} which then is emulated by additional +instructions. +For example, loading a value with @code{X+const} addressing with a +small non-negative @code{const < 64} to a register @var{Rn} is +performed as + +@example +adiw r26, const ; X += const +ld @var{Rn}, X ; @var{Rn} = *X +sbiw r26, const ; X -= const +@end example + +@item -mtiny-stack +@opindex mtiny-stack +Only change the lower 8@tie{}bits of the stack pointer. + +@item -mfract-convert-truncate +@opindex mfract-convert-truncate +Allow to use truncation instead of rounding towards zero for fractional fixed-point types. + +@item -nodevicelib +@opindex nodevicelib +Don't link against AVR-LibC's device specific library @code{lib.a}. + +@item -nodevicespecs +@opindex nodevicespecs +Don't add @option{-specs=device-specs/specs-@var{mcu}} to the compiler driver's +command line. The user takes responsibility for supplying the sub-processes +like compiler proper, assembler and linker with appropriate command line +options. This means that the user has to supply her private device specs +file by means of @option{-specs=@var{path-to-specs-file}}. There is no +more need for option @option{-mmcu=@var{mcu}}. + +This option can also serve as a replacement for the older way of +specifying custom device-specs files that needed @option{-B @var{some-path}} to point to a directory +which contains a folder named @code{device-specs} which contains a specs file named +@code{specs-@var{mcu}}, where @var{mcu} was specified by @option{-mmcu=@var{mcu}}. + +@item -Waddr-space-convert +@opindex Waddr-space-convert +@opindex Wno-addr-space-convert +Warn about conversions between address spaces in the case where the +resulting address space is not contained in the incoming address space. + +@item -Wmisspelled-isr +@opindex Wmisspelled-isr +@opindex Wno-misspelled-isr +Warn if the ISR is misspelled, i.e.@: without __vector prefix. +Enabled by default. +@end table + +@subsubsection @code{EIND} and Devices with More Than 128 Ki Bytes of Flash +@cindex @code{EIND} +Pointers in the implementation are 16@tie{}bits wide. +The address of a function or label is represented as word address so +that indirect jumps and calls can target any code address in the +range of 64@tie{}Ki words. + +In order to facilitate indirect jump on devices with more than 128@tie{}Ki +bytes of program memory space, there is a special function register called +@code{EIND} that serves as most significant part of the target address +when @code{EICALL} or @code{EIJMP} instructions are used. + +Indirect jumps and calls on these devices are handled as follows by +the compiler and are subject to some limitations: + +@itemize @bullet + +@item +The compiler never sets @code{EIND}. + +@item +The compiler uses @code{EIND} implicitly in @code{EICALL}/@code{EIJMP} +instructions or might read @code{EIND} directly in order to emulate an +indirect call/jump by means of a @code{RET} instruction. + +@item +The compiler assumes that @code{EIND} never changes during the startup +code or during the application. In particular, @code{EIND} is not +saved/restored in function or interrupt service routine +prologue/epilogue. + +@item +For indirect calls to functions and computed goto, the linker +generates @emph{stubs}. Stubs are jump pads sometimes also called +@emph{trampolines}. Thus, the indirect call/jump jumps to such a stub. +The stub contains a direct jump to the desired address. + +@item +Linker relaxation must be turned on so that the linker generates +the stubs correctly in all situations. See the compiler option +@option{-mrelax} and the linker option @option{--relax}. +There are corner cases where the linker is supposed to generate stubs +but aborts without relaxation and without a helpful error message. + +@item +The default linker script is arranged for code with @code{EIND = 0}. +If code is supposed to work for a setup with @code{EIND != 0}, a custom +linker script has to be used in order to place the sections whose +name start with @code{.trampolines} into the segment where @code{EIND} +points to. + +@item +The startup code from libgcc never sets @code{EIND}. +Notice that startup code is a blend of code from libgcc and AVR-LibC. +For the impact of AVR-LibC on @code{EIND}, see the +@w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC user manual}}. + +@item +It is legitimate for user-specific startup code to set up @code{EIND} +early, for example by means of initialization code located in +section @code{.init3}. Such code runs prior to general startup code +that initializes RAM and calls constructors, but after the bit +of startup code from AVR-LibC that sets @code{EIND} to the segment +where the vector table is located. +@example +#include + +static void +__attribute__((section(".init3"),naked,used,no_instrument_function)) +init3_set_eind (void) +@{ + __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" + "out %i0,r24" :: "n" (&EIND) : "r24","memory"); +@} +@end example + +@noindent +The @code{__trampolines_start} symbol is defined in the linker script. + +@item +Stubs are generated automatically by the linker if +the following two conditions are met: +@itemize @minus + +@item The address of a label is taken by means of the @code{gs} modifier +(short for @emph{generate stubs}) like so: +@example +LDI r24, lo8(gs(@var{func})) +LDI r25, hi8(gs(@var{func})) +@end example +@item The final location of that label is in a code segment +@emph{outside} the segment where the stubs are located. +@end itemize + +@item +The compiler emits such @code{gs} modifiers for code labels in the +following situations: +@itemize @minus +@item Taking address of a function or code label. +@item Computed goto. +@item If prologue-save function is used, see @option{-mcall-prologues} +command-line option. +@item Switch/case dispatch tables. If you do not want such dispatch +tables you can specify the @option{-fno-jump-tables} command-line option. +@item C and C++ constructors/destructors called during startup/shutdown. +@item If the tools hit a @code{gs()} modifier explained above. +@end itemize + +@item +Jumping to non-symbolic addresses like so is @emph{not} supported: + +@example +int main (void) +@{ + /* Call function at word address 0x2 */ + return ((int(*)(void)) 0x2)(); +@} +@end example + +Instead, a stub has to be set up, i.e.@: the function has to be called +through a symbol (@code{func_4} in the example): + +@example +int main (void) +@{ + extern int func_4 (void); + + /* Call function at byte address 0x4 */ + return func_4(); +@} +@end example + +and the application be linked with @option{-Wl,--defsym,func_4=0x4}. +Alternatively, @code{func_4} can be defined in the linker script. +@end itemize + +@subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers +@cindex @code{RAMPD} +@cindex @code{RAMPX} +@cindex @code{RAMPY} +@cindex @code{RAMPZ} +Some AVR devices support memories larger than the 64@tie{}KiB range +that can be accessed with 16-bit pointers. To access memory locations +outside this 64@tie{}KiB range, the content of a @code{RAMP} +register is used as high part of the address: +The @code{X}, @code{Y}, @code{Z} address register is concatenated +with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function +register, respectively, to get a wide address. Similarly, +@code{RAMPD} is used together with direct addressing. + +@itemize +@item +The startup code initializes the @code{RAMP} special function +registers with zero. + +@item +If a @ref{AVR Named Address Spaces,named address space} other than +generic or @code{__flash} is used, then @code{RAMPZ} is set +as needed before the operation. + +@item +If the device supports RAM larger than 64@tie{}KiB and the compiler +needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ} +is reset to zero after the operation. + +@item +If the device comes with a specific @code{RAMP} register, the ISR +prologue/epilogue saves/restores that SFR and initializes it with +zero in case the ISR code might (implicitly) use it. + +@item +RAM larger than 64@tie{}KiB is not supported by GCC for AVR targets. +If you use inline assembler to read from locations outside the +16-bit address range and change one of the @code{RAMP} registers, +you must reset it to zero after the access. + +@end itemize + +@subsubsection AVR Built-in Macros + +GCC defines several built-in macros so that the user code can test +for the presence or absence of features. Almost any of the following +built-in macros are deduced from device capabilities and thus +triggered by the @option{-mmcu=} command-line option. + +For even more AVR-specific built-in macros see +@ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}. + +@table @code + +@item __AVR_ARCH__ +Build-in macro that resolves to a decimal number that identifies the +architecture and depends on the @option{-mmcu=@var{mcu}} option. +Possible values are: + +@code{2}, @code{25}, @code{3}, @code{31}, @code{35}, +@code{4}, @code{5}, @code{51}, @code{6} + +for @var{mcu}=@code{avr2}, @code{avr25}, @code{avr3}, @code{avr31}, +@code{avr35}, @code{avr4}, @code{avr5}, @code{avr51}, @code{avr6}, + +respectively and + +@code{100}, +@code{102}, @code{103}, @code{104}, +@code{105}, @code{106}, @code{107} + +for @var{mcu}=@code{avrtiny}, +@code{avrxmega2}, @code{avrxmega3}, @code{avrxmega4}, +@code{avrxmega5}, @code{avrxmega6}, @code{avrxmega7}, respectively. +If @var{mcu} specifies a device, this built-in macro is set +accordingly. For example, with @option{-mmcu=atmega8} the macro is +defined to @code{4}. + +@item __AVR_@var{Device}__ +Setting @option{-mmcu=@var{device}} defines this built-in macro which reflects +the device's name. For example, @option{-mmcu=atmega8} defines the +built-in macro @code{__AVR_ATmega8__}, @option{-mmcu=attiny261a} defines +@code{__AVR_ATtiny261A__}, etc. + +The built-in macros' names follow +the scheme @code{__AVR_@var{Device}__} where @var{Device} is +the device name as from the AVR user manual. The difference between +@var{Device} in the built-in macro and @var{device} in +@option{-mmcu=@var{device}} is that the latter is always lowercase. + +If @var{device} is not a device but only a core architecture like +@samp{avr51}, this macro is not defined. + +@item __AVR_DEVICE_NAME__ +Setting @option{-mmcu=@var{device}} defines this built-in macro to +the device's name. For example, with @option{-mmcu=atmega8} the macro +is defined to @code{atmega8}. + +If @var{device} is not a device but only a core architecture like +@samp{avr51}, this macro is not defined. + +@item __AVR_XMEGA__ +The device / architecture belongs to the XMEGA family of devices. + +@item __AVR_HAVE_ELPM__ +The device has the @code{ELPM} instruction. + +@item __AVR_HAVE_ELPMX__ +The device has the @code{ELPM R@var{n},Z} and @code{ELPM +R@var{n},Z+} instructions. + +@item __AVR_HAVE_MOVW__ +The device has the @code{MOVW} instruction to perform 16-bit +register-register moves. + +@item __AVR_HAVE_LPMX__ +The device has the @code{LPM R@var{n},Z} and +@code{LPM R@var{n},Z+} instructions. + +@item __AVR_HAVE_MUL__ +The device has a hardware multiplier. + +@item __AVR_HAVE_JMP_CALL__ +The device has the @code{JMP} and @code{CALL} instructions. +This is the case for devices with more than 8@tie{}KiB of program +memory. + +@item __AVR_HAVE_EIJMP_EICALL__ +@itemx __AVR_3_BYTE_PC__ +The device has the @code{EIJMP} and @code{EICALL} instructions. +This is the case for devices with more than 128@tie{}KiB of program memory. +This also means that the program counter +(PC) is 3@tie{}bytes wide. + +@item __AVR_2_BYTE_PC__ +The program counter (PC) is 2@tie{}bytes wide. This is the case for devices +with up to 128@tie{}KiB of program memory. + +@item __AVR_HAVE_8BIT_SP__ +@itemx __AVR_HAVE_16BIT_SP__ +The stack pointer (SP) register is treated as 8-bit respectively +16-bit register by the compiler. +The definition of these macros is affected by @option{-mtiny-stack}. + +@item __AVR_HAVE_SPH__ +@itemx __AVR_SP8__ +The device has the SPH (high part of stack pointer) special function +register or has an 8-bit stack pointer, respectively. +The definition of these macros is affected by @option{-mmcu=} and +in the cases of @option{-mmcu=avr2} and @option{-mmcu=avr25} also +by @option{-msp8}. + +@item __AVR_HAVE_RAMPD__ +@itemx __AVR_HAVE_RAMPX__ +@itemx __AVR_HAVE_RAMPY__ +@itemx __AVR_HAVE_RAMPZ__ +The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY}, +@code{RAMPZ} special function register, respectively. + +@item __NO_INTERRUPTS__ +This macro reflects the @option{-mno-interrupts} command-line option. + +@item __AVR_ERRATA_SKIP__ +@itemx __AVR_ERRATA_SKIP_JMP_CALL__ +Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit +instructions because of a hardware erratum. Skip instructions are +@code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}. +The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also +set. + +@item __AVR_ISA_RMW__ +The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT). + +@item __AVR_SFR_OFFSET__=@var{offset} +Instructions that can address I/O special function registers directly +like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different +address as if addressed by an instruction to access RAM like @code{LD} +or @code{STS}. This offset depends on the device architecture and has +to be subtracted from the RAM address in order to get the +respective I/O@tie{}address. + +@item __AVR_SHORT_CALLS__ +The @option{-mshort-calls} command line option is set. + +@item __AVR_PM_BASE_ADDRESS__=@var{addr} +Some devices support reading from flash memory by means of @code{LD*} +instructions. The flash memory is seen in the data address space +at an offset of @code{__AVR_PM_BASE_ADDRESS__}. If this macro +is not defined, this feature is not available. If defined, +the address space is linear and there is no need to put +@code{.rodata} into RAM. This is handled by the default linker +description file, and is currently available for +@code{avrtiny} and @code{avrxmega3}. Even more convenient, +there is no need to use address spaces like @code{__flash} or +features like attribute @code{progmem} and @code{pgm_read_*}. + +@item __WITH_AVRLIBC__ +The compiler is configured to be used together with AVR-Libc. +See the @option{--with-avrlibc} configure option. + +@item __HAVE_DOUBLE_MULTILIB__ +Defined if @option{-mdouble=} acts as a multilib option. + +@item __HAVE_DOUBLE32__ +@itemx __HAVE_DOUBLE64__ +Defined if the compiler supports 32-bit double resp. 64-bit double. +The actual layout is specified by option @option{-mdouble=}. + +@item __DEFAULT_DOUBLE__ +The size in bits of @code{double} if @option{-mdouble=} is not set. +To test the layout of @code{double} in a program, use the built-in +macro @code{__SIZEOF_DOUBLE__}. + +@item __HAVE_LONG_DOUBLE32__ +@itemx __HAVE_LONG_DOUBLE64__ +@itemx __HAVE_LONG_DOUBLE_MULTILIB__ +@itemx __DEFAULT_LONG_DOUBLE__ +Same as above, but for @code{long double} instead of @code{double}. + +@item __WITH_DOUBLE_COMPARISON__ +Reflects the @code{--with-double-comparison=@{tristate|bool|libf7@}} +@w{@uref{https://gcc.gnu.org/install/configure.html#avr,configure option}} +and is defined to @code{2} or @code{3}. + +@item __WITH_LIBF7_LIBGCC__ +@itemx __WITH_LIBF7_MATH__ +@itemx __WITH_LIBF7_MATH_SYMBOLS__ +Reflects the @code{--with-libf7=@{libgcc|math|math-symbols@}} +@w{@uref{https://gcc.gnu.org/install/configure.html#avr,configure option}}. + +@end table + +@node Blackfin Options +@subsection Blackfin Options +@cindex Blackfin Options + +@table @gcctabopt +@item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} +@opindex mcpu= +Specifies the name of the target Blackfin processor. Currently, @var{cpu} +can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518}, +@samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526}, +@samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533}, +@samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539}, +@samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549}, +@samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m}, +@samp{bf561}, @samp{bf592}. + +The optional @var{sirevision} specifies the silicon revision of the target +Blackfin processor. Any workarounds available for the targeted silicon revision +are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled. +If @var{sirevision} is @samp{any}, all workarounds for the targeted processor +are enabled. The @code{__SILICON_REVISION__} macro is defined to two +hexadecimal digits representing the major and minor numbers in the silicon +revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__} +is not defined. If @var{sirevision} is @samp{any}, the +@code{__SILICON_REVISION__} is defined to be @code{0xffff}. +If this optional @var{sirevision} is not used, GCC assumes the latest known +silicon revision of the targeted Blackfin processor. + +GCC defines a preprocessor macro for the specified @var{cpu}. +For the @samp{bfin-elf} toolchain, this option causes the hardware BSP +provided by libgloss to be linked in if @option{-msim} is not given. + +Without this option, @samp{bf532} is used as the processor by default. + +Note that support for @samp{bf561} is incomplete. For @samp{bf561}, +only the preprocessor macro is defined. + +@item -msim +@opindex msim +Specifies that the program will be run on the simulator. This causes +the simulator BSP provided by libgloss to be linked in. This option +has effect only for @samp{bfin-elf} toolchain. +Certain other options, such as @option{-mid-shared-library} and +@option{-mfdpic}, imply @option{-msim}. + +@item -momit-leaf-frame-pointer +@opindex momit-leaf-frame-pointer +Don't keep the frame pointer in a register for leaf functions. This +avoids the instructions to save, set up and restore frame pointers and +makes an extra register available in leaf functions. + +@item -mspecld-anomaly +@opindex mspecld-anomaly +When enabled, the compiler ensures that the generated code does not +contain speculative loads after jump instructions. If this option is used, +@code{__WORKAROUND_SPECULATIVE_LOADS} is defined. + +@item -mno-specld-anomaly +@opindex mno-specld-anomaly +@opindex mspecld-anomaly +Don't generate extra code to prevent speculative loads from occurring. + +@item -mcsync-anomaly +@opindex mcsync-anomaly +When enabled, the compiler ensures that the generated code does not +contain CSYNC or SSYNC instructions too soon after conditional branches. +If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined. + +@item -mno-csync-anomaly +@opindex mno-csync-anomaly +@opindex mcsync-anomaly +Don't generate extra code to prevent CSYNC or SSYNC instructions from +occurring too soon after a conditional branch. + +@item -mlow64k +@opindex mlow64k +When enabled, the compiler is free to take advantage of the knowledge that +the entire program fits into the low 64k of memory. + +@item -mno-low64k +@opindex mno-low64k +Assume that the program is arbitrarily large. This is the default. + +@item -mstack-check-l1 +@opindex mstack-check-l1 +Do stack checking using information placed into L1 scratchpad memory by the +uClinux kernel. + +@item -mid-shared-library +@opindex mid-shared-library +Generate code that supports shared libraries via the library ID method. +This allows for execute in place and shared libraries in an environment +without virtual memory management. This option implies @option{-fPIC}. +With a @samp{bfin-elf} target, this option implies @option{-msim}. + +@item -mno-id-shared-library +@opindex mno-id-shared-library +@opindex mid-shared-library +Generate code that doesn't assume ID-based shared libraries are being used. +This is the default. + +@item -mleaf-id-shared-library +@opindex mleaf-id-shared-library +Generate code that supports shared libraries via the library ID method, +but assumes that this library or executable won't link against any other +ID shared libraries. That allows the compiler to use faster code for jumps +and calls. + +@item -mno-leaf-id-shared-library +@opindex mno-leaf-id-shared-library +@opindex mleaf-id-shared-library +Do not assume that the code being compiled won't link against any ID shared +libraries. Slower code is generated for jump and call insns. + +@item -mshared-library-id=n +@opindex mshared-library-id +Specifies the identification number of the ID-based shared library being +compiled. Specifying a value of 0 generates more compact code; specifying +other values forces the allocation of that number to the current +library but is no more space- or time-efficient than omitting this option. + +@item -msep-data +@opindex msep-data +Generate code that allows the data segment to be located in a different +area of memory from the text segment. This allows for execute in place in +an environment without virtual memory management by eliminating relocations +against the text section. + +@item -mno-sep-data +@opindex mno-sep-data +@opindex msep-data +Generate code that assumes that the data segment follows the text segment. +This is the default. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Tells the compiler to perform function calls by first loading the +address of the function into a register and then performing a subroutine +call on this register. This switch is needed if the target function +lies outside of the 24-bit addressing range of the offset-based +version of subroutine call instruction. + +This feature is not enabled by default. Specifying +@option{-mno-long-calls} restores the default behavior. Note these +switches have no effect on how the compiler generates code to handle +function calls via function pointers. + +@item -mfast-fp +@opindex mfast-fp +Link with the fast floating-point library. This library relaxes some of +the IEEE floating-point standard's rules for checking inputs against +Not-a-Number (NAN), in the interest of performance. + +@item -minline-plt +@opindex minline-plt +Enable inlining of PLT entries in function calls to functions that are +not known to bind locally. It has no effect without @option{-mfdpic}. + +@item -mmulticore +@opindex mmulticore +Build a standalone application for multicore Blackfin processors. +This option causes proper start files and link scripts supporting +multicore to be used, and defines the macro @code{__BFIN_MULTICORE}. +It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. + +This option can be used with @option{-mcorea} or @option{-mcoreb}, which +selects the one-application-per-core programming model. Without +@option{-mcorea} or @option{-mcoreb}, the single-application/dual-core +programming model is used. In this model, the main function of Core B +should be named as @code{coreb_main}. + +If this option is not used, the single-core application programming +model is used. + +@item -mcorea +@opindex mcorea +Build a standalone application for Core A of BF561 when using +the one-application-per-core programming model. Proper start files +and link scripts are used to support Core A, and the macro +@code{__BFIN_COREA} is defined. +This option can only be used in conjunction with @option{-mmulticore}. + +@item -mcoreb +@opindex mcoreb +Build a standalone application for Core B of BF561 when using +the one-application-per-core programming model. Proper start files +and link scripts are used to support Core B, and the macro +@code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main} +should be used instead of @code{main}. +This option can only be used in conjunction with @option{-mmulticore}. + +@item -msdram +@opindex msdram +Build a standalone application for SDRAM. Proper start files and +link scripts are used to put the application into SDRAM, and the macro +@code{__BFIN_SDRAM} is defined. +The loader should initialize SDRAM before loading the application. + +@item -micplb +@opindex micplb +Assume that ICPLBs are enabled at run time. This has an effect on certain +anomaly workarounds. For Linux targets, the default is to assume ICPLBs +are enabled; for standalone applications the default is off. +@end table + +@node C6X Options +@subsection C6X Options +@cindex C6X Options + +@table @gcctabopt +@item -march=@var{name} +@opindex march +This specifies the name of the target architecture. GCC uses this +name to determine what kind of instructions it can emit when generating +assembly code. Permissible names are: @samp{c62x}, +@samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}. + +@item -mbig-endian +@opindex mbig-endian +Generate code for a big-endian target. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a little-endian target. This is the default. + +@item -msim +@opindex msim +Choose startup files and linker script suitable for the simulator. + +@item -msdata=default +@opindex msdata=default +Put small global and static data in the @code{.neardata} section, +which is pointed to by register @code{B14}. Put small uninitialized +global and static data in the @code{.bss} section, which is adjacent +to the @code{.neardata} section. Put small read-only data into the +@code{.rodata} section. The corresponding sections used for large +pieces of data are @code{.fardata}, @code{.far} and @code{.const}. + +@item -msdata=all +@opindex msdata=all +Put all data, not just small objects, into the sections reserved for +small data, and use addressing relative to the @code{B14} register to +access them. + +@item -msdata=none +@opindex msdata=none +Make no use of the sections reserved for small data, and use absolute +addresses to access all data. Put all initialized global and static +data in the @code{.fardata} section, and all uninitialized data in the +@code{.far} section. Put all constant data into the @code{.const} +section. +@end table + +@node CRIS Options +@subsection CRIS Options +@cindex CRIS Options + +These options are defined specifically for the CRIS ports. + +@table @gcctabopt +@item -march=@var{architecture-type} +@itemx -mcpu=@var{architecture-type} +@opindex march +@opindex mcpu +Generate code for the specified architecture. The choices for +@var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for +respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@. +Default is @samp{v0}. + +@item -mtune=@var{architecture-type} +@opindex mtune +Tune to @var{architecture-type} everything applicable about the generated +code, except for the ABI and the set of available instructions. The +choices for @var{architecture-type} are the same as for +@option{-march=@var{architecture-type}}. + +@item -mmax-stack-frame=@var{n} +@opindex mmax-stack-frame +Warn when the stack frame of a function exceeds @var{n} bytes. + +@item -metrax4 +@itemx -metrax100 +@opindex metrax4 +@opindex metrax100 +The options @option{-metrax4} and @option{-metrax100} are synonyms for +@option{-march=v3} and @option{-march=v8} respectively. + +@item -mmul-bug-workaround +@itemx -mno-mul-bug-workaround +@opindex mmul-bug-workaround +@opindex mno-mul-bug-workaround +Work around a bug in the @code{muls} and @code{mulu} instructions for CPU +models where it applies. This option is disabled by default. + +@item -mpdebug +@opindex mpdebug +Enable CRIS-specific verbose debug-related information in the assembly +code. This option also has the effect of turning off the @samp{#NO_APP} +formatted-code indicator to the assembler at the beginning of the +assembly file. + +@item -mcc-init +@opindex mcc-init +Do not use condition-code results from previous instruction; always emit +compare and test instructions before use of condition codes. + +@item -mno-side-effects +@opindex mno-side-effects +@opindex mside-effects +Do not emit instructions with side effects in addressing modes other than +post-increment. + +@item -mstack-align +@itemx -mno-stack-align +@itemx -mdata-align +@itemx -mno-data-align +@itemx -mconst-align +@itemx -mno-const-align +@opindex mstack-align +@opindex mno-stack-align +@opindex mdata-align +@opindex mno-data-align +@opindex mconst-align +@opindex mno-const-align +These options (@samp{no-} options) arrange (eliminate arrangements) for the +stack frame, individual data and constants to be aligned for the maximum +single data access size for the chosen CPU model. The default is to +arrange for 32-bit alignment. ABI details such as structure layout are +not affected by these options. + +@item -m32-bit +@itemx -m16-bit +@itemx -m8-bit +@opindex m32-bit +@opindex m16-bit +@opindex m8-bit +Similar to the stack- data- and const-align options above, these options +arrange for stack frame, writable data and constants to all be 32-bit, +16-bit or 8-bit aligned. The default is 32-bit alignment. + +@item -mno-prologue-epilogue +@itemx -mprologue-epilogue +@opindex mno-prologue-epilogue +@opindex mprologue-epilogue +With @option{-mno-prologue-epilogue}, the normal function prologue and +epilogue which set up the stack frame are omitted and no return +instructions or return sequences are generated in the code. Use this +option only together with visual inspection of the compiled code: no +warnings or errors are generated when call-saved registers must be saved, +or storage for local variables needs to be allocated. + +@item -melf +@opindex melf +Legacy no-op option. + +@item -sim +@opindex sim +This option arranges +to link with input-output functions from a simulator library. Code, +initialized data and zero-initialized data are allocated consecutively. + +@item -sim2 +@opindex sim2 +Like @option{-sim}, but pass linker options to locate initialized data at +0x40000000 and zero-initialized data at 0x80000000. +@end table + +@node C-SKY Options +@subsection C-SKY Options +@cindex C-SKY Options + +GCC supports these options when compiling for C-SKY V2 processors. + +@table @gcctabopt + +@item -march=@var{arch} +@opindex march= +Specify the C-SKY target architecture. Valid values for @var{arch} are: +@samp{ck801}, @samp{ck802}, @samp{ck803}, @samp{ck807}, and @samp{ck810}. +The default is @samp{ck810}. + +@item -mcpu=@var{cpu} +@opindex mcpu= +Specify the C-SKY target processor. Valid values for @var{cpu} are: +@samp{ck801}, @samp{ck801t}, +@samp{ck802}, @samp{ck802t}, @samp{ck802j}, +@samp{ck803}, @samp{ck803h}, @samp{ck803t}, @samp{ck803ht}, +@samp{ck803f}, @samp{ck803fh}, @samp{ck803e}, @samp{ck803eh}, +@samp{ck803et}, @samp{ck803eht}, @samp{ck803ef}, @samp{ck803efh}, +@samp{ck803ft}, @samp{ck803eft}, @samp{ck803efht}, @samp{ck803r1}, +@samp{ck803hr1}, @samp{ck803tr1}, @samp{ck803htr1}, @samp{ck803fr1}, +@samp{ck803fhr1}, @samp{ck803er1}, @samp{ck803ehr1}, @samp{ck803etr1}, +@samp{ck803ehtr1}, @samp{ck803efr1}, @samp{ck803efhr1}, @samp{ck803ftr1}, +@samp{ck803eftr1}, @samp{ck803efhtr1}, +@samp{ck803s}, @samp{ck803st}, @samp{ck803se}, @samp{ck803sf}, +@samp{ck803sef}, @samp{ck803seft}, +@samp{ck807e}, @samp{ck807ef}, @samp{ck807}, @samp{ck807f}, +@samp{ck810e}, @samp{ck810et}, @samp{ck810ef}, @samp{ck810eft}, +@samp{ck810}, @samp{ck810v}, @samp{ck810f}, @samp{ck810t}, @samp{ck810fv}, +@samp{ck810tv}, @samp{ck810ft}, and @samp{ck810ftv}. + +@item -mbig-endian +@opindex mbig-endian +@itemx -EB +@opindex EB +@itemx -mlittle-endian +@opindex mlittle-endian +@itemx -EL +@opindex EL + +Select big- or little-endian code. The default is little-endian. + +@item -mfloat-abi=@var{name} +@opindex mfloat-abi +Specifies which floating-point ABI to use. Permissible values +are: @samp{soft}, @samp{softfp} and @samp{hard}. + +Specifying @samp{soft} causes GCC to generate output containing +library calls for floating-point operations. +@samp{softfp} allows the generation of code using hardware floating-point +instructions, but still uses the soft-float calling conventions. +@samp{hard} allows generation of floating-point instructions +and uses FPU-specific calling conventions. + +The default depends on the specific target configuration. Note that +the hard-float and soft-float ABIs are not link-compatible; you must +compile your entire program with the same ABI, and link with a +compatible set of libraries. + +@item -mhard-float +@opindex mhard-float +@itemx -msoft-float +@opindex msoft-float + +Select hardware or software floating-point implementations. +The default is soft float. + +@item -mdouble-float +@itemx -mno-double-float +@opindex mdouble-float +When @option{-mhard-float} is in effect, enable generation of +double-precision float instructions. This is the default except +when compiling for CK803. + +@item -mfdivdu +@itemx -mno-fdivdu +@opindex mfdivdu +When @option{-mhard-float} is in effect, enable generation of +@code{frecipd}, @code{fsqrtd}, and @code{fdivd} instructions. +This is the default except when compiling for CK803. + +@item -mfpu=@var{fpu} +@opindex mfpu= +Select the floating-point processor. This option can only be used with +@option{-mhard-float}. +Values for @var{fpu} are +@samp{fpv2_sf} (equivalent to @samp{-mno-double-float -mno-fdivdu}), +@samp{fpv2} (@samp{-mdouble-float -mno-divdu}), and +@samp{fpv2_divd} (@samp{-mdouble-float -mdivdu}). + +@item -melrw +@itemx -mno-elrw +@opindex melrw +Enable the extended @code{lrw} instruction. This option defaults to on +for CK801 and off otherwise. + +@item -mistack +@itemx -mno-istack +@opindex mistack +Enable interrupt stack instructions; the default is off. + +The @option{-mistack} option is required to handle the +@code{interrupt} and @code{isr} function attributes +(@pxref{C-SKY Function Attributes}). + +@item -mmp +@opindex mmp +Enable multiprocessor instructions; the default is off. + +@item -mcp +@opindex mcp +Enable coprocessor instructions; the default is off. + +@item -mcache +@opindex mcache +Enable coprocessor instructions; the default is off. + +@item -msecurity +@opindex msecurity +Enable C-SKY security instructions; the default is off. + +@item -mtrust +@opindex mtrust +Enable C-SKY trust instructions; the default is off. + +@item -mdsp +@opindex mdsp +@itemx -medsp +@opindex medsp +@itemx -mvdsp +@opindex mvdsp +Enable C-SKY DSP, Enhanced DSP, or Vector DSP instructions, respectively. +All of these options default to off. + +@item -mdiv +@itemx -mno-div +@opindex mdiv +Generate divide instructions. Default is off. + +@item -msmart +@itemx -mno-smart +@opindex msmart +Generate code for Smart Mode, using only registers numbered 0-7 to allow +use of 16-bit instructions. This option is ignored for CK801 where this +is the required behavior, and it defaults to on for CK802. +For other targets, the default is off. + +@item -mhigh-registers +@itemx -mno-high-registers +@opindex mhigh-registers +Generate code using the high registers numbered 16-31. This option +is not supported on CK801, CK802, or CK803, and is enabled by default +for other processors. + +@item -manchor +@itemx -mno-anchor +@opindex manchor +Generate code using global anchor symbol addresses. + +@item -mpushpop +@itemx -mno-pushpop +@opindex mpushpop +Generate code using @code{push} and @code{pop} instructions. This option +defaults to on. + +@item -mmultiple-stld +@itemx -mstm +@itemx -mno-multiple-stld +@itemx -mno-stm +@opindex mmultiple-stld +Generate code using @code{stm} and @code{ldm} instructions. This option +isn't supported on CK801 but is enabled by default on other processors. + +@item -mconstpool +@itemx -mno-constpool +@opindex mconstpool +Create constant pools in the compiler instead of deferring it to the +assembler. This option is the default and required for correct code +generation on CK801 and CK802, and is optional on other processors. + +@item -mstack-size +@item -mno-stack-size +@opindex mstack-size +Emit @code{.stack_size} directives for each function in the assembly +output. This option defaults to off. + +@item -mccrt +@itemx -mno-ccrt +@opindex mccrt +Generate code for the C-SKY compiler runtime instead of libgcc. This +option defaults to off. + +@item -mbranch-cost=@var{n} +@opindex mbranch-cost= +Set the branch costs to roughly @code{n} instructions. The default is 1. + +@item -msched-prolog +@itemx -mno-sched-prolog +@opindex msched-prolog +Permit scheduling of function prologue and epilogue sequences. Using +this option can result in code that is not compliant with the C-SKY V2 ABI +prologue requirements and that cannot be debugged or backtraced. +It is disabled by default. + +@item -msim +@opindex msim +Links the library libsemi.a which is in compatible with simulator. Applicable +to ELF compiler only. + +@end table + +@node Darwin Options +@subsection Darwin Options +@cindex Darwin options + +These options are defined for all architectures running the Darwin operating +system. + +FSF GCC on Darwin does not create ``fat'' object files; it creates +an object file for the single architecture that GCC was built to +target. Apple's GCC on Darwin does create ``fat'' files if multiple +@option{-arch} options are used; it does so by running the compiler or +linker multiple times and joining the results together with +@file{lipo}. + +The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or +@samp{i686}) is determined by the flags that specify the ISA +that GCC is targeting, like @option{-mcpu} or @option{-march}. The +@option{-force_cpusubtype_ALL} option can be used to override this. + +The Darwin tools vary in their behavior when presented with an ISA +mismatch. The assembler, @file{as}, only permits instructions to +be used that are valid for the subtype of the file it is generating, +so you cannot put 64-bit instructions in a @samp{ppc750} object file. +The linker for shared libraries, @file{/usr/bin/libtool}, fails +and prints an error if asked to create a shared library with a less +restrictive subtype than its input files (for instance, trying to put +a @samp{ppc970} object file in a @samp{ppc7400} library). The linker +for executables, @command{ld}, quietly gives the executable the most +restrictive subtype of any of its input files. + +@table @gcctabopt +@item -F@var{dir} +@opindex F +Add the framework directory @var{dir} to the head of the list of +directories to be searched for header files. These directories are +interleaved with those specified by @option{-I} options and are +scanned in a left-to-right order. + +A framework directory is a directory with frameworks in it. A +framework is a directory with a @file{Headers} and/or +@file{PrivateHeaders} directory contained directly in it that ends +in @file{.framework}. The name of a framework is the name of this +directory excluding the @file{.framework}. Headers associated with +the framework are found in one of those two directories, with +@file{Headers} being searched first. A subframework is a framework +directory that is in a framework's @file{Frameworks} directory. +Includes of subframework headers can only appear in a header of a +framework that contains the subframework, or in a sibling subframework +header. Two subframeworks are siblings if they occur in the same +framework. A subframework should not have the same name as a +framework; a warning is issued if this is violated. Currently a +subframework cannot have subframeworks; in the future, the mechanism +may be extended to support this. The standard frameworks can be found +in @file{/System/Library/Frameworks} and +@file{/Library/Frameworks}. An example include looks like +@code{#include }, where @file{Framework} denotes +the name of the framework and @file{header.h} is found in the +@file{PrivateHeaders} or @file{Headers} directory. + +@item -iframework@var{dir} +@opindex iframework +Like @option{-F} except the directory is a treated as a system +directory. The main difference between this @option{-iframework} and +@option{-F} is that with @option{-iframework} the compiler does not +warn about constructs contained within header files found via +@var{dir}. This option is valid only for the C family of languages. + +@item -gused +@opindex gused +Emit debugging information for symbols that are used. For stabs +debugging format, this enables @option{-feliminate-unused-debug-symbols}. +This is by default ON@. + +@item -gfull +@opindex gfull +Emit debugging information for all symbols and types. + +@item -mmacosx-version-min=@var{version} +The earliest version of MacOS X that this executable will run on +is @var{version}. Typical values of @var{version} include @code{10.1}, +@code{10.2}, and @code{10.3.9}. + +If the compiler was built to use the system's headers by default, +then the default for this option is the system version on which the +compiler is running, otherwise the default is to make choices that +are compatible with as many systems and code bases as possible. + +@item -mkernel +@opindex mkernel +Enable kernel development mode. The @option{-mkernel} option sets +@option{-static}, @option{-fno-common}, @option{-fno-use-cxa-atexit}, +@option{-fno-exceptions}, @option{-fno-non-call-exceptions}, +@option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where +applicable. This mode also sets @option{-mno-altivec}, +@option{-msoft-float}, @option{-fno-builtin} and +@option{-mlong-branch} for PowerPC targets. + +@item -mone-byte-bool +@opindex mone-byte-bool +Override the defaults for @code{bool} so that @code{sizeof(bool)==1}. +By default @code{sizeof(bool)} is @code{4} when compiling for +Darwin/PowerPC and @code{1} when compiling for Darwin/x86, so this +option has no effect on x86. + +@strong{Warning:} The @option{-mone-byte-bool} switch causes GCC +to generate code that is not binary compatible with code generated +without that switch. Using this switch may require recompiling all +other modules in a program, including system libraries. Use this +switch to conform to a non-default data model. + +@item -mfix-and-continue +@itemx -ffix-and-continue +@itemx -findirect-data +@opindex mfix-and-continue +@opindex ffix-and-continue +@opindex findirect-data +Generate code suitable for fast turnaround development, such as to +allow GDB to dynamically load @file{.o} files into already-running +programs. @option{-findirect-data} and @option{-ffix-and-continue} +are provided for backwards compatibility. + +@item -all_load +@opindex all_load +Loads all members of static archive libraries. +See man ld(1) for more information. + +@item -arch_errors_fatal +@opindex arch_errors_fatal +Cause the errors having to do with files that have the wrong architecture +to be fatal. + +@item -bind_at_load +@opindex bind_at_load +Causes the output file to be marked such that the dynamic linker will +bind all undefined references when the file is loaded or launched. + +@item -bundle +@opindex bundle +Produce a Mach-o bundle format file. +See man ld(1) for more information. + +@item -bundle_loader @var{executable} +@opindex bundle_loader +This option specifies the @var{executable} that will load the build +output file being linked. See man ld(1) for more information. + +@item -dynamiclib +@opindex dynamiclib +When passed this option, GCC produces a dynamic library instead of +an executable when linking, using the Darwin @file{libtool} command. + +@item -force_cpusubtype_ALL +@opindex force_cpusubtype_ALL +This causes GCC's output file to have the @samp{ALL} subtype, instead of +one controlled by the @option{-mcpu} or @option{-march} option. + +@item -allowable_client @var{client_name} +@itemx -client_name +@itemx -compatibility_version +@itemx -current_version +@itemx -dead_strip +@itemx -dependency-file +@itemx -dylib_file +@itemx -dylinker_install_name +@itemx -dynamic +@itemx -exported_symbols_list +@itemx -filelist +@need 800 +@itemx -flat_namespace +@itemx -force_flat_namespace +@itemx -headerpad_max_install_names +@itemx -image_base +@itemx -init +@itemx -install_name +@itemx -keep_private_externs +@itemx -multi_module +@itemx -multiply_defined +@itemx -multiply_defined_unused +@need 800 +@itemx -noall_load +@itemx -no_dead_strip_inits_and_terms +@itemx -nofixprebinding +@itemx -nomultidefs +@itemx -noprebind +@itemx -noseglinkedit +@itemx -pagezero_size +@itemx -prebind +@itemx -prebind_all_twolevel_modules +@itemx -private_bundle +@need 800 +@itemx -read_only_relocs +@itemx -sectalign +@itemx -sectobjectsymbols +@itemx -whyload +@itemx -seg1addr +@itemx -sectcreate +@itemx -sectobjectsymbols +@itemx -sectorder +@itemx -segaddr +@itemx -segs_read_only_addr +@need 800 +@itemx -segs_read_write_addr +@itemx -seg_addr_table +@itemx -seg_addr_table_filename +@itemx -seglinkedit +@itemx -segprot +@itemx -segs_read_only_addr +@itemx -segs_read_write_addr +@itemx -single_module +@itemx -static +@itemx -sub_library +@need 800 +@itemx -sub_umbrella +@itemx -twolevel_namespace +@itemx -umbrella +@itemx -undefined +@itemx -unexported_symbols_list +@itemx -weak_reference_mismatches +@itemx -whatsloaded +@opindex allowable_client +@opindex client_name +@opindex compatibility_version +@opindex current_version +@opindex dead_strip +@opindex dependency-file +@opindex dylib_file +@opindex dylinker_install_name +@opindex dynamic +@opindex exported_symbols_list +@opindex filelist +@opindex flat_namespace +@opindex force_flat_namespace +@opindex headerpad_max_install_names +@opindex image_base +@opindex init +@opindex install_name +@opindex keep_private_externs +@opindex multi_module +@opindex multiply_defined +@opindex multiply_defined_unused +@opindex noall_load +@opindex no_dead_strip_inits_and_terms +@opindex nofixprebinding +@opindex nomultidefs +@opindex noprebind +@opindex noseglinkedit +@opindex pagezero_size +@opindex prebind +@opindex prebind_all_twolevel_modules +@opindex private_bundle +@opindex read_only_relocs +@opindex sectalign +@opindex sectobjectsymbols +@opindex whyload +@opindex seg1addr +@opindex sectcreate +@opindex sectobjectsymbols +@opindex sectorder +@opindex segaddr +@opindex segs_read_only_addr +@opindex segs_read_write_addr +@opindex seg_addr_table +@opindex seg_addr_table_filename +@opindex seglinkedit +@opindex segprot +@opindex segs_read_only_addr +@opindex segs_read_write_addr +@opindex single_module +@opindex static +@opindex sub_library +@opindex sub_umbrella +@opindex twolevel_namespace +@opindex umbrella +@opindex undefined +@opindex unexported_symbols_list +@opindex weak_reference_mismatches +@opindex whatsloaded +These options are passed to the Darwin linker. The Darwin linker man page +describes them in detail. +@end table + +@node DEC Alpha Options +@subsection DEC Alpha Options + +These @samp{-m} options are defined for the DEC Alpha implementations: + +@table @gcctabopt +@item -mno-soft-float +@itemx -msoft-float +@opindex mno-soft-float +@opindex msoft-float +Use (do not use) the hardware floating-point instructions for +floating-point operations. When @option{-msoft-float} is specified, +functions in @file{libgcc.a} are used to perform floating-point +operations. Unless they are replaced by routines that emulate the +floating-point operations, or compiled in such a way as to call such +emulations routines, these routines issue floating-point +operations. If you are compiling for an Alpha without floating-point +operations, you must ensure that the library is built so as not to call +them. + +Note that Alpha implementations without floating-point operations are +required to have floating-point registers. + +@item -mfp-reg +@itemx -mno-fp-regs +@opindex mfp-reg +@opindex mno-fp-regs +Generate code that uses (does not use) the floating-point register set. +@option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point +register set is not used, floating-point operands are passed in integer +registers as if they were integers and floating-point results are passed +in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, +so any function with a floating-point argument or return value called by code +compiled with @option{-mno-fp-regs} must also be compiled with that +option. + +A typical use of this option is building a kernel that does not use, +and hence need not save and restore, any floating-point registers. + +@item -mieee +@opindex mieee +The Alpha architecture implements floating-point hardware optimized for +maximum performance. It is mostly compliant with the IEEE floating-point +standard. However, for full compliance, software assistance is +required. This option generates code fully IEEE-compliant code +@emph{except} that the @var{inexact-flag} is not maintained (see below). +If this option is turned on, the preprocessor macro @code{_IEEE_FP} is +defined during compilation. The resulting code is less efficient but is +able to correctly support denormalized numbers and exceptional IEEE +values such as not-a-number and plus/minus infinity. Other Alpha +compilers call this option @option{-ieee_with_no_inexact}. + +@item -mieee-with-inexact +@opindex mieee-with-inexact +This is like @option{-mieee} except the generated code also maintains +the IEEE @var{inexact-flag}. Turning on this option causes the +generated code to implement fully-compliant IEEE math. In addition to +@code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor +macro. On some Alpha implementations the resulting code may execute +significantly slower than the code generated by default. Since there is +very little code that depends on the @var{inexact-flag}, you should +normally not specify this option. Other Alpha compilers call this +option @option{-ieee_with_inexact}. + +@item -mfp-trap-mode=@var{trap-mode} +@opindex mfp-trap-mode +This option controls what floating-point related traps are enabled. +Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. +The trap mode can be set to one of four values: + +@table @samp +@item n +This is the default (normal) setting. The only traps that are enabled +are the ones that cannot be disabled in software (e.g., division by zero +trap). + +@item u +In addition to the traps enabled by @samp{n}, underflow traps are enabled +as well. + +@item su +Like @samp{u}, but the instructions are marked to be safe for software +completion (see Alpha architecture manual for details). + +@item sui +Like @samp{su}, but inexact traps are enabled as well. +@end table + +@item -mfp-rounding-mode=@var{rounding-mode} +@opindex mfp-rounding-mode +Selects the IEEE rounding mode. Other Alpha compilers call this option +@option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one +of: + +@table @samp +@item n +Normal IEEE rounding mode. Floating-point numbers are rounded towards +the nearest machine number or towards the even machine number in case +of a tie. + +@item m +Round towards minus infinity. + +@item c +Chopped rounding mode. Floating-point numbers are rounded towards zero. + +@item d +Dynamic rounding mode. A field in the floating-point control register +(@var{fpcr}, see Alpha architecture reference manual) controls the +rounding mode in effect. The C library initializes this register for +rounding towards plus infinity. Thus, unless your program modifies the +@var{fpcr}, @samp{d} corresponds to round towards plus infinity. +@end table + +@item -mtrap-precision=@var{trap-precision} +@opindex mtrap-precision +In the Alpha architecture, floating-point traps are imprecise. This +means without software assistance it is impossible to recover from a +floating trap and program execution normally needs to be terminated. +GCC can generate code that can assist operating system trap handlers +in determining the exact location that caused a floating-point trap. +Depending on the requirements of an application, different levels of +precisions can be selected: + +@table @samp +@item p +Program precision. This option is the default and means a trap handler +can only identify which program caused a floating-point exception. + +@item f +Function precision. The trap handler can determine the function that +caused a floating-point exception. + +@item i +Instruction precision. The trap handler can determine the exact +instruction that caused a floating-point exception. +@end table + +Other Alpha compilers provide the equivalent options called +@option{-scope_safe} and @option{-resumption_safe}. + +@item -mieee-conformant +@opindex mieee-conformant +This option marks the generated code as IEEE conformant. You must not +use this option unless you also specify @option{-mtrap-precision=i} and either +@option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect +is to emit the line @samp{.eflag 48} in the function prologue of the +generated assembly file. + +@item -mbuild-constants +@opindex mbuild-constants +Normally GCC examines a 32- or 64-bit integer constant to +see if it can construct it from smaller constants in two or three +instructions. If it cannot, it outputs the constant as a literal and +generates code to load it from the data segment at run time. + +Use this option to require GCC to construct @emph{all} integer constants +using code, even if it takes more instructions (the maximum is six). + +You typically use this option to build a shared library dynamic +loader. Itself a shared library, it must relocate itself in memory +before it can find the variables and constants in its own data segment. + +@item -mbwx +@itemx -mno-bwx +@itemx -mcix +@itemx -mno-cix +@itemx -mfix +@itemx -mno-fix +@itemx -mmax +@itemx -mno-max +@opindex mbwx +@opindex mno-bwx +@opindex mcix +@opindex mno-cix +@opindex mfix +@opindex mno-fix +@opindex mmax +@opindex mno-max +Indicate whether GCC should generate code to use the optional BWX, +CIX, FIX and MAX instruction sets. The default is to use the instruction +sets supported by the CPU type specified via @option{-mcpu=} option or that +of the CPU on which GCC was built if none is specified. + +@item -mfloat-vax +@itemx -mfloat-ieee +@opindex mfloat-vax +@opindex mfloat-ieee +Generate code that uses (does not use) VAX F and G floating-point +arithmetic instead of IEEE single and double precision. + +@item -mexplicit-relocs +@itemx -mno-explicit-relocs +@opindex mexplicit-relocs +@opindex mno-explicit-relocs +Older Alpha assemblers provided no way to generate symbol relocations +except via assembler macros. Use of these macros does not allow +optimal instruction scheduling. GNU binutils as of version 2.12 +supports a new syntax that allows the compiler to explicitly mark +which relocations should apply to which instructions. This option +is mostly useful for debugging, as GCC detects the capabilities of +the assembler when it is built and sets the default accordingly. + +@item -msmall-data +@itemx -mlarge-data +@opindex msmall-data +@opindex mlarge-data +When @option{-mexplicit-relocs} is in effect, static data is +accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} +is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} +(the @code{.sdata} and @code{.sbss} sections) and are accessed via +16-bit relocations off of the @code{$gp} register. This limits the +size of the small data area to 64KB, but allows the variables to be +directly accessed via a single instruction. + +The default is @option{-mlarge-data}. With this option the data area +is limited to just below 2GB@. Programs that require more than 2GB of +data must use @code{malloc} or @code{mmap} to allocate the data in the +heap instead of in the program's data segment. + +When generating code for shared libraries, @option{-fpic} implies +@option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. + +@item -msmall-text +@itemx -mlarge-text +@opindex msmall-text +@opindex mlarge-text +When @option{-msmall-text} is used, the compiler assumes that the +code of the entire program (or shared library) fits in 4MB, and is +thus reachable with a branch instruction. When @option{-msmall-data} +is used, the compiler can assume that all local symbols share the +same @code{$gp} value, and thus reduce the number of instructions +required for a function call from 4 to 1. + +The default is @option{-mlarge-text}. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set and instruction scheduling parameters for +machine type @var{cpu_type}. You can specify either the @samp{EV} +style name or the corresponding chip number. GCC supports scheduling +parameters for the EV4, EV5 and EV6 family of processors and +chooses the default values for the instruction set from the processor +you specify. If you do not specify a processor type, GCC defaults +to the processor on which the compiler was built. + +Supported values for @var{cpu_type} are + +@table @samp +@item ev4 +@itemx ev45 +@itemx 21064 +Schedules as an EV4 and has no instruction set extensions. + +@item ev5 +@itemx 21164 +Schedules as an EV5 and has no instruction set extensions. + +@item ev56 +@itemx 21164a +Schedules as an EV5 and supports the BWX extension. + +@item pca56 +@itemx 21164pc +@itemx 21164PC +Schedules as an EV5 and supports the BWX and MAX extensions. + +@item ev6 +@itemx 21264 +Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. + +@item ev67 +@itemx 21264a +Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. +@end table + +Native toolchains also support the value @samp{native}, +which selects the best architecture option for the host processor. +@option{-mcpu=native} has no effect if GCC does not recognize +the processor. + +@item -mtune=@var{cpu_type} +@opindex mtune +Set only the instruction scheduling parameters for machine type +@var{cpu_type}. The instruction set is not changed. + +Native toolchains also support the value @samp{native}, +which selects the best architecture option for the host processor. +@option{-mtune=native} has no effect if GCC does not recognize +the processor. + +@item -mmemory-latency=@var{time} +@opindex mmemory-latency +Sets the latency the scheduler should assume for typical memory +references as seen by the application. This number is highly +dependent on the memory access patterns used by the application +and the size of the external cache on the machine. + +Valid options for @var{time} are + +@table @samp +@item @var{number} +A decimal number representing clock cycles. + +@item L1 +@itemx L2 +@itemx L3 +@itemx main +The compiler contains estimates of the number of clock cycles for +``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches +(also called Dcache, Scache, and Bcache), as well as to main memory. +Note that L3 is only valid for EV5. + +@end table +@end table + +@node eBPF Options +@subsection eBPF Options +@cindex eBPF Options + +@table @gcctabopt +@item -mframe-limit=@var{bytes} +This specifies the hard limit for frame sizes, in bytes. Currently, +the value that can be specified should be less than or equal to +@samp{32767}. Defaults to whatever limit is imposed by the version of +the Linux kernel targeted. + +@item -mkernel=@var{version} +@opindex mkernel +This specifies the minimum version of the kernel that will run the +compiled program. GCC uses this version to determine which +instructions to use, what kernel helpers to allow, etc. Currently, +@var{version} can be one of @samp{4.0}, @samp{4.1}, @samp{4.2}, +@samp{4.3}, @samp{4.4}, @samp{4.5}, @samp{4.6}, @samp{4.7}, +@samp{4.8}, @samp{4.9}, @samp{4.10}, @samp{4.11}, @samp{4.12}, +@samp{4.13}, @samp{4.14}, @samp{4.15}, @samp{4.16}, @samp{4.17}, +@samp{4.18}, @samp{4.19}, @samp{4.20}, @samp{5.0}, @samp{5.1}, +@samp{5.2}, @samp{latest} and @samp{native}. + +@item -mbig-endian +@opindex mbig-endian +Generate code for a big-endian target. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a little-endian target. This is the default. + +@item -mjmpext +@opindex mjmpext +Enable generation of extra conditional-branch instructions. +Enabled for CPU v2 and above. + +@item -mjmp32 +@opindex mjmp32 +Enable 32-bit jump instructions. Enabled for CPU v3 and above. + +@item -malu32 +@opindex malu32 +Enable 32-bit ALU instructions. Enabled for CPU v3 and above. + +@item -mcpu=@var{version} +@opindex mcpu +This specifies which version of the eBPF ISA to target. Newer versions +may not be supported by all kernels. The default is @samp{v3}. + +Supported values for @var{version} are: + +@table @samp +@item v1 +The first stable eBPF ISA with no special features or extensions. + +@item v2 +Supports the jump extensions, as in @option{-mjmpext}. + +@item v3 +All features of v2, plus: +@itemize @minus +@item 32-bit jump operations, as in @option{-mjmp32} +@item 32-bit ALU operations, as in @option{-malu32} +@end itemize + +@end table + +@item -mco-re +@opindex mco-re +Enable BPF Compile Once - Run Everywhere (CO-RE) support. Requires and +is implied by @option{-gbtf}. + +@item -mno-co-re +@opindex mno-co-re +Disable BPF Compile Once - Run Everywhere (CO-RE) support. BPF CO-RE +support is enabled by default when generating BTF debug information for +the BPF target. + +@item -mxbpf +Generate code for an expanded version of BPF, which relaxes some of +the restrictions imposed by the BPF architecture: +@itemize @minus +@item Save and restore callee-saved registers at function entry and +exit, respectively. +@end itemize +@end table + +@node FR30 Options +@subsection FR30 Options +@cindex FR30 Options + +These options are defined specifically for the FR30 port. + +@table @gcctabopt + +@item -msmall-model +@opindex msmall-model +Use the small address space model. This can produce smaller code, but +it does assume that all symbolic values and addresses fit into a +20-bit range. + +@item -mno-lsim +@opindex mno-lsim +Assume that runtime support has been provided and so there is no need +to include the simulator library (@file{libsim.a}) on the linker +command line. + +@end table + +@node FT32 Options +@subsection FT32 Options +@cindex FT32 Options + +These options are defined specifically for the FT32 port. + +@table @gcctabopt + +@item -msim +@opindex msim +Specifies that the program will be run on the simulator. This causes +an alternate runtime startup and library to be linked. +You must not use this option when generating programs that will run on +real hardware; you must provide your own runtime library for whatever +I/O functions are needed. + +@item -mlra +@opindex mlra +Enable Local Register Allocation. This is still experimental for FT32, +so by default the compiler uses standard reload. + +@item -mnodiv +@opindex mnodiv +Do not use div and mod instructions. + +@item -mft32b +@opindex mft32b +Enable use of the extended instructions of the FT32B processor. + +@item -mcompress +@opindex mcompress +Compress all code using the Ft32B code compression scheme. + +@item -mnopm +@opindex mnopm +Do not generate code that reads program memory. + +@end table + +@node FRV Options +@subsection FRV Options +@cindex FRV Options + +@table @gcctabopt +@item -mgpr-32 +@opindex mgpr-32 + +Only use the first 32 general-purpose registers. + +@item -mgpr-64 +@opindex mgpr-64 + +Use all 64 general-purpose registers. + +@item -mfpr-32 +@opindex mfpr-32 + +Use only the first 32 floating-point registers. + +@item -mfpr-64 +@opindex mfpr-64 + +Use all 64 floating-point registers. + +@item -mhard-float +@opindex mhard-float + +Use hardware instructions for floating-point operations. + +@item -msoft-float +@opindex msoft-float + +Use library routines for floating-point operations. + +@item -malloc-cc +@opindex malloc-cc + +Dynamically allocate condition code registers. + +@item -mfixed-cc +@opindex mfixed-cc + +Do not try to dynamically allocate condition code registers, only +use @code{icc0} and @code{fcc0}. + +@item -mdword +@opindex mdword + +Change ABI to use double word insns. + +@item -mno-dword +@opindex mno-dword +@opindex mdword + +Do not use double word instructions. + +@item -mdouble +@opindex mdouble + +Use floating-point double instructions. + +@item -mno-double +@opindex mno-double + +Do not use floating-point double instructions. + +@item -mmedia +@opindex mmedia + +Use media instructions. + +@item -mno-media +@opindex mno-media + +Do not use media instructions. + +@item -mmuladd +@opindex mmuladd + +Use multiply and add/subtract instructions. + +@item -mno-muladd +@opindex mno-muladd + +Do not use multiply and add/subtract instructions. + +@item -mfdpic +@opindex mfdpic + +Select the FDPIC ABI, which uses function descriptors to represent +pointers to functions. Without any PIC/PIE-related options, it +implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it +assumes GOT entries and small data are within a 12-bit range from the +GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets +are computed with 32 bits. +With a @samp{bfin-elf} target, this option implies @option{-msim}. + +@item -minline-plt +@opindex minline-plt + +Enable inlining of PLT entries in function calls to functions that are +not known to bind locally. It has no effect without @option{-mfdpic}. +It's enabled by default if optimizing for speed and compiling for +shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an +optimization option such as @option{-O3} or above is present in the +command line. + +@item -mTLS +@opindex mTLS + +Assume a large TLS segment when generating thread-local code. + +@item -mtls +@opindex mtls + +Do not assume a large TLS segment when generating thread-local code. + +@item -mgprel-ro +@opindex mgprel-ro + +Enable the use of @code{GPREL} relocations in the FDPIC ABI for data +that is known to be in read-only sections. It's enabled by default, +except for @option{-fpic} or @option{-fpie}: even though it may help +make the global offset table smaller, it trades 1 instruction for 4. +With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4, +one of which may be shared by multiple symbols, and it avoids the need +for a GOT entry for the referenced symbol, so it's more likely to be a +win. If it is not, @option{-mno-gprel-ro} can be used to disable it. + +@item -multilib-library-pic +@opindex multilib-library-pic + +Link with the (library, not FD) pic libraries. It's implied by +@option{-mlibrary-pic}, as well as by @option{-fPIC} and +@option{-fpic} without @option{-mfdpic}. You should never have to use +it explicitly. + +@item -mlinked-fp +@opindex mlinked-fp + +Follow the EABI requirement of always creating a frame pointer whenever +a stack frame is allocated. This option is enabled by default and can +be disabled with @option{-mno-linked-fp}. + +@item -mlong-calls +@opindex mlong-calls + +Use indirect addressing to call functions outside the current +compilation unit. This allows the functions to be placed anywhere +within the 32-bit address space. + +@item -malign-labels +@opindex malign-labels + +Try to align labels to an 8-byte boundary by inserting NOPs into the +previous packet. This option only has an effect when VLIW packing +is enabled. It doesn't create new packets; it merely adds NOPs to +existing ones. + +@item -mlibrary-pic +@opindex mlibrary-pic + +Generate position-independent EABI code. + +@item -macc-4 +@opindex macc-4 + +Use only the first four media accumulator registers. + +@item -macc-8 +@opindex macc-8 + +Use all eight media accumulator registers. + +@item -mpack +@opindex mpack + +Pack VLIW instructions. + +@item -mno-pack +@opindex mno-pack + +Do not pack VLIW instructions. + +@item -mno-eflags +@opindex mno-eflags + +Do not mark ABI switches in e_flags. + +@item -mcond-move +@opindex mcond-move + +Enable the use of conditional-move instructions (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-cond-move +@opindex mno-cond-move + +Disable the use of conditional-move instructions. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mscc +@opindex mscc + +Enable the use of conditional set instructions (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-scc +@opindex mno-scc + +Disable the use of conditional set instructions. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mcond-exec +@opindex mcond-exec + +Enable the use of conditional execution (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-cond-exec +@opindex mno-cond-exec + +Disable the use of conditional execution. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mvliw-branch +@opindex mvliw-branch + +Run a pass to pack branches into VLIW instructions (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-vliw-branch +@opindex mno-vliw-branch + +Do not run a pass to pack branches into VLIW instructions. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mmulti-cond-exec +@opindex mmulti-cond-exec + +Enable optimization of @code{&&} and @code{||} in conditional execution +(default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-multi-cond-exec +@opindex mno-multi-cond-exec + +Disable optimization of @code{&&} and @code{||} in conditional execution. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mnested-cond-exec +@opindex mnested-cond-exec + +Enable nested conditional execution optimizations (default). + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -mno-nested-cond-exec +@opindex mno-nested-cond-exec + +Disable nested conditional execution optimizations. + +This switch is mainly for debugging the compiler and will likely be removed +in a future version. + +@item -moptimize-membar +@opindex moptimize-membar + +This switch removes redundant @code{membar} instructions from the +compiler-generated code. It is enabled by default. + +@item -mno-optimize-membar +@opindex mno-optimize-membar +@opindex moptimize-membar + +This switch disables the automatic removal of redundant @code{membar} +instructions from the generated code. + +@item -mtomcat-stats +@opindex mtomcat-stats + +Cause gas to print out tomcat statistics. + +@item -mcpu=@var{cpu} +@opindex mcpu + +Select the processor type for which to generate code. Possible values are +@samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450}, +@samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}. + +@end table + +@node GNU/Linux Options +@subsection GNU/Linux Options + +These @samp{-m} options are defined for GNU/Linux targets: + +@table @gcctabopt +@item -mglibc +@opindex mglibc +Use the GNU C library. This is the default except +on @samp{*-*-linux-*uclibc*}, @samp{*-*-linux-*musl*} and +@samp{*-*-linux-*android*} targets. + +@item -muclibc +@opindex muclibc +Use uClibc C library. This is the default on +@samp{*-*-linux-*uclibc*} targets. + +@item -mmusl +@opindex mmusl +Use the musl C library. This is the default on +@samp{*-*-linux-*musl*} targets. + +@item -mbionic +@opindex mbionic +Use Bionic C library. This is the default on +@samp{*-*-linux-*android*} targets. + +@item -mandroid +@opindex mandroid +Compile code compatible with Android platform. This is the default on +@samp{*-*-linux-*android*} targets. + +When compiling, this option enables @option{-mbionic}, @option{-fPIC}, +@option{-fno-exceptions} and @option{-fno-rtti} by default. When linking, +this option makes the GCC driver pass Android-specific options to the linker. +Finally, this option causes the preprocessor macro @code{__ANDROID__} +to be defined. + +@item -tno-android-cc +@opindex tno-android-cc +Disable compilation effects of @option{-mandroid}, i.e., do not enable +@option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and +@option{-fno-rtti} by default. + +@item -tno-android-ld +@opindex tno-android-ld +Disable linking effects of @option{-mandroid}, i.e., pass standard Linux +linking options to the linker. + +@end table + +@node H8/300 Options +@subsection H8/300 Options + +These @samp{-m} options are defined for the H8/300 implementations: + +@table @gcctabopt +@item -mrelax +@opindex mrelax +Shorten some address references at link time, when possible; uses the +linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, +ld, Using ld}, for a fuller description. + +@item -mh +@opindex mh +Generate code for the H8/300H@. + +@item -ms +@opindex ms +Generate code for the H8S@. + +@item -mn +@opindex mn +Generate code for the H8S and H8/300H in the normal mode. This switch +must be used either with @option{-mh} or @option{-ms}. + +@item -ms2600 +@opindex ms2600 +Generate code for the H8S/2600. This switch must be used with @option{-ms}. + +@item -mexr +@opindex mexr +Extended registers are stored on stack before execution of function +with monitor attribute. Default option is @option{-mexr}. +This option is valid only for H8S targets. + +@item -mno-exr +@opindex mno-exr +@opindex mexr +Extended registers are not stored on stack before execution of function +with monitor attribute. Default option is @option{-mno-exr}. +This option is valid only for H8S targets. + +@item -mint32 +@opindex mint32 +Make @code{int} data 32 bits by default. + +@item -malign-300 +@opindex malign-300 +On the H8/300H and H8S, use the same alignment rules as for the H8/300. +The default for the H8/300H and H8S is to align longs and floats on +4-byte boundaries. +@option{-malign-300} causes them to be aligned on 2-byte boundaries. +This option has no effect on the H8/300. +@end table + +@node HPPA Options +@subsection HPPA Options +@cindex HPPA Options + +These @samp{-m} options are defined for the HPPA family of computers: + +@table @gcctabopt +@item -march=@var{architecture-type} +@opindex march +Generate code for the specified architecture. The choices for +@var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA +1.1, and @samp{2.0} for PA 2.0 processors. Refer to +@file{/usr/lib/sched.models} on an HP-UX system to determine the proper +architecture option for your machine. Code compiled for lower numbered +architectures runs on higher numbered architectures, but not the +other way around. + +@item -mpa-risc-1-0 +@itemx -mpa-risc-1-1 +@itemx -mpa-risc-2-0 +@opindex mpa-risc-1-0 +@opindex mpa-risc-1-1 +@opindex mpa-risc-2-0 +Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. + +@item -mcaller-copies +@opindex mcaller-copies +The caller copies function arguments passed by hidden reference. This +option should be used with care as it is not compatible with the default +32-bit runtime. However, only aggregates larger than eight bytes are +passed by hidden reference and the option provides better compatibility +with OpenMP. + +@item -mjump-in-delay +@opindex mjump-in-delay +This option is ignored and provided for compatibility purposes only. + +@item -mdisable-fpregs +@opindex mdisable-fpregs +Prevent floating-point registers from being used in any manner. This is +necessary for compiling kernels that perform lazy context switching of +floating-point registers. If you use this option and attempt to perform +floating-point operations, the compiler aborts. + +@item -mdisable-indexing +@opindex mdisable-indexing +Prevent the compiler from using indexing address modes. This avoids some +rather obscure problems when compiling MIG generated code under MACH@. + +@item -mno-space-regs +@opindex mno-space-regs +@opindex mspace-regs +Generate code that assumes the target has no space registers. This allows +GCC to generate faster indirect calls and use unscaled index address modes. + +Such code is suitable for level 0 PA systems and kernels. + +@item -mfast-indirect-calls +@opindex mfast-indirect-calls +Generate code that assumes calls never cross space boundaries. This +allows GCC to emit code that performs faster indirect calls. + +This option does not work in the presence of shared libraries or nested +functions. + +@item -mfixed-range=@var{register-range} +@opindex mfixed-range +Generate code treating the given register range as fixed registers. +A fixed register is one that the register allocator cannot use. This is +useful when compiling kernel code. A register range is specified as +two registers separated by a dash. Multiple register ranges can be +specified separated by a comma. + +@item -mlong-load-store +@opindex mlong-load-store +Generate 3-instruction load and store sequences as sometimes required by +the HP-UX 10 linker. This is equivalent to the @samp{+k} option to +the HP compilers. + +@item -mportable-runtime +@opindex mportable-runtime +Use the portable calling conventions proposed by HP for ELF systems. + +@item -mgas +@opindex mgas +Enable the use of assembler directives only GAS understands. + +@item -mschedule=@var{cpu-type} +@opindex mschedule +Schedule code according to the constraints for the machine type +@var{cpu-type}. The choices for @var{cpu-type} are @samp{700} +@samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer +to @file{/usr/lib/sched.models} on an HP-UX system to determine the +proper scheduling option for your machine. The default scheduling is +@samp{8000}. + +@item -mlinker-opt +@opindex mlinker-opt +Enable the optimization pass in the HP-UX linker. Note this makes symbolic +debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 +linkers in which they give bogus error messages when linking some programs. + +@item -msoft-float +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all HPPA +targets. Normally the facilities of the machine's usual C compiler are +used, but this cannot be done directly in cross-compilation. You must make +your own arrangements to provide suitable library functions for +cross-compilation. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. + +@item -msio +@opindex msio +Generate the predefine, @code{_SIO}, for server IO@. The default is +@option{-mwsio}. This generates the predefines, @code{__hp9000s700}, +@code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These +options are available under HP-UX and HI-UX@. + +@item -mgnu-ld +@opindex mgnu-ld +Use options specific to GNU @command{ld}. +This passes @option{-shared} to @command{ld} when +building a shared library. It is the default when GCC is configured, +explicitly or implicitly, with the GNU linker. This option does not +affect which @command{ld} is called; it only changes what parameters +are passed to that @command{ld}. +The @command{ld} that is called is determined by the +@option{--with-ld} configure option, GCC's program search path, and +finally by the user's @env{PATH}. The linker used by GCC can be printed +using @samp{which `gcc -print-prog-name=ld`}. This option is only available +on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. + +@item -mhp-ld +@opindex mhp-ld +Use options specific to HP @command{ld}. +This passes @option{-b} to @command{ld} when building +a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all +links. It is the default when GCC is configured, explicitly or +implicitly, with the HP linker. This option does not affect +which @command{ld} is called; it only changes what parameters are passed to that +@command{ld}. +The @command{ld} that is called is determined by the @option{--with-ld} +configure option, GCC's program search path, and finally by the user's +@env{PATH}. The linker used by GCC can be printed using @samp{which +`gcc -print-prog-name=ld`}. This option is only available on the 64-bit +HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. + +@item -mlong-calls +@opindex mno-long-calls +@opindex mlong-calls +Generate code that uses long call sequences. This ensures that a call +is always able to reach linker generated stubs. The default is to generate +long calls only when the distance from the call site to the beginning +of the function or translation unit, as the case may be, exceeds a +predefined limit set by the branch type being used. The limits for +normal calls are 7,600,000 and 240,000 bytes, respectively for the +PA 2.0 and PA 1.X architectures. Sibcalls are always limited at +240,000 bytes. + +Distances are measured from the beginning of functions when using the +@option{-ffunction-sections} option, or when using the @option{-mgas} +and @option{-mno-portable-runtime} options together under HP-UX with +the SOM linker. + +It is normally not desirable to use this option as it degrades +performance. However, it may be useful in large applications, +particularly when partial linking is used to build the application. + +The types of long calls used depends on the capabilities of the +assembler and linker, and the type of code being generated. The +impact on systems that support long absolute calls, and long pic +symbol-difference or pc-relative calls should be relatively small. +However, an indirect call is used on 32-bit ELF systems in pic code +and it is quite long. + +@item -munix=@var{unix-std} +@opindex march +Generate compiler predefines and select a startfile for the specified +UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95} +and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95} +is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX +11.11 and later. The default values are @samp{93} for HP-UX 10.00, +@samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11 +and later. + +@option{-munix=93} provides the same predefines as GCC 3.3 and 3.4. +@option{-munix=95} provides additional predefines for @code{XOPEN_UNIX} +and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}. +@option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX}, +@code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and +@code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}. + +It is @emph{important} to note that this option changes the interfaces +for various library routines. It also affects the operational behavior +of the C library. Thus, @emph{extreme} care is needed in using this +option. + +Library code that is intended to operate with more than one UNIX +standard must test, set and restore the variable @code{__xpg4_extended_mask} +as appropriate. Most GNU software doesn't provide this capability. + +@item -nolibdld +@opindex nolibdld +Suppress the generation of link options to search libdld.sl when the +@option{-static} option is specified on HP-UX 10 and later. + +@item -static +@opindex static +The HP-UX implementation of setlocale in libc has a dependency on +libdld.sl. There isn't an archive version of libdld.sl. Thus, +when the @option{-static} option is specified, special link options +are needed to resolve this dependency. + +On HP-UX 10 and later, the GCC driver adds the necessary options to +link with libdld.sl when the @option{-static} option is specified. +This causes the resulting binary to be dynamic. On the 64-bit port, +the linkers generate dynamic binaries by default in any case. The +@option{-nolibdld} option can be used to prevent the GCC driver from +adding these link options. + +@item -threads +@opindex threads +Add support for multithreading with the @dfn{dce thread} library +under HP-UX@. This option sets flags for both the preprocessor and +linker. +@end table + +@node IA-64 Options +@subsection IA-64 Options +@cindex IA-64 Options + +These are the @samp{-m} options defined for the Intel IA-64 architecture. + +@table @gcctabopt +@item -mbig-endian +@opindex mbig-endian +Generate code for a big-endian target. This is the default for HP-UX@. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a little-endian target. This is the default for AIX5 +and GNU/Linux. + +@item -mgnu-as +@itemx -mno-gnu-as +@opindex mgnu-as +@opindex mno-gnu-as +Generate (or don't) code for the GNU assembler. This is the default. +@c Also, this is the default if the configure option @option{--with-gnu-as} +@c is used. + +@item -mgnu-ld +@itemx -mno-gnu-ld +@opindex mgnu-ld +@opindex mno-gnu-ld +Generate (or don't) code for the GNU linker. This is the default. +@c Also, this is the default if the configure option @option{--with-gnu-ld} +@c is used. + +@item -mno-pic +@opindex mno-pic +Generate code that does not use a global pointer register. The result +is not position independent code, and violates the IA-64 ABI@. + +@item -mvolatile-asm-stop +@itemx -mno-volatile-asm-stop +@opindex mvolatile-asm-stop +@opindex mno-volatile-asm-stop +Generate (or don't) a stop bit immediately before and after volatile asm +statements. + +@item -mregister-names +@itemx -mno-register-names +@opindex mregister-names +@opindex mno-register-names +Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for +the stacked registers. This may make assembler output more readable. + +@item -mno-sdata +@itemx -msdata +@opindex mno-sdata +@opindex msdata +Disable (or enable) optimizations that use the small data section. This may +be useful for working around optimizer bugs. + +@item -mconstant-gp +@opindex mconstant-gp +Generate code that uses a single constant global pointer value. This is +useful when compiling kernel code. + +@item -mauto-pic +@opindex mauto-pic +Generate code that is self-relocatable. This implies @option{-mconstant-gp}. +This is useful when compiling firmware code. + +@item -minline-float-divide-min-latency +@opindex minline-float-divide-min-latency +Generate code for inline divides of floating-point values +using the minimum latency algorithm. + +@item -minline-float-divide-max-throughput +@opindex minline-float-divide-max-throughput +Generate code for inline divides of floating-point values +using the maximum throughput algorithm. + +@item -mno-inline-float-divide +@opindex mno-inline-float-divide +Do not generate inline code for divides of floating-point values. + +@item -minline-int-divide-min-latency +@opindex minline-int-divide-min-latency +Generate code for inline divides of integer values +using the minimum latency algorithm. + +@item -minline-int-divide-max-throughput +@opindex minline-int-divide-max-throughput +Generate code for inline divides of integer values +using the maximum throughput algorithm. + +@item -mno-inline-int-divide +@opindex mno-inline-int-divide +@opindex minline-int-divide +Do not generate inline code for divides of integer values. + +@item -minline-sqrt-min-latency +@opindex minline-sqrt-min-latency +Generate code for inline square roots +using the minimum latency algorithm. + +@item -minline-sqrt-max-throughput +@opindex minline-sqrt-max-throughput +Generate code for inline square roots +using the maximum throughput algorithm. + +@item -mno-inline-sqrt +@opindex mno-inline-sqrt +Do not generate inline code for @code{sqrt}. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Do (don't) generate code that uses the fused multiply/add or multiply/subtract +instructions. The default is to use these instructions. + +@item -mno-dwarf2-asm +@itemx -mdwarf2-asm +@opindex mno-dwarf2-asm +@opindex mdwarf2-asm +Don't (or do) generate assembler code for the DWARF line number debugging +info. This may be useful when not using the GNU assembler. + +@item -mearly-stop-bits +@itemx -mno-early-stop-bits +@opindex mearly-stop-bits +@opindex mno-early-stop-bits +Allow stop bits to be placed earlier than immediately preceding the +instruction that triggered the stop bit. This can improve instruction +scheduling, but does not always do so. + +@item -mfixed-range=@var{register-range} +@opindex mfixed-range +Generate code treating the given register range as fixed registers. +A fixed register is one that the register allocator cannot use. This is +useful when compiling kernel code. A register range is specified as +two registers separated by a dash. Multiple register ranges can be +specified separated by a comma. + +@item -mtls-size=@var{tls-size} +@opindex mtls-size +Specify bit size of immediate TLS offsets. Valid values are 14, 22, and +64. + +@item -mtune=@var{cpu-type} +@opindex mtune +Tune the instruction scheduling for a particular CPU, Valid values are +@samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2}, +and @samp{mckinley}. + +@item -milp32 +@itemx -mlp64 +@opindex milp32 +@opindex mlp64 +Generate code for a 32-bit or 64-bit environment. +The 32-bit environment sets int, long and pointer to 32 bits. +The 64-bit environment sets int to 32 bits and long and pointer +to 64 bits. These are HP-UX specific flags. + +@item -mno-sched-br-data-spec +@itemx -msched-br-data-spec +@opindex mno-sched-br-data-spec +@opindex msched-br-data-spec +(Dis/En)able data speculative scheduling before reload. +This results in generation of @code{ld.a} instructions and +the corresponding check instructions (@code{ld.c} / @code{chk.a}). +The default setting is disabled. + +@item -msched-ar-data-spec +@itemx -mno-sched-ar-data-spec +@opindex msched-ar-data-spec +@opindex mno-sched-ar-data-spec +(En/Dis)able data speculative scheduling after reload. +This results in generation of @code{ld.a} instructions and +the corresponding check instructions (@code{ld.c} / @code{chk.a}). +The default setting is enabled. + +@item -mno-sched-control-spec +@itemx -msched-control-spec +@opindex mno-sched-control-spec +@opindex msched-control-spec +(Dis/En)able control speculative scheduling. This feature is +available only during region scheduling (i.e.@: before reload). +This results in generation of the @code{ld.s} instructions and +the corresponding check instructions @code{chk.s}. +The default setting is disabled. + +@item -msched-br-in-data-spec +@itemx -mno-sched-br-in-data-spec +@opindex msched-br-in-data-spec +@opindex mno-sched-br-in-data-spec +(En/Dis)able speculative scheduling of the instructions that +are dependent on the data speculative loads before reload. +This is effective only with @option{-msched-br-data-spec} enabled. +The default setting is enabled. + +@item -msched-ar-in-data-spec +@itemx -mno-sched-ar-in-data-spec +@opindex msched-ar-in-data-spec +@opindex mno-sched-ar-in-data-spec +(En/Dis)able speculative scheduling of the instructions that +are dependent on the data speculative loads after reload. +This is effective only with @option{-msched-ar-data-spec} enabled. +The default setting is enabled. + +@item -msched-in-control-spec +@itemx -mno-sched-in-control-spec +@opindex msched-in-control-spec +@opindex mno-sched-in-control-spec +(En/Dis)able speculative scheduling of the instructions that +are dependent on the control speculative loads. +This is effective only with @option{-msched-control-spec} enabled. +The default setting is enabled. + +@item -mno-sched-prefer-non-data-spec-insns +@itemx -msched-prefer-non-data-spec-insns +@opindex mno-sched-prefer-non-data-spec-insns +@opindex msched-prefer-non-data-spec-insns +If enabled, data-speculative instructions are chosen for schedule +only if there are no other choices at the moment. This makes +the use of the data speculation much more conservative. +The default setting is disabled. + +@item -mno-sched-prefer-non-control-spec-insns +@itemx -msched-prefer-non-control-spec-insns +@opindex mno-sched-prefer-non-control-spec-insns +@opindex msched-prefer-non-control-spec-insns +If enabled, control-speculative instructions are chosen for schedule +only if there are no other choices at the moment. This makes +the use of the control speculation much more conservative. +The default setting is disabled. + +@item -mno-sched-count-spec-in-critical-path +@itemx -msched-count-spec-in-critical-path +@opindex mno-sched-count-spec-in-critical-path +@opindex msched-count-spec-in-critical-path +If enabled, speculative dependencies are considered during +computation of the instructions priorities. This makes the use of the +speculation a bit more conservative. +The default setting is disabled. + +@item -msched-spec-ldc +@opindex msched-spec-ldc +Use a simple data speculation check. This option is on by default. + +@item -msched-control-spec-ldc +@opindex msched-spec-ldc +Use a simple check for control speculation. This option is on by default. + +@item -msched-stop-bits-after-every-cycle +@opindex msched-stop-bits-after-every-cycle +Place a stop bit after every cycle when scheduling. This option is on +by default. + +@item -msched-fp-mem-deps-zero-cost +@opindex msched-fp-mem-deps-zero-cost +Assume that floating-point stores and loads are not likely to cause a conflict +when placed into the same instruction group. This option is disabled by +default. + +@item -msel-sched-dont-check-control-spec +@opindex msel-sched-dont-check-control-spec +Generate checks for control speculation in selective scheduling. +This flag is disabled by default. + +@item -msched-max-memory-insns=@var{max-insns} +@opindex msched-max-memory-insns +Limit on the number of memory insns per instruction group, giving lower +priority to subsequent memory insns attempting to schedule in the same +instruction group. Frequently useful to prevent cache bank conflicts. +The default value is 1. + +@item -msched-max-memory-insns-hard-limit +@opindex msched-max-memory-insns-hard-limit +Makes the limit specified by @option{msched-max-memory-insns} a hard limit, +disallowing more than that number in an instruction group. +Otherwise, the limit is ``soft'', meaning that non-memory operations +are preferred when the limit is reached, but memory operations may still +be scheduled. + +@end table + +@node LM32 Options +@subsection LM32 Options +@cindex LM32 options + +These @option{-m} options are defined for the LatticeMico32 architecture: + +@table @gcctabopt +@item -mbarrel-shift-enabled +@opindex mbarrel-shift-enabled +Enable barrel-shift instructions. + +@item -mdivide-enabled +@opindex mdivide-enabled +Enable divide and modulus instructions. + +@item -mmultiply-enabled +@opindex multiply-enabled +Enable multiply instructions. + +@item -msign-extend-enabled +@opindex msign-extend-enabled +Enable sign extend instructions. + +@item -muser-enabled +@opindex muser-enabled +Enable user-defined instructions. + +@end table + +@node LoongArch Options +@subsection LoongArch Options +@cindex LoongArch Options + +These command-line options are defined for LoongArch targets: + +@table @gcctabopt +@item -march=@var{cpu-type} +@opindex -march +Generate instructions for the machine type @var{cpu-type}. In contrast to +@option{-mtune=@var{cpu-type}}, which merely tunes the generated code +for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC +to generate code that may not run at all on processors other than the one +indicated. Specifying @option{-march=@var{cpu-type}} implies +@option{-mtune=@var{cpu-type}}, except where noted otherwise. + +The choices for @var{cpu-type} are: + +@table @samp +@item native +This selects the CPU to generate code for at compilation time by determining +the processor type of the compiling machine. Using @option{-march=native} +enables all instruction subsets supported by the local machine (hence +the result might not run on different machines). Using @option{-mtune=native} +produces code optimized for the local machine under the constraints +of the selected instruction set. +@item loongarch64 +A generic CPU with 64-bit extensions. +@item la464 +LoongArch LA464 CPU with LBT, LSX, LASX, LVZ. +@end table + +@item -mtune=@var{cpu-type} +@opindex mtune +Optimize the output for the given processor, specified by microarchitecture +name. + +@item -mabi=@var{base-abi-type} +@opindex mabi +Generate code for the specified calling convention. +@var{base-abi-type} can be one of: +@table @samp +@item lp64d +Uses 64-bit general purpose registers and 32/64-bit floating-point +registers for parameter passing. Data model is LP64, where @samp{int} +is 32 bits, while @samp{long int} and pointers are 64 bits. +@item lp64f +Uses 64-bit general purpose registers and 32-bit floating-point +registers for parameter passing. Data model is LP64, where @samp{int} +is 32 bits, while @samp{long int} and pointers are 64 bits. +@item lp64s +Uses 64-bit general purpose registers and no floating-point +registers for parameter passing. Data model is LP64, where @samp{int} +is 32 bits, while @samp{long int} and pointers are 64 bits. +@end table + +@item -mfpu=@var{fpu-type} +@opindex mfpu +Generate code for the specified FPU type, which can be one of: +@table @samp +@item 64 +Allow the use of hardware floating-point instructions for 32-bit +and 64-bit operations. +@item 32 +Allow the use of hardware floating-point instructions for 32-bit +operations. +@item none +@item 0 +Prevent the use of hardware floating-point instructions. +@end table + +@item -msoft-float +@opindex msoft-float +Force @option{-mfpu=none} and prevents the use of floating-point +registers for parameter passing. This option may change the target +ABI. + +@item -msingle-float +@opindex -msingle-float +Force @option{-mfpu=32} and allow the use of 32-bit floating-point +registers for parameter passing. This option may change the target +ABI. + +@item -mdouble-float +@opindex -mdouble-float +Force @option{-mfpu=64} and allow the use of 32/64-bit floating-point +registers for parameter passing. This option may change the target +ABI. + +@item -mbranch-cost=@var{n} +@opindex -mbranch-cost +Set the cost of branches to roughly @var{n} instructions. + +@item -mcheck-zero-division +@itemx -mno-check-zero-divison +@opindex -mcheck-zero-division +Trap (do not trap) on integer division by zero. The default is +@option{-mcheck-zero-division} for @option{-O0} or @option{-Og}, and +@option{-mno-check-zero-division} for other optimization levels. + +@item -mcond-move-int +@itemx -mno-cond-move-int +@opindex -mcond-move-int +Conditional moves for integral data in general-purpose registers +are enabled (disabled). The default is @option{-mcond-move-int}. + +@item -mcond-move-float +@itemx -mno-cond-move-float +@opindex -mcond-move-float +Conditional moves for floating-point registers are enabled (disabled). +The default is @option{-mcond-move-float}. + +@item -mmemcpy +@itemx -mno-memcpy +@opindex -mmemcpy +Force (do not force) the use of @code{memcpy} for non-trivial block moves. +The default is @option{-mno-memcpy}, which allows GCC to inline most +constant-sized copies. Setting optimization level to @option{-Os} also +forces the use of @code{memcpy}, but @option{-mno-memcpy} may override this +behavior if explicitly specified, regardless of the order these options on +the command line. + +@item -mstrict-align +@itemx -mno-strict-align +@opindex -mstrict-align +Avoid or allow generating memory accesses that may not be aligned on a natural +object boundary as described in the architecture specification. The default is +@option{-mno-strict-align}. + +@item -msmall-data-limit=@var{number} +@opindex -msmall-data-limit +Put global and static data smaller than @var{number} bytes into a special +section (on some targets). The default value is 0. + +@item -mmax-inline-memcpy-size=@var{n} +@opindex -mmax-inline-memcpy-size +Inline all block moves (such as calls to @code{memcpy} or structure copies) +less than or equal to @var{n} bytes. The default value of @var{n} is 1024. + +@item -mcmodel=@var{code-model} +Set the code model to one of: +@table @samp +@item tiny-static (Not implemented yet) +@item tiny (Not implemented yet) + +@item normal +The text segment must be within 128MB addressing space. The data segment must +be within 2GB addressing space. + +@item medium +The text segment and data segment must be within 2GB addressing space. + +@item large (Not implemented yet) + +@item extreme +This mode does not limit the size of the code segment and data segment. +The @option{-mcmodel=extreme} option is incompatible with @option{-fplt} and +@option{-mno-explicit-relocs}. +@end table +The default code model is @code{normal}. + +@item -mexplicit-relocs +@itemx -mno-explicit-relocs +@opindex mexplicit-relocs +@opindex mno-explicit-relocs +Use or do not use assembler relocation operators when dealing with symbolic +addresses. The alternative is to use assembler macros instead, which may +limit optimization. The default value for the option is determined during +GCC build-time by detecting corresponding assembler support: +@code{-mexplicit-relocs} if said support is present, +@code{-mno-explicit-relocs} otherwise. This option is mostly useful for +debugging, or interoperation with assemblers different from the build-time +one. + +@item -mdirect-extern-access +@itemx -mno-direct-extern-access +@opindex mdirect-extern-access +Do not use or use GOT to access external symbols. The default is +@option{-mno-direct-extern-access}: GOT is used for external symbols with +default visibility, but not used for other external symbols. + +With @option{-mdirect-extern-access}, GOT is not used and all external +symbols are PC-relatively addressed. It is @strong{only} suitable for +environments where no dynamic link is performed, like firmwares, OS +kernels, executables linked with @option{-static} or @option{-static-pie}. +@option{-mdirect-extern-access} is not compatible with @option{-fPIC} or +@option{-fpic}. +@end table + +@node M32C Options +@subsection M32C Options +@cindex M32C options + +@table @gcctabopt +@item -mcpu=@var{name} +@opindex mcpu= +Select the CPU for which code is generated. @var{name} may be one of +@samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to +/60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for +the M32C/80 series. + +@item -msim +@opindex msim +Specifies that the program will be run on the simulator. This causes +an alternate runtime library to be linked in which supports, for +example, file I/O@. You must not use this option when generating +programs that will run on real hardware; you must provide your own +runtime library for whatever I/O functions are needed. + +@item -memregs=@var{number} +@opindex memregs= +Specifies the number of memory-based pseudo-registers GCC uses +during code generation. These pseudo-registers are used like real +registers, so there is a tradeoff between GCC's ability to fit the +code into available registers, and the performance penalty of using +memory instead of registers. Note that all modules in a program must +be compiled with the same value for this option. Because of that, you +must not use this option with GCC's default runtime libraries. + +@end table + +@node M32R/D Options +@subsection M32R/D Options +@cindex M32R/D options + +These @option{-m} options are defined for Renesas M32R/D architectures: + +@table @gcctabopt +@item -m32r2 +@opindex m32r2 +Generate code for the M32R/2@. + +@item -m32rx +@opindex m32rx +Generate code for the M32R/X@. + +@item -m32r +@opindex m32r +Generate code for the M32R@. This is the default. + +@item -mmodel=small +@opindex mmodel=small +Assume all objects live in the lower 16MB of memory (so that their addresses +can be loaded with the @code{ld24} instruction), and assume all subroutines +are reachable with the @code{bl} instruction. +This is the default. + +The addressability of a particular object can be set with the +@code{model} attribute. + +@item -mmodel=medium +@opindex mmodel=medium +Assume objects may be anywhere in the 32-bit address space (the compiler +generates @code{seth/add3} instructions to load their addresses), and +assume all subroutines are reachable with the @code{bl} instruction. + +@item -mmodel=large +@opindex mmodel=large +Assume objects may be anywhere in the 32-bit address space (the compiler +generates @code{seth/add3} instructions to load their addresses), and +assume subroutines may not be reachable with the @code{bl} instruction +(the compiler generates the much slower @code{seth/add3/jl} +instruction sequence). + +@item -msdata=none +@opindex msdata=none +Disable use of the small data area. Variables are put into +one of @code{.data}, @code{.bss}, or @code{.rodata} (unless the +@code{section} attribute has been specified). +This is the default. + +The small data area consists of sections @code{.sdata} and @code{.sbss}. +Objects may be explicitly put in the small data area with the +@code{section} attribute using one of these sections. + +@item -msdata=sdata +@opindex msdata=sdata +Put small global and static data in the small data area, but do not +generate special code to reference them. + +@item -msdata=use +@opindex msdata=use +Put small global and static data in the small data area, and generate +special instructions to reference them. + +@item -G @var{num} +@opindex G +@cindex smaller data references +Put global and static objects less than or equal to @var{num} bytes +into the small data or BSS sections instead of the normal data or BSS +sections. The default value of @var{num} is 8. +The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} +for this option to have any effect. + +All modules should be compiled with the same @option{-G @var{num}} value. +Compiling with different values of @var{num} may or may not work; if it +doesn't the linker gives an error message---incorrect code is not +generated. + +@item -mdebug +@opindex mdebug +Makes the M32R-specific code in the compiler display some statistics +that might help in debugging programs. + +@item -malign-loops +@opindex malign-loops +Align all loops to a 32-byte boundary. + +@item -mno-align-loops +@opindex mno-align-loops +Do not enforce a 32-byte alignment for loops. This is the default. + +@item -missue-rate=@var{number} +@opindex missue-rate=@var{number} +Issue @var{number} instructions per cycle. @var{number} can only be 1 +or 2. + +@item -mbranch-cost=@var{number} +@opindex mbranch-cost=@var{number} +@var{number} can only be 1 or 2. If it is 1 then branches are +preferred over conditional code, if it is 2, then the opposite applies. + +@item -mflush-trap=@var{number} +@opindex mflush-trap=@var{number} +Specifies the trap number to use to flush the cache. The default is +12. Valid numbers are between 0 and 15 inclusive. + +@item -mno-flush-trap +@opindex mno-flush-trap +Specifies that the cache cannot be flushed by using a trap. + +@item -mflush-func=@var{name} +@opindex mflush-func=@var{name} +Specifies the name of the operating system function to call to flush +the cache. The default is @samp{_flush_cache}, but a function call +is only used if a trap is not available. + +@item -mno-flush-func +@opindex mno-flush-func +Indicates that there is no OS function for flushing the cache. + +@end table + +@node M680x0 Options +@subsection M680x0 Options +@cindex M680x0 options + +These are the @samp{-m} options defined for M680x0 and ColdFire processors. +The default settings depend on which architecture was selected when +the compiler was configured; the defaults for the most common choices +are given below. + +@table @gcctabopt +@item -march=@var{arch} +@opindex march +Generate code for a specific M680x0 or ColdFire instruction set +architecture. Permissible values of @var{arch} for M680x0 +architectures are: @samp{68000}, @samp{68010}, @samp{68020}, +@samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire +architectures are selected according to Freescale's ISA classification +and the permissible values are: @samp{isaa}, @samp{isaaplus}, +@samp{isab} and @samp{isac}. + +GCC defines a macro @code{__mcf@var{arch}__} whenever it is generating +code for a ColdFire target. The @var{arch} in this macro is one of the +@option{-march} arguments given above. + +When used together, @option{-march} and @option{-mtune} select code +that runs on a family of similar processors but that is optimized +for a particular microarchitecture. + +@item -mcpu=@var{cpu} +@opindex mcpu +Generate code for a specific M680x0 or ColdFire processor. +The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020}, +@samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332} +and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table +below, which also classifies the CPUs into families: + +@multitable @columnfractions 0.20 0.80 +@headitem @strong{Family} @tab @strong{@samp{-mcpu} arguments} +@item @samp{51} @tab @samp{51} @samp{51ac} @samp{51ag} @samp{51cn} @samp{51em} @samp{51je} @samp{51jf} @samp{51jg} @samp{51jm} @samp{51mm} @samp{51qe} @samp{51qm} +@item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206} +@item @samp{5206e} @tab @samp{5206e} +@item @samp{5208} @tab @samp{5207} @samp{5208} +@item @samp{5211a} @tab @samp{5210a} @samp{5211a} +@item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213} +@item @samp{5216} @tab @samp{5214} @samp{5216} +@item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235} +@item @samp{5225} @tab @samp{5224} @samp{5225} +@item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259} +@item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x} +@item @samp{5249} @tab @samp{5249} +@item @samp{5250} @tab @samp{5250} +@item @samp{5271} @tab @samp{5270} @samp{5271} +@item @samp{5272} @tab @samp{5272} +@item @samp{5275} @tab @samp{5274} @samp{5275} +@item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x} +@item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017} +@item @samp{5307} @tab @samp{5307} +@item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x} +@item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x} +@item @samp{5407} @tab @samp{5407} +@item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485} +@end multitable + +@option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if +@var{arch} is compatible with @var{cpu}. Other combinations of +@option{-mcpu} and @option{-march} are rejected. + +GCC defines the macro @code{__mcf_cpu_@var{cpu}} when ColdFire target +@var{cpu} is selected. It also defines @code{__mcf_family_@var{family}}, +where the value of @var{family} is given by the table above. + +@item -mtune=@var{tune} +@opindex mtune +Tune the code for a particular microarchitecture within the +constraints set by @option{-march} and @option{-mcpu}. +The M680x0 microarchitectures are: @samp{68000}, @samp{68010}, +@samp{68020}, @samp{68030}, @samp{68040}, @samp{68060} +and @samp{cpu32}. The ColdFire microarchitectures +are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}. + +You can also use @option{-mtune=68020-40} for code that needs +to run relatively well on 68020, 68030 and 68040 targets. +@option{-mtune=68020-60} is similar but includes 68060 targets +as well. These two options select the same tuning decisions as +@option{-m68020-40} and @option{-m68020-60} respectively. + +GCC defines the macros @code{__mc@var{arch}} and @code{__mc@var{arch}__} +when tuning for 680x0 architecture @var{arch}. It also defines +@code{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std} +option is used. If GCC is tuning for a range of architectures, +as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60}, +it defines the macros for every architecture in the range. + +GCC also defines the macro @code{__m@var{uarch}__} when tuning for +ColdFire microarchitecture @var{uarch}, where @var{uarch} is one +of the arguments given above. + +@item -m68000 +@itemx -mc68000 +@opindex m68000 +@opindex mc68000 +Generate output for a 68000. This is the default +when the compiler is configured for 68000-based systems. +It is equivalent to @option{-march=68000}. + +Use this option for microcontrollers with a 68000 or EC000 core, +including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. + +@item -m68010 +@opindex m68010 +Generate output for a 68010. This is the default +when the compiler is configured for 68010-based systems. +It is equivalent to @option{-march=68010}. + +@item -m68020 +@itemx -mc68020 +@opindex m68020 +@opindex mc68020 +Generate output for a 68020. This is the default +when the compiler is configured for 68020-based systems. +It is equivalent to @option{-march=68020}. + +@item -m68030 +@opindex m68030 +Generate output for a 68030. This is the default when the compiler is +configured for 68030-based systems. It is equivalent to +@option{-march=68030}. + +@item -m68040 +@opindex m68040 +Generate output for a 68040. This is the default when the compiler is +configured for 68040-based systems. It is equivalent to +@option{-march=68040}. + +This option inhibits the use of 68881/68882 instructions that have to be +emulated by software on the 68040. Use this option if your 68040 does not +have code to emulate those instructions. + +@item -m68060 +@opindex m68060 +Generate output for a 68060. This is the default when the compiler is +configured for 68060-based systems. It is equivalent to +@option{-march=68060}. + +This option inhibits the use of 68020 and 68881/68882 instructions that +have to be emulated by software on the 68060. Use this option if your 68060 +does not have code to emulate those instructions. + +@item -mcpu32 +@opindex mcpu32 +Generate output for a CPU32. This is the default +when the compiler is configured for CPU32-based systems. +It is equivalent to @option{-march=cpu32}. + +Use this option for microcontrollers with a +CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, +68336, 68340, 68341, 68349 and 68360. + +@item -m5200 +@opindex m5200 +Generate output for a 520X ColdFire CPU@. This is the default +when the compiler is configured for 520X-based systems. +It is equivalent to @option{-mcpu=5206}, and is now deprecated +in favor of that option. + +Use this option for microcontroller with a 5200 core, including +the MCF5202, MCF5203, MCF5204 and MCF5206. + +@item -m5206e +@opindex m5206e +Generate output for a 5206e ColdFire CPU@. The option is now +deprecated in favor of the equivalent @option{-mcpu=5206e}. + +@item -m528x +@opindex m528x +Generate output for a member of the ColdFire 528X family. +The option is now deprecated in favor of the equivalent +@option{-mcpu=528x}. + +@item -m5307 +@opindex m5307 +Generate output for a ColdFire 5307 CPU@. The option is now deprecated +in favor of the equivalent @option{-mcpu=5307}. + +@item -m5407 +@opindex m5407 +Generate output for a ColdFire 5407 CPU@. The option is now deprecated +in favor of the equivalent @option{-mcpu=5407}. + +@item -mcfv4e +@opindex mcfv4e +Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x). +This includes use of hardware floating-point instructions. +The option is equivalent to @option{-mcpu=547x}, and is now +deprecated in favor of that option. + +@item -m68020-40 +@opindex m68020-40 +Generate output for a 68040, without using any of the new instructions. +This results in code that can run relatively efficiently on either a +68020/68881 or a 68030 or a 68040. The generated code does use the +68881 instructions that are emulated on the 68040. + +The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}. + +@item -m68020-60 +@opindex m68020-60 +Generate output for a 68060, without using any of the new instructions. +This results in code that can run relatively efficiently on either a +68020/68881 or a 68030 or a 68040. The generated code does use the +68881 instructions that are emulated on the 68060. + +The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}. + +@item -mhard-float +@itemx -m68881 +@opindex mhard-float +@opindex m68881 +Generate floating-point instructions. This is the default for 68020 +and above, and for ColdFire devices that have an FPU@. It defines the +macro @code{__HAVE_68881__} on M680x0 targets and @code{__mcffpu__} +on ColdFire targets. + +@item -msoft-float +@opindex msoft-float +Do not generate floating-point instructions; use library calls instead. +This is the default for 68000, 68010, and 68832 targets. It is also +the default for ColdFire devices that have no FPU. + +@item -mdiv +@itemx -mno-div +@opindex mdiv +@opindex mno-div +Generate (do not generate) ColdFire hardware divide and remainder +instructions. If @option{-march} is used without @option{-mcpu}, +the default is ``on'' for ColdFire architectures and ``off'' for M680x0 +architectures. Otherwise, the default is taken from the target CPU +(either the default CPU, or the one specified by @option{-mcpu}). For +example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for +@option{-mcpu=5206e}. + +GCC defines the macro @code{__mcfhwdiv__} when this option is enabled. + +@item -mshort +@opindex mshort +Consider type @code{int} to be 16 bits wide, like @code{short int}. +Additionally, parameters passed on the stack are also aligned to a +16-bit boundary even on targets whose API mandates promotion to 32-bit. + +@item -mno-short +@opindex mno-short +Do not consider type @code{int} to be 16 bits wide. This is the default. + +@item -mnobitfield +@itemx -mno-bitfield +@opindex mnobitfield +@opindex mno-bitfield +Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} +and @option{-m5200} options imply @w{@option{-mnobitfield}}. + +@item -mbitfield +@opindex mbitfield +Do use the bit-field instructions. The @option{-m68020} option implies +@option{-mbitfield}. This is the default if you use a configuration +designed for a 68020. + +@item -mrtd +@opindex mrtd +Use a different function-calling convention, in which functions +that take a fixed number of arguments return with the @code{rtd} +instruction, which pops their arguments while returning. This +saves one instruction in the caller since there is no need to pop +the arguments there. + +This calling convention is incompatible with the one normally +used on Unix, so you cannot use it if you need to call libraries +compiled with the Unix compiler. + +Also, you must provide function prototypes for all functions that +take variable numbers of arguments (including @code{printf}); +otherwise incorrect code is generated for calls to those +functions. + +In addition, seriously incorrect code results if you call a +function with too many arguments. (Normally, extra arguments are +harmlessly ignored.) + +The @code{rtd} instruction is supported by the 68010, 68020, 68030, +68040, 68060 and CPU32 processors, but not by the 68000 or 5200. + +The default is @option{-mno-rtd}. + +@item -malign-int +@itemx -mno-align-int +@opindex malign-int +@opindex mno-align-int +Control whether GCC aligns @code{int}, @code{long}, @code{long long}, +@code{float}, @code{double}, and @code{long double} variables on a 32-bit +boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). +Aligning variables on 32-bit boundaries produces code that runs somewhat +faster on processors with 32-bit busses at the expense of more memory. + +@strong{Warning:} if you use the @option{-malign-int} switch, GCC +aligns structures containing the above types differently than +most published application binary interface specifications for the m68k. + +@opindex mpcrel +Use the pc-relative addressing mode of the 68000 directly, instead of +using a global offset table. At present, this option implies @option{-fpic}, +allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is +not presently supported with @option{-mpcrel}, though this could be supported for +68020 and higher processors. + +@item -mno-strict-align +@itemx -mstrict-align +@opindex mno-strict-align +@opindex mstrict-align +Do not (do) assume that unaligned memory references are handled by +the system. + +@item -msep-data +Generate code that allows the data segment to be located in a different +area of memory from the text segment. This allows for execute-in-place in +an environment without virtual memory management. This option implies +@option{-fPIC}. + +@item -mno-sep-data +Generate code that assumes that the data segment follows the text segment. +This is the default. + +@item -mid-shared-library +Generate code that supports shared libraries via the library ID method. +This allows for execute-in-place and shared libraries in an environment +without virtual memory management. This option implies @option{-fPIC}. + +@item -mno-id-shared-library +Generate code that doesn't assume ID-based shared libraries are being used. +This is the default. + +@item -mshared-library-id=n +Specifies the identification number of the ID-based shared library being +compiled. Specifying a value of 0 generates more compact code; specifying +other values forces the allocation of that number to the current +library, but is no more space- or time-efficient than omitting this option. + +@item -mxgot +@itemx -mno-xgot +@opindex mxgot +@opindex mno-xgot +When generating position-independent code for ColdFire, generate code +that works if the GOT has more than 8192 entries. This code is +larger and slower than code generated without this option. On M680x0 +processors, this option is not needed; @option{-fPIC} suffices. + +GCC normally uses a single instruction to load values from the GOT@. +While this is relatively efficient, it only works if the GOT +is smaller than about 64k. Anything larger causes the linker +to report an error such as: + +@cindex relocation truncated to fit (ColdFire) +@smallexample +relocation truncated to fit: R_68K_GOT16O foobar +@end smallexample + +If this happens, you should recompile your code with @option{-mxgot}. +It should then work with very large GOTs. However, code generated with +@option{-mxgot} is less efficient, since it takes 4 instructions to fetch +the value of a global symbol. + +Note that some linkers, including newer versions of the GNU linker, +can create multiple GOTs and sort GOT entries. If you have such a linker, +you should only need to use @option{-mxgot} when compiling a single +object file that accesses more than 8192 GOT entries. Very few do. + +These options have no effect unless GCC is generating +position-independent code. + +@item -mlong-jump-table-offsets +@opindex mlong-jump-table-offsets +Use 32-bit offsets in @code{switch} tables. The default is to use +16-bit offsets. + +@end table + +@node MCore Options +@subsection MCore Options +@cindex MCore options + +These are the @samp{-m} options defined for the Motorola M*Core +processors. + +@table @gcctabopt + +@item -mhardlit +@itemx -mno-hardlit +@opindex mhardlit +@opindex mno-hardlit +Inline constants into the code stream if it can be done in two +instructions or less. + +@item -mdiv +@itemx -mno-div +@opindex mdiv +@opindex mno-div +Use the divide instruction. (Enabled by default). + +@item -mrelax-immediate +@itemx -mno-relax-immediate +@opindex mrelax-immediate +@opindex mno-relax-immediate +Allow arbitrary-sized immediates in bit operations. + +@item -mwide-bitfields +@itemx -mno-wide-bitfields +@opindex mwide-bitfields +@opindex mno-wide-bitfields +Always treat bit-fields as @code{int}-sized. + +@item -m4byte-functions +@itemx -mno-4byte-functions +@opindex m4byte-functions +@opindex mno-4byte-functions +Force all functions to be aligned to a 4-byte boundary. + +@item -mcallgraph-data +@itemx -mno-callgraph-data +@opindex mcallgraph-data +@opindex mno-callgraph-data +Emit callgraph information. + +@item -mslow-bytes +@itemx -mno-slow-bytes +@opindex mslow-bytes +@opindex mno-slow-bytes +Prefer word access when reading byte quantities. + +@item -mlittle-endian +@itemx -mbig-endian +@opindex mlittle-endian +@opindex mbig-endian +Generate code for a little-endian target. + +@item -m210 +@itemx -m340 +@opindex m210 +@opindex m340 +Generate code for the 210 processor. + +@item -mno-lsim +@opindex mno-lsim +Assume that runtime support has been provided and so omit the +simulator library (@file{libsim.a)} from the linker command line. + +@item -mstack-increment=@var{size} +@opindex mstack-increment +Set the maximum amount for a single stack increment operation. Large +values can increase the speed of programs that contain functions +that need a large amount of stack space, but they can also trigger a +segmentation fault if the stack is extended too much. The default +value is 0x1000. + +@end table + +@node MeP Options +@subsection MeP Options +@cindex MeP options + +@table @gcctabopt + +@item -mabsdiff +@opindex mabsdiff +Enables the @code{abs} instruction, which is the absolute difference +between two registers. + +@item -mall-opts +@opindex mall-opts +Enables all the optional instructions---average, multiply, divide, bit +operations, leading zero, absolute difference, min/max, clip, and +saturation. + + +@item -maverage +@opindex maverage +Enables the @code{ave} instruction, which computes the average of two +registers. + +@item -mbased=@var{n} +@opindex mbased= +Variables of size @var{n} bytes or smaller are placed in the +@code{.based} section by default. Based variables use the @code{$tp} +register as a base register, and there is a 128-byte limit to the +@code{.based} section. + +@item -mbitops +@opindex mbitops +Enables the bit operation instructions---bit test (@code{btstm}), set +(@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and +test-and-set (@code{tas}). + +@item -mc=@var{name} +@opindex mc= +Selects which section constant data is placed in. @var{name} may +be @samp{tiny}, @samp{near}, or @samp{far}. + +@item -mclip +@opindex mclip +Enables the @code{clip} instruction. Note that @option{-mclip} is not +useful unless you also provide @option{-mminmax}. + +@item -mconfig=@var{name} +@opindex mconfig= +Selects one of the built-in core configurations. Each MeP chip has +one or more modules in it; each module has a core CPU and a variety of +coprocessors, optional instructions, and peripherals. The +@code{MeP-Integrator} tool, not part of GCC, provides these +configurations through this option; using this option is the same as +using all the corresponding command-line options. The default +configuration is @samp{default}. + +@item -mcop +@opindex mcop +Enables the coprocessor instructions. By default, this is a 32-bit +coprocessor. Note that the coprocessor is normally enabled via the +@option{-mconfig=} option. + +@item -mcop32 +@opindex mcop32 +Enables the 32-bit coprocessor's instructions. + +@item -mcop64 +@opindex mcop64 +Enables the 64-bit coprocessor's instructions. + +@item -mivc2 +@opindex mivc2 +Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor. + +@item -mdc +@opindex mdc +Causes constant variables to be placed in the @code{.near} section. + +@item -mdiv +@opindex mdiv +Enables the @code{div} and @code{divu} instructions. + +@item -meb +@opindex meb +Generate big-endian code. + +@item -mel +@opindex mel +Generate little-endian code. + +@item -mio-volatile +@opindex mio-volatile +Tells the compiler that any variable marked with the @code{io} +attribute is to be considered volatile. + +@item -ml +@opindex ml +Causes variables to be assigned to the @code{.far} section by default. + +@item -mleadz +@opindex mleadz +Enables the @code{leadz} (leading zero) instruction. + +@item -mm +@opindex mm +Causes variables to be assigned to the @code{.near} section by default. + +@item -mminmax +@opindex mminmax +Enables the @code{min} and @code{max} instructions. + +@item -mmult +@opindex mmult +Enables the multiplication and multiply-accumulate instructions. + +@item -mno-opts +@opindex mno-opts +Disables all the optional instructions enabled by @option{-mall-opts}. + +@item -mrepeat +@opindex mrepeat +Enables the @code{repeat} and @code{erepeat} instructions, used for +low-overhead looping. + +@item -ms +@opindex ms +Causes all variables to default to the @code{.tiny} section. Note +that there is a 65536-byte limit to this section. Accesses to these +variables use the @code{%gp} base register. + +@item -msatur +@opindex msatur +Enables the saturation instructions. Note that the compiler does not +currently generate these itself, but this option is included for +compatibility with other tools, like @code{as}. + +@item -msdram +@opindex msdram +Link the SDRAM-based runtime instead of the default ROM-based runtime. + +@item -msim +@opindex msim +Link the simulator run-time libraries. + +@item -msimnovec +@opindex msimnovec +Link the simulator runtime libraries, excluding built-in support +for reset and exception vectors and tables. + +@item -mtf +@opindex mtf +Causes all functions to default to the @code{.far} section. Without +this option, functions default to the @code{.near} section. + +@item -mtiny=@var{n} +@opindex mtiny= +Variables that are @var{n} bytes or smaller are allocated to the +@code{.tiny} section. These variables use the @code{$gp} base +register. The default for this option is 4, but note that there's a +65536-byte limit to the @code{.tiny} section. + +@end table + +@node MicroBlaze Options +@subsection MicroBlaze Options +@cindex MicroBlaze Options + +@table @gcctabopt + +@item -msoft-float +@opindex msoft-float +Use software emulation for floating point (default). + +@item -mhard-float +@opindex mhard-float +Use hardware floating-point instructions. + +@item -mmemcpy +@opindex mmemcpy +Do not optimize block moves, use @code{memcpy}. + +@item -mno-clearbss +@opindex mno-clearbss +This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead. + +@item -mcpu=@var{cpu-type} +@opindex mcpu= +Use features of, and schedule code for, the given CPU. +Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}}, +where @var{X} is a major version, @var{YY} is the minor version, and +@var{Z} is compatibility code. Example values are @samp{v3.00.a}, +@samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v6.00.a}. + +@item -mxl-soft-mul +@opindex mxl-soft-mul +Use software multiply emulation (default). + +@item -mxl-soft-div +@opindex mxl-soft-div +Use software emulation for divides (default). + +@item -mxl-barrel-shift +@opindex mxl-barrel-shift +Use the hardware barrel shifter. + +@item -mxl-pattern-compare +@opindex mxl-pattern-compare +Use pattern compare instructions. + +@item -msmall-divides +@opindex msmall-divides +Use table lookup optimization for small signed integer divisions. + +@item -mxl-stack-check +@opindex mxl-stack-check +This option is deprecated. Use @option{-fstack-check} instead. + +@item -mxl-gp-opt +@opindex mxl-gp-opt +Use GP-relative @code{.sdata}/@code{.sbss} sections. + +@item -mxl-multiply-high +@opindex mxl-multiply-high +Use multiply high instructions for high part of 32x32 multiply. + +@item -mxl-float-convert +@opindex mxl-float-convert +Use hardware floating-point conversion instructions. + +@item -mxl-float-sqrt +@opindex mxl-float-sqrt +Use hardware floating-point square root instruction. + +@item -mbig-endian +@opindex mbig-endian +Generate code for a big-endian target. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code for a little-endian target. + +@item -mxl-reorder +@opindex mxl-reorder +Use reorder instructions (swap and byte reversed load/store). + +@item -mxl-mode-@var{app-model} +Select application model @var{app-model}. Valid models are +@table @samp +@item executable +normal executable (default), uses startup code @file{crt0.o}. + +@item xmdstub +for use with Xilinx Microprocessor Debugger (XMD) based +software intrusive debug agent called xmdstub. This uses startup file +@file{crt1.o} and sets the start address of the program to 0x800. + +@item bootstrap +for applications that are loaded using a bootloader. +This model uses startup file @file{crt2.o} which does not contain a processor +reset vector handler. This is suitable for transferring control on a +processor reset to the bootloader rather than the application. + +@item novectors +for applications that do not require any of the +MicroBlaze vectors. This option may be useful for applications running +within a monitoring application. This model uses @file{crt3.o} as a startup file. +@end table + +Option @option{-xl-mode-@var{app-model}} is a deprecated alias for +@option{-mxl-mode-@var{app-model}}. + +@item -mpic-data-is-text-relative +@opindex mpic-data-is-text-relative +Assume that the displacement between the text and data segments is fixed +at static link time. This allows data to be referenced by offset from start of +text address instead of GOT since PC-relative addressing is not supported. + +@end table + +@node MIPS Options +@subsection MIPS Options +@cindex MIPS options + +@table @gcctabopt + +@item -EB +@opindex EB +Generate big-endian code. + +@item -EL +@opindex EL +Generate little-endian code. This is the default for @samp{mips*el-*-*} +configurations. + +@item -march=@var{arch} +@opindex march +Generate code that runs on @var{arch}, which can be the name of a +generic MIPS ISA, or the name of a particular processor. +The ISA names are: +@samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, +@samp{mips32}, @samp{mips32r2}, @samp{mips32r3}, @samp{mips32r5}, +@samp{mips32r6}, @samp{mips64}, @samp{mips64r2}, @samp{mips64r3}, +@samp{mips64r5} and @samp{mips64r6}. +The processor names are: +@samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc}, +@samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd}, +@samp{5kc}, @samp{5kf}, +@samp{20kc}, +@samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1}, +@samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1}, +@samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn}, +@samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2}, +@samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1}, +@samp{i6400}, @samp{i6500}, +@samp{interaptiv}, +@samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a}, @samp{gs464}, +@samp{gs464e}, @samp{gs264e}, +@samp{m4k}, +@samp{m14k}, @samp{m14kc}, @samp{m14ke}, @samp{m14kec}, +@samp{m5100}, @samp{m5101}, +@samp{octeon}, @samp{octeon+}, @samp{octeon2}, @samp{octeon3}, +@samp{orion}, +@samp{p5600}, @samp{p6600}, +@samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400}, +@samp{r4600}, @samp{r4650}, @samp{r4700}, @samp{r5900}, +@samp{r6000}, @samp{r8000}, +@samp{rm7000}, @samp{rm9000}, +@samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000}, +@samp{sb1}, +@samp{sr71000}, +@samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300}, +@samp{vr5000}, @samp{vr5400}, @samp{vr5500}, +@samp{xlr} and @samp{xlp}. +The special value @samp{from-abi} selects the +most compatible architecture for the selected ABI (that is, +@samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@. + +The native Linux/GNU toolchain also supports the value @samp{native}, +which selects the best architecture option for the host processor. +@option{-march=native} has no effect if GCC does not recognize +the processor. + +In processor names, a final @samp{000} can be abbreviated as @samp{k} +(for example, @option{-march=r2k}). Prefixes are optional, and +@samp{vr} may be written @samp{r}. + +Names of the form @samp{@var{n}f2_1} refer to processors with +FPUs clocked at half the rate of the core, names of the form +@samp{@var{n}f1_1} refer to processors with FPUs clocked at the same +rate as the core, and names of the form @samp{@var{n}f3_2} refer to +processors with FPUs clocked a ratio of 3:2 with respect to the core. +For compatibility reasons, @samp{@var{n}f} is accepted as a synonym +for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are +accepted as synonyms for @samp{@var{n}f1_1}. + +GCC defines two macros based on the value of this option. The first +is @code{_MIPS_ARCH}, which gives the name of target architecture, as +a string. The second has the form @code{_MIPS_ARCH_@var{foo}}, +where @var{foo} is the capitalized value of @code{_MIPS_ARCH}@. +For example, @option{-march=r2000} sets @code{_MIPS_ARCH} +to @code{"r2000"} and defines the macro @code{_MIPS_ARCH_R2000}. + +Note that the @code{_MIPS_ARCH} macro uses the processor names given +above. In other words, it has the full prefix and does not +abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi}, +the macro names the resolved architecture (either @code{"mips1"} or +@code{"mips3"}). It names the default architecture when no +@option{-march} option is given. + +@item -mtune=@var{arch} +@opindex mtune +Optimize for @var{arch}. Among other things, this option controls +the way instructions are scheduled, and the perceived cost of arithmetic +operations. The list of @var{arch} values is the same as for +@option{-march}. + +When this option is not used, GCC optimizes for the processor +specified by @option{-march}. By using @option{-march} and +@option{-mtune} together, it is possible to generate code that +runs on a family of processors, but optimize the code for one +particular member of that family. + +@option{-mtune} defines the macros @code{_MIPS_TUNE} and +@code{_MIPS_TUNE_@var{foo}}, which work in the same way as the +@option{-march} ones described above. + +@item -mips1 +@opindex mips1 +Equivalent to @option{-march=mips1}. + +@item -mips2 +@opindex mips2 +Equivalent to @option{-march=mips2}. + +@item -mips3 +@opindex mips3 +Equivalent to @option{-march=mips3}. + +@item -mips4 +@opindex mips4 +Equivalent to @option{-march=mips4}. + +@item -mips32 +@opindex mips32 +Equivalent to @option{-march=mips32}. + +@item -mips32r3 +@opindex mips32r3 +Equivalent to @option{-march=mips32r3}. + +@item -mips32r5 +@opindex mips32r5 +Equivalent to @option{-march=mips32r5}. + +@item -mips32r6 +@opindex mips32r6 +Equivalent to @option{-march=mips32r6}. + +@item -mips64 +@opindex mips64 +Equivalent to @option{-march=mips64}. + +@item -mips64r2 +@opindex mips64r2 +Equivalent to @option{-march=mips64r2}. + +@item -mips64r3 +@opindex mips64r3 +Equivalent to @option{-march=mips64r3}. + +@item -mips64r5 +@opindex mips64r5 +Equivalent to @option{-march=mips64r5}. + +@item -mips64r6 +@opindex mips64r6 +Equivalent to @option{-march=mips64r6}. + +@item -mips16 +@itemx -mno-mips16 +@opindex mips16 +@opindex mno-mips16 +Generate (do not generate) MIPS16 code. If GCC is targeting a +MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@. + +MIPS16 code generation can also be controlled on a per-function basis +by means of @code{mips16} and @code{nomips16} attributes. +@xref{Function Attributes}, for more information. + +@item -mflip-mips16 +@opindex mflip-mips16 +Generate MIPS16 code on alternating functions. This option is provided +for regression testing of mixed MIPS16/non-MIPS16 code generation, and is +not intended for ordinary use in compiling user code. + +@item -minterlink-compressed +@itemx -mno-interlink-compressed +@opindex minterlink-compressed +@opindex mno-interlink-compressed +Require (do not require) that code using the standard (uncompressed) MIPS ISA +be link-compatible with MIPS16 and microMIPS code, and vice versa. + +For example, code using the standard ISA encoding cannot jump directly +to MIPS16 or microMIPS code; it must either use a call or an indirect jump. +@option{-minterlink-compressed} therefore disables direct jumps unless GCC +knows that the target of the jump is not compressed. + +@item -minterlink-mips16 +@itemx -mno-interlink-mips16 +@opindex minterlink-mips16 +@opindex mno-interlink-mips16 +Aliases of @option{-minterlink-compressed} and +@option{-mno-interlink-compressed}. These options predate the microMIPS ASE +and are retained for backwards compatibility. + +@item -mabi=32 +@itemx -mabi=o64 +@itemx -mabi=n32 +@itemx -mabi=64 +@itemx -mabi=eabi +@opindex mabi=32 +@opindex mabi=o64 +@opindex mabi=n32 +@opindex mabi=64 +@opindex mabi=eabi +Generate code for the given ABI@. + +Note that the EABI has a 32-bit and a 64-bit variant. GCC normally +generates 64-bit code when you select a 64-bit architecture, but you +can use @option{-mgp32} to get 32-bit code instead. + +For information about the O64 ABI, see +@uref{https://gcc.gnu.org/@/projects/@/mipso64-abi.html}. + +GCC supports a variant of the o32 ABI in which floating-point registers +are 64 rather than 32 bits wide. You can select this combination with +@option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1} +and @code{mfhc1} instructions and is therefore only supported for +MIPS32R2, MIPS32R3 and MIPS32R5 processors. + +The register assignments for arguments and return values remain the +same, but each scalar value is passed in a single 64-bit register +rather than a pair of 32-bit registers. For example, scalar +floating-point values are returned in @samp{$f0} only, not a +@samp{$f0}/@samp{$f1} pair. The set of call-saved registers also +remains the same in that the even-numbered double-precision registers +are saved. + +Two additional variants of the o32 ABI are supported to enable +a transition from 32-bit to 64-bit registers. These are FPXX +(@option{-mfpxx}) and FP64A (@option{-mfp64} @option{-mno-odd-spreg}). +The FPXX extension mandates that all code must execute correctly +when run using 32-bit or 64-bit registers. The code can be interlinked +with either FP32 or FP64, but not both. +The FP64A extension is similar to the FP64 extension but forbids the +use of odd-numbered single-precision registers. This can be used +in conjunction with the @code{FRE} mode of FPUs in MIPS32R5 +processors and allows both FP32 and FP64A code to interlink and +run in the same process without changing FPU modes. + +@item -mabicalls +@itemx -mno-abicalls +@opindex mabicalls +@opindex mno-abicalls +Generate (do not generate) code that is suitable for SVR4-style +dynamic objects. @option{-mabicalls} is the default for SVR4-based +systems. + +@item -mshared +@itemx -mno-shared +Generate (do not generate) code that is fully position-independent, +and that can therefore be linked into shared libraries. This option +only affects @option{-mabicalls}. + +All @option{-mabicalls} code has traditionally been position-independent, +regardless of options like @option{-fPIC} and @option{-fpic}. However, +as an extension, the GNU toolchain allows executables to use absolute +accesses for locally-binding symbols. It can also use shorter GP +initialization sequences and generate direct calls to locally-defined +functions. This mode is selected by @option{-mno-shared}. + +@option{-mno-shared} depends on binutils 2.16 or higher and generates +objects that can only be linked by the GNU linker. However, the option +does not affect the ABI of the final executable; it only affects the ABI +of relocatable objects. Using @option{-mno-shared} generally makes +executables both smaller and quicker. + +@option{-mshared} is the default. + +@item -mplt +@itemx -mno-plt +@opindex mplt +@opindex mno-plt +Assume (do not assume) that the static and dynamic linkers +support PLTs and copy relocations. This option only affects +@option{-mno-shared -mabicalls}. For the n64 ABI, this option +has no effect without @option{-msym32}. + +You can make @option{-mplt} the default by configuring +GCC with @option{--with-mips-plt}. The default is +@option{-mno-plt} otherwise. + +@item -mxgot +@itemx -mno-xgot +@opindex mxgot +@opindex mno-xgot +Lift (do not lift) the usual restrictions on the size of the global +offset table. + +GCC normally uses a single instruction to load values from the GOT@. +While this is relatively efficient, it only works if the GOT +is smaller than about 64k. Anything larger causes the linker +to report an error such as: + +@cindex relocation truncated to fit (MIPS) +@smallexample +relocation truncated to fit: R_MIPS_GOT16 foobar +@end smallexample + +If this happens, you should recompile your code with @option{-mxgot}. +This works with very large GOTs, although the code is also +less efficient, since it takes three instructions to fetch the +value of a global symbol. + +Note that some linkers can create multiple GOTs. If you have such a +linker, you should only need to use @option{-mxgot} when a single object +file accesses more than 64k's worth of GOT entries. Very few do. + +These options have no effect unless GCC is generating position +independent code. + +@item -mgp32 +@opindex mgp32 +Assume that general-purpose registers are 32 bits wide. + +@item -mgp64 +@opindex mgp64 +Assume that general-purpose registers are 64 bits wide. + +@item -mfp32 +@opindex mfp32 +Assume that floating-point registers are 32 bits wide. + +@item -mfp64 +@opindex mfp64 +Assume that floating-point registers are 64 bits wide. + +@item -mfpxx +@opindex mfpxx +Do not assume the width of floating-point registers. + +@item -mhard-float +@opindex mhard-float +Use floating-point coprocessor instructions. + +@item -msoft-float +@opindex msoft-float +Do not use floating-point coprocessor instructions. Implement +floating-point calculations using library calls instead. + +@item -mno-float +@opindex mno-float +Equivalent to @option{-msoft-float}, but additionally asserts that the +program being compiled does not perform any floating-point operations. +This option is presently supported only by some bare-metal MIPS +configurations, where it may select a special set of libraries +that lack all floating-point support (including, for example, the +floating-point @code{printf} formats). +If code compiled with @option{-mno-float} accidentally contains +floating-point operations, it is likely to suffer a link-time +or run-time failure. + +@item -msingle-float +@opindex msingle-float +Assume that the floating-point coprocessor only supports single-precision +operations. + +@item -mdouble-float +@opindex mdouble-float +Assume that the floating-point coprocessor supports double-precision +operations. This is the default. + +@item -modd-spreg +@itemx -mno-odd-spreg +@opindex modd-spreg +@opindex mno-odd-spreg +Enable the use of odd-numbered single-precision floating-point registers +for the o32 ABI. This is the default for processors that are known to +support these registers. When using the o32 FPXX ABI, @option{-mno-odd-spreg} +is set by default. + +@item -mabs=2008 +@itemx -mabs=legacy +@opindex mabs=2008 +@opindex mabs=legacy +These options control the treatment of the special not-a-number (NaN) +IEEE 754 floating-point data with the @code{abs.@i{fmt}} and +@code{neg.@i{fmt}} machine instructions. + +By default or when @option{-mabs=legacy} is used the legacy +treatment is selected. In this case these instructions are considered +arithmetic and avoided where correct operation is required and the +input operand might be a NaN. A longer sequence of instructions that +manipulate the sign bit of floating-point datum manually is used +instead unless the @option{-ffinite-math-only} option has also been +specified. + +The @option{-mabs=2008} option selects the IEEE 754-2008 treatment. In +this case these instructions are considered non-arithmetic and therefore +operating correctly in all cases, including in particular where the +input operand is a NaN. These instructions are therefore always used +for the respective operations. + +@item -mnan=2008 +@itemx -mnan=legacy +@opindex mnan=2008 +@opindex mnan=legacy +These options control the encoding of the special not-a-number (NaN) +IEEE 754 floating-point data. + +The @option{-mnan=legacy} option selects the legacy encoding. In this +case quiet NaNs (qNaNs) are denoted by the first bit of their trailing +significand field being 0, whereas signaling NaNs (sNaNs) are denoted +by the first bit of their trailing significand field being 1. + +The @option{-mnan=2008} option selects the IEEE 754-2008 encoding. In +this case qNaNs are denoted by the first bit of their trailing +significand field being 1, whereas sNaNs are denoted by the first bit of +their trailing significand field being 0. + +The default is @option{-mnan=legacy} unless GCC has been configured with +@option{--with-nan=2008}. + +@item -mllsc +@itemx -mno-llsc +@opindex mllsc +@opindex mno-llsc +Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to +implement atomic memory built-in functions. When neither option is +specified, GCC uses the instructions if the target architecture +supports them. + +@option{-mllsc} is useful if the runtime environment can emulate the +instructions and @option{-mno-llsc} can be useful when compiling for +nonstandard ISAs. You can make either option the default by +configuring GCC with @option{--with-llsc} and @option{--without-llsc} +respectively. @option{--with-llsc} is the default for some +configurations; see the installation documentation for details. + +@item -mdsp +@itemx -mno-dsp +@opindex mdsp +@opindex mno-dsp +Use (do not use) revision 1 of the MIPS DSP ASE@. +@xref{MIPS DSP Built-in Functions}. This option defines the +preprocessor macro @code{__mips_dsp}. It also defines +@code{__mips_dsp_rev} to 1. + +@item -mdspr2 +@itemx -mno-dspr2 +@opindex mdspr2 +@opindex mno-dspr2 +Use (do not use) revision 2 of the MIPS DSP ASE@. +@xref{MIPS DSP Built-in Functions}. This option defines the +preprocessor macros @code{__mips_dsp} and @code{__mips_dspr2}. +It also defines @code{__mips_dsp_rev} to 2. + +@item -msmartmips +@itemx -mno-smartmips +@opindex msmartmips +@opindex mno-smartmips +Use (do not use) the MIPS SmartMIPS ASE. + +@item -mpaired-single +@itemx -mno-paired-single +@opindex mpaired-single +@opindex mno-paired-single +Use (do not use) paired-single floating-point instructions. +@xref{MIPS Paired-Single Support}. This option requires +hardware floating-point support to be enabled. + +@item -mdmx +@itemx -mno-mdmx +@opindex mdmx +@opindex mno-mdmx +Use (do not use) MIPS Digital Media Extension instructions. +This option can only be used when generating 64-bit code and requires +hardware floating-point support to be enabled. + +@item -mips3d +@itemx -mno-mips3d +@opindex mips3d +@opindex mno-mips3d +Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}. +The option @option{-mips3d} implies @option{-mpaired-single}. + +@item -mmicromips +@itemx -mno-micromips +@opindex mmicromips +@opindex mno-mmicromips +Generate (do not generate) microMIPS code. + +MicroMIPS code generation can also be controlled on a per-function basis +by means of @code{micromips} and @code{nomicromips} attributes. +@xref{Function Attributes}, for more information. + +@item -mmt +@itemx -mno-mt +@opindex mmt +@opindex mno-mt +Use (do not use) MT Multithreading instructions. + +@item -mmcu +@itemx -mno-mcu +@opindex mmcu +@opindex mno-mcu +Use (do not use) the MIPS MCU ASE instructions. + +@item -meva +@itemx -mno-eva +@opindex meva +@opindex mno-eva +Use (do not use) the MIPS Enhanced Virtual Addressing instructions. + +@item -mvirt +@itemx -mno-virt +@opindex mvirt +@opindex mno-virt +Use (do not use) the MIPS Virtualization (VZ) instructions. + +@item -mxpa +@itemx -mno-xpa +@opindex mxpa +@opindex mno-xpa +Use (do not use) the MIPS eXtended Physical Address (XPA) instructions. + +@item -mcrc +@itemx -mno-crc +@opindex mcrc +@opindex mno-crc +Use (do not use) the MIPS Cyclic Redundancy Check (CRC) instructions. + +@item -mginv +@itemx -mno-ginv +@opindex mginv +@opindex mno-ginv +Use (do not use) the MIPS Global INValidate (GINV) instructions. + +@item -mloongson-mmi +@itemx -mno-loongson-mmi +@opindex mloongson-mmi +@opindex mno-loongson-mmi +Use (do not use) the MIPS Loongson MultiMedia extensions Instructions (MMI). + +@item -mloongson-ext +@itemx -mno-loongson-ext +@opindex mloongson-ext +@opindex mno-loongson-ext +Use (do not use) the MIPS Loongson EXTensions (EXT) instructions. + +@item -mloongson-ext2 +@itemx -mno-loongson-ext2 +@opindex mloongson-ext2 +@opindex mno-loongson-ext2 +Use (do not use) the MIPS Loongson EXTensions r2 (EXT2) instructions. + +@item -mlong64 +@opindex mlong64 +Force @code{long} types to be 64 bits wide. See @option{-mlong32} for +an explanation of the default and the way that the pointer size is +determined. + +@item -mlong32 +@opindex mlong32 +Force @code{long}, @code{int}, and pointer types to be 32 bits wide. + +The default size of @code{int}s, @code{long}s and pointers depends on +the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI +uses 64-bit @code{long}s, as does the 64-bit EABI; the others use +32-bit @code{long}s. Pointers are the same size as @code{long}s, +or the same size as integer registers, whichever is smaller. + +@item -msym32 +@itemx -mno-sym32 +@opindex msym32 +@opindex mno-sym32 +Assume (do not assume) that all symbols have 32-bit values, regardless +of the selected ABI@. This option is useful in combination with +@option{-mabi=64} and @option{-mno-abicalls} because it allows GCC +to generate shorter and faster references to symbolic addresses. + +@item -G @var{num} +@opindex G +Put definitions of externally-visible data in a small data section +if that data is no bigger than @var{num} bytes. GCC can then generate +more efficient accesses to the data; see @option{-mgpopt} for details. + +The default @option{-G} option depends on the configuration. + +@item -mlocal-sdata +@itemx -mno-local-sdata +@opindex mlocal-sdata +@opindex mno-local-sdata +Extend (do not extend) the @option{-G} behavior to local data too, +such as to static variables in C@. @option{-mlocal-sdata} is the +default for all configurations. + +If the linker complains that an application is using too much small data, +you might want to try rebuilding the less performance-critical parts with +@option{-mno-local-sdata}. You might also want to build large +libraries with @option{-mno-local-sdata}, so that the libraries leave +more room for the main program. + +@item -mextern-sdata +@itemx -mno-extern-sdata +@opindex mextern-sdata +@opindex mno-extern-sdata +Assume (do not assume) that externally-defined data is in +a small data section if the size of that data is within the @option{-G} limit. +@option{-mextern-sdata} is the default for all configurations. + +If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G +@var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var} +that is no bigger than @var{num} bytes, you must make sure that @var{Var} +is placed in a small data section. If @var{Var} is defined by another +module, you must either compile that module with a high-enough +@option{-G} setting or attach a @code{section} attribute to @var{Var}'s +definition. If @var{Var} is common, you must link the application +with a high-enough @option{-G} setting. + +The easiest way of satisfying these restrictions is to compile +and link every module with the same @option{-G} option. However, +you may wish to build a library that supports several different +small data limits. You can do this by compiling the library with +the highest supported @option{-G} setting and additionally using +@option{-mno-extern-sdata} to stop the library from making assumptions +about externally-defined data. + +@item -mgpopt +@itemx -mno-gpopt +@opindex mgpopt +@opindex mno-gpopt +Use (do not use) GP-relative accesses for symbols that are known to be +in a small data section; see @option{-G}, @option{-mlocal-sdata} and +@option{-mextern-sdata}. @option{-mgpopt} is the default for all +configurations. + +@option{-mno-gpopt} is useful for cases where the @code{$gp} register +might not hold the value of @code{_gp}. For example, if the code is +part of a library that might be used in a boot monitor, programs that +call boot monitor routines pass an unknown value in @code{$gp}. +(In such situations, the boot monitor itself is usually compiled +with @option{-G0}.) + +@option{-mno-gpopt} implies @option{-mno-local-sdata} and +@option{-mno-extern-sdata}. + +@item -membedded-data +@itemx -mno-embedded-data +@opindex membedded-data +@opindex mno-embedded-data +Allocate variables to the read-only data section first if possible, then +next in the small data section if possible, otherwise in data. This gives +slightly slower code than the default, but reduces the amount of RAM required +when executing, and thus may be preferred for some embedded systems. + +@item -muninit-const-in-rodata +@itemx -mno-uninit-const-in-rodata +@opindex muninit-const-in-rodata +@opindex mno-uninit-const-in-rodata +Put uninitialized @code{const} variables in the read-only data section. +This option is only meaningful in conjunction with @option{-membedded-data}. + +@item -mcode-readable=@var{setting} +@opindex mcode-readable +Specify whether GCC may generate code that reads from executable sections. +There are three possible settings: + +@table @gcctabopt +@item -mcode-readable=yes +Instructions may freely access executable sections. This is the +default setting. + +@item -mcode-readable=pcrel +MIPS16 PC-relative load instructions can access executable sections, +but other instructions must not do so. This option is useful on 4KSc +and 4KSd processors when the code TLBs have the Read Inhibit bit set. +It is also useful on processors that can be configured to have a dual +instruction/data SRAM interface and that, like the M4K, automatically +redirect PC-relative loads to the instruction RAM. + +@item -mcode-readable=no +Instructions must not access executable sections. This option can be +useful on targets that are configured to have a dual instruction/data +SRAM interface but that (unlike the M4K) do not automatically redirect +PC-relative loads to the instruction RAM. +@end table + +@item -msplit-addresses +@itemx -mno-split-addresses +@opindex msplit-addresses +@opindex mno-split-addresses +Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler +relocation operators. This option has been superseded by +@option{-mexplicit-relocs} but is retained for backwards compatibility. + +@item -mexplicit-relocs +@itemx -mno-explicit-relocs +@opindex mexplicit-relocs +@opindex mno-explicit-relocs +Use (do not use) assembler relocation operators when dealing with symbolic +addresses. The alternative, selected by @option{-mno-explicit-relocs}, +is to use assembler macros instead. + +@option{-mexplicit-relocs} is the default if GCC was configured +to use an assembler that supports relocation operators. + +@item -mcheck-zero-division +@itemx -mno-check-zero-division +@opindex mcheck-zero-division +@opindex mno-check-zero-division +Trap (do not trap) on integer division by zero. + +The default is @option{-mcheck-zero-division}. + +@item -mdivide-traps +@itemx -mdivide-breaks +@opindex mdivide-traps +@opindex mdivide-breaks +MIPS systems check for division by zero by generating either a +conditional trap or a break instruction. Using traps results in +smaller code, but is only supported on MIPS II and later. Also, some +versions of the Linux kernel have a bug that prevents trap from +generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to +allow conditional traps on architectures that support them and +@option{-mdivide-breaks} to force the use of breaks. + +The default is usually @option{-mdivide-traps}, but this can be +overridden at configure time using @option{--with-divide=breaks}. +Divide-by-zero checks can be completely disabled using +@option{-mno-check-zero-division}. + +@item -mload-store-pairs +@itemx -mno-load-store-pairs +@opindex mload-store-pairs +@opindex mno-load-store-pairs +Enable (disable) an optimization that pairs consecutive load or store +instructions to enable load/store bonding. This option is enabled by +default but only takes effect when the selected architecture is known +to support bonding. + +@item -munaligned-access +@itemx -mno-unaligned-access +@opindex munaligned-access +@opindex mno-unaligned-access +Enable (disable) direct unaligned access for MIPS Release 6. +MIPSr6 requires load/store unaligned-access support, +by hardware or trap&emulate. +So @option{-mno-unaligned-access} may be needed by kernel. + +@item -mmemcpy +@itemx -mno-memcpy +@opindex mmemcpy +@opindex mno-memcpy +Force (do not force) the use of @code{memcpy} for non-trivial block +moves. The default is @option{-mno-memcpy}, which allows GCC to inline +most constant-sized copies. + +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Disable (do not disable) use of the @code{jal} instruction. Calling +functions using @code{jal} is more efficient but requires the caller +and callee to be in the same 256 megabyte segment. + +This option has no effect on abicalls code. The default is +@option{-mno-long-calls}. + +@item -mmad +@itemx -mno-mad +@opindex mmad +@opindex mno-mad +Enable (disable) use of the @code{mad}, @code{madu} and @code{mul} +instructions, as provided by the R4650 ISA@. + +@item -mimadd +@itemx -mno-imadd +@opindex mimadd +@opindex mno-imadd +Enable (disable) use of the @code{madd} and @code{msub} integer +instructions. The default is @option{-mimadd} on architectures +that support @code{madd} and @code{msub} except for the 74k +architecture where it was found to generate slower code. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Enable (disable) use of the floating-point multiply-accumulate +instructions, when they are available. The default is +@option{-mfused-madd}. + +On the R8000 CPU when multiply-accumulate instructions are used, +the intermediate product is calculated to infinite precision +and is not subject to the FCSR Flush to Zero bit. This may be +undesirable in some circumstances. On other processors the result +is numerically identical to the equivalent computation using +separate multiply, add, subtract and negate instructions. + +@item -nocpp +@opindex nocpp +Tell the MIPS assembler to not run its preprocessor over user +assembler files (with a @samp{.s} suffix) when assembling them. + +@item -mfix-24k +@itemx -mno-fix-24k +@opindex mfix-24k +@opindex mno-fix-24k +Work around the 24K E48 (lost data on stores during refill) errata. +The workarounds are implemented by the assembler rather than by GCC@. + +@item -mfix-r4000 +@itemx -mno-fix-r4000 +@opindex mfix-r4000 +@opindex mno-fix-r4000 +Work around certain R4000 CPU errata: +@itemize @minus +@item +A double-word or a variable shift may give an incorrect result if executed +immediately after starting an integer division. +@item +A double-word or a variable shift may give an incorrect result if executed +while an integer multiplication is in progress. +@item +An integer division may give an incorrect result if started in a delay slot +of a taken branch or a jump. +@end itemize + +@item -mfix-r4400 +@itemx -mno-fix-r4400 +@opindex mfix-r4400 +@opindex mno-fix-r4400 +Work around certain R4400 CPU errata: +@itemize @minus +@item +A double-word or a variable shift may give an incorrect result if executed +immediately after starting an integer division. +@end itemize + +@item -mfix-r10000 +@itemx -mno-fix-r10000 +@opindex mfix-r10000 +@opindex mno-fix-r10000 +Work around certain R10000 errata: +@itemize @minus +@item +@code{ll}/@code{sc} sequences may not behave atomically on revisions +prior to 3.0. They may deadlock on revisions 2.6 and earlier. +@end itemize + +This option can only be used if the target architecture supports +branch-likely instructions. @option{-mfix-r10000} is the default when +@option{-march=r10000} is used; @option{-mno-fix-r10000} is the default +otherwise. + +@item -mfix-r5900 +@itemx -mno-fix-r5900 +@opindex mfix-r5900 +Do not attempt to schedule the preceding instruction into the delay slot +of a branch instruction placed at the end of a short loop of six +instructions or fewer and always schedule a @code{nop} instruction there +instead. The short loop bug under certain conditions causes loops to +execute only once or twice, due to a hardware bug in the R5900 chip. The +workaround is implemented by the assembler rather than by GCC@. + +@item -mfix-rm7000 +@itemx -mno-fix-rm7000 +@opindex mfix-rm7000 +Work around the RM7000 @code{dmult}/@code{dmultu} errata. The +workarounds are implemented by the assembler rather than by GCC@. + +@item -mfix-vr4120 +@itemx -mno-fix-vr4120 +@opindex mfix-vr4120 +Work around certain VR4120 errata: +@itemize @minus +@item +@code{dmultu} does not always produce the correct result. +@item +@code{div} and @code{ddiv} do not always produce the correct result if one +of the operands is negative. +@end itemize +The workarounds for the division errata rely on special functions in +@file{libgcc.a}. At present, these functions are only provided by +the @code{mips64vr*-elf} configurations. + +Other VR4120 errata require a NOP to be inserted between certain pairs of +instructions. These errata are handled by the assembler, not by GCC itself. + +@item -mfix-vr4130 +@opindex mfix-vr4130 +Work around the VR4130 @code{mflo}/@code{mfhi} errata. The +workarounds are implemented by the assembler rather than by GCC, +although GCC avoids using @code{mflo} and @code{mfhi} if the +VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi} +instructions are available instead. + +@item -mfix-sb1 +@itemx -mno-fix-sb1 +@opindex mfix-sb1 +Work around certain SB-1 CPU core errata. +(This flag currently works around the SB-1 revision 2 +``F1'' and ``F2'' floating-point errata.) + +@item -mr10k-cache-barrier=@var{setting} +@opindex mr10k-cache-barrier +Specify whether GCC should insert cache barriers to avoid the +side effects of speculation on R10K processors. + +In common with many processors, the R10K tries to predict the outcome +of a conditional branch and speculatively executes instructions from +the ``taken'' branch. It later aborts these instructions if the +predicted outcome is wrong. However, on the R10K, even aborted +instructions can have side effects. + +This problem only affects kernel stores and, depending on the system, +kernel loads. As an example, a speculatively-executed store may load +the target memory into cache and mark the cache line as dirty, even if +the store itself is later aborted. If a DMA operation writes to the +same area of memory before the ``dirty'' line is flushed, the cached +data overwrites the DMA-ed data. See the R10K processor manual +for a full description, including other potential problems. + +One workaround is to insert cache barrier instructions before every memory +access that might be speculatively executed and that might have side +effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}} +controls GCC's implementation of this workaround. It assumes that +aborted accesses to any byte in the following regions does not have +side effects: + +@enumerate +@item +the memory occupied by the current function's stack frame; + +@item +the memory occupied by an incoming stack argument; + +@item +the memory occupied by an object with a link-time-constant address. +@end enumerate + +It is the kernel's responsibility to ensure that speculative +accesses to these regions are indeed safe. + +If the input program contains a function declaration such as: + +@smallexample +void foo (void); +@end smallexample + +then the implementation of @code{foo} must allow @code{j foo} and +@code{jal foo} to be executed speculatively. GCC honors this +restriction for functions it compiles itself. It expects non-GCC +functions (such as hand-written assembly code) to do the same. + +The option has three forms: + +@table @gcctabopt +@item -mr10k-cache-barrier=load-store +Insert a cache barrier before a load or store that might be +speculatively executed and that might have side effects even +if aborted. + +@item -mr10k-cache-barrier=store +Insert a cache barrier before a store that might be speculatively +executed and that might have side effects even if aborted. + +@item -mr10k-cache-barrier=none +Disable the insertion of cache barriers. This is the default setting. +@end table + +@item -mflush-func=@var{func} +@itemx -mno-flush-func +@opindex mflush-func +Specifies the function to call to flush the I and D caches, or to not +call any such function. If called, the function must take the same +arguments as the common @code{_flush_func}, that is, the address of the +memory range for which the cache is being flushed, the size of the +memory range, and the number 3 (to flush both caches). The default +depends on the target GCC was configured for, but commonly is either +@code{_flush_func} or @code{__cpu_flush}. + +@item mbranch-cost=@var{num} +@opindex mbranch-cost +Set the cost of branches to roughly @var{num} ``simple'' instructions. +This cost is only a heuristic and is not guaranteed to produce +consistent results across releases. A zero cost redundantly selects +the default, which is based on the @option{-mtune} setting. + +@item -mbranch-likely +@itemx -mno-branch-likely +@opindex mbranch-likely +@opindex mno-branch-likely +Enable or disable use of Branch Likely instructions, regardless of the +default for the selected architecture. By default, Branch Likely +instructions may be generated if they are supported by the selected +architecture. An exception is for the MIPS32 and MIPS64 architectures +and processors that implement those architectures; for those, Branch +Likely instructions are not be generated by default because the MIPS32 +and MIPS64 architectures specifically deprecate their use. + +@item -mcompact-branches=never +@itemx -mcompact-branches=optimal +@itemx -mcompact-branches=always +@opindex mcompact-branches=never +@opindex mcompact-branches=optimal +@opindex mcompact-branches=always +These options control which form of branches will be generated. The +default is @option{-mcompact-branches=optimal}. + +The @option{-mcompact-branches=never} option ensures that compact branch +instructions will never be generated. + +The @option{-mcompact-branches=always} option ensures that a compact +branch instruction will be generated if available for MIPS Release 6 onwards. +If a compact branch instruction is not available (or pre-R6), +a delay slot form of the branch will be used instead. + +If it is used for MIPS16/microMIPS targets, it will be just ignored now. +The behaviour for MIPS16/microMIPS may change in future, +since they do have some compact branch instructions. + +The @option{-mcompact-branches=optimal} option will cause a delay slot +branch to be used if one is available in the current ISA and the delay +slot is successfully filled. If the delay slot is not filled, a compact +branch will be chosen if one is available. + +@item -mfp-exceptions +@itemx -mno-fp-exceptions +@opindex mfp-exceptions +Specifies whether FP exceptions are enabled. This affects how +FP instructions are scheduled for some processors. +The default is that FP exceptions are +enabled. + +For instance, on the SB-1, if FP exceptions are disabled, and we are emitting +64-bit code, then we can use both FP pipes. Otherwise, we can only use one +FP pipe. + +@item -mvr4130-align +@itemx -mno-vr4130-align +@opindex mvr4130-align +The VR4130 pipeline is two-way superscalar, but can only issue two +instructions together if the first one is 8-byte aligned. When this +option is enabled, GCC aligns pairs of instructions that it +thinks should execute in parallel. + +This option only has an effect when optimizing for the VR4130. +It normally makes code faster, but at the expense of making it bigger. +It is enabled by default at optimization level @option{-O3}. + +@item -msynci +@itemx -mno-synci +@opindex msynci +Enable (disable) generation of @code{synci} instructions on +architectures that support it. The @code{synci} instructions (if +enabled) are generated when @code{__builtin___clear_cache} is +compiled. + +This option defaults to @option{-mno-synci}, but the default can be +overridden by configuring GCC with @option{--with-synci}. + +When compiling code for single processor systems, it is generally safe +to use @code{synci}. However, on many multi-core (SMP) systems, it +does not invalidate the instruction caches on all cores and may lead +to undefined behavior. + +@item -mrelax-pic-calls +@itemx -mno-relax-pic-calls +@opindex mrelax-pic-calls +Try to turn PIC calls that are normally dispatched via register +@code{$25} into direct calls. This is only possible if the linker can +resolve the destination at link time and if the destination is within +range for a direct call. + +@option{-mrelax-pic-calls} is the default if GCC was configured to use +an assembler and a linker that support the @code{.reloc} assembly +directive and @option{-mexplicit-relocs} is in effect. With +@option{-mno-explicit-relocs}, this optimization can be performed by the +assembler and the linker alone without help from the compiler. + +@item -mmcount-ra-address +@itemx -mno-mcount-ra-address +@opindex mmcount-ra-address +@opindex mno-mcount-ra-address +Emit (do not emit) code that allows @code{_mcount} to modify the +calling function's return address. When enabled, this option extends +the usual @code{_mcount} interface with a new @var{ra-address} +parameter, which has type @code{intptr_t *} and is passed in register +@code{$12}. @code{_mcount} can then modify the return address by +doing both of the following: +@itemize +@item +Returning the new address in register @code{$31}. +@item +Storing the new address in @code{*@var{ra-address}}, +if @var{ra-address} is nonnull. +@end itemize + +The default is @option{-mno-mcount-ra-address}. + +@item -mframe-header-opt +@itemx -mno-frame-header-opt +@opindex mframe-header-opt +Enable (disable) frame header optimization in the o32 ABI. When using the +o32 ABI, calling functions will allocate 16 bytes on the stack for the called +function to write out register arguments. When enabled, this optimization +will suppress the allocation of the frame header if it can be determined that +it is unused. + +This optimization is off by default at all optimization levels. + +@item -mlxc1-sxc1 +@itemx -mno-lxc1-sxc1 +@opindex mlxc1-sxc1 +When applicable, enable (disable) the generation of @code{lwxc1}, +@code{swxc1}, @code{ldxc1}, @code{sdxc1} instructions. Enabled by default. + +@item -mmadd4 +@itemx -mno-madd4 +@opindex mmadd4 +When applicable, enable (disable) the generation of 4-operand @code{madd.s}, +@code{madd.d} and related instructions. Enabled by default. + +@end table + +@node MMIX Options +@subsection MMIX Options +@cindex MMIX Options + +These options are defined for the MMIX: + +@table @gcctabopt +@item -mlibfuncs +@itemx -mno-libfuncs +@opindex mlibfuncs +@opindex mno-libfuncs +Specify that intrinsic library functions are being compiled, passing all +values in registers, no matter the size. + +@item -mepsilon +@itemx -mno-epsilon +@opindex mepsilon +@opindex mno-epsilon +Generate floating-point comparison instructions that compare with respect +to the @code{rE} epsilon register. + +@item -mabi=mmixware +@itemx -mabi=gnu +@opindex mabi=mmixware +@opindex mabi=gnu +Generate code that passes function parameters and return values that (in +the called function) are seen as registers @code{$0} and up, as opposed to +the GNU ABI which uses global registers @code{$231} and up. + +@item -mzero-extend +@itemx -mno-zero-extend +@opindex mzero-extend +@opindex mno-zero-extend +When reading data from memory in sizes shorter than 64 bits, use (do not +use) zero-extending load instructions by default, rather than +sign-extending ones. + +@item -mknuthdiv +@itemx -mno-knuthdiv +@opindex mknuthdiv +@opindex mno-knuthdiv +Make the result of a division yielding a remainder have the same sign as +the divisor. With the default, @option{-mno-knuthdiv}, the sign of the +remainder follows the sign of the dividend. Both methods are +arithmetically valid, the latter being almost exclusively used. + +@item -mtoplevel-symbols +@itemx -mno-toplevel-symbols +@opindex mtoplevel-symbols +@opindex mno-toplevel-symbols +Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly +code can be used with the @code{PREFIX} assembly directive. + +@item -melf +@opindex melf +Generate an executable in the ELF format, rather than the default +@samp{mmo} format used by the @command{mmix} simulator. + +@item -mbranch-predict +@itemx -mno-branch-predict +@opindex mbranch-predict +@opindex mno-branch-predict +Use (do not use) the probable-branch instructions, when static branch +prediction indicates a probable branch. + +@item -mbase-addresses +@itemx -mno-base-addresses +@opindex mbase-addresses +@opindex mno-base-addresses +Generate (do not generate) code that uses @emph{base addresses}. Using a +base address automatically generates a request (handled by the assembler +and the linker) for a constant to be set up in a global register. The +register is used for one or more base address requests within the range 0 +to 255 from the value held in the register. The generally leads to short +and fast code, but the number of different data items that can be +addressed is limited. This means that a program that uses lots of static +data may require @option{-mno-base-addresses}. + +@item -msingle-exit +@itemx -mno-single-exit +@opindex msingle-exit +@opindex mno-single-exit +Force (do not force) generated code to have a single exit point in each +function. +@end table + +@node MN10300 Options +@subsection MN10300 Options +@cindex MN10300 options + +These @option{-m} options are defined for Matsushita MN10300 architectures: + +@table @gcctabopt +@item -mmult-bug +@opindex mmult-bug +Generate code to avoid bugs in the multiply instructions for the MN10300 +processors. This is the default. + +@item -mno-mult-bug +@opindex mno-mult-bug +Do not generate code to avoid bugs in the multiply instructions for the +MN10300 processors. + +@item -mam33 +@opindex mam33 +Generate code using features specific to the AM33 processor. + +@item -mno-am33 +@opindex mno-am33 +Do not generate code using features specific to the AM33 processor. This +is the default. + +@item -mam33-2 +@opindex mam33-2 +Generate code using features specific to the AM33/2.0 processor. + +@item -mam34 +@opindex mam34 +Generate code using features specific to the AM34 processor. + +@item -mtune=@var{cpu-type} +@opindex mtune +Use the timing characteristics of the indicated CPU type when +scheduling instructions. This does not change the targeted processor +type. The CPU type must be one of @samp{mn10300}, @samp{am33}, +@samp{am33-2} or @samp{am34}. + +@item -mreturn-pointer-on-d0 +@opindex mreturn-pointer-on-d0 +When generating a function that returns a pointer, return the pointer +in both @code{a0} and @code{d0}. Otherwise, the pointer is returned +only in @code{a0}, and attempts to call such functions without a prototype +result in errors. Note that this option is on by default; use +@option{-mno-return-pointer-on-d0} to disable it. + +@item -mno-crt0 +@opindex mno-crt0 +Do not link in the C run-time initialization object file. + +@item -mrelax +@opindex mrelax +Indicate to the linker that it should perform a relaxation optimization pass +to shorten branches, calls and absolute memory addresses. This option only +has an effect when used on the command line for the final link step. + +This option makes symbolic debugging impossible. + +@item -mliw +@opindex mliw +Allow the compiler to generate @emph{Long Instruction Word} +instructions if the target is the @samp{AM33} or later. This is the +default. This option defines the preprocessor macro @code{__LIW__}. + +@item -mno-liw +@opindex mno-liw +Do not allow the compiler to generate @emph{Long Instruction Word} +instructions. This option defines the preprocessor macro +@code{__NO_LIW__}. + +@item -msetlb +@opindex msetlb +Allow the compiler to generate the @emph{SETLB} and @emph{Lcc} +instructions if the target is the @samp{AM33} or later. This is the +default. This option defines the preprocessor macro @code{__SETLB__}. + +@item -mno-setlb +@opindex mno-setlb +Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc} +instructions. This option defines the preprocessor macro +@code{__NO_SETLB__}. + +@end table + +@node Moxie Options +@subsection Moxie Options +@cindex Moxie Options + +@table @gcctabopt + +@item -meb +@opindex meb +Generate big-endian code. This is the default for @samp{moxie-*-*} +configurations. + +@item -mel +@opindex mel +Generate little-endian code. + +@item -mmul.x +@opindex mmul.x +Generate mul.x and umul.x instructions. This is the default for +@samp{moxiebox-*-*} configurations. + +@item -mno-crt0 +@opindex mno-crt0 +Do not link in the C run-time initialization object file. + +@end table + +@node MSP430 Options +@subsection MSP430 Options +@cindex MSP430 Options + +These options are defined for the MSP430: + +@table @gcctabopt + +@item -masm-hex +@opindex masm-hex +Force assembly output to always use hex constants. Normally such +constants are signed decimals, but this option is available for +testsuite and/or aesthetic purposes. + +@item -mmcu= +@opindex mmcu= +Select the MCU to target. This is used to create a C preprocessor +symbol based upon the MCU name, converted to upper case and pre- and +post-fixed with @samp{__}. This in turn is used by the +@file{msp430.h} header file to select an MCU-specific supplementary +header file. + +The option also sets the ISA to use. If the MCU name is one that is +known to only support the 430 ISA then that is selected, otherwise the +430X ISA is selected. A generic MCU name of @samp{msp430} can also be +used to select the 430 ISA. Similarly the generic @samp{msp430x} MCU +name selects the 430X ISA. + +In addition an MCU-specific linker script is added to the linker +command line. The script's name is the name of the MCU with +@file{.ld} appended. Thus specifying @option{-mmcu=xxx} on the @command{gcc} +command line defines the C preprocessor symbol @code{__XXX__} and +cause the linker to search for a script called @file{xxx.ld}. + +The ISA and hardware multiply supported for the different MCUs is hard-coded +into GCC. However, an external @samp{devices.csv} file can be used to +extend device support beyond those that have been hard-coded. + +GCC searches for the @samp{devices.csv} file using the following methods in the +given precedence order, where the first method takes precendence over the +second which takes precedence over the third. + +@table @asis +@item Include path specified with @code{-I} and @code{-L} +@samp{devices.csv} will be searched for in each of the directories specified by +include paths and linker library search paths. +@item Path specified by the environment variable @samp{MSP430_GCC_INCLUDE_DIR} +Define the value of the global environment variable +@samp{MSP430_GCC_INCLUDE_DIR} +to the full path to the directory containing devices.csv, and GCC will search +this directory for devices.csv. If devices.csv is found, this directory will +also be registered as an include path, and linker library path. Header files +and linker scripts in this directory can therefore be used without manually +specifying @code{-I} and @code{-L} on the command line. +@item The @samp{msp430-elf@{,bare@}/include/devices} directory +Finally, GCC will examine @samp{msp430-elf@{,bare@}/include/devices} from the +toolchain root directory. This directory does not exist in a default +installation, but if the user has created it and copied @samp{devices.csv} +there, then the MCU data will be read. As above, this directory will +also be registered as an include path, and linker library path. + +@end table +If none of the above search methods find @samp{devices.csv}, then the +hard-coded MCU data is used. + + +@item -mwarn-mcu +@itemx -mno-warn-mcu +@opindex mwarn-mcu +@opindex mno-warn-mcu +This option enables or disables warnings about conflicts between the +MCU name specified by the @option{-mmcu} option and the ISA set by the +@option{-mcpu} option and/or the hardware multiply support set by the +@option{-mhwmult} option. It also toggles warnings about unrecognized +MCU names. This option is on by default. + +@item -mcpu= +@opindex mcpu= +Specifies the ISA to use. Accepted values are @samp{msp430}, +@samp{msp430x} and @samp{msp430xv2}. This option is deprecated. The +@option{-mmcu=} option should be used to select the ISA. + +@item -msim +@opindex msim +Link to the simulator runtime libraries and linker script. Overrides +any scripts that would be selected by the @option{-mmcu=} option. + +@item -mlarge +@opindex mlarge +Use large-model addressing (20-bit pointers, 20-bit @code{size_t}). + +@item -msmall +@opindex msmall +Use small-model addressing (16-bit pointers, 16-bit @code{size_t}). + +@item -mrelax +@opindex mrelax +This option is passed to the assembler and linker, and allows the +linker to perform certain optimizations that cannot be done until +the final link. + +@item mhwmult= +@opindex mhwmult= +Describes the type of hardware multiply supported by the target. +Accepted values are @samp{none} for no hardware multiply, @samp{16bit} +for the original 16-bit-only multiply supported by early MCUs. +@samp{32bit} for the 16/32-bit multiply supported by later MCUs and +@samp{f5series} for the 16/32-bit multiply supported by F5-series MCUs. +A value of @samp{auto} can also be given. This tells GCC to deduce +the hardware multiply support based upon the MCU name provided by the +@option{-mmcu} option. If no @option{-mmcu} option is specified or if +the MCU name is not recognized then no hardware multiply support is +assumed. @code{auto} is the default setting. + +Hardware multiplies are normally performed by calling a library +routine. This saves space in the generated code. When compiling at +@option{-O3} or higher however the hardware multiplier is invoked +inline. This makes for bigger, but faster code. + +The hardware multiply routines disable interrupts whilst running and +restore the previous interrupt state when they finish. This makes +them safe to use inside interrupt handlers as well as in normal code. + +@item -minrt +@opindex minrt +Enable the use of a minimum runtime environment - no static +initializers or constructors. This is intended for memory-constrained +devices. The compiler includes special symbols in some objects +that tell the linker and runtime which code fragments are required. + +@item -mtiny-printf +@opindex mtiny-printf +Enable reduced code size @code{printf} and @code{puts} library functions. +The @samp{tiny} implementations of these functions are not reentrant, so +must be used with caution in multi-threaded applications. + +Support for streams has been removed and the string to be printed will +always be sent to stdout via the @code{write} syscall. The string is not +buffered before it is sent to write. + +This option requires Newlib Nano IO, so GCC must be configured with +@samp{--enable-newlib-nano-formatted-io}. + +@item -mmax-inline-shift= +@opindex mmax-inline-shift= +This option takes an integer between 0 and 64 inclusive, and sets +the maximum number of inline shift instructions which should be emitted to +perform a shift operation by a constant amount. When this value needs to be +exceeded, an mspabi helper function is used instead. The default value is 4. + +This only affects cases where a shift by multiple positions cannot be +completed with a single instruction (e.g. all shifts >1 on the 430 ISA). + +Shifts of a 32-bit value are at least twice as costly, so the value passed for +this option is divided by 2 and the resulting value used instead. + +@item -mcode-region= +@itemx -mdata-region= +@opindex mcode-region +@opindex mdata-region +These options tell the compiler where to place functions and data that +do not have one of the @code{lower}, @code{upper}, @code{either} or +@code{section} attributes. Possible values are @code{lower}, +@code{upper}, @code{either} or @code{any}. The first three behave +like the corresponding attribute. The fourth possible value - +@code{any} - is the default. It leaves placement entirely up to the +linker script and how it assigns the standard sections +(@code{.text}, @code{.data}, etc) to the memory regions. + +@item -msilicon-errata= +@opindex msilicon-errata +This option passes on a request to assembler to enable the fixes for +the named silicon errata. + +@item -msilicon-errata-warn= +@opindex msilicon-errata-warn +This option passes on a request to the assembler to enable warning +messages when a silicon errata might need to be applied. + +@item -mwarn-devices-csv +@itemx -mno-warn-devices-csv +@opindex mwarn-devices-csv +@opindex mno-warn-devices-csv +Warn if @samp{devices.csv} is not found or there are problem parsing it +(default: on). + +@end table + +@node NDS32 Options +@subsection NDS32 Options +@cindex NDS32 Options + +These options are defined for NDS32 implementations: + +@table @gcctabopt + +@item -mbig-endian +@opindex mbig-endian +Generate code in big-endian mode. + +@item -mlittle-endian +@opindex mlittle-endian +Generate code in little-endian mode. + +@item -mreduced-regs +@opindex mreduced-regs +Use reduced-set registers for register allocation. + +@item -mfull-regs +@opindex mfull-regs +Use full-set registers for register allocation. + +@item -mcmov +@opindex mcmov +Generate conditional move instructions. + +@item -mno-cmov +@opindex mno-cmov +Do not generate conditional move instructions. + +@item -mext-perf +@opindex mext-perf +Generate performance extension instructions. + +@item -mno-ext-perf +@opindex mno-ext-perf +Do not generate performance extension instructions. + +@item -mext-perf2 +@opindex mext-perf2 +Generate performance extension 2 instructions. + +@item -mno-ext-perf2 +@opindex mno-ext-perf2 +Do not generate performance extension 2 instructions. + +@item -mext-string +@opindex mext-string +Generate string extension instructions. + +@item -mno-ext-string +@opindex mno-ext-string +Do not generate string extension instructions. + +@item -mv3push +@opindex mv3push +Generate v3 push25/pop25 instructions. + +@item -mno-v3push +@opindex mno-v3push +Do not generate v3 push25/pop25 instructions. + +@item -m16-bit +@opindex m16-bit +Generate 16-bit instructions. + +@item -mno-16-bit +@opindex mno-16-bit +Do not generate 16-bit instructions. + +@item -misr-vector-size=@var{num} +@opindex misr-vector-size +Specify the size of each interrupt vector, which must be 4 or 16. + +@item -mcache-block-size=@var{num} +@opindex mcache-block-size +Specify the size of each cache block, +which must be a power of 2 between 4 and 512. + +@item -march=@var{arch} +@opindex march +Specify the name of the target architecture. + +@item -mcmodel=@var{code-model} +@opindex mcmodel +Set the code model to one of +@table @asis +@item @samp{small} +All the data and read-only data segments must be within 512KB addressing space. +The text segment must be within 16MB addressing space. +@item @samp{medium} +The data segment must be within 512KB while the read-only data segment can be +within 4GB addressing space. The text segment should be still within 16MB +addressing space. +@item @samp{large} +All the text and data segments can be within 4GB addressing space. +@end table + +@item -mctor-dtor +@opindex mctor-dtor +Enable constructor/destructor feature. + +@item -mrelax +@opindex mrelax +Guide linker to relax instructions. + +@end table + +@node Nios II Options +@subsection Nios II Options +@cindex Nios II options +@cindex Altera Nios II options + +These are the options defined for the Altera Nios II processor. + +@table @gcctabopt + +@item -G @var{num} +@opindex G +@cindex smaller data references +Put global and static objects less than or equal to @var{num} bytes +into the small data or BSS sections instead of the normal data or BSS +sections. The default value of @var{num} is 8. + +@item -mgpopt=@var{option} +@itemx -mgpopt +@itemx -mno-gpopt +@opindex mgpopt +@opindex mno-gpopt +Generate (do not generate) GP-relative accesses. The following +@var{option} names are recognized: + +@table @samp + +@item none +Do not generate GP-relative accesses. + +@item local +Generate GP-relative accesses for small data objects that are not +external, weak, or uninitialized common symbols. +Also use GP-relative addressing for objects that +have been explicitly placed in a small data section via a @code{section} +attribute. + +@item global +As for @samp{local}, but also generate GP-relative accesses for +small data objects that are external, weak, or common. If you use this option, +you must ensure that all parts of your program (including libraries) are +compiled with the same @option{-G} setting. + +@item data +Generate GP-relative accesses for all data objects in the program. If you +use this option, the entire data and BSS segments +of your program must fit in 64K of memory and you must use an appropriate +linker script to allocate them within the addressable range of the +global pointer. + +@item all +Generate GP-relative addresses for function pointers as well as data +pointers. If you use this option, the entire text, data, and BSS segments +of your program must fit in 64K of memory and you must use an appropriate +linker script to allocate them within the addressable range of the +global pointer. + +@end table + +@option{-mgpopt} is equivalent to @option{-mgpopt=local}, and +@option{-mno-gpopt} is equivalent to @option{-mgpopt=none}. + +The default is @option{-mgpopt} except when @option{-fpic} or +@option{-fPIC} is specified to generate position-independent code. +Note that the Nios II ABI does not permit GP-relative accesses from +shared libraries. + +You may need to specify @option{-mno-gpopt} explicitly when building +programs that include large amounts of small data, including large +GOT data sections. In this case, the 16-bit offset for GP-relative +addressing may not be large enough to allow access to the entire +small data section. + +@item -mgprel-sec=@var{regexp} +@opindex mgprel-sec +This option specifies additional section names that can be accessed via +GP-relative addressing. It is most useful in conjunction with +@code{section} attributes on variable declarations +(@pxref{Common Variable Attributes}) and a custom linker script. +The @var{regexp} is a POSIX Extended Regular Expression. + +This option does not affect the behavior of the @option{-G} option, and +the specified sections are in addition to the standard @code{.sdata} +and @code{.sbss} small-data sections that are recognized by @option{-mgpopt}. + +@item -mr0rel-sec=@var{regexp} +@opindex mr0rel-sec +This option specifies names of sections that can be accessed via a +16-bit offset from @code{r0}; that is, in the low 32K or high 32K +of the 32-bit address space. It is most useful in conjunction with +@code{section} attributes on variable declarations +(@pxref{Common Variable Attributes}) and a custom linker script. +The @var{regexp} is a POSIX Extended Regular Expression. + +In contrast to the use of GP-relative addressing for small data, +zero-based addressing is never generated by default and there are no +conventional section names used in standard linker scripts for sections +in the low or high areas of memory. + +@item -mel +@itemx -meb +@opindex mel +@opindex meb +Generate little-endian (default) or big-endian (experimental) code, +respectively. + +@item -march=@var{arch} +@opindex march +This specifies the name of the target Nios II architecture. GCC uses this +name to determine what kind of instructions it can emit when generating +assembly code. Permissible names are: @samp{r1}, @samp{r2}. + +The preprocessor macro @code{__nios2_arch__} is available to programs, +with value 1 or 2, indicating the targeted ISA level. + +@item -mbypass-cache +@itemx -mno-bypass-cache +@opindex mno-bypass-cache +@opindex mbypass-cache +Force all load and store instructions to always bypass cache by +using I/O variants of the instructions. The default is not to +bypass the cache. + +@item -mno-cache-volatile +@itemx -mcache-volatile +@opindex mcache-volatile +@opindex mno-cache-volatile +Volatile memory access bypass the cache using the I/O variants of +the load and store instructions. The default is not to bypass the cache. + +@item -mno-fast-sw-div +@itemx -mfast-sw-div +@opindex mno-fast-sw-div +@opindex mfast-sw-div +Do not use table-based fast divide for small numbers. The default +is to use the fast divide at @option{-O3} and above. + +@item -mno-hw-mul +@itemx -mhw-mul +@itemx -mno-hw-mulx +@itemx -mhw-mulx +@itemx -mno-hw-div +@itemx -mhw-div +@opindex mno-hw-mul +@opindex mhw-mul +@opindex mno-hw-mulx +@opindex mhw-mulx +@opindex mno-hw-div +@opindex mhw-div +Enable or disable emitting @code{mul}, @code{mulx} and @code{div} family of +instructions by the compiler. The default is to emit @code{mul} +and not emit @code{div} and @code{mulx}. + +@item -mbmx +@itemx -mno-bmx +@itemx -mcdx +@itemx -mno-cdx +Enable or disable generation of Nios II R2 BMX (bit manipulation) and +CDX (code density) instructions. Enabling these instructions also +requires @option{-march=r2}. Since these instructions are optional +extensions to the R2 architecture, the default is not to emit them. + +@item -mcustom-@var{insn}=@var{N} +@itemx -mno-custom-@var{insn} +@opindex mcustom-@var{insn} +@opindex mno-custom-@var{insn} +Each @option{-mcustom-@var{insn}=@var{N}} option enables use of a +custom instruction with encoding @var{N} when generating code that uses +@var{insn}. For example, @option{-mcustom-fadds=253} generates custom +instruction 253 for single-precision floating-point add operations instead +of the default behavior of using a library call. + +The following values of @var{insn} are supported. Except as otherwise +noted, floating-point operations are expected to be implemented with +normal IEEE 754 semantics and correspond directly to the C operators or the +equivalent GCC built-in functions (@pxref{Other Builtins}). + +Single-precision floating point: +@table @asis + +@item @samp{fadds}, @samp{fsubs}, @samp{fdivs}, @samp{fmuls} +Binary arithmetic operations. + +@item @samp{fnegs} +Unary negation. + +@item @samp{fabss} +Unary absolute value. + +@item @samp{fcmpeqs}, @samp{fcmpges}, @samp{fcmpgts}, @samp{fcmples}, @samp{fcmplts}, @samp{fcmpnes} +Comparison operations. + +@item @samp{fmins}, @samp{fmaxs} +Floating-point minimum and maximum. These instructions are only +generated if @option{-ffinite-math-only} is specified. + +@item @samp{fsqrts} +Unary square root operation. + +@item @samp{fcoss}, @samp{fsins}, @samp{ftans}, @samp{fatans}, @samp{fexps}, @samp{flogs} +Floating-point trigonometric and exponential functions. These instructions +are only generated if @option{-funsafe-math-optimizations} is also specified. + +@end table + +Double-precision floating point: +@table @asis + +@item @samp{faddd}, @samp{fsubd}, @samp{fdivd}, @samp{fmuld} +Binary arithmetic operations. + +@item @samp{fnegd} +Unary negation. + +@item @samp{fabsd} +Unary absolute value. + +@item @samp{fcmpeqd}, @samp{fcmpged}, @samp{fcmpgtd}, @samp{fcmpled}, @samp{fcmpltd}, @samp{fcmpned} +Comparison operations. + +@item @samp{fmind}, @samp{fmaxd} +Double-precision minimum and maximum. These instructions are only +generated if @option{-ffinite-math-only} is specified. + +@item @samp{fsqrtd} +Unary square root operation. + +@item @samp{fcosd}, @samp{fsind}, @samp{ftand}, @samp{fatand}, @samp{fexpd}, @samp{flogd} +Double-precision trigonometric and exponential functions. These instructions +are only generated if @option{-funsafe-math-optimizations} is also specified. + +@end table + +Conversions: +@table @asis +@item @samp{fextsd} +Conversion from single precision to double precision. + +@item @samp{ftruncds} +Conversion from double precision to single precision. + +@item @samp{fixsi}, @samp{fixsu}, @samp{fixdi}, @samp{fixdu} +Conversion from floating point to signed or unsigned integer types, with +truncation towards zero. + +@item @samp{round} +Conversion from single-precision floating point to signed integer, +rounding to the nearest integer and ties away from zero. +This corresponds to the @code{__builtin_lroundf} function when +@option{-fno-math-errno} is used. + +@item @samp{floatis}, @samp{floatus}, @samp{floatid}, @samp{floatud} +Conversion from signed or unsigned integer types to floating-point types. + +@end table + +In addition, all of the following transfer instructions for internal +registers X and Y must be provided to use any of the double-precision +floating-point instructions. Custom instructions taking two +double-precision source operands expect the first operand in the +64-bit register X. The other operand (or only operand of a unary +operation) is given to the custom arithmetic instruction with the +least significant half in source register @var{src1} and the most +significant half in @var{src2}. A custom instruction that returns a +double-precision result returns the most significant 32 bits in the +destination register and the other half in 32-bit register Y. +GCC automatically generates the necessary code sequences to write +register X and/or read register Y when double-precision floating-point +instructions are used. + +@table @asis + +@item @samp{fwrx} +Write @var{src1} into the least significant half of X and @var{src2} into +the most significant half of X. + +@item @samp{fwry} +Write @var{src1} into Y. + +@item @samp{frdxhi}, @samp{frdxlo} +Read the most or least (respectively) significant half of X and store it in +@var{dest}. + +@item @samp{frdy} +Read the value of Y and store it into @var{dest}. +@end table + +Note that you can gain more local control over generation of Nios II custom +instructions by using the @code{target("custom-@var{insn}=@var{N}")} +and @code{target("no-custom-@var{insn}")} function attributes +(@pxref{Function Attributes}) +or pragmas (@pxref{Function Specific Option Pragmas}). + +@item -mcustom-fpu-cfg=@var{name} +@opindex mcustom-fpu-cfg + +This option enables a predefined, named set of custom instruction encodings +(see @option{-mcustom-@var{insn}} above). +Currently, the following sets are defined: + +@option{-mcustom-fpu-cfg=60-1} is equivalent to: +@gccoptlist{-mcustom-fmuls=252 @gol +-mcustom-fadds=253 @gol +-mcustom-fsubs=254 @gol +-fsingle-precision-constant} + +@option{-mcustom-fpu-cfg=60-2} is equivalent to: +@gccoptlist{-mcustom-fmuls=252 @gol +-mcustom-fadds=253 @gol +-mcustom-fsubs=254 @gol +-mcustom-fdivs=255 @gol +-fsingle-precision-constant} + +@option{-mcustom-fpu-cfg=72-3} is equivalent to: +@gccoptlist{-mcustom-floatus=243 @gol +-mcustom-fixsi=244 @gol +-mcustom-floatis=245 @gol +-mcustom-fcmpgts=246 @gol +-mcustom-fcmples=249 @gol +-mcustom-fcmpeqs=250 @gol +-mcustom-fcmpnes=251 @gol +-mcustom-fmuls=252 @gol +-mcustom-fadds=253 @gol +-mcustom-fsubs=254 @gol +-mcustom-fdivs=255 @gol +-fsingle-precision-constant} + +@option{-mcustom-fpu-cfg=fph2} is equivalent to: +@gccoptlist{-mcustom-fabss=224 @gol +-mcustom-fnegs=225 @gol +-mcustom-fcmpnes=226 @gol +-mcustom-fcmpeqs=227 @gol +-mcustom-fcmpges=228 @gol +-mcustom-fcmpgts=229 @gol +-mcustom-fcmples=230 @gol +-mcustom-fcmplts=231 @gol +-mcustom-fmaxs=232 @gol +-mcustom-fmins=233 @gol +-mcustom-round=248 @gol +-mcustom-fixsi=249 @gol +-mcustom-floatis=250 @gol +-mcustom-fsqrts=251 @gol +-mcustom-fmuls=252 @gol +-mcustom-fadds=253 @gol +-mcustom-fsubs=254 @gol +-mcustom-fdivs=255 @gol} + +Custom instruction assignments given by individual +@option{-mcustom-@var{insn}=} options override those given by +@option{-mcustom-fpu-cfg=}, regardless of the +order of the options on the command line. + +Note that you can gain more local control over selection of a FPU +configuration by using the @code{target("custom-fpu-cfg=@var{name}")} +function attribute (@pxref{Function Attributes}) +or pragma (@pxref{Function Specific Option Pragmas}). + +The name @var{fph2} is an abbreviation for @emph{Nios II Floating Point +Hardware 2 Component}. Please note that the custom instructions enabled by +@option{-mcustom-fmins=233} and @option{-mcustom-fmaxs=234} are only generated +if @option{-ffinite-math-only} is specified. The custom instruction enabled by +@option{-mcustom-round=248} is only generated if @option{-fno-math-errno} is +specified. In contrast to the other configurations, +@option{-fsingle-precision-constant} is not set. + +@end table + +These additional @samp{-m} options are available for the Altera Nios II +ELF (bare-metal) target: + +@table @gcctabopt + +@item -mhal +@opindex mhal +Link with HAL BSP. This suppresses linking with the GCC-provided C runtime +startup and termination code, and is typically used in conjunction with +@option{-msys-crt0=} to specify the location of the alternate startup code +provided by the HAL BSP. + +@item -msmallc +@opindex msmallc +Link with a limited version of the C library, @option{-lsmallc}, rather than +Newlib. + +@item -msys-crt0=@var{startfile} +@opindex msys-crt0 +@var{startfile} is the file name of the startfile (crt0) to use +when linking. This option is only useful in conjunction with @option{-mhal}. + +@item -msys-lib=@var{systemlib} +@opindex msys-lib +@var{systemlib} is the library name of the library that provides +low-level system calls required by the C library, +e.g.@: @code{read} and @code{write}. +This option is typically used to link with a library provided by a HAL BSP. + +@end table + +@node Nvidia PTX Options +@subsection Nvidia PTX Options +@cindex Nvidia PTX options +@cindex nvptx options + +These options are defined for Nvidia PTX: + +@table @gcctabopt + +@item -m64 +@opindex m64 +Ignored, but preserved for backward compatibility. Only 64-bit ABI is +supported. + +@item -march=@var{architecture-string} +@opindex march +Generate code for the specified PTX ISA target architecture +(e.g.@: @samp{sm_35}). Valid architecture strings are @samp{sm_30}, +@samp{sm_35}, @samp{sm_53}, @samp{sm_70}, @samp{sm_75} and +@samp{sm_80}. +The default depends on how the compiler has been configured, see +@option{--with-arch}. + +This option sets the value of the preprocessor macro +@code{__PTX_SM__}; for instance, for @samp{sm_35}, it has the value +@samp{350}. + +@item -misa=@var{architecture-string} +@opindex misa +Alias of @option{-march=}. + +@item -march-map=@var{architecture-string} +@opindex march +Select the closest available @option{-march=} value that is not more +capable. For instance, for @option{-march-map=sm_50} select +@option{-march=sm_35}, and for @option{-march-map=sm_53} select +@option{-march=sm_53}. + +@item -mptx=@var{version-string} +@opindex mptx +Generate code for the specified PTX ISA version (e.g.@: @samp{7.0}). +Valid version strings include @samp{3.1}, @samp{6.0}, @samp{6.3}, and +@samp{7.0}. The default PTX ISA version is 6.0, unless a higher +version is required for specified PTX ISA target architecture via +option @option{-march=}. + +This option sets the values of the preprocessor macros +@code{__PTX_ISA_VERSION_MAJOR__} and @code{__PTX_ISA_VERSION_MINOR__}; +for instance, for @samp{3.1} the macros have the values @samp{3} and +@samp{1}, respectively. + +@item -mmainkernel +@opindex mmainkernel +Link in code for a __main kernel. This is for stand-alone instead of +offloading execution. + +@item -moptimize +@opindex moptimize +Apply partitioned execution optimizations. This is the default when any +level of optimization is selected. + +@item -msoft-stack +@opindex msoft-stack +Generate code that does not use @code{.local} memory +directly for stack storage. Instead, a per-warp stack pointer is +maintained explicitly. This enables variable-length stack allocation (with +variable-length arrays or @code{alloca}), and when global memory is used for +underlying storage, makes it possible to access automatic variables from other +threads, or with atomic instructions. This code generation variant is used +for OpenMP offloading, but the option is exposed on its own for the purpose +of testing the compiler; to generate code suitable for linking into programs +using OpenMP offloading, use option @option{-mgomp}. + +@item -muniform-simt +@opindex muniform-simt +Switch to code generation variant that allows to execute all threads in each +warp, while maintaining memory state and side effects as if only one thread +in each warp was active outside of OpenMP SIMD regions. All atomic operations +and calls to runtime (malloc, free, vprintf) are conditionally executed (iff +current lane index equals the master lane index), and the register being +assigned is copied via a shuffle instruction from the master lane. Outside of +SIMD regions lane 0 is the master; inside, each thread sees itself as the +master. Shared memory array @code{int __nvptx_uni[]} stores all-zeros or +all-ones bitmasks for each warp, indicating current mode (0 outside of SIMD +regions). Each thread can bitwise-and the bitmask at position @code{tid.y} +with current lane index to compute the master lane index. + +@item -mgomp +@opindex mgomp +Generate code for use in OpenMP offloading: enables @option{-msoft-stack} and +@option{-muniform-simt} options, and selects corresponding multilib variant. + +@end table + +@node OpenRISC Options +@subsection OpenRISC Options +@cindex OpenRISC Options + +These options are defined for OpenRISC: + +@table @gcctabopt + +@item -mboard=@var{name} +@opindex mboard +Configure a board specific runtime. This will be passed to the linker for +newlib board library linking. The default is @code{or1ksim}. + +@item -mnewlib +@opindex mnewlib +This option is ignored; it is for compatibility purposes only. This used to +select linker and preprocessor options for use with newlib. + +@item -msoft-div +@itemx -mhard-div +@opindex msoft-div +@opindex mhard-div +Select software or hardware divide (@code{l.div}, @code{l.divu}) instructions. +This default is hardware divide. + +@item -msoft-mul +@itemx -mhard-mul +@opindex msoft-mul +@opindex mhard-mul +Select software or hardware multiply (@code{l.mul}, @code{l.muli}) instructions. +This default is hardware multiply. + +@item -msoft-float +@itemx -mhard-float +@opindex msoft-float +@opindex mhard-float +Select software or hardware for floating point operations. +The default is software. + +@item -mdouble-float +@opindex mdouble-float +When @option{-mhard-float} is selected, enables generation of double-precision +floating point instructions. By default functions from @file{libgcc} are used +to perform double-precision floating point operations. + +@item -munordered-float +@opindex munordered-float +When @option{-mhard-float} is selected, enables generation of unordered +floating point compare and set flag (@code{lf.sfun*}) instructions. By default +functions from @file{libgcc} are used to perform unordered floating point +compare and set flag operations. + +@item -mcmov +@opindex mcmov +Enable generation of conditional move (@code{l.cmov}) instructions. By +default the equivalent will be generated using set and branch. + +@item -mror +@opindex mror +Enable generation of rotate right (@code{l.ror}) instructions. By default +functions from @file{libgcc} are used to perform rotate right operations. + +@item -mrori +@opindex mrori +Enable generation of rotate right with immediate (@code{l.rori}) instructions. +By default functions from @file{libgcc} are used to perform rotate right with +immediate operations. + +@item -msext +@opindex msext +Enable generation of sign extension (@code{l.ext*}) instructions. By default +memory loads are used to perform sign extension. + +@item -msfimm +@opindex msfimm +Enable generation of compare and set flag with immediate (@code{l.sf*i}) +instructions. By default extra instructions will be generated to store the +immediate to a register first. + +@item -mshftimm +@opindex mshftimm +Enable generation of shift with immediate (@code{l.srai}, @code{l.srli}, +@code{l.slli}) instructions. By default extra instructions will be generated +to store the immediate to a register first. + +@item -mcmodel=small +@opindex mcmodel=small +Generate OpenRISC code for the small model: The GOT is limited to 64k. This is +the default model. + +@item -mcmodel=large +@opindex mcmodel=large +Generate OpenRISC code for the large model: The GOT may grow up to 4G in size. + + +@end table + +@node PDP-11 Options +@subsection PDP-11 Options +@cindex PDP-11 Options + +These options are defined for the PDP-11: + +@table @gcctabopt +@item -mfpu +@opindex mfpu +Use hardware FPP floating point. This is the default. (FIS floating +point on the PDP-11/40 is not supported.) Implies -m45. + +@item -msoft-float +@opindex msoft-float +Do not use hardware floating point. + +@item -mac0 +@opindex mac0 +Return floating-point results in ac0 (fr0 in Unix assembler syntax). + +@item -mno-ac0 +@opindex mno-ac0 +Return floating-point results in memory. This is the default. + +@item -m40 +@opindex m40 +Generate code for a PDP-11/40. Implies -msoft-float -mno-split. + +@item -m45 +@opindex m45 +Generate code for a PDP-11/45. This is the default. + +@item -m10 +@opindex m10 +Generate code for a PDP-11/10. Implies -msoft-float -mno-split. + +@item -mint16 +@itemx -mno-int32 +@opindex mint16 +@opindex mno-int32 +Use 16-bit @code{int}. This is the default. + +@item -mint32 +@itemx -mno-int16 +@opindex mint32 +@opindex mno-int16 +Use 32-bit @code{int}. + +@item -msplit +@opindex msplit +Target has split instruction and data space. Implies -m45. + +@item -munix-asm +@opindex munix-asm +Use Unix assembler syntax. + +@item -mdec-asm +@opindex mdec-asm +Use DEC assembler syntax. + +@item -mgnu-asm +@opindex mgnu-asm +Use GNU assembler syntax. This is the default. + +@item -mlra +@opindex mlra +Use the new LRA register allocator. By default, the old ``reload'' +allocator is used. +@end table + +@node picoChip Options +@subsection picoChip Options +@cindex picoChip options + +These @samp{-m} options are defined for picoChip implementations: + +@table @gcctabopt + +@item -mae=@var{ae_type} +@opindex mcpu +Set the instruction set, register set, and instruction scheduling +parameters for array element type @var{ae_type}. Supported values +for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}. + +@option{-mae=ANY} selects a completely generic AE type. Code +generated with this option runs on any of the other AE types. The +code is not as efficient as it would be if compiled for a specific +AE type, and some types of operation (e.g., multiplication) do not +work properly on all types of AE. + +@option{-mae=MUL} selects a MUL AE type. This is the most useful AE type +for compiled code, and is the default. + +@option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this +option may suffer from poor performance of byte (char) manipulation, +since the DSP AE does not provide hardware support for byte load/stores. + +@item -msymbol-as-address +Enable the compiler to directly use a symbol name as an address in a +load/store instruction, without first loading it into a +register. Typically, the use of this option generates larger +programs, which run faster than when the option isn't used. However, the +results vary from program to program, so it is left as a user option, +rather than being permanently enabled. + +@item -mno-inefficient-warnings +Disables warnings about the generation of inefficient code. These +warnings can be generated, for example, when compiling code that +performs byte-level memory operations on the MAC AE type. The MAC AE has +no hardware support for byte-level memory operations, so all byte +load/stores must be synthesized from word load/store operations. This is +inefficient and a warning is generated to indicate +that you should rewrite the code to avoid byte operations, or to target +an AE type that has the necessary hardware support. This option disables +these warnings. + +@end table + +@node PowerPC Options +@subsection PowerPC Options +@cindex PowerPC options + +These are listed under @xref{RS/6000 and PowerPC Options}. + +@node PRU Options +@subsection PRU Options +@cindex PRU Options + +These command-line options are defined for PRU target: + +@table @gcctabopt +@item -minrt +@opindex minrt +Link with a minimum runtime environment, with no support for static +initializers and constructors. Using this option can significantly reduce +the size of the final ELF binary. Beware that the compiler could still +generate code with static initializers and constructors. It is up to the +programmer to ensure that the source program will not use those features. + +@item -mmcu=@var{mcu} +@opindex mmcu +Specify the PRU MCU variant to use. Check Newlib for the exact list of +supported MCUs. + +@item -mno-relax +@opindex mno-relax +Make GCC pass the @option{--no-relax} command-line option to the linker +instead of the @option{--relax} option. + +@item -mloop +@opindex mloop +Allow (or do not allow) GCC to use the LOOP instruction. + +@item -mabi=@var{variant} +@opindex mabi +Specify the ABI variant to output code for. @option{-mabi=ti} selects the +unmodified TI ABI while @option{-mabi=gnu} selects a GNU variant that copes +more naturally with certain GCC assumptions. These are the differences: + +@table @samp +@item Function Pointer Size +TI ABI specifies that function (code) pointers are 16-bit, whereas GNU +supports only 32-bit data and code pointers. + +@item Optional Return Value Pointer +Function return values larger than 64 bits are passed by using a hidden +pointer as the first argument of the function. TI ABI, though, mandates that +the pointer can be NULL in case the caller is not using the returned value. +GNU always passes and expects a valid return value pointer. + +@end table + +The current @option{-mabi=ti} implementation simply raises a compile error +when any of the above code constructs is detected. As a consequence +the standard C library cannot be built and it is omitted when linking with +@option{-mabi=ti}. + +Relaxation is a GNU feature and for safety reasons is disabled when using +@option{-mabi=ti}. The TI toolchain does not emit relocations for QBBx +instructions, so the GNU linker cannot adjust them when shortening adjacent +LDI32 pseudo instructions. + +@end table + +@node RISC-V Options +@subsection RISC-V Options +@cindex RISC-V Options + +These command-line options are defined for RISC-V targets: + +@table @gcctabopt +@item -mbranch-cost=@var{n} +@opindex mbranch-cost +Set the cost of branches to roughly @var{n} instructions. + +@item -mplt +@itemx -mno-plt +@opindex plt +When generating PIC code, do or don't allow the use of PLTs. Ignored for +non-PIC. The default is @option{-mplt}. + +@item -mabi=@var{ABI-string} +@opindex mabi +Specify integer and floating-point calling convention. @var{ABI-string} +contains two parts: the size of integer types and the registers used for +floating-point types. For example @samp{-march=rv64ifd -mabi=lp64d} means that +@samp{long} and pointers are 64-bit (implicitly defining @samp{int} to be +32-bit), and that floating-point values up to 64 bits wide are passed in F +registers. Contrast this with @samp{-march=rv64ifd -mabi=lp64f}, which still +allows the compiler to generate code that uses the F and D extensions but only +allows floating-point values up to 32 bits long to be passed in registers; or +@samp{-march=rv64ifd -mabi=lp64}, in which no floating-point arguments will be +passed in registers. + +The default for this argument is system dependent, users who want a specific +calling convention should specify one explicitly. The valid calling +conventions are: @samp{ilp32}, @samp{ilp32f}, @samp{ilp32d}, @samp{lp64}, +@samp{lp64f}, and @samp{lp64d}. Some calling conventions are impossible to +implement on some ISAs: for example, @samp{-march=rv32if -mabi=ilp32d} is +invalid because the ABI requires 64-bit values be passed in F registers, but F +registers are only 32 bits wide. There is also the @samp{ilp32e} ABI that can +only be used with the @samp{rv32e} architecture. This ABI is not well +specified at present, and is subject to change. + +@item -mfdiv +@itemx -mno-fdiv +@opindex mfdiv +Do or don't use hardware floating-point divide and square root instructions. +This requires the F or D extensions for floating-point registers. The default +is to use them if the specified architecture has these instructions. + +@item -mdiv +@itemx -mno-div +@opindex mdiv +Do or don't use hardware instructions for integer division. This requires the +M extension. The default is to use them if the specified architecture has +these instructions. + +@item -misa-spec=@var{ISA-spec-string} +@opindex misa-spec +Specify the version of the RISC-V Unprivileged (formerly User-Level) +ISA specification to produce code conforming to. The possibilities +for @var{ISA-spec-string} are: +@table @code +@item 2.2 +Produce code conforming to version 2.2. +@item 20190608 +Produce code conforming to version 20190608. +@item 20191213 +Produce code conforming to version 20191213. +@end table +The default is @option{-misa-spec=20191213} unless GCC has been configured +with @option{--with-isa-spec=} specifying a different default version. + +@item -march=@var{ISA-string} +@opindex march +Generate code for given RISC-V ISA (e.g.@: @samp{rv64im}). ISA strings must be +lower-case. Examples include @samp{rv64i}, @samp{rv32g}, @samp{rv32e}, and +@samp{rv32imaf}. + +When @option{-march=} is not specified, use the setting from @option{-mcpu}. + +If both @option{-march} and @option{-mcpu=} are not specified, the default for +this argument is system dependent, users who want a specific architecture +extensions should specify one explicitly. + +@item -mcpu=@var{processor-string} +@opindex mcpu +Use architecture of and optimize the output for the given processor, specified +by particular CPU name. +Permissible values for this option are: @samp{sifive-e20}, @samp{sifive-e21}, +@samp{sifive-e24}, @samp{sifive-e31}, @samp{sifive-e34}, @samp{sifive-e76}, +@samp{sifive-s21}, @samp{sifive-s51}, @samp{sifive-s54}, @samp{sifive-s76}, +@samp{sifive-u54}, and @samp{sifive-u74}. + +@item -mtune=@var{processor-string} +@opindex mtune +Optimize the output for the given processor, specified by microarchitecture or +particular CPU name. Permissible values for this option are: @samp{rocket}, +@samp{sifive-3-series}, @samp{sifive-5-series}, @samp{sifive-7-series}, +@samp{thead-c906}, @samp{size}, and all valid options for @option{-mcpu=}. + +When @option{-mtune=} is not specified, use the setting from @option{-mcpu}, +the default is @samp{rocket} if both are not specified. + +The @samp{size} choice is not intended for use by end-users. This is used +when @option{-Os} is specified. It overrides the instruction cost info +provided by @option{-mtune=}, but does not override the pipeline info. This +helps reduce code size while still giving good performance. + +@item -mpreferred-stack-boundary=@var{num} +@opindex mpreferred-stack-boundary +Attempt to keep the stack boundary aligned to a 2 raised to @var{num} +byte boundary. If @option{-mpreferred-stack-boundary} is not specified, +the default is 4 (16 bytes or 128-bits). + +@strong{Warning:} If you use this switch, then you must build all modules with +the same value, including any libraries. This includes the system libraries +and startup modules. + +@item -msmall-data-limit=@var{n} +@opindex msmall-data-limit +Put global and static data smaller than @var{n} bytes into a special section +(on some targets). + +@item -msave-restore +@itemx -mno-save-restore +@opindex msave-restore +Do or don't use smaller but slower prologue and epilogue code that uses +library function calls. The default is to use fast inline prologues and +epilogues. + +@item -mshorten-memrefs +@itemx -mno-shorten-memrefs +@opindex mshorten-memrefs +Do or do not attempt to make more use of compressed load/store instructions by +replacing a load/store of 'base register + large offset' with a new load/store +of 'new base + small offset'. If the new base gets stored in a compressed +register, then the new load/store can be compressed. Currently targets 32-bit +integer load/stores only. + +@item -mstrict-align +@itemx -mno-strict-align +@opindex mstrict-align +Do not or do generate unaligned memory accesses. The default is set depending +on whether the processor we are optimizing for supports fast unaligned access +or not. + +@item -mcmodel=medlow +@opindex mcmodel=medlow +Generate code for the medium-low code model. The program and its statically +defined symbols must lie within a single 2 GiB address range and must lie +between absolute addresses @minus{}2 GiB and +2 GiB. Programs can be +statically or dynamically linked. This is the default code model. + +@item -mcmodel=medany +@opindex mcmodel=medany +Generate code for the medium-any code model. The program and its statically +defined symbols must be within any single 2 GiB address range. Programs can be +statically or dynamically linked. + +The code generated by the medium-any code model is position-independent, but is +not guaranteed to function correctly when linked into position-independent +executables or libraries. + +@item -mexplicit-relocs +@itemx -mno-exlicit-relocs +Use or do not use assembler relocation operators when dealing with symbolic +addresses. The alternative is to use assembler macros instead, which may +limit optimization. + +@item -mrelax +@itemx -mno-relax +@opindex mrelax +Take advantage of linker relaxations to reduce the number of instructions +required to materialize symbol addresses. The default is to take advantage of +linker relaxations. + +@item -mriscv-attribute +@itemx -mno-riscv-attribute +@opindex mriscv-attribute +Emit (do not emit) RISC-V attribute to record extra information into ELF +objects. This feature requires at least binutils 2.32. + +@item -mcsr-check +@itemx -mno-csr-check +@opindex mcsr-check +Enables or disables the CSR checking. + +@item -malign-data=@var{type} +@opindex malign-data +Control how GCC aligns variables and constants of array, structure, or union +types. Supported values for @var{type} are @samp{xlen} which uses x register +width as the alignment value, and @samp{natural} which uses natural alignment. +@samp{xlen} is the default. + +@item -mbig-endian +@opindex mbig-endian +Generate big-endian code. This is the default when GCC is configured for a +@samp{riscv64be-*-*} or @samp{riscv32be-*-*} target. + +@item -mlittle-endian +@opindex mlittle-endian +Generate little-endian code. This is the default when GCC is configured for a +@samp{riscv64-*-*} or @samp{riscv32-*-*} but not a @samp{riscv64be-*-*} or +@samp{riscv32be-*-*} target. + +@item -mstack-protector-guard=@var{guard} +@itemx -mstack-protector-guard-reg=@var{reg} +@itemx -mstack-protector-guard-offset=@var{offset} +@opindex mstack-protector-guard +@opindex mstack-protector-guard-reg +@opindex mstack-protector-guard-offset +Generate stack protection code using canary at @var{guard}. Supported +locations are @samp{global} for a global canary or @samp{tls} for per-thread +canary in the TLS block. + +With the latter choice the options +@option{-mstack-protector-guard-reg=@var{reg}} and +@option{-mstack-protector-guard-offset=@var{offset}} furthermore specify +which register to use as base register for reading the canary, +and from what offset from that base register. There is no default +register or offset as this is entirely for use within the Linux +kernel. +@end table + +@node RL78 Options +@subsection RL78 Options +@cindex RL78 Options + +@table @gcctabopt + +@item -msim +@opindex msim +Links in additional target libraries to support operation within a +simulator. + +@item -mmul=none +@itemx -mmul=g10 +@itemx -mmul=g13 +@itemx -mmul=g14 +@itemx -mmul=rl78 +@opindex mmul +Specifies the type of hardware multiplication and division support to +be used. The simplest is @code{none}, which uses software for both +multiplication and division. This is the default. The @code{g13} +value is for the hardware multiply/divide peripheral found on the +RL78/G13 (S2 core) targets. The @code{g14} value selects the use of +the multiplication and division instructions supported by the RL78/G14 +(S3 core) parts. The value @code{rl78} is an alias for @code{g14} and +the value @code{mg10} is an alias for @code{none}. + +In addition a C preprocessor macro is defined, based upon the setting +of this option. Possible values are: @code{__RL78_MUL_NONE__}, +@code{__RL78_MUL_G13__} or @code{__RL78_MUL_G14__}. + +@item -mcpu=g10 +@itemx -mcpu=g13 +@itemx -mcpu=g14 +@itemx -mcpu=rl78 +@opindex mcpu +Specifies the RL78 core to target. The default is the G14 core, also +known as an S3 core or just RL78. The G13 or S2 core does not have +multiply or divide instructions, instead it uses a hardware peripheral +for these operations. The G10 or S1 core does not have register +banks, so it uses a different calling convention. + +If this option is set it also selects the type of hardware multiply +support to use, unless this is overridden by an explicit +@option{-mmul=none} option on the command line. Thus specifying +@option{-mcpu=g13} enables the use of the G13 hardware multiply +peripheral and specifying @option{-mcpu=g10} disables the use of +hardware multiplications altogether. + +Note, although the RL78/G14 core is the default target, specifying +@option{-mcpu=g14} or @option{-mcpu=rl78} on the command line does +change the behavior of the toolchain since it also enables G14 +hardware multiply support. If these options are not specified on the +command line then software multiplication routines will be used even +though the code targets the RL78 core. This is for backwards +compatibility with older toolchains which did not have hardware +multiply and divide support. + +In addition a C preprocessor macro is defined, based upon the setting +of this option. Possible values are: @code{__RL78_G10__}, +@code{__RL78_G13__} or @code{__RL78_G14__}. + +@item -mg10 +@itemx -mg13 +@itemx -mg14 +@itemx -mrl78 +@opindex mg10 +@opindex mg13 +@opindex mg14 +@opindex mrl78 +These are aliases for the corresponding @option{-mcpu=} option. They +are provided for backwards compatibility. + +@item -mallregs +@opindex mallregs +Allow the compiler to use all of the available registers. By default +registers @code{r24..r31} are reserved for use in interrupt handlers. +With this option enabled these registers can be used in ordinary +functions as well. + +@item -m64bit-doubles +@itemx -m32bit-doubles +@opindex m64bit-doubles +@opindex m32bit-doubles +Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) +or 32 bits (@option{-m32bit-doubles}) in size. The default is +@option{-m32bit-doubles}. + +@item -msave-mduc-in-interrupts +@itemx -mno-save-mduc-in-interrupts +@opindex msave-mduc-in-interrupts +@opindex mno-save-mduc-in-interrupts +Specifies that interrupt handler functions should preserve the +MDUC registers. This is only necessary if normal code might use +the MDUC registers, for example because it performs multiplication +and division operations. The default is to ignore the MDUC registers +as this makes the interrupt handlers faster. The target option -mg13 +needs to be passed for this to work as this feature is only available +on the G13 target (S2 core). The MDUC registers will only be saved +if the interrupt handler performs a multiplication or division +operation or it calls another function. + +@end table + +@node RS/6000 and PowerPC Options +@subsection IBM RS/6000 and PowerPC Options +@cindex RS/6000 and PowerPC Options +@cindex IBM RS/6000 and PowerPC Options + +These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: +@table @gcctabopt +@item -mpowerpc-gpopt +@itemx -mno-powerpc-gpopt +@itemx -mpowerpc-gfxopt +@itemx -mno-powerpc-gfxopt +@need 800 +@itemx -mpowerpc64 +@itemx -mno-powerpc64 +@itemx -mmfcrf +@itemx -mno-mfcrf +@itemx -mpopcntb +@itemx -mno-popcntb +@itemx -mpopcntd +@itemx -mno-popcntd +@itemx -mfprnd +@itemx -mno-fprnd +@need 800 +@itemx -mcmpb +@itemx -mno-cmpb +@itemx -mhard-dfp +@itemx -mno-hard-dfp +@opindex mpowerpc-gpopt +@opindex mno-powerpc-gpopt +@opindex mpowerpc-gfxopt +@opindex mno-powerpc-gfxopt +@opindex mpowerpc64 +@opindex mno-powerpc64 +@opindex mmfcrf +@opindex mno-mfcrf +@opindex mpopcntb +@opindex mno-popcntb +@opindex mpopcntd +@opindex mno-popcntd +@opindex mfprnd +@opindex mno-fprnd +@opindex mcmpb +@opindex mno-cmpb +@opindex mhard-dfp +@opindex mno-hard-dfp +You use these options to specify which instructions are available on the +processor you are using. The default value of these options is +determined when configuring GCC@. Specifying the +@option{-mcpu=@var{cpu_type}} overrides the specification of these +options. We recommend you use the @option{-mcpu=@var{cpu_type}} option +rather than the options listed above. + +Specifying @option{-mpowerpc-gpopt} allows +GCC to use the optional PowerPC architecture instructions in the +General Purpose group, including floating-point square root. Specifying +@option{-mpowerpc-gfxopt} allows GCC to +use the optional PowerPC architecture instructions in the Graphics +group, including floating-point select. + +The @option{-mmfcrf} option allows GCC to generate the move from +condition register field instruction implemented on the POWER4 +processor and other processors that support the PowerPC V2.01 +architecture. +The @option{-mpopcntb} option allows GCC to generate the popcount and +double-precision FP reciprocal estimate instruction implemented on the +POWER5 processor and other processors that support the PowerPC V2.02 +architecture. +The @option{-mpopcntd} option allows GCC to generate the popcount +instruction implemented on the POWER7 processor and other processors +that support the PowerPC V2.06 architecture. +The @option{-mfprnd} option allows GCC to generate the FP round to +integer instructions implemented on the POWER5+ processor and other +processors that support the PowerPC V2.03 architecture. +The @option{-mcmpb} option allows GCC to generate the compare bytes +instruction implemented on the POWER6 processor and other processors +that support the PowerPC V2.05 architecture. +The @option{-mhard-dfp} option allows GCC to generate the decimal +floating-point instructions implemented on some POWER processors. + +The @option{-mpowerpc64} option allows GCC to generate the additional +64-bit instructions that are found in the full PowerPC64 architecture +and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to +@option{-mno-powerpc64}. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set architecture type, register usage, and +instruction scheduling parameters for machine type @var{cpu_type}. +Supported values for @var{cpu_type} are @samp{401}, @samp{403}, +@samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp}, +@samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603}, +@samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740}, +@samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823}, +@samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2}, +@samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500}, +@samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5}, +@samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+}, +@samp{power6}, @samp{power6x}, @samp{power7}, @samp{power8}, +@samp{power9}, @samp{power10}, @samp{powerpc}, @samp{powerpc64}, +@samp{powerpc64le}, @samp{rs64}, and @samp{native}. + +@option{-mcpu=powerpc}, @option{-mcpu=powerpc64}, and +@option{-mcpu=powerpc64le} specify pure 32-bit PowerPC (either +endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC +architecture machine types, with an appropriate, generic processor +model assumed for scheduling purposes. + +Specifying @samp{native} as cpu type detects and selects the +architecture option that corresponds to the host processor of the +system performing the compilation. +@option{-mcpu=native} has no effect if GCC does not recognize the +processor. + +The other options specify a specific processor. Code generated under +those options runs best on that processor, and may not run at all on +others. + +The @option{-mcpu} options automatically enable or disable the +following options: + +@gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol +-mpopcntb -mpopcntd -mpowerpc64 @gol +-mpowerpc-gpopt -mpowerpc-gfxopt @gol +-mmulhw -mdlmzb -mmfpgpr -mvsx @gol +-mcrypto -mhtm -mpower8-fusion -mpower8-vector @gol +-mquad-memory -mquad-memory-atomic -mfloat128 @gol +-mfloat128-hardware -mprefixed -mpcrel -mmma @gol +-mrop-protect} + +The particular options set for any particular CPU varies between +compiler versions, depending on what setting seems to produce optimal +code for that CPU; it doesn't necessarily reflect the actual hardware's +capabilities. If you wish to set an individual option to a particular +value, you may specify it after the @option{-mcpu} option, like +@option{-mcpu=970 -mno-altivec}. + +On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are +not enabled or disabled by the @option{-mcpu} option at present because +AIX does not have full support for these options. You may still +enable or disable them individually if you're sure it'll work in your +environment. + +@item -mtune=@var{cpu_type} +@opindex mtune +Set the instruction scheduling parameters for machine type +@var{cpu_type}, but do not set the architecture type or register usage, +as @option{-mcpu=@var{cpu_type}} does. The same +values for @var{cpu_type} are used for @option{-mtune} as for +@option{-mcpu}. If both are specified, the code generated uses the +architecture and registers set by @option{-mcpu}, but the +scheduling parameters set by @option{-mtune}. + +@item -mcmodel=small +@opindex mcmodel=small +Generate PowerPC64 code for the small model: The TOC is limited to +64k. + +@item -mcmodel=medium +@opindex mcmodel=medium +Generate PowerPC64 code for the medium model: The TOC and other static +data may be up to a total of 4G in size. This is the default for 64-bit +Linux. + +@item -mcmodel=large +@opindex mcmodel=large +Generate PowerPC64 code for the large model: The TOC may be up to 4G +in size. Other data and code is only limited by the 64-bit address +space. + +@item -maltivec +@itemx -mno-altivec +@opindex maltivec +@opindex mno-altivec +Generate code that uses (does not use) AltiVec instructions, and also +enable the use of built-in functions that allow more direct access to +the AltiVec instruction set. You may also need to set +@option{-mabi=altivec} to adjust the current ABI with AltiVec ABI +enhancements. + +When @option{-maltivec} is used, the element order for AltiVec intrinsics +such as @code{vec_splat}, @code{vec_extract}, and @code{vec_insert} +match array element order corresponding to the endianness of the +target. That is, element zero identifies the leftmost element in a +vector register when targeting a big-endian platform, and identifies +the rightmost element in a vector register when targeting a +little-endian platform. + +@item -mvrsave +@itemx -mno-vrsave +@opindex mvrsave +@opindex mno-vrsave +Generate VRSAVE instructions when generating AltiVec code. + +@item -msecure-plt +@opindex msecure-plt +Generate code that allows @command{ld} and @command{ld.so} +to build executables and shared +libraries with non-executable @code{.plt} and @code{.got} sections. +This is a PowerPC +32-bit SYSV ABI option. + +@item -mbss-plt +@opindex mbss-plt +Generate code that uses a BSS @code{.plt} section that @command{ld.so} +fills in, and +requires @code{.plt} and @code{.got} +sections that are both writable and executable. +This is a PowerPC 32-bit SYSV ABI option. + +@item -misel +@itemx -mno-isel +@opindex misel +@opindex mno-isel +This switch enables or disables the generation of ISEL instructions. + +@item -mvsx +@itemx -mno-vsx +@opindex mvsx +@opindex mno-vsx +Generate code that uses (does not use) vector/scalar (VSX) +instructions, and also enable the use of built-in functions that allow +more direct access to the VSX instruction set. + +@item -mcrypto +@itemx -mno-crypto +@opindex mcrypto +@opindex mno-crypto +Enable the use (disable) of the built-in functions that allow direct +access to the cryptographic instructions that were added in version +2.07 of the PowerPC ISA. + +@item -mhtm +@itemx -mno-htm +@opindex mhtm +@opindex mno-htm +Enable (disable) the use of the built-in functions that allow direct +access to the Hardware Transactional Memory (HTM) instructions that +were added in version 2.07 of the PowerPC ISA. + +@item -mpower8-fusion +@itemx -mno-power8-fusion +@opindex mpower8-fusion +@opindex mno-power8-fusion +Generate code that keeps (does not keeps) some integer operations +adjacent so that the instructions can be fused together on power8 and +later processors. + +@item -mpower8-vector +@itemx -mno-power8-vector +@opindex mpower8-vector +@opindex mno-power8-vector +Generate code that uses (does not use) the vector and scalar +instructions that were added in version 2.07 of the PowerPC ISA. Also +enable the use of built-in functions that allow more direct access to +the vector instructions. + +@item -mquad-memory +@itemx -mno-quad-memory +@opindex mquad-memory +@opindex mno-quad-memory +Generate code that uses (does not use) the non-atomic quad word memory +instructions. The @option{-mquad-memory} option requires use of +64-bit mode. + +@item -mquad-memory-atomic +@itemx -mno-quad-memory-atomic +@opindex mquad-memory-atomic +@opindex mno-quad-memory-atomic +Generate code that uses (does not use) the atomic quad word memory +instructions. The @option{-mquad-memory-atomic} option requires use of +64-bit mode. + +@item -mfloat128 +@itemx -mno-float128 +@opindex mfloat128 +@opindex mno-float128 +Enable/disable the @var{__float128} keyword for IEEE 128-bit floating point +and use either software emulation for IEEE 128-bit floating point or +hardware instructions. + +The VSX instruction set (@option{-mvsx}) must be enabled to use the IEEE +128-bit floating point support. The IEEE 128-bit floating point is only +supported on Linux. + +The default for @option{-mfloat128} is enabled on PowerPC Linux +systems using the VSX instruction set, and disabled on other systems. + +If you use the ISA 3.0 instruction set (@option{-mpower9-vector} or +@option{-mcpu=power9}) on a 64-bit system, the IEEE 128-bit floating +point support will also enable the generation of ISA 3.0 IEEE 128-bit +floating point instructions. Otherwise, if you do not specify to +generate ISA 3.0 instructions or you are targeting a 32-bit big endian +system, IEEE 128-bit floating point will be done with software +emulation. + +@item -mfloat128-hardware +@itemx -mno-float128-hardware +@opindex mfloat128-hardware +@opindex mno-float128-hardware +Enable/disable using ISA 3.0 hardware instructions to support the +@var{__float128} data type. + +The default for @option{-mfloat128-hardware} is enabled on PowerPC +Linux systems using the ISA 3.0 instruction set, and disabled on other +systems. + +@item -m32 +@itemx -m64 +@opindex m32 +@opindex m64 +Generate code for 32-bit or 64-bit environments of Darwin and SVR4 +targets (including GNU/Linux). The 32-bit environment sets int, long +and pointer to 32 bits and generates code that runs on any PowerPC +variant. The 64-bit environment sets int to 32 bits and long and +pointer to 64 bits, and generates code for PowerPC64, as for +@option{-mpowerpc64}. + +@item -mfull-toc +@itemx -mno-fp-in-toc +@itemx -mno-sum-in-toc +@itemx -mminimal-toc +@opindex mfull-toc +@opindex mno-fp-in-toc +@opindex mno-sum-in-toc +@opindex mminimal-toc +Modify generation of the TOC (Table Of Contents), which is created for +every executable file. The @option{-mfull-toc} option is selected by +default. In that case, GCC allocates at least one TOC entry for +each unique non-automatic variable reference in your program. GCC +also places floating-point constants in the TOC@. However, only +16,384 entries are available in the TOC@. + +If you receive a linker error message that saying you have overflowed +the available TOC space, you can reduce the amount of TOC space used +with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. +@option{-mno-fp-in-toc} prevents GCC from putting floating-point +constants in the TOC and @option{-mno-sum-in-toc} forces GCC to +generate code to calculate the sum of an address and a constant at +run time instead of putting that sum into the TOC@. You may specify one +or both of these options. Each causes GCC to produce very slightly +slower and larger code at the expense of conserving TOC space. + +If you still run out of space in the TOC even when you specify both of +these options, specify @option{-mminimal-toc} instead. This option causes +GCC to make only one TOC entry for every file. When you specify this +option, GCC produces code that is slower and larger but which +uses extremely little TOC space. You may wish to use this option +only on files that contain less frequently-executed code. + +@item -maix64 +@itemx -maix32 +@opindex maix64 +@opindex maix32 +Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit +@code{long} type, and the infrastructure needed to support them. +Specifying @option{-maix64} implies @option{-mpowerpc64}, +while @option{-maix32} disables the 64-bit ABI and +implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. + +@item -mxl-compat +@itemx -mno-xl-compat +@opindex mxl-compat +@opindex mno-xl-compat +Produce code that conforms more closely to IBM XL compiler semantics +when using AIX-compatible ABI@. Pass floating-point arguments to +prototyped functions beyond the register save area (RSA) on the stack +in addition to argument FPRs. Do not assume that most significant +double in 128-bit long double value is properly rounded when comparing +values and converting to double. Use XL symbol names for long double +support routines. + +The AIX calling convention was extended but not initially documented to +handle an obscure K&R C case of calling a function that takes the +address of its arguments with fewer arguments than declared. IBM XL +compilers access floating-point arguments that do not fit in the +RSA from the stack when a subroutine is compiled without +optimization. Because always storing floating-point arguments on the +stack is inefficient and rarely needed, this option is not enabled by +default and only is necessary when calling subroutines compiled by IBM +XL compilers without optimization. + +@item -mpe +@opindex mpe +Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an +application written to use message passing with special startup code to +enable the application to run. The system must have PE installed in the +standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file +must be overridden with the @option{-specs=} option to specify the +appropriate directory location. The Parallel Environment does not +support threads, so the @option{-mpe} option and the @option{-pthread} +option are incompatible. + +@item -malign-natural +@itemx -malign-power +@opindex malign-natural +@opindex malign-power +On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option +@option{-malign-natural} overrides the ABI-defined alignment of larger +types, such as floating-point doubles, on their natural size-based boundary. +The option @option{-malign-power} instructs GCC to follow the ABI-specified +alignment rules. GCC defaults to the standard alignment defined in the ABI@. + +On 64-bit Darwin, natural alignment is the default, and @option{-malign-power} +is not supported. + +@item -msoft-float +@itemx -mhard-float +@opindex msoft-float +@opindex mhard-float +Generate code that does not use (uses) the floating-point register set. +Software floating-point emulation is provided if you use the +@option{-msoft-float} option, and pass the option to GCC when linking. + +@item -mmultiple +@itemx -mno-multiple +@opindex mmultiple +@opindex mno-multiple +Generate code that uses (does not use) the load multiple word +instructions and the store multiple word instructions. These +instructions are generated by default on POWER systems, and not +generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian +PowerPC systems, since those instructions do not work when the +processor is in little-endian mode. The exceptions are PPC740 and +PPC750 which permit these instructions in little-endian mode. + +@item -mupdate +@itemx -mno-update +@opindex mupdate +@opindex mno-update +Generate code that uses (does not use) the load or store instructions +that update the base register to the address of the calculated memory +location. These instructions are generated by default. If you use +@option{-mno-update}, there is a small window between the time that the +stack pointer is updated and the address of the previous frame is +stored, which means code that walks the stack frame across interrupts or +signals may get corrupted data. + +@item -mavoid-indexed-addresses +@itemx -mno-avoid-indexed-addresses +@opindex mavoid-indexed-addresses +@opindex mno-avoid-indexed-addresses +Generate code that tries to avoid (not avoid) the use of indexed load +or store instructions. These instructions can incur a performance +penalty on Power6 processors in certain situations, such as when +stepping through large arrays that cross a 16M boundary. This option +is enabled by default when targeting Power6 and disabled otherwise. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Generate code that uses (does not use) the floating-point multiply and +accumulate instructions. These instructions are generated by default +if hardware floating point is used. The machine-dependent +@option{-mfused-madd} option is now mapped to the machine-independent +@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is +mapped to @option{-ffp-contract=off}. + +@item -mmulhw +@itemx -mno-mulhw +@opindex mmulhw +@opindex mno-mulhw +Generate code that uses (does not use) the half-word multiply and +multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. +These instructions are generated by default when targeting those +processors. + +@item -mdlmzb +@itemx -mno-dlmzb +@opindex mdlmzb +@opindex mno-dlmzb +Generate code that uses (does not use) the string-search @samp{dlmzb} +instruction on the IBM 405, 440, 464 and 476 processors. This instruction is +generated by default when targeting those processors. + +@item -mno-bit-align +@itemx -mbit-align +@opindex mno-bit-align +@opindex mbit-align +On System V.4 and embedded PowerPC systems do not (do) force structures +and unions that contain bit-fields to be aligned to the base type of the +bit-field. + +For example, by default a structure containing nothing but 8 +@code{unsigned} bit-fields of length 1 is aligned to a 4-byte +boundary and has a size of 4 bytes. By using @option{-mno-bit-align}, +the structure is aligned to a 1-byte boundary and is 1 byte in +size. + +@item -mno-strict-align +@itemx -mstrict-align +@opindex mno-strict-align +@opindex mstrict-align +On System V.4 and embedded PowerPC systems do not (do) assume that +unaligned memory references are handled by the system. + +@item -mrelocatable +@itemx -mno-relocatable +@opindex mrelocatable +@opindex mno-relocatable +Generate code that allows (does not allow) a static executable to be +relocated to a different address at run time. A simple embedded +PowerPC system loader should relocate the entire contents of +@code{.got2} and 4-byte locations listed in the @code{.fixup} section, +a table of 32-bit addresses generated by this option. For this to +work, all objects linked together must be compiled with +@option{-mrelocatable} or @option{-mrelocatable-lib}. +@option{-mrelocatable} code aligns the stack to an 8-byte boundary. + +@item -mrelocatable-lib +@itemx -mno-relocatable-lib +@opindex mrelocatable-lib +@opindex mno-relocatable-lib +Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a +@code{.fixup} section to allow static executables to be relocated at +run time, but @option{-mrelocatable-lib} does not use the smaller stack +alignment of @option{-mrelocatable}. Objects compiled with +@option{-mrelocatable-lib} may be linked with objects compiled with +any combination of the @option{-mrelocatable} options. + +@item -mno-toc +@itemx -mtoc +@opindex mno-toc +@opindex mtoc +On System V.4 and embedded PowerPC systems do not (do) assume that +register 2 contains a pointer to a global area pointing to the addresses +used in the program. + +@item -mlittle +@itemx -mlittle-endian +@opindex mlittle +@opindex mlittle-endian +On System V.4 and embedded PowerPC systems compile code for the +processor in little-endian mode. The @option{-mlittle-endian} option is +the same as @option{-mlittle}. + +@item -mbig +@itemx -mbig-endian +@opindex mbig +@opindex mbig-endian +On System V.4 and embedded PowerPC systems compile code for the +processor in big-endian mode. The @option{-mbig-endian} option is +the same as @option{-mbig}. + +@item -mdynamic-no-pic +@opindex mdynamic-no-pic +On Darwin and Mac OS X systems, compile code so that it is not +relocatable, but that its external references are relocatable. The +resulting code is suitable for applications, but not shared +libraries. + +@item -msingle-pic-base +@opindex msingle-pic-base +Treat the register used for PIC addressing as read-only, rather than +loading it in the prologue for each function. The runtime system is +responsible for initializing this register with an appropriate value +before execution begins. + +@item -mprioritize-restricted-insns=@var{priority} +@opindex mprioritize-restricted-insns +This option controls the priority that is assigned to +dispatch-slot restricted instructions during the second scheduling +pass. The argument @var{priority} takes the value @samp{0}, @samp{1}, +or @samp{2} to assign no, highest, or second-highest (respectively) +priority to dispatch-slot restricted +instructions. + +@item -msched-costly-dep=@var{dependence_type} +@opindex msched-costly-dep +This option controls which dependences are considered costly +by the target during instruction scheduling. The argument +@var{dependence_type} takes one of the following values: + +@table @asis +@item @samp{no} +No dependence is costly. + +@item @samp{all} +All dependences are costly. + +@item @samp{true_store_to_load} +A true dependence from store to load is costly. + +@item @samp{store_to_load} +Any dependence from store to load is costly. + +@item @var{number} +Any dependence for which the latency is greater than or equal to +@var{number} is costly. +@end table + +@item -minsert-sched-nops=@var{scheme} +@opindex minsert-sched-nops +This option controls which NOP insertion scheme is used during +the second scheduling pass. The argument @var{scheme} takes one of the +following values: + +@table @asis +@item @samp{no} +Don't insert NOPs. + +@item @samp{pad} +Pad with NOPs any dispatch group that has vacant issue slots, +according to the scheduler's grouping. + +@item @samp{regroup_exact} +Insert NOPs to force costly dependent insns into +separate groups. Insert exactly as many NOPs as needed to force an insn +to a new group, according to the estimated processor grouping. + +@item @var{number} +Insert NOPs to force costly dependent insns into +separate groups. Insert @var{number} NOPs to force an insn to a new group. +@end table + +@item -mcall-sysv +@opindex mcall-sysv +On System V.4 and embedded PowerPC systems compile code using calling +conventions that adhere to the March 1995 draft of the System V +Application Binary Interface, PowerPC processor supplement. This is the +default unless you configured GCC using @samp{powerpc-*-eabiaix}. + +@item -mcall-sysv-eabi +@itemx -mcall-eabi +@opindex mcall-sysv-eabi +@opindex mcall-eabi +Specify both @option{-mcall-sysv} and @option{-meabi} options. + +@item -mcall-sysv-noeabi +@opindex mcall-sysv-noeabi +Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. + +@item -mcall-aixdesc +@opindex m +On System V.4 and embedded PowerPC systems compile code for the AIX +operating system. + +@item -mcall-linux +@opindex mcall-linux +On System V.4 and embedded PowerPC systems compile code for the +Linux-based GNU system. + +@item -mcall-freebsd +@opindex mcall-freebsd +On System V.4 and embedded PowerPC systems compile code for the +FreeBSD operating system. + +@item -mcall-netbsd +@opindex mcall-netbsd +On System V.4 and embedded PowerPC systems compile code for the +NetBSD operating system. + +@item -mcall-openbsd +@opindex mcall-netbsd +On System V.4 and embedded PowerPC systems compile code for the +OpenBSD operating system. + +@item -mtraceback=@var{traceback_type} +@opindex mtraceback +Select the type of traceback table. Valid values for @var{traceback_type} +are @samp{full}, @samp{part}, and @samp{no}. + +@item -maix-struct-return +@opindex maix-struct-return +Return all structures in memory (as specified by the AIX ABI)@. + +@item -msvr4-struct-return +@opindex msvr4-struct-return +Return structures smaller than 8 bytes in registers (as specified by the +SVR4 ABI)@. + +@item -mabi=@var{abi-type} +@opindex mabi +Extend the current ABI with a particular extension, or remove such extension. +Valid values are: @samp{altivec}, @samp{no-altivec}, +@samp{ibmlongdouble}, @samp{ieeelongdouble}, +@samp{elfv1}, @samp{elfv2}, +and for AIX: @samp{vec-extabi}, @samp{vec-default}@. + +@item -mabi=ibmlongdouble +@opindex mabi=ibmlongdouble +Change the current ABI to use IBM extended-precision long double. +This is not likely to work if your system defaults to using IEEE +extended-precision long double. If you change the long double type +from IEEE extended-precision, the compiler will issue a warning unless +you use the @option{-Wno-psabi} option. Requires @option{-mlong-double-128} +to be enabled. + +@item -mabi=ieeelongdouble +@opindex mabi=ieeelongdouble +Change the current ABI to use IEEE extended-precision long double. +This is not likely to work if your system defaults to using IBM +extended-precision long double. If you change the long double type +from IBM extended-precision, the compiler will issue a warning unless +you use the @option{-Wno-psabi} option. Requires @option{-mlong-double-128} +to be enabled. + +@item -mabi=elfv1 +@opindex mabi=elfv1 +Change the current ABI to use the ELFv1 ABI. +This is the default ABI for big-endian PowerPC 64-bit Linux. +Overriding the default ABI requires special system support and is +likely to fail in spectacular ways. + +@item -mabi=elfv2 +@opindex mabi=elfv2 +Change the current ABI to use the ELFv2 ABI. +This is the default ABI for little-endian PowerPC 64-bit Linux. +Overriding the default ABI requires special system support and is +likely to fail in spectacular ways. + +@item -mgnu-attribute +@itemx -mno-gnu-attribute +@opindex mgnu-attribute +@opindex mno-gnu-attribute +Emit .gnu_attribute assembly directives to set tag/value pairs in a +.gnu.attributes section that specify ABI variations in function +parameters or return values. + +@item -mprototype +@itemx -mno-prototype +@opindex mprototype +@opindex mno-prototype +On System V.4 and embedded PowerPC systems assume that all calls to +variable argument functions are properly prototyped. Otherwise, the +compiler must insert an instruction before every non-prototyped call to +set or clear bit 6 of the condition code register (@code{CR}) to +indicate whether floating-point values are passed in the floating-point +registers in case the function takes variable arguments. With +@option{-mprototype}, only calls to prototyped variable argument functions +set or clear the bit. + +@item -msim +@opindex msim +On embedded PowerPC systems, assume that the startup module is called +@file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and +@file{libc.a}. This is the default for @samp{powerpc-*-eabisim} +configurations. + +@item -mmvme +@opindex mmvme +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libmvme.a} and +@file{libc.a}. + +@item -mads +@opindex mads +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libads.a} and +@file{libc.a}. + +@item -myellowknife +@opindex myellowknife +On embedded PowerPC systems, assume that the startup module is called +@file{crt0.o} and the standard C libraries are @file{libyk.a} and +@file{libc.a}. + +@item -mvxworks +@opindex mvxworks +On System V.4 and embedded PowerPC systems, specify that you are +compiling for a VxWorks system. + +@item -memb +@opindex memb +On embedded PowerPC systems, set the @code{PPC_EMB} bit in the ELF flags +header to indicate that @samp{eabi} extended relocations are used. + +@item -meabi +@itemx -mno-eabi +@opindex meabi +@opindex mno-eabi +On System V.4 and embedded PowerPC systems do (do not) adhere to the +Embedded Applications Binary Interface (EABI), which is a set of +modifications to the System V.4 specifications. Selecting @option{-meabi} +means that the stack is aligned to an 8-byte boundary, a function +@code{__eabi} is called from @code{main} to set up the EABI +environment, and the @option{-msdata} option can use both @code{r2} and +@code{r13} to point to two separate small data areas. Selecting +@option{-mno-eabi} means that the stack is aligned to a 16-byte boundary, +no EABI initialization function is called from @code{main}, and the +@option{-msdata} option only uses @code{r13} to point to a single +small data area. The @option{-meabi} option is on by default if you +configured GCC using one of the @samp{powerpc*-*-eabi*} options. + +@item -msdata=eabi +@opindex msdata=eabi +On System V.4 and embedded PowerPC systems, put small initialized +@code{const} global and static data in the @code{.sdata2} section, which +is pointed to by register @code{r2}. Put small initialized +non-@code{const} global and static data in the @code{.sdata} section, +which is pointed to by register @code{r13}. Put small uninitialized +global and static data in the @code{.sbss} section, which is adjacent to +the @code{.sdata} section. The @option{-msdata=eabi} option is +incompatible with the @option{-mrelocatable} option. The +@option{-msdata=eabi} option also sets the @option{-memb} option. + +@item -msdata=sysv +@opindex msdata=sysv +On System V.4 and embedded PowerPC systems, put small global and static +data in the @code{.sdata} section, which is pointed to by register +@code{r13}. Put small uninitialized global and static data in the +@code{.sbss} section, which is adjacent to the @code{.sdata} section. +The @option{-msdata=sysv} option is incompatible with the +@option{-mrelocatable} option. + +@item -msdata=default +@itemx -msdata +@opindex msdata=default +@opindex msdata +On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, +compile code the same as @option{-msdata=eabi}, otherwise compile code the +same as @option{-msdata=sysv}. + +@item -msdata=data +@opindex msdata=data +On System V.4 and embedded PowerPC systems, put small global +data in the @code{.sdata} section. Put small uninitialized global +data in the @code{.sbss} section. Do not use register @code{r13} +to address small data however. This is the default behavior unless +other @option{-msdata} options are used. + +@item -msdata=none +@itemx -mno-sdata +@opindex msdata=none +@opindex mno-sdata +On embedded PowerPC systems, put all initialized global and static data +in the @code{.data} section, and all uninitialized data in the +@code{.bss} section. + +@item -mreadonly-in-sdata +@opindex mreadonly-in-sdata +@opindex mno-readonly-in-sdata +Put read-only objects in the @code{.sdata} section as well. This is the +default. + +@item -mblock-move-inline-limit=@var{num} +@opindex mblock-move-inline-limit +Inline all block moves (such as calls to @code{memcpy} or structure +copies) less than or equal to @var{num} bytes. The minimum value for +@var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit +targets. The default value is target-specific. + +@item -mblock-compare-inline-limit=@var{num} +@opindex mblock-compare-inline-limit +Generate non-looping inline code for all block compares (such as calls +to @code{memcmp} or structure compares) less than or equal to @var{num} +bytes. If @var{num} is 0, all inline expansion (non-loop and loop) of +block compare is disabled. The default value is target-specific. + +@item -mblock-compare-inline-loop-limit=@var{num} +@opindex mblock-compare-inline-loop-limit +Generate an inline expansion using loop code for all block compares that +are less than or equal to @var{num} bytes, but greater than the limit +for non-loop inline block compare expansion. If the block length is not +constant, at most @var{num} bytes will be compared before @code{memcmp} +is called to compare the remainder of the block. The default value is +target-specific. + +@item -mstring-compare-inline-limit=@var{num} +@opindex mstring-compare-inline-limit +Compare at most @var{num} string bytes with inline code. +If the difference or end of string is not found at the +end of the inline compare a call to @code{strcmp} or @code{strncmp} will +take care of the rest of the comparison. The default is 64 bytes. + +@item -G @var{num} +@opindex G +@cindex smaller data references (PowerPC) +@cindex .sdata/.sdata2 references (PowerPC) +On embedded PowerPC systems, put global and static items less than or +equal to @var{num} bytes into the small data or BSS sections instead of +the normal data or BSS section. By default, @var{num} is 8. The +@option{-G @var{num}} switch is also passed to the linker. +All modules should be compiled with the same @option{-G @var{num}} value. + +@item -mregnames +@itemx -mno-regnames +@opindex mregnames +@opindex mno-regnames +On System V.4 and embedded PowerPC systems do (do not) emit register +names in the assembly language output using symbolic forms. + +@item -mlongcall +@itemx -mno-longcall +@opindex mlongcall +@opindex mno-longcall +By default assume that all calls are far away so that a longer and more +expensive calling sequence is required. This is required for calls +farther than 32 megabytes (33,554,432 bytes) from the current location. +A short call is generated if the compiler knows +the call cannot be that far away. This setting can be overridden by +the @code{shortcall} function attribute, or by @code{#pragma +longcall(0)}. + +Some linkers are capable of detecting out-of-range calls and generating +glue code on the fly. On these systems, long calls are unnecessary and +generate slower code. As of this writing, the AIX linker can do this, +as can the GNU linker for PowerPC/64. It is planned to add this feature +to the GNU linker for 32-bit PowerPC systems as well. + +On PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU linkers, +GCC can generate long calls using an inline PLT call sequence (see +@option{-mpltseq}). PowerPC with @option{-mbss-plt} and PowerPC64 +ELFv1 (big-endian) do not support inline PLT calls. + +On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr +callee, L42}, plus a @dfn{branch island} (glue code). The two target +addresses represent the callee and the branch island. The +Darwin/PPC linker prefers the first address and generates a @code{bl +callee} if the PPC @code{bl} instruction reaches the callee directly; +otherwise, the linker generates @code{bl L42} to call the branch +island. The branch island is appended to the body of the +calling function; it computes the full 32-bit address of the callee +and jumps to it. + +On Mach-O (Darwin) systems, this option directs the compiler emit to +the glue for every direct call, and the Darwin linker decides whether +to use or discard it. + +In the future, GCC may ignore all longcall specifications +when the linker is known to generate glue. + +@item -mpltseq +@itemx -mno-pltseq +@opindex mpltseq +@opindex mno-pltseq +Implement (do not implement) -fno-plt and long calls using an inline +PLT call sequence that supports lazy linking and long calls to +functions in dlopen'd shared libraries. Inline PLT calls are only +supported on PowerPC64 ELFv2 and 32-bit PowerPC systems with newer GNU +linkers, and are enabled by default if the support is detected when +configuring GCC, and, in the case of 32-bit PowerPC, if GCC is +configured with @option{--enable-secureplt}. @option{-mpltseq} code +and @option{-mbss-plt} 32-bit PowerPC relocatable objects may not be +linked together. + +@item -mtls-markers +@itemx -mno-tls-markers +@opindex mtls-markers +@opindex mno-tls-markers +Mark (do not mark) calls to @code{__tls_get_addr} with a relocation +specifying the function argument. The relocation allows the linker to +reliably associate function call with argument setup instructions for +TLS optimization, which in turn allows GCC to better schedule the +sequence. + +@item -mrecip +@itemx -mno-recip +@opindex mrecip +This option enables use of the reciprocal estimate and +reciprocal square root estimate instructions with additional +Newton-Raphson steps to increase precision instead of doing a divide or +square root and divide for floating-point arguments. You should use +the @option{-ffast-math} option when using @option{-mrecip} (or at +least @option{-funsafe-math-optimizations}, +@option{-ffinite-math-only}, @option{-freciprocal-math} and +@option{-fno-trapping-math}). Note that while the throughput of the +sequence is generally higher than the throughput of the non-reciprocal +instruction, the precision of the sequence can be decreased by up to 2 +ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square +roots. + +@item -mrecip=@var{opt} +@opindex mrecip=opt +This option controls which reciprocal estimate instructions +may be used. @var{opt} is a comma-separated list of options, which may +be preceded by a @code{!} to invert the option: + +@table @samp + +@item all +Enable all estimate instructions. + +@item default +Enable the default instructions, equivalent to @option{-mrecip}. + +@item none +Disable all estimate instructions, equivalent to @option{-mno-recip}. + +@item div +Enable the reciprocal approximation instructions for both +single and double precision. + +@item divf +Enable the single-precision reciprocal approximation instructions. + +@item divd +Enable the double-precision reciprocal approximation instructions. + +@item rsqrt +Enable the reciprocal square root approximation instructions for both +single and double precision. + +@item rsqrtf +Enable the single-precision reciprocal square root approximation instructions. + +@item rsqrtd +Enable the double-precision reciprocal square root approximation instructions. + +@end table + +So, for example, @option{-mrecip=all,!rsqrtd} enables +all of the reciprocal estimate instructions, except for the +@code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions +which handle the double-precision reciprocal square root calculations. + +@item -mrecip-precision +@itemx -mno-recip-precision +@opindex mrecip-precision +Assume (do not assume) that the reciprocal estimate instructions +provide higher-precision estimates than is mandated by the PowerPC +ABI. Selecting @option{-mcpu=power6}, @option{-mcpu=power7} or +@option{-mcpu=power8} automatically selects @option{-mrecip-precision}. +The double-precision square root estimate instructions are not generated by +default on low-precision machines, since they do not provide an +estimate that converges after three steps. + +@item -mveclibabi=@var{type} +@opindex mveclibabi +Specifies the ABI type to use for vectorizing intrinsics using an +external library. The only type supported at present is @samp{mass}, +which specifies to use IBM's Mathematical Acceleration Subsystem +(MASS) libraries for vectorizing intrinsics using external libraries. +GCC currently emits calls to @code{acosd2}, @code{acosf4}, +@code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4}, +@code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4}, +@code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4}, +@code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4}, +@code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4}, +@code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4}, +@code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4}, +@code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4}, +@code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4}, +@code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4}, +@code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2}, +@code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2}, +@code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code +for power7. Both @option{-ftree-vectorize} and +@option{-funsafe-math-optimizations} must also be enabled. The MASS +libraries must be specified at link time. + +@item -mfriz +@itemx -mno-friz +@opindex mfriz +Generate (do not generate) the @code{friz} instruction when the +@option{-funsafe-math-optimizations} option is used to optimize +rounding of floating-point values to 64-bit integer and back to floating +point. The @code{friz} instruction does not return the same value if +the floating-point number is too large to fit in an integer. + +@item -mpointers-to-nested-functions +@itemx -mno-pointers-to-nested-functions +@opindex mpointers-to-nested-functions +Generate (do not generate) code to load up the static chain register +(@code{r11}) when calling through a pointer on AIX and 64-bit Linux +systems where a function pointer points to a 3-word descriptor giving +the function address, TOC value to be loaded in register @code{r2}, and +static chain value to be loaded in register @code{r11}. The +@option{-mpointers-to-nested-functions} is on by default. You cannot +call through pointers to nested functions or pointers +to functions compiled in other languages that use the static chain if +you use @option{-mno-pointers-to-nested-functions}. + +@item -msave-toc-indirect +@itemx -mno-save-toc-indirect +@opindex msave-toc-indirect +Generate (do not generate) code to save the TOC value in the reserved +stack location in the function prologue if the function calls through +a pointer on AIX and 64-bit Linux systems. If the TOC value is not +saved in the prologue, it is saved just before the call through the +pointer. The @option{-mno-save-toc-indirect} option is the default. + +@item -mcompat-align-parm +@itemx -mno-compat-align-parm +@opindex mcompat-align-parm +Generate (do not generate) code to pass structure parameters with a +maximum alignment of 64 bits, for compatibility with older versions +of GCC. + +Older versions of GCC (prior to 4.9.0) incorrectly did not align a +structure parameter on a 128-bit boundary when that structure contained +a member requiring 128-bit alignment. This is corrected in more +recent versions of GCC. This option may be used to generate code +that is compatible with functions compiled with older versions of +GCC. + +The @option{-mno-compat-align-parm} option is the default. + +@item -mstack-protector-guard=@var{guard} +@itemx -mstack-protector-guard-reg=@var{reg} +@itemx -mstack-protector-guard-offset=@var{offset} +@itemx -mstack-protector-guard-symbol=@var{symbol} +@opindex mstack-protector-guard +@opindex mstack-protector-guard-reg +@opindex mstack-protector-guard-offset +@opindex mstack-protector-guard-symbol +Generate stack protection code using canary at @var{guard}. Supported +locations are @samp{global} for global canary or @samp{tls} for per-thread +canary in the TLS block (the default with GNU libc version 2.4 or later). + +With the latter choice the options +@option{-mstack-protector-guard-reg=@var{reg}} and +@option{-mstack-protector-guard-offset=@var{offset}} furthermore specify +which register to use as base register for reading the canary, and from what +offset from that base register. The default for those is as specified in the +relevant ABI. @option{-mstack-protector-guard-symbol=@var{symbol}} overrides +the offset with a symbol reference to a canary in the TLS block. + +@item -mpcrel +@itemx -mno-pcrel +@opindex mpcrel +@opindex mno-pcrel +Generate (do not generate) pc-relative addressing. The @option{-mpcrel} +option requires that the medium code model (@option{-mcmodel=medium}) +and prefixed addressing (@option{-mprefixed}) options are enabled. + +@item -mprefixed +@itemx -mno-prefixed +@opindex mprefixed +@opindex mno-prefixed +Generate (do not generate) addressing modes using prefixed load and +store instructions. The @option{-mprefixed} option requires that +the option @option{-mcpu=power10} (or later) is enabled. + +@item -mmma +@itemx -mno-mma +@opindex mmma +@opindex mno-mma +Generate (do not generate) the MMA instructions. The @option{-mma} +option requires that the option @option{-mcpu=power10} (or later) +is enabled. + +@item -mrop-protect +@itemx -mno-rop-protect +@opindex mrop-protect +@opindex mno-rop-protect +Generate (do not generate) ROP protection instructions when the target +processor supports them. Currently this option disables the shrink-wrap +optimization (@option{-fshrink-wrap}). + +@item -mprivileged +@itemx -mno-privileged +@opindex mprivileged +@opindex mno-privileged +Generate (do not generate) code that will run in privileged state. + +@item -mblock-ops-unaligned-vsx +@itemx -mno-block-ops-unaligned-vsx +@opindex block-ops-unaligned-vsx +@opindex no-block-ops-unaligned-vsx +Generate (do not generate) unaligned vsx loads and stores for +inline expansion of @code{memcpy} and @code{memmove}. + +@item --param rs6000-vect-unroll-limit= +The vectorizer will check with target information to determine whether it +would be beneficial to unroll the main vectorized loop and by how much. This +parameter sets the upper bound of how much the vectorizer will unroll the main +loop. The default value is four. + +@end table + +@node RX Options +@subsection RX Options +@cindex RX Options + +These command-line options are defined for RX targets: + +@table @gcctabopt +@item -m64bit-doubles +@itemx -m32bit-doubles +@opindex m64bit-doubles +@opindex m32bit-doubles +Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) +or 32 bits (@option{-m32bit-doubles}) in size. The default is +@option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only +works on 32-bit values, which is why the default is +@option{-m32bit-doubles}. + +@item -fpu +@itemx -nofpu +@opindex fpu +@opindex nofpu +Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX +floating-point hardware. The default is enabled for the RX600 +series and disabled for the RX200 series. + +Floating-point instructions are only generated for 32-bit floating-point +values, however, so the FPU hardware is not used for doubles if the +@option{-m64bit-doubles} option is used. + +@emph{Note} If the @option{-fpu} option is enabled then +@option{-funsafe-math-optimizations} is also enabled automatically. +This is because the RX FPU instructions are themselves unsafe. + +@item -mcpu=@var{name} +@opindex mcpu +Selects the type of RX CPU to be targeted. Currently three types are +supported, the generic @samp{RX600} and @samp{RX200} series hardware and +the specific @samp{RX610} CPU. The default is @samp{RX600}. + +The only difference between @samp{RX600} and @samp{RX610} is that the +@samp{RX610} does not support the @code{MVTIPL} instruction. + +The @samp{RX200} series does not have a hardware floating-point unit +and so @option{-nofpu} is enabled by default when this type is +selected. + +@item -mbig-endian-data +@itemx -mlittle-endian-data +@opindex mbig-endian-data +@opindex mlittle-endian-data +Store data (but not code) in the big-endian format. The default is +@option{-mlittle-endian-data}, i.e.@: to store data in the little-endian +format. + +@item -msmall-data-limit=@var{N} +@opindex msmall-data-limit +Specifies the maximum size in bytes of global and static variables +which can be placed into the small data area. Using the small data +area can lead to smaller and faster code, but the size of area is +limited and it is up to the programmer to ensure that the area does +not overflow. Also when the small data area is used one of the RX's +registers (usually @code{r13}) is reserved for use pointing to this +area, so it is no longer available for use by the compiler. This +could result in slower and/or larger code if variables are pushed onto +the stack instead of being held in this register. + +Note, common variables (variables that have not been initialized) and +constants are not placed into the small data area as they are assigned +to other sections in the output executable. + +The default value is zero, which disables this feature. Note, this +feature is not enabled by default with higher optimization levels +(@option{-O2} etc) because of the potentially detrimental effects of +reserving a register. It is up to the programmer to experiment and +discover whether this feature is of benefit to their program. See the +description of the @option{-mpid} option for a description of how the +actual register to hold the small data area pointer is chosen. + +@item -msim +@itemx -mno-sim +@opindex msim +@opindex mno-sim +Use the simulator runtime. The default is to use the libgloss +board-specific runtime. + +@item -mas100-syntax +@itemx -mno-as100-syntax +@opindex mas100-syntax +@opindex mno-as100-syntax +When generating assembler output use a syntax that is compatible with +Renesas's AS100 assembler. This syntax can also be handled by the GAS +assembler, but it has some restrictions so it is not generated by default. + +@item -mmax-constant-size=@var{N} +@opindex mmax-constant-size +Specifies the maximum size, in bytes, of a constant that can be used as +an operand in a RX instruction. Although the RX instruction set does +allow constants of up to 4 bytes in length to be used in instructions, +a longer value equates to a longer instruction. Thus in some +circumstances it can be beneficial to restrict the size of constants +that are used in instructions. Constants that are too big are instead +placed into a constant pool and referenced via register indirection. + +The value @var{N} can be between 0 and 4. A value of 0 (the default) +or 4 means that constants of any size are allowed. + +@item -mrelax +@opindex mrelax +Enable linker relaxation. Linker relaxation is a process whereby the +linker attempts to reduce the size of a program by finding shorter +versions of various instructions. Disabled by default. + +@item -mint-register=@var{N} +@opindex mint-register +Specify the number of registers to reserve for fast interrupt handler +functions. The value @var{N} can be between 0 and 4. A value of 1 +means that register @code{r13} is reserved for the exclusive use +of fast interrupt handlers. A value of 2 reserves @code{r13} and +@code{r12}. A value of 3 reserves @code{r13}, @code{r12} and +@code{r11}, and a value of 4 reserves @code{r13} through @code{r10}. +A value of 0, the default, does not reserve any registers. + +@item -msave-acc-in-interrupts +@opindex msave-acc-in-interrupts +Specifies that interrupt handler functions should preserve the +accumulator register. This is only necessary if normal code might use +the accumulator register, for example because it performs 64-bit +multiplications. The default is to ignore the accumulator as this +makes the interrupt handlers faster. + +@item -mpid +@itemx -mno-pid +@opindex mpid +@opindex mno-pid +Enables the generation of position independent data. When enabled any +access to constant data is done via an offset from a base address +held in a register. This allows the location of constant data to be +determined at run time without requiring the executable to be +relocated, which is a benefit to embedded applications with tight +memory constraints. Data that can be modified is not affected by this +option. + +Note, using this feature reserves a register, usually @code{r13}, for +the constant data base address. This can result in slower and/or +larger code, especially in complicated functions. + +The actual register chosen to hold the constant data base address +depends upon whether the @option{-msmall-data-limit} and/or the +@option{-mint-register} command-line options are enabled. Starting +with register @code{r13} and proceeding downwards, registers are +allocated first to satisfy the requirements of @option{-mint-register}, +then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it +is possible for the small data area register to be @code{r8} if both +@option{-mint-register=4} and @option{-mpid} are specified on the +command line. + +By default this feature is not enabled. The default can be restored +via the @option{-mno-pid} command-line option. + +@item -mno-warn-multiple-fast-interrupts +@itemx -mwarn-multiple-fast-interrupts +@opindex mno-warn-multiple-fast-interrupts +@opindex mwarn-multiple-fast-interrupts +Prevents GCC from issuing a warning message if it finds more than one +fast interrupt handler when it is compiling a file. The default is to +issue a warning for each extra fast interrupt handler found, as the RX +only supports one such interrupt. + +@item -mallow-string-insns +@itemx -mno-allow-string-insns +@opindex mallow-string-insns +@opindex mno-allow-string-insns +Enables or disables the use of the string manipulation instructions +@code{SMOVF}, @code{SCMPU}, @code{SMOVB}, @code{SMOVU}, @code{SUNTIL} +@code{SWHILE} and also the @code{RMPA} instruction. These +instructions may prefetch data, which is not safe to do if accessing +an I/O register. (See section 12.2.7 of the RX62N Group User's Manual +for more information). + +The default is to allow these instructions, but it is not possible for +GCC to reliably detect all circumstances where a string instruction +might be used to access an I/O register, so their use cannot be +disabled automatically. Instead it is reliant upon the programmer to +use the @option{-mno-allow-string-insns} option if their program +accesses I/O space. + +When the instructions are enabled GCC defines the C preprocessor +symbol @code{__RX_ALLOW_STRING_INSNS__}, otherwise it defines the +symbol @code{__RX_DISALLOW_STRING_INSNS__}. + +@item -mjsr +@itemx -mno-jsr +@opindex mjsr +@opindex mno-jsr +Use only (or not only) @code{JSR} instructions to access functions. +This option can be used when code size exceeds the range of @code{BSR} +instructions. Note that @option{-mno-jsr} does not mean to not use +@code{JSR} but instead means that any type of branch may be used. +@end table + +@emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}} +has special significance to the RX port when used with the +@code{interrupt} function attribute. This attribute indicates a +function intended to process fast interrupts. GCC ensures +that it only uses the registers @code{r10}, @code{r11}, @code{r12} +and/or @code{r13} and only provided that the normal use of the +corresponding registers have been restricted via the +@option{-ffixed-@var{reg}} or @option{-mint-register} command-line +options. + +@node S/390 and zSeries Options +@subsection S/390 and zSeries Options +@cindex S/390 and zSeries Options + +These are the @samp{-m} options defined for the S/390 and zSeries architecture. + +@table @gcctabopt +@item -mhard-float +@itemx -msoft-float +@opindex mhard-float +@opindex msoft-float +Use (do not use) the hardware floating-point instructions and registers +for floating-point operations. When @option{-msoft-float} is specified, +functions in @file{libgcc.a} are used to perform floating-point +operations. When @option{-mhard-float} is specified, the compiler +generates IEEE floating-point instructions. This is the default. + +@item -mhard-dfp +@itemx -mno-hard-dfp +@opindex mhard-dfp +@opindex mno-hard-dfp +Use (do not use) the hardware decimal-floating-point instructions for +decimal-floating-point operations. When @option{-mno-hard-dfp} is +specified, functions in @file{libgcc.a} are used to perform +decimal-floating-point operations. When @option{-mhard-dfp} is +specified, the compiler generates decimal-floating-point hardware +instructions. This is the default for @option{-march=z9-ec} or higher. + +@item -mlong-double-64 +@itemx -mlong-double-128 +@opindex mlong-double-64 +@opindex mlong-double-128 +These switches control the size of @code{long double} type. A size +of 64 bits makes the @code{long double} type equivalent to the @code{double} +type. This is the default. + +@item -mbackchain +@itemx -mno-backchain +@opindex mbackchain +@opindex mno-backchain +Store (do not store) the address of the caller's frame as backchain pointer +into the callee's stack frame. +A backchain may be needed to allow debugging using tools that do not understand +DWARF call frame information. +When @option{-mno-packed-stack} is in effect, the backchain pointer is stored +at the bottom of the stack frame; when @option{-mpacked-stack} is in effect, +the backchain is placed into the topmost word of the 96/160 byte register +save area. + +In general, code compiled with @option{-mbackchain} is call-compatible with +code compiled with @option{-mno-backchain}; however, use of the backchain +for debugging purposes usually requires that the whole binary is built with +@option{-mbackchain}. Note that the combination of @option{-mbackchain}, +@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order +to build a linux kernel use @option{-msoft-float}. + +The default is to not maintain the backchain. + +@item -mpacked-stack +@itemx -mno-packed-stack +@opindex mpacked-stack +@opindex mno-packed-stack +Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is +specified, the compiler uses the all fields of the 96/160 byte register save +area only for their default purpose; unused fields still take up stack space. +When @option{-mpacked-stack} is specified, register save slots are densely +packed at the top of the register save area; unused space is reused for other +purposes, allowing for more efficient use of the available stack space. +However, when @option{-mbackchain} is also in effect, the topmost word of +the save area is always used to store the backchain, and the return address +register is always saved two words below the backchain. + +As long as the stack frame backchain is not used, code generated with +@option{-mpacked-stack} is call-compatible with code generated with +@option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for +S/390 or zSeries generated code that uses the stack frame backchain at run +time, not just for debugging purposes. Such code is not call-compatible +with code compiled with @option{-mpacked-stack}. Also, note that the +combination of @option{-mbackchain}, +@option{-mpacked-stack} and @option{-mhard-float} is not supported. In order +to build a linux kernel use @option{-msoft-float}. + +The default is to not use the packed stack layout. + +@item -msmall-exec +@itemx -mno-small-exec +@opindex msmall-exec +@opindex mno-small-exec +Generate (or do not generate) code using the @code{bras} instruction +to do subroutine calls. +This only works reliably if the total executable size does not +exceed 64k. The default is to use the @code{basr} instruction instead, +which does not have this limitation. + +@item -m64 +@itemx -m31 +@opindex m64 +@opindex m31 +When @option{-m31} is specified, generate code compliant to the +GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate +code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in +particular to generate 64-bit instructions. For the @samp{s390} +targets, the default is @option{-m31}, while the @samp{s390x} +targets default to @option{-m64}. + +@item -mzarch +@itemx -mesa +@opindex mzarch +@opindex mesa +When @option{-mzarch} is specified, generate code using the +instructions available on z/Architecture. +When @option{-mesa} is specified, generate code using the +instructions available on ESA/390. Note that @option{-mesa} is +not possible with @option{-m64}. +When generating code compliant to the GNU/Linux for S/390 ABI, +the default is @option{-mesa}. When generating code compliant +to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}. + +@item -mhtm +@itemx -mno-htm +@opindex mhtm +@opindex mno-htm +The @option{-mhtm} option enables a set of builtins making use of +instructions available with the transactional execution facility +introduced with the IBM zEnterprise EC12 machine generation +@ref{S/390 System z Built-in Functions}. +@option{-mhtm} is enabled by default when using @option{-march=zEC12}. + +@item -mvx +@itemx -mno-vx +@opindex mvx +@opindex mno-vx +When @option{-mvx} is specified, generate code using the instructions +available with the vector extension facility introduced with the IBM +z13 machine generation. +This option changes the ABI for some vector type values with regard to +alignment and calling conventions. In case vector type values are +being used in an ABI-relevant context a GAS @samp{.gnu_attribute} +command will be added to mark the resulting binary with the ABI used. +@option{-mvx} is enabled by default when using @option{-march=z13}. + +@item -mzvector +@itemx -mno-zvector +@opindex mzvector +@opindex mno-zvector +The @option{-mzvector} option enables vector language extensions and +builtins using instructions available with the vector extension +facility introduced with the IBM z13 machine generation. +This option adds support for @samp{vector} to be used as a keyword to +define vector type variables and arguments. @samp{vector} is only +available when GNU extensions are enabled. It will not be expanded +when requesting strict standard compliance e.g.@: with @option{-std=c99}. +In addition to the GCC low-level builtins @option{-mzvector} enables +a set of builtins added for compatibility with AltiVec-style +implementations like Power and Cell. In order to make use of these +builtins the header file @file{vecintrin.h} needs to be included. +@option{-mzvector} is disabled by default. + +@item -mmvcle +@itemx -mno-mvcle +@opindex mmvcle +@opindex mno-mvcle +Generate (or do not generate) code using the @code{mvcle} instruction +to perform block moves. When @option{-mno-mvcle} is specified, +use a @code{mvc} loop instead. This is the default unless optimizing for +size. + +@item -mdebug +@itemx -mno-debug +@opindex mdebug +@opindex mno-debug +Print (or do not print) additional debug information when compiling. +The default is to not print debug information. + +@item -march=@var{cpu-type} +@opindex march +Generate code that runs on @var{cpu-type}, which is the name of a +system representing a certain processor type. Possible values for +@var{cpu-type} are @samp{z900}/@samp{arch5}, @samp{z990}/@samp{arch6}, +@samp{z9-109}, @samp{z9-ec}/@samp{arch7}, @samp{z10}/@samp{arch8}, +@samp{z196}/@samp{arch9}, @samp{zEC12}, @samp{z13}/@samp{arch11}, +@samp{z14}/@samp{arch12}, @samp{z15}/@samp{arch13}, +@samp{z16}/@samp{arch14}, and @samp{native}. + +The default is @option{-march=z900}. + +Specifying @samp{native} as cpu type can be used to select the best +architecture option for the host processor. +@option{-march=native} has no effect if GCC does not recognize the +processor. + +@item -mtune=@var{cpu-type} +@opindex mtune +Tune to @var{cpu-type} everything applicable about the generated code, +except for the ABI and the set of available instructions. +The list of @var{cpu-type} values is the same as for @option{-march}. +The default is the value used for @option{-march}. + +@item -mtpf-trace +@itemx -mno-tpf-trace +@opindex mtpf-trace +@opindex mno-tpf-trace +Generate code that adds (does not add) in TPF OS specific branches to trace +routines in the operating system. This option is off by default, even +when compiling for the TPF OS@. + +@item -mtpf-trace-skip +@itemx -mno-tpf-trace-skip +@opindex mtpf-trace-skip +@opindex mno-tpf-trace-skip +Generate code that changes (does not change) the default branch +targets enabled by @option{-mtpf-trace} to point to specialized trace +routines providing the ability of selectively skipping function trace +entries for the TPF OS. This option is off by default, even when +compiling for the TPF OS and specifying @option{-mtpf-trace}. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Generate code that uses (does not use) the floating-point multiply and +accumulate instructions. These instructions are generated by default if +hardware floating point is used. + +@item -mwarn-framesize=@var{framesize} +@opindex mwarn-framesize +Emit a warning if the current function exceeds the given frame size. Because +this is a compile-time check it doesn't need to be a real problem when the program +runs. It is intended to identify functions that most probably cause +a stack overflow. It is useful to be used in an environment with limited stack +size e.g.@: the linux kernel. + +@item -mwarn-dynamicstack +@opindex mwarn-dynamicstack +Emit a warning if the function calls @code{alloca} or uses dynamically-sized +arrays. This is generally a bad idea with a limited stack size. + +@item -mstack-guard=@var{stack-guard} +@itemx -mstack-size=@var{stack-size} +@opindex mstack-guard +@opindex mstack-size +If these options are provided the S/390 back end emits additional instructions in +the function prologue that trigger a trap if the stack size is @var{stack-guard} +bytes above the @var{stack-size} (remember that the stack on S/390 grows downward). +If the @var{stack-guard} option is omitted the smallest power of 2 larger than +the frame size of the compiled function is chosen. +These options are intended to be used to help debugging stack overflow problems. +The additionally emitted code causes only little overhead and hence can also be +used in production-like systems without greater performance degradation. The given +values have to be exact powers of 2 and @var{stack-size} has to be greater than +@var{stack-guard} without exceeding 64k. +In order to be efficient the extra code makes the assumption that the stack starts +at an address aligned to the value given by @var{stack-size}. +The @var{stack-guard} option can only be used in conjunction with @var{stack-size}. + +@item -mhotpatch=@var{pre-halfwords},@var{post-halfwords} +@opindex mhotpatch +If the hotpatch option is enabled, a ``hot-patching'' function +prologue is generated for all functions in the compilation unit. +The funtion label is prepended with the given number of two-byte +NOP instructions (@var{pre-halfwords}, maximum 1000000). After +the label, 2 * @var{post-halfwords} bytes are appended, using the +largest NOP like instructions the architecture allows (maximum +1000000). + +If both arguments are zero, hotpatching is disabled. + +This option can be overridden for individual functions with the +@code{hotpatch} attribute. +@end table + +@node Score Options +@subsection Score Options +@cindex Score Options + +These options are defined for Score implementations: + +@table @gcctabopt +@item -meb +@opindex meb +Compile code for big-endian mode. This is the default. + +@item -mel +@opindex mel +Compile code for little-endian mode. + +@item -mnhwloop +@opindex mnhwloop +Disable generation of @code{bcnz} instructions. + +@item -muls +@opindex muls +Enable generation of unaligned load and store instructions. + +@item -mmac +@opindex mmac +Enable the use of multiply-accumulate instructions. Disabled by default. + +@item -mscore5 +@opindex mscore5 +Specify the SCORE5 as the target architecture. + +@item -mscore5u +@opindex mscore5u +Specify the SCORE5U of the target architecture. + +@item -mscore7 +@opindex mscore7 +Specify the SCORE7 as the target architecture. This is the default. + +@item -mscore7d +@opindex mscore7d +Specify the SCORE7D as the target architecture. +@end table + +@node SH Options +@subsection SH Options + +These @samp{-m} options are defined for the SH implementations: + +@table @gcctabopt +@item -m1 +@opindex m1 +Generate code for the SH1. + +@item -m2 +@opindex m2 +Generate code for the SH2. + +@item -m2e +Generate code for the SH2e. + +@item -m2a-nofpu +@opindex m2a-nofpu +Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way +that the floating-point unit is not used. + +@item -m2a-single-only +@opindex m2a-single-only +Generate code for the SH2a-FPU, in such a way that no double-precision +floating-point operations are used. + +@item -m2a-single +@opindex m2a-single +Generate code for the SH2a-FPU assuming the floating-point unit is in +single-precision mode by default. + +@item -m2a +@opindex m2a +Generate code for the SH2a-FPU assuming the floating-point unit is in +double-precision mode by default. + +@item -m3 +@opindex m3 +Generate code for the SH3. + +@item -m3e +@opindex m3e +Generate code for the SH3e. + +@item -m4-nofpu +@opindex m4-nofpu +Generate code for the SH4 without a floating-point unit. + +@item -m4-single-only +@opindex m4-single-only +Generate code for the SH4 with a floating-point unit that only +supports single-precision arithmetic. + +@item -m4-single +@opindex m4-single +Generate code for the SH4 assuming the floating-point unit is in +single-precision mode by default. + +@item -m4 +@opindex m4 +Generate code for the SH4. + +@item -m4-100 +@opindex m4-100 +Generate code for SH4-100. + +@item -m4-100-nofpu +@opindex m4-100-nofpu +Generate code for SH4-100 in such a way that the +floating-point unit is not used. + +@item -m4-100-single +@opindex m4-100-single +Generate code for SH4-100 assuming the floating-point unit is in +single-precision mode by default. + +@item -m4-100-single-only +@opindex m4-100-single-only +Generate code for SH4-100 in such a way that no double-precision +floating-point operations are used. + +@item -m4-200 +@opindex m4-200 +Generate code for SH4-200. + +@item -m4-200-nofpu +@opindex m4-200-nofpu +Generate code for SH4-200 without in such a way that the +floating-point unit is not used. + +@item -m4-200-single +@opindex m4-200-single +Generate code for SH4-200 assuming the floating-point unit is in +single-precision mode by default. + +@item -m4-200-single-only +@opindex m4-200-single-only +Generate code for SH4-200 in such a way that no double-precision +floating-point operations are used. + +@item -m4-300 +@opindex m4-300 +Generate code for SH4-300. + +@item -m4-300-nofpu +@opindex m4-300-nofpu +Generate code for SH4-300 without in such a way that the +floating-point unit is not used. + +@item -m4-300-single +@opindex m4-300-single +Generate code for SH4-300 in such a way that no double-precision +floating-point operations are used. + +@item -m4-300-single-only +@opindex m4-300-single-only +Generate code for SH4-300 in such a way that no double-precision +floating-point operations are used. + +@item -m4-340 +@opindex m4-340 +Generate code for SH4-340 (no MMU, no FPU). + +@item -m4-500 +@opindex m4-500 +Generate code for SH4-500 (no FPU). Passes @option{-isa=sh4-nofpu} to the +assembler. + +@item -m4a-nofpu +@opindex m4a-nofpu +Generate code for the SH4al-dsp, or for a SH4a in such a way that the +floating-point unit is not used. + +@item -m4a-single-only +@opindex m4a-single-only +Generate code for the SH4a, in such a way that no double-precision +floating-point operations are used. + +@item -m4a-single +@opindex m4a-single +Generate code for the SH4a assuming the floating-point unit is in +single-precision mode by default. + +@item -m4a +@opindex m4a +Generate code for the SH4a. + +@item -m4al +@opindex m4al +Same as @option{-m4a-nofpu}, except that it implicitly passes +@option{-dsp} to the assembler. GCC doesn't generate any DSP +instructions at the moment. + +@item -mb +@opindex mb +Compile code for the processor in big-endian mode. + +@item -ml +@opindex ml +Compile code for the processor in little-endian mode. + +@item -mdalign +@opindex mdalign +Align doubles at 64-bit boundaries. Note that this changes the calling +conventions, and thus some functions from the standard C library do +not work unless you recompile it first with @option{-mdalign}. + +@item -mrelax +@opindex mrelax +Shorten some address references at link time, when possible; uses the +linker option @option{-relax}. + +@item -mbigtable +@opindex mbigtable +Use 32-bit offsets in @code{switch} tables. The default is to use +16-bit offsets. + +@item -mbitops +@opindex mbitops +Enable the use of bit manipulation instructions on SH2A. + +@item -mfmovd +@opindex mfmovd +Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for +alignment constraints. + +@item -mrenesas +@opindex mrenesas +Comply with the calling conventions defined by Renesas. + +@item -mno-renesas +@opindex mno-renesas +Comply with the calling conventions defined for GCC before the Renesas +conventions were available. This option is the default for all +targets of the SH toolchain. + +@item -mnomacsave +@opindex mnomacsave +Mark the @code{MAC} register as call-clobbered, even if +@option{-mrenesas} is given. + +@item -mieee +@itemx -mno-ieee +@opindex mieee +@opindex mno-ieee +Control the IEEE compliance of floating-point comparisons, which affects the +handling of cases where the result of a comparison is unordered. By default +@option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is +enabled @option{-mno-ieee} is implicitly set, which results in faster +floating-point greater-equal and less-equal comparisons. The implicit settings +can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}. + +@item -minline-ic_invalidate +@opindex minline-ic_invalidate +Inline code to invalidate instruction cache entries after setting up +nested function trampolines. +This option has no effect if @option{-musermode} is in effect and the selected +code generation option (e.g.@: @option{-m4}) does not allow the use of the @code{icbi} +instruction. +If the selected code generation option does not allow the use of the @code{icbi} +instruction, and @option{-musermode} is not in effect, the inlined code +manipulates the instruction cache address array directly with an associative +write. This not only requires privileged mode at run time, but it also +fails if the cache line had been mapped via the TLB and has become unmapped. + +@item -misize +@opindex misize +Dump instruction size and location in the assembly code. + +@item -mpadstruct +@opindex mpadstruct +This option is deprecated. It pads structures to multiple of 4 bytes, +which is incompatible with the SH ABI@. + +@item -matomic-model=@var{model} +@opindex matomic-model=@var{model} +Sets the model of atomic operations and additional parameters as a comma +separated list. For details on the atomic built-in functions see +@ref{__atomic Builtins}. The following models and parameters are supported: + +@table @samp + +@item none +Disable compiler generated atomic sequences and emit library calls for atomic +operations. This is the default if the target is not @code{sh*-*-linux*}. + +@item soft-gusa +Generate GNU/Linux compatible gUSA software atomic sequences for the atomic +built-in functions. The generated atomic sequences require additional support +from the interrupt/exception handling code of the system and are only suitable +for SH3* and SH4* single-core systems. This option is enabled by default when +the target is @code{sh*-*-linux*} and SH3* or SH4*. When the target is SH4A, +this option also partially utilizes the hardware atomic instructions +@code{movli.l} and @code{movco.l} to create more efficient code, unless +@samp{strict} is specified. + +@item soft-tcb +Generate software atomic sequences that use a variable in the thread control +block. This is a variation of the gUSA sequences which can also be used on +SH1* and SH2* targets. The generated atomic sequences require additional +support from the interrupt/exception handling code of the system and are only +suitable for single-core systems. When using this model, the @samp{gbr-offset=} +parameter has to be specified as well. + +@item soft-imask +Generate software atomic sequences that temporarily disable interrupts by +setting @code{SR.IMASK = 1111}. This model works only when the program runs +in privileged mode and is only suitable for single-core systems. Additional +support from the interrupt/exception handling code of the system is not +required. This model is enabled by default when the target is +@code{sh*-*-linux*} and SH1* or SH2*. + +@item hard-llcs +Generate hardware atomic sequences using the @code{movli.l} and @code{movco.l} +instructions only. This is only available on SH4A and is suitable for +multi-core systems. Since the hardware instructions support only 32 bit atomic +variables access to 8 or 16 bit variables is emulated with 32 bit accesses. +Code compiled with this option is also compatible with other software +atomic model interrupt/exception handling systems if executed on an SH4A +system. Additional support from the interrupt/exception handling code of the +system is not required for this model. + +@item gbr-offset= +This parameter specifies the offset in bytes of the variable in the thread +control block structure that should be used by the generated atomic sequences +when the @samp{soft-tcb} model has been selected. For other models this +parameter is ignored. The specified value must be an integer multiple of four +and in the range 0-1020. + +@item strict +This parameter prevents mixed usage of multiple atomic models, even if they +are compatible, and makes the compiler generate atomic sequences of the +specified model only. + +@end table + +@item -mtas +@opindex mtas +Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}. +Notice that depending on the particular hardware and software configuration +this can degrade overall performance due to the operand cache line flushes +that are implied by the @code{tas.b} instruction. On multi-core SH4A +processors the @code{tas.b} instruction must be used with caution since it +can result in data corruption for certain cache configurations. + +@item -mprefergot +@opindex mprefergot +When generating position-independent code, emit function calls using +the Global Offset Table instead of the Procedure Linkage Table. + +@item -musermode +@itemx -mno-usermode +@opindex musermode +@opindex mno-usermode +Don't allow (allow) the compiler generating privileged mode code. Specifying +@option{-musermode} also implies @option{-mno-inline-ic_invalidate} if the +inlined code would not work in user mode. @option{-musermode} is the default +when the target is @code{sh*-*-linux*}. If the target is SH1* or SH2* +@option{-musermode} has no effect, since there is no user mode. + +@item -multcost=@var{number} +@opindex multcost=@var{number} +Set the cost to assume for a multiply insn. + +@item -mdiv=@var{strategy} +@opindex mdiv=@var{strategy} +Set the division strategy to be used for integer division operations. +@var{strategy} can be one of: + +@table @samp + +@item call-div1 +Calls a library function that uses the single-step division instruction +@code{div1} to perform the operation. Division by zero calculates an +unspecified result and does not trap. This is the default except for SH4, +SH2A and SHcompact. + +@item call-fp +Calls a library function that performs the operation in double precision +floating point. Division by zero causes a floating-point exception. This is +the default for SHcompact with FPU. Specifying this for targets that do not +have a double precision FPU defaults to @code{call-div1}. + +@item call-table +Calls a library function that uses a lookup table for small divisors and +the @code{div1} instruction with case distinction for larger divisors. Division +by zero calculates an unspecified result and does not trap. This is the default +for SH4. Specifying this for targets that do not have dynamic shift +instructions defaults to @code{call-div1}. + +@end table + +When a division strategy has not been specified the default strategy is +selected based on the current target. For SH2A the default strategy is to +use the @code{divs} and @code{divu} instructions instead of library function +calls. + +@item -maccumulate-outgoing-args +@opindex maccumulate-outgoing-args +Reserve space once for outgoing arguments in the function prologue rather +than around each call. Generally beneficial for performance and size. Also +needed for unwinding to avoid changing the stack frame around conditional code. + +@item -mdivsi3_libfunc=@var{name} +@opindex mdivsi3_libfunc=@var{name} +Set the name of the library function used for 32-bit signed division to +@var{name}. +This only affects the name used in the @samp{call} division strategies, and +the compiler still expects the same sets of input/output/clobbered registers as +if this option were not present. + +@item -mfixed-range=@var{register-range} +@opindex mfixed-range +Generate code treating the given register range as fixed registers. +A fixed register is one that the register allocator cannot use. This is +useful when compiling kernel code. A register range is specified as +two registers separated by a dash. Multiple register ranges can be +specified separated by a comma. + +@item -mbranch-cost=@var{num} +@opindex mbranch-cost=@var{num} +Assume @var{num} to be the cost for a branch instruction. Higher numbers +make the compiler try to generate more branch-free code if possible. +If not specified the value is selected depending on the processor type that +is being compiled for. + +@item -mzdcbranch +@itemx -mno-zdcbranch +@opindex mzdcbranch +@opindex mno-zdcbranch +Assume (do not assume) that zero displacement conditional branch instructions +@code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the +compiler prefers zero displacement branch code sequences. This is +enabled by default when generating code for SH4 and SH4A. It can be explicitly +disabled by specifying @option{-mno-zdcbranch}. + +@item -mcbranch-force-delay-slot +@opindex mcbranch-force-delay-slot +Force the usage of delay slots for conditional branches, which stuffs the delay +slot with a @code{nop} if a suitable instruction cannot be found. By default +this option is disabled. It can be enabled to work around hardware bugs as +found in the original SH7055. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Generate code that uses (does not use) the floating-point multiply and +accumulate instructions. These instructions are generated by default +if hardware floating point is used. The machine-dependent +@option{-mfused-madd} option is now mapped to the machine-independent +@option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is +mapped to @option{-ffp-contract=off}. + +@item -mfsca +@itemx -mno-fsca +@opindex mfsca +@opindex mno-fsca +Allow or disallow the compiler to emit the @code{fsca} instruction for sine +and cosine approximations. The option @option{-mfsca} must be used in +combination with @option{-funsafe-math-optimizations}. It is enabled by default +when generating code for SH4A. Using @option{-mno-fsca} disables sine and cosine +approximations even if @option{-funsafe-math-optimizations} is in effect. + +@item -mfsrra +@itemx -mno-fsrra +@opindex mfsrra +@opindex mno-fsrra +Allow or disallow the compiler to emit the @code{fsrra} instruction for +reciprocal square root approximations. The option @option{-mfsrra} must be used +in combination with @option{-funsafe-math-optimizations} and +@option{-ffinite-math-only}. It is enabled by default when generating code for +SH4A. Using @option{-mno-fsrra} disables reciprocal square root approximations +even if @option{-funsafe-math-optimizations} and @option{-ffinite-math-only} are +in effect. + +@item -mpretend-cmove +@opindex mpretend-cmove +Prefer zero-displacement conditional branches for conditional move instruction +patterns. This can result in faster code on the SH4 processor. + +@item -mfdpic +@opindex fdpic +Generate code using the FDPIC ABI. + +@end table + +@node Solaris 2 Options +@subsection Solaris 2 Options +@cindex Solaris 2 options + +These @samp{-m} options are supported on Solaris 2: + +@table @gcctabopt +@item -mclear-hwcap +@opindex mclear-hwcap +@option{-mclear-hwcap} tells the compiler to remove the hardware +capabilities generated by the Solaris assembler. This is only necessary +when object files use ISA extensions not supported by the current +machine, but check at runtime whether or not to use them. + +@item -mimpure-text +@opindex mimpure-text +@option{-mimpure-text}, used in addition to @option{-shared}, tells +the compiler to not pass @option{-z text} to the linker when linking a +shared object. Using this option, you can link position-dependent +code into a shared object. + +@option{-mimpure-text} suppresses the ``relocations remain against +allocatable but non-writable sections'' linker error message. +However, the necessary relocations trigger copy-on-write, and the +shared object is not actually shared across processes. Instead of +using @option{-mimpure-text}, you should compile all source code with +@option{-fpic} or @option{-fPIC}. + +@end table + +These switches are supported in addition to the above on Solaris 2: + +@table @gcctabopt +@item -pthreads +@opindex pthreads +This is a synonym for @option{-pthread}. +@end table + +@node SPARC Options +@subsection SPARC Options +@cindex SPARC options + +These @samp{-m} options are supported on the SPARC: + +@table @gcctabopt +@item -mno-app-regs +@itemx -mapp-regs +@opindex mno-app-regs +@opindex mapp-regs +Specify @option{-mapp-regs} to generate output using the global registers +2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the +global register 1, each global register 2 through 4 is then treated as an +allocable register that is clobbered by function calls. This is the default. + +To be fully SVR4 ABI-compliant at the cost of some performance loss, +specify @option{-mno-app-regs}. You should compile libraries and system +software with this option. + +@item -mflat +@itemx -mno-flat +@opindex mflat +@opindex mno-flat +With @option{-mflat}, the compiler does not generate save/restore instructions +and uses a ``flat'' or single register window model. This model is compatible +with the regular register window model. The local registers and the input +registers (0--5) are still treated as ``call-saved'' registers and are +saved on the stack as needed. + +With @option{-mno-flat} (the default), the compiler generates save/restore +instructions (except for leaf functions). This is the normal operating mode. + +@item -mfpu +@itemx -mhard-float +@opindex mfpu +@opindex mhard-float +Generate output containing floating-point instructions. This is the +default. + +@item -mno-fpu +@itemx -msoft-float +@opindex mno-fpu +@opindex msoft-float +Generate output containing library calls for floating point. +@strong{Warning:} the requisite libraries are not available for all SPARC +targets. Normally the facilities of the machine's usual C compiler are +used, but this cannot be done directly in cross-compilation. You must make +your own arrangements to provide suitable library functions for +cross-compilation. The embedded targets @samp{sparc-*-aout} and +@samp{sparclite-*-*} do provide software floating-point support. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. + +@item -mhard-quad-float +@opindex mhard-quad-float +Generate output containing quad-word (long double) floating-point +instructions. + +@item -msoft-quad-float +@opindex msoft-quad-float +Generate output containing library calls for quad-word (long double) +floating-point instructions. The functions called are those specified +in the SPARC ABI@. This is the default. + +As of this writing, there are no SPARC implementations that have hardware +support for the quad-word floating-point instructions. They all invoke +a trap handler for one of these instructions, and then the trap handler +emulates the effect of the instruction. Because of the trap handler overhead, +this is much slower than calling the ABI library routines. Thus the +@option{-msoft-quad-float} option is the default. + +@item -mno-unaligned-doubles +@itemx -munaligned-doubles +@opindex mno-unaligned-doubles +@opindex munaligned-doubles +Assume that doubles have 8-byte alignment. This is the default. + +With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte +alignment only if they are contained in another type, or if they have an +absolute address. Otherwise, it assumes they have 4-byte alignment. +Specifying this option avoids some rare compatibility problems with code +generated by other compilers. It is not the default because it results +in a performance loss, especially for floating-point code. + +@item -muser-mode +@itemx -mno-user-mode +@opindex muser-mode +@opindex mno-user-mode +Do not generate code that can only run in supervisor mode. This is relevant +only for the @code{casa} instruction emitted for the LEON3 processor. This +is the default. + +@item -mfaster-structs +@itemx -mno-faster-structs +@opindex mfaster-structs +@opindex mno-faster-structs +With @option{-mfaster-structs}, the compiler assumes that structures +should have 8-byte alignment. This enables the use of pairs of +@code{ldd} and @code{std} instructions for copies in structure +assignment, in place of twice as many @code{ld} and @code{st} pairs. +However, the use of this changed alignment directly violates the SPARC +ABI@. Thus, it's intended only for use on targets where the developer +acknowledges that their resulting code is not directly in line with +the rules of the ABI@. + +@item -mstd-struct-return +@itemx -mno-std-struct-return +@opindex mstd-struct-return +@opindex mno-std-struct-return +With @option{-mstd-struct-return}, the compiler generates checking code +in functions returning structures or unions to detect size mismatches +between the two sides of function calls, as per the 32-bit ABI@. + +The default is @option{-mno-std-struct-return}. This option has no effect +in 64-bit mode. + +@item -mlra +@itemx -mno-lra +@opindex mlra +@opindex mno-lra +Enable Local Register Allocation. This is the default for SPARC since GCC 7 +so @option{-mno-lra} needs to be passed to get old Reload. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set, register set, and instruction scheduling parameters +for machine type @var{cpu_type}. Supported values for @var{cpu_type} are +@samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc}, +@samp{leon}, @samp{leon3}, @samp{leon3v7}, @samp{leon5}, @samp{sparclite}, +@samp{f930}, @samp{f934}, @samp{sparclite86x}, @samp{sparclet}, @samp{tsc701}, +@samp{v9}, @samp{ultrasparc}, @samp{ultrasparc3}, @samp{niagara}, +@samp{niagara2}, @samp{niagara3}, @samp{niagara4}, @samp{niagara7} and +@samp{m8}. + +Native Solaris and GNU/Linux toolchains also support the value @samp{native}, +which selects the best architecture option for the host processor. +@option{-mcpu=native} has no effect if GCC does not recognize +the processor. + +Default instruction scheduling parameters are used for values that select +an architecture and not an implementation. These are @samp{v7}, @samp{v8}, +@samp{sparclite}, @samp{sparclet}, @samp{v9}. + +Here is a list of each supported architecture and their supported +implementations. + +@table @asis +@item v7 +cypress, leon3v7 + +@item v8 +supersparc, hypersparc, leon, leon3, leon5 + +@item sparclite +f930, f934, sparclite86x + +@item sparclet +tsc701 + +@item v9 +ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4, +niagara7, m8 +@end table + +By default (unless configured otherwise), GCC generates code for the V7 +variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler +additionally optimizes it for the Cypress CY7C602 chip, as used in the +SPARCStation/SPARCServer 3xx series. This is also appropriate for the older +SPARCStation 1, 2, IPX etc. + +With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC +architecture. The only difference from V7 code is that the compiler emits +the integer multiply and integer divide instructions which exist in SPARC-V8 +but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally +optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and +2000 series. + +With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of +the SPARC architecture. This adds the integer multiply, integer divide step +and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7. +With @option{-mcpu=f930}, the compiler additionally optimizes it for the +Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With +@option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu +MB86934 chip, which is the more recent SPARClite with FPU@. + +With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of +the SPARC architecture. This adds the integer multiply, multiply/accumulate, +integer divide step and scan (@code{ffs}) instructions which exist in SPARClet +but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally +optimizes it for the TEMIC SPARClet chip. + +With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC +architecture. This adds 64-bit integer and floating-point move instructions, +3 additional floating-point condition code registers and conditional move +instructions. With @option{-mcpu=ultrasparc}, the compiler additionally +optimizes it for the Sun UltraSPARC I/II/IIi chips. With +@option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the +Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With +@option{-mcpu=niagara}, the compiler additionally optimizes it for +Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler +additionally optimizes it for Sun UltraSPARC T2 chips. With +@option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun +UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler +additionally optimizes it for Sun UltraSPARC T4 chips. With +@option{-mcpu=niagara7}, the compiler additionally optimizes it for +Oracle SPARC M7 chips. With @option{-mcpu=m8}, the compiler +additionally optimizes it for Oracle M8 chips. + +@item -mtune=@var{cpu_type} +@opindex mtune +Set the instruction scheduling parameters for machine type +@var{cpu_type}, but do not set the instruction set or register set that the +option @option{-mcpu=@var{cpu_type}} does. + +The same values for @option{-mcpu=@var{cpu_type}} can be used for +@option{-mtune=@var{cpu_type}}, but the only useful values are those +that select a particular CPU implementation. Those are +@samp{cypress}, @samp{supersparc}, @samp{hypersparc}, @samp{leon}, +@samp{leon3}, @samp{leon3v7}, @samp{leon5}, @samp{f930}, @samp{f934}, +@samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, +@samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, @samp{niagara3}, +@samp{niagara4}, @samp{niagara7} and @samp{m8}. With native Solaris +and GNU/Linux toolchains, @samp{native} can also be used. + +@item -mv8plus +@itemx -mno-v8plus +@opindex mv8plus +@opindex mno-v8plus +With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The +difference from the V8 ABI is that the global and out registers are +considered 64 bits wide. This is enabled by default on Solaris in 32-bit +mode for all SPARC-V9 processors. + +@item -mvis +@itemx -mno-vis +@opindex mvis +@opindex mno-vis +With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC +Visual Instruction Set extensions. The default is @option{-mno-vis}. + +@item -mvis2 +@itemx -mno-vis2 +@opindex mvis2 +@opindex mno-vis2 +With @option{-mvis2}, GCC generates code that takes advantage of +version 2.0 of the UltraSPARC Visual Instruction Set extensions. The +default is @option{-mvis2} when targeting a cpu that supports such +instructions, such as UltraSPARC-III and later. Setting @option{-mvis2} +also sets @option{-mvis}. + +@item -mvis3 +@itemx -mno-vis3 +@opindex mvis3 +@opindex mno-vis3 +With @option{-mvis3}, GCC generates code that takes advantage of +version 3.0 of the UltraSPARC Visual Instruction Set extensions. The +default is @option{-mvis3} when targeting a cpu that supports such +instructions, such as niagara-3 and later. Setting @option{-mvis3} +also sets @option{-mvis2} and @option{-mvis}. + +@item -mvis4 +@itemx -mno-vis4 +@opindex mvis4 +@opindex mno-vis4 +With @option{-mvis4}, GCC generates code that takes advantage of +version 4.0 of the UltraSPARC Visual Instruction Set extensions. The +default is @option{-mvis4} when targeting a cpu that supports such +instructions, such as niagara-7 and later. Setting @option{-mvis4} +also sets @option{-mvis3}, @option{-mvis2} and @option{-mvis}. + +@item -mvis4b +@itemx -mno-vis4b +@opindex mvis4b +@opindex mno-vis4b +With @option{-mvis4b}, GCC generates code that takes advantage of +version 4.0 of the UltraSPARC Visual Instruction Set extensions, plus +the additional VIS instructions introduced in the Oracle SPARC +Architecture 2017. The default is @option{-mvis4b} when targeting a +cpu that supports such instructions, such as m8 and later. Setting +@option{-mvis4b} also sets @option{-mvis4}, @option{-mvis3}, +@option{-mvis2} and @option{-mvis}. + +@item -mcbcond +@itemx -mno-cbcond +@opindex mcbcond +@opindex mno-cbcond +With @option{-mcbcond}, GCC generates code that takes advantage of the UltraSPARC +Compare-and-Branch-on-Condition instructions. The default is @option{-mcbcond} +when targeting a CPU that supports such instructions, such as Niagara-4 and +later. + +@item -mfmaf +@itemx -mno-fmaf +@opindex mfmaf +@opindex mno-fmaf +With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC +Fused Multiply-Add Floating-point instructions. The default is @option{-mfmaf} +when targeting a CPU that supports such instructions, such as Niagara-3 and +later. + +@item -mfsmuld +@itemx -mno-fsmuld +@opindex mfsmuld +@opindex mno-fsmuld +With @option{-mfsmuld}, GCC generates code that takes advantage of the +Floating-point Multiply Single to Double (FsMULd) instruction. The default is +@option{-mfsmuld} when targeting a CPU supporting the architecture versions V8 +or V9 with FPU except @option{-mcpu=leon}. + +@item -mpopc +@itemx -mno-popc +@opindex mpopc +@opindex mno-popc +With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC +Population Count instruction. The default is @option{-mpopc} +when targeting a CPU that supports such an instruction, such as Niagara-2 and +later. + +@item -msubxc +@itemx -mno-subxc +@opindex msubxc +@opindex mno-subxc +With @option{-msubxc}, GCC generates code that takes advantage of the UltraSPARC +Subtract-Extended-with-Carry instruction. The default is @option{-msubxc} +when targeting a CPU that supports such an instruction, such as Niagara-7 and +later. + +@item -mfix-at697f +@opindex mfix-at697f +Enable the documented workaround for the single erratum of the Atmel AT697F +processor (which corresponds to erratum #13 of the AT697E processor). + +@item -mfix-ut699 +@opindex mfix-ut699 +Enable the documented workarounds for the floating-point errata and the data +cache nullify errata of the UT699 processor. + +@item -mfix-ut700 +@opindex mfix-ut700 +Enable the documented workaround for the back-to-back store errata of +the UT699E/UT700 processor. + +@item -mfix-gr712rc +@opindex mfix-gr712rc +Enable the documented workaround for the back-to-back store errata of +the GR712RC processor. +@end table + +These @samp{-m} options are supported in addition to the above +on SPARC-V9 processors in 64-bit environments: + +@table @gcctabopt +@item -m32 +@itemx -m64 +@opindex m32 +@opindex m64 +Generate code for a 32-bit or 64-bit environment. +The 32-bit environment sets int, long and pointer to 32 bits. +The 64-bit environment sets int to 32 bits and long and pointer +to 64 bits. + +@item -mcmodel=@var{which} +@opindex mcmodel +Set the code model to one of + +@table @samp +@item medlow +The Medium/Low code model: 64-bit addresses, programs +must be linked in the low 32 bits of memory. Programs can be statically +or dynamically linked. + +@item medmid +The Medium/Middle code model: 64-bit addresses, programs +must be linked in the low 44 bits of memory, the text and data segments must +be less than 2GB in size and the data segment must be located within 2GB of +the text segment. + +@item medany +The Medium/Anywhere code model: 64-bit addresses, programs +may be linked anywhere in memory, the text and data segments must be less +than 2GB in size and the data segment must be located within 2GB of the +text segment. + +@item embmedany +The Medium/Anywhere code model for embedded systems: +64-bit addresses, the text and data segments must be less than 2GB in +size, both starting anywhere in memory (determined at link time). The +global register %g4 points to the base of the data segment. Programs +are statically linked and PIC is not supported. +@end table + +@item -mmemory-model=@var{mem-model} +@opindex mmemory-model +Set the memory model in force on the processor to one of + +@table @samp +@item default +The default memory model for the processor and operating system. + +@item rmo +Relaxed Memory Order + +@item pso +Partial Store Order + +@item tso +Total Store Order + +@item sc +Sequential Consistency +@end table + +These memory models are formally defined in Appendix D of the SPARC-V9 +architecture manual, as set in the processor's @code{PSTATE.MM} field. + +@item -mstack-bias +@itemx -mno-stack-bias +@opindex mstack-bias +@opindex mno-stack-bias +With @option{-mstack-bias}, GCC assumes that the stack pointer, and +frame pointer if present, are offset by @minus{}2047 which must be added back +when making stack frame references. This is the default in 64-bit mode. +Otherwise, assume no such offset is present. +@end table + +@node System V Options +@subsection Options for System V + +These additional options are available on System V Release 4 for +compatibility with other compilers on those systems: + +@table @gcctabopt +@item -G +@opindex G +Create a shared object. +It is recommended that @option{-symbolic} or @option{-shared} be used instead. + +@item -Qy +@opindex Qy +Identify the versions of each tool used by the compiler, in a +@code{.ident} assembler directive in the output. + +@item -Qn +@opindex Qn +Refrain from adding @code{.ident} directives to the output file (this is +the default). + +@item -YP,@var{dirs} +@opindex YP +Search the directories @var{dirs}, and no others, for libraries +specified with @option{-l}. + +@item -Ym,@var{dir} +@opindex Ym +Look in the directory @var{dir} to find the M4 preprocessor. +The assembler uses this option. +@c This is supposed to go with a -Yd for predefined M4 macro files, but +@c the generic assembler that comes with Solaris takes just -Ym. +@end table + +@node V850 Options +@subsection V850 Options +@cindex V850 Options + +These @samp{-m} options are defined for V850 implementations: + +@table @gcctabopt +@item -mlong-calls +@itemx -mno-long-calls +@opindex mlong-calls +@opindex mno-long-calls +Treat all calls as being far away (near). If calls are assumed to be +far away, the compiler always loads the function's address into a +register, and calls indirect through the pointer. + +@item -mno-ep +@itemx -mep +@opindex mno-ep +@opindex mep +Do not optimize (do optimize) basic blocks that use the same index +pointer 4 or more times to copy pointer into the @code{ep} register, and +use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} +option is on by default if you optimize. + +@item -mno-prolog-function +@itemx -mprolog-function +@opindex mno-prolog-function +@opindex mprolog-function +Do not use (do use) external functions to save and restore registers +at the prologue and epilogue of a function. The external functions +are slower, but use less code space if more than one function saves +the same number of registers. The @option{-mprolog-function} option +is on by default if you optimize. + +@item -mspace +@opindex mspace +Try to make the code as small as possible. At present, this just turns +on the @option{-mep} and @option{-mprolog-function} options. + +@item -mtda=@var{n} +@opindex mtda +Put static or global variables whose size is @var{n} bytes or less into +the tiny data area that register @code{ep} points to. The tiny data +area can hold up to 256 bytes in total (128 bytes for byte references). + +@item -msda=@var{n} +@opindex msda +Put static or global variables whose size is @var{n} bytes or less into +the small data area that register @code{gp} points to. The small data +area can hold up to 64 kilobytes. + +@item -mzda=@var{n} +@opindex mzda +Put static or global variables whose size is @var{n} bytes or less into +the first 32 kilobytes of memory. + +@item -mv850 +@opindex mv850 +Specify that the target processor is the V850. + +@item -mv850e3v5 +@opindex mv850e3v5 +Specify that the target processor is the V850E3V5. The preprocessor +constant @code{__v850e3v5__} is defined if this option is used. + +@item -mv850e2v4 +@opindex mv850e2v4 +Specify that the target processor is the V850E3V5. This is an alias for +the @option{-mv850e3v5} option. + +@item -mv850e2v3 +@opindex mv850e2v3 +Specify that the target processor is the V850E2V3. The preprocessor +constant @code{__v850e2v3__} is defined if this option is used. + +@item -mv850e2 +@opindex mv850e2 +Specify that the target processor is the V850E2. The preprocessor +constant @code{__v850e2__} is defined if this option is used. + +@item -mv850e1 +@opindex mv850e1 +Specify that the target processor is the V850E1. The preprocessor +constants @code{__v850e1__} and @code{__v850e__} are defined if +this option is used. + +@item -mv850es +@opindex mv850es +Specify that the target processor is the V850ES. This is an alias for +the @option{-mv850e1} option. + +@item -mv850e +@opindex mv850e +Specify that the target processor is the V850E@. The preprocessor +constant @code{__v850e__} is defined if this option is used. + +If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1} +nor @option{-mv850e2} nor @option{-mv850e2v3} nor @option{-mv850e3v5} +are defined then a default target processor is chosen and the +relevant @samp{__v850*__} preprocessor constant is defined. + +The preprocessor constants @code{__v850} and @code{__v851__} are always +defined, regardless of which processor variant is the target. + +@item -mdisable-callt +@itemx -mno-disable-callt +@opindex mdisable-callt +@opindex mno-disable-callt +This option suppresses generation of the @code{CALLT} instruction for the +v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 +architecture. + +This option is enabled by default when the RH850 ABI is +in use (see @option{-mrh850-abi}), and disabled by default when the +GCC ABI is in use. If @code{CALLT} instructions are being generated +then the C preprocessor symbol @code{__V850_CALLT__} is defined. + +@item -mrelax +@itemx -mno-relax +@opindex mrelax +@opindex mno-relax +Pass on (or do not pass on) the @option{-mrelax} command-line option +to the assembler. + +@item -mlong-jumps +@itemx -mno-long-jumps +@opindex mlong-jumps +@opindex mno-long-jumps +Disable (or re-enable) the generation of PC-relative jump instructions. + +@item -msoft-float +@itemx -mhard-float +@opindex msoft-float +@opindex mhard-float +Disable (or re-enable) the generation of hardware floating point +instructions. This option is only significant when the target +architecture is @samp{V850E2V3} or higher. If hardware floating point +instructions are being generated then the C preprocessor symbol +@code{__FPU_OK__} is defined, otherwise the symbol +@code{__NO_FPU__} is defined. + +@item -mloop +@opindex mloop +Enables the use of the e3v5 LOOP instruction. The use of this +instruction is not enabled by default when the e3v5 architecture is +selected because its use is still experimental. + +@item -mrh850-abi +@itemx -mghs +@opindex mrh850-abi +@opindex mghs +Enables support for the RH850 version of the V850 ABI. This is the +default. With this version of the ABI the following rules apply: + +@itemize +@item +Integer sized structures and unions are returned via a memory pointer +rather than a register. + +@item +Large structures and unions (more than 8 bytes in size) are passed by +value. + +@item +Functions are aligned to 16-bit boundaries. + +@item +The @option{-m8byte-align} command-line option is supported. + +@item +The @option{-mdisable-callt} command-line option is enabled by +default. The @option{-mno-disable-callt} command-line option is not +supported. +@end itemize + +When this version of the ABI is enabled the C preprocessor symbol +@code{__V850_RH850_ABI__} is defined. + +@item -mgcc-abi +@opindex mgcc-abi +Enables support for the old GCC version of the V850 ABI. With this +version of the ABI the following rules apply: + +@itemize +@item +Integer sized structures and unions are returned in register @code{r10}. + +@item +Large structures and unions (more than 8 bytes in size) are passed by +reference. + +@item +Functions are aligned to 32-bit boundaries, unless optimizing for +size. + +@item +The @option{-m8byte-align} command-line option is not supported. + +@item +The @option{-mdisable-callt} command-line option is supported but not +enabled by default. +@end itemize + +When this version of the ABI is enabled the C preprocessor symbol +@code{__V850_GCC_ABI__} is defined. + +@item -m8byte-align +@itemx -mno-8byte-align +@opindex m8byte-align +@opindex mno-8byte-align +Enables support for @code{double} and @code{long long} types to be +aligned on 8-byte boundaries. The default is to restrict the +alignment of all objects to at most 4-bytes. When +@option{-m8byte-align} is in effect the C preprocessor symbol +@code{__V850_8BYTE_ALIGN__} is defined. + +@item -mbig-switch +@opindex mbig-switch +Generate code suitable for big switch tables. Use this option only if +the assembler/linker complain about out of range branches within a switch +table. + +@item -mapp-regs +@opindex mapp-regs +This option causes r2 and r5 to be used in the code generated by +the compiler. This setting is the default. + +@item -mno-app-regs +@opindex mno-app-regs +This option causes r2 and r5 to be treated as fixed registers. + +@end table + +@node VAX Options +@subsection VAX Options +@cindex VAX options + +These @samp{-m} options are defined for the VAX: + +@table @gcctabopt +@item -munix +@opindex munix +Do not output certain jump instructions (@code{aobleq} and so on) +that the Unix assembler for the VAX cannot handle across long +ranges. + +@item -mgnu +@opindex mgnu +Do output those jump instructions, on the assumption that the +GNU assembler is being used. + +@item -mg +@opindex mg +Output code for G-format floating-point numbers instead of D-format. + +@item -mlra +@itemx -mno-lra +@opindex mlra +@opindex mno-lra +Enable Local Register Allocation. This is still experimental for the VAX, +so by default the compiler uses standard reload. +@end table + +@node Visium Options +@subsection Visium Options +@cindex Visium options + +@table @gcctabopt + +@item -mdebug +@opindex mdebug +A program which performs file I/O and is destined to run on an MCM target +should be linked with this option. It causes the libraries libc.a and +libdebug.a to be linked. The program should be run on the target under +the control of the GDB remote debugging stub. + +@item -msim +@opindex msim +A program which performs file I/O and is destined to run on the simulator +should be linked with option. This causes libraries libc.a and libsim.a to +be linked. + +@item -mfpu +@itemx -mhard-float +@opindex mfpu +@opindex mhard-float +Generate code containing floating-point instructions. This is the +default. + +@item -mno-fpu +@itemx -msoft-float +@opindex mno-fpu +@opindex msoft-float +Generate code containing library calls for floating-point. + +@option{-msoft-float} changes the calling convention in the output file; +therefore, it is only useful if you compile @emph{all} of a program with +this option. In particular, you need to compile @file{libgcc.a}, the +library that comes with GCC, with @option{-msoft-float} in order for +this to work. + +@item -mcpu=@var{cpu_type} +@opindex mcpu +Set the instruction set, register set, and instruction scheduling parameters +for machine type @var{cpu_type}. Supported values for @var{cpu_type} are +@samp{mcm}, @samp{gr5} and @samp{gr6}. + +@samp{mcm} is a synonym of @samp{gr5} present for backward compatibility. + +By default (unless configured otherwise), GCC generates code for the GR5 +variant of the Visium architecture. + +With @option{-mcpu=gr6}, GCC generates code for the GR6 variant of the Visium +architecture. The only difference from GR5 code is that the compiler will +generate block move instructions. + +@item -mtune=@var{cpu_type} +@opindex mtune +Set the instruction scheduling parameters for machine type @var{cpu_type}, +but do not set the instruction set or register set that the option +@option{-mcpu=@var{cpu_type}} would. + +@item -msv-mode +@opindex msv-mode +Generate code for the supervisor mode, where there are no restrictions on +the access to general registers. This is the default. + +@item -muser-mode +@opindex muser-mode +Generate code for the user mode, where the access to some general registers +is forbidden: on the GR5, registers r24 to r31 cannot be accessed in this +mode; on the GR6, only registers r29 to r31 are affected. +@end table + +@node VMS Options +@subsection VMS Options + +These @samp{-m} options are defined for the VMS implementations: + +@table @gcctabopt +@item -mvms-return-codes +@opindex mvms-return-codes +Return VMS condition codes from @code{main}. The default is to return POSIX-style +condition (e.g.@: error) codes. + +@item -mdebug-main=@var{prefix} +@opindex mdebug-main=@var{prefix} +Flag the first routine whose name starts with @var{prefix} as the main +routine for the debugger. + +@item -mmalloc64 +@opindex mmalloc64 +Default to 64-bit memory allocation routines. + +@item -mpointer-size=@var{size} +@opindex mpointer-size=@var{size} +Set the default size of pointers. Possible options for @var{size} are +@samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long} +for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers. +The later option disables @code{pragma pointer_size}. +@end table + +@node VxWorks Options +@subsection VxWorks Options +@cindex VxWorks Options + +The options in this section are defined for all VxWorks targets. +Options specific to the target hardware are listed with the other +options for that target. + +@table @gcctabopt +@item -mrtp +@opindex mrtp +GCC can generate code for both VxWorks kernels and real time processes +(RTPs). This option switches from the former to the latter. It also +defines the preprocessor macro @code{__RTP__}. + +@item -non-static +@opindex non-static +Link an RTP executable against shared libraries rather than static +libraries. The options @option{-static} and @option{-shared} can +also be used for RTPs (@pxref{Link Options}); @option{-static} +is the default. + +@item -Bstatic +@itemx -Bdynamic +@opindex Bstatic +@opindex Bdynamic +These options are passed down to the linker. They are defined for +compatibility with Diab. + +@item -Xbind-lazy +@opindex Xbind-lazy +Enable lazy binding of function calls. This option is equivalent to +@option{-Wl,-z,now} and is defined for compatibility with Diab. + +@item -Xbind-now +@opindex Xbind-now +Disable lazy binding of function calls. This option is the default and +is defined for compatibility with Diab. +@end table + +@node x86 Options +@subsection x86 Options +@cindex x86 Options + +These @samp{-m} options are defined for the x86 family of computers. + +@table @gcctabopt + +@item -march=@var{cpu-type} +@opindex march +Generate instructions for the machine type @var{cpu-type}. In contrast to +@option{-mtune=@var{cpu-type}}, which merely tunes the generated code +for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC +to generate code that may not run at all on processors other than the one +indicated. Specifying @option{-march=@var{cpu-type}} implies +@option{-mtune=@var{cpu-type}}, except where noted otherwise. + +The choices for @var{cpu-type} are: + +@table @samp +@item native +This selects the CPU to generate code for at compilation time by determining +the processor type of the compiling machine. Using @option{-march=native} +enables all instruction subsets supported by the local machine (hence +the result might not run on different machines). Using @option{-mtune=native} +produces code optimized for the local machine under the constraints +of the selected instruction set. + +@item x86-64 +A generic CPU with 64-bit extensions. + +@item x86-64-v2 +@itemx x86-64-v3 +@itemx x86-64-v4 +These choices for @var{cpu-type} select the corresponding +micro-architecture level from the x86-64 psABI. On ABIs other than +the x86-64 psABI they select the same CPU features as the x86-64 psABI +documents for the particular micro-architecture level. + +Since these @var{cpu-type} values do not have a corresponding +@option{-mtune} setting, using @option{-march} with these values enables +generic tuning. Specific tuning can be enabled using the +@option{-mtune=@var{other-cpu-type}} option with an appropriate +@var{other-cpu-type} value. + +@item i386 +Original Intel i386 CPU@. + +@item i486 +Intel i486 CPU@. (No scheduling is implemented for this chip.) + +@item i586 +@itemx pentium +Intel Pentium CPU with no MMX support. + +@item lakemont +Intel Lakemont MCU, based on Intel Pentium CPU. + +@item pentium-mmx +Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. + +@item pentiumpro +Intel Pentium Pro CPU@. + +@item i686 +When used with @option{-march}, the Pentium Pro +instruction set is used, so the code runs on all i686 family chips. +When used with @option{-mtune}, it has the same meaning as @samp{generic}. + +@item pentium2 +Intel Pentium II CPU, based on Pentium Pro core with MMX and FXSR instruction +set support. + +@item pentium3 +@itemx pentium3m +Intel Pentium III CPU, based on Pentium Pro core with MMX, FXSR and SSE +instruction set support. + +@item pentium-m +Intel Pentium M; low-power version of Intel Pentium III CPU +with MMX, SSE, SSE2 and FXSR instruction set support. Used by Centrino +notebooks. + +@item pentium4 +@itemx pentium4m +Intel Pentium 4 CPU with MMX, SSE, SSE2 and FXSR instruction set support. + +@item prescott +Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2, SSE3 and FXSR +instruction set support. + +@item nocona +Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, +SSE2, SSE3 and FXSR instruction set support. + +@item core2 +Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, CX16, +SAHF and FXSR instruction set support. + +@item nehalem +Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF and FXSR instruction set support. + +@item westmere +Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR and PCLMUL instruction set support. + +@item sandybridge +Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE and PCLMUL instruction set +support. + +@item ivybridge +Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND +and F16C instruction set support. + +@item haswell +Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, +F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE and HLE instruction set support. + +@item broadwell +Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, +F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX and PREFETCHW +instruction set support. + +@item skylake +Intel Skylake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, +F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, +CLFLUSHOPT, XSAVEC, XSAVES and SGX instruction set support. + +@item bonnell +Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3 +instruction set support. + +@item silvermont +Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW and RDRND +instruction set support. + +@item goldmont +Intel Goldmont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, +RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT and FSGSBASE instruction +set support. + +@item goldmont-plus +Intel Goldmont Plus CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, +SHA, RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, +RDPID and SGX instruction set support. + +@item tremont +Intel Tremont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, PCLMUL, PREFETCHW, RDRND, AES, SHA, +RDSEED, XSAVE, XSAVEC, XSAVES, XSAVEOPT, CLFLUSHOPT, FSGSBASE, PTWRITE, RDPID, +SGX, CLWB, GFNI-SSE, MOVDIRI, MOVDIR64B, CLDEMOTE and WAITPKG instruction set +support. + +@item sierraforest +Intel Sierra Forest CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, +XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, +MOVDIR64B, CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, +PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL, AVX-VNNI, +AVXIFMA, AVXVNNIINT8, AVXNECONVERT and CMPCCXADD instruction set support. + +@item grandridge +Intel Grand Ridge CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, +XSAVES, XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, +MOVDIR64B, CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, +PCONFIG, PKU, VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL, AVX-VNNI, +AVXIFMA, AVXVNNIINT8, AVXNECONVERT, CMPCCXADD and RAOINT instruction set +support. + +@item knl +Intel Knight's Landing CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, +RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, +AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1 instruction set support. + +@item knm +Intel Knights Mill CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, +RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, +AVX512PF, AVX512ER, AVX512F, AVX512CD and PREFETCHWT1, AVX5124VNNIW, +AVX5124FMAPS and AVX512VPOPCNTDQ instruction set support. + +@item skylake-avx512 +Intel Skylake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, +RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, +AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, +AVX512DQ and AVX512CD instruction set support. + +@item cannonlake +Intel Cannonlake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, +SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, +FSGSBASE, RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, +PREFETCHW, AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, +AVX512DQ, AVX512CD, PKU, AVX512VBMI, AVX512IFMA and SHA instruction set +support. + +@item icelake-client +Intel Icelake Client CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, +RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, +AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, +AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2 +, VPCLMULQDQ, AVX512BITALG, RDPID and AVX512VPOPCNTDQ instruction set support. + +@item icelake-server +Intel Icelake Server CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, +RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, +AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, +AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2 +, VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD and CLWB +instruction set support. + +@item cascadelake +Intel Cascadelake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, +F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, +CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ, +AVX512CD and AVX512VNNI instruction set support. + +@item cooperlake +Intel cooperlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, +F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, +CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, CLWB, AVX512VL, AVX512BW, AVX512DQ, +AVX512CD, AVX512VNNI and AVX512BF16 instruction set support. + +@item tigerlake +Intel Tigerlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, +F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, +CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD +PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, +VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, MOVDIRI, MOVDIR64B, CLWB, +AVX512VP2INTERSECT and KEYLOCKER instruction set support. + +@item sapphirerapids +Intel sapphirerapids CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, +RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, +AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, +AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, +VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, +MOVDIRI, MOVDIR64B, ENQCMD, CLDEMOTE, PTWRITE, WAITPKG, SERIALIZE, TSXLDTRK, +UINTR, AMX-BF16, AMX-TILE, AMX-INT8, AVX-VNNI, AVX512FP16 and AVX512BF16 +instruction set support. + +@item alderlake +Intel Alderlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, +SSE4.1, SSE4.2, POPCNT, AES, PREFETCHW, PCLMUL, RDRND, XSAVE, XSAVEC, XSAVES, +XSAVEOPT, FSGSBASE, PTWRITE, RDPID, SGX, GFNI-SSE, CLWB, MOVDIRI, MOVDIR64B, +CLDEMOTE, WAITPKG, ADCX, AVX, AVX2, BMI, BMI2, F16C, FMA, LZCNT, PCONFIG, PKU, +VAES, VPCLMULQDQ, SERIALIZE, HRESET, KL, WIDEKL and AVX-VNNI instruction set +support. + +@item rocketlake +Intel Rocketlake CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3 +, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, RDRND, +F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, AES, +CLFLUSHOPT, XSAVEC, XSAVES, AVX512F, AVX512VL, AVX512BW, AVX512DQ, AVX512CD +PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, +VPCLMULQDQ, AVX512BITALG, RDPID and AVX512VPOPCNTDQ instruction set support. + +@item graniterapids +Intel graniterapids CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, +SSSE3, SSE4.1, SSE4.2, POPCNT, CX16, SAHF, FXSR, AVX, XSAVE, PCLMUL, FSGSBASE, +RDRND, F16C, AVX2, BMI, BMI2, LZCNT, FMA, MOVBE, HLE, RDSEED, ADCX, PREFETCHW, +AES, CLFLUSHOPT, XSAVEC, XSAVES, SGX, AVX512F, AVX512VL, AVX512BW, AVX512DQ, +AVX512CD, PKU, AVX512VBMI, AVX512IFMA, SHA, AVX512VNNI, GFNI, VAES, AVX512VBMI2, +VPCLMULQDQ, AVX512BITALG, RDPID, AVX512VPOPCNTDQ, PCONFIG, WBNOINVD, CLWB, +MOVDIRI, MOVDIR64B, AVX512VP2INTERSECT, ENQCMD, CLDEMOTE, PTWRITE, WAITPKG, +SERIALIZE, TSXLDTRK, UINTR, AMX-BF16, AMX-TILE, AMX-INT8, AVX-VNNI, AVX512FP16, +AVX512BF16, AMX-FP16 and PREFETCHI instruction set support. + +@item k6 +AMD K6 CPU with MMX instruction set support. + +@item k6-2 +@itemx k6-3 +Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support. + +@item athlon +@itemx athlon-tbird +AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions +support. + +@item athlon-4 +@itemx athlon-xp +@itemx athlon-mp +Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE +instruction set support. + +@item k8 +@itemx opteron +@itemx athlon64 +@itemx athlon-fx +Processors based on the AMD K8 core with x86-64 instruction set support, +including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. +(This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit +instruction set extensions.) + +@item k8-sse3 +@itemx opteron-sse3 +@itemx athlon64-sse3 +Improved versions of AMD K8 cores with SSE3 instruction set support. + +@item amdfam10 +@itemx barcelona +CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This +supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit +instruction set extensions.) + +@item bdver1 +CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This +supersets FMA4, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, +SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) + +@item bdver2 +AMD Family 15h core based CPUs with x86-64 instruction set support. (This +supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCLMUL, CX16, MMX, +SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set +extensions.) + +@item bdver3 +AMD Family 15h core based CPUs with x86-64 instruction set support. (This +supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES, +PCLMUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and +64-bit instruction set extensions.) + +@item bdver4 +AMD Family 15h core based CPUs with x86-64 instruction set support. (This +supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP, +AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, +SSE4.2, ABM and 64-bit instruction set extensions.) + +@item znver1 +AMD Family 17h core based CPUs with x86-64 instruction set support. (This +supersets BMI, BMI2, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, MWAITX, +SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, +SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, and 64-bit +instruction set extensions.) + +@item znver2 +AMD Family 17h core based CPUs with x86-64 instruction set support. (This +supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, +MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, +SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, +WBNOINVD, and 64-bit instruction set extensions.) + +@item znver3 +AMD Family 19h core based CPUs with x86-64 instruction set support. (This +supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, +MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, +SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, +WBNOINVD, PKU, VPCLMULQDQ, VAES, and 64-bit instruction set extensions.) + +@item znver4 +AMD Family 19h core based CPUs with x86-64 instruction set support. (This +supersets BMI, BMI2, CLWB, F16C, FMA, FSGSBASE, AVX, AVX2, ADCX, RDSEED, +MWAITX, SHA, CLZERO, AES, PCLMUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, +SSSE3, SSE4.1, SSE4.2, ABM, XSAVEC, XSAVES, CLFLUSHOPT, POPCNT, RDPID, +WBNOINVD, PKU, VPCLMULQDQ, VAES, AVX512F, AVX512DQ, AVX512IFMA, AVX512CD, +AVX512BW, AVX512VL, AVX512BF16, AVX512VBMI, AVX512VBMI2, AVX512VNNI, +AVX512BITALG, AVX512VPOPCNTDQ, GFNI and 64-bit instruction set extensions.) + +@item btver1 +CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This +supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit +instruction set extensions.) + +@item btver2 +CPUs based on AMD Family 16h cores with x86-64 instruction set support. This +includes MOVBE, F16C, BMI, AVX, PCLMUL, AES, SSE4.2, SSE4.1, CX16, ABM, +SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions. + +@item winchip-c6 +IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction +set support. + +@item winchip2 +IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@: +instruction set support. + +@item c3 +VIA C3 CPU with MMX and 3DNow!@: instruction set support. +(No scheduling is implemented for this chip.) + +@item c3-2 +VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. +(No scheduling is implemented for this chip.) + +@item c7 +VIA C7 (Esther) CPU with MMX, SSE, SSE2 and SSE3 instruction set support. +(No scheduling is implemented for this chip.) + +@item samuel-2 +VIA Eden Samuel 2 CPU with MMX and 3DNow!@: instruction set support. +(No scheduling is implemented for this chip.) + +@item nehemiah +VIA Eden Nehemiah CPU with MMX and SSE instruction set support. +(No scheduling is implemented for this chip.) + +@item esther +VIA Eden Esther CPU with MMX, SSE, SSE2 and SSE3 instruction set support. +(No scheduling is implemented for this chip.) + +@item eden-x2 +VIA Eden X2 CPU with x86-64, MMX, SSE, SSE2 and SSE3 instruction set support. +(No scheduling is implemented for this chip.) + +@item eden-x4 +VIA Eden X4 CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, +AVX and AVX2 instruction set support. +(No scheduling is implemented for this chip.) + +@item nano +Generic VIA Nano CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 +instruction set support. +(No scheduling is implemented for this chip.) + +@item nano-1000 +VIA Nano 1xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 +instruction set support. +(No scheduling is implemented for this chip.) + +@item nano-2000 +VIA Nano 2xxx CPU with x86-64, MMX, SSE, SSE2, SSE3 and SSSE3 +instruction set support. +(No scheduling is implemented for this chip.) + +@item nano-3000 +VIA Nano 3xxx CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 +instruction set support. +(No scheduling is implemented for this chip.) + +@item nano-x2 +VIA Nano Dual Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 +instruction set support. +(No scheduling is implemented for this chip.) + +@item nano-x4 +VIA Nano Quad Core CPU with x86-64, MMX, SSE, SSE2, SSE3, SSSE3 and SSE4.1 +instruction set support. +(No scheduling is implemented for this chip.) + +@item lujiazui +ZHAOXIN lujiazui CPU with x86-64, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, +SSE4.2, AVX, POPCNT, AES, PCLMUL, RDRND, XSAVE, XSAVEOPT, FSGSBASE, CX16, +ABM, BMI, BMI2, F16C, FXSR, RDSEED instruction set support. + +@item geode +AMD Geode embedded processor with MMX and 3DNow!@: instruction set support. +@end table + +@item -mtune=@var{cpu-type} +@opindex mtune +Tune to @var{cpu-type} everything applicable about the generated code, except +for the ABI and the set of available instructions. +While picking a specific @var{cpu-type} schedules things appropriately +for that particular chip, the compiler does not generate any code that +cannot run on the default machine type unless you use a +@option{-march=@var{cpu-type}} option. +For example, if GCC is configured for i686-pc-linux-gnu +then @option{-mtune=pentium4} generates code that is tuned for Pentium 4 +but still runs on i686 machines. + +The choices for @var{cpu-type} are the same as for @option{-march}. +In addition, @option{-mtune} supports 2 extra choices for @var{cpu-type}: + +@table @samp +@item generic +Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors. +If you know the CPU on which your code will run, then you should use +the corresponding @option{-mtune} or @option{-march} option instead of +@option{-mtune=generic}. But, if you do not know exactly what CPU users +of your application will have, then you should use this option. + +As new processors are deployed in the marketplace, the behavior of this +option will change. Therefore, if you upgrade to a newer version of +GCC, code generation controlled by this option will change to reflect +the processors +that are most common at the time that version of GCC is released. + +There is no @option{-march=generic} option because @option{-march} +indicates the instruction set the compiler can use, and there is no +generic instruction set applicable to all processors. In contrast, +@option{-mtune} indicates the processor (or, in this case, collection of +processors) for which the code is optimized. + +@item intel +Produce code optimized for the most current Intel processors, which are +Haswell and Silvermont for this version of GCC. If you know the CPU +on which your code will run, then you should use the corresponding +@option{-mtune} or @option{-march} option instead of @option{-mtune=intel}. +But, if you want your application performs better on both Haswell and +Silvermont, then you should use this option. + +As new Intel processors are deployed in the marketplace, the behavior of +this option will change. Therefore, if you upgrade to a newer version of +GCC, code generation controlled by this option will change to reflect +the most current Intel processors at the time that version of GCC is +released. + +There is no @option{-march=intel} option because @option{-march} indicates +the instruction set the compiler can use, and there is no common +instruction set applicable to all processors. In contrast, +@option{-mtune} indicates the processor (or, in this case, collection of +processors) for which the code is optimized. +@end table + +@item -mcpu=@var{cpu-type} +@opindex mcpu +A deprecated synonym for @option{-mtune}. + +@item -mfpmath=@var{unit} +@opindex mfpmath +Generate floating-point arithmetic for selected unit @var{unit}. The choices +for @var{unit} are: + +@table @samp +@item 387 +Use the standard 387 floating-point coprocessor present on the majority of chips and +emulated otherwise. Code compiled with this option runs almost everywhere. +The temporary results are computed in 80-bit precision instead of the precision +specified by the type, resulting in slightly different results compared to most +of other chips. See @option{-ffloat-store} for more detailed description. + +This is the default choice for non-Darwin x86-32 targets. + +@item sse +Use scalar floating-point instructions present in the SSE instruction set. +This instruction set is supported by Pentium III and newer chips, +and in the AMD line +by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE +instruction set supports only single-precision arithmetic, thus the double and +extended-precision arithmetic are still done using 387. A later version, present +only in Pentium 4 and AMD x86-64 chips, supports double-precision +arithmetic too. + +For the x86-32 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse} +or @option{-msse2} switches to enable SSE extensions and make this option +effective. For the x86-64 compiler, these extensions are enabled by default. + +The resulting code should be considerably faster in the majority of cases and avoid +the numerical instability problems of 387 code, but may break some existing +code that expects temporaries to be 80 bits. + +This is the default choice for the x86-64 compiler, Darwin x86-32 targets, +and the default choice for x86-32 targets with the SSE2 instruction set +when @option{-ffast-math} is enabled. + +@item sse,387 +@itemx sse+387 +@itemx both +Attempt to utilize both instruction sets at once. This effectively doubles the +amount of available registers, and on chips with separate execution units for +387 and SSE the execution resources too. Use this option with care, as it is +still experimental, because the GCC register allocator does not model separate +functional units well, resulting in unstable performance. +@end table + +@item -masm=@var{dialect} +@opindex masm=@var{dialect} +Output assembly instructions using selected @var{dialect}. Also affects +which dialect is used for basic @code{asm} (@pxref{Basic Asm}) and +extended @code{asm} (@pxref{Extended Asm}). Supported choices (in dialect +order) are @samp{att} or @samp{intel}. The default is @samp{att}. Darwin does +not support @samp{intel}. + +@item -mieee-fp +@itemx -mno-ieee-fp +@opindex mieee-fp +@opindex mno-ieee-fp +Control whether or not the compiler uses IEEE floating-point +comparisons. These correctly handle the case where the result of a +comparison is unordered. + +@item -m80387 +@itemx -mhard-float +@opindex 80387 +@opindex mhard-float +Generate output containing 80387 instructions for floating point. + +@item -mno-80387 +@itemx -msoft-float +@opindex no-80387 +@opindex msoft-float +Generate output containing library calls for floating point. + +@strong{Warning:} the requisite libraries are not part of GCC@. +Normally the facilities of the machine's usual C compiler are used, but +this cannot be done directly in cross-compilation. You must make your +own arrangements to provide suitable library functions for +cross-compilation. + +On machines where a function returns floating-point results in the 80387 +register stack, some floating-point opcodes may be emitted even if +@option{-msoft-float} is used. + +@item -mno-fp-ret-in-387 +@opindex mno-fp-ret-in-387 +@opindex mfp-ret-in-387 +Do not use the FPU registers for return values of functions. + +The usual calling convention has functions return values of types +@code{float} and @code{double} in an FPU register, even if there +is no FPU@. The idea is that the operating system should emulate +an FPU@. + +The option @option{-mno-fp-ret-in-387} causes such values to be returned +in ordinary CPU registers instead. + +@item -mno-fancy-math-387 +@opindex mno-fancy-math-387 +@opindex mfancy-math-387 +Some 387 emulators do not support the @code{sin}, @code{cos} and +@code{sqrt} instructions for the 387. Specify this option to avoid +generating those instructions. +This option is overridden when @option{-march} +indicates that the target CPU always has an FPU and so the +instruction does not need emulation. These +instructions are not generated unless you also use the +@option{-funsafe-math-optimizations} switch. + +@item -malign-double +@itemx -mno-align-double +@opindex malign-double +@opindex mno-align-double +Control whether GCC aligns @code{double}, @code{long double}, and +@code{long long} variables on a two-word boundary or a one-word +boundary. Aligning @code{double} variables on a two-word boundary +produces code that runs somewhat faster on a Pentium at the +expense of more memory. + +On x86-64, @option{-malign-double} is enabled by default. + +@strong{Warning:} if you use the @option{-malign-double} switch, +structures containing the above types are aligned differently than +the published application binary interface specifications for the x86-32 +and are not binary compatible with structures in code compiled +without that switch. + +@item -m96bit-long-double +@itemx -m128bit-long-double +@opindex m96bit-long-double +@opindex m128bit-long-double +These switches control the size of @code{long double} type. The x86-32 +application binary interface specifies the size to be 96 bits, +so @option{-m96bit-long-double} is the default in 32-bit mode. + +Modern architectures (Pentium and newer) prefer @code{long double} +to be aligned to an 8- or 16-byte boundary. In arrays or structures +conforming to the ABI, this is not possible. So specifying +@option{-m128bit-long-double} aligns @code{long double} +to a 16-byte boundary by padding the @code{long double} with an additional +32-bit zero. + +In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as +its ABI specifies that @code{long double} is aligned on 16-byte boundary. + +Notice that neither of these options enable any extra precision over the x87 +standard of 80 bits for a @code{long double}. + +@strong{Warning:} if you override the default value for your target ABI, this +changes the size of +structures and arrays containing @code{long double} variables, +as well as modifying the function calling convention for functions taking +@code{long double}. Hence they are not binary-compatible +with code compiled without that switch. + +@item -mlong-double-64 +@itemx -mlong-double-80 +@itemx -mlong-double-128 +@opindex mlong-double-64 +@opindex mlong-double-80 +@opindex mlong-double-128 +These switches control the size of @code{long double} type. A size +of 64 bits makes the @code{long double} type equivalent to the @code{double} +type. This is the default for 32-bit Bionic C library. A size +of 128 bits makes the @code{long double} type equivalent to the +@code{__float128} type. This is the default for 64-bit Bionic C library. + +@strong{Warning:} if you override the default value for your target ABI, this +changes the size of +structures and arrays containing @code{long double} variables, +as well as modifying the function calling convention for functions taking +@code{long double}. Hence they are not binary-compatible +with code compiled without that switch. + +@item -malign-data=@var{type} +@opindex malign-data +Control how GCC aligns variables. Supported values for @var{type} are +@samp{compat} uses increased alignment value compatible uses GCC 4.8 +and earlier, @samp{abi} uses alignment value as specified by the +psABI, and @samp{cacheline} uses increased alignment value to match +the cache line size. @samp{compat} is the default. + +@item -mlarge-data-threshold=@var{threshold} +@opindex mlarge-data-threshold +When @option{-mcmodel=medium} is specified, data objects larger than +@var{threshold} are placed in the large data section. This value must be the +same across all objects linked into the binary, and defaults to 65535. + +@item -mrtd +@opindex mrtd +Use a different function-calling convention, in which functions that +take a fixed number of arguments return with the @code{ret @var{num}} +instruction, which pops their arguments while returning. This saves one +instruction in the caller since there is no need to pop the arguments +there. + +You can specify that an individual function is called with this calling +sequence with the function attribute @code{stdcall}. You can also +override the @option{-mrtd} option by using the function attribute +@code{cdecl}. @xref{Function Attributes}. + +@strong{Warning:} this calling convention is incompatible with the one +normally used on Unix, so you cannot use it if you need to call +libraries compiled with the Unix compiler. + +Also, you must provide function prototypes for all functions that +take variable numbers of arguments (including @code{printf}); +otherwise incorrect code is generated for calls to those +functions. + +In addition, seriously incorrect code results if you call a +function with too many arguments. (Normally, extra arguments are +harmlessly ignored.) + +@item -mregparm=@var{num} +@opindex mregparm +Control how many registers are used to pass integer arguments. By +default, no registers are used to pass arguments, and at most 3 +registers can be used. You can control this behavior for a specific +function by using the function attribute @code{regparm}. +@xref{Function Attributes}. + +@strong{Warning:} if you use this switch, and +@var{num} is nonzero, then you must build all modules with the same +value, including any libraries. This includes the system libraries and +startup modules. + +@item -msseregparm +@opindex msseregparm +Use SSE register passing conventions for float and double arguments +and return values. You can control this behavior for a specific +function by using the function attribute @code{sseregparm}. +@xref{Function Attributes}. + +@strong{Warning:} if you use this switch then you must build all +modules with the same value, including any libraries. This includes +the system libraries and startup modules. + +@item -mvect8-ret-in-mem +@opindex mvect8-ret-in-mem +Return 8-byte vectors in memory instead of MMX registers. This is the +default on VxWorks to match the ABI of the Sun Studio compilers until +version 12. @emph{Only} use this option if you need to remain +compatible with existing code produced by those previous compiler +versions or older versions of GCC@. + +@item -mpc32 +@itemx -mpc64 +@itemx -mpc80 +@opindex mpc32 +@opindex mpc64 +@opindex mpc80 + +Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32} +is specified, the significands of results of floating-point operations are +rounded to 24 bits (single precision); @option{-mpc64} rounds the +significands of results of floating-point operations to 53 bits (double +precision) and @option{-mpc80} rounds the significands of results of +floating-point operations to 64 bits (extended double precision), which is +the default. When this option is used, floating-point operations in higher +precisions are not available to the programmer without setting the FPU +control word explicitly. + +Setting the rounding of floating-point operations to less than the default +80 bits can speed some programs by 2% or more. Note that some mathematical +libraries assume that extended-precision (80-bit) floating-point operations +are enabled by default; routines in such libraries could suffer significant +loss of accuracy, typically through so-called ``catastrophic cancellation'', +when this option is used to set the precision to less than extended precision. + +@item -mstackrealign +@opindex mstackrealign +Realign the stack at entry. On the x86, the @option{-mstackrealign} +option generates an alternate prologue and epilogue that realigns the +run-time stack if necessary. This supports mixing legacy codes that keep +4-byte stack alignment with modern codes that keep 16-byte stack alignment for +SSE compatibility. See also the attribute @code{force_align_arg_pointer}, +applicable to individual functions. + +@item -mpreferred-stack-boundary=@var{num} +@opindex mpreferred-stack-boundary +Attempt to keep the stack boundary aligned to a 2 raised to @var{num} +byte boundary. If @option{-mpreferred-stack-boundary} is not specified, +the default is 4 (16 bytes or 128 bits). + +@strong{Warning:} When generating code for the x86-64 architecture with +SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be +used to keep the stack boundary aligned to 8 byte boundary. Since +x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and +intended to be used in controlled environment where stack space is +important limitation. This option leads to wrong code when functions +compiled with 16 byte stack alignment (such as functions from a standard +library) are called with misaligned stack. In this case, SSE +instructions may lead to misaligned memory access traps. In addition, +variable arguments are handled incorrectly for 16 byte aligned +objects (including x87 long double and __int128), leading to wrong +results. You must build all modules with +@option{-mpreferred-stack-boundary=3}, including any libraries. This +includes the system libraries and startup modules. + +@item -mincoming-stack-boundary=@var{num} +@opindex mincoming-stack-boundary +Assume the incoming stack is aligned to a 2 raised to @var{num} byte +boundary. If @option{-mincoming-stack-boundary} is not specified, +the one specified by @option{-mpreferred-stack-boundary} is used. + +On Pentium and Pentium Pro, @code{double} and @code{long double} values +should be aligned to an 8-byte boundary (see @option{-malign-double}) or +suffer significant run time performance penalties. On Pentium III, the +Streaming SIMD Extension (SSE) data type @code{__m128} may not work +properly if it is not 16-byte aligned. + +To ensure proper alignment of this values on the stack, the stack boundary +must be as aligned as that required by any value stored on the stack. +Further, every function must be generated such that it keeps the stack +aligned. Thus calling a function compiled with a higher preferred +stack boundary from a function compiled with a lower preferred stack +boundary most likely misaligns the stack. It is recommended that +libraries that use callbacks always use the default setting. + +This extra alignment does consume extra stack space, and generally +increases code size. Code that is sensitive to stack space usage, such +as embedded systems and operating system kernels, may want to reduce the +preferred alignment to @option{-mpreferred-stack-boundary=2}. + +@need 200 +@item -mmmx +@opindex mmmx +@need 200 +@itemx -msse +@opindex msse +@need 200 +@itemx -msse2 +@opindex msse2 +@need 200 +@itemx -msse3 +@opindex msse3 +@need 200 +@itemx -mssse3 +@opindex mssse3 +@need 200 +@itemx -msse4 +@opindex msse4 +@need 200 +@itemx -msse4a +@opindex msse4a +@need 200 +@itemx -msse4.1 +@opindex msse4.1 +@need 200 +@itemx -msse4.2 +@opindex msse4.2 +@need 200 +@itemx -mavx +@opindex mavx +@need 200 +@itemx -mavx2 +@opindex mavx2 +@need 200 +@itemx -mavx512f +@opindex mavx512f +@need 200 +@itemx -mavx512pf +@opindex mavx512pf +@need 200 +@itemx -mavx512er +@opindex mavx512er +@need 200 +@itemx -mavx512cd +@opindex mavx512cd +@need 200 +@itemx -mavx512vl +@opindex mavx512vl +@need 200 +@itemx -mavx512bw +@opindex mavx512bw +@need 200 +@itemx -mavx512dq +@opindex mavx512dq +@need 200 +@itemx -mavx512ifma +@opindex mavx512ifma +@need 200 +@itemx -mavx512vbmi +@opindex mavx512vbmi +@need 200 +@itemx -msha +@opindex msha +@need 200 +@itemx -maes +@opindex maes +@need 200 +@itemx -mpclmul +@opindex mpclmul +@need 200 +@itemx -mclflushopt +@opindex mclflushopt +@need 200 +@itemx -mclwb +@opindex mclwb +@need 200 +@itemx -mfsgsbase +@opindex mfsgsbase +@need 200 +@itemx -mptwrite +@opindex mptwrite +@need 200 +@itemx -mrdrnd +@opindex mrdrnd +@need 200 +@itemx -mf16c +@opindex mf16c +@need 200 +@itemx -mfma +@opindex mfma +@need 200 +@itemx -mpconfig +@opindex mpconfig +@need 200 +@itemx -mwbnoinvd +@opindex mwbnoinvd +@need 200 +@itemx -mfma4 +@opindex mfma4 +@need 200 +@itemx -mprfchw +@opindex mprfchw +@need 200 +@itemx -mrdpid +@opindex mrdpid +@need 200 +@itemx -mprefetchwt1 +@opindex mprefetchwt1 +@need 200 +@itemx -mrdseed +@opindex mrdseed +@need 200 +@itemx -msgx +@opindex msgx +@need 200 +@itemx -mxop +@opindex mxop +@need 200 +@itemx -mlwp +@opindex mlwp +@need 200 +@itemx -m3dnow +@opindex m3dnow +@need 200 +@itemx -m3dnowa +@opindex m3dnowa +@need 200 +@itemx -mpopcnt +@opindex mpopcnt +@need 200 +@itemx -mabm +@opindex mabm +@need 200 +@itemx -madx +@opindex madx +@need 200 +@itemx -mbmi +@opindex mbmi +@need 200 +@itemx -mbmi2 +@opindex mbmi2 +@need 200 +@itemx -mlzcnt +@opindex mlzcnt +@need 200 +@itemx -mfxsr +@opindex mfxsr +@need 200 +@itemx -mxsave +@opindex mxsave +@need 200 +@itemx -mxsaveopt +@opindex mxsaveopt +@need 200 +@itemx -mxsavec +@opindex mxsavec +@need 200 +@itemx -mxsaves +@opindex mxsaves +@need 200 +@itemx -mrtm +@opindex mrtm +@need 200 +@itemx -mhle +@opindex mhle +@need 200 +@itemx -mtbm +@opindex mtbm +@need 200 +@itemx -mmwaitx +@opindex mmwaitx +@need 200 +@itemx -mclzero +@opindex mclzero +@need 200 +@itemx -mpku +@opindex mpku +@need 200 +@itemx -mavx512vbmi2 +@opindex mavx512vbmi2 +@need 200 +@itemx -mavx512bf16 +@opindex mavx512bf16 +@need 200 +@itemx -mavx512fp16 +@opindex mavx512fp16 +@need 200 +@itemx -mgfni +@opindex mgfni +@need 200 +@itemx -mvaes +@opindex mvaes +@need 200 +@itemx -mwaitpkg +@opindex mwaitpkg +@need 200 +@itemx -mvpclmulqdq +@opindex mvpclmulqdq +@need 200 +@itemx -mavx512bitalg +@opindex mavx512bitalg +@need 200 +@itemx -mmovdiri +@opindex mmovdiri +@need 200 +@itemx -mmovdir64b +@opindex mmovdir64b +@need 200 +@itemx -menqcmd +@opindex menqcmd +@itemx -muintr +@opindex muintr +@need 200 +@itemx -mtsxldtrk +@opindex mtsxldtrk +@need 200 +@itemx -mavx512vpopcntdq +@opindex mavx512vpopcntdq +@need 200 +@itemx -mavx512vp2intersect +@opindex mavx512vp2intersect +@need 200 +@itemx -mavx5124fmaps +@opindex mavx5124fmaps +@need 200 +@itemx -mavx512vnni +@opindex mavx512vnni +@need 200 +@itemx -mavxvnni +@opindex mavxvnni +@need 200 +@itemx -mavx5124vnniw +@opindex mavx5124vnniw +@need 200 +@itemx -mcldemote +@opindex mcldemote +@need 200 +@itemx -mserialize +@opindex mserialize +@need 200 +@itemx -mamx-tile +@opindex mamx-tile +@need 200 +@itemx -mamx-int8 +@opindex mamx-int8 +@need 200 +@itemx -mamx-bf16 +@opindex mamx-bf16 +@need 200 +@itemx -mhreset +@opindex mhreset +@itemx -mkl +@opindex mkl +@need 200 +@itemx -mwidekl +@opindex mwidekl +@need 200 +@itemx -mavxifma +@opindex mavxifma +@need 200 +@itemx -mavxvnniint8 +@opindex mavxvnniint8 +@need 200 +@itemx -mavxneconvert +@opindex mavxneconvert +@need 200 +@itemx -mcmpccxadd +@opindex mcmpccxadd +@need 200 +@itemx -mamx-fp16 +@opindex mamx-fp16 +@need 200 +@itemx -mprefetchi +@opindex mprefetchi +@need 200 +@itemx -mraoint +@opindex mraoint +These switches enable the use of instructions in the MMX, SSE, +SSE2, SSE3, SSSE3, SSE4, SSE4A, SSE4.1, SSE4.2, AVX, AVX2, AVX512F, AVX512PF, +AVX512ER, AVX512CD, AVX512VL, AVX512BW, AVX512DQ, AVX512IFMA, AVX512VBMI, SHA, +AES, PCLMUL, CLFLUSHOPT, CLWB, FSGSBASE, PTWRITE, RDRND, F16C, FMA, PCONFIG, +WBNOINVD, FMA4, PREFETCHW, RDPID, PREFETCHWT1, RDSEED, SGX, XOP, LWP, +3DNow!@:, enhanced 3DNow!@:, POPCNT, ABM, ADX, BMI, BMI2, LZCNT, FXSR, XSAVE, +XSAVEOPT, XSAVEC, XSAVES, RTM, HLE, TBM, MWAITX, CLZERO, PKU, AVX512VBMI2, +GFNI, VAES, WAITPKG, VPCLMULQDQ, AVX512BITALG, MOVDIRI, MOVDIR64B, AVX512BF16, +ENQCMD, AVX512VPOPCNTDQ, AVX5124FMAPS, AVX512VNNI, AVX5124VNNIW, SERIALIZE, +UINTR, HRESET, AMXTILE, AMXINT8, AMXBF16, KL, WIDEKL, AVXVNNI, AVX512FP16, +AVXIFMA, AVXVNNIINT8, AVXNECONVERT, CMPCCXADD, AMX-FP16, PREFETCHI, RAOINT or +CLDEMOTE extended instruction sets. Each has a corresponding @option{-mno-} +option to disable use of these instructions. + +These extensions are also available as built-in functions: see +@ref{x86 Built-in Functions}, for details of the functions enabled and +disabled by these switches. + +To generate SSE/SSE2 instructions automatically from floating-point +code (as opposed to 387 instructions), see @option{-mfpmath=sse}. + +GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it +generates new AVX instructions or AVX equivalence for all SSEx instructions +when needed. + +These options enable GCC to use these extended instructions in +generated code, even without @option{-mfpmath=sse}. Applications that +perform run-time CPU detection must compile separate files for each +supported architecture, using the appropriate flags. In particular, +the file containing the CPU detection code should be compiled without +these options. + +@item -mdump-tune-features +@opindex mdump-tune-features +This option instructs GCC to dump the names of the x86 performance +tuning features and default settings. The names can be used in +@option{-mtune-ctrl=@var{feature-list}}. + +@item -mtune-ctrl=@var{feature-list} +@opindex mtune-ctrl=@var{feature-list} +This option is used to do fine grain control of x86 code generation features. +@var{feature-list} is a comma separated list of @var{feature} names. See also +@option{-mdump-tune-features}. When specified, the @var{feature} is turned +on if it is not preceded with @samp{^}, otherwise, it is turned off. +@option{-mtune-ctrl=@var{feature-list}} is intended to be used by GCC +developers. Using it may lead to code paths not covered by testing and can +potentially result in compiler ICEs or runtime errors. + +@item -mno-default +@opindex mno-default +This option instructs GCC to turn off all tunable features. See also +@option{-mtune-ctrl=@var{feature-list}} and @option{-mdump-tune-features}. + +@item -mcld +@opindex mcld +This option instructs GCC to emit a @code{cld} instruction in the prologue +of functions that use string instructions. String instructions depend on +the DF flag to select between autoincrement or autodecrement mode. While the +ABI specifies the DF flag to be cleared on function entry, some operating +systems violate this specification by not clearing the DF flag in their +exception dispatchers. The exception handler can be invoked with the DF flag +set, which leads to wrong direction mode when string instructions are used. +This option can be enabled by default on 32-bit x86 targets by configuring +GCC with the @option{--enable-cld} configure option. Generation of @code{cld} +instructions can be suppressed with the @option{-mno-cld} compiler option +in this case. + +@item -mvzeroupper +@opindex mvzeroupper +This option instructs GCC to emit a @code{vzeroupper} instruction +before a transfer of control flow out of the function to minimize +the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper} +intrinsics. + +@item -mprefer-avx128 +@opindex mprefer-avx128 +This option instructs GCC to use 128-bit AVX instructions instead of +256-bit AVX instructions in the auto-vectorizer. + +@item -mprefer-vector-width=@var{opt} +@opindex mprefer-vector-width +This option instructs GCC to use @var{opt}-bit vector width in instructions +instead of default on the selected platform. + +@item -mmove-max=@var{bits} +@opindex mmove-max +This option instructs GCC to set the maximum number of bits can be +moved from memory to memory efficiently to @var{bits}. The valid +@var{bits} are 128, 256 and 512. + +@item -mstore-max=@var{bits} +@opindex mstore-max +This option instructs GCC to set the maximum number of bits can be +stored to memory efficiently to @var{bits}. The valid @var{bits} are +128, 256 and 512. + +@table @samp +@item none +No extra limitations applied to GCC other than defined by the selected platform. + +@item 128 +Prefer 128-bit vector width for instructions. + +@item 256 +Prefer 256-bit vector width for instructions. + +@item 512 +Prefer 512-bit vector width for instructions. +@end table + +@item -mcx16 +@opindex mcx16 +This option enables GCC to generate @code{CMPXCHG16B} instructions in 64-bit +code to implement compare-and-exchange operations on 16-byte aligned 128-bit +objects. This is useful for atomic updates of data structures exceeding one +machine word in size. The compiler uses this instruction to implement +@ref{__sync Builtins}. However, for @ref{__atomic Builtins} operating on +128-bit integers, a library call is always used. + +@item -msahf +@opindex msahf +This option enables generation of @code{SAHF} instructions in 64-bit code. +Early Intel Pentium 4 CPUs with Intel 64 support, +prior to the introduction of Pentium 4 G1 step in December 2005, +lacked the @code{LAHF} and @code{SAHF} instructions +which are supported by AMD64. +These are load and store instructions, respectively, for certain status flags. +In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod}, +@code{drem}, and @code{remainder} built-in functions; +see @ref{Other Builtins} for details. + +@item -mmovbe +@opindex mmovbe +This option enables use of the @code{movbe} instruction to implement +@code{__builtin_bswap32} and @code{__builtin_bswap64}. + +@item -mshstk +@opindex mshstk +The @option{-mshstk} option enables shadow stack built-in functions +from x86 Control-flow Enforcement Technology (CET). + +@item -mcrc32 +@opindex mcrc32 +This option enables built-in functions @code{__builtin_ia32_crc32qi}, +@code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and +@code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction. + +@item -mmwait +@opindex mmwait +This option enables built-in functions @code{__builtin_ia32_monitor}, +and @code{__builtin_ia32_mwait} to generate the @code{monitor} and +@code{mwait} machine instructions. + +@item -mrecip +@opindex mrecip +This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions +(and their vectorized variants @code{RCPPS} and @code{RSQRTPS}) +with an additional Newton-Raphson step +to increase precision instead of @code{DIVSS} and @code{SQRTSS} +(and their vectorized +variants) for single-precision floating-point arguments. These instructions +are generated only when @option{-funsafe-math-optimizations} is enabled +together with @option{-ffinite-math-only} and @option{-fno-trapping-math}. +Note that while the throughput of the sequence is higher than the throughput +of the non-reciprocal instruction, the precision of the sequence can be +decreased by up to 2 ulp (i.e.@: the inverse of 1.0 equals 0.99999994). + +Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS} +(or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option +combination), and doesn't need @option{-mrecip}. + +Also note that GCC emits the above sequence with additional Newton-Raphson step +for vectorized single-float division and vectorized @code{sqrtf(@var{x})} +already with @option{-ffast-math} (or the above option combination), and +doesn't need @option{-mrecip}. + +@item -mrecip=@var{opt} +@opindex mrecip=opt +This option controls which reciprocal estimate instructions +may be used. @var{opt} is a comma-separated list of options, which may +be preceded by a @samp{!} to invert the option: + +@table @samp +@item all +Enable all estimate instructions. + +@item default +Enable the default instructions, equivalent to @option{-mrecip}. + +@item none +Disable all estimate instructions, equivalent to @option{-mno-recip}. + +@item div +Enable the approximation for scalar division. + +@item vec-div +Enable the approximation for vectorized division. + +@item sqrt +Enable the approximation for scalar square root. + +@item vec-sqrt +Enable the approximation for vectorized square root. +@end table + +So, for example, @option{-mrecip=all,!sqrt} enables +all of the reciprocal approximations, except for square root. + +@item -mveclibabi=@var{type} +@opindex mveclibabi +Specifies the ABI type to use for vectorizing intrinsics using an +external library. Supported values for @var{type} are @samp{svml} +for the Intel short +vector math library and @samp{acml} for the AMD math core library. +To use this option, both @option{-ftree-vectorize} and +@option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML +ABI-compatible library must be specified at link time. + +GCC currently emits calls to @code{vmldExp2}, +@code{vmldLn2}, @code{vmldLog102}, @code{vmldPow2}, +@code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2}, +@code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2}, +@code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2}, +@code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, +@code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4}, +@code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4}, +@code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4}, +@code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding +function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin}, +@code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2}, +@code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf}, +@code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f}, +@code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type +when @option{-mveclibabi=acml} is used. + +@item -mabi=@var{name} +@opindex mabi +Generate code for the specified calling convention. Permissible values +are @samp{sysv} for the ABI used on GNU/Linux and other systems, and +@samp{ms} for the Microsoft ABI. The default is to use the Microsoft +ABI when targeting Microsoft Windows and the SysV ABI on all other systems. +You can control this behavior for specific functions by +using the function attributes @code{ms_abi} and @code{sysv_abi}. +@xref{Function Attributes}. + +@item -mforce-indirect-call +@opindex mforce-indirect-call +Force all calls to functions to be indirect. This is useful +when using Intel Processor Trace where it generates more precise timing +information for function calls. + +@item -mmanual-endbr +@opindex mmanual-endbr +Insert ENDBR instruction at function entry only via the @code{cf_check} +function attribute. This is useful when used with the option +@option{-fcf-protection=branch} to control ENDBR insertion at the +function entry. + +@item -mcet-switch +@opindex mcet-switch +By default, CET instrumentation is turned off on switch statements that +use a jump table and indirect branch track is disabled. Since jump +tables are stored in read-only memory, this does not result in a direct +loss of hardening. But if the jump table index is attacker-controlled, +the indirect jump may not be constrained by CET. This option turns on +CET instrumentation to enable indirect branch track for switch statements +with jump tables which leads to the jump targets reachable via any indirect +jumps. + +@item -mcall-ms2sysv-xlogues +@opindex mcall-ms2sysv-xlogues +@opindex mno-call-ms2sysv-xlogues +Due to differences in 64-bit ABIs, any Microsoft ABI function that calls a +System V ABI function must consider RSI, RDI and XMM6-15 as clobbered. By +default, the code for saving and restoring these registers is emitted inline, +resulting in fairly lengthy prologues and epilogues. Using +@option{-mcall-ms2sysv-xlogues} emits prologues and epilogues that +use stubs in the static portion of libgcc to perform these saves and restores, +thus reducing function size at the cost of a few extra instructions. + +@item -mtls-dialect=@var{type} +@opindex mtls-dialect +Generate code to access thread-local storage using the @samp{gnu} or +@samp{gnu2} conventions. @samp{gnu} is the conservative default; +@samp{gnu2} is more efficient, but it may add compile- and run-time +requirements that cannot be satisfied on all systems. + +@item -mpush-args +@itemx -mno-push-args +@opindex mpush-args +@opindex mno-push-args +Use PUSH operations to store outgoing parameters. This method is shorter +and usually equally fast as method using SUB/MOV operations and is enabled +by default. In some cases disabling it may improve performance because of +improved scheduling and reduced dependencies. + +@item -maccumulate-outgoing-args +@opindex maccumulate-outgoing-args +If enabled, the maximum amount of space required for outgoing arguments is +computed in the function prologue. This is faster on most modern CPUs +because of reduced dependencies, improved scheduling and reduced stack usage +when the preferred stack boundary is not equal to 2. The drawback is a notable +increase in code size. This switch implies @option{-mno-push-args}. + +@item -mthreads +@opindex mthreads +Support thread-safe exception handling on MinGW. Programs that rely +on thread-safe exception handling must compile and link all code with the +@option{-mthreads} option. When compiling, @option{-mthreads} defines +@option{-D_MT}; when linking, it links in a special thread helper library +@option{-lmingwthrd} which cleans up per-thread exception-handling data. + +@item -mms-bitfields +@itemx -mno-ms-bitfields +@opindex mms-bitfields +@opindex mno-ms-bitfields + +Enable/disable bit-field layout compatible with the native Microsoft +Windows compiler. + +If @code{packed} is used on a structure, or if bit-fields are used, +it may be that the Microsoft ABI lays out the structure differently +than the way GCC normally does. Particularly when moving packed +data between functions compiled with GCC and the native Microsoft compiler +(either via function call or as data in a file), it may be necessary to access +either format. + +This option is enabled by default for Microsoft Windows +targets. This behavior can also be controlled locally by use of variable +or type attributes. For more information, see @ref{x86 Variable Attributes} +and @ref{x86 Type Attributes}. + +The Microsoft structure layout algorithm is fairly simple with the exception +of the bit-field packing. +The padding and alignment of members of structures and whether a bit-field +can straddle a storage-unit boundary are determine by these rules: + +@enumerate +@item Structure members are stored sequentially in the order in which they are +declared: the first member has the lowest memory address and the last member +the highest. + +@item Every data object has an alignment requirement. The alignment requirement +for all data except structures, unions, and arrays is either the size of the +object or the current packing size (specified with either the +@code{aligned} attribute or the @code{pack} pragma), +whichever is less. For structures, unions, and arrays, +the alignment requirement is the largest alignment requirement of its members. +Every object is allocated an offset so that: + +@smallexample +offset % alignment_requirement == 0 +@end smallexample + +@item Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation +unit if the integral types are the same size and if the next bit-field fits +into the current allocation unit without crossing the boundary imposed by the +common alignment requirements of the bit-fields. +@end enumerate + +MSVC interprets zero-length bit-fields in the following ways: + +@enumerate +@item If a zero-length bit-field is inserted between two bit-fields that +are normally coalesced, the bit-fields are not coalesced. + +For example: + +@smallexample +struct + @{ + unsigned long bf_1 : 12; + unsigned long : 0; + unsigned long bf_2 : 12; + @} t1; +@end smallexample + +@noindent +The size of @code{t1} is 8 bytes with the zero-length bit-field. If the +zero-length bit-field were removed, @code{t1}'s size would be 4 bytes. + +@item If a zero-length bit-field is inserted after a bit-field, @code{foo}, and the +alignment of the zero-length bit-field is greater than the member that follows it, +@code{bar}, @code{bar} is aligned as the type of the zero-length bit-field. + +For example: + +@smallexample +struct + @{ + char foo : 4; + short : 0; + char bar; + @} t2; + +struct + @{ + char foo : 4; + short : 0; + double bar; + @} t3; +@end smallexample + +@noindent +For @code{t2}, @code{bar} is placed at offset 2, rather than offset 1. +Accordingly, the size of @code{t2} is 4. For @code{t3}, the zero-length +bit-field does not affect the alignment of @code{bar} or, as a result, the size +of the structure. + +Taking this into account, it is important to note the following: + +@enumerate +@item If a zero-length bit-field follows a normal bit-field, the type of the +zero-length bit-field may affect the alignment of the structure as whole. For +example, @code{t2} has a size of 4 bytes, since the zero-length bit-field follows a +normal bit-field, and is of type short. + +@item Even if a zero-length bit-field is not followed by a normal bit-field, it may +still affect the alignment of the structure: + +@smallexample +struct + @{ + char foo : 6; + long : 0; + @} t4; +@end smallexample + +@noindent +Here, @code{t4} takes up 4 bytes. +@end enumerate + +@item Zero-length bit-fields following non-bit-field members are ignored: + +@smallexample +struct + @{ + char foo; + long : 0; + char bar; + @} t5; +@end smallexample + +@noindent +Here, @code{t5} takes up 2 bytes. +@end enumerate + + +@item -mno-align-stringops +@opindex mno-align-stringops +@opindex malign-stringops +Do not align the destination of inlined string operations. This switch reduces +code size and improves performance in case the destination is already aligned, +but GCC doesn't know about it. + +@item -minline-all-stringops +@opindex minline-all-stringops +By default GCC inlines string operations only when the destination is +known to be aligned to least a 4-byte boundary. +This enables more inlining and increases code +size, but may improve performance of code that depends on fast +@code{memcpy} and @code{memset} for short lengths. +The option enables inline expansion of @code{strlen} for all +pointer alignments. + +@item -minline-stringops-dynamically +@opindex minline-stringops-dynamically +For string operations of unknown size, use run-time checks with +inline code for small blocks and a library call for large blocks. + +@item -mstringop-strategy=@var{alg} +@opindex mstringop-strategy=@var{alg} +Override the internal decision heuristic for the particular algorithm to use +for inlining string operations. The allowed values for @var{alg} are: + +@table @samp +@item rep_byte +@itemx rep_4byte +@itemx rep_8byte +Expand using i386 @code{rep} prefix of the specified size. + +@item byte_loop +@itemx loop +@itemx unrolled_loop +Expand into an inline loop. + +@item libcall +Always use a library call. +@end table + +@item -mmemcpy-strategy=@var{strategy} +@opindex mmemcpy-strategy=@var{strategy} +Override the internal decision heuristic to decide if @code{__builtin_memcpy} +should be inlined and what inline algorithm to use when the expected size +of the copy operation is known. @var{strategy} +is a comma-separated list of @var{alg}:@var{max_size}:@var{dest_align} triplets. +@var{alg} is specified in @option{-mstringop-strategy}, @var{max_size} specifies +the max byte size with which inline algorithm @var{alg} is allowed. For the last +triplet, the @var{max_size} must be @code{-1}. The @var{max_size} of the triplets +in the list must be specified in increasing order. The minimal byte size for +@var{alg} is @code{0} for the first triplet and @code{@var{max_size} + 1} of the +preceding range. + +@item -mmemset-strategy=@var{strategy} +@opindex mmemset-strategy=@var{strategy} +The option is similar to @option{-mmemcpy-strategy=} except that it is to control +@code{__builtin_memset} expansion. + +@item -momit-leaf-frame-pointer +@opindex momit-leaf-frame-pointer +Don't keep the frame pointer in a register for leaf functions. This +avoids the instructions to save, set up, and restore frame pointers and +makes an extra register available in leaf functions. The option +@option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions, +which might make debugging harder. + +@item -mtls-direct-seg-refs +@itemx -mno-tls-direct-seg-refs +@opindex mtls-direct-seg-refs +Controls whether TLS variables may be accessed with offsets from the +TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit), +or whether the thread base pointer must be added. Whether or not this +is valid depends on the operating system, and whether it maps the +segment to cover the entire TLS area. + +For systems that use the GNU C Library, the default is on. + +@item -msse2avx +@itemx -mno-sse2avx +@opindex msse2avx +Specify that the assembler should encode SSE instructions with VEX +prefix. The option @option{-mavx} turns this on by default. + +@item -mfentry +@itemx -mno-fentry +@opindex mfentry +If profiling is active (@option{-pg}), put the profiling +counter call before the prologue. +Note: On x86 architectures the attribute @code{ms_hook_prologue} +isn't possible at the moment for @option{-mfentry} and @option{-pg}. + +@item -mrecord-mcount +@itemx -mno-record-mcount +@opindex mrecord-mcount +If profiling is active (@option{-pg}), generate a __mcount_loc section +that contains pointers to each profiling call. This is useful for +automatically patching and out calls. + +@item -mnop-mcount +@itemx -mno-nop-mcount +@opindex mnop-mcount +If profiling is active (@option{-pg}), generate the calls to +the profiling functions as NOPs. This is useful when they +should be patched in later dynamically. This is likely only +useful together with @option{-mrecord-mcount}. + +@item -minstrument-return=@var{type} +@opindex minstrument-return +Instrument function exit in -pg -mfentry instrumented functions with +call to specified function. This only instruments true returns ending +with ret, but not sibling calls ending with jump. Valid types +are @var{none} to not instrument, @var{call} to generate a call to __return__, +or @var{nop5} to generate a 5 byte nop. + +@item -mrecord-return +@itemx -mno-record-return +@opindex mrecord-return +Generate a __return_loc section pointing to all return instrumentation code. + +@item -mfentry-name=@var{name} +@opindex mfentry-name +Set name of __fentry__ symbol called at function entry for -pg -mfentry functions. + +@item -mfentry-section=@var{name} +@opindex mfentry-section +Set name of section to record -mrecord-mcount calls (default __mcount_loc). + +@item -mskip-rax-setup +@itemx -mno-skip-rax-setup +@opindex mskip-rax-setup +When generating code for the x86-64 architecture with SSE extensions +disabled, @option{-mskip-rax-setup} can be used to skip setting up RAX +register when there are no variable arguments passed in vector registers. + +@strong{Warning:} Since RAX register is used to avoid unnecessarily +saving vector registers on stack when passing variable arguments, the +impacts of this option are callees may waste some stack space, +misbehave or jump to a random location. GCC 4.4 or newer don't have +those issues, regardless the RAX register value. + +@item -m8bit-idiv +@itemx -mno-8bit-idiv +@opindex m8bit-idiv +On some processors, like Intel Atom, 8-bit unsigned integer divide is +much faster than 32-bit/64-bit integer divide. This option generates a +run-time check. If both dividend and divisor are within range of 0 +to 255, 8-bit unsigned integer divide is used instead of +32-bit/64-bit integer divide. + +@item -mavx256-split-unaligned-load +@itemx -mavx256-split-unaligned-store +@opindex mavx256-split-unaligned-load +@opindex mavx256-split-unaligned-store +Split 32-byte AVX unaligned load and store. + +@item -mstack-protector-guard=@var{guard} +@itemx -mstack-protector-guard-reg=@var{reg} +@itemx -mstack-protector-guard-offset=@var{offset} +@opindex mstack-protector-guard +@opindex mstack-protector-guard-reg +@opindex mstack-protector-guard-offset +Generate stack protection code using canary at @var{guard}. Supported +locations are @samp{global} for global canary or @samp{tls} for per-thread +canary in the TLS block (the default). This option has effect only when +@option{-fstack-protector} or @option{-fstack-protector-all} is specified. + +With the latter choice the options +@option{-mstack-protector-guard-reg=@var{reg}} and +@option{-mstack-protector-guard-offset=@var{offset}} furthermore specify +which segment register (@code{%fs} or @code{%gs}) to use as base register +for reading the canary, and from what offset from that base register. +The default for those is as specified in the relevant ABI. + +@item -mgeneral-regs-only +@opindex mgeneral-regs-only +Generate code that uses only the general-purpose registers. This +prevents the compiler from using floating-point, vector, mask and bound +registers. + +@item -mrelax-cmpxchg-loop +@opindex mrelax-cmpxchg-loop +Relax cmpxchg loop by emitting an early load and compare before cmpxchg, +execute pause if load value is not expected. This reduces excessive +cachline bouncing when and works for all atomic logic fetch builtins +that generates compare and swap loop. + +@item -mindirect-branch=@var{choice} +@opindex mindirect-branch +Convert indirect call and jump with @var{choice}. The default is +@samp{keep}, which keeps indirect call and jump unmodified. +@samp{thunk} converts indirect call and jump to call and return thunk. +@samp{thunk-inline} converts indirect call and jump to inlined call +and return thunk. @samp{thunk-extern} converts indirect call and jump +to external call and return thunk provided in a separate object file. +You can control this behavior for a specific function by using the +function attribute @code{indirect_branch}. @xref{Function Attributes}. + +Note that @option{-mcmodel=large} is incompatible with +@option{-mindirect-branch=thunk} and +@option{-mindirect-branch=thunk-extern} since the thunk function may +not be reachable in the large code model. + +Note that @option{-mindirect-branch=thunk-extern} is compatible with +@option{-fcf-protection=branch} since the external thunk can be made +to enable control-flow check. + +@item -mfunction-return=@var{choice} +@opindex mfunction-return +Convert function return with @var{choice}. The default is @samp{keep}, +which keeps function return unmodified. @samp{thunk} converts function +return to call and return thunk. @samp{thunk-inline} converts function +return to inlined call and return thunk. @samp{thunk-extern} converts +function return to external call and return thunk provided in a separate +object file. You can control this behavior for a specific function by +using the function attribute @code{function_return}. +@xref{Function Attributes}. + +Note that @option{-mindirect-return=thunk-extern} is compatible with +@option{-fcf-protection=branch} since the external thunk can be made +to enable control-flow check. + +Note that @option{-mcmodel=large} is incompatible with +@option{-mfunction-return=thunk} and +@option{-mfunction-return=thunk-extern} since the thunk function may +not be reachable in the large code model. + + +@item -mindirect-branch-register +@opindex mindirect-branch-register +Force indirect call and jump via register. + +@item -mharden-sls=@var{choice} +@opindex mharden-sls +Generate code to mitigate against straight line speculation (SLS) with +@var{choice}. The default is @samp{none} which disables all SLS +hardening. @samp{return} enables SLS hardening for function returns. +@samp{indirect-jmp} enables SLS hardening for indirect jumps. +@samp{all} enables all SLS hardening. + +@item -mindirect-branch-cs-prefix +@opindex mindirect-branch-cs-prefix +Add CS prefix to call and jmp to indirect thunk with branch target in +r8-r15 registers so that the call and jmp instruction length is 6 bytes +to allow them to be replaced with @samp{lfence; call *%r8-r15} or +@samp{lfence; jmp *%r8-r15} at run-time. + +@end table + +These @samp{-m} switches are supported in addition to the above +on x86-64 processors in 64-bit environments. + +@table @gcctabopt +@item -m32 +@itemx -m64 +@itemx -mx32 +@itemx -m16 +@itemx -miamcu +@opindex m32 +@opindex m64 +@opindex mx32 +@opindex m16 +@opindex miamcu +Generate code for a 16-bit, 32-bit or 64-bit environment. +The @option{-m32} option sets @code{int}, @code{long}, and pointer types +to 32 bits, and +generates code that runs on any i386 system. + +The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer +types to 64 bits, and generates code for the x86-64 architecture. +For Darwin only the @option{-m64} option also turns off the @option{-fno-pic} +and @option{-mdynamic-no-pic} options. + +The @option{-mx32} option sets @code{int}, @code{long}, and pointer types +to 32 bits, and +generates code for the x86-64 architecture. + +The @option{-m16} option is the same as @option{-m32}, except for that +it outputs the @code{.code16gcc} assembly directive at the beginning of +the assembly output so that the binary can run in 16-bit mode. + +The @option{-miamcu} option generates code which conforms to Intel MCU +psABI. It requires the @option{-m32} option to be turned on. + +@item -mno-red-zone +@opindex mno-red-zone +@opindex mred-zone +Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated +by the x86-64 ABI; it is a 128-byte area beyond the location of the +stack pointer that is not modified by signal or interrupt handlers +and therefore can be used for temporary data without adjusting the stack +pointer. The flag @option{-mno-red-zone} disables this red zone. + +@item -mcmodel=small +@opindex mcmodel=small +Generate code for the small code model: the program and its symbols must +be linked in the lower 2 GB of the address space. Pointers are 64 bits. +Programs can be statically or dynamically linked. This is the default +code model. + +@item -mcmodel=kernel +@opindex mcmodel=kernel +Generate code for the kernel code model. The kernel runs in the +negative 2 GB of the address space. +This model has to be used for Linux kernel code. + +@item -mcmodel=medium +@opindex mcmodel=medium +Generate code for the medium model: the program is linked in the lower 2 +GB of the address space. Small symbols are also placed there. Symbols +with sizes larger than @option{-mlarge-data-threshold} are put into +large data or BSS sections and can be located above 2GB. Programs can +be statically or dynamically linked. + +@item -mcmodel=large +@opindex mcmodel=large +Generate code for the large model. This model makes no assumptions +about addresses and sizes of sections. + +@item -maddress-mode=long +@opindex maddress-mode=long +Generate code for long address mode. This is only supported for 64-bit +and x32 environments. It is the default address mode for 64-bit +environments. + +@item -maddress-mode=short +@opindex maddress-mode=short +Generate code for short address mode. This is only supported for 32-bit +and x32 environments. It is the default address mode for 32-bit and +x32 environments. + +@item -mneeded +@itemx -mno-needed +@opindex mneeded +Emit GNU_PROPERTY_X86_ISA_1_NEEDED GNU property for Linux target to +indicate the micro-architecture ISA level required to execute the binary. + +@item -mno-direct-extern-access +@opindex mno-direct-extern-access +@opindex mdirect-extern-access +Without @option{-fpic} nor @option{-fPIC}, always use the GOT pointer +to access external symbols. With @option{-fpic} or @option{-fPIC}, +treat access to protected symbols as local symbols. The default is +@option{-mdirect-extern-access}. + +@strong{Warning:} shared libraries compiled with +@option{-mno-direct-extern-access} and executable compiled with +@option{-mdirect-extern-access} may not be binary compatible if +protected symbols are used in shared libraries and executable. +@end table + +@node x86 Windows Options +@subsection x86 Windows Options +@cindex x86 Windows Options +@cindex Windows Options for x86 + +These additional options are available for Microsoft Windows targets: + +@table @gcctabopt +@item -mconsole +@opindex mconsole +This option +specifies that a console application is to be generated, by +instructing the linker to set the PE header subsystem type +required for console applications. +This option is available for Cygwin and MinGW targets and is +enabled by default on those targets. + +@item -mdll +@opindex mdll +This option is available for Cygwin and MinGW targets. It +specifies that a DLL---a dynamic link library---is to be +generated, enabling the selection of the required runtime +startup object and entry point. + +@item -mnop-fun-dllimport +@opindex mnop-fun-dllimport +This option is available for Cygwin and MinGW targets. It +specifies that the @code{dllimport} attribute should be ignored. + +@item -mthreads +@opindex mthreads +This option is available for MinGW targets. It specifies +that MinGW-specific thread support is to be used. + +@item -municode +@opindex municode +This option is available for MinGW-w64 targets. It causes +the @code{UNICODE} preprocessor macro to be predefined, and +chooses Unicode-capable runtime startup code. + +@item -mwin32 +@opindex mwin32 +This option is available for Cygwin and MinGW targets. It +specifies that the typical Microsoft Windows predefined macros are to +be set in the pre-processor, but does not influence the choice +of runtime library/startup code. + +@item -mwindows +@opindex mwindows +This option is available for Cygwin and MinGW targets. It +specifies that a GUI application is to be generated by +instructing the linker to set the PE header subsystem type +appropriately. + +@item -fno-set-stack-executable +@opindex fno-set-stack-executable +@opindex fset-stack-executable +This option is available for MinGW targets. It specifies that +the executable flag for the stack used by nested functions isn't +set. This is necessary for binaries running in kernel mode of +Microsoft Windows, as there the User32 API, which is used to set executable +privileges, isn't available. + +@item -fwritable-relocated-rdata +@opindex fno-writable-relocated-rdata +@opindex fwritable-relocated-rdata +This option is available for MinGW and Cygwin targets. It specifies +that relocated-data in read-only section is put into the @code{.data} +section. This is a necessary for older runtimes not supporting +modification of @code{.rdata} sections for pseudo-relocation. + +@item -mpe-aligned-commons +@opindex mpe-aligned-commons +This option is available for Cygwin and MinGW targets. It +specifies that the GNU extension to the PE file format that +permits the correct alignment of COMMON variables should be +used when generating code. It is enabled by default if +GCC detects that the target assembler found during configuration +supports the feature. +@end table + +See also under @ref{x86 Options} for standard options. + +@node Xstormy16 Options +@subsection Xstormy16 Options +@cindex Xstormy16 Options + +These options are defined for Xstormy16: + +@table @gcctabopt +@item -msim +@opindex msim +Choose startup files and linker script suitable for the simulator. +@end table + +@node Xtensa Options +@subsection Xtensa Options +@cindex Xtensa Options + +These options are supported for Xtensa targets: + +@table @gcctabopt +@item -mconst16 +@itemx -mno-const16 +@opindex mconst16 +@opindex mno-const16 +Enable or disable use of @code{CONST16} instructions for loading +constant values. The @code{CONST16} instruction is currently not a +standard option from Tensilica. When enabled, @code{CONST16} +instructions are always used in place of the standard @code{L32R} +instructions. The use of @code{CONST16} is enabled by default only if +the @code{L32R} instruction is not available. + +@item -mfused-madd +@itemx -mno-fused-madd +@opindex mfused-madd +@opindex mno-fused-madd +Enable or disable use of fused multiply/add and multiply/subtract +instructions in the floating-point option. This has no effect if the +floating-point option is not also enabled. Disabling fused multiply/add +and multiply/subtract instructions forces the compiler to use separate +instructions for the multiply and add/subtract operations. This may be +desirable in some cases where strict IEEE 754-compliant results are +required: the fused multiply add/subtract instructions do not round the +intermediate result, thereby producing results with @emph{more} bits of +precision than specified by the IEEE standard. Disabling fused multiply +add/subtract instructions also ensures that the program output is not +sensitive to the compiler's ability to combine multiply and add/subtract +operations. + +@item -mserialize-volatile +@itemx -mno-serialize-volatile +@opindex mserialize-volatile +@opindex mno-serialize-volatile +When this option is enabled, GCC inserts @code{MEMW} instructions before +@code{volatile} memory references to guarantee sequential consistency. +The default is @option{-mserialize-volatile}. Use +@option{-mno-serialize-volatile} to omit the @code{MEMW} instructions. + +@item -mforce-no-pic +@opindex mforce-no-pic +For targets, like GNU/Linux, where all user-mode Xtensa code must be +position-independent code (PIC), this option disables PIC for compiling +kernel code. + +@item -mtext-section-literals +@itemx -mno-text-section-literals +@opindex mtext-section-literals +@opindex mno-text-section-literals +These options control the treatment of literal pools. The default is +@option{-mno-text-section-literals}, which places literals in a separate +section in the output file. This allows the literal pool to be placed +in a data RAM/ROM, and it also allows the linker to combine literal +pools from separate object files to remove redundant literals and +improve code size. With @option{-mtext-section-literals}, the literals +are interspersed in the text section in order to keep them as close as +possible to their references. This may be necessary for large assembly +files. Literals for each function are placed right before that function. + +@item -mauto-litpools +@itemx -mno-auto-litpools +@opindex mauto-litpools +@opindex mno-auto-litpools +These options control the treatment of literal pools. The default is +@option{-mno-auto-litpools}, which places literals in a separate +section in the output file unless @option{-mtext-section-literals} is +used. With @option{-mauto-litpools} the literals are interspersed in +the text section by the assembler. Compiler does not produce explicit +@code{.literal} directives and loads literals into registers with +@code{MOVI} instructions instead of @code{L32R} to let the assembler +do relaxation and place literals as necessary. This option allows +assembler to create several literal pools per function and assemble +very big functions, which may not be possible with +@option{-mtext-section-literals}. + +@item -mtarget-align +@itemx -mno-target-align +@opindex mtarget-align +@opindex mno-target-align +When this option is enabled, GCC instructs the assembler to +automatically align instructions to reduce branch penalties at the +expense of some code density. The assembler attempts to widen density +instructions to align branch targets and the instructions following call +instructions. If there are not enough preceding safe density +instructions to align a target, no widening is performed. The +default is @option{-mtarget-align}. These options do not affect the +treatment of auto-aligned instructions like @code{LOOP}, which the +assembler always aligns, either by widening density instructions or +by inserting NOP instructions. + +@item -mlongcalls +@itemx -mno-longcalls +@opindex mlongcalls +@opindex mno-longcalls +When this option is enabled, GCC instructs the assembler to translate +direct calls to indirect calls unless it can determine that the target +of a direct call is in the range allowed by the call instruction. This +translation typically occurs for calls to functions in other source +files. Specifically, the assembler translates a direct @code{CALL} +instruction into an @code{L32R} followed by a @code{CALLX} instruction. +The default is @option{-mno-longcalls}. This option should be used in +programs where the call target can potentially be out of range. This +option is implemented in the assembler, not the compiler, so the +assembly code generated by GCC still shows direct call +instructions---look at the disassembled object code to see the actual +instructions. Note that the assembler uses an indirect call for +every cross-file call, not just those that really are out of range. + +@item -mabi=@var{name} +@opindex mabi +Generate code for the specified ABI@. Permissible values are: @samp{call0}, +@samp{windowed}. Default ABI is chosen by the Xtensa core configuration. + +@item -mabi=call0 +@opindex mabi=call0 +When this option is enabled function parameters are passed in registers +@code{a2} through @code{a7}, registers @code{a12} through @code{a15} are +caller-saved, and register @code{a15} may be used as a frame pointer. +When this version of the ABI is enabled the C preprocessor symbol +@code{__XTENSA_CALL0_ABI__} is defined. + +@item -mabi=windowed +@opindex mabi=windowed +When this option is enabled function parameters are passed in registers +@code{a10} through @code{a15}, and called function rotates register window +by 8 registers on entry so that its arguments are found in registers +@code{a2} through @code{a7}. Register @code{a7} may be used as a frame +pointer. Register window is rotated 8 registers back upon return. +When this version of the ABI is enabled the C preprocessor symbol +@code{__XTENSA_WINDOWED_ABI__} is defined. + +@item -mextra-l32r-costs=@var{n} +@opindex mextra-l32r-costs +Specify an extra cost of instruction RAM/ROM access for @code{L32R} +instructions, in clock cycles. This affects, when optimizing for speed, +whether loading a constant from literal pool using @code{L32R} or +synthesizing the constant from a small one with a couple of arithmetic +instructions. The default value is 0. +@end table + +@node zSeries Options +@subsection zSeries Options +@cindex zSeries options + +These are listed under @xref{S/390 and zSeries Options}. + + +@c man end + +@node Spec Files +@section Specifying Subprocesses and the Switches to Pass to Them +@cindex Spec Files + +@command{gcc} is a driver program. It performs its job by invoking a +sequence of other programs to do the work of compiling, assembling and +linking. GCC interprets its command-line parameters and uses these to +deduce which programs it should invoke, and which command-line options +it ought to place on their command lines. This behavior is controlled +by @dfn{spec strings}. In most cases there is one spec string for each +program that GCC can invoke, but a few programs have multiple spec +strings to control their behavior. The spec strings built into GCC can +be overridden by using the @option{-specs=} command-line switch to specify +a spec file. + +@dfn{Spec files} are plain-text files that are used to construct spec +strings. They consist of a sequence of directives separated by blank +lines. The type of directive is determined by the first non-whitespace +character on the line, which can be one of the following: + +@table @code +@item %@var{command} +Issues a @var{command} to the spec file processor. The commands that can +appear here are: + +@table @code +@item %include <@var{file}> +@cindex @code{%include} +Search for @var{file} and insert its text at the current point in the +specs file. + +@item %include_noerr <@var{file}> +@cindex @code{%include_noerr} +Just like @samp{%include}, but do not generate an error message if the include +file cannot be found. + +@item %rename @var{old_name} @var{new_name} +@cindex @code{%rename} +Rename the spec string @var{old_name} to @var{new_name}. + +@end table + +@item *[@var{spec_name}]: +This tells the compiler to create, override or delete the named spec +string. All lines after this directive up to the next directive or +blank line are considered to be the text for the spec string. If this +results in an empty string then the spec is deleted. (Or, if the +spec did not exist, then nothing happens.) Otherwise, if the spec +does not currently exist a new spec is created. If the spec does +exist then its contents are overridden by the text of this +directive, unless the first character of that text is the @samp{+} +character, in which case the text is appended to the spec. + +@item [@var{suffix}]: +Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive +and up to the next directive or blank line are considered to make up the +spec string for the indicated suffix. When the compiler encounters an +input file with the named suffix, it processes the spec string in +order to work out how to compile that file. For example: + +@smallexample +.ZZ: +z-compile -input %i +@end smallexample + +This says that any input file whose name ends in @samp{.ZZ} should be +passed to the program @samp{z-compile}, which should be invoked with the +command-line switch @option{-input} and with the result of performing the +@samp{%i} substitution. (See below.) + +As an alternative to providing a spec string, the text following a +suffix directive can be one of the following: + +@table @code +@item @@@var{language} +This says that the suffix is an alias for a known @var{language}. This is +similar to using the @option{-x} command-line switch to GCC to specify a +language explicitly. For example: + +@smallexample +.ZZ: +@@c++ +@end smallexample + +Says that .ZZ files are, in fact, C++ source files. + +@item #@var{name} +This causes an error messages saying: + +@smallexample +@var{name} compiler not installed on this system. +@end smallexample +@end table + +GCC already has an extensive list of suffixes built into it. +This directive adds an entry to the end of the list of suffixes, but +since the list is searched from the end backwards, it is effectively +possible to override earlier entries using this technique. + +@end table + +GCC has the following spec strings built into it. Spec files can +override these strings or create their own. Note that individual +targets can also add their own spec strings to this list. + +@smallexample +asm Options to pass to the assembler +asm_final Options to pass to the assembler post-processor +cpp Options to pass to the C preprocessor +cc1 Options to pass to the C compiler +cc1plus Options to pass to the C++ compiler +endfile Object files to include at the end of the link +link Options to pass to the linker +lib Libraries to include on the command line to the linker +libgcc Decides which GCC support library to pass to the linker +linker Sets the name of the linker +predefines Defines to be passed to the C preprocessor +signed_char Defines to pass to CPP to say whether @code{char} is signed + by default +startfile Object files to include at the start of the link +@end smallexample + +Here is a small example of a spec file: + +@smallexample +%rename lib old_lib + +*lib: +--start-group -lgcc -lc -leval1 --end-group %(old_lib) +@end smallexample + +This example renames the spec called @samp{lib} to @samp{old_lib} and +then overrides the previous definition of @samp{lib} with a new one. +The new definition adds in some extra command-line options before +including the text of the old definition. + +@dfn{Spec strings} are a list of command-line options to be passed to their +corresponding program. In addition, the spec strings can contain +@samp{%}-prefixed sequences to substitute variable text or to +conditionally insert text into the command line. Using these constructs +it is possible to generate quite complex command lines. + +Here is a table of all defined @samp{%}-sequences for spec +strings. Note that spaces are not generated automatically around the +results of expanding these sequences. Therefore you can concatenate them +together or combine them with constant text in a single argument. + +@table @code +@item %% +Substitute one @samp{%} into the program name or argument. + +@item %" +Substitute an empty argument. + +@item %i +Substitute the name of the input file being processed. + +@item %b +Substitute the basename for outputs related with the input file being +processed. This is often the substring up to (and not including) the +last period and not including the directory but, unless %w is active, it +expands to the basename for auxiliary outputs, which may be influenced +by an explicit output name, and by various other options that control +how auxiliary outputs are named. + +@item %B +This is the same as @samp{%b}, but include the file suffix (text after +the last period). Without %w, it expands to the basename for dump +outputs. + +@item %d +Marks the argument containing or following the @samp{%d} as a +temporary file name, so that that file is deleted if GCC exits +successfully. Unlike @samp{%g}, this contributes no text to the +argument. + +@item %g@var{suffix} +Substitute a file name that has suffix @var{suffix} and is chosen +once per compilation, and mark the argument in the same way as +@samp{%d}. To reduce exposure to denial-of-service attacks, the file +name is now chosen in a way that is hard to predict even when previously +chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} +might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches +the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is +treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} +was simply substituted with a file name chosen once per compilation, +without regard to any appended suffix (which was therefore treated +just like ordinary text), making such attacks more likely to succeed. + +@item %u@var{suffix} +Like @samp{%g}, but generates a new temporary file name +each time it appears instead of once per compilation. + +@item %U@var{suffix} +Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a +new one if there is no such last file name. In the absence of any +@samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share +the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} +involves the generation of two distinct file names, one +for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was +simply substituted with a file name chosen for the previous @samp{%u}, +without regard to any appended suffix. + +@item %j@var{suffix} +Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is +writable, and if @option{-save-temps} is not used; +otherwise, substitute the name +of a temporary file, just like @samp{%u}. This temporary file is not +meant for communication between processes, but rather as a junk +disposal mechanism. + +@item %|@var{suffix} +@itemx %m@var{suffix} +Like @samp{%g}, except if @option{-pipe} is in effect. In that case +@samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at +all. These are the two most common ways to instruct a program that it +should read from standard input or write to standard output. If you +need something more elaborate you can use an @samp{%@{pipe:@code{X}@}} +construct: see for example @file{gcc/fortran/lang-specs.h}. + +@item %.@var{SUFFIX} +Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args +when it is subsequently output with @samp{%*}. @var{SUFFIX} is +terminated by the next space or %. + +@item %w +Marks the argument containing or following the @samp{%w} as the +designated output file of this compilation. This puts the argument +into the sequence of arguments that @samp{%o} substitutes. + +@item %V +Indicates that this compilation produces no output file. + +@item %o +Substitutes the names of all the output files, with spaces +automatically placed around them. You should write spaces +around the @samp{%o} as well or the results are undefined. +@samp{%o} is for use in the specs for running the linker. +Input files whose names have no recognized suffix are not compiled +at all, but they are included among the output files, so they are +linked. + +@item %O +Substitutes the suffix for object files. Note that this is +handled specially when it immediately follows @samp{%g, %u, or %U}, +because of the need for those to form complete file names. The +handling is such that @samp{%O} is treated exactly as if it had already +been substituted, except that @samp{%g, %u, and %U} do not currently +support additional @var{suffix} characters following @samp{%O} as they do +following, for example, @samp{.o}. + +@item %I +Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}), +@option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), +@option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options) +and @option{-imultilib} as necessary. + +@item %s +Current argument is the name of a library or startup file of some sort. +Search for that file in a standard list of directories and substitute +the full name found. The current working directory is included in the +list of directories scanned. + +@item %T +Current argument is the name of a linker script. Search for that file +in the current list of directories to scan for libraries. If the file +is located insert a @option{--script} option into the command line +followed by the full path name found. If the file is not found then +generate an error message. Note: the current working directory is not +searched. + +@item %e@var{str} +Print @var{str} as an error message. @var{str} is terminated by a newline. +Use this when inconsistent options are detected. + +@item %n@var{str} +Print @var{str} as a notice. @var{str} is terminated by a newline. + +@item %(@var{name}) +Substitute the contents of spec string @var{name} at this point. + +@item %x@{@var{option}@} +Accumulate an option for @samp{%X}. + +@item %X +Output the accumulated linker options specified by a @samp{%x} spec string. + +@item %Y +Output the accumulated assembler options specified by @option{-Wa}. + +@item %Z +Output the accumulated preprocessor options specified by @option{-Wp}. + +@item %M +Output @code{multilib_os_dir}. + +@item %R +Output the concatenation of @code{target_system_root} and @code{target_sysroot_suffix}. + +@item %a +Process the @code{asm} spec. This is used to compute the +switches to be passed to the assembler. + +@item %A +Process the @code{asm_final} spec. This is a spec string for +passing switches to an assembler post-processor, if such a program is +needed. + +@item %l +Process the @code{link} spec. This is the spec for computing the +command line passed to the linker. Typically it makes use of the +@samp{%L %G %S %D and %E} sequences. + +@item %D +Dump out a @option{-L} option for each directory that GCC believes might +contain startup files. If the target supports multilibs then the +current multilib directory is prepended to each of these paths. + +@item %L +Process the @code{lib} spec. This is a spec string for deciding which +libraries are included on the command line to the linker. + +@item %G +Process the @code{libgcc} spec. This is a spec string for deciding +which GCC support library is included on the command line to the linker. + +@item %S +Process the @code{startfile} spec. This is a spec for deciding which +object files are the first ones passed to the linker. Typically +this might be a file named @file{crt0.o}. + +@item %E +Process the @code{endfile} spec. This is a spec string that specifies +the last object files that are passed to the linker. + +@item %C +Process the @code{cpp} spec. This is used to construct the arguments +to be passed to the C preprocessor. + +@item %1 +Process the @code{cc1} spec. This is used to construct the options to be +passed to the actual C compiler (@command{cc1}). + +@item %2 +Process the @code{cc1plus} spec. This is used to construct the options to be +passed to the actual C++ compiler (@command{cc1plus}). + +@item %* +Substitute the variable part of a matched option. See below. +Note that each comma in the substituted string is replaced by +a single space. + +@item %S +Similar to @samp{% [] +@end smallexample + +It returns @code{result} if the comparison evaluates to true, and NULL if it doesn't. +The supported @code{comparison-op} values are: + +@table @code +@item >= +True if @code{switch} is a later (or same) version than @code{arg1} + +@item !> +Opposite of @code{>=} + +@item < +True if @code{switch} is an earlier version than @code{arg1} + +@item !< +Opposite of @code{<} + +@item >< +True if @code{switch} is @code{arg1} or later, and earlier than @code{arg2} + +@item <> +True if @code{switch} is earlier than @code{arg1}, or is @code{arg2} or later +@end table + +If the @code{switch} is not present at all, the condition is false unless the first character +of the @code{comparison-op} is @code{!}. + +@smallexample +%:version-compare(>= 10.3 mmacosx-version-min= -lmx) +@end smallexample + +The above example would add @option{-lmx} if @option{-mmacosx-version-min=10.3.9} was +passed. + +@item @code{include} +The @code{include} spec function behaves much like @code{%include}, with the advantage +that it can be nested inside a spec and thus be conditionalized. It takes one argument, +the filename, and looks for it in the startfile path. It always returns NULL. + +@smallexample +%@{static-libasan|static:%:include(libsanitizer.spec)%(link_libasan)@} +@end smallexample + +@item @code{pass-through-libs} +The @code{pass-through-libs} spec function takes any number of arguments. It +finds any @option{-l} options and any non-options ending in @file{.a} (which it +assumes are the names of linker input library archive files) and returns a +result containing all the found arguments each prepended by +@option{-plugin-opt=-pass-through=} and joined by spaces. This list is +intended to be passed to the LTO linker plugin. + +@smallexample +%:pass-through-libs(%G %L %G) +@end smallexample + +@item @code{print-asm-header} +The @code{print-asm-header} function takes no arguments and simply +prints a banner like: + +@smallexample +Assembler options +================= + +Use "-Wa,OPTION" to pass "OPTION" to the assembler. +@end smallexample + +It is used to separate compiler options from assembler options +in the @option{--target-help} output. + +@item @code{gt} +The @code{gt} spec function takes two or more arguments. It returns @code{""} (the +empty string) if the second-to-last argument is greater than the last argument, and NULL +otherwise. The following example inserts the @code{link_gomp} spec if the last +@option{-ftree-parallelize-loops=} option given on the command line is greater than 1: + +@smallexample +%@{%:gt(%@{ftree-parallelize-loops=*:%*@} 1):%:include(libgomp.spec)%(link_gomp)@} +@end smallexample + +@item @code{debug-level-gt} +The @code{debug-level-gt} spec function takes one argument and returns @code{""} (the +empty string) if @code{debug_info_level} is greater than the specified number, and NULL +otherwise. + +@smallexample +%@{%:debug-level-gt(0):%@{gdwarf*:--gdwarf2@}@} +@end smallexample +@end table + +@item %@{S@} +Substitutes the @code{-S} switch, if that switch is given to GCC@. +If that switch is not specified, this substitutes nothing. Note that +the leading dash is omitted when specifying this option, and it is +automatically inserted if the substitution is performed. Thus the spec +string @samp{%@{foo@}} matches the command-line option @option{-foo} +and outputs the command-line option @option{-foo}. + +@item %W@{S@} +Like %@{@code{S}@} but mark last argument supplied within as a file to be +deleted on failure. + +@item %@@@{S@} +Like %@{@code{S}@} but puts the result into a @code{FILE} and substitutes +@code{@@FILE} if an @code{@@file} argument has been supplied. + +@item %@{S*@} +Substitutes all the switches specified to GCC whose names start +with @code{-S}, but which also take an argument. This is used for +switches like @option{-o}, @option{-D}, @option{-I}, etc. +GCC considers @option{-o foo} as being +one switch whose name starts with @samp{o}. %@{o*@} substitutes this +text, including the space. Thus two arguments are generated. + +@item %@{S*&T*@} +Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options +(the order of @code{S} and @code{T} in the spec is not significant). +There can be any number of ampersand-separated variables; for each the +wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. + +@item %@{S:X@} +Substitutes @code{X}, if the @option{-S} switch is given to GCC@. + +@item %@{!S:X@} +Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@. + +@item %@{S*:X@} +Substitutes @code{X} if one or more switches whose names start with +@code{-S} are specified to GCC@. Normally @code{X} is substituted only +once, no matter how many such switches appeared. However, if @code{%*} +appears somewhere in @code{X}, then @code{X} is substituted once +for each matching switch, with the @code{%*} replaced by the part of +that switch matching the @code{*}. + +If @code{%*} appears as the last part of a spec sequence then a space +is added after the end of the last substitution. If there is more +text in the sequence, however, then a space is not generated. This +allows the @code{%*} substitution to be used as part of a larger +string. For example, a spec string like this: + +@smallexample +%@{mcu=*:--script=%*/memory.ld@} +@end smallexample + +@noindent +when matching an option like @option{-mcu=newchip} produces: + +@smallexample +--script=newchip/memory.ld +@end smallexample + +@item %@{.S:X@} +Substitutes @code{X}, if processing a file with suffix @code{S}. + +@item %@{!.S:X@} +Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}. + +@item %@{,S:X@} +Substitutes @code{X}, if processing a file for language @code{S}. + +@item %@{!,S:X@} +Substitutes @code{X}, if not processing a file for language @code{S}. + +@item %@{S|P:X@} +Substitutes @code{X} if either @code{-S} or @code{-P} is given to +GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and +@code{*} sequences as well, although they have a stronger binding than +the @samp{|}. If @code{%*} appears in @code{X}, all of the +alternatives must be starred, and only the first matching alternative +is substituted. + +For example, a spec string like this: + +@smallexample +%@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} +@end smallexample + +@noindent +outputs the following command-line options from the following input +command-line options: + +@smallexample +fred.c -foo -baz +jim.d -bar -boggle +-d fred.c -foo -baz -boggle +-d jim.d -bar -baz -boggle +@end smallexample + +@item %@{%:@var{function}(@var{args}):X@} + +Call function named @var{function} with args @var{args}. If the +function returns non-NULL, then @code{X} is substituted, if it returns +NULL, it isn't substituted. + +@item %@{S:X; T:Y; :D@} + +If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is +given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can +be as many clauses as you need. This may be combined with @code{.}, +@code{,}, @code{!}, @code{|}, and @code{*} as needed. + + +@end table + +The switch matching text @code{S} in a @samp{%@{S@}}, @samp{%@{S:X@}} +or similar construct can use a backslash to ignore the special meaning +of the character following it, thus allowing literal matching of a +character that is otherwise specially treated. For example, +@samp{%@{std=iso9899\:1999:X@}} substitutes @code{X} if the +@option{-std=iso9899:1999} option is given. + +The conditional text @code{X} in a @samp{%@{S:X@}} or similar +construct may contain other nested @samp{%} constructs or spaces, or +even newlines. They are processed as usual, as described above. +Trailing white space in @code{X} is ignored. White space may also +appear anywhere on the left side of the colon in these constructs, +except between @code{.} or @code{*} and the corresponding word. + +The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are +handled specifically in these constructs. If another value of +@option{-O} or the negated form of a @option{-f}, @option{-m}, or +@option{-W} switch is found later in the command line, the earlier +switch value is ignored, except with @{@code{S}*@} where @code{S} is +just one letter, which passes all matching options. + +The character @samp{|} at the beginning of the predicate text is used to +indicate that a command should be piped to the following command, but +only if @option{-pipe} is specified. + +It is built into GCC which switches take arguments and which do not. +(You might think it would be useful to generalize this to allow each +compiler's spec to say which switches take arguments. But this cannot +be done in a consistent fashion. GCC cannot even decide which input +files have been specified without knowing which switches take arguments, +and it must know which input files to compile in order to tell which +compilers to run). + +GCC also knows implicitly that arguments starting in @option{-l} are to be +treated as compiler output files, and passed to the linker in their +proper position among the other output files. + +@node Environment Variables +@section Environment Variables Affecting GCC +@cindex environment variables + +@c man begin ENVIRONMENT +This section describes several environment variables that affect how GCC +operates. Some of them work by specifying directories or prefixes to use +when searching for various kinds of files. Some are used to specify other +aspects of the compilation environment. + +Note that you can also specify places to search using options such as +@option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These +take precedence over places specified using environment variables, which +in turn take precedence over those specified by the configuration of GCC@. +@xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, +GNU Compiler Collection (GCC) Internals}. + +@table @env +@item LANG +@itemx LC_CTYPE +@c @itemx LC_COLLATE +@itemx LC_MESSAGES +@c @itemx LC_MONETARY +@c @itemx LC_NUMERIC +@c @itemx LC_TIME +@itemx LC_ALL +@findex LANG +@findex LC_CTYPE +@c @findex LC_COLLATE +@findex LC_MESSAGES +@c @findex LC_MONETARY +@c @findex LC_NUMERIC +@c @findex LC_TIME +@findex LC_ALL +@cindex locale +These environment variables control the way that GCC uses +localization information which allows GCC to work with different +national conventions. GCC inspects the locale categories +@env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do +so. These locale categories can be set to any value supported by your +installation. A typical value is @samp{en_GB.UTF-8} for English in the United +Kingdom encoded in UTF-8. + +The @env{LC_CTYPE} environment variable specifies character +classification. GCC uses it to determine the character boundaries in +a string; this is needed for some multibyte encodings that contain quote +and escape characters that are otherwise interpreted as a string +end or escape. + +The @env{LC_MESSAGES} environment variable specifies the language to +use in diagnostic messages. + +If the @env{LC_ALL} environment variable is set, it overrides the value +of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} +and @env{LC_MESSAGES} default to the value of the @env{LANG} +environment variable. If none of these variables are set, GCC +defaults to traditional C English behavior. + +@item TMPDIR +@findex TMPDIR +If @env{TMPDIR} is set, it specifies the directory to use for temporary +files. GCC uses temporary files to hold the output of one stage of +compilation which is to be used as input to the next stage: for example, +the output of the preprocessor, which is the input to the compiler +proper. + +@item GCC_COMPARE_DEBUG +@findex GCC_COMPARE_DEBUG +Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing +@option{-fcompare-debug} to the compiler driver. See the documentation +of this option for more details. + +@item GCC_EXEC_PREFIX +@findex GCC_EXEC_PREFIX +If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the +names of the subprograms executed by the compiler. No slash is added +when this prefix is combined with the name of a subprogram, but you can +specify a prefix that ends with a slash if you wish. + +If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out +an appropriate prefix to use based on the pathname it is invoked with. + +If GCC cannot find the subprogram using the specified prefix, it +tries looking in the usual places for the subprogram. + +The default value of @env{GCC_EXEC_PREFIX} is +@file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to +the installed compiler. In many cases @var{prefix} is the value +of @code{prefix} when you ran the @file{configure} script. + +Other prefixes specified with @option{-B} take precedence over this prefix. + +This prefix is also used for finding files such as @file{crt0.o} that are +used for linking. + +In addition, the prefix is used in an unusual way in finding the +directories to search for header files. For each of the standard +directories whose name normally begins with @samp{/usr/local/lib/gcc} +(more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries +replacing that beginning with the specified prefix to produce an +alternate directory name. Thus, with @option{-Bfoo/}, GCC searches +@file{foo/bar} just before it searches the standard directory +@file{/usr/local/lib/bar}. +If a standard directory begins with the configured +@var{prefix} then the value of @var{prefix} is replaced by +@env{GCC_EXEC_PREFIX} when looking for header files. + +@item COMPILER_PATH +@findex COMPILER_PATH +The value of @env{COMPILER_PATH} is a colon-separated list of +directories, much like @env{PATH}. GCC tries the directories thus +specified when searching for subprograms, if it cannot find the +subprograms using @env{GCC_EXEC_PREFIX}. + +@item LIBRARY_PATH +@findex LIBRARY_PATH +The value of @env{LIBRARY_PATH} is a colon-separated list of +directories, much like @env{PATH}. When configured as a native compiler, +GCC tries the directories thus specified when searching for special +linker files, if it cannot find them using @env{GCC_EXEC_PREFIX}. Linking +using GCC also uses these directories when searching for ordinary +libraries for the @option{-l} option (but directories specified with +@option{-L} come first). + +@item LANG +@findex LANG +@cindex locale definition +This variable is used to pass locale information to the compiler. One way in +which this information is used is to determine the character set to be used +when character literals, string literals and comments are parsed in C and C++. +When the compiler is configured to allow multibyte characters, +the following values for @env{LANG} are recognized: + +@table @samp +@item C-JIS +Recognize JIS characters. +@item C-SJIS +Recognize SJIS characters. +@item C-EUCJP +Recognize EUCJP characters. +@end table + +If @env{LANG} is not defined, or if it has some other value, then the +compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to +recognize and translate multibyte characters. + +@item GCC_EXTRA_DIAGNOSTIC_OUTPUT +@findex GCC_EXTRA_DIAGNOSTIC_OUTPUT +If @env{GCC_EXTRA_DIAGNOSTIC_OUTPUT} is set to one of the following values, +then additional text will be emitted to stderr when fix-it hints are +emitted. @option{-fdiagnostics-parseable-fixits} and +@option{-fno-diagnostics-parseable-fixits} take precedence over this +environment variable. + +@table @samp +@item fixits-v1 +Emit parseable fix-it hints, equivalent to +@option{-fdiagnostics-parseable-fixits}. In particular, columns are +expressed as a count of bytes, starting at byte 1 for the initial column. + +@item fixits-v2 +As @code{fixits-v1}, but columns are expressed as display columns, +as per @option{-fdiagnostics-column-unit=display}. +@end table + +@end table + +@noindent +Some additional environment variables affect the behavior of the +preprocessor. + +@include cppenv.texi + +@c man end + +@node Precompiled Headers +@section Using Precompiled Headers +@cindex precompiled headers +@cindex speed of compilation + +Often large projects have many header files that are included in every +source file. The time the compiler takes to process these header files +over and over again can account for nearly all of the time required to +build the project. To make builds faster, GCC allows you to +@dfn{precompile} a header file. + +To create a precompiled header file, simply compile it as you would any +other file, if necessary using the @option{-x} option to make the driver +treat it as a C or C++ header file. You may want to use a +tool like @command{make} to keep the precompiled header up-to-date when +the headers it contains change. + +A precompiled header file is searched for when @code{#include} is +seen in the compilation. As it searches for the included file +(@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the +compiler looks for a precompiled header in each directory just before it +looks for the include file in that directory. The name searched for is +the name specified in the @code{#include} with @samp{.gch} appended. If +the precompiled header file cannot be used, it is ignored. + +For instance, if you have @code{#include "all.h"}, and you have +@file{all.h.gch} in the same directory as @file{all.h}, then the +precompiled header file is used if possible, and the original +header is used otherwise. + +Alternatively, you might decide to put the precompiled header file in a +directory and use @option{-I} to ensure that directory is searched +before (or instead of) the directory containing the original header. +Then, if you want to check that the precompiled header file is always +used, you can put a file of the same name as the original header in this +directory containing an @code{#error} command. + +This also works with @option{-include}. So yet another way to use +precompiled headers, good for projects not designed with precompiled +header files in mind, is to simply take most of the header files used by +a project, include them from another header file, precompile that header +file, and @option{-include} the precompiled header. If the header files +have guards against multiple inclusion, they are skipped because +they've already been included (in the precompiled header). + +If you need to precompile the same header file for different +languages, targets, or compiler options, you can instead make a +@emph{directory} named like @file{all.h.gch}, and put each precompiled +header in the directory, perhaps using @option{-o}. It doesn't matter +what you call the files in the directory; every precompiled header in +the directory is considered. The first precompiled header +encountered in the directory that is valid for this compilation is +used; they're searched in no particular order. + +There are many other possibilities, limited only by your imagination, +good sense, and the constraints of your build system. + +A precompiled header file can be used only when these conditions apply: + +@itemize +@item +Only one precompiled header can be used in a particular compilation. + +@item +A precompiled header cannot be used once the first C token is seen. You +can have preprocessor directives before a precompiled header; you cannot +include a precompiled header from inside another header. + +@item +The precompiled header file must be produced for the same language as +the current compilation. You cannot use a C precompiled header for a C++ +compilation. + +@item +The precompiled header file must have been produced by the same compiler +binary as the current compilation is using. + +@item +Any macros defined before the precompiled header is included must +either be defined in the same way as when the precompiled header was +generated, or must not affect the precompiled header, which usually +means that they don't appear in the precompiled header at all. + +The @option{-D} option is one way to define a macro before a +precompiled header is included; using a @code{#define} can also do it. +There are also some options that define macros implicitly, like +@option{-O} and @option{-Wdeprecated}; the same rule applies to macros +defined this way. + +@item If debugging information is output when using the precompiled +header, using @option{-g} or similar, the same kind of debugging information +must have been output when building the precompiled header. However, +a precompiled header built using @option{-g} can be used in a compilation +when no debugging information is being output. + +@item The same @option{-m} options must generally be used when building +and using the precompiled header. @xref{Submodel Options}, +for any cases where this rule is relaxed. + +@item Each of the following options must be the same when building and using +the precompiled header: + +@gccoptlist{-fexceptions} + +@item +Some other command-line options starting with @option{-f}, +@option{-p}, or @option{-O} must be defined in the same way as when +the precompiled header was generated. At present, it's not clear +which options are safe to change and which are not; the safest choice +is to use exactly the same options when generating and using the +precompiled header. The following are known to be safe: + +@gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol +-fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol +-fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol +-pedantic-errors} + +@item Address space layout randomization (ASLR) can lead to not binary identical +PCH files. If you rely on stable PCH file contents disable ASLR when generating +PCH files. + +@end itemize + +For all of these except the last, the compiler automatically +ignores the precompiled header if the conditions aren't met. If you +find an option combination that doesn't work and doesn't cause the +precompiled header to be ignored, please consider filing a bug report, +see @ref{Bugs}. + +If you do use differing options when generating and using the +precompiled header, the actual behavior is a mixture of the +behavior for the options. For instance, if you use @option{-g} to +generate the precompiled header but not when using it, you may or may +not get debugging information for routines in the precompiled header. + +@node C++ Modules +@section C++ Modules +@cindex speed of compilation + +Modules are a C++20 language feature. As the name suggests, they +provides a modular compilation system, intending to provide both +faster builds and better library isolation. The ``Merging Modules'' +paper @uref{https://wg21.link/p1103}, provides the easiest to read set +of changes to the standard, although it does not capture later +changes. + +@emph{G++'s modules support is not complete.} Other than bugs, the +known missing pieces are: + +@table @emph + +@item Private Module Fragment +The Private Module Fragment is recognized, but an error is emitted. + +@item Partition definition visibility rules +Entities may be defined in implementation partitions, and those +definitions are not available outside of the module. This is not +implemented, and the definitions are available to extra-module use. + +@item Textual merging of reachable GM entities +Entities may be multiply defined across different header-units. +These must be de-duplicated, and this is implemented across imports, +or when an import redefines a textually-defined entity. However the +reverse is not implemented---textually redefining an entity that has +been defined in an imported header-unit. A redefinition error is +emitted. + +@item Translation-Unit local referencing rules +Papers p1815 (@uref{https://wg21.link/p1815}) and p2003 +(@uref{https://wg21.link/p2003}) add limitations on which entities an +exported region may reference (for instance, the entities an exported +template definition may reference). These are not fully implemented. + +@item Standard Library Header Units +The Standard Library is not provided as importable header units. If +you want to import such units, you must explicitly build them first. +If you do not do this with care, you may have multiple declarations, +which the module machinery must merge---compiler resource usage can be +affected by how you partition header files into header units. + +@end table + +Modular compilation is @emph{not} enabled with just the +@option{-std=c++20} option. You must explicitly enable it with the +@option{-fmodules-ts} option. It is independent of the language +version selected, although in pre-C++20 versions, it is of course an +extension. + +No new source file suffixes are required or supported. If you wish to +use a non-standard suffix (@pxref{Overall Options}), you also need +to provide a @option{-x c++} option too.@footnote{Some users like to +distinguish module interface files with a new suffix, such as naming +the source @code{module.cppm}, which involves +teaching all tools about the new suffix. A different scheme, such as +naming @code{module-m.cpp} would be less invasive.} + +Compiling a module interface unit produces an additional output (to +the assembly or object file), called a Compiled Module Interface +(CMI). This encodes the exported declarations of the module. +Importing a module reads in the CMI. The import graph is a Directed +Acyclic Graph (DAG). You must build imports before the importer. + +Header files may themselves be compiled to header units, which are a +transitional ability aiming at faster compilation. The +@option{-fmodule-header} option is used to enable this, and implies +the @option{-fmodules-ts} option. These CMIs are named by the fully +resolved underlying header file, and thus may be a complete pathname +containing subdirectories. If the header file is found at an absolute +pathname, the CMI location is still relative to a CMI root directory. + +As header files often have no suffix, you commonly have to specify a +@option{-x} option to tell the compiler the source is a header file. +You may use @option{-x c++-header}, @option{-x c++-user-header} or +@option{-x c++-system-header}. When used in conjunction with +@option{-fmodules-ts}, these all imply an appropriate +@option{-fmodule-header} option. The latter two variants use the +user or system include path to search for the file specified. This +allows you to, for instance, compile standard library header files as +header units, without needing to know exactly where they are +installed. Specifying the language as one of these variants also +inhibits output of the object file, as header files have no associated +object file. + +The @option{-fmodule-only} option disables generation of the +associated object file for compiling a module interface. Only the CMI +is generated. This option is implied when using the +@option{-fmodule-header} option. + +The @option{-flang-info-include-translate} and +@option{-flang-info-include-translate-not} options notes whether +include translation occurs or not. With no argument, the first will +note all include translation. The second will note all +non-translations of include files not known to intentionally be +textual. With an argument, queries about include translation of a +header files with that particular trailing pathname are noted. You +may repeat this form to cover several different header files. This +option may be helpful in determining whether include translation is +happening---if it is working correctly, it behaves as if it isn't +there at all. + +The @option{-flang-info-module-cmi} option can be used to determine +where the compiler is reading a CMI from. Without the option, the +compiler is silent when such a read is successful. This option has an +optional argument, which will restrict the notification to just the +set of named modules or header units specified. + +The @option{-Winvalid-imported-macros} option causes all imported macros +to be resolved at the end of compilation. Without this, imported +macros are only resolved when expanded or (re)defined. This option +detects conflicting import definitions for all macros. + +For details of the @option{-fmodule-mapper} family of options, +@pxref{C++ Module Mapper}. + +@menu +* C++ Module Mapper:: Module Mapper +* C++ Module Preprocessing:: Module Preprocessing +* C++ Compiled Module Interface:: Compiled Module Interface +@end menu + +@node C++ Module Mapper +@subsection Module Mapper +@cindex C++ Module Mapper + +A module mapper provides a server or file that the compiler queries to +determine the mapping between module names and CMI files. It is also +used to build CMIs on demand. @emph{Mapper functionality is in its +infancy and is intended for experimentation with build system +interactions.} + +You can specify a mapper with the @option{-fmodule-mapper=@var{val}} +option or @env{CXX_MODULE_MAPPER} environment variable. The value may +have one of the following forms: + +@table @gcctabopt + +@item @r{[}@var{hostname}@r{]}:@var{port}@r{[}?@var{ident}@r{]} +An optional hostname and a numeric port number to connect to. If the +hostname is omitted, the loopback address is used. If the hostname +corresponds to multiple IPV6 addresses, these are tried in turn, until +one is successful. If your host lacks IPv6, this form is +non-functional. If you must use IPv4 use +@option{-fmodule-mapper='|ncat @var{ipv4host} @var{port}'}. + +@item =@var{socket}@r{[}?@var{ident}@r{]} +A local domain socket. If your host lacks local domain sockets, this +form is non-functional. + +@item |@var{program}@r{[}?@var{ident}@r{]} @r{[}@var{args...}@r{]} +A program to spawn, and communicate with on its stdin/stdout streams. +Your @var{PATH} environment variable is searched for the program. +Arguments are separated by space characters, (it is not possible for +one of the arguments delivered to the program to contain a space). An +exception is if @var{program} begins with @@. In that case +@var{program} (sans @@) is looked for in the compiler's internal +binary directory. Thus the sample mapper-server can be specified +with @code{@@g++-mapper-server}. + +@item <>@r{[}?@var{ident}@r{]} +@item <>@var{inout}@r{[}?@var{ident}@r{]} +@item <@var{in}>@var{out}@r{[}?@var{ident}@r{]} +Named pipes or file descriptors to communicate over. The first form, +@option{<>}, communicates over stdin and stdout. The other forms +allow you to specify a file descriptor or name a pipe. A numeric value +is interpreted as a file descriptor, otherwise named pipe is opened. +The second form specifies a bidirectional pipe and the last form +allows specifying two independent pipes. Using file descriptors +directly in this manner is fragile in general, as it can require the +cooperation of intermediate processes. In particular using stdin & +stdout is fraught with danger as other compiler options might also +cause the compiler to read stdin or write stdout, and it can have +unfortunate interactions with signal delivery from the terminal. + +@item @var{file}@r{[}?@var{ident}@r{]} +A mapping file consisting of space-separated module-name, filename +pairs, one per line. Only the mappings for the direct imports and any +module export name need be provided. If other mappings are provided, +they override those stored in any imported CMI files. A repository +root may be specified in the mapping file by using @samp{$root} as the +module name in the first active line. Use of this option will disable +any default module->CMI name mapping. + +@end table + +As shown, an optional @var{ident} may suffix the first word of the +option, indicated by a @samp{?} prefix. The value is used in the +initial handshake with the module server, or to specify a prefix on +mapping file lines. In the server case, the main source file name is +used if no @var{ident} is specified. In the file case, all non-blank +lines are significant, unless a value is specified, in which case only +lines beginning with @var{ident} are significant. The @var{ident} +must be separated by whitespace from the module name. Be aware that +@samp{<}, @samp{>}, @samp{?}, and @samp{|} characters are often +significant to the shell, and therefore may need quoting. + +The mapper is connected to or loaded lazily, when the first module +mapping is required. The networking protocols are only supported on +hosts that provide networking. If no mapper is specified a default is +provided. + +A project-specific mapper is expected to be provided by the build +system that invokes the compiler. It is not expected that a +general-purpose server is provided for all compilations. As such, the +server will know the build configuration, the compiler it invoked, and +the environment (such as working directory) in which that is +operating. As it may parallelize builds, several compilations may +connect to the same socket. + +The default mapper generates CMI files in a @samp{gcm.cache} +directory. CMI files have a @samp{.gcm} suffix. The module unit name +is used directly to provide the basename. Header units construct a +relative path using the underlying header file name. If the path is +already relative, a @samp{,} directory is prepended. Internal +@samp{..} components are translated to @samp{,,}. No attempt is made +to canonicalize these filenames beyond that done by the preprocessor's +include search algorithm, as in general it is ambiguous when symbolic +links are present. + +The mapper protocol was published as ``A Module Mapper'' +@uref{https://wg21.link/p1184}. The implementation is provided by +@command{libcody}, @uref{https://github.com/urnathan/libcody}, +which specifies the canonical protocol definition. A proof of concept +server implementation embedded in @command{make} was described in +''Make Me A Module'', @uref{https://wg21.link/p1602}. + +@node C++ Module Preprocessing +@subsection Module Preprocessing +@cindex C++ Module Preprocessing + +Modules affect preprocessing because of header units and include +translation. Some uses of the preprocessor as a separate step either +do not produce a correct output, or require CMIs to be available. + +Header units import macros. These macros can affect later conditional +inclusion, which therefore can cascade to differing import sets. When +preprocessing, it is necessary to load the CMI. If a header unit is +unavailable, the preprocessor issues a warning and continue (when +not just preprocessing, an error is emitted). Detecting such imports +requires preprocessor tokenization of the input stream to phase 4 +(macro expansion). + +Include translation converts @code{#include}, @code{#include_next} and +@code{#import} directives to internal @code{import} declarations. +Whether a particular directive is translated is controlled by the +module mapper. Header unit names are canonicalized during +preprocessing. + +Dependency information can be emitted for macro import, extending the +functionality of @option{-MD} and @option{-MMD} options. Detection of +import declarations also requires phase 4 preprocessing, and thus +requires full preprocessing (or compilation). + +The @option{-M}, @option{-MM} and @option{-E -fdirectives-only} options halt +preprocessing before phase 4. + +The @option{-save-temps} option uses @option{-fdirectives-only} for +preprocessing, and preserve the macro definitions in the preprocessed +output. Usually you also want to use this option when explicitly +preprocessing a header-unit, or consuming such preprocessed output: + +@smallexample +g++ -fmodules-ts -E -fdirectives-only my-header.hh -o my-header.ii +g++ -x c++-header -fmodules-ts -fpreprocessed -fdirectives-only my-header.ii +@end smallexample + +@node C++ Compiled Module Interface +@subsection Compiled Module Interface +@cindex C++ Compiled Module Interface + +CMIs are an additional artifact when compiling named module +interfaces, partitions or header units. These are read when +importing. CMI contents are implementation-specific, and in GCC's +case tied to the compiler version. Consider them a rebuildable cache +artifact, not a distributable object. + +When creating an output CMI, any missing directory components are +created in a manner that is safe for concurrent builds creating +multiple, different, CMIs within a common subdirectory tree. + +CMI contents are written to a temporary file, which is then atomically +renamed. Observers either see old contents (if there is an +existing file), or complete new contents. They do not observe the +CMI during its creation. This is unlike object file writing, which +may be observed by an external process. + +CMIs are read in lazily, if the host OS provides @code{mmap} +functionality. Generally blocks are read when name lookup or template +instantiation occurs. To inhibit this, the @option{-fno-module-lazy} +option may be used. + +The @option{--param lazy-modules=@var{n}} parameter controls the limit +on the number of concurrently open module files during lazy loading. +Should more modules be imported, an LRU algorithm is used to determine +which files to close---until that file is needed again. This limit +may be exceeded with deep module dependency hierarchies. With large +code bases there may be more imports than the process limit of file +descriptors. By default, the limit is a few less than the per-process +file descriptor hard limit, if that is determinable.@footnote{Where +applicable the soft limit is incremented as needed towards the hard limit.} + +GCC CMIs use ELF32 as an architecture-neutral encapsulation mechanism. +You may use @command{readelf} to inspect them, although section +contents are largely undecipherable. There is a section named +@code{.gnu.c++.README}, which contains human-readable text. Other +than the first line, each line consists of @code{@var{tag}: @code{value}} +tuples. + +@smallexample +> @command{readelf -p.gnu.c++.README gcm.cache/foo.gcm} + +String dump of section '.gnu.c++.README': + [ 0] GNU C++ primary module interface + [ 21] compiler: 11.0.0 20201116 (experimental) [c++-modules revision 20201116-0454] + [ 6f] version: 2020/11/16-04:54 + [ 89] module: foo + [ 95] source: c_b.ii + [ a4] dialect: C++20/coroutines + [ be] cwd: /data/users/nathans/modules/obj/x86_64/gcc + [ ee] repository: gcm.cache + [ 104] buildtime: 2020/11/16 15:03:21 UTC + [ 127] localtime: 2020/11/16 07:03:21 PST + [ 14a] export: foo:part1 foo-part1.gcm +@end smallexample + +Amongst other things, this lists the source that was built, C++ +dialect used and imports of the module.@footnote{The precise contents +of this output may change.} The timestamp is the same value as that +provided by the @code{__DATE__} & @code{__TIME__} macros, and may be +explicitly specified with the environment variable +@code{SOURCE_DATE_EPOCH}. For further details +@pxref{Environment Variables}. + +A set of related CMIs may be copied, provided the relative pathnames +are preserved. + +The @code{.gnu.c++.README} contents do not affect CMI integrity, and +it may be removed or altered. The section numbering of the sections +whose names do not begin with @code{.gnu.c++.}, or are not the string +section is significant and must not be altered. diff --git a/gcc/doc/languages.texi b/gcc/doc/languages.texi new file mode 100644 index 00000000000..df36d7edfcf --- /dev/null +++ b/gcc/doc/languages.texi @@ -0,0 +1,36 @@ +@c Copyright (C) 2002-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Languages +@chapter Language Front Ends in GCC + +The interface to front ends for languages in GCC, and in particular +the @code{tree} structure (@pxref{GENERIC}), was initially designed for +C, and many aspects of it are still somewhat biased towards C and +C-like languages. It is, however, reasonably well suited to other +procedural languages, and front ends for many such languages have been +written for GCC@. + +Writing a compiler as a front end for GCC, rather than compiling +directly to assembler or generating C code which is then compiled by +GCC, has several advantages: + +@itemize @bullet +@item GCC front ends benefit from the support for many different +target machines already present in GCC@. +@item GCC front ends benefit from all the optimizations in GCC@. Some +of these, such as alias analysis, may work better when GCC is +compiling directly from source code than when it is compiling from +generated C code. +@item Better debugging information is generated when compiling +directly from source code than when going via intermediate generated C +code. +@end itemize + +Because of the advantages of writing a compiler as a GCC front end, +GCC front ends have also been created for languages very different +from those for which GCC was designed, such as the declarative +logic/functional language Mercury. For these reasons, it may also be +useful to implement compilers created for specialized purposes (for +example, as part of a research project) as GCC front ends. diff --git a/gcc/doc/libgcc.texi b/gcc/doc/libgcc.texi new file mode 100644 index 00000000000..99338334787 --- /dev/null +++ b/gcc/doc/libgcc.texi @@ -0,0 +1,2304 @@ +@c Copyright (C) 2003-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. +@c Contributed by Aldy Hernandez + +@node Libgcc +@chapter The GCC low-level runtime library + +GCC provides a low-level runtime library, @file{libgcc.a} or +@file{libgcc_s.so.1} on some platforms. GCC generates calls to +routines in this library automatically, whenever it needs to perform +some operation that is too complicated to emit inline code for. + +Most of the routines in @code{libgcc} handle arithmetic operations +that the target processor cannot perform directly. This includes +integer multiply and divide on some machines, and all floating-point +and fixed-point operations on other machines. @code{libgcc} also includes +routines for exception handling, and a handful of miscellaneous operations. + +Some of these routines can be defined in mostly machine-independent C@. +Others must be hand-written in assembly language for each processor +that needs them. + +GCC will also generate calls to C library routines, such as +@code{memcpy} and @code{memset}, in some cases. The set of routines +that GCC may possibly use is documented in @ref{Other +Builtins,,,gcc, Using the GNU Compiler Collection (GCC)}. + +These routines take arguments and return values of a specific machine +mode, not a specific C type. @xref{Machine Modes}, for an explanation +of this concept. For illustrative purposes, in this chapter the +floating point type @code{float} is assumed to correspond to @code{SFmode}; +@code{double} to @code{DFmode}; and @code{@w{long double}} to both +@code{TFmode} and @code{XFmode}. Similarly, the integer types @code{int} +and @code{@w{unsigned int}} correspond to @code{SImode}; @code{long} and +@code{@w{unsigned long}} to @code{DImode}; and @code{@w{long long}} and +@code{@w{unsigned long long}} to @code{TImode}. + +@menu +* Integer library routines:: +* Soft float library routines:: +* Decimal float library routines:: +* Fixed-point fractional library routines:: +* Exception handling routines:: +* Miscellaneous routines:: +@end menu + +@node Integer library routines +@section Routines for integer arithmetic + +The integer arithmetic routines are used on platforms that don't provide +hardware support for arithmetic operations on some modes. + +@subsection Arithmetic functions + +@deftypefn {Runtime Function} int __ashlsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __ashldi3 (long @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long} __ashlti3 (long long @var{a}, int @var{b}) +These functions return the result of shifting @var{a} left by @var{b} bits. +@end deftypefn + +@deftypefn {Runtime Function} int __ashrsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __ashrdi3 (long @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long} __ashrti3 (long long @var{a}, int @var{b}) +These functions return the result of arithmetically shifting @var{a} right +by @var{b} bits. +@end deftypefn + +@deftypefn {Runtime Function} int __divsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __divdi3 (long @var{a}, long @var{b}) +@deftypefnx {Runtime Function} {long long} __divti3 (long long @var{a}, long long @var{b}) +These functions return the quotient of the signed division of @var{a} and +@var{b}. +@end deftypefn + +@deftypefn {Runtime Function} int __lshrsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __lshrdi3 (long @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long} __lshrti3 (long long @var{a}, int @var{b}) +These functions return the result of logically shifting @var{a} right by +@var{b} bits. +@end deftypefn + +@deftypefn {Runtime Function} int __modsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __moddi3 (long @var{a}, long @var{b}) +@deftypefnx {Runtime Function} {long long} __modti3 (long long @var{a}, long long @var{b}) +These functions return the remainder of the signed division of @var{a} +and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} int __mulsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __muldi3 (long @var{a}, long @var{b}) +@deftypefnx {Runtime Function} {long long} __multi3 (long long @var{a}, long long @var{b}) +These functions return the product of @var{a} and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} long __negdi2 (long @var{a}) +@deftypefnx {Runtime Function} {long long} __negti2 (long long @var{a}) +These functions return the negation of @var{a}. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned int} __udivsi3 (unsigned int @var{a}, unsigned int @var{b}) +@deftypefnx {Runtime Function} {unsigned long} __udivdi3 (unsigned long @var{a}, unsigned long @var{b}) +@deftypefnx {Runtime Function} {unsigned long long} __udivti3 (unsigned long long @var{a}, unsigned long long @var{b}) +These functions return the quotient of the unsigned division of @var{a} +and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned long} __udivmoddi4 (unsigned long @var{a}, unsigned long @var{b}, unsigned long *@var{c}) +@deftypefnx {Runtime Function} {unsigned long long} __udivmodti4 (unsigned long long @var{a}, unsigned long long @var{b}, unsigned long long *@var{c}) +These functions calculate both the quotient and remainder of the unsigned +division of @var{a} and @var{b}. The return value is the quotient, and +the remainder is placed in variable pointed to by @var{c}. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned int} __umodsi3 (unsigned int @var{a}, unsigned int @var{b}) +@deftypefnx {Runtime Function} {unsigned long} __umoddi3 (unsigned long @var{a}, unsigned long @var{b}) +@deftypefnx {Runtime Function} {unsigned long long} __umodti3 (unsigned long long @var{a}, unsigned long long @var{b}) +These functions return the remainder of the unsigned division of @var{a} +and @var{b}. +@end deftypefn + +@subsection Comparison functions + +The following functions implement integral comparisons. These functions +implement a low-level compare, upon which the higher level comparison +operators (such as less than and greater than or equal to) can be +constructed. The returned values lie in the range zero to two, to allow +the high-level operators to be implemented by testing the returned +result using either signed or unsigned comparison. + +@deftypefn {Runtime Function} int __cmpdi2 (long @var{a}, long @var{b}) +@deftypefnx {Runtime Function} int __cmpti2 (long long @var{a}, long long @var{b}) +These functions perform a signed comparison of @var{a} and @var{b}. If +@var{a} is less than @var{b}, they return 0; if @var{a} is greater than +@var{b}, they return 2; and if @var{a} and @var{b} are equal they return 1. +@end deftypefn + +@deftypefn {Runtime Function} int __ucmpdi2 (unsigned long @var{a}, unsigned long @var{b}) +@deftypefnx {Runtime Function} int __ucmpti2 (unsigned long long @var{a}, unsigned long long @var{b}) +These functions perform an unsigned comparison of @var{a} and @var{b}. +If @var{a} is less than @var{b}, they return 0; if @var{a} is greater than +@var{b}, they return 2; and if @var{a} and @var{b} are equal they return 1. +@end deftypefn + +@subsection Trapping arithmetic functions + +The following functions implement trapping arithmetic. These functions +call the libc function @code{abort} upon signed arithmetic overflow. + +@deftypefn {Runtime Function} int __absvsi2 (int @var{a}) +@deftypefnx {Runtime Function} long __absvdi2 (long @var{a}) +These functions return the absolute value of @var{a}. +@end deftypefn + +@deftypefn {Runtime Function} int __addvsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __addvdi3 (long @var{a}, long @var{b}) +These functions return the sum of @var{a} and @var{b}; that is +@code{@var{a} + @var{b}}. +@end deftypefn + +@deftypefn {Runtime Function} int __mulvsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __mulvdi3 (long @var{a}, long @var{b}) +The functions return the product of @var{a} and @var{b}; that is +@code{@var{a} * @var{b}}. +@end deftypefn + +@deftypefn {Runtime Function} int __negvsi2 (int @var{a}) +@deftypefnx {Runtime Function} long __negvdi2 (long @var{a}) +These functions return the negation of @var{a}; that is @code{-@var{a}}. +@end deftypefn + +@deftypefn {Runtime Function} int __subvsi3 (int @var{a}, int @var{b}) +@deftypefnx {Runtime Function} long __subvdi3 (long @var{a}, long @var{b}) +These functions return the difference between @var{b} and @var{a}; +that is @code{@var{a} - @var{b}}. +@end deftypefn + +@subsection Bit operations + +@deftypefn {Runtime Function} int __clzsi2 (unsigned int @var{a}) +@deftypefnx {Runtime Function} int __clzdi2 (unsigned long @var{a}) +@deftypefnx {Runtime Function} int __clzti2 (unsigned long long @var{a}) +These functions return the number of leading 0-bits in @var{a}, starting +at the most significant bit position. If @var{a} is zero, the result is +undefined. +@end deftypefn + +@deftypefn {Runtime Function} int __ctzsi2 (unsigned int @var{a}) +@deftypefnx {Runtime Function} int __ctzdi2 (unsigned long @var{a}) +@deftypefnx {Runtime Function} int __ctzti2 (unsigned long long @var{a}) +These functions return the number of trailing 0-bits in @var{a}, starting +at the least significant bit position. If @var{a} is zero, the result is +undefined. +@end deftypefn + +@deftypefn {Runtime Function} int __ffsdi2 (unsigned long @var{a}) +@deftypefnx {Runtime Function} int __ffsti2 (unsigned long long @var{a}) +These functions return the index of the least significant 1-bit in @var{a}, +or the value zero if @var{a} is zero. The least significant bit is index +one. +@end deftypefn + +@deftypefn {Runtime Function} int __paritysi2 (unsigned int @var{a}) +@deftypefnx {Runtime Function} int __paritydi2 (unsigned long @var{a}) +@deftypefnx {Runtime Function} int __parityti2 (unsigned long long @var{a}) +These functions return the value zero if the number of bits set in +@var{a} is even, and the value one otherwise. +@end deftypefn + +@deftypefn {Runtime Function} int __popcountsi2 (unsigned int @var{a}) +@deftypefnx {Runtime Function} int __popcountdi2 (unsigned long @var{a}) +@deftypefnx {Runtime Function} int __popcountti2 (unsigned long long @var{a}) +These functions return the number of bits set in @var{a}. +@end deftypefn + +@deftypefn {Runtime Function} int32_t __bswapsi2 (int32_t @var{a}) +@deftypefnx {Runtime Function} int64_t __bswapdi2 (int64_t @var{a}) +These functions return the @var{a} byteswapped. +@end deftypefn + +@node Soft float library routines +@section Routines for floating point emulation +@cindex soft float library +@cindex arithmetic library +@cindex math library +@opindex msoft-float + +The software floating point library is used on machines which do not +have hardware support for floating point. It is also used whenever +@option{-msoft-float} is used to disable generation of floating point +instructions. (Not all targets support this switch.) + +For compatibility with other compilers, the floating point emulation +routines can be renamed with the @code{DECLARE_LIBRARY_RENAMES} macro +(@pxref{Library Calls}). In this section, the default names are used. + +Presently the library does not support @code{XFmode}, which is used +for @code{long double} on some architectures. + +@subsection Arithmetic functions + +@deftypefn {Runtime Function} float __addsf3 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} double __adddf3 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} {long double} __addtf3 (long double @var{a}, long double @var{b}) +@deftypefnx {Runtime Function} {long double} __addxf3 (long double @var{a}, long double @var{b}) +These functions return the sum of @var{a} and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} float __subsf3 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} double __subdf3 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} {long double} __subtf3 (long double @var{a}, long double @var{b}) +@deftypefnx {Runtime Function} {long double} __subxf3 (long double @var{a}, long double @var{b}) +These functions return the difference between @var{b} and @var{a}; +that is, @w{@math{@var{a} - @var{b}}}. +@end deftypefn + +@deftypefn {Runtime Function} float __mulsf3 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} double __muldf3 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} {long double} __multf3 (long double @var{a}, long double @var{b}) +@deftypefnx {Runtime Function} {long double} __mulxf3 (long double @var{a}, long double @var{b}) +These functions return the product of @var{a} and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} float __divsf3 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} double __divdf3 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} {long double} __divtf3 (long double @var{a}, long double @var{b}) +@deftypefnx {Runtime Function} {long double} __divxf3 (long double @var{a}, long double @var{b}) +These functions return the quotient of @var{a} and @var{b}; that is, +@w{@math{@var{a} / @var{b}}}. +@end deftypefn + +@deftypefn {Runtime Function} float __negsf2 (float @var{a}) +@deftypefnx {Runtime Function} double __negdf2 (double @var{a}) +@deftypefnx {Runtime Function} {long double} __negtf2 (long double @var{a}) +@deftypefnx {Runtime Function} {long double} __negxf2 (long double @var{a}) +These functions return the negation of @var{a}. They simply flip the +sign bit, so they can produce negative zero and negative NaN@. +@end deftypefn + +@subsection Conversion functions + +@deftypefn {Runtime Function} double __extendsfdf2 (float @var{a}) +@deftypefnx {Runtime Function} {long double} __extendsftf2 (float @var{a}) +@deftypefnx {Runtime Function} {long double} __extendsfxf2 (float @var{a}) +@deftypefnx {Runtime Function} {long double} __extenddftf2 (double @var{a}) +@deftypefnx {Runtime Function} {long double} __extenddfxf2 (double @var{a}) +These functions extend @var{a} to the wider mode of their return +type. +@end deftypefn + +@deftypefn {Runtime Function} double __truncxfdf2 (long double @var{a}) +@deftypefnx {Runtime Function} double __trunctfdf2 (long double @var{a}) +@deftypefnx {Runtime Function} float __truncxfsf2 (long double @var{a}) +@deftypefnx {Runtime Function} float __trunctfsf2 (long double @var{a}) +@deftypefnx {Runtime Function} float __truncdfsf2 (double @var{a}) +These functions truncate @var{a} to the narrower mode of their return +type, rounding toward zero. +@end deftypefn + +@deftypefn {Runtime Function} int __fixsfsi (float @var{a}) +@deftypefnx {Runtime Function} int __fixdfsi (double @var{a}) +@deftypefnx {Runtime Function} int __fixtfsi (long double @var{a}) +@deftypefnx {Runtime Function} int __fixxfsi (long double @var{a}) +These functions convert @var{a} to a signed integer, rounding toward zero. +@end deftypefn + +@deftypefn {Runtime Function} long __fixsfdi (float @var{a}) +@deftypefnx {Runtime Function} long __fixdfdi (double @var{a}) +@deftypefnx {Runtime Function} long __fixtfdi (long double @var{a}) +@deftypefnx {Runtime Function} long __fixxfdi (long double @var{a}) +These functions convert @var{a} to a signed long, rounding toward zero. +@end deftypefn + +@deftypefn {Runtime Function} {long long} __fixsfti (float @var{a}) +@deftypefnx {Runtime Function} {long long} __fixdfti (double @var{a}) +@deftypefnx {Runtime Function} {long long} __fixtfti (long double @var{a}) +@deftypefnx {Runtime Function} {long long} __fixxfti (long double @var{a}) +These functions convert @var{a} to a signed long long, rounding toward zero. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned int} __fixunssfsi (float @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fixunsdfsi (double @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fixunstfsi (long double @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fixunsxfsi (long double @var{a}) +These functions convert @var{a} to an unsigned integer, rounding +toward zero. Negative values all become zero. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned long} __fixunssfdi (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fixunsdfdi (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fixunstfdi (long double @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fixunsxfdi (long double @var{a}) +These functions convert @var{a} to an unsigned long, rounding +toward zero. Negative values all become zero. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned long long} __fixunssfti (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fixunsdfti (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fixunstfti (long double @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fixunsxfti (long double @var{a}) +These functions convert @var{a} to an unsigned long long, rounding +toward zero. Negative values all become zero. +@end deftypefn + +@deftypefn {Runtime Function} float __floatsisf (int @var{i}) +@deftypefnx {Runtime Function} double __floatsidf (int @var{i}) +@deftypefnx {Runtime Function} {long double} __floatsitf (int @var{i}) +@deftypefnx {Runtime Function} {long double} __floatsixf (int @var{i}) +These functions convert @var{i}, a signed integer, to floating point. +@end deftypefn + +@deftypefn {Runtime Function} float __floatdisf (long @var{i}) +@deftypefnx {Runtime Function} double __floatdidf (long @var{i}) +@deftypefnx {Runtime Function} {long double} __floatditf (long @var{i}) +@deftypefnx {Runtime Function} {long double} __floatdixf (long @var{i}) +These functions convert @var{i}, a signed long, to floating point. +@end deftypefn + +@deftypefn {Runtime Function} float __floattisf (long long @var{i}) +@deftypefnx {Runtime Function} double __floattidf (long long @var{i}) +@deftypefnx {Runtime Function} {long double} __floattitf (long long @var{i}) +@deftypefnx {Runtime Function} {long double} __floattixf (long long @var{i}) +These functions convert @var{i}, a signed long long, to floating point. +@end deftypefn + +@deftypefn {Runtime Function} float __floatunsisf (unsigned int @var{i}) +@deftypefnx {Runtime Function} double __floatunsidf (unsigned int @var{i}) +@deftypefnx {Runtime Function} {long double} __floatunsitf (unsigned int @var{i}) +@deftypefnx {Runtime Function} {long double} __floatunsixf (unsigned int @var{i}) +These functions convert @var{i}, an unsigned integer, to floating point. +@end deftypefn + +@deftypefn {Runtime Function} float __floatundisf (unsigned long @var{i}) +@deftypefnx {Runtime Function} double __floatundidf (unsigned long @var{i}) +@deftypefnx {Runtime Function} {long double} __floatunditf (unsigned long @var{i}) +@deftypefnx {Runtime Function} {long double} __floatundixf (unsigned long @var{i}) +These functions convert @var{i}, an unsigned long, to floating point. +@end deftypefn + +@deftypefn {Runtime Function} float __floatuntisf (unsigned long long @var{i}) +@deftypefnx {Runtime Function} double __floatuntidf (unsigned long long @var{i}) +@deftypefnx {Runtime Function} {long double} __floatuntitf (unsigned long long @var{i}) +@deftypefnx {Runtime Function} {long double} __floatuntixf (unsigned long long @var{i}) +These functions convert @var{i}, an unsigned long long, to floating point. +@end deftypefn + +@subsection Comparison functions + +There are two sets of basic comparison functions. + +@deftypefn {Runtime Function} int __cmpsf2 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} int __cmpdf2 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} int __cmptf2 (long double @var{a}, long double @var{b}) +These functions calculate @math{a <=> b}. That is, if @var{a} is less +than @var{b}, they return @minus{}1; if @var{a} is greater than @var{b}, they +return 1; and if @var{a} and @var{b} are equal they return 0. If +either argument is NaN they return 1, but you should not rely on this; +if NaN is a possibility, use one of the higher-level comparison +functions. +@end deftypefn + +@deftypefn {Runtime Function} int __unordsf2 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} int __unorddf2 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} int __unordtf2 (long double @var{a}, long double @var{b}) +These functions return a nonzero value if either argument is NaN, otherwise 0. +@end deftypefn + +There is also a complete group of higher level functions which +correspond directly to comparison operators. They implement the ISO C +semantics for floating-point comparisons, taking NaN into account. +Pay careful attention to the return values defined for each set. +Under the hood, all of these routines are implemented as + +@smallexample + if (__unord@var{X}f2 (a, b)) + return @var{E}; + return __cmp@var{X}f2 (a, b); +@end smallexample + +@noindent +where @var{E} is a constant chosen to give the proper behavior for +NaN@. Thus, the meaning of the return value is different for each set. +Do not rely on this implementation; only the semantics documented +below are guaranteed. + +@deftypefn {Runtime Function} int __eqsf2 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} int __eqdf2 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} int __eqtf2 (long double @var{a}, long double @var{b}) +These functions return zero if neither argument is NaN, and @var{a} and +@var{b} are equal. +@end deftypefn + +@deftypefn {Runtime Function} int __nesf2 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} int __nedf2 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} int __netf2 (long double @var{a}, long double @var{b}) +These functions return a nonzero value if either argument is NaN, or +if @var{a} and @var{b} are unequal. +@end deftypefn + +@deftypefn {Runtime Function} int __gesf2 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} int __gedf2 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} int __getf2 (long double @var{a}, long double @var{b}) +These functions return a value greater than or equal to zero if +neither argument is NaN, and @var{a} is greater than or equal to +@var{b}. +@end deftypefn + +@deftypefn {Runtime Function} int __ltsf2 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} int __ltdf2 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} int __lttf2 (long double @var{a}, long double @var{b}) +These functions return a value less than zero if neither argument is +NaN, and @var{a} is strictly less than @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} int __lesf2 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} int __ledf2 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} int __letf2 (long double @var{a}, long double @var{b}) +These functions return a value less than or equal to zero if neither +argument is NaN, and @var{a} is less than or equal to @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} int __gtsf2 (float @var{a}, float @var{b}) +@deftypefnx {Runtime Function} int __gtdf2 (double @var{a}, double @var{b}) +@deftypefnx {Runtime Function} int __gttf2 (long double @var{a}, long double @var{b}) +These functions return a value greater than zero if neither argument +is NaN, and @var{a} is strictly greater than @var{b}. +@end deftypefn + +@subsection Other floating-point functions + +@deftypefn {Runtime Function} float __powisf2 (float @var{a}, int @var{b}) +@deftypefnx {Runtime Function} double __powidf2 (double @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long double} __powitf2 (long double @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long double} __powixf2 (long double @var{a}, int @var{b}) +These functions convert raise @var{a} to the power @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} {complex float} __mulsc3 (float @var{a}, float @var{b}, float @var{c}, float @var{d}) +@deftypefnx {Runtime Function} {complex double} __muldc3 (double @var{a}, double @var{b}, double @var{c}, double @var{d}) +@deftypefnx {Runtime Function} {complex long double} __multc3 (long double @var{a}, long double @var{b}, long double @var{c}, long double @var{d}) +@deftypefnx {Runtime Function} {complex long double} __mulxc3 (long double @var{a}, long double @var{b}, long double @var{c}, long double @var{d}) +These functions return the product of @math{@var{a} + i@var{b}} and +@math{@var{c} + i@var{d}}, following the rules of C99 Annex G@. +@end deftypefn + +@deftypefn {Runtime Function} {complex float} __divsc3 (float @var{a}, float @var{b}, float @var{c}, float @var{d}) +@deftypefnx {Runtime Function} {complex double} __divdc3 (double @var{a}, double @var{b}, double @var{c}, double @var{d}) +@deftypefnx {Runtime Function} {complex long double} __divtc3 (long double @var{a}, long double @var{b}, long double @var{c}, long double @var{d}) +@deftypefnx {Runtime Function} {complex long double} __divxc3 (long double @var{a}, long double @var{b}, long double @var{c}, long double @var{d}) +These functions return the quotient of @math{@var{a} + i@var{b}} and +@math{@var{c} + i@var{d}} (i.e., @math{(@var{a} + i@var{b}) / (@var{c} ++ i@var{d})}), following the rules of C99 Annex G@. +@end deftypefn + +@node Decimal float library routines +@section Routines for decimal floating point emulation +@cindex decimal float library +@cindex IEEE 754-2008 + +The software decimal floating point library implements IEEE 754-2008 +decimal floating point arithmetic and is only activated on selected +targets. + +The software decimal floating point library supports either DPD +(Densely Packed Decimal) or BID (Binary Integer Decimal) encoding +as selected at configure time. + + +@subsection Arithmetic functions + +@deftypefn {Runtime Function} _Decimal32 __dpd_addsd3 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} _Decimal32 __bid_addsd3 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_adddd3 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} _Decimal64 __bid_adddd3 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_addtd3 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} _Decimal128 __bid_addtd3 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return the sum of @var{a} and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_subsd3 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} _Decimal32 __bid_subsd3 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_subdd3 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} _Decimal64 __bid_subdd3 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_subtd3 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} _Decimal128 __bid_subtd3 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return the difference between @var{b} and @var{a}; +that is, @w{@math{@var{a} - @var{b}}}. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_mulsd3 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} _Decimal32 __bid_mulsd3 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_muldd3 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} _Decimal64 __bid_muldd3 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_multd3 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} _Decimal128 __bid_multd3 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return the product of @var{a} and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_divsd3 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} _Decimal32 __bid_divsd3 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_divdd3 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} _Decimal64 __bid_divdd3 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_divtd3 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} _Decimal128 __bid_divtd3 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return the quotient of @var{a} and @var{b}; that is, +@w{@math{@var{a} / @var{b}}}. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_negsd2 (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __bid_negsd2 (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_negdd2 (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __bid_negdd2 (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_negtd2 (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __bid_negtd2 (_Decimal128 @var{a}) +These functions return the negation of @var{a}. They simply flip the +sign bit, so they can produce negative zero and negative NaN@. +@end deftypefn + +@subsection Conversion functions + +@deftypefn {Runtime Function} _Decimal64 __dpd_extendsddd2 (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __bid_extendsddd2 (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_extendsdtd2 (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __bid_extendsdtd2 (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_extendddtd2 (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __bid_extendddtd2 (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __dpd_truncddsd2 (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __bid_truncddsd2 (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __dpd_trunctdsd2 (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __bid_trunctdsd2 (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_trunctddd2 (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __bid_trunctddd2 (_Decimal128 @var{a}) +These functions convert the value @var{a} from one decimal floating type +to another. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal64 __dpd_extendsfdd (float @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __bid_extendsfdd (float @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_extendsftd (float @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __bid_extendsftd (float @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_extenddftd (double @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __bid_extenddftd (double @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_extendxftd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __bid_extendxftd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __dpd_truncdfsd (double @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __bid_truncdfsd (double @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __dpd_truncxfsd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __bid_truncxfsd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __dpd_trunctfsd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __bid_trunctfsd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_truncxfdd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __bid_truncxfdd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_trunctfdd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __bid_trunctfdd ({long double} @var{a}) +These functions convert the value of @var{a} from a binary floating type +to a decimal floating type of a different size. +@end deftypefn + +@deftypefn {Runtime Function} float __dpd_truncddsf (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} float __bid_truncddsf (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} float __dpd_trunctdsf (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} float __bid_trunctdsf (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} double __dpd_extendsddf (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} double __bid_extendsddf (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} double __dpd_trunctddf (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} double __bid_trunctddf (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} {long double} __dpd_extendsdxf (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} {long double} __bid_extendsdxf (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} {long double} __dpd_extendddxf (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} {long double} __bid_extendddxf (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} {long double} __dpd_trunctdxf (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} {long double} __bid_trunctdxf (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} {long double} __dpd_extendsdtf (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} {long double} __bid_extendsdtf (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} {long double} __dpd_extendddtf (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} {long double} __bid_extendddtf (_Decimal64 @var{a}) +These functions convert the value of @var{a} from a decimal floating type +to a binary floating type of a different size. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_extendsfsd (float @var{a}) +@deftypefnx {Runtime Function} _Decimal32 __bid_extendsfsd (float @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_extenddfdd (double @var{a}) +@deftypefnx {Runtime Function} _Decimal64 __bid_extenddfdd (double @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_extendtftd ({long double} @var{a}) +@deftypefnx {Runtime Function} _Decimal128 __bid_extendtftd ({long double} @var{a}) +@deftypefnx {Runtime Function} float __dpd_truncsdsf (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} float __bid_truncsdsf (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} double __dpd_truncdddf (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} double __bid_truncdddf (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} {long double} __dpd_trunctdtf (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} {long double} __bid_trunctdtf (_Decimal128 @var{a}) +These functions convert the value of @var{a} between decimal and +binary floating types of the same size. +@end deftypefn + +@deftypefn {Runtime Function} int __dpd_fixsdsi (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} int __bid_fixsdsi (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} int __dpd_fixddsi (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} int __bid_fixddsi (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} int __dpd_fixtdsi (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} int __bid_fixtdsi (_Decimal128 @var{a}) +These functions convert @var{a} to a signed integer. +@end deftypefn + +@deftypefn {Runtime Function} long __dpd_fixsddi (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} long __bid_fixsddi (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} long __dpd_fixdddi (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} long __bid_fixdddi (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} long __dpd_fixtddi (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} long __bid_fixtddi (_Decimal128 @var{a}) +These functions convert @var{a} to a signed long. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned int} __dpd_fixunssdsi (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __bid_fixunssdsi (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __dpd_fixunsddsi (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __bid_fixunsddsi (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __dpd_fixunstdsi (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __bid_fixunstdsi (_Decimal128 @var{a}) +These functions convert @var{a} to an unsigned integer. Negative values all become zero. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned long} __dpd_fixunssddi (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __bid_fixunssddi (_Decimal32 @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __dpd_fixunsdddi (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __bid_fixunsdddi (_Decimal64 @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __dpd_fixunstddi (_Decimal128 @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __bid_fixunstddi (_Decimal128 @var{a}) +These functions convert @var{a} to an unsigned long. Negative values +all become zero. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_floatsisd (int @var{i}) +@deftypefnx {Runtime Function} _Decimal32 __bid_floatsisd (int @var{i}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_floatsidd (int @var{i}) +@deftypefnx {Runtime Function} _Decimal64 __bid_floatsidd (int @var{i}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_floatsitd (int @var{i}) +@deftypefnx {Runtime Function} _Decimal128 __bid_floatsitd (int @var{i}) +These functions convert @var{i}, a signed integer, to decimal floating point. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_floatdisd (long @var{i}) +@deftypefnx {Runtime Function} _Decimal32 __bid_floatdisd (long @var{i}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_floatdidd (long @var{i}) +@deftypefnx {Runtime Function} _Decimal64 __bid_floatdidd (long @var{i}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_floatditd (long @var{i}) +@deftypefnx {Runtime Function} _Decimal128 __bid_floatditd (long @var{i}) +These functions convert @var{i}, a signed long, to decimal floating point. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_floatunssisd (unsigned int @var{i}) +@deftypefnx {Runtime Function} _Decimal32 __bid_floatunssisd (unsigned int @var{i}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_floatunssidd (unsigned int @var{i}) +@deftypefnx {Runtime Function} _Decimal64 __bid_floatunssidd (unsigned int @var{i}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_floatunssitd (unsigned int @var{i}) +@deftypefnx {Runtime Function} _Decimal128 __bid_floatunssitd (unsigned int @var{i}) +These functions convert @var{i}, an unsigned integer, to decimal floating point. +@end deftypefn + +@deftypefn {Runtime Function} _Decimal32 __dpd_floatunsdisd (unsigned long @var{i}) +@deftypefnx {Runtime Function} _Decimal32 __bid_floatunsdisd (unsigned long @var{i}) +@deftypefnx {Runtime Function} _Decimal64 __dpd_floatunsdidd (unsigned long @var{i}) +@deftypefnx {Runtime Function} _Decimal64 __bid_floatunsdidd (unsigned long @var{i}) +@deftypefnx {Runtime Function} _Decimal128 __dpd_floatunsditd (unsigned long @var{i}) +@deftypefnx {Runtime Function} _Decimal128 __bid_floatunsditd (unsigned long @var{i}) +These functions convert @var{i}, an unsigned long, to decimal floating point. +@end deftypefn + +@subsection Comparison functions + +@deftypefn {Runtime Function} int __dpd_unordsd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __bid_unordsd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __dpd_unorddd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __bid_unorddd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __dpd_unordtd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} int __bid_unordtd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return a nonzero value if either argument is NaN, otherwise 0. +@end deftypefn + +There is also a complete group of higher level functions which +correspond directly to comparison operators. They implement the ISO C +semantics for floating-point comparisons, taking NaN into account. +Pay careful attention to the return values defined for each set. +Under the hood, all of these routines are implemented as + +@smallexample + if (__bid_unord@var{X}d2 (a, b)) + return @var{E}; + return __bid_cmp@var{X}d2 (a, b); +@end smallexample + +@noindent +where @var{E} is a constant chosen to give the proper behavior for +NaN@. Thus, the meaning of the return value is different for each set. +Do not rely on this implementation; only the semantics documented +below are guaranteed. + +@deftypefn {Runtime Function} int __dpd_eqsd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __bid_eqsd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __dpd_eqdd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __bid_eqdd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __dpd_eqtd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} int __bid_eqtd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return zero if neither argument is NaN, and @var{a} and +@var{b} are equal. +@end deftypefn + +@deftypefn {Runtime Function} int __dpd_nesd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __bid_nesd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __dpd_nedd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __bid_nedd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __dpd_netd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} int __bid_netd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return a nonzero value if either argument is NaN, or +if @var{a} and @var{b} are unequal. +@end deftypefn + +@deftypefn {Runtime Function} int __dpd_gesd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __bid_gesd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __dpd_gedd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __bid_gedd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __dpd_getd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} int __bid_getd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return a value greater than or equal to zero if +neither argument is NaN, and @var{a} is greater than or equal to +@var{b}. +@end deftypefn + +@deftypefn {Runtime Function} int __dpd_ltsd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __bid_ltsd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __dpd_ltdd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __bid_ltdd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __dpd_lttd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} int __bid_lttd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return a value less than zero if neither argument is +NaN, and @var{a} is strictly less than @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} int __dpd_lesd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __bid_lesd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __dpd_ledd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __bid_ledd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __dpd_letd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} int __bid_letd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return a value less than or equal to zero if neither +argument is NaN, and @var{a} is less than or equal to @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} int __dpd_gtsd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __bid_gtsd2 (_Decimal32 @var{a}, _Decimal32 @var{b}) +@deftypefnx {Runtime Function} int __dpd_gtdd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __bid_gtdd2 (_Decimal64 @var{a}, _Decimal64 @var{b}) +@deftypefnx {Runtime Function} int __dpd_gttd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +@deftypefnx {Runtime Function} int __bid_gttd2 (_Decimal128 @var{a}, _Decimal128 @var{b}) +These functions return a value greater than zero if neither argument +is NaN, and @var{a} is strictly greater than @var{b}. +@end deftypefn + +@node Fixed-point fractional library routines +@section Routines for fixed-point fractional emulation +@cindex fixed-point fractional library +@cindex fractional types +@cindex Embedded C + +The software fixed-point library implements fixed-point fractional +arithmetic, and is only activated on selected targets. + +For ease of comprehension @code{fract} is an alias for the +@code{_Fract} type, @code{accum} an alias for @code{_Accum}, and +@code{sat} an alias for @code{_Sat}. + +For illustrative purposes, in this section the fixed-point fractional type +@code{@w{short fract}} is assumed to correspond to machine mode @code{QQmode}; +@code{@w{unsigned short fract}} to @code{UQQmode}; +@code{fract} to @code{HQmode}; +@code{@w{unsigned fract}} to @code{UHQmode}; +@code{@w{long fract}} to @code{SQmode}; +@code{@w{unsigned long fract}} to @code{USQmode}; +@code{@w{long long fract}} to @code{DQmode}; +and @code{@w{unsigned long long fract}} to @code{UDQmode}. +Similarly the fixed-point accumulator type +@code{@w{short accum}} corresponds to @code{HAmode}; +@code{@w{unsigned short accum}} to @code{UHAmode}; +@code{accum} to @code{SAmode}; +@code{@w{unsigned accum}} to @code{USAmode}; +@code{@w{long accum}} to @code{DAmode}; +@code{@w{unsigned long accum}} to @code{UDAmode}; +@code{@w{long long accum}} to @code{TAmode}; +and @code{@w{unsigned long long accum}} to @code{UTAmode}. + +@subsection Arithmetic functions + +@deftypefn {Runtime Function} {short fract} __addqq3 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {fract} __addhq3 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {long fract} __addsq3 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {long long fract} __adddq3 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned short fract} __adduqq3 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __adduhq3 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __addusq3 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __addudq3 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {short accum} __addha3 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {accum} __addsa3 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {long accum} __addda3 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {long long accum} __addta3 (long long accum @var{a}, long long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __adduha3 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __addusa3 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __adduda3 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __adduta3 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions return the sum of @var{a} and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __ssaddqq3 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {fract} __ssaddhq3 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {long fract} __ssaddsq3 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {long long fract} __ssadddq3 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {short accum} __ssaddha3 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {accum} __ssaddsa3 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {long accum} __ssaddda3 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {long long accum} __ssaddta3 (long long accum @var{a}, long long accum @var{b}) +These functions return the sum of @var{a} and @var{b} with signed saturation. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned short fract} __usadduqq3 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __usadduhq3 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __usaddusq3 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __usaddudq3 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __usadduha3 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __usaddusa3 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __usadduda3 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __usadduta3 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions return the sum of @var{a} and @var{b} with unsigned saturation. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __subqq3 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {fract} __subhq3 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {long fract} __subsq3 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {long long fract} __subdq3 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned short fract} __subuqq3 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __subuhq3 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __subusq3 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __subudq3 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {short accum} __subha3 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {accum} __subsa3 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {long accum} __subda3 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {long long accum} __subta3 (long long accum @var{a}, long long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __subuha3 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __subusa3 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __subuda3 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __subuta3 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions return the difference of @var{a} and @var{b}; +that is, @code{@var{a} - @var{b}}. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __sssubqq3 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {fract} __sssubhq3 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {long fract} __sssubsq3 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {long long fract} __sssubdq3 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {short accum} __sssubha3 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {accum} __sssubsa3 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {long accum} __sssubda3 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {long long accum} __sssubta3 (long long accum @var{a}, long long accum @var{b}) +These functions return the difference of @var{a} and @var{b} with signed +saturation; that is, @code{@var{a} - @var{b}}. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned short fract} __ussubuqq3 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __ussubuhq3 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __ussubusq3 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __ussubudq3 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __ussubuha3 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __ussubusa3 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __ussubuda3 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __ussubuta3 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions return the difference of @var{a} and @var{b} with unsigned +saturation; that is, @code{@var{a} - @var{b}}. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __mulqq3 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {fract} __mulhq3 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {long fract} __mulsq3 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {long long fract} __muldq3 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned short fract} __muluqq3 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __muluhq3 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __mulusq3 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __muludq3 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {short accum} __mulha3 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {accum} __mulsa3 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {long accum} __mulda3 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {long long accum} __multa3 (long long accum @var{a}, long long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __muluha3 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __mulusa3 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __muluda3 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __muluta3 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions return the product of @var{a} and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __ssmulqq3 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {fract} __ssmulhq3 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {long fract} __ssmulsq3 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {long long fract} __ssmuldq3 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {short accum} __ssmulha3 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {accum} __ssmulsa3 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {long accum} __ssmulda3 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {long long accum} __ssmulta3 (long long accum @var{a}, long long accum @var{b}) +These functions return the product of @var{a} and @var{b} with signed +saturation. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned short fract} __usmuluqq3 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __usmuluhq3 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __usmulusq3 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __usmuludq3 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __usmuluha3 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __usmulusa3 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __usmuluda3 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __usmuluta3 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions return the product of @var{a} and @var{b} with unsigned +saturation. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __divqq3 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {fract} __divhq3 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {long fract} __divsq3 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {long long fract} __divdq3 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {short accum} __divha3 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {accum} __divsa3 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {long accum} __divda3 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {long long accum} __divta3 (long long accum @var{a}, long long accum @var{b}) +These functions return the quotient of the signed division of @var{a} +and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned short fract} __udivuqq3 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __udivuhq3 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __udivusq3 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __udivudq3 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __udivuha3 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __udivusa3 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __udivuda3 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __udivuta3 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions return the quotient of the unsigned division of @var{a} +and @var{b}. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __ssdivqq3 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {fract} __ssdivhq3 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {long fract} __ssdivsq3 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {long long fract} __ssdivdq3 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {short accum} __ssdivha3 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {accum} __ssdivsa3 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {long accum} __ssdivda3 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {long long accum} __ssdivta3 (long long accum @var{a}, long long accum @var{b}) +These functions return the quotient of the signed division of @var{a} +and @var{b} with signed saturation. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned short fract} __usdivuqq3 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __usdivuhq3 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __usdivusq3 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __usdivudq3 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __usdivuha3 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __usdivusa3 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __usdivuda3 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __usdivuta3 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions return the quotient of the unsigned division of @var{a} +and @var{b} with unsigned saturation. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __negqq2 (short fract @var{a}) +@deftypefnx {Runtime Function} {fract} __neghq2 (fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __negsq2 (long fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __negdq2 (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __neguqq2 (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __neguhq2 (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __negusq2 (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __negudq2 (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __negha2 (short accum @var{a}) +@deftypefnx {Runtime Function} {accum} __negsa2 (accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __negda2 (long accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __negta2 (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __neguha2 (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __negusa2 (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __neguda2 (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __neguta2 (unsigned long long accum @var{a}) +These functions return the negation of @var{a}. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __ssnegqq2 (short fract @var{a}) +@deftypefnx {Runtime Function} {fract} __ssneghq2 (fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __ssnegsq2 (long fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __ssnegdq2 (long long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __ssnegha2 (short accum @var{a}) +@deftypefnx {Runtime Function} {accum} __ssnegsa2 (accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __ssnegda2 (long accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __ssnegta2 (long long accum @var{a}) +These functions return the negation of @var{a} with signed saturation. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned short fract} __usneguqq2 (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __usneguhq2 (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __usnegusq2 (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __usnegudq2 (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __usneguha2 (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __usnegusa2 (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __usneguda2 (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __usneguta2 (unsigned long long accum @var{a}) +These functions return the negation of @var{a} with unsigned saturation. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __ashlqq3 (short fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {fract} __ashlhq3 (fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long fract} __ashlsq3 (long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long fract} __ashldq3 (long long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned short fract} __ashluqq3 (unsigned short fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __ashluhq3 (unsigned fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __ashlusq3 (unsigned long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __ashludq3 (unsigned long long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {short accum} __ashlha3 (short accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {accum} __ashlsa3 (accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long accum} __ashlda3 (long accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long accum} __ashlta3 (long long accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __ashluha3 (unsigned short accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __ashlusa3 (unsigned accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __ashluda3 (unsigned long accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __ashluta3 (unsigned long long accum @var{a}, int @var{b}) +These functions return the result of shifting @var{a} left by @var{b} bits. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __ashrqq3 (short fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {fract} __ashrhq3 (fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long fract} __ashrsq3 (long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long fract} __ashrdq3 (long long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {short accum} __ashrha3 (short accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {accum} __ashrsa3 (accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long accum} __ashrda3 (long accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long accum} __ashrta3 (long long accum @var{a}, int @var{b}) +These functions return the result of arithmetically shifting @var{a} right +by @var{b} bits. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned short fract} __lshruqq3 (unsigned short fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __lshruhq3 (unsigned fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __lshrusq3 (unsigned long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __lshrudq3 (unsigned long long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __lshruha3 (unsigned short accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __lshrusa3 (unsigned accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __lshruda3 (unsigned long accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __lshruta3 (unsigned long long accum @var{a}, int @var{b}) +These functions return the result of logically shifting @var{a} right +by @var{b} bits. +@end deftypefn + +@deftypefn {Runtime Function} {fract} __ssashlhq3 (fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long fract} __ssashlsq3 (long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long fract} __ssashldq3 (long long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {short accum} __ssashlha3 (short accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {accum} __ssashlsa3 (accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long accum} __ssashlda3 (long accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {long long accum} __ssashlta3 (long long accum @var{a}, int @var{b}) +These functions return the result of shifting @var{a} left by @var{b} bits +with signed saturation. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned short fract} __usashluqq3 (unsigned short fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned fract} __usashluhq3 (unsigned fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long fract} __usashlusq3 (unsigned long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long long fract} __usashludq3 (unsigned long long fract @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned short accum} __usashluha3 (unsigned short accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned accum} __usashlusa3 (unsigned accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long accum} __usashluda3 (unsigned long accum @var{a}, int @var{b}) +@deftypefnx {Runtime Function} {unsigned long long accum} __usashluta3 (unsigned long long accum @var{a}, int @var{b}) +These functions return the result of shifting @var{a} left by @var{b} bits +with unsigned saturation. +@end deftypefn + +@subsection Comparison functions + +The following functions implement fixed-point comparisons. These functions +implement a low-level compare, upon which the higher level comparison +operators (such as less than and greater than or equal to) can be +constructed. The returned values lie in the range zero to two, to allow +the high-level operators to be implemented by testing the returned +result using either signed or unsigned comparison. + +@deftypefn {Runtime Function} {int} __cmpqq2 (short fract @var{a}, short fract @var{b}) +@deftypefnx {Runtime Function} {int} __cmphq2 (fract @var{a}, fract @var{b}) +@deftypefnx {Runtime Function} {int} __cmpsq2 (long fract @var{a}, long fract @var{b}) +@deftypefnx {Runtime Function} {int} __cmpdq2 (long long fract @var{a}, long long fract @var{b}) +@deftypefnx {Runtime Function} {int} __cmpuqq2 (unsigned short fract @var{a}, unsigned short fract @var{b}) +@deftypefnx {Runtime Function} {int} __cmpuhq2 (unsigned fract @var{a}, unsigned fract @var{b}) +@deftypefnx {Runtime Function} {int} __cmpusq2 (unsigned long fract @var{a}, unsigned long fract @var{b}) +@deftypefnx {Runtime Function} {int} __cmpudq2 (unsigned long long fract @var{a}, unsigned long long fract @var{b}) +@deftypefnx {Runtime Function} {int} __cmpha2 (short accum @var{a}, short accum @var{b}) +@deftypefnx {Runtime Function} {int} __cmpsa2 (accum @var{a}, accum @var{b}) +@deftypefnx {Runtime Function} {int} __cmpda2 (long accum @var{a}, long accum @var{b}) +@deftypefnx {Runtime Function} {int} __cmpta2 (long long accum @var{a}, long long accum @var{b}) +@deftypefnx {Runtime Function} {int} __cmpuha2 (unsigned short accum @var{a}, unsigned short accum @var{b}) +@deftypefnx {Runtime Function} {int} __cmpusa2 (unsigned accum @var{a}, unsigned accum @var{b}) +@deftypefnx {Runtime Function} {int} __cmpuda2 (unsigned long accum @var{a}, unsigned long accum @var{b}) +@deftypefnx {Runtime Function} {int} __cmputa2 (unsigned long long accum @var{a}, unsigned long long accum @var{b}) +These functions perform a signed or unsigned comparison of @var{a} and +@var{b} (depending on the selected machine mode). If @var{a} is less +than @var{b}, they return 0; if @var{a} is greater than @var{b}, they +return 2; and if @var{a} and @var{b} are equal they return 1. +@end deftypefn + +@subsection Conversion functions + +@deftypefn {Runtime Function} {fract} __fractqqhq2 (short fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractqqsq2 (short fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractqqdq2 (short fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractqqha (short fract @var{a}) +@deftypefnx {Runtime Function} {accum} __fractqqsa (short fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractqqda (short fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractqqta (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractqquqq (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractqquhq (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractqqusq (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractqqudq (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractqquha (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractqqusa (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractqquda (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractqquta (short fract @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractqqqi (short fract @var{a}) +@deftypefnx {Runtime Function} {short} __fractqqhi (short fract @var{a}) +@deftypefnx {Runtime Function} {int} __fractqqsi (short fract @var{a}) +@deftypefnx {Runtime Function} {long} __fractqqdi (short fract @var{a}) +@deftypefnx {Runtime Function} {long long} __fractqqti (short fract @var{a}) +@deftypefnx {Runtime Function} {float} __fractqqsf (short fract @var{a}) +@deftypefnx {Runtime Function} {double} __fractqqdf (short fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __fracthqqq2 (fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __fracthqsq2 (fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fracthqdq2 (fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __fracthqha (fract @var{a}) +@deftypefnx {Runtime Function} {accum} __fracthqsa (fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __fracthqda (fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fracthqta (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fracthquqq (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fracthquhq (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fracthqusq (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fracthqudq (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fracthquha (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fracthqusa (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fracthquda (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fracthquta (fract @var{a}) +@deftypefnx {Runtime Function} {signed char} __fracthqqi (fract @var{a}) +@deftypefnx {Runtime Function} {short} __fracthqhi (fract @var{a}) +@deftypefnx {Runtime Function} {int} __fracthqsi (fract @var{a}) +@deftypefnx {Runtime Function} {long} __fracthqdi (fract @var{a}) +@deftypefnx {Runtime Function} {long long} __fracthqti (fract @var{a}) +@deftypefnx {Runtime Function} {float} __fracthqsf (fract @var{a}) +@deftypefnx {Runtime Function} {double} __fracthqdf (fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractsqqq2 (long fract @var{a}) +@deftypefnx {Runtime Function} {fract} __fractsqhq2 (long fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractsqdq2 (long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractsqha (long fract @var{a}) +@deftypefnx {Runtime Function} {accum} __fractsqsa (long fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractsqda (long fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractsqta (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractsquqq (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractsquhq (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractsqusq (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractsqudq (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractsquha (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractsqusa (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractsquda (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractsquta (long fract @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractsqqi (long fract @var{a}) +@deftypefnx {Runtime Function} {short} __fractsqhi (long fract @var{a}) +@deftypefnx {Runtime Function} {int} __fractsqsi (long fract @var{a}) +@deftypefnx {Runtime Function} {long} __fractsqdi (long fract @var{a}) +@deftypefnx {Runtime Function} {long long} __fractsqti (long fract @var{a}) +@deftypefnx {Runtime Function} {float} __fractsqsf (long fract @var{a}) +@deftypefnx {Runtime Function} {double} __fractsqdf (long fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractdqqq2 (long long fract @var{a}) +@deftypefnx {Runtime Function} {fract} __fractdqhq2 (long long fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractdqsq2 (long long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractdqha (long long fract @var{a}) +@deftypefnx {Runtime Function} {accum} __fractdqsa (long long fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractdqda (long long fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractdqta (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractdquqq (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractdquhq (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractdqusq (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractdqudq (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractdquha (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractdqusa (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractdquda (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractdquta (long long fract @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractdqqi (long long fract @var{a}) +@deftypefnx {Runtime Function} {short} __fractdqhi (long long fract @var{a}) +@deftypefnx {Runtime Function} {int} __fractdqsi (long long fract @var{a}) +@deftypefnx {Runtime Function} {long} __fractdqdi (long long fract @var{a}) +@deftypefnx {Runtime Function} {long long} __fractdqti (long long fract @var{a}) +@deftypefnx {Runtime Function} {float} __fractdqsf (long long fract @var{a}) +@deftypefnx {Runtime Function} {double} __fractdqdf (long long fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __fracthaqq (short accum @var{a}) +@deftypefnx {Runtime Function} {fract} __fracthahq (short accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __fracthasq (short accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fracthadq (short accum @var{a}) +@deftypefnx {Runtime Function} {accum} __fracthasa2 (short accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __fracthada2 (short accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fracthata2 (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fracthauqq (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fracthauhq (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fracthausq (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fracthaudq (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fracthauha (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fracthausa (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fracthauda (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fracthauta (short accum @var{a}) +@deftypefnx {Runtime Function} {signed char} __fracthaqi (short accum @var{a}) +@deftypefnx {Runtime Function} {short} __fracthahi (short accum @var{a}) +@deftypefnx {Runtime Function} {int} __fracthasi (short accum @var{a}) +@deftypefnx {Runtime Function} {long} __fracthadi (short accum @var{a}) +@deftypefnx {Runtime Function} {long long} __fracthati (short accum @var{a}) +@deftypefnx {Runtime Function} {float} __fracthasf (short accum @var{a}) +@deftypefnx {Runtime Function} {double} __fracthadf (short accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractsaqq (accum @var{a}) +@deftypefnx {Runtime Function} {fract} __fractsahq (accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractsasq (accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractsadq (accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractsaha2 (accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractsada2 (accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractsata2 (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractsauqq (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractsauhq (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractsausq (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractsaudq (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractsauha (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractsausa (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractsauda (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractsauta (accum @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractsaqi (accum @var{a}) +@deftypefnx {Runtime Function} {short} __fractsahi (accum @var{a}) +@deftypefnx {Runtime Function} {int} __fractsasi (accum @var{a}) +@deftypefnx {Runtime Function} {long} __fractsadi (accum @var{a}) +@deftypefnx {Runtime Function} {long long} __fractsati (accum @var{a}) +@deftypefnx {Runtime Function} {float} __fractsasf (accum @var{a}) +@deftypefnx {Runtime Function} {double} __fractsadf (accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractdaqq (long accum @var{a}) +@deftypefnx {Runtime Function} {fract} __fractdahq (long accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractdasq (long accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractdadq (long accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractdaha2 (long accum @var{a}) +@deftypefnx {Runtime Function} {accum} __fractdasa2 (long accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractdata2 (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractdauqq (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractdauhq (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractdausq (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractdaudq (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractdauha (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractdausa (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractdauda (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractdauta (long accum @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractdaqi (long accum @var{a}) +@deftypefnx {Runtime Function} {short} __fractdahi (long accum @var{a}) +@deftypefnx {Runtime Function} {int} __fractdasi (long accum @var{a}) +@deftypefnx {Runtime Function} {long} __fractdadi (long accum @var{a}) +@deftypefnx {Runtime Function} {long long} __fractdati (long accum @var{a}) +@deftypefnx {Runtime Function} {float} __fractdasf (long accum @var{a}) +@deftypefnx {Runtime Function} {double} __fractdadf (long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fracttaqq (long long accum @var{a}) +@deftypefnx {Runtime Function} {fract} __fracttahq (long long accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __fracttasq (long long accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fracttadq (long long accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __fracttaha2 (long long accum @var{a}) +@deftypefnx {Runtime Function} {accum} __fracttasa2 (long long accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __fracttada2 (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fracttauqq (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fracttauhq (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fracttausq (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fracttaudq (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fracttauha (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fracttausa (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fracttauda (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fracttauta (long long accum @var{a}) +@deftypefnx {Runtime Function} {signed char} __fracttaqi (long long accum @var{a}) +@deftypefnx {Runtime Function} {short} __fracttahi (long long accum @var{a}) +@deftypefnx {Runtime Function} {int} __fracttasi (long long accum @var{a}) +@deftypefnx {Runtime Function} {long} __fracttadi (long long accum @var{a}) +@deftypefnx {Runtime Function} {long long} __fracttati (long long accum @var{a}) +@deftypefnx {Runtime Function} {float} __fracttasf (long long accum @var{a}) +@deftypefnx {Runtime Function} {double} __fracttadf (long long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractuqqqq (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {fract} __fractuqqhq (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractuqqsq (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractuqqdq (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractuqqha (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {accum} __fractuqqsa (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractuqqda (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractuqqta (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractuqquhq2 (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractuqqusq2 (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractuqqudq2 (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractuqquha (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractuqqusa (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractuqquda (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractuqquta (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractuqqqi (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {short} __fractuqqhi (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {int} __fractuqqsi (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long} __fractuqqdi (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long long} __fractuqqti (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {float} __fractuqqsf (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {double} __fractuqqdf (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractuhqqq (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {fract} __fractuhqhq (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractuhqsq (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractuhqdq (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractuhqha (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {accum} __fractuhqsa (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractuhqda (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractuhqta (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractuhquqq2 (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractuhqusq2 (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractuhqudq2 (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractuhquha (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractuhqusa (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractuhquda (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractuhquta (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractuhqqi (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {short} __fractuhqhi (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {int} __fractuhqsi (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long} __fractuhqdi (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long long} __fractuhqti (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {float} __fractuhqsf (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {double} __fractuhqdf (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractusqqq (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {fract} __fractusqhq (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractusqsq (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractusqdq (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractusqha (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {accum} __fractusqsa (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractusqda (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractusqta (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractusquqq2 (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractusquhq2 (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractusqudq2 (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractusquha (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractusqusa (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractusquda (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractusquta (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractusqqi (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {short} __fractusqhi (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {int} __fractusqsi (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long} __fractusqdi (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long long} __fractusqti (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {float} __fractusqsf (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {double} __fractusqdf (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractudqqq (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {fract} __fractudqhq (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractudqsq (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractudqdq (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractudqha (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {accum} __fractudqsa (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractudqda (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractudqta (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractudquqq2 (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractudquhq2 (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractudqusq2 (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractudquha (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractudqusa (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractudquda (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractudquta (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractudqqi (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {short} __fractudqhi (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {int} __fractudqsi (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long} __fractudqdi (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long long} __fractudqti (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {float} __fractudqsf (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {double} __fractudqdf (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractuhaqq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {fract} __fractuhahq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractuhasq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractuhadq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractuhaha (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {accum} __fractuhasa (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractuhada (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractuhata (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractuhauqq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractuhauhq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractuhausq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractuhaudq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractuhausa2 (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractuhauda2 (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractuhauta2 (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractuhaqi (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {short} __fractuhahi (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {int} __fractuhasi (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long} __fractuhadi (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long long} __fractuhati (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {float} __fractuhasf (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {double} __fractuhadf (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractusaqq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {fract} __fractusahq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractusasq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractusadq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractusaha (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {accum} __fractusasa (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractusada (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractusata (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractusauqq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractusauhq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractusausq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractusaudq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractusauha2 (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractusauda2 (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractusauta2 (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractusaqi (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {short} __fractusahi (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {int} __fractusasi (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long} __fractusadi (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long long} __fractusati (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {float} __fractusasf (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {double} __fractusadf (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractudaqq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {fract} __fractudahq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractudasq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractudadq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractudaha (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {accum} __fractudasa (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractudada (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractudata (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractudauqq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractudauhq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractudausq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractudaudq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractudauha2 (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractudausa2 (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractudauta2 (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractudaqi (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {short} __fractudahi (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {int} __fractudasi (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long} __fractudadi (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long long} __fractudati (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {float} __fractudasf (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {double} __fractudadf (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractutaqq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {fract} __fractutahq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractutasq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractutadq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractutaha (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {accum} __fractutasa (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractutada (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractutata (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractutauqq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractutauhq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractutausq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractutaudq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractutauha2 (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractutausa2 (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractutauda2 (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {signed char} __fractutaqi (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {short} __fractutahi (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {int} __fractutasi (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long} __fractutadi (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long long} __fractutati (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {float} __fractutasf (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {double} __fractutadf (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractqiqq (signed char @var{a}) +@deftypefnx {Runtime Function} {fract} __fractqihq (signed char @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractqisq (signed char @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractqidq (signed char @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractqiha (signed char @var{a}) +@deftypefnx {Runtime Function} {accum} __fractqisa (signed char @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractqida (signed char @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractqita (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractqiuqq (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractqiuhq (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractqiusq (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractqiudq (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractqiuha (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractqiusa (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractqiuda (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractqiuta (signed char @var{a}) +@deftypefnx {Runtime Function} {short fract} __fracthiqq (short @var{a}) +@deftypefnx {Runtime Function} {fract} __fracthihq (short @var{a}) +@deftypefnx {Runtime Function} {long fract} __fracthisq (short @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fracthidq (short @var{a}) +@deftypefnx {Runtime Function} {short accum} __fracthiha (short @var{a}) +@deftypefnx {Runtime Function} {accum} __fracthisa (short @var{a}) +@deftypefnx {Runtime Function} {long accum} __fracthida (short @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fracthita (short @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fracthiuqq (short @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fracthiuhq (short @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fracthiusq (short @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fracthiudq (short @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fracthiuha (short @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fracthiusa (short @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fracthiuda (short @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fracthiuta (short @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractsiqq (int @var{a}) +@deftypefnx {Runtime Function} {fract} __fractsihq (int @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractsisq (int @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractsidq (int @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractsiha (int @var{a}) +@deftypefnx {Runtime Function} {accum} __fractsisa (int @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractsida (int @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractsita (int @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractsiuqq (int @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractsiuhq (int @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractsiusq (int @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractsiudq (int @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractsiuha (int @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractsiusa (int @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractsiuda (int @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractsiuta (int @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractdiqq (long @var{a}) +@deftypefnx {Runtime Function} {fract} __fractdihq (long @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractdisq (long @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractdidq (long @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractdiha (long @var{a}) +@deftypefnx {Runtime Function} {accum} __fractdisa (long @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractdida (long @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractdita (long @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractdiuqq (long @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractdiuhq (long @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractdiusq (long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractdiudq (long @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractdiuha (long @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractdiusa (long @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractdiuda (long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractdiuta (long @var{a}) +@deftypefnx {Runtime Function} {short fract} __fracttiqq (long long @var{a}) +@deftypefnx {Runtime Function} {fract} __fracttihq (long long @var{a}) +@deftypefnx {Runtime Function} {long fract} __fracttisq (long long @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fracttidq (long long @var{a}) +@deftypefnx {Runtime Function} {short accum} __fracttiha (long long @var{a}) +@deftypefnx {Runtime Function} {accum} __fracttisa (long long @var{a}) +@deftypefnx {Runtime Function} {long accum} __fracttida (long long @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fracttita (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fracttiuqq (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fracttiuhq (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fracttiusq (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fracttiudq (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fracttiuha (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fracttiusa (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fracttiuda (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fracttiuta (long long @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractsfqq (float @var{a}) +@deftypefnx {Runtime Function} {fract} __fractsfhq (float @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractsfsq (float @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractsfdq (float @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractsfha (float @var{a}) +@deftypefnx {Runtime Function} {accum} __fractsfsa (float @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractsfda (float @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractsfta (float @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractsfuqq (float @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractsfuhq (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractsfusq (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractsfudq (float @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractsfuha (float @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractsfusa (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractsfuda (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractsfuta (float @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractdfqq (double @var{a}) +@deftypefnx {Runtime Function} {fract} __fractdfhq (double @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractdfsq (double @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractdfdq (double @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractdfha (double @var{a}) +@deftypefnx {Runtime Function} {accum} __fractdfsa (double @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractdfda (double @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractdfta (double @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractdfuqq (double @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractdfuhq (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractdfusq (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractdfudq (double @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractdfuha (double @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractdfusa (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractdfuda (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractdfuta (double @var{a}) +These functions convert from fractional and signed non-fractionals to +fractionals and signed non-fractionals, without saturation. +@end deftypefn + +@deftypefn {Runtime Function} {fract} __satfractqqhq2 (short fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractqqsq2 (short fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractqqdq2 (short fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractqqha (short fract @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractqqsa (short fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractqqda (short fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractqqta (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractqquqq (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractqquhq (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractqqusq (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractqqudq (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractqquha (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractqqusa (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractqquda (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractqquta (short fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfracthqqq2 (fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfracthqsq2 (fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfracthqdq2 (fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfracthqha (fract @var{a}) +@deftypefnx {Runtime Function} {accum} __satfracthqsa (fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfracthqda (fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfracthqta (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfracthquqq (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfracthquhq (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfracthqusq (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfracthqudq (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfracthquha (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfracthqusa (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfracthquda (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfracthquta (fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractsqqq2 (long fract @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractsqhq2 (long fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractsqdq2 (long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractsqha (long fract @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractsqsa (long fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractsqda (long fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractsqta (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractsquqq (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractsquhq (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractsqusq (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractsqudq (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractsquha (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractsqusa (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractsquda (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractsquta (long fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractdqqq2 (long long fract @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractdqhq2 (long long fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractdqsq2 (long long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractdqha (long long fract @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractdqsa (long long fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractdqda (long long fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractdqta (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractdquqq (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractdquhq (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractdqusq (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractdqudq (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractdquha (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractdqusa (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractdquda (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractdquta (long long fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfracthaqq (short accum @var{a}) +@deftypefnx {Runtime Function} {fract} __satfracthahq (short accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfracthasq (short accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfracthadq (short accum @var{a}) +@deftypefnx {Runtime Function} {accum} __satfracthasa2 (short accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfracthada2 (short accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfracthata2 (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfracthauqq (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfracthauhq (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfracthausq (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfracthaudq (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfracthauha (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfracthausa (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfracthauda (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfracthauta (short accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractsaqq (accum @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractsahq (accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractsasq (accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractsadq (accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractsaha2 (accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractsada2 (accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractsata2 (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractsauqq (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractsauhq (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractsausq (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractsaudq (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractsauha (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractsausa (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractsauda (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractsauta (accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractdaqq (long accum @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractdahq (long accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractdasq (long accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractdadq (long accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractdaha2 (long accum @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractdasa2 (long accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractdata2 (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractdauqq (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractdauhq (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractdausq (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractdaudq (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractdauha (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractdausa (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractdauda (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractdauta (long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfracttaqq (long long accum @var{a}) +@deftypefnx {Runtime Function} {fract} __satfracttahq (long long accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfracttasq (long long accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfracttadq (long long accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfracttaha2 (long long accum @var{a}) +@deftypefnx {Runtime Function} {accum} __satfracttasa2 (long long accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfracttada2 (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfracttauqq (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfracttauhq (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfracttausq (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfracttaudq (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfracttauha (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfracttausa (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfracttauda (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfracttauta (long long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractuqqqq (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractuqqhq (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractuqqsq (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractuqqdq (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractuqqha (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractuqqsa (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractuqqda (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractuqqta (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractuqquhq2 (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractuqqusq2 (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractuqqudq2 (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractuqquha (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractuqqusa (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractuqquda (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractuqquta (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractuhqqq (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractuhqhq (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractuhqsq (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractuhqdq (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractuhqha (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractuhqsa (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractuhqda (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractuhqta (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractuhquqq2 (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractuhqusq2 (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractuhqudq2 (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractuhquha (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractuhqusa (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractuhquda (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractuhquta (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractusqqq (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractusqhq (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractusqsq (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractusqdq (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractusqha (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractusqsa (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractusqda (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractusqta (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractusquqq2 (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractusquhq2 (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractusqudq2 (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractusquha (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractusqusa (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractusquda (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractusquta (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractudqqq (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractudqhq (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractudqsq (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractudqdq (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractudqha (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractudqsa (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractudqda (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractudqta (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractudquqq2 (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractudquhq2 (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractudqusq2 (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractudquha (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractudqusa (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractudquda (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractudquta (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractuhaqq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractuhahq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractuhasq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractuhadq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractuhaha (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractuhasa (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractuhada (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractuhata (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractuhauqq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractuhauhq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractuhausq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractuhaudq (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractuhausa2 (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractuhauda2 (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractuhauta2 (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractusaqq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractusahq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractusasq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractusadq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractusaha (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractusasa (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractusada (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractusata (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractusauqq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractusauhq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractusausq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractusaudq (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractusauha2 (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractusauda2 (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractusauta2 (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractudaqq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractudahq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractudasq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractudadq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractudaha (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractudasa (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractudada (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractudata (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractudauqq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractudauhq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractudausq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractudaudq (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractudauha2 (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractudausa2 (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractudauta2 (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractutaqq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractutahq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractutasq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractutadq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractutaha (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractutasa (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractutada (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractutata (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractutauqq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractutauhq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractutausq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractutaudq (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractutauha2 (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractutausa2 (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractutauda2 (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractqiqq (signed char @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractqihq (signed char @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractqisq (signed char @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractqidq (signed char @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractqiha (signed char @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractqisa (signed char @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractqida (signed char @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractqita (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractqiuqq (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractqiuhq (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractqiusq (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractqiudq (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractqiuha (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractqiusa (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractqiuda (signed char @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractqiuta (signed char @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfracthiqq (short @var{a}) +@deftypefnx {Runtime Function} {fract} __satfracthihq (short @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfracthisq (short @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfracthidq (short @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfracthiha (short @var{a}) +@deftypefnx {Runtime Function} {accum} __satfracthisa (short @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfracthida (short @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfracthita (short @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfracthiuqq (short @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfracthiuhq (short @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfracthiusq (short @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfracthiudq (short @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfracthiuha (short @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfracthiusa (short @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfracthiuda (short @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfracthiuta (short @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractsiqq (int @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractsihq (int @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractsisq (int @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractsidq (int @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractsiha (int @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractsisa (int @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractsida (int @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractsita (int @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractsiuqq (int @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractsiuhq (int @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractsiusq (int @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractsiudq (int @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractsiuha (int @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractsiusa (int @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractsiuda (int @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractsiuta (int @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractdiqq (long @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractdihq (long @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractdisq (long @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractdidq (long @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractdiha (long @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractdisa (long @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractdida (long @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractdita (long @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractdiuqq (long @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractdiuhq (long @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractdiusq (long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractdiudq (long @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractdiuha (long @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractdiusa (long @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractdiuda (long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractdiuta (long @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfracttiqq (long long @var{a}) +@deftypefnx {Runtime Function} {fract} __satfracttihq (long long @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfracttisq (long long @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfracttidq (long long @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfracttiha (long long @var{a}) +@deftypefnx {Runtime Function} {accum} __satfracttisa (long long @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfracttida (long long @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfracttita (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfracttiuqq (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfracttiuhq (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfracttiusq (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfracttiudq (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfracttiuha (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfracttiusa (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfracttiuda (long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfracttiuta (long long @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractsfqq (float @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractsfhq (float @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractsfsq (float @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractsfdq (float @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractsfha (float @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractsfsa (float @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractsfda (float @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractsfta (float @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractsfuqq (float @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractsfuhq (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractsfusq (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractsfudq (float @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractsfuha (float @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractsfusa (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractsfuda (float @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractsfuta (float @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractdfqq (double @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractdfhq (double @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractdfsq (double @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractdfdq (double @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractdfha (double @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractdfsa (double @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractdfda (double @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractdfta (double @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractdfuqq (double @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractdfuhq (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractdfusq (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractdfudq (double @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractdfuha (double @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractdfusa (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractdfuda (double @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractdfuta (double @var{a}) +The functions convert from fractional and signed non-fractionals to +fractionals, with saturation. +@end deftypefn + +@deftypefn {Runtime Function} {unsigned char} __fractunsqqqi (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsqqhi (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsqqsi (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsqqdi (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsqqti (short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunshqqi (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunshqhi (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunshqsi (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunshqdi (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunshqti (fract @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunssqqi (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunssqhi (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunssqsi (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunssqdi (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunssqti (long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsdqqi (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsdqhi (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsdqsi (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsdqdi (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsdqti (long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunshaqi (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunshahi (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunshasi (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunshadi (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunshati (short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunssaqi (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunssahi (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunssasi (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunssadi (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunssati (accum @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsdaqi (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsdahi (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsdasi (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsdadi (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsdati (long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunstaqi (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunstahi (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunstasi (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunstadi (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunstati (long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsuqqqi (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsuqqhi (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsuqqsi (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsuqqdi (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsuqqti (unsigned short fract @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsuhqqi (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsuhqhi (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsuhqsi (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsuhqdi (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsuhqti (unsigned fract @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsusqqi (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsusqhi (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsusqsi (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsusqdi (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsusqti (unsigned long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsudqqi (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsudqhi (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsudqsi (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsudqdi (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsudqti (unsigned long long fract @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsuhaqi (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsuhahi (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsuhasi (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsuhadi (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsuhati (unsigned short accum @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsusaqi (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsusahi (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsusasi (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsusadi (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsusati (unsigned accum @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsudaqi (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsudahi (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsudasi (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsudadi (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsudati (unsigned long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned char} __fractunsutaqi (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned short} __fractunsutahi (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned int} __fractunsutasi (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long} __fractunsutadi (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {unsigned long long} __fractunsutati (unsigned long long accum @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractunsqiqq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {fract} __fractunsqihq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractunsqisq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractunsqidq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractunsqiha (unsigned char @var{a}) +@deftypefnx {Runtime Function} {accum} __fractunsqisa (unsigned char @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractunsqida (unsigned char @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractunsqita (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractunsqiuqq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractunsqiuhq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractunsqiusq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractunsqiudq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractunsqiuha (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractunsqiusa (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractunsqiuda (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractunsqiuta (unsigned char @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractunshiqq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {fract} __fractunshihq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractunshisq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractunshidq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractunshiha (unsigned short @var{a}) +@deftypefnx {Runtime Function} {accum} __fractunshisa (unsigned short @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractunshida (unsigned short @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractunshita (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractunshiuqq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractunshiuhq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractunshiusq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractunshiudq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractunshiuha (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractunshiusa (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractunshiuda (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractunshiuta (unsigned short @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractunssiqq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {fract} __fractunssihq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractunssisq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractunssidq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractunssiha (unsigned int @var{a}) +@deftypefnx {Runtime Function} {accum} __fractunssisa (unsigned int @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractunssida (unsigned int @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractunssita (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractunssiuqq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractunssiuhq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractunssiusq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractunssiudq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractunssiuha (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractunssiusa (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractunssiuda (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractunssiuta (unsigned int @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractunsdiqq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {fract} __fractunsdihq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractunsdisq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractunsdidq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractunsdiha (unsigned long @var{a}) +@deftypefnx {Runtime Function} {accum} __fractunsdisa (unsigned long @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractunsdida (unsigned long @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractunsdita (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractunsdiuqq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractunsdiuhq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractunsdiusq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractunsdiudq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractunsdiuha (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractunsdiusa (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractunsdiuda (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractunsdiuta (unsigned long @var{a}) +@deftypefnx {Runtime Function} {short fract} __fractunstiqq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {fract} __fractunstihq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {long fract} __fractunstisq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {long long fract} __fractunstidq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {short accum} __fractunstiha (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {accum} __fractunstisa (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {long accum} __fractunstida (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {long long accum} __fractunstita (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __fractunstiuqq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __fractunstiuhq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __fractunstiusq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __fractunstiudq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __fractunstiuha (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __fractunstiusa (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __fractunstiuda (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __fractunstiuta (unsigned long long @var{a}) +These functions convert from fractionals to unsigned non-fractionals; +and from unsigned non-fractionals to fractionals, without saturation. +@end deftypefn + +@deftypefn {Runtime Function} {short fract} __satfractunsqiqq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractunsqihq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractunsqisq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractunsqidq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractunsqiha (unsigned char @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractunsqisa (unsigned char @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractunsqida (unsigned char @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractunsqita (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractunsqiuqq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractunsqiuhq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractunsqiusq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractunsqiudq (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractunsqiuha (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractunsqiusa (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractunsqiuda (unsigned char @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractunsqiuta (unsigned char @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractunshiqq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractunshihq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractunshisq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractunshidq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractunshiha (unsigned short @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractunshisa (unsigned short @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractunshida (unsigned short @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractunshita (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractunshiuqq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractunshiuhq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractunshiusq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractunshiudq (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractunshiuha (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractunshiusa (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractunshiuda (unsigned short @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractunshiuta (unsigned short @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractunssiqq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractunssihq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractunssisq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractunssidq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractunssiha (unsigned int @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractunssisa (unsigned int @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractunssida (unsigned int @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractunssita (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractunssiuqq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractunssiuhq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractunssiusq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractunssiudq (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractunssiuha (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractunssiusa (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractunssiuda (unsigned int @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractunssiuta (unsigned int @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractunsdiqq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractunsdihq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractunsdisq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractunsdidq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractunsdiha (unsigned long @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractunsdisa (unsigned long @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractunsdida (unsigned long @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractunsdita (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractunsdiuqq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractunsdiuhq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractunsdiusq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractunsdiudq (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractunsdiuha (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractunsdiusa (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractunsdiuda (unsigned long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractunsdiuta (unsigned long @var{a}) +@deftypefnx {Runtime Function} {short fract} __satfractunstiqq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {fract} __satfractunstihq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {long fract} __satfractunstisq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {long long fract} __satfractunstidq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {short accum} __satfractunstiha (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {accum} __satfractunstisa (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {long accum} __satfractunstida (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {long long accum} __satfractunstita (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned short fract} __satfractunstiuqq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned fract} __satfractunstiuhq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long fract} __satfractunstiusq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long fract} __satfractunstiudq (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned short accum} __satfractunstiuha (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned accum} __satfractunstiusa (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long accum} __satfractunstiuda (unsigned long long @var{a}) +@deftypefnx {Runtime Function} {unsigned long long accum} __satfractunstiuta (unsigned long long @var{a}) +These functions convert from unsigned non-fractionals to fractionals, +with saturation. +@end deftypefn + +@node Exception handling routines +@section Language-independent routines for exception handling + +document me! + +@smallexample + _Unwind_DeleteException + _Unwind_Find_FDE + _Unwind_ForcedUnwind + _Unwind_GetGR + _Unwind_GetIP + _Unwind_GetLanguageSpecificData + _Unwind_GetRegionStart + _Unwind_GetTextRelBase + _Unwind_GetDataRelBase + _Unwind_RaiseException + _Unwind_Resume + _Unwind_SetGR + _Unwind_SetIP + _Unwind_FindEnclosingFunction + _Unwind_SjLj_Register + _Unwind_SjLj_Unregister + _Unwind_SjLj_RaiseException + _Unwind_SjLj_ForcedUnwind + _Unwind_SjLj_Resume + __deregister_frame + __deregister_frame_info + __deregister_frame_info_bases + __register_frame + __register_frame_info + __register_frame_info_bases + __register_frame_info_table + __register_frame_info_table_bases + __register_frame_table +@end smallexample + +@node Miscellaneous routines +@section Miscellaneous runtime library routines + +@subsection Cache control functions +@deftypefn {Runtime Function} void __clear_cache (char *@var{beg}, char *@var{end}) +This function clears the instruction cache between @var{beg} and @var{end}. +@end deftypefn + +@subsection Split stack functions and variables +@deftypefn {Runtime Function} {void *} __splitstack_find (void *@var{segment_arg}, @ +void *@var{sp}, size_t @var{len}, void **@var{next_segment}, @ +void **@var{next_sp}, void **@var{initial_sp}) +When using @option{-fsplit-stack}, this call may be used to iterate +over the stack segments. It may be called like this: +@smallexample + void *next_segment = NULL; + void *next_sp = NULL; + void *initial_sp = NULL; + void *stack; + size_t stack_size; + while ((stack = __splitstack_find (next_segment, next_sp, + &stack_size, &next_segment, + &next_sp, &initial_sp)) + != NULL) + @{ + /* Stack segment starts at stack and is + stack_size bytes long. */ + @} +@end smallexample + +There is no way to iterate over the stack segments of a different +thread. However, what is permitted is for one thread to call this +with the @var{segment_arg} and @var{sp} arguments NULL, to pass +@var{next_segment}, @var{next_sp}, and @var{initial_sp} to a different +thread, and then to suspend one way or another. A different thread +may run the subsequent @code{__splitstack_find} iterations. Of +course, this will only work if the first thread is suspended while the +second thread is calling @code{__splitstack_find}. If not, the second +thread could be looking at the stack while it is changing, and +anything could happen. +@end deftypefn + +@defvar __morestack_segments +@defvarx __morestack_current_segment +@defvarx __morestack_initial_sp +Internal variables used by the @option{-fsplit-stack} implementation. +@end defvar diff --git a/gcc/doc/loop.texi b/gcc/doc/loop.texi new file mode 100644 index 00000000000..6e8657a074d --- /dev/null +++ b/gcc/doc/loop.texi @@ -0,0 +1,626 @@ +@c Copyright (C) 2006-2022 Free Software Foundation, Inc. +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@c --------------------------------------------------------------------- +@c Loop Representation +@c --------------------------------------------------------------------- + +@node Loop Analysis and Representation +@chapter Analysis and Representation of Loops + +GCC provides extensive infrastructure for work with natural loops, i.e., +strongly connected components of CFG with only one entry block. This +chapter describes representation of loops in GCC, both on GIMPLE and in +RTL, as well as the interfaces to loop-related analyses (induction +variable analysis and number of iterations analysis). + +@menu +* Loop representation:: Representation and analysis of loops. +* Loop querying:: Getting information about loops. +* Loop manipulation:: Loop manipulation functions. +* LCSSA:: Loop-closed SSA form. +* Scalar evolutions:: Induction variables on GIMPLE. +* loop-iv:: Induction variables on RTL. +* Number of iterations:: Number of iterations analysis. +* Dependency analysis:: Data dependency analysis. +@end menu + +@node Loop representation +@section Loop representation +@cindex Loop representation +@cindex Loop analysis + +This chapter describes the representation of loops in GCC, and functions +that can be used to build, modify and analyze this representation. Most +of the interfaces and data structures are declared in @file{cfgloop.h}. +Loop structures are analyzed and this information disposed or updated +at the discretion of individual passes. Still most of the generic +CFG manipulation routines are aware of loop structures and try to +keep them up-to-date. By this means an increasing part of the +compilation pipeline is setup to maintain loop structure across +passes to allow attaching meta information to individual loops +for consumption by later passes. + +In general, a natural loop has one entry block (header) and possibly +several back edges (latches) leading to the header from the inside of +the loop. Loops with several latches may appear if several loops share +a single header, or if there is a branching in the middle of the loop. +The representation of loops in GCC however allows only loops with a +single latch. During loop analysis, headers of such loops are split and +forwarder blocks are created in order to disambiguate their structures. +Heuristic based on profile information and structure of the induction +variables in the loops is used to determine whether the latches +correspond to sub-loops or to control flow in a single loop. This means +that the analysis sometimes changes the CFG, and if you run it in the +middle of an optimization pass, you must be able to deal with the new +blocks. You may avoid CFG changes by passing +@code{LOOPS_MAY_HAVE_MULTIPLE_LATCHES} flag to the loop discovery, +note however that most other loop manipulation functions will not work +correctly for loops with multiple latch edges (the functions that only +query membership of blocks to loops and subloop relationships, or +enumerate and test loop exits, can be expected to work). + +Body of the loop is the set of blocks that are dominated by its header, +and reachable from its latch against the direction of edges in CFG@. The +loops are organized in a containment hierarchy (tree) such that all the +loops immediately contained inside loop L are the children of L in the +tree. This tree is represented by the @code{struct loops} structure. +The root of this tree is a fake loop that contains all blocks in the +function. Each of the loops is represented in a @code{struct loop} +structure. Each loop is assigned an index (@code{num} field of the +@code{struct loop} structure), and the pointer to the loop is stored in +the corresponding field of the @code{larray} vector in the loops +structure. The indices do not have to be continuous, there may be +empty (@code{NULL}) entries in the @code{larray} created by deleting +loops. Also, there is no guarantee on the relative order of a loop +and its subloops in the numbering. The index of a loop never changes. + +The entries of the @code{larray} field should not be accessed directly. +The function @code{get_loop} returns the loop description for a loop with +the given index. @code{number_of_loops} function returns number of loops +in the function. To traverse all loops, use a range-based for loop with +class @code{loops_list} instance. The @code{flags} argument passed to the +constructor function of class @code{loops_list} is used to determine the +direction of traversal and the set of loops visited. Each loop is +guaranteed to be visited exactly once, regardless of the changes to the +loop tree, and the loops may be removed during the traversal. The newly +created loops are never traversed, if they need to be visited, this must +be done separately after their creation. + +Each basic block contains the reference to the innermost loop it belongs +to (@code{loop_father}). For this reason, it is only possible to have +one @code{struct loops} structure initialized at the same time for each +CFG@. The global variable @code{current_loops} contains the +@code{struct loops} structure. Many of the loop manipulation functions +assume that dominance information is up-to-date. + +The loops are analyzed through @code{loop_optimizer_init} function. The +argument of this function is a set of flags represented in an integer +bitmask. These flags specify what other properties of the loop +structures should be calculated/enforced and preserved later: + +@itemize +@item @code{LOOPS_MAY_HAVE_MULTIPLE_LATCHES}: If this flag is set, no +changes to CFG will be performed in the loop analysis, in particular, +loops with multiple latch edges will not be disambiguated. If a loop +has multiple latches, its latch block is set to NULL@. Most of +the loop manipulation functions will not work for loops in this shape. +No other flags that require CFG changes can be passed to +loop_optimizer_init. +@item @code{LOOPS_HAVE_PREHEADERS}: Forwarder blocks are created in such +a way that each loop has only one entry edge, and additionally, the +source block of this entry edge has only one successor. This creates a +natural place where the code can be moved out of the loop, and ensures +that the entry edge of the loop leads from its immediate super-loop. +@item @code{LOOPS_HAVE_SIMPLE_LATCHES}: Forwarder blocks are created to +force the latch block of each loop to have only one successor. This +ensures that the latch of the loop does not belong to any of its +sub-loops, and makes manipulation with the loops significantly easier. +Most of the loop manipulation functions assume that the loops are in +this shape. Note that with this flag, the ``normal'' loop without any +control flow inside and with one exit consists of two basic blocks. +@item @code{LOOPS_HAVE_MARKED_IRREDUCIBLE_REGIONS}: Basic blocks and +edges in the strongly connected components that are not natural loops +(have more than one entry block) are marked with +@code{BB_IRREDUCIBLE_LOOP} and @code{EDGE_IRREDUCIBLE_LOOP} flags. The +flag is not set for blocks and edges that belong to natural loops that +are in such an irreducible region (but it is set for the entry and exit +edges of such a loop, if they lead to/from this region). +@item @code{LOOPS_HAVE_RECORDED_EXITS}: The lists of exits are recorded +and updated for each loop. This makes some functions (e.g., +@code{get_loop_exit_edges}) more efficient. Some functions (e.g., +@code{single_exit}) can be used only if the lists of exits are +recorded. +@end itemize + +These properties may also be computed/enforced later, using functions +@code{create_preheaders}, @code{force_single_succ_latches}, +@code{mark_irreducible_loops} and @code{record_loop_exits}. +The properties can be queried using @code{loops_state_satisfies_p}. + +The memory occupied by the loops structures should be freed with +@code{loop_optimizer_finalize} function. When loop structures are +setup to be preserved across passes this function reduces the +information to be kept up-to-date to a minimum (only +@code{LOOPS_MAY_HAVE_MULTIPLE_LATCHES} set). + +The CFG manipulation functions in general do not update loop structures. +Specialized versions that additionally do so are provided for the most +common tasks. On GIMPLE, @code{cleanup_tree_cfg_loop} function can be +used to cleanup CFG while updating the loops structures if +@code{current_loops} is set. + +At the moment loop structure is preserved from the start of GIMPLE +loop optimizations until the end of RTL loop optimizations. During +this time a loop can be tracked by its @code{struct loop} and number. + +@node Loop querying +@section Loop querying +@cindex Loop querying + +The functions to query the information about loops are declared in +@file{cfgloop.h}. Some of the information can be taken directly from +the structures. @code{loop_father} field of each basic block contains +the innermost loop to that the block belongs. The most useful fields of +loop structure (that are kept up-to-date at all times) are: + +@itemize +@item @code{header}, @code{latch}: Header and latch basic blocks of the +loop. +@item @code{num_nodes}: Number of basic blocks in the loop (including +the basic blocks of the sub-loops). +@item @code{outer}, @code{inner}, @code{next}: The super-loop, the first +sub-loop, and the sibling of the loop in the loops tree. +@end itemize + +There are other fields in the loop structures, many of them used only by +some of the passes, or not updated during CFG changes; in general, they +should not be accessed directly. + +The most important functions to query loop structures are: + +@itemize +@item @code{loop_depth}: The depth of the loop in the loops tree, i.e., the +number of super-loops of the loop. +@item @code{flow_loops_dump}: Dumps the information about loops to a +file. +@item @code{verify_loop_structure}: Checks consistency of the loop +structures. +@item @code{loop_latch_edge}: Returns the latch edge of a loop. +@item @code{loop_preheader_edge}: If loops have preheaders, returns +the preheader edge of a loop. +@item @code{flow_loop_nested_p}: Tests whether loop is a sub-loop of +another loop. +@item @code{flow_bb_inside_loop_p}: Tests whether a basic block belongs +to a loop (including its sub-loops). +@item @code{find_common_loop}: Finds the common super-loop of two loops. +@item @code{superloop_at_depth}: Returns the super-loop of a loop with +the given depth. +@item @code{tree_num_loop_insns}, @code{num_loop_insns}: Estimates the +number of insns in the loop, on GIMPLE and on RTL. +@item @code{loop_exit_edge_p}: Tests whether edge is an exit from a +loop. +@item @code{mark_loop_exit_edges}: Marks all exit edges of all loops +with @code{EDGE_LOOP_EXIT} flag. +@item @code{get_loop_body}, @code{get_loop_body_in_dom_order}, +@code{get_loop_body_in_bfs_order}: Enumerates the basic blocks in the +loop in depth-first search order in reversed CFG, ordered by dominance +relation, and breath-first search order, respectively. +@item @code{single_exit}: Returns the single exit edge of the loop, or +@code{NULL} if the loop has more than one exit. You can only use this +function if @code{LOOPS_HAVE_RECORDED_EXITS} is used. +@item @code{get_loop_exit_edges}: Enumerates the exit edges of a loop. +@item @code{just_once_each_iteration_p}: Returns true if the basic block +is executed exactly once during each iteration of a loop (that is, it +does not belong to a sub-loop, and it dominates the latch of the loop). +@end itemize + +@node Loop manipulation +@section Loop manipulation +@cindex Loop manipulation + +The loops tree can be manipulated using the following functions: + +@itemize +@item @code{flow_loop_tree_node_add}: Adds a node to the tree. +@item @code{flow_loop_tree_node_remove}: Removes a node from the tree. +@item @code{add_bb_to_loop}: Adds a basic block to a loop. +@item @code{remove_bb_from_loops}: Removes a basic block from loops. +@end itemize + +Most low-level CFG functions update loops automatically. The following +functions handle some more complicated cases of CFG manipulations: + +@itemize +@item @code{remove_path}: Removes an edge and all blocks it dominates. +@item @code{split_loop_exit_edge}: Splits exit edge of the loop, +ensuring that PHI node arguments remain in the loop (this ensures that +loop-closed SSA form is preserved). Only useful on GIMPLE. +@end itemize + +Finally, there are some higher-level loop transformations implemented. +While some of them are written so that they should work on non-innermost +loops, they are mostly untested in that case, and at the moment, they +are only reliable for the innermost loops: + +@itemize +@item @code{create_iv}: Creates a new induction variable. Only works on +GIMPLE@. @code{standard_iv_increment_position} can be used to find a +suitable place for the iv increment. +@item @code{duplicate_loop_body_to_header_edge}, +@code{tree_duplicate_loop_body_to_header_edge}: These functions (on RTL and +on GIMPLE) duplicate the body of the loop prescribed number of times on +one of the edges entering loop header, thus performing either loop +unrolling or loop peeling. @code{can_duplicate_loop_p} +(@code{can_unroll_loop_p} on GIMPLE) must be true for the duplicated +loop. +@item @code{loop_version}: This function creates a copy of a loop, and +a branch before them that selects one of them depending on the +prescribed condition. This is useful for optimizations that need to +verify some assumptions in runtime (one of the copies of the loop is +usually left unchanged, while the other one is transformed in some way). +@item @code{tree_unroll_loop}: Unrolls the loop, including peeling the +extra iterations to make the number of iterations divisible by unroll +factor, updating the exit condition, and removing the exits that now +cannot be taken. Works only on GIMPLE. +@end itemize + +@node LCSSA +@section Loop-closed SSA form +@cindex LCSSA +@cindex Loop-closed SSA form + +Throughout the loop optimizations on tree level, one extra condition is +enforced on the SSA form: No SSA name is used outside of the loop in +that it is defined. The SSA form satisfying this condition is called +``loop-closed SSA form'' -- LCSSA@. To enforce LCSSA, PHI nodes must be +created at the exits of the loops for the SSA names that are used +outside of them. Only the real operands (not virtual SSA names) are +held in LCSSA, in order to save memory. + +There are various benefits of LCSSA: + +@itemize +@item Many optimizations (value range analysis, final value +replacement) are interested in the values that are defined in the loop +and used outside of it, i.e., exactly those for that we create new PHI +nodes. +@item In induction variable analysis, it is not necessary to specify the +loop in that the analysis should be performed -- the scalar evolution +analysis always returns the results with respect to the loop in that the +SSA name is defined. +@item It makes updating of SSA form during loop transformations simpler. +Without LCSSA, operations like loop unrolling may force creation of PHI +nodes arbitrarily far from the loop, while in LCSSA, the SSA form can be +updated locally. However, since we only keep real operands in LCSSA, we +cannot use this advantage (we could have local updating of real +operands, but it is not much more efficient than to use generic SSA form +updating for it as well; the amount of changes to SSA is the same). +@end itemize + +However, it also means LCSSA must be updated. This is usually +straightforward, unless you create a new value in loop and use it +outside, or unless you manipulate loop exit edges (functions are +provided to make these manipulations simple). +@code{rewrite_into_loop_closed_ssa} is used to rewrite SSA form to +LCSSA, and @code{verify_loop_closed_ssa} to check that the invariant of +LCSSA is preserved. + +@node Scalar evolutions +@section Scalar evolutions +@cindex Scalar evolutions +@cindex IV analysis on GIMPLE + +Scalar evolutions (SCEV) are used to represent results of induction +variable analysis on GIMPLE@. They enable us to represent variables with +complicated behavior in a simple and consistent way (we only use it to +express values of polynomial induction variables, but it is possible to +extend it). The interfaces to SCEV analysis are declared in +@file{tree-scalar-evolution.h}. To use scalar evolutions analysis, +@code{scev_initialize} must be used. To stop using SCEV, +@code{scev_finalize} should be used. SCEV analysis caches results in +order to save time and memory. This cache however is made invalid by +most of the loop transformations, including removal of code. If such a +transformation is performed, @code{scev_reset} must be called to clean +the caches. + +Given an SSA name, its behavior in loops can be analyzed using the +@code{analyze_scalar_evolution} function. The returned SCEV however +does not have to be fully analyzed and it may contain references to +other SSA names defined in the loop. To resolve these (potentially +recursive) references, @code{instantiate_parameters} or +@code{resolve_mixers} functions must be used. +@code{instantiate_parameters} is useful when you use the results of SCEV +only for some analysis, and when you work with whole nest of loops at +once. It will try replacing all SSA names by their SCEV in all loops, +including the super-loops of the current loop, thus providing a complete +information about the behavior of the variable in the loop nest. +@code{resolve_mixers} is useful if you work with only one loop at a +time, and if you possibly need to create code based on the value of the +induction variable. It will only resolve the SSA names defined in the +current loop, leaving the SSA names defined outside unchanged, even if +their evolution in the outer loops is known. + +The SCEV is a normal tree expression, except for the fact that it may +contain several special tree nodes. One of them is +@code{SCEV_NOT_KNOWN}, used for SSA names whose value cannot be +expressed. The other one is @code{POLYNOMIAL_CHREC}. Polynomial chrec +has three arguments -- base, step and loop (both base and step may +contain further polynomial chrecs). Type of the expression and of base +and step must be the same. A variable has evolution +@code{POLYNOMIAL_CHREC(base, step, loop)} if it is (in the specified +loop) equivalent to @code{x_1} in the following example + +@smallexample +while (@dots{}) + @{ + x_1 = phi (base, x_2); + x_2 = x_1 + step; + @} +@end smallexample + +Note that this includes the language restrictions on the operations. +For example, if we compile C code and @code{x} has signed type, then the +overflow in addition would cause undefined behavior, and we may assume +that this does not happen. Hence, the value with this SCEV cannot +overflow (which restricts the number of iterations of such a loop). + +In many cases, one wants to restrict the attention just to affine +induction variables. In this case, the extra expressive power of SCEV +is not useful, and may complicate the optimizations. In this case, +@code{simple_iv} function may be used to analyze a value -- the result +is a loop-invariant base and step. + +@node loop-iv +@section IV analysis on RTL +@cindex IV analysis on RTL + +The induction variable on RTL is simple and only allows analysis of +affine induction variables, and only in one loop at once. The interface +is declared in @file{cfgloop.h}. Before analyzing induction variables +in a loop L, @code{iv_analysis_loop_init} function must be called on L. +After the analysis (possibly calling @code{iv_analysis_loop_init} for +several loops) is finished, @code{iv_analysis_done} should be called. +The following functions can be used to access the results of the +analysis: + +@itemize +@item @code{iv_analyze}: Analyzes a single register used in the given +insn. If no use of the register in this insn is found, the following +insns are scanned, so that this function can be called on the insn +returned by get_condition. +@item @code{iv_analyze_result}: Analyzes result of the assignment in the +given insn. +@item @code{iv_analyze_expr}: Analyzes a more complicated expression. +All its operands are analyzed by @code{iv_analyze}, and hence they must +be used in the specified insn or one of the following insns. +@end itemize + +The description of the induction variable is provided in @code{struct +rtx_iv}. In order to handle subregs, the representation is a bit +complicated; if the value of the @code{extend} field is not +@code{UNKNOWN}, the value of the induction variable in the i-th +iteration is + +@smallexample +delta + mult * extend_@{extend_mode@} (subreg_@{mode@} (base + i * step)), +@end smallexample + +with the following exception: if @code{first_special} is true, then the +value in the first iteration (when @code{i} is zero) is @code{delta + +mult * base}. However, if @code{extend} is equal to @code{UNKNOWN}, +then @code{first_special} must be false, @code{delta} 0, @code{mult} 1 +and the value in the i-th iteration is + +@smallexample +subreg_@{mode@} (base + i * step) +@end smallexample + +The function @code{get_iv_value} can be used to perform these +calculations. + +@node Number of iterations +@section Number of iterations analysis +@cindex Number of iterations analysis + +Both on GIMPLE and on RTL, there are functions available to determine +the number of iterations of a loop, with a similar interface. The +number of iterations of a loop in GCC is defined as the number of +executions of the loop latch. In many cases, it is not possible to +determine the number of iterations unconditionally -- the determined +number is correct only if some assumptions are satisfied. The analysis +tries to verify these conditions using the information contained in the +program; if it fails, the conditions are returned together with the +result. The following information and conditions are provided by the +analysis: + +@itemize +@item @code{assumptions}: If this condition is false, the rest of +the information is invalid. +@item @code{noloop_assumptions} on RTL, @code{may_be_zero} on GIMPLE: If +this condition is true, the loop exits in the first iteration. +@item @code{infinite}: If this condition is true, the loop is infinite. +This condition is only available on RTL@. On GIMPLE, conditions for +finiteness of the loop are included in @code{assumptions}. +@item @code{niter_expr} on RTL, @code{niter} on GIMPLE: The expression +that gives number of iterations. The number of iterations is defined as +the number of executions of the loop latch. +@end itemize + +Both on GIMPLE and on RTL, it necessary for the induction variable +analysis framework to be initialized (SCEV on GIMPLE, loop-iv on RTL). +On GIMPLE, the results are stored to @code{struct tree_niter_desc} +structure. Number of iterations before the loop is exited through a +given exit can be determined using @code{number_of_iterations_exit} +function. On RTL, the results are returned in @code{struct niter_desc} +structure. The corresponding function is named +@code{check_simple_exit}. There are also functions that pass through +all the exits of a loop and try to find one with easy to determine +number of iterations -- @code{find_loop_niter} on GIMPLE and +@code{find_simple_exit} on RTL@. Finally, there are functions that +provide the same information, but additionally cache it, so that +repeated calls to number of iterations are not so costly -- +@code{number_of_latch_executions} on GIMPLE and @code{get_simple_loop_desc} +on RTL. + +Note that some of these functions may behave slightly differently than +others -- some of them return only the expression for the number of +iterations, and fail if there are some assumptions. The function +@code{number_of_latch_executions} works only for single-exit loops. +The function @code{number_of_cond_exit_executions} can be used to +determine number of executions of the exit condition of a single-exit +loop (i.e., the @code{number_of_latch_executions} increased by one). + +On GIMPLE, below constraint flags affect semantics of some APIs of number +of iterations analyzer: + +@itemize +@item @code{LOOP_C_INFINITE}: If this constraint flag is set, the loop +is known to be infinite. APIs like @code{number_of_iterations_exit} can +return false directly without doing any analysis. +@item @code{LOOP_C_FINITE}: If this constraint flag is set, the loop is +known to be finite, in other words, loop's number of iterations can be +computed with @code{assumptions} be true. +@end itemize + +Generally, the constraint flags are set/cleared by consumers which are +loop optimizers. It's also the consumers' responsibility to set/clear +constraints correctly. Failing to do that might result in hard to track +down bugs in scev/niter consumers. One typical use case is vectorizer: +it drives number of iterations analyzer by setting @code{LOOP_C_FINITE} +and vectorizes possibly infinite loop by versioning loop with analysis +result. In return, constraints set by consumers can also help number of +iterations analyzer in following optimizers. For example, @code{niter} +of a loop versioned under @code{assumptions} is valid unconditionally. + +Other constraints may be added in the future, for example, a constraint +indicating that loops' latch must roll thus @code{may_be_zero} would be +false unconditionally. + +@node Dependency analysis +@section Data Dependency Analysis +@cindex Data Dependency Analysis + +The code for the data dependence analysis can be found in +@file{tree-data-ref.cc} and its interface and data structures are +described in @file{tree-data-ref.h}. The function that computes the +data dependences for all the array and pointer references for a given +loop is @code{compute_data_dependences_for_loop}. This function is +currently used by the linear loop transform and the vectorization +passes. Before calling this function, one has to allocate two vectors: +a first vector will contain the set of data references that are +contained in the analyzed loop body, and the second vector will contain +the dependence relations between the data references. Thus if the +vector of data references is of size @code{n}, the vector containing the +dependence relations will contain @code{n*n} elements. However if the +analyzed loop contains side effects, such as calls that potentially can +interfere with the data references in the current analyzed loop, the +analysis stops while scanning the loop body for data references, and +inserts a single @code{chrec_dont_know} in the dependence relation +array. + +The data references are discovered in a particular order during the +scanning of the loop body: the loop body is analyzed in execution order, +and the data references of each statement are pushed at the end of the +data reference array. Two data references syntactically occur in the +program in the same order as in the array of data references. This +syntactic order is important in some classical data dependence tests, +and mapping this order to the elements of this array avoids costly +queries to the loop body representation. + +Three types of data references are currently handled: ARRAY_REF, +INDIRECT_REF and COMPONENT_REF@. The data structure for the data reference +is @code{data_reference}, where @code{data_reference_p} is a name of a +pointer to the data reference structure. The structure contains the +following elements: + +@itemize +@item @code{base_object_info}: Provides information about the base object +of the data reference and its access functions. These access functions +represent the evolution of the data reference in the loop relative to +its base, in keeping with the classical meaning of the data reference +access function for the support of arrays. For example, for a reference +@code{a.b[i][j]}, the base object is @code{a.b} and the access functions, +one for each array subscript, are: +@code{@{i_init, + i_step@}_1, @{j_init, +, j_step@}_2}. + +@item @code{first_location_in_loop}: Provides information about the first +location accessed by the data reference in the loop and about the access +function used to represent evolution relative to this location. This data +is used to support pointers, and is not used for arrays (for which we +have base objects). Pointer accesses are represented as a one-dimensional +access that starts from the first location accessed in the loop. For +example: + +@smallexample + for1 i + for2 j + *((int *)p + i + j) = a[i][j]; +@end smallexample + +The access function of the pointer access is @code{@{0, + 4B@}_for2} +relative to @code{p + i}. The access functions of the array are +@code{@{i_init, + i_step@}_for1} and @code{@{j_init, +, j_step@}_for2} +relative to @code{a}. + +Usually, the object the pointer refers to is either unknown, or we cannot +prove that the access is confined to the boundaries of a certain object. + +Two data references can be compared only if at least one of these two +representations has all its fields filled for both data references. + +The current strategy for data dependence tests is as follows: +If both @code{a} and @code{b} are represented as arrays, compare +@code{a.base_object} and @code{b.base_object}; +if they are equal, apply dependence tests (use access functions based on +base_objects). +Else if both @code{a} and @code{b} are represented as pointers, compare +@code{a.first_location} and @code{b.first_location}; +if they are equal, apply dependence tests (use access functions based on +first location). +However, if @code{a} and @code{b} are represented differently, only try +to prove that the bases are definitely different. + +@item Aliasing information. +@item Alignment information. +@end itemize + +The structure describing the relation between two data references is +@code{data_dependence_relation} and the shorter name for a pointer to +such a structure is @code{ddr_p}. This structure contains: + +@itemize +@item a pointer to each data reference, +@item a tree node @code{are_dependent} that is set to @code{chrec_known} +if the analysis has proved that there is no dependence between these two +data references, @code{chrec_dont_know} if the analysis was not able to +determine any useful result and potentially there could exist a +dependence between these data references, and @code{are_dependent} is +set to @code{NULL_TREE} if there exist a dependence relation between the +data references, and the description of this dependence relation is +given in the @code{subscripts}, @code{dir_vects}, and @code{dist_vects} +arrays, +@item a boolean that determines whether the dependence relation can be +represented by a classical distance vector, +@item an array @code{subscripts} that contains a description of each +subscript of the data references. Given two array accesses a +subscript is the tuple composed of the access functions for a given +dimension. For example, given @code{A[f1][f2][f3]} and +@code{B[g1][g2][g3]}, there are three subscripts: @code{(f1, g1), (f2, +g2), (f3, g3)}. +@item two arrays @code{dir_vects} and @code{dist_vects} that contain +classical representations of the data dependences under the form of +direction and distance dependence vectors, +@item an array of loops @code{loop_nest} that contains the loops to +which the distance and direction vectors refer to. +@end itemize + +Several functions for pretty printing the information extracted by the +data dependence analysis are available: @code{dump_ddrs} prints with a +maximum verbosity the details of a data dependence relations array, +@code{dump_dist_dir_vectors} prints only the classical distance and +direction vectors for a data dependence relations array, and +@code{dump_data_references} prints the details of the data references +contained in a data reference array. diff --git a/gcc/doc/lto-dump.texi b/gcc/doc/lto-dump.texi new file mode 100644 index 00000000000..d7fb346e25c --- /dev/null +++ b/gcc/doc/lto-dump.texi @@ -0,0 +1,131 @@ +@c Copyright (C) 2018-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ignore +@c man begin COPYRIGHT +Copyright @copyright{} 2017-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'' and ``Funding +Free Software'', the Front-Cover texts being (a) (see below), and with +the Back-Cover Texts being (b) (see below). A copy of the license is +included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename lto-dump +@settitle Tool for dumping LTO object files. +@end ignore + +@node lto-dump +@chapter @command{lto-dump}---Tool for dumping LTO object files. + +@menu +* lto-dump Intro:: Introduction to lto-dump. +* Invoking lto-dump:: How to use lto-dump. +@end menu + +@node lto-dump Intro +@section Introduction to @command{lto-dump} +@c man begin DESCRIPTION + +@command{lto-dump} is a tool you can use in conjunction with GCC to +dump link time optimization object files. + +@c man end + +@node Invoking lto-dump +@section Invoking @command{lto-dump} + +@smallexample +Usage: lto-dump @r{[}@var{OPTION}@r{]} ... @var{objfiles} +@end smallexample + +@command{lto-dump} accepts the following options: + +@ignore +@c man begin SYNOPSIS +lto-dump [@option{-list}] + [@option{-demangle}] + [@option{-defined-only}] + [@option{-print-value}] + [@option{-name-sort}] + [@option{-size-sort}] + [@option{-reverse-sort}] + [@option{-no-sort}] + [@option{-symbol=}] + [@option{-objects}] + [@option{-type-stats}] + [@option{-tree-stats}] + [@option{-gimple-stats}] + [@option{-dump-level=}] + [@option{-dump-body=}] + [@option{-help}] @var{lto-dump} +@c man end +@end ignore + +@c man begin OPTIONS +@table @gcctabopt +@item -list +Dumps list of details of functions and variables. + +@item -demangle +Dump the demangled output. + +@item -defined-only +Dump only the defined symbols. + +@item -print-value +Dump initial values of the variables. + +@item -name-sort +Sort the symbols alphabetically. + +@item -size-sort +Sort the symbols according to size. + +@item -reverse-sort +Dump the symbols in reverse order. + +@item -no-sort +Dump the symbols in order of occurrence. + +@item -symbol= +Dump the details of specific symbol. + +@item -objects +Dump the details of LTO objects. + +@item -type-stats +Dump the statistics of tree types. + +@item -tree-stats +Dump the statistics of trees. + +@item -gimple-stats +Dump the statistics of gimple statements. + +@item -dump-level= +For deciding the optimization level of body. + +@item -dump-body= +Dump the specific gimple body. + +@item -help +Display the dump tool help. + +@end table + +@c man end diff --git a/gcc/doc/lto.texi b/gcc/doc/lto.texi new file mode 100644 index 00000000000..8ee2a5bdc97 --- /dev/null +++ b/gcc/doc/lto.texi @@ -0,0 +1,591 @@ +@c Copyright (C) 2010-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. +@c Contributed by Jan Hubicka and +@c Diego Novillo + +@node LTO +@chapter Link Time Optimization +@cindex lto +@cindex whopr +@cindex wpa +@cindex ltrans + +Link Time Optimization (LTO) gives GCC the capability of +dumping its internal representation (GIMPLE) to disk, +so that all the different compilation units that make up +a single executable can be optimized as a single module. +This expands the scope of inter-procedural optimizations +to encompass the whole program (or, rather, everything +that is visible at link time). + +@menu +* LTO Overview:: Overview of LTO. +* LTO object file layout:: LTO file sections in ELF. +* IPA:: Using summary information in IPA passes. +* WHOPR:: Whole program assumptions, + linker plugin and symbol visibilities. +* Internal flags:: Internal flags controlling @code{lto1}. +@end menu + +@node LTO Overview +@section Design Overview + +Link time optimization is implemented as a GCC front end for a +bytecode representation of GIMPLE that is emitted in special sections +of @code{.o} files. Currently, LTO support is enabled in most +ELF-based systems, as well as darwin, cygwin and mingw systems. + +By default, object files generated with LTO support contain only GIMPLE +bytecode. Such objects are called ``slim'', and they require that +tools like @code{ar} and @code{nm} understand symbol tables of LTO +sections. For most targets these tools have been extended to use the +plugin infrastructure, so GCC can support ``slim'' objects consisting +of the intermediate code alone. + +GIMPLE bytecode could also be saved alongside final object code if +the @option{-ffat-lto-objects} option is passed, or if no plugin support +is detected for @code{ar} and @code{nm} when GCC is configured. It makes +the object files generated with LTO support larger than regular object +files. This ``fat'' object format allows to ship one set of fat +objects which could be used both for development and the production of +optimized builds. A, perhaps surprising, side effect of this feature +is that any mistake in the toolchain leads to LTO information not +being used (e.g.@: an older @code{libtool} calling @code{ld} directly). +This is both an advantage, as the system is more robust, and a +disadvantage, as the user is not informed that the optimization has +been disabled. + +At the highest level, LTO splits the compiler in two. The first half +(the ``writer'') produces a streaming representation of all the +internal data structures needed to optimize and generate code. This +includes declarations, types, the callgraph and the GIMPLE representation +of function bodies. + +When @option{-flto} is given during compilation of a source file, the +pass manager executes all the passes in @code{all_lto_gen_passes}. +Currently, this phase is composed of two IPA passes: + +@itemize @bullet +@item @code{pass_ipa_lto_gimple_out} +This pass executes the function @code{lto_output} in +@file{lto-streamer-out.cc}, which traverses the call graph encoding +every reachable declaration, type and function. This generates a +memory representation of all the file sections described below. + +@item @code{pass_ipa_lto_finish_out} +This pass executes the function @code{produce_asm_for_decls} in +@file{lto-streamer-out.cc}, which takes the memory image built in the +previous pass and encodes it in the corresponding ELF file sections. +@end itemize + +The second half of LTO support is the ``reader''. This is implemented +as the GCC front end @file{lto1} in @file{lto/lto.cc}. When +@file{collect2} detects a link set of @code{.o}/@code{.a} files with +LTO information and the @option{-flto} is enabled, it invokes +@file{lto1} which reads the set of files and aggregates them into a +single translation unit for optimization. The main entry point for +the reader is @file{lto/lto.cc}:@code{lto_main}. + +@subsection LTO modes of operation + +One of the main goals of the GCC link-time infrastructure was to allow +effective compilation of large programs. For this reason GCC implements two +link-time compilation modes. + +@enumerate +@item @emph{LTO mode}, in which the whole program is read into the +compiler at link-time and optimized in a similar way as if it +were a single source-level compilation unit. + +@item @emph{WHOPR or partitioned mode}, designed to utilize multiple +CPUs and/or a distributed compilation environment to quickly link +large applications. WHOPR stands for WHOle Program optimizeR (not to +be confused with the semantics of @option{-fwhole-program}). It +partitions the aggregated callgraph from many different @code{.o} +files and distributes the compilation of the sub-graphs to different +CPUs. + +Note that distributed compilation is not implemented yet, but since +the parallelism is facilitated via generating a @code{Makefile}, it +would be easy to implement. +@end enumerate + +WHOPR splits LTO into three main stages: +@enumerate +@item Local generation (LGEN) +This stage executes in parallel. Every file in the program is compiled +into the intermediate language and packaged together with the local +call-graph and summary information. This stage is the same for both +the LTO and WHOPR compilation mode. + +@item Whole Program Analysis (WPA) +WPA is performed sequentially. The global call-graph is generated, and +a global analysis procedure makes transformation decisions. The global +call-graph is partitioned to facilitate parallel optimization during +phase 3. The results of the WPA stage are stored into new object files +which contain the partitions of program expressed in the intermediate +language and the optimization decisions. + +@item Local transformations (LTRANS) +This stage executes in parallel. All the decisions made during phase 2 +are implemented locally in each partitioned object file, and the final +object code is generated. Optimizations which cannot be decided +efficiently during the phase 2 may be performed on the local +call-graph partitions. +@end enumerate + +WHOPR can be seen as an extension of the usual LTO mode of +compilation. In LTO, WPA and LTRANS are executed within a single +execution of the compiler, after the whole program has been read into +memory. + +When compiling in WHOPR mode, the callgraph is partitioned during +the WPA stage. The whole program is split into a given number of +partitions of roughly the same size. The compiler tries to +minimize the number of references which cross partition boundaries. +The main advantage of WHOPR is to allow the parallel execution of +LTRANS stages, which are the most time-consuming part of the +compilation process. Additionally, it avoids the need to load the +whole program into memory. + + +@node LTO object file layout +@section LTO file sections + +LTO information is stored in several ELF sections inside object files. +Data structures and enum codes for sections are defined in +@file{lto-streamer.h}. + +These sections are emitted from @file{lto-streamer-out.cc} and mapped +in all at once from @file{lto/lto.cc}:@code{lto_file_read}. The +individual functions dealing with the reading/writing of each section +are described below. + +@itemize @bullet +@item Command line options (@code{.gnu.lto_.opts}) + +This section contains the command line options used to generate the +object files. This is used at link time to determine the optimization +level and other settings when they are not explicitly specified at the +linker command line. + +Currently, GCC does not support combining LTO object files compiled +with different set of the command line options into a single binary. +At link time, the options given on the command line and the options +saved on all the files in a link-time set are applied globally. No +attempt is made at validating the combination of flags (other than the +usual validation done by option processing). This is implemented in +@file{lto/lto.cc}:@code{lto_read_all_file_options}. + + +@item Symbol table (@code{.gnu.lto_.symtab}) + +This table replaces the ELF symbol table for functions and variables +represented in the LTO IL. Symbols used and exported by the optimized +assembly code of ``fat'' objects might not match the ones used and +exported by the intermediate code. This table is necessary because +the intermediate code is less optimized and thus requires a separate +symbol table. + +Additionally, the binary code in the ``fat'' object will lack a call +to a function, since the call was optimized out at compilation time +after the intermediate language was streamed out. In some special +cases, the same optimization may not happen during link-time +optimization. This would lead to an undefined symbol if only one +symbol table was used. + +The symbol table is emitted in +@file{lto-streamer-out.cc}:@code{produce_symtab}. + + +@item Global declarations and types (@code{.gnu.lto_.decls}) + +This section contains an intermediate language dump of all +declarations and types required to represent the callgraph, static +variables and top-level debug info. + +The contents of this section are emitted in +@file{lto-streamer-out.cc}:@code{produce_asm_for_decls}. Types and +symbols are emitted in a topological order that preserves the sharing +of pointers when the file is read back in +(@file{lto.cc}:@code{read_cgraph_and_symbols}). + + +@item The callgraph (@code{.gnu.lto_.cgraph}) + +This section contains the basic data structure used by the GCC +inter-procedural optimization infrastructure. This section stores an +annotated multi-graph which represents the functions and call sites as +well as the variables, aliases and top-level @code{asm} statements. + +This section is emitted in +@file{lto-streamer-out.cc}:@code{output_cgraph} and read in +@file{lto-cgraph.cc}:@code{input_cgraph}. + + +@item IPA references (@code{.gnu.lto_.refs}) + +This section contains references between function and static +variables. It is emitted by @file{lto-cgraph.cc}:@code{output_refs} +and read by @file{lto-cgraph.cc}:@code{input_refs}. + + +@item Function bodies (@code{.gnu.lto_.function_body.}) + +This section contains function bodies in the intermediate language +representation. Every function body is in a separate section to allow +copying of the section independently to different object files or +reading the function on demand. + +Functions are emitted in +@file{lto-streamer-out.cc}:@code{output_function} and read in +@file{lto-streamer-in.cc}:@code{input_function}. + + +@item Static variable initializers (@code{.gnu.lto_.vars}) + +This section contains all the symbols in the global variable pool. It +is emitted by @file{lto-cgraph.cc}:@code{output_varpool} and read in +@file{lto-cgraph.cc}:@code{input_cgraph}. + +@item Summaries and optimization summaries used by IPA passes +(@code{.gnu.lto_.}, where @code{} is one of @code{jmpfuncs}, +@code{pureconst} or @code{reference}) + +These sections are used by IPA passes that need to emit summary +information during LTO generation to be read and aggregated at +link time. Each pass is responsible for implementing two pass manager +hooks: one for writing the summary and another for reading it in. The +format of these sections is entirely up to each individual pass. The +only requirement is that the writer and reader hooks agree on the +format. +@end itemize + + +@node IPA +@section Using summary information in IPA passes + +Programs are represented internally as a @emph{callgraph} (a +multi-graph where nodes are functions and edges are call sites) +and a @emph{varpool} (a list of static and external variables in +the program). + +The inter-procedural optimization is organized as a sequence of +individual passes, which operate on the callgraph and the +varpool. To make the implementation of WHOPR possible, every +inter-procedural optimization pass is split into several stages +that are executed at different times during WHOPR compilation: + +@itemize @bullet +@item LGEN time +@enumerate +@item @emph{Generate summary} (@code{generate_summary} in +@code{struct ipa_opt_pass_d}). This stage analyzes every function +body and variable initializer is examined and stores relevant +information into a pass-specific data structure. + +@item @emph{Write summary} (@code{write_summary} in +@code{struct ipa_opt_pass_d}). This stage writes all the +pass-specific information generated by @code{generate_summary}. +Summaries go into their own @code{LTO_section_*} sections that +have to be declared in @file{lto-streamer.h}:@code{enum +lto_section_type}. A new section is created by calling +@code{create_output_block} and data can be written using the +@code{lto_output_*} routines. +@end enumerate + +@item WPA time +@enumerate +@item @emph{Read summary} (@code{read_summary} in +@code{struct ipa_opt_pass_d}). This stage reads all the +pass-specific information in exactly the same order that it was +written by @code{write_summary}. + +@item @emph{Execute} (@code{execute} in @code{struct +opt_pass}). This performs inter-procedural propagation. This +must be done without actual access to the individual function +bodies or variable initializers. Typically, this results in a +transitive closure operation over the summary information of all +the nodes in the callgraph. + +@item @emph{Write optimization summary} +(@code{write_optimization_summary} in @code{struct +ipa_opt_pass_d}). This writes the result of the inter-procedural +propagation into the object file. This can use the same data +structures and helper routines used in @code{write_summary}. +@end enumerate + +@item LTRANS time +@enumerate +@item @emph{Read optimization summary} +(@code{read_optimization_summary} in @code{struct +ipa_opt_pass_d}). The counterpart to +@code{write_optimization_summary}. This reads the interprocedural +optimization decisions in exactly the same format emitted by +@code{write_optimization_summary}. + +@item @emph{Transform} (@code{function_transform} and +@code{variable_transform} in @code{struct ipa_opt_pass_d}). +The actual function bodies and variable initializers are updated +based on the information passed down from the @emph{Execute} stage. +@end enumerate +@end itemize + +The implementation of the inter-procedural passes are shared +between LTO, WHOPR and classic non-LTO compilation. + +@itemize +@item During the traditional file-by-file mode every pass executes its +own @emph{Generate summary}, @emph{Execute}, and @emph{Transform} +stages within the single execution context of the compiler. + +@item In LTO compilation mode, every pass uses @emph{Generate +summary} and @emph{Write summary} stages at compilation time, +while the @emph{Read summary}, @emph{Execute}, and +@emph{Transform} stages are executed at link time. + +@item In WHOPR mode all stages are used. +@end itemize + +To simplify development, the GCC pass manager differentiates +between normal inter-procedural passes (@pxref{Regular IPA passes}), +small inter-procedural passes (@pxref{Small IPA passes}) +and late inter-procedural passes (@pxref{Late IPA passes}). +A small or late IPA pass (@code{SIMPLE_IPA_PASS}) does +everything at once and thus cannot be executed during WPA in +WHOPR mode. It defines only the @emph{Execute} stage and during +this stage it accesses and modifies the function bodies. Such +passes are useful for optimization at LGEN or LTRANS time and are +used, for example, to implement early optimization before writing +object files. The simple inter-procedural passes can also be used +for easier prototyping and development of a new inter-procedural +pass. + + +@subsection Virtual clones + +One of the main challenges of introducing the WHOPR compilation +mode was addressing the interactions between optimization passes. +In LTO compilation mode, the passes are executed in a sequence, +each of which consists of analysis (or @emph{Generate summary}), +propagation (or @emph{Execute}) and @emph{Transform} stages. +Once the work of one pass is finished, the next pass sees the +updated program representation and can execute. This makes the +individual passes dependent on each other. + +In WHOPR mode all passes first execute their @emph{Generate +summary} stage. Then summary writing marks the end of the LGEN +stage. At WPA time, +the summaries are read back into memory and all passes run the +@emph{Execute} stage. Optimization summaries are streamed and +sent to LTRANS, where all the passes execute the @emph{Transform} +stage. + +Most optimization passes split naturally into analysis, +propagation and transformation stages. But some do not. The +main problem arises when one pass performs changes and the +following pass gets confused by seeing different callgraphs +between the @emph{Transform} stage and the @emph{Generate summary} +or @emph{Execute} stage. This means that the passes are required +to communicate their decisions with each other. + +To facilitate this communication, the GCC callgraph +infrastructure implements @emph{virtual clones}, a method of +representing the changes performed by the optimization passes in +the callgraph without needing to update function bodies. + +A @emph{virtual clone} in the callgraph is a function that has no +associated body, just a description of how to create its body based +on a different function (which itself may be a virtual clone). + +The description of function modifications includes adjustments to +the function's signature (which allows, for example, removing or +adding function arguments), substitutions to perform on the +function body, and, for inlined functions, a pointer to the +function that it will be inlined into. + +It is also possible to redirect any edge of the callgraph from a +function to its virtual clone. This implies updating of the call +site to adjust for the new function signature. + +Most of the transformations performed by inter-procedural +optimizations can be represented via virtual clones. For +instance, a constant propagation pass can produce a virtual clone +of the function which replaces one of its arguments by a +constant. The inliner can represent its decisions by producing a +clone of a function whose body will be later integrated into +a given function. + +Using @emph{virtual clones}, the program can be easily updated +during the @emph{Execute} stage, solving most of pass interactions +problems that would otherwise occur during @emph{Transform}. + +Virtual clones are later materialized in the LTRANS stage and +turned into real functions. Passes executed after the virtual +clone were introduced also perform their @emph{Transform} stage +on new functions, so for a pass there is no significant +difference between operating on a real function or a virtual +clone introduced before its @emph{Execute} stage. + +Optimization passes then work on virtual clones introduced before +their @emph{Execute} stage as if they were real functions. The +only difference is that clones are not visible during the +@emph{Generate Summary} stage. + +To keep function summaries updated, the callgraph interface +allows an optimizer to register a callback that is called every +time a new clone is introduced as well as when the actual +function or variable is generated or when a function or variable +is removed. These hooks are registered in the @emph{Generate +summary} stage and allow the pass to keep its information intact +until the @emph{Execute} stage. The same hooks can also be +registered during the @emph{Execute} stage to keep the +optimization summaries updated for the @emph{Transform} stage. + +@subsection IPA references + +GCC represents IPA references in the callgraph. For a function +or variable @code{A}, the @emph{IPA reference} is a list of all +locations where the address of @code{A} is taken and, when +@code{A} is a variable, a list of all direct stores and reads +to/from @code{A}. References represent an oriented multi-graph on +the union of nodes of the callgraph and the varpool. See +@file{ipa-reference.cc}:@code{ipa_reference_write_optimization_summary} +and +@file{ipa-reference.cc}:@code{ipa_reference_read_optimization_summary} +for details. + +@subsection Jump functions +Suppose that an optimization pass sees a function @code{A} and it +knows the values of (some of) its arguments. The @emph{jump +function} describes the value of a parameter of a given function +call in function @code{A} based on this knowledge. + +Jump functions are used by several optimizations, such as the +inter-procedural constant propagation pass and the +devirtualization pass. The inliner also uses jump functions to +perform inlining of callbacks. + +@node WHOPR +@section Whole program assumptions, linker plugin and symbol visibilities + +Link-time optimization gives relatively minor benefits when used +alone. The problem is that propagation of inter-procedural +information does not work well across functions and variables +that are called or referenced by other compilation units (such as +from a dynamically linked library). We say that such functions +and variables are @emph{externally visible}. + +To make the situation even more difficult, many applications +organize themselves as a set of shared libraries, and the default +ELF visibility rules allow one to overwrite any externally +visible symbol with a different symbol at runtime. This +basically disables any optimizations across such functions and +variables, because the compiler cannot be sure that the function +body it is seeing is the same function body that will be used at +runtime. Any function or variable not declared @code{static} in +the sources degrades the quality of inter-procedural +optimization. + +To avoid this problem the compiler must assume that it sees the +whole program when doing link-time optimization. Strictly +speaking, the whole program is rarely visible even at link-time. +Standard system libraries are usually linked dynamically or not +provided with the link-time information. In GCC, the whole +program option (@option{-fwhole-program}) asserts that every +function and variable defined in the current compilation +unit is static, except for function @code{main} (note: at +link time, the current unit is the union of all objects compiled +with LTO). Since some functions and variables need to +be referenced externally, for example by another DSO or from an +assembler file, GCC also provides the function and variable +attribute @code{externally_visible} which can be used to disable +the effect of @option{-fwhole-program} on a specific symbol. + +The whole program mode assumptions are slightly more complex in +C++, where inline functions in headers are put into @emph{COMDAT} +sections. COMDAT function and variables can be defined by +multiple object files and their bodies are unified at link-time +and dynamic link-time. COMDAT functions are changed to local only +when their address is not taken and thus un-sharing them with a +library is not harmful. COMDAT variables always remain externally +visible, however for readonly variables it is assumed that their +initializers cannot be overwritten by a different value. + +GCC provides the function and variable attribute +@code{visibility} that can be used to specify the visibility of +externally visible symbols (or alternatively an +@option{-fdefault-visibility} command line option). ELF defines +the @code{default}, @code{protected}, @code{hidden} and +@code{internal} visibilities. + +The most commonly used is visibility is @code{hidden}. It +specifies that the symbol cannot be referenced from outside of +the current shared library. Unfortunately, this information +cannot be used directly by the link-time optimization in the +compiler since the whole shared library also might contain +non-LTO objects and those are not visible to the compiler. + +GCC solves this problem using linker plugins. A @emph{linker +plugin} is an interface to the linker that allows an external +program to claim the ownership of a given object file. The linker +then performs the linking procedure by querying the plugin about +the symbol table of the claimed objects and once the linking +decisions are complete, the plugin is allowed to provide the +final object file before the actual linking is made. The linker +plugin obtains the symbol resolution information which specifies +which symbols provided by the claimed objects are bound from the +rest of a binary being linked. + +GCC is designed to be independent of the rest of the toolchain +and aims to support linkers without plugin support. For this +reason it does not use the linker plugin by default. Instead, +the object files are examined by @command{collect2} before being +passed to the linker and objects found to have LTO sections are +passed to @command{lto1} first. This mode does not work for +library archives. The decision on what object files from the +archive are needed depends on the actual linking and thus GCC +would have to implement the linker itself. The resolution +information is missing too and thus GCC needs to make an educated +guess based on @option{-fwhole-program}. Without the linker +plugin GCC also assumes that symbols are declared @code{hidden} +and not referred by non-LTO code by default. + +@node Internal flags +@section Internal flags controlling @code{lto1} + +The following flags are passed into @command{lto1} and are not +meant to be used directly from the command line. + +@itemize +@item -fwpa +@opindex fwpa +This option runs the serial part of the link-time optimizer +performing the inter-procedural propagation (WPA mode). The +compiler reads in summary information from all inputs and +performs an analysis based on summary information only. It +generates object files for subsequent runs of the link-time +optimizer where individual object files are optimized using both +summary information from the WPA mode and the actual function +bodies. It then drives the LTRANS phase. + +@item -fltrans +@opindex fltrans +This option runs the link-time optimizer in the +local-transformation (LTRANS) mode, which reads in output from a +previous run of the LTO in WPA mode. In the LTRANS mode, LTO +optimizes an object and produces the final assembly. + +@item -fltrans-output-list=@var{file} +@opindex fltrans-output-list +This option specifies a file to which the names of LTRANS output +files are written. This option is only meaningful in conjunction +with @option{-fwpa}. + +@item -fresolution=@var{file} +@opindex fresolution +This option specifies the linker resolution file. This option is +only meaningful in conjunction with @option{-fwpa} and as option +to pass through to the LTO linker plugin. +@end itemize diff --git a/gcc/doc/makefile.texi b/gcc/doc/makefile.texi new file mode 100644 index 00000000000..5186c1cd9d5 --- /dev/null +++ b/gcc/doc/makefile.texi @@ -0,0 +1,201 @@ +@c Copyright (C) 2001-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Makefile +@subsection Makefile Targets +@cindex makefile targets +@cindex targets, makefile + +These targets are available from the @samp{gcc} directory: + +@table @code +@item all +This is the default target. Depending on what your build/host/target +configuration is, it coordinates all the things that need to be built. + +@item doc +Produce info-formatted documentation and man pages. Essentially it +calls @samp{make man} and @samp{make info}. + +@item dvi +Produce DVI-formatted documentation. + +@item pdf +Produce PDF-formatted documentation. + +@item html +Produce HTML-formatted documentation. + +@item man +Generate man pages. + +@item info +Generate info-formatted pages. + +@item mostlyclean +Delete the files made while building the compiler. + +@item clean +That, and all the other files built by @samp{make all}. + +@item distclean +That, and all the files created by @command{configure}. + +@item maintainer-clean +Distclean plus any file that can be generated from other files. Note +that additional tools may be required beyond what is normally needed to +build GCC. + +@item srcextra +Generates files in the source directory that are not version-controlled but +should go into a release tarball. + +@item srcinfo +@itemx srcman +Copies the info-formatted and manpage documentation into the source +directory usually for the purpose of generating a release tarball. + +@item install +Installs GCC. + +@item uninstall +Deletes installed files, though this is not supported. + +@item check +Run the testsuite. This creates a @file{testsuite} subdirectory that +has various @file{.sum} and @file{.log} files containing the results of +the testing. You can run subsets with, for example, @samp{make check-gcc}. +You can specify specific tests by setting @env{RUNTESTFLAGS} to be the name +of the @file{.exp} file, optionally followed by (for some tests) an equals +and a file wildcard, like: + +@smallexample +make check-gcc RUNTESTFLAGS="execute.exp=19980413-*" +@end smallexample + +Note that running the testsuite may require additional tools be +installed, such as Tcl or DejaGnu. +@end table + +The toplevel tree from which you start GCC compilation is not +the GCC directory, but rather a complex Makefile that coordinates +the various steps of the build, including bootstrapping the compiler +and using the new compiler to build target libraries. + +When GCC is configured for a native configuration, the default action +for @command{make} is to do a full three-stage bootstrap. This means +that GCC is built three times---once with the native compiler, once with +the native-built compiler it just built, and once with the compiler it +built the second time. In theory, the last two should produce the same +results, which @samp{make compare} can check. Each stage is configured +separately and compiled into a separate directory, to minimize problems +due to ABI incompatibilities between the native compiler and GCC. + +If you do a change, rebuilding will also start from the first stage +and ``bubble'' up the change through the three stages. Each stage +is taken from its build directory (if it had been built previously), +rebuilt, and copied to its subdirectory. This will allow you to, for +example, continue a bootstrap after fixing a bug which causes the +stage2 build to crash. It does not provide as good coverage of the +compiler as bootstrapping from scratch, but it ensures that the new +code is syntactically correct (e.g., that you did not use GCC extensions +by mistake), and avoids spurious bootstrap comparison +failures@footnote{Except if the compiler was buggy and miscompiled +some of the files that were not modified. In this case, it's best +to use @command{make restrap}.}. + +Other targets available from the top level include: + +@table @code +@item bootstrap-lean +Like @code{bootstrap}, except that the various stages are removed once +they're no longer needed. This saves disk space. + +@item bootstrap2 +@itemx bootstrap2-lean +Performs only the first two stages of bootstrap. Unlike a three-stage +bootstrap, this does not perform a comparison to test that the compiler +is running properly. Note that the disk space required by a ``lean'' +bootstrap is approximately independent of the number of stages. + +@item stage@var{N}-bubble (@var{N} = 1@dots{}4, profile, feedback) +Rebuild all the stages up to @var{N}, with the appropriate flags, +``bubbling'' the changes as described above. + +@item all-stage@var{N} (@var{N} = 1@dots{}4, profile, feedback) +Assuming that stage @var{N} has already been built, rebuild it with the +appropriate flags. This is rarely needed. + +@item cleanstrap +Remove everything (@samp{make clean}) and rebuilds (@samp{make bootstrap}). + +@item compare +Compares the results of stages 2 and 3. This ensures that the compiler +is running properly, since it should produce the same object files +regardless of how it itself was compiled. + +@item distclean-stage@var{N} (@var{N} = 1@dots{}4, profile, feedback) +Wipe stage @var{N} and all the following ones. + +For example, +@samp{make distclean-stage3} wipes stage 3 and all the following ones, +so that another @command{make} then rebuilds them from scratch. +This can be useful if you're doing changes where +``bubbling'' the changes as described above is not sufficient, +but a full @command{make restrap} isn't necessary either. + +@item profiledbootstrap +Builds a compiler with profiling feedback information. In this case, +the second and third stages are named @samp{profile} and @samp{feedback}, +respectively. For more information, see the installation instructions. + +@item restrap +Restart a bootstrap, so that everything that was not built with +the system compiler is rebuilt. + +@item stage@var{N}-start (@var{N} = 1@dots{}4, profile, feedback) +For each package that is bootstrapped, rename directories so that, +for example, @file{gcc} points to the stage@var{N} GCC, compiled +with the stage@var{N-1} GCC@footnote{Customarily, the system compiler +is also termed the @file{stage0} GCC.}. + +You will invoke this target if you need to test or debug the +stage@var{N} GCC@. If you only need to execute GCC (but you need +not run @samp{make} either to rebuild it or to run test suites), +you should be able to work directly in the @file{stage@var{N}-gcc} +directory. This makes it easier to debug multiple stages in +parallel. + +@item stage +For each package that is bootstrapped, relocate its build directory +to indicate its stage. For example, if the @file{gcc} directory +points to the stage2 GCC, after invoking this target it will be +renamed to @file{stage2-gcc}. + +@end table + +If you wish to use non-default GCC flags when compiling the stage2 and +stage3 compilers, set @code{BOOT_CFLAGS} on the command line when doing +@samp{make}. + +Usually, the first stage only builds the languages that the compiler +is written in: typically, C and maybe Ada. If you are debugging a +miscompilation of a different stage2 front-end (for example, of the +Fortran front-end), you may want to have front-ends for other languages +in the first stage as well. To do so, set @code{STAGE1_LANGUAGES} +on the command line when doing @samp{make}. + +For example, in the aforementioned scenario of debugging a Fortran +front-end miscompilation caused by the stage1 compiler, you may need a +command like + +@example +make stage2-bubble STAGE1_LANGUAGES=c,fortran +@end example + +Alternatively, you can use per-language targets to build and test +languages that are not enabled by default in stage1. For example, +@command{make f951} will build a Fortran compiler even in the stage1 +build directory. + diff --git a/gcc/doc/match-and-simplify.texi b/gcc/doc/match-and-simplify.texi new file mode 100644 index 00000000000..b33d83518a7 --- /dev/null +++ b/gcc/doc/match-and-simplify.texi @@ -0,0 +1,453 @@ +@c Copyright (C) 2014-2022 Free Software Foundation, Inc. +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Match and Simplify +@chapter Match and Simplify +@cindex Match and Simplify + +The GIMPLE and GENERIC pattern matching project match-and-simplify +tries to address several issues. + +@enumerate +@item unify expression simplifications currently spread and duplicated + over separate files like fold-const.cc, gimple-fold.cc and builtins.cc +@item allow for a cheap way to implement building and simplifying + non-trivial GIMPLE expressions, avoiding the need to go through + building and simplifying GENERIC via fold_buildN and then + gimplifying via force_gimple_operand +@end enumerate + +To address these the project introduces a simple domain-specific language +to write expression simplifications from which code targeting GIMPLE +and GENERIC is auto-generated. The GENERIC variant follows the +fold_buildN API while for the GIMPLE variant and to address 2) new +APIs are introduced. + +@menu +* GIMPLE API:: +* The Language:: +@end menu + +@node GIMPLE API +@section GIMPLE API +@cindex GIMPLE API + +@deftypefn {GIMPLE function} tree gimple_simplify (enum tree_code, tree, tree, gimple_seq *, tree (*)(tree)) +@deftypefnx {GIMPLE function} tree gimple_simplify (enum tree_code, tree, tree, tree, gimple_seq *, tree (*)(tree)) +@deftypefnx {GIMPLE function} tree gimple_simplify (enum tree_code, tree, tree, tree, tree, gimple_seq *, tree (*)(tree)) +@deftypefnx {GIMPLE function} tree gimple_simplify (enum built_in_function, tree, tree, gimple_seq *, tree (*)(tree)) +@deftypefnx {GIMPLE function} tree gimple_simplify (enum built_in_function, tree, tree, tree, gimple_seq *, tree (*)(tree)) +@deftypefnx {GIMPLE function} tree gimple_simplify (enum built_in_function, tree, tree, tree, tree, gimple_seq *, tree (*)(tree)) +The main GIMPLE API entry to the expression simplifications mimicking +that of the GENERIC fold_@{unary,binary,ternary@} functions. +@end deftypefn + +thus providing n-ary overloads for operation or function. The +additional arguments are a gimple_seq where built statements are +inserted on (if @code{NULL} then simplifications requiring new statements +are not performed) and a valueization hook that can be used to +tie simplifications to a SSA lattice. + +In addition to those APIs @code{fold_stmt} is overloaded with +a valueization hook: + +@deftypefn bool fold_stmt (gimple_stmt_iterator *, tree (*)(tree)); +@end deftypefn + + +On top of these a @code{fold_buildN}-like API for GIMPLE is introduced: + +@deftypefn {GIMPLE function} tree gimple_build (gimple_seq *, location_t, enum tree_code, tree, tree, tree (*valueize) (tree) = NULL); +@deftypefnx {GIMPLE function} tree gimple_build (gimple_seq *, location_t, enum tree_code, tree, tree, tree, tree (*valueize) (tree) = NULL); +@deftypefnx {GIMPLE function} tree gimple_build (gimple_seq *, location_t, enum tree_code, tree, tree, tree, tree, tree (*valueize) (tree) = NULL); +@deftypefnx {GIMPLE function} tree gimple_build (gimple_seq *, location_t, enum built_in_function, tree, tree, tree (*valueize) (tree) = NULL); +@deftypefnx {GIMPLE function} tree gimple_build (gimple_seq *, location_t, enum built_in_function, tree, tree, tree, tree (*valueize) (tree) = NULL); +@deftypefnx {GIMPLE function} tree gimple_build (gimple_seq *, location_t, enum built_in_function, tree, tree, tree, tree, tree (*valueize) (tree) = NULL); +@deftypefnx {GIMPLE function} tree gimple_convert (gimple_seq *, location_t, tree, tree); +@end deftypefn + +which is supposed to replace @code{force_gimple_operand (fold_buildN (...), ...)} +and calls to @code{fold_convert}. Overloads without the @code{location_t} +argument exist. Built statements are inserted on the provided sequence +and simplification is performed using the optional valueization hook. + + +@node The Language +@section The Language +@cindex The Language + +The language in which to write expression simplifications resembles +other domain-specific languages GCC uses. Thus it is lispy. Let's +start with an example from the match.pd file: + +@smallexample +(simplify + (bit_and @@0 integer_all_onesp) + @@0) +@end smallexample + +This example contains all required parts of an expression simplification. +A simplification is wrapped inside a @code{(simplify ...)} expression. +That contains at least two operands - an expression that is matched +with the GIMPLE or GENERIC IL and a replacement expression that is +returned if the match was successful. + +Expressions have an operator ID, @code{bit_and} in this case. Expressions can +be lower-case tree codes with @code{_expr} stripped off or builtin +function code names in all-caps, like @code{BUILT_IN_SQRT}. + +@code{@@n} denotes a so-called capture. It captures the operand and lets +you refer to it in other places of the match-and-simplify. In the +above example it is referred to in the replacement expression. Captures +are @code{@@} followed by a number or an identifier. + +@smallexample +(simplify + (bit_xor @@0 @@0) + @{ build_zero_cst (type); @}) +@end smallexample + +In this example @code{@@0} is mentioned twice which constrains the matched +expression to have two equal operands. Usually matches are constrained +to equal types. If operands may be constants and conversions are involved, +matching by value might be preferred in which case use @code{@@@@0} to +denote a by-value match and the specific operand you want to refer to +in the result part. This example also introduces +operands written in C code. These can be used in the expression +replacements and are supposed to evaluate to a tree node which has to +be a valid GIMPLE operand (so you cannot generate expressions in C code). + +@smallexample +(simplify + (trunc_mod integer_zerop@@0 @@1) + (if (!integer_zerop (@@1)) + @@0)) +@end smallexample + +Here @code{@@0} captures the first operand of the trunc_mod expression +which is also predicated with @code{integer_zerop}. Expression operands +may be either expressions, predicates or captures. Captures +can be unconstrained or capture expressions or predicates. + +This example introduces an optional operand of simplify, +the if-expression. This condition is evaluated after the +expression matched in the IL and is required to evaluate to true +to enable the replacement expression in the second operand +position. The expression operand of the @code{if} is a standard C +expression which may contain references to captures. The @code{if} +has an optional third operand which may contain the replacement +expression that is enabled when the condition evaluates to false. + +A @code{if} expression can be used to specify a common condition +for multiple simplify patterns, avoiding the need +to repeat that multiple times: + +@smallexample +(if (!TYPE_SATURATING (type) + && !FLOAT_TYPE_P (type) && !FIXED_POINT_TYPE_P (type)) + (simplify + (minus (plus @@0 @@1) @@0) + @@1) + (simplify + (minus (minus @@0 @@1) @@0) + (negate @@1))) +@end smallexample + +Note that @code{if}s in outer position do not have the optional +else clause but instead have multiple then clauses. + +Ifs can be nested. + +There exists a @code{switch} expression which can be used to +chain conditions avoiding nesting @code{if}s too much: + +@smallexample +(simplify + (simple_comparison @@0 REAL_CST@@1) + (switch + /* a CMP (-0) -> a CMP 0 */ + (if (REAL_VALUE_MINUS_ZERO (TREE_REAL_CST (@@1))) + (cmp @@0 @{ build_real (TREE_TYPE (@@1), dconst0); @})) + /* x != NaN is always true, other ops are always false. */ + (if (REAL_VALUE_ISNAN (TREE_REAL_CST (@@1)) + && ! HONOR_SNANS (@@1)) + @{ constant_boolean_node (cmp == NE_EXPR, type); @}))) +@end smallexample + +Is equal to + +@smallexample +(simplify + (simple_comparison @@0 REAL_CST@@1) + (switch + /* a CMP (-0) -> a CMP 0 */ + (if (REAL_VALUE_MINUS_ZERO (TREE_REAL_CST (@@1))) + (cmp @@0 @{ build_real (TREE_TYPE (@@1), dconst0); @}) + /* x != NaN is always true, other ops are always false. */ + (if (REAL_VALUE_ISNAN (TREE_REAL_CST (@@1)) + && ! HONOR_SNANS (@@1)) + @{ constant_boolean_node (cmp == NE_EXPR, type); @})))) +@end smallexample + +which has the second @code{if} in the else operand of the first. +The @code{switch} expression takes @code{if} expressions as +operands (which may not have else clauses) and as a last operand +a replacement expression which should be enabled by default if +no other condition evaluated to true. + +Captures can also be used for capturing results of sub-expressions. + +@smallexample +#if GIMPLE +(simplify + (pointer_plus (addr@@2 @@0) INTEGER_CST_P@@1) + (if (is_gimple_min_invariant (@@2))) + @{ + poly_int64 off; + tree base = get_addr_base_and_unit_offset (@@0, &off); + off += tree_to_uhwi (@@1); + /* Now with that we should be able to simply write + (addr (mem_ref (addr @@base) (plus @@off @@1))) */ + build1 (ADDR_EXPR, type, + build2 (MEM_REF, TREE_TYPE (TREE_TYPE (@@2)), + build_fold_addr_expr (base), + build_int_cst (ptr_type_node, off))); + @}) +#endif +@end smallexample + +In the above example, @code{@@2} captures the result of the expression +@code{(addr @@0)}. For the outermost expression only its type can be +captured, and the keyword @code{type} is reserved for this purpose. The +above example also gives a way to conditionalize patterns to only apply +to @code{GIMPLE} or @code{GENERIC} by means of using the pre-defined +preprocessor macros @code{GIMPLE} and @code{GENERIC} and using +preprocessor directives. + +@smallexample +(simplify + (bit_and:c integral_op_p@@0 (bit_ior:c (bit_not @@0) @@1)) + (bit_and @@1 @@0)) +@end smallexample + +Here we introduce flags on match expressions. The flag used +above, @code{c}, denotes that the expression should +be also matched commutated. Thus the above match expression +is really the following four match expressions: + +@smallexample + (bit_and integral_op_p@@0 (bit_ior (bit_not @@0) @@1)) + (bit_and (bit_ior (bit_not @@0) @@1) integral_op_p@@0) + (bit_and integral_op_p@@0 (bit_ior @@1 (bit_not @@0))) + (bit_and (bit_ior @@1 (bit_not @@0)) integral_op_p@@0) +@end smallexample + +Usual canonicalizations you know from GENERIC expressions are +applied before matching, so for example constant operands always +come second in commutative expressions. + +The second supported flag is @code{s} which tells the code +generator to fail the pattern if the expression marked with +@code{s} does have more than one use and the simplification +results in an expression with more than one operator. +For example in + +@smallexample +(simplify + (pointer_plus (pointer_plus:s @@0 @@1) @@3) + (pointer_plus @@0 (plus @@1 @@3))) +@end smallexample + +this avoids the association if @code{(pointer_plus @@0 @@1)} is +used outside of the matched expression and thus it would stay +live and not trivially removed by dead code elimination. +Now consider @code{((x + 3) + -3)} with the temporary +holding @code{(x + 3)} used elsewhere. This simplifies down +to @code{x} which is desirable and thus flagging with @code{s} +does not prevent the transform. Now consider @code{((x + 3) + 1)} +which simplifies to @code{(x + 4)}. Despite being flagged with +@code{s} the simplification will be performed. The +simplification of @code{((x + a) + 1)} to @code{(x + (a + 1))} will +not performed in this case though. + +More features exist to avoid too much repetition. + +@smallexample +(for op (plus pointer_plus minus bit_ior bit_xor) + (simplify + (op @@0 integer_zerop) + @@0)) +@end smallexample + +A @code{for} expression can be used to repeat a pattern for each +operator specified, substituting @code{op}. @code{for} can be +nested and a @code{for} can have multiple operators to iterate. + +@smallexample +(for opa (plus minus) + opb (minus plus) + (for opc (plus minus) + (simplify... +@end smallexample + +In this example the pattern will be repeated four times with +@code{opa, opb, opc} being @code{plus, minus, plus}; +@code{plus, minus, minus}; @code{minus, plus, plus}; +@code{minus, plus, minus}. + +To avoid repeating operator lists in @code{for} you can name +them via + +@smallexample +(define_operator_list pmm plus minus mult) +@end smallexample + +and use them in @code{for} operator lists where they get expanded. + +@smallexample +(for opa (pmm trunc_div) + (simplify... +@end smallexample + +So this example iterates over @code{plus}, @code{minus}, @code{mult} +and @code{trunc_div}. + +Using operator lists can also remove the need to explicitly write +a @code{for}. All operator list uses that appear in a @code{simplify} +or @code{match} pattern in operator positions will implicitly +be added to a new @code{for}. For example + +@smallexample +(define_operator_list SQRT BUILT_IN_SQRTF BUILT_IN_SQRT BUILT_IN_SQRTL) +(define_operator_list POW BUILT_IN_POWF BUILT_IN_POW BUILT_IN_POWL) +(simplify + (SQRT (POW @@0 @@1)) + (POW (abs @@0) (mult @@1 @{ built_real (TREE_TYPE (@@1), dconsthalf); @}))) +@end smallexample + +is the same as + +@smallexample +(for SQRT (BUILT_IN_SQRTF BUILT_IN_SQRT BUILT_IN_SQRTL) + POW (BUILT_IN_POWF BUILT_IN_POW BUILT_IN_POWL) + (simplify + (SQRT (POW @@0 @@1)) + (POW (abs @@0) (mult @@1 @{ built_real (TREE_TYPE (@@1), dconsthalf); @})))) +@end smallexample + +@code{for}s and operator lists can include the special identifier +@code{null} that matches nothing and can never be generated. This can +be used to pad an operator list so that it has a standard form, +even if there isn't a suitable operator for every form. + +Another building block are @code{with} expressions in the +result expression which nest the generated code in a new C block +followed by its argument: + +@smallexample +(simplify + (convert (mult @@0 @@1)) + (with @{ tree utype = unsigned_type_for (type); @} + (convert (mult (convert:utype @@0) (convert:utype @@1))))) +@end smallexample + +This allows code nested in the @code{with} to refer to the declared +variables. In the above case we use the feature to specify the +type of a generated expression with the @code{:type} syntax where +@code{type} needs to be an identifier that refers to the desired type. +Usually the types of the generated result expressions are +determined from the context, but sometimes like in the above case +it is required that you specify them explicitly. + +Another modifier for generated expressions is @code{!} which +tells the machinery to only consider the simplification in case +the marked expression simplified to a simple operand. Consider +for example + +@smallexample +(simplify + (plus (vec_cond:s @@0 @@1 @@2) @@3) + (vec_cond @@0 (plus! @@1 @@3) (plus! @@2 @@3))) +@end smallexample + +which moves the outer @code{plus} operation to the inner arms +of the @code{vec_cond} expression but only if the actual plus +operations both simplify. Note that on @code{GENERIC} a simple +operand means that the result satisfies @code{!EXPR_P} which +can be limiting if the operation itself simplifies but the +remaining operand is an (unrelated) expression. + +As intermediate conversions are often optional there is a way to +avoid the need to repeat patterns both with and without such +conversions. Namely you can mark a conversion as being optional +with a @code{?}: + +@smallexample +(simplify + (eq (convert@@0 @@1) (convert@? @@2)) + (eq @@1 (convert @@2))) +@end smallexample + +which will match both @code{(eq (convert @@1) (convert @@2))} and +@code{(eq (convert @@1) @@2)}. The optional converts are supposed +to be all either present or not, thus +@code{(eq (convert@? @@1) (convert@? @@2))} will result in two +patterns only. If you want to match all four combinations you +have access to two additional conditional converts as in +@code{(eq (convert1@? @@1) (convert2@? @@2))}. + +The support for @code{?} marking extends to all unary operations +including predicates you declare yourself with @code{match}. + +Predicates available from the GCC middle-end need to be made +available explicitly via @code{define_predicates}: + +@smallexample +(define_predicates + integer_onep integer_zerop integer_all_onesp) +@end smallexample + +You can also define predicates using the pattern matching language +and the @code{match} form: + +@smallexample +(match negate_expr_p + INTEGER_CST + (if (TYPE_OVERFLOW_WRAPS (type) + || may_negate_without_overflow_p (t)))) +(match negate_expr_p + (negate @@0)) +@end smallexample + +This shows that for @code{match} expressions there is @code{t} +available which captures the outermost expression (something +not possible in the @code{simplify} context). As you can see +@code{match} has an identifier as first operand which is how +you refer to the predicate in patterns. Multiple @code{match} +for the same identifier add additional cases where the predicate +matches. + +Predicates can also match an expression in which case you need +to provide a template specifying the identifier and where to +get its operands from: + +@smallexample +(match (logical_inverted_value @@0) + (eq @@0 integer_zerop)) +(match (logical_inverted_value @@0) + (bit_not truth_valued_p@@0)) +@end smallexample + +You can use the above predicate like + +@smallexample +(simplify + (bit_and @@0 (logical_inverted_value @@0)) + @{ build_zero_cst (type); @}) +@end smallexample + +Which will match a bitwise and of an operand with its logical +inverted value. + diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi new file mode 100644 index 00000000000..d0a71ecbb80 --- /dev/null +++ b/gcc/doc/md.texi @@ -0,0 +1,11679 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@ifset INTERNALS +@node Machine Desc +@chapter Machine Descriptions +@cindex machine descriptions + +A machine description has two parts: a file of instruction patterns +(@file{.md} file) and a C header file of macro definitions. + +The @file{.md} file for a target machine contains a pattern for each +instruction that the target machine supports (or at least each instruction +that is worth telling the compiler about). It may also contain comments. +A semicolon causes the rest of the line to be a comment, unless the semicolon +is inside a quoted string. + +See the next chapter for information on the C header file. + +@menu +* Overview:: How the machine description is used. +* Patterns:: How to write instruction patterns. +* Example:: An explained example of a @code{define_insn} pattern. +* RTL Template:: The RTL template defines what insns match a pattern. +* Output Template:: The output template says how to make assembler code + from such an insn. +* Output Statement:: For more generality, write C code to output + the assembler code. +* Predicates:: Controlling what kinds of operands can be used + for an insn. +* Constraints:: Fine-tuning operand selection. +* Standard Names:: Names mark patterns to use for code generation. +* Pattern Ordering:: When the order of patterns makes a difference. +* Dependent Patterns:: Having one pattern may make you need another. +* Jump Patterns:: Special considerations for patterns for jump insns. +* Looping Patterns:: How to define patterns for special looping insns. +* Insn Canonicalizations::Canonicalization of Instructions +* Expander Definitions::Generating a sequence of several RTL insns + for a standard operation. +* Insn Splitting:: Splitting Instructions into Multiple Instructions. +* Including Patterns:: Including Patterns in Machine Descriptions. +* Peephole Definitions::Defining machine-specific peephole optimizations. +* Insn Attributes:: Specifying the value of attributes for generated insns. +* Conditional Execution::Generating @code{define_insn} patterns for + predication. +* Define Subst:: Generating @code{define_insn} and @code{define_expand} + patterns from other patterns. +* Constant Definitions::Defining symbolic constants that can be used in the + md file. +* Iterators:: Using iterators to generate patterns from a template. +@end menu + +@node Overview +@section Overview of How the Machine Description is Used + +There are three main conversions that happen in the compiler: + +@enumerate + +@item +The front end reads the source code and builds a parse tree. + +@item +The parse tree is used to generate an RTL insn list based on named +instruction patterns. + +@item +The insn list is matched against the RTL templates to produce assembler +code. + +@end enumerate + +For the generate pass, only the names of the insns matter, from either a +named @code{define_insn} or a @code{define_expand}. The compiler will +choose the pattern with the right name and apply the operands according +to the documentation later in this chapter, without regard for the RTL +template or operand constraints. Note that the names the compiler looks +for are hard-coded in the compiler---it will ignore unnamed patterns and +patterns with names it doesn't know about, but if you don't provide a +named pattern it needs, it will abort. + +If a @code{define_insn} is used, the template given is inserted into the +insn list. If a @code{define_expand} is used, one of three things +happens, based on the condition logic. The condition logic may manually +create new insns for the insn list, say via @code{emit_insn()}, and +invoke @code{DONE}. For certain named patterns, it may invoke @code{FAIL} to tell the +compiler to use an alternate way of performing that task. If it invokes +neither @code{DONE} nor @code{FAIL}, the template given in the pattern +is inserted, as if the @code{define_expand} were a @code{define_insn}. + +Once the insn list is generated, various optimization passes convert, +replace, and rearrange the insns in the insn list. This is where the +@code{define_split} and @code{define_peephole} patterns get used, for +example. + +Finally, the insn list's RTL is matched up with the RTL templates in the +@code{define_insn} patterns, and those patterns are used to emit the +final assembly code. For this purpose, each named @code{define_insn} +acts like it's unnamed, since the names are ignored. + +@node Patterns +@section Everything about Instruction Patterns +@cindex patterns +@cindex instruction patterns + +@findex define_insn +A @code{define_insn} expression is used to define instruction patterns +to which insns may be matched. A @code{define_insn} expression contains +an incomplete RTL expression, with pieces to be filled in later, operand +constraints that restrict how the pieces can be filled in, and an output +template or C code to generate the assembler output. + +A @code{define_insn} is an RTL expression containing four or five operands: + +@enumerate +@item +An optional name @var{n}. When a name is present, the compiler +automically generates a C++ function @samp{gen_@var{n}} that takes +the operands of the instruction as arguments and returns the instruction's +rtx pattern. The compiler also assigns the instruction a unique code +@samp{CODE_FOR_@var{n}}, with all such codes belonging to an enum +called @code{insn_code}. + +These names serve one of two purposes. The first is to indicate that the +instruction performs a certain standard job for the RTL-generation +pass of the compiler, such as a move, an addition, or a conditional +jump. The second is to help the target generate certain target-specific +operations, such as when implementing target-specific intrinsic functions. + +It is better to prefix target-specific names with the name of the +target, to avoid any clash with current or future standard names. + +The absence of a name is indicated by writing an empty string +where the name should go. Nameless instruction patterns are never +used for generating RTL code, but they may permit several simpler insns +to be combined later on. + +For the purpose of debugging the compiler, you may also specify a +name beginning with the @samp{*} character. Such a name is used only +for identifying the instruction in RTL dumps; it is equivalent to having +a nameless pattern for all other purposes. Names beginning with the +@samp{*} character are not required to be unique. + +The name may also have the form @samp{@@@var{n}}. This has the same +effect as a name @samp{@var{n}}, but in addition tells the compiler to +generate further helper functions; see @ref{Parameterized Names} for details. + +@item +The @dfn{RTL template}: This is a vector of incomplete RTL expressions +which describe the semantics of the instruction (@pxref{RTL Template}). +It is incomplete because it may contain @code{match_operand}, +@code{match_operator}, and @code{match_dup} expressions that stand for +operands of the instruction. + +If the vector has multiple elements, the RTL template is treated as a +@code{parallel} expression. + +@item +@cindex pattern conditions +@cindex conditions, in patterns +The condition: This is a string which contains a C expression. When the +compiler attempts to match RTL against a pattern, the condition is +evaluated. If the condition evaluates to @code{true}, the match is +permitted. The condition may be an empty string, which is treated +as always @code{true}. + +@cindex named patterns and conditions +For a named pattern, the condition may not depend on the data in the +insn being matched, but only the target-machine-type flags. The compiler +needs to test these conditions during initialization in order to learn +exactly which named instructions are available in a particular run. + +@findex operands +For nameless patterns, the condition is applied only when matching an +individual insn, and only after the insn has matched the pattern's +recognition template. The insn's operands may be found in the vector +@code{operands}. + +An instruction condition cannot become more restrictive as compilation +progresses. If the condition accepts a particular RTL instruction at +one stage of compilation, it must continue to accept that instruction +until the final pass. For example, @samp{!reload_completed} and +@samp{can_create_pseudo_p ()} are both invalid instruction conditions, +because they are true during the earlier RTL passes and false during +the later ones. For the same reason, if a condition accepts an +instruction before register allocation, it cannot later try to control +register allocation by excluding certain register or value combinations. + +Although a condition cannot become more restrictive as compilation +progresses, the condition for a nameless pattern @emph{can} become +more permissive. For example, a nameless instruction can require +@samp{reload_completed} to be true, in which case it only matches +after register allocation. + +@item +The @dfn{output template} or @dfn{output statement}: This is either +a string, or a fragment of C code which returns a string. + +When simple substitution isn't general enough, you can specify a piece +of C code to compute the output. @xref{Output Statement}. + +@item +The @dfn{insn attributes}: This is an optional vector containing the values of +attributes for insns matching this pattern (@pxref{Insn Attributes}). +@end enumerate + +@node Example +@section Example of @code{define_insn} +@cindex @code{define_insn} example + +Here is an example of an instruction pattern, taken from the machine +description for the 68000/68020. + +@smallexample +(define_insn "tstsi" + [(set (cc0) + (match_operand:SI 0 "general_operand" "rm"))] + "" + "* +@{ + if (TARGET_68020 || ! ADDRESS_REG_P (operands[0])) + return \"tstl %0\"; + return \"cmpl #0,%0\"; +@}") +@end smallexample + +@noindent +This can also be written using braced strings: + +@smallexample +(define_insn "tstsi" + [(set (cc0) + (match_operand:SI 0 "general_operand" "rm"))] + "" +@{ + if (TARGET_68020 || ! ADDRESS_REG_P (operands[0])) + return "tstl %0"; + return "cmpl #0,%0"; +@}) +@end smallexample + +This describes an instruction which sets the condition codes based on the +value of a general operand. It has no condition, so any insn with an RTL +description of the form shown may be matched to this pattern. The name +@samp{tstsi} means ``test a @code{SImode} value'' and tells the RTL +generation pass that, when it is necessary to test such a value, an insn +to do so can be constructed using this pattern. + +The output control string is a piece of C code which chooses which +output template to return based on the kind of operand and the specific +type of CPU for which code is being generated. + +@samp{"rm"} is an operand constraint. Its meaning is explained below. + +@node RTL Template +@section RTL Template +@cindex RTL insn template +@cindex generating insns +@cindex insns, generating +@cindex recognizing insns +@cindex insns, recognizing + +The RTL template is used to define which insns match the particular pattern +and how to find their operands. For named patterns, the RTL template also +says how to construct an insn from specified operands. + +Construction involves substituting specified operands into a copy of the +template. Matching involves determining the values that serve as the +operands in the insn being matched. Both of these activities are +controlled by special expression types that direct matching and +substitution of the operands. + +@table @code +@findex match_operand +@item (match_operand:@var{m} @var{n} @var{predicate} @var{constraint}) +This expression is a placeholder for operand number @var{n} of +the insn. When constructing an insn, operand number @var{n} +will be substituted at this point. When matching an insn, whatever +appears at this position in the insn will be taken as operand +number @var{n}; but it must satisfy @var{predicate} or this instruction +pattern will not match at all. + +Operand numbers must be chosen consecutively counting from zero in +each instruction pattern. There may be only one @code{match_operand} +expression in the pattern for each operand number. Usually operands +are numbered in the order of appearance in @code{match_operand} +expressions. In the case of a @code{define_expand}, any operand numbers +used only in @code{match_dup} expressions have higher values than all +other operand numbers. + +@var{predicate} is a string that is the name of a function that +accepts two arguments, an expression and a machine mode. +@xref{Predicates}. During matching, the function will be called with +the putative operand as the expression and @var{m} as the mode +argument (if @var{m} is not specified, @code{VOIDmode} will be used, +which normally causes @var{predicate} to accept any mode). If it +returns zero, this instruction pattern fails to match. +@var{predicate} may be an empty string; then it means no test is to be +done on the operand, so anything which occurs in this position is +valid. + +Most of the time, @var{predicate} will reject modes other than @var{m}---but +not always. For example, the predicate @code{address_operand} uses +@var{m} as the mode of memory ref that the address should be valid for. +Many predicates accept @code{const_int} nodes even though their mode is +@code{VOIDmode}. + +@var{constraint} controls reloading and the choice of the best register +class to use for a value, as explained later (@pxref{Constraints}). +If the constraint would be an empty string, it can be omitted. + +People are often unclear on the difference between the constraint and the +predicate. The predicate helps decide whether a given insn matches the +pattern. The constraint plays no role in this decision; instead, it +controls various decisions in the case of an insn which does match. + +@findex match_scratch +@item (match_scratch:@var{m} @var{n} @var{constraint}) +This expression is also a placeholder for operand number @var{n} +and indicates that operand must be a @code{scratch} or @code{reg} +expression. + +When matching patterns, this is equivalent to + +@smallexample +(match_operand:@var{m} @var{n} "scratch_operand" @var{constraint}) +@end smallexample + +but, when generating RTL, it produces a (@code{scratch}:@var{m}) +expression. + +If the last few expressions in a @code{parallel} are @code{clobber} +expressions whose operands are either a hard register or +@code{match_scratch}, the combiner can add or delete them when +necessary. @xref{Side Effects}. + +@findex match_dup +@item (match_dup @var{n}) +This expression is also a placeholder for operand number @var{n}. +It is used when the operand needs to appear more than once in the +insn. + +In construction, @code{match_dup} acts just like @code{match_operand}: +the operand is substituted into the insn being constructed. But in +matching, @code{match_dup} behaves differently. It assumes that operand +number @var{n} has already been determined by a @code{match_operand} +appearing earlier in the recognition template, and it matches only an +identical-looking expression. + +Note that @code{match_dup} should not be used to tell the compiler that +a particular register is being used for two operands (example: +@code{add} that adds one register to another; the second register is +both an input operand and the output operand). Use a matching +constraint (@pxref{Simple Constraints}) for those. @code{match_dup} is for the cases where one +operand is used in two places in the template, such as an instruction +that computes both a quotient and a remainder, where the opcode takes +two input operands but the RTL template has to refer to each of those +twice; once for the quotient pattern and once for the remainder pattern. + +@findex match_operator +@item (match_operator:@var{m} @var{n} @var{predicate} [@var{operands}@dots{}]) +This pattern is a kind of placeholder for a variable RTL expression +code. + +When constructing an insn, it stands for an RTL expression whose +expression code is taken from that of operand @var{n}, and whose +operands are constructed from the patterns @var{operands}. + +When matching an expression, it matches an expression if the function +@var{predicate} returns nonzero on that expression @emph{and} the +patterns @var{operands} match the operands of the expression. + +Suppose that the function @code{commutative_operator} is defined as +follows, to match any expression whose operator is one of the +commutative arithmetic operators of RTL and whose mode is @var{mode}: + +@smallexample +int +commutative_integer_operator (x, mode) + rtx x; + machine_mode mode; +@{ + enum rtx_code code = GET_CODE (x); + if (GET_MODE (x) != mode) + return 0; + return (GET_RTX_CLASS (code) == RTX_COMM_ARITH + || code == EQ || code == NE); +@} +@end smallexample + +Then the following pattern will match any RTL expression consisting +of a commutative operator applied to two general operands: + +@smallexample +(match_operator:SI 3 "commutative_operator" + [(match_operand:SI 1 "general_operand" "g") + (match_operand:SI 2 "general_operand" "g")]) +@end smallexample + +Here the vector @code{[@var{operands}@dots{}]} contains two patterns +because the expressions to be matched all contain two operands. + +When this pattern does match, the two operands of the commutative +operator are recorded as operands 1 and 2 of the insn. (This is done +by the two instances of @code{match_operand}.) Operand 3 of the insn +will be the entire commutative expression: use @code{GET_CODE +(operands[3])} to see which commutative operator was used. + +The machine mode @var{m} of @code{match_operator} works like that of +@code{match_operand}: it is passed as the second argument to the +predicate function, and that function is solely responsible for +deciding whether the expression to be matched ``has'' that mode. + +When constructing an insn, argument 3 of the gen-function will specify +the operation (i.e.@: the expression code) for the expression to be +made. It should be an RTL expression, whose expression code is copied +into a new expression whose operands are arguments 1 and 2 of the +gen-function. The subexpressions of argument 3 are not used; +only its expression code matters. + +When @code{match_operator} is used in a pattern for matching an insn, +it usually best if the operand number of the @code{match_operator} +is higher than that of the actual operands of the insn. This improves +register allocation because the register allocator often looks at +operands 1 and 2 of insns to see if it can do register tying. + +There is no way to specify constraints in @code{match_operator}. The +operand of the insn which corresponds to the @code{match_operator} +never has any constraints because it is never reloaded as a whole. +However, if parts of its @var{operands} are matched by +@code{match_operand} patterns, those parts may have constraints of +their own. + +@findex match_op_dup +@item (match_op_dup:@var{m} @var{n}[@var{operands}@dots{}]) +Like @code{match_dup}, except that it applies to operators instead of +operands. When constructing an insn, operand number @var{n} will be +substituted at this point. But in matching, @code{match_op_dup} behaves +differently. It assumes that operand number @var{n} has already been +determined by a @code{match_operator} appearing earlier in the +recognition template, and it matches only an identical-looking +expression. + +@findex match_parallel +@item (match_parallel @var{n} @var{predicate} [@var{subpat}@dots{}]) +This pattern is a placeholder for an insn that consists of a +@code{parallel} expression with a variable number of elements. This +expression should only appear at the top level of an insn pattern. + +When constructing an insn, operand number @var{n} will be substituted at +this point. When matching an insn, it matches if the body of the insn +is a @code{parallel} expression with at least as many elements as the +vector of @var{subpat} expressions in the @code{match_parallel}, if each +@var{subpat} matches the corresponding element of the @code{parallel}, +@emph{and} the function @var{predicate} returns nonzero on the +@code{parallel} that is the body of the insn. It is the responsibility +of the predicate to validate elements of the @code{parallel} beyond +those listed in the @code{match_parallel}. + +A typical use of @code{match_parallel} is to match load and store +multiple expressions, which can contain a variable number of elements +in a @code{parallel}. For example, + +@smallexample +(define_insn "" + [(match_parallel 0 "load_multiple_operation" + [(set (match_operand:SI 1 "gpc_reg_operand" "=r") + (match_operand:SI 2 "memory_operand" "m")) + (use (reg:SI 179)) + (clobber (reg:SI 179))])] + "" + "loadm 0,0,%1,%2") +@end smallexample + +This example comes from @file{a29k.md}. The function +@code{load_multiple_operation} is defined in @file{a29k.c} and checks +that subsequent elements in the @code{parallel} are the same as the +@code{set} in the pattern, except that they are referencing subsequent +registers and memory locations. + +An insn that matches this pattern might look like: + +@smallexample +(parallel + [(set (reg:SI 20) (mem:SI (reg:SI 100))) + (use (reg:SI 179)) + (clobber (reg:SI 179)) + (set (reg:SI 21) + (mem:SI (plus:SI (reg:SI 100) + (const_int 4)))) + (set (reg:SI 22) + (mem:SI (plus:SI (reg:SI 100) + (const_int 8))))]) +@end smallexample + +@findex match_par_dup +@item (match_par_dup @var{n} [@var{subpat}@dots{}]) +Like @code{match_op_dup}, but for @code{match_parallel} instead of +@code{match_operator}. + +@end table + +@node Output Template +@section Output Templates and Operand Substitution +@cindex output templates +@cindex operand substitution + +@cindex @samp{%} in template +@cindex percent sign +The @dfn{output template} is a string which specifies how to output the +assembler code for an instruction pattern. Most of the template is a +fixed string which is output literally. The character @samp{%} is used +to specify where to substitute an operand; it can also be used to +identify places where different variants of the assembler require +different syntax. + +In the simplest case, a @samp{%} followed by a digit @var{n} says to output +operand @var{n} at that point in the string. + +@samp{%} followed by a letter and a digit says to output an operand in an +alternate fashion. Four letters have standard, built-in meanings described +below. The machine description macro @code{PRINT_OPERAND} can define +additional letters with nonstandard meanings. + +@samp{%c@var{digit}} can be used to substitute an operand that is a +constant value without the syntax that normally indicates an immediate +operand. + +@samp{%n@var{digit}} is like @samp{%c@var{digit}} except that the value of +the constant is negated before printing. + +@samp{%a@var{digit}} can be used to substitute an operand as if it were a +memory reference, with the actual operand treated as the address. This may +be useful when outputting a ``load address'' instruction, because often the +assembler syntax for such an instruction requires you to write the operand +as if it were a memory reference. + +@samp{%l@var{digit}} is used to substitute a @code{label_ref} into a jump +instruction. + +@samp{%=} outputs a number which is unique to each instruction in the +entire compilation. This is useful for making local labels to be +referred to more than once in a single template that generates multiple +assembler instructions. + +@samp{%} followed by a punctuation character specifies a substitution that +does not use an operand. Only one case is standard: @samp{%%} outputs a +@samp{%} into the assembler code. Other nonstandard cases can be +defined in the @code{PRINT_OPERAND} macro. You must also define +which punctuation characters are valid with the +@code{PRINT_OPERAND_PUNCT_VALID_P} macro. + +@cindex \ +@cindex backslash +The template may generate multiple assembler instructions. Write the text +for the instructions, with @samp{\;} between them. + +@cindex matching operands +When the RTL contains two operands which are required by constraint to match +each other, the output template must refer only to the lower-numbered operand. +Matching operands are not always identical, and the rest of the compiler +arranges to put the proper RTL expression for printing into the lower-numbered +operand. + +One use of nonstandard letters or punctuation following @samp{%} is to +distinguish between different assembler languages for the same machine; for +example, Motorola syntax versus MIT syntax for the 68000. Motorola syntax +requires periods in most opcode names, while MIT syntax does not. For +example, the opcode @samp{movel} in MIT syntax is @samp{move.l} in Motorola +syntax. The same file of patterns is used for both kinds of output syntax, +but the character sequence @samp{%.} is used in each place where Motorola +syntax wants a period. The @code{PRINT_OPERAND} macro for Motorola syntax +defines the sequence to output a period; the macro for MIT syntax defines +it to do nothing. + +@cindex @code{#} in template +As a special case, a template consisting of the single character @code{#} +instructs the compiler to first split the insn, and then output the +resulting instructions separately. This helps eliminate redundancy in the +output templates. If you have a @code{define_insn} that needs to emit +multiple assembler instructions, and there is a matching @code{define_split} +already defined, then you can simply use @code{#} as the output template +instead of writing an output template that emits the multiple assembler +instructions. + +Note that @code{#} only has an effect while generating assembly code; +it does not affect whether a split occurs earlier. An associated +@code{define_split} must exist and it must be suitable for use after +register allocation. + +If the macro @code{ASSEMBLER_DIALECT} is defined, you can use construct +of the form @samp{@{option0|option1|option2@}} in the templates. These +describe multiple variants of assembler language syntax. +@xref{Instruction Output}. + +@node Output Statement +@section C Statements for Assembler Output +@cindex output statements +@cindex C statements for assembler output +@cindex generating assembler output + +Often a single fixed template string cannot produce correct and efficient +assembler code for all the cases that are recognized by a single +instruction pattern. For example, the opcodes may depend on the kinds of +operands; or some unfortunate combinations of operands may require extra +machine instructions. + +If the output control string starts with a @samp{@@}, then it is actually +a series of templates, each on a separate line. (Blank lines and +leading spaces and tabs are ignored.) The templates correspond to the +pattern's constraint alternatives (@pxref{Multi-Alternative}). For example, +if a target machine has a two-address add instruction @samp{addr} to add +into a register and another @samp{addm} to add a register to memory, you +might write this pattern: + +@smallexample +(define_insn "addsi3" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (plus:SI (match_operand:SI 1 "general_operand" "0,0") + (match_operand:SI 2 "general_operand" "g,r")))] + "" + "@@ + addr %2,%0 + addm %2,%0") +@end smallexample + +@cindex @code{*} in template +@cindex asterisk in template +If the output control string starts with a @samp{*}, then it is not an +output template but rather a piece of C program that should compute a +template. It should execute a @code{return} statement to return the +template-string you want. Most such templates use C string literals, which +require doublequote characters to delimit them. To include these +doublequote characters in the string, prefix each one with @samp{\}. + +If the output control string is written as a brace block instead of a +double-quoted string, it is automatically assumed to be C code. In that +case, it is not necessary to put in a leading asterisk, or to escape the +doublequotes surrounding C string literals. + +The operands may be found in the array @code{operands}, whose C data type +is @code{rtx []}. + +It is very common to select different ways of generating assembler code +based on whether an immediate operand is within a certain range. Be +careful when doing this, because the result of @code{INTVAL} is an +integer on the host machine. If the host machine has more bits in an +@code{int} than the target machine has in the mode in which the constant +will be used, then some of the bits you get from @code{INTVAL} will be +superfluous. For proper results, you must carefully disregard the +values of those bits. + +@findex output_asm_insn +It is possible to output an assembler instruction and then go on to output +or compute more of them, using the subroutine @code{output_asm_insn}. This +receives two arguments: a template-string and a vector of operands. The +vector may be @code{operands}, or it may be another array of @code{rtx} +that you declare locally and initialize yourself. + +@findex which_alternative +When an insn pattern has multiple alternatives in its constraints, often +the appearance of the assembler code is determined mostly by which alternative +was matched. When this is so, the C code can test the variable +@code{which_alternative}, which is the ordinal number of the alternative +that was actually satisfied (0 for the first, 1 for the second alternative, +etc.). + +For example, suppose there are two opcodes for storing zero, @samp{clrreg} +for registers and @samp{clrmem} for memory locations. Here is how +a pattern could use @code{which_alternative} to choose between them: + +@smallexample +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (const_int 0))] + "" + @{ + return (which_alternative == 0 + ? "clrreg %0" : "clrmem %0"); + @}) +@end smallexample + +The example above, where the assembler code to generate was +@emph{solely} determined by the alternative, could also have been specified +as follows, having the output control string start with a @samp{@@}: + +@smallexample +@group +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,m") + (const_int 0))] + "" + "@@ + clrreg %0 + clrmem %0") +@end group +@end smallexample + +If you just need a little bit of C code in one (or a few) alternatives, +you can use @samp{*} inside of a @samp{@@} multi-alternative template: + +@smallexample +@group +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,<,m") + (const_int 0))] + "" + "@@ + clrreg %0 + * return stack_mem_p (operands[0]) ? \"push 0\" : \"clrmem %0\"; + clrmem %0") +@end group +@end smallexample + +@node Predicates +@section Predicates +@cindex predicates +@cindex operand predicates +@cindex operator predicates + +A predicate determines whether a @code{match_operand} or +@code{match_operator} expression matches, and therefore whether the +surrounding instruction pattern will be used for that combination of +operands. GCC has a number of machine-independent predicates, and you +can define machine-specific predicates as needed. By convention, +predicates used with @code{match_operand} have names that end in +@samp{_operand}, and those used with @code{match_operator} have names +that end in @samp{_operator}. + +All predicates are boolean functions (in the mathematical sense) of +two arguments: the RTL expression that is being considered at that +position in the instruction pattern, and the machine mode that the +@code{match_operand} or @code{match_operator} specifies. In this +section, the first argument is called @var{op} and the second argument +@var{mode}. Predicates can be called from C as ordinary two-argument +functions; this can be useful in output templates or other +machine-specific code. + +Operand predicates can allow operands that are not actually acceptable +to the hardware, as long as the constraints give reload the ability to +fix them up (@pxref{Constraints}). However, GCC will usually generate +better code if the predicates specify the requirements of the machine +instructions as closely as possible. Reload cannot fix up operands +that must be constants (``immediate operands''); you must use a +predicate that allows only constants, or else enforce the requirement +in the extra condition. + +@cindex predicates and machine modes +@cindex normal predicates +@cindex special predicates +Most predicates handle their @var{mode} argument in a uniform manner. +If @var{mode} is @code{VOIDmode} (unspecified), then @var{op} can have +any mode. If @var{mode} is anything else, then @var{op} must have the +same mode, unless @var{op} is a @code{CONST_INT} or integer +@code{CONST_DOUBLE}. These RTL expressions always have +@code{VOIDmode}, so it would be counterproductive to check that their +mode matches. Instead, predicates that accept @code{CONST_INT} and/or +integer @code{CONST_DOUBLE} check that the value stored in the +constant will fit in the requested mode. + +Predicates with this behavior are called @dfn{normal}. +@command{genrecog} can optimize the instruction recognizer based on +knowledge of how normal predicates treat modes. It can also diagnose +certain kinds of common errors in the use of normal predicates; for +instance, it is almost always an error to use a normal predicate +without specifying a mode. + +Predicates that do something different with their @var{mode} argument +are called @dfn{special}. The generic predicates +@code{address_operand} and @code{pmode_register_operand} are special +predicates. @command{genrecog} does not do any optimizations or +diagnosis when special predicates are used. + +@menu +* Machine-Independent Predicates:: Predicates available to all back ends. +* Defining Predicates:: How to write machine-specific predicate + functions. +@end menu + +@node Machine-Independent Predicates +@subsection Machine-Independent Predicates +@cindex machine-independent predicates +@cindex generic predicates + +These are the generic predicates available to all back ends. They are +defined in @file{recog.cc}. The first category of predicates allow +only constant, or @dfn{immediate}, operands. + +@defun immediate_operand +This predicate allows any sort of constant that fits in @var{mode}. +It is an appropriate choice for instructions that take operands that +must be constant. +@end defun + +@defun const_int_operand +This predicate allows any @code{CONST_INT} expression that fits in +@var{mode}. It is an appropriate choice for an immediate operand that +does not allow a symbol or label. +@end defun + +@defun const_double_operand +This predicate accepts any @code{CONST_DOUBLE} expression that has +exactly @var{mode}. If @var{mode} is @code{VOIDmode}, it will also +accept @code{CONST_INT}. It is intended for immediate floating point +constants. +@end defun + +@noindent +The second category of predicates allow only some kind of machine +register. + +@defun register_operand +This predicate allows any @code{REG} or @code{SUBREG} expression that +is valid for @var{mode}. It is often suitable for arithmetic +instruction operands on a RISC machine. +@end defun + +@defun pmode_register_operand +This is a slight variant on @code{register_operand} which works around +a limitation in the machine-description reader. + +@smallexample +(match_operand @var{n} "pmode_register_operand" @var{constraint}) +@end smallexample + +@noindent +means exactly what + +@smallexample +(match_operand:P @var{n} "register_operand" @var{constraint}) +@end smallexample + +@noindent +would mean, if the machine-description reader accepted @samp{:P} +mode suffixes. Unfortunately, it cannot, because @code{Pmode} is an +alias for some other mode, and might vary with machine-specific +options. @xref{Misc}. +@end defun + +@defun scratch_operand +This predicate allows hard registers and @code{SCRATCH} expressions, +but not pseudo-registers. It is used internally by @code{match_scratch}; +it should not be used directly. +@end defun + +@noindent +The third category of predicates allow only some kind of memory reference. + +@defun memory_operand +This predicate allows any valid reference to a quantity of mode +@var{mode} in memory, as determined by the weak form of +@code{GO_IF_LEGITIMATE_ADDRESS} (@pxref{Addressing Modes}). +@end defun + +@defun address_operand +This predicate is a little unusual; it allows any operand that is a +valid expression for the @emph{address} of a quantity of mode +@var{mode}, again determined by the weak form of +@code{GO_IF_LEGITIMATE_ADDRESS}. To first order, if +@samp{@w{(mem:@var{mode} (@var{exp}))}} is acceptable to +@code{memory_operand}, then @var{exp} is acceptable to +@code{address_operand}. Note that @var{exp} does not necessarily have +the mode @var{mode}. +@end defun + +@defun indirect_operand +This is a stricter form of @code{memory_operand} which allows only +memory references with a @code{general_operand} as the address +expression. New uses of this predicate are discouraged, because +@code{general_operand} is very permissive, so it's hard to tell what +an @code{indirect_operand} does or does not allow. If a target has +different requirements for memory operands for different instructions, +it is better to define target-specific predicates which enforce the +hardware's requirements explicitly. +@end defun + +@defun push_operand +This predicate allows a memory reference suitable for pushing a value +onto the stack. This will be a @code{MEM} which refers to +@code{stack_pointer_rtx}, with a side effect in its address expression +(@pxref{Incdec}); which one is determined by the +@code{STACK_PUSH_CODE} macro (@pxref{Frame Layout}). +@end defun + +@defun pop_operand +This predicate allows a memory reference suitable for popping a value +off the stack. Again, this will be a @code{MEM} referring to +@code{stack_pointer_rtx}, with a side effect in its address +expression. However, this time @code{STACK_POP_CODE} is expected. +@end defun + +@noindent +The fourth category of predicates allow some combination of the above +operands. + +@defun nonmemory_operand +This predicate allows any immediate or register operand valid for @var{mode}. +@end defun + +@defun nonimmediate_operand +This predicate allows any register or memory operand valid for @var{mode}. +@end defun + +@defun general_operand +This predicate allows any immediate, register, or memory operand +valid for @var{mode}. +@end defun + +@noindent +Finally, there are two generic operator predicates. + +@defun comparison_operator +This predicate matches any expression which performs an arithmetic +comparison in @var{mode}; that is, @code{COMPARISON_P} is true for the +expression code. +@end defun + +@defun ordered_comparison_operator +This predicate matches any expression which performs an arithmetic +comparison in @var{mode} and whose expression code is valid for integer +modes; that is, the expression code will be one of @code{eq}, @code{ne}, +@code{lt}, @code{ltu}, @code{le}, @code{leu}, @code{gt}, @code{gtu}, +@code{ge}, @code{geu}. +@end defun + +@node Defining Predicates +@subsection Defining Machine-Specific Predicates +@cindex defining predicates +@findex define_predicate +@findex define_special_predicate + +Many machines have requirements for their operands that cannot be +expressed precisely using the generic predicates. You can define +additional predicates using @code{define_predicate} and +@code{define_special_predicate} expressions. These expressions have +three operands: + +@itemize @bullet +@item +The name of the predicate, as it will be referred to in +@code{match_operand} or @code{match_operator} expressions. + +@item +An RTL expression which evaluates to true if the predicate allows the +operand @var{op}, false if it does not. This expression can only use +the following RTL codes: + +@table @code +@item MATCH_OPERAND +When written inside a predicate expression, a @code{MATCH_OPERAND} +expression evaluates to true if the predicate it names would allow +@var{op}. The operand number and constraint are ignored. Due to +limitations in @command{genrecog}, you can only refer to generic +predicates and predicates that have already been defined. + +@item MATCH_CODE +This expression evaluates to true if @var{op} or a specified +subexpression of @var{op} has one of a given list of RTX codes. + +The first operand of this expression is a string constant containing a +comma-separated list of RTX code names (in lower case). These are the +codes for which the @code{MATCH_CODE} will be true. + +The second operand is a string constant which indicates what +subexpression of @var{op} to examine. If it is absent or the empty +string, @var{op} itself is examined. Otherwise, the string constant +must be a sequence of digits and/or lowercase letters. Each character +indicates a subexpression to extract from the current expression; for +the first character this is @var{op}, for the second and subsequent +characters it is the result of the previous character. A digit +@var{n} extracts @samp{@w{XEXP (@var{e}, @var{n})}}; a letter @var{l} +extracts @samp{@w{XVECEXP (@var{e}, 0, @var{n})}} where @var{n} is the +alphabetic ordinal of @var{l} (0 for `a', 1 for 'b', and so on). The +@code{MATCH_CODE} then examines the RTX code of the subexpression +extracted by the complete string. It is not possible to extract +components of an @code{rtvec} that is not at position 0 within its RTX +object. + +@item MATCH_TEST +This expression has one operand, a string constant containing a C +expression. The predicate's arguments, @var{op} and @var{mode}, are +available with those names in the C expression. The @code{MATCH_TEST} +evaluates to true if the C expression evaluates to a nonzero value. +@code{MATCH_TEST} expressions must not have side effects. + +@item AND +@itemx IOR +@itemx NOT +@itemx IF_THEN_ELSE +The basic @samp{MATCH_} expressions can be combined using these +logical operators, which have the semantics of the C operators +@samp{&&}, @samp{||}, @samp{!}, and @samp{@w{? :}} respectively. As +in Common Lisp, you may give an @code{AND} or @code{IOR} expression an +arbitrary number of arguments; this has exactly the same effect as +writing a chain of two-argument @code{AND} or @code{IOR} expressions. +@end table + +@item +An optional block of C code, which should execute +@samp{@w{return true}} if the predicate is found to match and +@samp{@w{return false}} if it does not. It must not have any side +effects. The predicate arguments, @var{op} and @var{mode}, are +available with those names. + +If a code block is present in a predicate definition, then the RTL +expression must evaluate to true @emph{and} the code block must +execute @samp{@w{return true}} for the predicate to allow the operand. +The RTL expression is evaluated first; do not re-check anything in the +code block that was checked in the RTL expression. +@end itemize + +The program @command{genrecog} scans @code{define_predicate} and +@code{define_special_predicate} expressions to determine which RTX +codes are possibly allowed. You should always make this explicit in +the RTL predicate expression, using @code{MATCH_OPERAND} and +@code{MATCH_CODE}. + +Here is an example of a simple predicate definition, from the IA64 +machine description: + +@smallexample +@group +;; @r{True if @var{op} is a @code{SYMBOL_REF} which refers to the sdata section.} +(define_predicate "small_addr_symbolic_operand" + (and (match_code "symbol_ref") + (match_test "SYMBOL_REF_SMALL_ADDR_P (op)"))) +@end group +@end smallexample + +@noindent +And here is another, showing the use of the C block. + +@smallexample +@group +;; @r{True if @var{op} is a register operand that is (or could be) a GR reg.} +(define_predicate "gr_register_operand" + (match_operand 0 "register_operand") +@{ + unsigned int regno; + if (GET_CODE (op) == SUBREG) + op = SUBREG_REG (op); + + regno = REGNO (op); + return (regno >= FIRST_PSEUDO_REGISTER || GENERAL_REGNO_P (regno)); +@}) +@end group +@end smallexample + +Predicates written with @code{define_predicate} automatically include +a test that @var{mode} is @code{VOIDmode}, or @var{op} has the same +mode as @var{mode}, or @var{op} is a @code{CONST_INT} or +@code{CONST_DOUBLE}. They do @emph{not} check specifically for +integer @code{CONST_DOUBLE}, nor do they test that the value of either +kind of constant fits in the requested mode. This is because +target-specific predicates that take constants usually have to do more +stringent value checks anyway. If you need the exact same treatment +of @code{CONST_INT} or @code{CONST_DOUBLE} that the generic predicates +provide, use a @code{MATCH_OPERAND} subexpression to call +@code{const_int_operand}, @code{const_double_operand}, or +@code{immediate_operand}. + +Predicates written with @code{define_special_predicate} do not get any +automatic mode checks, and are treated as having special mode handling +by @command{genrecog}. + +The program @command{genpreds} is responsible for generating code to +test predicates. It also writes a header file containing function +declarations for all machine-specific predicates. It is not necessary +to declare these predicates in @file{@var{cpu}-protos.h}. +@end ifset + +@c Most of this node appears by itself (in a different place) even +@c when the INTERNALS flag is clear. Passages that require the internals +@c manual's context are conditionalized to appear only in the internals manual. +@ifset INTERNALS +@node Constraints +@section Operand Constraints +@cindex operand constraints +@cindex constraints + +Each @code{match_operand} in an instruction pattern can specify +constraints for the operands allowed. The constraints allow you to +fine-tune matching within the set of operands allowed by the +predicate. + +@end ifset +@ifclear INTERNALS +@node Constraints +@section Constraints for @code{asm} Operands +@cindex operand constraints, @code{asm} +@cindex constraints, @code{asm} +@cindex @code{asm} constraints + +Here are specific details on what constraint letters you can use with +@code{asm} operands. +@end ifclear +Constraints can say whether +an operand may be in a register, and which kinds of register; whether the +operand can be a memory reference, and which kinds of address; whether the +operand may be an immediate constant, and which possible values it may +have. Constraints can also require two operands to match. +Side-effects aren't allowed in operands of inline @code{asm}, unless +@samp{<} or @samp{>} constraints are used, because there is no guarantee +that the side effects will happen exactly once in an instruction that can update +the addressing register. + +@ifset INTERNALS +@menu +* Simple Constraints:: Basic use of constraints. +* Multi-Alternative:: When an insn has two alternative constraint-patterns. +* Class Preferences:: Constraints guide which hard register to put things in. +* Modifiers:: More precise control over effects of constraints. +* Machine Constraints:: Existing constraints for some particular machines. +* Disable Insn Alternatives:: Disable insn alternatives using attributes. +* Define Constraints:: How to define machine-specific constraints. +* C Constraint Interface:: How to test constraints from C code. +@end menu +@end ifset + +@ifclear INTERNALS +@menu +* Simple Constraints:: Basic use of constraints. +* Multi-Alternative:: When an insn has two alternative constraint-patterns. +* Modifiers:: More precise control over effects of constraints. +* Machine Constraints:: Special constraints for some particular machines. +@end menu +@end ifclear + +@node Simple Constraints +@subsection Simple Constraints +@cindex simple constraints + +The simplest kind of constraint is a string full of letters, each of +which describes one kind of operand that is permitted. Here are +the letters that are allowed: + +@table @asis +@item whitespace +Whitespace characters are ignored and can be inserted at any position +except the first. This enables each alternative for different operands to +be visually aligned in the machine description even if they have different +number of constraints and modifiers. + +@cindex @samp{m} in constraint +@cindex memory references in constraints +@item @samp{m} +A memory operand is allowed, with any kind of address that the machine +supports in general. +Note that the letter used for the general memory constraint can be +re-defined by a back end using the @code{TARGET_MEM_CONSTRAINT} macro. + +@cindex offsettable address +@cindex @samp{o} in constraint +@item @samp{o} +A memory operand is allowed, but only if the address is +@dfn{offsettable}. This means that adding a small integer (actually, +the width in bytes of the operand, as determined by its machine mode) +may be added to the address and the result is also a valid memory +address. + +@cindex autoincrement/decrement addressing +For example, an address which is constant is offsettable; so is an +address that is the sum of a register and a constant (as long as a +slightly larger constant is also within the range of address-offsets +supported by the machine); but an autoincrement or autodecrement +address is not offsettable. More complicated indirect/indexed +addresses may or may not be offsettable depending on the other +addressing modes that the machine supports. + +Note that in an output operand which can be matched by another +operand, the constraint letter @samp{o} is valid only when accompanied +by both @samp{<} (if the target machine has predecrement addressing) +and @samp{>} (if the target machine has preincrement addressing). + +@cindex @samp{V} in constraint +@item @samp{V} +A memory operand that is not offsettable. In other words, anything that +would fit the @samp{m} constraint but not the @samp{o} constraint. + +@cindex @samp{<} in constraint +@item @samp{<} +A memory operand with autodecrement addressing (either predecrement or +postdecrement) is allowed. In inline @code{asm} this constraint is only +allowed if the operand is used exactly once in an instruction that can +handle the side effects. Not using an operand with @samp{<} in constraint +string in the inline @code{asm} pattern at all or using it in multiple +instructions isn't valid, because the side effects wouldn't be performed +or would be performed more than once. Furthermore, on some targets +the operand with @samp{<} in constraint string must be accompanied by +special instruction suffixes like @code{%U0} instruction suffix on PowerPC +or @code{%P0} on IA-64. + +@cindex @samp{>} in constraint +@item @samp{>} +A memory operand with autoincrement addressing (either preincrement or +postincrement) is allowed. In inline @code{asm} the same restrictions +as for @samp{<} apply. + +@cindex @samp{r} in constraint +@cindex registers in constraints +@item @samp{r} +A register operand is allowed provided that it is in a general +register. + +@cindex constants in constraints +@cindex @samp{i} in constraint +@item @samp{i} +An immediate integer operand (one with constant value) is allowed. +This includes symbolic constants whose values will be known only at +assembly time or later. + +@cindex @samp{n} in constraint +@item @samp{n} +An immediate integer operand with a known numeric value is allowed. +Many systems cannot support assembly-time constants for operands less +than a word wide. Constraints for these operands should use @samp{n} +rather than @samp{i}. + +@cindex @samp{I} in constraint +@item @samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P} +Other letters in the range @samp{I} through @samp{P} may be defined in +a machine-dependent fashion to permit immediate integer operands with +explicit integer values in specified ranges. For example, on the +68000, @samp{I} is defined to stand for the range of values 1 to 8. +This is the range permitted as a shift count in the shift +instructions. + +@cindex @samp{E} in constraint +@item @samp{E} +An immediate floating operand (expression code @code{const_double}) is +allowed, but only if the target floating point format is the same as +that of the host machine (on which the compiler is running). + +@cindex @samp{F} in constraint +@item @samp{F} +An immediate floating operand (expression code @code{const_double} or +@code{const_vector}) is allowed. + +@cindex @samp{G} in constraint +@cindex @samp{H} in constraint +@item @samp{G}, @samp{H} +@samp{G} and @samp{H} may be defined in a machine-dependent fashion to +permit immediate floating operands in particular ranges of values. + +@cindex @samp{s} in constraint +@item @samp{s} +An immediate integer operand whose value is not an explicit integer is +allowed. + +This might appear strange; if an insn allows a constant operand with a +value not known at compile time, it certainly must allow any known +value. So why use @samp{s} instead of @samp{i}? Sometimes it allows +better code to be generated. + +For example, on the 68000 in a fullword instruction it is possible to +use an immediate operand; but if the immediate value is between @minus{}128 +and 127, better code results from loading the value into a register and +using the register. This is because the load into the register can be +done with a @samp{moveq} instruction. We arrange for this to happen +by defining the letter @samp{K} to mean ``any integer outside the +range @minus{}128 to 127'', and then specifying @samp{Ks} in the operand +constraints. + +@cindex @samp{g} in constraint +@item @samp{g} +Any register, memory or immediate integer operand is allowed, except for +registers that are not general registers. + +@cindex @samp{X} in constraint +@item @samp{X} +@ifset INTERNALS +Any operand whatsoever is allowed, even if it does not satisfy +@code{general_operand}. This is normally used in the constraint of +a @code{match_scratch} when certain alternatives will not actually +require a scratch register. +@end ifset +@ifclear INTERNALS +Any operand whatsoever is allowed. +@end ifclear + +@cindex @samp{0} in constraint +@cindex digits in constraint +@item @samp{0}, @samp{1}, @samp{2}, @dots{} @samp{9} +An operand that matches the specified operand number is allowed. If a +digit is used together with letters within the same alternative, the +digit should come last. + +This number is allowed to be more than a single digit. If multiple +digits are encountered consecutively, they are interpreted as a single +decimal integer. There is scant chance for ambiguity, since to-date +it has never been desirable that @samp{10} be interpreted as matching +either operand 1 @emph{or} operand 0. Should this be desired, one +can use multiple alternatives instead. + +@cindex matching constraint +@cindex constraint, matching +This is called a @dfn{matching constraint} and what it really means is +that the assembler has only a single operand that fills two roles +@ifset INTERNALS +considered separate in the RTL insn. For example, an add insn has two +input operands and one output operand in the RTL, but on most CISC +@end ifset +@ifclear INTERNALS +which @code{asm} distinguishes. For example, an add instruction uses +two input operands and an output operand, but on most CISC +@end ifclear +machines an add instruction really has only two operands, one of them an +input-output operand: + +@smallexample +addl #35,r12 +@end smallexample + +Matching constraints are used in these circumstances. +More precisely, the two operands that match must include one input-only +operand and one output-only operand. Moreover, the digit must be a +smaller number than the number of the operand that uses it in the +constraint. + +@ifset INTERNALS +For operands to match in a particular case usually means that they +are identical-looking RTL expressions. But in a few special cases +specific kinds of dissimilarity are allowed. For example, @code{*x} +as an input operand will match @code{*x++} as an output operand. +For proper results in such cases, the output template should always +use the output-operand's number when printing the operand. +@end ifset + +@cindex load address instruction +@cindex push address instruction +@cindex address constraints +@cindex @samp{p} in constraint +@item @samp{p} +An operand that is a valid memory address is allowed. This is +for ``load address'' and ``push address'' instructions. + +@findex address_operand +@samp{p} in the constraint must be accompanied by @code{address_operand} +as the predicate in the @code{match_operand}. This predicate interprets +the mode specified in the @code{match_operand} as the mode of the memory +reference for which the address would be valid. + +@cindex other register constraints +@cindex extensible constraints +@item @var{other-letters} +Other letters can be defined in machine-dependent fashion to stand for +particular classes of registers or other arbitrary operand types. +@samp{d}, @samp{a} and @samp{f} are defined on the 68000/68020 to stand +for data, address and floating point registers. +@end table + +@ifset INTERNALS +In order to have valid assembler code, each operand must satisfy +its constraint. But a failure to do so does not prevent the pattern +from applying to an insn. Instead, it directs the compiler to modify +the code so that the constraint will be satisfied. Usually this is +done by copying an operand into a register. + +Contrast, therefore, the two instruction patterns that follow: + +@smallexample +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r") + (plus:SI (match_dup 0) + (match_operand:SI 1 "general_operand" "r")))] + "" + "@dots{}") +@end smallexample + +@noindent +which has two operands, one of which must appear in two places, and + +@smallexample +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r") + (plus:SI (match_operand:SI 1 "general_operand" "0") + (match_operand:SI 2 "general_operand" "r")))] + "" + "@dots{}") +@end smallexample + +@noindent +which has three operands, two of which are required by a constraint to be +identical. If we are considering an insn of the form + +@smallexample +(insn @var{n} @var{prev} @var{next} + (set (reg:SI 3) + (plus:SI (reg:SI 6) (reg:SI 109))) + @dots{}) +@end smallexample + +@noindent +the first pattern would not apply at all, because this insn does not +contain two identical subexpressions in the right place. The pattern would +say, ``That does not look like an add instruction; try other patterns''. +The second pattern would say, ``Yes, that's an add instruction, but there +is something wrong with it''. It would direct the reload pass of the +compiler to generate additional insns to make the constraint true. The +results might look like this: + +@smallexample +(insn @var{n2} @var{prev} @var{n} + (set (reg:SI 3) (reg:SI 6)) + @dots{}) + +(insn @var{n} @var{n2} @var{next} + (set (reg:SI 3) + (plus:SI (reg:SI 3) (reg:SI 109))) + @dots{}) +@end smallexample + +It is up to you to make sure that each operand, in each pattern, has +constraints that can handle any RTL expression that could be present for +that operand. (When multiple alternatives are in use, each pattern must, +for each possible combination of operand expressions, have at least one +alternative which can handle that combination of operands.) The +constraints don't need to @emph{allow} any possible operand---when this is +the case, they do not constrain---but they must at least point the way to +reloading any possible operand so that it will fit. + +@itemize @bullet +@item +If the constraint accepts whatever operands the predicate permits, +there is no problem: reloading is never necessary for this operand. + +For example, an operand whose constraints permit everything except +registers is safe provided its predicate rejects registers. + +An operand whose predicate accepts only constant values is safe +provided its constraints include the letter @samp{i}. If any possible +constant value is accepted, then nothing less than @samp{i} will do; +if the predicate is more selective, then the constraints may also be +more selective. + +@item +Any operand expression can be reloaded by copying it into a register. +So if an operand's constraints allow some kind of register, it is +certain to be safe. It need not permit all classes of registers; the +compiler knows how to copy a register into another register of the +proper class in order to make an instruction valid. + +@cindex nonoffsettable memory reference +@cindex memory reference, nonoffsettable +@item +A nonoffsettable memory reference can be reloaded by copying the +address into a register. So if the constraint uses the letter +@samp{o}, all memory references are taken care of. + +@item +A constant operand can be reloaded by allocating space in memory to +hold it as preinitialized data. Then the memory reference can be used +in place of the constant. So if the constraint uses the letters +@samp{o} or @samp{m}, constant operands are not a problem. + +@item +If the constraint permits a constant and a pseudo register used in an insn +was not allocated to a hard register and is equivalent to a constant, +the register will be replaced with the constant. If the predicate does +not permit a constant and the insn is re-recognized for some reason, the +compiler will crash. Thus the predicate must always recognize any +objects allowed by the constraint. +@end itemize + +If the operand's predicate can recognize registers, but the constraint does +not permit them, it can make the compiler crash. When this operand happens +to be a register, the reload pass will be stymied, because it does not know +how to copy a register temporarily into memory. + +If the predicate accepts a unary operator, the constraint applies to the +operand. For example, the MIPS processor at ISA level 3 supports an +instruction which adds two registers in @code{SImode} to produce a +@code{DImode} result, but only if the registers are correctly sign +extended. This predicate for the input operands accepts a +@code{sign_extend} of an @code{SImode} register. Write the constraint +to indicate the type of register that is required for the operand of the +@code{sign_extend}. +@end ifset + +@node Multi-Alternative +@subsection Multiple Alternative Constraints +@cindex multiple alternative constraints + +Sometimes a single instruction has multiple alternative sets of possible +operands. For example, on the 68000, a logical-or instruction can combine +register or an immediate value into memory, or it can combine any kind of +operand into a register; but it cannot combine one memory location into +another. + +These constraints are represented as multiple alternatives. An alternative +can be described by a series of letters for each operand. The overall +constraint for an operand is made from the letters for this operand +from the first alternative, a comma, the letters for this operand from +the second alternative, a comma, and so on until the last alternative. +All operands for a single instruction must have the same number of +alternatives. +@ifset INTERNALS +Here is how it is done for fullword logical-or on the 68000: + +@smallexample +(define_insn "iorsi3" + [(set (match_operand:SI 0 "general_operand" "=m,d") + (ior:SI (match_operand:SI 1 "general_operand" "%0,0") + (match_operand:SI 2 "general_operand" "dKs,dmKs")))] + @dots{}) +@end smallexample + +The first alternative has @samp{m} (memory) for operand 0, @samp{0} for +operand 1 (meaning it must match operand 0), and @samp{dKs} for operand +2. The second alternative has @samp{d} (data register) for operand 0, +@samp{0} for operand 1, and @samp{dmKs} for operand 2. The @samp{=} and +@samp{%} in the constraints apply to all the alternatives; their +meaning is explained in the next section (@pxref{Class Preferences}). + +If all the operands fit any one alternative, the instruction is valid. +Otherwise, for each alternative, the compiler counts how many instructions +must be added to copy the operands so that that alternative applies. +The alternative requiring the least copying is chosen. If two alternatives +need the same amount of copying, the one that comes first is chosen. +These choices can be altered with the @samp{?} and @samp{!} characters: + +@table @code +@cindex @samp{?} in constraint +@cindex question mark +@item ? +Disparage slightly the alternative that the @samp{?} appears in, +as a choice when no alternative applies exactly. The compiler regards +this alternative as one unit more costly for each @samp{?} that appears +in it. + +@cindex @samp{!} in constraint +@cindex exclamation point +@item ! +Disparage severely the alternative that the @samp{!} appears in. +This alternative can still be used if it fits without reloading, +but if reloading is needed, some other alternative will be used. + +@cindex @samp{^} in constraint +@cindex caret +@item ^ +This constraint is analogous to @samp{?} but it disparages slightly +the alternative only if the operand with the @samp{^} needs a reload. + +@cindex @samp{$} in constraint +@cindex dollar sign +@item $ +This constraint is analogous to @samp{!} but it disparages severely +the alternative only if the operand with the @samp{$} needs a reload. +@end table + +When an insn pattern has multiple alternatives in its constraints, often +the appearance of the assembler code is determined mostly by which +alternative was matched. When this is so, the C code for writing the +assembler code can use the variable @code{which_alternative}, which is +the ordinal number of the alternative that was actually satisfied (0 for +the first, 1 for the second alternative, etc.). @xref{Output Statement}. +@end ifset +@ifclear INTERNALS + +So the first alternative for the 68000's logical-or could be written as +@code{"+m" (output) : "ir" (input)}. The second could be @code{"+r" +(output): "irm" (input)}. However, the fact that two memory locations +cannot be used in a single instruction prevents simply using @code{"+rm" +(output) : "irm" (input)}. Using multi-alternatives, this might be +written as @code{"+m,r" (output) : "ir,irm" (input)}. This describes +all the available alternatives to the compiler, allowing it to choose +the most efficient one for the current conditions. + +There is no way within the template to determine which alternative was +chosen. However you may be able to wrap your @code{asm} statements with +builtins such as @code{__builtin_constant_p} to achieve the desired results. +@end ifclear + +@ifset INTERNALS +@node Class Preferences +@subsection Register Class Preferences +@cindex class preference constraints +@cindex register class preference constraints + +@cindex voting between constraint alternatives +The operand constraints have another function: they enable the compiler +to decide which kind of hardware register a pseudo register is best +allocated to. The compiler examines the constraints that apply to the +insns that use the pseudo register, looking for the machine-dependent +letters such as @samp{d} and @samp{a} that specify classes of registers. +The pseudo register is put in whichever class gets the most ``votes''. +The constraint letters @samp{g} and @samp{r} also vote: they vote in +favor of a general register. The machine description says which registers +are considered general. + +Of course, on some machines all registers are equivalent, and no register +classes are defined. Then none of this complexity is relevant. +@end ifset + +@node Modifiers +@subsection Constraint Modifier Characters +@cindex modifiers in constraints +@cindex constraint modifier characters + +@c prevent bad page break with this line +Here are constraint modifier characters. + +@table @samp +@cindex @samp{=} in constraint +@item = +Means that this operand is written to by this instruction: +the previous value is discarded and replaced by new data. + +@cindex @samp{+} in constraint +@item + +Means that this operand is both read and written by the instruction. + +When the compiler fixes up the operands to satisfy the constraints, +it needs to know which operands are read by the instruction and +which are written by it. @samp{=} identifies an operand which is only +written; @samp{+} identifies an operand that is both read and written; all +other operands are assumed to only be read. + +If you specify @samp{=} or @samp{+} in a constraint, you put it in the +first character of the constraint string. + +@cindex @samp{&} in constraint +@cindex earlyclobber operand +@item & +Means (in a particular alternative) that this operand is an +@dfn{earlyclobber} operand, which is written before the instruction is +finished using the input operands. Therefore, this operand may not lie +in a register that is read by the instruction or as part of any memory +address. + +@samp{&} applies only to the alternative in which it is written. In +constraints with multiple alternatives, sometimes one alternative +requires @samp{&} while others do not. See, for example, the +@samp{movdf} insn of the 68000. + +An operand which is read by the instruction can be tied to an earlyclobber +operand if its only use as an input occurs before the early result is +written. Adding alternatives of this form often allows GCC to produce +better code when only some of the read operands can be affected by the +earlyclobber. See, for example, the @samp{mulsi3} insn of the ARM@. + +Furthermore, if the @dfn{earlyclobber} operand is also a read/write +operand, then that operand is written only after it's used. + +@samp{&} does not obviate the need to write @samp{=} or @samp{+}. As +@dfn{earlyclobber} operands are always written, a read-only +@dfn{earlyclobber} operand is ill-formed and will be rejected by the +compiler. + +@cindex @samp{%} in constraint +@item % +Declares the instruction to be commutative for this operand and the +following operand. This means that the compiler may interchange the +two operands if that is the cheapest way to make all operands fit the +constraints. @samp{%} applies to all alternatives and must appear as +the first character in the constraint. Only read-only operands can use +@samp{%}. + +@ifset INTERNALS +This is often used in patterns for addition instructions +that really have only two operands: the result must go in one of the +arguments. Here for example, is how the 68000 halfword-add +instruction is defined: + +@smallexample +(define_insn "addhi3" + [(set (match_operand:HI 0 "general_operand" "=m,r") + (plus:HI (match_operand:HI 1 "general_operand" "%0,0") + (match_operand:HI 2 "general_operand" "di,g")))] + @dots{}) +@end smallexample +@end ifset +GCC can only handle one commutative pair in an asm; if you use more, +the compiler may fail. Note that you need not use the modifier if +the two alternatives are strictly identical; this would only waste +time in the reload pass. +@ifset INTERNALS +The modifier is not operational after +register allocation, so the result of @code{define_peephole2} +and @code{define_split}s performed after reload cannot rely on +@samp{%} to make the intended insn match. + +@cindex @samp{#} in constraint +@item # +Says that all following characters, up to the next comma, are to be +ignored as a constraint. They are significant only for choosing +register preferences. + +@cindex @samp{*} in constraint +@item * +Says that the following character should be ignored when choosing +register preferences. @samp{*} has no effect on the meaning of the +constraint as a constraint, and no effect on reloading. For LRA +@samp{*} additionally disparages slightly the alternative if the +following character matches the operand. + +Here is an example: the 68000 has an instruction to sign-extend a +halfword in a data register, and can also sign-extend a value by +copying it into an address register. While either kind of register is +acceptable, the constraints on an address-register destination are +less strict, so it is best if register allocation makes an address +register its goal. Therefore, @samp{*} is used so that the @samp{d} +constraint letter (for data register) is ignored when computing +register preferences. + +@smallexample +(define_insn "extendhisi2" + [(set (match_operand:SI 0 "general_operand" "=*d,a") + (sign_extend:SI + (match_operand:HI 1 "general_operand" "0,g")))] + @dots{}) +@end smallexample +@end ifset +@end table + +@node Machine Constraints +@subsection Constraints for Particular Machines +@cindex machine specific constraints +@cindex constraints, machine specific + +Whenever possible, you should use the general-purpose constraint letters +in @code{asm} arguments, since they will convey meaning more readily to +people reading your code. Failing that, use the constraint letters +that usually have very similar meanings across architectures. The most +commonly used constraints are @samp{m} and @samp{r} (for memory and +general-purpose registers respectively; @pxref{Simple Constraints}), and +@samp{I}, usually the letter indicating the most common +immediate-constant format. + +Each architecture defines additional constraints. These constraints +are used by the compiler itself for instruction generation, as well as +for @code{asm} statements; therefore, some of the constraints are not +particularly useful for @code{asm}. Here is a summary of some of the +machine-dependent constraints available on some particular machines; +it includes both constraints that are useful for @code{asm} and +constraints that aren't. The compiler source file mentioned in the +table heading for each architecture is the definitive reference for +the meanings of that architecture's constraints. + +@c Please keep this table alphabetized by target! +@table @emph +@item AArch64 family---@file{config/aarch64/constraints.md} +@table @code +@item k +The stack pointer register (@code{SP}) + +@item w +Floating point register, Advanced SIMD vector register or SVE vector register + +@item x +Like @code{w}, but restricted to registers 0 to 15 inclusive. + +@item y +Like @code{w}, but restricted to registers 0 to 7 inclusive. + +@item Upl +One of the low eight SVE predicate registers (@code{P0} to @code{P7}) + +@item Upa +Any of the SVE predicate registers (@code{P0} to @code{P15}) + +@item I +Integer constant that is valid as an immediate operand in an @code{ADD} +instruction + +@item J +Integer constant that is valid as an immediate operand in a @code{SUB} +instruction (once negated) + +@item K +Integer constant that can be used with a 32-bit logical instruction + +@item L +Integer constant that can be used with a 64-bit logical instruction + +@item M +Integer constant that is valid as an immediate operand in a 32-bit @code{MOV} +pseudo instruction. The @code{MOV} may be assembled to one of several different +machine instructions depending on the value + +@item N +Integer constant that is valid as an immediate operand in a 64-bit @code{MOV} +pseudo instruction + +@item S +An absolute symbolic address or a label reference + +@item Y +Floating point constant zero + +@item Z +Integer constant zero + +@item Ush +The high part (bits 12 and upwards) of the pc-relative address of a symbol +within 4GB of the instruction + +@item Q +A memory address which uses a single base register with no offset + +@item Ump +A memory address suitable for a load/store pair instruction in SI, DI, SF and +DF modes + +@end table + + +@item AMD GCN ---@file{config/gcn/constraints.md} +@table @code +@item I +Immediate integer in the range @minus{}16 to 64 + +@item J +Immediate 16-bit signed integer + +@item Kf +Immediate constant @minus{}1 + +@item L +Immediate 15-bit unsigned integer + +@item A +Immediate constant that can be inlined in an instruction encoding: integer +@minus{}16..64, or float 0.0, +/@minus{}0.5, +/@minus{}1.0, +/@minus{}2.0, ++/@minus{}4.0, 1.0/(2.0*PI) + +@item B +Immediate 32-bit signed integer that can be attached to an instruction encoding + +@item C +Immediate 32-bit integer in range @minus{}16..4294967295 (i.e. 32-bit unsigned +integer or @samp{A} constraint) + +@item DA +Immediate 64-bit constant that can be split into two @samp{A} constants + +@item DB +Immediate 64-bit constant that can be split into two @samp{B} constants + +@item U +Any @code{unspec} + +@item Y +Any @code{symbol_ref} or @code{label_ref} + +@item v +VGPR register + +@item Sg +SGPR register + +@item SD +SGPR registers valid for instruction destinations, including VCC, M0 and EXEC + +@item SS +SGPR registers valid for instruction sources, including VCC, M0, EXEC and SCC + +@item Sm +SGPR registers valid as a source for scalar memory instructions (excludes M0 +and EXEC) + +@item Sv +SGPR registers valid as a source or destination for vector instructions +(excludes EXEC) + +@item ca +All condition registers: SCC, VCCZ, EXECZ + +@item cs +Scalar condition register: SCC + +@item cV +Vector condition register: VCC, VCC_LO, VCC_HI + +@item e +EXEC register (EXEC_LO and EXEC_HI) + +@item RB +Memory operand with address space suitable for @code{buffer_*} instructions + +@item RF +Memory operand with address space suitable for @code{flat_*} instructions + +@item RS +Memory operand with address space suitable for @code{s_*} instructions + +@item RL +Memory operand with address space suitable for @code{ds_*} LDS instructions + +@item RG +Memory operand with address space suitable for @code{ds_*} GDS instructions + +@item RD +Memory operand with address space suitable for any @code{ds_*} instructions + +@item RM +Memory operand with address space suitable for @code{global_*} instructions + +@end table + + +@item ARC ---@file{config/arc/constraints.md} +@table @code +@item q +Registers usable in ARCompact 16-bit instructions: @code{r0}-@code{r3}, +@code{r12}-@code{r15}. This constraint can only match when the @option{-mq} +option is in effect. + +@item e +Registers usable as base-regs of memory addresses in ARCompact 16-bit memory +instructions: @code{r0}-@code{r3}, @code{r12}-@code{r15}, @code{sp}. +This constraint can only match when the @option{-mq} +option is in effect. +@item D +ARC FPX (dpfp) 64-bit registers. @code{D0}, @code{D1}. + +@item I +A signed 12-bit integer constant. + +@item Cal +constant for arithmetic/logical operations. This might be any constant +that can be put into a long immediate by the assmbler or linker without +involving a PIC relocation. + +@item K +A 3-bit unsigned integer constant. + +@item L +A 6-bit unsigned integer constant. + +@item CnL +One's complement of a 6-bit unsigned integer constant. + +@item CmL +Two's complement of a 6-bit unsigned integer constant. + +@item M +A 5-bit unsigned integer constant. + +@item O +A 7-bit unsigned integer constant. + +@item P +A 8-bit unsigned integer constant. + +@item H +Any const_double value. +@end table + +@item ARM family---@file{config/arm/constraints.md} +@table @code + +@item h +In Thumb state, the core registers @code{r8}-@code{r15}. + +@item k +The stack pointer register. + +@item l +In Thumb State the core registers @code{r0}-@code{r7}. In ARM state this +is an alias for the @code{r} constraint. + +@item t +VFP floating-point registers @code{s0}-@code{s31}. Used for 32 bit values. + +@item w +VFP floating-point registers @code{d0}-@code{d31} and the appropriate +subset @code{d0}-@code{d15} based on command line options. +Used for 64 bit values only. Not valid for Thumb1. + +@item y +The iWMMX co-processor registers. + +@item z +The iWMMX GR registers. + +@item G +The floating-point constant 0.0 + +@item I +Integer that is valid as an immediate operand in a data processing +instruction. That is, an integer in the range 0 to 255 rotated by a +multiple of 2 + +@item J +Integer in the range @minus{}4095 to 4095 + +@item K +Integer that satisfies constraint @samp{I} when inverted (ones complement) + +@item L +Integer that satisfies constraint @samp{I} when negated (twos complement) + +@item M +Integer in the range 0 to 32 + +@item Q +A memory reference where the exact address is in a single register +(`@samp{m}' is preferable for @code{asm} statements) + +@item R +An item in the constant pool + +@item S +A symbol in the text segment of the current file + +@item Uv +A memory reference suitable for VFP load/store insns (reg+constant offset) + +@item Uy +A memory reference suitable for iWMMXt load/store instructions. + +@item Uq +A memory reference suitable for the ARMv4 ldrsb instruction. +@end table + +@item AVR family---@file{config/avr/constraints.md} +@table @code +@item l +Registers from r0 to r15 + +@item a +Registers from r16 to r23 + +@item d +Registers from r16 to r31 + +@item w +Registers from r24 to r31. These registers can be used in @samp{adiw} command + +@item e +Pointer register (r26--r31) + +@item b +Base pointer register (r28--r31) + +@item q +Stack pointer register (SPH:SPL) + +@item t +Temporary register r0 + +@item x +Register pair X (r27:r26) + +@item y +Register pair Y (r29:r28) + +@item z +Register pair Z (r31:r30) + +@item I +Constant greater than @minus{}1, less than 64 + +@item J +Constant greater than @minus{}64, less than 1 + +@item K +Constant integer 2 + +@item L +Constant integer 0 + +@item M +Constant that fits in 8 bits + +@item N +Constant integer @minus{}1 + +@item O +Constant integer 8, 16, or 24 + +@item P +Constant integer 1 + +@item G +A floating point constant 0.0 + +@item Q +A memory address based on Y or Z pointer with displacement. +@end table + +@item Blackfin family---@file{config/bfin/constraints.md} +@table @code +@item a +P register + +@item d +D register + +@item z +A call clobbered P register. + +@item q@var{n} +A single register. If @var{n} is in the range 0 to 7, the corresponding D +register. If it is @code{A}, then the register P0. + +@item D +Even-numbered D register + +@item W +Odd-numbered D register + +@item e +Accumulator register. + +@item A +Even-numbered accumulator register. + +@item B +Odd-numbered accumulator register. + +@item b +I register + +@item v +B register + +@item f +M register + +@item c +Registers used for circular buffering, i.e.@: I, B, or L registers. + +@item C +The CC register. + +@item t +LT0 or LT1. + +@item k +LC0 or LC1. + +@item u +LB0 or LB1. + +@item x +Any D, P, B, M, I or L register. + +@item y +Additional registers typically used only in prologues and epilogues: RETS, +RETN, RETI, RETX, RETE, ASTAT, SEQSTAT and USP. + +@item w +Any register except accumulators or CC. + +@item Ksh +Signed 16 bit integer (in the range @minus{}32768 to 32767) + +@item Kuh +Unsigned 16 bit integer (in the range 0 to 65535) + +@item Ks7 +Signed 7 bit integer (in the range @minus{}64 to 63) + +@item Ku7 +Unsigned 7 bit integer (in the range 0 to 127) + +@item Ku5 +Unsigned 5 bit integer (in the range 0 to 31) + +@item Ks4 +Signed 4 bit integer (in the range @minus{}8 to 7) + +@item Ks3 +Signed 3 bit integer (in the range @minus{}3 to 4) + +@item Ku3 +Unsigned 3 bit integer (in the range 0 to 7) + +@item P@var{n} +Constant @var{n}, where @var{n} is a single-digit constant in the range 0 to 4. + +@item PA +An integer equal to one of the MACFLAG_XXX constants that is suitable for +use with either accumulator. + +@item PB +An integer equal to one of the MACFLAG_XXX constants that is suitable for +use only with accumulator A1. + +@item M1 +Constant 255. + +@item M2 +Constant 65535. + +@item J +An integer constant with exactly a single bit set. + +@item L +An integer constant with all bits set except exactly one. + +@item H + +@item Q +Any SYMBOL_REF. +@end table + +@item C-SKY---@file{config/csky/constraints.md} +@table @code + +@item a +The mini registers r0 - r7. + +@item b +The low registers r0 - r15. + +@item c +C register. + +@item y +HI and LO registers. + +@item l +LO register. + +@item h +HI register. + +@item v +Vector registers. + +@item z +Stack pointer register (SP). + +@item Q +A memory address which uses a base register with a short offset +or with a index register with its scale. + +@item W +A memory address which uses a base register with a index register +with its scale. +@end table + +@ifset INTERNALS +The C-SKY back end supports a large set of additional constraints +that are only useful for instruction selection or splitting rather +than inline asm, such as constraints representing constant integer +ranges accepted by particular instruction encodings. +Refer to the source code for details. +@end ifset + +@item Epiphany---@file{config/epiphany/constraints.md} +@table @code +@item U16 +An unsigned 16-bit constant. + +@item K +An unsigned 5-bit constant. + +@item L +A signed 11-bit constant. + +@item Cm1 +A signed 11-bit constant added to @minus{}1. +Can only match when the @option{-m1reg-@var{reg}} option is active. + +@item Cl1 +Left-shift of @minus{}1, i.e., a bit mask with a block of leading ones, the rest +being a block of trailing zeroes. +Can only match when the @option{-m1reg-@var{reg}} option is active. + +@item Cr1 +Right-shift of @minus{}1, i.e., a bit mask with a trailing block of ones, the +rest being zeroes. Or to put it another way, one less than a power of two. +Can only match when the @option{-m1reg-@var{reg}} option is active. + +@item Cal +Constant for arithmetic/logical operations. +This is like @code{i}, except that for position independent code, +no symbols / expressions needing relocations are allowed. + +@item Csy +Symbolic constant for call/jump instruction. + +@item Rcs +The register class usable in short insns. This is a register class +constraint, and can thus drive register allocation. +This constraint won't match unless @option{-mprefer-short-insn-regs} is +in effect. + +@item Rsc +The register class of registers that can be used to hold a +sibcall call address. I.e., a caller-saved register. + +@item Rct +Core control register class. + +@item Rgs +The register group usable in short insns. +This constraint does not use a register class, so that it only +passively matches suitable registers, and doesn't drive register allocation. + +@ifset INTERNALS +@item Car +Constant suitable for the addsi3_r pattern. This is a valid offset +For byte, halfword, or word addressing. +@end ifset + +@item Rra +Matches the return address if it can be replaced with the link register. + +@item Rcc +Matches the integer condition code register. + +@item Sra +Matches the return address if it is in a stack slot. + +@item Cfm +Matches control register values to switch fp mode, which are encapsulated in +@code{UNSPEC_FP_MODE}. +@end table + +@item FRV---@file{config/frv/frv.h} +@table @code +@item a +Register in the class @code{ACC_REGS} (@code{acc0} to @code{acc7}). + +@item b +Register in the class @code{EVEN_ACC_REGS} (@code{acc0} to @code{acc7}). + +@item c +Register in the class @code{CC_REGS} (@code{fcc0} to @code{fcc3} and +@code{icc0} to @code{icc3}). + +@item d +Register in the class @code{GPR_REGS} (@code{gr0} to @code{gr63}). + +@item e +Register in the class @code{EVEN_REGS} (@code{gr0} to @code{gr63}). +Odd registers are excluded not in the class but through the use of a machine +mode larger than 4 bytes. + +@item f +Register in the class @code{FPR_REGS} (@code{fr0} to @code{fr63}). + +@item h +Register in the class @code{FEVEN_REGS} (@code{fr0} to @code{fr63}). +Odd registers are excluded not in the class but through the use of a machine +mode larger than 4 bytes. + +@item l +Register in the class @code{LR_REG} (the @code{lr} register). + +@item q +Register in the class @code{QUAD_REGS} (@code{gr2} to @code{gr63}). +Register numbers not divisible by 4 are excluded not in the class but through +the use of a machine mode larger than 8 bytes. + +@item t +Register in the class @code{ICC_REGS} (@code{icc0} to @code{icc3}). + +@item u +Register in the class @code{FCC_REGS} (@code{fcc0} to @code{fcc3}). + +@item v +Register in the class @code{ICR_REGS} (@code{cc4} to @code{cc7}). + +@item w +Register in the class @code{FCR_REGS} (@code{cc0} to @code{cc3}). + +@item x +Register in the class @code{QUAD_FPR_REGS} (@code{fr0} to @code{fr63}). +Register numbers not divisible by 4 are excluded not in the class but through +the use of a machine mode larger than 8 bytes. + +@item z +Register in the class @code{SPR_REGS} (@code{lcr} and @code{lr}). + +@item A +Register in the class @code{QUAD_ACC_REGS} (@code{acc0} to @code{acc7}). + +@item B +Register in the class @code{ACCG_REGS} (@code{accg0} to @code{accg7}). + +@item C +Register in the class @code{CR_REGS} (@code{cc0} to @code{cc7}). + +@item G +Floating point constant zero + +@item I +6-bit signed integer constant + +@item J +10-bit signed integer constant + +@item L +16-bit signed integer constant + +@item M +16-bit unsigned integer constant + +@item N +12-bit signed integer constant that is negative---i.e.@: in the +range of @minus{}2048 to @minus{}1 + +@item O +Constant zero + +@item P +12-bit signed integer constant that is greater than zero---i.e.@: in the +range of 1 to 2047. + +@end table + +@item FT32---@file{config/ft32/constraints.md} +@table @code +@item A +An absolute address + +@item B +An offset address + +@item W +A register indirect memory operand + +@item e +An offset address. + +@item f +An offset address. + +@item O +The constant zero or one + +@item I +A 16-bit signed constant (@minus{}32768 @dots{} 32767) + +@item w +A bitfield mask suitable for bext or bins + +@item x +An inverted bitfield mask suitable for bext or bins + +@item L +A 16-bit unsigned constant, multiple of 4 (0 @dots{} 65532) + +@item S +A 20-bit signed constant (@minus{}524288 @dots{} 524287) + +@item b +A constant for a bitfield width (1 @dots{} 16) + +@item KA +A 10-bit signed constant (@minus{}512 @dots{} 511) + +@end table + +@item Hewlett-Packard PA-RISC---@file{config/pa/pa.h} +@table @code +@item a +General register 1 + +@item f +Floating point register + +@item q +Shift amount register + +@item x +Floating point register (deprecated) + +@item y +Upper floating point register (32-bit), floating point register (64-bit) + +@item Z +Any register + +@item I +Signed 11-bit integer constant + +@item J +Signed 14-bit integer constant + +@item K +Integer constant that can be deposited with a @code{zdepi} instruction + +@item L +Signed 5-bit integer constant + +@item M +Integer constant 0 + +@item N +Integer constant that can be loaded with a @code{ldil} instruction + +@item O +Integer constant whose value plus one is a power of 2 + +@item P +Integer constant that can be used for @code{and} operations in @code{depi} +and @code{extru} instructions + +@item S +Integer constant 31 + +@item U +Integer constant 63 + +@item G +Floating-point constant 0.0 + +@item A +A @code{lo_sum} data-linkage-table memory operand + +@item Q +A memory operand that can be used as the destination operand of an +integer store instruction + +@item R +A scaled or unscaled indexed memory operand + +@item T +A memory operand for floating-point loads and stores + +@item W +A register indirect memory operand +@end table + +@item Intel IA-64---@file{config/ia64/ia64.h} +@table @code +@item a +General register @code{r0} to @code{r3} for @code{addl} instruction + +@item b +Branch register + +@item c +Predicate register (@samp{c} as in ``conditional'') + +@item d +Application register residing in M-unit + +@item e +Application register residing in I-unit + +@item f +Floating-point register + +@item m +Memory operand. If used together with @samp{<} or @samp{>}, +the operand can have postincrement and postdecrement which +require printing with @samp{%Pn} on IA-64. + +@item G +Floating-point constant 0.0 or 1.0 + +@item I +14-bit signed integer constant + +@item J +22-bit signed integer constant + +@item K +8-bit signed integer constant for logical instructions + +@item L +8-bit adjusted signed integer constant for compare pseudo-ops + +@item M +6-bit unsigned integer constant for shift counts + +@item N +9-bit signed integer constant for load and store postincrements + +@item O +The constant zero + +@item P +0 or @minus{}1 for @code{dep} instruction + +@item Q +Non-volatile memory for floating-point loads and stores + +@item R +Integer constant in the range 1 to 4 for @code{shladd} instruction + +@item S +Memory operand except postincrement and postdecrement. This is +now roughly the same as @samp{m} when not used together with @samp{<} +or @samp{>}. +@end table + +@item M32C---@file{config/m32c/m32c.cc} +@table @code +@item Rsp +@itemx Rfb +@itemx Rsb +@samp{$sp}, @samp{$fb}, @samp{$sb}. + +@item Rcr +Any control register, when they're 16 bits wide (nothing if control +registers are 24 bits wide) + +@item Rcl +Any control register, when they're 24 bits wide. + +@item R0w +@itemx R1w +@itemx R2w +@itemx R3w +$r0, $r1, $r2, $r3. + +@item R02 +$r0 or $r2, or $r2r0 for 32 bit values. + +@item R13 +$r1 or $r3, or $r3r1 for 32 bit values. + +@item Rdi +A register that can hold a 64 bit value. + +@item Rhl +$r0 or $r1 (registers with addressable high/low bytes) + +@item R23 +$r2 or $r3 + +@item Raa +Address registers + +@item Raw +Address registers when they're 16 bits wide. + +@item Ral +Address registers when they're 24 bits wide. + +@item Rqi +Registers that can hold QI values. + +@item Rad +Registers that can be used with displacements ($a0, $a1, $sb). + +@item Rsi +Registers that can hold 32 bit values. + +@item Rhi +Registers that can hold 16 bit values. + +@item Rhc +Registers chat can hold 16 bit values, including all control +registers. + +@item Rra +$r0 through R1, plus $a0 and $a1. + +@item Rfl +The flags register. + +@item Rmm +The memory-based pseudo-registers $mem0 through $mem15. + +@item Rpi +Registers that can hold pointers (16 bit registers for r8c, m16c; 24 +bit registers for m32cm, m32c). + +@item Rpa +Matches multiple registers in a PARALLEL to form a larger register. +Used to match function return values. + +@item Is3 +@minus{}8 @dots{} 7 + +@item IS1 +@minus{}128 @dots{} 127 + +@item IS2 +@minus{}32768 @dots{} 32767 + +@item IU2 +0 @dots{} 65535 + +@item In4 +@minus{}8 @dots{} @minus{}1 or 1 @dots{} 8 + +@item In5 +@minus{}16 @dots{} @minus{}1 or 1 @dots{} 16 + +@item In6 +@minus{}32 @dots{} @minus{}1 or 1 @dots{} 32 + +@item IM2 +@minus{}65536 @dots{} @minus{}1 + +@item Ilb +An 8 bit value with exactly one bit set. + +@item Ilw +A 16 bit value with exactly one bit set. + +@item Sd +The common src/dest memory addressing modes. + +@item Sa +Memory addressed using $a0 or $a1. + +@item Si +Memory addressed with immediate addresses. + +@item Ss +Memory addressed using the stack pointer ($sp). + +@item Sf +Memory addressed using the frame base register ($fb). + +@item Ss +Memory addressed using the small base register ($sb). + +@item S1 +$r1h +@end table + +@item LoongArch---@file{config/loongarch/constraints.md} +@table @code +@item f +A floating-point register (if available). +@item k +A memory operand whose address is formed by a base register and +(optionally scaled) index register. +@item l +A signed 16-bit constant. +@item m +A memory operand whose address is formed by a base register and offset +that is suitable for use in instructions with the same addressing mode +as @code{st.w} and @code{ld.w}. +@item I +A signed 12-bit constant (for arithmetic instructions). +@item K +An unsigned 12-bit constant (for logic instructions). +@item ZB +An address that is held in a general-purpose register. +The offset is zero. +@item ZC +A memory operand whose address is formed by a base register and offset +that is suitable for use in instructions with the same addressing mode +as @code{ll.w} and @code{sc.w}. +@end table + +@item MicroBlaze---@file{config/microblaze/constraints.md} +@table @code +@item d +A general register (@code{r0} to @code{r31}). + +@item z +A status register (@code{rmsr}, @code{$fcc1} to @code{$fcc7}). + +@end table + +@item MIPS---@file{config/mips/constraints.md} +@table @code +@item d +A general-purpose register. This is equivalent to @code{r} unless +generating MIPS16 code, in which case the MIPS16 register set is used. + +@item f +A floating-point register (if available). + +@item h +Formerly the @code{hi} register. This constraint is no longer supported. + +@item l +The @code{lo} register. Use this register to store values that are +no bigger than a word. + +@item x +The concatenated @code{hi} and @code{lo} registers. Use this register +to store doubleword values. + +@item c +A register suitable for use in an indirect jump. This will always be +@code{$25} for @option{-mabicalls}. + +@item v +Register @code{$3}. Do not use this constraint in new code; +it is retained only for compatibility with glibc. + +@item y +Equivalent to @code{r}; retained for backwards compatibility. + +@item z +A floating-point condition code register. + +@item I +A signed 16-bit constant (for arithmetic instructions). + +@item J +Integer zero. + +@item K +An unsigned 16-bit constant (for logic instructions). + +@item L +A signed 32-bit constant in which the lower 16 bits are zero. +Such constants can be loaded using @code{lui}. + +@item M +A constant that cannot be loaded using @code{lui}, @code{addiu} +or @code{ori}. + +@item N +A constant in the range @minus{}65535 to @minus{}1 (inclusive). + +@item O +A signed 15-bit constant. + +@item P +A constant in the range 1 to 65535 (inclusive). + +@item G +Floating-point zero. + +@item R +An address that can be used in a non-macro load or store. + +@item ZC +A memory operand whose address is formed by a base register and offset +that is suitable for use in instructions with the same addressing mode +as @code{ll} and @code{sc}. + +@item ZD +An address suitable for a @code{prefetch} instruction, or for any other +instruction with the same addressing mode as @code{prefetch}. +@end table + +@item Motorola 680x0---@file{config/m68k/constraints.md} +@table @code +@item a +Address register + +@item d +Data register + +@item f +68881 floating-point register, if available + +@item I +Integer in the range 1 to 8 + +@item J +16-bit signed number + +@item K +Signed number whose magnitude is greater than 0x80 + +@item L +Integer in the range @minus{}8 to @minus{}1 + +@item M +Signed number whose magnitude is greater than 0x100 + +@item N +Range 24 to 31, rotatert:SI 8 to 1 expressed as rotate + +@item O +16 (for rotate using swap) + +@item P +Range 8 to 15, rotatert:HI 8 to 1 expressed as rotate + +@item R +Numbers that mov3q can handle + +@item G +Floating point constant that is not a 68881 constant + +@item S +Operands that satisfy 'm' when -mpcrel is in effect + +@item T +Operands that satisfy 's' when -mpcrel is not in effect + +@item Q +Address register indirect addressing mode + +@item U +Register offset addressing + +@item W +const_call_operand + +@item Cs +symbol_ref or const + +@item Ci +const_int + +@item C0 +const_int 0 + +@item Cj +Range of signed numbers that don't fit in 16 bits + +@item Cmvq +Integers valid for mvq + +@item Capsw +Integers valid for a moveq followed by a swap + +@item Cmvz +Integers valid for mvz + +@item Cmvs +Integers valid for mvs + +@item Ap +push_operand + +@item Ac +Non-register operands allowed in clr + +@end table + +@item Moxie---@file{config/moxie/constraints.md} +@table @code +@item A +An absolute address + +@item B +An offset address + +@item W +A register indirect memory operand + +@item I +A constant in the range of 0 to 255. + +@item N +A constant in the range of 0 to @minus{}255. + +@end table + +@item MSP430--@file{config/msp430/constraints.md} +@table @code + +@item R12 +Register R12. + +@item R13 +Register R13. + +@item K +Integer constant 1. + +@item L +Integer constant -1^20..1^19. + +@item M +Integer constant 1-4. + +@item Ya +Memory references which do not require an extended MOVX instruction. + +@item Yl +Memory reference, labels only. + +@item Ys +Memory reference, stack only. + +@end table + +@item NDS32---@file{config/nds32/constraints.md} +@table @code +@item w +LOW register class $r0 to $r7 constraint for V3/V3M ISA. +@item l +LOW register class $r0 to $r7. +@item d +MIDDLE register class $r0 to $r11, $r16 to $r19. +@item h +HIGH register class $r12 to $r14, $r20 to $r31. +@item t +Temporary assist register $ta (i.e.@: $r15). +@item k +Stack register $sp. +@item Iu03 +Unsigned immediate 3-bit value. +@item In03 +Negative immediate 3-bit value in the range of @minus{}7--0. +@item Iu04 +Unsigned immediate 4-bit value. +@item Is05 +Signed immediate 5-bit value. +@item Iu05 +Unsigned immediate 5-bit value. +@item In05 +Negative immediate 5-bit value in the range of @minus{}31--0. +@item Ip05 +Unsigned immediate 5-bit value for movpi45 instruction with range 16--47. +@item Iu06 +Unsigned immediate 6-bit value constraint for addri36.sp instruction. +@item Iu08 +Unsigned immediate 8-bit value. +@item Iu09 +Unsigned immediate 9-bit value. +@item Is10 +Signed immediate 10-bit value. +@item Is11 +Signed immediate 11-bit value. +@item Is15 +Signed immediate 15-bit value. +@item Iu15 +Unsigned immediate 15-bit value. +@item Ic15 +A constant which is not in the range of imm15u but ok for bclr instruction. +@item Ie15 +A constant which is not in the range of imm15u but ok for bset instruction. +@item It15 +A constant which is not in the range of imm15u but ok for btgl instruction. +@item Ii15 +A constant whose compliment value is in the range of imm15u +and ok for bitci instruction. +@item Is16 +Signed immediate 16-bit value. +@item Is17 +Signed immediate 17-bit value. +@item Is19 +Signed immediate 19-bit value. +@item Is20 +Signed immediate 20-bit value. +@item Ihig +The immediate value that can be simply set high 20-bit. +@item Izeb +The immediate value 0xff. +@item Izeh +The immediate value 0xffff. +@item Ixls +The immediate value 0x01. +@item Ix11 +The immediate value 0x7ff. +@item Ibms +The immediate value with power of 2. +@item Ifex +The immediate value with power of 2 minus 1. +@item U33 +Memory constraint for 333 format. +@item U45 +Memory constraint for 45 format. +@item U37 +Memory constraint for 37 format. +@end table + +@item Nios II family---@file{config/nios2/constraints.md} +@table @code + +@item I +Integer that is valid as an immediate operand in an +instruction taking a signed 16-bit number. Range +@minus{}32768 to 32767. + +@item J +Integer that is valid as an immediate operand in an +instruction taking an unsigned 16-bit number. Range +0 to 65535. + +@item K +Integer that is valid as an immediate operand in an +instruction taking only the upper 16-bits of a +32-bit number. Range 32-bit numbers with the lower +16-bits being 0. + +@item L +Integer that is valid as an immediate operand for a +shift instruction. Range 0 to 31. + +@item M +Integer that is valid as an immediate operand for +only the value 0. Can be used in conjunction with +the format modifier @code{z} to use @code{r0} +instead of @code{0} in the assembly output. + +@item N +Integer that is valid as an immediate operand for +a custom instruction opcode. Range 0 to 255. + +@item P +An immediate operand for R2 andchi/andci instructions. + +@item S +Matches immediates which are addresses in the small +data section and therefore can be added to @code{gp} +as a 16-bit immediate to re-create their 32-bit value. + +@item U +Matches constants suitable as an operand for the rdprs and +cache instructions. + +@item v +A memory operand suitable for Nios II R2 load/store +exclusive instructions. + +@item w +A memory operand suitable for load/store IO and cache +instructions. + +@ifset INTERNALS +@item T +A @code{const} wrapped @code{UNSPEC} expression, +representing a supported PIC or TLS relocation. +@end ifset + +@end table + +@item OpenRISC---@file{config/or1k/constraints.md} +@table @code +@item I +Integer that is valid as an immediate operand in an +instruction taking a signed 16-bit number. Range +@minus{}32768 to 32767. + +@item K +Integer that is valid as an immediate operand in an +instruction taking an unsigned 16-bit number. Range +0 to 65535. + +@item M +Signed 16-bit constant shifted left 16 bits. (Used with @code{l.movhi}) + +@item O +Zero + +@ifset INTERNALS +@item c +Register usable for sibcalls. +@end ifset + +@end table + +@item PDP-11---@file{config/pdp11/constraints.md} +@table @code +@item a +Floating point registers AC0 through AC3. These can be loaded from/to +memory with a single instruction. + +@item d +Odd numbered general registers (R1, R3, R5). These are used for +16-bit multiply operations. + +@item D +A memory reference that is encoded within the opcode, but not +auto-increment or auto-decrement. + +@item f +Any of the floating point registers (AC0 through AC5). + +@item G +Floating point constant 0. + +@item h +Floating point registers AC4 and AC5. These cannot be loaded from/to +memory with a single instruction. + +@item I +An integer constant that fits in 16 bits. + +@item J +An integer constant whose low order 16 bits are zero. + +@item K +An integer constant that does not meet the constraints for codes +@samp{I} or @samp{J}. + +@item L +The integer constant 1. + +@item M +The integer constant @minus{}1. + +@item N +The integer constant 0. + +@item O +Integer constants 0 through 3; shifts by these +amounts are handled as multiple single-bit shifts rather than a single +variable-length shift. + +@item Q +A memory reference which requires an additional word (address or +offset) after the opcode. + +@item R +A memory reference that is encoded within the opcode. + +@end table + +@item PowerPC and IBM RS6000---@file{config/rs6000/constraints.md} +@table @code +@item r +A general purpose register (GPR), @code{r0}@dots{}@code{r31}. + +@item b +A base register. Like @code{r}, but @code{r0} is not allowed, so +@code{r1}@dots{}@code{r31}. + +@item f +A floating point register (FPR), @code{f0}@dots{}@code{f31}. + +@item d +A floating point register. This is the same as @code{f} nowadays; +historically @code{f} was for single-precision and @code{d} was for +double-precision floating point. + +@item v +An Altivec vector register (VR), @code{v0}@dots{}@code{v31}. + +@item wa +A VSX register (VSR), @code{vs0}@dots{}@code{vs63}. This is either an +FPR (@code{vs0}@dots{}@code{vs31} are @code{f0}@dots{}@code{f31}) or a VR +(@code{vs32}@dots{}@code{vs63} are @code{v0}@dots{}@code{v31}). + +When using @code{wa}, you should use the @code{%x} output modifier, so that +the correct register number is printed. For example: + +@smallexample +asm ("xvadddp %x0,%x1,%x2" + : "=wa" (v1) + : "wa" (v2), "wa" (v3)); +@end smallexample + +You should not use @code{%x} for @code{v} operands: + +@smallexample +asm ("xsaddqp %0,%1,%2" + : "=v" (v1) + : "v" (v2), "v" (v3)); +@end smallexample + +@ifset INTERNALS +@item h +A special register (@code{vrsave}, @code{ctr}, or @code{lr}). +@end ifset + +@item c +The count register, @code{ctr}. + +@item l +The link register, @code{lr}. + +@item x +Condition register field 0, @code{cr0}. + +@item y +Any condition register field, @code{cr0}@dots{}@code{cr7}. + +@ifset INTERNALS +@item z +The carry bit, @code{XER[CA]}. + +@item we +Like @code{wa}, if @option{-mpower9-vector} and @option{-m64} are used; +otherwise, @code{NO_REGS}. + +@item wn +No register (@code{NO_REGS}). + +@item wr +Like @code{r}, if @option{-mpowerpc64} is used; otherwise, @code{NO_REGS}. + +@item wx +Like @code{d}, if @option{-mpowerpc-gfxopt} is used; otherwise, @code{NO_REGS}. + +@item wA +Like @code{b}, if @option{-mpowerpc64} is used; otherwise, @code{NO_REGS}. + +@item wB +Signed 5-bit constant integer that can be loaded into an Altivec register. + +@item wE +Vector constant that can be loaded with the XXSPLTIB instruction. + +@item wF +Memory operand suitable for power8 GPR load fusion. + +@item wL +Int constant that is the element number mfvsrld accesses in a vector. + +@item wM +Match vector constant with all 1's if the XXLORC instruction is available. + +@item wO +Memory operand suitable for the ISA 3.0 vector d-form instructions. + +@item wQ +Memory operand suitable for the load/store quad instructions. + +@item wS +Vector constant that can be loaded with XXSPLTIB & sign extension. + +@item wY +A memory operand for a DS-form instruction. + +@item wZ +An indexed or indirect memory operand, ignoring the bottom 4 bits. +@end ifset + +@item I +A signed 16-bit constant. + +@item J +An unsigned 16-bit constant shifted left 16 bits (use @code{L} instead +for @code{SImode} constants). + +@item K +An unsigned 16-bit constant. + +@item L +A signed 16-bit constant shifted left 16 bits. + +@ifset INTERNALS +@item M +An integer constant greater than 31. + +@item N +An exact power of 2. + +@item O +The integer constant zero. + +@item P +A constant whose negation is a signed 16-bit constant. +@end ifset + +@item eI +A signed 34-bit integer constant if prefixed instructions are supported. + +@item eP +A scalar floating point constant or a vector constant that can be +loaded to a VSX register with one prefixed instruction. + +@item eQ +An IEEE 128-bit constant that can be loaded into a VSX register with +the @code{lxvkq} instruction. + +@ifset INTERNALS +@item G +A floating point constant that can be loaded into a register with one +instruction per word. + +@item H +A floating point constant that can be loaded into a register using +three instructions. +@end ifset + +@item m +A memory operand. +Normally, @code{m} does not allow addresses that update the base register. +If the @code{<} or @code{>} constraint is also used, they are allowed and +therefore on PowerPC targets in that case it is only safe +to use @code{m<>} in an @code{asm} statement if that @code{asm} statement +accesses the operand exactly once. The @code{asm} statement must also +use @code{%U@var{}} as a placeholder for the ``update'' flag in the +corresponding load or store instruction. For example: + +@smallexample +asm ("st%U0 %1,%0" : "=m<>" (mem) : "r" (val)); +@end smallexample + +is correct but: + +@smallexample +asm ("st %1,%0" : "=m<>" (mem) : "r" (val)); +@end smallexample + +is not. + +@ifset INTERNALS +@item es +A ``stable'' memory operand; that is, one which does not include any +automodification of the base register. This used to be useful when +@code{m} allowed automodification of the base register, but as those +are now only allowed when @code{<} or @code{>} is used, @code{es} is +basically the same as @code{m} without @code{<} and @code{>}. +@end ifset + +@item Q +A memory operand addressed by just a base register. + +@ifset INTERNALS +@item Y +A memory operand for a DQ-form instruction. +@end ifset + +@item Z +A memory operand accessed with indexed or indirect addressing. + +@ifset INTERNALS +@item R +An AIX TOC entry. +@end ifset + +@item a +An indexed or indirect address. + +@ifset INTERNALS +@item U +A V.4 small data reference. + +@item W +A vector constant that does not require memory. + +@item j +The zero vector constant. +@end ifset + +@end table + +@item PRU---@file{config/pru/constraints.md} +@table @code +@item I +An unsigned 8-bit integer constant. + +@item J +An unsigned 16-bit integer constant. + +@item L +An unsigned 5-bit integer constant (for shift counts). + +@item T +A text segment (program memory) constant label. + +@item Z +Integer constant zero. + +@end table + +@item RL78---@file{config/rl78/constraints.md} +@table @code + +@item Int3 +An integer constant in the range 1 @dots{} 7. +@item Int8 +An integer constant in the range 0 @dots{} 255. +@item J +An integer constant in the range @minus{}255 @dots{} 0 +@item K +The integer constant 1. +@item L +The integer constant -1. +@item M +The integer constant 0. +@item N +The integer constant 2. +@item O +The integer constant -2. +@item P +An integer constant in the range 1 @dots{} 15. +@item Qbi +The built-in compare types--eq, ne, gtu, ltu, geu, and leu. +@item Qsc +The synthetic compare types--gt, lt, ge, and le. +@item Wab +A memory reference with an absolute address. +@item Wbc +A memory reference using @code{BC} as a base register, with an optional offset. +@item Wca +A memory reference using @code{AX}, @code{BC}, @code{DE}, or @code{HL} for the address, for calls. +@item Wcv +A memory reference using any 16-bit register pair for the address, for calls. +@item Wd2 +A memory reference using @code{DE} as a base register, with an optional offset. +@item Wde +A memory reference using @code{DE} as a base register, without any offset. +@item Wfr +Any memory reference to an address in the far address space. +@item Wh1 +A memory reference using @code{HL} as a base register, with an optional one-byte offset. +@item Whb +A memory reference using @code{HL} as a base register, with @code{B} or @code{C} as the index register. +@item Whl +A memory reference using @code{HL} as a base register, without any offset. +@item Ws1 +A memory reference using @code{SP} as a base register, with an optional one-byte offset. +@item Y +Any memory reference to an address in the near address space. +@item A +The @code{AX} register. +@item B +The @code{BC} register. +@item D +The @code{DE} register. +@item R +@code{A} through @code{L} registers. +@item S +The @code{SP} register. +@item T +The @code{HL} register. +@item Z08W +The 16-bit @code{R8} register. +@item Z10W +The 16-bit @code{R10} register. +@item Zint +The registers reserved for interrupts (@code{R24} to @code{R31}). +@item a +The @code{A} register. +@item b +The @code{B} register. +@item c +The @code{C} register. +@item d +The @code{D} register. +@item e +The @code{E} register. +@item h +The @code{H} register. +@item l +The @code{L} register. +@item v +The virtual registers. +@item w +The @code{PSW} register. +@item x +The @code{X} register. + +@end table + +@item RISC-V---@file{config/riscv/constraints.md} +@table @code + +@item f +A floating-point register (if available). + +@item I +An I-type 12-bit signed immediate. + +@item J +Integer zero. + +@item K +A 5-bit unsigned immediate for CSR access instructions. + +@item A +An address that is held in a general-purpose register. + +@item S +A constraint that matches an absolute symbolic address. + +@end table + +@item RX---@file{config/rx/constraints.md} +@table @code +@item Q +An address which does not involve register indirect addressing or +pre/post increment/decrement addressing. + +@item Symbol +A symbol reference. + +@item Int08 +A constant in the range @minus{}256 to 255, inclusive. + +@item Sint08 +A constant in the range @minus{}128 to 127, inclusive. + +@item Sint16 +A constant in the range @minus{}32768 to 32767, inclusive. + +@item Sint24 +A constant in the range @minus{}8388608 to 8388607, inclusive. + +@item Uint04 +A constant in the range 0 to 15, inclusive. + +@end table + +@item S/390 and zSeries---@file{config/s390/s390.h} +@table @code +@item a +Address register (general purpose register except r0) + +@item c +Condition code register + +@item d +Data register (arbitrary general purpose register) + +@item f +Floating-point register + +@item I +Unsigned 8-bit constant (0--255) + +@item J +Unsigned 12-bit constant (0--4095) + +@item K +Signed 16-bit constant (@minus{}32768--32767) + +@item L +Value appropriate as displacement. +@table @code +@item (0..4095) +for short displacement +@item (@minus{}524288..524287) +for long displacement +@end table + +@item M +Constant integer with a value of 0x7fffffff. + +@item N +Multiple letter constraint followed by 4 parameter letters. +@table @code +@item 0..9: +number of the part counting from most to least significant +@item H,Q: +mode of the part +@item D,S,H: +mode of the containing operand +@item 0,F: +value of the other parts (F---all bits set) +@end table +The constraint matches if the specified part of a constant +has a value different from its other parts. + +@item Q +Memory reference without index register and with short displacement. + +@item R +Memory reference with index register and short displacement. + +@item S +Memory reference without index register but with long displacement. + +@item T +Memory reference with index register and long displacement. + +@item U +Pointer with short displacement. + +@item W +Pointer with long displacement. + +@item Y +Shift count operand. + +@end table + +@need 1000 +@item SPARC---@file{config/sparc/sparc.h} +@table @code +@item f +Floating-point register on the SPARC-V8 architecture and +lower floating-point register on the SPARC-V9 architecture. + +@item e +Floating-point register. It is equivalent to @samp{f} on the +SPARC-V8 architecture and contains both lower and upper +floating-point registers on the SPARC-V9 architecture. + +@item c +Floating-point condition code register. + +@item d +Lower floating-point register. It is only valid on the SPARC-V9 +architecture when the Visual Instruction Set is available. + +@item b +Floating-point register. It is only valid on the SPARC-V9 architecture +when the Visual Instruction Set is available. + +@item h +64-bit global or out register for the SPARC-V8+ architecture. + +@item C +The constant all-ones, for floating-point. + +@item A +Signed 5-bit constant + +@item D +A vector constant + +@item I +Signed 13-bit constant + +@item J +Zero + +@item K +32-bit constant with the low 12 bits clear (a constant that can be +loaded with the @code{sethi} instruction) + +@item L +A constant in the range supported by @code{movcc} instructions (11-bit +signed immediate) + +@item M +A constant in the range supported by @code{movrcc} instructions (10-bit +signed immediate) + +@item N +Same as @samp{K}, except that it verifies that bits that are not in the +lower 32-bit range are all zero. Must be used instead of @samp{K} for +modes wider than @code{SImode} + +@item O +The constant 4096 + +@item G +Floating-point zero + +@item H +Signed 13-bit constant, sign-extended to 32 or 64 bits + +@item P +The constant -1 + +@item Q +Floating-point constant whose integral representation can +be moved into an integer register using a single sethi +instruction + +@item R +Floating-point constant whose integral representation can +be moved into an integer register using a single mov +instruction + +@item S +Floating-point constant whose integral representation can +be moved into an integer register using a high/lo_sum +instruction sequence + +@item T +Memory address aligned to an 8-byte boundary + +@item U +Even register + +@item W +Memory address for @samp{e} constraint registers + +@item w +Memory address with only a base register + +@item Y +Vector zero + +@end table + +@item TI C6X family---@file{config/c6x/constraints.md} +@table @code +@item a +Register file A (A0--A31). + +@item b +Register file B (B0--B31). + +@item A +Predicate registers in register file A (A0--A2 on C64X and +higher, A1 and A2 otherwise). + +@item B +Predicate registers in register file B (B0--B2). + +@item C +A call-used register in register file B (B0--B9, B16--B31). + +@item Da +Register file A, excluding predicate registers (A3--A31, +plus A0 if not C64X or higher). + +@item Db +Register file B, excluding predicate registers (B3--B31). + +@item Iu4 +Integer constant in the range 0 @dots{} 15. + +@item Iu5 +Integer constant in the range 0 @dots{} 31. + +@item In5 +Integer constant in the range @minus{}31 @dots{} 0. + +@item Is5 +Integer constant in the range @minus{}16 @dots{} 15. + +@item I5x +Integer constant that can be the operand of an ADDA or a SUBA insn. + +@item IuB +Integer constant in the range 0 @dots{} 65535. + +@item IsB +Integer constant in the range @minus{}32768 @dots{} 32767. + +@item IsC +Integer constant in the range @math{-2^{20}} @dots{} @math{2^{20} - 1}. + +@item Jc +Integer constant that is a valid mask for the clr instruction. + +@item Js +Integer constant that is a valid mask for the set instruction. + +@item Q +Memory location with A base register. + +@item R +Memory location with B base register. + +@ifset INTERNALS +@item S0 +On C64x+ targets, a GP-relative small data reference. + +@item S1 +Any kind of @code{SYMBOL_REF}, for use in a call address. + +@item Si +Any kind of immediate operand, unless it matches the S0 constraint. + +@item T +Memory location with B base register, but not using a long offset. + +@item W +A memory operand with an address that cannot be used in an unaligned access. + +@end ifset +@item Z +Register B14 (aka DP). + +@end table + +@item Visium---@file{config/visium/constraints.md} +@table @code +@item b +EAM register @code{mdb} + +@item c +EAM register @code{mdc} + +@item f +Floating point register + +@ifset INTERNALS +@item k +Register for sibcall optimization +@end ifset + +@item l +General register, but not @code{r29}, @code{r30} and @code{r31} + +@item t +Register @code{r1} + +@item u +Register @code{r2} + +@item v +Register @code{r3} + +@item G +Floating-point constant 0.0 + +@item J +Integer constant in the range 0 .. 65535 (16-bit immediate) + +@item K +Integer constant in the range 1 .. 31 (5-bit immediate) + +@item L +Integer constant in the range @minus{}65535 .. @minus{}1 (16-bit negative immediate) + +@item M +Integer constant @minus{}1 + +@item O +Integer constant 0 + +@item P +Integer constant 32 +@end table + +@item x86 family---@file{config/i386/constraints.md} +@table @code +@item R +Legacy register---the eight integer registers available on all +i386 processors (@code{a}, @code{b}, @code{c}, @code{d}, +@code{si}, @code{di}, @code{bp}, @code{sp}). + +@item q +Any register accessible as @code{@var{r}l}. In 32-bit mode, @code{a}, +@code{b}, @code{c}, and @code{d}; in 64-bit mode, any integer register. + +@item Q +Any register accessible as @code{@var{r}h}: @code{a}, @code{b}, +@code{c}, and @code{d}. + +@ifset INTERNALS +@item l +Any register that can be used as the index in a base+index memory +access: that is, any general register except the stack pointer. +@end ifset + +@item a +The @code{a} register. + +@item b +The @code{b} register. + +@item c +The @code{c} register. + +@item d +The @code{d} register. + +@item S +The @code{si} register. + +@item D +The @code{di} register. + +@item A +The @code{a} and @code{d} registers. This class is used for instructions +that return double word results in the @code{ax:dx} register pair. Single +word values will be allocated either in @code{ax} or @code{dx}. +For example on i386 the following implements @code{rdtsc}: + +@smallexample +unsigned long long rdtsc (void) +@{ + unsigned long long tick; + __asm__ __volatile__("rdtsc":"=A"(tick)); + return tick; +@} +@end smallexample + +This is not correct on x86-64 as it would allocate tick in either @code{ax} +or @code{dx}. You have to use the following variant instead: + +@smallexample +unsigned long long rdtsc (void) +@{ + unsigned int tickl, tickh; + __asm__ __volatile__("rdtsc":"=a"(tickl),"=d"(tickh)); + return ((unsigned long long)tickh << 32)|tickl; +@} +@end smallexample + +@item U +The call-clobbered integer registers. + +@item f +Any 80387 floating-point (stack) register. + +@item t +Top of 80387 floating-point stack (@code{%st(0)}). + +@item u +Second from top of 80387 floating-point stack (@code{%st(1)}). + +@ifset INTERNALS +@item Yk +Any mask register that can be used as a predicate, i.e.@: @code{k1-k7}. + +@item k +Any mask register. +@end ifset + +@item y +Any MMX register. + +@item x +Any SSE register. + +@item v +Any EVEX encodable SSE register (@code{%xmm0-%xmm31}). + +@ifset INTERNALS +@item w +Any bound register. +@end ifset + +@item Yz +First SSE register (@code{%xmm0}). + +@ifset INTERNALS +@item Yi +Any SSE register, when SSE2 and inter-unit moves are enabled. + +@item Yj +Any SSE register, when SSE2 and inter-unit moves from vector registers are enabled. + +@item Ym +Any MMX register, when inter-unit moves are enabled. + +@item Yn +Any MMX register, when inter-unit moves from vector registers are enabled. + +@item Yp +Any integer register when @code{TARGET_PARTIAL_REG_STALL} is disabled. + +@item Ya +Any integer register when zero extensions with @code{AND} are disabled. + +@item Yb +Any register that can be used as the GOT base when calling@* +@code{___tls_get_addr}: that is, any general register except @code{a} +and @code{sp} registers, for @option{-fno-plt} if linker supports it. +Otherwise, @code{b} register. + +@item Yf +Any x87 register when 80387 floating-point arithmetic is enabled. + +@item Yr +Lower SSE register when avoiding REX prefix and all SSE registers otherwise. + +@item Yv +For AVX512VL, any EVEX-encodable SSE register (@code{%xmm0-%xmm31}), +otherwise any SSE register. + +@item Yh +Any EVEX-encodable SSE register, that has number factor of four. + +@item Bf +Flags register operand. + +@item Bg +GOT memory operand. + +@item Bm +Vector memory operand. + +@item Bc +Constant memory operand. + +@item Bn +Memory operand without REX prefix. + +@item Bs +Sibcall memory operand. + +@item Bw +Call memory operand. + +@item Bz +Constant call address operand. + +@item BC +SSE constant -1 operand. +@end ifset + +@item I +Integer constant in the range 0 @dots{} 31, for 32-bit shifts. + +@item J +Integer constant in the range 0 @dots{} 63, for 64-bit shifts. + +@item K +Signed 8-bit integer constant. + +@item L +@code{0xFF} or @code{0xFFFF}, for andsi as a zero-extending move. + +@item M +0, 1, 2, or 3 (shifts for the @code{lea} instruction). + +@item N +Unsigned 8-bit integer constant (for @code{in} and @code{out} +instructions). + +@ifset INTERNALS +@item O +Integer constant in the range 0 @dots{} 127, for 128-bit shifts. +@end ifset + +@item G +Standard 80387 floating point constant. + +@item C +SSE constant zero operand. + +@item e +32-bit signed integer constant, or a symbolic reference known +to fit that range (for immediate operands in sign-extending x86-64 +instructions). + +@item We +32-bit signed integer constant, or a symbolic reference known +to fit that range (for sign-extending conversion operations that +require non-@code{VOIDmode} immediate operands). + +@item Wz +32-bit unsigned integer constant, or a symbolic reference known +to fit that range (for zero-extending conversion operations that +require non-@code{VOIDmode} immediate operands). + +@item Wd +128-bit integer constant where both the high and low 64-bit word +satisfy the @code{e} constraint. + +@item Z +32-bit unsigned integer constant, or a symbolic reference known +to fit that range (for immediate operands in zero-extending x86-64 +instructions). + +@item Tv +VSIB address operand. + +@item Ts +Address operand without segment register. + +@end table + +@item Xstormy16---@file{config/stormy16/stormy16.h} +@table @code +@item a +Register r0. + +@item b +Register r1. + +@item c +Register r2. + +@item d +Register r8. + +@item e +Registers r0 through r7. + +@item t +Registers r0 and r1. + +@item y +The carry register. + +@item z +Registers r8 and r9. + +@item I +A constant between 0 and 3 inclusive. + +@item J +A constant that has exactly one bit set. + +@item K +A constant that has exactly one bit clear. + +@item L +A constant between 0 and 255 inclusive. + +@item M +A constant between @minus{}255 and 0 inclusive. + +@item N +A constant between @minus{}3 and 0 inclusive. + +@item O +A constant between 1 and 4 inclusive. + +@item P +A constant between @minus{}4 and @minus{}1 inclusive. + +@item Q +A memory reference that is a stack push. + +@item R +A memory reference that is a stack pop. + +@item S +A memory reference that refers to a constant address of known value. + +@item T +The register indicated by Rx (not implemented yet). + +@item U +A constant that is not between 2 and 15 inclusive. + +@item Z +The constant 0. + +@end table + +@item Xtensa---@file{config/xtensa/constraints.md} +@table @code +@item a +General-purpose 32-bit register + +@item b +One-bit boolean register + +@item A +MAC16 40-bit accumulator register + +@item I +Signed 12-bit integer constant, for use in MOVI instructions + +@item J +Signed 8-bit integer constant, for use in ADDI instructions + +@item K +Integer constant valid for BccI instructions + +@item L +Unsigned constant valid for BccUI instructions + +@end table + +@end table + +@ifset INTERNALS +@node Disable Insn Alternatives +@subsection Disable insn alternatives using the @code{enabled} attribute +@cindex enabled + +There are three insn attributes that may be used to selectively disable +instruction alternatives: + +@table @code +@item enabled +Says whether an alternative is available on the current subtarget. + +@item preferred_for_size +Says whether an enabled alternative should be used in code that is +optimized for size. + +@item preferred_for_speed +Says whether an enabled alternative should be used in code that is +optimized for speed. +@end table + +All these attributes should use @code{(const_int 1)} to allow an alternative +or @code{(const_int 0)} to disallow it. The attributes must be a static +property of the subtarget; they cannot for example depend on the +current operands, on the current optimization level, on the location +of the insn within the body of a loop, on whether register allocation +has finished, or on the current compiler pass. + +The @code{enabled} attribute is a correctness property. It tells GCC to act +as though the disabled alternatives were never defined in the first place. +This is useful when adding new instructions to an existing pattern in +cases where the new instructions are only available for certain cpu +architecture levels (typically mapped to the @code{-march=} command-line +option). + +In contrast, the @code{preferred_for_size} and @code{preferred_for_speed} +attributes are strong optimization hints rather than correctness properties. +@code{preferred_for_size} tells GCC which alternatives to consider when +adding or modifying an instruction that GCC wants to optimize for size. +@code{preferred_for_speed} does the same thing for speed. Note that things +like code motion can lead to cases where code optimized for size uses +alternatives that are not preferred for size, and similarly for speed. + +Although @code{define_insn}s can in principle specify the @code{enabled} +attribute directly, it is often clearer to have subsiduary attributes +for each architectural feature of interest. The @code{define_insn}s +can then use these subsiduary attributes to say which alternatives +require which features. The example below does this for @code{cpu_facility}. + +E.g. the following two patterns could easily be merged using the @code{enabled} +attribute: + +@smallexample + +(define_insn "*movdi_old" + [(set (match_operand:DI 0 "register_operand" "=d") + (match_operand:DI 1 "register_operand" " d"))] + "!TARGET_NEW" + "lgr %0,%1") + +(define_insn "*movdi_new" + [(set (match_operand:DI 0 "register_operand" "=d,f,d") + (match_operand:DI 1 "register_operand" " d,d,f"))] + "TARGET_NEW" + "@@ + lgr %0,%1 + ldgr %0,%1 + lgdr %0,%1") + +@end smallexample + +to: + +@smallexample + +(define_insn "*movdi_combined" + [(set (match_operand:DI 0 "register_operand" "=d,f,d") + (match_operand:DI 1 "register_operand" " d,d,f"))] + "" + "@@ + lgr %0,%1 + ldgr %0,%1 + lgdr %0,%1" + [(set_attr "cpu_facility" "*,new,new")]) + +@end smallexample + +with the @code{enabled} attribute defined like this: + +@smallexample + +(define_attr "cpu_facility" "standard,new" (const_string "standard")) + +(define_attr "enabled" "" + (cond [(eq_attr "cpu_facility" "standard") (const_int 1) + (and (eq_attr "cpu_facility" "new") + (ne (symbol_ref "TARGET_NEW") (const_int 0))) + (const_int 1)] + (const_int 0))) + +@end smallexample + +@end ifset + +@ifset INTERNALS +@node Define Constraints +@subsection Defining Machine-Specific Constraints +@cindex defining constraints +@cindex constraints, defining + +Machine-specific constraints fall into two categories: register and +non-register constraints. Within the latter category, constraints +which allow subsets of all possible memory or address operands should +be specially marked, to give @code{reload} more information. + +Machine-specific constraints can be given names of arbitrary length, +but they must be entirely composed of letters, digits, underscores +(@samp{_}), and angle brackets (@samp{< >}). Like C identifiers, they +must begin with a letter or underscore. + +In order to avoid ambiguity in operand constraint strings, no +constraint can have a name that begins with any other constraint's +name. For example, if @code{x} is defined as a constraint name, +@code{xy} may not be, and vice versa. As a consequence of this rule, +no constraint may begin with one of the generic constraint letters: +@samp{E F V X g i m n o p r s}. + +Register constraints correspond directly to register classes. +@xref{Register Classes}. There is thus not much flexibility in their +definitions. + +@deffn {MD Expression} define_register_constraint name regclass docstring +All three arguments are string constants. +@var{name} is the name of the constraint, as it will appear in +@code{match_operand} expressions. If @var{name} is a multi-letter +constraint its length shall be the same for all constraints starting +with the same letter. @var{regclass} can be either the +name of the corresponding register class (@pxref{Register Classes}), +or a C expression which evaluates to the appropriate register class. +If it is an expression, it must have no side effects, and it cannot +look at the operand. The usual use of expressions is to map some +register constraints to @code{NO_REGS} when the register class +is not available on a given subarchitecture. + +@var{docstring} is a sentence documenting the meaning of the +constraint. Docstrings are explained further below. +@end deffn + +Non-register constraints are more like predicates: the constraint +definition gives a boolean expression which indicates whether the +constraint matches. + +@deffn {MD Expression} define_constraint name docstring exp +The @var{name} and @var{docstring} arguments are the same as for +@code{define_register_constraint}, but note that the docstring comes +immediately after the name for these expressions. @var{exp} is an RTL +expression, obeying the same rules as the RTL expressions in predicate +definitions. @xref{Defining Predicates}, for details. If it +evaluates true, the constraint matches; if it evaluates false, it +doesn't. Constraint expressions should indicate which RTL codes they +might match, just like predicate expressions. + +@code{match_test} C expressions have access to the +following variables: + +@table @var +@item op +The RTL object defining the operand. +@item mode +The machine mode of @var{op}. +@item ival +@samp{INTVAL (@var{op})}, if @var{op} is a @code{const_int}. +@item hval +@samp{CONST_DOUBLE_HIGH (@var{op})}, if @var{op} is an integer +@code{const_double}. +@item lval +@samp{CONST_DOUBLE_LOW (@var{op})}, if @var{op} is an integer +@code{const_double}. +@item rval +@samp{CONST_DOUBLE_REAL_VALUE (@var{op})}, if @var{op} is a floating-point +@code{const_double}. +@end table + +The @var{*val} variables should only be used once another piece of the +expression has verified that @var{op} is the appropriate kind of RTL +object. +@end deffn + +Most non-register constraints should be defined with +@code{define_constraint}. The remaining two definition expressions +are only appropriate for constraints that should be handled specially +by @code{reload} if they fail to match. + +@deffn {MD Expression} define_memory_constraint name docstring exp +Use this expression for constraints that match a subset of all memory +operands: that is, @code{reload} can make them match by converting the +operand to the form @samp{@w{(mem (reg @var{X}))}}, where @var{X} is a +base register (from the register class specified by +@code{BASE_REG_CLASS}, @pxref{Register Classes}). + +For example, on the S/390, some instructions do not accept arbitrary +memory references, but only those that do not make use of an index +register. The constraint letter @samp{Q} is defined to represent a +memory address of this type. If @samp{Q} is defined with +@code{define_memory_constraint}, a @samp{Q} constraint can handle any +memory operand, because @code{reload} knows it can simply copy the +memory address into a base register if required. This is analogous to +the way an @samp{o} constraint can handle any memory operand. + +The syntax and semantics are otherwise identical to +@code{define_constraint}. +@end deffn + +@deffn {MD Expression} define_special_memory_constraint name docstring exp +Use this expression for constraints that match a subset of all memory +operands: that is, @code{reload} cannot make them match by reloading +the address as it is described for @code{define_memory_constraint} or +such address reload is undesirable with the performance point of view. + +For example, @code{define_special_memory_constraint} can be useful if +specifically aligned memory is necessary or desirable for some insn +operand. + +The syntax and semantics are otherwise identical to +@code{define_memory_constraint}. +@end deffn + +@deffn {MD Expression} define_relaxed_memory_constraint name docstring exp +The test expression in a @code{define_memory_constraint} can assume +that @code{TARGET_LEGITIMATE_ADDRESS_P} holds for the address inside +a @code{mem} rtx and so it does not need to test this condition itself. +In other words, a @code{define_memory_constraint} test of the form: + +@smallexample +(match_test "mem") +@end smallexample + +is enough to test whether an rtx is a @code{mem} @emph{and} whether +its address satisfies @code{TARGET_MEM_CONSTRAINT} (which is usually +@samp{'m'}). Thus the conditions imposed by a @code{define_memory_constraint} +always apply on top of the conditions imposed by @code{TARGET_MEM_CONSTRAINT}. + +However, it is sometimes useful to define memory constraints that allow +addresses beyond those accepted by @code{TARGET_LEGITIMATE_ADDRESS_P}. +@code{define_relaxed_memory_constraint} exists for this case. +The test expression in a @code{define_relaxed_memory_constraint} is +applied with no preconditions, so that the expression can determine +``from scratch'' exactly which addresses are valid and which are not. + +The syntax and semantics are otherwise identical to +@code{define_memory_constraint}. +@end deffn + +@deffn {MD Expression} define_address_constraint name docstring exp +Use this expression for constraints that match a subset of all address +operands: that is, @code{reload} can make the constraint match by +converting the operand to the form @samp{@w{(reg @var{X})}}, again +with @var{X} a base register. + +Constraints defined with @code{define_address_constraint} can only be +used with the @code{address_operand} predicate, or machine-specific +predicates that work the same way. They are treated analogously to +the generic @samp{p} constraint. + +The syntax and semantics are otherwise identical to +@code{define_constraint}. +@end deffn + +For historical reasons, names beginning with the letters @samp{G H} +are reserved for constraints that match only @code{const_double}s, and +names beginning with the letters @samp{I J K L M N O P} are reserved +for constraints that match only @code{const_int}s. This may change in +the future. For the time being, constraints with these names must be +written in a stylized form, so that @code{genpreds} can tell you did +it correctly: + +@smallexample +@group +(define_constraint "[@var{GHIJKLMNOP}]@dots{}" + "@var{doc}@dots{}" + (and (match_code "const_int") ; @r{@code{const_double} for G/H} + @var{condition}@dots{})) ; @r{usually a @code{match_test}} +@end group +@end smallexample +@c the semicolons line up in the formatted manual + +It is fine to use names beginning with other letters for constraints +that match @code{const_double}s or @code{const_int}s. + +Each docstring in a constraint definition should be one or more complete +sentences, marked up in Texinfo format. @emph{They are currently unused.} +In the future they will be copied into the GCC manual, in @ref{Machine +Constraints}, replacing the hand-maintained tables currently found in +that section. Also, in the future the compiler may use this to give +more helpful diagnostics when poor choice of @code{asm} constraints +causes a reload failure. + +If you put the pseudo-Texinfo directive @samp{@@internal} at the +beginning of a docstring, then (in the future) it will appear only in +the internals manual's version of the machine-specific constraint tables. +Use this for constraints that should not appear in @code{asm} statements. + +@node C Constraint Interface +@subsection Testing constraints from C +@cindex testing constraints +@cindex constraints, testing + +It is occasionally useful to test a constraint from C code rather than +implicitly via the constraint string in a @code{match_operand}. The +generated file @file{tm_p.h} declares a few interfaces for working +with constraints. At present these are defined for all constraints +except @code{g} (which is equivalent to @code{general_operand}). + +Some valid constraint names are not valid C identifiers, so there is a +mangling scheme for referring to them from C@. Constraint names that +do not contain angle brackets or underscores are left unchanged. +Underscores are doubled, each @samp{<} is replaced with @samp{_l}, and +each @samp{>} with @samp{_g}. Here are some examples: + +@c the @c's prevent double blank lines in the printed manual. +@example +@multitable {Original} {Mangled} +@item @strong{Original} @tab @strong{Mangled} @c +@item @code{x} @tab @code{x} @c +@item @code{P42x} @tab @code{P42x} @c +@item @code{P4_x} @tab @code{P4__x} @c +@item @code{P4>x} @tab @code{P4_gx} @c +@item @code{P4>>} @tab @code{P4_g_g} @c +@item @code{P4_g>} @tab @code{P4__g_g} @c +@end multitable +@end example + +Throughout this section, the variable @var{c} is either a constraint +in the abstract sense, or a constant from @code{enum constraint_num}; +the variable @var{m} is a mangled constraint name (usually as part of +a larger identifier). + +@deftp Enum constraint_num +For each constraint except @code{g}, there is a corresponding +enumeration constant: @samp{CONSTRAINT_} plus the mangled name of the +constraint. Functions that take an @code{enum constraint_num} as an +argument expect one of these constants. +@end deftp + +@deftypefun {inline bool} satisfies_constraint_@var{m} (rtx @var{exp}) +For each non-register constraint @var{m} except @code{g}, there is +one of these functions; it returns @code{true} if @var{exp} satisfies the +constraint. These functions are only visible if @file{rtl.h} was included +before @file{tm_p.h}. +@end deftypefun + +@deftypefun bool constraint_satisfied_p (rtx @var{exp}, enum constraint_num @var{c}) +Like the @code{satisfies_constraint_@var{m}} functions, but the +constraint to test is given as an argument, @var{c}. If @var{c} +specifies a register constraint, this function will always return +@code{false}. +@end deftypefun + +@deftypefun {enum reg_class} reg_class_for_constraint (enum constraint_num @var{c}) +Returns the register class associated with @var{c}. If @var{c} is not +a register constraint, or those registers are not available for the +currently selected subtarget, returns @code{NO_REGS}. +@end deftypefun + +Here is an example use of @code{satisfies_constraint_@var{m}}. In +peephole optimizations (@pxref{Peephole Definitions}), operand +constraint strings are ignored, so if there are relevant constraints, +they must be tested in the C condition. In the example, the +optimization is applied if operand 2 does @emph{not} satisfy the +@samp{K} constraint. (This is a simplified version of a peephole +definition from the i386 machine description.) + +@smallexample +(define_peephole2 + [(match_scratch:SI 3 "r") + (set (match_operand:SI 0 "register_operand" "") + (mult:SI (match_operand:SI 1 "memory_operand" "") + (match_operand:SI 2 "immediate_operand" "")))] + + "!satisfies_constraint_K (operands[2])" + + [(set (match_dup 3) (match_dup 1)) + (set (match_dup 0) (mult:SI (match_dup 3) (match_dup 2)))] + + "") +@end smallexample + +@node Standard Names +@section Standard Pattern Names For Generation +@cindex standard pattern names +@cindex pattern names +@cindex names, pattern + +Here is a table of the instruction names that are meaningful in the RTL +generation pass of the compiler. Giving one of these names to an +instruction pattern tells the RTL generation pass that it can use the +pattern to accomplish a certain task. + +@table @asis +@cindex @code{mov@var{m}} instruction pattern +@item @samp{mov@var{m}} +Here @var{m} stands for a two-letter machine mode name, in lowercase. +This instruction pattern moves data with that machine mode from operand +1 to operand 0. For example, @samp{movsi} moves full-word data. + +If operand 0 is a @code{subreg} with mode @var{m} of a register whose +own mode is wider than @var{m}, the effect of this instruction is +to store the specified value in the part of the register that corresponds +to mode @var{m}. Bits outside of @var{m}, but which are within the +same target word as the @code{subreg} are undefined. Bits which are +outside the target word are left unchanged. + +This class of patterns is special in several ways. First of all, each +of these names up to and including full word size @emph{must} be defined, +because there is no other way to copy a datum from one place to another. +If there are patterns accepting operands in larger modes, +@samp{mov@var{m}} must be defined for integer modes of those sizes. + +Second, these patterns are not used solely in the RTL generation pass. +Even the reload pass can generate move insns to copy values from stack +slots into temporary registers. When it does so, one of the operands is +a hard register and the other is an operand that can need to be reloaded +into a register. + +@findex force_reg +Therefore, when given such a pair of operands, the pattern must generate +RTL which needs no reloading and needs no temporary registers---no +registers other than the operands. For example, if you support the +pattern with a @code{define_expand}, then in such a case the +@code{define_expand} mustn't call @code{force_reg} or any other such +function which might generate new pseudo registers. + +This requirement exists even for subword modes on a RISC machine where +fetching those modes from memory normally requires several insns and +some temporary registers. + +@findex change_address +During reload a memory reference with an invalid address may be passed +as an operand. Such an address will be replaced with a valid address +later in the reload pass. In this case, nothing may be done with the +address except to use it as it stands. If it is copied, it will not be +replaced with a valid address. No attempt should be made to make such +an address into a valid address and no routine (such as +@code{change_address}) that will do so may be called. Note that +@code{general_operand} will fail when applied to such an address. + +@findex reload_in_progress +The global variable @code{reload_in_progress} (which must be explicitly +declared if required) can be used to determine whether such special +handling is required. + +The variety of operands that have reloads depends on the rest of the +machine description, but typically on a RISC machine these can only be +pseudo registers that did not get hard registers, while on other +machines explicit memory references will get optional reloads. + +If a scratch register is required to move an object to or from memory, +it can be allocated using @code{gen_reg_rtx} prior to life analysis. + +If there are cases which need scratch registers during or after reload, +you must provide an appropriate secondary_reload target hook. + +@findex can_create_pseudo_p +The macro @code{can_create_pseudo_p} can be used to determine if it +is unsafe to create new pseudo registers. If this variable is nonzero, then +it is unsafe to call @code{gen_reg_rtx} to allocate a new pseudo. + +The constraints on a @samp{mov@var{m}} must permit moving any hard +register to any other hard register provided that +@code{TARGET_HARD_REGNO_MODE_OK} permits mode @var{m} in both registers and +@code{TARGET_REGISTER_MOVE_COST} applied to their classes returns a value +of 2. + +It is obligatory to support floating point @samp{mov@var{m}} +instructions into and out of any registers that can hold fixed point +values, because unions and structures (which have modes @code{SImode} or +@code{DImode}) can be in those registers and they may have floating +point members. + +There may also be a need to support fixed point @samp{mov@var{m}} +instructions in and out of floating point registers. Unfortunately, I +have forgotten why this was so, and I don't know whether it is still +true. If @code{TARGET_HARD_REGNO_MODE_OK} rejects fixed point values in +floating point registers, then the constraints of the fixed point +@samp{mov@var{m}} instructions must be designed to avoid ever trying to +reload into a floating point register. + +@cindex @code{reload_in} instruction pattern +@cindex @code{reload_out} instruction pattern +@item @samp{reload_in@var{m}} +@itemx @samp{reload_out@var{m}} +These named patterns have been obsoleted by the target hook +@code{secondary_reload}. + +Like @samp{mov@var{m}}, but used when a scratch register is required to +move between operand 0 and operand 1. Operand 2 describes the scratch +register. See the discussion of the @code{SECONDARY_RELOAD_CLASS} +macro in @pxref{Register Classes}. + +There are special restrictions on the form of the @code{match_operand}s +used in these patterns. First, only the predicate for the reload +operand is examined, i.e., @code{reload_in} examines operand 1, but not +the predicates for operand 0 or 2. Second, there may be only one +alternative in the constraints. Third, only a single register class +letter may be used for the constraint; subsequent constraint letters +are ignored. As a special exception, an empty constraint string +matches the @code{ALL_REGS} register class. This may relieve ports +of the burden of defining an @code{ALL_REGS} constraint letter just +for these patterns. + +@cindex @code{movstrict@var{m}} instruction pattern +@item @samp{movstrict@var{m}} +Like @samp{mov@var{m}} except that if operand 0 is a @code{subreg} +with mode @var{m} of a register whose natural mode is wider, +the @samp{movstrict@var{m}} instruction is guaranteed not to alter +any of the register except the part which belongs to mode @var{m}. + +@cindex @code{movmisalign@var{m}} instruction pattern +@item @samp{movmisalign@var{m}} +This variant of a move pattern is designed to load or store a value +from a memory address that is not naturally aligned for its mode. +For a store, the memory will be in operand 0; for a load, the memory +will be in operand 1. The other operand is guaranteed not to be a +memory, so that it's easy to tell whether this is a load or store. + +This pattern is used by the autovectorizer, and when expanding a +@code{MISALIGNED_INDIRECT_REF} expression. + +@cindex @code{load_multiple} instruction pattern +@item @samp{load_multiple} +Load several consecutive memory locations into consecutive registers. +Operand 0 is the first of the consecutive registers, operand 1 +is the first memory location, and operand 2 is a constant: the +number of consecutive registers. + +Define this only if the target machine really has such an instruction; +do not define this if the most efficient way of loading consecutive +registers from memory is to do them one at a time. + +On some machines, there are restrictions as to which consecutive +registers can be stored into memory, such as particular starting or +ending register numbers or only a range of valid counts. For those +machines, use a @code{define_expand} (@pxref{Expander Definitions}) +and make the pattern fail if the restrictions are not met. + +Write the generated insn as a @code{parallel} with elements being a +@code{set} of one register from the appropriate memory location (you may +also need @code{use} or @code{clobber} elements). Use a +@code{match_parallel} (@pxref{RTL Template}) to recognize the insn. See +@file{rs6000.md} for examples of the use of this insn pattern. + +@cindex @samp{store_multiple} instruction pattern +@item @samp{store_multiple} +Similar to @samp{load_multiple}, but store several consecutive registers +into consecutive memory locations. Operand 0 is the first of the +consecutive memory locations, operand 1 is the first register, and +operand 2 is a constant: the number of consecutive registers. + +@cindex @code{vec_load_lanes@var{m}@var{n}} instruction pattern +@item @samp{vec_load_lanes@var{m}@var{n}} +Perform an interleaved load of several vectors from memory operand 1 +into register operand 0. Both operands have mode @var{m}. The register +operand is viewed as holding consecutive vectors of mode @var{n}, +while the memory operand is a flat array that contains the same number +of elements. The operation is equivalent to: + +@smallexample +int c = GET_MODE_SIZE (@var{m}) / GET_MODE_SIZE (@var{n}); +for (j = 0; j < GET_MODE_NUNITS (@var{n}); j++) + for (i = 0; i < c; i++) + operand0[i][j] = operand1[j * c + i]; +@end smallexample + +For example, @samp{vec_load_lanestiv4hi} loads 8 16-bit values +from memory into a register of mode @samp{TI}@. The register +contains two consecutive vectors of mode @samp{V4HI}@. + +This pattern can only be used if: +@smallexample +TARGET_ARRAY_MODE_SUPPORTED_P (@var{n}, @var{c}) +@end smallexample +is true. GCC assumes that, if a target supports this kind of +instruction for some mode @var{n}, it also supports unaligned +loads for vectors of mode @var{n}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{vec_mask_load_lanes@var{m}@var{n}} instruction pattern +@item @samp{vec_mask_load_lanes@var{m}@var{n}} +Like @samp{vec_load_lanes@var{m}@var{n}}, but takes an additional +mask operand (operand 2) that specifies which elements of the destination +vectors should be loaded. Other elements of the destination +vectors are set to zero. The operation is equivalent to: + +@smallexample +int c = GET_MODE_SIZE (@var{m}) / GET_MODE_SIZE (@var{n}); +for (j = 0; j < GET_MODE_NUNITS (@var{n}); j++) + if (operand2[j]) + for (i = 0; i < c; i++) + operand0[i][j] = operand1[j * c + i]; + else + for (i = 0; i < c; i++) + operand0[i][j] = 0; +@end smallexample + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{vec_store_lanes@var{m}@var{n}} instruction pattern +@item @samp{vec_store_lanes@var{m}@var{n}} +Equivalent to @samp{vec_load_lanes@var{m}@var{n}}, with the memory +and register operands reversed. That is, the instruction is +equivalent to: + +@smallexample +int c = GET_MODE_SIZE (@var{m}) / GET_MODE_SIZE (@var{n}); +for (j = 0; j < GET_MODE_NUNITS (@var{n}); j++) + for (i = 0; i < c; i++) + operand0[j * c + i] = operand1[i][j]; +@end smallexample + +for a memory operand 0 and register operand 1. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{vec_mask_store_lanes@var{m}@var{n}} instruction pattern +@item @samp{vec_mask_store_lanes@var{m}@var{n}} +Like @samp{vec_store_lanes@var{m}@var{n}}, but takes an additional +mask operand (operand 2) that specifies which elements of the source +vectors should be stored. The operation is equivalent to: + +@smallexample +int c = GET_MODE_SIZE (@var{m}) / GET_MODE_SIZE (@var{n}); +for (j = 0; j < GET_MODE_NUNITS (@var{n}); j++) + if (operand2[j]) + for (i = 0; i < c; i++) + operand0[j * c + i] = operand1[i][j]; +@end smallexample + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{gather_load@var{m}@var{n}} instruction pattern +@item @samp{gather_load@var{m}@var{n}} +Load several separate memory locations into a vector of mode @var{m}. +Operand 1 is a scalar base address and operand 2 is a vector of mode @var{n} +containing offsets from that base. Operand 0 is a destination vector with +the same number of elements as @var{n}. For each element index @var{i}: + +@itemize @bullet +@item +extend the offset element @var{i} to address width, using zero +extension if operand 3 is 1 and sign extension if operand 3 is zero; +@item +multiply the extended offset by operand 4; +@item +add the result to the base; and +@item +load the value at that address into element @var{i} of operand 0. +@end itemize + +The value of operand 3 does not matter if the offsets are already +address width. + +@cindex @code{mask_gather_load@var{m}@var{n}} instruction pattern +@item @samp{mask_gather_load@var{m}@var{n}} +Like @samp{gather_load@var{m}@var{n}}, but takes an extra mask operand as +operand 5. Bit @var{i} of the mask is set if element @var{i} +of the result should be loaded from memory and clear if element @var{i} +of the result should be set to zero. + +@cindex @code{scatter_store@var{m}@var{n}} instruction pattern +@item @samp{scatter_store@var{m}@var{n}} +Store a vector of mode @var{m} into several distinct memory locations. +Operand 0 is a scalar base address and operand 1 is a vector of mode +@var{n} containing offsets from that base. Operand 4 is the vector of +values that should be stored, which has the same number of elements as +@var{n}. For each element index @var{i}: + +@itemize @bullet +@item +extend the offset element @var{i} to address width, using zero +extension if operand 2 is 1 and sign extension if operand 2 is zero; +@item +multiply the extended offset by operand 3; +@item +add the result to the base; and +@item +store element @var{i} of operand 4 to that address. +@end itemize + +The value of operand 2 does not matter if the offsets are already +address width. + +@cindex @code{mask_scatter_store@var{m}@var{n}} instruction pattern +@item @samp{mask_scatter_store@var{m}@var{n}} +Like @samp{scatter_store@var{m}@var{n}}, but takes an extra mask operand as +operand 5. Bit @var{i} of the mask is set if element @var{i} +of the result should be stored to memory. + +@cindex @code{vec_set@var{m}} instruction pattern +@item @samp{vec_set@var{m}} +Set given field in the vector value. Operand 0 is the vector to modify, +operand 1 is new value of field and operand 2 specify the field index. + +@cindex @code{vec_extract@var{m}@var{n}} instruction pattern +@item @samp{vec_extract@var{m}@var{n}} +Extract given field from the vector value. Operand 1 is the vector, operand 2 +specify field index and operand 0 place to store value into. The +@var{n} mode is the mode of the field or vector of fields that should be +extracted, should be either element mode of the vector mode @var{m}, or +a vector mode with the same element mode and smaller number of elements. +If @var{n} is a vector mode, the index is counted in units of that mode. + +@cindex @code{vec_init@var{m}@var{n}} instruction pattern +@item @samp{vec_init@var{m}@var{n}} +Initialize the vector to given values. Operand 0 is the vector to initialize +and operand 1 is parallel containing values for individual fields. The +@var{n} mode is the mode of the elements, should be either element mode of +the vector mode @var{m}, or a vector mode with the same element mode and +smaller number of elements. + +@cindex @code{vec_duplicate@var{m}} instruction pattern +@item @samp{vec_duplicate@var{m}} +Initialize vector output operand 0 so that each element has the value given +by scalar input operand 1. The vector has mode @var{m} and the scalar has +the mode appropriate for one element of @var{m}. + +This pattern only handles duplicates of non-constant inputs. Constant +vectors go through the @code{mov@var{m}} pattern instead. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{vec_series@var{m}} instruction pattern +@item @samp{vec_series@var{m}} +Initialize vector output operand 0 so that element @var{i} is equal to +operand 1 plus @var{i} times operand 2. In other words, create a linear +series whose base value is operand 1 and whose step is operand 2. + +The vector output has mode @var{m} and the scalar inputs have the mode +appropriate for one element of @var{m}. This pattern is not used for +floating-point vectors, in order to avoid having to specify the +rounding behavior for @var{i} > 1. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{while_ult@var{m}@var{n}} instruction pattern +@item @code{while_ult@var{m}@var{n}} +Set operand 0 to a mask that is true while incrementing operand 1 +gives a value that is less than operand 2, for a vector length up to operand 3. +Operand 0 has mode @var{n} and operands 1 and 2 are scalar integers of mode +@var{m}. Operand 3 should be omitted when @var{n} is a vector mode, and +a @code{CONST_INT} otherwise. The operation for vector modes is equivalent to: + +@smallexample +operand0[0] = operand1 < operand2; +for (i = 1; i < GET_MODE_NUNITS (@var{n}); i++) + operand0[i] = operand0[i - 1] && (operand1 + i < operand2); +@end smallexample + +And for non-vector modes the operation is equivalent to: + +@smallexample +operand0[0] = operand1 < operand2; +for (i = 1; i < operand3; i++) + operand0[i] = operand0[i - 1] && (operand1 + i < operand2); +@end smallexample + +@cindex @code{check_raw_ptrs@var{m}} instruction pattern +@item @samp{check_raw_ptrs@var{m}} +Check whether, given two pointers @var{a} and @var{b} and a length @var{len}, +a write of @var{len} bytes at @var{a} followed by a read of @var{len} bytes +at @var{b} can be split into interleaved byte accesses +@samp{@var{a}[0], @var{b}[0], @var{a}[1], @var{b}[1], @dots{}} +without affecting the dependencies between the bytes. Set operand 0 +to true if the split is possible and false otherwise. + +Operands 1, 2 and 3 provide the values of @var{a}, @var{b} and @var{len} +respectively. Operand 4 is a constant integer that provides the known +common alignment of @var{a} and @var{b}. All inputs have mode @var{m}. + +This split is possible if: + +@smallexample +@var{a} == @var{b} || @var{a} + @var{len} <= @var{b} || @var{b} + @var{len} <= @var{a} +@end smallexample + +You should only define this pattern if the target has a way of accelerating +the test without having to do the individual comparisons. + +@cindex @code{check_war_ptrs@var{m}} instruction pattern +@item @samp{check_war_ptrs@var{m}} +Like @samp{check_raw_ptrs@var{m}}, but with the read and write swapped round. +The split is possible in this case if: + +@smallexample +@var{b} <= @var{a} || @var{a} + @var{len} <= @var{b} +@end smallexample + +@cindex @code{vec_cmp@var{m}@var{n}} instruction pattern +@item @samp{vec_cmp@var{m}@var{n}} +Output a vector comparison. Operand 0 of mode @var{n} is the destination for +predicate in operand 1 which is a signed vector comparison with operands of +mode @var{m} in operands 2 and 3. Predicate is computed by element-wise +evaluation of the vector comparison with a truth value of all-ones and a false +value of all-zeros. + +@cindex @code{vec_cmpu@var{m}@var{n}} instruction pattern +@item @samp{vec_cmpu@var{m}@var{n}} +Similar to @code{vec_cmp@var{m}@var{n}} but perform unsigned vector comparison. + +@cindex @code{vec_cmpeq@var{m}@var{n}} instruction pattern +@item @samp{vec_cmpeq@var{m}@var{n}} +Similar to @code{vec_cmp@var{m}@var{n}} but perform equality or non-equality +vector comparison only. If @code{vec_cmp@var{m}@var{n}} +or @code{vec_cmpu@var{m}@var{n}} instruction pattern is supported, +it will be preferred over @code{vec_cmpeq@var{m}@var{n}}, so there is +no need to define this instruction pattern if the others are supported. + +@cindex @code{vcond@var{m}@var{n}} instruction pattern +@item @samp{vcond@var{m}@var{n}} +Output a conditional vector move. Operand 0 is the destination to +receive a combination of operand 1 and operand 2, which are of mode @var{m}, +dependent on the outcome of the predicate in operand 3 which is a signed +vector comparison with operands of mode @var{n} in operands 4 and 5. The +modes @var{m} and @var{n} should have the same size. Operand 0 +will be set to the value @var{op1} & @var{msk} | @var{op2} & ~@var{msk} +where @var{msk} is computed by element-wise evaluation of the vector +comparison with a truth value of all-ones and a false value of all-zeros. + +@cindex @code{vcondu@var{m}@var{n}} instruction pattern +@item @samp{vcondu@var{m}@var{n}} +Similar to @code{vcond@var{m}@var{n}} but performs unsigned vector +comparison. + +@cindex @code{vcondeq@var{m}@var{n}} instruction pattern +@item @samp{vcondeq@var{m}@var{n}} +Similar to @code{vcond@var{m}@var{n}} but performs equality or +non-equality vector comparison only. If @code{vcond@var{m}@var{n}} +or @code{vcondu@var{m}@var{n}} instruction pattern is supported, +it will be preferred over @code{vcondeq@var{m}@var{n}}, so there is +no need to define this instruction pattern if the others are supported. + +@cindex @code{vcond_mask_@var{m}@var{n}} instruction pattern +@item @samp{vcond_mask_@var{m}@var{n}} +Similar to @code{vcond@var{m}@var{n}} but operand 3 holds a pre-computed +result of vector comparison. + +@cindex @code{maskload@var{m}@var{n}} instruction pattern +@item @samp{maskload@var{m}@var{n}} +Perform a masked load of vector from memory operand 1 of mode @var{m} +into register operand 0. Mask is provided in register operand 2 of +mode @var{n}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{maskstore@var{m}@var{n}} instruction pattern +@item @samp{maskstore@var{m}@var{n}} +Perform a masked store of vector from register operand 1 of mode @var{m} +into memory operand 0. Mask is provided in register operand 2 of +mode @var{n}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{len_load_@var{m}} instruction pattern +@item @samp{len_load_@var{m}} +Load (operand 2 - operand 3) elements from vector memory operand 1 +into vector register operand 0, setting the other elements of +operand 0 to undefined values. Operands 0 and 1 have mode @var{m}, +which must be a vector mode. Operand 2 has whichever integer mode the +target prefers. Operand 3 conceptually has mode @code{QI}. + +Operand 2 can be a variable or a constant amount. Operand 3 specifies a +constant bias: it is either a constant 0 or a constant -1. The predicate on +operand 3 must only accept the bias values that the target actually supports. +GCC handles a bias of 0 more efficiently than a bias of -1. + +If (operand 2 - operand 3) exceeds the number of elements in mode +@var{m}, the behavior is undefined. + +If the target prefers the length to be measured in bytes rather than +elements, it should only implement this pattern for vectors of @code{QI} +elements. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{len_store_@var{m}} instruction pattern +@item @samp{len_store_@var{m}} +Store (operand 2 - operand 3) vector elements from vector register operand 1 +into memory operand 0, leaving the other elements of +operand 0 unchanged. Operands 0 and 1 have mode @var{m}, which must be +a vector mode. Operand 2 has whichever integer mode the target prefers. +Operand 3 conceptually has mode @code{QI}. + +Operand 2 can be a variable or a constant amount. Operand 3 specifies a +constant bias: it is either a constant 0 or a constant -1. The predicate on +operand 3 must only accept the bias values that the target actually supports. +GCC handles a bias of 0 more efficiently than a bias of -1. + +If (operand 2 - operand 3) exceeds the number of elements in mode +@var{m}, the behavior is undefined. + +If the target prefers the length to be measured in bytes +rather than elements, it should only implement this pattern for vectors +of @code{QI} elements. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{vec_perm@var{m}} instruction pattern +@item @samp{vec_perm@var{m}} +Output a (variable) vector permutation. Operand 0 is the destination +to receive elements from operand 1 and operand 2, which are of mode +@var{m}. Operand 3 is the @dfn{selector}. It is an integral mode +vector of the same width and number of elements as mode @var{m}. + +The input elements are numbered from 0 in operand 1 through +@math{2*@var{N}-1} in operand 2. The elements of the selector must +be computed modulo @math{2*@var{N}}. Note that if +@code{rtx_equal_p(operand1, operand2)}, this can be implemented +with just operand 1 and selector elements modulo @var{N}. + +In order to make things easy for a number of targets, if there is no +@samp{vec_perm} pattern for mode @var{m}, but there is for mode @var{q} +where @var{q} is a vector of @code{QImode} of the same width as @var{m}, +the middle-end will lower the mode @var{m} @code{VEC_PERM_EXPR} to +mode @var{q}. + +See also @code{TARGET_VECTORIZER_VEC_PERM_CONST}, which performs +the analogous operation for constant selectors. + +@cindex @code{push@var{m}1} instruction pattern +@item @samp{push@var{m}1} +Output a push instruction. Operand 0 is value to push. Used only when +@code{PUSH_ROUNDING} is defined. For historical reason, this pattern may be +missing and in such case an @code{mov} expander is used instead, with a +@code{MEM} expression forming the push operation. The @code{mov} expander +method is deprecated. + +@cindex @code{add@var{m}3} instruction pattern +@item @samp{add@var{m}3} +Add operand 2 and operand 1, storing the result in operand 0. All operands +must have mode @var{m}. This can be used even on two-address machines, by +means of constraints requiring operands 1 and 0 to be the same location. + +@cindex @code{ssadd@var{m}3} instruction pattern +@cindex @code{usadd@var{m}3} instruction pattern +@cindex @code{sub@var{m}3} instruction pattern +@cindex @code{sssub@var{m}3} instruction pattern +@cindex @code{ussub@var{m}3} instruction pattern +@cindex @code{mul@var{m}3} instruction pattern +@cindex @code{ssmul@var{m}3} instruction pattern +@cindex @code{usmul@var{m}3} instruction pattern +@cindex @code{div@var{m}3} instruction pattern +@cindex @code{ssdiv@var{m}3} instruction pattern +@cindex @code{udiv@var{m}3} instruction pattern +@cindex @code{usdiv@var{m}3} instruction pattern +@cindex @code{mod@var{m}3} instruction pattern +@cindex @code{umod@var{m}3} instruction pattern +@cindex @code{umin@var{m}3} instruction pattern +@cindex @code{umax@var{m}3} instruction pattern +@cindex @code{and@var{m}3} instruction pattern +@cindex @code{ior@var{m}3} instruction pattern +@cindex @code{xor@var{m}3} instruction pattern +@item @samp{ssadd@var{m}3}, @samp{usadd@var{m}3} +@itemx @samp{sub@var{m}3}, @samp{sssub@var{m}3}, @samp{ussub@var{m}3} +@itemx @samp{mul@var{m}3}, @samp{ssmul@var{m}3}, @samp{usmul@var{m}3} +@itemx @samp{div@var{m}3}, @samp{ssdiv@var{m}3} +@itemx @samp{udiv@var{m}3}, @samp{usdiv@var{m}3} +@itemx @samp{mod@var{m}3}, @samp{umod@var{m}3} +@itemx @samp{umin@var{m}3}, @samp{umax@var{m}3} +@itemx @samp{and@var{m}3}, @samp{ior@var{m}3}, @samp{xor@var{m}3} +Similar, for other arithmetic operations. + +@cindex @code{addv@var{m}4} instruction pattern +@item @samp{addv@var{m}4} +Like @code{add@var{m}3} but takes a @code{code_label} as operand 3 and +emits code to jump to it if signed overflow occurs during the addition. +This pattern is used to implement the built-in functions performing +signed integer addition with overflow checking. + +@cindex @code{subv@var{m}4} instruction pattern +@cindex @code{mulv@var{m}4} instruction pattern +@item @samp{subv@var{m}4}, @samp{mulv@var{m}4} +Similar, for other signed arithmetic operations. + +@cindex @code{uaddv@var{m}4} instruction pattern +@item @samp{uaddv@var{m}4} +Like @code{addv@var{m}4} but for unsigned addition. That is to +say, the operation is the same as signed addition but the jump +is taken only on unsigned overflow. + +@cindex @code{usubv@var{m}4} instruction pattern +@cindex @code{umulv@var{m}4} instruction pattern +@item @samp{usubv@var{m}4}, @samp{umulv@var{m}4} +Similar, for other unsigned arithmetic operations. + +@cindex @code{addptr@var{m}3} instruction pattern +@item @samp{addptr@var{m}3} +Like @code{add@var{m}3} but is guaranteed to only be used for address +calculations. The expanded code is not allowed to clobber the +condition code. It only needs to be defined if @code{add@var{m}3} +sets the condition code. If adds used for address calculations and +normal adds are not compatible it is required to expand a distinct +pattern (e.g.@: using an unspec). The pattern is used by LRA to emit +address calculations. @code{add@var{m}3} is used if +@code{addptr@var{m}3} is not defined. + +@cindex @code{fma@var{m}4} instruction pattern +@item @samp{fma@var{m}4} +Multiply operand 2 and operand 1, then add operand 3, storing the +result in operand 0 without doing an intermediate rounding step. All +operands must have mode @var{m}. This pattern is used to implement +the @code{fma}, @code{fmaf}, and @code{fmal} builtin functions from +the ISO C99 standard. + +@cindex @code{fms@var{m}4} instruction pattern +@item @samp{fms@var{m}4} +Like @code{fma@var{m}4}, except operand 3 subtracted from the +product instead of added to the product. This is represented +in the rtl as + +@smallexample +(fma:@var{m} @var{op1} @var{op2} (neg:@var{m} @var{op3})) +@end smallexample + +@cindex @code{fnma@var{m}4} instruction pattern +@item @samp{fnma@var{m}4} +Like @code{fma@var{m}4} except that the intermediate product +is negated before being added to operand 3. This is represented +in the rtl as + +@smallexample +(fma:@var{m} (neg:@var{m} @var{op1}) @var{op2} @var{op3}) +@end smallexample + +@cindex @code{fnms@var{m}4} instruction pattern +@item @samp{fnms@var{m}4} +Like @code{fms@var{m}4} except that the intermediate product +is negated before subtracting operand 3. This is represented +in the rtl as + +@smallexample +(fma:@var{m} (neg:@var{m} @var{op1}) @var{op2} (neg:@var{m} @var{op3})) +@end smallexample + +@cindex @code{min@var{m}3} instruction pattern +@cindex @code{max@var{m}3} instruction pattern +@item @samp{smin@var{m}3}, @samp{smax@var{m}3} +Signed minimum and maximum operations. When used with floating point, +if both operands are zeros, or if either operand is @code{NaN}, then +it is unspecified which of the two operands is returned as the result. + +@cindex @code{fmin@var{m}3} instruction pattern +@cindex @code{fmax@var{m}3} instruction pattern +@item @samp{fmin@var{m}3}, @samp{fmax@var{m}3} +IEEE-conformant minimum and maximum operations. If one operand is a quiet +@code{NaN}, then the other operand is returned. If both operands are quiet +@code{NaN}, then a quiet @code{NaN} is returned. In the case when gcc supports +signaling @code{NaN} (-fsignaling-nans) an invalid floating point exception is +raised and a quiet @code{NaN} is returned. + +All operands have mode @var{m}, which is a scalar or vector +floating-point mode. These patterns are not allowed to @code{FAIL}. + +@cindex @code{reduc_smin_scal_@var{m}} instruction pattern +@cindex @code{reduc_smax_scal_@var{m}} instruction pattern +@item @samp{reduc_smin_scal_@var{m}}, @samp{reduc_smax_scal_@var{m}} +Find the signed minimum/maximum of the elements of a vector. The vector is +operand 1, and operand 0 is the scalar result, with mode equal to the mode of +the elements of the input vector. + +@cindex @code{reduc_umin_scal_@var{m}} instruction pattern +@cindex @code{reduc_umax_scal_@var{m}} instruction pattern +@item @samp{reduc_umin_scal_@var{m}}, @samp{reduc_umax_scal_@var{m}} +Find the unsigned minimum/maximum of the elements of a vector. The vector is +operand 1, and operand 0 is the scalar result, with mode equal to the mode of +the elements of the input vector. + +@cindex @code{reduc_fmin_scal_@var{m}} instruction pattern +@cindex @code{reduc_fmax_scal_@var{m}} instruction pattern +@item @samp{reduc_fmin_scal_@var{m}}, @samp{reduc_fmax_scal_@var{m}} +Find the floating-point minimum/maximum of the elements of a vector, +using the same rules as @code{fmin@var{m}3} and @code{fmax@var{m}3}. +Operand 1 is a vector of mode @var{m} and operand 0 is the scalar +result, which has mode @code{GET_MODE_INNER (@var{m})}. + +@cindex @code{reduc_plus_scal_@var{m}} instruction pattern +@item @samp{reduc_plus_scal_@var{m}} +Compute the sum of the elements of a vector. The vector is operand 1, and +operand 0 is the scalar result, with mode equal to the mode of the elements of +the input vector. + +@cindex @code{reduc_and_scal_@var{m}} instruction pattern +@item @samp{reduc_and_scal_@var{m}} +@cindex @code{reduc_ior_scal_@var{m}} instruction pattern +@itemx @samp{reduc_ior_scal_@var{m}} +@cindex @code{reduc_xor_scal_@var{m}} instruction pattern +@itemx @samp{reduc_xor_scal_@var{m}} +Compute the bitwise @code{AND}/@code{IOR}/@code{XOR} reduction of the elements +of a vector of mode @var{m}. Operand 1 is the vector input and operand 0 +is the scalar result. The mode of the scalar result is the same as one +element of @var{m}. + +@cindex @code{extract_last_@var{m}} instruction pattern +@item @code{extract_last_@var{m}} +Find the last set bit in mask operand 1 and extract the associated element +of vector operand 2. Store the result in scalar operand 0. Operand 2 +has vector mode @var{m} while operand 0 has the mode appropriate for one +element of @var{m}. Operand 1 has the usual mask mode for vectors of mode +@var{m}; see @code{TARGET_VECTORIZE_GET_MASK_MODE}. + +@cindex @code{fold_extract_last_@var{m}} instruction pattern +@item @code{fold_extract_last_@var{m}} +If any bits of mask operand 2 are set, find the last set bit, extract +the associated element from vector operand 3, and store the result +in operand 0. Store operand 1 in operand 0 otherwise. Operand 3 +has mode @var{m} and operands 0 and 1 have the mode appropriate for +one element of @var{m}. Operand 2 has the usual mask mode for vectors +of mode @var{m}; see @code{TARGET_VECTORIZE_GET_MASK_MODE}. + +@cindex @code{fold_left_plus_@var{m}} instruction pattern +@item @code{fold_left_plus_@var{m}} +Take scalar operand 1 and successively add each element from vector +operand 2. Store the result in scalar operand 0. The vector has +mode @var{m} and the scalars have the mode appropriate for one +element of @var{m}. The operation is strictly in-order: there is +no reassociation. + +@cindex @code{mask_fold_left_plus_@var{m}} instruction pattern +@item @code{mask_fold_left_plus_@var{m}} +Like @samp{fold_left_plus_@var{m}}, but takes an additional mask operand +(operand 3) that specifies which elements of the source vector should be added. + +@cindex @code{sdot_prod@var{m}} instruction pattern +@item @samp{sdot_prod@var{m}} + +Compute the sum of the products of two signed elements. +Operand 1 and operand 2 are of the same mode. Their +product, which is of a wider mode, is computed and added to operand 3. +Operand 3 is of a mode equal or wider than the mode of the product. The +result is placed in operand 0, which is of the same mode as operand 3. + +Semantically the expressions perform the multiplication in the following signs + +@smallexample +sdot == + op0 = sign-ext (op1) * sign-ext (op2) + op3 +@dots{} +@end smallexample + +@cindex @code{udot_prod@var{m}} instruction pattern +@item @samp{udot_prod@var{m}} + +Compute the sum of the products of two unsigned elements. +Operand 1 and operand 2 are of the same mode. Their +product, which is of a wider mode, is computed and added to operand 3. +Operand 3 is of a mode equal or wider than the mode of the product. The +result is placed in operand 0, which is of the same mode as operand 3. + +Semantically the expressions perform the multiplication in the following signs + +@smallexample +udot == + op0 = zero-ext (op1) * zero-ext (op2) + op3 +@dots{} +@end smallexample + +@cindex @code{usdot_prod@var{m}} instruction pattern +@item @samp{usdot_prod@var{m}} +Compute the sum of the products of elements of different signs. +Operand 1 must be unsigned and operand 2 signed. Their +product, which is of a wider mode, is computed and added to operand 3. +Operand 3 is of a mode equal or wider than the mode of the product. The +result is placed in operand 0, which is of the same mode as operand 3. + +Semantically the expressions perform the multiplication in the following signs + +@smallexample +usdot == + op0 = ((signed-conv) zero-ext (op1)) * sign-ext (op2) + op3 +@dots{} +@end smallexample + +@cindex @code{ssad@var{m}} instruction pattern +@item @samp{ssad@var{m}} +@cindex @code{usad@var{m}} instruction pattern +@item @samp{usad@var{m}} +Compute the sum of absolute differences of two signed/unsigned elements. +Operand 1 and operand 2 are of the same mode. Their absolute difference, which +is of a wider mode, is computed and added to operand 3. Operand 3 is of a mode +equal or wider than the mode of the absolute difference. The result is placed +in operand 0, which is of the same mode as operand 3. + +@cindex @code{widen_ssum@var{m3}} instruction pattern +@item @samp{widen_ssum@var{m3}} +@cindex @code{widen_usum@var{m3}} instruction pattern +@itemx @samp{widen_usum@var{m3}} +Operands 0 and 2 are of the same mode, which is wider than the mode of +operand 1. Add operand 1 to operand 2 and place the widened result in +operand 0. (This is used express accumulation of elements into an accumulator +of a wider mode.) + +@cindex @code{smulhs@var{m3}} instruction pattern +@item @samp{smulhs@var{m3}} +@cindex @code{umulhs@var{m3}} instruction pattern +@itemx @samp{umulhs@var{m3}} +Signed/unsigned multiply high with scale. This is equivalent to the C code: +@smallexample +narrow op0, op1, op2; +@dots{} +op0 = (narrow) (((wide) op1 * (wide) op2) >> (N / 2 - 1)); +@end smallexample +where the sign of @samp{narrow} determines whether this is a signed +or unsigned operation, and @var{N} is the size of @samp{wide} in bits. + +@cindex @code{smulhrs@var{m3}} instruction pattern +@item @samp{smulhrs@var{m3}} +@cindex @code{umulhrs@var{m3}} instruction pattern +@itemx @samp{umulhrs@var{m3}} +Signed/unsigned multiply high with round and scale. This is +equivalent to the C code: +@smallexample +narrow op0, op1, op2; +@dots{} +op0 = (narrow) (((((wide) op1 * (wide) op2) >> (N / 2 - 2)) + 1) >> 1); +@end smallexample +where the sign of @samp{narrow} determines whether this is a signed +or unsigned operation, and @var{N} is the size of @samp{wide} in bits. + +@cindex @code{sdiv_pow2@var{m3}} instruction pattern +@item @samp{sdiv_pow2@var{m3}} +@cindex @code{sdiv_pow2@var{m3}} instruction pattern +@itemx @samp{sdiv_pow2@var{m3}} +Signed division by power-of-2 immediate. Equivalent to: +@smallexample +signed op0, op1; +@dots{} +op0 = op1 / (1 << imm); +@end smallexample + +@cindex @code{vec_shl_insert_@var{m}} instruction pattern +@item @samp{vec_shl_insert_@var{m}} +Shift the elements in vector input operand 1 left one element (i.e.@: +away from element 0) and fill the vacated element 0 with the scalar +in operand 2. Store the result in vector output operand 0. Operands +0 and 1 have mode @var{m} and operand 2 has the mode appropriate for +one element of @var{m}. + +@cindex @code{vec_shl_@var{m}} instruction pattern +@item @samp{vec_shl_@var{m}} +Whole vector left shift in bits, i.e.@: away from element 0. +Operand 1 is a vector to be shifted. +Operand 2 is an integer shift amount in bits. +Operand 0 is where the resulting shifted vector is stored. +The output and input vectors should have the same modes. + +@cindex @code{vec_shr_@var{m}} instruction pattern +@item @samp{vec_shr_@var{m}} +Whole vector right shift in bits, i.e.@: towards element 0. +Operand 1 is a vector to be shifted. +Operand 2 is an integer shift amount in bits. +Operand 0 is where the resulting shifted vector is stored. +The output and input vectors should have the same modes. + +@cindex @code{vec_pack_trunc_@var{m}} instruction pattern +@item @samp{vec_pack_trunc_@var{m}} +Narrow (demote) and merge the elements of two vectors. Operands 1 and 2 +are vectors of the same mode having N integral or floating point elements +of size S@. Operand 0 is the resulting vector in which 2*N elements of +size S/2 are concatenated after narrowing them down using truncation. + +@cindex @code{vec_pack_sbool_trunc_@var{m}} instruction pattern +@item @samp{vec_pack_sbool_trunc_@var{m}} +Narrow and merge the elements of two vectors. Operands 1 and 2 are vectors +of the same type having N boolean elements. Operand 0 is the resulting +vector in which 2*N elements are concatenated. The last operand (operand 3) +is the number of elements in the output vector 2*N as a @code{CONST_INT}. +This instruction pattern is used when all the vector input and output +operands have the same scalar mode @var{m} and thus using +@code{vec_pack_trunc_@var{m}} would be ambiguous. + +@cindex @code{vec_pack_ssat_@var{m}} instruction pattern +@cindex @code{vec_pack_usat_@var{m}} instruction pattern +@item @samp{vec_pack_ssat_@var{m}}, @samp{vec_pack_usat_@var{m}} +Narrow (demote) and merge the elements of two vectors. Operands 1 and 2 +are vectors of the same mode having N integral elements of size S. +Operand 0 is the resulting vector in which the elements of the two input +vectors are concatenated after narrowing them down using signed/unsigned +saturating arithmetic. + +@cindex @code{vec_pack_sfix_trunc_@var{m}} instruction pattern +@cindex @code{vec_pack_ufix_trunc_@var{m}} instruction pattern +@item @samp{vec_pack_sfix_trunc_@var{m}}, @samp{vec_pack_ufix_trunc_@var{m}} +Narrow, convert to signed/unsigned integral type and merge the elements +of two vectors. Operands 1 and 2 are vectors of the same mode having N +floating point elements of size S@. Operand 0 is the resulting vector +in which 2*N elements of size S/2 are concatenated. + +@cindex @code{vec_packs_float_@var{m}} instruction pattern +@cindex @code{vec_packu_float_@var{m}} instruction pattern +@item @samp{vec_packs_float_@var{m}}, @samp{vec_packu_float_@var{m}} +Narrow, convert to floating point type and merge the elements +of two vectors. Operands 1 and 2 are vectors of the same mode having N +signed/unsigned integral elements of size S@. Operand 0 is the resulting vector +in which 2*N elements of size S/2 are concatenated. + +@cindex @code{vec_unpacks_hi_@var{m}} instruction pattern +@cindex @code{vec_unpacks_lo_@var{m}} instruction pattern +@item @samp{vec_unpacks_hi_@var{m}}, @samp{vec_unpacks_lo_@var{m}} +Extract and widen (promote) the high/low part of a vector of signed +integral or floating point elements. The input vector (operand 1) has N +elements of size S@. Widen (promote) the high/low elements of the vector +using signed or floating point extension and place the resulting N/2 +values of size 2*S in the output vector (operand 0). + +@cindex @code{vec_unpacku_hi_@var{m}} instruction pattern +@cindex @code{vec_unpacku_lo_@var{m}} instruction pattern +@item @samp{vec_unpacku_hi_@var{m}}, @samp{vec_unpacku_lo_@var{m}} +Extract and widen (promote) the high/low part of a vector of unsigned +integral elements. The input vector (operand 1) has N elements of size S. +Widen (promote) the high/low elements of the vector using zero extension and +place the resulting N/2 values of size 2*S in the output vector (operand 0). + +@cindex @code{vec_unpacks_sbool_hi_@var{m}} instruction pattern +@cindex @code{vec_unpacks_sbool_lo_@var{m}} instruction pattern +@item @samp{vec_unpacks_sbool_hi_@var{m}}, @samp{vec_unpacks_sbool_lo_@var{m}} +Extract the high/low part of a vector of boolean elements that have scalar +mode @var{m}. The input vector (operand 1) has N elements, the output +vector (operand 0) has N/2 elements. The last operand (operand 2) is the +number of elements of the input vector N as a @code{CONST_INT}. These +patterns are used if both the input and output vectors have the same scalar +mode @var{m} and thus using @code{vec_unpacks_hi_@var{m}} or +@code{vec_unpacks_lo_@var{m}} would be ambiguous. + +@cindex @code{vec_unpacks_float_hi_@var{m}} instruction pattern +@cindex @code{vec_unpacks_float_lo_@var{m}} instruction pattern +@cindex @code{vec_unpacku_float_hi_@var{m}} instruction pattern +@cindex @code{vec_unpacku_float_lo_@var{m}} instruction pattern +@item @samp{vec_unpacks_float_hi_@var{m}}, @samp{vec_unpacks_float_lo_@var{m}} +@itemx @samp{vec_unpacku_float_hi_@var{m}}, @samp{vec_unpacku_float_lo_@var{m}} +Extract, convert to floating point type and widen the high/low part of a +vector of signed/unsigned integral elements. The input vector (operand 1) +has N elements of size S@. Convert the high/low elements of the vector using +floating point conversion and place the resulting N/2 values of size 2*S in +the output vector (operand 0). + +@cindex @code{vec_unpack_sfix_trunc_hi_@var{m}} instruction pattern +@cindex @code{vec_unpack_sfix_trunc_lo_@var{m}} instruction pattern +@cindex @code{vec_unpack_ufix_trunc_hi_@var{m}} instruction pattern +@cindex @code{vec_unpack_ufix_trunc_lo_@var{m}} instruction pattern +@item @samp{vec_unpack_sfix_trunc_hi_@var{m}}, +@itemx @samp{vec_unpack_sfix_trunc_lo_@var{m}} +@itemx @samp{vec_unpack_ufix_trunc_hi_@var{m}} +@itemx @samp{vec_unpack_ufix_trunc_lo_@var{m}} +Extract, convert to signed/unsigned integer type and widen the high/low part of a +vector of floating point elements. The input vector (operand 1) +has N elements of size S@. Convert the high/low elements of the vector +to integers and place the resulting N/2 values of size 2*S in +the output vector (operand 0). + +@cindex @code{vec_widen_umult_hi_@var{m}} instruction pattern +@cindex @code{vec_widen_umult_lo_@var{m}} instruction pattern +@cindex @code{vec_widen_smult_hi_@var{m}} instruction pattern +@cindex @code{vec_widen_smult_lo_@var{m}} instruction pattern +@cindex @code{vec_widen_umult_even_@var{m}} instruction pattern +@cindex @code{vec_widen_umult_odd_@var{m}} instruction pattern +@cindex @code{vec_widen_smult_even_@var{m}} instruction pattern +@cindex @code{vec_widen_smult_odd_@var{m}} instruction pattern +@item @samp{vec_widen_umult_hi_@var{m}}, @samp{vec_widen_umult_lo_@var{m}} +@itemx @samp{vec_widen_smult_hi_@var{m}}, @samp{vec_widen_smult_lo_@var{m}} +@itemx @samp{vec_widen_umult_even_@var{m}}, @samp{vec_widen_umult_odd_@var{m}} +@itemx @samp{vec_widen_smult_even_@var{m}}, @samp{vec_widen_smult_odd_@var{m}} +Signed/Unsigned widening multiplication. The two inputs (operands 1 and 2) +are vectors with N signed/unsigned elements of size S@. Multiply the high/low +or even/odd elements of the two vectors, and put the N/2 products of size 2*S +in the output vector (operand 0). A target shouldn't implement even/odd pattern +pair if it is less efficient than lo/hi one. + +@cindex @code{vec_widen_ushiftl_hi_@var{m}} instruction pattern +@cindex @code{vec_widen_ushiftl_lo_@var{m}} instruction pattern +@cindex @code{vec_widen_sshiftl_hi_@var{m}} instruction pattern +@cindex @code{vec_widen_sshiftl_lo_@var{m}} instruction pattern +@item @samp{vec_widen_ushiftl_hi_@var{m}}, @samp{vec_widen_ushiftl_lo_@var{m}} +@itemx @samp{vec_widen_sshiftl_hi_@var{m}}, @samp{vec_widen_sshiftl_lo_@var{m}} +Signed/Unsigned widening shift left. The first input (operand 1) is a vector +with N signed/unsigned elements of size S@. Operand 2 is a constant. Shift +the high/low elements of operand 1, and put the N/2 results of size 2*S in the +output vector (operand 0). + +@cindex @code{vec_widen_saddl_hi_@var{m}} instruction pattern +@cindex @code{vec_widen_saddl_lo_@var{m}} instruction pattern +@cindex @code{vec_widen_uaddl_hi_@var{m}} instruction pattern +@cindex @code{vec_widen_uaddl_lo_@var{m}} instruction pattern +@item @samp{vec_widen_uaddl_hi_@var{m}}, @samp{vec_widen_uaddl_lo_@var{m}} +@itemx @samp{vec_widen_saddl_hi_@var{m}}, @samp{vec_widen_saddl_lo_@var{m}} +Signed/Unsigned widening add long. Operands 1 and 2 are vectors with N +signed/unsigned elements of size S@. Add the high/low elements of 1 and 2 +together, widen the resulting elements and put the N/2 results of size 2*S in +the output vector (operand 0). + +@cindex @code{vec_widen_ssubl_hi_@var{m}} instruction pattern +@cindex @code{vec_widen_ssubl_lo_@var{m}} instruction pattern +@cindex @code{vec_widen_usubl_hi_@var{m}} instruction pattern +@cindex @code{vec_widen_usubl_lo_@var{m}} instruction pattern +@item @samp{vec_widen_usubl_hi_@var{m}}, @samp{vec_widen_usubl_lo_@var{m}} +@itemx @samp{vec_widen_ssubl_hi_@var{m}}, @samp{vec_widen_ssubl_lo_@var{m}} +Signed/Unsigned widening subtract long. Operands 1 and 2 are vectors with N +signed/unsigned elements of size S@. Subtract the high/low elements of 2 from +1 and widen the resulting elements. Put the N/2 results of size 2*S in the +output vector (operand 0). + +@cindex @code{vec_addsub@var{m}3} instruction pattern +@item @samp{vec_addsub@var{m}3} +Alternating subtract, add with even lanes doing subtract and odd +lanes doing addition. Operands 1 and 2 and the outout operand are vectors +with mode @var{m}. + +@cindex @code{vec_fmaddsub@var{m}4} instruction pattern +@item @samp{vec_fmaddsub@var{m}4} +Alternating multiply subtract, add with even lanes doing subtract and odd +lanes doing addition of the third operand to the multiplication result +of the first two operands. Operands 1, 2 and 3 and the outout operand are vectors +with mode @var{m}. + +@cindex @code{vec_fmsubadd@var{m}4} instruction pattern +@item @samp{vec_fmsubadd@var{m}4} +Alternating multiply add, subtract with even lanes doing addition and odd +lanes doing subtraction of the third operand to the multiplication result +of the first two operands. Operands 1, 2 and 3 and the outout operand are vectors +with mode @var{m}. + +These instructions are not allowed to @code{FAIL}. + +@cindex @code{mulhisi3} instruction pattern +@item @samp{mulhisi3} +Multiply operands 1 and 2, which have mode @code{HImode}, and store +a @code{SImode} product in operand 0. + +@cindex @code{mulqihi3} instruction pattern +@cindex @code{mulsidi3} instruction pattern +@item @samp{mulqihi3}, @samp{mulsidi3} +Similar widening-multiplication instructions of other widths. + +@cindex @code{umulqihi3} instruction pattern +@cindex @code{umulhisi3} instruction pattern +@cindex @code{umulsidi3} instruction pattern +@item @samp{umulqihi3}, @samp{umulhisi3}, @samp{umulsidi3} +Similar widening-multiplication instructions that do unsigned +multiplication. + +@cindex @code{usmulqihi3} instruction pattern +@cindex @code{usmulhisi3} instruction pattern +@cindex @code{usmulsidi3} instruction pattern +@item @samp{usmulqihi3}, @samp{usmulhisi3}, @samp{usmulsidi3} +Similar widening-multiplication instructions that interpret the first +operand as unsigned and the second operand as signed, then do a signed +multiplication. + +@cindex @code{smul@var{m}3_highpart} instruction pattern +@item @samp{smul@var{m}3_highpart} +Perform a signed multiplication of operands 1 and 2, which have mode +@var{m}, and store the most significant half of the product in operand 0. +The least significant half of the product is discarded. This may be +represented in RTL using a @code{smul_highpart} RTX expression. + +@cindex @code{umul@var{m}3_highpart} instruction pattern +@item @samp{umul@var{m}3_highpart} +Similar, but the multiplication is unsigned. This may be represented +in RTL using an @code{umul_highpart} RTX expression. + +@cindex @code{madd@var{m}@var{n}4} instruction pattern +@item @samp{madd@var{m}@var{n}4} +Multiply operands 1 and 2, sign-extend them to mode @var{n}, add +operand 3, and store the result in operand 0. Operands 1 and 2 +have mode @var{m} and operands 0 and 3 have mode @var{n}. +Both modes must be integer or fixed-point modes and @var{n} must be twice +the size of @var{m}. + +In other words, @code{madd@var{m}@var{n}4} is like +@code{mul@var{m}@var{n}3} except that it also adds operand 3. + +These instructions are not allowed to @code{FAIL}. + +@cindex @code{umadd@var{m}@var{n}4} instruction pattern +@item @samp{umadd@var{m}@var{n}4} +Like @code{madd@var{m}@var{n}4}, but zero-extend the multiplication +operands instead of sign-extending them. + +@cindex @code{ssmadd@var{m}@var{n}4} instruction pattern +@item @samp{ssmadd@var{m}@var{n}4} +Like @code{madd@var{m}@var{n}4}, but all involved operations must be +signed-saturating. + +@cindex @code{usmadd@var{m}@var{n}4} instruction pattern +@item @samp{usmadd@var{m}@var{n}4} +Like @code{umadd@var{m}@var{n}4}, but all involved operations must be +unsigned-saturating. + +@cindex @code{msub@var{m}@var{n}4} instruction pattern +@item @samp{msub@var{m}@var{n}4} +Multiply operands 1 and 2, sign-extend them to mode @var{n}, subtract the +result from operand 3, and store the result in operand 0. Operands 1 and 2 +have mode @var{m} and operands 0 and 3 have mode @var{n}. +Both modes must be integer or fixed-point modes and @var{n} must be twice +the size of @var{m}. + +In other words, @code{msub@var{m}@var{n}4} is like +@code{mul@var{m}@var{n}3} except that it also subtracts the result +from operand 3. + +These instructions are not allowed to @code{FAIL}. + +@cindex @code{umsub@var{m}@var{n}4} instruction pattern +@item @samp{umsub@var{m}@var{n}4} +Like @code{msub@var{m}@var{n}4}, but zero-extend the multiplication +operands instead of sign-extending them. + +@cindex @code{ssmsub@var{m}@var{n}4} instruction pattern +@item @samp{ssmsub@var{m}@var{n}4} +Like @code{msub@var{m}@var{n}4}, but all involved operations must be +signed-saturating. + +@cindex @code{usmsub@var{m}@var{n}4} instruction pattern +@item @samp{usmsub@var{m}@var{n}4} +Like @code{umsub@var{m}@var{n}4}, but all involved operations must be +unsigned-saturating. + +@cindex @code{divmod@var{m}4} instruction pattern +@item @samp{divmod@var{m}4} +Signed division that produces both a quotient and a remainder. +Operand 1 is divided by operand 2 to produce a quotient stored +in operand 0 and a remainder stored in operand 3. + +For machines with an instruction that produces both a quotient and a +remainder, provide a pattern for @samp{divmod@var{m}4} but do not +provide patterns for @samp{div@var{m}3} and @samp{mod@var{m}3}. This +allows optimization in the relatively common case when both the quotient +and remainder are computed. + +If an instruction that just produces a quotient or just a remainder +exists and is more efficient than the instruction that produces both, +write the output routine of @samp{divmod@var{m}4} to call +@code{find_reg_note} and look for a @code{REG_UNUSED} note on the +quotient or remainder and generate the appropriate instruction. + +@cindex @code{udivmod@var{m}4} instruction pattern +@item @samp{udivmod@var{m}4} +Similar, but does unsigned division. + +@anchor{shift patterns} +@cindex @code{ashl@var{m}3} instruction pattern +@cindex @code{ssashl@var{m}3} instruction pattern +@cindex @code{usashl@var{m}3} instruction pattern +@item @samp{ashl@var{m}3}, @samp{ssashl@var{m}3}, @samp{usashl@var{m}3} +Arithmetic-shift operand 1 left by a number of bits specified by operand +2, and store the result in operand 0. Here @var{m} is the mode of +operand 0 and operand 1; operand 2's mode is specified by the +instruction pattern, and the compiler will convert the operand to that +mode before generating the instruction. The shift or rotate expander +or instruction pattern should explicitly specify the mode of the operand 2, +it should never be @code{VOIDmode}. The meaning of out-of-range shift +counts can optionally be specified by @code{TARGET_SHIFT_TRUNCATION_MASK}. +@xref{TARGET_SHIFT_TRUNCATION_MASK}. Operand 2 is always a scalar type. + +@cindex @code{ashr@var{m}3} instruction pattern +@cindex @code{lshr@var{m}3} instruction pattern +@cindex @code{rotl@var{m}3} instruction pattern +@cindex @code{rotr@var{m}3} instruction pattern +@item @samp{ashr@var{m}3}, @samp{lshr@var{m}3}, @samp{rotl@var{m}3}, @samp{rotr@var{m}3} +Other shift and rotate instructions, analogous to the +@code{ashl@var{m}3} instructions. Operand 2 is always a scalar type. + +@cindex @code{vashl@var{m}3} instruction pattern +@cindex @code{vashr@var{m}3} instruction pattern +@cindex @code{vlshr@var{m}3} instruction pattern +@cindex @code{vrotl@var{m}3} instruction pattern +@cindex @code{vrotr@var{m}3} instruction pattern +@item @samp{vashl@var{m}3}, @samp{vashr@var{m}3}, @samp{vlshr@var{m}3}, @samp{vrotl@var{m}3}, @samp{vrotr@var{m}3} +Vector shift and rotate instructions that take vectors as operand 2 +instead of a scalar type. + +@cindex @code{avg@var{m}3_floor} instruction pattern +@cindex @code{uavg@var{m}3_floor} instruction pattern +@item @samp{avg@var{m}3_floor} +@itemx @samp{uavg@var{m}3_floor} +Signed and unsigned average instructions. These instructions add +operands 1 and 2 without truncation, divide the result by 2, +round towards -Inf, and store the result in operand 0. This is +equivalent to the C code: +@smallexample +narrow op0, op1, op2; +@dots{} +op0 = (narrow) (((wide) op1 + (wide) op2) >> 1); +@end smallexample +where the sign of @samp{narrow} determines whether this is a signed +or unsigned operation. + +@cindex @code{avg@var{m}3_ceil} instruction pattern +@cindex @code{uavg@var{m}3_ceil} instruction pattern +@item @samp{avg@var{m}3_ceil} +@itemx @samp{uavg@var{m}3_ceil} +Like @samp{avg@var{m}3_floor} and @samp{uavg@var{m}3_floor}, but round +towards +Inf. This is equivalent to the C code: +@smallexample +narrow op0, op1, op2; +@dots{} +op0 = (narrow) (((wide) op1 + (wide) op2 + 1) >> 1); +@end smallexample + +@cindex @code{bswap@var{m}2} instruction pattern +@item @samp{bswap@var{m}2} +Reverse the order of bytes of operand 1 and store the result in operand 0. + +@cindex @code{neg@var{m}2} instruction pattern +@cindex @code{ssneg@var{m}2} instruction pattern +@cindex @code{usneg@var{m}2} instruction pattern +@item @samp{neg@var{m}2}, @samp{ssneg@var{m}2}, @samp{usneg@var{m}2} +Negate operand 1 and store the result in operand 0. + +@cindex @code{negv@var{m}3} instruction pattern +@item @samp{negv@var{m}3} +Like @code{neg@var{m}2} but takes a @code{code_label} as operand 2 and +emits code to jump to it if signed overflow occurs during the negation. + +@cindex @code{abs@var{m}2} instruction pattern +@item @samp{abs@var{m}2} +Store the absolute value of operand 1 into operand 0. + +@cindex @code{sqrt@var{m}2} instruction pattern +@item @samp{sqrt@var{m}2} +Store the square root of operand 1 into operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{rsqrt@var{m}2} instruction pattern +@item @samp{rsqrt@var{m}2} +Store the reciprocal of the square root of operand 1 into operand 0. +Both operands have mode @var{m}, which is a scalar or vector +floating-point mode. + +On most architectures this pattern is only approximate, so either +its C condition or the @code{TARGET_OPTAB_SUPPORTED_P} hook should +check for the appropriate math flags. (Using the C condition is +more direct, but using @code{TARGET_OPTAB_SUPPORTED_P} can be useful +if a target-specific built-in also uses the @samp{rsqrt@var{m}2} +pattern.) + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{fmod@var{m}3} instruction pattern +@item @samp{fmod@var{m}3} +Store the remainder of dividing operand 1 by operand 2 into +operand 0, rounded towards zero to an integer. All operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{remainder@var{m}3} instruction pattern +@item @samp{remainder@var{m}3} +Store the remainder of dividing operand 1 by operand 2 into +operand 0, rounded to the nearest integer. All operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{scalb@var{m}3} instruction pattern +@item @samp{scalb@var{m}3} +Raise @code{FLT_RADIX} to the power of operand 2, multiply it by +operand 1, and store the result in operand 0. All operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{ldexp@var{m}3} instruction pattern +@item @samp{ldexp@var{m}3} +Raise 2 to the power of operand 2, multiply it by operand 1, and store +the result in operand 0. Operands 0 and 1 have mode @var{m}, which is +a scalar or vector floating-point mode. Operand 2's mode has +the same number of elements as @var{m} and each element is wide +enough to store an @code{int}. The integers are signed. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{cos@var{m}2} instruction pattern +@item @samp{cos@var{m}2} +Store the cosine of operand 1 into operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{sin@var{m}2} instruction pattern +@item @samp{sin@var{m}2} +Store the sine of operand 1 into operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{sincos@var{m}3} instruction pattern +@item @samp{sincos@var{m}3} +Store the cosine of operand 2 into operand 0 and the sine of +operand 2 into operand 1. All operands have mode @var{m}, +which is a scalar or vector floating-point mode. + +Targets that can calculate the sine and cosine simultaneously can +implement this pattern as opposed to implementing individual +@code{sin@var{m}2} and @code{cos@var{m}2} patterns. The @code{sin} +and @code{cos} built-in functions will then be expanded to the +@code{sincos@var{m}3} pattern, with one of the output values +left unused. + +@cindex @code{tan@var{m}2} instruction pattern +@item @samp{tan@var{m}2} +Store the tangent of operand 1 into operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{asin@var{m}2} instruction pattern +@item @samp{asin@var{m}2} +Store the arc sine of operand 1 into operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{acos@var{m}2} instruction pattern +@item @samp{acos@var{m}2} +Store the arc cosine of operand 1 into operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{atan@var{m}2} instruction pattern +@item @samp{atan@var{m}2} +Store the arc tangent of operand 1 into operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{fegetround@var{m}} instruction pattern +@item @samp{fegetround@var{m}} +Store the current machine floating-point rounding mode into operand 0. +Operand 0 has mode @var{m}, which is scalar. This pattern is used to +implement the @code{fegetround} function from the ISO C99 standard. + +@cindex @code{feclearexcept@var{m}} instruction pattern +@cindex @code{feraiseexcept@var{m}} instruction pattern +@item @samp{feclearexcept@var{m}} +@item @samp{feraiseexcept@var{m}} +Clears or raises the supported machine floating-point exceptions +represented by the bits in operand 1. Error status is stored as +nonzero value in operand 0. Both operands have mode @var{m}, which is +a scalar. These patterns are used to implement the +@code{feclearexcept} and @code{feraiseexcept} functions from the ISO +C99 standard. + +@cindex @code{exp@var{m}2} instruction pattern +@item @samp{exp@var{m}2} +Raise e (the base of natural logarithms) to the power of operand 1 +and store the result in operand 0. Both operands have mode @var{m}, +which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{expm1@var{m}2} instruction pattern +@item @samp{expm1@var{m}2} +Raise e (the base of natural logarithms) to the power of operand 1, +subtract 1, and store the result in operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. + +For inputs close to zero, the pattern is expected to be more +accurate than a separate @code{exp@var{m}2} and @code{sub@var{m}3} +would be. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{exp10@var{m}2} instruction pattern +@item @samp{exp10@var{m}2} +Raise 10 to the power of operand 1 and store the result in operand 0. +Both operands have mode @var{m}, which is a scalar or vector +floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{exp2@var{m}2} instruction pattern +@item @samp{exp2@var{m}2} +Raise 2 to the power of operand 1 and store the result in operand 0. +Both operands have mode @var{m}, which is a scalar or vector +floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{log@var{m}2} instruction pattern +@item @samp{log@var{m}2} +Store the natural logarithm of operand 1 into operand 0. Both operands +have mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{log1p@var{m}2} instruction pattern +@item @samp{log1p@var{m}2} +Add 1 to operand 1, compute the natural logarithm, and store +the result in operand 0. Both operands have mode @var{m}, which is +a scalar or vector floating-point mode. + +For inputs close to zero, the pattern is expected to be more +accurate than a separate @code{add@var{m}3} and @code{log@var{m}2} +would be. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{log10@var{m}2} instruction pattern +@item @samp{log10@var{m}2} +Store the base-10 logarithm of operand 1 into operand 0. Both operands +have mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{log2@var{m}2} instruction pattern +@item @samp{log2@var{m}2} +Store the base-2 logarithm of operand 1 into operand 0. Both operands +have mode @var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{logb@var{m}2} instruction pattern +@item @samp{logb@var{m}2} +Store the base-@code{FLT_RADIX} logarithm of operand 1 into operand 0. +Both operands have mode @var{m}, which is a scalar or vector +floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{significand@var{m}2} instruction pattern +@item @samp{significand@var{m}2} +Store the significand of floating-point operand 1 in operand 0. +Both operands have mode @var{m}, which is a scalar or vector +floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{pow@var{m}3} instruction pattern +@item @samp{pow@var{m}3} +Store the value of operand 1 raised to the exponent operand 2 +into operand 0. All operands have mode @var{m}, which is a scalar +or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{atan2@var{m}3} instruction pattern +@item @samp{atan2@var{m}3} +Store the arc tangent (inverse tangent) of operand 1 divided by +operand 2 into operand 0, using the signs of both arguments to +determine the quadrant of the result. All operands have mode +@var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{floor@var{m}2} instruction pattern +@item @samp{floor@var{m}2} +Store the largest integral value not greater than operand 1 in operand 0. +Both operands have mode @var{m}, which is a scalar or vector +floating-point mode. If @option{-ffp-int-builtin-inexact} is in +effect, the ``inexact'' exception may be raised for noninteger +operands; otherwise, it may not. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{btrunc@var{m}2} instruction pattern +@item @samp{btrunc@var{m}2} +Round operand 1 to an integer, towards zero, and store the result in +operand 0. Both operands have mode @var{m}, which is a scalar or +vector floating-point mode. If @option{-ffp-int-builtin-inexact} is +in effect, the ``inexact'' exception may be raised for noninteger +operands; otherwise, it may not. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{round@var{m}2} instruction pattern +@item @samp{round@var{m}2} +Round operand 1 to the nearest integer, rounding away from zero in the +event of a tie, and store the result in operand 0. Both operands have +mode @var{m}, which is a scalar or vector floating-point mode. If +@option{-ffp-int-builtin-inexact} is in effect, the ``inexact'' +exception may be raised for noninteger operands; otherwise, it may +not. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{ceil@var{m}2} instruction pattern +@item @samp{ceil@var{m}2} +Store the smallest integral value not less than operand 1 in operand 0. +Both operands have mode @var{m}, which is a scalar or vector +floating-point mode. If @option{-ffp-int-builtin-inexact} is in +effect, the ``inexact'' exception may be raised for noninteger +operands; otherwise, it may not. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{nearbyint@var{m}2} instruction pattern +@item @samp{nearbyint@var{m}2} +Round operand 1 to an integer, using the current rounding mode, and +store the result in operand 0. Do not raise an inexact condition when +the result is different from the argument. Both operands have mode +@var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{rint@var{m}2} instruction pattern +@item @samp{rint@var{m}2} +Round operand 1 to an integer, using the current rounding mode, and +store the result in operand 0. Raise an inexact condition when +the result is different from the argument. Both operands have mode +@var{m}, which is a scalar or vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{lrint@var{m}@var{n}2} +@item @samp{lrint@var{m}@var{n}2} +Convert operand 1 (valid for floating point mode @var{m}) to fixed +point mode @var{n} as a signed number according to the current +rounding mode and store in operand 0 (which has mode @var{n}). + +@cindex @code{lround@var{m}@var{n}2} +@item @samp{lround@var{m}@var{n}2} +Convert operand 1 (valid for floating point mode @var{m}) to fixed +point mode @var{n} as a signed number rounding to nearest and away +from zero and store in operand 0 (which has mode @var{n}). + +@cindex @code{lfloor@var{m}@var{n}2} +@item @samp{lfloor@var{m}@var{n}2} +Convert operand 1 (valid for floating point mode @var{m}) to fixed +point mode @var{n} as a signed number rounding down and store in +operand 0 (which has mode @var{n}). + +@cindex @code{lceil@var{m}@var{n}2} +@item @samp{lceil@var{m}@var{n}2} +Convert operand 1 (valid for floating point mode @var{m}) to fixed +point mode @var{n} as a signed number rounding up and store in +operand 0 (which has mode @var{n}). + +@cindex @code{copysign@var{m}3} instruction pattern +@item @samp{copysign@var{m}3} +Store a value with the magnitude of operand 1 and the sign of operand +2 into operand 0. All operands have mode @var{m}, which is a scalar or +vector floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{xorsign@var{m}3} instruction pattern +@item @samp{xorsign@var{m}3} +Equivalent to @samp{op0 = op1 * copysign (1.0, op2)}: store a value with +the magnitude of operand 1 and the sign of operand 2 into operand 0. +All operands have mode @var{m}, which is a scalar or vector +floating-point mode. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{issignaling@var{m}2} instruction pattern +@item @samp{issignaling@var{m}2} +Set operand 0 to 1 if operand 1 is a signaling NaN and to 0 otherwise. + +@cindex @code{cadd90@var{m}3} instruction pattern +@item @samp{cadd90@var{m}3} +Perform vector add and subtract on even/odd number pairs. The operation being +matched is semantically described as + +@smallexample + for (int i = 0; i < N; i += 2) + @{ + c[i] = a[i] - b[i+1]; + c[i+1] = a[i+1] + b[i]; + @} +@end smallexample + +This operation is semantically equivalent to performing a vector addition of +complex numbers in operand 1 with operand 2 rotated by 90 degrees around +the argand plane and storing the result in operand 0. + +In GCC lane ordering the real part of the number must be in the even lanes with +the imaginary part in the odd lanes. + +The operation is only supported for vector modes @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{cadd270@var{m}3} instruction pattern +@item @samp{cadd270@var{m}3} +Perform vector add and subtract on even/odd number pairs. The operation being +matched is semantically described as + +@smallexample + for (int i = 0; i < N; i += 2) + @{ + c[i] = a[i] + b[i+1]; + c[i+1] = a[i+1] - b[i]; + @} +@end smallexample + +This operation is semantically equivalent to performing a vector addition of +complex numbers in operand 1 with operand 2 rotated by 270 degrees around +the argand plane and storing the result in operand 0. + +In GCC lane ordering the real part of the number must be in the even lanes with +the imaginary part in the odd lanes. + +The operation is only supported for vector modes @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{cmla@var{m}4} instruction pattern +@item @samp{cmla@var{m}4} +Perform a vector multiply and accumulate that is semantically the same as +a multiply and accumulate of complex numbers. + +@smallexample + complex TYPE op0[N]; + complex TYPE op1[N]; + complex TYPE op2[N]; + complex TYPE op3[N]; + for (int i = 0; i < N; i += 1) + @{ + op0[i] = op1[i] * op2[i] + op3[i]; + @} +@end smallexample + +In GCC lane ordering the real part of the number must be in the even lanes with +the imaginary part in the odd lanes. + +The operation is only supported for vector modes @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{cmla_conj@var{m}4} instruction pattern +@item @samp{cmla_conj@var{m}4} +Perform a vector multiply by conjugate and accumulate that is semantically +the same as a multiply and accumulate of complex numbers where the second +multiply arguments is conjugated. + +@smallexample + complex TYPE op0[N]; + complex TYPE op1[N]; + complex TYPE op2[N]; + complex TYPE op3[N]; + for (int i = 0; i < N; i += 1) + @{ + op0[i] = op1[i] * conj (op2[i]) + op3[i]; + @} +@end smallexample + +In GCC lane ordering the real part of the number must be in the even lanes with +the imaginary part in the odd lanes. + +The operation is only supported for vector modes @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{cmls@var{m}4} instruction pattern +@item @samp{cmls@var{m}4} +Perform a vector multiply and subtract that is semantically the same as +a multiply and subtract of complex numbers. + +@smallexample + complex TYPE op0[N]; + complex TYPE op1[N]; + complex TYPE op2[N]; + complex TYPE op3[N]; + for (int i = 0; i < N; i += 1) + @{ + op0[i] = op1[i] * op2[i] - op3[i]; + @} +@end smallexample + +In GCC lane ordering the real part of the number must be in the even lanes with +the imaginary part in the odd lanes. + +The operation is only supported for vector modes @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{cmls_conj@var{m}4} instruction pattern +@item @samp{cmls_conj@var{m}4} +Perform a vector multiply by conjugate and subtract that is semantically +the same as a multiply and subtract of complex numbers where the second +multiply arguments is conjugated. + +@smallexample + complex TYPE op0[N]; + complex TYPE op1[N]; + complex TYPE op2[N]; + complex TYPE op3[N]; + for (int i = 0; i < N; i += 1) + @{ + op0[i] = op1[i] * conj (op2[i]) - op3[i]; + @} +@end smallexample + +In GCC lane ordering the real part of the number must be in the even lanes with +the imaginary part in the odd lanes. + +The operation is only supported for vector modes @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{cmul@var{m}4} instruction pattern +@item @samp{cmul@var{m}4} +Perform a vector multiply that is semantically the same as multiply of +complex numbers. + +@smallexample + complex TYPE op0[N]; + complex TYPE op1[N]; + complex TYPE op2[N]; + for (int i = 0; i < N; i += 1) + @{ + op0[i] = op1[i] * op2[i]; + @} +@end smallexample + +In GCC lane ordering the real part of the number must be in the even lanes with +the imaginary part in the odd lanes. + +The operation is only supported for vector modes @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{cmul_conj@var{m}4} instruction pattern +@item @samp{cmul_conj@var{m}4} +Perform a vector multiply by conjugate that is semantically the same as a +multiply of complex numbers where the second multiply arguments is conjugated. + +@smallexample + complex TYPE op0[N]; + complex TYPE op1[N]; + complex TYPE op2[N]; + for (int i = 0; i < N; i += 1) + @{ + op0[i] = op1[i] * conj (op2[i]); + @} +@end smallexample + +In GCC lane ordering the real part of the number must be in the even lanes with +the imaginary part in the odd lanes. + +The operation is only supported for vector modes @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{ffs@var{m}2} instruction pattern +@item @samp{ffs@var{m}2} +Store into operand 0 one plus the index of the least significant 1-bit +of operand 1. If operand 1 is zero, store zero. + +@var{m} is either a scalar or vector integer mode. When it is a scalar, +operand 1 has mode @var{m} but operand 0 can have whatever scalar +integer mode is suitable for the target. The compiler will insert +conversion instructions as necessary (typically to convert the result +to the same width as @code{int}). When @var{m} is a vector, both +operands must have mode @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{clrsb@var{m}2} instruction pattern +@item @samp{clrsb@var{m}2} +Count leading redundant sign bits. +Store into operand 0 the number of redundant sign bits in operand 1, starting +at the most significant bit position. +A redundant sign bit is defined as any sign bit after the first. As such, +this count will be one less than the count of leading sign bits. + +@var{m} is either a scalar or vector integer mode. When it is a scalar, +operand 1 has mode @var{m} but operand 0 can have whatever scalar +integer mode is suitable for the target. The compiler will insert +conversion instructions as necessary (typically to convert the result +to the same width as @code{int}). When @var{m} is a vector, both +operands must have mode @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{clz@var{m}2} instruction pattern +@item @samp{clz@var{m}2} +Store into operand 0 the number of leading 0-bits in operand 1, starting +at the most significant bit position. If operand 1 is 0, the +@code{CLZ_DEFINED_VALUE_AT_ZERO} (@pxref{Misc}) macro defines if +the result is undefined or has a useful value. + +@var{m} is either a scalar or vector integer mode. When it is a scalar, +operand 1 has mode @var{m} but operand 0 can have whatever scalar +integer mode is suitable for the target. The compiler will insert +conversion instructions as necessary (typically to convert the result +to the same width as @code{int}). When @var{m} is a vector, both +operands must have mode @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{ctz@var{m}2} instruction pattern +@item @samp{ctz@var{m}2} +Store into operand 0 the number of trailing 0-bits in operand 1, starting +at the least significant bit position. If operand 1 is 0, the +@code{CTZ_DEFINED_VALUE_AT_ZERO} (@pxref{Misc}) macro defines if +the result is undefined or has a useful value. + +@var{m} is either a scalar or vector integer mode. When it is a scalar, +operand 1 has mode @var{m} but operand 0 can have whatever scalar +integer mode is suitable for the target. The compiler will insert +conversion instructions as necessary (typically to convert the result +to the same width as @code{int}). When @var{m} is a vector, both +operands must have mode @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{popcount@var{m}2} instruction pattern +@item @samp{popcount@var{m}2} +Store into operand 0 the number of 1-bits in operand 1. + +@var{m} is either a scalar or vector integer mode. When it is a scalar, +operand 1 has mode @var{m} but operand 0 can have whatever scalar +integer mode is suitable for the target. The compiler will insert +conversion instructions as necessary (typically to convert the result +to the same width as @code{int}). When @var{m} is a vector, both +operands must have mode @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{parity@var{m}2} instruction pattern +@item @samp{parity@var{m}2} +Store into operand 0 the parity of operand 1, i.e.@: the number of 1-bits +in operand 1 modulo 2. + +@var{m} is either a scalar or vector integer mode. When it is a scalar, +operand 1 has mode @var{m} but operand 0 can have whatever scalar +integer mode is suitable for the target. The compiler will insert +conversion instructions as necessary (typically to convert the result +to the same width as @code{int}). When @var{m} is a vector, both +operands must have mode @var{m}. + +This pattern is not allowed to @code{FAIL}. + +@cindex @code{one_cmpl@var{m}2} instruction pattern +@item @samp{one_cmpl@var{m}2} +Store the bitwise-complement of operand 1 into operand 0. + +@cindex @code{cpymem@var{m}} instruction pattern +@item @samp{cpymem@var{m}} +Block copy instruction. The destination and source blocks of memory +are the first two operands, and both are @code{mem:BLK}s with an +address in mode @code{Pmode}. + +The number of bytes to copy is the third operand, in mode @var{m}. +Usually, you specify @code{Pmode} for @var{m}. However, if you can +generate better code knowing the range of valid lengths is smaller than +those representable in a full Pmode pointer, you should provide +a pattern with a +mode corresponding to the range of values you can handle efficiently +(e.g., @code{QImode} for values in the range 0--127; note we avoid numbers +that appear negative) and also a pattern with @code{Pmode}. + +The fourth operand is the known shared alignment of the source and +destination, in the form of a @code{const_int} rtx. Thus, if the +compiler knows that both source and destination are word-aligned, +it may provide the value 4 for this operand. + +Optional operands 5 and 6 specify expected alignment and size of block +respectively. The expected alignment differs from alignment in operand 4 +in a way that the blocks are not required to be aligned according to it in +all cases. This expected alignment is also in bytes, just like operand 4. +Expected size, when unknown, is set to @code{(const_int -1)}. + +Descriptions of multiple @code{cpymem@var{m}} patterns can only be +beneficial if the patterns for smaller modes have fewer restrictions +on their first, second and fourth operands. Note that the mode @var{m} +in @code{cpymem@var{m}} does not impose any restriction on the mode of +individually copied data units in the block. + +The @code{cpymem@var{m}} patterns need not give special consideration +to the possibility that the source and destination strings might +overlap. These patterns are used to do inline expansion of +@code{__builtin_memcpy}. + +@cindex @code{movmem@var{m}} instruction pattern +@item @samp{movmem@var{m}} +Block move instruction. The destination and source blocks of memory +are the first two operands, and both are @code{mem:BLK}s with an +address in mode @code{Pmode}. + +The number of bytes to copy is the third operand, in mode @var{m}. +Usually, you specify @code{Pmode} for @var{m}. However, if you can +generate better code knowing the range of valid lengths is smaller than +those representable in a full Pmode pointer, you should provide +a pattern with a +mode corresponding to the range of values you can handle efficiently +(e.g., @code{QImode} for values in the range 0--127; note we avoid numbers +that appear negative) and also a pattern with @code{Pmode}. + +The fourth operand is the known shared alignment of the source and +destination, in the form of a @code{const_int} rtx. Thus, if the +compiler knows that both source and destination are word-aligned, +it may provide the value 4 for this operand. + +Optional operands 5 and 6 specify expected alignment and size of block +respectively. The expected alignment differs from alignment in operand 4 +in a way that the blocks are not required to be aligned according to it in +all cases. This expected alignment is also in bytes, just like operand 4. +Expected size, when unknown, is set to @code{(const_int -1)}. + +Descriptions of multiple @code{movmem@var{m}} patterns can only be +beneficial if the patterns for smaller modes have fewer restrictions +on their first, second and fourth operands. Note that the mode @var{m} +in @code{movmem@var{m}} does not impose any restriction on the mode of +individually copied data units in the block. + +The @code{movmem@var{m}} patterns must correctly handle the case where +the source and destination strings overlap. These patterns are used to +do inline expansion of @code{__builtin_memmove}. + +@cindex @code{movstr} instruction pattern +@item @samp{movstr} +String copy instruction, with @code{stpcpy} semantics. Operand 0 is +an output operand in mode @code{Pmode}. The addresses of the +destination and source strings are operands 1 and 2, and both are +@code{mem:BLK}s with addresses in mode @code{Pmode}. The execution of +the expansion of this pattern should store in operand 0 the address in +which the @code{NUL} terminator was stored in the destination string. + +This pattern has also several optional operands that are same as in +@code{setmem}. + +@cindex @code{setmem@var{m}} instruction pattern +@item @samp{setmem@var{m}} +Block set instruction. The destination string is the first operand, +given as a @code{mem:BLK} whose address is in mode @code{Pmode}. The +number of bytes to set is the second operand, in mode @var{m}. The value to +initialize the memory with is the third operand. Targets that only support the +clearing of memory should reject any value that is not the constant 0. See +@samp{cpymem@var{m}} for a discussion of the choice of mode. + +The fourth operand is the known alignment of the destination, in the form +of a @code{const_int} rtx. Thus, if the compiler knows that the +destination is word-aligned, it may provide the value 4 for this +operand. + +Optional operands 5 and 6 specify expected alignment and size of block +respectively. The expected alignment differs from alignment in operand 4 +in a way that the blocks are not required to be aligned according to it in +all cases. This expected alignment is also in bytes, just like operand 4. +Expected size, when unknown, is set to @code{(const_int -1)}. +Operand 7 is the minimal size of the block and operand 8 is the +maximal size of the block (NULL if it cannot be represented as CONST_INT). +Operand 9 is the probable maximal size (i.e.@: we cannot rely on it for +correctness, but it can be used for choosing proper code sequence for a +given size). + +The use for multiple @code{setmem@var{m}} is as for @code{cpymem@var{m}}. + +@cindex @code{cmpstrn@var{m}} instruction pattern +@item @samp{cmpstrn@var{m}} +String compare instruction, with five operands. Operand 0 is the output; +it has mode @var{m}. The remaining four operands are like the operands +of @samp{cpymem@var{m}}. The two memory blocks specified are compared +byte by byte in lexicographic order starting at the beginning of each +string. The instruction is not allowed to prefetch more than one byte +at a time since either string may end in the first byte and reading past +that may access an invalid page or segment and cause a fault. The +comparison terminates early if the fetched bytes are different or if +they are equal to zero. The effect of the instruction is to store a +value in operand 0 whose sign indicates the result of the comparison. + +@cindex @code{cmpstr@var{m}} instruction pattern +@item @samp{cmpstr@var{m}} +String compare instruction, without known maximum length. Operand 0 is the +output; it has mode @var{m}. The second and third operand are the blocks of +memory to be compared; both are @code{mem:BLK} with an address in mode +@code{Pmode}. + +The fourth operand is the known shared alignment of the source and +destination, in the form of a @code{const_int} rtx. Thus, if the +compiler knows that both source and destination are word-aligned, +it may provide the value 4 for this operand. + +The two memory blocks specified are compared byte by byte in lexicographic +order starting at the beginning of each string. The instruction is not allowed +to prefetch more than one byte at a time since either string may end in the +first byte and reading past that may access an invalid page or segment and +cause a fault. The comparison will terminate when the fetched bytes +are different or if they are equal to zero. The effect of the +instruction is to store a value in operand 0 whose sign indicates the +result of the comparison. + +@cindex @code{cmpmem@var{m}} instruction pattern +@item @samp{cmpmem@var{m}} +Block compare instruction, with five operands like the operands +of @samp{cmpstr@var{m}}. The two memory blocks specified are compared +byte by byte in lexicographic order starting at the beginning of each +block. Unlike @samp{cmpstr@var{m}} the instruction can prefetch +any bytes in the two memory blocks. Also unlike @samp{cmpstr@var{m}} +the comparison will not stop if both bytes are zero. The effect of +the instruction is to store a value in operand 0 whose sign indicates +the result of the comparison. + +@cindex @code{strlen@var{m}} instruction pattern +@item @samp{strlen@var{m}} +Compute the length of a string, with three operands. +Operand 0 is the result (of mode @var{m}), operand 1 is +a @code{mem} referring to the first character of the string, +operand 2 is the character to search for (normally zero), +and operand 3 is a constant describing the known alignment +of the beginning of the string. + +@cindex @code{rawmemchr@var{m}} instruction pattern +@item @samp{rawmemchr@var{m}} +Scan memory referred to by operand 1 for the first occurrence of operand 2. +Operand 1 is a @code{mem} and operand 2 a @code{const_int} of mode @var{m}. +Operand 0 is the result, i.e., a pointer to the first occurrence of operand 2 +in the memory block given by operand 1. + +@cindex @code{float@var{m}@var{n}2} instruction pattern +@item @samp{float@var{m}@var{n}2} +Convert signed integer operand 1 (valid for fixed point mode @var{m}) to +floating point mode @var{n} and store in operand 0 (which has mode +@var{n}). + +@cindex @code{floatuns@var{m}@var{n}2} instruction pattern +@item @samp{floatuns@var{m}@var{n}2} +Convert unsigned integer operand 1 (valid for fixed point mode @var{m}) +to floating point mode @var{n} and store in operand 0 (which has mode +@var{n}). + +@cindex @code{fix@var{m}@var{n}2} instruction pattern +@item @samp{fix@var{m}@var{n}2} +Convert operand 1 (valid for floating point mode @var{m}) to fixed +point mode @var{n} as a signed number and store in operand 0 (which +has mode @var{n}). This instruction's result is defined only when +the value of operand 1 is an integer. + +If the machine description defines this pattern, it also needs to +define the @code{ftrunc} pattern. + +@cindex @code{fixuns@var{m}@var{n}2} instruction pattern +@item @samp{fixuns@var{m}@var{n}2} +Convert operand 1 (valid for floating point mode @var{m}) to fixed +point mode @var{n} as an unsigned number and store in operand 0 (which +has mode @var{n}). This instruction's result is defined only when the +value of operand 1 is an integer. + +@cindex @code{ftrunc@var{m}2} instruction pattern +@item @samp{ftrunc@var{m}2} +Convert operand 1 (valid for floating point mode @var{m}) to an +integer value, still represented in floating point mode @var{m}, and +store it in operand 0 (valid for floating point mode @var{m}). + +@cindex @code{fix_trunc@var{m}@var{n}2} instruction pattern +@item @samp{fix_trunc@var{m}@var{n}2} +Like @samp{fix@var{m}@var{n}2} but works for any floating point value +of mode @var{m} by converting the value to an integer. + +@cindex @code{fixuns_trunc@var{m}@var{n}2} instruction pattern +@item @samp{fixuns_trunc@var{m}@var{n}2} +Like @samp{fixuns@var{m}@var{n}2} but works for any floating point +value of mode @var{m} by converting the value to an integer. + +@cindex @code{trunc@var{m}@var{n}2} instruction pattern +@item @samp{trunc@var{m}@var{n}2} +Truncate operand 1 (valid for mode @var{m}) to mode @var{n} and +store in operand 0 (which has mode @var{n}). Both modes must be fixed +point or both floating point. + +@cindex @code{extend@var{m}@var{n}2} instruction pattern +@item @samp{extend@var{m}@var{n}2} +Sign-extend operand 1 (valid for mode @var{m}) to mode @var{n} and +store in operand 0 (which has mode @var{n}). Both modes must be fixed +point or both floating point. + +@cindex @code{zero_extend@var{m}@var{n}2} instruction pattern +@item @samp{zero_extend@var{m}@var{n}2} +Zero-extend operand 1 (valid for mode @var{m}) to mode @var{n} and +store in operand 0 (which has mode @var{n}). Both modes must be fixed +point. + +@cindex @code{fract@var{m}@var{n}2} instruction pattern +@item @samp{fract@var{m}@var{n}2} +Convert operand 1 of mode @var{m} to mode @var{n} and store in +operand 0 (which has mode @var{n}). Mode @var{m} and mode @var{n} +could be fixed-point to fixed-point, signed integer to fixed-point, +fixed-point to signed integer, floating-point to fixed-point, +or fixed-point to floating-point. +When overflows or underflows happen, the results are undefined. + +@cindex @code{satfract@var{m}@var{n}2} instruction pattern +@item @samp{satfract@var{m}@var{n}2} +Convert operand 1 of mode @var{m} to mode @var{n} and store in +operand 0 (which has mode @var{n}). Mode @var{m} and mode @var{n} +could be fixed-point to fixed-point, signed integer to fixed-point, +or floating-point to fixed-point. +When overflows or underflows happen, the instruction saturates the +results to the maximum or the minimum. + +@cindex @code{fractuns@var{m}@var{n}2} instruction pattern +@item @samp{fractuns@var{m}@var{n}2} +Convert operand 1 of mode @var{m} to mode @var{n} and store in +operand 0 (which has mode @var{n}). Mode @var{m} and mode @var{n} +could be unsigned integer to fixed-point, or +fixed-point to unsigned integer. +When overflows or underflows happen, the results are undefined. + +@cindex @code{satfractuns@var{m}@var{n}2} instruction pattern +@item @samp{satfractuns@var{m}@var{n}2} +Convert unsigned integer operand 1 of mode @var{m} to fixed-point mode +@var{n} and store in operand 0 (which has mode @var{n}). +When overflows or underflows happen, the instruction saturates the +results to the maximum or the minimum. + +@cindex @code{extv@var{m}} instruction pattern +@item @samp{extv@var{m}} +Extract a bit-field from register operand 1, sign-extend it, and store +it in operand 0. Operand 2 specifies the width of the field in bits +and operand 3 the starting bit, which counts from the most significant +bit if @samp{BITS_BIG_ENDIAN} is true and from the least significant bit +otherwise. + +Operands 0 and 1 both have mode @var{m}. Operands 2 and 3 have a +target-specific mode. + +@cindex @code{extvmisalign@var{m}} instruction pattern +@item @samp{extvmisalign@var{m}} +Extract a bit-field from memory operand 1, sign extend it, and store +it in operand 0. Operand 2 specifies the width in bits and operand 3 +the starting bit. The starting bit is always somewhere in the first byte of +operand 1; it counts from the most significant bit if @samp{BITS_BIG_ENDIAN} +is true and from the least significant bit otherwise. + +Operand 0 has mode @var{m} while operand 1 has @code{BLK} mode. +Operands 2 and 3 have a target-specific mode. + +The instruction must not read beyond the last byte of the bit-field. + +@cindex @code{extzv@var{m}} instruction pattern +@item @samp{extzv@var{m}} +Like @samp{extv@var{m}} except that the bit-field value is zero-extended. + +@cindex @code{extzvmisalign@var{m}} instruction pattern +@item @samp{extzvmisalign@var{m}} +Like @samp{extvmisalign@var{m}} except that the bit-field value is +zero-extended. + +@cindex @code{insv@var{m}} instruction pattern +@item @samp{insv@var{m}} +Insert operand 3 into a bit-field of register operand 0. Operand 1 +specifies the width of the field in bits and operand 2 the starting bit, +which counts from the most significant bit if @samp{BITS_BIG_ENDIAN} +is true and from the least significant bit otherwise. + +Operands 0 and 3 both have mode @var{m}. Operands 1 and 2 have a +target-specific mode. + +@cindex @code{insvmisalign@var{m}} instruction pattern +@item @samp{insvmisalign@var{m}} +Insert operand 3 into a bit-field of memory operand 0. Operand 1 +specifies the width of the field in bits and operand 2 the starting bit. +The starting bit is always somewhere in the first byte of operand 0; +it counts from the most significant bit if @samp{BITS_BIG_ENDIAN} +is true and from the least significant bit otherwise. + +Operand 3 has mode @var{m} while operand 0 has @code{BLK} mode. +Operands 1 and 2 have a target-specific mode. + +The instruction must not read or write beyond the last byte of the bit-field. + +@cindex @code{extv} instruction pattern +@item @samp{extv} +Extract a bit-field from operand 1 (a register or memory operand), where +operand 2 specifies the width in bits and operand 3 the starting bit, +and store it in operand 0. Operand 0 must have mode @code{word_mode}. +Operand 1 may have mode @code{byte_mode} or @code{word_mode}; often +@code{word_mode} is allowed only for registers. Operands 2 and 3 must +be valid for @code{word_mode}. + +The RTL generation pass generates this instruction only with constants +for operands 2 and 3 and the constant is never zero for operand 2. + +The bit-field value is sign-extended to a full word integer +before it is stored in operand 0. + +This pattern is deprecated; please use @samp{extv@var{m}} and +@code{extvmisalign@var{m}} instead. + +@cindex @code{extzv} instruction pattern +@item @samp{extzv} +Like @samp{extv} except that the bit-field value is zero-extended. + +This pattern is deprecated; please use @samp{extzv@var{m}} and +@code{extzvmisalign@var{m}} instead. + +@cindex @code{insv} instruction pattern +@item @samp{insv} +Store operand 3 (which must be valid for @code{word_mode}) into a +bit-field in operand 0, where operand 1 specifies the width in bits and +operand 2 the starting bit. Operand 0 may have mode @code{byte_mode} or +@code{word_mode}; often @code{word_mode} is allowed only for registers. +Operands 1 and 2 must be valid for @code{word_mode}. + +The RTL generation pass generates this instruction only with constants +for operands 1 and 2 and the constant is never zero for operand 1. + +This pattern is deprecated; please use @samp{insv@var{m}} and +@code{insvmisalign@var{m}} instead. + +@cindex @code{mov@var{mode}cc} instruction pattern +@item @samp{mov@var{mode}cc} +Conditionally move operand 2 or operand 3 into operand 0 according to the +comparison in operand 1. If the comparison is true, operand 2 is moved +into operand 0, otherwise operand 3 is moved. + +The mode of the operands being compared need not be the same as the operands +being moved. Some machines, sparc64 for example, have instructions that +conditionally move an integer value based on the floating point condition +codes and vice versa. + +If the machine does not have conditional move instructions, do not +define these patterns. + +@cindex @code{add@var{mode}cc} instruction pattern +@item @samp{add@var{mode}cc} +Similar to @samp{mov@var{mode}cc} but for conditional addition. Conditionally +move operand 2 or (operands 2 + operand 3) into operand 0 according to the +comparison in operand 1. If the comparison is false, operand 2 is moved into +operand 0, otherwise (operand 2 + operand 3) is moved. + +@cindex @code{cond_add@var{mode}} instruction pattern +@cindex @code{cond_sub@var{mode}} instruction pattern +@cindex @code{cond_mul@var{mode}} instruction pattern +@cindex @code{cond_div@var{mode}} instruction pattern +@cindex @code{cond_udiv@var{mode}} instruction pattern +@cindex @code{cond_mod@var{mode}} instruction pattern +@cindex @code{cond_umod@var{mode}} instruction pattern +@cindex @code{cond_and@var{mode}} instruction pattern +@cindex @code{cond_ior@var{mode}} instruction pattern +@cindex @code{cond_xor@var{mode}} instruction pattern +@cindex @code{cond_smin@var{mode}} instruction pattern +@cindex @code{cond_smax@var{mode}} instruction pattern +@cindex @code{cond_umin@var{mode}} instruction pattern +@cindex @code{cond_umax@var{mode}} instruction pattern +@cindex @code{cond_fmin@var{mode}} instruction pattern +@cindex @code{cond_fmax@var{mode}} instruction pattern +@cindex @code{cond_ashl@var{mode}} instruction pattern +@cindex @code{cond_ashr@var{mode}} instruction pattern +@cindex @code{cond_lshr@var{mode}} instruction pattern +@item @samp{cond_add@var{mode}} +@itemx @samp{cond_sub@var{mode}} +@itemx @samp{cond_mul@var{mode}} +@itemx @samp{cond_div@var{mode}} +@itemx @samp{cond_udiv@var{mode}} +@itemx @samp{cond_mod@var{mode}} +@itemx @samp{cond_umod@var{mode}} +@itemx @samp{cond_and@var{mode}} +@itemx @samp{cond_ior@var{mode}} +@itemx @samp{cond_xor@var{mode}} +@itemx @samp{cond_smin@var{mode}} +@itemx @samp{cond_smax@var{mode}} +@itemx @samp{cond_umin@var{mode}} +@itemx @samp{cond_umax@var{mode}} +@itemx @samp{cond_fmin@var{mode}} +@itemx @samp{cond_fmax@var{mode}} +@itemx @samp{cond_ashl@var{mode}} +@itemx @samp{cond_ashr@var{mode}} +@itemx @samp{cond_lshr@var{mode}} +When operand 1 is true, perform an operation on operands 2 and 3 and +store the result in operand 0, otherwise store operand 4 in operand 0. +The operation works elementwise if the operands are vectors. + +The scalar case is equivalent to: + +@smallexample +op0 = op1 ? op2 @var{op} op3 : op4; +@end smallexample + +while the vector case is equivalent to: + +@smallexample +for (i = 0; i < GET_MODE_NUNITS (@var{m}); i++) + op0[i] = op1[i] ? op2[i] @var{op} op3[i] : op4[i]; +@end smallexample + +where, for example, @var{op} is @code{+} for @samp{cond_add@var{mode}}. + +When defined for floating-point modes, the contents of @samp{op3[i]} +are not interpreted if @samp{op1[i]} is false, just like they would not +be in a normal C @samp{?:} condition. + +Operands 0, 2, 3 and 4 all have mode @var{m}. Operand 1 is a scalar +integer if @var{m} is scalar, otherwise it has the mode returned by +@code{TARGET_VECTORIZE_GET_MASK_MODE}. + +@samp{cond_@var{op}@var{mode}} generally corresponds to a conditional +form of @samp{@var{op}@var{mode}3}. As an exception, the vector forms +of shifts correspond to patterns like @code{vashl@var{mode}3} rather +than patterns like @code{ashl@var{mode}3}. + +@cindex @code{cond_fma@var{mode}} instruction pattern +@cindex @code{cond_fms@var{mode}} instruction pattern +@cindex @code{cond_fnma@var{mode}} instruction pattern +@cindex @code{cond_fnms@var{mode}} instruction pattern +@item @samp{cond_fma@var{mode}} +@itemx @samp{cond_fms@var{mode}} +@itemx @samp{cond_fnma@var{mode}} +@itemx @samp{cond_fnms@var{mode}} +Like @samp{cond_add@var{m}}, except that the conditional operation +takes 3 operands rather than two. For example, the vector form of +@samp{cond_fma@var{mode}} is equivalent to: + +@smallexample +for (i = 0; i < GET_MODE_NUNITS (@var{m}); i++) + op0[i] = op1[i] ? fma (op2[i], op3[i], op4[i]) : op5[i]; +@end smallexample + +@cindex @code{neg@var{mode}cc} instruction pattern +@item @samp{neg@var{mode}cc} +Similar to @samp{mov@var{mode}cc} but for conditional negation. Conditionally +move the negation of operand 2 or the unchanged operand 3 into operand 0 +according to the comparison in operand 1. If the comparison is true, the negation +of operand 2 is moved into operand 0, otherwise operand 3 is moved. + +@cindex @code{not@var{mode}cc} instruction pattern +@item @samp{not@var{mode}cc} +Similar to @samp{neg@var{mode}cc} but for conditional complement. +Conditionally move the bitwise complement of operand 2 or the unchanged +operand 3 into operand 0 according to the comparison in operand 1. +If the comparison is true, the complement of operand 2 is moved into +operand 0, otherwise operand 3 is moved. + +@cindex @code{cstore@var{mode}4} instruction pattern +@item @samp{cstore@var{mode}4} +Store zero or nonzero in operand 0 according to whether a comparison +is true. Operand 1 is a comparison operator. Operand 2 and operand 3 +are the first and second operand of the comparison, respectively. +You specify the mode that operand 0 must have when you write the +@code{match_operand} expression. The compiler automatically sees which +mode you have used and supplies an operand of that mode. + +The value stored for a true condition must have 1 as its low bit, or +else must be negative. Otherwise the instruction is not suitable and +you should omit it from the machine description. You describe to the +compiler exactly which value is stored by defining the macro +@code{STORE_FLAG_VALUE} (@pxref{Misc}). If a description cannot be +found that can be used for all the possible comparison operators, you +should pick one and use a @code{define_expand} to map all results +onto the one you chose. + +These operations may @code{FAIL}, but should do so only in relatively +uncommon cases; if they would @code{FAIL} for common cases involving +integer comparisons, it is best to restrict the predicates to not +allow these operands. Likewise if a given comparison operator will +always fail, independent of the operands (for floating-point modes, the +@code{ordered_comparison_operator} predicate is often useful in this case). + +If this pattern is omitted, the compiler will generate a conditional +branch---for example, it may copy a constant one to the target and branching +around an assignment of zero to the target---or a libcall. If the predicate +for operand 1 only rejects some operators, it will also try reordering the +operands and/or inverting the result value (e.g.@: by an exclusive OR). +These possibilities could be cheaper or equivalent to the instructions +used for the @samp{cstore@var{mode}4} pattern followed by those required +to convert a positive result from @code{STORE_FLAG_VALUE} to 1; in this +case, you can and should make operand 1's predicate reject some operators +in the @samp{cstore@var{mode}4} pattern, or remove the pattern altogether +from the machine description. + +@cindex @code{cbranch@var{mode}4} instruction pattern +@item @samp{cbranch@var{mode}4} +Conditional branch instruction combined with a compare instruction. +Operand 0 is a comparison operator. Operand 1 and operand 2 are the +first and second operands of the comparison, respectively. Operand 3 +is the @code{code_label} to jump to. + +@cindex @code{jump} instruction pattern +@item @samp{jump} +A jump inside a function; an unconditional branch. Operand 0 is the +@code{code_label} to jump to. This pattern name is mandatory on all +machines. + +@cindex @code{call} instruction pattern +@item @samp{call} +Subroutine call instruction returning no value. Operand 0 is the +function to call; operand 1 is the number of bytes of arguments pushed +as a @code{const_int}. Operand 2 is the result of calling the target +hook @code{TARGET_FUNCTION_ARG} with the second argument @code{arg} +yielding true for @code{arg.end_marker_p ()}, in a call after all +parameters have been passed to that hook. By default this is the first +register beyond those used for arguments in the call, or @code{NULL} if +all the argument-registers are used in the call. + +On most machines, operand 2 is not actually stored into the RTL +pattern. It is supplied for the sake of some RISC machines which need +to put this information into the assembler code; they can put it in +the RTL instead of operand 1. + +Operand 0 should be a @code{mem} RTX whose address is the address of the +function. Note, however, that this address can be a @code{symbol_ref} +expression even if it would not be a legitimate memory address on the +target machine. If it is also not a valid argument for a call +instruction, the pattern for this operation should be a +@code{define_expand} (@pxref{Expander Definitions}) that places the +address into a register and uses that register in the call instruction. + +@cindex @code{call_value} instruction pattern +@item @samp{call_value} +Subroutine call instruction returning a value. Operand 0 is the hard +register in which the value is returned. There are three more +operands, the same as the three operands of the @samp{call} +instruction (but with numbers increased by one). + +Subroutines that return @code{BLKmode} objects use the @samp{call} +insn. + +@cindex @code{call_pop} instruction pattern +@cindex @code{call_value_pop} instruction pattern +@item @samp{call_pop}, @samp{call_value_pop} +Similar to @samp{call} and @samp{call_value}, except used if defined and +if @code{RETURN_POPS_ARGS} is nonzero. They should emit a @code{parallel} +that contains both the function call and a @code{set} to indicate the +adjustment made to the frame pointer. + +For machines where @code{RETURN_POPS_ARGS} can be nonzero, the use of these +patterns increases the number of functions for which the frame pointer +can be eliminated, if desired. + +@cindex @code{untyped_call} instruction pattern +@item @samp{untyped_call} +Subroutine call instruction returning a value of any type. Operand 0 is +the function to call; operand 1 is a memory location where the result of +calling the function is to be stored; operand 2 is a @code{parallel} +expression where each element is a @code{set} expression that indicates +the saving of a function return value into the result block. + +This instruction pattern should be defined to support +@code{__builtin_apply} on machines where special instructions are needed +to call a subroutine with arbitrary arguments or to save the value +returned. This instruction pattern is required on machines that have +multiple registers that can hold a return value +(i.e.@: @code{FUNCTION_VALUE_REGNO_P} is true for more than one register). + +@cindex @code{return} instruction pattern +@item @samp{return} +Subroutine return instruction. This instruction pattern name should be +defined only if a single instruction can do all the work of returning +from a function. + +Like the @samp{mov@var{m}} patterns, this pattern is also used after the +RTL generation phase. In this case it is to support machines where +multiple instructions are usually needed to return from a function, but +some class of functions only requires one instruction to implement a +return. Normally, the applicable functions are those which do not need +to save any registers or allocate stack space. + +It is valid for this pattern to expand to an instruction using +@code{simple_return} if no epilogue is required. + +@cindex @code{simple_return} instruction pattern +@item @samp{simple_return} +Subroutine return instruction. This instruction pattern name should be +defined only if a single instruction can do all the work of returning +from a function on a path where no epilogue is required. This pattern +is very similar to the @code{return} instruction pattern, but it is emitted +only by the shrink-wrapping optimization on paths where the function +prologue has not been executed, and a function return should occur without +any of the effects of the epilogue. Additional uses may be introduced on +paths where both the prologue and the epilogue have executed. + +@findex reload_completed +@findex leaf_function_p +For such machines, the condition specified in this pattern should only +be true when @code{reload_completed} is nonzero and the function's +epilogue would only be a single instruction. For machines with register +windows, the routine @code{leaf_function_p} may be used to determine if +a register window push is required. + +Machines that have conditional return instructions should define patterns +such as + +@smallexample +(define_insn "" + [(set (pc) + (if_then_else (match_operator + 0 "comparison_operator" + [(reg:CC CC_REG) (const_int 0)]) + (return) + (pc)))] + "@var{condition}" + "@dots{}") +@end smallexample + +where @var{condition} would normally be the same condition specified on the +named @samp{return} pattern. + +@cindex @code{untyped_return} instruction pattern +@item @samp{untyped_return} +Untyped subroutine return instruction. This instruction pattern should +be defined to support @code{__builtin_return} on machines where special +instructions are needed to return a value of any type. + +Operand 0 is a memory location where the result of calling a function +with @code{__builtin_apply} is stored; operand 1 is a @code{parallel} +expression where each element is a @code{set} expression that indicates +the restoring of a function return value from the result block. + +@cindex @code{nop} instruction pattern +@item @samp{nop} +No-op instruction. This instruction pattern name should always be defined +to output a no-op in assembler code. @code{(const_int 0)} will do as an +RTL pattern. + +@cindex @code{indirect_jump} instruction pattern +@item @samp{indirect_jump} +An instruction to jump to an address which is operand zero. +This pattern name is mandatory on all machines. + +@cindex @code{casesi} instruction pattern +@item @samp{casesi} +Instruction to jump through a dispatch table, including bounds checking. +This instruction takes five operands: + +@enumerate +@item +The index to dispatch on, which has mode @code{SImode}. + +@item +The lower bound for indices in the table, an integer constant. + +@item +The total range of indices in the table---the largest index +minus the smallest one (both inclusive). + +@item +A label that precedes the table itself. + +@item +A label to jump to if the index has a value outside the bounds. +@end enumerate + +The table is an @code{addr_vec} or @code{addr_diff_vec} inside of a +@code{jump_table_data}. The number of elements in the table is one plus the +difference between the upper bound and the lower bound. + +@cindex @code{tablejump} instruction pattern +@item @samp{tablejump} +Instruction to jump to a variable address. This is a low-level +capability which can be used to implement a dispatch table when there +is no @samp{casesi} pattern. + +This pattern requires two operands: the address or offset, and a label +which should immediately precede the jump table. If the macro +@code{CASE_VECTOR_PC_RELATIVE} evaluates to a nonzero value then the first +operand is an offset which counts from the address of the table; otherwise, +it is an absolute address to jump to. In either case, the first operand has +mode @code{Pmode}. + +The @samp{tablejump} insn is always the last insn before the jump +table it uses. Its assembler code normally has no need to use the +second operand, but you should incorporate it in the RTL pattern so +that the jump optimizer will not delete the table as unreachable code. + + +@cindex @code{doloop_end} instruction pattern +@item @samp{doloop_end} +Conditional branch instruction that decrements a register and +jumps if the register is nonzero. Operand 0 is the register to +decrement and test; operand 1 is the label to jump to if the +register is nonzero. +@xref{Looping Patterns}. + +This optional instruction pattern should be defined for machines with +low-overhead looping instructions as the loop optimizer will try to +modify suitable loops to utilize it. The target hook +@code{TARGET_CAN_USE_DOLOOP_P} controls the conditions under which +low-overhead loops can be used. + +@cindex @code{doloop_begin} instruction pattern +@item @samp{doloop_begin} +Companion instruction to @code{doloop_end} required for machines that +need to perform some initialization, such as loading a special counter +register. Operand 1 is the associated @code{doloop_end} pattern and +operand 0 is the register that it decrements. + +If initialization insns do not always need to be emitted, use a +@code{define_expand} (@pxref{Expander Definitions}) and make it fail. + +@cindex @code{canonicalize_funcptr_for_compare} instruction pattern +@item @samp{canonicalize_funcptr_for_compare} +Canonicalize the function pointer in operand 1 and store the result +into operand 0. + +Operand 0 is always a @code{reg} and has mode @code{Pmode}; operand 1 +may be a @code{reg}, @code{mem}, @code{symbol_ref}, @code{const_int}, etc +and also has mode @code{Pmode}. + +Canonicalization of a function pointer usually involves computing +the address of the function which would be called if the function +pointer were used in an indirect call. + +Only define this pattern if function pointers on the target machine +can have different values but still call the same function when +used in an indirect call. + +@cindex @code{save_stack_block} instruction pattern +@cindex @code{save_stack_function} instruction pattern +@cindex @code{save_stack_nonlocal} instruction pattern +@cindex @code{restore_stack_block} instruction pattern +@cindex @code{restore_stack_function} instruction pattern +@cindex @code{restore_stack_nonlocal} instruction pattern +@item @samp{save_stack_block} +@itemx @samp{save_stack_function} +@itemx @samp{save_stack_nonlocal} +@itemx @samp{restore_stack_block} +@itemx @samp{restore_stack_function} +@itemx @samp{restore_stack_nonlocal} +Most machines save and restore the stack pointer by copying it to or +from an object of mode @code{Pmode}. Do not define these patterns on +such machines. + +Some machines require special handling for stack pointer saves and +restores. On those machines, define the patterns corresponding to the +non-standard cases by using a @code{define_expand} (@pxref{Expander +Definitions}) that produces the required insns. The three types of +saves and restores are: + +@enumerate +@item +@samp{save_stack_block} saves the stack pointer at the start of a block +that allocates a variable-sized object, and @samp{restore_stack_block} +restores the stack pointer when the block is exited. + +@item +@samp{save_stack_function} and @samp{restore_stack_function} do a +similar job for the outermost block of a function and are used when the +function allocates variable-sized objects or calls @code{alloca}. Only +the epilogue uses the restored stack pointer, allowing a simpler save or +restore sequence on some machines. + +@item +@samp{save_stack_nonlocal} is used in functions that contain labels +branched to by nested functions. It saves the stack pointer in such a +way that the inner function can use @samp{restore_stack_nonlocal} to +restore the stack pointer. The compiler generates code to restore the +frame and argument pointer registers, but some machines require saving +and restoring additional data such as register window information or +stack backchains. Place insns in these patterns to save and restore any +such required data. +@end enumerate + +When saving the stack pointer, operand 0 is the save area and operand 1 +is the stack pointer. The mode used to allocate the save area defaults +to @code{Pmode} but you can override that choice by defining the +@code{STACK_SAVEAREA_MODE} macro (@pxref{Storage Layout}). You must +specify an integral mode, or @code{VOIDmode} if no save area is needed +for a particular type of save (either because no save is needed or +because a machine-specific save area can be used). Operand 0 is the +stack pointer and operand 1 is the save area for restore operations. If +@samp{save_stack_block} is defined, operand 0 must not be +@code{VOIDmode} since these saves can be arbitrarily nested. + +A save area is a @code{mem} that is at a constant offset from +@code{virtual_stack_vars_rtx} when the stack pointer is saved for use by +nonlocal gotos and a @code{reg} in the other two cases. + +@cindex @code{allocate_stack} instruction pattern +@item @samp{allocate_stack} +Subtract (or add if @code{STACK_GROWS_DOWNWARD} is undefined) operand 1 from +the stack pointer to create space for dynamically allocated data. + +Store the resultant pointer to this space into operand 0. If you +are allocating space from the main stack, do this by emitting a +move insn to copy @code{virtual_stack_dynamic_rtx} to operand 0. +If you are allocating the space elsewhere, generate code to copy the +location of the space to operand 0. In the latter case, you must +ensure this space gets freed when the corresponding space on the main +stack is free. + +Do not define this pattern if all that must be done is the subtraction. +Some machines require other operations such as stack probes or +maintaining the back chain. Define this pattern to emit those +operations in addition to updating the stack pointer. + +@cindex @code{check_stack} instruction pattern +@item @samp{check_stack} +If stack checking (@pxref{Stack Checking}) cannot be done on your system by +probing the stack, define this pattern to perform the needed check and signal +an error if the stack has overflowed. The single operand is the address in +the stack farthest from the current stack pointer that you need to validate. +Normally, on platforms where this pattern is needed, you would obtain the +stack limit from a global or thread-specific variable or register. + +@cindex @code{probe_stack_address} instruction pattern +@item @samp{probe_stack_address} +If stack checking (@pxref{Stack Checking}) can be done on your system by +probing the stack but without the need to actually access it, define this +pattern and signal an error if the stack has overflowed. The single operand +is the memory address in the stack that needs to be probed. + +@cindex @code{probe_stack} instruction pattern +@item @samp{probe_stack} +If stack checking (@pxref{Stack Checking}) can be done on your system by +probing the stack but doing it with a ``store zero'' instruction is not valid +or optimal, define this pattern to do the probing differently and signal an +error if the stack has overflowed. The single operand is the memory reference +in the stack that needs to be probed. + +@cindex @code{nonlocal_goto} instruction pattern +@item @samp{nonlocal_goto} +Emit code to generate a non-local goto, e.g., a jump from one function +to a label in an outer function. This pattern has four arguments, +each representing a value to be used in the jump. The first +argument is to be loaded into the frame pointer, the second is +the address to branch to (code to dispatch to the actual label), +the third is the address of a location where the stack is saved, +and the last is the address of the label, to be placed in the +location for the incoming static chain. + +On most machines you need not define this pattern, since GCC will +already generate the correct code, which is to load the frame pointer +and static chain, restore the stack (using the +@samp{restore_stack_nonlocal} pattern, if defined), and jump indirectly +to the dispatcher. You need only define this pattern if this code will +not work on your machine. + +@cindex @code{nonlocal_goto_receiver} instruction pattern +@item @samp{nonlocal_goto_receiver} +This pattern, if defined, contains code needed at the target of a +nonlocal goto after the code already generated by GCC@. You will not +normally need to define this pattern. A typical reason why you might +need this pattern is if some value, such as a pointer to a global table, +must be restored when the frame pointer is restored. Note that a nonlocal +goto only occurs within a unit-of-translation, so a global table pointer +that is shared by all functions of a given module need not be restored. +There are no arguments. + +@cindex @code{exception_receiver} instruction pattern +@item @samp{exception_receiver} +This pattern, if defined, contains code needed at the site of an +exception handler that isn't needed at the site of a nonlocal goto. You +will not normally need to define this pattern. A typical reason why you +might need this pattern is if some value, such as a pointer to a global +table, must be restored after control flow is branched to the handler of +an exception. There are no arguments. + +@cindex @code{builtin_setjmp_setup} instruction pattern +@item @samp{builtin_setjmp_setup} +This pattern, if defined, contains additional code needed to initialize +the @code{jmp_buf}. You will not normally need to define this pattern. +A typical reason why you might need this pattern is if some value, such +as a pointer to a global table, must be restored. Though it is +preferred that the pointer value be recalculated if possible (given the +address of a label for instance). The single argument is a pointer to +the @code{jmp_buf}. Note that the buffer is five words long and that +the first three are normally used by the generic mechanism. + +@cindex @code{builtin_setjmp_receiver} instruction pattern +@item @samp{builtin_setjmp_receiver} +This pattern, if defined, contains code needed at the site of a +built-in setjmp that isn't needed at the site of a nonlocal goto. You +will not normally need to define this pattern. A typical reason why you +might need this pattern is if some value, such as a pointer to a global +table, must be restored. It takes one argument, which is the label +to which builtin_longjmp transferred control; this pattern may be emitted +at a small offset from that label. + +@cindex @code{builtin_longjmp} instruction pattern +@item @samp{builtin_longjmp} +This pattern, if defined, performs the entire action of the longjmp. +You will not normally need to define this pattern unless you also define +@code{builtin_setjmp_setup}. The single argument is a pointer to the +@code{jmp_buf}. + +@cindex @code{eh_return} instruction pattern +@item @samp{eh_return} +This pattern, if defined, affects the way @code{__builtin_eh_return}, +and thence the call frame exception handling library routines, are +built. It is intended to handle non-trivial actions needed along +the abnormal return path. + +The address of the exception handler to which the function should return +is passed as operand to this pattern. It will normally need to copied by +the pattern to some special register or memory location. +If the pattern needs to determine the location of the target call +frame in order to do so, it may use @code{EH_RETURN_STACKADJ_RTX}, +if defined; it will have already been assigned. + +If this pattern is not defined, the default action will be to simply +copy the return address to @code{EH_RETURN_HANDLER_RTX}. Either +that macro or this pattern needs to be defined if call frame exception +handling is to be used. + +@cindex @code{prologue} instruction pattern +@anchor{prologue instruction pattern} +@item @samp{prologue} +This pattern, if defined, emits RTL for entry to a function. The function +entry is responsible for setting up the stack frame, initializing the frame +pointer register, saving callee saved registers, etc. + +Using a prologue pattern is generally preferred over defining +@code{TARGET_ASM_FUNCTION_PROLOGUE} to emit assembly code for the prologue. + +The @code{prologue} pattern is particularly useful for targets which perform +instruction scheduling. + +@cindex @code{window_save} instruction pattern +@anchor{window_save instruction pattern} +@item @samp{window_save} +This pattern, if defined, emits RTL for a register window save. It should +be defined if the target machine has register windows but the window events +are decoupled from calls to subroutines. The canonical example is the SPARC +architecture. + +@cindex @code{epilogue} instruction pattern +@anchor{epilogue instruction pattern} +@item @samp{epilogue} +This pattern emits RTL for exit from a function. The function +exit is responsible for deallocating the stack frame, restoring callee saved +registers and emitting the return instruction. + +Using an epilogue pattern is generally preferred over defining +@code{TARGET_ASM_FUNCTION_EPILOGUE} to emit assembly code for the epilogue. + +The @code{epilogue} pattern is particularly useful for targets which perform +instruction scheduling or which have delay slots for their return instruction. + +@cindex @code{sibcall_epilogue} instruction pattern +@item @samp{sibcall_epilogue} +This pattern, if defined, emits RTL for exit from a function without the final +branch back to the calling function. This pattern will be emitted before any +sibling call (aka tail call) sites. + +The @code{sibcall_epilogue} pattern must not clobber any arguments used for +parameter passing or any stack slots for arguments passed to the current +function. + +@cindex @code{trap} instruction pattern +@item @samp{trap} +This pattern, if defined, signals an error, typically by causing some +kind of signal to be raised. + +@cindex @code{ctrap@var{MM}4} instruction pattern +@item @samp{ctrap@var{MM}4} +Conditional trap instruction. Operand 0 is a piece of RTL which +performs a comparison, and operands 1 and 2 are the arms of the +comparison. Operand 3 is the trap code, an integer. + +A typical @code{ctrap} pattern looks like + +@smallexample +(define_insn "ctrapsi4" + [(trap_if (match_operator 0 "trap_operator" + [(match_operand 1 "register_operand") + (match_operand 2 "immediate_operand")]) + (match_operand 3 "const_int_operand" "i"))] + "" + "@dots{}") +@end smallexample + +@cindex @code{prefetch} instruction pattern +@item @samp{prefetch} +This pattern, if defined, emits code for a non-faulting data prefetch +instruction. Operand 0 is the address of the memory to prefetch. Operand 1 +is a constant 1 if the prefetch is preparing for a write to the memory +address, or a constant 0 otherwise. Operand 2 is the expected degree of +temporal locality of the data and is a value between 0 and 3, inclusive; 0 +means that the data has no temporal locality, so it need not be left in the +cache after the access; 3 means that the data has a high degree of temporal +locality and should be left in all levels of cache possible; 1 and 2 mean, +respectively, a low or moderate degree of temporal locality. + +Targets that do not support write prefetches or locality hints can ignore +the values of operands 1 and 2. + +@cindex @code{blockage} instruction pattern +@item @samp{blockage} +This pattern defines a pseudo insn that prevents the instruction +scheduler and other passes from moving instructions and using register +equivalences across the boundary defined by the blockage insn. +This needs to be an UNSPEC_VOLATILE pattern or a volatile ASM. + +@cindex @code{memory_blockage} instruction pattern +@item @samp{memory_blockage} +This pattern, if defined, represents a compiler memory barrier, and will be +placed at points across which RTL passes may not propagate memory accesses. +This instruction needs to read and write volatile BLKmode memory. It does +not need to generate any machine instruction. If this pattern is not defined, +the compiler falls back to emitting an instruction corresponding +to @code{asm volatile ("" ::: "memory")}. + +@cindex @code{memory_barrier} instruction pattern +@item @samp{memory_barrier} +If the target memory model is not fully synchronous, then this pattern +should be defined to an instruction that orders both loads and stores +before the instruction with respect to loads and stores after the instruction. +This pattern has no operands. + +@cindex @code{speculation_barrier} instruction pattern +@item @samp{speculation_barrier} +If the target can support speculative execution, then this pattern should +be defined to an instruction that will block subsequent execution until +any prior speculation conditions has been resolved. The pattern must also +ensure that the compiler cannot move memory operations past the barrier, +so it needs to be an UNSPEC_VOLATILE pattern. The pattern has no +operands. + +If this pattern is not defined then the default expansion of +@code{__builtin_speculation_safe_value} will emit a warning. You can +suppress this warning by defining this pattern with a final condition +of @code{0} (zero), which tells the compiler that a speculation +barrier is not needed for this target. + +@cindex @code{sync_compare_and_swap@var{mode}} instruction pattern +@item @samp{sync_compare_and_swap@var{mode}} +This pattern, if defined, emits code for an atomic compare-and-swap +operation. Operand 1 is the memory on which the atomic operation is +performed. Operand 2 is the ``old'' value to be compared against the +current contents of the memory location. Operand 3 is the ``new'' value +to store in the memory if the compare succeeds. Operand 0 is the result +of the operation; it should contain the contents of the memory +before the operation. If the compare succeeds, this should obviously be +a copy of operand 2. + +This pattern must show that both operand 0 and operand 1 are modified. + +This pattern must issue any memory barrier instructions such that all +memory operations before the atomic operation occur before the atomic +operation and all memory operations after the atomic operation occur +after the atomic operation. + +For targets where the success or failure of the compare-and-swap +operation is available via the status flags, it is possible to +avoid a separate compare operation and issue the subsequent +branch or store-flag operation immediately after the compare-and-swap. +To this end, GCC will look for a @code{MODE_CC} set in the +output of @code{sync_compare_and_swap@var{mode}}; if the machine +description includes such a set, the target should also define special +@code{cbranchcc4} and/or @code{cstorecc4} instructions. GCC will then +be able to take the destination of the @code{MODE_CC} set and pass it +to the @code{cbranchcc4} or @code{cstorecc4} pattern as the first +operand of the comparison (the second will be @code{(const_int 0)}). + +For targets where the operating system may provide support for this +operation via library calls, the @code{sync_compare_and_swap_optab} +may be initialized to a function with the same interface as the +@code{__sync_val_compare_and_swap_@var{n}} built-in. If the entire +set of @var{__sync} builtins are supported via library calls, the +target can initialize all of the optabs at once with +@code{init_sync_libfuncs}. +For the purposes of C++11 @code{std::atomic::is_lock_free}, it is +assumed that these library calls do @emph{not} use any kind of +interruptable locking. + +@cindex @code{sync_add@var{mode}} instruction pattern +@cindex @code{sync_sub@var{mode}} instruction pattern +@cindex @code{sync_ior@var{mode}} instruction pattern +@cindex @code{sync_and@var{mode}} instruction pattern +@cindex @code{sync_xor@var{mode}} instruction pattern +@cindex @code{sync_nand@var{mode}} instruction pattern +@item @samp{sync_add@var{mode}}, @samp{sync_sub@var{mode}} +@itemx @samp{sync_ior@var{mode}}, @samp{sync_and@var{mode}} +@itemx @samp{sync_xor@var{mode}}, @samp{sync_nand@var{mode}} +These patterns emit code for an atomic operation on memory. +Operand 0 is the memory on which the atomic operation is performed. +Operand 1 is the second operand to the binary operator. + +This pattern must issue any memory barrier instructions such that all +memory operations before the atomic operation occur before the atomic +operation and all memory operations after the atomic operation occur +after the atomic operation. + +If these patterns are not defined, the operation will be constructed +from a compare-and-swap operation, if defined. + +@cindex @code{sync_old_add@var{mode}} instruction pattern +@cindex @code{sync_old_sub@var{mode}} instruction pattern +@cindex @code{sync_old_ior@var{mode}} instruction pattern +@cindex @code{sync_old_and@var{mode}} instruction pattern +@cindex @code{sync_old_xor@var{mode}} instruction pattern +@cindex @code{sync_old_nand@var{mode}} instruction pattern +@item @samp{sync_old_add@var{mode}}, @samp{sync_old_sub@var{mode}} +@itemx @samp{sync_old_ior@var{mode}}, @samp{sync_old_and@var{mode}} +@itemx @samp{sync_old_xor@var{mode}}, @samp{sync_old_nand@var{mode}} +These patterns emit code for an atomic operation on memory, +and return the value that the memory contained before the operation. +Operand 0 is the result value, operand 1 is the memory on which the +atomic operation is performed, and operand 2 is the second operand +to the binary operator. + +This pattern must issue any memory barrier instructions such that all +memory operations before the atomic operation occur before the atomic +operation and all memory operations after the atomic operation occur +after the atomic operation. + +If these patterns are not defined, the operation will be constructed +from a compare-and-swap operation, if defined. + +@cindex @code{sync_new_add@var{mode}} instruction pattern +@cindex @code{sync_new_sub@var{mode}} instruction pattern +@cindex @code{sync_new_ior@var{mode}} instruction pattern +@cindex @code{sync_new_and@var{mode}} instruction pattern +@cindex @code{sync_new_xor@var{mode}} instruction pattern +@cindex @code{sync_new_nand@var{mode}} instruction pattern +@item @samp{sync_new_add@var{mode}}, @samp{sync_new_sub@var{mode}} +@itemx @samp{sync_new_ior@var{mode}}, @samp{sync_new_and@var{mode}} +@itemx @samp{sync_new_xor@var{mode}}, @samp{sync_new_nand@var{mode}} +These patterns are like their @code{sync_old_@var{op}} counterparts, +except that they return the value that exists in the memory location +after the operation, rather than before the operation. + +@cindex @code{sync_lock_test_and_set@var{mode}} instruction pattern +@item @samp{sync_lock_test_and_set@var{mode}} +This pattern takes two forms, based on the capabilities of the target. +In either case, operand 0 is the result of the operand, operand 1 is +the memory on which the atomic operation is performed, and operand 2 +is the value to set in the lock. + +In the ideal case, this operation is an atomic exchange operation, in +which the previous value in memory operand is copied into the result +operand, and the value operand is stored in the memory operand. + +For less capable targets, any value operand that is not the constant 1 +should be rejected with @code{FAIL}. In this case the target may use +an atomic test-and-set bit operation. The result operand should contain +1 if the bit was previously set and 0 if the bit was previously clear. +The true contents of the memory operand are implementation defined. + +This pattern must issue any memory barrier instructions such that the +pattern as a whole acts as an acquire barrier, that is all memory +operations after the pattern do not occur until the lock is acquired. + +If this pattern is not defined, the operation will be constructed from +a compare-and-swap operation, if defined. + +@cindex @code{sync_lock_release@var{mode}} instruction pattern +@item @samp{sync_lock_release@var{mode}} +This pattern, if defined, releases a lock set by +@code{sync_lock_test_and_set@var{mode}}. Operand 0 is the memory +that contains the lock; operand 1 is the value to store in the lock. + +If the target doesn't implement full semantics for +@code{sync_lock_test_and_set@var{mode}}, any value operand which is not +the constant 0 should be rejected with @code{FAIL}, and the true contents +of the memory operand are implementation defined. + +This pattern must issue any memory barrier instructions such that the +pattern as a whole acts as a release barrier, that is the lock is +released only after all previous memory operations have completed. + +If this pattern is not defined, then a @code{memory_barrier} pattern +will be emitted, followed by a store of the value to the memory operand. + +@cindex @code{atomic_compare_and_swap@var{mode}} instruction pattern +@item @samp{atomic_compare_and_swap@var{mode}} +This pattern, if defined, emits code for an atomic compare-and-swap +operation with memory model semantics. Operand 2 is the memory on which +the atomic operation is performed. Operand 0 is an output operand which +is set to true or false based on whether the operation succeeded. Operand +1 is an output operand which is set to the contents of the memory before +the operation was attempted. Operand 3 is the value that is expected to +be in memory. Operand 4 is the value to put in memory if the expected +value is found there. Operand 5 is set to 1 if this compare and swap is to +be treated as a weak operation. Operand 6 is the memory model to be used +if the operation is a success. Operand 7 is the memory model to be used +if the operation fails. + +If memory referred to in operand 2 contains the value in operand 3, then +operand 4 is stored in memory pointed to by operand 2 and fencing based on +the memory model in operand 6 is issued. + +If memory referred to in operand 2 does not contain the value in operand 3, +then fencing based on the memory model in operand 7 is issued. + +If a target does not support weak compare-and-swap operations, or the port +elects not to implement weak operations, the argument in operand 5 can be +ignored. Note a strong implementation must be provided. + +If this pattern is not provided, the @code{__atomic_compare_exchange} +built-in functions will utilize the legacy @code{sync_compare_and_swap} +pattern with an @code{__ATOMIC_SEQ_CST} memory model. + +@cindex @code{atomic_load@var{mode}} instruction pattern +@item @samp{atomic_load@var{mode}} +This pattern implements an atomic load operation with memory model +semantics. Operand 1 is the memory address being loaded from. Operand 0 +is the result of the load. Operand 2 is the memory model to be used for +the load operation. + +If not present, the @code{__atomic_load} built-in function will either +resort to a normal load with memory barriers, or a compare-and-swap +operation if a normal load would not be atomic. + +@cindex @code{atomic_store@var{mode}} instruction pattern +@item @samp{atomic_store@var{mode}} +This pattern implements an atomic store operation with memory model +semantics. Operand 0 is the memory address being stored to. Operand 1 +is the value to be written. Operand 2 is the memory model to be used for +the operation. + +If not present, the @code{__atomic_store} built-in function will attempt to +perform a normal store and surround it with any required memory fences. If +the store would not be atomic, then an @code{__atomic_exchange} is +attempted with the result being ignored. + +@cindex @code{atomic_exchange@var{mode}} instruction pattern +@item @samp{atomic_exchange@var{mode}} +This pattern implements an atomic exchange operation with memory model +semantics. Operand 1 is the memory location the operation is performed on. +Operand 0 is an output operand which is set to the original value contained +in the memory pointed to by operand 1. Operand 2 is the value to be +stored. Operand 3 is the memory model to be used. + +If this pattern is not present, the built-in function +@code{__atomic_exchange} will attempt to preform the operation with a +compare and swap loop. + +@cindex @code{atomic_add@var{mode}} instruction pattern +@cindex @code{atomic_sub@var{mode}} instruction pattern +@cindex @code{atomic_or@var{mode}} instruction pattern +@cindex @code{atomic_and@var{mode}} instruction pattern +@cindex @code{atomic_xor@var{mode}} instruction pattern +@cindex @code{atomic_nand@var{mode}} instruction pattern +@item @samp{atomic_add@var{mode}}, @samp{atomic_sub@var{mode}} +@itemx @samp{atomic_or@var{mode}}, @samp{atomic_and@var{mode}} +@itemx @samp{atomic_xor@var{mode}}, @samp{atomic_nand@var{mode}} +These patterns emit code for an atomic operation on memory with memory +model semantics. Operand 0 is the memory on which the atomic operation is +performed. Operand 1 is the second operand to the binary operator. +Operand 2 is the memory model to be used by the operation. + +If these patterns are not defined, attempts will be made to use legacy +@code{sync} patterns, or equivalent patterns which return a result. If +none of these are available a compare-and-swap loop will be used. + +@cindex @code{atomic_fetch_add@var{mode}} instruction pattern +@cindex @code{atomic_fetch_sub@var{mode}} instruction pattern +@cindex @code{atomic_fetch_or@var{mode}} instruction pattern +@cindex @code{atomic_fetch_and@var{mode}} instruction pattern +@cindex @code{atomic_fetch_xor@var{mode}} instruction pattern +@cindex @code{atomic_fetch_nand@var{mode}} instruction pattern +@item @samp{atomic_fetch_add@var{mode}}, @samp{atomic_fetch_sub@var{mode}} +@itemx @samp{atomic_fetch_or@var{mode}}, @samp{atomic_fetch_and@var{mode}} +@itemx @samp{atomic_fetch_xor@var{mode}}, @samp{atomic_fetch_nand@var{mode}} +These patterns emit code for an atomic operation on memory with memory +model semantics, and return the original value. Operand 0 is an output +operand which contains the value of the memory location before the +operation was performed. Operand 1 is the memory on which the atomic +operation is performed. Operand 2 is the second operand to the binary +operator. Operand 3 is the memory model to be used by the operation. + +If these patterns are not defined, attempts will be made to use legacy +@code{sync} patterns. If none of these are available a compare-and-swap +loop will be used. + +@cindex @code{atomic_add_fetch@var{mode}} instruction pattern +@cindex @code{atomic_sub_fetch@var{mode}} instruction pattern +@cindex @code{atomic_or_fetch@var{mode}} instruction pattern +@cindex @code{atomic_and_fetch@var{mode}} instruction pattern +@cindex @code{atomic_xor_fetch@var{mode}} instruction pattern +@cindex @code{atomic_nand_fetch@var{mode}} instruction pattern +@item @samp{atomic_add_fetch@var{mode}}, @samp{atomic_sub_fetch@var{mode}} +@itemx @samp{atomic_or_fetch@var{mode}}, @samp{atomic_and_fetch@var{mode}} +@itemx @samp{atomic_xor_fetch@var{mode}}, @samp{atomic_nand_fetch@var{mode}} +These patterns emit code for an atomic operation on memory with memory +model semantics and return the result after the operation is performed. +Operand 0 is an output operand which contains the value after the +operation. Operand 1 is the memory on which the atomic operation is +performed. Operand 2 is the second operand to the binary operator. +Operand 3 is the memory model to be used by the operation. + +If these patterns are not defined, attempts will be made to use legacy +@code{sync} patterns, or equivalent patterns which return the result before +the operation followed by the arithmetic operation required to produce the +result. If none of these are available a compare-and-swap loop will be +used. + +@cindex @code{atomic_test_and_set} instruction pattern +@item @samp{atomic_test_and_set} +This pattern emits code for @code{__builtin_atomic_test_and_set}. +Operand 0 is an output operand which is set to true if the previous +previous contents of the byte was "set", and false otherwise. Operand 1 +is the @code{QImode} memory to be modified. Operand 2 is the memory +model to be used. + +The specific value that defines "set" is implementation defined, and +is normally based on what is performed by the native atomic test and set +instruction. + +@cindex @code{atomic_bit_test_and_set@var{mode}} instruction pattern +@cindex @code{atomic_bit_test_and_complement@var{mode}} instruction pattern +@cindex @code{atomic_bit_test_and_reset@var{mode}} instruction pattern +@item @samp{atomic_bit_test_and_set@var{mode}} +@itemx @samp{atomic_bit_test_and_complement@var{mode}} +@itemx @samp{atomic_bit_test_and_reset@var{mode}} +These patterns emit code for an atomic bitwise operation on memory with memory +model semantics, and return the original value of the specified bit. +Operand 0 is an output operand which contains the value of the specified bit +from the memory location before the operation was performed. Operand 1 is the +memory on which the atomic operation is performed. Operand 2 is the bit within +the operand, starting with least significant bit. Operand 3 is the memory model +to be used by the operation. Operand 4 is a flag - it is @code{const1_rtx} +if operand 0 should contain the original value of the specified bit in the +least significant bit of the operand, and @code{const0_rtx} if the bit should +be in its original position in the operand. +@code{atomic_bit_test_and_set@var{mode}} atomically sets the specified bit after +remembering its original value, @code{atomic_bit_test_and_complement@var{mode}} +inverts the specified bit and @code{atomic_bit_test_and_reset@var{mode}} clears +the specified bit. + +If these patterns are not defined, attempts will be made to use +@code{atomic_fetch_or@var{mode}}, @code{atomic_fetch_xor@var{mode}} or +@code{atomic_fetch_and@var{mode}} instruction patterns, or their @code{sync} +counterparts. If none of these are available a compare-and-swap +loop will be used. + +@cindex @code{atomic_add_fetch_cmp_0@var{mode}} instruction pattern +@cindex @code{atomic_sub_fetch_cmp_0@var{mode}} instruction pattern +@cindex @code{atomic_and_fetch_cmp_0@var{mode}} instruction pattern +@cindex @code{atomic_or_fetch_cmp_0@var{mode}} instruction pattern +@cindex @code{atomic_xor_fetch_cmp_0@var{mode}} instruction pattern +@item @samp{atomic_add_fetch_cmp_0@var{mode}} +@itemx @samp{atomic_sub_fetch_cmp_0@var{mode}} +@itemx @samp{atomic_and_fetch_cmp_0@var{mode}} +@itemx @samp{atomic_or_fetch_cmp_0@var{mode}} +@itemx @samp{atomic_xor_fetch_cmp_0@var{mode}} +These patterns emit code for an atomic operation on memory with memory +model semantics if the fetch result is used only in a comparison against +zero. +Operand 0 is an output operand which contains a boolean result of comparison +of the value after the operation against zero. Operand 1 is the memory on +which the atomic operation is performed. Operand 2 is the second operand +to the binary operator. Operand 3 is the memory model to be used by the +operation. Operand 4 is an integer holding the comparison code, one of +@code{EQ}, @code{NE}, @code{LT}, @code{GT}, @code{LE} or @code{GE}. + +If these patterns are not defined, attempts will be made to use separate +atomic operation and fetch pattern followed by comparison of the result +against zero. + +@cindex @code{mem_thread_fence} instruction pattern +@item @samp{mem_thread_fence} +This pattern emits code required to implement a thread fence with +memory model semantics. Operand 0 is the memory model to be used. + +For the @code{__ATOMIC_RELAXED} model no instructions need to be issued +and this expansion is not invoked. + +The compiler always emits a compiler memory barrier regardless of what +expanding this pattern produced. + +If this pattern is not defined, the compiler falls back to expanding the +@code{memory_barrier} pattern, then to emitting @code{__sync_synchronize} +library call, and finally to just placing a compiler memory barrier. + +@cindex @code{get_thread_pointer@var{mode}} instruction pattern +@cindex @code{set_thread_pointer@var{mode}} instruction pattern +@item @samp{get_thread_pointer@var{mode}} +@itemx @samp{set_thread_pointer@var{mode}} +These patterns emit code that reads/sets the TLS thread pointer. Currently, +these are only needed if the target needs to support the +@code{__builtin_thread_pointer} and @code{__builtin_set_thread_pointer} +builtins. + +The get/set patterns have a single output/input operand respectively, +with @var{mode} intended to be @code{Pmode}. + +@cindex @code{stack_protect_combined_set} instruction pattern +@item @samp{stack_protect_combined_set} +This pattern, if defined, moves a @code{ptr_mode} value from an address +whose declaration RTX is given in operand 1 to the memory in operand 0 +without leaving the value in a register afterward. If several +instructions are needed by the target to perform the operation (eg. to +load the address from a GOT entry then load the @code{ptr_mode} value +and finally store it), it is the backend's responsibility to ensure no +intermediate result gets spilled. This is to avoid leaking the value +some place that an attacker might use to rewrite the stack guard slot +after having clobbered it. + +If this pattern is not defined, then the address declaration is +expanded first in the standard way and a @code{stack_protect_set} +pattern is then generated to move the value from that address to the +address in operand 0. + +@cindex @code{stack_protect_set} instruction pattern +@item @samp{stack_protect_set} +This pattern, if defined, moves a @code{ptr_mode} value from the valid +memory location in operand 1 to the memory in operand 0 without leaving +the value in a register afterward. This is to avoid leaking the value +some place that an attacker might use to rewrite the stack guard slot +after having clobbered it. + +Note: on targets where the addressing modes do not allow to load +directly from stack guard address, the address is expanded in a standard +way first which could cause some spills. + +If this pattern is not defined, then a plain move pattern is generated. + +@cindex @code{stack_protect_combined_test} instruction pattern +@item @samp{stack_protect_combined_test} +This pattern, if defined, compares a @code{ptr_mode} value from an +address whose declaration RTX is given in operand 1 with the memory in +operand 0 without leaving the value in a register afterward and +branches to operand 2 if the values were equal. If several +instructions are needed by the target to perform the operation (eg. to +load the address from a GOT entry then load the @code{ptr_mode} value +and finally store it), it is the backend's responsibility to ensure no +intermediate result gets spilled. This is to avoid leaking the value +some place that an attacker might use to rewrite the stack guard slot +after having clobbered it. + +If this pattern is not defined, then the address declaration is +expanded first in the standard way and a @code{stack_protect_test} +pattern is then generated to compare the value from that address to the +value at the memory in operand 0. + +@cindex @code{stack_protect_test} instruction pattern +@item @samp{stack_protect_test} +This pattern, if defined, compares a @code{ptr_mode} value from the +valid memory location in operand 1 with the memory in operand 0 without +leaving the value in a register afterward and branches to operand 2 if +the values were equal. + +If this pattern is not defined, then a plain compare pattern and +conditional branch pattern is used. + +@cindex @code{clear_cache} instruction pattern +@item @samp{clear_cache} +This pattern, if defined, flushes the instruction cache for a region of +memory. The region is bounded to by the Pmode pointers in operand 0 +inclusive and operand 1 exclusive. + +If this pattern is not defined, a call to the library function +@code{__clear_cache} is used. + +@cindex @code{spaceship@var{m}3} instruction pattern +@item @samp{spaceship@var{m}3} +Initialize output operand 0 with mode of integer type to -1, 0, 1 or 2 +if operand 1 with mode @var{m} compares less than operand 2, equal to +operand 2, greater than operand 2 or is unordered with operand 2. +@var{m} should be a scalar floating point mode. + +This pattern is not allowed to @code{FAIL}. + +@end table + +@end ifset +@c Each of the following nodes are wrapped in separate +@c "@ifset INTERNALS" to work around memory limits for the default +@c configuration in older tetex distributions. Known to not work: +@c tetex-1.0.7, known to work: tetex-2.0.2. +@ifset INTERNALS +@node Pattern Ordering +@section When the Order of Patterns Matters +@cindex Pattern Ordering +@cindex Ordering of Patterns + +Sometimes an insn can match more than one instruction pattern. Then the +pattern that appears first in the machine description is the one used. +Therefore, more specific patterns (patterns that will match fewer things) +and faster instructions (those that will produce better code when they +do match) should usually go first in the description. + +In some cases the effect of ordering the patterns can be used to hide +a pattern when it is not valid. For example, the 68000 has an +instruction for converting a fullword to floating point and another +for converting a byte to floating point. An instruction converting +an integer to floating point could match either one. We put the +pattern to convert the fullword first to make sure that one will +be used rather than the other. (Otherwise a large integer might +be generated as a single-byte immediate quantity, which would not work.) +Instead of using this pattern ordering it would be possible to make the +pattern for convert-a-byte smart enough to deal properly with any +constant value. + +@end ifset +@ifset INTERNALS +@node Dependent Patterns +@section Interdependence of Patterns +@cindex Dependent Patterns +@cindex Interdependence of Patterns + +In some cases machines support instructions identical except for the +machine mode of one or more operands. For example, there may be +``sign-extend halfword'' and ``sign-extend byte'' instructions whose +patterns are + +@smallexample +(set (match_operand:SI 0 @dots{}) + (extend:SI (match_operand:HI 1 @dots{}))) + +(set (match_operand:SI 0 @dots{}) + (extend:SI (match_operand:QI 1 @dots{}))) +@end smallexample + +@noindent +Constant integers do not specify a machine mode, so an instruction to +extend a constant value could match either pattern. The pattern it +actually will match is the one that appears first in the file. For correct +results, this must be the one for the widest possible mode (@code{HImode}, +here). If the pattern matches the @code{QImode} instruction, the results +will be incorrect if the constant value does not actually fit that mode. + +Such instructions to extend constants are rarely generated because they are +optimized away, but they do occasionally happen in nonoptimized +compilations. + +If a constraint in a pattern allows a constant, the reload pass may +replace a register with a constant permitted by the constraint in some +cases. Similarly for memory references. Because of this substitution, +you should not provide separate patterns for increment and decrement +instructions. Instead, they should be generated from the same pattern +that supports register-register add insns by examining the operands and +generating the appropriate machine instruction. + +@end ifset +@ifset INTERNALS +@node Jump Patterns +@section Defining Jump Instruction Patterns +@cindex jump instruction patterns +@cindex defining jump instruction patterns + +GCC does not assume anything about how the machine realizes jumps. +The machine description should define a single pattern, usually +a @code{define_expand}, which expands to all the required insns. + +Usually, this would be a comparison insn to set the condition code +and a separate branch insn testing the condition code and branching +or not according to its value. For many machines, however, +separating compares and branches is limiting, which is why the +more flexible approach with one @code{define_expand} is used in GCC. +The machine description becomes clearer for architectures that +have compare-and-branch instructions but no condition code. It also +works better when different sets of comparison operators are supported +by different kinds of conditional branches (e.g.@: integer vs.@: +floating-point), or by conditional branches with respect to conditional stores. + +Two separate insns are always used on most machines that use a separate +condition code register (@pxref{Condition Code}). + +Even in this case having a single entry point for conditional branches +is advantageous, because it handles equally well the case where a single +comparison instruction records the results of both signed and unsigned +comparison of the given operands (with the branch insns coming in distinct +signed and unsigned flavors) as in the x86 or SPARC, and the case where +there are distinct signed and unsigned compare instructions and only +one set of conditional branch instructions as in the PowerPC. + +@end ifset +@ifset INTERNALS +@node Looping Patterns +@section Defining Looping Instruction Patterns +@cindex looping instruction patterns +@cindex defining looping instruction patterns + +Some machines have special jump instructions that can be utilized to +make loops more efficient. A common example is the 68000 @samp{dbra} +instruction which performs a decrement of a register and a branch if the +result was greater than zero. Other machines, in particular digital +signal processors (DSPs), have special block repeat instructions to +provide low-overhead loop support. For example, the TI TMS320C3x/C4x +DSPs have a block repeat instruction that loads special registers to +mark the top and end of a loop and to count the number of loop +iterations. This avoids the need for fetching and executing a +@samp{dbra}-like instruction and avoids pipeline stalls associated with +the jump. + +GCC has two special named patterns to support low overhead looping. +They are @samp{doloop_begin} and @samp{doloop_end}. These are emitted +by the loop optimizer for certain well-behaved loops with a finite +number of loop iterations using information collected during strength +reduction. + +The @samp{doloop_end} pattern describes the actual looping instruction +(or the implicit looping operation) and the @samp{doloop_begin} pattern +is an optional companion pattern that can be used for initialization +needed for some low-overhead looping instructions. + +Note that some machines require the actual looping instruction to be +emitted at the top of the loop (e.g., the TMS320C3x/C4x DSPs). Emitting +the true RTL for a looping instruction at the top of the loop can cause +problems with flow analysis. So instead, a dummy @code{doloop} insn is +emitted at the end of the loop. The machine dependent reorg pass checks +for the presence of this @code{doloop} insn and then searches back to +the top of the loop, where it inserts the true looping insn (provided +there are no instructions in the loop which would cause problems). Any +additional labels can be emitted at this point. In addition, if the +desired special iteration counter register was not allocated, this +machine dependent reorg pass could emit a traditional compare and jump +instruction pair. + +For the @samp{doloop_end} pattern, the loop optimizer allocates an +additional pseudo register as an iteration counter. This pseudo +register cannot be used within the loop (i.e., general induction +variables cannot be derived from it), however, in many cases the loop +induction variable may become redundant and removed by the flow pass. + +The @samp{doloop_end} pattern must have a specific structure to be +handled correctly by GCC. The example below is taken (slightly +simplified) from the PDP-11 target: + +@smallexample +@group +(define_expand "doloop_end" + [(parallel [(set (pc) + (if_then_else + (ne (match_operand:HI 0 "nonimmediate_operand" "+r,!m") + (const_int 1)) + (label_ref (match_operand 1 "" "")) + (pc))) + (set (match_dup 0) + (plus:HI (match_dup 0) + (const_int -1)))])] + "" + "@{ + if (GET_MODE (operands[0]) != HImode) + FAIL; + @}") + +(define_insn "doloop_end_insn" + [(set (pc) + (if_then_else + (ne (match_operand:HI 0 "nonimmediate_operand" "+r,!m") + (const_int 1)) + (label_ref (match_operand 1 "" "")) + (pc))) + (set (match_dup 0) + (plus:HI (match_dup 0) + (const_int -1)))] + "" + + @{ + if (which_alternative == 0) + return "sob %0,%l1"; + + /* emulate sob */ + output_asm_insn ("dec %0", operands); + return "bne %l1"; + @}) +@end group +@end smallexample + +The first part of the pattern describes the branch condition. GCC +supports three cases for the way the target machine handles the loop +counter: +@itemize @bullet +@item Loop terminates when the loop register decrements to zero. This +is represented by a @code{ne} comparison of the register (its old value) +with constant 1 (as in the example above). +@item Loop terminates when the loop register decrements to @minus{}1. +This is represented by a @code{ne} comparison of the register with +constant zero. +@item Loop terminates when the loop register decrements to a negative +value. This is represented by a @code{ge} comparison of the register +with constant zero. For this case, GCC will attach a @code{REG_NONNEG} +note to the @code{doloop_end} insn if it can determine that the register +will be non-negative. +@end itemize + +Since the @code{doloop_end} insn is a jump insn that also has an output, +the reload pass does not handle the output operand. Therefore, the +constraint must allow for that operand to be in memory rather than a +register. In the example shown above, that is handled (in the +@code{doloop_end_insn} pattern) by using a loop instruction sequence +that can handle memory operands when the memory alternative appears. + +GCC does not check the mode of the loop register operand when generating +the @code{doloop_end} pattern. If the pattern is only valid for some +modes but not others, the pattern should be a @code{define_expand} +pattern that checks the operand mode in the preparation code, and issues +@code{FAIL} if an unsupported mode is found. The example above does +this, since the machine instruction to be used only exists for +@code{HImode}. + +If the @code{doloop_end} pattern is a @code{define_expand}, there must +also be a @code{define_insn} or @code{define_insn_and_split} matching +the generated pattern. Otherwise, the compiler will fail during loop +optimization. + +@end ifset +@ifset INTERNALS +@node Insn Canonicalizations +@section Canonicalization of Instructions +@cindex canonicalization of instructions +@cindex insn canonicalization + +There are often cases where multiple RTL expressions could represent an +operation performed by a single machine instruction. This situation is +most commonly encountered with logical, branch, and multiply-accumulate +instructions. In such cases, the compiler attempts to convert these +multiple RTL expressions into a single canonical form to reduce the +number of insn patterns required. + +In addition to algebraic simplifications, following canonicalizations +are performed: + +@itemize @bullet +@item +For commutative and comparison operators, a constant is always made the +second operand. If a machine only supports a constant as the second +operand, only patterns that match a constant in the second operand need +be supplied. + +@item +For associative operators, a sequence of operators will always chain +to the left; for instance, only the left operand of an integer @code{plus} +can itself be a @code{plus}. @code{and}, @code{ior}, @code{xor}, +@code{plus}, @code{mult}, @code{smin}, @code{smax}, @code{umin}, and +@code{umax} are associative when applied to integers, and sometimes to +floating-point. + +@item +@cindex @code{neg}, canonicalization of +@cindex @code{not}, canonicalization of +@cindex @code{mult}, canonicalization of +@cindex @code{plus}, canonicalization of +@cindex @code{minus}, canonicalization of +For these operators, if only one operand is a @code{neg}, @code{not}, +@code{mult}, @code{plus}, or @code{minus} expression, it will be the +first operand. + +@item +In combinations of @code{neg}, @code{mult}, @code{plus}, and +@code{minus}, the @code{neg} operations (if any) will be moved inside +the operations as far as possible. For instance, +@code{(neg (mult A B))} is canonicalized as @code{(mult (neg A) B)}, but +@code{(plus (mult (neg B) C) A)} is canonicalized as +@code{(minus A (mult B C))}. + +@cindex @code{compare}, canonicalization of +@item +For the @code{compare} operator, a constant is always the second operand +if the first argument is a condition code register. + +@item +For instructions that inherently set a condition code register, the +@code{compare} operator is always written as the first RTL expression of +the @code{parallel} instruction pattern. For example, + +@smallexample +(define_insn "" + [(set (reg:CCZ FLAGS_REG) + (compare:CCZ + (plus:SI + (match_operand:SI 1 "register_operand" "%r") + (match_operand:SI 2 "register_operand" "r")) + (const_int 0))) + (set (match_operand:SI 0 "register_operand" "=r") + (plus:SI (match_dup 1) (match_dup 2)))] + "" + "addl %0, %1, %2") +@end smallexample + +@item +An operand of @code{neg}, @code{not}, @code{mult}, @code{plus}, or +@code{minus} is made the first operand under the same conditions as +above. + +@item +@code{(ltu (plus @var{a} @var{b}) @var{b})} is converted to +@code{(ltu (plus @var{a} @var{b}) @var{a})}. Likewise with @code{geu} instead +of @code{ltu}. + +@item +@code{(minus @var{x} (const_int @var{n}))} is converted to +@code{(plus @var{x} (const_int @var{-n}))}. + +@item +Within address computations (i.e., inside @code{mem}), a left shift is +converted into the appropriate multiplication by a power of two. + +@cindex @code{ior}, canonicalization of +@cindex @code{and}, canonicalization of +@cindex De Morgan's law +@item +De Morgan's Law is used to move bitwise negation inside a bitwise +logical-and or logical-or operation. If this results in only one +operand being a @code{not} expression, it will be the first one. + +A machine that has an instruction that performs a bitwise logical-and of one +operand with the bitwise negation of the other should specify the pattern +for that instruction as + +@smallexample +(define_insn "" + [(set (match_operand:@var{m} 0 @dots{}) + (and:@var{m} (not:@var{m} (match_operand:@var{m} 1 @dots{})) + (match_operand:@var{m} 2 @dots{})))] + "@dots{}" + "@dots{}") +@end smallexample + +@noindent +Similarly, a pattern for a ``NAND'' instruction should be written + +@smallexample +(define_insn "" + [(set (match_operand:@var{m} 0 @dots{}) + (ior:@var{m} (not:@var{m} (match_operand:@var{m} 1 @dots{})) + (not:@var{m} (match_operand:@var{m} 2 @dots{}))))] + "@dots{}" + "@dots{}") +@end smallexample + +In both cases, it is not necessary to include patterns for the many +logically equivalent RTL expressions. + +@cindex @code{xor}, canonicalization of +@item +The only possible RTL expressions involving both bitwise exclusive-or +and bitwise negation are @code{(xor:@var{m} @var{x} @var{y})} +and @code{(not:@var{m} (xor:@var{m} @var{x} @var{y}))}. + +@item +The sum of three items, one of which is a constant, will only appear in +the form + +@smallexample +(plus:@var{m} (plus:@var{m} @var{x} @var{y}) @var{constant}) +@end smallexample + +@cindex @code{zero_extract}, canonicalization of +@cindex @code{sign_extract}, canonicalization of +@item +Equality comparisons of a group of bits (usually a single bit) with zero +will be written using @code{zero_extract} rather than the equivalent +@code{and} or @code{sign_extract} operations. + +@cindex @code{mult}, canonicalization of +@item +@code{(sign_extend:@var{m1} (mult:@var{m2} (sign_extend:@var{m2} @var{x}) +(sign_extend:@var{m2} @var{y})))} is converted to @code{(mult:@var{m1} +(sign_extend:@var{m1} @var{x}) (sign_extend:@var{m1} @var{y}))}, and likewise +for @code{zero_extend}. + +@item +@code{(sign_extend:@var{m1} (mult:@var{m2} (ashiftrt:@var{m2} +@var{x} @var{s}) (sign_extend:@var{m2} @var{y})))} is converted +to @code{(mult:@var{m1} (sign_extend:@var{m1} (ashiftrt:@var{m2} +@var{x} @var{s})) (sign_extend:@var{m1} @var{y}))}, and likewise for +patterns using @code{zero_extend} and @code{lshiftrt}. If the second +operand of @code{mult} is also a shift, then that is extended also. +This transformation is only applied when it can be proven that the +original operation had sufficient precision to prevent overflow. + +@end itemize + +Further canonicalization rules are defined in the function +@code{commutative_operand_precedence} in @file{gcc/rtlanal.cc}. + +@end ifset +@ifset INTERNALS +@node Expander Definitions +@section Defining RTL Sequences for Code Generation +@cindex expander definitions +@cindex code generation RTL sequences +@cindex defining RTL sequences for code generation + +On some target machines, some standard pattern names for RTL generation +cannot be handled with single insn, but a sequence of RTL insns can +represent them. For these target machines, you can write a +@code{define_expand} to specify how to generate the sequence of RTL@. + +@findex define_expand +A @code{define_expand} is an RTL expression that looks almost like a +@code{define_insn}; but, unlike the latter, a @code{define_expand} is used +only for RTL generation and it can produce more than one RTL insn. + +A @code{define_expand} RTX has four operands: + +@itemize @bullet +@item +The name. Each @code{define_expand} must have a name, since the only +use for it is to refer to it by name. + +@item +The RTL template. This is a vector of RTL expressions representing +a sequence of separate instructions. Unlike @code{define_insn}, there +is no implicit surrounding @code{PARALLEL}. + +@item +The condition, a string containing a C expression. This expression is +used to express how the availability of this pattern depends on +subclasses of target machine, selected by command-line options when GCC +is run. This is just like the condition of a @code{define_insn} that +has a standard name. Therefore, the condition (if present) may not +depend on the data in the insn being matched, but only the +target-machine-type flags. The compiler needs to test these conditions +during initialization in order to learn exactly which named instructions +are available in a particular run. + +@item +The preparation statements, a string containing zero or more C +statements which are to be executed before RTL code is generated from +the RTL template. + +Usually these statements prepare temporary registers for use as +internal operands in the RTL template, but they can also generate RTL +insns directly by calling routines such as @code{emit_insn}, etc. +Any such insns precede the ones that come from the RTL template. + +@item +Optionally, a vector containing the values of attributes. @xref{Insn +Attributes}. +@end itemize + +Every RTL insn emitted by a @code{define_expand} must match some +@code{define_insn} in the machine description. Otherwise, the compiler +will crash when trying to generate code for the insn or trying to optimize +it. + +The RTL template, in addition to controlling generation of RTL insns, +also describes the operands that need to be specified when this pattern +is used. In particular, it gives a predicate for each operand. + +A true operand, which needs to be specified in order to generate RTL from +the pattern, should be described with a @code{match_operand} in its first +occurrence in the RTL template. This enters information on the operand's +predicate into the tables that record such things. GCC uses the +information to preload the operand into a register if that is required for +valid RTL code. If the operand is referred to more than once, subsequent +references should use @code{match_dup}. + +The RTL template may also refer to internal ``operands'' which are +temporary registers or labels used only within the sequence made by the +@code{define_expand}. Internal operands are substituted into the RTL +template with @code{match_dup}, never with @code{match_operand}. The +values of the internal operands are not passed in as arguments by the +compiler when it requests use of this pattern. Instead, they are computed +within the pattern, in the preparation statements. These statements +compute the values and store them into the appropriate elements of +@code{operands} so that @code{match_dup} can find them. + +There are two special macros defined for use in the preparation statements: +@code{DONE} and @code{FAIL}. Use them with a following semicolon, +as a statement. + +@table @code + +@findex DONE +@item DONE +Use the @code{DONE} macro to end RTL generation for the pattern. The +only RTL insns resulting from the pattern on this occasion will be +those already emitted by explicit calls to @code{emit_insn} within the +preparation statements; the RTL template will not be generated. + +@findex FAIL +@item FAIL +Make the pattern fail on this occasion. When a pattern fails, it means +that the pattern was not truly available. The calling routines in the +compiler will try other strategies for code generation using other patterns. + +Failure is currently supported only for binary (addition, multiplication, +shifting, etc.) and bit-field (@code{extv}, @code{extzv}, and @code{insv}) +operations. +@end table + +If the preparation falls through (invokes neither @code{DONE} nor +@code{FAIL}), then the @code{define_expand} acts like a +@code{define_insn} in that the RTL template is used to generate the +insn. + +The RTL template is not used for matching, only for generating the +initial insn list. If the preparation statement always invokes +@code{DONE} or @code{FAIL}, the RTL template may be reduced to a simple +list of operands, such as this example: + +@smallexample +@group +(define_expand "addsi3" + [(match_operand:SI 0 "register_operand" "") + (match_operand:SI 1 "register_operand" "") + (match_operand:SI 2 "register_operand" "")] + "" + " +@{ + handle_add (operands[0], operands[1], operands[2]); + DONE; +@}") +@end group +@end smallexample + +Here is an example, the definition of left-shift for the SPUR chip: + +@smallexample +@group +(define_expand "ashlsi3" + [(set (match_operand:SI 0 "register_operand" "") + (ashift:SI + (match_operand:SI 1 "register_operand" "") + (match_operand:SI 2 "nonmemory_operand" "")))] + "" + " +@{ + if (GET_CODE (operands[2]) != CONST_INT + || (unsigned) INTVAL (operands[2]) > 3) + FAIL; +@}") +@end group +@end smallexample + +@noindent +This example uses @code{define_expand} so that it can generate an RTL insn +for shifting when the shift-count is in the supported range of 0 to 3 but +fail in other cases where machine insns aren't available. When it fails, +the compiler tries another strategy using different patterns (such as, a +library call). + +If the compiler were able to handle nontrivial condition-strings in +patterns with names, then it would be possible to use a +@code{define_insn} in that case. Here is another case (zero-extension +on the 68000) which makes more use of the power of @code{define_expand}: + +@smallexample +(define_expand "zero_extendhisi2" + [(set (match_operand:SI 0 "general_operand" "") + (const_int 0)) + (set (strict_low_part + (subreg:HI + (match_dup 0) + 0)) + (match_operand:HI 1 "general_operand" ""))] + "" + "operands[1] = make_safe_from (operands[1], operands[0]);") +@end smallexample + +@noindent +@findex make_safe_from +Here two RTL insns are generated, one to clear the entire output operand +and the other to copy the input operand into its low half. This sequence +is incorrect if the input operand refers to [the old value of] the output +operand, so the preparation statement makes sure this isn't so. The +function @code{make_safe_from} copies the @code{operands[1]} into a +temporary register if it refers to @code{operands[0]}. It does this +by emitting another RTL insn. + +Finally, a third example shows the use of an internal operand. +Zero-extension on the SPUR chip is done by @code{and}-ing the result +against a halfword mask. But this mask cannot be represented by a +@code{const_int} because the constant value is too large to be legitimate +on this machine. So it must be copied into a register with +@code{force_reg} and then the register used in the @code{and}. + +@smallexample +(define_expand "zero_extendhisi2" + [(set (match_operand:SI 0 "register_operand" "") + (and:SI (subreg:SI + (match_operand:HI 1 "register_operand" "") + 0) + (match_dup 2)))] + "" + "operands[2] + = force_reg (SImode, GEN_INT (65535)); ") +@end smallexample + +@emph{Note:} If the @code{define_expand} is used to serve a +standard binary or unary arithmetic operation or a bit-field operation, +then the last insn it generates must not be a @code{code_label}, +@code{barrier} or @code{note}. It must be an @code{insn}, +@code{jump_insn} or @code{call_insn}. If you don't need a real insn +at the end, emit an insn to copy the result of the operation into +itself. Such an insn will generate no code, but it can avoid problems +in the compiler. + +@end ifset +@ifset INTERNALS +@node Insn Splitting +@section Defining How to Split Instructions +@cindex insn splitting +@cindex instruction splitting +@cindex splitting instructions + +There are two cases where you should specify how to split a pattern +into multiple insns. On machines that have instructions requiring +delay slots (@pxref{Delay Slots}) or that have instructions whose +output is not available for multiple cycles (@pxref{Processor pipeline +description}), the compiler phases that optimize these cases need to +be able to move insns into one-instruction delay slots. However, some +insns may generate more than one machine instruction. These insns +cannot be placed into a delay slot. + +Often you can rewrite the single insn as a list of individual insns, +each corresponding to one machine instruction. The disadvantage of +doing so is that it will cause the compilation to be slower and require +more space. If the resulting insns are too complex, it may also +suppress some optimizations. The compiler splits the insn if there is a +reason to believe that it might improve instruction or delay slot +scheduling. + +The insn combiner phase also splits putative insns. If three insns are +merged into one insn with a complex expression that cannot be matched by +some @code{define_insn} pattern, the combiner phase attempts to split +the complex pattern into two insns that are recognized. Usually it can +break the complex pattern into two patterns by splitting out some +subexpression. However, in some other cases, such as performing an +addition of a large constant in two insns on a RISC machine, the way to +split the addition into two insns is machine-dependent. + +@findex define_split +The @code{define_split} definition tells the compiler how to split a +complex insn into several simpler insns. It looks like this: + +@smallexample +(define_split + [@var{insn-pattern}] + "@var{condition}" + [@var{new-insn-pattern-1} + @var{new-insn-pattern-2} + @dots{}] + "@var{preparation-statements}") +@end smallexample + +@var{insn-pattern} is a pattern that needs to be split and +@var{condition} is the final condition to be tested, as in a +@code{define_insn}. When an insn matching @var{insn-pattern} and +satisfying @var{condition} is found, it is replaced in the insn list +with the insns given by @var{new-insn-pattern-1}, +@var{new-insn-pattern-2}, etc. + +The @var{preparation-statements} are similar to those statements that +are specified for @code{define_expand} (@pxref{Expander Definitions}) +and are executed before the new RTL is generated to prepare for the +generated code or emit some insns whose pattern is not fixed. Unlike +those in @code{define_expand}, however, these statements must not +generate any new pseudo-registers. Once reload has completed, they also +must not allocate any space in the stack frame. + +There are two special macros defined for use in the preparation statements: +@code{DONE} and @code{FAIL}. Use them with a following semicolon, +as a statement. + +@table @code + +@findex DONE +@item DONE +Use the @code{DONE} macro to end RTL generation for the splitter. The +only RTL insns generated as replacement for the matched input insn will +be those already emitted by explicit calls to @code{emit_insn} within +the preparation statements; the replacement pattern is not used. + +@findex FAIL +@item FAIL +Make the @code{define_split} fail on this occasion. When a @code{define_split} +fails, it means that the splitter was not truly available for the inputs +it was given, and the input insn will not be split. +@end table + +If the preparation falls through (invokes neither @code{DONE} nor +@code{FAIL}), then the @code{define_split} uses the replacement +template. + +Patterns are matched against @var{insn-pattern} in two different +circumstances. If an insn needs to be split for delay slot scheduling +or insn scheduling, the insn is already known to be valid, which means +that it must have been matched by some @code{define_insn} and, if +@code{reload_completed} is nonzero, is known to satisfy the constraints +of that @code{define_insn}. In that case, the new insn patterns must +also be insns that are matched by some @code{define_insn} and, if +@code{reload_completed} is nonzero, must also satisfy the constraints +of those definitions. + +As an example of this usage of @code{define_split}, consider the following +example from @file{a29k.md}, which splits a @code{sign_extend} from +@code{HImode} to @code{SImode} into a pair of shift insns: + +@smallexample +(define_split + [(set (match_operand:SI 0 "gen_reg_operand" "") + (sign_extend:SI (match_operand:HI 1 "gen_reg_operand" "")))] + "" + [(set (match_dup 0) + (ashift:SI (match_dup 1) + (const_int 16))) + (set (match_dup 0) + (ashiftrt:SI (match_dup 0) + (const_int 16)))] + " +@{ operands[1] = gen_lowpart (SImode, operands[1]); @}") +@end smallexample + +When the combiner phase tries to split an insn pattern, it is always the +case that the pattern is @emph{not} matched by any @code{define_insn}. +The combiner pass first tries to split a single @code{set} expression +and then the same @code{set} expression inside a @code{parallel}, but +followed by a @code{clobber} of a pseudo-reg to use as a scratch +register. In these cases, the combiner expects exactly one or two new insn +patterns to be generated. It will verify that these patterns match some +@code{define_insn} definitions, so you need not do this test in the +@code{define_split} (of course, there is no point in writing a +@code{define_split} that will never produce insns that match). + +Here is an example of this use of @code{define_split}, taken from +@file{rs6000.md}: + +@smallexample +(define_split + [(set (match_operand:SI 0 "gen_reg_operand" "") + (plus:SI (match_operand:SI 1 "gen_reg_operand" "") + (match_operand:SI 2 "non_add_cint_operand" "")))] + "" + [(set (match_dup 0) (plus:SI (match_dup 1) (match_dup 3))) + (set (match_dup 0) (plus:SI (match_dup 0) (match_dup 4)))] +" +@{ + int low = INTVAL (operands[2]) & 0xffff; + int high = (unsigned) INTVAL (operands[2]) >> 16; + + if (low & 0x8000) + high++, low |= 0xffff0000; + + operands[3] = GEN_INT (high << 16); + operands[4] = GEN_INT (low); +@}") +@end smallexample + +Here the predicate @code{non_add_cint_operand} matches any +@code{const_int} that is @emph{not} a valid operand of a single add +insn. The add with the smaller displacement is written so that it +can be substituted into the address of a subsequent operation. + +An example that uses a scratch register, from the same file, generates +an equality comparison of a register and a large constant: + +@smallexample +(define_split + [(set (match_operand:CC 0 "cc_reg_operand" "") + (compare:CC (match_operand:SI 1 "gen_reg_operand" "") + (match_operand:SI 2 "non_short_cint_operand" ""))) + (clobber (match_operand:SI 3 "gen_reg_operand" ""))] + "find_single_use (operands[0], insn, 0) + && (GET_CODE (*find_single_use (operands[0], insn, 0)) == EQ + || GET_CODE (*find_single_use (operands[0], insn, 0)) == NE)" + [(set (match_dup 3) (xor:SI (match_dup 1) (match_dup 4))) + (set (match_dup 0) (compare:CC (match_dup 3) (match_dup 5)))] + " +@{ + /* @r{Get the constant we are comparing against, C, and see what it + looks like sign-extended to 16 bits. Then see what constant + could be XOR'ed with C to get the sign-extended value.} */ + + int c = INTVAL (operands[2]); + int sextc = (c << 16) >> 16; + int xorv = c ^ sextc; + + operands[4] = GEN_INT (xorv); + operands[5] = GEN_INT (sextc); +@}") +@end smallexample + +To avoid confusion, don't write a single @code{define_split} that +accepts some insns that match some @code{define_insn} as well as some +insns that don't. Instead, write two separate @code{define_split} +definitions, one for the insns that are valid and one for the insns that +are not valid. + +The splitter is allowed to split jump instructions into sequence of +jumps or create new jumps in while splitting non-jump instructions. As +the control flow graph and branch prediction information needs to be updated, +several restriction apply. + +Splitting of jump instruction into sequence that over by another jump +instruction is always valid, as compiler expect identical behavior of new +jump. When new sequence contains multiple jump instructions or new labels, +more assistance is needed. Splitter is required to create only unconditional +jumps, or simple conditional jump instructions. Additionally it must attach a +@code{REG_BR_PROB} note to each conditional jump. A global variable +@code{split_branch_probability} holds the probability of the original branch in case +it was a simple conditional jump, @minus{}1 otherwise. To simplify +recomputing of edge frequencies, the new sequence is required to have only +forward jumps to the newly created labels. + +@findex define_insn_and_split +For the common case where the pattern of a define_split exactly matches the +pattern of a define_insn, use @code{define_insn_and_split}. It looks like +this: + +@smallexample +(define_insn_and_split + [@var{insn-pattern}] + "@var{condition}" + "@var{output-template}" + "@var{split-condition}" + [@var{new-insn-pattern-1} + @var{new-insn-pattern-2} + @dots{}] + "@var{preparation-statements}" + [@var{insn-attributes}]) + +@end smallexample + +@var{insn-pattern}, @var{condition}, @var{output-template}, and +@var{insn-attributes} are used as in @code{define_insn}. The +@var{new-insn-pattern} vector and the @var{preparation-statements} are used as +in a @code{define_split}. The @var{split-condition} is also used as in +@code{define_split}, with the additional behavior that if the condition starts +with @samp{&&}, the condition used for the split will be the constructed as a +logical ``and'' of the split condition with the insn condition. For example, +from i386.md: + +@smallexample +(define_insn_and_split "zero_extendhisi2_and" + [(set (match_operand:SI 0 "register_operand" "=r") + (zero_extend:SI (match_operand:HI 1 "register_operand" "0"))) + (clobber (reg:CC 17))] + "TARGET_ZERO_EXTEND_WITH_AND && !optimize_size" + "#" + "&& reload_completed" + [(parallel [(set (match_dup 0) + (and:SI (match_dup 0) (const_int 65535))) + (clobber (reg:CC 17))])] + "" + [(set_attr "type" "alu1")]) + +@end smallexample + +In this case, the actual split condition will be +@samp{TARGET_ZERO_EXTEND_WITH_AND && !optimize_size && reload_completed}. + +The @code{define_insn_and_split} construction provides exactly the same +functionality as two separate @code{define_insn} and @code{define_split} +patterns. It exists for compactness, and as a maintenance tool to prevent +having to ensure the two patterns' templates match. + +@findex define_insn_and_rewrite +It is sometimes useful to have a @code{define_insn_and_split} +that replaces specific operands of an instruction but leaves the +rest of the instruction pattern unchanged. You can do this directly +with a @code{define_insn_and_split}, but it requires a +@var{new-insn-pattern-1} that repeats most of the original @var{insn-pattern}. +There is also the complication that an implicit @code{parallel} in +@var{insn-pattern} must become an explicit @code{parallel} in +@var{new-insn-pattern-1}, which is easy to overlook. +A simpler alternative is to use @code{define_insn_and_rewrite}, which +is a form of @code{define_insn_and_split} that automatically generates +@var{new-insn-pattern-1} by replacing each @code{match_operand} +in @var{insn-pattern} with a corresponding @code{match_dup}, and each +@code{match_operator} in the pattern with a corresponding @code{match_op_dup}. +The arguments are otherwise identical to @code{define_insn_and_split}: + +@smallexample +(define_insn_and_rewrite + [@var{insn-pattern}] + "@var{condition}" + "@var{output-template}" + "@var{split-condition}" + "@var{preparation-statements}" + [@var{insn-attributes}]) +@end smallexample + +The @code{match_dup}s and @code{match_op_dup}s in the new +instruction pattern use any new operand values that the +@var{preparation-statements} store in the @code{operands} array, +as for a normal @code{define_insn_and_split}. @var{preparation-statements} +can also emit additional instructions before the new instruction. +They can even emit an entirely different sequence of instructions and +use @code{DONE} to avoid emitting a new form of the original +instruction. + +The split in a @code{define_insn_and_rewrite} is only intended +to apply to existing instructions that match @var{insn-pattern}. +@var{split-condition} must therefore start with @code{&&}, +so that the split condition applies on top of @var{condition}. + +Here is an example from the AArch64 SVE port, in which operand 1 is +known to be equivalent to an all-true constant and isn't used by the +output template: + +@smallexample +(define_insn_and_rewrite "*while_ult_cc" + [(set (reg:CC CC_REGNUM) + (compare:CC + (unspec:SI [(match_operand:PRED_ALL 1) + (unspec:PRED_ALL + [(match_operand:GPI 2 "aarch64_reg_or_zero" "rZ") + (match_operand:GPI 3 "aarch64_reg_or_zero" "rZ")] + UNSPEC_WHILE_LO)] + UNSPEC_PTEST_PTRUE) + (const_int 0))) + (set (match_operand:PRED_ALL 0 "register_operand" "=Upa") + (unspec:PRED_ALL [(match_dup 2) + (match_dup 3)] + UNSPEC_WHILE_LO))] + "TARGET_SVE" + "whilelo\t%0., %2, %3" + ;; Force the compiler to drop the unused predicate operand, so that we + ;; don't have an unnecessary PTRUE. + "&& !CONSTANT_P (operands[1])" + @{ + operands[1] = CONSTM1_RTX (mode); + @} +) +@end smallexample + +The splitter in this case simply replaces operand 1 with the constant +value that it is known to have. The equivalent @code{define_insn_and_split} +would be: + +@smallexample +(define_insn_and_split "*while_ult_cc" + [(set (reg:CC CC_REGNUM) + (compare:CC + (unspec:SI [(match_operand:PRED_ALL 1) + (unspec:PRED_ALL + [(match_operand:GPI 2 "aarch64_reg_or_zero" "rZ") + (match_operand:GPI 3 "aarch64_reg_or_zero" "rZ")] + UNSPEC_WHILE_LO)] + UNSPEC_PTEST_PTRUE) + (const_int 0))) + (set (match_operand:PRED_ALL 0 "register_operand" "=Upa") + (unspec:PRED_ALL [(match_dup 2) + (match_dup 3)] + UNSPEC_WHILE_LO))] + "TARGET_SVE" + "whilelo\t%0., %2, %3" + ;; Force the compiler to drop the unused predicate operand, so that we + ;; don't have an unnecessary PTRUE. + "&& !CONSTANT_P (operands[1])" + [(parallel + [(set (reg:CC CC_REGNUM) + (compare:CC + (unspec:SI [(match_dup 1) + (unspec:PRED_ALL [(match_dup 2) + (match_dup 3)] + UNSPEC_WHILE_LO)] + UNSPEC_PTEST_PTRUE) + (const_int 0))) + (set (match_dup 0) + (unspec:PRED_ALL [(match_dup 2) + (match_dup 3)] + UNSPEC_WHILE_LO))])] + @{ + operands[1] = CONSTM1_RTX (mode); + @} +) +@end smallexample + +@end ifset +@ifset INTERNALS +@node Including Patterns +@section Including Patterns in Machine Descriptions. +@cindex insn includes + +@findex include +The @code{include} pattern tells the compiler tools where to +look for patterns that are in files other than in the file +@file{.md}. This is used only at build time and there is no preprocessing allowed. + +It looks like: + +@smallexample + +(include + @var{pathname}) +@end smallexample + +For example: + +@smallexample + +(include "filestuff") + +@end smallexample + +Where @var{pathname} is a string that specifies the location of the file, +specifies the include file to be in @file{gcc/config/target/filestuff}. The +directory @file{gcc/config/target} is regarded as the default directory. + + +Machine descriptions may be split up into smaller more manageable subsections +and placed into subdirectories. + +By specifying: + +@smallexample + +(include "BOGUS/filestuff") + +@end smallexample + +the include file is specified to be in @file{gcc/config/@var{target}/BOGUS/filestuff}. + +Specifying an absolute path for the include file such as; +@smallexample + +(include "/u2/BOGUS/filestuff") + +@end smallexample +is permitted but is not encouraged. + +@subsection RTL Generation Tool Options for Directory Search +@cindex directory options .md +@cindex options, directory search +@cindex search options + +The @option{-I@var{dir}} option specifies directories to search for machine descriptions. +For example: + +@smallexample + +genrecog -I/p1/abc/proc1 -I/p2/abcd/pro2 target.md + +@end smallexample + + +Add the directory @var{dir} to the head of the list of directories to be +searched for header files. This can be used to override a system machine definition +file, substituting your own version, since these directories are +searched before the default machine description file directories. If you use more than +one @option{-I} option, the directories are scanned in left-to-right +order; the standard default directory come after. + + +@end ifset +@ifset INTERNALS +@node Peephole Definitions +@section Machine-Specific Peephole Optimizers +@cindex peephole optimizer definitions +@cindex defining peephole optimizers + +In addition to instruction patterns the @file{md} file may contain +definitions of machine-specific peephole optimizations. + +The combiner does not notice certain peephole optimizations when the data +flow in the program does not suggest that it should try them. For example, +sometimes two consecutive insns related in purpose can be combined even +though the second one does not appear to use a register computed in the +first one. A machine-specific peephole optimizer can detect such +opportunities. + +There are two forms of peephole definitions that may be used. The +original @code{define_peephole} is run at assembly output time to +match insns and substitute assembly text. Use of @code{define_peephole} +is deprecated. + +A newer @code{define_peephole2} matches insns and substitutes new +insns. The @code{peephole2} pass is run after register allocation +but before scheduling, which may result in much better code for +targets that do scheduling. + +@menu +* define_peephole:: RTL to Text Peephole Optimizers +* define_peephole2:: RTL to RTL Peephole Optimizers +@end menu + +@end ifset +@ifset INTERNALS +@node define_peephole +@subsection RTL to Text Peephole Optimizers +@findex define_peephole + +@need 1000 +A definition looks like this: + +@smallexample +(define_peephole + [@var{insn-pattern-1} + @var{insn-pattern-2} + @dots{}] + "@var{condition}" + "@var{template}" + "@var{optional-insn-attributes}") +@end smallexample + +@noindent +The last string operand may be omitted if you are not using any +machine-specific information in this machine description. If present, +it must obey the same rules as in a @code{define_insn}. + +In this skeleton, @var{insn-pattern-1} and so on are patterns to match +consecutive insns. The optimization applies to a sequence of insns when +@var{insn-pattern-1} matches the first one, @var{insn-pattern-2} matches +the next, and so on. + +Each of the insns matched by a peephole must also match a +@code{define_insn}. Peepholes are checked only at the last stage just +before code generation, and only optionally. Therefore, any insn which +would match a peephole but no @code{define_insn} will cause a crash in code +generation in an unoptimized compilation, or at various optimization +stages. + +The operands of the insns are matched with @code{match_operands}, +@code{match_operator}, and @code{match_dup}, as usual. What is not +usual is that the operand numbers apply to all the insn patterns in the +definition. So, you can check for identical operands in two insns by +using @code{match_operand} in one insn and @code{match_dup} in the +other. + +The operand constraints used in @code{match_operand} patterns do not have +any direct effect on the applicability of the peephole, but they will +be validated afterward, so make sure your constraints are general enough +to apply whenever the peephole matches. If the peephole matches +but the constraints are not satisfied, the compiler will crash. + +It is safe to omit constraints in all the operands of the peephole; or +you can write constraints which serve as a double-check on the criteria +previously tested. + +Once a sequence of insns matches the patterns, the @var{condition} is +checked. This is a C expression which makes the final decision whether to +perform the optimization (we do so if the expression is nonzero). If +@var{condition} is omitted (in other words, the string is empty) then the +optimization is applied to every sequence of insns that matches the +patterns. + +The defined peephole optimizations are applied after register allocation +is complete. Therefore, the peephole definition can check which +operands have ended up in which kinds of registers, just by looking at +the operands. + +@findex prev_active_insn +The way to refer to the operands in @var{condition} is to write +@code{operands[@var{i}]} for operand number @var{i} (as matched by +@code{(match_operand @var{i} @dots{})}). Use the variable @code{insn} +to refer to the last of the insns being matched; use +@code{prev_active_insn} to find the preceding insns. + +@findex dead_or_set_p +When optimizing computations with intermediate results, you can use +@var{condition} to match only when the intermediate results are not used +elsewhere. Use the C expression @code{dead_or_set_p (@var{insn}, +@var{op})}, where @var{insn} is the insn in which you expect the value +to be used for the last time (from the value of @code{insn}, together +with use of @code{prev_nonnote_insn}), and @var{op} is the intermediate +value (from @code{operands[@var{i}]}). + +Applying the optimization means replacing the sequence of insns with one +new insn. The @var{template} controls ultimate output of assembler code +for this combined insn. It works exactly like the template of a +@code{define_insn}. Operand numbers in this template are the same ones +used in matching the original sequence of insns. + +The result of a defined peephole optimizer does not need to match any of +the insn patterns in the machine description; it does not even have an +opportunity to match them. The peephole optimizer definition itself serves +as the insn pattern to control how the insn is output. + +Defined peephole optimizers are run as assembler code is being output, +so the insns they produce are never combined or rearranged in any way. + +Here is an example, taken from the 68000 machine description: + +@smallexample +(define_peephole + [(set (reg:SI 15) (plus:SI (reg:SI 15) (const_int 4))) + (set (match_operand:DF 0 "register_operand" "=f") + (match_operand:DF 1 "register_operand" "ad"))] + "FP_REG_P (operands[0]) && ! FP_REG_P (operands[1])" +@{ + rtx xoperands[2]; + xoperands[1] = gen_rtx_REG (SImode, REGNO (operands[1]) + 1); +#ifdef MOTOROLA + output_asm_insn ("move.l %1,(sp)", xoperands); + output_asm_insn ("move.l %1,-(sp)", operands); + return "fmove.d (sp)+,%0"; +#else + output_asm_insn ("movel %1,sp@@", xoperands); + output_asm_insn ("movel %1,sp@@-", operands); + return "fmoved sp@@+,%0"; +#endif +@}) +@end smallexample + +@need 1000 +The effect of this optimization is to change + +@smallexample +@group +jbsr _foobar +addql #4,sp +movel d1,sp@@- +movel d0,sp@@- +fmoved sp@@+,fp0 +@end group +@end smallexample + +@noindent +into + +@smallexample +@group +jbsr _foobar +movel d1,sp@@ +movel d0,sp@@- +fmoved sp@@+,fp0 +@end group +@end smallexample + +@ignore +@findex CC_REVERSED +If a peephole matches a sequence including one or more jump insns, you must +take account of the flags such as @code{CC_REVERSED} which specify that the +condition codes are represented in an unusual manner. The compiler +automatically alters any ordinary conditional jumps which occur in such +situations, but the compiler cannot alter jumps which have been replaced by +peephole optimizations. So it is up to you to alter the assembler code +that the peephole produces. Supply C code to write the assembler output, +and in this C code check the condition code status flags and change the +assembler code as appropriate. +@end ignore + +@var{insn-pattern-1} and so on look @emph{almost} like the second +operand of @code{define_insn}. There is one important difference: the +second operand of @code{define_insn} consists of one or more RTX's +enclosed in square brackets. Usually, there is only one: then the same +action can be written as an element of a @code{define_peephole}. But +when there are multiple actions in a @code{define_insn}, they are +implicitly enclosed in a @code{parallel}. Then you must explicitly +write the @code{parallel}, and the square brackets within it, in the +@code{define_peephole}. Thus, if an insn pattern looks like this, + +@smallexample +(define_insn "divmodsi4" + [(set (match_operand:SI 0 "general_operand" "=d") + (div:SI (match_operand:SI 1 "general_operand" "0") + (match_operand:SI 2 "general_operand" "dmsK"))) + (set (match_operand:SI 3 "general_operand" "=d") + (mod:SI (match_dup 1) (match_dup 2)))] + "TARGET_68020" + "divsl%.l %2,%3:%0") +@end smallexample + +@noindent +then the way to mention this insn in a peephole is as follows: + +@smallexample +(define_peephole + [@dots{} + (parallel + [(set (match_operand:SI 0 "general_operand" "=d") + (div:SI (match_operand:SI 1 "general_operand" "0") + (match_operand:SI 2 "general_operand" "dmsK"))) + (set (match_operand:SI 3 "general_operand" "=d") + (mod:SI (match_dup 1) (match_dup 2)))]) + @dots{}] + @dots{}) +@end smallexample + +@end ifset +@ifset INTERNALS +@node define_peephole2 +@subsection RTL to RTL Peephole Optimizers +@findex define_peephole2 + +The @code{define_peephole2} definition tells the compiler how to +substitute one sequence of instructions for another sequence, +what additional scratch registers may be needed and what their +lifetimes must be. + +@smallexample +(define_peephole2 + [@var{insn-pattern-1} + @var{insn-pattern-2} + @dots{}] + "@var{condition}" + [@var{new-insn-pattern-1} + @var{new-insn-pattern-2} + @dots{}] + "@var{preparation-statements}") +@end smallexample + +The definition is almost identical to @code{define_split} +(@pxref{Insn Splitting}) except that the pattern to match is not a +single instruction, but a sequence of instructions. + +It is possible to request additional scratch registers for use in the +output template. If appropriate registers are not free, the pattern +will simply not match. + +@findex match_scratch +@findex match_dup +Scratch registers are requested with a @code{match_scratch} pattern at +the top level of the input pattern. The allocated register (initially) will +be dead at the point requested within the original sequence. If the scratch +is used at more than a single point, a @code{match_dup} pattern at the +top level of the input pattern marks the last position in the input sequence +at which the register must be available. + +Here is an example from the IA-32 machine description: + +@smallexample +(define_peephole2 + [(match_scratch:SI 2 "r") + (parallel [(set (match_operand:SI 0 "register_operand" "") + (match_operator:SI 3 "arith_or_logical_operator" + [(match_dup 0) + (match_operand:SI 1 "memory_operand" "")])) + (clobber (reg:CC 17))])] + "! optimize_size && ! TARGET_READ_MODIFY" + [(set (match_dup 2) (match_dup 1)) + (parallel [(set (match_dup 0) + (match_op_dup 3 [(match_dup 0) (match_dup 2)])) + (clobber (reg:CC 17))])] + "") +@end smallexample + +@noindent +This pattern tries to split a load from its use in the hopes that we'll be +able to schedule around the memory load latency. It allocates a single +@code{SImode} register of class @code{GENERAL_REGS} (@code{"r"}) that needs +to be live only at the point just before the arithmetic. + +A real example requiring extended scratch lifetimes is harder to come by, +so here's a silly made-up example: + +@smallexample +(define_peephole2 + [(match_scratch:SI 4 "r") + (set (match_operand:SI 0 "" "") (match_operand:SI 1 "" "")) + (set (match_operand:SI 2 "" "") (match_dup 1)) + (match_dup 4) + (set (match_operand:SI 3 "" "") (match_dup 1))] + "/* @r{determine 1 does not overlap 0 and 2} */" + [(set (match_dup 4) (match_dup 1)) + (set (match_dup 0) (match_dup 4)) + (set (match_dup 2) (match_dup 4)) + (set (match_dup 3) (match_dup 4))] + "") +@end smallexample + +There are two special macros defined for use in the preparation statements: +@code{DONE} and @code{FAIL}. Use them with a following semicolon, +as a statement. + +@table @code + +@findex DONE +@item DONE +Use the @code{DONE} macro to end RTL generation for the peephole. The +only RTL insns generated as replacement for the matched input insn will +be those already emitted by explicit calls to @code{emit_insn} within +the preparation statements; the replacement pattern is not used. + +@findex FAIL +@item FAIL +Make the @code{define_peephole2} fail on this occasion. When a @code{define_peephole2} +fails, it means that the replacement was not truly available for the +particular inputs it was given. In that case, GCC may still apply a +later @code{define_peephole2} that also matches the given insn pattern. +(Note that this is different from @code{define_split}, where @code{FAIL} +prevents the input insn from being split at all.) +@end table + +If the preparation falls through (invokes neither @code{DONE} nor +@code{FAIL}), then the @code{define_peephole2} uses the replacement +template. + +@noindent +If we had not added the @code{(match_dup 4)} in the middle of the input +sequence, it might have been the case that the register we chose at the +beginning of the sequence is killed by the first or second @code{set}. + +@end ifset +@ifset INTERNALS +@node Insn Attributes +@section Instruction Attributes +@cindex insn attributes +@cindex instruction attributes + +In addition to describing the instruction supported by the target machine, +the @file{md} file also defines a group of @dfn{attributes} and a set of +values for each. Every generated insn is assigned a value for each attribute. +One possible attribute would be the effect that the insn has on the machine's +condition code. + +@menu +* Defining Attributes:: Specifying attributes and their values. +* Expressions:: Valid expressions for attribute values. +* Tagging Insns:: Assigning attribute values to insns. +* Attr Example:: An example of assigning attributes. +* Insn Lengths:: Computing the length of insns. +* Constant Attributes:: Defining attributes that are constant. +* Mnemonic Attribute:: Obtain the instruction mnemonic as attribute value. +* Delay Slots:: Defining delay slots required for a machine. +* Processor pipeline description:: Specifying information for insn scheduling. +@end menu + +@end ifset +@ifset INTERNALS +@node Defining Attributes +@subsection Defining Attributes and their Values +@cindex defining attributes and their values +@cindex attributes, defining + +@findex define_attr +The @code{define_attr} expression is used to define each attribute required +by the target machine. It looks like: + +@smallexample +(define_attr @var{name} @var{list-of-values} @var{default}) +@end smallexample + +@var{name} is a string specifying the name of the attribute being +defined. Some attributes are used in a special way by the rest of the +compiler. The @code{enabled} attribute can be used to conditionally +enable or disable insn alternatives (@pxref{Disable Insn +Alternatives}). The @code{predicable} attribute, together with a +suitable @code{define_cond_exec} (@pxref{Conditional Execution}), can +be used to automatically generate conditional variants of instruction +patterns. The @code{mnemonic} attribute can be used to check for the +instruction mnemonic (@pxref{Mnemonic Attribute}). The compiler +internally uses the names @code{ce_enabled} and @code{nonce_enabled}, +so they should not be used elsewhere as alternative names. + +@var{list-of-values} is either a string that specifies a comma-separated +list of values that can be assigned to the attribute, or a null string to +indicate that the attribute takes numeric values. + +@var{default} is an attribute expression that gives the value of this +attribute for insns that match patterns whose definition does not include +an explicit value for this attribute. @xref{Attr Example}, for more +information on the handling of defaults. @xref{Constant Attributes}, +for information on attributes that do not depend on any particular insn. + +@findex insn-attr.h +For each defined attribute, a number of definitions are written to the +@file{insn-attr.h} file. For cases where an explicit set of values is +specified for an attribute, the following are defined: + +@itemize @bullet +@item +A @samp{#define} is written for the symbol @samp{HAVE_ATTR_@var{name}}. + +@item +An enumerated class is defined for @samp{attr_@var{name}} with +elements of the form @samp{@var{upper-name}_@var{upper-value}} where +the attribute name and value are first converted to uppercase. + +@item +A function @samp{get_attr_@var{name}} is defined that is passed an insn and +returns the attribute value for that insn. +@end itemize + +For example, if the following is present in the @file{md} file: + +@smallexample +(define_attr "type" "branch,fp,load,store,arith" @dots{}) +@end smallexample + +@noindent +the following lines will be written to the file @file{insn-attr.h}. + +@smallexample +#define HAVE_ATTR_type 1 +enum attr_type @{TYPE_BRANCH, TYPE_FP, TYPE_LOAD, + TYPE_STORE, TYPE_ARITH@}; +extern enum attr_type get_attr_type (); +@end smallexample + +If the attribute takes numeric values, no @code{enum} type will be +defined and the function to obtain the attribute's value will return +@code{int}. + +There are attributes which are tied to a specific meaning. These +attributes are not free to use for other purposes: + +@table @code +@item length +The @code{length} attribute is used to calculate the length of emitted +code chunks. This is especially important when verifying branch +distances. @xref{Insn Lengths}. + +@item enabled +The @code{enabled} attribute can be defined to prevent certain +alternatives of an insn definition from being used during code +generation. @xref{Disable Insn Alternatives}. + +@item mnemonic +The @code{mnemonic} attribute can be defined to implement instruction +specific checks in e.g.@: the pipeline description. +@xref{Mnemonic Attribute}. +@end table + +For each of these special attributes, the corresponding +@samp{HAVE_ATTR_@var{name}} @samp{#define} is also written when the +attribute is not defined; in that case, it is defined as @samp{0}. + +@findex define_enum_attr +@anchor{define_enum_attr} +Another way of defining an attribute is to use: + +@smallexample +(define_enum_attr "@var{attr}" "@var{enum}" @var{default}) +@end smallexample + +This works in just the same way as @code{define_attr}, except that +the list of values is taken from a separate enumeration called +@var{enum} (@pxref{define_enum}). This form allows you to use +the same list of values for several attributes without having to +repeat the list each time. For example: + +@smallexample +(define_enum "processor" [ + model_a + model_b + @dots{} +]) +(define_enum_attr "arch" "processor" + (const (symbol_ref "target_arch"))) +(define_enum_attr "tune" "processor" + (const (symbol_ref "target_tune"))) +@end smallexample + +defines the same attributes as: + +@smallexample +(define_attr "arch" "model_a,model_b,@dots{}" + (const (symbol_ref "target_arch"))) +(define_attr "tune" "model_a,model_b,@dots{}" + (const (symbol_ref "target_tune"))) +@end smallexample + +but without duplicating the processor list. The second example defines two +separate C enums (@code{attr_arch} and @code{attr_tune}) whereas the first +defines a single C enum (@code{processor}). +@end ifset +@ifset INTERNALS +@node Expressions +@subsection Attribute Expressions +@cindex attribute expressions + +RTL expressions used to define attributes use the codes described above +plus a few specific to attribute definitions, to be discussed below. +Attribute value expressions must have one of the following forms: + +@table @code +@cindex @code{const_int} and attributes +@item (const_int @var{i}) +The integer @var{i} specifies the value of a numeric attribute. @var{i} +must be non-negative. + +The value of a numeric attribute can be specified either with a +@code{const_int}, or as an integer represented as a string in +@code{const_string}, @code{eq_attr} (see below), @code{attr}, +@code{symbol_ref}, simple arithmetic expressions, and @code{set_attr} +overrides on specific instructions (@pxref{Tagging Insns}). + +@cindex @code{const_string} and attributes +@item (const_string @var{value}) +The string @var{value} specifies a constant attribute value. +If @var{value} is specified as @samp{"*"}, it means that the default value of +the attribute is to be used for the insn containing this expression. +@samp{"*"} obviously cannot be used in the @var{default} expression +of a @code{define_attr}. + +If the attribute whose value is being specified is numeric, @var{value} +must be a string containing a non-negative integer (normally +@code{const_int} would be used in this case). Otherwise, it must +contain one of the valid values for the attribute. + +@cindex @code{if_then_else} and attributes +@item (if_then_else @var{test} @var{true-value} @var{false-value}) +@var{test} specifies an attribute test, whose format is defined below. +The value of this expression is @var{true-value} if @var{test} is true, +otherwise it is @var{false-value}. + +@cindex @code{cond} and attributes +@item (cond [@var{test1} @var{value1} @dots{}] @var{default}) +The first operand of this expression is a vector containing an even +number of expressions and consisting of pairs of @var{test} and @var{value} +expressions. The value of the @code{cond} expression is that of the +@var{value} corresponding to the first true @var{test} expression. If +none of the @var{test} expressions are true, the value of the @code{cond} +expression is that of the @var{default} expression. +@end table + +@var{test} expressions can have one of the following forms: + +@table @code +@cindex @code{const_int} and attribute tests +@item (const_int @var{i}) +This test is true if @var{i} is nonzero and false otherwise. + +@cindex @code{not} and attributes +@cindex @code{ior} and attributes +@cindex @code{and} and attributes +@item (not @var{test}) +@itemx (ior @var{test1} @var{test2}) +@itemx (and @var{test1} @var{test2}) +These tests are true if the indicated logical function is true. + +@cindex @code{match_operand} and attributes +@item (match_operand:@var{m} @var{n} @var{pred} @var{constraints}) +This test is true if operand @var{n} of the insn whose attribute value +is being determined has mode @var{m} (this part of the test is ignored +if @var{m} is @code{VOIDmode}) and the function specified by the string +@var{pred} returns a nonzero value when passed operand @var{n} and mode +@var{m} (this part of the test is ignored if @var{pred} is the null +string). + +The @var{constraints} operand is ignored and should be the null string. + +@cindex @code{match_test} and attributes +@item (match_test @var{c-expr}) +The test is true if C expression @var{c-expr} is true. In non-constant +attributes, @var{c-expr} has access to the following variables: + +@table @var +@item insn +The rtl instruction under test. +@item which_alternative +The @code{define_insn} alternative that @var{insn} matches. +@xref{Output Statement}. +@item operands +An array of @var{insn}'s rtl operands. +@end table + +@var{c-expr} behaves like the condition in a C @code{if} statement, +so there is no need to explicitly convert the expression into a boolean +0 or 1 value. For example, the following two tests are equivalent: + +@smallexample +(match_test "x & 2") +(match_test "(x & 2) != 0") +@end smallexample + +@cindex @code{le} and attributes +@cindex @code{leu} and attributes +@cindex @code{lt} and attributes +@cindex @code{gt} and attributes +@cindex @code{gtu} and attributes +@cindex @code{ge} and attributes +@cindex @code{geu} and attributes +@cindex @code{ne} and attributes +@cindex @code{eq} and attributes +@cindex @code{plus} and attributes +@cindex @code{minus} and attributes +@cindex @code{mult} and attributes +@cindex @code{div} and attributes +@cindex @code{mod} and attributes +@cindex @code{abs} and attributes +@cindex @code{neg} and attributes +@cindex @code{ashift} and attributes +@cindex @code{lshiftrt} and attributes +@cindex @code{ashiftrt} and attributes +@item (le @var{arith1} @var{arith2}) +@itemx (leu @var{arith1} @var{arith2}) +@itemx (lt @var{arith1} @var{arith2}) +@itemx (ltu @var{arith1} @var{arith2}) +@itemx (gt @var{arith1} @var{arith2}) +@itemx (gtu @var{arith1} @var{arith2}) +@itemx (ge @var{arith1} @var{arith2}) +@itemx (geu @var{arith1} @var{arith2}) +@itemx (ne @var{arith1} @var{arith2}) +@itemx (eq @var{arith1} @var{arith2}) +These tests are true if the indicated comparison of the two arithmetic +expressions is true. Arithmetic expressions are formed with +@code{plus}, @code{minus}, @code{mult}, @code{div}, @code{mod}, +@code{abs}, @code{neg}, @code{and}, @code{ior}, @code{xor}, @code{not}, +@code{ashift}, @code{lshiftrt}, and @code{ashiftrt} expressions. + +@findex get_attr +@code{const_int} and @code{symbol_ref} are always valid terms (@pxref{Insn +Lengths},for additional forms). @code{symbol_ref} is a string +denoting a C expression that yields an @code{int} when evaluated by the +@samp{get_attr_@dots{}} routine. It should normally be a global +variable. + +@findex eq_attr +@item (eq_attr @var{name} @var{value}) +@var{name} is a string specifying the name of an attribute. + +@var{value} is a string that is either a valid value for attribute +@var{name}, a comma-separated list of values, or @samp{!} followed by a +value or list. If @var{value} does not begin with a @samp{!}, this +test is true if the value of the @var{name} attribute of the current +insn is in the list specified by @var{value}. If @var{value} begins +with a @samp{!}, this test is true if the attribute's value is +@emph{not} in the specified list. + +For example, + +@smallexample +(eq_attr "type" "load,store") +@end smallexample + +@noindent +is equivalent to + +@smallexample +(ior (eq_attr "type" "load") (eq_attr "type" "store")) +@end smallexample + +If @var{name} specifies an attribute of @samp{alternative}, it refers to the +value of the compiler variable @code{which_alternative} +(@pxref{Output Statement}) and the values must be small integers. For +example, + +@smallexample +(eq_attr "alternative" "2,3") +@end smallexample + +@noindent +is equivalent to + +@smallexample +(ior (eq (symbol_ref "which_alternative") (const_int 2)) + (eq (symbol_ref "which_alternative") (const_int 3))) +@end smallexample + +Note that, for most attributes, an @code{eq_attr} test is simplified in cases +where the value of the attribute being tested is known for all insns matching +a particular pattern. This is by far the most common case. + +@findex attr_flag +@item (attr_flag @var{name}) +The value of an @code{attr_flag} expression is true if the flag +specified by @var{name} is true for the @code{insn} currently being +scheduled. + +@var{name} is a string specifying one of a fixed set of flags to test. +Test the flags @code{forward} and @code{backward} to determine the +direction of a conditional branch. + +This example describes a conditional branch delay slot which +can be nullified for forward branches that are taken (annul-true) or +for backward branches which are not taken (annul-false). + +@smallexample +(define_delay (eq_attr "type" "cbranch") + [(eq_attr "in_branch_delay" "true") + (and (eq_attr "in_branch_delay" "true") + (attr_flag "forward")) + (and (eq_attr "in_branch_delay" "true") + (attr_flag "backward"))]) +@end smallexample + +The @code{forward} and @code{backward} flags are false if the current +@code{insn} being scheduled is not a conditional branch. + +@code{attr_flag} is only used during delay slot scheduling and has no +meaning to other passes of the compiler. + +@findex attr +@item (attr @var{name}) +The value of another attribute is returned. This is most useful +for numeric attributes, as @code{eq_attr} and @code{attr_flag} +produce more efficient code for non-numeric attributes. +@end table + +@end ifset +@ifset INTERNALS +@node Tagging Insns +@subsection Assigning Attribute Values to Insns +@cindex tagging insns +@cindex assigning attribute values to insns + +The value assigned to an attribute of an insn is primarily determined by +which pattern is matched by that insn (or which @code{define_peephole} +generated it). Every @code{define_insn} and @code{define_peephole} can +have an optional last argument to specify the values of attributes for +matching insns. The value of any attribute not specified in a particular +insn is set to the default value for that attribute, as specified in its +@code{define_attr}. Extensive use of default values for attributes +permits the specification of the values for only one or two attributes +in the definition of most insn patterns, as seen in the example in the +next section. + +The optional last argument of @code{define_insn} and +@code{define_peephole} is a vector of expressions, each of which defines +the value for a single attribute. The most general way of assigning an +attribute's value is to use a @code{set} expression whose first operand is an +@code{attr} expression giving the name of the attribute being set. The +second operand of the @code{set} is an attribute expression +(@pxref{Expressions}) giving the value of the attribute. + +When the attribute value depends on the @samp{alternative} attribute +(i.e., which is the applicable alternative in the constraint of the +insn), the @code{set_attr_alternative} expression can be used. It +allows the specification of a vector of attribute expressions, one for +each alternative. + +@findex set_attr +When the generality of arbitrary attribute expressions is not required, +the simpler @code{set_attr} expression can be used, which allows +specifying a string giving either a single attribute value or a list +of attribute values, one for each alternative. + +The form of each of the above specifications is shown below. In each case, +@var{name} is a string specifying the attribute to be set. + +@table @code +@item (set_attr @var{name} @var{value-string}) +@var{value-string} is either a string giving the desired attribute value, +or a string containing a comma-separated list giving the values for +succeeding alternatives. The number of elements must match the number +of alternatives in the constraint of the insn pattern. + +Note that it may be useful to specify @samp{*} for some alternative, in +which case the attribute will assume its default value for insns matching +that alternative. + +@findex set_attr_alternative +@item (set_attr_alternative @var{name} [@var{value1} @var{value2} @dots{}]) +Depending on the alternative of the insn, the value will be one of the +specified values. This is a shorthand for using a @code{cond} with +tests on the @samp{alternative} attribute. + +@findex attr +@item (set (attr @var{name}) @var{value}) +The first operand of this @code{set} must be the special RTL expression +@code{attr}, whose sole operand is a string giving the name of the +attribute being set. @var{value} is the value of the attribute. +@end table + +The following shows three different ways of representing the same +attribute value specification: + +@smallexample +(set_attr "type" "load,store,arith") + +(set_attr_alternative "type" + [(const_string "load") (const_string "store") + (const_string "arith")]) + +(set (attr "type") + (cond [(eq_attr "alternative" "1") (const_string "load") + (eq_attr "alternative" "2") (const_string "store")] + (const_string "arith"))) +@end smallexample + +@need 1000 +@findex define_asm_attributes +The @code{define_asm_attributes} expression provides a mechanism to +specify the attributes assigned to insns produced from an @code{asm} +statement. It has the form: + +@smallexample +(define_asm_attributes [@var{attr-sets}]) +@end smallexample + +@noindent +where @var{attr-sets} is specified the same as for both the +@code{define_insn} and the @code{define_peephole} expressions. + +These values will typically be the ``worst case'' attribute values. For +example, they might indicate that the condition code will be clobbered. + +A specification for a @code{length} attribute is handled specially. The +way to compute the length of an @code{asm} insn is to multiply the +length specified in the expression @code{define_asm_attributes} by the +number of machine instructions specified in the @code{asm} statement, +determined by counting the number of semicolons and newlines in the +string. Therefore, the value of the @code{length} attribute specified +in a @code{define_asm_attributes} should be the maximum possible length +of a single machine instruction. + +@end ifset +@ifset INTERNALS +@node Attr Example +@subsection Example of Attribute Specifications +@cindex attribute specifications example +@cindex attribute specifications + +The judicious use of defaulting is important in the efficient use of +insn attributes. Typically, insns are divided into @dfn{types} and an +attribute, customarily called @code{type}, is used to represent this +value. This attribute is normally used only to define the default value +for other attributes. An example will clarify this usage. + +Assume we have a RISC machine with a condition code and in which only +full-word operations are performed in registers. Let us assume that we +can divide all insns into loads, stores, (integer) arithmetic +operations, floating point operations, and branches. + +Here we will concern ourselves with determining the effect of an insn on +the condition code and will limit ourselves to the following possible +effects: The condition code can be set unpredictably (clobbered), not +be changed, be set to agree with the results of the operation, or only +changed if the item previously set into the condition code has been +modified. + +Here is part of a sample @file{md} file for such a machine: + +@smallexample +(define_attr "type" "load,store,arith,fp,branch" (const_string "arith")) + +(define_attr "cc" "clobber,unchanged,set,change0" + (cond [(eq_attr "type" "load") + (const_string "change0") + (eq_attr "type" "store,branch") + (const_string "unchanged") + (eq_attr "type" "arith") + (if_then_else (match_operand:SI 0 "" "") + (const_string "set") + (const_string "clobber"))] + (const_string "clobber"))) + +(define_insn "" + [(set (match_operand:SI 0 "general_operand" "=r,r,m") + (match_operand:SI 1 "general_operand" "r,m,r"))] + "" + "@@ + move %0,%1 + load %0,%1 + store %0,%1" + [(set_attr "type" "arith,load,store")]) +@end smallexample + +Note that we assume in the above example that arithmetic operations +performed on quantities smaller than a machine word clobber the condition +code since they will set the condition code to a value corresponding to the +full-word result. + +@end ifset +@ifset INTERNALS +@node Insn Lengths +@subsection Computing the Length of an Insn +@cindex insn lengths, computing +@cindex computing the length of an insn + +For many machines, multiple types of branch instructions are provided, each +for different length branch displacements. In most cases, the assembler +will choose the correct instruction to use. However, when the assembler +cannot do so, GCC can when a special attribute, the @code{length} +attribute, is defined. This attribute must be defined to have numeric +values by specifying a null string in its @code{define_attr}. + +In the case of the @code{length} attribute, two additional forms of +arithmetic terms are allowed in test expressions: + +@table @code +@cindex @code{match_dup} and attributes +@item (match_dup @var{n}) +This refers to the address of operand @var{n} of the current insn, which +must be a @code{label_ref}. + +@cindex @code{pc} and attributes +@item (pc) +For non-branch instructions and backward branch instructions, this refers +to the address of the current insn. But for forward branch instructions, +this refers to the address of the next insn, because the length of the +current insn is to be computed. +@end table + +@cindex @code{addr_vec}, length of +@cindex @code{addr_diff_vec}, length of +For normal insns, the length will be determined by value of the +@code{length} attribute. In the case of @code{addr_vec} and +@code{addr_diff_vec} insn patterns, the length is computed as +the number of vectors multiplied by the size of each vector. + +Lengths are measured in addressable storage units (bytes). + +Note that it is possible to call functions via the @code{symbol_ref} +mechanism to compute the length of an insn. However, if you use this +mechanism you must provide dummy clauses to express the maximum length +without using the function call. You can see an example of this in the +@code{pa} machine description for the @code{call_symref} pattern. + +The following macros can be used to refine the length computation: + +@table @code +@findex ADJUST_INSN_LENGTH +@item ADJUST_INSN_LENGTH (@var{insn}, @var{length}) +If defined, modifies the length assigned to instruction @var{insn} as a +function of the context in which it is used. @var{length} is an lvalue +that contains the initially computed length of the insn and should be +updated with the correct length of the insn. + +This macro will normally not be required. A case in which it is +required is the ROMP@. On this machine, the size of an @code{addr_vec} +insn must be increased by two to compensate for the fact that alignment +may be required. +@end table + +@findex get_attr_length +The routine that returns @code{get_attr_length} (the value of the +@code{length} attribute) can be used by the output routine to +determine the form of the branch instruction to be written, as the +example below illustrates. + +As an example of the specification of variable-length branches, consider +the IBM 360. If we adopt the convention that a register will be set to +the starting address of a function, we can jump to labels within 4k of +the start using a four-byte instruction. Otherwise, we need a six-byte +sequence to load the address from memory and then branch to it. + +On such a machine, a pattern for a branch instruction might be specified +as follows: + +@smallexample +(define_insn "jump" + [(set (pc) + (label_ref (match_operand 0 "" "")))] + "" +@{ + return (get_attr_length (insn) == 4 + ? "b %l0" : "l r15,=a(%l0); br r15"); +@} + [(set (attr "length") + (if_then_else (lt (match_dup 0) (const_int 4096)) + (const_int 4) + (const_int 6)))]) +@end smallexample + +@end ifset +@ifset INTERNALS +@node Constant Attributes +@subsection Constant Attributes +@cindex constant attributes + +A special form of @code{define_attr}, where the expression for the +default value is a @code{const} expression, indicates an attribute that +is constant for a given run of the compiler. Constant attributes may be +used to specify which variety of processor is used. For example, + +@smallexample +(define_attr "cpu" "m88100,m88110,m88000" + (const + (cond [(symbol_ref "TARGET_88100") (const_string "m88100") + (symbol_ref "TARGET_88110") (const_string "m88110")] + (const_string "m88000")))) + +(define_attr "memory" "fast,slow" + (const + (if_then_else (symbol_ref "TARGET_FAST_MEM") + (const_string "fast") + (const_string "slow")))) +@end smallexample + +The routine generated for constant attributes has no parameters as it +does not depend on any particular insn. RTL expressions used to define +the value of a constant attribute may use the @code{symbol_ref} form, +but may not use either the @code{match_operand} form or @code{eq_attr} +forms involving insn attributes. + +@end ifset +@ifset INTERNALS +@node Mnemonic Attribute +@subsection Mnemonic Attribute +@cindex mnemonic attribute + +The @code{mnemonic} attribute is a string type attribute holding the +instruction mnemonic for an insn alternative. The attribute values +will automatically be generated by the machine description parser if +there is an attribute definition in the md file: + +@smallexample +(define_attr "mnemonic" "unknown" (const_string "unknown")) +@end smallexample + +The default value can be freely chosen as long as it does not collide +with any of the instruction mnemonics. This value will be used +whenever the machine description parser is not able to determine the +mnemonic string. This might be the case for output templates +containing more than a single instruction as in +@code{"mvcle\t%0,%1,0\;jo\t.-4"}. + +The @code{mnemonic} attribute set is not generated automatically if the +instruction string is generated via C code. + +An existing @code{mnemonic} attribute set in an insn definition will not +be overriden by the md file parser. That way it is possible to +manually set the instruction mnemonics for the cases where the md file +parser fails to determine it automatically. + +The @code{mnemonic} attribute is useful for dealing with instruction +specific properties in the pipeline description without defining +additional insn attributes. + +@smallexample +(define_attr "ooo_expanded" "" + (cond [(eq_attr "mnemonic" "dlr,dsgr,d,dsgf,stam,dsgfr,dlgr") + (const_int 1)] + (const_int 0))) +@end smallexample + +@end ifset +@ifset INTERNALS +@node Delay Slots +@subsection Delay Slot Scheduling +@cindex delay slots, defining + +The insn attribute mechanism can be used to specify the requirements for +delay slots, if any, on a target machine. An instruction is said to +require a @dfn{delay slot} if some instructions that are physically +after the instruction are executed as if they were located before it. +Classic examples are branch and call instructions, which often execute +the following instruction before the branch or call is performed. + +On some machines, conditional branch instructions can optionally +@dfn{annul} instructions in the delay slot. This means that the +instruction will not be executed for certain branch outcomes. Both +instructions that annul if the branch is true and instructions that +annul if the branch is false are supported. + +Delay slot scheduling differs from instruction scheduling in that +determining whether an instruction needs a delay slot is dependent only +on the type of instruction being generated, not on data flow between the +instructions. See the next section for a discussion of data-dependent +instruction scheduling. + +@findex define_delay +The requirement of an insn needing one or more delay slots is indicated +via the @code{define_delay} expression. It has the following form: + +@smallexample +(define_delay @var{test} + [@var{delay-1} @var{annul-true-1} @var{annul-false-1} + @var{delay-2} @var{annul-true-2} @var{annul-false-2} + @dots{}]) +@end smallexample + +@var{test} is an attribute test that indicates whether this +@code{define_delay} applies to a particular insn. If so, the number of +required delay slots is determined by the length of the vector specified +as the second argument. An insn placed in delay slot @var{n} must +satisfy attribute test @var{delay-n}. @var{annul-true-n} is an +attribute test that specifies which insns may be annulled if the branch +is true. Similarly, @var{annul-false-n} specifies which insns in the +delay slot may be annulled if the branch is false. If annulling is not +supported for that delay slot, @code{(nil)} should be coded. + +For example, in the common case where branch and call insns require +a single delay slot, which may contain any insn other than a branch or +call, the following would be placed in the @file{md} file: + +@smallexample +(define_delay (eq_attr "type" "branch,call") + [(eq_attr "type" "!branch,call") (nil) (nil)]) +@end smallexample + +Multiple @code{define_delay} expressions may be specified. In this +case, each such expression specifies different delay slot requirements +and there must be no insn for which tests in two @code{define_delay} +expressions are both true. + +For example, if we have a machine that requires one delay slot for branches +but two for calls, no delay slot can contain a branch or call insn, +and any valid insn in the delay slot for the branch can be annulled if the +branch is true, we might represent this as follows: + +@smallexample +(define_delay (eq_attr "type" "branch") + [(eq_attr "type" "!branch,call") + (eq_attr "type" "!branch,call") + (nil)]) + +(define_delay (eq_attr "type" "call") + [(eq_attr "type" "!branch,call") (nil) (nil) + (eq_attr "type" "!branch,call") (nil) (nil)]) +@end smallexample +@c the above is *still* too long. --mew 4feb93 + +@end ifset +@ifset INTERNALS +@node Processor pipeline description +@subsection Specifying processor pipeline description +@cindex processor pipeline description +@cindex processor functional units +@cindex instruction latency time +@cindex interlock delays +@cindex data dependence delays +@cindex reservation delays +@cindex pipeline hazard recognizer +@cindex automaton based pipeline description +@cindex regular expressions +@cindex deterministic finite state automaton +@cindex automaton based scheduler +@cindex RISC +@cindex VLIW + +To achieve better performance, most modern processors +(super-pipelined, superscalar @acronym{RISC}, and @acronym{VLIW} +processors) have many @dfn{functional units} on which several +instructions can be executed simultaneously. An instruction starts +execution if its issue conditions are satisfied. If not, the +instruction is stalled until its conditions are satisfied. Such +@dfn{interlock (pipeline) delay} causes interruption of the fetching +of successor instructions (or demands nop instructions, e.g.@: for some +MIPS processors). + +There are two major kinds of interlock delays in modern processors. +The first one is a data dependence delay determining @dfn{instruction +latency time}. The instruction execution is not started until all +source data have been evaluated by prior instructions (there are more +complex cases when the instruction execution starts even when the data +are not available but will be ready in given time after the +instruction execution start). Taking the data dependence delays into +account is simple. The data dependence (true, output, and +anti-dependence) delay between two instructions is given by a +constant. In most cases this approach is adequate. The second kind +of interlock delays is a reservation delay. The reservation delay +means that two instructions under execution will be in need of shared +processors resources, i.e.@: buses, internal registers, and/or +functional units, which are reserved for some time. Taking this kind +of delay into account is complex especially for modern @acronym{RISC} +processors. + +The task of exploiting more processor parallelism is solved by an +instruction scheduler. For a better solution to this problem, the +instruction scheduler has to have an adequate description of the +processor parallelism (or @dfn{pipeline description}). GCC +machine descriptions describe processor parallelism and functional +unit reservations for groups of instructions with the aid of +@dfn{regular expressions}. + +The GCC instruction scheduler uses a @dfn{pipeline hazard recognizer} to +figure out the possibility of the instruction issue by the processor +on a given simulated processor cycle. The pipeline hazard recognizer is +automatically generated from the processor pipeline description. The +pipeline hazard recognizer generated from the machine description +is based on a deterministic finite state automaton (@acronym{DFA}): +the instruction issue is possible if there is a transition from one +automaton state to another one. This algorithm is very fast, and +furthermore, its speed is not dependent on processor +complexity@footnote{However, the size of the automaton depends on +processor complexity. To limit this effect, machine descriptions +can split orthogonal parts of the machine description among several +automata: but then, since each of these must be stepped independently, +this does cause a small decrease in the algorithm's performance.}. + +@cindex automaton based pipeline description +The rest of this section describes the directives that constitute +an automaton-based processor pipeline description. The order of +these constructions within the machine description file is not +important. + +@findex define_automaton +@cindex pipeline hazard recognizer +The following optional construction describes names of automata +generated and used for the pipeline hazards recognition. Sometimes +the generated finite state automaton used by the pipeline hazard +recognizer is large. If we use more than one automaton and bind functional +units to the automata, the total size of the automata is usually +less than the size of the single automaton. If there is no one such +construction, only one finite state automaton is generated. + +@smallexample +(define_automaton @var{automata-names}) +@end smallexample + +@var{automata-names} is a string giving names of the automata. The +names are separated by commas. All the automata should have unique names. +The automaton name is used in the constructions @code{define_cpu_unit} and +@code{define_query_cpu_unit}. + +@findex define_cpu_unit +@cindex processor functional units +Each processor functional unit used in the description of instruction +reservations should be described by the following construction. + +@smallexample +(define_cpu_unit @var{unit-names} [@var{automaton-name}]) +@end smallexample + +@var{unit-names} is a string giving the names of the functional units +separated by commas. Don't use name @samp{nothing}, it is reserved +for other goals. + +@var{automaton-name} is a string giving the name of the automaton with +which the unit is bound. The automaton should be described in +construction @code{define_automaton}. You should give +@dfn{automaton-name}, if there is a defined automaton. + +The assignment of units to automata are constrained by the uses of the +units in insn reservations. The most important constraint is: if a +unit reservation is present on a particular cycle of an alternative +for an insn reservation, then some unit from the same automaton must +be present on the same cycle for the other alternatives of the insn +reservation. The rest of the constraints are mentioned in the +description of the subsequent constructions. + +@findex define_query_cpu_unit +@cindex querying function unit reservations +The following construction describes CPU functional units analogously +to @code{define_cpu_unit}. The reservation of such units can be +queried for an automaton state. The instruction scheduler never +queries reservation of functional units for given automaton state. So +as a rule, you don't need this construction. This construction could +be used for future code generation goals (e.g.@: to generate +@acronym{VLIW} insn templates). + +@smallexample +(define_query_cpu_unit @var{unit-names} [@var{automaton-name}]) +@end smallexample + +@var{unit-names} is a string giving names of the functional units +separated by commas. + +@var{automaton-name} is a string giving the name of the automaton with +which the unit is bound. + +@findex define_insn_reservation +@cindex instruction latency time +@cindex regular expressions +@cindex data bypass +The following construction is the major one to describe pipeline +characteristics of an instruction. + +@smallexample +(define_insn_reservation @var{insn-name} @var{default_latency} + @var{condition} @var{regexp}) +@end smallexample + +@var{default_latency} is a number giving latency time of the +instruction. There is an important difference between the old +description and the automaton based pipeline description. The latency +time is used for all dependencies when we use the old description. In +the automaton based pipeline description, the given latency time is only +used for true dependencies. The cost of anti-dependencies is always +zero and the cost of output dependencies is the difference between +latency times of the producing and consuming insns (if the difference +is negative, the cost is considered to be zero). You can always +change the default costs for any description by using the target hook +@code{TARGET_SCHED_ADJUST_COST} (@pxref{Scheduling}). + +@var{insn-name} is a string giving the internal name of the insn. The +internal names are used in constructions @code{define_bypass} and in +the automaton description file generated for debugging. The internal +name has nothing in common with the names in @code{define_insn}. It is a +good practice to use insn classes described in the processor manual. + +@var{condition} defines what RTL insns are described by this +construction. You should remember that you will be in trouble if +@var{condition} for two or more different +@code{define_insn_reservation} constructions is TRUE for an insn. In +this case what reservation will be used for the insn is not defined. +Such cases are not checked during generation of the pipeline hazards +recognizer because in general recognizing that two conditions may have +the same value is quite difficult (especially if the conditions +contain @code{symbol_ref}). It is also not checked during the +pipeline hazard recognizer work because it would slow down the +recognizer considerably. + +@var{regexp} is a string describing the reservation of the cpu's functional +units by the instruction. The reservations are described by a regular +expression according to the following syntax: + +@smallexample + regexp = regexp "," oneof + | oneof + + oneof = oneof "|" allof + | allof + + allof = allof "+" repeat + | repeat + + repeat = element "*" number + | element + + element = cpu_function_unit_name + | reservation_name + | result_name + | "nothing" + | "(" regexp ")" +@end smallexample + +@itemize @bullet +@item +@samp{,} is used for describing the start of the next cycle in +the reservation. + +@item +@samp{|} is used for describing a reservation described by the first +regular expression @strong{or} a reservation described by the second +regular expression @strong{or} etc. + +@item +@samp{+} is used for describing a reservation described by the first +regular expression @strong{and} a reservation described by the +second regular expression @strong{and} etc. + +@item +@samp{*} is used for convenience and simply means a sequence in which +the regular expression are repeated @var{number} times with cycle +advancing (see @samp{,}). + +@item +@samp{cpu_function_unit_name} denotes reservation of the named +functional unit. + +@item +@samp{reservation_name} --- see description of construction +@samp{define_reservation}. + +@item +@samp{nothing} denotes no unit reservations. +@end itemize + +@findex define_reservation +Sometimes unit reservations for different insns contain common parts. +In such case, you can simplify the pipeline description by describing +the common part by the following construction + +@smallexample +(define_reservation @var{reservation-name} @var{regexp}) +@end smallexample + +@var{reservation-name} is a string giving name of @var{regexp}. +Functional unit names and reservation names are in the same name +space. So the reservation names should be different from the +functional unit names and cannot be the reserved name @samp{nothing}. + +@findex define_bypass +@cindex instruction latency time +@cindex data bypass +The following construction is used to describe exceptions in the +latency time for given instruction pair. This is so called bypasses. + +@smallexample +(define_bypass @var{number} @var{out_insn_names} @var{in_insn_names} + [@var{guard}]) +@end smallexample + +@var{number} defines when the result generated by the instructions +given in string @var{out_insn_names} will be ready for the +instructions given in string @var{in_insn_names}. Each of these +strings is a comma-separated list of filename-style globs and +they refer to the names of @code{define_insn_reservation}s. +For example: +@smallexample +(define_bypass 1 "cpu1_load_*, cpu1_store_*" "cpu1_load_*") +@end smallexample +defines a bypass between instructions that start with +@samp{cpu1_load_} or @samp{cpu1_store_} and those that start with +@samp{cpu1_load_}. + +@var{guard} is an optional string giving the name of a C function which +defines an additional guard for the bypass. The function will get the +two insns as parameters. If the function returns zero the bypass will +be ignored for this case. The additional guard is necessary to +recognize complicated bypasses, e.g.@: when the consumer is only an address +of insn @samp{store} (not a stored value). + +If there are more one bypass with the same output and input insns, the +chosen bypass is the first bypass with a guard in description whose +guard function returns nonzero. If there is no such bypass, then +bypass without the guard function is chosen. + +@findex exclusion_set +@findex presence_set +@findex final_presence_set +@findex absence_set +@findex final_absence_set +@cindex VLIW +@cindex RISC +The following five constructions are usually used to describe +@acronym{VLIW} processors, or more precisely, to describe a placement +of small instructions into @acronym{VLIW} instruction slots. They +can be used for @acronym{RISC} processors, too. + +@smallexample +(exclusion_set @var{unit-names} @var{unit-names}) +(presence_set @var{unit-names} @var{patterns}) +(final_presence_set @var{unit-names} @var{patterns}) +(absence_set @var{unit-names} @var{patterns}) +(final_absence_set @var{unit-names} @var{patterns}) +@end smallexample + +@var{unit-names} is a string giving names of functional units +separated by commas. + +@var{patterns} is a string giving patterns of functional units +separated by comma. Currently pattern is one unit or units +separated by white-spaces. + +The first construction (@samp{exclusion_set}) means that each +functional unit in the first string cannot be reserved simultaneously +with a unit whose name is in the second string and vice versa. For +example, the construction is useful for describing processors +(e.g.@: some SPARC processors) with a fully pipelined floating point +functional unit which can execute simultaneously only single floating +point insns or only double floating point insns. + +The second construction (@samp{presence_set}) means that each +functional unit in the first string cannot be reserved unless at +least one of pattern of units whose names are in the second string is +reserved. This is an asymmetric relation. For example, it is useful +for description that @acronym{VLIW} @samp{slot1} is reserved after +@samp{slot0} reservation. We could describe it by the following +construction + +@smallexample +(presence_set "slot1" "slot0") +@end smallexample + +Or @samp{slot1} is reserved only after @samp{slot0} and unit @samp{b0} +reservation. In this case we could write + +@smallexample +(presence_set "slot1" "slot0 b0") +@end smallexample + +The third construction (@samp{final_presence_set}) is analogous to +@samp{presence_set}. The difference between them is when checking is +done. When an instruction is issued in given automaton state +reflecting all current and planned unit reservations, the automaton +state is changed. The first state is a source state, the second one +is a result state. Checking for @samp{presence_set} is done on the +source state reservation, checking for @samp{final_presence_set} is +done on the result reservation. This construction is useful to +describe a reservation which is actually two subsequent reservations. +For example, if we use + +@smallexample +(presence_set "slot1" "slot0") +@end smallexample + +the following insn will be never issued (because @samp{slot1} requires +@samp{slot0} which is absent in the source state). + +@smallexample +(define_reservation "insn_and_nop" "slot0 + slot1") +@end smallexample + +but it can be issued if we use analogous @samp{final_presence_set}. + +The forth construction (@samp{absence_set}) means that each functional +unit in the first string can be reserved only if each pattern of units +whose names are in the second string is not reserved. This is an +asymmetric relation (actually @samp{exclusion_set} is analogous to +this one but it is symmetric). For example it might be useful in a +@acronym{VLIW} description to say that @samp{slot0} cannot be reserved +after either @samp{slot1} or @samp{slot2} have been reserved. This +can be described as: + +@smallexample +(absence_set "slot0" "slot1, slot2") +@end smallexample + +Or @samp{slot2} cannot be reserved if @samp{slot0} and unit @samp{b0} +are reserved or @samp{slot1} and unit @samp{b1} are reserved. In +this case we could write + +@smallexample +(absence_set "slot2" "slot0 b0, slot1 b1") +@end smallexample + +All functional units mentioned in a set should belong to the same +automaton. + +The last construction (@samp{final_absence_set}) is analogous to +@samp{absence_set} but checking is done on the result (state) +reservation. See comments for @samp{final_presence_set}. + +@findex automata_option +@cindex deterministic finite state automaton +@cindex nondeterministic finite state automaton +@cindex finite state automaton minimization +You can control the generator of the pipeline hazard recognizer with +the following construction. + +@smallexample +(automata_option @var{options}) +@end smallexample + +@var{options} is a string giving options which affect the generated +code. Currently there are the following options: + +@itemize @bullet +@item +@dfn{no-minimization} makes no minimization of the automaton. This is +only worth to do when we are debugging the description and need to +look more accurately at reservations of states. + +@item +@dfn{time} means printing time statistics about the generation of +automata. + +@item +@dfn{stats} means printing statistics about the generated automata +such as the number of DFA states, NDFA states and arcs. + +@item +@dfn{v} means a generation of the file describing the result automata. +The file has suffix @samp{.dfa} and can be used for the description +verification and debugging. + +@item +@dfn{w} means a generation of warning instead of error for +non-critical errors. + +@item +@dfn{no-comb-vect} prevents the automaton generator from generating +two data structures and comparing them for space efficiency. Using +a comb vector to represent transitions may be better, but it can be +very expensive to construct. This option is useful if the build +process spends an unacceptably long time in genautomata. + +@item +@dfn{ndfa} makes nondeterministic finite state automata. This affects +the treatment of operator @samp{|} in the regular expressions. The +usual treatment of the operator is to try the first alternative and, +if the reservation is not possible, the second alternative. The +nondeterministic treatment means trying all alternatives, some of them +may be rejected by reservations in the subsequent insns. + +@item +@dfn{collapse-ndfa} modifies the behavior of the generator when +producing an automaton. An additional state transition to collapse a +nondeterministic @acronym{NDFA} state to a deterministic @acronym{DFA} +state is generated. It can be triggered by passing @code{const0_rtx} to +state_transition. In such an automaton, cycle advance transitions are +available only for these collapsed states. This option is useful for +ports that want to use the @code{ndfa} option, but also want to use +@code{define_query_cpu_unit} to assign units to insns issued in a cycle. + +@item +@dfn{progress} means output of a progress bar showing how many states +were generated so far for automaton being processed. This is useful +during debugging a @acronym{DFA} description. If you see too many +generated states, you could interrupt the generator of the pipeline +hazard recognizer and try to figure out a reason for generation of the +huge automaton. +@end itemize + +As an example, consider a superscalar @acronym{RISC} machine which can +issue three insns (two integer insns and one floating point insn) on +the cycle but can finish only two insns. To describe this, we define +the following functional units. + +@smallexample +(define_cpu_unit "i0_pipeline, i1_pipeline, f_pipeline") +(define_cpu_unit "port0, port1") +@end smallexample + +All simple integer insns can be executed in any integer pipeline and +their result is ready in two cycles. The simple integer insns are +issued into the first pipeline unless it is reserved, otherwise they +are issued into the second pipeline. Integer division and +multiplication insns can be executed only in the second integer +pipeline and their results are ready correspondingly in 9 and 4 +cycles. The integer division is not pipelined, i.e.@: the subsequent +integer division insn cannot be issued until the current division +insn finished. Floating point insns are fully pipelined and their +results are ready in 3 cycles. Where the result of a floating point +insn is used by an integer insn, an additional delay of one cycle is +incurred. To describe all of this we could specify + +@smallexample +(define_cpu_unit "div") + +(define_insn_reservation "simple" 2 (eq_attr "type" "int") + "(i0_pipeline | i1_pipeline), (port0 | port1)") + +(define_insn_reservation "mult" 4 (eq_attr "type" "mult") + "i1_pipeline, nothing*2, (port0 | port1)") + +(define_insn_reservation "div" 9 (eq_attr "type" "div") + "i1_pipeline, div*7, div + (port0 | port1)") + +(define_insn_reservation "float" 3 (eq_attr "type" "float") + "f_pipeline, nothing, (port0 | port1)) + +(define_bypass 4 "float" "simple,mult,div") +@end smallexample + +To simplify the description we could describe the following reservation + +@smallexample +(define_reservation "finish" "port0|port1") +@end smallexample + +and use it in all @code{define_insn_reservation} as in the following +construction + +@smallexample +(define_insn_reservation "simple" 2 (eq_attr "type" "int") + "(i0_pipeline | i1_pipeline), finish") +@end smallexample + + +@end ifset +@ifset INTERNALS +@node Conditional Execution +@section Conditional Execution +@cindex conditional execution +@cindex predication + +A number of architectures provide for some form of conditional +execution, or predication. The hallmark of this feature is the +ability to nullify most of the instructions in the instruction set. +When the instruction set is large and not entirely symmetric, it +can be quite tedious to describe these forms directly in the +@file{.md} file. An alternative is the @code{define_cond_exec} template. + +@findex define_cond_exec +@smallexample +(define_cond_exec + [@var{predicate-pattern}] + "@var{condition}" + "@var{output-template}" + "@var{optional-insn-attribues}") +@end smallexample + +@var{predicate-pattern} is the condition that must be true for the +insn to be executed at runtime and should match a relational operator. +One can use @code{match_operator} to match several relational operators +at once. Any @code{match_operand} operands must have no more than one +alternative. + +@var{condition} is a C expression that must be true for the generated +pattern to match. + +@findex current_insn_predicate +@var{output-template} is a string similar to the @code{define_insn} +output template (@pxref{Output Template}), except that the @samp{*} +and @samp{@@} special cases do not apply. This is only useful if the +assembly text for the predicate is a simple prefix to the main insn. +In order to handle the general case, there is a global variable +@code{current_insn_predicate} that will contain the entire predicate +if the current insn is predicated, and will otherwise be @code{NULL}. + +@var{optional-insn-attributes} is an optional vector of attributes that gets +appended to the insn attributes of the produced cond_exec rtx. It can +be used to add some distinguishing attribute to cond_exec rtxs produced +that way. An example usage would be to use this attribute in conjunction +with attributes on the main pattern to disable particular alternatives under +certain conditions. + +When @code{define_cond_exec} is used, an implicit reference to +the @code{predicable} instruction attribute is made. +@xref{Insn Attributes}. This attribute must be a boolean (i.e.@: have +exactly two elements in its @var{list-of-values}), with the possible +values being @code{no} and @code{yes}. The default and all uses in +the insns must be a simple constant, not a complex expressions. It +may, however, depend on the alternative, by using a comma-separated +list of values. If that is the case, the port should also define an +@code{enabled} attribute (@pxref{Disable Insn Alternatives}), which +should also allow only @code{no} and @code{yes} as its values. + +For each @code{define_insn} for which the @code{predicable} +attribute is true, a new @code{define_insn} pattern will be +generated that matches a predicated version of the instruction. +For example, + +@smallexample +(define_insn "addsi" + [(set (match_operand:SI 0 "register_operand" "r") + (plus:SI (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r")))] + "@var{test1}" + "add %2,%1,%0") + +(define_cond_exec + [(ne (match_operand:CC 0 "register_operand" "c") + (const_int 0))] + "@var{test2}" + "(%0)") +@end smallexample + +@noindent +generates a new pattern + +@smallexample +(define_insn "" + [(cond_exec + (ne (match_operand:CC 3 "register_operand" "c") (const_int 0)) + (set (match_operand:SI 0 "register_operand" "r") + (plus:SI (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r"))))] + "(@var{test2}) && (@var{test1})" + "(%3) add %2,%1,%0") +@end smallexample + +@end ifset +@ifset INTERNALS +@node Define Subst +@section RTL Templates Transformations +@cindex define_subst + +For some hardware architectures there are common cases when the RTL +templates for the instructions can be derived from the other RTL +templates using simple transformations. E.g., @file{i386.md} contains +an RTL template for the ordinary @code{sub} instruction--- +@code{*subsi_1}, and for the @code{sub} instruction with subsequent +zero-extension---@code{*subsi_1_zext}. Such cases can be easily +implemented by a single meta-template capable of generating a modified +case based on the initial one: + +@findex define_subst +@smallexample +(define_subst "@var{name}" + [@var{input-template}] + "@var{condition}" + [@var{output-template}]) +@end smallexample +@var{input-template} is a pattern describing the source RTL template, +which will be transformed. + +@var{condition} is a C expression that is conjunct with the condition +from the input-template to generate a condition to be used in the +output-template. + +@var{output-template} is a pattern that will be used in the resulting +template. + +@code{define_subst} mechanism is tightly coupled with the notion of the +subst attribute (@pxref{Subst Iterators}). The use of +@code{define_subst} is triggered by a reference to a subst attribute in +the transforming RTL template. This reference initiates duplication of +the source RTL template and substitution of the attributes with their +values. The source RTL template is left unchanged, while the copy is +transformed by @code{define_subst}. This transformation can fail in the +case when the source RTL template is not matched against the +input-template of the @code{define_subst}. In such case the copy is +deleted. + +@code{define_subst} can be used only in @code{define_insn} and +@code{define_expand}, it cannot be used in other expressions (e.g.@: in +@code{define_insn_and_split}). + +@menu +* Define Subst Example:: Example of @code{define_subst} work. +* Define Subst Pattern Matching:: Process of template comparison. +* Define Subst Output Template:: Generation of output template. +@end menu + +@node Define Subst Example +@subsection @code{define_subst} Example +@cindex define_subst + +To illustrate how @code{define_subst} works, let us examine a simple +template transformation. + +Suppose there are two kinds of instructions: one that touches flags and +the other that does not. The instructions of the second type could be +generated with the following @code{define_subst}: + +@smallexample +(define_subst "add_clobber_subst" + [(set (match_operand:SI 0 "" "") + (match_operand:SI 1 "" ""))] + "" + [(set (match_dup 0) + (match_dup 1)) + (clobber (reg:CC FLAGS_REG))]) +@end smallexample + +This @code{define_subst} can be applied to any RTL pattern containing +@code{set} of mode SI and generates a copy with clobber when it is +applied. + +Assume there is an RTL template for a @code{max} instruction to be used +in @code{define_subst} mentioned above: + +@smallexample +(define_insn "maxsi" + [(set (match_operand:SI 0 "register_operand" "=r") + (max:SI + (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r")))] + "" + "max\t@{%2, %1, %0|%0, %1, %2@}" + [@dots{}]) +@end smallexample + +To mark the RTL template for @code{define_subst} application, +subst-attributes are used. They should be declared in advance: + +@smallexample +(define_subst_attr "add_clobber_name" "add_clobber_subst" "_noclobber" "_clobber") +@end smallexample + +Here @samp{add_clobber_name} is the attribute name, +@samp{add_clobber_subst} is the name of the corresponding +@code{define_subst}, the third argument (@samp{_noclobber}) is the +attribute value that would be substituted into the unchanged version of +the source RTL template, and the last argument (@samp{_clobber}) is the +value that would be substituted into the second, transformed, +version of the RTL template. + +Once the subst-attribute has been defined, it should be used in RTL +templates which need to be processed by the @code{define_subst}. So, +the original RTL template should be changed: + +@smallexample +(define_insn "maxsi" + [(set (match_operand:SI 0 "register_operand" "=r") + (max:SI + (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r")))] + "" + "max\t@{%2, %1, %0|%0, %1, %2@}" + [@dots{}]) +@end smallexample + +The result of the @code{define_subst} usage would look like the following: + +@smallexample +(define_insn "maxsi_noclobber" + [(set (match_operand:SI 0 "register_operand" "=r") + (max:SI + (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r")))] + "" + "max\t@{%2, %1, %0|%0, %1, %2@}" + [@dots{}]) +(define_insn "maxsi_clobber" + [(set (match_operand:SI 0 "register_operand" "=r") + (max:SI + (match_operand:SI 1 "register_operand" "r") + (match_operand:SI 2 "register_operand" "r"))) + (clobber (reg:CC FLAGS_REG))] + "" + "max\t@{%2, %1, %0|%0, %1, %2@}" + [@dots{}]) +@end smallexample + +@node Define Subst Pattern Matching +@subsection Pattern Matching in @code{define_subst} +@cindex define_subst + +All expressions, allowed in @code{define_insn} or @code{define_expand}, +are allowed in the input-template of @code{define_subst}, except +@code{match_par_dup}, @code{match_scratch}, @code{match_parallel}. The +meanings of expressions in the input-template were changed: + +@code{match_operand} matches any expression (possibly, a subtree in +RTL-template), if modes of the @code{match_operand} and this expression +are the same, or mode of the @code{match_operand} is @code{VOIDmode}, or +this expression is @code{match_dup}, @code{match_op_dup}. If the +expression is @code{match_operand} too, and predicate of +@code{match_operand} from the input pattern is not empty, then the +predicates are compared. That can be used for more accurate filtering +of accepted RTL-templates. + +@code{match_operator} matches common operators (like @code{plus}, +@code{minus}), @code{unspec}, @code{unspec_volatile} operators and +@code{match_operator}s from the original pattern if the modes match and +@code{match_operator} from the input pattern has the same number of +operands as the operator from the original pattern. + +@node Define Subst Output Template +@subsection Generation of output template in @code{define_subst} +@cindex define_subst + +If all necessary checks for @code{define_subst} application pass, a new +RTL-pattern, based on the output-template, is created to replace the old +template. Like in input-patterns, meanings of some RTL expressions are +changed when they are used in output-patterns of a @code{define_subst}. +Thus, @code{match_dup} is used for copying the whole expression from the +original pattern, which matched corresponding @code{match_operand} from +the input pattern. + +@code{match_dup N} is used in the output template to be replaced with +the expression from the original pattern, which matched +@code{match_operand N} from the input pattern. As a consequence, +@code{match_dup} cannot be used to point to @code{match_operand}s from +the output pattern, it should always refer to a @code{match_operand} +from the input pattern. If a @code{match_dup N} occurs more than once +in the output template, its first occurrence is replaced with the +expression from the original pattern, and the subsequent expressions +are replaced with @code{match_dup N}, i.e., a reference to the first +expression. + +In the output template one can refer to the expressions from the +original pattern and create new ones. For instance, some operands could +be added by means of standard @code{match_operand}. + +After replacing @code{match_dup} with some RTL-subtree from the original +pattern, it could happen that several @code{match_operand}s in the +output pattern have the same indexes. It is unknown, how many and what +indexes would be used in the expression which would replace +@code{match_dup}, so such conflicts in indexes are inevitable. To +overcome this issue, @code{match_operands} and @code{match_operators}, +which were introduced into the output pattern, are renumerated when all +@code{match_dup}s are replaced. + +Number of alternatives in @code{match_operand}s introduced into the +output template @code{M} could differ from the number of alternatives in +the original pattern @code{N}, so in the resultant pattern there would +be @code{N*M} alternatives. Thus, constraints from the original pattern +would be duplicated @code{N} times, constraints from the output pattern +would be duplicated @code{M} times, producing all possible combinations. +@end ifset + +@ifset INTERNALS +@node Constant Definitions +@section Constant Definitions +@cindex constant definitions +@findex define_constants + +Using literal constants inside instruction patterns reduces legibility and +can be a maintenance problem. + +To overcome this problem, you may use the @code{define_constants} +expression. It contains a vector of name-value pairs. From that +point on, wherever any of the names appears in the MD file, it is as +if the corresponding value had been written instead. You may use +@code{define_constants} multiple times; each appearance adds more +constants to the table. It is an error to redefine a constant with +a different value. + +To come back to the a29k load multiple example, instead of + +@smallexample +(define_insn "" + [(match_parallel 0 "load_multiple_operation" + [(set (match_operand:SI 1 "gpc_reg_operand" "=r") + (match_operand:SI 2 "memory_operand" "m")) + (use (reg:SI 179)) + (clobber (reg:SI 179))])] + "" + "loadm 0,0,%1,%2") +@end smallexample + +You could write: + +@smallexample +(define_constants [ + (R_BP 177) + (R_FC 178) + (R_CR 179) + (R_Q 180) +]) + +(define_insn "" + [(match_parallel 0 "load_multiple_operation" + [(set (match_operand:SI 1 "gpc_reg_operand" "=r") + (match_operand:SI 2 "memory_operand" "m")) + (use (reg:SI R_CR)) + (clobber (reg:SI R_CR))])] + "" + "loadm 0,0,%1,%2") +@end smallexample + +The constants that are defined with a define_constant are also output +in the insn-codes.h header file as #defines. + +@cindex enumerations +@findex define_c_enum +You can also use the machine description file to define enumerations. +Like the constants defined by @code{define_constant}, these enumerations +are visible to both the machine description file and the main C code. + +The syntax is as follows: + +@smallexample +(define_c_enum "@var{name}" [ + @var{value0} + @var{value1} + (@var{value32} 32) + @var{value33} + @dots{} + @var{valuen} +]) +@end smallexample + +This definition causes the equivalent of the following C code to appear +in @file{insn-constants.h}: + +@smallexample +enum @var{name} @{ + @var{value0} = 0, + @var{value1} = 1, + @var{value32} = 32, + @var{value33} = 33, + @dots{} + @var{valuen} = @var{n} +@}; +#define NUM_@var{cname}_VALUES (@var{n} + 1) +@end smallexample + +where @var{cname} is the capitalized form of @var{name}. +It also makes each @var{valuei} available in the machine description +file, just as if it had been declared with: + +@smallexample +(define_constants [(@var{valuei} @var{i})]) +@end smallexample + +Each @var{valuei} is usually an upper-case identifier and usually +begins with @var{cname}. + +You can split the enumeration definition into as many statements as +you like. The above example is directly equivalent to: + +@smallexample +(define_c_enum "@var{name}" [@var{value0}]) +(define_c_enum "@var{name}" [@var{value1}]) +@dots{} +(define_c_enum "@var{name}" [@var{valuen}]) +@end smallexample + +Splitting the enumeration helps to improve the modularity of each +individual @code{.md} file. For example, if a port defines its +synchronization instructions in a separate @file{sync.md} file, +it is convenient to define all synchronization-specific enumeration +values in @file{sync.md} rather than in the main @file{.md} file. + +Some enumeration names have special significance to GCC: + +@table @code +@item unspecv +@findex unspec_volatile +If an enumeration called @code{unspecv} is defined, GCC will use it +when printing out @code{unspec_volatile} expressions. For example: + +@smallexample +(define_c_enum "unspecv" [ + UNSPECV_BLOCKAGE +]) +@end smallexample + +causes GCC to print @samp{(unspec_volatile @dots{} 0)} as: + +@smallexample +(unspec_volatile ... UNSPECV_BLOCKAGE) +@end smallexample + +@item unspec +@findex unspec +If an enumeration called @code{unspec} is defined, GCC will use +it when printing out @code{unspec} expressions. GCC will also use +it when printing out @code{unspec_volatile} expressions unless an +@code{unspecv} enumeration is also defined. You can therefore +decide whether to keep separate enumerations for volatile and +non-volatile expressions or whether to use the same enumeration +for both. +@end table + +@findex define_enum +@anchor{define_enum} +Another way of defining an enumeration is to use @code{define_enum}: + +@smallexample +(define_enum "@var{name}" [ + @var{value0} + @var{value1} + @dots{} + @var{valuen} +]) +@end smallexample + +This directive implies: + +@smallexample +(define_c_enum "@var{name}" [ + @var{cname}_@var{cvalue0} + @var{cname}_@var{cvalue1} + @dots{} + @var{cname}_@var{cvaluen} +]) +@end smallexample + +@findex define_enum_attr +where @var{cvaluei} is the capitalized form of @var{valuei}. +However, unlike @code{define_c_enum}, the enumerations defined +by @code{define_enum} can be used in attribute specifications +(@pxref{define_enum_attr}). +@end ifset +@ifset INTERNALS +@node Iterators +@section Iterators +@cindex iterators in @file{.md} files + +Ports often need to define similar patterns for more than one machine +mode or for more than one rtx code. GCC provides some simple iterator +facilities to make this process easier. + +@menu +* Mode Iterators:: Generating variations of patterns for different modes. +* Code Iterators:: Doing the same for codes. +* Int Iterators:: Doing the same for integers. +* Subst Iterators:: Generating variations of patterns for define_subst. +* Parameterized Names:: Specifying iterator values in C++ code. +@end menu + +@node Mode Iterators +@subsection Mode Iterators +@cindex mode iterators in @file{.md} files + +Ports often need to define similar patterns for two or more different modes. +For example: + +@itemize @bullet +@item +If a processor has hardware support for both single and double +floating-point arithmetic, the @code{SFmode} patterns tend to be +very similar to the @code{DFmode} ones. + +@item +If a port uses @code{SImode} pointers in one configuration and +@code{DImode} pointers in another, it will usually have very similar +@code{SImode} and @code{DImode} patterns for manipulating pointers. +@end itemize + +Mode iterators allow several patterns to be instantiated from one +@file{.md} file template. They can be used with any type of +rtx-based construct, such as a @code{define_insn}, +@code{define_split}, or @code{define_peephole2}. + +@menu +* Defining Mode Iterators:: Defining a new mode iterator. +* Substitutions:: Combining mode iterators with substitutions +* Examples:: Examples +@end menu + +@node Defining Mode Iterators +@subsubsection Defining Mode Iterators +@findex define_mode_iterator + +The syntax for defining a mode iterator is: + +@smallexample +(define_mode_iterator @var{name} [(@var{mode1} "@var{cond1}") @dots{} (@var{moden} "@var{condn}")]) +@end smallexample + +This allows subsequent @file{.md} file constructs to use the mode suffix +@code{:@var{name}}. Every construct that does so will be expanded +@var{n} times, once with every use of @code{:@var{name}} replaced by +@code{:@var{mode1}}, once with every use replaced by @code{:@var{mode2}}, +and so on. In the expansion for a particular @var{modei}, every +C condition will also require that @var{condi} be true. + +For example: + +@smallexample +(define_mode_iterator P [(SI "Pmode == SImode") (DI "Pmode == DImode")]) +@end smallexample + +defines a new mode suffix @code{:P}. Every construct that uses +@code{:P} will be expanded twice, once with every @code{:P} replaced +by @code{:SI} and once with every @code{:P} replaced by @code{:DI}. +The @code{:SI} version will only apply if @code{Pmode == SImode} and +the @code{:DI} version will only apply if @code{Pmode == DImode}. + +As with other @file{.md} conditions, an empty string is treated +as ``always true''. @code{(@var{mode} "")} can also be abbreviated +to @code{@var{mode}}. For example: + +@smallexample +(define_mode_iterator GPR [SI (DI "TARGET_64BIT")]) +@end smallexample + +means that the @code{:DI} expansion only applies if @code{TARGET_64BIT} +but that the @code{:SI} expansion has no such constraint. + +Iterators are applied in the order they are defined. This can be +significant if two iterators are used in a construct that requires +substitutions. @xref{Substitutions}. + +@node Substitutions +@subsubsection Substitution in Mode Iterators +@findex define_mode_attr + +If an @file{.md} file construct uses mode iterators, each version of the +construct will often need slightly different strings or modes. For +example: + +@itemize @bullet +@item +When a @code{define_expand} defines several @code{add@var{m}3} patterns +(@pxref{Standard Names}), each expander will need to use the +appropriate mode name for @var{m}. + +@item +When a @code{define_insn} defines several instruction patterns, +each instruction will often use a different assembler mnemonic. + +@item +When a @code{define_insn} requires operands with different modes, +using an iterator for one of the operand modes usually requires a specific +mode for the other operand(s). +@end itemize + +GCC supports such variations through a system of ``mode attributes''. +There are two standard attributes: @code{mode}, which is the name of +the mode in lower case, and @code{MODE}, which is the same thing in +upper case. You can define other attributes using: + +@smallexample +(define_mode_attr @var{name} [(@var{mode1} "@var{value1}") @dots{} (@var{moden} "@var{valuen}")]) +@end smallexample + +where @var{name} is the name of the attribute and @var{valuei} +is the value associated with @var{modei}. + +When GCC replaces some @var{:iterator} with @var{:mode}, it will scan +each string and mode in the pattern for sequences of the form +@code{<@var{iterator}:@var{attr}>}, where @var{attr} is the name of a +mode attribute. If the attribute is defined for @var{mode}, the whole +@code{<@dots{}>} sequence will be replaced by the appropriate attribute +value. + +For example, suppose an @file{.md} file has: + +@smallexample +(define_mode_iterator P [(SI "Pmode == SImode") (DI "Pmode == DImode")]) +(define_mode_attr load [(SI "lw") (DI "ld")]) +@end smallexample + +If one of the patterns that uses @code{:P} contains the string +@code{"\t%0,%1"}, the @code{SI} version of that pattern +will use @code{"lw\t%0,%1"} and the @code{DI} version will use +@code{"ld\t%0,%1"}. + +Here is an example of using an attribute for a mode: + +@smallexample +(define_mode_iterator LONG [SI DI]) +(define_mode_attr SHORT [(SI "HI") (DI "SI")]) +(define_insn @dots{} + (sign_extend:LONG (match_operand: @dots{})) @dots{}) +@end smallexample + +The @code{@var{iterator}:} prefix may be omitted, in which case the +substitution will be attempted for every iterator expansion. + +@node Examples +@subsubsection Mode Iterator Examples + +Here is an example from the MIPS port. It defines the following +modes and attributes (among others): + +@smallexample +(define_mode_iterator GPR [SI (DI "TARGET_64BIT")]) +(define_mode_attr d [(SI "") (DI "d")]) +@end smallexample + +and uses the following template to define both @code{subsi3} +and @code{subdi3}: + +@smallexample +(define_insn "sub3" + [(set (match_operand:GPR 0 "register_operand" "=d") + (minus:GPR (match_operand:GPR 1 "register_operand" "d") + (match_operand:GPR 2 "register_operand" "d")))] + "" + "subu\t%0,%1,%2" + [(set_attr "type" "arith") + (set_attr "mode" "")]) +@end smallexample + +This is exactly equivalent to: + +@smallexample +(define_insn "subsi3" + [(set (match_operand:SI 0 "register_operand" "=d") + (minus:SI (match_operand:SI 1 "register_operand" "d") + (match_operand:SI 2 "register_operand" "d")))] + "" + "subu\t%0,%1,%2" + [(set_attr "type" "arith") + (set_attr "mode" "SI")]) + +(define_insn "subdi3" + [(set (match_operand:DI 0 "register_operand" "=d") + (minus:DI (match_operand:DI 1 "register_operand" "d") + (match_operand:DI 2 "register_operand" "d")))] + "TARGET_64BIT" + "dsubu\t%0,%1,%2" + [(set_attr "type" "arith") + (set_attr "mode" "DI")]) +@end smallexample + +@node Code Iterators +@subsection Code Iterators +@cindex code iterators in @file{.md} files +@findex define_code_iterator +@findex define_code_attr + +Code iterators operate in a similar way to mode iterators. @xref{Mode Iterators}. + +The construct: + +@smallexample +(define_code_iterator @var{name} [(@var{code1} "@var{cond1}") @dots{} (@var{coden} "@var{condn}")]) +@end smallexample + +defines a pseudo rtx code @var{name} that can be instantiated as +@var{codei} if condition @var{condi} is true. Each @var{codei} +must have the same rtx format. @xref{RTL Classes}. + +As with mode iterators, each pattern that uses @var{name} will be +expanded @var{n} times, once with all uses of @var{name} replaced by +@var{code1}, once with all uses replaced by @var{code2}, and so on. +@xref{Defining Mode Iterators}. + +It is possible to define attributes for codes as well as for modes. +There are two standard code attributes: @code{code}, the name of the +code in lower case, and @code{CODE}, the name of the code in upper case. +Other attributes are defined using: + +@smallexample +(define_code_attr @var{name} [(@var{code1} "@var{value1}") @dots{} (@var{coden} "@var{valuen}")]) +@end smallexample + +Instruction patterns can use code attributes as rtx codes, which can be +useful if two sets of codes act in tandem. For example, the following +@code{define_insn} defines two patterns, one calculating a signed absolute +difference and another calculating an unsigned absolute difference: + +@smallexample +(define_code_iterator any_max [smax umax]) +(define_code_attr paired_min [(smax "smin") (umax "umin")]) +(define_insn @dots{} + [(set (match_operand:SI 0 @dots{}) + (minus:SI (any_max:SI (match_operand:SI 1 @dots{}) + (match_operand:SI 2 @dots{})) + (:SI (match_dup 1) (match_dup 2))))] + @dots{}) +@end smallexample + +The signed version of the instruction uses @code{smax} and @code{smin} +while the unsigned version uses @code{umax} and @code{umin}. There +are no versions that pair @code{smax} with @code{umin} or @code{umax} +with @code{smin}. + +Here's an example of code iterators in action, taken from the MIPS port: + +@smallexample +(define_code_iterator any_cond [unordered ordered unlt unge uneq ltgt unle ungt + eq ne gt ge lt le gtu geu ltu leu]) + +(define_expand "b" + [(set (pc) + (if_then_else (any_cond:CC (cc0) + (const_int 0)) + (label_ref (match_operand 0 "")) + (pc)))] + "" +@{ + gen_conditional_branch (operands, ); + DONE; +@}) +@end smallexample + +This is equivalent to: + +@smallexample +(define_expand "bunordered" + [(set (pc) + (if_then_else (unordered:CC (cc0) + (const_int 0)) + (label_ref (match_operand 0 "")) + (pc)))] + "" +@{ + gen_conditional_branch (operands, UNORDERED); + DONE; +@}) + +(define_expand "bordered" + [(set (pc) + (if_then_else (ordered:CC (cc0) + (const_int 0)) + (label_ref (match_operand 0 "")) + (pc)))] + "" +@{ + gen_conditional_branch (operands, ORDERED); + DONE; +@}) + +@dots{} +@end smallexample + +@node Int Iterators +@subsection Int Iterators +@cindex int iterators in @file{.md} files +@findex define_int_iterator +@findex define_int_attr + +Int iterators operate in a similar way to code iterators. @xref{Code Iterators}. + +The construct: + +@smallexample +(define_int_iterator @var{name} [(@var{int1} "@var{cond1}") @dots{} (@var{intn} "@var{condn}")]) +@end smallexample + +defines a pseudo integer constant @var{name} that can be instantiated as +@var{inti} if condition @var{condi} is true. Each @var{int} must have the +same rtx format. @xref{RTL Classes}. Int iterators can appear in only +those rtx fields that have 'i', 'n', 'w', or 'p' as the specifier. This +means that each @var{int} has to be a constant defined using define_constant +or define_c_enum. + +As with mode and code iterators, each pattern that uses @var{name} will be +expanded @var{n} times, once with all uses of @var{name} replaced by +@var{int1}, once with all uses replaced by @var{int2}, and so on. +@xref{Defining Mode Iterators}. + +It is possible to define attributes for ints as well as for codes and modes. +Attributes are defined using: + +@smallexample +(define_int_attr @var{name} [(@var{int1} "@var{value1}") @dots{} (@var{intn} "@var{valuen}")]) +@end smallexample + +Here's an example of int iterators in action, taken from the ARM port: + +@smallexample +(define_int_iterator QABSNEG [UNSPEC_VQABS UNSPEC_VQNEG]) + +(define_int_attr absneg [(UNSPEC_VQABS "abs") (UNSPEC_VQNEG "neg")]) + +(define_insn "neon_vq" + [(set (match_operand:VDQIW 0 "s_register_operand" "=w") + (unspec:VDQIW [(match_operand:VDQIW 1 "s_register_operand" "w") + (match_operand:SI 2 "immediate_operand" "i")] + QABSNEG))] + "TARGET_NEON" + "vq.\t%0, %1" + [(set_attr "type" "neon_vqneg_vqabs")] +) + +@end smallexample + +This is equivalent to: + +@smallexample +(define_insn "neon_vqabs" + [(set (match_operand:VDQIW 0 "s_register_operand" "=w") + (unspec:VDQIW [(match_operand:VDQIW 1 "s_register_operand" "w") + (match_operand:SI 2 "immediate_operand" "i")] + UNSPEC_VQABS))] + "TARGET_NEON" + "vqabs.\t%0, %1" + [(set_attr "type" "neon_vqneg_vqabs")] +) + +(define_insn "neon_vqneg" + [(set (match_operand:VDQIW 0 "s_register_operand" "=w") + (unspec:VDQIW [(match_operand:VDQIW 1 "s_register_operand" "w") + (match_operand:SI 2 "immediate_operand" "i")] + UNSPEC_VQNEG))] + "TARGET_NEON" + "vqneg.\t%0, %1" + [(set_attr "type" "neon_vqneg_vqabs")] +) + +@end smallexample + +@node Subst Iterators +@subsection Subst Iterators +@cindex subst iterators in @file{.md} files +@findex define_subst +@findex define_subst_attr + +Subst iterators are special type of iterators with the following +restrictions: they could not be declared explicitly, they always have +only two values, and they do not have explicit dedicated name. +Subst-iterators are triggered only when corresponding subst-attribute is +used in RTL-pattern. + +Subst iterators transform templates in the following way: the templates +are duplicated, the subst-attributes in these templates are replaced +with the corresponding values, and a new attribute is implicitly added +to the given @code{define_insn}/@code{define_expand}. The name of the +added attribute matches the name of @code{define_subst}. Such +attributes are declared implicitly, and it is not allowed to have a +@code{define_attr} named as a @code{define_subst}. + +Each subst iterator is linked to a @code{define_subst}. It is declared +implicitly by the first appearance of the corresponding +@code{define_subst_attr}, and it is not allowed to define it explicitly. + +Declarations of subst-attributes have the following syntax: + +@findex define_subst_attr +@smallexample +(define_subst_attr "@var{name}" + "@var{subst-name}" + "@var{no-subst-value}" + "@var{subst-applied-value}") +@end smallexample + +@var{name} is a string with which the given subst-attribute could be +referred to. + +@var{subst-name} shows which @code{define_subst} should be applied to an +RTL-template if the given subst-attribute is present in the +RTL-template. + +@var{no-subst-value} is a value with which subst-attribute would be +replaced in the first copy of the original RTL-template. + +@var{subst-applied-value} is a value with which subst-attribute would be +replaced in the second copy of the original RTL-template. + +@node Parameterized Names +@subsection Parameterized Names +@cindex @samp{@@} in instruction pattern names +Ports sometimes need to apply iterators using C++ code, in order to +get the code or RTL pattern for a specific instruction. For example, +suppose we have the @samp{neon_vq} pattern given above: + +@smallexample +(define_int_iterator QABSNEG [UNSPEC_VQABS UNSPEC_VQNEG]) + +(define_int_attr absneg [(UNSPEC_VQABS "abs") (UNSPEC_VQNEG "neg")]) + +(define_insn "neon_vq" + [(set (match_operand:VDQIW 0 "s_register_operand" "=w") + (unspec:VDQIW [(match_operand:VDQIW 1 "s_register_operand" "w") + (match_operand:SI 2 "immediate_operand" "i")] + QABSNEG))] + @dots{} +) +@end smallexample + +A port might need to generate this pattern for a variable +@samp{QABSNEG} value and a variable @samp{VDQIW} mode. There are two +ways of doing this. The first is to build the rtx for the pattern +directly from C++ code; this is a valid technique and avoids any risk +of combinatorial explosion. The second is to prefix the instruction +name with the special character @samp{@@}, which tells GCC to generate +the four additional functions below. In each case, @var{name} is the +name of the instruction without the leading @samp{@@} character, +without the @samp{<@dots{}>} placeholders, and with any underscore +before a @samp{<@dots{}>} placeholder removed if keeping it would +lead to a double or trailing underscore. + +@table @samp +@item insn_code maybe_code_for_@var{name} (@var{i1}, @var{i2}, @dots{}) +See whether replacing the first @samp{<@dots{}>} placeholder with +iterator value @var{i1}, the second with iterator value @var{i2}, and +so on, gives a valid instruction. Return its code if so, otherwise +return @code{CODE_FOR_nothing}. + +@item insn_code code_for_@var{name} (@var{i1}, @var{i2}, @dots{}) +Same, but abort the compiler if the requested instruction does not exist. + +@item rtx maybe_gen_@var{name} (@var{i1}, @var{i2}, @dots{}, @var{op0}, @var{op1}, @dots{}) +Check for a valid instruction in the same way as +@code{maybe_code_for_@var{name}}. If the instruction exists, +generate an instance of it using the operand values given by @var{op0}, +@var{op1}, and so on, otherwise return null. + +@item rtx gen_@var{name} (@var{i1}, @var{i2}, @dots{}, @var{op0}, @var{op1}, @dots{}) +Same, but abort the compiler if the requested instruction does not exist, +or if the instruction generator invoked the @code{FAIL} macro. +@end table + +For example, changing the pattern above to: + +@smallexample +(define_insn "@@neon_vq" + [(set (match_operand:VDQIW 0 "s_register_operand" "=w") + (unspec:VDQIW [(match_operand:VDQIW 1 "s_register_operand" "w") + (match_operand:SI 2 "immediate_operand" "i")] + QABSNEG))] + @dots{} +) +@end smallexample + +would define the same patterns as before, but in addition would generate +the four functions below: + +@smallexample +insn_code maybe_code_for_neon_vq (int, machine_mode); +insn_code code_for_neon_vq (int, machine_mode); +rtx maybe_gen_neon_vq (int, machine_mode, rtx, rtx, rtx); +rtx gen_neon_vq (int, machine_mode, rtx, rtx, rtx); +@end smallexample + +Calling @samp{code_for_neon_vq (UNSPEC_VQABS, V8QImode)} +would then give @code{CODE_FOR_neon_vqabsv8qi}. + +It is possible to have multiple @samp{@@} patterns with the same +name and same types of iterator. For example: + +@smallexample +(define_insn "@@some_arithmetic_op" + [(set (match_operand:INTEGER_MODES 0 "register_operand") @dots{})] + @dots{} +) + +(define_insn "@@some_arithmetic_op" + [(set (match_operand:FLOAT_MODES 0 "register_operand") @dots{})] + @dots{} +) +@end smallexample + +would produce a single set of functions that handles both +@code{INTEGER_MODES} and @code{FLOAT_MODES}. + +It is also possible for these @samp{@@} patterns to have different +numbers of operands from each other. For example, patterns with +a binary rtl code might take three operands (one output and two inputs) +while patterns with a ternary rtl code might take four operands (one +output and three inputs). This combination would produce separate +@samp{maybe_gen_@var{name}} and @samp{gen_@var{name}} functions for +each operand count, but it would still produce a single +@samp{maybe_code_for_@var{name}} and a single @samp{code_for_@var{name}}. + +@end ifset diff --git a/gcc/doc/objc.texi b/gcc/doc/objc.texi new file mode 100644 index 00000000000..147785d4818 --- /dev/null +++ b/gcc/doc/objc.texi @@ -0,0 +1,1210 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Objective-C +@comment node-name, next, previous, up + +@chapter GNU Objective-C Features + +This document is meant to describe some of the GNU Objective-C +features. It is not intended to teach you Objective-C. There are +several resources on the Internet that present the language. + +@menu +* GNU Objective-C runtime API:: +* Executing code before main:: +* Type encoding:: +* Garbage Collection:: +* Constant string objects:: +* compatibility_alias:: +* Exceptions:: +* Synchronization:: +* Fast enumeration:: +* Messaging with the GNU Objective-C runtime:: +@end menu + +@c ========================================================================= +@node GNU Objective-C runtime API +@section GNU Objective-C Runtime API + +This section is specific for the GNU Objective-C runtime. If you are +using a different runtime, you can skip it. + +The GNU Objective-C runtime provides an API that allows you to +interact with the Objective-C runtime system, querying the live +runtime structures and even manipulating them. This allows you for +example to inspect and navigate classes, methods and protocols; to +define new classes or new methods, and even to modify existing classes +or protocols. + +If you are using a ``Foundation'' library such as GNUstep-Base, this +library will provide you with a rich set of functionality to do most +of the inspection tasks, and you probably will only need direct access +to the GNU Objective-C runtime API to define new classes or methods. + +@menu +* Modern GNU Objective-C runtime API:: +* Traditional GNU Objective-C runtime API:: +@end menu + +@c ========================================================================= +@node Modern GNU Objective-C runtime API +@subsection Modern GNU Objective-C Runtime API + +The GNU Objective-C runtime provides an API which is similar to the +one provided by the ``Objective-C 2.0'' Apple/NeXT Objective-C +runtime. The API is documented in the public header files of the GNU +Objective-C runtime: + +@itemize @bullet + +@item +@file{objc/objc.h}: this is the basic Objective-C header file, +defining the basic Objective-C types such as @code{id}, @code{Class} +and @code{BOOL}. You have to include this header to do almost +anything with Objective-C. + +@item +@file{objc/runtime.h}: this header declares most of the public runtime +API functions allowing you to inspect and manipulate the Objective-C +runtime data structures. These functions are fairly standardized +across Objective-C runtimes and are almost identical to the Apple/NeXT +Objective-C runtime ones. It does not declare functions in some +specialized areas (constructing and forwarding message invocations, +threading) which are in the other headers below. You have to include +@file{objc/objc.h} and @file{objc/runtime.h} to use any of the +functions, such as @code{class_getName()}, declared in +@file{objc/runtime.h}. + +@item +@file{objc/message.h}: this header declares public functions used to +construct, deconstruct and forward message invocations. Because +messaging is done in quite a different way on different runtimes, +functions in this header are specific to the GNU Objective-C runtime +implementation. + +@item +@file{objc/objc-exception.h}: this header declares some public +functions related to Objective-C exceptions. For example functions in +this header allow you to throw an Objective-C exception from plain +C/C++ code. + +@item +@file{objc/objc-sync.h}: this header declares some public functions +related to the Objective-C @code{@@synchronized()} syntax, allowing +you to emulate an Objective-C @code{@@synchronized()} block in plain +C/C++ code. + +@item +@file{objc/thr.h}: this header declares a public runtime API threading +layer that is only provided by the GNU Objective-C runtime. It +declares functions such as @code{objc_mutex_lock()}, which provide a +platform-independent set of threading functions. + +@end itemize + +The header files contain detailed documentation for each function in +the GNU Objective-C runtime API. + +@c ========================================================================= +@node Traditional GNU Objective-C runtime API +@subsection Traditional GNU Objective-C Runtime API + +The GNU Objective-C runtime used to provide a different API, which we +call the ``traditional'' GNU Objective-C runtime API. Functions +belonging to this API are easy to recognize because they use a +different naming convention, such as @code{class_get_super_class()} +(traditional API) instead of @code{class_getSuperclass()} (modern +API). Software using this API includes the file +@file{objc/objc-api.h} where it is declared. + +Starting with GCC 4.7.0, the traditional GNU runtime API is no longer +available. + +@c ========================================================================= +@node Executing code before main +@section @code{+load}: Executing Code before @code{main} + +This section is specific for the GNU Objective-C runtime. If you are +using a different runtime, you can skip it. + +The GNU Objective-C runtime provides a way that allows you to execute +code before the execution of the program enters the @code{main} +function. The code is executed on a per-class and a per-category basis, +through a special class method @code{+load}. + +This facility is very useful if you want to initialize global variables +which can be accessed by the program directly, without sending a message +to the class first. The usual way to initialize global variables, in the +@code{+initialize} method, might not be useful because +@code{+initialize} is only called when the first message is sent to a +class object, which in some cases could be too late. + +Suppose for example you have a @code{FileStream} class that declares +@code{Stdin}, @code{Stdout} and @code{Stderr} as global variables, like +below: + +@smallexample + +FileStream *Stdin = nil; +FileStream *Stdout = nil; +FileStream *Stderr = nil; + +@@implementation FileStream + ++ (void)initialize +@{ + Stdin = [[FileStream new] initWithFd:0]; + Stdout = [[FileStream new] initWithFd:1]; + Stderr = [[FileStream new] initWithFd:2]; +@} + +/* @r{Other methods here} */ +@@end + +@end smallexample + +In this example, the initialization of @code{Stdin}, @code{Stdout} and +@code{Stderr} in @code{+initialize} occurs too late. The programmer can +send a message to one of these objects before the variables are actually +initialized, thus sending messages to the @code{nil} object. The +@code{+initialize} method which actually initializes the global +variables is not invoked until the first message is sent to the class +object. The solution would require these variables to be initialized +just before entering @code{main}. + +The correct solution of the above problem is to use the @code{+load} +method instead of @code{+initialize}: + +@smallexample + +@@implementation FileStream + ++ (void)load +@{ + Stdin = [[FileStream new] initWithFd:0]; + Stdout = [[FileStream new] initWithFd:1]; + Stderr = [[FileStream new] initWithFd:2]; +@} + +/* @r{Other methods here} */ +@@end + +@end smallexample + +The @code{+load} is a method that is not overridden by categories. If a +class and a category of it both implement @code{+load}, both methods are +invoked. This allows some additional initializations to be performed in +a category. + +This mechanism is not intended to be a replacement for @code{+initialize}. +You should be aware of its limitations when you decide to use it +instead of @code{+initialize}. + +@menu +* What you can and what you cannot do in +load:: +@end menu + + +@node What you can and what you cannot do in +load +@subsection What You Can and Cannot Do in @code{+load} + +@code{+load} is to be used only as a last resort. Because it is +executed very early, most of the Objective-C runtime machinery will +not be ready when @code{+load} is executed; hence @code{+load} works +best for executing C code that is independent on the Objective-C +runtime. + +The @code{+load} implementation in the GNU runtime guarantees you the +following things: + +@itemize @bullet + +@item +you can write whatever C code you like; + +@item +you can allocate and send messages to objects whose class is implemented +in the same file; + +@item +the @code{+load} implementation of all super classes of a class are +executed before the @code{+load} of that class is executed; + +@item +the @code{+load} implementation of a class is executed before the +@code{+load} implementation of any category. + +@end itemize + +In particular, the following things, even if they can work in a +particular case, are not guaranteed: + +@itemize @bullet + +@item +allocation of or sending messages to arbitrary objects; + +@item +allocation of or sending messages to objects whose classes have a +category implemented in the same file; + +@item +sending messages to Objective-C constant strings (@code{@@"this is a +constant string"}); + +@end itemize + +You should make no assumptions about receiving @code{+load} in sibling +classes when you write @code{+load} of a class. The order in which +sibling classes receive @code{+load} is not guaranteed. + +The order in which @code{+load} and @code{+initialize} are called could +be problematic if this matters. If you don't allocate objects inside +@code{+load}, it is guaranteed that @code{+load} is called before +@code{+initialize}. If you create an object inside @code{+load} the +@code{+initialize} method of object's class is invoked even if +@code{+load} was not invoked. Note if you explicitly call @code{+load} +on a class, @code{+initialize} will be called first. To avoid possible +problems try to implement only one of these methods. + +The @code{+load} method is also invoked when a bundle is dynamically +loaded into your running program. This happens automatically without any +intervening operation from you. When you write bundles and you need to +write @code{+load} you can safely create and send messages to objects whose +classes already exist in the running program. The same restrictions as +above apply to classes defined in bundle. + + + +@node Type encoding +@section Type Encoding + +This is an advanced section. Type encodings are used extensively by +the compiler and by the runtime, but you generally do not need to know +about them to use Objective-C. + +The Objective-C compiler generates type encodings for all the types. +These type encodings are used at runtime to find out information about +selectors and methods and about objects and classes. + +The types are encoded in the following way: + +@c @sp 1 + +@multitable @columnfractions .25 .75 +@item @code{_Bool} +@tab @code{B} +@item @code{char} +@tab @code{c} +@item @code{unsigned char} +@tab @code{C} +@item @code{short} +@tab @code{s} +@item @code{unsigned short} +@tab @code{S} +@item @code{int} +@tab @code{i} +@item @code{unsigned int} +@tab @code{I} +@item @code{long} +@tab @code{l} +@item @code{unsigned long} +@tab @code{L} +@item @code{long long} +@tab @code{q} +@item @code{unsigned long long} +@tab @code{Q} +@item @code{float} +@tab @code{f} +@item @code{double} +@tab @code{d} +@item @code{long double} +@tab @code{D} +@item @code{void} +@tab @code{v} +@item @code{id} +@tab @code{@@} +@item @code{Class} +@tab @code{#} +@item @code{SEL} +@tab @code{:} +@item @code{char*} +@tab @code{*} +@item @code{enum} +@tab an @code{enum} is encoded exactly as the integer type that the compiler uses for it, which depends on the enumeration +values. Often the compiler users @code{unsigned int}, which is then encoded as @code{I}. +@item unknown type +@tab @code{?} +@item Complex types +@tab @code{j} followed by the inner type. For example @code{_Complex double} is encoded as "jd". +@item bit-fields +@tab @code{b} followed by the starting position of the bit-field, the type of the bit-field and the size of the bit-field (the bit-fields encoding was changed from the NeXT's compiler encoding, see below) +@end multitable + +@c @sp 1 + +The encoding of bit-fields has changed to allow bit-fields to be +properly handled by the runtime functions that compute sizes and +alignments of types that contain bit-fields. The previous encoding +contained only the size of the bit-field. Using only this information +it is not possible to reliably compute the size occupied by the +bit-field. This is very important in the presence of the Boehm's +garbage collector because the objects are allocated using the typed +memory facility available in this collector. The typed memory +allocation requires information about where the pointers are located +inside the object. + +The position in the bit-field is the position, counting in bits, of the +bit closest to the beginning of the structure. + +The non-atomic types are encoded as follows: + +@c @sp 1 + +@multitable @columnfractions .2 .8 +@item pointers +@tab @samp{^} followed by the pointed type. +@item arrays +@tab @samp{[} followed by the number of elements in the array followed by the type of the elements followed by @samp{]} +@item structures +@tab @samp{@{} followed by the name of the structure (or @samp{?} if the structure is unnamed), the @samp{=} sign, the type of the members and by @samp{@}} +@item unions +@tab @samp{(} followed by the name of the structure (or @samp{?} if the union is unnamed), the @samp{=} sign, the type of the members followed by @samp{)} +@item vectors +@tab @samp{![} followed by the vector_size (the number of bytes composing the vector) followed by a comma, followed by the alignment (in bytes) of the vector, followed by the type of the elements followed by @samp{]} +@end multitable + +Here are some types and their encodings, as they are generated by the +compiler on an i386 machine: + +@sp 1 + +@multitable @columnfractions .60 .40 +@headitem Objective-C type +@tab Compiler encoding +@item +@smallexample +int a[10]; +@end smallexample +@tab @code{[10i]} +@item +@smallexample +struct @{ + int i; + float f[3]; + int a:3; + int b:2; + char c; +@} +@end smallexample +@tab @code{@{?=i[3f]b128i3b131i2c@}} +@item +@smallexample +int a __attribute__ ((vector_size (16))); +@end smallexample +@tab @code{![16,16i]} (alignment depends on the machine) +@end multitable + +@sp 1 + +In addition to the types the compiler also encodes the type +specifiers. The table below describes the encoding of the current +Objective-C type specifiers: + +@sp 1 + +@multitable @columnfractions .25 .75 +@headitem Specifier +@tab Encoding +@item @code{const} +@tab @code{r} +@item @code{in} +@tab @code{n} +@item @code{inout} +@tab @code{N} +@item @code{out} +@tab @code{o} +@item @code{bycopy} +@tab @code{O} +@item @code{byref} +@tab @code{R} +@item @code{oneway} +@tab @code{V} +@end multitable + +@sp 1 + +The type specifiers are encoded just before the type. Unlike types +however, the type specifiers are only encoded when they appear in method +argument types. + +Note how @code{const} interacts with pointers: + +@sp 1 + +@multitable @columnfractions .25 .75 +@headitem Objective-C type +@tab Compiler encoding +@item +@smallexample +const int +@end smallexample +@tab @code{ri} +@item +@smallexample +const int* +@end smallexample +@tab @code{^ri} +@item +@smallexample +int *const +@end smallexample +@tab @code{r^i} +@end multitable + +@sp 1 + +@code{const int*} is a pointer to a @code{const int}, and so is +encoded as @code{^ri}. @code{int* const}, instead, is a @code{const} +pointer to an @code{int}, and so is encoded as @code{r^i}. + +Finally, there is a complication when encoding @code{const char *} +versus @code{char * const}. Because @code{char *} is encoded as +@code{*} and not as @code{^c}, there is no way to express the fact +that @code{r} applies to the pointer or to the pointee. + +Hence, it is assumed as a convention that @code{r*} means @code{const +char *} (since it is what is most often meant), and there is no way to +encode @code{char *const}. @code{char *const} would simply be encoded +as @code{*}, and the @code{const} is lost. + +@menu +* Legacy type encoding:: +* @@encode:: +* Method signatures:: +@end menu + +@node Legacy type encoding +@subsection Legacy Type Encoding + +Unfortunately, historically GCC used to have a number of bugs in its +encoding code. The NeXT runtime expects GCC to emit type encodings in +this historical format (compatible with GCC-3.3), so when using the +NeXT runtime, GCC will introduce on purpose a number of incorrect +encodings: + +@itemize @bullet + +@item +the read-only qualifier of the pointee gets emitted before the '^'. +The read-only qualifier of the pointer itself gets ignored, unless it +is a typedef. Also, the 'r' is only emitted for the outermost type. + +@item +32-bit longs are encoded as 'l' or 'L', but not always. For typedefs, +the compiler uses 'i' or 'I' instead if encoding a struct field or a +pointer. + +@item +@code{enum}s are always encoded as 'i' (int) even if they are actually +unsigned or long. + +@end itemize + +In addition to that, the NeXT runtime uses a different encoding for +bitfields. It encodes them as @code{b} followed by the size, without +a bit offset or the underlying field type. + +@node @@encode +@subsection @code{@@encode} + +GNU Objective-C supports the @code{@@encode} syntax that allows you to +create a type encoding from a C/Objective-C type. For example, +@code{@@encode(int)} is compiled by the compiler into @code{"i"}. + +@code{@@encode} does not support type qualifiers other than +@code{const}. For example, @code{@@encode(const char*)} is valid and +is compiled into @code{"r*"}, while @code{@@encode(bycopy char *)} is +invalid and will cause a compilation error. + +@node Method signatures +@subsection Method Signatures + +This section documents the encoding of method types, which is rarely +needed to use Objective-C. You should skip it at a first reading; the +runtime provides functions that will work on methods and can walk +through the list of parameters and interpret them for you. These +functions are part of the public ``API'' and are the preferred way to +interact with method signatures from user code. + +But if you need to debug a problem with method signatures and need to +know how they are implemented (i.e., the ``ABI''), read on. + +Methods have their ``signature'' encoded and made available to the +runtime. The ``signature'' encodes all the information required to +dynamically build invocations of the method at runtime: return type +and arguments. + +The ``signature'' is a null-terminated string, composed of the following: + +@itemize @bullet + +@item +The return type, including type qualifiers. For example, a method +returning @code{int} would have @code{i} here. + +@item +The total size (in bytes) required to pass all the parameters. This +includes the two hidden parameters (the object @code{self} and the +method selector @code{_cmd}). + +@item +Each argument, with the type encoding, followed by the offset (in +bytes) of the argument in the list of parameters. + +@end itemize + +For example, a method with no arguments and returning @code{int} would +have the signature @code{i8@@0:4} if the size of a pointer is 4. The +signature is interpreted as follows: the @code{i} is the return type +(an @code{int}), the @code{8} is the total size of the parameters in +bytes (two pointers each of size 4), the @code{@@0} is the first +parameter (an object at byte offset @code{0}) and @code{:4} is the +second parameter (a @code{SEL} at byte offset @code{4}). + +You can easily find more examples by running the ``strings'' program +on an Objective-C object file compiled by GCC. You'll see a lot of +strings that look very much like @code{i8@@0:4}. They are signatures +of Objective-C methods. + + +@node Garbage Collection +@section Garbage Collection + +This section is specific for the GNU Objective-C runtime. If you are +using a different runtime, you can skip it. + +Support for garbage collection with the GNU runtime has been added by +using a powerful conservative garbage collector, known as the +Boehm-Demers-Weiser conservative garbage collector. + +To enable the support for it you have to configure the compiler using +an additional argument, @w{@option{--enable-objc-gc}}. This will +build the boehm-gc library, and build an additional runtime library +which has several enhancements to support the garbage collector. The +new library has a new name, @file{libobjc_gc.a} to not conflict with +the non-garbage-collected library. + +When the garbage collector is used, the objects are allocated using the +so-called typed memory allocation mechanism available in the +Boehm-Demers-Weiser collector. This mode requires precise information on +where pointers are located inside objects. This information is computed +once per class, immediately after the class has been initialized. + +There is a new runtime function @code{class_ivar_set_gcinvisible()} +which can be used to declare a so-called @dfn{weak pointer} +reference. Such a pointer is basically hidden for the garbage collector; +this can be useful in certain situations, especially when you want to +keep track of the allocated objects, yet allow them to be +collected. This kind of pointers can only be members of objects, you +cannot declare a global pointer as a weak reference. Every type which is +a pointer type can be declared a weak pointer, including @code{id}, +@code{Class} and @code{SEL}. + +Here is an example of how to use this feature. Suppose you want to +implement a class whose instances hold a weak pointer reference; the +following class does this: + +@smallexample + +@@interface WeakPointer : Object +@{ + const void* weakPointer; +@} + +- initWithPointer:(const void*)p; +- (const void*)weakPointer; +@@end + + +@@implementation WeakPointer + ++ (void)initialize +@{ + if (self == objc_lookUpClass ("WeakPointer")) + class_ivar_set_gcinvisible (self, "weakPointer", YES); +@} + +- initWithPointer:(const void*)p +@{ + weakPointer = p; + return self; +@} + +- (const void*)weakPointer +@{ + return weakPointer; +@} + +@@end + +@end smallexample + +Weak pointers are supported through a new type character specifier +represented by the @samp{!} character. The +@code{class_ivar_set_gcinvisible()} function adds or removes this +specifier to the string type description of the instance variable named +as argument. + +@c ========================================================================= +@node Constant string objects +@section Constant String Objects + +GNU Objective-C provides constant string objects that are generated +directly by the compiler. You declare a constant string object by +prefixing a C constant string with the character @samp{@@}: + +@smallexample + id myString = @@"this is a constant string object"; +@end smallexample + +The constant string objects are by default instances of the +@code{NXConstantString} class which is provided by the GNU Objective-C +runtime. To get the definition of this class you must include the +@file{objc/NXConstStr.h} header file. + +User defined libraries may want to implement their own constant string +class. To be able to support them, the GNU Objective-C compiler provides +a new command line options @option{-fconstant-string-class=@var{class-name}}. +The provided class should adhere to a strict structure, the same +as @code{NXConstantString}'s structure: + +@smallexample + +@@interface MyConstantStringClass +@{ + Class isa; + char *c_string; + unsigned int len; +@} +@@end + +@end smallexample + +@code{NXConstantString} inherits from @code{Object}; user class +libraries may choose to inherit the customized constant string class +from a different class than @code{Object}. There is no requirement in +the methods the constant string class has to implement, but the final +ivar layout of the class must be the compatible with the given +structure. + +When the compiler creates the statically allocated constant string +object, the @code{c_string} field will be filled by the compiler with +the string; the @code{length} field will be filled by the compiler with +the string length; the @code{isa} pointer will be filled with +@code{NULL} by the compiler, and it will later be fixed up automatically +at runtime by the GNU Objective-C runtime library to point to the class +which was set by the @option{-fconstant-string-class} option when the +object file is loaded (if you wonder how it works behind the scenes, the +name of the class to use, and the list of static objects to fixup, are +stored by the compiler in the object file in a place where the GNU +runtime library will find them at runtime). + +As a result, when a file is compiled with the +@option{-fconstant-string-class} option, all the constant string objects +will be instances of the class specified as argument to this option. It +is possible to have multiple compilation units referring to different +constant string classes, neither the compiler nor the linker impose any +restrictions in doing this. + +@c ========================================================================= +@node compatibility_alias +@section @code{compatibility_alias} + +The keyword @code{@@compatibility_alias} allows you to define a class name +as equivalent to another class name. For example: + +@smallexample +@@compatibility_alias WOApplication GSWApplication; +@end smallexample + +tells the compiler that each time it encounters @code{WOApplication} as +a class name, it should replace it with @code{GSWApplication} (that is, +@code{WOApplication} is just an alias for @code{GSWApplication}). + +There are some constraints on how this can be used--- + +@itemize @bullet + +@item @code{WOApplication} (the alias) must not be an existing class; + +@item @code{GSWApplication} (the real class) must be an existing class. + +@end itemize + +@c ========================================================================= +@node Exceptions +@section Exceptions + +GNU Objective-C provides exception support built into the language, as +in the following example: + +@smallexample + @@try @{ + @dots{} + @@throw expr; + @dots{} + @} + @@catch (AnObjCClass *exc) @{ + @dots{} + @@throw expr; + @dots{} + @@throw; + @dots{} + @} + @@catch (AnotherClass *exc) @{ + @dots{} + @} + @@catch (id allOthers) @{ + @dots{} + @} + @@finally @{ + @dots{} + @@throw expr; + @dots{} + @} +@end smallexample + +The @code{@@throw} statement may appear anywhere in an Objective-C or +Objective-C++ program; when used inside of a @code{@@catch} block, the +@code{@@throw} may appear without an argument (as shown above), in +which case the object caught by the @code{@@catch} will be rethrown. + +Note that only (pointers to) Objective-C objects may be thrown and +caught using this scheme. When an object is thrown, it will be caught +by the nearest @code{@@catch} clause capable of handling objects of +that type, analogously to how @code{catch} blocks work in C++ and +Java. A @code{@@catch(id @dots{})} clause (as shown above) may also +be provided to catch any and all Objective-C exceptions not caught by +previous @code{@@catch} clauses (if any). + +The @code{@@finally} clause, if present, will be executed upon exit +from the immediately preceding @code{@@try @dots{} @@catch} section. +This will happen regardless of whether any exceptions are thrown, +caught or rethrown inside the @code{@@try @dots{} @@catch} section, +analogously to the behavior of the @code{finally} clause in Java. + +There are several caveats to using the new exception mechanism: + +@itemize @bullet +@item +The @option{-fobjc-exceptions} command line option must be used when +compiling Objective-C files that use exceptions. + +@item +With the GNU runtime, exceptions are always implemented as ``native'' +exceptions and it is recommended that the @option{-fexceptions} and +@option{-shared-libgcc} options are used when linking. + +@item +With the NeXT runtime, although currently designed to be binary +compatible with @code{NS_HANDLER}-style idioms provided by the +@code{NSException} class, the new exceptions can only be used on Mac +OS X 10.3 (Panther) and later systems, due to additional functionality +needed in the NeXT Objective-C runtime. + +@item +As mentioned above, the new exceptions do not support handling +types other than Objective-C objects. Furthermore, when used from +Objective-C++, the Objective-C exception model does not interoperate with C++ +exceptions at this time. This means you cannot @code{@@throw} an exception +from Objective-C and @code{catch} it in C++, or vice versa +(i.e., @code{throw @dots{} @@catch}). +@end itemize + +@c ========================================================================= +@node Synchronization +@section Synchronization + +GNU Objective-C provides support for synchronized blocks: + +@smallexample + @@synchronized (ObjCClass *guard) @{ + @dots{} + @} +@end smallexample + +Upon entering the @code{@@synchronized} block, a thread of execution +shall first check whether a lock has been placed on the corresponding +@code{guard} object by another thread. If it has, the current thread +shall wait until the other thread relinquishes its lock. Once +@code{guard} becomes available, the current thread will place its own +lock on it, execute the code contained in the @code{@@synchronized} +block, and finally relinquish the lock (thereby making @code{guard} +available to other threads). + +Unlike Java, Objective-C does not allow for entire methods to be +marked @code{@@synchronized}. Note that throwing exceptions out of +@code{@@synchronized} blocks is allowed, and will cause the guarding +object to be unlocked properly. + +Because of the interactions between synchronization and exception +handling, you can only use @code{@@synchronized} when compiling with +exceptions enabled, that is with the command line option +@option{-fobjc-exceptions}. + + +@c ========================================================================= +@node Fast enumeration +@section Fast Enumeration + +@menu +* Using fast enumeration:: +* c99-like fast enumeration syntax:: +* Fast enumeration details:: +* Fast enumeration protocol:: +@end menu + +@c ================================ +@node Using fast enumeration +@subsection Using Fast Enumeration + +GNU Objective-C provides support for the fast enumeration syntax: + +@smallexample + id array = @dots{}; + id object; + + for (object in array) + @{ + /* Do something with 'object' */ + @} +@end smallexample + +@code{array} needs to be an Objective-C object (usually a collection +object, for example an array, a dictionary or a set) which implements +the ``Fast Enumeration Protocol'' (see below). If you are using a +Foundation library such as GNUstep Base or Apple Cocoa Foundation, all +collection objects in the library implement this protocol and can be +used in this way. + +The code above would iterate over all objects in @code{array}. For +each of them, it assigns it to @code{object}, then executes the +@code{Do something with 'object'} statements. + +Here is a fully worked-out example using a Foundation library (which +provides the implementation of @code{NSArray}, @code{NSString} and +@code{NSLog}): + +@smallexample + NSArray *array = [NSArray arrayWithObjects: @@"1", @@"2", @@"3", nil]; + NSString *object; + + for (object in array) + NSLog (@@"Iterating over %@@", object); +@end smallexample + + +@c ================================ +@node c99-like fast enumeration syntax +@subsection C99-Like Fast Enumeration Syntax + +A c99-like declaration syntax is also allowed: + +@smallexample + id array = @dots{}; + + for (id object in array) + @{ + /* Do something with 'object' */ + @} +@end smallexample + +this is completely equivalent to: + +@smallexample + id array = @dots{}; + + @{ + id object; + for (object in array) + @{ + /* Do something with 'object' */ + @} + @} +@end smallexample + +but can save some typing. + +Note that the option @option{-std=c99} is not required to allow this +syntax in Objective-C. + +@c ================================ +@node Fast enumeration details +@subsection Fast Enumeration Details + +Here is a more technical description with the gory details. Consider the code + +@smallexample + for (@var{object expression} in @var{collection expression}) + @{ + @var{statements} + @} +@end smallexample + +here is what happens when you run it: + +@itemize @bullet +@item +@code{@var{collection expression}} is evaluated exactly once and the +result is used as the collection object to iterate over. This means +it is safe to write code such as @code{for (object in [NSDictionary +keyEnumerator]) @dots{}}. + +@item +the iteration is implemented by the compiler by repeatedly getting +batches of objects from the collection object using the fast +enumeration protocol (see below), then iterating over all objects in +the batch. This is faster than a normal enumeration where objects are +retrieved one by one (hence the name ``fast enumeration''). + +@item +if there are no objects in the collection, then +@code{@var{object expression}} is set to @code{nil} and the loop +immediately terminates. + +@item +if there are objects in the collection, then for each object in the +collection (in the order they are returned) @code{@var{object expression}} +is set to the object, then @code{@var{statements}} are executed. + +@item +@code{@var{statements}} can contain @code{break} and @code{continue} +commands, which will abort the iteration or skip to the next loop +iteration as expected. + +@item +when the iteration ends because there are no more objects to iterate +over, @code{@var{object expression}} is set to @code{nil}. This allows +you to determine whether the iteration finished because a @code{break} +command was used (in which case @code{@var{object expression}} will remain +set to the last object that was iterated over) or because it iterated +over all the objects (in which case @code{@var{object expression}} will be +set to @code{nil}). + +@item +@code{@var{statements}} must not make any changes to the collection +object; if they do, it is a hard error and the fast enumeration +terminates by invoking @code{objc_enumerationMutation}, a runtime +function that normally aborts the program but which can be customized +by Foundation libraries via @code{objc_set_mutation_handler} to do +something different, such as raising an exception. + +@end itemize + +@c ================================ +@node Fast enumeration protocol +@subsection Fast Enumeration Protocol + +If you want your own collection object to be usable with fast +enumeration, you need to have it implement the method + +@smallexample +- (unsigned long) countByEnumeratingWithState: (NSFastEnumerationState *)state + objects: (id *)objects + count: (unsigned long)len; +@end smallexample + +where @code{NSFastEnumerationState} must be defined in your code as follows: + +@smallexample +typedef struct +@{ + unsigned long state; + id *itemsPtr; + unsigned long *mutationsPtr; + unsigned long extra[5]; +@} NSFastEnumerationState; +@end smallexample + +If no @code{NSFastEnumerationState} is defined in your code, the +compiler will automatically replace @code{NSFastEnumerationState *} +with @code{struct __objcFastEnumerationState *}, where that type is +silently defined by the compiler in an identical way. This can be +confusing and we recommend that you define +@code{NSFastEnumerationState} (as shown above) instead. + +The method is called repeatedly during a fast enumeration to retrieve +batches of objects. Each invocation of the method should retrieve the +next batch of objects. + +The return value of the method is the number of objects in the current +batch; this should not exceed @code{len}, which is the maximum size of +a batch as requested by the caller. The batch itself is returned in +the @code{itemsPtr} field of the @code{NSFastEnumerationState} struct. + +To help with returning the objects, the @code{objects} array is a C +array preallocated by the caller (on the stack) of size @code{len}. +In many cases you can put the objects you want to return in that +@code{objects} array, then do @code{itemsPtr = objects}. But you +don't have to; if your collection already has the objects to return in +some form of C array, it could return them from there instead. + +The @code{state} and @code{extra} fields of the +@code{NSFastEnumerationState} structure allows your collection object +to keep track of the state of the enumeration. In a simple array +implementation, @code{state} may keep track of the index of the last +object that was returned, and @code{extra} may be unused. + +The @code{mutationsPtr} field of the @code{NSFastEnumerationState} is +used to keep track of mutations. It should point to a number; before +working on each object, the fast enumeration loop will check that this +number has not changed. If it has, a mutation has happened and the +fast enumeration will abort. So, @code{mutationsPtr} could be set to +point to some sort of version number of your collection, which is +increased by one every time there is a change (for example when an +object is added or removed). Or, if you are content with less strict +mutation checks, it could point to the number of objects in your +collection or some other value that can be checked to perform an +approximate check that the collection has not been mutated. + +Finally, note how we declared the @code{len} argument and the return +value to be of type @code{unsigned long}. They could also be declared +to be of type @code{unsigned int} and everything would still work. + +@c ========================================================================= +@node Messaging with the GNU Objective-C runtime +@section Messaging with the GNU Objective-C Runtime + +This section is specific for the GNU Objective-C runtime. If you are +using a different runtime, you can skip it. + +The implementation of messaging in the GNU Objective-C runtime is +designed to be portable, and so is based on standard C. + +Sending a message in the GNU Objective-C runtime is composed of two +separate steps. First, there is a call to the lookup function, +@code{objc_msg_lookup ()} (or, in the case of messages to super, +@code{objc_msg_lookup_super ()}). This runtime function takes as +argument the receiver and the selector of the method to be called; it +returns the @code{IMP}, that is a pointer to the function implementing +the method. The second step of method invocation consists of casting +this pointer function to the appropriate function pointer type, and +calling the function pointed to it with the right arguments. + +For example, when the compiler encounters a method invocation such as +@code{[object init]}, it compiles it into a call to +@code{objc_msg_lookup (object, @@selector(init))} followed by a cast +of the returned value to the appropriate function pointer type, and +then it calls it. + +@menu +* Dynamically registering methods:: +* Forwarding hook:: +@end menu + +@c ========================================================================= +@node Dynamically registering methods +@subsection Dynamically Registering Methods + +If @code{objc_msg_lookup()} does not find a suitable method +implementation, because the receiver does not implement the required +method, it tries to see if the class can dynamically register the +method. + +To do so, the runtime checks if the class of the receiver implements +the method + +@smallexample ++ (BOOL) resolveInstanceMethod: (SEL)selector; +@end smallexample + +in the case of an instance method, or + +@smallexample ++ (BOOL) resolveClassMethod: (SEL)selector; +@end smallexample + +in the case of a class method. If the class implements it, the +runtime invokes it, passing as argument the selector of the original +method, and if it returns @code{YES}, the runtime tries the lookup +again, which could now succeed if a matching method was added +dynamically by @code{+resolveInstanceMethod:} or +@code{+resolveClassMethod:}. + +This allows classes to dynamically register methods (by adding them to +the class using @code{class_addMethod}) when they are first called. +To do so, a class should implement @code{+resolveInstanceMethod:} (or, +depending on the case, @code{+resolveClassMethod:}) and have it +recognize the selectors of methods that can be registered dynamically +at runtime, register them, and return @code{YES}. It should return +@code{NO} for methods that it does not dynamically registered at +runtime. + +If @code{+resolveInstanceMethod:} (or @code{+resolveClassMethod:}) is +not implemented or returns @code{NO}, the runtime then tries the +forwarding hook. + +Support for @code{+resolveInstanceMethod:} and +@code{resolveClassMethod:} was added to the GNU Objective-C runtime in +GCC version 4.6. + +@c ========================================================================= +@node Forwarding hook +@subsection Forwarding Hook + +The GNU Objective-C runtime provides a hook, called +@code{__objc_msg_forward2}, which is called by +@code{objc_msg_lookup()} when it cannot find a method implementation in +the runtime tables and after calling @code{+resolveInstanceMethod:} +and @code{+resolveClassMethod:} has been attempted and did not succeed +in dynamically registering the method. + +To configure the hook, you set the global variable +@code{__objc_msg_forward2} to a function with the same argument and +return types of @code{objc_msg_lookup()}. When +@code{objc_msg_lookup()} cannot find a method implementation, it +invokes the hook function you provided to get a method implementation +to return. So, in practice @code{__objc_msg_forward2} allows you to +extend @code{objc_msg_lookup()} by adding some custom code that is +called to do a further lookup when no standard method implementation +can be found using the normal lookup. + +This hook is generally reserved for ``Foundation'' libraries such as +GNUstep Base, which use it to implement their high-level method +forwarding API, typically based around the @code{forwardInvocation:} +method. So, unless you are implementing your own ``Foundation'' +library, you should not set this hook. + +In a typical forwarding implementation, the @code{__objc_msg_forward2} +hook function determines the argument and return type of the method +that is being looked up, and then creates a function that takes these +arguments and has that return type, and returns it to the caller. +Creating this function is non-trivial and is typically performed using +a dedicated library such as @code{libffi}. + +The forwarding method implementation thus created is returned by +@code{objc_msg_lookup()} and is executed as if it was a normal method +implementation. When the forwarding method implementation is called, +it is usually expected to pack all arguments into some sort of object +(typically, an @code{NSInvocation} in a ``Foundation'' library), and +hand it over to the programmer (@code{forwardInvocation:}) who is then +allowed to manipulate the method invocation using a high-level API +provided by the ``Foundation'' library. For example, the programmer +may want to examine the method invocation arguments and name and +potentially change them before forwarding the method invocation to one +or more local objects (@code{performInvocation:}) or even to remote +objects (by using Distributed Objects or some other mechanism). When +all this completes, the return value is passed back and must be +returned correctly to the original caller. + +Note that the GNU Objective-C runtime currently provides no support +for method forwarding or method invocations other than the +@code{__objc_msg_forward2} hook. + +If the forwarding hook does not exist or returns @code{NULL}, the +runtime currently attempts forwarding using an older, deprecated API, +and if that fails, it aborts the program. In future versions of the +GNU Objective-C runtime, the runtime will immediately abort. diff --git a/gcc/doc/optinfo.texi b/gcc/doc/optinfo.texi new file mode 100644 index 00000000000..c0244630341 --- /dev/null +++ b/gcc/doc/optinfo.texi @@ -0,0 +1,246 @@ +@c Copyright (C) 2013-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@cindex optimization dumps + +This section is describes dump infrastructure which is common to both +pass dumps as well as optimization dumps. The goal for this +infrastructure is to provide both gcc developers and users detailed +information about various compiler transformations and optimizations. + +@menu +* Dump setup:: Setup of optimization dumps. +* Optimization groups:: Groups made up of optimization passes. +* Dump files and streams:: Dump output file names and streams. +* Dump output verbosity:: How much information to dump. +* Dump types:: Various types of dump functions. +* Dump examples:: Sample usage. +@end menu + +@node Dump setup +@subsection Dump setup +@cindex dump setup + +A dump_manager class is defined in @file{dumpfile.h}. Various passes +register dumping pass-specific information via @code{dump_register} in +@file{passes.cc}. During the registration, an optimization pass can +select its optimization group (@pxref{Optimization groups}). After +that optimization information corresponding to the entire group +(presumably from multiple passes) can be output via command-line +switches. Note that if a pass does not fit into any of the pre-defined +groups, it can select @code{OPTGROUP_NONE}. + +Note that in general, a pass need not know its dump output file name, +whether certain flags are enabled, etc. However, for legacy reasons, +passes could also call @code{dump_begin} which returns a stream in +case the particular pass has optimization dumps enabled. A pass could +call @code{dump_end} when the dump has ended. These methods should go +away once all the passes are converted to use the new dump +infrastructure. + +The recommended way to setup the dump output is via @code{dump_start} +and @code{dump_end}. + +@node Optimization groups +@subsection Optimization groups +@cindex optimization groups +The optimization passes are grouped into several categories. Currently +defined categories in @file{dumpfile.h} are + +@ftable @code + +@item OPTGROUP_IPA +IPA optimization passes. Enabled by @option{-ipa} + +@item OPTGROUP_LOOP +Loop optimization passes. Enabled by @option{-loop}. + +@item OPTGROUP_INLINE +Inlining passes. Enabled by @option{-inline}. + +@item OPTGROUP_OMP +OMP (Offloading and Multi Processing) passes. Enabled by +@option{-omp}. + +@item OPTGROUP_VEC +Vectorization passes. Enabled by @option{-vec}. + +@item OPTGROUP_OTHER +All other optimization passes which do not fall into one of the above. + +@item OPTGROUP_ALL +All optimization passes. Enabled by @option{-optall}. + +@end ftable + +By using groups a user could selectively enable optimization +information only for a group of passes. By default, the optimization +information for all the passes is dumped. + +@node Dump files and streams +@subsection Dump files and streams +@cindex optimization info file names + +There are two separate output streams available for outputting +optimization information from passes. Note that both these streams +accept @code{stderr} and @code{stdout} as valid streams and thus it is +possible to dump output to standard output or error. This is specially +handy for outputting all available information in a single file by +redirecting @code{stderr}. + +@table @code +@item @code{pstream} +This stream is for pass-specific dump output. For example, +@option{-fdump-tree-vect=foo.v} dumps tree vectorization pass output +into the given file name @file{foo.v}. If the file name is not provided, +the default file name is based on the source file and pass number. Note +that one could also use special file names @code{stdout} and +@code{stderr} for dumping to standard output and standard error +respectively. + +@item @code{alt_stream} +This steam is used for printing optimization specific output in +response to the @option{-fopt-info}. Again a file name can be given. If +the file name is not given, it defaults to @code{stderr}. +@end table + +@node Dump output verbosity +@subsection Dump output verbosity +@cindex dump verbosity + +The dump verbosity has the following options + +@table @samp +@item optimized +Print information when an optimization is successfully applied. It is +up to a pass to decide which information is relevant. For example, the +vectorizer passes print the source location of loops which got +successfully vectorized. + +@item missed +Print information about missed optimizations. Individual passes +control which information to include in the output. For example, + +@smallexample +gcc -O2 -ftree-vectorize -fopt-info-vec-missed +@end smallexample + +will print information about missed optimization opportunities from +vectorization passes on stderr. + +@item note +Print verbose information about optimizations, such as certain +transformations, more detailed messages about decisions etc. + +@item all +Print detailed optimization information. This includes +@var{optimized}, @var{missed}, and @var{note}. +@end table + +@node Dump types +@subsection Dump types +@cindex dump types + +@ftable @code + +@item dump_printf + +This is a generic method for doing formatted output. It takes an +additional argument @code{dump_kind} which signifies the type of +dump. This method outputs information only when the dumps are enabled +for this particular @code{dump_kind}. Note that the caller doesn't +need to know if the particular dump is enabled or not, or even the +file name. The caller only needs to decide which dump output +information is relevant, and under what conditions. This determines +the associated flags. + +Consider the following example from @file{loop-unroll.cc} where an +informative message about a loop (along with its location) is printed +when any of the following flags is enabled +@itemize @minus + +@item optimization messages +@item RTL dumps +@item detailed dumps + +@end itemize + +@example +int report_flags = MSG_OPTIMIZED_LOCATIONS | TDF_RTL | TDF_DETAILS; +dump_printf_loc (report_flags, insn, + "loop turned into non-loop; it never loops.\n"); +@end example + +@item dump_basic_block +Output basic block. +@item dump_generic_expr +Output generic expression. +@item dump_gimple_stmt +Output gimple statement. + +Note that the above methods also have variants prefixed with +@code{_loc}, such as @code{dump_printf_loc}, which are similar except +they also output the source location information. The @code{_loc} variants +take a @code{const dump_location_t &}. This class can be constructed from +a @code{gimple *} or from a @code{rtx_insn *}, and so callers can pass +a @code{gimple *} or a @code{rtx_insn *} as the @code{_loc} argument. +The @code{dump_location_t} constructor will extract the source location +from the statement or instruction, along with the profile count, and +the location in GCC's own source code (or the plugin) from which the dump +call was emitted. Only the source location is currently used. +There is also a @code{dump_user_location_t} class, capturing the +source location and profile count, but not the dump emission location, +so that locations in the user's code can be passed around. This +can also be constructed from a @code{gimple *} and from a @code{rtx_insn *}, +and it too can be passed as the @code{_loc} argument. + +@end ftable + +@node Dump examples +@subsection Dump examples +@cindex dump examples + +@smallexample +gcc -O3 -fopt-info-missed=missed.all +@end smallexample + +outputs missed optimization report from all the passes into +@file{missed.all}. + +As another example, +@smallexample +gcc -O3 -fopt-info-inline-optimized-missed=inline.txt +@end smallexample + +will output information about missed optimizations as well as +optimized locations from all the inlining passes into +@file{inline.txt}. + +If the @var{filename} is provided, then the dumps from all the +applicable optimizations are concatenated into the @file{filename}. +Otherwise the dump is output onto @file{stderr}. If @var{options} is +omitted, it defaults to @option{optimized-optall}, which means dump +all information about successful optimizations from all the passes. +In the following example, the optimization information is output on +to @file{stderr}. + +@smallexample +gcc -O3 -fopt-info +@end smallexample + +Note that @option{-fopt-info-vec-missed} behaves the same as +@option{-fopt-info-missed-vec}. The order of the optimization group +names and message types listed after @option{-fopt-info} does not matter. + +As another example, consider + +@smallexample +gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt +@end smallexample + +Here the two output file names @file{vec.miss} and @file{loop.opt} are +in conflict since only one output file is allowed. In this case, only +the first option takes effect and the subsequent options are +ignored. Thus only the @file{vec.miss} is produced which containts +dumps from the vectorizer about missed opportunities. diff --git a/gcc/doc/options.texi b/gcc/doc/options.texi new file mode 100644 index 00000000000..17ba923890e --- /dev/null +++ b/gcc/doc/options.texi @@ -0,0 +1,590 @@ +@c Copyright (C) 2003-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Options +@chapter Option specification files +@cindex option specification files +@cindex @samp{optc-gen.awk} + +Most GCC command-line options are described by special option +definition files, the names of which conventionally end in +@code{.opt}. This chapter describes the format of these files. + +@menu +* Option file format:: The general layout of the files +* Option properties:: Supported option properties +@end menu + +@node Option file format +@section Option file format + +Option files are a simple list of records in which each field occupies +its own line and in which the records themselves are separated by +blank lines. Comments may appear on their own line anywhere within +the file and are preceded by semicolons. Whitespace is allowed before +the semicolon. + +The files can contain the following types of record: + +@itemize @bullet +@item +A language definition record. These records have two fields: the +string @samp{Language} and the name of the language. Once a language +has been declared in this way, it can be used as an option property. +@xref{Option properties}. + +@item +A target specific save record to save additional information. These +records have two fields: the string @samp{TargetSave}, and a +declaration type to go in the @code{cl_target_option} structure. + +@item +A variable record to define a variable used to store option +information. These records have two fields: the string +@samp{Variable}, and a declaration of the type and name of the +variable, optionally with an initializer (but without any trailing +@samp{;}). These records may be used for variables used for many +options where declaring the initializer in a single option definition +record, or duplicating it in many records, would be inappropriate, or +for variables set in option handlers rather than referenced by +@code{Var} properties. + +@item +A variable record to define a variable used to store option +information. These records have two fields: the string +@samp{TargetVariable}, and a declaration of the type and name of the +variable, optionally with an initializer (but without any trailing +@samp{;}). @samp{TargetVariable} is a combination of @samp{Variable} +and @samp{TargetSave} records in that the variable is defined in the +@code{gcc_options} structure, but these variables are also stored in +the @code{cl_target_option} structure. The variables are saved in the +target save code and restored in the target restore code. + +@item +A variable record to record any additional files that the +@file{options.h} file should include. This is useful to provide +enumeration or structure definitions needed for target variables. +These records have two fields: the string @samp{HeaderInclude} and the +name of the include file. + +@item +A variable record to record any additional files that the +@file{options.cc} or @file{options-save.cc} file should include. This +is useful to provide +inline functions needed for target variables and/or @code{#ifdef} +sequences to properly set up the initialization. These records have +two fields: the string @samp{SourceInclude} and the name of the +include file. + +@item +An enumeration record to define a set of strings that may be used as +arguments to an option or options. These records have three fields: +the string @samp{Enum}, a space-separated list of properties and help +text used to describe the set of strings in @option{--help} output. +Properties use the same format as option properties; the following are +valid: +@table @code +@item Name(@var{name}) +This property is required; @var{name} must be a name (suitable for use +in C identifiers) used to identify the set of strings in @code{Enum} +option properties. + +@item Type(@var{type}) +This property is required; @var{type} is the C type for variables set +by options using this enumeration together with @code{Var}. + +@item UnknownError(@var{message}) +The message @var{message} will be used as an error message if the +argument is invalid; for enumerations without @code{UnknownError}, a +generic error message is used. @var{message} should contain a single +@samp{%qs} format, which will be used to format the invalid argument. +@end table + +@item +An enumeration value record to define one of the strings in a set +given in an @samp{Enum} record. These records have two fields: the +string @samp{EnumValue} and a space-separated list of properties. +Properties use the same format as option properties; the following are +valid: +@table @code +@item Enum(@var{name}) +This property is required; @var{name} says which @samp{Enum} record +this @samp{EnumValue} record corresponds to. + +@item String(@var{string}) +This property is required; @var{string} is the string option argument +being described by this record. + +@item Value(@var{value}) +This property is required; it says what value (representable as +@code{int}) should be used for the given string. + +@item Canonical +This property is optional. If present, it says the present string is +the canonical one among all those with the given value. Other strings +yielding that value will be mapped to this one so specs do not need to +handle them. + +@item DriverOnly +This property is optional. If present, the present string will only +be accepted by the driver. This is used for cases such as +@option{-march=native} that are processed by the driver so that +@samp{gcc -v} shows how the options chosen depended on the system on +which the compiler was run. + +@item Set(@var{number}) +This property is optional, required for enumerations used in +@code{EnumSet} options. @var{number} should be decimal number between +1 and 64 inclusive and divides the enumeration into a set of +sets of mutually exclusive arguments. Arguments with the same +@var{number} can't be specified together in the same option, but +arguments with different @var{number} can. @var{value} needs to be +chosen such that a mask of all @var{value} values from the same set +@var{number} bitwise ored doesn't overlap with masks for other sets. +When @code{-foption=arg_from_set1,arg_from_set4} and +@code{-fno-option=arg_from_set3} are used, the effect is that previous +value of the @code{Var} will get bits from set 1 and 4 masks cleared, +ored @code{Value} of @code{arg_from_set1} and @code{arg_from_set4} +and then will get bits from set 3 mask cleared. +@end table + +@item +An option definition record. These records have the following fields: +@enumerate +@item +the name of the option, with the leading ``-'' removed +@item +a space-separated list of option properties (@pxref{Option properties}) +@item +the help text to use for @option{--help} (omitted if the second field +contains the @code{Undocumented} property). +@end enumerate + +By default, all options beginning with ``f'', ``W'' or ``m'' are +implicitly assumed to take a ``no-'' form. This form should not be +listed separately. If an option beginning with one of these letters +does not have a ``no-'' form, you can use the @code{RejectNegative} +property to reject it. + +The help text is automatically line-wrapped before being displayed. +Normally the name of the option is printed on the left-hand side of +the output and the help text is printed on the right. However, if the +help text contains a tab character, the text to the left of the tab is +used instead of the option's name and the text to the right of the +tab forms the help text. This allows you to elaborate on what type +of argument the option takes. + +There is no support for different help texts for different languages. +If an option is supported for multiple languages, use a generic +description that is correct for all of them. + +If an option has multiple option definition records (in different +front ends' @file{*.opt} files, and/or @file{gcc/common.opt}, for +example), convention is to not duplicate the help text for each of +them, but instead put a comment like @code{; documented in common.opt} +in place of the help text for all but one of the multiple option +definition records. + +@item +A target mask record. These records have one field of the form +@samp{Mask(@var{x})}. The options-processing script will automatically +allocate a bit in @code{target_flags} (@pxref{Run-time Target}) for +each mask name @var{x} and set the macro @code{MASK_@var{x}} to the +appropriate bitmask. It will also declare a @code{TARGET_@var{x}} +macro that has the value 1 when bit @code{MASK_@var{x}} is set and +0 otherwise. + +They are primarily intended to declare target masks that are not +associated with user options, either because these masks represent +internal switches or because the options are not available on all +configurations and yet the masks always need to be defined. +@end itemize + +@node Option properties +@section Option properties + +The second field of an option record can specify any of the following +properties. When an option takes an argument, it is enclosed in parentheses +following the option property name. The parser that handles option files +is quite simplistic, and will be tricked by any nested parentheses within +the argument text itself; in this case, the entire option argument can +be wrapped in curly braces within the parentheses to demarcate it, e.g.: + +@smallexample +Condition(@{defined (USE_CYGWIN_LIBSTDCXX_WRAPPERS)@}) +@end smallexample + +@table @code +@item Common +The option is available for all languages and targets. + +@item Target +The option is available for all languages but is target-specific. + +@item Driver +The option is handled by the compiler driver using code not shared +with the compilers proper (@file{cc1} etc.). + +@item @var{language} +The option is available when compiling for the given language. + +It is possible to specify several different languages for the same +option. Each @var{language} must have been declared by an earlier +@code{Language} record. @xref{Option file format}. + +@item RejectDriver +The option is only handled by the compilers proper (@file{cc1} etc.)@: +and should not be accepted by the driver. + +@item RejectNegative +The option does not have a ``no-'' form. All options beginning with +``f'', ``W'' or ``m'' are assumed to have a ``no-'' form unless this +property is used. + +@item Negative(@var{othername}) +The option will turn off another option @var{othername}, which is +the option name with the leading ``-'' removed. This chain action will +propagate through the @code{Negative} property of the option to be +turned off. The driver will prune options, removing those that are +turned off by some later option. This pruning is not done for options +with @code{Joined} or @code{JoinedOrMissing} properties, unless the +options have both the @code{RejectNegative} property and the @code{Negative} +property mentions itself. + +As a consequence, if you have a group of mutually-exclusive +options, their @code{Negative} properties should form a circular chain. +For example, if options @option{-@var{a}}, @option{-@var{b}} and +@option{-@var{c}} are mutually exclusive, their respective @code{Negative} +properties should be @samp{Negative(@var{b})}, @samp{Negative(@var{c})} +and @samp{Negative(@var{a})}. + +@item Joined +@itemx Separate +The option takes a mandatory argument. @code{Joined} indicates +that the option and argument can be included in the same @code{argv} +entry (as with @code{-mflush-func=@var{name}}, for example). +@code{Separate} indicates that the option and argument can be +separate @code{argv} entries (as with @code{-o}). An option is +allowed to have both of these properties. + +@item JoinedOrMissing +The option takes an optional argument. If the argument is given, +it will be part of the same @code{argv} entry as the option itself. + +This property cannot be used alongside @code{Joined} or @code{Separate}. + +@item MissingArgError(@var{message}) +For an option marked @code{Joined} or @code{Separate}, the message +@var{message} will be used as an error message if the mandatory +argument is missing; for options without @code{MissingArgError}, a +generic error message is used. @var{message} should contain a single +@samp{%qs} format, which will be used to format the name of the option +passed. + +@item Args(@var{n}) +For an option marked @code{Separate}, indicate that it takes @var{n} +arguments. The default is 1. + +@item UInteger +The option's argument is a non-negative integer consisting of either +decimal or hexadecimal digits interpreted as @code{int}. Hexadecimal +integers may optionally start with the @code{0x} or @code{0X} prefix. +The option parser validates and converts the argument before passing +it to the relevant option handler. @code{UInteger} should also be used +with options like @code{-falign-loops} where both @code{-falign-loops} +and @code{-falign-loops}=@var{n} are supported to make sure the saved +options are given a full integer. Positive values of the argument in +excess of @code{INT_MAX} wrap around zero. + +@item Host_Wide_Int +The option's argument is a non-negative integer consisting of either +decimal or hexadecimal digits interpreted as the widest integer type +on the host. As with an @code{UInteger} argument, hexadecimal integers +may optionally start with the @code{0x} or @code{0X} prefix. The option +parser validates and converts the argument before passing it to +the relevant option handler. @code{Host_Wide_Int} should be used with +options that need to accept very large values. Positive values of +the argument in excess of @code{HOST_WIDE_INT_M1U} are assigned +@code{HOST_WIDE_INT_M1U}. + +@item IntegerRange(@var{n}, @var{m}) +The options's arguments are integers of type @code{int}. The option's +parser validates that the value of an option integer argument is within +the closed range [@var{n}, @var{m}]. + +@item ByteSize +A property applicable only to @code{UInteger} or @code{Host_Wide_Int} +arguments. The option's integer argument is interpreted as if in infinite +precision using saturation arithmetic in the corresponding type. The argument +may be followed by a @samp{byte-size} suffix designating a multiple of bytes +such as @code{kB} and @code{KiB} for kilobyte and kibibyte, respectively, +@code{MB} and @code{MiB} for megabyte and mebibyte, @code{GB} and @code{GiB} +for gigabyte and gigibyte, and so on. @code{ByteSize} should be used for +with options that take a very large argument representing a size in bytes, +such as @option{-Wlarger-than=}. + +@item ToLower +The option's argument should be converted to lowercase as part of +putting it in canonical form, and before comparing with the strings +indicated by any @code{Enum} property. + +@item NoDriverArg +For an option marked @code{Separate}, the option only takes an +argument in the compiler proper, not in the driver. This is for +compatibility with existing options that are used both directly and +via @option{-Wp,}; new options should not have this property. + +@item Var(@var{var}) +The state of this option should be stored in variable @var{var} +(actually a macro for @code{global_options.x_@var{var}}). +The way that the state is stored depends on the type of option: + +@item WarnRemoved +The option is removed and every usage of such option will +result in a warning. We use it option backward compatibility. + +@item Var(@var{var}, @var{set}) +The option controls an integer variable @var{var} and is active when +@var{var} equals @var{set}. The option parser will set @var{var} to +@var{set} when the positive form of the option is used and @code{!@var{set}} +when the ``no-'' form is used. + +@var{var} is declared in the same way as for the single-argument form +described above. + +@itemize @bullet +@item +If the option uses the @code{Mask} or @code{InverseMask} properties, +@var{var} is the integer variable that contains the mask. + +@item +If the option is a normal on/off switch, @var{var} is an integer +variable that is nonzero when the option is enabled. The options +parser will set the variable to 1 when the positive form of the +option is used and 0 when the ``no-'' form is used. + +@item +If the option takes an argument and has the @code{UInteger} property, +@var{var} is an integer variable that stores the value of the argument. + +@item +If the option takes an argument and has the @code{Enum} property, +@var{var} is a variable (type given in the @code{Type} property of the +@samp{Enum} record whose @code{Name} property has the same argument as +the @code{Enum} property of this option) that stores the value of the +argument. + +@item +If the option has the @code{Defer} property, @var{var} is a pointer to +a @code{VEC(cl_deferred_option,heap)} that stores the option for later +processing. (@var{var} is declared with type @code{void *} and needs +to be cast to @code{VEC(cl_deferred_option,heap)} before use.) + +@item +Otherwise, if the option takes an argument, @var{var} is a pointer to +the argument string. The pointer will be null if the argument is optional +and wasn't given. +@end itemize + +The option-processing script will usually zero-initialize @var{var}. +You can modify this behavior using @code{Init}. + +@item Init(@var{value}) +The variable specified by the @code{Var} property should be statically +initialized to @var{value}. If more than one option using the same +variable specifies @code{Init}, all must specify the same initializer. + +@item Mask(@var{name}) +The option is associated with a bit in the @code{target_flags} +variable (@pxref{Run-time Target}) and is active when that bit is set. +You may also specify @code{Var} to select a variable other than +@code{target_flags}. + +The options-processing script will automatically allocate a unique bit +for the option. If the option is attached to @samp{target_flags}, +the script will set the macro @code{MASK_@var{name}} to the appropriate +bitmask. It will also declare a @code{TARGET_@var{name}} macro that has +the value 1 when the option is active and 0 otherwise. If you use @code{Var} +to attach the option to a different variable, the bitmask macro with be +called @code{OPTION_MASK_@var{name}}. + +@item InverseMask(@var{othername}) +@itemx InverseMask(@var{othername}, @var{thisname}) +The option is the inverse of another option that has the +@code{Mask(@var{othername})} property. If @var{thisname} is given, +the options-processing script will declare a @code{TARGET_@var{thisname}} +macro that is 1 when the option is active and 0 otherwise. + +@item Enum(@var{name}) +The option's argument is a string from the set of strings associated +with the corresponding @samp{Enum} record. The string is checked and +converted to the integer specified in the corresponding +@samp{EnumValue} record before being passed to option handlers. + +@item EnumSet +Must be used together with the @code{Enum(@var{name})} property. +Corresponding @samp{Enum} record must use @code{Set} properties. +The option's argument is either a string from the set like for +@code{Enum(@var{name})}, but with a slightly different behavior that +the whole @code{Var} isn't overwritten, but only the bits in all the +enumeration values with the same set bitwise ored together. +Or option's argument can be a comma separated list of strings where +each string is from a different @code{Set(@var{number})}. + +@item EnumBitSet +Must be used together with the @code{Enum(@var{name})} property. +Similar to @samp{EnumSet}, but corresponding @samp{Enum} record must +not use @code{Set} properties, each @code{EnumValue} should have +@code{Value} that is a power of 2, each value is treated as its own +set and its value as the set's mask, so there are no mutually +exclusive arguments. + +@item Defer +The option should be stored in a vector, specified with @code{Var}, +for later processing. + +@item Alias(@var{opt}) +@itemx Alias(@var{opt}, @var{arg}) +@itemx Alias(@var{opt}, @var{posarg}, @var{negarg}) +The option is an alias for @option{-@var{opt}} (or the negative form +of that option, depending on @code{NegativeAlias}). In the first form, +any argument passed to the alias is considered to be passed to +@option{-@var{opt}}, and @option{-@var{opt}} is considered to be +negated if the alias is used in negated form. In the second form, the +alias may not be negated or have an argument, and @var{posarg} is +considered to be passed as an argument to @option{-@var{opt}}. In the +third form, the alias may not have an argument, if the alias is used +in the positive form then @var{posarg} is considered to be passed to +@option{-@var{opt}}, and if the alias is used in the negative form +then @var{negarg} is considered to be passed to @option{-@var{opt}}. + +Aliases should not specify @code{Var} or @code{Mask} or +@code{UInteger}. Aliases should normally specify the same languages +as the target of the alias; the flags on the target will be used to +determine any diagnostic for use of an option for the wrong language, +while those on the alias will be used to identify what command-line +text is the option and what text is any argument to that option. + +When an @code{Alias} definition is used for an option, driver specs do +not need to handle it and no @samp{OPT_} enumeration value is defined +for it; only the canonical form of the option will be seen in those +places. + +@item NegativeAlias +For an option marked with @code{Alias(@var{opt})}, the option is +considered to be an alias for the positive form of @option{-@var{opt}} +if negated and for the negative form of @option{-@var{opt}} if not +negated. @code{NegativeAlias} may not be used with the forms of +@code{Alias} taking more than one argument. + +@item Ignore +This option is ignored apart from printing any warning specified using +@code{Warn}. The option will not be seen by specs and no @samp{OPT_} +enumeration value is defined for it. + +@item SeparateAlias +For an option marked with @code{Joined}, @code{Separate} and +@code{Alias}, the option only acts as an alias when passed a separate +argument; with a joined argument it acts as a normal option, with an +@samp{OPT_} enumeration value. This is for compatibility with the +Java @option{-d} option and should not be used for new options. + +@item Warn(@var{message}) +If this option is used, output the warning @var{message}. +@var{message} is a format string, either taking a single operand with +a @samp{%qs} format which is the option name, or not taking any +operands, which is passed to the @samp{warning} function. If an alias +is marked @code{Warn}, the target of the alias must not also be marked +@code{Warn}. + +@item Warning +This is a warning option and should be shown as such in +@option{--help} output. This flag does not currently affect anything +other than @option{--help}. + +@item Optimization +This is an optimization option. It should be shown as such in +@option{--help} output, and any associated variable named using +@code{Var} should be saved and restored when the optimization level is +changed with @code{optimize} attributes. + +@item PerFunction +This is an option that can be overridden on a per-function basis. +@code{Optimization} implies @code{PerFunction}, but options that do not +affect executable code generation may use this flag instead, so that the +option is not taken into account in ways that might affect executable +code generation. + +@item Param +This is an option that is a parameter. + +@item Undocumented +The option is deliberately missing documentation and should not +be included in the @option{--help} output. + +@item Condition(@var{cond}) +The option should only be accepted if preprocessor condition +@var{cond} is true. Note that any C declarations associated with the +option will be present even if @var{cond} is false; @var{cond} simply +controls whether the option is accepted and whether it is printed in +the @option{--help} output. + +@item Save +Build the @code{cl_target_option} structure to hold a copy of the +option, add the functions @code{cl_target_option_save} and +@code{cl_target_option_restore} to save and restore the options. + +@item SetByCombined +The option may also be set by a combined option such as +@option{-ffast-math}. This causes the @code{gcc_options} struct to +have a field @code{frontend_set_@var{name}}, where @code{@var{name}} +is the name of the field holding the value of this option (without the +leading @code{x_}). This gives the front end a way to indicate that +the value has been set explicitly and should not be changed by the +combined option. For example, some front ends use this to prevent +@option{-ffast-math} and @option{-fno-fast-math} from changing the +value of @option{-fmath-errno} for languages that do not use +@code{errno}. + +@item EnabledBy(@var{opt}) +@itemx EnabledBy(@var{opt} || @var{opt2}) +@itemx EnabledBy(@var{opt} && @var{opt2}) +If not explicitly set, the option is set to the value of +@option{-@var{opt}}; multiple options can be given, separated by +@code{||}. The third form using @code{&&} specifies that the option is +only set if both @var{opt} and @var{opt2} are set. The options @var{opt} +and @var{opt2} must have the @code{Common} property; otherwise, use +@code{LangEnabledBy}. + +@item LangEnabledBy(@var{language}, @var{opt}) +@itemx LangEnabledBy(@var{language}, @var{opt}, @var{posarg}, @var{negarg}) +When compiling for the given language, the option is set to the value +of @option{-@var{opt}}, if not explicitly set. @var{opt} can be also a list +of @code{||} separated options. In the second form, if +@var{opt} is used in the positive form then @var{posarg} is considered +to be passed to the option, and if @var{opt} is used in the negative +form then @var{negarg} is considered to be passed to the option. It +is possible to specify several different languages. Each +@var{language} must have been declared by an earlier @code{Language} +record. @xref{Option file format}. + +@item NoDWARFRecord +The option is omitted from the producer string written by +@option{-grecord-gcc-switches}. + +@item PchIgnore +Even if this is a target option, this option will not be recorded / compared +to determine if a precompiled header file matches. + +@item CPP(@var{var}) +The state of this option should be kept in sync with the preprocessor +option @var{var}. If this property is set, then properties @code{Var} +and @code{Init} must be set as well. + +@item CppReason(@var{CPP_W_Enum}) +This warning option corresponds to @code{cpplib.h} warning reason code +@var{CPP_W_Enum}. This should only be used for warning options of the +C-family front-ends. + +@end table diff --git a/gcc/doc/passes.texi b/gcc/doc/passes.texi new file mode 100644 index 00000000000..9e8b4f50ad6 --- /dev/null +++ b/gcc/doc/passes.texi @@ -0,0 +1,1196 @@ +@c markers: BUG TODO + +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Passes +@chapter Passes and Files of the Compiler +@cindex passes and files of the compiler +@cindex files and passes of the compiler +@cindex compiler passes and files +@cindex pass dumps + +This chapter is dedicated to giving an overview of the optimization and +code generation passes of the compiler. In the process, it describes +some of the language front end interface, though this description is no +where near complete. + +@menu +* Parsing pass:: The language front end turns text into bits. +* Gimplification pass:: The bits are turned into something we can optimize. +* Pass manager:: Sequencing the optimization passes. +* IPA passes:: Inter-procedural optimizations. +* Tree SSA passes:: Optimizations on a high-level representation. +* RTL passes:: Optimizations on a low-level representation. +* Optimization info:: Dumping optimization information from passes. +@end menu + +@node Parsing pass +@section Parsing pass +@cindex GENERIC +@findex lang_hooks.parse_file +The language front end is invoked only once, via +@code{lang_hooks.parse_file}, to parse the entire input. The language +front end may use any intermediate language representation deemed +appropriate. The C front end uses GENERIC trees (@pxref{GENERIC}), plus +a double handful of language specific tree codes defined in +@file{c-common.def}. The Fortran front end uses a completely different +private representation. + +@cindex GIMPLE +@cindex gimplification +@cindex gimplifier +@cindex language-independent intermediate representation +@cindex intermediate representation lowering +@cindex lowering, language-dependent intermediate representation +At some point the front end must translate the representation used in the +front end to a representation understood by the language-independent +portions of the compiler. Current practice takes one of two forms. +The C front end manually invokes the gimplifier (@pxref{GIMPLE}) on each function, +and uses the gimplifier callbacks to convert the language-specific tree +nodes directly to GIMPLE before passing the function off to be compiled. +The Fortran front end converts from a private representation to GENERIC, +which is later lowered to GIMPLE when the function is compiled. Which +route to choose probably depends on how well GENERIC (plus extensions) +can be made to match up with the source language and necessary parsing +data structures. + +BUG: Gimplification must occur before nested function lowering, +and nested function lowering must be done by the front end before +passing the data off to cgraph. + +TODO: Cgraph should control nested function lowering. It would +only be invoked when it is certain that the outer-most function +is used. + +TODO: Cgraph needs a gimplify_function callback. It should be +invoked when (1) it is certain that the function is used, (2) +warning flags specified by the user require some amount of +compilation in order to honor, (3) the language indicates that +semantic analysis is not complete until gimplification occurs. +Hum@dots{} this sounds overly complicated. Perhaps we should just +have the front end gimplify always; in most cases it's only one +function call. + +The front end needs to pass all function definitions and top level +declarations off to the middle-end so that they can be compiled and +emitted to the object file. For a simple procedural language, it is +usually most convenient to do this as each top level declaration or +definition is seen. There is also a distinction to be made between +generating functional code and generating complete debug information. +The only thing that is absolutely required for functional code is that +function and data @emph{definitions} be passed to the middle-end. For +complete debug information, function, data and type declarations +should all be passed as well. + +@findex rest_of_decl_compilation +@findex rest_of_type_compilation +@findex cgraph_finalize_function +In any case, the front end needs each complete top-level function or +data declaration, and each data definition should be passed to +@code{rest_of_decl_compilation}. Each complete type definition should +be passed to @code{rest_of_type_compilation}. Each function definition +should be passed to @code{cgraph_finalize_function}. + +TODO: I know rest_of_compilation currently has all sorts of +RTL generation semantics. I plan to move all code generation +bits (both Tree and RTL) to compile_function. Should we hide +cgraph from the front ends and move back to rest_of_compilation +as the official interface? Possibly we should rename all three +interfaces such that the names match in some meaningful way and +that is more descriptive than "rest_of". + +The middle-end will, at its option, emit the function and data +definitions immediately or queue them for later processing. + +@node Gimplification pass +@section Gimplification pass + +@cindex gimplification +@cindex GIMPLE +@dfn{Gimplification} is a whimsical term for the process of converting +the intermediate representation of a function into the GIMPLE language +(@pxref{GIMPLE}). The term stuck, and so words like ``gimplification'', +``gimplify'', ``gimplifier'' and the like are sprinkled throughout this +section of code. + +While a front end may certainly choose to generate GIMPLE directly if +it chooses, this can be a moderately complex process unless the +intermediate language used by the front end is already fairly simple. +Usually it is easier to generate GENERIC trees plus extensions +and let the language-independent gimplifier do most of the work. + +@findex gimplify_function_tree +@findex gimplify_expr +@findex lang_hooks.gimplify_expr +The main entry point to this pass is @code{gimplify_function_tree} +located in @file{gimplify.cc}. From here we process the entire +function gimplifying each statement in turn. The main workhorse +for this pass is @code{gimplify_expr}. Approximately everything +passes through here at least once, and it is from here that we +invoke the @code{lang_hooks.gimplify_expr} callback. + +The callback should examine the expression in question and return +@code{GS_UNHANDLED} if the expression is not a language specific +construct that requires attention. Otherwise it should alter the +expression in some way to such that forward progress is made toward +producing valid GIMPLE@. If the callback is certain that the +transformation is complete and the expression is valid GIMPLE, it +should return @code{GS_ALL_DONE}. Otherwise it should return +@code{GS_OK}, which will cause the expression to be processed again. +If the callback encounters an error during the transformation (because +the front end is relying on the gimplification process to finish +semantic checks), it should return @code{GS_ERROR}. + +@node Pass manager +@section Pass manager + +The pass manager is located in @file{passes.cc}, @file{tree-optimize.c} +and @file{tree-pass.h}. +It processes passes as described in @file{passes.def}. +Its job is to run all of the individual passes in the correct order, +and take care of standard bookkeeping that applies to every pass. + +The theory of operation is that each pass defines a structure that +represents everything we need to know about that pass---when it +should be run, how it should be run, what intermediate language +form or on-the-side data structures it needs. We register the pass +to be run in some particular order, and the pass manager arranges +for everything to happen in the correct order. + +The actuality doesn't completely live up to the theory at present. +Command-line switches and @code{timevar_id_t} enumerations must still +be defined elsewhere. The pass manager validates constraints but does +not attempt to (re-)generate data structures or lower intermediate +language form based on the requirements of the next pass. Nevertheless, +what is present is useful, and a far sight better than nothing at all. + +Each pass should have a unique name. +Each pass may have its own dump file (for GCC debugging purposes). +Passes with a name starting with a star do not dump anything. +Sometimes passes are supposed to share a dump file / option name. +To still give these unique names, you can use a prefix that is delimited +by a space from the part that is used for the dump file / option name. +E.g. When the pass name is "ud dce", the name used for dump file/options +is "dce". + +TODO: describe the global variables set up by the pass manager, +and a brief description of how a new pass should use it. +I need to look at what info RTL passes use first@enddots{} + +@node IPA passes +@section Inter-procedural optimization passes +@cindex IPA passes +@cindex inter-procedural optimization passes + +The inter-procedural optimization (IPA) passes use call graph +information to perform transformations across function boundaries. +IPA is a critical part of link-time optimization (LTO) and +whole-program (WHOPR) optimization, and these passes are structured +with the needs of LTO and WHOPR in mind by dividing their operations +into stages. For detailed discussion of the LTO/WHOPR IPA pass stages +and interfaces, see @ref{IPA}. + +The following briefly describes the inter-procedural optimization (IPA) +passes, which are split into small IPA passes, regular IPA passes, +and late IPA passes, according to the LTO/WHOPR processing model. + +@menu +* Small IPA passes:: +* Regular IPA passes:: +* Late IPA passes:: +@end menu + +@node Small IPA passes +@subsection Small IPA passes +@cindex small IPA passes +A small IPA pass is a pass derived from @code{simple_ipa_opt_pass}. +As described in @ref{IPA}, it does everything at once and +defines only the @emph{Execute} stage. During this +stage it accesses and modifies the function bodies. +No @code{generate_summary}, @code{read_summary}, or @code{write_summary} +hooks are defined. + +@itemize @bullet +@item IPA free lang data + +This pass frees resources that are used by the front end but are +not needed once it is done. It is located in @file{tree.cc} and is described by +@code{pass_ipa_free_lang_data}. + +@item IPA function and variable visibility + +This is a local function pass handling visibilities of all symbols. This +happens before LTO streaming, so @option{-fwhole-program} should be ignored +at this level. It is located in @file{ipa-visibility.cc} and is described by +@code{pass_ipa_function_and_variable_visibility}. + +@item IPA remove symbols + +This pass performs reachability analysis and reclaims all unreachable nodes. +It is located in @file{passes.cc} and is described by +@code{pass_ipa_remove_symbols}. + +@item IPA OpenACC + +This is a pass group for OpenACC processing. It is located in +@file{tree-ssa-loop.cc} and is described by @code{pass_ipa_oacc}. + +@item IPA points-to analysis + +This is a tree-based points-to analysis pass. The idea behind this analyzer +is to generate set constraints from the program, then solve the resulting +constraints in order to generate the points-to sets. It is located in +@file{tree-ssa-structalias.cc} and is described by @code{pass_ipa_pta}. + +@item IPA OpenACC kernels + +This is a pass group for processing OpenACC kernels regions. It is a +subpass of the IPA OpenACC pass group that runs on offloaded functions +containing OpenACC kernels loops. It is located in +@file{tree-ssa-loop.cc} and is described by +@code{pass_ipa_oacc_kernels}. + +@item Target clone + +This is a pass for parsing functions with multiple target attributes. +It is located in @file{multiple_target.cc} and is described by +@code{pass_target_clone}. + +@item IPA auto profile + +This pass uses AutoFDO profiling data to annotate the control flow graph. +It is located in @file{auto-profile.cc} and is described by +@code{pass_ipa_auto_profile}. + +@item IPA tree profile + +This pass does profiling for all functions in the call graph. +It calculates branch +probabilities and basic block execution counts. It is located +in @file{tree-profile.cc} and is described by @code{pass_ipa_tree_profile}. + +@item IPA free function summary + +This pass is a small IPA pass when argument @code{small_p} is true. +It releases inline function summaries and call summaries. +It is located in @file{ipa-fnsummary.cc} and is described by +@code{pass_ipa_free_free_fn_summary}. + +@item IPA increase alignment + +This pass increases the alignment of global arrays to improve +vectorization. It is located in @file{tree-vectorizer.cc} +and is described by @code{pass_ipa_increase_alignment}. + +@item IPA transactional memory + +This pass is for transactional memory support. +It is located in @file{trans-mem.cc} and is described by +@code{pass_ipa_tm}. + +@item IPA lower emulated TLS + +This pass lowers thread-local storage (TLS) operations +to emulation functions provided by libgcc. +It is located in @file{tree-emutls.cc} and is described by +@code{pass_ipa_lower_emutls}. + +@end itemize + +@node Regular IPA passes +@subsection Regular IPA passes +@cindex regular IPA passes + +A regular IPA pass is a pass derived from @code{ipa_opt_pass_d} that +is executed in WHOPR compilation. Regular IPA passes may have summary +hooks implemented in any of the LGEN, WPA or LTRANS stages (@pxref{IPA}). + +@itemize @bullet +@item IPA whole program visibility + +This pass performs various optimizations involving symbol visibility +with @option{-fwhole-program}, including symbol privatization, +discovering local functions, and dismantling comdat groups. It is +located in @file{ipa-visibility.cc} and is described by +@code{pass_ipa_whole_program_visibility}. + +@item IPA profile + +The IPA profile pass propagates profiling frequencies across the call +graph. It is located in @file{ipa-profile.cc} and is described by +@code{pass_ipa_profile}. + +@item IPA identical code folding + +This is the inter-procedural identical code folding pass. +The goal of this transformation is to discover functions +and read-only variables that have exactly the same semantics. It is +located in @file{ipa-icf.cc} and is described by @code{pass_ipa_icf}. + +@item IPA devirtualization + +This pass performs speculative devirtualization based on the type +inheritance graph. When a polymorphic call has only one likely target +in the unit, it is turned into a speculative call. It is located in +@file{ipa-devirt.cc} and is described by @code{pass_ipa_devirt}. + +@item IPA constant propagation + +The goal of this pass is to discover functions that are always invoked +with some arguments with the same known constant values and to modify +the functions accordingly. It can also do partial specialization and +type-based devirtualization. It is located in @file{ipa-cp.cc} and is +described by @code{pass_ipa_cp}. + +@item IPA scalar replacement of aggregates + +This pass can replace an aggregate parameter with a set of other parameters +representing part of the original, turning those passed by reference +into new ones which pass the value directly. It also removes unused +function return values and unused function parameters. This pass is +located in @file{ipa-sra.cc} and is described by @code{pass_ipa_sra}. + +@item IPA constructor/destructor merge + +This pass merges multiple constructors and destructors for static +objects into single functions. It's only run at LTO time unless the +target doesn't support constructors and destructors natively. The +pass is located in @file{ipa.cc} and is described by +@code{pass_ipa_cdtor_merge}. + +@item IPA function summary + +This pass provides function analysis for inter-procedural passes. +It collects estimates of function body size, execution time, and frame +size for each function. It also estimates information about function +calls: call statement size, time and how often the parameters change +for each call. It is located in @file{ipa-fnsummary.cc} and is +described by @code{pass_ipa_fn_summary}. + +@item IPA inline + +The IPA inline pass handles function inlining with whole-program +knowledge. Small functions that are candidates for inlining are +ordered in increasing badness, bounded by unit growth parameters. +Unreachable functions are removed from the call graph. Functions called +once and not exported from the unit are inlined. This pass is located in +@file{ipa-inline.cc} and is described by @code{pass_ipa_inline}. + +@item IPA pure/const analysis + +This pass marks functions as being either const (@code{TREE_READONLY}) or +pure (@code{DECL_PURE_P}). The per-function information is produced +by @code{pure_const_generate_summary}, then the global information is computed +by performing a transitive closure over the call graph. It is located in +@file{ipa-pure-const.cc} and is described by @code{pass_ipa_pure_const}. + +@item IPA free function summary + +This pass is a regular IPA pass when argument @code{small_p} is false. +It releases inline function summaries and call summaries. +It is located in @file{ipa-fnsummary.cc} and is described by +@code{pass_ipa_free_fn_summary}. + +@item IPA reference + +This pass gathers information about how variables whose scope is +confined to the compilation unit are used. It is located in +@file{ipa-reference.cc} and is described by @code{pass_ipa_reference}. + +@item IPA single use + +This pass checks whether variables are used by a single function. +It is located in @file{ipa.cc} and is described by +@code{pass_ipa_single_use}. + +@item IPA comdats + +This pass looks for static symbols that are used exclusively +within one comdat group, and moves them into that comdat group. It is +located in @file{ipa-comdats.cc} and is described by +@code{pass_ipa_comdats}. + +@end itemize + +@node Late IPA passes +@subsection Late IPA passes +@cindex late IPA passes + +Late IPA passes are simple IPA passes executed after +the regular passes. In WHOPR mode the passes are executed after +partitioning and thus see just parts of the compiled unit. + +@itemize @bullet +@item Materialize all clones + +Once all functions from compilation unit are in memory, produce all clones +and update all calls. It is located in @file{ipa.cc} and is described by +@code{pass_materialize_all_clones}. + +@item IPA points-to analysis + +Points-to analysis; this is the same as the points-to-analysis pass +run with the small IPA passes (@pxref{Small IPA passes}). + +@item OpenMP simd clone + +This is the OpenMP constructs' SIMD clone pass. It creates the appropriate +SIMD clones for functions tagged as elemental SIMD functions. +It is located in @file{omp-simd-clone.cc} and is described by +@code{pass_omp_simd_clone}. + +@end itemize + +@node Tree SSA passes +@section Tree SSA passes + +The following briefly describes the Tree optimization passes that are +run after gimplification and what source files they are located in. + +@itemize @bullet +@item Remove useless statements + +This pass is an extremely simple sweep across the gimple code in which +we identify obviously dead code and remove it. Here we do things like +simplify @code{if} statements with constant conditions, remove +exception handling constructs surrounding code that obviously cannot +throw, remove lexical bindings that contain no variables, and other +assorted simplistic cleanups. The idea is to get rid of the obvious +stuff quickly rather than wait until later when it's more work to get +rid of it. This pass is located in @file{tree-cfg.cc} and described by +@code{pass_remove_useless_stmts}. + +@item OpenMP lowering + +If OpenMP generation (@option{-fopenmp}) is enabled, this pass lowers +OpenMP constructs into GIMPLE. + +Lowering of OpenMP constructs involves creating replacement +expressions for local variables that have been mapped using data +sharing clauses, exposing the control flow of most synchronization +directives and adding region markers to facilitate the creation of the +control flow graph. The pass is located in @file{omp-low.cc} and is +described by @code{pass_lower_omp}. + +@item OpenMP expansion + +If OpenMP generation (@option{-fopenmp}) is enabled, this pass expands +parallel regions into their own functions to be invoked by the thread +library. The pass is located in @file{omp-low.cc} and is described by +@code{pass_expand_omp}. + +@item Lower control flow + +This pass flattens @code{if} statements (@code{COND_EXPR}) +and moves lexical bindings (@code{BIND_EXPR}) out of line. After +this pass, all @code{if} statements will have exactly two @code{goto} +statements in its @code{then} and @code{else} arms. Lexical binding +information for each statement will be found in @code{TREE_BLOCK} rather +than being inferred from its position under a @code{BIND_EXPR}. This +pass is found in @file{gimple-low.cc} and is described by +@code{pass_lower_cf}. + +@item Lower exception handling control flow + +This pass decomposes high-level exception handling constructs +(@code{TRY_FINALLY_EXPR} and @code{TRY_CATCH_EXPR}) into a form +that explicitly represents the control flow involved. After this +pass, @code{lookup_stmt_eh_region} will return a non-negative +number for any statement that may have EH control flow semantics; +examine @code{tree_can_throw_internal} or @code{tree_can_throw_external} +for exact semantics. Exact control flow may be extracted from +@code{foreach_reachable_handler}. The EH region nesting tree is defined +in @file{except.h} and built in @file{except.cc}. The lowering pass +itself is in @file{tree-eh.cc} and is described by @code{pass_lower_eh}. + +@item Build the control flow graph + +This pass decomposes a function into basic blocks and creates all of +the edges that connect them. It is located in @file{tree-cfg.cc} and +is described by @code{pass_build_cfg}. + +@item Find all referenced variables + +This pass walks the entire function and collects an array of all +variables referenced in the function, @code{referenced_vars}. The +index at which a variable is found in the array is used as a UID +for the variable within this function. This data is needed by the +SSA rewriting routines. The pass is located in @file{tree-dfa.cc} +and is described by @code{pass_referenced_vars}. + +@item Enter static single assignment form + +This pass rewrites the function such that it is in SSA form. After +this pass, all @code{is_gimple_reg} variables will be referenced by +@code{SSA_NAME}, and all occurrences of other variables will be +annotated with @code{VDEFS} and @code{VUSES}; PHI nodes will have +been inserted as necessary for each basic block. This pass is +located in @file{tree-ssa.cc} and is described by @code{pass_build_ssa}. + +@item Warn for uninitialized variables + +This pass scans the function for uses of @code{SSA_NAME}s that +are fed by default definition. For non-parameter variables, such +uses are uninitialized. The pass is run twice, before and after +optimization (if turned on). In the first pass we only warn for uses that are +positively uninitialized; in the second pass we warn for uses that +are possibly uninitialized. The pass is located in @file{tree-ssa.cc} +and is defined by @code{pass_early_warn_uninitialized} and +@code{pass_late_warn_uninitialized}. + +@item Dead code elimination + +This pass scans the function for statements without side effects whose +result is unused. It does not do memory life analysis, so any value +that is stored in memory is considered used. The pass is run multiple +times throughout the optimization process. It is located in +@file{tree-ssa-dce.cc} and is described by @code{pass_dce}. + +@item Dominator optimizations + +This pass performs trivial dominator-based copy and constant propagation, +expression simplification, and jump threading. It is run multiple times +throughout the optimization process. It is located in @file{tree-ssa-dom.cc} +and is described by @code{pass_dominator}. + +@item Forward propagation of single-use variables + +This pass attempts to remove redundant computation by substituting +variables that are used once into the expression that uses them and +seeing if the result can be simplified. It is located in +@file{tree-ssa-forwprop.cc} and is described by @code{pass_forwprop}. + +@item Copy Renaming + +This pass attempts to change the name of compiler temporaries involved in +copy operations such that SSA->normal can coalesce the copy away. When compiler +temporaries are copies of user variables, it also renames the compiler +temporary to the user variable resulting in better use of user symbols. It is +located in @file{tree-ssa-copyrename.c} and is described by +@code{pass_copyrename}. + +@item PHI node optimizations + +This pass recognizes forms of PHI inputs that can be represented as +conditional expressions and rewrites them into straight line code. +It is located in @file{tree-ssa-phiopt.cc} and is described by +@code{pass_phiopt}. + +@item May-alias optimization + +This pass performs a flow sensitive SSA-based points-to analysis. +The resulting may-alias, must-alias, and escape analysis information +is used to promote variables from in-memory addressable objects to +non-aliased variables that can be renamed into SSA form. We also +update the @code{VDEF}/@code{VUSE} memory tags for non-renameable +aggregates so that we get fewer false kills. The pass is located +in @file{tree-ssa-alias.cc} and is described by @code{pass_may_alias}. + +Interprocedural points-to information is located in +@file{tree-ssa-structalias.cc} and described by @code{pass_ipa_pta}. + +@item Profiling + +This pass instruments the function in order to collect runtime block +and value profiling data. Such data may be fed back into the compiler +on a subsequent run so as to allow optimization based on expected +execution frequencies. The pass is located in @file{tree-profile.cc} and +is described by @code{pass_ipa_tree_profile}. + +@item Static profile estimation + +This pass implements series of heuristics to guess propababilities +of branches. The resulting predictions are turned into edge profile +by propagating branches across the control flow graphs. +The pass is located in @file{tree-profile.cc} and is described by +@code{pass_profile}. + +@item Lower complex arithmetic + +This pass rewrites complex arithmetic operations into their component +scalar arithmetic operations. The pass is located in @file{tree-complex.cc} +and is described by @code{pass_lower_complex}. + +@item Scalar replacement of aggregates + +This pass rewrites suitable non-aliased local aggregate variables into +a set of scalar variables. The resulting scalar variables are +rewritten into SSA form, which allows subsequent optimization passes +to do a significantly better job with them. The pass is located in +@file{tree-sra.cc} and is described by @code{pass_sra}. + +@item Dead store elimination + +This pass eliminates stores to memory that are subsequently overwritten +by another store, without any intervening loads. The pass is located +in @file{tree-ssa-dse.cc} and is described by @code{pass_dse}. + +@item Tail recursion elimination + +This pass transforms tail recursion into a loop. It is located in +@file{tree-tailcall.cc} and is described by @code{pass_tail_recursion}. + +@item Forward store motion + +This pass sinks stores and assignments down the flowgraph closer to their +use point. The pass is located in @file{tree-ssa-sink.cc} and is +described by @code{pass_sink_code}. + +@item Partial redundancy elimination + +This pass eliminates partially redundant computations, as well as +performing load motion. The pass is located in @file{tree-ssa-pre.cc} +and is described by @code{pass_pre}. + +Just before partial redundancy elimination, if +@option{-funsafe-math-optimizations} is on, GCC tries to convert +divisions to multiplications by the reciprocal. The pass is located +in @file{tree-ssa-math-opts.cc} and is described by +@code{pass_cse_reciprocal}. + +@item Full redundancy elimination + +This is a simpler form of PRE that only eliminates redundancies that +occur on all paths. It is located in @file{tree-ssa-pre.cc} and +described by @code{pass_fre}. + +@item Loop optimization + +The main driver of the pass is placed in @file{tree-ssa-loop.cc} +and described by @code{pass_loop}. + +The optimizations performed by this pass are: + +Loop invariant motion. This pass moves only invariants that +would be hard to handle on RTL level (function calls, operations that expand to +nontrivial sequences of insns). With @option{-funswitch-loops} it also moves +operands of conditions that are invariant out of the loop, so that we can use +just trivial invariantness analysis in loop unswitching. The pass also includes +store motion. The pass is implemented in @file{tree-ssa-loop-im.cc}. + +Canonical induction variable creation. This pass creates a simple counter +for number of iterations of the loop and replaces the exit condition of the +loop using it, in case when a complicated analysis is necessary to determine +the number of iterations. Later optimizations then may determine the number +easily. The pass is implemented in @file{tree-ssa-loop-ivcanon.cc}. + +Induction variable optimizations. This pass performs standard induction +variable optimizations, including strength reduction, induction variable +merging and induction variable elimination. The pass is implemented in +@file{tree-ssa-loop-ivopts.cc}. + +Loop unswitching. This pass moves the conditional jumps that are invariant +out of the loops. To achieve this, a duplicate of the loop is created for +each possible outcome of conditional jump(s). The pass is implemented in +@file{tree-ssa-loop-unswitch.cc}. + +Loop splitting. If a loop contains a conditional statement that is +always true for one part of the iteration space and false for the other +this pass splits the loop into two, one dealing with one side the other +only with the other, thereby removing one inner-loop conditional. The +pass is implemented in @file{tree-ssa-loop-split.cc}. + +The optimizations also use various utility functions contained in +@file{tree-ssa-loop-manip.cc}, @file{cfgloop.cc}, @file{cfgloopanal.cc} and +@file{cfgloopmanip.cc}. + +Vectorization. This pass transforms loops to operate on vector types +instead of scalar types. Data parallelism across loop iterations is exploited +to group data elements from consecutive iterations into a vector and operate +on them in parallel. Depending on available target support the loop is +conceptually unrolled by a factor @code{VF} (vectorization factor), which is +the number of elements operated upon in parallel in each iteration, and the +@code{VF} copies of each scalar operation are fused to form a vector operation. +Additional loop transformations such as peeling and versioning may take place +to align the number of iterations, and to align the memory accesses in the +loop. +The pass is implemented in @file{tree-vectorizer.cc} (the main driver), +@file{tree-vect-loop.cc} and @file{tree-vect-loop-manip.cc} (loop specific parts +and general loop utilities), @file{tree-vect-slp} (loop-aware SLP +functionality), @file{tree-vect-stmts.cc}, @file{tree-vect-data-refs.cc} and +@file{tree-vect-slp-patterns.cc} containing the SLP pattern matcher. +Analysis of data references is in @file{tree-data-ref.cc}. + +SLP Vectorization. This pass performs vectorization of straight-line code. The +pass is implemented in @file{tree-vectorizer.cc} (the main driver), +@file{tree-vect-slp.cc}, @file{tree-vect-stmts.cc} and +@file{tree-vect-data-refs.cc}. + +Autoparallelization. This pass splits the loop iteration space to run +into several threads. The pass is implemented in @file{tree-parloops.cc}. + +Graphite is a loop transformation framework based on the polyhedral +model. Graphite stands for Gimple Represented as Polyhedra. The +internals of this infrastructure are documented in +@w{@uref{https://gcc.gnu.org/wiki/Graphite}}. The passes working on +this representation are implemented in the various @file{graphite-*} +files. + +@item Tree level if-conversion for vectorizer + +This pass applies if-conversion to simple loops to help vectorizer. +We identify if convertible loops, if-convert statements and merge +basic blocks in one big block. The idea is to present loop in such +form so that vectorizer can have one to one mapping between statements +and available vector operations. This pass is located in +@file{tree-if-conv.cc} and is described by @code{pass_if_conversion}. + +@item Conditional constant propagation + +This pass relaxes a lattice of values in order to identify those +that must be constant even in the presence of conditional branches. +The pass is located in @file{tree-ssa-ccp.cc} and is described +by @code{pass_ccp}. + +A related pass that works on memory loads and stores, and not just +register values, is located in @file{tree-ssa-ccp.cc} and described by +@code{pass_store_ccp}. + +@item Conditional copy propagation + +This is similar to constant propagation but the lattice of values is +the ``copy-of'' relation. It eliminates redundant copies from the +code. The pass is located in @file{tree-ssa-copy.cc} and described by +@code{pass_copy_prop}. + +A related pass that works on memory copies, and not just register +copies, is located in @file{tree-ssa-copy.cc} and described by +@code{pass_store_copy_prop}. + +@item Value range propagation + +This transformation is similar to constant propagation but +instead of propagating single constant values, it propagates +known value ranges. The implementation is based on Patterson's +range propagation algorithm (Accurate Static Branch Prediction by +Value Range Propagation, J. R. C. Patterson, PLDI '95). In +contrast to Patterson's algorithm, this implementation does not +propagate branch probabilities nor it uses more than a single +range per SSA name. This means that the current implementation +cannot be used for branch prediction (though adapting it would +not be difficult). The pass is located in @file{tree-vrp.cc} and is +described by @code{pass_vrp}. + +@item Folding built-in functions + +This pass simplifies built-in functions, as applicable, with constant +arguments or with inferable string lengths. It is located in +@file{tree-ssa-ccp.cc} and is described by @code{pass_fold_builtins}. + +@item Split critical edges + +This pass identifies critical edges and inserts empty basic blocks +such that the edge is no longer critical. The pass is located in +@file{tree-cfg.cc} and is described by @code{pass_split_crit_edges}. + +@item Control dependence dead code elimination + +This pass is a stronger form of dead code elimination that can +eliminate unnecessary control flow statements. It is located +in @file{tree-ssa-dce.cc} and is described by @code{pass_cd_dce}. + +@item Tail call elimination + +This pass identifies function calls that may be rewritten into +jumps. No code transformation is actually applied here, but the +data and control flow problem is solved. The code transformation +requires target support, and so is delayed until RTL@. In the +meantime @code{CALL_EXPR_TAILCALL} is set indicating the possibility. +The pass is located in @file{tree-tailcall.cc} and is described by +@code{pass_tail_calls}. The RTL transformation is handled by +@code{fixup_tail_calls} in @file{calls.cc}. + +@item Warn for function return without value + +For non-void functions, this pass locates return statements that do +not specify a value and issues a warning. Such a statement may have +been injected by falling off the end of the function. This pass is +run last so that we have as much time as possible to prove that the +statement is not reachable. It is located in @file{tree-cfg.cc} and +is described by @code{pass_warn_function_return}. + +@item Leave static single assignment form + +This pass rewrites the function such that it is in normal form. At +the same time, we eliminate as many single-use temporaries as possible, +so the intermediate language is no longer GIMPLE, but GENERIC@. The +pass is located in @file{tree-outof-ssa.cc} and is described by +@code{pass_del_ssa}. + +@item Merge PHI nodes that feed into one another + +This is part of the CFG cleanup passes. It attempts to join PHI nodes +from a forwarder CFG block into another block with PHI nodes. The +pass is located in @file{tree-cfgcleanup.cc} and is described by +@code{pass_merge_phi}. + +@item Return value optimization + +If a function always returns the same local variable, and that local +variable is an aggregate type, then the variable is replaced with the +return value for the function (i.e., the function's DECL_RESULT). This +is equivalent to the C++ named return value optimization applied to +GIMPLE@. The pass is located in @file{tree-nrv.cc} and is described by +@code{pass_nrv}. + +@item Return slot optimization + +If a function returns a memory object and is called as @code{var = +foo()}, this pass tries to change the call so that the address of +@code{var} is sent to the caller to avoid an extra memory copy. This +pass is located in @code{tree-nrv.cc} and is described by +@code{pass_return_slot}. + +@item Optimize calls to @code{__builtin_object_size} + +This is a propagation pass similar to CCP that tries to remove calls +to @code{__builtin_object_size} when the size of the object can be +computed at compile-time. This pass is located in +@file{tree-object-size.cc} and is described by +@code{pass_object_sizes}. + +@item Loop invariant motion + +This pass removes expensive loop-invariant computations out of loops. +The pass is located in @file{tree-ssa-loop.cc} and described by +@code{pass_lim}. + +@item Loop nest optimizations + +This is a family of loop transformations that works on loop nests. It +includes loop interchange, scaling, skewing and reversal and they are +all geared to the optimization of data locality in array traversals +and the removal of dependencies that hamper optimizations such as loop +parallelization and vectorization. The pass is located in +@file{tree-loop-linear.c} and described by +@code{pass_linear_transform}. + +@item Removal of empty loops + +This pass removes loops with no code in them. The pass is located in +@file{tree-ssa-loop-ivcanon.cc} and described by +@code{pass_empty_loop}. + +@item Unrolling of small loops + +This pass completely unrolls loops with few iterations. The pass +is located in @file{tree-ssa-loop-ivcanon.cc} and described by +@code{pass_complete_unroll}. + +@item Predictive commoning + +This pass makes the code reuse the computations from the previous +iterations of the loops, especially loads and stores to memory. +It does so by storing the values of these computations to a bank +of temporary variables that are rotated at the end of loop. To avoid +the need for this rotation, the loop is then unrolled and the copies +of the loop body are rewritten to use the appropriate version of +the temporary variable. This pass is located in @file{tree-predcom.cc} +and described by @code{pass_predcom}. + +@item Array prefetching + +This pass issues prefetch instructions for array references inside +loops. The pass is located in @file{tree-ssa-loop-prefetch.cc} and +described by @code{pass_loop_prefetch}. + +@item Reassociation + +This pass rewrites arithmetic expressions to enable optimizations that +operate on them, like redundancy elimination and vectorization. The +pass is located in @file{tree-ssa-reassoc.cc} and described by +@code{pass_reassoc}. + +@item Optimization of @code{stdarg} functions + +This pass tries to avoid the saving of register arguments into the +stack on entry to @code{stdarg} functions. If the function doesn't +use any @code{va_start} macros, no registers need to be saved. If +@code{va_start} macros are used, the @code{va_list} variables don't +escape the function, it is only necessary to save registers that will +be used in @code{va_arg} macros. For instance, if @code{va_arg} is +only used with integral types in the function, floating point +registers don't need to be saved. This pass is located in +@code{tree-stdarg.cc} and described by @code{pass_stdarg}. + +@end itemize + +@node RTL passes +@section RTL passes + +The following briefly describes the RTL generation and optimization +passes that are run after the Tree optimization passes. + +@itemize @bullet +@item RTL generation + +@c Avoiding overfull is tricky here. +The source files for RTL generation include +@file{stmt.cc}, +@file{calls.cc}, +@file{expr.cc}, +@file{explow.cc}, +@file{expmed.cc}, +@file{function.cc}, +@file{optabs.cc} +and @file{emit-rtl.cc}. +Also, the file +@file{insn-emit.cc}, generated from the machine description by the +program @code{genemit}, is used in this pass. The header file +@file{expr.h} is used for communication within this pass. + +@findex genflags +@findex gencodes +The header files @file{insn-flags.h} and @file{insn-codes.h}, +generated from the machine description by the programs @code{genflags} +and @code{gencodes}, tell this pass which standard names are available +for use and which patterns correspond to them. + +@item Generation of exception landing pads + +This pass generates the glue that handles communication between the +exception handling library routines and the exception handlers within +the function. Entry points in the function that are invoked by the +exception handling library are called @dfn{landing pads}. The code +for this pass is located in @file{except.cc}. + +@item Control flow graph cleanup + +This pass removes unreachable code, simplifies jumps to next, jumps to +jump, jumps across jumps, etc. The pass is run multiple times. +For historical reasons, it is occasionally referred to as the ``jump +optimization pass''. The bulk of the code for this pass is in +@file{cfgcleanup.cc}, and there are support routines in @file{cfgrtl.cc} +and @file{jump.cc}. + +@item Forward propagation of single-def values + +This pass attempts to remove redundant computation by substituting +variables that come from a single definition, and +seeing if the result can be simplified. It performs copy propagation +and addressing mode selection. The pass is run twice, with values +being propagated into loops only on the second run. The code is +located in @file{fwprop.cc}. + +@item Common subexpression elimination + +This pass removes redundant computation within basic blocks, and +optimizes addressing modes based on cost. The pass is run twice. +The code for this pass is located in @file{cse.cc}. + +@item Global common subexpression elimination + +This pass performs two +different types of GCSE depending on whether you are optimizing for +size or not (LCM based GCSE tends to increase code size for a gain in +speed, while Morel-Renvoise based GCSE does not). +When optimizing for size, GCSE is done using Morel-Renvoise Partial +Redundancy Elimination, with the exception that it does not try to move +invariants out of loops---that is left to the loop optimization pass. +If MR PRE GCSE is done, code hoisting (aka unification) is also done, as +well as load motion. +If you are optimizing for speed, LCM (lazy code motion) based GCSE is +done. LCM is based on the work of Knoop, Ruthing, and Steffen. LCM +based GCSE also does loop invariant code motion. We also perform load +and store motion when optimizing for speed. +Regardless of which type of GCSE is used, the GCSE pass also performs +global constant and copy propagation. +The source file for this pass is @file{gcse.cc}, and the LCM routines +are in @file{lcm.cc}. + +@item Loop optimization + +This pass performs several loop related optimizations. +The source files @file{cfgloopanal.cc} and @file{cfgloopmanip.cc} contain +generic loop analysis and manipulation code. Initialization and finalization +of loop structures is handled by @file{loop-init.cc}. +A loop invariant motion pass is implemented in @file{loop-invariant.cc}. +Basic block level optimizations---unrolling, and peeling loops--- +are implemented in @file{loop-unroll.cc}. +Replacing of the exit condition of loops by special machine-dependent +instructions is handled by @file{loop-doloop.cc}. + +@item Jump bypassing + +This pass is an aggressive form of GCSE that transforms the control +flow graph of a function by propagating constants into conditional +branch instructions. The source file for this pass is @file{gcse.cc}. + +@item If conversion + +This pass attempts to replace conditional branches and surrounding +assignments with arithmetic, boolean value producing comparison +instructions, and conditional move instructions. In the very last +invocation after reload/LRA, it will generate predicated instructions +when supported by the target. The code is located in @file{ifcvt.cc}. + +@item Web construction + +This pass splits independent uses of each pseudo-register. This can +improve effect of the other transformation, such as CSE or register +allocation. The code for this pass is located in @file{web.cc}. + +@item Instruction combination + +This pass attempts to combine groups of two or three instructions that +are related by data flow into single instructions. It combines the +RTL expressions for the instructions by substitution, simplifies the +result using algebra, and then attempts to match the result against +the machine description. The code is located in @file{combine.cc}. + +@item Mode switching optimization + +This pass looks for instructions that require the processor to be in a +specific ``mode'' and minimizes the number of mode changes required to +satisfy all users. What these modes are, and what they apply to are +completely target-specific. The code for this pass is located in +@file{mode-switching.cc}. + +@cindex modulo scheduling +@cindex sms, swing, software pipelining +@item Modulo scheduling + +This pass looks at innermost loops and reorders their instructions +by overlapping different iterations. Modulo scheduling is performed +immediately before instruction scheduling. The code for this pass is +located in @file{modulo-sched.cc}. + +@item Instruction scheduling + +This pass looks for instructions whose output will not be available by +the time that it is used in subsequent instructions. Memory loads and +floating point instructions often have this behavior on RISC machines. +It re-orders instructions within a basic block to try to separate the +definition and use of items that otherwise would cause pipeline +stalls. This pass is performed twice, before and after register +allocation. The code for this pass is located in @file{haifa-sched.cc}, +@file{sched-deps.cc}, @file{sched-ebb.cc}, @file{sched-rgn.cc} and +@file{sched-vis.c}. + +@item Register allocation + +These passes make sure that all occurrences of pseudo registers are +eliminated, either by allocating them to a hard register, replacing +them by an equivalent expression (e.g.@: a constant) or by placing +them on the stack. This is done in several subpasses: + +@itemize @bullet +@item +The integrated register allocator (@acronym{IRA}). It is called +integrated because coalescing, register live range splitting, and hard +register preferencing are done on-the-fly during coloring. It also +has better integration with the reload/LRA pass. Pseudo-registers spilled +by the allocator or the reload/LRA have still a chance to get +hard-registers if the reload/LRA evicts some pseudo-registers from +hard-registers. The allocator helps to choose better pseudos for +spilling based on their live ranges and to coalesce stack slots +allocated for the spilled pseudo-registers. IRA is a regional +register allocator which is transformed into Chaitin-Briggs allocator +if there is one region. By default, IRA chooses regions using +register pressure but the user can force it to use one region or +regions corresponding to all loops. + +Source files of the allocator are @file{ira.cc}, @file{ira-build.cc}, +@file{ira-costs.cc}, @file{ira-conflicts.cc}, @file{ira-color.cc}, +@file{ira-emit.cc}, @file{ira-lives}, plus header files @file{ira.h} +and @file{ira-int.h} used for the communication between the allocator +and the rest of the compiler and between the IRA files. + +@cindex reloading +@item +Reloading. This pass renumbers pseudo registers with the hardware +registers numbers they were allocated. Pseudo registers that did not +get hard registers are replaced with stack slots. Then it finds +instructions that are invalid because a value has failed to end up in +a register, or has ended up in a register of the wrong kind. It fixes +up these instructions by reloading the problematical values +temporarily into registers. Additional instructions are generated to +do the copying. + +The reload pass also optionally eliminates the frame pointer and inserts +instructions to save and restore call-clobbered registers around calls. + +Source files are @file{reload.cc} and @file{reload1.cc}, plus the header +@file{reload.h} used for communication between them. + +@cindex Local Register Allocator (LRA) +@item +This pass is a modern replacement of the reload pass. Source files +are @file{lra.cc}, @file{lra-assign.c}, @file{lra-coalesce.cc}, +@file{lra-constraints.cc}, @file{lra-eliminations.cc}, +@file{lra-lives.cc}, @file{lra-remat.cc}, @file{lra-spills.cc}, the +header @file{lra-int.h} used for communication between them, and the +header @file{lra.h} used for communication between LRA and the rest of +compiler. + +Unlike the reload pass, intermediate LRA decisions are reflected in +RTL as much as possible. This reduces the number of target-dependent +macros and hooks, leaving instruction constraints as the primary +source of control. + +LRA is run on targets for which TARGET_LRA_P returns true. +@end itemize + +@item Basic block reordering + +This pass implements profile guided code positioning. If profile +information is not available, various types of static analysis are +performed to make the predictions normally coming from the profile +feedback (IE execution frequency, branch probability, etc). It is +implemented in the file @file{bb-reorder.cc}, and the various +prediction routines are in @file{predict.cc}. + +@item Variable tracking + +This pass computes where the variables are stored at each +position in code and generates notes describing the variable locations +to RTL code. The location lists are then generated according to these +notes to debug information if the debugging information format supports +location lists. The code is located in @file{var-tracking.cc}. + +@item Delayed branch scheduling + +This optional pass attempts to find instructions that can go into the +delay slots of other instructions, usually jumps and calls. The code +for this pass is located in @file{reorg.cc}. + +@item Branch shortening + +On many RISC machines, branch instructions have a limited range. +Thus, longer sequences of instructions must be used for long branches. +In this pass, the compiler figures out what how far each instruction +will be from each other instruction, and therefore whether the usual +instructions, or the longer sequences, must be used for each branch. +The code for this pass is located in @file{final.cc}. + +@item Register-to-stack conversion + +Conversion from usage of some hard registers to usage of a register +stack may be done at this point. Currently, this is supported only +for the floating-point registers of the Intel 80387 coprocessor. The +code for this pass is located in @file{reg-stack.cc}. + +@item Final + +This pass outputs the assembler code for the function. The source files +are @file{final.cc} plus @file{insn-output.cc}; the latter is generated +automatically from the machine description by the tool @file{genoutput}. +The header file @file{conditions.h} is used for communication between +these files. + +@item Debugging information output + +This is run after final because it must output the stack slot offsets +for pseudo registers that did not get hard registers. Source files +are @file{dwarfout.c} for +DWARF symbol table format, files @file{dwarf2out.cc} and @file{dwarf2asm.cc} +for DWARF2 symbol table format, and @file{vmsdbgout.cc} for VMS debug +symbol table format. + +@end itemize + +@node Optimization info +@section Optimization info +@include optinfo.texi diff --git a/gcc/doc/plugins.texi b/gcc/doc/plugins.texi new file mode 100644 index 00000000000..6d1a5fa7607 --- /dev/null +++ b/gcc/doc/plugins.texi @@ -0,0 +1,562 @@ +@c Copyright (C) 2009-2022 Free Software Foundation, Inc. +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Plugins +@chapter Plugins +@cindex Plugins + +GCC plugins are loadable modules that provide extra features to the +compiler. Like GCC itself they can be distributed in source and +binary forms. + +GCC plugins provide developers with a rich subset of +the GCC API to allow them to extend GCC as they see fit. +Whether it is writing an additional optimization pass, +transforming code, or analyzing information, plugins +can be quite useful. + +@menu +* Plugins loading:: How can we load plugins. +* Plugin API:: The APIs for plugins. +* Plugins pass:: How a plugin interact with the pass manager. +* Plugins GC:: How a plugin Interact with GCC Garbage Collector. +* Plugins description:: Giving information about a plugin itself. +* Plugins attr:: Registering custom attributes or pragmas. +* Plugins recording:: Recording information about pass execution. +* Plugins gate:: Controlling which passes are being run. +* Plugins tracking:: Keeping track of available passes. +* Plugins building:: How can we build a plugin. +@end menu + +@node Plugins loading +@section Loading Plugins + +Plugins are supported on platforms that support @option{-ldl +-rdynamic} as well as Windows/MinGW. They are loaded by the compiler +using @code{dlopen} or equivalent and invoked at pre-determined +locations in the compilation process. + +Plugins are loaded with + +@option{-fplugin=/path/to/@var{name}.@var{ext}} @option{-fplugin-arg-@var{name}-@var{key1}[=@var{value1}]} + +Where @var{name} is the plugin name and @var{ext} is the platform-specific +dynamic library extension. It should be @code{dll} on Windows/MinGW, +@code{dylib} on Darwin/Mac OS X, and @code{so} on all other platforms. +The plugin arguments are parsed by GCC and passed to respective +plugins as key-value pairs. Multiple plugins can be invoked by +specifying multiple @option{-fplugin} arguments. + +A plugin can be simply given by its short name (no dots or +slashes). When simply passing @option{-fplugin=@var{name}}, the plugin is +loaded from the @file{plugin} directory, so @option{-fplugin=@var{name}} is +the same as @option{-fplugin=`gcc -print-file-name=plugin`/@var{name}.@var{ext}}, +using backquote shell syntax to query the @file{plugin} directory. + +@node Plugin API +@section Plugin API + +Plugins are activated by the compiler at specific events as defined in +@file{gcc-plugin.h}. For each event of interest, the plugin should +call @code{register_callback} specifying the name of the event and +address of the callback function that will handle that event. + +The header @file{gcc-plugin.h} must be the first gcc header to be included. + +@subsection Plugin license check + +Every plugin should define the global symbol @code{plugin_is_GPL_compatible} +to assert that it has been licensed under a GPL-compatible license. +If this symbol does not exist, the compiler will emit a fatal error +and exit with the error message: + +@smallexample +fatal error: plugin @var{name} is not licensed under a GPL-compatible license +@var{name}: undefined symbol: plugin_is_GPL_compatible +compilation terminated +@end smallexample + +The declared type of the symbol should be int, to match a forward declaration +in @file{gcc-plugin.h} that suppresses C++ mangling. It does not need to be in +any allocated section, though. The compiler merely asserts that +the symbol exists in the global scope. Something like this is enough: + +@smallexample +int plugin_is_GPL_compatible; +@end smallexample + +@subsection Plugin initialization + +Every plugin should export a function called @code{plugin_init} that +is called right after the plugin is loaded. This function is +responsible for registering all the callbacks required by the plugin +and do any other required initialization. + +This function is called from @code{compile_file} right before invoking +the parser. The arguments to @code{plugin_init} are: + +@itemize @bullet +@item @code{plugin_info}: Plugin invocation information. +@item @code{version}: GCC version. +@end itemize + +The @code{plugin_info} struct is defined as follows: + +@smallexample +struct plugin_name_args +@{ + char *base_name; /* Short name of the plugin + (filename without .so suffix). */ + const char *full_name; /* Path to the plugin as specified with + -fplugin=. */ + int argc; /* Number of arguments specified with + -fplugin-arg-.... */ + struct plugin_argument *argv; /* Array of ARGC key-value pairs. */ + const char *version; /* Version string provided by plugin. */ + const char *help; /* Help string provided by plugin. */ +@} +@end smallexample + +If initialization fails, @code{plugin_init} must return a non-zero +value. Otherwise, it should return 0. + +The version of the GCC compiler loading the plugin is described by the +following structure: + +@smallexample +struct plugin_gcc_version +@{ + const char *basever; + const char *datestamp; + const char *devphase; + const char *revision; + const char *configuration_arguments; +@}; +@end smallexample + +The function @code{plugin_default_version_check} takes two pointers to +such structure and compare them field by field. It can be used by the +plugin's @code{plugin_init} function. + +The version of GCC used to compile the plugin can be found in the symbol +@code{gcc_version} defined in the header @file{plugin-version.h}. The +recommended version check to perform looks like + +@smallexample +#include "plugin-version.h" +... + +int +plugin_init (struct plugin_name_args *plugin_info, + struct plugin_gcc_version *version) +@{ + if (!plugin_default_version_check (version, &gcc_version)) + return 1; + +@} +@end smallexample + +but you can also check the individual fields if you want a less strict check. + +@subsection Plugin callbacks + +Callback functions have the following prototype: + +@smallexample +/* The prototype for a plugin callback function. + gcc_data - event-specific data provided by GCC + user_data - plugin-specific data provided by the plug-in. */ +typedef void (*plugin_callback_func)(void *gcc_data, void *user_data); +@end smallexample + +Callbacks can be invoked at the following pre-determined events: + + +@smallexample +enum plugin_event +@{ + PLUGIN_START_PARSE_FUNCTION, /* Called before parsing the body of a function. */ + PLUGIN_FINISH_PARSE_FUNCTION, /* After finishing parsing a function. */ + PLUGIN_PASS_MANAGER_SETUP, /* To hook into pass manager. */ + PLUGIN_FINISH_TYPE, /* After finishing parsing a type. */ + PLUGIN_FINISH_DECL, /* After finishing parsing a declaration. */ + PLUGIN_FINISH_UNIT, /* Useful for summary processing. */ + PLUGIN_PRE_GENERICIZE, /* Allows to see low level AST in C and C++ frontends. */ + PLUGIN_FINISH, /* Called before GCC exits. */ + PLUGIN_INFO, /* Information about the plugin. */ + PLUGIN_GGC_START, /* Called at start of GCC Garbage Collection. */ + PLUGIN_GGC_MARKING, /* Extend the GGC marking. */ + PLUGIN_GGC_END, /* Called at end of GGC. */ + PLUGIN_REGISTER_GGC_ROOTS, /* Register an extra GGC root table. */ + PLUGIN_ATTRIBUTES, /* Called during attribute registration */ + PLUGIN_START_UNIT, /* Called before processing a translation unit. */ + PLUGIN_PRAGMAS, /* Called during pragma registration. */ + /* Called before first pass from all_passes. */ + PLUGIN_ALL_PASSES_START, + /* Called after last pass from all_passes. */ + PLUGIN_ALL_PASSES_END, + /* Called before first ipa pass. */ + PLUGIN_ALL_IPA_PASSES_START, + /* Called after last ipa pass. */ + PLUGIN_ALL_IPA_PASSES_END, + /* Allows to override pass gate decision for current_pass. */ + PLUGIN_OVERRIDE_GATE, + /* Called before executing a pass. */ + PLUGIN_PASS_EXECUTION, + /* Called before executing subpasses of a GIMPLE_PASS in + execute_ipa_pass_list. */ + PLUGIN_EARLY_GIMPLE_PASSES_START, + /* Called after executing subpasses of a GIMPLE_PASS in + execute_ipa_pass_list. */ + PLUGIN_EARLY_GIMPLE_PASSES_END, + /* Called when a pass is first instantiated. */ + PLUGIN_NEW_PASS, +/* Called when a file is #include-d or given via the #line directive. + This could happen many times. The event data is the included file path, + as a const char* pointer. */ + PLUGIN_INCLUDE_FILE, + + /* Called when -fanalyzer starts. The event data is an + ana::plugin_analyzer_init_iface *. */ + PLUGIN_ANALYZER_INIT, + + PLUGIN_EVENT_FIRST_DYNAMIC /* Dummy event used for indexing callback + array. */ +@}; +@end smallexample + +In addition, plugins can also look up the enumerator of a named event, +and / or generate new events dynamically, by calling the function +@code{get_named_event_id}. + +To register a callback, the plugin calls @code{register_callback} with +the arguments: + +@itemize +@item @code{char *name}: Plugin name. +@item @code{int event}: The event code. +@item @code{plugin_callback_func callback}: The function that handles @code{event}. +@item @code{void *user_data}: Pointer to plugin-specific data. +@end itemize + +For the @i{PLUGIN_PASS_MANAGER_SETUP}, @i{PLUGIN_INFO}, and +@i{PLUGIN_REGISTER_GGC_ROOTS} pseudo-events the @code{callback} should be null, +and the @code{user_data} is specific. + +When the @i{PLUGIN_PRAGMAS} event is triggered (with a null pointer as +data from GCC), plugins may register their own pragmas. Notice that +pragmas are not available from @file{lto1}, so plugins used with +@code{-flto} option to GCC during link-time optimization cannot use +pragmas and do not even see functions like @code{c_register_pragma} or +@code{pragma_lex}. + +The @i{PLUGIN_INCLUDE_FILE} event, with a @code{const char*} file path as +GCC data, is triggered for processing of @code{#include} or +@code{#line} directives. + +The @i{PLUGIN_FINISH} event is the last time that plugins can call GCC +functions, notably emit diagnostics with @code{warning}, @code{error} +etc. + + +@node Plugins pass +@section Interacting with the pass manager + +There needs to be a way to add/reorder/remove passes dynamically. This +is useful for both analysis plugins (plugging in after a certain pass +such as CFG or an IPA pass) and optimization plugins. + +Basic support for inserting new passes or replacing existing passes is +provided. A plugin registers a new pass with GCC by calling +@code{register_callback} with the @code{PLUGIN_PASS_MANAGER_SETUP} +event and a pointer to a @code{struct register_pass_info} object defined as follows + +@smallexample +enum pass_positioning_ops +@{ + PASS_POS_INSERT_AFTER, // Insert after the reference pass. + PASS_POS_INSERT_BEFORE, // Insert before the reference pass. + PASS_POS_REPLACE // Replace the reference pass. +@}; + +struct register_pass_info +@{ + struct opt_pass *pass; /* New pass provided by the plugin. */ + const char *reference_pass_name; /* Name of the reference pass for hooking + up the new pass. */ + int ref_pass_instance_number; /* Insert the pass at the specified + instance number of the reference pass. */ + /* Do it for every instance if it is 0. */ + enum pass_positioning_ops pos_op; /* how to insert the new pass. */ +@}; + + +/* Sample plugin code that registers a new pass. */ +int +plugin_init (struct plugin_name_args *plugin_info, + struct plugin_gcc_version *version) +@{ + struct register_pass_info pass_info; + + ... + + /* Code to fill in the pass_info object with new pass information. */ + + ... + + /* Register the new pass. */ + register_callback (plugin_info->base_name, PLUGIN_PASS_MANAGER_SETUP, NULL, &pass_info); + + ... +@} +@end smallexample + + +@node Plugins GC +@section Interacting with the GCC Garbage Collector + +Some plugins may want to be informed when GGC (the GCC Garbage +Collector) is running. They can register callbacks for the +@code{PLUGIN_GGC_START} and @code{PLUGIN_GGC_END} events (for which +the callback is called with a null @code{gcc_data}) to be notified of +the start or end of the GCC garbage collection. + +Some plugins may need to have GGC mark additional data. This can be +done by registering a callback (called with a null @code{gcc_data}) +for the @code{PLUGIN_GGC_MARKING} event. Such callbacks can call the +@code{ggc_set_mark} routine, preferably through the @code{ggc_mark} macro +(and conversely, these routines should usually not be used in plugins +outside of the @code{PLUGIN_GGC_MARKING} event). Plugins that wish to hold +weak references to gc data may also use this event to drop weak references when +the object is about to be collected. The @code{ggc_marked_p} function can be +used to tell if an object is marked, or is about to be collected. The +@code{gt_clear_cache} overloads which some types define may also be of use in +managing weak references. + +Some plugins may need to add extra GGC root tables, e.g.@: to handle their own +@code{GTY}-ed data. This can be done with the @code{PLUGIN_REGISTER_GGC_ROOTS} +pseudo-event with a null callback and the extra root table (of type @code{struct +ggc_root_tab*}) as @code{user_data}. Running the + @code{gengtype -p @var{source-dir} @var{file-list} @var{plugin*.c} ...} +utility generates these extra root tables. + +You should understand the details of memory management inside GCC +before using @code{PLUGIN_GGC_MARKING} or @code{PLUGIN_REGISTER_GGC_ROOTS}. + + +@node Plugins description +@section Giving information about a plugin + +A plugin should give some information to the user about itself. This +uses the following structure: + +@smallexample +struct plugin_info +@{ + const char *version; + const char *help; +@}; +@end smallexample + +Such a structure is passed as the @code{user_data} by the plugin's +init routine using @code{register_callback} with the +@code{PLUGIN_INFO} pseudo-event and a null callback. + +@node Plugins attr +@section Registering custom attributes or pragmas + +For analysis (or other) purposes it is useful to be able to add custom +attributes or pragmas. + +The @code{PLUGIN_ATTRIBUTES} callback is called during attribute +registration. Use the @code{register_attribute} function to register +custom attributes. + +@smallexample +/* Attribute handler callback */ +static tree +handle_user_attribute (tree *node, tree name, tree args, + int flags, bool *no_add_attrs) +@{ + return NULL_TREE; +@} + +/* Attribute definition */ +static struct attribute_spec user_attr = + @{ "user", 1, 1, false, false, false, false, handle_user_attribute, NULL @}; + +/* Plugin callback called during attribute registration. +Registered with register_callback (plugin_name, PLUGIN_ATTRIBUTES, register_attributes, NULL) +*/ +static void +register_attributes (void *event_data, void *data) +@{ + warning (0, G_("Callback to register attributes")); + register_attribute (&user_attr); +@} + +@end smallexample + + +The @i{PLUGIN_PRAGMAS} callback is called once during pragmas +registration. Use the @code{c_register_pragma}, +@code{c_register_pragma_with_data}, +@code{c_register_pragma_with_expansion}, +@code{c_register_pragma_with_expansion_and_data} functions to register +custom pragmas and their handlers (which often want to call +@code{pragma_lex}) from @file{c-family/c-pragma.h}. + +@smallexample +/* Plugin callback called during pragmas registration. Registered with + register_callback (plugin_name, PLUGIN_PRAGMAS, + register_my_pragma, NULL); +*/ +static void +register_my_pragma (void *event_data, void *data) +@{ + warning (0, G_("Callback to register pragmas")); + c_register_pragma ("GCCPLUGIN", "sayhello", handle_pragma_sayhello); +@} +@end smallexample + +It is suggested to pass @code{"GCCPLUGIN"} (or a short name identifying +your plugin) as the ``space'' argument of your pragma. + +Pragmas registered with @code{c_register_pragma_with_expansion} or +@code{c_register_pragma_with_expansion_and_data} support +preprocessor expansions. For example: + +@smallexample +#define NUMBER 10 +#pragma GCCPLUGIN foothreshold (NUMBER) +@end smallexample + +@node Plugins recording +@section Recording information about pass execution + +The event PLUGIN_PASS_EXECUTION passes the pointer to the executed pass +(the same as current_pass) as @code{gcc_data} to the callback. You can also +inspect cfun to find out about which function this pass is executed for. +Note that this event will only be invoked if the gate check (if +applicable, modified by PLUGIN_OVERRIDE_GATE) succeeds. +You can use other hooks, like @code{PLUGIN_ALL_PASSES_START}, +@code{PLUGIN_ALL_PASSES_END}, @code{PLUGIN_ALL_IPA_PASSES_START}, +@code{PLUGIN_ALL_IPA_PASSES_END}, @code{PLUGIN_EARLY_GIMPLE_PASSES_START}, +and/or @code{PLUGIN_EARLY_GIMPLE_PASSES_END} to manipulate global state +in your plugin(s) in order to get context for the pass execution. + + +@node Plugins gate +@section Controlling which passes are being run + +After the original gate function for a pass is called, its result +- the gate status - is stored as an integer. +Then the event @code{PLUGIN_OVERRIDE_GATE} is invoked, with a pointer +to the gate status in the @code{gcc_data} parameter to the callback function. +A nonzero value of the gate status means that the pass is to be executed. +You can both read and write the gate status via the passed pointer. + + +@node Plugins tracking +@section Keeping track of available passes + +When your plugin is loaded, you can inspect the various +pass lists to determine what passes are available. However, other +plugins might add new passes. Also, future changes to GCC might cause +generic passes to be added after plugin loading. +When a pass is first added to one of the pass lists, the event +@code{PLUGIN_NEW_PASS} is invoked, with the callback parameter +@code{gcc_data} pointing to the new pass. + + +@node Plugins building +@section Building GCC plugins + +If plugins are enabled, GCC installs the headers needed to build a +plugin (somewhere in the installation tree, e.g.@: under +@file{/usr/local}). In particular a @file{plugin/include} directory +is installed, containing all the header files needed to build plugins. + +On most systems, you can query this @code{plugin} directory by +invoking @command{gcc -print-file-name=plugin} (replace if needed +@command{gcc} with the appropriate program path). + +Inside plugins, this @code{plugin} directory name can be queried by +calling @code{default_plugin_dir_name ()}. + +Plugins may know, when they are compiled, the GCC version for which +@file{plugin-version.h} is provided. The constant macros +@code{GCCPLUGIN_VERSION_MAJOR}, @code{GCCPLUGIN_VERSION_MINOR}, +@code{GCCPLUGIN_VERSION_PATCHLEVEL}, @code{GCCPLUGIN_VERSION} are +integer numbers, so a plugin could ensure it is built for GCC 4.7 with +@smallexample +#if GCCPLUGIN_VERSION != 4007 +#error this GCC plugin is for GCC 4.7 +#endif +@end smallexample + +The following GNU Makefile excerpt shows how to build a simple plugin: + +@smallexample +HOST_GCC=g++ +TARGET_GCC=gcc +PLUGIN_SOURCE_FILES= plugin1.c plugin2.cc +GCCPLUGINS_DIR:= $(shell $(TARGET_GCC) -print-file-name=plugin) +CXXFLAGS+= -I$(GCCPLUGINS_DIR)/include -fPIC -fno-rtti -O2 + +plugin.so: $(PLUGIN_SOURCE_FILES) + $(HOST_GCC) -shared $(CXXFLAGS) $^ -o $@@ +@end smallexample + +A single source file plugin may be built with @code{g++ -I`gcc +-print-file-name=plugin`/include -fPIC -shared -fno-rtti -O2 plugin.cc -o +plugin.so}, using backquote shell syntax to query the @file{plugin} +directory. + +Plugin support on Windows/MinGW has a number of limitations and +additional requirements. When building a plugin on Windows we have to +link an import library for the corresponding backend executable, for +example, @file{cc1.exe}, @file{cc1plus.exe}, etc., in order to gain +access to the symbols provided by GCC. This means that on Windows a +plugin is language-specific, for example, for C, C++, etc. If you wish +to use your plugin with multiple languages, then you will need to +build multiple plugin libraries and either instruct your users on how +to load the correct version or provide a compiler wrapper that does +this automatically. + +Additionally, on Windows the plugin library has to export the +@code{plugin_is_GPL_compatible} and @code{plugin_init} symbols. If you +do not wish to modify the source code of your plugin, then you can use +the @option{-Wl,--export-all-symbols} option or provide a suitable DEF +file. Alternatively, you can export just these two symbols by decorating +them with @code{__declspec(dllexport)}, for example: + +@smallexample +#ifdef _WIN32 +__declspec(dllexport) +#endif +int plugin_is_GPL_compatible; + +#ifdef _WIN32 +__declspec(dllexport) +#endif +int plugin_init (plugin_name_args *, plugin_gcc_version *) +@end smallexample + +The import libraries are installed into the @code{plugin} directory +and their names are derived by appending the @code{.a} extension to +the backend executable names, for example, @file{cc1.exe.a}, +@file{cc1plus.exe.a}, etc. The following command line shows how to +build the single source file plugin on Windows to be used with the C++ +compiler: + +@smallexample +g++ -I`gcc -print-file-name=plugin`/include -shared -Wl,--export-all-symbols \ +-o plugin.dll plugin.cc `gcc -print-file-name=plugin`/cc1plus.exe.a +@end smallexample + +When a plugin needs to use @command{gengtype}, be sure that both +@file{gengtype} and @file{gtype.state} have the same version as the +GCC for which the plugin is built. diff --git a/gcc/doc/poly-int.texi b/gcc/doc/poly-int.texi new file mode 100644 index 00000000000..d60bb02aabf --- /dev/null +++ b/gcc/doc/poly-int.texi @@ -0,0 +1,1060 @@ +@node poly_int +@chapter Sizes and offsets as runtime invariants +@cindex polynomial integers +@findex poly_int + +GCC allows the size of a hardware register to be a runtime invariant +rather than a compile-time constant. This in turn means that various +sizes and offsets must also be runtime invariants rather than +compile-time constants, such as: + +@itemize @bullet +@item +the size of a general @code{machine_mode} (@pxref{Machine Modes}); + +@item +the size of a spill slot; + +@item +the offset of something within a stack frame; + +@item +the number of elements in a vector; + +@item +the size and offset of a @code{mem} rtx (@pxref{Regs and Memory}); and + +@item +the byte offset in a @code{subreg} rtx (@pxref{Regs and Memory}). +@end itemize + +The motivating example is the Arm SVE ISA, whose vector registers can be +any multiple of 128 bits between 128 and 2048 inclusive. The compiler +normally produces code that works for all SVE register sizes, with the +actual size only being known at runtime. + +GCC's main representation of such runtime invariants is the +@code{poly_int} class. This chapter describes what @code{poly_int} +does, lists the available operations, and gives some general +usage guidelines. + +@menu +* Overview of @code{poly_int}:: +* Consequences of using @code{poly_int}:: +* Comparisons involving @code{poly_int}:: +* Arithmetic on @code{poly_int}s:: +* Alignment of @code{poly_int}s:: +* Computing bounds on @code{poly_int}s:: +* Converting @code{poly_int}s:: +* Miscellaneous @code{poly_int} routines:: +* Guidelines for using @code{poly_int}:: +@end menu + +@node Overview of @code{poly_int} +@section Overview of @code{poly_int} + +@cindex @code{poly_int}, runtime value +We define indeterminates @var{x1}, @dots{}, @var{xn} whose values are +only known at runtime and use polynomials of the form: + +@smallexample +@var{c0} + @var{c1} * @var{x1} + @dots{} + @var{cn} * @var{xn} +@end smallexample + +to represent a size or offset whose value might depend on some +of these indeterminates. The coefficients @var{c0}, @dots{}, @var{cn} +are always known at compile time, with the @var{c0} term being the +``constant'' part that does not depend on any runtime value. + +GCC uses the @code{poly_int} class to represent these coefficients. +The class has two template parameters: the first specifies the number of +coefficients (@var{n} + 1) and the second specifies the type of the +coefficients. For example, @samp{poly_int<2, unsigned short>} represents +a polynomial with two coefficients (and thus one indeterminate), with each +coefficient having type @code{unsigned short}. When @var{n} is 0, +the class degenerates to a single compile-time constant @var{c0}. + +@cindex @code{poly_int}, template parameters +@findex NUM_POLY_INT_COEFFS +The number of coefficients needed for compilation is a fixed +property of each target and is specified by the configuration macro +@code{NUM_POLY_INT_COEFFS}. The default value is 1, since most targets +do not have such runtime invariants. Targets that need a different +value should @code{#define} the macro in their @file{@var{cpu}-modes.def} +file. @xref{Back End}. + +@cindex @code{poly_int}, invariant range +@code{poly_int} makes the simplifying requirement that each indeterminate +must be a nonnegative integer. An indeterminate value of 0 should usually +represent the minimum possible runtime value, with @var{c0} specifying +the value in that case. + +For example, when targetting the Arm SVE ISA, the single indeterminate +represents the number of 128-bit blocks in a vector @emph{beyond the minimum +length of 128 bits}. Thus the number of 64-bit doublewords in a vector +is 2 + 2 * @var{x1}. If an aggregate has a single SVE vector and 16 +additional bytes, its total size is 32 + 16 * @var{x1} bytes. + +The header file @file{poly-int-types.h} provides typedefs for the +most common forms of @code{poly_int}, all having +@code{NUM_POLY_INT_COEFFS} coefficients: + +@cindex @code{poly_int}, main typedefs +@table @code +@item poly_uint16 +a @samp{poly_int} with @code{unsigned short} coefficients. + +@item poly_int64 +a @samp{poly_int} with @code{HOST_WIDE_INT} coefficients. + +@item poly_uint64 +a @samp{poly_int} with @code{unsigned HOST_WIDE_INT} coefficients. + +@item poly_offset_int +a @samp{poly_int} with @code{offset_int} coefficients. + +@item poly_wide_int +a @samp{poly_int} with @code{wide_int} coefficients. + +@item poly_widest_int +a @samp{poly_int} with @code{widest_int} coefficients. +@end table + +Since the main purpose of @code{poly_int} is to represent sizes and +offsets, the last two typedefs are only rarely used. + +@node Consequences of using @code{poly_int} +@section Consequences of using @code{poly_int} + +The two main consequences of using polynomial sizes and offsets are that: + +@itemize +@item +there is no total ordering between the values at compile time, and + +@item +some operations might yield results that cannot be expressed as a +@code{poly_int}. +@end itemize + +For example, if @var{x} is a runtime invariant, we cannot tell at +compile time whether: + +@smallexample +3 + 4@var{x} <= 1 + 5@var{x} +@end smallexample + +since the condition is false when @var{x} <= 1 and true when @var{x} >= 2. + +Similarly, @code{poly_int} cannot represent the result of: + +@smallexample +(3 + 4@var{x}) * (1 + 5@var{x}) +@end smallexample + +since it cannot (and in practice does not need to) store powers greater +than one. It also cannot represent the result of: + +@smallexample +(3 + 4@var{x}) / (1 + 5@var{x}) +@end smallexample + +The following sections describe how we deal with these restrictions. + +@cindex @code{poly_int}, use in target-independent code +As described earlier, a @code{poly_int<1, @var{T}>} has no indeterminates +and so degenerates to a compile-time constant of type @var{T}. It would +be possible in that case to do all normal arithmetic on the @var{T}, +and to compare the @var{T} using the normal C++ operators. We deliberately +prevent target-independent code from doing this, since the compiler needs +to support other @code{poly_int<@var{n}, @var{T}>} as well, regardless of +the current target's @code{NUM_POLY_INT_COEFFS}. + +@cindex @code{poly_int}, use in target-specific code +However, it would be very artificial to force target-specific code +to follow these restrictions if the target has no runtime indeterminates. +There is therefore an implicit conversion from @code{poly_int<1, @var{T}>} +to @var{T} when compiling target-specific translation units. + +@node Comparisons involving @code{poly_int} +@section Comparisons involving @code{poly_int} + +In general we need to compare sizes and offsets in two situations: +those in which the values need to be ordered, and those in which +the values can be unordered. More loosely, the distinction is often +between values that have a definite link (usually because they refer to the +same underlying register or memory location) and values that have +no definite link. An example of the former is the relationship between +the inner and outer sizes of a subreg, where we must know at compile time +whether the subreg is paradoxical, partial, or complete. An example of +the latter is alias analysis: we might want to check whether two +arbitrary memory references overlap. + +Referring back to the examples in the previous section, it makes sense +to ask whether a memory reference of size @samp{3 + 4@var{x}} overlaps +one of size @samp{1 + 5@var{x}}, but it does not make sense to have a +subreg in which the outer mode has @samp{3 + 4@var{x}} bytes and the +inner mode has @samp{1 + 5@var{x}} bytes (or vice versa). Such subregs +are always invalid and should trigger an internal compiler error +if formed. + +The underlying operators are the same in both cases, but the distinction +affects how they are used. + +@menu +* Comparison functions for @code{poly_int}:: +* Properties of the @code{poly_int} comparisons:: +* Comparing potentially-unordered @code{poly_int}s:: +* Comparing ordered @code{poly_int}s:: +* Checking for a @code{poly_int} marker value:: +* Range checks on @code{poly_int}s:: +* Sorting @code{poly_int}s:: +@end menu + +@node Comparison functions for @code{poly_int} +@subsection Comparison functions for @code{poly_int} + +@code{poly_int} provides the following routines for checking whether +a particular condition ``may be'' (might be) true: + +@example +maybe_lt maybe_le maybe_eq maybe_ge maybe_gt + maybe_ne +@end example + +The functions have their natural meaning: + +@table @samp +@item maybe_lt(@var{a}, @var{b}) +Return true if @var{a} might be less than @var{b}. + +@item maybe_le(@var{a}, @var{b}) +Return true if @var{a} might be less than or equal to @var{b}. + +@item maybe_eq(@var{a}, @var{b}) +Return true if @var{a} might be equal to @var{b}. + +@item maybe_ne(@var{a}, @var{b}) +Return true if @var{a} might not be equal to @var{b}. + +@item maybe_ge(@var{a}, @var{b}) +Return true if @var{a} might be greater than or equal to @var{b}. + +@item maybe_gt(@var{a}, @var{b}) +Return true if @var{a} might be greater than @var{b}. +@end table + +For readability, @code{poly_int} also provides ``known'' inverses of these +functions: + +@example +known_lt (@var{a}, @var{b}) == !maybe_ge (@var{a}, @var{b}) +known_le (@var{a}, @var{b}) == !maybe_gt (@var{a}, @var{b}) +known_eq (@var{a}, @var{b}) == !maybe_ne (@var{a}, @var{b}) +known_ge (@var{a}, @var{b}) == !maybe_lt (@var{a}, @var{b}) +known_gt (@var{a}, @var{b}) == !maybe_le (@var{a}, @var{b}) +known_ne (@var{a}, @var{b}) == !maybe_eq (@var{a}, @var{b}) +@end example + +@node Properties of the @code{poly_int} comparisons +@subsection Properties of the @code{poly_int} comparisons + +All ``maybe'' relations except @code{maybe_ne} are transitive, so for example: + +@smallexample +maybe_lt (@var{a}, @var{b}) && maybe_lt (@var{b}, @var{c}) implies maybe_lt (@var{a}, @var{c}) +@end smallexample + +for all @var{a}, @var{b} and @var{c}. @code{maybe_lt}, @code{maybe_gt} +and @code{maybe_ne} are irreflexive, so for example: + +@smallexample +!maybe_lt (@var{a}, @var{a}) +@end smallexample + +is true for all @var{a}. @code{maybe_le}, @code{maybe_eq} and @code{maybe_ge} +are reflexive, so for example: + +@smallexample +maybe_le (@var{a}, @var{a}) +@end smallexample + +is true for all @var{a}. @code{maybe_eq} and @code{maybe_ne} are symmetric, so: + +@smallexample +maybe_eq (@var{a}, @var{b}) == maybe_eq (@var{b}, @var{a}) +maybe_ne (@var{a}, @var{b}) == maybe_ne (@var{b}, @var{a}) +@end smallexample + +for all @var{a} and @var{b}. In addition: + +@smallexample +maybe_le (@var{a}, @var{b}) == maybe_lt (@var{a}, @var{b}) || maybe_eq (@var{a}, @var{b}) +maybe_ge (@var{a}, @var{b}) == maybe_gt (@var{a}, @var{b}) || maybe_eq (@var{a}, @var{b}) +maybe_lt (@var{a}, @var{b}) == maybe_gt (@var{b}, @var{a}) +maybe_le (@var{a}, @var{b}) == maybe_ge (@var{b}, @var{a}) +@end smallexample + +However: + +@smallexample +maybe_le (@var{a}, @var{b}) && maybe_le (@var{b}, @var{a}) does not imply !maybe_ne (@var{a}, @var{b}) [== known_eq (@var{a}, @var{b})] +maybe_ge (@var{a}, @var{b}) && maybe_ge (@var{b}, @var{a}) does not imply !maybe_ne (@var{a}, @var{b}) [== known_eq (@var{a}, @var{b})] +@end smallexample + +One example is again @samp{@var{a} == 3 + 4@var{x}} +and @samp{@var{b} == 1 + 5@var{x}}, where @samp{maybe_le (@var{a}, @var{b})}, +@samp{maybe_ge (@var{a}, @var{b})} and @samp{maybe_ne (@var{a}, @var{b})} +all hold. @code{maybe_le} and @code{maybe_ge} are therefore not antisymetric +and do not form a partial order. + +From the above, it follows that: + +@itemize @bullet +@item +All ``known'' relations except @code{known_ne} are transitive. + +@item +@code{known_lt}, @code{known_ne} and @code{known_gt} are irreflexive. + +@item +@code{known_le}, @code{known_eq} and @code{known_ge} are reflexive. +@end itemize + +Also: + +@smallexample +known_lt (@var{a}, @var{b}) == known_gt (@var{b}, @var{a}) +known_le (@var{a}, @var{b}) == known_ge (@var{b}, @var{a}) +known_lt (@var{a}, @var{b}) implies !known_lt (@var{b}, @var{a}) [asymmetry] +known_gt (@var{a}, @var{b}) implies !known_gt (@var{b}, @var{a}) +known_le (@var{a}, @var{b}) && known_le (@var{b}, @var{a}) == known_eq (@var{a}, @var{b}) [== !maybe_ne (@var{a}, @var{b})] +known_ge (@var{a}, @var{b}) && known_ge (@var{b}, @var{a}) == known_eq (@var{a}, @var{b}) [== !maybe_ne (@var{a}, @var{b})] +@end smallexample + +@code{known_le} and @code{known_ge} are therefore antisymmetric and are +partial orders. However: + +@smallexample +known_le (@var{a}, @var{b}) does not imply known_lt (@var{a}, @var{b}) || known_eq (@var{a}, @var{b}) +known_ge (@var{a}, @var{b}) does not imply known_gt (@var{a}, @var{b}) || known_eq (@var{a}, @var{b}) +@end smallexample + +For example, @samp{known_le (4, 4 + 4@var{x})} holds because the runtime +indeterminate @var{x} is a nonnegative integer, but neither +@code{known_lt (4, 4 + 4@var{x})} nor @code{known_eq (4, 4 + 4@var{x})} hold. + +@node Comparing potentially-unordered @code{poly_int}s +@subsection Comparing potentially-unordered @code{poly_int}s + +In cases where there is no definite link between two @code{poly_int}s, +we can usually make a conservatively-correct assumption. For example, +the conservative assumption for alias analysis is that two references +@emph{might} alias. + +One way of checking whether [@var{begin1}, @var{end1}) might overlap +[@var{begin2}, @var{end2}) using the @code{poly_int} comparisons is: + +@smallexample +maybe_gt (@var{end1}, @var{begin2}) && maybe_gt (@var{end2}, @var{begin1}) +@end smallexample + +and another (equivalent) way is: + +@smallexample +!(known_le (@var{end1}, @var{begin2}) || known_le (@var{end2}, @var{begin1})) +@end smallexample + +However, in this particular example, it is better to use the range helper +functions instead. @xref{Range checks on @code{poly_int}s}. + +@node Comparing ordered @code{poly_int}s +@subsection Comparing ordered @code{poly_int}s + +In cases where there is a definite link between two @code{poly_int}s, +such as the outer and inner sizes of subregs, we usually require the sizes +to be ordered by the @code{known_le} partial order. @code{poly_int} provides +the following utility functions for ordered values: + +@table @samp +@item ordered_p (@var{a}, @var{b}) +Return true if @var{a} and @var{b} are ordered by the @code{known_le} +partial order. + +@item ordered_min (@var{a}, @var{b}) +Assert that @var{a} and @var{b} are ordered by @code{known_le} and return the +minimum of the two. When using this function, please add a comment explaining +why the values are known to be ordered. + +@item ordered_max (@var{a}, @var{b}) +Assert that @var{a} and @var{b} are ordered by @code{known_le} and return the +maximum of the two. When using this function, please add a comment explaining +why the values are known to be ordered. +@end table + +For example, if a subreg has an outer mode of size @var{outer} and an +inner mode of size @var{inner}: + +@itemize @bullet +@item +the subreg is complete if known_eq (@var{inner}, @var{outer}) + +@item +otherwise, the subreg is paradoxical if known_le (@var{inner}, @var{outer}) + +@item +otherwise, the subreg is partial if known_le (@var{outer}, @var{inner}) + +@item +otherwise, the subreg is ill-formed +@end itemize + +Thus the subreg is only valid if +@samp{ordered_p (@var{outer}, @var{inner})} is true. If this condition +is already known to be true then: + +@itemize @bullet +@item +the subreg is complete if known_eq (@var{inner}, @var{outer}) + +@item +the subreg is paradoxical if maybe_lt (@var{inner}, @var{outer}) + +@item +the subreg is partial if maybe_lt (@var{outer}, @var{inner}) +@end itemize + +with the three conditions being mutually exclusive. + +Code that checks whether a subreg is valid would therefore generally +check whether @code{ordered_p} holds (in addition to whatever other +checks are required for subreg validity). Code that is dealing +with existing subregs can assert that @code{ordered_p} holds +and use either of the classifications above. + +@node Checking for a @code{poly_int} marker value +@subsection Checking for a @code{poly_int} marker value + +It is sometimes useful to have a special ``marker value'' that is not +meant to be taken literally. For example, some code uses a size +of -1 to represent an unknown size, rather than having to carry around +a separate boolean to say whether the size is known. + +The best way of checking whether something is a marker value is +@code{known_eq}. Conversely the best way of checking whether something +is @emph{not} a marker value is @code{maybe_ne}. + +Thus in the size example just mentioned, @samp{known_eq (size, -1)} would +check for an unknown size and @samp{maybe_ne (size, -1)} would check for a +known size. + +@node Range checks on @code{poly_int}s +@subsection Range checks on @code{poly_int}s + +As well as the core comparisons +(@pxref{Comparison functions for @code{poly_int}}), @code{poly_int} provides +utilities for various kinds of range check. In each case the range +is represented by a start position and a size rather than a start +position and an end position; this is because the former is used +much more often than the latter in GCC@. Also, the sizes can be +-1 (or all ones for unsigned sizes) to indicate a range with a known +start position but an unknown size. All other sizes must be nonnegative. +A range of size 0 does not contain anything or overlap anything. + +@table @samp +@item known_size_p (@var{size}) +Return true if @var{size} represents a known range size, false if it +is -1 or all ones (for signed and unsigned types respectively). + +@item ranges_maybe_overlap_p (@var{pos1}, @var{size1}, @var{pos2}, @var{size2}) +Return true if the range described by @var{pos1} and @var{size1} @emph{might} +overlap the range described by @var{pos2} and @var{size2} (in other words, +return true if we cannot prove that the ranges are disjoint). + +@item ranges_known_overlap_p (@var{pos1}, @var{size1}, @var{pos2}, @var{size2}) +Return true if the range described by @var{pos1} and @var{size1} is known to +overlap the range described by @var{pos2} and @var{size2}. + +@item known_subrange_p (@var{pos1}, @var{size1}, @var{pos2}, @var{size2}) +Return true if the range described by @var{pos1} and @var{size1} is known to +be contained in the range described by @var{pos2} and @var{size2}. + +@item maybe_in_range_p (@var{value}, @var{pos}, @var{size}) +Return true if @var{value} @emph{might} be in the range described by +@var{pos} and @var{size} (in other words, return true if we cannot +prove that @var{value} is outside that range). + +@item known_in_range_p (@var{value}, @var{pos}, @var{size}) +Return true if @var{value} is known to be in the range described +by @var{pos} and @var{size}. + +@item endpoint_representable_p (@var{pos}, @var{size}) +Return true if the range described by @var{pos} and @var{size} is +open-ended or if the endpoint (@var{pos} + @var{size}) is representable +in the same type as @var{pos} and @var{size}. The function returns false +if adding @var{size} to @var{pos} makes conceptual sense but could overflow. +@end table + +There is also a @code{poly_int} version of the @code{IN_RANGE_P} macro: + +@table @samp +@item coeffs_in_range_p (@var{x}, @var{lower}, @var{upper}) +Return true if every coefficient of @var{x} is in the inclusive range +[@var{lower}, @var{upper}]. This function can be useful when testing +whether an operation would cause the values of coefficients to +overflow. + +Note that the function does not indicate whether @var{x} itself is in the +given range. @var{x} can be either a constant or a @code{poly_int}. +@end table + +@node Sorting @code{poly_int}s +@subsection Sorting @code{poly_int}s + +@code{poly_int} provides the following routine for sorting: + +@table @samp +@item compare_sizes_for_sort (@var{a}, @var{b}) +Compare @var{a} and @var{b} in reverse lexicographical order (that is, +compare the highest-indexed coefficients first). This can be useful when +sorting data structures, since it has the effect of separating constant +and non-constant values. If all values are nonnegative, the constant +values come first. + +Note that the values do not necessarily end up in numerical order. +For example, @samp{1 + 1@var{x}} would come after @samp{100} in the sort order, +but may well be less than @samp{100} at run time. +@end table + +@node Arithmetic on @code{poly_int}s +@section Arithmetic on @code{poly_int}s + +Addition, subtraction, negation and bit inversion all work normally for +@code{poly_int}s. Multiplication by a constant multiplier and left +shifting by a constant shift amount also work normally. General +multiplication of two @code{poly_int}s is not supported and is not +useful in practice. + +Other operations are only conditionally supported: the operation +might succeed or might fail, depending on the inputs. + +This section describes both types of operation. + +@menu +* Using @code{poly_int} with C++ arithmetic operators:: +* @code{wi} arithmetic on @code{poly_int}s:: +* Division of @code{poly_int}s:: +* Other @code{poly_int} arithmetic:: +@end menu + +@node Using @code{poly_int} with C++ arithmetic operators +@subsection Using @code{poly_int} with C++ arithmetic operators + +The following C++ expressions are supported, where @var{p1} and @var{p2} +are @code{poly_int}s and where @var{c1} and @var{c2} are scalars: + +@smallexample +-@var{p1} +~@var{p1} + +@var{p1} + @var{p2} +@var{p1} + @var{c2} +@var{c1} + @var{p2} + +@var{p1} - @var{p2} +@var{p1} - @var{c2} +@var{c1} - @var{p2} + +@var{c1} * @var{p2} +@var{p1} * @var{c2} + +@var{p1} << @var{c2} + +@var{p1} += @var{p2} +@var{p1} += @var{c2} + +@var{p1} -= @var{p2} +@var{p1} -= @var{c2} + +@var{p1} *= @var{c2} +@var{p1} <<= @var{c2} +@end smallexample + +These arithmetic operations handle integer ranks in a similar way +to C++. The main difference is that every coefficient narrower than +@code{HOST_WIDE_INT} promotes to @code{HOST_WIDE_INT}, whereas in +C++ everything narrower than @code{int} promotes to @code{int}. +For example: + +@smallexample +poly_uint16 + int -> poly_int64 +unsigned int + poly_uint16 -> poly_int64 +poly_int64 + int -> poly_int64 +poly_int32 + poly_uint64 -> poly_uint64 +uint64 + poly_int64 -> poly_uint64 +poly_offset_int + int32 -> poly_offset_int +offset_int + poly_uint16 -> poly_offset_int +@end smallexample + +In the first two examples, both coefficients are narrower than +@code{HOST_WIDE_INT}, so the result has coefficients of type +@code{HOST_WIDE_INT}. In the other examples, the coefficient +with the highest rank ``wins''. + +If one of the operands is @code{wide_int} or @code{poly_wide_int}, +the rules are the same as for @code{wide_int} arithmetic. + +@node @code{wi} arithmetic on @code{poly_int}s +@subsection @code{wi} arithmetic on @code{poly_int}s + +As well as the C++ operators, @code{poly_int} supports the following +@code{wi} routines: + +@smallexample +wi::neg (@var{p1}, &@var{overflow}) + +wi::add (@var{p1}, @var{p2}) +wi::add (@var{p1}, @var{c2}) +wi::add (@var{c1}, @var{p1}) +wi::add (@var{p1}, @var{p2}, @var{sign}, &@var{overflow}) + +wi::sub (@var{p1}, @var{p2}) +wi::sub (@var{p1}, @var{c2}) +wi::sub (@var{c1}, @var{p1}) +wi::sub (@var{p1}, @var{p2}, @var{sign}, &@var{overflow}) + +wi::mul (@var{p1}, @var{c2}) +wi::mul (@var{c1}, @var{p1}) +wi::mul (@var{p1}, @var{c2}, @var{sign}, &@var{overflow}) + +wi::lshift (@var{p1}, @var{c2}) +@end smallexample + +These routines just check whether overflow occurs on any individual +coefficient; it is not possible to know at compile time whether the +final runtime value would overflow. + +@node Division of @code{poly_int}s +@subsection Division of @code{poly_int}s + +Division of @code{poly_int}s is possible for certain inputs. The functions +for division return true if the operation is possible and in most cases +return the results by pointer. The routines are: + +@table @samp +@item multiple_p (@var{a}, @var{b}) +@itemx multiple_p (@var{a}, @var{b}, &@var{quotient}) +Return true if @var{a} is an exact multiple of @var{b}, storing the result +in @var{quotient} if so. There are overloads for various combinations +of polynomial and constant @var{a}, @var{b} and @var{quotient}. + +@item constant_multiple_p (@var{a}, @var{b}) +@itemx constant_multiple_p (@var{a}, @var{b}, &@var{quotient}) +Like @code{multiple_p}, but also test whether the multiple is a +compile-time constant. + +@item can_div_trunc_p (@var{a}, @var{b}, &@var{quotient}) +@itemx can_div_trunc_p (@var{a}, @var{b}, &@var{quotient}, &@var{remainder}) +Return true if we can calculate @samp{trunc (@var{a} / @var{b})} at compile +time, storing the result in @var{quotient} and @var{remainder} if so. + +@item can_div_away_from_zero_p (@var{a}, @var{b}, &@var{quotient}) +Return true if we can calculate @samp{@var{a} / @var{b}} at compile time, +rounding away from zero. Store the result in @var{quotient} if so. + +Note that this is true if and only if @code{can_div_trunc_p} is true. +The only difference is in the rounding of the result. +@end table + +There is also an asserting form of division: + +@table @samp +@item exact_div (@var{a}, @var{b}) +Assert that @var{a} is a multiple of @var{b} and return +@samp{@var{a} / @var{b}}. The result is a @code{poly_int} if @var{a} +is a @code{poly_int}. +@end table + +@node Other @code{poly_int} arithmetic +@subsection Other @code{poly_int} arithmetic + +There are tentative routines for other operations besides division: + +@table @samp +@item can_ior_p (@var{a}, @var{b}, &@var{result}) +Return true if we can calculate @samp{@var{a} | @var{b}} at compile time, +storing the result in @var{result} if so. +@end table + +Also, ANDs with a value @samp{(1 << @var{y}) - 1} or its inverse can be +treated as alignment operations. @xref{Alignment of @code{poly_int}s}. + +In addition, the following miscellaneous routines are available: + +@table @samp +@item coeff_gcd (@var{a}) +Return the greatest common divisor of all nonzero coefficients in +@var{a}, or zero if @var{a} is known to be zero. + +@item common_multiple (@var{a}, @var{b}) +Return a value that is a multiple of both @var{a} and @var{b}, where +one value is a @code{poly_int} and the other is a scalar. The result +will be the least common multiple for some indeterminate values but +not necessarily for all. + +@item force_common_multiple (@var{a}, @var{b}) +Return a value that is a multiple of both @code{poly_int} @var{a} and +@code{poly_int} @var{b}, asserting that such a value exists. The +result will be the least common multiple for some indeterminate values +but not necessarily for all. + +When using this routine, please add a comment explaining why the +assertion is known to hold. +@end table + +Please add any other operations that you find to be useful. + +@node Alignment of @code{poly_int}s +@section Alignment of @code{poly_int}s + +@code{poly_int} provides various routines for aligning values and for querying +misalignments. In each case the alignment must be a power of 2. + +@table @samp +@item can_align_p (@var{value}, @var{align}) +Return true if we can align @var{value} up or down to the nearest multiple +of @var{align} at compile time. The answer is the same for both directions. + +@item can_align_down (@var{value}, @var{align}, &@var{aligned}) +Return true if @code{can_align_p}; if so, set @var{aligned} to the greatest +aligned value that is less than or equal to @var{value}. + +@item can_align_up (@var{value}, @var{align}, &@var{aligned}) +Return true if @code{can_align_p}; if so, set @var{aligned} to the lowest +aligned value that is greater than or equal to @var{value}. + +@item known_equal_after_align_down (@var{a}, @var{b}, @var{align}) +Return true if we can align @var{a} and @var{b} down to the nearest +@var{align} boundary at compile time and if the two results are equal. + +@item known_equal_after_align_up (@var{a}, @var{b}, @var{align}) +Return true if we can align @var{a} and @var{b} up to the nearest +@var{align} boundary at compile time and if the two results are equal. + +@item aligned_lower_bound (@var{value}, @var{align}) +Return a result that is no greater than @var{value} and that is aligned +to @var{align}. The result will the closest aligned value for some +indeterminate values but not necessarily for all. + +For example, suppose we are allocating an object of @var{size} bytes +in a downward-growing stack whose current limit is given by @var{limit}. +If the object requires @var{align} bytes of alignment, the new stack +limit is given by: + +@smallexample +aligned_lower_bound (@var{limit} - @var{size}, @var{align}) +@end smallexample + +@item aligned_upper_bound (@var{value}, @var{align}) +Likewise return a result that is no less than @var{value} and that is +aligned to @var{align}. This is the routine that would be used for +upward-growing stacks in the scenario just described. + +@item known_misalignment (@var{value}, @var{align}, &@var{misalign}) +Return true if we can calculate the misalignment of @var{value} +with respect to @var{align} at compile time, storing the result in +@var{misalign} if so. + +@item known_alignment (@var{value}) +Return the minimum alignment that @var{value} is known to have +(in other words, the largest alignment that can be guaranteed +whatever the values of the indeterminates turn out to be). +Return 0 if @var{value} is known to be 0. + +@item force_align_down (@var{value}, @var{align}) +Assert that @var{value} can be aligned down to @var{align} at compile +time and return the result. When using this routine, please add a +comment explaining why the assertion is known to hold. + +@item force_align_up (@var{value}, @var{align}) +Likewise, but aligning up. + +@item force_align_down_and_div (@var{value}, @var{align}) +Divide the result of @code{force_align_down} by @var{align}. Again, +please add a comment explaining why the assertion in @code{force_align_down} +is known to hold. + +@item force_align_up_and_div (@var{value}, @var{align}) +Likewise for @code{force_align_up}. + +@item force_get_misalignment (@var{value}, @var{align}) +Assert that we can calculate the misalignment of @var{value} with +respect to @var{align} at compile time and return the misalignment. +When using this function, please add a comment explaining why +the assertion is known to hold. +@end table + +@node Computing bounds on @code{poly_int}s +@section Computing bounds on @code{poly_int}s + +@code{poly_int} also provides routines for calculating lower and upper bounds: + +@table @samp +@item constant_lower_bound (@var{a}) +Assert that @var{a} is nonnegative and return the smallest value it can have. + +@item constant_lower_bound_with_limit (@var{a}, @var{b}) +Return the least value @var{a} can have, given that the context in +which @var{a} appears guarantees that the answer is no less than @var{b}. +In other words, the caller is asserting that @var{a} is greater than or +equal to @var{b} even if @samp{known_ge (@var{a}, @var{b})} doesn't hold. + +@item constant_upper_bound_with_limit (@var{a}, @var{b}) +Return the greatest value @var{a} can have, given that the context in +which @var{a} appears guarantees that the answer is no greater than @var{b}. +In other words, the caller is asserting that @var{a} is less than or equal +to @var{b} even if @samp{known_le (@var{a}, @var{b})} doesn't hold. + +@item lower_bound (@var{a}, @var{b}) +Return a value that is always less than or equal to both @var{a} and @var{b}. +It will be the greatest such value for some indeterminate values +but necessarily for all. + +@item upper_bound (@var{a}, @var{b}) +Return a value that is always greater than or equal to both @var{a} and +@var{b}. It will be the least such value for some indeterminate values +but necessarily for all. +@end table + +@node Converting @code{poly_int}s +@section Converting @code{poly_int}s + +A @code{poly_int<@var{n}, @var{T}>} can be constructed from up to +@var{n} individual @var{T} coefficients, with the remaining coefficients +being implicitly zero. In particular, this means that every +@code{poly_int<@var{n}, @var{T}>} can be constructed from a single +scalar @var{T}, or something compatible with @var{T}. + +Also, a @code{poly_int<@var{n}, @var{T}>} can be constructed from +a @code{poly_int<@var{n}, @var{U}>} if @var{T} can be constructed +from @var{U}. + +The following functions provide other forms of conversion, +or test whether such a conversion would succeed. + +@table @samp +@item @var{value}.is_constant () +Return true if @code{poly_int} @var{value} is a compile-time constant. + +@item @var{value}.is_constant (&@var{c1}) +Return true if @code{poly_int} @var{value} is a compile-time constant, +storing it in @var{c1} if so. @var{c1} must be able to hold all +constant values of @var{value} without loss of precision. + +@item @var{value}.to_constant () +Assert that @var{value} is a compile-time constant and return its value. +When using this function, please add a comment explaining why the +condition is known to hold (for example, because an earlier phase +of analysis rejected non-constants). + +@item @var{value}.to_shwi (&@var{p2}) +Return true if @samp{poly_int<@var{N}, @var{T}>} @var{value} can be +represented without loss of precision as a +@samp{poly_int<@var{N}, @code{HOST_WIDE_INT}>}, storing it in that +form in @var{p2} if so. + +@item @var{value}.to_uhwi (&@var{p2}) +Return true if @samp{poly_int<@var{N}, @var{T}>} @var{value} can be +represented without loss of precision as a +@samp{poly_int<@var{N}, @code{unsigned HOST_WIDE_INT}>}, storing it in that +form in @var{p2} if so. + +@item @var{value}.force_shwi () +Forcibly convert each coefficient of @samp{poly_int<@var{N}, @var{T}>} +@var{value} to @code{HOST_WIDE_INT}, truncating any that are out of range. +Return the result as a @samp{poly_int<@var{N}, @code{HOST_WIDE_INT}>}. + +@item @var{value}.force_uhwi () +Forcibly convert each coefficient of @samp{poly_int<@var{N}, @var{T}>} +@var{value} to @code{unsigned HOST_WIDE_INT}, truncating any that are +out of range. Return the result as a +@samp{poly_int<@var{N}, @code{unsigned HOST_WIDE_INT}>}. + +@item wi::shwi (@var{value}, @var{precision}) +Return a @code{poly_int} with the same value as @var{value}, but with +the coefficients converted from @code{HOST_WIDE_INT} to @code{wide_int}. +@var{precision} specifies the precision of the @code{wide_int} cofficients; +if this is wider than a @code{HOST_WIDE_INT}, the coefficients of +@var{value} will be sign-extended to fit. + +@item wi::uhwi (@var{value}, @var{precision}) +Like @code{wi::shwi}, except that @var{value} has coefficients of +type @code{unsigned HOST_WIDE_INT}. If @var{precision} is wider than +a @code{HOST_WIDE_INT}, the coefficients of @var{value} will be +zero-extended to fit. + +@item wi::sext (@var{value}, @var{precision}) +Return a @code{poly_int} of the same type as @var{value}, sign-extending +every coefficient from the low @var{precision} bits. This in effect +applies @code{wi::sext} to each coefficient individually. + +@item wi::zext (@var{value}, @var{precision}) +Like @code{wi::sext}, but for zero extension. + +@item poly_wide_int::from (@var{value}, @var{precision}, @var{sign}) +Convert @var{value} to a @code{poly_wide_int} in which each coefficient +has @var{precision} bits. Extend the coefficients according to +@var{sign} if the coefficients have fewer bits. + +@item poly_offset_int::from (@var{value}, @var{sign}) +Convert @var{value} to a @code{poly_offset_int}, extending its coefficients +according to @var{sign} if they have fewer bits than @code{offset_int}. + +@item poly_widest_int::from (@var{value}, @var{sign}) +Convert @var{value} to a @code{poly_widest_int}, extending its coefficients +according to @var{sign} if they have fewer bits than @code{widest_int}. +@end table + +@node Miscellaneous @code{poly_int} routines +@section Miscellaneous @code{poly_int} routines + +@table @samp +@item print_dec (@var{value}, @var{file}, @var{sign}) +@itemx print_dec (@var{value}, @var{file}) +Print @var{value} to @var{file} as a decimal value, interpreting +the coefficients according to @var{sign}. The final argument is +optional if @var{value} has an inherent sign; for example, +@code{poly_int64} values print as signed by default and +@code{poly_uint64} values print as unsigned by default. + +This is a simply a @code{poly_int} version of a wide-int routine. +@end table + +@node Guidelines for using @code{poly_int} +@section Guidelines for using @code{poly_int} + +One of the main design goals of @code{poly_int} was to make it easy +to write target-independent code that handles variable-sized registers +even when the current target has fixed-sized registers. There are two +aspects to this: + +@itemize +@item +The set of @code{poly_int} operations should be complete enough that +the question in most cases becomes ``Can we do this operation on these +particular @code{poly_int} values? If not, bail out'' rather than +``Are these @code{poly_int} values constant? If so, do the operation, +otherwise bail out''. + +@item +If target-independent code compiles and runs correctly on a target +with one value of @code{NUM_POLY_INT_COEFFS}, and if the code does not +use asserting functions like @code{to_constant}, it is reasonable to +assume that the code also works on targets with other values of +@code{NUM_POLY_INT_COEFFS}. There is no need to check this during +everyday development. +@end itemize + +So the general principle is: if target-independent code is dealing +with a @code{poly_int} value, it is better to operate on it as a +@code{poly_int} if at all possible, choosing conservatively-correct +behavior if a particular operation fails. For example, the following +code handles an index @code{pos} into a sequence of vectors that each +have @code{nunits} elements: + +@smallexample +/* Calculate which vector contains the result, and which lane of + that vector we need. */ +if (!can_div_trunc_p (pos, nunits, &vec_entry, &vec_index)) + @{ + if (dump_enabled_p ()) + dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location, + "Cannot determine which vector holds the" + " final result.\n"); + return false; + @} +@end smallexample + +However, there are some contexts in which operating on a +@code{poly_int} is not possible or does not make sense. One example +is when handling static initializers, since no current target supports +the concept of a variable-length static initializer. In these +situations, a reasonable fallback is: + +@smallexample +if (@var{poly_value}.is_constant (&@var{const_value})) + @{ + @dots{} + /* Operate on @var{const_value}. */ + @dots{} + @} +else + @{ + @dots{} + /* Conservatively correct fallback. */ + @dots{} + @} +@end smallexample + +@code{poly_int} also provides some asserting functions like +@code{to_constant}. Please only use these functions if there is a +good theoretical reason to believe that the assertion cannot fire. +For example, if some work is divided into an analysis phase and an +implementation phase, the analysis phase might reject inputs that are +not @code{is_constant}, in which case the implementation phase can +reasonably use @code{to_constant} on the remaining inputs. The assertions +should not be used to discover whether a condition ever occurs ``in the +field''; in other words, they should not be used to restrict code to +constants at first, with the intention of only implementing a +@code{poly_int} version if a user hits the assertion. + +If a particular asserting function like @code{to_constant} is needed +more than once for the same reason, it is probably worth adding a +helper function or macro for that situation, so that the justification +only needs to be given once. For example: + +@smallexample +/* Return the size of an element in a vector of size SIZE, given that + the vector has NELTS elements. The return value is in the same units + as SIZE (either bits or bytes). + + to_constant () is safe in this situation because vector elements are + always constant-sized scalars. */ +#define vector_element_size(SIZE, NELTS) \ + (exact_div (SIZE, NELTS).to_constant ()) +@end smallexample + +Target-specific code in @file{config/@var{cpu}} only needs to handle +non-constant @code{poly_int}s if @code{NUM_POLY_INT_COEFFS} is greater +than one. For other targets, @code{poly_int} degenerates to a compile-time +constant and is often interchangable with a normal scalar integer. +There are two main exceptions: + +@itemize +@item +Sometimes an explicit cast to an integer type might be needed, such as to +resolve ambiguities in a @code{?:} expression, or when passing values +through @code{...} to things like print functions. + +@item +Target macros are included in target-independent code and so do not +have access to the implicit conversion to a scalar integer. +If this becomes a problem for a particular target macro, the +possible solutions, in order of preference, are: + +@itemize +@item +Convert the target macro to a target hook (for all targets). + +@item +Put the target's implementation of the target macro in its +@file{@var{cpu}.c} file and call it from the target macro in the +@file{@var{cpu}.h} file. + +@item +Add @code{to_constant ()} calls where necessary. The previous option +is preferable because it will help with any future conversion of the +macro to a hook. +@end itemize +@end itemize + diff --git a/gcc/doc/portability.texi b/gcc/doc/portability.texi new file mode 100644 index 00000000000..3e1ad5fe55b --- /dev/null +++ b/gcc/doc/portability.texi @@ -0,0 +1,39 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Portability +@chapter GCC and Portability +@cindex portability +@cindex GCC and portability + +GCC itself aims to be portable to any machine where @code{int} is at least +a 32-bit type. It aims to target machines with a flat (non-segmented) byte +addressed data address space (the code address space can be separate). +Target ABIs may have 8, 16, 32 or 64-bit @code{int} type. @code{char} +can be wider than 8 bits. + +GCC gets most of the information about the target machine from a machine +description which gives an algebraic formula for each of the machine's +instructions. This is a very clean way to describe the target. But when +the compiler needs information that is difficult to express in this +fashion, ad-hoc parameters have been defined for machine descriptions. +The purpose of portability is to reduce the total work needed on the +compiler; it was not of interest for its own sake. + +@cindex endianness +@cindex autoincrement addressing, availability +@findex abort +GCC does not contain machine dependent code, but it does contain code +that depends on machine parameters such as endianness (whether the most +significant byte has the highest or lowest address of the bytes in a word) +and the availability of autoincrement addressing. In the RTL-generation +pass, it is often necessary to have multiple strategies for generating code +for a particular kind of syntax tree, strategies that are usable for different +combinations of parameters. Often, not all possible cases have been +addressed, but only the common ones or only the ones that have been +encountered. As a result, a new target may require additional +strategies. You will know +if this happens because the compiler will call @code{abort}. Fortunately, +the new strategies can be added in a machine-independent fashion, and will +affect only the target machines that need them. diff --git a/gcc/doc/rtl.texi b/gcc/doc/rtl.texi new file mode 100644 index 00000000000..43c9ee8bffe --- /dev/null +++ b/gcc/doc/rtl.texi @@ -0,0 +1,5258 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node RTL +@chapter RTL Representation +@cindex RTL representation +@cindex representation of RTL +@cindex Register Transfer Language (RTL) + +The last part of the compiler work is done on a low-level intermediate +representation called Register Transfer Language. In this language, the +instructions to be output are described, pretty much one by one, in an +algebraic form that describes what the instruction does. + +RTL is inspired by Lisp lists. It has both an internal form, made up of +structures that point at other structures, and a textual form that is used +in the machine description and in printed debugging dumps. The textual +form uses nested parentheses to indicate the pointers in the internal form. + +@menu +* RTL Objects:: Expressions vs vectors vs strings vs integers. +* RTL Classes:: Categories of RTL expression objects, and their structure. +* Accessors:: Macros to access expression operands or vector elts. +* Special Accessors:: Macros to access specific annotations on RTL. +* Flags:: Other flags in an RTL expression. +* Machine Modes:: Describing the size and format of a datum. +* Constants:: Expressions with constant values. +* Regs and Memory:: Expressions representing register contents or memory. +* Arithmetic:: Expressions representing arithmetic on other expressions. +* Comparisons:: Expressions representing comparison of expressions. +* Bit-Fields:: Expressions representing bit-fields in memory or reg. +* Vector Operations:: Expressions involving vector datatypes. +* Conversions:: Extending, truncating, floating or fixing. +* RTL Declarations:: Declaring volatility, constancy, etc. +* Side Effects:: Expressions for storing in registers, etc. +* Incdec:: Embedded side-effects for autoincrement addressing. +* Assembler:: Representing @code{asm} with operands. +* Debug Information:: Expressions representing debugging information. +* Insns:: Expression types for entire insns. +* Calls:: RTL representation of function call insns. +* RTL SSA:: An on-the-side SSA form for RTL +* Sharing:: Some expressions are unique; others *must* be copied. +* Reading RTL:: Reading textual RTL from a file. +@end menu + +@node RTL Objects +@section RTL Object Types +@cindex RTL object types + +@cindex RTL integers +@cindex RTL strings +@cindex RTL vectors +@cindex RTL expression +@cindex RTX (See RTL) +RTL uses five kinds of objects: expressions, integers, wide integers, +strings and vectors. Expressions are the most important ones. An RTL +expression (``RTX'', for short) is a C structure, but it is usually +referred to with a pointer; a type that is given the typedef name +@code{rtx}. + +An integer is simply an @code{int}; their written form uses decimal +digits. A wide integer is an integral object whose type is +@code{HOST_WIDE_INT}; their written form uses decimal digits. + +A string is a sequence of characters. In core it is represented as a +@code{char *} in usual C fashion, and it is written in C syntax as well. +However, strings in RTL may never be null. If you write an empty string in +a machine description, it is represented in core as a null pointer rather +than as a pointer to a null character. In certain contexts, these null +pointers instead of strings are valid. Within RTL code, strings are most +commonly found inside @code{symbol_ref} expressions, but they appear in +other contexts in the RTL expressions that make up machine descriptions. + +In a machine description, strings are normally written with double +quotes, as you would in C@. However, strings in machine descriptions may +extend over many lines, which is invalid C, and adjacent string +constants are not concatenated as they are in C@. Any string constant +may be surrounded with a single set of parentheses. Sometimes this +makes the machine description easier to read. + +There is also a special syntax for strings, which can be useful when C +code is embedded in a machine description. Wherever a string can +appear, it is also valid to write a C-style brace block. The entire +brace block, including the outermost pair of braces, is considered to be +the string constant. Double quote characters inside the braces are not +special. Therefore, if you write string constants in the C code, you +need not escape each quote character with a backslash. + +A vector contains an arbitrary number of pointers to expressions. The +number of elements in the vector is explicitly present in the vector. +The written form of a vector consists of square brackets +(@samp{[@dots{}]}) surrounding the elements, in sequence and with +whitespace separating them. Vectors of length zero are not created; +null pointers are used instead. + +@cindex expression codes +@cindex codes, RTL expression +@findex GET_CODE +@findex PUT_CODE +Expressions are classified by @dfn{expression codes} (also called RTX +codes). The expression code is a name defined in @file{rtl.def}, which is +also (in uppercase) a C enumeration constant. The possible expression +codes and their meanings are machine-independent. The code of an RTX can +be extracted with the macro @code{GET_CODE (@var{x})} and altered with +@code{PUT_CODE (@var{x}, @var{newcode})}. + +The expression code determines how many operands the expression contains, +and what kinds of objects they are. In RTL, unlike Lisp, you cannot tell +by looking at an operand what kind of object it is. Instead, you must know +from its context---from the expression code of the containing expression. +For example, in an expression of code @code{subreg}, the first operand is +to be regarded as an expression and the second operand as a polynomial +integer. In an expression of code @code{plus}, there are two operands, +both of which are to be regarded as expressions. In a @code{symbol_ref} +expression, there is one operand, which is to be regarded as a string. + +Expressions are written as parentheses containing the name of the +expression type, its flags and machine mode if any, and then the operands +of the expression (separated by spaces). + +Expression code names in the @samp{md} file are written in lowercase, +but when they appear in C code they are written in uppercase. In this +manual, they are shown as follows: @code{const_int}. + +@cindex (nil) +@cindex nil +In a few contexts a null pointer is valid where an expression is normally +wanted. The written form of this is @code{(nil)}. + +@node RTL Classes +@section RTL Classes and Formats +@cindex RTL classes +@cindex classes of RTX codes +@cindex RTX codes, classes of +@findex GET_RTX_CLASS + +The various expression codes are divided into several @dfn{classes}, +which are represented by single characters. You can determine the class +of an RTX code with the macro @code{GET_RTX_CLASS (@var{code})}. +Currently, @file{rtl.def} defines these classes: + +@table @code +@item RTX_OBJ +An RTX code that represents an actual object, such as a register +(@code{REG}) or a memory location (@code{MEM}, @code{SYMBOL_REF}). +@code{LO_SUM} is also included; instead, @code{SUBREG} and +@code{STRICT_LOW_PART} are not in this class, but in class +@code{RTX_EXTRA}. + +@item RTX_CONST_OBJ +An RTX code that represents a constant object. @code{HIGH} is also +included in this class. + +@item RTX_COMPARE +An RTX code for a non-symmetric comparison, such as @code{GEU} or +@code{LT}. + +@item RTX_COMM_COMPARE +An RTX code for a symmetric (commutative) comparison, such as @code{EQ} +or @code{ORDERED}. + +@item RTX_UNARY +An RTX code for a unary arithmetic operation, such as @code{NEG}, +@code{NOT}, or @code{ABS}. This category also includes value extension +(sign or zero) and conversions between integer and floating point. + +@item RTX_COMM_ARITH +An RTX code for a commutative binary operation, such as @code{PLUS} or +@code{AND}. @code{NE} and @code{EQ} are comparisons, so they have class +@code{RTX_COMM_COMPARE}. + +@item RTX_BIN_ARITH +An RTX code for a non-commutative binary operation, such as @code{MINUS}, +@code{DIV}, or @code{ASHIFTRT}. + +@item RTX_BITFIELD_OPS +An RTX code for a bit-field operation. Currently only +@code{ZERO_EXTRACT} and @code{SIGN_EXTRACT}. These have three inputs +and are lvalues (so they can be used for insertion as well). +@xref{Bit-Fields}. + +@item RTX_TERNARY +An RTX code for other three input operations. Currently only +@code{IF_THEN_ELSE}, @code{VEC_MERGE}, @code{SIGN_EXTRACT}, +@code{ZERO_EXTRACT}, and @code{FMA}. + +@item RTX_INSN +An RTX code for an entire instruction: @code{INSN}, @code{JUMP_INSN}, and +@code{CALL_INSN}. @xref{Insns}. + +@item RTX_MATCH +An RTX code for something that matches in insns, such as +@code{MATCH_DUP}. These only occur in machine descriptions. + +@item RTX_AUTOINC +An RTX code for an auto-increment addressing mode, such as +@code{POST_INC}. @samp{XEXP (@var{x}, 0)} gives the auto-modified +register. + +@item RTX_EXTRA +All other RTX codes. This category includes the remaining codes used +only in machine descriptions (@code{DEFINE_*}, etc.). It also includes +all the codes describing side effects (@code{SET}, @code{USE}, +@code{CLOBBER}, etc.) and the non-insns that may appear on an insn +chain, such as @code{NOTE}, @code{BARRIER}, and @code{CODE_LABEL}. +@code{SUBREG} is also part of this class. +@end table + +@cindex RTL format +For each expression code, @file{rtl.def} specifies the number of +contained objects and their kinds using a sequence of characters +called the @dfn{format} of the expression code. For example, +the format of @code{subreg} is @samp{ep}. + +@cindex RTL format characters +These are the most commonly used format characters: + +@table @code +@item e +An expression (actually a pointer to an expression). + +@item i +An integer. + +@item w +A wide integer. + +@item s +A string. + +@item E +A vector of expressions. +@end table + +A few other format characters are used occasionally: + +@table @code +@item u +@samp{u} is equivalent to @samp{e} except that it is printed differently +in debugging dumps. It is used for pointers to insns. + +@item n +@samp{n} is equivalent to @samp{i} except that it is printed differently +in debugging dumps. It is used for the line number or code number of a +@code{note} insn. + +@item S +@samp{S} indicates a string which is optional. In the RTL objects in +core, @samp{S} is equivalent to @samp{s}, but when the object is read, +from an @samp{md} file, the string value of this operand may be omitted. +An omitted string is taken to be the null string. + +@item V +@samp{V} indicates a vector which is optional. In the RTL objects in +core, @samp{V} is equivalent to @samp{E}, but when the object is read +from an @samp{md} file, the vector value of this operand may be omitted. +An omitted vector is effectively the same as a vector of no elements. + +@item B +@samp{B} indicates a pointer to basic block structure. + +@item p +A polynomial integer. At present this is used only for @code{SUBREG_BYTE}. + +@item 0 +@samp{0} means a slot whose contents do not fit any normal category. +@samp{0} slots are not printed at all in dumps, and are often used in +special ways by small parts of the compiler. +@end table + +There are macros to get the number of operands and the format +of an expression code: + +@table @code +@findex GET_RTX_LENGTH +@item GET_RTX_LENGTH (@var{code}) +Number of operands of an RTX of code @var{code}. + +@findex GET_RTX_FORMAT +@item GET_RTX_FORMAT (@var{code}) +The format of an RTX of code @var{code}, as a C string. +@end table + +Some classes of RTX codes always have the same format. For example, it +is safe to assume that all comparison operations have format @code{ee}. + +@table @code +@item RTX_UNARY +All codes of this class have format @code{e}. + +@item RTX_BIN_ARITH +@itemx RTX_COMM_ARITH +@itemx RTX_COMM_COMPARE +@itemx RTX_COMPARE +All codes of these classes have format @code{ee}. + +@item RTX_BITFIELD_OPS +@itemx RTX_TERNARY +All codes of these classes have format @code{eee}. + +@item RTX_INSN +All codes of this class have formats that begin with @code{iuueiee}. +@xref{Insns}. Note that not all RTL objects linked onto an insn chain +are of class @code{RTX_INSN}. + +@item RTX_CONST_OBJ +@itemx RTX_OBJ +@itemx RTX_MATCH +@itemx RTX_EXTRA +You can make no assumptions about the format of these codes. +@end table + +@node Accessors +@section Access to Operands +@cindex accessors +@cindex access to operands +@cindex operand access + +@findex XEXP +@findex XINT +@findex XWINT +@findex XSTR +Operands of expressions are accessed using the macros @code{XEXP}, +@code{XINT}, @code{XWINT} and @code{XSTR}. Each of these macros takes +two arguments: an expression-pointer (RTX) and an operand number +(counting from zero). Thus, + +@smallexample +XEXP (@var{x}, 2) +@end smallexample + +@noindent +accesses operand 2 of expression @var{x}, as an expression. + +@smallexample +XINT (@var{x}, 2) +@end smallexample + +@noindent +accesses the same operand as an integer. @code{XSTR}, used in the same +fashion, would access it as a string. + +Any operand can be accessed as an integer, as an expression or as a string. +You must choose the correct method of access for the kind of value actually +stored in the operand. You would do this based on the expression code of +the containing expression. That is also how you would know how many +operands there are. + +For example, if @var{x} is an @code{int_list} expression, you know that it has +two operands which can be correctly accessed as @code{XINT (@var{x}, 0)} +and @code{XEXP (@var{x}, 1)}. Incorrect accesses like +@code{XEXP (@var{x}, 0)} and @code{XINT (@var{x}, 1)} would compile, +but would trigger an internal compiler error when rtl checking is enabled. +Nothing stops you from writing @code{XEXP (@var{x}, 28)} either, but +this will access memory past the end of the expression with +unpredictable results. + +Access to operands which are vectors is more complicated. You can use the +macro @code{XVEC} to get the vector-pointer itself, or the macros +@code{XVECEXP} and @code{XVECLEN} to access the elements and length of a +vector. + +@table @code +@findex XVEC +@item XVEC (@var{exp}, @var{idx}) +Access the vector-pointer which is operand number @var{idx} in @var{exp}. + +@findex XVECLEN +@item XVECLEN (@var{exp}, @var{idx}) +Access the length (number of elements) in the vector which is +in operand number @var{idx} in @var{exp}. This value is an @code{int}. + +@findex XVECEXP +@item XVECEXP (@var{exp}, @var{idx}, @var{eltnum}) +Access element number @var{eltnum} in the vector which is +in operand number @var{idx} in @var{exp}. This value is an RTX@. + +It is up to you to make sure that @var{eltnum} is not negative +and is less than @code{XVECLEN (@var{exp}, @var{idx})}. +@end table + +All the macros defined in this section expand into lvalues and therefore +can be used to assign the operands, lengths and vector elements as well as +to access them. + +@node Special Accessors +@section Access to Special Operands +@cindex access to special operands + +Some RTL nodes have special annotations associated with them. + +@table @code +@item MEM +@table @code +@findex MEM_ALIAS_SET +@item MEM_ALIAS_SET (@var{x}) +If 0, @var{x} is not in any alias set, and may alias anything. Otherwise, +@var{x} can only alias @code{MEM}s in a conflicting alias set. This value +is set in a language-dependent manner in the front-end, and should not be +altered in the back-end. In some front-ends, these numbers may correspond +in some way to types, or other language-level entities, but they need not, +and the back-end makes no such assumptions. +These set numbers are tested with @code{alias_sets_conflict_p}. + +@findex MEM_EXPR +@item MEM_EXPR (@var{x}) +If this register is known to hold the value of some user-level +declaration, this is that tree node. It may also be a +@code{COMPONENT_REF}, in which case this is some field reference, +and @code{TREE_OPERAND (@var{x}, 0)} contains the declaration, +or another @code{COMPONENT_REF}, or null if there is no compile-time +object associated with the reference. + +@findex MEM_OFFSET_KNOWN_P +@item MEM_OFFSET_KNOWN_P (@var{x}) +True if the offset of the memory reference from @code{MEM_EXPR} is known. +@samp{MEM_OFFSET (@var{x})} provides the offset if so. + +@findex MEM_OFFSET +@item MEM_OFFSET (@var{x}) +The offset from the start of @code{MEM_EXPR}. The value is only valid if +@samp{MEM_OFFSET_KNOWN_P (@var{x})} is true. + +@findex MEM_SIZE_KNOWN_P +@item MEM_SIZE_KNOWN_P (@var{x}) +True if the size of the memory reference is known. +@samp{MEM_SIZE (@var{x})} provides its size if so. + +@findex MEM_SIZE +@item MEM_SIZE (@var{x}) +The size in bytes of the memory reference. +This is mostly relevant for @code{BLKmode} references as otherwise +the size is implied by the mode. The value is only valid if +@samp{MEM_SIZE_KNOWN_P (@var{x})} is true. + +@findex MEM_ALIGN +@item MEM_ALIGN (@var{x}) +The known alignment in bits of the memory reference. + +@findex MEM_ADDR_SPACE +@item MEM_ADDR_SPACE (@var{x}) +The address space of the memory reference. This will commonly be zero +for the generic address space. +@end table + +@item REG +@table @code +@findex ORIGINAL_REGNO +@item ORIGINAL_REGNO (@var{x}) +This field holds the number the register ``originally'' had; for a +pseudo register turned into a hard reg this will hold the old pseudo +register number. + +@findex REG_EXPR +@item REG_EXPR (@var{x}) +If this register is known to hold the value of some user-level +declaration, this is that tree node. + +@findex REG_OFFSET +@item REG_OFFSET (@var{x}) +If this register is known to hold the value of some user-level +declaration, this is the offset into that logical storage. +@end table + +@item SYMBOL_REF +@table @code +@findex SYMBOL_REF_DECL +@item SYMBOL_REF_DECL (@var{x}) +If the @code{symbol_ref} @var{x} was created for a @code{VAR_DECL} or +a @code{FUNCTION_DECL}, that tree is recorded here. If this value is +null, then @var{x} was created by back end code generation routines, +and there is no associated front end symbol table entry. + +@code{SYMBOL_REF_DECL} may also point to a tree of class @code{'c'}, +that is, some sort of constant. In this case, the @code{symbol_ref} +is an entry in the per-file constant pool; again, there is no associated +front end symbol table entry. + +@findex SYMBOL_REF_CONSTANT +@item SYMBOL_REF_CONSTANT (@var{x}) +If @samp{CONSTANT_POOL_ADDRESS_P (@var{x})} is true, this is the constant +pool entry for @var{x}. It is null otherwise. + +@findex SYMBOL_REF_DATA +@item SYMBOL_REF_DATA (@var{x}) +A field of opaque type used to store @code{SYMBOL_REF_DECL} or +@code{SYMBOL_REF_CONSTANT}. + +@findex SYMBOL_REF_FLAGS +@item SYMBOL_REF_FLAGS (@var{x}) +In a @code{symbol_ref}, this is used to communicate various predicates +about the symbol. Some of these are common enough to be computed by +common code, some are specific to the target. The common bits are: + +@table @code +@findex SYMBOL_REF_FUNCTION_P +@findex SYMBOL_FLAG_FUNCTION +@item SYMBOL_FLAG_FUNCTION +Set if the symbol refers to a function. + +@findex SYMBOL_REF_LOCAL_P +@findex SYMBOL_FLAG_LOCAL +@item SYMBOL_FLAG_LOCAL +Set if the symbol is local to this ``module''. +See @code{TARGET_BINDS_LOCAL_P}. + +@findex SYMBOL_REF_EXTERNAL_P +@findex SYMBOL_FLAG_EXTERNAL +@item SYMBOL_FLAG_EXTERNAL +Set if this symbol is not defined in this translation unit. +Note that this is not the inverse of @code{SYMBOL_FLAG_LOCAL}. + +@findex SYMBOL_REF_SMALL_P +@findex SYMBOL_FLAG_SMALL +@item SYMBOL_FLAG_SMALL +Set if the symbol is located in the small data section. +See @code{TARGET_IN_SMALL_DATA_P}. + +@findex SYMBOL_FLAG_TLS_SHIFT +@findex SYMBOL_REF_TLS_MODEL +@item SYMBOL_REF_TLS_MODEL (@var{x}) +This is a multi-bit field accessor that returns the @code{tls_model} +to be used for a thread-local storage symbol. It returns zero for +non-thread-local symbols. + +@findex SYMBOL_REF_HAS_BLOCK_INFO_P +@findex SYMBOL_FLAG_HAS_BLOCK_INFO +@item SYMBOL_FLAG_HAS_BLOCK_INFO +Set if the symbol has @code{SYMBOL_REF_BLOCK} and +@code{SYMBOL_REF_BLOCK_OFFSET} fields. + +@findex SYMBOL_REF_ANCHOR_P +@findex SYMBOL_FLAG_ANCHOR +@cindex @option{-fsection-anchors} +@item SYMBOL_FLAG_ANCHOR +Set if the symbol is used as a section anchor. ``Section anchors'' +are symbols that have a known position within an @code{object_block} +and that can be used to access nearby members of that block. +They are used to implement @option{-fsection-anchors}. + +If this flag is set, then @code{SYMBOL_FLAG_HAS_BLOCK_INFO} will be too. +@end table + +Bits beginning with @code{SYMBOL_FLAG_MACH_DEP} are available for +the target's use. +@end table + +@findex SYMBOL_REF_BLOCK +@item SYMBOL_REF_BLOCK (@var{x}) +If @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})}, this is the +@samp{object_block} structure to which the symbol belongs, +or @code{NULL} if it has not been assigned a block. + +@findex SYMBOL_REF_BLOCK_OFFSET +@item SYMBOL_REF_BLOCK_OFFSET (@var{x}) +If @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})}, this is the offset of @var{x} +from the first object in @samp{SYMBOL_REF_BLOCK (@var{x})}. The value is +negative if @var{x} has not yet been assigned to a block, or it has not +been given an offset within that block. +@end table + +@node Flags +@section Flags in an RTL Expression +@cindex flags in RTL expression + +RTL expressions contain several flags (one-bit bit-fields) +that are used in certain types of expression. Most often they +are accessed with the following macros, which expand into lvalues. + +@table @code +@findex CROSSING_JUMP_P +@cindex @code{jump_insn} and @samp{/j} +@item CROSSING_JUMP_P (@var{x}) +Nonzero in a @code{jump_insn} if it crosses between hot and cold sections, +which could potentially be very far apart in the executable. The presence +of this flag indicates to other optimizations that this branching instruction +should not be ``collapsed'' into a simpler branching construct. It is used +when the optimization to partition basic blocks into hot and cold sections +is turned on. + +@findex CONSTANT_POOL_ADDRESS_P +@cindex @code{symbol_ref} and @samp{/u} +@cindex @code{unchanging}, in @code{symbol_ref} +@item CONSTANT_POOL_ADDRESS_P (@var{x}) +Nonzero in a @code{symbol_ref} if it refers to part of the current +function's constant pool. For most targets these addresses are in a +@code{.rodata} section entirely separate from the function, but for +some targets the addresses are close to the beginning of the function. +In either case GCC assumes these addresses can be addressed directly, +perhaps with the help of base registers. +Stored in the @code{unchanging} field and printed as @samp{/u}. + +@findex INSN_ANNULLED_BRANCH_P +@cindex @code{jump_insn} and @samp{/u} +@cindex @code{call_insn} and @samp{/u} +@cindex @code{insn} and @samp{/u} +@cindex @code{unchanging}, in @code{jump_insn}, @code{call_insn} and @code{insn} +@item INSN_ANNULLED_BRANCH_P (@var{x}) +In a @code{jump_insn}, @code{call_insn}, or @code{insn} indicates +that the branch is an annulling one. See the discussion under +@code{sequence} below. Stored in the @code{unchanging} field and +printed as @samp{/u}. + +@findex INSN_DELETED_P +@cindex @code{insn} and @samp{/v} +@cindex @code{call_insn} and @samp{/v} +@cindex @code{jump_insn} and @samp{/v} +@cindex @code{code_label} and @samp{/v} +@cindex @code{jump_table_data} and @samp{/v} +@cindex @code{barrier} and @samp{/v} +@cindex @code{note} and @samp{/v} +@cindex @code{volatil}, in @code{insn}, @code{call_insn}, @code{jump_insn}, @code{code_label}, @code{jump_table_data}, @code{barrier}, and @code{note} +@item INSN_DELETED_P (@var{x}) +In an @code{insn}, @code{call_insn}, @code{jump_insn}, @code{code_label}, +@code{jump_table_data}, @code{barrier}, or @code{note}, +nonzero if the insn has been deleted. Stored in the +@code{volatil} field and printed as @samp{/v}. + +@findex INSN_FROM_TARGET_P +@cindex @code{insn} and @samp{/s} +@cindex @code{jump_insn} and @samp{/s} +@cindex @code{call_insn} and @samp{/s} +@cindex @code{in_struct}, in @code{insn} and @code{jump_insn} and @code{call_insn} +@item INSN_FROM_TARGET_P (@var{x}) +In an @code{insn} or @code{jump_insn} or @code{call_insn} in a delay +slot of a branch, indicates that the insn +is from the target of the branch. If the branch insn has +@code{INSN_ANNULLED_BRANCH_P} set, this insn will only be executed if +the branch is taken. For annulled branches with +@code{INSN_FROM_TARGET_P} clear, the insn will be executed only if the +branch is not taken. When @code{INSN_ANNULLED_BRANCH_P} is not set, +this insn will always be executed. Stored in the @code{in_struct} +field and printed as @samp{/s}. + +@findex LABEL_PRESERVE_P +@cindex @code{code_label} and @samp{/i} +@cindex @code{note} and @samp{/i} +@cindex @code{in_struct}, in @code{code_label} and @code{note} +@item LABEL_PRESERVE_P (@var{x}) +In a @code{code_label} or @code{note}, indicates that the label is referenced by +code or data not visible to the RTL of a given function. +Labels referenced by a non-local goto will have this bit set. Stored +in the @code{in_struct} field and printed as @samp{/s}. + +@findex LABEL_REF_NONLOCAL_P +@cindex @code{label_ref} and @samp{/v} +@cindex @code{reg_label} and @samp{/v} +@cindex @code{volatil}, in @code{label_ref} and @code{reg_label} +@item LABEL_REF_NONLOCAL_P (@var{x}) +In @code{label_ref} and @code{reg_label} expressions, nonzero if this is +a reference to a non-local label. +Stored in the @code{volatil} field and printed as @samp{/v}. + +@findex MEM_KEEP_ALIAS_SET_P +@cindex @code{mem} and @samp{/j} +@cindex @code{jump}, in @code{mem} +@item MEM_KEEP_ALIAS_SET_P (@var{x}) +In @code{mem} expressions, 1 if we should keep the alias set for this +mem unchanged when we access a component. Set to 1, for example, when we +are already in a non-addressable component of an aggregate. +Stored in the @code{jump} field and printed as @samp{/j}. + +@findex MEM_VOLATILE_P +@cindex @code{mem} and @samp{/v} +@cindex @code{asm_input} and @samp{/v} +@cindex @code{asm_operands} and @samp{/v} +@cindex @code{volatil}, in @code{mem}, @code{asm_operands}, and @code{asm_input} +@item MEM_VOLATILE_P (@var{x}) +In @code{mem}, @code{asm_operands}, and @code{asm_input} expressions, +nonzero for volatile memory references. +Stored in the @code{volatil} field and printed as @samp{/v}. + +@findex MEM_NOTRAP_P +@cindex @code{mem} and @samp{/c} +@cindex @code{call}, in @code{mem} +@item MEM_NOTRAP_P (@var{x}) +In @code{mem}, nonzero for memory references that will not trap. +Stored in the @code{call} field and printed as @samp{/c}. + +@findex MEM_POINTER +@cindex @code{mem} and @samp{/f} +@cindex @code{frame_related}, in @code{mem} +@item MEM_POINTER (@var{x}) +Nonzero in a @code{mem} if the memory reference holds a pointer. +Stored in the @code{frame_related} field and printed as @samp{/f}. + +@findex MEM_READONLY_P +@cindex @code{mem} and @samp{/u} +@cindex @code{unchanging}, in @code{mem} +@item MEM_READONLY_P (@var{x}) +Nonzero in a @code{mem}, if the memory is statically allocated and read-only. + +Read-only in this context means never modified during the lifetime of the +program, not necessarily in ROM or in write-disabled pages. A common +example of the later is a shared library's global offset table. This +table is initialized by the runtime loader, so the memory is technically +writable, but after control is transferred from the runtime loader to the +application, this memory will never be subsequently modified. + +Stored in the @code{unchanging} field and printed as @samp{/u}. + +@findex PREFETCH_SCHEDULE_BARRIER_P +@cindex @code{prefetch} and @samp{/v} +@cindex @code{volatile}, in @code{prefetch} +@item PREFETCH_SCHEDULE_BARRIER_P (@var{x}) +In a @code{prefetch}, indicates that the prefetch is a scheduling barrier. +No other INSNs will be moved over it. +Stored in the @code{volatil} field and printed as @samp{/v}. + +@findex REG_FUNCTION_VALUE_P +@cindex @code{reg} and @samp{/i} +@cindex @code{return_val}, in @code{reg} +@item REG_FUNCTION_VALUE_P (@var{x}) +Nonzero in a @code{reg} if it is the place in which this function's +value is going to be returned. (This happens only in a hard +register.) Stored in the @code{return_val} field and printed as +@samp{/i}. + +@findex REG_POINTER +@cindex @code{reg} and @samp{/f} +@cindex @code{frame_related}, in @code{reg} +@item REG_POINTER (@var{x}) +Nonzero in a @code{reg} if the register holds a pointer. Stored in the +@code{frame_related} field and printed as @samp{/f}. + +@findex REG_USERVAR_P +@cindex @code{reg} and @samp{/v} +@cindex @code{volatil}, in @code{reg} +@item REG_USERVAR_P (@var{x}) +In a @code{reg}, nonzero if it corresponds to a variable present in +the user's source code. Zero for temporaries generated internally by +the compiler. Stored in the @code{volatil} field and printed as +@samp{/v}. + +The same hard register may be used also for collecting the values of +functions called by this one, but @code{REG_FUNCTION_VALUE_P} is zero +in this kind of use. + +@findex RTL_CONST_CALL_P +@cindex @code{call_insn} and @samp{/u} +@cindex @code{unchanging}, in @code{call_insn} +@item RTL_CONST_CALL_P (@var{x}) +In a @code{call_insn} indicates that the insn represents a call to a +const function. Stored in the @code{unchanging} field and printed as +@samp{/u}. + +@findex RTL_PURE_CALL_P +@cindex @code{call_insn} and @samp{/i} +@cindex @code{return_val}, in @code{call_insn} +@item RTL_PURE_CALL_P (@var{x}) +In a @code{call_insn} indicates that the insn represents a call to a +pure function. Stored in the @code{return_val} field and printed as +@samp{/i}. + +@findex RTL_CONST_OR_PURE_CALL_P +@cindex @code{call_insn} and @samp{/u} or @samp{/i} +@item RTL_CONST_OR_PURE_CALL_P (@var{x}) +In a @code{call_insn}, true if @code{RTL_CONST_CALL_P} or +@code{RTL_PURE_CALL_P} is true. + +@findex RTL_LOOPING_CONST_OR_PURE_CALL_P +@cindex @code{call_insn} and @samp{/c} +@cindex @code{call}, in @code{call_insn} +@item RTL_LOOPING_CONST_OR_PURE_CALL_P (@var{x}) +In a @code{call_insn} indicates that the insn represents a possibly +infinite looping call to a const or pure function. Stored in the +@code{call} field and printed as @samp{/c}. Only true if one of +@code{RTL_CONST_CALL_P} or @code{RTL_PURE_CALL_P} is true. + +@findex RTX_FRAME_RELATED_P +@cindex @code{insn} and @samp{/f} +@cindex @code{call_insn} and @samp{/f} +@cindex @code{jump_insn} and @samp{/f} +@cindex @code{barrier} and @samp{/f} +@cindex @code{set} and @samp{/f} +@cindex @code{frame_related}, in @code{insn}, @code{call_insn}, @code{jump_insn}, @code{barrier}, and @code{set} +@item RTX_FRAME_RELATED_P (@var{x}) +Nonzero in an @code{insn}, @code{call_insn}, @code{jump_insn}, +@code{barrier}, or @code{set} which is part of a function prologue +and sets the stack pointer, sets the frame pointer, or saves a register. +This flag should also be set on an instruction that sets up a temporary +register to use in place of the frame pointer. +Stored in the @code{frame_related} field and printed as @samp{/f}. + +In particular, on RISC targets where there are limits on the sizes of +immediate constants, it is sometimes impossible to reach the register +save area directly from the stack pointer. In that case, a temporary +register is used that is near enough to the register save area, and the +Canonical Frame Address, i.e., DWARF2's logical frame pointer, register +must (temporarily) be changed to be this temporary register. So, the +instruction that sets this temporary register must be marked as +@code{RTX_FRAME_RELATED_P}. + +If the marked instruction is overly complex (defined in terms of what +@code{dwarf2out_frame_debug_expr} can handle), you will also have to +create a @code{REG_FRAME_RELATED_EXPR} note and attach it to the +instruction. This note should contain a simple expression of the +computation performed by this instruction, i.e., one that +@code{dwarf2out_frame_debug_expr} can handle. + +This flag is required for exception handling support on targets with RTL +prologues. + +@findex SCHED_GROUP_P +@cindex @code{insn} and @samp{/s} +@cindex @code{call_insn} and @samp{/s} +@cindex @code{jump_insn} and @samp{/s} +@cindex @code{jump_table_data} and @samp{/s} +@cindex @code{in_struct}, in @code{insn}, @code{call_insn}, @code{jump_insn} and @code{jump_table_data} +@item SCHED_GROUP_P (@var{x}) +During instruction scheduling, in an @code{insn}, @code{call_insn}, +@code{jump_insn} or @code{jump_table_data}, indicates that the +previous insn must be scheduled together with this insn. This is used to +ensure that certain groups of instructions will not be split up by the +instruction scheduling pass, for example, @code{use} insns before +a @code{call_insn} may not be separated from the @code{call_insn}. +Stored in the @code{in_struct} field and printed as @samp{/s}. + +@findex SET_IS_RETURN_P +@cindex @code{insn} and @samp{/j} +@cindex @code{jump}, in @code{insn} +@item SET_IS_RETURN_P (@var{x}) +For a @code{set}, nonzero if it is for a return. +Stored in the @code{jump} field and printed as @samp{/j}. + +@findex SIBLING_CALL_P +@cindex @code{call_insn} and @samp{/j} +@cindex @code{jump}, in @code{call_insn} +@item SIBLING_CALL_P (@var{x}) +For a @code{call_insn}, nonzero if the insn is a sibling call. +Stored in the @code{jump} field and printed as @samp{/j}. + +@findex STRING_POOL_ADDRESS_P +@cindex @code{symbol_ref} and @samp{/f} +@cindex @code{frame_related}, in @code{symbol_ref} +@item STRING_POOL_ADDRESS_P (@var{x}) +For a @code{symbol_ref} expression, nonzero if it addresses this function's +string constant pool. +Stored in the @code{frame_related} field and printed as @samp{/f}. + +@findex SUBREG_PROMOTED_UNSIGNED_P +@cindex @code{subreg} and @samp{/u} and @samp{/v} +@cindex @code{unchanging}, in @code{subreg} +@cindex @code{volatil}, in @code{subreg} +@item SUBREG_PROMOTED_UNSIGNED_P (@var{x}) +Returns a value greater then zero for a @code{subreg} that has +@code{SUBREG_PROMOTED_VAR_P} nonzero if the object being referenced is kept +zero-extended, zero if it is kept sign-extended, and less then zero if it is +extended some other way via the @code{ptr_extend} instruction. +Stored in the @code{unchanging} +field and @code{volatil} field, printed as @samp{/u} and @samp{/v}. +This macro may only be used to get the value it may not be used to change +the value. Use @code{SUBREG_PROMOTED_UNSIGNED_SET} to change the value. + +@findex SUBREG_PROMOTED_UNSIGNED_SET +@cindex @code{subreg} and @samp{/u} +@cindex @code{unchanging}, in @code{subreg} +@cindex @code{volatil}, in @code{subreg} +@item SUBREG_PROMOTED_UNSIGNED_SET (@var{x}) +Set the @code{unchanging} and @code{volatil} fields in a @code{subreg} +to reflect zero, sign, or other extension. If @code{volatil} is +zero, then @code{unchanging} as nonzero means zero extension and as +zero means sign extension. If @code{volatil} is nonzero then some +other type of extension was done via the @code{ptr_extend} instruction. + +@findex SUBREG_PROMOTED_VAR_P +@cindex @code{subreg} and @samp{/s} +@cindex @code{in_struct}, in @code{subreg} +@item SUBREG_PROMOTED_VAR_P (@var{x}) +Nonzero in a @code{subreg} if it was made when accessing an object that +was promoted to a wider mode in accord with the @code{PROMOTED_MODE} machine +description macro (@pxref{Storage Layout}). In this case, the mode of +the @code{subreg} is the declared mode of the object and the mode of +@code{SUBREG_REG} is the mode of the register that holds the object. +Promoted variables are always either sign- or zero-extended to the wider +mode on every assignment. Stored in the @code{in_struct} field and +printed as @samp{/s}. + +@findex SYMBOL_REF_USED +@cindex @code{used}, in @code{symbol_ref} +@item SYMBOL_REF_USED (@var{x}) +In a @code{symbol_ref}, indicates that @var{x} has been used. This is +normally only used to ensure that @var{x} is only declared external +once. Stored in the @code{used} field. + +@findex SYMBOL_REF_WEAK +@cindex @code{symbol_ref} and @samp{/i} +@cindex @code{return_val}, in @code{symbol_ref} +@item SYMBOL_REF_WEAK (@var{x}) +In a @code{symbol_ref}, indicates that @var{x} has been declared weak. +Stored in the @code{return_val} field and printed as @samp{/i}. + +@findex SYMBOL_REF_FLAG +@cindex @code{symbol_ref} and @samp{/v} +@cindex @code{volatil}, in @code{symbol_ref} +@item SYMBOL_REF_FLAG (@var{x}) +In a @code{symbol_ref}, this is used as a flag for machine-specific purposes. +Stored in the @code{volatil} field and printed as @samp{/v}. + +Most uses of @code{SYMBOL_REF_FLAG} are historic and may be subsumed +by @code{SYMBOL_REF_FLAGS}. Certainly use of @code{SYMBOL_REF_FLAGS} +is mandatory if the target requires more than one bit of storage. +@end table + +These are the fields to which the above macros refer: + +@table @code +@findex call +@cindex @samp{/c} in RTL dump +@item call +In a @code{mem}, 1 means that the memory reference will not trap. + +In a @code{call}, 1 means that this pure or const call may possibly +infinite loop. + +In an RTL dump, this flag is represented as @samp{/c}. + +@findex frame_related +@cindex @samp{/f} in RTL dump +@item frame_related +In an @code{insn} or @code{set} expression, 1 means that it is part of +a function prologue and sets the stack pointer, sets the frame pointer, +saves a register, or sets up a temporary register to use in place of the +frame pointer. + +In @code{reg} expressions, 1 means that the register holds a pointer. + +In @code{mem} expressions, 1 means that the memory reference holds a pointer. + +In @code{symbol_ref} expressions, 1 means that the reference addresses +this function's string constant pool. + +In an RTL dump, this flag is represented as @samp{/f}. + +@findex in_struct +@cindex @samp{/s} in RTL dump +@item in_struct +In @code{reg} expressions, it is 1 if the register has its entire life +contained within the test expression of some loop. + +In @code{subreg} expressions, 1 means that the @code{subreg} is accessing +an object that has had its mode promoted from a wider mode. + +In @code{label_ref} expressions, 1 means that the referenced label is +outside the innermost loop containing the insn in which the @code{label_ref} +was found. + +In @code{code_label} expressions, it is 1 if the label may never be deleted. +This is used for labels which are the target of non-local gotos. Such a +label that would have been deleted is replaced with a @code{note} of type +@code{NOTE_INSN_DELETED_LABEL}. + +In an @code{insn} during dead-code elimination, 1 means that the insn is +dead code. + +In an @code{insn} or @code{jump_insn} during reorg for an insn in the +delay slot of a branch, +1 means that this insn is from the target of the branch. + +In an @code{insn} during instruction scheduling, 1 means that this insn +must be scheduled as part of a group together with the previous insn. + +In an RTL dump, this flag is represented as @samp{/s}. + +@findex return_val +@cindex @samp{/i} in RTL dump +@item return_val +In @code{reg} expressions, 1 means the register contains +the value to be returned by the current function. On +machines that pass parameters in registers, the same register number +may be used for parameters as well, but this flag is not set on such +uses. + +In @code{symbol_ref} expressions, 1 means the referenced symbol is weak. + +In @code{call} expressions, 1 means the call is pure. + +In an RTL dump, this flag is represented as @samp{/i}. + +@findex jump +@cindex @samp{/j} in RTL dump +@item jump +In a @code{mem} expression, 1 means we should keep the alias set for this +mem unchanged when we access a component. + +In a @code{set}, 1 means it is for a return. + +In a @code{call_insn}, 1 means it is a sibling call. + +In a @code{jump_insn}, 1 means it is a crossing jump. + +In an RTL dump, this flag is represented as @samp{/j}. + +@findex unchanging +@cindex @samp{/u} in RTL dump +@item unchanging +In @code{reg} and @code{mem} expressions, 1 means +that the value of the expression never changes. + +In @code{subreg} expressions, it is 1 if the @code{subreg} references an +unsigned object whose mode has been promoted to a wider mode. + +In an @code{insn} or @code{jump_insn} in the delay slot of a branch +instruction, 1 means an annulling branch should be used. + +In a @code{symbol_ref} expression, 1 means that this symbol addresses +something in the per-function constant pool. + +In a @code{call_insn} 1 means that this instruction is a call to a const +function. + +In an RTL dump, this flag is represented as @samp{/u}. + +@findex used +@item used +This flag is used directly (without an access macro) at the end of RTL +generation for a function, to count the number of times an expression +appears in insns. Expressions that appear more than once are copied, +according to the rules for shared structure (@pxref{Sharing}). + +For a @code{reg}, it is used directly (without an access macro) by the +leaf register renumbering code to ensure that each register is only +renumbered once. + +In a @code{symbol_ref}, it indicates that an external declaration for +the symbol has already been written. + +@findex volatil +@cindex @samp{/v} in RTL dump +@item volatil +@cindex volatile memory references +In a @code{mem}, @code{asm_operands}, or @code{asm_input} +expression, it is 1 if the memory +reference is volatile. Volatile memory references may not be deleted, +reordered or combined. + +In a @code{symbol_ref} expression, it is used for machine-specific +purposes. + +In a @code{reg} expression, it is 1 if the value is a user-level variable. +0 indicates an internal compiler temporary. + +In an @code{insn}, 1 means the insn has been deleted. + +In @code{label_ref} and @code{reg_label} expressions, 1 means a reference +to a non-local label. + +In @code{prefetch} expressions, 1 means that the containing insn is a +scheduling barrier. + +In an RTL dump, this flag is represented as @samp{/v}. +@end table + +@node Machine Modes +@section Machine Modes +@cindex machine modes + +@findex machine_mode +A machine mode describes a size of data object and the representation used +for it. In the C code, machine modes are represented by an enumeration +type, @code{machine_mode}, defined in @file{machmode.def}. Each RTL +expression has room for a machine mode and so do certain kinds of tree +expressions (declarations and types, to be precise). + +In debugging dumps and machine descriptions, the machine mode of an RTL +expression is written after the expression code with a colon to separate +them. The letters @samp{mode} which appear at the end of each machine mode +name are omitted. For example, @code{(reg:SI 38)} is a @code{reg} +expression with machine mode @code{SImode}. If the mode is +@code{VOIDmode}, it is not written at all. + +Here is a table of machine modes. The term ``byte'' below refers to an +object of @code{BITS_PER_UNIT} bits (@pxref{Storage Layout}). + +@table @code +@findex BImode +@item BImode +``Bit'' mode represents a single bit, for predicate registers. + +@findex QImode +@item QImode +``Quarter-Integer'' mode represents a single byte treated as an integer. + +@findex HImode +@item HImode +``Half-Integer'' mode represents a two-byte integer. + +@findex PSImode +@item PSImode +``Partial Single Integer'' mode represents an integer which occupies +four bytes but which doesn't really use all four. On some machines, +this is the right mode to use for pointers. + +@findex SImode +@item SImode +``Single Integer'' mode represents a four-byte integer. + +@findex PDImode +@item PDImode +``Partial Double Integer'' mode represents an integer which occupies +eight bytes but which doesn't really use all eight. On some machines, +this is the right mode to use for certain pointers. + +@findex DImode +@item DImode +``Double Integer'' mode represents an eight-byte integer. + +@findex TImode +@item TImode +``Tetra Integer'' (?) mode represents a sixteen-byte integer. + +@findex OImode +@item OImode +``Octa Integer'' (?) mode represents a thirty-two-byte integer. + +@findex XImode +@item XImode +``Hexadeca Integer'' (?) mode represents a sixty-four-byte integer. + +@findex QFmode +@item QFmode +``Quarter-Floating'' mode represents a quarter-precision (single byte) +floating point number. + +@findex HFmode +@item HFmode +``Half-Floating'' mode represents a half-precision (two byte) floating +point number. + +@findex TQFmode +@item TQFmode +``Three-Quarter-Floating'' (?) mode represents a three-quarter-precision +(three byte) floating point number. + +@findex SFmode +@item SFmode +``Single Floating'' mode represents a four byte floating point number. +In the common case, of a processor with IEEE arithmetic and 8-bit bytes, +this is a single-precision IEEE floating point number; it can also be +used for double-precision (on processors with 16-bit bytes) and +single-precision VAX and IBM types. + +@findex DFmode +@item DFmode +``Double Floating'' mode represents an eight byte floating point number. +In the common case, of a processor with IEEE arithmetic and 8-bit bytes, +this is a double-precision IEEE floating point number. + +@findex XFmode +@item XFmode +``Extended Floating'' mode represents an IEEE extended floating point +number. This mode only has 80 meaningful bits (ten bytes). Some +processors require such numbers to be padded to twelve bytes, others +to sixteen; this mode is used for either. + +@findex SDmode +@item SDmode +``Single Decimal Floating'' mode represents a four byte decimal +floating point number (as distinct from conventional binary floating +point). + +@findex DDmode +@item DDmode +``Double Decimal Floating'' mode represents an eight byte decimal +floating point number. + +@findex TDmode +@item TDmode +``Tetra Decimal Floating'' mode represents a sixteen byte decimal +floating point number all 128 of whose bits are meaningful. + +@findex TFmode +@item TFmode +``Tetra Floating'' mode represents a sixteen byte floating point number +all 128 of whose bits are meaningful. One common use is the +IEEE quad-precision format. + +@findex QQmode +@item QQmode +``Quarter-Fractional'' mode represents a single byte treated as a signed +fractional number. The default format is ``s.7''. + +@findex HQmode +@item HQmode +``Half-Fractional'' mode represents a two-byte signed fractional number. +The default format is ``s.15''. + +@findex SQmode +@item SQmode +``Single Fractional'' mode represents a four-byte signed fractional number. +The default format is ``s.31''. + +@findex DQmode +@item DQmode +``Double Fractional'' mode represents an eight-byte signed fractional number. +The default format is ``s.63''. + +@findex TQmode +@item TQmode +``Tetra Fractional'' mode represents a sixteen-byte signed fractional number. +The default format is ``s.127''. + +@findex UQQmode +@item UQQmode +``Unsigned Quarter-Fractional'' mode represents a single byte treated as an +unsigned fractional number. The default format is ``.8''. + +@findex UHQmode +@item UHQmode +``Unsigned Half-Fractional'' mode represents a two-byte unsigned fractional +number. The default format is ``.16''. + +@findex USQmode +@item USQmode +``Unsigned Single Fractional'' mode represents a four-byte unsigned fractional +number. The default format is ``.32''. + +@findex UDQmode +@item UDQmode +``Unsigned Double Fractional'' mode represents an eight-byte unsigned +fractional number. The default format is ``.64''. + +@findex UTQmode +@item UTQmode +``Unsigned Tetra Fractional'' mode represents a sixteen-byte unsigned +fractional number. The default format is ``.128''. + +@findex HAmode +@item HAmode +``Half-Accumulator'' mode represents a two-byte signed accumulator. +The default format is ``s8.7''. + +@findex SAmode +@item SAmode +``Single Accumulator'' mode represents a four-byte signed accumulator. +The default format is ``s16.15''. + +@findex DAmode +@item DAmode +``Double Accumulator'' mode represents an eight-byte signed accumulator. +The default format is ``s32.31''. + +@findex TAmode +@item TAmode +``Tetra Accumulator'' mode represents a sixteen-byte signed accumulator. +The default format is ``s64.63''. + +@findex UHAmode +@item UHAmode +``Unsigned Half-Accumulator'' mode represents a two-byte unsigned accumulator. +The default format is ``8.8''. + +@findex USAmode +@item USAmode +``Unsigned Single Accumulator'' mode represents a four-byte unsigned +accumulator. The default format is ``16.16''. + +@findex UDAmode +@item UDAmode +``Unsigned Double Accumulator'' mode represents an eight-byte unsigned +accumulator. The default format is ``32.32''. + +@findex UTAmode +@item UTAmode +``Unsigned Tetra Accumulator'' mode represents a sixteen-byte unsigned +accumulator. The default format is ``64.64''. + +@findex CCmode +@item CCmode +``Condition Code'' mode represents the value of a condition code, which +is a machine-specific set of bits used to represent the result of a +comparison operation. Other machine-specific modes may also be used for +the condition code. (@pxref{Condition Code}). + +@findex BLKmode +@item BLKmode +``Block'' mode represents values that are aggregates to which none of +the other modes apply. In RTL, only memory references can have this mode, +and only if they appear in string-move or vector instructions. On machines +which have no such instructions, @code{BLKmode} will not appear in RTL@. + +@findex VOIDmode +@item VOIDmode +Void mode means the absence of a mode or an unspecified mode. +For example, RTL expressions of code @code{const_int} have mode +@code{VOIDmode} because they can be taken to have whatever mode the context +requires. In debugging dumps of RTL, @code{VOIDmode} is expressed by +the absence of any mode. + +@findex QCmode +@findex HCmode +@findex SCmode +@findex DCmode +@findex XCmode +@findex TCmode +@item QCmode, HCmode, SCmode, DCmode, XCmode, TCmode +These modes stand for a complex number represented as a pair of floating +point values. The floating point values are in @code{QFmode}, +@code{HFmode}, @code{SFmode}, @code{DFmode}, @code{XFmode}, and +@code{TFmode}, respectively. + +@findex CQImode +@findex CHImode +@findex CSImode +@findex CDImode +@findex CTImode +@findex COImode +@findex CPSImode +@item CQImode, CHImode, CSImode, CDImode, CTImode, COImode, CPSImode +These modes stand for a complex number represented as a pair of integer +values. The integer values are in @code{QImode}, @code{HImode}, +@code{SImode}, @code{DImode}, @code{TImode}, @code{OImode}, and @code{PSImode}, +respectively. + +@findex BND32mode +@findex BND64mode +@item BND32mode BND64mode +These modes stand for bounds for pointer of 32 and 64 bit size respectively. +Mode size is double pointer mode size. +@end table + +The machine description defines @code{Pmode} as a C macro which expands +into the machine mode used for addresses. Normally this is the mode +whose size is @code{BITS_PER_WORD}, @code{SImode} on 32-bit machines. + +The only modes which a machine description @i{must} support are +@code{QImode}, and the modes corresponding to @code{BITS_PER_WORD}, +@code{FLOAT_TYPE_SIZE} and @code{DOUBLE_TYPE_SIZE}. +The compiler will attempt to use @code{DImode} for 8-byte structures and +unions, but this can be prevented by overriding the definition of +@code{MAX_FIXED_MODE_SIZE}. Alternatively, you can have the compiler +use @code{TImode} for 16-byte structures and unions. Likewise, you can +arrange for the C type @code{short int} to avoid using @code{HImode}. + +@cindex mode classes +Very few explicit references to machine modes remain in the compiler and +these few references will soon be removed. Instead, the machine modes +are divided into mode classes. These are represented by the enumeration +type @code{enum mode_class} defined in @file{machmode.h}. The possible +mode classes are: + +@table @code +@findex MODE_INT +@item MODE_INT +Integer modes. By default these are @code{BImode}, @code{QImode}, +@code{HImode}, @code{SImode}, @code{DImode}, @code{TImode}, and +@code{OImode}. + +@findex MODE_PARTIAL_INT +@item MODE_PARTIAL_INT +The ``partial integer'' modes, @code{PQImode}, @code{PHImode}, +@code{PSImode} and @code{PDImode}. + +@findex MODE_FLOAT +@item MODE_FLOAT +Floating point modes. By default these are @code{QFmode}, +@code{HFmode}, @code{TQFmode}, @code{SFmode}, @code{DFmode}, +@code{XFmode} and @code{TFmode}. + +@findex MODE_DECIMAL_FLOAT +@item MODE_DECIMAL_FLOAT +Decimal floating point modes. By default these are @code{SDmode}, +@code{DDmode} and @code{TDmode}. + +@findex MODE_FRACT +@item MODE_FRACT +Signed fractional modes. By default these are @code{QQmode}, @code{HQmode}, +@code{SQmode}, @code{DQmode} and @code{TQmode}. + +@findex MODE_UFRACT +@item MODE_UFRACT +Unsigned fractional modes. By default these are @code{UQQmode}, @code{UHQmode}, +@code{USQmode}, @code{UDQmode} and @code{UTQmode}. + +@findex MODE_ACCUM +@item MODE_ACCUM +Signed accumulator modes. By default these are @code{HAmode}, +@code{SAmode}, @code{DAmode} and @code{TAmode}. + +@findex MODE_UACCUM +@item MODE_UACCUM +Unsigned accumulator modes. By default these are @code{UHAmode}, +@code{USAmode}, @code{UDAmode} and @code{UTAmode}. + +@findex MODE_COMPLEX_INT +@item MODE_COMPLEX_INT +Complex integer modes. (These are not currently implemented). + +@findex MODE_COMPLEX_FLOAT +@item MODE_COMPLEX_FLOAT +Complex floating point modes. By default these are @code{QCmode}, +@code{HCmode}, @code{SCmode}, @code{DCmode}, @code{XCmode}, and +@code{TCmode}. + +@findex MODE_CC +@item MODE_CC +Modes representing condition code values. These are @code{CCmode} plus +any @code{CC_MODE} modes listed in the @file{@var{machine}-modes.def}. +@xref{Jump Patterns}, +also see @ref{Condition Code}. + +@findex MODE_POINTER_BOUNDS +@item MODE_POINTER_BOUNDS +Pointer bounds modes. Used to represent values of pointer bounds type. +Operations in these modes may be executed as NOPs depending on hardware +features and environment setup. + +@findex MODE_OPAQUE +@item MODE_OPAQUE +This is a mode class for modes that don't want to provide operations +other than register moves, memory moves, loads, stores, and +@code{unspec}s. They have a size and precision and that's all. + +@findex MODE_RANDOM +@item MODE_RANDOM +This is a catchall mode class for modes which don't fit into the above +classes. Currently @code{VOIDmode} and @code{BLKmode} are in +@code{MODE_RANDOM}. +@end table + +@cindex machine mode wrapper classes +@code{machmode.h} also defines various wrapper classes that combine a +@code{machine_mode} with a static assertion that a particular +condition holds. The classes are: + +@table @code +@findex scalar_int_mode +@item scalar_int_mode +A mode that has class @code{MODE_INT} or @code{MODE_PARTIAL_INT}. + +@findex scalar_float_mode +@item scalar_float_mode +A mode that has class @code{MODE_FLOAT} or @code{MODE_DECIMAL_FLOAT}. + +@findex scalar_mode +@item scalar_mode +A mode that holds a single numerical value. In practice this means +that the mode is a @code{scalar_int_mode}, is a @code{scalar_float_mode}, +or has class @code{MODE_FRACT}, @code{MODE_UFRACT}, @code{MODE_ACCUM}, +@code{MODE_UACCUM} or @code{MODE_POINTER_BOUNDS}. + +@findex complex_mode +@item complex_mode +A mode that has class @code{MODE_COMPLEX_INT} or @code{MODE_COMPLEX_FLOAT}. + +@findex fixed_size_mode +@item fixed_size_mode +A mode whose size is known at compile time. +@end table + +Named modes use the most constrained of the available wrapper classes, +if one exists, otherwise they use @code{machine_mode}. For example, +@code{QImode} is a @code{scalar_int_mode}, @code{SFmode} is a +@code{scalar_float_mode} and @code{BLKmode} is a plain +@code{machine_mode}. It is possible to refer to any mode as a raw +@code{machine_mode} by adding the @code{E_} prefix, where @code{E} +stands for ``enumeration''. For example, the raw @code{machine_mode} +names of the modes just mentioned are @code{E_QImode}, @code{E_SFmode} +and @code{E_BLKmode} respectively. + +The wrapper classes implicitly convert to @code{machine_mode} and to any +wrapper class that represents a more general condition; for example +@code{scalar_int_mode} and @code{scalar_float_mode} both convert +to @code{scalar_mode} and all three convert to @code{fixed_size_mode}. +The classes act like @code{machine_mode}s that accept only certain +named modes. + +@findex opt_mode +@file{machmode.h} also defines a template class @code{opt_mode<@var{T}>} +that holds a @code{T} or nothing, where @code{T} can be either +@code{machine_mode} or one of the wrapper classes above. The main +operations on an @code{opt_mode<@var{T}>} @var{x} are as follows: + +@table @samp +@item @var{x}.exists () +Return true if @var{x} holds a mode rather than nothing. + +@item @var{x}.exists (&@var{y}) +Return true if @var{x} holds a mode rather than nothing, storing the +mode in @var{y} if so. @var{y} must be assignment-compatible with @var{T}. + +@item @var{x}.require () +Assert that @var{x} holds a mode rather than nothing and return that mode. + +@item @var{x} = @var{y} +Set @var{x} to @var{y}, where @var{y} is a @var{T} or implicitly converts +to a @var{T}. +@end table + +The default constructor sets an @code{opt_mode<@var{T}>} to nothing. +There is also a constructor that takes an initial value of type @var{T}. + +It is possible to use the @file{is-a.h} accessors on a @code{machine_mode} +or machine mode wrapper @var{x}: + +@table @samp +@findex is_a +@item is_a <@var{T}> (@var{x}) +Return true if @var{x} meets the conditions for wrapper class @var{T}. + +@item is_a <@var{T}> (@var{x}, &@var{y}) +Return true if @var{x} meets the conditions for wrapper class @var{T}, +storing it in @var{y} if so. @var{y} must be assignment-compatible with +@var{T}. + +@item as_a <@var{T}> (@var{x}) +Assert that @var{x} meets the conditions for wrapper class @var{T} +and return it as a @var{T}. + +@item dyn_cast <@var{T}> (@var{x}) +Return an @code{opt_mode<@var{T}>} that holds @var{x} if @var{x} meets +the conditions for wrapper class @var{T} and that holds nothing otherwise. +@end table + +The purpose of these wrapper classes is to give stronger static type +checking. For example, if a function takes a @code{scalar_int_mode}, +a caller that has a general @code{machine_mode} must either check or +assert that the code is indeed a scalar integer first, using one of +the functions above. + +The wrapper classes are normal C++ classes, with user-defined +constructors. Sometimes it is useful to have a POD version of +the same type, particularly if the type appears in a @code{union}. +The template class @code{pod_mode<@var{T}>} provides a POD version +of wrapper class @var{T}. It is assignment-compatible with @var{T} +and implicitly converts to both @code{machine_mode} and @var{T}. + +Here are some C macros that relate to machine modes: + +@table @code +@findex GET_MODE +@item GET_MODE (@var{x}) +Returns the machine mode of the RTX @var{x}. + +@findex PUT_MODE +@item PUT_MODE (@var{x}, @var{newmode}) +Alters the machine mode of the RTX @var{x} to be @var{newmode}. + +@findex NUM_MACHINE_MODES +@item NUM_MACHINE_MODES +Stands for the number of machine modes available on the target +machine. This is one greater than the largest numeric value of any +machine mode. + +@findex GET_MODE_NAME +@item GET_MODE_NAME (@var{m}) +Returns the name of mode @var{m} as a string. + +@findex GET_MODE_CLASS +@item GET_MODE_CLASS (@var{m}) +Returns the mode class of mode @var{m}. + +@findex GET_MODE_WIDER_MODE +@item GET_MODE_WIDER_MODE (@var{m}) +Returns the next wider natural mode. For example, the expression +@code{GET_MODE_WIDER_MODE (QImode)} returns @code{HImode}. + +@findex GET_MODE_SIZE +@item GET_MODE_SIZE (@var{m}) +Returns the size in bytes of a datum of mode @var{m}. + +@findex GET_MODE_BITSIZE +@item GET_MODE_BITSIZE (@var{m}) +Returns the size in bits of a datum of mode @var{m}. + +@findex GET_MODE_IBIT +@item GET_MODE_IBIT (@var{m}) +Returns the number of integral bits of a datum of fixed-point mode @var{m}. + +@findex GET_MODE_FBIT +@item GET_MODE_FBIT (@var{m}) +Returns the number of fractional bits of a datum of fixed-point mode @var{m}. + +@findex GET_MODE_MASK +@item GET_MODE_MASK (@var{m}) +Returns a bitmask containing 1 for all bits in a word that fit within +mode @var{m}. This macro can only be used for modes whose bitsize is +less than or equal to @code{HOST_BITS_PER_INT}. + +@findex GET_MODE_ALIGNMENT +@item GET_MODE_ALIGNMENT (@var{m}) +Return the required alignment, in bits, for an object of mode @var{m}. + +@findex GET_MODE_UNIT_SIZE +@item GET_MODE_UNIT_SIZE (@var{m}) +Returns the size in bytes of the subunits of a datum of mode @var{m}. +This is the same as @code{GET_MODE_SIZE} except in the case of complex +modes. For them, the unit size is the size of the real or imaginary +part. + +@findex GET_MODE_NUNITS +@item GET_MODE_NUNITS (@var{m}) +Returns the number of units contained in a mode, i.e., +@code{GET_MODE_SIZE} divided by @code{GET_MODE_UNIT_SIZE}. + +@findex GET_CLASS_NARROWEST_MODE +@item GET_CLASS_NARROWEST_MODE (@var{c}) +Returns the narrowest mode in mode class @var{c}. +@end table + +The following 3 variables are defined on every target. They can be +used to allocate buffers that are guaranteed to be large enough to +hold any value that can be represented on the target. The first two +can be overridden by defining them in the target's mode.def file, +however, the value must be a constant that can determined very early +in the compilation process. The third symbol cannot be overridden. + +@table @code +@findex BITS_PER_UNIT +@item BITS_PER_UNIT +The number of bits in an addressable storage unit (byte). If you do +not define this, the default is 8. + +@findex MAX_BITSIZE_MODE_ANY_INT +@item MAX_BITSIZE_MODE_ANY_INT +The maximum bitsize of any mode that is used in integer math. This +should be overridden by the target if it uses large integers as +containers for larger vectors but otherwise never uses the contents to +compute integer values. + +@findex MAX_BITSIZE_MODE_ANY_MODE +@item MAX_BITSIZE_MODE_ANY_MODE +The bitsize of the largest mode on the target. The default value is +the largest mode size given in the mode definition file, which is +always correct for targets whose modes have a fixed size. Targets +that might increase the size of a mode beyond this default should define +@code{MAX_BITSIZE_MODE_ANY_MODE} to the actual upper limit in +@file{@var{machine}-modes.def}. +@end table + +@findex byte_mode +@findex word_mode +The global variables @code{byte_mode} and @code{word_mode} contain modes +whose classes are @code{MODE_INT} and whose bitsizes are either +@code{BITS_PER_UNIT} or @code{BITS_PER_WORD}, respectively. On 32-bit +machines, these are @code{QImode} and @code{SImode}, respectively. + +@node Constants +@section Constant Expression Types +@cindex RTL constants +@cindex RTL constant expression types + +The simplest RTL expressions are those that represent constant values. + +@table @code +@findex const_int +@item (const_int @var{i}) +This type of expression represents the integer value @var{i}. @var{i} +is customarily accessed with the macro @code{INTVAL} as in +@code{INTVAL (@var{exp})}, which is equivalent to @code{XWINT (@var{exp}, 0)}. + +Constants generated for modes with fewer bits than in +@code{HOST_WIDE_INT} must be sign extended to full width (e.g., with +@code{gen_int_mode}). For constants for modes with more bits than in +@code{HOST_WIDE_INT} the implied high order bits of that constant are +copies of the top bit. Note however that values are neither +inherently signed nor inherently unsigned; where necessary, signedness +is determined by the rtl operation instead. + +@findex const0_rtx +@findex const1_rtx +@findex const2_rtx +@findex constm1_rtx +There is only one expression object for the integer value zero; it is +the value of the variable @code{const0_rtx}. Likewise, the only +expression for integer value one is found in @code{const1_rtx}, the only +expression for integer value two is found in @code{const2_rtx}, and the +only expression for integer value negative one is found in +@code{constm1_rtx}. Any attempt to create an expression of code +@code{const_int} and value zero, one, two or negative one will return +@code{const0_rtx}, @code{const1_rtx}, @code{const2_rtx} or +@code{constm1_rtx} as appropriate. + +@findex const_true_rtx +Similarly, there is only one object for the integer whose value is +@code{STORE_FLAG_VALUE}. It is found in @code{const_true_rtx}. If +@code{STORE_FLAG_VALUE} is one, @code{const_true_rtx} and +@code{const1_rtx} will point to the same object. If +@code{STORE_FLAG_VALUE} is @minus{}1, @code{const_true_rtx} and +@code{constm1_rtx} will point to the same object. + +@findex const_double +@item (const_double:@var{m} @var{i0} @var{i1} @dots{}) +This represents either a floating-point constant of mode @var{m} or +(on older ports that do not define +@code{TARGET_SUPPORTS_WIDE_INT}) an integer constant too large to fit +into @code{HOST_BITS_PER_WIDE_INT} bits but small enough to fit within +twice that number of bits. In the latter case, @var{m} will be +@code{VOIDmode}. For integral values constants for modes with more +bits than twice the number in @code{HOST_WIDE_INT} the implied high +order bits of that constant are copies of the top bit of +@code{CONST_DOUBLE_HIGH}. Note however that integral values are +neither inherently signed nor inherently unsigned; where necessary, +signedness is determined by the rtl operation instead. + +On more modern ports, @code{CONST_DOUBLE} only represents floating +point values. New ports define @code{TARGET_SUPPORTS_WIDE_INT} to +make this designation. + +@findex CONST_DOUBLE_LOW +If @var{m} is @code{VOIDmode}, the bits of the value are stored in +@var{i0} and @var{i1}. @var{i0} is customarily accessed with the macro +@code{CONST_DOUBLE_LOW} and @var{i1} with @code{CONST_DOUBLE_HIGH}. + +If the constant is floating point (regardless of its precision), then +the number of integers used to store the value depends on the size of +@code{REAL_VALUE_TYPE} (@pxref{Floating Point}). The integers +represent a floating point number, but not precisely in the target +machine's or host machine's floating point format. To convert them to +the precise bit pattern used by the target machine, use the macro +@code{REAL_VALUE_TO_TARGET_DOUBLE} and friends (@pxref{Data Output}). + +@findex const_double_zero +The host dependency for the number of integers used to store a double +value makes it problematic for machine descriptions to use expressions +of code @code{const_double} and therefore a syntactic alias has been +provided: + +@smallexample +(const_double_zero:@var{m}) +@end smallexample + +standing for: + +@smallexample +(const_double:@var{m} 0 0 @dots{}) +@end smallexample + +for matching the floating-point value zero, possibly the only useful one. + +@findex CONST_WIDE_INT +@item (const_wide_int:@var{m} @var{nunits} @var{elt0} @dots{}) +This contains an array of @code{HOST_WIDE_INT}s that is large enough +to hold any constant that can be represented on the target. This form +of rtl is only used on targets that define +@code{TARGET_SUPPORTS_WIDE_INT} to be nonzero and then +@code{CONST_DOUBLE}s are only used to hold floating-point values. If +the target leaves @code{TARGET_SUPPORTS_WIDE_INT} defined as 0, +@code{CONST_WIDE_INT}s are not used and @code{CONST_DOUBLE}s are as +they were before. + +The values are stored in a compressed format. The higher-order +0s or -1s are not represented if they are just the logical sign +extension of the number that is represented. + +@findex CONST_WIDE_INT_VEC +@item CONST_WIDE_INT_VEC (@var{code}) +Returns the entire array of @code{HOST_WIDE_INT}s that are used to +store the value. This macro should be rarely used. + +@findex CONST_WIDE_INT_NUNITS +@item CONST_WIDE_INT_NUNITS (@var{code}) +The number of @code{HOST_WIDE_INT}s used to represent the number. +Note that this generally is smaller than the number of +@code{HOST_WIDE_INT}s implied by the mode size. + +@findex CONST_WIDE_INT_ELT +@item CONST_WIDE_INT_ELT (@var{code},@var{i}) +Returns the @code{i}th element of the array. Element 0 is contains +the low order bits of the constant. + +@findex const_fixed +@item (const_fixed:@var{m} @dots{}) +Represents a fixed-point constant of mode @var{m}. +The operand is a data structure of type @code{struct fixed_value} and +is accessed with the macro @code{CONST_FIXED_VALUE}. The high part of +data is accessed with @code{CONST_FIXED_VALUE_HIGH}; the low part is +accessed with @code{CONST_FIXED_VALUE_LOW}. + +@findex const_poly_int +@item (const_poly_int:@var{m} [@var{c0} @var{c1} @dots{}]) +Represents a @code{poly_int}-style polynomial integer with coefficients +@var{c0}, @var{c1}, @dots{}. The coefficients are @code{wide_int}-based +integers rather than rtxes. @code{CONST_POLY_INT_COEFFS} gives the +values of individual coefficients (which is mostly only useful in +low-level routines) and @code{const_poly_int_value} gives the full +@code{poly_int} value. + +@findex const_vector +@item (const_vector:@var{m} [@var{x0} @var{x1} @dots{}]) +Represents a vector constant. The values in square brackets are +elements of the vector, which are always @code{const_int}, +@code{const_wide_int}, @code{const_double} or @code{const_fixed} +expressions. + +Each vector constant @var{v} is treated as a specific instance of an +arbitrary-length sequence that itself contains +@samp{CONST_VECTOR_NPATTERNS (@var{v})} interleaved patterns. Each +pattern has the form: + +@smallexample +@{ @var{base0}, @var{base1}, @var{base1} + @var{step}, @var{base1} + @var{step} * 2, @dots{} @} +@end smallexample + +The first three elements in each pattern are enough to determine the +values of the other elements. However, if all @var{step}s are zero, +only the first two elements are needed. If in addition each @var{base1} +is equal to the corresponding @var{base0}, only the first element in +each pattern is needed. The number of determining elements per pattern +is given by @samp{CONST_VECTOR_NELTS_PER_PATTERN (@var{v})}. + +For example, the constant: + +@smallexample +@{ 0, 1, 2, 6, 3, 8, 4, 10, 5, 12, 6, 14, 7, 16, 8, 18 @} +@end smallexample + +is interpreted as an interleaving of the sequences: + +@smallexample +@{ 0, 2, 3, 4, 5, 6, 7, 8 @} +@{ 1, 6, 8, 10, 12, 14, 16, 18 @} +@end smallexample + +where the sequences are represented by the following patterns: + +@smallexample +@var{base0} == 0, @var{base1} == 2, @var{step} == 1 +@var{base0} == 1, @var{base1} == 6, @var{step} == 2 +@end smallexample + +In this case: + +@smallexample +CONST_VECTOR_NPATTERNS (@var{v}) == 2 +CONST_VECTOR_NELTS_PER_PATTERN (@var{v}) == 3 +@end smallexample + +Thus the first 6 elements (@samp{@{ 0, 1, 2, 6, 3, 8 @}}) are enough +to determine the whole sequence; we refer to them as the ``encoded'' +elements. They are the only elements present in the square brackets +for variable-length @code{const_vector}s (i.e.@: for +@code{const_vector}s whose mode @var{m} has a variable number of +elements). However, as a convenience to code that needs to handle +both @code{const_vector}s and @code{parallel}s, all elements are +present in the square brackets for fixed-length @code{const_vector}s; +the encoding scheme simply reduces the amount of work involved in +processing constants that follow a regular pattern. + +Sometimes this scheme can create two possible encodings of the same +vector. For example @{ 0, 1 @} could be seen as two patterns with +one element each or one pattern with two elements (@var{base0} and +@var{base1}). The canonical encoding is always the one with the +fewest patterns or (if both encodings have the same number of +petterns) the one with the fewest encoded elements. + +@samp{const_vector_encoding_nelts (@var{v})} gives the total number of +encoded elements in @var{v}, which is 6 in the example above. +@code{CONST_VECTOR_ENCODED_ELT (@var{v}, @var{i})} accesses the value +of encoded element @var{i}. + +@samp{CONST_VECTOR_DUPLICATE_P (@var{v})} is true if @var{v} simply contains +repeated instances of @samp{CONST_VECTOR_NPATTERNS (@var{v})} values. This is +a shorthand for testing @samp{CONST_VECTOR_NELTS_PER_PATTERN (@var{v}) == 1}. + +@samp{CONST_VECTOR_STEPPED_P (@var{v})} is true if at least one +pattern in @var{v} has a nonzero step. This is a shorthand for +testing @samp{CONST_VECTOR_NELTS_PER_PATTERN (@var{v}) == 3}. + +@code{CONST_VECTOR_NUNITS (@var{v})} gives the total number of elements +in @var{v}; it is a shorthand for getting the number of units in +@samp{GET_MODE (@var{v})}. + +The utility function @code{const_vector_elt} gives the value of an +arbitrary element as an @code{rtx}. @code{const_vector_int_elt} gives +the same value as a @code{wide_int}. + +@findex const_string +@item (const_string @var{str}) +Represents a constant string with value @var{str}. Currently this is +used only for insn attributes (@pxref{Insn Attributes}) since constant +strings in C are placed in memory. + +@findex symbol_ref +@item (symbol_ref:@var{mode} @var{symbol}) +Represents the value of an assembler label for data. @var{symbol} is +a string that describes the name of the assembler label. If it starts +with a @samp{*}, the label is the rest of @var{symbol} not including +the @samp{*}. Otherwise, the label is @var{symbol}, usually prefixed +with @samp{_}. + +The @code{symbol_ref} contains a mode, which is usually @code{Pmode}. +Usually that is the only mode for which a symbol is directly valid. + +@findex label_ref +@item (label_ref:@var{mode} @var{label}) +Represents the value of an assembler label for code. It contains one +operand, an expression, which must be a @code{code_label} or a @code{note} +of type @code{NOTE_INSN_DELETED_LABEL} that appears in the instruction +sequence to identify the place where the label should go. + +The reason for using a distinct expression type for code label +references is so that jump optimization can distinguish them. + +The @code{label_ref} contains a mode, which is usually @code{Pmode}. +Usually that is the only mode for which a label is directly valid. + +@findex const +@item (const:@var{m} @var{exp}) +Represents a constant that is the result of an assembly-time +arithmetic computation. The operand, @var{exp}, contains only +@code{const_int}, @code{symbol_ref}, @code{label_ref} or @code{unspec} +expressions, combined with @code{plus} and @code{minus}. Any such +@code{unspec}s are target-specific and typically represent some form +of relocation operator. @var{m} should be a valid address mode. + +@findex high +@item (high:@var{m} @var{exp}) +Represents the high-order bits of @var{exp}. +The number of bits is machine-dependent and is +normally the number of bits specified in an instruction that initializes +the high order bits of a register. It is used with @code{lo_sum} to +represent the typical two-instruction sequence used in RISC machines to +reference large immediate values and/or link-time constants such +as global memory addresses. In the latter case, @var{m} is @code{Pmode} +and @var{exp} is usually a constant expression involving @code{symbol_ref}. +@end table + +@findex CONST0_RTX +@findex CONST1_RTX +@findex CONST2_RTX +The macro @code{CONST0_RTX (@var{mode})} refers to an expression with +value 0 in mode @var{mode}. If mode @var{mode} is of mode class +@code{MODE_INT}, it returns @code{const0_rtx}. If mode @var{mode} is of +mode class @code{MODE_FLOAT}, it returns a @code{CONST_DOUBLE} +expression in mode @var{mode}. Otherwise, it returns a +@code{CONST_VECTOR} expression in mode @var{mode}. Similarly, the macro +@code{CONST1_RTX (@var{mode})} refers to an expression with value 1 in +mode @var{mode} and similarly for @code{CONST2_RTX}. The +@code{CONST1_RTX} and @code{CONST2_RTX} macros are undefined +for vector modes. + +@node Regs and Memory +@section Registers and Memory +@cindex RTL register expressions +@cindex RTL memory expressions + +Here are the RTL expression types for describing access to machine +registers and to main memory. + +@table @code +@findex reg +@cindex hard registers +@cindex pseudo registers +@item (reg:@var{m} @var{n}) +For small values of the integer @var{n} (those that are less than +@code{FIRST_PSEUDO_REGISTER}), this stands for a reference to machine +register number @var{n}: a @dfn{hard register}. For larger values of +@var{n}, it stands for a temporary value or @dfn{pseudo register}. +The compiler's strategy is to generate code assuming an unlimited +number of such pseudo registers, and later convert them into hard +registers or into memory references. + +@var{m} is the machine mode of the reference. It is necessary because +machines can generally refer to each register in more than one mode. +For example, a register may contain a full word but there may be +instructions to refer to it as a half word or as a single byte, as +well as instructions to refer to it as a floating point number of +various precisions. + +Even for a register that the machine can access in only one mode, +the mode must always be specified. + +The symbol @code{FIRST_PSEUDO_REGISTER} is defined by the machine +description, since the number of hard registers on the machine is an +invariant characteristic of the machine. Note, however, that not +all of the machine registers must be general registers. All the +machine registers that can be used for storage of data are given +hard register numbers, even those that can be used only in certain +instructions or can hold only certain types of data. + +A hard register may be accessed in various modes throughout one +function, but each pseudo register is given a natural mode +and is accessed only in that mode. When it is necessary to describe +an access to a pseudo register using a nonnatural mode, a @code{subreg} +expression is used. + +A @code{reg} expression with a machine mode that specifies more than +one word of data may actually stand for several consecutive registers. +If in addition the register number specifies a hardware register, then +it actually represents several consecutive hardware registers starting +with the specified one. + +Each pseudo register number used in a function's RTL code is +represented by a unique @code{reg} expression. + +@findex FIRST_VIRTUAL_REGISTER +@findex LAST_VIRTUAL_REGISTER +Some pseudo register numbers, those within the range of +@code{FIRST_VIRTUAL_REGISTER} to @code{LAST_VIRTUAL_REGISTER} only +appear during the RTL generation phase and are eliminated before the +optimization phases. These represent locations in the stack frame that +cannot be determined until RTL generation for the function has been +completed. The following virtual register numbers are defined: + +@table @code +@findex VIRTUAL_INCOMING_ARGS_REGNUM +@item VIRTUAL_INCOMING_ARGS_REGNUM +This points to the first word of the incoming arguments passed on the +stack. Normally these arguments are placed there by the caller, but the +callee may have pushed some arguments that were previously passed in +registers. + +@cindex @code{FIRST_PARM_OFFSET} and virtual registers +@cindex @code{ARG_POINTER_REGNUM} and virtual registers +When RTL generation is complete, this virtual register is replaced +by the sum of the register given by @code{ARG_POINTER_REGNUM} and the +value of @code{FIRST_PARM_OFFSET}. + +@findex VIRTUAL_STACK_VARS_REGNUM +@cindex @code{FRAME_GROWS_DOWNWARD} and virtual registers +@item VIRTUAL_STACK_VARS_REGNUM +If @code{FRAME_GROWS_DOWNWARD} is defined to a nonzero value, this points +to immediately above the first variable on the stack. Otherwise, it points +to the first variable on the stack. + +@cindex @code{TARGET_STARTING_FRAME_OFFSET} and virtual registers +@cindex @code{FRAME_POINTER_REGNUM} and virtual registers +@code{VIRTUAL_STACK_VARS_REGNUM} is replaced with the sum of the +register given by @code{FRAME_POINTER_REGNUM} and the value +@code{TARGET_STARTING_FRAME_OFFSET}. + +@findex VIRTUAL_STACK_DYNAMIC_REGNUM +@item VIRTUAL_STACK_DYNAMIC_REGNUM +This points to the location of dynamically allocated memory on the stack +immediately after the stack pointer has been adjusted by the amount of +memory desired. + +@cindex @code{STACK_DYNAMIC_OFFSET} and virtual registers +@cindex @code{STACK_POINTER_REGNUM} and virtual registers +This virtual register is replaced by the sum of the register given by +@code{STACK_POINTER_REGNUM} and the value @code{STACK_DYNAMIC_OFFSET}. + +@findex VIRTUAL_OUTGOING_ARGS_REGNUM +@item VIRTUAL_OUTGOING_ARGS_REGNUM +This points to the location in the stack at which outgoing arguments +should be written when the stack is pre-pushed (arguments pushed using +push insns should always use @code{STACK_POINTER_REGNUM}). + +@cindex @code{STACK_POINTER_OFFSET} and virtual registers +This virtual register is replaced by the sum of the register given by +@code{STACK_POINTER_REGNUM} and the value @code{STACK_POINTER_OFFSET}. +@end table + +@findex subreg +@item (subreg:@var{m1} @var{reg:m2} @var{bytenum}) + +@code{subreg} expressions are used to refer to a register in a machine +mode other than its natural one, or to refer to one register of +a multi-part @code{reg} that actually refers to several registers. + +Each pseudo register has a natural mode. If it is necessary to +operate on it in a different mode, the register must be +enclosed in a @code{subreg}. + +There are currently three supported types for the first operand of a +@code{subreg}: +@itemize +@item pseudo registers +This is the most common case. Most @code{subreg}s have pseudo +@code{reg}s as their first operand. + +@item mem +@code{subreg}s of @code{mem} were common in earlier versions of GCC and +are still supported. During the reload pass these are replaced by plain +@code{mem}s. On machines that do not do instruction scheduling, use of +@code{subreg}s of @code{mem} are still used, but this is no longer +recommended. Such @code{subreg}s are considered to be +@code{register_operand}s rather than @code{memory_operand}s before and +during reload. Because of this, the scheduling passes cannot properly +schedule instructions with @code{subreg}s of @code{mem}, so for machines +that do scheduling, @code{subreg}s of @code{mem} should never be used. +To support this, the combine and recog passes have explicit code to +inhibit the creation of @code{subreg}s of @code{mem} when +@code{INSN_SCHEDULING} is defined. + +The use of @code{subreg}s of @code{mem} after the reload pass is an area +that is not well understood and should be avoided. There is still some +code in the compiler to support this, but this code has possibly rotted. +This use of @code{subreg}s is discouraged and will most likely not be +supported in the future. + +@item hard registers +It is seldom necessary to wrap hard registers in @code{subreg}s; such +registers would normally reduce to a single @code{reg} rtx. This use of +@code{subreg}s is discouraged and may not be supported in the future. + +@end itemize + +@code{subreg}s of @code{subreg}s are not supported. Using +@code{simplify_gen_subreg} is the recommended way to avoid this problem. + +@code{subreg}s come in two distinct flavors, each having its own +usage and rules: + +@table @asis +@item Paradoxical subregs +When @var{m1} is strictly wider than @var{m2}, the @code{subreg} +expression is called @dfn{paradoxical}. The canonical test for this +class of @code{subreg} is: + +@smallexample +paradoxical_subreg_p (@var{m1}, @var{m2}) +@end smallexample + +Paradoxical @code{subreg}s can be used as both lvalues and rvalues. +When used as an lvalue, the low-order bits of the source value +are stored in @var{reg} and the high-order bits are discarded. +When used as an rvalue, the low-order bits of the @code{subreg} are +taken from @var{reg} while the high-order bits may or may not be +defined. + +The high-order bits of rvalues are defined in the following circumstances: + +@itemize +@item @code{subreg}s of @code{mem} +When @var{m2} is smaller than a word, the macro @code{LOAD_EXTEND_OP}, +can control how the high-order bits are defined. + +@item @code{subreg} of @code{reg}s +The upper bits are defined when @code{SUBREG_PROMOTED_VAR_P} is true. +@code{SUBREG_PROMOTED_UNSIGNED_P} describes what the upper bits hold. +Such subregs usually represent local variables, register variables +and parameter pseudo variables that have been promoted to a wider mode. + +@end itemize + +@var{bytenum} is always zero for a paradoxical @code{subreg}, even on +big-endian targets. + +For example, the paradoxical @code{subreg}: + +@smallexample +(set (subreg:SI (reg:HI @var{x}) 0) @var{y}) +@end smallexample + +stores the lower 2 bytes of @var{y} in @var{x} and discards the upper +2 bytes. A subsequent: + +@smallexample +(set @var{z} (subreg:SI (reg:HI @var{x}) 0)) +@end smallexample + +would set the lower two bytes of @var{z} to @var{y} and set the upper +two bytes to an unknown value assuming @code{SUBREG_PROMOTED_VAR_P} is +false. + +@item Normal subregs +When @var{m1} is at least as narrow as @var{m2} the @code{subreg} +expression is called @dfn{normal}. + +@findex REGMODE_NATURAL_SIZE +Normal @code{subreg}s restrict consideration to certain bits of +@var{reg}. For this purpose, @var{reg} is divided into +individually-addressable blocks in which each block has: + +@smallexample +REGMODE_NATURAL_SIZE (@var{m2}) +@end smallexample + +bytes. Usually the value is @code{UNITS_PER_WORD}; that is, +most targets usually treat each word of a register as being +independently addressable. + +There are two types of normal @code{subreg}. If @var{m1} is known +to be no bigger than a block, the @code{subreg} refers to the +least-significant part (or @dfn{lowpart}) of one block of @var{reg}. +If @var{m1} is known to be larger than a block, the @code{subreg} refers +to two or more complete blocks. + +When used as an lvalue, @code{subreg} is a block-based accessor. +Storing to a @code{subreg} modifies all the blocks of @var{reg} that +overlap the @code{subreg}, but it leaves the other blocks of @var{reg} +alone. + +When storing to a normal @code{subreg} that is smaller than a block, +the other bits of the referenced block are usually left in an undefined +state. This laxity makes it easier to generate efficient code for +such instructions. To represent an instruction that preserves all the +bits outside of those in the @code{subreg}, use @code{strict_low_part} +or @code{zero_extract} around the @code{subreg}. + +@var{bytenum} must identify the offset of the first byte of the +@code{subreg} from the start of @var{reg}, assuming that @var{reg} is +laid out in memory order. The memory order of bytes is defined by +two target macros, @code{WORDS_BIG_ENDIAN} and @code{BYTES_BIG_ENDIAN}: + +@itemize +@item +@cindex @code{WORDS_BIG_ENDIAN}, effect on @code{subreg} +@code{WORDS_BIG_ENDIAN}, if set to 1, says that byte number zero is +part of the most significant word; otherwise, it is part of the least +significant word. + +@item +@cindex @code{BYTES_BIG_ENDIAN}, effect on @code{subreg} +@code{BYTES_BIG_ENDIAN}, if set to 1, says that byte number zero is +the most significant byte within a word; otherwise, it is the least +significant byte within a word. +@end itemize + +@cindex @code{FLOAT_WORDS_BIG_ENDIAN}, (lack of) effect on @code{subreg} +On a few targets, @code{FLOAT_WORDS_BIG_ENDIAN} disagrees with +@code{WORDS_BIG_ENDIAN}. However, most parts of the compiler treat +floating point values as if they had the same endianness as integer +values. This works because they handle them solely as a collection of +integer values, with no particular numerical value. Only real.cc and +the runtime libraries care about @code{FLOAT_WORDS_BIG_ENDIAN}. + +Thus, + +@smallexample +(subreg:HI (reg:SI @var{x}) 2) +@end smallexample + +on a @code{BYTES_BIG_ENDIAN}, @samp{UNITS_PER_WORD == 4} target is the same as + +@smallexample +(subreg:HI (reg:SI @var{x}) 0) +@end smallexample + +on a little-endian, @samp{UNITS_PER_WORD == 4} target. Both +@code{subreg}s access the lower two bytes of register @var{x}. + +Note that the byte offset is a polynomial integer; it may not be a +compile-time constant on targets with variable-sized modes. However, +the restrictions above mean that there are only a certain set of +acceptable offsets for a given combination of @var{m1} and @var{m2}. +The compiler can always tell which blocks a valid subreg occupies, and +whether the subreg is a lowpart of a block. + +@end table + +A @code{MODE_PARTIAL_INT} mode behaves as if it were as wide as the +corresponding @code{MODE_INT} mode, except that it has a number of +undefined bits, which are determined by the precision of the +mode. + +For example, on a little-endian target which defines @code{PSImode} +to have a precision of 20 bits: + +@smallexample +(subreg:PSI (reg:SI 0) 0) +@end smallexample + +accesses the low 20 bits of @samp{(reg:SI 0)}. + +@findex REGMODE_NATURAL_SIZE +Continuing with a @code{PSImode} precision of 20 bits, if we assume +@samp{REGMODE_NATURAL_SIZE (DImode) <= 4}, +then the following two @code{subreg}s: + +@smallexample +(subreg:PSI (reg:DI 0) 0) +(subreg:PSI (reg:DI 0) 4) +@end smallexample + +represent accesses to the low 20 bits of the two halves of +@samp{(reg:DI 0)}. + +If @samp{REGMODE_NATURAL_SIZE (PSImode) <= 2} then these two @code{subreg}s: + +@smallexample +(subreg:HI (reg:PSI 0) 0) +(subreg:HI (reg:PSI 0) 2) +@end smallexample + +represent independent 2-byte accesses that together span the whole +of @samp{(reg:PSI 0)}. Storing to the first @code{subreg} does not +affect the value of the second, and vice versa, so the assignment: + +@smallexample +(set (subreg:HI (reg:PSI 0) 0) (reg:HI 4)) +@end smallexample + +sets the low 16 bits of @samp{(reg:PSI 0)} to @samp{(reg:HI 4)}, and +the high 4 defined bits of @samp{(reg:PSI 0)} retain their +original value. The behavior here is the same as for +normal @code{subreg}s, when there are no +@code{MODE_PARTIAL_INT} modes involved. + +@cindex @code{TARGET_CAN_CHANGE_MODE_CLASS} and subreg semantics +The rules above apply to both pseudo @var{reg}s and hard @var{reg}s. +If the semantics are not correct for particular combinations of +@var{m1}, @var{m2} and hard @var{reg}, the target-specific code +must ensure that those combinations are never used. For example: + +@smallexample +TARGET_CAN_CHANGE_MODE_CLASS (@var{m2}, @var{m1}, @var{class}) +@end smallexample + +must be false for every class @var{class} that includes @var{reg}. + +GCC must be able to determine at compile time whether a subreg is +paradoxical, whether it occupies a whole number of blocks, or whether +it is a lowpart of a block. This means that certain combinations of +variable-sized mode are not permitted. For example, if @var{m2} +holds @var{n} @code{SI} values, where @var{n} is greater than zero, +it is not possible to form a @code{DI} @code{subreg} of it; such a +@code{subreg} would be paradoxical when @var{n} is 1 but not when +@var{n} is greater than 1. + +@findex SUBREG_REG +@findex SUBREG_BYTE +The first operand of a @code{subreg} expression is customarily accessed +with the @code{SUBREG_REG} macro and the second operand is customarily +accessed with the @code{SUBREG_BYTE} macro. + +It has been several years since a platform in which +@code{BYTES_BIG_ENDIAN} not equal to @code{WORDS_BIG_ENDIAN} has +been tested. Anyone wishing to support such a platform in the future +may be confronted with code rot. + +@findex scratch +@cindex scratch operands +@item (scratch:@var{m}) +This represents a scratch register that will be required for the +execution of a single instruction and not used subsequently. It is +converted into a @code{reg} by either the local register allocator or +the reload pass. + +@code{scratch} is usually present inside a @code{clobber} operation +(@pxref{Side Effects}). + +On some machines, the condition code register is given a register number +and a @code{reg} is used. +Other machines store condition codes in general +registers; in such cases a pseudo register should be used. + +Some machines, such as the SPARC and RS/6000, have two sets of +arithmetic instructions, one that sets and one that does not set the +condition code. This is best handled by normally generating the +instruction that does not set the condition code, and making a pattern +that both performs the arithmetic and sets the condition code register. +For examples, search for @samp{addcc} and @samp{andcc} in @file{sparc.md}. + +@findex pc +@item (pc) +@cindex program counter +This represents the machine's program counter. It has no operands and +may not have a machine mode. @code{(pc)} may be validly used only in +certain specific contexts in jump instructions. + +@findex pc_rtx +There is only one expression object of code @code{pc}; it is the value +of the variable @code{pc_rtx}. Any attempt to create an expression of +code @code{pc} will return @code{pc_rtx}. + +All instructions that do not jump alter the program counter implicitly +by incrementing it, but there is no need to mention this in the RTL@. + +@findex mem +@item (mem:@var{m} @var{addr} @var{alias}) +This RTX represents a reference to main memory at an address +represented by the expression @var{addr}. @var{m} specifies how large +a unit of memory is accessed. @var{alias} specifies an alias set for the +reference. In general two items are in different alias sets if they cannot +reference the same memory address. + +The construct @code{(mem:BLK (scratch))} is considered to alias all +other memories. Thus it may be used as a memory barrier in epilogue +stack deallocation patterns. + +@findex concat +@item (concat@var{m} @var{rtx} @var{rtx}) +This RTX represents the concatenation of two other RTXs. This is used +for complex values. It should only appear in the RTL attached to +declarations and during RTL generation. It should not appear in the +ordinary insn chain. + +@findex concatn +@item (concatn@var{m} [@var{rtx} @dots{}]) +This RTX represents the concatenation of all the @var{rtx} to make a +single value. Like @code{concat}, this should only appear in +declarations, and not in the insn chain. +@end table + +@node Arithmetic +@section RTL Expressions for Arithmetic +@cindex arithmetic, in RTL +@cindex math, in RTL +@cindex RTL expressions for arithmetic + +Unless otherwise specified, all the operands of arithmetic expressions +must be valid for mode @var{m}. An operand is valid for mode @var{m} +if it has mode @var{m}, or if it is a @code{const_int} or +@code{const_double} and @var{m} is a mode of class @code{MODE_INT}. + +For commutative binary operations, constants should be placed in the +second operand. + +@table @code +@findex plus +@findex ss_plus +@findex us_plus +@cindex RTL sum +@cindex RTL addition +@cindex RTL addition with signed saturation +@cindex RTL addition with unsigned saturation +@item (plus:@var{m} @var{x} @var{y}) +@itemx (ss_plus:@var{m} @var{x} @var{y}) +@itemx (us_plus:@var{m} @var{x} @var{y}) + +These three expressions all represent the sum of the values +represented by @var{x} and @var{y} carried out in machine mode +@var{m}. They differ in their behavior on overflow of integer modes. +@code{plus} wraps round modulo the width of @var{m}; @code{ss_plus} +saturates at the maximum signed value representable in @var{m}; +@code{us_plus} saturates at the maximum unsigned value. + +@c ??? What happens on overflow of floating point modes? + +@findex lo_sum +@item (lo_sum:@var{m} @var{x} @var{y}) + +This expression represents the sum of @var{x} and the low-order bits +of @var{y}. It is used with @code{high} (@pxref{Constants}) to +represent the typical two-instruction sequence used in RISC machines to +reference large immediate values and/or link-time constants such +as global memory addresses. In the latter case, @var{m} is @code{Pmode} +and @var{y} is usually a constant expression involving @code{symbol_ref}. + +The number of low order bits is machine-dependent but is +normally the number of bits in mode @var{m} minus the number of +bits set by @code{high}. + +@findex minus +@findex ss_minus +@findex us_minus +@cindex RTL difference +@cindex RTL subtraction +@cindex RTL subtraction with signed saturation +@cindex RTL subtraction with unsigned saturation +@item (minus:@var{m} @var{x} @var{y}) +@itemx (ss_minus:@var{m} @var{x} @var{y}) +@itemx (us_minus:@var{m} @var{x} @var{y}) + +These three expressions represent the result of subtracting @var{y} +from @var{x}, carried out in mode @var{M}. Behavior on overflow is +the same as for the three variants of @code{plus} (see above). + +@findex compare +@cindex RTL comparison +@item (compare:@var{m} @var{x} @var{y}) +Represents the result of subtracting @var{y} from @var{x} for purposes +of comparison. The result is computed without overflow, as if with +infinite precision. + +Of course, machines cannot really subtract with infinite precision. +However, they can pretend to do so when only the sign of the result will +be used, which is the case when the result is stored in the condition +code. And that is the @emph{only} way this kind of expression may +validly be used: as a value to be stored in the condition codes, in a +register. @xref{Comparisons}. + +The mode @var{m} is not related to the modes of @var{x} and @var{y}, but +instead is the mode of the condition code value. It is some mode in class +@code{MODE_CC}, often @code{CCmode}. @xref{Condition Code}. If @var{m} +is @code{CCmode}, the operation returns sufficient +information (in an unspecified format) so that any comparison operator +can be applied to the result of the @code{COMPARE} operation. For other +modes in class @code{MODE_CC}, the operation only returns a subset of +this information. + +Normally, @var{x} and @var{y} must have the same mode. Otherwise, +@code{compare} is valid only if the mode of @var{x} is in class +@code{MODE_INT} and @var{y} is a @code{const_int} or +@code{const_double} with mode @code{VOIDmode}. The mode of @var{x} +determines what mode the comparison is to be done in; thus it must not +be @code{VOIDmode}. + +If one of the operands is a constant, it should be placed in the +second operand and the comparison code adjusted as appropriate. + +A @code{compare} specifying two @code{VOIDmode} constants is not valid +since there is no way to know in what mode the comparison is to be +performed; the comparison must either be folded during the compilation +or the first operand must be loaded into a register while its mode is +still known. + +@findex neg +@findex ss_neg +@findex us_neg +@cindex negation +@cindex negation with signed saturation +@cindex negation with unsigned saturation +@item (neg:@var{m} @var{x}) +@itemx (ss_neg:@var{m} @var{x}) +@itemx (us_neg:@var{m} @var{x}) +These two expressions represent the negation (subtraction from zero) of +the value represented by @var{x}, carried out in mode @var{m}. They +differ in the behavior on overflow of integer modes. In the case of +@code{neg}, the negation of the operand may be a number not representable +in mode @var{m}, in which case it is truncated to @var{m}. @code{ss_neg} +and @code{us_neg} ensure that an out-of-bounds result saturates to the +maximum or minimum signed or unsigned value. + +@findex mult +@findex ss_mult +@findex us_mult +@cindex multiplication +@cindex product +@cindex multiplication with signed saturation +@cindex multiplication with unsigned saturation +@item (mult:@var{m} @var{x} @var{y}) +@itemx (ss_mult:@var{m} @var{x} @var{y}) +@itemx (us_mult:@var{m} @var{x} @var{y}) +Represents the signed product of the values represented by @var{x} and +@var{y} carried out in machine mode @var{m}. +@code{ss_mult} and @code{us_mult} ensure that an out-of-bounds result +saturates to the maximum or minimum signed or unsigned value. + +Some machines support a multiplication that generates a product wider +than the operands. Write the pattern for this as + +@smallexample +(mult:@var{m} (sign_extend:@var{m} @var{x}) (sign_extend:@var{m} @var{y})) +@end smallexample + +where @var{m} is wider than the modes of @var{x} and @var{y}, which need +not be the same. + +For unsigned widening multiplication, use the same idiom, but with +@code{zero_extend} instead of @code{sign_extend}. + +@findex smul_highpart +@findex umul_highpart +@cindex high-part multiplication +@cindex multiplication high part +@item (smul_highpart:@var{m} @var{x} @var{y}) +@itemx (umul_highpart:@var{m} @var{x} @var{y}) +Represents the high-part multiplication of @var{x} and @var{y} carried +out in machine mode @var{m}. @code{smul_highpart} returns the high part +of a signed multiplication, @code{umul_highpart} returns the high part +of an unsigned multiplication. + +@findex fma +@cindex fused multiply-add +@item (fma:@var{m} @var{x} @var{y} @var{z}) +Represents the @code{fma}, @code{fmaf}, and @code{fmal} builtin +functions, which compute @samp{@var{x} * @var{y} + @var{z}} +without doing an intermediate rounding step. + +@findex div +@findex ss_div +@cindex division +@cindex signed division +@cindex signed division with signed saturation +@cindex quotient +@item (div:@var{m} @var{x} @var{y}) +@itemx (ss_div:@var{m} @var{x} @var{y}) +Represents the quotient in signed division of @var{x} by @var{y}, +carried out in machine mode @var{m}. If @var{m} is a floating point +mode, it represents the exact quotient; otherwise, the integerized +quotient. +@code{ss_div} ensures that an out-of-bounds result saturates to the maximum +or minimum signed value. + +Some machines have division instructions in which the operands and +quotient widths are not all the same; you should represent +such instructions using @code{truncate} and @code{sign_extend} as in, + +@smallexample +(truncate:@var{m1} (div:@var{m2} @var{x} (sign_extend:@var{m2} @var{y}))) +@end smallexample + +@findex udiv +@cindex unsigned division +@cindex unsigned division with unsigned saturation +@cindex division +@item (udiv:@var{m} @var{x} @var{y}) +@itemx (us_div:@var{m} @var{x} @var{y}) +Like @code{div} but represents unsigned division. +@code{us_div} ensures that an out-of-bounds result saturates to the maximum +or minimum unsigned value. + +@findex mod +@findex umod +@cindex remainder +@cindex division +@item (mod:@var{m} @var{x} @var{y}) +@itemx (umod:@var{m} @var{x} @var{y}) +Like @code{div} and @code{udiv} but represent the remainder instead of +the quotient. + +@findex smin +@findex smax +@cindex signed minimum +@cindex signed maximum +@item (smin:@var{m} @var{x} @var{y}) +@itemx (smax:@var{m} @var{x} @var{y}) +Represents the smaller (for @code{smin}) or larger (for @code{smax}) of +@var{x} and @var{y}, interpreted as signed values in mode @var{m}. +When used with floating point, if both operands are zeros, or if either +operand is @code{NaN}, then it is unspecified which of the two operands +is returned as the result. + +@findex umin +@findex umax +@cindex unsigned minimum and maximum +@item (umin:@var{m} @var{x} @var{y}) +@itemx (umax:@var{m} @var{x} @var{y}) +Like @code{smin} and @code{smax}, but the values are interpreted as unsigned +integers. + +@findex not +@cindex complement, bitwise +@cindex bitwise complement +@item (not:@var{m} @var{x}) +Represents the bitwise complement of the value represented by @var{x}, +carried out in mode @var{m}, which must be a fixed-point machine mode. + +@findex and +@cindex logical-and, bitwise +@cindex bitwise logical-and +@item (and:@var{m} @var{x} @var{y}) +Represents the bitwise logical-and of the values represented by +@var{x} and @var{y}, carried out in machine mode @var{m}, which must be +a fixed-point machine mode. + +@findex ior +@cindex inclusive-or, bitwise +@cindex bitwise inclusive-or +@item (ior:@var{m} @var{x} @var{y}) +Represents the bitwise inclusive-or of the values represented by @var{x} +and @var{y}, carried out in machine mode @var{m}, which must be a +fixed-point mode. + +@findex xor +@cindex exclusive-or, bitwise +@cindex bitwise exclusive-or +@item (xor:@var{m} @var{x} @var{y}) +Represents the bitwise exclusive-or of the values represented by @var{x} +and @var{y}, carried out in machine mode @var{m}, which must be a +fixed-point mode. + +@findex ashift +@findex ss_ashift +@findex us_ashift +@cindex left shift +@cindex shift +@cindex arithmetic shift +@cindex arithmetic shift with signed saturation +@cindex arithmetic shift with unsigned saturation +@item (ashift:@var{m} @var{x} @var{c}) +@itemx (ss_ashift:@var{m} @var{x} @var{c}) +@itemx (us_ashift:@var{m} @var{x} @var{c}) +These three expressions represent the result of arithmetically shifting @var{x} +left by @var{c} places. They differ in their behavior on overflow of integer +modes. An @code{ashift} operation is a plain shift with no special behavior +in case of a change in the sign bit; @code{ss_ashift} and @code{us_ashift} +saturates to the minimum or maximum representable value if any of the bits +shifted out differs from the final sign bit. + +@var{x} have mode @var{m}, a fixed-point machine mode. @var{c} +be a fixed-point mode or be a constant with mode @code{VOIDmode}; which +mode is determined by the mode called for in the machine description +entry for the left-shift instruction. For example, on the VAX, the mode +of @var{c} is @code{QImode} regardless of @var{m}. + +@findex lshiftrt +@cindex right shift +@findex ashiftrt +@item (lshiftrt:@var{m} @var{x} @var{c}) +@itemx (ashiftrt:@var{m} @var{x} @var{c}) +Like @code{ashift} but for right shift. Unlike the case for left shift, +these two operations are distinct. + +@findex rotate +@cindex rotate +@cindex left rotate +@findex rotatert +@cindex right rotate +@item (rotate:@var{m} @var{x} @var{c}) +@itemx (rotatert:@var{m} @var{x} @var{c}) +Similar but represent left and right rotate. If @var{c} is a constant, +use @code{rotate}. + +@findex abs +@findex ss_abs +@cindex absolute value +@item (abs:@var{m} @var{x}) +@item (ss_abs:@var{m} @var{x}) +Represents the absolute value of @var{x}, computed in mode @var{m}. +@code{ss_abs} ensures that an out-of-bounds result saturates to the +maximum signed value. + + +@findex sqrt +@cindex square root +@item (sqrt:@var{m} @var{x}) +Represents the square root of @var{x}, computed in mode @var{m}. +Most often @var{m} will be a floating point mode. + +@findex ffs +@item (ffs:@var{m} @var{x}) +Represents one plus the index of the least significant 1-bit in +@var{x}, represented as an integer of mode @var{m}. (The value is +zero if @var{x} is zero.) The mode of @var{x} must be @var{m} +or @code{VOIDmode}. + +@findex clrsb +@item (clrsb:@var{m} @var{x}) +Represents the number of redundant leading sign bits in @var{x}, +represented as an integer of mode @var{m}, starting at the most +significant bit position. This is one less than the number of leading +sign bits (either 0 or 1), with no special cases. The mode of @var{x} +must be @var{m} or @code{VOIDmode}. + +@findex clz +@item (clz:@var{m} @var{x}) +Represents the number of leading 0-bits in @var{x}, represented as an +integer of mode @var{m}, starting at the most significant bit position. +If @var{x} is zero, the value is determined by +@code{CLZ_DEFINED_VALUE_AT_ZERO} (@pxref{Misc}). Note that this is one of +the few expressions that is not invariant under widening. The mode of +@var{x} must be @var{m} or @code{VOIDmode}. + +@findex ctz +@item (ctz:@var{m} @var{x}) +Represents the number of trailing 0-bits in @var{x}, represented as an +integer of mode @var{m}, starting at the least significant bit position. +If @var{x} is zero, the value is determined by +@code{CTZ_DEFINED_VALUE_AT_ZERO} (@pxref{Misc}). Except for this case, +@code{ctz(x)} is equivalent to @code{ffs(@var{x}) - 1}. The mode of +@var{x} must be @var{m} or @code{VOIDmode}. + +@findex popcount +@item (popcount:@var{m} @var{x}) +Represents the number of 1-bits in @var{x}, represented as an integer of +mode @var{m}. The mode of @var{x} must be @var{m} or @code{VOIDmode}. + +@findex parity +@item (parity:@var{m} @var{x}) +Represents the number of 1-bits modulo 2 in @var{x}, represented as an +integer of mode @var{m}. The mode of @var{x} must be @var{m} or +@code{VOIDmode}. + +@findex bswap +@item (bswap:@var{m} @var{x}) +Represents the value @var{x} with the order of bytes reversed, carried out +in mode @var{m}, which must be a fixed-point machine mode. +The mode of @var{x} must be @var{m} or @code{VOIDmode}. +@end table + +@node Comparisons +@section Comparison Operations +@cindex RTL comparison operations + +Comparison operators test a relation on two operands and are considered +to represent a machine-dependent nonzero value described by, but not +necessarily equal to, @code{STORE_FLAG_VALUE} (@pxref{Misc}) +if the relation holds, or zero if it does not, for comparison operators +whose results have a `MODE_INT' mode, +@code{FLOAT_STORE_FLAG_VALUE} (@pxref{Misc}) if the relation holds, or +zero if it does not, for comparison operators that return floating-point +values, and a vector of either @code{VECTOR_STORE_FLAG_VALUE} (@pxref{Misc}) +if the relation holds, or of zeros if it does not, for comparison operators +that return vector results. +The mode of the comparison operation is independent of the mode +of the data being compared. If the comparison operation is being tested +(e.g., the first operand of an @code{if_then_else}), the mode must be +@code{VOIDmode}. + +@cindex condition codes +A comparison operation compares two data +objects. The mode of the comparison is determined by the operands; they +must both be valid for a common machine mode. A comparison with both +operands constant would be invalid as the machine mode could not be +deduced from it, but such a comparison should never exist in RTL due to +constant folding. + +Usually only one style +of comparisons is supported on a particular machine, but the combine +pass will try to merge operations to produce code like +@code{(eq @var{x} @var{y})}, +in case it exists in the context of the particular insn involved. + +Inequality comparisons come in two flavors, signed and unsigned. Thus, +there are distinct expression codes @code{gt} and @code{gtu} for signed and +unsigned greater-than. These can produce different results for the same +pair of integer values: for example, 1 is signed greater-than @minus{}1 but not +unsigned greater-than, because @minus{}1 when regarded as unsigned is actually +@code{0xffffffff} which is greater than 1. + +The signed comparisons are also used for floating point values. Floating +point comparisons are distinguished by the machine modes of the operands. + +@table @code +@findex eq +@cindex equal +@item (eq:@var{m} @var{x} @var{y}) +@code{STORE_FLAG_VALUE} if the values represented by @var{x} and @var{y} +are equal, otherwise 0. + +@findex ne +@cindex not equal +@item (ne:@var{m} @var{x} @var{y}) +@code{STORE_FLAG_VALUE} if the values represented by @var{x} and @var{y} +are not equal, otherwise 0. + +@findex gt +@cindex greater than +@item (gt:@var{m} @var{x} @var{y}) +@code{STORE_FLAG_VALUE} if the @var{x} is greater than @var{y}. If they +are fixed-point, the comparison is done in a signed sense. + +@findex gtu +@cindex greater than +@cindex unsigned greater than +@item (gtu:@var{m} @var{x} @var{y}) +Like @code{gt} but does unsigned comparison, on fixed-point numbers only. + +@findex lt +@cindex less than +@findex ltu +@cindex unsigned less than +@item (lt:@var{m} @var{x} @var{y}) +@itemx (ltu:@var{m} @var{x} @var{y}) +Like @code{gt} and @code{gtu} but test for ``less than''. + +@findex ge +@cindex greater than +@findex geu +@cindex unsigned greater than +@item (ge:@var{m} @var{x} @var{y}) +@itemx (geu:@var{m} @var{x} @var{y}) +Like @code{gt} and @code{gtu} but test for ``greater than or equal''. + +@findex le +@cindex less than or equal +@findex leu +@cindex unsigned less than +@item (le:@var{m} @var{x} @var{y}) +@itemx (leu:@var{m} @var{x} @var{y}) +Like @code{gt} and @code{gtu} but test for ``less than or equal''. + +@findex if_then_else +@item (if_then_else @var{cond} @var{then} @var{else}) +This is not a comparison operation but is listed here because it is +always used in conjunction with a comparison operation. To be +precise, @var{cond} is a comparison expression. This expression +represents a choice, according to @var{cond}, between the value +represented by @var{then} and the one represented by @var{else}. + +On most machines, @code{if_then_else} expressions are valid only +to express conditional jumps. + +@findex cond +@item (cond [@var{test1} @var{value1} @var{test2} @var{value2} @dots{}] @var{default}) +Similar to @code{if_then_else}, but more general. Each of @var{test1}, +@var{test2}, @dots{} is performed in turn. The result of this expression is +the @var{value} corresponding to the first nonzero test, or @var{default} if +none of the tests are nonzero expressions. + +This is currently not valid for instruction patterns and is supported only +for insn attributes. @xref{Insn Attributes}. +@end table + +@node Bit-Fields +@section Bit-Fields +@cindex bit-fields + +Special expression codes exist to represent bit-field instructions. + +@table @code +@findex sign_extract +@cindex @code{BITS_BIG_ENDIAN}, effect on @code{sign_extract} +@item (sign_extract:@var{m} @var{loc} @var{size} @var{pos}) +This represents a reference to a sign-extended bit-field contained or +starting in @var{loc} (a memory or register reference). The bit-field +is @var{size} bits wide and starts at bit @var{pos}. The compilation +option @code{BITS_BIG_ENDIAN} says which end of the memory unit +@var{pos} counts from. + +If @var{loc} is in memory, its mode must be a single-byte integer mode. +If @var{loc} is in a register, the mode to use is specified by the +operand of the @code{insv} or @code{extv} pattern +(@pxref{Standard Names}) and is usually a full-word integer mode, +which is the default if none is specified. + +The mode of @var{pos} is machine-specific and is also specified +in the @code{insv} or @code{extv} pattern. + +The mode @var{m} is the same as the mode that would be used for +@var{loc} if it were a register. + +A @code{sign_extract} cannot appear as an lvalue, or part thereof, +in RTL. + +@findex zero_extract +@item (zero_extract:@var{m} @var{loc} @var{size} @var{pos}) +Like @code{sign_extract} but refers to an unsigned or zero-extended +bit-field. The same sequence of bits are extracted, but they +are filled to an entire word with zeros instead of by sign-extension. + +Unlike @code{sign_extract}, this type of expressions can be lvalues +in RTL; they may appear on the left side of an assignment, indicating +insertion of a value into the specified bit-field. +@end table + +@node Vector Operations +@section Vector Operations +@cindex vector operations + +All normal RTL expressions can be used with vector modes; they are +interpreted as operating on each part of the vector independently. +Additionally, there are a few new expressions to describe specific vector +operations. + +@table @code +@findex vec_merge +@item (vec_merge:@var{m} @var{vec1} @var{vec2} @var{items}) +This describes a merge operation between two vectors. The result is a vector +of mode @var{m}; its elements are selected from either @var{vec1} or +@var{vec2}. Which elements are selected is described by @var{items}, which +is a bit mask represented by a @code{const_int}; a zero bit indicates the +corresponding element in the result vector is taken from @var{vec2} while +a set bit indicates it is taken from @var{vec1}. + +@findex vec_select +@item (vec_select:@var{m} @var{vec1} @var{selection}) +This describes an operation that selects parts of a vector. @var{vec1} is +the source vector, and @var{selection} is a @code{parallel} that contains a +@code{const_int} (or another expression, if the selection can be made at +runtime) for each of the subparts of the result vector, giving the number of +the source subpart that should be stored into it. The result mode @var{m} is +either the submode for a single element of @var{vec1} (if only one subpart is +selected), or another vector mode with that element submode (if multiple +subparts are selected). + +@findex vec_concat +@item (vec_concat:@var{m} @var{x1} @var{x2}) +Describes a vector concat operation. The result is a concatenation of the +vectors or scalars @var{x1} and @var{x2}; its length is the sum of the +lengths of the two inputs. + +@findex vec_duplicate +@item (vec_duplicate:@var{m} @var{x}) +This operation converts a scalar into a vector or a small vector into a +larger one by duplicating the input values. The output vector mode must have +the same submodes as the input vector mode or the scalar modes, and the +number of output parts must be an integer multiple of the number of input +parts. + +@findex vec_series +@item (vec_series:@var{m} @var{base} @var{step}) +This operation creates a vector in which element @var{i} is equal to +@samp{@var{base} + @var{i}*@var{step}}. @var{m} must be a vector integer mode. +@end table + +@node Conversions +@section Conversions +@cindex conversions +@cindex machine mode conversions + +All conversions between machine modes must be represented by +explicit conversion operations. For example, an expression +which is the sum of a byte and a full word cannot be written as +@code{(plus:SI (reg:QI 34) (reg:SI 80))} because the @code{plus} +operation requires two operands of the same machine mode. +Therefore, the byte-sized operand is enclosed in a conversion +operation, as in + +@smallexample +(plus:SI (sign_extend:SI (reg:QI 34)) (reg:SI 80)) +@end smallexample + +The conversion operation is not a mere placeholder, because there +may be more than one way of converting from a given starting mode +to the desired final mode. The conversion operation code says how +to do it. + +For all conversion operations, @var{x} must not be @code{VOIDmode} +because the mode in which to do the conversion would not be known. +The conversion must either be done at compile-time or @var{x} +must be placed into a register. + +@table @code +@findex sign_extend +@item (sign_extend:@var{m} @var{x}) +Represents the result of sign-extending the value @var{x} +to machine mode @var{m}. @var{m} must be a fixed-point mode +and @var{x} a fixed-point value of a mode narrower than @var{m}. + +@findex zero_extend +@item (zero_extend:@var{m} @var{x}) +Represents the result of zero-extending the value @var{x} +to machine mode @var{m}. @var{m} must be a fixed-point mode +and @var{x} a fixed-point value of a mode narrower than @var{m}. + +@findex float_extend +@item (float_extend:@var{m} @var{x}) +Represents the result of extending the value @var{x} +to machine mode @var{m}. @var{m} must be a floating point mode +and @var{x} a floating point value of a mode narrower than @var{m}. + +@findex truncate +@item (truncate:@var{m} @var{x}) +Represents the result of truncating the value @var{x} +to machine mode @var{m}. @var{m} must be a fixed-point mode +and @var{x} a fixed-point value of a mode wider than @var{m}. + +@findex ss_truncate +@item (ss_truncate:@var{m} @var{x}) +Represents the result of truncating the value @var{x} +to machine mode @var{m}, using signed saturation in the case of +overflow. Both @var{m} and the mode of @var{x} must be fixed-point +modes. + +@findex us_truncate +@item (us_truncate:@var{m} @var{x}) +Represents the result of truncating the value @var{x} +to machine mode @var{m}, using unsigned saturation in the case of +overflow. Both @var{m} and the mode of @var{x} must be fixed-point +modes. + +@findex float_truncate +@item (float_truncate:@var{m} @var{x}) +Represents the result of truncating the value @var{x} +to machine mode @var{m}. @var{m} must be a floating point mode +and @var{x} a floating point value of a mode wider than @var{m}. + +@findex float +@item (float:@var{m} @var{x}) +Represents the result of converting fixed point value @var{x}, +regarded as signed, to floating point mode @var{m}. + +@findex unsigned_float +@item (unsigned_float:@var{m} @var{x}) +Represents the result of converting fixed point value @var{x}, +regarded as unsigned, to floating point mode @var{m}. + +@findex fix +@item (fix:@var{m} @var{x}) +When @var{m} is a floating-point mode, represents the result of +converting floating point value @var{x} (valid for mode @var{m}) to an +integer, still represented in floating point mode @var{m}, by rounding +towards zero. + +When @var{m} is a fixed-point mode, represents the result of +converting floating point value @var{x} to mode @var{m}, regarded as +signed. How rounding is done is not specified, so this operation may +be used validly in compiling C code only for integer-valued operands. + +@findex unsigned_fix +@item (unsigned_fix:@var{m} @var{x}) +Represents the result of converting floating point value @var{x} to +fixed point mode @var{m}, regarded as unsigned. How rounding is done +is not specified. + +@findex fract_convert +@item (fract_convert:@var{m} @var{x}) +Represents the result of converting fixed-point value @var{x} to +fixed-point mode @var{m}, signed integer value @var{x} to +fixed-point mode @var{m}, floating-point value @var{x} to +fixed-point mode @var{m}, fixed-point value @var{x} to integer mode @var{m} +regarded as signed, or fixed-point value @var{x} to floating-point mode @var{m}. +When overflows or underflows happen, the results are undefined. + +@findex sat_fract +@item (sat_fract:@var{m} @var{x}) +Represents the result of converting fixed-point value @var{x} to +fixed-point mode @var{m}, signed integer value @var{x} to +fixed-point mode @var{m}, or floating-point value @var{x} to +fixed-point mode @var{m}. +When overflows or underflows happen, the results are saturated to the +maximum or the minimum. + +@findex unsigned_fract_convert +@item (unsigned_fract_convert:@var{m} @var{x}) +Represents the result of converting fixed-point value @var{x} to +integer mode @var{m} regarded as unsigned, or unsigned integer value @var{x} to +fixed-point mode @var{m}. +When overflows or underflows happen, the results are undefined. + +@findex unsigned_sat_fract +@item (unsigned_sat_fract:@var{m} @var{x}) +Represents the result of converting unsigned integer value @var{x} to +fixed-point mode @var{m}. +When overflows or underflows happen, the results are saturated to the +maximum or the minimum. +@end table + +@node RTL Declarations +@section Declarations +@cindex RTL declarations +@cindex declarations, RTL + +Declaration expression codes do not represent arithmetic operations +but rather state assertions about their operands. + +@table @code +@findex strict_low_part +@cindex @code{subreg}, in @code{strict_low_part} +@item (strict_low_part (subreg:@var{m} (reg:@var{n} @var{r}) 0)) +This expression code is used in only one context: as the destination operand of a +@code{set} expression. In addition, the operand of this expression +must be a non-paradoxical @code{subreg} expression. + +The presence of @code{strict_low_part} says that the part of the +register which is meaningful in mode @var{n}, but is not part of +mode @var{m}, is not to be altered. Normally, an assignment to such +a subreg is allowed to have undefined effects on the rest of the +register when @var{m} is smaller than @samp{REGMODE_NATURAL_SIZE (@var{n})}. +@end table + +@node Side Effects +@section Side Effect Expressions +@cindex RTL side effect expressions + +The expression codes described so far represent values, not actions. +But machine instructions never produce values; they are meaningful +only for their side effects on the state of the machine. Special +expression codes are used to represent side effects. + +The body of an instruction is always one of these side effect codes; +the codes described above, which represent values, appear only as +the operands of these. + +@table @code +@findex set +@item (set @var{lval} @var{x}) +Represents the action of storing the value of @var{x} into the place +represented by @var{lval}. @var{lval} must be an expression +representing a place that can be stored in: @code{reg} (or @code{subreg}, +@code{strict_low_part} or @code{zero_extract}), @code{mem}, @code{pc}, +or @code{parallel}. + +If @var{lval} is a @code{reg}, @code{subreg} or @code{mem}, it has a +machine mode; then @var{x} must be valid for that mode. + +If @var{lval} is a @code{reg} whose machine mode is less than the full +width of the register, then it means that the part of the register +specified by the machine mode is given the specified value and the +rest of the register receives an undefined value. Likewise, if +@var{lval} is a @code{subreg} whose machine mode is narrower than +the mode of the register, the rest of the register can be changed in +an undefined way. + +If @var{lval} is a @code{strict_low_part} of a subreg, then the part +of the register specified by the machine mode of the @code{subreg} is +given the value @var{x} and the rest of the register is not changed. + +If @var{lval} is a @code{zero_extract}, then the referenced part of +the bit-field (a memory or register reference) specified by the +@code{zero_extract} is given the value @var{x} and the rest of the +bit-field is not changed. Note that @code{sign_extract} cannot +appear in @var{lval}. + +If @var{lval} is a @code{parallel}, it is used to represent the case of +a function returning a structure in multiple registers. Each element +of the @code{parallel} is an @code{expr_list} whose first operand is a +@code{reg} and whose second operand is a @code{const_int} representing the +offset (in bytes) into the structure at which the data in that register +corresponds. The first element may be null to indicate that the structure +is also passed partly in memory. + +@cindex jump instructions and @code{set} +@cindex @code{if_then_else} usage +If @var{lval} is @code{(pc)}, we have a jump instruction, and the +possibilities for @var{x} are very limited. It may be a +@code{label_ref} expression (unconditional jump). It may be an +@code{if_then_else} (conditional jump), in which case either the +second or the third operand must be @code{(pc)} (for the case which +does not jump) and the other of the two must be a @code{label_ref} +(for the case which does jump). @var{x} may also be a @code{mem} or +@code{(plus:SI (pc) @var{y})}, where @var{y} may be a @code{reg} or a +@code{mem}; these unusual patterns are used to represent jumps through +branch tables. + +If @var{lval} is not @code{(pc)}, the mode of +@var{lval} must not be @code{VOIDmode} and the mode of @var{x} must be +valid for the mode of @var{lval}. + +@findex SET_DEST +@findex SET_SRC +@var{lval} is customarily accessed with the @code{SET_DEST} macro and +@var{x} with the @code{SET_SRC} macro. + +@findex return +@item (return) +As the sole expression in a pattern, represents a return from the +current function, on machines where this can be done with one +instruction, such as VAXen. On machines where a multi-instruction +``epilogue'' must be executed in order to return from the function, +returning is done by jumping to a label which precedes the epilogue, and +the @code{return} expression code is never used. + +Inside an @code{if_then_else} expression, represents the value to be +placed in @code{pc} to return to the caller. + +Note that an insn pattern of @code{(return)} is logically equivalent to +@code{(set (pc) (return))}, but the latter form is never used. + +@findex simple_return +@item (simple_return) +Like @code{(return)}, but truly represents only a function return, while +@code{(return)} may represent an insn that also performs other functions +of the function epilogue. Like @code{(return)}, this may also occur in +conditional jumps. + +@findex call +@item (call @var{function} @var{nargs}) +Represents a function call. @var{function} is a @code{mem} expression +whose address is the address of the function to be called. +@var{nargs} is an expression which can be used for two purposes: on +some machines it represents the number of bytes of stack argument; on +others, it represents the number of argument registers. + +Each machine has a standard machine mode which @var{function} must +have. The machine description defines macro @code{FUNCTION_MODE} to +expand into the requisite mode name. The purpose of this mode is to +specify what kind of addressing is allowed, on machines where the +allowed kinds of addressing depend on the machine mode being +addressed. + +@findex clobber +@item (clobber @var{x}) +Represents the storing or possible storing of an unpredictable, +undescribed value into @var{x}, which must be a @code{reg}, +@code{scratch}, @code{parallel} or @code{mem} expression. + +One place this is used is in string instructions that store standard +values into particular hard registers. It may not be worth the +trouble to describe the values that are stored, but it is essential to +inform the compiler that the registers will be altered, lest it +attempt to keep data in them across the string instruction. + +If @var{x} is @code{(mem:BLK (const_int 0))} or +@code{(mem:BLK (scratch))}, it means that all memory +locations must be presumed clobbered. If @var{x} is a @code{parallel}, +it has the same meaning as a @code{parallel} in a @code{set} expression. + +Note that the machine description classifies certain hard registers as +``call-clobbered''. All function call instructions are assumed by +default to clobber these registers, so there is no need to use +@code{clobber} expressions to indicate this fact. Also, each function +call is assumed to have the potential to alter any memory location, +unless the function is declared @code{const}. + +If the last group of expressions in a @code{parallel} are each a +@code{clobber} expression whose arguments are @code{reg} or +@code{match_scratch} (@pxref{RTL Template}) expressions, the combiner +phase can add the appropriate @code{clobber} expressions to an insn it +has constructed when doing so will cause a pattern to be matched. + +This feature can be used, for example, on a machine that whose multiply +and add instructions don't use an MQ register but which has an +add-accumulate instruction that does clobber the MQ register. Similarly, +a combined instruction might require a temporary register while the +constituent instructions might not. + +When a @code{clobber} expression for a register appears inside a +@code{parallel} with other side effects, the register allocator +guarantees that the register is unoccupied both before and after that +insn if it is a hard register clobber. For pseudo-register clobber, +the register allocator and the reload pass do not assign the same hard +register to the clobber and the input operands if there is an insn +alternative containing the @samp{&} constraint (@pxref{Modifiers}) for +the clobber and the hard register is in register classes of the +clobber in the alternative. You can clobber either a specific hard +register, a pseudo register, or a @code{scratch} expression; in the +latter two cases, GCC will allocate a hard register that is available +there for use as a temporary. + +For instructions that require a temporary register, you should use +@code{scratch} instead of a pseudo-register because this will allow the +combiner phase to add the @code{clobber} when required. You do this by +coding (@code{clobber} (@code{match_scratch} @dots{})). If you do +clobber a pseudo register, use one which appears nowhere else---generate +a new one each time. Otherwise, you may confuse CSE@. + +There is one other known use for clobbering a pseudo register in a +@code{parallel}: when one of the input operands of the insn is also +clobbered by the insn. In this case, using the same pseudo register in +the clobber and elsewhere in the insn produces the expected results. + +@findex use +@item (use @var{x}) +Represents the use of the value of @var{x}. It indicates that the +value in @var{x} at this point in the program is needed, even though +it may not be apparent why this is so. Therefore, the compiler will +not attempt to delete previous instructions whose only effect is to +store a value in @var{x}. @var{x} must be a @code{reg} expression. + +In some situations, it may be tempting to add a @code{use} of a +register in a @code{parallel} to describe a situation where the value +of a special register will modify the behavior of the instruction. +A hypothetical example might be a pattern for an addition that can +either wrap around or use saturating addition depending on the value +of a special control register: + +@smallexample +(parallel [(set (reg:SI 2) (unspec:SI [(reg:SI 3) + (reg:SI 4)] 0)) + (use (reg:SI 1))]) +@end smallexample + +@noindent + +This will not work, several of the optimizers only look at expressions +locally; it is very likely that if you have multiple insns with +identical inputs to the @code{unspec}, they will be optimized away even +if register 1 changes in between. + +This means that @code{use} can @emph{only} be used to describe +that the register is live. You should think twice before adding +@code{use} statements, more often you will want to use @code{unspec} +instead. The @code{use} RTX is most commonly useful to describe that +a fixed register is implicitly used in an insn. It is also safe to use +in patterns where the compiler knows for other reasons that the result +of the whole pattern is variable, such as @samp{cpymem@var{m}} or +@samp{call} patterns. + +During the reload phase, an insn that has a @code{use} as pattern +can carry a reg_equal note. These @code{use} insns will be deleted +before the reload phase exits. + +During the delayed branch scheduling phase, @var{x} may be an insn. +This indicates that @var{x} previously was located at this place in the +code and its data dependencies need to be taken into account. These +@code{use} insns will be deleted before the delayed branch scheduling +phase exits. + +@findex parallel +@item (parallel [@var{x0} @var{x1} @dots{}]) +Represents several side effects performed in parallel. The square +brackets stand for a vector; the operand of @code{parallel} is a +vector of expressions. @var{x0}, @var{x1} and so on are individual +side effect expressions---expressions of code @code{set}, @code{call}, +@code{return}, @code{simple_return}, @code{clobber} or @code{use}. + +``In parallel'' means that first all the values used in the individual +side-effects are computed, and second all the actual side-effects are +performed. For example, + +@smallexample +(parallel [(set (reg:SI 1) (mem:SI (reg:SI 1))) + (set (mem:SI (reg:SI 1)) (reg:SI 1))]) +@end smallexample + +@noindent +says unambiguously that the values of hard register 1 and the memory +location addressed by it are interchanged. In both places where +@code{(reg:SI 1)} appears as a memory address it refers to the value +in register 1 @emph{before} the execution of the insn. + +It follows that it is @emph{incorrect} to use @code{parallel} and +expect the result of one @code{set} to be available for the next one. +For example, people sometimes attempt to represent a jump-if-zero +instruction this way: + +@smallexample +(parallel [(set (reg:CC CC_REG) (reg:SI 34)) + (set (pc) (if_then_else + (eq (reg:CC CC_REG) (const_int 0)) + (label_ref @dots{}) + (pc)))]) +@end smallexample + +@noindent +But this is incorrect, because it says that the jump condition depends +on the condition code value @emph{before} this instruction, not on the +new value that is set by this instruction. + +@cindex peephole optimization, RTL representation +Peephole optimization, which takes place together with final assembly +code output, can produce insns whose patterns consist of a @code{parallel} +whose elements are the operands needed to output the resulting +assembler code---often @code{reg}, @code{mem} or constant expressions. +This would not be well-formed RTL at any other stage in compilation, +but it is OK then because no further optimization remains to be done. + +@findex cond_exec +@item (cond_exec [@var{cond} @var{expr}]) +Represents a conditionally executed expression. The @var{expr} is +executed only if the @var{cond} is nonzero. The @var{cond} expression +must not have side-effects, but the @var{expr} may very well have +side-effects. + +@findex sequence +@item (sequence [@var{insns} @dots{}]) +Represents a sequence of insns. If a @code{sequence} appears in the +chain of insns, then each of the @var{insns} that appears in the sequence +must be suitable for appearing in the chain of insns, i.e.@: must satisfy +the @code{INSN_P} predicate. + +After delay-slot scheduling is completed, an insn and all the insns that +reside in its delay slots are grouped together into a @code{sequence}. +The insn requiring the delay slot is the first insn in the vector; +subsequent insns are to be placed in the delay slot. + +@code{INSN_ANNULLED_BRANCH_P} is set on an insn in a delay slot to +indicate that a branch insn should be used that will conditionally annul +the effect of the insns in the delay slots. In such a case, +@code{INSN_FROM_TARGET_P} indicates that the insn is from the target of +the branch and should be executed only if the branch is taken; otherwise +the insn should be executed only if the branch is not taken. +@xref{Delay Slots}. + +Some back ends also use @code{sequence} objects for purposes other than +delay-slot groups. This is not supported in the common parts of the +compiler, which treat such sequences as delay-slot groups. + +DWARF2 Call Frame Address (CFA) adjustments are sometimes also expressed +using @code{sequence} objects as the value of a @code{RTX_FRAME_RELATED_P} +note. This only happens if the CFA adjustments cannot be easily derived +from the pattern of the instruction to which the note is attached. In +such cases, the value of the note is used instead of best-guesing the +semantics of the instruction. The back end can attach notes containing +a @code{sequence} of @code{set} patterns that express the effect of the +parent instruction. +@end table + +These expression codes appear in place of a side effect, as the body of +an insn, though strictly speaking they do not always describe side +effects as such: + +@table @code +@findex asm_input +@item (asm_input @var{s}) +Represents literal assembler code as described by the string @var{s}. + +@findex unspec +@findex unspec_volatile +@item (unspec [@var{operands} @dots{}] @var{index}) +@itemx (unspec_volatile [@var{operands} @dots{}] @var{index}) +Represents a machine-specific operation on @var{operands}. @var{index} +selects between multiple machine-specific operations. +@code{unspec_volatile} is used for volatile operations and operations +that may trap; @code{unspec} is used for other operations. + +These codes may appear inside a @code{pattern} of an +insn, inside a @code{parallel}, or inside an expression. + +@findex addr_vec +@item (addr_vec:@var{m} [@var{lr0} @var{lr1} @dots{}]) +Represents a table of jump addresses. The vector elements @var{lr0}, +etc., are @code{label_ref} expressions. The mode @var{m} specifies +how much space is given to each address; normally @var{m} would be +@code{Pmode}. + +@findex addr_diff_vec +@item (addr_diff_vec:@var{m} @var{base} [@var{lr0} @var{lr1} @dots{}] @var{min} @var{max} @var{flags}) +Represents a table of jump addresses expressed as offsets from +@var{base}. The vector elements @var{lr0}, etc., are @code{label_ref} +expressions and so is @var{base}. The mode @var{m} specifies how much +space is given to each address-difference. @var{min} and @var{max} +are set up by branch shortening and hold a label with a minimum and a +maximum address, respectively. @var{flags} indicates the relative +position of @var{base}, @var{min} and @var{max} to the containing insn +and of @var{min} and @var{max} to @var{base}. See rtl.def for details. + +@findex prefetch +@item (prefetch:@var{m} @var{addr} @var{rw} @var{locality}) +Represents prefetch of memory at address @var{addr}. +Operand @var{rw} is 1 if the prefetch is for data to be written, 0 otherwise; +targets that do not support write prefetches should treat this as a normal +prefetch. +Operand @var{locality} specifies the amount of temporal locality; 0 if there +is none or 1, 2, or 3 for increasing levels of temporal locality; +targets that do not support locality hints should ignore this. + +This insn is used to minimize cache-miss latency by moving data into a +cache before it is accessed. It should use only non-faulting data prefetch +instructions. +@end table + +@node Incdec +@section Embedded Side-Effects on Addresses +@cindex RTL preincrement +@cindex RTL postincrement +@cindex RTL predecrement +@cindex RTL postdecrement + +Six special side-effect expression codes appear as memory addresses. + +@table @code +@findex pre_dec +@item (pre_dec:@var{m} @var{x}) +Represents the side effect of decrementing @var{x} by a standard +amount and represents also the value that @var{x} has after being +decremented. @var{x} must be a @code{reg} or @code{mem}, but most +machines allow only a @code{reg}. @var{m} must be the machine mode +for pointers on the machine in use. The amount @var{x} is decremented +by is the length in bytes of the machine mode of the containing memory +reference of which this expression serves as the address. Here is an +example of its use: + +@smallexample +(mem:DF (pre_dec:SI (reg:SI 39))) +@end smallexample + +@noindent +This says to decrement pseudo register 39 by the length of a @code{DFmode} +value and use the result to address a @code{DFmode} value. + +@findex pre_inc +@item (pre_inc:@var{m} @var{x}) +Similar, but specifies incrementing @var{x} instead of decrementing it. + +@findex post_dec +@item (post_dec:@var{m} @var{x}) +Represents the same side effect as @code{pre_dec} but a different +value. The value represented here is the value @var{x} has @i{before} +being decremented. + +@findex post_inc +@item (post_inc:@var{m} @var{x}) +Similar, but specifies incrementing @var{x} instead of decrementing it. + +@findex post_modify +@item (post_modify:@var{m} @var{x} @var{y}) + +Represents the side effect of setting @var{x} to @var{y} and +represents @var{x} before @var{x} is modified. @var{x} must be a +@code{reg} or @code{mem}, but most machines allow only a @code{reg}. +@var{m} must be the machine mode for pointers on the machine in use. + +The expression @var{y} must be one of three forms: +@code{(plus:@var{m} @var{x} @var{z})}, +@code{(minus:@var{m} @var{x} @var{z})}, or +@code{(plus:@var{m} @var{x} @var{i})}, +where @var{z} is an index register and @var{i} is a constant. + +Here is an example of its use: + +@smallexample +(mem:SF (post_modify:SI (reg:SI 42) (plus (reg:SI 42) + (reg:SI 48)))) +@end smallexample + +This says to modify pseudo register 42 by adding the contents of pseudo +register 48 to it, after the use of what ever 42 points to. + +@findex pre_modify +@item (pre_modify:@var{m} @var{x} @var{expr}) +Similar except side effects happen before the use. +@end table + +These embedded side effect expressions must be used with care. Instruction +patterns may not use them. Until the @samp{flow} pass of the compiler, +they may occur only to represent pushes onto the stack. The @samp{flow} +pass finds cases where registers are incremented or decremented in one +instruction and used as an address shortly before or after; these cases are +then transformed to use pre- or post-increment or -decrement. + +If a register used as the operand of these expressions is used in +another address in an insn, the original value of the register is used. +Uses of the register outside of an address are not permitted within the +same insn as a use in an embedded side effect expression because such +insns behave differently on different machines and hence must be treated +as ambiguous and disallowed. + +An instruction that can be represented with an embedded side effect +could also be represented using @code{parallel} containing an additional +@code{set} to describe how the address register is altered. This is not +done because machines that allow these operations at all typically +allow them wherever a memory address is called for. Describing them as +additional parallel stores would require doubling the number of entries +in the machine description. + +@node Assembler +@section Assembler Instructions as Expressions +@cindex assembler instructions in RTL + +@cindex @code{asm_operands}, usage +The RTX code @code{asm_operands} represents a value produced by a +user-specified assembler instruction. It is used to represent +an @code{asm} statement with arguments. An @code{asm} statement with +a single output operand, like this: + +@smallexample +asm ("foo %1,%2,%0" : "=a" (outputvar) : "g" (x + y), "di" (*z)); +@end smallexample + +@noindent +is represented using a single @code{asm_operands} RTX which represents +the value that is stored in @code{outputvar}: + +@smallexample +(set @var{rtx-for-outputvar} + (asm_operands "foo %1,%2,%0" "a" 0 + [@var{rtx-for-addition-result} @var{rtx-for-*z}] + [(asm_input:@var{m1} "g") + (asm_input:@var{m2} "di")])) +@end smallexample + +@noindent +Here the operands of the @code{asm_operands} RTX are the assembler +template string, the output-operand's constraint, the index-number of the +output operand among the output operands specified, a vector of input +operand RTX's, and a vector of input-operand modes and constraints. The +mode @var{m1} is the mode of the sum @code{x+y}; @var{m2} is that of +@code{*z}. + +When an @code{asm} statement has multiple output values, its insn has +several such @code{set} RTX's inside of a @code{parallel}. Each @code{set} +contains an @code{asm_operands}; all of these share the same assembler +template and vectors, but each contains the constraint for the respective +output operand. They are also distinguished by the output-operand index +number, which is 0, 1, @dots{} for successive output operands. + +@node Debug Information +@section Variable Location Debug Information in RTL +@cindex Variable Location Debug Information in RTL + +Variable tracking relies on @code{MEM_EXPR} and @code{REG_EXPR} +annotations to determine what user variables memory and register +references refer to. + +Variable tracking at assignments uses these notes only when they refer +to variables that live at fixed locations (e.g., addressable +variables, global non-automatic variables). For variables whose +location may vary, it relies on the following types of notes. + +@table @code +@findex var_location +@item (var_location:@var{mode} @var{var} @var{exp} @var{stat}) +Binds variable @code{var}, a tree, to value @var{exp}, an RTL +expression. It appears only in @code{NOTE_INSN_VAR_LOCATION} and +@code{DEBUG_INSN}s, with slightly different meanings. @var{mode}, if +present, represents the mode of @var{exp}, which is useful if it is a +modeless expression. @var{stat} is only meaningful in notes, +indicating whether the variable is known to be initialized or +uninitialized. + +@findex debug_expr +@item (debug_expr:@var{mode} @var{decl}) +Stands for the value bound to the @code{DEBUG_EXPR_DECL} @var{decl}, +that points back to it, within value expressions in +@code{VAR_LOCATION} nodes. + +@findex debug_implicit_ptr +@item (debug_implicit_ptr:@var{mode} @var{decl}) +Stands for the location of a @var{decl} that is no longer addressable. + +@findex entry_value +@item (entry_value:@var{mode} @var{decl}) +Stands for the value a @var{decl} had at the entry point of the +containing function. + +@findex debug_parameter_ref +@item (debug_parameter_ref:@var{mode} @var{decl}) +Refers to a parameter that was completely optimized out. + +@findex debug_marker +@item (debug_marker:@var{mode}) +Marks a program location. With @code{VOIDmode}, it stands for the +beginning of a statement, a recommended inspection point logically after +all prior side effects, and before any subsequent side effects. With +@code{BLKmode}, it indicates an inline entry point: the lexical block +encoded in the @code{INSN_LOCATION} is the enclosing block that encloses +the inlined function. + +@end table + +@node Insns +@section Insns +@cindex insns + +The RTL representation of the code for a function is a doubly-linked +chain of objects called @dfn{insns}. Insns are expressions with +special codes that are used for no other purpose. Some insns are +actual instructions; others represent dispatch tables for @code{switch} +statements; others represent labels to jump to or various sorts of +declarative information. + +In addition to its own specific data, each insn must have a unique +id-number that distinguishes it from all other insns in the current +function (after delayed branch scheduling, copies of an insn with the +same id-number may be present in multiple places in a function, but +these copies will always be identical and will only appear inside a +@code{sequence}), and chain pointers to the preceding and following +insns. These three fields occupy the same position in every insn, +independent of the expression code of the insn. They could be accessed +with @code{XEXP} and @code{XINT}, but instead three special macros are +always used: + +@table @code +@findex INSN_UID +@item INSN_UID (@var{i}) +Accesses the unique id of insn @var{i}. + +@findex PREV_INSN +@item PREV_INSN (@var{i}) +Accesses the chain pointer to the insn preceding @var{i}. +If @var{i} is the first insn, this is a null pointer. + +@findex NEXT_INSN +@item NEXT_INSN (@var{i}) +Accesses the chain pointer to the insn following @var{i}. +If @var{i} is the last insn, this is a null pointer. +@end table + +@findex get_insns +@findex get_last_insn +The first insn in the chain is obtained by calling @code{get_insns}; the +last insn is the result of calling @code{get_last_insn}. Within the +chain delimited by these insns, the @code{NEXT_INSN} and +@code{PREV_INSN} pointers must always correspond: if @var{insn} is not +the first insn, + +@smallexample +NEXT_INSN (PREV_INSN (@var{insn})) == @var{insn} +@end smallexample + +@noindent +is always true and if @var{insn} is not the last insn, + +@smallexample +PREV_INSN (NEXT_INSN (@var{insn})) == @var{insn} +@end smallexample + +@noindent +is always true. + +After delay slot scheduling, some of the insns in the chain might be +@code{sequence} expressions, which contain a vector of insns. The value +of @code{NEXT_INSN} in all but the last of these insns is the next insn +in the vector; the value of @code{NEXT_INSN} of the last insn in the vector +is the same as the value of @code{NEXT_INSN} for the @code{sequence} in +which it is contained. Similar rules apply for @code{PREV_INSN}. + +This means that the above invariants are not necessarily true for insns +inside @code{sequence} expressions. Specifically, if @var{insn} is the +first insn in a @code{sequence}, @code{NEXT_INSN (PREV_INSN (@var{insn}))} +is the insn containing the @code{sequence} expression, as is the value +of @code{PREV_INSN (NEXT_INSN (@var{insn}))} if @var{insn} is the last +insn in the @code{sequence} expression. You can use these expressions +to find the containing @code{sequence} expression. + +Every insn has one of the following expression codes: + +@table @code +@findex insn +@item insn +The expression code @code{insn} is used for instructions that do not jump +and do not do function calls. @code{sequence} expressions are always +contained in insns with code @code{insn} even if one of those insns +should jump or do function calls. + +Insns with code @code{insn} have four additional fields beyond the three +mandatory ones listed above. These four are described in a table below. + +@findex jump_insn +@item jump_insn +The expression code @code{jump_insn} is used for instructions that may +jump (or, more generally, may contain @code{label_ref} expressions to +which @code{pc} can be set in that instruction). If there is an +instruction to return from the current function, it is recorded as a +@code{jump_insn}. + +@findex JUMP_LABEL +@code{jump_insn} insns have the same extra fields as @code{insn} insns, +accessed in the same way and in addition contain a field +@code{JUMP_LABEL} which is defined once jump optimization has completed. + +For simple conditional and unconditional jumps, this field contains +the @code{code_label} to which this insn will (possibly conditionally) +branch. In a more complex jump, @code{JUMP_LABEL} records one of the +labels that the insn refers to; other jump target labels are recorded +as @code{REG_LABEL_TARGET} notes. The exception is @code{addr_vec} +and @code{addr_diff_vec}, where @code{JUMP_LABEL} is @code{NULL_RTX} +and the only way to find the labels is to scan the entire body of the +insn. + +Return insns count as jumps, but their @code{JUMP_LABEL} is @code{RETURN} +or @code{SIMPLE_RETURN}. + +@findex call_insn +@item call_insn +The expression code @code{call_insn} is used for instructions that may do +function calls. It is important to distinguish these instructions because +they imply that certain registers and memory locations may be altered +unpredictably. + +@findex CALL_INSN_FUNCTION_USAGE +@code{call_insn} insns have the same extra fields as @code{insn} insns, +accessed in the same way and in addition contain a field +@code{CALL_INSN_FUNCTION_USAGE}, which contains a list (chain of +@code{expr_list} expressions) containing @code{use}, @code{clobber} and +sometimes @code{set} expressions that denote hard registers and +@code{mem}s used or clobbered by the called function. + +A @code{mem} generally points to a stack slot in which arguments passed +to the libcall by reference (@pxref{Register Arguments, +TARGET_PASS_BY_REFERENCE}) are stored. If the argument is +caller-copied (@pxref{Register Arguments, TARGET_CALLEE_COPIES}), +the stack slot will be mentioned in @code{clobber} and @code{use} +entries; if it's callee-copied, only a @code{use} will appear, and the +@code{mem} may point to addresses that are not stack slots. + +Registers occurring inside a @code{clobber} in this list augment +registers specified in @code{CALL_USED_REGISTERS} (@pxref{Register +Basics}). + +If the list contains a @code{set} involving two registers, it indicates +that the function returns one of its arguments. Such a @code{set} may +look like a no-op if the same register holds the argument and the return +value. + +@findex code_label +@findex CODE_LABEL_NUMBER +@item code_label +A @code{code_label} insn represents a label that a jump insn can jump +to. It contains two special fields of data in addition to the three +standard ones. @code{CODE_LABEL_NUMBER} is used to hold the @dfn{label +number}, a number that identifies this label uniquely among all the +labels in the compilation (not just in the current function). +Ultimately, the label is represented in the assembler output as an +assembler label, usually of the form @samp{L@var{n}} where @var{n} is +the label number. + +When a @code{code_label} appears in an RTL expression, it normally +appears within a @code{label_ref} which represents the address of +the label, as a number. + +Besides as a @code{code_label}, a label can also be represented as a +@code{note} of type @code{NOTE_INSN_DELETED_LABEL}. + +@findex LABEL_NUSES +The field @code{LABEL_NUSES} is only defined once the jump optimization +phase is completed. It contains the number of times this label is +referenced in the current function. + +@findex LABEL_KIND +@findex SET_LABEL_KIND +@findex LABEL_ALT_ENTRY_P +@cindex alternate entry points +The field @code{LABEL_KIND} differentiates four different types of +labels: @code{LABEL_NORMAL}, @code{LABEL_STATIC_ENTRY}, +@code{LABEL_GLOBAL_ENTRY}, and @code{LABEL_WEAK_ENTRY}. The only labels +that do not have type @code{LABEL_NORMAL} are @dfn{alternate entry +points} to the current function. These may be static (visible only in +the containing translation unit), global (exposed to all translation +units), or weak (global, but can be overridden by another symbol with the +same name). + +Much of the compiler treats all four kinds of label identically. Some +of it needs to know whether or not a label is an alternate entry point; +for this purpose, the macro @code{LABEL_ALT_ENTRY_P} is provided. It is +equivalent to testing whether @samp{LABEL_KIND (label) == LABEL_NORMAL}. +The only place that cares about the distinction between static, global, +and weak alternate entry points, besides the front-end code that creates +them, is the function @code{output_alternate_entry_point}, in +@file{final.cc}. + +To set the kind of a label, use the @code{SET_LABEL_KIND} macro. + +@findex jump_table_data +@item jump_table_data +A @code{jump_table_data} insn is a placeholder for the jump-table data +of a @code{casesi} or @code{tablejump} insn. They are placed after +a @code{tablejump_p} insn. A @code{jump_table_data} insn is not part o +a basic blockm but it is associated with the basic block that ends with +the @code{tablejump_p} insn. The @code{PATTERN} of a @code{jump_table_data} +is always either an @code{addr_vec} or an @code{addr_diff_vec}, and a +@code{jump_table_data} insn is always preceded by a @code{code_label}. +The @code{tablejump_p} insn refers to that @code{code_label} via its +@code{JUMP_LABEL}. + +@findex barrier +@item barrier +Barriers are placed in the instruction stream when control cannot flow +past them. They are placed after unconditional jump instructions to +indicate that the jumps are unconditional and after calls to +@code{volatile} functions, which do not return (e.g., @code{exit}). +They contain no information beyond the three standard fields. + +@findex note +@findex NOTE_LINE_NUMBER +@findex NOTE_SOURCE_FILE +@item note +@code{note} insns are used to represent additional debugging and +declarative information. They contain two nonstandard fields, an +integer which is accessed with the macro @code{NOTE_LINE_NUMBER} and a +string accessed with @code{NOTE_SOURCE_FILE}. + +If @code{NOTE_LINE_NUMBER} is positive, the note represents the +position of a source line and @code{NOTE_SOURCE_FILE} is the source file name +that the line came from. These notes control generation of line +number data in the assembler output. + +Otherwise, @code{NOTE_LINE_NUMBER} is not really a line number but a +code with one of the following values (and @code{NOTE_SOURCE_FILE} +must contain a null pointer): + +@table @code +@findex NOTE_INSN_DELETED +@item NOTE_INSN_DELETED +Such a note is completely ignorable. Some passes of the compiler +delete insns by altering them into notes of this kind. + +@findex NOTE_INSN_DELETED_LABEL +@item NOTE_INSN_DELETED_LABEL +This marks what used to be a @code{code_label}, but was not used for other +purposes than taking its address and was transformed to mark that no +code jumps to it. + +@findex NOTE_INSN_BLOCK_BEG +@findex NOTE_INSN_BLOCK_END +@item NOTE_INSN_BLOCK_BEG +@itemx NOTE_INSN_BLOCK_END +These types of notes indicate the position of the beginning and end +of a level of scoping of variable names. They control the output +of debugging information. + +@findex NOTE_INSN_EH_REGION_BEG +@findex NOTE_INSN_EH_REGION_END +@item NOTE_INSN_EH_REGION_BEG +@itemx NOTE_INSN_EH_REGION_END +These types of notes indicate the position of the beginning and end of a +level of scoping for exception handling. @code{NOTE_EH_HANDLER} +identifies which region is associated with these notes. + +@findex NOTE_INSN_FUNCTION_BEG +@item NOTE_INSN_FUNCTION_BEG +Appears at the start of the function body, after the function +prologue. + +@findex NOTE_INSN_VAR_LOCATION +@findex NOTE_VAR_LOCATION +@item NOTE_INSN_VAR_LOCATION +This note is used to generate variable location debugging information. +It indicates that the user variable in its @code{VAR_LOCATION} operand +is at the location given in the RTL expression, or holds a value that +can be computed by evaluating the RTL expression from that static +point in the program up to the next such note for the same user +variable. + +@findex NOTE_INSN_BEGIN_STMT +@item NOTE_INSN_BEGIN_STMT +This note is used to generate @code{is_stmt} markers in line number +debugging information. It indicates the beginning of a user +statement. + +@findex NOTE_INSN_INLINE_ENTRY +@item NOTE_INSN_INLINE_ENTRY +This note is used to generate @code{entry_pc} for inlined subroutines in +debugging information. It indicates an inspection point at which all +arguments for the inlined function have been bound, and before its first +statement. + +@end table + +These codes are printed symbolically when they appear in debugging dumps. + +@findex debug_insn +@findex INSN_VAR_LOCATION +@item debug_insn +The expression code @code{debug_insn} is used for pseudo-instructions +that hold debugging information for variable tracking at assignments +(see @option{-fvar-tracking-assignments} option). They are the RTL +representation of @code{GIMPLE_DEBUG} statements +(@ref{@code{GIMPLE_DEBUG}}), with a @code{VAR_LOCATION} operand that +binds a user variable tree to an RTL representation of the +@code{value} in the corresponding statement. A @code{DEBUG_EXPR} in +it stands for the value bound to the corresponding +@code{DEBUG_EXPR_DECL}. + +@code{GIMPLE_DEBUG_BEGIN_STMT} and @code{GIMPLE_DEBUG_INLINE_ENTRY} are +expanded to RTL as a @code{DEBUG_INSN} with a @code{DEBUG_MARKER} +@code{PATTERN}; the difference is the RTL mode: the former's +@code{DEBUG_MARKER} is @code{VOIDmode}, whereas the latter is +@code{BLKmode}; information about the inlined function can be taken from +the lexical block encoded in the @code{INSN_LOCATION}. These +@code{DEBUG_INSN}s, that do not carry @code{VAR_LOCATION} information, +just @code{DEBUG_MARKER}s, can be detected by testing +@code{DEBUG_MARKER_INSN_P}, whereas those that do can be recognized as +@code{DEBUG_BIND_INSN_P}. + +Throughout optimization passes, @code{DEBUG_INSN}s are not reordered +with respect to each other, particularly during scheduling. Binding +information is kept in pseudo-instruction form, so that, unlike notes, +it gets the same treatment and adjustments that regular instructions +would. It is the variable tracking pass that turns these +pseudo-instructions into @code{NOTE_INSN_VAR_LOCATION}, +@code{NOTE_INSN_BEGIN_STMT} and @code{NOTE_INSN_INLINE_ENTRY} notes, +analyzing control flow, value equivalences and changes to registers and +memory referenced in value expressions, propagating the values of debug +temporaries and determining expressions that can be used to compute the +value of each user variable at as many points (ranges, actually) in the +program as possible. + +Unlike @code{NOTE_INSN_VAR_LOCATION}, the value expression in an +@code{INSN_VAR_LOCATION} denotes a value at that specific point in the +program, rather than an expression that can be evaluated at any later +point before an overriding @code{VAR_LOCATION} is encountered. E.g., +if a user variable is bound to a @code{REG} and then a subsequent insn +modifies the @code{REG}, the note location would keep mapping the user +variable to the register across the insn, whereas the insn location +would keep the variable bound to the value, so that the variable +tracking pass would emit another location note for the variable at the +point in which the register is modified. + +@end table + +@cindex @code{TImode}, in @code{insn} +@cindex @code{HImode}, in @code{insn} +@cindex @code{QImode}, in @code{insn} +The machine mode of an insn is normally @code{VOIDmode}, but some +phases use the mode for various purposes. + +The common subexpression elimination pass sets the mode of an insn to +@code{QImode} when it is the first insn in a block that has already +been processed. + +The second Haifa scheduling pass, for targets that can multiple issue, +sets the mode of an insn to @code{TImode} when it is believed that the +instruction begins an issue group. That is, when the instruction +cannot issue simultaneously with the previous. This may be relied on +by later passes, in particular machine-dependent reorg. + +Here is a table of the extra fields of @code{insn}, @code{jump_insn} +and @code{call_insn} insns: + +@table @code +@findex PATTERN +@item PATTERN (@var{i}) +An expression for the side effect performed by this insn. This must +be one of the following codes: @code{set}, @code{call}, @code{use}, +@code{clobber}, @code{return}, @code{simple_return}, @code{asm_input}, +@code{asm_output}, @code{addr_vec}, @code{addr_diff_vec}, +@code{trap_if}, @code{unspec}, @code{unspec_volatile}, +@code{parallel}, @code{cond_exec}, or @code{sequence}. If it is a +@code{parallel}, each element of the @code{parallel} must be one these +codes, except that @code{parallel} expressions cannot be nested and +@code{addr_vec} and @code{addr_diff_vec} are not permitted inside a +@code{parallel} expression. + +@findex INSN_CODE +@item INSN_CODE (@var{i}) +An integer that says which pattern in the machine description matches +this insn, or @minus{}1 if the matching has not yet been attempted. + +Such matching is never attempted and this field remains @minus{}1 on an insn +whose pattern consists of a single @code{use}, @code{clobber}, +@code{asm_input}, @code{addr_vec} or @code{addr_diff_vec} expression. + +@findex asm_noperands +Matching is also never attempted on insns that result from an @code{asm} +statement. These contain at least one @code{asm_operands} expression. +The function @code{asm_noperands} returns a non-negative value for +such insns. + +In the debugging output, this field is printed as a number followed by +a symbolic representation that locates the pattern in the @file{md} +file as some small positive or negative offset from a named pattern. + +@findex REG_NOTES +@item REG_NOTES (@var{i}) +A list (chain of @code{expr_list}, @code{insn_list} and @code{int_list} +expressions) giving miscellaneous information about the insn. It is often +information pertaining to the registers used in this insn. +@end table + +The @code{REG_NOTES} field of an insn is a chain that includes +@code{expr_list} and @code{int_list} expressions as well as @code{insn_list} +expressions. There are several +kinds of register notes, which are distinguished by the machine mode, which +in a register note is really understood as being an @code{enum reg_note}. +The first operand @var{op} of the note is data whose meaning depends on +the kind of note. + +@findex REG_NOTE_KIND +@findex PUT_REG_NOTE_KIND +The macro @code{REG_NOTE_KIND (@var{x})} returns the kind of +register note. Its counterpart, the macro @code{PUT_REG_NOTE_KIND +(@var{x}, @var{newkind})} sets the register note type of @var{x} to be +@var{newkind}. + +Register notes are of three classes: They may say something about an +input to an insn, they may say something about an output of an insn, or +they may create a linkage between two insns. + +These register notes annotate inputs to an insn: + +@table @code +@findex REG_DEAD +@item REG_DEAD +The value in @var{op} dies in this insn; that is to say, altering the +value immediately after this insn would not affect the future behavior +of the program. + +It does not follow that the register @var{op} has no useful value after +this insn since @var{op} is not necessarily modified by this insn. +Rather, no subsequent instruction uses the contents of @var{op}. + +@findex REG_UNUSED +@item REG_UNUSED +The register @var{op} being set by this insn will not be used in a +subsequent insn. This differs from a @code{REG_DEAD} note, which +indicates that the value in an input will not be used subsequently. +These two notes are independent; both may be present for the same +register. + +@findex REG_INC +@item REG_INC +The register @var{op} is incremented (or decremented; at this level +there is no distinction) by an embedded side effect inside this insn. +This means it appears in a @code{post_inc}, @code{pre_inc}, +@code{post_dec} or @code{pre_dec} expression. + +@findex REG_NONNEG +@item REG_NONNEG +The register @var{op} is known to have a nonnegative value when this +insn is reached. This is used by special looping instructions +that terminate when the register goes negative. + +The @code{REG_NONNEG} note is added only to @samp{doloop_end} +insns, if its pattern uses a @code{ge} condition. + +@findex REG_LABEL_OPERAND +@item REG_LABEL_OPERAND +This insn uses @var{op}, a @code{code_label} or a @code{note} of type +@code{NOTE_INSN_DELETED_LABEL}, but is not a @code{jump_insn}, or it +is a @code{jump_insn} that refers to the operand as an ordinary +operand. The label may still eventually be a jump target, but if so +in an indirect jump in a subsequent insn. The presence of this note +allows jump optimization to be aware that @var{op} is, in fact, being +used, and flow optimization to build an accurate flow graph. + +@findex REG_LABEL_TARGET +@item REG_LABEL_TARGET +This insn is a @code{jump_insn} but not an @code{addr_vec} or +@code{addr_diff_vec}. It uses @var{op}, a @code{code_label} as a +direct or indirect jump target. Its purpose is similar to that of +@code{REG_LABEL_OPERAND}. This note is only present if the insn has +multiple targets; the last label in the insn (in the highest numbered +insn-field) goes into the @code{JUMP_LABEL} field and does not have a +@code{REG_LABEL_TARGET} note. @xref{Insns, JUMP_LABEL}. + +@findex REG_SETJMP +@item REG_SETJMP +Appears attached to each @code{CALL_INSN} to @code{setjmp} or a +related function. +@end table + +The following notes describe attributes of outputs of an insn: + +@table @code +@findex REG_EQUIV +@findex REG_EQUAL +@item REG_EQUIV +@itemx REG_EQUAL +This note is only valid on an insn that sets only one register and +indicates that that register will be equal to @var{op} at run time; the +scope of this equivalence differs between the two types of notes. The +value which the insn explicitly copies into the register may look +different from @var{op}, but they will be equal at run time. If the +output of the single @code{set} is a @code{strict_low_part} or +@code{zero_extract} expression, the note refers to the register that +is contained in its first operand. + +For @code{REG_EQUIV}, the register is equivalent to @var{op} throughout +the entire function, and could validly be replaced in all its +occurrences by @var{op}. (``Validly'' here refers to the data flow of +the program; simple replacement may make some insns invalid.) For +example, when a constant is loaded into a register that is never +assigned any other value, this kind of note is used. + +When a parameter is copied into a pseudo-register at entry to a function, +a note of this kind records that the register is equivalent to the stack +slot where the parameter was passed. Although in this case the register +may be set by other insns, it is still valid to replace the register +by the stack slot throughout the function. + +A @code{REG_EQUIV} note is also used on an instruction which copies a +register parameter into a pseudo-register at entry to a function, if +there is a stack slot where that parameter could be stored. Although +other insns may set the pseudo-register, it is valid for the compiler to +replace the pseudo-register by stack slot throughout the function, +provided the compiler ensures that the stack slot is properly +initialized by making the replacement in the initial copy instruction as +well. This is used on machines for which the calling convention +allocates stack space for register parameters. See +@code{REG_PARM_STACK_SPACE} in @ref{Stack Arguments}. + +In the case of @code{REG_EQUAL}, the register that is set by this insn +will be equal to @var{op} at run time at the end of this insn but not +necessarily elsewhere in the function. In this case, @var{op} +is typically an arithmetic expression. For example, when a sequence of +insns such as a library call is used to perform an arithmetic operation, +this kind of note is attached to the insn that produces or copies the +final value. + +These two notes are used in different ways by the compiler passes. +@code{REG_EQUAL} is used by passes prior to register allocation (such as +common subexpression elimination and loop optimization) to tell them how +to think of that value. @code{REG_EQUIV} notes are used by register +allocation to indicate that there is an available substitute expression +(either a constant or a @code{mem} expression for the location of a +parameter on the stack) that may be used in place of a register if +insufficient registers are available. + +Except for stack homes for parameters, which are indicated by a +@code{REG_EQUIV} note and are not useful to the early optimization +passes and pseudo registers that are equivalent to a memory location +throughout their entire life, which is not detected until later in +the compilation, all equivalences are initially indicated by an attached +@code{REG_EQUAL} note. In the early stages of register allocation, a +@code{REG_EQUAL} note is changed into a @code{REG_EQUIV} note if +@var{op} is a constant and the insn represents the only set of its +destination register. + +Thus, compiler passes prior to register allocation need only check for +@code{REG_EQUAL} notes and passes subsequent to register allocation +need only check for @code{REG_EQUIV} notes. +@end table + +These notes describe linkages between insns. They occur in pairs: one +insn has one of a pair of notes that points to a second insn, which has +the inverse note pointing back to the first insn. + +@table @code +@findex REG_DEP_TRUE +@item REG_DEP_TRUE +This indicates a true dependence (a read after write dependence). + +@findex REG_DEP_OUTPUT +@item REG_DEP_OUTPUT +This indicates an output dependence (a write after write dependence). + +@findex REG_DEP_ANTI +@item REG_DEP_ANTI +This indicates an anti dependence (a write after read dependence). + +@end table + +These notes describe information gathered from gcov profile data. They +are stored in the @code{REG_NOTES} field of an insn. + +@table @code +@findex REG_BR_PROB +@item REG_BR_PROB +This is used to specify the ratio of branches to non-branches of a +branch insn according to the profile data. The note is represented +as an @code{int_list} expression whose integer value is an encoding +of @code{profile_probability} type. @code{profile_probability} provide +member function @code{from_reg_br_prob_note} and @code{to_reg_br_prob_note} +to extract and store the probability into the RTL encoding. + +@findex REG_BR_PRED +@item REG_BR_PRED +These notes are found in JUMP insns after delayed branch scheduling +has taken place. They indicate both the direction and the likelihood +of the JUMP@. The format is a bitmask of ATTR_FLAG_* values. + +@findex REG_FRAME_RELATED_EXPR +@item REG_FRAME_RELATED_EXPR +This is used on an RTX_FRAME_RELATED_P insn wherein the attached expression +is used in place of the actual insn pattern. This is done in cases where +the pattern is either complex or misleading. +@end table + +The note @code{REG_CALL_NOCF_CHECK} is used in conjunction with the +@option{-fcf-protection=branch} option. The note is set if a +@code{nocf_check} attribute is specified for a function type or a +pointer to function type. The note is stored in the @code{REG_NOTES} +field of an insn. + +@table @code +@findex REG_CALL_NOCF_CHECK +@item REG_CALL_NOCF_CHECK +Users have control through the @code{nocf_check} attribute to identify +which calls to a function should be skipped from control-flow instrumentation +when the option @option{-fcf-protection=branch} is specified. The compiler +puts a @code{REG_CALL_NOCF_CHECK} note on each @code{CALL_INSN} instruction +that has a function type marked with a @code{nocf_check} attribute. +@end table + +For convenience, the machine mode in an @code{insn_list} or +@code{expr_list} is printed using these symbolic codes in debugging dumps. + +@findex insn_list +@findex expr_list +The only difference between the expression codes @code{insn_list} and +@code{expr_list} is that the first operand of an @code{insn_list} is +assumed to be an insn and is printed in debugging dumps as the insn's +unique id; the first operand of an @code{expr_list} is printed in the +ordinary way as an expression. + +@node Calls +@section RTL Representation of Function-Call Insns +@cindex calling functions in RTL +@cindex RTL function-call insns +@cindex function-call insns + +Insns that call subroutines have the RTL expression code @code{call_insn}. +These insns must satisfy special rules, and their bodies must use a special +RTL expression code, @code{call}. + +@cindex @code{call} usage +A @code{call} expression has two operands, as follows: + +@smallexample +(call (mem:@var{fm} @var{addr}) @var{nbytes}) +@end smallexample + +@noindent +Here @var{nbytes} is an operand that represents the number of bytes of +argument data being passed to the subroutine, @var{fm} is a machine mode +(which must equal as the definition of the @code{FUNCTION_MODE} macro in +the machine description) and @var{addr} represents the address of the +subroutine. + +For a subroutine that returns no value, the @code{call} expression as +shown above is the entire body of the insn, except that the insn might +also contain @code{use} or @code{clobber} expressions. + +@cindex @code{BLKmode}, and function return values +For a subroutine that returns a value whose mode is not @code{BLKmode}, +the value is returned in a hard register. If this register's number is +@var{r}, then the body of the call insn looks like this: + +@smallexample +(set (reg:@var{m} @var{r}) + (call (mem:@var{fm} @var{addr}) @var{nbytes})) +@end smallexample + +@noindent +This RTL expression makes it clear (to the optimizer passes) that the +appropriate register receives a useful value in this insn. + +When a subroutine returns a @code{BLKmode} value, it is handled by +passing to the subroutine the address of a place to store the value. +So the call insn itself does not ``return'' any value, and it has the +same RTL form as a call that returns nothing. + +On some machines, the call instruction itself clobbers some register, +for example to contain the return address. @code{call_insn} insns +on these machines should have a body which is a @code{parallel} +that contains both the @code{call} expression and @code{clobber} +expressions that indicate which registers are destroyed. Similarly, +if the call instruction requires some register other than the stack +pointer that is not explicitly mentioned in its RTL, a @code{use} +subexpression should mention that register. + +Functions that are called are assumed to modify all registers listed in +the configuration macro @code{CALL_USED_REGISTERS} (@pxref{Register +Basics}) and, with the exception of @code{const} functions and library +calls, to modify all of memory. + +Insns containing just @code{use} expressions directly precede the +@code{call_insn} insn to indicate which registers contain inputs to the +function. Similarly, if registers other than those in +@code{CALL_USED_REGISTERS} are clobbered by the called function, insns +containing a single @code{clobber} follow immediately after the call to +indicate which registers. + +@node RTL SSA +@section On-the-Side SSA Form for RTL +@cindex SSA, RTL form +@cindex RTL SSA + +The patterns of an individual RTL instruction describe which registers +are inputs to that instruction and which registers are outputs from +that instruction. However, it is often useful to know where the +definition of a register input comes from and where the result of +a register output is used. One way of obtaining this information +is to use the RTL SSA form, which provides a Static Single Assignment +representation of the RTL instructions. + +The RTL SSA code is located in the @file{rtl-ssa} subdirectory of the GCC +source tree. This section only gives a brief overview of it; please +see the comments in the source code for more details. + +@menu +* Using RTL SSA:: What a pass needs to do to use the RTL SSA form +* RTL SSA Instructions:: How instructions are represented and organized +* RTL SSA Basic Blocks:: How instructions are grouped into blocks +* RTL SSA Resources:: How registers and memory are represented +* RTL SSA Accesses:: How register and memory accesses are represented +* RTL SSA Phi Nodes:: How multiple sources are combined into one +* RTL SSA Access Lists:: How accesses are chained together +* Changing RTL Instructions:: How to use the RTL SSA framework to change insns +@end menu + +@node Using RTL SSA +@subsection Using RTL SSA in a pass + +A pass that wants to use the RTL SSA form should start with the following: + +@smallexample +#define INCLUDE_ALGORITHM +#define INCLUDE_FUNCTIONAL +#include "config.h" +#include "system.h" +#include "coretypes.h" +#include "backend.h" +#include "rtl.h" +#include "df.h" +#include "rtl-ssa.h" +@end smallexample + +All the RTL SSA code is contained in the @code{rtl_ssa} namespace, +so most passes will then want to do: + +@smallexample +using namespace rtl_ssa; +@end smallexample + +However, this is purely a matter of taste, and the examples in the rest of +this section do not require it. + +The RTL SSA represention is an optional on-the-side feature that applies +on top of the normal RTL instructions. It is currently local to individual +RTL passes and is not maintained across passes. + +However, in order to allow the RTL SSA information to be preserved across +passes in future, @samp{crtl->ssa} points to the current function's +SSA form (if any). Passes that want to use the RTL SSA form should +first do: + +@smallexample +crtl->ssa = new rtl_ssa::function_info (@var{fn}); +@end smallexample + +where @var{fn} is the function that the pass is processing. +(Passes that are @code{using namespace rtl_ssa} do not need +the @samp{rtl_ssa::}.) + +Once the pass has finished with the SSA form, it should do the following: + +@smallexample +free_dominance_info (CDI_DOMINATORS); +if (crtl->ssa->perform_pending_updates ()) + cleanup_cfg (0); + +delete crtl->ssa; +crtl->ssa = nullptr; +@end smallexample + +The @code{free_dominance_info} call is necessary because +dominance information is not currently maintained between RTL passes. +The next two lines commit any changes to the RTL instructions that +were queued for later; see the comment above the declaration of +@code{perform_pending_updates} for details. The final two lines +discard the RTL SSA form and free the associated memory. + +@node RTL SSA Instructions +@subsection RTL SSA Instructions + +@cindex RPO +@cindex reverse postorder +@cindex instructions, RTL SSA +@findex rtl_ssa::insn_info +RTL SSA instructions are represented by an @code{rtl_ssa::insn_info}. +These instructions are chained together in a single list that follows +a reverse postorder (RPO) traversal of the function. This means that +if any path through the function can execute an instruction @var{I1} +and then later execute an instruction @var{I2} for the first time, +@var{I1} appears before @var{I2} in the list@footnote{Note that this +order is different from the order of the underlying RTL instructions, +which follow machine code order instead.}. + +Two RTL SSA instructions can be compared to find which instruction +occurs earlier than the other in the RPO@. One way to do this is +to use the C++ comparison operators, such as: + +@example +*@var{insn1} < *@var{insn2} +@end example + +Another way is to use the @code{compare_with} function: + +@example +@var{insn1}->compare_with (@var{insn2}) +@end example + +This expression is greater than zero if @var{insn1} comes after @var{insn2} +in the RPO, less than zero if @var{insn1} comes before @var{insn2} in the +RPO, or zero if @var{insn1} and @var{insn2} are the same. This order is +maintained even if instructions are added to the function or moved around. + +The main purpose of @code{rtl_ssa::insn_info} is to hold +SSA information about an instruction. However, it also caches +certain properties of the instruction, such as whether it is an +inline assembly instruction, whether it has volatile accesses, and so on. + +@node RTL SSA Basic Blocks +@subsection RTL SSA Basic Blocks + +@cindex basic blocks, RTL SSA +@findex basic_block +@findex rtl_ssa::bb_info +RTL SSA instructions (@pxref{RTL SSA Instructions}) are organized into +basic blocks, with each block being represented by an @code{rtl_ssa:bb_info}. +There is a one-to-one mapping between these @code{rtl_ssa:bb_info} +structures and the underlying CFG @code{basic_block} structures +(@pxref{Basic Blocks}). + +@cindex ``real'' instructions, RTL SSA +@anchor{real RTL SSA insns} +If a CFG basic block @var{bb} contains an RTL instruction @var{insn}, +the RTL SSA represenation of @var{bb} also contains an RTL SSA representation +of @var{insn}@footnote{Note that this excludes non-instruction things like +@code{note}s and @code{barrier}s that also appear in the chain of RTL +instructions.}. Within RTL SSA, these instructions are referred to as +``real'' instructions. These real instructions fall into two groups: +debug instructions and nondebug instructions. Only nondebug instructions +should affect code generation decisions. + +In addition, each RTL SSA basic block has two ``artificial'' +instructions: a ``head'' instruction that comes before all the real +instructions and an ``end'' instruction that comes after all real +instructions. These instructions exist to represent things that +are conceptually defined or used at the start and end of a basic block. +The instructions always exist, even if they do not currently do anything. + +Like instructions, these blocks are chained together in a reverse +postorder. This list includes the entry block (which always comes +first) and the exit block (which always comes last). + +@cindex extended basic blocks, RTL SSA +@findex rtl_ssa::ebb_info +RTL SSA basic blocks are chained together into ``extended basic blocks'' +(EBBs), represented by an @code{rtl_ssa::ebb_info}. Extended basic +blocks contain one or more basic blocks. They have the property +that if a block @var{bby} comes immediately after a block @var{bbx} +in an EBB, then @var{bby} can only be reached by @var{bbx}; in other words, +@var{bbx} is the sole predecessor of @var{bby}. + +Each extended basic block starts with an artificial ``phi node'' +instruction. This instruction defines all phi nodes for the EBB +(@pxref{RTL SSA Phi Nodes}). (Individual blocks in an EBB do not +need phi nodes because their live values can only come from one source.) + +The contents of a function are therefore represented using a +four-level hierarchy: + +@itemize @bullet +@item +functions (@code{rtl_ssa::function_info}), which contain @dots{} + +@item +extended basic blocks (@code{rtl_ssa::ebb_info}), which contain @dots{} + +@item +basic blocks (@code{rtl_ssa::bb_info}), which contain @dots{} + +@item +instructions (@code{rtl_ssa::insn_info}) +@end itemize + +In dumps, a basic block is identified as @code{bb@var{n}}, where @var{n} +is the index of the associated CFG @code{basic_block} structure. +An EBB is in turn identified by the index of its first block. +For example, an EBB that contains @samp{bb10}, @code{bb5}, @code{bb6} +and @code{bb9} is identified as @var{ebb10}. + +@node RTL SSA Resources +@subsection RTL SSA Resources + +The RTL SSA form tracks two types of ``resource'': registers and memory. +Each hard and pseudo register is a separate resource. Memory is a +single unified resource, like it is in GIMPLE (@pxref{GIMPLE}). + +Each resource has a unique identifier. The unique identifier for a +register is simply its register number. The unique identifier for +memory is a special register number called @code{MEM_REGNO}. + +Since resource numbers so closely match register numbers, it is sometimes +convenient to refer to them simply as register numbers, or ``regnos'' +for short. However, the RTL SSA form also provides an abstraction +of resources in the form of @code{rtl_ssa::resource_info}. +This is a lightweight class that records both the regno of a resource +and the @code{machine_mode} that the resource has (@pxref{Machine Modes}). +It has functions for testing whether a resource is a register or memory. +In principle it could be extended to other kinds of resource in future. + +@node RTL SSA Accesses +@subsection RTL SSA Register and Memory Accesses + +In the RTL SSA form, most reads or writes of a resource are +represented as a @code{rtl_ssa::access_info}@footnote{The exceptions +are call clobbers, which are generally represented separately. +See the comment above @code{rtl_ssa::insn_info} for details.}. +These @code{rtl_ssa::access_info}s are organized into the following +class hierarchy: + +@findex rtl_ssa::access_info +@findex rtl_ssa::use_info +@findex rtl_ssa::def_info +@findex rtl_ssa::clobber_info +@findex rtl_ssa::set_info +@findex rtl_ssa::phi_info +@smallexample +rtl_ssa::access_info + | + +-- rtl_ssa::use_info + | + +-- rtl_ssa::def_info + | + +-- rtl_ssa::clobber_info + | + +-- rtl_ssa::set_info + | + +-- rtl_ssa::phi_info +@end smallexample + +A @code{rtl_ssa::use_info} represents a read or use of a resource and +a @code{rtl_ssa::def_info} represents a write or definition of a resource. +As in the main RTL representation, there are two basic types of +definition: clobbers and sets. The difference is that a clobber +leaves the register with an unspecified value that cannot be used +or relied on by later instructions, while a set leaves the register +with a known value that later instructions could use if they wanted to. +A @code{rtl_ssa::clobber_info} represents a clobber and +a @code{rtl_ssa::set_info} represent a set. + +Each @code{rtl_ssa::use_info} records which single @code{rtl_ssa::set_info} +provides the value of the resource; this is null if the resource is +completely undefined at the point of use. Each @code{rtl_ssa::set_info} +in turn records all the @code{rtl_ssa::use_info}s that use its value. + +If a value of a resource can come from multiple sources, +a @code{rtl_ssa::phi_info} brings those multiple sources together +into a single definition (@pxref{RTL SSA Phi Nodes}). + +@node RTL SSA Phi Nodes +@subsection RTL SSA Phi Nodes + +@cindex phi nodes, RTL SSA +@findex rtl_ssa::phi_info +If a resource is live on entry to an extended basic block and if the +resource's value can come from multiple sources, the extended basic block +has a ``phi node'' that collects together these multiple sources. +The phi node conceptually has one input for each incoming edge of +the extended basic block, with the input specifying the value of +the resource on that edge. For example, suppose a function contains +the following RTL: + +@smallexample +;; Basic block bb3 +@dots{} +(set (reg:SI R1) (const_int 0)) ;; A +(set (pc) (label_ref bb5)) + +;; Basic block bb4 +@dots{} +(set (reg:SI R1) (const_int 1)) ;; B +;; Fall through + +;; Basic block bb5 +;; preds: bb3, bb4 +;; live in: R1 @dots{} +(code_label bb5) +@dots{} +(set (reg:SI @var{R2}) + (plus:SI (reg:SI R1) @dots{})) ;; C +@end smallexample + +The value of R1 on entry to block 5 can come from either A or B@. +The extended basic block that contains block 5 would therefore have a +phi node with two inputs: the first input would have the value of +R1 defined by A and the second input would have the value of +R1 defined by B@. This phi node would then provide the value of +R1 for C (assuming that R1 does not change again between +the start of block 5 and C). + +Since RTL is not a ``native'' SSA representation, these phi nodes +simply collect together definitions that already exist. Each input +to a phi node for a resource @var{R} is itself a definition of +resource @var{R} (or is null if the resource is completely +undefined for a particular incoming edge). This is in contrast +to a native SSA representation like GIMPLE, where the phi inputs +can be arbitrary expressions. As a result, RTL SSA phi nodes +never involve ``hidden'' moves: all moves are instead explicit. + +Phi nodes are represented as a @code{rtl_ssa::phi_node}. +Each input to a phi node is represented as an @code{rtl_ssa::use_info}. + +@node RTL SSA Access Lists +@subsection RTL SSA Access Lists + +All the definitions of a resource are chained together in reverse postorder. +In general, this list can contain an arbitrary mix of both sets +(@code{rtl_ssa::set_info}) and clobbers (@code{rtl_ssa::clobber_info}). +However, it is often useful to skip over all intervening clobbers +of a resource in order to find the next set. The list is constructed +in such a way that this can be done in amortized constant time. + +All uses (@code{rtl_ssa::use_info}) of a given set are also chained +together into a list. This list of uses is divided into three parts: + +@enumerate +@item +uses by ``real'' nondebug instructions (@pxref{real RTL SSA insns}) + +@item +uses by real debug instructions + +@item +uses by phi nodes (@pxref{RTL SSA Phi Nodes}) +@end enumerate + +The first and second parts individually follow reverse postorder. +The third part has no particular order. + +@cindex degenerate phi node, RTL SSA +The last use by a real nondebug instruction always comes earlier in +the reverse postorder than the next definition of the resource (if any). +This means that the accesses follow a linear sequence of the form: + +@itemize @bullet +@item +first definition of resource R + +@itemize @bullet +@item +first use by a real nondebug instruction of the first definition of resource R + +@item +@dots{} + +@item +last use by a real nondebug instruction of the first definition of resource R +@end itemize + +@item +second definition of resource R + +@itemize @bullet +@item +first use by a real nondebug instruction of the second definition of resource R + +@item +@dots{} + +@item +last use by a real nondebug instruction of the second definition of resource R +@end itemize + +@item +@dots{} + +@item +last definition of resource R + +@itemize @bullet +@item +first use by a real nondebug instruction of the last definition of resource R + +@item +@dots{} + +@item +last use by a real nondebug instruction of the last definition of resource R +@end itemize +@end itemize + +(Note that clobbers never have uses; only sets do.) + +This linear view is easy to achieve when there is only a single definition +of a resource, which is commonly true for pseudo registers. However, +things are more complex if code has a structure like the following: + +@smallexample +// ebb2, bb2 +R = @var{va}; // A +if (@dots{}) + @{ + // ebb2, bb3 + use1 (R); // B + @dots{} + R = @var{vc}; // C + @} +else + @{ + // ebb4, bb4 + use2 (R); // D + @} +@end smallexample + +The list of accesses would begin as follows: + +@itemize @bullet +@item +definition of R by A + +@itemize @bullet +@item +use of A's definition of R by B +@end itemize + +@item +definition of R by C +@end itemize + +The next access to R is in D, but the value of R that D uses comes from +A rather than C@. + +This is resolved by adding a phi node for @code{ebb4}. All inputs to this +phi node have the same value, which in the example above is A's definition +of R@. In other circumstances, it would not be necessary to create a phi +node when all inputs are equal, so these phi nodes are referred to as +``degenerate'' phi nodes. + +The full list of accesses to R is therefore: + +@itemize @bullet +@item +definition of R by A + +@itemize @bullet +@item +use of A's definition of R by B +@end itemize + +@item +definition of R by C + +@item +definition of R by ebb4's phi instruction, with the input coming from A + +@itemize @bullet +@item +use of the ebb4's R phi definition of R by B +@end itemize +@end itemize + +Note that A's definition is also used by ebb4's phi node, but this +use belongs to the third part of the use list described above and +so does not form part of the linear sequence. + +It is possible to ``look through'' any degenerate phi to the ultimate +definition using the function @code{look_through_degenerate_phi}. +Note that the input to a degenerate phi is never itself provided +by a degenerate phi. + +At present, the SSA form takes this principle one step further +and guarantees that, for any given resource @var{res}, one of the +following is true: + +@itemize +@item +The resource has a single definition @var{def}, which is not a phi node. +Excluding uses of undefined registers, all uses of @var{res} by real +nondebug instructions use the value provided by @var{def}. + +@item +Excluding uses of undefined registers, all uses of @var{res} use +values provided by definitions that occur earlier in the same +extended basic block. These definitions might come from phi nodes +or from real instructions. +@end itemize + +@node Changing RTL Instructions +@subsection Using the RTL SSA framework to change instructions + +@findex rtl_ssa::insn_change +There are various routines that help to change a single RTL instruction +or a group of RTL instructions while keeping the RTL SSA form up-to-date. +This section first describes the process for changing a single instruction, +then goes on to describe the differences when changing multiple instructions. + +@menu +* Changing One RTL SSA Instruction:: +* Changing Multiple RTL SSA Instructions:: +@end menu + +@node Changing One RTL SSA Instruction +@subsubsection Changing One RTL SSA Instruction + +Before making a change, passes should first use a statement like the +following: + +@smallexample +auto attempt = crtl->ssa->new_change_attempt (); +@end smallexample + +Here, @code{attempt} is an RAII object that should remain in scope +for the entire change attempt. It automatically frees temporary +memory related to the changes when it goes out of scope. + +Next, the pass should create an @code{rtl_ssa::insn_change} object +for the instruction that it wants to change. This object specifies +several things: + +@itemize @bullet +@item +what the instruction's new list of uses should be (@code{new_uses}). +By default this is the same as the instruction's current list of uses. + +@item +what the instruction's new list of definitions should be (@code{new_defs}). +By default this is the same as the instruction's current list of +definitions. + +@item +where the instruction should be located (@code{move_range}). +This is a range of instructions after which the instruction could +be placed, represented as an @code{rtl_ssa::insn_range}. +By default the instruction must remain at its current position. +@end itemize + +If a pass was attempting to change all these properties of an instruction +@code{insn}, it might do something like this: + +@smallexample +rtl_ssa::insn_change change (insn); +change.new_defs = @dots{}; +change.new_uses = @dots{}; +change.move_range = @dots{}; +@end smallexample + +This @code{rtl_ssa::insn_change} only describes something that the +pass @emph{might} do; at this stage, nothing has actually changed. + +As noted above, the default @code{move_range} requires the instruction +to remain where it is. At the other extreme, it is possible to allow +the instruction to move anywhere within its extended basic block, +provided that all the new uses and definitions can be performed +at the new location. The way to do this is: + +@smallexample +change.move_range = insn->ebb ()->insn_range (); +@end smallexample + +In either case, the next step is to make sure that move range is +consistent with the new uses and definitions. The way to do this is: + +@smallexample +if (!rtl_ssa::restrict_movement (change)) + return false; +@end smallexample + +This function tries to limit @code{move_range} to a range of instructions +at which @code{new_uses} and @code{new_defs} can be correctly performed. +It returns true on success or false if no suitable location exists. + +The pass should also tentatively change the pattern of the instruction +to whatever form the pass wants the instruction to have. This should use +the facilities provided by @file{recog.cc}. For example: + +@smallexample +rtl_insn *rtl = insn->rtl (); +insn_change_watermark watermark; +validate_change (rtl, &PATTERN (rtl), new_pat, 1); +@end smallexample + +will tentatively replace @code{insn}'s pattern with @code{new_pat}. + +These changes and the construction of the @code{rtl_ssa::insn_change} +can happen in either order or be interleaved. + +After the tentative changes to the instruction are complete, +the pass should check whether the new pattern matches a target +instruction or satisfies the requirements of an inline asm: + +@smallexample +if (!rtl_ssa::recog (change)) + return false; +@end smallexample + +This step might change the instruction pattern further in order to +make it match. It might also add new definitions or restrict the range +of the move. For example, if the new pattern did not match in its original +form, but could be made to match by adding a clobber of the flags +register, @code{rtl_ssa::recog} will check whether the flags register +is free at an appropriate point. If so, it will add a clobber of the +flags register to @code{new_defs} and restrict @code{move_range} to +the locations at which the flags register can be safely clobbered. + +Even if the proposed new instruction is valid according to +@code{rtl_ssa::recog}, the change might not be worthwhile. +For example, when optimizing for speed, the new instruction might +turn out to be slower than the original one. When optimizing for +size, the new instruction might turn out to be bigger than the +original one. + +Passes should check for this case using @code{change_is_worthwhile}. +For example: + +@smallexample +if (!rtl_ssa::change_is_worthwhile (change)) + return false; +@end smallexample + +If the change passes this test too then the pass can perform the change using: + +@smallexample +confirm_change_group (); +crtl->ssa->change_insn (change); +@end smallexample + +Putting all this together, the change has the following form: + +@smallexample +auto attempt = crtl->ssa->new_change_attempt (); + +rtl_ssa::insn_change change (insn); +change.new_defs = @dots{}; +change.new_uses = @dots{}; +change.move_range = @dots{}; + +if (!rtl_ssa::restrict_movement (change)) + return false; + +insn_change_watermark watermark; +// Use validate_change etc. to change INSN's pattern. +@dots{} +if (!rtl_ssa::recog (change) + || !rtl_ssa::change_is_worthwhile (change)) + return false; + +confirm_change_group (); +crtl->ssa->change_insn (change); +@end smallexample + +@node Changing Multiple RTL SSA Instructions +@subsubsection Changing Multiple RTL SSA Instructions + +The process for changing multiple instructions is similar +to the process for changing single instructions +(@pxref{Changing One RTL SSA Instruction}). The pass should +again start the change attempt with: + +@smallexample +auto attempt = crtl->ssa->new_change_attempt (); +@end smallexample + +and keep @code{attempt} in scope for the duration of the change +attempt. It should then construct an @code{rtl_ssa::insn_change} +for each change that it wants to make. + +After this, it should combine the changes into a sequence of +@code{rtl_ssa::insn_change} pointers. This sequence must be in +reverse postorder; the instructions will remain strictly in the +order that the sequence specifies. + +For example, if a pass is changing exactly two instructions, +it might do: + +@smallexample +rtl_ssa::insn_change *changes[] = @{ &change1, change2 @}; +@end smallexample + +where @code{change1}'s instruction must come before @code{change2}'s. +Alternatively, if the pass is changing a variable number of +instructions, it might build up the sequence in a +@code{vec}. + +By default, @code{rtl_ssa::restrict_movement} assumes that all +instructions other than the one passed to it will remain in their +current positions and will retain their current uses and definitions. +When changing multiple instructions, it is usually more effective +to ignore the other instructions that are changing. The sequencing +described above ensures that the changing instructions remain +in the correct order with respect to each other. +The way to do this is: + +@smallexample +if (!rtl_ssa::restrict_movement (change, insn_is_changing (changes))) + return false; +@end smallexample + +Similarly, when @code{rtl_ssa::restrict_movement} is detecting +whether a register can be clobbered, it by default assumes that +all other instructions will remain in their current positions and +retain their current form. It is again more effective to ignore +changing instructions (which might, for example, no longer need +to clobber the flags register). The way to do this is: + +@smallexample +if (!rtl_ssa::recog (change, insn_is_changing (changes))) + return false; +@end smallexample + +When changing multiple instructions, the important question is usually +not whether each individual change is worthwhile, but whether the changes +as a whole are worthwhile. The way to test this is: + +@smallexample +if (!rtl_ssa::changes_are_worthwhile (changes)) + return false; +@end smallexample + +The process for changing single instructions makes sure that one +@code{rtl_ssa::insn_change} in isolation is valid. But when changing +multiple instructions, it is also necessary to test whether the +sequence as a whole is valid. For example, it might be impossible +to satisfy all of the @code{move_range}s at once. + +Therefore, once the pass has a sequence of changes that are +individually correct, it should use: + +@smallexample +if (!crtl->ssa->verify_insn_changes (changes)) + return false; +@end smallexample + +to check whether the sequence as a whole is valid. If all checks pass, +the final step is: + +@smallexample +confirm_change_group (); +crtl->ssa->change_insns (changes); +@end smallexample + +Putting all this together, the process for a two-instruction change is: + +@smallexample +auto attempt = crtl->ssa->new_change_attempt (); + +rtl_ssa::insn_change change (insn1); +change1.new_defs = @dots{}; +change1.new_uses = @dots{}; +change1.move_range = @dots{}; + +rtl_ssa::insn_change change (insn2); +change2.new_defs = @dots{}; +change2.new_uses = @dots{}; +change2.move_range = @dots{}; + +rtl_ssa::insn_change *changes[] = @{ &change1, change2 @}; + +auto is_changing = insn_is_changing (changes); +if (!rtl_ssa::restrict_movement (change1, is_changing) + || !rtl_ssa::restrict_movement (change2, is_changing)) + return false; + +insn_change_watermark watermark; +// Use validate_change etc. to change INSN1's and INSN2's patterns. +@dots{} +if (!rtl_ssa::recog (change1, is_changing) + || !rtl_ssa::recog (change2, is_changing) + || !rtl_ssa::changes_are_worthwhile (changes) + || !crtl->ssa->verify_insn_changes (changes)) + return false; + +confirm_change_group (); +crtl->ssa->change_insns (changes); +@end smallexample + +@node Sharing +@section Structure Sharing Assumptions +@cindex sharing of RTL components +@cindex RTL structure sharing assumptions + +The compiler assumes that certain kinds of RTL expressions are unique; +there do not exist two distinct objects representing the same value. +In other cases, it makes an opposite assumption: that no RTL expression +object of a certain kind appears in more than one place in the +containing structure. + +These assumptions refer to a single function; except for the RTL +objects that describe global variables and external functions, +and a few standard objects such as small integer constants, +no RTL objects are common to two functions. + +@itemize @bullet +@cindex @code{reg}, RTL sharing +@item +Each pseudo-register has only a single @code{reg} object to represent it, +and therefore only a single machine mode. + +@cindex symbolic label +@cindex @code{symbol_ref}, RTL sharing +@item +For any symbolic label, there is only one @code{symbol_ref} object +referring to it. + +@cindex @code{const_int}, RTL sharing +@item +All @code{const_int} expressions with equal values are shared. + +@cindex @code{const_poly_int}, RTL sharing +@item +All @code{const_poly_int} expressions with equal modes and values +are shared. + +@cindex @code{pc}, RTL sharing +@item +There is only one @code{pc} expression. + +@cindex @code{const_double}, RTL sharing +@item +There is only one @code{const_double} expression with value 0 for +each floating point mode. Likewise for values 1 and 2. + +@cindex @code{const_vector}, RTL sharing +@item +There is only one @code{const_vector} expression with value 0 for +each vector mode, be it an integer or a double constant vector. + +@cindex @code{label_ref}, RTL sharing +@cindex @code{scratch}, RTL sharing +@item +No @code{label_ref} or @code{scratch} appears in more than one place in +the RTL structure; in other words, it is safe to do a tree-walk of all +the insns in the function and assume that each time a @code{label_ref} +or @code{scratch} is seen it is distinct from all others that are seen. + +@cindex @code{mem}, RTL sharing +@item +Only one @code{mem} object is normally created for each static +variable or stack slot, so these objects are frequently shared in all +the places they appear. However, separate but equal objects for these +variables are occasionally made. + +@cindex @code{asm_operands}, RTL sharing +@item +When a single @code{asm} statement has multiple output operands, a +distinct @code{asm_operands} expression is made for each output operand. +However, these all share the vector which contains the sequence of input +operands. This sharing is used later on to test whether two +@code{asm_operands} expressions come from the same statement, so all +optimizations must carefully preserve the sharing if they copy the +vector at all. + +@item +No RTL object appears in more than one place in the RTL structure +except as described above. Many passes of the compiler rely on this +by assuming that they can modify RTL objects in place without unwanted +side-effects on other insns. + +@findex unshare_all_rtl +@item +During initial RTL generation, shared structure is freely introduced. +After all the RTL for a function has been generated, all shared +structure is copied by @code{unshare_all_rtl} in @file{emit-rtl.cc}, +after which the above rules are guaranteed to be followed. + +@findex copy_rtx_if_shared +@item +During the combiner pass, shared structure within an insn can exist +temporarily. However, the shared structure is copied before the +combiner is finished with the insn. This is done by calling +@code{copy_rtx_if_shared}, which is a subroutine of +@code{unshare_all_rtl}. +@end itemize + +@node Reading RTL +@section Reading RTL + +To read an RTL object from a file, call @code{read_rtx}. It takes one +argument, a stdio stream, and returns a single RTL object. This routine +is defined in @file{read-rtl.cc}. It is not available in the compiler +itself, only the various programs that generate the compiler back end +from the machine description. + +People frequently have the idea of using RTL stored as text in a file as +an interface between a language front end and the bulk of GCC@. This +idea is not feasible. + +GCC was designed to use RTL internally only. Correct RTL for a given +program is very dependent on the particular target machine. And the RTL +does not contain all the information about the program. + +The proper way to interface GCC to a new language front end is with +the ``tree'' data structure, described in the files @file{tree.h} and +@file{tree.def}. The documentation for this structure (@pxref{GENERIC}) +is incomplete. diff --git a/gcc/doc/service.texi b/gcc/doc/service.texi new file mode 100644 index 00000000000..28f90ddfc94 --- /dev/null +++ b/gcc/doc/service.texi @@ -0,0 +1,27 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Service +@chapter How To Get Help with GCC + +If you need help installing, using or changing GCC, there are two +ways to find it: + +@itemize @bullet +@item +Send a message to a suitable network mailing list. First try +@email{gcc-help@@gcc.gnu.org} (for help installing or using GCC), and if +that brings no response, try @email{gcc@@gcc.gnu.org}. For help +changing GCC, ask @email{gcc@@gcc.gnu.org}. If you think you have found +a bug in GCC, please report it following the instructions at +@pxref{Bug Reporting}. + +@item +Look in the service directory for someone who might help you for a fee. +The service directory is found at +@uref{https://www.fsf.org/resources/service}. +@end itemize + +For further information, see +@uref{https://gcc.gnu.org/faq.html#support}. diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi new file mode 100644 index 00000000000..766266942f9 --- /dev/null +++ b/gcc/doc/sourcebuild.texi @@ -0,0 +1,3987 @@ +@c Copyright (C) 2002-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Source Tree +@chapter Source Tree Structure and Build System + +This chapter describes the structure of the GCC source tree, and how +GCC is built. The user documentation for building and installing GCC +is in a separate manual (@uref{https://gcc.gnu.org/install/}), with +which it is presumed that you are familiar. + +@menu +* Configure Terms:: Configuration terminology and history. +* Top Level:: The top level source directory. +* gcc Directory:: The @file{gcc} subdirectory. +@end menu + +@include configterms.texi + +@node Top Level +@section Top Level Source Directory + +The top level source directory in a GCC distribution contains several +files and directories that are shared with other software +distributions such as that of GNU Binutils. It also contains several +subdirectories that contain parts of GCC and its runtime libraries: + +@table @file +@item c++tools +Contains the sources for the g++-mapper-server, a tool used with +C++ modules. + +@item config +Autoconf macros and Makefile fragments used throughout the tree. + +@item contrib +Contributed scripts that may be found useful in conjunction with GCC@. +One of these, @file{contrib/texi2pod.pl}, is used to generate man +pages from Texinfo manuals as part of the GCC build process. + +@item fixincludes +The support for fixing system headers to work with GCC@. See +@file{fixincludes/README} for more information. The headers fixed by +this mechanism are installed in @file{@var{libsubdir}/include-fixed}. +Along with those headers, @file{README-fixinc} is also installed, as +@file{@var{libsubdir}/include-fixed/README}. + +@item gcc +The main sources of GCC itself (except for runtime libraries), +including optimizers, support for different target architectures, +language front ends, and testsuites. @xref{gcc Directory, , The +@file{gcc} Subdirectory}, for details. + +@item gnattools +Support tools for GNAT. + +@item gotools +Support tools for Go. + +@item include +Headers for the @code{libiberty} library. + +@item intl +GNU @code{libintl}, from GNU @code{gettext}, for systems which do not +include it in @code{libc}. + +@item libada +The Ada runtime library. + +@item libatomic +The runtime support library for atomic operations (e.g.@: for @code{__sync} +and @code{__atomic}). + +@item libbacktrace +A library that allows gcc to produce backtraces when it crashes. + +@item libcc1 +A library that allows gdb to make use of the compiler. + +@item libcody +A compiler dynamism library to allow communication between compilers and +build systems, for purposes such as C++ modules. + +@item libcpp +The C preprocessor library. + +@item libdecnumber +The Decimal Float support library. + +@item libffi +The @code{libffi} library, used as part of the Go runtime library. + +@item libgcc +The GCC runtime library. + +@item libgfortran +The Fortran runtime library. + +@item libgo +The Go runtime library. The bulk of this library is mirrored from the +@uref{https://github.com/@/golang/go, master Go repository}. + +@item libgomp +The GNU Offloading and Multi Processing Runtime Library. + +@item libiberty +The @code{libiberty} library, used for portability and for some +generally useful data structures and algorithms. @xref{Top, , +Introduction, libiberty, @sc{gnu} libiberty}, for more information +about this library. + +@item libitm +The runtime support library for transactional memory. + +@item libobjc +The Objective-C and Objective-C++ runtime library. + +@item libphobos +The D standard and runtime library. The bulk of this library is mirrored +from the @uref{https://github.com/@/dlang, master D repositories}. + +@item libquadmath +The runtime support library for quad-precision math operations. + +@item libsanitizer +Libraries for various sanitizers. The bulk of this directory is mirrored +from the @uref{https://github.com/google/sanitizers, Google sanitizers +repositories}. + +@item libssp +The Stack protector runtime library. + +@item libstdc++-v3 +The C++ runtime library. + +@item libvtv +The vtable verification library. + +@item lto-plugin +Plugin used by the linker if link-time optimizations are enabled. + +@item maintainer-scripts +Scripts used by the @code{gccadmin} account on @code{gcc.gnu.org}. + +@item zlib +The @code{zlib} compression library, used for compressing and +uncompressing GCC's intermediate language in LTO object files. +@end table + +The build system in the top level directory, including how recursion +into subdirectories works and how building runtime libraries for +multilibs is handled, is documented in a separate manual, included +with GNU Binutils. @xref{Top, , GNU configure and build system, +configure, The GNU configure and build system}, for details. + +@node gcc Directory +@section The @file{gcc} Subdirectory + +The @file{gcc} directory contains many files that are part of the C +sources of GCC, other files used as part of the configuration and +build process, and subdirectories including documentation and a +testsuite. The files that are sources of GCC are documented in a +separate chapter. @xref{Passes, , Passes and Files of the Compiler}. + +@menu +* Subdirectories:: Subdirectories of @file{gcc}. +* Configuration:: The configuration process, and the files it uses. +* Build:: The build system in the @file{gcc} directory. +* Makefile:: Targets in @file{gcc/Makefile}. +* Library Files:: Library source files and headers under @file{gcc/}. +* Headers:: Headers installed by GCC. +* Documentation:: Building documentation in GCC. +* Front End:: Anatomy of a language front end. +* Back End:: Anatomy of a target back end. +@end menu + +@node Subdirectories +@subsection Subdirectories of @file{gcc} + +The @file{gcc} directory contains the following subdirectories: + +@table @file +@item @var{language} +Subdirectories for various languages. Directories containing a file +@file{config-lang.in} are language subdirectories. The contents of +the subdirectories @file{c} (for C), @file{cp} (for C++), +@file{objc} (for Objective-C), @file{objcp} (for Objective-C++), +and @file{lto} (for LTO) are documented in this +manual (@pxref{Passes, , Passes and Files of the Compiler}); +those for other languages are not. @xref{Front End, , +Anatomy of a Language Front End}, for details of the files in these +directories. + +@item common +Source files shared between the compiler drivers (such as +@command{gcc}) and the compilers proper (such as @file{cc1}). If an +architecture defines target hooks shared between those places, it also +has a subdirectory in @file{common/config}. @xref{Target Structure}. + +@item config +Configuration files for supported architectures and operating +systems. @xref{Back End, , Anatomy of a Target Back End}, for +details of the files in this directory. + +@item doc +Texinfo documentation for GCC, together with automatically generated +man pages and support for converting the installation manual to +HTML@. @xref{Documentation}. + +@item ginclude +System headers installed by GCC, mainly those required by the C +standard of freestanding implementations. @xref{Headers, , Headers +Installed by GCC}, for details of when these and other headers are +installed. + +@item po +Message catalogs with translations of messages produced by GCC into +various languages, @file{@var{language}.po}. This directory also +contains @file{gcc.pot}, the template for these message catalogues, +@file{exgettext}, a wrapper around @command{gettext} to extract the +messages from the GCC sources and create @file{gcc.pot}, which is run +by @samp{make gcc.pot}, and @file{EXCLUDES}, a list of files from +which messages should not be extracted. + +@item testsuite +The GCC testsuites (except for those for runtime libraries). +@xref{Testsuites}. +@end table + +@node Configuration +@subsection Configuration in the @file{gcc} Directory + +The @file{gcc} directory is configured with an Autoconf-generated +script @file{configure}. The @file{configure} script is generated +from @file{configure.ac} and @file{aclocal.m4}. From the files +@file{configure.ac} and @file{acconfig.h}, Autoheader generates the +file @file{config.in}. The file @file{cstamp-h.in} is used as a +timestamp. + +@menu +* Config Fragments:: Scripts used by @file{configure}. +* System Config:: The @file{config.build}, @file{config.host}, and + @file{config.gcc} files. +* Configuration Files:: Files created by running @file{configure}. +@end menu + +@node Config Fragments +@subsubsection Scripts Used by @file{configure} + +@file{configure} uses some other scripts to help in its work: + +@itemize @bullet +@item The standard GNU @file{config.sub} and @file{config.guess} +files, kept in the top level directory, are used. + +@item The file @file{config.gcc} is used to handle configuration +specific to the particular target machine. The file +@file{config.build} is used to handle configuration specific to the +particular build machine. The file @file{config.host} is used to handle +configuration specific to the particular host machine. (In general, +these should only be used for features that cannot reasonably be tested in +Autoconf feature tests.) +@xref{System Config, , The @file{config.build}; @file{config.host}; +and @file{config.gcc} Files}, for details of the contents of these files. + +@item Each language subdirectory has a file +@file{@var{language}/config-lang.in} that is used for +front-end-specific configuration. @xref{Front End Config, , The Front +End @file{config-lang.in} File}, for details of this file. + +@item A helper script @file{configure.frag} is used as part of +creating the output of @file{configure}. +@end itemize + +@node System Config +@subsubsection The @file{config.build}; @file{config.host}; and @file{config.gcc} Files + +The @file{config.build} file contains specific rules for particular systems +which GCC is built on. This should be used as rarely as possible, as the +behavior of the build system can always be detected by autoconf. + +The @file{config.host} file contains specific rules for particular systems +which GCC will run on. This is rarely needed. + +The @file{config.gcc} file contains specific rules for particular systems +which GCC will generate code for. This is usually needed. + +Each file has a list of the shell variables it sets, with descriptions, at the +top of the file. + +FIXME: document the contents of these files, and what variables should +be set to control build, host and target configuration. + +@include configfiles.texi + +@node Build +@subsection Build System in the @file{gcc} Directory + +FIXME: describe the build system, including what is built in what +stages. Also list the various source files that are used in the build +process but aren't source files of GCC itself and so aren't documented +below (@pxref{Passes}). + +@include makefile.texi + +@node Library Files +@subsection Library Source Files and Headers under the @file{gcc} Directory + +FIXME: list here, with explanation, all the C source files and headers +under the @file{gcc} directory that aren't built into the GCC +executable but rather are part of runtime libraries and object files, +such as @file{crtstuff.c} and @file{unwind-dw2.c}. @xref{Headers, , +Headers Installed by GCC}, for more information about the +@file{ginclude} directory. + +@node Headers +@subsection Headers Installed by GCC + +In general, GCC expects the system C library to provide most of the +headers to be used with it. However, GCC will fix those headers if +necessary to make them work with GCC, and will install some headers +required of freestanding implementations. These headers are installed +in @file{@var{libsubdir}/include}. Headers for non-C runtime +libraries are also installed by GCC; these are not documented here. +(FIXME: document them somewhere.) + +Several of the headers GCC installs are in the @file{ginclude} +directory. These headers, @file{iso646.h}, +@file{stdarg.h}, @file{stdbool.h}, and @file{stddef.h}, +are installed in @file{@var{libsubdir}/include}, +unless the target Makefile fragment (@pxref{Target Fragment}) +overrides this by setting @code{USER_H}. + +In addition to these headers and those generated by fixing system +headers to work with GCC, some other headers may also be installed in +@file{@var{libsubdir}/include}. @file{config.gcc} may set +@code{extra_headers}; this specifies additional headers under +@file{config} to be installed on some systems. + +GCC installs its own version of @code{}, from @file{ginclude/float.h}. +This is done to cope with command-line options that change the +representation of floating point numbers. + +GCC also installs its own version of @code{}; this is generated +from @file{glimits.h}, together with @file{limitx.h} and +@file{limity.h} if the system also has its own version of +@code{}. (GCC provides its own header because it is +required of ISO C freestanding implementations, but needs to include +the system header from its own header as well because other standards +such as POSIX specify additional values to be defined in +@code{}.) The system's @code{} header is used via +@file{@var{libsubdir}/include/syslimits.h}, which is copied from +@file{gsyslimits.h} if it does not need fixing to work with GCC; if it +needs fixing, @file{syslimits.h} is the fixed copy. + +GCC can also install @code{}. It will do this when +@file{config.gcc} sets @code{use_gcc_tgmath} to @code{yes}. + +@node Documentation +@subsection Building Documentation + +The main GCC documentation is in the form of manuals in Texinfo +format. These are installed in Info format; DVI versions may be +generated by @samp{make dvi}, PDF versions by @samp{make pdf}, and +HTML versions by @samp{make html}. In addition, some man pages are +generated from the Texinfo manuals, there are some other text files +with miscellaneous documentation, and runtime libraries have their own +documentation outside the @file{gcc} directory. FIXME: document the +documentation for runtime libraries somewhere. + +@menu +* Texinfo Manuals:: GCC manuals in Texinfo format. +* Man Page Generation:: Generating man pages from Texinfo manuals. +* Miscellaneous Docs:: Miscellaneous text files with documentation. +@end menu + +@node Texinfo Manuals +@subsubsection Texinfo Manuals + +The manuals for GCC as a whole, and the C and C++ front ends, are in +files @file{doc/*.texi}. Other front ends have their own manuals in +files @file{@var{language}/*.texi}. Common files +@file{doc/include/*.texi} are provided which may be included in +multiple manuals; the following files are in @file{doc/include}: + +@table @file +@item fdl.texi +The GNU Free Documentation License. +@item funding.texi +The section ``Funding Free Software''. +@item gcc-common.texi +Common definitions for manuals. +@item gpl_v3.texi +The GNU General Public License. +@item texinfo.tex +A copy of @file{texinfo.tex} known to work with the GCC manuals. +@end table + +DVI-formatted manuals are generated by @samp{make dvi}, which uses +@command{texi2dvi} (via the Makefile macro @code{$(TEXI2DVI)}). +PDF-formatted manuals are generated by @samp{make pdf}, which uses +@command{texi2pdf} (via the Makefile macro @code{$(TEXI2PDF)}). HTML +formatted manuals are generated by @samp{make html}. Info +manuals are generated by @samp{make info} (which is run as part of +a bootstrap); this generates the manuals in the source directory, +using @command{makeinfo} via the Makefile macro @code{$(MAKEINFO)}, +and they are included in release distributions. + +Manuals are also provided on the GCC web site, in both HTML and +PostScript forms. This is done via the script +@file{maintainer-scripts/update_web_docs_git}. Each manual to be +provided online must be listed in the definition of @code{MANUALS} in +that file; a file @file{@var{name}.texi} must only appear once in the +source tree, and the output manual must have the same name as the +source file. (However, other Texinfo files, included in manuals but +not themselves the root files of manuals, may have names that appear +more than once in the source tree.) The manual file +@file{@var{name}.texi} should only include other files in its own +directory or in @file{doc/include}. HTML manuals will be generated by +@samp{makeinfo --html}, PostScript manuals by @command{texi2dvi} +and @command{dvips}, and PDF manuals by @command{texi2pdf}. +All Texinfo files that are parts of manuals must +be version-controlled, even if they are generated files, for the +generation of online manuals to work. + +The installation manual, @file{doc/install.texi}, is also provided on +the GCC web site. The HTML version is generated by the script +@file{doc/install.texi2html}. + +@node Man Page Generation +@subsubsection Man Page Generation + +Because of user demand, in addition to full Texinfo manuals, man pages +are provided which contain extracts from those manuals. These man +pages are generated from the Texinfo manuals using +@file{contrib/texi2pod.pl} and @command{pod2man}. (The man page for +@command{g++}, @file{cp/g++.1}, just contains a @samp{.so} reference +to @file{gcc.1}, but all the other man pages are generated from +Texinfo manuals.) + +Because many systems may not have the necessary tools installed to +generate the man pages, they are only generated if the +@file{configure} script detects that recent enough tools are +installed, and the Makefiles allow generating man pages to fail +without aborting the build. Man pages are also included in release +distributions. They are generated in the source directory. + +Magic comments in Texinfo files starting @samp{@@c man} control what +parts of a Texinfo file go into a man page. Only a subset of Texinfo +is supported by @file{texi2pod.pl}, and it may be necessary to add +support for more Texinfo features to this script when generating new +man pages. To improve the man page output, some special Texinfo +macros are provided in @file{doc/include/gcc-common.texi} which +@file{texi2pod.pl} understands: + +@table @code +@item @@gcctabopt +Use in the form @samp{@@table @@gcctabopt} for tables of options, +where for printed output the effect of @samp{@@code} is better than +that of @samp{@@option} but for man page output a different effect is +wanted. +@item @@gccoptlist +Use for summary lists of options in manuals. +@item @@gol +Use at the end of each line inside @samp{@@gccoptlist}. This is +necessary to avoid problems with differences in how the +@samp{@@gccoptlist} macro is handled by different Texinfo formatters. +@end table + +FIXME: describe the @file{texi2pod.pl} input language and magic +comments in more detail. + +@node Miscellaneous Docs +@subsubsection Miscellaneous Documentation + +In addition to the formal documentation that is installed by GCC, +there are several other text files in the @file{gcc} subdirectory +with miscellaneous documentation: + +@table @file +@item ABOUT-GCC-NLS +Notes on GCC's Native Language Support. FIXME: this should be part of +this manual rather than a separate file. +@item ABOUT-NLS +Notes on the Free Translation Project. +@item COPYING +@itemx COPYING3 +The GNU General Public License, Versions 2 and 3. +@item COPYING.LIB +@itemx COPYING3.LIB +The GNU Lesser General Public License, Versions 2.1 and 3. +@item *ChangeLog* +@itemx */ChangeLog* +Change log files for various parts of GCC@. +@item LANGUAGES +Details of a few changes to the GCC front-end interface. FIXME: the +information in this file should be part of general documentation of +the front-end interface in this manual. +@item ONEWS +Information about new features in old versions of GCC@. (For recent +versions, the information is on the GCC web site.) +@item README.Portability +Information about portability issues when writing code in GCC@. FIXME: +why isn't this part of this manual or of the GCC Coding Conventions? +@end table + +FIXME: document such files in subdirectories, at least @file{config}, +@file{c}, @file{cp}, @file{objc}, @file{testsuite}. + +@node Front End +@subsection Anatomy of a Language Front End + +A front end for a language in GCC has the following parts: + +@itemize @bullet +@item +A directory @file{@var{language}} under @file{gcc} containing source +files for that front end. @xref{Front End Directory, , The Front End +@file{@var{language}} Directory}, for details. +@item +A mention of the language in the list of supported languages in +@file{gcc/doc/install.texi}. +@item +A mention of the name under which the language's runtime library is +recognized by @option{--enable-shared=@var{package}} in the +documentation of that option in @file{gcc/doc/install.texi}. +@item +A mention of any special prerequisites for building the front end in +the documentation of prerequisites in @file{gcc/doc/install.texi}. +@item +Details of contributors to that front end in +@file{gcc/doc/contrib.texi}. If the details are in that front end's +own manual then there should be a link to that manual's list in +@file{contrib.texi}. +@item +Information about support for that language in +@file{gcc/doc/frontends.texi}. +@item +Information about standards for that language, and the front end's +support for them, in @file{gcc/doc/standards.texi}. This may be a +link to such information in the front end's own manual. +@item +Details of source file suffixes for that language and @option{-x +@var{lang}} options supported, in @file{gcc/doc/invoke.texi}. +@item +Entries in @code{default_compilers} in @file{gcc.cc} for source file +suffixes for that language. +@item +Preferably testsuites, which may be under @file{gcc/testsuite} or +runtime library directories. FIXME: document somewhere how to write +testsuite harnesses. +@item +Probably a runtime library for the language, outside the @file{gcc} +directory. FIXME: document this further. +@item +Details of the directories of any runtime libraries in +@file{gcc/doc/sourcebuild.texi}. +@item +Check targets in @file{Makefile.def} for the top-level @file{Makefile} +to check just the compiler or the compiler and runtime library for the +language. +@end itemize + +If the front end is added to the official GCC source repository, the +following are also necessary: + +@itemize @bullet +@item +At least one Bugzilla component for bugs in that front end and runtime +libraries. This category needs to be added to the Bugzilla database. +@item +Normally, one or more maintainers of that front end listed in +@file{MAINTAINERS}. +@item +Mentions on the GCC web site in @file{index.html} and +@file{frontends.html}, with any relevant links on +@file{readings.html}. (Front ends that are not an official part of +GCC may also be listed on @file{frontends.html}, with relevant links.) +@item +A news item on @file{index.html}, and possibly an announcement on the +@email{gcc-announce@@gcc.gnu.org} mailing list. +@item +The front end's manuals should be mentioned in +@file{maintainer-scripts/update_web_docs_git} (@pxref{Texinfo Manuals}) +and the online manuals should be linked to from +@file{onlinedocs/index.html}. +@item +Any old releases or CVS repositories of the front end, before its +inclusion in GCC, should be made available on the GCC web site at +@uref{https://gcc.gnu.org/pub/gcc/old-releases/}. +@item +The release and snapshot script @file{maintainer-scripts/gcc_release} +should be updated to generate appropriate tarballs for this front end. +@item +If this front end includes its own version files that include the +current date, @file{maintainer-scripts/update_version} should be +updated accordingly. +@end itemize + +@menu +* Front End Directory:: The front end @file{@var{language}} directory. +* Front End Config:: The front end @file{config-lang.in} file. +* Front End Makefile:: The front end @file{Make-lang.in} file. +@end menu + +@node Front End Directory +@subsubsection The Front End @file{@var{language}} Directory + +A front end @file{@var{language}} directory contains the source files +of that front end (but not of any runtime libraries, which should be +outside the @file{gcc} directory). This includes documentation, and +possibly some subsidiary programs built alongside the front end. +Certain files are special and other parts of the compiler depend on +their names: + +@table @file +@item config-lang.in +This file is required in all language subdirectories. @xref{Front End +Config, , The Front End @file{config-lang.in} File}, for details of +its contents +@item Make-lang.in +This file is required in all language subdirectories. @xref{Front End +Makefile, , The Front End @file{Make-lang.in} File}, for details of its +contents. +@item lang.opt +This file registers the set of switches that the front end accepts on +the command line, and their @option{--help} text. @xref{Options}. +@item lang-specs.h +This file provides entries for @code{default_compilers} in +@file{gcc.cc} which override the default of giving an error that a +compiler for that language is not installed. +@item @var{language}-tree.def +This file, which need not exist, defines any language-specific tree +codes. +@end table + +@node Front End Config +@subsubsection The Front End @file{config-lang.in} File + +Each language subdirectory contains a @file{config-lang.in} file. +This file is a shell script that may define some variables describing +the language: + +@table @code +@item language +This definition must be present, and gives the name of the language +for some purposes such as arguments to @option{--enable-languages}. +@item lang_requires +If defined, this variable lists (space-separated) language front ends +other than C that this front end requires to be enabled (with the +names given being their @code{language} settings). For example, the +Obj-C++ front end depends on the C++ and ObjC front ends, so sets +@samp{lang_requires="objc c++"}. +@item subdir_requires +If defined, this variable lists (space-separated) front end directories +other than C that this front end requires to be present. For example, +the Objective-C++ front end uses source files from the C++ and +Objective-C front ends, so sets @samp{subdir_requires="cp objc"}. +@item target_libs +If defined, this variable lists (space-separated) targets in the top +level @file{Makefile} to build the runtime libraries for this +language, such as @code{target-libobjc}. +@item lang_dirs +If defined, this variable lists (space-separated) top level +directories (parallel to @file{gcc}), apart from the runtime libraries, +that should not be configured if this front end is not built. +@item build_by_default +If defined to @samp{no}, this language front end is not built unless +enabled in a @option{--enable-languages} argument. Otherwise, front +ends are built by default, subject to any special logic in +@file{configure.ac} (as is present to disable the Ada front end if the +Ada compiler is not already installed). +@item boot_language +If defined to @samp{yes}, this front end is built in stage1 of the +bootstrap. This is only relevant to front ends written in their own +languages. +@item compilers +If defined, a space-separated list of compiler executables that will +be run by the driver. The names here will each end +with @samp{\$(exeext)}. +@item outputs +If defined, a space-separated list of files that should be generated +by @file{configure} substituting values in them. This mechanism can +be used to create a file @file{@var{language}/Makefile} from +@file{@var{language}/Makefile.in}, but this is deprecated, building +everything from the single @file{gcc/Makefile} is preferred. +@item gtfiles +If defined, a space-separated list of files that should be scanned by +@file{gengtype.cc} to generate the garbage collection tables and routines for +this language. This excludes the files that are common to all front +ends. @xref{Type Information}. + +@end table + +@node Front End Makefile +@subsubsection The Front End @file{Make-lang.in} File + +Each language subdirectory contains a @file{Make-lang.in} file. It contains +targets @code{@var{lang}.@var{hook}} (where @code{@var{lang}} is the +setting of @code{language} in @file{config-lang.in}) for the following +values of @code{@var{hook}}, and any other Makefile rules required to +build those targets (which may if necessary use other Makefiles +specified in @code{outputs} in @file{config-lang.in}, although this is +deprecated). It also adds any testsuite targets that can use the +standard rule in @file{gcc/Makefile.in} to the variable +@code{lang_checks}. + +@table @code +@item all.cross +@itemx start.encap +@itemx rest.encap +FIXME: exactly what goes in each of these targets? +@item tags +Build an @command{etags} @file{TAGS} file in the language subdirectory +in the source tree. +@item info +Build info documentation for the front end, in the build directory. +This target is only called by @samp{make bootstrap} if a suitable +version of @command{makeinfo} is available, so does not need to check +for this, and should fail if an error occurs. +@item dvi +Build DVI documentation for the front end, in the build directory. +This should be done using @code{$(TEXI2DVI)}, with appropriate +@option{-I} arguments pointing to directories of included files. +@item pdf +Build PDF documentation for the front end, in the build directory. +This should be done using @code{$(TEXI2PDF)}, with appropriate +@option{-I} arguments pointing to directories of included files. +@item html +Build HTML documentation for the front end, in the build directory. +@item man +Build generated man pages for the front end from Texinfo manuals +(@pxref{Man Page Generation}), in the build directory. This target +is only called if the necessary tools are available, but should ignore +errors so as not to stop the build if errors occur; man pages are +optional and the tools involved may be installed in a broken way. +@item install-common +Install everything that is part of the front end, apart from the +compiler executables listed in @code{compilers} in +@file{config-lang.in}. +@item install-info +Install info documentation for the front end, if it is present in the +source directory. This target should have dependencies on info files +that should be installed. +@item install-man +Install man pages for the front end. This target should ignore +errors. +@item install-plugin +Install headers needed for plugins. +@item srcextra +Copies its dependencies into the source directory. This generally should +be used for generated files such as Bison output files which are not +version-controlled, but should be included in any release tarballs. This +target will be executed during a bootstrap if +@samp{--enable-generated-files-in-srcdir} was specified as a +@file{configure} option. +@item srcinfo +@itemx srcman +Copies its dependencies into the source directory. These targets will be +executed during a bootstrap if @samp{--enable-generated-files-in-srcdir} +was specified as a @file{configure} option. +@item uninstall +Uninstall files installed by installing the compiler. This is +currently documented not to be supported, so the hook need not do +anything. +@item mostlyclean +@itemx clean +@itemx distclean +@itemx maintainer-clean +The language parts of the standard GNU +@samp{*clean} targets. @xref{Standard Targets, , Standard Targets for +Users, standards, GNU Coding Standards}, for details of the standard +targets. For GCC, @code{maintainer-clean} should delete +all generated files in the source directory that are not version-controlled, +but should not delete anything that is. +@end table + +@file{Make-lang.in} must also define a variable @code{@var{lang}_OBJS} +to a list of host object files that are used by that language. + +@node Back End +@subsection Anatomy of a Target Back End + +A back end for a target architecture in GCC has the following parts: + +@itemize @bullet +@item +A directory @file{@var{machine}} under @file{gcc/config}, containing a +machine description @file{@var{machine}.md} file (@pxref{Machine Desc, +, Machine Descriptions}), header files @file{@var{machine}.h} and +@file{@var{machine}-protos.h} and a source file @file{@var{machine}.c} +(@pxref{Target Macros, , Target Description Macros and Functions}), +possibly a target Makefile fragment @file{t-@var{machine}} +(@pxref{Target Fragment, , The Target Makefile Fragment}), and maybe +some other files. The names of these files may be changed from the +defaults given by explicit specifications in @file{config.gcc}. +@item +If necessary, a file @file{@var{machine}-modes.def} in the +@file{@var{machine}} directory, containing additional machine modes to +represent condition codes. @xref{Condition Code}, for further details. +@item +An optional @file{@var{machine}.opt} file in the @file{@var{machine}} +directory, containing a list of target-specific options. You can also +add other option files using the @code{extra_options} variable in +@file{config.gcc}. @xref{Options}. +@item +Entries in @file{config.gcc} (@pxref{System Config, , The +@file{config.gcc} File}) for the systems with this target +architecture. +@item +Documentation in @file{gcc/doc/invoke.texi} for any command-line +options supported by this target (@pxref{Run-time Target, , Run-time +Target Specification}). This means both entries in the summary table +of options and details of the individual options. +@item +Documentation in @file{gcc/doc/extend.texi} for any target-specific +attributes supported (@pxref{Target Attributes, , Defining +target-specific uses of @code{__attribute__}}), including where the +same attribute is already supported on some targets, which are +enumerated in the manual. +@item +Documentation in @file{gcc/doc/extend.texi} for any target-specific +pragmas supported. +@item +Documentation in @file{gcc/doc/extend.texi} of any target-specific +built-in functions supported. +@item +Documentation in @file{gcc/doc/extend.texi} of any target-specific +format checking styles supported. +@item +Documentation in @file{gcc/doc/md.texi} of any target-specific +constraint letters (@pxref{Machine Constraints, , Constraints for +Particular Machines}). +@item +A note in @file{gcc/doc/contrib.texi} under the person or people who +contributed the target support. +@item +Entries in @file{gcc/doc/install.texi} for all target triplets +supported with this target architecture, giving details of any special +notes about installation for this target, or saying that there are no +special notes if there are none. +@item +Possibly other support outside the @file{gcc} directory for runtime +libraries. FIXME: reference docs for this. The @code{libstdc++} porting +manual needs to be installed as info for this to work, or to be a +chapter of this manual. +@end itemize + +The @file{@var{machine}.h} header is included very early in GCC's +standard sequence of header files, while @file{@var{machine}-protos.h} +is included late in the sequence. Thus @file{@var{machine}-protos.h} +can include declarations referencing types that are not defined when +@file{@var{machine}.h} is included, specifically including those from +@file{rtl.h} and @file{tree.h}. Since both RTL and tree types may not +be available in every context where @file{@var{machine}-protos.h} is +included, in this file you should guard declarations using these types +inside appropriate @code{#ifdef RTX_CODE} or @code{#ifdef TREE_CODE} +conditional code segments. + +If the backend uses shared data structures that require @code{GTY} markers +for garbage collection (@pxref{Type Information}), you must declare those +in @file{@var{machine}.h} rather than @file{@var{machine}-protos.h}. +Any definitions required for building libgcc must also go in +@file{@var{machine}.h}. + +GCC uses the macro @code{IN_TARGET_CODE} to distinguish between +machine-specific @file{.c} and @file{.cc} files and +machine-independent @file{.c} and @file{.cc} files. Machine-specific +files should use the directive: + +@example +#define IN_TARGET_CODE 1 +@end example + +before including @code{config.h}. + +If the back end is added to the official GCC source repository, the +following are also necessary: + +@itemize @bullet +@item +An entry for the target architecture in @file{readings.html} on the +GCC web site, with any relevant links. +@item +Details of the properties of the back end and target architecture in +@file{backends.html} on the GCC web site. +@item +A news item about the contribution of support for that target +architecture, in @file{index.html} on the GCC web site. +@item +Normally, one or more maintainers of that target listed in +@file{MAINTAINERS}. Some existing architectures may be unmaintained, +but it would be unusual to add support for a target that does not have +a maintainer when support is added. +@item +Target triplets covering all @file{config.gcc} stanzas for the target, +in the list in @file{contrib/config-list.mk}. +@end itemize + +@node Testsuites +@chapter Testsuites + +GCC contains several testsuites to help maintain compiler quality. +Most of the runtime libraries and language front ends in GCC have +testsuites. Currently only the C language testsuites are documented +here; FIXME: document the others. + +@menu +* Test Idioms:: Idioms used in testsuite code. +* Test Directives:: Directives used within DejaGnu tests. +* Ada Tests:: The Ada language testsuites. +* C Tests:: The C language testsuites. +* LTO Testing:: Support for testing link-time optimizations. +* gcov Testing:: Support for testing gcov. +* profopt Testing:: Support for testing profile-directed optimizations. +* compat Testing:: Support for testing binary compatibility. +* Torture Tests:: Support for torture testing using multiple options. +* GIMPLE Tests:: Support for testing GIMPLE passes. +* RTL Tests:: Support for testing RTL passes. +@end menu + +@node Test Idioms +@section Idioms Used in Testsuite Code + +In general, C testcases have a trailing @file{-@var{n}.c}, starting +with @file{-1.c}, in case other testcases with similar names are added +later. If the test is a test of some well-defined feature, it should +have a name referring to that feature such as +@file{@var{feature}-1.c}. If it does not test a well-defined feature +but just happens to exercise a bug somewhere in the compiler, and a +bug report has been filed for this bug in the GCC bug database, +@file{pr@var{bug-number}-1.c} is the appropriate form of name. +Otherwise (for miscellaneous bugs not filed in the GCC bug database), +and previously more generally, test cases are named after the date on +which they were added. This allows people to tell at a glance whether +a test failure is because of a recently found bug that has not yet +been fixed, or whether it may be a regression, but does not give any +other information about the bug or where discussion of it may be +found. Some other language testsuites follow similar conventions. + +In the @file{gcc.dg} testsuite, it is often necessary to test that an +error is indeed a hard error and not just a warning---for example, +where it is a constraint violation in the C standard, which must +become an error with @option{-pedantic-errors}. The following idiom, +where the first line shown is line @var{line} of the file and the line +that generates the error, is used for this: + +@smallexample +/* @{ dg-bogus "warning" "warning in place of error" @} */ +/* @{ dg-error "@var{regexp}" "@var{message}" @{ target *-*-* @} @var{line} @} */ +@end smallexample + +It may be necessary to check that an expression is an integer constant +expression and has a certain value. To check that @code{@var{E}} has +value @code{@var{V}}, an idiom similar to the following is used: + +@smallexample +char x[((E) == (V) ? 1 : -1)]; +@end smallexample + +In @file{gcc.dg} tests, @code{__typeof__} is sometimes used to make +assertions about the types of expressions. See, for example, +@file{gcc.dg/c99-condexpr-1.c}. The more subtle uses depend on the +exact rules for the types of conditional expressions in the C +standard; see, for example, @file{gcc.dg/c99-intconst-1.c}. + +It is useful to be able to test that optimizations are being made +properly. This cannot be done in all cases, but it can be done where +the optimization will lead to code being optimized away (for example, +where flow analysis or alias analysis should show that certain code +cannot be called) or to functions not being called because they have +been expanded as built-in functions. Such tests go in +@file{gcc.c-torture/execute}. Where code should be optimized away, a +call to a nonexistent function such as @code{link_failure ()} may be +inserted; a definition + +@smallexample +#ifndef __OPTIMIZE__ +void +link_failure (void) +@{ + abort (); +@} +#endif +@end smallexample + +@noindent +will also be needed so that linking still succeeds when the test is +run without optimization. When all calls to a built-in function +should have been optimized and no calls to the non-built-in version of +the function should remain, that function may be defined as +@code{static} to call @code{abort ()} (although redeclaring a function +as static may not work on all targets). + +All testcases must be portable. Target-specific testcases must have +appropriate code to avoid causing failures on unsupported systems; +unfortunately, the mechanisms for this differ by directory. + +FIXME: discuss non-C testsuites here. + +@node Test Directives +@section Directives used within DejaGnu tests + +@menu +* Directives:: Syntax and descriptions of test directives. +* Selectors:: Selecting targets to which a test applies. +* Effective-Target Keywords:: Keywords describing target attributes. +* Add Options:: Features for @code{dg-add-options} +* Require Support:: Variants of @code{dg-require-@var{support}} +* Final Actions:: Commands for use in @code{dg-final} +@end menu + +@node Directives +@subsection Syntax and Descriptions of test directives + +Test directives appear within comments in a test source file and begin +with @code{dg-}. Some of these are defined within DejaGnu and others +are local to the GCC testsuite. + +The order in which test directives appear in a test can be important: +directives local to GCC sometimes override information used by the +DejaGnu directives, which know nothing about the GCC directives, so the +DejaGnu directives must precede GCC directives. + +Several test directives include selectors (@pxref{Selectors, , }) +which are usually preceded by the keyword @code{target} or @code{xfail}. + +@subsubsection Specify how to build the test + +@table @code +@item @{ dg-do @var{do-what-keyword} [@{ target/xfail @var{selector} @}] @} +@var{do-what-keyword} specifies how the test is compiled and whether +it is executed. It is one of: + +@table @code +@item preprocess +Compile with @option{-E} to run only the preprocessor. +@item compile +Compile with @option{-S} to produce an assembly code file. +@item assemble +Compile with @option{-c} to produce a relocatable object file. +@item link +Compile, assemble, and link to produce an executable file. +@item run +Produce and run an executable file, which is expected to return +an exit code of 0. +@end table + +The default is @code{compile}. That can be overridden for a set of +tests by redefining @code{dg-do-what-default} within the @code{.exp} +file for those tests. + +If the directive includes the optional @samp{@{ target @var{selector} @}} +then the test is skipped unless the target system matches the +@var{selector}. + +If @var{do-what-keyword} is @code{run} and the directive includes +the optional @samp{@{ xfail @var{selector} @}} and the selector is met +then the test is expected to fail. The @code{xfail} clause is ignored +for other values of @var{do-what-keyword}; those tests can use +directive @code{dg-xfail-if}. +@end table + +@subsubsection Specify additional compiler options + +@table @code +@item @{ dg-options @var{options} [@{ target @var{selector} @}] @} +This DejaGnu directive provides a list of compiler options, to be used +if the target system matches @var{selector}, that replace the default +options used for this set of tests. + +@item @{ dg-add-options @var{feature} @dots{} @} +Add any compiler options that are needed to access certain features. +This directive does nothing on targets that enable the features by +default, or that don't provide them at all. It must come after +all @code{dg-options} directives. +For supported values of @var{feature} see @ref{Add Options, ,}. + +@item @{ dg-additional-options @var{options} [@{ target @var{selector} @}] @} +This directive provides a list of compiler options, to be used +if the target system matches @var{selector}, that are added to the default +options used for this set of tests. +@end table + +@subsubsection Modify the test timeout value + +The normal timeout limit, in seconds, is found by searching the +following in order: + +@itemize @bullet +@item the value defined by an earlier @code{dg-timeout} directive in +the test + +@item variable @var{tool_timeout} defined by the set of tests + +@item @var{gcc},@var{timeout} set in the target board + +@item 300 +@end itemize + +@table @code +@item @{ dg-timeout @var{n} [@{target @var{selector} @}] @} +Set the time limit for the compilation and for the execution of the test +to the specified number of seconds. + +@item @{ dg-timeout-factor @var{x} [@{ target @var{selector} @}] @} +Multiply the normal time limit for compilation and execution of the test +by the specified floating-point factor. +@end table + +@subsubsection Skip a test for some targets + +@table @code +@item @{ dg-skip-if @var{comment} @{ @var{selector} @} [@{ @var{include-opts} @} [@{ @var{exclude-opts} @}]] @} +Arguments @var{include-opts} and @var{exclude-opts} are lists in which +each element is a string of zero or more GCC options. +Skip the test if all of the following conditions are met: +@itemize @bullet +@item the test system is included in @var{selector} + +@item for at least one of the option strings in @var{include-opts}, +every option from that string is in the set of options with which +the test would be compiled; use @samp{"*"} for an @var{include-opts} list +that matches any options; that is the default if @var{include-opts} is +not specified + +@item for each of the option strings in @var{exclude-opts}, at least one +option from that string is not in the set of options with which the test +would be compiled; use @samp{""} for an empty @var{exclude-opts} list; +that is the default if @var{exclude-opts} is not specified +@end itemize + +For example, to skip a test if option @code{-Os} is present: + +@smallexample +/* @{ dg-skip-if "" @{ *-*-* @} @{ "-Os" @} @{ "" @} @} */ +@end smallexample + +To skip a test if both options @code{-O2} and @code{-g} are present: + +@smallexample +/* @{ dg-skip-if "" @{ *-*-* @} @{ "-O2 -g" @} @{ "" @} @} */ +@end smallexample + +To skip a test if either @code{-O2} or @code{-O3} is present: + +@smallexample +/* @{ dg-skip-if "" @{ *-*-* @} @{ "-O2" "-O3" @} @{ "" @} @} */ +@end smallexample + +To skip a test unless option @code{-Os} is present: + +@smallexample +/* @{ dg-skip-if "" @{ *-*-* @} @{ "*" @} @{ "-Os" @} @} */ +@end smallexample + +To skip a test if either @code{-O2} or @code{-O3} is used with @code{-g} +but not if @code{-fpic} is also present: + +@smallexample +/* @{ dg-skip-if "" @{ *-*-* @} @{ "-O2 -g" "-O3 -g" @} @{ "-fpic" @} @} */ +@end smallexample + +@item @{ dg-require-effective-target @var{keyword} [@{ target @var{selector} @}] @} +Skip the test if the test target, including current multilib flags, +is not covered by the effective-target keyword. +If the directive includes the optional @samp{@{ @var{selector} @}} +then the effective-target test is only performed if the target system +matches the @var{selector}. +This directive must appear after any @code{dg-do} directive in the test +and before any @code{dg-additional-sources} directive. +@xref{Effective-Target Keywords, , }. + +@item @{ dg-require-@var{support} args @} +Skip the test if the target does not provide the required support. +These directives must appear after any @code{dg-do} directive in the test +and before any @code{dg-additional-sources} directive. +They require at least one argument, which can be an empty string if the +specific procedure does not examine the argument. +@xref{Require Support, , }, for a complete list of these directives. +@end table + +@subsubsection Expect a test to fail for some targets + +@table @code +@item @{ dg-xfail-if @var{comment} @{ @var{selector} @} [@{ @var{include-opts} @} [@{ @var{exclude-opts} @}]] @} +Expect the test to fail if the conditions (which are the same as for +@code{dg-skip-if}) are met. This does not affect the execute step. + +@item @{ dg-xfail-run-if @var{comment} @{ @var{selector} @} [@{ @var{include-opts} @} [@{ @var{exclude-opts} @}]] @} +Expect the execute step of a test to fail if the conditions (which are +the same as for @code{dg-skip-if}) are met. +@end table + +@subsubsection Expect the compiler to crash + +@table @code +@item @{ dg-ice @var{comment} [@{ @var{selector} @} [@{ @var{include-opts} @} [@{ @var{exclude-opts} @}]]] @} +Expect the compiler to crash with an internal compiler error and return +a nonzero exit status if the conditions (which are the same as for +@code{dg-skip-if}) are met. Used for tests that test bugs that have not been +fixed yet. +@end table + +@subsubsection Expect the test executable to fail + +@table @code +@item @{ dg-shouldfail @var{comment} [@{ @var{selector} @} [@{ @var{include-opts} @} [@{ @var{exclude-opts} @}]]] @} +Expect the test executable to return a nonzero exit status if the +conditions (which are the same as for @code{dg-skip-if}) are met. +@end table + +@subsubsection Verify compiler messages +Where @var{line} is an accepted argument for these commands, a value of @samp{0} +can be used if there is no line associated with the message. + +@table @code +@item @{ dg-error @var{regexp} [@var{comment} [@{ target/xfail @var{selector} @} [@var{line}] ]] @} +This DejaGnu directive appears on a source line that is expected to get +an error message, or else specifies the source line associated with the +message. If there is no message for that line or if the text of that +message is not matched by @var{regexp} then the check fails and +@var{comment} is included in the @code{FAIL} message. The check does +not look for the string @samp{error} unless it is part of @var{regexp}. + +@item @{ dg-warning @var{regexp} [@var{comment} [@{ target/xfail @var{selector} @} [@var{line}] ]] @} +This DejaGnu directive appears on a source line that is expected to get +a warning message, or else specifies the source line associated with the +message. If there is no message for that line or if the text of that +message is not matched by @var{regexp} then the check fails and +@var{comment} is included in the @code{FAIL} message. The check does +not look for the string @samp{warning} unless it is part of @var{regexp}. + +@item @{ dg-message @var{regexp} [@var{comment} [@{ target/xfail @var{selector} @} [@var{line}] ]] @} +The line is expected to get a message other than an error or warning. +If there is no message for that line or if the text of that message is +not matched by @var{regexp} then the check fails and @var{comment} is +included in the @code{FAIL} message. + +@item @{ dg-note @var{regexp} [@var{comment} [@{ target/xfail @var{selector} @} [@var{line}] ]] @} +The line is expected to get a @samp{note} message. +If there is no message for that line or if the text of that message is +not matched by @var{regexp} then the check fails and @var{comment} is +included in the @code{FAIL} message. + +By default, any @emph{excess} @samp{note} messages are pruned, meaning +their appearance doesn't trigger @emph{excess errors}. +However, if @samp{dg-note} is used at least once in a testcase, +they're not pruned and instead must @emph{all} be handled explicitly. +Thus, if looking for just single instances of messages with +@samp{note: } prefixes without caring for all of them, use +@samp{dg-message "note: [@dots{}]"} instead of @samp{dg-note}, or use +@samp{dg-note} together with @samp{dg-prune-output "note: "}. + +@item @{ dg-bogus @var{regexp} [@var{comment} [@{ target/xfail @var{selector} @} [@var{line}] ]] @} +This DejaGnu directive appears on a source line that should not get a +message matching @var{regexp}, or else specifies the source line +associated with the bogus message. It is usually used with @samp{xfail} +to indicate that the message is a known problem for a particular set of +targets. + +@item @{ dg-line @var{linenumvar} @} +This DejaGnu directive sets the variable @var{linenumvar} to the line number of +the source line. The variable @var{linenumvar} can then be used in subsequent +@code{dg-error}, @code{dg-warning}, @code{dg-message}, @code{dg-note} +and @code{dg-bogus} +directives. For example: + +@smallexample +int a; /* @{ dg-line first_def_a @} */ +float a; /* @{ dg-error "conflicting types of" @} */ +/* @{ dg-message "previous declaration of" "" @{ target *-*-* @} first_def_a @} */ +@end smallexample + +@item @{ dg-excess-errors @var{comment} [@{ target/xfail @var{selector} @}] @} +This DejaGnu directive indicates that the test is expected to fail due +to compiler messages that are not handled by @samp{dg-error}, +@samp{dg-warning}, @code{dg-message}, @samp{dg-note} or +@samp{dg-bogus}. +For this directive @samp{xfail} +has the same effect as @samp{target}. + +@item @{ dg-prune-output @var{regexp} @} +Prune messages matching @var{regexp} from the test output. +@end table + +@subsubsection Verify output of the test executable + +@table @code +@item @{ dg-output @var{regexp} [@{ target/xfail @var{selector} @}] @} +This DejaGnu directive compares @var{regexp} to the combined output +that the test executable writes to @file{stdout} and @file{stderr}. +@end table + +@subsubsection Specify environment variables for a test + +@table @code +@item @{ dg-set-compiler-env-var @var{var_name} "@var{var_value}" @} +Specify that the environment variable @var{var_name} needs to be set +to @var{var_value} before invoking the compiler on the test file. + +@item @{ dg-set-target-env-var @var{var_name} "@var{var_value}" @} +Specify that the environment variable @var{var_name} needs to be set +to @var{var_value} before execution of the program created by the test. +@end table + +@subsubsection Specify additional files for a test + +@table @code +@item @{ dg-additional-files "@var{filelist}" @} +Specify additional files, other than source files, that must be copied +to the system where the compiler runs. + +@item @{ dg-additional-sources "@var{filelist}" @} +Specify additional source files to appear in the compile line +following the main test file. +@end table + +@subsubsection Add checks at the end of a test + +@table @code +@item @{ dg-final @{ @var{local-directive} @} @} +This DejaGnu directive is placed within a comment anywhere in the +source file and is processed after the test has been compiled and run. +Multiple @samp{dg-final} commands are processed in the order in which +they appear in the source file. @xref{Final Actions, , }, for a list +of directives that can be used within @code{dg-final}. +@end table + +@node Selectors +@subsection Selecting targets to which a test applies + +Several test directives include @var{selector}s to limit the targets +for which a test is run or to declare that a test is expected to fail +on particular targets. + +A selector is: +@itemize @bullet +@item one or more target triplets, possibly including wildcard characters; +use @samp{*-*-*} to match any target +@item a single effective-target keyword (@pxref{Effective-Target Keywords}) +@item a list of compiler options that should be included or excluded +(as described in more detail below) +@item a logical expression +@end itemize + +Depending on the context, the selector specifies whether a test is +skipped and reported as unsupported or is expected to fail. A context +that allows either @samp{target} or @samp{xfail} also allows +@samp{@{ target @var{selector1} xfail @var{selector2} @}} +to skip the test for targets that don't match @var{selector1} and the +test to fail for targets that match @var{selector2}. + +A selector expression appears within curly braces and uses a single +logical operator: one of @samp{!}, @samp{&&}, or @samp{||}. An +operand is one of the following: + +@itemize @bullet +@item +another selector expression, in curly braces + +@item +an effective-target keyword, such as @code{lp64} + +@item +a single target triplet + +@item +a list of target triplets within quotes or curly braces + +@item +one of the following: + +@table @samp +@item @{ any-opts @var{opt1} @dots{} @var{optn} @} +Each of @var{opt1} to @var{optn} is a space-separated list of option globs. +The selector expression evaluates to true if, for one of these strings, +every glob in the string matches an option that was passed to the compiler. +For example: + +@smallexample +@{ any-opts "-O3 -flto" "-O[2g]" @} +@end smallexample + +is true if any of the following are true: + +@itemize @bullet +@item +@option{-O2} was passed to the compiler + +@item +@option{-Og} was passed to the compiler + +@item +both @option{-O3} and @option{-flto} were passed to the compiler +@end itemize + +This kind of selector can only be used within @code{dg-final} directives. +Use @code{dg-skip-if}, @code{dg-xfail-if} or @code{dg-xfail-run-if} to +skip whole tests based on options, or to mark them as expected to fail +with certain options. + +@item @{ no-opts @var{opt1} @dots{} @var{optn} @} +As for @code{any-opts} above, each of @var{opt1} to @var{optn} is a +space-separated list of option globs. The selector expression +evaluates to true if, for all of these strings, there is at least +one glob that does not match an option that was passed to the compiler. +It is shorthand for: + +@smallexample +@{ ! @{ any-opts @var{opt1} @dots{} @var{optn} @} @} +@end smallexample + +For example: + +@smallexample +@{ no-opts "-O3 -flto" "-O[2g]" @} +@end smallexample + +is true if all of the following are true: + +@itemize @bullet +@item +@option{-O2} was not passed to the compiler + +@item +@option{-Og} was not passed to the compiler + +@item +at least one of @option{-O3} or @option{-flto} was not passed to the compiler +@end itemize + +Like @code{any-opts}, this kind of selector can only be used within +@code{dg-final} directives. + +@end table +@end itemize + +Here are some examples of full target selectors: + +@smallexample +@{ target @{ ! "hppa*-*-* ia64*-*-*" @} @} +@{ target @{ powerpc*-*-* && lp64 @} @} +@{ xfail @{ lp64 || vect_no_align @} @} +@{ xfail @{ aarch64*-*-* && @{ any-opts "-O2" @} @} @} +@end smallexample + +@node Effective-Target Keywords +@subsection Keywords describing target attributes + +Effective-target keywords identify sets of targets that support +particular functionality. They are used to limit tests to be run only +for particular targets, or to specify that particular sets of targets +are expected to fail some tests. + +Effective-target keywords are defined in @file{lib/target-supports.exp} in +the GCC testsuite, with the exception of those that are documented as +being local to a particular test directory. + +The @samp{effective target} takes into account all of the compiler options +with which the test will be compiled, including the multilib options. +By convention, keywords ending in @code{_nocache} can also include options +specified for the particular test in an earlier @code{dg-options} or +@code{dg-add-options} directive. + +@subsubsection Endianness + +@table @code +@item be +Target uses big-endian memory order for multi-byte and multi-word data. + +@item le +Target uses little-endian memory order for multi-byte and multi-word data. +@end table + +@subsubsection Data type sizes + +@table @code +@item ilp32 +Target has 32-bit @code{int}, @code{long}, and pointers. + +@item lp64 +Target has 32-bit @code{int}, 64-bit @code{long} and pointers. + +@item llp64 +Target has 32-bit @code{int} and @code{long}, 64-bit @code{long long} +and pointers. + +@item double64 +Target has 64-bit @code{double}. + +@item double64plus +Target has @code{double} that is 64 bits or longer. + +@item longdouble128 +Target has 128-bit @code{long double}. + +@item int32plus +Target has @code{int} that is at 32 bits or longer. + +@item int16 +Target has @code{int} that is 16 bits or shorter. + +@item longlong64 +Target has 64-bit @code{long long}. + +@item long_neq_int +Target has @code{int} and @code{long} with different sizes. + +@item short_eq_int +Target has @code{short} and @code{int} with the same size. + +@item ptr_eq_short +Target has pointers (@code{void *}) and @code{short} with the same size. + +@item int_eq_float +Target has @code{int} and @code{float} with the same size. + +@item ptr_eq_long +Target has pointers (@code{void *}) and @code{long} with the same size. + +@item large_double +Target supports @code{double} that is longer than @code{float}. + +@item large_long_double +Target supports @code{long double} that is longer than @code{double}. + +@item ptr32plus +Target has pointers that are 32 bits or longer. + +@item size20plus +Target has a 20-bit or larger address space, so supports at least +16-bit array and structure sizes. + +@item size24plus +Target has a 24-bit or larger address space, so supports at least +20-bit array and structure sizes. + +@item size32plus +Target has a 32-bit or larger address space, so supports at least +24-bit array and structure sizes. + +@item 4byte_wchar_t +Target has @code{wchar_t} that is at least 4 bytes. + +@item float@var{n} +Target has the @code{_Float@var{n}} type. + +@item float@var{n}x +Target has the @code{_Float@var{n}x} type. + +@item float@var{n}_runtime +Target has the @code{_Float@var{n}} type, including runtime support +for any options added with @code{dg-add-options}. + +@item float@var{n}x_runtime +Target has the @code{_Float@var{n}x} type, including runtime support +for any options added with @code{dg-add-options}. + +@item floatn_nx_runtime +Target has runtime support for any options added with +@code{dg-add-options} for any @code{_Float@var{n}} or +@code{_Float@var{n}x} type. + +@item inf +Target supports floating point infinite (@code{inf}) for type +@code{double}. + +@item inff +Target supports floating point infinite (@code{inf}) for type +@code{float}. +@end table +@subsubsection Fortran-specific attributes + +@table @code +@item fortran_integer_16 +Target supports Fortran @code{integer} that is 16 bytes or longer. + +@item fortran_real_10 +Target supports Fortran @code{real} that is 10 bytes or longer. + +@item fortran_real_16 +Target supports Fortran @code{real} that is 16 bytes or longer. + +@item fortran_large_int +Target supports Fortran @code{integer} kinds larger than @code{integer(8)}. + +@item fortran_large_real +Target supports Fortran @code{real} kinds larger than @code{real(8)}. +@end table + +@subsubsection Vector-specific attributes + +@table @code +@item vect_align_stack_vars +The target's ABI allows stack variables to be aligned to the preferred +vector alignment. + +@item vect_avg_qi +Target supports both signed and unsigned averaging operations on vectors +of bytes. + +@item vect_mulhrs_hi +Target supports both signed and unsigned multiply-high-with-round-and-scale +operations on vectors of half-words. + +@item vect_sdiv_pow2_si +Target supports signed division by constant power-of-2 operations +on vectors of 4-byte integers. + +@item vect_condition +Target supports vector conditional operations. + +@item vect_cond_mixed +Target supports vector conditional operations where comparison operands +have different type from the value operands. + +@item vect_double +Target supports hardware vectors of @code{double}. + +@item vect_double_cond_arith +Target supports conditional addition, subtraction, multiplication, +division, minimum and maximum on vectors of @code{double}, via the +@code{cond_} optabs. + +@item vect_element_align_preferred +The target's preferred vector alignment is the same as the element +alignment. + +@item vect_float +Target supports hardware vectors of @code{float} when +@option{-funsafe-math-optimizations} is in effect. + +@item vect_float_strict +Target supports hardware vectors of @code{float} when +@option{-funsafe-math-optimizations} is not in effect. +This implies @code{vect_float}. + +@item vect_int +Target supports hardware vectors of @code{int}. + +@item vect_long +Target supports hardware vectors of @code{long}. + +@item vect_long_long +Target supports hardware vectors of @code{long long}. + +@item vect_check_ptrs +Target supports the @code{check_raw_ptrs} and @code{check_war_ptrs} +optabs on vectors. + +@item vect_fully_masked +Target supports fully-masked (also known as fully-predicated) loops, +so that vector loops can handle partial as well as full vectors. + +@item vect_masked_load +Target supports vector masked loads. + +@item vect_masked_store +Target supports vector masked stores. + +@item vect_gather_load_ifn +Target supports vector gather loads using internal functions +(rather than via built-in functions or emulation). + +@item vect_scatter_store +Target supports vector scatter stores. + +@item vect_aligned_arrays +Target aligns arrays to vector alignment boundary. + +@item vect_hw_misalign +Target supports a vector misalign access. + +@item vect_no_align +Target does not support a vector alignment mechanism. + +@item vect_peeling_profitable +Target might require to peel loops for alignment purposes. + +@item vect_no_int_min_max +Target does not support a vector min and max instruction on @code{int}. + +@item vect_no_int_add +Target does not support a vector add instruction on @code{int}. + +@item vect_no_bitwise +Target does not support vector bitwise instructions. + +@item vect_bool_cmp +Target supports comparison of @code{bool} vectors for at least one +vector length. + +@item vect_char_add +Target supports addition of @code{char} vectors for at least one +vector length. + +@item vect_char_mult +Target supports @code{vector char} multiplication. + +@item vect_short_mult +Target supports @code{vector short} multiplication. + +@item vect_int_mult +Target supports @code{vector int} multiplication. + +@item vect_long_mult +Target supports 64 bit @code{vector long} multiplication. + +@item vect_extract_even_odd +Target supports vector even/odd element extraction. + +@item vect_extract_even_odd_wide +Target supports vector even/odd element extraction of vectors with elements +@code{SImode} or larger. + +@item vect_interleave +Target supports vector interleaving. + +@item vect_strided +Target supports vector interleaving and extract even/odd. + +@item vect_strided_wide +Target supports vector interleaving and extract even/odd for wide +element types. + +@item vect_perm +Target supports vector permutation. + +@item vect_perm_byte +Target supports permutation of vectors with 8-bit elements. + +@item vect_perm_short +Target supports permutation of vectors with 16-bit elements. + +@item vect_perm3_byte +Target supports permutation of vectors with 8-bit elements, and for the +default vector length it is possible to permute: +@example +@{ a0, a1, a2, b0, b1, b2, @dots{} @} +@end example +to: +@example +@{ a0, a0, a0, b0, b0, b0, @dots{} @} +@{ a1, a1, a1, b1, b1, b1, @dots{} @} +@{ a2, a2, a2, b2, b2, b2, @dots{} @} +@end example +using only two-vector permutes, regardless of how long the sequence is. + +@item vect_perm3_int +Like @code{vect_perm3_byte}, but for 32-bit elements. + +@item vect_perm3_short +Like @code{vect_perm3_byte}, but for 16-bit elements. + +@item vect_shift +Target supports a hardware vector shift operation. + +@item vect_unaligned_possible +Target prefers vectors to have an alignment greater than element +alignment, but also allows unaligned vector accesses in some +circumstances. + +@item vect_variable_length +Target has variable-length vectors. + +@item vect64 +Target supports vectors of 64 bits. + +@item vect32 +Target supports vectors of 32 bits. + +@item vect_widen_sum_hi_to_si +Target supports a vector widening summation of @code{short} operands +into @code{int} results, or can promote (unpack) from @code{short} +to @code{int}. + +@item vect_widen_sum_qi_to_hi +Target supports a vector widening summation of @code{char} operands +into @code{short} results, or can promote (unpack) from @code{char} +to @code{short}. + +@item vect_widen_sum_qi_to_si +Target supports a vector widening summation of @code{char} operands +into @code{int} results. + +@item vect_widen_mult_qi_to_hi +Target supports a vector widening multiplication of @code{char} operands +into @code{short} results, or can promote (unpack) from @code{char} to +@code{short} and perform non-widening multiplication of @code{short}. + +@item vect_widen_mult_hi_to_si +Target supports a vector widening multiplication of @code{short} operands +into @code{int} results, or can promote (unpack) from @code{short} to +@code{int} and perform non-widening multiplication of @code{int}. + +@item vect_widen_mult_si_to_di_pattern +Target supports a vector widening multiplication of @code{int} operands +into @code{long} results. + +@item vect_sdot_qi +Target supports a vector dot-product of @code{signed char}. + +@item vect_udot_qi +Target supports a vector dot-product of @code{unsigned char}. + +@item vect_usdot_qi +Target supports a vector dot-product where one operand of the multiply is +@code{signed char} and the other of @code{unsigned char}. + +@item vect_sdot_hi +Target supports a vector dot-product of @code{signed short}. + +@item vect_udot_hi +Target supports a vector dot-product of @code{unsigned short}. + +@item vect_pack_trunc +Target supports a vector demotion (packing) of @code{short} to @code{char} +and from @code{int} to @code{short} using modulo arithmetic. + +@item vect_unpack +Target supports a vector promotion (unpacking) of @code{char} to @code{short} +and from @code{char} to @code{int}. + +@item vect_intfloat_cvt +Target supports conversion from @code{signed int} to @code{float}. + +@item vect_uintfloat_cvt +Target supports conversion from @code{unsigned int} to @code{float}. + +@item vect_floatint_cvt +Target supports conversion from @code{float} to @code{signed int}. + +@item vect_floatuint_cvt +Target supports conversion from @code{float} to @code{unsigned int}. + +@item vect_intdouble_cvt +Target supports conversion from @code{signed int} to @code{double}. + +@item vect_doubleint_cvt +Target supports conversion from @code{double} to @code{signed int}. + +@item vect_max_reduc +Target supports max reduction for vectors. + +@item vect_sizes_16B_8B +Target supports 16- and 8-bytes vectors. + +@item vect_sizes_32B_16B +Target supports 32- and 16-bytes vectors. + +@item vect_logical_reduc +Target supports AND, IOR and XOR reduction on vectors. + +@item vect_fold_extract_last +Target supports the @code{fold_extract_last} optab. + +@item vect_len_load_store +Target supports the @code{len_load} and @code{len_store} optabs. + +@item vect_partial_vectors_usage_1 +Target supports loop vectorization with partial vectors and +@code{vect-partial-vector-usage} is set to 1. + +@item vect_partial_vectors_usage_2 +Target supports loop vectorization with partial vectors and +@code{vect-partial-vector-usage} is set to 2. + +@item vect_partial_vectors +Target supports loop vectorization with partial vectors and +@code{vect-partial-vector-usage} is nonzero. + +@item vect_slp_v2qi_store_align +Target supports vectorization of 2-byte char stores with 2-byte aligned +address at plain @option{-O2}. + +@item vect_slp_v4qi_store_align +Target supports vectorization of 4-byte char stores with 4-byte aligned +address at plain @option{-O2}. + +@item vect_slp_v4qi_store_unalign +Target supports vectorization of 4-byte char stores with unaligned address +at plain @option{-O2}. + +@item struct_4char_block_move +Target supports block move for 8-byte aligned 4-byte size struct initialization. + +@item vect_slp_v4qi_store_unalign_1 +Target supports vectorization of 4-byte char stores with unaligned address +or store them with constant pool at plain @option{-O2}. + +@item struct_8char_block_move +Target supports block move for 8-byte aligned 8-byte size struct initialization. + +@item vect_slp_v8qi_store_unalign_1 +Target supports vectorization of 8-byte char stores with unaligned address +or store them with constant pool at plain @option{-O2}. + +@item struct_16char_block_move +Target supports block move for 8-byte aligned 16-byte size struct +initialization. + +@item vect_slp_v16qi_store_unalign_1 +Target supports vectorization of 16-byte char stores with unaligned address +or store them with constant pool at plain @option{-O2}. + +@item vect_slp_v2hi_store_align +Target supports vectorization of 4-byte short stores with 4-byte aligned +addressat plain @option{-O2}. + +@item vect_slp_v2hi_store_unalign +Target supports vectorization of 4-byte short stores with unaligned address +at plain @option{-O2}. + +@item vect_slp_v4hi_store_unalign +Target supports vectorization of 8-byte short stores with unaligned address +at plain @option{-O2}. + +@item vect_slp_v2si_store_align +Target supports vectorization of 8-byte int stores with 8-byte aligned address +at plain @option{-O2}. + +@item vect_slp_v4si_store_unalign +Target supports vectorization of 16-byte int stores with unaligned address +at plain @option{-O2}. +@end table + +@subsubsection Thread Local Storage attributes + +@table @code +@item tls +Target supports thread-local storage. + +@item tls_native +Target supports native (rather than emulated) thread-local storage. + +@item tls_runtime +Test system supports executing TLS executables. +@end table + +@subsubsection Decimal floating point attributes + +@table @code +@item dfp +Targets supports compiling decimal floating point extension to C. + +@item dfp_nocache +Including the options used to compile this particular test, the +target supports compiling decimal floating point extension to C. + +@item dfprt +Test system can execute decimal floating point tests. + +@item dfprt_nocache +Including the options used to compile this particular test, the +test system can execute decimal floating point tests. + +@item hard_dfp +Target generates decimal floating point instructions with current options. + +@item dfp_bid +Target uses the BID format for decimal floating point. +@end table + +@subsubsection ARM-specific attributes + +@table @code +@item arm32 +ARM target generates 32-bit code. + +@item arm_little_endian +ARM target that generates little-endian code. + +@item arm_eabi +ARM target adheres to the ABI for the ARM Architecture. + +@item arm_fp_ok +@anchor{arm_fp_ok} +ARM target defines @code{__ARM_FP} using @code{-mfloat-abi=softfp} or +equivalent options. Some multilibs may be incompatible with these +options. + +@item arm_fp_dp_ok +@anchor{arm_fp_dp_ok} +ARM target defines @code{__ARM_FP} with double-precision support using +@code{-mfloat-abi=softfp} or equivalent options. Some multilibs may +be incompatible with these options. + +@item arm_hf_eabi +ARM target adheres to the VFP and Advanced SIMD Register Arguments +variant of the ABI for the ARM Architecture (as selected with +@code{-mfloat-abi=hard}). + +@item arm_softfloat +ARM target uses emulated floating point operations. + +@item arm_hard_vfp_ok +ARM target supports @code{-mfpu=vfp -mfloat-abi=hard}. +Some multilibs may be incompatible with these options. + +@item arm_iwmmxt_ok +ARM target supports @code{-mcpu=iwmmxt}. +Some multilibs may be incompatible with this option. + +@item arm_neon +ARM target supports generating NEON instructions. + +@item arm_tune_string_ops_prefer_neon +Test CPU tune supports inlining string operations with NEON instructions. + +@item arm_neon_hw +Test system supports executing NEON instructions. + +@item arm_neonv2_hw +Test system supports executing NEON v2 instructions. + +@item arm_neon_ok +@anchor{arm_neon_ok} +ARM Target supports @code{-mfpu=neon -mfloat-abi=softfp} or compatible +options. Some multilibs may be incompatible with these options. + +@item arm_neon_ok_no_float_abi +@anchor{arm_neon_ok_no_float_abi} +ARM Target supports NEON with @code{-mfpu=neon}, but without any +-mfloat-abi= option. Some multilibs may be incompatible with this +option. + +@item arm_neonv2_ok +@anchor{arm_neonv2_ok} +ARM Target supports @code{-mfpu=neon-vfpv4 -mfloat-abi=softfp} or compatible +options. Some multilibs may be incompatible with these options. + +@item arm_fp16_ok +@anchor{arm_fp16_ok} +Target supports options to generate VFP half-precision floating-point +instructions. Some multilibs may be incompatible with these +options. This test is valid for ARM only. + +@item arm_fp16_hw +Target supports executing VFP half-precision floating-point +instructions. This test is valid for ARM only. + +@item arm_neon_fp16_ok +@anchor{arm_neon_fp16_ok} +ARM Target supports @code{-mfpu=neon-fp16 -mfloat-abi=softfp} or compatible +options, including @code{-mfp16-format=ieee} if necessary to obtain the +@code{__fp16} type. Some multilibs may be incompatible with these options. + +@item arm_neon_fp16_hw +Test system supports executing Neon half-precision float instructions. +(Implies previous.) + +@item arm_fp16_alternative_ok +ARM target supports the ARM FP16 alternative format. Some multilibs +may be incompatible with the options needed. + +@item arm_fp16_none_ok +ARM target supports specifying none as the ARM FP16 format. + +@item arm_thumb1_ok +ARM target generates Thumb-1 code for @code{-mthumb}. + +@item arm_thumb2_ok +ARM target generates Thumb-2 code for @code{-mthumb}. + +@item arm_nothumb +ARM target that is not using Thumb. + +@item arm_vfp_ok +ARM target supports @code{-mfpu=vfp -mfloat-abi=softfp}. +Some multilibs may be incompatible with these options. + +@item arm_vfp3_ok +@anchor{arm_vfp3_ok} +ARM target supports @code{-mfpu=vfp3 -mfloat-abi=softfp}. +Some multilibs may be incompatible with these options. + +@item arm_arch_v8a_hard_ok +@anchor{arm_arch_v8a_hard_ok} +The compiler is targeting @code{arm*-*-*} and can compile and assemble code +using the options @code{-march=armv8-a -mfpu=neon-fp-armv8 -mfloat-abi=hard}. +This is not enough to guarantee that linking works. + +@item arm_arch_v8a_hard_multilib +The compiler is targeting @code{arm*-*-*} and can build programs using +the options @code{-march=armv8-a -mfpu=neon-fp-armv8 -mfloat-abi=hard}. +The target can also run the resulting binaries. + +@item arm_v8_vfp_ok +ARM target supports @code{-mfpu=fp-armv8 -mfloat-abi=softfp}. +Some multilibs may be incompatible with these options. + +@item arm_v8_neon_ok +ARM target supports @code{-mfpu=neon-fp-armv8 -mfloat-abi=softfp}. +Some multilibs may be incompatible with these options. + +@item arm_v8_1a_neon_ok +@anchor{arm_v8_1a_neon_ok} +ARM target supports options to generate ARMv8.1-A Adv.SIMD instructions. +Some multilibs may be incompatible with these options. + +@item arm_v8_1a_neon_hw +ARM target supports executing ARMv8.1-A Adv.SIMD instructions. Some +multilibs may be incompatible with the options needed. Implies +arm_v8_1a_neon_ok. + +@item arm_acq_rel +ARM target supports acquire-release instructions. + +@item arm_v8_2a_fp16_scalar_ok +@anchor{arm_v8_2a_fp16_scalar_ok} +ARM target supports options to generate instructions for ARMv8.2-A and +scalar instructions from the FP16 extension. Some multilibs may be +incompatible with these options. + +@item arm_v8_2a_fp16_scalar_hw +ARM target supports executing instructions for ARMv8.2-A and scalar +instructions from the FP16 extension. Some multilibs may be +incompatible with these options. Implies arm_v8_2a_fp16_neon_ok. + +@item arm_v8_2a_fp16_neon_ok +@anchor{arm_v8_2a_fp16_neon_ok} +ARM target supports options to generate instructions from ARMv8.2-A with +the FP16 extension. Some multilibs may be incompatible with these +options. Implies arm_v8_2a_fp16_scalar_ok. + +@item arm_v8_2a_fp16_neon_hw +ARM target supports executing instructions from ARMv8.2-A with the FP16 +extension. Some multilibs may be incompatible with these options. +Implies arm_v8_2a_fp16_neon_ok and arm_v8_2a_fp16_scalar_hw. + +@item arm_v8_2a_dotprod_neon_ok +@anchor{arm_v8_2a_dotprod_neon_ok} +ARM target supports options to generate instructions from ARMv8.2-A with +the Dot Product extension. Some multilibs may be incompatible with these +options. + +@item arm_v8_2a_dotprod_neon_hw +ARM target supports executing instructions from ARMv8.2-A with the Dot +Product extension. Some multilibs may be incompatible with these options. +Implies arm_v8_2a_dotprod_neon_ok. + +@item arm_v8_2a_i8mm_neon_hw +ARM target supports executing instructions from ARMv8.2-A with the 8-bit +Matrix Multiply extension. Some multilibs may be incompatible with these +options. Implies arm_v8_2a_i8mm_ok. + +@item arm_fp16fml_neon_ok +@anchor{arm_fp16fml_neon_ok} +ARM target supports extensions to generate the @code{VFMAL} and @code{VFMLS} +half-precision floating-point instructions available from ARMv8.2-A and +onwards. Some multilibs may be incompatible with these options. + +@item arm_v8_2a_bf16_neon_ok +ARM target supports options to generate instructions from ARMv8.2-A with +the BFloat16 extension (bf16). Some multilibs may be incompatible with these +options. + +@item arm_v8_2a_i8mm_ok +ARM target supports options to generate instructions from ARMv8.2-A with +the 8-Bit Integer Matrix Multiply extension (i8mm). Some multilibs may be +incompatible with these options. + +@item arm_v8_1m_mve_ok +ARM target supports options to generate instructions from ARMv8.1-M with +the M-Profile Vector Extension (MVE). Some multilibs may be incompatible +with these options. + +@item arm_v8_1m_mve_fp_ok +ARM target supports options to generate instructions from ARMv8.1-M with +the Half-precision floating-point instructions (HP), Floating-point Extension +(FP) along with M-Profile Vector Extension (MVE). Some multilibs may be +incompatible with these options. + +@item arm_mve_hw +Test system supports executing MVE instructions. + +@item arm_v8m_main_cde +ARM target supports options to generate instructions from ARMv8-M with +the Custom Datapath Extension (CDE). Some multilibs may be incompatible +with these options. + +@item arm_v8m_main_cde_fp +ARM target supports options to generate instructions from ARMv8-M with +the Custom Datapath Extension (CDE) and floating-point (VFP). +Some multilibs may be incompatible with these options. + +@item arm_v8_1m_main_cde_mve +ARM target supports options to generate instructions from ARMv8.1-M with +the Custom Datapath Extension (CDE) and M-Profile Vector Extension (MVE). +Some multilibs may be incompatible with these options. + +@item arm_prefer_ldrd_strd +ARM target prefers @code{LDRD} and @code{STRD} instructions over +@code{LDM} and @code{STM} instructions. + +@item arm_thumb1_movt_ok +ARM target generates Thumb-1 code for @code{-mthumb} with @code{MOVW} +and @code{MOVT} instructions available. + +@item arm_thumb1_cbz_ok +ARM target generates Thumb-1 code for @code{-mthumb} with +@code{CBZ} and @code{CBNZ} instructions available. + +@item arm_divmod_simode +ARM target for which divmod transform is disabled, if it supports hardware +div instruction. + +@item arm_cmse_ok +ARM target supports ARMv8-M Security Extensions, enabled by the @code{-mcmse} +option. + +@item arm_cmse_hw +Test system supports executing CMSE instructions. + +@item arm_coproc1_ok +@anchor{arm_coproc1_ok} +ARM target supports the following coprocessor instructions: @code{CDP}, +@code{LDC}, @code{STC}, @code{MCR} and @code{MRC}. + +@item arm_coproc2_ok +@anchor{arm_coproc2_ok} +ARM target supports all the coprocessor instructions also listed as supported +in @ref{arm_coproc1_ok} in addition to the following: @code{CDP2}, @code{LDC2}, +@code{LDC2l}, @code{STC2}, @code{STC2l}, @code{MCR2} and @code{MRC2}. + +@item arm_coproc3_ok +@anchor{arm_coproc3_ok} +ARM target supports all the coprocessor instructions also listed as supported +in @ref{arm_coproc2_ok} in addition the following: @code{MCRR} and @code{MRRC}. + +@item arm_coproc4_ok +ARM target supports all the coprocessor instructions also listed as supported +in @ref{arm_coproc3_ok} in addition the following: @code{MCRR2} and @code{MRRC2}. + +@item arm_simd32_ok +@anchor{arm_simd32_ok} +ARM Target supports options suitable for accessing the SIMD32 intrinsics from +@code{arm_acle.h}. +Some multilibs may be incompatible with these options. + +@item arm_sat_ok +@anchor{arm_sat_ok} +ARM Target supports options suitable for accessing the saturation +intrinsics from @code{arm_acle.h}. +Some multilibs may be incompatible with these options. + +@item arm_dsp_ok +@anchor{arm_dsp_ok} +ARM Target supports options suitable for accessing the DSP intrinsics +from @code{arm_acle.h}. +Some multilibs may be incompatible with these options. + +@item arm_softfp_ok +@anchor{arm_softfp_ok} +ARM target supports the @code{-mfloat-abi=softfp} option. + +@item arm_hard_ok +@anchor{arm_hard_ok} +ARM target supports the @code{-mfloat-abi=hard} option. + +@item arm_mve +@anchor{arm_mve} +ARM target supports generating MVE instructions. + +@item arm_v8_1_lob_ok +@anchor{arm_v8_1_lob_ok} +ARM Target supports executing the Armv8.1-M Mainline Low Overhead Loop +instructions @code{DLS} and @code{LE}. +Some multilibs may be incompatible with these options. + +@item arm_thumb2_no_arm_v8_1_lob +ARM target where Thumb-2 is used without options but does not support +executing the Armv8.1-M Mainline Low Overhead Loop instructions +@code{DLS} and @code{LE}. + +@item arm_thumb2_ok_no_arm_v8_1_lob +ARM target generates Thumb-2 code for @code{-mthumb} but does not +support executing the Armv8.1-M Mainline Low Overhead Loop +instructions @code{DLS} and @code{LE}. + +@end table + +@subsubsection AArch64-specific attributes + +@table @code +@item aarch64_asm__ok +AArch64 assembler supports the architecture extension @code{ext} via the +@code{.arch_extension} pseudo-op. +@item aarch64_tiny +AArch64 target which generates instruction sequences for tiny memory model. +@item aarch64_small +AArch64 target which generates instruction sequences for small memory model. +@item aarch64_large +AArch64 target which generates instruction sequences for large memory model. +@item aarch64_little_endian +AArch64 target which generates instruction sequences for little endian. +@item aarch64_big_endian +AArch64 target which generates instruction sequences for big endian. +@item aarch64_small_fpic +Binutils installed on test system supports relocation types required by -fpic +for AArch64 small memory model. +@item aarch64_sve_hw +AArch64 target that is able to generate and execute SVE code (regardless of +whether it does so by default). +@item aarch64_sve128_hw +@itemx aarch64_sve256_hw +@itemx aarch64_sve512_hw +@itemx aarch64_sve1024_hw +@itemx aarch64_sve2048_hw +Like @code{aarch64_sve_hw}, but also test for an exact hardware vector length. + +@item aarch64_fjcvtzs_hw +AArch64 target that is able to generate and execute armv8.3-a FJCVTZS +instruction. +@end table + +@subsubsection MIPS-specific attributes + +@table @code +@item mips64 +MIPS target supports 64-bit instructions. + +@item nomips16 +MIPS target does not produce MIPS16 code. + +@item mips16_attribute +MIPS target can generate MIPS16 code. + +@item mips_loongson +MIPS target is a Loongson-2E or -2F target using an ABI that supports +the Loongson vector modes. + +@item mips_msa +MIPS target supports @code{-mmsa}, MIPS SIMD Architecture (MSA). + +@item mips_newabi_large_long_double +MIPS target supports @code{long double} larger than @code{double} +when using the new ABI. + +@item mpaired_single +MIPS target supports @code{-mpaired-single}. +@end table + +@subsubsection MSP430-specific attributes + +@table @code +@item msp430_small +MSP430 target has the small memory model enabled (@code{-msmall}). + +@item msp430_large +MSP430 target has the large memory model enabled (@code{-mlarge}). +@end table + +@subsubsection PowerPC-specific attributes + +@table @code + +@item dfp_hw +PowerPC target supports executing hardware DFP instructions. + +@item p8vector_hw +PowerPC target supports executing VSX instructions (ISA 2.07). + +@item powerpc64 +Test system supports executing 64-bit instructions. + +@item powerpc_altivec +PowerPC target supports AltiVec. + +@item powerpc_altivec_ok +PowerPC target supports @code{-maltivec}. + +@item powerpc_eabi_ok +PowerPC target supports @code{-meabi}. + +@item powerpc_elfv2 +PowerPC target supports @code{-mabi=elfv2}. + +@item powerpc_fprs +PowerPC target supports floating-point registers. + +@item powerpc_hard_double +PowerPC target supports hardware double-precision floating-point. + +@item powerpc_htm_ok +PowerPC target supports @code{-mhtm} + +@item powerpc_p8vector_ok +PowerPC target supports @code{-mpower8-vector} + +@item powerpc_popcntb_ok +PowerPC target supports the @code{popcntb} instruction, indicating +that this target supports @code{-mcpu=power5}. + +@item powerpc_ppu_ok +PowerPC target supports @code{-mcpu=cell}. + +@item powerpc_spe +PowerPC target supports PowerPC SPE. + +@item powerpc_spe_nocache +Including the options used to compile this particular test, the +PowerPC target supports PowerPC SPE. + +@item powerpc_spu +PowerPC target supports PowerPC SPU. + +@item powerpc_vsx_ok +PowerPC target supports @code{-mvsx}. + +@item powerpc_405_nocache +Including the options used to compile this particular test, the +PowerPC target supports PowerPC 405. + +@item ppc_recip_hw +PowerPC target supports executing reciprocal estimate instructions. + +@item vmx_hw +PowerPC target supports executing AltiVec instructions. + +@item vsx_hw +PowerPC target supports executing VSX instructions (ISA 2.06). + +@item has_arch_pwr5 +PowerPC target pre-defines macro _ARCH_PWR5 which means the @code{-mcpu} +setting is Power5 or later. + +@item has_arch_pwr6 +PowerPC target pre-defines macro _ARCH_PWR6 which means the @code{-mcpu} +setting is Power6 or later. + +@item has_arch_pwr7 +PowerPC target pre-defines macro _ARCH_PWR7 which means the @code{-mcpu} +setting is Power7 or later. + +@item has_arch_pwr8 +PowerPC target pre-defines macro _ARCH_PWR8 which means the @code{-mcpu} +setting is Power8 or later. + +@item has_arch_pwr9 +PowerPC target pre-defines macro _ARCH_PWR9 which means the @code{-mcpu} +setting is Power9 or later. +@end table + +@subsubsection RISC-V specific attributes + +@table @code + +@item rv32 +Test system has an integer register width of 32 bits. + +@item rv64 +Test system has an integer register width of 64 bits. + +@end table + +@subsubsection Other hardware attributes + +@c Please keep this table sorted alphabetically. +@table @code +@item autoincdec +Target supports autoincrement/decrement addressing. + +@item avx +Target supports compiling @code{avx} instructions. + +@item avx_runtime +Target supports the execution of @code{avx} instructions. + +@item avx2 +Target supports compiling @code{avx2} instructions. + +@item avx2_runtime +Target supports the execution of @code{avx2} instructions. + +@item avxvnni +Target supports the execution of @code{avxvnni} instructions. + +@item avx512f +Target supports compiling @code{avx512f} instructions. + +@item avx512f_runtime +Target supports the execution of @code{avx512f} instructions. + +@item avx512vp2intersect +Target supports the execution of @code{avx512vp2intersect} instructions. + +@item avxifma +Target supports the execution of @code{avxifma} instructions. + +@item avxneconvert +Target supports the execution of @code{avxneconvert} instructions. + +@item avxvnniint8 +Target supports the execution of @code{avxvnniint8} instructions. + +@item amx_tile +Target supports the execution of @code{amx-tile} instructions. + +@item amx_int8 +Target supports the execution of @code{amx-int8} instructions. + +@item amx_bf16 +Target supports the execution of @code{amx-bf16} instructions. + +@item amx_fp16 +Target supports the execution of @code{amx-fp16} instructions. + +@item cell_hw +Test system can execute AltiVec and Cell PPU instructions. + +@item cmpccxadd +Target supports the execution of @code{cmpccxadd} instructions. + +@item coldfire_fpu +Target uses a ColdFire FPU. + +@item divmod +Target supporting hardware divmod insn or divmod libcall. + +@item divmod_simode +Target supporting hardware divmod insn or divmod libcall for SImode. + +@item hard_float +Target supports FPU instructions. + +@item non_strict_align +Target does not require strict alignment. + +@item pie_copyreloc +The x86-64 target linker supports PIE with copy reloc. + +@item prefetchi +Target supports the execution of @code{prefetchi} instructions. + +@item raoint +Target supports the execution of @code{raoint} instructions. + +@item rdrand +Target supports x86 @code{rdrand} instruction. + +@item sqrt_insn +Target has a square root instruction that the compiler can generate. + +@item sse +Target supports compiling @code{sse} instructions. + +@item sse_runtime +Target supports the execution of @code{sse} instructions. + +@item sse2 +Target supports compiling @code{sse2} instructions. + +@item sse2_runtime +Target supports the execution of @code{sse2} instructions. + +@item sync_char_short +Target supports atomic operations on @code{char} and @code{short}. + +@item sync_int_long +Target supports atomic operations on @code{int} and @code{long}. + +@item ultrasparc_hw +Test environment appears to run executables on a simulator that +accepts only @code{EM_SPARC} executables and chokes on @code{EM_SPARC32PLUS} +or @code{EM_SPARCV9} executables. + +@item vect_cmdline_needed +Target requires a command line argument to enable a SIMD instruction set. + +@item xorsign +Target supports the xorsign optab expansion. + +@end table + +@subsubsection Environment attributes + +@table @code +@item c +The language for the compiler under test is C. + +@item c++ +The language for the compiler under test is C++. + +@item c99_runtime +Target provides a full C99 runtime. + +@item correct_iso_cpp_string_wchar_protos +Target @code{string.h} and @code{wchar.h} headers provide C++ required +overloads for @code{strchr} etc. functions. + +@item d_runtime +Target provides the D runtime. + +@item d_runtime_has_std_library +Target provides the D standard library (Phobos). + +@item dummy_wcsftime +Target uses a dummy @code{wcsftime} function that always returns zero. + +@item fd_truncate +Target can truncate a file from a file descriptor, as used by +@file{libgfortran/io/unix.c:fd_truncate}; i.e.@: @code{ftruncate} or +@code{chsize}. + +@item fenv +Target provides @file{fenv.h} include file. + +@item fenv_exceptions +Target supports @file{fenv.h} with all the standard IEEE exceptions +and floating-point exceptions are raised by arithmetic operations. + +@item fenv_exceptions_dfp +Target supports @file{fenv.h} with all the standard IEEE exceptions +and floating-point exceptions are raised by arithmetic operations for +decimal floating point. + +@item fileio +Target offers such file I/O library functions as @code{fopen}, +@code{fclose}, @code{tmpnam}, and @code{remove}. This is a link-time +requirement for the presence of the functions in the library; even if +they fail at runtime, the requirement is still regarded as satisfied. + +@item freestanding +Target is @samp{freestanding} as defined in section 4 of the C99 standard. +Effectively, it is a target which supports no extra headers or libraries +other than what is considered essential. + +@item gettimeofday +Target supports @code{gettimeofday}. + +@item init_priority +Target supports constructors with initialization priority arguments. + +@item inttypes_types +Target has the basic signed and unsigned types in @code{inttypes.h}. +This is for tests that GCC's notions of these types agree with those +in the header, as some systems have only @code{inttypes.h}. + +@item lax_strtofp +Target might have errors of a few ULP in string to floating-point +conversion functions and overflow is not always detected correctly by +those functions. + +@item mempcpy +Target provides @code{mempcpy} function. + +@item mmap +Target supports @code{mmap}. + +@item newlib +Target supports Newlib. + +@item newlib_nano_io +GCC was configured with @code{--enable-newlib-nano-formatted-io}, which reduces +the code size of Newlib formatted I/O functions. + +@item pow10 +Target provides @code{pow10} function. + +@item pthread +Target can compile using @code{pthread.h} with no errors or warnings. + +@item pthread_h +Target has @code{pthread.h}. + +@item run_expensive_tests +Expensive testcases (usually those that consume excessive amounts of CPU +time) should be run on this target. This can be enabled by setting the +@env{GCC_TEST_RUN_EXPENSIVE} environment variable to a non-empty string. + +@item simulator +Test system runs executables on a simulator (i.e.@: slowly) rather than +hardware (i.e.@: fast). + +@item signal +Target has @code{signal.h}. + +@item stabs +Target supports the stabs debugging format. + +@item stdint_types +Target has the basic signed and unsigned C types in @code{stdint.h}. +This will be obsolete when GCC ensures a working @code{stdint.h} for +all targets. + +@item stdint_types_mbig_endian +Target accepts the option @option{-mbig-endian} and @code{stdint.h} +can be included without error when @option{-mbig-endian} is passed. + +@item stpcpy +Target provides @code{stpcpy} function. + +@item sysconf +Target supports @code{sysconf}. + +@item trampolines +Target supports trampolines. + +@item two_plus_gigs +Target supports linking programs with 2+GiB of data. + +@item uclibc +Target supports uClibc. + +@item unwrapped +Target does not use a status wrapper. + +@item vxworks_kernel +Target is a VxWorks kernel. + +@item vxworks_rtp +Target is a VxWorks RTP. + +@item wchar +Target supports wide characters. +@end table + +@subsubsection Other attributes + +@table @code +@item R_flag_in_section +Target supports the 'R' flag in .section directive in assembly inputs. + +@item automatic_stack_alignment +Target supports automatic stack alignment. + +@item branch_cost +Target supports @option{-branch-cost=N}. + +@item cxa_atexit +Target uses @code{__cxa_atexit}. + +@item default_packed +@anchor{default_packed} +Target has packed layout of structure members by default. + +@item exceptions +Target supports exceptions. + +@item exceptions_enabled +Target supports exceptions and they are enabled in the current +testing configuration. + +@item fgraphite +Target supports Graphite optimizations. + +@item fixed_point +Target supports fixed-point extension to C. + +@item fopenacc +Target supports OpenACC via @option{-fopenacc}. + +@item fopenmp +Target supports OpenMP via @option{-fopenmp}. + +@item fpic +Target supports @option{-fpic} and @option{-fPIC}. + +@item freorder +Target supports @option{-freorder-blocks-and-partition}. + +@item fstack_protector +Target supports @option{-fstack-protector}. + +@item gas +Target uses GNU @command{as}. + +@item gc_sections +Target supports @option{--gc-sections}. + +@item gld +Target uses GNU @command{ld}. + +@item keeps_null_pointer_checks +Target keeps null pointer checks, either due to the use of +@option{-fno-delete-null-pointer-checks} or hardwired into the target. + +@item llvm_binutils +Target is using an LLVM assembler and/or linker, instead of GNU Binutils. + +@item lra +Target supports local register allocator (LRA). + +@item lto +Compiler has been configured to support link-time optimization (LTO). + +@item lto_incremental +Compiler and linker support link-time optimization relocatable linking +with @option{-r} and @option{-flto} options. + +@item naked_functions +Target supports the @code{naked} function attribute. + +@item named_sections +Target supports named sections. + +@item natural_alignment_32 +Target uses natural alignment (aligned to type size) for types of +32 bits or less. + +@item target_natural_alignment_64 +Target uses natural alignment (aligned to type size) for types of +64 bits or less. + +@item no_alignment_constraints +Target defines __BIGGEST_ALIGNMENT__=1. Hence target imposes +no alignment constraints. This is similar, but not necessarily +the same as @ref{default_packed}. Although @code{BIGGEST_FIELD_ALIGNMENT} +defaults to @code{BIGGEST_ALIGNMENT} for most targets, it is possible +for a target to set those two with different values and have different +alignment constraints for aggregate and non-aggregate types. + +@item noinit +Target supports the @code{noinit} variable attribute. + +@item nonpic +Target does not generate PIC by default. + +@item o_flag_in_section +Target supports the 'o' flag in .section directive in assembly inputs. + +@item offload_gcn +Target has been configured for OpenACC/OpenMP offloading on AMD GCN. + +@item persistent +Target supports the @code{persistent} variable attribute. + +@item pie_enabled +Target generates PIE by default. + +@item pcc_bitfield_type_matters +Target defines @code{PCC_BITFIELD_TYPE_MATTERS}. + +@item pe_aligned_commons +Target supports @option{-mpe-aligned-commons}. + +@item pie +Target supports @option{-pie}, @option{-fpie} and @option{-fPIE}. + +@item rdynamic +Target supports @option{-rdynamic}. + +@item scalar_all_fma +Target supports all four fused multiply-add optabs for both @code{float} +and @code{double}. These optabs are: @code{fma_optab}, @code{fms_optab}, +@code{fnma_optab} and @code{fnms_optab}. + +@item section_anchors +Target supports section anchors. + +@item short_enums +Target defaults to short enums. + +@item stack_size +@anchor{stack_size_et} +Target has limited stack size. The stack size limit can be obtained using the +STACK_SIZE macro defined by @ref{stack_size_ao,,@code{dg-add-options} feature +@code{stack_size}}. + +@item static +Target supports @option{-static}. + +@item static_libgfortran +Target supports statically linking @samp{libgfortran}. + +@item string_merging +Target supports merging string constants at link time. + +@item ucn +Target supports compiling and assembling UCN. + +@item ucn_nocache +Including the options used to compile this particular test, the +target supports compiling and assembling UCN. + +@item unaligned_stack +Target does not guarantee that its @code{STACK_BOUNDARY} is greater than +or equal to the required vector alignment. + +@item vector_alignment_reachable +Vector alignment is reachable for types of 32 bits or less. + +@item vector_alignment_reachable_for_64bit +Vector alignment is reachable for types of 64 bits or less. + +@item vma_equals_lma +Target generates executable with VMA equal to LMA for .data section. + +@item wchar_t_char16_t_compatible +Target supports @code{wchar_t} that is compatible with @code{char16_t}. + +@item wchar_t_char32_t_compatible +Target supports @code{wchar_t} that is compatible with @code{char32_t}. + +@item comdat_group +Target uses comdat groups. + +@item indirect_calls +Target supports indirect calls, i.e. calls where the target is not +constant. + +@item lgccjit +Target supports -lgccjit, i.e. libgccjit.so can be linked into jit tests. + +@item __OPTIMIZE__ +Optimizations are enabled (@code{__OPTIMIZE__}) per the current +compiler flags. +@end table + +@subsubsection Local to tests in @code{gcc.target/i386} + +@table @code +@item 3dnow +Target supports compiling @code{3dnow} instructions. + +@item aes +Target supports compiling @code{aes} instructions. + +@item fma4 +Target supports compiling @code{fma4} instructions. + +@item mfentry +Target supports the @code{-mfentry} option that alters the +position of profiling calls such that they precede the prologue. + +@item ms_hook_prologue +Target supports attribute @code{ms_hook_prologue}. + +@item pclmul +Target supports compiling @code{pclmul} instructions. + +@item sse3 +Target supports compiling @code{sse3} instructions. + +@item sse4 +Target supports compiling @code{sse4} instructions. + +@item sse4a +Target supports compiling @code{sse4a} instructions. + +@item ssse3 +Target supports compiling @code{ssse3} instructions. + +@item vaes +Target supports compiling @code{vaes} instructions. + +@item vpclmul +Target supports compiling @code{vpclmul} instructions. + +@item xop +Target supports compiling @code{xop} instructions. +@end table + +@subsubsection Local to tests in @code{gcc.test-framework} + +@table @code +@item no +Always returns 0. + +@item yes +Always returns 1. +@end table + +@node Add Options +@subsection Features for @code{dg-add-options} + +The supported values of @var{feature} for directive @code{dg-add-options} +are: + +@table @code +@item arm_fp +@code{__ARM_FP} definition. Only ARM targets support this feature, and only then +in certain modes; see the @ref{arm_fp_ok,,arm_fp_ok effective target +keyword}. + +@item arm_fp_dp +@code{__ARM_FP} definition with double-precision support. Only ARM +targets support this feature, and only then in certain modes; see the +@ref{arm_fp_dp_ok,,arm_fp_dp_ok effective target keyword}. + +@item arm_neon +NEON support. Only ARM targets support this feature, and only then +in certain modes; see the @ref{arm_neon_ok,,arm_neon_ok effective target +keyword}. + +@item arm_fp16 +VFP half-precision floating point support. This does not select the +FP16 format; for that, use @ref{arm_fp16_ieee,,arm_fp16_ieee} or +@ref{arm_fp16_alternative,,arm_fp16_alternative} instead. This +feature is only supported by ARM targets and then only in certain +modes; see the @ref{arm_fp16_ok,,arm_fp16_ok effective target +keyword}. + +@item arm_fp16_ieee +@anchor{arm_fp16_ieee} +ARM IEEE 754-2008 format VFP half-precision floating point support. +This feature is only supported by ARM targets and then only in certain +modes; see the @ref{arm_fp16_ok,,arm_fp16_ok effective target +keyword}. + +@item arm_fp16_alternative +@anchor{arm_fp16_alternative} +ARM Alternative format VFP half-precision floating point support. +This feature is only supported by ARM targets and then only in certain +modes; see the @ref{arm_fp16_ok,,arm_fp16_ok effective target +keyword}. + +@item arm_neon_fp16 +NEON and half-precision floating point support. Only ARM targets +support this feature, and only then in certain modes; see +the @ref{arm_neon_fp16_ok,,arm_neon_fp16_ok effective target keyword}. + +@item arm_vfp3 +arm vfp3 floating point support; see +the @ref{arm_vfp3_ok,,arm_vfp3_ok effective target keyword}. + +@item arm_arch_v8a_hard +Add options for ARMv8-A and the hard-float variant of the AAPCS, +if this is supported by the compiler; see the +@ref{arm_arch_v8a_hard_ok,,arm_arch_v8a_hard_ok} effective target keyword. + +@item arm_v8_1a_neon +Add options for ARMv8.1-A with Adv.SIMD support, if this is supported +by the target; see the @ref{arm_v8_1a_neon_ok,,arm_v8_1a_neon_ok} +effective target keyword. + +@item arm_v8_2a_fp16_scalar +Add options for ARMv8.2-A with scalar FP16 support, if this is +supported by the target; see the +@ref{arm_v8_2a_fp16_scalar_ok,,arm_v8_2a_fp16_scalar_ok} effective +target keyword. + +@item arm_v8_2a_fp16_neon +Add options for ARMv8.2-A with Adv.SIMD FP16 support, if this is +supported by the target; see the +@ref{arm_v8_2a_fp16_neon_ok,,arm_v8_2a_fp16_neon_ok} effective target +keyword. + +@item arm_v8_2a_dotprod_neon +Add options for ARMv8.2-A with Adv.SIMD Dot Product support, if this is +supported by the target; see the +@ref{arm_v8_2a_dotprod_neon_ok} effective target keyword. + +@item arm_fp16fml_neon +Add options to enable generation of the @code{VFMAL} and @code{VFMSL} +instructions, if this is supported by the target; see the +@ref{arm_fp16fml_neon_ok} effective target keyword. + +@item arm_dsp +Add options for ARM DSP intrinsics support, if this is supported by +the target; see the @ref{arm_dsp_ok,,arm_dsp_ok effective target +keyword}. + +@item bind_pic_locally +Add the target-specific flags needed to enable functions to bind +locally when using pic/PIC passes in the testsuite. + +@item float@var{n} +Add the target-specific flags needed to use the @code{_Float@var{n}} type. + +@item float@var{n}x +Add the target-specific flags needed to use the @code{_Float@var{n}x} type. + +@item ieee +Add the target-specific flags needed to enable full IEEE +compliance mode. + +@item mips16_attribute +@code{mips16} function attributes. +Only MIPS targets support this feature, and only then in certain modes. + +@item stack_size +@anchor{stack_size_ao} +Add the flags needed to define macro STACK_SIZE and set it to the stack size +limit associated with the @ref{stack_size_et,,@code{stack_size} effective +target}. + +@item sqrt_insn +Add the target-specific flags needed to enable hardware square root +instructions, if any. + +@item tls +Add the target-specific flags needed to use thread-local storage. +@end table + +@node Require Support +@subsection Variants of @code{dg-require-@var{support}} + +A few of the @code{dg-require} directives take arguments. + +@table @code +@item dg-require-iconv @var{codeset} +Skip the test if the target does not support iconv. @var{codeset} is +the codeset to convert to. + +@item dg-require-profiling @var{profopt} +Skip the test if the target does not support profiling with option +@var{profopt}. + +@item dg-require-stack-check @var{check} +Skip the test if the target does not support the @code{-fstack-check} +option. If @var{check} is @code{""}, support for @code{-fstack-check} +is checked, for @code{-fstack-check=("@var{check}")} otherwise. + +@item dg-require-stack-size @var{size} +Skip the test if the target does not support a stack size of @var{size}. + +@item dg-require-visibility @var{vis} +Skip the test if the target does not support the @code{visibility} attribute. +If @var{vis} is @code{""}, support for @code{visibility("hidden")} is +checked, for @code{visibility("@var{vis}")} otherwise. +@end table + +The original @code{dg-require} directives were defined before there +was support for effective-target keywords. The directives that do not +take arguments could be replaced with effective-target keywords. + +@table @code +@item dg-require-alias "" +Skip the test if the target does not support the @samp{alias} attribute. + +@item dg-require-ascii-locale "" +Skip the test if the host does not support an ASCII locale. + +@item dg-require-compat-dfp "" +Skip this test unless both compilers in a @file{compat} testsuite +support decimal floating point. + +@item dg-require-cxa-atexit "" +Skip the test if the target does not support @code{__cxa_atexit}. +This is equivalent to @code{dg-require-effective-target cxa_atexit}. + +@item dg-require-dll "" +Skip the test if the target does not support DLL attributes. + +@item dg-require-dot "" +Skip the test if the host does not have @command{dot}. + +@item dg-require-fork "" +Skip the test if the target does not support @code{fork}. + +@item dg-require-gc-sections "" +Skip the test if the target's linker does not support the +@code{--gc-sections} flags. +This is equivalent to @code{dg-require-effective-target gc-sections}. + +@item dg-require-host-local "" +Skip the test if the host is remote, rather than the same as the build +system. Some tests are incompatible with DejaGnu's handling of remote +hosts, which involves copying the source file to the host and compiling +it with a relative path and "@code{-o a.out}". + +@item dg-require-mkfifo "" +Skip the test if the target does not support @code{mkfifo}. + +@item dg-require-named-sections "" +Skip the test is the target does not support named sections. +This is equivalent to @code{dg-require-effective-target named_sections}. + +@item dg-require-weak "" +Skip the test if the target does not support weak symbols. + +@item dg-require-weak-override "" +Skip the test if the target does not support overriding weak symbols. +@end table + +@node Final Actions +@subsection Commands for use in @code{dg-final} + +The GCC testsuite defines the following directives to be used within +@code{dg-final}. + +@subsubsection Scan a particular file + +@table @code +@item scan-file @var{filename} @var{regexp} [@{ target/xfail @var{selector} @}] +Passes if @var{regexp} matches text in @var{filename}. +@item scan-file-not @var{filename} @var{regexp} [@{ target/xfail @var{selector} @}] +Passes if @var{regexp} does not match text in @var{filename}. +@item scan-module @var{module} @var{regexp} [@{ target/xfail @var{selector} @}] +Passes if @var{regexp} matches in Fortran module @var{module}. +@item dg-check-dot @var{filename} +Passes if @var{filename} is a valid @file{.dot} file (by running +@code{dot -Tpng} on it, and verifying the exit code is 0). +@item scan-sarif-file @var{regexp} [@{ target/xfail @var{selector} @}] +Passes if @var{regexp} matches text in the file generated by +@option{-fdiagnostics-format=sarif-file}. +@item scan-sarif-file-not @var{regexp} [@{ target/xfail @var{selector} @}] +Passes if @var{regexp} does not match text in the file generated by +@option{-fdiagnostics-format=sarif-file}. +@end table + +@subsubsection Scan the assembly output + +@table @code +@item scan-assembler @var{regex} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} matches text in the test's assembler output. + +@item scan-assembler-not @var{regex} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} does not match text in the test's assembler output. + +@item scan-assembler-times @var{regex} @var{num} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} is matched exactly @var{num} times in the test's +assembler output. + +@item scan-assembler-dem @var{regex} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} matches text in the test's demangled assembler output. + +@item scan-assembler-dem-not @var{regex} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} does not match text in the test's demangled assembler +output. + +@item scan-assembler-symbol-section @var{functions} @var{section} [@{ target/xfail @var{selector} @}] +Passes if @var{functions} are all in @var{section}. The caller needs to +allow for @code{USER_LABEL_PREFIX} and different section name conventions. + +@item scan-symbol-section @var{filename} @var{functions} @var{section} [@{ target/xfail @var{selector} @}] +Passes if @var{functions} are all in @var{section}in @var{filename}. +The same caveats as for @code{scan-assembler-symbol-section} apply. + +@item scan-hidden @var{symbol} [@{ target/xfail @var{selector} @}] +Passes if @var{symbol} is defined as a hidden symbol in the test's +assembly output. + +@item scan-not-hidden @var{symbol} [@{ target/xfail @var{selector} @}] +Passes if @var{symbol} is not defined as a hidden symbol in the test's +assembly output. + +@item check-function-bodies @var{prefix} @var{terminator} [@var{options} [@{ target/xfail @var{selector} @}]] +Looks through the source file for comments that give the expected assembly +output for selected functions. Each line of expected output starts with the +prefix string @var{prefix} and the expected output for a function as a whole +is followed by a line that starts with the string @var{terminator}. +Specifying an empty terminator is equivalent to specifying @samp{"*/"}. + +@var{options}, if specified, is a list of regular expressions, each of +which matches a full command-line option. A non-empty list prevents +the test from running unless all of the given options are present on the +command line. This can help if a source file is compiled both with +and without optimization, since it is rarely useful to check the full +function body for unoptimized code. + +The first line of the expected output for a function @var{fn} has the form: + +@smallexample +@var{prefix} @var{fn}: [@{ target/xfail @var{selector} @}] +@end smallexample + +Subsequent lines of the expected output also start with @var{prefix}. +In both cases, whitespace after @var{prefix} is not significant. + +The test discards assembly directives such as @code{.cfi_startproc} +and local label definitions such as @code{.LFB0} from the compiler's +assembly output. It then matches the result against the expected +output for a function as a single regular expression. This means that +later lines can use backslashes to refer back to @samp{(@dots{})} +captures on earlier lines. For example: + +@smallexample +/* @{ dg-final @{ check-function-bodies "**" "" "-DCHECK_ASM" @} @} */ +@dots{} +/* +** add_w0_s8_m: +** mov (z[0-9]+\.b), w0 +** add z0\.b, p0/m, z0\.b, \1 +** ret +*/ +svint8_t add_w0_s8_m (@dots{}) @{ @dots{} @} +@dots{} +/* +** add_b0_s8_m: +** mov (z[0-9]+\.b), b0 +** add z1\.b, p0/m, z1\.b, \1 +** ret +*/ +svint8_t add_b0_s8_m (@dots{}) @{ @dots{} @} +@end smallexample + +checks whether the implementations of @code{add_w0_s8_m} and +@code{add_b0_s8_m} match the regular expressions given. The test only +runs when @samp{-DCHECK_ASM} is passed on the command line. + +It is possible to create non-capturing multi-line regular expression +groups of the form @samp{(@var{a}|@var{b}|@dots{})} by putting the +@samp{(}, @samp{|} and @samp{)} on separate lines (each still using +@var{prefix}). For example: + +@smallexample +/* +** cmple_f16_tied: +** ( +** fcmge p0\.h, p0/z, z1\.h, z0\.h +** | +** fcmle p0\.h, p0/z, z0\.h, z1\.h +** ) +** ret +*/ +svbool_t cmple_f16_tied (@dots{}) @{ @dots{} @} +@end smallexample + +checks whether @code{cmple_f16_tied} is implemented by the +@code{fcmge} instruction followed by @code{ret} or by the +@code{fcmle} instruction followed by @code{ret}. The test is +still a single regular rexpression. + +A line containing just: + +@smallexample +@var{prefix} ... +@end smallexample + +stands for zero or more unmatched lines; the whitespace after +@var{prefix} is again not significant. + +@end table + +@subsubsection Scan optimization dump files + +These commands are available for @var{kind} of @code{tree}, @code{ltrans-tree}, +@code{offload-tree}, @code{rtl}, @code{offload-rtl}, @code{ipa}, and +@code{wpa-ipa}. + +@table @code +@item scan-@var{kind}-dump @var{regex} @var{suffix} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} matches text in the dump file with suffix @var{suffix}. + +@item scan-@var{kind}-dump-not @var{regex} @var{suffix} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} does not match text in the dump file with suffix +@var{suffix}. + +@item scan-@var{kind}-dump-times @var{regex} @var{num} @var{suffix} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} is found exactly @var{num} times in the dump file +with suffix @var{suffix}. + +@item scan-@var{kind}-dump-dem @var{regex} @var{suffix} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} matches demangled text in the dump file with +suffix @var{suffix}. + +@item scan-@var{kind}-dump-dem-not @var{regex} @var{suffix} [@{ target/xfail @var{selector} @}] +Passes if @var{regex} does not match demangled text in the dump file with +suffix @var{suffix}. +@end table + +The @var{suffix} argument which describes the dump file to be scanned +may contain a glob pattern that must expand to exactly one file +name. This is useful if, e.g., different pass instances are executed +depending on torture testing command-line flags, producing dump files +whose names differ only in their pass instance number suffix. For +example, to scan instances 1, 2, 3 of a tree pass ``mypass'' for +occurrences of the string ``code has been optimized'', use: +@smallexample +/* @{ dg-options "-fdump-tree-mypass" @} */ +/* @{ dg-final @{ scan-tree-dump "code has been optimized" "mypass\[1-3\]" @} @} */ +@end smallexample + + +@subsubsection Check for output files + +@table @code +@item output-exists [@{ target/xfail @var{selector} @}] +Passes if compiler output file exists. + +@item output-exists-not [@{ target/xfail @var{selector} @}] +Passes if compiler output file does not exist. + +@item scan-symbol @var{regexp} [@{ target/xfail @var{selector} @}] +Passes if the pattern is present in the final executable. + +@item scan-symbol-not @var{regexp} [@{ target/xfail @var{selector} @}] +Passes if the pattern is absent from the final executable. +@end table + +@subsubsection Checks for @command{gcov} tests + +@table @code +@item run-gcov @var{sourcefile} +Check line counts in @command{gcov} tests. + +@item run-gcov [branches] [calls] @{ @var{opts} @var{sourcefile} @} +Check branch and/or call counts, in addition to line counts, in +@command{gcov} tests. + +@item run-gcov-pytest @{ @var{sourcefile} @var{pytest_file} @} +Check output of @command{gcov} intermediate format with a pytest +script. +@end table + +@subsubsection Clean up generated test files + +Usually the test-framework removes files that were generated during +testing. If a testcase, for example, uses any dumping mechanism to +inspect a passes dump file, the testsuite recognized the dump option +passed to the tool and schedules a final cleanup to remove these files. + +There are, however, following additional cleanup directives that can be +used to annotate a testcase "manually". +@table @code +@item cleanup-coverage-files +Removes coverage data files generated for this test. + +@item cleanup-modules "@var{list-of-extra-modules}" +Removes Fortran module files generated for this test, excluding the +module names listed in keep-modules. +Cleaning up module files is usually done automatically by the testsuite +by looking at the source files and removing the modules after the test +has been executed. +@smallexample +module MoD1 +end module MoD1 +module Mod2 +end module Mod2 +module moD3 +end module moD3 +module mod4 +end module mod4 +! @{ dg-final @{ cleanup-modules "mod1 mod2" @} @} ! redundant +! @{ dg-final @{ keep-modules "mod3 mod4" @} @} +@end smallexample + +@item keep-modules "@var{list-of-modules-not-to-delete}" +Whitespace separated list of module names that should not be deleted by +cleanup-modules. +If the list of modules is empty, all modules defined in this file are kept. +@smallexample +module maybe_unneeded +end module maybe_unneeded +module keep1 +end module keep1 +module keep2 +end module keep2 +! @{ dg-final @{ keep-modules "keep1 keep2" @} @} ! just keep these two +! @{ dg-final @{ keep-modules "" @} @} ! keep all +@end smallexample + +@item dg-keep-saved-temps "@var{list-of-suffixes-not-to-delete}" +Whitespace separated list of suffixes that should not be deleted +automatically in a testcase that uses @option{-save-temps}. +@smallexample +// @{ dg-options "-save-temps -fpch-preprocess -I." @} +int main() @{ return 0; @} +// @{ dg-keep-saved-temps ".s" @} ! just keep assembler file +// @{ dg-keep-saved-temps ".s" ".i" @} ! ... and .i +// @{ dg-keep-saved-temps ".ii" ".o" @} ! or just .ii and .o +@end smallexample + +@item cleanup-profile-file +Removes profiling files generated for this test. + +@end table + +@node Ada Tests +@section Ada Language Testsuites + +The Ada testsuite includes executable tests from the ACATS +testsuite, publicly available at +@uref{http://www.ada-auth.org/acats.html}. + +These tests are integrated in the GCC testsuite in the +@file{ada/acats} directory, and +enabled automatically when running @code{make check}, assuming +the Ada language has been enabled when configuring GCC@. + +You can also run the Ada testsuite independently, using +@code{make check-ada}, or run a subset of the tests by specifying which +chapter to run, e.g.: + +@smallexample +$ make check-ada CHAPTERS="c3 c9" +@end smallexample + +The tests are organized by directory, each directory corresponding to +a chapter of the Ada Reference Manual. So for example, @file{c9} corresponds +to chapter 9, which deals with tasking features of the language. + +The tests are run using two @command{sh} scripts: @file{run_acats} and +@file{run_all.sh}. To run the tests using a simulator or a cross +target, see the small +customization section at the top of @file{run_all.sh}. + +These tests are run using the build tree: they can be run without doing +a @code{make install}. + +@node C Tests +@section C Language Testsuites + +GCC contains the following C language testsuites, in the +@file{gcc/testsuite} directory: + +@table @file +@item gcc.dg +This contains tests of particular features of the C compiler, using the +more modern @samp{dg} harness. Correctness tests for various compiler +features should go here if possible. + +Magic comments determine whether the file +is preprocessed, compiled, linked or run. In these tests, error and warning +message texts are compared against expected texts or regular expressions +given in comments. These tests are run with the options @samp{-ansi -pedantic} +unless other options are given in the test. Except as noted below they +are not run with multiple optimization options. +@item gcc.dg/compat +This subdirectory contains tests for binary compatibility using +@file{lib/compat.exp}, which in turn uses the language-independent support +(@pxref{compat Testing, , Support for testing binary compatibility}). +@item gcc.dg/cpp +This subdirectory contains tests of the preprocessor. +@item gcc.dg/debug +This subdirectory contains tests for debug formats. Tests in this +subdirectory are run for each debug format that the compiler supports. +@item gcc.dg/format +This subdirectory contains tests of the @option{-Wformat} format +checking. Tests in this directory are run with and without +@option{-DWIDE}. +@item gcc.dg/noncompile +This subdirectory contains tests of code that should not compile and +does not need any special compilation options. They are run with +multiple optimization options, since sometimes invalid code crashes +the compiler with optimization. +@item gcc.dg/special +FIXME: describe this. + +@item gcc.c-torture +This contains particular code fragments which have historically broken easily. +These tests are run with multiple optimization options, so tests for features +which only break at some optimization levels belong here. This also contains +tests to check that certain optimizations occur. It might be worthwhile to +separate the correctness tests cleanly from the code quality tests, but +it hasn't been done yet. + +@item gcc.c-torture/compat +FIXME: describe this. + +This directory should probably not be used for new tests. +@item gcc.c-torture/compile +This testsuite contains test cases that should compile, but do not +need to link or run. These test cases are compiled with several +different combinations of optimization options. All warnings are +disabled for these test cases, so this directory is not suitable if +you wish to test for the presence or absence of compiler warnings. +While special options can be set, and tests disabled on specific +platforms, by the use of @file{.x} files, mostly these test cases +should not contain platform dependencies. FIXME: discuss how defines +such as @code{STACK_SIZE} are used. +@item gcc.c-torture/execute +This testsuite contains test cases that should compile, link and run; +otherwise the same comments as for @file{gcc.c-torture/compile} apply. +@item gcc.c-torture/execute/ieee +This contains tests which are specific to IEEE floating point. +@item gcc.c-torture/unsorted +FIXME: describe this. + +This directory should probably not be used for new tests. +@item gcc.misc-tests +This directory contains C tests that require special handling. Some +of these tests have individual expect files, and others share +special-purpose expect files: + +@table @file +@item @code{bprob*.c} +Test @option{-fbranch-probabilities} using +@file{gcc.misc-tests/bprob.exp}, which +in turn uses the generic, language-independent framework +(@pxref{profopt Testing, , Support for testing profile-directed +optimizations}). + +@item @code{gcov*.c} +Test @command{gcov} output using @file{gcov.exp}, which in turn uses the +language-independent support (@pxref{gcov Testing, , Support for testing gcov}). + +@item @code{i386-pf-*.c} +Test i386-specific support for data prefetch using @file{i386-prefetch.exp}. +@end table + +@item gcc.test-framework +@table @file +@item @code{dg-*.c} +Test the testsuite itself using @file{gcc.test-framework/test-framework.exp}. +@end table + +@end table + +FIXME: merge in @file{testsuite/README.gcc} and discuss the format of +test cases and magic comments more. + +@node LTO Testing +@section Support for testing link-time optimizations + +Tests for link-time optimizations usually require multiple source files +that are compiled separately, perhaps with different sets of options. +There are several special-purpose test directives used for these tests. + +@table @code +@item @{ dg-lto-do @var{do-what-keyword} @} +@var{do-what-keyword} specifies how the test is compiled and whether +it is executed. It is one of: + +@table @code +@item assemble +Compile with @option{-c} to produce a relocatable object file. +@item link +Compile, assemble, and link to produce an executable file. +@item run +Produce and run an executable file, which is expected to return +an exit code of 0. +@end table + +The default is @code{assemble}. That can be overridden for a set of +tests by redefining @code{dg-do-what-default} within the @code{.exp} +file for those tests. + +Unlike @code{dg-do}, @code{dg-lto-do} does not support an optional +@samp{target} or @samp{xfail} list. Use @code{dg-skip-if}, +@code{dg-xfail-if}, or @code{dg-xfail-run-if}. + +@item @{ dg-lto-options @{ @{ @var{options} @} [@{ @var{options} @}] @} [@{ target @var{selector} @}]@} +This directive provides a list of one or more sets of compiler options +to override @var{LTO_OPTIONS}. Each test will be compiled and run with +each of these sets of options. + +@item @{ dg-extra-ld-options @var{options} [@{ target @var{selector} @}]@} +This directive adds @var{options} to the linker options used. + +@item @{ dg-suppress-ld-options @var{options} [@{ target @var{selector} @}]@} +This directive removes @var{options} from the set of linker options used. +@end table + +@node gcov Testing +@section Support for testing @command{gcov} + +Language-independent support for testing @command{gcov}, and for checking +that branch profiling produces expected values, is provided by the +expect file @file{lib/gcov.exp}. @command{gcov} tests also rely on procedures +in @file{lib/gcc-dg.exp} to compile and run the test program. A typical +@command{gcov} test contains the following DejaGnu commands within comments: + +@smallexample +@{ dg-options "--coverage" @} +@{ dg-do run @{ target native @} @} +@{ dg-final @{ run-gcov sourcefile @} @} +@end smallexample + +Checks of @command{gcov} output can include line counts, branch percentages, +and call return percentages. All of these checks are requested via +commands that appear in comments in the test's source file. +Commands to check line counts are processed by default. +Commands to check branch percentages and call return percentages are +processed if the @command{run-gcov} command has arguments @code{branches} +or @code{calls}, respectively. For example, the following specifies +checking both, as well as passing @option{-b} to @command{gcov}: + +@smallexample +@{ dg-final @{ run-gcov branches calls @{ -b sourcefile @} @} @} +@end smallexample + +A line count command appears within a comment on the source line +that is expected to get the specified count and has the form +@code{count(@var{cnt})}. A test should only check line counts for +lines that will get the same count for any architecture. + +Commands to check branch percentages (@code{branch}) and call +return percentages (@code{returns}) are very similar to each other. +A beginning command appears on or before the first of a range of +lines that will report the percentage, and the ending command +follows that range of lines. The beginning command can include a +list of percentages, all of which are expected to be found within +the range. A range is terminated by the next command of the same +kind. A command @code{branch(end)} or @code{returns(end)} marks +the end of a range without starting a new one. For example: + +@smallexample +if (i > 10 && j > i && j < 20) /* @r{branch(27 50 75)} */ + /* @r{branch(end)} */ + foo (i, j); +@end smallexample + +For a call return percentage, the value specified is the +percentage of calls reported to return. For a branch percentage, +the value is either the expected percentage or 100 minus that +value, since the direction of a branch can differ depending on the +target or the optimization level. + +Not all branches and calls need to be checked. A test should not +check for branches that might be optimized away or replaced with +predicated instructions. Don't check for calls inserted by the +compiler or ones that might be inlined or optimized away. + +A single test can check for combinations of line counts, branch +percentages, and call return percentages. The command to check a +line count must appear on the line that will report that count, but +commands to check branch percentages and call return percentages can +bracket the lines that report them. + +@node profopt Testing +@section Support for testing profile-directed optimizations + +The file @file{profopt.exp} provides language-independent support for +checking correct execution of a test built with profile-directed +optimization. This testing requires that a test program be built and +executed twice. The first time it is compiled to generate profile +data, and the second time it is compiled to use the data that was +generated during the first execution. The second execution is to +verify that the test produces the expected results. + +To check that the optimization actually generated better code, a +test can be built and run a third time with normal optimizations to +verify that the performance is better with the profile-directed +optimizations. @file{profopt.exp} has the beginnings of this kind +of support. + +@file{profopt.exp} provides generic support for profile-directed +optimizations. Each set of tests that uses it provides information +about a specific optimization: + +@table @code +@item tool +tool being tested, e.g., @command{gcc} + +@item profile_option +options used to generate profile data + +@item feedback_option +options used to optimize using that profile data + +@item prof_ext +suffix of profile data files + +@item PROFOPT_OPTIONS +list of options with which to run each test, similar to the lists for +torture tests + +@item @{ dg-final-generate @{ @var{local-directive} @} @} +This directive is similar to @code{dg-final}, but the +@var{local-directive} is run after the generation of profile data. + +@item @{ dg-final-use @{ @var{local-directive} @} @} +The @var{local-directive} is run after the profile data have been +used. +@end table + +@node compat Testing +@section Support for testing binary compatibility + +The file @file{compat.exp} provides language-independent support for +binary compatibility testing. It supports testing interoperability of +two compilers that follow the same ABI, or of multiple sets of +compiler options that should not affect binary compatibility. It is +intended to be used for testsuites that complement ABI testsuites. + +A test supported by this framework has three parts, each in a +separate source file: a main program and two pieces that interact +with each other to split up the functionality being tested. + +@table @file +@item @var{testname}_main.@var{suffix} +Contains the main program, which calls a function in file +@file{@var{testname}_x.@var{suffix}}. + +@item @var{testname}_x.@var{suffix} +Contains at least one call to a function in +@file{@var{testname}_y.@var{suffix}}. + +@item @var{testname}_y.@var{suffix} +Shares data with, or gets arguments from, +@file{@var{testname}_x.@var{suffix}}. +@end table + +Within each test, the main program and one functional piece are +compiled by the GCC under test. The other piece can be compiled by +an alternate compiler. If no alternate compiler is specified, +then all three source files are all compiled by the GCC under test. +You can specify pairs of sets of compiler options. The first element +of such a pair specifies options used with the GCC under test, and the +second element of the pair specifies options used with the alternate +compiler. Each test is compiled with each pair of options. + +@file{compat.exp} defines default pairs of compiler options. +These can be overridden by defining the environment variable +@env{COMPAT_OPTIONS} as: + +@smallexample +COMPAT_OPTIONS="[list [list @{@var{tst1}@} @{@var{alt1}@}] + @dots{}[list @{@var{tstn}@} @{@var{altn}@}]]" +@end smallexample + +where @var{tsti} and @var{alti} are lists of options, with @var{tsti} +used by the compiler under test and @var{alti} used by the alternate +compiler. For example, with +@code{[list [list @{-g -O0@} @{-O3@}] [list @{-fpic@} @{-fPIC -O2@}]]}, +the test is first built with @option{-g -O0} by the compiler under +test and with @option{-O3} by the alternate compiler. The test is +built a second time using @option{-fpic} by the compiler under test +and @option{-fPIC -O2} by the alternate compiler. + +An alternate compiler is specified by defining an environment +variable to be the full pathname of an installed compiler; for C +define @env{ALT_CC_UNDER_TEST}, and for C++ define +@env{ALT_CXX_UNDER_TEST}. These will be written to the +@file{site.exp} file used by DejaGnu. The default is to build each +test with the compiler under test using the first of each pair of +compiler options from @env{COMPAT_OPTIONS}. When +@env{ALT_CC_UNDER_TEST} or +@env{ALT_CXX_UNDER_TEST} is @code{same}, each test is built using +the compiler under test but with combinations of the options from +@env{COMPAT_OPTIONS}. + +To run only the C++ compatibility suite using the compiler under test +and another version of GCC using specific compiler options, do the +following from @file{@var{objdir}/gcc}: + +@smallexample +rm site.exp +make -k \ + ALT_CXX_UNDER_TEST=$@{alt_prefix@}/bin/g++ \ + COMPAT_OPTIONS="@var{lists as shown above}" \ + check-c++ \ + RUNTESTFLAGS="compat.exp" +@end smallexample + +A test that fails when the source files are compiled with different +compilers, but passes when the files are compiled with the same +compiler, demonstrates incompatibility of the generated code or +runtime support. A test that fails for the alternate compiler but +passes for the compiler under test probably tests for a bug that was +fixed in the compiler under test but is present in the alternate +compiler. + +The binary compatibility tests support a small number of test framework +commands that appear within comments in a test file. + +@table @code +@item dg-require-* +These commands can be used in @file{@var{testname}_main.@var{suffix}} +to skip the test if specific support is not available on the target. + +@item dg-options +The specified options are used for compiling this particular source +file, appended to the options from @env{COMPAT_OPTIONS}. When this +command appears in @file{@var{testname}_main.@var{suffix}} the options +are also used to link the test program. + +@item dg-xfail-if +This command can be used in a secondary source file to specify that +compilation is expected to fail for particular options on particular +targets. +@end table + +@node Torture Tests +@section Support for torture testing using multiple options + +Throughout the compiler testsuite there are several directories whose +tests are run multiple times, each with a different set of options. +These are known as torture tests. +@file{lib/torture-options.exp} defines procedures to +set up these lists: + +@table @code +@item torture-init +Initialize use of torture lists. +@item set-torture-options +Set lists of torture options to use for tests with and without loops. +Optionally combine a set of torture options with a set of other +options, as is done with Objective-C runtime options. +@item torture-finish +Finalize use of torture lists. +@end table + +The @file{.exp} file for a set of tests that use torture options must +include calls to these three procedures if: + +@itemize @bullet +@item It calls @code{gcc-dg-runtest} and overrides @var{DG_TORTURE_OPTIONS}. + +@item It calls @var{$@{tool@}}@code{-torture} or +@var{$@{tool@}}@code{-torture-execute}, where @var{tool} is @code{c}, +@code{fortran}, or @code{objc}. + +@item It calls @code{dg-pch}. +@end itemize + +It is not necessary for a @file{.exp} file that calls @code{gcc-dg-runtest} +to call the torture procedures if the tests should use the list in +@var{DG_TORTURE_OPTIONS} defined in @file{gcc-dg.exp}. + +Most uses of torture options can override the default lists by defining +@var{TORTURE_OPTIONS} or add to the default list by defining +@var{ADDITIONAL_TORTURE_OPTIONS}. Define these in a @file{.dejagnurc} +file or add them to the @file{site.exp} file; for example + +@smallexample +set ADDITIONAL_TORTURE_OPTIONS [list \ + @{ -O2 -ftree-loop-linear @} \ + @{ -O2 -fpeel-loops @} ] +@end smallexample + +@node GIMPLE Tests +@section Support for testing GIMPLE passes + +As of gcc 7, C functions can be tagged with @code{__GIMPLE} to indicate +that the function body will be GIMPLE, rather than C. The compiler requires +the option @option{-fgimple} to enable this functionality. For example: + +@smallexample +/* @{ dg-do compile @} */ +/* @{ dg-options "-O -fgimple" @} */ + +void __GIMPLE (startwith ("dse2")) foo () +@{ + int a; + +bb_2: + if (a > 4) + goto bb_3; + else + goto bb_4; + +bb_3: + a_2 = 10; + goto bb_5; + +bb_4: + a_3 = 20; + +bb_5: + a_1 = __PHI (bb_3: a_2, bb_4: a_3); + a_4 = a_1 + 4; + + return; +@} +@end smallexample + +The @code{startwith} argument indicates at which pass to begin. + +Use the dump modifier @code{-gimple} (e.g.@: @option{-fdump-tree-all-gimple}) +to make tree dumps more closely follow the format accepted by the GIMPLE +parser. + +Example DejaGnu tests of GIMPLE can be seen in the source tree at +@file{gcc/testsuite/gcc.dg/gimplefe-*.c}. + +The @code{__GIMPLE} parser is integrated with the C tokenizer and +preprocessor, so it should be possible to use macros to build out +test coverage. + +@node RTL Tests +@section Support for testing RTL passes + +As of gcc 7, C functions can be tagged with @code{__RTL} to indicate that the +function body will be RTL, rather than C. For example: + +@smallexample +double __RTL (startwith ("ira")) test (struct foo *f, const struct bar *b) +@{ + (function "test" + [...snip; various directives go in here...] + ) ;; function "test" +@} +@end smallexample + +The @code{startwith} argument indicates at which pass to begin. + +The parser expects the RTL body to be in the format emitted by this +dumping function: + +@smallexample +DEBUG_FUNCTION void +print_rtx_function (FILE *outfile, function *fn, bool compact); +@end smallexample + +when "compact" is true. So you can capture RTL in the correct format +from the debugger using: + +@smallexample +(gdb) print_rtx_function (stderr, cfun, true); +@end smallexample + +and copy and paste the output into the body of the C function. + +Example DejaGnu tests of RTL can be seen in the source tree under +@file{gcc/testsuite/gcc.dg/rtl}. + +The @code{__RTL} parser is not integrated with the C tokenizer or +preprocessor, and works simply by reading the relevant lines within +the braces. In particular, the RTL body must be on separate lines from +the enclosing braces, and the preprocessor is not usable within it. diff --git a/gcc/doc/standards.texi b/gcc/doc/standards.texi new file mode 100644 index 00000000000..f878615ca30 --- /dev/null +++ b/gcc/doc/standards.texi @@ -0,0 +1,336 @@ +@c Copyright (C) 2000-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Standards +@chapter Language Standards Supported by GCC + +For each language compiled by GCC for which there is a standard, GCC +attempts to follow one or more versions of that standard, possibly +with some exceptions, and possibly with some extensions. + +@section C Language +@cindex C standard +@cindex C standards +@cindex ANSI C standard +@cindex ANSI C +@cindex ANSI C89 +@cindex C89 +@cindex ANSI X3.159-1989 +@cindex X3.159-1989 +@cindex ISO C standard +@cindex ISO C +@cindex ISO C90 +@cindex ISO/IEC 9899 +@cindex ISO 9899 +@cindex C90 +@cindex ISO C94 +@cindex C94 +@cindex ISO C95 +@cindex C95 +@cindex ISO C99 +@cindex C99 +@cindex ISO C9X +@cindex C9X +@cindex ISO C11 +@cindex C11 +@cindex ISO C1X +@cindex C1X +@cindex ISO C17 +@cindex C17 +@cindex ISO C2X +@cindex C2X +@cindex Technical Corrigenda +@cindex TC1 +@cindex Technical Corrigendum 1 +@cindex TC2 +@cindex Technical Corrigendum 2 +@cindex TC3 +@cindex Technical Corrigendum 3 +@cindex AMD1 +@cindex freestanding implementation +@cindex freestanding environment +@cindex hosted implementation +@cindex hosted environment +@findex __STDC_HOSTED__ + +@opindex std +@opindex ansi +@opindex pedantic +@opindex pedantic-errors +The original ANSI C standard (X3.159-1989) was ratified in 1989 and +published in 1990. This standard was ratified as an ISO standard +(ISO/IEC 9899:1990) later in 1990. There were no technical +differences between these publications, although the sections of the +ANSI standard were renumbered and became clauses in the ISO standard. +The ANSI +standard, but not the ISO standard, also came with a Rationale +document. +This standard, in both its forms, is commonly known as @dfn{C89}, or +occasionally as @dfn{C90}, from the dates of ratification. +To select this standard in GCC, use one of the options +@option{-ansi}, @option{-std=c90} or @option{-std=iso9899:1990}; to obtain +all the diagnostics required by the standard, you should also specify +@option{-pedantic} (or @option{-pedantic-errors} if you want them to be +errors rather than warnings). @xref{C Dialect Options,,Options +Controlling C Dialect}. + +Errors in the 1990 ISO C standard were corrected in two Technical +Corrigenda published in 1994 and 1996. GCC does not support the +uncorrected version. + +An amendment to the 1990 standard was published in 1995. This +amendment added digraphs and @code{__STDC_VERSION__} to the language, +but otherwise concerned the library. This amendment is commonly known +as @dfn{AMD1}; the amended standard is sometimes known as @dfn{C94} or +@dfn{C95}. To select this standard in GCC, use the option +@option{-std=iso9899:199409} (with, as for other standard versions, +@option{-pedantic} to receive all required diagnostics). + +A new edition of the ISO C standard was published in 1999 as ISO/IEC +9899:1999, and is commonly known as @dfn{C99}. (While in +development, drafts of this standard version were referred to as +@dfn{C9X}.) GCC has substantially +complete support for this standard version; see +@uref{https://gcc.gnu.org/c99status.html} for details. To select this +standard, use @option{-std=c99} or @option{-std=iso9899:1999}. + +Errors in the 1999 ISO C standard were corrected in three Technical +Corrigenda published in 2001, 2004 and 2007. GCC does not support the +uncorrected version. + +A fourth version of the C standard, known as @dfn{C11}, was published +in 2011 as ISO/IEC 9899:2011. (While in development, drafts of this +standard version were referred to as @dfn{C1X}.) +GCC has substantially complete support +for this standard, enabled with @option{-std=c11} or +@option{-std=iso9899:2011}. A version with corrections integrated was +prepared in 2017 and published in 2018 as ISO/IEC 9899:2018; it is +known as @dfn{C17} and is supported with @option{-std=c17} or +@option{-std=iso9899:2017}; the corrections are also applied with +@option{-std=c11}, and the only difference between the options is the +value of @code{__STDC_VERSION__}. + +A further version of the C standard, known as @dfn{C2X}, is under +development; experimental and incomplete support for this is enabled +with @option{-std=c2x}. + +By default, GCC provides some extensions to the C language that, on +rare occasions conflict with the C standard. @xref{C +Extensions,,Extensions to the C Language Family}. +Some features that are part of the C99 standard +are accepted as extensions in C90 mode, and some features that are part +of the C11 standard are accepted as extensions in C90 and C99 modes. +Use of the +@option{-std} options listed above disables these extensions where +they conflict with the C standard version selected. You may also +select an extended version of the C language explicitly with +@option{-std=gnu90} (for C90 with GNU extensions), @option{-std=gnu99} +(for C99 with GNU extensions) or @option{-std=gnu11} (for C11 with GNU +extensions). + +The default, if no C language dialect options are given, +is @option{-std=gnu17}. + +The ISO C standard defines (in clause 4) two classes of conforming +implementation. A @dfn{conforming hosted implementation} supports the +whole standard including all the library facilities; a @dfn{conforming +freestanding implementation} is only required to provide certain +library facilities: those in @code{}, @code{}, +@code{}, and @code{}; since AMD1, also those in +@code{}; since C99, also those in @code{} and +@code{}; and since C11, also those in @code{} +and @code{}. In addition, complex types, added in C99, are not +required for freestanding implementations. + +The standard also defines two environments for programs, a +@dfn{freestanding environment}, required of all implementations and +which may not have library facilities beyond those required of +freestanding implementations, where the handling of program startup +and termination are implementation-defined; and a @dfn{hosted +environment}, which is not required, in which all the library +facilities are provided and startup is through a function @code{int +main (void)} or @code{int main (int, char *[])}. An OS kernel is an example +of a program running in a freestanding environment; +a program using the facilities of an +operating system is an example of a program running in a hosted environment. + +@opindex ffreestanding +GCC aims towards being usable as a conforming freestanding +implementation, or as the compiler for a conforming hosted +implementation. By default, it acts as the compiler for a hosted +implementation, defining @code{__STDC_HOSTED__} as @code{1} and +presuming that when the names of ISO C functions are used, they have +the semantics defined in the standard. To make it act as a conforming +freestanding implementation for a freestanding environment, use the +option @option{-ffreestanding}; it then defines +@code{__STDC_HOSTED__} to @code{0} and does not make assumptions about the +meanings of function names from the standard library, with exceptions +noted below. To build an OS kernel, you may well still need to make +your own arrangements for linking and startup. +@xref{C Dialect Options,,Options Controlling C Dialect}. + +GCC does not provide the library facilities required only of hosted +implementations, nor yet all the facilities required by C99 of +freestanding implementations on all platforms. +To use the facilities of a hosted +environment, you need to find them elsewhere (for example, in the +GNU C library). @xref{Standard Libraries,,Standard Libraries}. + +Most of the compiler support routines used by GCC are present in +@file{libgcc}, but there are a few exceptions. GCC requires the +freestanding environment provide @code{memcpy}, @code{memmove}, +@code{memset} and @code{memcmp}. +Finally, if @code{__builtin_trap} is used, and the target does +not implement the @code{trap} pattern, then GCC emits a call +to @code{abort}. + +For references to Technical Corrigenda, Rationale documents and +information concerning the history of C that is available online, see +@uref{https://gcc.gnu.org/readings.html} + +@section C++ Language + +GCC supports the original ISO C++ standard published in 1998, +and the 2011, 2014, 2017 and mostly 2020 revisions. + +The original ISO C++ standard was published as the ISO standard (ISO/IEC +14882:1998) and amended by a Technical Corrigenda published in 2003 +(ISO/IEC 14882:2003). These standards are referred to as C++98 and +C++03, respectively. GCC implements the majority of C++98 (@code{export} +is a notable exception) and most of the changes in C++03. To select +this standard in GCC, use one of the options @option{-ansi}, +@option{-std=c++98}, or @option{-std=c++03}; to obtain all the diagnostics +required by the standard, you should also specify @option{-pedantic} (or +@option{-pedantic-errors} if you want them to be errors rather than +warnings). + +A revised ISO C++ standard was published in 2011 as ISO/IEC +14882:2011, and is referred to as C++11; before its publication it was +commonly referred to as C++0x. C++11 contains several changes to the +C++ language, all of which have been implemented in GCC@. For details +see @uref{https://gcc.gnu.org/projects/@/cxx-status.html#cxx11}. +To select this standard in GCC, use the option @option{-std=c++11}. + +Another revised ISO C++ standard was published in 2014 as ISO/IEC +14882:2014, and is referred to as C++14; before its publication it was +sometimes referred to as C++1y. C++14 contains several further +changes to the C++ language, all of which have been implemented in GCC@. +For details see @uref{https://gcc.gnu.org/projects/@/cxx-status.html#cxx14}. +To select this standard in GCC, use the option @option{-std=c++14}. + +The C++ language was further revised in 2017 and ISO/IEC 14882:2017 was +published. This is referred to as C++17, and before publication was +often referred to as C++1z. GCC supports all the changes in that +specification. For further details see +@uref{https://gcc.gnu.org/projects/@/cxx-status.html#cxx17}. Use the option +@option{-std=c++17} to select this variant of C++. + +Another revised ISO C++ standard was published in 2020 as ISO/IEC +14882:2020, and is referred to as C++20; before its publication it was +sometimes referred to as C++2a. GCC supports most of the changes in the +new specification. For further details see +@uref{https://gcc.gnu.org/projects/@/cxx-status.html#cxx20}. +To select this standard in GCC, use the option @option{-std=c++20}. + +More information about the C++ standards is available on the ISO C++ +committee's web site at @uref{http://www.open-std.org/@/jtc1/@/sc22/@/wg21/}. + +To obtain all the diagnostics required by any of the standard versions +described above you should specify @option{-pedantic} +or @option{-pedantic-errors}, otherwise GCC will allow some non-ISO C++ +features as extensions. @xref{Warning Options}. + +By default, GCC also provides some additional extensions to the C++ language +that on rare occasions conflict with the C++ standard. @xref{C++ +Dialect Options,Options Controlling C++ Dialect}. Use of the +@option{-std} options listed above disables these extensions where they +they conflict with the C++ standard version selected. You may also +select an extended version of the C++ language explicitly with +@option{-std=gnu++98} (for C++98 with GNU extensions), or +@option{-std=gnu++11} (for C++11 with GNU extensions), or +@option{-std=gnu++14} (for C++14 with GNU extensions), or +@option{-std=gnu++17} (for C++17 with GNU extensions), or +@option{-std=gnu++20} (for C++20 with GNU extensions). + +The default, if +no C++ language dialect options are given, is @option{-std=gnu++17}. + +@section Objective-C and Objective-C++ Languages +@cindex Objective-C +@cindex Objective-C++ + +GCC supports ``traditional'' Objective-C (also known as ``Objective-C +1.0'') and contains support for the Objective-C exception and +synchronization syntax. It has also support for a number of +``Objective-C 2.0'' language extensions, including properties, fast +enumeration (only for Objective-C), method attributes and the +@@optional and @@required keywords in protocols. GCC supports +Objective-C++ and features available in Objective-C are also available +in Objective-C++@. + +GCC by default uses the GNU Objective-C runtime library, which is part +of GCC and is not the same as the Apple/NeXT Objective-C runtime +library used on Apple systems. There are a number of differences +documented in this manual. The options @option{-fgnu-runtime} and +@option{-fnext-runtime} allow you to switch between producing output +that works with the GNU Objective-C runtime library and output that +works with the Apple/NeXT Objective-C runtime library. + +There is no formal written standard for Objective-C or Objective-C++@. +The authoritative manual on traditional Objective-C (1.0) is +``Object-Oriented Programming and the Objective-C Language'': +@uref{http://www.gnustep.org/@/resources/@/documentation/@/ObjectivCBook.pdf} +is the original NeXTstep document. + +The Objective-C exception and synchronization syntax (that is, the +keywords @code{@@try}, @code{@@throw}, @code{@@catch}, +@code{@@finally} and @code{@@synchronized}) is +supported by GCC and is enabled with the option +@option{-fobjc-exceptions}. The syntax is briefly documented in this +manual and in the Objective-C 2.0 manuals from Apple. + +The Objective-C 2.0 language extensions and features are automatically +enabled; they include properties (via the @code{@@property}, +@code{@@synthesize} and +@code{@@dynamic keywords}), fast enumeration (not available in +Objective-C++), attributes for methods (such as @code{deprecated}, +@code{noreturn}, @code{sentinel}, @code{format}), +the @code{unused} attribute for method arguments, the +@code{@@package} keyword for instance variables and the @code{@@optional} and +@code{@@required} keywords in protocols. You can disable all these +Objective-C 2.0 language extensions with the option +@option{-fobjc-std=objc1}, which causes the compiler to recognize the +same Objective-C language syntax recognized by GCC 4.0, and to produce +an error if one of the new features is used. + +GCC has currently no support for non-fragile instance variables. + +The authoritative manual on Objective-C 2.0 is available from Apple: +@itemize +@item +@uref{https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/Introduction/Introduction.html} +@end itemize + +For more information concerning the history of Objective-C that is +available online, see @uref{https://gcc.gnu.org/readings.html} + +@section Go Language + +As of the GCC 4.7.1 release, GCC supports the Go 1 language standard, +described at @uref{https://golang.org/doc/go1}. + +@section D language + +GCC supports the D 2.0 programming language. The D language itself is +currently defined by its reference implementation and supporting language +specification, described at @uref{https://dlang.org/spec/spec.html}. + +@section References for Other Languages + +@xref{Top, GNAT Reference Manual, About This Guide, gnat_rm, +GNAT Reference Manual}, for information on standard +conformance and compatibility of the Ada compiler. + +@xref{Standards,,Standards, gfortran, The GNU Fortran Compiler}, for details +of standards supported by GNU Fortran. diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi new file mode 100644 index 00000000000..8572313b308 --- /dev/null +++ b/gcc/doc/tm.texi @@ -0,0 +1,12436 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Target Macros +@chapter Target Description Macros and Functions +@cindex machine description macros +@cindex target description macros +@cindex macros, target description +@cindex @file{tm.h} macros + +In addition to the file @file{@var{machine}.md}, a machine description +includes a C header file conventionally given the name +@file{@var{machine}.h} and a C source file named @file{@var{machine}.c}. +The header file defines numerous macros that convey the information +about the target machine that does not fit into the scheme of the +@file{.md} file. The file @file{tm.h} should be a link to +@file{@var{machine}.h}. The header file @file{config.h} includes +@file{tm.h} and most compiler source files include @file{config.h}. The +source file defines a variable @code{targetm}, which is a structure +containing pointers to functions and data relating to the target +machine. @file{@var{machine}.c} should also contain their definitions, +if they are not defined elsewhere in GCC, and other functions called +through the macros defined in the @file{.h} file. + +@menu +* Target Structure:: The @code{targetm} variable. +* Driver:: Controlling how the driver runs the compilation passes. +* Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}. +* Per-Function Data:: Defining data structures for per-function information. +* Storage Layout:: Defining sizes and alignments of data. +* Type Layout:: Defining sizes and properties of basic user data types. +* Registers:: Naming and describing the hardware registers. +* Register Classes:: Defining the classes of hardware registers. +* Stack and Calling:: Defining which way the stack grows and by how much. +* Varargs:: Defining the varargs macros. +* Trampolines:: Code set up at run time to enter a nested function. +* Library Calls:: Controlling how library routines are implicitly called. +* Addressing Modes:: Defining addressing modes valid for memory operands. +* Anchored Addresses:: Defining how @option{-fsection-anchors} should work. +* Condition Code:: Defining how insns update the condition code. +* Costs:: Defining relative costs of different operations. +* Scheduling:: Adjusting the behavior of the instruction scheduler. +* Sections:: Dividing storage into text, data, and other sections. +* PIC:: Macros for position independent code. +* Assembler Format:: Defining how to write insns and pseudo-ops to output. +* Debugging Info:: Defining the format of debugging output. +* Floating Point:: Handling floating point for cross-compilers. +* Mode Switching:: Insertion of mode-switching instructions. +* Target Attributes:: Defining target-specific uses of @code{__attribute__}. +* Emulated TLS:: Emulated TLS support. +* MIPS Coprocessors:: MIPS coprocessor support and how to customize it. +* PCH Target:: Validity checking for precompiled headers. +* C++ ABI:: Controlling C++ ABI changes. +* D Language and ABI:: Controlling D ABI changes. +* Named Address Spaces:: Adding support for named address spaces +* Misc:: Everything else. +@end menu + +@node Target Structure +@section The Global @code{targetm} Variable +@cindex target hooks +@cindex target functions + +@deftypevar {struct gcc_target} targetm +The target @file{.c} file must define the global @code{targetm} variable +which contains pointers to functions and data relating to the target +machine. The variable is declared in @file{target.h}; +@file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is +used to initialize the variable, and macros for the default initializers +for elements of the structure. The @file{.c} file should override those +macros for which the default definition is inappropriate. For example: +@smallexample +#include "target.h" +#include "target-def.h" + +/* @r{Initialize the GCC target structure.} */ + +#undef TARGET_COMP_TYPE_ATTRIBUTES +#define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes + +struct gcc_target targetm = TARGET_INITIALIZER; +@end smallexample +@end deftypevar + +Where a macro should be defined in the @file{.c} file in this manner to +form part of the @code{targetm} structure, it is documented below as a +``Target Hook'' with a prototype. Many macros will change in future +from being defined in the @file{.h} file to being part of the +@code{targetm} structure. + +Similarly, there is a @code{targetcm} variable for hooks that are +specific to front ends for C-family languages, documented as ``C +Target Hook''. This is declared in @file{c-family/c-target.h}, the +initializer @code{TARGETCM_INITIALIZER} in +@file{c-family/c-target-def.h}. If targets initialize @code{targetcm} +themselves, they should set @code{target_has_targetcm=yes} in +@file{config.gcc}; otherwise a default definition is used. + +Similarly, there is a @code{targetm_common} variable for hooks that +are shared between the compiler driver and the compilers proper, +documented as ``Common Target Hook''. This is declared in +@file{common/common-target.h}, the initializer +@code{TARGETM_COMMON_INITIALIZER} in +@file{common/common-target-def.h}. If targets initialize +@code{targetm_common} themselves, they should set +@code{target_has_targetm_common=yes} in @file{config.gcc}; otherwise a +default definition is used. + +Similarly, there is a @code{targetdm} variable for hooks that are +specific to the D language front end, documented as ``D Target Hook''. +This is declared in @file{d/d-target.h}, the initializer +@code{TARGETDM_INITIALIZER} in @file{d/d-target-def.h}. If targets +initialize @code{targetdm} themselves, they should set +@code{target_has_targetdm=yes} in @file{config.gcc}; otherwise a default +definition is used. + +@node Driver +@section Controlling the Compilation Driver, @file{gcc} +@cindex driver +@cindex controlling the compilation driver + +@c prevent bad page break with this line +You can control the compilation driver. + +@defmac DRIVER_SELF_SPECS +A list of specs for the driver itself. It should be a suitable +initializer for an array of strings, with no surrounding braces. + +The driver applies these specs to its own command line between loading +default @file{specs} files (but not command-line specified ones) and +choosing the multilib directory or running any subcommands. It +applies them in the order given, so each spec can depend on the +options added by earlier ones. It is also possible to remove options +using @samp{%<@var{option}} in the usual way. + +This macro can be useful when a port has several interdependent target +options. It provides a way of standardizing the command line so +that the other specs are easier to write. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac OPTION_DEFAULT_SPECS +A list of specs used to support configure-time default options (i.e.@: +@option{--with} options) in the driver. It should be a suitable initializer +for an array of structures, each containing two strings, without the +outermost pair of surrounding braces. + +The first item in the pair is the name of the default. This must match +the code in @file{config.gcc} for the target. The second item is a spec +to apply if a default with this name was specified. The string +@samp{%(VALUE)} in the spec will be replaced by the value of the default +everywhere it occurs. + +The driver will apply these specs to its own command line between loading +default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using +the same mechanism as @code{DRIVER_SELF_SPECS}. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CPP_SPEC +A C string constant that tells the GCC driver program options to +pass to CPP@. It can also specify how to translate options you +give to GCC into options for GCC to pass to the CPP@. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CPLUSPLUS_CPP_SPEC +This macro is just like @code{CPP_SPEC}, but is used for C++, rather +than C@. If you do not define this macro, then the value of +@code{CPP_SPEC} (if any) will be used instead. +@end defmac + +@defmac CC1_SPEC +A C string constant that tells the GCC driver program options to +pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language +front ends. +It can also specify how to translate options you give to GCC into options +for GCC to pass to front ends. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CC1PLUS_SPEC +A C string constant that tells the GCC driver program options to +pass to @code{cc1plus}. It can also specify how to translate options you +give to GCC into options for GCC to pass to the @code{cc1plus}. + +Do not define this macro if it does not need to do anything. +Note that everything defined in CC1_SPEC is already passed to +@code{cc1plus} so there is no need to duplicate the contents of +CC1_SPEC in CC1PLUS_SPEC@. +@end defmac + +@defmac ASM_SPEC +A C string constant that tells the GCC driver program options to +pass to the assembler. It can also specify how to translate options +you give to GCC into options for GCC to pass to the assembler. +See the file @file{sun3.h} for an example of this. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac ASM_FINAL_SPEC +A C string constant that tells the GCC driver program how to +run any programs which cleanup after the normal assembler. +Normally, this is not needed. See the file @file{mips.h} for +an example of this. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac AS_NEEDS_DASH_FOR_PIPED_INPUT +Define this macro, with no value, if the driver should give the assembler +an argument consisting of a single dash, @option{-}, to instruct it to +read from its standard input (which will be a pipe connected to the +output of the compiler proper). This argument is given after any +@option{-o} option specifying the name of the output file. + +If you do not define this macro, the assembler is assumed to read its +standard input if given no non-option arguments. If your assembler +cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct; +see @file{mips.h} for instance. +@end defmac + +@defmac LINK_SPEC +A C string constant that tells the GCC driver program options to +pass to the linker. It can also specify how to translate options you +give to GCC into options for GCC to pass to the linker. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac LIB_SPEC +Another C string constant used much like @code{LINK_SPEC}. The difference +between the two is that @code{LIB_SPEC} is used at the end of the +command given to the linker. + +If this macro is not defined, a default is provided that +loads the standard C library from the usual place. See @file{gcc.cc}. +@end defmac + +@defmac LIBGCC_SPEC +Another C string constant that tells the GCC driver program +how and when to place a reference to @file{libgcc.a} into the +linker command line. This constant is placed both before and after +the value of @code{LIB_SPEC}. + +If this macro is not defined, the GCC driver provides a default that +passes the string @option{-lgcc} to the linker. +@end defmac + +@defmac REAL_LIBGCC_SPEC +By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the +@code{LIBGCC_SPEC} is not directly used by the driver program but is +instead modified to refer to different versions of @file{libgcc.a} +depending on the values of the command line flags @option{-static}, +@option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On +targets where these modifications are inappropriate, define +@code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the +driver how to place a reference to @file{libgcc} on the link command +line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified. +@end defmac + +@defmac USE_LD_AS_NEEDED +A macro that controls the modifications to @code{LIBGCC_SPEC} +mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be +generated that uses @option{--as-needed} or equivalent options and the +shared @file{libgcc} in place of the +static exception handler library, when linking without any of +@code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}. +@end defmac + +@defmac LINK_EH_SPEC +If defined, this C string constant is added to @code{LINK_SPEC}. +When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects +the modifications to @code{LIBGCC_SPEC} mentioned in +@code{REAL_LIBGCC_SPEC}. +@end defmac + +@defmac STARTFILE_SPEC +Another C string constant used much like @code{LINK_SPEC}. The +difference between the two is that @code{STARTFILE_SPEC} is used at +the very beginning of the command given to the linker. + +If this macro is not defined, a default is provided that loads the +standard C startup file from the usual place. See @file{gcc.cc}. +@end defmac + +@defmac ENDFILE_SPEC +Another C string constant used much like @code{LINK_SPEC}. The +difference between the two is that @code{ENDFILE_SPEC} is used at +the very end of the command given to the linker. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac THREAD_MODEL_SPEC +GCC @code{-v} will print the thread model GCC was configured to use. +However, this doesn't work on platforms that are multilibbed on thread +models, such as AIX 4.3. On such platforms, define +@code{THREAD_MODEL_SPEC} such that it evaluates to a string without +blanks that names one of the recognized thread models. @code{%*}, the +default value of this macro, will expand to the value of +@code{thread_file} set in @file{config.gcc}. +@end defmac + +@defmac SYSROOT_SUFFIX_SPEC +Define this macro to add a suffix to the target sysroot when GCC is +configured with a sysroot. This will cause GCC to search for usr/lib, +et al, within sysroot+suffix. +@end defmac + +@defmac SYSROOT_HEADERS_SUFFIX_SPEC +Define this macro to add a headers_suffix to the target sysroot when +GCC is configured with a sysroot. This will cause GCC to pass the +updated sysroot+headers_suffix to CPP, causing it to search for +usr/include, et al, within sysroot+headers_suffix. +@end defmac + +@defmac EXTRA_SPECS +Define this macro to provide additional specifications to put in the +@file{specs} file that can be used in various specifications like +@code{CC1_SPEC}. + +The definition should be an initializer for an array of structures, +containing a string constant, that defines the specification name, and a +string constant that provides the specification. + +Do not define this macro if it does not need to do anything. + +@code{EXTRA_SPECS} is useful when an architecture contains several +related targets, which have various @code{@dots{}_SPECS} which are similar +to each other, and the maintainer would like one central place to keep +these definitions. + +For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to +define either @code{_CALL_SYSV} when the System V calling sequence is +used or @code{_CALL_AIX} when the older AIX-based calling sequence is +used. + +The @file{config/rs6000/rs6000.h} target file defines: + +@smallexample +#define EXTRA_SPECS \ + @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @}, + +#define CPP_SYS_DEFAULT "" +@end smallexample + +The @file{config/rs6000/sysv.h} target file defines: +@smallexample +#undef CPP_SPEC +#define CPP_SPEC \ +"%@{posix: -D_POSIX_SOURCE @} \ +%@{mcall-sysv: -D_CALL_SYSV @} \ +%@{!mcall-sysv: %(cpp_sysv_default) @} \ +%@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}" + +#undef CPP_SYSV_DEFAULT +#define CPP_SYSV_DEFAULT "-D_CALL_SYSV" +@end smallexample + +while the @file{config/rs6000/eabiaix.h} target file defines +@code{CPP_SYSV_DEFAULT} as: + +@smallexample +#undef CPP_SYSV_DEFAULT +#define CPP_SYSV_DEFAULT "-D_CALL_AIX" +@end smallexample +@end defmac + +@defmac LINK_LIBGCC_SPECIAL_1 +Define this macro if the driver program should find the library +@file{libgcc.a}. If you do not define this macro, the driver program will pass +the argument @option{-lgcc} to tell the linker to do the search. +@end defmac + +@defmac LINK_GCC_C_SEQUENCE_SPEC +The sequence in which libgcc and libc are specified to the linker. +By default this is @code{%G %L %G}. +@end defmac + +@defmac POST_LINK_SPEC +Define this macro to add additional steps to be executed after linker. +The default value of this macro is empty string. +@end defmac + +@defmac LINK_COMMAND_SPEC +A C string constant giving the complete command line need to execute the +linker. When you do this, you will need to update your port each time a +change is made to the link command line within @file{gcc.cc}. Therefore, +define this macro only if you need to completely redefine the command +line for invoking the linker and there is no other way to accomplish +the effect you need. Overriding this macro may be avoidable by overriding +@code{LINK_GCC_C_SEQUENCE_SPEC} instead. +@end defmac + +@deftypevr {Common Target Hook} bool TARGET_ALWAYS_STRIP_DOTDOT +True if @file{..} components should always be removed from directory names +computed relative to GCC's internal directories, false (default) if such +components should be preserved and directory names containing them passed +to other tools such as the linker. +@end deftypevr + +@defmac MULTILIB_DEFAULTS +Define this macro as a C expression for the initializer of an array of +string to tell the driver program which options are defaults for this +target and thus do not need to be handled specially when using +@code{MULTILIB_OPTIONS}. + +Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in +the target makefile fragment or if none of the options listed in +@code{MULTILIB_OPTIONS} are set by default. +@xref{Target Fragment}. +@end defmac + +@defmac RELATIVE_PREFIX_NOT_LINKDIR +Define this macro to tell @command{gcc} that it should only translate +a @option{-B} prefix into a @option{-L} linker option if the prefix +indicates an absolute file name. +@end defmac + +@defmac MD_EXEC_PREFIX +If defined, this macro is an additional prefix to try after +@code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched +when the compiler is built as a cross +compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it +to the list of directories used to find the assembler in @file{configure.ac}. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX +Define this macro as a C string constant if you wish to override the +standard choice of @code{libdir} as the default prefix to +try when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX_1 +Define this macro as a C string constant if you wish to override the +standard choice of @code{/lib} as a prefix to try after the default prefix +when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX_2 +Define this macro as a C string constant if you wish to override the +standard choice of @code{/lib} as yet another prefix to try after the +default prefix when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac MD_STARTFILE_PREFIX +If defined, this macro supplies an additional prefix to try after the +standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the +compiler is built as a cross compiler. +@end defmac + +@defmac MD_STARTFILE_PREFIX_1 +If defined, this macro supplies yet another prefix to try after the +standard prefixes. It is not searched when the compiler is built as a +cross compiler. +@end defmac + +@defmac INIT_ENVIRONMENT +Define this macro as a C string constant if you wish to set environment +variables for programs called by the driver, such as the assembler and +loader. The driver passes the value of this macro to @code{putenv} to +initialize the necessary environment variables. +@end defmac + +@defmac LOCAL_INCLUDE_DIR +Define this macro as a C string constant if you wish to override the +standard choice of @file{/usr/local/include} as the default prefix to +try when searching for local header files. @code{LOCAL_INCLUDE_DIR} +comes before @code{NATIVE_SYSTEM_HEADER_DIR} (set in +@file{config.gcc}, normally @file{/usr/include}) in the search order. + +Cross compilers do not search either @file{/usr/local/include} or its +replacement. +@end defmac + +@defmac NATIVE_SYSTEM_HEADER_COMPONENT +The ``component'' corresponding to @code{NATIVE_SYSTEM_HEADER_DIR}. +See @code{INCLUDE_DEFAULTS}, below, for the description of components. +If you do not define this macro, no component is used. +@end defmac + +@defmac INCLUDE_DEFAULTS +Define this macro if you wish to override the entire default search path +for include files. For a native compiler, the default search path +usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR}, +@code{GPLUSPLUS_INCLUDE_DIR}, and +@code{NATIVE_SYSTEM_HEADER_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR} +and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile}, +and specify private search areas for GCC@. The directory +@code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs. + +The definition should be an initializer for an array of structures. +Each array element should have four elements: the directory name (a +string constant), the component name (also a string constant), a flag +for C++-only directories, +and a flag showing that the includes in the directory don't need to be +wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of +the array with a null element. + +The component name denotes what GNU package the include file is part of, +if any, in all uppercase letters. For example, it might be @samp{GCC} +or @samp{BINUTILS}. If the package is part of a vendor-supplied +operating system, code the component name as @samp{0}. + +For example, here is the definition used for VAX/VMS: + +@smallexample +#define INCLUDE_DEFAULTS \ +@{ \ + @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \ + @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \ + @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \ + @{ ".", 0, 0, 0@}, \ + @{ 0, 0, 0, 0@} \ +@} +@end smallexample +@end defmac + +Here is the order of prefixes tried for exec files: + +@enumerate +@item +Any prefixes specified by the user with @option{-B}. + +@item +The environment variable @code{GCC_EXEC_PREFIX} or, if @code{GCC_EXEC_PREFIX} +is not set and the compiler has not been installed in the configure-time +@var{prefix}, the location in which the compiler has actually been installed. + +@item +The directories specified by the environment variable @code{COMPILER_PATH}. + +@item +The macro @code{STANDARD_EXEC_PREFIX}, if the compiler has been installed +in the configured-time @var{prefix}. + +@item +The location @file{/usr/libexec/gcc/}, but only if this is a native compiler. + +@item +The location @file{/usr/lib/gcc/}, but only if this is a native compiler. + +@item +The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native +compiler. +@end enumerate + +Here is the order of prefixes tried for startfiles: + +@enumerate +@item +Any prefixes specified by the user with @option{-B}. + +@item +The environment variable @code{GCC_EXEC_PREFIX} or its automatically determined +value based on the installed toolchain location. + +@item +The directories specified by the environment variable @code{LIBRARY_PATH} +(or port-specific name; native only, cross compilers do not use this). + +@item +The macro @code{STANDARD_EXEC_PREFIX}, but only if the toolchain is installed +in the configured @var{prefix} or this is a native compiler. + +@item +The location @file{/usr/lib/gcc/}, but only if this is a native compiler. + +@item +The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native +compiler. + +@item +The macro @code{MD_STARTFILE_PREFIX}, if defined, but only if this is a +native compiler, or we have a target system root. + +@item +The macro @code{MD_STARTFILE_PREFIX_1}, if defined, but only if this is a +native compiler, or we have a target system root. + +@item +The macro @code{STANDARD_STARTFILE_PREFIX}, with any sysroot modifications. +If this path is relative it will be prefixed by @code{GCC_EXEC_PREFIX} and +the machine suffix or @code{STANDARD_EXEC_PREFIX} and the machine suffix. + +@item +The macro @code{STANDARD_STARTFILE_PREFIX_1}, but only if this is a native +compiler, or we have a target system root. The default for this macro is +@file{/lib/}. + +@item +The macro @code{STANDARD_STARTFILE_PREFIX_2}, but only if this is a native +compiler, or we have a target system root. The default for this macro is +@file{/usr/lib/}. +@end enumerate + +@node Run-time Target +@section Run-time Target Specification +@cindex run-time target specification +@cindex predefined macros +@cindex target specifications + +@c prevent bad page break with this line +Here are run-time target specifications. + +@defmac TARGET_CPU_CPP_BUILTINS () +This function-like macro expands to a block of code that defines +built-in preprocessor macros and assertions for the target CPU, using +the functions @code{builtin_define}, @code{builtin_define_std} and +@code{builtin_assert}. When the front end +calls this macro it provides a trailing semicolon, and since it has +finished command line option processing your code can use those +results freely. + +@code{builtin_assert} takes a string in the form you pass to the +command-line option @option{-A}, such as @code{cpu=mips}, and creates +the assertion. @code{builtin_define} takes a string in the form +accepted by option @option{-D} and unconditionally defines the macro. + +@code{builtin_define_std} takes a string representing the name of an +object-like macro. If it doesn't lie in the user's namespace, +@code{builtin_define_std} defines it unconditionally. Otherwise, it +defines a version with two leading underscores, and another version +with two leading and trailing underscores, and defines the original +only if an ISO standard was not requested on the command line. For +example, passing @code{unix} defines @code{__unix}, @code{__unix__} +and possibly @code{unix}; passing @code{_mips} defines @code{__mips}, +@code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64} +defines only @code{_ABI64}. + +You can also test for the C dialect being compiled. The variable +@code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus} +or @code{clk_objective_c}. Note that if we are preprocessing +assembler, this variable will be @code{clk_c} but the function-like +macro @code{preprocessing_asm_p()} will return true, so you might want +to check for that first. If you need to check for strict ANSI, the +variable @code{flag_iso} can be used. The function-like macro +@code{preprocessing_trad_p()} can be used to check for traditional +preprocessing. +@end defmac + +@defmac TARGET_OS_CPP_BUILTINS () +Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional +and is used for the target operating system instead. +@end defmac + +@defmac TARGET_OBJFMT_CPP_BUILTINS () +Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional +and is used for the target object format. @file{elfos.h} uses this +macro to define @code{__ELF__}, so you probably do not need to define +it yourself. +@end defmac + +@deftypevar {extern int} target_flags +This variable is declared in @file{options.h}, which is included before +any target-specific headers. +@end deftypevar + +@deftypevr {Common Target Hook} int TARGET_DEFAULT_TARGET_FLAGS +This variable specifies the initial value of @code{target_flags}. +Its default setting is 0. +@end deftypevr + +@cindex optional hardware or system features +@cindex features, optional, in system conventions + +@deftypefn {Common Target Hook} bool TARGET_HANDLE_OPTION (struct gcc_options *@var{opts}, struct gcc_options *@var{opts_set}, const struct cl_decoded_option *@var{decoded}, location_t @var{loc}) +This hook is called whenever the user specifies one of the +target-specific options described by the @file{.opt} definition files +(@pxref{Options}). It has the opportunity to do some option-specific +processing and should return true if the option is valid. The default +definition does nothing but return true. + +@var{decoded} specifies the option and its arguments. @var{opts} and +@var{opts_set} are the @code{gcc_options} structures to be used for +storing option state, and @var{loc} is the location at which the +option was passed (@code{UNKNOWN_LOCATION} except for options passed +via attributes). +@end deftypefn + +@deftypefn {C Target Hook} bool TARGET_HANDLE_C_OPTION (size_t @var{code}, const char *@var{arg}, int @var{value}) +This target hook is called whenever the user specifies one of the +target-specific C language family options described by the @file{.opt} +definition files(@pxref{Options}). It has the opportunity to do some +option-specific processing and should return true if the option is +valid. The arguments are like for @code{TARGET_HANDLE_OPTION}. The +default definition does nothing but return false. + +In general, you should use @code{TARGET_HANDLE_OPTION} to handle +options. However, if processing an option requires routines that are +only available in the C (and related language) front ends, then you +should use @code{TARGET_HANDLE_C_OPTION} instead. +@end deftypefn + +@deftypefn {C Target Hook} tree TARGET_OBJC_CONSTRUCT_STRING_OBJECT (tree @var{string}) +Targets may provide a string object type that can be used within +and between C, C++ and their respective Objective-C dialects. +A string object might, for example, embed encoding and length information. +These objects are considered opaque to the compiler and handled as references. +An ideal implementation makes the composition of the string object +match that of the Objective-C @code{NSString} (@code{NXString} for GNUStep), +allowing efficient interworking between C-only and Objective-C code. +If a target implements string objects then this hook should return a +reference to such an object constructed from the normal `C' string +representation provided in @var{string}. +At present, the hook is used by Objective-C only, to obtain a + common-format string object when the target provides one. +@end deftypefn + +@deftypefn {C Target Hook} void TARGET_OBJC_DECLARE_UNRESOLVED_CLASS_REFERENCE (const char *@var{classname}) +Declare that Objective C class @var{classname} is referenced +by the current TU. +@end deftypefn + +@deftypefn {C Target Hook} void TARGET_OBJC_DECLARE_CLASS_DEFINITION (const char *@var{classname}) +Declare that Objective C class @var{classname} is defined +by the current TU. +@end deftypefn + +@deftypefn {C Target Hook} bool TARGET_STRING_OBJECT_REF_TYPE_P (const_tree @var{stringref}) +If a target implements string objects then this hook should return +@code{true} if @var{stringref} is a valid reference to such an object. +@end deftypefn + +@deftypefn {C Target Hook} void TARGET_CHECK_STRING_OBJECT_FORMAT_ARG (tree @var{format_arg}, tree @var{args_list}) +If a target implements string objects then this hook should +provide a facility to check the function arguments in @var{args_list} +against the format specifiers in @var{format_arg} where the type of +@var{format_arg} is one recognized as a valid string reference type. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE (void) +This target function is similar to the hook @code{TARGET_OPTION_OVERRIDE} +but is called when the optimize level is changed via an attribute or +pragma or when it is reset at the end of the code affected by the +attribute or pragma. It is not called at the beginning of compilation +when @code{TARGET_OPTION_OVERRIDE} is called so if you want to perform these +actions then, you should have @code{TARGET_OPTION_OVERRIDE} call +@code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE}. +@end deftypefn + +@defmac C_COMMON_OVERRIDE_OPTIONS +This is similar to the @code{TARGET_OPTION_OVERRIDE} hook +but is only used in the C +language frontends (C, Objective-C, C++, Objective-C++) and so can be +used to alter option flag variables which only exist in those +frontends. +@end defmac + +@deftypevr {Common Target Hook} {const struct default_options *} TARGET_OPTION_OPTIMIZATION_TABLE +Some machines may desire to change what optimizations are performed for +various optimization levels. This variable, if defined, describes +options to enable at particular sets of optimization levels. These +options are processed once +just after the optimization level is determined and before the remainder +of the command options have been parsed, so may be overridden by other +options passed explicitly. + +This processing is run once at program startup and when the optimization +options are changed via @code{#pragma GCC optimize} or by using the +@code{optimize} attribute. +@end deftypevr + +@deftypefn {Common Target Hook} void TARGET_OPTION_INIT_STRUCT (struct gcc_options *@var{opts}) +Set target-dependent initial values of fields in @var{opts}. +@end deftypefn + +@deftypefn {Common Target Hook} {const char *} TARGET_COMPUTE_MULTILIB (const struct switchstr *@var{switches}, int @var{n_switches}, const char *@var{multilib_dir}, const char *@var{multilib_defaults}, const char *@var{multilib_select}, const char *@var{multilib_matches}, const char *@var{multilib_exclusions}, const char *@var{multilib_reuse}) +Some targets like RISC-V might have complicated multilib reuse rules which +are hard to implement with the current multilib scheme. This hook allows +targets to override the result from the built-in multilib mechanism. +@var{switches} is the raw option list with @var{n_switches} items; +@var{multilib_dir} is the multi-lib result which is computed by the built-in +multi-lib mechanism; +@var{multilib_defaults} is the default options list for multi-lib; +@var{multilib_select} is the string containing the list of supported +multi-libs, and the option checking list. +@var{multilib_matches}, @var{multilib_exclusions}, and @var{multilib_reuse} +are corresponding to @var{MULTILIB_MATCHES}, @var{MULTILIB_EXCLUSIONS}, +and @var{MULTILIB_REUSE}. +The default definition does nothing but return @var{multilib_dir} directly. +@end deftypefn + + +@defmac SWITCHABLE_TARGET +Some targets need to switch between substantially different subtargets +during compilation. For example, the MIPS target has one subtarget for +the traditional MIPS architecture and another for MIPS16. Source code +can switch between these two subarchitectures using the @code{mips16} +and @code{nomips16} attributes. + +Such subtargets can differ in things like the set of available +registers, the set of available instructions, the costs of various +operations, and so on. GCC caches a lot of this type of information +in global variables, and recomputing them for each subtarget takes a +significant amount of time. The compiler therefore provides a facility +for maintaining several versions of the global variables and quickly +switching between them; see @file{target-globals.h} for details. + +Define this macro to 1 if your target needs this facility. The default +is 0. +@end defmac + +@deftypefn {Target Hook} bool TARGET_FLOAT_EXCEPTIONS_ROUNDING_SUPPORTED_P (void) +Returns true if the target supports IEEE 754 floating-point exceptions +and rounding modes, false otherwise. This is intended to relate to the +@code{float} and @code{double} types, but not necessarily @code{long double}. +By default, returns true if the @code{adddf3} instruction pattern is +available and false otherwise, on the assumption that hardware floating +point supports exceptions and rounding modes but software floating point +does not. +@end deftypefn + +@node Per-Function Data +@section Defining data structures for per-function information. +@cindex per-function data +@cindex data structures + +If the target needs to store information on a per-function basis, GCC +provides a macro and a couple of variables to allow this. Note, just +using statics to store the information is a bad idea, since GCC supports +nested functions, so you can be halfway through encoding one function +when another one comes along. + +GCC defines a data structure called @code{struct function} which +contains all of the data specific to an individual function. This +structure contains a field called @code{machine} whose type is +@code{struct machine_function *}, which can be used by targets to point +to their own specific data. + +If a target needs per-function specific data it should define the type +@code{struct machine_function} and also the macro @code{INIT_EXPANDERS}. +This macro should be used to initialize the function pointer +@code{init_machine_status}. This pointer is explained below. + +One typical use of per-function, target specific data is to create an +RTX to hold the register containing the function's return address. This +RTX can then be used to implement the @code{__builtin_return_address} +function, for level 0. + +Note---earlier implementations of GCC used a single data area to hold +all of the per-function information. Thus when processing of a nested +function began the old per-function data had to be pushed onto a +stack, and when the processing was finished, it had to be popped off the +stack. GCC used to provide function pointers called +@code{save_machine_status} and @code{restore_machine_status} to handle +the saving and restoring of the target specific information. Since the +single data area approach is no longer used, these pointers are no +longer supported. + +@defmac INIT_EXPANDERS +Macro called to initialize any target specific information. This macro +is called once per function, before generation of any RTL has begun. +The intention of this macro is to allow the initialization of the +function pointer @code{init_machine_status}. +@end defmac + +@deftypevar {void (*)(struct function *)} init_machine_status +If this function pointer is non-@code{NULL} it will be called once per +function, before function compilation starts, in order to allow the +target to perform any target specific initialization of the +@code{struct function} structure. It is intended that this would be +used to initialize the @code{machine} of that structure. + +@code{struct machine_function} structures are expected to be freed by GC@. +Generally, any memory that they reference must be allocated by using +GC allocation, including the structure itself. +@end deftypevar + +@node Storage Layout +@section Storage Layout +@cindex storage layout + +Note that the definitions of the macros in this table which are sizes or +alignments measured in bits do not need to be constant. They can be C +expressions that refer to static variables, such as the @code{target_flags}. +@xref{Run-time Target}. + +@defmac BITS_BIG_ENDIAN +Define this macro to have the value 1 if the most significant bit in a +byte has the lowest number; otherwise define it to have the value zero. +This means that bit-field instructions count from the most significant +bit. If the machine has no bit-field instructions, then this must still +be defined, but it doesn't matter which value it is defined to. This +macro need not be a constant. + +This macro does not affect the way structure fields are packed into +bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}. +@end defmac + +@defmac BYTES_BIG_ENDIAN +Define this macro to have the value 1 if the most significant byte in a +word has the lowest number. This macro need not be a constant. +@end defmac + +@defmac WORDS_BIG_ENDIAN +Define this macro to have the value 1 if, in a multiword object, the +most significant word has the lowest number. This applies to both +memory locations and registers; see @code{REG_WORDS_BIG_ENDIAN} if the +order of words in memory is not the same as the order in registers. This +macro need not be a constant. +@end defmac + +@defmac REG_WORDS_BIG_ENDIAN +On some machines, the order of words in a multiword object differs between +registers in memory. In such a situation, define this macro to describe +the order of words in a register. The macro @code{WORDS_BIG_ENDIAN} controls +the order of words in memory. +@end defmac + +@defmac FLOAT_WORDS_BIG_ENDIAN +Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or +@code{TFmode} floating point numbers are stored in memory with the word +containing the sign bit at the lowest address; otherwise define it to +have the value 0. This macro need not be a constant. + +You need not define this macro if the ordering is the same as for +multi-word integers. +@end defmac + +@defmac BITS_PER_WORD +Number of bits in a word. If you do not define this macro, the default +is @code{BITS_PER_UNIT * UNITS_PER_WORD}. +@end defmac + +@defmac MAX_BITS_PER_WORD +Maximum number of bits in a word. If this is undefined, the default is +@code{BITS_PER_WORD}. Otherwise, it is the constant value that is the +largest value that @code{BITS_PER_WORD} can have at run-time. +@end defmac + +@defmac UNITS_PER_WORD +Number of storage units in a word; normally the size of a general-purpose +register, a power of two from 1 or 8. +@end defmac + +@defmac MIN_UNITS_PER_WORD +Minimum number of units in a word. If this is undefined, the default is +@code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the +smallest value that @code{UNITS_PER_WORD} can have at run-time. +@end defmac + +@defmac POINTER_SIZE +Width of a pointer, in bits. You must specify a value no wider than the +width of @code{Pmode}. If it is not equal to the width of @code{Pmode}, +you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify +a value the default is @code{BITS_PER_WORD}. +@end defmac + +@defmac POINTERS_EXTEND_UNSIGNED +A C expression that determines how pointers should be extended from +@code{ptr_mode} to either @code{Pmode} or @code{word_mode}. It is +greater than zero if pointers should be zero-extended, zero if they +should be sign-extended, and negative if some other sort of conversion +is needed. In the last case, the extension is done by the target's +@code{ptr_extend} instruction. + +You need not define this macro if the @code{ptr_mode}, @code{Pmode} +and @code{word_mode} are all the same width. +@end defmac + +@defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type}) +A macro to update @var{m} and @var{unsignedp} when an object whose type +is @var{type} and which has the specified mode and signedness is to be +stored in a register. This macro is only called when @var{type} is a +scalar type. + +On most RISC machines, which only have operations that operate on a full +register, define this macro to set @var{m} to @code{word_mode} if +@var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most +cases, only integer modes should be widened because wider-precision +floating-point operations are usually more expensive than their narrower +counterparts. + +For most machines, the macro definition does not change @var{unsignedp}. +However, some machines, have instructions that preferentially handle +either signed or unsigned quantities of certain modes. For example, on +the DEC Alpha, 32-bit loads from memory and 32-bit add instructions +sign-extend the result to 64 bits. On such machines, set +@var{unsignedp} according to which kind of extension is more efficient. + +Do not define this macro if it would never modify @var{m}. +@end defmac + +@deftypefn {Target Hook} {enum flt_eval_method} TARGET_C_EXCESS_PRECISION (enum excess_precision_type @var{type}) +Return a value, with the same meaning as the C99 macro +@code{FLT_EVAL_METHOD} that describes which excess precision should be +applied. @var{type} is either @code{EXCESS_PRECISION_TYPE_IMPLICIT}, +@code{EXCESS_PRECISION_TYPE_FAST}, +@code{EXCESS_PRECISION_TYPE_STANDARD}, or +@code{EXCESS_PRECISION_TYPE_FLOAT16}. For +@code{EXCESS_PRECISION_TYPE_IMPLICIT}, the target should return which +precision and range operations will be implictly evaluated in regardless +of the excess precision explicitly added. For +@code{EXCESS_PRECISION_TYPE_STANDARD}, +@code{EXCESS_PRECISION_TYPE_FLOAT16}, and +@code{EXCESS_PRECISION_TYPE_FAST}, the target should return the +explicit excess precision that should be added depending on the +value set for @option{-fexcess-precision=@r{[}standard@r{|}fast@r{|}16@r{]}}. +Note that unpredictable explicit excess precision does not make sense, +so a target should never return @code{FLT_EVAL_METHOD_UNPREDICTABLE} +when @var{type} is @code{EXCESS_PRECISION_TYPE_STANDARD}, +@code{EXCESS_PRECISION_TYPE_FLOAT16} or +@code{EXCESS_PRECISION_TYPE_FAST}. +@end deftypefn +Return a value, with the same meaning as the C99 macro +@code{FLT_EVAL_METHOD} that describes which excess precision should be +applied. + +@deftypefn {Target Hook} machine_mode TARGET_PROMOTE_FUNCTION_MODE (const_tree @var{type}, machine_mode @var{mode}, int *@var{punsignedp}, const_tree @var{funtype}, int @var{for_return}) +Like @code{PROMOTE_MODE}, but it is applied to outgoing function arguments or +function return values. The target hook should return the new mode +and possibly change @code{*@var{punsignedp}} if the promotion should +change signedness. This function is called only for scalar @emph{or +pointer} types. + +@var{for_return} allows to distinguish the promotion of arguments and +return values. If it is @code{1}, a return value is being promoted and +@code{TARGET_FUNCTION_VALUE} must perform the same promotions done here. +If it is @code{2}, the returned mode should be that of the register in +which an incoming parameter is copied, or the outgoing result is computed; +then the hook should return the same mode as @code{promote_mode}, though +the signedness may be different. + +@var{type} can be NULL when promoting function arguments of libcalls. + +The default is to not promote arguments and return values. You can +also define the hook to @code{default_promote_function_mode_always_promote} +if you would like to apply the same rules given by @code{PROMOTE_MODE}. +@end deftypefn + +@defmac PARM_BOUNDARY +Normal alignment required for function parameters on the stack, in +bits. All stack parameters receive at least this much alignment +regardless of data type. On most machines, this is the same as the +size of an integer. +@end defmac + +@defmac STACK_BOUNDARY +Define this macro to the minimum alignment enforced by hardware for the +stack pointer on this machine. The definition is a C expression for the +desired alignment (measured in bits). This value is used as a default +if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines, +this should be the same as @code{PARM_BOUNDARY}. +@end defmac + +@defmac PREFERRED_STACK_BOUNDARY +Define this macro if you wish to preserve a certain alignment for the +stack pointer, greater than what the hardware enforces. The definition +is a C expression for the desired alignment (measured in bits). This +macro must evaluate to a value equal to or larger than +@code{STACK_BOUNDARY}. +@end defmac + +@defmac INCOMING_STACK_BOUNDARY +Define this macro if the incoming stack boundary may be different +from @code{PREFERRED_STACK_BOUNDARY}. This macro must evaluate +to a value equal to or larger than @code{STACK_BOUNDARY}. +@end defmac + +@defmac FUNCTION_BOUNDARY +Alignment required for a function entry point, in bits. +@end defmac + +@defmac BIGGEST_ALIGNMENT +Biggest alignment that any data type can require on this machine, in +bits. Note that this is not the biggest alignment that is supported, +just the biggest alignment that, when violated, may cause a fault. +@end defmac + +@deftypevr {Target Hook} HOST_WIDE_INT TARGET_ABSOLUTE_BIGGEST_ALIGNMENT +If defined, this target hook specifies the absolute biggest alignment +that a type or variable can have on this machine, otherwise, +@code{BIGGEST_ALIGNMENT} is used. +@end deftypevr + +@defmac MALLOC_ABI_ALIGNMENT +Alignment, in bits, a C conformant malloc implementation has to +provide. If not defined, the default value is @code{BITS_PER_WORD}. +@end defmac + +@defmac ATTRIBUTE_ALIGNED_VALUE +Alignment used by the @code{__attribute__ ((aligned))} construct. If +not defined, the default value is @code{BIGGEST_ALIGNMENT}. +@end defmac + +@defmac MINIMUM_ATOMIC_ALIGNMENT +If defined, the smallest alignment, in bits, that can be given to an +object that can be referenced in one operation, without disturbing any +nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger +on machines that don't have byte or half-word store operations. +@end defmac + +@defmac BIGGEST_FIELD_ALIGNMENT +Biggest alignment that any structure or union field can require on this +machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for +structure and union fields only, unless the field alignment has been set +by the @code{__attribute__ ((aligned (@var{n})))} construct. +@end defmac + +@defmac ADJUST_FIELD_ALIGN (@var{field}, @var{type}, @var{computed}) +An expression for the alignment of a structure field @var{field} of +type @var{type} if the alignment computed in the usual way (including +applying of @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the +alignment) is @var{computed}. It overrides alignment only if the +field alignment has not been set by the +@code{__attribute__ ((aligned (@var{n})))} construct. Note that @var{field} +may be @code{NULL_TREE} in case we just query for the minimum alignment +of a field of type @var{type} in structure context. +@end defmac + +@defmac MAX_STACK_ALIGNMENT +Biggest stack alignment guaranteed by the backend. Use this macro +to specify the maximum alignment of a variable on stack. + +If not defined, the default value is @code{STACK_BOUNDARY}. + +@c FIXME: The default should be @code{PREFERRED_STACK_BOUNDARY}. +@c But the fix for PR 32893 indicates that we can only guarantee +@c maximum stack alignment on stack up to @code{STACK_BOUNDARY}, not +@c @code{PREFERRED_STACK_BOUNDARY}, if stack alignment isn't supported. +@end defmac + +@defmac MAX_OFILE_ALIGNMENT +Biggest alignment supported by the object file format of this machine. +Use this macro to limit the alignment which can be specified using the +@code{__attribute__ ((aligned (@var{n})))} construct for functions and +objects with static storage duration. The alignment of automatic +objects may exceed the object file format maximum up to the maximum +supported by GCC. If not defined, the default value is +@code{BIGGEST_ALIGNMENT}. + +On systems that use ELF, the default (in @file{config/elfos.h}) is +the largest supported 32-bit ELF section alignment representable on +a 32-bit host e.g.@: @samp{(((uint64_t) 1 << 28) * 8)}. +On 32-bit ELF the largest supported section alignment in bits is +@samp{(0x80000000 * 8)}, but this is not representable on 32-bit hosts. +@end defmac + +@deftypefn {Target Hook} void TARGET_LOWER_LOCAL_DECL_ALIGNMENT (tree @var{decl}) +Define this hook to lower alignment of local, parm or result +decl @samp{(@var{decl})}. +@end deftypefn + +@deftypefn {Target Hook} HOST_WIDE_INT TARGET_STATIC_RTX_ALIGNMENT (machine_mode @var{mode}) +This hook returns the preferred alignment in bits for a +statically-allocated rtx, such as a constant pool entry. @var{mode} +is the mode of the rtx. The default implementation returns +@samp{GET_MODE_ALIGNMENT (@var{mode})}. +@end deftypefn + +@defmac DATA_ALIGNMENT (@var{type}, @var{basic-align}) +If defined, a C expression to compute the alignment for a variable in +the static store. @var{type} is the data type, and @var{basic-align} is +the alignment that the object would ordinarily have. The value of this +macro is used instead of that alignment to align the object. + +If this macro is not defined, then @var{basic-align} is used. + +@findex strcpy +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. Another is to cause character +arrays to be word-aligned so that @code{strcpy} calls that copy +constants to character arrays can be done inline. +@end defmac + +@defmac DATA_ABI_ALIGNMENT (@var{type}, @var{basic-align}) +Similar to @code{DATA_ALIGNMENT}, but for the cases where the ABI mandates +some alignment increase, instead of optimization only purposes. E.g.@ +AMD x86-64 psABI says that variables with array type larger than 15 bytes +must be aligned to 16 byte boundaries. + +If this macro is not defined, then @var{basic-align} is used. +@end defmac + +@deftypefn {Target Hook} HOST_WIDE_INT TARGET_CONSTANT_ALIGNMENT (const_tree @var{constant}, HOST_WIDE_INT @var{basic_align}) +This hook returns the alignment in bits of a constant that is being +placed in memory. @var{constant} is the constant and @var{basic_align} +is the alignment that the object would ordinarily have. + +The default definition just returns @var{basic_align}. + +The typical use of this hook is to increase alignment for string +constants to be word aligned so that @code{strcpy} calls that copy +constants can be done inline. The function +@code{constant_alignment_word_strings} provides such a definition. +@end deftypefn + +@defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align}) +If defined, a C expression to compute the alignment for a variable in +the local store. @var{type} is the data type, and @var{basic-align} is +the alignment that the object would ordinarily have. The value of this +macro is used instead of that alignment to align the object. + +If this macro is not defined, then @var{basic-align} is used. + +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. + +If the value of this macro has a type, it should be an unsigned type. +@end defmac + +@deftypefn {Target Hook} HOST_WIDE_INT TARGET_VECTOR_ALIGNMENT (const_tree @var{type}) +This hook can be used to define the alignment for a vector of type +@var{type}, in order to comply with a platform ABI. The default is to +require natural alignment for vector types. The alignment returned by +this hook must be a power-of-two multiple of the default alignment of +the vector element type. +@end deftypefn + +@defmac STACK_SLOT_ALIGNMENT (@var{type}, @var{mode}, @var{basic-align}) +If defined, a C expression to compute the alignment for stack slot. +@var{type} is the data type, @var{mode} is the widest mode available, +and @var{basic-align} is the alignment that the slot would ordinarily +have. The value of this macro is used instead of that alignment to +align the slot. + +If this macro is not defined, then @var{basic-align} is used when +@var{type} is @code{NULL}. Otherwise, @code{LOCAL_ALIGNMENT} will +be used. + +This macro is to set alignment of stack slot to the maximum alignment +of all possible modes which the slot may have. + +If the value of this macro has a type, it should be an unsigned type. +@end defmac + +@defmac LOCAL_DECL_ALIGNMENT (@var{decl}) +If defined, a C expression to compute the alignment for a local +variable @var{decl}. + +If this macro is not defined, then +@code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))} +is used. + +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. + +If the value of this macro has a type, it should be an unsigned type. +@end defmac + +@defmac MINIMUM_ALIGNMENT (@var{exp}, @var{mode}, @var{align}) +If defined, a C expression to compute the minimum required alignment +for dynamic stack realignment purposes for @var{exp} (a type or decl), +@var{mode}, assuming normal alignment @var{align}. + +If this macro is not defined, then @var{align} will be used. +@end defmac + +@defmac EMPTY_FIELD_BOUNDARY +Alignment in bits to be given to a structure bit-field that follows an +empty field such as @code{int : 0;}. + +If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro. +@end defmac + +@defmac STRUCTURE_SIZE_BOUNDARY +Number of bits which any structure or union's size must be a multiple of. +Each structure or union's size is rounded up to a multiple of this. + +If you do not define this macro, the default is the same as +@code{BITS_PER_UNIT}. +@end defmac + +@defmac STRICT_ALIGNMENT +Define this macro to be the value 1 if instructions will fail to work +if given data not on the nominal alignment. If instructions will merely +go slower in that case, define this macro as 0. +@end defmac + +@defmac PCC_BITFIELD_TYPE_MATTERS +Define this if you wish to imitate the way many other C compilers handle +alignment of bit-fields and the structures that contain them. + +The behavior is that the type written for a named bit-field (@code{int}, +@code{short}, or other integer type) imposes an alignment for the entire +structure, as if the structure really did contain an ordinary field of +that type. In addition, the bit-field is placed within the structure so +that it would fit within such a field, not crossing a boundary for it. + +Thus, on most machines, a named bit-field whose type is written as +@code{int} would not cross a four-byte boundary, and would force +four-byte alignment for the whole structure. (The alignment used may +not be four bytes; it is controlled by the other alignment parameters.) + +An unnamed bit-field will not affect the alignment of the containing +structure. + +If the macro is defined, its definition should be a C expression; +a nonzero value for the expression enables this behavior. + +Note that if this macro is not defined, or its value is zero, some +bit-fields may cross more than one alignment boundary. The compiler can +support such references if there are @samp{insv}, @samp{extv}, and +@samp{extzv} insns that can directly reference memory. + +The other known way of making bit-fields work is to define +@code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}. +Then every structure can be accessed with fullwords. + +Unless the machine has bit-field instructions or you define +@code{STRUCTURE_SIZE_BOUNDARY} that way, you must define +@code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value. + +If your aim is to make GCC use the same conventions for laying out +bit-fields as are used by another compiler, here is how to investigate +what the other compiler does. Compile and run this program: + +@smallexample +struct foo1 +@{ + char x; + char :0; + char y; +@}; + +struct foo2 +@{ + char x; + int :0; + char y; +@}; + +main () +@{ + printf ("Size of foo1 is %d\n", + sizeof (struct foo1)); + printf ("Size of foo2 is %d\n", + sizeof (struct foo2)); + exit (0); +@} +@end smallexample + +If this prints 2 and 5, then the compiler's behavior is what you would +get from @code{PCC_BITFIELD_TYPE_MATTERS}. +@end defmac + +@defmac BITFIELD_NBYTES_LIMITED +Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited +to aligning a bit-field within the structure. +@end defmac + +@deftypefn {Target Hook} bool TARGET_ALIGN_ANON_BITFIELD (void) +When @code{PCC_BITFIELD_TYPE_MATTERS} is true this hook will determine +whether unnamed bitfields affect the alignment of the containing +structure. The hook should return true if the structure should inherit +the alignment requirements of an unnamed bitfield's type. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_NARROW_VOLATILE_BITFIELD (void) +This target hook should return @code{true} if accesses to volatile bitfields +should use the narrowest mode possible. It should return @code{false} if +these accesses should use the bitfield container type. + +The default is @code{false}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_MEMBER_TYPE_FORCES_BLK (const_tree @var{field}, machine_mode @var{mode}) +Return true if a structure, union or array containing @var{field} should +be accessed using @code{BLKMODE}. + +If @var{field} is the only field in the structure, @var{mode} is its +mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the +case where structures of one field would require the structure's mode to +retain the field's mode. + +Normally, this is not needed. +@end deftypefn + +@defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified}) +Define this macro as an expression for the alignment of a type (given +by @var{type} as a tree node) if the alignment computed in the usual +way is @var{computed} and the alignment explicitly specified was +@var{specified}. + +The default is to use @var{specified} if it is larger; otherwise, use +the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT} +@end defmac + +@defmac MAX_FIXED_MODE_SIZE +An integer expression for the size in bits of the largest integer +machine mode that should actually be used. All integer machine modes of +this size or smaller can be used for structures and unions with the +appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE +(DImode)} is assumed. +@end defmac + +@defmac STACK_SAVEAREA_MODE (@var{save_level}) +If defined, an expression of type @code{machine_mode} that +specifies the mode of the save area operand of a +@code{save_stack_@var{level}} named pattern (@pxref{Standard Names}). +@var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or +@code{SAVE_NONLOCAL} and selects which of the three named patterns is +having its mode specified. + +You need not define this macro if it always returns @code{Pmode}. You +would most commonly define this macro if the +@code{save_stack_@var{level}} patterns need to support both a 32- and a +64-bit mode. +@end defmac + +@defmac STACK_SIZE_MODE +If defined, an expression of type @code{machine_mode} that +specifies the mode of the size increment operand of an +@code{allocate_stack} named pattern (@pxref{Standard Names}). + +You need not define this macro if it always returns @code{word_mode}. +You would most commonly define this macro if the @code{allocate_stack} +pattern needs to support both a 32- and a 64-bit mode. +@end defmac + +@deftypefn {Target Hook} scalar_int_mode TARGET_LIBGCC_CMP_RETURN_MODE (void) +This target hook should return the mode to be used for the return value +of compare instructions expanded to libgcc calls. If not defined +@code{word_mode} is returned which is the right choice for a majority of +targets. +@end deftypefn + +@deftypefn {Target Hook} scalar_int_mode TARGET_LIBGCC_SHIFT_COUNT_MODE (void) +This target hook should return the mode to be used for the shift count operand +of shift instructions expanded to libgcc calls. If not defined +@code{word_mode} is returned which is the right choice for a majority of +targets. +@end deftypefn + +@deftypefn {Target Hook} scalar_int_mode TARGET_UNWIND_WORD_MODE (void) +Return machine mode to be used for @code{_Unwind_Word} type. +The default is to use @code{word_mode}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (const_tree @var{record_type}) +This target hook returns @code{true} if bit-fields in the given +@var{record_type} are to be laid out following the rules of Microsoft +Visual C/C++, namely: (i) a bit-field won't share the same storage +unit with the previous bit-field if their underlying types have +different sizes, and the bit-field will be aligned to the highest +alignment of the underlying types of itself and of the previous +bit-field; (ii) a zero-sized bit-field will affect the alignment of +the whole enclosing structure, even if it is unnamed; except that +(iii) a zero-sized bit-field will be disregarded unless it follows +another bit-field of nonzero size. If this hook returns @code{true}, +other macros that control bit-field layout are ignored. + +When a bit-field is inserted into a packed record, the whole size +of the underlying type is used by one or more same-size adjacent +bit-fields (that is, if its long:3, 32 bits is used in the record, +and any additional adjacent long bit-fields are packed into the same +chunk of 32 bits. However, if the size changes, a new field of that +size is allocated). In an unpacked record, this is the same as using +alignment, but not equivalent when packing. + +If both MS bit-fields and @samp{__attribute__((packed))} are used, +the latter will take precedence. If @samp{__attribute__((packed))} is +used on a single field when MS bit-fields are in use, it will take +precedence for that field, but the alignment of the rest of the structure +may affect its placement. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_DECIMAL_FLOAT_SUPPORTED_P (void) +Returns true if the target supports decimal floating point. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_FIXED_POINT_SUPPORTED_P (void) +Returns true if the target supports fixed-point arithmetic. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_EXPAND_TO_RTL_HOOK (void) +This hook is called just before expansion into rtl, allowing the target +to perform additional initializations or analysis before the expansion. +For example, the rs6000 port uses it to allocate a scratch stack slot +for use in copying SDmode values between memory and floating point +registers whenever the function being expanded has any SDmode +usage. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_INSTANTIATE_DECLS (void) +This hook allows the backend to perform additional instantiations on rtl +that are not actually in any insns yet, but will be later. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_MANGLE_TYPE (const_tree @var{type}) +If your target defines any fundamental types, or any types your target +uses should be mangled differently from the default, define this hook +to return the appropriate encoding for these types as part of a C++ +mangled name. The @var{type} argument is the tree structure representing +the type to be mangled. The hook may be applied to trees which are +not target-specific fundamental types; it should return @code{NULL} +for all such types, as well as arguments it does not recognize. If the +return value is not @code{NULL}, it must point to a statically-allocated +string constant. + +Target-specific fundamental types might be new fundamental types or +qualified versions of ordinary fundamental types. Encode new +fundamental types as @samp{@w{u @var{n} @var{name}}}, where @var{name} +is the name used for the type in source code, and @var{n} is the +length of @var{name} in decimal. Encode qualified versions of +ordinary types as @samp{@w{U @var{n} @var{name} @var{code}}}, where +@var{name} is the name used for the type qualifier in source code, +@var{n} is the length of @var{name} as above, and @var{code} is the +code used to represent the unqualified version of this type. (See +@code{write_builtin_type} in @file{cp/mangle.cc} for the list of +codes.) In both cases the spaces are for clarity; do not include any +spaces in your string. + +This hook is applied to types prior to typedef resolution. If the mangled +name for a particular type depends only on that type's main variant, you +can perform typedef resolution yourself using @code{TYPE_MAIN_VARIANT} +before mangling. + +The default version of this hook always returns @code{NULL}, which is +appropriate for a target that does not define any new fundamental +types. +@end deftypefn + +@node Type Layout +@section Layout of Source Language Data Types + +These macros define the sizes and other characteristics of the standard +basic data types used in programs being compiled. Unlike the macros in +the previous section, these apply to specific features of C and related +languages, rather than to fundamental aspects of storage layout. + +@defmac INT_TYPE_SIZE +A C expression for the size in bits of the type @code{int} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac SHORT_TYPE_SIZE +A C expression for the size in bits of the type @code{short} on the +target machine. If you don't define this, the default is half a word. +(If this would be less than one storage unit, it is rounded up to one +unit.) +@end defmac + +@defmac LONG_TYPE_SIZE +A C expression for the size in bits of the type @code{long} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac ADA_LONG_TYPE_SIZE +On some machines, the size used for the Ada equivalent of the type +@code{long} by a native Ada compiler differs from that used by C@. In +that situation, define this macro to be a C expression to be used for +the size of that type. If you don't define this, the default is the +value of @code{LONG_TYPE_SIZE}. +@end defmac + +@defmac LONG_LONG_TYPE_SIZE +A C expression for the size in bits of the type @code{long long} on the +target machine. If you don't define this, the default is two +words. If you want to support GNU Ada on your machine, the value of this +macro must be at least 64. +@end defmac + +@defmac CHAR_TYPE_SIZE +A C expression for the size in bits of the type @code{char} on the +target machine. If you don't define this, the default is +@code{BITS_PER_UNIT}. +@end defmac + +@defmac BOOL_TYPE_SIZE +A C expression for the size in bits of the C++ type @code{bool} and +C99 type @code{_Bool} on the target machine. If you don't define +this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}. +@end defmac + +@defmac FLOAT_TYPE_SIZE +A C expression for the size in bits of the type @code{float} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac DOUBLE_TYPE_SIZE +A C expression for the size in bits of the type @code{double} on the +target machine. If you don't define this, the default is two +words. +@end defmac + +@defmac LONG_DOUBLE_TYPE_SIZE +A C expression for the size in bits of the type @code{long double} on +the target machine. If you don't define this, the default is two +words. +@end defmac + +@defmac SHORT_FRACT_TYPE_SIZE +A C expression for the size in bits of the type @code{short _Fract} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT}. +@end defmac + +@defmac FRACT_TYPE_SIZE +A C expression for the size in bits of the type @code{_Fract} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 2}. +@end defmac + +@defmac LONG_FRACT_TYPE_SIZE +A C expression for the size in bits of the type @code{long _Fract} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 4}. +@end defmac + +@defmac LONG_LONG_FRACT_TYPE_SIZE +A C expression for the size in bits of the type @code{long long _Fract} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 8}. +@end defmac + +@defmac SHORT_ACCUM_TYPE_SIZE +A C expression for the size in bits of the type @code{short _Accum} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 2}. +@end defmac + +@defmac ACCUM_TYPE_SIZE +A C expression for the size in bits of the type @code{_Accum} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 4}. +@end defmac + +@defmac LONG_ACCUM_TYPE_SIZE +A C expression for the size in bits of the type @code{long _Accum} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 8}. +@end defmac + +@defmac LONG_LONG_ACCUM_TYPE_SIZE +A C expression for the size in bits of the type @code{long long _Accum} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 16}. +@end defmac + +@defmac LIBGCC2_GNU_PREFIX +This macro corresponds to the @code{TARGET_LIBFUNC_GNU_PREFIX} target +hook and should be defined if that hook is overriden to be true. It +causes function names in libgcc to be changed to use a @code{__gnu_} +prefix for their name rather than the default @code{__}. A port which +uses this macro should also arrange to use @file{t-gnu-prefix} in +the libgcc @file{config.host}. +@end defmac + +@defmac WIDEST_HARDWARE_FP_SIZE +A C expression for the size in bits of the widest floating-point format +supported by the hardware. If you define this macro, you must specify a +value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}. +If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE} +is the default. +@end defmac + +@defmac DEFAULT_SIGNED_CHAR +An expression whose value is 1 or 0, according to whether the type +@code{char} should be signed or unsigned by default. The user can +always override this default with the options @option{-fsigned-char} +and @option{-funsigned-char}. +@end defmac + +@deftypefn {Target Hook} bool TARGET_DEFAULT_SHORT_ENUMS (void) +This target hook should return true if the compiler should give an +@code{enum} type only as many bytes as it takes to represent the range +of possible values of that type. It should return false if all +@code{enum} types should be allocated like @code{int}. + +The default is to return false. +@end deftypefn + +@defmac SIZE_TYPE +A C expression for a string describing the name of the data type to use +for size values. The typedef name @code{size_t} is defined using the +contents of the string. + +The string can contain more than one keyword. If so, separate them with +spaces, and write first any length keyword, then @code{unsigned} if +appropriate, and finally @code{int}. The string must exactly match one +of the data type names defined in the function +@code{c_common_nodes_and_builtins} in the file @file{c-family/c-common.cc}. +You may not omit @code{int} or change the order---that would cause the +compiler to crash on startup. + +If you don't define this macro, the default is @code{"long unsigned +int"}. +@end defmac + +@defmac SIZETYPE +GCC defines internal types (@code{sizetype}, @code{ssizetype}, +@code{bitsizetype} and @code{sbitsizetype}) for expressions +dealing with size. This macro is a C expression for a string describing +the name of the data type from which the precision of @code{sizetype} +is extracted. + +The string has the same restrictions as @code{SIZE_TYPE} string. + +If you don't define this macro, the default is @code{SIZE_TYPE}. +@end defmac + +@defmac PTRDIFF_TYPE +A C expression for a string describing the name of the data type to use +for the result of subtracting two pointers. The typedef name +@code{ptrdiff_t} is defined using the contents of the string. See +@code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is @code{"long int"}. +@end defmac + +@defmac WCHAR_TYPE +A C expression for a string describing the name of the data type to use +for wide characters. The typedef name @code{wchar_t} is defined using +the contents of the string. See @code{SIZE_TYPE} above for more +information. + +If you don't define this macro, the default is @code{"int"}. +@end defmac + +@defmac WCHAR_TYPE_SIZE +A C expression for the size in bits of the data type for wide +characters. This is used in @code{cpp}, which cannot make use of +@code{WCHAR_TYPE}. +@end defmac + +@defmac WINT_TYPE +A C expression for a string describing the name of the data type to +use for wide characters passed to @code{printf} and returned from +@code{getwc}. The typedef name @code{wint_t} is defined using the +contents of the string. See @code{SIZE_TYPE} above for more +information. + +If you don't define this macro, the default is @code{"unsigned int"}. +@end defmac + +@defmac INTMAX_TYPE +A C expression for a string describing the name of the data type that +can represent any value of any standard or extended signed integer type. +The typedef name @code{intmax_t} is defined using the contents of the +string. See @code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is the first of +@code{"int"}, @code{"long int"}, or @code{"long long int"} that has as +much precision as @code{long long int}. +@end defmac + +@defmac UINTMAX_TYPE +A C expression for a string describing the name of the data type that +can represent any value of any standard or extended unsigned integer +type. The typedef name @code{uintmax_t} is defined using the contents +of the string. See @code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is the first of +@code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long +unsigned int"} that has as much precision as @code{long long unsigned +int}. +@end defmac + +@defmac SIG_ATOMIC_TYPE +@defmacx INT8_TYPE +@defmacx INT16_TYPE +@defmacx INT32_TYPE +@defmacx INT64_TYPE +@defmacx UINT8_TYPE +@defmacx UINT16_TYPE +@defmacx UINT32_TYPE +@defmacx UINT64_TYPE +@defmacx INT_LEAST8_TYPE +@defmacx INT_LEAST16_TYPE +@defmacx INT_LEAST32_TYPE +@defmacx INT_LEAST64_TYPE +@defmacx UINT_LEAST8_TYPE +@defmacx UINT_LEAST16_TYPE +@defmacx UINT_LEAST32_TYPE +@defmacx UINT_LEAST64_TYPE +@defmacx INT_FAST8_TYPE +@defmacx INT_FAST16_TYPE +@defmacx INT_FAST32_TYPE +@defmacx INT_FAST64_TYPE +@defmacx UINT_FAST8_TYPE +@defmacx UINT_FAST16_TYPE +@defmacx UINT_FAST32_TYPE +@defmacx UINT_FAST64_TYPE +@defmacx INTPTR_TYPE +@defmacx UINTPTR_TYPE +C expressions for the standard types @code{sig_atomic_t}, +@code{int8_t}, @code{int16_t}, @code{int32_t}, @code{int64_t}, +@code{uint8_t}, @code{uint16_t}, @code{uint32_t}, @code{uint64_t}, +@code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t}, +@code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t}, +@code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t}, +@code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t}, +@code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t}, +@code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t}. See +@code{SIZE_TYPE} above for more information. + +If any of these macros evaluates to a null pointer, the corresponding +type is not supported; if GCC is configured to provide +@code{} in such a case, the header provided may not conform +to C99, depending on the type in question. The defaults for all of +these macros are null pointers. +@end defmac + +@defmac TARGET_PTRMEMFUNC_VBIT_LOCATION +The C++ compiler represents a pointer-to-member-function with a struct +that looks like: + +@smallexample + struct @{ + union @{ + void (*fn)(); + ptrdiff_t vtable_index; + @}; + ptrdiff_t delta; + @}; +@end smallexample + +@noindent +The C++ compiler must use one bit to indicate whether the function that +will be called through a pointer-to-member-function is virtual. +Normally, we assume that the low-order bit of a function pointer must +always be zero. Then, by ensuring that the vtable_index is odd, we can +distinguish which variant of the union is in use. But, on some +platforms function pointers can be odd, and so this doesn't work. In +that case, we use the low-order bit of the @code{delta} field, and shift +the remainder of the @code{delta} field to the left. + +GCC will automatically make the right selection about where to store +this bit using the @code{FUNCTION_BOUNDARY} setting for your platform. +However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY} +set such that functions always start at even addresses, but the lowest +bit of pointers to functions indicate whether the function at that +address is in ARM or Thumb mode. If this is the case of your +architecture, you should define this macro to +@code{ptrmemfunc_vbit_in_delta}. + +In general, you should not have to define this macro. On architectures +in which function addresses are always even, according to +@code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to +@code{ptrmemfunc_vbit_in_pfn}. +@end defmac + +@defmac TARGET_VTABLE_USES_DESCRIPTORS +Normally, the C++ compiler uses function pointers in vtables. This +macro allows the target to change to use ``function descriptors'' +instead. Function descriptors are found on targets for whom a +function pointer is actually a small data structure. Normally the +data structure consists of the actual code address plus a data +pointer to which the function's data is relative. + +If vtables are used, the value of this macro should be the number +of words that the function descriptor occupies. +@end defmac + +@defmac TARGET_VTABLE_ENTRY_ALIGN +By default, the vtable entries are void pointers, the so the alignment +is the same as pointer alignment. The value of this macro specifies +the alignment of the vtable entry in bits. It should be defined only +when special alignment is necessary. */ +@end defmac + +@defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE +There are a few non-descriptor entries in the vtable at offsets below +zero. If these entries must be padded (say, to preserve the alignment +specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number +of words in each data entry. +@end defmac + +@node Registers +@section Register Usage +@cindex register usage + +This section explains how to describe what registers the target machine +has, and how (in general) they can be used. + +The description of which registers a specific instruction can use is +done with register classes; see @ref{Register Classes}. For information +on using registers to access a stack frame, see @ref{Frame Registers}. +For passing values in registers, see @ref{Register Arguments}. +For returning values in registers, see @ref{Scalar Return}. + +@menu +* Register Basics:: Number and kinds of registers. +* Allocation Order:: Order in which registers are allocated. +* Values in Registers:: What kinds of values each reg can hold. +* Leaf Functions:: Renumbering registers for leaf functions. +* Stack Registers:: Handling a register stack such as 80387. +@end menu + +@node Register Basics +@subsection Basic Characteristics of Registers + +@c prevent bad page break with this line +Registers have various characteristics. + +@defmac FIRST_PSEUDO_REGISTER +Number of hardware registers known to the compiler. They receive +numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first +pseudo register's number really is assigned the number +@code{FIRST_PSEUDO_REGISTER}. +@end defmac + +@defmac FIXED_REGISTERS +@cindex fixed register +An initializer that says which registers are used for fixed purposes +all throughout the compiled code and are therefore not available for +general allocation. These would include the stack pointer, the frame +pointer (except on machines where that can be used as a general +register when no frame pointer is needed), the program counter on +machines where that is considered one of the addressable registers, +and any other numbered register with a standard use. + +This information is expressed as a sequence of numbers, separated by +commas and surrounded by braces. The @var{n}th number is 1 if +register @var{n} is fixed, 0 otherwise. + +The table initialized from this macro, and the table initialized by +the following one, may be overridden at run time either automatically, +by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by +the user with the command options @option{-ffixed-@var{reg}}, +@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}. +@end defmac + +@defmac CALL_USED_REGISTERS +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +Like @code{FIXED_REGISTERS} but has 1 for each register that is +clobbered (in general) by function calls as well as for fixed +registers. This macro therefore identifies the registers that are not +available for general allocation of values that must live across +function calls. + +If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler +automatically saves it on function entry and restores it on function +exit, if the register is used within the function. + +Exactly one of @code{CALL_USED_REGISTERS} and @code{CALL_REALLY_USED_REGISTERS} +must be defined. Modern ports should define @code{CALL_REALLY_USED_REGISTERS}. +@end defmac + +@defmac CALL_REALLY_USED_REGISTERS +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +Like @code{CALL_USED_REGISTERS} except this macro doesn't require +that the entire set of @code{FIXED_REGISTERS} be included. +(@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}). + +Exactly one of @code{CALL_USED_REGISTERS} and @code{CALL_REALLY_USED_REGISTERS} +must be defined. Modern ports should define @code{CALL_REALLY_USED_REGISTERS}. +@end defmac + +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +@deftypefn {Target Hook} {const predefined_function_abi &} TARGET_FNTYPE_ABI (const_tree @var{type}) +Return the ABI used by a function with type @var{type}; see the +definition of @code{predefined_function_abi} for details of the ABI +descriptor. Targets only need to define this hook if they support +interoperability between several ABIs in the same translation unit. +@end deftypefn + +@deftypefn {Target Hook} {const predefined_function_abi &} TARGET_INSN_CALLEE_ABI (const rtx_insn *@var{insn}) +This hook returns a description of the ABI used by the target of +call instruction @var{insn}; see the definition of +@code{predefined_function_abi} for details of the ABI descriptor. +Only the global function @code{insn_callee_abi} should call this hook +directly. + +Targets only need to define this hook if they support +interoperability between several ABIs in the same translation unit. +@end deftypefn + +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +@deftypefn {Target Hook} bool TARGET_HARD_REGNO_CALL_PART_CLOBBERED (unsigned int @var{abi_id}, unsigned int @var{regno}, machine_mode @var{mode}) +ABIs usually specify that calls must preserve the full contents +of a particular register, or that calls can alter any part of a +particular register. This information is captured by the target macro +@code{CALL_REALLY_USED_REGISTERS}. However, some ABIs specify that calls +must preserve certain bits of a particular register but can alter others. +This hook should return true if this applies to at least one of the +registers in @samp{(reg:@var{mode} @var{regno})}, and if as a result the +call would alter part of the @var{mode} value. For example, if a call +preserves the low 32 bits of a 64-bit hard register @var{regno} but can +clobber the upper 32 bits, this hook should return true for a 64-bit mode +but false for a 32-bit mode. + +The value of @var{abi_id} comes from the @code{predefined_function_abi} +structure that describes the ABI of the call; see the definition of the +structure for more details. If (as is usual) the target uses the same ABI +for all functions in a translation unit, @var{abi_id} is always 0. + +The default implementation returns false, which is correct +for targets that don't have partly call-clobbered registers. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_GET_MULTILIB_ABI_NAME (void) +This hook returns name of multilib ABI name. +@end deftypefn + +@findex fixed_regs +@findex call_used_regs +@findex global_regs +@findex reg_names +@findex reg_class_contents +@deftypefn {Target Hook} void TARGET_CONDITIONAL_REGISTER_USAGE (void) +This hook may conditionally modify five variables +@code{fixed_regs}, @code{call_used_regs}, @code{global_regs}, +@code{reg_names}, and @code{reg_class_contents}, to take into account +any dependence of these register sets on target flags. The first three +of these are of type @code{char []} (interpreted as boolean vectors). +@code{global_regs} is a @code{const char *[]}, and +@code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is +called, @code{fixed_regs}, @code{call_used_regs}, +@code{reg_class_contents}, and @code{reg_names} have been initialized +from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS}, +@code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively. +@code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}}, +@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}} +command options have been applied. + +@cindex disabling certain registers +@cindex controlling register usage +If the usage of an entire class of registers depends on the target +flags, you may indicate this to GCC by using this macro to modify +@code{fixed_regs} and @code{call_used_regs} to 1 for each of the +registers in the classes which should not be used by GCC@. Also make +@code{define_register_constraint}s return @code{NO_REGS} for constraints +that shouldn't be used. + +(However, if this class is not included in @code{GENERAL_REGS} and all +of the insn patterns whose constraints permit this class are +controlled by target switches, then GCC will automatically avoid using +these registers when the target switches are opposed to them.) +@end deftypefn + +@defmac INCOMING_REGNO (@var{out}) +Define this macro if the target machine has register windows. This C +expression returns the register number as seen by the called function +corresponding to the register number @var{out} as seen by the calling +function. Return @var{out} if register number @var{out} is not an +outbound register. +@end defmac + +@defmac OUTGOING_REGNO (@var{in}) +Define this macro if the target machine has register windows. This C +expression returns the register number as seen by the calling function +corresponding to the register number @var{in} as seen by the called +function. Return @var{in} if register number @var{in} is not an inbound +register. +@end defmac + +@defmac LOCAL_REGNO (@var{regno}) +Define this macro if the target machine has register windows. This C +expression returns true if the register is call-saved but is in the +register window. Unlike most call-saved registers, such registers +need not be explicitly restored on function exit or during non-local +gotos. +@end defmac + +@defmac PC_REGNUM +If the program counter has a register number, define this as that +register number. Otherwise, do not define it. +@end defmac + +@node Allocation Order +@subsection Order of Allocation of Registers +@cindex order of register allocation +@cindex register allocation order + +@c prevent bad page break with this line +Registers are allocated in order. + +@defmac REG_ALLOC_ORDER +If defined, an initializer for a vector of integers, containing the +numbers of hard registers in the order in which GCC should prefer +to use them (from most preferred to least). + +If this macro is not defined, registers are used lowest numbered first +(all else being equal). + +One use of this macro is on machines where the highest numbered +registers must always be saved and the save-multiple-registers +instruction supports only sequences of consecutive registers. On such +machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists +the highest numbered allocable register first. +@end defmac + +@defmac ADJUST_REG_ALLOC_ORDER +A C statement (sans semicolon) to choose the order in which to allocate +hard registers for pseudo-registers local to a basic block. + +Store the desired register order in the array @code{reg_alloc_order}. +Element 0 should be the register to allocate first; element 1, the next +register; and so on. + +The macro body should not assume anything about the contents of +@code{reg_alloc_order} before execution of the macro. + +On most machines, it is not necessary to define this macro. +@end defmac + +@defmac HONOR_REG_ALLOC_ORDER +Normally, IRA tries to estimate the costs for saving a register in the +prologue and restoring it in the epilogue. This discourages it from +using call-saved registers. If a machine wants to ensure that IRA +allocates registers in the order given by REG_ALLOC_ORDER even if some +call-saved registers appear earlier than call-used ones, then define this +macro as a C expression to nonzero. Default is 0. +@end defmac + +@defmac IRA_HARD_REGNO_ADD_COST_MULTIPLIER (@var{regno}) +In some case register allocation order is not enough for the +Integrated Register Allocator (@acronym{IRA}) to generate a good code. +If this macro is defined, it should return a floating point value +based on @var{regno}. The cost of using @var{regno} for a pseudo will +be increased by approximately the pseudo's usage frequency times the +value returned by this macro. Not defining this macro is equivalent +to having it always return @code{0.0}. + +On most machines, it is not necessary to define this macro. +@end defmac + +@node Values in Registers +@subsection How Values Fit in Registers + +This section discusses the macros that describe which kinds of values +(specifically, which machine modes) each register can hold, and how many +consecutive registers are needed for a given mode. + +@deftypefn {Target Hook} {unsigned int} TARGET_HARD_REGNO_NREGS (unsigned int @var{regno}, machine_mode @var{mode}) +This hook returns the number of consecutive hard registers, starting +at register number @var{regno}, required to hold a value of mode +@var{mode}. This hook must never return zero, even if a register +cannot hold the requested mode - indicate that with +@code{TARGET_HARD_REGNO_MODE_OK} and/or +@code{TARGET_CAN_CHANGE_MODE_CLASS} instead. + +The default definition returns the number of words in @var{mode}. +@end deftypefn + +@defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode}) +A C expression that is nonzero if a value of mode @var{mode}, stored +in memory, ends with padding that causes it to take up more space than +in registers starting at register number @var{regno} (as determined by +multiplying GCC's notion of the size of the register when containing +this mode by the number of registers returned by +@code{TARGET_HARD_REGNO_NREGS}). By default this is zero. + +For example, if a floating-point value is stored in three 32-bit +registers but takes up 128 bits in memory, then this would be +nonzero. + +This macros only needs to be defined if there are cases where +@code{subreg_get_info} +would otherwise wrongly determine that a @code{subreg} can be +represented by an offset to the register number, when in fact such a +@code{subreg} would contain some of the padding not stored in +registers and so not be representable. +@end defmac + +@defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode}) +For values of @var{regno} and @var{mode} for which +@code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression +returning the greater number of registers required to hold the value +including any padding. In the example above, the value would be four. +@end defmac + +@defmac REGMODE_NATURAL_SIZE (@var{mode}) +Define this macro if the natural size of registers that hold values +of mode @var{mode} is not the word size. It is a C expression that +should give the natural size in bytes for the specified mode. It is +used by the register allocator to try to optimize its results. This +happens for example on SPARC 64-bit where the natural size of +floating-point registers is still 32-bit. +@end defmac + +@deftypefn {Target Hook} bool TARGET_HARD_REGNO_MODE_OK (unsigned int @var{regno}, machine_mode @var{mode}) +This hook returns true if it is permissible to store a value +of mode @var{mode} in hard register number @var{regno} (or in several +registers starting with that one). The default definition returns true +unconditionally. + +You need not include code to check for the numbers of fixed registers, +because the allocation mechanism considers them to be always occupied. + +@cindex register pairs +On some machines, double-precision values must be kept in even/odd +register pairs. You can implement that by defining this hook to reject +odd register numbers for such modes. + +The minimum requirement for a mode to be OK in a register is that the +@samp{mov@var{mode}} instruction pattern support moves between the +register and other hard register in the same class and that moving a +value into the register and back out not alter it. + +Since the same instruction used to move @code{word_mode} will work for +all narrower integer modes, it is not necessary on any machine for +this hook to distinguish between these modes, provided you define +patterns @samp{movhi}, etc., to take advantage of this. This is +useful because of the interaction between @code{TARGET_HARD_REGNO_MODE_OK} +and @code{TARGET_MODES_TIEABLE_P}; it is very desirable for all integer +modes to be tieable. + +Many machines have special registers for floating point arithmetic. +Often people assume that floating point machine modes are allowed only +in floating point registers. This is not true. Any registers that +can hold integers can safely @emph{hold} a floating point machine +mode, whether or not floating arithmetic can be done on it in those +registers. Integer move instructions can be used to move the values. + +On some machines, though, the converse is true: fixed-point machine +modes may not go in floating registers. This is true if the floating +registers normalize any value stored in them, because storing a +non-floating value there would garble it. In this case, +@code{TARGET_HARD_REGNO_MODE_OK} should reject fixed-point machine modes in +floating registers. But if the floating registers do not automatically +normalize, if you can store any bit pattern in one and retrieve it +unchanged without a trap, then any machine mode may go in a floating +register, so you can define this hook to say so. + +The primary significance of special floating registers is rather that +they are the registers acceptable in floating point arithmetic +instructions. However, this is of no concern to +@code{TARGET_HARD_REGNO_MODE_OK}. You handle it by writing the proper +constraints for those instructions. + +On some machines, the floating registers are especially slow to access, +so that it is better to store a value in a stack frame than in such a +register if floating point arithmetic is not being done. As long as the +floating registers are not in class @code{GENERAL_REGS}, they will not +be used unless some pattern's constraint asks for one. +@end deftypefn + +@defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to}) +A C expression that is nonzero if it is OK to rename a hard register +@var{from} to another hard register @var{to}. + +One common use of this macro is to prevent renaming of a register to +another register that is not saved by a prologue in an interrupt +handler. + +The default is always nonzero. +@end defmac + +@deftypefn {Target Hook} bool TARGET_MODES_TIEABLE_P (machine_mode @var{mode1}, machine_mode @var{mode2}) +This hook returns true if a value of mode @var{mode1} is accessible +in mode @var{mode2} without copying. + +If @code{TARGET_HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and +@code{TARGET_HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always +the same for any @var{r}, then +@code{TARGET_MODES_TIEABLE_P (@var{mode1}, @var{mode2})} +should be true. If they differ for any @var{r}, you should define +this hook to return false unless some other mechanism ensures the +accessibility of the value in a narrower mode. + +You should define this hook to return true in as many cases as +possible since doing so will allow GCC to perform better register +allocation. The default definition returns true unconditionally. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_HARD_REGNO_SCRATCH_OK (unsigned int @var{regno}) +This target hook should return @code{true} if it is OK to use a hard register +@var{regno} as scratch reg in peephole2. + +One common use of this macro is to prevent using of a register that +is not saved by a prologue in an interrupt handler. + +The default version of this hook always returns @code{true}. +@end deftypefn + +@defmac AVOID_CCMODE_COPIES +Define this macro if the compiler should avoid copies to/from @code{CCmode} +registers. You should only define this macro if support for copying to/from +@code{CCmode} is incomplete. +@end defmac + +@node Leaf Functions +@subsection Handling Leaf Functions + +@cindex leaf functions +@cindex functions, leaf +On some machines, a leaf function (i.e., one which makes no calls) can run +more efficiently if it does not make its own register window. Often this +means it is required to receive its arguments in the registers where they +are passed by the caller, instead of the registers where they would +normally arrive. + +The special treatment for leaf functions generally applies only when +other conditions are met; for example, often they may use only those +registers for its own variables and temporaries. We use the term ``leaf +function'' to mean a function that is suitable for this special +handling, so that functions with no calls are not necessarily ``leaf +functions''. + +GCC assigns register numbers before it knows whether the function is +suitable for leaf function treatment. So it needs to renumber the +registers in order to output a leaf function. The following macros +accomplish this. + +@defmac LEAF_REGISTERS +Name of a char vector, indexed by hard register number, which +contains 1 for a register that is allowable in a candidate for leaf +function treatment. + +If leaf function treatment involves renumbering the registers, then the +registers marked here should be the ones before renumbering---those that +GCC would ordinarily allocate. The registers which will actually be +used in the assembler code, after renumbering, should not be marked with 1 +in this vector. + +Define this macro only if the target machine offers a way to optimize +the treatment of leaf functions. +@end defmac + +@defmac LEAF_REG_REMAP (@var{regno}) +A C expression whose value is the register number to which @var{regno} +should be renumbered, when a function is treated as a leaf function. + +If @var{regno} is a register number which should not appear in a leaf +function before renumbering, then the expression should yield @minus{}1, which +will cause the compiler to abort. + +Define this macro only if the target machine offers a way to optimize the +treatment of leaf functions, and registers need to be renumbered to do +this. +@end defmac + +@findex current_function_is_leaf +@findex current_function_uses_only_leaf_regs +@code{TARGET_ASM_FUNCTION_PROLOGUE} and +@code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions +specially. They can test the C variable @code{current_function_is_leaf} +which is nonzero for leaf functions. @code{current_function_is_leaf} is +set prior to local register allocation and is valid for the remaining +compiler passes. They can also test the C variable +@code{current_function_uses_only_leaf_regs} which is nonzero for leaf +functions which only use leaf registers. +@code{current_function_uses_only_leaf_regs} is valid after all passes +that modify the instructions have been run and is only useful if +@code{LEAF_REGISTERS} is defined. +@c changed this to fix overfull. ALSO: why the "it" at the beginning +@c of the next paragraph?! --mew 2feb93 + +@node Stack Registers +@subsection Registers That Form a Stack + +There are special features to handle computers where some of the +``registers'' form a stack. Stack registers are normally written by +pushing onto the stack, and are numbered relative to the top of the +stack. + +Currently, GCC can only handle one group of stack-like registers, and +they must be consecutively numbered. Furthermore, the existing +support for stack-like registers is specific to the 80387 floating +point coprocessor. If you have a new architecture that uses +stack-like registers, you will need to do substantial work on +@file{reg-stack.cc} and write your machine description to cooperate +with it, as well as defining these macros. + +@defmac STACK_REGS +Define this if the machine has any stack-like registers. +@end defmac + +@defmac STACK_REG_COVER_CLASS +This is a cover class containing the stack registers. Define this if +the machine has any stack-like registers. +@end defmac + +@defmac FIRST_STACK_REG +The number of the first stack-like register. This one is the top +of the stack. +@end defmac + +@defmac LAST_STACK_REG +The number of the last stack-like register. This one is the bottom of +the stack. +@end defmac + +@node Register Classes +@section Register Classes +@cindex register class definitions +@cindex class definitions, register + +On many machines, the numbered registers are not all equivalent. +For example, certain registers may not be allowed for indexed addressing; +certain registers may not be allowed in some instructions. These machine +restrictions are described to the compiler using @dfn{register classes}. + +You define a number of register classes, giving each one a name and saying +which of the registers belong to it. Then you can specify register classes +that are allowed as operands to particular instruction patterns. + +@findex ALL_REGS +@findex NO_REGS +In general, each register will belong to several classes. In fact, one +class must be named @code{ALL_REGS} and contain all the registers. Another +class must be named @code{NO_REGS} and contain no registers. Often the +union of two classes will be another class; however, this is not required. + +@findex GENERAL_REGS +One of the classes must be named @code{GENERAL_REGS}. There is nothing +terribly special about the name, but the operand constraint letters +@samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is +the same as @code{ALL_REGS}, just define it as a macro which expands +to @code{ALL_REGS}. + +Order the classes so that if class @var{x} is contained in class @var{y} +then @var{x} has a lower class number than @var{y}. + +The way classes other than @code{GENERAL_REGS} are specified in operand +constraints is through machine-dependent operand constraint letters. +You can define such letters to correspond to various classes, then use +them in operand constraints. + +You must define the narrowest register classes for allocatable +registers, so that each class either has no subclasses, or that for +some mode, the move cost between registers within the class is +cheaper than moving a register in the class to or from memory +(@pxref{Costs}). + +You should define a class for the union of two classes whenever some +instruction allows both classes. For example, if an instruction allows +either a floating point (coprocessor) register or a general register for a +certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS} +which includes both of them. Otherwise you will get suboptimal code, +or even internal compiler errors when reload cannot find a register in the +class computed via @code{reg_class_subunion}. + +You must also specify certain redundant information about the register +classes: for each class, which classes contain it and which ones are +contained in it; for each pair of classes, the largest class contained +in their union. + +When a value occupying several consecutive registers is expected in a +certain class, all the registers used must belong to that class. +Therefore, register classes cannot be used to enforce a requirement for +a register pair to start with an even-numbered register. The way to +specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK}. + +Register classes used for input-operands of bitwise-and or shift +instructions have a special requirement: each such class must have, for +each fixed-point machine mode, a subclass whose registers can transfer that +mode to or from memory. For example, on some machines, the operations for +single-byte values (@code{QImode}) are limited to certain registers. When +this is so, each register class that is used in a bitwise-and or shift +instruction must have a subclass consisting of registers from which +single-byte values can be loaded or stored. This is so that +@code{PREFERRED_RELOAD_CLASS} can always have a possible value to return. + +@deftp {Data type} {enum reg_class} +An enumerated type that must be defined with all the register class names +as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS} +must be the last register class, followed by one more enumerated value, +@code{LIM_REG_CLASSES}, which is not a register class but rather +tells how many classes there are. + +Each register class has a number, which is the value of casting +the class name to type @code{int}. The number serves as an index +in many of the tables described below. +@end deftp + +@defmac N_REG_CLASSES +The number of distinct register classes, defined as follows: + +@smallexample +#define N_REG_CLASSES (int) LIM_REG_CLASSES +@end smallexample +@end defmac + +@defmac REG_CLASS_NAMES +An initializer containing the names of the register classes as C string +constants. These names are used in writing some of the debugging dumps. +@end defmac + +@defmac REG_CLASS_CONTENTS +An initializer containing the contents of the register classes, as integers +which are bit masks. The @var{n}th integer specifies the contents of class +@var{n}. The way the integer @var{mask} is interpreted is that +register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1. + +When the machine has more than 32 registers, an integer does not suffice. +Then the integers are replaced by sub-initializers, braced groupings containing +several integers. Each sub-initializer must be suitable as an initializer +for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}. +In this situation, the first integer in each sub-initializer corresponds to +registers 0 through 31, the second integer to registers 32 through 63, and +so on. +@end defmac + +@defmac REGNO_REG_CLASS (@var{regno}) +A C expression whose value is a register class containing hard register +@var{regno}. In general there is more than one such class; choose a class +which is @dfn{minimal}, meaning that no smaller class also contains the +register. +@end defmac + +@defmac BASE_REG_CLASS +A macro whose definition is the name of the class to which a valid +base register must belong. A base register is one used in an address +which is the register value plus a displacement. +@end defmac + +@defmac MODE_BASE_REG_CLASS (@var{mode}) +This is a variation of the @code{BASE_REG_CLASS} macro which allows +the selection of a base register in a mode dependent manner. If +@var{mode} is VOIDmode then it should return the same value as +@code{BASE_REG_CLASS}. +@end defmac + +@defmac MODE_BASE_REG_REG_CLASS (@var{mode}) +A C expression whose value is the register class to which a valid +base register must belong in order to be used in a base plus index +register address. You should define this macro if base plus index +addresses have different requirements than other base register uses. +@end defmac + +@defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{address_space}, @var{outer_code}, @var{index_code}) +A C expression whose value is the register class to which a valid +base register for a memory reference in mode @var{mode} to address +space @var{address_space} must belong. @var{outer_code} and @var{index_code} +define the context in which the base register occurs. @var{outer_code} is +the code of the immediately enclosing expression (@code{MEM} for the top level +of an address, @code{ADDRESS} for something that occurs in an +@code{address_operand}). @var{index_code} is the code of the corresponding +index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise. +@end defmac + +@defmac INDEX_REG_CLASS +A macro whose definition is the name of the class to which a valid +index register must belong. An index register is one used in an +address where its value is either multiplied by a scale factor or +added to another register (as well as added to a displacement). +@end defmac + +@defmac REGNO_OK_FOR_BASE_P (@var{num}) +A C expression which is nonzero if register number @var{num} is +suitable for use as a base register in operand addresses. +@end defmac + +@defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode}) +A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that +that expression may examine the mode of the memory reference in +@var{mode}. You should define this macro if the mode of the memory +reference affects whether a register may be used as a base register. If +you define this macro, the compiler will use it instead of +@code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for +addresses that appear outside a @code{MEM}, i.e., as an +@code{address_operand}. +@end defmac + +@defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode}) +A C expression which is nonzero if register number @var{num} is suitable for +use as a base register in base plus index operand addresses, accessing +memory in mode @var{mode}. It may be either a suitable hard register or a +pseudo register that has been allocated such a hard register. You should +define this macro if base plus index addresses have different requirements +than other base register uses. + +Use of this macro is deprecated; please use the more general +@code{REGNO_MODE_CODE_OK_FOR_BASE_P}. +@end defmac + +@defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{address_space}, @var{outer_code}, @var{index_code}) +A C expression which is nonzero if register number @var{num} is +suitable for use as a base register in operand addresses, accessing +memory in mode @var{mode} in address space @var{address_space}. +This is similar to @code{REGNO_MODE_OK_FOR_BASE_P}, except +that that expression may examine the context in which the register +appears in the memory reference. @var{outer_code} is the code of the +immediately enclosing expression (@code{MEM} if at the top level of the +address, @code{ADDRESS} for something that occurs in an +@code{address_operand}). @var{index_code} is the code of the +corresponding index expression if @var{outer_code} is @code{PLUS}; +@code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses +that appear outside a @code{MEM}, i.e., as an @code{address_operand}. +@end defmac + +@defmac REGNO_OK_FOR_INDEX_P (@var{num}) +A C expression which is nonzero if register number @var{num} is +suitable for use as an index register in operand addresses. It may be +either a suitable hard register or a pseudo register that has been +allocated such a hard register. + +The difference between an index register and a base register is that +the index register may be scaled. If an address involves the sum of +two registers, neither one of them scaled, then either one may be +labeled the ``base'' and the other the ``index''; but whichever +labeling is used must fit the machine's constraints of which registers +may serve in each capacity. The compiler will try both labelings, +looking for one that is valid, and will reload one or both registers +only if neither labeling works. +@end defmac + +@deftypefn {Target Hook} reg_class_t TARGET_PREFERRED_RENAME_CLASS (reg_class_t @var{rclass}) +A target hook that places additional preference on the register +class to use when it is necessary to rename a register in class +@var{rclass} to another class, or perhaps @var{NO_REGS}, if no +preferred register class is found or hook @code{preferred_rename_class} +is not implemented. +Sometimes returning a more restrictive class makes better code. For +example, on ARM, thumb-2 instructions using @code{LO_REGS} may be +smaller than instructions using @code{GENERIC_REGS}. By returning +@code{LO_REGS} from @code{preferred_rename_class}, code size can +be reduced. +@end deftypefn + +@deftypefn {Target Hook} reg_class_t TARGET_PREFERRED_RELOAD_CLASS (rtx @var{x}, reg_class_t @var{rclass}) +A target hook that places additional restrictions on the register class +to use when it is necessary to copy value @var{x} into a register in class +@var{rclass}. The value is a register class; perhaps @var{rclass}, or perhaps +another, smaller class. + +The default version of this hook always returns value of @code{rclass} argument. + +Sometimes returning a more restrictive class makes better code. For +example, on the 68000, when @var{x} is an integer constant that is in range +for a @samp{moveq} instruction, the value of this macro is always +@code{DATA_REGS} as long as @var{rclass} includes the data registers. +Requiring a data register guarantees that a @samp{moveq} will be used. + +One case where @code{TARGET_PREFERRED_RELOAD_CLASS} must not return +@var{rclass} is if @var{x} is a legitimate constant which cannot be +loaded into some register class. By returning @code{NO_REGS} you can +force @var{x} into a memory location. For example, rs6000 can load +immediate values into general-purpose registers, but does not have an +instruction for loading an immediate value into a floating-point +register, so @code{TARGET_PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when +@var{x} is a floating-point constant. If the constant can't be loaded +into any kind of register, code generation will be better if +@code{TARGET_LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead +of using @code{TARGET_PREFERRED_RELOAD_CLASS}. + +If an insn has pseudos in it after register allocation, reload will go +through the alternatives and call repeatedly @code{TARGET_PREFERRED_RELOAD_CLASS} +to find the best one. Returning @code{NO_REGS}, in this case, makes +reload add a @code{!} in front of the constraint: the x86 back-end uses +this feature to discourage usage of 387 registers when math is done in +the SSE registers (and vice versa). +@end deftypefn + +@defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class}) +A C expression that places additional restrictions on the register class +to use when it is necessary to copy value @var{x} into a register in class +@var{class}. The value is a register class; perhaps @var{class}, or perhaps +another, smaller class. On many machines, the following definition is +safe: + +@smallexample +#define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS +@end smallexample + +Sometimes returning a more restrictive class makes better code. For +example, on the 68000, when @var{x} is an integer constant that is in range +for a @samp{moveq} instruction, the value of this macro is always +@code{DATA_REGS} as long as @var{class} includes the data registers. +Requiring a data register guarantees that a @samp{moveq} will be used. + +One case where @code{PREFERRED_RELOAD_CLASS} must not return +@var{class} is if @var{x} is a legitimate constant which cannot be +loaded into some register class. By returning @code{NO_REGS} you can +force @var{x} into a memory location. For example, rs6000 can load +immediate values into general-purpose registers, but does not have an +instruction for loading an immediate value into a floating-point +register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when +@var{x} is a floating-point constant. If the constant cannot be loaded +into any kind of register, code generation will be better if +@code{TARGET_LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead +of using @code{TARGET_PREFERRED_RELOAD_CLASS}. + +If an insn has pseudos in it after register allocation, reload will go +through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS} +to find the best one. Returning @code{NO_REGS}, in this case, makes +reload add a @code{!} in front of the constraint: the x86 back-end uses +this feature to discourage usage of 387 registers when math is done in +the SSE registers (and vice versa). +@end defmac + +@deftypefn {Target Hook} reg_class_t TARGET_PREFERRED_OUTPUT_RELOAD_CLASS (rtx @var{x}, reg_class_t @var{rclass}) +Like @code{TARGET_PREFERRED_RELOAD_CLASS}, but for output reloads instead of +input reloads. + +The default version of this hook always returns value of @code{rclass} +argument. + +You can also use @code{TARGET_PREFERRED_OUTPUT_RELOAD_CLASS} to discourage +reload from using some alternatives, like @code{TARGET_PREFERRED_RELOAD_CLASS}. +@end deftypefn + +@defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class}) +A C expression that places additional restrictions on the register class +to use when it is necessary to be able to hold a value of mode +@var{mode} in a reload register for which class @var{class} would +ordinarily be used. + +Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when +there are certain modes that simply cannot go in certain reload classes. + +The value is a register class; perhaps @var{class}, or perhaps another, +smaller class. + +Don't define this macro unless the target machine has limitations which +require the macro to do something nontrivial. +@end defmac + +@deftypefn {Target Hook} reg_class_t TARGET_SECONDARY_RELOAD (bool @var{in_p}, rtx @var{x}, reg_class_t @var{reload_class}, machine_mode @var{reload_mode}, secondary_reload_info *@var{sri}) +Many machines have some registers that cannot be copied directly to or +from memory or even from other types of registers. An example is the +@samp{MQ} register, which on most machines, can only be copied to or +from general registers, but not memory. Below, we shall be using the +term 'intermediate register' when a move operation cannot be performed +directly, but has to be done by copying the source into the intermediate +register first, and then copying the intermediate register to the +destination. An intermediate register always has the same mode as +source and destination. Since it holds the actual value being copied, +reload might apply optimizations to re-use an intermediate register +and eliding the copy from the source when it can determine that the +intermediate register still holds the required value. + +Another kind of secondary reload is required on some machines which +allow copying all registers to and from memory, but require a scratch +register for stores to some memory locations (e.g., those with symbolic +address on the RT, and those with certain symbolic address on the SPARC +when compiling PIC)@. Scratch registers need not have the same mode +as the value being copied, and usually hold a different value than +that being copied. Special patterns in the md file are needed to +describe how the copy is performed with the help of the scratch register; +these patterns also describe the number, register class(es) and mode(s) +of the scratch register(s). + +In some cases, both an intermediate and a scratch register are required. + +For input reloads, this target hook is called with nonzero @var{in_p}, +and @var{x} is an rtx that needs to be copied to a register of class +@var{reload_class} in @var{reload_mode}. For output reloads, this target +hook is called with zero @var{in_p}, and a register of class @var{reload_class} +needs to be copied to rtx @var{x} in @var{reload_mode}. + +If copying a register of @var{reload_class} from/to @var{x} requires +an intermediate register, the hook @code{secondary_reload} should +return the register class required for this intermediate register. +If no intermediate register is required, it should return NO_REGS. +If more than one intermediate register is required, describe the one +that is closest in the copy chain to the reload register. + +If scratch registers are needed, you also have to describe how to +perform the copy from/to the reload register to/from this +closest intermediate register. Or if no intermediate register is +required, but still a scratch register is needed, describe the +copy from/to the reload register to/from the reload operand @var{x}. + +You do this by setting @code{sri->icode} to the instruction code of a pattern +in the md file which performs the move. Operands 0 and 1 are the output +and input of this copy, respectively. Operands from operand 2 onward are +for scratch operands. These scratch operands must have a mode, and a +single-register-class +@c [later: or memory] +output constraint. + +When an intermediate register is used, the @code{secondary_reload} +hook will be called again to determine how to copy the intermediate +register to/from the reload operand @var{x}, so your hook must also +have code to handle the register class of the intermediate operand. + +@c [For later: maybe we'll allow multi-alternative reload patterns - +@c the port maintainer could name a mov pattern that has clobbers - +@c and match the constraints of input and output to determine the required +@c alternative. A restriction would be that constraints used to match +@c against reloads registers would have to be written as register class +@c constraints, or we need a new target macro / hook that tells us if an +@c arbitrary constraint can match an unknown register of a given class. +@c Such a macro / hook would also be useful in other places.] + + +@var{x} might be a pseudo-register or a @code{subreg} of a +pseudo-register, which could either be in a hard register or in memory. +Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is +in memory and the hard register number if it is in a register. + +Scratch operands in memory (constraint @code{"=m"} / @code{"=&m"}) are +currently not supported. For the time being, you will have to continue +to use @code{TARGET_SECONDARY_MEMORY_NEEDED} for that purpose. + +@code{copy_cost} also uses this target hook to find out how values are +copied. If you want it to include some extra cost for the need to allocate +(a) scratch register(s), set @code{sri->extra_cost} to the additional cost. +Or if two dependent moves are supposed to have a lower cost than the sum +of the individual moves due to expected fortuitous scheduling and/or special +forwarding logic, you can set @code{sri->extra_cost} to a negative amount. +@end deftypefn + +@defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +@defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +@defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +These macros are obsolete, new ports should use the target hook +@code{TARGET_SECONDARY_RELOAD} instead. + +These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD} +target hook. Older ports still define these macros to indicate to the +reload phase that it may +need to allocate at least one register for a reload in addition to the +register to contain the data. Specifically, if copying @var{x} to a +register @var{class} in @var{mode} requires an intermediate register, +you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the +largest register class all of whose registers can be used as +intermediate registers or scratch registers. + +If copying a register @var{class} in @var{mode} to @var{x} requires an +intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS} +was supposed to be defined to return the largest register +class required. If the +requirements for input and output reloads were the same, the macro +@code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both +macros identically. + +The values returned by these macros are often @code{GENERAL_REGS}. +Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x} +can be directly copied to or from a register of @var{class} in +@var{mode} without requiring a scratch register. Do not define this +macro if it would always return @code{NO_REGS}. + +If a scratch register is required (either with or without an +intermediate register), you were supposed to define patterns for +@samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required +(@pxref{Standard Names}. These patterns, which were normally +implemented with a @code{define_expand}, should be similar to the +@samp{mov@var{m}} patterns, except that operand 2 is the scratch +register. + +These patterns need constraints for the reload register and scratch +register that +contain a single register class. If the original reload register (whose +class is @var{class}) can meet the constraint given in the pattern, the +value returned by these macros is used for the class of the scratch +register. Otherwise, two additional reload registers are required. +Their classes are obtained from the constraints in the insn pattern. + +@var{x} might be a pseudo-register or a @code{subreg} of a +pseudo-register, which could either be in a hard register or in memory. +Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is +in memory and the hard register number if it is in a register. + +These macros should not be used in the case where a particular class of +registers can only be copied to memory and not to another class of +registers. In that case, secondary reload registers are not needed and +would not be helpful. Instead, a stack location must be used to perform +the copy and the @code{mov@var{m}} pattern should use memory as an +intermediate storage. This case often occurs between floating-point and +general registers. +@end defmac + +@deftypefn {Target Hook} bool TARGET_SECONDARY_MEMORY_NEEDED (machine_mode @var{mode}, reg_class_t @var{class1}, reg_class_t @var{class2}) +Certain machines have the property that some registers cannot be copied +to some other registers without using memory. Define this hook on +those machines to return true if objects of mode @var{m} in registers +of @var{class1} can only be copied to registers of class @var{class2} by + storing a register of @var{class1} into memory and loading that memory +location into a register of @var{class2}. The default definition returns +false for all inputs. +@end deftypefn + +@defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode}) +Normally when @code{TARGET_SECONDARY_MEMORY_NEEDED} is defined, the compiler +allocates a stack slot for a memory location needed for register copies. +If this macro is defined, the compiler instead uses the memory location +defined by this macro. + +Do not define this macro if you do not define +@code{TARGET_SECONDARY_MEMORY_NEEDED}. +@end defmac + +@deftypefn {Target Hook} machine_mode TARGET_SECONDARY_MEMORY_NEEDED_MODE (machine_mode @var{mode}) +If @code{TARGET_SECONDARY_MEMORY_NEEDED} tells the compiler to use memory +when moving between two particular registers of mode @var{mode}, +this hook specifies the mode that the memory should have. + +The default depends on @code{TARGET_LRA_P}. Without LRA, the default +is to use a word-sized mode for integral modes that are smaller than a +a word. This is right thing to do on most machines because it ensures +that all bits of the register are copied and prevents accesses to the +registers in a narrower mode, which some machines prohibit for +floating-point registers. + +However, this default behavior is not correct on some machines, such as +the DEC Alpha, that store short integers in floating-point registers +differently than in integer registers. On those machines, the default +widening will not work correctly and you must define this hook to +suppress that widening in some cases. See the file @file{alpha.cc} for +details. + +With LRA, the default is to use @var{mode} unmodified. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SELECT_EARLY_REMAT_MODES (sbitmap @var{modes}) +On some targets, certain modes cannot be held in registers around a +standard ABI call and are relatively expensive to spill to the stack. +The early rematerialization pass can help in such cases by aggressively +recomputing values after calls, so that they don't need to be spilled. + +This hook returns the set of such modes by setting the associated bits +in @var{modes}. The default implementation selects no modes, which has +the effect of disabling the early rematerialization pass. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CLASS_LIKELY_SPILLED_P (reg_class_t @var{rclass}) +A target hook which returns @code{true} if pseudos that have been assigned +to registers of class @var{rclass} would likely be spilled because +registers of @var{rclass} are needed for spill registers. + +The default version of this target hook returns @code{true} if @var{rclass} +has exactly one register and @code{false} otherwise. On most machines, this +default should be used. For generally register-starved machines, such as +i386, or machines with right register constraints, such as SH, this hook +can be used to avoid excessive spilling. + +This hook is also used by some of the global intra-procedural code +transformations to throtle code motion, to avoid increasing register +pressure. +@end deftypefn + +@deftypefn {Target Hook} {unsigned char} TARGET_CLASS_MAX_NREGS (reg_class_t @var{rclass}, machine_mode @var{mode}) +A target hook returns the maximum number of consecutive registers +of class @var{rclass} needed to hold a value of mode @var{mode}. + +This is closely related to the macro @code{TARGET_HARD_REGNO_NREGS}. +In fact, the value returned by @code{TARGET_CLASS_MAX_NREGS (@var{rclass}, +@var{mode})} target hook should be the maximum value of +@code{TARGET_HARD_REGNO_NREGS (@var{regno}, @var{mode})} for all @var{regno} +values in the class @var{rclass}. + +This target hook helps control the handling of multiple-word values +in the reload pass. + +The default version of this target hook returns the size of @var{mode} +in words. +@end deftypefn + +@defmac CLASS_MAX_NREGS (@var{class}, @var{mode}) +A C expression for the maximum number of consecutive registers +of class @var{class} needed to hold a value of mode @var{mode}. + +This is closely related to the macro @code{TARGET_HARD_REGNO_NREGS}. In fact, +the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})} +should be the maximum value of @code{TARGET_HARD_REGNO_NREGS (@var{regno}, +@var{mode})} for all @var{regno} values in the class @var{class}. + +This macro helps control the handling of multiple-word values +in the reload pass. +@end defmac + +@deftypefn {Target Hook} bool TARGET_CAN_CHANGE_MODE_CLASS (machine_mode @var{from}, machine_mode @var{to}, reg_class_t @var{rclass}) +This hook returns true if it is possible to bitcast values held in +registers of class @var{rclass} from mode @var{from} to mode @var{to} +and if doing so preserves the low-order bits that are common to both modes. +The result is only meaningful if @var{rclass} has registers that can hold +both @code{from} and @code{to}. The default implementation returns true. + +As an example of when such bitcasting is invalid, loading 32-bit integer or +floating-point objects into floating-point registers on Alpha extends them +to 64 bits. Therefore loading a 64-bit object and then storing it as a +32-bit object does not store the low-order 32 bits, as would be the case +for a normal register. Therefore, @file{alpha.h} defines +@code{TARGET_CAN_CHANGE_MODE_CLASS} to return: + +@smallexample +(GET_MODE_SIZE (from) == GET_MODE_SIZE (to) + || !reg_classes_intersect_p (FLOAT_REGS, rclass)) +@end smallexample + +Even if storing from a register in mode @var{to} would be valid, +if both @var{from} and @code{raw_reg_mode} for @var{rclass} are wider +than @code{word_mode}, then we must prevent @var{to} narrowing the +mode. This happens when the middle-end assumes that it can load +or store pieces of an @var{N}-word pseudo, and that the pseudo will +eventually be allocated to @var{N} @code{word_mode} hard registers. +Failure to prevent this kind of mode change will result in the +entire @code{raw_reg_mode} being modified instead of the partial +value that the middle-end intended. +@end deftypefn + +@deftypefn {Target Hook} reg_class_t TARGET_IRA_CHANGE_PSEUDO_ALLOCNO_CLASS (int, @var{reg_class_t}, @var{reg_class_t}) +A target hook which can change allocno class for given pseudo from + allocno and best class calculated by IRA. + + The default version of this target hook always returns given class. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_LRA_P (void) +A target hook which returns true if we use LRA instead of reload pass. + +The default version of this target hook returns true. New ports +should use LRA, and existing ports are encouraged to convert. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_REGISTER_PRIORITY (int) +A target hook which returns the register priority number to which the +register @var{hard_regno} belongs to. The bigger the number, the +more preferable the hard register usage (when all other conditions are +the same). This hook can be used to prefer some hard register over +others in LRA. For example, some x86-64 register usage needs +additional prefix which makes instructions longer. The hook can +return lower priority number for such registers make them less favorable +and as result making the generated code smaller. + +The default version of this target hook returns always zero. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_REGISTER_USAGE_LEVELING_P (void) +A target hook which returns true if we need register usage leveling. +That means if a few hard registers are equally good for the +assignment, we choose the least used hard register. The register +usage leveling may be profitable for some targets. Don't use the +usage leveling for targets with conditional execution or targets +with big register files as it hurts if-conversion and cross-jumping +optimizations. + +The default version of this target hook returns always false. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_DIFFERENT_ADDR_DISPLACEMENT_P (void) +A target hook which returns true if an address with the same structure +can have different maximal legitimate displacement. For example, the +displacement can depend on memory mode or on operand combinations in +the insn. + +The default version of this target hook returns always false. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CANNOT_SUBSTITUTE_MEM_EQUIV_P (rtx @var{subst}) +A target hook which returns @code{true} if @var{subst} can't +substitute safely pseudos with equivalent memory values during +register allocation. +The default version of this target hook returns @code{false}. +On most machines, this default should be used. For generally +machines with non orthogonal register usage for addressing, such +as SH, this hook can be used to avoid excessive spilling. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_LEGITIMIZE_ADDRESS_DISPLACEMENT (rtx *@var{offset1}, rtx *@var{offset2}, poly_int64 @var{orig_offset}, machine_mode @var{mode}) +This hook tries to split address offset @var{orig_offset} into +two parts: one that should be added to the base address to create +a local anchor point, and an additional offset that can be applied +to the anchor to address a value of mode @var{mode}. The idea is that +the local anchor could be shared by other accesses to nearby locations. + +The hook returns true if it succeeds, storing the offset of the +anchor from the base in @var{offset1} and the offset of the final address +from the anchor in @var{offset2}. The default implementation returns false. +@end deftypefn + +@deftypefn {Target Hook} reg_class_t TARGET_SPILL_CLASS (reg_class_t, @var{machine_mode}) +This hook defines a class of registers which could be used for spilling +pseudos of the given mode and class, or @code{NO_REGS} if only memory +should be used. Not defining this hook is equivalent to returning +@code{NO_REGS} for all inputs. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ADDITIONAL_ALLOCNO_CLASS_P (reg_class_t) +This hook should return @code{true} if given class of registers should +be an allocno class in any way. Usually RA uses only one register +class from all classes containing the same register set. In some +complicated cases, you need to have two or more such classes as +allocno ones for RA correct work. Not defining this hook is +equivalent to returning @code{false} for all inputs. +@end deftypefn + +@deftypefn {Target Hook} scalar_int_mode TARGET_CSTORE_MODE (enum insn_code @var{icode}) +This hook defines the machine mode to use for the boolean result of +conditional store patterns. The ICODE argument is the instruction code +for the cstore being performed. Not definiting this hook is the same +as accepting the mode encoded into operand 0 of the cstore expander +patterns. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_COMPUTE_PRESSURE_CLASSES (enum reg_class *@var{pressure_classes}) +A target hook which lets a backend compute the set of pressure classes to +be used by those optimization passes which take register pressure into +account, as opposed to letting IRA compute them. It returns the number of +register classes stored in the array @var{pressure_classes}. +@end deftypefn + +@node Stack and Calling +@section Stack Layout and Calling Conventions +@cindex calling conventions + +@c prevent bad page break with this line +This describes the stack layout and calling conventions. + +@menu +* Frame Layout:: +* Exception Handling:: +* Stack Checking:: +* Frame Registers:: +* Elimination:: +* Stack Arguments:: +* Register Arguments:: +* Scalar Return:: +* Aggregate Return:: +* Caller Saves:: +* Function Entry:: +* Profiling:: +* Tail Calls:: +* Shrink-wrapping separate components:: +* Stack Smashing Protection:: +* Miscellaneous Register Hooks:: +@end menu + +@node Frame Layout +@subsection Basic Stack Layout +@cindex stack frame layout +@cindex frame layout + +@c prevent bad page break with this line +Here is the basic stack layout. + +@defmac STACK_GROWS_DOWNWARD +Define this macro to be true if pushing a word onto the stack moves the stack +pointer to a smaller address, and false otherwise. +@end defmac + +@defmac STACK_PUSH_CODE +This macro defines the operation used when something is pushed +on the stack. In RTL, a push operation will be +@code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})} + +The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC}, +and @code{POST_INC}. Which of these is correct depends on +the stack direction and on whether the stack pointer points +to the last item on the stack or whether it points to the +space for the next item on the stack. + +The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is +true, which is almost always right, and @code{PRE_INC} otherwise, +which is often wrong. +@end defmac + +@defmac FRAME_GROWS_DOWNWARD +Define this macro to nonzero value if the addresses of local variable slots +are at negative offsets from the frame pointer. +@end defmac + +@defmac ARGS_GROW_DOWNWARD +Define this macro if successive arguments to a function occupy decreasing +addresses on the stack. +@end defmac + +@deftypefn {Target Hook} HOST_WIDE_INT TARGET_STARTING_FRAME_OFFSET (void) +This hook returns the offset from the frame pointer to the first local +variable slot to be allocated. If @code{FRAME_GROWS_DOWNWARD}, it is the +offset to @emph{end} of the first slot allocated, otherwise it is the +offset to @emph{beginning} of the first slot allocated. The default +implementation returns 0. +@end deftypefn + +@defmac STACK_ALIGNMENT_NEEDED +Define to zero to disable final alignment of the stack during reload. +The nonzero default for this macro is suitable for most ports. + +On ports where @code{TARGET_STARTING_FRAME_OFFSET} is nonzero or where there +is a register save block following the local block that doesn't require +alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable +stack alignment and do it in the backend. +@end defmac + +@defmac STACK_POINTER_OFFSET +Offset from the stack pointer register to the first location at which +outgoing arguments are placed. If not specified, the default value of +zero is used. This is the proper value for most machines. + +If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above +the first location at which outgoing arguments are placed. +@end defmac + +@defmac FIRST_PARM_OFFSET (@var{fundecl}) +Offset from the argument pointer register to the first argument's +address. On some machines it may depend on the data type of the +function. + +If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above +the first argument's address. +@end defmac + +@defmac STACK_DYNAMIC_OFFSET (@var{fundecl}) +Offset from the stack pointer register to an item dynamically allocated +on the stack, e.g., by @code{alloca}. + +The default value for this macro is @code{STACK_POINTER_OFFSET} plus the +length of the outgoing arguments. The default is correct for most +machines. See @file{function.cc} for details. +@end defmac + +@defmac INITIAL_FRAME_ADDRESS_RTX +A C expression whose value is RTL representing the address of the initial +stack frame. This address is passed to @code{RETURN_ADDR_RTX} and +@code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable +default value will be used. Define this macro in order to make frame pointer +elimination work in the presence of @code{__builtin_frame_address (count)} and +@code{__builtin_return_address (count)} for @code{count} not equal to zero. +@end defmac + +@defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr}) +A C expression whose value is RTL representing the address in a stack +frame where the pointer to the caller's frame is stored. Assume that +@var{frameaddr} is an RTL expression for the address of the stack frame +itself. + +If you don't define this macro, the default is to return the value +of @var{frameaddr}---that is, the stack frame address is also the +address of the stack word that points to the previous frame. +@end defmac + +@defmac SETUP_FRAME_ADDRESSES +A C expression that produces the machine-specific code to +setup the stack so that arbitrary frames can be accessed. For example, +on the SPARC, we must flush all of the register windows to the stack +before we can access arbitrary stack frames. You will seldom need to +define this macro. The default is to do nothing. +@end defmac + +@deftypefn {Target Hook} rtx TARGET_BUILTIN_SETJMP_FRAME_VALUE (void) +This target hook should return an rtx that is used to store +the address of the current frame into the built in @code{setjmp} buffer. +The default value, @code{virtual_stack_vars_rtx}, is correct for most +machines. One reason you may need to define this target hook is if +@code{hard_frame_pointer_rtx} is the appropriate value on your machine. +@end deftypefn + +@defmac FRAME_ADDR_RTX (@var{frameaddr}) +A C expression whose value is RTL representing the value of the frame +address for the current frame. @var{frameaddr} is the frame pointer +of the current frame. This is used for __builtin_frame_address. +You need only define this macro if the frame address is not the same +as the frame pointer. Most machines do not need to define it. +@end defmac + +@defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr}) +A C expression whose value is RTL representing the value of the return +address for the frame @var{count} steps up from the current frame, after +the prologue. @var{frameaddr} is the frame pointer of the @var{count} +frame, or the frame pointer of the @var{count} @minus{} 1 frame if +@code{RETURN_ADDR_IN_PREVIOUS_FRAME} is nonzero. + +The value of the expression must always be the correct address when +@var{count} is zero, but may be @code{NULL_RTX} if there is no way to +determine the return address of other frames. +@end defmac + +@defmac RETURN_ADDR_IN_PREVIOUS_FRAME +Define this macro to nonzero value if the return address of a particular +stack frame is accessed from the frame pointer of the previous stack +frame. The zero default for this macro is suitable for most ports. +@end defmac + +@defmac INCOMING_RETURN_ADDR_RTX +A C expression whose value is RTL representing the location of the +incoming return address at the beginning of any function, before the +prologue. This RTL is either a @code{REG}, indicating that the return +value is saved in @samp{REG}, or a @code{MEM} representing a location in +the stack. + +You only need to define this macro if you want to support call frame +debugging information like that provided by DWARF 2. + +If this RTL is a @code{REG}, you should also define +@code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}. +@end defmac + +@defmac DWARF_ALT_FRAME_RETURN_COLUMN +A C expression whose value is an integer giving a DWARF 2 column +number that may be used as an alternative return column. The column +must not correspond to any gcc hard register (that is, it must not +be in the range of @code{DWARF_FRAME_REGNUM}). + +This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a +general register, but an alternative column needs to be used for signal +frames. Some targets have also used different frame return columns +over time. +@end defmac + +@defmac DWARF_ZERO_REG +A C expression whose value is an integer giving a DWARF 2 register +number that is considered to always have the value zero. This should +only be defined if the target has an architected zero register, and +someone decided it was a good idea to use that register number to +terminate the stack backtrace. New ports should avoid this. +@end defmac + +@defmac DWARF_VERSION_DEFAULT +A C expression whose value is the default dwarf standard version we'll honor +and advertise when generating dwarf debug information, in absence of +an explicit @option{-gdwarf-@var{version}} option on the command line. +@end defmac + +@deftypefn {Target Hook} void TARGET_DWARF_HANDLE_FRAME_UNSPEC (const char *@var{label}, rtx @var{pattern}, int @var{index}) +This target hook allows the backend to emit frame-related insns that +contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging +info engine will invoke it on insns of the form +@smallexample +(set (reg) (unspec [@dots{}] UNSPEC_INDEX)) +@end smallexample +and +@smallexample +(set (reg) (unspec_volatile [@dots{}] UNSPECV_INDEX)). +@end smallexample +to let the backend emit the call frame instructions. @var{label} is +the CFI label attached to the insn, @var{pattern} is the pattern of +the insn and @var{index} is @code{UNSPEC_INDEX} or @code{UNSPECV_INDEX}. +@end deftypefn + +@deftypefn {Target Hook} {unsigned int} TARGET_DWARF_POLY_INDETERMINATE_VALUE (unsigned int @var{i}, unsigned int *@var{factor}, int *@var{offset}) +Express the value of @code{poly_int} indeterminate @var{i} as a DWARF +expression, with @var{i} counting from 1. Return the number of a DWARF +register @var{R} and set @samp{*@var{factor}} and @samp{*@var{offset}} such +that the value of the indeterminate is: +@smallexample +value_of(@var{R}) / @var{factor} - @var{offset} +@end smallexample + +A target only needs to define this hook if it sets +@samp{NUM_POLY_INT_COEFFS} to a value greater than 1. +@end deftypefn + +@defmac INCOMING_FRAME_SP_OFFSET +A C expression whose value is an integer giving the offset, in bytes, +from the value of the stack pointer register to the top of the stack +frame at the beginning of any function, before the prologue. The top of +the frame is defined to be the value of the stack pointer in the +previous frame, just before the call instruction. + +You only need to define this macro if you want to support call frame +debugging information like that provided by DWARF 2. +@end defmac + +@defmac DEFAULT_INCOMING_FRAME_SP_OFFSET +Like @code{INCOMING_FRAME_SP_OFFSET}, but must be the same for all +functions of the same ABI, and when using GAS @code{.cfi_*} directives +must also agree with the default CFI GAS emits. Define this macro +only if @code{INCOMING_FRAME_SP_OFFSET} can have different values +between different functions of the same ABI or when +@code{INCOMING_FRAME_SP_OFFSET} does not agree with GAS default CFI. +@end defmac + +@defmac ARG_POINTER_CFA_OFFSET (@var{fundecl}) +A C expression whose value is an integer giving the offset, in bytes, +from the argument pointer to the canonical frame address (cfa). The +final value should coincide with that calculated by +@code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable +during virtual register instantiation. + +The default value for this macro is +@code{FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size}, +which is correct for most machines; in general, the arguments are found +immediately before the stack frame. Note that this is not the case on +some targets that save registers into the caller's frame, such as SPARC +and rs6000, and so such targets need to define this macro. + +You only need to define this macro if the default is incorrect, and you +want to support call frame debugging information like that provided by +DWARF 2. +@end defmac + +@defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl}) +If defined, a C expression whose value is an integer giving the offset +in bytes from the frame pointer to the canonical frame address (cfa). +The final value should coincide with that calculated by +@code{INCOMING_FRAME_SP_OFFSET}. + +Normally the CFA is calculated as an offset from the argument pointer, +via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is +variable due to the ABI, this may not be possible. If this macro is +defined, it implies that the virtual register instantiation should be +based on the frame pointer instead of the argument pointer. Only one +of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET} +should be defined. +@end defmac + +@defmac CFA_FRAME_BASE_OFFSET (@var{fundecl}) +If defined, a C expression whose value is an integer giving the offset +in bytes from the canonical frame address (cfa) to the frame base used +in DWARF 2 debug information. The default is zero. A different value +may reduce the size of debug information on some ports. +@end defmac + +@node Exception Handling +@subsection Exception Handling Support +@cindex exception handling + +@defmac EH_RETURN_DATA_REGNO (@var{N}) +A C expression whose value is the @var{N}th register number used for +data by exception handlers, or @code{INVALID_REGNUM} if fewer than +@var{N} registers are usable. + +The exception handling library routines communicate with the exception +handlers via a set of agreed upon registers. Ideally these registers +should be call-clobbered; it is possible to use call-saved registers, +but may negatively impact code size. The target must support at least +2 data registers, but should define 4 if there are enough free registers. + +You must define this macro if you want to support call frame exception +handling like that provided by DWARF 2. +@end defmac + +@defmac EH_RETURN_STACKADJ_RTX +A C expression whose value is RTL representing a location in which +to store a stack adjustment to be applied before function return. +This is used to unwind the stack to an exception handler's call frame. +It will be assigned zero on code paths that return normally. + +Typically this is a call-clobbered hard register that is otherwise +untouched by the epilogue, but could also be a stack slot. + +Do not define this macro if the stack pointer is saved and restored +by the regular prolog and epilog code in the call frame itself; in +this case, the exception handling library routines will update the +stack location to be restored in place. Otherwise, you must define +this macro if you want to support call frame exception handling like +that provided by DWARF 2. +@end defmac + +@defmac EH_RETURN_HANDLER_RTX +A C expression whose value is RTL representing a location in which +to store the address of an exception handler to which we should +return. It will not be assigned on code paths that return normally. + +Typically this is the location in the call frame at which the normal +return address is stored. For targets that return by popping an +address off the stack, this might be a memory address just below +the @emph{target} call frame rather than inside the current call +frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already +been assigned, so it may be used to calculate the location of the +target call frame. + +Some targets have more complex requirements than storing to an +address calculable during initial code generation. In that case +the @code{eh_return} instruction pattern should be used instead. + +If you want to support call frame exception handling, you must +define either this macro or the @code{eh_return} instruction pattern. +@end defmac + +@defmac RETURN_ADDR_OFFSET +If defined, an integer-valued C expression for which rtl will be generated +to add it to the exception handler address before it is searched in the +exception handling tables, and to subtract it again from the address before +using it to return to the exception handler. +@end defmac + +@defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global}) +This macro chooses the encoding of pointers embedded in the exception +handling sections. If at all possible, this should be defined such +that the exception handling section will not require dynamic relocations, +and so may be read-only. + +@var{code} is 0 for data, 1 for code labels, 2 for function pointers. +@var{global} is true if the symbol may be affected by dynamic relocations. +The macro should return a combination of the @code{DW_EH_PE_*} defines +as found in @file{dwarf2.h}. + +If this macro is not defined, pointers will not be encoded but +represented directly. +@end defmac + +@defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done}) +This macro allows the target to emit whatever special magic is required +to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}. +Generic code takes care of pc-relative and indirect encodings; this must +be defined if the target uses text-relative or data-relative encodings. + +This is a C statement that branches to @var{done} if the format was +handled. @var{encoding} is the format chosen, @var{size} is the number +of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF} +to be emitted. +@end defmac + +@defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs}) +This macro allows the target to add CPU and operating system specific +code to the call-frame unwinder for use when there is no unwind data +available. The most common reason to implement this macro is to unwind +through signal frames. + +This macro is called from @code{uw_frame_state_for} in +@file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and +@file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; +@var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra} +for the address of the code being executed and @code{context->cfa} for +the stack pointer value. If the frame can be decoded, the register +save addresses should be updated in @var{fs} and the macro should +evaluate to @code{_URC_NO_REASON}. If the frame cannot be decoded, +the macro should evaluate to @code{_URC_END_OF_STACK}. + +For proper signal handling in Java this macro is accompanied by +@code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers. +@end defmac + +@defmac MD_HANDLE_UNWABI (@var{context}, @var{fs}) +This macro allows the target to add operating system specific code to the +call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive, +usually used for signal or interrupt frames. + +This macro is called from @code{uw_update_context} in libgcc's +@file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; +@var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi} +for the abi and context in the @code{.unwabi} directive. If the +@code{.unwabi} directive can be handled, the register save addresses should +be updated in @var{fs}. +@end defmac + +@defmac TARGET_USES_WEAK_UNWIND_INFO +A C expression that evaluates to true if the target requires unwind +info to be given comdat linkage. Define it to be @code{1} if comdat +linkage is necessary. The default is @code{0}. +@end defmac + +@node Stack Checking +@subsection Specifying How Stack Checking is Done + +GCC will check that stack references are within the boundaries of the +stack, if the option @option{-fstack-check} is specified, in one of +three ways: + +@enumerate +@item +If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC +will assume that you have arranged for full stack checking to be done +at appropriate places in the configuration files. GCC will not do +other special processing. + +@item +If @code{STACK_CHECK_BUILTIN} is zero and the value of the +@code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume +that you have arranged for static stack checking (checking of the +static stack frame of functions) to be done at appropriate places +in the configuration files. GCC will only emit code to do dynamic +stack checking (checking on dynamic stack allocations) using the third +approach below. + +@item +If neither of the above are true, GCC will generate code to periodically +``probe'' the stack pointer using the values of the macros defined below. +@end enumerate + +If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined, +GCC will change its allocation strategy for large objects if the option +@option{-fstack-check} is specified: they will always be allocated +dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes. + +@defmac STACK_CHECK_BUILTIN +A nonzero value if stack checking is done by the configuration files in a +machine-dependent manner. You should define this macro if stack checking +is required by the ABI of your machine or if you would like to do stack +checking in some more efficient way than the generic approach. The default +value of this macro is zero. +@end defmac + +@defmac STACK_CHECK_STATIC_BUILTIN +A nonzero value if static stack checking is done by the configuration files +in a machine-dependent manner. You should define this macro if you would +like to do static stack checking in some more efficient way than the generic +approach. The default value of this macro is zero. +@end defmac + +@defmac STACK_CHECK_PROBE_INTERVAL_EXP +An integer specifying the interval at which GCC must generate stack probe +instructions, defined as 2 raised to this integer. You will normally +define this macro so that the interval be no larger than the size of +the ``guard pages'' at the end of a stack area. The default value +of 12 (4096-byte interval) is suitable for most systems. +@end defmac + +@defmac STACK_CHECK_MOVING_SP +An integer which is nonzero if GCC should move the stack pointer page by page +when doing probes. This can be necessary on systems where the stack pointer +contains the bottom address of the memory area accessible to the executing +thread at any point in time. In this situation an alternate signal stack +is required in order to be able to recover from a stack overflow. The +default value of this macro is zero. +@end defmac + +@defmac STACK_CHECK_PROTECT +The number of bytes of stack needed to recover from a stack overflow, for +languages where such a recovery is supported. The default value of 4KB/8KB +with the @code{setjmp}/@code{longjmp}-based exception handling mechanism and +8KB/12KB with other exception handling mechanisms should be adequate for most +architectures and operating systems. +@end defmac + +The following macros are relevant only if neither STACK_CHECK_BUILTIN +nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether +in the opposite case. + +@defmac STACK_CHECK_MAX_FRAME_SIZE +The maximum size of a stack frame, in bytes. GCC will generate probe +instructions in non-leaf functions to ensure at least this many bytes of +stack are available. If a stack frame is larger than this size, stack +checking will not be reliable and GCC will issue a warning. The +default is chosen so that GCC only generates one instruction on most +systems. You should normally not change the default value of this macro. +@end defmac + +@defmac STACK_CHECK_FIXED_FRAME_SIZE +GCC uses this value to generate the above warning message. It +represents the amount of fixed frame used by a function, not including +space for any callee-saved registers, temporaries and user variables. +You need only specify an upper bound for this amount and will normally +use the default of four words. +@end defmac + +@defmac STACK_CHECK_MAX_VAR_SIZE +The maximum size, in bytes, of an object that GCC will place in the +fixed area of the stack frame when the user specifies +@option{-fstack-check}. +GCC computed the default from the values of the above macros and you will +normally not need to override that default. +@end defmac + +@deftypefn {Target Hook} HOST_WIDE_INT TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE (void) +Some targets have an ABI defined interval for which no probing needs to be done. +When a probe does need to be done this same interval is used as the probe distance +up when doing stack clash protection for alloca. +On such targets this value can be set to override the default probing up interval. +Define this variable to return nonzero if such a probe range is required or zero otherwise. +Defining this hook also requires your functions which make use of alloca to have at least 8 byes +of outgoing arguments. If this is not the case the stack will be corrupted. +You need not define this macro if it would always have the value zero. +@end deftypefn + +@need 2000 +@node Frame Registers +@subsection Registers That Address the Stack Frame + +@c prevent bad page break with this line +This discusses registers that address the stack frame. + +@defmac STACK_POINTER_REGNUM +The register number of the stack pointer register, which must also be a +fixed register according to @code{FIXED_REGISTERS}. On most machines, +the hardware determines which register this is. +@end defmac + +@defmac FRAME_POINTER_REGNUM +The register number of the frame pointer register, which is used to +access automatic variables in the stack frame. On some machines, the +hardware determines which register this is. On other machines, you can +choose any register you wish for this purpose. +@end defmac + +@defmac HARD_FRAME_POINTER_REGNUM +On some machines the offset between the frame pointer and starting +offset of the automatic variables is not known until after register +allocation has been done (for example, because the saved registers are +between these two locations). On those machines, define +@code{FRAME_POINTER_REGNUM} the number of a special, fixed register to +be used internally until the offset is known, and define +@code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number +used for the frame pointer. + +You should define this macro only in the very rare circumstances when it +is not possible to calculate the offset between the frame pointer and +the automatic variables until after register allocation has been +completed. When this macro is defined, you must also indicate in your +definition of @code{ELIMINABLE_REGS} how to eliminate +@code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM} +or @code{STACK_POINTER_REGNUM}. + +Do not define this macro if it would be the same as +@code{FRAME_POINTER_REGNUM}. +@end defmac + +@defmac ARG_POINTER_REGNUM +The register number of the arg pointer register, which is used to access +the function's argument list. On some machines, this is the same as the +frame pointer register. On some machines, the hardware determines which +register this is. On other machines, you can choose any register you +wish for this purpose. If this is not the same register as the frame +pointer register, then you must mark it as a fixed register according to +@code{FIXED_REGISTERS}, or arrange to be able to eliminate it +(@pxref{Elimination}). +@end defmac + +@defmac HARD_FRAME_POINTER_IS_FRAME_POINTER +Define this to a preprocessor constant that is nonzero if +@code{hard_frame_pointer_rtx} and @code{frame_pointer_rtx} should be +the same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM +== FRAME_POINTER_REGNUM)}; you only need to define this macro if that +definition is not suitable for use in preprocessor conditionals. +@end defmac + +@defmac HARD_FRAME_POINTER_IS_ARG_POINTER +Define this to a preprocessor constant that is nonzero if +@code{hard_frame_pointer_rtx} and @code{arg_pointer_rtx} should be the +same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM == +ARG_POINTER_REGNUM)}; you only need to define this macro if that +definition is not suitable for use in preprocessor conditionals. +@end defmac + +@defmac RETURN_ADDRESS_POINTER_REGNUM +The register number of the return address pointer register, which is used to +access the current function's return address from the stack. On some +machines, the return address is not at a fixed offset from the frame +pointer or stack pointer or argument pointer. This register can be defined +to point to the return address on the stack, and then be converted by +@code{ELIMINABLE_REGS} into either the frame pointer or stack pointer. + +Do not define this macro unless there is no other way to get the return +address from the stack. +@end defmac + +@defmac STATIC_CHAIN_REGNUM +@defmacx STATIC_CHAIN_INCOMING_REGNUM +Register numbers used for passing a function's static chain pointer. If +register windows are used, the register number as seen by the called +function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register +number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If +these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need +not be defined. + +The static chain register need not be a fixed register. + +If the static chain is passed in memory, these macros should not be +defined; instead, the @code{TARGET_STATIC_CHAIN} hook should be used. +@end defmac + +@deftypefn {Target Hook} rtx TARGET_STATIC_CHAIN (const_tree @var{fndecl_or_type}, bool @var{incoming_p}) +This hook replaces the use of @code{STATIC_CHAIN_REGNUM} et al for +targets that may use different static chain locations for different +nested functions. This may be required if the target has function +attributes that affect the calling conventions of the function and +those calling conventions use different static chain locations. + +The default version of this hook uses @code{STATIC_CHAIN_REGNUM} et al. + +If the static chain is passed in memory, this hook should be used to +provide rtx giving @code{mem} expressions that denote where they are stored. +Often the @code{mem} expression as seen by the caller will be at an offset +from the stack pointer and the @code{mem} expression as seen by the callee +will be at an offset from the frame pointer. +@findex stack_pointer_rtx +@findex frame_pointer_rtx +@findex arg_pointer_rtx +The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and +@code{arg_pointer_rtx} will have been initialized and should be used +to refer to those items. +@end deftypefn + +@defmac DWARF_FRAME_REGISTERS +This macro specifies the maximum number of hard registers that can be +saved in a call frame. This is used to size data structures used in +DWARF2 exception handling. + +Prior to GCC 3.0, this macro was needed in order to establish a stable +exception handling ABI in the face of adding new hard registers for ISA +extensions. In GCC 3.0 and later, the EH ABI is insulated from changes +in the number of hard registers. Nevertheless, this macro can still be +used to reduce the runtime memory requirements of the exception handling +routines, which can be substantial if the ISA contains a lot of +registers that are not call-saved. + +If this macro is not defined, it defaults to +@code{FIRST_PSEUDO_REGISTER}. +@end defmac + +@defmac PRE_GCC3_DWARF_FRAME_REGISTERS + +This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided +for backward compatibility in pre GCC 3.0 compiled code. + +If this macro is not defined, it defaults to +@code{DWARF_FRAME_REGISTERS}. +@end defmac + +@defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno}) + +Define this macro if the target's representation for dwarf registers +is different than the internal representation for unwind column. +Given a dwarf register, this macro should return the internal unwind +column number to use instead. +@end defmac + +@defmac DWARF_FRAME_REGNUM (@var{regno}) + +Define this macro if the target's representation for dwarf registers +used in .eh_frame or .debug_frame is different from that used in other +debug info sections. Given a GCC hard register number, this macro +should return the .eh_frame register number. The default is +@code{DEBUGGER_REGNO (@var{regno})}. + +@end defmac + +@defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh}) + +Define this macro to map register numbers held in the call frame info +that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that +should be output in .debug_frame (@code{@var{for_eh}} is zero) and +.eh_frame (@code{@var{for_eh}} is nonzero). The default is to +return @code{@var{regno}}. + +@end defmac + +@defmac REG_VALUE_IN_UNWIND_CONTEXT + +Define this macro if the target stores register values as +@code{_Unwind_Word} type in unwind context. It should be defined if +target register size is larger than the size of @code{void *}. The +default is to store register values as @code{void *} type. + +@end defmac + +@defmac ASSUME_EXTENDED_UNWIND_CONTEXT + +Define this macro to be 1 if the target always uses extended unwind +context with version, args_size and by_value fields. If it is undefined, +it will be defined to 1 when @code{REG_VALUE_IN_UNWIND_CONTEXT} is +defined and 0 otherwise. + +@end defmac + +@defmac DWARF_LAZY_REGISTER_VALUE (@var{regno}, @var{value}) +Define this macro if the target has pseudo DWARF registers whose +values need to be computed lazily on demand by the unwinder (such as when +referenced in a CFA expression). The macro returns true if @var{regno} +is such a register and stores its value in @samp{*@var{value}} if so. +@end defmac + +@node Elimination +@subsection Eliminating Frame Pointer and Arg Pointer + +@c prevent bad page break with this line +This is about eliminating the frame pointer and arg pointer. + +@deftypefn {Target Hook} bool TARGET_FRAME_POINTER_REQUIRED (void) +This target hook should return @code{true} if a function must have and use +a frame pointer. This target hook is called in the reload pass. If its return +value is @code{true} the function will have a frame pointer. + +This target hook can in principle examine the current function and decide +according to the facts, but on most machines the constant @code{false} or the +constant @code{true} suffices. Use @code{false} when the machine allows code +to be generated with no frame pointer, and doing so saves some time or space. +Use @code{true} when there is no possible advantage to avoiding a frame +pointer. + +In certain cases, the compiler does not know how to produce valid code +without a frame pointer. The compiler recognizes those cases and +automatically gives the function a frame pointer regardless of what +@code{targetm.frame_pointer_required} returns. You don't need to worry about +them. + +In a function that does not require a frame pointer, the frame pointer +register can be allocated for ordinary usage, unless you mark it as a +fixed register. See @code{FIXED_REGISTERS} for more information. + +Default return value is @code{false}. +@end deftypefn + +@defmac ELIMINABLE_REGS +This macro specifies a table of register pairs used to eliminate +unneeded registers that point into the stack frame. + +The definition of this macro is a list of structure initializations, each +of which specifies an original and replacement register. + +On some machines, the position of the argument pointer is not known until +the compilation is completed. In such a case, a separate hard register +must be used for the argument pointer. This register can be eliminated by +replacing it with either the frame pointer or the argument pointer, +depending on whether or not the frame pointer has been eliminated. + +In this case, you might specify: +@smallexample +#define ELIMINABLE_REGS \ +@{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \ + @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \ + @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@} +@end smallexample + +Note that the elimination of the argument pointer with the stack pointer is +specified first since that is the preferred elimination. +@end defmac + +@deftypefn {Target Hook} bool TARGET_CAN_ELIMINATE (const int @var{from_reg}, const int @var{to_reg}) +This target hook should return @code{true} if the compiler is allowed to +try to replace register number @var{from_reg} with register number +@var{to_reg}. This target hook will usually be @code{true}, since most of the +cases preventing register elimination are things that the compiler already +knows about. + +Default return value is @code{true}. +@end deftypefn + +@defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var}) +This macro returns the initial difference between the specified pair +of registers. The value would be computed from information +such as the result of @code{get_frame_size ()} and the tables of +registers @code{df_regs_ever_live_p} and @code{call_used_regs}. +@end defmac + +@deftypefn {Target Hook} void TARGET_COMPUTE_FRAME_LAYOUT (void) +This target hook is called once each time the frame layout needs to be +recalculated. The calculations can be cached by the target and can then +be used by @code{INITIAL_ELIMINATION_OFFSET} instead of re-computing the +layout on every invocation of that hook. This is particularly useful +for targets that have an expensive frame layout function. Implementing +this callback is optional. +@end deftypefn + +@node Stack Arguments +@subsection Passing Function Arguments on the Stack +@cindex arguments on stack +@cindex stack arguments + +The macros in this section control how arguments are passed +on the stack. See the following section for other macros that +control passing certain arguments in registers. + +@deftypefn {Target Hook} bool TARGET_PROMOTE_PROTOTYPES (const_tree @var{fntype}) +This target hook returns @code{true} if an argument declared in a +prototype as an integral type smaller than @code{int} should actually be +passed as an @code{int}. In addition to avoiding errors in certain +cases of mismatch, it also makes for better code on certain machines. +The default is to not promote prototypes. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_PUSH_ARGUMENT (unsigned int @var{npush}) +This target hook returns @code{true} if push instructions will be +used to pass outgoing arguments. When the push instruction usage is +optional, @var{npush} is nonzero to indicate the number of bytes to +push. Otherwise, @var{npush} is zero. If the target machine does not +have a push instruction or push instruction should be avoided, +@code{false} should be returned. That directs GCC to use an alternate +strategy: to allocate the entire argument block and then store the +arguments into it. If this target hook may return @code{true}, +@code{PUSH_ROUNDING} must be defined. +@end deftypefn + +@defmac PUSH_ARGS_REVERSED +A C expression. If nonzero, function arguments will be evaluated from +last to first, rather than from first to last. If this macro is not +defined, it defaults to @code{PUSH_ARGS} on targets where the stack +and args grow in opposite directions, and 0 otherwise. +@end defmac + +@defmac PUSH_ROUNDING (@var{npushed}) +A C expression that is the number of bytes actually pushed onto the +stack when an instruction attempts to push @var{npushed} bytes. + +On some machines, the definition + +@smallexample +#define PUSH_ROUNDING(BYTES) (BYTES) +@end smallexample + +@noindent +will suffice. But on other machines, instructions that appear +to push one byte actually push two bytes in an attempt to maintain +alignment. Then the definition should be + +@smallexample +#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) +@end smallexample + +If the value of this macro has a type, it should be an unsigned type. +@end defmac + +@findex outgoing_args_size +@findex crtl->outgoing_args_size +@defmac ACCUMULATE_OUTGOING_ARGS +A C expression. If nonzero, the maximum amount of space required for outgoing arguments +will be computed and placed into +@code{crtl->outgoing_args_size}. No space will be pushed +onto the stack for each call; instead, the function prologue should +increase the stack frame size by this amount. + +Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS} +is not proper. +@end defmac + +@defmac REG_PARM_STACK_SPACE (@var{fndecl}) +Define this macro if functions should assume that stack space has been +allocated for arguments even when their values are passed in +registers. + +The value of this macro is the size, in bytes, of the area reserved for +arguments passed in registers for the function represented by @var{fndecl}, +which can be zero if GCC is calling a library function. +The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself +of the function. + +This space can be allocated by the caller, or be a part of the +machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says +which. +@end defmac +@c above is overfull. not sure what to do. --mew 5feb93 did +@c something, not sure if it looks good. --mew 10feb93 + +@defmac INCOMING_REG_PARM_STACK_SPACE (@var{fndecl}) +Like @code{REG_PARM_STACK_SPACE}, but for incoming register arguments. +Define this macro if space guaranteed when compiling a function body +is different to space required when making a call, a situation that +can arise with K&R style function definitions. +@end defmac + +@defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype}) +Define this to a nonzero value if it is the responsibility of the +caller to allocate the area reserved for arguments passed in registers +when calling a function of @var{fntype}. @var{fntype} may be NULL +if the function called is a library function. + +If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls +whether the space for these arguments counts in the value of +@code{crtl->outgoing_args_size}. +@end defmac + +@defmac STACK_PARMS_IN_REG_PARM_AREA +Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the +stack parameters don't skip the area specified by it. +@c i changed this, makes more sens and it should have taken care of the +@c overfull.. not as specific, tho. --mew 5feb93 + +Normally, when a parameter is not passed in registers, it is placed on the +stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro +suppresses this behavior and causes the parameter to be passed on the +stack in its natural location. +@end defmac + +@deftypefn {Target Hook} poly_int64 TARGET_RETURN_POPS_ARGS (tree @var{fundecl}, tree @var{funtype}, poly_int64 @var{size}) +This target hook returns the number of bytes of its own arguments that +a function pops on returning, or 0 if the function pops no arguments +and the caller must therefore pop them all after the function returns. + +@var{fundecl} is a C variable whose value is a tree node that describes +the function in question. Normally it is a node of type +@code{FUNCTION_DECL} that describes the declaration of the function. +From this you can obtain the @code{DECL_ATTRIBUTES} of the function. + +@var{funtype} is a C variable whose value is a tree node that +describes the function in question. Normally it is a node of type +@code{FUNCTION_TYPE} that describes the data type of the function. +From this it is possible to obtain the data types of the value and +arguments (if known). + +When a call to a library function is being considered, @var{fundecl} +will contain an identifier node for the library function. Thus, if +you need to distinguish among various library functions, you can do so +by their names. Note that ``library function'' in this context means +a function used to perform arithmetic, whose name is known specially +in the compiler and was not mentioned in the C code being compiled. + +@var{size} is the number of bytes of arguments passed on the +stack. If a variable number of bytes is passed, it is zero, and +argument popping will always be the responsibility of the calling function. + +On the VAX, all functions always pop their arguments, so the definition +of this macro is @var{size}. On the 68000, using the standard +calling convention, no functions pop their arguments, so the value of +the macro is always 0 in this case. But an alternative calling +convention is available in which functions that take a fixed number of +arguments pop them but other functions (such as @code{printf}) pop +nothing (the caller pops all). When this convention is in use, +@var{funtype} is examined to determine whether a function takes a fixed +number of arguments. +@end deftypefn + +@defmac CALL_POPS_ARGS (@var{cum}) +A C expression that should indicate the number of bytes a call sequence +pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS} +when compiling a function call. + +@var{cum} is the variable in which all arguments to the called function +have been accumulated. + +On certain architectures, such as the SH5, a call trampoline is used +that pops certain registers off the stack, depending on the arguments +that have been passed to the function. Since this is a property of the +call site, not of the called function, @code{RETURN_POPS_ARGS} is not +appropriate. +@end defmac + +@node Register Arguments +@subsection Passing Arguments in Registers +@cindex arguments in registers +@cindex registers arguments + +This section describes the macros which let you control how various +types of arguments are passed in registers or how they are arranged in +the stack. + +@deftypefn {Target Hook} rtx TARGET_FUNCTION_ARG (cumulative_args_t @var{ca}, const function_arg_info @var{&arg}) +Return an RTX indicating whether function argument @var{arg} is passed +in a register and if so, which register. Argument @var{ca} summarizes all +the previous arguments. + +The return value is usually either a @code{reg} RTX for the hard +register in which to pass the argument, or zero to pass the argument +on the stack. + +The value of the expression can also be a @code{parallel} RTX@. This is +used when an argument is passed in multiple locations. The mode of the +@code{parallel} should be the mode of the entire argument. The +@code{parallel} holds any number of @code{expr_list} pairs; each one +describes where part of the argument is passed. In each +@code{expr_list} the first operand must be a @code{reg} RTX for the hard +register in which to pass this part of the argument, and the mode of the +register RTX indicates how large this part of the argument is. The +second operand of the @code{expr_list} is a @code{const_int} which gives +the offset in bytes into the entire argument of where this part starts. +As a special exception the first @code{expr_list} in the @code{parallel} +RTX may have a first operand of zero. This indicates that the entire +argument is also stored on the stack. + +The last time this hook is called, it is called with @code{MODE == +VOIDmode}, and its result is passed to the @code{call} or @code{call_value} +pattern as operands 2 and 3 respectively. + +@cindex @file{stdarg.h} and register arguments +The usual way to make the ISO library @file{stdarg.h} work on a +machine where some arguments are usually passed in registers, is to +cause nameless arguments to be passed on the stack instead. This is +done by making @code{TARGET_FUNCTION_ARG} return 0 whenever +@var{named} is @code{false}. + +@cindex @code{TARGET_MUST_PASS_IN_STACK}, and @code{TARGET_FUNCTION_ARG} +@cindex @code{REG_PARM_STACK_SPACE}, and @code{TARGET_FUNCTION_ARG} +You may use the hook @code{targetm.calls.must_pass_in_stack} +in the definition of this macro to determine if this argument is of a +type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE} +is not defined and @code{TARGET_FUNCTION_ARG} returns nonzero for such an +argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is +defined, the argument will be computed in the stack and then loaded into +a register. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_MUST_PASS_IN_STACK (const function_arg_info @var{&arg}) +This target hook should return @code{true} if we should not pass @var{arg} +solely in registers. The file @file{expr.h} defines a +definition that is usually appropriate, refer to @file{expr.h} for additional +documentation. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_FUNCTION_INCOMING_ARG (cumulative_args_t @var{ca}, const function_arg_info @var{&arg}) +Define this hook if the caller and callee on the target have different +views of where arguments are passed. Also define this hook if there are +functions that are never directly called, but are invoked by the hardware +and which have nonstandard calling conventions. + +In this case @code{TARGET_FUNCTION_ARG} computes the register in +which the caller passes the value, and +@code{TARGET_FUNCTION_INCOMING_ARG} should be defined in a similar +fashion to tell the function being called where the arguments will +arrive. + +@code{TARGET_FUNCTION_INCOMING_ARG} can also return arbitrary address +computation using hard register, which can be forced into a register, +so that it can be used to pass special arguments. + +If @code{TARGET_FUNCTION_INCOMING_ARG} is not defined, +@code{TARGET_FUNCTION_ARG} serves both purposes. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_USE_PSEUDO_PIC_REG (void) +This hook should return 1 in case pseudo register should be created +for pic_offset_table_rtx during function expand. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_INIT_PIC_REG (void) +Perform a target dependent initialization of pic_offset_table_rtx. +This hook is called at the start of register allocation. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_ARG_PARTIAL_BYTES (cumulative_args_t @var{cum}, const function_arg_info @var{&arg}) +This target hook returns the number of bytes at the beginning of an +argument that must be put in registers. The value must be zero for +arguments that are passed entirely in registers or that are entirely +pushed on the stack. + +On some machines, certain arguments must be passed partially in +registers and partially in memory. On these machines, typically the +first few words of arguments are passed in registers, and the rest +on the stack. If a multi-word argument (a @code{double} or a +structure) crosses that boundary, its first few words must be passed +in registers and the rest must be pushed. This macro tells the +compiler when this occurs, and how many bytes should go in registers. + +@code{TARGET_FUNCTION_ARG} for these arguments should return the first +register to be used by the caller for this argument; likewise +@code{TARGET_FUNCTION_INCOMING_ARG}, for the called function. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_PASS_BY_REFERENCE (cumulative_args_t @var{cum}, const function_arg_info @var{&arg}) +This target hook should return @code{true} if argument @var{arg} at the +position indicated by @var{cum} should be passed by reference. This +predicate is queried after target independent reasons for being +passed by reference, such as @code{TREE_ADDRESSABLE (@var{arg}.type)}. + +If the hook returns true, a copy of that argument is made in memory and a +pointer to the argument is passed instead of the argument itself. +The pointer is passed in whatever way is appropriate for passing a pointer +to that type. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CALLEE_COPIES (cumulative_args_t @var{cum}, const function_arg_info @var{&arg}) +The function argument described by the parameters to this hook is +known to be passed by reference. The hook should return true if the +function argument should be copied by the callee instead of copied +by the caller. + +For any argument for which the hook returns true, if it can be +determined that the argument is not modified, then a copy need +not be generated. + +The default version of this hook always returns false. +@end deftypefn + +@defmac CUMULATIVE_ARGS +A C type for declaring a variable that is used as the first argument +of @code{TARGET_FUNCTION_ARG} and other related values. For some +target machines, the type @code{int} suffices and can hold the number +of bytes of argument so far. + +There is no need to record in @code{CUMULATIVE_ARGS} anything about the +arguments that have been passed on the stack. The compiler has other +variables to keep track of that. For target machines on which all +arguments are passed on the stack, there is no need to store anything in +@code{CUMULATIVE_ARGS}; however, the data structure must exist and +should not be empty, so use @code{int}. +@end defmac + +@defmac OVERRIDE_ABI_FORMAT (@var{fndecl}) +If defined, this macro is called before generating any code for a +function, but after the @var{cfun} descriptor for the function has been +created. The back end may use this macro to update @var{cfun} to +reflect an ABI other than that which would normally be used by default. +If the compiler is generating code for a compiler-generated function, +@var{fndecl} may be @code{NULL}. +@end defmac + +@defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args}) +A C statement (sans semicolon) for initializing the variable +@var{cum} for the state at the beginning of the argument list. The +variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype} +is the tree node for the data type of the function which will receive +the args, or 0 if the args are to a compiler support library function. +For direct calls that are not libcalls, @var{fndecl} contain the +declaration node of the function. @var{fndecl} is also set when +@code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function +being compiled. @var{n_named_args} is set to the number of named +arguments, including a structure return address if it is passed as a +parameter, when making a call. When processing incoming arguments, +@var{n_named_args} is set to @minus{}1. + +When processing a call to a compiler support library function, +@var{libname} identifies which one. It is a @code{symbol_ref} rtx which +contains the name of the function, as a string. @var{libname} is 0 when +an ordinary C function call is being processed. Thus, each time this +macro is called, either @var{libname} or @var{fntype} is nonzero, but +never both of them at once. +@end defmac + +@defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname}) +Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls, +it gets a @code{MODE} argument instead of @var{fntype}, that would be +@code{NULL}. @var{indirect} would always be zero, too. If this macro +is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, +0)} is used instead. +@end defmac + +@defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname}) +Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of +finding the arguments for the function being compiled. If this macro is +undefined, @code{INIT_CUMULATIVE_ARGS} is used instead. + +The value passed for @var{libname} is always 0, since library routines +with special calling conventions are never compiled with GCC@. The +argument @var{libname} exists for symmetry with +@code{INIT_CUMULATIVE_ARGS}. +@c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe. +@c --mew 5feb93 i switched the order of the sentences. --mew 10feb93 +@end defmac + +@deftypefn {Target Hook} void TARGET_FUNCTION_ARG_ADVANCE (cumulative_args_t @var{ca}, const function_arg_info @var{&arg}) +This hook updates the summarizer variable pointed to by @var{ca} to +advance past argument @var{arg} in the argument list. Once this is done, +the variable @var{cum} is suitable for analyzing the @emph{following} +argument with @code{TARGET_FUNCTION_ARG}, etc. + +This hook need not do anything if the argument in question was passed +on the stack. The compiler knows how to track the amount of stack space +used for arguments without any special help. +@end deftypefn + +@deftypefn {Target Hook} HOST_WIDE_INT TARGET_FUNCTION_ARG_OFFSET (machine_mode @var{mode}, const_tree @var{type}) +This hook returns the number of bytes to add to the offset of an +argument of type @var{type} and mode @var{mode} when passed in memory. +This is needed for the SPU, which passes @code{char} and @code{short} +arguments in the preferred slot that is in the middle of the quad word +instead of starting at the top. The default implementation returns 0. +@end deftypefn + +@deftypefn {Target Hook} pad_direction TARGET_FUNCTION_ARG_PADDING (machine_mode @var{mode}, const_tree @var{type}) +This hook determines whether, and in which direction, to pad out +an argument of mode @var{mode} and type @var{type}. It returns +@code{PAD_UPWARD} to insert padding above the argument, @code{PAD_DOWNWARD} +to insert padding below the argument, or @code{PAD_NONE} to inhibit padding. + +The @emph{amount} of padding is not controlled by this hook, but by +@code{TARGET_FUNCTION_ARG_ROUND_BOUNDARY}. It is always just enough +to reach the next multiple of that boundary. + +This hook has a default definition that is right for most systems. +For little-endian machines, the default is to pad upward. For +big-endian machines, the default is to pad downward for an argument of +constant size shorter than an @code{int}, and upward otherwise. +@end deftypefn + +@defmac PAD_VARARGS_DOWN +If defined, a C expression which determines whether the default +implementation of va_arg will attempt to pad down before reading the +next argument, if that argument is smaller than its aligned space as +controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such +arguments are padded down if @code{BYTES_BIG_ENDIAN} is true. +@end defmac + +@defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first}) +Specify padding for the last element of a block move between registers and +memory. @var{first} is nonzero if this is the only element. Defining this +macro allows better control of register function parameters on big-endian +machines, without using @code{PARALLEL} rtl. In particular, +@code{MUST_PASS_IN_STACK} need not test padding and mode of types in +registers, as there is no longer a "wrong" part of a register; For example, +a three byte aggregate may be passed in the high part of a register if so +required. +@end defmac + +@deftypefn {Target Hook} {unsigned int} TARGET_FUNCTION_ARG_BOUNDARY (machine_mode @var{mode}, const_tree @var{type}) +This hook returns the alignment boundary, in bits, of an argument +with the specified mode and type. The default hook returns +@code{PARM_BOUNDARY} for all arguments. +@end deftypefn + +@deftypefn {Target Hook} {unsigned int} TARGET_FUNCTION_ARG_ROUND_BOUNDARY (machine_mode @var{mode}, const_tree @var{type}) +Normally, the size of an argument is rounded up to @code{PARM_BOUNDARY}, +which is the default value for this hook. You can define this hook to +return a different value if an argument size must be rounded to a larger +value. +@end deftypefn + +@defmac FUNCTION_ARG_REGNO_P (@var{regno}) +A C expression that is nonzero if @var{regno} is the number of a hard +register in which function arguments are sometimes passed. This does +@emph{not} include implicit arguments such as the static chain and +the structure-value address. On many machines, no registers can be +used for this purpose since all function arguments are pushed on the +stack. +@end defmac + +@deftypefn {Target Hook} bool TARGET_SPLIT_COMPLEX_ARG (const_tree @var{type}) +This hook should return true if parameter of type @var{type} are passed +as two scalar parameters. By default, GCC will attempt to pack complex +arguments into the target's word size. Some ABIs require complex arguments +to be split and treated as their individual components. For example, on +AIX64, complex floats should be passed in a pair of floating point +registers, even though a complex float would fit in one 64-bit floating +point register. + +The default value of this hook is @code{NULL}, which is treated as always +false. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_BUILD_BUILTIN_VA_LIST (void) +This hook returns a type node for @code{va_list} for the target. +The default version of the hook returns @code{void*}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_ENUM_VA_LIST_P (int @var{idx}, const char **@var{pname}, tree *@var{ptree}) +This target hook is used in function @code{c_common_nodes_and_builtins} +to iterate through the target specific builtin types for va_list. The +variable @var{idx} is used as iterator. @var{pname} has to be a pointer +to a @code{const char *} and @var{ptree} a pointer to a @code{tree} typed +variable. +The arguments @var{pname} and @var{ptree} are used to store the result of +this macro and are set to the name of the va_list builtin type and its +internal type. +If the return value of this macro is zero, then there is no more element. +Otherwise the @var{IDX} should be increased for the next call of this +macro to iterate through all types. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_FN_ABI_VA_LIST (tree @var{fndecl}) +This hook returns the va_list type of the calling convention specified by +@var{fndecl}. +The default version of this hook returns @code{va_list_type_node}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_CANONICAL_VA_LIST_TYPE (tree @var{type}) +This hook returns the va_list type of the calling convention specified by the +type of @var{type}. If @var{type} is not a valid va_list type, it returns +@code{NULL_TREE}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_GIMPLIFY_VA_ARG_EXPR (tree @var{valist}, tree @var{type}, gimple_seq *@var{pre_p}, gimple_seq *@var{post_p}) +This hook performs target-specific gimplification of +@code{VA_ARG_EXPR}. The first two parameters correspond to the +arguments to @code{va_arg}; the latter two are as in +@code{gimplify.cc:gimplify_expr}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VALID_POINTER_MODE (scalar_int_mode @var{mode}) +Define this to return nonzero if the port can handle pointers +with machine mode @var{mode}. The default version of this +hook returns true for both @code{ptr_mode} and @code{Pmode}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_REF_MAY_ALIAS_ERRNO (ao_ref *@var{ref}) +Define this to return nonzero if the memory reference @var{ref} +may alias with the system C library errno location. The default +version of this hook assumes the system C library errno location +is either a declaration of type int or accessed by dereferencing +a pointer to int. +@end deftypefn + +@deftypefn {Target Hook} machine_mode TARGET_TRANSLATE_MODE_ATTRIBUTE (machine_mode @var{mode}) +Define this hook if during mode attribute processing, the port should +translate machine_mode @var{mode} to another mode. For example, rs6000's +@code{KFmode}, when it is the same as @code{TFmode}. + +The default version of the hook returns that mode that was passed in. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCALAR_MODE_SUPPORTED_P (scalar_mode @var{mode}) +Define this to return nonzero if the port is prepared to handle +insns involving scalar mode @var{mode}. For a scalar mode to be +considered supported, all the basic arithmetic and comparisons +must work. + +The default version of this hook returns true for any mode +required to handle the basic C types (as defined by the port). +Included here are the double-word arithmetic supported by the +code in @file{optabs.cc}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VECTOR_MODE_SUPPORTED_P (machine_mode @var{mode}) +Define this to return nonzero if the port is prepared to handle +insns involving vector mode @var{mode}. At the very least, it +must have move patterns for this mode. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_COMPATIBLE_VECTOR_TYPES_P (const_tree @var{type1}, const_tree @var{type2}) +Return true if there is no target-specific reason for treating +vector types @var{type1} and @var{type2} as distinct types. The caller +has already checked for target-independent reasons, meaning that the +types are known to have the same mode, to have the same number of elements, +and to have what the caller considers to be compatible element types. + +The main reason for defining this hook is to reject pairs of types +that are handled differently by the target's calling convention. +For example, when a new @var{N}-bit vector architecture is added +to a target, the target may want to handle normal @var{N}-bit +@code{VECTOR_TYPE} arguments and return values in the same way as +before, to maintain backwards compatibility. However, it may also +provide new, architecture-specific @code{VECTOR_TYPE}s that are passed +and returned in a more efficient way. It is then important to maintain +a distinction between the ``normal'' @code{VECTOR_TYPE}s and the new +architecture-specific ones. + +The default implementation returns true, which is correct for most targets. +@end deftypefn + +@deftypefn {Target Hook} opt_machine_mode TARGET_ARRAY_MODE (machine_mode @var{mode}, unsigned HOST_WIDE_INT @var{nelems}) +Return the mode that GCC should use for an array that has +@var{nelems} elements, with each element having mode @var{mode}. +Return no mode if the target has no special requirements. In the +latter case, GCC looks for an integer mode of the appropriate size +if available and uses BLKmode otherwise. Usually the search for the +integer mode is limited to @code{MAX_FIXED_MODE_SIZE}, but the +@code{TARGET_ARRAY_MODE_SUPPORTED_P} hook allows a larger mode to be +used in specific cases. + +The main use of this hook is to specify that an array of vectors should +also have a vector mode. The default implementation returns no mode. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ARRAY_MODE_SUPPORTED_P (machine_mode @var{mode}, unsigned HOST_WIDE_INT @var{nelems}) +Return true if GCC should try to use a scalar mode to store an array +of @var{nelems} elements, given that each element has mode @var{mode}. +Returning true here overrides the usual @code{MAX_FIXED_MODE} limit +and allows GCC to use any defined integer mode. + +One use of this hook is to support vector load and store operations +that operate on several homogeneous vectors. For example, ARM NEON +has operations like: + +@smallexample +int8x8x3_t vld3_s8 (const int8_t *) +@end smallexample + +where the return type is defined as: + +@smallexample +typedef struct int8x8x3_t +@{ + int8x8_t val[3]; +@} int8x8x3_t; +@end smallexample + +If this hook allows @code{val} to have a scalar mode, then +@code{int8x8x3_t} can have the same mode. GCC can then store +@code{int8x8x3_t}s in registers rather than forcing them onto the stack. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P (scalar_float_mode @var{mode}) +Define this to return nonzero if libgcc provides support for the +floating-point mode @var{mode}, which is known to pass +@code{TARGET_SCALAR_MODE_SUPPORTED_P}. The default version of this +hook returns true for all of @code{SFmode}, @code{DFmode}, +@code{XFmode} and @code{TFmode}, if such modes exist. +@end deftypefn + +@deftypefn {Target Hook} opt_scalar_float_mode TARGET_FLOATN_MODE (int @var{n}, bool @var{extended}) +Define this to return the machine mode to use for the type +@code{_Float@var{n}}, if @var{extended} is false, or the type +@code{_Float@var{n}x}, if @var{extended} is true. If such a type is not +supported, return @code{opt_scalar_float_mode ()}. The default version of +this hook returns @code{SFmode} for @code{_Float32}, @code{DFmode} for +@code{_Float64} and @code{_Float32x} and @code{TFmode} for +@code{_Float128}, if those modes exist and satisfy the requirements for +those types and pass @code{TARGET_SCALAR_MODE_SUPPORTED_P} and +@code{TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P}; for @code{_Float64x}, it +returns the first of @code{XFmode} and @code{TFmode} that exists and +satisfies the same requirements; for other types, it returns +@code{opt_scalar_float_mode ()}. The hook is only called for values +of @var{n} and @var{extended} that are valid according to +ISO/IEC TS 18661-3:2015; that is, @var{n} is one of 32, 64, 128, or, +if @var{extended} is false, 16 or greater than 128 and a multiple of 32. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_FLOATN_BUILTIN_P (int @var{func}) +Define this to return true if the @code{_Float@var{n}} and +@code{_Float@var{n}x} built-in functions should implicitly enable the +built-in function without the @code{__builtin_} prefix in addition to the +normal built-in function with the @code{__builtin_} prefix. The default is +to only enable built-in functions without the @code{__builtin_} prefix for +the GNU C langauge. In strict ANSI/ISO mode, the built-in function without +the @code{__builtin_} prefix is not enabled. The argument @code{FUNC} is the +@code{enum built_in_function} id of the function to be enabled. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P (machine_mode @var{mode}) +Define this to return nonzero for machine modes for which the port has +small register classes. If this target hook returns nonzero for a given +@var{mode}, the compiler will try to minimize the lifetime of registers +in @var{mode}. The hook may be called with @code{VOIDmode} as argument. +In this case, the hook is expected to return nonzero if it returns nonzero +for any mode. + +On some machines, it is risky to let hard registers live across arbitrary +insns. Typically, these machines have instructions that require values +to be in specific registers (like an accumulator), and reload will fail +if the required hard register is used for another purpose across such an +insn. + +Passes before reload do not know which hard registers will be used +in an instruction, but the machine modes of the registers set or used in +the instruction are already known. And for some machines, register +classes are small for, say, integer registers but not for floating point +registers. For example, the AMD x86-64 architecture requires specific +registers for the legacy x86 integer instructions, but there are many +SSE registers for floating point operations. On such targets, a good +strategy may be to return nonzero from this hook for @code{INTEGRAL_MODE_P} +machine modes but zero for the SSE register classes. + +The default version of this hook returns false for any mode. It is always +safe to redefine this hook to return with a nonzero value. But if you +unnecessarily define it, you will reduce the amount of optimizations +that can be performed in some cases. If you do not define this hook +to return a nonzero value when it is required, the compiler will run out +of spill registers and print a fatal error message. +@end deftypefn + +@node Scalar Return +@subsection How Scalar Function Values Are Returned +@cindex return values in registers +@cindex values, returned by functions +@cindex scalars, returned as values + +This section discusses the macros that control returning scalars as +values---values that can fit in registers. + +@deftypefn {Target Hook} rtx TARGET_FUNCTION_VALUE (const_tree @var{ret_type}, const_tree @var{fn_decl_or_type}, bool @var{outgoing}) + +Define this to return an RTX representing the place where a function +returns or receives a value of data type @var{ret_type}, a tree node +representing a data type. @var{fn_decl_or_type} is a tree node +representing @code{FUNCTION_DECL} or @code{FUNCTION_TYPE} of a +function being called. If @var{outgoing} is false, the hook should +compute the register in which the caller will see the return value. +Otherwise, the hook should return an RTX representing the place where +a function returns a value. + +On many machines, only @code{TYPE_MODE (@var{ret_type})} is relevant. +(Actually, on most machines, scalar values are returned in the same +place regardless of mode.) The value of the expression is usually a +@code{reg} RTX for the hard register where the return value is stored. +The value can also be a @code{parallel} RTX, if the return value is in +multiple places. See @code{TARGET_FUNCTION_ARG} for an explanation of the +@code{parallel} form. Note that the callee will populate every +location specified in the @code{parallel}, but if the first element of +the @code{parallel} contains the whole return value, callers will use +that element as the canonical location and ignore the others. The m68k +port uses this type of @code{parallel} to return pointers in both +@samp{%a0} (the canonical location) and @samp{%d0}. + +If @code{TARGET_PROMOTE_FUNCTION_RETURN} returns true, you must apply +the same promotion rules specified in @code{PROMOTE_MODE} if +@var{valtype} is a scalar type. + +If the precise function being called is known, @var{func} is a tree +node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null +pointer. This makes it possible to use a different value-returning +convention for specific functions when all their calls are +known. + +Some target machines have ``register windows'' so that the register in +which a function returns its value is not the same as the one in which +the caller sees the value. For such machines, you should return +different RTX depending on @var{outgoing}. + +@code{TARGET_FUNCTION_VALUE} is not used for return values with +aggregate data types, because these are returned in another way. See +@code{TARGET_STRUCT_VALUE_RTX} and related macros, below. +@end deftypefn + +@defmac FUNCTION_VALUE (@var{valtype}, @var{func}) +This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for +a new target instead. +@end defmac + +@defmac LIBCALL_VALUE (@var{mode}) +A C expression to create an RTX representing the place where a library +function returns a value of mode @var{mode}. + +Note that ``library function'' in this context means a compiler +support routine, used to perform arithmetic, whose name is known +specially by the compiler and was not mentioned in the C code being +compiled. +@end defmac + +@deftypefn {Target Hook} rtx TARGET_LIBCALL_VALUE (machine_mode @var{mode}, const_rtx @var{fun}) +Define this hook if the back-end needs to know the name of the libcall +function in order to determine where the result should be returned. + +The mode of the result is given by @var{mode} and the name of the called +library function is given by @var{fun}. The hook should return an RTX +representing the place where the library function result will be returned. + +If this hook is not defined, then LIBCALL_VALUE will be used. +@end deftypefn + +@defmac FUNCTION_VALUE_REGNO_P (@var{regno}) +A C expression that is nonzero if @var{regno} is the number of a hard +register in which the values of called function may come back. + +A register whose use for returning values is limited to serving as the +second of a pair (for a value of type @code{double}, say) need not be +recognized by this macro. So for most machines, this definition +suffices: + +@smallexample +#define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) +@end smallexample + +If the machine has register windows, so that the caller and the called +function use different registers for the return value, this macro +should recognize only the caller's register numbers. + +This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE_REGNO_P} +for a new target instead. +@end defmac + +@deftypefn {Target Hook} bool TARGET_FUNCTION_VALUE_REGNO_P (const unsigned int @var{regno}) +A target hook that return @code{true} if @var{regno} is the number of a hard +register in which the values of called function may come back. + +A register whose use for returning values is limited to serving as the +second of a pair (for a value of type @code{double}, say) need not be +recognized by this target hook. + +If the machine has register windows, so that the caller and the called +function use different registers for the return value, this target hook +should recognize only the caller's register numbers. + +If this hook is not defined, then FUNCTION_VALUE_REGNO_P will be used. +@end deftypefn + +@defmac APPLY_RESULT_SIZE +Define this macro if @samp{untyped_call} and @samp{untyped_return} +need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for +saving and restoring an arbitrary return value. +@end defmac + +@deftypevr {Target Hook} bool TARGET_OMIT_STRUCT_RETURN_REG +Normally, when a function returns a structure by memory, the address +is passed as an invisible pointer argument, but the compiler also +arranges to return the address from the function like it would a normal +pointer return value. Define this to true if that behavior is +undesirable on your target. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_RETURN_IN_MSB (const_tree @var{type}) +This hook should return true if values of type @var{type} are returned +at the most significant end of a register (in other words, if they are +padded at the least significant end). You can assume that @var{type} +is returned in a register; the caller is required to check this. + +Note that the register provided by @code{TARGET_FUNCTION_VALUE} must +be able to hold the complete return value. For example, if a 1-, 2- +or 3-byte structure is returned at the most significant end of a +4-byte register, @code{TARGET_FUNCTION_VALUE} should provide an +@code{SImode} rtx. +@end deftypefn + +@node Aggregate Return +@subsection How Large Values Are Returned +@cindex aggregates as return values +@cindex large return values +@cindex returning aggregate values +@cindex structure value address + +When a function value's mode is @code{BLKmode} (and in some other +cases), the value is not returned according to +@code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the +caller passes the address of a block of memory in which the value +should be stored. This address is called the @dfn{structure value +address}. + +This section describes how to control returning structure values in +memory. + +@deftypefn {Target Hook} bool TARGET_RETURN_IN_MEMORY (const_tree @var{type}, const_tree @var{fntype}) +This target hook should return a nonzero value to say to return the +function value in memory, just as large structures are always returned. +Here @var{type} will be the data type of the value, and @var{fntype} +will be the type of the function doing the returning, or @code{NULL} for +libcalls. + +Note that values of mode @code{BLKmode} must be explicitly handled +by this function. Also, the option @option{-fpcc-struct-return} +takes effect regardless of this macro. On most systems, it is +possible to leave the hook undefined; this causes a default +definition to be used, whose value is the constant 1 for @code{BLKmode} +values, and 0 otherwise. + +Do not use this hook to indicate that structures and unions should always +be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN} +to indicate this. +@end deftypefn + +@defmac DEFAULT_PCC_STRUCT_RETURN +Define this macro to be 1 if all structure and union return values must be +in memory. Since this results in slower code, this should be defined +only if needed for compatibility with other compilers or with an ABI@. +If you define this macro to be 0, then the conventions used for structure +and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY} +target hook. + +If not defined, this defaults to the value 1. +@end defmac + +@deftypefn {Target Hook} rtx TARGET_STRUCT_VALUE_RTX (tree @var{fndecl}, int @var{incoming}) +This target hook should return the location of the structure value +address (normally a @code{mem} or @code{reg}), or 0 if the address is +passed as an ``invisible'' first argument. Note that @var{fndecl} may +be @code{NULL}, for libcalls. You do not need to define this target +hook if the address is always passed as an ``invisible'' first +argument. + +On some architectures the place where the structure value address +is found by the called function is not the same place that the +caller put it. This can be due to register windows, or it could +be because the function prologue moves it to a different place. +@var{incoming} is @code{1} or @code{2} when the location is needed in +the context of the called function, and @code{0} in the context of +the caller. + +If @var{incoming} is nonzero and the address is to be found on the +stack, return a @code{mem} which refers to the frame pointer. If +@var{incoming} is @code{2}, the result is being used to fetch the +structure value address at the beginning of a function. If you need +to emit adjusting code, you should do it at this point. +@end deftypefn + +@defmac PCC_STATIC_STRUCT_RETURN +Define this macro if the usual system convention on the target machine +for returning structures and unions is for the called function to return +the address of a static variable containing the value. + +Do not define this if the usual system convention is for the caller to +pass an address to the subroutine. + +This macro has effect in @option{-fpcc-struct-return} mode, but it does +nothing when you use @option{-freg-struct-return} mode. +@end defmac + +@deftypefn {Target Hook} fixed_size_mode TARGET_GET_RAW_RESULT_MODE (int @var{regno}) +This target hook returns the mode to be used when accessing raw return +registers in @code{__builtin_return}. Define this macro if the value +in @var{reg_raw_mode} is not correct. +@end deftypefn + +@deftypefn {Target Hook} fixed_size_mode TARGET_GET_RAW_ARG_MODE (int @var{regno}) +This target hook returns the mode to be used when accessing raw argument +registers in @code{__builtin_apply_args}. Define this macro if the value +in @var{reg_raw_mode} is not correct. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_EMPTY_RECORD_P (const_tree @var{type}) +This target hook returns true if the type is an empty record. The default +is to return @code{false}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_WARN_PARAMETER_PASSING_ABI (cumulative_args_t @var{ca}, tree @var{type}) +This target hook warns about the change in empty class parameter passing +ABI. +@end deftypefn + +@node Caller Saves +@subsection Caller-Saves Register Allocation + +If you enable it, GCC can save registers around function calls. This +makes it possible to use call-clobbered registers to hold variables that +must live across calls. + +@defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs}) +A C expression specifying which mode is required for saving @var{nregs} +of a pseudo-register in call-clobbered hard register @var{regno}. If +@var{regno} is unsuitable for caller save, @code{VOIDmode} should be +returned. For most machines this macro need not be defined since GCC +will select the smallest suitable mode. +@end defmac + +@node Function Entry +@subsection Function Entry and Exit +@cindex function entry and exit +@cindex prologue +@cindex epilogue + +This section describes the macros that output function entry +(@dfn{prologue}) and exit (@dfn{epilogue}) code. + +@deftypefn {Target Hook} void TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY (FILE *@var{file}, unsigned HOST_WIDE_INT @var{patch_area_size}, bool @var{record_p}) +Generate a patchable area at the function start, consisting of +@var{patch_area_size} NOP instructions. If the target supports named +sections and if @var{record_p} is true, insert a pointer to the current +location in the table of patchable functions. The default implementation +of the hook places the table of pointers in the special section named +@code{__patchable_function_entries}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}) +If defined, a function that outputs the assembler code for entry to a +function. The prologue is responsible for setting up the stack frame, +initializing the frame pointer register, saving registers that must be +saved, and allocating @var{size} additional bytes of storage for the +local variables. @var{file} is a stdio stream to which the assembler +code should be output. + +The label for the beginning of the function need not be output by this +macro. That has already been done when the macro is run. + +@findex regs_ever_live +To determine which registers to save, the macro can refer to the array +@code{regs_ever_live}: element @var{r} is nonzero if hard register +@var{r} is used anywhere within the function. This implies the function +prologue should save register @var{r}, provided it is not one of the +call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use +@code{regs_ever_live}.) + +On machines that have ``register windows'', the function entry code does +not save on the stack the registers that are in the windows, even if +they are supposed to be preserved by function calls; instead it takes +appropriate steps to ``push'' the register stack, if any non-call-used +registers are used in the function. + +@findex frame_pointer_needed +On machines where functions may or may not have frame-pointers, the +function entry code must vary accordingly; it must set up the frame +pointer if one is wanted, and not otherwise. To determine whether a +frame pointer is in wanted, the macro can refer to the variable +@code{frame_pointer_needed}. The variable's value will be 1 at run +time in a function that needs a frame pointer. @xref{Elimination}. + +The function entry code is responsible for allocating any stack space +required for the function. This stack space consists of the regions +listed below. In most cases, these regions are allocated in the +order listed, with the last listed region closest to the top of the +stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and +the highest address if it is not defined). You can use a different order +for a machine if doing so is more convenient or required for +compatibility reasons. Except in cases where required by standard +or by a debugger, there is no reason why the stack layout used by GCC +need agree with that used by other compilers for a machine. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file}) +If defined, a function that outputs assembler code at the end of a +prologue. This should be used when the function prologue is being +emitted as RTL, and you have some extra assembler that needs to be +emitted. @xref{prologue instruction pattern}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file}) +If defined, a function that outputs assembler code at the start of an +epilogue. This should be used when the function epilogue is being +emitted as RTL, and you have some extra assembler that needs to be +emitted. @xref{epilogue instruction pattern}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}) +If defined, a function that outputs the assembler code for exit from a +function. The epilogue is responsible for restoring the saved +registers and stack pointer to their values when the function was +called, and returning control to the caller. This macro takes the +same argument as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the +registers to restore are determined from @code{regs_ever_live} and +@code{CALL_USED_REGISTERS} in the same way. + +On some machines, there is a single instruction that does all the work +of returning from the function. On these machines, give that +instruction the name @samp{return} and do not define the macro +@code{TARGET_ASM_FUNCTION_EPILOGUE} at all. + +Do not define a pattern named @samp{return} if you want the +@code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target +switches to control whether return instructions or epilogues are used, +define a @samp{return} pattern with a validity condition that tests the +target switches appropriately. If the @samp{return} pattern's validity +condition is false, epilogues will be used. + +On machines where functions may or may not have frame-pointers, the +function exit code must vary accordingly. Sometimes the code for these +two cases is completely different. To determine whether a frame pointer +is wanted, the macro can refer to the variable +@code{frame_pointer_needed}. The variable's value will be 1 when compiling +a function that needs a frame pointer. + +Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and +@code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially. +The C variable @code{current_function_is_leaf} is nonzero for such a +function. @xref{Leaf Functions}. + +On some machines, some functions pop their arguments on exit while +others leave that for the caller to do. For example, the 68020 when +given @option{-mrtd} pops arguments in functions that take a fixed +number of arguments. + +@findex pops_args +@findex crtl->args.pops_args +Your definition of the macro @code{RETURN_POPS_ARGS} decides which +functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE} +needs to know what was decided. The number of bytes of the current +function's arguments that this function should pop is available in +@code{crtl->args.pops_args}. @xref{Scalar Return}. +@end deftypefn + +@itemize @bullet +@item +@findex pretend_args_size +@findex crtl->args.pretend_args_size +A region of @code{crtl->args.pretend_args_size} bytes of +uninitialized space just underneath the first argument arriving on the +stack. (This may not be at the very start of the allocated stack region +if the calling sequence has pushed anything else since pushing the stack +arguments. But usually, on such machines, nothing else has been pushed +yet, because the function prologue itself does all the pushing.) This +region is used on machines where an argument may be passed partly in +registers and partly in memory, and, in some cases to support the +features in @code{}. + +@item +An area of memory used to save certain registers used by the function. +The size of this area, which may also include space for such things as +the return address and pointers to previous stack frames, is +machine-specific and usually depends on which registers have been used +in the function. Machines with register windows often do not require +a save area. + +@item +A region of at least @var{size} bytes, possibly rounded up to an allocation +boundary, to contain the local variables of the function. On some machines, +this region and the save area may occur in the opposite order, with the +save area closer to the top of the stack. + +@item +@cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames +Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of +@code{crtl->outgoing_args_size} bytes to be used for outgoing +argument lists of the function. @xref{Stack Arguments}. +@end itemize + +@defmac EXIT_IGNORE_STACK +Define this macro as a C expression that is nonzero if the return +instruction or the function epilogue ignores the value of the stack +pointer; in other words, if it is safe to delete an instruction to +adjust the stack pointer before a return from the function. The +default is 0. + +Note that this macro's value is relevant only for functions for which +frame pointers are maintained. It is never safe to delete a final +stack adjustment in a function that has no frame pointer, and the +compiler knows this regardless of @code{EXIT_IGNORE_STACK}. +@end defmac + +@defmac EPILOGUE_USES (@var{regno}) +Define this macro as a C expression that is nonzero for registers that are +used by the epilogue or the @samp{return} pattern. The stack and frame +pointer registers are already assumed to be used as needed. +@end defmac + +@defmac EH_USES (@var{regno}) +Define this macro as a C expression that is nonzero for registers that are +used by the exception handling mechanism, and so should be considered live +on entry to an exception edge. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_MI_THUNK (FILE *@var{file}, tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, tree @var{function}) +A function that outputs the assembler code for a thunk +function, used to implement C++ virtual function calls with multiple +inheritance. The thunk acts as a wrapper around a virtual function, +adjusting the implicit object parameter before handing control off to +the real function. + +First, emit code to add the integer @var{delta} to the location that +contains the incoming first argument. Assume that this argument +contains a pointer, and is the one used to pass the @code{this} pointer +in C++. This is the incoming argument @emph{before} the function prologue, +e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of +all other incoming arguments. + +Then, if @var{vcall_offset} is nonzero, an additional adjustment should be +made after adding @code{delta}. In particular, if @var{p} is the +adjusted pointer, the following adjustment should be made: + +@smallexample +p += (*((ptrdiff_t **)p))[vcall_offset/sizeof(ptrdiff_t)] +@end smallexample + +After the additions, emit code to jump to @var{function}, which is a +@code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does +not touch the return address. Hence returning from @var{FUNCTION} will +return to whoever called the current @samp{thunk}. + +The effect must be as if @var{function} had been called directly with +the adjusted first argument. This macro is responsible for emitting all +of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE} +and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked. + +The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function} +have already been extracted from it.) It might possibly be useful on +some targets, but probably not. + +If you do not define this macro, the target-independent code in the C++ +front end will generate a less efficient heavyweight thunk that calls +@var{function} instead of jumping to it. The generic approach does +not support varargs. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ASM_CAN_OUTPUT_MI_THUNK (const_tree @var{thunk_fndecl}, HOST_WIDE_INT @var{delta}, HOST_WIDE_INT @var{vcall_offset}, const_tree @var{function}) +A function that returns true if TARGET_ASM_OUTPUT_MI_THUNK would be able +to output the assembler code for the thunk function specified by the +arguments it is passed, and false otherwise. In the latter case, the +generic approach will be used by the C++ front end, with the limitations +previously exposed. +@end deftypefn + +@node Profiling +@subsection Generating Code for Profiling +@cindex profiling, code generation + +These macros will help you generate code for profiling. + +@defmac FUNCTION_PROFILER (@var{file}, @var{labelno}) +A C statement or compound statement to output to @var{file} some +assembler code to call the profiling subroutine @code{mcount}. + +@findex mcount +The details of how @code{mcount} expects to be called are determined by +your operating system environment, not by GCC@. To figure them out, +compile a small program for profiling using the system's installed C +compiler and look at the assembler code that results. + +Older implementations of @code{mcount} expect the address of a counter +variable to be loaded into some register. The name of this variable is +@samp{LP} followed by the number @var{labelno}, so you would generate +the name using @samp{LP%d} in a @code{fprintf}. +@end defmac + +@defmac PROFILE_HOOK +A C statement or compound statement to output to @var{file} some assembly +code to call the profiling subroutine @code{mcount} even the target does +not support profiling. +@end defmac + +@defmac NO_PROFILE_COUNTERS +Define this macro to be an expression with a nonzero value if the +@code{mcount} subroutine on your system does not need a counter variable +allocated for each function. This is true for almost all modern +implementations. If you define this macro, you must not use the +@var{labelno} argument to @code{FUNCTION_PROFILER}. +@end defmac + +@defmac PROFILE_BEFORE_PROLOGUE +Define this macro if the code for function profiling should come before +the function prologue. Normally, the profiling code comes after. +@end defmac + +@deftypefn {Target Hook} bool TARGET_KEEP_LEAF_WHEN_PROFILED (void) +This target hook returns true if the target wants the leaf flag for +the current function to stay true even if it calls mcount. This might +make sense for targets using the leaf flag only to determine whether a +stack frame needs to be generated or not and for which the call to +mcount is generated before the function prologue. +@end deftypefn + +@node Tail Calls +@subsection Permitting tail calls +@cindex tail calls + +@deftypefn {Target Hook} bool TARGET_FUNCTION_OK_FOR_SIBCALL (tree @var{decl}, tree @var{exp}) +True if it is OK to do sibling call optimization for the specified +call expression @var{exp}. @var{decl} will be the called function, +or @code{NULL} if this is an indirect call. + +It is not uncommon for limitations of calling conventions to prevent +tail calls to functions outside the current unit of translation, or +during PIC compilation. The hook is used to enforce these restrictions, +as the @code{sibcall} md pattern cannot fail, or fall over to a +``normal'' call. The criteria for successful sibling call optimization +may vary greatly between different architectures. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_EXTRA_LIVE_ON_ENTRY (bitmap @var{regs}) +Add any hard registers to @var{regs} that are live on entry to the +function. This hook only needs to be defined to provide registers that +cannot be found by examination of FUNCTION_ARG_REGNO_P, the callee saved +registers, STATIC_CHAIN_INCOMING_REGNUM, STATIC_CHAIN_REGNUM, +TARGET_STRUCT_VALUE_RTX, FRAME_POINTER_REGNUM, EH_USES, +FRAME_POINTER_REGNUM, ARG_POINTER_REGNUM, and the PIC_OFFSET_TABLE_REGNUM. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SET_UP_BY_PROLOGUE (struct hard_reg_set_container *@var{}) +This hook should add additional registers that are computed by the prologue +to the hard regset for shrink-wrapping optimization purposes. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_WARN_FUNC_RETURN (tree) +True if a function's return statements should be checked for matching +the function's return type. This includes checking for falling off the end +of a non-void function. Return false if no such check should be made. +@end deftypefn + +@node Shrink-wrapping separate components +@subsection Shrink-wrapping separate components +@cindex shrink-wrapping separate components + +The prologue may perform a variety of target dependent tasks such as +saving callee-saved registers, saving the return address, aligning the +stack, creating a stack frame, initializing the PIC register, setting +up the static chain, etc. + +On some targets some of these tasks may be independent of others and +thus may be shrink-wrapped separately. These independent tasks are +referred to as components and are handled generically by the target +independent parts of GCC. + +Using the following hooks those prologue or epilogue components can be +shrink-wrapped separately, so that the initialization (and possibly +teardown) those components do is not done as frequently on execution +paths where this would unnecessary. + +What exactly those components are is up to the target code; the generic +code treats them abstractly, as a bit in an @code{sbitmap}. These +@code{sbitmap}s are allocated by the @code{shrink_wrap.get_separate_components} +and @code{shrink_wrap.components_for_bb} hooks, and deallocated by the +generic code. + +@deftypefn {Target Hook} sbitmap TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS (void) +This hook should return an @code{sbitmap} with the bits set for those +components that can be separately shrink-wrapped in the current function. +Return @code{NULL} if the current function should not get any separate +shrink-wrapping. +Don't define this hook if it would always return @code{NULL}. +If it is defined, the other hooks in this group have to be defined as well. +@end deftypefn + +@deftypefn {Target Hook} sbitmap TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB (basic_block) +This hook should return an @code{sbitmap} with the bits set for those +components where either the prologue component has to be executed before +the @code{basic_block}, or the epilogue component after it, or both. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS (sbitmap @var{components}, edge @var{e}, sbitmap @var{edge_components}, bool @var{is_prologue}) +This hook should clear the bits in the @var{components} bitmap for those +components in @var{edge_components} that the target cannot handle on edge +@var{e}, where @var{is_prologue} says if this is for a prologue or an +epilogue instead. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS (sbitmap) +Emit prologue insns for the components indicated by the parameter. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS (sbitmap) +Emit epilogue insns for the components indicated by the parameter. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS (sbitmap) +Mark the components in the parameter as handled, so that the +@code{prologue} and @code{epilogue} named patterns know to ignore those +components. The target code should not hang on to the @code{sbitmap}, it +will be deleted after this call. +@end deftypefn + +@node Stack Smashing Protection +@subsection Stack smashing protection +@cindex stack smashing protection + +@deftypefn {Target Hook} tree TARGET_STACK_PROTECT_GUARD (void) +This hook returns a @code{DECL} node for the external variable to use +for the stack protection guard. This variable is initialized by the +runtime to some random value and is used to initialize the guard value +that is placed at the top of the local stack frame. The type of this +variable must be @code{ptr_type_node}. + +The default version of this hook creates a variable called +@samp{__stack_chk_guard}, which is normally defined in @file{libgcc2.c}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_STACK_PROTECT_FAIL (void) +This hook returns a @code{CALL_EXPR} that alerts the runtime that the +stack protect guard variable has been modified. This expression should +involve a call to a @code{noreturn} function. + +The default version of this hook invokes a function called +@samp{__stack_chk_fail}, taking no arguments. This function is +normally defined in @file{libgcc2.c}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_STACK_PROTECT_RUNTIME_ENABLED_P (void) +Returns true if the target wants GCC's default stack protect runtime support, +otherwise return false. The default implementation always returns true. +@end deftypefn + +@deftypefn {Common Target Hook} bool TARGET_SUPPORTS_SPLIT_STACK (bool @var{report}, struct gcc_options *@var{opts}) +Whether this target supports splitting the stack when the options +described in @var{opts} have been passed. This is called +after options have been parsed, so the target may reject splitting +the stack in some configurations. The default version of this hook +returns false. If @var{report} is true, this function may issue a warning +or error; if @var{report} is false, it must simply return a value +@end deftypefn + +@deftypefn {Common Target Hook} {vec} TARGET_GET_VALID_OPTION_VALUES (int @var{option_code}, const char *@var{prefix}) +The hook is used for options that have a non-trivial list of +possible option values. OPTION_CODE is option code of opt_code +enum type. PREFIX is used for bash completion and allows an implementation +to return more specific completion based on the prefix. All string values +should be allocated from heap memory and consumers should release them. +The result will be pruned to cases with PREFIX if not NULL. +@end deftypefn + +@node Miscellaneous Register Hooks +@subsection Miscellaneous register hooks +@cindex miscellaneous register hooks + +@deftypevr {Target Hook} bool TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS +Set to true if each call that binds to a local definition explicitly +clobbers or sets all non-fixed registers modified by performing the call. +That is, by the call pattern itself, or by code that might be inserted by the +linker (e.g.@: stubs, veneers, branch islands), but not including those +modifiable by the callee. The affected registers may be mentioned explicitly +in the call pattern, or included as clobbers in CALL_INSN_FUNCTION_USAGE. +The default version of this hook is set to false. The purpose of this hook +is to enable the fipa-ra optimization. +@end deftypevr + +@node Varargs +@section Implementing the Varargs Macros +@cindex varargs implementation + +GCC comes with an implementation of @code{} and +@code{} that work without change on machines that pass arguments +on the stack. Other machines require their own implementations of +varargs, and the two machine independent header files must have +conditionals to include it. + +ISO @code{} differs from traditional @code{} mainly in +the calling convention for @code{va_start}. The traditional +implementation takes just one argument, which is the variable in which +to store the argument pointer. The ISO implementation of +@code{va_start} takes an additional second argument. The user is +supposed to write the last named argument of the function here. + +However, @code{va_start} should not use this argument. The way to find +the end of the named arguments is with the built-in functions described +below. + +@defmac __builtin_saveregs () +Use this built-in function to save the argument registers in memory so +that the varargs mechanism can access them. Both ISO and traditional +versions of @code{va_start} must use @code{__builtin_saveregs}, unless +you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead. + +On some machines, @code{__builtin_saveregs} is open-coded under the +control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On +other machines, it calls a routine written in assembler language, +found in @file{libgcc2.c}. + +Code generated for the call to @code{__builtin_saveregs} appears at the +beginning of the function, as opposed to where the call to +@code{__builtin_saveregs} is written, regardless of what the code is. +This is because the registers must be saved before the function starts +to use them for its own purposes. +@c i rewrote the first sentence above to fix an overfull hbox. --mew +@c 10feb93 +@end defmac + +@defmac __builtin_next_arg (@var{lastarg}) +This builtin returns the address of the first anonymous stack +argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it +returns the address of the location above the first anonymous stack +argument. Use it in @code{va_start} to initialize the pointer for +fetching arguments from the stack. Also use it in @code{va_start} to +verify that the second parameter @var{lastarg} is the last named argument +of the current function. +@end defmac + +@defmac __builtin_classify_type (@var{object}) +Since each machine has its own conventions for which data types are +passed in which kind of register, your implementation of @code{va_arg} +has to embody these conventions. The easiest way to categorize the +specified data type is to use @code{__builtin_classify_type} together +with @code{sizeof} and @code{__alignof__}. + +@code{__builtin_classify_type} ignores the value of @var{object}, +considering only its data type. It returns an integer describing what +kind of type that is---integer, floating, pointer, structure, and so on. + +The file @file{typeclass.h} defines an enumeration that you can use to +interpret the values of @code{__builtin_classify_type}. +@end defmac + +These machine description macros help implement varargs: + +@deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN_SAVEREGS (void) +If defined, this hook produces the machine-specific code for a call to +@code{__builtin_saveregs}. This code will be moved to the very +beginning of the function, before any parameter access are made. The +return value of this function should be an RTX that contains the value +to use as the return of @code{__builtin_saveregs}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SETUP_INCOMING_VARARGS (cumulative_args_t @var{args_so_far}, const function_arg_info @var{&arg}, int *@var{pretend_args_size}, int @var{second_time}) +This target hook offers an alternative to using +@code{__builtin_saveregs} and defining the hook +@code{TARGET_EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous +register arguments into the stack so that all the arguments appear to +have been passed consecutively on the stack. Once this is done, you can +use the standard implementation of varargs that works for machines that +pass all their arguments on the stack. + +The argument @var{args_so_far} points to the @code{CUMULATIVE_ARGS} data +structure, containing the values that are obtained after processing the +named arguments. The argument @var{arg} describes the last of these named +arguments. The argument @var{arg} should not be used if the function type +satisfies @code{TYPE_NO_NAMED_ARGS_STDARG_P}, since in that case there are +no named arguments and all arguments are accessed with @code{va_arg}. + +The target hook should do two things: first, push onto the stack all the +argument registers @emph{not} used for the named arguments, and second, +store the size of the data thus pushed into the @code{int}-valued +variable pointed to by @var{pretend_args_size}. The value that you +store here will serve as additional offset for setting up the stack +frame. + +Because you must generate code to push the anonymous arguments at +compile time without knowing their data types, +@code{TARGET_SETUP_INCOMING_VARARGS} is only useful on machines that +have just a single category of argument register and use it uniformly +for all data types. + +If the argument @var{second_time} is nonzero, it means that the +arguments of the function are being analyzed for the second time. This +happens for an inline function, which is not actually compiled until the +end of the source file. The hook @code{TARGET_SETUP_INCOMING_VARARGS} should +not generate any instructions in this case. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_STRICT_ARGUMENT_NAMING (cumulative_args_t @var{ca}) +Define this hook to return @code{true} if the location where a function +argument is passed depends on whether or not it is a named argument. + +This hook controls how the @var{named} argument to @code{TARGET_FUNCTION_ARG} +is set for varargs and stdarg functions. If this hook returns +@code{true}, the @var{named} argument is always true for named +arguments, and false for unnamed arguments. If it returns @code{false}, +but @code{TARGET_PRETEND_OUTGOING_VARARGS_NAMED} returns @code{true}, +then all arguments are treated as named. Otherwise, all named arguments +except the last are treated as named. + +You need not define this hook if it always returns @code{false}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_CALL_ARGS (rtx, @var{tree}) +While generating RTL for a function call, this target hook is invoked once +for each argument passed to the function, either a register returned by +@code{TARGET_FUNCTION_ARG} or a memory location. It is called just +before the point where argument registers are stored. The type of the +function to be called is also passed as the second argument; it is +@code{NULL_TREE} for libcalls. The @code{TARGET_END_CALL_ARGS} hook is +invoked just after the code to copy the return reg has been emitted. +This functionality can be used to perform special setup of call argument +registers if a target needs it. +For functions without arguments, the hook is called once with @code{pc_rtx} +passed instead of an argument register. +Most ports do not need to implement anything for this hook. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_END_CALL_ARGS (void) +This target hook is invoked while generating RTL for a function call, +just after the point where the return reg is copied into a pseudo. It +signals that all the call argument and return registers for the just +emitted call are now no longer in use. +Most ports do not need to implement anything for this hook. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_PRETEND_OUTGOING_VARARGS_NAMED (cumulative_args_t @var{ca}) +If you need to conditionally change ABIs so that one works with +@code{TARGET_SETUP_INCOMING_VARARGS}, but the other works like neither +@code{TARGET_SETUP_INCOMING_VARARGS} nor @code{TARGET_STRICT_ARGUMENT_NAMING} was +defined, then define this hook to return @code{true} if +@code{TARGET_SETUP_INCOMING_VARARGS} is used, @code{false} otherwise. +Otherwise, you should not define this hook. +@end deftypefn + +@node Trampolines +@section Support for Nested Functions +@cindex support for nested functions +@cindex trampolines for nested functions +@cindex descriptors for nested functions +@cindex nested functions, support for + +Taking the address of a nested function requires special compiler +handling to ensure that the static chain register is loaded when +the function is invoked via an indirect call. + +GCC has traditionally supported nested functions by creating an +executable @dfn{trampoline} at run time when the address of a nested +function is taken. This is a small piece of code which normally +resides on the stack, in the stack frame of the containing function. +The trampoline loads the static chain register and then jumps to the +real address of the nested function. + +The use of trampolines requires an executable stack, which is a +security risk. To avoid this problem, GCC also supports another +strategy: using descriptors for nested functions. Under this model, +taking the address of a nested function results in a pointer to a +non-executable function descriptor object. Initializing the static chain +from the descriptor is handled at indirect call sites. + +On some targets, including HPPA and IA-64, function descriptors may be +mandated by the ABI or be otherwise handled in a target-specific way +by the back end in its code generation strategy for indirect calls. +GCC also provides its own generic descriptor implementation to support the +@option{-fno-trampolines} option. In this case runtime detection of +function descriptors at indirect call sites relies on descriptor +pointers being tagged with a bit that is never set in bare function +addresses. Since GCC's generic function descriptors are +not ABI-compliant, this option is typically used only on a +per-language basis (notably by Ada) or when it can otherwise be +applied to the whole program. + +For languages other than Ada, the @code{-ftrampolines} and +@code{-fno-trampolines} options currently have no effect, and +trampolines are always generated on platforms that need them +for nested functions. + +Define the following hook if your backend either implements ABI-specified +descriptor support, or can use GCC's generic descriptor implementation +for nested functions. + +@deftypevr {Target Hook} int TARGET_CUSTOM_FUNCTION_DESCRIPTORS +If the target can use GCC's generic descriptor mechanism for nested +functions, define this hook to a power of 2 representing an unused bit +in function pointers which can be used to differentiate descriptors at +run time. This value gives the number of bytes by which descriptor +pointers are misaligned compared to function pointers. For example, on +targets that require functions to be aligned to a 4-byte boundary, a +value of either 1 or 2 is appropriate unless the architecture already +reserves the bit for another purpose, such as on ARM. + +Define this hook to 0 if the target implements ABI support for +function descriptors in its standard calling sequence, like for example +HPPA or IA-64. + +Using descriptors for nested functions +eliminates the need for trampolines that reside on the stack and require +it to be made executable. +@end deftypevr + +The following macros tell GCC how to generate code to allocate and +initialize an executable trampoline. You can also use this interface +if your back end needs to create ABI-specified non-executable descriptors; in +this case the "trampoline" created is the descriptor containing data only. + +The instructions in an executable trampoline must do two things: load +a constant address into the static chain register, and jump to the real +address of the nested function. On CISC machines such as the m68k, +this requires two instructions, a move immediate and a jump. Then the +two addresses exist in the trampoline as word-long immediate operands. +On RISC machines, it is often necessary to load each address into a +register in two parts. Then pieces of each address form separate +immediate operands. + +The code generated to initialize the trampoline must store the variable +parts---the static chain value and the function address---into the +immediate operands of the instructions. On a CISC machine, this is +simply a matter of copying each address to a memory reference at the +proper offset from the start of the trampoline. On a RISC machine, it +may be necessary to take out pieces of the address and store them +separately. + +@deftypefn {Target Hook} void TARGET_ASM_TRAMPOLINE_TEMPLATE (FILE *@var{f}) +This hook is called by @code{assemble_trampoline_template} to output, +on the stream @var{f}, assembler code for a block of data that contains +the constant parts of a trampoline. This code should not include a +label---the label is taken care of automatically. + +If you do not define this hook, it means no template is needed +for the target. Do not define this hook on systems where the block move +code to copy the trampoline into place would be larger than the code +to generate it on the spot. +@end deftypefn + +@defmac TRAMPOLINE_SECTION +Return the section into which the trampoline template is to be placed +(@pxref{Sections}). The default value is @code{readonly_data_section}. +@end defmac + +@defmac TRAMPOLINE_SIZE +A C expression for the size in bytes of the trampoline, as an integer. +@end defmac + +@defmac TRAMPOLINE_ALIGNMENT +Alignment required for trampolines, in bits. + +If you don't define this macro, the value of @code{FUNCTION_ALIGNMENT} +is used for aligning trampolines. +@end defmac + +@deftypefn {Target Hook} void TARGET_TRAMPOLINE_INIT (rtx @var{m_tramp}, tree @var{fndecl}, rtx @var{static_chain}) +This hook is called to initialize a trampoline. +@var{m_tramp} is an RTX for the memory block for the trampoline; @var{fndecl} +is the @code{FUNCTION_DECL} for the nested function; @var{static_chain} is an +RTX for the static chain value that should be passed to the function +when it is called. + +If the target defines @code{TARGET_ASM_TRAMPOLINE_TEMPLATE}, then the +first thing this hook should do is emit a block move into @var{m_tramp} +from the memory block returned by @code{assemble_trampoline_template}. +Note that the block move need only cover the constant parts of the +trampoline. If the target isolates the variable parts of the trampoline +to the end, not all @code{TRAMPOLINE_SIZE} bytes need be copied. + +If the target requires any other actions, such as flushing caches +(possibly calling function maybe_emit_call_builtin___clear_cache) or +enabling stack execution, these actions should be performed after +initializing the trampoline proper. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_EMIT_CALL_BUILTIN___CLEAR_CACHE (rtx @var{begin}, rtx @var{end}) +On targets that do not define a @code{clear_cache} insn expander, +but that define the @code{CLEAR_CACHE_INSN} macro, +maybe_emit_call_builtin___clear_cache relies on this target hook +to clear an address range in the instruction cache. + +The default implementation calls the @code{__clear_cache} builtin, +taking the assembler name from the builtin declaration. Overriding +definitions may call alternate functions, with alternate calling +conventions, or emit alternate RTX to perform the job. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_TRAMPOLINE_ADJUST_ADDRESS (rtx @var{addr}) +This hook should perform any machine-specific adjustment in +the address of the trampoline. Its argument contains the address of the +memory block that was passed to @code{TARGET_TRAMPOLINE_INIT}. In case +the address to be used for a function call should be different from the +address at which the template was stored, the different address should +be returned; otherwise @var{addr} should be returned unchanged. +If this hook is not defined, @var{addr} will be used for function calls. +@end deftypefn + +Implementing trampolines is difficult on many machines because they have +separate instruction and data caches. Writing into a stack location +fails to clear the memory in the instruction cache, so when the program +jumps to that location, it executes the old contents. + +Here are two possible solutions. One is to clear the relevant parts of +the instruction cache whenever a trampoline is set up. The other is to +make all trampolines identical, by having them jump to a standard +subroutine. The former technique makes trampoline execution faster; the +latter makes initialization faster. + +To clear the instruction cache when a trampoline is initialized, define +the following macro. + +@defmac CLEAR_INSN_CACHE (@var{beg}, @var{end}) +If defined, expands to a C expression clearing the @emph{instruction +cache} in the specified interval. The definition of this macro would +typically be a series of @code{asm} statements. Both @var{beg} and +@var{end} are pointer expressions. +@end defmac + +To use a standard subroutine, define the following macro. In addition, +you must make sure that the instructions in a trampoline fill an entire +cache line with identical instructions, or else ensure that the +beginning of the trampoline code is always aligned at the same point in +its cache line. Look in @file{m68k.h} as a guide. + +@defmac TRANSFER_FROM_TRAMPOLINE +Define this macro if trampolines need a special subroutine to do their +work. The macro should expand to a series of @code{asm} statements +which will be compiled with GCC@. They go in a library function named +@code{__transfer_from_trampoline}. + +If you need to avoid executing the ordinary prologue code of a compiled +C function when you jump to the subroutine, you can do so by placing a +special label of your own in the assembler code. Use one @code{asm} +statement to generate an assembler label, and another to make the label +global. Then trampolines can use that label to jump directly to your +special assembler code. +@end defmac + +@node Library Calls +@section Implicit Calls to Library Routines +@cindex library subroutine names +@cindex @file{libgcc.a} + +@c prevent bad page break with this line +Here is an explanation of implicit calls to library routines. + +@defmac DECLARE_LIBRARY_RENAMES +This macro, if defined, should expand to a piece of C code that will get +expanded when compiling functions for libgcc.a. It can be used to +provide alternate names for GCC's internal library functions if there +are ABI-mandated names that the compiler should provide. +@end defmac + +@findex set_optab_libfunc +@findex init_one_libfunc +@deftypefn {Target Hook} void TARGET_INIT_LIBFUNCS (void) +This hook should declare additional library routines or rename +existing ones, using the functions @code{set_optab_libfunc} and +@code{init_one_libfunc} defined in @file{optabs.cc}. +@code{init_optabs} calls this macro after initializing all the normal +library routines. + +The default is to do nothing. Most ports don't need to define this hook. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_LIBFUNC_GNU_PREFIX +If false (the default), internal library routines start with two +underscores. If set to true, these routines start with @code{__gnu_} +instead. E.g., @code{__muldi3} changes to @code{__gnu_muldi3}. This +currently only affects functions defined in @file{libgcc2.c}. If this +is set to true, the @file{tm.h} file must also +@code{#define LIBGCC2_GNU_PREFIX}. +@end deftypevr + +@defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison}) +This macro should return @code{true} if the library routine that +implements the floating point comparison operator @var{comparison} in +mode @var{mode} will return a boolean, and @var{false} if it will +return a tristate. + +GCC's own floating point libraries return tristates from the +comparison operators, so the default returns false always. Most ports +don't need to define this macro. +@end defmac + +@defmac TARGET_LIB_INT_CMP_BIASED +This macro should evaluate to @code{true} if the integer comparison +functions (like @code{__cmpdi2}) return 0 to indicate that the first +operand is smaller than the second, 1 to indicate that they are equal, +and 2 to indicate that the first operand is greater than the second. +If this macro evaluates to @code{false} the comparison functions return +@minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines +in @file{libgcc.a}, you do not need to define this macro. +@end defmac + +@defmac TARGET_HAS_NO_HW_DIVIDE +This macro should be defined if the target has no hardware divide +instructions. If this macro is defined, GCC will use an algorithm which +make use of simple logical and arithmetic operations for 64-bit +division. If the macro is not defined, GCC will use an algorithm which +make use of a 64-bit by 32-bit divide primitive. +@end defmac + +@cindex @code{EDOM}, implicit usage +@findex matherr +@defmac TARGET_EDOM +The value of @code{EDOM} on the target machine, as a C integer constant +expression. If you don't define this macro, GCC does not attempt to +deposit the value of @code{EDOM} into @code{errno} directly. Look in +@file{/usr/include/errno.h} to find the value of @code{EDOM} on your +system. + +If you do not define @code{TARGET_EDOM}, then compiled code reports +domain errors by calling the library function and letting it report the +error. If mathematical functions on your system use @code{matherr} when +there is an error, then you should leave @code{TARGET_EDOM} undefined so +that @code{matherr} is used normally. +@end defmac + +@cindex @code{errno}, implicit usage +@defmac GEN_ERRNO_RTX +Define this macro as a C expression to create an rtl expression that +refers to the global ``variable'' @code{errno}. (On certain systems, +@code{errno} may not actually be a variable.) If you don't define this +macro, a reasonable default is used. +@end defmac + +@deftypefn {Target Hook} bool TARGET_LIBC_HAS_FUNCTION (enum function_class @var{fn_class}, tree @var{type}) +This hook determines whether a function from a class of functions +@var{fn_class} is present in the target C library. If @var{type} is NULL, +the caller asks for support for all standard (float, double, long double) +types. If @var{type} is non-NULL, the caller asks for support for a +specific type. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_LIBC_HAS_FAST_FUNCTION (int @var{fcode}) +This hook determines whether a function from a class of functions +@code{(enum function_class)}@var{fcode} has a fast implementation. +@end deftypefn + +@defmac NEXT_OBJC_RUNTIME +Set this macro to 1 to use the "NeXT" Objective-C message sending conventions +by default. This calling convention involves passing the object, the selector +and the method arguments all at once to the method-lookup library function. +This is the usual setting when targeting Darwin/Mac OS X systems, which have +the NeXT runtime installed. + +If the macro is set to 0, the "GNU" Objective-C message sending convention +will be used by default. This convention passes just the object and the +selector to the method-lookup function, which returns a pointer to the method. + +In either case, it remains possible to select code-generation for the alternate +scheme, by means of compiler command line switches. +@end defmac + +@node Addressing Modes +@section Addressing Modes +@cindex addressing modes + +@c prevent bad page break with this line +This is about addressing modes. + +@defmac HAVE_PRE_INCREMENT +@defmacx HAVE_PRE_DECREMENT +@defmacx HAVE_POST_INCREMENT +@defmacx HAVE_POST_DECREMENT +A C expression that is nonzero if the machine supports pre-increment, +pre-decrement, post-increment, or post-decrement addressing respectively. +@end defmac + +@defmac HAVE_PRE_MODIFY_DISP +@defmacx HAVE_POST_MODIFY_DISP +A C expression that is nonzero if the machine supports pre- or +post-address side-effect generation involving constants other than +the size of the memory operand. +@end defmac + +@defmac HAVE_PRE_MODIFY_REG +@defmacx HAVE_POST_MODIFY_REG +A C expression that is nonzero if the machine supports pre- or +post-address side-effect generation involving a register displacement. +@end defmac + +@defmac CONSTANT_ADDRESS_P (@var{x}) +A C expression that is 1 if the RTX @var{x} is a constant which +is a valid address. On most machines the default definition of +@code{(CONSTANT_P (@var{x}) && GET_CODE (@var{x}) != CONST_DOUBLE)} +is acceptable, but a few machines are more restrictive as to which +constant addresses are supported. +@end defmac + +@defmac CONSTANT_P (@var{x}) +@code{CONSTANT_P}, which is defined by target-independent code, +accepts integer-values expressions whose values are not explicitly +known, such as @code{symbol_ref}, @code{label_ref}, and @code{high} +expressions and @code{const} arithmetic expressions, in addition to +@code{const_int} and @code{const_double} expressions. +@end defmac + +@defmac MAX_REGS_PER_ADDRESS +A number, the maximum number of registers that can appear in a valid +memory address. Note that it is up to you to specify a value equal to +the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever +accept. +@end defmac + +@deftypefn {Target Hook} bool TARGET_LEGITIMATE_ADDRESS_P (machine_mode @var{mode}, rtx @var{x}, bool @var{strict}) +A function that returns whether @var{x} (an RTX) is a legitimate memory +address on the target machine for a memory operand of mode @var{mode}. + +Legitimate addresses are defined in two variants: a strict variant and a +non-strict one. The @var{strict} parameter chooses which variant is +desired by the caller. + +The strict variant is used in the reload pass. It must be defined so +that any pseudo-register that has not been allocated a hard register is +considered a memory reference. This is because in contexts where some +kind of register is required, a pseudo-register with no hard register +must be rejected. For non-hard registers, the strict variant should look +up the @code{reg_renumber} array; it should then proceed using the hard +register number in the array, or treat the pseudo as a memory reference +if the array holds @code{-1}. + +The non-strict variant is used in other passes. It must be defined to +accept all pseudo-registers in every context where some kind of +register is required. + +Normally, constant addresses which are the sum of a @code{symbol_ref} +and an integer are stored inside a @code{const} RTX to mark them as +constant. Therefore, there is no need to recognize such sums +specifically as legitimate addresses. Normally you would simply +recognize any @code{const} as legitimate. + +Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant +sums that are not marked with @code{const}. It assumes that a naked +@code{plus} indicates indexing. If so, then you @emph{must} reject such +naked constant sums as illegitimate addresses, so that none of them will +be given to @code{PRINT_OPERAND_ADDRESS}. + +@cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation +On some machines, whether a symbolic address is legitimate depends on +the section that the address refers to. On these machines, define the +target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information +into the @code{symbol_ref}, and then check for it here. When you see a +@code{const}, you will have to look inside it to find the +@code{symbol_ref} in order to determine the section. @xref{Assembler +Format}. + +@cindex @code{GO_IF_LEGITIMATE_ADDRESS} +Some ports are still using a deprecated legacy substitute for +this hook, the @code{GO_IF_LEGITIMATE_ADDRESS} macro. This macro +has this syntax: + +@example +#define GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label}) +@end example + +@noindent +and should @code{goto @var{label}} if the address @var{x} is a valid +address on the target machine for a memory operand of mode @var{mode}. + +@findex REG_OK_STRICT +Compiler source files that want to use the strict variant of this +macro define the macro @code{REG_OK_STRICT}. You should use an +@code{#ifdef REG_OK_STRICT} conditional to define the strict variant in +that case and the non-strict variant otherwise. + +Using the hook is usually simpler because it limits the number of +files that are recompiled when changes are made. +@end deftypefn + +@defmac TARGET_MEM_CONSTRAINT +A single character to be used instead of the default @code{'m'} +character for general memory addresses. This defines the constraint +letter which matches the memory addresses accepted by +@code{TARGET_LEGITIMATE_ADDRESS_P}. Define this macro if you want to +support new address formats in your back end without changing the +semantics of the @code{'m'} constraint. This is necessary in order to +preserve functionality of inline assembly constructs using the +@code{'m'} constraint. +@end defmac + +@defmac FIND_BASE_TERM (@var{x}) +A C expression to determine the base term of address @var{x}, +or to provide a simplified version of @var{x} from which @file{alias.cc} +can easily find the base term. This macro is used in only two places: +@code{find_base_value} and @code{find_base_term} in @file{alias.cc}. + +It is always safe for this macro to not be defined. It exists so +that alias analysis can understand machine-dependent addresses. + +The typical use of this macro is to handle addresses containing +a label_ref or symbol_ref within an UNSPEC@. +@end defmac + +@deftypefn {Target Hook} rtx TARGET_LEGITIMIZE_ADDRESS (rtx @var{x}, rtx @var{oldx}, machine_mode @var{mode}) +This hook is given an invalid memory address @var{x} for an +operand of mode @var{mode} and should try to return a valid memory +address. + +@findex break_out_memory_refs +@var{x} will always be the result of a call to @code{break_out_memory_refs}, +and @var{oldx} will be the operand that was given to that function to produce +@var{x}. + +The code of the hook should not alter the substructure of +@var{x}. If it transforms @var{x} into a more legitimate form, it +should return the new @var{x}. + +It is not necessary for this hook to come up with a legitimate address, +with the exception of native TLS addresses (@pxref{Emulated TLS}). +The compiler has standard ways of doing so in all cases. In fact, if +the target supports only emulated TLS, it +is safe to omit this hook or make it return @var{x} if it cannot find +a valid way to legitimize the address. But often a machine-dependent +strategy can generate better code. +@end deftypefn + +@defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) +A C compound statement that attempts to replace @var{x}, which is an address +that needs reloading, with a valid memory address for an operand of mode +@var{mode}. @var{win} will be a C statement label elsewhere in the code. +It is not necessary to define this macro, but it might be useful for +performance reasons. + +For example, on the i386, it is sometimes possible to use a single +reload register instead of two by reloading a sum of two pseudo +registers into a register. On the other hand, for number of RISC +processors offsets are limited so that often an intermediate address +needs to be generated in order to address a stack slot. By defining +@code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses +generated for adjacent some stack slots can be made identical, and thus +be shared. + +@emph{Note}: This macro should be used with caution. It is necessary +to know something of how reload works in order to effectively use this, +and it is quite easy to produce macros that build in too much knowledge +of reload internals. + +@emph{Note}: This macro must be able to reload an address created by a +previous invocation of this macro. If it fails to handle such addresses +then the compiler may generate incorrect code or abort. + +@findex push_reload +The macro definition should use @code{push_reload} to indicate parts that +need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually +suitable to be passed unaltered to @code{push_reload}. + +The code generated by this macro must not alter the substructure of +@var{x}. If it transforms @var{x} into a more legitimate form, it +should assign @var{x} (which will always be a C variable) a new value. +This also applies to parts that you change indirectly by calling +@code{push_reload}. + +@findex strict_memory_address_p +The macro definition may use @code{strict_memory_address_p} to test if +the address has become legitimate. + +@findex copy_rtx +If you want to change only a part of @var{x}, one standard way of doing +this is to use @code{copy_rtx}. Note, however, that it unshares only a +single level of rtl. Thus, if the part to be changed is not at the +top level, you'll need to replace first the top level. +It is not necessary for this macro to come up with a legitimate +address; but often a machine-dependent strategy can generate better code. +@end defmac + +@deftypefn {Target Hook} bool TARGET_MODE_DEPENDENT_ADDRESS_P (const_rtx @var{addr}, addr_space_t @var{addrspace}) +This hook returns @code{true} if memory address @var{addr} in address +space @var{addrspace} can have +different meanings depending on the machine mode of the memory +reference it is used for or if the address is valid for some modes +but not others. + +Autoincrement and autodecrement addresses typically have mode-dependent +effects because the amount of the increment or decrement is the size +of the operand being addressed. Some machines have other mode-dependent +addresses. Many RISC machines have no mode-dependent addresses. + +You may assume that @var{addr} is a valid address for the machine. + +The default version of this hook returns @code{false}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_LEGITIMATE_CONSTANT_P (machine_mode @var{mode}, rtx @var{x}) +This hook returns true if @var{x} is a legitimate constant for a +@var{mode}-mode immediate operand on the target machine. You can assume that +@var{x} satisfies @code{CONSTANT_P}, so you need not check this. + +The default definition returns true. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_PRECOMPUTE_TLS_P (machine_mode @var{mode}, rtx @var{x}) +This hook returns true if @var{x} is a TLS operand on the target +machine that should be pre-computed when used as the argument in a call. +You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not +check this. + +The default definition returns false. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_DELEGITIMIZE_ADDRESS (rtx @var{x}) +This hook is used to undo the possibly obfuscating effects of the +@code{LEGITIMIZE_ADDRESS} and @code{LEGITIMIZE_RELOAD_ADDRESS} target +macros. Some backend implementations of these macros wrap symbol +references inside an @code{UNSPEC} rtx to represent PIC or similar +addressing modes. This target hook allows GCC's optimizers to understand +the semantics of these opaque @code{UNSPEC}s by converting them back +into their original form. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CONST_NOT_OK_FOR_DEBUG_P (rtx @var{x}) +This hook should return true if @var{x} should not be emitted into +debug sections. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CANNOT_FORCE_CONST_MEM (machine_mode @var{mode}, rtx @var{x}) +This hook should return true if @var{x} is of a form that cannot (or +should not) be spilled to the constant pool. @var{mode} is the mode +of @var{x}. + +The default version of this hook returns false. + +The primary reason to define this hook is to prevent reload from +deciding that a non-legitimate constant would be better reloaded +from the constant pool instead of spilling and reloading a register +holding the constant. This restriction is often true of addresses +of TLS symbols for various targets. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_USE_BLOCKS_FOR_CONSTANT_P (machine_mode @var{mode}, const_rtx @var{x}) +This hook should return true if pool entries for constant @var{x} can +be placed in an @code{object_block} structure. @var{mode} is the mode +of @var{x}. + +The default version returns false for all constants. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_USE_BLOCKS_FOR_DECL_P (const_tree @var{decl}) +This hook should return true if pool entries for @var{decl} should +be placed in an @code{object_block} structure. + +The default version returns true for all decls. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_BUILTIN_RECIPROCAL (tree @var{fndecl}) +This hook should return the DECL of a function that implements the +reciprocal of the machine-specific builtin function @var{fndecl}, or +@code{NULL_TREE} if such a function is not available. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD (void) +This hook should return the DECL of a function @var{f} that given an +address @var{addr} as an argument returns a mask @var{m} that can be +used to extract from two vectors the relevant data that resides in +@var{addr} in case @var{addr} is not properly aligned. + +The autovectorizer, when vectorizing a load operation from an address +@var{addr} that may be unaligned, will generate two vector loads from +the two aligned addresses around @var{addr}. It then generates a +@code{REALIGN_LOAD} operation to extract the relevant data from the +two loaded vectors. The first two arguments to @code{REALIGN_LOAD}, +@var{v1} and @var{v2}, are the two vectors, each of size @var{VS}, and +the third argument, @var{OFF}, defines how the data will be extracted +from these two vectors: if @var{OFF} is 0, then the returned vector is +@var{v2}; otherwise, the returned vector is composed from the last +@var{VS}-@var{OFF} elements of @var{v1} concatenated to the first +@var{OFF} elements of @var{v2}. + +If this hook is defined, the autovectorizer will generate a call +to @var{f} (using the DECL tree that this hook returns) and will +use the return value of @var{f} as the argument @var{OFF} to +@code{REALIGN_LOAD}. Therefore, the mask @var{m} returned by @var{f} +should comply with the semantics expected by @code{REALIGN_LOAD} +described above. +If this hook is not defined, then @var{addr} will be used as +the argument @var{OFF} to @code{REALIGN_LOAD}, in which case the low +log2(@var{VS}) @minus{} 1 bits of @var{addr} will be considered. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST (enum vect_cost_for_stmt @var{type_of_cost}, tree @var{vectype}, int @var{misalign}) +Returns cost of different scalar or vector statements for vectorization cost model. +For vector memory operations the cost may depend on type (@var{vectype}) and +misalignment value (@var{misalign}). +@end deftypefn + +@deftypefn {Target Hook} poly_uint64 TARGET_VECTORIZE_PREFERRED_VECTOR_ALIGNMENT (const_tree @var{type}) +This hook returns the preferred alignment in bits for accesses to +vectors of type @var{type} in vectorized code. This might be less than +or greater than the ABI-defined value returned by +@code{TARGET_VECTOR_ALIGNMENT}. It can be equal to the alignment of +a single element, in which case the vectorizer will not try to optimize +for alignment. + +The default hook returns @code{TYPE_ALIGN (@var{type})}, which is +correct for most targets. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE (const_tree @var{type}, bool @var{is_packed}) +Return true if vector alignment is reachable (by peeling N iterations) +for the given scalar type @var{type}. @var{is_packed} is false if the scalar +access using @var{type} is known to be naturally aligned. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VECTORIZE_VEC_PERM_CONST (machine_mode @var{mode}, machine_mode @var{op_mode}, rtx @var{output}, rtx @var{in0}, rtx @var{in1}, const vec_perm_indices @var{&sel}) +This hook is used to test whether the target can permute up to two +vectors of mode @var{op_mode} using the permutation vector @code{sel}, +producing a vector of mode @var{mode}. The hook is also used to emit such +a permutation. + +When the hook is being used to test whether the target supports a permutation, +@var{in0}, @var{in1}, and @var{out} are all null. When the hook is being used +to emit a permutation, @var{in0} and @var{in1} are the source vectors of mode +@var{op_mode} and @var{out} is the destination vector of mode @var{mode}. +@var{in1} is the same as @var{in0} if @var{sel} describes a permutation on one +vector instead of two. + +Return true if the operation is possible, emitting instructions for it +if rtxes are provided. + +@cindex @code{vec_perm@var{m}} instruction pattern +If the hook returns false for a mode with multibyte elements, GCC will +try the equivalent byte operation. If that also fails, it will try forcing +the selector into a register and using the @var{vec_perm@var{mode}} +instruction pattern. There is no need for the hook to handle these two +implementation approaches itself. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION (unsigned @var{code}, tree @var{vec_type_out}, tree @var{vec_type_in}) +This hook should return the decl of a function that implements the +vectorized variant of the function with the @code{combined_fn} code +@var{code} or @code{NULL_TREE} if such a function is not available. +The return type of the vectorized function shall be of vector type +@var{vec_type_out} and the argument types should be @var{vec_type_in}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_MD_VECTORIZED_FUNCTION (tree @var{fndecl}, tree @var{vec_type_out}, tree @var{vec_type_in}) +This hook should return the decl of a function that implements the +vectorized variant of target built-in function @code{fndecl}. The +return type of the vectorized function shall be of vector type +@var{vec_type_out} and the argument types should be @var{vec_type_in}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT (machine_mode @var{mode}, const_tree @var{type}, int @var{misalignment}, bool @var{is_packed}) +This hook should return true if the target supports misaligned vector +store/load of a specific factor denoted in the @var{misalignment} +parameter. The vector store/load should be of machine mode @var{mode} and +the elements in the vectors should be of type @var{type}. @var{is_packed} +parameter is true if the memory access is defined in a packed struct. +@end deftypefn + +@deftypefn {Target Hook} machine_mode TARGET_VECTORIZE_PREFERRED_SIMD_MODE (scalar_mode @var{mode}) +This hook should return the preferred mode for vectorizing scalar +mode @var{mode}. The default is +equal to @code{word_mode}, because the vectorizer can do some +transformations even in absence of specialized @acronym{SIMD} hardware. +@end deftypefn + +@deftypefn {Target Hook} machine_mode TARGET_VECTORIZE_SPLIT_REDUCTION (machine_mode) +This hook should return the preferred mode to split the final reduction +step on @var{mode} to. The reduction is then carried out reducing upper +against lower halves of vectors recursively until the specified mode is +reached. The default is @var{mode} which means no splitting. +@end deftypefn + +@deftypefn {Target Hook} {unsigned int} TARGET_VECTORIZE_AUTOVECTORIZE_VECTOR_MODES (vector_modes *@var{modes}, bool @var{all}) +If using the mode returned by @code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE} +is not the only approach worth considering, this hook should add one mode to +@var{modes} for each useful alternative approach. These modes are then +passed to @code{TARGET_VECTORIZE_RELATED_MODE} to obtain the vector mode +for a given element mode. + +The modes returned in @var{modes} should use the smallest element mode +possible for the vectorization approach that they represent, preferring +integer modes over floating-poing modes in the event of a tie. The first +mode should be the @code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE} for its +element mode. + +If @var{all} is true, add suitable vector modes even when they are generally +not expected to be worthwhile. + +The hook returns a bitmask of flags that control how the modes in +@var{modes} are used. The flags are: +@table @code +@item VECT_COMPARE_COSTS +Tells the loop vectorizer to try all the provided modes and pick the one +with the lowest cost. By default the vectorizer will choose the first +mode that works. +@end table + +The hook does not need to do anything if the vector returned by +@code{TARGET_VECTORIZE_PREFERRED_SIMD_MODE} is the only one relevant +for autovectorization. The default implementation adds no modes and +returns 0. +@end deftypefn + +@deftypefn {Target Hook} opt_machine_mode TARGET_VECTORIZE_RELATED_MODE (machine_mode @var{vector_mode}, scalar_mode @var{element_mode}, poly_uint64 @var{nunits}) +If a piece of code is using vector mode @var{vector_mode} and also wants +to operate on elements of mode @var{element_mode}, return the vector mode +it should use for those elements. If @var{nunits} is nonzero, ensure that +the mode has exactly @var{nunits} elements, otherwise pick whichever vector +size pairs the most naturally with @var{vector_mode}. Return an empty +@code{opt_machine_mode} if there is no supported vector mode with the +required properties. + +There is no prescribed way of handling the case in which @var{nunits} +is zero. One common choice is to pick a vector mode with the same size +as @var{vector_mode}; this is the natural choice if the target has a +fixed vector size. Another option is to choose a vector mode with the +same number of elements as @var{vector_mode}; this is the natural choice +if the target has a fixed number of elements. Alternatively, the hook +might choose a middle ground, such as trying to keep the number of +elements as similar as possible while applying maximum and minimum +vector sizes. + +The default implementation uses @code{mode_for_vector} to find the +requested mode, returning a mode with the same size as @var{vector_mode} +when @var{nunits} is zero. This is the correct behavior for most targets. +@end deftypefn + +@deftypefn {Target Hook} opt_machine_mode TARGET_VECTORIZE_GET_MASK_MODE (machine_mode @var{mode}) +Return the mode to use for a vector mask that holds one boolean +result for each element of vector mode @var{mode}. The returned mask mode +can be a vector of integers (class @code{MODE_VECTOR_INT}), a vector of +booleans (class @code{MODE_VECTOR_BOOL}) or a scalar integer (class +@code{MODE_INT}). Return an empty @code{opt_machine_mode} if no such +mask mode exists. + +The default implementation returns a @code{MODE_VECTOR_INT} with the +same size and number of elements as @var{mode}, if such a mode exists. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VECTORIZE_EMPTY_MASK_IS_EXPENSIVE (unsigned @var{ifn}) +This hook returns true if masked internal function @var{ifn} (really of +type @code{internal_fn}) should be considered expensive when the mask is +all zeros. GCC can then try to branch around the instruction instead. +@end deftypefn + +@deftypefn {Target Hook} {class vector_costs *} TARGET_VECTORIZE_CREATE_COSTS (vec_info *@var{vinfo}, bool @var{costing_for_scalar}) +This hook should initialize target-specific data structures in preparation +for modeling the costs of vectorizing a loop or basic block. The default +allocates three unsigned integers for accumulating costs for the prologue, +body, and epilogue of the loop or basic block. If @var{loop_info} is +non-NULL, it identifies the loop being vectorized; otherwise a single block +is being vectorized. If @var{costing_for_scalar} is true, it indicates the +current cost model is for the scalar version of a loop or block; otherwise +it is for the vector version. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_GATHER (const_tree @var{mem_vectype}, const_tree @var{index_type}, int @var{scale}) +Target builtin that implements vector gather operation. @var{mem_vectype} +is the vector type of the load and @var{index_type} is scalar type of +the index, scaled by @var{scale}. +The default is @code{NULL_TREE} which means to not vectorize gather +loads. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_VECTORIZE_BUILTIN_SCATTER (const_tree @var{vectype}, const_tree @var{index_type}, int @var{scale}) +Target builtin that implements vector scatter operation. @var{vectype} +is the vector type of the store and @var{index_type} is scalar type of +the index, scaled by @var{scale}. +The default is @code{NULL_TREE} which means to not vectorize scatter +stores. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN (struct cgraph_node *@var{}, struct cgraph_simd_clone *@var{}, @var{tree}, @var{int}) +This hook should set @var{vecsize_mangle}, @var{vecsize_int}, @var{vecsize_float} +fields in @var{simd_clone} structure pointed by @var{clone_info} argument and also +@var{simdlen} field if it was previously 0. +@var{vecsize_mangle} is a marker for the backend only. @var{vecsize_int} and +@var{vecsize_float} should be left zero on targets where the number of lanes is +not determined by the bitsize (in which case @var{simdlen} is always used). +The hook should return 0 if SIMD clones shouldn't be emitted, +or number of @var{vecsize_mangle} variants that should be emitted. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SIMD_CLONE_ADJUST (struct cgraph_node *@var{}) +This hook should add implicit @code{attribute(target("..."))} attribute +to SIMD clone @var{node} if needed. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SIMD_CLONE_USABLE (struct cgraph_node *@var{}) +This hook should return -1 if SIMD clone @var{node} shouldn't be used +in vectorized loops in current function, or non-negative number if it is +usable. In that case, the smaller the number is, the more desirable it is +to use it. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SIMT_VF (void) +Return number of threads in SIMT thread group on the target. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_OMP_DEVICE_KIND_ARCH_ISA (enum omp_device_kind_arch_isa @var{trait}, const char *@var{name}) +Return 1 if @var{trait} @var{name} is present in the OpenMP context's +device trait set, return 0 if not present in any OpenMP context in the +whole translation unit, or -1 if not present in the current OpenMP context +but might be present in another OpenMP context in the same TU. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_GOACC_VALIDATE_DIMS (tree @var{decl}, int *@var{dims}, int @var{fn_level}, unsigned @var{used}) +This hook should check the launch dimensions provided for an OpenACC +compute region, or routine. Defaulted values are represented as -1 +and non-constant values as 0. The @var{fn_level} is negative for the +function corresponding to the compute region. For a routine it is the +outermost level at which partitioned execution may be spawned. The hook +should verify non-default values. If DECL is NULL, global defaults +are being validated and unspecified defaults should be filled in. +Diagnostics should be issued as appropriate. Return +true, if changes have been made. You must override this hook to +provide dimensions larger than 1. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_GOACC_DIM_LIMIT (int @var{axis}) +This hook should return the maximum size of a particular dimension, +or zero if unbounded. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_GOACC_FORK_JOIN (gcall *@var{call}, const int *@var{dims}, bool @var{is_fork}) +This hook can be used to convert IFN_GOACC_FORK and IFN_GOACC_JOIN +function calls to target-specific gimple, or indicate whether they +should be retained. It is executed during the oacc_device_lower pass. +It should return true, if the call should be retained. It should +return false, if it is to be deleted (either because target-specific +gimple has been inserted before it, or there is no need for it). +The default hook returns false, if there are no RTL expanders for them. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_GOACC_REDUCTION (gcall *@var{call}) +This hook is used by the oacc_transform pass to expand calls to the +@var{GOACC_REDUCTION} internal function, into a sequence of gimple +instructions. @var{call} is gimple statement containing the call to +the function. This hook removes statement @var{call} after the +expanded sequence has been inserted. This hook is also responsible +for allocating any storage for reductions when necessary. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_PREFERRED_ELSE_VALUE (unsigned @var{ifn}, tree @var{type}, unsigned @var{nops}, tree *@var{ops}) +This hook returns the target's preferred final argument for a call +to conditional internal function @var{ifn} (really of type +@code{internal_fn}). @var{type} specifies the return type of the +function and @var{ops} are the operands to the conditional operation, +of which there are @var{nops}. + +For example, if @var{ifn} is @code{IFN_COND_ADD}, the hook returns +a value of type @var{type} that should be used when @samp{@var{ops}[0]} +and @samp{@var{ops}[1]} are conditionally added together. + +This hook is only relevant if the target supports conditional patterns +like @code{cond_add@var{m}}. The default implementation returns a zero +constant of type @var{type}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_GOACC_ADJUST_PRIVATE_DECL (location_t @var{loc}, tree @var{var}, int @var{level}) +This hook, if defined, is used by accelerator target back-ends to adjust +OpenACC variable declarations that should be made private to the given +parallelism level (i.e. @code{GOMP_DIM_GANG}, @code{GOMP_DIM_WORKER} or +@code{GOMP_DIM_VECTOR}). A typical use for this hook is to force variable +declarations at the @code{gang} level to reside in GPU shared memory. +@var{loc} may be used for diagnostic purposes. + +You may also use the @code{TARGET_GOACC_EXPAND_VAR_DECL} hook if the +adjusted variable declaration needs to be expanded to RTL in a non-standard +way. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_GOACC_EXPAND_VAR_DECL (tree @var{var}) +This hook, if defined, is used by accelerator target back-ends to expand +specially handled kinds of @code{VAR_DECL} expressions. A particular use is +to place variables with specific attributes inside special accelarator +memories. A return value of @code{NULL} indicates that the target does not +handle this @code{VAR_DECL}, and normal RTL expanding is resumed. + +Only define this hook if your accelerator target needs to expand certain +@code{VAR_DECL} nodes in a way that differs from the default. You can also adjust +private variables at OpenACC device-lowering time using the +@code{TARGET_GOACC_ADJUST_PRIVATE_DECL} target hook. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_GOACC_CREATE_WORKER_BROADCAST_RECORD (tree @var{rec}, bool @var{sender}, const char *@var{name}, unsigned HOST_WIDE_INT @var{offset}) +Create a record used to propagate local-variable state from an active +worker to other workers. A possible implementation might adjust the type +of REC to place the new variable in shared GPU memory. + +Presence of this target hook indicates that middle end neutering/broadcasting +be used. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_GOACC_SHARED_MEM_LAYOUT (unsigned HOST_WIDE_INT *@var{}, unsigned HOST_WIDE_INT *@var{}, @var{int[]}, unsigned @var{HOST_WIDE_INT[]}, unsigned @var{HOST_WIDE_INT[]}) +Lay out a fixed shared-memory region on the target. The LO and HI +arguments should be set to a range of addresses that can be used for worker +broadcasting. The dimensions, reduction size and gang-private size +arguments are for the current offload region. +@end deftypefn + +@node Anchored Addresses +@section Anchored Addresses +@cindex anchored addresses +@cindex @option{-fsection-anchors} + +GCC usually addresses every static object as a separate entity. +For example, if we have: + +@smallexample +static int a, b, c; +int foo (void) @{ return a + b + c; @} +@end smallexample + +the code for @code{foo} will usually calculate three separate symbolic +addresses: those of @code{a}, @code{b} and @code{c}. On some targets, +it would be better to calculate just one symbolic address and access +the three variables relative to it. The equivalent pseudocode would +be something like: + +@smallexample +int foo (void) +@{ + register int *xr = &x; + return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; +@} +@end smallexample + +(which isn't valid C). We refer to shared addresses like @code{x} as +``section anchors''. Their use is controlled by @option{-fsection-anchors}. + +The hooks below describe the target properties that GCC needs to know +in order to make effective use of section anchors. It won't use +section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET} +or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value. + +@deftypevr {Target Hook} HOST_WIDE_INT TARGET_MIN_ANCHOR_OFFSET +The minimum offset that should be applied to a section anchor. +On most targets, it should be the smallest offset that can be +applied to a base register while still giving a legitimate address +for every mode. The default value is 0. +@end deftypevr + +@deftypevr {Target Hook} HOST_WIDE_INT TARGET_MAX_ANCHOR_OFFSET +Like @code{TARGET_MIN_ANCHOR_OFFSET}, but the maximum (inclusive) +offset that should be applied to section anchors. The default +value is 0. +@end deftypevr + +@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_ANCHOR (rtx @var{x}) +Write the assembly code to define section anchor @var{x}, which is a +@code{SYMBOL_REF} for which @samp{SYMBOL_REF_ANCHOR_P (@var{x})} is true. +The hook is called with the assembly output position set to the beginning +of @code{SYMBOL_REF_BLOCK (@var{x})}. + +If @code{ASM_OUTPUT_DEF} is available, the hook's default definition uses +it to define the symbol as @samp{. + SYMBOL_REF_BLOCK_OFFSET (@var{x})}. +If @code{ASM_OUTPUT_DEF} is not available, the hook's default definition +is @code{NULL}, which disables the use of section anchors altogether. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_USE_ANCHORS_FOR_SYMBOL_P (const_rtx @var{x}) +Return true if GCC should attempt to use anchors to access @code{SYMBOL_REF} +@var{x}. You can assume @samp{SYMBOL_REF_HAS_BLOCK_INFO_P (@var{x})} and +@samp{!SYMBOL_REF_ANCHOR_P (@var{x})}. + +The default version is correct for most targets, but you might need to +intercept this hook to handle things like target-specific attributes +or target-specific sections. +@end deftypefn + +@node Condition Code +@section Condition Code Status +@cindex condition code status + +Condition codes in GCC are represented as registers, +which provides better schedulability for +architectures that do have a condition code register, but on which +most instructions do not affect it. The latter category includes +most RISC machines. + +Implicit clobbering would pose a strong restriction on the placement of +the definition and use of the condition code. In the past the definition +and use were always adjacent. However, recent changes to support trapping +arithmetic may result in the definition and user being in different blocks. +Thus, there may be a @code{NOTE_INSN_BASIC_BLOCK} between them. Additionally, +the definition may be the source of exception handling edges. + +These restrictions can prevent important +optimizations on some machines. For example, on the IBM RS/6000, there +is a delay for taken branches unless the condition code register is set +three instructions earlier than the conditional branch. The instruction +scheduler cannot perform this optimization if it is not permitted to +separate the definition and use of the condition code register. + +If there is a specific +condition code register in the machine, use a hard register. If the +condition code or comparison result can be placed in any general register, +or if there are multiple condition registers, use a pseudo register. +Registers used to store the condition code value will usually have a mode +that is in class @code{MODE_CC}. + +Alternatively, you can use @code{BImode} if the comparison operator is +specified already in the compare instruction. In this case, you are not +interested in most macros in this section. + +@menu +* MODE_CC Condition Codes:: Modern representation of condition codes. +@end menu + +@node MODE_CC Condition Codes +@subsection Representation of condition codes using registers +@findex CCmode +@findex MODE_CC + +@defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y}) +On many machines, the condition code may be produced by other instructions +than compares, for example the branch can use directly the condition +code set by a subtract instruction. However, on some machines +when the condition code is set this way some bits (such as the overflow +bit) are not set in the same way as a test instruction, so that a different +branch instruction must be used for some conditional branches. When +this happens, use the machine mode of the condition code register to +record different formats of the condition code register. Modes can +also be used to record which compare instruction (e.g.@: a signed or an +unsigned comparison) produced the condition codes. + +If other modes than @code{CCmode} are required, add them to +@file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose +a mode given an operand of a compare. This is needed because the modes +have to be chosen not only during RTL generation but also, for example, +by instruction combination. The result of @code{SELECT_CC_MODE} should +be consistent with the mode used in the patterns; for example to support +the case of the add on the SPARC discussed above, we have the pattern + +@smallexample +(define_insn "" + [(set (reg:CCNZ 0) + (compare:CCNZ + (plus:SI (match_operand:SI 0 "register_operand" "%r") + (match_operand:SI 1 "arith_operand" "rI")) + (const_int 0)))] + "" + "@dots{}") +@end smallexample + +@noindent +together with a @code{SELECT_CC_MODE} that returns @code{CCNZmode} +for comparisons whose argument is a @code{plus}: + +@smallexample +#define SELECT_CC_MODE(OP,X,Y) \ + (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ + ? ((OP == LT || OP == LE || OP == GT || OP == GE) \ + ? CCFPEmode : CCFPmode) \ + : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ + || GET_CODE (X) == NEG || GET_CODE (x) == ASHIFT) \ + ? CCNZmode : CCmode)) +@end smallexample + +Another reason to use modes is to retain information on which operands +were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in +this section. + +You should define this macro if and only if you define extra CC modes +in @file{@var{machine}-modes.def}. +@end defmac + +@deftypefn {Target Hook} void TARGET_CANONICALIZE_COMPARISON (int *@var{code}, rtx *@var{op0}, rtx *@var{op1}, bool @var{op0_preserve_value}) +On some machines not all possible comparisons are defined, but you can +convert an invalid comparison into a valid one. For example, the Alpha +does not have a @code{GT} comparison, but you can use an @code{LT} +comparison instead and swap the order of the operands. + +On such machines, implement this hook to do any required conversions. +@var{code} is the initial comparison code and @var{op0} and @var{op1} +are the left and right operands of the comparison, respectively. If +@var{op0_preserve_value} is @code{true} the implementation is not +allowed to change the value of @var{op0} since the value might be used +in RTXs which aren't comparisons. E.g. the implementation is not +allowed to swap operands in that case. + +GCC will not assume that the comparison resulting from this macro is +valid but will see if the resulting insn matches a pattern in the +@file{md} file. + +You need not to implement this hook if it would never change the +comparison code or operands. +@end deftypefn + +@defmac REVERSIBLE_CC_MODE (@var{mode}) +A C expression whose value is one if it is always safe to reverse a +comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE} +can ever return @var{mode} for a floating-point inequality comparison, +then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero. + +You need not define this macro if it would always returns zero or if the +floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}. +For example, here is the definition used on the SPARC, where floating-point +inequality comparisons are given either @code{CCFPEmode} or @code{CCFPmode}: + +@smallexample +#define REVERSIBLE_CC_MODE(MODE) \ + ((MODE) != CCFPEmode && (MODE) != CCFPmode) +@end smallexample +@end defmac + +@defmac REVERSE_CONDITION (@var{code}, @var{mode}) +A C expression whose value is reversed condition code of the @var{code} for +comparison done in CC_MODE @var{mode}. The macro is used only in case +@code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case +machine has some non-standard way how to reverse certain conditionals. For +instance in case all floating point conditions are non-trapping, compiler may +freely convert unordered compares to ordered ones. Then definition may look +like: + +@smallexample +#define REVERSE_CONDITION(CODE, MODE) \ + ((MODE) != CCFPmode ? reverse_condition (CODE) \ + : reverse_condition_maybe_unordered (CODE)) +@end smallexample +@end defmac + +@deftypefn {Target Hook} bool TARGET_FIXED_CONDITION_CODE_REGS (unsigned int *@var{p1}, unsigned int *@var{p2}) +On targets which use a hard +register rather than a pseudo-register to hold condition codes, the +regular CSE passes are often not able to identify cases in which the +hard register is set to a common value. Use this hook to enable a +small pass which optimizes such cases. This hook should return true +to enable this pass, and it should set the integers to which its +arguments point to the hard register numbers used for condition codes. +When there is only one such register, as is true on most systems, the +integer pointed to by @var{p2} should be set to +@code{INVALID_REGNUM}. + +The default version of this hook returns false. +@end deftypefn + +@deftypefn {Target Hook} machine_mode TARGET_CC_MODES_COMPATIBLE (machine_mode @var{m1}, machine_mode @var{m2}) +On targets which use multiple condition code modes in class +@code{MODE_CC}, it is sometimes the case that a comparison can be +validly done in more than one mode. On such a system, define this +target hook to take two mode arguments and to return a mode in which +both comparisons may be validly done. If there is no such mode, +return @code{VOIDmode}. + +The default version of this hook checks whether the modes are the +same. If they are, it returns that mode. If they are different, it +returns @code{VOIDmode}. +@end deftypefn + +@deftypevr {Target Hook} {unsigned int} TARGET_FLAGS_REGNUM +If the target has a dedicated flags register, and it needs to use the +post-reload comparison elimination pass, or the delay slot filler pass, +then this value should be set appropriately. +@end deftypevr + +@node Costs +@section Describing Relative Costs of Operations +@cindex costs of instructions +@cindex relative costs +@cindex speed of instructions + +These macros let you describe the relative speed of various operations +on the target machine. + +@defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to}) +A C expression for the cost of moving data of mode @var{mode} from a +register in class @var{from} to one in class @var{to}. The classes are +expressed using the enumeration values such as @code{GENERAL_REGS}. A +value of 2 is the default; other values are interpreted relative to +that. + +It is not required that the cost always equal 2 when @var{from} is the +same as @var{to}; on some machines it is expensive to move between +registers if they are not general registers. + +If reload sees an insn consisting of a single @code{set} between two +hard registers, and if @code{REGISTER_MOVE_COST} applied to their +classes returns a value of 2, reload does not check to ensure that the +constraints of the insn are met. Setting a cost of other than 2 will +allow reload to verify that the constraints are met. You should do this +if the @samp{mov@var{m}} pattern's constraints do not allow such copying. + +These macros are obsolete, new ports should use the target hook +@code{TARGET_REGISTER_MOVE_COST} instead. +@end defmac + +@deftypefn {Target Hook} int TARGET_REGISTER_MOVE_COST (machine_mode @var{mode}, reg_class_t @var{from}, reg_class_t @var{to}) +This target hook should return the cost of moving data of mode @var{mode} +from a register in class @var{from} to one in class @var{to}. The classes +are expressed using the enumeration values such as @code{GENERAL_REGS}. +A value of 2 is the default; other values are interpreted relative to +that. + +It is not required that the cost always equal 2 when @var{from} is the +same as @var{to}; on some machines it is expensive to move between +registers if they are not general registers. + +If reload sees an insn consisting of a single @code{set} between two +hard registers, and if @code{TARGET_REGISTER_MOVE_COST} applied to their +classes returns a value of 2, reload does not check to ensure that the +constraints of the insn are met. Setting a cost of other than 2 will +allow reload to verify that the constraints are met. You should do this +if the @samp{mov@var{m}} pattern's constraints do not allow such copying. + +The default version of this function returns 2. +@end deftypefn + +@defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) +A C expression for the cost of moving data of mode @var{mode} between a +register of class @var{class} and memory; @var{in} is zero if the value +is to be written to memory, nonzero if it is to be read in. This cost +is relative to those in @code{REGISTER_MOVE_COST}. If moving between +registers and memory is more expensive than between two registers, you +should define this macro to express the relative cost. + +If you do not define this macro, GCC uses a default cost of 4 plus +the cost of copying via a secondary reload register, if one is +needed. If your machine requires a secondary reload register to copy +between memory and a register of @var{class} but the reload mechanism is +more complex than copying via an intermediate, define this macro to +reflect the actual cost of the move. + +GCC defines the function @code{memory_move_secondary_cost} if +secondary reloads are needed. It computes the costs due to copying via +a secondary register. If your machine copies from memory using a +secondary register in the conventional way but the default base value of +4 is not correct for your machine, define this macro to add some other +value to the result of that function. The arguments to that function +are the same as to this macro. + +These macros are obsolete, new ports should use the target hook +@code{TARGET_MEMORY_MOVE_COST} instead. +@end defmac + +@deftypefn {Target Hook} int TARGET_MEMORY_MOVE_COST (machine_mode @var{mode}, reg_class_t @var{rclass}, bool @var{in}) +This target hook should return the cost of moving data of mode @var{mode} +between a register of class @var{rclass} and memory; @var{in} is @code{false} +if the value is to be written to memory, @code{true} if it is to be read in. +This cost is relative to those in @code{TARGET_REGISTER_MOVE_COST}. +If moving between registers and memory is more expensive than between two +registers, you should add this target hook to express the relative cost. + +If you do not add this target hook, GCC uses a default cost of 4 plus +the cost of copying via a secondary reload register, if one is +needed. If your machine requires a secondary reload register to copy +between memory and a register of @var{rclass} but the reload mechanism is +more complex than copying via an intermediate, use this target hook to +reflect the actual cost of the move. + +GCC defines the function @code{memory_move_secondary_cost} if +secondary reloads are needed. It computes the costs due to copying via +a secondary register. If your machine copies from memory using a +secondary register in the conventional way but the default base value of +4 is not correct for your machine, use this target hook to add some other +value to the result of that function. The arguments to that function +are the same as to this target hook. +@end deftypefn + +@defmac BRANCH_COST (@var{speed_p}, @var{predictable_p}) +A C expression for the cost of a branch instruction. A value of 1 is +the default; other values are interpreted relative to that. Parameter +@var{speed_p} is true when the branch in question should be optimized +for speed. When it is false, @code{BRANCH_COST} should return a value +optimal for code size rather than performance. @var{predictable_p} is +true for well-predicted branches. On many architectures the +@code{BRANCH_COST} can be reduced then. +@end defmac + +Here are additional macros which do not specify precise relative costs, +but only that certain actions are more expensive than GCC would +ordinarily expect. + +@defmac SLOW_BYTE_ACCESS +Define this macro as a C expression which is nonzero if accessing less +than a word of memory (i.e.@: a @code{char} or a @code{short}) is no +faster than accessing a word of memory, i.e., if such access +require more than one instruction or if there is no difference in cost +between byte and (aligned) word loads. + +When this macro is not defined, the compiler will access a field by +finding the smallest containing object; when it is defined, a fullword +load will be used if alignment permits. Unless bytes accesses are +faster than word accesses, using word accesses is preferable since it +may eliminate subsequent memory access if subsequent accesses occur to +other fields in the same word of the structure, but to different bytes. +@end defmac + +@deftypefn {Target Hook} bool TARGET_SLOW_UNALIGNED_ACCESS (machine_mode @var{mode}, unsigned int @var{align}) +This hook returns true if memory accesses described by the +@var{mode} and @var{alignment} parameters have a cost many times greater +than aligned accesses, for example if they are emulated in a trap handler. +This hook is invoked only for unaligned accesses, i.e.@: when +@code{@var{alignment} < GET_MODE_ALIGNMENT (@var{mode})}. + +When this hook returns true, the compiler will act as if +@code{STRICT_ALIGNMENT} were true when generating code for block +moves. This can cause significantly more instructions to be produced. +Therefore, do not make this hook return true if unaligned accesses only +add a cycle or two to the time for a memory access. + +The hook must return true whenever @code{STRICT_ALIGNMENT} is true. +The default implementation returns @code{STRICT_ALIGNMENT}. +@end deftypefn + +@defmac MOVE_RATIO (@var{speed}) +The threshold of number of scalar memory-to-memory move insns, @emph{below} +which a sequence of insns should be generated instead of a +string move insn or a library call. Increasing the value will always +make code faster, but eventually incurs high cost in increased code size. + +Note that on machines where the corresponding move insn is a +@code{define_expand} that emits a sequence of insns, this macro counts +the number of such sequences. + +The parameter @var{speed} is true if the code is currently being +optimized for speed rather than size. + +If you don't define this, a reasonable default is used. +@end defmac + +@deftypefn {Target Hook} bool TARGET_USE_BY_PIECES_INFRASTRUCTURE_P (unsigned HOST_WIDE_INT @var{size}, unsigned int @var{alignment}, enum by_pieces_operation @var{op}, bool @var{speed_p}) +GCC will attempt several strategies when asked to copy between +two areas of memory, or to set, clear or store to memory, for example +when copying a @code{struct}. The @code{by_pieces} infrastructure +implements such memory operations as a sequence of load, store or move +insns. Alternate strategies are to expand the +@code{cpymem} or @code{setmem} optabs, to emit a library call, or to emit +unit-by-unit, loop-based operations. + +This target hook should return true if, for a memory operation with a +given @var{size} and @var{alignment}, using the @code{by_pieces} +infrastructure is expected to result in better code generation. +Both @var{size} and @var{alignment} are measured in terms of storage +units. + +The parameter @var{op} is one of: @code{CLEAR_BY_PIECES}, +@code{MOVE_BY_PIECES}, @code{SET_BY_PIECES}, @code{STORE_BY_PIECES} or +@code{COMPARE_BY_PIECES}. These describe the type of memory operation +under consideration. + +The parameter @var{speed_p} is true if the code is currently being +optimized for speed rather than size. + +Returning true for higher values of @var{size} can improve code generation +for speed if the target does not provide an implementation of the +@code{cpymem} or @code{setmem} standard names, if the @code{cpymem} or +@code{setmem} implementation would be more expensive than a sequence of +insns, or if the overhead of a library call would dominate that of +the body of the memory operation. + +Returning true for higher values of @code{size} may also cause an increase +in code size, for example where the number of insns emitted to perform a +move would be greater than that of a library call. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_OVERLAP_OP_BY_PIECES_P (void) +This target hook should return true if when the @code{by_pieces} +infrastructure is used, an offset adjusted unaligned memory operation +in the smallest integer mode for the last piece operation of a memory +region can be generated to avoid doing more than one smaller operations. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_COMPARE_BY_PIECES_BRANCH_RATIO (machine_mode @var{mode}) +When expanding a block comparison in MODE, gcc can try to reduce the +number of branches at the expense of more memory operations. This hook +allows the target to override the default choice. It should return the +factor by which branches should be reduced over the plain expansion with +one comparison per @var{mode}-sized piece. A port can also prevent a +particular mode from being used for block comparisons by returning a +negative number from this hook. +@end deftypefn + +@defmac MOVE_MAX_PIECES +A C expression used by @code{move_by_pieces} to determine the largest unit +a load or store used to copy memory is. Defaults to @code{MOVE_MAX}. +@end defmac + +@defmac STORE_MAX_PIECES +A C expression used by @code{store_by_pieces} to determine the largest unit +a store used to memory is. Defaults to @code{MOVE_MAX_PIECES}, or two times +the size of @code{HOST_WIDE_INT}, whichever is smaller. +@end defmac + +@defmac COMPARE_MAX_PIECES +A C expression used by @code{compare_by_pieces} to determine the largest unit +a load or store used to compare memory is. Defaults to +@code{MOVE_MAX_PIECES}. +@end defmac + +@defmac CLEAR_RATIO (@var{speed}) +The threshold of number of scalar move insns, @emph{below} which a sequence +of insns should be generated to clear memory instead of a string clear insn +or a library call. Increasing the value will always make code faster, but +eventually incurs high cost in increased code size. + +The parameter @var{speed} is true if the code is currently being +optimized for speed rather than size. + +If you don't define this, a reasonable default is used. +@end defmac + +@defmac SET_RATIO (@var{speed}) +The threshold of number of scalar move insns, @emph{below} which a sequence +of insns should be generated to set memory to a constant value, instead of +a block set insn or a library call. +Increasing the value will always make code faster, but +eventually incurs high cost in increased code size. + +The parameter @var{speed} is true if the code is currently being +optimized for speed rather than size. + +If you don't define this, it defaults to the value of @code{MOVE_RATIO}. +@end defmac + +@defmac USE_LOAD_POST_INCREMENT (@var{mode}) +A C expression used to determine whether a load postincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_INCREMENT}. +@end defmac + +@defmac USE_LOAD_POST_DECREMENT (@var{mode}) +A C expression used to determine whether a load postdecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_DECREMENT}. +@end defmac + +@defmac USE_LOAD_PRE_INCREMENT (@var{mode}) +A C expression used to determine whether a load preincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_INCREMENT}. +@end defmac + +@defmac USE_LOAD_PRE_DECREMENT (@var{mode}) +A C expression used to determine whether a load predecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_DECREMENT}. +@end defmac + +@defmac USE_STORE_POST_INCREMENT (@var{mode}) +A C expression used to determine whether a store postincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_INCREMENT}. +@end defmac + +@defmac USE_STORE_POST_DECREMENT (@var{mode}) +A C expression used to determine whether a store postdecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_DECREMENT}. +@end defmac + +@defmac USE_STORE_PRE_INCREMENT (@var{mode}) +This macro is used to determine whether a store preincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_INCREMENT}. +@end defmac + +@defmac USE_STORE_PRE_DECREMENT (@var{mode}) +This macro is used to determine whether a store predecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_DECREMENT}. +@end defmac + +@defmac NO_FUNCTION_CSE +Define this macro to be true if it is as good or better to call a constant +function address than to call an address kept in a register. +@end defmac + +@defmac LOGICAL_OP_NON_SHORT_CIRCUIT +Define this macro if a non-short-circuit operation produced by +@samp{fold_range_test ()} is optimal. This macro defaults to true if +@code{BRANCH_COST} is greater than or equal to the value 2. +@end defmac + +@deftypefn {Target Hook} bool TARGET_OPTAB_SUPPORTED_P (int @var{op}, machine_mode @var{mode1}, machine_mode @var{mode2}, optimization_type @var{opt_type}) +Return true if the optimizers should use optab @var{op} with +modes @var{mode1} and @var{mode2} for optimization type @var{opt_type}. +The optab is known to have an associated @file{.md} instruction +whose C condition is true. @var{mode2} is only meaningful for conversion +optabs; for direct optabs it is a copy of @var{mode1}. + +For example, when called with @var{op} equal to @code{rint_optab} and +@var{mode1} equal to @code{DFmode}, the hook should say whether the +optimizers should use optab @code{rintdf2}. + +The default hook returns true for all inputs. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_RTX_COSTS (rtx @var{x}, machine_mode @var{mode}, int @var{outer_code}, int @var{opno}, int *@var{total}, bool @var{speed}) +This target hook describes the relative costs of RTL expressions. + +The cost may depend on the precise form of the expression, which is +available for examination in @var{x}, and the fact that @var{x} appears +as operand @var{opno} of an expression with rtx code @var{outer_code}. +That is, the hook can assume that there is some rtx @var{y} such +that @samp{GET_CODE (@var{y}) == @var{outer_code}} and such that +either (a) @samp{XEXP (@var{y}, @var{opno}) == @var{x}} or +(b) @samp{XVEC (@var{y}, @var{opno})} contains @var{x}. + +@var{mode} is @var{x}'s machine mode, or for cases like @code{const_int} that +do not have a mode, the mode in which @var{x} is used. + +In implementing this hook, you can use the construct +@code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast +instructions. + +On entry to the hook, @code{*@var{total}} contains a default estimate +for the cost of the expression. The hook should modify this value as +necessary. Traditionally, the default costs are @code{COSTS_N_INSNS (5)} +for multiplications, @code{COSTS_N_INSNS (7)} for division and modulus +operations, and @code{COSTS_N_INSNS (1)} for all other operations. + +When optimizing for code size, i.e.@: when @code{speed} is +false, this target hook should be used to estimate the relative +size cost of an expression, again relative to @code{COSTS_N_INSNS}. + +The hook returns true when all subexpressions of @var{x} have been +processed, and false when @code{rtx_cost} should recurse. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_ADDRESS_COST (rtx @var{address}, machine_mode @var{mode}, addr_space_t @var{as}, bool @var{speed}) +This hook computes the cost of an addressing mode that contains +@var{address}. If not defined, the cost is computed from +the @var{address} expression and the @code{TARGET_RTX_COST} hook. + +For most CISC machines, the default cost is a good approximation of the +true cost of the addressing mode. However, on RISC machines, all +instructions normally have the same length and execution time. Hence +all addresses will have equal costs. + +In cases where more than one form of an address is known, the form with +the lowest cost will be used. If multiple forms have the same, lowest, +cost, the one that is the most complex will be used. + +For example, suppose an address that is equal to the sum of a register +and a constant is used twice in the same basic block. When this macro +is not defined, the address will be computed in a register and memory +references will be indirect through that register. On machines where +the cost of the addressing mode containing the sum is no higher than +that of a simple indirect reference, this will produce an additional +instruction and possibly require an additional register. Proper +specification of this macro eliminates this overhead for such machines. + +This hook is never called with an invalid address. + +On machines where an address involving more than one register is as +cheap as an address computation involving only one register, defining +@code{TARGET_ADDRESS_COST} to reflect this can cause two registers to +be live over a region of code where only one would have been if +@code{TARGET_ADDRESS_COST} were not defined in that manner. This effect +should be considered in the definition of this macro. Equivalent costs +should probably only be given to addresses with different numbers of +registers on machines with lots of registers. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_INSN_COST (rtx_insn *@var{insn}, bool @var{speed}) +This target hook describes the relative costs of RTL instructions. + +In implementing this hook, you can use the construct +@code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast +instructions. + +When optimizing for code size, i.e.@: when @code{speed} is +false, this target hook should be used to estimate the relative +size cost of an expression, again relative to @code{COSTS_N_INSNS}. +@end deftypefn + +@deftypefn {Target Hook} {unsigned int} TARGET_MAX_NOCE_IFCVT_SEQ_COST (edge @var{e}) +This hook returns a value in the same units as @code{TARGET_RTX_COSTS}, +giving the maximum acceptable cost for a sequence generated by the RTL +if-conversion pass when conditional execution is not available. +The RTL if-conversion pass attempts to convert conditional operations +that would require a branch to a series of unconditional operations and +@code{mov@var{mode}cc} insns. This hook returns the maximum cost of the +unconditional instructions and the @code{mov@var{mode}cc} insns. +RTL if-conversion is cancelled if the cost of the converted sequence +is greater than the value returned by this hook. + +@code{e} is the edge between the basic block containing the conditional +branch to the basic block which would be executed if the condition +were true. + +The default implementation of this hook uses the +@code{max-rtl-if-conversion-[un]predictable} parameters if they are set, +and uses a multiple of @code{BRANCH_COST} otherwise. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_NOCE_CONVERSION_PROFITABLE_P (rtx_insn *@var{seq}, struct noce_if_info *@var{if_info}) +This hook returns true if the instruction sequence @code{seq} is a good +candidate as a replacement for the if-convertible sequence described in +@code{if_info}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_NEW_ADDRESS_PROFITABLE_P (rtx @var{memref}, rtx_insn * @var{insn}, rtx @var{new_addr}) +Return @code{true} if it is profitable to replace the address in +@var{memref} with @var{new_addr}. This allows targets to prevent the +scheduler from undoing address optimizations. The instruction containing the +memref is @var{insn}. The default implementation returns @code{true}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_NO_SPECULATION_IN_DELAY_SLOTS_P (void) +This predicate controls the use of the eager delay slot filler to disallow +speculatively executed instructions being placed in delay slots. Targets +such as certain MIPS architectures possess both branches with and without +delay slots. As the eager delay slot filler can decrease performance, +disabling it is beneficial when ordinary branches are available. Use of +delay slot branches filled using the basic filler is often still desirable +as the delay slot can hide a pipeline bubble. +@end deftypefn + +@deftypefn {Target Hook} HOST_WIDE_INT TARGET_ESTIMATED_POLY_VALUE (poly_int64 @var{val}, poly_value_estimate_kind @var{kind}) +Return an estimate of the runtime value of @var{val}, for use in +things like cost calculations or profiling frequencies. @var{kind} is used +to ask for the minimum, maximum, and likely estimates of the value through +the @code{POLY_VALUE_MIN}, @code{POLY_VALUE_MAX} and +@code{POLY_VALUE_LIKELY} values. The default +implementation returns the lowest possible value of @var{val}. +@end deftypefn + +@node Scheduling +@section Adjusting the Instruction Scheduler + +The instruction scheduler may need a fair amount of machine-specific +adjustment in order to produce good code. GCC provides several target +hooks for this purpose. It is usually enough to define just a few of +them: try the first ones in this list first. + +@deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void) +This hook returns the maximum number of instructions that can ever +issue at the same time on the target machine. The default is one. +Although the insn scheduler can define itself the possibility of issue +an insn on the same cycle, the value can serve as an additional +constraint to issue insns on the same simulated processor cycle (see +hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}). +This value must be constant over the entire compilation. If you need +it to vary depending on what the instructions are, you must use +@samp{TARGET_SCHED_VARIABLE_ISSUE}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx_insn *@var{insn}, int @var{more}) +This hook is executed by the scheduler after it has scheduled an insn +from the ready list. It should return the number of insns which can +still be issued in the current cycle. The default is +@samp{@w{@var{more} - 1}} for insns other than @code{CLOBBER} and +@code{USE}, which normally are not counted against the issue rate. +You should define this hook if some insns take more machine resources +than others, so that fewer insns can follow them in the same cycle. +@var{file} is either a null pointer, or a stdio stream to write any +debug output to. @var{verbose} is the verbose level provided by +@option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that +was scheduled. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx_insn *@var{insn}, int @var{dep_type1}, rtx_insn *@var{dep_insn}, int @var{cost}, unsigned int @var{dw}) +This function corrects the value of @var{cost} based on the +relationship between @var{insn} and @var{dep_insn} through a +dependence of type dep_type, and strength @var{dw}. It should return the new +value. The default is to make no adjustment to @var{cost}. This can be +used for example to specify to the scheduler using the traditional pipeline +description that an output- or anti-dependence does not incur the same cost +as a data-dependence. If the scheduler using the automaton based pipeline +description, the cost of anti-dependence is zero and the cost of +output-dependence is maximum of one and the difference of latency +times of the first and the second insns. If these values are not +acceptable, you could use the hook to modify them too. See also +@pxref{Processor pipeline description}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx_insn *@var{insn}, int @var{priority}) +This hook adjusts the integer scheduling priority @var{priority} of +@var{insn}. It should return the new priority. Increase the priority to +execute @var{insn} earlier, reduce the priority to execute @var{insn} +later. Do not define this hook if you do not need to adjust the +scheduling priorities of insns. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx_insn **@var{ready}, int *@var{n_readyp}, int @var{clock}) +This hook is executed by the scheduler after it has scheduled the ready +list, to allow the machine description to reorder it (for example to +combine two small instructions together on @samp{VLIW} machines). +@var{file} is either a null pointer, or a stdio stream to write any +debug output to. @var{verbose} is the verbose level provided by +@option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready +list of instructions that are ready to be scheduled. @var{n_readyp} is +a pointer to the number of elements in the ready list. The scheduler +reads the ready list in reverse order, starting with +@var{ready}[@var{*n_readyp} @minus{} 1] and going to @var{ready}[0]. @var{clock} +is the timer tick of the scheduler. You may modify the ready list and +the number of ready insns. The return value is the number of insns that +can issue this cycle; normally this is just @code{issue_rate}. See also +@samp{TARGET_SCHED_REORDER2}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx_insn **@var{ready}, int *@var{n_readyp}, int @var{clock}) +Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That +function is called whenever the scheduler starts a new cycle. This one +is called once per iteration over a cycle, immediately after +@samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and +return the number of insns to be scheduled in the same cycle. Defining +this hook can be useful if there are frequent situations where +scheduling one insn causes other insns to become ready in the same +cycle. These other insns can then be taken into account properly. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCHED_MACRO_FUSION_P (void) +This hook is used to check whether target platform supports macro fusion. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCHED_MACRO_FUSION_PAIR_P (rtx_insn *@var{prev}, rtx_insn *@var{curr}) +This hook is used to check whether two insns should be macro fused for +a target microarchitecture. If this hook returns true for the given insn pair +(@var{prev} and @var{curr}), the scheduler will put them into a sched +group, and they will not be scheduled apart. The two insns will be either +two SET insns or a compare and a conditional jump and this hook should +validate any dependencies needed to fuse the two insns together. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK (rtx_insn *@var{head}, rtx_insn *@var{tail}) +This hook is called after evaluation forward dependencies of insns in +chain given by two parameter values (@var{head} and @var{tail} +correspondingly) but before insns scheduling of the insn chain. For +example, it can be used for better insn classification if it requires +analysis of dependencies. This hook can use backward and forward +dependencies of the insn scheduler because they are already +calculated. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready}) +This hook is executed by the scheduler at the beginning of each block of +instructions that are to be scheduled. @var{file} is either a null +pointer, or a stdio stream to write any debug output to. @var{verbose} +is the verbose level provided by @option{-fsched-verbose-@var{n}}. +@var{max_ready} is the maximum number of insns in the current scheduling +region that can be live at the same time. This can be used to allocate +scratch space if it is needed, e.g.@: by @samp{TARGET_SCHED_REORDER}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose}) +This hook is executed by the scheduler at the end of each block of +instructions that are to be scheduled. It can be used to perform +cleanup of any actions done by the other scheduling hooks. @var{file} +is either a null pointer, or a stdio stream to write any debug output +to. @var{verbose} is the verbose level provided by +@option{-fsched-verbose-@var{n}}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT_GLOBAL (FILE *@var{file}, int @var{verbose}, int @var{old_max_uid}) +This hook is executed by the scheduler after function level initializations. +@var{file} is either a null pointer, or a stdio stream to write any debug output to. +@var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. +@var{old_max_uid} is the maximum insn uid when scheduling begins. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FINISH_GLOBAL (FILE *@var{file}, int @var{verbose}) +This is the cleanup hook corresponding to @code{TARGET_SCHED_INIT_GLOBAL}. +@var{file} is either a null pointer, or a stdio stream to write any debug output to. +@var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_SCHED_DFA_PRE_CYCLE_INSN (void) +The hook returns an RTL insn. The automaton state used in the +pipeline hazard recognizer is changed as if the insn were scheduled +when the new simulated processor cycle starts. Usage of the hook may +simplify the automaton pipeline description for some @acronym{VLIW} +processors. If the hook is defined, it is used only for the automaton +based pipeline description. The default is not to change the state +when the new simulated processor cycle starts. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void) +The hook can be used to initialize data used by the previous hook. +@end deftypefn + +@deftypefn {Target Hook} {rtx_insn *} TARGET_SCHED_DFA_POST_CYCLE_INSN (void) +The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used +to changed the state as if the insn were scheduled when the new +simulated processor cycle finishes. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void) +The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but +used to initialize data used by the previous hook. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE (void) +The hook to notify target that the current simulated cycle is about to finish. +The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used +to change the state in more complicated situations - e.g., when advancing +state on a single insn is not enough. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_DFA_POST_ADVANCE_CYCLE (void) +The hook to notify target that new simulated cycle has just started. +The hook is analogous to @samp{TARGET_SCHED_DFA_POST_CYCLE_INSN} but used +to change the state in more complicated situations - e.g., when advancing +state on a single insn is not enough. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void) +This hook controls better choosing an insn from the ready insn queue +for the @acronym{DFA}-based insn scheduler. Usually the scheduler +chooses the first insn from the queue. If the hook returns a positive +value, an additional scheduler code tries all permutations of +@samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()} +subsequent ready insns to choose an insn whose issue will result in +maximal number of issued insns on the same cycle. For the +@acronym{VLIW} processor, the code could actually solve the problem of +packing simple insns into the @acronym{VLIW} insn. Of course, if the +rules of @acronym{VLIW} packing are described in the automaton. + +This code also could be used for superscalar @acronym{RISC} +processors. Let us consider a superscalar @acronym{RISC} processor +with 3 pipelines. Some insns can be executed in pipelines @var{A} or +@var{B}, some insns can be executed only in pipelines @var{B} or +@var{C}, and one insn can be executed in pipeline @var{B}. The +processor may issue the 1st insn into @var{A} and the 2nd one into +@var{B}. In this case, the 3rd insn will wait for freeing @var{B} +until the next cycle. If the scheduler issues the 3rd insn the first, +the processor could issue all 3 insns per cycle. + +Actually this code demonstrates advantages of the automaton based +pipeline hazard recognizer. We try quickly and easy many insn +schedules to choose the best one. + +The default is no multipass scheduling. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD (rtx_insn *@var{insn}, int @var{ready_index}) + +This hook controls what insns from the ready insn queue will be +considered for the multipass insn scheduling. If the hook returns +zero for @var{insn}, the insn will be considered in multipass scheduling. +Positive return values will remove @var{insn} from consideration on +the current round of multipass scheduling. +Negative return values will remove @var{insn} from consideration for given +number of cycles. +Backends should be careful about returning non-zero for highest priority +instruction at position 0 in the ready list. @var{ready_index} is passed +to allow backends make correct judgements. + +The default is that any ready insns can be chosen to be issued. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BEGIN (void *@var{data}, signed char *@var{ready_try}, int @var{n_ready}, bool @var{first_cycle_insn_p}) +This hook prepares the target backend for a new round of multipass +scheduling. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_ISSUE (void *@var{data}, signed char *@var{ready_try}, int @var{n_ready}, rtx_insn *@var{insn}, const void *@var{prev_data}) +This hook is called when multipass scheduling evaluates instruction INSN. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BACKTRACK (const void *@var{data}, signed char *@var{ready_try}, int @var{n_ready}) +This is called when multipass scheduling backtracks from evaluation of +an instruction. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_END (const void *@var{data}) +This hook notifies the target about the result of the concluded current +round of multipass scheduling. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_INIT (void *@var{data}) +This hook initializes target-specific data used in multipass scheduling. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FIRST_CYCLE_MULTIPASS_FINI (void *@var{data}) +This hook finalizes target-specific data used in multipass scheduling. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_DFA_NEW_CYCLE (FILE *@var{dump}, int @var{verbose}, rtx_insn *@var{insn}, int @var{last_clock}, int @var{clock}, int *@var{sort_p}) +This hook is called by the insn scheduler before issuing @var{insn} +on cycle @var{clock}. If the hook returns nonzero, +@var{insn} is not issued on this processor cycle. Instead, +the processor cycle is advanced. If *@var{sort_p} +is zero, the insn ready queue is not sorted on the new cycle +start as usually. @var{dump} and @var{verbose} specify the file and +verbosity level to use for debugging output. +@var{last_clock} and @var{clock} are, respectively, the +processor cycle on which the previous insn has been issued, +and the current processor cycle. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCHED_IS_COSTLY_DEPENDENCE (struct _dep *@var{_dep}, int @var{cost}, int @var{distance}) +This hook is used to define which dependences are considered costly by +the target, so costly that it is not advisable to schedule the insns that +are involved in the dependence too close to one another. The parameters +to this hook are as follows: The first parameter @var{_dep} is the dependence +being evaluated. The second parameter @var{cost} is the cost of the +dependence as estimated by the scheduler, and the third +parameter @var{distance} is the distance in cycles between the two insns. +The hook returns @code{true} if considering the distance between the two +insns the dependence between them is considered costly by the target, +and @code{false} otherwise. + +Defining this hook can be useful in multiple-issue out-of-order machines, +where (a) it's practically hopeless to predict the actual data/resource +delays, however: (b) there's a better chance to predict the actual grouping +that will be formed, and (c) correctly emulating the grouping can be very +important. In such targets one may want to allow issuing dependent insns +closer to one another---i.e., closer than the dependence distance; however, +not in cases of ``costly dependences'', which this hooks allows to define. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_H_I_D_EXTENDED (void) +This hook is called by the insn scheduler after emitting a new instruction to +the instruction stream. The hook notifies a target backend to extend its +per instruction data structures. +@end deftypefn + +@deftypefn {Target Hook} {void *} TARGET_SCHED_ALLOC_SCHED_CONTEXT (void) +Return a pointer to a store large enough to hold target scheduling context. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_INIT_SCHED_CONTEXT (void *@var{tc}, bool @var{clean_p}) +Initialize store pointed to by @var{tc} to hold target scheduling context. +It @var{clean_p} is true then initialize @var{tc} as if scheduler is at the +beginning of the block. Otherwise, copy the current context into @var{tc}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_CONTEXT (void *@var{tc}) +Copy target scheduling context pointed to by @var{tc} to the current context. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_CLEAR_SCHED_CONTEXT (void *@var{tc}) +Deallocate internal data in target scheduling context pointed to by @var{tc}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FREE_SCHED_CONTEXT (void *@var{tc}) +Deallocate a store for target scheduling context pointed to by @var{tc}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_SPECULATE_INSN (rtx_insn *@var{insn}, unsigned int @var{dep_status}, rtx *@var{new_pat}) +This hook is called by the insn scheduler when @var{insn} has only +speculative dependencies and therefore can be scheduled speculatively. +The hook is used to check if the pattern of @var{insn} has a speculative +version and, in case of successful check, to generate that speculative +pattern. The hook should return 1, if the instruction has a speculative form, +or @minus{}1, if it doesn't. @var{request} describes the type of requested +speculation. If the return value equals 1 then @var{new_pat} is assigned +the generated speculative pattern. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCHED_NEEDS_BLOCK_P (unsigned int @var{dep_status}) +This hook is called by the insn scheduler during generation of recovery code +for @var{insn}. It should return @code{true}, if the corresponding check +instruction should branch to recovery code, or @code{false} otherwise. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_SCHED_GEN_SPEC_CHECK (rtx_insn *@var{insn}, rtx_insn *@var{label}, unsigned int @var{ds}) +This hook is called by the insn scheduler to generate a pattern for recovery +check instruction. If @var{mutate_p} is zero, then @var{insn} is a +speculative instruction for which the check should be generated. +@var{label} is either a label of a basic block, where recovery code should +be emitted, or a null pointer, when requested check doesn't branch to +recovery code (a simple check). If @var{mutate_p} is nonzero, then +a pattern for a branchy check corresponding to a simple check denoted by +@var{insn} should be generated. In this case @var{label} can't be null. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_SET_SCHED_FLAGS (struct spec_info_def *@var{spec_info}) +This hook is used by the insn scheduler to find out what features should be +enabled/used. +The structure *@var{spec_info} should be filled in by the target. +The structure describes speculation types that can be used in the scheduler. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCHED_CAN_SPECULATE_INSN (rtx_insn *@var{insn}) +Some instructions should never be speculated by the schedulers, usually + because the instruction is too expensive to get this wrong. Often such + instructions have long latency, and often they are not fully modeled in the + pipeline descriptions. This hook should return @code{false} if @var{insn} + should not be speculated. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_SCHED_SMS_RES_MII (struct ddg *@var{g}) +This hook is called by the swing modulo scheduler to calculate a +resource-based lower bound which is based on the resources available in +the machine and the resources required by each instruction. The target +backend can use @var{g} to calculate such bound. A very simple lower +bound will be used in case this hook is not implemented: the total number +of instructions divided by the issue rate. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SCHED_DISPATCH (rtx_insn *@var{insn}, int @var{x}) +This hook is called by Haifa Scheduler. It returns true if dispatch scheduling +is supported in hardware and the condition specified in the parameter is true. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_DISPATCH_DO (rtx_insn *@var{insn}, int @var{x}) +This hook is called by Haifa Scheduler. It performs the operation specified +in its second parameter. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_SCHED_EXPOSED_PIPELINE +True if the processor has an exposed pipeline, which means that not just +the order of instructions is important for correctness when scheduling, but +also the latencies of operations. +@end deftypevr + +@deftypefn {Target Hook} int TARGET_SCHED_REASSOCIATION_WIDTH (unsigned int @var{opc}, machine_mode @var{mode}) +This hook is called by tree reassociator to determine a level of +parallelism required in output calculations chain. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SCHED_FUSION_PRIORITY (rtx_insn *@var{insn}, int @var{max_pri}, int *@var{fusion_pri}, int *@var{pri}) +This hook is called by scheduling fusion pass. It calculates fusion +priorities for each instruction passed in by parameter. The priorities +are returned via pointer parameters. + +@var{insn} is the instruction whose priorities need to be calculated. +@var{max_pri} is the maximum priority can be returned in any cases. +@var{fusion_pri} is the pointer parameter through which @var{insn}'s +fusion priority should be calculated and returned. +@var{pri} is the pointer parameter through which @var{insn}'s priority +should be calculated and returned. + +Same @var{fusion_pri} should be returned for instructions which should +be scheduled together. Different @var{pri} should be returned for +instructions with same @var{fusion_pri}. @var{fusion_pri} is the major +sort key, @var{pri} is the minor sort key. All instructions will be +scheduled according to the two priorities. All priorities calculated +should be between 0 (exclusive) and @var{max_pri} (inclusive). To avoid +false dependencies, @var{fusion_pri} of instructions which need to be +scheduled together should be smaller than @var{fusion_pri} of irrelevant +instructions. + +Given below example: + +@smallexample + ldr r10, [r1, 4] + add r4, r4, r10 + ldr r15, [r2, 8] + sub r5, r5, r15 + ldr r11, [r1, 0] + add r4, r4, r11 + ldr r16, [r2, 12] + sub r5, r5, r16 +@end smallexample + +On targets like ARM/AArch64, the two pairs of consecutive loads should be +merged. Since peephole2 pass can't help in this case unless consecutive +loads are actually next to each other in instruction flow. That's where +this scheduling fusion pass works. This hook calculates priority for each +instruction based on its fustion type, like: + +@smallexample + ldr r10, [r1, 4] ; fusion_pri=99, pri=96 + add r4, r4, r10 ; fusion_pri=100, pri=100 + ldr r15, [r2, 8] ; fusion_pri=98, pri=92 + sub r5, r5, r15 ; fusion_pri=100, pri=100 + ldr r11, [r1, 0] ; fusion_pri=99, pri=100 + add r4, r4, r11 ; fusion_pri=100, pri=100 + ldr r16, [r2, 12] ; fusion_pri=98, pri=88 + sub r5, r5, r16 ; fusion_pri=100, pri=100 +@end smallexample + +Scheduling fusion pass then sorts all ready to issue instructions according +to the priorities. As a result, instructions of same fusion type will be +pushed together in instruction flow, like: + +@smallexample + ldr r11, [r1, 0] + ldr r10, [r1, 4] + ldr r15, [r2, 8] + ldr r16, [r2, 12] + add r4, r4, r10 + sub r5, r5, r15 + add r4, r4, r11 + sub r5, r5, r16 +@end smallexample + +Now peephole2 pass can simply merge the two pairs of loads. + +Since scheduling fusion pass relies on peephole2 to do real fusion +work, it is only enabled by default when peephole2 is in effect. + +This is firstly introduced on ARM/AArch64 targets, please refer to +the hook implementation for how different fusion types are supported. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_EXPAND_DIVMOD_LIBFUNC (rtx @var{libfunc}, machine_mode @var{mode}, rtx @var{op0}, rtx @var{op1}, rtx *@var{quot}, rtx *@var{rem}) +Define this hook for enabling divmod transform if the port does not have +hardware divmod insn but defines target-specific divmod libfuncs. +@end deftypefn + +@node Sections +@section Dividing the Output into Sections (Texts, Data, @dots{}) +@c the above section title is WAY too long. maybe cut the part between +@c the (...)? --mew 10feb93 + +An object file is divided into sections containing different types of +data. In the most common case, there are three sections: the @dfn{text +section}, which holds instructions and read-only data; the @dfn{data +section}, which holds initialized writable data; and the @dfn{bss +section}, which holds uninitialized data. Some systems have other kinds +of sections. + +@file{varasm.cc} provides several well-known sections, such as +@code{text_section}, @code{data_section} and @code{bss_section}. +The normal way of controlling a @code{@var{foo}_section} variable +is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro, +as described below. The macros are only read once, when @file{varasm.cc} +initializes itself, so their values must be run-time constants. +They may however depend on command-line flags. + +@emph{Note:} Some run-time files, such @file{crtstuff.c}, also make +use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them +to be string literals. + +Some assemblers require a different string to be written every time a +section is selected. If your assembler falls into this category, you +should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use +@code{get_unnamed_section} to set up the sections. + +You must always create a @code{text_section}, either by defining +@code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section} +in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of +@code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not +create a distinct @code{readonly_data_section}, the default is to +reuse @code{text_section}. + +All the other @file{varasm.cc} sections are optional, and are null +if the target does not provide them. + +@defmac TEXT_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation that should precede instructions and read-only data. +Normally @code{"\t.text"} is right. +@end defmac + +@defmac HOT_TEXT_SECTION_NAME +If defined, a C string constant for the name of the section containing most +frequently executed functions of the program. If not defined, GCC will provide +a default definition if the target supports named sections. +@end defmac + +@defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME +If defined, a C string constant for the name of the section containing unlikely +executed functions in the program. +@end defmac + +@defmac DATA_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation to identify the following data as writable initialized +data. Normally @code{"\t.data"} is right. +@end defmac + +@defmac SDATA_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +initialized, writable small data. +@end defmac + +@defmac READONLY_DATA_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation to identify the following data as read-only initialized +data. +@end defmac + +@defmac BSS_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +uninitialized global data. If not defined, and +@code{ASM_OUTPUT_ALIGNED_BSS} not defined, +uninitialized global data will be output in the data section if +@option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be +used. +@end defmac + +@defmac SBSS_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +uninitialized, writable small data. +@end defmac + +@defmac TLS_COMMON_ASM_OP +If defined, a C expression whose value is a string containing the +assembler operation to identify the following data as thread-local +common data. The default is @code{".tls_common"}. +@end defmac + +@defmac TLS_SECTION_ASM_FLAG +If defined, a C expression whose value is a character constant +containing the flag used to mark a section as a TLS section. The +default is @code{'T'}. +@end defmac + +@defmac INIT_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +initialization code. If not defined, GCC will assume such a section does +not exist. This section has no corresponding @code{init_section} +variable; it is used entirely in runtime code. +@end defmac + +@defmac FINI_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +finalization code. If not defined, GCC will assume such a section does +not exist. This section has no corresponding @code{fini_section} +variable; it is used entirely in runtime code. +@end defmac + +@defmac INIT_ARRAY_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +part of the @code{.init_array} (or equivalent) section. If not +defined, GCC will assume such a section does not exist. Do not define +both this macro and @code{INIT_SECTION_ASM_OP}. +@end defmac + +@defmac FINI_ARRAY_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +part of the @code{.fini_array} (or equivalent) section. If not +defined, GCC will assume such a section does not exist. Do not define +both this macro and @code{FINI_SECTION_ASM_OP}. +@end defmac + +@defmac MACH_DEP_SECTION_ASM_FLAG +If defined, a C expression whose value is a character constant +containing the flag used to mark a machine-dependent section. This +corresponds to the @code{SECTION_MACH_DEP} section flag. +@end defmac + +@defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function}) +If defined, an ASM statement that switches to a different section +via @var{section_op}, calls @var{function}, and switches back to +the text section. This is used in @file{crtstuff.c} if +@code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls +to initialization and finalization functions from the init and fini +sections. By default, this macro uses a simple function call. Some +ports need hand-crafted assembly code to avoid dependencies on +registers initialized in the function prologue or to ensure that +constant pools don't end up too far way in the text section. +@end defmac + +@defmac TARGET_LIBGCC_SDATA_SECTION +If defined, a string which names the section into which small +variables defined in crtstuff and libgcc should go. This is useful +when the target has options for optimizing access to small data, and +you want the crtstuff and libgcc routines to be conservative in what +they expect of your application yet liberal in what your application +expects. For example, for targets with a @code{.sdata} section (like +MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't +require small data support from your application, but use this macro +to put small data into @code{.sdata} so that your application can +access these variables whether it uses small data or not. +@end defmac + +@defmac FORCE_CODE_SECTION_ALIGN +If defined, an ASM statement that aligns a code section to some +arbitrary boundary. This is used to force all fragments of the +@code{.init} and @code{.fini} sections to have to same alignment +and thus prevent the linker from having to add any padding. +@end defmac + +@defmac JUMP_TABLES_IN_TEXT_SECTION +Define this macro to be an expression with a nonzero value if jump +tables (for @code{tablejump} insns) should be output in the text +section, along with the assembler instructions. Otherwise, the +readonly data section is used. + +This macro is irrelevant if there is no separate readonly data section. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_INIT_SECTIONS (void) +Define this hook if you need to do something special to set up the +@file{varasm.cc} sections, or if your target has some special sections +of its own that you need to create. + +GCC calls this hook after processing the command line, but before writing +any assembly code, and before calling any of the section-returning hooks +described below. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_ASM_RELOC_RW_MASK (void) +Return a mask describing how relocations should be treated when +selecting sections. Bit 1 should be set if global relocations +should be placed in a read-write section; bit 0 should be set if +local relocations should be placed in a read-write section. + +The default version of this function returns 3 when @option{-fpic} +is in effect, and 0 otherwise. The hook is typically redefined +when the target cannot support (some kinds of) dynamic relocations +in read-only sections even in executables. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ASM_GENERATE_PIC_ADDR_DIFF_VEC (void) +Return true to generate ADDR_DIF_VEC table +or false to generate ADDR_VEC table for jumps in case of -fPIC. + +The default version of this function returns true if flag_pic +equals true and false otherwise +@end deftypefn + +@deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align}) +Return the section into which @var{exp} should be placed. You can +assume that @var{exp} is either a @code{VAR_DECL} node or a constant of +some sort. @var{reloc} indicates whether the initial value of @var{exp} +requires link-time relocations. Bit 0 is set when variable contains +local relocations only, while bit 1 is set for global relocations. +@var{align} is the constant alignment in bits. + +The default version of this function takes care of putting read-only +variables in @code{readonly_data_section}. + +See also @var{USE_SELECT_SECTION_FOR_FUNCTIONS}. +@end deftypefn + +@defmac USE_SELECT_SECTION_FOR_FUNCTIONS +Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called +for @code{FUNCTION_DECL}s as well as for variables and constants. + +In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the +function has been determined to be likely to be called, and nonzero if +it is unlikely to be called. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc}) +Build up a unique section name, expressed as a @code{STRING_CST} node, +and assign it to @samp{DECL_SECTION_NAME (@var{decl})}. +As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether +the initial value of @var{exp} requires link-time relocations. + +The default version of this function appends the symbol name to the +ELF section name that would normally be used for the symbol. For +example, the function @code{foo} would be placed in @code{.text.foo}. +Whatever the actual target object format, this is often good enough. +@end deftypefn + +@deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_RODATA_SECTION (tree @var{decl}, bool @var{relocatable}) +Return the readonly data or reloc readonly data section associated with +@samp{DECL_SECTION_NAME (@var{decl})}. @var{relocatable} selects the latter +over the former. +The default version of this function selects @code{.gnu.linkonce.r.name} if +the function's section is @code{.gnu.linkonce.t.name}, @code{.rodata.name} +or @code{.data.rel.ro.name} if function is in @code{.text.name}, and +the normal readonly-data or reloc readonly data section otherwise. +@end deftypefn + +@deftypevr {Target Hook} {const char *} TARGET_ASM_MERGEABLE_RODATA_PREFIX +Usually, the compiler uses the prefix @code{".rodata"} to construct +section names for mergeable constant data. Define this macro to override +the string if a different section name should be used. +@end deftypevr + +@deftypefn {Target Hook} {section *} TARGET_ASM_TM_CLONE_TABLE_SECTION (void) +Return the section that should be used for transactional memory clone +tables. +@end deftypefn + +@deftypefn {Target Hook} {section *} TARGET_ASM_SELECT_RTX_SECTION (machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align}) +Return the section into which a constant @var{x}, of mode @var{mode}, +should be placed. You can assume that @var{x} is some kind of +constant in RTL@. The argument @var{mode} is redundant except in the +case of a @code{const_int} rtx. @var{align} is the constant alignment +in bits. + +The default version of this function takes care of putting symbolic +constants in @code{flag_pic} mode in @code{data_section} and everything +else in @code{readonly_data_section}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_MANGLE_DECL_ASSEMBLER_NAME (tree @var{decl}, tree @var{id}) +Define this hook if you need to postprocess the assembler name generated +by target-independent code. The @var{id} provided to this hook will be +the computed name (e.g., the macro @code{DECL_NAME} of the @var{decl} in C, +or the mangled name of the @var{decl} in C++). The return value of the +hook is an @code{IDENTIFIER_NODE} for the appropriate mangled name on +your target system. The default implementation of this hook just +returns the @var{id} provided. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, rtx @var{rtl}, int @var{new_decl_p}) +Define this hook if references to a symbol or a constant must be +treated differently depending on something about the variable or +function named by the symbol (such as what section it is in). + +The hook is executed immediately after rtl has been created for +@var{decl}, which may be a variable or function declaration or +an entry in the constant pool. In either case, @var{rtl} is the +rtl in question. Do @emph{not} use @code{DECL_RTL (@var{decl})} +in this hook; that field may not have been initialized yet. + +In the case of a constant, it is safe to assume that the rtl is +a @code{mem} whose address is a @code{symbol_ref}. Most decls +will also have this form, but that is not guaranteed. Global +register variables, for instance, will have a @code{reg} for their +rtl. (Normally the right thing to do with such unusual rtl is +leave it alone.) + +The @var{new_decl_p} argument will be true if this is the first time +that @code{TARGET_ENCODE_SECTION_INFO} has been invoked on this decl. It will +be false for subsequent invocations, which will happen for duplicate +declarations. Whether or not anything must be done for the duplicate +declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}. +@var{new_decl_p} is always true when the hook is called for a constant. + +@cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO} +The usual thing for this hook to do is to record flags in the +@code{symbol_ref}, using @code{SYMBOL_REF_FLAG} or @code{SYMBOL_REF_FLAGS}. +Historically, the name string was modified if it was necessary to +encode more than one bit of information, but this practice is now +discouraged; use @code{SYMBOL_REF_FLAGS}. + +The default definition of this hook, @code{default_encode_section_info} +in @file{varasm.cc}, sets a number of commonly-useful bits in +@code{SYMBOL_REF_FLAGS}. Check whether the default does what you need +before overriding it. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_STRIP_NAME_ENCODING (const char *@var{name}) +Decode @var{name} and return the real name part, sans +the characters that @code{TARGET_ENCODE_SECTION_INFO} +may have added. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (const_tree @var{exp}) +Returns true if @var{exp} should be placed into a ``small data'' section. +The default version of this hook always returns false. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_HAVE_SRODATA_SECTION +Contains the value true if the target places read-only +``small data'' into a separate section. The default value is false. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_PROFILE_BEFORE_PROLOGUE (void) +It returns true if target wants profile code emitted before prologue. + +The default version of this hook use the target macro +@code{PROFILE_BEFORE_PROLOGUE}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (const_tree @var{exp}) +Returns true if @var{exp} names an object for which name resolution +rules must resolve to the current ``module'' (dynamic shared library +or executable image). + +The default version of this hook implements the name resolution rules +for ELF, which has a looser model of global name binding than other +currently supported object file formats. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_HAVE_TLS +Contains the value true if the target supports thread-local storage. +The default value is false. +@end deftypevr + + +@node PIC +@section Position Independent Code +@cindex position independent code +@cindex PIC + +This section describes macros that help implement generation of position +independent code. Simply defining these macros is not enough to +generate valid PIC; you must also add support to the hook +@code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro +@code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You +must modify the definition of @samp{movsi} to do something appropriate +when the source operand contains a symbolic address. You may also +need to alter the handling of switch statements so that they use +relative addresses. +@c i rearranged the order of the macros above to try to force one of +@c them to the next line, to eliminate an overfull hbox. --mew 10feb93 + +@defmac PIC_OFFSET_TABLE_REGNUM +The register number of the register used to address a table of static +data addresses in memory. In some cases this register is defined by a +processor's ``application binary interface'' (ABI)@. When this macro +is defined, RTL is generated for this register once, as with the stack +pointer and frame pointer registers. If this macro is not defined, it +is up to the machine-dependent files to allocate such a register (if +necessary). Note that this register must be fixed when in use (e.g.@: +when @code{flag_pic} is true). +@end defmac + +@defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED +A C expression that is nonzero if the register defined by +@code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. If not defined, +the default is zero. Do not define +this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined. +@end defmac + +@defmac LEGITIMATE_PIC_OPERAND_P (@var{x}) +A C expression that is nonzero if @var{x} is a legitimate immediate +operand on the target machine when generating position independent code. +You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not +check this. You can also assume @var{flag_pic} is true, so you need not +check it either. You need not define this macro if all constants +(including @code{SYMBOL_REF}) can be immediate operands when generating +position independent code. +@end defmac + +@node Assembler Format +@section Defining the Output Assembler Language + +This section describes macros whose principal purpose is to describe how +to write instructions in assembler language---rather than what the +instructions do. + +@menu +* File Framework:: Structural information for the assembler file. +* Data Output:: Output of constants (numbers, strings, addresses). +* Uninitialized Data:: Output of uninitialized variables. +* Label Output:: Output and generation of labels. +* Initialization:: General principles of initialization + and termination routines. +* Macros for Initialization:: + Specific macros that control the handling of + initialization and termination routines. +* Instruction Output:: Output of actual instructions. +* Dispatch Tables:: Output of jump tables. +* Exception Region Output:: Output of exception region code. +* Alignment Output:: Pseudo ops for alignment and skipping data. +@end menu + +@node File Framework +@subsection The Overall Framework of an Assembler File +@cindex assembler format +@cindex output of assembler code + +@c prevent bad page break with this line +This describes the overall framework of an assembly file. + +@findex default_file_start +@deftypefn {Target Hook} void TARGET_ASM_FILE_START (void) +Output to @code{asm_out_file} any text which the assembler expects to +find at the beginning of a file. The default behavior is controlled +by two flags, documented below. Unless your target's assembler is +quite unusual, if you override the default, you should call +@code{default_file_start} at some point in your target hook. This +lets other target files rely on these variables. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_ASM_FILE_START_APP_OFF +If this flag is true, the text of the macro @code{ASM_APP_OFF} will be +printed as the very first line in the assembly file, unless +@option{-fverbose-asm} is in effect. (If that macro has been defined +to the empty string, this variable has no effect.) With the normal +definition of @code{ASM_APP_OFF}, the effect is to notify the GNU +assembler that it need not bother stripping comments or extra +whitespace from its input. This allows it to work a bit faster. + +The default is false. You should not set it to true unless you have +verified that your port does not generate any extra whitespace or +comments that will cause GAS to issue errors in NO_APP mode. +@end deftypevr + +@deftypevr {Target Hook} bool TARGET_ASM_FILE_START_FILE_DIRECTIVE +If this flag is true, @code{output_file_directive} will be called +for the primary source file, immediately after printing +@code{ASM_APP_OFF} (if that is enabled). Most ELF assemblers expect +this to be done. The default is false. +@end deftypevr + +@deftypefn {Target Hook} void TARGET_ASM_FILE_END (void) +Output to @code{asm_out_file} any text which the assembler expects +to find at the end of a file. The default is to output nothing. +@end deftypefn + +@deftypefun void file_end_indicate_exec_stack () +Some systems use a common convention, the @samp{.note.GNU-stack} +special section, to indicate whether or not an object file relies on +the stack being executable. If your system uses this convention, you +should define @code{TARGET_ASM_FILE_END} to this function. If you +need to do other things in that hook, have your hook function call +this function. +@end deftypefun + +@deftypefn {Target Hook} void TARGET_ASM_LTO_START (void) +Output to @code{asm_out_file} any text which the assembler expects +to find at the start of an LTO section. The default is to output +nothing. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_LTO_END (void) +Output to @code{asm_out_file} any text which the assembler expects +to find at the end of an LTO section. The default is to output +nothing. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_CODE_END (void) +Output to @code{asm_out_file} any text which is needed before emitting +unwind info and debug info at the end of a file. Some targets emit +here PIC setup thunks that cannot be emitted at the end of file, +because they couldn't have unwind info then. The default is to output +nothing. +@end deftypefn + +@defmac ASM_COMMENT_START +A C string constant describing how to begin a comment in the target +assembler language. The compiler assumes that the comment will end at +the end of the line. +@end defmac + +@defmac ASM_APP_ON +A C string constant for text to be output before each @code{asm} +statement or group of consecutive ones. Normally this is +@code{"#APP"}, which is a comment that has no effect on most +assemblers but tells the GNU assembler that it must check the lines +that follow for all valid assembler constructs. +@end defmac + +@defmac ASM_APP_OFF +A C string constant for text to be output after each @code{asm} +statement or group of consecutive ones. Normally this is +@code{"#NO_APP"}, which tells the GNU assembler to resume making the +time-saving assumptions that are valid for ordinary compiler output. +@end defmac + +@defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) +A C statement to output COFF information or DWARF debugging information +which indicates that filename @var{name} is the current source file to +the stdio stream @var{stream}. + +This macro need not be defined if the standard form of output +for the file format in use is appropriate. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_SOURCE_FILENAME (FILE *@var{file}, const char *@var{name}) +Output DWARF debugging information which indicates that filename +@var{name} is the current source file to the stdio stream @var{file}. + +This target hook need not be defined if the standard form of output +for the file format in use is appropriate. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_IDENT (const char *@var{name}) +Output a string based on @var{name}, suitable for the @samp{#ident} +directive, or the equivalent directive or pragma in non-C-family languages. +If this hook is not defined, nothing is output for the @samp{#ident} +directive. +@end deftypefn + +@defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string}) +A C statement to output the string @var{string} to the stdio stream +@var{stream}. If you do not call the function @code{output_quoted_string} +in your config files, GCC will only call it to output filenames to +the assembler source. So you can use it to canonicalize the format +of the filename using this macro. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, tree @var{decl}) +Output assembly directives to switch to section @var{name}. The section +should have attributes as specified by @var{flags}, which is a bit mask +of the @code{SECTION_*} flags defined in @file{output.h}. If @var{decl} +is non-NULL, it is the @code{VAR_DECL} or @code{FUNCTION_DECL} with which +this section is associated. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ASM_ELF_FLAGS_NUMERIC (unsigned int @var{flags}, unsigned int *@var{num}) +This hook can be used to encode ELF section flags for which no letter +code has been defined in the assembler. It is called by +@code{default_asm_named_section} whenever the section flags need to be +emitted in the assembler output. If the hook returns true, then the +numerical value for ELF section flags should be calculated from +@var{flags} and saved in @var{*num}; the value is printed out instead of the +normal sequence of letter codes. If the hook is not defined, or if it +returns false, then @var{num} is ignored and the traditional letter sequence +is emitted. +@end deftypefn + +@deftypefn {Target Hook} {section *} TARGET_ASM_FUNCTION_SECTION (tree @var{decl}, enum node_frequency @var{freq}, bool @var{startup}, bool @var{exit}) +Return preferred text (sub)section for function @var{decl}. +Main purpose of this function is to separate cold, normal and hot +functions. @var{startup} is true when function is known to be used only +at startup (from static constructors or it is @code{main()}). +@var{exit} is true when function is known to be used only at exit +(from static destructors). +Return NULL if function should go to default text section. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_FUNCTION_SWITCHED_TEXT_SECTIONS (FILE *@var{file}, tree @var{decl}, bool @var{new_is_cold}) +Used by the target to emit any assembler directives or additional +labels needed when a function is partitioned between different +sections. Output should be written to @var{file}. The function +decl is available as @var{decl} and the new section is `cold' if +@var{new_is_cold} is @code{true}. +@end deftypefn + +@deftypevr {Common Target Hook} bool TARGET_HAVE_NAMED_SECTIONS +This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. +It must not be modified by command-line option processing. +@end deftypevr + +@anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS} +@deftypevr {Target Hook} bool TARGET_HAVE_SWITCHABLE_BSS_SECTIONS +This flag is true if we can create zeroed data by switching to a BSS +section and then using @code{ASM_OUTPUT_SKIP} to allocate the space. +This is true on most ELF targets. +@end deftypevr + +@deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc}) +Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION} +based on a variable or function decl, a section name, and whether or not the +declaration's initializer may contain runtime relocations. @var{decl} may be +null, in which case read-write data should be assumed. + +The default version of this function handles choosing code vs data, +read-only vs read-write data, and @code{flag_pic}. You should only +need to override this if your target has special flags that might be +set via @code{__attribute__}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_RECORD_GCC_SWITCHES (const char *@var{}) +Provides the target with the ability to record the gcc command line +switches provided as argument. + +By default this hook is set to NULL, but an example implementation is +provided for ELF based targets. Called @var{elf_record_gcc_switches}, +it records the switches as ASCII text inside a new, string mergeable +section in the assembler output file. The name of the new section is +provided by the @code{TARGET_ASM_RECORD_GCC_SWITCHES_SECTION} target +hook. +@end deftypefn + +@deftypevr {Target Hook} {const char *} TARGET_ASM_RECORD_GCC_SWITCHES_SECTION +This is the name of the section that will be created by the example +ELF implementation of the @code{TARGET_ASM_RECORD_GCC_SWITCHES} target +hook. +@end deftypevr + +@need 2000 +@node Data Output +@subsection Output of Data + + +@deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_PSI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_PDI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_PTI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_PSI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_PDI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_PTI_OP +@deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP +These hooks specify assembly directives for creating certain kinds +of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a +byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an +aligned two-byte object, and so on. Any of the hooks may be +@code{NULL}, indicating that no suitable directive is available. + +The compiler will print these strings at the start of a new line, +followed immediately by the object's initial value. In most cases, +the string should contain a tab, a pseudo-op, and then another tab. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p}) +The @code{assemble_integer} function uses this hook to output an +integer object. @var{x} is the object's value, @var{size} is its size +in bytes and @var{aligned_p} indicates whether it is aligned. The +function should return @code{true} if it was able to output the +object. If it returns false, @code{assemble_integer} will try to +split the object into smaller parts. + +The default implementation of this hook will use the +@code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false} +when the relevant string is @code{NULL}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_DECL_END (void) +Define this hook if the target assembler requires a special marker to +terminate an initialized variable declaration. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA (FILE *@var{file}, rtx @var{x}) +A target hook to recognize @var{rtx} patterns that @code{output_addr_const} +can't deal with, and output assembly code to @var{file} corresponding to +the pattern @var{x}. This may be used to allow machine-dependent +@code{UNSPEC}s to appear within constants. + +If target hook fails to recognize a pattern, it must return @code{false}, +so that a standard error message is printed. If it prints an error message +itself, by calling, for example, @code{output_operand_lossage}, it may just +return @code{true}. +@end deftypefn + +@defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len}) +A C statement to output to the stdio stream @var{stream} an assembler +instruction to assemble a string constant containing the @var{len} +bytes at @var{ptr}. @var{ptr} will be a C expression of type +@code{char *} and @var{len} a C expression of type @code{int}. + +If the assembler has a @code{.ascii} pseudo-op as found in the +Berkeley Unix assembler, do not define the macro +@code{ASM_OUTPUT_ASCII}. +@end defmac + +@defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n}) +A C statement to output word @var{n} of a function descriptor for +@var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS} +is defined, and is otherwise unused. +@end defmac + +@defmac CONSTANT_POOL_BEFORE_FUNCTION +You may define this macro as a C expression. You should define the +expression to have a nonzero value if GCC should output the constant +pool for a function before the code for the function, or a zero value if +GCC should output the constant pool after the function. If you do +not define this macro, the usual case, GCC will output the constant +pool before the function. +@end defmac + +@defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size}) +A C statement to output assembler commands to define the start of the +constant pool for a function. @var{funname} is a string giving +the name of the function. Should the return type of the function +be required, it can be obtained via @var{fundecl}. @var{size} +is the size, in bytes, of the constant pool that will be written +immediately after this call. + +If no constant-pool prefix is required, the usual case, this macro need +not be defined. +@end defmac + +@defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto}) +A C statement (with or without semicolon) to output a constant in the +constant pool, if it needs special treatment. (This macro need not do +anything for RTL expressions that can be output normally.) + +The argument @var{file} is the standard I/O stream to output the +assembler code on. @var{x} is the RTL expression for the constant to +output, and @var{mode} is the machine mode (in case @var{x} is a +@samp{const_int}). @var{align} is the required alignment for the value +@var{x}; you should output an assembler directive to force this much +alignment. + +The argument @var{labelno} is a number to use in an internal label for +the address of this pool entry. The definition of this macro is +responsible for outputting the label definition at the proper place. +Here is how to do this: + +@smallexample +@code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno}); +@end smallexample + +When you output a pool entry specially, you should end with a +@code{goto} to the label @var{jumpto}. This will prevent the same pool +entry from being output a second time in the usual manner. + +You need not define this macro if it would do nothing. +@end defmac + +@defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size}) +A C statement to output assembler commands to at the end of the constant +pool for a function. @var{funname} is a string giving the name of the +function. Should the return type of the function be required, you can +obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the +constant pool that GCC wrote immediately before this call. + +If no constant-pool epilogue is required, the usual case, you need not +define this macro. +@end defmac + +@defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR}) +Define this macro as a C expression which is nonzero if @var{C} is +used as a logical line separator by the assembler. @var{STR} points +to the position in the string where @var{C} was found; this can be used if +a line separator uses multiple characters. + +If you do not define this macro, the default is that only +the character @samp{;} is treated as a logical line separator. +@end defmac + +@deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN +@deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN +These target hooks are C string constants, describing the syntax in the +assembler for grouping arithmetic expressions. If not overridden, they +default to normal parentheses, which is correct for most assemblers. +@end deftypevr + +These macros are provided by @file{real.h} for writing the definitions +of @code{ASM_OUTPUT_DOUBLE} and the like: + +@defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l}) +These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the +target's floating point representation, and store its bit pattern in +the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and +@code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a +simple @code{long int}. For the others, it should be an array of +@code{long int}. The number of elements in this array is determined +by the size of the desired target floating point data type: 32 bits of +it go in each @code{long int} array element. Each array element holds +32 bits of the result, even if @code{long int} is wider than 32 bits +on the host machine. + +The array element values are designed so that you can print them out +using @code{fprintf} in the order they should appear in the target +machine's memory. +@end defmac + +@node Uninitialized Data +@subsection Output of Uninitialized Variables + +Each of the macros in this section is used to do the whole job of +outputting a single uninitialized variable. + +@defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a common-label named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. It is +possible that @var{size} may be zero, for instance if a struct with no +other member than a zero-length array is defined. In this case, the +backend must output a symbol definition that allocates at least one +byte, both so that the address of the resulting object does not compare +equal to any other, and because some object formats cannot even express +the concept of a zero-sized common symbol, as that is how they represent +an ordinary undefined external. + +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +This macro controls how the assembler definitions of uninitialized +common global variables are output. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the +variable to be output, if there is one, or @code{NULL_TREE} if there +is no corresponding variable. If you define this macro, GCC will use it +in place of both @code{ASM_OUTPUT_COMMON} and +@code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see +the variable's decl in order to chose what to output. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of uninitialized global @var{decl} named +@var{name} whose size is @var{size} bytes. The variable @var{alignment} +is the alignment specified as the number of bits. + +Try to use function @code{asm_output_aligned_bss} defined in file +@file{varasm.cc} when defining this macro. If unable, use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name itself; +before and after that, output the additional assembler syntax for defining +the name, and a newline. + +There are two ways of handling global BSS@. One is to define this macro. +The other is to have @code{TARGET_ASM_SELECT_SECTION} return a +switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}). +You do not need to do both. + +Some languages do not have @code{common} data, and require a +non-common form of global BSS in order to handle uninitialized globals +efficiently. C++ is one example of this. However, if the target does +not support global BSS, the front end may choose to make globals +common in order to save space in the object file. +@end defmac + +@defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a local-common-label named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. + +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +This macro controls how the assembler definitions of uninitialized +static variables are output. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_ALIGNED_LOCAL} except that @var{decl} of the +variable to be output, if there is one, or @code{NULL_TREE} if there +is no corresponding variable. If you define this macro, GCC will use it +in place of both @code{ASM_OUTPUT_LOCAL} and +@code{ASM_OUTPUT_ALIGNED_LOCAL}. Define this macro when you need to see +the variable's decl in order to chose what to output. +@end defmac + +@node Label Output +@subsection Output and Generation of Labels + +@c prevent bad page break with this line +This is about outputting labels. + +@findex assemble_name +@defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a label named @var{name}. +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. A default +definition of this macro is provided which is correct for most systems. +@end defmac + +@defmac ASM_OUTPUT_FUNCTION_LABEL (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a label named @var{name} of +a function. +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. A default +definition of this macro is provided which is correct for most systems. + +If this macro is not defined, then the function name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). +@end defmac + +@findex assemble_name_raw +@defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name}) +Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known +to refer to a compiler-generated label. The default definition uses +@code{assemble_name_raw}, which is like @code{assemble_name} except +that it is more efficient. +@end defmac + +@defmac SIZE_ASM_OP +A C string containing the appropriate assembler directive to specify the +size of a symbol, without any arguments. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other +systems, the default is not to define this macro. + +Define this macro only if it is correct to use the default definitions +of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE} +for your system. If you need your own custom definitions of those +macros, or if you do not need explicit symbol sizes at all, do not +define this macro. +@end defmac + +@defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler that the size of the +symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}. +If you define @code{SIZE_ASM_OP}, a default definition of this macro is +provided. +@end defmac + +@defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler to calculate the size of +the symbol @var{name} by subtracting its address from the current +address. + +If you define @code{SIZE_ASM_OP}, a default definition of this macro is +provided. The default assumes that the assembler recognizes a special +@samp{.} symbol as referring to the current address, and can calculate +the difference between this and another symbol. If your assembler does +not recognize @samp{.} or cannot do calculations with it, you will need +to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique. +@end defmac + +@defmac NO_DOLLAR_IN_LABEL +Define this macro if the assembler does not accept the character +@samp{$} in label names. By default constructors and destructors in +G++ have @samp{$} in the identifiers. If this macro is defined, +@samp{.} is used instead. +@end defmac + +@defmac NO_DOT_IN_LABEL +Define this macro if the assembler does not accept the character +@samp{.} in label names. By default constructors and destructors in G++ +have names that use @samp{.}. If this macro is defined, these names +are rewritten to avoid @samp{.}. +@end defmac + +@defmac TYPE_ASM_OP +A C string containing the appropriate assembler directive to specify the +type of a symbol, without any arguments. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other +systems, the default is not to define this macro. + +Define this macro only if it is correct to use the default definition of +@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own +custom definition of this macro, or if you do not need explicit symbol +types at all, do not define this macro. +@end defmac + +@defmac TYPE_OPERAND_FMT +A C string which specifies (using @code{printf} syntax) the format of +the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems, +the default is not to define this macro. + +Define this macro only if it is correct to use the default definition of +@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own +custom definition of this macro, or if you do not need explicit symbol +types at all, do not define this macro. +@end defmac + +@defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler that the type of the +symbol @var{name} is @var{type}. @var{type} is a C string; currently, +that string is always either @samp{"function"} or @samp{"object"}, but +you should not count on this. + +If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default +definition of this macro is provided. +@end defmac + +@defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of a +function which is being defined. This macro is responsible for +outputting the label definition (perhaps using +@code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the +@code{FUNCTION_DECL} tree node representing the function. + +If this macro is not defined, then the function name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_FUNCTION_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the size of a function +which is being defined. The argument @var{name} is the name of the +function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node +representing the function. + +If this macro is not defined, then the function size is not defined. + +You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_COLD_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of a +cold function partition which is being defined. This macro is responsible +for outputting the label definition (perhaps using +@code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the +@code{FUNCTION_DECL} tree node representing the function. + +If this macro is not defined, then the cold partition name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_COLD_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the size of a cold function +partition which is being defined. The argument @var{name} is the name of the +cold partition of the function. The argument @var{decl} is the +@code{FUNCTION_DECL} tree node representing the function. + +If this macro is not defined, then the partition size is not defined. + +You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of an +initialized variable which is being defined. This macro must output the +label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument +@var{decl} is the @code{VAR_DECL} tree node representing the variable. + +If this macro is not defined, then the variable name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or +@code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_DECLARE_CONSTANT_NAME (FILE *@var{file}, const char *@var{name}, const_tree @var{expr}, HOST_WIDE_INT @var{size}) +A target hook to output to the stdio stream @var{file} any text necessary +for declaring the name @var{name} of a constant which is being defined. This +target hook is responsible for outputting the label definition (perhaps using +@code{assemble_label}). The argument @var{exp} is the value of the constant, +and @var{size} is the size of the constant in bytes. The @var{name} +will be an internal label. + +The default version of this target hook, define the @var{name} in the +usual manner as a label (by means of @code{assemble_label}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in this target hook. +@end deftypefn + +@defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for claiming a register @var{regno} +for a global variable @var{decl} with name @var{name}. + +If you don't define this macro, that is equivalent to defining it to do +nothing. +@end defmac + +@defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend}) +A C statement (sans semicolon) to finish up declaring a variable name +once the compiler has processed its initializer fully and thus has had a +chance to determine the size of an array when controlled by an +initializer. This is used on systems where it's necessary to declare +something about the size of the object. + +If you don't define this macro, that is equivalent to defining it to do +nothing. + +You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or +@code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name}) +This target hook is a function to output to the stdio stream +@var{stream} some commands that will make the label @var{name} global; +that is, available for reference from other files. + +The default implementation relies on a proper definition of +@code{GLOBAL_ASM_OP}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_DECL_NAME (FILE *@var{stream}, tree @var{decl}) +This target hook is a function to output to the stdio stream +@var{stream} some commands that will make the name associated with @var{decl} +global; that is, available for reference from other files. + +The default implementation uses the TARGET_ASM_GLOBALIZE_LABEL target hook. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_UNDEFINED_DECL (FILE *@var{stream}, const char *@var{name}, const_tree @var{decl}) +This target hook is a function to output to the stdio stream +@var{stream} some commands that will declare the name associated with +@var{decl} which is not defined in the current translation unit. Most +assemblers do not require anything to be output in this case. +@end deftypefn + +@defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} some commands that will make the label @var{name} weak; +that is, available for reference from other files but only used if +no other definition is available. Use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name +itself; before and after that, output the additional assembler syntax +for making that name weak, and a newline. + +If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not +support weak symbols and you should not define the @code{SUPPORTS_WEAK} +macro. +@end defmac + +@defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value}) +Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and +@code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function +or variable decl. If @var{value} is not @code{NULL}, this C statement +should output to the stdio stream @var{stream} assembler code which +defines (equates) the weak symbol @var{name} to have the value +@var{value}. If @var{value} is @code{NULL}, it should output commands +to make @var{name} weak. +@end defmac + +@defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value}) +Outputs a directive that enables @var{name} to be used to refer to +symbol @var{value} with weak-symbol semantics. @code{decl} is the +declaration of @code{name}. +@end defmac + +@defmac SUPPORTS_WEAK +A preprocessor constant expression which evaluates to true if the target +supports weak symbols. + +If you don't define this macro, @file{defaults.h} provides a default +definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL} +is defined, the default definition is @samp{1}; otherwise, it is @samp{0}. +@end defmac + +@defmac TARGET_SUPPORTS_WEAK +A C expression which evaluates to true if the target supports weak symbols. + +If you don't define this macro, @file{defaults.h} provides a default +definition. The default definition is @samp{(SUPPORTS_WEAK)}. Define +this macro if you want to control weak symbol support with a compiler +flag such as @option{-melf}. +@end defmac + +@defmac MAKE_DECL_ONE_ONLY (@var{decl}) +A C statement (sans semicolon) to mark @var{decl} to be emitted as a +public symbol such that extra copies in multiple translation units will +be discarded by the linker. Define this macro if your object file +format provides support for this concept, such as the @samp{COMDAT} +section flags in the Microsoft Windows PE/COFF format, and this support +requires changes to @var{decl}, such as putting it in a separate section. +@end defmac + +@defmac SUPPORTS_ONE_ONLY +A C expression which evaluates to true if the target supports one-only +semantics. + +If you don't define this macro, @file{varasm.cc} provides a default +definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default +definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if +you want to control one-only symbol support with a compiler flag, or if +setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to +be emitted as one-only. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, int @var{visibility}) +This target hook is a function to output to @var{asm_out_file} some +commands that will make the symbol(s) associated with @var{decl} have +hidden, protected or internal visibility as specified by @var{visibility}. +@end deftypefn + +@defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC +A C expression that evaluates to true if the target's linker expects +that weak symbols do not appear in a static archive's table of contents. +The default is @code{0}. + +Leaving weak symbols out of an archive's table of contents means that, +if a symbol will only have a definition in one translation unit and +will have undefined references from other translation units, that +symbol should not be weak. Defining this macro to be nonzero will +thus have the effect that certain symbols that would normally be weak +(explicit template instantiations, and vtables for polymorphic classes +with noninline key methods) will instead be nonweak. + +The C++ ABI requires this macro to be zero. Define this macro for +targets where full C++ ABI compliance is impossible and where linker +restrictions require weak symbols to be left out of a static archive's +table of contents. +@end defmac + +@defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name of an external +symbol named @var{name} which is referenced in this compilation but +not defined. The value of @var{decl} is the tree node for the +declaration. + +This macro need not be defined if it does not need to output anything. +The GNU assembler and most Unix assemblers don't require anything. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_EXTERNAL_LIBCALL (rtx @var{symref}) +This target hook is a function to output to @var{asm_out_file} an assembler +pseudo-op to declare a library function name external. The name of the +library function is given by @var{symref}, which is a @code{symbol_ref}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_MARK_DECL_PRESERVED (const char *@var{symbol}) +This target hook is a function to output to @var{asm_out_file} an assembler +directive to annotate @var{symbol} as used. The Darwin target uses the +.no_dead_code_strip directive. +@end deftypefn + +@defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a reference in assembler syntax to a label named +@var{name}. This should add @samp{_} to the front of the name, if that +is customary on your operating system, as it is in most Berkeley Unix +systems. This macro is used in @code{assemble_name}. +@end defmac + +@deftypefn {Target Hook} tree TARGET_MANGLE_ASSEMBLER_NAME (const char *@var{name}) +Given a symbol @var{name}, perform same mangling as @code{varasm.cc}'s +@code{assemble_name}, but in memory rather than to a file stream, returning +result as an @code{IDENTIFIER_NODE}. Required for correct LTO symtabs. The +default implementation calls the @code{TARGET_STRIP_NAME_ENCODING} hook and +then prepends the @code{USER_LABEL_PREFIX}, if any. +@end deftypefn + +@defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym}) +A C statement (sans semicolon) to output a reference to +@code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name} +will be used to output the name of the symbol. This macro may be used +to modify the way a symbol is referenced depending on information +encoded by @code{TARGET_ENCODE_SECTION_INFO}. +@end defmac + +@defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf}) +A C statement (sans semicolon) to output a reference to @var{buf}, the +result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined, +@code{assemble_name} will be used to output the name of the symbol. +This macro is not used by @code{output_asm_label}, or the @code{%l} +specifier that calls it; the intention is that this macro should be set +when it is necessary to output a label differently when its address is +being taken. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_INTERNAL_LABEL (FILE *@var{stream}, const char *@var{prefix}, unsigned long @var{labelno}) +A function to output to the stdio stream @var{stream} a label whose +name is made from the string @var{prefix} and the number @var{labelno}. + +It is absolutely essential that these labels be distinct from the labels +used for user-level functions and variables. Otherwise, certain programs +will have name conflicts with internal labels. + +It is desirable to exclude internal labels from the symbol table of the +object file. Most assemblers have a naming convention for labels that +should be excluded; on many systems, the letter @samp{L} at the +beginning of a label has this effect. You should find out what +convention your system uses, and follow it. + +The default version of this function utilizes @code{ASM_GENERATE_INTERNAL_LABEL}. +@end deftypefn + +@defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num}) +A C statement to output to the stdio stream @var{stream} a debug info +label whose name is made from the string @var{prefix} and the number +@var{num}. This is useful for VLIW targets, where debug info labels +may need to be treated differently than branch target labels. On some +systems, branch target labels must be at the beginning of instruction +bundles, but debug info labels can occur in the middle of instruction +bundles. + +If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be +used. +@end defmac + +@defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num}) +A C statement to store into the string @var{string} a label whose name +is made from the string @var{prefix} and the number @var{num}. + +This string, when output subsequently by @code{assemble_name}, should +produce the output that @code{(*targetm.asm_out.internal_label)} would produce +with the same @var{prefix} and @var{num}. + +If the string begins with @samp{*}, then @code{assemble_name} will +output the rest of the string unchanged. It is often convenient for +@code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the +string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets +to output the string, and may change it. (Of course, +@code{ASM_OUTPUT_LABELREF} is also part of your machine description, so +you should know what it does on your machine.) +@end defmac + +@defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number}) +A C expression to assign to @var{outvar} (which is a variable of type +@code{char *}) a newly allocated string made from the string +@var{name} and the number @var{number}, with some suitable punctuation +added. Use @code{alloca} to get space for the string. + +The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to +produce an assembler label for an internal static variable whose name is +@var{name}. Therefore, the string must be such as to result in valid +assembler code. The argument @var{number} is different each time this +macro is executed; it prevents conflicts between similarly-named +internal static variables in different scopes. + +Ideally this string should not be a valid C identifier, to prevent any +conflict with the user's own symbols. Most assemblers allow periods +or percent signs in assembler symbols; putting at least one of these +between the name and the number will suffice. + +If this macro is not defined, a default definition will be provided +which is correct for most systems. +@end defmac + +@defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol @var{name} to have the value @var{value}. + +@findex SET_ASM_OP +If @code{SET_ASM_OP} is defined, a default definition is provided which is +correct for most systems. +@end defmac + +@defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol whose tree node is @var{decl_of_name} +to have the value of the tree node @var{decl_of_value}. This macro will +be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if +the tree nodes are available. + +@findex SET_ASM_OP +If @code{SET_ASM_OP} is defined, a default definition is provided which is +correct for most systems. +@end defmac + +@defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value}) +A C statement that evaluates to true if the assembler code which defines +(equates) the symbol whose tree node is @var{decl_of_name} to have the value +of the tree node @var{decl_of_value} should be emitted near the end of the +current compilation unit. The default is to not defer output of defines. +This macro affects defines output by @samp{ASM_OUTPUT_DEF} and +@samp{ASM_OUTPUT_DEF_FROM_DECLS}. +@end defmac + +@defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the weak symbol @var{name} to have the value +@var{value}. If @var{value} is @code{NULL}, it defines @var{name} as +an undefined weak symbol. + +Define this macro if the target only supports weak aliases; define +@code{ASM_OUTPUT_DEF} instead if possible. +@end defmac + +@defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name}) +Define this macro to override the default assembler names used for +Objective-C methods. + +The default name is a unique method number followed by the name of the +class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of +the category is also included in the assembler name (e.g.@: +@samp{_1_Foo_Bar}). + +These names are safe on most systems, but make debugging difficult since +the method's selector is not present in the name. Therefore, particular +systems define other ways of computing names. + +@var{buf} is an expression of type @code{char *} which gives you a +buffer in which to store the name; its length is as long as +@var{class_name}, @var{cat_name} and @var{sel_name} put together, plus +50 characters extra. + +The argument @var{is_inst} specifies whether the method is an instance +method or a class method; @var{class_name} is the name of the class; +@var{cat_name} is the name of the category (or @code{NULL} if the method is not +in a category); and @var{sel_name} is the name of the selector. + +On systems where the assembler can handle quoted names, you can use this +macro to provide more human-readable names. +@end defmac + +@node Initialization +@subsection How Initialization Functions Are Handled +@cindex initialization routines +@cindex termination routines +@cindex constructors, output of +@cindex destructors, output of + +The compiled code for certain languages includes @dfn{constructors} +(also called @dfn{initialization routines})---functions to initialize +data in the program when the program is started. These functions need +to be called before the program is ``started''---that is to say, before +@code{main} is called. + +Compiling some languages generates @dfn{destructors} (also called +@dfn{termination routines}) that should be called when the program +terminates. + +To make the initialization and termination functions work, the compiler +must output something in the assembler code to cause those functions to +be called at the appropriate time. When you port the compiler to a new +system, you need to specify how to do this. + +There are two major ways that GCC currently supports the execution of +initialization and termination functions. Each way has two variants. +Much of the structure is common to all four variations. + +@findex __CTOR_LIST__ +@findex __DTOR_LIST__ +The linker must build two lists of these functions---a list of +initialization functions, called @code{__CTOR_LIST__}, and a list of +termination functions, called @code{__DTOR_LIST__}. + +Each list always begins with an ignored function pointer (which may hold +0, @minus{}1, or a count of the function pointers after it, depending on +the environment). This is followed by a series of zero or more function +pointers to constructors (or destructors), followed by a function +pointer containing zero. + +Depending on the operating system and its executable file format, either +@file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup +time and exit time. Constructors are called in reverse order of the +list; destructors in forward order. + +The best way to handle static constructors works only for object file +formats which provide arbitrarily-named sections. A section is set +aside for a list of constructors, and another for a list of destructors. +Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each +object file that defines an initialization function also puts a word in +the constructor section to point to that function. The linker +accumulates all these words into one contiguous @samp{.ctors} section. +Termination functions are handled similarly. + +This method will be chosen as the default by @file{target-def.h} if +@code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not +support arbitrary sections, but does support special designated +constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP} +and @code{DTORS_SECTION_ASM_OP} to achieve the same effect. + +When arbitrary sections are available, there are two variants, depending +upon how the code in @file{crtstuff.c} is called. On systems that +support a @dfn{.init} section which is executed at program startup, +parts of @file{crtstuff.c} are compiled into that section. The +program is linked by the @command{gcc} driver like this: + +@smallexample +ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o +@end smallexample + +The prologue of a function (@code{__init}) appears in the @code{.init} +section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise +for the function @code{__fini} in the @dfn{.fini} section. Normally these +files are provided by the operating system or by the GNU C library, but +are provided by GCC for a few targets. + +The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets) +compiled from @file{crtstuff.c}. They contain, among other things, code +fragments within the @code{.init} and @code{.fini} sections that branch +to routines in the @code{.text} section. The linker will pull all parts +of a section together, which results in a complete @code{__init} function +that invokes the routines we need at startup. + +To use this variant, you must define the @code{INIT_SECTION_ASM_OP} +macro properly. + +If no init section is available, when GCC compiles any function called +@code{main} (or more accurately, any function designated as a program +entry point by the language front end calling @code{expand_main_function}), +it inserts a procedure call to @code{__main} as the first executable code +after the function prologue. The @code{__main} function is defined +in @file{libgcc2.c} and runs the global constructors. + +In file formats that don't support arbitrary sections, there are again +two variants. In the simplest variant, the GNU linker (GNU @code{ld}) +and an `a.out' format must be used. In this case, +@code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs} +entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__}, +and with the address of the void function containing the initialization +code as its value. The GNU linker recognizes this as a request to add +the value to a @dfn{set}; the values are accumulated, and are eventually +placed in the executable as a vector in the format described above, with +a leading (ignored) count and a trailing zero element. +@code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init +section is available, the absence of @code{INIT_SECTION_ASM_OP} causes +the compilation of @code{main} to call @code{__main} as above, starting +the initialization process. + +The last variant uses neither arbitrary sections nor the GNU linker. +This is preferable when you want to do dynamic linking and when using +file formats which the GNU linker does not support, such as `ECOFF'@. In +this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and +termination functions are recognized simply by their names. This requires +an extra program in the linkage step, called @command{collect2}. This program +pretends to be the linker, for use with GCC; it does its job by running +the ordinary linker, but also arranges to include the vectors of +initialization and termination functions. These functions are called +via @code{__main} as described above. In order to use this method, +@code{use_collect2} must be defined in the target in @file{config.gcc}. + +@ifinfo +The following section describes the specific macros that control and +customize the handling of initialization and termination functions. +@end ifinfo + +@node Macros for Initialization +@subsection Macros Controlling Initialization Routines + +Here are the macros that control how the compiler handles initialization +and termination functions: + +@defmac INIT_SECTION_ASM_OP +If defined, a C string constant, including spacing, for the assembler +operation to identify the following data as initialization code. If not +defined, GCC will assume such a section does not exist. When you are +using special sections for initialization and termination functions, this +macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to +run the initialization functions. +@end defmac + +@defmac HAS_INIT_SECTION +If defined, @code{main} will not call @code{__main} as described above. +This macro should be defined for systems that control start-up code +on a symbol-by-symbol basis, such as OSF/1, and should not +be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}. +@end defmac + +@defmac LD_INIT_SWITCH +If defined, a C string constant for a switch that tells the linker that +the following symbol is an initialization routine. +@end defmac + +@defmac LD_FINI_SWITCH +If defined, a C string constant for a switch that tells the linker that +the following symbol is a finalization routine. +@end defmac + +@defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func}) +If defined, a C statement that will write a function that can be +automatically called when a shared library is loaded. The function +should call @var{func}, which takes no arguments. If not defined, and +the object format requires an explicit initialization function, then a +function called @code{_GLOBAL__DI} will be generated. + +This function and the following one are used by collect2 when linking a +shared library that needs constructors or destructors, or has DWARF2 +exception tables embedded in the code. +@end defmac + +@defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func}) +If defined, a C statement that will write a function that can be +automatically called when a shared library is unloaded. The function +should call @var{func}, which takes no arguments. If not defined, and +the object format requires an explicit finalization function, then a +function called @code{_GLOBAL__DD} will be generated. +@end defmac + +@defmac INVOKE__main +If defined, @code{main} will call @code{__main} despite the presence of +@code{INIT_SECTION_ASM_OP}. This macro should be defined for systems +where the init section is not actually run automatically, but is still +useful for collecting the lists of constructors and destructors. +@end defmac + +@defmac SUPPORTS_INIT_PRIORITY +If nonzero, the C++ @code{init_priority} attribute is supported and the +compiler should emit instructions to control the order of initialization +of objects. If zero, the compiler will issue an error message upon +encountering an @code{init_priority} attribute. +@end defmac + +@deftypevr {Target Hook} bool TARGET_HAVE_CTORS_DTORS +This value is true if the target supports some ``native'' method of +collecting constructors and destructors to be run at startup and exit. +It is false if we must use @command{collect2}. +@end deftypevr + +@deftypevr {Target Hook} bool TARGET_DTORS_FROM_CXA_ATEXIT +This value is true if the target wants destructors to be queued to be +run from __cxa_atexit. If this is the case then, for each priority level, +a new constructor will be entered that registers the destructors for that +level with __cxa_atexit (and there will be no destructors emitted). +It is false the method implied by @code{have_ctors_dtors} is used. +@end deftypevr + +@deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority}) +If defined, a function that outputs assembler code to arrange to call +the function referenced by @var{symbol} at initialization time. + +Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking +no arguments and with no return value. If the target supports initialization +priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY}; +otherwise it must be @code{DEFAULT_INIT_PRIORITY}. + +If this macro is not defined by the target, a suitable default will +be chosen if (1) the target supports arbitrary section names, (2) the +target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2} +is not defined. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority}) +This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination +functions rather than initialization functions. +@end deftypefn + +If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine +generated for the generated object file will have static linkage. + +If your system uses @command{collect2} as the means of processing +constructors, then that program normally uses @command{nm} to scan +an object file for constructor functions to be called. + +On certain kinds of systems, you can define this macro to make +@command{collect2} work faster (and, in some cases, make it work at all): + +@defmac OBJECT_FORMAT_COFF +Define this macro if the system uses COFF (Common Object File Format) +object files, so that @command{collect2} can assume this format and scan +object files directly for dynamic constructor/destructor functions. + +This macro is effective only in a native compiler; @command{collect2} as +part of a cross compiler always uses @command{nm} for the target machine. +@end defmac + +@defmac REAL_NM_FILE_NAME +Define this macro as a C string constant containing the file name to use +to execute @command{nm}. The default is to search the path normally for +@command{nm}. +@end defmac + +@defmac NM_FLAGS +@command{collect2} calls @command{nm} to scan object files for static +constructors and destructors and LTO info. By default, @option{-n} is +passed. Define @code{NM_FLAGS} to a C string constant if other options +are needed to get the same output format as GNU @command{nm -n} +produces. +@end defmac + +If your system supports shared libraries and has a program to list the +dynamic dependencies of a given library or executable, you can define +these macros to enable support for running initialization and +termination functions in shared libraries: + +@defmac LDD_SUFFIX +Define this macro to a C string constant containing the name of the program +which lists dynamic dependencies, like @command{ldd} under SunOS 4. +@end defmac + +@defmac PARSE_LDD_OUTPUT (@var{ptr}) +Define this macro to be C code that extracts filenames from the output +of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable +of type @code{char *} that points to the beginning of a line of output +from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the +code must advance @var{ptr} to the beginning of the filename on that +line. Otherwise, it must set @var{ptr} to @code{NULL}. +@end defmac + +@defmac SHLIB_SUFFIX +Define this macro to a C string constant containing the default shared +library extension of the target (e.g., @samp{".so"}). @command{collect2} +strips version information after this suffix when generating global +constructor and destructor names. This define is only needed on targets +that use @command{collect2} to process constructors and destructors. +@end defmac + +@node Instruction Output +@subsection Output of Assembler Instructions + +@c prevent bad page break with this line +This describes assembler instruction output. + +@defmac REGISTER_NAMES +A C initializer containing the assembler's names for the machine +registers, each one as a C string constant. This is what translates +register numbers in the compiler into assembler language. +@end defmac + +@defmac ADDITIONAL_REGISTER_NAMES +If defined, a C initializer for an array of structures containing a name +and a register number. This macro defines additional names for hard +registers, thus allowing the @code{asm} option in declarations to refer +to registers using alternate names. +@end defmac + +@defmac OVERLAPPING_REGISTER_NAMES +If defined, a C initializer for an array of structures containing a +name, a register number and a count of the number of consecutive +machine registers the name overlaps. This macro defines additional +names for hard registers, thus allowing the @code{asm} option in +declarations to refer to registers using alternate names. Unlike +@code{ADDITIONAL_REGISTER_NAMES}, this macro should be used when the +register name implies multiple underlying registers. + +This macro should be used when it is important that a clobber in an +@code{asm} statement clobbers all the underlying values implied by the +register name. For example, on ARM, clobbering the double-precision +VFP register ``d0'' implies clobbering both single-precision registers +``s0'' and ``s1''. +@end defmac + +@defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr}) +Define this macro if you are using an unusual assembler that +requires different names for the machine instructions. + +The definition is a C statement or statements which output an +assembler instruction opcode to the stdio stream @var{stream}. The +macro-operand @var{ptr} is a variable of type @code{char *} which +points to the opcode name in its ``internal'' form---the form that is +written in the machine description. The definition should output the +opcode name to @var{stream}, performing any translation you desire, and +increment the variable @var{ptr} to point at the end of the opcode +so that it will not be output twice. + +In fact, your macro definition may process less than the entire opcode +name, or more than the opcode name; but if you want to process text +that includes @samp{%}-sequences to substitute operands, you must take +care of the substitution yourself. Just be sure to increment +@var{ptr} over whatever text should not be output normally. + +@findex recog_data.operand +If you need to look at the operand values, they can be found as the +elements of @code{recog_data.operand}. + +If the macro definition does nothing, the instruction is output +in the usual way. +@end defmac + +@defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands}) +If defined, a C statement to be executed just prior to the output of +assembler code for @var{insn}, to modify the extracted operands so +they will be output differently. + +Here the argument @var{opvec} is the vector containing the operands +extracted from @var{insn}, and @var{noperands} is the number of +elements of the vector which contain meaningful data for this insn. +The contents of this vector are what will be used to convert the insn +template into assembler code, so you can change the assembler output +by changing the contents of the vector. + +This macro is useful when various assembler syntaxes share a single +file of instruction patterns; by defining this macro differently, you +can cause a large class of instructions to be output differently (such +as with rearranged operands). Naturally, variations in assembler +syntax affecting individual insn patterns ought to be handled by +writing conditional output routines in those patterns. + +If this macro is not defined, it is equivalent to a null statement. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_FINAL_POSTSCAN_INSN (FILE *@var{file}, rtx_insn *@var{insn}, rtx *@var{opvec}, int @var{noperands}) +If defined, this target hook is a function which is executed just after the +output of assembler code for @var{insn}, to change the mode of the assembler +if necessary. + +Here the argument @var{opvec} is the vector containing the operands +extracted from @var{insn}, and @var{noperands} is the number of +elements of the vector which contain meaningful data for this insn. +The contents of this vector are what was used to convert the insn +template into assembler code, so you can change the assembler mode +by checking the contents of the vector. +@end deftypefn + +@defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code}) +A C compound statement to output to stdio stream @var{stream} the +assembler syntax for an instruction operand @var{x}. @var{x} is an +RTL expression. + +@var{code} is a value that can be used to specify one of several ways +of printing the operand. It is used when identical operands must be +printed differently depending on the context. @var{code} comes from +the @samp{%} specification that was used to request printing of the +operand. If the specification was just @samp{%@var{digit}} then +@var{code} is 0; if the specification was @samp{%@var{ltr} +@var{digit}} then @var{code} is the ASCII code for @var{ltr}. + +@findex reg_names +If @var{x} is a register, this macro should print the register's name. +The names can be found in an array @code{reg_names} whose type is +@code{char *[]}. @code{reg_names} is initialized from +@code{REGISTER_NAMES}. + +When the machine description has a specification @samp{%@var{punct}} +(a @samp{%} followed by a punctuation character), this macro is called +with a null pointer for @var{x} and the punctuation character for +@var{code}. +@end defmac + +@defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code}) +A C expression which evaluates to true if @var{code} is a valid +punctuation character for use in the @code{PRINT_OPERAND} macro. If +@code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no +punctuation characters (except for the standard one, @samp{%}) are used +in this way. +@end defmac + +@defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x}) +A C compound statement to output to stdio stream @var{stream} the +assembler syntax for an instruction operand that is a memory reference +whose address is @var{x}. @var{x} is an RTL expression. + +@cindex @code{TARGET_ENCODE_SECTION_INFO} usage +On some machines, the syntax for a symbolic address depends on the +section that the address refers to. On these machines, define the hook +@code{TARGET_ENCODE_SECTION_INFO} to store the information into the +@code{symbol_ref}, and then check for it here. @xref{Assembler +Format}. +@end defmac + +@findex dbr_sequence_length +@defmac DBR_OUTPUT_SEQEND (@var{file}) +A C statement, to be executed after all slot-filler instructions have +been output. If necessary, call @code{dbr_sequence_length} to +determine the number of slots filled in a sequence (zero if not +currently outputting a sequence), to decide how many no-ops to output, +or whatever. + +Don't define this macro if it has nothing to do, but it is helpful in +reading assembly output if the extent of the delay sequence is made +explicit (e.g.@: with white space). +@end defmac + +@findex final_sequence +Note that output routines for instructions with delay slots must be +prepared to deal with not being output as part of a sequence +(i.e.@: when the scheduling pass is not run, or when no slot fillers could be +found.) The variable @code{final_sequence} is null when not +processing a sequence, otherwise it contains the @code{sequence} rtx +being output. + +@findex asm_fprintf +@defmac REGISTER_PREFIX +@defmacx LOCAL_LABEL_PREFIX +@defmacx USER_LABEL_PREFIX +@defmacx IMMEDIATE_PREFIX +If defined, C string expressions to be used for the @samp{%R}, @samp{%L}, +@samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see +@file{final.cc}). These are useful when a single @file{md} file must +support multiple assembler formats. In that case, the various @file{tm.h} +files can define these macros differently. +@end defmac + +@defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format}) +If defined this macro should expand to a series of @code{case} +statements which will be parsed inside the @code{switch} statement of +the @code{asm_fprintf} function. This allows targets to define extra +printf formats which may useful when generating their assembler +statements. Note that uppercase letters are reserved for future +generic extensions to asm_fprintf, and so are not available to target +specific code. The output file is given by the parameter @var{file}. +The varargs input pointer is @var{argptr} and the rest of the format +string, starting the character after the one that is being switched +upon, is pointed to by @var{format}. +@end defmac + +@defmac ASSEMBLER_DIALECT +If your target supports multiple dialects of assembler language (such as +different opcodes), define this macro as a C expression that gives the +numeric index of the assembler language dialect to use, with zero as the +first variant. + +If this macro is defined, you may use constructs of the form +@smallexample +@samp{@{option0|option1|option2@dots{}@}} +@end smallexample +@noindent +in the output templates of patterns (@pxref{Output Template}) or in the +first argument of @code{asm_fprintf}. This construct outputs +@samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of +@code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters +within these strings retain their usual meaning. If there are fewer +alternatives within the braces than the value of +@code{ASSEMBLER_DIALECT}, the construct outputs nothing. If it's needed +to print curly braces or @samp{|} character in assembler output directly, +@samp{%@{}, @samp{%@}} and @samp{%|} can be used. + +If you do not define this macro, the characters @samp{@{}, @samp{|} and +@samp{@}} do not have any special meaning when used in templates or +operands to @code{asm_fprintf}. + +Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX}, +@code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express +the variations in assembler language syntax with that mechanism. Define +@code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax +if the syntax variant are larger and involve such things as different +opcodes or operand order. +@end defmac + +@defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno}) +A C expression to output to @var{stream} some assembler code +which will push hard register number @var{regno} onto the stack. +The code need not be optimal, since this macro is used only when +profiling. +@end defmac + +@defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno}) +A C expression to output to @var{stream} some assembler code +which will pop hard register number @var{regno} off of the stack. +The code need not be optimal, since this macro is used only when +profiling. +@end defmac + +@node Dispatch Tables +@subsection Output of Dispatch Tables + +@c prevent bad page break with this line +This concerns dispatch tables. + +@cindex dispatch table +@defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel}) +A C statement to output to the stdio stream @var{stream} an assembler +pseudo-instruction to generate a difference between two labels. +@var{value} and @var{rel} are the numbers of two internal labels. The +definitions of these labels are output using +@code{(*targetm.asm_out.internal_label)}, and they must be printed in the same +way here. For example, + +@smallexample +fprintf (@var{stream}, "\t.word L%d-L%d\n", + @var{value}, @var{rel}) +@end smallexample + +You must provide this macro on machines where the addresses in a +dispatch table are relative to the table's own address. If defined, GCC +will also use this macro on all machines when producing PIC@. +@var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the +mode and flags can be read. +@end defmac + +@defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value}) +This macro should be provided on machines where the addresses +in a dispatch table are absolute. + +The definition should be a C statement to output to the stdio stream +@var{stream} an assembler pseudo-instruction to generate a reference to +a label. @var{value} is the number of an internal label whose +definition is output using @code{(*targetm.asm_out.internal_label)}. +For example, + +@smallexample +fprintf (@var{stream}, "\t.word L%d\n", @var{value}) +@end smallexample +@end defmac + +@defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table}) +Define this if the label before a jump-table needs to be output +specially. The first three arguments are the same as for +@code{(*targetm.asm_out.internal_label)}; the fourth argument is the +jump-table which follows (a @code{jump_table_data} containing an +@code{addr_vec} or @code{addr_diff_vec}). + +This feature is used on system V to output a @code{swbeg} statement +for the table. + +If this macro is not defined, these labels are output with +@code{(*targetm.asm_out.internal_label)}. +@end defmac + +@defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table}) +Define this if something special must be output at the end of a +jump-table. The definition should be a C statement to be executed +after the assembler code for the table is written. It should write +the appropriate code to stdio stream @var{stream}. The argument +@var{table} is the jump-table insn, and @var{num} is the label-number +of the preceding label. + +If this macro is not defined, nothing special is output at the end of +the jump-table. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_POST_CFI_STARTPROC (FILE *@var{}, @var{tree}) +This target hook is used to emit assembly strings required by the target +after the .cfi_startproc directive. The first argument is the file stream to +write the strings to and the second argument is the function's declaration. The +expected use is to add more .cfi_* directives. + +The default is to not output any assembly strings. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_EMIT_UNWIND_LABEL (FILE *@var{stream}, tree @var{decl}, int @var{for_eh}, int @var{empty}) +This target hook emits a label at the beginning of each FDE@. It +should be defined on targets where FDEs need special labels, and it +should write the appropriate label, for the FDE associated with the +function declaration @var{decl}, to the stdio stream @var{stream}. +The third argument, @var{for_eh}, is a boolean: true if this is for an +exception table. The fourth argument, @var{empty}, is a boolean: +true if this is a placeholder label for an omitted FDE@. + +The default is that FDEs are not given nonlocal labels. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL (FILE *@var{stream}) +This target hook emits a label at the beginning of the exception table. +It should be defined on targets where it is desirable for the table +to be broken up according to function. + +The default is that no label is emitted. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_EMIT_EXCEPT_PERSONALITY (rtx @var{personality}) +If the target implements @code{TARGET_ASM_UNWIND_EMIT}, this hook may be +used to emit a directive to install a personality hook into the unwind +info. This hook should not be used if dwarf2 unwind info is used. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ASM_UNWIND_EMIT (FILE *@var{stream}, rtx_insn *@var{insn}) +This target hook emits assembly directives required to unwind the +given instruction. This is only used when @code{TARGET_EXCEPT_UNWIND_INFO} +returns @code{UI_TARGET}. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_ASM_MAKE_EH_SYMBOL_INDIRECT (rtx @var{origsymbol}, bool @var{pubvis}) +If necessary, modify personality and LSDA references to handle indirection. +The original symbol is in @code{origsymbol} and if @code{pubvis} is true +the symbol is visible outside the TU. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_ASM_UNWIND_EMIT_BEFORE_INSN +True if the @code{TARGET_ASM_UNWIND_EMIT} hook should be called before +the assembly for @var{insn} has been emitted, false if the hook should +be called afterward. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_ASM_SHOULD_RESTORE_CFA_STATE (void) +For DWARF-based unwind frames, two CFI instructions provide for save and +restore of register state. GCC maintains the current frame address (CFA) +separately from the register bank but the unwinder in libgcc preserves this +state along with the registers (and this is expected by the code that writes +the unwind frames). This hook allows the target to specify that the CFA data +is not saved/restored along with the registers by the target unwinder so that +suitable additional instructions should be emitted to restore it. +@end deftypefn + +@node Exception Region Output +@subsection Assembler Commands for Exception Regions + +@c prevent bad page break with this line + +This describes commands marking the start and the end of an exception +region. + +@defmac EH_FRAME_SECTION_NAME +If defined, a C string constant for the name of the section containing +exception handling frame unwind information. If not defined, GCC will +provide a default definition if the target supports named sections. +@file{crtstuff.c} uses this macro to switch to the appropriate section. + +You should define this symbol if your target supports DWARF 2 frame +unwind information and the default definition does not work. +@end defmac + +@defmac EH_FRAME_THROUGH_COLLECT2 +If defined, DWARF 2 frame unwind information will identified by +specially named labels. The collect2 process will locate these +labels and generate code to register the frames. + +This might be necessary, for instance, if the system linker will not +place the eh_frames in-between the sentinals from @file{crtstuff.c}, +or if the system linker does garbage collection and sections cannot +be marked as not to be collected. +@end defmac + +@defmac EH_TABLES_CAN_BE_READ_ONLY +Define this macro to 1 if your target is such that no frame unwind +information encoding used with non-PIC code will ever require a +runtime relocation, but the linker may not support merging read-only +and read-write sections into a single read-write section. +@end defmac + +@defmac MASK_RETURN_ADDR +An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so +that it does not contain any extraneous set bits in it. +@end defmac + +@defmac DWARF2_UNWIND_INFO +Define this macro to 0 if your target supports DWARF 2 frame unwind +information, but it does not yet work with exception handling. +Otherwise, if your target supports this information (if it defines +@code{INCOMING_RETURN_ADDR_RTX} and @code{OBJECT_FORMAT_ELF}), +GCC will provide a default definition of 1. +@end defmac + +@deftypefn {Common Target Hook} {enum unwind_info_type} TARGET_EXCEPT_UNWIND_INFO (struct gcc_options *@var{opts}) +This hook defines the mechanism that will be used for exception handling +by the target. If the target has ABI specified unwind tables, the hook +should return @code{UI_TARGET}. If the target is to use the +@code{setjmp}/@code{longjmp}-based exception handling scheme, the hook +should return @code{UI_SJLJ}. If the target supports DWARF 2 frame unwind +information, the hook should return @code{UI_DWARF2}. + +A target may, if exceptions are disabled, choose to return @code{UI_NONE}. +This may end up simplifying other parts of target-specific code. The +default implementation of this hook never returns @code{UI_NONE}. + +Note that the value returned by this hook should be constant. It should +not depend on anything except the command-line switches described by +@var{opts}. In particular, the +setting @code{UI_SJLJ} must be fixed at compiler start-up as C pre-processor +macros and builtin functions related to exception handling are set up +depending on this setting. + +The default implementation of the hook first honors the +@option{--enable-sjlj-exceptions} configure option, then +@code{DWARF2_UNWIND_INFO}, and finally defaults to @code{UI_SJLJ}. If +@code{DWARF2_UNWIND_INFO} depends on command-line options, the target +must define this hook so that @var{opts} is used correctly. +@end deftypefn + +@deftypevr {Common Target Hook} bool TARGET_UNWIND_TABLES_DEFAULT +This variable should be set to @code{true} if the target ABI requires unwinding +tables even when exceptions are not used. It must not be modified by +command-line option processing. +@end deftypevr + +@defmac DONT_USE_BUILTIN_SETJMP +Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme +should use the @code{setjmp}/@code{longjmp} functions from the C library +instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery. +@end defmac + +@defmac JMP_BUF_SIZE +This macro has no effect unless @code{DONT_USE_BUILTIN_SETJMP} is also +defined. Define this macro if the default size of @code{jmp_buf} buffer +for the @code{setjmp}/@code{longjmp}-based exception handling mechanism +is not large enough, or if it is much too large. +The default size is @code{FIRST_PSEUDO_REGISTER * sizeof(void *)}. +@end defmac + +@defmac DWARF_CIE_DATA_ALIGNMENT +This macro need only be defined if the target might save registers in the +function prologue at an offset to the stack pointer that is not aligned to +@code{UNITS_PER_WORD}. The definition should be the negative minimum +alignment if @code{STACK_GROWS_DOWNWARD} is true, and the positive +minimum alignment otherwise. @xref{DWARF}. Only applicable if +the target supports DWARF 2 frame unwind information. +@end defmac + +@deftypevr {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO +Contains the value true if the target should add a zero word onto the +end of a Dwarf-2 frame info section when used for exception handling. +Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and +true otherwise. +@end deftypevr + +@deftypefn {Target Hook} rtx TARGET_DWARF_REGISTER_SPAN (rtx @var{reg}) +Given a register, this hook should return a parallel of registers to +represent where to find the register pieces. Define this hook if the +register and its mode are represented in Dwarf in non-contiguous +locations, or if the register should be represented in more than one +register in Dwarf. Otherwise, this hook should return @code{NULL_RTX}. +If not defined, the default is to return @code{NULL_RTX}. +@end deftypefn + +@deftypefn {Target Hook} machine_mode TARGET_DWARF_FRAME_REG_MODE (int @var{regno}) +Given a register, this hook should return the mode which the +corresponding Dwarf frame register should have. This is normally +used to return a smaller mode than the raw mode to prevent call +clobbered parts of a register altering the frame register size +@end deftypefn + +@deftypefn {Target Hook} void TARGET_INIT_DWARF_REG_SIZES_EXTRA (tree @var{address}) +If some registers are represented in Dwarf-2 unwind information in +multiple pieces, define this hook to fill in information about the +sizes of those pieces in the table used by the unwinder at runtime. +It will be called by @code{expand_builtin_init_dwarf_reg_sizes} after +filling in a single size corresponding to each hard register; +@var{address} is the address of the table. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ASM_TTYPE (rtx @var{sym}) +This hook is used to output a reference from a frame unwinding table to +the type_info object identified by @var{sym}. It should return @code{true} +if the reference was output. Returning @code{false} will cause the +reference to be output using the normal Dwarf2 routines. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_ARM_EABI_UNWINDER +This flag should be set to @code{true} on targets that use an ARM EABI +based unwinding library, and @code{false} on other targets. This effects +the format of unwinding tables, and how the unwinder in entered after +running a cleanup. The default is @code{false}. +@end deftypevr + +@node Alignment Output +@subsection Assembler Commands for Alignment + +@c prevent bad page break with this line +This describes commands for alignment. + +@defmac JUMP_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which is +a common destination of jumps and has no fallthru incoming edge. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @var{align_jumps} in the target's +@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's +selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation. +@end defmac + +@defmac LABEL_ALIGN_AFTER_BARRIER (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which follows +a @code{BARRIER}. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. +@end defmac + +@defmac LOOP_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label} that heads +a frequently executed basic block (usually the header of a loop). + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @code{align_loops} in the target's +@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's +selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation. +@end defmac + +@defmac LABEL_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}. +If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment, +the maximum of the specified values is used. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @code{align_labels} in the target's +@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's +selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation. +@end defmac + +@defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes}) +A C statement to output to the stdio stream @var{stream} an assembler +instruction to advance the location counter by @var{nbytes} bytes. +Those bytes should be zero when loaded. @var{nbytes} will be a C +expression of type @code{unsigned HOST_WIDE_INT}. +@end defmac + +@defmac ASM_NO_SKIP_IN_TEXT +Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the +text section because it fails to put zeros in the bytes that are skipped. +This is true on many Unix systems, where the pseudo--op to skip bytes +produces no-op instructions rather than zeros when used in the text +section. +@end defmac + +@defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power}) +A C statement to output to the stdio stream @var{stream} an assembler +command to advance the location counter to a multiple of 2 to the +@var{power} bytes. @var{power} will be a C expression of type @code{int}. +@end defmac + +@defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power}) +Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used +for padding, if necessary. +@end defmac + +@defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip}) +A C statement to output to the stdio stream @var{stream} an assembler +command to advance the location counter to a multiple of 2 to the +@var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to +satisfy the alignment request. @var{power} and @var{max_skip} will be +a C expression of type @code{int}. +@end defmac + +@need 3000 +@node Debugging Info +@section Controlling Debugging Information Format + +@c prevent bad page break with this line +This describes how to specify debugging information. + +@menu +* All Debuggers:: Macros that affect all debugging formats uniformly. +* DWARF:: Macros for DWARF format. +* VMS Debug:: Macros for VMS debug format. +* CTF Debug:: Macros for CTF debug format. +* BTF Debug:: Macros for BTF debug format. +@end menu + +@node All Debuggers +@subsection Macros Affecting All Debugging Formats + +@c prevent bad page break with this line +These macros affect all debugging formats. + +@defmac DEBUGGER_REGNO (@var{regno}) +A C expression that returns the debugger register number for the compiler +register number @var{regno}. In the default macro provided, the value +of this expression will be @var{regno} itself. But sometimes there are +some registers that the compiler knows about and debugger does not, or vice +versa. In such cases, some register may need to have one number in the +compiler and another for debugger@. + +If two registers have consecutive numbers inside GCC, and they can be +used as a pair to hold a multiword value, then they @emph{must} have +consecutive numbers after renumbering with @code{DEBUGGER_REGNO}. +Otherwise, debuggers will be unable to access such a pair, because they +expect register pairs to be consecutive in their own numbering scheme. + +If you find yourself defining @code{DEBUGGER_REGNO} in way that +does not preserve register pairs, then what you must do instead is +redefine the actual register numbering scheme. +@end defmac + +@defmac DEBUGGER_AUTO_OFFSET (@var{x}) +A C expression that returns the integer offset value for an automatic +variable having address @var{x} (an RTL expression). The default +computation assumes that @var{x} is based on the frame-pointer and +gives the offset from the frame-pointer. This is required for targets +that produce debugging output for debugger and allow the frame-pointer to be +eliminated when the @option{-g} option is used. +@end defmac + +@defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x}) +A C expression that returns the integer offset value for an argument +having address @var{x} (an RTL expression). The nominal offset is +@var{offset}. +@end defmac + +@defmac PREFERRED_DEBUGGING_TYPE +A C expression that returns the type of debugging output GCC should +produce when the user specifies just @option{-g}. Define +this if you have arranged for GCC to support more than one format of +debugging output. Currently, the allowable values are +@code{DWARF2_DEBUG}, @code{VMS_DEBUG}, +and @code{VMS_AND_DWARF2_DEBUG}. + +When the user specifies @option{-ggdb}, GCC normally also uses the +value of this macro to select the debugging output format, but with two +exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the +value @code{DWARF2_DEBUG}. + +The value of this macro only affects the default debugging output; the +user can always get a specific type of output by using @option{-gdwarf-2}, +or @option{-gvms}. +@end defmac + +@defmac DEFAULT_GDB_EXTENSIONS +Define this macro to control whether GCC should by default generate +GDB's extended version of debugging information. If you don't define the +macro, the default is 1: always generate the extended information +if there is any occasion to. +@end defmac + +@need 2000 +@node DWARF +@subsection Macros for DWARF Output + +@c prevent bad page break with this line +Here are macros for DWARF output. + +@defmac DWARF2_DEBUGGING_INFO +Define this macro if GCC should produce dwarf version 2 format +debugging output in response to the @option{-g} option. + +To support optional call frame debugging information, you must also +define @code{INCOMING_RETURN_ADDR_RTX} and either set +@code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the +prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save} +as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't. +@end defmac + +@deftypefn {Target Hook} int TARGET_DWARF_CALLING_CONVENTION (const_tree @var{function}) +Define this to enable the dwarf attribute @code{DW_AT_calling_convention} to +be emitted for each function. Instead of an integer return the enum +value for the @code{DW_CC_} tag. +@end deftypefn + +@defmac DWARF2_FRAME_INFO +Define this macro to a nonzero value if GCC should always output +Dwarf 2 frame information. If @code{TARGET_EXCEPT_UNWIND_INFO} +(@pxref{Exception Region Output}) returns @code{UI_DWARF2}, and +exceptions are enabled, GCC will output this information not matter +how you define @code{DWARF2_FRAME_INFO}. +@end defmac + +@deftypefn {Target Hook} {enum unwind_info_type} TARGET_DEBUG_UNWIND_INFO (void) +This hook defines the mechanism that will be used for describing frame +unwind information to the debugger. Normally the hook will return +@code{UI_DWARF2} if DWARF 2 debug information is enabled, and +return @code{UI_NONE} otherwise. + +A target may return @code{UI_DWARF2} even when DWARF 2 debug information +is disabled in order to always output DWARF 2 frame information. + +A target may return @code{UI_TARGET} if it has ABI specified unwind tables. +This will suppress generation of the normal debug frame unwind information. +@end deftypefn + +@defmac DWARF2_ASM_LINE_DEBUG_INFO +Define this macro to be a nonzero value if the assembler can generate Dwarf 2 +line debug info sections. This will result in much more compact line number +tables, and hence is desirable if it works. +@end defmac + +@defmac DWARF2_ASM_VIEW_DEBUG_INFO +Define this macro to be a nonzero value if the assembler supports view +assignment and verification in @code{.loc}. If it does not, but the +user enables location views, the compiler may have to fallback to +internal line number tables. +@end defmac + +@deftypefn {Target Hook} int TARGET_RESET_LOCATION_VIEW (rtx_insn *@var{}) +This hook, if defined, enables -ginternal-reset-location-views, and +uses its result to override cases in which the estimated min insn +length might be nonzero even when a PC advance (i.e., a view reset) +cannot be taken for granted. + +If the hook is defined, it must return a positive value to indicate +the insn definitely advances the PC, and so the view number can be +safely assumed to be reset; a negative value to mean the insn +definitely does not advance the PC, and os the view number must not +be reset; or zero to decide based on the estimated insn length. + +If insn length is to be regarded as reliable, set the hook to +@code{hook_int_rtx_insn_0}. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_WANT_DEBUG_PUB_SECTIONS +True if the @code{.debug_pubtypes} and @code{.debug_pubnames} sections +should be emitted. These sections are not used on most platforms, and +in particular GDB does not use them. +@end deftypevr + +@deftypevr {Target Hook} bool TARGET_DELAY_SCHED2 +True if sched2 is not to be run at its normal place. +This usually means it will be run as part of machine-specific reorg. +@end deftypevr + +@deftypevr {Target Hook} bool TARGET_DELAY_VARTRACK +True if vartrack is not to be run at its normal place. +This usually means it will be run as part of machine-specific reorg. +@end deftypevr + +@deftypevr {Target Hook} bool TARGET_NO_REGISTER_ALLOCATION +True if register allocation and the passes +following it should not be run. Usually true only for virtual assembler +targets. +@end deftypevr + +@defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) +A C statement to issue assembly directives that create a difference +@var{lab1} minus @var{lab2}, using an integer of the given @var{size}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_VMS_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) +A C statement to issue assembly directives that create a difference +between the two given labels in system defined units, e.g.@: instruction +slots on IA64 VMS, using an integer of the given size. +@end defmac + +@defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{offset}, @var{section}) +A C statement to issue assembly directives that create a +section-relative reference to the given @var{label} plus @var{offset}, using +an integer of the given @var{size}. The label is known to be defined in the +given @var{section}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label}) +A C statement to issue assembly directives that create a self-relative +reference to the given @var{label}, using an integer of the given @var{size}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_DATAREL (@var{stream}, @var{size}, @var{label}) +A C statement to issue assembly directives that create a reference to the +given @var{label} relative to the dbase, using an integer of the given @var{size}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_TABLE_REF (@var{label}) +A C statement to issue assembly directives that create a reference to +the DWARF table identifier @var{label} from the current section. This +is used on some systems to avoid garbage collecting a DWARF table which +is referenced by a function. +@end defmac + +@deftypefn {Target Hook} void TARGET_ASM_OUTPUT_DWARF_DTPREL (FILE *@var{file}, int @var{size}, rtx @var{x}) +If defined, this target hook is a function which outputs a DTP-relative +reference to the given TLS symbol of the specified size. +@end deftypefn + +@need 2000 +@node VMS Debug +@subsection Macros for VMS Debug Format + +@c prevent bad page break with this line +Here are macros for VMS debug format. + +@defmac VMS_DEBUGGING_INFO +Define this macro if GCC should produce debugging output for VMS +in response to the @option{-g} option. The default behavior for VMS +is to generate minimal debug info for a traceback in the absence of +@option{-g} unless explicitly overridden with @option{-g0}. This +behavior is controlled by @code{TARGET_OPTION_OPTIMIZATION} and +@code{TARGET_OPTION_OVERRIDE}. +@end defmac + +@need 2000 +@node CTF Debug +@subsection Macros for CTF Debug Format + +@c prevent bad page break with this line +Here are macros for CTF debug format. + +@defmac CTF_DEBUGGING_INFO +Define this macro if GCC should produce debugging output in CTF debug +format in response to the @option{-gctf} option. +@end defmac + +@need 2000 +@node BTF Debug +@subsection Macros for BTF Debug Format + +@c prevent bad page break with this line +Here are macros for BTF debug format. + +@defmac BTF_DEBUGGING_INFO +Define this macro if GCC should produce debugging output in BTF debug +format in response to the @option{-gbtf} option. +@end defmac + +@node Floating Point +@section Cross Compilation and Floating Point +@cindex cross compilation and floating point +@cindex floating point and cross compilation + +While all modern machines use twos-complement representation for integers, +there are a variety of representations for floating point numbers. This +means that in a cross-compiler the representation of floating point numbers +in the compiled program may be different from that used in the machine +doing the compilation. + +Because different representation systems may offer different amounts of +range and precision, all floating point constants must be represented in +the target machine's format. Therefore, the cross compiler cannot +safely use the host machine's floating point arithmetic; it must emulate +the target's arithmetic. To ensure consistency, GCC always uses +emulation to work with floating point values, even when the host and +target floating point formats are identical. + +The following macros are provided by @file{real.h} for the compiler to +use. All parts of the compiler which generate or optimize +floating-point calculations must use these macros. They may evaluate +their operands more than once, so operands must not have side effects. + +@defmac REAL_VALUE_TYPE +The C data type to be used to hold a floating point value in the target +machine's format. Typically this is a @code{struct} containing an +array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque +quantity. +@end defmac + +@deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x}) +Truncates @var{x} to a signed integer, rounding toward zero. +@end deftypefn + +@deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x}) +Truncates @var{x} to an unsigned integer, rounding toward zero. If +@var{x} is negative, returns zero. +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, machine_mode @var{mode}) +Converts @var{string} into a floating point number in the target machine's +representation for mode @var{mode}. This routine can handle both +decimal and hexadecimal floating point constants, using the syntax +defined by the C language for both. +@end deftypefn + +@deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x}) +Returns 1 if @var{x} is negative (including negative zero), 0 otherwise. +@end deftypefn + +@deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x}) +Determines whether @var{x} represents infinity (positive or negative). +@end deftypefn + +@deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x}) +Determines whether @var{x} represents a ``NaN'' (not-a-number). +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x}) +Returns the negative of the floating point value @var{x}. +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x}) +Returns the absolute value of @var{x}. +@end deftypefn + +@node Mode Switching +@section Mode Switching Instructions +@cindex mode switching +The following macros control mode switching optimizations: + +@defmac OPTIMIZE_MODE_SWITCHING (@var{entity}) +Define this macro if the port needs extra instructions inserted for mode +switching in an optimizing compilation. + +For an example, the SH4 can perform both single and double precision +floating point operations, but to perform a single precision operation, +the FPSCR PR bit has to be cleared, while for a double precision +operation, this bit has to be set. Changing the PR bit requires a general +purpose register as a scratch register, hence these FPSCR sets have to +be inserted before reload, i.e.@: you cannot put this into instruction emitting +or @code{TARGET_MACHINE_DEPENDENT_REORG}. + +You can have multiple entities that are mode-switched, and select at run time +which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should +return nonzero for any @var{entity} that needs mode-switching. +If you define this macro, you also have to define +@code{NUM_MODES_FOR_MODE_SWITCHING}, @code{TARGET_MODE_NEEDED}, +@code{TARGET_MODE_PRIORITY} and @code{TARGET_MODE_EMIT}. +@code{TARGET_MODE_AFTER}, @code{TARGET_MODE_ENTRY}, and @code{TARGET_MODE_EXIT} +are optional. +@end defmac + +@defmac NUM_MODES_FOR_MODE_SWITCHING +If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as +initializer for an array of integers. Each initializer element +N refers to an entity that needs mode switching, and specifies the number +of different modes that might need to be set for this entity. +The position of the initializer in the initializer---starting counting at +zero---determines the integer that is used to refer to the mode-switched +entity in question. +In macros that take mode arguments / yield a mode result, modes are +represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode +switch is needed / supplied. +@end defmac + +@deftypefn {Target Hook} void TARGET_MODE_EMIT (int @var{entity}, int @var{mode}, int @var{prev_mode}, HARD_REG_SET @var{regs_live}) +Generate one or more insns to set @var{entity} to @var{mode}. +@var{hard_reg_live} is the set of hard registers live at the point where +the insn(s) are to be inserted. @var{prev_moxde} indicates the mode +to switch from. Sets of a lower numbered entity will be emitted before +sets of a higher numbered entity to a mode of the same or lower priority. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_MODE_NEEDED (int @var{entity}, rtx_insn *@var{insn}) +@var{entity} is an integer specifying a mode-switched entity. +If @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro +to return an integer value not larger than the corresponding element +in @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} +must be switched into prior to the execution of @var{insn}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_MODE_AFTER (int @var{entity}, int @var{mode}, rtx_insn *@var{insn}) +@var{entity} is an integer specifying a mode-switched entity. +If this macro is defined, it is evaluated for every @var{insn} during mode +switching. It determines the mode that an insn results +in (if different from the incoming mode). +@end deftypefn + +@deftypefn {Target Hook} int TARGET_MODE_ENTRY (int @var{entity}) +If this macro is defined, it is evaluated for every @var{entity} that +needs mode switching. It should evaluate to an integer, which is a mode +that @var{entity} is assumed to be switched to at function entry. +If @code{TARGET_MODE_ENTRY} is defined then @code{TARGET_MODE_EXIT} +must be defined. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_MODE_EXIT (int @var{entity}) +If this macro is defined, it is evaluated for every @var{entity} that +needs mode switching. It should evaluate to an integer, which is a mode +that @var{entity} is assumed to be switched to at function exit. +If @code{TARGET_MODE_EXIT} is defined then @code{TARGET_MODE_ENTRY} +must be defined. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_MODE_PRIORITY (int @var{entity}, int @var{n}) +This macro specifies the order in which modes for @var{entity} +are processed. 0 is the highest priority, +@code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the lowest. +The value of the macro should be an integer designating a mode +for @var{entity}. For any fixed @var{entity}, @code{mode_priority} +(@var{entity}, @var{n}) shall be a bijection in 0 @dots{} +@code{num_modes_for_mode_switching[@var{entity}] - 1}. +@end deftypefn + +@node Target Attributes +@section Defining target-specific uses of @code{__attribute__} +@cindex target attributes +@cindex machine attributes +@cindex attributes, target-specific + +Target-specific attributes may be defined for functions, data and types. +These are described using the following target hooks; they also need to +be documented in @file{extend.texi}. + +@deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE +If defined, this target hook points to an array of @samp{struct +attribute_spec} (defined in @file{tree-core.h}) specifying the machine +specific attributes for this target and some of the restrictions on the +entities to which these attributes are applied and the arguments they +take. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P (const_tree @var{name}) +If defined, this target hook is a function which returns true if the +machine-specific attribute named @var{name} expects an identifier +given as its first argument to be passed on as a plain identifier, not +subjected to name lookup. If this is not defined, the default is +false for all machine-specific attributes. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (const_tree @var{type1}, const_tree @var{type2}) +If defined, this target hook is a function which returns zero if the attributes on +@var{type1} and @var{type2} are incompatible, one if they are compatible, +and two if they are nearly compatible (which causes a warning to be +generated). If this is not defined, machine-specific attributes are +supposed always to be compatible. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type}) +If defined, this target hook is a function which assigns default attributes to +the newly defined @var{type}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) +Define this target hook if the merging of type attributes needs special +handling. If defined, the result is a list of the combined +@code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed +that @code{comptypes} has already been called and returned 1. This +function may call @code{merge_attributes} to handle machine-independent +merging. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl}) +Define this target hook if the merging of decl attributes needs special +handling. If defined, the result is a list of the combined +@code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}. +@var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of +when this is needed are when one attribute overrides another, or when an +attribute is nullified by a subsequent definition. This function may +call @code{merge_attributes} to handle machine-independent merging. + +@findex TARGET_DLLIMPORT_DECL_ATTRIBUTES +If the only target-specific handling you require is @samp{dllimport} +for Microsoft Windows targets, you should define the macro +@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES} to @code{1}. The compiler +will then define a function called +@code{merge_dllimport_decl_attributes} which can then be defined as +the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. You can also +add @code{handle_dll_attribute} in the attribute table for your port +to perform initial processing of the @samp{dllimport} and +@samp{dllexport} attributes. This is done in @file{i386/cygwin.h} and +@file{i386/i386.cc}, for example. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VALID_DLLIMPORT_ATTRIBUTE_P (const_tree @var{decl}) +@var{decl} is a variable or function with @code{__attribute__((dllimport))} +specified. Use this hook if the target needs to add extra validation +checks to @code{handle_dll_attribute}. +@end deftypefn + +@defmac TARGET_DECLSPEC +Define this macro to a nonzero value if you want to treat +@code{__declspec(X)} as equivalent to @code{__attribute((X))}. By +default, this behavior is enabled only for targets that define +@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation +of @code{__declspec} is via a built-in macro, but you should not rely +on this implementation detail. +@end defmac + +@deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr}) +Define this target hook if you want to be able to add attributes to a decl +when it is being created. This is normally useful for back ends which +wish to implement a pragma by using the attributes which correspond to +the pragma's effect. The @var{node} argument is the decl which is being +created. The @var{attr_ptr} argument is a pointer to the attribute list +for this decl. The list itself should not be modified, since it may be +shared with other decls, but attributes may be chained on the head of +the list and @code{*@var{attr_ptr}} modified to point to the new +attributes, or a copy of the list may be made if further changes are +needed. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_HANDLE_GENERIC_ATTRIBUTE (tree *@var{node}, tree @var{name}, tree @var{args}, int @var{flags}, bool *@var{no_add_attrs}) +Define this target hook if you want to be able to perform additional +target-specific processing of an attribute which is handled generically +by a front end. The arguments are the same as those which are passed to +attribute handlers. So far this only affects the @var{noinit} and +@var{section} attribute. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (const_tree @var{fndecl}) +@cindex inlining +This target hook returns @code{true} if it is OK to inline @var{fndecl} +into the current function, despite its having target-specific +attributes, @code{false} otherwise. By default, if a function has a +target specific attribute attached to it, it will not be inlined. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_OPTION_VALID_ATTRIBUTE_P (tree @var{fndecl}, tree @var{name}, tree @var{args}, int @var{flags}) +This hook is called to parse @code{attribute(target("..."))}, which +allows setting target-specific options on individual functions. +These function-specific options may differ +from the options specified on the command line. The hook should return +@code{true} if the options are valid. + +The hook should set the @code{DECL_FUNCTION_SPECIFIC_TARGET} field in +the function declaration to hold a pointer to a target-specific +@code{struct cl_target_option} structure. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_OPTION_SAVE (struct cl_target_option *@var{ptr}, struct gcc_options *@var{opts}, struct gcc_options *@var{opts_set}) +This hook is called to save any additional target-specific information +in the @code{struct cl_target_option} structure for function-specific +options from the @code{struct gcc_options} structure. +@xref{Option file format}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_OPTION_RESTORE (struct gcc_options *@var{opts}, struct gcc_options *@var{opts_set}, struct cl_target_option *@var{ptr}) +This hook is called to restore any additional target-specific +information in the @code{struct cl_target_option} structure for +function-specific options to the @code{struct gcc_options} structure. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_OPTION_POST_STREAM_IN (struct cl_target_option *@var{ptr}) +This hook is called to update target-specific information in the +@code{struct cl_target_option} structure after it is streamed in from +LTO bytecode. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_OPTION_PRINT (FILE *@var{file}, int @var{indent}, struct cl_target_option *@var{ptr}) +This hook is called to print any additional target-specific +information in the @code{struct cl_target_option} structure for +function-specific options. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_OPTION_PRAGMA_PARSE (tree @var{args}, tree @var{pop_target}) +This target hook parses the options for @code{#pragma GCC target}, which +sets the target-specific options for functions that occur later in the +input stream. The options accepted should be the same as those handled by the +@code{TARGET_OPTION_VALID_ATTRIBUTE_P} hook. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_OPTION_OVERRIDE (void) +Sometimes certain combinations of command options do not make sense on +a particular target machine. You can override the hook +@code{TARGET_OPTION_OVERRIDE} to take account of this. This hooks is called +once just after all the command options have been parsed. + +Don't use this hook to turn on various extra optimizations for +@option{-O}. That is what @code{TARGET_OPTION_OPTIMIZATION} is for. + +If you need to do something whenever the optimization level is +changed via the optimize attribute or pragma, see +@code{TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE} +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_OPTION_FUNCTION_VERSIONS (tree @var{decl1}, tree @var{decl2}) +This target hook returns @code{true} if @var{DECL1} and @var{DECL2} are +versions of the same function. @var{DECL1} and @var{DECL2} are function +versions if and only if they have the same function signature and +different target specific attributes, that is, they are compiled for +different target machines. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CAN_INLINE_P (tree @var{caller}, tree @var{callee}) +This target hook returns @code{false} if the @var{caller} function +cannot inline @var{callee}, based on target specific information. By +default, inlining is not allowed if the callee function has function +specific target options and the caller does not use the same options. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_UPDATE_IPA_FN_TARGET_INFO (unsigned int& @var{info}, const gimple* @var{stmt}) +Allow target to analyze all gimple statements for the given function to +record and update some target specific information for inlining. A typical +example is that a caller with one isa feature disabled is normally not +allowed to inline a callee with that same isa feature enabled even which is +attributed by always_inline, but with the conservative analysis on all +statements of the callee if we are able to guarantee the callee does not +exploit any instructions from the mismatch isa feature, it would be safe to +allow the caller to inline the callee. +@var{info} is one @code{unsigned int} value to record information in which +one set bit indicates one corresponding feature is detected in the analysis, +@var{stmt} is the statement being analyzed. Return true if target still +need to analyze the subsequent statements, otherwise return false to stop +subsequent analysis. +The default version of this hook returns false. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_NEED_IPA_FN_TARGET_INFO (const_tree @var{decl}, unsigned int& @var{info}) +Allow target to check early whether it is necessary to analyze all gimple +statements in the given function to update target specific information for +inlining. See hook @code{update_ipa_fn_target_info} for usage example of +target specific information. This hook is expected to be invoked ahead of +the iterating with hook @code{update_ipa_fn_target_info}. +@var{decl} is the function being analyzed, @var{info} is the same as what +in hook @code{update_ipa_fn_target_info}, target can do one time update +into @var{info} without iterating for some case. Return true if target +decides to analyze all gimple statements to collect information, otherwise +return false. +The default version of this hook returns false. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_RELAYOUT_FUNCTION (tree @var{fndecl}) +This target hook fixes function @var{fndecl} after attributes are processed. +Default does nothing. On ARM, the default function's alignment is updated +with the attribute target. +@end deftypefn + +@node Emulated TLS +@section Emulating TLS +@cindex Emulated TLS + +For targets whose psABI does not provide Thread Local Storage via +specific relocations and instruction sequences, an emulation layer is +used. A set of target hooks allows this emulation layer to be +configured for the requirements of a particular target. For instance +the psABI may in fact specify TLS support in terms of an emulation +layer. + +The emulation layer works by creating a control object for every TLS +object. To access the TLS object, a lookup function is provided +which, when given the address of the control object, will return the +address of the current thread's instance of the TLS object. + +@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_GET_ADDRESS +Contains the name of the helper function that uses a TLS control +object to locate a TLS instance. The default causes libgcc's +emulated TLS helper function to be used. +@end deftypevr + +@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_REGISTER_COMMON +Contains the name of the helper function that should be used at +program startup to register TLS objects that are implicitly +initialized to zero. If this is @code{NULL}, all TLS objects will +have explicit initializers. The default causes libgcc's emulated TLS +registration function to be used. +@end deftypevr + +@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_VAR_SECTION +Contains the name of the section in which TLS control variables should +be placed. The default of @code{NULL} allows these to be placed in +any section. +@end deftypevr + +@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_TMPL_SECTION +Contains the name of the section in which TLS initializers should be +placed. The default of @code{NULL} allows these to be placed in any +section. +@end deftypevr + +@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_VAR_PREFIX +Contains the prefix to be prepended to TLS control variable names. +The default of @code{NULL} uses a target-specific prefix. +@end deftypevr + +@deftypevr {Target Hook} {const char *} TARGET_EMUTLS_TMPL_PREFIX +Contains the prefix to be prepended to TLS initializer objects. The +default of @code{NULL} uses a target-specific prefix. +@end deftypevr + +@deftypefn {Target Hook} tree TARGET_EMUTLS_VAR_FIELDS (tree @var{type}, tree *@var{name}) +Specifies a function that generates the FIELD_DECLs for a TLS control +object type. @var{type} is the RECORD_TYPE the fields are for and +@var{name} should be filled with the structure tag, if the default of +@code{__emutls_object} is unsuitable. The default creates a type suitable +for libgcc's emulated TLS function. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_EMUTLS_VAR_INIT (tree @var{var}, tree @var{decl}, tree @var{tmpl_addr}) +Specifies a function that generates the CONSTRUCTOR to initialize a +TLS control object. @var{var} is the TLS control object, @var{decl} +is the TLS object and @var{tmpl_addr} is the address of the +initializer. The default initializes libgcc's emulated TLS control object. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_EMUTLS_VAR_ALIGN_FIXED +Specifies whether the alignment of TLS control variable objects is +fixed and should not be increased as some backends may do to optimize +single objects. The default is false. +@end deftypevr + +@deftypevr {Target Hook} bool TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS +Specifies whether a DWARF @code{DW_OP_form_tls_address} location descriptor +may be used to describe emulated TLS control objects. +@end deftypevr + +@node MIPS Coprocessors +@section Defining coprocessor specifics for MIPS targets. +@cindex MIPS coprocessor-definition macros + +The MIPS specification allows MIPS implementations to have as many as 4 +coprocessors, each with as many as 32 private registers. GCC supports +accessing these registers and transferring values between the registers +and memory using asm-ized variables. For example: + +@smallexample + register unsigned int cp0count asm ("c0r1"); + unsigned int d; + + d = cp0count + 3; +@end smallexample + +(``c0r1'' is the default name of register 1 in coprocessor 0; alternate +names may be added as described below, or the default names may be +overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.) + +Coprocessor registers are assumed to be epilogue-used; sets to them will +be preserved even if it does not appear that the register is used again +later in the function. + +Another note: according to the MIPS spec, coprocessor 1 (if present) is +the FPU@. One accesses COP1 registers through standard mips +floating-point support; they are not included in this mechanism. + +@node PCH Target +@section Parameters for Precompiled Header Validity Checking +@cindex parameters, precompiled headers + +@deftypefn {Target Hook} {void *} TARGET_GET_PCH_VALIDITY (size_t *@var{sz}) +This hook returns a pointer to the data needed by +@code{TARGET_PCH_VALID_P} and sets +@samp{*@var{sz}} to the size of the data in bytes. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_PCH_VALID_P (const void *@var{data}, size_t @var{sz}) +This hook checks whether the options used to create a PCH file are +compatible with the current settings. It returns @code{NULL} +if so and a suitable error message if not. Error messages will +be presented to the user and must be localized using @samp{_(@var{msg})}. + +@var{data} is the data that was returned by @code{TARGET_GET_PCH_VALIDITY} +when the PCH file was created and @var{sz} is the size of that data in bytes. +It's safe to assume that the data was created by the same version of the +compiler, so no format checking is needed. + +The default definition of @code{default_pch_valid_p} should be +suitable for most targets. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_CHECK_PCH_TARGET_FLAGS (int @var{pch_flags}) +If this hook is nonnull, the default implementation of +@code{TARGET_PCH_VALID_P} will use it to check for compatible values +of @code{target_flags}. @var{pch_flags} specifies the value that +@code{target_flags} had when the PCH file was created. The return +value is the same as for @code{TARGET_PCH_VALID_P}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_PREPARE_PCH_SAVE (void) +Called before writing out a PCH file. If the target has some +garbage-collected data that needs to be in a particular state on PCH loads, +it can use this hook to enforce that state. Very few targets need +to do anything here. +@end deftypefn + +@node C++ ABI +@section C++ ABI parameters +@cindex parameters, c++ abi + +@deftypefn {Target Hook} tree TARGET_CXX_GUARD_TYPE (void) +Define this hook to override the integer type used for guard variables. +These are used to implement one-time construction of static objects. The +default is long_long_integer_type_node. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_GUARD_MASK_BIT (void) +This hook determines how guard variables are used. It should return +@code{false} (the default) if the first byte should be used. A return value of +@code{true} indicates that only the least significant bit should be used. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_CXX_GET_COOKIE_SIZE (tree @var{type}) +This hook returns the size of the cookie to use when allocating an array +whose elements have the indicated @var{type}. Assumes that it is already +known that a cookie is needed. The default is +@code{max(sizeof (size_t), alignof(type))}, as defined in section 2.7 of the +IA64/Generic C++ ABI@. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_COOKIE_HAS_SIZE (void) +This hook should return @code{true} if the element size should be stored in +array cookies. The default is to return @code{false}. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_CXX_IMPORT_EXPORT_CLASS (tree @var{type}, int @var{import_export}) +If defined by a backend this hook allows the decision made to export +class @var{type} to be overruled. Upon entry @var{import_export} +will contain 1 if the class is going to be exported, @minus{}1 if it is going +to be imported and 0 otherwise. This function should return the +modified value and perform any other actions necessary to support the +backend's targeted operating system. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_CDTOR_RETURNS_THIS (void) +This hook should return @code{true} if constructors and destructors return +the address of the object created/destroyed. The default is to return +@code{false}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_KEY_METHOD_MAY_BE_INLINE (void) +This hook returns true if the key method for a class (i.e., the method +which, if defined in the current translation unit, causes the virtual +table to be emitted) may be an inline function. Under the standard +Itanium C++ ABI the key method may be an inline function so long as +the function is not declared inline in the class definition. Under +some variants of the ABI, an inline function can never be the key +method. The default is to return @code{true}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY (tree @var{decl}) +@var{decl} is a virtual table, virtual table table, typeinfo object, +or other similar implicit class data object that will be emitted with +external linkage in this translation unit. No ELF visibility has been +explicitly specified. If the target needs to specify a visibility +other than that of the containing class, use this hook to set +@code{DECL_VISIBILITY} and @code{DECL_VISIBILITY_SPECIFIED}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT (void) +This hook returns true (the default) if virtual tables and other +similar implicit class data objects are always COMDAT if they have +external linkage. If this hook returns false, then class data for +classes whose virtual table will be emitted in only one translation +unit will not be COMDAT. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_LIBRARY_RTTI_COMDAT (void) +This hook returns true (the default) if the RTTI information for +the basic types which is defined in the C++ runtime should always +be COMDAT, false if it should not be COMDAT. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_USE_AEABI_ATEXIT (void) +This hook returns true if @code{__aeabi_atexit} (as defined by the ARM EABI) +should be used to register static destructors when @option{-fuse-cxa-atexit} +is in effect. The default is to return false to use @code{__cxa_atexit}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT (void) +This hook returns true if the target @code{atexit} function can be used +in the same manner as @code{__cxa_atexit} to register C++ static +destructors. This requires that @code{atexit}-registered functions in +shared libraries are run in the correct order when the libraries are +unloaded. The default is to return false. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_CXX_ADJUST_CLASS_AT_DEFINITION (tree @var{type}) +@var{type} is a C++ class (i.e., RECORD_TYPE or UNION_TYPE) that has just +been defined. Use this hook to make adjustments to the class (eg, tweak +visibility or perform any other required target modifications). +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_CXX_DECL_MANGLING_CONTEXT (const_tree @var{decl}) +Return target-specific mangling context of @var{decl} or @code{NULL_TREE}. +@end deftypefn + +@node D Language and ABI +@section D ABI parameters +@cindex parameters, d abi + +@deftypefn {D Target Hook} void TARGET_D_CPU_VERSIONS (void) +Declare all environmental version identifiers relating to the target CPU +using the function @code{builtin_version}, which takes a string representing +the name of the version. Version identifiers predefined by this hook apply +to all modules that are being compiled and imported. +@end deftypefn + +@deftypefn {D Target Hook} void TARGET_D_OS_VERSIONS (void) +Similarly to @code{TARGET_D_CPU_VERSIONS}, but is used for versions +relating to the target operating system. +@end deftypefn + +@deftypefn {D Target Hook} void TARGET_D_REGISTER_CPU_TARGET_INFO (void) +Register all target information keys relating to the target CPU using the +function @code{d_add_target_info_handlers}, which takes a +@samp{struct d_target_info_spec} (defined in @file{d/d-target.h}). The keys +added by this hook are made available at compile time by the +@code{__traits(getTargetInfo)} extension, the result is an expression +describing the requested target information. +@end deftypefn + +@deftypefn {D Target Hook} void TARGET_D_REGISTER_OS_TARGET_INFO (void) +Same as @code{TARGET_D_CPU_TARGET_INFO}, but is used for keys relating to +the target operating system. +@end deftypefn + +@deftypevr {D Target Hook} {const char *} TARGET_D_MINFO_SECTION +Contains the name of the section in which module info references should be +placed. By default, the compiler puts all module info symbols in the +@code{"minfo"} section. Define this macro to override the string if a +different section name should be used. This section is expected to be +bracketed by two symbols @code{TARGET_D_MINFO_SECTION_START} and +@code{TARGET_D_MINFO_SECTION_END} to indicate the start and end address of +the section, so that the runtime library can collect all modules for each +loaded shared library and executable. Setting the value to @code{NULL} +disables the use of sections for storing module info altogether. +@end deftypevr + +@deftypevr {D Target Hook} {const char *} TARGET_D_MINFO_SECTION_START +If @code{TARGET_D_MINFO_SECTION} is defined, then this must also be defined +as the name of the symbol indicating the start address of the module info +section +@end deftypevr + +@deftypevr {D Target Hook} {const char *} TARGET_D_MINFO_SECTION_END +If @code{TARGET_D_MINFO_SECTION} is defined, then this must also be defined +as the name of the symbol indicating the end address of the module info +section +@end deftypevr + +@deftypefn {D Target Hook} bool TARGET_D_HAS_STDCALL_CONVENTION (unsigned int *@var{link_system}, unsigned int *@var{link_windows}) +Returns @code{true} if the target supports the stdcall calling convention. +The hook should also set @var{link_system} to @code{1} if the @code{stdcall} +attribute should be applied to functions with @code{extern(System)} linkage, +and @var{link_windows} to @code{1} to apply @code{stdcall} to functions with +@code{extern(Windows)} linkage. +@end deftypefn + +@deftypevr {D Target Hook} bool TARGET_D_TEMPLATES_ALWAYS_COMDAT +This flag is true if instantiated functions and variables are always COMDAT +if they have external linkage. If this flag is false, then instantiated +decls will be emitted as weak symbols. The default is @code{false}. +@end deftypevr + +@node Named Address Spaces +@section Adding support for named address spaces +@cindex named address spaces + +The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275 +standards committee, @cite{Programming Languages - C - Extensions to +support embedded processors}, specifies a syntax for embedded +processors to specify alternate address spaces. You can configure a +GCC port to support section 5.1 of the draft report to add support for +address spaces other than the default address space. These address +spaces are new keywords that are similar to the @code{volatile} and +@code{const} type attributes. + +Pointers to named address spaces can have a different size than +pointers to the generic address space. + +For example, the SPU port uses the @code{__ea} address space to refer +to memory in the host processor, rather than memory local to the SPU +processor. Access to memory in the @code{__ea} address space involves +issuing DMA operations to move data between the host processor and the +local processor memory address space. Pointers in the @code{__ea} +address space are either 32 bits or 64 bits based on the +@option{-mea32} or @option{-mea64} switches (native SPU pointers are +always 32 bits). + +Internally, address spaces are represented as a small integer in the +range 0 to 15 with address space 0 being reserved for the generic +address space. + +To register a named address space qualifier keyword with the C front end, +the target may call the @code{c_register_addr_space} routine. For example, +the SPU port uses the following to declare @code{__ea} as the keyword for +named address space #1: +@smallexample +#define ADDR_SPACE_EA 1 +c_register_addr_space ("__ea", ADDR_SPACE_EA); +@end smallexample + +@deftypefn {Target Hook} scalar_int_mode TARGET_ADDR_SPACE_POINTER_MODE (addr_space_t @var{address_space}) +Define this to return the machine mode to use for pointers to +@var{address_space} if the target supports named address spaces. +The default version of this hook returns @code{ptr_mode}. +@end deftypefn + +@deftypefn {Target Hook} scalar_int_mode TARGET_ADDR_SPACE_ADDRESS_MODE (addr_space_t @var{address_space}) +Define this to return the machine mode to use for addresses in +@var{address_space} if the target supports named address spaces. +The default version of this hook returns @code{Pmode}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ADDR_SPACE_VALID_POINTER_MODE (scalar_int_mode @var{mode}, addr_space_t @var{as}) +Define this to return nonzero if the port can handle pointers +with machine mode @var{mode} to address space @var{as}. This target +hook is the same as the @code{TARGET_VALID_POINTER_MODE} target hook, +except that it includes explicit named address space support. The default +version of this hook returns true for the modes returned by either the +@code{TARGET_ADDR_SPACE_POINTER_MODE} or @code{TARGET_ADDR_SPACE_ADDRESS_MODE} +target hooks for the given address space. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P (machine_mode @var{mode}, rtx @var{exp}, bool @var{strict}, addr_space_t @var{as}) +Define this to return true if @var{exp} is a valid address for mode +@var{mode} in the named address space @var{as}. The @var{strict} +parameter says whether strict addressing is in effect after reload has +finished. This target hook is the same as the +@code{TARGET_LEGITIMATE_ADDRESS_P} target hook, except that it includes +explicit named address space support. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS (rtx @var{x}, rtx @var{oldx}, machine_mode @var{mode}, addr_space_t @var{as}) +Define this to modify an invalid address @var{x} to be a valid address +with mode @var{mode} in the named address space @var{as}. This target +hook is the same as the @code{TARGET_LEGITIMIZE_ADDRESS} target hook, +except that it includes explicit named address space support. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ADDR_SPACE_SUBSET_P (addr_space_t @var{subset}, addr_space_t @var{superset}) +Define this to return whether the @var{subset} named address space is +contained within the @var{superset} named address space. Pointers to +a named address space that is a subset of another named address space +will be converted automatically without a cast if used together in +arithmetic operations. Pointers to a superset address space can be +converted to pointers to a subset address space via explicit casts. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID (addr_space_t @var{as}) +Define this to modify the default handling of address 0 for the +address space. Return true if 0 should be considered a valid address. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_ADDR_SPACE_CONVERT (rtx @var{op}, tree @var{from_type}, tree @var{to_type}) +Define this to convert the pointer expression represented by the RTL +@var{op} with type @var{from_type} that points to a named address +space to a new pointer expression with type @var{to_type} that points +to a different named address space. When this hook it called, it is +guaranteed that one of the two address spaces is a subset of the other, +as determined by the @code{TARGET_ADDR_SPACE_SUBSET_P} target hook. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_ADDR_SPACE_DEBUG (addr_space_t @var{as}) +Define this to define how the address space is encoded in dwarf. +The result is the value to be used with @code{DW_AT_address_class}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ADDR_SPACE_DIAGNOSE_USAGE (addr_space_t @var{as}, location_t @var{loc}) +Define this hook if the availability of an address space depends on +command line options and some diagnostics should be printed when the +address space is used. This hook is called during parsing and allows +to emit a better diagnostic compared to the case where the address space +was not registered with @code{c_register_addr_space}. @var{as} is +the address space as registered with @code{c_register_addr_space}. +@var{loc} is the location of the address space qualifier token. +The default implementation does nothing. +@end deftypefn + +@node Misc +@section Miscellaneous Parameters +@cindex parameters, miscellaneous + +@c prevent bad page break with this line +Here are several miscellaneous parameters. + +@defmac HAS_LONG_COND_BRANCH +Define this boolean macro to indicate whether or not your architecture +has conditional branches that can span all of memory. It is used in +conjunction with an optimization that partitions hot and cold basic +blocks into separate sections of the executable. If this macro is +set to false, gcc will convert any conditional branches that attempt +to cross between sections into unconditional branches or indirect jumps. +@end defmac + +@defmac HAS_LONG_UNCOND_BRANCH +Define this boolean macro to indicate whether or not your architecture +has unconditional branches that can span all of memory. It is used in +conjunction with an optimization that partitions hot and cold basic +blocks into separate sections of the executable. If this macro is +set to false, gcc will convert any unconditional branches that attempt +to cross between sections into indirect jumps. +@end defmac + +@defmac CASE_VECTOR_MODE +An alias for a machine mode name. This is the machine mode that +elements of a jump-table should have. +@end defmac + +@defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body}) +Optional: return the preferred mode for an @code{addr_diff_vec} +when the minimum and maximum offset are known. If you define this, +it enables extra code in branch shortening to deal with @code{addr_diff_vec}. +To make this work, you also have to define @code{INSN_ALIGN} and +make the alignment for @code{addr_diff_vec} explicit. +The @var{body} argument is provided so that the offset_unsigned and scale +flags can be updated. +@end defmac + +@defmac CASE_VECTOR_PC_RELATIVE +Define this macro to be a C expression to indicate when jump-tables +should contain relative addresses. You need not define this macro if +jump-tables never contain relative addresses, or jump-tables should +contain relative addresses only when @option{-fPIC} or @option{-fPIC} +is in effect. +@end defmac + +@deftypefn {Target Hook} {unsigned int} TARGET_CASE_VALUES_THRESHOLD (void) +This function return the smallest number of different values for which it +is best to use a jump-table instead of a tree of conditional branches. +The default is four for machines with a @code{casesi} instruction and +five otherwise. This is best for most machines. +@end deftypefn + +@defmac WORD_REGISTER_OPERATIONS +Define this macro to 1 if operations between registers with integral mode +smaller than a word are always performed on the entire register. To be +more explicit, if you start with a pair of @code{word_mode} registers with +known values and you do a subword, for example @code{QImode}, addition on +the low part of the registers, then the compiler may consider that the +result has a known value in @code{word_mode} too if the macro is defined +to 1. Most RISC machines have this property and most CISC machines do not. +@end defmac + +@deftypefn {Target Hook} {unsigned int} TARGET_MIN_ARITHMETIC_PRECISION (void) +On some RISC architectures with 64-bit registers, the processor also +maintains 32-bit condition codes that make it possible to do real 32-bit +arithmetic, although the operations are performed on the full registers. + +On such architectures, defining this hook to 32 tells the compiler to try +using 32-bit arithmetical operations setting the condition codes instead +of doing full 64-bit arithmetic. + +More generally, define this hook on RISC architectures if you want the +compiler to try using arithmetical operations setting the condition codes +with a precision lower than the word precision. + +You need not define this hook if @code{WORD_REGISTER_OPERATIONS} is not +defined to 1. +@end deftypefn + +@defmac LOAD_EXTEND_OP (@var{mem_mode}) +Define this macro to be a C expression indicating when insns that read +memory in @var{mem_mode}, an integral mode narrower than a word, set the +bits outside of @var{mem_mode} to be either the sign-extension or the +zero-extension of the data read. Return @code{SIGN_EXTEND} for values +of @var{mem_mode} for which the +insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and +@code{UNKNOWN} for other modes. + +This macro is not called with @var{mem_mode} non-integral or with a width +greater than or equal to @code{BITS_PER_WORD}, so you may return any +value in this case. Do not define this macro if it would always return +@code{UNKNOWN}. On machines where this macro is defined, you will normally +define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}. + +You may return a non-@code{UNKNOWN} value even if for some hard registers +the sign extension is not performed, if for the @code{REGNO_REG_CLASS} +of these hard registers @code{TARGET_CAN_CHANGE_MODE_CLASS} returns false +when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any +integral mode larger than this but not larger than @code{word_mode}. + +You must return @code{UNKNOWN} if for some hard registers that allow this +mode, @code{TARGET_CAN_CHANGE_MODE_CLASS} says that they cannot change to +@code{word_mode}, but that they can change to another integral mode that +is larger then @var{mem_mode} but still smaller than @code{word_mode}. +@end defmac + +@defmac SHORT_IMMEDIATES_SIGN_EXTEND +Define this macro to 1 if loading short immediate values into registers sign +extends. +@end defmac + +@deftypefn {Target Hook} {unsigned int} TARGET_MIN_DIVISIONS_FOR_RECIP_MUL (machine_mode @var{mode}) +When @option{-ffast-math} is in effect, GCC tries to optimize +divisions by the same divisor, by turning them into multiplications by +the reciprocal. This target hook specifies the minimum number of divisions +that should be there for GCC to perform the optimization for a variable +of mode @var{mode}. The default implementation returns 3 if the machine +has an instruction for the division, and 2 if it does not. +@end deftypefn + +@defmac MOVE_MAX +The maximum number of bytes that a single instruction can move quickly +between memory and registers or between two memory locations. +@end defmac + +@defmac MAX_MOVE_MAX +The maximum number of bytes that a single instruction can move quickly +between memory and registers or between two memory locations. If this +is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the +constant value that is the largest value that @code{MOVE_MAX} can have +at run-time. +@end defmac + +@defmac SHIFT_COUNT_TRUNCATED +A C expression that is nonzero if on this machine the number of bits +actually used for the count of a shift operation is equal to the number +of bits needed to represent the size of the object being shifted. When +this macro is nonzero, the compiler will assume that it is safe to omit +a sign-extend, zero-extend, and certain bitwise `and' instructions that +truncates the count of a shift operation. On machines that have +instructions that act on bit-fields at variable positions, which may +include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED} +also enables deletion of truncations of the values that serve as +arguments to bit-field instructions. + +If both types of instructions truncate the count (for shifts) and +position (for bit-field operations), or if no variable-position bit-field +instructions exist, you should define this macro. + +However, on some machines, such as the 80386 and the 680x0, truncation +only applies to shift operations and not the (real or pretended) +bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on +such machines. Instead, add patterns to the @file{md} file that include +the implied truncation of the shift instructions. + +You need not define this macro if it would always have the value of zero. +@end defmac + +@anchor{TARGET_SHIFT_TRUNCATION_MASK} +@deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_SHIFT_TRUNCATION_MASK (machine_mode @var{mode}) +This function describes how the standard shift patterns for @var{mode} +deal with shifts by negative amounts or by more than the width of the mode. +@xref{shift patterns}. + +On many machines, the shift patterns will apply a mask @var{m} to the +shift count, meaning that a fixed-width shift of @var{x} by @var{y} is +equivalent to an arbitrary-width shift of @var{x} by @var{y & m}. If +this is true for mode @var{mode}, the function should return @var{m}, +otherwise it should return 0. A return value of 0 indicates that no +particular behavior is guaranteed. + +Note that, unlike @code{SHIFT_COUNT_TRUNCATED}, this function does +@emph{not} apply to general shift rtxes; it applies only to instructions +that are generated by the named shift patterns. + +The default implementation of this function returns +@code{GET_MODE_BITSIZE (@var{mode}) - 1} if @code{SHIFT_COUNT_TRUNCATED} +and 0 otherwise. This definition is always safe, but if +@code{SHIFT_COUNT_TRUNCATED} is false, and some shift patterns +nevertheless truncate the shift count, you may get better code +by overriding it. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_TRULY_NOOP_TRUNCATION (poly_uint64 @var{outprec}, poly_uint64 @var{inprec}) +This hook returns true if it is safe to ``convert'' a value of +@var{inprec} bits to one of @var{outprec} bits (where @var{outprec} is +smaller than @var{inprec}) by merely operating on it as if it had only +@var{outprec} bits. The default returns true unconditionally, which +is correct for most machines. When @code{TARGET_TRULY_NOOP_TRUNCATION} +returns false, the machine description should provide a @code{trunc} +optab to specify the RTL that performs the required truncation. + +If @code{TARGET_MODES_TIEABLE_P} returns false for a pair of modes, +suboptimal code can result if this hook returns true for the corresponding +mode sizes. Making this hook return false in such cases may improve things. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_MODE_REP_EXTENDED (scalar_int_mode @var{mode}, scalar_int_mode @var{rep_mode}) +The representation of an integral mode can be such that the values +are always extended to a wider integral mode. Return +@code{SIGN_EXTEND} if values of @var{mode} are represented in +sign-extended form to @var{rep_mode}. Return @code{UNKNOWN} +otherwise. (Currently, none of the targets use zero-extended +representation this way so unlike @code{LOAD_EXTEND_OP}, +@code{TARGET_MODE_REP_EXTENDED} is expected to return either +@code{SIGN_EXTEND} or @code{UNKNOWN}. Also no target extends +@var{mode} to @var{rep_mode} so that @var{rep_mode} is not the next +widest integral mode and currently we take advantage of this fact.) + +Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN} +value even if the extension is not performed on certain hard registers +as long as for the @code{REGNO_REG_CLASS} of these hard registers +@code{TARGET_CAN_CHANGE_MODE_CLASS} returns false. + +Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP} +describe two related properties. If you define +@code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want +to define @code{LOAD_EXTEND_OP (mode)} to return the same type of +extension. + +In order to enforce the representation of @code{mode}, +@code{TARGET_TRULY_NOOP_TRUNCATION} should return false when truncating to +@code{mode}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_SETJMP_PRESERVES_NONVOLATILE_REGS_P (void) +On some targets, it is assumed that the compiler will spill all pseudos + that are live across a call to @code{setjmp}, while other targets treat + @code{setjmp} calls as normal function calls. + + This hook returns false if @code{setjmp} calls do not preserve all + non-volatile registers so that gcc that must spill all pseudos that are + live across @code{setjmp} calls. Define this to return true if the + target does not need to spill all pseudos live across @code{setjmp} calls. + The default implementation conservatively assumes all pseudos must be + spilled across @code{setjmp} calls. +@end deftypefn + +@defmac STORE_FLAG_VALUE +A C expression describing the value returned by a comparison operator +with an integral mode and stored by a store-flag instruction +(@samp{cstore@var{mode}4}) when the condition is true. This description must +apply to @emph{all} the @samp{cstore@var{mode}4} patterns and all the +comparison operators whose results have a @code{MODE_INT} mode. + +A value of 1 or @minus{}1 means that the instruction implementing the +comparison operator returns exactly 1 or @minus{}1 when the comparison is true +and 0 when the comparison is false. Otherwise, the value indicates +which bits of the result are guaranteed to be 1 when the comparison is +true. This value is interpreted in the mode of the comparison +operation, which is given by the mode of the first operand in the +@samp{cstore@var{mode}4} pattern. Either the low bit or the sign bit of +@code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by +the compiler. + +If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will +generate code that depends only on the specified bits. It can also +replace comparison operators with equivalent operations if they cause +the required bits to be set, even if the remaining bits are undefined. +For example, on a machine whose comparison operators return an +@code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as +@samp{0x80000000}, saying that just the sign bit is relevant, the +expression + +@smallexample +(ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0)) +@end smallexample + +@noindent +can be converted to + +@smallexample +(ashift:SI @var{x} (const_int @var{n})) +@end smallexample + +@noindent +where @var{n} is the appropriate shift count to move the bit being +tested into the sign bit. + +There is no way to describe a machine that always sets the low-order bit +for a true value, but does not guarantee the value of any other bits, +but we do not know of any machine that has such an instruction. If you +are trying to port GCC to such a machine, include an instruction to +perform a logical-and of the result with 1 in the pattern for the +comparison operators and let us know at @email{gcc@@gcc.gnu.org}. + +Often, a machine will have multiple instructions that obtain a value +from a comparison (or the condition codes). Here are rules to guide the +choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions +to be used: + +@itemize @bullet +@item +Use the shortest sequence that yields a valid definition for +@code{STORE_FLAG_VALUE}. It is more efficient for the compiler to +``normalize'' the value (convert it to, e.g., 1 or 0) than for the +comparison operators to do so because there may be opportunities to +combine the normalization with other operations. + +@item +For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being +slightly preferred on machines with expensive jumps and 1 preferred on +other machines. + +@item +As a second choice, choose a value of @samp{0x80000001} if instructions +exist that set both the sign and low-order bits but do not define the +others. + +@item +Otherwise, use a value of @samp{0x80000000}. +@end itemize + +Many machines can produce both the value chosen for +@code{STORE_FLAG_VALUE} and its negation in the same number of +instructions. On those machines, you should also define a pattern for +those cases, e.g., one matching + +@smallexample +(set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C}))) +@end smallexample + +Some machines can also perform @code{and} or @code{plus} operations on +condition code values with less instructions than the corresponding +@samp{cstore@var{mode}4} insn followed by @code{and} or @code{plus}. On those +machines, define the appropriate patterns. Use the names @code{incscc} +and @code{decscc}, respectively, for the patterns which perform +@code{plus} or @code{minus} operations on condition code values. See +@file{rs6000.md} for some examples. The GNU Superoptimizer can be used to +find such instruction sequences on other machines. + +If this macro is not defined, the default value, 1, is used. You need +not define @code{STORE_FLAG_VALUE} if the machine has no store-flag +instructions, or if the value generated by these instructions is 1. +@end defmac + +@defmac FLOAT_STORE_FLAG_VALUE (@var{mode}) +A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is +returned when comparison operators with floating-point results are true. +Define this macro on machines that have comparison operations that return +floating-point values. If there are no such operations, do not define +this macro. +@end defmac + +@defmac VECTOR_STORE_FLAG_VALUE (@var{mode}) +A C expression that gives an rtx representing the nonzero true element +for vector comparisons. The returned rtx should be valid for the inner +mode of @var{mode} which is guaranteed to be a vector mode. Define +this macro on machines that have vector comparison operations that +return a vector result. If there are no such operations, do not define +this macro. Typically, this macro is defined as @code{const1_rtx} or +@code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent +the compiler optimizing such vector comparison operations for the +given mode. +@end defmac + +@defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) +@defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) +A C expression that indicates whether the architecture defines a value +for @code{clz} or @code{ctz} with a zero operand. +A result of @code{0} indicates the value is undefined. +If the value is defined for only the RTL expression, the macro should +evaluate to @code{1}; if the value applies also to the corresponding optab +entry (which is normally the case if it expands directly into +the corresponding RTL), then the macro should evaluate to @code{2}. +In the cases where the value is defined, @var{value} should be set to +this value. + +If this macro is not defined, the value of @code{clz} or +@code{ctz} at zero is assumed to be undefined. + +This macro must be defined if the target's expansion for @code{ffs} +relies on a particular value to get correct results. Otherwise it +is not necessary, though it may be used to optimize some corner cases, and +to provide a default expansion for the @code{ffs} optab. + +Note that regardless of this macro the ``definedness'' of @code{clz} +and @code{ctz} at zero do @emph{not} extend to the builtin functions +visible to the user. Thus one may be free to adjust the value at will +to match the target expansion of these operations without fear of +breaking the API@. +@end defmac + +@defmac Pmode +An alias for the machine mode for pointers. On most machines, define +this to be the integer mode corresponding to the width of a hardware +pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines. +On some machines you must define this to be one of the partial integer +modes, such as @code{PSImode}. + +The width of @code{Pmode} must be at least as large as the value of +@code{POINTER_SIZE}. If it is not equal, you must define the macro +@code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended +to @code{Pmode}. +@end defmac + +@defmac FUNCTION_MODE +An alias for the machine mode used for memory references to functions +being called, in @code{call} RTL expressions. On most CISC machines, +where an instruction can begin at any byte address, this should be +@code{QImode}. On most RISC machines, where all instructions have fixed +size and alignment, this should be a mode with the same size and alignment +as the machine instruction words - typically @code{SImode} or @code{HImode}. +@end defmac + +@defmac STDC_0_IN_SYSTEM_HEADERS +In normal operation, the preprocessor expands @code{__STDC__} to the +constant 1, to signify that GCC conforms to ISO Standard C@. On some +hosts, like Solaris, the system compiler uses a different convention, +where @code{__STDC__} is normally 0, but is 1 if the user specifies +strict conformance to the C Standard. + +Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host +convention when processing system header files, but when processing user +files @code{__STDC__} will always expand to 1. +@end defmac + +@deftypefn {C Target Hook} {const char *} TARGET_C_PREINCLUDE (void) +Define this hook to return the name of a header file to be included at +the start of all compilations, as if it had been included with +@code{#include <@var{file}>}. If this hook returns @code{NULL}, or is +not defined, or the header is not found, or if the user specifies +@option{-ffreestanding} or @option{-nostdinc}, no header is included. + +This hook can be used together with a header provided by the system C +library to implement ISO C requirements for certain macros to be +predefined that describe properties of the whole implementation rather +than just the compiler. +@end deftypefn + +@deftypefn {C Target Hook} bool TARGET_CXX_IMPLICIT_EXTERN_C (const char*@var{}) +Define this hook to add target-specific C++ implicit extern C functions. +If this function returns true for the name of a file-scope function, that +function implicitly gets extern "C" linkage rather than whatever language +linkage the declaration would normally have. An example of such function +is WinMain on Win32 targets. +@end deftypefn + +@defmac SYSTEM_IMPLICIT_EXTERN_C +Define this macro if the system header files do not support C++@. +This macro handles system header files by pretending that system +header files are enclosed in @samp{extern "C" @{@dots{}@}}. +@end defmac + +@findex #pragma +@findex pragma +@defmac REGISTER_TARGET_PRAGMAS () +Define this macro if you want to implement any target-specific pragmas. +If defined, it is a C expression which makes a series of calls to +@code{c_register_pragma} or @code{c_register_pragma_with_expansion} +for each pragma. The macro may also do any +setup required for the pragmas. + +The primary reason to define this macro is to provide compatibility with +other compilers for the same target. In general, we discourage +definition of target-specific pragmas for GCC@. + +If the pragma can be implemented by attributes then you should consider +defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well. + +Preprocessor macros that appear on pragma lines are not expanded. All +@samp{#pragma} directives that do not match any registered pragma are +silently ignored, unless the user specifies @option{-Wunknown-pragmas}. +@end defmac + +@deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) +@deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) + +Each call to @code{c_register_pragma} or +@code{c_register_pragma_with_expansion} establishes one pragma. The +@var{callback} routine will be called when the preprocessor encounters a +pragma of the form + +@smallexample +#pragma [@var{space}] @var{name} @dots{} +@end smallexample + +@var{space} is the case-sensitive namespace of the pragma, or +@code{NULL} to put the pragma in the global namespace. The callback +routine receives @var{pfile} as its first argument, which can be passed +on to cpplib's functions if necessary. You can lex tokens after the +@var{name} by calling @code{pragma_lex}. Tokens that are not read by the +callback will be silently ignored. The end of the line is indicated by +a token of type @code{CPP_EOF}. Macro expansion occurs on the +arguments of pragmas registered with +@code{c_register_pragma_with_expansion} but not on the arguments of +pragmas registered with @code{c_register_pragma}. + +Note that the use of @code{pragma_lex} is specific to the C and C++ +compilers. It will not work in the Java or Fortran compilers, or any +other language compilers for that matter. Thus if @code{pragma_lex} is going +to be called from target-specific code, it must only be done so when +building the C and C++ compilers. This can be done by defining the +variables @code{c_target_objs} and @code{cxx_target_objs} in the +target entry in the @file{config.gcc} file. These variables should name +the target-specific, language-specific object file which contains the +code that uses @code{pragma_lex}. Note it will also be necessary to add a +rule to the makefile fragment pointed to by @code{tmake_file} that shows +how to build this object file. +@end deftypefun + +@defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION +Define this macro if macros should be expanded in the +arguments of @samp{#pragma pack}. +@end defmac + +@defmac TARGET_DEFAULT_PACK_STRUCT +If your target requires a structure packing default other than 0 (meaning +the machine default), define this macro to the necessary value (in bytes). +This must be a value that would also be valid to use with +@samp{#pragma pack()} (that is, a small power of two). +@end defmac + +@defmac DOLLARS_IN_IDENTIFIERS +Define this macro to control use of the character @samp{$} in +identifier names for the C family of languages. 0 means @samp{$} is +not allowed by default; 1 means it is allowed. 1 is the default; +there is no need to define this macro in that case. +@end defmac + +@defmac INSN_SETS_ARE_DELAYED (@var{insn}) +Define this macro as a C expression that is nonzero if it is safe for the +delay slot scheduler to place instructions in the delay slot of @var{insn}, +even if they appear to use a resource set or clobbered in @var{insn}. +@var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that +every @code{call_insn} has this behavior. On machines where some @code{insn} +or @code{jump_insn} is really a function call and hence has this behavior, +you should define this macro. + +You need not define this macro if it would always return zero. +@end defmac + +@defmac INSN_REFERENCES_ARE_DELAYED (@var{insn}) +Define this macro as a C expression that is nonzero if it is safe for the +delay slot scheduler to place instructions in the delay slot of @var{insn}, +even if they appear to set or clobber a resource referenced in @var{insn}. +@var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where +some @code{insn} or @code{jump_insn} is really a function call and its operands +are registers whose use is actually in the subroutine it calls, you should +define this macro. Doing so allows the delay slot scheduler to move +instructions which copy arguments into the argument registers into the delay +slot of @var{insn}. + +You need not define this macro if it would always return zero. +@end defmac + +@defmac MULTIPLE_SYMBOL_SPACES +Define this macro as a C expression that is nonzero if, in some cases, +global symbols from one translation unit may not be bound to undefined +symbols in another translation unit without user intervention. For +instance, under Microsoft Windows symbols must be explicitly imported +from shared libraries (DLLs). + +You need not define this macro if it would always evaluate to zero. +@end defmac + +@deftypefn {Target Hook} {rtx_insn *} TARGET_MD_ASM_ADJUST (vec& @var{outputs}, vec& @var{inputs}, vec& @var{input_modes}, vec& @var{constraints}, vec& @var{clobbers}, HARD_REG_SET& @var{clobbered_regs}, location_t @var{loc}) +This target hook may add @dfn{clobbers} to @var{clobbers} and +@var{clobbered_regs} for any hard regs the port wishes to automatically +clobber for an asm. The @var{outputs} and @var{inputs} may be inspected +to avoid clobbering a register that is already used by the asm. @var{loc} +is the source location of the asm. + +It may modify the @var{outputs}, @var{inputs}, @var{input_modes}, and +@var{constraints} as necessary for other pre-processing. In this case the +return value is a sequence of insns to emit after the asm. Note that +changes to @var{inputs} must be accompanied by the corresponding changes +to @var{input_modes}. +@end deftypefn + +@defmac MATH_LIBRARY +Define this macro as a C string constant for the linker argument to link +in the system math library, minus the initial @samp{"-l"}, or +@samp{""} if the target does not have a +separate math library. + +You need only define this macro if the default of @samp{"m"} is wrong. +@end defmac + +@defmac LIBRARY_PATH_ENV +Define this macro as a C string constant for the environment variable that +specifies where the linker should look for libraries. + +You need only define this macro if the default of @samp{"LIBRARY_PATH"} +is wrong. +@end defmac + +@defmac TARGET_POSIX_IO +Define this macro if the target supports the following POSIX@ file +functions, access, mkdir and file locking with fcntl / F_SETLKW@. +Defining @code{TARGET_POSIX_IO} will enable the test coverage code +to use file locking when exiting a program, which avoids race conditions +if the program has forked. It will also create directories at run-time +for cross-profiling. +@end defmac + +@defmac MAX_CONDITIONAL_EXECUTE + +A C expression for the maximum number of instructions to execute via +conditional execution instructions instead of a branch. A value of +@code{BRANCH_COST}+1 is the default. +@end defmac + +@defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr}) +Used if the target needs to perform machine-dependent modifications on the +conditionals used for turning basic blocks into conditionally executed code. +@var{ce_info} points to a data structure, @code{struct ce_if_block}, which +contains information about the currently processed blocks. @var{true_expr} +and @var{false_expr} are the tests that are used for converting the +then-block and the else-block, respectively. Set either @var{true_expr} or +@var{false_expr} to a null pointer if the tests cannot be converted. +@end defmac + +@defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr}) +Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated +if-statements into conditions combined by @code{and} and @code{or} operations. +@var{bb} contains the basic block that contains the test that is currently +being processed and about to be turned into a condition. +@end defmac + +@defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn}) +A C expression to modify the @var{PATTERN} of an @var{INSN} that is to +be converted to conditional execution format. @var{ce_info} points to +a data structure, @code{struct ce_if_block}, which contains information +about the currently processed blocks. +@end defmac + +@defmac IFCVT_MODIFY_FINAL (@var{ce_info}) +A C expression to perform any final machine dependent modifications in +converting code to conditional execution. The involved basic blocks +can be found in the @code{struct ce_if_block} structure that is pointed +to by @var{ce_info}. +@end defmac + +@defmac IFCVT_MODIFY_CANCEL (@var{ce_info}) +A C expression to cancel any machine dependent modifications in +converting code to conditional execution. The involved basic blocks +can be found in the @code{struct ce_if_block} structure that is pointed +to by @var{ce_info}. +@end defmac + +@defmac IFCVT_MACHDEP_INIT (@var{ce_info}) +A C expression to initialize any machine specific data for if-conversion +of the if-block in the @code{struct ce_if_block} structure that is pointed +to by @var{ce_info}. +@end defmac + +@deftypefn {Target Hook} void TARGET_MACHINE_DEPENDENT_REORG (void) +If non-null, this hook performs a target-specific pass over the +instruction stream. The compiler will run it at all optimization levels, +just before the point at which it normally does delayed-branch scheduling. + +The exact purpose of the hook varies from target to target. Some use +it to do transformations that are necessary for correctness, such as +laying out in-function constant pools or avoiding hardware hazards. +Others use it as an opportunity to do some machine-dependent optimizations. + +You need not implement the hook if it has nothing to do. The default +definition is null. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_INIT_BUILTINS (void) +Define this hook if you have any machine-specific built-in functions +that need to be defined. It should be a function that performs the +necessary setup. + +Machine specific built-in functions can be useful to expand special machine +instructions that would otherwise not normally be generated because +they have no equivalent in the source language (for example, SIMD vector +instructions or prefetch instructions). + +To create a built-in function, call the function +@code{lang_hooks.builtin_function} +which is defined by the language front end. You can use any type nodes set +up by @code{build_common_tree_nodes}; +only language front ends that use those two functions will call +@samp{TARGET_INIT_BUILTINS}. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_BUILTIN_DECL (unsigned @var{code}, bool @var{initialize_p}) +Define this hook if you have any machine-specific built-in functions +that need to be defined. It should be a function that returns the +builtin function declaration for the builtin function code @var{code}. +If there is no such builtin and it cannot be initialized at this time +if @var{initialize_p} is true the function should return @code{NULL_TREE}. +If @var{code} is out of range the function should return +@code{error_mark_node}. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, machine_mode @var{mode}, int @var{ignore}) + +Expand a call to a machine specific built-in function that was set up by +@samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the +function call; the result should go to @var{target} if that is +convenient, and have mode @var{mode} if that is convenient. +@var{subtarget} may be used as the target for computing one of +@var{exp}'s operands. @var{ignore} is nonzero if the value is to be +ignored. This function should return the result of the call to the +built-in function. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_RESOLVE_OVERLOADED_BUILTIN (unsigned int @var{loc}, tree @var{fndecl}, void *@var{arglist}) +Select a replacement for a machine specific built-in function that +was set up by @samp{TARGET_INIT_BUILTINS}. This is done +@emph{before} regular type checking, and so allows the target to +implement a crude form of function overloading. @var{fndecl} is the +declaration of the built-in function. @var{arglist} is the list of +arguments passed to the built-in function. The result is a +complete expression that implements the operation, usually +another @code{CALL_EXPR}. +@var{arglist} really has type @samp{VEC(tree,gc)*} +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CHECK_BUILTIN_CALL (location_t @var{loc}, vec @var{arg_loc}, tree @var{fndecl}, tree @var{orig_fndecl}, unsigned int @var{nargs}, tree *@var{args}) +Perform semantic checking on a call to a machine-specific built-in +function after its arguments have been constrained to the function +signature. Return true if the call is valid, otherwise report an error +and return false. + +This hook is called after @code{TARGET_RESOLVE_OVERLOADED_BUILTIN}. +The call was originally to built-in function @var{orig_fndecl}, +but after the optional @code{TARGET_RESOLVE_OVERLOADED_BUILTIN} +step is now to built-in function @var{fndecl}. @var{loc} is the +location of the call and @var{args} is an array of function arguments, +of which there are @var{nargs}. @var{arg_loc} specifies the location +of each argument. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_FOLD_BUILTIN (tree @var{fndecl}, int @var{n_args}, tree *@var{argp}, bool @var{ignore}) +Fold a call to a machine specific built-in function that was set up by +@samp{TARGET_INIT_BUILTINS}. @var{fndecl} is the declaration of the +built-in function. @var{n_args} is the number of arguments passed to +the function; the arguments themselves are pointed to by @var{argp}. +The result is another tree, valid for both GIMPLE and GENERIC, +containing a simplified expression for the call's result. If +@var{ignore} is true the value will be ignored. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_GIMPLE_FOLD_BUILTIN (gimple_stmt_iterator *@var{gsi}) +Fold a call to a machine specific built-in function that was set up +by @samp{TARGET_INIT_BUILTINS}. @var{gsi} points to the gimple +statement holding the function call. Returns true if any change +was made to the GIMPLE stream. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_COMPARE_VERSION_PRIORITY (tree @var{decl1}, tree @var{decl2}) +This hook is used to compare the target attributes in two functions to +determine which function's features get higher priority. This is used +during function multi-versioning to figure out the order in which two +versions must be dispatched. A function version with a higher priority +is checked for dispatching earlier. @var{decl1} and @var{decl2} are + the two function decls that will be compared. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_GET_FUNCTION_VERSIONS_DISPATCHER (void *@var{decl}) +This hook is used to get the dispatcher function for a set of function +versions. The dispatcher function is called to invoke the right function +version at run-time. @var{decl} is one version from a set of semantically +identical versions. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_GENERATE_VERSION_DISPATCHER_BODY (void *@var{arg}) +This hook is used to generate the dispatcher logic to invoke the right +function version at run-time for a given set of function versions. +@var{arg} points to the callgraph node of the dispatcher function whose +body must be generated. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_PREDICT_DOLOOP_P (class loop *@var{loop}) +Return true if we can predict it is possible to use a low-overhead loop +for a particular loop. The parameter @var{loop} is a pointer to the loop. +This target hook is required only when the target supports low-overhead +loops, and will help ivopts to make some decisions. +The default version of this hook returns false. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_HAVE_COUNT_REG_DECR_P +Return true if the target supports hardware count register for decrement +and branch. +The default value is false. +@end deftypevr + +@deftypevr {Target Hook} int64_t TARGET_DOLOOP_COST_FOR_GENERIC +One IV candidate dedicated for doloop is introduced in IVOPTs, we can +calculate the computation cost of adopting it to any generic IV use by +function get_computation_cost as before. But for targets which have +hardware count register support for decrement and branch, it may have to +move IV value from hardware count register to general purpose register +while doloop IV candidate is used for generic IV uses. It probably takes +expensive penalty. This hook allows target owners to define the cost for +this especially for generic IV uses. +The default value is zero. +@end deftypevr + +@deftypevr {Target Hook} int64_t TARGET_DOLOOP_COST_FOR_ADDRESS +One IV candidate dedicated for doloop is introduced in IVOPTs, we can +calculate the computation cost of adopting it to any address IV use by +function get_computation_cost as before. But for targets which have +hardware count register support for decrement and branch, it may have to +move IV value from hardware count register to general purpose register +while doloop IV candidate is used for address IV uses. It probably takes +expensive penalty. This hook allows target owners to define the cost for +this escpecially for address IV uses. +The default value is zero. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_CAN_USE_DOLOOP_P (const widest_int @var{&iterations}, const widest_int @var{&iterations_max}, unsigned int @var{loop_depth}, bool @var{entered_at_top}) +Return true if it is possible to use low-overhead loops (@code{doloop_end} +and @code{doloop_begin}) for a particular loop. @var{iterations} gives the +exact number of iterations, or 0 if not known. @var{iterations_max} gives +the maximum number of iterations, or 0 if not known. @var{loop_depth} is +the nesting depth of the loop, with 1 for innermost loops, 2 for loops that +contain innermost loops, and so on. @var{entered_at_top} is true if the +loop is only entered from the top. + +This hook is only used if @code{doloop_end} is available. The default +implementation returns true. You can use @code{can_use_doloop_if_innermost} +if the loop must be the innermost, and if there are no other restrictions. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_INVALID_WITHIN_DOLOOP (const rtx_insn *@var{insn}) + +Take an instruction in @var{insn} and return NULL if it is valid within a +low-overhead loop, otherwise return a string explaining why doloop +could not be applied. + +Many targets use special registers for low-overhead looping. For any +instruction that clobbers these this function should return a string indicating +the reason why the doloop could not be applied. +By default, the RTL loop optimizer does not use a present doloop pattern for +loops containing function calls or branch on table instructions. +@end deftypefn + +@deftypefn {Target Hook} machine_mode TARGET_PREFERRED_DOLOOP_MODE (machine_mode @var{mode}) +This hook takes a @var{mode} for a doloop IV, where @code{mode} is the +original mode for the operation. If the target prefers an alternate +@code{mode} for the operation, then this hook should return that mode; +otherwise the original @code{mode} should be returned. For example, on a +64-bit target, @code{DImode} might be preferred over @code{SImode}. Both the +original and the returned modes should be @code{MODE_INT}. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_LEGITIMATE_COMBINED_INSN (rtx_insn *@var{insn}) +Take an instruction in @var{insn} and return @code{false} if the instruction +is not appropriate as a combination of two or more instructions. The +default is to accept all instructions. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_CAN_FOLLOW_JUMP (const rtx_insn *@var{follower}, const rtx_insn *@var{followee}) +FOLLOWER and FOLLOWEE are JUMP_INSN instructions; +return true if FOLLOWER may be modified to follow FOLLOWEE; +false, if it can't. +For example, on some targets, certain kinds of branches can't be made to +follow through a hot/cold partitioning. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_COMMUTATIVE_P (const_rtx @var{x}, int @var{outer_code}) +This target hook returns @code{true} if @var{x} is considered to be commutative. +Usually, this is just COMMUTATIVE_P (@var{x}), but the HP PA doesn't consider +PLUS to be commutative inside a MEM@. @var{outer_code} is the rtx code +of the enclosing rtl, if known, otherwise it is UNKNOWN. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_ALLOCATE_INITIAL_VALUE (rtx @var{hard_reg}) + +When the initial value of a hard register has been copied in a pseudo +register, it is often not necessary to actually allocate another register +to this pseudo register, because the original hard register or a stack slot +it has been saved into can be used. @code{TARGET_ALLOCATE_INITIAL_VALUE} +is called at the start of register allocation once for each hard register +that had its initial value copied by using +@code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}. +Possible values are @code{NULL_RTX}, if you don't want +to do any special allocation, a @code{REG} rtx---that would typically be +the hard register itself, if it is known not to be clobbered---or a +@code{MEM}. +If you are returning a @code{MEM}, this is only a hint for the allocator; +it might decide to use another register anyways. +You may use @code{current_function_is_leaf} or +@code{REG_N_SETS} in the hook to determine if the hard +register in question will not be clobbered. +The default value of this hook is @code{NULL}, which disables any special +allocation. +@end deftypefn + +@deftypefn {Target Hook} int TARGET_UNSPEC_MAY_TRAP_P (const_rtx @var{x}, unsigned @var{flags}) +This target hook returns nonzero if @var{x}, an @code{unspec} or +@code{unspec_volatile} operation, might cause a trap. Targets can use +this hook to enhance precision of analysis for @code{unspec} and +@code{unspec_volatile} operations. You may call @code{may_trap_p_1} +to analyze inner elements of @var{x} in which case @var{flags} should be +passed along. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_SET_CURRENT_FUNCTION (tree @var{decl}) +The compiler invokes this hook whenever it changes its current function +context (@code{cfun}). You can define this function if +the back end needs to perform any initialization or reset actions on a +per-function basis. For example, it may be used to implement function +attributes that affect register usage or code generation patterns. +The argument @var{decl} is the declaration for the new function context, +and may be null to indicate that the compiler has left a function context +and is returning to processing at the top level. +The default hook function does nothing. + +GCC sets @code{cfun} to a dummy function context during initialization of +some parts of the back end. The hook function is not invoked in this +situation; you need not worry about the hook being invoked recursively, +or when the back end is in a partially-initialized state. +@code{cfun} might be @code{NULL} to indicate processing at top level, +outside of any function scope. +@end deftypefn + +@defmac TARGET_OBJECT_SUFFIX +Define this macro to be a C string representing the suffix for object +files on your target machine. If you do not define this macro, GCC will +use @samp{.o} as the suffix for object files. +@end defmac + +@defmac TARGET_EXECUTABLE_SUFFIX +Define this macro to be a C string representing the suffix to be +automatically added to executable files on your target machine. If you +do not define this macro, GCC will use the null string as the suffix for +executable files. +@end defmac + +@defmac COLLECT_EXPORT_LIST +If defined, @code{collect2} will scan the individual object files +specified on its command line and create an export list for the linker. +Define this macro for systems like AIX, where the linker discards +object files that are not referenced from @code{main} and uses export +lists. +@end defmac + +@deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void) +This target hook returns @code{true} past the point in which new jump +instructions could be created. On machines that require a register for +every jump such as the SHmedia ISA of SH5, this point would typically be +reload, so this target hook should be defined to a function such as: + +@smallexample +static bool +cannot_modify_jumps_past_reload_p () +@{ + return (reload_completed || reload_in_progress); +@} +@end smallexample +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_HAVE_CONDITIONAL_EXECUTION (void) +This target hook returns true if the target supports conditional execution. +This target hook is required only when the target has several different +modes and they have different conditional execution capability, such as ARM. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_GEN_CCMP_FIRST (rtx_insn **@var{prep_seq}, rtx_insn **@var{gen_seq}, int @var{code}, tree @var{op0}, tree @var{op1}) +This function prepares to emit a comparison insn for the first compare in a + sequence of conditional comparisions. It returns an appropriate comparison + with @code{CC} for passing to @code{gen_ccmp_next} or @code{cbranch_optab}. + The insns to prepare the compare are saved in @var{prep_seq} and the compare + insns are saved in @var{gen_seq}. They will be emitted when all the + compares in the conditional comparision are generated without error. + @var{code} is the @code{rtx_code} of the compare for @var{op0} and @var{op1}. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_GEN_CCMP_NEXT (rtx_insn **@var{prep_seq}, rtx_insn **@var{gen_seq}, rtx @var{prev}, int @var{cmp_code}, tree @var{op0}, tree @var{op1}, int @var{bit_code}) +This function prepares to emit a conditional comparison within a sequence + of conditional comparisons. It returns an appropriate comparison with + @code{CC} for passing to @code{gen_ccmp_next} or @code{cbranch_optab}. + The insns to prepare the compare are saved in @var{prep_seq} and the compare + insns are saved in @var{gen_seq}. They will be emitted when all the + compares in the conditional comparision are generated without error. The + @var{prev} expression is the result of a prior call to @code{gen_ccmp_first} + or @code{gen_ccmp_next}. It may return @code{NULL} if the combination of + @var{prev} and this comparison is not supported, otherwise the result must + be appropriate for passing to @code{gen_ccmp_next} or @code{cbranch_optab}. + @var{code} is the @code{rtx_code} of the compare for @var{op0} and @var{op1}. + @var{bit_code} is @code{AND} or @code{IOR}, which is the op on the compares. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_GEN_MEMSET_SCRATCH_RTX (machine_mode @var{mode}) +This hook should return an rtx for a scratch register in @var{mode} to +be used when expanding memset calls. The backend can use a hard scratch +register to avoid stack realignment when expanding memset. The default +is @code{gen_reg_rtx}. +@end deftypefn + +@deftypefn {Target Hook} unsigned TARGET_LOOP_UNROLL_ADJUST (unsigned @var{nunroll}, class loop *@var{loop}) +This target hook returns a new value for the number of times @var{loop} +should be unrolled. The parameter @var{nunroll} is the number of times +the loop is to be unrolled. The parameter @var{loop} is a pointer to +the loop, which is going to be checked for unrolling. This target hook +is required only when the target has special constraints like maximum +number of memory accesses. +@end deftypefn + +@defmac POWI_MAX_MULTS +If defined, this macro is interpreted as a signed integer C expression +that specifies the maximum number of floating point multiplications +that should be emitted when expanding exponentiation by an integer +constant inline. When this value is defined, exponentiation requiring +more than this number of multiplications is implemented by calling the +system library's @code{pow}, @code{powf} or @code{powl} routines. +The default value places no upper bound on the multiplication count. +@end defmac + +@deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) +This target hook should register any extra include files for the +target. The parameter @var{stdinc} indicates if normal include files +are present. The parameter @var{sysroot} is the system root directory. +The parameter @var{iprefix} is the prefix for the gcc directory. +@end deftypefn + +@deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) +This target hook should register any extra include files for the +target before any standard headers. The parameter @var{stdinc} +indicates if normal include files are present. The parameter +@var{sysroot} is the system root directory. The parameter +@var{iprefix} is the prefix for the gcc directory. +@end deftypefn + +@deftypefn Macro void TARGET_OPTF (char *@var{path}) +This target hook should register special include paths for the target. +The parameter @var{path} is the include to register. On Darwin +systems, this is used for Framework includes, which have semantics +that are different from @option{-I}. +@end deftypefn + +@defmac bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl}) +This target macro returns @code{true} if it is safe to use a local alias +for a virtual function @var{fndecl} when constructing thunks, +@code{false} otherwise. By default, the macro returns @code{true} for all +functions, if a target supports aliases (i.e.@: defines +@code{ASM_OUTPUT_DEF}), @code{false} otherwise, +@end defmac + +@defmac TARGET_FORMAT_TYPES +If defined, this macro is the name of a global variable containing +target-specific format checking information for the @option{-Wformat} +option. The default is to have no target-specific format checks. +@end defmac + +@defmac TARGET_N_FORMAT_TYPES +If defined, this macro is the number of entries in +@code{TARGET_FORMAT_TYPES}. +@end defmac + +@defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES +If defined, this macro is the name of a global variable containing +target-specific format overrides for the @option{-Wformat} option. The +default is to have no target-specific format overrides. If defined, +@code{TARGET_FORMAT_TYPES} and @code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT} +must be defined, too. +@end defmac + +@defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT +If defined, this macro specifies the number of entries in +@code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}. +@end defmac + +@defmac TARGET_OVERRIDES_FORMAT_INIT +If defined, this macro specifies the optional initialization +routine for target specific customizations of the system printf +and scanf formatter settings. +@end defmac + +@deftypefn {Target Hook} {const char *} TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN (const_tree @var{typelist}, const_tree @var{funcdecl}, const_tree @var{val}) +If defined, this macro returns the diagnostic message when it is +illegal to pass argument @var{val} to function @var{funcdecl} +with prototype @var{typelist}. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_INVALID_CONVERSION (const_tree @var{fromtype}, const_tree @var{totype}) +If defined, this macro returns the diagnostic message when it is +invalid to convert from @var{fromtype} to @var{totype}, or @code{NULL} +if validity should be determined by the front end. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_INVALID_UNARY_OP (int @var{op}, const_tree @var{type}) +If defined, this macro returns the diagnostic message when it is +invalid to apply operation @var{op} (where unary plus is denoted by +@code{CONVERT_EXPR}) to an operand of type @var{type}, or @code{NULL} +if validity should be determined by the front end. +@end deftypefn + +@deftypefn {Target Hook} {const char *} TARGET_INVALID_BINARY_OP (int @var{op}, const_tree @var{type1}, const_tree @var{type2}) +If defined, this macro returns the diagnostic message when it is +invalid to apply operation @var{op} to operands of types @var{type1} +and @var{type2}, or @code{NULL} if validity should be determined by +the front end. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_PROMOTED_TYPE (const_tree @var{type}) +If defined, this target hook returns the type to which values of +@var{type} should be promoted when they appear in expressions, +analogous to the integer promotions, or @code{NULL_TREE} to use the +front end's normal promotion rules. This hook is useful when there are +target-specific types with special promotion rules. +This is currently used only by the C and C++ front ends. +@end deftypefn + +@deftypefn {Target Hook} tree TARGET_CONVERT_TO_TYPE (tree @var{type}, tree @var{expr}) +If defined, this hook returns the result of converting @var{expr} to +@var{type}. It should return the converted expression, +or @code{NULL_TREE} to apply the front end's normal conversion rules. +This hook is useful when there are target-specific types with special +conversion rules. +This is currently used only by the C and C++ front ends. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_VERIFY_TYPE_CONTEXT (location_t @var{loc}, type_context_kind @var{context}, const_tree @var{type}, bool @var{silent_p}) +If defined, this hook returns false if there is a target-specific reason +why type @var{type} cannot be used in the source language context described +by @var{context}. When @var{silent_p} is false, the hook also reports an +error against @var{loc} for invalid uses of @var{type}. + +Calls to this hook should be made through the global function +@code{verify_type_context}, which makes the @var{silent_p} parameter +default to false and also handles @code{error_mark_node}. + +The default implementation always returns true. +@end deftypefn + +@defmac OBJC_JBLEN +This macro determines the size of the objective C jump buffer for the +NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value. +@end defmac + +@defmac LIBGCC2_UNWIND_ATTRIBUTE +Define this macro if any target-specific attributes need to be attached +to the functions in @file{libgcc} that provide low-level support for +call stack unwinding. It is used in declarations in @file{unwind-generic.h} +and the associated definitions of those functions. +@end defmac + +@deftypefn {Target Hook} void TARGET_UPDATE_STACK_BOUNDARY (void) +Define this macro to update the current function stack boundary if +necessary. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_GET_DRAP_RTX (void) +This hook should return an rtx for Dynamic Realign Argument Pointer (DRAP) if a +different argument pointer register is needed to access the function's +argument list due to stack realignment. Return @code{NULL} if no DRAP +is needed. +@end deftypefn + +@deftypefn {Target Hook} HARD_REG_SET TARGET_ZERO_CALL_USED_REGS (HARD_REG_SET @var{selected_regs}) +This target hook emits instructions to zero the subset of @var{selected_regs} +that could conceivably contain values that are useful to an attacker. +Return the set of registers that were actually cleared. + +For most targets, the returned set of registers is a subset of +@var{selected_regs}, however, for some of the targets (for example MIPS), +clearing some registers that are in the @var{selected_regs} requires +clearing other call used registers that are not in the @var{selected_regs}, +under such situation, the returned set of registers must be a subset of all +call used registers. + +The default implementation uses normal move instructions to zero +all the registers in @var{selected_regs}. Define this hook if the +target has more efficient ways of zeroing certain registers, +or if you believe that certain registers would never contain +values that are useful to an attacker. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS (void) +When optimization is disabled, this hook indicates whether or not +arguments should be allocated to stack slots. Normally, GCC allocates +stacks slots for arguments when not optimizing in order to make +debugging easier. However, when a function is declared with +@code{__attribute__((naked))}, there is no stack frame, and the compiler +cannot safely move arguments from the registers in which they are passed +to the stack. Therefore, this hook should return true in general, but +false for naked functions. The default implementation always returns true. +@end deftypefn + +@deftypevr {Target Hook} {unsigned HOST_WIDE_INT} TARGET_CONST_ANCHOR +On some architectures it can take multiple instructions to synthesize +a constant. If there is another constant already in a register that +is close enough in value then it is preferable that the new constant +is computed from this register using immediate addition or +subtraction. We accomplish this through CSE. Besides the value of +the constant we also add a lower and an upper constant anchor to the +available expressions. These are then queried when encountering new +constants. The anchors are computed by rounding the constant up and +down to a multiple of the value of @code{TARGET_CONST_ANCHOR}. +@code{TARGET_CONST_ANCHOR} should be the maximum positive value +accepted by immediate-add plus one. We currently assume that the +value of @code{TARGET_CONST_ANCHOR} is a power of 2. For example, on +MIPS, where add-immediate takes a 16-bit signed value, +@code{TARGET_CONST_ANCHOR} is set to @samp{0x8000}. The default value +is zero, which disables this optimization. +@end deftypevr + +@deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_ASAN_SHADOW_OFFSET (void) +Return the offset bitwise ored into shifted address to get corresponding +Address Sanitizer shadow memory address. NULL if Address Sanitizer is not +supported by the target. May return 0 if Address Sanitizer is not supported +by a subtarget. +@end deftypefn + +@deftypefn {Target Hook} {unsigned HOST_WIDE_INT} TARGET_MEMMODEL_CHECK (unsigned HOST_WIDE_INT @var{val}) +Validate target specific memory model mask bits. When NULL no target specific +memory model bits are allowed. +@end deftypefn + +@deftypevr {Target Hook} {unsigned char} TARGET_ATOMIC_TEST_AND_SET_TRUEVAL +This value should be set if the result written by +@code{atomic_test_and_set} is not exactly 1, i.e.@: the +@code{bool} @code{true}. +@end deftypevr + +@deftypefn {Target Hook} bool TARGET_HAS_IFUNC_P (void) +It returns true if the target supports GNU indirect functions. +The support includes the assembler, linker and dynamic linker. +The default value of this hook is based on target's libc. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_IFUNC_REF_LOCAL_OK (void) +Return true if it is OK to reference indirect function resolvers +locally. The default is to return false. +@end deftypefn + +@deftypefn {Target Hook} {unsigned int} TARGET_ATOMIC_ALIGN_FOR_MODE (machine_mode @var{mode}) +If defined, this function returns an appropriate alignment in bits for an +atomic object of machine_mode @var{mode}. If 0 is returned then the +default alignment for the specified mode is used. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_ATOMIC_ASSIGN_EXPAND_FENV (tree *@var{hold}, tree *@var{clear}, tree *@var{update}) +ISO C11 requires atomic compound assignments that may raise floating-point +exceptions to raise exceptions corresponding to the arithmetic operation +whose result was successfully stored in a compare-and-exchange sequence. +This requires code equivalent to calls to @code{feholdexcept}, +@code{feclearexcept} and @code{feupdateenv} to be generated at +appropriate points in the compare-and-exchange sequence. This hook should +set @code{*@var{hold}} to an expression equivalent to the call to +@code{feholdexcept}, @code{*@var{clear}} to an expression equivalent to +the call to @code{feclearexcept} and @code{*@var{update}} to an expression +equivalent to the call to @code{feupdateenv}. The three expressions are +@code{NULL_TREE} on entry to the hook and may be left as @code{NULL_TREE} +if no code is required in a particular place. The default implementation +leaves all three expressions as @code{NULL_TREE}. The +@code{__atomic_feraiseexcept} function from @code{libatomic} may be of use +as part of the code generated in @code{*@var{update}}. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_RECORD_OFFLOAD_SYMBOL (tree) +Used when offloaded functions are seen in the compilation unit and no named +sections are available. It is called once for each symbol that must be +recorded in the offload function and variable table. +@end deftypefn + +@deftypefn {Target Hook} {char *} TARGET_OFFLOAD_OPTIONS (void) +Used when writing out the list of options into an LTO file. It should +translate any relevant target-specific options (such as the ABI in use) +into one of the @option{-foffload} options that exist as a common interface +to express such options. It should return a string containing these options, +separated by spaces, which the caller will free. + +@end deftypefn + +@defmac TARGET_SUPPORTS_WIDE_INT + +On older ports, large integers are stored in @code{CONST_DOUBLE} rtl +objects. Newer ports define @code{TARGET_SUPPORTS_WIDE_INT} to be nonzero +to indicate that large integers are stored in +@code{CONST_WIDE_INT} rtl objects. The @code{CONST_WIDE_INT} allows +very large integer constants to be represented. @code{CONST_DOUBLE} +is limited to twice the size of the host's @code{HOST_WIDE_INT} +representation. + +Converting a port mostly requires looking for the places where +@code{CONST_DOUBLE}s are used with @code{VOIDmode} and replacing that +code with code that accesses @code{CONST_WIDE_INT}s. @samp{"grep -i +const_double"} at the port level gets you to 95% of the changes that +need to be made. There are a few places that require a deeper look. + +@itemize @bullet +@item +There is no equivalent to @code{hval} and @code{lval} for +@code{CONST_WIDE_INT}s. This would be difficult to express in the md +language since there are a variable number of elements. + +Most ports only check that @code{hval} is either 0 or -1 to see if the +value is small. As mentioned above, this will no longer be necessary +since small constants are always @code{CONST_INT}. Of course there +are still a few exceptions, the alpha's constraint used by the zap +instruction certainly requires careful examination by C code. +However, all the current code does is pass the hval and lval to C +code, so evolving the c code to look at the @code{CONST_WIDE_INT} is +not really a large change. + +@item +Because there is no standard template that ports use to materialize +constants, there is likely to be some futzing that is unique to each +port in this code. + +@item +The rtx costs may have to be adjusted to properly account for larger +constants that are represented as @code{CONST_WIDE_INT}. +@end itemize + +All and all it does not take long to convert ports that the +maintainer is familiar with. + +@end defmac + +@deftypefn {Target Hook} bool TARGET_HAVE_SPECULATION_SAFE_VALUE (bool @var{active}) +This hook is used to determine the level of target support for + @code{__builtin_speculation_safe_value}. If called with an argument + of false, it returns true if the target has been modified to support + this builtin. If called with an argument of true, it returns true + if the target requires active mitigation execution might be speculative. + + The default implementation returns false if the target does not define + a pattern named @code{speculation_barrier}. Else it returns true + for the first case and whether the pattern is enabled for the current + compilation for the second case. + + For targets that have no processors that can execute instructions + speculatively an alternative implemenation of this hook is available: + simply redefine this hook to @code{speculation_safe_value_not_needed} + along with your other target hooks. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_SPECULATION_SAFE_VALUE (machine_mode @var{mode}, rtx @var{result}, rtx @var{val}, rtx @var{failval}) +This target hook can be used to generate a target-specific code + sequence that implements the @code{__builtin_speculation_safe_value} + built-in function. The function must always return @var{val} in + @var{result} in mode @var{mode} when the cpu is not executing + speculatively, but must never return that when speculating until it + is known that the speculation will not be unwound. The hook supports + two primary mechanisms for implementing the requirements. The first + is to emit a speculation barrier which forces the processor to wait + until all prior speculative operations have been resolved; the second + is to use a target-specific mechanism that can track the speculation + state and to return @var{failval} if it can determine that + speculation must be unwound at a later time. + + The default implementation simply copies @var{val} to @var{result} and + emits a @code{speculation_barrier} instruction if that is defined. +@end deftypefn + +@deftypefn {Target Hook} void TARGET_RUN_TARGET_SELFTESTS (void) +If selftests are enabled, run any selftests for this target. +@end deftypefn + +@deftypefn {Target Hook} bool TARGET_MEMTAG_CAN_TAG_ADDRESSES () +True if the backend architecture naturally supports ignoring some region +of pointers. This feature means that @option{-fsanitize=hwaddress} can +work. + +At preset, this feature does not support address spaces. It also requires +@code{Pmode} to be the same as @code{ptr_mode}. +@end deftypefn + +@deftypefn {Target Hook} uint8_t TARGET_MEMTAG_TAG_SIZE () +Return the size of a tag (in bits) for this platform. + +The default returns 8. +@end deftypefn + +@deftypefn {Target Hook} uint8_t TARGET_MEMTAG_GRANULE_SIZE () +Return the size in real memory that each byte in shadow memory refers to. +I.e. if a variable is @var{X} bytes long in memory, then this hook should +return the value @var{Y} such that the tag in shadow memory spans +@var{X}/@var{Y} bytes. + +Most variables will need to be aligned to this amount since two variables +that are neighbors in memory and share a tag granule would need to share +the same tag. + +The default returns 16. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_MEMTAG_INSERT_RANDOM_TAG (rtx @var{untagged}, rtx @var{target}) +Return an RTX representing the value of @var{untagged} but with a +(possibly) random tag in it. +Put that value into @var{target} if it is convenient to do so. +This function is used to generate a tagged base for the current stack frame. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_MEMTAG_ADD_TAG (rtx @var{base}, poly_int64 @var{addr_offset}, uint8_t @var{tag_offset}) +Return an RTX that represents the result of adding @var{addr_offset} to +the address in pointer @var{base} and @var{tag_offset} to the tag in pointer +@var{base}. +The resulting RTX must either be a valid memory address or be able to get +put into an operand with @code{force_operand}. + +Unlike other memtag hooks, this must return an expression and not emit any +RTL. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_MEMTAG_SET_TAG (rtx @var{untagged_base}, rtx @var{tag}, rtx @var{target}) +Return an RTX representing @var{untagged_base} but with the tag @var{tag}. +Try and store this in @var{target} if convenient. +@var{untagged_base} is required to have a zero tag when this hook is called. +The default of this hook is to set the top byte of @var{untagged_base} to +@var{tag}. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_MEMTAG_EXTRACT_TAG (rtx @var{tagged_pointer}, rtx @var{target}) +Return an RTX representing the tag stored in @var{tagged_pointer}. +Store the result in @var{target} if it is convenient. +The default represents the top byte of the original pointer. +@end deftypefn + +@deftypefn {Target Hook} rtx TARGET_MEMTAG_UNTAGGED_POINTER (rtx @var{tagged_pointer}, rtx @var{target}) +Return an RTX representing @var{tagged_pointer} with its tag set to zero. +Store the result in @var{target} if convenient. +The default clears the top byte of the original pointer. +@end deftypefn + +@deftypefn {Target Hook} HOST_WIDE_INT TARGET_GCOV_TYPE_SIZE (void) +Returns the gcov type size in bits. This type is used for example for +counters incremented by profiling and code-coverage events. The default +value is 64, if the type size of long long is greater than 32, otherwise the +default value is 32. A 64-bit type is recommended to avoid overflows of the +counters. If the @option{-fprofile-update=atomic} is used, then the +counters are incremented using atomic operations. Targets not supporting +64-bit atomic operations may override the default value and request a 32-bit +type. +@end deftypefn + +@deftypevr {Target Hook} bool TARGET_HAVE_SHADOW_CALL_STACK +This value is true if the target platform supports +@option{-fsanitize=shadow-call-stack}. The default value is false. +@end deftypevr diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in new file mode 100644 index 00000000000..986e8f0da09 --- /dev/null +++ b/gcc/doc/tm.texi.in @@ -0,0 +1,7984 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Target Macros +@chapter Target Description Macros and Functions +@cindex machine description macros +@cindex target description macros +@cindex macros, target description +@cindex @file{tm.h} macros + +In addition to the file @file{@var{machine}.md}, a machine description +includes a C header file conventionally given the name +@file{@var{machine}.h} and a C source file named @file{@var{machine}.c}. +The header file defines numerous macros that convey the information +about the target machine that does not fit into the scheme of the +@file{.md} file. The file @file{tm.h} should be a link to +@file{@var{machine}.h}. The header file @file{config.h} includes +@file{tm.h} and most compiler source files include @file{config.h}. The +source file defines a variable @code{targetm}, which is a structure +containing pointers to functions and data relating to the target +machine. @file{@var{machine}.c} should also contain their definitions, +if they are not defined elsewhere in GCC, and other functions called +through the macros defined in the @file{.h} file. + +@menu +* Target Structure:: The @code{targetm} variable. +* Driver:: Controlling how the driver runs the compilation passes. +* Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}. +* Per-Function Data:: Defining data structures for per-function information. +* Storage Layout:: Defining sizes and alignments of data. +* Type Layout:: Defining sizes and properties of basic user data types. +* Registers:: Naming and describing the hardware registers. +* Register Classes:: Defining the classes of hardware registers. +* Stack and Calling:: Defining which way the stack grows and by how much. +* Varargs:: Defining the varargs macros. +* Trampolines:: Code set up at run time to enter a nested function. +* Library Calls:: Controlling how library routines are implicitly called. +* Addressing Modes:: Defining addressing modes valid for memory operands. +* Anchored Addresses:: Defining how @option{-fsection-anchors} should work. +* Condition Code:: Defining how insns update the condition code. +* Costs:: Defining relative costs of different operations. +* Scheduling:: Adjusting the behavior of the instruction scheduler. +* Sections:: Dividing storage into text, data, and other sections. +* PIC:: Macros for position independent code. +* Assembler Format:: Defining how to write insns and pseudo-ops to output. +* Debugging Info:: Defining the format of debugging output. +* Floating Point:: Handling floating point for cross-compilers. +* Mode Switching:: Insertion of mode-switching instructions. +* Target Attributes:: Defining target-specific uses of @code{__attribute__}. +* Emulated TLS:: Emulated TLS support. +* MIPS Coprocessors:: MIPS coprocessor support and how to customize it. +* PCH Target:: Validity checking for precompiled headers. +* C++ ABI:: Controlling C++ ABI changes. +* D Language and ABI:: Controlling D ABI changes. +* Named Address Spaces:: Adding support for named address spaces +* Misc:: Everything else. +@end menu + +@node Target Structure +@section The Global @code{targetm} Variable +@cindex target hooks +@cindex target functions + +@deftypevar {struct gcc_target} targetm +The target @file{.c} file must define the global @code{targetm} variable +which contains pointers to functions and data relating to the target +machine. The variable is declared in @file{target.h}; +@file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is +used to initialize the variable, and macros for the default initializers +for elements of the structure. The @file{.c} file should override those +macros for which the default definition is inappropriate. For example: +@smallexample +#include "target.h" +#include "target-def.h" + +/* @r{Initialize the GCC target structure.} */ + +#undef TARGET_COMP_TYPE_ATTRIBUTES +#define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes + +struct gcc_target targetm = TARGET_INITIALIZER; +@end smallexample +@end deftypevar + +Where a macro should be defined in the @file{.c} file in this manner to +form part of the @code{targetm} structure, it is documented below as a +``Target Hook'' with a prototype. Many macros will change in future +from being defined in the @file{.h} file to being part of the +@code{targetm} structure. + +Similarly, there is a @code{targetcm} variable for hooks that are +specific to front ends for C-family languages, documented as ``C +Target Hook''. This is declared in @file{c-family/c-target.h}, the +initializer @code{TARGETCM_INITIALIZER} in +@file{c-family/c-target-def.h}. If targets initialize @code{targetcm} +themselves, they should set @code{target_has_targetcm=yes} in +@file{config.gcc}; otherwise a default definition is used. + +Similarly, there is a @code{targetm_common} variable for hooks that +are shared between the compiler driver and the compilers proper, +documented as ``Common Target Hook''. This is declared in +@file{common/common-target.h}, the initializer +@code{TARGETM_COMMON_INITIALIZER} in +@file{common/common-target-def.h}. If targets initialize +@code{targetm_common} themselves, they should set +@code{target_has_targetm_common=yes} in @file{config.gcc}; otherwise a +default definition is used. + +Similarly, there is a @code{targetdm} variable for hooks that are +specific to the D language front end, documented as ``D Target Hook''. +This is declared in @file{d/d-target.h}, the initializer +@code{TARGETDM_INITIALIZER} in @file{d/d-target-def.h}. If targets +initialize @code{targetdm} themselves, they should set +@code{target_has_targetdm=yes} in @file{config.gcc}; otherwise a default +definition is used. + +@node Driver +@section Controlling the Compilation Driver, @file{gcc} +@cindex driver +@cindex controlling the compilation driver + +@c prevent bad page break with this line +You can control the compilation driver. + +@defmac DRIVER_SELF_SPECS +A list of specs for the driver itself. It should be a suitable +initializer for an array of strings, with no surrounding braces. + +The driver applies these specs to its own command line between loading +default @file{specs} files (but not command-line specified ones) and +choosing the multilib directory or running any subcommands. It +applies them in the order given, so each spec can depend on the +options added by earlier ones. It is also possible to remove options +using @samp{%<@var{option}} in the usual way. + +This macro can be useful when a port has several interdependent target +options. It provides a way of standardizing the command line so +that the other specs are easier to write. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac OPTION_DEFAULT_SPECS +A list of specs used to support configure-time default options (i.e.@: +@option{--with} options) in the driver. It should be a suitable initializer +for an array of structures, each containing two strings, without the +outermost pair of surrounding braces. + +The first item in the pair is the name of the default. This must match +the code in @file{config.gcc} for the target. The second item is a spec +to apply if a default with this name was specified. The string +@samp{%(VALUE)} in the spec will be replaced by the value of the default +everywhere it occurs. + +The driver will apply these specs to its own command line between loading +default @file{specs} files and processing @code{DRIVER_SELF_SPECS}, using +the same mechanism as @code{DRIVER_SELF_SPECS}. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CPP_SPEC +A C string constant that tells the GCC driver program options to +pass to CPP@. It can also specify how to translate options you +give to GCC into options for GCC to pass to the CPP@. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CPLUSPLUS_CPP_SPEC +This macro is just like @code{CPP_SPEC}, but is used for C++, rather +than C@. If you do not define this macro, then the value of +@code{CPP_SPEC} (if any) will be used instead. +@end defmac + +@defmac CC1_SPEC +A C string constant that tells the GCC driver program options to +pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language +front ends. +It can also specify how to translate options you give to GCC into options +for GCC to pass to front ends. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac CC1PLUS_SPEC +A C string constant that tells the GCC driver program options to +pass to @code{cc1plus}. It can also specify how to translate options you +give to GCC into options for GCC to pass to the @code{cc1plus}. + +Do not define this macro if it does not need to do anything. +Note that everything defined in CC1_SPEC is already passed to +@code{cc1plus} so there is no need to duplicate the contents of +CC1_SPEC in CC1PLUS_SPEC@. +@end defmac + +@defmac ASM_SPEC +A C string constant that tells the GCC driver program options to +pass to the assembler. It can also specify how to translate options +you give to GCC into options for GCC to pass to the assembler. +See the file @file{sun3.h} for an example of this. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac ASM_FINAL_SPEC +A C string constant that tells the GCC driver program how to +run any programs which cleanup after the normal assembler. +Normally, this is not needed. See the file @file{mips.h} for +an example of this. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac AS_NEEDS_DASH_FOR_PIPED_INPUT +Define this macro, with no value, if the driver should give the assembler +an argument consisting of a single dash, @option{-}, to instruct it to +read from its standard input (which will be a pipe connected to the +output of the compiler proper). This argument is given after any +@option{-o} option specifying the name of the output file. + +If you do not define this macro, the assembler is assumed to read its +standard input if given no non-option arguments. If your assembler +cannot read standard input at all, use a @samp{%@{pipe:%e@}} construct; +see @file{mips.h} for instance. +@end defmac + +@defmac LINK_SPEC +A C string constant that tells the GCC driver program options to +pass to the linker. It can also specify how to translate options you +give to GCC into options for GCC to pass to the linker. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac LIB_SPEC +Another C string constant used much like @code{LINK_SPEC}. The difference +between the two is that @code{LIB_SPEC} is used at the end of the +command given to the linker. + +If this macro is not defined, a default is provided that +loads the standard C library from the usual place. See @file{gcc.cc}. +@end defmac + +@defmac LIBGCC_SPEC +Another C string constant that tells the GCC driver program +how and when to place a reference to @file{libgcc.a} into the +linker command line. This constant is placed both before and after +the value of @code{LIB_SPEC}. + +If this macro is not defined, the GCC driver provides a default that +passes the string @option{-lgcc} to the linker. +@end defmac + +@defmac REAL_LIBGCC_SPEC +By default, if @code{ENABLE_SHARED_LIBGCC} is defined, the +@code{LIBGCC_SPEC} is not directly used by the driver program but is +instead modified to refer to different versions of @file{libgcc.a} +depending on the values of the command line flags @option{-static}, +@option{-shared}, @option{-static-libgcc}, and @option{-shared-libgcc}. On +targets where these modifications are inappropriate, define +@code{REAL_LIBGCC_SPEC} instead. @code{REAL_LIBGCC_SPEC} tells the +driver how to place a reference to @file{libgcc} on the link command +line, but, unlike @code{LIBGCC_SPEC}, it is used unmodified. +@end defmac + +@defmac USE_LD_AS_NEEDED +A macro that controls the modifications to @code{LIBGCC_SPEC} +mentioned in @code{REAL_LIBGCC_SPEC}. If nonzero, a spec will be +generated that uses @option{--as-needed} or equivalent options and the +shared @file{libgcc} in place of the +static exception handler library, when linking without any of +@code{-static}, @code{-static-libgcc}, or @code{-shared-libgcc}. +@end defmac + +@defmac LINK_EH_SPEC +If defined, this C string constant is added to @code{LINK_SPEC}. +When @code{USE_LD_AS_NEEDED} is zero or undefined, it also affects +the modifications to @code{LIBGCC_SPEC} mentioned in +@code{REAL_LIBGCC_SPEC}. +@end defmac + +@defmac STARTFILE_SPEC +Another C string constant used much like @code{LINK_SPEC}. The +difference between the two is that @code{STARTFILE_SPEC} is used at +the very beginning of the command given to the linker. + +If this macro is not defined, a default is provided that loads the +standard C startup file from the usual place. See @file{gcc.cc}. +@end defmac + +@defmac ENDFILE_SPEC +Another C string constant used much like @code{LINK_SPEC}. The +difference between the two is that @code{ENDFILE_SPEC} is used at +the very end of the command given to the linker. + +Do not define this macro if it does not need to do anything. +@end defmac + +@defmac THREAD_MODEL_SPEC +GCC @code{-v} will print the thread model GCC was configured to use. +However, this doesn't work on platforms that are multilibbed on thread +models, such as AIX 4.3. On such platforms, define +@code{THREAD_MODEL_SPEC} such that it evaluates to a string without +blanks that names one of the recognized thread models. @code{%*}, the +default value of this macro, will expand to the value of +@code{thread_file} set in @file{config.gcc}. +@end defmac + +@defmac SYSROOT_SUFFIX_SPEC +Define this macro to add a suffix to the target sysroot when GCC is +configured with a sysroot. This will cause GCC to search for usr/lib, +et al, within sysroot+suffix. +@end defmac + +@defmac SYSROOT_HEADERS_SUFFIX_SPEC +Define this macro to add a headers_suffix to the target sysroot when +GCC is configured with a sysroot. This will cause GCC to pass the +updated sysroot+headers_suffix to CPP, causing it to search for +usr/include, et al, within sysroot+headers_suffix. +@end defmac + +@defmac EXTRA_SPECS +Define this macro to provide additional specifications to put in the +@file{specs} file that can be used in various specifications like +@code{CC1_SPEC}. + +The definition should be an initializer for an array of structures, +containing a string constant, that defines the specification name, and a +string constant that provides the specification. + +Do not define this macro if it does not need to do anything. + +@code{EXTRA_SPECS} is useful when an architecture contains several +related targets, which have various @code{@dots{}_SPECS} which are similar +to each other, and the maintainer would like one central place to keep +these definitions. + +For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to +define either @code{_CALL_SYSV} when the System V calling sequence is +used or @code{_CALL_AIX} when the older AIX-based calling sequence is +used. + +The @file{config/rs6000/rs6000.h} target file defines: + +@smallexample +#define EXTRA_SPECS \ + @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @}, + +#define CPP_SYS_DEFAULT "" +@end smallexample + +The @file{config/rs6000/sysv.h} target file defines: +@smallexample +#undef CPP_SPEC +#define CPP_SPEC \ +"%@{posix: -D_POSIX_SOURCE @} \ +%@{mcall-sysv: -D_CALL_SYSV @} \ +%@{!mcall-sysv: %(cpp_sysv_default) @} \ +%@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}" + +#undef CPP_SYSV_DEFAULT +#define CPP_SYSV_DEFAULT "-D_CALL_SYSV" +@end smallexample + +while the @file{config/rs6000/eabiaix.h} target file defines +@code{CPP_SYSV_DEFAULT} as: + +@smallexample +#undef CPP_SYSV_DEFAULT +#define CPP_SYSV_DEFAULT "-D_CALL_AIX" +@end smallexample +@end defmac + +@defmac LINK_LIBGCC_SPECIAL_1 +Define this macro if the driver program should find the library +@file{libgcc.a}. If you do not define this macro, the driver program will pass +the argument @option{-lgcc} to tell the linker to do the search. +@end defmac + +@defmac LINK_GCC_C_SEQUENCE_SPEC +The sequence in which libgcc and libc are specified to the linker. +By default this is @code{%G %L %G}. +@end defmac + +@defmac POST_LINK_SPEC +Define this macro to add additional steps to be executed after linker. +The default value of this macro is empty string. +@end defmac + +@defmac LINK_COMMAND_SPEC +A C string constant giving the complete command line need to execute the +linker. When you do this, you will need to update your port each time a +change is made to the link command line within @file{gcc.cc}. Therefore, +define this macro only if you need to completely redefine the command +line for invoking the linker and there is no other way to accomplish +the effect you need. Overriding this macro may be avoidable by overriding +@code{LINK_GCC_C_SEQUENCE_SPEC} instead. +@end defmac + +@hook TARGET_ALWAYS_STRIP_DOTDOT + +@defmac MULTILIB_DEFAULTS +Define this macro as a C expression for the initializer of an array of +string to tell the driver program which options are defaults for this +target and thus do not need to be handled specially when using +@code{MULTILIB_OPTIONS}. + +Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in +the target makefile fragment or if none of the options listed in +@code{MULTILIB_OPTIONS} are set by default. +@xref{Target Fragment}. +@end defmac + +@defmac RELATIVE_PREFIX_NOT_LINKDIR +Define this macro to tell @command{gcc} that it should only translate +a @option{-B} prefix into a @option{-L} linker option if the prefix +indicates an absolute file name. +@end defmac + +@defmac MD_EXEC_PREFIX +If defined, this macro is an additional prefix to try after +@code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched +when the compiler is built as a cross +compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it +to the list of directories used to find the assembler in @file{configure.ac}. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX +Define this macro as a C string constant if you wish to override the +standard choice of @code{libdir} as the default prefix to +try when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX_1 +Define this macro as a C string constant if you wish to override the +standard choice of @code{/lib} as a prefix to try after the default prefix +when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX_1} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac STANDARD_STARTFILE_PREFIX_2 +Define this macro as a C string constant if you wish to override the +standard choice of @code{/lib} as yet another prefix to try after the +default prefix when searching for startup files such as @file{crt0.o}. +@code{STANDARD_STARTFILE_PREFIX_2} is not searched when the compiler +is built as a cross compiler. +@end defmac + +@defmac MD_STARTFILE_PREFIX +If defined, this macro supplies an additional prefix to try after the +standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the +compiler is built as a cross compiler. +@end defmac + +@defmac MD_STARTFILE_PREFIX_1 +If defined, this macro supplies yet another prefix to try after the +standard prefixes. It is not searched when the compiler is built as a +cross compiler. +@end defmac + +@defmac INIT_ENVIRONMENT +Define this macro as a C string constant if you wish to set environment +variables for programs called by the driver, such as the assembler and +loader. The driver passes the value of this macro to @code{putenv} to +initialize the necessary environment variables. +@end defmac + +@defmac LOCAL_INCLUDE_DIR +Define this macro as a C string constant if you wish to override the +standard choice of @file{/usr/local/include} as the default prefix to +try when searching for local header files. @code{LOCAL_INCLUDE_DIR} +comes before @code{NATIVE_SYSTEM_HEADER_DIR} (set in +@file{config.gcc}, normally @file{/usr/include}) in the search order. + +Cross compilers do not search either @file{/usr/local/include} or its +replacement. +@end defmac + +@defmac NATIVE_SYSTEM_HEADER_COMPONENT +The ``component'' corresponding to @code{NATIVE_SYSTEM_HEADER_DIR}. +See @code{INCLUDE_DEFAULTS}, below, for the description of components. +If you do not define this macro, no component is used. +@end defmac + +@defmac INCLUDE_DEFAULTS +Define this macro if you wish to override the entire default search path +for include files. For a native compiler, the default search path +usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR}, +@code{GPLUSPLUS_INCLUDE_DIR}, and +@code{NATIVE_SYSTEM_HEADER_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR} +and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile}, +and specify private search areas for GCC@. The directory +@code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs. + +The definition should be an initializer for an array of structures. +Each array element should have four elements: the directory name (a +string constant), the component name (also a string constant), a flag +for C++-only directories, +and a flag showing that the includes in the directory don't need to be +wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of +the array with a null element. + +The component name denotes what GNU package the include file is part of, +if any, in all uppercase letters. For example, it might be @samp{GCC} +or @samp{BINUTILS}. If the package is part of a vendor-supplied +operating system, code the component name as @samp{0}. + +For example, here is the definition used for VAX/VMS: + +@smallexample +#define INCLUDE_DEFAULTS \ +@{ \ + @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \ + @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \ + @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \ + @{ ".", 0, 0, 0@}, \ + @{ 0, 0, 0, 0@} \ +@} +@end smallexample +@end defmac + +Here is the order of prefixes tried for exec files: + +@enumerate +@item +Any prefixes specified by the user with @option{-B}. + +@item +The environment variable @code{GCC_EXEC_PREFIX} or, if @code{GCC_EXEC_PREFIX} +is not set and the compiler has not been installed in the configure-time +@var{prefix}, the location in which the compiler has actually been installed. + +@item +The directories specified by the environment variable @code{COMPILER_PATH}. + +@item +The macro @code{STANDARD_EXEC_PREFIX}, if the compiler has been installed +in the configured-time @var{prefix}. + +@item +The location @file{/usr/libexec/gcc/}, but only if this is a native compiler. + +@item +The location @file{/usr/lib/gcc/}, but only if this is a native compiler. + +@item +The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native +compiler. +@end enumerate + +Here is the order of prefixes tried for startfiles: + +@enumerate +@item +Any prefixes specified by the user with @option{-B}. + +@item +The environment variable @code{GCC_EXEC_PREFIX} or its automatically determined +value based on the installed toolchain location. + +@item +The directories specified by the environment variable @code{LIBRARY_PATH} +(or port-specific name; native only, cross compilers do not use this). + +@item +The macro @code{STANDARD_EXEC_PREFIX}, but only if the toolchain is installed +in the configured @var{prefix} or this is a native compiler. + +@item +The location @file{/usr/lib/gcc/}, but only if this is a native compiler. + +@item +The macro @code{MD_EXEC_PREFIX}, if defined, but only if this is a native +compiler. + +@item +The macro @code{MD_STARTFILE_PREFIX}, if defined, but only if this is a +native compiler, or we have a target system root. + +@item +The macro @code{MD_STARTFILE_PREFIX_1}, if defined, but only if this is a +native compiler, or we have a target system root. + +@item +The macro @code{STANDARD_STARTFILE_PREFIX}, with any sysroot modifications. +If this path is relative it will be prefixed by @code{GCC_EXEC_PREFIX} and +the machine suffix or @code{STANDARD_EXEC_PREFIX} and the machine suffix. + +@item +The macro @code{STANDARD_STARTFILE_PREFIX_1}, but only if this is a native +compiler, or we have a target system root. The default for this macro is +@file{/lib/}. + +@item +The macro @code{STANDARD_STARTFILE_PREFIX_2}, but only if this is a native +compiler, or we have a target system root. The default for this macro is +@file{/usr/lib/}. +@end enumerate + +@node Run-time Target +@section Run-time Target Specification +@cindex run-time target specification +@cindex predefined macros +@cindex target specifications + +@c prevent bad page break with this line +Here are run-time target specifications. + +@defmac TARGET_CPU_CPP_BUILTINS () +This function-like macro expands to a block of code that defines +built-in preprocessor macros and assertions for the target CPU, using +the functions @code{builtin_define}, @code{builtin_define_std} and +@code{builtin_assert}. When the front end +calls this macro it provides a trailing semicolon, and since it has +finished command line option processing your code can use those +results freely. + +@code{builtin_assert} takes a string in the form you pass to the +command-line option @option{-A}, such as @code{cpu=mips}, and creates +the assertion. @code{builtin_define} takes a string in the form +accepted by option @option{-D} and unconditionally defines the macro. + +@code{builtin_define_std} takes a string representing the name of an +object-like macro. If it doesn't lie in the user's namespace, +@code{builtin_define_std} defines it unconditionally. Otherwise, it +defines a version with two leading underscores, and another version +with two leading and trailing underscores, and defines the original +only if an ISO standard was not requested on the command line. For +example, passing @code{unix} defines @code{__unix}, @code{__unix__} +and possibly @code{unix}; passing @code{_mips} defines @code{__mips}, +@code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64} +defines only @code{_ABI64}. + +You can also test for the C dialect being compiled. The variable +@code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus} +or @code{clk_objective_c}. Note that if we are preprocessing +assembler, this variable will be @code{clk_c} but the function-like +macro @code{preprocessing_asm_p()} will return true, so you might want +to check for that first. If you need to check for strict ANSI, the +variable @code{flag_iso} can be used. The function-like macro +@code{preprocessing_trad_p()} can be used to check for traditional +preprocessing. +@end defmac + +@defmac TARGET_OS_CPP_BUILTINS () +Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional +and is used for the target operating system instead. +@end defmac + +@defmac TARGET_OBJFMT_CPP_BUILTINS () +Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional +and is used for the target object format. @file{elfos.h} uses this +macro to define @code{__ELF__}, so you probably do not need to define +it yourself. +@end defmac + +@deftypevar {extern int} target_flags +This variable is declared in @file{options.h}, which is included before +any target-specific headers. +@end deftypevar + +@hook TARGET_DEFAULT_TARGET_FLAGS +This variable specifies the initial value of @code{target_flags}. +Its default setting is 0. +@end deftypevr + +@cindex optional hardware or system features +@cindex features, optional, in system conventions + +@hook TARGET_HANDLE_OPTION +This hook is called whenever the user specifies one of the +target-specific options described by the @file{.opt} definition files +(@pxref{Options}). It has the opportunity to do some option-specific +processing and should return true if the option is valid. The default +definition does nothing but return true. + +@var{decoded} specifies the option and its arguments. @var{opts} and +@var{opts_set} are the @code{gcc_options} structures to be used for +storing option state, and @var{loc} is the location at which the +option was passed (@code{UNKNOWN_LOCATION} except for options passed +via attributes). +@end deftypefn + +@hook TARGET_HANDLE_C_OPTION +This target hook is called whenever the user specifies one of the +target-specific C language family options described by the @file{.opt} +definition files(@pxref{Options}). It has the opportunity to do some +option-specific processing and should return true if the option is +valid. The arguments are like for @code{TARGET_HANDLE_OPTION}. The +default definition does nothing but return false. + +In general, you should use @code{TARGET_HANDLE_OPTION} to handle +options. However, if processing an option requires routines that are +only available in the C (and related language) front ends, then you +should use @code{TARGET_HANDLE_C_OPTION} instead. +@end deftypefn + +@hook TARGET_OBJC_CONSTRUCT_STRING_OBJECT + +@hook TARGET_OBJC_DECLARE_UNRESOLVED_CLASS_REFERENCE + +@hook TARGET_OBJC_DECLARE_CLASS_DEFINITION + +@hook TARGET_STRING_OBJECT_REF_TYPE_P + +@hook TARGET_CHECK_STRING_OBJECT_FORMAT_ARG + +@hook TARGET_OVERRIDE_OPTIONS_AFTER_CHANGE + +@defmac C_COMMON_OVERRIDE_OPTIONS +This is similar to the @code{TARGET_OPTION_OVERRIDE} hook +but is only used in the C +language frontends (C, Objective-C, C++, Objective-C++) and so can be +used to alter option flag variables which only exist in those +frontends. +@end defmac + +@hook TARGET_OPTION_OPTIMIZATION_TABLE +Some machines may desire to change what optimizations are performed for +various optimization levels. This variable, if defined, describes +options to enable at particular sets of optimization levels. These +options are processed once +just after the optimization level is determined and before the remainder +of the command options have been parsed, so may be overridden by other +options passed explicitly. + +This processing is run once at program startup and when the optimization +options are changed via @code{#pragma GCC optimize} or by using the +@code{optimize} attribute. +@end deftypevr + +@hook TARGET_OPTION_INIT_STRUCT + +@hook TARGET_COMPUTE_MULTILIB + + +@defmac SWITCHABLE_TARGET +Some targets need to switch between substantially different subtargets +during compilation. For example, the MIPS target has one subtarget for +the traditional MIPS architecture and another for MIPS16. Source code +can switch between these two subarchitectures using the @code{mips16} +and @code{nomips16} attributes. + +Such subtargets can differ in things like the set of available +registers, the set of available instructions, the costs of various +operations, and so on. GCC caches a lot of this type of information +in global variables, and recomputing them for each subtarget takes a +significant amount of time. The compiler therefore provides a facility +for maintaining several versions of the global variables and quickly +switching between them; see @file{target-globals.h} for details. + +Define this macro to 1 if your target needs this facility. The default +is 0. +@end defmac + +@hook TARGET_FLOAT_EXCEPTIONS_ROUNDING_SUPPORTED_P + +@node Per-Function Data +@section Defining data structures for per-function information. +@cindex per-function data +@cindex data structures + +If the target needs to store information on a per-function basis, GCC +provides a macro and a couple of variables to allow this. Note, just +using statics to store the information is a bad idea, since GCC supports +nested functions, so you can be halfway through encoding one function +when another one comes along. + +GCC defines a data structure called @code{struct function} which +contains all of the data specific to an individual function. This +structure contains a field called @code{machine} whose type is +@code{struct machine_function *}, which can be used by targets to point +to their own specific data. + +If a target needs per-function specific data it should define the type +@code{struct machine_function} and also the macro @code{INIT_EXPANDERS}. +This macro should be used to initialize the function pointer +@code{init_machine_status}. This pointer is explained below. + +One typical use of per-function, target specific data is to create an +RTX to hold the register containing the function's return address. This +RTX can then be used to implement the @code{__builtin_return_address} +function, for level 0. + +Note---earlier implementations of GCC used a single data area to hold +all of the per-function information. Thus when processing of a nested +function began the old per-function data had to be pushed onto a +stack, and when the processing was finished, it had to be popped off the +stack. GCC used to provide function pointers called +@code{save_machine_status} and @code{restore_machine_status} to handle +the saving and restoring of the target specific information. Since the +single data area approach is no longer used, these pointers are no +longer supported. + +@defmac INIT_EXPANDERS +Macro called to initialize any target specific information. This macro +is called once per function, before generation of any RTL has begun. +The intention of this macro is to allow the initialization of the +function pointer @code{init_machine_status}. +@end defmac + +@deftypevar {void (*)(struct function *)} init_machine_status +If this function pointer is non-@code{NULL} it will be called once per +function, before function compilation starts, in order to allow the +target to perform any target specific initialization of the +@code{struct function} structure. It is intended that this would be +used to initialize the @code{machine} of that structure. + +@code{struct machine_function} structures are expected to be freed by GC@. +Generally, any memory that they reference must be allocated by using +GC allocation, including the structure itself. +@end deftypevar + +@node Storage Layout +@section Storage Layout +@cindex storage layout + +Note that the definitions of the macros in this table which are sizes or +alignments measured in bits do not need to be constant. They can be C +expressions that refer to static variables, such as the @code{target_flags}. +@xref{Run-time Target}. + +@defmac BITS_BIG_ENDIAN +Define this macro to have the value 1 if the most significant bit in a +byte has the lowest number; otherwise define it to have the value zero. +This means that bit-field instructions count from the most significant +bit. If the machine has no bit-field instructions, then this must still +be defined, but it doesn't matter which value it is defined to. This +macro need not be a constant. + +This macro does not affect the way structure fields are packed into +bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}. +@end defmac + +@defmac BYTES_BIG_ENDIAN +Define this macro to have the value 1 if the most significant byte in a +word has the lowest number. This macro need not be a constant. +@end defmac + +@defmac WORDS_BIG_ENDIAN +Define this macro to have the value 1 if, in a multiword object, the +most significant word has the lowest number. This applies to both +memory locations and registers; see @code{REG_WORDS_BIG_ENDIAN} if the +order of words in memory is not the same as the order in registers. This +macro need not be a constant. +@end defmac + +@defmac REG_WORDS_BIG_ENDIAN +On some machines, the order of words in a multiword object differs between +registers in memory. In such a situation, define this macro to describe +the order of words in a register. The macro @code{WORDS_BIG_ENDIAN} controls +the order of words in memory. +@end defmac + +@defmac FLOAT_WORDS_BIG_ENDIAN +Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or +@code{TFmode} floating point numbers are stored in memory with the word +containing the sign bit at the lowest address; otherwise define it to +have the value 0. This macro need not be a constant. + +You need not define this macro if the ordering is the same as for +multi-word integers. +@end defmac + +@defmac BITS_PER_WORD +Number of bits in a word. If you do not define this macro, the default +is @code{BITS_PER_UNIT * UNITS_PER_WORD}. +@end defmac + +@defmac MAX_BITS_PER_WORD +Maximum number of bits in a word. If this is undefined, the default is +@code{BITS_PER_WORD}. Otherwise, it is the constant value that is the +largest value that @code{BITS_PER_WORD} can have at run-time. +@end defmac + +@defmac UNITS_PER_WORD +Number of storage units in a word; normally the size of a general-purpose +register, a power of two from 1 or 8. +@end defmac + +@defmac MIN_UNITS_PER_WORD +Minimum number of units in a word. If this is undefined, the default is +@code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the +smallest value that @code{UNITS_PER_WORD} can have at run-time. +@end defmac + +@defmac POINTER_SIZE +Width of a pointer, in bits. You must specify a value no wider than the +width of @code{Pmode}. If it is not equal to the width of @code{Pmode}, +you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify +a value the default is @code{BITS_PER_WORD}. +@end defmac + +@defmac POINTERS_EXTEND_UNSIGNED +A C expression that determines how pointers should be extended from +@code{ptr_mode} to either @code{Pmode} or @code{word_mode}. It is +greater than zero if pointers should be zero-extended, zero if they +should be sign-extended, and negative if some other sort of conversion +is needed. In the last case, the extension is done by the target's +@code{ptr_extend} instruction. + +You need not define this macro if the @code{ptr_mode}, @code{Pmode} +and @code{word_mode} are all the same width. +@end defmac + +@defmac PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type}) +A macro to update @var{m} and @var{unsignedp} when an object whose type +is @var{type} and which has the specified mode and signedness is to be +stored in a register. This macro is only called when @var{type} is a +scalar type. + +On most RISC machines, which only have operations that operate on a full +register, define this macro to set @var{m} to @code{word_mode} if +@var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most +cases, only integer modes should be widened because wider-precision +floating-point operations are usually more expensive than their narrower +counterparts. + +For most machines, the macro definition does not change @var{unsignedp}. +However, some machines, have instructions that preferentially handle +either signed or unsigned quantities of certain modes. For example, on +the DEC Alpha, 32-bit loads from memory and 32-bit add instructions +sign-extend the result to 64 bits. On such machines, set +@var{unsignedp} according to which kind of extension is more efficient. + +Do not define this macro if it would never modify @var{m}. +@end defmac + +@hook TARGET_C_EXCESS_PRECISION +Return a value, with the same meaning as the C99 macro +@code{FLT_EVAL_METHOD} that describes which excess precision should be +applied. + +@hook TARGET_PROMOTE_FUNCTION_MODE + +@defmac PARM_BOUNDARY +Normal alignment required for function parameters on the stack, in +bits. All stack parameters receive at least this much alignment +regardless of data type. On most machines, this is the same as the +size of an integer. +@end defmac + +@defmac STACK_BOUNDARY +Define this macro to the minimum alignment enforced by hardware for the +stack pointer on this machine. The definition is a C expression for the +desired alignment (measured in bits). This value is used as a default +if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines, +this should be the same as @code{PARM_BOUNDARY}. +@end defmac + +@defmac PREFERRED_STACK_BOUNDARY +Define this macro if you wish to preserve a certain alignment for the +stack pointer, greater than what the hardware enforces. The definition +is a C expression for the desired alignment (measured in bits). This +macro must evaluate to a value equal to or larger than +@code{STACK_BOUNDARY}. +@end defmac + +@defmac INCOMING_STACK_BOUNDARY +Define this macro if the incoming stack boundary may be different +from @code{PREFERRED_STACK_BOUNDARY}. This macro must evaluate +to a value equal to or larger than @code{STACK_BOUNDARY}. +@end defmac + +@defmac FUNCTION_BOUNDARY +Alignment required for a function entry point, in bits. +@end defmac + +@defmac BIGGEST_ALIGNMENT +Biggest alignment that any data type can require on this machine, in +bits. Note that this is not the biggest alignment that is supported, +just the biggest alignment that, when violated, may cause a fault. +@end defmac + +@hook TARGET_ABSOLUTE_BIGGEST_ALIGNMENT + +@defmac MALLOC_ABI_ALIGNMENT +Alignment, in bits, a C conformant malloc implementation has to +provide. If not defined, the default value is @code{BITS_PER_WORD}. +@end defmac + +@defmac ATTRIBUTE_ALIGNED_VALUE +Alignment used by the @code{__attribute__ ((aligned))} construct. If +not defined, the default value is @code{BIGGEST_ALIGNMENT}. +@end defmac + +@defmac MINIMUM_ATOMIC_ALIGNMENT +If defined, the smallest alignment, in bits, that can be given to an +object that can be referenced in one operation, without disturbing any +nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger +on machines that don't have byte or half-word store operations. +@end defmac + +@defmac BIGGEST_FIELD_ALIGNMENT +Biggest alignment that any structure or union field can require on this +machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for +structure and union fields only, unless the field alignment has been set +by the @code{__attribute__ ((aligned (@var{n})))} construct. +@end defmac + +@defmac ADJUST_FIELD_ALIGN (@var{field}, @var{type}, @var{computed}) +An expression for the alignment of a structure field @var{field} of +type @var{type} if the alignment computed in the usual way (including +applying of @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the +alignment) is @var{computed}. It overrides alignment only if the +field alignment has not been set by the +@code{__attribute__ ((aligned (@var{n})))} construct. Note that @var{field} +may be @code{NULL_TREE} in case we just query for the minimum alignment +of a field of type @var{type} in structure context. +@end defmac + +@defmac MAX_STACK_ALIGNMENT +Biggest stack alignment guaranteed by the backend. Use this macro +to specify the maximum alignment of a variable on stack. + +If not defined, the default value is @code{STACK_BOUNDARY}. + +@c FIXME: The default should be @code{PREFERRED_STACK_BOUNDARY}. +@c But the fix for PR 32893 indicates that we can only guarantee +@c maximum stack alignment on stack up to @code{STACK_BOUNDARY}, not +@c @code{PREFERRED_STACK_BOUNDARY}, if stack alignment isn't supported. +@end defmac + +@defmac MAX_OFILE_ALIGNMENT +Biggest alignment supported by the object file format of this machine. +Use this macro to limit the alignment which can be specified using the +@code{__attribute__ ((aligned (@var{n})))} construct for functions and +objects with static storage duration. The alignment of automatic +objects may exceed the object file format maximum up to the maximum +supported by GCC. If not defined, the default value is +@code{BIGGEST_ALIGNMENT}. + +On systems that use ELF, the default (in @file{config/elfos.h}) is +the largest supported 32-bit ELF section alignment representable on +a 32-bit host e.g.@: @samp{(((uint64_t) 1 << 28) * 8)}. +On 32-bit ELF the largest supported section alignment in bits is +@samp{(0x80000000 * 8)}, but this is not representable on 32-bit hosts. +@end defmac + +@hook TARGET_LOWER_LOCAL_DECL_ALIGNMENT + +@hook TARGET_STATIC_RTX_ALIGNMENT + +@defmac DATA_ALIGNMENT (@var{type}, @var{basic-align}) +If defined, a C expression to compute the alignment for a variable in +the static store. @var{type} is the data type, and @var{basic-align} is +the alignment that the object would ordinarily have. The value of this +macro is used instead of that alignment to align the object. + +If this macro is not defined, then @var{basic-align} is used. + +@findex strcpy +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. Another is to cause character +arrays to be word-aligned so that @code{strcpy} calls that copy +constants to character arrays can be done inline. +@end defmac + +@defmac DATA_ABI_ALIGNMENT (@var{type}, @var{basic-align}) +Similar to @code{DATA_ALIGNMENT}, but for the cases where the ABI mandates +some alignment increase, instead of optimization only purposes. E.g.@ +AMD x86-64 psABI says that variables with array type larger than 15 bytes +must be aligned to 16 byte boundaries. + +If this macro is not defined, then @var{basic-align} is used. +@end defmac + +@hook TARGET_CONSTANT_ALIGNMENT + +@defmac LOCAL_ALIGNMENT (@var{type}, @var{basic-align}) +If defined, a C expression to compute the alignment for a variable in +the local store. @var{type} is the data type, and @var{basic-align} is +the alignment that the object would ordinarily have. The value of this +macro is used instead of that alignment to align the object. + +If this macro is not defined, then @var{basic-align} is used. + +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. + +If the value of this macro has a type, it should be an unsigned type. +@end defmac + +@hook TARGET_VECTOR_ALIGNMENT + +@defmac STACK_SLOT_ALIGNMENT (@var{type}, @var{mode}, @var{basic-align}) +If defined, a C expression to compute the alignment for stack slot. +@var{type} is the data type, @var{mode} is the widest mode available, +and @var{basic-align} is the alignment that the slot would ordinarily +have. The value of this macro is used instead of that alignment to +align the slot. + +If this macro is not defined, then @var{basic-align} is used when +@var{type} is @code{NULL}. Otherwise, @code{LOCAL_ALIGNMENT} will +be used. + +This macro is to set alignment of stack slot to the maximum alignment +of all possible modes which the slot may have. + +If the value of this macro has a type, it should be an unsigned type. +@end defmac + +@defmac LOCAL_DECL_ALIGNMENT (@var{decl}) +If defined, a C expression to compute the alignment for a local +variable @var{decl}. + +If this macro is not defined, then +@code{LOCAL_ALIGNMENT (TREE_TYPE (@var{decl}), DECL_ALIGN (@var{decl}))} +is used. + +One use of this macro is to increase alignment of medium-size data to +make it all fit in fewer cache lines. + +If the value of this macro has a type, it should be an unsigned type. +@end defmac + +@defmac MINIMUM_ALIGNMENT (@var{exp}, @var{mode}, @var{align}) +If defined, a C expression to compute the minimum required alignment +for dynamic stack realignment purposes for @var{exp} (a type or decl), +@var{mode}, assuming normal alignment @var{align}. + +If this macro is not defined, then @var{align} will be used. +@end defmac + +@defmac EMPTY_FIELD_BOUNDARY +Alignment in bits to be given to a structure bit-field that follows an +empty field such as @code{int : 0;}. + +If @code{PCC_BITFIELD_TYPE_MATTERS} is true, it overrides this macro. +@end defmac + +@defmac STRUCTURE_SIZE_BOUNDARY +Number of bits which any structure or union's size must be a multiple of. +Each structure or union's size is rounded up to a multiple of this. + +If you do not define this macro, the default is the same as +@code{BITS_PER_UNIT}. +@end defmac + +@defmac STRICT_ALIGNMENT +Define this macro to be the value 1 if instructions will fail to work +if given data not on the nominal alignment. If instructions will merely +go slower in that case, define this macro as 0. +@end defmac + +@defmac PCC_BITFIELD_TYPE_MATTERS +Define this if you wish to imitate the way many other C compilers handle +alignment of bit-fields and the structures that contain them. + +The behavior is that the type written for a named bit-field (@code{int}, +@code{short}, or other integer type) imposes an alignment for the entire +structure, as if the structure really did contain an ordinary field of +that type. In addition, the bit-field is placed within the structure so +that it would fit within such a field, not crossing a boundary for it. + +Thus, on most machines, a named bit-field whose type is written as +@code{int} would not cross a four-byte boundary, and would force +four-byte alignment for the whole structure. (The alignment used may +not be four bytes; it is controlled by the other alignment parameters.) + +An unnamed bit-field will not affect the alignment of the containing +structure. + +If the macro is defined, its definition should be a C expression; +a nonzero value for the expression enables this behavior. + +Note that if this macro is not defined, or its value is zero, some +bit-fields may cross more than one alignment boundary. The compiler can +support such references if there are @samp{insv}, @samp{extv}, and +@samp{extzv} insns that can directly reference memory. + +The other known way of making bit-fields work is to define +@code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}. +Then every structure can be accessed with fullwords. + +Unless the machine has bit-field instructions or you define +@code{STRUCTURE_SIZE_BOUNDARY} that way, you must define +@code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value. + +If your aim is to make GCC use the same conventions for laying out +bit-fields as are used by another compiler, here is how to investigate +what the other compiler does. Compile and run this program: + +@smallexample +struct foo1 +@{ + char x; + char :0; + char y; +@}; + +struct foo2 +@{ + char x; + int :0; + char y; +@}; + +main () +@{ + printf ("Size of foo1 is %d\n", + sizeof (struct foo1)); + printf ("Size of foo2 is %d\n", + sizeof (struct foo2)); + exit (0); +@} +@end smallexample + +If this prints 2 and 5, then the compiler's behavior is what you would +get from @code{PCC_BITFIELD_TYPE_MATTERS}. +@end defmac + +@defmac BITFIELD_NBYTES_LIMITED +Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited +to aligning a bit-field within the structure. +@end defmac + +@hook TARGET_ALIGN_ANON_BITFIELD + +@hook TARGET_NARROW_VOLATILE_BITFIELD + +@hook TARGET_MEMBER_TYPE_FORCES_BLK + +@defmac ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified}) +Define this macro as an expression for the alignment of a type (given +by @var{type} as a tree node) if the alignment computed in the usual +way is @var{computed} and the alignment explicitly specified was +@var{specified}. + +The default is to use @var{specified} if it is larger; otherwise, use +the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT} +@end defmac + +@defmac MAX_FIXED_MODE_SIZE +An integer expression for the size in bits of the largest integer +machine mode that should actually be used. All integer machine modes of +this size or smaller can be used for structures and unions with the +appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE +(DImode)} is assumed. +@end defmac + +@defmac STACK_SAVEAREA_MODE (@var{save_level}) +If defined, an expression of type @code{machine_mode} that +specifies the mode of the save area operand of a +@code{save_stack_@var{level}} named pattern (@pxref{Standard Names}). +@var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or +@code{SAVE_NONLOCAL} and selects which of the three named patterns is +having its mode specified. + +You need not define this macro if it always returns @code{Pmode}. You +would most commonly define this macro if the +@code{save_stack_@var{level}} patterns need to support both a 32- and a +64-bit mode. +@end defmac + +@defmac STACK_SIZE_MODE +If defined, an expression of type @code{machine_mode} that +specifies the mode of the size increment operand of an +@code{allocate_stack} named pattern (@pxref{Standard Names}). + +You need not define this macro if it always returns @code{word_mode}. +You would most commonly define this macro if the @code{allocate_stack} +pattern needs to support both a 32- and a 64-bit mode. +@end defmac + +@hook TARGET_LIBGCC_CMP_RETURN_MODE + +@hook TARGET_LIBGCC_SHIFT_COUNT_MODE + +@hook TARGET_UNWIND_WORD_MODE + +@hook TARGET_MS_BITFIELD_LAYOUT_P + +@hook TARGET_DECIMAL_FLOAT_SUPPORTED_P + +@hook TARGET_FIXED_POINT_SUPPORTED_P + +@hook TARGET_EXPAND_TO_RTL_HOOK + +@hook TARGET_INSTANTIATE_DECLS + +@hook TARGET_MANGLE_TYPE + +@node Type Layout +@section Layout of Source Language Data Types + +These macros define the sizes and other characteristics of the standard +basic data types used in programs being compiled. Unlike the macros in +the previous section, these apply to specific features of C and related +languages, rather than to fundamental aspects of storage layout. + +@defmac INT_TYPE_SIZE +A C expression for the size in bits of the type @code{int} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac SHORT_TYPE_SIZE +A C expression for the size in bits of the type @code{short} on the +target machine. If you don't define this, the default is half a word. +(If this would be less than one storage unit, it is rounded up to one +unit.) +@end defmac + +@defmac LONG_TYPE_SIZE +A C expression for the size in bits of the type @code{long} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac ADA_LONG_TYPE_SIZE +On some machines, the size used for the Ada equivalent of the type +@code{long} by a native Ada compiler differs from that used by C@. In +that situation, define this macro to be a C expression to be used for +the size of that type. If you don't define this, the default is the +value of @code{LONG_TYPE_SIZE}. +@end defmac + +@defmac LONG_LONG_TYPE_SIZE +A C expression for the size in bits of the type @code{long long} on the +target machine. If you don't define this, the default is two +words. If you want to support GNU Ada on your machine, the value of this +macro must be at least 64. +@end defmac + +@defmac CHAR_TYPE_SIZE +A C expression for the size in bits of the type @code{char} on the +target machine. If you don't define this, the default is +@code{BITS_PER_UNIT}. +@end defmac + +@defmac BOOL_TYPE_SIZE +A C expression for the size in bits of the C++ type @code{bool} and +C99 type @code{_Bool} on the target machine. If you don't define +this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}. +@end defmac + +@defmac FLOAT_TYPE_SIZE +A C expression for the size in bits of the type @code{float} on the +target machine. If you don't define this, the default is one word. +@end defmac + +@defmac DOUBLE_TYPE_SIZE +A C expression for the size in bits of the type @code{double} on the +target machine. If you don't define this, the default is two +words. +@end defmac + +@defmac LONG_DOUBLE_TYPE_SIZE +A C expression for the size in bits of the type @code{long double} on +the target machine. If you don't define this, the default is two +words. +@end defmac + +@defmac SHORT_FRACT_TYPE_SIZE +A C expression for the size in bits of the type @code{short _Fract} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT}. +@end defmac + +@defmac FRACT_TYPE_SIZE +A C expression for the size in bits of the type @code{_Fract} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 2}. +@end defmac + +@defmac LONG_FRACT_TYPE_SIZE +A C expression for the size in bits of the type @code{long _Fract} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 4}. +@end defmac + +@defmac LONG_LONG_FRACT_TYPE_SIZE +A C expression for the size in bits of the type @code{long long _Fract} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 8}. +@end defmac + +@defmac SHORT_ACCUM_TYPE_SIZE +A C expression for the size in bits of the type @code{short _Accum} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 2}. +@end defmac + +@defmac ACCUM_TYPE_SIZE +A C expression for the size in bits of the type @code{_Accum} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 4}. +@end defmac + +@defmac LONG_ACCUM_TYPE_SIZE +A C expression for the size in bits of the type @code{long _Accum} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 8}. +@end defmac + +@defmac LONG_LONG_ACCUM_TYPE_SIZE +A C expression for the size in bits of the type @code{long long _Accum} on +the target machine. If you don't define this, the default is +@code{BITS_PER_UNIT * 16}. +@end defmac + +@defmac LIBGCC2_GNU_PREFIX +This macro corresponds to the @code{TARGET_LIBFUNC_GNU_PREFIX} target +hook and should be defined if that hook is overriden to be true. It +causes function names in libgcc to be changed to use a @code{__gnu_} +prefix for their name rather than the default @code{__}. A port which +uses this macro should also arrange to use @file{t-gnu-prefix} in +the libgcc @file{config.host}. +@end defmac + +@defmac WIDEST_HARDWARE_FP_SIZE +A C expression for the size in bits of the widest floating-point format +supported by the hardware. If you define this macro, you must specify a +value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}. +If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE} +is the default. +@end defmac + +@defmac DEFAULT_SIGNED_CHAR +An expression whose value is 1 or 0, according to whether the type +@code{char} should be signed or unsigned by default. The user can +always override this default with the options @option{-fsigned-char} +and @option{-funsigned-char}. +@end defmac + +@hook TARGET_DEFAULT_SHORT_ENUMS + +@defmac SIZE_TYPE +A C expression for a string describing the name of the data type to use +for size values. The typedef name @code{size_t} is defined using the +contents of the string. + +The string can contain more than one keyword. If so, separate them with +spaces, and write first any length keyword, then @code{unsigned} if +appropriate, and finally @code{int}. The string must exactly match one +of the data type names defined in the function +@code{c_common_nodes_and_builtins} in the file @file{c-family/c-common.cc}. +You may not omit @code{int} or change the order---that would cause the +compiler to crash on startup. + +If you don't define this macro, the default is @code{"long unsigned +int"}. +@end defmac + +@defmac SIZETYPE +GCC defines internal types (@code{sizetype}, @code{ssizetype}, +@code{bitsizetype} and @code{sbitsizetype}) for expressions +dealing with size. This macro is a C expression for a string describing +the name of the data type from which the precision of @code{sizetype} +is extracted. + +The string has the same restrictions as @code{SIZE_TYPE} string. + +If you don't define this macro, the default is @code{SIZE_TYPE}. +@end defmac + +@defmac PTRDIFF_TYPE +A C expression for a string describing the name of the data type to use +for the result of subtracting two pointers. The typedef name +@code{ptrdiff_t} is defined using the contents of the string. See +@code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is @code{"long int"}. +@end defmac + +@defmac WCHAR_TYPE +A C expression for a string describing the name of the data type to use +for wide characters. The typedef name @code{wchar_t} is defined using +the contents of the string. See @code{SIZE_TYPE} above for more +information. + +If you don't define this macro, the default is @code{"int"}. +@end defmac + +@defmac WCHAR_TYPE_SIZE +A C expression for the size in bits of the data type for wide +characters. This is used in @code{cpp}, which cannot make use of +@code{WCHAR_TYPE}. +@end defmac + +@defmac WINT_TYPE +A C expression for a string describing the name of the data type to +use for wide characters passed to @code{printf} and returned from +@code{getwc}. The typedef name @code{wint_t} is defined using the +contents of the string. See @code{SIZE_TYPE} above for more +information. + +If you don't define this macro, the default is @code{"unsigned int"}. +@end defmac + +@defmac INTMAX_TYPE +A C expression for a string describing the name of the data type that +can represent any value of any standard or extended signed integer type. +The typedef name @code{intmax_t} is defined using the contents of the +string. See @code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is the first of +@code{"int"}, @code{"long int"}, or @code{"long long int"} that has as +much precision as @code{long long int}. +@end defmac + +@defmac UINTMAX_TYPE +A C expression for a string describing the name of the data type that +can represent any value of any standard or extended unsigned integer +type. The typedef name @code{uintmax_t} is defined using the contents +of the string. See @code{SIZE_TYPE} above for more information. + +If you don't define this macro, the default is the first of +@code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long +unsigned int"} that has as much precision as @code{long long unsigned +int}. +@end defmac + +@defmac SIG_ATOMIC_TYPE +@defmacx INT8_TYPE +@defmacx INT16_TYPE +@defmacx INT32_TYPE +@defmacx INT64_TYPE +@defmacx UINT8_TYPE +@defmacx UINT16_TYPE +@defmacx UINT32_TYPE +@defmacx UINT64_TYPE +@defmacx INT_LEAST8_TYPE +@defmacx INT_LEAST16_TYPE +@defmacx INT_LEAST32_TYPE +@defmacx INT_LEAST64_TYPE +@defmacx UINT_LEAST8_TYPE +@defmacx UINT_LEAST16_TYPE +@defmacx UINT_LEAST32_TYPE +@defmacx UINT_LEAST64_TYPE +@defmacx INT_FAST8_TYPE +@defmacx INT_FAST16_TYPE +@defmacx INT_FAST32_TYPE +@defmacx INT_FAST64_TYPE +@defmacx UINT_FAST8_TYPE +@defmacx UINT_FAST16_TYPE +@defmacx UINT_FAST32_TYPE +@defmacx UINT_FAST64_TYPE +@defmacx INTPTR_TYPE +@defmacx UINTPTR_TYPE +C expressions for the standard types @code{sig_atomic_t}, +@code{int8_t}, @code{int16_t}, @code{int32_t}, @code{int64_t}, +@code{uint8_t}, @code{uint16_t}, @code{uint32_t}, @code{uint64_t}, +@code{int_least8_t}, @code{int_least16_t}, @code{int_least32_t}, +@code{int_least64_t}, @code{uint_least8_t}, @code{uint_least16_t}, +@code{uint_least32_t}, @code{uint_least64_t}, @code{int_fast8_t}, +@code{int_fast16_t}, @code{int_fast32_t}, @code{int_fast64_t}, +@code{uint_fast8_t}, @code{uint_fast16_t}, @code{uint_fast32_t}, +@code{uint_fast64_t}, @code{intptr_t}, and @code{uintptr_t}. See +@code{SIZE_TYPE} above for more information. + +If any of these macros evaluates to a null pointer, the corresponding +type is not supported; if GCC is configured to provide +@code{} in such a case, the header provided may not conform +to C99, depending on the type in question. The defaults for all of +these macros are null pointers. +@end defmac + +@defmac TARGET_PTRMEMFUNC_VBIT_LOCATION +The C++ compiler represents a pointer-to-member-function with a struct +that looks like: + +@smallexample + struct @{ + union @{ + void (*fn)(); + ptrdiff_t vtable_index; + @}; + ptrdiff_t delta; + @}; +@end smallexample + +@noindent +The C++ compiler must use one bit to indicate whether the function that +will be called through a pointer-to-member-function is virtual. +Normally, we assume that the low-order bit of a function pointer must +always be zero. Then, by ensuring that the vtable_index is odd, we can +distinguish which variant of the union is in use. But, on some +platforms function pointers can be odd, and so this doesn't work. In +that case, we use the low-order bit of the @code{delta} field, and shift +the remainder of the @code{delta} field to the left. + +GCC will automatically make the right selection about where to store +this bit using the @code{FUNCTION_BOUNDARY} setting for your platform. +However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY} +set such that functions always start at even addresses, but the lowest +bit of pointers to functions indicate whether the function at that +address is in ARM or Thumb mode. If this is the case of your +architecture, you should define this macro to +@code{ptrmemfunc_vbit_in_delta}. + +In general, you should not have to define this macro. On architectures +in which function addresses are always even, according to +@code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to +@code{ptrmemfunc_vbit_in_pfn}. +@end defmac + +@defmac TARGET_VTABLE_USES_DESCRIPTORS +Normally, the C++ compiler uses function pointers in vtables. This +macro allows the target to change to use ``function descriptors'' +instead. Function descriptors are found on targets for whom a +function pointer is actually a small data structure. Normally the +data structure consists of the actual code address plus a data +pointer to which the function's data is relative. + +If vtables are used, the value of this macro should be the number +of words that the function descriptor occupies. +@end defmac + +@defmac TARGET_VTABLE_ENTRY_ALIGN +By default, the vtable entries are void pointers, the so the alignment +is the same as pointer alignment. The value of this macro specifies +the alignment of the vtable entry in bits. It should be defined only +when special alignment is necessary. */ +@end defmac + +@defmac TARGET_VTABLE_DATA_ENTRY_DISTANCE +There are a few non-descriptor entries in the vtable at offsets below +zero. If these entries must be padded (say, to preserve the alignment +specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number +of words in each data entry. +@end defmac + +@node Registers +@section Register Usage +@cindex register usage + +This section explains how to describe what registers the target machine +has, and how (in general) they can be used. + +The description of which registers a specific instruction can use is +done with register classes; see @ref{Register Classes}. For information +on using registers to access a stack frame, see @ref{Frame Registers}. +For passing values in registers, see @ref{Register Arguments}. +For returning values in registers, see @ref{Scalar Return}. + +@menu +* Register Basics:: Number and kinds of registers. +* Allocation Order:: Order in which registers are allocated. +* Values in Registers:: What kinds of values each reg can hold. +* Leaf Functions:: Renumbering registers for leaf functions. +* Stack Registers:: Handling a register stack such as 80387. +@end menu + +@node Register Basics +@subsection Basic Characteristics of Registers + +@c prevent bad page break with this line +Registers have various characteristics. + +@defmac FIRST_PSEUDO_REGISTER +Number of hardware registers known to the compiler. They receive +numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first +pseudo register's number really is assigned the number +@code{FIRST_PSEUDO_REGISTER}. +@end defmac + +@defmac FIXED_REGISTERS +@cindex fixed register +An initializer that says which registers are used for fixed purposes +all throughout the compiled code and are therefore not available for +general allocation. These would include the stack pointer, the frame +pointer (except on machines where that can be used as a general +register when no frame pointer is needed), the program counter on +machines where that is considered one of the addressable registers, +and any other numbered register with a standard use. + +This information is expressed as a sequence of numbers, separated by +commas and surrounded by braces. The @var{n}th number is 1 if +register @var{n} is fixed, 0 otherwise. + +The table initialized from this macro, and the table initialized by +the following one, may be overridden at run time either automatically, +by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by +the user with the command options @option{-ffixed-@var{reg}}, +@option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}. +@end defmac + +@defmac CALL_USED_REGISTERS +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +Like @code{FIXED_REGISTERS} but has 1 for each register that is +clobbered (in general) by function calls as well as for fixed +registers. This macro therefore identifies the registers that are not +available for general allocation of values that must live across +function calls. + +If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler +automatically saves it on function entry and restores it on function +exit, if the register is used within the function. + +Exactly one of @code{CALL_USED_REGISTERS} and @code{CALL_REALLY_USED_REGISTERS} +must be defined. Modern ports should define @code{CALL_REALLY_USED_REGISTERS}. +@end defmac + +@defmac CALL_REALLY_USED_REGISTERS +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +Like @code{CALL_USED_REGISTERS} except this macro doesn't require +that the entire set of @code{FIXED_REGISTERS} be included. +(@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}). + +Exactly one of @code{CALL_USED_REGISTERS} and @code{CALL_REALLY_USED_REGISTERS} +must be defined. Modern ports should define @code{CALL_REALLY_USED_REGISTERS}. +@end defmac + +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +@hook TARGET_FNTYPE_ABI + +@hook TARGET_INSN_CALLEE_ABI + +@cindex call-used register +@cindex call-clobbered register +@cindex call-saved register +@hook TARGET_HARD_REGNO_CALL_PART_CLOBBERED + +@hook TARGET_GET_MULTILIB_ABI_NAME + +@findex fixed_regs +@findex call_used_regs +@findex global_regs +@findex reg_names +@findex reg_class_contents +@hook TARGET_CONDITIONAL_REGISTER_USAGE + +@defmac INCOMING_REGNO (@var{out}) +Define this macro if the target machine has register windows. This C +expression returns the register number as seen by the called function +corresponding to the register number @var{out} as seen by the calling +function. Return @var{out} if register number @var{out} is not an +outbound register. +@end defmac + +@defmac OUTGOING_REGNO (@var{in}) +Define this macro if the target machine has register windows. This C +expression returns the register number as seen by the calling function +corresponding to the register number @var{in} as seen by the called +function. Return @var{in} if register number @var{in} is not an inbound +register. +@end defmac + +@defmac LOCAL_REGNO (@var{regno}) +Define this macro if the target machine has register windows. This C +expression returns true if the register is call-saved but is in the +register window. Unlike most call-saved registers, such registers +need not be explicitly restored on function exit or during non-local +gotos. +@end defmac + +@defmac PC_REGNUM +If the program counter has a register number, define this as that +register number. Otherwise, do not define it. +@end defmac + +@node Allocation Order +@subsection Order of Allocation of Registers +@cindex order of register allocation +@cindex register allocation order + +@c prevent bad page break with this line +Registers are allocated in order. + +@defmac REG_ALLOC_ORDER +If defined, an initializer for a vector of integers, containing the +numbers of hard registers in the order in which GCC should prefer +to use them (from most preferred to least). + +If this macro is not defined, registers are used lowest numbered first +(all else being equal). + +One use of this macro is on machines where the highest numbered +registers must always be saved and the save-multiple-registers +instruction supports only sequences of consecutive registers. On such +machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists +the highest numbered allocable register first. +@end defmac + +@defmac ADJUST_REG_ALLOC_ORDER +A C statement (sans semicolon) to choose the order in which to allocate +hard registers for pseudo-registers local to a basic block. + +Store the desired register order in the array @code{reg_alloc_order}. +Element 0 should be the register to allocate first; element 1, the next +register; and so on. + +The macro body should not assume anything about the contents of +@code{reg_alloc_order} before execution of the macro. + +On most machines, it is not necessary to define this macro. +@end defmac + +@defmac HONOR_REG_ALLOC_ORDER +Normally, IRA tries to estimate the costs for saving a register in the +prologue and restoring it in the epilogue. This discourages it from +using call-saved registers. If a machine wants to ensure that IRA +allocates registers in the order given by REG_ALLOC_ORDER even if some +call-saved registers appear earlier than call-used ones, then define this +macro as a C expression to nonzero. Default is 0. +@end defmac + +@defmac IRA_HARD_REGNO_ADD_COST_MULTIPLIER (@var{regno}) +In some case register allocation order is not enough for the +Integrated Register Allocator (@acronym{IRA}) to generate a good code. +If this macro is defined, it should return a floating point value +based on @var{regno}. The cost of using @var{regno} for a pseudo will +be increased by approximately the pseudo's usage frequency times the +value returned by this macro. Not defining this macro is equivalent +to having it always return @code{0.0}. + +On most machines, it is not necessary to define this macro. +@end defmac + +@node Values in Registers +@subsection How Values Fit in Registers + +This section discusses the macros that describe which kinds of values +(specifically, which machine modes) each register can hold, and how many +consecutive registers are needed for a given mode. + +@hook TARGET_HARD_REGNO_NREGS + +@defmac HARD_REGNO_NREGS_HAS_PADDING (@var{regno}, @var{mode}) +A C expression that is nonzero if a value of mode @var{mode}, stored +in memory, ends with padding that causes it to take up more space than +in registers starting at register number @var{regno} (as determined by +multiplying GCC's notion of the size of the register when containing +this mode by the number of registers returned by +@code{TARGET_HARD_REGNO_NREGS}). By default this is zero. + +For example, if a floating-point value is stored in three 32-bit +registers but takes up 128 bits in memory, then this would be +nonzero. + +This macros only needs to be defined if there are cases where +@code{subreg_get_info} +would otherwise wrongly determine that a @code{subreg} can be +represented by an offset to the register number, when in fact such a +@code{subreg} would contain some of the padding not stored in +registers and so not be representable. +@end defmac + +@defmac HARD_REGNO_NREGS_WITH_PADDING (@var{regno}, @var{mode}) +For values of @var{regno} and @var{mode} for which +@code{HARD_REGNO_NREGS_HAS_PADDING} returns nonzero, a C expression +returning the greater number of registers required to hold the value +including any padding. In the example above, the value would be four. +@end defmac + +@defmac REGMODE_NATURAL_SIZE (@var{mode}) +Define this macro if the natural size of registers that hold values +of mode @var{mode} is not the word size. It is a C expression that +should give the natural size in bytes for the specified mode. It is +used by the register allocator to try to optimize its results. This +happens for example on SPARC 64-bit where the natural size of +floating-point registers is still 32-bit. +@end defmac + +@hook TARGET_HARD_REGNO_MODE_OK + +@defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to}) +A C expression that is nonzero if it is OK to rename a hard register +@var{from} to another hard register @var{to}. + +One common use of this macro is to prevent renaming of a register to +another register that is not saved by a prologue in an interrupt +handler. + +The default is always nonzero. +@end defmac + +@hook TARGET_MODES_TIEABLE_P + +@hook TARGET_HARD_REGNO_SCRATCH_OK + +@defmac AVOID_CCMODE_COPIES +Define this macro if the compiler should avoid copies to/from @code{CCmode} +registers. You should only define this macro if support for copying to/from +@code{CCmode} is incomplete. +@end defmac + +@node Leaf Functions +@subsection Handling Leaf Functions + +@cindex leaf functions +@cindex functions, leaf +On some machines, a leaf function (i.e., one which makes no calls) can run +more efficiently if it does not make its own register window. Often this +means it is required to receive its arguments in the registers where they +are passed by the caller, instead of the registers where they would +normally arrive. + +The special treatment for leaf functions generally applies only when +other conditions are met; for example, often they may use only those +registers for its own variables and temporaries. We use the term ``leaf +function'' to mean a function that is suitable for this special +handling, so that functions with no calls are not necessarily ``leaf +functions''. + +GCC assigns register numbers before it knows whether the function is +suitable for leaf function treatment. So it needs to renumber the +registers in order to output a leaf function. The following macros +accomplish this. + +@defmac LEAF_REGISTERS +Name of a char vector, indexed by hard register number, which +contains 1 for a register that is allowable in a candidate for leaf +function treatment. + +If leaf function treatment involves renumbering the registers, then the +registers marked here should be the ones before renumbering---those that +GCC would ordinarily allocate. The registers which will actually be +used in the assembler code, after renumbering, should not be marked with 1 +in this vector. + +Define this macro only if the target machine offers a way to optimize +the treatment of leaf functions. +@end defmac + +@defmac LEAF_REG_REMAP (@var{regno}) +A C expression whose value is the register number to which @var{regno} +should be renumbered, when a function is treated as a leaf function. + +If @var{regno} is a register number which should not appear in a leaf +function before renumbering, then the expression should yield @minus{}1, which +will cause the compiler to abort. + +Define this macro only if the target machine offers a way to optimize the +treatment of leaf functions, and registers need to be renumbered to do +this. +@end defmac + +@findex current_function_is_leaf +@findex current_function_uses_only_leaf_regs +@code{TARGET_ASM_FUNCTION_PROLOGUE} and +@code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions +specially. They can test the C variable @code{current_function_is_leaf} +which is nonzero for leaf functions. @code{current_function_is_leaf} is +set prior to local register allocation and is valid for the remaining +compiler passes. They can also test the C variable +@code{current_function_uses_only_leaf_regs} which is nonzero for leaf +functions which only use leaf registers. +@code{current_function_uses_only_leaf_regs} is valid after all passes +that modify the instructions have been run and is only useful if +@code{LEAF_REGISTERS} is defined. +@c changed this to fix overfull. ALSO: why the "it" at the beginning +@c of the next paragraph?! --mew 2feb93 + +@node Stack Registers +@subsection Registers That Form a Stack + +There are special features to handle computers where some of the +``registers'' form a stack. Stack registers are normally written by +pushing onto the stack, and are numbered relative to the top of the +stack. + +Currently, GCC can only handle one group of stack-like registers, and +they must be consecutively numbered. Furthermore, the existing +support for stack-like registers is specific to the 80387 floating +point coprocessor. If you have a new architecture that uses +stack-like registers, you will need to do substantial work on +@file{reg-stack.cc} and write your machine description to cooperate +with it, as well as defining these macros. + +@defmac STACK_REGS +Define this if the machine has any stack-like registers. +@end defmac + +@defmac STACK_REG_COVER_CLASS +This is a cover class containing the stack registers. Define this if +the machine has any stack-like registers. +@end defmac + +@defmac FIRST_STACK_REG +The number of the first stack-like register. This one is the top +of the stack. +@end defmac + +@defmac LAST_STACK_REG +The number of the last stack-like register. This one is the bottom of +the stack. +@end defmac + +@node Register Classes +@section Register Classes +@cindex register class definitions +@cindex class definitions, register + +On many machines, the numbered registers are not all equivalent. +For example, certain registers may not be allowed for indexed addressing; +certain registers may not be allowed in some instructions. These machine +restrictions are described to the compiler using @dfn{register classes}. + +You define a number of register classes, giving each one a name and saying +which of the registers belong to it. Then you can specify register classes +that are allowed as operands to particular instruction patterns. + +@findex ALL_REGS +@findex NO_REGS +In general, each register will belong to several classes. In fact, one +class must be named @code{ALL_REGS} and contain all the registers. Another +class must be named @code{NO_REGS} and contain no registers. Often the +union of two classes will be another class; however, this is not required. + +@findex GENERAL_REGS +One of the classes must be named @code{GENERAL_REGS}. There is nothing +terribly special about the name, but the operand constraint letters +@samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is +the same as @code{ALL_REGS}, just define it as a macro which expands +to @code{ALL_REGS}. + +Order the classes so that if class @var{x} is contained in class @var{y} +then @var{x} has a lower class number than @var{y}. + +The way classes other than @code{GENERAL_REGS} are specified in operand +constraints is through machine-dependent operand constraint letters. +You can define such letters to correspond to various classes, then use +them in operand constraints. + +You must define the narrowest register classes for allocatable +registers, so that each class either has no subclasses, or that for +some mode, the move cost between registers within the class is +cheaper than moving a register in the class to or from memory +(@pxref{Costs}). + +You should define a class for the union of two classes whenever some +instruction allows both classes. For example, if an instruction allows +either a floating point (coprocessor) register or a general register for a +certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS} +which includes both of them. Otherwise you will get suboptimal code, +or even internal compiler errors when reload cannot find a register in the +class computed via @code{reg_class_subunion}. + +You must also specify certain redundant information about the register +classes: for each class, which classes contain it and which ones are +contained in it; for each pair of classes, the largest class contained +in their union. + +When a value occupying several consecutive registers is expected in a +certain class, all the registers used must belong to that class. +Therefore, register classes cannot be used to enforce a requirement for +a register pair to start with an even-numbered register. The way to +specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK}. + +Register classes used for input-operands of bitwise-and or shift +instructions have a special requirement: each such class must have, for +each fixed-point machine mode, a subclass whose registers can transfer that +mode to or from memory. For example, on some machines, the operations for +single-byte values (@code{QImode}) are limited to certain registers. When +this is so, each register class that is used in a bitwise-and or shift +instruction must have a subclass consisting of registers from which +single-byte values can be loaded or stored. This is so that +@code{PREFERRED_RELOAD_CLASS} can always have a possible value to return. + +@deftp {Data type} {enum reg_class} +An enumerated type that must be defined with all the register class names +as enumerated values. @code{NO_REGS} must be first. @code{ALL_REGS} +must be the last register class, followed by one more enumerated value, +@code{LIM_REG_CLASSES}, which is not a register class but rather +tells how many classes there are. + +Each register class has a number, which is the value of casting +the class name to type @code{int}. The number serves as an index +in many of the tables described below. +@end deftp + +@defmac N_REG_CLASSES +The number of distinct register classes, defined as follows: + +@smallexample +#define N_REG_CLASSES (int) LIM_REG_CLASSES +@end smallexample +@end defmac + +@defmac REG_CLASS_NAMES +An initializer containing the names of the register classes as C string +constants. These names are used in writing some of the debugging dumps. +@end defmac + +@defmac REG_CLASS_CONTENTS +An initializer containing the contents of the register classes, as integers +which are bit masks. The @var{n}th integer specifies the contents of class +@var{n}. The way the integer @var{mask} is interpreted is that +register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1. + +When the machine has more than 32 registers, an integer does not suffice. +Then the integers are replaced by sub-initializers, braced groupings containing +several integers. Each sub-initializer must be suitable as an initializer +for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}. +In this situation, the first integer in each sub-initializer corresponds to +registers 0 through 31, the second integer to registers 32 through 63, and +so on. +@end defmac + +@defmac REGNO_REG_CLASS (@var{regno}) +A C expression whose value is a register class containing hard register +@var{regno}. In general there is more than one such class; choose a class +which is @dfn{minimal}, meaning that no smaller class also contains the +register. +@end defmac + +@defmac BASE_REG_CLASS +A macro whose definition is the name of the class to which a valid +base register must belong. A base register is one used in an address +which is the register value plus a displacement. +@end defmac + +@defmac MODE_BASE_REG_CLASS (@var{mode}) +This is a variation of the @code{BASE_REG_CLASS} macro which allows +the selection of a base register in a mode dependent manner. If +@var{mode} is VOIDmode then it should return the same value as +@code{BASE_REG_CLASS}. +@end defmac + +@defmac MODE_BASE_REG_REG_CLASS (@var{mode}) +A C expression whose value is the register class to which a valid +base register must belong in order to be used in a base plus index +register address. You should define this macro if base plus index +addresses have different requirements than other base register uses. +@end defmac + +@defmac MODE_CODE_BASE_REG_CLASS (@var{mode}, @var{address_space}, @var{outer_code}, @var{index_code}) +A C expression whose value is the register class to which a valid +base register for a memory reference in mode @var{mode} to address +space @var{address_space} must belong. @var{outer_code} and @var{index_code} +define the context in which the base register occurs. @var{outer_code} is +the code of the immediately enclosing expression (@code{MEM} for the top level +of an address, @code{ADDRESS} for something that occurs in an +@code{address_operand}). @var{index_code} is the code of the corresponding +index expression if @var{outer_code} is @code{PLUS}; @code{SCRATCH} otherwise. +@end defmac + +@defmac INDEX_REG_CLASS +A macro whose definition is the name of the class to which a valid +index register must belong. An index register is one used in an +address where its value is either multiplied by a scale factor or +added to another register (as well as added to a displacement). +@end defmac + +@defmac REGNO_OK_FOR_BASE_P (@var{num}) +A C expression which is nonzero if register number @var{num} is +suitable for use as a base register in operand addresses. +@end defmac + +@defmac REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode}) +A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that +that expression may examine the mode of the memory reference in +@var{mode}. You should define this macro if the mode of the memory +reference affects whether a register may be used as a base register. If +you define this macro, the compiler will use it instead of +@code{REGNO_OK_FOR_BASE_P}. The mode may be @code{VOIDmode} for +addresses that appear outside a @code{MEM}, i.e., as an +@code{address_operand}. +@end defmac + +@defmac REGNO_MODE_OK_FOR_REG_BASE_P (@var{num}, @var{mode}) +A C expression which is nonzero if register number @var{num} is suitable for +use as a base register in base plus index operand addresses, accessing +memory in mode @var{mode}. It may be either a suitable hard register or a +pseudo register that has been allocated such a hard register. You should +define this macro if base plus index addresses have different requirements +than other base register uses. + +Use of this macro is deprecated; please use the more general +@code{REGNO_MODE_CODE_OK_FOR_BASE_P}. +@end defmac + +@defmac REGNO_MODE_CODE_OK_FOR_BASE_P (@var{num}, @var{mode}, @var{address_space}, @var{outer_code}, @var{index_code}) +A C expression which is nonzero if register number @var{num} is +suitable for use as a base register in operand addresses, accessing +memory in mode @var{mode} in address space @var{address_space}. +This is similar to @code{REGNO_MODE_OK_FOR_BASE_P}, except +that that expression may examine the context in which the register +appears in the memory reference. @var{outer_code} is the code of the +immediately enclosing expression (@code{MEM} if at the top level of the +address, @code{ADDRESS} for something that occurs in an +@code{address_operand}). @var{index_code} is the code of the +corresponding index expression if @var{outer_code} is @code{PLUS}; +@code{SCRATCH} otherwise. The mode may be @code{VOIDmode} for addresses +that appear outside a @code{MEM}, i.e., as an @code{address_operand}. +@end defmac + +@defmac REGNO_OK_FOR_INDEX_P (@var{num}) +A C expression which is nonzero if register number @var{num} is +suitable for use as an index register in operand addresses. It may be +either a suitable hard register or a pseudo register that has been +allocated such a hard register. + +The difference between an index register and a base register is that +the index register may be scaled. If an address involves the sum of +two registers, neither one of them scaled, then either one may be +labeled the ``base'' and the other the ``index''; but whichever +labeling is used must fit the machine's constraints of which registers +may serve in each capacity. The compiler will try both labelings, +looking for one that is valid, and will reload one or both registers +only if neither labeling works. +@end defmac + +@hook TARGET_PREFERRED_RENAME_CLASS + +@hook TARGET_PREFERRED_RELOAD_CLASS + +@defmac PREFERRED_RELOAD_CLASS (@var{x}, @var{class}) +A C expression that places additional restrictions on the register class +to use when it is necessary to copy value @var{x} into a register in class +@var{class}. The value is a register class; perhaps @var{class}, or perhaps +another, smaller class. On many machines, the following definition is +safe: + +@smallexample +#define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS +@end smallexample + +Sometimes returning a more restrictive class makes better code. For +example, on the 68000, when @var{x} is an integer constant that is in range +for a @samp{moveq} instruction, the value of this macro is always +@code{DATA_REGS} as long as @var{class} includes the data registers. +Requiring a data register guarantees that a @samp{moveq} will be used. + +One case where @code{PREFERRED_RELOAD_CLASS} must not return +@var{class} is if @var{x} is a legitimate constant which cannot be +loaded into some register class. By returning @code{NO_REGS} you can +force @var{x} into a memory location. For example, rs6000 can load +immediate values into general-purpose registers, but does not have an +instruction for loading an immediate value into a floating-point +register, so @code{PREFERRED_RELOAD_CLASS} returns @code{NO_REGS} when +@var{x} is a floating-point constant. If the constant cannot be loaded +into any kind of register, code generation will be better if +@code{TARGET_LEGITIMATE_CONSTANT_P} makes the constant illegitimate instead +of using @code{TARGET_PREFERRED_RELOAD_CLASS}. + +If an insn has pseudos in it after register allocation, reload will go +through the alternatives and call repeatedly @code{PREFERRED_RELOAD_CLASS} +to find the best one. Returning @code{NO_REGS}, in this case, makes +reload add a @code{!} in front of the constraint: the x86 back-end uses +this feature to discourage usage of 387 registers when math is done in +the SSE registers (and vice versa). +@end defmac + +@hook TARGET_PREFERRED_OUTPUT_RELOAD_CLASS + +@defmac LIMIT_RELOAD_CLASS (@var{mode}, @var{class}) +A C expression that places additional restrictions on the register class +to use when it is necessary to be able to hold a value of mode +@var{mode} in a reload register for which class @var{class} would +ordinarily be used. + +Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when +there are certain modes that simply cannot go in certain reload classes. + +The value is a register class; perhaps @var{class}, or perhaps another, +smaller class. + +Don't define this macro unless the target machine has limitations which +require the macro to do something nontrivial. +@end defmac + +@hook TARGET_SECONDARY_RELOAD + +@defmac SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +@defmacx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +@defmacx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) +These macros are obsolete, new ports should use the target hook +@code{TARGET_SECONDARY_RELOAD} instead. + +These are obsolete macros, replaced by the @code{TARGET_SECONDARY_RELOAD} +target hook. Older ports still define these macros to indicate to the +reload phase that it may +need to allocate at least one register for a reload in addition to the +register to contain the data. Specifically, if copying @var{x} to a +register @var{class} in @var{mode} requires an intermediate register, +you were supposed to define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the +largest register class all of whose registers can be used as +intermediate registers or scratch registers. + +If copying a register @var{class} in @var{mode} to @var{x} requires an +intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS} +was supposed to be defined to return the largest register +class required. If the +requirements for input and output reloads were the same, the macro +@code{SECONDARY_RELOAD_CLASS} should have been used instead of defining both +macros identically. + +The values returned by these macros are often @code{GENERAL_REGS}. +Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x} +can be directly copied to or from a register of @var{class} in +@var{mode} without requiring a scratch register. Do not define this +macro if it would always return @code{NO_REGS}. + +If a scratch register is required (either with or without an +intermediate register), you were supposed to define patterns for +@samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required +(@pxref{Standard Names}. These patterns, which were normally +implemented with a @code{define_expand}, should be similar to the +@samp{mov@var{m}} patterns, except that operand 2 is the scratch +register. + +These patterns need constraints for the reload register and scratch +register that +contain a single register class. If the original reload register (whose +class is @var{class}) can meet the constraint given in the pattern, the +value returned by these macros is used for the class of the scratch +register. Otherwise, two additional reload registers are required. +Their classes are obtained from the constraints in the insn pattern. + +@var{x} might be a pseudo-register or a @code{subreg} of a +pseudo-register, which could either be in a hard register or in memory. +Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is +in memory and the hard register number if it is in a register. + +These macros should not be used in the case where a particular class of +registers can only be copied to memory and not to another class of +registers. In that case, secondary reload registers are not needed and +would not be helpful. Instead, a stack location must be used to perform +the copy and the @code{mov@var{m}} pattern should use memory as an +intermediate storage. This case often occurs between floating-point and +general registers. +@end defmac + +@hook TARGET_SECONDARY_MEMORY_NEEDED + +@defmac SECONDARY_MEMORY_NEEDED_RTX (@var{mode}) +Normally when @code{TARGET_SECONDARY_MEMORY_NEEDED} is defined, the compiler +allocates a stack slot for a memory location needed for register copies. +If this macro is defined, the compiler instead uses the memory location +defined by this macro. + +Do not define this macro if you do not define +@code{TARGET_SECONDARY_MEMORY_NEEDED}. +@end defmac + +@hook TARGET_SECONDARY_MEMORY_NEEDED_MODE + +@hook TARGET_SELECT_EARLY_REMAT_MODES + +@hook TARGET_CLASS_LIKELY_SPILLED_P + +@hook TARGET_CLASS_MAX_NREGS + +@defmac CLASS_MAX_NREGS (@var{class}, @var{mode}) +A C expression for the maximum number of consecutive registers +of class @var{class} needed to hold a value of mode @var{mode}. + +This is closely related to the macro @code{TARGET_HARD_REGNO_NREGS}. In fact, +the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})} +should be the maximum value of @code{TARGET_HARD_REGNO_NREGS (@var{regno}, +@var{mode})} for all @var{regno} values in the class @var{class}. + +This macro helps control the handling of multiple-word values +in the reload pass. +@end defmac + +@hook TARGET_CAN_CHANGE_MODE_CLASS + +@hook TARGET_IRA_CHANGE_PSEUDO_ALLOCNO_CLASS + +@hook TARGET_LRA_P + +@hook TARGET_REGISTER_PRIORITY + +@hook TARGET_REGISTER_USAGE_LEVELING_P + +@hook TARGET_DIFFERENT_ADDR_DISPLACEMENT_P + +@hook TARGET_CANNOT_SUBSTITUTE_MEM_EQUIV_P + +@hook TARGET_LEGITIMIZE_ADDRESS_DISPLACEMENT + +@hook TARGET_SPILL_CLASS + +@hook TARGET_ADDITIONAL_ALLOCNO_CLASS_P + +@hook TARGET_CSTORE_MODE + +@hook TARGET_COMPUTE_PRESSURE_CLASSES + +@node Stack and Calling +@section Stack Layout and Calling Conventions +@cindex calling conventions + +@c prevent bad page break with this line +This describes the stack layout and calling conventions. + +@menu +* Frame Layout:: +* Exception Handling:: +* Stack Checking:: +* Frame Registers:: +* Elimination:: +* Stack Arguments:: +* Register Arguments:: +* Scalar Return:: +* Aggregate Return:: +* Caller Saves:: +* Function Entry:: +* Profiling:: +* Tail Calls:: +* Shrink-wrapping separate components:: +* Stack Smashing Protection:: +* Miscellaneous Register Hooks:: +@end menu + +@node Frame Layout +@subsection Basic Stack Layout +@cindex stack frame layout +@cindex frame layout + +@c prevent bad page break with this line +Here is the basic stack layout. + +@defmac STACK_GROWS_DOWNWARD +Define this macro to be true if pushing a word onto the stack moves the stack +pointer to a smaller address, and false otherwise. +@end defmac + +@defmac STACK_PUSH_CODE +This macro defines the operation used when something is pushed +on the stack. In RTL, a push operation will be +@code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})} + +The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC}, +and @code{POST_INC}. Which of these is correct depends on +the stack direction and on whether the stack pointer points +to the last item on the stack or whether it points to the +space for the next item on the stack. + +The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is +true, which is almost always right, and @code{PRE_INC} otherwise, +which is often wrong. +@end defmac + +@defmac FRAME_GROWS_DOWNWARD +Define this macro to nonzero value if the addresses of local variable slots +are at negative offsets from the frame pointer. +@end defmac + +@defmac ARGS_GROW_DOWNWARD +Define this macro if successive arguments to a function occupy decreasing +addresses on the stack. +@end defmac + +@hook TARGET_STARTING_FRAME_OFFSET + +@defmac STACK_ALIGNMENT_NEEDED +Define to zero to disable final alignment of the stack during reload. +The nonzero default for this macro is suitable for most ports. + +On ports where @code{TARGET_STARTING_FRAME_OFFSET} is nonzero or where there +is a register save block following the local block that doesn't require +alignment to @code{STACK_BOUNDARY}, it may be beneficial to disable +stack alignment and do it in the backend. +@end defmac + +@defmac STACK_POINTER_OFFSET +Offset from the stack pointer register to the first location at which +outgoing arguments are placed. If not specified, the default value of +zero is used. This is the proper value for most machines. + +If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above +the first location at which outgoing arguments are placed. +@end defmac + +@defmac FIRST_PARM_OFFSET (@var{fundecl}) +Offset from the argument pointer register to the first argument's +address. On some machines it may depend on the data type of the +function. + +If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above +the first argument's address. +@end defmac + +@defmac STACK_DYNAMIC_OFFSET (@var{fundecl}) +Offset from the stack pointer register to an item dynamically allocated +on the stack, e.g., by @code{alloca}. + +The default value for this macro is @code{STACK_POINTER_OFFSET} plus the +length of the outgoing arguments. The default is correct for most +machines. See @file{function.cc} for details. +@end defmac + +@defmac INITIAL_FRAME_ADDRESS_RTX +A C expression whose value is RTL representing the address of the initial +stack frame. This address is passed to @code{RETURN_ADDR_RTX} and +@code{DYNAMIC_CHAIN_ADDRESS}. If you don't define this macro, a reasonable +default value will be used. Define this macro in order to make frame pointer +elimination work in the presence of @code{__builtin_frame_address (count)} and +@code{__builtin_return_address (count)} for @code{count} not equal to zero. +@end defmac + +@defmac DYNAMIC_CHAIN_ADDRESS (@var{frameaddr}) +A C expression whose value is RTL representing the address in a stack +frame where the pointer to the caller's frame is stored. Assume that +@var{frameaddr} is an RTL expression for the address of the stack frame +itself. + +If you don't define this macro, the default is to return the value +of @var{frameaddr}---that is, the stack frame address is also the +address of the stack word that points to the previous frame. +@end defmac + +@defmac SETUP_FRAME_ADDRESSES +A C expression that produces the machine-specific code to +setup the stack so that arbitrary frames can be accessed. For example, +on the SPARC, we must flush all of the register windows to the stack +before we can access arbitrary stack frames. You will seldom need to +define this macro. The default is to do nothing. +@end defmac + +@hook TARGET_BUILTIN_SETJMP_FRAME_VALUE + +@defmac FRAME_ADDR_RTX (@var{frameaddr}) +A C expression whose value is RTL representing the value of the frame +address for the current frame. @var{frameaddr} is the frame pointer +of the current frame. This is used for __builtin_frame_address. +You need only define this macro if the frame address is not the same +as the frame pointer. Most machines do not need to define it. +@end defmac + +@defmac RETURN_ADDR_RTX (@var{count}, @var{frameaddr}) +A C expression whose value is RTL representing the value of the return +address for the frame @var{count} steps up from the current frame, after +the prologue. @var{frameaddr} is the frame pointer of the @var{count} +frame, or the frame pointer of the @var{count} @minus{} 1 frame if +@code{RETURN_ADDR_IN_PREVIOUS_FRAME} is nonzero. + +The value of the expression must always be the correct address when +@var{count} is zero, but may be @code{NULL_RTX} if there is no way to +determine the return address of other frames. +@end defmac + +@defmac RETURN_ADDR_IN_PREVIOUS_FRAME +Define this macro to nonzero value if the return address of a particular +stack frame is accessed from the frame pointer of the previous stack +frame. The zero default for this macro is suitable for most ports. +@end defmac + +@defmac INCOMING_RETURN_ADDR_RTX +A C expression whose value is RTL representing the location of the +incoming return address at the beginning of any function, before the +prologue. This RTL is either a @code{REG}, indicating that the return +value is saved in @samp{REG}, or a @code{MEM} representing a location in +the stack. + +You only need to define this macro if you want to support call frame +debugging information like that provided by DWARF 2. + +If this RTL is a @code{REG}, you should also define +@code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}. +@end defmac + +@defmac DWARF_ALT_FRAME_RETURN_COLUMN +A C expression whose value is an integer giving a DWARF 2 column +number that may be used as an alternative return column. The column +must not correspond to any gcc hard register (that is, it must not +be in the range of @code{DWARF_FRAME_REGNUM}). + +This macro can be useful if @code{DWARF_FRAME_RETURN_COLUMN} is set to a +general register, but an alternative column needs to be used for signal +frames. Some targets have also used different frame return columns +over time. +@end defmac + +@defmac DWARF_ZERO_REG +A C expression whose value is an integer giving a DWARF 2 register +number that is considered to always have the value zero. This should +only be defined if the target has an architected zero register, and +someone decided it was a good idea to use that register number to +terminate the stack backtrace. New ports should avoid this. +@end defmac + +@defmac DWARF_VERSION_DEFAULT +A C expression whose value is the default dwarf standard version we'll honor +and advertise when generating dwarf debug information, in absence of +an explicit @option{-gdwarf-@var{version}} option on the command line. +@end defmac + +@hook TARGET_DWARF_HANDLE_FRAME_UNSPEC + +@hook TARGET_DWARF_POLY_INDETERMINATE_VALUE + +@defmac INCOMING_FRAME_SP_OFFSET +A C expression whose value is an integer giving the offset, in bytes, +from the value of the stack pointer register to the top of the stack +frame at the beginning of any function, before the prologue. The top of +the frame is defined to be the value of the stack pointer in the +previous frame, just before the call instruction. + +You only need to define this macro if you want to support call frame +debugging information like that provided by DWARF 2. +@end defmac + +@defmac DEFAULT_INCOMING_FRAME_SP_OFFSET +Like @code{INCOMING_FRAME_SP_OFFSET}, but must be the same for all +functions of the same ABI, and when using GAS @code{.cfi_*} directives +must also agree with the default CFI GAS emits. Define this macro +only if @code{INCOMING_FRAME_SP_OFFSET} can have different values +between different functions of the same ABI or when +@code{INCOMING_FRAME_SP_OFFSET} does not agree with GAS default CFI. +@end defmac + +@defmac ARG_POINTER_CFA_OFFSET (@var{fundecl}) +A C expression whose value is an integer giving the offset, in bytes, +from the argument pointer to the canonical frame address (cfa). The +final value should coincide with that calculated by +@code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable +during virtual register instantiation. + +The default value for this macro is +@code{FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size}, +which is correct for most machines; in general, the arguments are found +immediately before the stack frame. Note that this is not the case on +some targets that save registers into the caller's frame, such as SPARC +and rs6000, and so such targets need to define this macro. + +You only need to define this macro if the default is incorrect, and you +want to support call frame debugging information like that provided by +DWARF 2. +@end defmac + +@defmac FRAME_POINTER_CFA_OFFSET (@var{fundecl}) +If defined, a C expression whose value is an integer giving the offset +in bytes from the frame pointer to the canonical frame address (cfa). +The final value should coincide with that calculated by +@code{INCOMING_FRAME_SP_OFFSET}. + +Normally the CFA is calculated as an offset from the argument pointer, +via @code{ARG_POINTER_CFA_OFFSET}, but if the argument pointer is +variable due to the ABI, this may not be possible. If this macro is +defined, it implies that the virtual register instantiation should be +based on the frame pointer instead of the argument pointer. Only one +of @code{FRAME_POINTER_CFA_OFFSET} and @code{ARG_POINTER_CFA_OFFSET} +should be defined. +@end defmac + +@defmac CFA_FRAME_BASE_OFFSET (@var{fundecl}) +If defined, a C expression whose value is an integer giving the offset +in bytes from the canonical frame address (cfa) to the frame base used +in DWARF 2 debug information. The default is zero. A different value +may reduce the size of debug information on some ports. +@end defmac + +@node Exception Handling +@subsection Exception Handling Support +@cindex exception handling + +@defmac EH_RETURN_DATA_REGNO (@var{N}) +A C expression whose value is the @var{N}th register number used for +data by exception handlers, or @code{INVALID_REGNUM} if fewer than +@var{N} registers are usable. + +The exception handling library routines communicate with the exception +handlers via a set of agreed upon registers. Ideally these registers +should be call-clobbered; it is possible to use call-saved registers, +but may negatively impact code size. The target must support at least +2 data registers, but should define 4 if there are enough free registers. + +You must define this macro if you want to support call frame exception +handling like that provided by DWARF 2. +@end defmac + +@defmac EH_RETURN_STACKADJ_RTX +A C expression whose value is RTL representing a location in which +to store a stack adjustment to be applied before function return. +This is used to unwind the stack to an exception handler's call frame. +It will be assigned zero on code paths that return normally. + +Typically this is a call-clobbered hard register that is otherwise +untouched by the epilogue, but could also be a stack slot. + +Do not define this macro if the stack pointer is saved and restored +by the regular prolog and epilog code in the call frame itself; in +this case, the exception handling library routines will update the +stack location to be restored in place. Otherwise, you must define +this macro if you want to support call frame exception handling like +that provided by DWARF 2. +@end defmac + +@defmac EH_RETURN_HANDLER_RTX +A C expression whose value is RTL representing a location in which +to store the address of an exception handler to which we should +return. It will not be assigned on code paths that return normally. + +Typically this is the location in the call frame at which the normal +return address is stored. For targets that return by popping an +address off the stack, this might be a memory address just below +the @emph{target} call frame rather than inside the current call +frame. If defined, @code{EH_RETURN_STACKADJ_RTX} will have already +been assigned, so it may be used to calculate the location of the +target call frame. + +Some targets have more complex requirements than storing to an +address calculable during initial code generation. In that case +the @code{eh_return} instruction pattern should be used instead. + +If you want to support call frame exception handling, you must +define either this macro or the @code{eh_return} instruction pattern. +@end defmac + +@defmac RETURN_ADDR_OFFSET +If defined, an integer-valued C expression for which rtl will be generated +to add it to the exception handler address before it is searched in the +exception handling tables, and to subtract it again from the address before +using it to return to the exception handler. +@end defmac + +@defmac ASM_PREFERRED_EH_DATA_FORMAT (@var{code}, @var{global}) +This macro chooses the encoding of pointers embedded in the exception +handling sections. If at all possible, this should be defined such +that the exception handling section will not require dynamic relocations, +and so may be read-only. + +@var{code} is 0 for data, 1 for code labels, 2 for function pointers. +@var{global} is true if the symbol may be affected by dynamic relocations. +The macro should return a combination of the @code{DW_EH_PE_*} defines +as found in @file{dwarf2.h}. + +If this macro is not defined, pointers will not be encoded but +represented directly. +@end defmac + +@defmac ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX (@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done}) +This macro allows the target to emit whatever special magic is required +to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}. +Generic code takes care of pc-relative and indirect encodings; this must +be defined if the target uses text-relative or data-relative encodings. + +This is a C statement that branches to @var{done} if the format was +handled. @var{encoding} is the format chosen, @var{size} is the number +of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF} +to be emitted. +@end defmac + +@defmac MD_FALLBACK_FRAME_STATE_FOR (@var{context}, @var{fs}) +This macro allows the target to add CPU and operating system specific +code to the call-frame unwinder for use when there is no unwind data +available. The most common reason to implement this macro is to unwind +through signal frames. + +This macro is called from @code{uw_frame_state_for} in +@file{unwind-dw2.c}, @file{unwind-dw2-xtensa.c} and +@file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; +@var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra} +for the address of the code being executed and @code{context->cfa} for +the stack pointer value. If the frame can be decoded, the register +save addresses should be updated in @var{fs} and the macro should +evaluate to @code{_URC_NO_REASON}. If the frame cannot be decoded, +the macro should evaluate to @code{_URC_END_OF_STACK}. + +For proper signal handling in Java this macro is accompanied by +@code{MAKE_THROW_FRAME}, defined in @file{libjava/include/*-signal.h} headers. +@end defmac + +@defmac MD_HANDLE_UNWABI (@var{context}, @var{fs}) +This macro allows the target to add operating system specific code to the +call-frame unwinder to handle the IA-64 @code{.unwabi} unwinding directive, +usually used for signal or interrupt frames. + +This macro is called from @code{uw_update_context} in libgcc's +@file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; +@var{fs} is an @code{_Unwind_FrameState}. Examine @code{fs->unwabi} +for the abi and context in the @code{.unwabi} directive. If the +@code{.unwabi} directive can be handled, the register save addresses should +be updated in @var{fs}. +@end defmac + +@defmac TARGET_USES_WEAK_UNWIND_INFO +A C expression that evaluates to true if the target requires unwind +info to be given comdat linkage. Define it to be @code{1} if comdat +linkage is necessary. The default is @code{0}. +@end defmac + +@node Stack Checking +@subsection Specifying How Stack Checking is Done + +GCC will check that stack references are within the boundaries of the +stack, if the option @option{-fstack-check} is specified, in one of +three ways: + +@enumerate +@item +If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC +will assume that you have arranged for full stack checking to be done +at appropriate places in the configuration files. GCC will not do +other special processing. + +@item +If @code{STACK_CHECK_BUILTIN} is zero and the value of the +@code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume +that you have arranged for static stack checking (checking of the +static stack frame of functions) to be done at appropriate places +in the configuration files. GCC will only emit code to do dynamic +stack checking (checking on dynamic stack allocations) using the third +approach below. + +@item +If neither of the above are true, GCC will generate code to periodically +``probe'' the stack pointer using the values of the macros defined below. +@end enumerate + +If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined, +GCC will change its allocation strategy for large objects if the option +@option{-fstack-check} is specified: they will always be allocated +dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes. + +@defmac STACK_CHECK_BUILTIN +A nonzero value if stack checking is done by the configuration files in a +machine-dependent manner. You should define this macro if stack checking +is required by the ABI of your machine or if you would like to do stack +checking in some more efficient way than the generic approach. The default +value of this macro is zero. +@end defmac + +@defmac STACK_CHECK_STATIC_BUILTIN +A nonzero value if static stack checking is done by the configuration files +in a machine-dependent manner. You should define this macro if you would +like to do static stack checking in some more efficient way than the generic +approach. The default value of this macro is zero. +@end defmac + +@defmac STACK_CHECK_PROBE_INTERVAL_EXP +An integer specifying the interval at which GCC must generate stack probe +instructions, defined as 2 raised to this integer. You will normally +define this macro so that the interval be no larger than the size of +the ``guard pages'' at the end of a stack area. The default value +of 12 (4096-byte interval) is suitable for most systems. +@end defmac + +@defmac STACK_CHECK_MOVING_SP +An integer which is nonzero if GCC should move the stack pointer page by page +when doing probes. This can be necessary on systems where the stack pointer +contains the bottom address of the memory area accessible to the executing +thread at any point in time. In this situation an alternate signal stack +is required in order to be able to recover from a stack overflow. The +default value of this macro is zero. +@end defmac + +@defmac STACK_CHECK_PROTECT +The number of bytes of stack needed to recover from a stack overflow, for +languages where such a recovery is supported. The default value of 4KB/8KB +with the @code{setjmp}/@code{longjmp}-based exception handling mechanism and +8KB/12KB with other exception handling mechanisms should be adequate for most +architectures and operating systems. +@end defmac + +The following macros are relevant only if neither STACK_CHECK_BUILTIN +nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether +in the opposite case. + +@defmac STACK_CHECK_MAX_FRAME_SIZE +The maximum size of a stack frame, in bytes. GCC will generate probe +instructions in non-leaf functions to ensure at least this many bytes of +stack are available. If a stack frame is larger than this size, stack +checking will not be reliable and GCC will issue a warning. The +default is chosen so that GCC only generates one instruction on most +systems. You should normally not change the default value of this macro. +@end defmac + +@defmac STACK_CHECK_FIXED_FRAME_SIZE +GCC uses this value to generate the above warning message. It +represents the amount of fixed frame used by a function, not including +space for any callee-saved registers, temporaries and user variables. +You need only specify an upper bound for this amount and will normally +use the default of four words. +@end defmac + +@defmac STACK_CHECK_MAX_VAR_SIZE +The maximum size, in bytes, of an object that GCC will place in the +fixed area of the stack frame when the user specifies +@option{-fstack-check}. +GCC computed the default from the values of the above macros and you will +normally not need to override that default. +@end defmac + +@hook TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE + +@need 2000 +@node Frame Registers +@subsection Registers That Address the Stack Frame + +@c prevent bad page break with this line +This discusses registers that address the stack frame. + +@defmac STACK_POINTER_REGNUM +The register number of the stack pointer register, which must also be a +fixed register according to @code{FIXED_REGISTERS}. On most machines, +the hardware determines which register this is. +@end defmac + +@defmac FRAME_POINTER_REGNUM +The register number of the frame pointer register, which is used to +access automatic variables in the stack frame. On some machines, the +hardware determines which register this is. On other machines, you can +choose any register you wish for this purpose. +@end defmac + +@defmac HARD_FRAME_POINTER_REGNUM +On some machines the offset between the frame pointer and starting +offset of the automatic variables is not known until after register +allocation has been done (for example, because the saved registers are +between these two locations). On those machines, define +@code{FRAME_POINTER_REGNUM} the number of a special, fixed register to +be used internally until the offset is known, and define +@code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number +used for the frame pointer. + +You should define this macro only in the very rare circumstances when it +is not possible to calculate the offset between the frame pointer and +the automatic variables until after register allocation has been +completed. When this macro is defined, you must also indicate in your +definition of @code{ELIMINABLE_REGS} how to eliminate +@code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM} +or @code{STACK_POINTER_REGNUM}. + +Do not define this macro if it would be the same as +@code{FRAME_POINTER_REGNUM}. +@end defmac + +@defmac ARG_POINTER_REGNUM +The register number of the arg pointer register, which is used to access +the function's argument list. On some machines, this is the same as the +frame pointer register. On some machines, the hardware determines which +register this is. On other machines, you can choose any register you +wish for this purpose. If this is not the same register as the frame +pointer register, then you must mark it as a fixed register according to +@code{FIXED_REGISTERS}, or arrange to be able to eliminate it +(@pxref{Elimination}). +@end defmac + +@defmac HARD_FRAME_POINTER_IS_FRAME_POINTER +Define this to a preprocessor constant that is nonzero if +@code{hard_frame_pointer_rtx} and @code{frame_pointer_rtx} should be +the same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM +== FRAME_POINTER_REGNUM)}; you only need to define this macro if that +definition is not suitable for use in preprocessor conditionals. +@end defmac + +@defmac HARD_FRAME_POINTER_IS_ARG_POINTER +Define this to a preprocessor constant that is nonzero if +@code{hard_frame_pointer_rtx} and @code{arg_pointer_rtx} should be the +same. The default definition is @samp{(HARD_FRAME_POINTER_REGNUM == +ARG_POINTER_REGNUM)}; you only need to define this macro if that +definition is not suitable for use in preprocessor conditionals. +@end defmac + +@defmac RETURN_ADDRESS_POINTER_REGNUM +The register number of the return address pointer register, which is used to +access the current function's return address from the stack. On some +machines, the return address is not at a fixed offset from the frame +pointer or stack pointer or argument pointer. This register can be defined +to point to the return address on the stack, and then be converted by +@code{ELIMINABLE_REGS} into either the frame pointer or stack pointer. + +Do not define this macro unless there is no other way to get the return +address from the stack. +@end defmac + +@defmac STATIC_CHAIN_REGNUM +@defmacx STATIC_CHAIN_INCOMING_REGNUM +Register numbers used for passing a function's static chain pointer. If +register windows are used, the register number as seen by the called +function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register +number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If +these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need +not be defined. + +The static chain register need not be a fixed register. + +If the static chain is passed in memory, these macros should not be +defined; instead, the @code{TARGET_STATIC_CHAIN} hook should be used. +@end defmac + +@hook TARGET_STATIC_CHAIN + +@defmac DWARF_FRAME_REGISTERS +This macro specifies the maximum number of hard registers that can be +saved in a call frame. This is used to size data structures used in +DWARF2 exception handling. + +Prior to GCC 3.0, this macro was needed in order to establish a stable +exception handling ABI in the face of adding new hard registers for ISA +extensions. In GCC 3.0 and later, the EH ABI is insulated from changes +in the number of hard registers. Nevertheless, this macro can still be +used to reduce the runtime memory requirements of the exception handling +routines, which can be substantial if the ISA contains a lot of +registers that are not call-saved. + +If this macro is not defined, it defaults to +@code{FIRST_PSEUDO_REGISTER}. +@end defmac + +@defmac PRE_GCC3_DWARF_FRAME_REGISTERS + +This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided +for backward compatibility in pre GCC 3.0 compiled code. + +If this macro is not defined, it defaults to +@code{DWARF_FRAME_REGISTERS}. +@end defmac + +@defmac DWARF_REG_TO_UNWIND_COLUMN (@var{regno}) + +Define this macro if the target's representation for dwarf registers +is different than the internal representation for unwind column. +Given a dwarf register, this macro should return the internal unwind +column number to use instead. +@end defmac + +@defmac DWARF_FRAME_REGNUM (@var{regno}) + +Define this macro if the target's representation for dwarf registers +used in .eh_frame or .debug_frame is different from that used in other +debug info sections. Given a GCC hard register number, this macro +should return the .eh_frame register number. The default is +@code{DEBUGGER_REGNO (@var{regno})}. + +@end defmac + +@defmac DWARF2_FRAME_REG_OUT (@var{regno}, @var{for_eh}) + +Define this macro to map register numbers held in the call frame info +that GCC has collected using @code{DWARF_FRAME_REGNUM} to those that +should be output in .debug_frame (@code{@var{for_eh}} is zero) and +.eh_frame (@code{@var{for_eh}} is nonzero). The default is to +return @code{@var{regno}}. + +@end defmac + +@defmac REG_VALUE_IN_UNWIND_CONTEXT + +Define this macro if the target stores register values as +@code{_Unwind_Word} type in unwind context. It should be defined if +target register size is larger than the size of @code{void *}. The +default is to store register values as @code{void *} type. + +@end defmac + +@defmac ASSUME_EXTENDED_UNWIND_CONTEXT + +Define this macro to be 1 if the target always uses extended unwind +context with version, args_size and by_value fields. If it is undefined, +it will be defined to 1 when @code{REG_VALUE_IN_UNWIND_CONTEXT} is +defined and 0 otherwise. + +@end defmac + +@defmac DWARF_LAZY_REGISTER_VALUE (@var{regno}, @var{value}) +Define this macro if the target has pseudo DWARF registers whose +values need to be computed lazily on demand by the unwinder (such as when +referenced in a CFA expression). The macro returns true if @var{regno} +is such a register and stores its value in @samp{*@var{value}} if so. +@end defmac + +@node Elimination +@subsection Eliminating Frame Pointer and Arg Pointer + +@c prevent bad page break with this line +This is about eliminating the frame pointer and arg pointer. + +@hook TARGET_FRAME_POINTER_REQUIRED + +@defmac ELIMINABLE_REGS +This macro specifies a table of register pairs used to eliminate +unneeded registers that point into the stack frame. + +The definition of this macro is a list of structure initializations, each +of which specifies an original and replacement register. + +On some machines, the position of the argument pointer is not known until +the compilation is completed. In such a case, a separate hard register +must be used for the argument pointer. This register can be eliminated by +replacing it with either the frame pointer or the argument pointer, +depending on whether or not the frame pointer has been eliminated. + +In this case, you might specify: +@smallexample +#define ELIMINABLE_REGS \ +@{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \ + @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \ + @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@} +@end smallexample + +Note that the elimination of the argument pointer with the stack pointer is +specified first since that is the preferred elimination. +@end defmac + +@hook TARGET_CAN_ELIMINATE + +@defmac INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var}) +This macro returns the initial difference between the specified pair +of registers. The value would be computed from information +such as the result of @code{get_frame_size ()} and the tables of +registers @code{df_regs_ever_live_p} and @code{call_used_regs}. +@end defmac + +@hook TARGET_COMPUTE_FRAME_LAYOUT + +@node Stack Arguments +@subsection Passing Function Arguments on the Stack +@cindex arguments on stack +@cindex stack arguments + +The macros in this section control how arguments are passed +on the stack. See the following section for other macros that +control passing certain arguments in registers. + +@hook TARGET_PROMOTE_PROTOTYPES + +@hook TARGET_PUSH_ARGUMENT + +@defmac PUSH_ARGS_REVERSED +A C expression. If nonzero, function arguments will be evaluated from +last to first, rather than from first to last. If this macro is not +defined, it defaults to @code{PUSH_ARGS} on targets where the stack +and args grow in opposite directions, and 0 otherwise. +@end defmac + +@defmac PUSH_ROUNDING (@var{npushed}) +A C expression that is the number of bytes actually pushed onto the +stack when an instruction attempts to push @var{npushed} bytes. + +On some machines, the definition + +@smallexample +#define PUSH_ROUNDING(BYTES) (BYTES) +@end smallexample + +@noindent +will suffice. But on other machines, instructions that appear +to push one byte actually push two bytes in an attempt to maintain +alignment. Then the definition should be + +@smallexample +#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) +@end smallexample + +If the value of this macro has a type, it should be an unsigned type. +@end defmac + +@findex outgoing_args_size +@findex crtl->outgoing_args_size +@defmac ACCUMULATE_OUTGOING_ARGS +A C expression. If nonzero, the maximum amount of space required for outgoing arguments +will be computed and placed into +@code{crtl->outgoing_args_size}. No space will be pushed +onto the stack for each call; instead, the function prologue should +increase the stack frame size by this amount. + +Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS} +is not proper. +@end defmac + +@defmac REG_PARM_STACK_SPACE (@var{fndecl}) +Define this macro if functions should assume that stack space has been +allocated for arguments even when their values are passed in +registers. + +The value of this macro is the size, in bytes, of the area reserved for +arguments passed in registers for the function represented by @var{fndecl}, +which can be zero if GCC is calling a library function. +The argument @var{fndecl} can be the FUNCTION_DECL, or the type itself +of the function. + +This space can be allocated by the caller, or be a part of the +machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says +which. +@end defmac +@c above is overfull. not sure what to do. --mew 5feb93 did +@c something, not sure if it looks good. --mew 10feb93 + +@defmac INCOMING_REG_PARM_STACK_SPACE (@var{fndecl}) +Like @code{REG_PARM_STACK_SPACE}, but for incoming register arguments. +Define this macro if space guaranteed when compiling a function body +is different to space required when making a call, a situation that +can arise with K&R style function definitions. +@end defmac + +@defmac OUTGOING_REG_PARM_STACK_SPACE (@var{fntype}) +Define this to a nonzero value if it is the responsibility of the +caller to allocate the area reserved for arguments passed in registers +when calling a function of @var{fntype}. @var{fntype} may be NULL +if the function called is a library function. + +If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls +whether the space for these arguments counts in the value of +@code{crtl->outgoing_args_size}. +@end defmac + +@defmac STACK_PARMS_IN_REG_PARM_AREA +Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the +stack parameters don't skip the area specified by it. +@c i changed this, makes more sens and it should have taken care of the +@c overfull.. not as specific, tho. --mew 5feb93 + +Normally, when a parameter is not passed in registers, it is placed on the +stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro +suppresses this behavior and causes the parameter to be passed on the +stack in its natural location. +@end defmac + +@hook TARGET_RETURN_POPS_ARGS + +@defmac CALL_POPS_ARGS (@var{cum}) +A C expression that should indicate the number of bytes a call sequence +pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS} +when compiling a function call. + +@var{cum} is the variable in which all arguments to the called function +have been accumulated. + +On certain architectures, such as the SH5, a call trampoline is used +that pops certain registers off the stack, depending on the arguments +that have been passed to the function. Since this is a property of the +call site, not of the called function, @code{RETURN_POPS_ARGS} is not +appropriate. +@end defmac + +@node Register Arguments +@subsection Passing Arguments in Registers +@cindex arguments in registers +@cindex registers arguments + +This section describes the macros which let you control how various +types of arguments are passed in registers or how they are arranged in +the stack. + +@hook TARGET_FUNCTION_ARG + +@hook TARGET_MUST_PASS_IN_STACK + +@hook TARGET_FUNCTION_INCOMING_ARG + +@hook TARGET_USE_PSEUDO_PIC_REG + +@hook TARGET_INIT_PIC_REG + +@hook TARGET_ARG_PARTIAL_BYTES + +@hook TARGET_PASS_BY_REFERENCE + +@hook TARGET_CALLEE_COPIES + +@defmac CUMULATIVE_ARGS +A C type for declaring a variable that is used as the first argument +of @code{TARGET_FUNCTION_ARG} and other related values. For some +target machines, the type @code{int} suffices and can hold the number +of bytes of argument so far. + +There is no need to record in @code{CUMULATIVE_ARGS} anything about the +arguments that have been passed on the stack. The compiler has other +variables to keep track of that. For target machines on which all +arguments are passed on the stack, there is no need to store anything in +@code{CUMULATIVE_ARGS}; however, the data structure must exist and +should not be empty, so use @code{int}. +@end defmac + +@defmac OVERRIDE_ABI_FORMAT (@var{fndecl}) +If defined, this macro is called before generating any code for a +function, but after the @var{cfun} descriptor for the function has been +created. The back end may use this macro to update @var{cfun} to +reflect an ABI other than that which would normally be used by default. +If the compiler is generating code for a compiler-generated function, +@var{fndecl} may be @code{NULL}. +@end defmac + +@defmac INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{fndecl}, @var{n_named_args}) +A C statement (sans semicolon) for initializing the variable +@var{cum} for the state at the beginning of the argument list. The +variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype} +is the tree node for the data type of the function which will receive +the args, or 0 if the args are to a compiler support library function. +For direct calls that are not libcalls, @var{fndecl} contain the +declaration node of the function. @var{fndecl} is also set when +@code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function +being compiled. @var{n_named_args} is set to the number of named +arguments, including a structure return address if it is passed as a +parameter, when making a call. When processing incoming arguments, +@var{n_named_args} is set to @minus{}1. + +When processing a call to a compiler support library function, +@var{libname} identifies which one. It is a @code{symbol_ref} rtx which +contains the name of the function, as a string. @var{libname} is 0 when +an ordinary C function call is being processed. Thus, each time this +macro is called, either @var{libname} or @var{fntype} is nonzero, but +never both of them at once. +@end defmac + +@defmac INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname}) +Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls, +it gets a @code{MODE} argument instead of @var{fntype}, that would be +@code{NULL}. @var{indirect} would always be zero, too. If this macro +is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, +0)} is used instead. +@end defmac + +@defmac INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname}) +Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of +finding the arguments for the function being compiled. If this macro is +undefined, @code{INIT_CUMULATIVE_ARGS} is used instead. + +The value passed for @var{libname} is always 0, since library routines +with special calling conventions are never compiled with GCC@. The +argument @var{libname} exists for symmetry with +@code{INIT_CUMULATIVE_ARGS}. +@c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe. +@c --mew 5feb93 i switched the order of the sentences. --mew 10feb93 +@end defmac + +@hook TARGET_FUNCTION_ARG_ADVANCE + +@hook TARGET_FUNCTION_ARG_OFFSET + +@hook TARGET_FUNCTION_ARG_PADDING + +@defmac PAD_VARARGS_DOWN +If defined, a C expression which determines whether the default +implementation of va_arg will attempt to pad down before reading the +next argument, if that argument is smaller than its aligned space as +controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such +arguments are padded down if @code{BYTES_BIG_ENDIAN} is true. +@end defmac + +@defmac BLOCK_REG_PADDING (@var{mode}, @var{type}, @var{first}) +Specify padding for the last element of a block move between registers and +memory. @var{first} is nonzero if this is the only element. Defining this +macro allows better control of register function parameters on big-endian +machines, without using @code{PARALLEL} rtl. In particular, +@code{MUST_PASS_IN_STACK} need not test padding and mode of types in +registers, as there is no longer a "wrong" part of a register; For example, +a three byte aggregate may be passed in the high part of a register if so +required. +@end defmac + +@hook TARGET_FUNCTION_ARG_BOUNDARY + +@hook TARGET_FUNCTION_ARG_ROUND_BOUNDARY + +@defmac FUNCTION_ARG_REGNO_P (@var{regno}) +A C expression that is nonzero if @var{regno} is the number of a hard +register in which function arguments are sometimes passed. This does +@emph{not} include implicit arguments such as the static chain and +the structure-value address. On many machines, no registers can be +used for this purpose since all function arguments are pushed on the +stack. +@end defmac + +@hook TARGET_SPLIT_COMPLEX_ARG + +@hook TARGET_BUILD_BUILTIN_VA_LIST + +@hook TARGET_ENUM_VA_LIST_P + +@hook TARGET_FN_ABI_VA_LIST + +@hook TARGET_CANONICAL_VA_LIST_TYPE + +@hook TARGET_GIMPLIFY_VA_ARG_EXPR + +@hook TARGET_VALID_POINTER_MODE + +@hook TARGET_REF_MAY_ALIAS_ERRNO + +@hook TARGET_TRANSLATE_MODE_ATTRIBUTE + +@hook TARGET_SCALAR_MODE_SUPPORTED_P + +@hook TARGET_VECTOR_MODE_SUPPORTED_P + +@hook TARGET_COMPATIBLE_VECTOR_TYPES_P + +@hook TARGET_ARRAY_MODE + +@hook TARGET_ARRAY_MODE_SUPPORTED_P + +@hook TARGET_LIBGCC_FLOATING_MODE_SUPPORTED_P + +@hook TARGET_FLOATN_MODE + +@hook TARGET_FLOATN_BUILTIN_P + +@hook TARGET_SMALL_REGISTER_CLASSES_FOR_MODE_P + +@node Scalar Return +@subsection How Scalar Function Values Are Returned +@cindex return values in registers +@cindex values, returned by functions +@cindex scalars, returned as values + +This section discusses the macros that control returning scalars as +values---values that can fit in registers. + +@hook TARGET_FUNCTION_VALUE + +@defmac FUNCTION_VALUE (@var{valtype}, @var{func}) +This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE} for +a new target instead. +@end defmac + +@defmac LIBCALL_VALUE (@var{mode}) +A C expression to create an RTX representing the place where a library +function returns a value of mode @var{mode}. + +Note that ``library function'' in this context means a compiler +support routine, used to perform arithmetic, whose name is known +specially by the compiler and was not mentioned in the C code being +compiled. +@end defmac + +@hook TARGET_LIBCALL_VALUE + +@defmac FUNCTION_VALUE_REGNO_P (@var{regno}) +A C expression that is nonzero if @var{regno} is the number of a hard +register in which the values of called function may come back. + +A register whose use for returning values is limited to serving as the +second of a pair (for a value of type @code{double}, say) need not be +recognized by this macro. So for most machines, this definition +suffices: + +@smallexample +#define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) +@end smallexample + +If the machine has register windows, so that the caller and the called +function use different registers for the return value, this macro +should recognize only the caller's register numbers. + +This macro has been deprecated. Use @code{TARGET_FUNCTION_VALUE_REGNO_P} +for a new target instead. +@end defmac + +@hook TARGET_FUNCTION_VALUE_REGNO_P + +@defmac APPLY_RESULT_SIZE +Define this macro if @samp{untyped_call} and @samp{untyped_return} +need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for +saving and restoring an arbitrary return value. +@end defmac + +@hook TARGET_OMIT_STRUCT_RETURN_REG + +@hook TARGET_RETURN_IN_MSB + +@node Aggregate Return +@subsection How Large Values Are Returned +@cindex aggregates as return values +@cindex large return values +@cindex returning aggregate values +@cindex structure value address + +When a function value's mode is @code{BLKmode} (and in some other +cases), the value is not returned according to +@code{TARGET_FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the +caller passes the address of a block of memory in which the value +should be stored. This address is called the @dfn{structure value +address}. + +This section describes how to control returning structure values in +memory. + +@hook TARGET_RETURN_IN_MEMORY + +@defmac DEFAULT_PCC_STRUCT_RETURN +Define this macro to be 1 if all structure and union return values must be +in memory. Since this results in slower code, this should be defined +only if needed for compatibility with other compilers or with an ABI@. +If you define this macro to be 0, then the conventions used for structure +and union return values are decided by the @code{TARGET_RETURN_IN_MEMORY} +target hook. + +If not defined, this defaults to the value 1. +@end defmac + +@hook TARGET_STRUCT_VALUE_RTX + +@defmac PCC_STATIC_STRUCT_RETURN +Define this macro if the usual system convention on the target machine +for returning structures and unions is for the called function to return +the address of a static variable containing the value. + +Do not define this if the usual system convention is for the caller to +pass an address to the subroutine. + +This macro has effect in @option{-fpcc-struct-return} mode, but it does +nothing when you use @option{-freg-struct-return} mode. +@end defmac + +@hook TARGET_GET_RAW_RESULT_MODE + +@hook TARGET_GET_RAW_ARG_MODE + +@hook TARGET_EMPTY_RECORD_P + +@hook TARGET_WARN_PARAMETER_PASSING_ABI + +@node Caller Saves +@subsection Caller-Saves Register Allocation + +If you enable it, GCC can save registers around function calls. This +makes it possible to use call-clobbered registers to hold variables that +must live across calls. + +@defmac HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs}) +A C expression specifying which mode is required for saving @var{nregs} +of a pseudo-register in call-clobbered hard register @var{regno}. If +@var{regno} is unsuitable for caller save, @code{VOIDmode} should be +returned. For most machines this macro need not be defined since GCC +will select the smallest suitable mode. +@end defmac + +@node Function Entry +@subsection Function Entry and Exit +@cindex function entry and exit +@cindex prologue +@cindex epilogue + +This section describes the macros that output function entry +(@dfn{prologue}) and exit (@dfn{epilogue}) code. + +@hook TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY + +@hook TARGET_ASM_FUNCTION_PROLOGUE + +@hook TARGET_ASM_FUNCTION_END_PROLOGUE + +@hook TARGET_ASM_FUNCTION_BEGIN_EPILOGUE + +@hook TARGET_ASM_FUNCTION_EPILOGUE + +@itemize @bullet +@item +@findex pretend_args_size +@findex crtl->args.pretend_args_size +A region of @code{crtl->args.pretend_args_size} bytes of +uninitialized space just underneath the first argument arriving on the +stack. (This may not be at the very start of the allocated stack region +if the calling sequence has pushed anything else since pushing the stack +arguments. But usually, on such machines, nothing else has been pushed +yet, because the function prologue itself does all the pushing.) This +region is used on machines where an argument may be passed partly in +registers and partly in memory, and, in some cases to support the +features in @code{}. + +@item +An area of memory used to save certain registers used by the function. +The size of this area, which may also include space for such things as +the return address and pointers to previous stack frames, is +machine-specific and usually depends on which registers have been used +in the function. Machines with register windows often do not require +a save area. + +@item +A region of at least @var{size} bytes, possibly rounded up to an allocation +boundary, to contain the local variables of the function. On some machines, +this region and the save area may occur in the opposite order, with the +save area closer to the top of the stack. + +@item +@cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames +Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of +@code{crtl->outgoing_args_size} bytes to be used for outgoing +argument lists of the function. @xref{Stack Arguments}. +@end itemize + +@defmac EXIT_IGNORE_STACK +Define this macro as a C expression that is nonzero if the return +instruction or the function epilogue ignores the value of the stack +pointer; in other words, if it is safe to delete an instruction to +adjust the stack pointer before a return from the function. The +default is 0. + +Note that this macro's value is relevant only for functions for which +frame pointers are maintained. It is never safe to delete a final +stack adjustment in a function that has no frame pointer, and the +compiler knows this regardless of @code{EXIT_IGNORE_STACK}. +@end defmac + +@defmac EPILOGUE_USES (@var{regno}) +Define this macro as a C expression that is nonzero for registers that are +used by the epilogue or the @samp{return} pattern. The stack and frame +pointer registers are already assumed to be used as needed. +@end defmac + +@defmac EH_USES (@var{regno}) +Define this macro as a C expression that is nonzero for registers that are +used by the exception handling mechanism, and so should be considered live +on entry to an exception edge. +@end defmac + +@hook TARGET_ASM_OUTPUT_MI_THUNK + +@hook TARGET_ASM_CAN_OUTPUT_MI_THUNK + +@node Profiling +@subsection Generating Code for Profiling +@cindex profiling, code generation + +These macros will help you generate code for profiling. + +@defmac FUNCTION_PROFILER (@var{file}, @var{labelno}) +A C statement or compound statement to output to @var{file} some +assembler code to call the profiling subroutine @code{mcount}. + +@findex mcount +The details of how @code{mcount} expects to be called are determined by +your operating system environment, not by GCC@. To figure them out, +compile a small program for profiling using the system's installed C +compiler and look at the assembler code that results. + +Older implementations of @code{mcount} expect the address of a counter +variable to be loaded into some register. The name of this variable is +@samp{LP} followed by the number @var{labelno}, so you would generate +the name using @samp{LP%d} in a @code{fprintf}. +@end defmac + +@defmac PROFILE_HOOK +A C statement or compound statement to output to @var{file} some assembly +code to call the profiling subroutine @code{mcount} even the target does +not support profiling. +@end defmac + +@defmac NO_PROFILE_COUNTERS +Define this macro to be an expression with a nonzero value if the +@code{mcount} subroutine on your system does not need a counter variable +allocated for each function. This is true for almost all modern +implementations. If you define this macro, you must not use the +@var{labelno} argument to @code{FUNCTION_PROFILER}. +@end defmac + +@defmac PROFILE_BEFORE_PROLOGUE +Define this macro if the code for function profiling should come before +the function prologue. Normally, the profiling code comes after. +@end defmac + +@hook TARGET_KEEP_LEAF_WHEN_PROFILED + +@node Tail Calls +@subsection Permitting tail calls +@cindex tail calls + +@hook TARGET_FUNCTION_OK_FOR_SIBCALL + +@hook TARGET_EXTRA_LIVE_ON_ENTRY + +@hook TARGET_SET_UP_BY_PROLOGUE + +@hook TARGET_WARN_FUNC_RETURN + +@node Shrink-wrapping separate components +@subsection Shrink-wrapping separate components +@cindex shrink-wrapping separate components + +The prologue may perform a variety of target dependent tasks such as +saving callee-saved registers, saving the return address, aligning the +stack, creating a stack frame, initializing the PIC register, setting +up the static chain, etc. + +On some targets some of these tasks may be independent of others and +thus may be shrink-wrapped separately. These independent tasks are +referred to as components and are handled generically by the target +independent parts of GCC. + +Using the following hooks those prologue or epilogue components can be +shrink-wrapped separately, so that the initialization (and possibly +teardown) those components do is not done as frequently on execution +paths where this would unnecessary. + +What exactly those components are is up to the target code; the generic +code treats them abstractly, as a bit in an @code{sbitmap}. These +@code{sbitmap}s are allocated by the @code{shrink_wrap.get_separate_components} +and @code{shrink_wrap.components_for_bb} hooks, and deallocated by the +generic code. + +@hook TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS + +@hook TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB + +@hook TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS + +@hook TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS + +@hook TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS + +@hook TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS + +@node Stack Smashing Protection +@subsection Stack smashing protection +@cindex stack smashing protection + +@hook TARGET_STACK_PROTECT_GUARD + +@hook TARGET_STACK_PROTECT_FAIL + +@hook TARGET_STACK_PROTECT_RUNTIME_ENABLED_P + +@hook TARGET_SUPPORTS_SPLIT_STACK + +@hook TARGET_GET_VALID_OPTION_VALUES + +@node Miscellaneous Register Hooks +@subsection Miscellaneous register hooks +@cindex miscellaneous register hooks + +@hook TARGET_CALL_FUSAGE_CONTAINS_NON_CALLEE_CLOBBERS + +@node Varargs +@section Implementing the Varargs Macros +@cindex varargs implementation + +GCC comes with an implementation of @code{} and +@code{} that work without change on machines that pass arguments +on the stack. Other machines require their own implementations of +varargs, and the two machine independent header files must have +conditionals to include it. + +ISO @code{} differs from traditional @code{} mainly in +the calling convention for @code{va_start}. The traditional +implementation takes just one argument, which is the variable in which +to store the argument pointer. The ISO implementation of +@code{va_start} takes an additional second argument. The user is +supposed to write the last named argument of the function here. + +However, @code{va_start} should not use this argument. The way to find +the end of the named arguments is with the built-in functions described +below. + +@defmac __builtin_saveregs () +Use this built-in function to save the argument registers in memory so +that the varargs mechanism can access them. Both ISO and traditional +versions of @code{va_start} must use @code{__builtin_saveregs}, unless +you use @code{TARGET_SETUP_INCOMING_VARARGS} (see below) instead. + +On some machines, @code{__builtin_saveregs} is open-coded under the +control of the target hook @code{TARGET_EXPAND_BUILTIN_SAVEREGS}. On +other machines, it calls a routine written in assembler language, +found in @file{libgcc2.c}. + +Code generated for the call to @code{__builtin_saveregs} appears at the +beginning of the function, as opposed to where the call to +@code{__builtin_saveregs} is written, regardless of what the code is. +This is because the registers must be saved before the function starts +to use them for its own purposes. +@c i rewrote the first sentence above to fix an overfull hbox. --mew +@c 10feb93 +@end defmac + +@defmac __builtin_next_arg (@var{lastarg}) +This builtin returns the address of the first anonymous stack +argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it +returns the address of the location above the first anonymous stack +argument. Use it in @code{va_start} to initialize the pointer for +fetching arguments from the stack. Also use it in @code{va_start} to +verify that the second parameter @var{lastarg} is the last named argument +of the current function. +@end defmac + +@defmac __builtin_classify_type (@var{object}) +Since each machine has its own conventions for which data types are +passed in which kind of register, your implementation of @code{va_arg} +has to embody these conventions. The easiest way to categorize the +specified data type is to use @code{__builtin_classify_type} together +with @code{sizeof} and @code{__alignof__}. + +@code{__builtin_classify_type} ignores the value of @var{object}, +considering only its data type. It returns an integer describing what +kind of type that is---integer, floating, pointer, structure, and so on. + +The file @file{typeclass.h} defines an enumeration that you can use to +interpret the values of @code{__builtin_classify_type}. +@end defmac + +These machine description macros help implement varargs: + +@hook TARGET_EXPAND_BUILTIN_SAVEREGS + +@hook TARGET_SETUP_INCOMING_VARARGS + +@hook TARGET_STRICT_ARGUMENT_NAMING + +@hook TARGET_CALL_ARGS + +@hook TARGET_END_CALL_ARGS + +@hook TARGET_PRETEND_OUTGOING_VARARGS_NAMED + +@node Trampolines +@section Support for Nested Functions +@cindex support for nested functions +@cindex trampolines for nested functions +@cindex descriptors for nested functions +@cindex nested functions, support for + +Taking the address of a nested function requires special compiler +handling to ensure that the static chain register is loaded when +the function is invoked via an indirect call. + +GCC has traditionally supported nested functions by creating an +executable @dfn{trampoline} at run time when the address of a nested +function is taken. This is a small piece of code which normally +resides on the stack, in the stack frame of the containing function. +The trampoline loads the static chain register and then jumps to the +real address of the nested function. + +The use of trampolines requires an executable stack, which is a +security risk. To avoid this problem, GCC also supports another +strategy: using descriptors for nested functions. Under this model, +taking the address of a nested function results in a pointer to a +non-executable function descriptor object. Initializing the static chain +from the descriptor is handled at indirect call sites. + +On some targets, including HPPA and IA-64, function descriptors may be +mandated by the ABI or be otherwise handled in a target-specific way +by the back end in its code generation strategy for indirect calls. +GCC also provides its own generic descriptor implementation to support the +@option{-fno-trampolines} option. In this case runtime detection of +function descriptors at indirect call sites relies on descriptor +pointers being tagged with a bit that is never set in bare function +addresses. Since GCC's generic function descriptors are +not ABI-compliant, this option is typically used only on a +per-language basis (notably by Ada) or when it can otherwise be +applied to the whole program. + +For languages other than Ada, the @code{-ftrampolines} and +@code{-fno-trampolines} options currently have no effect, and +trampolines are always generated on platforms that need them +for nested functions. + +Define the following hook if your backend either implements ABI-specified +descriptor support, or can use GCC's generic descriptor implementation +for nested functions. + +@hook TARGET_CUSTOM_FUNCTION_DESCRIPTORS + +The following macros tell GCC how to generate code to allocate and +initialize an executable trampoline. You can also use this interface +if your back end needs to create ABI-specified non-executable descriptors; in +this case the "trampoline" created is the descriptor containing data only. + +The instructions in an executable trampoline must do two things: load +a constant address into the static chain register, and jump to the real +address of the nested function. On CISC machines such as the m68k, +this requires two instructions, a move immediate and a jump. Then the +two addresses exist in the trampoline as word-long immediate operands. +On RISC machines, it is often necessary to load each address into a +register in two parts. Then pieces of each address form separate +immediate operands. + +The code generated to initialize the trampoline must store the variable +parts---the static chain value and the function address---into the +immediate operands of the instructions. On a CISC machine, this is +simply a matter of copying each address to a memory reference at the +proper offset from the start of the trampoline. On a RISC machine, it +may be necessary to take out pieces of the address and store them +separately. + +@hook TARGET_ASM_TRAMPOLINE_TEMPLATE + +@defmac TRAMPOLINE_SECTION +Return the section into which the trampoline template is to be placed +(@pxref{Sections}). The default value is @code{readonly_data_section}. +@end defmac + +@defmac TRAMPOLINE_SIZE +A C expression for the size in bytes of the trampoline, as an integer. +@end defmac + +@defmac TRAMPOLINE_ALIGNMENT +Alignment required for trampolines, in bits. + +If you don't define this macro, the value of @code{FUNCTION_ALIGNMENT} +is used for aligning trampolines. +@end defmac + +@hook TARGET_TRAMPOLINE_INIT + +@hook TARGET_EMIT_CALL_BUILTIN___CLEAR_CACHE + +@hook TARGET_TRAMPOLINE_ADJUST_ADDRESS + +Implementing trampolines is difficult on many machines because they have +separate instruction and data caches. Writing into a stack location +fails to clear the memory in the instruction cache, so when the program +jumps to that location, it executes the old contents. + +Here are two possible solutions. One is to clear the relevant parts of +the instruction cache whenever a trampoline is set up. The other is to +make all trampolines identical, by having them jump to a standard +subroutine. The former technique makes trampoline execution faster; the +latter makes initialization faster. + +To clear the instruction cache when a trampoline is initialized, define +the following macro. + +@defmac CLEAR_INSN_CACHE (@var{beg}, @var{end}) +If defined, expands to a C expression clearing the @emph{instruction +cache} in the specified interval. The definition of this macro would +typically be a series of @code{asm} statements. Both @var{beg} and +@var{end} are pointer expressions. +@end defmac + +To use a standard subroutine, define the following macro. In addition, +you must make sure that the instructions in a trampoline fill an entire +cache line with identical instructions, or else ensure that the +beginning of the trampoline code is always aligned at the same point in +its cache line. Look in @file{m68k.h} as a guide. + +@defmac TRANSFER_FROM_TRAMPOLINE +Define this macro if trampolines need a special subroutine to do their +work. The macro should expand to a series of @code{asm} statements +which will be compiled with GCC@. They go in a library function named +@code{__transfer_from_trampoline}. + +If you need to avoid executing the ordinary prologue code of a compiled +C function when you jump to the subroutine, you can do so by placing a +special label of your own in the assembler code. Use one @code{asm} +statement to generate an assembler label, and another to make the label +global. Then trampolines can use that label to jump directly to your +special assembler code. +@end defmac + +@node Library Calls +@section Implicit Calls to Library Routines +@cindex library subroutine names +@cindex @file{libgcc.a} + +@c prevent bad page break with this line +Here is an explanation of implicit calls to library routines. + +@defmac DECLARE_LIBRARY_RENAMES +This macro, if defined, should expand to a piece of C code that will get +expanded when compiling functions for libgcc.a. It can be used to +provide alternate names for GCC's internal library functions if there +are ABI-mandated names that the compiler should provide. +@end defmac + +@findex set_optab_libfunc +@findex init_one_libfunc +@hook TARGET_INIT_LIBFUNCS + +@hook TARGET_LIBFUNC_GNU_PREFIX + +@defmac FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison}) +This macro should return @code{true} if the library routine that +implements the floating point comparison operator @var{comparison} in +mode @var{mode} will return a boolean, and @var{false} if it will +return a tristate. + +GCC's own floating point libraries return tristates from the +comparison operators, so the default returns false always. Most ports +don't need to define this macro. +@end defmac + +@defmac TARGET_LIB_INT_CMP_BIASED +This macro should evaluate to @code{true} if the integer comparison +functions (like @code{__cmpdi2}) return 0 to indicate that the first +operand is smaller than the second, 1 to indicate that they are equal, +and 2 to indicate that the first operand is greater than the second. +If this macro evaluates to @code{false} the comparison functions return +@minus{}1, 0, and 1 instead of 0, 1, and 2. If the target uses the routines +in @file{libgcc.a}, you do not need to define this macro. +@end defmac + +@defmac TARGET_HAS_NO_HW_DIVIDE +This macro should be defined if the target has no hardware divide +instructions. If this macro is defined, GCC will use an algorithm which +make use of simple logical and arithmetic operations for 64-bit +division. If the macro is not defined, GCC will use an algorithm which +make use of a 64-bit by 32-bit divide primitive. +@end defmac + +@cindex @code{EDOM}, implicit usage +@findex matherr +@defmac TARGET_EDOM +The value of @code{EDOM} on the target machine, as a C integer constant +expression. If you don't define this macro, GCC does not attempt to +deposit the value of @code{EDOM} into @code{errno} directly. Look in +@file{/usr/include/errno.h} to find the value of @code{EDOM} on your +system. + +If you do not define @code{TARGET_EDOM}, then compiled code reports +domain errors by calling the library function and letting it report the +error. If mathematical functions on your system use @code{matherr} when +there is an error, then you should leave @code{TARGET_EDOM} undefined so +that @code{matherr} is used normally. +@end defmac + +@cindex @code{errno}, implicit usage +@defmac GEN_ERRNO_RTX +Define this macro as a C expression to create an rtl expression that +refers to the global ``variable'' @code{errno}. (On certain systems, +@code{errno} may not actually be a variable.) If you don't define this +macro, a reasonable default is used. +@end defmac + +@hook TARGET_LIBC_HAS_FUNCTION + +@hook TARGET_LIBC_HAS_FAST_FUNCTION + +@defmac NEXT_OBJC_RUNTIME +Set this macro to 1 to use the "NeXT" Objective-C message sending conventions +by default. This calling convention involves passing the object, the selector +and the method arguments all at once to the method-lookup library function. +This is the usual setting when targeting Darwin/Mac OS X systems, which have +the NeXT runtime installed. + +If the macro is set to 0, the "GNU" Objective-C message sending convention +will be used by default. This convention passes just the object and the +selector to the method-lookup function, which returns a pointer to the method. + +In either case, it remains possible to select code-generation for the alternate +scheme, by means of compiler command line switches. +@end defmac + +@node Addressing Modes +@section Addressing Modes +@cindex addressing modes + +@c prevent bad page break with this line +This is about addressing modes. + +@defmac HAVE_PRE_INCREMENT +@defmacx HAVE_PRE_DECREMENT +@defmacx HAVE_POST_INCREMENT +@defmacx HAVE_POST_DECREMENT +A C expression that is nonzero if the machine supports pre-increment, +pre-decrement, post-increment, or post-decrement addressing respectively. +@end defmac + +@defmac HAVE_PRE_MODIFY_DISP +@defmacx HAVE_POST_MODIFY_DISP +A C expression that is nonzero if the machine supports pre- or +post-address side-effect generation involving constants other than +the size of the memory operand. +@end defmac + +@defmac HAVE_PRE_MODIFY_REG +@defmacx HAVE_POST_MODIFY_REG +A C expression that is nonzero if the machine supports pre- or +post-address side-effect generation involving a register displacement. +@end defmac + +@defmac CONSTANT_ADDRESS_P (@var{x}) +A C expression that is 1 if the RTX @var{x} is a constant which +is a valid address. On most machines the default definition of +@code{(CONSTANT_P (@var{x}) && GET_CODE (@var{x}) != CONST_DOUBLE)} +is acceptable, but a few machines are more restrictive as to which +constant addresses are supported. +@end defmac + +@defmac CONSTANT_P (@var{x}) +@code{CONSTANT_P}, which is defined by target-independent code, +accepts integer-values expressions whose values are not explicitly +known, such as @code{symbol_ref}, @code{label_ref}, and @code{high} +expressions and @code{const} arithmetic expressions, in addition to +@code{const_int} and @code{const_double} expressions. +@end defmac + +@defmac MAX_REGS_PER_ADDRESS +A number, the maximum number of registers that can appear in a valid +memory address. Note that it is up to you to specify a value equal to +the maximum number that @code{TARGET_LEGITIMATE_ADDRESS_P} would ever +accept. +@end defmac + +@hook TARGET_LEGITIMATE_ADDRESS_P + +@defmac TARGET_MEM_CONSTRAINT +A single character to be used instead of the default @code{'m'} +character for general memory addresses. This defines the constraint +letter which matches the memory addresses accepted by +@code{TARGET_LEGITIMATE_ADDRESS_P}. Define this macro if you want to +support new address formats in your back end without changing the +semantics of the @code{'m'} constraint. This is necessary in order to +preserve functionality of inline assembly constructs using the +@code{'m'} constraint. +@end defmac + +@defmac FIND_BASE_TERM (@var{x}) +A C expression to determine the base term of address @var{x}, +or to provide a simplified version of @var{x} from which @file{alias.cc} +can easily find the base term. This macro is used in only two places: +@code{find_base_value} and @code{find_base_term} in @file{alias.cc}. + +It is always safe for this macro to not be defined. It exists so +that alias analysis can understand machine-dependent addresses. + +The typical use of this macro is to handle addresses containing +a label_ref or symbol_ref within an UNSPEC@. +@end defmac + +@hook TARGET_LEGITIMIZE_ADDRESS + +@defmac LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) +A C compound statement that attempts to replace @var{x}, which is an address +that needs reloading, with a valid memory address for an operand of mode +@var{mode}. @var{win} will be a C statement label elsewhere in the code. +It is not necessary to define this macro, but it might be useful for +performance reasons. + +For example, on the i386, it is sometimes possible to use a single +reload register instead of two by reloading a sum of two pseudo +registers into a register. On the other hand, for number of RISC +processors offsets are limited so that often an intermediate address +needs to be generated in order to address a stack slot. By defining +@code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses +generated for adjacent some stack slots can be made identical, and thus +be shared. + +@emph{Note}: This macro should be used with caution. It is necessary +to know something of how reload works in order to effectively use this, +and it is quite easy to produce macros that build in too much knowledge +of reload internals. + +@emph{Note}: This macro must be able to reload an address created by a +previous invocation of this macro. If it fails to handle such addresses +then the compiler may generate incorrect code or abort. + +@findex push_reload +The macro definition should use @code{push_reload} to indicate parts that +need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually +suitable to be passed unaltered to @code{push_reload}. + +The code generated by this macro must not alter the substructure of +@var{x}. If it transforms @var{x} into a more legitimate form, it +should assign @var{x} (which will always be a C variable) a new value. +This also applies to parts that you change indirectly by calling +@code{push_reload}. + +@findex strict_memory_address_p +The macro definition may use @code{strict_memory_address_p} to test if +the address has become legitimate. + +@findex copy_rtx +If you want to change only a part of @var{x}, one standard way of doing +this is to use @code{copy_rtx}. Note, however, that it unshares only a +single level of rtl. Thus, if the part to be changed is not at the +top level, you'll need to replace first the top level. +It is not necessary for this macro to come up with a legitimate +address; but often a machine-dependent strategy can generate better code. +@end defmac + +@hook TARGET_MODE_DEPENDENT_ADDRESS_P + +@hook TARGET_LEGITIMATE_CONSTANT_P + +@hook TARGET_PRECOMPUTE_TLS_P + +@hook TARGET_DELEGITIMIZE_ADDRESS + +@hook TARGET_CONST_NOT_OK_FOR_DEBUG_P + +@hook TARGET_CANNOT_FORCE_CONST_MEM + +@hook TARGET_USE_BLOCKS_FOR_CONSTANT_P + +@hook TARGET_USE_BLOCKS_FOR_DECL_P + +@hook TARGET_BUILTIN_RECIPROCAL + +@hook TARGET_VECTORIZE_BUILTIN_MASK_FOR_LOAD + +@hook TARGET_VECTORIZE_BUILTIN_VECTORIZATION_COST + +@hook TARGET_VECTORIZE_PREFERRED_VECTOR_ALIGNMENT + +@hook TARGET_VECTORIZE_VECTOR_ALIGNMENT_REACHABLE + +@hook TARGET_VECTORIZE_VEC_PERM_CONST + +@hook TARGET_VECTORIZE_BUILTIN_VECTORIZED_FUNCTION + +@hook TARGET_VECTORIZE_BUILTIN_MD_VECTORIZED_FUNCTION + +@hook TARGET_VECTORIZE_SUPPORT_VECTOR_MISALIGNMENT + +@hook TARGET_VECTORIZE_PREFERRED_SIMD_MODE + +@hook TARGET_VECTORIZE_SPLIT_REDUCTION + +@hook TARGET_VECTORIZE_AUTOVECTORIZE_VECTOR_MODES + +@hook TARGET_VECTORIZE_RELATED_MODE + +@hook TARGET_VECTORIZE_GET_MASK_MODE + +@hook TARGET_VECTORIZE_EMPTY_MASK_IS_EXPENSIVE + +@hook TARGET_VECTORIZE_CREATE_COSTS + +@hook TARGET_VECTORIZE_BUILTIN_GATHER + +@hook TARGET_VECTORIZE_BUILTIN_SCATTER + +@hook TARGET_SIMD_CLONE_COMPUTE_VECSIZE_AND_SIMDLEN + +@hook TARGET_SIMD_CLONE_ADJUST + +@hook TARGET_SIMD_CLONE_USABLE + +@hook TARGET_SIMT_VF + +@hook TARGET_OMP_DEVICE_KIND_ARCH_ISA + +@hook TARGET_GOACC_VALIDATE_DIMS + +@hook TARGET_GOACC_DIM_LIMIT + +@hook TARGET_GOACC_FORK_JOIN + +@hook TARGET_GOACC_REDUCTION + +@hook TARGET_PREFERRED_ELSE_VALUE + +@hook TARGET_GOACC_ADJUST_PRIVATE_DECL + +@hook TARGET_GOACC_EXPAND_VAR_DECL + +@hook TARGET_GOACC_CREATE_WORKER_BROADCAST_RECORD + +@hook TARGET_GOACC_SHARED_MEM_LAYOUT + +@node Anchored Addresses +@section Anchored Addresses +@cindex anchored addresses +@cindex @option{-fsection-anchors} + +GCC usually addresses every static object as a separate entity. +For example, if we have: + +@smallexample +static int a, b, c; +int foo (void) @{ return a + b + c; @} +@end smallexample + +the code for @code{foo} will usually calculate three separate symbolic +addresses: those of @code{a}, @code{b} and @code{c}. On some targets, +it would be better to calculate just one symbolic address and access +the three variables relative to it. The equivalent pseudocode would +be something like: + +@smallexample +int foo (void) +@{ + register int *xr = &x; + return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; +@} +@end smallexample + +(which isn't valid C). We refer to shared addresses like @code{x} as +``section anchors''. Their use is controlled by @option{-fsection-anchors}. + +The hooks below describe the target properties that GCC needs to know +in order to make effective use of section anchors. It won't use +section anchors at all unless either @code{TARGET_MIN_ANCHOR_OFFSET} +or @code{TARGET_MAX_ANCHOR_OFFSET} is set to a nonzero value. + +@hook TARGET_MIN_ANCHOR_OFFSET + +@hook TARGET_MAX_ANCHOR_OFFSET + +@hook TARGET_ASM_OUTPUT_ANCHOR + +@hook TARGET_USE_ANCHORS_FOR_SYMBOL_P + +@node Condition Code +@section Condition Code Status +@cindex condition code status + +Condition codes in GCC are represented as registers, +which provides better schedulability for +architectures that do have a condition code register, but on which +most instructions do not affect it. The latter category includes +most RISC machines. + +Implicit clobbering would pose a strong restriction on the placement of +the definition and use of the condition code. In the past the definition +and use were always adjacent. However, recent changes to support trapping +arithmetic may result in the definition and user being in different blocks. +Thus, there may be a @code{NOTE_INSN_BASIC_BLOCK} between them. Additionally, +the definition may be the source of exception handling edges. + +These restrictions can prevent important +optimizations on some machines. For example, on the IBM RS/6000, there +is a delay for taken branches unless the condition code register is set +three instructions earlier than the conditional branch. The instruction +scheduler cannot perform this optimization if it is not permitted to +separate the definition and use of the condition code register. + +If there is a specific +condition code register in the machine, use a hard register. If the +condition code or comparison result can be placed in any general register, +or if there are multiple condition registers, use a pseudo register. +Registers used to store the condition code value will usually have a mode +that is in class @code{MODE_CC}. + +Alternatively, you can use @code{BImode} if the comparison operator is +specified already in the compare instruction. In this case, you are not +interested in most macros in this section. + +@menu +* MODE_CC Condition Codes:: Modern representation of condition codes. +@end menu + +@node MODE_CC Condition Codes +@subsection Representation of condition codes using registers +@findex CCmode +@findex MODE_CC + +@defmac SELECT_CC_MODE (@var{op}, @var{x}, @var{y}) +On many machines, the condition code may be produced by other instructions +than compares, for example the branch can use directly the condition +code set by a subtract instruction. However, on some machines +when the condition code is set this way some bits (such as the overflow +bit) are not set in the same way as a test instruction, so that a different +branch instruction must be used for some conditional branches. When +this happens, use the machine mode of the condition code register to +record different formats of the condition code register. Modes can +also be used to record which compare instruction (e.g.@: a signed or an +unsigned comparison) produced the condition codes. + +If other modes than @code{CCmode} are required, add them to +@file{@var{machine}-modes.def} and define @code{SELECT_CC_MODE} to choose +a mode given an operand of a compare. This is needed because the modes +have to be chosen not only during RTL generation but also, for example, +by instruction combination. The result of @code{SELECT_CC_MODE} should +be consistent with the mode used in the patterns; for example to support +the case of the add on the SPARC discussed above, we have the pattern + +@smallexample +(define_insn "" + [(set (reg:CCNZ 0) + (compare:CCNZ + (plus:SI (match_operand:SI 0 "register_operand" "%r") + (match_operand:SI 1 "arith_operand" "rI")) + (const_int 0)))] + "" + "@dots{}") +@end smallexample + +@noindent +together with a @code{SELECT_CC_MODE} that returns @code{CCNZmode} +for comparisons whose argument is a @code{plus}: + +@smallexample +#define SELECT_CC_MODE(OP,X,Y) \ + (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ + ? ((OP == LT || OP == LE || OP == GT || OP == GE) \ + ? CCFPEmode : CCFPmode) \ + : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ + || GET_CODE (X) == NEG || GET_CODE (x) == ASHIFT) \ + ? CCNZmode : CCmode)) +@end smallexample + +Another reason to use modes is to retain information on which operands +were used by the comparison; see @code{REVERSIBLE_CC_MODE} later in +this section. + +You should define this macro if and only if you define extra CC modes +in @file{@var{machine}-modes.def}. +@end defmac + +@hook TARGET_CANONICALIZE_COMPARISON + +@defmac REVERSIBLE_CC_MODE (@var{mode}) +A C expression whose value is one if it is always safe to reverse a +comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE} +can ever return @var{mode} for a floating-point inequality comparison, +then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero. + +You need not define this macro if it would always returns zero or if the +floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}. +For example, here is the definition used on the SPARC, where floating-point +inequality comparisons are given either @code{CCFPEmode} or @code{CCFPmode}: + +@smallexample +#define REVERSIBLE_CC_MODE(MODE) \ + ((MODE) != CCFPEmode && (MODE) != CCFPmode) +@end smallexample +@end defmac + +@defmac REVERSE_CONDITION (@var{code}, @var{mode}) +A C expression whose value is reversed condition code of the @var{code} for +comparison done in CC_MODE @var{mode}. The macro is used only in case +@code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case +machine has some non-standard way how to reverse certain conditionals. For +instance in case all floating point conditions are non-trapping, compiler may +freely convert unordered compares to ordered ones. Then definition may look +like: + +@smallexample +#define REVERSE_CONDITION(CODE, MODE) \ + ((MODE) != CCFPmode ? reverse_condition (CODE) \ + : reverse_condition_maybe_unordered (CODE)) +@end smallexample +@end defmac + +@hook TARGET_FIXED_CONDITION_CODE_REGS + +@hook TARGET_CC_MODES_COMPATIBLE + +@hook TARGET_FLAGS_REGNUM + +@node Costs +@section Describing Relative Costs of Operations +@cindex costs of instructions +@cindex relative costs +@cindex speed of instructions + +These macros let you describe the relative speed of various operations +on the target machine. + +@defmac REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to}) +A C expression for the cost of moving data of mode @var{mode} from a +register in class @var{from} to one in class @var{to}. The classes are +expressed using the enumeration values such as @code{GENERAL_REGS}. A +value of 2 is the default; other values are interpreted relative to +that. + +It is not required that the cost always equal 2 when @var{from} is the +same as @var{to}; on some machines it is expensive to move between +registers if they are not general registers. + +If reload sees an insn consisting of a single @code{set} between two +hard registers, and if @code{REGISTER_MOVE_COST} applied to their +classes returns a value of 2, reload does not check to ensure that the +constraints of the insn are met. Setting a cost of other than 2 will +allow reload to verify that the constraints are met. You should do this +if the @samp{mov@var{m}} pattern's constraints do not allow such copying. + +These macros are obsolete, new ports should use the target hook +@code{TARGET_REGISTER_MOVE_COST} instead. +@end defmac + +@hook TARGET_REGISTER_MOVE_COST + +@defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) +A C expression for the cost of moving data of mode @var{mode} between a +register of class @var{class} and memory; @var{in} is zero if the value +is to be written to memory, nonzero if it is to be read in. This cost +is relative to those in @code{REGISTER_MOVE_COST}. If moving between +registers and memory is more expensive than between two registers, you +should define this macro to express the relative cost. + +If you do not define this macro, GCC uses a default cost of 4 plus +the cost of copying via a secondary reload register, if one is +needed. If your machine requires a secondary reload register to copy +between memory and a register of @var{class} but the reload mechanism is +more complex than copying via an intermediate, define this macro to +reflect the actual cost of the move. + +GCC defines the function @code{memory_move_secondary_cost} if +secondary reloads are needed. It computes the costs due to copying via +a secondary register. If your machine copies from memory using a +secondary register in the conventional way but the default base value of +4 is not correct for your machine, define this macro to add some other +value to the result of that function. The arguments to that function +are the same as to this macro. + +These macros are obsolete, new ports should use the target hook +@code{TARGET_MEMORY_MOVE_COST} instead. +@end defmac + +@hook TARGET_MEMORY_MOVE_COST + +@defmac BRANCH_COST (@var{speed_p}, @var{predictable_p}) +A C expression for the cost of a branch instruction. A value of 1 is +the default; other values are interpreted relative to that. Parameter +@var{speed_p} is true when the branch in question should be optimized +for speed. When it is false, @code{BRANCH_COST} should return a value +optimal for code size rather than performance. @var{predictable_p} is +true for well-predicted branches. On many architectures the +@code{BRANCH_COST} can be reduced then. +@end defmac + +Here are additional macros which do not specify precise relative costs, +but only that certain actions are more expensive than GCC would +ordinarily expect. + +@defmac SLOW_BYTE_ACCESS +Define this macro as a C expression which is nonzero if accessing less +than a word of memory (i.e.@: a @code{char} or a @code{short}) is no +faster than accessing a word of memory, i.e., if such access +require more than one instruction or if there is no difference in cost +between byte and (aligned) word loads. + +When this macro is not defined, the compiler will access a field by +finding the smallest containing object; when it is defined, a fullword +load will be used if alignment permits. Unless bytes accesses are +faster than word accesses, using word accesses is preferable since it +may eliminate subsequent memory access if subsequent accesses occur to +other fields in the same word of the structure, but to different bytes. +@end defmac + +@hook TARGET_SLOW_UNALIGNED_ACCESS + +@defmac MOVE_RATIO (@var{speed}) +The threshold of number of scalar memory-to-memory move insns, @emph{below} +which a sequence of insns should be generated instead of a +string move insn or a library call. Increasing the value will always +make code faster, but eventually incurs high cost in increased code size. + +Note that on machines where the corresponding move insn is a +@code{define_expand} that emits a sequence of insns, this macro counts +the number of such sequences. + +The parameter @var{speed} is true if the code is currently being +optimized for speed rather than size. + +If you don't define this, a reasonable default is used. +@end defmac + +@hook TARGET_USE_BY_PIECES_INFRASTRUCTURE_P + +@hook TARGET_OVERLAP_OP_BY_PIECES_P + +@hook TARGET_COMPARE_BY_PIECES_BRANCH_RATIO + +@defmac MOVE_MAX_PIECES +A C expression used by @code{move_by_pieces} to determine the largest unit +a load or store used to copy memory is. Defaults to @code{MOVE_MAX}. +@end defmac + +@defmac STORE_MAX_PIECES +A C expression used by @code{store_by_pieces} to determine the largest unit +a store used to memory is. Defaults to @code{MOVE_MAX_PIECES}, or two times +the size of @code{HOST_WIDE_INT}, whichever is smaller. +@end defmac + +@defmac COMPARE_MAX_PIECES +A C expression used by @code{compare_by_pieces} to determine the largest unit +a load or store used to compare memory is. Defaults to +@code{MOVE_MAX_PIECES}. +@end defmac + +@defmac CLEAR_RATIO (@var{speed}) +The threshold of number of scalar move insns, @emph{below} which a sequence +of insns should be generated to clear memory instead of a string clear insn +or a library call. Increasing the value will always make code faster, but +eventually incurs high cost in increased code size. + +The parameter @var{speed} is true if the code is currently being +optimized for speed rather than size. + +If you don't define this, a reasonable default is used. +@end defmac + +@defmac SET_RATIO (@var{speed}) +The threshold of number of scalar move insns, @emph{below} which a sequence +of insns should be generated to set memory to a constant value, instead of +a block set insn or a library call. +Increasing the value will always make code faster, but +eventually incurs high cost in increased code size. + +The parameter @var{speed} is true if the code is currently being +optimized for speed rather than size. + +If you don't define this, it defaults to the value of @code{MOVE_RATIO}. +@end defmac + +@defmac USE_LOAD_POST_INCREMENT (@var{mode}) +A C expression used to determine whether a load postincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_INCREMENT}. +@end defmac + +@defmac USE_LOAD_POST_DECREMENT (@var{mode}) +A C expression used to determine whether a load postdecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_DECREMENT}. +@end defmac + +@defmac USE_LOAD_PRE_INCREMENT (@var{mode}) +A C expression used to determine whether a load preincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_INCREMENT}. +@end defmac + +@defmac USE_LOAD_PRE_DECREMENT (@var{mode}) +A C expression used to determine whether a load predecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_DECREMENT}. +@end defmac + +@defmac USE_STORE_POST_INCREMENT (@var{mode}) +A C expression used to determine whether a store postincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_INCREMENT}. +@end defmac + +@defmac USE_STORE_POST_DECREMENT (@var{mode}) +A C expression used to determine whether a store postdecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_POST_DECREMENT}. +@end defmac + +@defmac USE_STORE_PRE_INCREMENT (@var{mode}) +This macro is used to determine whether a store preincrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_INCREMENT}. +@end defmac + +@defmac USE_STORE_PRE_DECREMENT (@var{mode}) +This macro is used to determine whether a store predecrement is a good +thing to use for a given mode. Defaults to the value of +@code{HAVE_PRE_DECREMENT}. +@end defmac + +@defmac NO_FUNCTION_CSE +Define this macro to be true if it is as good or better to call a constant +function address than to call an address kept in a register. +@end defmac + +@defmac LOGICAL_OP_NON_SHORT_CIRCUIT +Define this macro if a non-short-circuit operation produced by +@samp{fold_range_test ()} is optimal. This macro defaults to true if +@code{BRANCH_COST} is greater than or equal to the value 2. +@end defmac + +@hook TARGET_OPTAB_SUPPORTED_P + +@hook TARGET_RTX_COSTS + +@hook TARGET_ADDRESS_COST + +@hook TARGET_INSN_COST + +@hook TARGET_MAX_NOCE_IFCVT_SEQ_COST + +@hook TARGET_NOCE_CONVERSION_PROFITABLE_P + +@hook TARGET_NEW_ADDRESS_PROFITABLE_P + +@hook TARGET_NO_SPECULATION_IN_DELAY_SLOTS_P + +@hook TARGET_ESTIMATED_POLY_VALUE + +@node Scheduling +@section Adjusting the Instruction Scheduler + +The instruction scheduler may need a fair amount of machine-specific +adjustment in order to produce good code. GCC provides several target +hooks for this purpose. It is usually enough to define just a few of +them: try the first ones in this list first. + +@hook TARGET_SCHED_ISSUE_RATE + +@hook TARGET_SCHED_VARIABLE_ISSUE + +@hook TARGET_SCHED_ADJUST_COST + +@hook TARGET_SCHED_ADJUST_PRIORITY + +@hook TARGET_SCHED_REORDER + +@hook TARGET_SCHED_REORDER2 + +@hook TARGET_SCHED_MACRO_FUSION_P + +@hook TARGET_SCHED_MACRO_FUSION_PAIR_P + +@hook TARGET_SCHED_DEPENDENCIES_EVALUATION_HOOK + +@hook TARGET_SCHED_INIT + +@hook TARGET_SCHED_FINISH + +@hook TARGET_SCHED_INIT_GLOBAL + +@hook TARGET_SCHED_FINISH_GLOBAL + +@hook TARGET_SCHED_DFA_PRE_CYCLE_INSN + +@hook TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN + +@hook TARGET_SCHED_DFA_POST_CYCLE_INSN + +@hook TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN + +@hook TARGET_SCHED_DFA_PRE_ADVANCE_CYCLE + +@hook TARGET_SCHED_DFA_POST_ADVANCE_CYCLE + +@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD + +@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD_GUARD + +@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BEGIN + +@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_ISSUE + +@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_BACKTRACK + +@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_END + +@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_INIT + +@hook TARGET_SCHED_FIRST_CYCLE_MULTIPASS_FINI + +@hook TARGET_SCHED_DFA_NEW_CYCLE + +@hook TARGET_SCHED_IS_COSTLY_DEPENDENCE + +@hook TARGET_SCHED_H_I_D_EXTENDED + +@hook TARGET_SCHED_ALLOC_SCHED_CONTEXT + +@hook TARGET_SCHED_INIT_SCHED_CONTEXT + +@hook TARGET_SCHED_SET_SCHED_CONTEXT + +@hook TARGET_SCHED_CLEAR_SCHED_CONTEXT + +@hook TARGET_SCHED_FREE_SCHED_CONTEXT + +@hook TARGET_SCHED_SPECULATE_INSN + +@hook TARGET_SCHED_NEEDS_BLOCK_P + +@hook TARGET_SCHED_GEN_SPEC_CHECK + +@hook TARGET_SCHED_SET_SCHED_FLAGS + +@hook TARGET_SCHED_CAN_SPECULATE_INSN + +@hook TARGET_SCHED_SMS_RES_MII + +@hook TARGET_SCHED_DISPATCH + +@hook TARGET_SCHED_DISPATCH_DO + +@hook TARGET_SCHED_EXPOSED_PIPELINE + +@hook TARGET_SCHED_REASSOCIATION_WIDTH + +@hook TARGET_SCHED_FUSION_PRIORITY + +@hook TARGET_EXPAND_DIVMOD_LIBFUNC + +@node Sections +@section Dividing the Output into Sections (Texts, Data, @dots{}) +@c the above section title is WAY too long. maybe cut the part between +@c the (...)? --mew 10feb93 + +An object file is divided into sections containing different types of +data. In the most common case, there are three sections: the @dfn{text +section}, which holds instructions and read-only data; the @dfn{data +section}, which holds initialized writable data; and the @dfn{bss +section}, which holds uninitialized data. Some systems have other kinds +of sections. + +@file{varasm.cc} provides several well-known sections, such as +@code{text_section}, @code{data_section} and @code{bss_section}. +The normal way of controlling a @code{@var{foo}_section} variable +is to define the associated @code{@var{FOO}_SECTION_ASM_OP} macro, +as described below. The macros are only read once, when @file{varasm.cc} +initializes itself, so their values must be run-time constants. +They may however depend on command-line flags. + +@emph{Note:} Some run-time files, such @file{crtstuff.c}, also make +use of the @code{@var{FOO}_SECTION_ASM_OP} macros, and expect them +to be string literals. + +Some assemblers require a different string to be written every time a +section is selected. If your assembler falls into this category, you +should define the @code{TARGET_ASM_INIT_SECTIONS} hook and use +@code{get_unnamed_section} to set up the sections. + +You must always create a @code{text_section}, either by defining +@code{TEXT_SECTION_ASM_OP} or by initializing @code{text_section} +in @code{TARGET_ASM_INIT_SECTIONS}. The same is true of +@code{data_section} and @code{DATA_SECTION_ASM_OP}. If you do not +create a distinct @code{readonly_data_section}, the default is to +reuse @code{text_section}. + +All the other @file{varasm.cc} sections are optional, and are null +if the target does not provide them. + +@defmac TEXT_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation that should precede instructions and read-only data. +Normally @code{"\t.text"} is right. +@end defmac + +@defmac HOT_TEXT_SECTION_NAME +If defined, a C string constant for the name of the section containing most +frequently executed functions of the program. If not defined, GCC will provide +a default definition if the target supports named sections. +@end defmac + +@defmac UNLIKELY_EXECUTED_TEXT_SECTION_NAME +If defined, a C string constant for the name of the section containing unlikely +executed functions in the program. +@end defmac + +@defmac DATA_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation to identify the following data as writable initialized +data. Normally @code{"\t.data"} is right. +@end defmac + +@defmac SDATA_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +initialized, writable small data. +@end defmac + +@defmac READONLY_DATA_SECTION_ASM_OP +A C expression whose value is a string, including spacing, containing the +assembler operation to identify the following data as read-only initialized +data. +@end defmac + +@defmac BSS_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +uninitialized global data. If not defined, and +@code{ASM_OUTPUT_ALIGNED_BSS} not defined, +uninitialized global data will be output in the data section if +@option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be +used. +@end defmac + +@defmac SBSS_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +uninitialized, writable small data. +@end defmac + +@defmac TLS_COMMON_ASM_OP +If defined, a C expression whose value is a string containing the +assembler operation to identify the following data as thread-local +common data. The default is @code{".tls_common"}. +@end defmac + +@defmac TLS_SECTION_ASM_FLAG +If defined, a C expression whose value is a character constant +containing the flag used to mark a section as a TLS section. The +default is @code{'T'}. +@end defmac + +@defmac INIT_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +initialization code. If not defined, GCC will assume such a section does +not exist. This section has no corresponding @code{init_section} +variable; it is used entirely in runtime code. +@end defmac + +@defmac FINI_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +finalization code. If not defined, GCC will assume such a section does +not exist. This section has no corresponding @code{fini_section} +variable; it is used entirely in runtime code. +@end defmac + +@defmac INIT_ARRAY_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +part of the @code{.init_array} (or equivalent) section. If not +defined, GCC will assume such a section does not exist. Do not define +both this macro and @code{INIT_SECTION_ASM_OP}. +@end defmac + +@defmac FINI_ARRAY_SECTION_ASM_OP +If defined, a C expression whose value is a string, including spacing, +containing the assembler operation to identify the following data as +part of the @code{.fini_array} (or equivalent) section. If not +defined, GCC will assume such a section does not exist. Do not define +both this macro and @code{FINI_SECTION_ASM_OP}. +@end defmac + +@defmac MACH_DEP_SECTION_ASM_FLAG +If defined, a C expression whose value is a character constant +containing the flag used to mark a machine-dependent section. This +corresponds to the @code{SECTION_MACH_DEP} section flag. +@end defmac + +@defmac CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function}) +If defined, an ASM statement that switches to a different section +via @var{section_op}, calls @var{function}, and switches back to +the text section. This is used in @file{crtstuff.c} if +@code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls +to initialization and finalization functions from the init and fini +sections. By default, this macro uses a simple function call. Some +ports need hand-crafted assembly code to avoid dependencies on +registers initialized in the function prologue or to ensure that +constant pools don't end up too far way in the text section. +@end defmac + +@defmac TARGET_LIBGCC_SDATA_SECTION +If defined, a string which names the section into which small +variables defined in crtstuff and libgcc should go. This is useful +when the target has options for optimizing access to small data, and +you want the crtstuff and libgcc routines to be conservative in what +they expect of your application yet liberal in what your application +expects. For example, for targets with a @code{.sdata} section (like +MIPS), you could compile crtstuff with @code{-G 0} so that it doesn't +require small data support from your application, but use this macro +to put small data into @code{.sdata} so that your application can +access these variables whether it uses small data or not. +@end defmac + +@defmac FORCE_CODE_SECTION_ALIGN +If defined, an ASM statement that aligns a code section to some +arbitrary boundary. This is used to force all fragments of the +@code{.init} and @code{.fini} sections to have to same alignment +and thus prevent the linker from having to add any padding. +@end defmac + +@defmac JUMP_TABLES_IN_TEXT_SECTION +Define this macro to be an expression with a nonzero value if jump +tables (for @code{tablejump} insns) should be output in the text +section, along with the assembler instructions. Otherwise, the +readonly data section is used. + +This macro is irrelevant if there is no separate readonly data section. +@end defmac + +@hook TARGET_ASM_INIT_SECTIONS + +@hook TARGET_ASM_RELOC_RW_MASK + +@hook TARGET_ASM_GENERATE_PIC_ADDR_DIFF_VEC + +@hook TARGET_ASM_SELECT_SECTION + +@defmac USE_SELECT_SECTION_FOR_FUNCTIONS +Define this macro if you wish TARGET_ASM_SELECT_SECTION to be called +for @code{FUNCTION_DECL}s as well as for variables and constants. + +In the case of a @code{FUNCTION_DECL}, @var{reloc} will be zero if the +function has been determined to be likely to be called, and nonzero if +it is unlikely to be called. +@end defmac + +@hook TARGET_ASM_UNIQUE_SECTION + +@hook TARGET_ASM_FUNCTION_RODATA_SECTION + +@hook TARGET_ASM_MERGEABLE_RODATA_PREFIX + +@hook TARGET_ASM_TM_CLONE_TABLE_SECTION + +@hook TARGET_ASM_SELECT_RTX_SECTION + +@hook TARGET_MANGLE_DECL_ASSEMBLER_NAME + +@hook TARGET_ENCODE_SECTION_INFO + +@hook TARGET_STRIP_NAME_ENCODING + +@hook TARGET_IN_SMALL_DATA_P + +@hook TARGET_HAVE_SRODATA_SECTION + +@hook TARGET_PROFILE_BEFORE_PROLOGUE + +@hook TARGET_BINDS_LOCAL_P + +@hook TARGET_HAVE_TLS + + +@node PIC +@section Position Independent Code +@cindex position independent code +@cindex PIC + +This section describes macros that help implement generation of position +independent code. Simply defining these macros is not enough to +generate valid PIC; you must also add support to the hook +@code{TARGET_LEGITIMATE_ADDRESS_P} and to the macro +@code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You +must modify the definition of @samp{movsi} to do something appropriate +when the source operand contains a symbolic address. You may also +need to alter the handling of switch statements so that they use +relative addresses. +@c i rearranged the order of the macros above to try to force one of +@c them to the next line, to eliminate an overfull hbox. --mew 10feb93 + +@defmac PIC_OFFSET_TABLE_REGNUM +The register number of the register used to address a table of static +data addresses in memory. In some cases this register is defined by a +processor's ``application binary interface'' (ABI)@. When this macro +is defined, RTL is generated for this register once, as with the stack +pointer and frame pointer registers. If this macro is not defined, it +is up to the machine-dependent files to allocate such a register (if +necessary). Note that this register must be fixed when in use (e.g.@: +when @code{flag_pic} is true). +@end defmac + +@defmac PIC_OFFSET_TABLE_REG_CALL_CLOBBERED +A C expression that is nonzero if the register defined by +@code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. If not defined, +the default is zero. Do not define +this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined. +@end defmac + +@defmac LEGITIMATE_PIC_OPERAND_P (@var{x}) +A C expression that is nonzero if @var{x} is a legitimate immediate +operand on the target machine when generating position independent code. +You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not +check this. You can also assume @var{flag_pic} is true, so you need not +check it either. You need not define this macro if all constants +(including @code{SYMBOL_REF}) can be immediate operands when generating +position independent code. +@end defmac + +@node Assembler Format +@section Defining the Output Assembler Language + +This section describes macros whose principal purpose is to describe how +to write instructions in assembler language---rather than what the +instructions do. + +@menu +* File Framework:: Structural information for the assembler file. +* Data Output:: Output of constants (numbers, strings, addresses). +* Uninitialized Data:: Output of uninitialized variables. +* Label Output:: Output and generation of labels. +* Initialization:: General principles of initialization + and termination routines. +* Macros for Initialization:: + Specific macros that control the handling of + initialization and termination routines. +* Instruction Output:: Output of actual instructions. +* Dispatch Tables:: Output of jump tables. +* Exception Region Output:: Output of exception region code. +* Alignment Output:: Pseudo ops for alignment and skipping data. +@end menu + +@node File Framework +@subsection The Overall Framework of an Assembler File +@cindex assembler format +@cindex output of assembler code + +@c prevent bad page break with this line +This describes the overall framework of an assembly file. + +@findex default_file_start +@hook TARGET_ASM_FILE_START + +@hook TARGET_ASM_FILE_START_APP_OFF + +@hook TARGET_ASM_FILE_START_FILE_DIRECTIVE + +@hook TARGET_ASM_FILE_END + +@deftypefun void file_end_indicate_exec_stack () +Some systems use a common convention, the @samp{.note.GNU-stack} +special section, to indicate whether or not an object file relies on +the stack being executable. If your system uses this convention, you +should define @code{TARGET_ASM_FILE_END} to this function. If you +need to do other things in that hook, have your hook function call +this function. +@end deftypefun + +@hook TARGET_ASM_LTO_START + +@hook TARGET_ASM_LTO_END + +@hook TARGET_ASM_CODE_END + +@defmac ASM_COMMENT_START +A C string constant describing how to begin a comment in the target +assembler language. The compiler assumes that the comment will end at +the end of the line. +@end defmac + +@defmac ASM_APP_ON +A C string constant for text to be output before each @code{asm} +statement or group of consecutive ones. Normally this is +@code{"#APP"}, which is a comment that has no effect on most +assemblers but tells the GNU assembler that it must check the lines +that follow for all valid assembler constructs. +@end defmac + +@defmac ASM_APP_OFF +A C string constant for text to be output after each @code{asm} +statement or group of consecutive ones. Normally this is +@code{"#NO_APP"}, which tells the GNU assembler to resume making the +time-saving assumptions that are valid for ordinary compiler output. +@end defmac + +@defmac ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) +A C statement to output COFF information or DWARF debugging information +which indicates that filename @var{name} is the current source file to +the stdio stream @var{stream}. + +This macro need not be defined if the standard form of output +for the file format in use is appropriate. +@end defmac + +@hook TARGET_ASM_OUTPUT_SOURCE_FILENAME + +@hook TARGET_ASM_OUTPUT_IDENT + +@defmac OUTPUT_QUOTED_STRING (@var{stream}, @var{string}) +A C statement to output the string @var{string} to the stdio stream +@var{stream}. If you do not call the function @code{output_quoted_string} +in your config files, GCC will only call it to output filenames to +the assembler source. So you can use it to canonicalize the format +of the filename using this macro. +@end defmac + +@hook TARGET_ASM_NAMED_SECTION + +@hook TARGET_ASM_ELF_FLAGS_NUMERIC + +@hook TARGET_ASM_FUNCTION_SECTION + +@hook TARGET_ASM_FUNCTION_SWITCHED_TEXT_SECTIONS + +@hook TARGET_HAVE_NAMED_SECTIONS +This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. +It must not be modified by command-line option processing. +@end deftypevr + +@anchor{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS} +@hook TARGET_HAVE_SWITCHABLE_BSS_SECTIONS + +@hook TARGET_SECTION_TYPE_FLAGS + +@hook TARGET_ASM_RECORD_GCC_SWITCHES + +@hook TARGET_ASM_RECORD_GCC_SWITCHES_SECTION + +@need 2000 +@node Data Output +@subsection Output of Data + + +@hook TARGET_ASM_BYTE_OP + +@hook TARGET_ASM_INTEGER + +@hook TARGET_ASM_DECL_END + +@hook TARGET_ASM_OUTPUT_ADDR_CONST_EXTRA + +@defmac ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len}) +A C statement to output to the stdio stream @var{stream} an assembler +instruction to assemble a string constant containing the @var{len} +bytes at @var{ptr}. @var{ptr} will be a C expression of type +@code{char *} and @var{len} a C expression of type @code{int}. + +If the assembler has a @code{.ascii} pseudo-op as found in the +Berkeley Unix assembler, do not define the macro +@code{ASM_OUTPUT_ASCII}. +@end defmac + +@defmac ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n}) +A C statement to output word @var{n} of a function descriptor for +@var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS} +is defined, and is otherwise unused. +@end defmac + +@defmac CONSTANT_POOL_BEFORE_FUNCTION +You may define this macro as a C expression. You should define the +expression to have a nonzero value if GCC should output the constant +pool for a function before the code for the function, or a zero value if +GCC should output the constant pool after the function. If you do +not define this macro, the usual case, GCC will output the constant +pool before the function. +@end defmac + +@defmac ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size}) +A C statement to output assembler commands to define the start of the +constant pool for a function. @var{funname} is a string giving +the name of the function. Should the return type of the function +be required, it can be obtained via @var{fundecl}. @var{size} +is the size, in bytes, of the constant pool that will be written +immediately after this call. + +If no constant-pool prefix is required, the usual case, this macro need +not be defined. +@end defmac + +@defmac ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto}) +A C statement (with or without semicolon) to output a constant in the +constant pool, if it needs special treatment. (This macro need not do +anything for RTL expressions that can be output normally.) + +The argument @var{file} is the standard I/O stream to output the +assembler code on. @var{x} is the RTL expression for the constant to +output, and @var{mode} is the machine mode (in case @var{x} is a +@samp{const_int}). @var{align} is the required alignment for the value +@var{x}; you should output an assembler directive to force this much +alignment. + +The argument @var{labelno} is a number to use in an internal label for +the address of this pool entry. The definition of this macro is +responsible for outputting the label definition at the proper place. +Here is how to do this: + +@smallexample +@code{(*targetm.asm_out.internal_label)} (@var{file}, "LC", @var{labelno}); +@end smallexample + +When you output a pool entry specially, you should end with a +@code{goto} to the label @var{jumpto}. This will prevent the same pool +entry from being output a second time in the usual manner. + +You need not define this macro if it would do nothing. +@end defmac + +@defmac ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size}) +A C statement to output assembler commands to at the end of the constant +pool for a function. @var{funname} is a string giving the name of the +function. Should the return type of the function be required, you can +obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the +constant pool that GCC wrote immediately before this call. + +If no constant-pool epilogue is required, the usual case, you need not +define this macro. +@end defmac + +@defmac IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}, @var{STR}) +Define this macro as a C expression which is nonzero if @var{C} is +used as a logical line separator by the assembler. @var{STR} points +to the position in the string where @var{C} was found; this can be used if +a line separator uses multiple characters. + +If you do not define this macro, the default is that only +the character @samp{;} is treated as a logical line separator. +@end defmac + +@hook TARGET_ASM_OPEN_PAREN + +These macros are provided by @file{real.h} for writing the definitions +of @code{ASM_OUTPUT_DOUBLE} and the like: + +@defmac REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL32 (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL64 (@var{x}, @var{l}) +@defmacx REAL_VALUE_TO_TARGET_DECIMAL128 (@var{x}, @var{l}) +These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the +target's floating point representation, and store its bit pattern in +the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE} and +@code{REAL_VALUE_TO_TARGET_DECIMAL32}, this variable should be a +simple @code{long int}. For the others, it should be an array of +@code{long int}. The number of elements in this array is determined +by the size of the desired target floating point data type: 32 bits of +it go in each @code{long int} array element. Each array element holds +32 bits of the result, even if @code{long int} is wider than 32 bits +on the host machine. + +The array element values are designed so that you can print them out +using @code{fprintf} in the order they should appear in the target +machine's memory. +@end defmac + +@node Uninitialized Data +@subsection Output of Uninitialized Variables + +Each of the macros in this section is used to do the whole job of +outputting a single uninitialized variable. + +@defmac ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a common-label named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. It is +possible that @var{size} may be zero, for instance if a struct with no +other member than a zero-length array is defined. In this case, the +backend must output a symbol definition that allocates at least one +byte, both so that the address of the resulting object does not compare +equal to any other, and because some object formats cannot even express +the concept of a zero-sized common symbol, as that is how they represent +an ordinary undefined external. + +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +This macro controls how the assembler definitions of uninitialized +common global variables are output. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the +variable to be output, if there is one, or @code{NULL_TREE} if there +is no corresponding variable. If you define this macro, GCC will use it +in place of both @code{ASM_OUTPUT_COMMON} and +@code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see +the variable's decl in order to chose what to output. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of uninitialized global @var{decl} named +@var{name} whose size is @var{size} bytes. The variable @var{alignment} +is the alignment specified as the number of bits. + +Try to use function @code{asm_output_aligned_bss} defined in file +@file{varasm.cc} when defining this macro. If unable, use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name itself; +before and after that, output the additional assembler syntax for defining +the name, and a newline. + +There are two ways of handling global BSS@. One is to define this macro. +The other is to have @code{TARGET_ASM_SELECT_SECTION} return a +switchable BSS section (@pxref{TARGET_HAVE_SWITCHABLE_BSS_SECTIONS}). +You do not need to do both. + +Some languages do not have @code{common} data, and require a +non-common form of global BSS in order to handle uninitialized globals +efficiently. C++ is one example of this. However, if the target does +not support global BSS, the front end may choose to make globals +common in order to save space in the object file. +@end defmac + +@defmac ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a local-common-label named +@var{name} whose size is @var{size} bytes. The variable @var{rounded} +is the size rounded up to whatever alignment the caller wants. + +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. + +This macro controls how the assembler definitions of uninitialized +static variables are output. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a +separate, explicit argument. If you define this macro, it is used in +place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in +handling the required alignment of the variable. The alignment is specified +as the number of bits. +@end defmac + +@defmac ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) +Like @code{ASM_OUTPUT_ALIGNED_LOCAL} except that @var{decl} of the +variable to be output, if there is one, or @code{NULL_TREE} if there +is no corresponding variable. If you define this macro, GCC will use it +in place of both @code{ASM_OUTPUT_LOCAL} and +@code{ASM_OUTPUT_ALIGNED_LOCAL}. Define this macro when you need to see +the variable's decl in order to chose what to output. +@end defmac + +@node Label Output +@subsection Output and Generation of Labels + +@c prevent bad page break with this line +This is about outputting labels. + +@findex assemble_name +@defmac ASM_OUTPUT_LABEL (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a label named @var{name}. +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. A default +definition of this macro is provided which is correct for most systems. +@end defmac + +@defmac ASM_OUTPUT_FUNCTION_LABEL (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} the assembler definition of a label named @var{name} of +a function. +Use the expression @code{assemble_name (@var{stream}, @var{name})} to +output the name itself; before and after that, output the additional +assembler syntax for defining the name, and a newline. A default +definition of this macro is provided which is correct for most systems. + +If this macro is not defined, then the function name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). +@end defmac + +@findex assemble_name_raw +@defmac ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{name}) +Identical to @code{ASM_OUTPUT_LABEL}, except that @var{name} is known +to refer to a compiler-generated label. The default definition uses +@code{assemble_name_raw}, which is like @code{assemble_name} except +that it is more efficient. +@end defmac + +@defmac SIZE_ASM_OP +A C string containing the appropriate assembler directive to specify the +size of a symbol, without any arguments. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other +systems, the default is not to define this macro. + +Define this macro only if it is correct to use the default definitions +of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE} +for your system. If you need your own custom definitions of those +macros, or if you do not need explicit symbol sizes at all, do not +define this macro. +@end defmac + +@defmac ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler that the size of the +symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}. +If you define @code{SIZE_ASM_OP}, a default definition of this macro is +provided. +@end defmac + +@defmac ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler to calculate the size of +the symbol @var{name} by subtracting its address from the current +address. + +If you define @code{SIZE_ASM_OP}, a default definition of this macro is +provided. The default assumes that the assembler recognizes a special +@samp{.} symbol as referring to the current address, and can calculate +the difference between this and another symbol. If your assembler does +not recognize @samp{.} or cannot do calculations with it, you will need +to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique. +@end defmac + +@defmac NO_DOLLAR_IN_LABEL +Define this macro if the assembler does not accept the character +@samp{$} in label names. By default constructors and destructors in +G++ have @samp{$} in the identifiers. If this macro is defined, +@samp{.} is used instead. +@end defmac + +@defmac NO_DOT_IN_LABEL +Define this macro if the assembler does not accept the character +@samp{.} in label names. By default constructors and destructors in G++ +have names that use @samp{.}. If this macro is defined, these names +are rewritten to avoid @samp{.}. +@end defmac + +@defmac TYPE_ASM_OP +A C string containing the appropriate assembler directive to specify the +type of a symbol, without any arguments. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other +systems, the default is not to define this macro. + +Define this macro only if it is correct to use the default definition of +@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own +custom definition of this macro, or if you do not need explicit symbol +types at all, do not define this macro. +@end defmac + +@defmac TYPE_OPERAND_FMT +A C string which specifies (using @code{printf} syntax) the format of +the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the +default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems, +the default is not to define this macro. + +Define this macro only if it is correct to use the default definition of +@code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own +custom definition of this macro, or if you do not need explicit symbol +types at all, do not define this macro. +@end defmac + +@defmac ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a directive telling the assembler that the type of the +symbol @var{name} is @var{type}. @var{type} is a C string; currently, +that string is always either @samp{"function"} or @samp{"object"}, but +you should not count on this. + +If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default +definition of this macro is provided. +@end defmac + +@defmac ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of a +function which is being defined. This macro is responsible for +outputting the label definition (perhaps using +@code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the +@code{FUNCTION_DECL} tree node representing the function. + +If this macro is not defined, then the function name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_FUNCTION_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the size of a function +which is being defined. The argument @var{name} is the name of the +function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node +representing the function. + +If this macro is not defined, then the function size is not defined. + +You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_COLD_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of a +cold function partition which is being defined. This macro is responsible +for outputting the label definition (perhaps using +@code{ASM_OUTPUT_FUNCTION_LABEL}). The argument @var{decl} is the +@code{FUNCTION_DECL} tree node representing the function. + +If this macro is not defined, then the cold partition name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_COLD_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the size of a cold function +partition which is being defined. The argument @var{name} is the name of the +cold partition of the function. The argument @var{decl} is the +@code{FUNCTION_DECL} tree node representing the function. + +If this macro is not defined, then the partition size is not defined. + +You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition +of this macro. +@end defmac + +@defmac ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name @var{name} of an +initialized variable which is being defined. This macro must output the +label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument +@var{decl} is the @code{VAR_DECL} tree node representing the variable. + +If this macro is not defined, then the variable name is defined in the +usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). + +You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or +@code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro. +@end defmac + +@hook TARGET_ASM_DECLARE_CONSTANT_NAME + +@defmac ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for claiming a register @var{regno} +for a global variable @var{decl} with name @var{name}. + +If you don't define this macro, that is equivalent to defining it to do +nothing. +@end defmac + +@defmac ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend}) +A C statement (sans semicolon) to finish up declaring a variable name +once the compiler has processed its initializer fully and thus has had a +chance to determine the size of an array when controlled by an +initializer. This is used on systems where it's necessary to declare +something about the size of the object. + +If you don't define this macro, that is equivalent to defining it to do +nothing. + +You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or +@code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro. +@end defmac + +@hook TARGET_ASM_GLOBALIZE_LABEL + +@hook TARGET_ASM_GLOBALIZE_DECL_NAME + +@hook TARGET_ASM_ASSEMBLE_UNDEFINED_DECL + +@defmac ASM_WEAKEN_LABEL (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} some commands that will make the label @var{name} weak; +that is, available for reference from other files but only used if +no other definition is available. Use the expression +@code{assemble_name (@var{stream}, @var{name})} to output the name +itself; before and after that, output the additional assembler syntax +for making that name weak, and a newline. + +If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not +support weak symbols and you should not define the @code{SUPPORTS_WEAK} +macro. +@end defmac + +@defmac ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value}) +Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and +@code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function +or variable decl. If @var{value} is not @code{NULL}, this C statement +should output to the stdio stream @var{stream} assembler code which +defines (equates) the weak symbol @var{name} to have the value +@var{value}. If @var{value} is @code{NULL}, it should output commands +to make @var{name} weak. +@end defmac + +@defmac ASM_OUTPUT_WEAKREF (@var{stream}, @var{decl}, @var{name}, @var{value}) +Outputs a directive that enables @var{name} to be used to refer to +symbol @var{value} with weak-symbol semantics. @code{decl} is the +declaration of @code{name}. +@end defmac + +@defmac SUPPORTS_WEAK +A preprocessor constant expression which evaluates to true if the target +supports weak symbols. + +If you don't define this macro, @file{defaults.h} provides a default +definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL} +is defined, the default definition is @samp{1}; otherwise, it is @samp{0}. +@end defmac + +@defmac TARGET_SUPPORTS_WEAK +A C expression which evaluates to true if the target supports weak symbols. + +If you don't define this macro, @file{defaults.h} provides a default +definition. The default definition is @samp{(SUPPORTS_WEAK)}. Define +this macro if you want to control weak symbol support with a compiler +flag such as @option{-melf}. +@end defmac + +@defmac MAKE_DECL_ONE_ONLY (@var{decl}) +A C statement (sans semicolon) to mark @var{decl} to be emitted as a +public symbol such that extra copies in multiple translation units will +be discarded by the linker. Define this macro if your object file +format provides support for this concept, such as the @samp{COMDAT} +section flags in the Microsoft Windows PE/COFF format, and this support +requires changes to @var{decl}, such as putting it in a separate section. +@end defmac + +@defmac SUPPORTS_ONE_ONLY +A C expression which evaluates to true if the target supports one-only +semantics. + +If you don't define this macro, @file{varasm.cc} provides a default +definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default +definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if +you want to control one-only symbol support with a compiler flag, or if +setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to +be emitted as one-only. +@end defmac + +@hook TARGET_ASM_ASSEMBLE_VISIBILITY + +@defmac TARGET_WEAK_NOT_IN_ARCHIVE_TOC +A C expression that evaluates to true if the target's linker expects +that weak symbols do not appear in a static archive's table of contents. +The default is @code{0}. + +Leaving weak symbols out of an archive's table of contents means that, +if a symbol will only have a definition in one translation unit and +will have undefined references from other translation units, that +symbol should not be weak. Defining this macro to be nonzero will +thus have the effect that certain symbols that would normally be weak +(explicit template instantiations, and vtables for polymorphic classes +with noninline key methods) will instead be nonweak. + +The C++ ABI requires this macro to be zero. Define this macro for +targets where full C++ ABI compliance is impossible and where linker +restrictions require weak symbols to be left out of a static archive's +table of contents. +@end defmac + +@defmac ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} any text necessary for declaring the name of an external +symbol named @var{name} which is referenced in this compilation but +not defined. The value of @var{decl} is the tree node for the +declaration. + +This macro need not be defined if it does not need to output anything. +The GNU assembler and most Unix assemblers don't require anything. +@end defmac + +@hook TARGET_ASM_EXTERNAL_LIBCALL + +@hook TARGET_ASM_MARK_DECL_PRESERVED + +@defmac ASM_OUTPUT_LABELREF (@var{stream}, @var{name}) +A C statement (sans semicolon) to output to the stdio stream +@var{stream} a reference in assembler syntax to a label named +@var{name}. This should add @samp{_} to the front of the name, if that +is customary on your operating system, as it is in most Berkeley Unix +systems. This macro is used in @code{assemble_name}. +@end defmac + +@hook TARGET_MANGLE_ASSEMBLER_NAME + +@defmac ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym}) +A C statement (sans semicolon) to output a reference to +@code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name} +will be used to output the name of the symbol. This macro may be used +to modify the way a symbol is referenced depending on information +encoded by @code{TARGET_ENCODE_SECTION_INFO}. +@end defmac + +@defmac ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf}) +A C statement (sans semicolon) to output a reference to @var{buf}, the +result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined, +@code{assemble_name} will be used to output the name of the symbol. +This macro is not used by @code{output_asm_label}, or the @code{%l} +specifier that calls it; the intention is that this macro should be set +when it is necessary to output a label differently when its address is +being taken. +@end defmac + +@hook TARGET_ASM_INTERNAL_LABEL + +@defmac ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num}) +A C statement to output to the stdio stream @var{stream} a debug info +label whose name is made from the string @var{prefix} and the number +@var{num}. This is useful for VLIW targets, where debug info labels +may need to be treated differently than branch target labels. On some +systems, branch target labels must be at the beginning of instruction +bundles, but debug info labels can occur in the middle of instruction +bundles. + +If this macro is not defined, then @code{(*targetm.asm_out.internal_label)} will be +used. +@end defmac + +@defmac ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num}) +A C statement to store into the string @var{string} a label whose name +is made from the string @var{prefix} and the number @var{num}. + +This string, when output subsequently by @code{assemble_name}, should +produce the output that @code{(*targetm.asm_out.internal_label)} would produce +with the same @var{prefix} and @var{num}. + +If the string begins with @samp{*}, then @code{assemble_name} will +output the rest of the string unchanged. It is often convenient for +@code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the +string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets +to output the string, and may change it. (Of course, +@code{ASM_OUTPUT_LABELREF} is also part of your machine description, so +you should know what it does on your machine.) +@end defmac + +@defmac ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number}) +A C expression to assign to @var{outvar} (which is a variable of type +@code{char *}) a newly allocated string made from the string +@var{name} and the number @var{number}, with some suitable punctuation +added. Use @code{alloca} to get space for the string. + +The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to +produce an assembler label for an internal static variable whose name is +@var{name}. Therefore, the string must be such as to result in valid +assembler code. The argument @var{number} is different each time this +macro is executed; it prevents conflicts between similarly-named +internal static variables in different scopes. + +Ideally this string should not be a valid C identifier, to prevent any +conflict with the user's own symbols. Most assemblers allow periods +or percent signs in assembler symbols; putting at least one of these +between the name and the number will suffice. + +If this macro is not defined, a default definition will be provided +which is correct for most systems. +@end defmac + +@defmac ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol @var{name} to have the value @var{value}. + +@findex SET_ASM_OP +If @code{SET_ASM_OP} is defined, a default definition is provided which is +correct for most systems. +@end defmac + +@defmac ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the symbol whose tree node is @var{decl_of_name} +to have the value of the tree node @var{decl_of_value}. This macro will +be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if +the tree nodes are available. + +@findex SET_ASM_OP +If @code{SET_ASM_OP} is defined, a default definition is provided which is +correct for most systems. +@end defmac + +@defmac TARGET_DEFERRED_OUTPUT_DEFS (@var{decl_of_name}, @var{decl_of_value}) +A C statement that evaluates to true if the assembler code which defines +(equates) the symbol whose tree node is @var{decl_of_name} to have the value +of the tree node @var{decl_of_value} should be emitted near the end of the +current compilation unit. The default is to not defer output of defines. +This macro affects defines output by @samp{ASM_OUTPUT_DEF} and +@samp{ASM_OUTPUT_DEF_FROM_DECLS}. +@end defmac + +@defmac ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value}) +A C statement to output to the stdio stream @var{stream} assembler code +which defines (equates) the weak symbol @var{name} to have the value +@var{value}. If @var{value} is @code{NULL}, it defines @var{name} as +an undefined weak symbol. + +Define this macro if the target only supports weak aliases; define +@code{ASM_OUTPUT_DEF} instead if possible. +@end defmac + +@defmac OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name}) +Define this macro to override the default assembler names used for +Objective-C methods. + +The default name is a unique method number followed by the name of the +class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of +the category is also included in the assembler name (e.g.@: +@samp{_1_Foo_Bar}). + +These names are safe on most systems, but make debugging difficult since +the method's selector is not present in the name. Therefore, particular +systems define other ways of computing names. + +@var{buf} is an expression of type @code{char *} which gives you a +buffer in which to store the name; its length is as long as +@var{class_name}, @var{cat_name} and @var{sel_name} put together, plus +50 characters extra. + +The argument @var{is_inst} specifies whether the method is an instance +method or a class method; @var{class_name} is the name of the class; +@var{cat_name} is the name of the category (or @code{NULL} if the method is not +in a category); and @var{sel_name} is the name of the selector. + +On systems where the assembler can handle quoted names, you can use this +macro to provide more human-readable names. +@end defmac + +@node Initialization +@subsection How Initialization Functions Are Handled +@cindex initialization routines +@cindex termination routines +@cindex constructors, output of +@cindex destructors, output of + +The compiled code for certain languages includes @dfn{constructors} +(also called @dfn{initialization routines})---functions to initialize +data in the program when the program is started. These functions need +to be called before the program is ``started''---that is to say, before +@code{main} is called. + +Compiling some languages generates @dfn{destructors} (also called +@dfn{termination routines}) that should be called when the program +terminates. + +To make the initialization and termination functions work, the compiler +must output something in the assembler code to cause those functions to +be called at the appropriate time. When you port the compiler to a new +system, you need to specify how to do this. + +There are two major ways that GCC currently supports the execution of +initialization and termination functions. Each way has two variants. +Much of the structure is common to all four variations. + +@findex __CTOR_LIST__ +@findex __DTOR_LIST__ +The linker must build two lists of these functions---a list of +initialization functions, called @code{__CTOR_LIST__}, and a list of +termination functions, called @code{__DTOR_LIST__}. + +Each list always begins with an ignored function pointer (which may hold +0, @minus{}1, or a count of the function pointers after it, depending on +the environment). This is followed by a series of zero or more function +pointers to constructors (or destructors), followed by a function +pointer containing zero. + +Depending on the operating system and its executable file format, either +@file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup +time and exit time. Constructors are called in reverse order of the +list; destructors in forward order. + +The best way to handle static constructors works only for object file +formats which provide arbitrarily-named sections. A section is set +aside for a list of constructors, and another for a list of destructors. +Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each +object file that defines an initialization function also puts a word in +the constructor section to point to that function. The linker +accumulates all these words into one contiguous @samp{.ctors} section. +Termination functions are handled similarly. + +This method will be chosen as the default by @file{target-def.h} if +@code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not +support arbitrary sections, but does support special designated +constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP} +and @code{DTORS_SECTION_ASM_OP} to achieve the same effect. + +When arbitrary sections are available, there are two variants, depending +upon how the code in @file{crtstuff.c} is called. On systems that +support a @dfn{.init} section which is executed at program startup, +parts of @file{crtstuff.c} are compiled into that section. The +program is linked by the @command{gcc} driver like this: + +@smallexample +ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o +@end smallexample + +The prologue of a function (@code{__init}) appears in the @code{.init} +section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise +for the function @code{__fini} in the @dfn{.fini} section. Normally these +files are provided by the operating system or by the GNU C library, but +are provided by GCC for a few targets. + +The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets) +compiled from @file{crtstuff.c}. They contain, among other things, code +fragments within the @code{.init} and @code{.fini} sections that branch +to routines in the @code{.text} section. The linker will pull all parts +of a section together, which results in a complete @code{__init} function +that invokes the routines we need at startup. + +To use this variant, you must define the @code{INIT_SECTION_ASM_OP} +macro properly. + +If no init section is available, when GCC compiles any function called +@code{main} (or more accurately, any function designated as a program +entry point by the language front end calling @code{expand_main_function}), +it inserts a procedure call to @code{__main} as the first executable code +after the function prologue. The @code{__main} function is defined +in @file{libgcc2.c} and runs the global constructors. + +In file formats that don't support arbitrary sections, there are again +two variants. In the simplest variant, the GNU linker (GNU @code{ld}) +and an `a.out' format must be used. In this case, +@code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs} +entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__}, +and with the address of the void function containing the initialization +code as its value. The GNU linker recognizes this as a request to add +the value to a @dfn{set}; the values are accumulated, and are eventually +placed in the executable as a vector in the format described above, with +a leading (ignored) count and a trailing zero element. +@code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init +section is available, the absence of @code{INIT_SECTION_ASM_OP} causes +the compilation of @code{main} to call @code{__main} as above, starting +the initialization process. + +The last variant uses neither arbitrary sections nor the GNU linker. +This is preferable when you want to do dynamic linking and when using +file formats which the GNU linker does not support, such as `ECOFF'@. In +this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and +termination functions are recognized simply by their names. This requires +an extra program in the linkage step, called @command{collect2}. This program +pretends to be the linker, for use with GCC; it does its job by running +the ordinary linker, but also arranges to include the vectors of +initialization and termination functions. These functions are called +via @code{__main} as described above. In order to use this method, +@code{use_collect2} must be defined in the target in @file{config.gcc}. + +@ifinfo +The following section describes the specific macros that control and +customize the handling of initialization and termination functions. +@end ifinfo + +@node Macros for Initialization +@subsection Macros Controlling Initialization Routines + +Here are the macros that control how the compiler handles initialization +and termination functions: + +@defmac INIT_SECTION_ASM_OP +If defined, a C string constant, including spacing, for the assembler +operation to identify the following data as initialization code. If not +defined, GCC will assume such a section does not exist. When you are +using special sections for initialization and termination functions, this +macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to +run the initialization functions. +@end defmac + +@defmac HAS_INIT_SECTION +If defined, @code{main} will not call @code{__main} as described above. +This macro should be defined for systems that control start-up code +on a symbol-by-symbol basis, such as OSF/1, and should not +be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}. +@end defmac + +@defmac LD_INIT_SWITCH +If defined, a C string constant for a switch that tells the linker that +the following symbol is an initialization routine. +@end defmac + +@defmac LD_FINI_SWITCH +If defined, a C string constant for a switch that tells the linker that +the following symbol is a finalization routine. +@end defmac + +@defmac COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func}) +If defined, a C statement that will write a function that can be +automatically called when a shared library is loaded. The function +should call @var{func}, which takes no arguments. If not defined, and +the object format requires an explicit initialization function, then a +function called @code{_GLOBAL__DI} will be generated. + +This function and the following one are used by collect2 when linking a +shared library that needs constructors or destructors, or has DWARF2 +exception tables embedded in the code. +@end defmac + +@defmac COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func}) +If defined, a C statement that will write a function that can be +automatically called when a shared library is unloaded. The function +should call @var{func}, which takes no arguments. If not defined, and +the object format requires an explicit finalization function, then a +function called @code{_GLOBAL__DD} will be generated. +@end defmac + +@defmac INVOKE__main +If defined, @code{main} will call @code{__main} despite the presence of +@code{INIT_SECTION_ASM_OP}. This macro should be defined for systems +where the init section is not actually run automatically, but is still +useful for collecting the lists of constructors and destructors. +@end defmac + +@defmac SUPPORTS_INIT_PRIORITY +If nonzero, the C++ @code{init_priority} attribute is supported and the +compiler should emit instructions to control the order of initialization +of objects. If zero, the compiler will issue an error message upon +encountering an @code{init_priority} attribute. +@end defmac + +@hook TARGET_HAVE_CTORS_DTORS + +@hook TARGET_DTORS_FROM_CXA_ATEXIT + +@hook TARGET_ASM_CONSTRUCTOR + +@hook TARGET_ASM_DESTRUCTOR + +If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine +generated for the generated object file will have static linkage. + +If your system uses @command{collect2} as the means of processing +constructors, then that program normally uses @command{nm} to scan +an object file for constructor functions to be called. + +On certain kinds of systems, you can define this macro to make +@command{collect2} work faster (and, in some cases, make it work at all): + +@defmac OBJECT_FORMAT_COFF +Define this macro if the system uses COFF (Common Object File Format) +object files, so that @command{collect2} can assume this format and scan +object files directly for dynamic constructor/destructor functions. + +This macro is effective only in a native compiler; @command{collect2} as +part of a cross compiler always uses @command{nm} for the target machine. +@end defmac + +@defmac REAL_NM_FILE_NAME +Define this macro as a C string constant containing the file name to use +to execute @command{nm}. The default is to search the path normally for +@command{nm}. +@end defmac + +@defmac NM_FLAGS +@command{collect2} calls @command{nm} to scan object files for static +constructors and destructors and LTO info. By default, @option{-n} is +passed. Define @code{NM_FLAGS} to a C string constant if other options +are needed to get the same output format as GNU @command{nm -n} +produces. +@end defmac + +If your system supports shared libraries and has a program to list the +dynamic dependencies of a given library or executable, you can define +these macros to enable support for running initialization and +termination functions in shared libraries: + +@defmac LDD_SUFFIX +Define this macro to a C string constant containing the name of the program +which lists dynamic dependencies, like @command{ldd} under SunOS 4. +@end defmac + +@defmac PARSE_LDD_OUTPUT (@var{ptr}) +Define this macro to be C code that extracts filenames from the output +of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable +of type @code{char *} that points to the beginning of a line of output +from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the +code must advance @var{ptr} to the beginning of the filename on that +line. Otherwise, it must set @var{ptr} to @code{NULL}. +@end defmac + +@defmac SHLIB_SUFFIX +Define this macro to a C string constant containing the default shared +library extension of the target (e.g., @samp{".so"}). @command{collect2} +strips version information after this suffix when generating global +constructor and destructor names. This define is only needed on targets +that use @command{collect2} to process constructors and destructors. +@end defmac + +@node Instruction Output +@subsection Output of Assembler Instructions + +@c prevent bad page break with this line +This describes assembler instruction output. + +@defmac REGISTER_NAMES +A C initializer containing the assembler's names for the machine +registers, each one as a C string constant. This is what translates +register numbers in the compiler into assembler language. +@end defmac + +@defmac ADDITIONAL_REGISTER_NAMES +If defined, a C initializer for an array of structures containing a name +and a register number. This macro defines additional names for hard +registers, thus allowing the @code{asm} option in declarations to refer +to registers using alternate names. +@end defmac + +@defmac OVERLAPPING_REGISTER_NAMES +If defined, a C initializer for an array of structures containing a +name, a register number and a count of the number of consecutive +machine registers the name overlaps. This macro defines additional +names for hard registers, thus allowing the @code{asm} option in +declarations to refer to registers using alternate names. Unlike +@code{ADDITIONAL_REGISTER_NAMES}, this macro should be used when the +register name implies multiple underlying registers. + +This macro should be used when it is important that a clobber in an +@code{asm} statement clobbers all the underlying values implied by the +register name. For example, on ARM, clobbering the double-precision +VFP register ``d0'' implies clobbering both single-precision registers +``s0'' and ``s1''. +@end defmac + +@defmac ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr}) +Define this macro if you are using an unusual assembler that +requires different names for the machine instructions. + +The definition is a C statement or statements which output an +assembler instruction opcode to the stdio stream @var{stream}. The +macro-operand @var{ptr} is a variable of type @code{char *} which +points to the opcode name in its ``internal'' form---the form that is +written in the machine description. The definition should output the +opcode name to @var{stream}, performing any translation you desire, and +increment the variable @var{ptr} to point at the end of the opcode +so that it will not be output twice. + +In fact, your macro definition may process less than the entire opcode +name, or more than the opcode name; but if you want to process text +that includes @samp{%}-sequences to substitute operands, you must take +care of the substitution yourself. Just be sure to increment +@var{ptr} over whatever text should not be output normally. + +@findex recog_data.operand +If you need to look at the operand values, they can be found as the +elements of @code{recog_data.operand}. + +If the macro definition does nothing, the instruction is output +in the usual way. +@end defmac + +@defmac FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands}) +If defined, a C statement to be executed just prior to the output of +assembler code for @var{insn}, to modify the extracted operands so +they will be output differently. + +Here the argument @var{opvec} is the vector containing the operands +extracted from @var{insn}, and @var{noperands} is the number of +elements of the vector which contain meaningful data for this insn. +The contents of this vector are what will be used to convert the insn +template into assembler code, so you can change the assembler output +by changing the contents of the vector. + +This macro is useful when various assembler syntaxes share a single +file of instruction patterns; by defining this macro differently, you +can cause a large class of instructions to be output differently (such +as with rearranged operands). Naturally, variations in assembler +syntax affecting individual insn patterns ought to be handled by +writing conditional output routines in those patterns. + +If this macro is not defined, it is equivalent to a null statement. +@end defmac + +@hook TARGET_ASM_FINAL_POSTSCAN_INSN + +@defmac PRINT_OPERAND (@var{stream}, @var{x}, @var{code}) +A C compound statement to output to stdio stream @var{stream} the +assembler syntax for an instruction operand @var{x}. @var{x} is an +RTL expression. + +@var{code} is a value that can be used to specify one of several ways +of printing the operand. It is used when identical operands must be +printed differently depending on the context. @var{code} comes from +the @samp{%} specification that was used to request printing of the +operand. If the specification was just @samp{%@var{digit}} then +@var{code} is 0; if the specification was @samp{%@var{ltr} +@var{digit}} then @var{code} is the ASCII code for @var{ltr}. + +@findex reg_names +If @var{x} is a register, this macro should print the register's name. +The names can be found in an array @code{reg_names} whose type is +@code{char *[]}. @code{reg_names} is initialized from +@code{REGISTER_NAMES}. + +When the machine description has a specification @samp{%@var{punct}} +(a @samp{%} followed by a punctuation character), this macro is called +with a null pointer for @var{x} and the punctuation character for +@var{code}. +@end defmac + +@defmac PRINT_OPERAND_PUNCT_VALID_P (@var{code}) +A C expression which evaluates to true if @var{code} is a valid +punctuation character for use in the @code{PRINT_OPERAND} macro. If +@code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no +punctuation characters (except for the standard one, @samp{%}) are used +in this way. +@end defmac + +@defmac PRINT_OPERAND_ADDRESS (@var{stream}, @var{x}) +A C compound statement to output to stdio stream @var{stream} the +assembler syntax for an instruction operand that is a memory reference +whose address is @var{x}. @var{x} is an RTL expression. + +@cindex @code{TARGET_ENCODE_SECTION_INFO} usage +On some machines, the syntax for a symbolic address depends on the +section that the address refers to. On these machines, define the hook +@code{TARGET_ENCODE_SECTION_INFO} to store the information into the +@code{symbol_ref}, and then check for it here. @xref{Assembler +Format}. +@end defmac + +@findex dbr_sequence_length +@defmac DBR_OUTPUT_SEQEND (@var{file}) +A C statement, to be executed after all slot-filler instructions have +been output. If necessary, call @code{dbr_sequence_length} to +determine the number of slots filled in a sequence (zero if not +currently outputting a sequence), to decide how many no-ops to output, +or whatever. + +Don't define this macro if it has nothing to do, but it is helpful in +reading assembly output if the extent of the delay sequence is made +explicit (e.g.@: with white space). +@end defmac + +@findex final_sequence +Note that output routines for instructions with delay slots must be +prepared to deal with not being output as part of a sequence +(i.e.@: when the scheduling pass is not run, or when no slot fillers could be +found.) The variable @code{final_sequence} is null when not +processing a sequence, otherwise it contains the @code{sequence} rtx +being output. + +@findex asm_fprintf +@defmac REGISTER_PREFIX +@defmacx LOCAL_LABEL_PREFIX +@defmacx USER_LABEL_PREFIX +@defmacx IMMEDIATE_PREFIX +If defined, C string expressions to be used for the @samp{%R}, @samp{%L}, +@samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see +@file{final.cc}). These are useful when a single @file{md} file must +support multiple assembler formats. In that case, the various @file{tm.h} +files can define these macros differently. +@end defmac + +@defmac ASM_FPRINTF_EXTENSIONS (@var{file}, @var{argptr}, @var{format}) +If defined this macro should expand to a series of @code{case} +statements which will be parsed inside the @code{switch} statement of +the @code{asm_fprintf} function. This allows targets to define extra +printf formats which may useful when generating their assembler +statements. Note that uppercase letters are reserved for future +generic extensions to asm_fprintf, and so are not available to target +specific code. The output file is given by the parameter @var{file}. +The varargs input pointer is @var{argptr} and the rest of the format +string, starting the character after the one that is being switched +upon, is pointed to by @var{format}. +@end defmac + +@defmac ASSEMBLER_DIALECT +If your target supports multiple dialects of assembler language (such as +different opcodes), define this macro as a C expression that gives the +numeric index of the assembler language dialect to use, with zero as the +first variant. + +If this macro is defined, you may use constructs of the form +@smallexample +@samp{@{option0|option1|option2@dots{}@}} +@end smallexample +@noindent +in the output templates of patterns (@pxref{Output Template}) or in the +first argument of @code{asm_fprintf}. This construct outputs +@samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of +@code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters +within these strings retain their usual meaning. If there are fewer +alternatives within the braces than the value of +@code{ASSEMBLER_DIALECT}, the construct outputs nothing. If it's needed +to print curly braces or @samp{|} character in assembler output directly, +@samp{%@{}, @samp{%@}} and @samp{%|} can be used. + +If you do not define this macro, the characters @samp{@{}, @samp{|} and +@samp{@}} do not have any special meaning when used in templates or +operands to @code{asm_fprintf}. + +Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX}, +@code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express +the variations in assembler language syntax with that mechanism. Define +@code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax +if the syntax variant are larger and involve such things as different +opcodes or operand order. +@end defmac + +@defmac ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno}) +A C expression to output to @var{stream} some assembler code +which will push hard register number @var{regno} onto the stack. +The code need not be optimal, since this macro is used only when +profiling. +@end defmac + +@defmac ASM_OUTPUT_REG_POP (@var{stream}, @var{regno}) +A C expression to output to @var{stream} some assembler code +which will pop hard register number @var{regno} off of the stack. +The code need not be optimal, since this macro is used only when +profiling. +@end defmac + +@node Dispatch Tables +@subsection Output of Dispatch Tables + +@c prevent bad page break with this line +This concerns dispatch tables. + +@cindex dispatch table +@defmac ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel}) +A C statement to output to the stdio stream @var{stream} an assembler +pseudo-instruction to generate a difference between two labels. +@var{value} and @var{rel} are the numbers of two internal labels. The +definitions of these labels are output using +@code{(*targetm.asm_out.internal_label)}, and they must be printed in the same +way here. For example, + +@smallexample +fprintf (@var{stream}, "\t.word L%d-L%d\n", + @var{value}, @var{rel}) +@end smallexample + +You must provide this macro on machines where the addresses in a +dispatch table are relative to the table's own address. If defined, GCC +will also use this macro on all machines when producing PIC@. +@var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the +mode and flags can be read. +@end defmac + +@defmac ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value}) +This macro should be provided on machines where the addresses +in a dispatch table are absolute. + +The definition should be a C statement to output to the stdio stream +@var{stream} an assembler pseudo-instruction to generate a reference to +a label. @var{value} is the number of an internal label whose +definition is output using @code{(*targetm.asm_out.internal_label)}. +For example, + +@smallexample +fprintf (@var{stream}, "\t.word L%d\n", @var{value}) +@end smallexample +@end defmac + +@defmac ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table}) +Define this if the label before a jump-table needs to be output +specially. The first three arguments are the same as for +@code{(*targetm.asm_out.internal_label)}; the fourth argument is the +jump-table which follows (a @code{jump_table_data} containing an +@code{addr_vec} or @code{addr_diff_vec}). + +This feature is used on system V to output a @code{swbeg} statement +for the table. + +If this macro is not defined, these labels are output with +@code{(*targetm.asm_out.internal_label)}. +@end defmac + +@defmac ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table}) +Define this if something special must be output at the end of a +jump-table. The definition should be a C statement to be executed +after the assembler code for the table is written. It should write +the appropriate code to stdio stream @var{stream}. The argument +@var{table} is the jump-table insn, and @var{num} is the label-number +of the preceding label. + +If this macro is not defined, nothing special is output at the end of +the jump-table. +@end defmac + +@hook TARGET_ASM_POST_CFI_STARTPROC + +@hook TARGET_ASM_EMIT_UNWIND_LABEL + +@hook TARGET_ASM_EMIT_EXCEPT_TABLE_LABEL + +@hook TARGET_ASM_EMIT_EXCEPT_PERSONALITY + +@hook TARGET_ASM_UNWIND_EMIT + +@hook TARGET_ASM_MAKE_EH_SYMBOL_INDIRECT + +@hook TARGET_ASM_UNWIND_EMIT_BEFORE_INSN + +@hook TARGET_ASM_SHOULD_RESTORE_CFA_STATE + +@node Exception Region Output +@subsection Assembler Commands for Exception Regions + +@c prevent bad page break with this line + +This describes commands marking the start and the end of an exception +region. + +@defmac EH_FRAME_SECTION_NAME +If defined, a C string constant for the name of the section containing +exception handling frame unwind information. If not defined, GCC will +provide a default definition if the target supports named sections. +@file{crtstuff.c} uses this macro to switch to the appropriate section. + +You should define this symbol if your target supports DWARF 2 frame +unwind information and the default definition does not work. +@end defmac + +@defmac EH_FRAME_THROUGH_COLLECT2 +If defined, DWARF 2 frame unwind information will identified by +specially named labels. The collect2 process will locate these +labels and generate code to register the frames. + +This might be necessary, for instance, if the system linker will not +place the eh_frames in-between the sentinals from @file{crtstuff.c}, +or if the system linker does garbage collection and sections cannot +be marked as not to be collected. +@end defmac + +@defmac EH_TABLES_CAN_BE_READ_ONLY +Define this macro to 1 if your target is such that no frame unwind +information encoding used with non-PIC code will ever require a +runtime relocation, but the linker may not support merging read-only +and read-write sections into a single read-write section. +@end defmac + +@defmac MASK_RETURN_ADDR +An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so +that it does not contain any extraneous set bits in it. +@end defmac + +@defmac DWARF2_UNWIND_INFO +Define this macro to 0 if your target supports DWARF 2 frame unwind +information, but it does not yet work with exception handling. +Otherwise, if your target supports this information (if it defines +@code{INCOMING_RETURN_ADDR_RTX} and @code{OBJECT_FORMAT_ELF}), +GCC will provide a default definition of 1. +@end defmac + +@hook TARGET_EXCEPT_UNWIND_INFO +This hook defines the mechanism that will be used for exception handling +by the target. If the target has ABI specified unwind tables, the hook +should return @code{UI_TARGET}. If the target is to use the +@code{setjmp}/@code{longjmp}-based exception handling scheme, the hook +should return @code{UI_SJLJ}. If the target supports DWARF 2 frame unwind +information, the hook should return @code{UI_DWARF2}. + +A target may, if exceptions are disabled, choose to return @code{UI_NONE}. +This may end up simplifying other parts of target-specific code. The +default implementation of this hook never returns @code{UI_NONE}. + +Note that the value returned by this hook should be constant. It should +not depend on anything except the command-line switches described by +@var{opts}. In particular, the +setting @code{UI_SJLJ} must be fixed at compiler start-up as C pre-processor +macros and builtin functions related to exception handling are set up +depending on this setting. + +The default implementation of the hook first honors the +@option{--enable-sjlj-exceptions} configure option, then +@code{DWARF2_UNWIND_INFO}, and finally defaults to @code{UI_SJLJ}. If +@code{DWARF2_UNWIND_INFO} depends on command-line options, the target +must define this hook so that @var{opts} is used correctly. +@end deftypefn + +@hook TARGET_UNWIND_TABLES_DEFAULT +This variable should be set to @code{true} if the target ABI requires unwinding +tables even when exceptions are not used. It must not be modified by +command-line option processing. +@end deftypevr + +@defmac DONT_USE_BUILTIN_SETJMP +Define this macro to 1 if the @code{setjmp}/@code{longjmp}-based scheme +should use the @code{setjmp}/@code{longjmp} functions from the C library +instead of the @code{__builtin_setjmp}/@code{__builtin_longjmp} machinery. +@end defmac + +@defmac JMP_BUF_SIZE +This macro has no effect unless @code{DONT_USE_BUILTIN_SETJMP} is also +defined. Define this macro if the default size of @code{jmp_buf} buffer +for the @code{setjmp}/@code{longjmp}-based exception handling mechanism +is not large enough, or if it is much too large. +The default size is @code{FIRST_PSEUDO_REGISTER * sizeof(void *)}. +@end defmac + +@defmac DWARF_CIE_DATA_ALIGNMENT +This macro need only be defined if the target might save registers in the +function prologue at an offset to the stack pointer that is not aligned to +@code{UNITS_PER_WORD}. The definition should be the negative minimum +alignment if @code{STACK_GROWS_DOWNWARD} is true, and the positive +minimum alignment otherwise. @xref{DWARF}. Only applicable if +the target supports DWARF 2 frame unwind information. +@end defmac + +@hook TARGET_TERMINATE_DW2_EH_FRAME_INFO + +@hook TARGET_DWARF_REGISTER_SPAN + +@hook TARGET_DWARF_FRAME_REG_MODE + +@hook TARGET_INIT_DWARF_REG_SIZES_EXTRA + +@hook TARGET_ASM_TTYPE + +@hook TARGET_ARM_EABI_UNWINDER + +@node Alignment Output +@subsection Assembler Commands for Alignment + +@c prevent bad page break with this line +This describes commands for alignment. + +@defmac JUMP_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which is +a common destination of jumps and has no fallthru incoming edge. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @var{align_jumps} in the target's +@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's +selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation. +@end defmac + +@defmac LABEL_ALIGN_AFTER_BARRIER (@var{label}) +The alignment (log base 2) to put in front of @var{label}, which follows +a @code{BARRIER}. + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. +@end defmac + +@defmac LOOP_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label} that heads +a frequently executed basic block (usually the header of a loop). + +This macro need not be defined if you don't want any special alignment +to be done at such a time. Most machine descriptions do not currently +define the macro. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @code{align_loops} in the target's +@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's +selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation. +@end defmac + +@defmac LABEL_ALIGN (@var{label}) +The alignment (log base 2) to put in front of @var{label}. +If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment, +the maximum of the specified values is used. + +Unless it's necessary to inspect the @var{label} parameter, it is better +to set the variable @code{align_labels} in the target's +@code{TARGET_OPTION_OVERRIDE}. Otherwise, you should try to honor the user's +selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation. +@end defmac + +@defmac ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes}) +A C statement to output to the stdio stream @var{stream} an assembler +instruction to advance the location counter by @var{nbytes} bytes. +Those bytes should be zero when loaded. @var{nbytes} will be a C +expression of type @code{unsigned HOST_WIDE_INT}. +@end defmac + +@defmac ASM_NO_SKIP_IN_TEXT +Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the +text section because it fails to put zeros in the bytes that are skipped. +This is true on many Unix systems, where the pseudo--op to skip bytes +produces no-op instructions rather than zeros when used in the text +section. +@end defmac + +@defmac ASM_OUTPUT_ALIGN (@var{stream}, @var{power}) +A C statement to output to the stdio stream @var{stream} an assembler +command to advance the location counter to a multiple of 2 to the +@var{power} bytes. @var{power} will be a C expression of type @code{int}. +@end defmac + +@defmac ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power}) +Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used +for padding, if necessary. +@end defmac + +@defmac ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip}) +A C statement to output to the stdio stream @var{stream} an assembler +command to advance the location counter to a multiple of 2 to the +@var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to +satisfy the alignment request. @var{power} and @var{max_skip} will be +a C expression of type @code{int}. +@end defmac + +@need 3000 +@node Debugging Info +@section Controlling Debugging Information Format + +@c prevent bad page break with this line +This describes how to specify debugging information. + +@menu +* All Debuggers:: Macros that affect all debugging formats uniformly. +* DWARF:: Macros for DWARF format. +* VMS Debug:: Macros for VMS debug format. +* CTF Debug:: Macros for CTF debug format. +* BTF Debug:: Macros for BTF debug format. +@end menu + +@node All Debuggers +@subsection Macros Affecting All Debugging Formats + +@c prevent bad page break with this line +These macros affect all debugging formats. + +@defmac DEBUGGER_REGNO (@var{regno}) +A C expression that returns the debugger register number for the compiler +register number @var{regno}. In the default macro provided, the value +of this expression will be @var{regno} itself. But sometimes there are +some registers that the compiler knows about and debugger does not, or vice +versa. In such cases, some register may need to have one number in the +compiler and another for debugger@. + +If two registers have consecutive numbers inside GCC, and they can be +used as a pair to hold a multiword value, then they @emph{must} have +consecutive numbers after renumbering with @code{DEBUGGER_REGNO}. +Otherwise, debuggers will be unable to access such a pair, because they +expect register pairs to be consecutive in their own numbering scheme. + +If you find yourself defining @code{DEBUGGER_REGNO} in way that +does not preserve register pairs, then what you must do instead is +redefine the actual register numbering scheme. +@end defmac + +@defmac DEBUGGER_AUTO_OFFSET (@var{x}) +A C expression that returns the integer offset value for an automatic +variable having address @var{x} (an RTL expression). The default +computation assumes that @var{x} is based on the frame-pointer and +gives the offset from the frame-pointer. This is required for targets +that produce debugging output for debugger and allow the frame-pointer to be +eliminated when the @option{-g} option is used. +@end defmac + +@defmac DEBUGGER_ARG_OFFSET (@var{offset}, @var{x}) +A C expression that returns the integer offset value for an argument +having address @var{x} (an RTL expression). The nominal offset is +@var{offset}. +@end defmac + +@defmac PREFERRED_DEBUGGING_TYPE +A C expression that returns the type of debugging output GCC should +produce when the user specifies just @option{-g}. Define +this if you have arranged for GCC to support more than one format of +debugging output. Currently, the allowable values are +@code{DWARF2_DEBUG}, @code{VMS_DEBUG}, +and @code{VMS_AND_DWARF2_DEBUG}. + +When the user specifies @option{-ggdb}, GCC normally also uses the +value of this macro to select the debugging output format, but with two +exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined, GCC uses the +value @code{DWARF2_DEBUG}. + +The value of this macro only affects the default debugging output; the +user can always get a specific type of output by using @option{-gdwarf-2}, +or @option{-gvms}. +@end defmac + +@defmac DEFAULT_GDB_EXTENSIONS +Define this macro to control whether GCC should by default generate +GDB's extended version of debugging information. If you don't define the +macro, the default is 1: always generate the extended information +if there is any occasion to. +@end defmac + +@need 2000 +@node DWARF +@subsection Macros for DWARF Output + +@c prevent bad page break with this line +Here are macros for DWARF output. + +@defmac DWARF2_DEBUGGING_INFO +Define this macro if GCC should produce dwarf version 2 format +debugging output in response to the @option{-g} option. + +To support optional call frame debugging information, you must also +define @code{INCOMING_RETURN_ADDR_RTX} and either set +@code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the +prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save} +as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't. +@end defmac + +@hook TARGET_DWARF_CALLING_CONVENTION + +@defmac DWARF2_FRAME_INFO +Define this macro to a nonzero value if GCC should always output +Dwarf 2 frame information. If @code{TARGET_EXCEPT_UNWIND_INFO} +(@pxref{Exception Region Output}) returns @code{UI_DWARF2}, and +exceptions are enabled, GCC will output this information not matter +how you define @code{DWARF2_FRAME_INFO}. +@end defmac + +@hook TARGET_DEBUG_UNWIND_INFO + +@defmac DWARF2_ASM_LINE_DEBUG_INFO +Define this macro to be a nonzero value if the assembler can generate Dwarf 2 +line debug info sections. This will result in much more compact line number +tables, and hence is desirable if it works. +@end defmac + +@defmac DWARF2_ASM_VIEW_DEBUG_INFO +Define this macro to be a nonzero value if the assembler supports view +assignment and verification in @code{.loc}. If it does not, but the +user enables location views, the compiler may have to fallback to +internal line number tables. +@end defmac + +@hook TARGET_RESET_LOCATION_VIEW + +@hook TARGET_WANT_DEBUG_PUB_SECTIONS + +@hook TARGET_DELAY_SCHED2 + +@hook TARGET_DELAY_VARTRACK + +@hook TARGET_NO_REGISTER_ALLOCATION + +@defmac ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) +A C statement to issue assembly directives that create a difference +@var{lab1} minus @var{lab2}, using an integer of the given @var{size}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_VMS_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) +A C statement to issue assembly directives that create a difference +between the two given labels in system defined units, e.g.@: instruction +slots on IA64 VMS, using an integer of the given size. +@end defmac + +@defmac ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}, @var{offset}, @var{section}) +A C statement to issue assembly directives that create a +section-relative reference to the given @var{label} plus @var{offset}, using +an integer of the given @var{size}. The label is known to be defined in the +given @var{section}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label}) +A C statement to issue assembly directives that create a self-relative +reference to the given @var{label}, using an integer of the given @var{size}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_DATAREL (@var{stream}, @var{size}, @var{label}) +A C statement to issue assembly directives that create a reference to the +given @var{label} relative to the dbase, using an integer of the given @var{size}. +@end defmac + +@defmac ASM_OUTPUT_DWARF_TABLE_REF (@var{label}) +A C statement to issue assembly directives that create a reference to +the DWARF table identifier @var{label} from the current section. This +is used on some systems to avoid garbage collecting a DWARF table which +is referenced by a function. +@end defmac + +@hook TARGET_ASM_OUTPUT_DWARF_DTPREL + +@need 2000 +@node VMS Debug +@subsection Macros for VMS Debug Format + +@c prevent bad page break with this line +Here are macros for VMS debug format. + +@defmac VMS_DEBUGGING_INFO +Define this macro if GCC should produce debugging output for VMS +in response to the @option{-g} option. The default behavior for VMS +is to generate minimal debug info for a traceback in the absence of +@option{-g} unless explicitly overridden with @option{-g0}. This +behavior is controlled by @code{TARGET_OPTION_OPTIMIZATION} and +@code{TARGET_OPTION_OVERRIDE}. +@end defmac + +@need 2000 +@node CTF Debug +@subsection Macros for CTF Debug Format + +@c prevent bad page break with this line +Here are macros for CTF debug format. + +@defmac CTF_DEBUGGING_INFO +Define this macro if GCC should produce debugging output in CTF debug +format in response to the @option{-gctf} option. +@end defmac + +@need 2000 +@node BTF Debug +@subsection Macros for BTF Debug Format + +@c prevent bad page break with this line +Here are macros for BTF debug format. + +@defmac BTF_DEBUGGING_INFO +Define this macro if GCC should produce debugging output in BTF debug +format in response to the @option{-gbtf} option. +@end defmac + +@node Floating Point +@section Cross Compilation and Floating Point +@cindex cross compilation and floating point +@cindex floating point and cross compilation + +While all modern machines use twos-complement representation for integers, +there are a variety of representations for floating point numbers. This +means that in a cross-compiler the representation of floating point numbers +in the compiled program may be different from that used in the machine +doing the compilation. + +Because different representation systems may offer different amounts of +range and precision, all floating point constants must be represented in +the target machine's format. Therefore, the cross compiler cannot +safely use the host machine's floating point arithmetic; it must emulate +the target's arithmetic. To ensure consistency, GCC always uses +emulation to work with floating point values, even when the host and +target floating point formats are identical. + +The following macros are provided by @file{real.h} for the compiler to +use. All parts of the compiler which generate or optimize +floating-point calculations must use these macros. They may evaluate +their operands more than once, so operands must not have side effects. + +@defmac REAL_VALUE_TYPE +The C data type to be used to hold a floating point value in the target +machine's format. Typically this is a @code{struct} containing an +array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque +quantity. +@end defmac + +@deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x}) +Truncates @var{x} to a signed integer, rounding toward zero. +@end deftypefn + +@deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x}) +Truncates @var{x} to an unsigned integer, rounding toward zero. If +@var{x} is negative, returns zero. +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, machine_mode @var{mode}) +Converts @var{string} into a floating point number in the target machine's +representation for mode @var{mode}. This routine can handle both +decimal and hexadecimal floating point constants, using the syntax +defined by the C language for both. +@end deftypefn + +@deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x}) +Returns 1 if @var{x} is negative (including negative zero), 0 otherwise. +@end deftypefn + +@deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x}) +Determines whether @var{x} represents infinity (positive or negative). +@end deftypefn + +@deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x}) +Determines whether @var{x} represents a ``NaN'' (not-a-number). +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x}) +Returns the negative of the floating point value @var{x}. +@end deftypefn + +@deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x}) +Returns the absolute value of @var{x}. +@end deftypefn + +@node Mode Switching +@section Mode Switching Instructions +@cindex mode switching +The following macros control mode switching optimizations: + +@defmac OPTIMIZE_MODE_SWITCHING (@var{entity}) +Define this macro if the port needs extra instructions inserted for mode +switching in an optimizing compilation. + +For an example, the SH4 can perform both single and double precision +floating point operations, but to perform a single precision operation, +the FPSCR PR bit has to be cleared, while for a double precision +operation, this bit has to be set. Changing the PR bit requires a general +purpose register as a scratch register, hence these FPSCR sets have to +be inserted before reload, i.e.@: you cannot put this into instruction emitting +or @code{TARGET_MACHINE_DEPENDENT_REORG}. + +You can have multiple entities that are mode-switched, and select at run time +which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should +return nonzero for any @var{entity} that needs mode-switching. +If you define this macro, you also have to define +@code{NUM_MODES_FOR_MODE_SWITCHING}, @code{TARGET_MODE_NEEDED}, +@code{TARGET_MODE_PRIORITY} and @code{TARGET_MODE_EMIT}. +@code{TARGET_MODE_AFTER}, @code{TARGET_MODE_ENTRY}, and @code{TARGET_MODE_EXIT} +are optional. +@end defmac + +@defmac NUM_MODES_FOR_MODE_SWITCHING +If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as +initializer for an array of integers. Each initializer element +N refers to an entity that needs mode switching, and specifies the number +of different modes that might need to be set for this entity. +The position of the initializer in the initializer---starting counting at +zero---determines the integer that is used to refer to the mode-switched +entity in question. +In macros that take mode arguments / yield a mode result, modes are +represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode +switch is needed / supplied. +@end defmac + +@hook TARGET_MODE_EMIT + +@hook TARGET_MODE_NEEDED + +@hook TARGET_MODE_AFTER + +@hook TARGET_MODE_ENTRY + +@hook TARGET_MODE_EXIT + +@hook TARGET_MODE_PRIORITY + +@node Target Attributes +@section Defining target-specific uses of @code{__attribute__} +@cindex target attributes +@cindex machine attributes +@cindex attributes, target-specific + +Target-specific attributes may be defined for functions, data and types. +These are described using the following target hooks; they also need to +be documented in @file{extend.texi}. + +@hook TARGET_ATTRIBUTE_TABLE + +@hook TARGET_ATTRIBUTE_TAKES_IDENTIFIER_P + +@hook TARGET_COMP_TYPE_ATTRIBUTES + +@hook TARGET_SET_DEFAULT_TYPE_ATTRIBUTES + +@hook TARGET_MERGE_TYPE_ATTRIBUTES + +@hook TARGET_MERGE_DECL_ATTRIBUTES + +@hook TARGET_VALID_DLLIMPORT_ATTRIBUTE_P + +@defmac TARGET_DECLSPEC +Define this macro to a nonzero value if you want to treat +@code{__declspec(X)} as equivalent to @code{__attribute((X))}. By +default, this behavior is enabled only for targets that define +@code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. The current implementation +of @code{__declspec} is via a built-in macro, but you should not rely +on this implementation detail. +@end defmac + +@hook TARGET_INSERT_ATTRIBUTES + +@hook TARGET_HANDLE_GENERIC_ATTRIBUTE + +@hook TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P + +@hook TARGET_OPTION_VALID_ATTRIBUTE_P + +@hook TARGET_OPTION_SAVE + +@hook TARGET_OPTION_RESTORE + +@hook TARGET_OPTION_POST_STREAM_IN + +@hook TARGET_OPTION_PRINT + +@hook TARGET_OPTION_PRAGMA_PARSE + +@hook TARGET_OPTION_OVERRIDE + +@hook TARGET_OPTION_FUNCTION_VERSIONS + +@hook TARGET_CAN_INLINE_P + +@hook TARGET_UPDATE_IPA_FN_TARGET_INFO + +@hook TARGET_NEED_IPA_FN_TARGET_INFO + +@hook TARGET_RELAYOUT_FUNCTION + +@node Emulated TLS +@section Emulating TLS +@cindex Emulated TLS + +For targets whose psABI does not provide Thread Local Storage via +specific relocations and instruction sequences, an emulation layer is +used. A set of target hooks allows this emulation layer to be +configured for the requirements of a particular target. For instance +the psABI may in fact specify TLS support in terms of an emulation +layer. + +The emulation layer works by creating a control object for every TLS +object. To access the TLS object, a lookup function is provided +which, when given the address of the control object, will return the +address of the current thread's instance of the TLS object. + +@hook TARGET_EMUTLS_GET_ADDRESS + +@hook TARGET_EMUTLS_REGISTER_COMMON + +@hook TARGET_EMUTLS_VAR_SECTION + +@hook TARGET_EMUTLS_TMPL_SECTION + +@hook TARGET_EMUTLS_VAR_PREFIX + +@hook TARGET_EMUTLS_TMPL_PREFIX + +@hook TARGET_EMUTLS_VAR_FIELDS + +@hook TARGET_EMUTLS_VAR_INIT + +@hook TARGET_EMUTLS_VAR_ALIGN_FIXED + +@hook TARGET_EMUTLS_DEBUG_FORM_TLS_ADDRESS + +@node MIPS Coprocessors +@section Defining coprocessor specifics for MIPS targets. +@cindex MIPS coprocessor-definition macros + +The MIPS specification allows MIPS implementations to have as many as 4 +coprocessors, each with as many as 32 private registers. GCC supports +accessing these registers and transferring values between the registers +and memory using asm-ized variables. For example: + +@smallexample + register unsigned int cp0count asm ("c0r1"); + unsigned int d; + + d = cp0count + 3; +@end smallexample + +(``c0r1'' is the default name of register 1 in coprocessor 0; alternate +names may be added as described below, or the default names may be +overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.) + +Coprocessor registers are assumed to be epilogue-used; sets to them will +be preserved even if it does not appear that the register is used again +later in the function. + +Another note: according to the MIPS spec, coprocessor 1 (if present) is +the FPU@. One accesses COP1 registers through standard mips +floating-point support; they are not included in this mechanism. + +@node PCH Target +@section Parameters for Precompiled Header Validity Checking +@cindex parameters, precompiled headers + +@hook TARGET_GET_PCH_VALIDITY + +@hook TARGET_PCH_VALID_P + +@hook TARGET_CHECK_PCH_TARGET_FLAGS + +@hook TARGET_PREPARE_PCH_SAVE + +@node C++ ABI +@section C++ ABI parameters +@cindex parameters, c++ abi + +@hook TARGET_CXX_GUARD_TYPE + +@hook TARGET_CXX_GUARD_MASK_BIT + +@hook TARGET_CXX_GET_COOKIE_SIZE + +@hook TARGET_CXX_COOKIE_HAS_SIZE + +@hook TARGET_CXX_IMPORT_EXPORT_CLASS + +@hook TARGET_CXX_CDTOR_RETURNS_THIS + +@hook TARGET_CXX_KEY_METHOD_MAY_BE_INLINE + +@hook TARGET_CXX_DETERMINE_CLASS_DATA_VISIBILITY + +@hook TARGET_CXX_CLASS_DATA_ALWAYS_COMDAT + +@hook TARGET_CXX_LIBRARY_RTTI_COMDAT + +@hook TARGET_CXX_USE_AEABI_ATEXIT + +@hook TARGET_CXX_USE_ATEXIT_FOR_CXA_ATEXIT + +@hook TARGET_CXX_ADJUST_CLASS_AT_DEFINITION + +@hook TARGET_CXX_DECL_MANGLING_CONTEXT + +@node D Language and ABI +@section D ABI parameters +@cindex parameters, d abi + +@hook TARGET_D_CPU_VERSIONS + +@hook TARGET_D_OS_VERSIONS + +@hook TARGET_D_REGISTER_CPU_TARGET_INFO + +@hook TARGET_D_REGISTER_OS_TARGET_INFO + +@hook TARGET_D_MINFO_SECTION + +@hook TARGET_D_MINFO_SECTION_START + +@hook TARGET_D_MINFO_SECTION_END + +@hook TARGET_D_HAS_STDCALL_CONVENTION + +@hook TARGET_D_TEMPLATES_ALWAYS_COMDAT + +@node Named Address Spaces +@section Adding support for named address spaces +@cindex named address spaces + +The draft technical report of the ISO/IEC JTC1 S22 WG14 N1275 +standards committee, @cite{Programming Languages - C - Extensions to +support embedded processors}, specifies a syntax for embedded +processors to specify alternate address spaces. You can configure a +GCC port to support section 5.1 of the draft report to add support for +address spaces other than the default address space. These address +spaces are new keywords that are similar to the @code{volatile} and +@code{const} type attributes. + +Pointers to named address spaces can have a different size than +pointers to the generic address space. + +For example, the SPU port uses the @code{__ea} address space to refer +to memory in the host processor, rather than memory local to the SPU +processor. Access to memory in the @code{__ea} address space involves +issuing DMA operations to move data between the host processor and the +local processor memory address space. Pointers in the @code{__ea} +address space are either 32 bits or 64 bits based on the +@option{-mea32} or @option{-mea64} switches (native SPU pointers are +always 32 bits). + +Internally, address spaces are represented as a small integer in the +range 0 to 15 with address space 0 being reserved for the generic +address space. + +To register a named address space qualifier keyword with the C front end, +the target may call the @code{c_register_addr_space} routine. For example, +the SPU port uses the following to declare @code{__ea} as the keyword for +named address space #1: +@smallexample +#define ADDR_SPACE_EA 1 +c_register_addr_space ("__ea", ADDR_SPACE_EA); +@end smallexample + +@hook TARGET_ADDR_SPACE_POINTER_MODE + +@hook TARGET_ADDR_SPACE_ADDRESS_MODE + +@hook TARGET_ADDR_SPACE_VALID_POINTER_MODE + +@hook TARGET_ADDR_SPACE_LEGITIMATE_ADDRESS_P + +@hook TARGET_ADDR_SPACE_LEGITIMIZE_ADDRESS + +@hook TARGET_ADDR_SPACE_SUBSET_P + +@hook TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID + +@hook TARGET_ADDR_SPACE_CONVERT + +@hook TARGET_ADDR_SPACE_DEBUG + +@hook TARGET_ADDR_SPACE_DIAGNOSE_USAGE + +@node Misc +@section Miscellaneous Parameters +@cindex parameters, miscellaneous + +@c prevent bad page break with this line +Here are several miscellaneous parameters. + +@defmac HAS_LONG_COND_BRANCH +Define this boolean macro to indicate whether or not your architecture +has conditional branches that can span all of memory. It is used in +conjunction with an optimization that partitions hot and cold basic +blocks into separate sections of the executable. If this macro is +set to false, gcc will convert any conditional branches that attempt +to cross between sections into unconditional branches or indirect jumps. +@end defmac + +@defmac HAS_LONG_UNCOND_BRANCH +Define this boolean macro to indicate whether or not your architecture +has unconditional branches that can span all of memory. It is used in +conjunction with an optimization that partitions hot and cold basic +blocks into separate sections of the executable. If this macro is +set to false, gcc will convert any unconditional branches that attempt +to cross between sections into indirect jumps. +@end defmac + +@defmac CASE_VECTOR_MODE +An alias for a machine mode name. This is the machine mode that +elements of a jump-table should have. +@end defmac + +@defmac CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body}) +Optional: return the preferred mode for an @code{addr_diff_vec} +when the minimum and maximum offset are known. If you define this, +it enables extra code in branch shortening to deal with @code{addr_diff_vec}. +To make this work, you also have to define @code{INSN_ALIGN} and +make the alignment for @code{addr_diff_vec} explicit. +The @var{body} argument is provided so that the offset_unsigned and scale +flags can be updated. +@end defmac + +@defmac CASE_VECTOR_PC_RELATIVE +Define this macro to be a C expression to indicate when jump-tables +should contain relative addresses. You need not define this macro if +jump-tables never contain relative addresses, or jump-tables should +contain relative addresses only when @option{-fPIC} or @option{-fPIC} +is in effect. +@end defmac + +@hook TARGET_CASE_VALUES_THRESHOLD + +@defmac WORD_REGISTER_OPERATIONS +Define this macro to 1 if operations between registers with integral mode +smaller than a word are always performed on the entire register. To be +more explicit, if you start with a pair of @code{word_mode} registers with +known values and you do a subword, for example @code{QImode}, addition on +the low part of the registers, then the compiler may consider that the +result has a known value in @code{word_mode} too if the macro is defined +to 1. Most RISC machines have this property and most CISC machines do not. +@end defmac + +@hook TARGET_MIN_ARITHMETIC_PRECISION + +@defmac LOAD_EXTEND_OP (@var{mem_mode}) +Define this macro to be a C expression indicating when insns that read +memory in @var{mem_mode}, an integral mode narrower than a word, set the +bits outside of @var{mem_mode} to be either the sign-extension or the +zero-extension of the data read. Return @code{SIGN_EXTEND} for values +of @var{mem_mode} for which the +insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and +@code{UNKNOWN} for other modes. + +This macro is not called with @var{mem_mode} non-integral or with a width +greater than or equal to @code{BITS_PER_WORD}, so you may return any +value in this case. Do not define this macro if it would always return +@code{UNKNOWN}. On machines where this macro is defined, you will normally +define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}. + +You may return a non-@code{UNKNOWN} value even if for some hard registers +the sign extension is not performed, if for the @code{REGNO_REG_CLASS} +of these hard registers @code{TARGET_CAN_CHANGE_MODE_CLASS} returns false +when the @var{from} mode is @var{mem_mode} and the @var{to} mode is any +integral mode larger than this but not larger than @code{word_mode}. + +You must return @code{UNKNOWN} if for some hard registers that allow this +mode, @code{TARGET_CAN_CHANGE_MODE_CLASS} says that they cannot change to +@code{word_mode}, but that they can change to another integral mode that +is larger then @var{mem_mode} but still smaller than @code{word_mode}. +@end defmac + +@defmac SHORT_IMMEDIATES_SIGN_EXTEND +Define this macro to 1 if loading short immediate values into registers sign +extends. +@end defmac + +@hook TARGET_MIN_DIVISIONS_FOR_RECIP_MUL + +@defmac MOVE_MAX +The maximum number of bytes that a single instruction can move quickly +between memory and registers or between two memory locations. +@end defmac + +@defmac MAX_MOVE_MAX +The maximum number of bytes that a single instruction can move quickly +between memory and registers or between two memory locations. If this +is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the +constant value that is the largest value that @code{MOVE_MAX} can have +at run-time. +@end defmac + +@defmac SHIFT_COUNT_TRUNCATED +A C expression that is nonzero if on this machine the number of bits +actually used for the count of a shift operation is equal to the number +of bits needed to represent the size of the object being shifted. When +this macro is nonzero, the compiler will assume that it is safe to omit +a sign-extend, zero-extend, and certain bitwise `and' instructions that +truncates the count of a shift operation. On machines that have +instructions that act on bit-fields at variable positions, which may +include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED} +also enables deletion of truncations of the values that serve as +arguments to bit-field instructions. + +If both types of instructions truncate the count (for shifts) and +position (for bit-field operations), or if no variable-position bit-field +instructions exist, you should define this macro. + +However, on some machines, such as the 80386 and the 680x0, truncation +only applies to shift operations and not the (real or pretended) +bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on +such machines. Instead, add patterns to the @file{md} file that include +the implied truncation of the shift instructions. + +You need not define this macro if it would always have the value of zero. +@end defmac + +@anchor{TARGET_SHIFT_TRUNCATION_MASK} +@hook TARGET_SHIFT_TRUNCATION_MASK + +@hook TARGET_TRULY_NOOP_TRUNCATION + +@hook TARGET_MODE_REP_EXTENDED + +@hook TARGET_SETJMP_PRESERVES_NONVOLATILE_REGS_P + +@defmac STORE_FLAG_VALUE +A C expression describing the value returned by a comparison operator +with an integral mode and stored by a store-flag instruction +(@samp{cstore@var{mode}4}) when the condition is true. This description must +apply to @emph{all} the @samp{cstore@var{mode}4} patterns and all the +comparison operators whose results have a @code{MODE_INT} mode. + +A value of 1 or @minus{}1 means that the instruction implementing the +comparison operator returns exactly 1 or @minus{}1 when the comparison is true +and 0 when the comparison is false. Otherwise, the value indicates +which bits of the result are guaranteed to be 1 when the comparison is +true. This value is interpreted in the mode of the comparison +operation, which is given by the mode of the first operand in the +@samp{cstore@var{mode}4} pattern. Either the low bit or the sign bit of +@code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by +the compiler. + +If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will +generate code that depends only on the specified bits. It can also +replace comparison operators with equivalent operations if they cause +the required bits to be set, even if the remaining bits are undefined. +For example, on a machine whose comparison operators return an +@code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as +@samp{0x80000000}, saying that just the sign bit is relevant, the +expression + +@smallexample +(ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0)) +@end smallexample + +@noindent +can be converted to + +@smallexample +(ashift:SI @var{x} (const_int @var{n})) +@end smallexample + +@noindent +where @var{n} is the appropriate shift count to move the bit being +tested into the sign bit. + +There is no way to describe a machine that always sets the low-order bit +for a true value, but does not guarantee the value of any other bits, +but we do not know of any machine that has such an instruction. If you +are trying to port GCC to such a machine, include an instruction to +perform a logical-and of the result with 1 in the pattern for the +comparison operators and let us know at @email{gcc@@gcc.gnu.org}. + +Often, a machine will have multiple instructions that obtain a value +from a comparison (or the condition codes). Here are rules to guide the +choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions +to be used: + +@itemize @bullet +@item +Use the shortest sequence that yields a valid definition for +@code{STORE_FLAG_VALUE}. It is more efficient for the compiler to +``normalize'' the value (convert it to, e.g., 1 or 0) than for the +comparison operators to do so because there may be opportunities to +combine the normalization with other operations. + +@item +For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being +slightly preferred on machines with expensive jumps and 1 preferred on +other machines. + +@item +As a second choice, choose a value of @samp{0x80000001} if instructions +exist that set both the sign and low-order bits but do not define the +others. + +@item +Otherwise, use a value of @samp{0x80000000}. +@end itemize + +Many machines can produce both the value chosen for +@code{STORE_FLAG_VALUE} and its negation in the same number of +instructions. On those machines, you should also define a pattern for +those cases, e.g., one matching + +@smallexample +(set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C}))) +@end smallexample + +Some machines can also perform @code{and} or @code{plus} operations on +condition code values with less instructions than the corresponding +@samp{cstore@var{mode}4} insn followed by @code{and} or @code{plus}. On those +machines, define the appropriate patterns. Use the names @code{incscc} +and @code{decscc}, respectively, for the patterns which perform +@code{plus} or @code{minus} operations on condition code values. See +@file{rs6000.md} for some examples. The GNU Superoptimizer can be used to +find such instruction sequences on other machines. + +If this macro is not defined, the default value, 1, is used. You need +not define @code{STORE_FLAG_VALUE} if the machine has no store-flag +instructions, or if the value generated by these instructions is 1. +@end defmac + +@defmac FLOAT_STORE_FLAG_VALUE (@var{mode}) +A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is +returned when comparison operators with floating-point results are true. +Define this macro on machines that have comparison operations that return +floating-point values. If there are no such operations, do not define +this macro. +@end defmac + +@defmac VECTOR_STORE_FLAG_VALUE (@var{mode}) +A C expression that gives an rtx representing the nonzero true element +for vector comparisons. The returned rtx should be valid for the inner +mode of @var{mode} which is guaranteed to be a vector mode. Define +this macro on machines that have vector comparison operations that +return a vector result. If there are no such operations, do not define +this macro. Typically, this macro is defined as @code{const1_rtx} or +@code{constm1_rtx}. This macro may return @code{NULL_RTX} to prevent +the compiler optimizing such vector comparison operations for the +given mode. +@end defmac + +@defmac CLZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) +@defmacx CTZ_DEFINED_VALUE_AT_ZERO (@var{mode}, @var{value}) +A C expression that indicates whether the architecture defines a value +for @code{clz} or @code{ctz} with a zero operand. +A result of @code{0} indicates the value is undefined. +If the value is defined for only the RTL expression, the macro should +evaluate to @code{1}; if the value applies also to the corresponding optab +entry (which is normally the case if it expands directly into +the corresponding RTL), then the macro should evaluate to @code{2}. +In the cases where the value is defined, @var{value} should be set to +this value. + +If this macro is not defined, the value of @code{clz} or +@code{ctz} at zero is assumed to be undefined. + +This macro must be defined if the target's expansion for @code{ffs} +relies on a particular value to get correct results. Otherwise it +is not necessary, though it may be used to optimize some corner cases, and +to provide a default expansion for the @code{ffs} optab. + +Note that regardless of this macro the ``definedness'' of @code{clz} +and @code{ctz} at zero do @emph{not} extend to the builtin functions +visible to the user. Thus one may be free to adjust the value at will +to match the target expansion of these operations without fear of +breaking the API@. +@end defmac + +@defmac Pmode +An alias for the machine mode for pointers. On most machines, define +this to be the integer mode corresponding to the width of a hardware +pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines. +On some machines you must define this to be one of the partial integer +modes, such as @code{PSImode}. + +The width of @code{Pmode} must be at least as large as the value of +@code{POINTER_SIZE}. If it is not equal, you must define the macro +@code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended +to @code{Pmode}. +@end defmac + +@defmac FUNCTION_MODE +An alias for the machine mode used for memory references to functions +being called, in @code{call} RTL expressions. On most CISC machines, +where an instruction can begin at any byte address, this should be +@code{QImode}. On most RISC machines, where all instructions have fixed +size and alignment, this should be a mode with the same size and alignment +as the machine instruction words - typically @code{SImode} or @code{HImode}. +@end defmac + +@defmac STDC_0_IN_SYSTEM_HEADERS +In normal operation, the preprocessor expands @code{__STDC__} to the +constant 1, to signify that GCC conforms to ISO Standard C@. On some +hosts, like Solaris, the system compiler uses a different convention, +where @code{__STDC__} is normally 0, but is 1 if the user specifies +strict conformance to the C Standard. + +Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host +convention when processing system header files, but when processing user +files @code{__STDC__} will always expand to 1. +@end defmac + +@hook TARGET_C_PREINCLUDE + +@hook TARGET_CXX_IMPLICIT_EXTERN_C + +@defmac SYSTEM_IMPLICIT_EXTERN_C +Define this macro if the system header files do not support C++@. +This macro handles system header files by pretending that system +header files are enclosed in @samp{extern "C" @{@dots{}@}}. +@end defmac + +@findex #pragma +@findex pragma +@defmac REGISTER_TARGET_PRAGMAS () +Define this macro if you want to implement any target-specific pragmas. +If defined, it is a C expression which makes a series of calls to +@code{c_register_pragma} or @code{c_register_pragma_with_expansion} +for each pragma. The macro may also do any +setup required for the pragmas. + +The primary reason to define this macro is to provide compatibility with +other compilers for the same target. In general, we discourage +definition of target-specific pragmas for GCC@. + +If the pragma can be implemented by attributes then you should consider +defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well. + +Preprocessor macros that appear on pragma lines are not expanded. All +@samp{#pragma} directives that do not match any registered pragma are +silently ignored, unless the user specifies @option{-Wunknown-pragmas}. +@end defmac + +@deftypefun void c_register_pragma (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) +@deftypefunx void c_register_pragma_with_expansion (const char *@var{space}, const char *@var{name}, void (*@var{callback}) (struct cpp_reader *)) + +Each call to @code{c_register_pragma} or +@code{c_register_pragma_with_expansion} establishes one pragma. The +@var{callback} routine will be called when the preprocessor encounters a +pragma of the form + +@smallexample +#pragma [@var{space}] @var{name} @dots{} +@end smallexample + +@var{space} is the case-sensitive namespace of the pragma, or +@code{NULL} to put the pragma in the global namespace. The callback +routine receives @var{pfile} as its first argument, which can be passed +on to cpplib's functions if necessary. You can lex tokens after the +@var{name} by calling @code{pragma_lex}. Tokens that are not read by the +callback will be silently ignored. The end of the line is indicated by +a token of type @code{CPP_EOF}. Macro expansion occurs on the +arguments of pragmas registered with +@code{c_register_pragma_with_expansion} but not on the arguments of +pragmas registered with @code{c_register_pragma}. + +Note that the use of @code{pragma_lex} is specific to the C and C++ +compilers. It will not work in the Java or Fortran compilers, or any +other language compilers for that matter. Thus if @code{pragma_lex} is going +to be called from target-specific code, it must only be done so when +building the C and C++ compilers. This can be done by defining the +variables @code{c_target_objs} and @code{cxx_target_objs} in the +target entry in the @file{config.gcc} file. These variables should name +the target-specific, language-specific object file which contains the +code that uses @code{pragma_lex}. Note it will also be necessary to add a +rule to the makefile fragment pointed to by @code{tmake_file} that shows +how to build this object file. +@end deftypefun + +@defmac HANDLE_PRAGMA_PACK_WITH_EXPANSION +Define this macro if macros should be expanded in the +arguments of @samp{#pragma pack}. +@end defmac + +@defmac TARGET_DEFAULT_PACK_STRUCT +If your target requires a structure packing default other than 0 (meaning +the machine default), define this macro to the necessary value (in bytes). +This must be a value that would also be valid to use with +@samp{#pragma pack()} (that is, a small power of two). +@end defmac + +@defmac DOLLARS_IN_IDENTIFIERS +Define this macro to control use of the character @samp{$} in +identifier names for the C family of languages. 0 means @samp{$} is +not allowed by default; 1 means it is allowed. 1 is the default; +there is no need to define this macro in that case. +@end defmac + +@defmac INSN_SETS_ARE_DELAYED (@var{insn}) +Define this macro as a C expression that is nonzero if it is safe for the +delay slot scheduler to place instructions in the delay slot of @var{insn}, +even if they appear to use a resource set or clobbered in @var{insn}. +@var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that +every @code{call_insn} has this behavior. On machines where some @code{insn} +or @code{jump_insn} is really a function call and hence has this behavior, +you should define this macro. + +You need not define this macro if it would always return zero. +@end defmac + +@defmac INSN_REFERENCES_ARE_DELAYED (@var{insn}) +Define this macro as a C expression that is nonzero if it is safe for the +delay slot scheduler to place instructions in the delay slot of @var{insn}, +even if they appear to set or clobber a resource referenced in @var{insn}. +@var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where +some @code{insn} or @code{jump_insn} is really a function call and its operands +are registers whose use is actually in the subroutine it calls, you should +define this macro. Doing so allows the delay slot scheduler to move +instructions which copy arguments into the argument registers into the delay +slot of @var{insn}. + +You need not define this macro if it would always return zero. +@end defmac + +@defmac MULTIPLE_SYMBOL_SPACES +Define this macro as a C expression that is nonzero if, in some cases, +global symbols from one translation unit may not be bound to undefined +symbols in another translation unit without user intervention. For +instance, under Microsoft Windows symbols must be explicitly imported +from shared libraries (DLLs). + +You need not define this macro if it would always evaluate to zero. +@end defmac + +@hook TARGET_MD_ASM_ADJUST + +@defmac MATH_LIBRARY +Define this macro as a C string constant for the linker argument to link +in the system math library, minus the initial @samp{"-l"}, or +@samp{""} if the target does not have a +separate math library. + +You need only define this macro if the default of @samp{"m"} is wrong. +@end defmac + +@defmac LIBRARY_PATH_ENV +Define this macro as a C string constant for the environment variable that +specifies where the linker should look for libraries. + +You need only define this macro if the default of @samp{"LIBRARY_PATH"} +is wrong. +@end defmac + +@defmac TARGET_POSIX_IO +Define this macro if the target supports the following POSIX@ file +functions, access, mkdir and file locking with fcntl / F_SETLKW@. +Defining @code{TARGET_POSIX_IO} will enable the test coverage code +to use file locking when exiting a program, which avoids race conditions +if the program has forked. It will also create directories at run-time +for cross-profiling. +@end defmac + +@defmac MAX_CONDITIONAL_EXECUTE + +A C expression for the maximum number of instructions to execute via +conditional execution instructions instead of a branch. A value of +@code{BRANCH_COST}+1 is the default. +@end defmac + +@defmac IFCVT_MODIFY_TESTS (@var{ce_info}, @var{true_expr}, @var{false_expr}) +Used if the target needs to perform machine-dependent modifications on the +conditionals used for turning basic blocks into conditionally executed code. +@var{ce_info} points to a data structure, @code{struct ce_if_block}, which +contains information about the currently processed blocks. @var{true_expr} +and @var{false_expr} are the tests that are used for converting the +then-block and the else-block, respectively. Set either @var{true_expr} or +@var{false_expr} to a null pointer if the tests cannot be converted. +@end defmac + +@defmac IFCVT_MODIFY_MULTIPLE_TESTS (@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr}) +Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated +if-statements into conditions combined by @code{and} and @code{or} operations. +@var{bb} contains the basic block that contains the test that is currently +being processed and about to be turned into a condition. +@end defmac + +@defmac IFCVT_MODIFY_INSN (@var{ce_info}, @var{pattern}, @var{insn}) +A C expression to modify the @var{PATTERN} of an @var{INSN} that is to +be converted to conditional execution format. @var{ce_info} points to +a data structure, @code{struct ce_if_block}, which contains information +about the currently processed blocks. +@end defmac + +@defmac IFCVT_MODIFY_FINAL (@var{ce_info}) +A C expression to perform any final machine dependent modifications in +converting code to conditional execution. The involved basic blocks +can be found in the @code{struct ce_if_block} structure that is pointed +to by @var{ce_info}. +@end defmac + +@defmac IFCVT_MODIFY_CANCEL (@var{ce_info}) +A C expression to cancel any machine dependent modifications in +converting code to conditional execution. The involved basic blocks +can be found in the @code{struct ce_if_block} structure that is pointed +to by @var{ce_info}. +@end defmac + +@defmac IFCVT_MACHDEP_INIT (@var{ce_info}) +A C expression to initialize any machine specific data for if-conversion +of the if-block in the @code{struct ce_if_block} structure that is pointed +to by @var{ce_info}. +@end defmac + +@hook TARGET_MACHINE_DEPENDENT_REORG + +@hook TARGET_INIT_BUILTINS + +@hook TARGET_BUILTIN_DECL + +@hook TARGET_EXPAND_BUILTIN + +@hook TARGET_RESOLVE_OVERLOADED_BUILTIN + +@hook TARGET_CHECK_BUILTIN_CALL + +@hook TARGET_FOLD_BUILTIN + +@hook TARGET_GIMPLE_FOLD_BUILTIN + +@hook TARGET_COMPARE_VERSION_PRIORITY + +@hook TARGET_GET_FUNCTION_VERSIONS_DISPATCHER + +@hook TARGET_GENERATE_VERSION_DISPATCHER_BODY + +@hook TARGET_PREDICT_DOLOOP_P + +@hook TARGET_HAVE_COUNT_REG_DECR_P + +@hook TARGET_DOLOOP_COST_FOR_GENERIC + +@hook TARGET_DOLOOP_COST_FOR_ADDRESS + +@hook TARGET_CAN_USE_DOLOOP_P + +@hook TARGET_INVALID_WITHIN_DOLOOP + +@hook TARGET_PREFERRED_DOLOOP_MODE + +@hook TARGET_LEGITIMATE_COMBINED_INSN + +@hook TARGET_CAN_FOLLOW_JUMP + +@hook TARGET_COMMUTATIVE_P + +@hook TARGET_ALLOCATE_INITIAL_VALUE + +@hook TARGET_UNSPEC_MAY_TRAP_P + +@hook TARGET_SET_CURRENT_FUNCTION + +@defmac TARGET_OBJECT_SUFFIX +Define this macro to be a C string representing the suffix for object +files on your target machine. If you do not define this macro, GCC will +use @samp{.o} as the suffix for object files. +@end defmac + +@defmac TARGET_EXECUTABLE_SUFFIX +Define this macro to be a C string representing the suffix to be +automatically added to executable files on your target machine. If you +do not define this macro, GCC will use the null string as the suffix for +executable files. +@end defmac + +@defmac COLLECT_EXPORT_LIST +If defined, @code{collect2} will scan the individual object files +specified on its command line and create an export list for the linker. +Define this macro for systems like AIX, where the linker discards +object files that are not referenced from @code{main} and uses export +lists. +@end defmac + +@hook TARGET_CANNOT_MODIFY_JUMPS_P + +@hook TARGET_HAVE_CONDITIONAL_EXECUTION + +@hook TARGET_GEN_CCMP_FIRST + +@hook TARGET_GEN_CCMP_NEXT + +@hook TARGET_GEN_MEMSET_SCRATCH_RTX + +@hook TARGET_LOOP_UNROLL_ADJUST + +@defmac POWI_MAX_MULTS +If defined, this macro is interpreted as a signed integer C expression +that specifies the maximum number of floating point multiplications +that should be emitted when expanding exponentiation by an integer +constant inline. When this value is defined, exponentiation requiring +more than this number of multiplications is implemented by calling the +system library's @code{pow}, @code{powf} or @code{powl} routines. +The default value places no upper bound on the multiplication count. +@end defmac + +@deftypefn Macro void TARGET_EXTRA_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) +This target hook should register any extra include files for the +target. The parameter @var{stdinc} indicates if normal include files +are present. The parameter @var{sysroot} is the system root directory. +The parameter @var{iprefix} is the prefix for the gcc directory. +@end deftypefn + +@deftypefn Macro void TARGET_EXTRA_PRE_INCLUDES (const char *@var{sysroot}, const char *@var{iprefix}, int @var{stdinc}) +This target hook should register any extra include files for the +target before any standard headers. The parameter @var{stdinc} +indicates if normal include files are present. The parameter +@var{sysroot} is the system root directory. The parameter +@var{iprefix} is the prefix for the gcc directory. +@end deftypefn + +@deftypefn Macro void TARGET_OPTF (char *@var{path}) +This target hook should register special include paths for the target. +The parameter @var{path} is the include to register. On Darwin +systems, this is used for Framework includes, which have semantics +that are different from @option{-I}. +@end deftypefn + +@defmac bool TARGET_USE_LOCAL_THUNK_ALIAS_P (tree @var{fndecl}) +This target macro returns @code{true} if it is safe to use a local alias +for a virtual function @var{fndecl} when constructing thunks, +@code{false} otherwise. By default, the macro returns @code{true} for all +functions, if a target supports aliases (i.e.@: defines +@code{ASM_OUTPUT_DEF}), @code{false} otherwise, +@end defmac + +@defmac TARGET_FORMAT_TYPES +If defined, this macro is the name of a global variable containing +target-specific format checking information for the @option{-Wformat} +option. The default is to have no target-specific format checks. +@end defmac + +@defmac TARGET_N_FORMAT_TYPES +If defined, this macro is the number of entries in +@code{TARGET_FORMAT_TYPES}. +@end defmac + +@defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES +If defined, this macro is the name of a global variable containing +target-specific format overrides for the @option{-Wformat} option. The +default is to have no target-specific format overrides. If defined, +@code{TARGET_FORMAT_TYPES} and @code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT} +must be defined, too. +@end defmac + +@defmac TARGET_OVERRIDES_FORMAT_ATTRIBUTES_COUNT +If defined, this macro specifies the number of entries in +@code{TARGET_OVERRIDES_FORMAT_ATTRIBUTES}. +@end defmac + +@defmac TARGET_OVERRIDES_FORMAT_INIT +If defined, this macro specifies the optional initialization +routine for target specific customizations of the system printf +and scanf formatter settings. +@end defmac + +@hook TARGET_INVALID_ARG_FOR_UNPROTOTYPED_FN + +@hook TARGET_INVALID_CONVERSION + +@hook TARGET_INVALID_UNARY_OP + +@hook TARGET_INVALID_BINARY_OP + +@hook TARGET_PROMOTED_TYPE + +@hook TARGET_CONVERT_TO_TYPE + +@hook TARGET_VERIFY_TYPE_CONTEXT + +@defmac OBJC_JBLEN +This macro determines the size of the objective C jump buffer for the +NeXT runtime. By default, OBJC_JBLEN is defined to an innocuous value. +@end defmac + +@defmac LIBGCC2_UNWIND_ATTRIBUTE +Define this macro if any target-specific attributes need to be attached +to the functions in @file{libgcc} that provide low-level support for +call stack unwinding. It is used in declarations in @file{unwind-generic.h} +and the associated definitions of those functions. +@end defmac + +@hook TARGET_UPDATE_STACK_BOUNDARY + +@hook TARGET_GET_DRAP_RTX + +@hook TARGET_ZERO_CALL_USED_REGS + +@hook TARGET_ALLOCATE_STACK_SLOTS_FOR_ARGS + +@hook TARGET_CONST_ANCHOR + +@hook TARGET_ASAN_SHADOW_OFFSET + +@hook TARGET_MEMMODEL_CHECK + +@hook TARGET_ATOMIC_TEST_AND_SET_TRUEVAL + +@hook TARGET_HAS_IFUNC_P + +@hook TARGET_IFUNC_REF_LOCAL_OK + +@hook TARGET_ATOMIC_ALIGN_FOR_MODE + +@hook TARGET_ATOMIC_ASSIGN_EXPAND_FENV + +@hook TARGET_RECORD_OFFLOAD_SYMBOL + +@hook TARGET_OFFLOAD_OPTIONS + +@defmac TARGET_SUPPORTS_WIDE_INT + +On older ports, large integers are stored in @code{CONST_DOUBLE} rtl +objects. Newer ports define @code{TARGET_SUPPORTS_WIDE_INT} to be nonzero +to indicate that large integers are stored in +@code{CONST_WIDE_INT} rtl objects. The @code{CONST_WIDE_INT} allows +very large integer constants to be represented. @code{CONST_DOUBLE} +is limited to twice the size of the host's @code{HOST_WIDE_INT} +representation. + +Converting a port mostly requires looking for the places where +@code{CONST_DOUBLE}s are used with @code{VOIDmode} and replacing that +code with code that accesses @code{CONST_WIDE_INT}s. @samp{"grep -i +const_double"} at the port level gets you to 95% of the changes that +need to be made. There are a few places that require a deeper look. + +@itemize @bullet +@item +There is no equivalent to @code{hval} and @code{lval} for +@code{CONST_WIDE_INT}s. This would be difficult to express in the md +language since there are a variable number of elements. + +Most ports only check that @code{hval} is either 0 or -1 to see if the +value is small. As mentioned above, this will no longer be necessary +since small constants are always @code{CONST_INT}. Of course there +are still a few exceptions, the alpha's constraint used by the zap +instruction certainly requires careful examination by C code. +However, all the current code does is pass the hval and lval to C +code, so evolving the c code to look at the @code{CONST_WIDE_INT} is +not really a large change. + +@item +Because there is no standard template that ports use to materialize +constants, there is likely to be some futzing that is unique to each +port in this code. + +@item +The rtx costs may have to be adjusted to properly account for larger +constants that are represented as @code{CONST_WIDE_INT}. +@end itemize + +All and all it does not take long to convert ports that the +maintainer is familiar with. + +@end defmac + +@hook TARGET_HAVE_SPECULATION_SAFE_VALUE + +@hook TARGET_SPECULATION_SAFE_VALUE + +@hook TARGET_RUN_TARGET_SELFTESTS + +@hook TARGET_MEMTAG_CAN_TAG_ADDRESSES + +@hook TARGET_MEMTAG_TAG_SIZE + +@hook TARGET_MEMTAG_GRANULE_SIZE + +@hook TARGET_MEMTAG_INSERT_RANDOM_TAG + +@hook TARGET_MEMTAG_ADD_TAG + +@hook TARGET_MEMTAG_SET_TAG + +@hook TARGET_MEMTAG_EXTRACT_TAG + +@hook TARGET_MEMTAG_UNTAGGED_POINTER + +@hook TARGET_GCOV_TYPE_SIZE + +@hook TARGET_HAVE_SHADOW_CALL_STACK diff --git a/gcc/doc/tree-ssa.texi b/gcc/doc/tree-ssa.texi new file mode 100644 index 00000000000..f962ef9b1ee --- /dev/null +++ b/gcc/doc/tree-ssa.texi @@ -0,0 +1,826 @@ +@c Copyright (C) 2004-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@c --------------------------------------------------------------------- +@c Tree SSA +@c --------------------------------------------------------------------- + +@node Tree SSA +@chapter Analysis and Optimization of GIMPLE tuples +@cindex Tree SSA +@cindex Optimization infrastructure for GIMPLE + +GCC uses three main intermediate languages to represent the program +during compilation: GENERIC, GIMPLE and RTL@. GENERIC is a +language-independent representation generated by each front end. It +is used to serve as an interface between the parser and optimizer. +GENERIC is a common representation that is able to represent programs +written in all the languages supported by GCC@. + +GIMPLE and RTL are used to optimize the program. GIMPLE is used for +target and language independent optimizations (e.g., inlining, +constant propagation, tail call elimination, redundancy elimination, +etc). Much like GENERIC, GIMPLE is a language independent, tree based +representation. However, it differs from GENERIC in that the GIMPLE +grammar is more restrictive: expressions contain no more than 3 +operands (except function calls), it has no control flow structures +and expressions with side effects are only allowed on the right hand +side of assignments. See the chapter describing GENERIC and GIMPLE +for more details. + +This chapter describes the data structures and functions used in the +GIMPLE optimizers (also known as ``tree optimizers'' or ``middle +end''). In particular, it focuses on all the macros, data structures, +functions and programming constructs needed to implement optimization +passes for GIMPLE@. + +@menu +* Annotations:: Attributes for variables. +* SSA Operands:: SSA names referenced by GIMPLE statements. +* SSA:: Static Single Assignment representation. +* Alias analysis:: Representing aliased loads and stores. +* Memory model:: Memory model used by the middle-end. +@end menu + +@node Annotations +@section Annotations +@cindex annotations + +The optimizers need to associate attributes with variables during the +optimization process. For instance, we need to know whether a +variable has aliases. All these attributes are stored in data +structures called annotations which are then linked to the field +@code{ann} in @code{struct tree_common}. + + +@node SSA Operands +@section SSA Operands +@cindex operands +@cindex virtual operands +@cindex real operands +@findex update_stmt + +Almost every GIMPLE statement will contain a reference to a variable +or memory location. Since statements come in different shapes and +sizes, their operands are going to be located at various spots inside +the statement's tree. To facilitate access to the statement's +operands, they are organized into lists associated inside each +statement's annotation. Each element in an operand list is a pointer +to a @code{VAR_DECL}, @code{PARM_DECL} or @code{SSA_NAME} tree node. +This provides a very convenient way of examining and replacing +operands. + +Data flow analysis and optimization is done on all tree nodes +representing variables. Any node for which @code{SSA_VAR_P} returns +nonzero is considered when scanning statement operands. However, not +all @code{SSA_VAR_P} variables are processed in the same way. For the +purposes of optimization, we need to distinguish between references to +local scalar variables and references to globals, statics, structures, +arrays, aliased variables, etc. The reason is simple, the compiler +can gather complete data flow information for a local scalar. On the +other hand, a global variable may be modified by a function call, it +may not be possible to keep track of all the elements of an array or +the fields of a structure, etc. + +The operand scanner gathers two kinds of operands: @dfn{real} and +@dfn{virtual}. An operand for which @code{is_gimple_reg} returns true +is considered real, otherwise it is a virtual operand. We also +distinguish between uses and definitions. An operand is used if its +value is loaded by the statement (e.g., the operand at the RHS of an +assignment). If the statement assigns a new value to the operand, the +operand is considered a definition (e.g., the operand at the LHS of +an assignment). + +Virtual and real operands also have very different data flow +properties. Real operands are unambiguous references to the +full object that they represent. For instance, given + +@smallexample +@{ + int a, b; + a = b +@} +@end smallexample + +Since @code{a} and @code{b} are non-aliased locals, the statement +@code{a = b} will have one real definition and one real use because +variable @code{a} is completely modified with the contents of +variable @code{b}. Real definition are also known as @dfn{killing +definitions}. Similarly, the use of @code{b} reads all its bits. + +In contrast, virtual operands are used with variables that can have +a partial or ambiguous reference. This includes structures, arrays, +globals, and aliased variables. In these cases, we have two types of +definitions. For globals, structures, and arrays, we can determine from +a statement whether a variable of these types has a killing definition. +If the variable does, then the statement is marked as having a +@dfn{must definition} of that variable. However, if a statement is only +defining a part of the variable (i.e.@: a field in a structure), or if we +know that a statement might define the variable but we cannot say for sure, +then we mark that statement as having a @dfn{may definition}. For +instance, given + +@smallexample +@{ + int a, b, *p; + + if (@dots{}) + p = &a; + else + p = &b; + *p = 5; + return *p; +@} +@end smallexample + +The assignment @code{*p = 5} may be a definition of @code{a} or +@code{b}. If we cannot determine statically where @code{p} is +pointing to at the time of the store operation, we create virtual +definitions to mark that statement as a potential definition site for +@code{a} and @code{b}. Memory loads are similarly marked with virtual +use operands. Virtual operands are shown in tree dumps right before +the statement that contains them. To request a tree dump with virtual +operands, use the @option{-vops} option to @option{-fdump-tree}: + +@smallexample +@{ + int a, b, *p; + + if (@dots{}) + p = &a; + else + p = &b; + # a = VDEF + # b = VDEF + *p = 5; + + # VUSE + # VUSE + return *p; +@} +@end smallexample + +Notice that @code{VDEF} operands have two copies of the referenced +variable. This indicates that this is not a killing definition of +that variable. In this case we refer to it as a @dfn{may definition} +or @dfn{aliased store}. The presence of the second copy of the +variable in the @code{VDEF} operand will become important when the +function is converted into SSA form. This will be used to link all +the non-killing definitions to prevent optimizations from making +incorrect assumptions about them. + +Operands are updated as soon as the statement is finished via a call +to @code{update_stmt}. If statement elements are changed via +@code{SET_USE} or @code{SET_DEF}, then no further action is required +(i.e., those macros take care of updating the statement). If changes +are made by manipulating the statement's tree directly, then a call +must be made to @code{update_stmt} when complete. Calling one of the +@code{bsi_insert} routines or @code{bsi_replace} performs an implicit +call to @code{update_stmt}. + +@subsection Operand Iterators And Access Routines +@cindex Operand Iterators +@cindex Operand Access Routines + +Operands are collected by @file{tree-ssa-operands.cc}. They are stored +inside each statement's annotation and can be accessed through either the +operand iterators or an access routine. + +The following access routines are available for examining operands: + +@enumerate +@item @code{SINGLE_SSA_@{USE,DEF,TREE@}_OPERAND}: These accessors will return +NULL unless there is exactly one operand matching the specified flags. If +there is exactly one operand, the operand is returned as either a @code{tree}, +@code{def_operand_p}, or @code{use_operand_p}. + +@smallexample +tree t = SINGLE_SSA_TREE_OPERAND (stmt, flags); +use_operand_p u = SINGLE_SSA_USE_OPERAND (stmt, SSA_ALL_VIRTUAL_USES); +def_operand_p d = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_ALL_DEFS); +@end smallexample + +@item @code{ZERO_SSA_OPERANDS}: This macro returns true if there are no +operands matching the specified flags. + +@smallexample +if (ZERO_SSA_OPERANDS (stmt, SSA_OP_ALL_VIRTUALS)) + return; +@end smallexample + +@item @code{NUM_SSA_OPERANDS}: This macro Returns the number of operands +matching 'flags'. This actually executes a loop to perform the count, so +only use this if it is really needed. + +@smallexample +int count = NUM_SSA_OPERANDS (stmt, flags) +@end smallexample +@end enumerate + + +If you wish to iterate over some or all operands, use the +@code{FOR_EACH_SSA_@{USE,DEF,TREE@}_OPERAND} iterator. For example, to print +all the operands for a statement: + +@smallexample +void +print_ops (tree stmt) +@{ + ssa_op_iter; + tree var; + + FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_ALL_OPERANDS) + print_generic_expr (stderr, var, TDF_SLIM); +@} +@end smallexample + + +How to choose the appropriate iterator: + +@enumerate +@item Determine whether you are need to see the operand pointers, or just the +trees, and choose the appropriate macro: + +@smallexample +Need Macro: +---- ------- +use_operand_p FOR_EACH_SSA_USE_OPERAND +def_operand_p FOR_EACH_SSA_DEF_OPERAND +tree FOR_EACH_SSA_TREE_OPERAND +@end smallexample + +@item You need to declare a variable of the type you are interested +in, and an ssa_op_iter structure which serves as the loop controlling +variable. + +@item Determine which operands you wish to use, and specify the flags of +those you are interested in. They are documented in +@file{tree-ssa-operands.h}: + +@smallexample +#define SSA_OP_USE 0x01 /* @r{Real USE operands.} */ +#define SSA_OP_DEF 0x02 /* @r{Real DEF operands.} */ +#define SSA_OP_VUSE 0x04 /* @r{VUSE operands.} */ +#define SSA_OP_VDEF 0x08 /* @r{VDEF operands.} */ + +/* @r{These are commonly grouped operand flags.} */ +#define SSA_OP_VIRTUAL_USES (SSA_OP_VUSE) +#define SSA_OP_VIRTUAL_DEFS (SSA_OP_VDEF) +#define SSA_OP_ALL_VIRTUALS (SSA_OP_VIRTUAL_USES | SSA_OP_VIRTUAL_DEFS) +#define SSA_OP_ALL_USES (SSA_OP_VIRTUAL_USES | SSA_OP_USE) +#define SSA_OP_ALL_DEFS (SSA_OP_VIRTUAL_DEFS | SSA_OP_DEF) +#define SSA_OP_ALL_OPERANDS (SSA_OP_ALL_USES | SSA_OP_ALL_DEFS) +@end smallexample +@end enumerate + +So if you want to look at the use pointers for all the @code{USE} and +@code{VUSE} operands, you would do something like: + +@smallexample + use_operand_p use_p; + ssa_op_iter iter; + + FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, (SSA_OP_USE | SSA_OP_VUSE)) + @{ + process_use_ptr (use_p); + @} +@end smallexample + +The @code{TREE} macro is basically the same as the @code{USE} and +@code{DEF} macros, only with the use or def dereferenced via +@code{USE_FROM_PTR (use_p)} and @code{DEF_FROM_PTR (def_p)}. Since we +aren't using operand pointers, use and defs flags can be mixed. + +@smallexample + tree var; + ssa_op_iter iter; + + FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_VUSE) + @{ + print_generic_expr (stderr, var, TDF_SLIM); + @} +@end smallexample + +@code{VDEF}s are broken into two flags, one for the +@code{DEF} portion (@code{SSA_OP_VDEF}) and one for the USE portion +(@code{SSA_OP_VUSE}). + +There are many examples in the code, in addition to the documentation +in @file{tree-ssa-operands.h} and @file{ssa-iterators.h}. + +There are also a couple of variants on the stmt iterators regarding PHI +nodes. + +@code{FOR_EACH_PHI_ARG} Works exactly like +@code{FOR_EACH_SSA_USE_OPERAND}, except it works over @code{PHI} arguments +instead of statement operands. + +@smallexample +/* Look at every virtual PHI use. */ +FOR_EACH_PHI_ARG (use_p, phi_stmt, iter, SSA_OP_VIRTUAL_USES) +@{ + my_code; +@} + +/* Look at every real PHI use. */ +FOR_EACH_PHI_ARG (use_p, phi_stmt, iter, SSA_OP_USES) + my_code; + +/* Look at every PHI use. */ +FOR_EACH_PHI_ARG (use_p, phi_stmt, iter, SSA_OP_ALL_USES) + my_code; +@end smallexample + +@code{FOR_EACH_PHI_OR_STMT_@{USE,DEF@}} works exactly like +@code{FOR_EACH_SSA_@{USE,DEF@}_OPERAND}, except it will function on +either a statement or a @code{PHI} node. These should be used when it is +appropriate but they are not quite as efficient as the individual +@code{FOR_EACH_PHI} and @code{FOR_EACH_SSA} routines. + +@smallexample +FOR_EACH_PHI_OR_STMT_USE (use_operand_p, stmt, iter, flags) + @{ + my_code; + @} + +FOR_EACH_PHI_OR_STMT_DEF (def_operand_p, phi, iter, flags) + @{ + my_code; + @} +@end smallexample + +@subsection Immediate Uses +@cindex Immediate Uses + +Immediate use information is now always available. Using the immediate use +iterators, you may examine every use of any @code{SSA_NAME}. For instance, +to change each use of @code{ssa_var} to @code{ssa_var2} and call fold_stmt on +each stmt after that is done: + +@smallexample + use_operand_p imm_use_p; + imm_use_iterator iterator; + tree ssa_var, stmt; + + + FOR_EACH_IMM_USE_STMT (stmt, iterator, ssa_var) + @{ + FOR_EACH_IMM_USE_ON_STMT (imm_use_p, iterator) + SET_USE (imm_use_p, ssa_var_2); + fold_stmt (stmt); + @} +@end smallexample + +There are 2 iterators which can be used. @code{FOR_EACH_IMM_USE_FAST} is +used when the immediate uses are not changed, i.e., you are looking at the +uses, but not setting them. + +If they do get changed, then care must be taken that things are not changed +under the iterators, so use the @code{FOR_EACH_IMM_USE_STMT} and +@code{FOR_EACH_IMM_USE_ON_STMT} iterators. They attempt to preserve the +sanity of the use list by moving all the uses for a statement into +a controlled position, and then iterating over those uses. Then the +optimization can manipulate the stmt when all the uses have been +processed. This is a little slower than the FAST version since it adds a +placeholder element and must sort through the list a bit for each statement. +This placeholder element must be also be removed if the loop is +terminated early; a destructor takes care of that when leaving the +@code{FOR_EACH_IMM_USE_STMT} scope. + +There are checks in @code{verify_ssa} which verify that the immediate use list +is up to date, as well as checking that an optimization didn't break from the +loop without using this macro. It is safe to simply 'break'; from a +@code{FOR_EACH_IMM_USE_FAST} traverse. + +Some useful functions and macros: +@enumerate +@item @code{has_zero_uses (ssa_var)} : Returns true if there are no uses of +@code{ssa_var}. +@item @code{has_single_use (ssa_var)} : Returns true if there is only a +single use of @code{ssa_var}. +@item @code{single_imm_use (ssa_var, use_operand_p *ptr, tree *stmt)} : +Returns true if there is only a single use of @code{ssa_var}, and also returns +the use pointer and statement it occurs in, in the second and third parameters. +@item @code{num_imm_uses (ssa_var)} : Returns the number of immediate uses of +@code{ssa_var}. It is better not to use this if possible since it simply +utilizes a loop to count the uses. +@item @code{PHI_ARG_INDEX_FROM_USE (use_p)} : Given a use within a @code{PHI} +node, return the index number for the use. An assert is triggered if the use +isn't located in a @code{PHI} node. +@item @code{USE_STMT (use_p)} : Return the statement a use occurs in. +@end enumerate + +Note that uses are not put into an immediate use list until their statement is +actually inserted into the instruction stream via a @code{bsi_*} routine. + +It is also still possible to utilize lazy updating of statements, but this +should be used only when absolutely required. Both alias analysis and the +dominator optimizations currently do this. + +When lazy updating is being used, the immediate use information is out of date +and cannot be used reliably. Lazy updating is achieved by simply marking +statements modified via calls to @code{gimple_set_modified} instead of +@code{update_stmt}. When lazy updating is no longer required, all the +modified statements must have @code{update_stmt} called in order to bring them +up to date. This must be done before the optimization is finished, or +@code{verify_ssa} will trigger an abort. + +This is done with a simple loop over the instruction stream: +@smallexample + block_stmt_iterator bsi; + basic_block bb; + FOR_EACH_BB (bb) + @{ + for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi)) + update_stmt_if_modified (bsi_stmt (bsi)); + @} +@end smallexample + +@node SSA +@section Static Single Assignment +@cindex SSA +@cindex static single assignment + +Most of the tree optimizers rely on the data flow information provided +by the Static Single Assignment (SSA) form. We implement the SSA form +as described in @cite{R. Cytron, J. Ferrante, B. Rosen, M. Wegman, and +K. Zadeck. Efficiently Computing Static Single Assignment Form and the +Control Dependence Graph. ACM Transactions on Programming Languages +and Systems, 13(4):451-490, October 1991}. + +The SSA form is based on the premise that program variables are +assigned in exactly one location in the program. Multiple assignments +to the same variable create new versions of that variable. Naturally, +actual programs are seldom in SSA form initially because variables +tend to be assigned multiple times. The compiler modifies the program +representation so that every time a variable is assigned in the code, +a new version of the variable is created. Different versions of the +same variable are distinguished by subscripting the variable name with +its version number. Variables used in the right-hand side of +expressions are renamed so that their version number matches that of +the most recent assignment. + +We represent variable versions using @code{SSA_NAME} nodes. The +renaming process in @file{tree-ssa.cc} wraps every real and +virtual operand with an @code{SSA_NAME} node which contains +the version number and the statement that created the +@code{SSA_NAME}. Only definitions and virtual definitions may +create new @code{SSA_NAME} nodes. + +@cindex PHI nodes +Sometimes, flow of control makes it impossible to determine the +most recent version of a variable. In these cases, the compiler +inserts an artificial definition for that variable called +@dfn{PHI function} or @dfn{PHI node}. This new definition merges +all the incoming versions of the variable to create a new name +for it. For instance, + +@smallexample +if (@dots{}) + a_1 = 5; +else if (@dots{}) + a_2 = 2; +else + a_3 = 13; + +# a_4 = PHI +return a_4; +@end smallexample + +Since it is not possible to determine which of the three branches +will be taken at runtime, we don't know which of @code{a_1}, +@code{a_2} or @code{a_3} to use at the return statement. So, the +SSA renamer creates a new version @code{a_4} which is assigned +the result of ``merging'' @code{a_1}, @code{a_2} and @code{a_3}. +Hence, PHI nodes mean ``one of these operands. I don't know +which''. + +The following functions can be used to examine PHI nodes + +@defun gimple_phi_result (@var{phi}) +Returns the @code{SSA_NAME} created by PHI node @var{phi} (i.e., +@var{phi}'s LHS)@. +@end defun + +@defun gimple_phi_num_args (@var{phi}) +Returns the number of arguments in @var{phi}. This number is exactly +the number of incoming edges to the basic block holding @var{phi}@. +@end defun + +@defun gimple_phi_arg (@var{phi}, @var{i}) +Returns @var{i}th argument of @var{phi}@. +@end defun + +@defun gimple_phi_arg_edge (@var{phi}, @var{i}) +Returns the incoming edge for the @var{i}th argument of @var{phi}. +@end defun + +@defun gimple_phi_arg_def (@var{phi}, @var{i}) +Returns the @code{SSA_NAME} for the @var{i}th argument of @var{phi}. +@end defun + + +@subsection Preserving the SSA form +@findex update_ssa +@cindex preserving SSA form +Some optimization passes make changes to the function that +invalidate the SSA property. This can happen when a pass has +added new symbols or changed the program so that variables that +were previously aliased aren't anymore. Whenever something like this +happens, the affected symbols must be renamed into SSA form again. +Transformations that emit new code or replicate existing statements +will also need to update the SSA form@. + +Since GCC implements two different SSA forms for register and virtual +variables, keeping the SSA form up to date depends on whether you are +updating register or virtual names. In both cases, the general idea +behind incremental SSA updates is similar: when new SSA names are +created, they typically are meant to replace other existing names in +the program@. + +For instance, given the following code: + +@smallexample + 1 L0: + 2 x_1 = PHI (0, x_5) + 3 if (x_1 < 10) + 4 if (x_1 > 7) + 5 y_2 = 0 + 6 else + 7 y_3 = x_1 + x_7 + 8 endif + 9 x_5 = x_1 + 1 + 10 goto L0; + 11 endif +@end smallexample + +Suppose that we insert new names @code{x_10} and @code{x_11} (lines +@code{4} and @code{8})@. + +@smallexample + 1 L0: + 2 x_1 = PHI (0, x_5) + 3 if (x_1 < 10) + 4 x_10 = @dots{} + 5 if (x_1 > 7) + 6 y_2 = 0 + 7 else + 8 x_11 = @dots{} + 9 y_3 = x_1 + x_7 + 10 endif + 11 x_5 = x_1 + 1 + 12 goto L0; + 13 endif +@end smallexample + +We want to replace all the uses of @code{x_1} with the new definitions +of @code{x_10} and @code{x_11}. Note that the only uses that should +be replaced are those at lines @code{5}, @code{9} and @code{11}. +Also, the use of @code{x_7} at line @code{9} should @emph{not} be +replaced (this is why we cannot just mark symbol @code{x} for +renaming)@. + +Additionally, we may need to insert a PHI node at line @code{11} +because that is a merge point for @code{x_10} and @code{x_11}. So the +use of @code{x_1} at line @code{11} will be replaced with the new PHI +node. The insertion of PHI nodes is optional. They are not strictly +necessary to preserve the SSA form, and depending on what the caller +inserted, they may not even be useful for the optimizers@. + +Updating the SSA form is a two step process. First, the pass has to +identify which names need to be updated and/or which symbols need to +be renamed into SSA form for the first time. When new names are +introduced to replace existing names in the program, the mapping +between the old and the new names are registered by calling +@code{register_new_name_mapping} (note that if your pass creates new +code by duplicating basic blocks, the call to @code{tree_duplicate_bb} +will set up the necessary mappings automatically). + +After the replacement mappings have been registered and new symbols +marked for renaming, a call to @code{update_ssa} makes the registered +changes. This can be done with an explicit call or by creating +@code{TODO} flags in the @code{tree_opt_pass} structure for your pass. +There are several @code{TODO} flags that control the behavior of +@code{update_ssa}: + +@itemize @bullet +@item @code{TODO_update_ssa}. Update the SSA form inserting PHI nodes +for newly exposed symbols and virtual names marked for updating. +When updating real names, only insert PHI nodes for a real name +@code{O_j} in blocks reached by all the new and old definitions for +@code{O_j}. If the iterated dominance frontier for @code{O_j} +is not pruned, we may end up inserting PHI nodes in blocks that +have one or more edges with no incoming definition for +@code{O_j}. This would lead to uninitialized warnings for +@code{O_j}'s symbol@. + +@item @code{TODO_update_ssa_no_phi}. Update the SSA form without +inserting any new PHI nodes at all. This is used by passes that +have either inserted all the PHI nodes themselves or passes that +need only to patch use-def and def-def chains for virtuals +(e.g., DCE)@. + + +@item @code{TODO_update_ssa_full_phi}. Insert PHI nodes everywhere +they are needed. No pruning of the IDF is done. This is used +by passes that need the PHI nodes for @code{O_j} even if it +means that some arguments will come from the default definition +of @code{O_j}'s symbol (e.g., @code{pass_linear_transform})@. + +WARNING: If you need to use this flag, chances are that your +pass may be doing something wrong. Inserting PHI nodes for an +old name where not all edges carry a new replacement may lead to +silent codegen errors or spurious uninitialized warnings@. + +@item @code{TODO_update_ssa_only_virtuals}. Passes that update the +SSA form on their own may want to delegate the updating of +virtual names to the generic updater. Since FUD chains are +easier to maintain, this simplifies the work they need to do. +NOTE: If this flag is used, any OLD->NEW mappings for real names +are explicitly destroyed and only the symbols marked for +renaming are processed@. +@end itemize + +@subsection Examining @code{SSA_NAME} nodes +@cindex examining SSA_NAMEs + +The following macros can be used to examine @code{SSA_NAME} nodes + +@defmac SSA_NAME_DEF_STMT (@var{var}) +Returns the statement @var{s} that creates the @code{SSA_NAME} +@var{var}. If @var{s} is an empty statement (i.e., @code{IS_EMPTY_STMT +(@var{s})} returns @code{true}), it means that the first reference to +this variable is a USE or a VUSE@. +@end defmac + +@defmac SSA_NAME_VERSION (@var{var}) +Returns the version number of the @code{SSA_NAME} object @var{var}. +@end defmac + + +@subsection Walking the dominator tree + +@deftypefn {Tree SSA function} void walk_dominator_tree (@var{walk_data}, @var{bb}) + +This function walks the dominator tree for the current CFG calling a +set of callback functions defined in @var{struct dom_walk_data} in +@file{domwalk.h}. The call back functions you need to define give you +hooks to execute custom code at various points during traversal: + +@enumerate +@item Once to initialize any local data needed while processing +@var{bb} and its children. This local data is pushed into an +internal stack which is automatically pushed and popped as the +walker traverses the dominator tree. + +@item Once before traversing all the statements in the @var{bb}. + +@item Once for every statement inside @var{bb}. + +@item Once after traversing all the statements and before recursing +into @var{bb}'s dominator children. + +@item It then recurses into all the dominator children of @var{bb}. + +@item After recursing into all the dominator children of @var{bb} it +can, optionally, traverse every statement in @var{bb} again +(i.e., repeating steps 2 and 3). + +@item Once after walking the statements in @var{bb} and @var{bb}'s +dominator children. At this stage, the block local data stack +is popped. +@end enumerate +@end deftypefn + +@node Alias analysis +@section Alias analysis +@cindex alias +@cindex flow-sensitive alias analysis +@cindex flow-insensitive alias analysis + +Alias analysis in GIMPLE SSA form consists of two pieces. First +the virtual SSA web ties conflicting memory accesses and provides +a SSA use-def chain and SSA immediate-use chains for walking +possibly dependent memory accesses. Second an alias-oracle can +be queried to disambiguate explicit and implicit memory references. + +@enumerate +@item Memory SSA form. + +All statements that may use memory have exactly one accompanied use of +a virtual SSA name that represents the state of memory at the +given point in the IL. + +All statements that may define memory have exactly one accompanied +definition of a virtual SSA name using the previous state of memory +and defining the new state of memory after the given point in the IL. + +@smallexample +int i; +int foo (void) +@{ + # .MEM_3 = VDEF <.MEM_2(D)> + i = 1; + # VUSE <.MEM_3> + return i; +@} +@end smallexample + +The virtual SSA names in this case are @code{.MEM_2(D)} and +@code{.MEM_3}. The store to the global variable @code{i} +defines @code{.MEM_3} invalidating @code{.MEM_2(D)}. The +load from @code{i} uses that new state @code{.MEM_3}. + +The virtual SSA web serves as constraints to SSA optimizers +preventing illegitimate code-motion and optimization. It +also provides a way to walk related memory statements. + +@item Points-to and escape analysis. + +Points-to analysis builds a set of constraints from the GIMPLE +SSA IL representing all pointer operations and facts we do +or do not know about pointers. Solving this set of constraints +yields a conservatively correct solution for each pointer +variable in the program (though we are only interested in +SSA name pointers) as to what it may possibly point to. + +This points-to solution for a given SSA name pointer is stored +in the @code{pt_solution} sub-structure of the +@code{SSA_NAME_PTR_INFO} record. The following accessor +functions are available: + +@itemize @bullet +@item @code{pt_solution_includes} +@item @code{pt_solutions_intersect} +@end itemize + +Points-to analysis also computes the solution for two special +set of pointers, @code{ESCAPED} and @code{CALLUSED}. Those +represent all memory that has escaped the scope of analysis +or that is used by pure or nested const calls. + +@item Type-based alias analysis + +Type-based alias analysis is frontend dependent though generic +support is provided by the middle-end in @code{alias.cc}. TBAA +code is used by both tree optimizers and RTL optimizers. + +Every language that wishes to perform language-specific alias analysis +should define a function that computes, given a @code{tree} +node, an alias set for the node. Nodes in different alias sets are not +allowed to alias. For an example, see the C front-end function +@code{c_get_alias_set}. + +@item Tree alias-oracle + +The tree alias-oracle provides means to disambiguate two memory +references and memory references against statements. The following +queries are available: + +@itemize @bullet +@item @code{refs_may_alias_p} +@item @code{ref_maybe_used_by_stmt_p} +@item @code{stmt_may_clobber_ref_p} +@end itemize + +In addition to those two kind of statement walkers are available +walking statements related to a reference ref. +@code{walk_non_aliased_vuses} walks over dominating memory defining +statements and calls back if the statement does not clobber ref +providing the non-aliased VUSE. The walk stops at +the first clobbering statement or if asked to. +@code{walk_aliased_vdefs} walks over dominating memory defining +statements and calls back on each statement clobbering ref +providing its aliasing VDEF. The walk stops if asked to. + +@end enumerate + + +@node Memory model +@section Memory model +@cindex memory model + +The memory model used by the middle-end models that of the C/C++ +languages. The middle-end has the notion of an effective type +of a memory region which is used for type-based alias analysis. + +The following is a refinement of ISO C99 6.5/6, clarifying the block copy case +to follow common sense and extending the concept of a dynamic effective +type to objects with a declared type as required for C++. + +@smallexample +The effective type of an object for an access to its stored value is +the declared type of the object or the effective type determined by +a previous store to it. If a value is stored into an object through +an lvalue having a type that is not a character type, then the +type of the lvalue becomes the effective type of the object for that +access and for subsequent accesses that do not modify the stored value. +If a value is copied into an object using @code{memcpy} or @code{memmove}, +or is copied as an array of character type, then the effective type +of the modified object for that access and for subsequent accesses that +do not modify the value is undetermined. For all other accesses to an +object, the effective type of the object is simply the type of the +lvalue used for the access. +@end smallexample + diff --git a/gcc/doc/trouble.texi b/gcc/doc/trouble.texi new file mode 100644 index 00000000000..c3f4d396bc5 --- /dev/null +++ b/gcc/doc/trouble.texi @@ -0,0 +1,1197 @@ +@c Copyright (C) 1988-2022 Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node Trouble +@chapter Known Causes of Trouble with GCC +@cindex bugs, known +@cindex installation trouble +@cindex known causes of trouble + +This section describes known problems that affect users of GCC@. Most +of these are not GCC bugs per se---if they were, we would fix them. +But the result for a user may be like the result of a bug. + +Some of these problems are due to bugs in other software, some are +missing features that are too much work to add, and some are places +where people's opinions differ as to what is best. + +@menu +* Actual Bugs:: Bugs we will fix later. +* Interoperation:: Problems using GCC with other compilers, + and with certain linkers, assemblers and debuggers. +* Incompatibilities:: GCC is incompatible with traditional C. +* Fixed Headers:: GCC uses corrected versions of system header files. + This is necessary, but doesn't always work smoothly. +* Standard Libraries:: GCC uses the system C library, which might not be + compliant with the ISO C standard. +* Disappointments:: Regrettable things we cannot change, but not quite bugs. +* C++ Misunderstandings:: Common misunderstandings with GNU C++. +* Non-bugs:: Things we think are right, but some others disagree. +* Warnings and Errors:: Which problems in your code get warnings, + and which get errors. +@end menu + +@node Actual Bugs +@section Actual Bugs We Haven't Fixed Yet + +@itemize @bullet +@item +The @code{fixincludes} script interacts badly with automounters; if the +directory of system header files is automounted, it tends to be +unmounted while @code{fixincludes} is running. This would seem to be a +bug in the automounter. We don't know any good way to work around it. +@end itemize + +@node Interoperation +@section Interoperation + +This section lists various difficulties encountered in using GCC +together with other compilers or with the assemblers, linkers, +libraries and debuggers on certain systems. + +@itemize @bullet +@item +On many platforms, GCC supports a different ABI for C++ than do other +compilers, so the object files compiled by GCC cannot be used with object +files generated by another C++ compiler. + +An area where the difference is most apparent is name mangling. The use +of different name mangling is intentional, to protect you from more subtle +problems. +Compilers differ as to many internal details of C++ implementation, +including: how class instances are laid out, how multiple inheritance is +implemented, and how virtual function calls are handled. If the name +encoding were made the same, your programs would link against libraries +provided from other compilers---but the programs would then crash when +run. Incompatible libraries are then detected at link time, rather than +at run time. + +@item +On some BSD systems, including some versions of Ultrix, use of profiling +causes static variable destructors (currently used only in C++) not to +be run. + +@item +On a SPARC, GCC aligns all values of type @code{double} on an 8-byte +boundary, and it expects every @code{double} to be so aligned. The Sun +compiler usually gives @code{double} values 8-byte alignment, with one +exception: function arguments of type @code{double} may not be aligned. + +As a result, if a function compiled with Sun CC takes the address of an +argument of type @code{double} and passes this pointer of type +@code{double *} to a function compiled with GCC, dereferencing the +pointer may cause a fatal signal. + +One way to solve this problem is to compile your entire program with GCC@. +Another solution is to modify the function that is compiled with +Sun CC to copy the argument into a local variable; local variables +are always properly aligned. A third solution is to modify the function +that uses the pointer to dereference it via the following function +@code{access_double} instead of directly with @samp{*}: + +@smallexample +inline double +access_double (double *unaligned_ptr) +@{ + union d2i @{ double d; int i[2]; @}; + + union d2i *p = (union d2i *) unaligned_ptr; + union d2i u; + + u.i[0] = p->i[0]; + u.i[1] = p->i[1]; + + return u.d; +@} +@end smallexample + +@noindent +Storing into the pointer can be done likewise with the same union. + +@item +On Solaris, the @code{malloc} function in the @file{libmalloc.a} library +may allocate memory that is only 4 byte aligned. Since GCC on the +SPARC assumes that doubles are 8 byte aligned, this may result in a +fatal signal if doubles are stored in memory allocated by the +@file{libmalloc.a} library. + +The solution is to not use the @file{libmalloc.a} library. Use instead +@code{malloc} and related functions from @file{libc.a}; they do not have +this problem. + +@item +On the HP PA machine, ADB sometimes fails to work on functions compiled +with GCC@. Specifically, it fails to work on functions that use +@code{alloca} or variable-size arrays. This is because GCC doesn't +generate HP-UX unwind descriptors for such functions. It may even be +impossible to generate them. + +@item +Debugging (@option{-g}) is not supported on the HP PA machine, unless you use +the preliminary GNU tools. + +@item +Taking the address of a label may generate errors from the HP-UX +PA assembler. GAS for the PA does not have this problem. + +@item +Using floating point parameters for indirect calls to static functions +will not work when using the HP assembler. There simply is no way for GCC +to specify what registers hold arguments for static functions when using +the HP assembler. GAS for the PA does not have this problem. + +@item +In extremely rare cases involving some very large functions you may +receive errors from the HP linker complaining about an out of bounds +unconditional branch offset. This used to occur more often in previous +versions of GCC, but is now exceptionally rare. If you should run +into it, you can work around by making your function smaller. + +@item +GCC compiled code sometimes emits warnings from the HP-UX assembler of +the form: + +@smallexample +(warning) Use of GR3 when + frame >= 8192 may cause conflict. +@end smallexample + +These warnings are harmless and can be safely ignored. + +@item +In extremely rare cases involving some very large functions you may +receive errors from the AIX Assembler complaining about a displacement +that is too large. If you should run into it, you can work around by +making your function smaller. + +@item +The @file{libstdc++.a} library in GCC relies on the SVR4 dynamic +linker semantics which merges global symbols between libraries and +applications, especially necessary for C++ streams functionality. +This is not the default behavior of AIX shared libraries and dynamic +linking. @file{libstdc++.a} is built on AIX with ``runtime-linking'' +enabled so that symbol merging can occur. To utilize this feature, +the application linked with @file{libstdc++.a} must include the +@option{-Wl,-brtl} flag on the link line. G++ cannot impose this +because this option may interfere with the semantics of the user +program and users may not always use @samp{g++} to link his or her +application. Applications are not required to use the +@option{-Wl,-brtl} flag on the link line---the rest of the +@file{libstdc++.a} library which is not dependent on the symbol +merging semantics will continue to function correctly. + +@item +An application can interpose its own definition of functions for +functions invoked by @file{libstdc++.a} with ``runtime-linking'' +enabled on AIX@. To accomplish this the application must be linked +with ``runtime-linking'' option and the functions explicitly must be +exported by the application (@option{-Wl,-brtl,-bE:exportfile}). + +@item +AIX on the RS/6000 provides support (NLS) for environments outside of +the United States. Compilers and assemblers use NLS to support +locale-specific representations of various objects including +floating-point numbers (@samp{.} vs @samp{,} for separating decimal +fractions). There have been problems reported where the library linked +with GCC does not produce the same floating-point formats that the +assembler accepts. If you have this problem, set the @env{LANG} +environment variable to @samp{C} or @samp{En_US}. + +@item +@opindex fdollars-in-identifiers +Even if you specify @option{-fdollars-in-identifiers}, +you cannot successfully use @samp{$} in identifiers on the RS/6000 due +to a restriction in the IBM assembler. GAS supports these +identifiers. + +@end itemize + +@node Incompatibilities +@section Incompatibilities of GCC +@cindex incompatibilities of GCC +@opindex traditional + +There are several noteworthy incompatibilities between GNU C and K&R +(non-ISO) versions of C@. + +@itemize @bullet +@cindex string constants +@cindex read-only strings +@cindex shared strings +@item +GCC normally makes string constants read-only. If several +identical-looking string constants are used, GCC stores only one +copy of the string. + +@cindex @code{mktemp}, and constant strings +One consequence is that you cannot call @code{mktemp} with a string +constant argument. The function @code{mktemp} always alters the +string its argument points to. + +@cindex @code{sscanf}, and constant strings +@cindex @code{fscanf}, and constant strings +@cindex @code{scanf}, and constant strings +Another consequence is that @code{sscanf} does not work on some very +old systems when passed a string constant as its format control string +or input. This is because @code{sscanf} incorrectly tries to write +into the string constant. Likewise @code{fscanf} and @code{scanf}. + +The solution to these problems is to change the program to use +@code{char}-array variables with initialization strings for these +purposes instead of string constants. + +@item +@code{-2147483648} is positive. + +This is because 2147483648 cannot fit in the type @code{int}, so +(following the ISO C rules) its data type is @code{unsigned long int}. +Negating this value yields 2147483648 again. + +@item +GCC does not substitute macro arguments when they appear inside of +string constants. For example, the following macro in GCC + +@smallexample +#define foo(a) "a" +@end smallexample + +@noindent +will produce output @code{"a"} regardless of what the argument @var{a} is. + +@cindex @code{setjmp} incompatibilities +@cindex @code{longjmp} incompatibilities +@item +When you use @code{setjmp} and @code{longjmp}, the only automatic +variables guaranteed to remain valid are those declared +@code{volatile}. This is a consequence of automatic register +allocation. Consider this function: + +@smallexample +jmp_buf j; + +foo () +@{ + int a, b; + + a = fun1 (); + if (setjmp (j)) + return a; + + a = fun2 (); + /* @r{@code{longjmp (j)} may occur in @code{fun3}.} */ + return a + fun3 (); +@} +@end smallexample + +Here @code{a} may or may not be restored to its first value when the +@code{longjmp} occurs. If @code{a} is allocated in a register, then +its first value is restored; otherwise, it keeps the last value stored +in it. + +@opindex W +If you use the @option{-W} option with the @option{-O} option, you will +get a warning when GCC thinks such a problem might be possible. + +@item +Programs that use preprocessing directives in the middle of macro +arguments do not work with GCC@. For example, a program like this +will not work: + +@smallexample +@group +foobar ( +#define luser + hack) +@end group +@end smallexample + +ISO C does not permit such a construct. + +@item +K&R compilers allow comments to cross over an inclusion boundary +(i.e.@: started in an include file and ended in the including file). + +@cindex external declaration scope +@cindex scope of external declarations +@cindex declaration scope +@item +Declarations of external variables and functions within a block apply +only to the block containing the declaration. In other words, they +have the same scope as any other declaration in the same place. + +In some other C compilers, an @code{extern} declaration affects all the +rest of the file even if it happens within a block. + +@item +In traditional C, you can combine @code{long}, etc., with a typedef name, +as shown here: + +@smallexample +typedef int foo; +typedef long foo bar; +@end smallexample + +In ISO C, this is not allowed: @code{long} and other type modifiers +require an explicit @code{int}. + +@cindex typedef names as function parameters +@item +PCC allows typedef names to be used as function parameters. + +@item +Traditional C allows the following erroneous pair of declarations to +appear together in a given scope: + +@smallexample +typedef int foo; +typedef foo foo; +@end smallexample + +@item +GCC treats all characters of identifiers as significant. According to +K&R-1 (2.2), ``No more than the first eight characters are significant, +although more may be used.''. Also according to K&R-1 (2.2), ``An +identifier is a sequence of letters and digits; the first character must +be a letter. The underscore _ counts as a letter.'', but GCC also +allows dollar signs in identifiers. + +@cindex whitespace +@item +PCC allows whitespace in the middle of compound assignment operators +such as @samp{+=}. GCC, following the ISO standard, does not +allow this. + +@cindex apostrophes +@cindex @code{'} +@item +GCC complains about unterminated character constants inside of +preprocessing conditionals that fail. Some programs have English +comments enclosed in conditionals that are guaranteed to fail; if these +comments contain apostrophes, GCC will probably report an error. For +example, this code would produce an error: + +@smallexample +#if 0 +You can't expect this to work. +#endif +@end smallexample + +The best solution to such a problem is to put the text into an actual +C comment delimited by @samp{/*@dots{}*/}. + +@item +Many user programs contain the declaration @samp{long time ();}. In the +past, the system header files on many systems did not actually declare +@code{time}, so it did not matter what type your program declared it to +return. But in systems with ISO C headers, @code{time} is declared to +return @code{time_t}, and if that is not the same as @code{long}, then +@samp{long time ();} is erroneous. + +The solution is to change your program to use appropriate system headers +(@code{} on systems with ISO C headers) and not to declare +@code{time} if the system header files declare it, or failing that to +use @code{time_t} as the return type of @code{time}. + +@cindex @code{float} as function value type +@item +When compiling functions that return @code{float}, PCC converts it to +a double. GCC actually returns a @code{float}. If you are concerned +with PCC compatibility, you should declare your functions to return +@code{double}; you might as well say what you mean. + +@cindex structures +@cindex unions +@item +When compiling functions that return structures or unions, GCC +output code normally uses a method different from that used on most +versions of Unix. As a result, code compiled with GCC cannot call +a structure-returning function compiled with PCC, and vice versa. + +The method used by GCC is as follows: a structure or union which is +1, 2, 4 or 8 bytes long is returned like a scalar. A structure or union +with any other size is stored into an address supplied by the caller +(usually in a special, fixed register, but on some machines it is passed +on the stack). The target hook @code{TARGET_STRUCT_VALUE_RTX} +tells GCC where to pass this address. + +By contrast, PCC on most target machines returns structures and unions +of any size by copying the data into an area of static storage, and then +returning the address of that storage as if it were a pointer value. +The caller must copy the data from that memory area to the place where +the value is wanted. GCC does not use this method because it is +slower and nonreentrant. + +On some newer machines, PCC uses a reentrant convention for all +structure and union returning. GCC on most of these machines uses a +compatible convention when returning structures and unions in memory, +but still returns small structures and unions in registers. + +@opindex fpcc-struct-return +You can tell GCC to use a compatible convention for all structure and +union returning with the option @option{-fpcc-struct-return}. + +@cindex preprocessing tokens +@cindex preprocessing numbers +@item +GCC complains about program fragments such as @samp{0x74ae-0x4000} +which appear to be two hexadecimal constants separated by the minus +operator. Actually, this string is a single @dfn{preprocessing token}. +Each such token must correspond to one token in C@. Since this does not, +GCC prints an error message. Although it may appear obvious that what +is meant is an operator and two values, the ISO C standard specifically +requires that this be treated as erroneous. + +A @dfn{preprocessing token} is a @dfn{preprocessing number} if it +begins with a digit and is followed by letters, underscores, digits, +periods and @samp{e+}, @samp{e-}, @samp{E+}, @samp{E-}, @samp{p+}, +@samp{p-}, @samp{P+}, or @samp{P-} character sequences. (In strict C90 +mode, the sequences @samp{p+}, @samp{p-}, @samp{P+} and @samp{P-} cannot +appear in preprocessing numbers.) + +To make the above program fragment valid, place whitespace in front of +the minus sign. This whitespace will end the preprocessing number. +@end itemize + +@node Fixed Headers +@section Fixed Header Files + +GCC needs to install corrected versions of some system header files. +This is because most target systems have some header files that won't +work with GCC unless they are changed. Some have bugs, some are +incompatible with ISO C, and some depend on special features of other +compilers. + +Installing GCC automatically creates and installs the fixed header +files, by running a program called @code{fixincludes}. Normally, you +don't need to pay attention to this. But there are cases where it +doesn't do the right thing automatically. + +@itemize @bullet +@item +If you update the system's header files, such as by installing a new +system version, the fixed header files of GCC are not automatically +updated. They can be updated using the @command{mkheaders} script +installed in +@file{@var{libexecdir}/gcc/@var{target}/@var{version}/install-tools/}. + +@item +On some systems, header file directories contain +machine-specific symbolic links in certain places. This makes it +possible to share most of the header files among hosts running the +same version of the system on different machine models. + +The programs that fix the header files do not understand this special +way of using symbolic links; therefore, the directory of fixed header +files is good only for the machine model used to build it. + +It is possible to make separate sets of fixed header files for the +different machine models, and arrange a structure of symbolic links so +as to use the proper set, but you'll have to do this by hand. +@end itemize + +@node Standard Libraries +@section Standard Libraries + +@opindex Wall +GCC by itself attempts to be a conforming freestanding implementation. +@xref{Standards,,Language Standards Supported by GCC}, for details of +what this means. Beyond the library facilities required of such an +implementation, the rest of the C library is supplied by the vendor of +the operating system. If that C library doesn't conform to the C +standards, then your programs might get warnings (especially when using +@option{-Wall}) that you don't expect. + +For example, the @code{sprintf} function on SunOS 4.1.3 returns +@code{char *} while the C standard says that @code{sprintf} returns an +@code{int}. The @code{fixincludes} program could make the prototype for +this function match the Standard, but that would be wrong, since the +function will still return @code{char *}. + +If you need a Standard compliant library, then you need to find one, as +GCC does not provide one. The GNU C library (called @code{glibc}) +provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for +GNU/Linux and HURD-based GNU systems; no recent version of it supports +other systems, though some very old versions did. Version 2.2 of the +GNU C library includes nearly complete C99 support. You could also ask +your operating system vendor if newer libraries are available. + +@node Disappointments +@section Disappointments and Misunderstandings + +These problems are perhaps regrettable, but we don't know any practical +way around them. + +@itemize @bullet +@item +Certain local variables aren't recognized by debuggers when you compile +with optimization. + +This occurs because sometimes GCC optimizes the variable out of +existence. There is no way to tell the debugger how to compute the +value such a variable ``would have had'', and it is not clear that would +be desirable anyway. So GCC simply does not mention the eliminated +variable when it writes debugging information. + +You have to expect a certain amount of disagreement between the +executable and your source code, when you use optimization. + +@cindex conflicting types +@cindex scope of declaration +@item +Users often think it is a bug when GCC reports an error for code +like this: + +@smallexample +int foo (struct mumble *); + +struct mumble @{ @dots{} @}; + +int foo (struct mumble *x) +@{ @dots{} @} +@end smallexample + +This code really is erroneous, because the scope of @code{struct +mumble} in the prototype is limited to the argument list containing it. +It does not refer to the @code{struct mumble} defined with file scope +immediately below---they are two unrelated types with similar names in +different scopes. + +But in the definition of @code{foo}, the file-scope type is used +because that is available to be inherited. Thus, the definition and +the prototype do not match, and you get an error. + +This behavior may seem silly, but it's what the ISO standard specifies. +It is easy enough for you to make your code work by moving the +definition of @code{struct mumble} above the prototype. It's not worth +being incompatible with ISO C just to avoid an error for the example +shown above. + +@item +Accesses to bit-fields even in volatile objects works by accessing larger +objects, such as a byte or a word. You cannot rely on what size of +object is accessed in order to read or write the bit-field; it may even +vary for a given bit-field according to the precise usage. + +If you care about controlling the amount of memory that is accessed, use +volatile but do not use bit-fields. + +@item +GCC comes with shell scripts to fix certain known problems in system +header files. They install corrected copies of various header files in +a special directory where only GCC will normally look for them. The +scripts adapt to various systems by searching all the system header +files for the problem cases that we know about. + +If new system header files are installed, nothing automatically arranges +to update the corrected header files. They can be updated using the +@command{mkheaders} script installed in +@file{@var{libexecdir}/gcc/@var{target}/@var{version}/install-tools/}. + +@item +@cindex floating point precision +On 68000 and x86 systems, for instance, you can get paradoxical results +if you test the precise values of floating point numbers. For example, +you can find that a floating point value which is not a NaN is not equal +to itself. This results from the fact that the floating point registers +hold a few more bits of precision than fit in a @code{double} in memory. +Compiled code moves values between memory and floating point registers +at its convenience, and moving them into memory truncates them. + +@opindex ffloat-store +You can partially avoid this problem by using the @option{-ffloat-store} +option (@pxref{Optimize Options}). + +@item +On AIX and other platforms without weak symbol support, templates +need to be instantiated explicitly and symbols for static members +of templates will not be generated. + +@item +On AIX, GCC scans object files and library archives for static +constructors and destructors when linking an application before the +linker prunes unreferenced symbols. This is necessary to prevent the +AIX linker from mistakenly assuming that static constructor or +destructor are unused and removing them before the scanning can occur. +All static constructors and destructors found will be referenced even +though the modules in which they occur may not be used by the program. +This may lead to both increased executable size and unexpected symbol +references. +@end itemize + +@node C++ Misunderstandings +@section Common Misunderstandings with GNU C++ + +@cindex misunderstandings in C++ +@cindex surprises in C++ +@cindex C++ misunderstandings +C++ is a complex language and an evolving one, and its standard +definition (the ISO C++ standard) was only recently completed. As a +result, your C++ compiler may occasionally surprise you, even when its +behavior is correct. This section discusses some areas that frequently +give rise to questions of this sort. + +@menu +* Static Definitions:: Static member declarations are not definitions +* Name lookup:: Name lookup, templates, and accessing members of base classes +* Temporaries:: Temporaries may vanish before you expect +* Copy Assignment:: Copy Assignment operators copy virtual bases twice +@end menu + +@node Static Definitions +@subsection Declare @emph{and} Define Static Members + +@cindex C++ static data, declaring and defining +@cindex static data in C++, declaring and defining +@cindex declaring static data in C++ +@cindex defining static data in C++ +When a class has static data members, it is not enough to @emph{declare} +the static member; you must also @emph{define} it. For example: + +@smallexample +class Foo +@{ + @dots{} + void method(); + static int bar; +@}; +@end smallexample + +This declaration only establishes that the class @code{Foo} has an +@code{int} named @code{Foo::bar}, and a member function named +@code{Foo::method}. But you still need to define @emph{both} +@code{method} and @code{bar} elsewhere. According to the ISO +standard, you must supply an initializer in one (and only one) source +file, such as: + +@smallexample +int Foo::bar = 0; +@end smallexample + +Other C++ compilers may not correctly implement the standard behavior. +As a result, when you switch to @command{g++} from one of these compilers, +you may discover that a program that appeared to work correctly in fact +does not conform to the standard: @command{g++} reports as undefined +symbols any static data members that lack definitions. + + +@node Name lookup +@subsection Name Lookup, Templates, and Accessing Members of Base Classes + +@cindex base class members +@cindex two-stage name lookup +@cindex dependent name lookup + +The C++ standard prescribes that all names that are not dependent on +template parameters are bound to their present definitions when parsing +a template function or class.@footnote{The C++ standard just uses the +term ``dependent'' for names that depend on the type or value of +template parameters. This shorter term will also be used in the rest of +this section.} Only names that are dependent are looked up at the point +of instantiation. For example, consider + +@smallexample + void foo(double); + + struct A @{ + template + void f () @{ + foo (1); // @r{1} + int i = N; // @r{2} + T t; + t.bar(); // @r{3} + foo (t); // @r{4} + @} + + static const int N; + @}; +@end smallexample + +Here, the names @code{foo} and @code{N} appear in a context that does +not depend on the type of @code{T}. The compiler will thus require that +they are defined in the context of use in the template, not only before +the point of instantiation, and will here use @code{::foo(double)} and +@code{A::N}, respectively. In particular, it will convert the integer +value to a @code{double} when passing it to @code{::foo(double)}. + +Conversely, @code{bar} and the call to @code{foo} in the fourth marked +line are used in contexts that do depend on the type of @code{T}, so +they are only looked up at the point of instantiation, and you can +provide declarations for them after declaring the template, but before +instantiating it. In particular, if you instantiate @code{A::f}, +the last line will call an overloaded @code{::foo(int)} if one was +provided, even if after the declaration of @code{struct A}. + +This distinction between lookup of dependent and non-dependent names is +called two-stage (or dependent) name lookup. G++ implements it +since version 3.4. + +Two-stage name lookup sometimes leads to situations with behavior +different from non-template codes. The most common is probably this: + +@smallexample + template struct Base @{ + int i; + @}; + + template struct Derived : public Base @{ + int get_i() @{ return i; @} + @}; +@end smallexample + +In @code{get_i()}, @code{i} is not used in a dependent context, so the +compiler will look for a name declared at the enclosing namespace scope +(which is the global scope here). It will not look into the base class, +since that is dependent and you may declare specializations of +@code{Base} even after declaring @code{Derived}, so the compiler cannot +really know what @code{i} would refer to. If there is no global +variable @code{i}, then you will get an error message. + +In order to make it clear that you want the member of the base class, +you need to defer lookup until instantiation time, at which the base +class is known. For this, you need to access @code{i} in a dependent +context, by either using @code{this->i} (remember that @code{this} is of +type @code{Derived*}, so is obviously dependent), or using +@code{Base::i}. Alternatively, @code{Base::i} might be brought +into scope by a @code{using}-declaration. + +Another, similar example involves calling member functions of a base +class: + +@smallexample + template struct Base @{ + int f(); + @}; + + template struct Derived : Base @{ + int g() @{ return f(); @}; + @}; +@end smallexample + +Again, the call to @code{f()} is not dependent on template arguments +(there are no arguments that depend on the type @code{T}, and it is also +not otherwise specified that the call should be in a dependent context). +Thus a global declaration of such a function must be available, since +the one in the base class is not visible until instantiation time. The +compiler will consequently produce the following error message: + +@smallexample + x.cc: In member function `int Derived::g()': + x.cc:6: error: there are no arguments to `f' that depend on a template + parameter, so a declaration of `f' must be available + x.cc:6: error: (if you use `-fpermissive', G++ will accept your code, but + allowing the use of an undeclared name is deprecated) +@end smallexample + +To make the code valid either use @code{this->f()}, or +@code{Base::f()}. Using the @option{-fpermissive} flag will also let +the compiler accept the code, by marking all function calls for which no +declaration is visible at the time of definition of the template for +later lookup at instantiation time, as if it were a dependent call. +We do not recommend using @option{-fpermissive} to work around invalid +code, and it will also only catch cases where functions in base classes +are called, not where variables in base classes are used (as in the +example above). + +Note that some compilers (including G++ versions prior to 3.4) get these +examples wrong and accept above code without an error. Those compilers +do not implement two-stage name lookup correctly. + + +@node Temporaries +@subsection Temporaries May Vanish Before You Expect + +@cindex temporaries, lifetime of +@cindex portions of temporary objects, pointers to +It is dangerous to use pointers or references to @emph{portions} of a +temporary object. The compiler may very well delete the object before +you expect it to, leaving a pointer to garbage. The most common place +where this problem crops up is in classes like string classes, +especially ones that define a conversion function to type @code{char *} +or @code{const char *}---which is one reason why the standard +@code{string} class requires you to call the @code{c_str} member +function. However, any class that returns a pointer to some internal +structure is potentially subject to this problem. + +For example, a program may use a function @code{strfunc} that returns +@code{string} objects, and another function @code{charfunc} that +operates on pointers to @code{char}: + +@smallexample +string strfunc (); +void charfunc (const char *); + +void +f () +@{ + const char *p = strfunc().c_str(); + @dots{} + charfunc (p); + @dots{} + charfunc (p); +@} +@end smallexample + +@noindent +In this situation, it may seem reasonable to save a pointer to the C +string returned by the @code{c_str} member function and use that rather +than call @code{c_str} repeatedly. However, the temporary string +created by the call to @code{strfunc} is destroyed after @code{p} is +initialized, at which point @code{p} is left pointing to freed memory. + +Code like this may run successfully under some other compilers, +particularly obsolete cfront-based compilers that delete temporaries +along with normal local variables. However, the GNU C++ behavior is +standard-conforming, so if your program depends on late destruction of +temporaries it is not portable. + +The safe way to write such code is to give the temporary a name, which +forces it to remain until the end of the scope of the name. For +example: + +@smallexample +const string& tmp = strfunc (); +charfunc (tmp.c_str ()); +@end smallexample + +@node Copy Assignment +@subsection Implicit Copy-Assignment for Virtual Bases + +When a base class is virtual, only one subobject of the base class +belongs to each full object. Also, the constructors and destructors are +invoked only once, and called from the most-derived class. However, such +objects behave unspecified when being assigned. For example: + +@smallexample +struct Base@{ + char *name; + Base(const char *n) : name(strdup(n))@{@} + Base& operator= (const Base& other)@{ + free (name); + name = strdup (other.name); + return *this; + @} +@}; + +struct A:virtual Base@{ + int val; + A():Base("A")@{@} +@}; + +struct B:virtual Base@{ + int bval; + B():Base("B")@{@} +@}; + +struct Derived:public A, public B@{ + Derived():Base("Derived")@{@} +@}; + +void func(Derived &d1, Derived &d2) +@{ + d1 = d2; +@} +@end smallexample + +The C++ standard specifies that @samp{Base::Base} is only called once +when constructing or copy-constructing a Derived object. It is +unspecified whether @samp{Base::operator=} is called more than once when +the implicit copy-assignment for Derived objects is invoked (as it is +inside @samp{func} in the example). + +G++ implements the ``intuitive'' algorithm for copy-assignment: assign all +direct bases, then assign all members. In that algorithm, the virtual +base subobject can be encountered more than once. In the example, copying +proceeds in the following order: @samp{name} (via @code{strdup}), +@samp{val}, @samp{name} again, and @samp{bval}. + +If application code relies on copy-assignment, a user-defined +copy-assignment operator removes any uncertainties. With such an +operator, the application can define whether and how the virtual base +subobject is assigned. + +@node Non-bugs +@section Certain Changes We Don't Want to Make + +This section lists changes that people frequently request, but which +we do not make because we think GCC is better without them. + +@itemize @bullet +@item +Checking the number and type of arguments to a function which has an +old-fashioned definition and no prototype. + +Such a feature would work only occasionally---only for calls that appear +in the same file as the called function, following the definition. The +only way to check all calls reliably is to add a prototype for the +function. But adding a prototype eliminates the motivation for this +feature. So the feature is not worthwhile. + +@item +Warning about using an expression whose type is signed as a shift count. + +Shift count operands are probably signed more often than unsigned. +Warning about this would cause far more annoyance than good. + +@item +Warning about assigning a signed value to an unsigned variable. + +Such assignments must be very common; warning about them would cause +more annoyance than good. + +@item +Warning when a non-void function value is ignored. + +C contains many standard functions that return a value that most +programs choose to ignore. One obvious example is @code{printf}. +Warning about this practice only leads the defensive programmer to +clutter programs with dozens of casts to @code{void}. Such casts are +required so frequently that they become visual noise. Writing those +casts becomes so automatic that they no longer convey useful +information about the intentions of the programmer. For functions +where the return value should never be ignored, use the +@code{warn_unused_result} function attribute (@pxref{Function +Attributes}). + +@item +@opindex fshort-enums +Making @option{-fshort-enums} the default. + +This would cause storage layout to be incompatible with most other C +compilers. And it doesn't seem very important, given that you can get +the same result in other ways. The case where it matters most is when +the enumeration-valued object is inside a structure, and in that case +you can specify a field width explicitly. + +@item +Making bit-fields unsigned by default on particular machines where ``the +ABI standard'' says to do so. + +The ISO C standard leaves it up to the implementation whether a bit-field +declared plain @code{int} is signed or not. This in effect creates two +alternative dialects of C@. + +@opindex fsigned-bitfields +@opindex funsigned-bitfields +The GNU C compiler supports both dialects; you can specify the signed +dialect with @option{-fsigned-bitfields} and the unsigned dialect with +@option{-funsigned-bitfields}. However, this leaves open the question of +which dialect to use by default. + +Currently, the preferred dialect makes plain bit-fields signed, because +this is simplest. Since @code{int} is the same as @code{signed int} in +every other context, it is cleanest for them to be the same in bit-fields +as well. + +Some computer manufacturers have published Application Binary Interface +standards which specify that plain bit-fields should be unsigned. It is +a mistake, however, to say anything about this issue in an ABI@. This is +because the handling of plain bit-fields distinguishes two dialects of C@. +Both dialects are meaningful on every type of machine. Whether a +particular object file was compiled using signed bit-fields or unsigned +is of no concern to other object files, even if they access the same +bit-fields in the same data structures. + +A given program is written in one or the other of these two dialects. +The program stands a chance to work on most any machine if it is +compiled with the proper dialect. It is unlikely to work at all if +compiled with the wrong dialect. + +Many users appreciate the GNU C compiler because it provides an +environment that is uniform across machines. These users would be +inconvenienced if the compiler treated plain bit-fields differently on +certain machines. + +Occasionally users write programs intended only for a particular machine +type. On these occasions, the users would benefit if the GNU C compiler +were to support by default the same dialect as the other compilers on +that machine. But such applications are rare. And users writing a +program to run on more than one type of machine cannot possibly benefit +from this kind of compatibility. + +This is why GCC does and will treat plain bit-fields in the same +fashion on all types of machines (by default). + +There are some arguments for making bit-fields unsigned by default on all +machines. If, for example, this becomes a universal de facto standard, +it would make sense for GCC to go along with it. This is something +to be considered in the future. + +(Of course, users strongly concerned about portability should indicate +explicitly in each bit-field whether it is signed or not. In this way, +they write programs which have the same meaning in both C dialects.) + +@item +@opindex ansi +@opindex std +Undefining @code{__STDC__} when @option{-ansi} is not used. + +Currently, GCC defines @code{__STDC__} unconditionally. This provides +good results in practice. + +Programmers normally use conditionals on @code{__STDC__} to ask whether +it is safe to use certain features of ISO C, such as function +prototypes or ISO token concatenation. Since plain @command{gcc} supports +all the features of ISO C, the correct answer to these questions is +``yes''. + +Some users try to use @code{__STDC__} to check for the availability of +certain library facilities. This is actually incorrect usage in an ISO +C program, because the ISO C standard says that a conforming +freestanding implementation should define @code{__STDC__} even though it +does not have the library facilities. @samp{gcc -ansi -pedantic} is a +conforming freestanding implementation, and it is therefore required to +define @code{__STDC__}, even though it does not come with an ISO C +library. + +Sometimes people say that defining @code{__STDC__} in a compiler that +does not completely conform to the ISO C standard somehow violates the +standard. This is illogical. The standard is a standard for compilers +that claim to support ISO C, such as @samp{gcc -ansi}---not for other +compilers such as plain @command{gcc}. Whatever the ISO C standard says +is relevant to the design of plain @command{gcc} without @option{-ansi} only +for pragmatic reasons, not as a requirement. + +GCC normally defines @code{__STDC__} to be 1, and in addition +defines @code{__STRICT_ANSI__} if you specify the @option{-ansi} option, +or a @option{-std} option for strict conformance to some version of ISO C@. +On some hosts, system include files use a different convention, where +@code{__STDC__} is normally 0, but is 1 if the user specifies strict +conformance to the C Standard. GCC follows the host convention when +processing system include files, but when processing user files it follows +the usual GNU C convention. + +@item +Undefining @code{__STDC__} in C++. + +Programs written to compile with C++-to-C translators get the +value of @code{__STDC__} that goes with the C compiler that is +subsequently used. These programs must test @code{__STDC__} +to determine what kind of C preprocessor that compiler uses: +whether they should concatenate tokens in the ISO C fashion +or in the traditional fashion. + +These programs work properly with GNU C++ if @code{__STDC__} is defined. +They would not work otherwise. + +In addition, many header files are written to provide prototypes in ISO +C but not in traditional C@. Many of these header files can work without +change in C++ provided @code{__STDC__} is defined. If @code{__STDC__} +is not defined, they will all fail, and will all need to be changed to +test explicitly for C++ as well. + +@item +Deleting ``empty'' loops. + +Historically, GCC has not deleted ``empty'' loops under the +assumption that the most likely reason you would put one in a program is +to have a delay, so deleting them will not make real programs run any +faster. + +However, the rationale here is that optimization of a nonempty loop +cannot produce an empty one. This held for carefully written C compiled +with less powerful optimizers but is not always the case for carefully +written C++ or with more powerful optimizers. +Thus GCC will remove operations from loops whenever it can determine +those operations are not externally visible (apart from the time taken +to execute them, of course). In case the loop can be proved to be finite, +GCC will also remove the loop itself. + +Be aware of this when performing timing tests, for instance the +following loop can be completely removed, provided +@code{some_expression} can provably not change any global state. + +@smallexample +@{ + int sum = 0; + int ix; + + for (ix = 0; ix != 10000; ix++) + sum += some_expression; +@} +@end smallexample + +Even though @code{sum} is accumulated in the loop, no use is made of +that summation, so the accumulation can be removed. + +@item +Making side effects happen in the same order as in some other compiler. + +@cindex side effects, order of evaluation +@cindex order of evaluation, side effects +It is never safe to depend on the order of evaluation of side effects. +For example, a function call like this may very well behave differently +from one compiler to another: + +@smallexample +void func (int, int); + +int i = 2; +func (i++, i++); +@end smallexample + +There is no guarantee (in either the C or the C++ standard language +definitions) that the increments will be evaluated in any particular +order. Either increment might happen first. @code{func} might get the +arguments @samp{2, 3}, or it might get @samp{3, 2}, or even @samp{2, 2}. + +@item +Making certain warnings into errors by default. + +Some ISO C testsuites report failure when the compiler does not produce +an error message for a certain program. + +@opindex pedantic-errors +ISO C requires a ``diagnostic'' message for certain kinds of invalid +programs, but a warning is defined by GCC to count as a diagnostic. If +GCC produces a warning but not an error, that is correct ISO C support. +If testsuites call this ``failure'', they should be run with the GCC +option @option{-pedantic-errors}, which will turn these warnings into +errors. + +@end itemize + +@node Warnings and Errors +@section Warning Messages and Error Messages + +@cindex error messages +@cindex warnings vs errors +@cindex messages, warning and error +The GNU compiler can produce two kinds of diagnostics: errors and +warnings. Each kind has a different purpose: + +@itemize @w{} +@item +@dfn{Errors} report problems that make it impossible to compile your +program. GCC reports errors with the source file name and line +number where the problem is apparent. + +@item +@dfn{Warnings} report other unusual conditions in your code that +@emph{may} indicate a problem, although compilation can (and does) +proceed. Warning messages also report the source file name and line +number, but include the text @samp{warning:} to distinguish them +from error messages. +@end itemize + +Warnings may indicate danger points where you should check to make sure +that your program really does what you intend; or the use of obsolete +features; or the use of nonstandard features of GNU C or C++. Many +warnings are issued only if you ask for them, with one of the @option{-W} +options (for instance, @option{-Wall} requests a variety of useful +warnings). + +@opindex pedantic +@opindex pedantic-errors +GCC always tries to compile your program if possible; it never +gratuitously rejects a program whose meaning is clear merely because +(for instance) it fails to conform to a standard. In some cases, +however, the C and C++ standards specify that certain extensions are +forbidden, and a diagnostic @emph{must} be issued by a conforming +compiler. The @option{-pedantic} option tells GCC to issue warnings in +such cases; @option{-pedantic-errors} says to make them errors instead. +This does not mean that @emph{all} non-ISO constructs get warnings +or errors. + +@xref{Warning Options,,Options to Request or Suppress Warnings}, for +more detail on these and related command-line options. diff --git a/gcc/doc/ux.texi b/gcc/doc/ux.texi new file mode 100644 index 00000000000..1e27b2b0c09 --- /dev/null +++ b/gcc/doc/ux.texi @@ -0,0 +1,661 @@ +@c Copyright (C) 2018-2022 Free Software Foundation, Inc. +@c Free Software Foundation, Inc. +@c This is part of the GCC manual. +@c For copying conditions, see the file gcc.texi. + +@node User Experience Guidelines +@chapter User Experience Guidelines +@cindex user experience guidelines +@cindex guidelines, user experience + +To borrow a slogan from +@uref{https://elm-lang.org/news/compilers-as-assistants, Elm}, + +@quotation +@strong{Compilers should be assistants, not adversaries.} A compiler should +not just detect bugs, it should then help you understand why there is a bug. +It should not berate you in a robot voice, it should give you specific hints +that help you write better code. Ultimately, a compiler should make +programming faster and more fun! +@author Evan Czaplicki +@end quotation + +This chapter provides guidelines on how to implement diagnostics and +command-line options in ways that we hope achieve the above ideal. + +@menu +* Guidelines for Diagnostics:: How to implement diagnostics. +* Guidelines for Options:: Guidelines for command-line options. +@end menu + + +@node Guidelines for Diagnostics +@section Guidelines for Diagnostics +@cindex guidelines for diagnostics +@cindex diagnostics, guidelines for + +@subsection Talk in terms of the user's code + +Diagnostics should be worded in terms of the user's source code, and the +source language, rather than GCC's own implementation details. + +@subsection Diagnostics are actionable +@cindex diagnostics, actionable + +A good diagnostic is @dfn{actionable}: it should assist the user in +taking action. + +Consider what an end user will want to do when encountering a diagnostic. + +Given an error, an end user will think: ``How do I fix this?'' + +Given a warning, an end user will think: + +@itemize @bullet +@item +``Is this a real problem?'' +@item +``Do I care?'' +@item +if they decide it's genuine: ``How do I fix this?'' +@end itemize + +A good diagnostic provides pertinent information to allow the user to +easily answer the above questions. + +@subsection The user's attention is important + +A perfect compiler would issue a warning on every aspect of the user's +source code that ought to be fixed, and issue no other warnings. +Naturally, this ideal is impossible to achieve. + +@cindex signal-to-noise ratio (metaphorical usage for diagnostics) +@cindex diagnostics, false positive +@cindex diagnostics, true positive +@cindex false positive +@cindex true positive + +Warnings should have a good @dfn{signal-to-noise ratio}: we should have few +@dfn{false positives} (falsely issuing a warning when no warning is +warranted) and few @dfn{false negatives} (failing to issue a warning when +one @emph{is} justified). + +Note that a false positive can mean, in practice, a warning that the +user doesn't agree with. Ideally a diagnostic should contain enough +information to allow the user to make an informed choice about whether +they should care (and how to fix it), but a balance must be drawn against +overloading the user with irrelevant data. + +@subsection Sometimes the user didn't write the code + +GCC is typically used in two different ways: + +@itemize @bullet +@item +Semi-interactive usage: GCC is used as a development tool when the user +is writing code, as the ``compile'' part of the ``edit-compile-debug'' +cycle. The user is actively hacking on the code themself (perhaps a +project they wrote, or someone else's), where they just made a change +to the code and want to see what happens, and to be warned about +mistakes. + +@item +Batch rebuilds: where the user is recompiling one or more existing +packages, and GCC is a detail that's being invoked by various build +scripts. Examples include a user trying to bring up an operating system +consisting of hundreds of packages on a new CPU architecture, where the +packages were written by many different people, or simply rebuilding +packages after a dependency changed, where the user is hoping +``nothing breaks'', since they are unfamiliar with the code. +@end itemize + +Keep both of these styles of usage in mind when implementing diagnostics. + +@subsection Precision of Wording + +Provide the user with details that allow them to identify what the +problem is. For example, the vaguely-worded message: + +@smallexample +demo.c:1:1: warning: 'noinline' attribute ignored [-Wattributes] + 1 | int foo __attribute__((noinline)); + | ^~~ +@end smallexample + +@noindent +doesn't tell the user why the attribute was ignored, or what kind of +entity the compiler thought the attribute was being applied to (the +source location for the diagnostic is also poor; +@pxref{input_location_example,,discussion of @code{input_location}}). +A better message would be: + +@smallexample +demo.c:1:24: warning: attribute 'noinline' on variable 'foo' was + ignored [-Wattributes] + 1 | int foo __attribute__((noinline)); + | ~~~ ~~~~~~~~~~~~~~~^~~~~~~~~ +demo.c:1:24: note: attribute 'noinline' is only applicable to functions +@end smallexample + +@noindent +which spells out the missing information (and fixes the location +information, as discussed below). + +The above example uses a note to avoid a combinatorial explosion of possible +messages. + +@subsection Try the diagnostic on real-world code + +It's worth testing a new warning on many instances of real-world code, +written by different people, and seeing what it complains about, and +what it doesn't complain about. + +This may suggest heuristics that silence common false positives. + +It may also suggest ways to improve the precision of the message. + +@subsection Make mismatches clear + +Many diagnostics relate to a mismatch between two different places in the +user's source code. Examples include: +@itemize @bullet + @item + a type mismatch, where the type at a usage site does not match the type + at a declaration + + @item + the argument count at a call site does not match the parameter count + at the declaration + + @item + something is erroneously duplicated (e.g.@: an error, due to breaking a + uniqueness requirement, or a warning, if it's suggestive of a bug) + + @item + an ``opened'' syntactic construct (such as an open-parenthesis) is not + closed + + @c TODO: more examples? +@end itemize + +In each case, the diagnostic should indicate @strong{both} pertinent +locations (so that the user can easily see the problem and how to fix it). + +The standard way to do this is with a note (via @code{inform}). For +example: + +@smallexample + auto_diagnostic_group d; + if (warning_at (loc, OPT_Wduplicated_cond, + "duplicated % condition")) + inform (EXPR_LOCATION (t), "previously used here"); +@end smallexample + +@noindent +which leads to: + +@smallexample +demo.c: In function 'test': +demo.c:5:17: warning: duplicated 'if' condition [-Wduplicated-cond] + 5 | else if (flag > 3) + | ~~~~~^~~ +demo.c:3:12: note: previously used here + 3 | if (flag > 3) + | ~~~~~^~~ +@end smallexample + +@noindent +The @code{inform} call should be guarded by the return value from the +@code{warning_at} call so that the note isn't emitted when the warning +is suppressed. + +For cases involving punctuation where the locations might be near +each other, they can be conditionally consolidated via +@code{gcc_rich_location::add_location_if_nearby}: + +@smallexample + auto_diagnostic_group d; + gcc_rich_location richloc (primary_loc); + bool added secondary = richloc.add_location_if_nearby (secondary_loc); + error_at (&richloc, "main message"); + if (!added secondary) + inform (secondary_loc, "message for secondary"); +@end smallexample + +@noindent +This will emit either one diagnostic with two locations: +@smallexample + demo.c:42:10: error: main message + (foo) + ~ ^ +@end smallexample + +@noindent +or two diagnostics: + +@smallexample + demo.c:42:4: error: main message + foo) + ^ + demo.c:40:2: note: message for secondary + ( + ^ +@end smallexample + +@subsection Location Information +@cindex diagnostics, locations +@cindex location information +@cindex source code, location information +@cindex caret + +GCC's @code{location_t} type can support both ordinary locations, +and locations relating to a macro expansion. + +As of GCC 6, ordinary locations changed from supporting just a +point in the user's source code to supporting three points: the +@dfn{caret} location, plus a start and a finish: + +@smallexample + a = foo && bar; + ~~~~^~~~~~ + | | | + | | finish + | caret + start +@end smallexample + +Tokens coming out of libcpp have locations of the form @code{caret == start}, +such as for @code{foo} here: + +@smallexample + a = foo && bar; + ^~~ + | | + | finish + caret == start +@end smallexample + +Compound expressions should be reported using the location of the +expression as a whole, rather than just of one token within it. + +For example, in @code{-Wformat}, rather than underlining just the first +token of a bad argument: + +@smallexample + printf("hello %i %s", (long)0, "world"); + ~^ ~ + %li +@end smallexample + +@noindent +the whole of the expression should be underlined, so that the user can +easily identify what is being referred to: + +@smallexample + printf("hello %i %s", (long)0, "world"); + ~^ ~~~~~~~ + %li +@end smallexample + +@c this was r251239 + +Avoid using the @code{input_location} global, and the diagnostic functions +that implicitly use it---use @code{error_at} and @code{warning_at} rather +than @code{error} and @code{warning}, and provide the most appropriate +@code{location_t} value available at that phase of the compilation. It's +possible to supply secondary @code{location_t} values via +@code{rich_location}. + +@noindent +@anchor{input_location_example} +For example, in the example of imprecise wording above, generating the +diagnostic using @code{warning}: + +@smallexample + // BAD: implicitly uses @code{input_location} + warning (OPT_Wattributes, "%qE attribute ignored", name); +@end smallexample + +@noindent +leads to: + +@smallexample +// BAD: uses @code{input_location} +demo.c:1:1: warning: 'noinline' attribute ignored [-Wattributes] + 1 | int foo __attribute__((noinline)); + | ^~~ +@end smallexample + +@noindent +which thus happened to use the location of the @code{int} token, rather +than that of the attribute. Using @code{warning_at} with the location of +the attribute, providing the location of the declaration in question +as a secondary location, and adding a note: + +@smallexample + auto_diagnostic_group d; + gcc_rich_location richloc (attrib_loc); + richloc.add_range (decl_loc); + if (warning_at (OPT_Wattributes, &richloc, + "attribute %qE on variable %qE was ignored", name)) + inform (attrib_loc, "attribute %qE is only applicable to functions"); +@end smallexample + +@noindent +would lead to: + +@smallexample +// OK: use location of attribute, with a secondary location +demo.c:1:24: warning: attribute 'noinline' on variable 'foo' was + ignored [-Wattributes] + 1 | int foo __attribute__((noinline)); + | ~~~ ~~~~~~~~~~~~~~~^~~~~~~~~ +demo.c:1:24: note: attribute 'noinline' is only applicable to functions +@end smallexample + +@c TODO labelling of ranges + +@subsection Coding Conventions + +See the @uref{https://gcc.gnu.org/codingconventions.html#Diagnostics, +diagnostics section} of the GCC coding conventions. + +In the C++ front end, when comparing two types in a message, use @samp{%H} +and @samp{%I} rather than @samp{%T}, as this allows the diagnostics +subsystem to highlight differences between template-based types. +For example, rather than using @samp{%qT}: + +@smallexample + // BAD: a pair of %qT used in C++ front end for type comparison + error_at (loc, "could not convert %qE from %qT to %qT", expr, + TREE_TYPE (expr), type); +@end smallexample + +@noindent +which could lead to: + +@smallexample +error: could not convert 'map()' from 'map' + to 'map' +@end smallexample + +@noindent +using @samp{%H} and @samp{%I} (via @samp{%qH} and @samp{%qI}): + +@smallexample + // OK: compare types in C++ front end via %qH and %qI + error_at (loc, "could not convert %qE from %qH to %qI", expr, + TREE_TYPE (expr), type); +@end smallexample + +@noindent +allows the above output to be simplified to: + +@smallexample +error: could not convert 'map()' from 'map<[...],double>' + to 'map<[...],int>' +@end smallexample + +@noindent +where the @code{double} and @code{int} are colorized to highlight them. + +@c %H and %I were added in r248698. + +@subsection Group logically-related diagnostics + +Use @code{auto_diagnostic_group} when issuing multiple related +diagnostics (seen in various examples on this page). This informs the +diagnostic subsystem that all diagnostics issued within the lifetime +of the @code{auto_diagnostic_group} are related. For example, +@option{-fdiagnostics-format=json} will treat the first diagnostic +emitted within the group as a top-level diagnostic, and all subsequent +diagnostics within the group as its children. + +@subsection Quoting +Text should be quoted by either using the @samp{q} modifier in a directive +such as @samp{%qE}, or by enclosing the quoted text in a pair of @samp{%<} +and @samp{%>} directives, and never by using explicit quote characters. +The directives handle the appropriate quote characters for each language +and apply the correct color or highlighting. + +The following elements should be quoted in GCC diagnostics: + +@itemize @bullet +@item +Language keywords. +@item +Tokens. +@item +Boolean, numerical, character, and string constants that appear in the +source code. +@item +Identifiers, including function, macro, type, and variable names. +@end itemize + +Other elements such as numbers that do not refer to numeric constants that +appear in the source code should not be quoted. For example, in the message: + +@smallexample +argument %d of %qE must be a pointer type +@end smallexample + +@noindent +since the argument number does not refer to a numerical constant in the +source code it should not be quoted. + +@subsection Spelling and Terminology + +See the @uref{https://gcc.gnu.org/codingconventions.html#Spelling +Spelling, terminology and markup} section of the GCC coding conventions. + +@subsection Fix-it hints +@cindex fix-it hints +@cindex diagnostics guidelines, fix-it hints + +GCC's diagnostic subsystem can emit @dfn{fix-it hints}: small suggested +edits to the user's source code. + +They are printed by default underneath the code in question. They +can also be viewed via @option{-fdiagnostics-generate-patch} and +@option{-fdiagnostics-parseable-fixits}. With the latter, an IDE +ought to be able to offer to automatically apply the suggested fix. + +Fix-it hints contain code fragments, and thus they should not be marked +for translation. + +Fix-it hints can be added to a diagnostic by using a @code{rich_location} +rather than a @code{location_t} - the fix-it hints are added to the +@code{rich_location} using one of the various @code{add_fixit} member +functions of @code{rich_location}. They are documented with +@code{rich_location} in @file{libcpp/line-map.h}. +It's easiest to use the @code{gcc_rich_location} subclass of +@code{rich_location} found in @file{gcc-rich-location.h}, as this +implicitly supplies the @code{line_table} variable. + +For example: + +@smallexample + if (const char *suggestion = hint.suggestion ()) + @{ + gcc_rich_location richloc (location); + richloc.add_fixit_replace (suggestion); + error_at (&richloc, + "%qE does not name a type; did you mean %qs?", + id, suggestion); + @} +@end smallexample + +@noindent +which can lead to: + +@smallexample +spellcheck-typenames.C:73:1: error: 'singed' does not name a type; did + you mean 'signed'? + 73 | singed char ch; + | ^~~~~~ + | signed +@end smallexample + +Non-trivial edits can be built up by adding multiple fix-it hints to one +@code{rich_location}. It's best to express the edits in terms of the +locations of individual tokens. Various handy functions for adding +fix-it hints for idiomatic C and C++ can be seen in +@file{gcc-rich-location.h}. + +@subsubsection Fix-it hints should work + +When implementing a fix-it hint, please verify that the suggested edit +leads to fixed, compilable code. (Unfortunately, this currently must be +done by hand using @option{-fdiagnostics-generate-patch}. It would be +good to have an automated way of verifying that fix-it hints actually fix +the code). + +For example, a ``gotcha'' here is to forget to add a space when adding a +missing reserved word. Consider a C++ fix-it hint that adds +@code{typename} in front of a template declaration. A naive way to +implement this might be: + +@smallexample +gcc_rich_location richloc (loc); +// BAD: insertion is missing a trailing space +richloc.add_fixit_insert_before ("typename"); +error_at (&richloc, "need % before %<%T::%E%> because " + "%qT is a dependent scope", + parser->scope, id, parser->scope); +@end smallexample + +@noindent +When applied to the code, this might lead to: + +@smallexample +T::type x; +@end smallexample + +@noindent +being ``corrected'' to: + +@smallexample +typenameT::type x; +@end smallexample + +@noindent +In this case, the correct thing to do is to add a trailing space after +@code{typename}: + +@smallexample +gcc_rich_location richloc (loc); +// OK: note that here we have a trailing space +richloc.add_fixit_insert_before ("typename "); +error_at (&richloc, "need % before %<%T::%E%> because " + "%qT is a dependent scope", + parser->scope, id, parser->scope); +@end smallexample + +@noindent +leading to this corrected code: + +@smallexample +typename T::type x; +@end smallexample + +@subsubsection Express deletion in terms of deletion, not replacement + +It's best to express deletion suggestions in terms of deletion fix-it +hints, rather than replacement fix-it hints. For example, consider this: + +@smallexample + auto_diagnostic_group d; + gcc_rich_location richloc (location_of (retval)); + tree name = DECL_NAME (arg); + richloc.add_fixit_replace (IDENTIFIER_POINTER (name)); + warning_at (&richloc, OPT_Wredundant_move, + "redundant move in return statement"); +@end smallexample + +@noindent +which is intended to e.g.@: replace a @code{std::move} with the underlying +value: + +@smallexample + return std::move (retval); + ~~~~~~~~~~^~~~~~~~ + retval +@end smallexample + +@noindent +where the change has been expressed as replacement, replacing +with the name of the declaration. +This works for simple cases, but consider this case: + +@smallexample +#ifdef SOME_CONFIG_FLAG +# define CONFIGURY_GLOBAL global_a +#else +# define CONFIGURY_GLOBAL global_b +#endif + +int fn () +@{ + return std::move (CONFIGURY_GLOBAL /* some comment */); +@} +@end smallexample + +@noindent +The above implementation erroneously strips out the macro and the +comment in the fix-it hint: + +@smallexample + return std::move (CONFIGURY_GLOBAL /* some comment */); + ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + global_a +@end smallexample + +@noindent +and thus this resulting code: + +@smallexample + return global_a; +@end smallexample + +@noindent +It's better to do deletions in terms of deletions; deleting the +@code{std::move (} and the trailing close-paren, leading to +this: + +@smallexample + return std::move (CONFIGURY_GLOBAL /* some comment */); + ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + CONFIGURY_GLOBAL /* some comment */ +@end smallexample + +@noindent +and thus this result: + +@smallexample + return CONFIGURY_GLOBAL /* some comment */; +@end smallexample + +@noindent +Unfortunately, the pertinent @code{location_t} values are not always +available. + +@c the above was https://gcc.gnu.org/ml/gcc-patches/2018-08/msg01474.html + +@subsubsection Multiple suggestions + +In the rare cases where you need to suggest more than one mutually +exclusive solution to a problem, this can be done by emitting +multiple notes and calling +@code{rich_location::fixits_cannot_be_auto_applied} on each note's +@code{rich_location}. If this is called, then the fix-it hints in +the @code{rich_location} will be printed, but will not be added to +generated patches. + + +@node Guidelines for Options +@section Guidelines for Options +@cindex command-line options, guidelines for +@cindex options, guidelines for +@cindex guidelines for options + +@c TODO diff --git a/gcc/fortran/gfc-internals.texi b/gcc/fortran/gfc-internals.texi new file mode 100644 index 00000000000..1409e286105 --- /dev/null +++ b/gcc/fortran/gfc-internals.texi @@ -0,0 +1,968 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename gfc-internals.info +@set copyrights-gfortran 2007-2022 + +@include gcc-common.texi + +@synindex tp cp + +@settitle GNU Fortran Compiler Internals + +@c %**end of header + +@c Use with @@smallbook. + +@c %** start of document + +@c Cause even numbered pages to be printed on the left hand side of +@c the page and odd numbered pages to be printed on the right hand +@c side of the page. Using this, you can print on both sides of a +@c sheet of paper and have the text on the same part of the sheet. + +@c The text on right hand pages is pushed towards the right hand +@c margin and the text on left hand pages is pushed toward the left +@c hand margin. +@c (To provide the reverse effect, set bindingoffset to -0.75in.) + +@c @tex +@c \global\bindingoffset=0.75in +@c \global\normaloffset =0.75in +@c @end tex + +@copying +Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``Funding Free Software'', the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end copying + +@ifinfo +@dircategory Software development +@direntry +* gfortran: (gfortran). The GNU Fortran Compiler. +@end direntry +This file documents the internals of the GNU Fortran +compiler, (@command{gfortran}). + +Published by the Free Software Foundation +51 Franklin Street, Fifth Floor +Boston, MA 02110-1301 USA + +@insertcopying +@end ifinfo + + +@setchapternewpage odd +@titlepage +@title GNU Fortran Internals +@versionsubtitle +@author The @t{gfortran} team +@page +@vskip 0pt plus 1filll +Published by the Free Software Foundation@* +51 Franklin Street, Fifth Floor@* +Boston, MA 02110-1301, USA@* +@c Last printed ??ber, 19??.@* +@c Printed copies are available for $? each.@* +@c ISBN ??? +@sp 1 +@insertcopying +@end titlepage + +@summarycontents +@contents + +@page + +@c --------------------------------------------------------------------- +@c TexInfo table of contents. +@c --------------------------------------------------------------------- + +@ifnottex +@node Top +@top Introduction +@cindex Introduction + +This manual documents the internals of @command{gfortran}, +the GNU Fortran compiler. + +@ifset DEVELOPMENT +@emph{Warning:} This document, and the compiler it describes, are still +under development. While efforts are made to keep it up-to-date, it might +not accurately reflect the status of the most recent GNU Fortran compiler. +@end ifset + +@comment +@comment When you add a new menu item, please keep the right hand +@comment aligned to the same column. Do not use tabs. This provides +@comment better formatting. +@comment +@menu +* Introduction:: About this manual. +* User Interface:: Code that Interacts with the User. +* Frontend Data Structures:: + Data structures used by the frontend +* Object Orientation:: Internals of Fortran 2003 OOP features. +* Translating to GENERIC:: + Generating the intermediate language for later stages. +* LibGFortran:: The LibGFortran Runtime Library. +* GNU Free Documentation License:: + How you can copy and share this manual. +* Index:: Index of this documentation. +@end menu +@end ifnottex + +@c --------------------------------------------------------------------- +@c Introduction +@c --------------------------------------------------------------------- + +@node Introduction +@chapter Introduction + +@c The following duplicates the text on the TexInfo table of contents. +@iftex +This manual documents the internals of @command{gfortran}, the GNU Fortran +compiler. + +@ifset DEVELOPMENT +@emph{Warning:} This document, and the compiler it describes, are still +under development. While efforts are made to keep it up-to-date, it +might not accurately reflect the status of the most recent GNU Fortran +compiler. +@end ifset +@end iftex + +At present, this manual is very much a work in progress, containing +miscellaneous notes about the internals of the compiler. It is hoped +that at some point in the future it will become a reasonably complete +guide; in the interim, GNU Fortran developers are strongly encouraged to +contribute to it as a way of keeping notes while working on the +compiler. + + +@c --------------------------------------------------------------------- +@c Code that Interacts with the User +@c --------------------------------------------------------------------- + +@node User Interface +@chapter Code that Interacts with the User + +@menu +* Command-Line Options:: Command-Line Options. +* Error Handling:: Error Handling. +@end menu + + +@c --------------------------------------------------------------------- +@c Command-Line Options +@c --------------------------------------------------------------------- + +@node Command-Line Options +@section Command-Line Options + +Command-line options for @command{gfortran} involve four interrelated +pieces within the Fortran compiler code. + +The relevant command-line flag is defined in @file{lang.opt}, according +to the documentation in @ref{Options,, Options, gccint, GNU Compiler +Collection Internals}. This is then processed by the overall GCC +machinery to create the code that enables @command{gfortran} and +@command{gcc} to recognize the option in the command-line arguments and +call the relevant handler function. + +This generated code calls the @code{gfc_handle_option} code in +@file{options.cc} with an enumerator variable indicating which option is +to be processed, and the relevant integer or string values associated +with that option flag. Typically, @code{gfc_handle_option} uses these +arguments to set global flags which record the option states. + +The global flags that record the option states are stored in the +@code{gfc_option_t} struct, which is defined in @file{gfortran.h}. +Before the options are processed, initial values for these flags are set +in @code{gfc_init_option} in @file{options.cc}; these become the default +values for the options. + + + +@c --------------------------------------------------------------------- +@c Error Handling +@c --------------------------------------------------------------------- + +@node Error Handling +@section Error Handling + +The GNU Fortran compiler's parser operates by testing each piece of +source code against a variety of matchers. In some cases, if these +matchers do not match the source code, they will store an error message +in a buffer. If the parser later finds a matcher that does correctly +match the source code, then the buffered error is discarded. However, +if the parser cannot find a match, then the buffered error message is +reported to the user. This enables the compiler to provide more +meaningful error messages even in the many cases where (erroneous) +Fortran syntax is ambiguous due to things like the absence of reserved +keywords. + +As an example of how this works, consider the following line: +@smallexample +IF = 3 +@end smallexample +Hypothetically, this may get passed to the matcher for an @code{IF} +statement. Since this could plausibly be an erroneous @code{IF} +statement, the matcher will buffer an error message reporting the +absence of an expected @samp{(} following an @code{IF}. Since no +matchers reported an error-free match, however, the parser will also try +matching this against a variable assignment. When @code{IF} is a valid +variable, this will be parsed as an assignment statement, and the error +discarded. However, when @code{IF} is not a valid variable, this +buffered error message will be reported to the user. + +The error handling code is implemented in @file{error.cc}. Errors are +normally entered into the buffer with the @code{gfc_error} function. +Warnings go through a similar buffering process, and are entered into +the buffer with @code{gfc_warning}. There is also a special-purpose +function, @code{gfc_notify_std}, for things which have an error/warning +status that depends on the currently-selected language standard. + +The @code{gfc_error_check} function checks the buffer for errors, +reports the error message to the user if one exists, clears the buffer, +and returns a flag to the user indicating whether or not an error +existed. To check the state of the buffer without changing its state or +reporting the errors, the @code{gfc_error_flag_test} function can be +used. The @code{gfc_clear_error} function will clear out any errors in +the buffer, without reporting them. The @code{gfc_warning_check} and +@code{gfc_clear_warning} functions provide equivalent functionality for +the warning buffer. + +Only one error and one warning can be in the buffers at a time, and +buffering another will overwrite the existing one. In cases where one +may wish to work on a smaller piece of source code without disturbing an +existing error state, the @code{gfc_push_error}, @code{gfc_pop_error}, +and @code{gfc_free_error} mechanism exists to implement a stack for the +error buffer. + +For cases where an error or warning should be reported immediately +rather than buffered, the @code{gfc_error_now} and +@code{gfc_warning_now} functions can be used. Normally, the compiler +will continue attempting to parse the program after an error has +occurred, but if this is not appropriate, the @code{gfc_fatal_error} +function should be used instead. For errors that are always the result +of a bug somewhere in the compiler, the @code{gfc_internal_error} +function should be used. + +The syntax for the strings used to produce the error/warning message in +the various error and warning functions is similar to the @code{printf} +syntax, with @samp{%}-escapes to insert variable values. The details, +and the allowable codes, are documented in the @code{error_print} +function in @file{error.cc}. + +@c --------------------------------------------------------------------- +@c Frontend Data Structures +@c --------------------------------------------------------------------- + +@node Frontend Data Structures +@chapter Frontend Data Structures +@cindex data structures + +This chapter should describe the details necessary to understand how +the various @code{gfc_*} data are used and interact. In general it is +advisable to read the code in @file{dump-parse-tree.cc} as its routines +should exhaust all possible valid combinations of content for these +structures. + +@menu +* gfc_code:: Representation of Executable Statements. +* gfc_expr:: Representation of Values and Expressions. +@end menu + + +@c gfc_code +@c -------- + +@node gfc_code +@section @code{gfc_code} +@cindex statement chaining +@tindex @code{gfc_code} +@tindex @code{struct gfc_code} + +The executable statements in a program unit are represented by a +nested chain of @code{gfc_code} structures. The type of statement is +identified by the @code{op} member of the structure, the different +possible values are enumerated in @code{gfc_exec_op}. A special +member of this @code{enum} is @code{EXEC_NOP} which is used to +represent the various @code{END} statements if they carry a label. +Depending on the type of statement some of the other fields will be +filled in. Fields that are generally applicable are the @code{next} +and @code{here} fields. The former points to the next statement in +the current block or is @code{NULL} if the current statement is the +last in a block, @code{here} points to the statement label of the +current statement. + +If the current statement is one of @code{IF}, @code{DO}, @code{SELECT} +it starts a block, i.e.@: a nested level in the program. In order to +represent this, the @code{block} member is set to point to a +@code{gfc_code} structure whose @code{next} member starts the chain of +statements inside the block; this structure's @code{op} member should be set to +the same value as the parent structure's @code{op} member. The @code{SELECT} +and @code{IF} statements may contain various blocks (the chain of @code{ELSE IF} +and @code{ELSE} blocks or the various @code{CASE}s, respectively). These chains +are linked-lists formed by the @code{block} members. + +Consider the following example code: + +@example +IF (foo < 20) THEN + PRINT *, "Too small" + foo = 20 +ELSEIF (foo > 50) THEN + PRINT *, "Too large" + foo = 50 +ELSE + PRINT *, "Good" +END IF +@end example + +This statement-block will be represented in the internal gfortran tree as +follows, were the horizontal link-chains are those induced by the @code{next} +members and vertical links down are those of @code{block}. @samp{==|} and +@samp{--|} mean @code{NULL} pointers to mark the end of a chain: + +@example +... ==> IF ==> ... + | + +--> IF foo < 20 ==> PRINT *, "Too small" ==> foo = 20 ==| + | + +--> IF foo > 50 ==> PRINT *, "Too large" ==> foo = 50 ==| + | + +--> ELSE ==> PRINT *, "Good" ==| + | + +--| +@end example + + +@subsection IF Blocks + +Conditionals are represented by @code{gfc_code} structures with their +@code{op} member set to @code{EXEC_IF}. This structure's @code{block} +member must point to another @code{gfc_code} node that is the header of the +if-block. This header's @code{op} member must be set to @code{EXEC_IF}, too, +its @code{expr} member holds the condition to check for, and its @code{next} +should point to the code-chain of the statements to execute if the condition is +true. + +If in addition an @code{ELSEIF} or @code{ELSE} block is present, the +@code{block} member of the if-block-header node points to yet another +@code{gfc_code} structure that is the header of the elseif- or else-block. Its +structure is identical to that of the if-block-header, except that in case of an +@code{ELSE} block without a new condition the @code{expr} member should be +@code{NULL}. This block can itself have its @code{block} member point to the +next @code{ELSEIF} or @code{ELSE} block if there's a chain of them. + + +@subsection Loops + +@code{DO} loops are stored in the tree as @code{gfc_code} nodes with their +@code{op} set to @code{EXEC_DO} for a @code{DO} loop with iterator variable and +to @code{EXEC_DO_WHILE} for infinite @code{DO}s and @code{DO WHILE} blocks. +Their @code{block} member should point to a @code{gfc_code} structure heading +the code-chain of the loop body; its @code{op} member should be set to +@code{EXEC_DO} or @code{EXEC_DO_WHILE}, too, respectively. + +For @code{DO WHILE} loops, the loop condition is stored on the top +@code{gfc_code} structure's @code{expr} member; @code{DO} forever loops are +simply @code{DO WHILE} loops with a constant @code{.TRUE.} loop condition in +the internal representation. + +Similarly, @code{DO} loops with an iterator have instead of the condition their +@code{ext.iterator} member set to the correct values for the loop iterator +variable and its range. + + +@subsection @code{SELECT} Statements + +A @code{SELECT} block is introduced by a @code{gfc_code} structure with an +@code{op} member of @code{EXEC_SELECT} and @code{expr} containing the expression +to evaluate and test. Its @code{block} member starts a list of @code{gfc_code} +structures linked together by their @code{block} members that stores the various +@code{CASE} parts. + +Each @code{CASE} node has its @code{op} member set to @code{EXEC_SELECT}, too, +its @code{next} member points to the code-chain to be executed in the current +case-block, and @code{extx.case_list} contains the case-values this block +corresponds to. The @code{block} member links to the next case in the list. + + +@subsection @code{BLOCK} and @code{ASSOCIATE} + +The code related to a @code{BLOCK} statement is stored inside an +@code{gfc_code} structure (say @var{c}) +with @code{c.op} set to @code{EXEC_BLOCK}. The +@code{gfc_namespace} holding the locally defined variables of the +@code{BLOCK} is stored in @code{c.ext.block.ns}. The code inside the +construct is in @code{c.code}. + +@code{ASSOCIATE} constructs are based on @code{BLOCK} and thus also have +the internal storage structure described above (including @code{EXEC_BLOCK}). +However, for them @code{c.ext.block.assoc} is set additionally and points +to a linked list of @code{gfc_association_list} structures. Those +structures basically store a link of associate-names to target expressions. +The associate-names themselves are still also added to the @code{BLOCK}'s +namespace as ordinary symbols, but they have their @code{gfc_symbol}'s +member @code{assoc} set also pointing to the association-list structure. +This way associate-names can be distinguished from ordinary variables +and their target expressions identified. + +For association to expressions (as opposed to variables), at the very beginning +of the @code{BLOCK} construct assignments are automatically generated to +set the corresponding variables to their target expressions' values, and +later on the compiler simply disallows using such associate-names in contexts +that may change the value. + + +@c gfc_expr +@c -------- + +@node gfc_expr +@section @code{gfc_expr} +@tindex @code{gfc_expr} +@tindex @code{struct gfc_expr} + +Expressions and ``values'', including constants, variable-, array- and +component-references as well as complex expressions consisting of operators and +function calls are internally represented as one or a whole tree of +@code{gfc_expr} objects. The member @code{expr_type} specifies the overall +type of an expression (for instance, @code{EXPR_CONSTANT} for constants or +@code{EXPR_VARIABLE} for variable references). The members @code{ts} and +@code{rank} as well as @code{shape}, which can be @code{NULL}, specify +the type, rank and, if applicable, shape of the whole expression or expression +tree of which the current structure is the root. @code{where} is the locus of +this expression in the source code. + +Depending on the flavor of the expression being described by the object +(that is, the value of its @code{expr_type} member), the corresponding structure +in the @code{value} union will usually contain additional data describing the +expression's value in a type-specific manner. The @code{ref} member is used to +build chains of (array-, component- and substring-) references if the expression +in question contains such references, see below for details. + + +@subsection Constants + +Scalar constants are represented by @code{gfc_expr} nodes with their +@code{expr_type} set to @code{EXPR_CONSTANT}. The constant's value shall +already be known at compile-time and is stored in the @code{logical}, +@code{integer}, @code{real}, @code{complex} or @code{character} struct inside +@code{value}, depending on the constant's type specification. + + +@subsection Operators + +Operator-expressions are expressions that are the result of the execution of +some operator on one or two operands. The expressions have an @code{expr_type} +of @code{EXPR_OP}. Their @code{value.op} structure contains additional data. + +@code{op1} and optionally @code{op2} if the operator is binary point to the +two operands, and @code{operator} or @code{uop} describe the operator that +should be evaluated on these operands, where @code{uop} describes a user-defined +operator. + + +@subsection Function Calls + +If the expression is the return value of a function-call, its @code{expr_type} +is set to @code{EXPR_FUNCTION}, and @code{symtree} must point to the symtree +identifying the function to be called. @code{value.function.actual} holds the +actual arguments given to the function as a linked list of +@code{gfc_actual_arglist} nodes. + +The other members of @code{value.function} describe the function being called +in more detail, containing a link to the intrinsic symbol or user-defined +function symbol if the call is to an intrinsic or external function, +respectively. These values are determined during resolution-phase from the +structure's @code{symtree} member. + +A special case of function calls are ``component calls'' to type-bound +procedures; those have the @code{expr_type} @code{EXPR_COMPCALL} with +@code{value.compcall} containing the argument list and the procedure called, +while @code{symtree} and @code{ref} describe the object on which the procedure +was called in the same way as a @code{EXPR_VARIABLE} expression would. +@xref{Type-bound Procedures}. + + +@subsection Array- and Structure-Constructors + +Array- and structure-constructors (one could probably call them ``array-'' and +``derived-type constants'') are @code{gfc_expr} structures with their +@code{expr_type} member set to @code{EXPR_ARRAY} or @code{EXPR_STRUCTURE}, +respectively. For structure constructors, @code{symtree} points to the +derived-type symbol for the type being constructed. + +The values for initializing each array element or structure component are +stored as linked-list of @code{gfc_constructor} nodes in the +@code{value.constructor} member. + + +@subsection Null + +@code{NULL} is a special value for pointers; it can be of different base types. +Such a @code{NULL} value is represented in the internal tree by a +@code{gfc_expr} node with @code{expr_type} @code{EXPR_NULL}. If the base type +of the @code{NULL} expression is known, it is stored in @code{ts} (that's for +instance the case for default-initializers of @code{ALLOCATABLE} components), +but this member can also be set to @code{BT_UNKNOWN} if the information is not +available (for instance, when the expression is a pointer-initializer +@code{NULL()}). + + +@subsection Variables and Reference Expressions + +Variable references are @code{gfc_expr} structures with their @code{expr_type} +set to @code{EXPR_VARIABLE}; their @code{symtree} should point to the variable +that is referenced. + +For this type of expression, it's also possible to chain array-, component- +or substring-references to the original expression to get something like +@samp{struct%component(2:5)}, where @code{component} is either an array or +a @code{CHARACTER} member of @code{struct} that is of some derived-type. Such a +chain of references is achieved by a linked list headed by @code{ref} of the +@code{gfc_expr} node. For the example above it would be (@samp{==|} is the +last @code{NULL} pointer): + +@smallexample +EXPR_VARIABLE(struct) ==> REF_COMPONENT(component) ==> REF_ARRAY(2:5) ==| +@end smallexample + +If @code{component} is a string rather than an array, the last element would be +a @code{REF_SUBSTRING} reference, of course. If the variable itself or some +component referenced is an array and the expression should reference the whole +array rather than being followed by an array-element or -section reference, a +@code{REF_ARRAY} reference must be built as the last element in the chain with +an array-reference type of @code{AR_FULL}. Consider this example code: + +@smallexample +TYPE :: mytype + INTEGER :: array(42) +END TYPE mytype + +TYPE(mytype) :: variable +INTEGER :: local_array(5) + +CALL do_something (variable%array, local_array) +@end smallexample + +The @code{gfc_expr} nodes representing the arguments to the @samp{do_something} +call will have a reference-chain like this: + +@smallexample +EXPR_VARIABLE(variable) ==> REF_COMPONENT(array) ==> REF_ARRAY(FULL) ==| +EXPR_VARIABLE(local_array) ==> REF_ARRAY(FULL) ==| +@end smallexample + + +@subsection Constant Substring References + +@code{EXPR_SUBSTRING} is a special type of expression that encodes a substring +reference of a constant string, as in the following code snippet: + +@smallexample +x = "abcde"(1:2) +@end smallexample + +In this case, @code{value.character} contains the full string's data as if it +was a string constant, but the @code{ref} member is also set and points to a +substring reference as described in the subsection above. + + +@c --------------------------------------------------------------------- +@c F2003 OOP +@c --------------------------------------------------------------------- + +@node Object Orientation +@chapter Internals of Fortran 2003 OOP Features + +@menu +* Type-bound Procedures:: Type-bound procedures. +* Type-bound Operators:: Type-bound operators. +@end menu + + +@c Type-bound procedures +@c --------------------- + +@node Type-bound Procedures +@section Type-bound Procedures + +Type-bound procedures are stored in the @code{tb_sym_root} of the namespace +@code{f2k_derived} associated with the derived-type symbol as @code{gfc_symtree} +nodes. The name and symbol of these symtrees corresponds to the binding-name +of the procedure, i.e. the name that is used to call it from the context of an +object of the derived-type. + +In addition, this type of symtrees stores in @code{n.tb} a struct of type +@code{gfc_typebound_proc} containing the additional data needed: The +binding attributes (like @code{PASS} and @code{NOPASS}, @code{NON_OVERRIDABLE} +or the access-specifier), the binding's target(s) and, if the current binding +overrides or extends an inherited binding of the same name, @code{overridden} +points to this binding's @code{gfc_typebound_proc} structure. + + +@subsection Specific Bindings +@c -------------------------- + +For specific bindings (declared with @code{PROCEDURE}), if they have a +passed-object argument, the passed-object dummy argument is first saved by its +name, and later during resolution phase the corresponding argument is looked for +and its position remembered as @code{pass_arg_num} in @code{gfc_typebound_proc}. +The binding's target procedure is pointed-to by @code{u.specific}. + +@code{DEFERRED} bindings are just like ordinary specific bindings, except +that their @code{deferred} flag is set of course and that @code{u.specific} +points to their ``interface'' defining symbol (might be an abstract interface) +instead of the target procedure. + +At the moment, all type-bound procedure calls are statically dispatched and +transformed into ordinary procedure calls at resolution time; their actual +argument list is updated to include at the right position the passed-object +argument, if applicable, and then a simple procedure call to the binding's +target procedure is built. To handle dynamic dispatch in the future, this will +be extended to allow special code generation during the trans-phase to dispatch +based on the object's dynamic type. + + +@subsection Generic Bindings +@c ------------------------- + +Bindings declared as @code{GENERIC} store the specific bindings they target as +a linked list using nodes of type @code{gfc_tbp_generic} in @code{u.generic}. +For each specific target, the parser records its symtree and during resolution +this symtree is bound to the corresponding @code{gfc_typebound_proc} structure +of the specific target. + +Calls to generic bindings are handled entirely in the resolution-phase, where +for the actual argument list present the matching specific binding is found +and the call's target procedure (@code{value.compcall.tbp}) is re-pointed to +the found specific binding and this call is subsequently handled by the logic +for specific binding calls. + + +@subsection Calls to Type-bound Procedures +@c --------------------------------------- + +Calls to type-bound procedures are stored in the parse-tree as @code{gfc_expr} +nodes of type @code{EXPR_COMPCALL}. Their @code{value.compcall.actual} saves +the actual argument list of the call and @code{value.compcall.tbp} points to the +@code{gfc_typebound_proc} structure of the binding to be called. The object +in whose context the procedure was called is saved by combination of +@code{symtree} and @code{ref}, as if the expression was of type +@code{EXPR_VARIABLE}. + +For code like this: +@smallexample +CALL myobj%procedure (arg1, arg2) +@end smallexample +@noindent +the @code{CALL} is represented in the parse-tree as a @code{gfc_code} node of +type @code{EXEC_COMPCALL}. The @code{expr} member of this node holds an +expression of type @code{EXPR_COMPCALL} of the same structure as mentioned above +except that its target procedure is of course a @code{SUBROUTINE} and not a +@code{FUNCTION}. + +Expressions that are generated internally (as expansion of a type-bound +operator call) may also use additional flags and members. +@code{value.compcall.ignore_pass} signals that even though a @code{PASS} +attribute may be present the actual argument list should not be updated because +it already contains the passed-object. +@code{value.compcall.base_object} overrides, if it is set, the base-object +(that is normally stored in @code{symtree} and @code{ref} as mentioned above); +this is needed because type-bound operators can be called on a base-object that +need not be of type @code{EXPR_VARIABLE} and thus representable in this way. +Finally, if @code{value.compcall.assign} is set, the call was produced in +expansion of a type-bound assignment; this means that proper dependency-checking +needs to be done when relevant. + + +@c Type-bound operators +@c -------------------- + +@node Type-bound Operators +@section Type-bound Operators + +Type-bound operators are in fact basically just @code{GENERIC} procedure +bindings and are represented much in the same way as those (see +@ref{Type-bound Procedures}). + +They come in two flavours: +User-defined operators (like @code{.MYOPERATOR.}) +are stored in the @code{f2k_derived} namespace's @code{tb_uop_root} +symtree exactly like ordinary type-bound procedures are stored in +@code{tb_sym_root}; their symtrees' names are the operator-names (e.g. +@samp{myoperator} in the example). +Intrinsic operators on the other hand are stored in the namespace's +array member @code{tb_op} indexed by the intrinsic operator's enum +value. Those need not be packed into @code{gfc_symtree} structures and are +only @code{gfc_typebound_proc} instances. + +When an operator call or assignment is found that cannot be handled in +another way (i.e. neither matches an intrinsic nor interface operator +definition) but that contains a derived-type expression, all type-bound +operators defined on that derived-type are checked for a match with +the operator call. If there's indeed a relevant definition, the +operator call is replaced with an internally generated @code{GENERIC} +type-bound procedure call to the respective definition and that call is +further processed. + +@c --------------------------------------------------------------------- +@c - Translating to GENERIC +@c --------------------------------------------------------------------- + +@node Translating to GENERIC +@chapter Generating the intermediate language for later stages. + +This chapter deals with the transformation of gfortran's frontend data +structures to the intermediate language used by the later stages of +the compiler, the so-called middle end. + +Data structures relating to this are found in the source files +@file{trans*.h} and @file{trans-*.c}. + +@menu +* Basic Data Structures:: Basic data structures. +* Converting Expressions:: Converting expressions to tree. +* Translating Statements:: Translating statements. +* Accessing Declarations:: Accessing declarations. +@end menu + +@node Basic Data Structures +@section Basic data structures + +Gfortran creates GENERIC as an intermediate language for the +middle-end. Details about GENERIC can be found in the GCC manual. + +The basic data structure of GENERIC is a @code{tree}. Everything in +GENERIC is a @code{tree}, including types and statements. Fortunately +for the gfortran programmer, @code{tree} variables are +garbage-collected, so doing memory management for them is not +necessary. + +@code{tree} expressions are built using functions such as, for +example, @code{fold_build2_loc}. For two tree variables @code{a} and +@code{b}, both of which have the type @code{gfc_arry_index_type}, +calculation @code{c = a * b} would be done by + +@smallexample +c = fold_build2_loc (input_location, MULT_EXPR, + gfc_array_index_type, a, b); +@end smallexample + +The types have to agree, otherwise internal compiler errors will occur +at a later stage. Expressions can be converted to a different type +using @code{fold_convert}. + +Accessing individual members in the @code{tree} structures should not +be done. Rather, access should be done via macros. + +One basic data structure is the @code{stmtblock_t} struct. This is +used for holding a list of statements, expressed as @code{tree} +expressions. If a block is created using @code{gfc_start_block}, it +has its own scope for variables; if it is created using +@code{gfc_init_block}, it does not have its own scope. + +It is possible to +@itemize @bullet +@item Add an expression to the end of a block using + @code{gfc_add_expr_to_block} +@item Add an expression to the beginning of a block using + @code{void gfc_prepend_expr_to_block} +@item Make a block into a single @code{tree} using + @code{gfc_finish_block}. For example, this is needed to put the + contents of a block into the @code{if} or @code{else} branch of + a @code{COND_EXPR}. +@end itemize + +Variables are also @code{tree} expressions, they can be created using +@code{gfc_create_var}. Assigning to a variable can be done with +@code{gfc_add_modify}. + +An example: Creating a default integer type variable in the current +scope with the prefix ``everything'' in the @code{stmt_block} +@code{block} and assigning the value 42 would be + +@smallexample +tree var, *block; +/* Initialize block somewhere here. */ +var = gfc_create_var (integer_type_node, "everything"); +gfc_add_modify (block, var, build_int_cst (integer_type_node, 42)); +@end smallexample + +@node Converting Expressions +@section Converting Expressions to tree + +Converting expressions to @code{tree} is done by functions called +@code{gfc_conv_*}. + +The central data structure for a GENERIC expression is the +@code{gfc_se} structure. Its @code{expr} member is a @code{tree} that +holds the value of the expression. A @code{gfc_se} structure is +initialized using @code{gfc_init_se}; it needs to be embedded in an +outer @code{gfc_se}. + +Evaluating Fortran expressions often require things to be done before +and after evaluation of the expression, for example code for the +allocation of a temporary variable and its subsequent deallocation. +Therefore, @code{gfc_se} contains the members @code{pre} and +@code{post}, which point to @code{stmt_block} blocks for code that +needs to be executed before and after evaluation of the expression. + +When using a local @code{gfc_se} to convert some expression, it is +often necessary to add the generated @code{pre} and @code{post} blocks +to the @code{pre} or @code{post} blocks of the outer @code{gfc_se}. +Code like this (lifted from @file{trans-expr.cc}) is fairly common: + +@smallexample +gfc_se cont_se; +tree cont_var; + +/* cont_var = is_contiguous (expr); . */ +gfc_init_se (&cont_se, parmse); +gfc_conv_is_contiguous_expr (&cont_se, expr); +gfc_add_block_to_block (&se->pre, &(&cont_se)->pre); +gfc_add_modify (&se->pre, cont_var, cont_se.expr); +gfc_add_block_to_block (&se->pre, &(&cont_se)->post); +@end smallexample + +Conversion functions which need a @code{gfc_se} structure will have a +corresponding argument. + +@code{gfc_se} also contains pointers to a @code{gfc_ss} and a +@code{gfc_loopinfo} structure. These are needed by the scalarizer. + +@node Translating Statements +@section Translating statements +Translating statements to @code{tree} is done by functions called +@code{gfc_trans_*}. These functions usually get passed a +@code{gfc_code} structure, evaluate any expressions and then +return a @code{tree} structure. + +@node Accessing Declarations +@section Accessing declarations + +@code{gfc_symbol}, @code{gfc_charlen} and other front-end structures +contain a @code{backend_decl} variable, which contains the @code{tree} +used for accessing that entity in the middle-end. + +Accessing declarations is usually done by functions called +@code{gfc_get*}. + +@c --------------------------------------------------------------------- +@c LibGFortran +@c --------------------------------------------------------------------- + +@node LibGFortran +@chapter The LibGFortran Runtime Library + +@menu +* Symbol Versioning:: Symbol Versioning. +@end menu + + +@c --------------------------------------------------------------------- +@c Symbol Versioning +@c --------------------------------------------------------------------- + +@node Symbol Versioning +@section Symbol Versioning +@comment Based on https://gcc.gnu.org/wiki/SymbolVersioning, +@comment as of 2006-11-05, written by Janne Blomqvist. + +In general, this capability exists only on a few platforms, thus there +is a need for configure magic so that it is used only on those targets +where it is supported. + +The central concept in symbol versioning is the so-called map file, +which specifies the version node(s) exported symbols are labeled with. +Also, the map file is used to hide local symbols. + +Some relevant references: +@itemize @bullet +@item +@uref{https://sourceware.org/binutils/docs/ld/VERSION.html, +GNU @command{ld} manual} + +@item +@uref{https://www.akkadia.org/drepper/symbol-versioning, ELF Symbol +Versioning - Ulrich Depper} + +@item +@uref{https://www.akkadia.org/drepper/dsohowto.pdf, How to Write Shared +Libraries - Ulrich Drepper (see Chapter 3)} + +@end itemize + +If one adds a new symbol to a library that should be exported, the new +symbol should be mentioned in the map file and a new version node +defined, e.g., if one adds a new symbols @code{foo} and @code{bar} to +libgfortran for the next GCC release, the following should be added to +the map file: +@smallexample +GFORTRAN_1.1 @{ + global: + foo; + bar; +@} GFORTRAN_1.0; +@end smallexample +@noindent +where @code{GFORTRAN_1.0} is the version node of the current release, +and @code{GFORTRAN_1.1} is the version node of the next release where +foo and bar are made available. + +If one wants to change an existing interface, it is possible by using +some asm trickery (from the @command{ld} manual referenced above): + +@smallexample +__asm__(".symver original_foo,foo@@"); +__asm__(".symver old_foo,foo@@VERS_1.1"); +__asm__(".symver old_foo1,foo@@VERS_1.2"); +__asm__(".symver new_foo,foo@@VERS_2.0"); +@end smallexample + +In this example, @code{foo@@} represents the symbol @code{foo} bound to +the unspecified base version of the symbol. The source file that +contains this example would define 4 C functions: @code{original_foo}, +@code{old_foo}, @code{old_foo1}, and @code{new_foo}. + +In this case the map file must contain @code{foo} in @code{VERS_1.1} +and @code{VERS_1.2} as well as in @code{VERS_2.0}. + + +@c --------------------------------------------------------------------- +@c GNU Free Documentation License +@c --------------------------------------------------------------------- + +@include fdl.texi + + +@c --------------------------------------------------------------------- +@c Index +@c --------------------------------------------------------------------- + +@node Index +@unnumbered Index + +@printindex cp + +@bye diff --git a/gcc/fortran/gfortran.texi b/gcc/fortran/gfortran.texi new file mode 100644 index 00000000000..4b4ecd528a7 --- /dev/null +++ b/gcc/fortran/gfortran.texi @@ -0,0 +1,5573 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename gfortran.info +@set copyrights-gfortran 1999-2022 + +@include gcc-common.texi + +@settitle The GNU Fortran Compiler + +@c Create a separate index for command line options +@defcodeindex op +@c Merge the standard indexes into a single one. +@syncodeindex fn cp +@syncodeindex vr cp +@syncodeindex ky cp +@syncodeindex pg cp +@syncodeindex tp cp + +@c TODO: The following "Part" definitions are included here temporarily +@c until they are incorporated into the official Texinfo distribution. +@c They borrow heavily from Texinfo's \unnchapentry definitions. + +@tex +\gdef\part#1#2{% + \pchapsepmacro + \gdef\thischapter{} + \begingroup + \vglue\titlepagetopglue + \titlefonts \rm + \leftline{Part #1:@* #2} + \vskip4pt \hrule height 4pt width \hsize \vskip4pt + \endgroup + \writetocentry{part}{#2}{#1} +} +\gdef\blankpart{% + \writetocentry{blankpart}{}{} +} +% Part TOC-entry definition for summary contents. +\gdef\dosmallpartentry#1#2#3#4{% + \vskip .5\baselineskip plus.2\baselineskip + \begingroup + \let\rm=\bf \rm + \tocentry{Part #2: #1}{\doshortpageno\bgroup#4\egroup} + \endgroup +} +\gdef\dosmallblankpartentry#1#2#3#4{% + \vskip .5\baselineskip plus.2\baselineskip +} +% Part TOC-entry definition for regular contents. This has to be +% equated to an existing entry to not cause problems when the PDF +% outline is created. +\gdef\dopartentry#1#2#3#4{% + \unnchapentry{Part #2: #1}{}{#3}{#4} +} +\gdef\doblankpartentry#1#2#3#4{} +@end tex + +@c %**end of header + +@c Use with @@smallbook. + +@c %** start of document + +@c Cause even numbered pages to be printed on the left hand side of +@c the page and odd numbered pages to be printed on the right hand +@c side of the page. Using this, you can print on both sides of a +@c sheet of paper and have the text on the same part of the sheet. + +@c The text on right hand pages is pushed towards the right hand +@c margin and the text on left hand pages is pushed toward the left +@c hand margin. +@c (To provide the reverse effect, set bindingoffset to -0.75in.) + +@c @tex +@c \global\bindingoffset=0.75in +@c \global\normaloffset =0.75in +@c @end tex + +@copying +Copyright @copyright{} @value{copyrights-gfortran} Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``Funding Free Software'', the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end copying + +@ifinfo +@dircategory Software development +@direntry +* gfortran: (gfortran). The GNU Fortran Compiler. +@end direntry +This file documents the use and the internals of +the GNU Fortran compiler, (@command{gfortran}). + +Published by the Free Software Foundation +51 Franklin Street, Fifth Floor +Boston, MA 02110-1301 USA + +@insertcopying +@end ifinfo + + +@setchapternewpage odd +@titlepage +@title Using GNU Fortran +@versionsubtitle +@author The @t{gfortran} team +@page +@vskip 0pt plus 1filll +Published by the Free Software Foundation@* +51 Franklin Street, Fifth Floor@* +Boston, MA 02110-1301, USA@* +@c Last printed ??ber, 19??.@* +@c Printed copies are available for $? each.@* +@c ISBN ??? +@sp 1 +@insertcopying +@end titlepage + +@c TODO: The following "Part" definitions are included here temporarily +@c until they are incorporated into the official Texinfo distribution. + +@tex +\global\let\partentry=\dosmallpartentry +\global\let\blankpartentry=\dosmallblankpartentry +@end tex +@summarycontents + +@tex +\global\let\partentry=\dopartentry +\global\let\blankpartentry=\doblankpartentry +@end tex +@contents + +@page + +@c --------------------------------------------------------------------- +@c TexInfo table of contents. +@c --------------------------------------------------------------------- + +@ifnottex +@node Top +@top Introduction +@cindex Introduction + +This manual documents the use of @command{gfortran}, +the GNU Fortran compiler. You can find in this manual how to invoke +@command{gfortran}, as well as its features and incompatibilities. + +@ifset DEVELOPMENT +@emph{Warning:} This document, and the compiler it describes, are still +under development. While efforts are made to keep it up-to-date, it might +not accurately reflect the status of the most recent GNU Fortran compiler. +@end ifset + +@comment +@comment When you add a new menu item, please keep the right hand +@comment aligned to the same column. Do not use tabs. This provides +@comment better formatting. +@comment +@menu +* Introduction:: + +Part I: Invoking GNU Fortran +* Invoking GNU Fortran:: Command options supported by @command{gfortran}. +* Runtime:: Influencing runtime behavior with environment variables. + +Part II: Language Reference +* Compiler Characteristics:: User-visible implementation details. +* Extensions:: Language extensions implemented by GNU Fortran. +* Mixed-Language Programming:: Interoperability with C +* Coarray Programming:: +* Intrinsic Procedures:: Intrinsic procedures supported by GNU Fortran. +* Intrinsic Modules:: Intrinsic modules supported by GNU Fortran. + +* Contributing:: How you can help. +* Copying:: GNU General Public License says + how you can copy and share GNU Fortran. +* GNU Free Documentation License:: + How you can copy and share this manual. +* Funding:: How to help assure continued work for free software. +* Option Index:: Index of command line options +* Keyword Index:: Index of concepts +@end menu +@end ifnottex + +@c --------------------------------------------------------------------- +@c Introduction +@c --------------------------------------------------------------------- + +@node Introduction +@chapter Introduction + +@c The following duplicates the text on the TexInfo table of contents. +@iftex +This manual documents the use of @command{gfortran}, the GNU Fortran +compiler. You can find in this manual how to invoke @command{gfortran}, +as well as its features and incompatibilities. + +@ifset DEVELOPMENT +@emph{Warning:} This document, and the compiler it describes, are still +under development. While efforts are made to keep it up-to-date, it +might not accurately reflect the status of the most recent GNU Fortran +compiler. +@end ifset +@end iftex + +@menu +* About GNU Fortran:: What you should know about the GNU Fortran compiler. +* GNU Fortran and GCC:: You can compile Fortran, C, or other programs. +* Standards:: Standards supported by GNU Fortran. +@end menu + + +@c --------------------------------------------------------------------- +@c About GNU Fortran +@c --------------------------------------------------------------------- + +@node About GNU Fortran +@section About GNU Fortran + +The GNU Fortran compiler is the successor to @command{g77}, the +Fortran 77 front end included in GCC prior to version 4 (released in +2005). While it is backward-compatible with most @command{g77} +extensions and command-line options, @command{gfortran} is a completely new +implemention designed to support more modern dialects of Fortran. +GNU Fortran implements the Fortran 77, 90 and 95 standards +completely, most of the Fortran 2003 and 2008 standards, and some +features from the 2018 standard. It also implements several extensions +including OpenMP and OpenACC support for parallel programming. + +The GNU Fortran compiler passes the +@uref{http://www.fortran-2000.com/ArnaudRecipes/fcvs21_f95.html, +NIST Fortran 77 Test Suite}, and produces acceptable results on the +@uref{https://www.netlib.org/lapack/faq.html, LAPACK Test Suite}. +It also provides respectable performance on +the @uref{https://polyhedron.com/?page_id=175, +Polyhedron Fortran compiler benchmarks} and the +@uref{https://www.netlib.org/benchmark/livermore, +Livermore Fortran Kernels test}. It has been used to compile a number of +large real-world programs, including +@uref{http://hirlam.org/, the HARMONIE and HIRLAM weather forecasting code} and +@uref{https://github.com/dylan-jayatilaka/tonto, +the Tonto quantum chemistry package}; see +@url{https://gcc.gnu.org/@/wiki/@/GfortranApps} for an extended list. + +GNU Fortran provides the following functionality: + +@itemize @bullet +@item +Read a program, stored in a file and containing @dfn{source code} +instructions written in Fortran 77. + +@item +Translate the program into instructions a computer +can carry out more quickly than it takes to translate the +original Fortran instructions. +The result after compilation of a program is +@dfn{machine code}, +which is efficiently translated and processed +by a machine such as your computer. +Humans usually are not as good writing machine code +as they are at writing Fortran (or C++, Ada, or Java), +because it is easy to make tiny mistakes writing machine code. + +@item +Provide information about the reasons why +the compiler may be unable to create a binary from the source code, +for example if the source code is flawed. +The Fortran language standards require that the compiler can point out +mistakes in your code. +An incorrect usage of the language causes an @dfn{error message}. + +The compiler also attempts to diagnose cases where your +program contains a correct usage of the language, +but instructs the computer to do something questionable. +This kind of diagnostic message is called a @dfn{warning message}. + +@item +Provide optional information about the translation passes +from the source code to machine code. +This can help you to find the cause of +certain bugs which may not be obvious in the source code, +but may be more easily found at a lower level compiler output. +It also helps developers to find bugs in the compiler itself. + +@item +Provide information in the generated machine code that can +make it easier to find bugs in the program (using a debugging tool, +called a @dfn{debugger}, such as the GNU Debugger @command{gdb}). + +@item +Locate and gather machine code already generated to +perform actions requested by statements in the program. +This machine code is organized into @dfn{modules} and is located +and @dfn{linked} to the user program. +@end itemize + +The GNU Fortran compiler consists of several components: + +@itemize @bullet +@item +A version of the @command{gcc} command +(which also might be installed as the system's @command{cc} command) +that also understands and accepts Fortran source code. +The @command{gcc} command is the @dfn{driver} program for +all the languages in the GNU Compiler Collection (GCC); +With @command{gcc}, +you can compile the source code of any language for +which a front end is available in GCC. + +@item +The @command{gfortran} command itself, +which also might be installed as the +system's @command{f95} command. +@command{gfortran} is just another driver program, +but specifically for the Fortran compiler only. +The primary difference between the @command{gcc} and @command{gfortran} +commands is that the latter automatically links the correct libraries +to your program. + +@item +A collection of run-time libraries. +These libraries contain the machine code needed to support +capabilities of the Fortran language that are not directly +provided by the machine code generated by the +@command{gfortran} compilation phase, +such as intrinsic functions and subroutines, +and routines for interaction with files and the operating system. +@c and mechanisms to spawn, +@c unleash and pause threads in parallelized code. + +@item +The Fortran compiler itself, (@command{f951}). +This is the GNU Fortran parser and code generator, +linked to and interfaced with the GCC backend library. +@command{f951} ``translates'' the source code to +assembler code. You would typically not use this +program directly; +instead, the @command{gcc} or @command{gfortran} driver +programs call it for you. +@end itemize + + +@c --------------------------------------------------------------------- +@c GNU Fortran and GCC +@c --------------------------------------------------------------------- + +@node GNU Fortran and GCC +@section GNU Fortran and GCC +@cindex GNU Compiler Collection +@cindex GCC + +GNU Fortran is a part of GCC, the @dfn{GNU Compiler Collection}. GCC +consists of a collection of front ends for various languages, which +translate the source code into a language-independent form called +@dfn{GENERIC}. This is then processed by a common middle end which +provides optimization, and then passed to one of a collection of back +ends which generate code for different computer architectures and +operating systems. + +Functionally, this is implemented with a driver program (@command{gcc}) +which provides the command-line interface for the compiler. It calls +the relevant compiler front-end program (e.g., @command{f951} for +Fortran) for each file in the source code, and then calls the assembler +and linker as appropriate to produce the compiled output. In a copy of +GCC that has been compiled with Fortran language support enabled, +@command{gcc} recognizes files with @file{.f}, @file{.for}, @file{.ftn}, +@file{.f90}, @file{.f95}, @file{.f03} and @file{.f08} extensions as +Fortran source code, and compiles it accordingly. A @command{gfortran} +driver program is also provided, which is identical to @command{gcc} +except that it automatically links the Fortran runtime libraries into the +compiled program. + +Source files with @file{.f}, @file{.for}, @file{.fpp}, @file{.ftn}, @file{.F}, +@file{.FOR}, @file{.FPP}, and @file{.FTN} extensions are treated as fixed form. +Source files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.f08}, +@file{.F90}, @file{.F95}, @file{.F03} and @file{.F08} extensions are +treated as free form. The capitalized versions of either form are run +through preprocessing. Source files with the lower case @file{.fpp} +extension are also run through preprocessing. + +This manual specifically documents the Fortran front end, which handles +the programming language's syntax and semantics. The aspects of GCC +that relate to the optimization passes and the back-end code generation +are documented in the GCC manual; see +@ref{Top,,Introduction,gcc,Using the GNU Compiler Collection (GCC)}. +The two manuals together provide a complete reference for the GNU +Fortran compiler. + +@c --------------------------------------------------------------------- +@c Standards +@c --------------------------------------------------------------------- + +@node Standards +@section Standards +@cindex Standards + +@menu +* Fortran 95 status:: +* Fortran 2003 status:: +* Fortran 2008 status:: +* Fortran 2018 status:: +@end menu + +Fortran is developed by the Working Group 5 of Sub-Committee 22 of the +Joint Technical Committee 1 of the International Organization for +Standardization and the International Electrotechnical Commission (IEC). +This group is known as @uref{http://www.nag.co.uk/sc22wg5/, WG5}. +Official Fortran standard documents are available for purchase +from ISO; a collection of free documents (typically final drafts) are +also available on the @uref{https://gcc.gnu.org/wiki/GFortranStandards, wiki}. + +The GNU Fortran compiler implements ISO/IEC 1539:1997 (Fortran 95). +As such, it can also compile essentially all standard-compliant +Fortran 90 and Fortran 77 programs. It also supports the ISO/IEC +TR-15581 enhancements to allocatable arrays. + +GNU Fortran also supports almost all of ISO/IEC 1539-1:2004 +(Fortran 2003) and ISO/IEC 1539-1:2010 (Fortran 2008). +It has partial support for features introduced in ISO/IEC +1539:2018 (Fortran 2018), the most recent version of the Fortran +language standard, including full support for the Technical Specification +@code{Further Interoperability of Fortran with C} (ISO/IEC TS 29113:2012). +More details on support for these standards can be +found in the following sections of the documentation. + +Additionally, the GNU Fortran compilers supports the OpenMP specification +(version 4.5 and partial support of the features of the 5.0 version, +@url{https://openmp.org/@/specifications/}). +There also is support for the OpenACC specification (targeting +version 2.6, @uref{https://www.openacc.org/}). See +@uref{https://gcc.gnu.org/wiki/OpenACC} for more information. + +@node Fortran 95 status +@subsection Fortran 95 status +@cindex Varying length strings +@cindex strings, varying length +@cindex conditional compilation + +The Fortran 95 standard specifies in Part 2 (ISO/IEC 1539-2:2000) +varying length character strings. While GNU Fortran currently does not +support such strings directly, there exist two Fortran implementations +for them, which work with GNU Fortran. One can be found at +@uref{http://user.astro.wisc.edu/~townsend/static.php?ref=iso-varying-string}. + +Deferred-length character strings of Fortran 2003 supports part of +the features of @code{ISO_VARYING_STRING} and should be considered as +replacement. (Namely, allocatable or pointers of the type +@code{character(len=:)}.) + +Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines +Conditional Compilation, which is not widely used and not directly +supported by the GNU Fortran compiler. You can use the program coco +to preprocess such files (@uref{http://www.daniellnagle.com/coco.html}). + +@node Fortran 2003 status +@subsection Fortran 2003 status + +GNU Fortran implements the Fortran 2003 (ISO/IEC 1539-1:2004) standard +except for finalization support, which is incomplete. +See the +@uref{https://gcc.gnu.org/wiki/Fortran2003, wiki page} for a full list +of new features introduced by Fortran 2003 and their implementation status. + +@node Fortran 2008 status +@subsection Fortran 2008 status + +The GNU Fortran compiler supports almost all features of Fortran 2008; +the @uref{https://gcc.gnu.org/wiki/Fortran2008Status, wiki} +has some information about the current implementation status. +In particular, the following are not yet supported: + +@itemize @bullet +@item +@code{DO CONCURRENT} and @code{FORALL} do not recognize a +type-spec in the loop header. + +@item +The change to permit any constant expression in subscripts and +nested implied-do limits in a @code{DATA} statement has not been implemented. +@end itemize + + +@node Fortran 2018 status +@subsection Fortran 2018 status + +Fortran 2018 (ISO/IEC 1539:2018) is the most recent version +of the Fortran language standard. GNU Fortran implements some of the +new features of this standard: + +@itemize @bullet +@item +All Fortran 2018 features derived from ISO/IEC TS 29113:2012, +``Further Interoperability of Fortran with C'', are supported by GNU Fortran. +This includes assumed-type and assumed-rank objects and +the @code{SELECT RANK} construct as well as the parts relating to +@code{BIND(C)} functions. +See also @ref{Further Interoperability of Fortran with C}. + +@item +GNU Fortran supports a subset of features derived from ISO/IEC TS 18508:2015, +``Additional Parallel Features in Fortran'': + +@itemize @bullet +@item +The new atomic ADD, CAS, FETCH and ADD/OR/XOR, OR and XOR intrinsics. + +@item +The @code{CO_MIN} and @code{CO_MAX} and @code{SUM} reduction intrinsics, +and the @code{CO_BROADCAST} and @code{CO_REDUCE} intrinsic, except that those +do not support polymorphic types or types with allocatable, pointer or +polymorphic components. + +@item +Events (@code{EVENT POST}, @code{EVENT WAIT}, @code{EVENT_QUERY}). + +@item +Failed images (@code{FAIL IMAGE}, @code{IMAGE_STATUS}, +@code{FAILED_IMAGES}, @code{STOPPED_IMAGES}). + +@end itemize + +@item +An @code{ERROR STOP} statement is permitted in a @code{PURE} +procedure. + +@item +GNU Fortran supports the @code{IMPLICIT NONE} statement with an +@code{implicit-none-spec-list}. + +@item +The behavior of the @code{INQUIRE} statement with the @code{RECL=} +specifier now conforms to Fortran 2018. + +@end itemize + + +@c ===================================================================== +@c PART I: INVOCATION REFERENCE +@c ===================================================================== + +@tex +\part{I}{Invoking GNU Fortran} +@end tex + +@c --------------------------------------------------------------------- +@c Compiler Options +@c --------------------------------------------------------------------- + +@include invoke.texi + + +@c --------------------------------------------------------------------- +@c Runtime +@c --------------------------------------------------------------------- + +@node Runtime +@chapter Runtime: Influencing runtime behavior with environment variables +@cindex environment variable + +The behavior of the @command{gfortran} can be influenced by +environment variables. + +Malformed environment variables are silently ignored. + +@menu +* TMPDIR:: Directory for scratch files +* GFORTRAN_STDIN_UNIT:: Unit number for standard input +* GFORTRAN_STDOUT_UNIT:: Unit number for standard output +* GFORTRAN_STDERR_UNIT:: Unit number for standard error +* GFORTRAN_UNBUFFERED_ALL:: Do not buffer I/O for all units +* GFORTRAN_UNBUFFERED_PRECONNECTED:: Do not buffer I/O for preconnected units. +* GFORTRAN_SHOW_LOCUS:: Show location for runtime errors +* GFORTRAN_OPTIONAL_PLUS:: Print leading + where permitted +* GFORTRAN_LIST_SEPARATOR:: Separator for list output +* GFORTRAN_CONVERT_UNIT:: Set conversion for unformatted I/O +* GFORTRAN_ERROR_BACKTRACE:: Show backtrace on run-time errors +* GFORTRAN_FORMATTED_BUFFER_SIZE:: Buffer size for formatted files +* GFORTRAN_UNFORMATTED_BUFFER_SIZE:: Buffer size for unformatted files +@end menu + +@node TMPDIR +@section @env{TMPDIR}---Directory for scratch files + +When opening a file with @code{STATUS='SCRATCH'}, GNU Fortran tries to +create the file in one of the potential directories by testing each +directory in the order below. + +@enumerate +@item +The environment variable @env{TMPDIR}, if it exists. + +@item +On the MinGW target, the directory returned by the @code{GetTempPath} +function. Alternatively, on the Cygwin target, the @env{TMP} and +@env{TEMP} environment variables, if they exist, in that order. + +@item +The @code{P_tmpdir} macro if it is defined, otherwise the directory +@file{/tmp}. +@end enumerate + +@node GFORTRAN_STDIN_UNIT +@section @env{GFORTRAN_STDIN_UNIT}---Unit number for standard input + +This environment variable can be used to select the unit number +preconnected to standard input. This must be a positive integer. +The default value is 5. + +@node GFORTRAN_STDOUT_UNIT +@section @env{GFORTRAN_STDOUT_UNIT}---Unit number for standard output + +This environment variable can be used to select the unit number +preconnected to standard output. This must be a positive integer. +The default value is 6. + +@node GFORTRAN_STDERR_UNIT +@section @env{GFORTRAN_STDERR_UNIT}---Unit number for standard error + +This environment variable can be used to select the unit number +preconnected to standard error. This must be a positive integer. +The default value is 0. + +@node GFORTRAN_UNBUFFERED_ALL +@section @env{GFORTRAN_UNBUFFERED_ALL}---Do not buffer I/O on all units + +This environment variable controls whether all I/O is unbuffered. If +the first letter is @samp{y}, @samp{Y} or @samp{1}, all I/O is +unbuffered. This will slow down small sequential reads and writes. If +the first letter is @samp{n}, @samp{N} or @samp{0}, I/O is buffered. +This is the default. + +@node GFORTRAN_UNBUFFERED_PRECONNECTED +@section @env{GFORTRAN_UNBUFFERED_PRECONNECTED}---Do not buffer I/O on preconnected units + +The environment variable named @env{GFORTRAN_UNBUFFERED_PRECONNECTED} controls +whether I/O on a preconnected unit (i.e.@: STDOUT or STDERR) is unbuffered. If +the first letter is @samp{y}, @samp{Y} or @samp{1}, I/O is unbuffered. This +will slow down small sequential reads and writes. If the first letter +is @samp{n}, @samp{N} or @samp{0}, I/O is buffered. This is the default. + +@node GFORTRAN_SHOW_LOCUS +@section @env{GFORTRAN_SHOW_LOCUS}---Show location for runtime errors + +If the first letter is @samp{y}, @samp{Y} or @samp{1}, filename and +line numbers for runtime errors are printed. If the first letter is +@samp{n}, @samp{N} or @samp{0}, do not print filename and line numbers +for runtime errors. The default is to print the location. + +@node GFORTRAN_OPTIONAL_PLUS +@section @env{GFORTRAN_OPTIONAL_PLUS}---Print leading + where permitted + +If the first letter is @samp{y}, @samp{Y} or @samp{1}, +a plus sign is printed +where permitted by the Fortran standard. If the first letter +is @samp{n}, @samp{N} or @samp{0}, a plus sign is not printed +in most cases. Default is not to print plus signs. + +@node GFORTRAN_LIST_SEPARATOR +@section @env{GFORTRAN_LIST_SEPARATOR}---Separator for list output + +This environment variable specifies the separator when writing +list-directed output. It may contain any number of spaces and +at most one comma. If you specify this on the command line, +be sure to quote spaces, as in +@smallexample +$ GFORTRAN_LIST_SEPARATOR=' , ' ./a.out +@end smallexample +when @command{a.out} is the compiled Fortran program that you want to run. +Default is a single space. + +@node GFORTRAN_CONVERT_UNIT +@section @env{GFORTRAN_CONVERT_UNIT}---Set conversion for unformatted I/O + +By setting the @env{GFORTRAN_CONVERT_UNIT} variable, it is possible +to change the representation of data for unformatted files. +The syntax for the @env{GFORTRAN_CONVERT_UNIT} variable for +most systems is: +@smallexample +GFORTRAN_CONVERT_UNIT: mode | mode ';' exception | exception ; +mode: 'native' | 'swap' | 'big_endian' | 'little_endian' ; +exception: mode ':' unit_list | unit_list ; +unit_list: unit_spec | unit_list unit_spec ; +unit_spec: INTEGER | INTEGER '-' INTEGER ; +@end smallexample +The variable consists of an optional default mode, followed by +a list of optional exceptions, which are separated by semicolons +from the preceding default and each other. Each exception consists +of a format and a comma-separated list of units. Valid values for +the modes are the same as for the @code{CONVERT} specifier: + +@itemize @w{} +@item @code{NATIVE} Use the native format. This is the default. +@item @code{SWAP} Swap between little- and big-endian. +@item @code{LITTLE_ENDIAN} Use the little-endian format +for unformatted files. +@item @code{BIG_ENDIAN} Use the big-endian format for unformatted files. +@end itemize +For POWER systems which support @option{-mabi=ieeelongdouble}, +there are additional options, which can be combined with the +others with commas. Those are +@itemize @w{} +@item @code{R16_IEEE} Use IEEE 128-bit format for @code{REAL(KIND=16)}. +@item @code{R16_IBM} Use IBM @code{long double} format for +@code{REAL(KIND=16)}. +@end itemize +A missing mode for an exception is taken to mean @code{BIG_ENDIAN}. +Examples of values for @env{GFORTRAN_CONVERT_UNIT} are: +@itemize @w{} +@item @code{'big_endian'} Do all unformatted I/O in big_endian mode. +@item @code{'little_endian;native:10-20,25'} Do all unformatted I/O +in little_endian mode, except for units 10 to 20 and 25, which are in +native format. +@item @code{'10-20'} Units 10 to 20 are big-endian, the rest is native. +@item @code{'big_endian,r16_ibm'} Do all unformatted I/O in big-endian +mode and use IBM long double for output of @code{REAL(KIND=16)} values. +@end itemize + +Setting the environment variables should be done on the command +line or via the @command{export} +command for @command{sh}-compatible shells and via @command{setenv} +for @command{csh}-compatible shells. + +Example for @command{sh}: +@smallexample +$ gfortran foo.f90 +$ GFORTRAN_CONVERT_UNIT='big_endian;native:10-20' ./a.out +@end smallexample + +Example code for @command{csh}: +@smallexample +% gfortran foo.f90 +% setenv GFORTRAN_CONVERT_UNIT 'big_endian;native:10-20' +% ./a.out +@end smallexample + +Using anything but the native representation for unformatted data +carries a significant speed overhead. If speed in this area matters +to you, it is best if you use this only for data that needs to be +portable. + +@xref{CONVERT specifier}, for an alternative way to specify the +data representation for unformatted files. @xref{Runtime Options}, for +setting a default data representation for the whole program. The +@code{CONVERT} specifier overrides the @option{-fconvert} compile options. + +@emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT +environment variable will override the CONVERT specifier in the +open statement}. This is to give control over data formats to +users who do not have the source code of their program available. + +@node GFORTRAN_ERROR_BACKTRACE +@section @env{GFORTRAN_ERROR_BACKTRACE}---Show backtrace on run-time errors + +If the @env{GFORTRAN_ERROR_BACKTRACE} variable is set to @samp{y}, +@samp{Y} or @samp{1} (only the first letter is relevant) then a +backtrace is printed when a serious run-time error occurs. To disable +the backtracing, set the variable to @samp{n}, @samp{N}, @samp{0}. +Default is to print a backtrace unless the @option{-fno-backtrace} +compile option was used. + +@node GFORTRAN_FORMATTED_BUFFER_SIZE +@section @env{GFORTRAN_FORMATTED_BUFFER_SIZE}---Set buffer size for formatted I/O + +The @env{GFORTRAN_FORMATTED_BUFFER_SIZE} environment variable +specifies buffer size in bytes to be used for formatted output. +The default value is 8192. + +@node GFORTRAN_UNFORMATTED_BUFFER_SIZE +@section @env{GFORTRAN_UNFORMATTED_BUFFER_SIZE}---Set buffer size for unformatted I/O + +The @env{GFORTRAN_UNFORMATTED_BUFFER_SIZE} environment variable +specifies buffer size in bytes to be used for unformatted output. +The default value is 131072. + +@c ===================================================================== +@c PART II: LANGUAGE REFERENCE +@c ===================================================================== + +@tex +\part{II}{Language Reference} +@end tex + + + +@c --------------------------------------------------------------------- +@c Compiler Characteristics +@c --------------------------------------------------------------------- + +@node Compiler Characteristics +@chapter Compiler Characteristics + +This chapter describes certain characteristics of the GNU Fortran +compiler, that are not specified by the Fortran standard, but which +might in some way or another become visible to the programmer. + +@menu +* KIND Type Parameters:: +* Internal representation of LOGICAL variables:: +* Evaluation of logical expressions:: +* MAX and MIN intrinsics with REAL NaN arguments:: +* Thread-safety of the runtime library:: +* Data consistency and durability:: +* Files opened without an explicit ACTION= specifier:: +* File operations on symbolic links:: +* File format of unformatted sequential files:: +* Asynchronous I/O:: +@end menu + + +@node KIND Type Parameters +@section KIND Type Parameters +@cindex kind + +The @code{KIND} type parameters supported by GNU Fortran for the primitive +data types are: + +@table @code + +@item INTEGER +1, 2, 4, 8*, 16*, default: 4** + +@item LOGICAL +1, 2, 4, 8*, 16*, default: 4** + +@item REAL +4, 8, 10*, 16*, default: 4*** + +@item COMPLEX +4, 8, 10*, 16*, default: 4*** + +@item DOUBLE PRECISION +4, 8, 10*, 16*, default: 8*** + +@item CHARACTER +1, 4, default: 1 + +@end table + +@noindent +* not available on all systems @* +** unless @option{-fdefault-integer-8} is used @* +*** unless @option{-fdefault-real-8} is used (see @ref{Fortran Dialect Options}) + +@noindent +The @code{KIND} value matches the storage size in bytes, except for +@code{COMPLEX} where the storage size is twice as much (or both real and +imaginary part are a real value of the given size). It is recommended to use +the @ref{SELECTED_CHAR_KIND}, @ref{SELECTED_INT_KIND} and +@ref{SELECTED_REAL_KIND} intrinsics or the @code{INT8}, @code{INT16}, +@code{INT32}, @code{INT64}, @code{REAL32}, @code{REAL64}, and @code{REAL128} +parameters of the @code{ISO_FORTRAN_ENV} module instead of the concrete values. +The available kind parameters can be found in the constant arrays +@code{CHARACTER_KINDS}, @code{INTEGER_KINDS}, @code{LOGICAL_KINDS} and +@code{REAL_KINDS} in the @ref{ISO_FORTRAN_ENV} module. For C interoperability, +the kind parameters of the @ref{ISO_C_BINDING} module should be used. + + +@node Internal representation of LOGICAL variables +@section Internal representation of LOGICAL variables +@cindex logical, variable representation + +The Fortran standard does not specify how variables of @code{LOGICAL} +type are represented, beyond requiring that @code{LOGICAL} variables +of default kind have the same storage size as default @code{INTEGER} +and @code{REAL} variables. The GNU Fortran internal representation is +as follows. + +A @code{LOGICAL(KIND=N)} variable is represented as an +@code{INTEGER(KIND=N)} variable, however, with only two permissible +values: @code{1} for @code{.TRUE.} and @code{0} for +@code{.FALSE.}. Any other integer value results in undefined behavior. + +See also @ref{Argument passing conventions} and @ref{Interoperability with C}. + + +@node Evaluation of logical expressions +@section Evaluation of logical expressions + +The Fortran standard does not require the compiler to evaluate all parts of an +expression, if they do not contribute to the final result. For logical +expressions with @code{.AND.} or @code{.OR.} operators, in particular, GNU +Fortran will optimize out function calls (even to impure functions) if the +result of the expression can be established without them. However, since not +all compilers do that, and such an optimization can potentially modify the +program flow and subsequent results, GNU Fortran throws warnings for such +situations with the @option{-Wfunction-elimination} flag. + + +@node MAX and MIN intrinsics with REAL NaN arguments +@section MAX and MIN intrinsics with REAL NaN arguments +@cindex MAX, MIN, NaN + +The Fortran standard does not specify what the result of the +@code{MAX} and @code{MIN} intrinsics are if one of the arguments is a +@code{NaN}. Accordingly, the GNU Fortran compiler does not specify +that either, as this allows for faster and more compact code to be +generated. If the programmer wishes to take some specific action in +case one of the arguments is a @code{NaN}, it is necessary to +explicitly test the arguments before calling @code{MAX} or @code{MIN}, +e.g. with the @code{IEEE_IS_NAN} function from the intrinsic module +@code{IEEE_ARITHMETIC}. + + +@node Thread-safety of the runtime library +@section Thread-safety of the runtime library +@cindex thread-safety, threads + +GNU Fortran can be used in programs with multiple threads, e.g.@: by +using OpenMP, by calling OS thread handling functions via the +@code{ISO_C_BINDING} facility, or by GNU Fortran compiled library code +being called from a multi-threaded program. + +The GNU Fortran runtime library, (@code{libgfortran}), supports being +called concurrently from multiple threads with the following +exceptions. + +During library initialization, the C @code{getenv} function is used, +which need not be thread-safe. Similarly, the @code{getenv} +function is used to implement the @code{GET_ENVIRONMENT_VARIABLE} and +@code{GETENV} intrinsics. It is the responsibility of the user to +ensure that the environment is not being updated concurrently when any +of these actions are taking place. + +The @code{EXECUTE_COMMAND_LINE} and @code{SYSTEM} intrinsics are +implemented with the @code{system} function, which need not be +thread-safe. It is the responsibility of the user to ensure that +@code{system} is not called concurrently. + +For platforms not supporting thread-safe POSIX functions, further +functionality might not be thread-safe. For details, please consult +the documentation for your operating system. + +The GNU Fortran runtime library uses various C library functions that +depend on the locale, such as @code{strtod} and @code{snprintf}. In +order to work correctly in locale-aware programs that set the locale +using @code{setlocale}, the locale is reset to the default ``C'' +locale while executing a formatted @code{READ} or @code{WRITE} +statement. On targets supporting the POSIX 2008 per-thread locale +functions (e.g. @code{newlocale}, @code{uselocale}, +@code{freelocale}), these are used and thus the global locale set +using @code{setlocale} or the per-thread locales in other threads are +not affected. However, on targets lacking this functionality, the +global LC_NUMERIC locale is set to ``C'' during the formatted I/O. +Thus, on such targets it's not safe to call @code{setlocale} +concurrently from another thread while a Fortran formatted I/O +operation is in progress. Also, other threads doing something +dependent on the LC_NUMERIC locale might not work correctly if a +formatted I/O operation is in progress in another thread. + +@node Data consistency and durability +@section Data consistency and durability +@cindex consistency, durability + +This section contains a brief overview of data and metadata +consistency and durability issues when doing I/O. + +With respect to durability, GNU Fortran makes no effort to ensure that +data is committed to stable storage. If this is required, the GNU +Fortran programmer can use the intrinsic @code{FNUM} to retrieve the +low level file descriptor corresponding to an open Fortran unit. Then, +using e.g. the @code{ISO_C_BINDING} feature, one can call the +underlying system call to flush dirty data to stable storage, such as +@code{fsync} on POSIX, @code{_commit} on MingW, or @code{fcntl(fd, +F_FULLSYNC, 0)} on Mac OS X. The following example shows how to call +fsync: + +@smallexample + ! Declare the interface for POSIX fsync function + interface + function fsync (fd) bind(c,name="fsync") + use iso_c_binding, only: c_int + integer(c_int), value :: fd + integer(c_int) :: fsync + end function fsync + end interface + + ! Variable declaration + integer :: ret + + ! Opening unit 10 + open (10,file="foo") + + ! ... + ! Perform I/O on unit 10 + ! ... + + ! Flush and sync + flush(10) + ret = fsync(fnum(10)) + + ! Handle possible error + if (ret /= 0) stop "Error calling FSYNC" +@end smallexample + +With respect to consistency, for regular files GNU Fortran uses +buffered I/O in order to improve performance. This buffer is flushed +automatically when full and in some other situations, e.g. when +closing a unit. It can also be explicitly flushed with the +@code{FLUSH} statement. Also, the buffering can be turned off with the +@code{GFORTRAN_UNBUFFERED_ALL} and +@code{GFORTRAN_UNBUFFERED_PRECONNECTED} environment variables. Special +files, such as terminals and pipes, are always unbuffered. Sometimes, +however, further things may need to be done in order to allow other +processes to see data that GNU Fortran has written, as follows. + +The Windows platform supports a relaxed metadata consistency model, +where file metadata is written to the directory lazily. This means +that, for instance, the @code{dir} command can show a stale size for a +file. One can force a directory metadata update by closing the unit, +or by calling @code{_commit} on the file descriptor. Note, though, +that @code{_commit} will force all dirty data to stable storage, which +is often a very slow operation. + +The Network File System (NFS) implements a relaxed consistency model +called open-to-close consistency. Closing a file forces dirty data and +metadata to be flushed to the server, and opening a file forces the +client to contact the server in order to revalidate cached +data. @code{fsync} will also force a flush of dirty data and metadata +to the server. Similar to @code{open} and @code{close}, acquiring and +releasing @code{fcntl} file locks, if the server supports them, will +also force cache validation and flushing dirty data and metadata. + + +@node Files opened without an explicit ACTION= specifier +@section Files opened without an explicit ACTION= specifier +@cindex open, action + +The Fortran standard says that if an @code{OPEN} statement is executed +without an explicit @code{ACTION=} specifier, the default value is +processor dependent. GNU Fortran behaves as follows: + +@enumerate +@item Attempt to open the file with @code{ACTION='READWRITE'} +@item If that fails, try to open with @code{ACTION='READ'} +@item If that fails, try to open with @code{ACTION='WRITE'} +@item If that fails, generate an error +@end enumerate + + +@node File operations on symbolic links +@section File operations on symbolic links +@cindex file, symbolic link + +This section documents the behavior of GNU Fortran for file operations on +symbolic links, on systems that support them. + +@itemize + +@item Results of INQUIRE statements of the ``inquire by file'' form will +relate to the target of the symbolic link. For example, +@code{INQUIRE(FILE="foo",EXIST=ex)} will set @var{ex} to @var{.true.} if +@var{foo} is a symbolic link pointing to an existing file, and @var{.false.} +if @var{foo} points to an non-existing file (``dangling'' symbolic link). + +@item Using the @code{OPEN} statement with a @code{STATUS="NEW"} specifier +on a symbolic link will result in an error condition, whether the symbolic +link points to an existing target or is dangling. + +@item If a symbolic link was connected, using the @code{CLOSE} statement +with a @code{STATUS="DELETE"} specifier will cause the symbolic link itself +to be deleted, not its target. + +@end itemize + +@node File format of unformatted sequential files +@section File format of unformatted sequential files +@cindex file, unformatted sequential +@cindex unformatted sequential +@cindex sequential, unformatted +@cindex record marker +@cindex subrecord + +Unformatted sequential files are stored as logical records using +record markers. Each logical record consists of one of more +subrecords. + +Each subrecord consists of a leading record marker, the data written +by the user program, and a trailing record marker. The record markers +are four-byte integers by default, and eight-byte integers if the +@option{-fmax-subrecord-length=8} option (which exists for backwards +compability only) is in effect. + +The representation of the record markers is that of unformatted files +given with the @option{-fconvert} option, the @ref{CONVERT specifier} +in an open statement or the @ref{GFORTRAN_CONVERT_UNIT} environment +variable. + +The maximum number of bytes of user data in a subrecord is 2147483639 +(2 GiB - 9) for a four-byte record marker. This limit can be lowered +with the @option{-fmax-subrecord-length} option, although this is +rarely useful. If the length of a logical record exceeds this limit, +the data is distributed among several subrecords. + +The absolute of the number stored in the record markers is the number +of bytes of user data in the corresponding subrecord. If the leading +record marker of a subrecord contains a negative number, another +subrecord follows the current one. If the trailing record marker +contains a negative number, then there is a preceding subrecord. + +In the most simple case, with only one subrecord per logical record, +both record markers contain the number of bytes of user data in the +record. + +The format for unformatted sequential data can be duplicated using +unformatted stream, as shown in the example program for an unformatted +record containing a single subrecord: + +@smallexample +program main + use iso_fortran_env, only: int32 + implicit none + integer(int32) :: i + real, dimension(10) :: a, b + call random_number(a) + open (10,file='test.dat',form='unformatted',access='stream') + inquire (iolength=i) a + write (10) i, a, i + close (10) + open (10,file='test.dat',form='unformatted') + read (10) b + if (all (a == b)) print *,'success!' +end program main +@end smallexample + +@node Asynchronous I/O +@section Asynchronous I/O +@cindex input/output, asynchronous +@cindex asynchronous I/O + +Asynchronous I/O is supported if the program is linked against the +POSIX thread library. If that is not the case, all I/O is performed +as synchronous. On systems which do not support pthread condition +variables, such as AIX, I/O is also performed as synchronous. + +On some systems, such as Darwin or Solaris, the POSIX thread library +is always linked in, so asynchronous I/O is always performed. On other +sytems, such as Linux, it is necessary to specify @option{-pthread}, +@option{-lpthread} or @option{-fopenmp} during the linking step. + +@c --------------------------------------------------------------------- +@c Extensions +@c --------------------------------------------------------------------- + +@c Maybe this chapter should be merged with the 'Standards' section, +@c whenever that is written :-) + +@node Extensions +@chapter Extensions +@cindex extensions + +The two sections below detail the extensions to standard Fortran that are +implemented in GNU Fortran, as well as some of the popular or +historically important extensions that are not (or not yet) implemented. +For the latter case, we explain the alternatives available to GNU Fortran +users, including replacement by standard-conforming code or GNU +extensions. + +@menu +* Extensions implemented in GNU Fortran:: +* Extensions not implemented in GNU Fortran:: +@end menu + + +@node Extensions implemented in GNU Fortran +@section Extensions implemented in GNU Fortran +@cindex extensions, implemented + +GNU Fortran implements a number of extensions over standard Fortran. +This chapter contains information on their syntax and meaning. There +are currently two categories of GNU Fortran extensions, those that +provide functionality beyond that provided by any standard, and those +that are supported by GNU Fortran purely for backward compatibility +with legacy compilers. By default, @option{-std=gnu} allows the +compiler to accept both types of extensions, but to warn about the use +of the latter. Specifying either @option{-std=f95}, +@option{-std=f2003}, @option{-std=f2008}, or @option{-std=f2018} +disables both types of extensions, and @option{-std=legacy} allows +both without warning. The special compile flag @option{-fdec} enables +additional compatibility extensions along with those enabled by +@option{-std=legacy}. + +@menu +* Old-style kind specifications:: +* Old-style variable initialization:: +* Extensions to namelist:: +* X format descriptor without count field:: +* Commas in FORMAT specifications:: +* Missing period in FORMAT specifications:: +* Default widths for F@comma{} G and I format descriptors:: +* I/O item lists:: +* @code{Q} exponent-letter:: +* BOZ literal constants:: +* Real array indices:: +* Unary operators:: +* Implicitly convert LOGICAL and INTEGER values:: +* Hollerith constants support:: +* Character conversion:: +* Cray pointers:: +* CONVERT specifier:: +* OpenMP:: +* OpenACC:: +* Argument list functions:: +* Read/Write after EOF marker:: +* STRUCTURE and RECORD:: +* UNION and MAP:: +* Type variants for integer intrinsics:: +* AUTOMATIC and STATIC attributes:: +* Extended math intrinsics:: +* Form feed as whitespace:: +* TYPE as an alias for PRINT:: +* %LOC as an rvalue:: +* .XOR. operator:: +* Bitwise logical operators:: +* Extended I/O specifiers:: +* Legacy PARAMETER statements:: +* Default exponents:: +@end menu + +@node Old-style kind specifications +@subsection Old-style kind specifications +@cindex kind, old-style + +GNU Fortran allows old-style kind specifications in declarations. These +look like: +@smallexample + TYPESPEC*size x,y,z +@end smallexample +@noindent +where @code{TYPESPEC} is a basic type (@code{INTEGER}, @code{REAL}, +etc.), and where @code{size} is a byte count corresponding to the +storage size of a valid kind for that type. (For @code{COMPLEX} +variables, @code{size} is the total size of the real and imaginary +parts.) The statement then declares @code{x}, @code{y} and @code{z} to +be of type @code{TYPESPEC} with the appropriate kind. This is +equivalent to the standard-conforming declaration +@smallexample + TYPESPEC(k) x,y,z +@end smallexample +@noindent +where @code{k} is the kind parameter suitable for the intended precision. As +kind parameters are implementation-dependent, use the @code{KIND}, +@code{SELECTED_INT_KIND} and @code{SELECTED_REAL_KIND} intrinsics to retrieve +the correct value, for instance @code{REAL*8 x} can be replaced by: +@smallexample +INTEGER, PARAMETER :: dbl = KIND(1.0d0) +REAL(KIND=dbl) :: x +@end smallexample + +@node Old-style variable initialization +@subsection Old-style variable initialization + +GNU Fortran allows old-style initialization of variables of the +form: +@smallexample + INTEGER i/1/,j/2/ + REAL x(2,2) /3*0.,1./ +@end smallexample +The syntax for the initializers is as for the @code{DATA} statement, but +unlike in a @code{DATA} statement, an initializer only applies to the +variable immediately preceding the initialization. In other words, +something like @code{INTEGER I,J/2,3/} is not valid. This style of +initialization is only allowed in declarations without double colons +(@code{::}); the double colons were introduced in Fortran 90, which also +introduced a standard syntax for initializing variables in type +declarations. + +Examples of standard-conforming code equivalent to the above example +are: +@smallexample +! Fortran 90 + INTEGER :: i = 1, j = 2 + REAL :: x(2,2) = RESHAPE((/0.,0.,0.,1./),SHAPE(x)) +! Fortran 77 + INTEGER i, j + REAL x(2,2) + DATA i/1/, j/2/, x/3*0.,1./ +@end smallexample + +Note that variables which are explicitly initialized in declarations +or in @code{DATA} statements automatically acquire the @code{SAVE} +attribute. + +@node Extensions to namelist +@subsection Extensions to namelist +@cindex Namelist + +GNU Fortran fully supports the Fortran 95 standard for namelist I/O +including array qualifiers, substrings and fully qualified derived types. +The output from a namelist write is compatible with namelist read. The +output has all names in upper case and indentation to column 1 after the +namelist name. Two extensions are permitted: + +Old-style use of @samp{$} instead of @samp{&} +@smallexample +$MYNML + X(:)%Y(2) = 1.0 2.0 3.0 + CH(1:4) = "abcd" +$END +@end smallexample + +It should be noted that the default terminator is @samp{/} rather than +@samp{&END}. + +Querying of the namelist when inputting from stdin. After at least +one space, entering @samp{?} sends to stdout the namelist name and the names of +the variables in the namelist: +@smallexample + ? + +&mynml + x + x%y + ch +&end +@end smallexample + +Entering @samp{=?} outputs the namelist to stdout, as if +@code{WRITE(*,NML = mynml)} had been called: +@smallexample +=? + +&MYNML + X(1)%Y= 0.000000 , 1.000000 , 0.000000 , + X(2)%Y= 0.000000 , 2.000000 , 0.000000 , + X(3)%Y= 0.000000 , 3.000000 , 0.000000 , + CH=abcd, / +@end smallexample + +To aid this dialog, when input is from stdin, errors send their +messages to stderr and execution continues, even if @code{IOSTAT} is set. + +@code{PRINT} namelist is permitted. This causes an error if +@option{-std=f95} is used. +@smallexample +PROGRAM test_print + REAL, dimension (4) :: x = (/1.0, 2.0, 3.0, 4.0/) + NAMELIST /mynml/ x + PRINT mynml +END PROGRAM test_print +@end smallexample + +Expanded namelist reads are permitted. This causes an error if +@option{-std=f95} is used. In the following example, the first element +of the array will be given the value 0.00 and the two succeeding +elements will be given the values 1.00 and 2.00. +@smallexample +&MYNML + X(1,1) = 0.00 , 1.00 , 2.00 +/ +@end smallexample + +When writing a namelist, if no @code{DELIM=} is specified, by default a +double quote is used to delimit character strings. If -std=F95, F2003, +or F2008, etc, the delim status is set to 'none'. Defaulting to +quotes ensures that namelists with character strings can be subsequently +read back in accurately. + +@node X format descriptor without count field +@subsection @code{X} format descriptor without count field + +To support legacy codes, GNU Fortran permits the count field of the +@code{X} edit descriptor in @code{FORMAT} statements to be omitted. +When omitted, the count is implicitly assumed to be one. + +@smallexample + PRINT 10, 2, 3 +10 FORMAT (I1, X, I1) +@end smallexample + +@node Commas in FORMAT specifications +@subsection Commas in @code{FORMAT} specifications + +To support legacy codes, GNU Fortran allows the comma separator +to be omitted immediately before and after character string edit +descriptors in @code{FORMAT} statements. A comma with no following format +decriptor is permited if the @option{-fdec-blank-format-item} is given on +the command line. This is considered non-conforming code and is +discouraged. + +@smallexample + PRINT 10, 2, 3 +10 FORMAT ('FOO='I1' BAR='I2) + print 20, 5, 6 +20 FORMAT (I3, I3,) +@end smallexample + + +@node Missing period in FORMAT specifications +@subsection Missing period in @code{FORMAT} specifications + +To support legacy codes, GNU Fortran allows missing periods in format +specifications if and only if @option{-std=legacy} is given on the +command line. This is considered non-conforming code and is +discouraged. + +@smallexample + REAL :: value + READ(*,10) value +10 FORMAT ('F4') +@end smallexample + +@node Default widths for F@comma{} G and I format descriptors +@subsection Default widths for @code{F}, @code{G} and @code{I} format descriptors + +To support legacy codes, GNU Fortran allows width to be omitted from format +specifications if and only if @option{-fdec-format-defaults} is given on the +command line. Default widths will be used. This is considered non-conforming +code and is discouraged. + +@smallexample + REAL :: value1 + INTEGER :: value2 + WRITE(*,10) value1, value1, value2 +10 FORMAT ('F, G, I') +@end smallexample + + +@node I/O item lists +@subsection I/O item lists +@cindex I/O item lists + +To support legacy codes, GNU Fortran allows the input item list +of the @code{READ} statement, and the output item lists of the +@code{WRITE} and @code{PRINT} statements, to start with a comma. + +@node @code{Q} exponent-letter +@subsection @code{Q} exponent-letter +@cindex @code{Q} exponent-letter + +GNU Fortran accepts real literal constants with an exponent-letter +of @code{Q}, for example, @code{1.23Q45}. The constant is interpreted +as a @code{REAL(16)} entity on targets that support this type. If +the target does not support @code{REAL(16)} but has a @code{REAL(10)} +type, then the real-literal-constant will be interpreted as a +@code{REAL(10)} entity. In the absence of @code{REAL(16)} and +@code{REAL(10)}, an error will occur. + +@node BOZ literal constants +@subsection BOZ literal constants +@cindex BOZ literal constants + +Besides decimal constants, Fortran also supports binary (@code{b}), +octal (@code{o}) and hexadecimal (@code{z}) integer constants. The +syntax is: @samp{prefix quote digits quote}, where the prefix is +either @code{b}, @code{o} or @code{z}, quote is either @code{'} or +@code{"} and the digits are @code{0} or @code{1} for binary, +between @code{0} and @code{7} for octal, and between @code{0} and +@code{F} for hexadecimal. (Example: @code{b'01011101'}.) + +Up to Fortran 95, BOZ literal constants were only allowed to initialize +integer variables in DATA statements. Since Fortran 2003 BOZ literal +constants are also allowed as actual arguments to the @code{REAL}, +@code{DBLE}, @code{INT} and @code{CMPLX} intrinsic functions. +The BOZ literal constant is simply a string of bits, which is padded +or truncated as needed, during conversion to a numeric type. The +Fortran standard states that the treatment of the sign bit is processor +dependent. Gfortran interprets the sign bit as a user would expect. + +As a deprecated extension, GNU Fortran allows hexadecimal BOZ literal +constants to be specified using the @code{X} prefix. That the BOZ literal +constant can also be specified by adding a suffix to the string, for +example, @code{Z'ABC'} and @code{'ABC'X} are equivalent. Additionally, +as extension, BOZ literals are permitted in some contexts outside of +@code{DATA} and the intrinsic functions listed in the Fortran standard. +Use @option{-fallow-invalid-boz} to enable the extension. + +@node Real array indices +@subsection Real array indices +@cindex array, indices of type real + +As an extension, GNU Fortran allows the use of @code{REAL} expressions +or variables as array indices. + +@node Unary operators +@subsection Unary operators +@cindex operators, unary + +As an extension, GNU Fortran allows unary plus and unary minus operators +to appear as the second operand of binary arithmetic operators without +the need for parenthesis. + +@smallexample + X = Y * -Z +@end smallexample + +@node Implicitly convert LOGICAL and INTEGER values +@subsection Implicitly convert @code{LOGICAL} and @code{INTEGER} values +@cindex conversion, to integer +@cindex conversion, to logical + +As an extension for backwards compatibility with other compilers, GNU +Fortran allows the implicit conversion of @code{LOGICAL} values to +@code{INTEGER} values and vice versa. When converting from a +@code{LOGICAL} to an @code{INTEGER}, @code{.FALSE.} is interpreted as +zero, and @code{.TRUE.} is interpreted as one. When converting from +@code{INTEGER} to @code{LOGICAL}, the value zero is interpreted as +@code{.FALSE.} and any nonzero value is interpreted as @code{.TRUE.}. + +@smallexample + LOGICAL :: l + l = 1 +@end smallexample +@smallexample + INTEGER :: i + i = .TRUE. +@end smallexample + +However, there is no implicit conversion of @code{INTEGER} values in +@code{if}-statements, nor of @code{LOGICAL} or @code{INTEGER} values +in I/O operations. + +@node Hollerith constants support +@subsection Hollerith constants support +@cindex Hollerith constants + +GNU Fortran supports Hollerith constants in assignments, @code{DATA} +statements, function and subroutine arguments. A Hollerith constant is +written as a string of characters preceded by an integer constant +indicating the character count, and the letter @code{H} or +@code{h}, and stored in bytewise fashion in a numeric (@code{INTEGER}, +@code{REAL}, or @code{COMPLEX}), @code{LOGICAL} or @code{CHARACTER} variable. +The constant will be padded with spaces or truncated to fit the size of +the variable in which it is stored. + +Examples of valid uses of Hollerith constants: +@smallexample + complex*16 x(2) + data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/ + x(1) = 16HABCDEFGHIJKLMNOP + call foo (4h abc) +@end smallexample + +Examples of Hollerith constants: +@smallexample + integer*4 a + a = 0H ! Invalid, at least one character is needed. + a = 4HAB12 ! Valid + a = 8H12345678 ! Valid, but the Hollerith constant will be truncated. + a = 3Hxyz ! Valid, but the Hollerith constant will be padded. +@end smallexample + +In general, Hollerith constants were used to provide a rudimentary +facility for handling character strings in early Fortran compilers, +prior to the introduction of @code{CHARACTER} variables in Fortran 77; +in those cases, the standard-compliant equivalent is to convert the +program to use proper character strings. On occasion, there may be a +case where the intent is specifically to initialize a numeric variable +with a given byte sequence. In these cases, the same result can be +obtained by using the @code{TRANSFER} statement, as in this example. +@smallexample + integer(kind=4) :: a + a = transfer ("abcd", a) ! equivalent to: a = 4Habcd +@end smallexample + +The use of the @option{-fdec} option extends support of Hollerith constants +to comparisons: +@smallexample + integer*4 a + a = 4hABCD + if (a .ne. 4habcd) then + write(*,*) "no match" + end if +@end smallexample + +Supported types are numeric (@code{INTEGER}, @code{REAL}, or @code{COMPLEX}), +and @code{CHARACTER}. + +@node Character conversion +@subsection Character conversion +@cindex conversion, to character + +Allowing character literals to be used in a similar way to Hollerith constants +is a non-standard extension. This feature is enabled using +-fdec-char-conversions and only applies to character literals of @code{kind=1}. + +Character literals can be used in @code{DATA} statements and assignments with +numeric (@code{INTEGER}, @code{REAL}, or @code{COMPLEX}) or @code{LOGICAL} +variables. Like Hollerith constants they are copied byte-wise fashion. The +constant will be padded with spaces or truncated to fit the size of the +variable in which it is stored. + +Examples: +@smallexample + integer*4 x + data x / 'abcd' / + + x = 'A' ! Will be padded. + x = 'ab1234' ! Will be truncated. +@end smallexample + + +@node Cray pointers +@subsection Cray pointers +@cindex pointer, Cray + +Cray pointers are part of a non-standard extension that provides a +C-like pointer in Fortran. This is accomplished through a pair of +variables: an integer "pointer" that holds a memory address, and a +"pointee" that is used to dereference the pointer. + +Pointer/pointee pairs are declared in statements of the form: +@smallexample + pointer ( , ) +@end smallexample +or, +@smallexample + pointer ( , ), ( , ), ... +@end smallexample +The pointer is an integer that is intended to hold a memory address. +The pointee may be an array or scalar. +If an assumed-size array is permitted within the scoping unit, a +pointee can be an assumed-size array. +That is, the last dimension may be left unspecified by using a @code{*} +in place of a value. A pointee cannot be an assumed shape array. +No space is allocated for the pointee. + +The pointee may have its type declared before or after the pointer +statement, and its array specification (if any) may be declared +before, during, or after the pointer statement. The pointer may be +declared as an integer prior to the pointer statement. However, some +machines have default integer sizes that are different than the size +of a pointer, and so the following code is not portable: +@smallexample + integer ipt + pointer (ipt, iarr) +@end smallexample +If a pointer is declared with a kind that is too small, the compiler +will issue a warning; the resulting binary will probably not work +correctly, because the memory addresses stored in the pointers may be +truncated. It is safer to omit the first line of the above example; +if explicit declaration of ipt's type is omitted, then the compiler +will ensure that ipt is an integer variable large enough to hold a +pointer. + +Pointer arithmetic is valid with Cray pointers, but it is not the same +as C pointer arithmetic. Cray pointers are just ordinary integers, so +the user is responsible for determining how many bytes to add to a +pointer in order to increment it. Consider the following example: +@smallexample + real target(10) + real pointee(10) + pointer (ipt, pointee) + ipt = loc (target) + ipt = ipt + 1 +@end smallexample +The last statement does not set @code{ipt} to the address of +@code{target(1)}, as it would in C pointer arithmetic. Adding @code{1} +to @code{ipt} just adds one byte to the address stored in @code{ipt}. + +Any expression involving the pointee will be translated to use the +value stored in the pointer as the base address. + +To get the address of elements, this extension provides an intrinsic +function @code{LOC()}. The @code{LOC()} function is equivalent to the +@code{&} operator in C, except the address is cast to an integer type: +@smallexample + real ar(10) + pointer(ipt, arpte(10)) + real arpte + ipt = loc(ar) ! Makes arpte is an alias for ar + arpte(1) = 1.0 ! Sets ar(1) to 1.0 +@end smallexample +The pointer can also be set by a call to the @code{MALLOC} intrinsic +(see @ref{MALLOC}). + +Cray pointees often are used to alias an existing variable. For +example: +@smallexample + integer target(10) + integer iarr(10) + pointer (ipt, iarr) + ipt = loc(target) +@end smallexample +As long as @code{ipt} remains unchanged, @code{iarr} is now an alias for +@code{target}. The optimizer, however, will not detect this aliasing, so +it is unsafe to use @code{iarr} and @code{target} simultaneously. Using +a pointee in any way that violates the Fortran aliasing rules or +assumptions is illegal. It is the user's responsibility to avoid doing +this; the compiler works under the assumption that no such aliasing +occurs. + +Cray pointers will work correctly when there is no aliasing (i.e., when +they are used to access a dynamically allocated block of memory), and +also in any routine where a pointee is used, but any variable with which +it shares storage is not used. Code that violates these rules may not +run as the user intends. This is not a bug in the optimizer; any code +that violates the aliasing rules is illegal. (Note that this is not +unique to GNU Fortran; any Fortran compiler that supports Cray pointers +will ``incorrectly'' optimize code with illegal aliasing.) + +There are a number of restrictions on the attributes that can be applied +to Cray pointers and pointees. Pointees may not have the +@code{ALLOCATABLE}, @code{INTENT}, @code{OPTIONAL}, @code{DUMMY}, +@code{TARGET}, @code{INTRINSIC}, or @code{POINTER} attributes. Pointers +may not have the @code{DIMENSION}, @code{POINTER}, @code{TARGET}, +@code{ALLOCATABLE}, @code{EXTERNAL}, or @code{INTRINSIC} attributes, nor +may they be function results. Pointees may not occur in more than one +pointer statement. A pointee cannot be a pointer. Pointees cannot occur +in equivalence, common, or data statements. + +A Cray pointer may also point to a function or a subroutine. For +example, the following excerpt is valid: +@smallexample + implicit none + external sub + pointer (subptr,subpte) + external subpte + subptr = loc(sub) + call subpte() + [...] + subroutine sub + [...] + end subroutine sub +@end smallexample + +A pointer may be modified during the course of a program, and this +will change the location to which the pointee refers. However, when +pointees are passed as arguments, they are treated as ordinary +variables in the invoked function. Subsequent changes to the pointer +will not change the base address of the array that was passed. + +@node CONVERT specifier +@subsection @code{CONVERT} specifier +@cindex @code{CONVERT} specifier + +GNU Fortran allows the conversion of unformatted data between little- +and big-endian representation to facilitate moving of data +between different systems. The conversion can be indicated with +the @code{CONVERT} specifier on the @code{OPEN} statement. +@xref{GFORTRAN_CONVERT_UNIT}, for an alternative way of specifying +the data format via an environment variable. + +Valid values for @code{CONVERT} on most systems are: +@itemize @w{} +@item @code{CONVERT='NATIVE'} Use the native format. This is the default. +@item @code{CONVERT='SWAP'} Swap between little- and big-endian. +@item @code{CONVERT='LITTLE_ENDIAN'} Use the little-endian representation +for unformatted files. +@item @code{CONVERT='BIG_ENDIAN'} Use the big-endian representation for +unformatted files. +@end itemize +On POWER systems which support @option{-mabi=ieeelongdouble}, +there are additional options, which can be combined with the others +with commas. Those are +@itemize @w{} +@item @code{CONVERT='R16_IEEE'} Use IEEE 128-bit format for +@code{REAL(KIND=16)}. +@item @code{CONVERT='R16_IBM'} Use IBM @code{long double} format for +real@code{REAL(KIND=16)}. +@end itemize + +Using the option could look like this: +@smallexample + open(file='big.dat',form='unformatted',access='sequential', & + convert='big_endian') +@end smallexample + +The value of the conversion can be queried by using +@code{INQUIRE(CONVERT=ch)}. The values returned are +@code{'BIG_ENDIAN'} and @code{'LITTLE_ENDIAN'}. + +@code{CONVERT} works between big- and little-endian for +@code{INTEGER} values of all supported kinds and for @code{REAL} +on IEEE systems of kinds 4 and 8. Conversion between different +``extended double'' types on different architectures such as +m68k and x86_64, which GNU Fortran +supports as @code{REAL(KIND=10)} and @code{REAL(KIND=16)}, will +probably not work. + +@emph{Note that the values specified via the GFORTRAN_CONVERT_UNIT +environment variable will override the CONVERT specifier in the +open statement}. This is to give control over data formats to +users who do not have the source code of their program available. + +Using anything but the native representation for unformatted data +carries a significant speed overhead. If speed in this area matters +to you, it is best if you use this only for data that needs to be +portable. + +@node OpenMP +@subsection OpenMP +@cindex OpenMP + +OpenMP (Open Multi-Processing) is an application programming +interface (API) that supports multi-platform shared memory +multiprocessing programming in C/C++ and Fortran on many +architectures, including Unix and Microsoft Windows platforms. +It consists of a set of compiler directives, library routines, +and environment variables that influence run-time behavior. + +GNU Fortran strives to be compatible to the +@uref{https://openmp.org/specifications/, +OpenMP Application Program Interface v4.5}. + +To enable the processing of the OpenMP directive @code{!$omp} in +free-form source code; the @code{c$omp}, @code{*$omp} and @code{!$omp} +directives in fixed form; the @code{!$} conditional compilation sentinels +in free form; and the @code{c$}, @code{*$} and @code{!$} sentinels +in fixed form, @command{gfortran} needs to be invoked with the +@option{-fopenmp}. This also arranges for automatic linking of the +GNU Offloading and Multi Processing Runtime Library +@ref{Top,,libgomp,libgomp,GNU Offloading and Multi Processing Runtime +Library}. + +The OpenMP Fortran runtime library routines are provided both in a +form of a Fortran 90 module named @code{omp_lib} and in a form of +a Fortran @code{include} file named @file{omp_lib.h}. + +An example of a parallelized loop taken from Appendix A.1 of +the OpenMP Application Program Interface v2.5: +@smallexample +SUBROUTINE A1(N, A, B) + INTEGER I, N + REAL B(N), A(N) +!$OMP PARALLEL DO !I is private by default + DO I=2,N + B(I) = (A(I) + A(I-1)) / 2.0 + ENDDO +!$OMP END PARALLEL DO +END SUBROUTINE A1 +@end smallexample + +Please note: +@itemize +@item +@option{-fopenmp} implies @option{-frecursive}, i.e., all local arrays +will be allocated on the stack. When porting existing code to OpenMP, +this may lead to surprising results, especially to segmentation faults +if the stacksize is limited. + +@item +On glibc-based systems, OpenMP enabled applications cannot be statically +linked due to limitations of the underlying pthreads-implementation. It +might be possible to get a working solution if +@command{-Wl,--whole-archive -lpthread -Wl,--no-whole-archive} is added +to the command line. However, this is not supported by @command{gcc} and +thus not recommended. +@end itemize + +@node OpenACC +@subsection OpenACC +@cindex OpenACC + +OpenACC is an application programming interface (API) that supports +offloading of code to accelerator devices. It consists of a set of +compiler directives, library routines, and environment variables that +influence run-time behavior. + +GNU Fortran strives to be compatible to the +@uref{https://www.openacc.org/, OpenACC Application Programming +Interface v2.6}. + +To enable the processing of the OpenACC directive @code{!$acc} in +free-form source code; the @code{c$acc}, @code{*$acc} and @code{!$acc} +directives in fixed form; the @code{!$} conditional compilation +sentinels in free form; and the @code{c$}, @code{*$} and @code{!$} +sentinels in fixed form, @command{gfortran} needs to be invoked with +the @option{-fopenacc}. This also arranges for automatic linking of +the GNU Offloading and Multi Processing Runtime Library +@ref{Top,,libgomp,libgomp,GNU Offloading and Multi Processing Runtime +Library}. + +The OpenACC Fortran runtime library routines are provided both in a +form of a Fortran 90 module named @code{openacc} and in a form of a +Fortran @code{include} file named @file{openacc_lib.h}. + +@node Argument list functions +@subsection Argument list functions @code{%VAL}, @code{%REF} and @code{%LOC} +@cindex argument list functions +@cindex @code{%VAL} +@cindex @code{%REF} +@cindex @code{%LOC} + +GNU Fortran supports argument list functions @code{%VAL}, @code{%REF} +and @code{%LOC} statements, for backward compatibility with g77. +It is recommended that these should be used only for code that is +accessing facilities outside of GNU Fortran, such as operating system +or windowing facilities. It is best to constrain such uses to isolated +portions of a program--portions that deal specifically and exclusively +with low-level, system-dependent facilities. Such portions might well +provide a portable interface for use by the program as a whole, but are +themselves not portable, and should be thoroughly tested each time they +are rebuilt using a new compiler or version of a compiler. + +@code{%VAL} passes a scalar argument by value, @code{%REF} passes it by +reference and @code{%LOC} passes its memory location. Since gfortran +already passes scalar arguments by reference, @code{%REF} is in effect +a do-nothing. @code{%LOC} has the same effect as a Fortran pointer. + +An example of passing an argument by value to a C subroutine foo.: +@smallexample +C +C prototype void foo_ (float x); +C + external foo + real*4 x + x = 3.14159 + call foo (%VAL (x)) + end +@end smallexample + +For details refer to the g77 manual +@uref{https://gcc.gnu.org/@/onlinedocs/@/gcc-3.4.6/@/g77/@/index.html#Top}. + +Also, @code{c_by_val.f} and its partner @code{c_by_val.c} of the +GNU Fortran testsuite are worth a look. + +@node Read/Write after EOF marker +@subsection Read/Write after EOF marker +@cindex @code{EOF} +@cindex @code{BACKSPACE} +@cindex @code{REWIND} + +Some legacy codes rely on allowing @code{READ} or @code{WRITE} after the +EOF file marker in order to find the end of a file. GNU Fortran normally +rejects these codes with a run-time error message and suggests the user +consider @code{BACKSPACE} or @code{REWIND} to properly position +the file before the EOF marker. As an extension, the run-time error may +be disabled using -std=legacy. + + +@node STRUCTURE and RECORD +@subsection @code{STRUCTURE} and @code{RECORD} +@cindex @code{STRUCTURE} +@cindex @code{RECORD} + +Record structures are a pre-Fortran-90 vendor extension to create +user-defined aggregate data types. Support for record structures in GNU +Fortran can be enabled with the @option{-fdec-structure} compile flag. +If you have a choice, you should instead use Fortran 90's ``derived types'', +which have a different syntax. + +In many cases, record structures can easily be converted to derived types. +To convert, replace @code{STRUCTURE /}@var{structure-name}@code{/} +by @code{TYPE} @var{type-name}. Additionally, replace +@code{RECORD /}@var{structure-name}@code{/} by +@code{TYPE(}@var{type-name}@code{)}. Finally, in the component access, +replace the period (@code{.}) by the percent sign (@code{%}). + +Here is an example of code using the non portable record structure syntax: + +@example +! Declaring a structure named ``item'' and containing three fields: +! an integer ID, an description string and a floating-point price. +STRUCTURE /item/ + INTEGER id + CHARACTER(LEN=200) description + REAL price +END STRUCTURE + +! Define two variables, an single record of type ``item'' +! named ``pear'', and an array of items named ``store_catalog'' +RECORD /item/ pear, store_catalog(100) + +! We can directly access the fields of both variables +pear.id = 92316 +pear.description = "juicy D'Anjou pear" +pear.price = 0.15 +store_catalog(7).id = 7831 +store_catalog(7).description = "milk bottle" +store_catalog(7).price = 1.2 + +! We can also manipulate the whole structure +store_catalog(12) = pear +print *, store_catalog(12) +@end example + +@noindent +This code can easily be rewritten in the Fortran 90 syntax as following: + +@example +! ``STRUCTURE /name/ ... END STRUCTURE'' becomes +! ``TYPE name ... END TYPE'' +TYPE item + INTEGER id + CHARACTER(LEN=200) description + REAL price +END TYPE + +! ``RECORD /name/ variable'' becomes ``TYPE(name) variable'' +TYPE(item) pear, store_catalog(100) + +! Instead of using a dot (.) to access fields of a record, the +! standard syntax uses a percent sign (%) +pear%id = 92316 +pear%description = "juicy D'Anjou pear" +pear%price = 0.15 +store_catalog(7)%id = 7831 +store_catalog(7)%description = "milk bottle" +store_catalog(7)%price = 1.2 + +! Assignments of a whole variable do not change +store_catalog(12) = pear +print *, store_catalog(12) +@end example + +@noindent +GNU Fortran implements STRUCTURES like derived types with the following +rules and exceptions: + +@itemize @bullet +@item Structures act like derived types with the @code{SEQUENCE} attribute. +Otherwise they may contain no specifiers. + +@item Structures may contain a special field with the name @code{%FILL}. +This will create an anonymous component which cannot be accessed but occupies +space just as if a component of the same type was declared in its place, useful +for alignment purposes. As an example, the following structure will consist +of at least sixteen bytes: + +@smallexample +structure /padded/ + character(4) start + character(8) %FILL + character(4) end +end structure +@end smallexample + +@item Structures may share names with other symbols. For example, the following +is invalid for derived types, but valid for structures: + +@smallexample +structure /header/ + ! ... +end structure +record /header/ header +@end smallexample + +@item Structure types may be declared nested within another parent structure. +The syntax is: +@smallexample +structure /type-name/ + ... + structure [//] +... +@end smallexample + +The type name may be ommitted, in which case the structure type itself is +anonymous, and other structures of the same type cannot be instantiated. The +following shows some examples: + +@example +structure /appointment/ + ! nested structure definition: app_time is an array of two 'time' + structure /time/ app_time (2) + integer(1) hour, minute + end structure + character(10) memo +end structure + +! The 'time' structure is still usable +record /time/ now +now = time(5, 30) + +... + +structure /appointment/ + ! anonymous nested structure definition + structure start, end + integer(1) hour, minute + end structure + character(10) memo +end structure +@end example + +@item Structures may contain @code{UNION} blocks. For more detail see the +section on @ref{UNION and MAP}. + +@item Structures support old-style initialization of components, like +those described in @ref{Old-style variable initialization}. For array +initializers, an initializer may contain a repeat specification of the form +@code{ * }. The value of the integer +indicates the number of times to repeat the constant initializer when expanding +the initializer list. +@end itemize + +@node UNION and MAP +@subsection @code{UNION} and @code{MAP} +@cindex @code{UNION} +@cindex @code{MAP} + +Unions are an old vendor extension which were commonly used with the +non-standard @ref{STRUCTURE and RECORD} extensions. Use of @code{UNION} and +@code{MAP} is automatically enabled with @option{-fdec-structure}. + +A @code{UNION} declaration occurs within a structure; within the definition of +each union is a number of @code{MAP} blocks. Each @code{MAP} shares storage +with its sibling maps (in the same union), and the size of the union is the +size of the largest map within it, just as with unions in C. The major +difference is that component references do not indicate which union or map the +component is in (the compiler gets to figure that out). + +Here is a small example: +@smallexample +structure /myunion/ +union + map + character(2) w0, w1, w2 + end map + map + character(6) long + end map +end union +end structure + +record /myunion/ rec +! After this assignment... +rec.long = 'hello!' + +! The following is true: +! rec.w0 === 'he' +! rec.w1 === 'll' +! rec.w2 === 'o!' +@end smallexample + +The two maps share memory, and the size of the union is ultimately six bytes: + +@example +0 1 2 3 4 5 6 Byte offset +------------------------------- +| | | | | | | +------------------------------- + +^ W0 ^ W1 ^ W2 ^ + \-------/ \-------/ \-------/ + +^ LONG ^ + \---------------------------/ +@end example + +Following is an example mirroring the layout of an Intel x86_64 register: + +@example +structure /reg/ + union ! U0 ! rax + map + character(16) rx + end map + map + character(8) rh ! rah + union ! U1 + map + character(8) rl ! ral + end map + map + character(8) ex ! eax + end map + map + character(4) eh ! eah + union ! U2 + map + character(4) el ! eal + end map + map + character(4) x ! ax + end map + map + character(2) h ! ah + character(2) l ! al + end map + end union + end map + end union + end map + end union +end structure +record /reg/ a + +! After this assignment... +a.rx = 'AAAAAAAA.BBB.C.D' + +! The following is true: +a.rx === 'AAAAAAAA.BBB.C.D' +a.rh === 'AAAAAAAA' +a.rl === '.BBB.C.D' +a.ex === '.BBB.C.D' +a.eh === '.BBB' +a.el === '.C.D' +a.x === '.C.D' +a.h === '.C' +a.l === '.D' +@end example + +@node Type variants for integer intrinsics +@subsection Type variants for integer intrinsics +@cindex intrinsics, integer + +Similar to the D/C prefixes to real functions to specify the input/output +types, GNU Fortran offers B/I/J/K prefixes to integer functions for +compatibility with DEC programs. The types implied by each are: + +@example +@code{B} - @code{INTEGER(kind=1)} +@code{I} - @code{INTEGER(kind=2)} +@code{J} - @code{INTEGER(kind=4)} +@code{K} - @code{INTEGER(kind=8)} +@end example + +GNU Fortran supports these with the flag @option{-fdec-intrinsic-ints}. +Intrinsics for which prefixed versions are available and in what form are noted +in @ref{Intrinsic Procedures}. The complete list of supported intrinsics is +here: + +@multitable @columnfractions .2 .2 .2 .2 .2 + +@headitem Intrinsic @tab B @tab I @tab J @tab K + +@item @code{@ref{ABS}} + @tab @code{BABS} @tab @code{IIABS} @tab @code{JIABS} @tab @code{KIABS} +@item @code{@ref{BTEST}} + @tab @code{BBTEST} @tab @code{BITEST} @tab @code{BJTEST} @tab @code{BKTEST} +@item @code{@ref{IAND}} + @tab @code{BIAND} @tab @code{IIAND} @tab @code{JIAND} @tab @code{KIAND} +@item @code{@ref{IBCLR}} + @tab @code{BBCLR} @tab @code{IIBCLR} @tab @code{JIBCLR} @tab @code{KIBCLR} +@item @code{@ref{IBITS}} + @tab @code{BBITS} @tab @code{IIBITS} @tab @code{JIBITS} @tab @code{KIBITS} +@item @code{@ref{IBSET}} + @tab @code{BBSET} @tab @code{IIBSET} @tab @code{JIBSET} @tab @code{KIBSET} +@item @code{@ref{IEOR}} + @tab @code{BIEOR} @tab @code{IIEOR} @tab @code{JIEOR} @tab @code{KIEOR} +@item @code{@ref{IOR}} + @tab @code{BIOR} @tab @code{IIOR} @tab @code{JIOR} @tab @code{KIOR} +@item @code{@ref{ISHFT}} + @tab @code{BSHFT} @tab @code{IISHFT} @tab @code{JISHFT} @tab @code{KISHFT} +@item @code{@ref{ISHFTC}} + @tab @code{BSHFTC} @tab @code{IISHFTC} @tab @code{JISHFTC} @tab @code{KISHFTC} +@item @code{@ref{MOD}} + @tab @code{BMOD} @tab @code{IMOD} @tab @code{JMOD} @tab @code{KMOD} +@item @code{@ref{NOT}} + @tab @code{BNOT} @tab @code{INOT} @tab @code{JNOT} @tab @code{KNOT} +@item @code{@ref{REAL}} + @tab @code{--} @tab @code{FLOATI} @tab @code{FLOATJ} @tab @code{FLOATK} +@end multitable + +@node AUTOMATIC and STATIC attributes +@subsection @code{AUTOMATIC} and @code{STATIC} attributes +@cindex variable attributes +@cindex @code{AUTOMATIC} +@cindex @code{STATIC} + +With @option{-fdec-static} GNU Fortran supports the DEC extended attributes +@code{STATIC} and @code{AUTOMATIC} to provide explicit specification of entity +storage. These follow the syntax of the Fortran standard @code{SAVE} attribute. + +@code{STATIC} is exactly equivalent to @code{SAVE}, and specifies that +an entity should be allocated in static memory. As an example, @code{STATIC} +local variables will retain their values across multiple calls to a function. + +Entities marked @code{AUTOMATIC} will be stack automatic whenever possible. +@code{AUTOMATIC} is the default for local variables smaller than +@option{-fmax-stack-var-size}, unless @option{-fno-automatic} is given. This +attribute overrides @option{-fno-automatic}, @option{-fmax-stack-var-size}, and +blanket @code{SAVE} statements. + + +Examples: + +@example +subroutine f + integer, automatic :: i ! automatic variable + integer x, y ! static variables + save + ... +endsubroutine +@end example +@example +subroutine f + integer a, b, c, x, y, z + static :: x + save y + automatic z, c + ! a, b, c, and z are automatic + ! x and y are static +endsubroutine +@end example +@example +! Compiled with -fno-automatic +subroutine f + integer a, b, c, d + automatic :: a + ! a is automatic; b, c, and d are static +endsubroutine +@end example + +@node Extended math intrinsics +@subsection Extended math intrinsics +@cindex intrinsics, math +@cindex intrinsics, trigonometric functions + +GNU Fortran supports an extended list of mathematical intrinsics with the +compile flag @option{-fdec-math} for compatability with legacy code. +These intrinsics are described fully in @ref{Intrinsic Procedures} where it is +noted that they are extensions and should be avoided whenever possible. + +Specifically, @option{-fdec-math} enables the @ref{COTAN} intrinsic, and +trigonometric intrinsics which accept or produce values in degrees instead of +radians. Here is a summary of the new intrinsics: + +@multitable @columnfractions .5 .5 +@headitem Radians @tab Degrees +@item @code{@ref{ACOS}} @tab @code{@ref{ACOSD}}* +@item @code{@ref{ASIN}} @tab @code{@ref{ASIND}}* +@item @code{@ref{ATAN}} @tab @code{@ref{ATAND}}* +@item @code{@ref{ATAN2}} @tab @code{@ref{ATAN2D}}* +@item @code{@ref{COS}} @tab @code{@ref{COSD}}* +@item @code{@ref{COTAN}}* @tab @code{@ref{COTAND}}* +@item @code{@ref{SIN}} @tab @code{@ref{SIND}}* +@item @code{@ref{TAN}} @tab @code{@ref{TAND}}* +@end multitable + +* Enabled with @option{-fdec-math}. + +For advanced users, it may be important to know the implementation of these +functions. They are simply wrappers around the standard radian functions, which +have more accurate builtin versions. These functions convert their arguments +(or results) to degrees (or radians) by taking the value modulus 360 (or 2*pi) +and then multiplying it by a constant radian-to-degree (or degree-to-radian) +factor, as appropriate. The factor is computed at compile-time as 180/pi (or +pi/180). + +@node Form feed as whitespace +@subsection Form feed as whitespace +@cindex form feed whitespace + +Historically, legacy compilers allowed insertion of form feed characters ('\f', +ASCII 0xC) at the beginning of lines for formatted output to line printers, +though the Fortran standard does not mention this. GNU Fortran supports the +interpretation of form feed characters in source as whitespace for +compatibility. + +@node TYPE as an alias for PRINT +@subsection TYPE as an alias for PRINT +@cindex type alias print +For compatibility, GNU Fortran will interpret @code{TYPE} statements as +@code{PRINT} statements with the flag @option{-fdec}. With this flag asserted, +the following two examples are equivalent: + +@smallexample +TYPE *, 'hello world' +@end smallexample + +@smallexample +PRINT *, 'hello world' +@end smallexample + +@node %LOC as an rvalue +@subsection %LOC as an rvalue +@cindex LOC +Normally @code{%LOC} is allowed only in parameter lists. However the intrinsic +function @code{LOC} does the same thing, and is usable as the right-hand-side of +assignments. For compatibility, GNU Fortran supports the use of @code{%LOC} as +an alias for the builtin @code{LOC} with @option{-std=legacy}. With this +feature enabled the following two examples are equivalent: + +@smallexample +integer :: i, l +l = %loc(i) +call sub(l) +@end smallexample + +@smallexample +integer :: i +call sub(%loc(i)) +@end smallexample + +@node .XOR. operator +@subsection .XOR. operator +@cindex operators, xor + +GNU Fortran supports @code{.XOR.} as a logical operator with @code{-std=legacy} +for compatibility with legacy code. @code{.XOR.} is equivalent to +@code{.NEQV.}. That is, the output is true if and only if the inputs differ. + +@node Bitwise logical operators +@subsection Bitwise logical operators +@cindex logical, bitwise + +With @option{-fdec}, GNU Fortran relaxes the type constraints on +logical operators to allow integer operands, and performs the corresponding +bitwise operation instead. This flag is for compatibility only, and should be +avoided in new code. Consider: + +@smallexample + INTEGER :: i, j + i = z'33' + j = z'cc' + print *, i .AND. j +@end smallexample + +In this example, compiled with @option{-fdec}, GNU Fortran will +replace the @code{.AND.} operation with a call to the intrinsic +@code{@ref{IAND}} function, yielding the bitwise-and of @code{i} and @code{j}. + +Note that this conversion will occur if at least one operand is of integral +type. As a result, a logical operand will be converted to an integer when the +other operand is an integer in a logical operation. In this case, +@code{.TRUE.} is converted to @code{1} and @code{.FALSE.} to @code{0}. + +Here is the mapping of logical operator to bitwise intrinsic used with +@option{-fdec}: + +@multitable @columnfractions .25 .25 .5 +@headitem Operator @tab Intrinsic @tab Bitwise operation +@item @code{.NOT.} @tab @code{@ref{NOT}} @tab complement +@item @code{.AND.} @tab @code{@ref{IAND}} @tab intersection +@item @code{.OR.} @tab @code{@ref{IOR}} @tab union +@item @code{.NEQV.} @tab @code{@ref{IEOR}} @tab exclusive or +@item @code{.EQV.} @tab @code{@ref{NOT}(@ref{IEOR})} @tab complement of exclusive or +@end multitable + +@node Extended I/O specifiers +@subsection Extended I/O specifiers +@cindex @code{CARRIAGECONTROL} +@cindex @code{READONLY} +@cindex @code{SHARE} +@cindex @code{SHARED} +@cindex @code{NOSHARED} +@cindex I/O specifiers + +GNU Fortran supports the additional legacy I/O specifiers +@code{CARRIAGECONTROL}, @code{READONLY}, and @code{SHARE} with the +compile flag @option{-fdec}, for compatibility. + +@table @code +@item CARRIAGECONTROL +The @code{CARRIAGECONTROL} specifier allows a user to control line +termination settings between output records for an I/O unit. The specifier has +no meaning for readonly files. When @code{CARRAIGECONTROL} is specified upon +opening a unit for formatted writing, the exact @code{CARRIAGECONTROL} setting +determines what characters to write between output records. The syntax is: + +@smallexample +OPEN(..., CARRIAGECONTROL=cc) +@end smallexample + +Where @emph{cc} is a character expression that evaluates to one of the +following values: + +@multitable @columnfractions .2 .8 +@item @code{'LIST'} @tab One line feed between records (default) +@item @code{'FORTRAN'} @tab Legacy interpretation of the first character (see below) +@item @code{'NONE'} @tab No separator between records +@end multitable + +With @code{CARRIAGECONTROL='FORTRAN'}, when a record is written, the first +character of the input record is not written, and instead determines the output +record separator as follows: + +@multitable @columnfractions .3 .3 .4 +@headitem Leading character @tab Meaning @tab Output separating character(s) +@item @code{'+'} @tab Overprinting @tab Carriage return only +@item @code{'-'} @tab New line @tab Line feed and carriage return +@item @code{'0'} @tab Skip line @tab Two line feeds and carriage return +@item @code{'1'} @tab New page @tab Form feed and carriage return +@item @code{'$'} @tab Prompting @tab Line feed (no carriage return) +@item @code{CHAR(0)} @tab Overprinting (no advance) @tab None +@end multitable + +@item READONLY +The @code{READONLY} specifier may be given upon opening a unit, and is +equivalent to specifying @code{ACTION='READ'}, except that the file may not be +deleted on close (i.e. @code{CLOSE} with @code{STATUS="DELETE"}). The syntax +is: + +@smallexample +@code{OPEN(..., READONLY)} +@end smallexample + +@item SHARE +The @code{SHARE} specifier allows system-level locking on a unit upon opening +it for controlled access from multiple processes/threads. The @code{SHARE} +specifier has several forms: + +@smallexample +OPEN(..., SHARE=sh) +OPEN(..., SHARED) +OPEN(..., NOSHARED) +@end smallexample + +Where @emph{sh} in the first form is a character expression that evaluates to +a value as seen in the table below. The latter two forms are aliases +for particular values of @emph{sh}: + +@multitable @columnfractions .3 .3 .4 +@headitem Explicit form @tab Short form @tab Meaning +@item @code{SHARE='DENYRW'} @tab @code{NOSHARED} @tab Exclusive (write) lock +@item @code{SHARE='DENYNONE'} @tab @code{SHARED} @tab Shared (read) lock +@end multitable + +In general only one process may hold an exclusive (write) lock for a given file +at a time, whereas many processes may hold shared (read) locks for the same +file. + +The behavior of locking may vary with your operating system. On POSIX systems, +locking is implemented with @code{fcntl}. Consult your corresponding operating +system's manual pages for further details. Locking via @code{SHARE=} is not +supported on other systems. + +@end table + +@node Legacy PARAMETER statements +@subsection Legacy PARAMETER statements +@cindex PARAMETER + +For compatibility, GNU Fortran supports legacy PARAMETER statements without +parentheses with @option{-std=legacy}. A warning is emitted if used with +@option{-std=gnu}, and an error is acknowledged with a real Fortran standard +flag (@option{-std=f95}, etc...). These statements take the following form: + +@smallexample +implicit real (E) +parameter e = 2.718282 +real c +parameter c = 3.0e8 +@end smallexample + +@node Default exponents +@subsection Default exponents +@cindex exponent + +For compatibility, GNU Fortran supports a default exponent of zero in real +constants with @option{-fdec}. For example, @code{9e} would be +interpreted as @code{9e0}, rather than an error. + + +@node Extensions not implemented in GNU Fortran +@section Extensions not implemented in GNU Fortran +@cindex extensions, not implemented + +The long history of the Fortran language, its wide use and broad +userbase, the large number of different compiler vendors and the lack of +some features crucial to users in the first standards have lead to the +existence of a number of important extensions to the language. While +some of the most useful or popular extensions are supported by the GNU +Fortran compiler, not all existing extensions are supported. This section +aims at listing these extensions and offering advice on how best make +code that uses them running with the GNU Fortran compiler. + +@c More can be found here: +@c -- https://gcc.gnu.org/onlinedocs/gcc-3.4.6/g77/Missing-Features.html +@c -- the list of Fortran and libgfortran bugs closed as WONTFIX: +@c http://tinyurl.com/2u4h5y + +@menu +* ENCODE and DECODE statements:: +* Variable FORMAT expressions:: +@c * TYPE and ACCEPT I/O Statements:: +@c * DEFAULTFILE, DISPOSE and RECORDTYPE I/O specifiers:: +@c * Omitted arguments in procedure call:: +* Alternate complex function syntax:: +* Volatile COMMON blocks:: +* OPEN( ... NAME=):: +* Q edit descriptor:: +@end menu + +@node ENCODE and DECODE statements +@subsection @code{ENCODE} and @code{DECODE} statements +@cindex @code{ENCODE} +@cindex @code{DECODE} + +GNU Fortran does not support the @code{ENCODE} and @code{DECODE} +statements. These statements are best replaced by @code{READ} and +@code{WRITE} statements involving internal files (@code{CHARACTER} +variables and arrays), which have been part of the Fortran standard since +Fortran 77. For example, replace a code fragment like + +@smallexample + INTEGER*1 LINE(80) + REAL A, B, C +c ... Code that sets LINE + DECODE (80, 9000, LINE) A, B, C + 9000 FORMAT (1X, 3(F10.5)) +@end smallexample + +@noindent +with the following: + +@smallexample + CHARACTER(LEN=80) LINE + REAL A, B, C +c ... Code that sets LINE + READ (UNIT=LINE, FMT=9000) A, B, C + 9000 FORMAT (1X, 3(F10.5)) +@end smallexample + +Similarly, replace a code fragment like + +@smallexample + INTEGER*1 LINE(80) + REAL A, B, C +c ... Code that sets A, B and C + ENCODE (80, 9000, LINE) A, B, C + 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5)) +@end smallexample + +@noindent +with the following: + +@smallexample + CHARACTER(LEN=80) LINE + REAL A, B, C +c ... Code that sets A, B and C + WRITE (UNIT=LINE, FMT=9000) A, B, C + 9000 FORMAT (1X, 'OUTPUT IS ', 3(F10.5)) +@end smallexample + + +@node Variable FORMAT expressions +@subsection Variable @code{FORMAT} expressions +@cindex @code{FORMAT} + +A variable @code{FORMAT} expression is format statement which includes +angle brackets enclosing a Fortran expression: @code{FORMAT(I)}. GNU +Fortran does not support this legacy extension. The effect of variable +format expressions can be reproduced by using the more powerful (and +standard) combination of internal output and string formats. For example, +replace a code fragment like this: + +@smallexample + WRITE(6,20) INT1 + 20 FORMAT(I) +@end smallexample + +@noindent +with the following: + +@smallexample +c Variable declaration + CHARACTER(LEN=20) FMT +c +c Other code here... +c + WRITE(FMT,'("(I", I0, ")")') N+1 + WRITE(6,FMT) INT1 +@end smallexample + +@noindent +or with: + +@smallexample +c Variable declaration + CHARACTER(LEN=20) FMT +c +c Other code here... +c + WRITE(FMT,*) N+1 + WRITE(6,"(I" // ADJUSTL(FMT) // ")") INT1 +@end smallexample + + +@node Alternate complex function syntax +@subsection Alternate complex function syntax +@cindex Complex function + +Some Fortran compilers, including @command{g77}, let the user declare +complex functions with the syntax @code{COMPLEX FUNCTION name*16()}, as +well as @code{COMPLEX*16 FUNCTION name()}. Both are non-standard, legacy +extensions. @command{gfortran} accepts the latter form, which is more +common, but not the former. + + +@node Volatile COMMON blocks +@subsection Volatile @code{COMMON} blocks +@cindex @code{VOLATILE} +@cindex @code{COMMON} + +Some Fortran compilers, including @command{g77}, let the user declare +@code{COMMON} with the @code{VOLATILE} attribute. This is +invalid standard Fortran syntax and is not supported by +@command{gfortran}. Note that @command{gfortran} accepts +@code{VOLATILE} variables in @code{COMMON} blocks since revision 4.3. + + +@node OPEN( ... NAME=) +@subsection @code{OPEN( ... NAME=)} +@cindex @code{NAME} + +Some Fortran compilers, including @command{g77}, let the user declare +@code{OPEN( ... NAME=)}. This is +invalid standard Fortran syntax and is not supported by +@command{gfortran}. @code{OPEN( ... NAME=)} should be replaced +with @code{OPEN( ... FILE=)}. + +@node Q edit descriptor +@subsection @code{Q} edit descriptor +@cindex @code{Q} edit descriptor + +Some Fortran compilers provide the @code{Q} edit descriptor, which +transfers the number of characters left within an input record into an +integer variable. + +A direct replacement of the @code{Q} edit descriptor is not available +in @command{gfortran}. How to replicate its functionality using +standard-conforming code depends on what the intent of the original +code is. + +Options to replace @code{Q} may be to read the whole line into a +character variable and then counting the number of non-blank +characters left using @code{LEN_TRIM}. Another method may be to use +formatted stream, read the data up to the position where the @code{Q} +descriptor occurred, use @code{INQUIRE} to get the file position, +count the characters up to the next @code{NEW_LINE} and then start +reading from the position marked previously. + + +@c --------------------------------------------------------------------- +@c --------------------------------------------------------------------- +@c Mixed-Language Programming +@c --------------------------------------------------------------------- + +@node Mixed-Language Programming +@chapter Mixed-Language Programming +@cindex Interoperability +@cindex Mixed-language programming + +@menu +* Interoperability with C:: +* GNU Fortran Compiler Directives:: +* Non-Fortran Main Program:: +* Naming and argument-passing conventions:: +@end menu + +This chapter is about mixed-language interoperability, but also +applies if you link Fortran code compiled by different compilers. In +most cases, use of the C Binding features of the Fortran 2003 and +later standards is sufficient. + +For example, it is possible to mix Fortran code with C++ code as well +as C, if you declare the interface functions as @code{extern "C"} on +the C++ side and @code{BIND(C)} on the Fortran side, and follow the +rules for interoperability with C. Note that you cannot manipulate +C++ class objects in Fortran or vice versa except as opaque pointers. + +You can use the @command{gfortran} command to link both Fortran and +non-Fortran code into the same program, or you can use @command{gcc} +or @command{g++} if you also add an explicit @option{-lgfortran} option +to link with the Fortran library. If your main program is written in +C or some other language instead of Fortran, see +@ref{Non-Fortran Main Program}, below. + +@node Interoperability with C +@section Interoperability with C +@cindex interoperability with C +@cindex C interoperability + +@menu +* Intrinsic Types:: +* Derived Types and struct:: +* Interoperable Global Variables:: +* Interoperable Subroutines and Functions:: +* Working with C Pointers:: +* Further Interoperability of Fortran with C:: +@end menu + +Since Fortran 2003 (ISO/IEC 1539-1:2004(E)) there is a +standardized way to generate procedure and derived-type +declarations and global variables that are interoperable with C +(ISO/IEC 9899:1999). The @code{BIND(C)} attribute has been added +to inform the compiler that a symbol shall be interoperable with C; +also, some constraints are added. Note, however, that not +all C features have a Fortran equivalent or vice versa. For instance, +neither C's unsigned integers nor C's functions with variable number +of arguments have an equivalent in Fortran. + +Note that array dimensions are reversely ordered in C and that arrays in +C always start with index 0 while in Fortran they start by default with +1. Thus, an array declaration @code{A(n,m)} in Fortran matches +@code{A[m][n]} in C and accessing the element @code{A(i,j)} matches +@code{A[j-1][i-1]}. The element following @code{A(i,j)} (C: @code{A[j-1][i-1]}; +assuming @math{i < n}) in memory is @code{A(i+1,j)} (C: @code{A[j-1][i]}). + +@node Intrinsic Types +@subsection Intrinsic Types +@cindex C intrinsic type interoperability +@cindex intrinsic type interoperability with C +@cindex interoperability, intrinsic type + +In order to ensure that exactly the same variable type and kind is used +in C and Fortran, you should use the named constants for kind parameters +that are defined in the @code{ISO_C_BINDING} intrinsic module. +That module contains named constants of character type representing +the escaped special characters in C, such as newline. +For a list of the constants, see @ref{ISO_C_BINDING}. + +For logical types, please note that the Fortran standard only guarantees +interoperability between C99's @code{_Bool} and Fortran's @code{C_Bool}-kind +logicals and C99 defines that @code{true} has the value 1 and @code{false} +the value 0. Using any other integer value with GNU Fortran's @code{LOGICAL} +(with any kind parameter) gives an undefined result. (Passing other integer +values than 0 and 1 to GCC's @code{_Bool} is also undefined, unless the +integer is explicitly or implicitly casted to @code{_Bool}.) + +@node Derived Types and struct +@subsection Derived Types and struct +@cindex C derived type and struct interoperability +@cindex derived type interoperability with C +@cindex interoperability, derived type and struct + +For compatibility of derived types with @code{struct}, use +the @code{BIND(C)} attribute in the type declaration. For instance, the +following type declaration + +@smallexample + USE ISO_C_BINDING + TYPE, BIND(C) :: myType + INTEGER(C_INT) :: i1, i2 + INTEGER(C_SIGNED_CHAR) :: i3 + REAL(C_DOUBLE) :: d1 + COMPLEX(C_FLOAT_COMPLEX) :: c1 + CHARACTER(KIND=C_CHAR) :: str(5) + END TYPE +@end smallexample + +@noindent +matches the following @code{struct} declaration in C + +@smallexample + struct @{ + int i1, i2; + /* Note: "char" might be signed or unsigned. */ + signed char i3; + double d1; + float _Complex c1; + char str[5]; + @} myType; +@end smallexample + +Derived types with the C binding attribute shall not have the @code{sequence} +attribute, type parameters, the @code{extends} attribute, nor type-bound +procedures. Every component must be of interoperable type and kind and may not +have the @code{pointer} or @code{allocatable} attribute. The names of the +components are irrelevant for interoperability. + +As there exist no direct Fortran equivalents, neither unions nor structs +with bit field or variable-length array members are interoperable. + +@node Interoperable Global Variables +@subsection Interoperable Global Variables +@cindex C variable interoperability +@cindex variable interoperability with C +@cindex interoperability, variable + +Variables can be made accessible from C using the C binding attribute, +optionally together with specifying a binding name. Those variables +have to be declared in the declaration part of a @code{MODULE}, +be of interoperable type, and have neither the @code{pointer} nor +the @code{allocatable} attribute. + +@smallexample + MODULE m + USE myType_module + USE ISO_C_BINDING + integer(C_INT), bind(C, name="_MyProject_flags") :: global_flag + type(myType), bind(C) :: tp + END MODULE +@end smallexample + +Here, @code{_MyProject_flags} is the case-sensitive name of the variable +as seen from C programs while @code{global_flag} is the case-insensitive +name as seen from Fortran. If no binding name is specified, as for +@var{tp}, the C binding name is the (lowercase) Fortran binding name. +If a binding name is specified, only a single variable may be after the +double colon. Note of warning: You cannot use a global variable to +access @var{errno} of the C library as the C standard allows it to be +a macro. Use the @code{IERRNO} intrinsic (GNU extension) instead. + +@node Interoperable Subroutines and Functions +@subsection Interoperable Subroutines and Functions +@cindex C procedure interoperability +@cindex procedure interoperability with C +@cindex function interoperability with C +@cindex subroutine interoperability with C +@cindex interoperability, subroutine and function + +Subroutines and functions have to have the @code{BIND(C)} attribute to +be compatible with C. The dummy argument declaration is relatively +straightforward. However, one needs to be careful because C uses +call-by-value by default while Fortran behaves usually similar to +call-by-reference. Furthermore, strings and pointers are handled +differently. + +To pass a variable by value, use the @code{VALUE} attribute. +Thus, the following C prototype + +@smallexample +@code{int func(int i, int *j)} +@end smallexample + +@noindent +matches the Fortran declaration + +@smallexample + integer(c_int) function func(i,j) + use iso_c_binding, only: c_int + integer(c_int), VALUE :: i + integer(c_int) :: j +@end smallexample + +Note that pointer arguments also frequently need the @code{VALUE} attribute, +see @ref{Working with C Pointers}. + +Strings are handled quite differently in C and Fortran. In C a string +is a @code{NUL}-terminated array of characters while in Fortran each string +has a length associated with it and is thus not terminated (by e.g. +@code{NUL}). For example, if you want to use the following C function, + +@smallexample + #include + void print_C(char *string) /* equivalent: char string[] */ + @{ + printf("%s\n", string); + @} +@end smallexample + +@noindent +to print ``Hello World'' from Fortran, you can call it using + +@smallexample + use iso_c_binding, only: C_CHAR, C_NULL_CHAR + interface + subroutine print_c(string) bind(C, name="print_C") + use iso_c_binding, only: c_char + character(kind=c_char) :: string(*) + end subroutine print_c + end interface + call print_c(C_CHAR_"Hello World"//C_NULL_CHAR) +@end smallexample + +As the example shows, you need to ensure that the +string is @code{NUL} terminated. Additionally, the dummy argument +@var{string} of @code{print_C} is a length-one assumed-size +array; using @code{character(len=*)} is not allowed. The example +above uses @code{c_char_"Hello World"} to ensure the string +literal has the right type; typically the default character +kind and @code{c_char} are the same and thus @code{"Hello World"} +is equivalent. However, the standard does not guarantee this. + +The use of strings is now further illustrated using the C library +function @code{strncpy}, whose prototype is + +@smallexample + char *strncpy(char *restrict s1, const char *restrict s2, size_t n); +@end smallexample + +@noindent +The function @code{strncpy} copies at most @var{n} characters from +string @var{s2} to @var{s1} and returns @var{s1}. In the following +example, we ignore the return value: + +@smallexample + use iso_c_binding + implicit none + character(len=30) :: str,str2 + interface + ! Ignore the return value of strncpy -> subroutine + ! "restrict" is always assumed if we do not pass a pointer + subroutine strncpy(dest, src, n) bind(C) + import + character(kind=c_char), intent(out) :: dest(*) + character(kind=c_char), intent(in) :: src(*) + integer(c_size_t), value, intent(in) :: n + end subroutine strncpy + end interface + str = repeat('X',30) ! Initialize whole string with 'X' + call strncpy(str, c_char_"Hello World"//C_NULL_CHAR, & + len(c_char_"Hello World",kind=c_size_t)) + print '(a)', str ! prints: "Hello WorldXXXXXXXXXXXXXXXXXXX" + end +@end smallexample + +The intrinsic procedures are described in @ref{Intrinsic Procedures}. + +@node Working with C Pointers +@subsection Working with C Pointers +@cindex C pointers +@cindex pointers, C + +C pointers are represented in Fortran via the special opaque derived +type @code{type(c_ptr)} (with private components). C pointers are distinct +from Fortran objects with the @code{POINTER} attribute. Thus one needs to +use intrinsic conversion procedures to convert from or to C pointers. +For some applications, using an assumed type (@code{TYPE(*)}) can be +an alternative to a C pointer, and you can also use library routines +to access Fortran pointers from C. See @ref{Further Interoperability +of Fortran with C}. + +Here is an example of using C pointers in Fortran: + +@smallexample + use iso_c_binding + type(c_ptr) :: cptr1, cptr2 + integer, target :: array(7), scalar + integer, pointer :: pa(:), ps + cptr1 = c_loc(array(1)) ! The programmer needs to ensure that the + ! array is contiguous if required by the C + ! procedure + cptr2 = c_loc(scalar) + call c_f_pointer(cptr2, ps) + call c_f_pointer(cptr2, pa, shape=[7]) +@end smallexample + +When converting C to Fortran arrays, the one-dimensional @code{SHAPE} argument +has to be passed. + +If a pointer is a dummy argument of an interoperable procedure, it usually +has to be declared using the @code{VALUE} attribute. @code{void*} +matches @code{TYPE(C_PTR), VALUE}, while @code{TYPE(C_PTR)} alone +matches @code{void**}. + +Procedure pointers are handled analogously to pointers; the C type is +@code{TYPE(C_FUNPTR)} and the intrinsic conversion procedures are +@code{C_F_PROCPOINTER} and @code{C_FUNLOC}. + +Let us consider two examples of actually passing a procedure pointer from +C to Fortran and vice versa. Note that these examples are also very +similar to passing ordinary pointers between both languages. First, +consider this code in C: + +@smallexample +/* Procedure implemented in Fortran. */ +void get_values (void (*)(double)); + +/* Call-back routine we want called from Fortran. */ +void +print_it (double x) +@{ + printf ("Number is %f.\n", x); +@} + +/* Call Fortran routine and pass call-back to it. */ +void +foobar () +@{ + get_values (&print_it); +@} +@end smallexample + +A matching implementation for @code{get_values} in Fortran, that correctly +receives the procedure pointer from C and is able to call it, is given +in the following @code{MODULE}: + +@smallexample +MODULE m + IMPLICIT NONE + + ! Define interface of call-back routine. + ABSTRACT INTERFACE + SUBROUTINE callback (x) + USE, INTRINSIC :: ISO_C_BINDING + REAL(KIND=C_DOUBLE), INTENT(IN), VALUE :: x + END SUBROUTINE callback + END INTERFACE + +CONTAINS + + ! Define C-bound procedure. + SUBROUTINE get_values (cproc) BIND(C) + USE, INTRINSIC :: ISO_C_BINDING + TYPE(C_FUNPTR), INTENT(IN), VALUE :: cproc + + PROCEDURE(callback), POINTER :: proc + + ! Convert C to Fortran procedure pointer. + CALL C_F_PROCPOINTER (cproc, proc) + + ! Call it. + CALL proc (1.0_C_DOUBLE) + CALL proc (-42.0_C_DOUBLE) + CALL proc (18.12_C_DOUBLE) + END SUBROUTINE get_values + +END MODULE m +@end smallexample + +Next, we want to call a C routine that expects a procedure pointer argument +and pass it a Fortran procedure (which clearly must be interoperable!). +Again, the C function may be: + +@smallexample +int +call_it (int (*func)(int), int arg) +@{ + return func (arg); +@} +@end smallexample + +It can be used as in the following Fortran code: + +@smallexample +MODULE m + USE, INTRINSIC :: ISO_C_BINDING + IMPLICIT NONE + + ! Define interface of C function. + INTERFACE + INTEGER(KIND=C_INT) FUNCTION call_it (func, arg) BIND(C) + USE, INTRINSIC :: ISO_C_BINDING + TYPE(C_FUNPTR), INTENT(IN), VALUE :: func + INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg + END FUNCTION call_it + END INTERFACE + +CONTAINS + + ! Define procedure passed to C function. + ! It must be interoperable! + INTEGER(KIND=C_INT) FUNCTION double_it (arg) BIND(C) + INTEGER(KIND=C_INT), INTENT(IN), VALUE :: arg + double_it = arg + arg + END FUNCTION double_it + + ! Call C function. + SUBROUTINE foobar () + TYPE(C_FUNPTR) :: cproc + INTEGER(KIND=C_INT) :: i + + ! Get C procedure pointer. + cproc = C_FUNLOC (double_it) + + ! Use it. + DO i = 1_C_INT, 10_C_INT + PRINT *, call_it (cproc, i) + END DO + END SUBROUTINE foobar + +END MODULE m +@end smallexample + +@node Further Interoperability of Fortran with C +@subsection Further Interoperability of Fortran with C +@cindex Further Interoperability of Fortran with C +@cindex TS 29113 +@cindex array descriptor +@cindex dope vector +@cindex assumed-type +@cindex assumed-rank + +GNU Fortran implements the Technical Specification ISO/IEC TS +29113:2012, which extends the interoperability support of Fortran 2003 +and Fortran 2008 and is now part of the 2018 Fortran standard. +Besides removing some restrictions and constraints, the Technical +Specification adds assumed-type (@code{TYPE(*)}) and assumed-rank +(@code{DIMENSION(..)}) variables and allows for interoperability of +assumed-shape, assumed-rank, and deferred-shape arrays, as well as +allocatables and pointers. Objects of these types are passed to +@code{BIND(C)} functions as descriptors with a standard interface, +declared in the header file @code{}. + +Note: Currently, GNU Fortran does not use internally the array descriptor +(dope vector) as specified in the Technical Specification, but uses +an array descriptor with different fields in functions without the +@code{BIND(C)} attribute. Arguments to functions marked @code{BIND(C)} +are converted to the specified form. If you need to access GNU Fortran's +internal array descriptor, you can use the Chasm Language Interoperability +Tools, @url{http://chasm-interop.sourceforge.net/}. + +@node GNU Fortran Compiler Directives +@section GNU Fortran Compiler Directives + +@menu +* ATTRIBUTES directive:: +* UNROLL directive:: +* BUILTIN directive:: +* IVDEP directive:: +* VECTOR directive:: +* NOVECTOR directive:: +@end menu + +@node ATTRIBUTES directive +@subsection ATTRIBUTES directive + +The Fortran standard describes how a conforming program shall +behave; however, the exact implementation is not standardized. In order +to allow the user to choose specific implementation details, compiler +directives can be used to set attributes of variables and procedures +which are not part of the standard. Whether a given attribute is +supported and its exact effects depend on both the operating system and +on the processor; see +@ref{Top,,C Extensions,gcc,Using the GNU Compiler Collection (GCC)} +for details. + +For procedures and procedure pointers, the following attributes can +be used to change the calling convention: + +@itemize +@item @code{CDECL} -- standard C calling convention +@item @code{STDCALL} -- convention where the called procedure pops the stack +@item @code{FASTCALL} -- part of the arguments are passed via registers +instead using the stack +@end itemize + +Besides changing the calling convention, the attributes also influence +the decoration of the symbol name, e.g., by a leading underscore or by +a trailing at-sign followed by the number of bytes on the stack. When +assigning a procedure to a procedure pointer, both should use the same +calling convention. + +On some systems, procedures and global variables (module variables and +@code{COMMON} blocks) need special handling to be accessible when they +are in a shared library. The following attributes are available: + +@itemize +@item @code{DLLEXPORT} -- provide a global pointer to a pointer in the DLL +@item @code{DLLIMPORT} -- reference the function or variable using a +global pointer +@end itemize + +For dummy arguments, the @code{NO_ARG_CHECK} attribute can be used; in +other compilers, it is also known as @code{IGNORE_TKR}. For dummy arguments +with this attribute actual arguments of any type and kind (similar to +@code{TYPE(*)}), scalars and arrays of any rank (no equivalent +in Fortran standard) are accepted. As with @code{TYPE(*)}, the argument +is unlimited polymorphic and no type information is available. +Additionally, the argument may only be passed to dummy arguments +with the @code{NO_ARG_CHECK} attribute and as argument to the +@code{PRESENT} intrinsic function and to @code{C_LOC} of the +@code{ISO_C_BINDING} module. + +Variables with @code{NO_ARG_CHECK} attribute shall be of assumed-type +(@code{TYPE(*)}; recommended) or of type @code{INTEGER}, @code{LOGICAL}, +@code{REAL} or @code{COMPLEX}. They shall not have the @code{ALLOCATE}, +@code{CODIMENSION}, @code{INTENT(OUT)}, @code{POINTER} or @code{VALUE} +attribute; furthermore, they shall be either scalar or of assumed-size +(@code{dimension(*)}). As @code{TYPE(*)}, the @code{NO_ARG_CHECK} attribute +requires an explicit interface. + +@itemize +@item @code{NO_ARG_CHECK} -- disable the type, kind and rank checking +@item @code{DEPRECATED} -- print a warning when using a such-tagged +deprecated procedure, variable or parameter; the warning can be suppressed +with @option{-Wno-deprecated-declarations}. +@end itemize + + +The attributes are specified using the syntax + +@code{!GCC$ ATTRIBUTES} @var{attribute-list} @code{::} @var{variable-list} + +where in free-form source code only whitespace is allowed before @code{!GCC$} +and in fixed-form source code @code{!GCC$}, @code{cGCC$} or @code{*GCC$} shall +start in the first column. + +For procedures, the compiler directives shall be placed into the body +of the procedure; for variables and procedure pointers, they shall be in +the same declaration part as the variable or procedure pointer. + + +@node UNROLL directive +@subsection UNROLL directive + +The syntax of the directive is + +@code{!GCC$ unroll N} + +You can use this directive to control how many times a loop should be unrolled. +It must be placed immediately before a @code{DO} loop and applies only to the +loop that follows. N is an integer constant specifying the unrolling factor. +The values of 0 and 1 block any unrolling of the loop. + + +@node BUILTIN directive +@subsection BUILTIN directive + +The syntax of the directive is + +@code{!GCC$ BUILTIN (B) attributes simd FLAGS IF('target')} + +You can use this directive to define which middle-end built-ins provide vector +implementations. @code{B} is name of the middle-end built-in. @code{FLAGS} +are optional and must be either "(inbranch)" or "(notinbranch)". +@code{IF} statement is optional and is used to filter multilib ABIs +for the built-in that should be vectorized. Example usage: + +@smallexample +!GCC$ builtin (sinf) attributes simd (notinbranch) if('x86_64') +@end smallexample + +The purpose of the directive is to provide an API among the GCC compiler and +the GNU C Library which would define vector implementations of math routines. + + +@node IVDEP directive +@subsection IVDEP directive + +The syntax of the directive is + +@code{!GCC$ ivdep} + +This directive tells the compiler to ignore vector dependencies in the +following loop. It must be placed immediately before a @code{DO} loop +and applies only to the loop that follows. + +Sometimes the compiler may not have sufficient information to decide +whether a particular loop is vectorizable due to potential +dependencies between iterations. The purpose of the directive is to +tell the compiler that vectorization is safe. + +This directive is intended for annotation of existing code. For new +code it is recommended to consider OpenMP SIMD directives as potential +alternative. + + +@node VECTOR directive +@subsection VECTOR directive + +The syntax of the directive is + +@code{!GCC$ vector} + +This directive tells the compiler to vectorize the following loop. It +must be placed immediately before a @code{DO} loop and applies only to +the loop that follows. + + +@node NOVECTOR directive +@subsection NOVECTOR directive + +The syntax of the directive is + +@code{!GCC$ novector} + +This directive tells the compiler to not vectorize the following loop. +It must be placed immediately before a @code{DO} loop and applies only +to the loop that follows. + + +@node Non-Fortran Main Program +@section Non-Fortran Main Program + +@menu +* _gfortran_set_args:: Save command-line arguments +* _gfortran_set_options:: Set library option flags +* _gfortran_set_convert:: Set endian conversion +* _gfortran_set_record_marker:: Set length of record markers +* _gfortran_set_fpe:: Set when a Floating Point Exception should be raised +* _gfortran_set_max_subrecord_length:: Set subrecord length +@end menu + +Even if you are doing mixed-language programming, it is very +likely that you do not need to know or use the information in this +section. Since it is about the internal structure of GNU Fortran, +it may also change in GCC minor releases. + +When you compile a @code{PROGRAM} with GNU Fortran, a function +with the name @code{main} (in the symbol table of the object file) +is generated, which initializes the libgfortran library and then +calls the actual program which uses the name @code{MAIN__}, for +historic reasons. If you link GNU Fortran compiled procedures +to, e.g., a C or C++ program or to a Fortran program compiled by +a different compiler, the libgfortran library is not initialized +and thus a few intrinsic procedures do not work properly, e.g. +those for obtaining the command-line arguments. + +Therefore, if your @code{PROGRAM} is not compiled with +GNU Fortran and the GNU Fortran compiled procedures require +intrinsics relying on the library initialization, you need to +initialize the library yourself. Using the default options, +gfortran calls @code{_gfortran_set_args} and +@code{_gfortran_set_options}. The initialization of the former +is needed if the called procedures access the command line +(and for backtracing); the latter sets some flags based on the +standard chosen or to enable backtracing. In typical programs, +it is not necessary to call any initialization function. + +If your @code{PROGRAM} is compiled with GNU Fortran, you shall +not call any of the following functions. The libgfortran +initialization functions are shown in C syntax but using C +bindings they are also accessible from Fortran. + + +@node _gfortran_set_args +@subsection @code{_gfortran_set_args} --- Save command-line arguments +@fnindex _gfortran_set_args +@cindex libgfortran initialization, set_args + +@table @asis +@item @emph{Description}: +@code{_gfortran_set_args} saves the command-line arguments; this +initialization is required if any of the command-line intrinsics +is called. Additionally, it shall be called if backtracing is +enabled (see @code{_gfortran_set_options}). + +@item @emph{Syntax}: +@code{void _gfortran_set_args (int argc, char *argv[])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{argc} @tab number of command line argument strings +@item @var{argv} @tab the command-line argument strings; argv[0] +is the pathname of the executable itself. +@end multitable + +@item @emph{Example}: +@smallexample +int main (int argc, char *argv[]) +@{ + /* Initialize libgfortran. */ + _gfortran_set_args (argc, argv); + return 0; +@} +@end smallexample +@end table + + +@node _gfortran_set_options +@subsection @code{_gfortran_set_options} --- Set library option flags +@fnindex _gfortran_set_options +@cindex libgfortran initialization, set_options + +@table @asis +@item @emph{Description}: +@code{_gfortran_set_options} sets several flags related to the Fortran +standard to be used, whether backtracing should be enabled +and whether range checks should be performed. The syntax allows for +upward compatibility since the number of passed flags is specified; for +non-passed flags, the default value is used. See also +@pxref{Code Gen Options}. Please note that not all flags are actually +used. + +@item @emph{Syntax}: +@code{void _gfortran_set_options (int num, int options[])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{num} @tab number of options passed +@item @var{argv} @tab The list of flag values +@end multitable + +@item @emph{option flag list}: +@multitable @columnfractions .15 .70 +@item @var{option}[0] @tab Allowed standard; can give run-time errors +if e.g. an input-output edit descriptor is invalid in a given +standard. Possible values are (bitwise or-ed) @code{GFC_STD_F77} (1), +@code{GFC_STD_F95_OBS} (2), @code{GFC_STD_F95_DEL} (4), +@code{GFC_STD_F95} (8), @code{GFC_STD_F2003} (16), @code{GFC_STD_GNU} +(32), @code{GFC_STD_LEGACY} (64), @code{GFC_STD_F2008} (128), +@code{GFC_STD_F2008_OBS} (256), @code{GFC_STD_F2008_TS} (512), +@code{GFC_STD_F2018} (1024), @code{GFC_STD_F2018_OBS} (2048), and +@code{GFC_STD=F2018_DEL} (4096). Default: @code{GFC_STD_F95_OBS | +GFC_STD_F95_DEL | GFC_STD_F95 | GFC_STD_F2003 | GFC_STD_F2008 | +GFC_STD_F2008_TS | GFC_STD_F2008_OBS | GFC_STD_F77 | GFC_STD_F2018 | +GFC_STD_F2018_OBS | GFC_STD_F2018_DEL | GFC_STD_GNU | GFC_STD_LEGACY}. +@item @var{option}[1] @tab Standard-warning flag; prints a warning to +standard error. Default: @code{GFC_STD_F95_DEL | GFC_STD_LEGACY}. +@item @var{option}[2] @tab If non zero, enable pedantic checking. +Default: off. +@item @var{option}[3] @tab Unused. +@item @var{option}[4] @tab If non zero, enable backtracing on run-time +errors. Default: off. (Default in the compiler: on.) +Note: Installs a signal handler and requires command-line +initialization using @code{_gfortran_set_args}. +@item @var{option}[5] @tab If non zero, supports signed zeros. +Default: enabled. +@item @var{option}[6] @tab Enables run-time checking. Possible values +are (bitwise or-ed): GFC_RTCHECK_BOUNDS (1), GFC_RTCHECK_ARRAY_TEMPS (2), +GFC_RTCHECK_RECURSION (4), GFC_RTCHECK_DO (8), GFC_RTCHECK_POINTER (16), +GFC_RTCHECK_MEM (32), GFC_RTCHECK_BITS (64). +Default: disabled. +@item @var{option}[7] @tab Unused. +@item @var{option}[8] @tab Show a warning when invoking @code{STOP} and +@code{ERROR STOP} if a floating-point exception occurred. Possible values +are (bitwise or-ed) @code{GFC_FPE_INVALID} (1), @code{GFC_FPE_DENORMAL} (2), +@code{GFC_FPE_ZERO} (4), @code{GFC_FPE_OVERFLOW} (8), +@code{GFC_FPE_UNDERFLOW} (16), @code{GFC_FPE_INEXACT} (32). Default: None (0). +(Default in the compiler: @code{GFC_FPE_INVALID | GFC_FPE_DENORMAL | +GFC_FPE_ZERO | GFC_FPE_OVERFLOW | GFC_FPE_UNDERFLOW}.) +@end multitable + +@item @emph{Example}: +@smallexample + /* Use gfortran 4.9 default options. */ + static int options[] = @{68, 511, 0, 0, 1, 1, 0, 0, 31@}; + _gfortran_set_options (9, &options); +@end smallexample +@end table + + +@node _gfortran_set_convert +@subsection @code{_gfortran_set_convert} --- Set endian conversion +@fnindex _gfortran_set_convert +@cindex libgfortran initialization, set_convert + +@table @asis +@item @emph{Description}: +@code{_gfortran_set_convert} set the representation of data for +unformatted files. + +@item @emph{Syntax}: +@code{void _gfortran_set_convert (int conv)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{conv} @tab Endian conversion, possible values: +GFC_CONVERT_NATIVE (0, default), GFC_CONVERT_SWAP (1), +GFC_CONVERT_BIG (2), GFC_CONVERT_LITTLE (3). +@end multitable + +@item @emph{Example}: +@smallexample +int main (int argc, char *argv[]) +@{ + /* Initialize libgfortran. */ + _gfortran_set_args (argc, argv); + _gfortran_set_convert (1); + return 0; +@} +@end smallexample +@end table + + +@node _gfortran_set_record_marker +@subsection @code{_gfortran_set_record_marker} --- Set length of record markers +@fnindex _gfortran_set_record_marker +@cindex libgfortran initialization, set_record_marker + +@table @asis +@item @emph{Description}: +@code{_gfortran_set_record_marker} sets the length of record markers +for unformatted files. + +@item @emph{Syntax}: +@code{void _gfortran_set_record_marker (int val)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{val} @tab Length of the record marker; valid values +are 4 and 8. Default is 4. +@end multitable + +@item @emph{Example}: +@smallexample +int main (int argc, char *argv[]) +@{ + /* Initialize libgfortran. */ + _gfortran_set_args (argc, argv); + _gfortran_set_record_marker (8); + return 0; +@} +@end smallexample +@end table + + +@node _gfortran_set_fpe +@subsection @code{_gfortran_set_fpe} --- Enable floating point exception traps +@fnindex _gfortran_set_fpe +@cindex libgfortran initialization, set_fpe + +@table @asis +@item @emph{Description}: +@code{_gfortran_set_fpe} enables floating point exception traps for +the specified exceptions. On most systems, this will result in a +SIGFPE signal being sent and the program being aborted. + +@item @emph{Syntax}: +@code{void _gfortran_set_fpe (int val)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{option}[0] @tab IEEE exceptions. Possible values are +(bitwise or-ed) zero (0, default) no trapping, +@code{GFC_FPE_INVALID} (1), @code{GFC_FPE_DENORMAL} (2), +@code{GFC_FPE_ZERO} (4), @code{GFC_FPE_OVERFLOW} (8), +@code{GFC_FPE_UNDERFLOW} (16), and @code{GFC_FPE_INEXACT} (32). +@end multitable + +@item @emph{Example}: +@smallexample +int main (int argc, char *argv[]) +@{ + /* Initialize libgfortran. */ + _gfortran_set_args (argc, argv); + /* FPE for invalid operations such as SQRT(-1.0). */ + _gfortran_set_fpe (1); + return 0; +@} +@end smallexample +@end table + + +@node _gfortran_set_max_subrecord_length +@subsection @code{_gfortran_set_max_subrecord_length} --- Set subrecord length +@fnindex _gfortran_set_max_subrecord_length +@cindex libgfortran initialization, set_max_subrecord_length + +@table @asis +@item @emph{Description}: +@code{_gfortran_set_max_subrecord_length} set the maximum length +for a subrecord. This option only makes sense for testing and +debugging of unformatted I/O. + +@item @emph{Syntax}: +@code{void _gfortran_set_max_subrecord_length (int val)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{val} @tab the maximum length for a subrecord; +the maximum permitted value is 2147483639, which is also +the default. +@end multitable + +@item @emph{Example}: +@smallexample +int main (int argc, char *argv[]) +@{ + /* Initialize libgfortran. */ + _gfortran_set_args (argc, argv); + _gfortran_set_max_subrecord_length (8); + return 0; +@} +@end smallexample +@end table + + +@node Naming and argument-passing conventions +@section Naming and argument-passing conventions + +This section gives an overview about the naming convention of procedures +and global variables and about the argument passing conventions used by +GNU Fortran. If a C binding has been specified, the naming convention +and some of the argument-passing conventions change. If possible, +mixed-language and mixed-compiler projects should use the better defined +C binding for interoperability. See @pxref{Interoperability with C}. + +@menu +* Naming conventions:: +* Argument passing conventions:: +@end menu + + +@node Naming conventions +@subsection Naming conventions + +According the Fortran standard, valid Fortran names consist of a letter +between @code{A} to @code{Z}, @code{a} to @code{z}, digits @code{0}, +@code{1} to @code{9} and underscores (@code{_}) with the restriction +that names may only start with a letter. As vendor extension, the +dollar sign (@code{$}) is additionally permitted with the option +@option{-fdollar-ok}, but not as first character and only if the +target system supports it. + +By default, the procedure name is the lower-cased Fortran name with an +appended underscore (@code{_}); using @option{-fno-underscoring} no +underscore is appended while @code{-fsecond-underscore} appends two +underscores. Depending on the target system and the calling convention, +the procedure might be additionally dressed; for instance, on 32bit +Windows with @code{stdcall}, an at-sign @code{@@} followed by an integer +number is appended. For the changing the calling convention, see +@pxref{GNU Fortran Compiler Directives}. + +For common blocks, the same convention is used, i.e. by default an +underscore is appended to the lower-cased Fortran name. Blank commons +have the name @code{__BLNK__}. + +For procedures and variables declared in the specification space of a +module, the name is formed by @code{__}, followed by the lower-cased +module name, @code{_MOD_}, and the lower-cased Fortran name. Note that +no underscore is appended. + + +@node Argument passing conventions +@subsection Argument passing conventions + +Subroutines do not return a value (matching C99's @code{void}) while +functions either return a value as specified in the platform ABI or +the result variable is passed as hidden argument to the function and +no result is returned. A hidden result variable is used when the +result variable is an array or of type @code{CHARACTER}. + +Arguments are passed according to the platform ABI. In particular, +complex arguments might not be compatible to a struct with two real +components for the real and imaginary part. The argument passing +matches the one of C99's @code{_Complex}. Functions with scalar +complex result variables return their value and do not use a +by-reference argument. Note that with the @option{-ff2c} option, +the argument passing is modified and no longer completely matches +the platform ABI. Some other Fortran compilers use @code{f2c} +semantic by default; this might cause problems with +interoperablility. + +GNU Fortran passes most arguments by reference, i.e. by passing a +pointer to the data. Note that the compiler might use a temporary +variable into which the actual argument has been copied, if required +semantically (copy-in/copy-out). + +For arguments with @code{ALLOCATABLE} and @code{POINTER} +attribute (including procedure pointers), a pointer to the pointer +is passed such that the pointer address can be modified in the +procedure. + +For dummy arguments with the @code{VALUE} attribute: Scalar arguments +of the type @code{INTEGER}, @code{LOGICAL}, @code{REAL} and +@code{COMPLEX} are passed by value according to the platform ABI. +(As vendor extension and not recommended, using @code{%VAL()} in the +call to a procedure has the same effect.) For @code{TYPE(C_PTR)} and +procedure pointers, the pointer itself is passed such that it can be +modified without affecting the caller. +@c FIXME: Document how VALUE is handled for CHARACTER, TYPE, +@c CLASS and arrays, i.e. whether the copy-in is done in the caller +@c or in the callee. + +For Boolean (@code{LOGICAL}) arguments, please note that GCC expects +only the integer value 0 and 1. If a GNU Fortran @code{LOGICAL} +variable contains another integer value, the result is undefined. +As some other Fortran compilers use @math{-1} for @code{.TRUE.}, +extra care has to be taken -- such as passing the value as +@code{INTEGER}. (The same value restriction also applies to other +front ends of GCC, e.g. to GCC's C99 compiler for @code{_Bool} +or GCC's Ada compiler for @code{Boolean}.) + +For arguments of @code{CHARACTER} type, the character length is passed +as a hidden argument at the end of the argument list. For +deferred-length strings, the value is passed by reference, otherwise +by value. The character length has the C type @code{size_t} (or +@code{INTEGER(kind=C_SIZE_T)} in Fortran). Note that this is +different to older versions of the GNU Fortran compiler, where the +type of the hidden character length argument was a C @code{int}. In +order to retain compatibility with older versions, one can e.g. for +the following Fortran procedure + +@smallexample +subroutine fstrlen (s, a) + character(len=*) :: s + integer :: a + print*, len(s) +end subroutine fstrlen +@end smallexample + +define the corresponding C prototype as follows: + +@smallexample +#if __GNUC__ > 7 +typedef size_t fortran_charlen_t; +#else +typedef int fortran_charlen_t; +#endif + +void fstrlen_ (char*, int*, fortran_charlen_t); +@end smallexample + +In order to avoid such compiler-specific details, for new code it is +instead recommended to use the ISO_C_BINDING feature. + +Note with C binding, @code{CHARACTER(len=1)} result variables are +returned according to the platform ABI and no hidden length argument +is used for dummy arguments; with @code{VALUE}, those variables are +passed by value. + +For @code{OPTIONAL} dummy arguments, an absent argument is denoted +by a NULL pointer, except for scalar dummy arguments of type +@code{INTEGER}, @code{LOGICAL}, @code{REAL} and @code{COMPLEX} +which have the @code{VALUE} attribute. For those, a hidden Boolean +argument (@code{logical(kind=C_bool),value}) is used to indicate +whether the argument is present. + +Arguments which are assumed-shape, assumed-rank or deferred-rank +arrays or, with @option{-fcoarray=lib}, allocatable scalar coarrays use +an array descriptor. All other arrays pass the address of the +first element of the array. With @option{-fcoarray=lib}, the token +and the offset belonging to nonallocatable coarrays dummy arguments +are passed as hidden argument along the character length hidden +arguments. The token is an opaque pointer identifying the coarray +and the offset is a passed-by-value integer of kind @code{C_PTRDIFF_T}, +denoting the byte offset between the base address of the coarray and +the passed scalar or first element of the passed array. + +The arguments are passed in the following order +@itemize @bullet +@item Result variable, when the function result is passed by reference +@item Character length of the function result, if it is a of type +@code{CHARACTER} and no C binding is used +@item The arguments in the order in which they appear in the Fortran +declaration +@item The present status for optional arguments with value attribute, +which are internally passed by value +@item The character length and/or coarray token and offset for the first +argument which is a @code{CHARACTER} or a nonallocatable coarray dummy +argument, followed by the hidden arguments of the next dummy argument +of such a type +@end itemize + + +@c --------------------------------------------------------------------- +@c Coarray Programming +@c --------------------------------------------------------------------- + +@node Coarray Programming +@chapter Coarray Programming +@cindex Coarrays + +@menu +* Type and enum ABI Documentation:: +* Function ABI Documentation:: +@end menu + + +@node Type and enum ABI Documentation +@section Type and enum ABI Documentation + +@menu +* caf_token_t:: +* caf_register_t:: +* caf_deregister_t:: +* caf_reference_t:: +* caf_team_t:: +@end menu + +@node caf_token_t +@subsection @code{caf_token_t} + +Typedef of type @code{void *} on the compiler side. Can be any data +type on the library side. + +@node caf_register_t +@subsection @code{caf_register_t} + +Indicates which kind of coarray variable should be registered. + +@verbatim +typedef enum caf_register_t { + CAF_REGTYPE_COARRAY_STATIC, + CAF_REGTYPE_COARRAY_ALLOC, + CAF_REGTYPE_LOCK_STATIC, + CAF_REGTYPE_LOCK_ALLOC, + CAF_REGTYPE_CRITICAL, + CAF_REGTYPE_EVENT_STATIC, + CAF_REGTYPE_EVENT_ALLOC, + CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY, + CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY +} +caf_register_t; +@end verbatim + +The values @code{CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY} and +@code{CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY} are for allocatable components +in derived type coarrays only. The first one sets up the token without +allocating memory for allocatable component. The latter one only allocates the +memory for an allocatable component in a derived type coarray. The token +needs to be setup previously by the REGISTER_ONLY. This allows to have +allocatable components un-allocated on some images. The status whether an +allocatable component is allocated on a remote image can be queried by +@code{_caf_is_present} which used internally by the @code{ALLOCATED} +intrinsic. + +@node caf_deregister_t +@subsection @code{caf_deregister_t} + +@verbatim +typedef enum caf_deregister_t { + CAF_DEREGTYPE_COARRAY_DEREGISTER, + CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY +} +caf_deregister_t; +@end verbatim + +Allows to specifiy the type of deregistration of a coarray object. The +@code{CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY} flag is only allowed for +allocatable components in derived type coarrays. + +@node caf_reference_t +@subsection @code{caf_reference_t} + +The structure used for implementing arbitrary reference chains. +A @code{CAF_REFERENCE_T} allows to specify a component reference or any kind +of array reference of any rank supported by gfortran. For array references all +kinds as known by the compiler/Fortran standard are supported indicated by +a @code{MODE}. + +@verbatim +typedef enum caf_ref_type_t { + /* Reference a component of a derived type, either regular one or an + allocatable or pointer type. For regular ones idx in caf_reference_t is + set to -1. */ + CAF_REF_COMPONENT, + /* Reference an allocatable array. */ + CAF_REF_ARRAY, + /* Reference a non-allocatable/non-pointer array. I.e., the coarray object + has no array descriptor associated and the addressing is done + completely using the ref. */ + CAF_REF_STATIC_ARRAY +} caf_ref_type_t; +@end verbatim + +@verbatim +typedef enum caf_array_ref_t { + /* No array ref. This terminates the array ref. */ + CAF_ARR_REF_NONE = 0, + /* Reference array elements given by a vector. Only for this mode + caf_reference_t.u.a.dim[i].v is valid. */ + CAF_ARR_REF_VECTOR, + /* A full array ref (:). */ + CAF_ARR_REF_FULL, + /* Reference a range on elements given by start, end and stride. */ + CAF_ARR_REF_RANGE, + /* Only a single item is referenced given in the start member. */ + CAF_ARR_REF_SINGLE, + /* An array ref of the kind (i:), where i is an arbitrary valid index in the + array. The index i is given in the start member. */ + CAF_ARR_REF_OPEN_END, + /* An array ref of the kind (:i), where the lower bound of the array ref + is given by the remote side. The index i is given in the end member. */ + CAF_ARR_REF_OPEN_START +} caf_array_ref_t; +@end verbatim + +@verbatim +/* References to remote components of a derived type. */ +typedef struct caf_reference_t { + /* A pointer to the next ref or NULL. */ + struct caf_reference_t *next; + /* The type of the reference. */ + /* caf_ref_type_t, replaced by int to allow specification in fortran FE. */ + int type; + /* The size of an item referenced in bytes. I.e. in an array ref this is + the factor to advance the array pointer with to get to the next item. + For component refs this gives just the size of the element referenced. */ + size_t item_size; + union { + struct { + /* The offset (in bytes) of the component in the derived type. + Unused for allocatable or pointer components. */ + ptrdiff_t offset; + /* The offset (in bytes) to the caf_token associated with this + component. NULL, when not allocatable/pointer ref. */ + ptrdiff_t caf_token_offset; + } c; + struct { + /* The mode of the array ref. See CAF_ARR_REF_*. */ + /* caf_array_ref_t, replaced by unsigend char to allow specification in + fortran FE. */ + unsigned char mode[GFC_MAX_DIMENSIONS]; + /* The type of a static array. Unset for array's with descriptors. */ + int static_array_type; + /* Subscript refs (s) or vector refs (v). */ + union { + struct { + /* The start and end boundary of the ref and the stride. */ + index_type start, end, stride; + } s; + struct { + /* nvec entries of kind giving the elements to reference. */ + void *vector; + /* The number of entries in vector. */ + size_t nvec; + /* The integer kind used for the elements in vector. */ + int kind; + } v; + } dim[GFC_MAX_DIMENSIONS]; + } a; + } u; +} caf_reference_t; +@end verbatim + +The references make up a single linked list of reference operations. The +@code{NEXT} member links to the next reference or NULL to indicate the end of +the chain. Component and array refs can be arbitrarily mixed as long as they +comply to the Fortran standard. + +@emph{NOTES} +The member @code{STATIC_ARRAY_TYPE} is used only when the @code{TYPE} is +@code{CAF_REF_STATIC_ARRAY}. The member gives the type of the data referenced. +Because no array descriptor is available for a descriptor-less array and +type conversion still needs to take place the type is transported here. + +At the moment @code{CAF_ARR_REF_VECTOR} is not implemented in the front end for +descriptor-less arrays. The library caf_single has untested support for it. + +@node caf_team_t +@subsection @code{caf_team_t} + +Opaque pointer to represent a team-handle. This type is a stand-in for the +future implementation of teams. It is about to change without further notice. + +@node Function ABI Documentation +@section Function ABI Documentation + +@menu +* _gfortran_caf_init:: Initialiation function +* _gfortran_caf_finish:: Finalization function +* _gfortran_caf_this_image:: Querying the image number +* _gfortran_caf_num_images:: Querying the maximal number of images +* _gfortran_caf_image_status :: Query the status of an image +* _gfortran_caf_failed_images :: Get an array of the indexes of the failed images +* _gfortran_caf_stopped_images :: Get an array of the indexes of the stopped images +* _gfortran_caf_register:: Registering coarrays +* _gfortran_caf_deregister:: Deregistering coarrays +* _gfortran_caf_is_present:: Query whether an allocatable or pointer component in a derived type coarray is allocated +* _gfortran_caf_send:: Sending data from a local image to a remote image +* _gfortran_caf_get:: Getting data from a remote image +* _gfortran_caf_sendget:: Sending data between remote images +* _gfortran_caf_send_by_ref:: Sending data from a local image to a remote image using enhanced references +* _gfortran_caf_get_by_ref:: Getting data from a remote image using enhanced references +* _gfortran_caf_sendget_by_ref:: Sending data between remote images using enhanced references +* _gfortran_caf_lock:: Locking a lock variable +* _gfortran_caf_unlock:: Unlocking a lock variable +* _gfortran_caf_event_post:: Post an event +* _gfortran_caf_event_wait:: Wait that an event occurred +* _gfortran_caf_event_query:: Query event count +* _gfortran_caf_sync_all:: All-image barrier +* _gfortran_caf_sync_images:: Barrier for selected images +* _gfortran_caf_sync_memory:: Wait for completion of segment-memory operations +* _gfortran_caf_error_stop:: Error termination with exit code +* _gfortran_caf_error_stop_str:: Error termination with string +* _gfortran_caf_fail_image :: Mark the image failed and end its execution +* _gfortran_caf_atomic_define:: Atomic variable assignment +* _gfortran_caf_atomic_ref:: Atomic variable reference +* _gfortran_caf_atomic_cas:: Atomic compare and swap +* _gfortran_caf_atomic_op:: Atomic operation +* _gfortran_caf_co_broadcast:: Sending data to all images +* _gfortran_caf_co_max:: Collective maximum reduction +* _gfortran_caf_co_min:: Collective minimum reduction +* _gfortran_caf_co_sum:: Collective summing reduction +* _gfortran_caf_co_reduce:: Generic collective reduction +@end menu + + +@node _gfortran_caf_init +@subsection @code{_gfortran_caf_init} --- Initialiation function +@cindex Coarray, _gfortran_caf_init + +@table @asis +@item @emph{Description}: +This function is called at startup of the program before the Fortran main +program, if the latter has been compiled with @option{-fcoarray=lib}. +It takes as arguments the command-line arguments of the program. It is +permitted to pass two @code{NULL} pointers as argument; if non-@code{NULL}, +the library is permitted to modify the arguments. + +@item @emph{Syntax}: +@code{void _gfortran_caf_init (int *argc, char ***argv)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{argc} @tab intent(inout) An integer pointer with the number of +arguments passed to the program or @code{NULL}. +@item @var{argv} @tab intent(inout) A pointer to an array of strings with the +command-line arguments or @code{NULL}. +@end multitable + +@item @emph{NOTES} +The function is modelled after the initialization function of the Message +Passing Interface (MPI) specification. Due to the way coarray registration +works, it might not be the first call to the library. If the main program is +not written in Fortran and only a library uses coarrays, it can happen that +this function is never called. Therefore, it is recommended that the library +does not rely on the passed arguments and whether the call has been done. +@end table + + +@node _gfortran_caf_finish +@subsection @code{_gfortran_caf_finish} --- Finalization function +@cindex Coarray, _gfortran_caf_finish + +@table @asis +@item @emph{Description}: +This function is called at the end of the Fortran main program, if it has +been compiled with the @option{-fcoarray=lib} option. + +@item @emph{Syntax}: +@code{void _gfortran_caf_finish (void)} + +@item @emph{NOTES} +For non-Fortran programs, it is recommended to call the function at the end +of the main program. To ensure that the shutdown is also performed for +programs where this function is not explicitly invoked, for instance +non-Fortran programs or calls to the system's exit() function, the library +can use a destructor function. Note that programs can also be terminated +using the STOP and ERROR STOP statements; those use different library calls. +@end table + + +@node _gfortran_caf_this_image +@subsection @code{_gfortran_caf_this_image} --- Querying the image number +@cindex Coarray, _gfortran_caf_this_image + +@table @asis +@item @emph{Description}: +This function returns the current image number, which is a positive number. + +@item @emph{Syntax}: +@code{int _gfortran_caf_this_image (int distance)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{distance} @tab As specified for the @code{this_image} intrinsic +in TS18508. Shall be a non-negative number. +@end multitable + +@item @emph{NOTES} +If the Fortran intrinsic @code{this_image} is invoked without an argument, which +is the only permitted form in Fortran 2008, GCC passes @code{0} as +first argument. +@end table + + +@node _gfortran_caf_num_images +@subsection @code{_gfortran_caf_num_images} --- Querying the maximal number of images +@cindex Coarray, _gfortran_caf_num_images + +@table @asis +@item @emph{Description}: +This function returns the number of images in the current team, if +@var{distance} is 0 or the number of images in the parent team at the specified +distance. If failed is -1, the function returns the number of all images at +the specified distance; if it is 0, the function returns the number of +nonfailed images, and if it is 1, it returns the number of failed images. + +@item @emph{Syntax}: +@code{int _gfortran_caf_num_images(int distance, int failed)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{distance} @tab the distance from this image to the ancestor. +Shall be positive. +@item @var{failed} @tab shall be -1, 0, or 1 +@end multitable + +@item @emph{NOTES} +This function follows TS18508. If the num_image intrinsic has no arguments, +then the compiler passes @code{distance=0} and @code{failed=-1} to the function. +@end table + + +@node _gfortran_caf_image_status +@subsection @code{_gfortran_caf_image_status} --- Query the status of an image +@cindex Coarray, _gfortran_caf_image_status + +@table @asis +@item @emph{Description}: +Get the status of the image given by the id @var{image} of the team given by +@var{team}. Valid results are zero, for image is ok, @code{STAT_STOPPED_IMAGE} +from the ISO_FORTRAN_ENV module to indicate that the image has been stopped and +@code{STAT_FAILED_IMAGE} also from ISO_FORTRAN_ENV to indicate that the image +has executed a @code{FAIL IMAGE} statement. + +@item @emph{Syntax}: +@code{int _gfortran_caf_image_status (int image, caf_team_t * team)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{image} @tab the positive scalar id of the image in the current TEAM. +@item @var{team} @tab optional; team on the which the inquiry is to be +performed. +@end multitable + +@item @emph{NOTES} +This function follows TS18508. Because team-functionality is not yet +implemented a null-pointer is passed for the @var{team} argument at the moment. +@end table + + +@node _gfortran_caf_failed_images +@subsection @code{_gfortran_caf_failed_images} --- Get an array of the indexes of the failed images +@cindex Coarray, _gfortran_caf_failed_images + +@table @asis +@item @emph{Description}: +Get an array of image indexes in the current @var{team} that have failed. The +array is sorted ascendingly. When @var{team} is not provided the current team +is to be used. When @var{kind} is provided then the resulting array is of that +integer kind else it is of default integer kind. The returns an unallocated +size zero array when no images have failed. + +@item @emph{Syntax}: +@code{int _gfortran_caf_failed_images (caf_team_t * team, int * kind)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{team} @tab optional; team on the which the inquiry is to be +performed. +@item @var{image} @tab optional; the kind of the resulting integer array. +@end multitable + +@item @emph{NOTES} +This function follows TS18508. Because team-functionality is not yet +implemented a null-pointer is passed for the @var{team} argument at the moment. +@end table + + +@node _gfortran_caf_stopped_images +@subsection @code{_gfortran_caf_stopped_images} --- Get an array of the indexes of the stopped images +@cindex Coarray, _gfortran_caf_stopped_images + +@table @asis +@item @emph{Description}: +Get an array of image indexes in the current @var{team} that have stopped. The +array is sorted ascendingly. When @var{team} is not provided the current team +is to be used. When @var{kind} is provided then the resulting array is of that +integer kind else it is of default integer kind. The returns an unallocated +size zero array when no images have failed. + +@item @emph{Syntax}: +@code{int _gfortran_caf_stopped_images (caf_team_t * team, int * kind)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{team} @tab optional; team on the which the inquiry is to be +performed. +@item @var{image} @tab optional; the kind of the resulting integer array. +@end multitable + +@item @emph{NOTES} +This function follows TS18508. Because team-functionality is not yet +implemented a null-pointer is passed for the @var{team} argument at the moment. +@end table + + +@node _gfortran_caf_register +@subsection @code{_gfortran_caf_register} --- Registering coarrays +@cindex Coarray, _gfortran_caf_register + +@table @asis +@item @emph{Description}: +Registers memory for a coarray and creates a token to identify the coarray. The +routine is called for both coarrays with @code{SAVE} attribute and using an +explicit @code{ALLOCATE} statement. If an error occurs and @var{STAT} is a +@code{NULL} pointer, the function shall abort with printing an error message +and starting the error termination. If no error occurs and @var{STAT} is +present, it shall be set to zero. Otherwise, it shall be set to a positive +value and, if not-@code{NULL}, @var{ERRMSG} shall be set to a string describing +the failure. The routine shall register the memory provided in the +@code{DATA}-component of the array descriptor @var{DESC}, when that component +is non-@code{NULL}, else it shall allocate sufficient memory and provide a +pointer to it in the @code{DATA}-component of @var{DESC}. The array descriptor +has rank zero, when a scalar object is to be registered and the array +descriptor may be invalid after the call to @code{_gfortran_caf_register}. +When an array is to be allocated the descriptor persists. + +For @code{CAF_REGTYPE_COARRAY_STATIC} and @code{CAF_REGTYPE_COARRAY_ALLOC}, +the passed size is the byte size requested. For @code{CAF_REGTYPE_LOCK_STATIC}, +@code{CAF_REGTYPE_LOCK_ALLOC} and @code{CAF_REGTYPE_CRITICAL} it is the array +size or one for a scalar. + +When @code{CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY} is used, then only a token +for an allocatable or pointer component is created. The @code{SIZE} parameter +is not used then. On the contrary when +@code{CAF_REGTYPE_COARRAY_ALLOC_ALLOCATE_ONLY} is specified, then the +@var{token} needs to be registered by a previous call with regtype +@code{CAF_REGTYPE_COARRAY_ALLOC_REGISTER_ONLY} and either the memory specified +in the @var{DESC}'s data-ptr is registered or allocate when the data-ptr is +@code{NULL}. + +@item @emph{Syntax}: +@code{void caf_register (size_t size, caf_register_t type, caf_token_t *token, +gfc_descriptor_t *desc, int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{size} @tab For normal coarrays, the byte size of the coarray to be +allocated; for lock types and event types, the number of elements. +@item @var{type} @tab one of the caf_register_t types. +@item @var{token} @tab intent(out) An opaque pointer identifying the coarray. +@item @var{desc} @tab intent(inout) The (pseudo) array descriptor. +@item @var{stat} @tab intent(out) For allocatable coarrays, stores the STAT=; +may be @code{NULL} +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be @code{NULL} +@item @var{errmsg_len} @tab the buffer size of errmsg. +@end multitable + +@item @emph{NOTES} +Nonallocatable coarrays have to be registered prior use from remote images. +In order to guarantee this, they have to be registered before the main +program. This can be achieved by creating constructor functions. That is what +GCC does such that also for nonallocatable coarrays the memory is allocated and +no static memory is used. The token permits to identify the coarray; to the +processor, the token is a nonaliasing pointer. The library can, for instance, +store the base address of the coarray in the token, some handle or a more +complicated struct. The library may also store the array descriptor +@var{DESC} when its rank is non-zero. + +For lock types, the value shall only be used for checking the allocation +status. Note that for critical blocks, the locking is only required on one +image; in the locking statement, the processor shall always pass an +image index of one for critical-block lock variables +(@code{CAF_REGTYPE_CRITICAL}). For lock types and critical-block variables, +the initial value shall be unlocked (or, respectively, not in critical +section) such as the value false; for event types, the initial state should +be no event, e.g. zero. +@end table + + +@node _gfortran_caf_deregister +@subsection @code{_gfortran_caf_deregister} --- Deregistering coarrays +@cindex Coarray, _gfortran_caf_deregister + +@table @asis +@item @emph{Description}: +Called to free or deregister the memory of a coarray; the processor calls this +function for automatic and explicit deallocation. In case of an error, this +function shall fail with an error message, unless the @var{STAT} variable is +not null. The library is only expected to free memory it allocated itself +during a call to @code{_gfortran_caf_register}. + +@item @emph{Syntax}: +@code{void caf_deregister (caf_token_t *token, caf_deregister_t type, +int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab the token to free. +@item @var{type} @tab the type of action to take for the coarray. A +@code{CAF_DEREGTYPE_COARRAY_DEALLOCATE_ONLY} is allowed only for allocatable or +pointer components of derived type coarrays. The action only deallocates the +local memory without deleting the token. +@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set +to an error message; may be NULL +@item @var{errmsg_len} @tab the buffer size of errmsg. +@end multitable + +@item @emph{NOTES} +For nonalloatable coarrays this function is never called. If a cleanup is +required, it has to be handled via the finish, stop and error stop functions, +and via destructors. +@end table + + +@node _gfortran_caf_is_present +@subsection @code{_gfortran_caf_is_present} --- Query whether an allocatable or pointer component in a derived type coarray is allocated +@cindex Coarray, _gfortran_caf_is_present + +@table @asis +@item @emph{Description}: +Used to query the coarray library whether an allocatable component in a derived +type coarray is allocated on a remote image. + +@item @emph{Syntax}: +@code{void _gfortran_caf_is_present (caf_token_t token, int image_index, +gfc_reference_t *ref)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab An opaque pointer identifying the coarray. +@item @var{image_index} @tab The ID of the remote image; must be a positive +number. +@item @var{ref} @tab A chain of references to address the allocatable or +pointer component in the derived type coarray. The object reference needs to be +a scalar or a full array reference, respectively. +@end multitable + +@end table + +@node _gfortran_caf_send +@subsection @code{_gfortran_caf_send} --- Sending data from a local image to a remote image +@cindex Coarray, _gfortran_caf_send + +@table @asis +@item @emph{Description}: +Called to send a scalar, an array section or a whole array from a local +to a remote image identified by the image_index. + +@item @emph{Syntax}: +@code{void _gfortran_caf_send (caf_token_t token, size_t offset, +int image_index, gfc_descriptor_t *dest, caf_vector_t *dst_vector, +gfc_descriptor_t *src, int dst_kind, int src_kind, bool may_require_tmp, +int *stat)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{offset} @tab intent(in) By which amount of bytes the actual data is +shifted compared to the base address of the coarray. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number. +@item @var{dest} @tab intent(in) Array descriptor for the remote image for the +bounds and the size. The @code{base_addr} shall not be accessed. +@item @var{dst_vector} @tab intent(in) If not NULL, it contains the vector +subscript of the destination array; the values are relative to the dimension +triplet of the dest argument. +@item @var{src} @tab intent(in) Array descriptor of the local array to be +transferred to the remote image +@item @var{dst_kind} @tab intent(in) Kind of the destination argument +@item @var{src_kind} @tab intent(in) Kind of the source argument +@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when +it is known at compile time that the @var{dest} and @var{src} either cannot +overlap or overlap (fully or partially) such that walking @var{src} and +@var{dest} in element wise element order (honoring the stride value) will not +lead to wrong results. Otherwise, the value is @code{true}. +@item @var{stat} @tab intent(out) when non-NULL give the result of the +operation, i.e., zero on success and non-zero on error. When NULL and an error +occurs, then an error message is printed and the program is terminated. +@end multitable + +@item @emph{NOTES} +It is permitted to have @var{image_index} equal the current image; the memory +of the send-to and the send-from might (partially) overlap in that case. The +implementation has to take care that it handles this case, e.g. using +@code{memmove} which handles (partially) overlapping memory. If +@var{may_require_tmp} is true, the library might additionally create a +temporary variable, unless additional checks show that this is not required +(e.g. because walking backward is possible or because both arrays are +contiguous and @code{memmove} takes care of overlap issues). + +Note that the assignment of a scalar to an array is permitted. In addition, +the library has to handle numeric-type conversion and for strings, padding +and different character kinds. +@end table + + +@node _gfortran_caf_get +@subsection @code{_gfortran_caf_get} --- Getting data from a remote image +@cindex Coarray, _gfortran_caf_get + +@table @asis +@item @emph{Description}: +Called to get an array section or a whole array from a remote, +image identified by the image_index. + +@item @emph{Syntax}: +@code{void _gfortran_caf_get (caf_token_t token, size_t offset, +int image_index, gfc_descriptor_t *src, caf_vector_t *src_vector, +gfc_descriptor_t *dest, int src_kind, int dst_kind, bool may_require_tmp, +int *stat)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{offset} @tab intent(in) By which amount of bytes the actual data is +shifted compared to the base address of the coarray. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number. +@item @var{dest} @tab intent(out) Array descriptor of the local array to store +the data retrieved from the remote image +@item @var{src} @tab intent(in) Array descriptor for the remote image for the +bounds and the size. The @code{base_addr} shall not be accessed. +@item @var{src_vector} @tab intent(in) If not NULL, it contains the vector +subscript of the source array; the values are relative to the dimension +triplet of the @var{src} argument. +@item @var{dst_kind} @tab intent(in) Kind of the destination argument +@item @var{src_kind} @tab intent(in) Kind of the source argument +@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when +it is known at compile time that the @var{dest} and @var{src} either cannot +overlap or overlap (fully or partially) such that walking @var{src} and +@var{dest} in element wise element order (honoring the stride value) will not +lead to wrong results. Otherwise, the value is @code{true}. +@item @var{stat} @tab intent(out) When non-NULL give the result of the +operation, i.e., zero on success and non-zero on error. When NULL and an error +occurs, then an error message is printed and the program is terminated. +@end multitable + +@item @emph{NOTES} +It is permitted to have @var{image_index} equal the current image; the memory of +the send-to and the send-from might (partially) overlap in that case. The +implementation has to take care that it handles this case, e.g. using +@code{memmove} which handles (partially) overlapping memory. If +@var{may_require_tmp} is true, the library might additionally create a +temporary variable, unless additional checks show that this is not required +(e.g. because walking backward is possible or because both arrays are +contiguous and @code{memmove} takes care of overlap issues). + +Note that the library has to handle numeric-type conversion and for strings, +padding and different character kinds. +@end table + + +@node _gfortran_caf_sendget +@subsection @code{_gfortran_caf_sendget} --- Sending data between remote images +@cindex Coarray, _gfortran_caf_sendget + +@table @asis +@item @emph{Description}: +Called to send a scalar, an array section or a whole array from a remote image +identified by the @var{src_image_index} to a remote image identified by the +@var{dst_image_index}. + +@item @emph{Syntax}: +@code{void _gfortran_caf_sendget (caf_token_t dst_token, size_t dst_offset, +int dst_image_index, gfc_descriptor_t *dest, caf_vector_t *dst_vector, +caf_token_t src_token, size_t src_offset, int src_image_index, +gfc_descriptor_t *src, caf_vector_t *src_vector, int dst_kind, int src_kind, +bool may_require_tmp, int *stat)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{dst_token} @tab intent(in) An opaque pointer identifying the +destination coarray. +@item @var{dst_offset} @tab intent(in) By which amount of bytes the actual data +is shifted compared to the base address of the destination coarray. +@item @var{dst_image_index} @tab intent(in) The ID of the destination remote +image; must be a positive number. +@item @var{dest} @tab intent(in) Array descriptor for the destination +remote image for the bounds and the size. The @code{base_addr} shall not be +accessed. +@item @var{dst_vector} @tab intent(int) If not NULL, it contains the vector +subscript of the destination array; the values are relative to the dimension +triplet of the @var{dest} argument. +@item @var{src_token} @tab intent(in) An opaque pointer identifying the source +coarray. +@item @var{src_offset} @tab intent(in) By which amount of bytes the actual data +is shifted compared to the base address of the source coarray. +@item @var{src_image_index} @tab intent(in) The ID of the source remote image; +must be a positive number. +@item @var{src} @tab intent(in) Array descriptor of the local array to be +transferred to the remote image. +@item @var{src_vector} @tab intent(in) Array descriptor of the local array to +be transferred to the remote image +@item @var{dst_kind} @tab intent(in) Kind of the destination argument +@item @var{src_kind} @tab intent(in) Kind of the source argument +@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when +it is known at compile time that the @var{dest} and @var{src} either cannot +overlap or overlap (fully or partially) such that walking @var{src} and +@var{dest} in element wise element order (honoring the stride value) will not +lead to wrong results. Otherwise, the value is @code{true}. +@item @var{stat} @tab intent(out) when non-NULL give the result of the +operation, i.e., zero on success and non-zero on error. When NULL and an error +occurs, then an error message is printed and the program is terminated. +@end multitable + +@item @emph{NOTES} +It is permitted to have the same image index for both @var{src_image_index} and +@var{dst_image_index}; the memory of the send-to and the send-from might +(partially) overlap in that case. The implementation has to take care that it +handles this case, e.g. using @code{memmove} which handles (partially) +overlapping memory. If @var{may_require_tmp} is true, the library +might additionally create a temporary variable, unless additional checks show +that this is not required (e.g. because walking backward is possible or because +both arrays are contiguous and @code{memmove} takes care of overlap issues). + +Note that the assignment of a scalar to an array is permitted. In addition, +the library has to handle numeric-type conversion and for strings, padding and +different character kinds. +@end table + +@node _gfortran_caf_send_by_ref +@subsection @code{_gfortran_caf_send_by_ref} --- Sending data from a local image to a remote image with enhanced referencing options +@cindex Coarray, _gfortran_caf_send_by_ref + +@table @asis +@item @emph{Description}: +Called to send a scalar, an array section or a whole array from a local to a +remote image identified by the @var{image_index}. + +@item @emph{Syntax}: +@code{void _gfortran_caf_send_by_ref (caf_token_t token, int image_index, +gfc_descriptor_t *src, caf_reference_t *refs, int dst_kind, int src_kind, +bool may_require_tmp, bool dst_reallocatable, int *stat, int dst_type)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number. +@item @var{src} @tab intent(in) Array descriptor of the local array to be +transferred to the remote image +@item @var{refs} @tab intent(in) The references on the remote array to store +the data given by src. Guaranteed to have at least one entry. +@item @var{dst_kind} @tab intent(in) Kind of the destination argument +@item @var{src_kind} @tab intent(in) Kind of the source argument +@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when +it is known at compile time that the @var{dest} and @var{src} either cannot +overlap or overlap (fully or partially) such that walking @var{src} and +@var{dest} in element wise element order (honoring the stride value) will not +lead to wrong results. Otherwise, the value is @code{true}. +@item @var{dst_reallocatable} @tab intent(in) Set when the destination is of +allocatable or pointer type and the refs will allow reallocation, i.e., the ref +is a full array or component ref. +@item @var{stat} @tab intent(out) When non-@code{NULL} give the result of the +operation, i.e., zero on success and non-zero on error. When @code{NULL} and +an error occurs, then an error message is printed and the program is terminated. +@item @var{dst_type} @tab intent(in) Give the type of the destination. When +the destination is not an array, than the precise type, e.g. of a component in +a derived type, is not known, but provided here. +@end multitable + +@item @emph{NOTES} +It is permitted to have @var{image_index} equal the current image; the memory of +the send-to and the send-from might (partially) overlap in that case. The +implementation has to take care that it handles this case, e.g. using +@code{memmove} which handles (partially) overlapping memory. If +@var{may_require_tmp} is true, the library might additionally create a +temporary variable, unless additional checks show that this is not required +(e.g. because walking backward is possible or because both arrays are +contiguous and @code{memmove} takes care of overlap issues). + +Note that the assignment of a scalar to an array is permitted. In addition, +the library has to handle numeric-type conversion and for strings, padding +and different character kinds. + +Because of the more complicated references possible some operations may be +unsupported by certain libraries. The library is expected to issue a precise +error message why the operation is not permitted. +@end table + + +@node _gfortran_caf_get_by_ref +@subsection @code{_gfortran_caf_get_by_ref} --- Getting data from a remote image using enhanced references +@cindex Coarray, _gfortran_caf_get_by_ref + +@table @asis +@item @emph{Description}: +Called to get a scalar, an array section or a whole array from a remote image +identified by the @var{image_index}. + +@item @emph{Syntax}: +@code{void _gfortran_caf_get_by_ref (caf_token_t token, int image_index, +caf_reference_t *refs, gfc_descriptor_t *dst, int dst_kind, int src_kind, +bool may_require_tmp, bool dst_reallocatable, int *stat, int src_type)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number. +@item @var{refs} @tab intent(in) The references to apply to the remote structure +to get the data. +@item @var{dst} @tab intent(in) Array descriptor of the local array to store +the data transferred from the remote image. May be reallocated where needed +and when @var{DST_REALLOCATABLE} allows it. +@item @var{dst_kind} @tab intent(in) Kind of the destination argument +@item @var{src_kind} @tab intent(in) Kind of the source argument +@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when +it is known at compile time that the @var{dest} and @var{src} either cannot +overlap or overlap (fully or partially) such that walking @var{src} and +@var{dest} in element wise element order (honoring the stride value) will not +lead to wrong results. Otherwise, the value is @code{true}. +@item @var{dst_reallocatable} @tab intent(in) Set when @var{DST} is of +allocatable or pointer type and its refs allow reallocation, i.e., the full +array or a component is referenced. +@item @var{stat} @tab intent(out) When non-@code{NULL} give the result of the +operation, i.e., zero on success and non-zero on error. When @code{NULL} and an +error occurs, then an error message is printed and the program is terminated. +@item @var{src_type} @tab intent(in) Give the type of the source. When the +source is not an array, than the precise type, e.g. of a component in a +derived type, is not known, but provided here. +@end multitable + +@item @emph{NOTES} +It is permitted to have @code{image_index} equal the current image; the memory +of the send-to and the send-from might (partially) overlap in that case. The +implementation has to take care that it handles this case, e.g. using +@code{memmove} which handles (partially) overlapping memory. If +@var{may_require_tmp} is true, the library might additionally create a +temporary variable, unless additional checks show that this is not required +(e.g. because walking backward is possible or because both arrays are +contiguous and @code{memmove} takes care of overlap issues). + +Note that the library has to handle numeric-type conversion and for strings, +padding and different character kinds. + +Because of the more complicated references possible some operations may be +unsupported by certain libraries. The library is expected to issue a precise +error message why the operation is not permitted. +@end table + + +@node _gfortran_caf_sendget_by_ref +@subsection @code{_gfortran_caf_sendget_by_ref} --- Sending data between remote images using enhanced references on both sides +@cindex Coarray, _gfortran_caf_sendget_by_ref + +@table @asis +@item @emph{Description}: +Called to send a scalar, an array section or a whole array from a remote image +identified by the @var{src_image_index} to a remote image identified by the +@var{dst_image_index}. + +@item @emph{Syntax}: +@code{void _gfortran_caf_sendget_by_ref (caf_token_t dst_token, +int dst_image_index, caf_reference_t *dst_refs, +caf_token_t src_token, int src_image_index, caf_reference_t *src_refs, +int dst_kind, int src_kind, bool may_require_tmp, int *dst_stat, +int *src_stat, int dst_type, int src_type)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{dst_token} @tab intent(in) An opaque pointer identifying the +destination coarray. +@item @var{dst_image_index} @tab intent(in) The ID of the destination remote +image; must be a positive number. +@item @var{dst_refs} @tab intent(in) The references on the remote array to store +the data given by the source. Guaranteed to have at least one entry. +@item @var{src_token} @tab intent(in) An opaque pointer identifying the source +coarray. +@item @var{src_image_index} @tab intent(in) The ID of the source remote image; +must be a positive number. +@item @var{src_refs} @tab intent(in) The references to apply to the remote +structure to get the data. +@item @var{dst_kind} @tab intent(in) Kind of the destination argument +@item @var{src_kind} @tab intent(in) Kind of the source argument +@item @var{may_require_tmp} @tab intent(in) The variable is @code{false} when +it is known at compile time that the @var{dest} and @var{src} either cannot +overlap or overlap (fully or partially) such that walking @var{src} and +@var{dest} in element wise element order (honoring the stride value) will not +lead to wrong results. Otherwise, the value is @code{true}. +@item @var{dst_stat} @tab intent(out) when non-@code{NULL} give the result of +the send-operation, i.e., zero on success and non-zero on error. When +@code{NULL} and an error occurs, then an error message is printed and the +program is terminated. +@item @var{src_stat} @tab intent(out) When non-@code{NULL} give the result of +the get-operation, i.e., zero on success and non-zero on error. When +@code{NULL} and an error occurs, then an error message is printed and the +program is terminated. +@item @var{dst_type} @tab intent(in) Give the type of the destination. When +the destination is not an array, than the precise type, e.g. of a component in +a derived type, is not known, but provided here. +@item @var{src_type} @tab intent(in) Give the type of the source. When the +source is not an array, than the precise type, e.g. of a component in a +derived type, is not known, but provided here. +@end multitable + +@item @emph{NOTES} +It is permitted to have the same image index for both @var{src_image_index} and +@var{dst_image_index}; the memory of the send-to and the send-from might +(partially) overlap in that case. The implementation has to take care that it +handles this case, e.g. using @code{memmove} which handles (partially) +overlapping memory. If @var{may_require_tmp} is true, the library +might additionally create a temporary variable, unless additional checks show +that this is not required (e.g. because walking backward is possible or because +both arrays are contiguous and @code{memmove} takes care of overlap issues). + +Note that the assignment of a scalar to an array is permitted. In addition, +the library has to handle numeric-type conversion and for strings, padding and +different character kinds. + +Because of the more complicated references possible some operations may be +unsupported by certain libraries. The library is expected to issue a precise +error message why the operation is not permitted. +@end table + + +@node _gfortran_caf_lock +@subsection @code{_gfortran_caf_lock} --- Locking a lock variable +@cindex Coarray, _gfortran_caf_lock + +@table @asis +@item @emph{Description}: +Acquire a lock on the given image on a scalar locking variable or for the +given array element for an array-valued variable. If the @var{acquired_lock} +is @code{NULL}, the function returns after having obtained the lock. If it is +non-@code{NULL}, then @var{acquired_lock} is assigned the value true (one) when +the lock could be obtained and false (zero) otherwise. Locking a lock variable +which has already been locked by the same image is an error. + +@item @emph{Syntax}: +@code{void _gfortran_caf_lock (caf_token_t token, size_t index, int image_index, +int *acquired_lock, int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{index} @tab intent(in) Array index; first array index is 0. For +scalars, it is always 0. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number. +@item @var{acquired_lock} @tab intent(out) If not NULL, it returns whether lock +could be obtained. +@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTES} +This function is also called for critical blocks; for those, the array index +is always zero and the image index is one. Libraries are permitted to use other +images for critical-block locking variables. +@end table + +@node _gfortran_caf_unlock +@subsection @code{_gfortran_caf_lock} --- Unlocking a lock variable +@cindex Coarray, _gfortran_caf_unlock + +@table @asis +@item @emph{Description}: +Release a lock on the given image on a scalar locking variable or for the +given array element for an array-valued variable. Unlocking a lock variable +which is unlocked or has been locked by a different image is an error. + +@item @emph{Syntax}: +@code{void _gfortran_caf_unlock (caf_token_t token, size_t index, int image_index, +int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{index} @tab intent(in) Array index; first array index is 0. For +scalars, it is always 0. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number. +@item @var{stat} @tab intent(out) For allocatable coarrays, stores the STAT=; +may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTES} +This function is also called for critical block; for those, the array index +is always zero and the image index is one. Libraries are permitted to use other +images for critical-block locking variables. +@end table + +@node _gfortran_caf_event_post +@subsection @code{_gfortran_caf_event_post} --- Post an event +@cindex Coarray, _gfortran_caf_event_post + +@table @asis +@item @emph{Description}: +Increment the event count of the specified event variable. + +@item @emph{Syntax}: +@code{void _gfortran_caf_event_post (caf_token_t token, size_t index, +int image_index, int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{index} @tab intent(in) Array index; first array index is 0. For +scalars, it is always 0. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number; zero indicates the current image, when accessed noncoindexed. +@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTES} +This acts like an atomic add of one to the remote image's event variable. +The statement is an image-control statement but does not imply sync memory. +Still, all preceeding push communications of this image to the specified +remote image have to be completed before @code{event_wait} on the remote +image returns. +@end table + + + +@node _gfortran_caf_event_wait +@subsection @code{_gfortran_caf_event_wait} --- Wait that an event occurred +@cindex Coarray, _gfortran_caf_event_wait + +@table @asis +@item @emph{Description}: +Wait until the event count has reached at least the specified +@var{until_count}; if so, atomically decrement the event variable by this +amount and return. + +@item @emph{Syntax}: +@code{void _gfortran_caf_event_wait (caf_token_t token, size_t index, +int until_count, int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{index} @tab intent(in) Array index; first array index is 0. For +scalars, it is always 0. +@item @var{until_count} @tab intent(in) The number of events which have to be +available before the function returns. +@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTES} +This function only operates on a local coarray. It acts like a loop checking +atomically the value of the event variable, breaking if the value is greater +or equal the requested number of counts. Before the function returns, the +event variable has to be decremented by the requested @var{until_count} value. +A possible implementation would be a busy loop for a certain number of spins +(possibly depending on the number of threads relative to the number of available +cores) followed by another waiting strategy such as a sleeping wait (possibly +with an increasing number of sleep time) or, if possible, a futex wait. + +The statement is an image-control statement but does not imply sync memory. +Still, all preceeding push communications of this image to the specified +remote image have to be completed before @code{event_wait} on the remote +image returns. +@end table + + + +@node _gfortran_caf_event_query +@subsection @code{_gfortran_caf_event_query} --- Query event count +@cindex Coarray, _gfortran_caf_event_query + +@table @asis +@item @emph{Description}: +Return the event count of the specified event variable. + +@item @emph{Syntax}: +@code{void _gfortran_caf_event_query (caf_token_t token, size_t index, +int image_index, int *count, int *stat)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{index} @tab intent(in) Array index; first array index is 0. For +scalars, it is always 0. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number; zero indicates the current image when accessed noncoindexed. +@item @var{count} @tab intent(out) The number of events currently posted to +the event variable. +@item @var{stat} @tab intent(out) Stores the STAT=; may be NULL. +@end multitable + +@item @emph{NOTES} +The typical use is to check the local event variable to only call +@code{event_wait} when the data is available. However, a coindexed variable +is permitted; there is no ordering or synchronization implied. It acts like +an atomic fetch of the value of the event variable. +@end table + + + +@node _gfortran_caf_sync_all +@subsection @code{_gfortran_caf_sync_all} --- All-image barrier +@cindex Coarray, _gfortran_caf_sync_all + +@table @asis +@item @emph{Description}: +Synchronization of all images in the current team; the program only continues +on a given image after this function has been called on all images of the +current team. Additionally, it ensures that all pending data transfers of +previous segment have completed. + +@item @emph{Syntax}: +@code{void _gfortran_caf_sync_all (int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable +@end table + + + +@node _gfortran_caf_sync_images +@subsection @code{_gfortran_caf_sync_images} --- Barrier for selected images +@cindex Coarray, _gfortran_caf_sync_images + +@table @asis +@item @emph{Description}: +Synchronization between the specified images; the program only continues on a +given image after this function has been called on all images specified for +that image. Note that one image can wait for all other images in the current +team (e.g. via @code{sync images(*)}) while those only wait for that specific +image. Additionally, @code{sync images} ensures that all pending data +transfers of previous segments have completed. + +@item @emph{Syntax}: +@code{void _gfortran_caf_sync_images (int count, int images[], int *stat, +char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{count} @tab intent(in) The number of images which are provided in +the next argument. For a zero-sized array, the value is zero. For +@code{sync images (*)}, the value is @math{-1}. +@item @var{images} @tab intent(in) An array with the images provided by the +user. If @var{count} is zero, a NULL pointer is passed. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable +@end table + + + +@node _gfortran_caf_sync_memory +@subsection @code{_gfortran_caf_sync_memory} --- Wait for completion of segment-memory operations +@cindex Coarray, _gfortran_caf_sync_memory + +@table @asis +@item @emph{Description}: +Acts as optimization barrier between different segments. It also ensures that +all pending memory operations of this image have been completed. + +@item @emph{Syntax}: +@code{void _gfortran_caf_sync_memory (int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTE} A simple implementation could be +@code{__asm__ __volatile__ ("":::"memory")} to prevent code movements. +@end table + + + +@node _gfortran_caf_error_stop +@subsection @code{_gfortran_caf_error_stop} --- Error termination with exit code +@cindex Coarray, _gfortran_caf_error_stop + +@table @asis +@item @emph{Description}: +Invoked for an @code{ERROR STOP} statement which has an integer argument. The +function should terminate the program with the specified exit code. + + +@item @emph{Syntax}: +@code{void _gfortran_caf_error_stop (int error)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{error} @tab intent(in) The exit status to be used. +@end multitable +@end table + + + +@node _gfortran_caf_error_stop_str +@subsection @code{_gfortran_caf_error_stop_str} --- Error termination with string +@cindex Coarray, _gfortran_caf_error_stop_str + +@table @asis +@item @emph{Description}: +Invoked for an @code{ERROR STOP} statement which has a string as argument. The +function should terminate the program with a nonzero-exit code. + +@item @emph{Syntax}: +@code{void _gfortran_caf_error_stop (const char *string, size_t len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{string} @tab intent(in) the error message (not zero terminated) +@item @var{len} @tab intent(in) the length of the string +@end multitable +@end table + + + +@node _gfortran_caf_fail_image +@subsection @code{_gfortran_caf_fail_image} --- Mark the image failed and end its execution +@cindex Coarray, _gfortran_caf_fail_image + +@table @asis +@item @emph{Description}: +Invoked for an @code{FAIL IMAGE} statement. The function should terminate the +current image. + +@item @emph{Syntax}: +@code{void _gfortran_caf_fail_image ()} + +@item @emph{NOTES} +This function follows TS18508. +@end table + + + +@node _gfortran_caf_atomic_define +@subsection @code{_gfortran_caf_atomic_define} --- Atomic variable assignment +@cindex Coarray, _gfortran_caf_atomic_define + +@table @asis +@item @emph{Description}: +Assign atomically a value to an integer or logical variable. + +@item @emph{Syntax}: +@code{void _gfortran_caf_atomic_define (caf_token_t token, size_t offset, +int image_index, void *value, int *stat, int type, int kind)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{offset} @tab intent(in) By which amount of bytes the actual data is +shifted compared to the base address of the coarray. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number; zero indicates the current image when used noncoindexed. +@item @var{value} @tab intent(in) the value to be assigned, passed by reference +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{type} @tab intent(in) The data type, i.e. @code{BT_INTEGER} (1) or +@code{BT_LOGICAL} (2). +@item @var{kind} @tab intent(in) The kind value (only 4; always @code{int}) +@end multitable +@end table + + + +@node _gfortran_caf_atomic_ref +@subsection @code{_gfortran_caf_atomic_ref} --- Atomic variable reference +@cindex Coarray, _gfortran_caf_atomic_ref + +@table @asis +@item @emph{Description}: +Reference atomically a value of a kind-4 integer or logical variable. + +@item @emph{Syntax}: +@code{void _gfortran_caf_atomic_ref (caf_token_t token, size_t offset, +int image_index, void *value, int *stat, int type, int kind)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{offset} @tab intent(in) By which amount of bytes the actual data is +shifted compared to the base address of the coarray. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number; zero indicates the current image when used noncoindexed. +@item @var{value} @tab intent(out) The variable assigned the atomically +referenced variable. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{type} @tab the data type, i.e. @code{BT_INTEGER} (1) or +@code{BT_LOGICAL} (2). +@item @var{kind} @tab The kind value (only 4; always @code{int}) +@end multitable +@end table + + + +@node _gfortran_caf_atomic_cas +@subsection @code{_gfortran_caf_atomic_cas} --- Atomic compare and swap +@cindex Coarray, _gfortran_caf_atomic_cas + +@table @asis +@item @emph{Description}: +Atomic compare and swap of a kind-4 integer or logical variable. Assigns +atomically the specified value to the atomic variable, if the latter has +the value specified by the passed condition value. + +@item @emph{Syntax}: +@code{void _gfortran_caf_atomic_cas (caf_token_t token, size_t offset, +int image_index, void *old, void *compare, void *new_val, int *stat, +int type, int kind)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{offset} @tab intent(in) By which amount of bytes the actual data is +shifted compared to the base address of the coarray. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number; zero indicates the current image when used noncoindexed. +@item @var{old} @tab intent(out) The value which the atomic variable had +just before the cas operation. +@item @var{compare} @tab intent(in) The value used for comparision. +@item @var{new_val} @tab intent(in) The new value for the atomic variable, +assigned to the atomic variable, if @code{compare} equals the value of the +atomic variable. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{type} @tab intent(in) the data type, i.e. @code{BT_INTEGER} (1) or +@code{BT_LOGICAL} (2). +@item @var{kind} @tab intent(in) The kind value (only 4; always @code{int}) +@end multitable +@end table + + + +@node _gfortran_caf_atomic_op +@subsection @code{_gfortran_caf_atomic_op} --- Atomic operation +@cindex Coarray, _gfortran_caf_atomic_op + +@table @asis +@item @emph{Description}: +Apply an operation atomically to an atomic integer or logical variable. +After the operation, @var{old} contains the value just before the operation, +which, respectively, adds (GFC_CAF_ATOMIC_ADD) atomically the @code{value} to +the atomic integer variable or does a bitwise AND, OR or exclusive OR +between the atomic variable and @var{value}; the result is then stored in the +atomic variable. + +@item @emph{Syntax}: +@code{void _gfortran_caf_atomic_op (int op, caf_token_t token, size_t offset, +int image_index, void *value, void *old, int *stat, int type, int kind)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{op} @tab intent(in) the operation to be performed; possible values +@code{GFC_CAF_ATOMIC_ADD} (1), @code{GFC_CAF_ATOMIC_AND} (2), +@code{GFC_CAF_ATOMIC_OR} (3), @code{GFC_CAF_ATOMIC_XOR} (4). +@item @var{token} @tab intent(in) An opaque pointer identifying the coarray. +@item @var{offset} @tab intent(in) By which amount of bytes the actual data is +shifted compared to the base address of the coarray. +@item @var{image_index} @tab intent(in) The ID of the remote image; must be a +positive number; zero indicates the current image when used noncoindexed. +@item @var{old} @tab intent(out) The value which the atomic variable had +just before the atomic operation. +@item @var{val} @tab intent(in) The new value for the atomic variable, +assigned to the atomic variable, if @code{compare} equals the value of the +atomic variable. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{type} @tab intent(in) the data type, i.e. @code{BT_INTEGER} (1) or +@code{BT_LOGICAL} (2) +@item @var{kind} @tab intent(in) the kind value (only 4; always @code{int}) +@end multitable +@end table + + + + +@node _gfortran_caf_co_broadcast +@subsection @code{_gfortran_caf_co_broadcast} --- Sending data to all images +@cindex Coarray, _gfortran_caf_co_broadcast + +@table @asis +@item @emph{Description}: +Distribute a value from a given image to all other images in the team. Has to +be called collectively. + +@item @emph{Syntax}: +@code{void _gfortran_caf_co_broadcast (gfc_descriptor_t *a, +int source_image, int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{a} @tab intent(inout) An array descriptor with the data to be +broadcasted (on @var{source_image}) or to be received (other images). +@item @var{source_image} @tab intent(in) The ID of the image from which the +data should be broadcasted. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg. +@end multitable +@end table + + + +@node _gfortran_caf_co_max +@subsection @code{_gfortran_caf_co_max} --- Collective maximum reduction +@cindex Coarray, _gfortran_caf_co_max + +@table @asis +@item @emph{Description}: +Calculates for each array element of the variable @var{a} the maximum +value for that element in the current team; if @var{result_image} has the +value 0, the result shall be stored on all images, otherwise, only on the +specified image. This function operates on numeric values and character +strings. + +@item @emph{Syntax}: +@code{void _gfortran_caf_co_max (gfc_descriptor_t *a, int result_image, +int *stat, char *errmsg, int a_len, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{a} @tab intent(inout) An array descriptor for the data to be +processed. On the destination image(s) the result overwrites the old content. +@item @var{result_image} @tab intent(in) The ID of the image to which the +reduced value should be copied to; if zero, it has to be copied to all images. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{a_len} @tab intent(in) the string length of argument @var{a} +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTES} +If @var{result_image} is nonzero, the data in the array descriptor @var{a} on +all images except of the specified one become undefined; hence, the library may +make use of this. +@end table + + + +@node _gfortran_caf_co_min +@subsection @code{_gfortran_caf_co_min} --- Collective minimum reduction +@cindex Coarray, _gfortran_caf_co_min + +@table @asis +@item @emph{Description}: +Calculates for each array element of the variable @var{a} the minimum +value for that element in the current team; if @var{result_image} has the +value 0, the result shall be stored on all images, otherwise, only on the +specified image. This function operates on numeric values and character +strings. + +@item @emph{Syntax}: +@code{void _gfortran_caf_co_min (gfc_descriptor_t *a, int result_image, +int *stat, char *errmsg, int a_len, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{a} @tab intent(inout) An array descriptor for the data to be +processed. On the destination image(s) the result overwrites the old content. +@item @var{result_image} @tab intent(in) The ID of the image to which the +reduced value should be copied to; if zero, it has to be copied to all images. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{a_len} @tab intent(in) the string length of argument @var{a} +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTES} +If @var{result_image} is nonzero, the data in the array descriptor @var{a} on +all images except of the specified one become undefined; hence, the library may +make use of this. +@end table + + + +@node _gfortran_caf_co_sum +@subsection @code{_gfortran_caf_co_sum} --- Collective summing reduction +@cindex Coarray, _gfortran_caf_co_sum + +@table @asis +@item @emph{Description}: +Calculates for each array element of the variable @var{a} the sum of all +values for that element in the current team; if @var{result_image} has the +value 0, the result shall be stored on all images, otherwise, only on the +specified image. This function operates on numeric values only. + +@item @emph{Syntax}: +@code{void _gfortran_caf_co_sum (gfc_descriptor_t *a, int result_image, +int *stat, char *errmsg, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{a} @tab intent(inout) An array descriptor with the data to be +processed. On the destination image(s) the result overwrites the old content. +@item @var{result_image} @tab intent(in) The ID of the image to which the +reduced value should be copied to; if zero, it has to be copied to all images. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTES} +If @var{result_image} is nonzero, the data in the array descriptor @var{a} on +all images except of the specified one become undefined; hence, the library may +make use of this. +@end table + + + +@node _gfortran_caf_co_reduce +@subsection @code{_gfortran_caf_co_reduce} --- Generic collective reduction +@cindex Coarray, _gfortran_caf_co_reduce + +@table @asis +@item @emph{Description}: +Calculates for each array element of the variable @var{a} the reduction +value for that element in the current team; if @var{result_image} has the +value 0, the result shall be stored on all images, otherwise, only on the +specified image. The @var{opr} is a pure function doing a mathematically +commutative and associative operation. + +The @var{opr_flags} denote the following; the values are bitwise ored. +@code{GFC_CAF_BYREF} (1) if the result should be returned +by reference; @code{GFC_CAF_HIDDENLEN} (2) whether the result and argument +string lengths shall be specified as hidden arguments; +@code{GFC_CAF_ARG_VALUE} (4) whether the arguments shall be passed by value, +@code{GFC_CAF_ARG_DESC} (8) whether the arguments shall be passed by descriptor. + + +@item @emph{Syntax}: +@code{void _gfortran_caf_co_reduce (gfc_descriptor_t *a, +void * (*opr) (void *, void *), int opr_flags, int result_image, +int *stat, char *errmsg, int a_len, size_t errmsg_len)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{a} @tab intent(inout) An array descriptor with the data to be +processed. On the destination image(s) the result overwrites the old content. +@item @var{opr} @tab intent(in) Function pointer to the reduction function +@item @var{opr_flags} @tab intent(in) Flags regarding the reduction function +@item @var{result_image} @tab intent(in) The ID of the image to which the +reduced value should be copied to; if zero, it has to be copied to all images. +@item @var{stat} @tab intent(out) Stores the status STAT= and may be NULL. +@item @var{errmsg} @tab intent(out) When an error occurs, this will be set to +an error message; may be NULL. +@item @var{a_len} @tab intent(in) the string length of argument @var{a} +@item @var{errmsg_len} @tab intent(in) the buffer size of errmsg +@end multitable + +@item @emph{NOTES} +If @var{result_image} is nonzero, the data in the array descriptor @var{a} on +all images except of the specified one become undefined; hence, the library may +make use of this. + +For character arguments, the result is passed as first argument, followed +by the result string length, next come the two string arguments, followed +by the two hidden string length arguments. With C binding, there are no hidden +arguments and by-reference passing and either only a single character is passed +or an array descriptor. +@end table + + +@c Intrinsic Procedures +@c --------------------------------------------------------------------- + +@include intrinsic.texi + + +@tex +\blankpart +@end tex + +@c --------------------------------------------------------------------- +@c Contributing +@c --------------------------------------------------------------------- + +@node Contributing +@unnumbered Contributing +@cindex Contributing + +Free software is only possible if people contribute to efforts +to create it. +We're always in need of more people helping out with ideas +and comments, writing documentation and contributing code. + +If you want to contribute to GNU Fortran, +have a look at the long lists of projects you can take on. +Some of these projects are small, +some of them are large; +some are completely orthogonal to the rest of what is +happening on GNU Fortran, +but others are ``mainstream'' projects in need of enthusiastic hackers. +All of these projects are important! +We will eventually get around to the things here, +but they are also things doable by someone who is willing and able. + +@menu +* Contributors:: +* Projects:: +@end menu + + +@node Contributors +@section Contributors to GNU Fortran +@cindex Contributors +@cindex Credits +@cindex Authors + +Most of the parser was hand-crafted by @emph{Andy Vaught}, who is +also the initiator of the whole project. Thanks Andy! +Most of the interface with GCC was written by @emph{Paul Brook}. + +The following individuals have contributed code and/or +ideas and significant help to the GNU Fortran project +(in alphabetical order): + +@itemize @minus +@item Janne Blomqvist +@item Steven Bosscher +@item Paul Brook +@item Tobias Burnus +@item Fran@,{c}ois-Xavier Coudert +@item Bud Davis +@item Jerry DeLisle +@item Erik Edelmann +@item Bernhard Fischer +@item Daniel Franke +@item Richard Guenther +@item Richard Henderson +@item Katherine Holcomb +@item Jakub Jelinek +@item Niels Kristian Bech Jensen +@item Steven Johnson +@item Steven G. Kargl +@item Thomas Koenig +@item Asher Langton +@item H. J. Lu +@item Toon Moene +@item Brooks Moses +@item Andrew Pinski +@item Tim Prince +@item Christopher D. Rickett +@item Richard Sandiford +@item Tobias Schl@"uter +@item Roger Sayle +@item Paul Thomas +@item Andy Vaught +@item Feng Wang +@item Janus Weil +@item Daniel Kraft +@end itemize + +The following people have contributed bug reports, +smaller or larger patches, +and much needed feedback and encouragement for the +GNU Fortran project: + +@itemize @minus +@item Bill Clodius +@item Dominique d'Humi@`eres +@item Kate Hedstrom +@item Erik Schnetter +@item Gerhard Steinmetz +@item Joost VandeVondele +@end itemize + +Many other individuals have helped debug, +test and improve the GNU Fortran compiler over the past few years, +and we welcome you to do the same! +If you already have done so, +and you would like to see your name listed in the +list above, please contact us. + + +@node Projects +@section Projects + +@table @emph + +@item Help build the test suite +Solicit more code for donation to the test suite: the more extensive the +testsuite, the smaller the risk of breaking things in the future! We can +keep code private on request. + +@item Bug hunting/squishing +Find bugs and write more test cases! Test cases are especially very +welcome, because it allows us to concentrate on fixing bugs instead of +isolating them. Going through the bugzilla database at +@url{https://gcc.gnu.org/@/bugzilla/} to reduce testcases posted there and +add more information (for example, for which version does the testcase +work, for which versions does it fail?) is also very helpful. + +@item Missing features +For a larger project, consider working on the missing features required for +Fortran language standards compliance (@pxref{Standards}), or contributing +to the implementation of extensions such as OpenMP (@pxref{OpenMP}) or +OpenACC (@pxref{OpenACC}) that are under active development. Again, +contributing test cases for these features is useful too! + +@end table + + +@c --------------------------------------------------------------------- +@c GNU General Public License +@c --------------------------------------------------------------------- + +@include gpl_v3.texi + + + +@c --------------------------------------------------------------------- +@c GNU Free Documentation License +@c --------------------------------------------------------------------- + +@include fdl.texi + + + +@c --------------------------------------------------------------------- +@c Funding Free Software +@c --------------------------------------------------------------------- + +@include funding.texi + +@c --------------------------------------------------------------------- +@c Indices +@c --------------------------------------------------------------------- + +@node Option Index +@unnumbered Option Index +@command{gfortran}'s command line options are indexed here without any +initial @samp{-} or @samp{--}. Where an option has both positive and +negative forms (such as -foption and -fno-option), relevant entries in +the manual are indexed under the most appropriate form; it may sometimes +be useful to look up both forms. +@printindex op + +@node Keyword Index +@unnumbered Keyword Index +@printindex cp + +@bye diff --git a/gcc/fortran/intrinsic.texi b/gcc/fortran/intrinsic.texi new file mode 100644 index 00000000000..55f53fc1137 --- /dev/null +++ b/gcc/fortran/intrinsic.texi @@ -0,0 +1,15435 @@ +@ignore +Copyright (C) 2005-2022 Free Software Foundation, Inc. +This is part of the GNU Fortran manual. +For copying conditions, see the file gfortran.texi. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``Funding Free Software'', the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the gfdl(7) man page. + + +Some basic guidelines for editing this document: + + (1) The intrinsic procedures are to be listed in alphabetical order. + (2) The generic name is to be used. + (3) The specific names are included in the function index and in a + table at the end of the node (See ABS entry). + (4) Try to maintain the same style for each entry. + + +@end ignore + +@tex +\gdef\acosd{\mathop{\rm acosd}\nolimits} +\gdef\asind{\mathop{\rm asind}\nolimits} +\gdef\atand{\mathop{\rm atand}\nolimits} +\gdef\acos{\mathop{\rm acos}\nolimits} +\gdef\asin{\mathop{\rm asin}\nolimits} +\gdef\atan{\mathop{\rm atan}\nolimits} +\gdef\acosh{\mathop{\rm acosh}\nolimits} +\gdef\asinh{\mathop{\rm asinh}\nolimits} +\gdef\atanh{\mathop{\rm atanh}\nolimits} +\gdef\cosd{\mathop{\rm cosd}\nolimits} +@end tex + + +@node Intrinsic Procedures +@chapter Intrinsic Procedures +@cindex intrinsic procedures + +@menu +* Introduction: Introduction to Intrinsics +* @code{ABORT}: ABORT, Abort the program +* @code{ABS}: ABS, Absolute value +* @code{ACCESS}: ACCESS, Checks file access modes +* @code{ACHAR}: ACHAR, Character in @acronym{ASCII} collating sequence +* @code{ACOS}: ACOS, Arccosine function +* @code{ACOSD}: ACOSD, Arccosine function, degrees +* @code{ACOSH}: ACOSH, Inverse hyperbolic cosine function +* @code{ADJUSTL}: ADJUSTL, Left adjust a string +* @code{ADJUSTR}: ADJUSTR, Right adjust a string +* @code{AIMAG}: AIMAG, Imaginary part of complex number +* @code{AINT}: AINT, Truncate to a whole number +* @code{ALARM}: ALARM, Set an alarm clock +* @code{ALL}: ALL, Determine if all values are true +* @code{ALLOCATED}: ALLOCATED, Status of allocatable entity +* @code{AND}: AND, Bitwise logical AND +* @code{ANINT}: ANINT, Nearest whole number +* @code{ANY}: ANY, Determine if any values are true +* @code{ASIN}: ASIN, Arcsine function +* @code{ASIND}: ASIND, Arcsine function, degrees +* @code{ASINH}: ASINH, Inverse hyperbolic sine function +* @code{ASSOCIATED}: ASSOCIATED, Status of a pointer or pointer/target pair +* @code{ATAN}: ATAN, Arctangent function +* @code{ATAND}: ATAND, Arctangent function, degrees +* @code{ATAN2}: ATAN2, Arctangent function +* @code{ATAN2D}: ATAN2D, Arctangent function, degrees +* @code{ATANH}: ATANH, Inverse hyperbolic tangent function +* @code{ATOMIC_ADD}: ATOMIC_ADD, Atomic ADD operation +* @code{ATOMIC_AND}: ATOMIC_AND, Atomic bitwise AND operation +* @code{ATOMIC_CAS}: ATOMIC_CAS, Atomic compare and swap +* @code{ATOMIC_DEFINE}: ATOMIC_DEFINE, Setting a variable atomically +* @code{ATOMIC_FETCH_ADD}: ATOMIC_FETCH_ADD, Atomic ADD operation with prior fetch +* @code{ATOMIC_FETCH_AND}: ATOMIC_FETCH_AND, Atomic bitwise AND operation with prior fetch +* @code{ATOMIC_FETCH_OR}: ATOMIC_FETCH_OR, Atomic bitwise OR operation with prior fetch +* @code{ATOMIC_FETCH_XOR}: ATOMIC_FETCH_XOR, Atomic bitwise XOR operation with prior fetch +* @code{ATOMIC_OR}: ATOMIC_OR, Atomic bitwise OR operation +* @code{ATOMIC_REF}: ATOMIC_REF, Obtaining the value of a variable atomically +* @code{ATOMIC_XOR}: ATOMIC_XOR, Atomic bitwise OR operation +* @code{BACKTRACE}: BACKTRACE, Show a backtrace +* @code{BESSEL_J0}: BESSEL_J0, Bessel function of the first kind of order 0 +* @code{BESSEL_J1}: BESSEL_J1, Bessel function of the first kind of order 1 +* @code{BESSEL_JN}: BESSEL_JN, Bessel function of the first kind +* @code{BESSEL_Y0}: BESSEL_Y0, Bessel function of the second kind of order 0 +* @code{BESSEL_Y1}: BESSEL_Y1, Bessel function of the second kind of order 1 +* @code{BESSEL_YN}: BESSEL_YN, Bessel function of the second kind +* @code{BGE}: BGE, Bitwise greater than or equal to +* @code{BGT}: BGT, Bitwise greater than +* @code{BIT_SIZE}: BIT_SIZE, Bit size inquiry function +* @code{BLE}: BLE, Bitwise less than or equal to +* @code{BLT}: BLT, Bitwise less than +* @code{BTEST}: BTEST, Bit test function +* @code{C_ASSOCIATED}: C_ASSOCIATED, Status of a C pointer +* @code{C_F_POINTER}: C_F_POINTER, Convert C into Fortran pointer +* @code{C_F_PROCPOINTER}: C_F_PROCPOINTER, Convert C into Fortran procedure pointer +* @code{C_FUNLOC}: C_FUNLOC, Obtain the C address of a procedure +* @code{C_LOC}: C_LOC, Obtain the C address of an object +* @code{C_SIZEOF}: C_SIZEOF, Size in bytes of an expression +* @code{CEILING}: CEILING, Integer ceiling function +* @code{CHAR}: CHAR, Integer-to-character conversion function +* @code{CHDIR}: CHDIR, Change working directory +* @code{CHMOD}: CHMOD, Change access permissions of files +* @code{CMPLX}: CMPLX, Complex conversion function +* @code{CO_BROADCAST}: CO_BROADCAST, Copy a value to all images the current set of images +* @code{CO_MAX}: CO_MAX, Maximal value on the current set of images +* @code{CO_MIN}: CO_MIN, Minimal value on the current set of images +* @code{CO_REDUCE}: CO_REDUCE, Reduction of values on the current set of images +* @code{CO_SUM}: CO_SUM, Sum of values on the current set of images +* @code{COMMAND_ARGUMENT_COUNT}: COMMAND_ARGUMENT_COUNT, Get number of command line arguments +* @code{COMPILER_OPTIONS}: COMPILER_OPTIONS, Options passed to the compiler +* @code{COMPILER_VERSION}: COMPILER_VERSION, Compiler version string +* @code{COMPLEX}: COMPLEX, Complex conversion function +* @code{CONJG}: CONJG, Complex conjugate function +* @code{COS}: COS, Cosine function +* @code{COSD}: COSD, Cosine function, degrees +* @code{COSH}: COSH, Hyperbolic cosine function +* @code{COTAN}: COTAN, Cotangent function +* @code{COTAND}: COTAND, Cotangent function, degrees +* @code{COUNT}: COUNT, Count occurrences of TRUE in an array +* @code{CPU_TIME}: CPU_TIME, CPU time subroutine +* @code{CSHIFT}: CSHIFT, Circular shift elements of an array +* @code{CTIME}: CTIME, Subroutine (or function) to convert a time into a string +* @code{DATE_AND_TIME}: DATE_AND_TIME, Date and time subroutine +* @code{DBLE}: DBLE, Double precision conversion function +* @code{DCMPLX}: DCMPLX, Double complex conversion function +* @code{DIGITS}: DIGITS, Significant digits function +* @code{DIM}: DIM, Positive difference +* @code{DOT_PRODUCT}: DOT_PRODUCT, Dot product function +* @code{DPROD}: DPROD, Double product function +* @code{DREAL}: DREAL, Double real part function +* @code{DSHIFTL}: DSHIFTL, Combined left shift +* @code{DSHIFTR}: DSHIFTR, Combined right shift +* @code{DTIME}: DTIME, Execution time subroutine (or function) +* @code{EOSHIFT}: EOSHIFT, End-off shift elements of an array +* @code{EPSILON}: EPSILON, Epsilon function +* @code{ERF}: ERF, Error function +* @code{ERFC}: ERFC, Complementary error function +* @code{ERFC_SCALED}: ERFC_SCALED, Exponentially-scaled complementary error function +* @code{ETIME}: ETIME, Execution time subroutine (or function) +* @code{EVENT_QUERY}: EVENT_QUERY, Query whether a coarray event has occurred +* @code{EXECUTE_COMMAND_LINE}: EXECUTE_COMMAND_LINE, Execute a shell command +* @code{EXIT}: EXIT, Exit the program with status. +* @code{EXP}: EXP, Exponential function +* @code{EXPONENT}: EXPONENT, Exponent function +* @code{EXTENDS_TYPE_OF}: EXTENDS_TYPE_OF, Query dynamic type for extension +* @code{FDATE}: FDATE, Subroutine (or function) to get the current time as a string +* @code{FGET}: FGET, Read a single character in stream mode from stdin +* @code{FGETC}: FGETC, Read a single character in stream mode +* @code{FINDLOC}: FINDLOC, Search an array for a value +* @code{FLOOR}: FLOOR, Integer floor function +* @code{FLUSH}: FLUSH, Flush I/O unit(s) +* @code{FNUM}: FNUM, File number function +* @code{FPUT}: FPUT, Write a single character in stream mode to stdout +* @code{FPUTC}: FPUTC, Write a single character in stream mode +* @code{FRACTION}: FRACTION, Fractional part of the model representation +* @code{FREE}: FREE, Memory de-allocation subroutine +* @code{FSEEK}: FSEEK, Low level file positioning subroutine +* @code{FSTAT}: FSTAT, Get file status +* @code{FTELL}: FTELL, Current stream position +* @code{GAMMA}: GAMMA, Gamma function +* @code{GERROR}: GERROR, Get last system error message +* @code{GETARG}: GETARG, Get command line arguments +* @code{GET_COMMAND}: GET_COMMAND, Get the entire command line +* @code{GET_COMMAND_ARGUMENT}: GET_COMMAND_ARGUMENT, Get command line arguments +* @code{GETCWD}: GETCWD, Get current working directory +* @code{GETENV}: GETENV, Get an environmental variable +* @code{GET_ENVIRONMENT_VARIABLE}: GET_ENVIRONMENT_VARIABLE, Get an environmental variable +* @code{GETGID}: GETGID, Group ID function +* @code{GETLOG}: GETLOG, Get login name +* @code{GETPID}: GETPID, Process ID function +* @code{GETUID}: GETUID, User ID function +* @code{GMTIME}: GMTIME, Convert time to GMT info +* @code{HOSTNM}: HOSTNM, Get system host name +* @code{HUGE}: HUGE, Largest number of a kind +* @code{HYPOT}: HYPOT, Euclidean distance function +* @code{IACHAR}: IACHAR, Code in @acronym{ASCII} collating sequence +* @code{IALL}: IALL, Bitwise AND of array elements +* @code{IAND}: IAND, Bitwise logical and +* @code{IANY}: IANY, Bitwise OR of array elements +* @code{IARGC}: IARGC, Get the number of command line arguments +* @code{IBCLR}: IBCLR, Clear bit +* @code{IBITS}: IBITS, Bit extraction +* @code{IBSET}: IBSET, Set bit +* @code{ICHAR}: ICHAR, Character-to-integer conversion function +* @code{IDATE}: IDATE, Current local time (day/month/year) +* @code{IEOR}: IEOR, Bitwise logical exclusive or +* @code{IERRNO}: IERRNO, Function to get the last system error number +* @code{IMAGE_INDEX}: IMAGE_INDEX, Cosubscript to image index conversion +* @code{INDEX}: INDEX intrinsic, Position of a substring within a string +* @code{INT}: INT, Convert to integer type +* @code{INT2}: INT2, Convert to 16-bit integer type +* @code{INT8}: INT8, Convert to 64-bit integer type +* @code{IOR}: IOR, Bitwise logical or +* @code{IPARITY}: IPARITY, Bitwise XOR of array elements +* @code{IRAND}: IRAND, Integer pseudo-random number +* @code{IS_CONTIGUOUS}: IS_CONTIGUOUS, Test whether an array is contiguous +* @code{IS_IOSTAT_END}: IS_IOSTAT_END, Test for end-of-file value +* @code{IS_IOSTAT_EOR}: IS_IOSTAT_EOR, Test for end-of-record value +* @code{ISATTY}: ISATTY, Whether a unit is a terminal device +* @code{ISHFT}: ISHFT, Shift bits +* @code{ISHFTC}: ISHFTC, Shift bits circularly +* @code{ISNAN}: ISNAN, Tests for a NaN +* @code{ITIME}: ITIME, Current local time (hour/minutes/seconds) +* @code{KILL}: KILL, Send a signal to a process +* @code{KIND}: KIND, Kind of an entity +* @code{LBOUND}: LBOUND, Lower dimension bounds of an array +* @code{LCOBOUND}: LCOBOUND, Lower codimension bounds of an array +* @code{LEADZ}: LEADZ, Number of leading zero bits of an integer +* @code{LEN}: LEN, Length of a character entity +* @code{LEN_TRIM}: LEN_TRIM, Length of a character entity without trailing blank characters +* @code{LGE}: LGE, Lexical greater than or equal +* @code{LGT}: LGT, Lexical greater than +* @code{LINK}: LINK, Create a hard link +* @code{LLE}: LLE, Lexical less than or equal +* @code{LLT}: LLT, Lexical less than +* @code{LNBLNK}: LNBLNK, Index of the last non-blank character in a string +* @code{LOC}: LOC, Returns the address of a variable +* @code{LOG}: LOG, Logarithm function +* @code{LOG10}: LOG10, Base 10 logarithm function +* @code{LOG_GAMMA}: LOG_GAMMA, Logarithm of the Gamma function +* @code{LOGICAL}: LOGICAL, Convert to logical type +* @code{LSHIFT}: LSHIFT, Left shift bits +* @code{LSTAT}: LSTAT, Get file status +* @code{LTIME}: LTIME, Convert time to local time info +* @code{MALLOC}: MALLOC, Dynamic memory allocation function +* @code{MASKL}: MASKL, Left justified mask +* @code{MASKR}: MASKR, Right justified mask +* @code{MATMUL}: MATMUL, matrix multiplication +* @code{MAX}: MAX, Maximum value of an argument list +* @code{MAXEXPONENT}: MAXEXPONENT, Maximum exponent of a real kind +* @code{MAXLOC}: MAXLOC, Location of the maximum value within an array +* @code{MAXVAL}: MAXVAL, Maximum value of an array +* @code{MCLOCK}: MCLOCK, Time function +* @code{MCLOCK8}: MCLOCK8, Time function (64-bit) +* @code{MERGE}: MERGE, Merge arrays +* @code{MERGE_BITS}: MERGE_BITS, Merge of bits under mask +* @code{MIN}: MIN, Minimum value of an argument list +* @code{MINEXPONENT}: MINEXPONENT, Minimum exponent of a real kind +* @code{MINLOC}: MINLOC, Location of the minimum value within an array +* @code{MINVAL}: MINVAL, Minimum value of an array +* @code{MOD}: MOD, Remainder function +* @code{MODULO}: MODULO, Modulo function +* @code{MOVE_ALLOC}: MOVE_ALLOC, Move allocation from one object to another +* @code{MVBITS}: MVBITS, Move bits from one integer to another +* @code{NEAREST}: NEAREST, Nearest representable number +* @code{NEW_LINE}: NEW_LINE, New line character +* @code{NINT}: NINT, Nearest whole number +* @code{NORM2}: NORM2, Euclidean vector norm +* @code{NOT}: NOT, Logical negation +* @code{NULL}: NULL, Function that returns an disassociated pointer +* @code{NUM_IMAGES}: NUM_IMAGES, Number of images +* @code{OR}: OR, Bitwise logical OR +* @code{PACK}: PACK, Pack an array into an array of rank one +* @code{PARITY}: PARITY, Reduction with exclusive OR +* @code{PERROR}: PERROR, Print system error message +* @code{POPCNT}: POPCNT, Number of bits set +* @code{POPPAR}: POPPAR, Parity of the number of bits set +* @code{PRECISION}: PRECISION, Decimal precision of a real kind +* @code{PRESENT}: PRESENT, Determine whether an optional dummy argument is specified +* @code{PRODUCT}: PRODUCT, Product of array elements +* @code{RADIX}: RADIX, Base of a data model +* @code{RAN}: RAN, Real pseudo-random number +* @code{RAND}: RAND, Real pseudo-random number +* @code{RANDOM_INIT}: RANDOM_INIT, Initialize pseudo-random number generator +* @code{RANDOM_NUMBER}: RANDOM_NUMBER, Pseudo-random number +* @code{RANDOM_SEED}: RANDOM_SEED, Initialize a pseudo-random number sequence +* @code{RANGE}: RANGE, Decimal exponent range +* @code{RANK} : RANK, Rank of a data object +* @code{REAL}: REAL, Convert to real type +* @code{RENAME}: RENAME, Rename a file +* @code{REPEAT}: REPEAT, Repeated string concatenation +* @code{RESHAPE}: RESHAPE, Function to reshape an array +* @code{RRSPACING}: RRSPACING, Reciprocal of the relative spacing +* @code{RSHIFT}: RSHIFT, Right shift bits +* @code{SAME_TYPE_AS}: SAME_TYPE_AS, Query dynamic types for equality +* @code{SCALE}: SCALE, Scale a real value +* @code{SCAN}: SCAN, Scan a string for the presence of a set of characters +* @code{SECNDS}: SECNDS, Time function +* @code{SECOND}: SECOND, CPU time function +* @code{SELECTED_CHAR_KIND}: SELECTED_CHAR_KIND, Choose character kind +* @code{SELECTED_INT_KIND}: SELECTED_INT_KIND, Choose integer kind +* @code{SELECTED_REAL_KIND}: SELECTED_REAL_KIND, Choose real kind +* @code{SET_EXPONENT}: SET_EXPONENT, Set the exponent of the model +* @code{SHAPE}: SHAPE, Determine the shape of an array +* @code{SHIFTA}: SHIFTA, Right shift with fill +* @code{SHIFTL}: SHIFTL, Left shift +* @code{SHIFTR}: SHIFTR, Right shift +* @code{SIGN}: SIGN, Sign copying function +* @code{SIGNAL}: SIGNAL, Signal handling subroutine (or function) +* @code{SIN}: SIN, Sine function +* @code{SIND}: SIND, Sine function, degrees +* @code{SINH}: SINH, Hyperbolic sine function +* @code{SIZE}: SIZE, Function to determine the size of an array +* @code{SIZEOF}: SIZEOF, Determine the size in bytes of an expression +* @code{SLEEP}: SLEEP, Sleep for the specified number of seconds +* @code{SPACING}: SPACING, Smallest distance between two numbers of a given type +* @code{SPREAD}: SPREAD, Add a dimension to an array +* @code{SQRT}: SQRT, Square-root function +* @code{SRAND}: SRAND, Reinitialize the random number generator +* @code{STAT}: STAT, Get file status +* @code{STORAGE_SIZE}: STORAGE_SIZE, Storage size in bits +* @code{SUM}: SUM, Sum of array elements +* @code{SYMLNK}: SYMLNK, Create a symbolic link +* @code{SYSTEM}: SYSTEM, Execute a shell command +* @code{SYSTEM_CLOCK}: SYSTEM_CLOCK, Time function +* @code{TAN}: TAN, Tangent function +* @code{TAND}: TAND, Tangent function, degrees +* @code{TANH}: TANH, Hyperbolic tangent function +* @code{THIS_IMAGE}: THIS_IMAGE, Cosubscript index of this image +* @code{TIME}: TIME, Time function +* @code{TIME8}: TIME8, Time function (64-bit) +* @code{TINY}: TINY, Smallest positive number of a real kind +* @code{TRAILZ}: TRAILZ, Number of trailing zero bits of an integer +* @code{TRANSFER}: TRANSFER, Transfer bit patterns +* @code{TRANSPOSE}: TRANSPOSE, Transpose an array of rank two +* @code{TRIM}: TRIM, Remove trailing blank characters of a string +* @code{TTYNAM}: TTYNAM, Get the name of a terminal device +* @code{UBOUND}: UBOUND, Upper dimension bounds of an array +* @code{UCOBOUND}: UCOBOUND, Upper codimension bounds of an array +* @code{UMASK}: UMASK, Set the file creation mask +* @code{UNLINK}: UNLINK, Remove a file from the file system +* @code{UNPACK}: UNPACK, Unpack an array of rank one into an array +* @code{VERIFY}: VERIFY, Scan a string for the absence of a set of characters +* @code{XOR}: XOR, Bitwise logical exclusive or +@end menu + +@node Introduction to Intrinsics +@section Introduction to intrinsic procedures + +The intrinsic procedures provided by GNU Fortran include procedures required +by the Fortran 95 and later supported standards, and a set of intrinsic +procedures for backwards compatibility with G77. Any conflict between +a description here and a description in the Fortran standards is +unintentional, and the standard(s) should be considered authoritative. + +The enumeration of the @code{KIND} type parameter is processor defined in +the Fortran 95 standard. GNU Fortran defines the default integer type and +default real type by @code{INTEGER(KIND=4)} and @code{REAL(KIND=4)}, +respectively. The standard mandates that both data types shall have +another kind, which have more precision. On typical target architectures +supported by @command{gfortran}, this kind type parameter is @code{KIND=8}. +Hence, @code{REAL(KIND=8)} and @code{DOUBLE PRECISION} are equivalent. +In the description of generic intrinsic procedures, the kind type parameter +will be specified by @code{KIND=*}, and in the description of specific +names for an intrinsic procedure the kind type parameter will be explicitly +given (e.g., @code{REAL(KIND=4)} or @code{REAL(KIND=8)}). Finally, for +brevity the optional @code{KIND=} syntax will be omitted. + +Many of the intrinsic procedures take one or more optional arguments. +This document follows the convention used in the Fortran 95 standard, +and denotes such arguments by square brackets. + +GNU Fortran offers the @option{-std=} command-line option, +which can be used to restrict the set of intrinsic procedures to a +given standard. By default, @command{gfortran} sets the @option{-std=gnu} +option, and so all intrinsic procedures described here are accepted. There +is one caveat. For a select group of intrinsic procedures, @command{g77} +implemented both a function and a subroutine. Both classes +have been implemented in @command{gfortran} for backwards compatibility +with @command{g77}. It is noted here that these functions and subroutines +cannot be intermixed in a given subprogram. In the descriptions that follow, +the applicable standard for each intrinsic procedure is noted. + + + +@node ABORT +@section @code{ABORT} --- Abort the program +@fnindex ABORT +@cindex program termination, with core dump +@cindex terminate program, with core dump +@cindex core, dump + +@table @asis +@item @emph{Description}: +@code{ABORT} causes immediate termination of the program. On operating +systems that support a core dump, @code{ABORT} will produce a core dump. +It will also print a backtrace, unless @code{-fno-backtrace} is given. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL ABORT} + +@item @emph{Return value}: +Does not return. + +@item @emph{Example}: +@smallexample +program test_abort + integer :: i = 1, j = 2 + if (i /= j) call abort +end program test_abort +@end smallexample + +@item @emph{See also}: +@ref{EXIT}, @gol +@ref{KILL}, @gol +@ref{BACKTRACE} +@end table + + + +@node ABS +@section @code{ABS} --- Absolute value +@fnindex ABS +@fnindex CABS +@fnindex DABS +@fnindex IABS +@fnindex ZABS +@fnindex CDABS +@fnindex BABS +@fnindex IIABS +@fnindex JIABS +@fnindex KIABS +@cindex absolute value + +@table @asis +@item @emph{Description}: +@code{ABS(A)} computes the absolute value of @code{A}. + +@item @emph{Standard}: +Fortran 77 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ABS(A)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab The type of the argument shall be an @code{INTEGER}, +@code{REAL}, or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and +kind as the argument except the return value is @code{REAL} for a +@code{COMPLEX} argument. + +@item @emph{Example}: +@smallexample +program test_abs + integer :: i = -1 + real :: x = -1.e0 + complex :: z = (-1.e0,0.e0) + i = abs(i) + x = abs(x) + x = abs(z) +end program test_abs +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ABS(A)} @tab @code{REAL(4) A} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{CABS(A)} @tab @code{COMPLEX(4) A} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DABS(A)} @tab @code{REAL(8) A} @tab @code{REAL(8)} @tab Fortran 77 and later +@item @code{IABS(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab Fortran 77 and later +@item @code{BABS(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IIABS(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JIABS(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KIABS(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@item @code{ZABS(A)} @tab @code{COMPLEX(8) A} @tab @code{REAL(8)} @tab GNU extension +@item @code{CDABS(A)} @tab @code{COMPLEX(8) A} @tab @code{REAL(8)} @tab GNU extension +@end multitable +@end table + + + +@node ACCESS +@section @code{ACCESS} --- Checks file access modes +@fnindex ACCESS +@cindex file system, access mode + +@table @asis +@item @emph{Description}: +@code{ACCESS(NAME, MODE)} checks whether the file @var{NAME} +exists, is readable, writable or executable. Except for the +executable check, @code{ACCESS} can be replaced by +Fortran 95's @code{INQUIRE}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = ACCESS(NAME, MODE)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NAME} @tab Scalar @code{CHARACTER} of default kind with the +file name. Trailing blank are ignored unless the character @code{achar(0)} +is present, then all characters up to and excluding @code{achar(0)} are +used as file name. +@item @var{MODE} @tab Scalar @code{CHARACTER} of default kind with the +file access mode, may be any concatenation of @code{"r"} (readable), +@code{"w"} (writable) and @code{"x"} (executable), or @code{" "} to check +for existence. +@end multitable + +@item @emph{Return value}: +Returns a scalar @code{INTEGER}, which is @code{0} if the file is +accessible in the given mode; otherwise or if an invalid argument +has been given for @code{MODE} the value @code{1} is returned. + +@item @emph{Example}: +@smallexample +program access_test + implicit none + character(len=*), parameter :: file = 'test.dat' + character(len=*), parameter :: file2 = 'test.dat '//achar(0) + if(access(file,' ') == 0) print *, trim(file),' is exists' + if(access(file,'r') == 0) print *, trim(file),' is readable' + if(access(file,'w') == 0) print *, trim(file),' is writable' + if(access(file,'x') == 0) print *, trim(file),' is executable' + if(access(file2,'rwx') == 0) & + print *, trim(file2),' is readable, writable and executable' +end program access_test +@end smallexample +@end table + + + +@node ACHAR +@section @code{ACHAR} --- Character in @acronym{ASCII} collating sequence +@fnindex ACHAR +@cindex @acronym{ASCII} collating sequence +@cindex collating sequence, @acronym{ASCII} + +@table @asis +@item @emph{Description}: +@code{ACHAR(I)} returns the character located at position @code{I} +in the @acronym{ASCII} collating sequence. + +@item @emph{Standard}: +Fortran 77 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ACHAR(I [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{CHARACTER} with a length of one. +If the @var{KIND} argument is present, the return value is of the +specified kind and of the default kind otherwise. + +@item @emph{Example}: +@smallexample +program test_achar + character c + c = achar(32) +end program test_achar +@end smallexample + +@item @emph{Note}: +See @ref{ICHAR} for a discussion of converting between numerical values +and formatted string representations. + +@item @emph{See also}: +@ref{CHAR}, @gol +@ref{IACHAR}, @gol +@ref{ICHAR} +@end table + + + +@node ACOS +@section @code{ACOS} --- Arccosine function +@fnindex ACOS +@fnindex DACOS +@cindex trigonometric function, cosine, inverse +@cindex cosine, inverse + +@table @asis +@item @emph{Description}: +@code{ACOS(X)} computes the arccosine of @var{X} (inverse of @code{COS(X)}). + +@item @emph{Standard}: +Fortran 77 and later, for a complex argument Fortran 2008 or later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ACOS(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall either be @code{REAL} with a magnitude that is +less than or equal to one - or the type shall be @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +The real part of the result is in radians and lies in the range +@math{0 \leq \Re \acos(x) \leq \pi}. + +@item @emph{Example}: +@smallexample +program test_acos + real(8) :: x = 0.866_8 + x = acos(x) +end program test_acos +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ACOS(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DACOS(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{COS} @gol +Degrees function: @gol +@ref{ACOSD} +@end table + + + +@node ACOSD +@section @code{ACOSD} --- Arccosine function, degrees +@fnindex ACOSD +@fnindex DACOSD +@cindex trigonometric function, cosine, inverse, degrees +@cindex cosine, inverse, degrees + +@table @asis +@item @emph{Description}: +@code{ACOSD(X)} computes the arccosine of @var{X} in degrees (inverse of +@code{COSD(X)}). + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math} + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ACOSD(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall either be @code{REAL} with a magnitude that is +less than or equal to one - or the type shall be @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +The real part of the result is in degrees and lies in the range +@math{0 \leq \Re \acos(x) \leq 180}. + +@item @emph{Example}: +@smallexample +program test_acosd + real(8) :: x = 0.866_8 + x = acosd(x) +end program test_acosd +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ACOSD(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DACOSD(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{COSD} @gol +Radians function: @gol +@ref{ACOS} @gol +@end table + + + +@node ACOSH +@section @code{ACOSH} --- Inverse hyperbolic cosine function +@fnindex ACOSH +@fnindex DACOSH +@cindex area hyperbolic cosine +@cindex inverse hyperbolic cosine +@cindex hyperbolic function, cosine, inverse +@cindex cosine, hyperbolic, inverse + +@table @asis +@item @emph{Description}: +@code{ACOSH(X)} computes the inverse hyperbolic cosine of @var{X}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ACOSH(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has the same type and kind as @var{X}. If @var{X} is +complex, the imaginary part of the result is in radians and lies between +@math{ 0 \leq \Im \acosh(x) \leq \pi}. + +@item @emph{Example}: +@smallexample +PROGRAM test_acosh + REAL(8), DIMENSION(3) :: x = (/ 1.0, 2.0, 3.0 /) + WRITE (*,*) ACOSH(x) +END PROGRAM +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DACOSH(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{COSH} +@end table + + + +@node ADJUSTL +@section @code{ADJUSTL} --- Left adjust a string +@fnindex ADJUSTL +@cindex string, adjust left +@cindex adjust string + +@table @asis +@item @emph{Description}: +@code{ADJUSTL(STRING)} will left adjust a string by removing leading spaces. +Spaces are inserted at the end of the string as needed. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ADJUSTL(STRING)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab The type shall be @code{CHARACTER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{CHARACTER} and of the same kind as +@var{STRING} where leading spaces are removed and the same number of +spaces are inserted on the end of @var{STRING}. + +@item @emph{Example}: +@smallexample +program test_adjustl + character(len=20) :: str = ' gfortran' + str = adjustl(str) + print *, str +end program test_adjustl +@end smallexample + +@item @emph{See also}: +@ref{ADJUSTR}, @gol +@ref{TRIM} +@end table + + + +@node ADJUSTR +@section @code{ADJUSTR} --- Right adjust a string +@fnindex ADJUSTR +@cindex string, adjust right +@cindex adjust string + +@table @asis +@item @emph{Description}: +@code{ADJUSTR(STRING)} will right adjust a string by removing trailing spaces. +Spaces are inserted at the start of the string as needed. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ADJUSTR(STRING)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STR} @tab The type shall be @code{CHARACTER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{CHARACTER} and of the same kind as +@var{STRING} where trailing spaces are removed and the same number of +spaces are inserted at the start of @var{STRING}. + +@item @emph{Example}: +@smallexample +program test_adjustr + character(len=20) :: str = 'gfortran' + str = adjustr(str) + print *, str +end program test_adjustr +@end smallexample + +@item @emph{See also}: +@ref{ADJUSTL}, @gol +@ref{TRIM} +@end table + + + +@node AIMAG +@section @code{AIMAG} --- Imaginary part of complex number +@fnindex AIMAG +@fnindex DIMAG +@fnindex IMAG +@fnindex IMAGPART +@cindex complex numbers, imaginary part + +@table @asis +@item @emph{Description}: +@code{AIMAG(Z)} yields the imaginary part of complex argument @code{Z}. +The @code{IMAG(Z)} and @code{IMAGPART(Z)} intrinsic functions are provided +for compatibility with @command{g77}, and their use in new code is +strongly discouraged. + +@item @emph{Standard}: +Fortran 77 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = AIMAG(Z)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{Z} @tab The type of the argument shall be @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} with the +kind type parameter of the argument. + +@item @emph{Example}: +@smallexample +program test_aimag + complex(4) z4 + complex(8) z8 + z4 = cmplx(1.e0_4, 0.e0_4) + z8 = cmplx(0.e0_8, 1.e0_8) + print *, aimag(z4), dimag(z8) +end program test_aimag +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{AIMAG(Z)} @tab @code{COMPLEX Z} @tab @code{REAL} @tab Fortran 77 and later +@item @code{DIMAG(Z)} @tab @code{COMPLEX(8) Z} @tab @code{REAL(8)} @tab GNU extension +@item @code{IMAG(Z)} @tab @code{COMPLEX Z} @tab @code{REAL} @tab GNU extension +@item @code{IMAGPART(Z)} @tab @code{COMPLEX Z} @tab @code{REAL} @tab GNU extension +@end multitable +@end table + + + +@node AINT +@section @code{AINT} --- Truncate to a whole number +@fnindex AINT +@fnindex DINT +@cindex floor +@cindex rounding, floor + +@table @asis +@item @emph{Description}: +@code{AINT(A [, KIND])} truncates its argument to a whole number. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = AINT(A [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab The type of the argument shall be @code{REAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} with the kind type parameter of the +argument if the optional @var{KIND} is absent; otherwise, the kind +type parameter will be given by @var{KIND}. If the magnitude of +@var{X} is less than one, @code{AINT(X)} returns zero. If the +magnitude is equal to or greater than one then it returns the largest +whole number that does not exceed its magnitude. The sign is the same +as the sign of @var{X}. + +@item @emph{Example}: +@smallexample +program test_aint + real(4) x4 + real(8) x8 + x4 = 1.234E0_4 + x8 = 4.321_8 + print *, aint(x4), dint(x8) + x8 = aint(x4,8) +end program test_aint +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{AINT(A)} @tab @code{REAL(4) A} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DINT(A)} @tab @code{REAL(8) A} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable +@end table + + + +@node ALARM +@section @code{ALARM} --- Execute a routine after a given delay +@fnindex ALARM +@cindex delayed execution + +@table @asis +@item @emph{Description}: +@code{ALARM(SECONDS, HANDLER [, STATUS])} causes external subroutine @var{HANDLER} +to be executed after a delay of @var{SECONDS} by using @code{alarm(2)} to +set up a signal and @code{signal(2)} to catch it. If @var{STATUS} is +supplied, it will be returned with the number of seconds remaining until +any previously scheduled alarm was due to be delivered, or zero if there +was no previously scheduled alarm. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL ALARM(SECONDS, HANDLER [, STATUS])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SECONDS} @tab The type of the argument shall be a scalar +@code{INTEGER}. It is @code{INTENT(IN)}. +@item @var{HANDLER} @tab Signal handler (@code{INTEGER FUNCTION} or +@code{SUBROUTINE}) or dummy/global @code{INTEGER} scalar. The scalar +values may be either @code{SIG_IGN=1} to ignore the alarm generated +or @code{SIG_DFL=0} to set the default action. It is @code{INTENT(IN)}. +@item @var{STATUS} @tab (Optional) @var{STATUS} shall be a scalar +variable of the default @code{INTEGER} kind. It is @code{INTENT(OUT)}. +@end multitable + +@item @emph{Example}: +@smallexample +program test_alarm + external handler_print + integer i + call alarm (3, handler_print, i) + print *, i + call sleep(10) +end program test_alarm +@end smallexample +This will cause the external routine @var{handler_print} to be called +after 3 seconds. +@end table + + + +@node ALL +@section @code{ALL} --- All values in @var{MASK} along @var{DIM} are true +@fnindex ALL +@cindex array, apply condition +@cindex array, condition testing + +@table @asis +@item @emph{Description}: +@code{ALL(MASK [, DIM])} determines if all the values are true in @var{MASK} +in the array along dimension @var{DIM}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = ALL(MASK [, DIM])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{MASK} @tab The type of the argument shall be @code{LOGICAL} and +it shall not be scalar. +@item @var{DIM} @tab (Optional) @var{DIM} shall be a scalar integer +with a value that lies between one and the rank of @var{MASK}. +@end multitable + +@item @emph{Return value}: +@code{ALL(MASK)} returns a scalar value of type @code{LOGICAL} where +the kind type parameter is the same as the kind type parameter of +@var{MASK}. If @var{DIM} is present, then @code{ALL(MASK, DIM)} returns +an array with the rank of @var{MASK} minus 1. The shape is determined from +the shape of @var{MASK} where the @var{DIM} dimension is elided. + +@table @asis +@item (A) +@code{ALL(MASK)} is true if all elements of @var{MASK} are true. +It also is true if @var{MASK} has zero size; otherwise, it is false. +@item (B) +If the rank of @var{MASK} is one, then @code{ALL(MASK,DIM)} is equivalent +to @code{ALL(MASK)}. If the rank is greater than one, then @code{ALL(MASK,DIM)} +is determined by applying @code{ALL} to the array sections. +@end table + +@item @emph{Example}: +@smallexample +program test_all + logical l + l = all((/.true., .true., .true./)) + print *, l + call section + contains + subroutine section + integer a(2,3), b(2,3) + a = 1 + b = 1 + b(2,2) = 2 + print *, all(a .eq. b, 1) + print *, all(a .eq. b, 2) + end subroutine section +end program test_all +@end smallexample +@end table + + + +@node ALLOCATED +@section @code{ALLOCATED} --- Status of an allocatable entity +@fnindex ALLOCATED +@cindex allocation, status + +@table @asis +@item @emph{Description}: +@code{ALLOCATED(ARRAY)} and @code{ALLOCATED(SCALAR)} check the allocation +status of @var{ARRAY} and @var{SCALAR}, respectively. + +@item @emph{Standard}: +Fortran 90 and later. Note, the @code{SCALAR=} keyword and allocatable +scalar entities are available in Fortran 2003 and later. + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = ALLOCATED(ARRAY)} +@item @code{RESULT = ALLOCATED(SCALAR)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab The argument shall be an @code{ALLOCATABLE} array. +@item @var{SCALAR} @tab The argument shall be an @code{ALLOCATABLE} scalar. +@end multitable + +@item @emph{Return value}: +The return value is a scalar @code{LOGICAL} with the default logical +kind type parameter. If the argument is allocated, then the result is +@code{.TRUE.}; otherwise, it returns @code{.FALSE.} + +@item @emph{Example}: +@smallexample +program test_allocated + integer :: i = 4 + real(4), allocatable :: x(:) + if (.not. allocated(x)) allocate(x(i)) +end program test_allocated +@end smallexample +@end table + + + +@node AND +@section @code{AND} --- Bitwise logical AND +@fnindex AND +@cindex bitwise logical and +@cindex logical and, bitwise + +@table @asis +@item @emph{Description}: +Bitwise logical @code{AND}. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. For integer arguments, programmers should consider +the use of the @ref{IAND} intrinsic defined by the Fortran standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = AND(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be either a scalar @code{INTEGER} +type or a scalar @code{LOGICAL} type or a boz-literal-constant. +@item @var{J} @tab The type shall be the same as the type of @var{I} or +a boz-literal-constant. @var{I} and @var{J} shall not both be +boz-literal-constants. If either @var{I} or @var{J} is a +boz-literal-constant, then the other argument must be a scalar @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return type is either a scalar @code{INTEGER} or a scalar +@code{LOGICAL}. If the kind type parameters differ, then the +smaller kind type is implicitly converted to larger kind, and the +return has the larger kind. A boz-literal-constant is +converted to an @code{INTEGER} with the kind type parameter of +the other argument as-if a call to @ref{INT} occurred. + +@item @emph{Example}: +@smallexample +PROGRAM test_and + LOGICAL :: T = .TRUE., F = .FALSE. + INTEGER :: a, b + DATA a / Z'F' /, b / Z'3' / + + WRITE (*,*) AND(T, T), AND(T, F), AND(F, T), AND(F, F) + WRITE (*,*) AND(a, b) +END PROGRAM +@end smallexample + +@item @emph{See also}: +Fortran 95 elemental function: @gol +@ref{IAND} +@end table + + + +@node ANINT +@section @code{ANINT} --- Nearest whole number +@fnindex ANINT +@fnindex DNINT +@cindex ceiling +@cindex rounding, ceiling + +@table @asis +@item @emph{Description}: +@code{ANINT(A [, KIND])} rounds its argument to the nearest whole number. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ANINT(A [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab The type of the argument shall be @code{REAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type real with the kind type parameter of the +argument if the optional @var{KIND} is absent; otherwise, the kind +type parameter will be given by @var{KIND}. If @var{A} is greater than +zero, @code{ANINT(A)} returns @code{AINT(X+0.5)}. If @var{A} is +less than or equal to zero then it returns @code{AINT(X-0.5)}. + +@item @emph{Example}: +@smallexample +program test_anint + real(4) x4 + real(8) x8 + x4 = 1.234E0_4 + x8 = 4.321_8 + print *, anint(x4), dnint(x8) + x8 = anint(x4,8) +end program test_anint +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ANINT(A)} @tab @code{REAL(4) A} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DNINT(A)} @tab @code{REAL(8) A} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable +@end table + + + +@node ANY +@section @code{ANY} --- Any value in @var{MASK} along @var{DIM} is true +@fnindex ANY +@cindex array, apply condition +@cindex array, condition testing + +@table @asis +@item @emph{Description}: +@code{ANY(MASK [, DIM])} determines if any of the values in the logical array +@var{MASK} along dimension @var{DIM} are @code{.TRUE.}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = ANY(MASK [, DIM])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{MASK} @tab The type of the argument shall be @code{LOGICAL} and +it shall not be scalar. +@item @var{DIM} @tab (Optional) @var{DIM} shall be a scalar integer +with a value that lies between one and the rank of @var{MASK}. +@end multitable + +@item @emph{Return value}: +@code{ANY(MASK)} returns a scalar value of type @code{LOGICAL} where +the kind type parameter is the same as the kind type parameter of +@var{MASK}. If @var{DIM} is present, then @code{ANY(MASK, DIM)} returns +an array with the rank of @var{MASK} minus 1. The shape is determined from +the shape of @var{MASK} where the @var{DIM} dimension is elided. + +@table @asis +@item (A) +@code{ANY(MASK)} is true if any element of @var{MASK} is true; +otherwise, it is false. It also is false if @var{MASK} has zero size. +@item (B) +If the rank of @var{MASK} is one, then @code{ANY(MASK,DIM)} is equivalent +to @code{ANY(MASK)}. If the rank is greater than one, then @code{ANY(MASK,DIM)} +is determined by applying @code{ANY} to the array sections. +@end table + +@item @emph{Example}: +@smallexample +program test_any + logical l + l = any((/.true., .true., .true./)) + print *, l + call section + contains + subroutine section + integer a(2,3), b(2,3) + a = 1 + b = 1 + b(2,2) = 2 + print *, any(a .eq. b, 1) + print *, any(a .eq. b, 2) + end subroutine section +end program test_any +@end smallexample +@end table + + + +@node ASIN +@section @code{ASIN} --- Arcsine function +@fnindex ASIN +@fnindex DASIN +@cindex trigonometric function, sine, inverse +@cindex sine, inverse + +@table @asis +@item @emph{Description}: +@code{ASIN(X)} computes the arcsine of its @var{X} (inverse of @code{SIN(X)}). + +@item @emph{Standard}: +Fortran 77 and later, for a complex argument Fortran 2008 or later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ASIN(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be either @code{REAL} and a magnitude that is +less than or equal to one - or be @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +The real part of the result is in radians and lies in the range +@math{-\pi/2 \leq \Re \asin(x) \leq \pi/2}. + +@item @emph{Example}: +@smallexample +program test_asin + real(8) :: x = 0.866_8 + x = asin(x) +end program test_asin +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ASIN(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DASIN(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{SIN} @gol +Degrees function: @gol +@ref{ASIND} +@end table + + + +@node ASIND +@section @code{ASIND} --- Arcsine function, degrees +@fnindex ASIND +@fnindex DASIND +@cindex trigonometric function, sine, inverse, degrees +@cindex sine, inverse, degrees + +@table @asis +@item @emph{Description}: +@code{ASIND(X)} computes the arcsine of its @var{X} in degrees (inverse of +@code{SIND(X)}). + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math}. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ASIND(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be either @code{REAL} and a magnitude that is +less than or equal to one - or be @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +The real part of the result is in degrees and lies in the range +@math{-90 \leq \Re \asin(x) \leq 90}. + +@item @emph{Example}: +@smallexample +program test_asind + real(8) :: x = 0.866_8 + x = asind(x) +end program test_asind +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ASIND(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DASIND(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{SIND} @gol +Radians function: @gol +@ref{ASIN} +@end table + + + +@node ASINH +@section @code{ASINH} --- Inverse hyperbolic sine function +@fnindex ASINH +@fnindex DASINH +@cindex area hyperbolic sine +@cindex inverse hyperbolic sine +@cindex hyperbolic function, sine, inverse +@cindex sine, hyperbolic, inverse + +@table @asis +@item @emph{Description}: +@code{ASINH(X)} computes the inverse hyperbolic sine of @var{X}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ASINH(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. If @var{X} is +complex, the imaginary part of the result is in radians and lies between +@math{-\pi/2 \leq \Im \asinh(x) \leq \pi/2}. + +@item @emph{Example}: +@smallexample +PROGRAM test_asinh + REAL(8), DIMENSION(3) :: x = (/ -1.0, 0.0, 1.0 /) + WRITE (*,*) ASINH(x) +END PROGRAM +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DASINH(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension. +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{SINH} +@end table + + + +@node ASSOCIATED +@section @code{ASSOCIATED} --- Status of a pointer or pointer/target pair +@fnindex ASSOCIATED +@cindex pointer, status +@cindex association status + +@table @asis +@item @emph{Description}: +@code{ASSOCIATED(POINTER [, TARGET])} determines the status of the pointer +@var{POINTER} or if @var{POINTER} is associated with the target @var{TARGET}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = ASSOCIATED(POINTER [, TARGET])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{POINTER} @tab @var{POINTER} shall have the @code{POINTER} attribute +and it can be of any type. +@item @var{TARGET} @tab (Optional) @var{TARGET} shall be a pointer or +a target. It must have the same type, kind type parameter, and +array rank as @var{POINTER}. +@end multitable +The association status of neither @var{POINTER} nor @var{TARGET} shall be +undefined. + +@item @emph{Return value}: +@code{ASSOCIATED(POINTER)} returns a scalar value of type @code{LOGICAL(4)}. +There are several cases: +@table @asis +@item (A) When the optional @var{TARGET} is not present then +@code{ASSOCIATED(POINTER)} is true if @var{POINTER} is associated with a target; otherwise, it returns false. +@item (B) If @var{TARGET} is present and a scalar target, the result is true if +@var{TARGET} is not a zero-sized storage sequence and the target associated with @var{POINTER} occupies the same storage units. If @var{POINTER} is +disassociated, the result is false. +@item (C) If @var{TARGET} is present and an array target, the result is true if +@var{TARGET} and @var{POINTER} have the same shape, are not zero-sized arrays, +are arrays whose elements are not zero-sized storage sequences, and +@var{TARGET} and @var{POINTER} occupy the same storage units in array element +order. +As in case(B), the result is false, if @var{POINTER} is disassociated. +@item (D) If @var{TARGET} is present and an scalar pointer, the result is true +if @var{TARGET} is associated with @var{POINTER}, the target associated with +@var{TARGET} are not zero-sized storage sequences and occupy the same storage +units. +The result is false, if either @var{TARGET} or @var{POINTER} is disassociated. +@item (E) If @var{TARGET} is present and an array pointer, the result is true if +target associated with @var{POINTER} and the target associated with @var{TARGET} +have the same shape, are not zero-sized arrays, are arrays whose elements are +not zero-sized storage sequences, and @var{TARGET} and @var{POINTER} occupy +the same storage units in array element order. +The result is false, if either @var{TARGET} or @var{POINTER} is disassociated. +@end table + +@item @emph{Example}: +@smallexample +program test_associated + implicit none + real, target :: tgt(2) = (/1., 2./) + real, pointer :: ptr(:) + ptr => tgt + if (associated(ptr) .eqv. .false.) call abort + if (associated(ptr,tgt) .eqv. .false.) call abort +end program test_associated +@end smallexample + +@item @emph{See also}: +@ref{NULL} +@end table + + + +@node ATAN +@section @code{ATAN} --- Arctangent function +@fnindex ATAN +@fnindex DATAN +@cindex trigonometric function, tangent, inverse +@cindex tangent, inverse + +@table @asis +@item @emph{Description}: +@code{ATAN(X)} computes the arctangent of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later, for a complex argument and for two arguments +Fortran 2008 or later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = ATAN(X)} +@item @code{RESULT = ATAN(Y, X)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}; +if @var{Y} is present, @var{X} shall be REAL. +@item @var{Y} @tab The type and kind type parameter shall be the same as @var{X}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +If @var{Y} is present, the result is identical to @code{ATAN2(Y,X)}. +Otherwise, it the arcus tangent of @var{X}, where the real part of +the result is in radians and lies in the range +@math{-\pi/2 \leq \Re \atan(x) \leq \pi/2}. + +@item @emph{Example}: +@smallexample +program test_atan + real(8) :: x = 2.866_8 + x = atan(x) +end program test_atan +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ATAN(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DATAN(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{TAN} @gol +Degrees function: @gol +@ref{ATAND} +@end table + + + +@node ATAND +@section @code{ATAND} --- Arctangent function, degrees +@fnindex ATAND +@fnindex DATAND +@cindex trigonometric function, tangent, inverse, degrees +@cindex tangent, inverse, degrees + +@table @asis +@item @emph{Description}: +@code{ATAND(X)} computes the arctangent of @var{X} in degrees (inverse of +@ref{TAND}). + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math}. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = ATAND(X)} +@item @code{RESULT = ATAND(Y, X)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}; +if @var{Y} is present, @var{X} shall be REAL. +@item @var{Y} @tab The type and kind type parameter shall be the same as @var{X}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +If @var{Y} is present, the result is identical to @code{ATAND2(Y,X)}. +Otherwise, it is the arcus tangent of @var{X}, where the real part of +the result is in degrees and lies in the range +@math{-90 \leq \Re \atand(x) \leq 90}. + +@item @emph{Example}: +@smallexample +program test_atand + real(8) :: x = 2.866_8 + x = atand(x) +end program test_atand +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .23 .23 .20 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ATAND(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DATAND(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{TAND} @gol +Radians function: @gol +@ref{ATAN} +@end table + + + +@node ATAN2 +@section @code{ATAN2} --- Arctangent function +@fnindex ATAN2 +@fnindex DATAN2 +@cindex trigonometric function, tangent, inverse +@cindex tangent, inverse + +@table @asis +@item @emph{Description}: +@code{ATAN2(Y, X)} computes the principal value of the argument +function of the complex number @math{X + i Y}. This function can +be used to transform from Cartesian into polar coordinates and +allows to determine the angle in the correct quadrant. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ATAN2(Y, X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{Y} @tab The type shall be @code{REAL}. +@item @var{X} @tab The type and kind type parameter shall be the same as @var{Y}. +If @var{Y} is zero, then @var{X} must be nonzero. +@end multitable + +@item @emph{Return value}: +The return value has the same type and kind type parameter as @var{Y}. It +is the principal value of the complex number @math{X + i Y}. If @var{X} +is nonzero, then it lies in the range @math{-\pi \le \atan (x) \leq \pi}. +The sign is positive if @var{Y} is positive. If @var{Y} is zero, then +the return value is zero if @var{X} is strictly positive, @math{\pi} if +@var{X} is negative and @var{Y} is positive zero (or the processor does +not handle signed zeros), and @math{-\pi} if @var{X} is negative and +@var{Y} is negative zero. Finally, if @var{X} is zero, then the +magnitude of the result is @math{\pi/2}. + +@item @emph{Example}: +@smallexample +program test_atan2 + real(4) :: x = 1.e0_4, y = 0.5e0_4 + x = atan2(y,x) +end program test_atan2 +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .22 .22 .20 .32 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ATAN2(X, Y)} @tab @code{REAL(4) X, Y} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DATAN2(X, Y)} @tab @code{REAL(8) X, Y} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +Alias: @gol +@ref{ATAN} @gol +Degrees function: @gol +@ref{ATAN2D} +@end table + + + +@node ATAN2D +@section @code{ATAN2D} --- Arctangent function, degrees +@fnindex ATAN2D +@fnindex DATAN2D +@cindex trigonometric function, tangent, inverse, degrees +@cindex tangent, inverse, degrees + +@table @asis +@item @emph{Description}: +@code{ATAN2D(Y, X)} computes the principal value of the argument +function of the complex number @math{X + i Y} in degrees. This function can +be used to transform from Cartesian into polar coordinates and +allows to determine the angle in the correct quadrant. + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math}. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ATAN2D(Y, X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{Y} @tab The type shall be @code{REAL}. +@item @var{X} @tab The type and kind type parameter shall be the same as @var{Y}. +If @var{Y} is zero, then @var{X} must be nonzero. +@end multitable + +@item @emph{Return value}: +The return value has the same type and kind type parameter as @var{Y}. It +is the principal value of the complex number @math{X + i Y}. If @var{X} +is nonzero, then it lies in the range @math{-180 \le \atan (x) \leq 180}. +The sign is positive if @var{Y} is positive. If @var{Y} is zero, then +the return value is zero if @var{X} is strictly positive, @math{180} if +@var{X} is negative and @var{Y} is positive zero (or the processor does +not handle signed zeros), and @math{-180} if @var{X} is negative and +@var{Y} is negative zero. Finally, if @var{X} is zero, then the +magnitude of the result is @math{90}. + +@item @emph{Example}: +@smallexample +program test_atan2d + real(4) :: x = 1.e0_4, y = 0.5e0_4 + x = atan2d(y,x) +end program test_atan2d +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .23 .23 .20 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ATAN2D(X, Y)} @tab @code{REAL(4) X, Y} @tab @code{REAL(4)} @tab GNU extension +@item @code{DATAN2D(X, Y)} @tab @code{REAL(8) X, Y} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Alias: @gol +@ref{ATAND} @gol +Radians function: @gol +@ref{ATAN2} +@end table + + + +@node ATANH +@section @code{ATANH} --- Inverse hyperbolic tangent function +@fnindex ATANH +@fnindex DATANH +@cindex area hyperbolic tangent +@cindex inverse hyperbolic tangent +@cindex hyperbolic function, tangent, inverse +@cindex tangent, hyperbolic, inverse + +@table @asis +@item @emph{Description}: +@code{ATANH(X)} computes the inverse hyperbolic tangent of @var{X}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ATANH(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}. If @var{X} is +complex, the imaginary part of the result is in radians and lies between +@math{-\pi/2 \leq \Im \atanh(x) \leq \pi/2}. + +@item @emph{Example}: +@smallexample +PROGRAM test_atanh + REAL, DIMENSION(3) :: x = (/ -1.0, 0.0, 1.0 /) + WRITE (*,*) ATANH(x) +END PROGRAM +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DATANH(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{TANH} +@end table + + + +@node ATOMIC_ADD +@section @code{ATOMIC_ADD} --- Atomic ADD operation +@fnindex ATOMIC_ADD +@cindex Atomic subroutine, add + +@table @asis +@item @emph{Description}: +@code{ATOMIC_ADD(ATOM, VALUE)} atomically adds the value of @var{VALUE} to the +variable @var{ATOM}. When @var{STAT} is present and the invocation was +successful, it is assigned the value 0. If it is present and the invocation +has failed, it is assigned a positive value; in particular, for a coindexed +@var{ATOM}, if the remote image has stopped, it is assigned the value of +@code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote image has +failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_ADD (ATOM, VALUE [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of integer +type with @code{ATOMIC_INT_KIND} kind. +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*] + call atomic_add (atom[1], this_image()) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_FETCH_ADD}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_AND}, @gol +@ref{ATOMIC_OR}, @gol +@ref{ATOMIC_XOR} +@end table + + + + +@node ATOMIC_AND +@section @code{ATOMIC_AND} --- Atomic bitwise AND operation +@fnindex ATOMIC_AND +@cindex Atomic subroutine, AND + +@table @asis +@item @emph{Description}: +@code{ATOMIC_AND(ATOM, VALUE)} atomically defines @var{ATOM} with the bitwise +AND between the values of @var{ATOM} and @var{VALUE}. When @var{STAT} is present +and the invocation was successful, it is assigned the value 0. If it is present +and the invocation has failed, it is assigned a positive value; in particular, +for a coindexed @var{ATOM}, if the remote image has stopped, it is assigned the +value of @code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote +image has failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_AND (ATOM, VALUE [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of integer +type with @code{ATOMIC_INT_KIND} kind. +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*] + call atomic_and (atom[1], int(b'10100011101')) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_FETCH_AND}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_ADD}, @gol +@ref{ATOMIC_OR}, @gol +@ref{ATOMIC_XOR} +@end table + + + +@node ATOMIC_CAS +@section @code{ATOMIC_CAS} --- Atomic compare and swap +@fnindex ATOMIC_DEFINE +@cindex Atomic subroutine, compare and swap + +@table @asis +@item @emph{Description}: +@code{ATOMIC_CAS} compares the variable @var{ATOM} with the value of +@var{COMPARE}; if the value is the same, @var{ATOM} is set to the value +of @var{NEW}. Additionally, @var{OLD} is set to the value of @var{ATOM} +that was used for the comparison. When @var{STAT} is present and the invocation +was successful, it is assigned the value 0. If it is present and the invocation +has failed, it is assigned a positive value; in particular, for a coindexed +@var{ATOM}, if the remote image has stopped, it is assigned the value of +@code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote image has +failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_CAS (ATOM, OLD, COMPARE, NEW [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of either integer +type with @code{ATOMIC_INT_KIND} kind or logical type with +@code{ATOMIC_LOGICAL_KIND} kind. +@item @var{OLD} @tab Scalar of the same type and kind as @var{ATOM}. +@item @var{COMPARE} @tab Scalar variable of the same type and kind as +@var{ATOM}. +@item @var{NEW} @tab Scalar variable of the same type as @var{ATOM}. If kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + logical(atomic_logical_kind) :: atom[*], prev + call atomic_cas (atom[1], prev, .false., .true.)) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_REF}, @gol +@ref{ISO_FORTRAN_ENV} +@end table + + + +@node ATOMIC_DEFINE +@section @code{ATOMIC_DEFINE} --- Setting a variable atomically +@fnindex ATOMIC_DEFINE +@cindex Atomic subroutine, define + +@table @asis +@item @emph{Description}: +@code{ATOMIC_DEFINE(ATOM, VALUE)} defines the variable @var{ATOM} with the value +@var{VALUE} atomically. When @var{STAT} is present and the invocation was +successful, it is assigned the value 0. If it is present and the invocation +has failed, it is assigned a positive value; in particular, for a coindexed +@var{ATOM}, if the remote image has stopped, it is assigned the value of +@code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote image has +failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +Fortran 2008 and later; with @var{STAT}, TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_DEFINE (ATOM, VALUE [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of either integer +type with @code{ATOMIC_INT_KIND} kind or logical type with +@code{ATOMIC_LOGICAL_KIND} kind. + +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*] + call atomic_define (atom[1], this_image()) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_REF}, @gol +@ref{ATOMIC_CAS}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_ADD}, @gol +@ref{ATOMIC_AND}, @gol +@ref{ATOMIC_OR}, @gol +@ref{ATOMIC_XOR} +@end table + + + +@node ATOMIC_FETCH_ADD +@section @code{ATOMIC_FETCH_ADD} --- Atomic ADD operation with prior fetch +@fnindex ATOMIC_FETCH_ADD +@cindex Atomic subroutine, ADD with fetch + +@table @asis +@item @emph{Description}: +@code{ATOMIC_FETCH_ADD(ATOM, VALUE, OLD)} atomically stores the value of +@var{ATOM} in @var{OLD} and adds the value of @var{VALUE} to the +variable @var{ATOM}. When @var{STAT} is present and the invocation was +successful, it is assigned the value 0. If it is present and the invocation +has failed, it is assigned a positive value; in particular, for a coindexed +@var{ATOM}, if the remote image has stopped, it is assigned the value of +@code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote image has +failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_FETCH_ADD (ATOM, VALUE, old [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of integer +type with @code{ATOMIC_INT_KIND} kind. +@code{ATOMIC_LOGICAL_KIND} kind. + +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{OLD} @tab Scalar of the same type and kind as @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*], old + call atomic_add (atom[1], this_image(), old) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_ADD}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_FETCH_AND}, @gol +@ref{ATOMIC_FETCH_OR}, @gol +@ref{ATOMIC_FETCH_XOR} +@end table + + + +@node ATOMIC_FETCH_AND +@section @code{ATOMIC_FETCH_AND} --- Atomic bitwise AND operation with prior fetch +@fnindex ATOMIC_FETCH_AND +@cindex Atomic subroutine, AND with fetch + +@table @asis +@item @emph{Description}: +@code{ATOMIC_AND(ATOM, VALUE)} atomically stores the value of @var{ATOM} in +@var{OLD} and defines @var{ATOM} with the bitwise AND between the values of +@var{ATOM} and @var{VALUE}. When @var{STAT} is present and the invocation was +successful, it is assigned the value 0. If it is present and the invocation has +failed, it is assigned a positive value; in particular, for a coindexed +@var{ATOM}, if the remote image has stopped, it is assigned the value of +@code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote image has +failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_FETCH_AND (ATOM, VALUE, OLD [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of integer +type with @code{ATOMIC_INT_KIND} kind. +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{OLD} @tab Scalar of the same type and kind as @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*], old + call atomic_fetch_and (atom[1], int(b'10100011101'), old) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_AND}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_FETCH_ADD}, @gol +@ref{ATOMIC_FETCH_OR}, @gol +@ref{ATOMIC_FETCH_XOR} +@end table + + + +@node ATOMIC_FETCH_OR +@section @code{ATOMIC_FETCH_OR} --- Atomic bitwise OR operation with prior fetch +@fnindex ATOMIC_FETCH_OR +@cindex Atomic subroutine, OR with fetch + +@table @asis +@item @emph{Description}: +@code{ATOMIC_OR(ATOM, VALUE)} atomically stores the value of @var{ATOM} in +@var{OLD} and defines @var{ATOM} with the bitwise OR between the values of +@var{ATOM} and @var{VALUE}. When @var{STAT} is present and the invocation was +successful, it is assigned the value 0. If it is present and the invocation has +failed, it is assigned a positive value; in particular, for a coindexed +@var{ATOM}, if the remote image has stopped, it is assigned the value of +@code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote image has +failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_FETCH_OR (ATOM, VALUE, OLD [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of integer +type with @code{ATOMIC_INT_KIND} kind. +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{OLD} @tab Scalar of the same type and kind as @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*], old + call atomic_fetch_or (atom[1], int(b'10100011101'), old) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_OR}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_FETCH_ADD}, @gol +@ref{ATOMIC_FETCH_AND}, @gol +@ref{ATOMIC_FETCH_XOR} +@end table + + + +@node ATOMIC_FETCH_XOR +@section @code{ATOMIC_FETCH_XOR} --- Atomic bitwise XOR operation with prior fetch +@fnindex ATOMIC_FETCH_XOR +@cindex Atomic subroutine, XOR with fetch + +@table @asis +@item @emph{Description}: +@code{ATOMIC_XOR(ATOM, VALUE)} atomically stores the value of @var{ATOM} in +@var{OLD} and defines @var{ATOM} with the bitwise XOR between the values of +@var{ATOM} and @var{VALUE}. When @var{STAT} is present and the invocation was +successful, it is assigned the value 0. If it is present and the invocation has +failed, it is assigned a positive value; in particular, for a coindexed +@var{ATOM}, if the remote image has stopped, it is assigned the value of +@code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote image has +failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_FETCH_XOR (ATOM, VALUE, OLD [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of integer +type with @code{ATOMIC_INT_KIND} kind. +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{OLD} @tab Scalar of the same type and kind as @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*], old + call atomic_fetch_xor (atom[1], int(b'10100011101'), old) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_XOR}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_FETCH_ADD}, @gol +@ref{ATOMIC_FETCH_AND}, @gol +@ref{ATOMIC_FETCH_OR} +@end table + + + +@node ATOMIC_OR +@section @code{ATOMIC_OR} --- Atomic bitwise OR operation +@fnindex ATOMIC_OR +@cindex Atomic subroutine, OR + +@table @asis +@item @emph{Description}: +@code{ATOMIC_OR(ATOM, VALUE)} atomically defines @var{ATOM} with the bitwise +AND between the values of @var{ATOM} and @var{VALUE}. When @var{STAT} is present +and the invocation was successful, it is assigned the value 0. If it is present +and the invocation has failed, it is assigned a positive value; in particular, +for a coindexed @var{ATOM}, if the remote image has stopped, it is assigned the +value of @code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote +image has failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_OR (ATOM, VALUE [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of integer +type with @code{ATOMIC_INT_KIND} kind. +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*] + call atomic_or (atom[1], int(b'10100011101')) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_FETCH_OR}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_ADD}, @gol +@ref{ATOMIC_OR}, @gol +@ref{ATOMIC_XOR} +@end table + + + +@node ATOMIC_REF +@section @code{ATOMIC_REF} --- Obtaining the value of a variable atomically +@fnindex ATOMIC_REF +@cindex Atomic subroutine, reference + +@table @asis +@item @emph{Description}: +@code{ATOMIC_DEFINE(ATOM, VALUE)} atomically assigns the value of the +variable @var{ATOM} to @var{VALUE}. When @var{STAT} is present and the +invocation was successful, it is assigned the value 0. If it is present and the +invocation has failed, it is assigned a positive value; in particular, for a +coindexed @var{ATOM}, if the remote image has stopped, it is assigned the value +of @code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote image +has failed, the value @code{STAT_FAILED_IMAGE}. + + +@item @emph{Standard}: +Fortran 2008 and later; with @var{STAT}, TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_REF(VALUE, ATOM [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{ATOM} @tab Scalar coarray or coindexed variable of either integer +type with @code{ATOMIC_INT_KIND} kind or logical type with +@code{ATOMIC_LOGICAL_KIND} kind. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + logical(atomic_logical_kind) :: atom[*] + logical :: val + call atomic_ref (atom, .false.) + ! ... + call atomic_ref (atom, val) + if (val) then + print *, "Obtained" + end if +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_CAS}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_FETCH_ADD}, @gol +@ref{ATOMIC_FETCH_AND}, @gol +@ref{ATOMIC_FETCH_OR}, @gol +@ref{ATOMIC_FETCH_XOR} +@end table + + +@node ATOMIC_XOR +@section @code{ATOMIC_XOR} --- Atomic bitwise OR operation +@fnindex ATOMIC_XOR +@cindex Atomic subroutine, XOR + +@table @asis +@item @emph{Description}: +@code{ATOMIC_AND(ATOM, VALUE)} atomically defines @var{ATOM} with the bitwise +XOR between the values of @var{ATOM} and @var{VALUE}. When @var{STAT} is present +and the invocation was successful, it is assigned the value 0. If it is present +and the invocation has failed, it is assigned a positive value; in particular, +for a coindexed @var{ATOM}, if the remote image has stopped, it is assigned the +value of @code{ISO_FORTRAN_ENV}'s @code{STAT_STOPPED_IMAGE} and if the remote +image has failed, the value @code{STAT_FAILED_IMAGE}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: +Atomic subroutine + +@item @emph{Syntax}: +@code{CALL ATOMIC_XOR (ATOM, VALUE [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ATOM} @tab Scalar coarray or coindexed variable of integer +type with @code{ATOMIC_INT_KIND} kind. +@item @var{VALUE} @tab Scalar of the same type as @var{ATOM}. If the kind +is different, the value is converted to the kind of @var{ATOM}. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + integer(atomic_int_kind) :: atom[*] + call atomic_xor (atom[1], int(b'10100011101')) +end program atomic +@end smallexample + +@item @emph{See also}: +@ref{ATOMIC_DEFINE}, @gol +@ref{ATOMIC_FETCH_XOR}, @gol +@ref{ISO_FORTRAN_ENV}, @gol +@ref{ATOMIC_ADD}, @gol +@ref{ATOMIC_OR}, @gol +@ref{ATOMIC_XOR} +@end table + + +@node BACKTRACE +@section @code{BACKTRACE} --- Show a backtrace +@fnindex BACKTRACE +@cindex backtrace + +@table @asis +@item @emph{Description}: +@code{BACKTRACE} shows a backtrace at an arbitrary place in user code. Program +execution continues normally afterwards. The backtrace information is printed +to the unit corresponding to @code{ERROR_UNIT} in @code{ISO_FORTRAN_ENV}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL BACKTRACE} + +@item @emph{Arguments}: +None + +@item @emph{See also}: +@ref{ABORT} +@end table + + + +@node BESSEL_J0 +@section @code{BESSEL_J0} --- Bessel function of the first kind of order 0 +@fnindex BESSEL_J0 +@fnindex BESJ0 +@fnindex DBESJ0 +@cindex Bessel function, first kind + +@table @asis +@item @emph{Description}: +@code{BESSEL_J0(X)} computes the Bessel function of the first kind of +order 0 of @var{X}. This function is available under the name +@code{BESJ0} as a GNU extension. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BESSEL_J0(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} and lies in the +range @math{ - 0.4027... \leq Bessel (0,x) \leq 1}. It has the same +kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_besj0 + real(8) :: x = 0.0_8 + x = bessel_j0(x) +end program test_besj0 +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .21 .22 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DBESJ0(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable +@end table + + + +@node BESSEL_J1 +@section @code{BESSEL_J1} --- Bessel function of the first kind of order 1 +@fnindex BESSEL_J1 +@fnindex BESJ1 +@fnindex DBESJ1 +@cindex Bessel function, first kind + +@table @asis +@item @emph{Description}: +@code{BESSEL_J1(X)} computes the Bessel function of the first kind of +order 1 of @var{X}. This function is available under the name +@code{BESJ1} as a GNU extension. + +@item @emph{Standard}: +Fortran 2008 + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BESSEL_J1(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} and lies in the +range @math{ - 0.5818... \leq Bessel (0,x) \leq 0.5818 }. It has the same +kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_besj1 + real(8) :: x = 1.0_8 + x = bessel_j1(x) +end program test_besj1 +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DBESJ1(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable +@end table + + + +@node BESSEL_JN +@section @code{BESSEL_JN} --- Bessel function of the first kind +@fnindex BESSEL_JN +@fnindex BESJN +@fnindex DBESJN +@cindex Bessel function, first kind + +@table @asis +@item @emph{Description}: +@code{BESSEL_JN(N, X)} computes the Bessel function of the first kind of +order @var{N} of @var{X}. This function is available under the name +@code{BESJN} as a GNU extension. If @var{N} and @var{X} are arrays, +their ranks and shapes shall conform. + +@code{BESSEL_JN(N1, N2, X)} returns an array with the Bessel functions +of the first kind of the orders @var{N1} to @var{N2}. + +@item @emph{Standard}: +Fortran 2008 and later, negative @var{N} is allowed as GNU extension + +@item @emph{Class}: +Elemental function, except for the transformational function +@code{BESSEL_JN(N1, N2, X)} + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = BESSEL_JN(N, X)} +@item @code{RESULT = BESSEL_JN(N1, N2, X)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{N} @tab Shall be a scalar or an array of type @code{INTEGER}. +@item @var{N1} @tab Shall be a non-negative scalar of type @code{INTEGER}. +@item @var{N2} @tab Shall be a non-negative scalar of type @code{INTEGER}. +@item @var{X} @tab Shall be a scalar or an array of type @code{REAL}; +for @code{BESSEL_JN(N1, N2, X)} it shall be scalar. +@end multitable + +@item @emph{Return value}: +The return value is a scalar of type @code{REAL}. It has the same +kind as @var{X}. + +@item @emph{Note}: +The transformational function uses a recurrence algorithm which might, +for some values of @var{X}, lead to different results than calls to +the elemental function. + +@item @emph{Example}: +@smallexample +program test_besjn + real(8) :: x = 1.0_8 + x = bessel_jn(5,x) +end program test_besjn +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .22 .22 .20 .32 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DBESJN(N, X)} @tab @code{INTEGER N} @tab @code{REAL(8)} @tab GNU extension +@item @tab @code{REAL(8) X} @tab @tab +@end multitable +@end table + + + +@node BESSEL_Y0 +@section @code{BESSEL_Y0} --- Bessel function of the second kind of order 0 +@fnindex BESSEL_Y0 +@fnindex BESY0 +@fnindex DBESY0 +@cindex Bessel function, second kind + +@table @asis +@item @emph{Description}: +@code{BESSEL_Y0(X)} computes the Bessel function of the second kind of +order 0 of @var{X}. This function is available under the name +@code{BESY0} as a GNU extension. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BESSEL_Y0(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL}. It has the same kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_besy0 + real(8) :: x = 0.0_8 + x = bessel_y0(x) +end program test_besy0 +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DBESY0(X)}@tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable +@end table + + + +@node BESSEL_Y1 +@section @code{BESSEL_Y1} --- Bessel function of the second kind of order 1 +@fnindex BESSEL_Y1 +@fnindex BESY1 +@fnindex DBESY1 +@cindex Bessel function, second kind + +@table @asis +@item @emph{Description}: +@code{BESSEL_Y1(X)} computes the Bessel function of the second kind of +order 1 of @var{X}. This function is available under the name +@code{BESY1} as a GNU extension. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BESSEL_Y1(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL}. It has the same kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_besy1 + real(8) :: x = 1.0_8 + x = bessel_y1(x) +end program test_besy1 +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DBESY1(X)}@tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable +@end table + + + +@node BESSEL_YN +@section @code{BESSEL_YN} --- Bessel function of the second kind +@fnindex BESSEL_YN +@fnindex BESYN +@fnindex DBESYN +@cindex Bessel function, second kind + +@table @asis +@item @emph{Description}: +@code{BESSEL_YN(N, X)} computes the Bessel function of the second kind of +order @var{N} of @var{X}. This function is available under the name +@code{BESYN} as a GNU extension. If @var{N} and @var{X} are arrays, +their ranks and shapes shall conform. + +@code{BESSEL_YN(N1, N2, X)} returns an array with the Bessel functions +of the first kind of the orders @var{N1} to @var{N2}. + +@item @emph{Standard}: +Fortran 2008 and later, negative @var{N} is allowed as GNU extension + +@item @emph{Class}: +Elemental function, except for the transformational function +@code{BESSEL_YN(N1, N2, X)} + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = BESSEL_YN(N, X)} +@item @code{RESULT = BESSEL_YN(N1, N2, X)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{N} @tab Shall be a scalar or an array of type @code{INTEGER} . +@item @var{N1} @tab Shall be a non-negative scalar of type @code{INTEGER}. +@item @var{N2} @tab Shall be a non-negative scalar of type @code{INTEGER}. +@item @var{X} @tab Shall be a scalar or an array of type @code{REAL}; +for @code{BESSEL_YN(N1, N2, X)} it shall be scalar. +@end multitable + +@item @emph{Return value}: +The return value is a scalar of type @code{REAL}. It has the same +kind as @var{X}. + +@item @emph{Note}: +The transformational function uses a recurrence algorithm which might, +for some values of @var{X}, lead to different results than calls to +the elemental function. + +@item @emph{Example}: +@smallexample +program test_besyn + real(8) :: x = 1.0_8 + x = bessel_yn(5,x) +end program test_besyn +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DBESYN(N,X)} @tab @code{INTEGER N} @tab @code{REAL(8)} @tab GNU extension +@item @tab @code{REAL(8) X} @tab @tab +@end multitable +@end table + + + +@node BGE +@section @code{BGE} --- Bitwise greater than or equal to +@fnindex BGE +@cindex bitwise comparison + +@table @asis +@item @emph{Description}: +Determines whether an integral is a bitwise greater than or equal to +another. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BGE(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of @code{INTEGER} type. +@item @var{J} @tab Shall be of @code{INTEGER} type, and of the same kind +as @var{I}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{LOGICAL} and of the default kind. + +@item @emph{See also}: +@ref{BGT}, @gol +@ref{BLE}, @gol +@ref{BLT} +@end table + + + +@node BGT +@section @code{BGT} --- Bitwise greater than +@fnindex BGT +@cindex bitwise comparison + +@table @asis +@item @emph{Description}: +Determines whether an integral is a bitwise greater than another. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BGT(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of @code{INTEGER} type. +@item @var{J} @tab Shall be of @code{INTEGER} type, and of the same kind +as @var{I}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{LOGICAL} and of the default kind. + +@item @emph{See also}: +@ref{BGE}, @gol +@ref{BLE}, @gol +@ref{BLT} +@end table + + + +@node BIT_SIZE +@section @code{BIT_SIZE} --- Bit size inquiry function +@fnindex BIT_SIZE +@cindex bits, number of +@cindex size of a variable, in bits + +@table @asis +@item @emph{Description}: +@code{BIT_SIZE(I)} returns the number of bits (integer precision plus sign bit) +represented by the type of @var{I}. The result of @code{BIT_SIZE(I)} is +independent of the actual value of @var{I}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = BIT_SIZE(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} + +@item @emph{Example}: +@smallexample +program test_bit_size + integer :: i = 123 + integer :: size + size = bit_size(i) + print *, size +end program test_bit_size +@end smallexample +@end table + + + +@node BLE +@section @code{BLE} --- Bitwise less than or equal to +@fnindex BLE +@cindex bitwise comparison + +@table @asis +@item @emph{Description}: +Determines whether an integral is a bitwise less than or equal to +another. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BLE(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of @code{INTEGER} type. +@item @var{J} @tab Shall be of @code{INTEGER} type, and of the same kind +as @var{I}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{LOGICAL} and of the default kind. + +@item @emph{See also}: +@ref{BGT}, @gol +@ref{BGE}, @gol +@ref{BLT} +@end table + + + +@node BLT +@section @code{BLT} --- Bitwise less than +@fnindex BLT +@cindex bitwise comparison + +@table @asis +@item @emph{Description}: +Determines whether an integral is a bitwise less than another. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BLT(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of @code{INTEGER} type. +@item @var{J} @tab Shall be of @code{INTEGER} type, and of the same kind +as @var{I}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{LOGICAL} and of the default kind. + +@item @emph{See also}: +@ref{BGE}, @gol +@ref{BGT}, @gol +@ref{BLE} +@end table + + + +@node BTEST +@section @code{BTEST} --- Bit test function +@fnindex BTEST +@fnindex BBTEST +@fnindex BITEST +@fnindex BJTEST +@fnindex BKTEST +@cindex bits, testing + +@table @asis +@item @emph{Description}: +@code{BTEST(I,POS)} returns logical @code{.TRUE.} if the bit at @var{POS} +in @var{I} is set. The counting of the bits starts at 0. + +@item @emph{Standard}: +Fortran 90 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = BTEST(I, POS)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{POS} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{LOGICAL} + +@item @emph{Example}: +@smallexample +program test_btest + integer :: i = 32768 + 1024 + 64 + integer :: pos + logical :: bool + do pos=0,16 + bool = btest(i, pos) + print *, pos, bool + end do +end program test_btest +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .21 .28 .18 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{BTEST(I,POS)} @tab @code{INTEGER I,POS} @tab @code{LOGICAL} @tab Fortran 95 and later +@item @code{BBTEST(I,POS)} @tab @code{INTEGER(1) I,POS} @tab @code{LOGICAL(1)} @tab GNU extension +@item @code{BITEST(I,POS)} @tab @code{INTEGER(2) I,POS} @tab @code{LOGICAL(2)} @tab GNU extension +@item @code{BJTEST(I,POS)} @tab @code{INTEGER(4) I,POS} @tab @code{LOGICAL(4)} @tab GNU extension +@item @code{BKTEST(I,POS)} @tab @code{INTEGER(8) I,POS} @tab @code{LOGICAL(8)} @tab GNU extension +@end multitable +@end table + +@node C_ASSOCIATED +@section @code{C_ASSOCIATED} --- Status of a C pointer +@fnindex C_ASSOCIATED +@cindex association status, C pointer +@cindex pointer, C association status + +@table @asis +@item @emph{Description}: +@code{C_ASSOCIATED(c_ptr_1[, c_ptr_2])} determines the status of the C pointer +@var{c_ptr_1} or if @var{c_ptr_1} is associated with the target @var{c_ptr_2}. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = C_ASSOCIATED(c_ptr_1[, c_ptr_2])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{c_ptr_1} @tab Scalar of the type @code{C_PTR} or @code{C_FUNPTR}. +@item @var{c_ptr_2} @tab (Optional) Scalar of the same type as @var{c_ptr_1}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{LOGICAL}; it is @code{.false.} if either +@var{c_ptr_1} is a C NULL pointer or if @var{c_ptr1} and @var{c_ptr_2} +point to different addresses. + +@item @emph{Example}: +@smallexample +subroutine association_test(a,b) + use iso_c_binding, only: c_associated, c_loc, c_ptr + implicit none + real, pointer :: a + type(c_ptr) :: b + if(c_associated(b, c_loc(a))) & + stop 'b and a do not point to same target' +end subroutine association_test +@end smallexample + +@item @emph{See also}: +@ref{C_LOC}, @gol +@ref{C_FUNLOC} +@end table + + +@node C_F_POINTER +@section @code{C_F_POINTER} --- Convert C into Fortran pointer +@fnindex C_F_POINTER +@cindex pointer, convert C to Fortran + +@table @asis +@item @emph{Description}: +@code{C_F_POINTER(CPTR, FPTR[, SHAPE])} assigns the target of the C pointer +@var{CPTR} to the Fortran pointer @var{FPTR} and specifies its shape. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL C_F_POINTER(CPTR, FPTR[, SHAPE])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{CPTR} @tab scalar of the type @code{C_PTR}. It is +@code{INTENT(IN)}. +@item @var{FPTR} @tab pointer interoperable with @var{cptr}. It is +@code{INTENT(OUT)}. +@item @var{SHAPE} @tab (Optional) Rank-one array of type @code{INTEGER} +with @code{INTENT(IN)}. It shall be present +if and only if @var{fptr} is an array. The size +must be equal to the rank of @var{fptr}. +@end multitable + +@item @emph{Example}: +@smallexample +program main + use iso_c_binding + implicit none + interface + subroutine my_routine(p) bind(c,name='myC_func') + import :: c_ptr + type(c_ptr), intent(out) :: p + end subroutine + end interface + type(c_ptr) :: cptr + real,pointer :: a(:) + call my_routine(cptr) + call c_f_pointer(cptr, a, [12]) +end program main +@end smallexample + +@item @emph{See also}: +@ref{C_LOC}, @gol +@ref{C_F_PROCPOINTER} +@end table + + +@node C_F_PROCPOINTER +@section @code{C_F_PROCPOINTER} --- Convert C into Fortran procedure pointer +@fnindex C_F_PROCPOINTER +@cindex pointer, C address of pointers + +@table @asis +@item @emph{Description}: +@code{C_F_PROCPOINTER(CPTR, FPTR)} Assign the target of the C function pointer +@var{CPTR} to the Fortran procedure pointer @var{FPTR}. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL C_F_PROCPOINTER(cptr, fptr)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{CPTR} @tab scalar of the type @code{C_FUNPTR}. It is +@code{INTENT(IN)}. +@item @var{FPTR} @tab procedure pointer interoperable with @var{cptr}. It is +@code{INTENT(OUT)}. +@end multitable + +@item @emph{Example}: +@smallexample +program main + use iso_c_binding + implicit none + abstract interface + function func(a) + import :: c_float + real(c_float), intent(in) :: a + real(c_float) :: func + end function + end interface + interface + function getIterFunc() bind(c,name="getIterFunc") + import :: c_funptr + type(c_funptr) :: getIterFunc + end function + end interface + type(c_funptr) :: cfunptr + procedure(func), pointer :: myFunc + cfunptr = getIterFunc() + call c_f_procpointer(cfunptr, myFunc) +end program main +@end smallexample + +@item @emph{See also}: +@ref{C_LOC}, @gol +@ref{C_F_POINTER} +@end table + + +@node C_FUNLOC +@section @code{C_FUNLOC} --- Obtain the C address of a procedure +@fnindex C_FUNLOC +@cindex pointer, C address of procedures + +@table @asis +@item @emph{Description}: +@code{C_FUNLOC(x)} determines the C address of the argument. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = C_FUNLOC(x)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{x} @tab Interoperable function or pointer to such function. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{C_FUNPTR} and contains the C address +of the argument. + +@item @emph{Example}: +@smallexample +module x + use iso_c_binding + implicit none +contains + subroutine sub(a) bind(c) + real(c_float) :: a + a = sqrt(a)+5.0 + end subroutine sub +end module x +program main + use iso_c_binding + use x + implicit none + interface + subroutine my_routine(p) bind(c,name='myC_func') + import :: c_funptr + type(c_funptr), intent(in) :: p + end subroutine + end interface + call my_routine(c_funloc(sub)) +end program main +@end smallexample + +@item @emph{See also}: +@ref{C_ASSOCIATED}, @gol +@ref{C_LOC}, @gol +@ref{C_F_POINTER}, @gol +@ref{C_F_PROCPOINTER} +@end table + + +@node C_LOC +@section @code{C_LOC} --- Obtain the C address of an object +@fnindex C_LOC +@cindex procedure pointer, convert C to Fortran + +@table @asis +@item @emph{Description}: +@code{C_LOC(X)} determines the C address of the argument. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = C_LOC(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .10 .75 +@item @var{X} @tab Shall have either the POINTER or TARGET attribute. It shall not be a coindexed object. It shall either be a variable with interoperable type and kind type parameters, or be a scalar, nonpolymorphic variable with no length type parameters. + +@end multitable + +@item @emph{Return value}: +The return value is of type @code{C_PTR} and contains the C address +of the argument. + +@item @emph{Example}: +@smallexample +subroutine association_test(a,b) + use iso_c_binding, only: c_associated, c_loc, c_ptr + implicit none + real, pointer :: a + type(c_ptr) :: b + if(c_associated(b, c_loc(a))) & + stop 'b and a do not point to same target' +end subroutine association_test +@end smallexample + +@item @emph{See also}: +@ref{C_ASSOCIATED}, @gol +@ref{C_FUNLOC}, @gol +@ref{C_F_POINTER}, @gol +@ref{C_F_PROCPOINTER} +@end table + + +@node C_SIZEOF +@section @code{C_SIZEOF} --- Size in bytes of an expression +@fnindex C_SIZEOF +@cindex expression size +@cindex size of an expression + +@table @asis +@item @emph{Description}: +@code{C_SIZEOF(X)} calculates the number of bytes of storage the +expression @code{X} occupies. + +@item @emph{Standard}: +Fortran 2008 + +@item @emph{Class}: +Inquiry function of the module @code{ISO_C_BINDING} + +@item @emph{Syntax}: +@code{N = C_SIZEOF(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The argument shall be an interoperable data entity. +@end multitable + +@item @emph{Return value}: +The return value is of type integer and of the system-dependent kind +@code{C_SIZE_T} (from the @code{ISO_C_BINDING} module). Its value is the +number of bytes occupied by the argument. If the argument has the +@code{POINTER} attribute, the number of bytes of the storage area pointed +to is returned. If the argument is of a derived type with @code{POINTER} +or @code{ALLOCATABLE} components, the return value does not account for +the sizes of the data pointed to by these components. + +@item @emph{Example}: +@smallexample + use iso_c_binding + integer(c_int) :: i + real(c_float) :: r, s(5) + print *, (c_sizeof(s)/c_sizeof(r) == 5) + end +@end smallexample +The example will print @code{T} unless you are using a platform +where default @code{REAL} variables are unusually padded. + +@item @emph{See also}: +@ref{SIZEOF}, @gol +@ref{STORAGE_SIZE} +@end table + + +@node CEILING +@section @code{CEILING} --- Integer ceiling function +@fnindex CEILING +@cindex ceiling +@cindex rounding, ceiling + +@table @asis +@item @emph{Description}: +@code{CEILING(A)} returns the least integer greater than or equal to @var{A}. + +@item @emph{Standard}: +Fortran 95 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = CEILING(A [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab The type shall be @code{REAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER(KIND)} if @var{KIND} is present +and a default-kind @code{INTEGER} otherwise. + +@item @emph{Example}: +@smallexample +program test_ceiling + real :: x = 63.29 + real :: y = -63.59 + print *, ceiling(x) ! returns 64 + print *, ceiling(y) ! returns -63 +end program test_ceiling +@end smallexample + +@item @emph{See also}: +@ref{FLOOR}, @gol +@ref{NINT} +@end table + + + +@node CHAR +@section @code{CHAR} --- Character conversion function +@fnindex CHAR +@cindex conversion, to character + +@table @asis +@item @emph{Description}: +@code{CHAR(I [, KIND])} returns the character represented by the integer @var{I}. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = CHAR(I [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{CHARACTER(1)} + +@item @emph{Example}: +@smallexample +program test_char + integer :: i = 74 + character(1) :: c + c = char(i) + print *, i, c ! returns 'J' +end program test_char +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .19 .19 .25 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{CHAR(I)} @tab @code{INTEGER I} @tab @code{CHARACTER(LEN=1)} @tab Fortran 77 and later +@end multitable + +@item @emph{Note}: +See @ref{ICHAR} for a discussion of converting between numerical values +and formatted string representations. + +@item @emph{See also}: +@ref{ACHAR}, @gol +@ref{IACHAR}, @gol +@ref{ICHAR} + +@end table + + + +@node CHDIR +@section @code{CHDIR} --- Change working directory +@fnindex CHDIR +@cindex system, working directory + +@table @asis +@item @emph{Description}: +Change current working directory to a specified path. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL CHDIR(NAME [, STATUS])} +@item @code{STATUS = CHDIR(NAME)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NAME} @tab The type shall be @code{CHARACTER} of default +kind and shall specify a valid path within the file system. +@item @var{STATUS} @tab (Optional) @code{INTEGER} status flag of the default +kind. Returns 0 on success, and a system specific and nonzero error code +otherwise. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_chdir + CHARACTER(len=255) :: path + CALL getcwd(path) + WRITE(*,*) TRIM(path) + CALL chdir("/tmp") + CALL getcwd(path) + WRITE(*,*) TRIM(path) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{GETCWD} +@end table + + + +@node CHMOD +@section @code{CHMOD} --- Change access permissions of files +@fnindex CHMOD +@cindex file system, change access mode + +@table @asis +@item @emph{Description}: +@code{CHMOD} changes the permissions of a file. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL CHMOD(NAME, MODE[, STATUS])} +@item @code{STATUS = CHMOD(NAME, MODE)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 + +@item @var{NAME} @tab Scalar @code{CHARACTER} of default kind with the +file name. Trailing blanks are ignored unless the character +@code{achar(0)} is present, then all characters up to and excluding +@code{achar(0)} are used as the file name. + +@item @var{MODE} @tab Scalar @code{CHARACTER} of default kind giving the +file permission. @var{MODE} uses the same syntax as the @code{chmod} utility +as defined by the POSIX standard. The argument shall either be a string of +a nonnegative octal number or a symbolic mode. + +@item @var{STATUS} @tab (optional) scalar @code{INTEGER}, which is +@code{0} on success and nonzero otherwise. +@end multitable + +@item @emph{Return value}: +In either syntax, @var{STATUS} is set to @code{0} on success and nonzero +otherwise. + +@item @emph{Example}: +@code{CHMOD} as subroutine +@smallexample +program chmod_test + implicit none + integer :: status + call chmod('test.dat','u+x',status) + print *, 'Status: ', status +end program chmod_test +@end smallexample +@code{CHMOD} as function: +@smallexample +program chmod_test + implicit none + integer :: status + status = chmod('test.dat','u+x') + print *, 'Status: ', status +end program chmod_test +@end smallexample + +@end table + + + +@node CMPLX +@section @code{CMPLX} --- Complex conversion function +@fnindex CMPLX +@cindex complex numbers, conversion to +@cindex conversion, to complex + +@table @asis +@item @emph{Description}: +@code{CMPLX(X [, Y [, KIND]])} returns a complex number where @var{X} is converted to +the real component. If @var{Y} is present it is converted to the imaginary +component. If @var{Y} is not present then the imaginary component is set to +0.0. If @var{X} is complex then @var{Y} must not be present. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = CMPLX(X [, Y [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type may be @code{INTEGER}, @code{REAL}, +or @code{COMPLEX}. +@item @var{Y} @tab (Optional; only allowed if @var{X} is not +@code{COMPLEX}.) May be @code{INTEGER} or @code{REAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of @code{COMPLEX} type, with a kind equal to +@var{KIND} if it is specified. If @var{KIND} is not specified, the +result is of the default @code{COMPLEX} kind, regardless of the kinds of +@var{X} and @var{Y}. + +@item @emph{Example}: +@smallexample +program test_cmplx + integer :: i = 42 + real :: x = 3.14 + complex :: z + z = cmplx(i, x) + print *, z, cmplx(x) +end program test_cmplx +@end smallexample + +@item @emph{See also}: +@ref{COMPLEX} +@end table + + + +@node CO_BROADCAST +@section @code{CO_BROADCAST} --- Copy a value to all images the current set of images +@fnindex CO_BROADCAST +@cindex Collectives, value broadcasting + +@table @asis +@item @emph{Description}: +@code{CO_BROADCAST} copies the value of argument @var{A} on the image with +image index @code{SOURCE_IMAGE} to all images in the current team. @var{A} +becomes defined as if by intrinsic assignment. If the execution was +successful and @var{STAT} is present, it is assigned the value zero. If the +execution failed, @var{STAT} gets assigned a nonzero value and, if present, +@var{ERRMSG} gets assigned a value describing the occurred error. + +@item @emph{Standard}: +Technical Specification (TS) 18508 or later + +@item @emph{Class}: +Collective subroutine + +@item @emph{Syntax}: +@code{CALL CO_BROADCAST(A, SOURCE_IMAGE [, STAT, ERRMSG])} + +@item @emph{Arguments}: +@multitable @columnfractions .20 .65 +@item @var{A} @tab INTENT(INOUT) argument; shall have the same +dynamic type and type parameters on all images of the current team. If it +is an array, it shall have the same shape on all images. +@item @var{SOURCE_IMAGE} @tab a scalar integer expression. +It shall have the same value on all images and refer to an +image of the current team. +@item @var{STAT} @tab (optional) a scalar integer variable +@item @var{ERRMSG} @tab (optional) a scalar character variable +@end multitable + +@item @emph{Example}: +@smallexample +program test + integer :: val(3) + if (this_image() == 1) then + val = [1, 5, 3] + end if + call co_broadcast (val, source_image=1) + print *, this_image, ":", val +end program test +@end smallexample + +@item @emph{See also}: +@ref{CO_MAX}, @gol +@ref{CO_MIN}, @gol +@ref{CO_SUM}, @gol +@ref{CO_REDUCE} +@end table + + + +@node CO_MAX +@section @code{CO_MAX} --- Maximal value on the current set of images +@fnindex CO_MAX +@cindex Collectives, maximal value + +@table @asis +@item @emph{Description}: +@code{CO_MAX} determines element-wise the maximal value of @var{A} on all +images of the current team. If @var{RESULT_IMAGE} is present, the maximum +values are returned in @var{A} on the specified image only and the value +of @var{A} on the other images become undefined. If @var{RESULT_IMAGE} is +not present, the value is returned on all images. If the execution was +successful and @var{STAT} is present, it is assigned the value zero. If the +execution failed, @var{STAT} gets assigned a nonzero value and, if present, +@var{ERRMSG} gets assigned a value describing the occurred error. + +@item @emph{Standard}: +Technical Specification (TS) 18508 or later + +@item @emph{Class}: +Collective subroutine + +@item @emph{Syntax}: +@code{CALL CO_MAX(A [, RESULT_IMAGE, STAT, ERRMSG])} + +@item @emph{Arguments}: +@multitable @columnfractions .20 .65 +@item @var{A} @tab shall be an integer, real or character variable, +which has the same type and type parameters on all images of the team. +@item @var{RESULT_IMAGE} @tab (optional) a scalar integer expression; if +present, it shall have the same value on all images and refer to an +image of the current team. +@item @var{STAT} @tab (optional) a scalar integer variable +@item @var{ERRMSG} @tab (optional) a scalar character variable +@end multitable + +@item @emph{Example}: +@smallexample +program test + integer :: val + val = this_image () + call co_max (val, result_image=1) + if (this_image() == 1) then + write(*,*) "Maximal value", val ! prints num_images() + end if +end program test +@end smallexample + +@item @emph{See also}: +@ref{CO_MIN}, @gol +@ref{CO_SUM}, @gol +@ref{CO_REDUCE}, @gol +@ref{CO_BROADCAST} +@end table + + + +@node CO_MIN +@section @code{CO_MIN} --- Minimal value on the current set of images +@fnindex CO_MIN +@cindex Collectives, minimal value + +@table @asis +@item @emph{Description}: +@code{CO_MIN} determines element-wise the minimal value of @var{A} on all +images of the current team. If @var{RESULT_IMAGE} is present, the minimal +values are returned in @var{A} on the specified image only and the value +of @var{A} on the other images become undefined. If @var{RESULT_IMAGE} is +not present, the value is returned on all images. If the execution was +successful and @var{STAT} is present, it is assigned the value zero. If the +execution failed, @var{STAT} gets assigned a nonzero value and, if present, +@var{ERRMSG} gets assigned a value describing the occurred error. + +@item @emph{Standard}: +Technical Specification (TS) 18508 or later + +@item @emph{Class}: +Collective subroutine + +@item @emph{Syntax}: +@code{CALL CO_MIN(A [, RESULT_IMAGE, STAT, ERRMSG])} + +@item @emph{Arguments}: +@multitable @columnfractions .20 .65 +@item @var{A} @tab shall be an integer, real or character variable, +which has the same type and type parameters on all images of the team. +@item @var{RESULT_IMAGE} @tab (optional) a scalar integer expression; if +present, it shall have the same value on all images and refer to an +image of the current team. +@item @var{STAT} @tab (optional) a scalar integer variable +@item @var{ERRMSG} @tab (optional) a scalar character variable +@end multitable + +@item @emph{Example}: +@smallexample +program test + integer :: val + val = this_image () + call co_min (val, result_image=1) + if (this_image() == 1) then + write(*,*) "Minimal value", val ! prints 1 + end if +end program test +@end smallexample + +@item @emph{See also}: +@ref{CO_MAX}, @gol +@ref{CO_SUM}, @gol +@ref{CO_REDUCE}, @gol +@ref{CO_BROADCAST} +@end table + + + +@node CO_REDUCE +@section @code{CO_REDUCE} --- Reduction of values on the current set of images +@fnindex CO_REDUCE +@cindex Collectives, generic reduction + +@table @asis +@item @emph{Description}: +@code{CO_REDUCE} determines element-wise the reduction of the value of @var{A} +on all images of the current team. The pure function passed as @var{OPERATION} +is used to pairwise reduce the values of @var{A} by passing either the value +of @var{A} of different images or the result values of such a reduction as +argument. If @var{A} is an array, the deduction is done element wise. If +@var{RESULT_IMAGE} is present, the result values are returned in @var{A} on +the specified image only and the value of @var{A} on the other images become +undefined. If @var{RESULT_IMAGE} is not present, the value is returned on all +images. If the execution was successful and @var{STAT} is present, it is +assigned the value zero. If the execution failed, @var{STAT} gets assigned +a nonzero value and, if present, @var{ERRMSG} gets assigned a value describing +the occurred error. + +@item @emph{Standard}: +Technical Specification (TS) 18508 or later + +@item @emph{Class}: +Collective subroutine + +@item @emph{Syntax}: +@code{CALL CO_REDUCE(A, OPERATION, [, RESULT_IMAGE, STAT, ERRMSG])} + +@item @emph{Arguments}: +@multitable @columnfractions .20 .65 +@item @var{A} @tab is an @code{INTENT(INOUT)} argument and shall be +nonpolymorphic. If it is allocatable, it shall be allocated; if it is a pointer, +it shall be associated. @var{A} shall have the same type and type parameters on +all images of the team; if it is an array, it shall have the same shape on all +images. +@item @var{OPERATION} @tab pure function with two scalar nonallocatable +arguments, which shall be nonpolymorphic and have the same type and type +parameters as @var{A}. The function shall return a nonallocatable scalar of +the same type and type parameters as @var{A}. The function shall be the same on +all images and with regards to the arguments mathematically commutative and +associative. Note that @var{OPERATION} may not be an elemental function, unless +it is an intrisic function. +@item @var{RESULT_IMAGE} @tab (optional) a scalar integer expression; if +present, it shall have the same value on all images and refer to an +image of the current team. +@item @var{STAT} @tab (optional) a scalar integer variable +@item @var{ERRMSG} @tab (optional) a scalar character variable +@end multitable + +@item @emph{Example}: +@smallexample +program test + integer :: val + val = this_image () + call co_reduce (val, result_image=1, operation=myprod) + if (this_image() == 1) then + write(*,*) "Product value", val ! prints num_images() factorial + end if +contains + pure function myprod(a, b) + integer, value :: a, b + integer :: myprod + myprod = a * b + end function myprod +end program test +@end smallexample + +@item @emph{Note}: +While the rules permit in principle an intrinsic function, none of the +intrinsics in the standard fulfill the criteria of having a specific +function, which takes two arguments of the same type and returning that +type as result. + +@item @emph{See also}: +@ref{CO_MIN}, @gol +@ref{CO_MAX}, @gol +@ref{CO_SUM}, @gol +@ref{CO_BROADCAST} +@end table + + + +@node CO_SUM +@section @code{CO_SUM} --- Sum of values on the current set of images +@fnindex CO_SUM +@cindex Collectives, sum of values + +@table @asis +@item @emph{Description}: +@code{CO_SUM} sums up the values of each element of @var{A} on all +images of the current team. If @var{RESULT_IMAGE} is present, the summed-up +values are returned in @var{A} on the specified image only and the value +of @var{A} on the other images become undefined. If @var{RESULT_IMAGE} is +not present, the value is returned on all images. If the execution was +successful and @var{STAT} is present, it is assigned the value zero. If the +execution failed, @var{STAT} gets assigned a nonzero value and, if present, +@var{ERRMSG} gets assigned a value describing the occurred error. + +@item @emph{Standard}: +Technical Specification (TS) 18508 or later + +@item @emph{Class}: +Collective subroutine + +@item @emph{Syntax}: +@code{CALL CO_SUM(A [, RESULT_IMAGE, STAT, ERRMSG])} + +@item @emph{Arguments}: +@multitable @columnfractions .20 .65 +@item @var{A} @tab shall be an integer, real or complex variable, +which has the same type and type parameters on all images of the team. +@item @var{RESULT_IMAGE} @tab (optional) a scalar integer expression; if +present, it shall have the same value on all images and refer to an +image of the current team. +@item @var{STAT} @tab (optional) a scalar integer variable +@item @var{ERRMSG} @tab (optional) a scalar character variable +@end multitable + +@item @emph{Example}: +@smallexample +program test + integer :: val + val = this_image () + call co_sum (val, result_image=1) + if (this_image() == 1) then + write(*,*) "The sum is ", val ! prints (n**2 + n)/2, + ! with n = num_images() + end if +end program test +@end smallexample + +@item @emph{See also}: +@ref{CO_MAX}, @gol +@ref{CO_MIN}, @gol +@ref{CO_REDUCE}, @gol +@ref{CO_BROADCAST} +@end table + + + +@node COMMAND_ARGUMENT_COUNT +@section @code{COMMAND_ARGUMENT_COUNT} --- Get number of command line arguments +@fnindex COMMAND_ARGUMENT_COUNT +@cindex command-line arguments +@cindex command-line arguments, number of +@cindex arguments, to program + +@table @asis +@item @emph{Description}: +@code{COMMAND_ARGUMENT_COUNT} returns the number of arguments passed on the +command line when the containing program was invoked. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = COMMAND_ARGUMENT_COUNT()} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item None +@end multitable + +@item @emph{Return value}: +The return value is an @code{INTEGER} of default kind. + +@item @emph{Example}: +@smallexample +program test_command_argument_count + integer :: count + count = command_argument_count() + print *, count +end program test_command_argument_count +@end smallexample + +@item @emph{See also}: +@ref{GET_COMMAND}, @gol +@ref{GET_COMMAND_ARGUMENT} +@end table + + + +@node COMPILER_OPTIONS +@section @code{COMPILER_OPTIONS} --- Options passed to the compiler +@fnindex COMPILER_OPTIONS +@cindex flags inquiry function +@cindex options inquiry function +@cindex compiler flags inquiry function + +@table @asis +@item @emph{Description}: +@code{COMPILER_OPTIONS} returns a string with the options used for +compiling. + +@item @emph{Standard}: +Fortran 2008 + +@item @emph{Class}: +Inquiry function of the module @code{ISO_FORTRAN_ENV} + +@item @emph{Syntax}: +@code{STR = COMPILER_OPTIONS()} + +@item @emph{Arguments}: +None + +@item @emph{Return value}: +The return value is a default-kind string with system-dependent length. +It contains the compiler flags used to compile the file, which called +the @code{COMPILER_OPTIONS} intrinsic. + +@item @emph{Example}: +@smallexample + use iso_fortran_env + print '(4a)', 'This file was compiled by ', & + compiler_version(), ' using the options ', & + compiler_options() + end +@end smallexample + +@item @emph{See also}: +@ref{COMPILER_VERSION}, @gol +@ref{ISO_FORTRAN_ENV} +@end table + + + +@node COMPILER_VERSION +@section @code{COMPILER_VERSION} --- Compiler version string +@fnindex COMPILER_VERSION +@cindex compiler, name and version +@cindex version of the compiler + +@table @asis +@item @emph{Description}: +@code{COMPILER_VERSION} returns a string with the name and the +version of the compiler. + +@item @emph{Standard}: +Fortran 2008 + +@item @emph{Class}: +Inquiry function of the module @code{ISO_FORTRAN_ENV} + +@item @emph{Syntax}: +@code{STR = COMPILER_VERSION()} + +@item @emph{Arguments}: +None + +@item @emph{Return value}: +The return value is a default-kind string with system-dependent length. +It contains the name of the compiler and its version number. + +@item @emph{Example}: +@smallexample + use iso_fortran_env + print '(4a)', 'This file was compiled by ', & + compiler_version(), ' using the options ', & + compiler_options() + end +@end smallexample + +@item @emph{See also}: +@ref{COMPILER_OPTIONS}, @gol +@ref{ISO_FORTRAN_ENV} +@end table + + + +@node COMPLEX +@section @code{COMPLEX} --- Complex conversion function +@fnindex COMPLEX +@cindex complex numbers, conversion to +@cindex conversion, to complex + +@table @asis +@item @emph{Description}: +@code{COMPLEX(X, Y)} returns a complex number where @var{X} is converted +to the real component and @var{Y} is converted to the imaginary +component. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = COMPLEX(X, Y)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type may be @code{INTEGER} or @code{REAL}. +@item @var{Y} @tab The type may be @code{INTEGER} or @code{REAL}. +@end multitable + +@item @emph{Return value}: +If @var{X} and @var{Y} are both of @code{INTEGER} type, then the return +value is of default @code{COMPLEX} type. + +If @var{X} and @var{Y} are of @code{REAL} type, or one is of @code{REAL} +type and one is of @code{INTEGER} type, then the return value is of +@code{COMPLEX} type with a kind equal to that of the @code{REAL} +argument with the highest precision. + +@item @emph{Example}: +@smallexample +program test_complex + integer :: i = 42 + real :: x = 3.14 + print *, complex(i, x) +end program test_complex +@end smallexample + +@item @emph{See also}: +@ref{CMPLX} +@end table + + + +@node CONJG +@section @code{CONJG} --- Complex conjugate function +@fnindex CONJG +@fnindex DCONJG +@cindex complex conjugate + +@table @asis +@item @emph{Description}: +@code{CONJG(Z)} returns the conjugate of @var{Z}. If @var{Z} is @code{(x, y)} +then the result is @code{(x, -y)} + +@item @emph{Standard}: +Fortran 77 and later, has an overload that is a GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{Z = CONJG(Z)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{Z} @tab The type shall be @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{COMPLEX}. + +@item @emph{Example}: +@smallexample +program test_conjg + complex :: z = (2.0, 3.0) + complex(8) :: dz = (2.71_8, -3.14_8) + z= conjg(z) + print *, z + dz = dconjg(dz) + print *, dz +end program test_conjg +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DCONJG(Z)} @tab @code{COMPLEX(8) Z} @tab @code{COMPLEX(8)} @tab GNU extension +@end multitable +@end table + + + +@node COS +@section @code{COS} --- Cosine function +@fnindex COS +@fnindex DCOS +@fnindex CCOS +@fnindex ZCOS +@fnindex CDCOS +@cindex trigonometric function, cosine +@cindex cosine + +@table @asis +@item @emph{Description}: +@code{COS(X)} computes the cosine of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = COS(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or +@code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. The real part +of the result is in radians. If @var{X} is of the type @code{REAL}, +the return value lies in the range @math{ -1 \leq \cos (x) \leq 1}. + +@item @emph{Example}: +@smallexample +program test_cos + real :: x = 0.0 + x = cos(x) +end program test_cos +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{COS(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DCOS(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@item @code{CCOS(X)} @tab @code{COMPLEX(4) X} @tab @code{COMPLEX(4)} @tab Fortran 77 and later +@item @code{ZCOS(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@item @code{CDCOS(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{ACOS} @gol +Degrees function: @gol +@ref{COSD} +@end table + + + +@node COSD +@section @code{COSD} --- Cosine function, degrees +@fnindex COSD +@fnindex DCOSD +@fnindex CCOSD +@fnindex ZCOSD +@fnindex CDCOSD +@cindex trigonometric function, cosine, degrees +@cindex cosine, degrees + +@table @asis +@item @emph{Description}: +@code{COSD(X)} computes the cosine of @var{X} in degrees. + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math}. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = COSD(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or +@code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. The real part +of the result is in degrees. If @var{X} is of the type @code{REAL}, +the return value lies in the range @math{ -1 \leq \cosd (x) \leq 1}. + +@item @emph{Example}: +@smallexample +program test_cosd + real :: x = 0.0 + x = cosd(x) +end program test_cosd +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{COSD(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DCOSD(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@item @code{CCOSD(X)} @tab @code{COMPLEX(4) X} @tab @code{COMPLEX(4)} @tab GNU extension +@item @code{ZCOSD(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@item @code{CDCOSD(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{ACOSD} @gol +Radians function: @gol +@ref{COS} +@end table + + + +@node COSH +@section @code{COSH} --- Hyperbolic cosine function +@fnindex COSH +@fnindex DCOSH +@cindex hyperbolic cosine +@cindex hyperbolic function, cosine +@cindex cosine, hyperbolic + +@table @asis +@item @emph{Description}: +@code{COSH(X)} computes the hyperbolic cosine of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later, for a complex argument Fortran 2008 or later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{X = COSH(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}. If @var{X} is +complex, the imaginary part of the result is in radians. If @var{X} +is @code{REAL}, the return value has a lower bound of one, +@math{\cosh (x) \geq 1}. + +@item @emph{Example}: +@smallexample +program test_cosh + real(8) :: x = 1.0_8 + x = cosh(x) +end program test_cosh +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{COSH(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DCOSH(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{ACOSH} +@end table + + + +@node COTAN +@section @code{COTAN} --- Cotangent function +@fnindex COTAN +@fnindex DCOTAN +@cindex trigonometric function, cotangent +@cindex cotangent + +@table @asis +@item @emph{Description}: +@code{COTAN(X)} computes the cotangent of @var{X}. Equivalent to @code{COS(x)} +divided by @code{SIN(x)}, or @code{1 / TAN(x)}. + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math}. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = COTAN(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}, and its value is in radians. + +@item @emph{Example}: +@smallexample +program test_cotan + real(8) :: x = 0.165_8 + x = cotan(x) +end program test_cotan +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{COTAN(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DCOTAN(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Converse function: @gol +@ref{TAN} @gol +Degrees function: @gol +@ref{COTAND} +@end table + + + +@node COTAND +@section @code{COTAND} --- Cotangent function, degrees +@fnindex COTAND +@fnindex DCOTAND +@cindex trigonometric function, cotangent, degrees +@cindex cotangent, degrees + +@table @asis +@item @emph{Description}: +@code{COTAND(X)} computes the cotangent of @var{X} in degrees. Equivalent to +@code{COSD(x)} divided by @code{SIND(x)}, or @code{1 / TAND(x)}. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math}. + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = COTAND(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}, and its value is in degrees. + +@item @emph{Example}: +@smallexample +program test_cotand + real(8) :: x = 0.165_8 + x = cotand(x) +end program test_cotand +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{COTAND(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DCOTAND(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Converse function: @gol +@ref{TAND} @gol +Radians function: @gol +@ref{COTAN} +@end table + + + +@node COUNT +@section @code{COUNT} --- Count function +@fnindex COUNT +@cindex array, conditionally count elements +@cindex array, element counting +@cindex array, number of elements + +@table @asis +@item @emph{Description}: + +Counts the number of @code{.TRUE.} elements in a logical @var{MASK}, +or, if the @var{DIM} argument is supplied, counts the number of +elements along each row of the array in the @var{DIM} direction. +If the array has zero size, or all of the elements of @var{MASK} are +@code{.FALSE.}, then the result is @code{0}. + +@item @emph{Standard}: +Fortran 90 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = COUNT(MASK [, DIM, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{MASK} @tab The type shall be @code{LOGICAL}. +@item @var{DIM} @tab (Optional) The type shall be @code{INTEGER}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. +If @var{DIM} is present, the result is an array with a rank one less +than the rank of @var{ARRAY}, and a size corresponding to the shape +of @var{ARRAY} with the @var{DIM} dimension removed. + +@item @emph{Example}: +@smallexample +program test_count + integer, dimension(2,3) :: a, b + logical, dimension(2,3) :: mask + a = reshape( (/ 1, 2, 3, 4, 5, 6 /), (/ 2, 3 /)) + b = reshape( (/ 0, 7, 3, 4, 5, 8 /), (/ 2, 3 /)) + print '(3i3)', a(1,:) + print '(3i3)', a(2,:) + print * + print '(3i3)', b(1,:) + print '(3i3)', b(2,:) + print * + mask = a.ne.b + print '(3l3)', mask(1,:) + print '(3l3)', mask(2,:) + print * + print '(3i3)', count(mask) + print * + print '(3i3)', count(mask, 1) + print * + print '(3i3)', count(mask, 2) +end program test_count +@end smallexample +@end table + + + +@node CPU_TIME +@section @code{CPU_TIME} --- CPU elapsed time in seconds +@fnindex CPU_TIME +@cindex time, elapsed + +@table @asis +@item @emph{Description}: +Returns a @code{REAL} value representing the elapsed CPU time in +seconds. This is useful for testing segments of code to determine +execution time. + +If a time source is available, time will be reported with microsecond +resolution. If no time source is available, @var{TIME} is set to +@code{-1.0}. + +Note that @var{TIME} may contain a, system dependent, arbitrary offset +and may not start with @code{0.0}. For @code{CPU_TIME}, the absolute +value is meaningless, only differences between subsequent calls to +this subroutine, as shown in the example below, should be used. + + +@item @emph{Standard}: +Fortran 95 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL CPU_TIME(TIME)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{TIME} @tab The type shall be @code{REAL} with @code{INTENT(OUT)}. +@end multitable + +@item @emph{Return value}: +None + +@item @emph{Example}: +@smallexample +program test_cpu_time + real :: start, finish + call cpu_time(start) + ! put code to test here + call cpu_time(finish) + print '("Time = ",f6.3," seconds.")',finish-start +end program test_cpu_time +@end smallexample + +@item @emph{See also}: +@ref{SYSTEM_CLOCK}, @gol +@ref{DATE_AND_TIME} +@end table + + + +@node CSHIFT +@section @code{CSHIFT} --- Circular shift elements of an array +@fnindex CSHIFT +@cindex array, shift circularly +@cindex array, permutation +@cindex array, rotate + +@table @asis +@item @emph{Description}: +@code{CSHIFT(ARRAY, SHIFT [, DIM])} performs a circular shift on elements of +@var{ARRAY} along the dimension of @var{DIM}. If @var{DIM} is omitted it is +taken to be @code{1}. @var{DIM} is a scalar of type @code{INTEGER} in the +range of @math{1 \leq DIM \leq n)} where @math{n} is the rank of @var{ARRAY}. +If the rank of @var{ARRAY} is one, then all elements of @var{ARRAY} are shifted +by @var{SHIFT} places. If rank is greater than one, then all complete rank one +sections of @var{ARRAY} along the given dimension are shifted. Elements +shifted out one end of each rank one section are shifted back in the other end. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = CSHIFT(ARRAY, SHIFT [, DIM])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of any type. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@item @var{DIM} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +Returns an array of same type and rank as the @var{ARRAY} argument. + +@item @emph{Example}: +@smallexample +program test_cshift + integer, dimension(3,3) :: a + a = reshape( (/ 1, 2, 3, 4, 5, 6, 7, 8, 9 /), (/ 3, 3 /)) + print '(3i3)', a(1,:) + print '(3i3)', a(2,:) + print '(3i3)', a(3,:) + a = cshift(a, SHIFT=(/1, 2, -1/), DIM=2) + print * + print '(3i3)', a(1,:) + print '(3i3)', a(2,:) + print '(3i3)', a(3,:) +end program test_cshift +@end smallexample +@end table + + + +@node CTIME +@section @code{CTIME} --- Convert a time into a string +@fnindex CTIME +@cindex time, conversion to string +@cindex conversion, to string + +@table @asis +@item @emph{Description}: +@code{CTIME} converts a system time value, such as returned by +@ref{TIME8}, to a string. The output will be of the form @samp{Sat +Aug 19 18:13:14 1995}. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL CTIME(TIME, RESULT)}. +@item @code{RESULT = CTIME(TIME)}. +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{TIME} @tab The type shall be of type @code{INTEGER}. +@item @var{RESULT} @tab The type shall be of type @code{CHARACTER} and +of default kind. It is an @code{INTENT(OUT)} argument. If the length +of this variable is too short for the time and date string to fit +completely, it will be blank on procedure return. +@end multitable + +@item @emph{Return value}: +The converted date and time as a string. + +@item @emph{Example}: +@smallexample +program test_ctime + integer(8) :: i + character(len=30) :: date + i = time8() + + ! Do something, main part of the program + + call ctime(i,date) + print *, 'Program was started on ', date +end program test_ctime +@end smallexample + +@item @emph{See Also}: +@ref{DATE_AND_TIME}, @gol +@ref{GMTIME}, @gol +@ref{LTIME}, @gol +@ref{TIME}, @gol +@ref{TIME8} +@end table + + + +@node DATE_AND_TIME +@section @code{DATE_AND_TIME} --- Date and time subroutine +@fnindex DATE_AND_TIME +@cindex date, current +@cindex current date +@cindex time, current +@cindex current time + +@table @asis +@item @emph{Description}: +@code{DATE_AND_TIME(DATE, TIME, ZONE, VALUES)} gets the corresponding date and +time information from the real-time system clock. @var{DATE} is +@code{INTENT(OUT)} and has form ccyymmdd. @var{TIME} is @code{INTENT(OUT)} and +has form hhmmss.sss. @var{ZONE} is @code{INTENT(OUT)} and has form (+-)hhmm, +representing the difference with respect to Coordinated Universal Time (UTC). +Unavailable time and date parameters return blanks. + +@var{VALUES} is @code{INTENT(OUT)} and provides the following: + +@multitable @columnfractions .15 .70 +@item @code{VALUE(1)}: @tab The year +@item @code{VALUE(2)}: @tab The month +@item @code{VALUE(3)}: @tab The day of the month +@item @code{VALUE(4)}: @tab Time difference with UTC in minutes +@item @code{VALUE(5)}: @tab The hour of the day +@item @code{VALUE(6)}: @tab The minutes of the hour +@item @code{VALUE(7)}: @tab The seconds of the minute +@item @code{VALUE(8)}: @tab The milliseconds of the second +@end multitable + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL DATE_AND_TIME([DATE, TIME, ZONE, VALUES])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{DATE} @tab (Optional) The type shall be @code{CHARACTER(LEN=8)} +or larger, and of default kind. +@item @var{TIME} @tab (Optional) The type shall be @code{CHARACTER(LEN=10)} +or larger, and of default kind. +@item @var{ZONE} @tab (Optional) The type shall be @code{CHARACTER(LEN=5)} +or larger, and of default kind. +@item @var{VALUES}@tab (Optional) The type shall be @code{INTEGER(8)}. +@end multitable + +@item @emph{Return value}: +None + +@item @emph{Example}: +@smallexample +program test_time_and_date + character(8) :: date + character(10) :: time + character(5) :: zone + integer,dimension(8) :: values + ! using keyword arguments + call date_and_time(date,time,zone,values) + call date_and_time(DATE=date,ZONE=zone) + call date_and_time(TIME=time) + call date_and_time(VALUES=values) + print '(a,2x,a,2x,a)', date, time, zone + print '(8i5)', values +end program test_time_and_date +@end smallexample + +@item @emph{See also}: +@ref{CPU_TIME}, @gol +@ref{SYSTEM_CLOCK} +@end table + + + +@node DBLE +@section @code{DBLE} --- Double conversion function +@fnindex DBLE +@cindex conversion, to real + +@table @asis +@item @emph{Description}: +@code{DBLE(A)} Converts @var{A} to double precision real type. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = DBLE(A)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab The type shall be @code{INTEGER}, @code{REAL}, +or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of type double precision real. + +@item @emph{Example}: +@smallexample +program test_dble + real :: x = 2.18 + integer :: i = 5 + complex :: z = (2.3,1.14) + print *, dble(x), dble(i), dble(z) +end program test_dble +@end smallexample + +@item @emph{See also}: +@ref{REAL} +@end table + + + +@node DCMPLX +@section @code{DCMPLX} --- Double complex conversion function +@fnindex DCMPLX +@cindex complex numbers, conversion to +@cindex conversion, to complex + +@table @asis +@item @emph{Description}: +@code{DCMPLX(X [,Y])} returns a double complex number where @var{X} is +converted to the real component. If @var{Y} is present it is converted to the +imaginary component. If @var{Y} is not present then the imaginary component is +set to 0.0. If @var{X} is complex then @var{Y} must not be present. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = DCMPLX(X [, Y])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type may be @code{INTEGER}, @code{REAL}, +or @code{COMPLEX}. +@item @var{Y} @tab (Optional if @var{X} is not @code{COMPLEX}.) May be +@code{INTEGER} or @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{COMPLEX(8)} + +@item @emph{Example}: +@smallexample +program test_dcmplx + integer :: i = 42 + real :: x = 3.14 + complex :: z + z = cmplx(i, x) + print *, dcmplx(i) + print *, dcmplx(x) + print *, dcmplx(z) + print *, dcmplx(x,i) +end program test_dcmplx +@end smallexample +@end table + + +@node DIGITS +@section @code{DIGITS} --- Significant binary digits function +@fnindex DIGITS +@cindex model representation, significant digits + +@table @asis +@item @emph{Description}: +@code{DIGITS(X)} returns the number of significant binary digits of the internal +model representation of @var{X}. For example, on a system using a 32-bit +floating point representation, a default real number would likely return 24. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = DIGITS(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type may be @code{INTEGER} or @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER}. + +@item @emph{Example}: +@smallexample +program test_digits + integer :: i = 12345 + real :: x = 3.143 + real(8) :: y = 2.33 + print *, digits(i) + print *, digits(x) + print *, digits(y) +end program test_digits +@end smallexample +@end table + + + +@node DIM +@section @code{DIM} --- Positive difference +@fnindex DIM +@fnindex IDIM +@fnindex DDIM +@cindex positive difference + +@table @asis +@item @emph{Description}: +@code{DIM(X,Y)} returns the difference @code{X-Y} if the result is positive; +otherwise returns zero. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = DIM(X, Y)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{INTEGER} or @code{REAL} +@item @var{Y} @tab The type shall be the same type and kind as @var{X}. (As +a GNU extension, arguments of different kinds are permitted.) +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} or @code{REAL}. (As a GNU +extension, kind is the largest kind of the actual arguments.) + +@item @emph{Example}: +@smallexample +program test_dim + integer :: i + real(8) :: x + i = dim(4, 15) + x = dim(4.345_8, 2.111_8) + print *, i + print *, x +end program test_dim +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .26 .20 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DIM(X,Y)} @tab @code{REAL(4) X, Y} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{IDIM(X,Y)} @tab @code{INTEGER(4) X, Y} @tab @code{INTEGER(4)} @tab Fortran 77 and later +@item @code{DDIM(X,Y)} @tab @code{REAL(8) X, Y} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable +@end table + + + +@node DOT_PRODUCT +@section @code{DOT_PRODUCT} --- Dot product function +@fnindex DOT_PRODUCT +@cindex dot product +@cindex vector product +@cindex product, vector + +@table @asis +@item @emph{Description}: +@code{DOT_PRODUCT(VECTOR_A, VECTOR_B)} computes the dot product multiplication +of two vectors @var{VECTOR_A} and @var{VECTOR_B}. The two vectors may be +either numeric or logical and must be arrays of rank one and of equal size. If +the vectors are @code{INTEGER} or @code{REAL}, the result is +@code{SUM(VECTOR_A*VECTOR_B)}. If the vectors are @code{COMPLEX}, the result +is @code{SUM(CONJG(VECTOR_A)*VECTOR_B)}. If the vectors are @code{LOGICAL}, +the result is @code{ANY(VECTOR_A .AND. VECTOR_B)}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = DOT_PRODUCT(VECTOR_A, VECTOR_B)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{VECTOR_A} @tab The type shall be numeric or @code{LOGICAL}, rank 1. +@item @var{VECTOR_B} @tab The type shall be numeric if @var{VECTOR_A} is of numeric type or @code{LOGICAL} if @var{VECTOR_A} is of type @code{LOGICAL}. @var{VECTOR_B} shall be a rank-one array. +@end multitable + +@item @emph{Return value}: +If the arguments are numeric, the return value is a scalar of numeric type, +@code{INTEGER}, @code{REAL}, or @code{COMPLEX}. If the arguments are +@code{LOGICAL}, the return value is @code{.TRUE.} or @code{.FALSE.}. + +@item @emph{Example}: +@smallexample +program test_dot_prod + integer, dimension(3) :: a, b + a = (/ 1, 2, 3 /) + b = (/ 4, 5, 6 /) + print '(3i3)', a + print * + print '(3i3)', b + print * + print *, dot_product(a,b) +end program test_dot_prod +@end smallexample +@end table + + + +@node DPROD +@section @code{DPROD} --- Double product function +@fnindex DPROD +@cindex product, double-precision + +@table @asis +@item @emph{Description}: +@code{DPROD(X,Y)} returns the product @code{X*Y}. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = DPROD(X, Y)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@item @var{Y} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL(8)}. + +@item @emph{Example}: +@smallexample +program test_dprod + real :: x = 5.2 + real :: y = 2.3 + real(8) :: d + d = dprod(x,y) + print *, d +end program test_dprod +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DPROD(X,Y)} @tab @code{REAL(4) X, Y} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@end table + + +@node DREAL +@section @code{DREAL} --- Double real part function +@fnindex DREAL +@cindex complex numbers, real part + +@table @asis +@item @emph{Description}: +@code{DREAL(Z)} returns the real part of complex variable @var{Z}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = DREAL(A)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab The type shall be @code{COMPLEX(8)}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL(8)}. + +@item @emph{Example}: +@smallexample +program test_dreal + complex(8) :: z = (1.3_8,7.2_8) + print *, dreal(z) +end program test_dreal +@end smallexample + +@item @emph{See also}: +@ref{AIMAG} + +@end table + + + +@node DSHIFTL +@section @code{DSHIFTL} --- Combined left shift +@fnindex DSHIFTL +@cindex left shift, combined +@cindex shift, left + +@table @asis +@item @emph{Description}: +@code{DSHIFTL(I, J, SHIFT)} combines bits of @var{I} and @var{J}. The +rightmost @var{SHIFT} bits of the result are the leftmost @var{SHIFT} +bits of @var{J}, and the remaining bits are the rightmost bits of +@var{I}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = DSHIFTL(I, J, SHIFT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER} or a BOZ constant. +@item @var{J} @tab Shall be of type @code{INTEGER} or a BOZ constant. +If both @var{I} and @var{J} have integer type, then they shall have +the same kind type parameter. @var{I} and @var{J} shall not both be +BOZ constants. +@item @var{SHIFT} @tab Shall be of type @code{INTEGER}. It shall +be nonnegative. If @var{I} is not a BOZ constant, then @var{SHIFT} +shall be less than or equal to @code{BIT_SIZE(I)}; otherwise, +@var{SHIFT} shall be less than or equal to @code{BIT_SIZE(J)}. +@end multitable + +@item @emph{Return value}: +If either @var{I} or @var{J} is a BOZ constant, it is first converted +as if by the intrinsic function @code{INT} to an integer type with the +kind type parameter of the other. + +@item @emph{See also}: +@ref{DSHIFTR} +@end table + + +@node DSHIFTR +@section @code{DSHIFTR} --- Combined right shift +@fnindex DSHIFTR +@cindex right shift, combined +@cindex shift, right + +@table @asis +@item @emph{Description}: +@code{DSHIFTR(I, J, SHIFT)} combines bits of @var{I} and @var{J}. The +leftmost @var{SHIFT} bits of the result are the rightmost @var{SHIFT} +bits of @var{I}, and the remaining bits are the leftmost bits of +@var{J}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = DSHIFTR(I, J, SHIFT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER} or a BOZ constant. +@item @var{J} @tab Shall be of type @code{INTEGER} or a BOZ constant. +If both @var{I} and @var{J} have integer type, then they shall have +the same kind type parameter. @var{I} and @var{J} shall not both be +BOZ constants. +@item @var{SHIFT} @tab Shall be of type @code{INTEGER}. It shall +be nonnegative. If @var{I} is not a BOZ constant, then @var{SHIFT} +shall be less than or equal to @code{BIT_SIZE(I)}; otherwise, +@var{SHIFT} shall be less than or equal to @code{BIT_SIZE(J)}. +@end multitable + +@item @emph{Return value}: +If either @var{I} or @var{J} is a BOZ constant, it is first converted +as if by the intrinsic function @code{INT} to an integer type with the +kind type parameter of the other. + +@item @emph{See also}: +@ref{DSHIFTL} +@end table + + +@node DTIME +@section @code{DTIME} --- Execution time subroutine (or function) +@fnindex DTIME +@cindex time, elapsed +@cindex elapsed time + +@table @asis +@item @emph{Description}: +@code{DTIME(VALUES, TIME)} initially returns the number of seconds of runtime +since the start of the process's execution in @var{TIME}. @var{VALUES} +returns the user and system components of this time in @code{VALUES(1)} and +@code{VALUES(2)} respectively. @var{TIME} is equal to @code{VALUES(1) + +VALUES(2)}. + +Subsequent invocations of @code{DTIME} return values accumulated since the +previous invocation. + +On some systems, the underlying timings are represented using types with +sufficiently small limits that overflows (wrap around) are possible, such as +32-bit types. Therefore, the values returned by this intrinsic might be, or +become, negative, or numerically less than previous values, during a single +run of the compiled program. + +Please note, that this implementation is thread safe if used within OpenMP +directives, i.e., its state will be consistent while called from multiple +threads. However, if @code{DTIME} is called from multiple threads, the result +is still the time since the last invocation. This may not give the intended +results. If possible, use @code{CPU_TIME} instead. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@var{VALUES} and @var{TIME} are @code{INTENT(OUT)} and provide the following: + +@multitable @columnfractions .15 .70 +@item @code{VALUES(1)}: @tab User time in seconds. +@item @code{VALUES(2)}: @tab System time in seconds. +@item @code{TIME}: @tab Run time since start in seconds. +@end multitable + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL DTIME(VALUES, TIME)}. +@item @code{TIME = DTIME(VALUES)}, (not recommended). +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{VALUES}@tab The type shall be @code{REAL(4), DIMENSION(2)}. +@item @var{TIME}@tab The type shall be @code{REAL(4)}. +@end multitable + +@item @emph{Return value}: +Elapsed time in seconds since the last invocation or since the start of program +execution if not called before. + +@item @emph{Example}: +@smallexample +program test_dtime + integer(8) :: i, j + real, dimension(2) :: tarray + real :: result + call dtime(tarray, result) + print *, result + print *, tarray(1) + print *, tarray(2) + do i=1,100000000 ! Just a delay + j = i * i - i + end do + call dtime(tarray, result) + print *, result + print *, tarray(1) + print *, tarray(2) +end program test_dtime +@end smallexample + +@item @emph{See also}: +@ref{CPU_TIME} + +@end table + + + +@node EOSHIFT +@section @code{EOSHIFT} --- End-off shift elements of an array +@fnindex EOSHIFT +@cindex array, shift + +@table @asis +@item @emph{Description}: +@code{EOSHIFT(ARRAY, SHIFT[, BOUNDARY, DIM])} performs an end-off shift on +elements of @var{ARRAY} along the dimension of @var{DIM}. If @var{DIM} is +omitted it is taken to be @code{1}. @var{DIM} is a scalar of type +@code{INTEGER} in the range of @math{1 \leq DIM \leq n)} where @math{n} is the +rank of @var{ARRAY}. If the rank of @var{ARRAY} is one, then all elements of +@var{ARRAY} are shifted by @var{SHIFT} places. If rank is greater than one, +then all complete rank one sections of @var{ARRAY} along the given dimension are +shifted. Elements shifted out one end of each rank one section are dropped. If +@var{BOUNDARY} is present then the corresponding value of from @var{BOUNDARY} +is copied back in the other end. If @var{BOUNDARY} is not present then the +following are copied in depending on the type of @var{ARRAY}. + +@multitable @columnfractions .15 .80 +@item @emph{Array Type} @tab @emph{Boundary Value} +@item Numeric @tab 0 of the type and kind of @var{ARRAY}. +@item Logical @tab @code{.FALSE.}. +@item Character(@var{len}) @tab @var{len} blanks. +@end multitable + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = EOSHIFT(ARRAY, SHIFT [, BOUNDARY, DIM])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab May be any type, not scalar. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@item @var{BOUNDARY} @tab Same type as @var{ARRAY}. +@item @var{DIM} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +Returns an array of same type and rank as the @var{ARRAY} argument. + +@item @emph{Example}: +@smallexample +program test_eoshift + integer, dimension(3,3) :: a + a = reshape( (/ 1, 2, 3, 4, 5, 6, 7, 8, 9 /), (/ 3, 3 /)) + print '(3i3)', a(1,:) + print '(3i3)', a(2,:) + print '(3i3)', a(3,:) + a = EOSHIFT(a, SHIFT=(/1, 2, 1/), BOUNDARY=-5, DIM=2) + print * + print '(3i3)', a(1,:) + print '(3i3)', a(2,:) + print '(3i3)', a(3,:) +end program test_eoshift +@end smallexample +@end table + + + +@node EPSILON +@section @code{EPSILON} --- Epsilon function +@fnindex EPSILON +@cindex model representation, epsilon + +@table @asis +@item @emph{Description}: +@code{EPSILON(X)} returns the smallest number @var{E} of the same kind +as @var{X} such that @math{1 + E > 1}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = EPSILON(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of same type as the argument. + +@item @emph{Example}: +@smallexample +program test_epsilon + real :: x = 3.143 + real(8) :: y = 2.33 + print *, EPSILON(x) + print *, EPSILON(y) +end program test_epsilon +@end smallexample +@end table + + + +@node ERF +@section @code{ERF} --- Error function +@fnindex ERF +@cindex error function + +@table @asis +@item @emph{Description}: +@code{ERF(X)} computes the error function of @var{X}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ERF(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL}, of the same kind as +@var{X} and lies in the range @math{-1 \leq erf (x) \leq 1 }. + +@item @emph{Example}: +@smallexample +program test_erf + real(8) :: x = 0.17_8 + x = erf(x) +end program test_erf +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DERF(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable +@end table + + + +@node ERFC +@section @code{ERFC} --- Error function +@fnindex ERFC +@cindex error function, complementary + +@table @asis +@item @emph{Description}: +@code{ERFC(X)} computes the complementary error function of @var{X}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ERFC(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} and of the same kind as @var{X}. +It lies in the range @math{ 0 \leq erfc (x) \leq 2 }. + +@item @emph{Example}: +@smallexample +program test_erfc + real(8) :: x = 0.17_8 + x = erfc(x) +end program test_erfc +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DERFC(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable +@end table + + + +@node ERFC_SCALED +@section @code{ERFC_SCALED} --- Error function +@fnindex ERFC_SCALED +@cindex error function, complementary, exponentially-scaled + +@table @asis +@item @emph{Description}: +@code{ERFC_SCALED(X)} computes the exponentially-scaled complementary +error function of @var{X}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ERFC_SCALED(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} and of the same kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_erfc_scaled + real(8) :: x = 0.17_8 + x = erfc_scaled(x) +end program test_erfc_scaled +@end smallexample +@end table + + + +@node ETIME +@section @code{ETIME} --- Execution time subroutine (or function) +@fnindex ETIME +@cindex time, elapsed + +@table @asis +@item @emph{Description}: +@code{ETIME(VALUES, TIME)} returns the number of seconds of runtime +since the start of the process's execution in @var{TIME}. @var{VALUES} +returns the user and system components of this time in @code{VALUES(1)} and +@code{VALUES(2)} respectively. @var{TIME} is equal to @code{VALUES(1) + VALUES(2)}. + +On some systems, the underlying timings are represented using types with +sufficiently small limits that overflows (wrap around) are possible, such as +32-bit types. Therefore, the values returned by this intrinsic might be, or +become, negative, or numerically less than previous values, during a single +run of the compiled program. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@var{VALUES} and @var{TIME} are @code{INTENT(OUT)} and provide the following: + +@multitable @columnfractions .15 .70 +@item @code{VALUES(1)}: @tab User time in seconds. +@item @code{VALUES(2)}: @tab System time in seconds. +@item @code{TIME}: @tab Run time since start in seconds. +@end multitable + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL ETIME(VALUES, TIME)}. +@item @code{TIME = ETIME(VALUES)}, (not recommended). +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{VALUES}@tab The type shall be @code{REAL(4), DIMENSION(2)}. +@item @var{TIME}@tab The type shall be @code{REAL(4)}. +@end multitable + +@item @emph{Return value}: +Elapsed time in seconds since the start of program execution. + +@item @emph{Example}: +@smallexample +program test_etime + integer(8) :: i, j + real, dimension(2) :: tarray + real :: result + call ETIME(tarray, result) + print *, result + print *, tarray(1) + print *, tarray(2) + do i=1,100000000 ! Just a delay + j = i * i - i + end do + call ETIME(tarray, result) + print *, result + print *, tarray(1) + print *, tarray(2) +end program test_etime +@end smallexample + +@item @emph{See also}: +@ref{CPU_TIME} + +@end table + + + +@node EVENT_QUERY +@section @code{EVENT_QUERY} --- Query whether a coarray event has occurred +@fnindex EVENT_QUERY +@cindex Events, EVENT_QUERY + +@table @asis +@item @emph{Description}: +@code{EVENT_QUERY} assignes the number of events to @var{COUNT} which have been +posted to the @var{EVENT} variable and not yet been removed by calling +@code{EVENT WAIT}. When @var{STAT} is present and the invocation was successful, +it is assigned the value 0. If it is present and the invocation has failed, +it is assigned a positive value and @var{COUNT} is assigned the value @math{-1}. + +@item @emph{Standard}: +TS 18508 or later + +@item @emph{Class}: + subroutine + +@item @emph{Syntax}: +@code{CALL EVENT_QUERY (EVENT, COUNT [, STAT])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{EVENT} @tab (intent(IN)) Scalar of type @code{EVENT_TYPE}, +defined in @code{ISO_FORTRAN_ENV}; shall not be coindexed. +@item @var{COUNT} @tab (intent(out))Scalar integer with at least the +precision of default integer. +@item @var{STAT} @tab (optional) Scalar default-kind integer variable. +@end multitable + +@item @emph{Example}: +@smallexample +program atomic + use iso_fortran_env + implicit none + type(event_type) :: event_value_has_been_set[*] + integer :: cnt + if (this_image() == 1) then + call event_query (event_value_has_been_set, cnt) + if (cnt > 0) write(*,*) "Value has been set" + elseif (this_image() == 2) then + event post (event_value_has_been_set[1]) + end if +end program atomic +@end smallexample + +@end table + + + +@node EXECUTE_COMMAND_LINE +@section @code{EXECUTE_COMMAND_LINE} --- Execute a shell command +@fnindex EXECUTE_COMMAND_LINE +@cindex system, system call +@cindex command line + +@table @asis +@item @emph{Description}: +@code{EXECUTE_COMMAND_LINE} runs a shell command, synchronously or +asynchronously. + +The @code{COMMAND} argument is passed to the shell and executed (The +shell is @code{sh} on Unix systems, and @code{cmd.exe} on Windows.). +If @code{WAIT} is present and has the value false, the execution of +the command is asynchronous if the system supports it; otherwise, the +command is executed synchronously using the C library's @code{system} +call. + +The three last arguments allow the user to get status information. After +synchronous execution, @code{EXITSTAT} contains the integer exit code of +the command, as returned by @code{system}. @code{CMDSTAT} is set to zero +if the command line was executed (whatever its exit status was). +@code{CMDMSG} is assigned an error message if an error has occurred. + +Note that the @code{system} function need not be thread-safe. It is +the responsibility of the user to ensure that @code{system} is not +called concurrently. + +For asynchronous execution on supported targets, the POSIX +@code{posix_spawn} or @code{fork} functions are used. Also, a signal +handler for the @code{SIGCHLD} signal is installed. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL EXECUTE_COMMAND_LINE(COMMAND [, WAIT, EXITSTAT, CMDSTAT, CMDMSG ])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{COMMAND} @tab Shall be a default @code{CHARACTER} scalar. +@item @var{WAIT} @tab (Optional) Shall be a default @code{LOGICAL} scalar. +@item @var{EXITSTAT} @tab (Optional) Shall be an @code{INTEGER} of the +default kind. +@item @var{CMDSTAT} @tab (Optional) Shall be an @code{INTEGER} of the +default kind. +@item @var{CMDMSG} @tab (Optional) Shall be an @code{CHARACTER} scalar of the +default kind. +@end multitable + +@item @emph{Example}: +@smallexample +program test_exec + integer :: i + + call execute_command_line ("external_prog.exe", exitstat=i) + print *, "Exit status of external_prog.exe was ", i + + call execute_command_line ("reindex_files.exe", wait=.false.) + print *, "Now reindexing files in the background" + +end program test_exec +@end smallexample + + +@item @emph{Note}: + +Because this intrinsic is implemented in terms of the @code{system} +function call, its behavior with respect to signaling is processor +dependent. In particular, on POSIX-compliant systems, the SIGINT and +SIGQUIT signals will be ignored, and the SIGCHLD will be blocked. As +such, if the parent process is terminated, the child process might not be +terminated alongside. + + +@item @emph{See also}: +@ref{SYSTEM} +@end table + + + +@node EXIT +@section @code{EXIT} --- Exit the program with status. +@fnindex EXIT +@cindex program termination +@cindex terminate program + +@table @asis +@item @emph{Description}: +@code{EXIT} causes immediate termination of the program with status. If status +is omitted it returns the canonical @emph{success} for the system. All Fortran +I/O units are closed. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL EXIT([STATUS])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STATUS} @tab Shall be an @code{INTEGER} of the default kind. +@end multitable + +@item @emph{Return value}: +@code{STATUS} is passed to the parent process on exit. + +@item @emph{Example}: +@smallexample +program test_exit + integer :: STATUS = 0 + print *, 'This program is going to exit.' + call EXIT(STATUS) +end program test_exit +@end smallexample + +@item @emph{See also}: +@ref{ABORT}, @gol +@ref{KILL} +@end table + + + +@node EXP +@section @code{EXP} --- Exponential function +@fnindex EXP +@fnindex DEXP +@fnindex CEXP +@fnindex ZEXP +@fnindex CDEXP +@cindex exponential function +@cindex logarithm function, inverse + +@table @asis +@item @emph{Description}: +@code{EXP(X)} computes the base @math{e} exponential of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = EXP(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or +@code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_exp + real :: x = 1.0 + x = exp(x) +end program test_exp +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{EXP(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DEXP(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@item @code{CEXP(X)} @tab @code{COMPLEX(4) X} @tab @code{COMPLEX(4)} @tab Fortran 77 and later +@item @code{ZEXP(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@item @code{CDEXP(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@end multitable +@end table + + + +@node EXPONENT +@section @code{EXPONENT} --- Exponent function +@fnindex EXPONENT +@cindex real number, exponent +@cindex floating point, exponent + +@table @asis +@item @emph{Description}: +@code{EXPONENT(X)} returns the value of the exponent part of @var{X}. If @var{X} +is zero the value returned is zero. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = EXPONENT(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type default @code{INTEGER}. + +@item @emph{Example}: +@smallexample +program test_exponent + real :: x = 1.0 + integer :: i + i = exponent(x) + print *, i + print *, exponent(0.0) +end program test_exponent +@end smallexample +@end table + + + +@node EXTENDS_TYPE_OF +@section @code{EXTENDS_TYPE_OF} --- Query dynamic type for extension +@fnindex EXTENDS_TYPE_OF + +@table @asis +@item @emph{Description}: +Query dynamic type for extension. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = EXTENDS_TYPE_OF(A, MOLD)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be an object of extensible declared type or +unlimited polymorphic. +@item @var{MOLD} @tab Shall be an object of extensible declared type or +unlimited polymorphic. +@end multitable + +@item @emph{Return value}: +The return value is a scalar of type default logical. It is true if and only if +the dynamic type of A is an extension type of the dynamic type of MOLD. + + +@item @emph{See also}: +@ref{SAME_TYPE_AS} +@end table + + + +@node FDATE +@section @code{FDATE} --- Get the current time as a string +@fnindex FDATE +@cindex time, current +@cindex current time +@cindex date, current +@cindex current date + +@table @asis +@item @emph{Description}: +@code{FDATE(DATE)} returns the current date (using the same format as +@ref{CTIME}) in @var{DATE}. It is equivalent to @code{CALL CTIME(DATE, +TIME())}. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL FDATE(DATE)}. +@item @code{DATE = FDATE()}. +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{DATE}@tab The type shall be of type @code{CHARACTER} of the +default kind. It is an @code{INTENT(OUT)} argument. If the length of +this variable is too short for the date and time string to fit +completely, it will be blank on procedure return. +@end multitable + +@item @emph{Return value}: +The current date and time as a string. + +@item @emph{Example}: +@smallexample +program test_fdate + integer(8) :: i, j + character(len=30) :: date + call fdate(date) + print *, 'Program started on ', date + do i = 1, 100000000 ! Just a delay + j = i * i - i + end do + call fdate(date) + print *, 'Program ended on ', date +end program test_fdate +@end smallexample + +@item @emph{See also}: +@ref{DATE_AND_TIME}, @gol +@ref{CTIME} +@end table + + +@node FGET +@section @code{FGET} --- Read a single character in stream mode from stdin +@fnindex FGET +@cindex read character, stream mode +@cindex stream mode, read character +@cindex file operation, read character + +@table @asis +@item @emph{Description}: +Read a single character in stream mode from stdin by bypassing normal +formatted output. Stream I/O should not be mixed with normal record-oriented +(formatted or unformatted) I/O on the same unit; the results are unpredictable. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +Note that the @code{FGET} intrinsic is provided for backwards compatibility with +@command{g77}. GNU Fortran provides the Fortran 2003 Stream facility. +Programmers should consider the use of new stream IO feature in new code +for future portability. See also @ref{Fortran 2003 status}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL FGET(C [, STATUS])} +@item @code{STATUS = FGET(C)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{C} @tab The type shall be @code{CHARACTER} and of default +kind. +@item @var{STATUS} @tab (Optional) status flag of type @code{INTEGER}. +Returns 0 on success, -1 on end-of-file, and a system specific positive +error code otherwise. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_fget + INTEGER, PARAMETER :: strlen = 100 + INTEGER :: status, i = 1 + CHARACTER(len=strlen) :: str = "" + + WRITE (*,*) 'Enter text:' + DO + CALL fget(str(i:i), status) + if (status /= 0 .OR. i > strlen) exit + i = i + 1 + END DO + WRITE (*,*) TRIM(str) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{FGETC}, @gol +@ref{FPUT}, @gol +@ref{FPUTC} +@end table + + + +@node FGETC +@section @code{FGETC} --- Read a single character in stream mode +@fnindex FGETC +@cindex read character, stream mode +@cindex stream mode, read character +@cindex file operation, read character + +@table @asis +@item @emph{Description}: +Read a single character in stream mode by bypassing normal formatted output. +Stream I/O should not be mixed with normal record-oriented (formatted or +unformatted) I/O on the same unit; the results are unpredictable. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +Note that the @code{FGET} intrinsic is provided for backwards compatibility +with @command{g77}. GNU Fortran provides the Fortran 2003 Stream facility. +Programmers should consider the use of new stream IO feature in new code +for future portability. See also @ref{Fortran 2003 status}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL FGETC(UNIT, C [, STATUS])} +@item @code{STATUS = FGETC(UNIT, C)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{UNIT} @tab The type shall be @code{INTEGER}. +@item @var{C} @tab The type shall be @code{CHARACTER} and of default +kind. +@item @var{STATUS} @tab (Optional) status flag of type @code{INTEGER}. +Returns 0 on success, -1 on end-of-file and a system specific positive +error code otherwise. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_fgetc + INTEGER :: fd = 42, status + CHARACTER :: c + + OPEN(UNIT=fd, FILE="/etc/passwd", ACTION="READ", STATUS = "OLD") + DO + CALL fgetc(fd, c, status) + IF (status /= 0) EXIT + call fput(c) + END DO + CLOSE(UNIT=fd) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{FGET}, @gol +@ref{FPUT}, @gol +@ref{FPUTC} +@end table + +@node FINDLOC +@section @code{FINDLOC} --- Search an array for a value +@fnindex FINDLOC +@cindex findloc + +@table @asis +@item @emph{Description}: +Determines the location of the element in the array with the value +given in the @var{VALUE} argument, or, if the @var{DIM} argument is +supplied, determines the locations of the elements equal to the +@var{VALUE} argument element along each +row of the array in the @var{DIM} direction. If @var{MASK} is +present, only the elements for which @var{MASK} is @code{.TRUE.} are +considered. If more than one element in the array has the value +@var{VALUE}, the location returned is that of the first such element +in array element order if the @var{BACK} is not present or if it is +@code{.FALSE.}. If @var{BACK} is true, the location returned is that +of the last such element. If the array has zero size, or all of the +elements of @var{MASK} are @code{.FALSE.}, then the result is an array +of zeroes. Similarly, if @var{DIM} is supplied and all of the +elements of @var{MASK} along a given row are zero, the result value +for that row is zero. + +@item @emph{Standard}: +Fortran 2008 and later. + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = FINDLOC(ARRAY, VALUE, DIM [, MASK] [,KIND] [,BACK])} +@item @code{RESULT = FINDLOC(ARRAY, VALUE, [, MASK] [,KIND] [,BACK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of intrinsic type. +@item @var{VALUE} @tab A scalar of intrinsic type which is in type +conformance with @var{ARRAY}. +@item @var{DIM} @tab (Optional) Shall be a scalar of type +@code{INTEGER}, with a value between one and the rank of @var{ARRAY}, +inclusive. It may not be an optional dummy argument. +@item @var{MASK} @tab (Optional) Shall be of type @code{LOGICAL}, +and conformable with @var{ARRAY}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@item @var{BACK} @tab (Optional) A scalar of type @code{LOGICAL}. +@end multitable + +@item @emph{Return value}: +If @var{DIM} is absent, the result is a rank-one array with a length +equal to the rank of @var{ARRAY}. If @var{DIM} is present, the result +is an array with a rank one less than the rank of @var{ARRAY}, and a +size corresponding to the size of @var{ARRAY} with the @var{DIM} +dimension removed. If @var{DIM} is present and @var{ARRAY} has a rank +of one, the result is a scalar. If the optional argument @var{KIND} +is present, the result is an integer of kind @var{KIND}, otherwise it +is of default kind. + +@item @emph{See also}: +@ref{MAXLOC}, @gol +@ref{MINLOC} + +@end table + +@node FLOOR +@section @code{FLOOR} --- Integer floor function +@fnindex FLOOR +@cindex floor +@cindex rounding, floor + +@table @asis +@item @emph{Description}: +@code{FLOOR(A)} returns the greatest integer less than or equal to @var{X}. + +@item @emph{Standard}: +Fortran 95 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = FLOOR(A [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab The type shall be @code{REAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER(KIND)} if @var{KIND} is present +and of default-kind @code{INTEGER} otherwise. + +@item @emph{Example}: +@smallexample +program test_floor + real :: x = 63.29 + real :: y = -63.59 + print *, floor(x) ! returns 63 + print *, floor(y) ! returns -64 +end program test_floor +@end smallexample + +@item @emph{See also}: +@ref{CEILING}, @gol +@ref{NINT} +@end table + + + +@node FLUSH +@section @code{FLUSH} --- Flush I/O unit(s) +@fnindex FLUSH +@cindex file operation, flush + +@table @asis +@item @emph{Description}: +Flushes Fortran unit(s) currently open for output. Without the optional +argument, all units are flushed, otherwise just the unit specified. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL FLUSH(UNIT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{UNIT} @tab (Optional) The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Note}: +Beginning with the Fortran 2003 standard, there is a @code{FLUSH} +statement that should be preferred over the @code{FLUSH} intrinsic. + +The @code{FLUSH} intrinsic and the Fortran 2003 @code{FLUSH} statement +have identical effect: they flush the runtime library's I/O buffer so +that the data becomes visible to other processes. This does not guarantee +that the data is committed to disk. + +On POSIX systems, you can request that all data is transferred to the +storage device by calling the @code{fsync} function, with the POSIX file +descriptor of the I/O unit as argument (retrieved with GNU intrinsic +@code{FNUM}). The following example shows how: + +@smallexample + ! Declare the interface for POSIX fsync function + interface + function fsync (fd) bind(c,name="fsync") + use iso_c_binding, only: c_int + integer(c_int), value :: fd + integer(c_int) :: fsync + end function fsync + end interface + + ! Variable declaration + integer :: ret + + ! Opening unit 10 + open (10,file="foo") + + ! ... + ! Perform I/O on unit 10 + ! ... + + ! Flush and sync + flush(10) + ret = fsync(fnum(10)) + + ! Handle possible error + if (ret /= 0) stop "Error calling FSYNC" +@end smallexample + +@end table + + + +@node FNUM +@section @code{FNUM} --- File number function +@fnindex FNUM +@cindex file operation, file number + +@table @asis +@item @emph{Description}: +@code{FNUM(UNIT)} returns the POSIX file descriptor number corresponding to the +open Fortran I/O unit @code{UNIT}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = FNUM(UNIT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{UNIT} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} + +@item @emph{Example}: +@smallexample +program test_fnum + integer :: i + open (unit=10, status = "scratch") + i = fnum(10) + print *, i + close (10) +end program test_fnum +@end smallexample +@end table + + + +@node FPUT +@section @code{FPUT} --- Write a single character in stream mode to stdout +@fnindex FPUT +@cindex write character, stream mode +@cindex stream mode, write character +@cindex file operation, write character + +@table @asis +@item @emph{Description}: +Write a single character in stream mode to stdout by bypassing normal +formatted output. Stream I/O should not be mixed with normal record-oriented +(formatted or unformatted) I/O on the same unit; the results are unpredictable. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +Note that the @code{FGET} intrinsic is provided for backwards compatibility with +@command{g77}. GNU Fortran provides the Fortran 2003 Stream facility. +Programmers should consider the use of new stream IO feature in new code +for future portability. See also @ref{Fortran 2003 status}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL FPUT(C [, STATUS])} +@item @code{STATUS = FPUT(C)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{C} @tab The type shall be @code{CHARACTER} and of default +kind. +@item @var{STATUS} @tab (Optional) status flag of type @code{INTEGER}. +Returns 0 on success, -1 on end-of-file and a system specific positive +error code otherwise. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_fput + CHARACTER(len=10) :: str = "gfortran" + INTEGER :: i + DO i = 1, len_trim(str) + CALL fput(str(i:i)) + END DO +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{FPUTC}, @gol +@ref{FGET}, @gol +@ref{FGETC} +@end table + + + +@node FPUTC +@section @code{FPUTC} --- Write a single character in stream mode +@fnindex FPUTC +@cindex write character, stream mode +@cindex stream mode, write character +@cindex file operation, write character + +@table @asis +@item @emph{Description}: +Write a single character in stream mode by bypassing normal formatted +output. Stream I/O should not be mixed with normal record-oriented +(formatted or unformatted) I/O on the same unit; the results are unpredictable. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +Note that the @code{FGET} intrinsic is provided for backwards compatibility with +@command{g77}. GNU Fortran provides the Fortran 2003 Stream facility. +Programmers should consider the use of new stream IO feature in new code +for future portability. See also @ref{Fortran 2003 status}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL FPUTC(UNIT, C [, STATUS])} +@item @code{STATUS = FPUTC(UNIT, C)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{UNIT} @tab The type shall be @code{INTEGER}. +@item @var{C} @tab The type shall be @code{CHARACTER} and of default +kind. +@item @var{STATUS} @tab (Optional) status flag of type @code{INTEGER}. +Returns 0 on success, -1 on end-of-file and a system specific positive +error code otherwise. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_fputc + CHARACTER(len=10) :: str = "gfortran" + INTEGER :: fd = 42, i + + OPEN(UNIT = fd, FILE = "out", ACTION = "WRITE", STATUS="NEW") + DO i = 1, len_trim(str) + CALL fputc(fd, str(i:i)) + END DO + CLOSE(fd) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{FPUT}, @gol +@ref{FGET}, @gol +@ref{FGETC} +@end table + + + +@node FRACTION +@section @code{FRACTION} --- Fractional part of the model representation +@fnindex FRACTION +@cindex real number, fraction +@cindex floating point, fraction + +@table @asis +@item @emph{Description}: +@code{FRACTION(X)} returns the fractional part of the model +representation of @code{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{Y = FRACTION(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type of the argument shall be a @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as the argument. +The fractional part of the model representation of @code{X} is returned; +it is @code{X * RADIX(X)**(-EXPONENT(X))}. + +@item @emph{Example}: +@smallexample +program test_fraction + real :: x + x = 178.1387e-4 + print *, fraction(x), x * radix(x)**(-exponent(x)) +end program test_fraction +@end smallexample + +@end table + + + +@node FREE +@section @code{FREE} --- Frees memory +@fnindex FREE +@cindex pointer, cray + +@table @asis +@item @emph{Description}: +Frees memory previously allocated by @code{MALLOC}. The @code{FREE} +intrinsic is an extension intended to be used with Cray pointers, and is +provided in GNU Fortran to allow user to compile legacy code. For +new code using Fortran 95 pointers, the memory de-allocation intrinsic is +@code{DEALLOCATE}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL FREE(PTR)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{PTR} @tab The type shall be @code{INTEGER}. It represents the +location of the memory that should be de-allocated. +@end multitable + +@item @emph{Return value}: +None + +@item @emph{Example}: +See @code{MALLOC} for an example. + +@item @emph{See also}: +@ref{MALLOC} +@end table + + + +@node FSEEK +@section @code{FSEEK} --- Low level file positioning subroutine +@fnindex FSEEK +@cindex file operation, seek +@cindex file operation, position + +@table @asis +@item @emph{Description}: +Moves @var{UNIT} to the specified @var{OFFSET}. If @var{WHENCE} +is set to 0, the @var{OFFSET} is taken as an absolute value @code{SEEK_SET}, +if set to 1, @var{OFFSET} is taken to be relative to the current position +@code{SEEK_CUR}, and if set to 2 relative to the end of the file @code{SEEK_END}. +On error, @var{STATUS} is set to a nonzero value. If @var{STATUS} the seek +fails silently. + +This intrinsic routine is not fully backwards compatible with @command{g77}. +In @command{g77}, the @code{FSEEK} takes a statement label instead of a +@var{STATUS} variable. If FSEEK is used in old code, change +@smallexample + CALL FSEEK(UNIT, OFFSET, WHENCE, *label) +@end smallexample +to +@smallexample + INTEGER :: status + CALL FSEEK(UNIT, OFFSET, WHENCE, status) + IF (status /= 0) GOTO label +@end smallexample + +Please note that GNU Fortran provides the Fortran 2003 Stream facility. +Programmers should consider the use of new stream IO feature in new code +for future portability. See also @ref{Fortran 2003 status}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL FSEEK(UNIT, OFFSET, WHENCE[, STATUS])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{UNIT} @tab Shall be a scalar of type @code{INTEGER}. +@item @var{OFFSET} @tab Shall be a scalar of type @code{INTEGER}. +@item @var{WHENCE} @tab Shall be a scalar of type @code{INTEGER}. +Its value shall be either 0, 1 or 2. +@item @var{STATUS} @tab (Optional) shall be a scalar of type +@code{INTEGER(4)}. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_fseek + INTEGER, PARAMETER :: SEEK_SET = 0, SEEK_CUR = 1, SEEK_END = 2 + INTEGER :: fd, offset, ierr + + ierr = 0 + offset = 5 + fd = 10 + + OPEN(UNIT=fd, FILE="fseek.test") + CALL FSEEK(fd, offset, SEEK_SET, ierr) ! move to OFFSET + print *, FTELL(fd), ierr + + CALL FSEEK(fd, 0, SEEK_END, ierr) ! move to end + print *, FTELL(fd), ierr + + CALL FSEEK(fd, 0, SEEK_SET, ierr) ! move to beginning + print *, FTELL(fd), ierr + + CLOSE(UNIT=fd) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{FTELL} +@end table + + + +@node FSTAT +@section @code{FSTAT} --- Get file status +@fnindex FSTAT +@cindex file system, file status + +@table @asis +@item @emph{Description}: +@code{FSTAT} is identical to @ref{STAT}, except that information about an +already opened file is obtained. + +The elements in @code{VALUES} are the same as described by @ref{STAT}. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL FSTAT(UNIT, VALUES [, STATUS])} +@item @code{STATUS = FSTAT(UNIT, VALUES)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{UNIT} @tab An open I/O unit number of type @code{INTEGER}. +@item @var{VALUES} @tab The type shall be @code{INTEGER(4), DIMENSION(13)}. +@item @var{STATUS} @tab (Optional) status flag of type @code{INTEGER(4)}. Returns 0 +on success and a system specific error code otherwise. +@end multitable + +@item @emph{Example}: +See @ref{STAT} for an example. + +@item @emph{See also}: +To stat a link: @gol +@ref{LSTAT} @gol +To stat a file: @gol +@ref{STAT} +@end table + + + +@node FTELL +@section @code{FTELL} --- Current stream position +@fnindex FTELL +@cindex file operation, position + +@table @asis +@item @emph{Description}: +Retrieves the current position within an open file. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL FTELL(UNIT, OFFSET)} +@item @code{OFFSET = FTELL(UNIT)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{OFFSET} @tab Shall of type @code{INTEGER}. +@item @var{UNIT} @tab Shall of type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +In either syntax, @var{OFFSET} is set to the current offset of unit +number @var{UNIT}, or to @math{-1} if the unit is not currently open. + +@item @emph{Example}: +@smallexample +PROGRAM test_ftell + INTEGER :: i + OPEN(10, FILE="temp.dat") + CALL ftell(10,i) + WRITE(*,*) i +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{FSEEK} +@end table + + + +@node GAMMA +@section @code{GAMMA} --- Gamma function +@fnindex GAMMA +@fnindex DGAMMA +@cindex Gamma function +@cindex Factorial function + +@table @asis +@item @emph{Description}: +@code{GAMMA(X)} computes Gamma (@math{\Gamma}) of @var{X}. For positive, +integer values of @var{X} the Gamma function simplifies to the factorial +function @math{\Gamma(x)=(x-1)!}. + +@tex +$$ +\Gamma(x) = \int_0^\infty t^{x-1}{\rm e}^{-t}\,{\rm d}t +$$ +@end tex + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{X = GAMMA(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL} and neither zero +nor a negative integer. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} of the same kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_gamma + real :: x = 1.0 + x = gamma(x) ! returns 1.0 +end program test_gamma +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DGAMMA(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Logarithm of the Gamma function: @gol +@ref{LOG_GAMMA} +@end table + + + +@node GERROR +@section @code{GERROR} --- Get last system error message +@fnindex GERROR +@cindex system, error handling + +@table @asis +@item @emph{Description}: +Returns the system error message corresponding to the last system error. +This resembles the functionality of @code{strerror(3)} in C. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL GERROR(RESULT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{RESULT} @tab Shall be of type @code{CHARACTER} and of default kind. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_gerror + CHARACTER(len=100) :: msg + CALL gerror(msg) + WRITE(*,*) msg +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{IERRNO}, @gol +@ref{PERROR} +@end table + + + +@node GETARG +@section @code{GETARG} --- Get command line arguments +@fnindex GETARG +@cindex command-line arguments +@cindex arguments, to program + +@table @asis +@item @emph{Description}: +Retrieve the @var{POS}-th argument that was passed on the +command line when the containing program was invoked. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. In new code, programmers should consider the use of +the @ref{GET_COMMAND_ARGUMENT} intrinsic defined by the Fortran 2003 +standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL GETARG(POS, VALUE)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{POS} @tab Shall be of type @code{INTEGER} and not wider than +the default integer kind; @math{@var{POS} \geq 0} +@item @var{VALUE} @tab Shall be of type @code{CHARACTER} and of default +kind. +@end multitable + +@item @emph{Return value}: +After @code{GETARG} returns, the @var{VALUE} argument holds the +@var{POS}th command line argument. If @var{VALUE} cannot hold the +argument, it is truncated to fit the length of @var{VALUE}. If there are +less than @var{POS} arguments specified at the command line, @var{VALUE} +will be filled with blanks. If @math{@var{POS} = 0}, @var{VALUE} is set +to the name of the program (on systems that support this feature). + +@item @emph{Example}: +@smallexample +PROGRAM test_getarg + INTEGER :: i + CHARACTER(len=32) :: arg + + DO i = 1, iargc() + CALL getarg(i, arg) + WRITE (*,*) arg + END DO +END PROGRAM +@end smallexample + +@item @emph{See also}: +GNU Fortran 77 compatibility function: @gol +@ref{IARGC} @gol +Fortran 2003 functions and subroutines: @gol +@ref{GET_COMMAND}, @gol +@ref{GET_COMMAND_ARGUMENT}, @gol +@ref{COMMAND_ARGUMENT_COUNT} +@end table + + + +@node GET_COMMAND +@section @code{GET_COMMAND} --- Get the entire command line +@fnindex GET_COMMAND +@cindex command-line arguments +@cindex arguments, to program + +@table @asis +@item @emph{Description}: +Retrieve the entire command line that was used to invoke the program. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL GET_COMMAND([COMMAND, LENGTH, STATUS])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{COMMAND} @tab (Optional) shall be of type @code{CHARACTER} and +of default kind. +@item @var{LENGTH} @tab (Optional) Shall be of type @code{INTEGER} and of +default kind. +@item @var{STATUS} @tab (Optional) Shall be of type @code{INTEGER} and of +default kind. +@end multitable + +@item @emph{Return value}: +If @var{COMMAND} is present, stores the entire command line that was used +to invoke the program in @var{COMMAND}. If @var{LENGTH} is present, it is +assigned the length of the command line. If @var{STATUS} is present, it +is assigned 0 upon success of the command, -1 if @var{COMMAND} is too +short to store the command line, or a positive value in case of an error. + +@item @emph{Example}: +@smallexample +PROGRAM test_get_command + CHARACTER(len=255) :: cmd + CALL get_command(cmd) + WRITE (*,*) TRIM(cmd) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{GET_COMMAND_ARGUMENT}, @gol +@ref{COMMAND_ARGUMENT_COUNT} +@end table + + + +@node GET_COMMAND_ARGUMENT +@section @code{GET_COMMAND_ARGUMENT} --- Get command line arguments +@fnindex GET_COMMAND_ARGUMENT +@cindex command-line arguments +@cindex arguments, to program + +@table @asis +@item @emph{Description}: +Retrieve the @var{NUMBER}-th argument that was passed on the +command line when the containing program was invoked. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL GET_COMMAND_ARGUMENT(NUMBER [, VALUE, LENGTH, STATUS])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NUMBER} @tab Shall be a scalar of type @code{INTEGER} and of +default kind, @math{@var{NUMBER} \geq 0} +@item @var{VALUE} @tab (Optional) Shall be a scalar of type @code{CHARACTER} +and of default kind. +@item @var{LENGTH} @tab (Optional) Shall be a scalar of type @code{INTEGER} +and of default kind. +@item @var{STATUS} @tab (Optional) Shall be a scalar of type @code{INTEGER} +and of default kind. +@end multitable + +@item @emph{Return value}: +After @code{GET_COMMAND_ARGUMENT} returns, the @var{VALUE} argument holds the +@var{NUMBER}-th command line argument. If @var{VALUE} cannot hold the argument, it is +truncated to fit the length of @var{VALUE}. If there are less than @var{NUMBER} +arguments specified at the command line, @var{VALUE} will be filled with blanks. +If @math{@var{NUMBER} = 0}, @var{VALUE} is set to the name of the program (on +systems that support this feature). The @var{LENGTH} argument contains the +length of the @var{NUMBER}-th command line argument. If the argument retrieval +fails, @var{STATUS} is a positive number; if @var{VALUE} contains a truncated +command line argument, @var{STATUS} is -1; and otherwise the @var{STATUS} is +zero. + +@item @emph{Example}: +@smallexample +PROGRAM test_get_command_argument + INTEGER :: i + CHARACTER(len=32) :: arg + + i = 0 + DO + CALL get_command_argument(i, arg) + IF (LEN_TRIM(arg) == 0) EXIT + + WRITE (*,*) TRIM(arg) + i = i+1 + END DO +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{GET_COMMAND}, @gol +@ref{COMMAND_ARGUMENT_COUNT} +@end table + + + +@node GETCWD +@section @code{GETCWD} --- Get current working directory +@fnindex GETCWD +@cindex system, working directory + +@table @asis +@item @emph{Description}: +Get current working directory. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL GETCWD(C [, STATUS])} +@item @code{STATUS = GETCWD(C)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{C} @tab The type shall be @code{CHARACTER} and of default kind. +@item @var{STATUS} @tab (Optional) status flag. Returns 0 on success, +a system specific and nonzero error code otherwise. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_getcwd + CHARACTER(len=255) :: cwd + CALL getcwd(cwd) + WRITE(*,*) TRIM(cwd) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{CHDIR} +@end table + + + +@node GETENV +@section @code{GETENV} --- Get an environmental variable +@fnindex GETENV +@cindex environment variable + +@table @asis +@item @emph{Description}: +Get the @var{VALUE} of the environmental variable @var{NAME}. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. In new code, programmers should consider the use of +the @ref{GET_ENVIRONMENT_VARIABLE} intrinsic defined by the Fortran +2003 standard. + +Note that @code{GETENV} need not be thread-safe. It is the +responsibility of the user to ensure that the environment is not being +updated concurrently with a call to the @code{GETENV} intrinsic. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL GETENV(NAME, VALUE)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NAME} @tab Shall be of type @code{CHARACTER} and of default kind. +@item @var{VALUE} @tab Shall be of type @code{CHARACTER} and of default kind. +@end multitable + +@item @emph{Return value}: +Stores the value of @var{NAME} in @var{VALUE}. If @var{VALUE} is +not large enough to hold the data, it is truncated. If @var{NAME} +is not set, @var{VALUE} will be filled with blanks. + +@item @emph{Example}: +@smallexample +PROGRAM test_getenv + CHARACTER(len=255) :: homedir + CALL getenv("HOME", homedir) + WRITE (*,*) TRIM(homedir) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{GET_ENVIRONMENT_VARIABLE} +@end table + + + +@node GET_ENVIRONMENT_VARIABLE +@section @code{GET_ENVIRONMENT_VARIABLE} --- Get an environmental variable +@fnindex GET_ENVIRONMENT_VARIABLE +@cindex environment variable + +@table @asis +@item @emph{Description}: +Get the @var{VALUE} of the environmental variable @var{NAME}. + +Note that @code{GET_ENVIRONMENT_VARIABLE} need not be thread-safe. It +is the responsibility of the user to ensure that the environment is +not being updated concurrently with a call to the +@code{GET_ENVIRONMENT_VARIABLE} intrinsic. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL GET_ENVIRONMENT_VARIABLE(NAME[, VALUE, LENGTH, STATUS, TRIM_NAME)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NAME} @tab Shall be a scalar of type @code{CHARACTER} +and of default kind. +@item @var{VALUE} @tab (Optional) Shall be a scalar of type @code{CHARACTER} +and of default kind. +@item @var{LENGTH} @tab (Optional) Shall be a scalar of type @code{INTEGER} +and of default kind. +@item @var{STATUS} @tab (Optional) Shall be a scalar of type @code{INTEGER} +and of default kind. +@item @var{TRIM_NAME} @tab (Optional) Shall be a scalar of type @code{LOGICAL} +and of default kind. +@end multitable + +@item @emph{Return value}: +Stores the value of @var{NAME} in @var{VALUE}. If @var{VALUE} is +not large enough to hold the data, it is truncated. If @var{NAME} +is not set, @var{VALUE} will be filled with blanks. Argument @var{LENGTH} +contains the length needed for storing the environment variable @var{NAME} +or zero if it is not present. @var{STATUS} is -1 if @var{VALUE} is present +but too short for the environment variable; it is 1 if the environment +variable does not exist and 2 if the processor does not support environment +variables; in all other cases @var{STATUS} is zero. If @var{TRIM_NAME} is +present with the value @code{.FALSE.}, the trailing blanks in @var{NAME} +are significant; otherwise they are not part of the environment variable +name. + +@item @emph{Example}: +@smallexample +PROGRAM test_getenv + CHARACTER(len=255) :: homedir + CALL get_environment_variable("HOME", homedir) + WRITE (*,*) TRIM(homedir) +END PROGRAM +@end smallexample +@end table + + + +@node GETGID +@section @code{GETGID} --- Group ID function +@fnindex GETGID +@cindex system, group ID + +@table @asis +@item @emph{Description}: +Returns the numerical group ID of the current process. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = GETGID()} + +@item @emph{Return value}: +The return value of @code{GETGID} is an @code{INTEGER} of the default +kind. + + +@item @emph{Example}: +See @code{GETPID} for an example. + +@item @emph{See also}: +@ref{GETPID}, @gol +@ref{GETUID} +@end table + + + +@node GETLOG +@section @code{GETLOG} --- Get login name +@fnindex GETLOG +@cindex system, login name +@cindex login name + +@table @asis +@item @emph{Description}: +Gets the username under which the program is running. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL GETLOG(C)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{C} @tab Shall be of type @code{CHARACTER} and of default kind. +@end multitable + +@item @emph{Return value}: +Stores the current user name in @var{C}. (On systems where POSIX +functions @code{geteuid} and @code{getpwuid} are not available, and +the @code{getlogin} function is not implemented either, this will +return a blank string.) + +@item @emph{Example}: +@smallexample +PROGRAM TEST_GETLOG + CHARACTER(32) :: login + CALL GETLOG(login) + WRITE(*,*) login +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{GETUID} +@end table + + + +@node GETPID +@section @code{GETPID} --- Process ID function +@fnindex GETPID +@cindex system, process ID +@cindex process ID + +@table @asis +@item @emph{Description}: +Returns the numerical process identifier of the current process. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = GETPID()} + +@item @emph{Return value}: +The return value of @code{GETPID} is an @code{INTEGER} of the default +kind. + + +@item @emph{Example}: +@smallexample +program info + print *, "The current process ID is ", getpid() + print *, "Your numerical user ID is ", getuid() + print *, "Your numerical group ID is ", getgid() +end program info +@end smallexample + +@item @emph{See also}: +@ref{GETGID}, @gol +@ref{GETUID} +@end table + + + +@node GETUID +@section @code{GETUID} --- User ID function +@fnindex GETUID +@cindex system, user ID +@cindex user id + +@table @asis +@item @emph{Description}: +Returns the numerical user ID of the current process. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = GETUID()} + +@item @emph{Return value}: +The return value of @code{GETUID} is an @code{INTEGER} of the default +kind. + + +@item @emph{Example}: +See @code{GETPID} for an example. + +@item @emph{See also}: +@ref{GETPID}, @gol +@ref{GETLOG} +@end table + + + +@node GMTIME +@section @code{GMTIME} --- Convert time to GMT info +@fnindex GMTIME +@cindex time, conversion to GMT info + +@table @asis +@item @emph{Description}: +Given a system time value @var{TIME} (as provided by the @ref{TIME} +intrinsic), fills @var{VALUES} with values extracted from it appropriate +to the UTC time zone (Universal Coordinated Time, also known in some +countries as GMT, Greenwich Mean Time), using @code{gmtime(3)}. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. In new code, programmers should consider the use of +the @ref{DATE_AND_TIME} intrinsic defined by the Fortran 95 +standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL GMTIME(TIME, VALUES)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{TIME} @tab An @code{INTEGER} scalar expression +corresponding to a system time, with @code{INTENT(IN)}. +@item @var{VALUES} @tab A default @code{INTEGER} array with 9 elements, +with @code{INTENT(OUT)}. +@end multitable + +@item @emph{Return value}: +The elements of @var{VALUES} are assigned as follows: +@enumerate +@item Seconds after the minute, range 0--59 or 0--61 to allow for leap +seconds +@item Minutes after the hour, range 0--59 +@item Hours past midnight, range 0--23 +@item Day of month, range 1--31 +@item Number of months since January, range 0--11 +@item Years since 1900 +@item Number of days since Sunday, range 0--6 +@item Days since January 1, range 0--365 +@item Daylight savings indicator: positive if daylight savings is in +effect, zero if not, and negative if the information is not available. +@end enumerate + +@item @emph{See also}: +@ref{DATE_AND_TIME}, @gol +@ref{CTIME}, @gol +@ref{LTIME}, @gol +@ref{TIME}, @gol +@ref{TIME8} +@end table + + + +@node HOSTNM +@section @code{HOSTNM} --- Get system host name +@fnindex HOSTNM +@cindex system, host name + +@table @asis +@item @emph{Description}: +Retrieves the host name of the system on which the program is running. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL HOSTNM(C [, STATUS])} +@item @code{STATUS = HOSTNM(NAME)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{C} @tab Shall of type @code{CHARACTER} and of default kind. +@item @var{STATUS} @tab (Optional) status flag of type @code{INTEGER}. +Returns 0 on success, or a system specific error code otherwise. +@end multitable + +@item @emph{Return value}: +In either syntax, @var{NAME} is set to the current hostname if it can +be obtained, or to a blank string otherwise. + +@end table + + + +@node HUGE +@section @code{HUGE} --- Largest number of a kind +@fnindex HUGE +@cindex limits, largest number +@cindex model representation, largest number + +@table @asis +@item @emph{Description}: +@code{HUGE(X)} returns the largest number that is not an infinity in +the model of the type of @code{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = HUGE(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL} or @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X} + +@item @emph{Example}: +@smallexample +program test_huge_tiny + print *, huge(0), huge(0.0), huge(0.0d0) + print *, tiny(0.0), tiny(0.0d0) +end program test_huge_tiny +@end smallexample +@end table + + + +@node HYPOT +@section @code{HYPOT} --- Euclidean distance function +@fnindex HYPOT +@cindex Euclidean distance + +@table @asis +@item @emph{Description}: +@code{HYPOT(X,Y)} is the Euclidean distance function. It is equal to +@math{\sqrt{X^2 + Y^2}}, without undue underflow or overflow. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = HYPOT(X, Y)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@item @var{Y} @tab The type and kind type parameter shall be the same as +@var{X}. +@end multitable + +@item @emph{Return value}: +The return value has the same type and kind type parameter as @var{X}. + +@item @emph{Example}: +@smallexample +program test_hypot + real(4) :: x = 1.e0_4, y = 0.5e0_4 + x = hypot(x,y) +end program test_hypot +@end smallexample +@end table + + + +@node IACHAR +@section @code{IACHAR} --- Code in @acronym{ASCII} collating sequence +@fnindex IACHAR +@cindex @acronym{ASCII} collating sequence +@cindex collating sequence, @acronym{ASCII} +@cindex conversion, to integer + +@table @asis +@item @emph{Description}: +@code{IACHAR(C)} returns the code for the @acronym{ASCII} character +in the first character position of @code{C}. + +@item @emph{Standard}: +Fortran 95 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IACHAR(C [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{C} @tab Shall be a scalar @code{CHARACTER}, with @code{INTENT(IN)} +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. + +@item @emph{Example}: +@smallexample +program test_iachar + integer i + i = iachar(' ') +end program test_iachar +@end smallexample + +@item @emph{Note}: +See @ref{ICHAR} for a discussion of converting between numerical values +and formatted string representations. + +@item @emph{See also}: +@ref{ACHAR}, @gol +@ref{CHAR}, @gol +@ref{ICHAR} +@end table + + + +@node IALL +@section @code{IALL} --- Bitwise AND of array elements +@fnindex IALL +@cindex array, AND +@cindex bits, AND of array elements + +@table @asis +@item @emph{Description}: +Reduces with bitwise AND the elements of @var{ARRAY} along dimension @var{DIM} +if the corresponding element in @var{MASK} is @code{TRUE}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = IALL(ARRAY[, MASK])} +@item @code{RESULT = IALL(ARRAY, DIM[, MASK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER} +@item @var{DIM} @tab (Optional) shall be a scalar of type +@code{INTEGER} with a value in the range from 1 to n, where n +equals the rank of @var{ARRAY}. +@item @var{MASK} @tab (Optional) shall be of type @code{LOGICAL} +and either be a scalar or an array of the same shape as @var{ARRAY}. +@end multitable + +@item @emph{Return value}: +The result is of the same type as @var{ARRAY}. + +If @var{DIM} is absent, a scalar with the bitwise ALL of all elements in +@var{ARRAY} is returned. Otherwise, an array of rank n-1, where n equals +the rank of @var{ARRAY}, and a shape similar to that of @var{ARRAY} with +dimension @var{DIM} dropped is returned. + +@item @emph{Example}: +@smallexample +PROGRAM test_iall + INTEGER(1) :: a(2) + + a(1) = b'00100100' + a(2) = b'01101010' + + ! prints 00100000 + PRINT '(b8.8)', IALL(a) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{IANY}, @gol +@ref{IPARITY}, @gol +@ref{IAND} +@end table + + + +@node IAND +@section @code{IAND} --- Bitwise logical and +@fnindex IAND +@fnindex BIAND +@fnindex IIAND +@fnindex JIAND +@fnindex KIAND +@cindex bitwise logical and +@cindex logical and, bitwise + +@table @asis +@item @emph{Description}: +Bitwise logical @code{AND}. + +@item @emph{Standard}: +Fortran 90 and later, with boz-literal-constant Fortran 2008 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IAND(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER} or a boz-literal-constant. +@item @var{J} @tab The type shall be @code{INTEGER} with the same +kind type parameter as @var{I} or a boz-literal-constant. +@var{I} and @var{J} shall not both be boz-literal-constants. +@end multitable + +@item @emph{Return value}: +The return type is @code{INTEGER} with the kind type parameter of the +arguments. +A boz-literal-constant is converted to an @code{INTEGER} with the kind +type parameter of the other argument as-if a call to @ref{INT} occurred. + +@item @emph{Example}: +@smallexample +PROGRAM test_iand + INTEGER :: a, b + DATA a / Z'F' /, b / Z'3' / + WRITE (*,*) IAND(a, b) +END PROGRAM +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{IAND(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BIAND(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IIAND(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JIAND(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KIAND(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{IOR}, @gol +@ref{IEOR}, @gol +@ref{IBITS}, @gol +@ref{IBSET}, @gol +@ref{IBCLR}, @gol +@ref{NOT} +@end table + + + +@node IANY +@section @code{IANY} --- Bitwise OR of array elements +@fnindex IANY +@cindex array, OR +@cindex bits, OR of array elements + +@table @asis +@item @emph{Description}: +Reduces with bitwise OR (inclusive or) the elements of @var{ARRAY} along +dimension @var{DIM} if the corresponding element in @var{MASK} is @code{TRUE}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = IANY(ARRAY[, MASK])} +@item @code{RESULT = IANY(ARRAY, DIM[, MASK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER} +@item @var{DIM} @tab (Optional) shall be a scalar of type +@code{INTEGER} with a value in the range from 1 to n, where n +equals the rank of @var{ARRAY}. +@item @var{MASK} @tab (Optional) shall be of type @code{LOGICAL} +and either be a scalar or an array of the same shape as @var{ARRAY}. +@end multitable + +@item @emph{Return value}: +The result is of the same type as @var{ARRAY}. + +If @var{DIM} is absent, a scalar with the bitwise OR of all elements in +@var{ARRAY} is returned. Otherwise, an array of rank n-1, where n equals +the rank of @var{ARRAY}, and a shape similar to that of @var{ARRAY} with +dimension @var{DIM} dropped is returned. + +@item @emph{Example}: +@smallexample +PROGRAM test_iany + INTEGER(1) :: a(2) + + a(1) = b'00100100' + a(2) = b'01101010' + + ! prints 01101110 + PRINT '(b8.8)', IANY(a) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{IPARITY}, @gol +@ref{IALL}, @gol +@ref{IOR} +@end table + + + +@node IARGC +@section @code{IARGC} --- Get the number of command line arguments +@fnindex IARGC +@cindex command-line arguments +@cindex command-line arguments, number of +@cindex arguments, to program + +@table @asis +@item @emph{Description}: +@code{IARGC} returns the number of arguments passed on the +command line when the containing program was invoked. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. In new code, programmers should consider the use of +the @ref{COMMAND_ARGUMENT_COUNT} intrinsic defined by the Fortran 2003 +standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = IARGC()} + +@item @emph{Arguments}: +None + +@item @emph{Return value}: +The number of command line arguments, type @code{INTEGER(4)}. + +@item @emph{Example}: +See @ref{GETARG} + +@item @emph{See also}: +GNU Fortran 77 compatibility subroutine: @gol +@ref{GETARG} @gol +Fortran 2003 functions and subroutines: @gol +@ref{GET_COMMAND}, @gol +@ref{GET_COMMAND_ARGUMENT}, @gol +@ref{COMMAND_ARGUMENT_COUNT} +@end table + + + +@node IBCLR +@section @code{IBCLR} --- Clear bit +@fnindex IBCLR +@fnindex BBCLR +@fnindex IIBCLR +@fnindex JIBCLR +@fnindex KIBCLR +@cindex bits, unset +@cindex bits, clear + +@table @asis +@item @emph{Description}: +@code{IBCLR} returns the value of @var{I} with the bit at position +@var{POS} set to zero. + +@item @emph{Standard}: +Fortran 90 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IBCLR(I, POS)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{POS} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{IBCLR(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BBCLR(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IIBCLR(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JIBCLR(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KIBCLR(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{IBITS}, @gol +@ref{IBSET}, @gol +@ref{IAND}, @gol +@ref{IOR}, @gol +@ref{IEOR}, @gol +@ref{MVBITS} +@end table + + + +@node IBITS +@section @code{IBITS} --- Bit extraction +@fnindex IBITS +@fnindex BBITS +@fnindex IIBITS +@fnindex JIBITS +@fnindex KIBITS +@cindex bits, get +@cindex bits, extract + +@table @asis +@item @emph{Description}: +@code{IBITS} extracts a field of length @var{LEN} from @var{I}, +starting from bit position @var{POS} and extending left for @var{LEN} +bits. The result is right-justified and the remaining bits are +zeroed. The value of @code{POS+LEN} must be less than or equal to the +value @code{BIT_SIZE(I)}. + +@item @emph{Standard}: +Fortran 90 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IBITS(I, POS, LEN)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{POS} @tab The type shall be @code{INTEGER}. +@item @var{LEN} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{IBITS(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BBITS(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IIBITS(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JIBITS(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KIBITS(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{BIT_SIZE}, @gol +@ref{IBCLR}, @gol +@ref{IBSET}, @gol +@ref{IAND}, @gol +@ref{IOR}, @gol +@ref{IEOR} +@end table + + + +@node IBSET +@section @code{IBSET} --- Set bit +@fnindex IBSET +@fnindex BBSET +@fnindex IIBSET +@fnindex JIBSET +@fnindex KIBSET +@cindex bits, set + +@table @asis +@item @emph{Description}: +@code{IBSET} returns the value of @var{I} with the bit at position +@var{POS} set to one. + +@item @emph{Standard}: +Fortran 90 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IBSET(I, POS)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{POS} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{IBSET(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BBSET(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IIBSET(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JIBSET(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KIBSET(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{IBCLR}, @gol +@ref{IBITS}, @gol +@ref{IAND}, @gol +@ref{IOR}, @gol +@ref{IEOR}, @gol +@ref{MVBITS} +@end table + + + +@node ICHAR +@section @code{ICHAR} --- Character-to-integer conversion function +@fnindex ICHAR +@cindex conversion, to integer + +@table @asis +@item @emph{Description}: +@code{ICHAR(C)} returns the code for the character in the first character +position of @code{C} in the system's native character set. +The correspondence between characters and their codes is not necessarily +the same across different GNU Fortran implementations. + +@item @emph{Standard}: +Fortran 77 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ICHAR(C [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{C} @tab Shall be a scalar @code{CHARACTER}, with @code{INTENT(IN)} +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. + +@item @emph{Example}: +@smallexample +program test_ichar + integer i + i = ichar(' ') +end program test_ichar +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ICHAR(C)} @tab @code{CHARACTER C} @tab @code{INTEGER(4)} @tab Fortran 77 and later +@end multitable + +@item @emph{Note}: +No intrinsic exists to convert between a numeric value and a formatted +character string representation -- for instance, given the +@code{CHARACTER} value @code{'154'}, obtaining an @code{INTEGER} or +@code{REAL} value with the value 154, or vice versa. Instead, this +functionality is provided by internal-file I/O, as in the following +example: +@smallexample +program read_val + integer value + character(len=10) string, string2 + string = '154' + + ! Convert a string to a numeric value + read (string,'(I10)') value + print *, value + + ! Convert a value to a formatted string + write (string2,'(I10)') value + print *, string2 +end program read_val +@end smallexample + +@item @emph{See also}: +@ref{ACHAR}, @gol +@ref{CHAR}, @gol +@ref{IACHAR} +@end table + + + +@node IDATE +@section @code{IDATE} --- Get current local time subroutine (day/month/year) +@fnindex IDATE +@cindex date, current +@cindex current date + +@table @asis +@item @emph{Description}: +@code{IDATE(VALUES)} Fills @var{VALUES} with the numerical values at the +current local time. The day (in the range 1-31), month (in the range 1-12), +and year appear in elements 1, 2, and 3 of @var{VALUES}, respectively. +The year has four significant digits. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. In new code, programmers should consider the use of +the @ref{DATE_AND_TIME} intrinsic defined by the Fortran 95 +standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL IDATE(VALUES)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{VALUES} @tab The type shall be @code{INTEGER, DIMENSION(3)} and +the kind shall be the default integer kind. +@end multitable + +@item @emph{Return value}: +Does not return anything. + +@item @emph{Example}: +@smallexample +program test_idate + integer, dimension(3) :: tarray + call idate(tarray) + print *, tarray(1) + print *, tarray(2) + print *, tarray(3) +end program test_idate +@end smallexample + +@item @emph{See also}: +@ref{DATE_AND_TIME} +@end table + + +@node IEOR +@section @code{IEOR} --- Bitwise logical exclusive or +@fnindex IEOR +@fnindex BIEOR +@fnindex IIEOR +@fnindex JIEOR +@fnindex KIEOR +@cindex bitwise logical exclusive or +@cindex logical exclusive or, bitwise + +@table @asis +@item @emph{Description}: +@code{IEOR} returns the bitwise Boolean exclusive-OR of @var{I} and +@var{J}. + +@item @emph{Standard}: +Fortran 90 and later, with boz-literal-constant Fortran 2008 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IEOR(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER} or a boz-literal-constant. +@item @var{J} @tab The type shall be @code{INTEGER} with the same +kind type parameter as @var{I} or a boz-literal-constant. +@var{I} and @var{J} shall not both be boz-literal-constants. +@end multitable + +@item @emph{Return value}: +The return type is @code{INTEGER} with the kind type parameter of the +arguments. +A boz-literal-constant is converted to an @code{INTEGER} with the kind +type parameter of the other argument as-if a call to @ref{INT} occurred. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{IEOR(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BIEOR(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IIEOR(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JIEOR(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KIEOR(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{IOR}, @gol +@ref{IAND}, @gol +@ref{IBITS}, @gol +@ref{IBSET}, @gol +@ref{IBCLR}, @gol +@ref{NOT} +@end table + + + +@node IERRNO +@section @code{IERRNO} --- Get the last system error number +@fnindex IERRNO +@cindex system, error handling + +@table @asis +@item @emph{Description}: +Returns the last system error number, as given by the C @code{errno} +variable. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = IERRNO()} + +@item @emph{Arguments}: +None + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the default integer +kind. + +@item @emph{See also}: +@ref{PERROR} +@end table + + + +@node IMAGE_INDEX +@section @code{IMAGE_INDEX} --- Function that converts a cosubscript to an image index +@fnindex IMAGE_INDEX +@cindex coarray, @code{IMAGE_INDEX} +@cindex images, cosubscript to image index conversion + +@table @asis +@item @emph{Description}: +Returns the image index belonging to a cosubscript. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Inquiry function. + +@item @emph{Syntax}: +@code{RESULT = IMAGE_INDEX(COARRAY, SUB)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{COARRAY} @tab Coarray of any type. +@item @var{SUB} @tab default integer rank-1 array of a size equal to +the corank of @var{COARRAY}. +@end multitable + + +@item @emph{Return value}: +Scalar default integer with the value of the image index which corresponds +to the cosubscripts. For invalid cosubscripts the result is zero. + +@item @emph{Example}: +@smallexample +INTEGER :: array[2,-1:4,8,*] +! Writes 28 (or 0 if there are fewer than 28 images) +WRITE (*,*) IMAGE_INDEX (array, [2,0,3,1]) +@end smallexample + +@item @emph{See also}: +@ref{THIS_IMAGE}, @gol +@ref{NUM_IMAGES} +@end table + + + +@node INDEX intrinsic +@section @code{INDEX} --- Position of a substring within a string +@fnindex INDEX +@cindex substring position +@cindex string, find substring + +@table @asis +@item @emph{Description}: +Returns the position of the start of the first occurrence of string +@var{SUBSTRING} as a substring in @var{STRING}, counting from one. If +@var{SUBSTRING} is not present in @var{STRING}, zero is returned. If +the @var{BACK} argument is present and true, the return value is the +start of the last occurrence rather than the first. + +@item @emph{Standard}: +Fortran 77 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = INDEX(STRING, SUBSTRING [, BACK [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab Shall be a scalar @code{CHARACTER}, with +@code{INTENT(IN)} +@item @var{SUBSTRING} @tab Shall be a scalar @code{CHARACTER}, with +@code{INTENT(IN)} +@item @var{BACK} @tab (Optional) Shall be a scalar @code{LOGICAL}, with +@code{INTENT(IN)} +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. + +@item @emph{Specific names}: +@multitable @columnfractions .35 .15 .17 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{INDEX(STRING,SUBSTRING)} @tab @code{CHARACTER} @tab @code{INTEGER(4)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{SCAN}, @gol +@ref{VERIFY} +@end table + + + +@node INT +@section @code{INT} --- Convert to integer type +@fnindex INT +@fnindex IFIX +@fnindex IDINT +@cindex conversion, to integer + +@table @asis +@item @emph{Description}: +Convert to integer type + +@item @emph{Standard}: +Fortran 77 and later, with boz-literal-constant Fortran 2008 and later. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = INT(A [, KIND))} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be of type @code{INTEGER}, +@code{REAL}, or @code{COMPLEX} or a boz-literal-constant. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +These functions return a @code{INTEGER} variable or array under +the following rules: + +@table @asis +@item (A) +If @var{A} is of type @code{INTEGER}, @code{INT(A) = A} +@item (B) +If @var{A} is of type @code{REAL} and @math{|A| < 1}, @code{INT(A)} +equals @code{0}. If @math{|A| \geq 1}, then @code{INT(A)} is the integer +whose magnitude is the largest integer that does not exceed the magnitude +of @var{A} and whose sign is the same as the sign of @var{A}. +@item (C) +If @var{A} is of type @code{COMPLEX}, rule B is applied to the real part of @var{A}. +@end table + +@item @emph{Example}: +@smallexample +program test_int + integer :: i = 42 + complex :: z = (-3.7, 1.0) + print *, int(i) + print *, int(z), int(z,8) +end program +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{INT(A)} @tab @code{REAL(4) A} @tab @code{INTEGER} @tab Fortran 77 and later +@item @code{IFIX(A)} @tab @code{REAL(4) A} @tab @code{INTEGER} @tab Fortran 77 and later +@item @code{IDINT(A)} @tab @code{REAL(8) A} @tab @code{INTEGER} @tab Fortran 77 and later +@end multitable + +@end table + + +@node INT2 +@section @code{INT2} --- Convert to 16-bit integer type +@fnindex INT2 +@cindex conversion, to integer + +@table @asis +@item @emph{Description}: +Convert to a @code{KIND=2} integer type. This is equivalent to the +standard @code{INT} intrinsic with an optional argument of +@code{KIND=2}, and is only included for backwards compatibility. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = INT2(A)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be of type @code{INTEGER}, +@code{REAL}, or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is a @code{INTEGER(2)} variable. + +@item @emph{See also}: +@ref{INT}, @gol +@ref{INT8} +@end table + + + +@node INT8 +@section @code{INT8} --- Convert to 64-bit integer type +@fnindex INT8 +@cindex conversion, to integer + +@table @asis +@item @emph{Description}: +Convert to a @code{KIND=8} integer type. This is equivalent to the +standard @code{INT} intrinsic with an optional argument of +@code{KIND=8}, and is only included for backwards compatibility. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = INT8(A)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be of type @code{INTEGER}, +@code{REAL}, or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is a @code{INTEGER(8)} variable. + +@item @emph{See also}: +@ref{INT}, @gol +@ref{INT2} +@end table + + + +@node IOR +@section @code{IOR} --- Bitwise logical or +@fnindex IOR +@fnindex BIOR +@fnindex IIOR +@fnindex JIOR +@fnindex KIOR +@cindex bitwise logical or +@cindex logical or, bitwise + +@table @asis +@item @emph{Description}: +@code{IOR} returns the bitwise Boolean inclusive-OR of @var{I} and +@var{J}. + +@item @emph{Standard}: +Fortran 90 and later, with boz-literal-constant Fortran 2008 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IOR(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER} or a boz-literal-constant. +@item @var{J} @tab The type shall be @code{INTEGER} with the same +kind type parameter as @var{I} or a boz-literal-constant. +@var{I} and @var{J} shall not both be boz-literal-constants. +@end multitable + +@item @emph{Return value}: +The return type is @code{INTEGER} with the kind type parameter of the +arguments. +A boz-literal-constant is converted to an @code{INTEGER} with the kind +type parameter of the other argument as-if a call to @ref{INT} occurred. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{IOR(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BIOR(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IIOR(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JIOR(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KIOR(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{IEOR}, @gol +@ref{IAND}, @gol +@ref{IBITS}, @gol +@ref{IBSET}, @gol +@ref{IBCLR}, @gol +@ref{NOT} +@end table + + + +@node IPARITY +@section @code{IPARITY} --- Bitwise XOR of array elements +@fnindex IPARITY +@cindex array, parity +@cindex array, XOR +@cindex bits, XOR of array elements + +@table @asis +@item @emph{Description}: +Reduces with bitwise XOR (exclusive or) the elements of @var{ARRAY} along +dimension @var{DIM} if the corresponding element in @var{MASK} is @code{TRUE}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = IPARITY(ARRAY[, MASK])} +@item @code{RESULT = IPARITY(ARRAY, DIM[, MASK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER} +@item @var{DIM} @tab (Optional) shall be a scalar of type +@code{INTEGER} with a value in the range from 1 to n, where n +equals the rank of @var{ARRAY}. +@item @var{MASK} @tab (Optional) shall be of type @code{LOGICAL} +and either be a scalar or an array of the same shape as @var{ARRAY}. +@end multitable + +@item @emph{Return value}: +The result is of the same type as @var{ARRAY}. + +If @var{DIM} is absent, a scalar with the bitwise XOR of all elements in +@var{ARRAY} is returned. Otherwise, an array of rank n-1, where n equals +the rank of @var{ARRAY}, and a shape similar to that of @var{ARRAY} with +dimension @var{DIM} dropped is returned. + +@item @emph{Example}: +@smallexample +PROGRAM test_iparity + INTEGER(1) :: a(2) + + a(1) = int(b'00100100', 1) + a(2) = int(b'01101010', 1) + + ! prints 01001110 + PRINT '(b8.8)', IPARITY(a) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{IANY}, @gol +@ref{IALL}, @gol +@ref{IEOR}, @gol +@ref{PARITY} +@end table + + + +@node IRAND +@section @code{IRAND} --- Integer pseudo-random number +@fnindex IRAND +@cindex random number generation + +@table @asis +@item @emph{Description}: +@code{IRAND(FLAG)} returns a pseudo-random number from a uniform +distribution between 0 and a system-dependent limit (which is in most +cases 2147483647). If @var{FLAG} is 0, the next number +in the current sequence is returned; if @var{FLAG} is 1, the generator +is restarted by @code{CALL SRAND(0)}; if @var{FLAG} has any other value, +it is used as a new seed with @code{SRAND}. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. It implements a simple modulo generator as provided +by @command{g77}. For new code, one should consider the use of +@ref{RANDOM_NUMBER} as it implements a superior algorithm. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = IRAND(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be a scalar @code{INTEGER} of kind 4. +@end multitable + +@item @emph{Return value}: +The return value is of @code{INTEGER(kind=4)} type. + +@item @emph{Example}: +@smallexample +program test_irand + integer,parameter :: seed = 86456 + + call srand(seed) + print *, irand(), irand(), irand(), irand() + print *, irand(seed), irand(), irand(), irand() +end program test_irand +@end smallexample + +@end table + + + +@node IS_CONTIGUOUS +@section @code{IS_CONTIGUOUS} --- Test whether an array is contiguous +@fnindex IS_IOSTAT_EOR +@cindex array, contiguity + +@table @asis +@item @emph{Description}: +@code{IS_CONTIGUOUS} tests whether an array is contiguous. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = IS_CONTIGUOUS(ARRAY)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of any type. +@end multitable + +@item @emph{Return value}: +Returns a @code{LOGICAL} of the default kind, which @code{.TRUE.} if +@var{ARRAY} is contiguous and false otherwise. + +@item @emph{Example}: +@smallexample +program test + integer :: a(10) + a = [1,2,3,4,5,6,7,8,9,10] + call sub (a) ! every element, is contiguous + call sub (a(::2)) ! every other element, is noncontiguous +contains + subroutine sub (x) + integer :: x(:) + if (is_contiguous (x)) then + write (*,*) 'X is contiguous' + else + write (*,*) 'X is not contiguous' + end if + end subroutine sub +end program test +@end smallexample +@end table + + + +@node IS_IOSTAT_END +@section @code{IS_IOSTAT_END} --- Test for end-of-file value +@fnindex IS_IOSTAT_END +@cindex @code{IOSTAT}, end of file + +@table @asis +@item @emph{Description}: +@code{IS_IOSTAT_END} tests whether an variable has the value of the I/O +status ``end of file''. The function is equivalent to comparing the variable +with the @code{IOSTAT_END} parameter of the intrinsic module +@code{ISO_FORTRAN_ENV}. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IS_IOSTAT_END(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of the type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +Returns a @code{LOGICAL} of the default kind, which @code{.TRUE.} if +@var{I} has the value which indicates an end of file condition for +@code{IOSTAT=} specifiers, and is @code{.FALSE.} otherwise. + +@item @emph{Example}: +@smallexample +PROGRAM iostat + IMPLICIT NONE + INTEGER :: stat, i + OPEN(88, FILE='test.dat') + READ(88, *, IOSTAT=stat) i + IF(IS_IOSTAT_END(stat)) STOP 'END OF FILE' +END PROGRAM +@end smallexample +@end table + + + +@node IS_IOSTAT_EOR +@section @code{IS_IOSTAT_EOR} --- Test for end-of-record value +@fnindex IS_IOSTAT_EOR +@cindex @code{IOSTAT}, end of record + +@table @asis +@item @emph{Description}: +@code{IS_IOSTAT_EOR} tests whether an variable has the value of the I/O +status ``end of record''. The function is equivalent to comparing the +variable with the @code{IOSTAT_EOR} parameter of the intrinsic module +@code{ISO_FORTRAN_ENV}. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = IS_IOSTAT_EOR(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of the type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +Returns a @code{LOGICAL} of the default kind, which @code{.TRUE.} if +@var{I} has the value which indicates an end of file condition for +@code{IOSTAT=} specifiers, and is @code{.FALSE.} otherwise. + +@item @emph{Example}: +@smallexample +PROGRAM iostat + IMPLICIT NONE + INTEGER :: stat, i(50) + OPEN(88, FILE='test.dat', FORM='UNFORMATTED') + READ(88, IOSTAT=stat) i + IF(IS_IOSTAT_EOR(stat)) STOP 'END OF RECORD' +END PROGRAM +@end smallexample +@end table + + +@node ISATTY +@section @code{ISATTY} --- Whether a unit is a terminal device +@fnindex ISATTY +@cindex system, terminal + +@table @asis +@item @emph{Description}: +Determine whether a unit is connected to a terminal device. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = ISATTY(UNIT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{UNIT} @tab Shall be a scalar @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +Returns @code{.TRUE.} if the @var{UNIT} is connected to a terminal +device, @code{.FALSE.} otherwise. + +@item @emph{Example}: +@smallexample +PROGRAM test_isatty + INTEGER(kind=1) :: unit + DO unit = 1, 10 + write(*,*) isatty(unit=unit) + END DO +END PROGRAM +@end smallexample +@item @emph{See also}: +@ref{TTYNAM} +@end table + + + +@node ISHFT +@section @code{ISHFT} --- Shift bits +@fnindex ISHFT +@fnindex BSHFT +@fnindex IISHFT +@fnindex JISHFT +@fnindex KISHFT +@cindex bits, shift + +@table @asis +@item @emph{Description}: +@code{ISHFT} returns a value corresponding to @var{I} with all of the +bits shifted @var{SHIFT} places. A value of @var{SHIFT} greater than +zero corresponds to a left shift, a value of zero corresponds to no +shift, and a value less than zero corresponds to a right shift. If the +absolute value of @var{SHIFT} is greater than @code{BIT_SIZE(I)}, the +value is undefined. Bits shifted out from the left end or right end are +lost; zeros are shifted in from the opposite end. + +@item @emph{Standard}: +Fortran 90 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ISHFT(I, SHIFT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ISHFT(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BSHFT(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IISHFT(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JISHFT(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KISHFT(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{ISHFTC} +@end table + + + +@node ISHFTC +@section @code{ISHFTC} --- Shift bits circularly +@fnindex ISHFTC +@fnindex BSHFTC +@fnindex IISHFTC +@fnindex JISHFTC +@fnindex KISHFTC +@cindex bits, shift circular + +@table @asis +@item @emph{Description}: +@code{ISHFTC} returns a value corresponding to @var{I} with the +rightmost @var{SIZE} bits shifted circularly @var{SHIFT} places; that +is, bits shifted out one end are shifted into the opposite end. A value +of @var{SHIFT} greater than zero corresponds to a left shift, a value of +zero corresponds to no shift, and a value less than zero corresponds to +a right shift. The absolute value of @var{SHIFT} must be less than +@var{SIZE}. If the @var{SIZE} argument is omitted, it is taken to be +equivalent to @code{BIT_SIZE(I)}. + +@item @emph{Standard}: +Fortran 90 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = ISHFTC(I, SHIFT [, SIZE])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@item @var{SIZE} @tab (Optional) The type shall be @code{INTEGER}; +the value must be greater than zero and less than or equal to +@code{BIT_SIZE(I)}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ISHFTC(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BSHFTC(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IISHFTC(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JISHFTC(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KISHFTC(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{ISHFT} +@end table + + + +@node ISNAN +@section @code{ISNAN} --- Test for a NaN +@fnindex ISNAN +@cindex IEEE, ISNAN + +@table @asis +@item @emph{Description}: +@code{ISNAN} tests whether a floating-point value is an IEEE +Not-a-Number (NaN). +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{ISNAN(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Variable of the type @code{REAL}. + +@end multitable + +@item @emph{Return value}: +Returns a default-kind @code{LOGICAL}. The returned value is @code{TRUE} +if @var{X} is a NaN and @code{FALSE} otherwise. + +@item @emph{Example}: +@smallexample +program test_nan + implicit none + real :: x + x = -1.0 + x = sqrt(x) + if (isnan(x)) stop '"x" is a NaN' +end program test_nan +@end smallexample +@end table + + + +@node ITIME +@section @code{ITIME} --- Get current local time subroutine (hour/minutes/seconds) +@fnindex ITIME +@cindex time, current +@cindex current time + +@table @asis +@item @emph{Description}: +@code{ITIME(VALUES)} Fills @var{VALUES} with the numerical values at the +current local time. The hour (in the range 1-24), minute (in the range 1-60), +and seconds (in the range 1-60) appear in elements 1, 2, and 3 of @var{VALUES}, +respectively. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. In new code, programmers should consider the use of +the @ref{DATE_AND_TIME} intrinsic defined by the Fortran 95 +standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL ITIME(VALUES)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{VALUES} @tab The type shall be @code{INTEGER, DIMENSION(3)} +and the kind shall be the default integer kind. +@end multitable + +@item @emph{Return value}: +Does not return anything. + + +@item @emph{Example}: +@smallexample +program test_itime + integer, dimension(3) :: tarray + call itime(tarray) + print *, tarray(1) + print *, tarray(2) + print *, tarray(3) +end program test_itime +@end smallexample + +@item @emph{See also}: +@ref{DATE_AND_TIME} +@end table + + + +@node KILL +@section @code{KILL} --- Send a signal to a process +@fnindex KILL + +@table @asis +@item @emph{Description}: +Sends the signal specified by @var{SIG} to the process @var{PID}. +See @code{kill(2)}. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. +@item @emph{Standard}: +GNU extension + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL KILL(PID, SIG [, STATUS])} +@item @code{STATUS = KILL(PID, SIG)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{PID} @tab Shall be a scalar @code{INTEGER} with @code{INTENT(IN)}. +@item @var{SIG} @tab Shall be a scalar @code{INTEGER} with @code{INTENT(IN)}. +@item @var{STATUS} @tab [Subroutine](Optional) +Shall be a scalar @code{INTEGER}. +Returns 0 on success; otherwise a system-specific error code is returned. +@item @var{STATUS} @tab [Function] The kind type parameter is that of +@code{pid}. +Returns 0 on success; otherwise a system-specific error code is returned. +@end multitable + +@item @emph{See also}: +@ref{ABORT}, @gol +@ref{EXIT} +@end table + + +@node KIND +@section @code{KIND} --- Kind of an entity +@fnindex KIND +@cindex kind + +@table @asis +@item @emph{Description}: +@code{KIND(X)} returns the kind value of the entity @var{X}. + +@item @emph{Standard}: +Fortran 95 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{K = KIND(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{LOGICAL}, @code{INTEGER}, +@code{REAL}, @code{COMPLEX} or @code{CHARACTER}. It may be scalar or +array valued. +@end multitable + +@item @emph{Return value}: +The return value is a scalar of type @code{INTEGER} and of the default +integer kind. + +@item @emph{Example}: +@smallexample +program test_kind + integer,parameter :: kc = kind(' ') + integer,parameter :: kl = kind(.true.) + + print *, "The default character kind is ", kc + print *, "The default logical kind is ", kl +end program test_kind +@end smallexample + +@end table + + + +@node LBOUND +@section @code{LBOUND} --- Lower dimension bounds of an array +@fnindex LBOUND +@cindex array, lower bound + +@table @asis +@item @emph{Description}: +Returns the lower bounds of an array, or a single lower bound +along the @var{DIM} dimension. +@item @emph{Standard}: +Fortran 90 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = LBOUND(ARRAY [, DIM [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array, of any type. +@item @var{DIM} @tab (Optional) Shall be a scalar @code{INTEGER}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. +If @var{DIM} is absent, the result is an array of the lower bounds of +@var{ARRAY}. If @var{DIM} is present, the result is a scalar +corresponding to the lower bound of the array along that dimension. If +@var{ARRAY} is an expression rather than a whole array or array +structure component, or if it has a zero extent along the relevant +dimension, the lower bound is taken to be 1. + +@item @emph{See also}: +@ref{UBOUND}, @gol +@ref{LCOBOUND} +@end table + + + +@node LCOBOUND +@section @code{LCOBOUND} --- Lower codimension bounds of an array +@fnindex LCOBOUND +@cindex coarray, lower bound + +@table @asis +@item @emph{Description}: +Returns the lower bounds of a coarray, or a single lower cobound +along the @var{DIM} codimension. +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = LCOBOUND(COARRAY [, DIM [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an coarray, of any type. +@item @var{DIM} @tab (Optional) Shall be a scalar @code{INTEGER}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. +If @var{DIM} is absent, the result is an array of the lower cobounds of +@var{COARRAY}. If @var{DIM} is present, the result is a scalar +corresponding to the lower cobound of the array along that codimension. + +@item @emph{See also}: +@ref{UCOBOUND}, @gol +@ref{LBOUND} +@end table + + + +@node LEADZ +@section @code{LEADZ} --- Number of leading zero bits of an integer +@fnindex LEADZ +@cindex zero bits + +@table @asis +@item @emph{Description}: +@code{LEADZ} returns the number of leading zero bits of an integer. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LEADZ(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The type of the return value is the default @code{INTEGER}. +If all the bits of @code{I} are zero, the result value is @code{BIT_SIZE(I)}. + +@item @emph{Example}: +@smallexample +PROGRAM test_leadz + WRITE (*,*) BIT_SIZE(1) ! prints 32 + WRITE (*,*) LEADZ(1) ! prints 31 +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{BIT_SIZE}, @gol +@ref{TRAILZ}, @gol +@ref{POPCNT}, @gol +@ref{POPPAR} +@end table + + + +@node LEN +@section @code{LEN} --- Length of a character entity +@fnindex LEN +@cindex string, length + +@table @asis +@item @emph{Description}: +Returns the length of a character string. If @var{STRING} is an array, +the length of an element of @var{STRING} is returned. Note that +@var{STRING} need not be defined when this intrinsic is invoked, since +only the length, not the content, of @var{STRING} is needed. + +@item @emph{Standard}: +Fortran 77 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{L = LEN(STRING [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab Shall be a scalar or array of type +@code{CHARACTER}, with @code{INTENT(IN)} +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. + + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{LEN(STRING)} @tab @code{CHARACTER} @tab @code{INTEGER} @tab Fortran 77 and later +@end multitable + + +@item @emph{See also}: +@ref{LEN_TRIM}, @gol +@ref{ADJUSTL}, @gol +@ref{ADJUSTR} +@end table + + + +@node LEN_TRIM +@section @code{LEN_TRIM} --- Length of a character entity without trailing blank characters +@fnindex LEN_TRIM +@cindex string, length, without trailing whitespace + +@table @asis +@item @emph{Description}: +Returns the length of a character string, ignoring any trailing blanks. + +@item @emph{Standard}: +Fortran 90 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LEN_TRIM(STRING [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab Shall be a scalar of type @code{CHARACTER}, +with @code{INTENT(IN)} +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. + +@item @emph{See also}: +@ref{LEN}, @gol +@ref{ADJUSTL}, @gol +@ref{ADJUSTR} +@end table + + + +@node LGE +@section @code{LGE} --- Lexical greater than or equal +@fnindex LGE +@cindex lexical comparison of strings +@cindex string, comparison + +@table @asis +@item @emph{Description}: +Determines whether one string is lexically greater than or equal to +another string, where the two strings are interpreted as containing +ASCII character codes. If the String A and String B are not the same +length, the shorter is compared as if spaces were appended to it to form +a value that has the same length as the longer. + +In general, the lexical comparison intrinsics @code{LGE}, @code{LGT}, +@code{LLE}, and @code{LLT} differ from the corresponding intrinsic +operators @code{.GE.}, @code{.GT.}, @code{.LE.}, and @code{.LT.}, in +that the latter use the processor's character ordering (which is not +ASCII on some targets), whereas the former always use the ASCII +ordering. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LGE(STRING_A, STRING_B)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING_A} @tab Shall be of default @code{CHARACTER} type. +@item @var{STRING_B} @tab Shall be of default @code{CHARACTER} type. +@end multitable + +@item @emph{Return value}: +Returns @code{.TRUE.} if @code{STRING_A >= STRING_B}, and @code{.FALSE.} +otherwise, based on the ASCII ordering. + +@item @emph{Specific names}: +@multitable @columnfractions .34 .16 .17 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{LGE(STRING_A,STRING_B)} @tab @code{CHARACTER} @tab @code{LOGICAL} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{LGT}, @gol +@ref{LLE}, @gol +@ref{LLT} +@end table + + + +@node LGT +@section @code{LGT} --- Lexical greater than +@fnindex LGT +@cindex lexical comparison of strings +@cindex string, comparison + +@table @asis +@item @emph{Description}: +Determines whether one string is lexically greater than another string, +where the two strings are interpreted as containing ASCII character +codes. If the String A and String B are not the same length, the +shorter is compared as if spaces were appended to it to form a value +that has the same length as the longer. + +In general, the lexical comparison intrinsics @code{LGE}, @code{LGT}, +@code{LLE}, and @code{LLT} differ from the corresponding intrinsic +operators @code{.GE.}, @code{.GT.}, @code{.LE.}, and @code{.LT.}, in +that the latter use the processor's character ordering (which is not +ASCII on some targets), whereas the former always use the ASCII +ordering. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LGT(STRING_A, STRING_B)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING_A} @tab Shall be of default @code{CHARACTER} type. +@item @var{STRING_B} @tab Shall be of default @code{CHARACTER} type. +@end multitable + +@item @emph{Return value}: +Returns @code{.TRUE.} if @code{STRING_A > STRING_B}, and @code{.FALSE.} +otherwise, based on the ASCII ordering. + +@item @emph{Specific names}: +@multitable @columnfractions .34 .16 .17 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{LGT(STRING_A,STRING_B)} @tab @code{CHARACTER} @tab @code{LOGICAL} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{LGE}, @gol +@ref{LLE}, @gol +@ref{LLT} +@end table + + + +@node LINK +@section @code{LINK} --- Create a hard link +@fnindex LINK +@cindex file system, create link +@cindex file system, hard link + +@table @asis +@item @emph{Description}: +Makes a (hard) link from file @var{PATH1} to @var{PATH2}. A null +character (@code{CHAR(0)}) can be used to mark the end of the names in +@var{PATH1} and @var{PATH2}; otherwise, trailing blanks in the file +names are ignored. If the @var{STATUS} argument is supplied, it +contains 0 on success or a nonzero error code upon return; see +@code{link(2)}. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL LINK(PATH1, PATH2 [, STATUS])} +@item @code{STATUS = LINK(PATH1, PATH2)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{PATH1} @tab Shall be of default @code{CHARACTER} type. +@item @var{PATH2} @tab Shall be of default @code{CHARACTER} type. +@item @var{STATUS} @tab (Optional) Shall be of default @code{INTEGER} type. +@end multitable + +@item @emph{See also}: +@ref{SYMLNK}, @gol +@ref{UNLINK} +@end table + + + +@node LLE +@section @code{LLE} --- Lexical less than or equal +@fnindex LLE +@cindex lexical comparison of strings +@cindex string, comparison + +@table @asis +@item @emph{Description}: +Determines whether one string is lexically less than or equal to another +string, where the two strings are interpreted as containing ASCII +character codes. If the String A and String B are not the same length, +the shorter is compared as if spaces were appended to it to form a value +that has the same length as the longer. + +In general, the lexical comparison intrinsics @code{LGE}, @code{LGT}, +@code{LLE}, and @code{LLT} differ from the corresponding intrinsic +operators @code{.GE.}, @code{.GT.}, @code{.LE.}, and @code{.LT.}, in +that the latter use the processor's character ordering (which is not +ASCII on some targets), whereas the former always use the ASCII +ordering. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LLE(STRING_A, STRING_B)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING_A} @tab Shall be of default @code{CHARACTER} type. +@item @var{STRING_B} @tab Shall be of default @code{CHARACTER} type. +@end multitable + +@item @emph{Return value}: +Returns @code{.TRUE.} if @code{STRING_A <= STRING_B}, and @code{.FALSE.} +otherwise, based on the ASCII ordering. + +@item @emph{Specific names}: +@multitable @columnfractions .34 .16 .17 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{LLE(STRING_A,STRING_B)} @tab @code{CHARACTER} @tab @code{LOGICAL} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{LGE}, @gol +@ref{LGT}, @gol +@ref{LLT} +@end table + + + +@node LLT +@section @code{LLT} --- Lexical less than +@fnindex LLT +@cindex lexical comparison of strings +@cindex string, comparison + +@table @asis +@item @emph{Description}: +Determines whether one string is lexically less than another string, +where the two strings are interpreted as containing ASCII character +codes. If the String A and String B are not the same length, the +shorter is compared as if spaces were appended to it to form a value +that has the same length as the longer. + +In general, the lexical comparison intrinsics @code{LGE}, @code{LGT}, +@code{LLE}, and @code{LLT} differ from the corresponding intrinsic +operators @code{.GE.}, @code{.GT.}, @code{.LE.}, and @code{.LT.}, in +that the latter use the processor's character ordering (which is not +ASCII on some targets), whereas the former always use the ASCII +ordering. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LLT(STRING_A, STRING_B)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING_A} @tab Shall be of default @code{CHARACTER} type. +@item @var{STRING_B} @tab Shall be of default @code{CHARACTER} type. +@end multitable + +@item @emph{Return value}: +Returns @code{.TRUE.} if @code{STRING_A < STRING_B}, and @code{.FALSE.} +otherwise, based on the ASCII ordering. + +@item @emph{Specific names}: +@multitable @columnfractions .34 .16 .17 .30 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{LLT(STRING_A,STRING_B)} @tab @code{CHARACTER} @tab @code{LOGICAL} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{LGE}, @gol +@ref{LGT}, @gol +@ref{LLE} +@end table + + + +@node LNBLNK +@section @code{LNBLNK} --- Index of the last non-blank character in a string +@fnindex LNBLNK +@cindex string, find non-blank character + +@table @asis +@item @emph{Description}: +Returns the length of a character string, ignoring any trailing blanks. +This is identical to the standard @code{LEN_TRIM} intrinsic, and is only +included for backwards compatibility. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LNBLNK(STRING)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab Shall be a scalar of type @code{CHARACTER}, +with @code{INTENT(IN)} +@end multitable + +@item @emph{Return value}: +The return value is of @code{INTEGER(kind=4)} type. + +@item @emph{See also}: +@ref{INDEX intrinsic}, @gol +@ref{LEN_TRIM} +@end table + + + +@node LOC +@section @code{LOC} --- Returns the address of a variable +@fnindex LOC +@cindex location of a variable in memory + +@table @asis +@item @emph{Description}: +@code{LOC(X)} returns the address of @var{X} as an integer. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = LOC(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Variable of any type. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER}, with a @code{KIND} +corresponding to the size (in bytes) of a memory address on the target +machine. + +@item @emph{Example}: +@smallexample +program test_loc + integer :: i + real :: r + i = loc(r) + print *, i +end program test_loc +@end smallexample +@end table + + + +@node LOG +@section @code{LOG} --- Natural logarithm function +@fnindex LOG +@fnindex ALOG +@fnindex DLOG +@fnindex CLOG +@fnindex ZLOG +@fnindex CDLOG +@cindex exponential function, inverse +@cindex logarithm function +@cindex natural logarithm function + +@table @asis +@item @emph{Description}: +@code{LOG(X)} computes the natural logarithm of @var{X}, i.e. the +logarithm to the base @math{e}. + +@item @emph{Standard}: +Fortran 77 and later, has GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LOG(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or +@code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} or @code{COMPLEX}. +The kind type parameter is the same as @var{X}. +If @var{X} is @code{COMPLEX}, the imaginary part @math{\omega} is in the range +@math{-\pi < \omega \leq \pi}. + +@item @emph{Example}: +@smallexample +program test_log + real(8) :: x = 2.7182818284590451_8 + complex :: z = (1.0, 2.0) + x = log(x) ! will yield (approximately) 1 + z = log(z) +end program test_log +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ALOG(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 or later +@item @code{DLOG(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 or later +@item @code{CLOG(X)} @tab @code{COMPLEX(4) X} @tab @code{COMPLEX(4)} @tab Fortran 77 or later +@item @code{ZLOG(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@item @code{CDLOG(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@end multitable +@end table + + + +@node LOG10 +@section @code{LOG10} --- Base 10 logarithm function +@fnindex LOG10 +@fnindex ALOG10 +@fnindex DLOG10 +@cindex exponential function, inverse +@cindex logarithm function with base 10 +@cindex base 10 logarithm function + +@table @asis +@item @emph{Description}: +@code{LOG10(X)} computes the base 10 logarithm of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LOG10(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} or @code{COMPLEX}. +The kind type parameter is the same as @var{X}. + +@item @emph{Example}: +@smallexample +program test_log10 + real(8) :: x = 10.0_8 + x = log10(x) +end program test_log10 +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{ALOG10(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DLOG10(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable +@end table + + + +@node LOG_GAMMA +@section @code{LOG_GAMMA} --- Logarithm of the Gamma function +@fnindex LOG_GAMMA +@fnindex LGAMMA +@fnindex ALGAMA +@fnindex DLGAMA +@cindex Gamma function, logarithm of + +@table @asis +@item @emph{Description}: +@code{LOG_GAMMA(X)} computes the natural logarithm of the absolute value +of the Gamma (@math{\Gamma}) function. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{X = LOG_GAMMA(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL} and neither zero +nor a negative integer. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} of the same kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_log_gamma + real :: x = 1.0 + x = lgamma(x) ! returns 0.0 +end program test_log_gamma +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{LGAMMA(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{ALGAMA(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DLGAMA(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Gamma function: @gol +@ref{GAMMA} +@end table + + + +@node LOGICAL +@section @code{LOGICAL} --- Convert to logical type +@fnindex LOGICAL +@cindex conversion, to logical + +@table @asis +@item @emph{Description}: +Converts one kind of @code{LOGICAL} variable to another. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LOGICAL(L [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{L} @tab The type shall be @code{LOGICAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is a @code{LOGICAL} value equal to @var{L}, with a +kind corresponding to @var{KIND}, or of the default logical kind if +@var{KIND} is not given. + +@item @emph{See also}: +@ref{INT}, @gol +@ref{REAL}, @gol +@ref{CMPLX} +@end table + + + +@node LSHIFT +@section @code{LSHIFT} --- Left shift bits +@fnindex LSHIFT +@cindex bits, shift left + +@table @asis +@item @emph{Description}: +@code{LSHIFT} returns a value corresponding to @var{I} with all of the +bits shifted left by @var{SHIFT} places. @var{SHIFT} shall be +nonnegative and less than or equal to @code{BIT_SIZE(I)}, otherwise +the result value is undefined. Bits shifted out from the left end are +lost; zeros are shifted in from the opposite end. + +This function has been superseded by the @code{ISHFT} intrinsic, which +is standard in Fortran 95 and later, and the @code{SHIFTL} intrinsic, +which is standard in Fortran 2008 and later. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = LSHIFT(I, SHIFT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{See also}: +@ref{ISHFT}, @gol +@ref{ISHFTC}, @gol +@ref{RSHIFT}, @gol +@ref{SHIFTA}, @gol +@ref{SHIFTL}, @gol +@ref{SHIFTR} +@end table + + + +@node LSTAT +@section @code{LSTAT} --- Get file status +@fnindex LSTAT +@cindex file system, file status + +@table @asis +@item @emph{Description}: +@code{LSTAT} is identical to @ref{STAT}, except that if path is a +symbolic link, then the link itself is statted, not the file that it +refers to. + +The elements in @code{VALUES} are the same as described by @ref{STAT}. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL LSTAT(NAME, VALUES [, STATUS])} +@item @code{STATUS = LSTAT(NAME, VALUES)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NAME} @tab The type shall be @code{CHARACTER} of the default +kind, a valid path within the file system. +@item @var{VALUES} @tab The type shall be @code{INTEGER(4), DIMENSION(13)}. +@item @var{STATUS} @tab (Optional) status flag of type @code{INTEGER(4)}. +Returns 0 on success and a system specific error code otherwise. +@end multitable + +@item @emph{Example}: +See @ref{STAT} for an example. + +@item @emph{See also}: +To stat an open file: @gol +@ref{FSTAT} @gol +To stat a file: @gol +@ref{STAT} +@end table + + + +@node LTIME +@section @code{LTIME} --- Convert time to local time info +@fnindex LTIME +@cindex time, conversion to local time info + +@table @asis +@item @emph{Description}: +Given a system time value @var{TIME} (as provided by the @ref{TIME} +intrinsic), fills @var{VALUES} with values extracted from it appropriate +to the local time zone using @code{localtime(3)}. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. In new code, programmers should consider the use of +the @ref{DATE_AND_TIME} intrinsic defined by the Fortran 95 +standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL LTIME(TIME, VALUES)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{TIME} @tab An @code{INTEGER} scalar expression +corresponding to a system time, with @code{INTENT(IN)}. +@item @var{VALUES} @tab A default @code{INTEGER} array with 9 elements, +with @code{INTENT(OUT)}. +@end multitable + +@item @emph{Return value}: +The elements of @var{VALUES} are assigned as follows: +@enumerate +@item Seconds after the minute, range 0--59 or 0--61 to allow for leap +seconds +@item Minutes after the hour, range 0--59 +@item Hours past midnight, range 0--23 +@item Day of month, range 1--31 +@item Number of months since January, range 0--11 +@item Years since 1900 +@item Number of days since Sunday, range 0--6 +@item Days since January 1, range 0--365 +@item Daylight savings indicator: positive if daylight savings is in +effect, zero if not, and negative if the information is not available. +@end enumerate + +@item @emph{See also}: +@ref{DATE_AND_TIME}, @gol +@ref{CTIME}, @gol +@ref{GMTIME}, @gol +@ref{TIME}, @gol +@ref{TIME8} +@end table + + + +@node MALLOC +@section @code{MALLOC} --- Allocate dynamic memory +@fnindex MALLOC +@cindex pointer, cray + +@table @asis +@item @emph{Description}: +@code{MALLOC(SIZE)} allocates @var{SIZE} bytes of dynamic memory and +returns the address of the allocated memory. The @code{MALLOC} intrinsic +is an extension intended to be used with Cray pointers, and is provided +in GNU Fortran to allow the user to compile legacy code. For new code +using Fortran 95 pointers, the memory allocation intrinsic is +@code{ALLOCATE}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{PTR = MALLOC(SIZE)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SIZE} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER(K)}, with @var{K} such that +variables of type @code{INTEGER(K)} have the same size as +C pointers (@code{sizeof(void *)}). + +@item @emph{Example}: +The following example demonstrates the use of @code{MALLOC} and +@code{FREE} with Cray pointers. + +@smallexample +program test_malloc + implicit none + integer i + real*8 x(*), z + pointer(ptr_x,x) + + ptr_x = malloc(20*8) + do i = 1, 20 + x(i) = sqrt(1.0d0 / i) + end do + z = 0 + do i = 1, 20 + z = z + x(i) + print *, z + end do + call free(ptr_x) +end program test_malloc +@end smallexample + +@item @emph{See also}: +@ref{FREE} +@end table + + + +@node MASKL +@section @code{MASKL} --- Left justified mask +@fnindex MASKL +@cindex mask, left justified + +@table @asis +@item @emph{Description}: +@code{MASKL(I[, KIND])} has its leftmost @var{I} bits set to 1, and the +remaining bits set to 0. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = MASKL(I[, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER}. +@item @var{KIND} @tab Shall be a scalar constant expression of type +@code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER}. If @var{KIND} is present, it +specifies the kind value of the return type; otherwise, it is of the +default integer kind. + +@item @emph{See also}: +@ref{MASKR} +@end table + + + +@node MASKR +@section @code{MASKR} --- Right justified mask +@fnindex MASKR +@cindex mask, right justified + +@table @asis +@item @emph{Description}: +@code{MASKL(I[, KIND])} has its rightmost @var{I} bits set to 1, and the +remaining bits set to 0. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = MASKR(I[, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER}. +@item @var{KIND} @tab Shall be a scalar constant expression of type +@code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER}. If @var{KIND} is present, it +specifies the kind value of the return type; otherwise, it is of the +default integer kind. + +@item @emph{See also}: +@ref{MASKL} +@end table + + + +@node MATMUL +@section @code{MATMUL} --- matrix multiplication +@fnindex MATMUL +@cindex matrix multiplication +@cindex product, matrix + +@table @asis +@item @emph{Description}: +Performs a matrix multiplication on numeric or logical arguments. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = MATMUL(MATRIX_A, MATRIX_B)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{MATRIX_A} @tab An array of @code{INTEGER}, +@code{REAL}, @code{COMPLEX}, or @code{LOGICAL} type, with a rank of +one or two. +@item @var{MATRIX_B} @tab An array of @code{INTEGER}, +@code{REAL}, or @code{COMPLEX} type if @var{MATRIX_A} is of a numeric +type; otherwise, an array of @code{LOGICAL} type. The rank shall be one +or two, and the first (or only) dimension of @var{MATRIX_B} shall be +equal to the last (or only) dimension of @var{MATRIX_A}. +@var{MATRIX_A} and @var{MATRIX_B} shall not both be rank one arrays. +@end multitable + +@item @emph{Return value}: +The matrix product of @var{MATRIX_A} and @var{MATRIX_B}. The type and +kind of the result follow the usual type and kind promotion rules, as +for the @code{*} or @code{.AND.} operators. +@end table + + + +@node MAX +@section @code{MAX} --- Maximum value of an argument list +@fnindex MAX +@fnindex MAX0 +@fnindex AMAX0 +@fnindex MAX1 +@fnindex AMAX1 +@fnindex DMAX1 +@cindex maximum value + +@table @asis +@item @emph{Description}: +Returns the argument with the largest (most positive) value. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = MAX(A1, A2 [, A3 [, ...]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A1} @tab The type shall be @code{INTEGER} or +@code{REAL}. +@item @var{A2}, @var{A3}, ... @tab An expression of the same type and kind +as @var{A1}. (As a GNU extension, arguments of different kinds are +permitted.) +@end multitable + +@item @emph{Return value}: +The return value corresponds to the maximum value among the arguments, +and has the same type and kind as the first argument. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{MAX0(A1)} @tab @code{INTEGER(4) A1} @tab @code{INTEGER(4)} @tab Fortran 77 and later +@item @code{AMAX0(A1)} @tab @code{INTEGER(4) A1} @tab @code{REAL(MAX(X))} @tab Fortran 77 and later +@item @code{MAX1(A1)} @tab @code{REAL A1} @tab @code{INT(MAX(X))} @tab Fortran 77 and later +@item @code{AMAX1(A1)} @tab @code{REAL(4) A1} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DMAX1(A1)} @tab @code{REAL(8) A1} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{MAXLOC} @gol +@ref{MAXVAL}, @gol +@ref{MIN} +@end table + + + +@node MAXEXPONENT +@section @code{MAXEXPONENT} --- Maximum exponent of a real kind +@fnindex MAXEXPONENT +@cindex model representation, maximum exponent + +@table @asis +@item @emph{Description}: +@code{MAXEXPONENT(X)} returns the maximum exponent in the model of the +type of @code{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = MAXEXPONENT(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the default integer +kind. + +@item @emph{Example}: +@smallexample +program exponents + real(kind=4) :: x + real(kind=8) :: y + + print *, minexponent(x), maxexponent(x) + print *, minexponent(y), maxexponent(y) +end program exponents +@end smallexample +@end table + + + +@node MAXLOC +@section @code{MAXLOC} --- Location of the maximum value within an array +@fnindex MAXLOC +@cindex array, location of maximum element + +@table @asis +@item @emph{Description}: +Determines the location of the element in the array with the maximum +value, or, if the @var{DIM} argument is supplied, determines the +locations of the maximum element along each row of the array in the +@var{DIM} direction. If @var{MASK} is present, only the elements for +which @var{MASK} is @code{.TRUE.} are considered. If more than one +element in the array has the maximum value, the location returned is +that of the first such element in array element order if the +@var{BACK} is not present, or is false; if @var{BACK} is true, the location +returned is that of the last such element. If the array has zero +size, or all of the elements of @var{MASK} are @code{.FALSE.}, then +the result is an array of zeroes. Similarly, if @var{DIM} is supplied +and all of the elements of @var{MASK} along a given row are zero, the +result value for that row is zero. + +@item @emph{Standard}: +Fortran 95 and later; @var{ARRAY} of @code{CHARACTER} and the +@var{KIND} argument are available in Fortran 2003 and later. +The @var{BACK} argument is available in Fortran 2008 and later. + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = MAXLOC(ARRAY, DIM [, MASK] [,KIND] [,BACK])} +@item @code{RESULT = MAXLOC(ARRAY [, MASK] [,KIND] [,BACK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER} or +@code{REAL}. +@item @var{DIM} @tab (Optional) Shall be a scalar of type +@code{INTEGER}, with a value between one and the rank of @var{ARRAY}, +inclusive. It may not be an optional dummy argument. +@item @var{MASK} @tab Shall be of type @code{LOGICAL}, +and conformable with @var{ARRAY}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@item @var{BACK} @tab (Optional) A scalar of type @code{LOGICAL}. +@end multitable + +@item @emph{Return value}: +If @var{DIM} is absent, the result is a rank-one array with a length +equal to the rank of @var{ARRAY}. If @var{DIM} is present, the result +is an array with a rank one less than the rank of @var{ARRAY}, and a +size corresponding to the size of @var{ARRAY} with the @var{DIM} +dimension removed. If @var{DIM} is present and @var{ARRAY} has a rank +of one, the result is a scalar. If the optional argument @var{KIND} +is present, the result is an integer of kind @var{KIND}, otherwise it +is of default kind. + +@item @emph{See also}: +@ref{FINDLOC}, @gol +@ref{MAX}, @gol +@ref{MAXVAL} +@end table + + + +@node MAXVAL +@section @code{MAXVAL} --- Maximum value of an array +@fnindex MAXVAL +@cindex array, maximum value +@cindex maximum value + +@table @asis +@item @emph{Description}: +Determines the maximum value of the elements in an array value, or, if +the @var{DIM} argument is supplied, determines the maximum value along +each row of the array in the @var{DIM} direction. If @var{MASK} is +present, only the elements for which @var{MASK} is @code{.TRUE.} are +considered. If the array has zero size, or all of the elements of +@var{MASK} are @code{.FALSE.}, then the result is @code{-HUGE(ARRAY)} +if @var{ARRAY} is numeric, or a string of nulls if @var{ARRAY} is of character +type. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = MAXVAL(ARRAY, DIM [, MASK])} +@item @code{RESULT = MAXVAL(ARRAY [, MASK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER} or +@code{REAL}. +@item @var{DIM} @tab (Optional) Shall be a scalar of type +@code{INTEGER}, with a value between one and the rank of @var{ARRAY}, +inclusive. It may not be an optional dummy argument. +@item @var{MASK} @tab (Optional) Shall be of type @code{LOGICAL}, +and conformable with @var{ARRAY}. +@end multitable + +@item @emph{Return value}: +If @var{DIM} is absent, or if @var{ARRAY} has a rank of one, the result +is a scalar. If @var{DIM} is present, the result is an array with a +rank one less than the rank of @var{ARRAY}, and a size corresponding to +the size of @var{ARRAY} with the @var{DIM} dimension removed. In all +cases, the result is of the same type and kind as @var{ARRAY}. + +@item @emph{See also}: +@ref{MAX}, @gol +@ref{MAXLOC} +@end table + + + +@node MCLOCK +@section @code{MCLOCK} --- Time function +@fnindex MCLOCK +@cindex time, clock ticks +@cindex clock ticks + +@table @asis +@item @emph{Description}: +Returns the number of clock ticks since the start of the process, based +on the function @code{clock(3)} in the C standard library. + +This intrinsic is not fully portable, such as to systems with 32-bit +@code{INTEGER} types but supporting times wider than 32 bits. Therefore, +the values returned by this intrinsic might be, or become, negative, or +numerically less than previous values, during a single run of the +compiled program. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = MCLOCK()} + +@item @emph{Return value}: +The return value is a scalar of type @code{INTEGER(4)}, equal to the +number of clock ticks since the start of the process, or @code{-1} if +the system does not support @code{clock(3)}. + +@item @emph{See also}: +@ref{CTIME}, @gol +@ref{GMTIME}, @gol +@ref{LTIME}, @gol +@ref{MCLOCK}, @gol +@ref{TIME} +@end table + + + +@node MCLOCK8 +@section @code{MCLOCK8} --- Time function (64-bit) +@fnindex MCLOCK8 +@cindex time, clock ticks +@cindex clock ticks + +@table @asis +@item @emph{Description}: +Returns the number of clock ticks since the start of the process, based +on the function @code{clock(3)} in the C standard library. + +@emph{Warning:} this intrinsic does not increase the range of the timing +values over that returned by @code{clock(3)}. On a system with a 32-bit +@code{clock(3)}, @code{MCLOCK8} will return a 32-bit value, even though +it is converted to a 64-bit @code{INTEGER(8)} value. That means +overflows of the 32-bit value can still occur. Therefore, the values +returned by this intrinsic might be or become negative or numerically +less than previous values during a single run of the compiled program. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = MCLOCK8()} + +@item @emph{Return value}: +The return value is a scalar of type @code{INTEGER(8)}, equal to the +number of clock ticks since the start of the process, or @code{-1} if +the system does not support @code{clock(3)}. + +@item @emph{See also}: +@ref{CTIME}, @gol +@ref{GMTIME}, @gol +@ref{LTIME}, @gol +@ref{MCLOCK}, @gol +@ref{TIME8} +@end table + + + +@node MERGE +@section @code{MERGE} --- Merge variables +@fnindex MERGE +@cindex array, merge arrays +@cindex array, combine arrays + +@table @asis +@item @emph{Description}: +Select values from two arrays according to a logical mask. The result +is equal to @var{TSOURCE} if @var{MASK} is @code{.TRUE.}, or equal to +@var{FSOURCE} if it is @code{.FALSE.}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = MERGE(TSOURCE, FSOURCE, MASK)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{TSOURCE} @tab May be of any type. +@item @var{FSOURCE} @tab Shall be of the same type and type parameters +as @var{TSOURCE}. +@item @var{MASK} @tab Shall be of type @code{LOGICAL}. +@end multitable + +@item @emph{Return value}: +The result is of the same type and type parameters as @var{TSOURCE}. + +@end table + + + +@node MERGE_BITS +@section @code{MERGE_BITS} --- Merge of bits under mask +@fnindex MERGE_BITS +@cindex bits, merge + +@table @asis +@item @emph{Description}: +@code{MERGE_BITS(I, J, MASK)} merges the bits of @var{I} and @var{J} +as determined by the mask. The i-th bit of the result is equal to the +i-th bit of @var{I} if the i-th bit of @var{MASK} is 1; it is equal to +the i-th bit of @var{J} otherwise. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = MERGE_BITS(I, J, MASK)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER} or a boz-literal-constant. +@item @var{J} @tab Shall be of type @code{INTEGER} with the same +kind type parameter as @var{I} or a boz-literal-constant. +@var{I} and @var{J} shall not both be boz-literal-constants. +@item @var{MASK} @tab Shall be of type @code{INTEGER} or a boz-literal-constant +and of the same kind as @var{I}. +@end multitable + +@item @emph{Return value}: +The result is of the same type and kind as @var{I}. + +@end table + + + +@node MIN +@section @code{MIN} --- Minimum value of an argument list +@fnindex MIN +@fnindex MIN0 +@fnindex AMIN0 +@fnindex MIN1 +@fnindex AMIN1 +@fnindex DMIN1 +@cindex minimum value + +@table @asis +@item @emph{Description}: +Returns the argument with the smallest (most negative) value. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = MIN(A1, A2 [, A3, ...])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A1} @tab The type shall be @code{INTEGER} or +@code{REAL}. +@item @var{A2}, @var{A3}, ... @tab An expression of the same type and kind +as @var{A1}. (As a GNU extension, arguments of different kinds are +permitted.) +@end multitable + +@item @emph{Return value}: +The return value corresponds to the minimum value among the arguments, +and has the same type and kind as the first argument. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{MIN0(A1)} @tab @code{INTEGER(4) A1} @tab @code{INTEGER(4)} @tab Fortran 77 and later +@item @code{AMIN0(A1)} @tab @code{INTEGER(4) A1} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{MIN1(A1)} @tab @code{REAL A1} @tab @code{INTEGER(4)} @tab Fortran 77 and later +@item @code{AMIN1(A1)} @tab @code{REAL(4) A1} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DMIN1(A1)} @tab @code{REAL(8) A1} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{MAX}, @gol +@ref{MINLOC}, @gol +@ref{MINVAL} +@end table + + + +@node MINEXPONENT +@section @code{MINEXPONENT} --- Minimum exponent of a real kind +@fnindex MINEXPONENT +@cindex model representation, minimum exponent + +@table @asis +@item @emph{Description}: +@code{MINEXPONENT(X)} returns the minimum exponent in the model of the +type of @code{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = MINEXPONENT(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the default integer +kind. + +@item @emph{Example}: +See @code{MAXEXPONENT} for an example. +@end table + + + +@node MINLOC +@section @code{MINLOC} --- Location of the minimum value within an array +@fnindex MINLOC +@cindex array, location of minimum element + +@table @asis +@item @emph{Description}: +Determines the location of the element in the array with the minimum +value, or, if the @var{DIM} argument is supplied, determines the +locations of the minimum element along each row of the array in the +@var{DIM} direction. If @var{MASK} is present, only the elements for +which @var{MASK} is @code{.TRUE.} are considered. If more than one +element in the array has the minimum value, the location returned is +that of the first such element in array element order if the +@var{BACK} is not present, or is false; if @var{BACK} is true, the location +returned is that of the last such element. If the array has +zero size, or all of the elements of @var{MASK} are @code{.FALSE.}, then +the result is an array of zeroes. Similarly, if @var{DIM} is supplied +and all of the elements of @var{MASK} along a given row are zero, the +result value for that row is zero. + +@item @emph{Standard}: +Fortran 90 and later; @var{ARRAY} of @code{CHARACTER} and the +@var{KIND} argument are available in Fortran 2003 and later. +The @var{BACK} argument is available in Fortran 2008 and later. + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = MINLOC(ARRAY, DIM [, MASK] [,KIND] [,BACK])} +@item @code{RESULT = MINLOC(ARRAY [, MASK], [,KIND] [,BACK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER}, +@code{REAL} or @code{CHARACTER}. +@item @var{DIM} @tab (Optional) Shall be a scalar of type +@code{INTEGER}, with a value between one and the rank of @var{ARRAY}, +inclusive. It may not be an optional dummy argument. +@item @var{MASK} @tab Shall be of type @code{LOGICAL}, +and conformable with @var{ARRAY}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@item @var{BACK} @tab (Optional) A scalar of type @code{LOGICAL}. +@end multitable + +@item @emph{Return value}: +If @var{DIM} is absent, the result is a rank-one array with a length +equal to the rank of @var{ARRAY}. If @var{DIM} is present, the result +is an array with a rank one less than the rank of @var{ARRAY}, and a +size corresponding to the size of @var{ARRAY} with the @var{DIM} +dimension removed. If @var{DIM} is present and @var{ARRAY} has a rank +of one, the result is a scalar. If the optional argument @var{KIND} +is present, the result is an integer of kind @var{KIND}, otherwise it +is of default kind. + +@item @emph{See also}: +@ref{FINDLOC}, @gol +@ref{MIN}, @gol +@ref{MINVAL} +@end table + + + +@node MINVAL +@section @code{MINVAL} --- Minimum value of an array +@fnindex MINVAL +@cindex array, minimum value +@cindex minimum value + +@table @asis +@item @emph{Description}: +Determines the minimum value of the elements in an array value, or, if +the @var{DIM} argument is supplied, determines the minimum value along +each row of the array in the @var{DIM} direction. If @var{MASK} is +present, only the elements for which @var{MASK} is @code{.TRUE.} are +considered. If the array has zero size, or all of the elements of +@var{MASK} are @code{.FALSE.}, then the result is @code{HUGE(ARRAY)} if +@var{ARRAY} is numeric, or a string of @code{CHAR(255)} characters if +@var{ARRAY} is of character type. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = MINVAL(ARRAY, DIM [, MASK])} +@item @code{RESULT = MINVAL(ARRAY [, MASK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER} or +@code{REAL}. +@item @var{DIM} @tab (Optional) Shall be a scalar of type +@code{INTEGER}, with a value between one and the rank of @var{ARRAY}, +inclusive. It may not be an optional dummy argument. +@item @var{MASK} @tab Shall be of type @code{LOGICAL}, +and conformable with @var{ARRAY}. +@end multitable + +@item @emph{Return value}: +If @var{DIM} is absent, or if @var{ARRAY} has a rank of one, the result +is a scalar. If @var{DIM} is present, the result is an array with a +rank one less than the rank of @var{ARRAY}, and a size corresponding to +the size of @var{ARRAY} with the @var{DIM} dimension removed. In all +cases, the result is of the same type and kind as @var{ARRAY}. + +@item @emph{See also}: +@ref{MIN}, @gol +@ref{MINLOC} +@end table + + + +@node MOD +@section @code{MOD} --- Remainder function +@fnindex MOD +@fnindex AMOD +@fnindex DMOD +@fnindex BMOD +@fnindex IMOD +@fnindex JMOD +@fnindex KMOD +@cindex remainder +@cindex division, remainder + +@table @asis +@item @emph{Description}: +@code{MOD(A,P)} computes the remainder of the division of A by P@. + +@item @emph{Standard}: +Fortran 77 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = MOD(A, P)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be a scalar of type @code{INTEGER} or @code{REAL}. +@item @var{P} @tab Shall be a scalar of the same type and kind as @var{A} +and not equal to zero. (As a GNU extension, arguments of different kinds are +permitted.) +@end multitable + +@item @emph{Return value}: +The return value is the result of @code{A - (INT(A/P) * P)}. The type +and kind of the return value is the same as that of the arguments. The +returned value has the same sign as A and a magnitude less than the +magnitude of P. (As a GNU extension, kind is the largest kind of the actual +arguments.) + +@item @emph{Example}: +@smallexample +program test_mod + print *, mod(17,3) + print *, mod(17.5,5.5) + print *, mod(17.5d0,5.5) + print *, mod(17.5,5.5d0) + + print *, mod(-17,3) + print *, mod(-17.5,5.5) + print *, mod(-17.5d0,5.5) + print *, mod(-17.5,5.5d0) + + print *, mod(17,-3) + print *, mod(17.5,-5.5) + print *, mod(17.5d0,-5.5) + print *, mod(17.5,-5.5d0) +end program test_mod +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .25 .20 .31 +@headitem Name @tab Arguments @tab Return type @tab Standard +@item @code{MOD(A,P)} @tab @code{INTEGER A,P} @tab @code{INTEGER} @tab Fortran 77 and later +@item @code{AMOD(A,P)} @tab @code{REAL(4) A,P} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DMOD(A,P)} @tab @code{REAL(8) A,P} @tab @code{REAL(8)} @tab Fortran 77 and later +@item @code{BMOD(A,P)} @tab @code{INTEGER(1) A,P} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IMOD(A,P)} @tab @code{INTEGER(2) A,P} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JMOD(A,P)} @tab @code{INTEGER(4) A,P} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KMOD(A,P)} @tab @code{INTEGER(8) A,P} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{MODULO} + +@end table + + + +@node MODULO +@section @code{MODULO} --- Modulo function +@fnindex MODULO +@cindex modulo +@cindex division, modulo + +@table @asis +@item @emph{Description}: +@code{MODULO(A,P)} computes the @var{A} modulo @var{P}. + +@item @emph{Standard}: +Fortran 95 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = MODULO(A, P)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be a scalar of type @code{INTEGER} or @code{REAL}. +@item @var{P} @tab Shall be a scalar of the same type and kind as @var{A}. +It shall not be zero. (As a GNU extension, arguments of different kinds are +permitted.) +@end multitable + +@item @emph{Return value}: +The type and kind of the result are those of the arguments. (As a GNU +extension, kind is the largest kind of the actual arguments.) +@table @asis +@item If @var{A} and @var{P} are of type @code{INTEGER}: +@code{MODULO(A,P)} has the value @var{R} such that @code{A=Q*P+R}, where +@var{Q} is an integer and @var{R} is between 0 (inclusive) and @var{P} +(exclusive). +@item If @var{A} and @var{P} are of type @code{REAL}: +@code{MODULO(A,P)} has the value of @code{A - FLOOR (A / P) * P}. +@end table +The returned value has the same sign as P and a magnitude less than +the magnitude of P. + +@item @emph{Example}: +@smallexample +program test_modulo + print *, modulo(17,3) + print *, modulo(17.5,5.5) + + print *, modulo(-17,3) + print *, modulo(-17.5,5.5) + + print *, modulo(17,-3) + print *, modulo(17.5,-5.5) +end program +@end smallexample + +@item @emph{See also}: +@ref{MOD} + +@end table + + + +@node MOVE_ALLOC +@section @code{MOVE_ALLOC} --- Move allocation from one object to another +@fnindex MOVE_ALLOC +@cindex moving allocation +@cindex allocation, moving + +@table @asis +@item @emph{Description}: +@code{MOVE_ALLOC(FROM, TO)} moves the allocation from @var{FROM} to +@var{TO}. @var{FROM} will become deallocated in the process. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Pure subroutine + +@item @emph{Syntax}: +@code{CALL MOVE_ALLOC(FROM, TO)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{FROM} @tab @code{ALLOCATABLE}, @code{INTENT(INOUT)}, may be +of any type and kind. +@item @var{TO} @tab @code{ALLOCATABLE}, @code{INTENT(OUT)}, shall be +of the same type, kind and rank as @var{FROM}. +@end multitable + +@item @emph{Return value}: +None + +@item @emph{Example}: +@smallexample +program test_move_alloc + integer, allocatable :: a(:), b(:) + + allocate(a(3)) + a = [ 1, 2, 3 ] + call move_alloc(a, b) + print *, allocated(a), allocated(b) + print *, b +end program test_move_alloc +@end smallexample +@end table + + + +@node MVBITS +@section @code{MVBITS} --- Move bits from one integer to another +@fnindex MVBITS +@fnindex BMVBITS +@fnindex IMVBITS +@fnindex JMVBITS +@fnindex KMVBITS +@cindex bits, move + +@table @asis +@item @emph{Description}: +Moves @var{LEN} bits from positions @var{FROMPOS} through +@code{FROMPOS+LEN-1} of @var{FROM} to positions @var{TOPOS} through +@code{TOPOS+LEN-1} of @var{TO}. The portion of argument @var{TO} not +affected by the movement of bits is unchanged. The values of +@code{FROMPOS+LEN-1} and @code{TOPOS+LEN-1} must be less than +@code{BIT_SIZE(FROM)}. + +@item @emph{Standard}: +Fortran 90 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental subroutine + +@item @emph{Syntax}: +@code{CALL MVBITS(FROM, FROMPOS, LEN, TO, TOPOS)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{FROM} @tab The type shall be @code{INTEGER}. +@item @var{FROMPOS} @tab The type shall be @code{INTEGER}. +@item @var{LEN} @tab The type shall be @code{INTEGER}. +@item @var{TO} @tab The type shall be @code{INTEGER}, of the +same kind as @var{FROM}. +@item @var{TOPOS} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{MVBITS(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 90 and later +@item @code{BMVBITS(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{IMVBITS(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JMVBITS(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KMVBITS(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{IBCLR}, @gol +@ref{IBSET}, @gol +@ref{IBITS}, @gol +@ref{IAND}, @gol +@ref{IOR}, @gol +@ref{IEOR} +@end table + + + +@node NEAREST +@section @code{NEAREST} --- Nearest representable number +@fnindex NEAREST +@cindex real number, nearest different +@cindex floating point, nearest different + +@table @asis +@item @emph{Description}: +@code{NEAREST(X, S)} returns the processor-representable number nearest +to @code{X} in the direction indicated by the sign of @code{S}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = NEAREST(X, S)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL}. +@item @var{S} @tab Shall be of type @code{REAL} and +not equal to zero. +@end multitable + +@item @emph{Return value}: +The return value is of the same type as @code{X}. If @code{S} is +positive, @code{NEAREST} returns the processor-representable number +greater than @code{X} and nearest to it. If @code{S} is negative, +@code{NEAREST} returns the processor-representable number smaller than +@code{X} and nearest to it. + +@item @emph{Example}: +@smallexample +program test_nearest + real :: x, y + x = nearest(42.0, 1.0) + y = nearest(42.0, -1.0) + write (*,"(3(G20.15))") x, y, x - y +end program test_nearest +@end smallexample +@end table + + + +@node NEW_LINE +@section @code{NEW_LINE} --- New line character +@fnindex NEW_LINE +@cindex newline +@cindex output, newline + +@table @asis +@item @emph{Description}: +@code{NEW_LINE(C)} returns the new-line character. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = NEW_LINE(C)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{C} @tab The argument shall be a scalar or array of the +type @code{CHARACTER}. +@end multitable + +@item @emph{Return value}: +Returns a @var{CHARACTER} scalar of length one with the new-line character of +the same kind as parameter @var{C}. + +@item @emph{Example}: +@smallexample +program newline + implicit none + write(*,'(A)') 'This is record 1.'//NEW_LINE('A')//'This is record 2.' +end program newline +@end smallexample +@end table + + + +@node NINT +@section @code{NINT} --- Nearest whole number +@fnindex NINT +@fnindex IDNINT +@cindex rounding, nearest whole number + +@table @asis +@item @emph{Description}: +@code{NINT(A)} rounds its argument to the nearest whole number. + +@item @emph{Standard}: +Fortran 77 and later, with @var{KIND} argument Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = NINT(A [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab The type of the argument shall be @code{REAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +Returns @var{A} with the fractional portion of its magnitude eliminated by +rounding to the nearest whole number and with its sign preserved, +converted to an @code{INTEGER} of the default kind. + +@item @emph{Example}: +@smallexample +program test_nint + real(4) x4 + real(8) x8 + x4 = 1.234E0_4 + x8 = 4.321_8 + print *, nint(x4), idnint(x8) +end program test_nint +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return Type @tab Standard +@item @code{NINT(A)} @tab @code{REAL(4) A} @tab @code{INTEGER} @tab Fortran 77 and later +@item @code{IDNINT(A)} @tab @code{REAL(8) A} @tab @code{INTEGER} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{CEILING}, @gol +@ref{FLOOR} +@end table + + + +@node NORM2 +@section @code{NORM2} --- Euclidean vector norms +@fnindex NORM2 +@cindex Euclidean vector norm +@cindex L2 vector norm +@cindex norm, Euclidean + +@table @asis +@item @emph{Description}: +Calculates the Euclidean vector norm (@math{L_2} norm) +of @var{ARRAY} along dimension @var{DIM}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = NORM2(ARRAY[, DIM])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{REAL} +@item @var{DIM} @tab (Optional) shall be a scalar of type +@code{INTEGER} with a value in the range from 1 to n, where n +equals the rank of @var{ARRAY}. +@end multitable + +@item @emph{Return value}: +The result is of the same type as @var{ARRAY}. + +If @var{DIM} is absent, a scalar with the square root of the sum of all +elements in @var{ARRAY} squared is returned. Otherwise, an array of +rank @math{n-1}, where @math{n} equals the rank of @var{ARRAY}, and a +shape similar to that of @var{ARRAY} with dimension @var{DIM} dropped +is returned. + +@item @emph{Example}: +@smallexample +PROGRAM test_sum + REAL :: x(5) = [ real :: 1, 2, 3, 4, 5 ] + print *, NORM2(x) ! = sqrt(55.) ~ 7.416 +END PROGRAM +@end smallexample +@end table + + + +@node NOT +@section @code{NOT} --- Logical negation +@fnindex NOT +@fnindex BNOT +@fnindex INOT +@fnindex JNOT +@fnindex KNOT +@cindex bits, negate +@cindex bitwise logical not +@cindex logical not, bitwise + +@table @asis +@item @emph{Description}: +@code{NOT} returns the bitwise Boolean inverse of @var{I}. + +@item @emph{Standard}: +Fortran 90 and later, has overloads that are GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = NOT(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return type is @code{INTEGER}, of the same kind as the +argument. + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{NOT(A)} @tab @code{INTEGER A} @tab @code{INTEGER} @tab Fortran 95 and later +@item @code{BNOT(A)} @tab @code{INTEGER(1) A} @tab @code{INTEGER(1)} @tab GNU extension +@item @code{INOT(A)} @tab @code{INTEGER(2) A} @tab @code{INTEGER(2)} @tab GNU extension +@item @code{JNOT(A)} @tab @code{INTEGER(4) A} @tab @code{INTEGER(4)} @tab GNU extension +@item @code{KNOT(A)} @tab @code{INTEGER(8) A} @tab @code{INTEGER(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +@ref{IAND}, @gol +@ref{IEOR}, @gol +@ref{IOR}, @gol +@ref{IBITS}, @gol +@ref{IBSET}, @gol +@ref{IBCLR} +@end table + + + +@node NULL +@section @code{NULL} --- Function that returns an disassociated pointer +@fnindex NULL +@cindex pointer, status +@cindex pointer, disassociated + +@table @asis +@item @emph{Description}: +Returns a disassociated pointer. + +If @var{MOLD} is present, a disassociated pointer of the same type is +returned, otherwise the type is determined by context. + +In Fortran 95, @var{MOLD} is optional. Please note that Fortran 2003 +includes cases where it is required. + +@item @emph{Standard}: +Fortran 95 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{PTR => NULL([MOLD])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{MOLD} @tab (Optional) shall be a pointer of any association +status and of any type. +@end multitable + +@item @emph{Return value}: +A disassociated pointer. + +@item @emph{Example}: +@smallexample +REAL, POINTER, DIMENSION(:) :: VEC => NULL () +@end smallexample + +@item @emph{See also}: +@ref{ASSOCIATED} +@end table + + + +@node NUM_IMAGES +@section @code{NUM_IMAGES} --- Function that returns the number of images +@fnindex NUM_IMAGES +@cindex coarray, @code{NUM_IMAGES} +@cindex images, number of + +@table @asis +@item @emph{Description}: +Returns the number of images. + +@item @emph{Standard}: +Fortran 2008 and later. With @var{DISTANCE} or @var{FAILED} argument, +Technical Specification (TS) 18508 or later + + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = NUM_IMAGES(DISTANCE, FAILED)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{DISTANCE} @tab (optional, intent(in)) Nonnegative scalar integer +@item @var{FAILED} @tab (optional, intent(in)) Scalar logical expression +@end multitable + +@item @emph{Return value}: +Scalar default-kind integer. If @var{DISTANCE} is not present or has value 0, +the number of images in the current team is returned. For values smaller or +equal distance to the initial team, it returns the number of images index +on the ancestor team which has a distance of @var{DISTANCE} from the invoking +team. If @var{DISTANCE} is larger than the distance to the initial team, the +number of images of the initial team is returned. If @var{FAILED} is not present +the total number of images is returned; if it has the value @code{.TRUE.}, +the number of failed images is returned, otherwise, the number of images which +do have not the failed status. + +@item @emph{Example}: +@smallexample +INTEGER :: value[*] +INTEGER :: i +value = THIS_IMAGE() +SYNC ALL +IF (THIS_IMAGE() == 1) THEN + DO i = 1, NUM_IMAGES() + WRITE(*,'(2(a,i0))') 'value[', i, '] is ', value[i] + END DO +END IF +@end smallexample + +@item @emph{See also}: +@ref{THIS_IMAGE}, @gol +@ref{IMAGE_INDEX} +@end table + + + +@node OR +@section @code{OR} --- Bitwise logical OR +@fnindex OR +@cindex bitwise logical or +@cindex logical or, bitwise + +@table @asis +@item @emph{Description}: +Bitwise logical @code{OR}. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. For integer arguments, programmers should consider +the use of the @ref{IOR} intrinsic defined by the Fortran standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = OR(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be either a scalar @code{INTEGER} +type or a scalar @code{LOGICAL} type or a boz-literal-constant. +@item @var{J} @tab The type shall be the same as the type of @var{I} or +a boz-literal-constant. @var{I} and @var{J} shall not both be +boz-literal-constants. If either @var{I} and @var{J} is a +boz-literal-constant, then the other argument must be a scalar @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return type is either a scalar @code{INTEGER} or a scalar +@code{LOGICAL}. If the kind type parameters differ, then the +smaller kind type is implicitly converted to larger kind, and the +return has the larger kind. A boz-literal-constant is +converted to an @code{INTEGER} with the kind type parameter of +the other argument as-if a call to @ref{INT} occurred. + +@item @emph{Example}: +@smallexample +PROGRAM test_or + LOGICAL :: T = .TRUE., F = .FALSE. + INTEGER :: a, b + DATA a / Z'F' /, b / Z'3' / + + WRITE (*,*) OR(T, T), OR(T, F), OR(F, T), OR(F, F) + WRITE (*,*) OR(a, b) +END PROGRAM +@end smallexample + +@item @emph{See also}: +Fortran 95 elemental function: @gol +@ref{IOR} +@end table + + + +@node PACK +@section @code{PACK} --- Pack an array into an array of rank one +@fnindex PACK +@cindex array, packing +@cindex array, reduce dimension +@cindex array, gather elements + +@table @asis +@item @emph{Description}: +Stores the elements of @var{ARRAY} in an array of rank one. + +The beginning of the resulting array is made up of elements whose @var{MASK} +equals @code{TRUE}. Afterwards, positions are filled with elements taken from +@var{VECTOR}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = PACK(ARRAY, MASK[,VECTOR])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of any type. +@item @var{MASK} @tab Shall be an array of type @code{LOGICAL} and +of the same size as @var{ARRAY}. Alternatively, it may be a @code{LOGICAL} +scalar. +@item @var{VECTOR} @tab (Optional) shall be an array of the same type +as @var{ARRAY} and of rank one. If present, the number of elements in +@var{VECTOR} shall be equal to or greater than the number of true elements +in @var{MASK}. If @var{MASK} is scalar, the number of elements in +@var{VECTOR} shall be equal to or greater than the number of elements in +@var{ARRAY}. +@end multitable + +@item @emph{Return value}: +The result is an array of rank one and the same type as that of @var{ARRAY}. +If @var{VECTOR} is present, the result size is that of @var{VECTOR}, the +number of @code{TRUE} values in @var{MASK} otherwise. + +@item @emph{Example}: +Gathering nonzero elements from an array: +@smallexample +PROGRAM test_pack_1 + INTEGER :: m(6) + m = (/ 1, 0, 0, 0, 5, 0 /) + WRITE(*, FMT="(6(I0, ' '))") pack(m, m /= 0) ! "1 5" +END PROGRAM +@end smallexample + +Gathering nonzero elements from an array and appending elements from @var{VECTOR}: +@smallexample +PROGRAM test_pack_2 + INTEGER :: m(4) + m = (/ 1, 0, 0, 2 /) + ! The following results in "1 2 3 4" + WRITE(*, FMT="(4(I0, ' '))") pack(m, m /= 0, (/ 0, 0, 3, 4 /)) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{UNPACK} +@end table + + + +@node PARITY +@section @code{PARITY} --- Reduction with exclusive OR +@fnindex PARITY +@cindex Parity +@cindex Reduction, XOR +@cindex XOR reduction + +@table @asis +@item @emph{Description}: +Calculates the parity, i.e. the reduction using @code{.XOR.}, +of @var{MASK} along dimension @var{DIM}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = PARITY(MASK[, DIM])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{MASK} @tab Shall be an array of type @code{LOGICAL} +@item @var{DIM} @tab (Optional) shall be a scalar of type +@code{INTEGER} with a value in the range from 1 to n, where n +equals the rank of @var{MASK}. +@end multitable + +@item @emph{Return value}: +The result is of the same type as @var{MASK}. + +If @var{DIM} is absent, a scalar with the parity of all elements in +@var{MASK} is returned, i.e. true if an odd number of elements is +@code{.true.} and false otherwise. If @var{DIM} is present, an array +of rank @math{n-1}, where @math{n} equals the rank of @var{ARRAY}, +and a shape similar to that of @var{MASK} with dimension @var{DIM} +dropped is returned. + +@item @emph{Example}: +@smallexample +PROGRAM test_sum + LOGICAL :: x(2) = [ .true., .false. ] + print *, PARITY(x) ! prints "T" (true). +END PROGRAM +@end smallexample +@end table + + + +@node PERROR +@section @code{PERROR} --- Print system error message +@fnindex PERROR +@cindex system, error handling + +@table @asis +@item @emph{Description}: +Prints (on the C @code{stderr} stream) a newline-terminated error +message corresponding to the last system error. This is prefixed by +@var{STRING}, a colon and a space. See @code{perror(3)}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL PERROR(STRING)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab A scalar of type @code{CHARACTER} and of the +default kind. +@end multitable + +@item @emph{See also}: +@ref{IERRNO} +@end table + + + +@node POPCNT +@section @code{POPCNT} --- Number of bits set +@fnindex POPCNT +@cindex binary representation +@cindex bits set + +@table @asis +@item @emph{Description}: +@code{POPCNT(I)} returns the number of bits set ('1' bits) in the binary +representation of @code{I}. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = POPCNT(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the default integer +kind. + +@item @emph{Example}: +@smallexample +program test_population + print *, popcnt(127), poppar(127) + print *, popcnt(huge(0_4)), poppar(huge(0_4)) + print *, popcnt(huge(0_8)), poppar(huge(0_8)) +end program test_population +@end smallexample +@item @emph{See also}: +@ref{POPPAR}, @gol +@ref{LEADZ}, @gol +@ref{TRAILZ} +@end table + + + +@node POPPAR +@section @code{POPPAR} --- Parity of the number of bits set +@fnindex POPPAR +@cindex binary representation +@cindex parity + +@table @asis +@item @emph{Description}: +@code{POPPAR(I)} returns parity of the integer @code{I}, i.e. the parity +of the number of bits set ('1' bits) in the binary representation of +@code{I}. It is equal to 0 if @code{I} has an even number of bits set, +and 1 for an odd number of '1' bits. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = POPPAR(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the default integer +kind. + +@item @emph{Example}: +@smallexample +program test_population + print *, popcnt(127), poppar(127) + print *, popcnt(huge(0_4)), poppar(huge(0_4)) + print *, popcnt(huge(0_8)), poppar(huge(0_8)) +end program test_population +@end smallexample +@item @emph{See also}: +@ref{POPCNT}, @gol +@ref{LEADZ}, @gol +@ref{TRAILZ} +@end table + + + +@node PRECISION +@section @code{PRECISION} --- Decimal precision of a real kind +@fnindex PRECISION +@cindex model representation, precision + +@table @asis +@item @emph{Description}: +@code{PRECISION(X)} returns the decimal precision in the model of the +type of @code{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = PRECISION(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL} or @code{COMPLEX}. It may +be scalar or valued. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the default integer +kind. + +@item @emph{Example}: +@smallexample +program prec_and_range + real(kind=4) :: x(2) + complex(kind=8) :: y + + print *, precision(x), range(x) + print *, precision(y), range(y) +end program prec_and_range +@end smallexample +@item @emph{See also}: +@ref{SELECTED_REAL_KIND}, @gol +@ref{RANGE} +@end table + + + +@node PRESENT +@section @code{PRESENT} --- Determine whether an optional dummy argument is specified +@fnindex PRESENT + +@table @asis +@item @emph{Description}: +Determines whether an optional dummy argument is present. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = PRESENT(A)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab May be of any type and may be a pointer, scalar or array +value, or a dummy procedure. It shall be the name of an optional dummy argument +accessible within the current subroutine or function. +@end multitable + +@item @emph{Return value}: +Returns either @code{TRUE} if the optional argument @var{A} is present, or +@code{FALSE} otherwise. + +@item @emph{Example}: +@smallexample +PROGRAM test_present + WRITE(*,*) f(), f(42) ! "F T" +CONTAINS + LOGICAL FUNCTION f(x) + INTEGER, INTENT(IN), OPTIONAL :: x + f = PRESENT(x) + END FUNCTION +END PROGRAM +@end smallexample +@end table + + + +@node PRODUCT +@section @code{PRODUCT} --- Product of array elements +@fnindex PRODUCT +@cindex array, product +@cindex array, multiply elements +@cindex array, conditionally multiply elements +@cindex multiply array elements + +@table @asis +@item @emph{Description}: +Multiplies the elements of @var{ARRAY} along dimension @var{DIM} if +the corresponding element in @var{MASK} is @code{TRUE}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = PRODUCT(ARRAY[, MASK])} +@item @code{RESULT = PRODUCT(ARRAY, DIM[, MASK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER}, +@code{REAL} or @code{COMPLEX}. +@item @var{DIM} @tab (Optional) shall be a scalar of type +@code{INTEGER} with a value in the range from 1 to n, where n +equals the rank of @var{ARRAY}. +@item @var{MASK} @tab (Optional) shall be of type @code{LOGICAL} +and either be a scalar or an array of the same shape as @var{ARRAY}. +@end multitable + +@item @emph{Return value}: +The result is of the same type as @var{ARRAY}. + +If @var{DIM} is absent, a scalar with the product of all elements in +@var{ARRAY} is returned. Otherwise, an array of rank n-1, where n equals +the rank of @var{ARRAY}, and a shape similar to that of @var{ARRAY} with +dimension @var{DIM} dropped is returned. + + +@item @emph{Example}: +@smallexample +PROGRAM test_product + INTEGER :: x(5) = (/ 1, 2, 3, 4 ,5 /) + print *, PRODUCT(x) ! all elements, product = 120 + print *, PRODUCT(x, MASK=MOD(x, 2)==1) ! odd elements, product = 15 +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{SUM} +@end table + + + +@node RADIX +@section @code{RADIX} --- Base of a model number +@fnindex RADIX +@cindex model representation, base +@cindex model representation, radix + +@table @asis +@item @emph{Description}: +@code{RADIX(X)} returns the base of the model representing the entity @var{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = RADIX(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{INTEGER} or @code{REAL} +@end multitable + +@item @emph{Return value}: +The return value is a scalar of type @code{INTEGER} and of the default +integer kind. + +@item @emph{Example}: +@smallexample +program test_radix + print *, "The radix for the default integer kind is", radix(0) + print *, "The radix for the default real kind is", radix(0.0) +end program test_radix +@end smallexample +@item @emph{See also}: +@ref{SELECTED_REAL_KIND} +@end table + + + +@node RAN +@section @code{RAN} --- Real pseudo-random number +@fnindex RAN +@cindex random number generation + +@table @asis +@item @emph{Description}: +For compatibility with HP FORTRAN 77/iX, the @code{RAN} intrinsic is +provided as an alias for @code{RAND}. See @ref{RAND} for complete +documentation. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{See also}: +@ref{RAND}, @gol +@ref{RANDOM_NUMBER} +@end table + + + +@node RAND +@section @code{RAND} --- Real pseudo-random number +@fnindex RAND +@cindex random number generation + +@table @asis +@item @emph{Description}: +@code{RAND(FLAG)} returns a pseudo-random number from a uniform +distribution between 0 and 1. If @var{FLAG} is 0, the next number +in the current sequence is returned; if @var{FLAG} is 1, the generator +is restarted by @code{CALL SRAND(0)}; if @var{FLAG} has any other value, +it is used as a new seed with @code{SRAND}. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. It implements a simple modulo generator as provided +by @command{g77}. For new code, one should consider the use of +@ref{RANDOM_NUMBER} as it implements a superior algorithm. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = RAND(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be a scalar @code{INTEGER} of kind 4. +@end multitable + +@item @emph{Return value}: +The return value is of @code{REAL} type and the default kind. + +@item @emph{Example}: +@smallexample +program test_rand + integer,parameter :: seed = 86456 + + call srand(seed) + print *, rand(), rand(), rand(), rand() + print *, rand(seed), rand(), rand(), rand() +end program test_rand +@end smallexample + +@item @emph{See also}: +@ref{SRAND}, @gol +@ref{RANDOM_NUMBER} + +@end table + + +@node RANDOM_INIT +@section @code{RANDOM_INIT} --- Initialize a pseudo-random number generator +@fnindex RANDOM_INIT +@cindex random number generation, initialization + +@table @asis +@item @emph{Description}: +Initializes the state of the pseudorandom number generator used by +@code{RANDOM_NUMBER}. + +@item @emph{Standard}: +Fortran 2018 + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL RANDOM_INIT(REPEATABLE, IMAGE_DISTINCT)} + +@item @emph{Arguments}: +@multitable @columnfractions .25 .70 +@item @var{REPEATABLE} @tab Shall be a scalar with a @code{LOGICAL} type, +and it is @code{INTENT(IN)}. If it is @code{.true.}, the seed is set to +a processor-dependent value that is the same each time @code{RANDOM_INIT} +is called from the same image. The term ``same image'' means a single +instance of program execution. The sequence of random numbers is different +for repeated execution of the program. If it is @code{.false.}, the seed +is set to a processor-dependent value. +@item @var{IMAGE_DISTINCT} @tab Shall be a scalar with a +@code{LOGICAL} type, and it is @code{INTENT(IN)}. If it is @code{.true.}, +the seed is set to a processor-dependent value that is distinct from th +seed set by a call to @code{RANDOM_INIT} in another image. If it is +@code{.false.}, the seed is set to a value that does depend which image called +@code{RANDOM_INIT}. +@end multitable + +@item @emph{Example}: +@smallexample +program test_random_seed + implicit none + real x(3), y(3) + call random_init(.true., .true.) + call random_number(x) + call random_init(.true., .true.) + call random_number(y) + ! x and y are the same sequence + if (any(x /= y)) call abort +end program test_random_seed +@end smallexample + +@item @emph{See also}: +@ref{RANDOM_NUMBER}, @gol +@ref{RANDOM_SEED} +@end table + + +@node RANDOM_NUMBER +@section @code{RANDOM_NUMBER} --- Pseudo-random number +@fnindex RANDOM_NUMBER +@cindex random number generation + +@table @asis +@item @emph{Description}: +Returns a single pseudorandom number or an array of pseudorandom numbers +from the uniform distribution over the range @math{ 0 \leq x < 1}. + +The runtime-library implements the xoshiro256** pseudorandom number +generator (PRNG). This generator has a period of @math{2^{256} - 1}, +and when using multiple threads up to @math{2^{128}} threads can each +generate @math{2^{128}} random numbers before any aliasing occurs. + +Note that in a multi-threaded program (e.g. using OpenMP directives), +each thread will have its own random number state. For details of the +seeding procedure, see the documentation for the @code{RANDOM_SEED} +intrinsic. + + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL RANDOM_NUMBER(HARVEST)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{HARVEST} @tab Shall be a scalar or an array of type @code{REAL}. +@end multitable + +@item @emph{Example}: +@smallexample +program test_random_number + REAL :: r(5,5) + CALL RANDOM_NUMBER(r) +end program +@end smallexample + +@item @emph{See also}: +@ref{RANDOM_SEED}, @gol +@ref{RANDOM_INIT} +@end table + + + +@node RANDOM_SEED +@section @code{RANDOM_SEED} --- Initialize a pseudo-random number sequence +@fnindex RANDOM_SEED +@cindex random number generation, seeding +@cindex seeding a random number generator + +@table @asis +@item @emph{Description}: +Restarts or queries the state of the pseudorandom number generator used by +@code{RANDOM_NUMBER}. + +If @code{RANDOM_SEED} is called without arguments, it is seeded with +random data retrieved from the operating system. + +As an extension to the Fortran standard, the GFortran +@code{RANDOM_NUMBER} supports multiple threads. Each thread in a +multi-threaded program has its own seed. When @code{RANDOM_SEED} is +called either without arguments or with the @var{PUT} argument, the +given seed is copied into a master seed as well as the seed of the +current thread. When a new thread uses @code{RANDOM_NUMBER} for the +first time, the seed is copied from the master seed, and forwarded +@math{N * 2^{128}} steps to guarantee that the random stream does not +alias any other stream in the system, where @var{N} is the number of +threads that have used @code{RANDOM_NUMBER} so far during the program +execution. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL RANDOM_SEED([SIZE, PUT, GET])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SIZE} @tab (Optional) Shall be a scalar and of type default +@code{INTEGER}, with @code{INTENT(OUT)}. It specifies the minimum size +of the arrays used with the @var{PUT} and @var{GET} arguments. +@item @var{PUT} @tab (Optional) Shall be an array of type default +@code{INTEGER} and rank one. It is @code{INTENT(IN)} and the size of +the array must be larger than or equal to the number returned by the +@var{SIZE} argument. +@item @var{GET} @tab (Optional) Shall be an array of type default +@code{INTEGER} and rank one. It is @code{INTENT(OUT)} and the size +of the array must be larger than or equal to the number returned by +the @var{SIZE} argument. +@end multitable + +@item @emph{Example}: +@smallexample +program test_random_seed + implicit none + integer, allocatable :: seed(:) + integer :: n + + call random_seed(size = n) + allocate(seed(n)) + call random_seed(get=seed) + write (*, *) seed +end program test_random_seed +@end smallexample + +@item @emph{See also}: +@ref{RANDOM_NUMBER}, @gol +@ref{RANDOM_INIT} +@end table + + + +@node RANGE +@section @code{RANGE} --- Decimal exponent range +@fnindex RANGE +@cindex model representation, range + +@table @asis +@item @emph{Description}: +@code{RANGE(X)} returns the decimal exponent range in the model of the +type of @code{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = RANGE(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{INTEGER}, @code{REAL} +or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the default integer +kind. + +@item @emph{Example}: +See @code{PRECISION} for an example. +@item @emph{See also}: +@ref{SELECTED_REAL_KIND}, @gol +@ref{PRECISION} +@end table + + + +@node RANK +@section @code{RANK} --- Rank of a data object +@fnindex RANK +@cindex rank + +@table @asis +@item @emph{Description}: +@code{RANK(A)} returns the rank of a scalar or array data object. + +@item @emph{Standard}: +Technical Specification (TS) 29113 + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = RANK(A)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab can be of any type +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the default integer +kind. For arrays, their rank is returned; for scalars zero is returned. + +@item @emph{Example}: +@smallexample +program test_rank + integer :: a + real, allocatable :: b(:,:) + + print *, rank(a), rank(b) ! Prints: 0 2 +end program test_rank +@end smallexample + +@end table + + + +@node REAL +@section @code{REAL} --- Convert to real type +@fnindex REAL +@fnindex REALPART +@fnindex FLOAT +@fnindex DFLOAT +@fnindex FLOATI +@fnindex FLOATJ +@fnindex FLOATK +@fnindex SNGL +@cindex conversion, to real +@cindex complex numbers, real part + +@table @asis +@item @emph{Description}: +@code{REAL(A [, KIND])} converts its argument @var{A} to a real type. The +@code{REALPART} function is provided for compatibility with @command{g77}, +and its use is strongly discouraged. + +@item @emph{Standard}: +Fortran 77 and later, with @var{KIND} argument Fortran 90 and later, has GNU extensions + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = REAL(A [, KIND])} +@item @code{RESULT = REALPART(Z)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be @code{INTEGER}, @code{REAL}, or +@code{COMPLEX}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +These functions return a @code{REAL} variable or array under +the following rules: + +@table @asis +@item (A) +@code{REAL(A)} is converted to a default real type if @var{A} is an +integer or real variable. +@item (B) +@code{REAL(A)} is converted to a real type with the kind type parameter +of @var{A} if @var{A} is a complex variable. +@item (C) +@code{REAL(A, KIND)} is converted to a real type with kind type +parameter @var{KIND} if @var{A} is a complex, integer, or real +variable. +@end table + +@item @emph{Example}: +@smallexample +program test_real + complex :: x = (1.0, 2.0) + print *, real(x), real(x,8), realpart(x) +end program test_real +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{FLOAT(A)} @tab @code{INTEGER(4)} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DFLOAT(A)} @tab @code{INTEGER(4)} @tab @code{REAL(8)} @tab GNU extension +@item @code{FLOATI(A)} @tab @code{INTEGER(2)} @tab @code{REAL(4)} @tab GNU extension (-fdec) +@item @code{FLOATJ(A)} @tab @code{INTEGER(4)} @tab @code{REAL(4)} @tab GNU extension (-fdec) +@item @code{FLOATK(A)} @tab @code{INTEGER(8)} @tab @code{REAL(4)} @tab GNU extension (-fdec) +@item @code{SNGL(A)} @tab @code{REAL(8)} @tab @code{REAL(4)} @tab Fortran 77 and later +@end multitable + + +@item @emph{See also}: +@ref{DBLE} + +@end table + + + +@node RENAME +@section @code{RENAME} --- Rename a file +@fnindex RENAME +@cindex file system, rename file + +@table @asis +@item @emph{Description}: +Renames a file from file @var{PATH1} to @var{PATH2}. A null +character (@code{CHAR(0)}) can be used to mark the end of the names in +@var{PATH1} and @var{PATH2}; otherwise, trailing blanks in the file +names are ignored. If the @var{STATUS} argument is supplied, it +contains 0 on success or a nonzero error code upon return; see +@code{rename(2)}. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL RENAME(PATH1, PATH2 [, STATUS])} +@item @code{STATUS = RENAME(PATH1, PATH2)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{PATH1} @tab Shall be of default @code{CHARACTER} type. +@item @var{PATH2} @tab Shall be of default @code{CHARACTER} type. +@item @var{STATUS} @tab (Optional) Shall be of default @code{INTEGER} type. +@end multitable + +@item @emph{See also}: +@ref{LINK} + +@end table + + + +@node REPEAT +@section @code{REPEAT} --- Repeated string concatenation +@fnindex REPEAT +@cindex string, repeat +@cindex string, concatenate + +@table @asis +@item @emph{Description}: +Concatenates @var{NCOPIES} copies of a string. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = REPEAT(STRING, NCOPIES)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab Shall be scalar and of type @code{CHARACTER}. +@item @var{NCOPIES} @tab Shall be scalar and of type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +A new scalar of type @code{CHARACTER} built up from @var{NCOPIES} copies +of @var{STRING}. + +@item @emph{Example}: +@smallexample +program test_repeat + write(*,*) repeat("x", 5) ! "xxxxx" +end program +@end smallexample +@end table + + + +@node RESHAPE +@section @code{RESHAPE} --- Function to reshape an array +@fnindex RESHAPE +@cindex array, change dimensions +@cindex array, transmogrify + +@table @asis +@item @emph{Description}: +Reshapes @var{SOURCE} to correspond to @var{SHAPE}. If necessary, +the new array may be padded with elements from @var{PAD} or permuted +as defined by @var{ORDER}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = RESHAPE(SOURCE, SHAPE[, PAD, ORDER])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SOURCE} @tab Shall be an array of any type. +@item @var{SHAPE} @tab Shall be of type @code{INTEGER} and an +array of rank one. Its values must be positive or zero. +@item @var{PAD} @tab (Optional) shall be an array of the same +type as @var{SOURCE}. +@item @var{ORDER} @tab (Optional) shall be of type @code{INTEGER} +and an array of the same shape as @var{SHAPE}. Its values shall +be a permutation of the numbers from 1 to n, where n is the size of +@var{SHAPE}. If @var{ORDER} is absent, the natural ordering shall +be assumed. +@end multitable + +@item @emph{Return value}: +The result is an array of shape @var{SHAPE} with the same type as +@var{SOURCE}. + +@item @emph{Example}: +@smallexample +PROGRAM test_reshape + INTEGER, DIMENSION(4) :: x + WRITE(*,*) SHAPE(x) ! prints "4" + WRITE(*,*) SHAPE(RESHAPE(x, (/2, 2/))) ! prints "2 2" +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{SHAPE} +@end table + + + +@node RRSPACING +@section @code{RRSPACING} --- Reciprocal of the relative spacing +@fnindex RRSPACING +@cindex real number, relative spacing +@cindex floating point, relative spacing + + +@table @asis +@item @emph{Description}: +@code{RRSPACING(X)} returns the reciprocal of the relative spacing of +model numbers near @var{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = RRSPACING(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +The value returned is equal to +@code{ABS(FRACTION(X)) * FLOAT(RADIX(X))**DIGITS(X)}. + +@item @emph{See also}: +@ref{SPACING} +@end table + + + +@node RSHIFT +@section @code{RSHIFT} --- Right shift bits +@fnindex RSHIFT +@cindex bits, shift right + +@table @asis +@item @emph{Description}: +@code{RSHIFT} returns a value corresponding to @var{I} with all of the +bits shifted right by @var{SHIFT} places. @var{SHIFT} shall be +nonnegative and less than or equal to @code{BIT_SIZE(I)}, otherwise +the result value is undefined. Bits shifted out from the right end +are lost. The fill is arithmetic: the bits shifted in from the left +end are equal to the leftmost bit, which in two's complement +representation is the sign bit. + +This function has been superseded by the @code{SHIFTA} intrinsic, which +is standard in Fortran 2008 and later. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = RSHIFT(I, SHIFT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{See also}: +@ref{ISHFT}, @gol +@ref{ISHFTC}, @gol +@ref{LSHIFT}, @gol +@ref{SHIFTA}, @gol +@ref{SHIFTR}, @gol +@ref{SHIFTL} + +@end table + + + +@node SAME_TYPE_AS +@section @code{SAME_TYPE_AS} --- Query dynamic types for equality +@fnindex SAME_TYPE_AS + +@table @asis +@item @emph{Description}: +Query dynamic types for equality. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = SAME_TYPE_AS(A, B)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be an object of extensible declared type or +unlimited polymorphic. +@item @var{B} @tab Shall be an object of extensible declared type or +unlimited polymorphic. +@end multitable + +@item @emph{Return value}: +The return value is a scalar of type default logical. It is true if and +only if the dynamic type of A is the same as the dynamic type of B. + +@item @emph{See also}: +@ref{EXTENDS_TYPE_OF} + +@end table + + + +@node SCALE +@section @code{SCALE} --- Scale a real value +@fnindex SCALE +@cindex real number, scale +@cindex floating point, scale + +@table @asis +@item @emph{Description}: +@code{SCALE(X,I)} returns @code{X * RADIX(X)**I}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SCALE(X, I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type of the argument shall be a @code{REAL}. +@item @var{I} @tab The type of the argument shall be a @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +Its value is @code{X * RADIX(X)**I}. + +@item @emph{Example}: +@smallexample +program test_scale + real :: x = 178.1387e-4 + integer :: i = 5 + print *, scale(x,i), x*radix(x)**i +end program test_scale +@end smallexample + +@end table + + + +@node SCAN +@section @code{SCAN} --- Scan a string for the presence of a set of characters +@fnindex SCAN +@cindex string, find subset + +@table @asis +@item @emph{Description}: +Scans a @var{STRING} for any of the characters in a @var{SET} +of characters. + +If @var{BACK} is either absent or equals @code{FALSE}, this function +returns the position of the leftmost character of @var{STRING} that is +in @var{SET}. If @var{BACK} equals @code{TRUE}, the rightmost position +is returned. If no character of @var{SET} is found in @var{STRING}, the +result is zero. + +@item @emph{Standard}: +Fortran 90 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SCAN(STRING, SET[, BACK [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab Shall be of type @code{CHARACTER}. +@item @var{SET} @tab Shall be of type @code{CHARACTER}. +@item @var{BACK} @tab (Optional) shall be of type @code{LOGICAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. + +@item @emph{Example}: +@smallexample +PROGRAM test_scan + WRITE(*,*) SCAN("FORTRAN", "AO") ! 2, found 'O' + WRITE(*,*) SCAN("FORTRAN", "AO", .TRUE.) ! 6, found 'A' + WRITE(*,*) SCAN("FORTRAN", "C++") ! 0, found none +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{INDEX intrinsic}, @gol +@ref{VERIFY} +@end table + + + +@node SECNDS +@section @code{SECNDS} --- Time function +@fnindex SECNDS +@cindex time, elapsed +@cindex elapsed time + +@table @asis +@item @emph{Description}: +@code{SECNDS(X)} gets the time in seconds from the real-time system clock. +@var{X} is a reference time, also in seconds. If this is zero, the time in +seconds from midnight is returned. This function is non-standard and its +use is discouraged. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = SECNDS (X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{T} @tab Shall be of type @code{REAL(4)}. +@item @var{X} @tab Shall be of type @code{REAL(4)}. +@end multitable + +@item @emph{Return value}: +None + +@item @emph{Example}: +@smallexample +program test_secnds + integer :: i + real(4) :: t1, t2 + print *, secnds (0.0) ! seconds since midnight + t1 = secnds (0.0) ! reference time + do i = 1, 10000000 ! do something + end do + t2 = secnds (t1) ! elapsed time + print *, "Something took ", t2, " seconds." +end program test_secnds +@end smallexample +@end table + + + +@node SECOND +@section @code{SECOND} --- CPU time function +@fnindex SECOND +@cindex time, elapsed +@cindex elapsed time + +@table @asis +@item @emph{Description}: +Returns a @code{REAL(4)} value representing the elapsed CPU time in +seconds. This provides the same functionality as the standard +@code{CPU_TIME} intrinsic, and is only included for backwards +compatibility. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL SECOND(TIME)} +@item @code{TIME = SECOND()} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{TIME} @tab Shall be of type @code{REAL(4)}. +@end multitable + +@item @emph{Return value}: +In either syntax, @var{TIME} is set to the process's current runtime in +seconds. + +@item @emph{See also}: +@ref{CPU_TIME} + +@end table + + + +@node SELECTED_CHAR_KIND +@section @code{SELECTED_CHAR_KIND} --- Choose character kind +@fnindex SELECTED_CHAR_KIND +@cindex character kind +@cindex kind, character + +@table @asis +@item @emph{Description}: + +@code{SELECTED_CHAR_KIND(NAME)} returns the kind value for the character +set named @var{NAME}, if a character set with such a name is supported, +or @math{-1} otherwise. Currently, supported character sets include +``ASCII'' and ``DEFAULT'', which are equivalent, and ``ISO_10646'' +(Universal Character Set, UCS-4) which is commonly known as Unicode. + +@item @emph{Standard}: +Fortran 2003 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = SELECTED_CHAR_KIND(NAME)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NAME} @tab Shall be a scalar and of the default character type. +@end multitable + +@item @emph{Example}: +@smallexample +program character_kind + use iso_fortran_env + implicit none + integer, parameter :: ascii = selected_char_kind ("ascii") + integer, parameter :: ucs4 = selected_char_kind ('ISO_10646') + + character(kind=ascii, len=26) :: alphabet + character(kind=ucs4, len=30) :: hello_world + + alphabet = ascii_"abcdefghijklmnopqrstuvwxyz" + hello_world = ucs4_'Hello World and Ni Hao -- ' & + // char (int (z'4F60'), ucs4) & + // char (int (z'597D'), ucs4) + + write (*,*) alphabet + + open (output_unit, encoding='UTF-8') + write (*,*) trim (hello_world) +end program character_kind +@end smallexample +@end table + + + +@node SELECTED_INT_KIND +@section @code{SELECTED_INT_KIND} --- Choose integer kind +@fnindex SELECTED_INT_KIND +@cindex integer kind +@cindex kind, integer + +@table @asis +@item @emph{Description}: +@code{SELECTED_INT_KIND(R)} return the kind value of the smallest integer +type that can represent all values ranging from @math{-10^R} (exclusive) +to @math{10^R} (exclusive). If there is no integer kind that accommodates +this range, @code{SELECTED_INT_KIND} returns @math{-1}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = SELECTED_INT_KIND(R)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{R} @tab Shall be a scalar and of type @code{INTEGER}. +@end multitable + +@item @emph{Example}: +@smallexample +program large_integers + integer,parameter :: k5 = selected_int_kind(5) + integer,parameter :: k15 = selected_int_kind(15) + integer(kind=k5) :: i5 + integer(kind=k15) :: i15 + + print *, huge(i5), huge(i15) + + ! The following inequalities are always true + print *, huge(i5) >= 10_k5**5-1 + print *, huge(i15) >= 10_k15**15-1 +end program large_integers +@end smallexample +@end table + + + +@node SELECTED_REAL_KIND +@section @code{SELECTED_REAL_KIND} --- Choose real kind +@fnindex SELECTED_REAL_KIND +@cindex real kind +@cindex kind, real +@cindex radix, real + +@table @asis +@item @emph{Description}: +@code{SELECTED_REAL_KIND(P,R)} returns the kind value of a real data type +with decimal precision of at least @code{P} digits, exponent range of +at least @code{R}, and with a radix of @code{RADIX}. + +@item @emph{Standard}: +Fortran 90 and later, with @code{RADIX} Fortran 2008 or later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = SELECTED_REAL_KIND([P, R, RADIX])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{P} @tab (Optional) shall be a scalar and of type @code{INTEGER}. +@item @var{R} @tab (Optional) shall be a scalar and of type @code{INTEGER}. +@item @var{RADIX} @tab (Optional) shall be a scalar and of type @code{INTEGER}. +@end multitable +Before Fortran 2008, at least one of the arguments @var{R} or @var{P} shall +be present; since Fortran 2008, they are assumed to be zero if absent. + +@item @emph{Return value}: + +@code{SELECTED_REAL_KIND} returns the value of the kind type parameter of +a real data type with decimal precision of at least @code{P} digits, a +decimal exponent range of at least @code{R}, and with the requested +@code{RADIX}. If the @code{RADIX} parameter is absent, real kinds with +any radix can be returned. If more than one real data type meet the +criteria, the kind of the data type with the smallest decimal precision +is returned. If no real data type matches the criteria, the result is +@table @asis +@item -1 if the processor does not support a real data type with a +precision greater than or equal to @code{P}, but the @code{R} and +@code{RADIX} requirements can be fulfilled +@item -2 if the processor does not support a real type with an exponent +range greater than or equal to @code{R}, but @code{P} and @code{RADIX} +are fulfillable +@item -3 if @code{RADIX} but not @code{P} and @code{R} requirements +are fulfillable +@item -4 if @code{RADIX} and either @code{P} or @code{R} requirements +are fulfillable +@item -5 if there is no real type with the given @code{RADIX} +@end table + +@item @emph{Example}: +@smallexample +program real_kinds + integer,parameter :: p6 = selected_real_kind(6) + integer,parameter :: p10r100 = selected_real_kind(10,100) + integer,parameter :: r400 = selected_real_kind(r=400) + real(kind=p6) :: x + real(kind=p10r100) :: y + real(kind=r400) :: z + + print *, precision(x), range(x) + print *, precision(y), range(y) + print *, precision(z), range(z) +end program real_kinds +@end smallexample +@item @emph{See also}: +@ref{PRECISION}, @gol +@ref{RANGE}, @gol +@ref{RADIX} +@end table + + + +@node SET_EXPONENT +@section @code{SET_EXPONENT} --- Set the exponent of the model +@fnindex SET_EXPONENT +@cindex real number, set exponent +@cindex floating point, set exponent + +@table @asis +@item @emph{Description}: +@code{SET_EXPONENT(X, I)} returns the real number whose fractional part +is that of @var{X} and whose exponent part is @var{I}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SET_EXPONENT(X, I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL}. +@item @var{I} @tab Shall be of type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X}. +The real number whose fractional part +is that of @var{X} and whose exponent part if @var{I} is returned; +it is @code{FRACTION(X) * RADIX(X)**I}. + +@item @emph{Example}: +@smallexample +PROGRAM test_setexp + REAL :: x = 178.1387e-4 + INTEGER :: i = 17 + PRINT *, SET_EXPONENT(x, i), FRACTION(x) * RADIX(x)**i +END PROGRAM +@end smallexample + +@end table + + + +@node SHAPE +@section @code{SHAPE} --- Determine the shape of an array +@fnindex SHAPE +@cindex array, shape + +@table @asis +@item @emph{Description}: +Determines the shape of an array. + +@item @emph{Standard}: +Fortran 90 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = SHAPE(SOURCE [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SOURCE} @tab Shall be an array or scalar of any type. +If @var{SOURCE} is a pointer it must be associated and allocatable +arrays must be allocated. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +An @code{INTEGER} array of rank one with as many elements as @var{SOURCE} +has dimensions. The elements of the resulting array correspond to the extend +of @var{SOURCE} along the respective dimensions. If @var{SOURCE} is a scalar, +the result is the rank one array of size zero. If @var{KIND} is absent, the +return value has the default integer kind otherwise the specified kind. + +@item @emph{Example}: +@smallexample +PROGRAM test_shape + INTEGER, DIMENSION(-1:1, -1:2) :: A + WRITE(*,*) SHAPE(A) ! (/ 3, 4 /) + WRITE(*,*) SIZE(SHAPE(42)) ! (/ /) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{RESHAPE}, @gol +@ref{SIZE} +@end table + + + +@node SHIFTA +@section @code{SHIFTA} --- Right shift with fill +@fnindex SHIFTA +@cindex bits, shift right +@cindex shift, right with fill + +@table @asis +@item @emph{Description}: +@code{SHIFTA} returns a value corresponding to @var{I} with all of the +bits shifted right by @var{SHIFT} places. @var{SHIFT} that be +nonnegative and less than or equal to @code{BIT_SIZE(I)}, otherwise +the result value is undefined. Bits shifted out from the right end +are lost. The fill is arithmetic: the bits shifted in from the left +end are equal to the leftmost bit, which in two's complement +representation is the sign bit. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SHIFTA(I, SHIFT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{See also}: +@ref{SHIFTL}, @gol +@ref{SHIFTR} +@end table + + + +@node SHIFTL +@section @code{SHIFTL} --- Left shift +@fnindex SHIFTL +@cindex bits, shift left +@cindex shift, left + +@table @asis +@item @emph{Description}: +@code{SHIFTL} returns a value corresponding to @var{I} with all of the +bits shifted left by @var{SHIFT} places. @var{SHIFT} shall be +nonnegative and less than or equal to @code{BIT_SIZE(I)}, otherwise +the result value is undefined. Bits shifted out from the left end are +lost, and bits shifted in from the right end are set to 0. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SHIFTL(I, SHIFT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{See also}: +@ref{SHIFTA}, @gol +@ref{SHIFTR} +@end table + + + +@node SHIFTR +@section @code{SHIFTR} --- Right shift +@fnindex SHIFTR +@cindex bits, shift right +@cindex shift, right + +@table @asis +@item @emph{Description}: +@code{SHIFTR} returns a value corresponding to @var{I} with all of the +bits shifted right by @var{SHIFT} places. @var{SHIFT} shall be +nonnegative and less than or equal to @code{BIT_SIZE(I)}, otherwise +the result value is undefined. Bits shifted out from the right end +are lost, and bits shifted in from the left end are set to 0. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SHIFTR(I, SHIFT)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be @code{INTEGER}. +@item @var{SHIFT} @tab The type shall be @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of the same kind as +@var{I}. + +@item @emph{See also}: +@ref{SHIFTA}, @gol +@ref{SHIFTL} +@end table + + + +@node SIGN +@section @code{SIGN} --- Sign copying function +@fnindex SIGN +@fnindex ISIGN +@fnindex DSIGN +@cindex sign copying + +@table @asis +@item @emph{Description}: +@code{SIGN(A,B)} returns the value of @var{A} with the sign of @var{B}. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SIGN(A, B)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be of type @code{INTEGER} or @code{REAL} +@item @var{B} @tab Shall be of the same type and kind as @var{A}. +@end multitable + +@item @emph{Return value}: +The kind of the return value is that of @var{A} and @var{B}. +If @math{B \ge 0} then the result is @code{ABS(A)}, else +it is @code{-ABS(A)}. + +@item @emph{Example}: +@smallexample +program test_sign + print *, sign(-12,1) + print *, sign(-12,0) + print *, sign(-12,-1) + + print *, sign(-12.,1.) + print *, sign(-12.,0.) + print *, sign(-12.,-1.) +end program test_sign +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .26 .20 .30 +@headitem Name @tab Arguments @tab Return type @tab Standard +@item @code{SIGN(A,B)} @tab @code{REAL(4) A, B} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{ISIGN(A,B)} @tab @code{INTEGER(4) A, B} @tab @code{INTEGER(4)} @tab Fortran 77 and later +@item @code{DSIGN(A,B)} @tab @code{REAL(8) A, B} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable +@end table + + + +@node SIGNAL +@section @code{SIGNAL} --- Signal handling subroutine (or function) +@fnindex SIGNAL +@cindex system, signal handling + +@table @asis +@item @emph{Description}: +@code{SIGNAL(NUMBER, HANDLER [, STATUS])} causes external subroutine +@var{HANDLER} to be executed with a single integer argument when signal +@var{NUMBER} occurs. If @var{HANDLER} is an integer, it can be used to +turn off handling of signal @var{NUMBER} or revert to its default +action. See @code{signal(2)}. + +If @code{SIGNAL} is called as a subroutine and the @var{STATUS} argument +is supplied, it is set to the value returned by @code{signal(2)}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL SIGNAL(NUMBER, HANDLER [, STATUS])} +@item @code{STATUS = SIGNAL(NUMBER, HANDLER)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NUMBER} @tab Shall be a scalar integer, with @code{INTENT(IN)} +@item @var{HANDLER}@tab Signal handler (@code{INTEGER FUNCTION} or +@code{SUBROUTINE}) or dummy/global @code{INTEGER} scalar. +@code{INTEGER}. It is @code{INTENT(IN)}. +@item @var{STATUS} @tab (Optional) @var{STATUS} shall be a scalar +integer. It has @code{INTENT(OUT)}. +@end multitable +@c TODO: What should the interface of the handler be? Does it take arguments? + +@item @emph{Return value}: +The @code{SIGNAL} function returns the value returned by @code{signal(2)}. + +@item @emph{Example}: +@smallexample +program test_signal + intrinsic signal + external handler_print + + call signal (12, handler_print) + call signal (10, 1) + + call sleep (30) +end program test_signal +@end smallexample +@end table + + + +@node SIN +@section @code{SIN} --- Sine function +@fnindex SIN +@fnindex DSIN +@fnindex CSIN +@fnindex ZSIN +@fnindex CDSIN +@cindex trigonometric function, sine +@cindex sine + +@table @asis +@item @emph{Description}: +@code{SIN(X)} computes the sine of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SIN(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or +@code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_sin + real :: x = 0.0 + x = sin(x) +end program test_sin +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{SIN(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DSIN(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@item @code{CSIN(X)} @tab @code{COMPLEX(4) X} @tab @code{COMPLEX(4)} @tab Fortran 77 and later +@item @code{ZSIN(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@item @code{CDSIN(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{ASIN} @gol +Degrees function: @gol +@ref{SIND} +@end table + + + +@node SIND +@section @code{SIND} --- Sine function, degrees +@fnindex SIND +@fnindex DSIND +@fnindex CSIND +@fnindex ZSIND +@fnindex CDSIND +@cindex trigonometric function, sine, degrees +@cindex sine, degrees + +@table @asis +@item @emph{Description}: +@code{SIND(X)} computes the sine of @var{X} in degrees. + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math}. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SIND(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or +@code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}, and its value is in degrees. + +@item @emph{Example}: +@smallexample +program test_sind + real :: x = 0.0 + x = sind(x) +end program test_sind +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{SIND(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DSIND(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@item @code{CSIND(X)} @tab @code{COMPLEX(4) X} @tab @code{COMPLEX(4)} @tab GNU extension +@item @code{ZSIND(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@item @code{CDSIND(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{ASIND} @gol +Radians function: @gol +@ref{SIN} @gol +@end table + + + +@node SINH +@section @code{SINH} --- Hyperbolic sine function +@fnindex SINH +@fnindex DSINH +@cindex hyperbolic sine +@cindex hyperbolic function, sine +@cindex sine, hyperbolic + +@table @asis +@item @emph{Description}: +@code{SINH(X)} computes the hyperbolic sine of @var{X}. + +@item @emph{Standard}: +Fortran 90 and later, for a complex argument Fortran 2008 or later, has +a GNU extension + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SINH(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}. + +@item @emph{Example}: +@smallexample +program test_sinh + real(8) :: x = - 1.0_8 + x = sinh(x) +end program test_sinh +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{DSINH(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 90 and later +@end multitable + +@item @emph{See also}: +@ref{ASINH} +@end table + + + +@node SIZE +@section @code{SIZE} --- Determine the size of an array +@fnindex SIZE +@cindex array, size +@cindex array, number of elements +@cindex array, count elements + +@table @asis +@item @emph{Description}: +Determine the extent of @var{ARRAY} along a specified dimension @var{DIM}, +or the total number of elements in @var{ARRAY} if @var{DIM} is absent. + +@item @emph{Standard}: +Fortran 90 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = SIZE(ARRAY[, DIM [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of any type. If @var{ARRAY} is +a pointer it must be associated and allocatable arrays must be allocated. +@item @var{DIM} @tab (Optional) shall be a scalar of type @code{INTEGER} +and its value shall be in the range from 1 to n, where n equals the rank +of @var{ARRAY}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. + +@item @emph{Example}: +@smallexample +PROGRAM test_size + WRITE(*,*) SIZE((/ 1, 2 /)) ! 2 +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{SHAPE}, @gol +@ref{RESHAPE} +@end table + + +@node SIZEOF +@section @code{SIZEOF} --- Size in bytes of an expression +@fnindex SIZEOF +@cindex expression size +@cindex size of an expression + +@table @asis +@item @emph{Description}: +@code{SIZEOF(X)} calculates the number of bytes of storage the +expression @code{X} occupies. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{N = SIZEOF(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The argument shall be of any type, rank or shape. +@end multitable + +@item @emph{Return value}: +The return value is of type integer and of the system-dependent kind +@var{C_SIZE_T} (from the @var{ISO_C_BINDING} module). Its value is the +number of bytes occupied by the argument. If the argument has the +@code{POINTER} attribute, the number of bytes of the storage area pointed +to is returned. If the argument is of a derived type with @code{POINTER} +or @code{ALLOCATABLE} components, the return value does not account for +the sizes of the data pointed to by these components. If the argument is +polymorphic, the size according to the dynamic type is returned. The argument +may not be a procedure or procedure pointer. Note that the code assumes for +arrays that those are contiguous; for contiguous arrays, it returns the +storage or an array element multiplied by the size of the array. + +@item @emph{Example}: +@smallexample + integer :: i + real :: r, s(5) + print *, (sizeof(s)/sizeof(r) == 5) + end +@end smallexample +The example will print @code{.TRUE.} unless you are using a platform +where default @code{REAL} variables are unusually padded. + +@item @emph{See also}: +@ref{C_SIZEOF}, @gol +@ref{STORAGE_SIZE} +@end table + + +@node SLEEP +@section @code{SLEEP} --- Sleep for the specified number of seconds +@fnindex SLEEP +@cindex delayed execution + +@table @asis +@item @emph{Description}: +Calling this subroutine causes the process to pause for @var{SECONDS} seconds. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL SLEEP(SECONDS)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SECONDS} @tab The type shall be of default @code{INTEGER}. +@end multitable + +@item @emph{Example}: +@smallexample +program test_sleep + call sleep(5) +end +@end smallexample +@end table + + + +@node SPACING +@section @code{SPACING} --- Smallest distance between two numbers of a given type +@fnindex SPACING +@cindex real number, relative spacing +@cindex floating point, relative spacing + +@table @asis +@item @emph{Description}: +Determines the distance between the argument @var{X} and the nearest +adjacent number of the same type. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SPACING(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL}. +@end multitable + +@item @emph{Return value}: +The result is of the same type as the input argument @var{X}. + +@item @emph{Example}: +@smallexample +PROGRAM test_spacing + INTEGER, PARAMETER :: SGL = SELECTED_REAL_KIND(p=6, r=37) + INTEGER, PARAMETER :: DBL = SELECTED_REAL_KIND(p=13, r=200) + + WRITE(*,*) spacing(1.0_SGL) ! "1.1920929E-07" on i686 + WRITE(*,*) spacing(1.0_DBL) ! "2.220446049250313E-016" on i686 +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{RRSPACING} +@end table + + + +@node SPREAD +@section @code{SPREAD} --- Add a dimension to an array +@fnindex SPREAD +@cindex array, increase dimension +@cindex array, duplicate elements +@cindex array, duplicate dimensions + +@table @asis +@item @emph{Description}: +Replicates a @var{SOURCE} array @var{NCOPIES} times along a specified +dimension @var{DIM}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = SPREAD(SOURCE, DIM, NCOPIES)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SOURCE} @tab Shall be a scalar or an array of any type and +a rank less than seven. +@item @var{DIM} @tab Shall be a scalar of type @code{INTEGER} with a +value in the range from 1 to n+1, where n equals the rank of @var{SOURCE}. +@item @var{NCOPIES} @tab Shall be a scalar of type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The result is an array of the same type as @var{SOURCE} and has rank n+1 +where n equals the rank of @var{SOURCE}. + +@item @emph{Example}: +@smallexample +PROGRAM test_spread + INTEGER :: a = 1, b(2) = (/ 1, 2 /) + WRITE(*,*) SPREAD(A, 1, 2) ! "1 1" + WRITE(*,*) SPREAD(B, 1, 2) ! "1 1 2 2" +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{UNPACK} +@end table + + + +@node SQRT +@section @code{SQRT} --- Square-root function +@fnindex SQRT +@fnindex DSQRT +@fnindex CSQRT +@fnindex ZSQRT +@fnindex CDSQRT +@cindex root +@cindex square-root + +@table @asis +@item @emph{Description}: +@code{SQRT(X)} computes the square root of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = SQRT(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or +@code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{REAL} or @code{COMPLEX}. +The kind type parameter is the same as @var{X}. + +@item @emph{Example}: +@smallexample +program test_sqrt + real(8) :: x = 2.0_8 + complex :: z = (1.0, 2.0) + x = sqrt(x) + z = sqrt(z) +end program test_sqrt +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{SQRT(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DSQRT(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@item @code{CSQRT(X)} @tab @code{COMPLEX(4) X} @tab @code{COMPLEX(4)} @tab Fortran 77 and later +@item @code{ZSQRT(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@item @code{CDSQRT(X)} @tab @code{COMPLEX(8) X} @tab @code{COMPLEX(8)} @tab GNU extension +@end multitable +@end table + + + +@node SRAND +@section @code{SRAND} --- Reinitialize the random number generator +@fnindex SRAND +@cindex random number generation, seeding +@cindex seeding a random number generator + +@table @asis +@item @emph{Description}: +@code{SRAND} reinitializes the pseudo-random number generator +called by @code{RAND} and @code{IRAND}. The new seed used by the +generator is specified by the required argument @var{SEED}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL SRAND(SEED)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SEED} @tab Shall be a scalar @code{INTEGER(kind=4)}. +@end multitable + +@item @emph{Return value}: +Does not return anything. + +@item @emph{Example}: +See @code{RAND} and @code{IRAND} for examples. + +@item @emph{Notes}: +The Fortran standard specifies the intrinsic subroutines +@code{RANDOM_SEED} to initialize the pseudo-random number +generator and @code{RANDOM_NUMBER} to generate pseudo-random numbers. +These subroutines should be used in new codes. + +Please note that in GNU Fortran, these two sets of intrinsics (@code{RAND}, +@code{IRAND} and @code{SRAND} on the one hand, @code{RANDOM_NUMBER} and +@code{RANDOM_SEED} on the other hand) access two independent +pseudo-random number generators. + +@item @emph{See also}: +@ref{RAND}, @gol +@ref{RANDOM_SEED}, @gol +@ref{RANDOM_NUMBER} +@end table + + + +@node STAT +@section @code{STAT} --- Get file status +@fnindex STAT +@cindex file system, file status + +@table @asis +@item @emph{Description}: +This function returns information about a file. No permissions are required on +the file itself, but execute (search) permission is required on all of the +directories in path that lead to the file. + +The elements that are obtained and stored in the array @code{VALUES}: +@multitable @columnfractions .15 .70 +@item @code{VALUES(1)} @tab Device ID +@item @code{VALUES(2)} @tab Inode number +@item @code{VALUES(3)} @tab File mode +@item @code{VALUES(4)} @tab Number of links +@item @code{VALUES(5)} @tab Owner's uid +@item @code{VALUES(6)} @tab Owner's gid +@item @code{VALUES(7)} @tab ID of device containing directory entry for file (0 if not available) +@item @code{VALUES(8)} @tab File size (bytes) +@item @code{VALUES(9)} @tab Last access time +@item @code{VALUES(10)} @tab Last modification time +@item @code{VALUES(11)} @tab Last file status change time +@item @code{VALUES(12)} @tab Preferred I/O block size (-1 if not available) +@item @code{VALUES(13)} @tab Number of blocks allocated (-1 if not available) +@end multitable + +Not all these elements are relevant on all systems. +If an element is not relevant, it is returned as 0. + +This intrinsic is provided in both subroutine and function forms; however, +only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL STAT(NAME, VALUES [, STATUS])} +@item @code{STATUS = STAT(NAME, VALUES)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{NAME} @tab The type shall be @code{CHARACTER}, of the +default kind and a valid path within the file system. +@item @var{VALUES} @tab The type shall be @code{INTEGER(4), DIMENSION(13)}. +@item @var{STATUS} @tab (Optional) status flag of type @code{INTEGER(4)}. Returns 0 +on success and a system specific error code otherwise. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_stat + INTEGER, DIMENSION(13) :: buff + INTEGER :: status + + CALL STAT("/etc/passwd", buff, status) + + IF (status == 0) THEN + WRITE (*, FMT="('Device ID:', T30, I19)") buff(1) + WRITE (*, FMT="('Inode number:', T30, I19)") buff(2) + WRITE (*, FMT="('File mode (octal):', T30, O19)") buff(3) + WRITE (*, FMT="('Number of links:', T30, I19)") buff(4) + WRITE (*, FMT="('Owner''s uid:', T30, I19)") buff(5) + WRITE (*, FMT="('Owner''s gid:', T30, I19)") buff(6) + WRITE (*, FMT="('Device where located:', T30, I19)") buff(7) + WRITE (*, FMT="('File size:', T30, I19)") buff(8) + WRITE (*, FMT="('Last access time:', T30, A19)") CTIME(buff(9)) + WRITE (*, FMT="('Last modification time', T30, A19)") CTIME(buff(10)) + WRITE (*, FMT="('Last status change time:', T30, A19)") CTIME(buff(11)) + WRITE (*, FMT="('Preferred block size:', T30, I19)") buff(12) + WRITE (*, FMT="('No. of blocks allocated:', T30, I19)") buff(13) + END IF +END PROGRAM +@end smallexample + +@item @emph{See also}: +To stat an open file: @gol +@ref{FSTAT} @gol +To stat a link: @gol +@ref{LSTAT} +@end table + + + +@node STORAGE_SIZE +@section @code{STORAGE_SIZE} --- Storage size in bits +@fnindex STORAGE_SIZE +@cindex storage size + +@table @asis +@item @emph{Description}: +Returns the storage size of argument @var{A} in bits. +@item @emph{Standard}: +Fortran 2008 and later +@item @emph{Class}: +Inquiry function +@item @emph{Syntax}: +@code{RESULT = STORAGE_SIZE(A [, KIND])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{A} @tab Shall be a scalar or array of any type. +@item @var{KIND} @tab (Optional) shall be a scalar integer constant expression. +@end multitable + +@item @emph{Return Value}: +The result is a scalar integer with the kind type parameter specified by KIND +(or default integer type if KIND is missing). The result value is the size +expressed in bits for an element of an array that has the dynamic type and type +parameters of A. + +@item @emph{See also}: +@ref{C_SIZEOF}, @gol +@ref{SIZEOF} +@end table + + + +@node SUM +@section @code{SUM} --- Sum of array elements +@fnindex SUM +@cindex array, sum +@cindex array, add elements +@cindex array, conditionally add elements +@cindex sum array elements + +@table @asis +@item @emph{Description}: +Adds the elements of @var{ARRAY} along dimension @var{DIM} if +the corresponding element in @var{MASK} is @code{TRUE}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = SUM(ARRAY[, MASK])} +@item @code{RESULT = SUM(ARRAY, DIM[, MASK])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array of type @code{INTEGER}, +@code{REAL} or @code{COMPLEX}. +@item @var{DIM} @tab (Optional) shall be a scalar of type +@code{INTEGER} with a value in the range from 1 to n, where n +equals the rank of @var{ARRAY}. +@item @var{MASK} @tab (Optional) shall be of type @code{LOGICAL} +and either be a scalar or an array of the same shape as @var{ARRAY}. +@end multitable + +@item @emph{Return value}: +The result is of the same type as @var{ARRAY}. + +If @var{DIM} is absent, a scalar with the sum of all elements in @var{ARRAY} +is returned. Otherwise, an array of rank n-1, where n equals the rank of +@var{ARRAY}, and a shape similar to that of @var{ARRAY} with dimension @var{DIM} +dropped is returned. + +@item @emph{Example}: +@smallexample +PROGRAM test_sum + INTEGER :: x(5) = (/ 1, 2, 3, 4 ,5 /) + print *, SUM(x) ! all elements, sum = 15 + print *, SUM(x, MASK=MOD(x, 2)==1) ! odd elements, sum = 9 +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{PRODUCT} +@end table + + + +@node SYMLNK +@section @code{SYMLNK} --- Create a symbolic link +@fnindex SYMLNK +@cindex file system, create link +@cindex file system, soft link + +@table @asis +@item @emph{Description}: +Makes a symbolic link from file @var{PATH1} to @var{PATH2}. A null +character (@code{CHAR(0)}) can be used to mark the end of the names in +@var{PATH1} and @var{PATH2}; otherwise, trailing blanks in the file +names are ignored. If the @var{STATUS} argument is supplied, it +contains 0 on success or a nonzero error code upon return; see +@code{symlink(2)}. If the system does not supply @code{symlink(2)}, +@code{ENOSYS} is returned. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL SYMLNK(PATH1, PATH2 [, STATUS])} +@item @code{STATUS = SYMLNK(PATH1, PATH2)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{PATH1} @tab Shall be of default @code{CHARACTER} type. +@item @var{PATH2} @tab Shall be of default @code{CHARACTER} type. +@item @var{STATUS} @tab (Optional) Shall be of default @code{INTEGER} type. +@end multitable + +@item @emph{See also}: +@ref{LINK}, @gol +@ref{UNLINK} +@end table + + + +@node SYSTEM +@section @code{SYSTEM} --- Execute a shell command +@fnindex SYSTEM +@cindex system, system call + +@table @asis +@item @emph{Description}: +Passes the command @var{COMMAND} to a shell (see @code{system(3)}). If +argument @var{STATUS} is present, it contains the value returned by +@code{system(3)}, which is presumably 0 if the shell command succeeded. +Note that which shell is used to invoke the command is system-dependent +and environment-dependent. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. + +Note that the @code{system} function need not be thread-safe. It is +the responsibility of the user to ensure that @code{system} is not +called concurrently. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL SYSTEM(COMMAND [, STATUS])} +@item @code{STATUS = SYSTEM(COMMAND)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{COMMAND} @tab Shall be of default @code{CHARACTER} type. +@item @var{STATUS} @tab (Optional) Shall be of default @code{INTEGER} type. +@end multitable + +@item @emph{See also}: +@ref{EXECUTE_COMMAND_LINE}, which is part of the Fortran 2008 standard +and should considered in new code for future portability. +@end table + + + +@node SYSTEM_CLOCK +@section @code{SYSTEM_CLOCK} --- Time function +@fnindex SYSTEM_CLOCK +@cindex time, clock ticks +@cindex clock ticks + +@table @asis +@item @emph{Description}: +Determines the @var{COUNT} of a processor clock since an unspecified +time in the past modulo @var{COUNT_MAX}, @var{COUNT_RATE} determines +the number of clock ticks per second. If the platform supports a +monotonic clock, that clock is used and can, depending on the platform +clock implementation, provide up to nanosecond resolution. If a +monotonic clock is not available, the implementation falls back to a +realtime clock. + +@var{COUNT_RATE} is system dependent and can vary depending on the kind of +the arguments. For @var{kind=4} arguments (and smaller integer kinds), +@var{COUNT} represents milliseconds, while for @var{kind=8} arguments (and +larger integer kinds), @var{COUNT} typically represents micro- or +nanoseconds depending on resolution of the underlying platform clock. +@var{COUNT_MAX} usually equals @code{HUGE(COUNT_MAX)}. Note that the +millisecond resolution of the @var{kind=4} version implies that the +@var{COUNT} will wrap around in roughly 25 days. In order to avoid issues +with the wrap around and for more precise timing, please use the +@var{kind=8} version. + +If there is no clock, or querying the clock fails, @var{COUNT} is set +to @code{-HUGE(COUNT)}, and @var{COUNT_RATE} and @var{COUNT_MAX} are +set to zero. + +When running on a platform using the GNU C library (glibc) version +2.16 or older, or a derivative thereof, the high resolution monotonic +clock is available only when linking with the @var{rt} library. This +can be done explicitly by adding the @code{-lrt} flag when linking the +application, but is also done implicitly when using OpenMP. + +On the Windows platform, the version with @var{kind=4} arguments uses +the @code{GetTickCount} function, whereas the @var{kind=8} version +uses @code{QueryPerformanceCounter} and +@code{QueryPerformanceCounterFrequency}. For more information, and +potential caveats, please see the platform documentation. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Subroutine + +@item @emph{Syntax}: +@code{CALL SYSTEM_CLOCK([COUNT, COUNT_RATE, COUNT_MAX])} + +@item @emph{Arguments}: +@multitable @columnfractions .20 .65 +@item @var{COUNT} @tab (Optional) shall be a scalar of type +@code{INTEGER} with @code{INTENT(OUT)}. +@item @var{COUNT_RATE} @tab (Optional) shall be a scalar of type +@code{INTEGER} or @code{REAL}, with @code{INTENT(OUT)}. +@item @var{COUNT_MAX} @tab (Optional) shall be a scalar of type +@code{INTEGER} with @code{INTENT(OUT)}. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_system_clock + INTEGER :: count, count_rate, count_max + CALL SYSTEM_CLOCK(count, count_rate, count_max) + WRITE(*,*) count, count_rate, count_max +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{DATE_AND_TIME}, @gol +@ref{CPU_TIME} +@end table + + + +@node TAN +@section @code{TAN} --- Tangent function +@fnindex TAN +@fnindex DTAN +@cindex trigonometric function, tangent +@cindex tangent + +@table @asis +@item @emph{Description}: +@code{TAN(X)} computes the tangent of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later, for a complex argument Fortran 2008 or later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = TAN(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}, and its value is in radians. + +@item @emph{Example}: +@smallexample +program test_tan + real(8) :: x = 0.165_8 + x = tan(x) +end program test_tan +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{TAN(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DTAN(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{ATAN} @gol +Degrees function: @gol +@ref{TAND} +@end table + + + +@node TAND +@section @code{TAND} --- Tangent function, degrees +@fnindex TAND +@fnindex DTAND +@cindex trigonometric function, tangent, degrees +@cindex tangent, degrees + +@table @asis +@item @emph{Description}: +@code{TAND(X)} computes the tangent of @var{X} in degrees. + +This function is for compatibility only and should be avoided in favor of +standard constructs wherever possible. + +@item @emph{Standard}: +GNU extension, enabled with @option{-fdec-math}. + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = TAND(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}, and its value is in degrees. + +@item @emph{Example}: +@smallexample +program test_tand + real(8) :: x = 0.165_8 + x = tand(x) +end program test_tand +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{TAND(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab GNU extension +@item @code{DTAND(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab GNU extension +@end multitable + +@item @emph{See also}: +Inverse function: @gol +@ref{ATAND} @gol +Radians function: @gol +@ref{TAN} +@end table + + + +@node TANH +@section @code{TANH} --- Hyperbolic tangent function +@fnindex TANH +@fnindex DTANH +@cindex hyperbolic tangent +@cindex hyperbolic function, tangent +@cindex tangent, hyperbolic + +@table @asis +@item @emph{Description}: +@code{TANH(X)} computes the hyperbolic tangent of @var{X}. + +@item @emph{Standard}: +Fortran 77 and later, for a complex argument Fortran 2008 or later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{X = TANH(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab The type shall be @code{REAL} or @code{COMPLEX}. +@end multitable + +@item @emph{Return value}: +The return value has same type and kind as @var{X}. If @var{X} is +complex, the imaginary part of the result is in radians. If @var{X} +is @code{REAL}, the return value lies in the range +@math{ - 1 \leq tanh(x) \leq 1 }. + +@item @emph{Example}: +@smallexample +program test_tanh + real(8) :: x = 2.1_8 + x = tanh(x) +end program test_tanh +@end smallexample + +@item @emph{Specific names}: +@multitable @columnfractions .20 .23 .20 .33 +@headitem Name @tab Argument @tab Return type @tab Standard +@item @code{TANH(X)} @tab @code{REAL(4) X} @tab @code{REAL(4)} @tab Fortran 77 and later +@item @code{DTANH(X)} @tab @code{REAL(8) X} @tab @code{REAL(8)} @tab Fortran 77 and later +@end multitable + +@item @emph{See also}: +@ref{ATANH} +@end table + + + +@node THIS_IMAGE +@section @code{THIS_IMAGE} --- Function that returns the cosubscript index of this image +@fnindex THIS_IMAGE +@cindex coarray, @code{THIS_IMAGE} +@cindex images, index of this image + +@table @asis +@item @emph{Description}: +Returns the cosubscript for this image. + +@item @emph{Standard}: +Fortran 2008 and later. With @var{DISTANCE} argument, +Technical Specification (TS) 18508 or later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{RESULT = THIS_IMAGE()} +@item @code{RESULT = THIS_IMAGE(DISTANCE)} +@item @code{RESULT = THIS_IMAGE(COARRAY [, DIM])} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{DISTANCE} @tab (optional, intent(in)) Nonnegative scalar integer +(not permitted together with @var{COARRAY}). +@item @var{COARRAY} @tab Coarray of any type (optional; if @var{DIM} +present, required). +@item @var{DIM} @tab default integer scalar (optional). If present, +@var{DIM} shall be between one and the corank of @var{COARRAY}. +@end multitable + + +@item @emph{Return value}: +Default integer. If @var{COARRAY} is not present, it is scalar; if +@var{DISTANCE} is not present or has value 0, its value is the image index on +the invoking image for the current team, for values smaller or equal +distance to the initial team, it returns the image index on the ancestor team +which has a distance of @var{DISTANCE} from the invoking team. If +@var{DISTANCE} is larger than the distance to the initial team, the image +index of the initial team is returned. Otherwise when the @var{COARRAY} is +present, if @var{DIM} is not present, a rank-1 array with corank elements is +returned, containing the cosubscripts for @var{COARRAY} specifying the invoking +image. If @var{DIM} is present, a scalar is returned, with the value of +the @var{DIM} element of @code{THIS_IMAGE(COARRAY)}. + +@item @emph{Example}: +@smallexample +INTEGER :: value[*] +INTEGER :: i +value = THIS_IMAGE() +SYNC ALL +IF (THIS_IMAGE() == 1) THEN + DO i = 1, NUM_IMAGES() + WRITE(*,'(2(a,i0))') 'value[', i, '] is ', value[i] + END DO +END IF + +! Check whether the current image is the initial image +IF (THIS_IMAGE(HUGE(1)) /= THIS_IMAGE()) + error stop "something is rotten here" +@end smallexample + +@item @emph{See also}: +@ref{NUM_IMAGES}, @gol +@ref{IMAGE_INDEX} +@end table + + + +@node TIME +@section @code{TIME} --- Time function +@fnindex TIME +@cindex time, current +@cindex current time + +@table @asis +@item @emph{Description}: +Returns the current time encoded as an integer (in the manner of the +function @code{time(3)} in the C standard library). This value is +suitable for passing to @ref{CTIME}, @ref{GMTIME}, and @ref{LTIME}. + +This intrinsic is not fully portable, such as to systems with 32-bit +@code{INTEGER} types but supporting times wider than 32 bits. Therefore, +the values returned by this intrinsic might be, or become, negative, or +numerically less than previous values, during a single run of the +compiled program. + +See @ref{TIME8}, for information on a similar intrinsic that might be +portable to more GNU Fortran implementations, though to fewer Fortran +compilers. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = TIME()} + +@item @emph{Return value}: +The return value is a scalar of type @code{INTEGER(4)}. + +@item @emph{See also}: +@ref{DATE_AND_TIME}, @gol +@ref{CTIME}, @gol +@ref{GMTIME}, @gol +@ref{LTIME}, @gol +@ref{MCLOCK}, @gol +@ref{TIME8} +@end table + + + +@node TIME8 +@section @code{TIME8} --- Time function (64-bit) +@fnindex TIME8 +@cindex time, current +@cindex current time + +@table @asis +@item @emph{Description}: +Returns the current time encoded as an integer (in the manner of the +function @code{time(3)} in the C standard library). This value is +suitable for passing to @ref{CTIME}, @ref{GMTIME}, and @ref{LTIME}. + +@emph{Warning:} this intrinsic does not increase the range of the timing +values over that returned by @code{time(3)}. On a system with a 32-bit +@code{time(3)}, @code{TIME8} will return a 32-bit value, even though +it is converted to a 64-bit @code{INTEGER(8)} value. That means +overflows of the 32-bit value can still occur. Therefore, the values +returned by this intrinsic might be or become negative or numerically +less than previous values during a single run of the compiled program. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = TIME8()} + +@item @emph{Return value}: +The return value is a scalar of type @code{INTEGER(8)}. + +@item @emph{See also}: +@ref{DATE_AND_TIME}, @gol +@ref{CTIME}, @gol +@ref{GMTIME}, @gol +@ref{LTIME}, @gol +@ref{MCLOCK8}, @gol +@ref{TIME} +@end table + + + +@node TINY +@section @code{TINY} --- Smallest positive number of a real kind +@fnindex TINY +@cindex limits, smallest number +@cindex model representation, smallest number + +@table @asis +@item @emph{Description}: +@code{TINY(X)} returns the smallest positive (non zero) number +in the model of the type of @code{X}. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = TINY(X)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{X} @tab Shall be of type @code{REAL}. +@end multitable + +@item @emph{Return value}: +The return value is of the same type and kind as @var{X} + +@item @emph{Example}: +See @code{HUGE} for an example. +@end table + + + +@node TRAILZ +@section @code{TRAILZ} --- Number of trailing zero bits of an integer +@fnindex TRAILZ +@cindex zero bits + +@table @asis +@item @emph{Description}: +@code{TRAILZ} returns the number of trailing zero bits of an integer. + +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = TRAILZ(I)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab Shall be of type @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The type of the return value is the default @code{INTEGER}. +If all the bits of @code{I} are zero, the result value is @code{BIT_SIZE(I)}. + +@item @emph{Example}: +@smallexample +PROGRAM test_trailz + WRITE (*,*) TRAILZ(8) ! prints 3 +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{BIT_SIZE}, @gol +@ref{LEADZ}, @gol +@ref{POPPAR}, @gol +@ref{POPCNT} +@end table + + + +@node TRANSFER +@section @code{TRANSFER} --- Transfer bit patterns +@fnindex TRANSFER +@cindex bits, move +@cindex type cast + +@table @asis +@item @emph{Description}: +Interprets the bitwise representation of @var{SOURCE} in memory as if it +is the representation of a variable or array of the same type and type +parameters as @var{MOLD}. + +This is approximately equivalent to the C concept of @emph{casting} one +type to another. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = TRANSFER(SOURCE, MOLD[, SIZE])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{SOURCE} @tab Shall be a scalar or an array of any type. +@item @var{MOLD} @tab Shall be a scalar or an array of any type. +@item @var{SIZE} @tab (Optional) shall be a scalar of type +@code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The result has the same type as @var{MOLD}, with the bit level +representation of @var{SOURCE}. If @var{SIZE} is present, the result is +a one-dimensional array of length @var{SIZE}. If @var{SIZE} is absent +but @var{MOLD} is an array (of any size or shape), the result is a one- +dimensional array of the minimum length needed to contain the entirety +of the bitwise representation of @var{SOURCE}. If @var{SIZE} is absent +and @var{MOLD} is a scalar, the result is a scalar. + +If the bitwise representation of the result is longer than that of +@var{SOURCE}, then the leading bits of the result correspond to those of +@var{SOURCE} and any trailing bits are filled arbitrarily. + +When the resulting bit representation does not correspond to a valid +representation of a variable of the same type as @var{MOLD}, the results +are undefined, and subsequent operations on the result cannot be +guaranteed to produce sensible behavior. For example, it is possible to +create @code{LOGICAL} variables for which @code{@var{VAR}} and +@code{.NOT.@var{VAR}} both appear to be true. + +@item @emph{Example}: +@smallexample +PROGRAM test_transfer + integer :: x = 2143289344 + print *, transfer(x, 1.0) ! prints "NaN" on i686 +END PROGRAM +@end smallexample +@end table + + + +@node TRANSPOSE +@section @code{TRANSPOSE} --- Transpose an array of rank two +@fnindex TRANSPOSE +@cindex array, transpose +@cindex matrix, transpose +@cindex transpose + +@table @asis +@item @emph{Description}: +Transpose an array of rank two. Element (i, j) of the result has the value +@code{MATRIX(j, i)}, for all i, j. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = TRANSPOSE(MATRIX)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{MATRIX} @tab Shall be an array of any type and have a rank of two. +@end multitable + +@item @emph{Return value}: +The result has the same type as @var{MATRIX}, and has shape +@code{(/ m, n /)} if @var{MATRIX} has shape @code{(/ n, m /)}. +@end table + + + +@node TRIM +@section @code{TRIM} --- Remove trailing blank characters of a string +@fnindex TRIM +@cindex string, remove trailing whitespace + +@table @asis +@item @emph{Description}: +Removes trailing blank characters of a string. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = TRIM(STRING)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab Shall be a scalar of type @code{CHARACTER}. +@end multitable + +@item @emph{Return value}: +A scalar of type @code{CHARACTER} which length is that of @var{STRING} +less the number of trailing blanks. + +@item @emph{Example}: +@smallexample +PROGRAM test_trim + CHARACTER(len=10), PARAMETER :: s = "GFORTRAN " + WRITE(*,*) LEN(s), LEN(TRIM(s)) ! "10 8", with/without trailing blanks +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{ADJUSTL}, @gol +@ref{ADJUSTR} +@end table + + + +@node TTYNAM +@section @code{TTYNAM} --- Get the name of a terminal device +@fnindex TTYNAM +@cindex system, terminal + +@table @asis +@item @emph{Description}: +Get the name of a terminal device. For more information, +see @code{ttyname(3)}. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL TTYNAM(UNIT, NAME)} +@item @code{NAME = TTYNAM(UNIT)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{UNIT} @tab Shall be a scalar @code{INTEGER}. +@item @var{NAME} @tab Shall be of type @code{CHARACTER}. +@end multitable + +@item @emph{Example}: +@smallexample +PROGRAM test_ttynam + INTEGER :: unit + DO unit = 1, 10 + IF (isatty(unit=unit)) write(*,*) ttynam(unit) + END DO +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{ISATTY} +@end table + + + +@node UBOUND +@section @code{UBOUND} --- Upper dimension bounds of an array +@fnindex UBOUND +@cindex array, upper bound + +@table @asis +@item @emph{Description}: +Returns the upper bounds of an array, or a single upper bound +along the @var{DIM} dimension. +@item @emph{Standard}: +Fortran 90 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = UBOUND(ARRAY [, DIM [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an array, of any type. +@item @var{DIM} @tab (Optional) Shall be a scalar @code{INTEGER}. +@item @var{KIND}@tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. +If @var{DIM} is absent, the result is an array of the upper bounds of +@var{ARRAY}. If @var{DIM} is present, the result is a scalar +corresponding to the upper bound of the array along that dimension. If +@var{ARRAY} is an expression rather than a whole array or array +structure component, or if it has a zero extent along the relevant +dimension, the upper bound is taken to be the number of elements along +the relevant dimension. + +@item @emph{See also}: +@ref{LBOUND}, @gol +@ref{LCOBOUND} +@end table + + + +@node UCOBOUND +@section @code{UCOBOUND} --- Upper codimension bounds of an array +@fnindex UCOBOUND +@cindex coarray, upper bound + +@table @asis +@item @emph{Description}: +Returns the upper cobounds of a coarray, or a single upper cobound +along the @var{DIM} codimension. +@item @emph{Standard}: +Fortran 2008 and later + +@item @emph{Class}: +Inquiry function + +@item @emph{Syntax}: +@code{RESULT = UCOBOUND(COARRAY [, DIM [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{ARRAY} @tab Shall be an coarray, of any type. +@item @var{DIM} @tab (Optional) Shall be a scalar @code{INTEGER}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. +If @var{DIM} is absent, the result is an array of the lower cobounds of +@var{COARRAY}. If @var{DIM} is present, the result is a scalar +corresponding to the lower cobound of the array along that codimension. + +@item @emph{See also}: +@ref{LCOBOUND}, @gol +@ref{LBOUND} +@end table + + + +@node UMASK +@section @code{UMASK} --- Set the file creation mask +@fnindex UMASK +@cindex file system, file creation mask + +@table @asis +@item @emph{Description}: +Sets the file creation mask to @var{MASK}. If called as a function, it +returns the old value. If called as a subroutine and argument @var{OLD} +if it is supplied, it is set to the old value. See @code{umask(2)}. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL UMASK(MASK [, OLD])} +@item @code{OLD = UMASK(MASK)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{MASK} @tab Shall be a scalar of type @code{INTEGER}. +@item @var{OLD} @tab (Optional) Shall be a scalar of type +@code{INTEGER}. +@end multitable + +@end table + + + +@node UNLINK +@section @code{UNLINK} --- Remove a file from the file system +@fnindex UNLINK +@cindex file system, remove file + +@table @asis +@item @emph{Description}: +Unlinks the file @var{PATH}. A null character (@code{CHAR(0)}) can be +used to mark the end of the name in @var{PATH}; otherwise, trailing +blanks in the file name are ignored. If the @var{STATUS} argument is +supplied, it contains 0 on success or a nonzero error code upon return; +see @code{unlink(2)}. + +This intrinsic is provided in both subroutine and function forms; +however, only one form can be used in any given program unit. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Subroutine, function + +@item @emph{Syntax}: +@multitable @columnfractions .80 +@item @code{CALL UNLINK(PATH [, STATUS])} +@item @code{STATUS = UNLINK(PATH)} +@end multitable + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{PATH} @tab Shall be of default @code{CHARACTER} type. +@item @var{STATUS} @tab (Optional) Shall be of default @code{INTEGER} type. +@end multitable + +@item @emph{See also}: +@ref{LINK}, @gol +@ref{SYMLNK} +@end table + + + +@node UNPACK +@section @code{UNPACK} --- Unpack an array of rank one into an array +@fnindex UNPACK +@cindex array, unpacking +@cindex array, increase dimension +@cindex array, scatter elements + +@table @asis +@item @emph{Description}: +Store the elements of @var{VECTOR} in an array of higher rank. + +@item @emph{Standard}: +Fortran 90 and later + +@item @emph{Class}: +Transformational function + +@item @emph{Syntax}: +@code{RESULT = UNPACK(VECTOR, MASK, FIELD)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{VECTOR} @tab Shall be an array of any type and rank one. It +shall have at least as many elements as @var{MASK} has @code{TRUE} values. +@item @var{MASK} @tab Shall be an array of type @code{LOGICAL}. +@item @var{FIELD} @tab Shall be of the same type as @var{VECTOR} and have +the same shape as @var{MASK}. +@end multitable + +@item @emph{Return value}: +The resulting array corresponds to @var{FIELD} with @code{TRUE} elements +of @var{MASK} replaced by values from @var{VECTOR} in array element order. + +@item @emph{Example}: +@smallexample +PROGRAM test_unpack + integer :: vector(2) = (/1,1/) + logical :: mask(4) = (/ .TRUE., .FALSE., .FALSE., .TRUE. /) + integer :: field(2,2) = 0, unity(2,2) + + ! result: unity matrix + unity = unpack(vector, reshape(mask, (/2,2/)), field) +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{PACK}, @gol +@ref{SPREAD} +@end table + + + +@node VERIFY +@section @code{VERIFY} --- Scan a string for characters not a given set +@fnindex VERIFY +@cindex string, find missing set + +@table @asis +@item @emph{Description}: +Verifies that all the characters in @var{STRING} belong to the set of +characters in @var{SET}. + +If @var{BACK} is either absent or equals @code{FALSE}, this function +returns the position of the leftmost character of @var{STRING} that is +not in @var{SET}. If @var{BACK} equals @code{TRUE}, the rightmost +position is returned. If all characters of @var{STRING} are found in +@var{SET}, the result is zero. + +@item @emph{Standard}: +Fortran 90 and later, with @var{KIND} argument Fortran 2003 and later + +@item @emph{Class}: +Elemental function + +@item @emph{Syntax}: +@code{RESULT = VERIFY(STRING, SET[, BACK [, KIND]])} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{STRING} @tab Shall be of type @code{CHARACTER}. +@item @var{SET} @tab Shall be of type @code{CHARACTER}. +@item @var{BACK} @tab (Optional) shall be of type @code{LOGICAL}. +@item @var{KIND} @tab (Optional) An @code{INTEGER} initialization +expression indicating the kind parameter of the result. +@end multitable + +@item @emph{Return value}: +The return value is of type @code{INTEGER} and of kind @var{KIND}. If +@var{KIND} is absent, the return value is of default integer kind. + +@item @emph{Example}: +@smallexample +PROGRAM test_verify + WRITE(*,*) VERIFY("FORTRAN", "AO") ! 1, found 'F' + WRITE(*,*) VERIFY("FORTRAN", "FOO") ! 3, found 'R' + WRITE(*,*) VERIFY("FORTRAN", "C++") ! 1, found 'F' + WRITE(*,*) VERIFY("FORTRAN", "C++", .TRUE.) ! 7, found 'N' + WRITE(*,*) VERIFY("FORTRAN", "FORTRAN") ! 0' found none +END PROGRAM +@end smallexample + +@item @emph{See also}: +@ref{SCAN}, @gol +@ref{INDEX intrinsic} +@end table + + + +@node XOR +@section @code{XOR} --- Bitwise logical exclusive OR +@fnindex XOR +@cindex bitwise logical exclusive or +@cindex logical exclusive or, bitwise + +@table @asis +@item @emph{Description}: +Bitwise logical exclusive or. + +This intrinsic routine is provided for backwards compatibility with +GNU Fortran 77. For integer arguments, programmers should consider +the use of the @ref{IEOR} intrinsic and for logical arguments the +@code{.NEQV.} operator, which are both defined by the Fortran standard. + +@item @emph{Standard}: +GNU extension + +@item @emph{Class}: +Function + +@item @emph{Syntax}: +@code{RESULT = XOR(I, J)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{I} @tab The type shall be either a scalar @code{INTEGER} +type or a scalar @code{LOGICAL} type or a boz-literal-constant. +@item @var{J} @tab The type shall be the same as the type of @var{I} or +a boz-literal-constant. @var{I} and @var{J} shall not both be +boz-literal-constants. If either @var{I} and @var{J} is a +boz-literal-constant, then the other argument must be a scalar @code{INTEGER}. +@end multitable + +@item @emph{Return value}: +The return type is either a scalar @code{INTEGER} or a scalar +@code{LOGICAL}. If the kind type parameters differ, then the +smaller kind type is implicitly converted to larger kind, and the +return has the larger kind. A boz-literal-constant is +converted to an @code{INTEGER} with the kind type parameter of +the other argument as-if a call to @ref{INT} occurred. + +@item @emph{Example}: +@smallexample +PROGRAM test_xor + LOGICAL :: T = .TRUE., F = .FALSE. + INTEGER :: a, b + DATA a / Z'F' /, b / Z'3' / + + WRITE (*,*) XOR(T, T), XOR(T, F), XOR(F, T), XOR(F, F) + WRITE (*,*) XOR(a, b) +END PROGRAM +@end smallexample + +@item @emph{See also}: +Fortran 95 elemental function: @gol +@ref{IEOR} +@end table + + + +@node Intrinsic Modules +@chapter Intrinsic Modules +@cindex intrinsic Modules + +@menu +* ISO_FORTRAN_ENV:: +* ISO_C_BINDING:: +* IEEE modules:: +* OpenMP Modules OMP_LIB and OMP_LIB_KINDS:: +* OpenACC Module OPENACC:: +@end menu + +@node ISO_FORTRAN_ENV +@section @code{ISO_FORTRAN_ENV} +@table @asis +@item @emph{Standard}: +Fortran 2003 and later, except when otherwise noted +@end table + +The @code{ISO_FORTRAN_ENV} module provides the following scalar default-integer +named constants: + +@table @asis +@item @code{ATOMIC_INT_KIND}: +Default-kind integer constant to be used as kind parameter when defining +integer variables used in atomic operations. (Fortran 2008 or later.) + +@item @code{ATOMIC_LOGICAL_KIND}: +Default-kind integer constant to be used as kind parameter when defining +logical variables used in atomic operations. (Fortran 2008 or later.) + +@item @code{CHARACTER_KINDS}: +Default-kind integer constant array of rank one containing the supported kind +parameters of the @code{CHARACTER} type. (Fortran 2008 or later.) + +@item @code{CHARACTER_STORAGE_SIZE}: +Size in bits of the character storage unit. + +@item @code{ERROR_UNIT}: +Identifies the preconnected unit used for error reporting. + +@item @code{FILE_STORAGE_SIZE}: +Size in bits of the file-storage unit. + +@item @code{INPUT_UNIT}: +Identifies the preconnected unit identified by the asterisk +(@code{*}) in @code{READ} statement. + +@item @code{INT8}, @code{INT16}, @code{INT32}, @code{INT64}: +Kind type parameters to specify an INTEGER type with a storage +size of 16, 32, and 64 bits. It is negative if a target platform +does not support the particular kind. (Fortran 2008 or later.) + +@item @code{INTEGER_KINDS}: +Default-kind integer constant array of rank one containing the supported kind +parameters of the @code{INTEGER} type. (Fortran 2008 or later.) + +@item @code{IOSTAT_END}: +The value assigned to the variable passed to the @code{IOSTAT=} specifier of +an input/output statement if an end-of-file condition occurred. + +@item @code{IOSTAT_EOR}: +The value assigned to the variable passed to the @code{IOSTAT=} specifier of +an input/output statement if an end-of-record condition occurred. + +@item @code{IOSTAT_INQUIRE_INTERNAL_UNIT}: +Scalar default-integer constant, used by @code{INQUIRE} for the +@code{IOSTAT=} specifier to denote an that a unit number identifies an +internal unit. (Fortran 2008 or later.) + +@item @code{NUMERIC_STORAGE_SIZE}: +The size in bits of the numeric storage unit. + +@item @code{LOGICAL_KINDS}: +Default-kind integer constant array of rank one containing the supported kind +parameters of the @code{LOGICAL} type. (Fortran 2008 or later.) + +@item @code{OUTPUT_UNIT}: +Identifies the preconnected unit identified by the asterisk +(@code{*}) in @code{WRITE} statement. + +@item @code{REAL32}, @code{REAL64}, @code{REAL128}: +Kind type parameters to specify a REAL type with a storage +size of 32, 64, and 128 bits. It is negative if a target platform +does not support the particular kind. (Fortran 2008 or later.) + +@item @code{REAL_KINDS}: +Default-kind integer constant array of rank one containing the supported kind +parameters of the @code{REAL} type. (Fortran 2008 or later.) + +@item @code{STAT_LOCKED}: +Scalar default-integer constant used as STAT= return value by @code{LOCK} to +denote that the lock variable is locked by the executing image. (Fortran 2008 +or later.) + +@item @code{STAT_LOCKED_OTHER_IMAGE}: +Scalar default-integer constant used as STAT= return value by @code{UNLOCK} to +denote that the lock variable is locked by another image. (Fortran 2008 or +later.) + +@item @code{STAT_STOPPED_IMAGE}: +Positive, scalar default-integer constant used as STAT= return value if the +argument in the statement requires synchronisation with an image, which has +initiated the termination of the execution. (Fortran 2008 or later.) + +@item @code{STAT_FAILED_IMAGE}: +Positive, scalar default-integer constant used as STAT= return value if the +argument in the statement requires communication with an image, which has +is in the failed state. (TS 18508 or later.) + +@item @code{STAT_UNLOCKED}: +Scalar default-integer constant used as STAT= return value by @code{UNLOCK} to +denote that the lock variable is unlocked. (Fortran 2008 or later.) +@end table + +The module provides the following derived type: + +@table @asis +@item @code{LOCK_TYPE}: +Derived type with private components to be use with the @code{LOCK} and +@code{UNLOCK} statement. A variable of its type has to be always declared +as coarray and may not appear in a variable-definition context. +(Fortran 2008 or later.) +@end table + +The module also provides the following intrinsic procedures: +@ref{COMPILER_OPTIONS} and @ref{COMPILER_VERSION}. + + + +@node ISO_C_BINDING +@section @code{ISO_C_BINDING} +@table @asis +@item @emph{Standard}: +Fortran 2003 and later, GNU extensions +@end table + +The following intrinsic procedures are provided by the module; their +definition can be found in the section Intrinsic Procedures of this +manual. + +@table @asis +@item @code{C_ASSOCIATED} +@item @code{C_F_POINTER} +@item @code{C_F_PROCPOINTER} +@item @code{C_FUNLOC} +@item @code{C_LOC} +@item @code{C_SIZEOF} +@end table +@c TODO: Vertical spacing between C_FUNLOC and C_LOC wrong in PDF, +@c don't really know why. + +The @code{ISO_C_BINDING} module provides the following named constants of +type default integer, which can be used as KIND type parameters. + +In addition to the integer named constants required by the Fortran 2003 +standard and @code{C_PTRDIFF_T} of TS 29113, GNU Fortran provides as an +extension named constants for the 128-bit integer types supported by the +C compiler: @code{C_INT128_T, C_INT_LEAST128_T, C_INT_FAST128_T}. +Furthermore, if @code{_Float128} is supported in C, the named constants +@code{C_FLOAT128} and @code{C_FLOAT128_COMPLEX} are defined. + +@multitable @columnfractions .19 .32 .34 .15 +@headitem Fortran Type @tab Named constant @tab C type @tab Extension +@item @code{INTEGER}@tab @code{C_INT} @tab @code{int} +@item @code{INTEGER}@tab @code{C_SHORT} @tab @code{short int} +@item @code{INTEGER}@tab @code{C_LONG} @tab @code{long int} +@item @code{INTEGER}@tab @code{C_LONG_LONG} @tab @code{long long int} +@item @code{INTEGER}@tab @code{C_SIGNED_CHAR} @tab @code{signed char}/@code{unsigned char} +@item @code{INTEGER}@tab @code{C_SIZE_T} @tab @code{size_t} +@item @code{INTEGER}@tab @code{C_INT8_T} @tab @code{int8_t} +@item @code{INTEGER}@tab @code{C_INT16_T} @tab @code{int16_t} +@item @code{INTEGER}@tab @code{C_INT32_T} @tab @code{int32_t} +@item @code{INTEGER}@tab @code{C_INT64_T} @tab @code{int64_t} +@item @code{INTEGER}@tab @code{C_INT128_T} @tab @code{int128_t} @tab Ext. +@item @code{INTEGER}@tab @code{C_INT_LEAST8_T} @tab @code{int_least8_t} +@item @code{INTEGER}@tab @code{C_INT_LEAST16_T} @tab @code{int_least16_t} +@item @code{INTEGER}@tab @code{C_INT_LEAST32_T} @tab @code{int_least32_t} +@item @code{INTEGER}@tab @code{C_INT_LEAST64_T} @tab @code{int_least64_t} +@item @code{INTEGER}@tab @code{C_INT_LEAST128_T}@tab @code{int_least128_t} @tab Ext. +@item @code{INTEGER}@tab @code{C_INT_FAST8_T} @tab @code{int_fast8_t} +@item @code{INTEGER}@tab @code{C_INT_FAST16_T} @tab @code{int_fast16_t} +@item @code{INTEGER}@tab @code{C_INT_FAST32_T} @tab @code{int_fast32_t} +@item @code{INTEGER}@tab @code{C_INT_FAST64_T} @tab @code{int_fast64_t} +@item @code{INTEGER}@tab @code{C_INT_FAST128_T} @tab @code{int_fast128_t} @tab Ext. +@item @code{INTEGER}@tab @code{C_INTMAX_T} @tab @code{intmax_t} +@item @code{INTEGER}@tab @code{C_INTPTR_T} @tab @code{intptr_t} +@item @code{INTEGER}@tab @code{C_PTRDIFF_T} @tab @code{ptrdiff_t} @tab TS 29113 +@item @code{REAL} @tab @code{C_FLOAT} @tab @code{float} +@item @code{REAL} @tab @code{C_DOUBLE} @tab @code{double} +@item @code{REAL} @tab @code{C_LONG_DOUBLE} @tab @code{long double} +@item @code{REAL} @tab @code{C_FLOAT128} @tab @code{_Float128} @tab Ext. +@item @code{COMPLEX}@tab @code{C_FLOAT_COMPLEX} @tab @code{float _Complex} +@item @code{COMPLEX}@tab @code{C_DOUBLE_COMPLEX}@tab @code{double _Complex} +@item @code{COMPLEX}@tab @code{C_LONG_DOUBLE_COMPLEX}@tab @code{long double _Complex} +@item @code{COMPLEX}@tab @code{C_FLOAT128_COMPLEX} @tab @code{_Float128 _Complex} @tab Ext. +@item @code{LOGICAL}@tab @code{C_BOOL} @tab @code{_Bool} +@item @code{CHARACTER}@tab @code{C_CHAR} @tab @code{char} +@end multitable + +Additionally, the following parameters of type @code{CHARACTER(KIND=C_CHAR)} +are defined. + +@multitable @columnfractions .20 .45 .15 +@headitem Name @tab C definition @tab Value +@item @code{C_NULL_CHAR} @tab null character @tab @code{'\0'} +@item @code{C_ALERT} @tab alert @tab @code{'\a'} +@item @code{C_BACKSPACE} @tab backspace @tab @code{'\b'} +@item @code{C_FORM_FEED} @tab form feed @tab @code{'\f'} +@item @code{C_NEW_LINE} @tab new line @tab @code{'\n'} +@item @code{C_CARRIAGE_RETURN} @tab carriage return @tab @code{'\r'} +@item @code{C_HORIZONTAL_TAB} @tab horizontal tab @tab @code{'\t'} +@item @code{C_VERTICAL_TAB} @tab vertical tab @tab @code{'\v'} +@end multitable + +Moreover, the following two named constants are defined: + +@multitable @columnfractions .20 .80 +@headitem Name @tab Type +@item @code{C_NULL_PTR} @tab @code{C_PTR} +@item @code{C_NULL_FUNPTR} @tab @code{C_FUNPTR} +@end multitable + +Both are equivalent to the value @code{NULL} in C. + + + +@node IEEE modules +@section IEEE modules: @code{IEEE_EXCEPTIONS}, @code{IEEE_ARITHMETIC}, and @code{IEEE_FEATURES} +@table @asis +@item @emph{Standard}: +Fortran 2003 and later +@end table + +The @code{IEEE_EXCEPTIONS}, @code{IEEE_ARITHMETIC}, and @code{IEEE_FEATURES} +intrinsic modules provide support for exceptions and IEEE arithmetic, as +defined in Fortran 2003 and later standards, and the IEC 60559:1989 standard +(@emph{Binary floating-point arithmetic for microprocessor systems}). These +modules are only provided on the following supported platforms: + +@itemize @bullet +@item i386 and x86_64 processors +@item platforms which use the GNU C Library (glibc) +@item platforms with support for SysV/386 routines for floating point +interface (including Solaris and BSDs) +@item platforms with the AIX OS +@end itemize + +For full compliance with the Fortran standards, code using the +@code{IEEE_EXCEPTIONS} or @code{IEEE_ARITHMETIC} modules should be compiled +with the following options: @code{-fno-unsafe-math-optimizations +-frounding-math -fsignaling-nans}. + + + +@node OpenMP Modules OMP_LIB and OMP_LIB_KINDS +@section OpenMP Modules @code{OMP_LIB} and @code{OMP_LIB_KINDS} +@table @asis +@item @emph{Standard}: +OpenMP Application Program Interface v4.5, +OpenMP Application Program Interface v5.0 (partially supported) and +OpenMP Application Program Interface v5.1 (partially supported). +@end table + +The OpenMP Fortran runtime library routines are provided both in +a form of two Fortran modules, named @code{OMP_LIB} and +@code{OMP_LIB_KINDS}, and in a form of a Fortran @code{include} file named +@file{omp_lib.h}. The procedures provided by @code{OMP_LIB} can be found +in the @ref{Top,,Introduction,libgomp,GNU Offloading and Multi +Processing Runtime Library} manual, +the named constants defined in the modules are listed +below. + +For details refer to the actual +@uref{https://www.openmp.org/wp-content/uploads/openmp-4.5.pdf, +OpenMP Application Program Interface v4.5} and +@uref{https://www.openmp.org/wp-content/uploads/OpenMP-API-Specification-5.0.pdf, +OpenMP Application Program Interface v5.0}. + +@code{OMP_LIB_KINDS} provides the following scalar default-integer +named constants: + +@table @asis +@item @code{omp_allocator_handle_kind} +@item @code{omp_alloctrait_key_kind} +@item @code{omp_alloctrait_val_kind} +@item @code{omp_depend_kind} +@item @code{omp_lock_kind} +@item @code{omp_lock_hint_kind} +@item @code{omp_nest_lock_kind} +@item @code{omp_pause_resource_kind} +@item @code{omp_memspace_handle_kind} +@item @code{omp_proc_bind_kind} +@item @code{omp_sched_kind} +@item @code{omp_sync_hint_kind} +@end table + +@code{OMP_LIB} provides the scalar default-integer +named constant @code{openmp_version} with a value of the form +@var{yyyymm}, where @code{yyyy} is the year and @var{mm} the month +of the OpenMP version; for OpenMP v4.5 the value is @code{201511}. + +The following derived type: + +@table @asis +@item @code{omp_alloctrait} +@end table + +The following scalar integer named constants of the +kind @code{omp_sched_kind}: + +@table @asis +@item @code{omp_sched_static} +@item @code{omp_sched_dynamic} +@item @code{omp_sched_guided} +@item @code{omp_sched_auto} +@end table + +And the following scalar integer named constants of the +kind @code{omp_proc_bind_kind}: + +@table @asis +@item @code{omp_proc_bind_false} +@item @code{omp_proc_bind_true} +@item @code{omp_proc_bind_primary} +@item @code{omp_proc_bind_master} +@item @code{omp_proc_bind_close} +@item @code{omp_proc_bind_spread} +@end table + +The following scalar integer named constants are of the +kind @code{omp_lock_hint_kind}: + +@table @asis +@item @code{omp_lock_hint_none} +@item @code{omp_lock_hint_uncontended} +@item @code{omp_lock_hint_contended} +@item @code{omp_lock_hint_nonspeculative} +@item @code{omp_lock_hint_speculative} +@item @code{omp_sync_hint_none} +@item @code{omp_sync_hint_uncontended} +@item @code{omp_sync_hint_contended} +@item @code{omp_sync_hint_nonspeculative} +@item @code{omp_sync_hint_speculative} +@end table + +And the following two scalar integer named constants are of the +kind @code{omp_pause_resource_kind}: + +@table @asis +@item @code{omp_pause_soft} +@item @code{omp_pause_hard} +@end table + +The following scalar integer named constants are of the kind +@code{omp_alloctrait_key_kind}: + +@table @asis +@item @code{omp_atk_sync_hint} +@item @code{omp_atk_alignment} +@item @code{omp_atk_access} +@item @code{omp_atk_pool_size} +@item @code{omp_atk_fallback} +@item @code{omp_atk_fb_data} +@item @code{omp_atk_pinned} +@item @code{omp_atk_partition} +@end table + +The following scalar integer named constants are of the kind +@code{omp_alloctrait_val_kind}: + +@table @asis +@code{omp_alloctrait_key_kind}: +@item @code{omp_atv_default} +@item @code{omp_atv_false} +@item @code{omp_atv_true} +@item @code{omp_atv_contended} +@item @code{omp_atv_uncontended} +@item @code{omp_atv_serialized} +@item @code{omp_atv_sequential} +@item @code{omp_atv_private} +@item @code{omp_atv_all} +@item @code{omp_atv_thread} +@item @code{omp_atv_pteam} +@item @code{omp_atv_cgroup} +@item @code{omp_atv_default_mem_fb} +@item @code{omp_atv_null_fb} +@item @code{omp_atv_abort_fb} +@item @code{omp_atv_allocator_fb} +@item @code{omp_atv_environment} +@item @code{omp_atv_nearest} +@item @code{omp_atv_blocked} +@end table + +The following scalar integer named constants are of the kind +@code{omp_allocator_handle_kind}: + +@table @asis +@item @code{omp_null_allocator} +@item @code{omp_default_mem_alloc} +@item @code{omp_large_cap_mem_alloc} +@item @code{omp_const_mem_alloc} +@item @code{omp_high_bw_mem_alloc} +@item @code{omp_low_lat_mem_alloc} +@item @code{omp_cgroup_mem_alloc} +@item @code{omp_pteam_mem_alloc} +@item @code{omp_thread_mem_alloc} +@end table + +The following scalar integer named constants are of the kind +@code{omp_memspace_handle_kind}: + +@table @asis +@item @code{omp_default_mem_space} +@item @code{omp_large_cap_mem_space} +@item @code{omp_const_mem_space} +@item @code{omp_high_bw_mem_space} +@item @code{omp_low_lat_mem_space} +@end table + + + +@node OpenACC Module OPENACC +@section OpenACC Module @code{OPENACC} +@table @asis +@item @emph{Standard}: +OpenACC Application Programming Interface v2.6 +@end table + + +The OpenACC Fortran runtime library routines are provided both in a +form of a Fortran 90 module, named @code{OPENACC}, and in form of a +Fortran @code{include} file named @file{openacc_lib.h}. The +procedures provided by @code{OPENACC} can be found in the +@ref{Top,,Introduction,libgomp,GNU Offloading and Multi Processing +Runtime Library} manual, the named constants defined in the modules +are listed below. + +For details refer to the actual +@uref{https://www.openacc.org/, +OpenACC Application Programming Interface v2.6}. + +@code{OPENACC} provides the scalar default-integer +named constant @code{openacc_version} with a value of the form +@var{yyyymm}, where @code{yyyy} is the year and @var{mm} the month +of the OpenACC version; for OpenACC v2.6 the value is @code{201711}. diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi new file mode 100644 index 00000000000..58502d38ac8 --- /dev/null +++ b/gcc/fortran/invoke.texi @@ -0,0 +1,2133 @@ +@c Copyright (C) 2004-2022 Free Software Foundation, Inc. +@c This is part of the GNU Fortran manual. +@c For copying conditions, see the file gfortran.texi. + +@ignore +@c man begin COPYRIGHT +Copyright @copyright{} 2004-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``Funding Free Software'', the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the gfdl(7) man page. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@c Set file name and title for the man page. +@setfilename gfortran +@settitle GNU Fortran compiler. +@c man begin SYNOPSIS +gfortran [@option{-c}|@option{-S}|@option{-E}] + [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] + [@option{-W}@var{warn}@dots{}] [@option{-pedantic}] + [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] + [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] + [@option{-f}@var{option}@dots{}] + [@option{-m}@var{machine-option}@dots{}] + [@option{-o} @var{outfile}] @var{infile}@dots{} + +Only the most useful options are listed here; see below for the +remainder. +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), +cpp(1), gcov(1), gcc(1), as(1), ld(1), gdb(1), dbx(1) +and the Info entries for @file{gcc}, @file{cpp}, @file{gfortran}, @file{as}, +@file{ld}, @file{binutils} and @file{gdb}. +@c man end +@c man begin BUGS +For instructions on reporting bugs, see +@w{@value{BUGURL}}. +@c man end +@c man begin AUTHOR +See the Info entry for @command{gfortran} for contributors to GCC and +GNU Fortran. +@c man end +@end ignore + +@node Invoking GNU Fortran +@chapter GNU Fortran Command Options +@cindex GNU Fortran command options +@cindex command options +@cindex options, @command{gfortran} command + +@c man begin DESCRIPTION + +The @command{gfortran} command supports all the options supported by the +@command{gcc} command. Only options specific to GNU Fortran are documented +here. + +@xref{Invoking GCC,,GCC Command Options,gcc,Using the GNU Compiler +Collection (GCC)}, for information +on the non-Fortran-specific aspects of the @command{gcc} command (and, +therefore, the @command{gfortran} command). + +@cindex options, negative forms +All GCC and GNU Fortran options +are accepted both by @command{gfortran} and by @command{gcc} +(as well as any other drivers built at the same time, +such as @command{g++}), +since adding GNU Fortran to the GCC distribution +enables acceptance of GNU Fortran options +by all of the relevant drivers. + +In some cases, options have positive and negative forms; +the negative form of @option{-ffoo} would be @option{-fno-foo}. +This manual documents only one of these two forms, whichever +one is not the default. +@c man end + +@menu +* Option Summary:: Brief list of all @command{gfortran} options, + without explanations. +* Fortran Dialect Options:: Controlling the variant of Fortran language + compiled. +* Preprocessing Options:: Enable and customize preprocessing. +* Error and Warning Options:: How picky should the compiler be? +* Debugging Options:: Symbol tables, measurements, and debugging dumps. +* Directory Options:: Where to find module files +* Link Options :: Influencing the linking step +* Runtime Options:: Influencing runtime behavior +* Code Gen Options:: Specifying conventions for function calls, data layout + and register usage. +* Interoperability Options:: Options for interoperability with other + languages. +* Environment Variables:: Environment variables that affect @command{gfortran}. +@end menu + +@node Option Summary +@section Option summary + +@c man begin OPTIONS + +Here is a summary of all the options specific to GNU Fortran, grouped +by type. Explanations are in the following sections. + +@table @emph +@item Fortran Language Options +@xref{Fortran Dialect Options,,Options controlling Fortran dialect}. +@gccoptlist{-fall-intrinsics -fallow-argument-mismatch -fallow-invalid-boz @gol +-fbackslash -fcray-pointer -fd-lines-as-code -fd-lines-as-comments @gol +-fdec -fdec-char-conversions -fdec-structure -fdec-intrinsic-ints @gol +-fdec-static -fdec-math -fdec-include -fdec-format-defaults @gol +-fdec-blank-format-item -fdefault-double-8 -fdefault-integer-8 @gol +-fdefault-real-8 -fdefault-real-10 -fdefault-real-16 -fdollar-ok @gol +-ffixed-line-length-@var{n} -ffixed-line-length-none -fpad-source @gol +-ffree-form -ffree-line-length-@var{n} -ffree-line-length-none @gol +-fimplicit-none -finteger-4-integer-8 -fmax-identifier-length @gol +-fmodule-private -ffixed-form -fno-range-check -fopenacc -fopenmp @gol +-freal-4-real-10 -freal-4-real-16 -freal-4-real-8 -freal-8-real-10 @gol +-freal-8-real-16 -freal-8-real-4 -std=@var{std} -ftest-forall-temp +} + +@item Preprocessing Options +@xref{Preprocessing Options,,Enable and customize preprocessing}. +@gccoptlist{-A-@var{question}@r{[}=@var{answer}@r{]} +-A@var{question}=@var{answer} -C -CC -D@var{macro}@r{[}=@var{defn}@r{]} +-H -P @gol +-U@var{macro} -cpp -dD -dI -dM -dN -dU -fworking-directory +-imultilib @var{dir} @gol +-iprefix @var{file} -iquote -isysroot @var{dir} -isystem @var{dir} -nocpp +-nostdinc @gol +-undef +} + +@item Error and Warning Options +@xref{Error and Warning Options,,Options to request or suppress errors +and warnings}. +@gccoptlist{-Waliasing -Wall -Wampersand -Warray-bounds @gol +-Wc-binding-type -Wcharacter-truncation -Wconversion @gol +-Wdo-subscript -Wfunction-elimination -Wimplicit-interface @gol +-Wimplicit-procedure -Wintrinsic-shadow -Wuse-without-only @gol +-Wintrinsics-std -Wline-truncation -Wno-align-commons @gol +-Wno-overwrite-recursive -Wno-tabs -Wreal-q-constant -Wsurprising @gol +-Wunderflow -Wunused-parameter -Wrealloc-lhs -Wrealloc-lhs-all @gol +-Wfrontend-loop-interchange -Wtarget-lifetime -fmax-errors=@var{n} @gol +-fsyntax-only -pedantic @gol +-pedantic-errors @gol +} + +@item Debugging Options +@xref{Debugging Options,,Options for debugging your program or GNU Fortran}. +@gccoptlist{-fbacktrace -fdump-fortran-optimized -fdump-fortran-original @gol +-fdebug-aux-vars -fdump-fortran-global -fdump-parse-tree -ffpe-trap=@var{list} @gol +-ffpe-summary=@var{list} +} + +@item Directory Options +@xref{Directory Options,,Options for directory search}. +@gccoptlist{-I@var{dir} -J@var{dir} -fintrinsic-modules-path @var{dir}} + +@item Link Options +@xref{Link Options,,Options for influencing the linking step}. +@gccoptlist{-static-libgfortran -static-libquadmath} + +@item Runtime Options +@xref{Runtime Options,,Options for influencing runtime behavior}. +@gccoptlist{-fconvert=@var{conversion} -fmax-subrecord-length=@var{length} @gol +-frecord-marker=@var{length} -fsign-zero +} + +@item Interoperability Options +@xref{Interoperability Options,,Options for interoperability}. +@gccoptlist{-fc-prototypes -fc-prototypes-external} + +@item Code Generation Options +@xref{Code Gen Options,,Options for code generation conventions}. +@gccoptlist{-faggressive-function-elimination -fblas-matmul-limit=@var{n} @gol +-fbounds-check -ftail-call-workaround -ftail-call-workaround=@var{n} @gol +-fcheck-array-temporaries @gol +-fcheck=@var{} @gol +-fcoarray=@var{} -fexternal-blas -ff2c @gol +-ffrontend-loop-interchange -ffrontend-optimize @gol +-finit-character=@var{n} -finit-integer=@var{n} -finit-local-zero @gol +-finit-derived -finit-logical=@var{} @gol +-finit-real=@var{} +-finline-matmul-limit=@var{n} @gol +-finline-arg-packing -fmax-array-constructor=@var{n} @gol +-fmax-stack-var-size=@var{n} -fno-align-commons -fno-automatic @gol +-fno-protect-parens -fno-underscoring -fsecond-underscore @gol +-fpack-derived -frealloc-lhs -frecursive -frepack-arrays @gol +-fshort-enums -fstack-arrays +} +@end table + +@node Fortran Dialect Options +@section Options controlling Fortran dialect +@cindex dialect options +@cindex language, dialect options +@cindex options, dialect + +The following options control the details of the Fortran dialect +accepted by the compiler: + +@table @gcctabopt +@item -ffree-form +@itemx -ffixed-form +@opindex @code{ffree-form} +@opindex @code{ffixed-form} +@cindex options, Fortran dialect +@cindex file format, free +@cindex file format, fixed +Specify the layout used by the source file. The free form layout +was introduced in Fortran 90. Fixed form was traditionally used in +older Fortran programs. When neither option is specified, the source +form is determined by the file extension. + +@item -fall-intrinsics +@opindex @code{fall-intrinsics} +This option causes all intrinsic procedures (including the GNU-specific +extensions) to be accepted. This can be useful with @option{-std=} to +force standard-compliance but get access to the full range of intrinsics +available with @command{gfortran}. As a consequence, @option{-Wintrinsics-std} +will be ignored and no user-defined procedure with the same name as any +intrinsic will be called except when it is explicitly declared @code{EXTERNAL}. + +@item -fallow-argument-mismatch +@opindex @code{fallow-argument-mismatch} +Some code contains calls to external procedures with mismatches +between the calls and the procedure definition, or with mismatches +between different calls. Such code is non-conforming, and will usually +be flagged with an error. This options degrades the error to a +warning, which can only be disabled by disabling all warnings via +@option{-w}. Only a single occurrence per argument is flagged by this +warning. @option{-fallow-argument-mismatch} is implied by +@option{-std=legacy}. + +Using this option is @emph{strongly} discouraged. It is possible to +provide standard-conforming code which allows different types of +arguments by using an explicit interface and @code{TYPE(*)}. + +@item -fallow-invalid-boz +@opindex @code{allow-invalid-boz} +A BOZ literal constant can occur in a limited number of contexts in +standard conforming Fortran. This option degrades an error condition +to a warning, and allows a BOZ literal constant to appear where the +Fortran standard would otherwise prohibit its use. + +@item -fd-lines-as-code +@itemx -fd-lines-as-comments +@opindex @code{fd-lines-as-code} +@opindex @code{fd-lines-as-comments} +Enable special treatment for lines beginning with @code{d} or @code{D} +in fixed form sources. If the @option{-fd-lines-as-code} option is +given they are treated as if the first column contained a blank. If the +@option{-fd-lines-as-comments} option is given, they are treated as +comment lines. + +@item -fdec +@opindex @code{fdec} +DEC compatibility mode. Enables extensions and other features that mimic +the default behavior of older compilers (such as DEC). +These features are non-standard and should be avoided at all costs. +For details on GNU Fortran's implementation of these extensions see the +full documentation. + +Other flags enabled by this switch are: +@option{-fdollar-ok} @option{-fcray-pointer} @option{-fdec-char-conversions} +@option{-fdec-structure} @option{-fdec-intrinsic-ints} @option{-fdec-static} +@option{-fdec-math} @option{-fdec-include} @option{-fdec-blank-format-item} +@option{-fdec-format-defaults} + +If @option{-fd-lines-as-code}/@option{-fd-lines-as-comments} are unset, then +@option{-fdec} also sets @option{-fd-lines-as-comments}. + +@item -fdec-char-conversions +@opindex @code{fdec-char-conversions} +Enable the use of character literals in assignments and @code{DATA} statements +for non-character variables. + +@item -fdec-structure +@opindex @code{fdec-structure} +Enable DEC @code{STRUCTURE} and @code{RECORD} as well as @code{UNION}, +@code{MAP}, and dot ('.') as a member separator (in addition to '%'). This is +provided for compatibility only; Fortran 90 derived types should be used +instead where possible. + +@item -fdec-intrinsic-ints +@opindex @code{fdec-intrinsic-ints} +Enable B/I/J/K kind variants of existing integer functions (e.g. BIAND, IIAND, +JIAND, etc...). For a complete list of intrinsics see the full documentation. + +@item -fdec-math +@opindex @code{fdec-math} +Enable legacy math intrinsics such as COTAN and degree-valued trigonometric +functions (e.g. TAND, ATAND, etc...) for compatability with older code. + +@item -fdec-static +@opindex @code{fdec-static} +Enable DEC-style STATIC and AUTOMATIC attributes to explicitly specify +the storage of variables and other objects. + +@item -fdec-include +@opindex @code{fdec-include} +Enable parsing of INCLUDE as a statement in addition to parsing it as +INCLUDE line. When parsed as INCLUDE statement, INCLUDE does not have to +be on a single line and can use line continuations. + +@item -fdec-format-defaults +@opindex @code{fdec-format-defaults} +Enable format specifiers F, G and I to be used without width specifiers, +default widths will be used instead. + +@item -fdec-blank-format-item +@opindex @code{fdec-blank-format-item} +Enable a blank format item at the end of a format specification i.e. nothing +following the final comma. + +@item -fdollar-ok +@opindex @code{fdollar-ok} +@cindex @code{$} +@cindex symbol names +@cindex character set +Allow @samp{$} as a valid non-first character in a symbol name. Symbols +that start with @samp{$} are rejected since it is unclear which rules to +apply to implicit typing as different vendors implement different rules. +Using @samp{$} in @code{IMPLICIT} statements is also rejected. + +@item -fbackslash +@opindex @code{backslash} +@cindex backslash +@cindex escape characters +Change the interpretation of backslashes in string literals from a single +backslash character to ``C-style'' escape characters. The following +combinations are expanded @code{\a}, @code{\b}, @code{\f}, @code{\n}, +@code{\r}, @code{\t}, @code{\v}, @code{\\}, and @code{\0} to the ASCII +characters alert, backspace, form feed, newline, carriage return, +horizontal tab, vertical tab, backslash, and NUL, respectively. +Additionally, @code{\x}@var{nn}, @code{\u}@var{nnnn} and +@code{\U}@var{nnnnnnnn} (where each @var{n} is a hexadecimal digit) are +translated into the Unicode characters corresponding to the specified code +points. All other combinations of a character preceded by \ are +unexpanded. + +@item -fmodule-private +@opindex @code{fmodule-private} +@cindex module entities +@cindex private +Set the default accessibility of module entities to @code{PRIVATE}. +Use-associated entities will not be accessible unless they are explicitly +declared as @code{PUBLIC}. + +@item -ffixed-line-length-@var{n} +@opindex @code{ffixed-line-length-}@var{n} +@cindex file format, fixed +Set column after which characters are ignored in typical fixed-form +lines in the source file, and, unless @code{-fno-pad-source}, through which +spaces are assumed (as if padded to that length) after the ends of short +fixed-form lines. + +Popular values for @var{n} include 72 (the +standard and the default), 80 (card image), and 132 (corresponding +to ``extended-source'' options in some popular compilers). +@var{n} may also be @samp{none}, meaning that the entire line is meaningful +and that continued character constants never have implicit spaces appended +to them to fill out the line. +@option{-ffixed-line-length-0} means the same thing as +@option{-ffixed-line-length-none}. + +@item -fno-pad-source +@opindex @code{fpad-source} +By default fixed-form lines have spaces assumed (as if padded to that length) +after the ends of short fixed-form lines. This is not done either if +@option{-ffixed-line-length-0}, @option{-ffixed-line-length-none} or +if @option{-fno-pad-source} option is used. With any of those options +continued character constants never have implicit spaces appended +to them to fill out the line. + +@item -ffree-line-length-@var{n} +@opindex @code{ffree-line-length-}@var{n} +@cindex file format, free +Set column after which characters are ignored in typical free-form +lines in the source file. The default value is 132. +@var{n} may be @samp{none}, meaning that the entire line is meaningful. +@option{-ffree-line-length-0} means the same thing as +@option{-ffree-line-length-none}. + +@item -fmax-identifier-length=@var{n} +@opindex @code{fmax-identifier-length=}@var{n} +Specify the maximum allowed identifier length. Typical values are +31 (Fortran 95) and 63 (Fortran 2003 and later). + +@item -fimplicit-none +@opindex @code{fimplicit-none} +Specify that no implicit typing is allowed, unless overridden by explicit +@code{IMPLICIT} statements. This is the equivalent of adding +@code{implicit none} to the start of every procedure. + +@item -fcray-pointer +@opindex @code{fcray-pointer} +Enable the Cray pointer extension, which provides C-like pointer +functionality. + +@item -fopenacc +@opindex @code{fopenacc} +@cindex OpenACC +Enable the OpenACC extensions. This includes OpenACC @code{!$acc} +directives in free form and @code{c$acc}, @code{*$acc} and +@code{!$acc} directives in fixed form, @code{!$} conditional +compilation sentinels in free form and @code{c$}, @code{*$} and +@code{!$} sentinels in fixed form, and when linking arranges for the +OpenACC runtime library to be linked in. + +@item -fopenmp +@opindex @code{fopenmp} +@cindex OpenMP +Enable the OpenMP extensions. This includes OpenMP @code{!$omp} directives +in free form +and @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form, +@code{!$} conditional compilation sentinels in free form +and @code{c$}, @code{*$} and @code{!$} sentinels in fixed form, +and when linking arranges for the OpenMP runtime library to be linked +in. The option @option{-fopenmp} implies @option{-frecursive}. + +@item -fno-range-check +@opindex @code{frange-check} +Disable range checking on results of simplification of constant +expressions during compilation. For example, GNU Fortran will give +an error at compile time when simplifying @code{a = 1. / 0}. +With this option, no error will be given and @code{a} will be assigned +the value @code{+Infinity}. If an expression evaluates to a value +outside of the relevant range of [@code{-HUGE()}:@code{HUGE()}], +then the expression will be replaced by @code{-Inf} or @code{+Inf} +as appropriate. +Similarly, @code{DATA i/Z'FFFFFFFF'/} will result in an integer overflow +on most systems, but with @option{-fno-range-check} the value will +``wrap around'' and @code{i} will be initialized to @math{-1} instead. + +@item -fdefault-integer-8 +@opindex @code{fdefault-integer-8} +Set the default integer and logical types to an 8 byte wide type. This option +also affects the kind of integer constants like @code{42}. Unlike +@option{-finteger-4-integer-8}, it does not promote variables with explicit +kind declaration. + +@item -fdefault-real-8 +@opindex @code{fdefault-real-8} +Set the default real type to an 8 byte wide type. This option also affects +the kind of non-double real constants like @code{1.0}. This option promotes +the default width of @code{DOUBLE PRECISION} and double real constants +like @code{1.d0} to 16 bytes if possible. If @code{-fdefault-double-8} +is given along with @code{fdefault-real-8}, @code{DOUBLE PRECISION} +and double real constants are not promoted. Unlike @option{-freal-4-real-8}, +@code{fdefault-real-8} does not promote variables with explicit kind +declarations. + +@item -fdefault-real-10 +@opindex @code{fdefault-real-10} +Set the default real type to an 10 byte wide type. This option also affects +the kind of non-double real constants like @code{1.0}. This option promotes +the default width of @code{DOUBLE PRECISION} and double real constants +like @code{1.d0} to 16 bytes if possible. If @code{-fdefault-double-8} +is given along with @code{fdefault-real-10}, @code{DOUBLE PRECISION} +and double real constants are not promoted. Unlike @option{-freal-4-real-10}, +@code{fdefault-real-10} does not promote variables with explicit kind +declarations. + +@item -fdefault-real-16 +@opindex @code{fdefault-real-16} +Set the default real type to an 16 byte wide type. This option also affects +the kind of non-double real constants like @code{1.0}. This option promotes +the default width of @code{DOUBLE PRECISION} and double real constants +like @code{1.d0} to 16 bytes if possible. If @code{-fdefault-double-8} +is given along with @code{fdefault-real-16}, @code{DOUBLE PRECISION} +and double real constants are not promoted. Unlike @option{-freal-4-real-16}, +@code{fdefault-real-16} does not promote variables with explicit kind +declarations. + +@item -fdefault-double-8 +@opindex @code{fdefault-double-8} +Set the @code{DOUBLE PRECISION} type and double real constants +like @code{1.d0} to an 8 byte wide type. Do nothing if this +is already the default. This option prevents @option{-fdefault-real-8}, +@option{-fdefault-real-10}, and @option{-fdefault-real-16}, +from promoting @code{DOUBLE PRECISION} and double real constants like +@code{1.d0} to 16 bytes. + +@item -finteger-4-integer-8 +@opindex @code{finteger-4-integer-8} +Promote all @code{INTEGER(KIND=4)} entities to an @code{INTEGER(KIND=8)} +entities. If @code{KIND=8} is unavailable, then an error will be issued. +This option should be used with care and may not be suitable for your codes. +Areas of possible concern include calls to external procedures, +alignment in @code{EQUIVALENCE} and/or @code{COMMON}, generic interfaces, +BOZ literal constant conversion, and I/O. Inspection of the intermediate +representation of the translated Fortran code, produced by +@option{-fdump-tree-original}, is suggested. + +@item -freal-4-real-8 +@itemx -freal-4-real-10 +@itemx -freal-4-real-16 +@itemx -freal-8-real-4 +@itemx -freal-8-real-10 +@itemx -freal-8-real-16 +@opindex @code{freal-4-real-8} +@opindex @code{freal-4-real-10} +@opindex @code{freal-4-real-16} +@opindex @code{freal-8-real-4} +@opindex @code{freal-8-real-10} +@opindex @code{freal-8-real-16} +@cindex options, real kind type promotion +Promote all @code{REAL(KIND=M)} entities to @code{REAL(KIND=N)} entities. +If @code{REAL(KIND=N)} is unavailable, then an error will be issued. +The @code{-freal-4-} flags also affect the default real kind and the +@code{-freal-8-} flags also the double-precision real kind. All other +real-kind types are unaffected by this option. The promotion is also +applied to real literal constants of default and double-precision kind +and a specified kind number of 4 or 8, respectively. +However, @code{-fdefault-real-8}, @code{-fdefault-real-10}, +@code{-fdefault-real-10}, and @code{-fdefault-double-8} take precedence +for the default and double-precision real kinds, both for real literal +constants and for declarations without a kind number. +Note that for @code{REAL(KIND=KIND(1.0))} the literal may get promoted and +then the result may get promoted again. +These options should be used with care and may not be suitable for your +codes. Areas of possible concern include calls to external procedures, +alignment in @code{EQUIVALENCE} and/or @code{COMMON}, generic interfaces, +BOZ literal constant conversion, and I/O and calls to intrinsic procedures +when passing a value to the @code{kind=} dummy argument. Inspection of the +intermediate representation of the translated Fortran code, produced by +@option{-fdump-fortran-original} or @option{-fdump-tree-original}, is suggested. + +@item -std=@var{std} +@opindex @code{std=}@var{std} option +Specify the standard to which the program is expected to conform, +which may be one of @samp{f95}, @samp{f2003}, @samp{f2008}, +@samp{f2018}, @samp{gnu}, or @samp{legacy}. The default value for +@var{std} is @samp{gnu}, which specifies a superset of the latest +Fortran standard that includes all of the extensions supported by GNU +Fortran, although warnings will be given for obsolete extensions not +recommended for use in new code. The @samp{legacy} value is +equivalent but without the warnings for obsolete extensions, and may +be useful for old non-standard programs. The @samp{f95}, +@samp{f2003}, @samp{f2008}, and @samp{f2018} values specify strict +conformance to the Fortran 95, Fortran 2003, Fortran 2008 and Fortran +2018 standards, respectively; errors are given for all extensions +beyond the relevant language standard, and warnings are given for the +Fortran 77 features that are permitted but obsolescent in later +standards. The deprecated option @samp{-std=f2008ts} acts as an alias for +@samp{-std=f2018}. It is only present for backwards compatibility with +earlier gfortran versions and should not be used any more. + +@item -ftest-forall-temp +@opindex @code{ftest-forall-temp} +Enhance test coverage by forcing most forall assignments to use temporary. + +@end table + +@node Preprocessing Options +@section Enable and customize preprocessing +@cindex preprocessor +@cindex options, preprocessor +@cindex CPP +@cindex FPP +@cindex Conditional compilation +@cindex Preprocessing +@cindex preprocessor, include file handling + +Many Fortran compilers including GNU Fortran allow passing the source code +through a C preprocessor (CPP; sometimes also called the Fortran preprocessor, +FPP) to allow for conditional compilation. In the case of GNU Fortran, +this is the GNU C Preprocessor in the traditional mode. On systems with +case-preserving file names, the preprocessor is automatically invoked if the +filename extension is @file{.F}, @file{.FOR}, @file{.FTN}, @file{.fpp}, +@file{.FPP}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. To manually +invoke the preprocessor on any file, use @option{-cpp}, to disable +preprocessing on files where the preprocessor is run automatically, use +@option{-nocpp}. + +If a preprocessed file includes another file with the Fortran @code{INCLUDE} +statement, the included file is not preprocessed. To preprocess included +files, use the equivalent preprocessor statement @code{#include}. + +If GNU Fortran invokes the preprocessor, @code{__GFORTRAN__} +is defined. The macros @code{__GNUC__}, @code{__GNUC_MINOR__} and +@code{__GNUC_PATCHLEVEL__} can be used to determine the version of the +compiler. See @ref{Top,,Overview,cpp,The C Preprocessor} for details. + +GNU Fortran supports a number of @code{INTEGER} and @code{REAL} kind types +in additional to the kind types required by the Fortran standard. +The availability of any given kind type is architecture dependent. The +following pre-defined preprocessor macros can be used to conditionally +include code for these additional kind types: @code{__GFC_INT_1__}, +@code{__GFC_INT_2__}, @code{__GFC_INT_8__}, @code{__GFC_INT_16__}, +@code{__GFC_REAL_10__}, and @code{__GFC_REAL_16__}. + +While CPP is the de-facto standard for preprocessing Fortran code, +Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines +Conditional Compilation, which is not widely used and not directly +supported by the GNU Fortran compiler. You can use the program coco +to preprocess such files (@uref{http://www.daniellnagle.com/coco.html}). + +The following options control preprocessing of Fortran code: + +@table @gcctabopt +@item -cpp +@itemx -nocpp +@opindex @code{cpp} +@opindex @code{fpp} +@cindex preprocessor, enable +@cindex preprocessor, disable +Enable preprocessing. The preprocessor is automatically invoked if +the file extension is @file{.fpp}, @file{.FPP}, @file{.F}, @file{.FOR}, +@file{.FTN}, @file{.F90}, @file{.F95}, @file{.F03} or @file{.F08}. Use +this option to manually enable preprocessing of any kind of Fortran file. + +To disable preprocessing of files with any of the above listed extensions, +use the negative form: @option{-nocpp}. + +The preprocessor is run in traditional mode. Any restrictions of the +file-format, especially the limits on line length, apply for +preprocessed output as well, so it might be advisable to use the +@option{-ffree-line-length-none} or @option{-ffixed-line-length-none} +options. + +@item -dM +@opindex @code{dM} +@cindex preprocessor, debugging +@cindex debugging, preprocessor +Instead of the normal output, generate a list of @code{'#define'} +directives for all the macros defined during the execution of the +preprocessor, including predefined macros. This gives you a way +of finding out what is predefined in your version of the preprocessor. +Assuming you have no file @file{foo.f90}, the command +@smallexample + touch foo.f90; gfortran -cpp -E -dM foo.f90 +@end smallexample +will show all the predefined macros. + +@item -dD +@opindex @code{dD} +@cindex preprocessor, debugging +@cindex debugging, preprocessor +Like @option{-dM} except in two respects: it does not include the +predefined macros, and it outputs both the @code{#define} directives +and the result of preprocessing. Both kinds of output go to the +standard output file. + +@item -dN +@opindex @code{dN} +@cindex preprocessor, debugging +@cindex debugging, preprocessor +Like @option{-dD}, but emit only the macro names, not their expansions. + +@item -dU +@opindex @code{dU} +@cindex preprocessor, debugging +@cindex debugging, preprocessor +Like @option{dD} except that only macros that are expanded, or whose +definedness is tested in preprocessor directives, are output; the +output is delayed until the use or test of the macro; and @code{'#undef'} +directives are also output for macros tested but undefined at the time. + +@item -dI +@opindex @code{dI} +@cindex preprocessor, debugging +@cindex debugging, preprocessor +Output @code{'#include'} directives in addition to the result +of preprocessing. + +@item -fworking-directory +@opindex @code{fworking-directory} +@cindex preprocessor, working directory +Enable generation of linemarkers in the preprocessor output that will +let the compiler know the current working directory at the time of +preprocessing. When this option is enabled, the preprocessor will emit, +after the initial linemarker, a second linemarker with the current +working directory followed by two slashes. GCC will use this directory, +when it is present in the preprocessed input, as the directory emitted +as the current working directory in some debugging information formats. +This option is implicitly enabled if debugging information is enabled, +but this can be inhibited with the negated form +@option{-fno-working-directory}. If the @option{-P} flag is present +in the command line, this option has no effect, since no @code{#line} +directives are emitted whatsoever. + +@item -idirafter @var{dir} +@opindex @code{idirafter @var{dir}} +@cindex preprocessing, include path +Search @var{dir} for include files, but do it after all directories +specified with @option{-I} and the standard system directories have +been exhausted. @var{dir} is treated as a system include directory. +If dir begins with @code{=}, then the @code{=} will be replaced by +the sysroot prefix; see @option{--sysroot} and @option{-isysroot}. + +@item -imultilib @var{dir} +@opindex @code{imultilib @var{dir}} +@cindex preprocessing, include path +Use @var{dir} as a subdirectory of the directory containing target-specific +C++ headers. + +@item -iprefix @var{prefix} +@opindex @code{iprefix @var{prefix}} +@cindex preprocessing, include path +Specify @var{prefix} as the prefix for subsequent @option{-iwithprefix} +options. If the @var{prefix} represents a directory, you should include +the final @code{'/'}. + +@item -isysroot @var{dir} +@opindex @code{isysroot @var{dir}} +@cindex preprocessing, include path +This option is like the @option{--sysroot} option, but applies only to +header files. See the @option{--sysroot} option for more information. + +@item -iquote @var{dir} +@opindex @code{iquote @var{dir}} +@cindex preprocessing, include path +Search @var{dir} only for header files requested with @code{#include "file"}; +they are not searched for @code{#include }, before all directories +specified by @option{-I} and before the standard system directories. If +@var{dir} begins with @code{=}, then the @code{=} will be replaced by the +sysroot prefix; see @option{--sysroot} and @option{-isysroot}. + +@item -isystem @var{dir} +@opindex @code{isystem @var{dir}} +@cindex preprocessing, include path +Search @var{dir} for header files, after all directories specified by +@option{-I} but before the standard system directories. Mark it as a +system directory, so that it gets the same special treatment as is +applied to the standard system directories. If @var{dir} begins with +@code{=}, then the @code{=} will be replaced by the sysroot prefix; +see @option{--sysroot} and @option{-isysroot}. + +@item -nostdinc +@opindex @code{nostdinc} +Do not search the standard system directories for header files. Only +the directories you have specified with @option{-I} options (and the +directory of the current file, if appropriate) are searched. + +@item -undef +@opindex @code{undef} +Do not predefine any system-specific or GCC-specific macros. +The standard predefined macros remain defined. + +@item -A@var{predicate}=@var{answer} +@opindex @code{A@var{predicate}=@var{answer}} +@cindex preprocessing, assertion +Make an assertion with the predicate @var{predicate} and answer @var{answer}. +This form is preferred to the older form -A predicate(answer), which is still +supported, because it does not use shell special characters. + +@item -A-@var{predicate}=@var{answer} +@opindex @code{A-@var{predicate}=@var{answer}} +@cindex preprocessing, assertion +Cancel an assertion with the predicate @var{predicate} and answer @var{answer}. + +@item -C +@opindex @code{C} +@cindex preprocessing, keep comments +Do not discard comments. All comments are passed through to the output +file, except for comments in processed directives, which are deleted +along with the directive. + +You should be prepared for side effects when using @option{-C}; it causes +the preprocessor to treat comments as tokens in their own right. For example, +comments appearing at the start of what would be a directive line have the +effect of turning that line into an ordinary source line, since the first +token on the line is no longer a @code{'#'}. + +Warning: this currently handles C-Style comments only. The preprocessor +does not yet recognize Fortran-style comments. + +@item -CC +@opindex @code{CC} +@cindex preprocessing, keep comments +Do not discard comments, including during macro expansion. This is like +@option{-C}, except that comments contained within macros are also passed +through to the output file where the macro is expanded. + +In addition to the side-effects of the @option{-C} option, the @option{-CC} +option causes all C++-style comments inside a macro to be converted to C-style +comments. This is to prevent later use of that macro from inadvertently +commenting out the remainder of the source line. The @option{-CC} option +is generally used to support lint comments. + +Warning: this currently handles C- and C++-Style comments only. The +preprocessor does not yet recognize Fortran-style comments. + +@item -D@var{name} +@opindex @code{D@var{name}} +@cindex preprocessing, define macros +Predefine name as a macro, with definition @code{1}. + +@item -D@var{name}=@var{definition} +@opindex @code{D@var{name}=@var{definition}} +@cindex preprocessing, define macros +The contents of @var{definition} are tokenized and processed as if they +appeared during translation phase three in a @code{'#define'} directive. +In particular, the definition will be truncated by embedded newline +characters. + +If you are invoking the preprocessor from a shell or shell-like program +you may need to use the shell's quoting syntax to protect characters such +as spaces that have a meaning in the shell syntax. + +If you wish to define a function-like macro on the command line, write +its argument list with surrounding parentheses before the equals sign +(if any). Parentheses are meaningful to most shells, so you will need +to quote the option. With sh and csh, @code{-D'name(args...)=definition'} +works. + +@option{-D} and @option{-U} options are processed in the order they are +given on the command line. All -imacros file and -include file options +are processed after all -D and -U options. + +@item -H +@opindex @code{H} +Print the name of each header file used, in addition to other normal +activities. Each name is indented to show how deep in the @code{'#include'} +stack it is. + +@item -P +@opindex @code{P} +@cindex preprocessing, no linemarkers +Inhibit generation of linemarkers in the output from the preprocessor. +This might be useful when running the preprocessor on something that +is not C code, and will be sent to a program which might be confused +by the linemarkers. + +@item -U@var{name} +@opindex @code{U@var{name}} +@cindex preprocessing, undefine macros +Cancel any previous definition of @var{name}, either built in or provided +with a @option{-D} option. +@end table + + +@node Error and Warning Options +@section Options to request or suppress errors and warnings +@cindex options, warnings +@cindex options, errors +@cindex warnings, suppressing +@cindex messages, error +@cindex messages, warning +@cindex suppressing warnings + +Errors are diagnostic messages that report that the GNU Fortran compiler +cannot compile the relevant piece of source code. The compiler will +continue to process the program in an attempt to report further errors +to aid in debugging, but will not produce any compiled output. + +Warnings are diagnostic messages that report constructions which +are not inherently erroneous but which are risky or suggest there is +likely to be a bug in the program. Unless @option{-Werror} is specified, +they do not prevent compilation of the program. + +You can request many specific warnings with options beginning @option{-W}, +for example @option{-Wimplicit} to request warnings on implicit +declarations. Each of these specific warning options also has a +negative form beginning @option{-Wno-} to turn off warnings; +for example, @option{-Wno-implicit}. This manual lists only one of the +two forms, whichever is not the default. + +These options control the amount and kinds of errors and warnings produced +by GNU Fortran: + +@table @gcctabopt +@item -fmax-errors=@var{n} +@opindex @code{fmax-errors=}@var{n} +@cindex errors, limiting +Limits the maximum number of error messages to @var{n}, at which point +GNU Fortran bails out rather than attempting to continue processing the +source code. If @var{n} is 0, there is no limit on the number of error +messages produced. + +@item -fsyntax-only +@opindex @code{fsyntax-only} +@cindex syntax checking +Check the code for syntax errors, but do not actually compile it. This +will generate module files for each module present in the code, but no +other output file. + +@item -Wpedantic +@itemx -pedantic +@opindex @code{pedantic} +@opindex @code{Wpedantic} +Issue warnings for uses of extensions to Fortran. +@option{-pedantic} also applies to C-language constructs where they +occur in GNU Fortran source files, such as use of @samp{\e} in a +character constant within a directive like @code{#include}. + +Valid Fortran programs should compile properly with or without +this option. +However, without this option, certain GNU extensions and traditional +Fortran features are supported as well. +With this option, many of them are rejected. + +Some users try to use @option{-pedantic} to check programs for conformance. +They soon find that it does not do quite what they want---it finds some +nonstandard practices, but not all. +However, improvements to GNU Fortran in this area are welcome. + +This should be used in conjunction with @option{-std=f95}, +@option{-std=f2003}, @option{-std=f2008} or @option{-std=f2018}. + +@item -pedantic-errors +@opindex @code{pedantic-errors} +Like @option{-pedantic}, except that errors are produced rather than +warnings. + +@item -Wall +@opindex @code{Wall} +@cindex all warnings +@cindex warnings, all +Enables commonly used warning options pertaining to usage that +we recommend avoiding and that we believe are easy to avoid. +This currently includes @option{-Waliasing}, @option{-Wampersand}, +@option{-Wconversion}, @option{-Wsurprising}, @option{-Wc-binding-type}, +@option{-Wintrinsics-std}, @option{-Wtabs}, @option{-Wintrinsic-shadow}, +@option{-Wline-truncation}, @option{-Wtarget-lifetime}, +@option{-Winteger-division}, @option{-Wreal-q-constant}, @option{-Wunused} +and @option{-Wundefined-do-loop}. + +@item -Waliasing +@opindex @code{Waliasing} +@cindex aliasing +@cindex warnings, aliasing +Warn about possible aliasing of dummy arguments. Specifically, it warns +if the same actual argument is associated with a dummy argument with +@code{INTENT(IN)} and a dummy argument with @code{INTENT(OUT)} in a call +with an explicit interface. + +The following example will trigger the warning. +@smallexample + interface + subroutine bar(a,b) + integer, intent(in) :: a + integer, intent(out) :: b + end subroutine + end interface + integer :: a + + call bar(a,a) +@end smallexample + +@item -Wampersand +@opindex @code{Wampersand} +@cindex warnings, ampersand +@cindex @code{&} +Warn about missing ampersand in continued character constants. The +warning is given with @option{-Wampersand}, @option{-pedantic}, +@option{-std=f95}, @option{-std=f2003}, @option{-std=f2008} and +@option{-std=f2018}. Note: With no ampersand given in a continued +character constant, GNU Fortran assumes continuation at the first +non-comment, non-whitespace character after the ampersand that +initiated the continuation. + +@item -Warray-temporaries +@opindex @code{Warray-temporaries} +@cindex warnings, array temporaries +Warn about array temporaries generated by the compiler. The information +generated by this warning is sometimes useful in optimization, in order to +avoid such temporaries. + +@item -Wc-binding-type +@opindex @code{Wc-binding-type} +@cindex warning, C binding type +Warn if the a variable might not be C interoperable. In particular, warn if +the variable has been declared using an intrinsic type with default kind +instead of using a kind parameter defined for C interoperability in the +intrinsic @code{ISO_C_Binding} module. This option is implied by +@option{-Wall}. + +@item -Wcharacter-truncation +@opindex @code{Wcharacter-truncation} +@cindex warnings, character truncation +Warn when a character assignment will truncate the assigned string. + +@item -Wline-truncation +@opindex @code{Wline-truncation} +@cindex warnings, line truncation +Warn when a source code line will be truncated. This option is +implied by @option{-Wall}. For free-form source code, the default is +@option{-Werror=line-truncation} such that truncations are reported as +error. + +@item -Wconversion +@opindex @code{Wconversion} +@cindex warnings, conversion +@cindex conversion +Warn about implicit conversions that are likely to change the value of +the expression after conversion. Implied by @option{-Wall}. + +@item -Wconversion-extra +@opindex @code{Wconversion-extra} +@cindex warnings, conversion +@cindex conversion +Warn about implicit conversions between different types and kinds. This +option does @emph{not} imply @option{-Wconversion}. + +@item -Wextra +@opindex @code{Wextra} +@cindex extra warnings +@cindex warnings, extra +Enables some warning options for usages of language features which +may be problematic. This currently includes @option{-Wcompare-reals}, +@option{-Wunused-parameter} and @option{-Wdo-subscript}. + +@item -Wfrontend-loop-interchange +@opindex @code{Wfrontend-loop-interchange} +@cindex warnings, loop interchange +@cindex loop interchange, warning +Warn when using @option{-ffrontend-loop-interchange} for performing loop +interchanges. + +@item -Wimplicit-interface +@opindex @code{Wimplicit-interface} +@cindex warnings, implicit interface +Warn if a procedure is called without an explicit interface. +Note this only checks that an explicit interface is present. It does not +check that the declared interfaces are consistent across program units. + +@item -Wimplicit-procedure +@opindex @code{Wimplicit-procedure} +@cindex warnings, implicit procedure +Warn if a procedure is called that has neither an explicit interface +nor has been declared as @code{EXTERNAL}. + +@item -Winteger-division +@opindex @code{Winteger-division} +@cindex warnings, integer division +@cindex warnings, division of integers +Warn if a constant integer division truncates its result. +As an example, 3/5 evaluates to 0. + +@item -Wintrinsics-std +@opindex @code{Wintrinsics-std} +@cindex warnings, non-standard intrinsics +@cindex warnings, intrinsics of other standards +Warn if @command{gfortran} finds a procedure named like an intrinsic not +available in the currently selected standard (with @option{-std}) and treats +it as @code{EXTERNAL} procedure because of this. @option{-fall-intrinsics} can +be used to never trigger this behavior and always link to the intrinsic +regardless of the selected standard. + +@item -Wno-overwrite-recursive +@opindex @code{Woverwrite-recursive} +@cindex warnings, overwrite recursive +Do not warn when @option{-fno-automatic} is used with @option{-frecursive}. Recursion +will be broken if the relevant local variables do not have the attribute +@code{AUTOMATIC} explicitly declared. This option can be used to suppress the warning +when it is known that recursion is not broken. Useful for build environments that use +@option{-Werror}. + +@item -Wreal-q-constant +@opindex @code{Wreal-q-constant} +@cindex warnings, @code{q} exponent-letter +Produce a warning if a real-literal-constant contains a @code{q} +exponent-letter. + +@item -Wsurprising +@opindex @code{Wsurprising} +@cindex warnings, suspicious code +Produce a warning when ``suspicious'' code constructs are encountered. +While technically legal these usually indicate that an error has been made. + +This currently produces a warning under the following circumstances: + +@itemize @bullet +@item +An INTEGER SELECT construct has a CASE that can never be matched as its +lower value is greater than its upper value. + +@item +A LOGICAL SELECT construct has three CASE statements. + +@item +A TRANSFER specifies a source that is shorter than the destination. + +@item +The type of a function result is declared more than once with the same type. If +@option{-pedantic} or standard-conforming mode is enabled, this is an error. + +@item +A @code{CHARACTER} variable is declared with negative length. + +@item +With @option{-fopenmp}, for fixed-form source code, when an @code{omx} +vendor-extension sentinel is encountered. (The equivalent @code{ompx}, +used in free-form source code, is diagnosed by default.) +@end itemize + +@item -Wtabs +@opindex @code{Wtabs} +@cindex warnings, tabs +@cindex tabulators +By default, tabs are accepted as whitespace, but tabs are not members +of the Fortran Character Set. For continuation lines, a tab followed +by a digit between 1 and 9 is supported. @option{-Wtabs} will cause a +warning to be issued if a tab is encountered. Note, @option{-Wtabs} is +active for @option{-pedantic}, @option{-std=f95}, @option{-std=f2003}, +@option{-std=f2008}, @option{-std=f2018} and +@option{-Wall}. + +@item -Wundefined-do-loop +@opindex @code{Wundefined-do-loop} +@cindex warnings, undefined do loop +Warn if a DO loop with step either 1 or -1 yields an underflow or an overflow +during iteration of an induction variable of the loop. +This option is implied by @option{-Wall}. + +@item -Wunderflow +@opindex @code{Wunderflow} +@cindex warnings, underflow +@cindex underflow +Produce a warning when numerical constant expressions are +encountered, which yield an UNDERFLOW during compilation. Enabled by default. + +@item -Wintrinsic-shadow +@opindex @code{Wintrinsic-shadow} +@cindex warnings, intrinsic +@cindex intrinsic +Warn if a user-defined procedure or module procedure has the same name as an +intrinsic; in this case, an explicit interface or @code{EXTERNAL} or +@code{INTRINSIC} declaration might be needed to get calls later resolved to +the desired intrinsic/procedure. This option is implied by @option{-Wall}. + +@item -Wuse-without-only +@opindex @code{Wuse-without-only} +@cindex warnings, use statements +@cindex intrinsic +Warn if a @code{USE} statement has no @code{ONLY} qualifier and +thus implicitly imports all public entities of the used module. + +@item -Wunused-dummy-argument +@opindex @code{Wunused-dummy-argument} +@cindex warnings, unused dummy argument +@cindex unused dummy argument +@cindex dummy argument, unused +Warn about unused dummy arguments. This option is implied by @option{-Wall}. + +@item -Wunused-parameter +@opindex @code{Wunused-parameter} +@cindex warnings, unused parameter +@cindex unused parameter +Contrary to @command{gcc}'s meaning of @option{-Wunused-parameter}, +@command{gfortran}'s implementation of this option does not warn +about unused dummy arguments (see @option{-Wunused-dummy-argument}), +but about unused @code{PARAMETER} values. @option{-Wunused-parameter} +is implied by @option{-Wextra} if also @option{-Wunused} or +@option{-Wall} is used. + +@item -Walign-commons +@opindex @code{Walign-commons} +@cindex warnings, alignment of @code{COMMON} blocks +@cindex alignment of @code{COMMON} blocks +By default, @command{gfortran} warns about any occasion of variables being +padded for proper alignment inside a @code{COMMON} block. This warning can be turned +off via @option{-Wno-align-commons}. See also @option{-falign-commons}. + +@item -Wfunction-elimination +@opindex @code{Wfunction-elimination} +@cindex function elimination +@cindex warnings, function elimination +Warn if any calls to impure functions are eliminated by the optimizations +enabled by the @option{-ffrontend-optimize} option. +This option is implied by @option{-Wextra}. + +@item -Wrealloc-lhs +@opindex @code{Wrealloc-lhs} +@cindex Reallocate the LHS in assignments, notification +Warn when the compiler might insert code to for allocation or reallocation of +an allocatable array variable of intrinsic type in intrinsic assignments. In +hot loops, the Fortran 2003 reallocation feature may reduce the performance. +If the array is already allocated with the correct shape, consider using a +whole-array array-spec (e.g. @code{(:,:,:)}) for the variable on the left-hand +side to prevent the reallocation check. Note that in some cases the warning +is shown, even if the compiler will optimize reallocation checks away. For +instance, when the right-hand side contains the same variable multiplied by +a scalar. See also @option{-frealloc-lhs}. + +@item -Wrealloc-lhs-all +@opindex @code{Wrealloc-lhs-all} +Warn when the compiler inserts code to for allocation or reallocation of an +allocatable variable; this includes scalars and derived types. + +@item -Wcompare-reals +@opindex @code{Wcompare-reals} +Warn when comparing real or complex types for equality or inequality. +This option is implied by @option{-Wextra}. + +@item -Wtarget-lifetime +@opindex @code{Wtargt-lifetime} +Warn if the pointer in a pointer assignment might be longer than the its +target. This option is implied by @option{-Wall}. + +@item -Wzerotrip +@opindex @code{Wzerotrip} +Warn if a @code{DO} loop is known to execute zero times at compile +time. This option is implied by @option{-Wall}. + +@item -Wdo-subscript +@opindex @code{Wdo-subscript} +Warn if an array subscript inside a DO loop could lead to an +out-of-bounds access even if the compiler cannot prove that the +statement is actually executed, in cases like +@smallexample + real a(3) + do i=1,4 + if (condition(i)) then + a(i) = 1.2 + end if + end do +@end smallexample +This option is implied by @option{-Wextra}. + +@item -Werror +@opindex @code{Werror} +@cindex warnings, to errors +Turns all warnings into errors. +@end table + +@xref{Warning Options,,Options to Request or Suppress Errors and +Warnings, gcc,Using the GNU Compiler Collection (GCC)}, for information on +more options offered by the GBE shared by @command{gfortran}, @command{gcc} +and other GNU compilers. + +Some of these have no effect when compiling programs written in Fortran. + +@node Debugging Options +@section Options for debugging your program or GNU Fortran +@cindex options, debugging +@cindex debugging information options + +GNU Fortran has various special options that are used for debugging +either your program or the GNU Fortran compiler. + +@table @gcctabopt +@item -fdump-fortran-original +@opindex @code{fdump-fortran-original} +Output the internal parse tree after translating the source program +into internal representation. This option is mostly useful for +debugging the GNU Fortran compiler itself. The output generated by +this option might change between releases. This option may also +generate internal compiler errors for features which have only +recently been added. + +@item -fdump-fortran-optimized +@opindex @code{fdump-fortran-optimized} +Output the parse tree after front-end optimization. Mostly useful for +debugging the GNU Fortran compiler itself. The output generated by +this option might change between releases. This option may also +generate internal compiler errors for features which have only +recently been added. + +@item -fdump-parse-tree +@opindex @code{fdump-parse-tree} +Output the internal parse tree after translating the source program +into internal representation. Mostly useful for debugging the GNU +Fortran compiler itself. The output generated by this option might +change between releases. This option may also generate internal +compiler errors for features which have only recently been added. This +option is deprecated; use @code{-fdump-fortran-original} instead. + +@item -fdebug-aux-vars +@opindex @code{fdebug-aux-vars} +Renames internal variables created by the gfortran front end and makes +them accessible to a debugger. The name of the internal variables then +start with upper-case letters followed by an underscore. This option is +useful for debugging the compiler's code generation together with +@code{-fdump-tree-original} and enabling debugging of the executable +program by using @code{-g} or @code{-ggdb3}. + +@item -fdump-fortran-global +@opindex @code{fdump-fortran-global} +Output a list of the global identifiers after translating into +middle-end representation. Mostly useful for debugging the GNU Fortran +compiler itself. The output generated by this option might change +between releases. This option may also generate internal compiler +errors for features which have only recently been added. + +@item -ffpe-trap=@var{list} +@opindex @code{ffpe-trap=}@var{list} +Specify a list of floating point exception traps to enable. On most +systems, if a floating point exception occurs and the trap for that +exception is enabled, a SIGFPE signal will be sent and the program +being aborted, producing a core file useful for debugging. @var{list} +is a (possibly empty) comma-separated list of the following +exceptions: @samp{invalid} (invalid floating point operation, such as +@code{SQRT(-1.0)}), @samp{zero} (division by zero), @samp{overflow} +(overflow in a floating point operation), @samp{underflow} (underflow +in a floating point operation), @samp{inexact} (loss of precision +during operation), and @samp{denormal} (operation performed on a +denormal value). The first five exceptions correspond to the five +IEEE 754 exceptions, whereas the last one (@samp{denormal}) is not +part of the IEEE 754 standard but is available on some common +architectures such as x86. + +The first three exceptions (@samp{invalid}, @samp{zero}, and +@samp{overflow}) often indicate serious errors, and unless the program +has provisions for dealing with these exceptions, enabling traps for +these three exceptions is probably a good idea. + +If the option is used more than once in the command line, the lists will +be joined: '@code{ffpe-trap=}@var{list1} @code{ffpe-trap=}@var{list2}' +is equivalent to @code{ffpe-trap=}@var{list1},@var{list2}. + +Note that once enabled an exception cannot be disabled (no negative form). + +Many, if not most, floating point operations incur loss of precision +due to rounding, and hence the @code{ffpe-trap=inexact} is likely to +be uninteresting in practice. + +By default no exception traps are enabled. + +@item -ffpe-summary=@var{list} +@opindex @code{ffpe-summary=}@var{list} +Specify a list of floating-point exceptions, whose flag status is printed +to @code{ERROR_UNIT} when invoking @code{STOP} and @code{ERROR STOP}. +@var{list} can be either @samp{none}, @samp{all} or a comma-separated list +of the following exceptions: @samp{invalid}, @samp{zero}, @samp{overflow}, +@samp{underflow}, @samp{inexact} and @samp{denormal}. (See +@option{-ffpe-trap} for a description of the exceptions.) + +If the option is used more than once in the command line, only the +last one will be used. + +By default, a summary for all exceptions but @samp{inexact} is shown. + +@item -fno-backtrace +@opindex @code{fno-backtrace} +@cindex backtrace +@cindex trace +When a serious runtime error is encountered or a deadly signal is +emitted (segmentation fault, illegal instruction, bus error, +floating-point exception, and the other POSIX signals that have the +action @samp{core}), the Fortran runtime library tries to output a +backtrace of the error. @code{-fno-backtrace} disables the backtrace +generation. This option only has influence for compilation of the +Fortran main program. + +@end table + +@xref{Debugging Options,,Options for Debugging Your Program or GCC, +gcc,Using the GNU Compiler Collection (GCC)}, for more information on +debugging options. + +@node Directory Options +@section Options for directory search +@cindex directory, options +@cindex options, directory search +@cindex search path +@cindex @code{INCLUDE} directive +@cindex directive, @code{INCLUDE} +These options affect how GNU Fortran searches +for files specified by the @code{INCLUDE} directive and where it searches +for previously compiled modules. + +It also affects the search paths used by @command{cpp} when used to preprocess +Fortran source. + +@table @gcctabopt +@item -I@var{dir} +@opindex @code{I}@var{dir} +@cindex directory, search paths for inclusion +@cindex inclusion, directory search paths for +@cindex search paths, for included files +@cindex paths, search +@cindex module search path +These affect interpretation of the @code{INCLUDE} directive +(as well as of the @code{#include} directive of the @command{cpp} +preprocessor). + +Also note that the general behavior of @option{-I} and +@code{INCLUDE} is pretty much the same as of @option{-I} with +@code{#include} in the @command{cpp} preprocessor, with regard to +looking for @file{header.gcc} files and other such things. + +This path is also used to search for @file{.mod} files when previously +compiled modules are required by a @code{USE} statement. + +@xref{Directory Options,,Options for Directory Search, +gcc,Using the GNU Compiler Collection (GCC)}, for information on the +@option{-I} option. + +@item -J@var{dir} +@opindex @code{J}@var{dir} +@opindex @code{M}@var{dir} +@cindex paths, search +@cindex module search path +This option specifies where to put @file{.mod} files for compiled modules. +It is also added to the list of directories to searched by an @code{USE} +statement. + +The default is the current directory. + +@item -fintrinsic-modules-path @var{dir} +@opindex @code{fintrinsic-modules-path} @var{dir} +@cindex paths, search +@cindex module search path +This option specifies the location of pre-compiled intrinsic modules, if +they are not in the default location expected by the compiler. +@end table + +@node Link Options +@section Influencing the linking step +@cindex options, linking +@cindex linking, static + +These options come into play when the compiler links object files into an +executable output file. They are meaningless if the compiler is not doing +a link step. + +@table @gcctabopt +@item -static-libgfortran +@opindex @code{static-libgfortran} +On systems that provide @file{libgfortran} as a shared and a static +library, this option forces the use of the static version. If no +shared version of @file{libgfortran} was built when the compiler was +configured, this option has no effect. +@end table + + +@table @gcctabopt +@item -static-libquadmath +@opindex @code{static-libquadmath} +On systems that provide @file{libquadmath} as a shared and a static +library, this option forces the use of the static version. If no +shared version of @file{libquadmath} was built when the compiler was +configured, this option has no effect. + +Please note that the @file{libquadmath} runtime library is licensed under the +GNU Lesser General Public License (LGPL), and linking it statically introduces +requirements when redistributing the resulting binaries. +@end table + + +@node Runtime Options +@section Influencing runtime behavior +@cindex options, runtime + +These options affect the runtime behavior of programs compiled with GNU Fortran. + +@table @gcctabopt +@item -fconvert=@var{conversion} +@opindex @code{fconvert=}@var{conversion} +Specify the representation of data for unformatted files. Valid +values for conversion on most systems are: @samp{native}, the default; +@samp{swap}, swap between big- and little-endian; @samp{big-endian}, use +big-endian representation for unformatted files; @samp{little-endian}, use +little-endian representation for unformatted files. + +On POWER systems which suppport @option{-mabi=ieeelongdouble}, +there are additional options, which can be combined with others with +commas. Those are +@itemize @w{} +@item @option{-fconvert=r16_ieee} Use IEEE 128-bit format for +@code{REAL(KIND=16)}. +@item @option{-fconvert=r16_ibm} Use IBM long double format for +@code{REAL(KIND=16)}. +@end itemize + +@emph{This option has an effect only when used in the main program. +The @code{CONVERT} specifier and the GFORTRAN_CONVERT_UNIT environment +variable override the default specified by @option{-fconvert}.} + +@item -frecord-marker=@var{length} +@opindex @code{frecord-marker=}@var{length} +Specify the length of record markers for unformatted files. +Valid values for @var{length} are 4 and 8. Default is 4. +@emph{This is different from previous versions of @command{gfortran}}, +which specified a default record marker length of 8 on most +systems. If you want to read or write files compatible +with earlier versions of @command{gfortran}, use @option{-frecord-marker=8}. + +@item -fmax-subrecord-length=@var{length} +@opindex @code{fmax-subrecord-length=}@var{length} +Specify the maximum length for a subrecord. The maximum permitted +value for length is 2147483639, which is also the default. Only +really useful for use by the gfortran testsuite. + +@item -fsign-zero +@opindex @code{fsign-zero} +When enabled, floating point numbers of value zero with the sign bit set +are written as negative number in formatted output and treated as +negative in the @code{SIGN} intrinsic. @option{-fno-sign-zero} does not +print the negative sign of zero values (or values rounded to zero for I/O) +and regards zero as positive number in the @code{SIGN} intrinsic for +compatibility with Fortran 77. The default is @option{-fsign-zero}. +@end table + +@node Code Gen Options +@section Options for code generation conventions +@cindex code generation, conventions +@cindex options, code generation +@cindex options, run-time + +These machine-independent options control the interface conventions +used in code generation. + +Most of them have both positive and negative forms; the negative form +of @option{-ffoo} would be @option{-fno-foo}. In the table below, only +one of the forms is listed---the one which is not the default. You +can figure out the other form by either removing @option{no-} or adding +it. + +@table @gcctabopt +@item -fno-automatic +@opindex @code{fno-automatic} +@cindex @code{SAVE} statement +@cindex statement, @code{SAVE} +Treat each program unit (except those marked as RECURSIVE) as if the +@code{SAVE} statement were specified for every local variable and array +referenced in it. Does not affect common blocks. (Some Fortran compilers +provide this option under the name @option{-static} or @option{-save}.) +The default, which is @option{-fautomatic}, uses the stack for local +variables smaller than the value given by @option{-fmax-stack-var-size}. +Use the option @option{-frecursive} to use no static memory. + +Local variables or arrays having an explicit @code{SAVE} attribute are +silently ignored unless the @option{-pedantic} option is added. + +@item -ff2c +@opindex ff2c +@cindex calling convention +@cindex @command{f2c} calling convention +@cindex @command{g77} calling convention +@cindex libf2c calling convention +Generate code designed to be compatible with code generated +by @command{g77} and @command{f2c}. + +The calling conventions used by @command{g77} (originally implemented +in @command{f2c}) require functions that return type +default @code{REAL} to actually return the C type @code{double}, and +functions that return type @code{COMPLEX} to return the values via an +extra argument in the calling sequence that points to where to +store the return value. Under the default GNU calling conventions, such +functions simply return their results as they would in GNU +C---default @code{REAL} functions return the C type @code{float}, and +@code{COMPLEX} functions return the GNU C type @code{complex}. +Additionally, this option implies the @option{-fsecond-underscore} +option, unless @option{-fno-second-underscore} is explicitly requested. + +This does not affect the generation of code that interfaces with +the @command{libgfortran} library. + +@emph{Caution:} It is not a good idea to mix Fortran code compiled with +@option{-ff2c} with code compiled with the default @option{-fno-f2c} +calling conventions as, calling @code{COMPLEX} or default @code{REAL} +functions between program parts which were compiled with different +calling conventions will break at execution time. + +@emph{Caution:} This will break code which passes intrinsic functions +of type default @code{REAL} or @code{COMPLEX} as actual arguments, as +the library implementations use the @option{-fno-f2c} calling conventions. + +@item -fno-underscoring +@opindex @code{fno-underscoring} +@cindex underscore +@cindex symbol names, underscores +@cindex transforming symbol names +@cindex symbol names, transforming +Do not transform names of entities specified in the Fortran +source file by appending underscores to them. + +With @option{-funderscoring} in effect, GNU Fortran appends one +underscore to external names with no underscores. This is done to ensure +compatibility with code produced by many UNIX Fortran compilers. + +@emph{Caution}: The default behavior of GNU Fortran is +incompatible with @command{f2c} and @command{g77}, please use the +@option{-ff2c} option if you want object files compiled with +GNU Fortran to be compatible with object code created with these +tools. + +Use of @option{-fno-underscoring} is not recommended unless you are +experimenting with issues such as integration of GNU Fortran into +existing system environments (vis-@`{a}-vis existing libraries, tools, +and so on). + +For example, with @option{-funderscoring}, and assuming that @code{j()} and +@code{max_count()} are external functions while @code{my_var} and +@code{lvar} are local variables, a statement like +@smallexample +I = J() + MAX_COUNT (MY_VAR, LVAR) +@end smallexample +@noindent +is implemented as something akin to: +@smallexample +i = j_() + max_count__(&my_var__, &lvar); +@end smallexample + +With @option{-fno-underscoring}, the same statement is implemented as: + +@smallexample +i = j() + max_count(&my_var, &lvar); +@end smallexample + +Use of @option{-fno-underscoring} allows direct specification of +user-defined names while debugging and when interfacing GNU Fortran +code with other languages. + +Note that just because the names match does @emph{not} mean that the +interface implemented by GNU Fortran for an external name matches the +interface implemented by some other language for that same name. +That is, getting code produced by GNU Fortran to link to code produced +by some other compiler using this or any other method can be only a +small part of the overall solution---getting the code generated by +both compilers to agree on issues other than naming can require +significant effort, and, unlike naming disagreements, linkers normally +cannot detect disagreements in these other areas. + +Also, note that with @option{-fno-underscoring}, the lack of appended +underscores introduces the very real possibility that a user-defined +external name will conflict with a name in a system library, which +could make finding unresolved-reference bugs quite difficult in some +cases---they might occur at program run time, and show up only as +buggy behavior at run time. + +In future versions of GNU Fortran we hope to improve naming and linking +issues so that debugging always involves using the names as they appear +in the source, even if the names as seen by the linker are mangled to +prevent accidental linking between procedures with incompatible +interfaces. + +@item -fsecond-underscore +@opindex @code{fsecond-underscore} +@cindex underscore +@cindex symbol names, underscores +@cindex transforming symbol names +@cindex symbol names, transforming +@cindex @command{f2c} calling convention +@cindex @command{g77} calling convention +@cindex libf2c calling convention +By default, GNU Fortran appends an underscore to external +names. If this option is used GNU Fortran appends two +underscores to names with underscores and one underscore to external names +with no underscores. GNU Fortran also appends two underscores to +internal names with underscores to avoid naming collisions with external +names. + +This option has no effect if @option{-fno-underscoring} is +in effect. It is implied by the @option{-ff2c} option. + +Otherwise, with this option, an external name such as @code{MAX_COUNT} +is implemented as a reference to the link-time external symbol +@code{max_count__}, instead of @code{max_count_}. This is required +for compatibility with @command{g77} and @command{f2c}, and is implied +by use of the @option{-ff2c} option. + +@item -fcoarray=@var{} +@opindex @code{fcoarray} +@cindex coarrays + +@table @asis +@item @samp{none} +Disable coarray support; using coarray declarations and image-control +statements will produce a compile-time error. (Default) + +@item @samp{single} +Single-image mode, i.e. @code{num_images()} is always one. + +@item @samp{lib} +Library-based coarray parallelization; a suitable GNU Fortran coarray +library needs to be linked. +@end table + + +@item -fcheck=@var{} +@opindex @code{fcheck} +@cindex array, bounds checking +@cindex bit intrinsics checking +@cindex bounds checking +@cindex pointer checking +@cindex memory checking +@cindex range checking +@cindex subscript checking +@cindex checking subscripts +@cindex run-time checking +@cindex checking array temporaries + +Enable the generation of run-time checks; the argument shall be +a comma-delimited list of the following keywords. Prefixing a check with +@option{no-} disables it if it was activated by a previous specification. + +@table @asis +@item @samp{all} +Enable all run-time test of @option{-fcheck}. + +@item @samp{array-temps} +Warns at run time when for passing an actual argument a temporary array +had to be generated. The information generated by this warning is +sometimes useful in optimization, in order to avoid such temporaries. + +Note: The warning is only printed once per location. + +@item @samp{bits} +Enable generation of run-time checks for invalid arguments to the bit +manipulation intrinsics. + +@item @samp{bounds} +Enable generation of run-time checks for array subscripts +and against the declared minimum and maximum values. It also +checks array indices for assumed and deferred +shape arrays against the actual allocated bounds and ensures that all string +lengths are equal for character array constructors without an explicit +typespec. + +Some checks require that @option{-fcheck=bounds} is set for +the compilation of the main program. + +Note: In the future this may also include other forms of checking, e.g., +checking substring references. + +@item @samp{do} +Enable generation of run-time checks for invalid modification of loop +iteration variables. + +@item @samp{mem} +Enable generation of run-time checks for memory allocation. +Note: This option does not affect explicit allocations using the +@code{ALLOCATE} statement, which will be always checked. + +@item @samp{pointer} +Enable generation of run-time checks for pointers and allocatables. + +@item @samp{recursion} +Enable generation of run-time checks for recursively called subroutines and +functions which are not marked as recursive. See also @option{-frecursive}. +Note: This check does not work for OpenMP programs and is disabled if used +together with @option{-frecursive} and @option{-fopenmp}. +@end table + +Example: Assuming you have a file @file{foo.f90}, the command +@smallexample + gfortran -fcheck=all,no-array-temps foo.f90 +@end smallexample +will compile the file with all checks enabled as specified above except +warnings for generated array temporaries. + + +@item -fbounds-check +@opindex @code{fbounds-check} +@c Note: This option is also referred in gcc's manpage +Deprecated alias for @option{-fcheck=bounds}. + +@item -ftail-call-workaround +@itemx -ftail-call-workaround=@var{n} +@opindex @code{tail-call-workaround} +Some C interfaces to Fortran codes violate the gfortran ABI by +omitting the hidden character length arguments as described in +@xref{Argument passing conventions}. This can lead to crashes +because pushing arguments for tail calls can overflow the stack. + +To provide a workaround for existing binary packages, this option +disables tail call optimization for gfortran procedures with character +arguments. With @option{-ftail-call-workaround=2} tail call optimization +is disabled in all gfortran procedures with character arguments, +with @option{-ftail-call-workaround=1} or equivalent +@option{-ftail-call-workaround} only in gfortran procedures with character +arguments that call implicitly prototyped procedures. + +Using this option can lead to problems including crashes due to +insufficient stack space. + +It is @emph{very strongly} recommended to fix the code in question. +The @option{-fc-prototypes-external} option can be used to generate +prototypes which conform to gfortran's ABI, for inclusion in the +source code. + +Support for this option will likely be withdrawn in a future release +of gfortran. + +The negative form, @option{-fno-tail-call-workaround} or equivalent +@option{-ftail-call-workaround=0}, can be used to disable this option. + +Default is currently @option{-ftail-call-workaround}, this will change +in future releases. + +@item -fcheck-array-temporaries +@opindex @code{fcheck-array-temporaries} +Deprecated alias for @option{-fcheck=array-temps}. + +@item -fmax-array-constructor=@var{n} +@opindex @code{fmax-array-constructor} +This option can be used to increase the upper limit permitted in +array constructors. The code below requires this option to expand +the array at compile time. + +@smallexample +program test +implicit none +integer j +integer, parameter :: n = 100000 +integer, parameter :: i(n) = (/ (2*j, j = 1, n) /) +print '(10(I0,1X))', i +end program test +@end smallexample + +@emph{Caution: This option can lead to long compile times and excessively +large object files.} + +The default value for @var{n} is 65535. + + +@item -fmax-stack-var-size=@var{n} +@opindex @code{fmax-stack-var-size} +This option specifies the size in bytes of the largest array that will be put +on the stack; if the size is exceeded static memory is used (except in +procedures marked as RECURSIVE). Use the option @option{-frecursive} to +allow for recursive procedures which do not have a RECURSIVE attribute or +for parallel programs. Use @option{-fno-automatic} to never use the stack. + +This option currently only affects local arrays declared with constant +bounds, and may not apply to all character variables. +Future versions of GNU Fortran may improve this behavior. + +The default value for @var{n} is 65536. + +@item -fstack-arrays +@opindex @code{fstack-arrays} +Adding this option will make the Fortran compiler put all arrays of +unknown size and array temporaries onto stack memory. If your program uses very +large local arrays it is possible that you will have to extend your runtime +limits for stack memory on some operating systems. This flag is enabled +by default at optimization level @option{-Ofast} unless +@option{-fmax-stack-var-size} is specified. + +@item -fpack-derived +@opindex @code{fpack-derived} +@cindex structure packing +This option tells GNU Fortran to pack derived type members as closely as +possible. Code compiled with this option is likely to be incompatible +with code compiled without this option, and may execute slower. + +@item -frepack-arrays +@opindex @code{frepack-arrays} +@cindex repacking arrays +In some circumstances GNU Fortran may pass assumed shape array +sections via a descriptor describing a noncontiguous area of memory. +This option adds code to the function prologue to repack the data into +a contiguous block at runtime. + +This should result in faster accesses to the array. However it can introduce +significant overhead to the function call, especially when the passed data +is noncontiguous. + +@item -fshort-enums +@opindex @code{fshort-enums} +This option is provided for interoperability with C code that was +compiled with the @option{-fshort-enums} option. It will make +GNU Fortran choose the smallest @code{INTEGER} kind a given +enumerator set will fit in, and give all its enumerators this kind. + +@item -finline-arg-packing +@opindex @code{finline-arg-packing} +When passing an assumed-shape argument of a procedure as actual +argument to an assumed-size or explicit size or as argument to a +procedure that does not have an explicit interface, the argument may +have to be packed, that is put into contiguous memory. An example is +the call to @code{foo} in +@smallexample + subroutine foo(a) + real, dimension(*) :: a + end subroutine foo + subroutine bar(b) + real, dimension(:) :: b + call foo(b) + end subroutine bar +@end smallexample + +When @option{-finline-arg-packing} is in effect, this packing will be +performed by inline code. This allows for more optimization while +increasing code size. + +@option{-finline-arg-packing} is implied by any of the @option{-O} options +except when optimizing for size via @option{-Os}. If the code +contains a very large number of argument that have to be packed, code +size and also compilation time may become excessive. If that is the +case, it may be better to disable this option. Instances of packing +can be found by using @option{-Warray-temporaries}. + +@item -fexternal-blas +@opindex @code{fexternal-blas} +This option will make @command{gfortran} generate calls to BLAS functions +for some matrix operations like @code{MATMUL}, instead of using our own +algorithms, if the size of the matrices involved is larger than a given +limit (see @option{-fblas-matmul-limit}). This may be profitable if an +optimized vendor BLAS library is available. The BLAS library will have +to be specified at link time. + +@item -fblas-matmul-limit=@var{n} +@opindex @code{fblas-matmul-limit} +Only significant when @option{-fexternal-blas} is in effect. +Matrix multiplication of matrices with size larger than (or equal to) @var{n} +will be performed by calls to BLAS functions, while others will be +handled by @command{gfortran} internal algorithms. If the matrices +involved are not square, the size comparison is performed using the +geometric mean of the dimensions of the argument and result matrices. + +The default value for @var{n} is 30. + +@item -finline-matmul-limit=@var{n} +@opindex @code{finline-matmul-limit} +When front-end optimization is active, some calls to the @code{MATMUL} +intrinsic function will be inlined. This may result in code size +increase if the size of the matrix cannot be determined at compile +time, as code for both cases is generated. Setting +@code{-finline-matmul-limit=0} will disable inlining in all cases. +Setting this option with a value of @var{n} will produce inline code +for matrices with size up to @var{n}. If the matrices involved are not +square, the size comparison is performed using the geometric mean of +the dimensions of the argument and result matrices. + +The default value for @var{n} is 30. The @code{-fblas-matmul-limit} +can be used to change this value. + +@item -frecursive +@opindex @code{frecursive} +Allow indirect recursion by forcing all local arrays to be allocated +on the stack. This flag cannot be used together with +@option{-fmax-stack-var-size=} or @option{-fno-automatic}. + +@item -finit-local-zero +@itemx -finit-derived +@itemx -finit-integer=@var{n} +@itemx -finit-real=@var{} +@itemx -finit-logical=@var{} +@itemx -finit-character=@var{n} +@opindex @code{finit-local-zero} +@opindex @code{finit-derived} +@opindex @code{finit-integer} +@opindex @code{finit-real} +@opindex @code{finit-logical} +@opindex @code{finit-character} +The @option{-finit-local-zero} option instructs the compiler to +initialize local @code{INTEGER}, @code{REAL}, and @code{COMPLEX} +variables to zero, @code{LOGICAL} variables to false, and +@code{CHARACTER} variables to a string of null bytes. Finer-grained +initialization options are provided by the +@option{-finit-integer=@var{n}}, +@option{-finit-real=@var{}} (which also initializes +the real and imaginary parts of local @code{COMPLEX} variables), +@option{-finit-logical=@var{}}, and +@option{-finit-character=@var{n}} (where @var{n} is an ASCII character +value) options. + +With @option{-finit-derived}, components of derived type variables will be +initialized according to these flags. Components whose type is not covered by +an explicit @option{-finit-*} flag will be treated as described above with +@option{-finit-local-zero}. + +These options do not initialize +@itemize @bullet +@item +objects with the POINTER attribute +@item +allocatable arrays +@item +variables that appear in an @code{EQUIVALENCE} statement. +@end itemize +(These limitations may be removed in future releases). + +Note that the @option{-finit-real=nan} option initializes @code{REAL} +and @code{COMPLEX} variables with a quiet NaN. For a signalling NaN +use @option{-finit-real=snan}; note, however, that compile-time +optimizations may convert them into quiet NaN and that trapping +needs to be enabled (e.g. via @option{-ffpe-trap}). + +The @option{-finit-integer} option will parse the value into an +integer of type @code{INTEGER(kind=C_LONG)} on the host. Said value +is then assigned to the integer variables in the Fortran code, which +might result in wraparound if the value is too large for the kind. + +Finally, note that enabling any of the @option{-finit-*} options will +silence warnings that would have been emitted by @option{-Wuninitialized} +for the affected local variables. + +@item -falign-commons +@opindex @code{falign-commons} +@cindex alignment of @code{COMMON} blocks +By default, @command{gfortran} enforces proper alignment of all variables in a +@code{COMMON} block by padding them as needed. On certain platforms this is mandatory, +on others it increases performance. If a @code{COMMON} block is not declared with +consistent data types everywhere, this padding can cause trouble, and +@option{-fno-align-commons} can be used to disable automatic alignment. The +same form of this option should be used for all files that share a @code{COMMON} block. +To avoid potential alignment issues in @code{COMMON} blocks, it is recommended to order +objects from largest to smallest. + +@item -fno-protect-parens +@opindex @code{fno-protect-parens} +@cindex re-association of parenthesized expressions +By default the parentheses in expression are honored for all optimization +levels such that the compiler does not do any re-association. Using +@option{-fno-protect-parens} allows the compiler to reorder @code{REAL} and +@code{COMPLEX} expressions to produce faster code. Note that for the re-association +optimization @option{-fno-signed-zeros} and @option{-fno-trapping-math} +need to be in effect. The parentheses protection is enabled by default, unless +@option{-Ofast} is given. + +@item -frealloc-lhs +@opindex @code{frealloc-lhs} +@cindex Reallocate the LHS in assignments +An allocatable left-hand side of an intrinsic assignment is automatically +(re)allocated if it is either unallocated or has a different shape. The +option is enabled by default except when @option{-std=f95} is given. See +also @option{-Wrealloc-lhs}. + +@item -faggressive-function-elimination +@opindex @code{faggressive-function-elimination} +@cindex Elimination of functions with identical argument lists +Functions with identical argument lists are eliminated within +statements, regardless of whether these functions are marked +@code{PURE} or not. For example, in +@smallexample + a = f(b,c) + f(b,c) +@end smallexample +there will only be a single call to @code{f}. This option only works +if @option{-ffrontend-optimize} is in effect. + +@item -ffrontend-optimize +@opindex @code{frontend-optimize} +@cindex Front-end optimization +This option performs front-end optimization, based on manipulating +parts the Fortran parse tree. Enabled by default by any @option{-O} option +except @option{-O0} and @option{-Og}. Optimizations enabled by this option +include: +@itemize @bullet +@item inlining calls to @code{MATMUL}, +@item elimination of identical function calls within expressions, +@item removing unnecessary calls to @code{TRIM} in comparisons and assignments, +@item replacing @code{TRIM(a)} with @code{a(1:LEN_TRIM(a))} and +@item short-circuiting of logical operators (@code{.AND.} and @code{.OR.}). +@end itemize +It can be deselected by specifying @option{-fno-frontend-optimize}. + +@item -ffrontend-loop-interchange +@opindex @code{frontend-loop-interchange} +@cindex loop interchange, Fortran +Attempt to interchange loops in the Fortran front end where +profitable. Enabled by default by any @option{-O} option. +At the moment, this option only affects @code{FORALL} and +@code{DO CONCURRENT} statements with several forall triplets. +@end table + +@xref{Code Gen Options,,Options for Code Generation Conventions, +gcc,Using the GNU Compiler Collection (GCC)}, for information on more options +offered by the GBE +shared by @command{gfortran}, @command{gcc}, and other GNU compilers. + +@c man end + +@node Interoperability Options +@section Options for interoperability with other languages + +@table @asis + +@item -fc-prototypes +@opindex @code{c-prototypes} +@cindex Generating C prototypes from Fortran BIND(C) enteties +This option will generate C prototypes from @code{BIND(C)} variable +declarations, types and procedure interfaces and writes them to +standard output. @code{ENUM} is not yet supported. + +The generated prototypes may need inclusion of an appropriate header, +such as @code{} or @code{}. For types which are +not specified using the appropriate kind from the @code{iso_c_binding} +module, a warning is added as a comment to the code. + +For function pointers, a pointer to a function returning @code{int} +without an explicit argument list is generated. + +Example of use: +@smallexample +$ gfortran -fc-prototypes -fsyntax-only foo.f90 > foo.h +@end smallexample +where the C code intended for interoperating with the Fortran code +then uses @code{#include "foo.h"}. + +@item -fc-prototypes-external +@opindex @code{c-prototypes-external} +@cindex Generating C prototypes from external procedures +This option will generate C prototypes from external functions and +subroutines and write them to standard output. This may be useful for +making sure that C bindings to Fortran code are correct. This option +does not generate prototypes for @code{BIND(C)} procedures, use +@option{-fc-prototypes} for that. + +The generated prototypes may need inclusion of an appropriate +header, such as @code{} or @code{}. + +This is primarily meant for legacy code to ensure that existing C +bindings match what @command{gfortran} emits. The generated C +prototypes should be correct for the current version of the compiler, +but may not match what other compilers or earlier versions of +@command{gfortran} need. For new developments, use of the +@code{BIND(C)} features is recommended. + +Example of use: +@smallexample +$ gfortran -fc-prototypes-external -fsyntax-only foo.f > foo.h +@end smallexample +where the C code intended for interoperating with the Fortran code +then uses @code{#include "foo.h"}. +@end table + +@node Environment Variables +@section Environment variables affecting @command{gfortran} +@cindex environment variable + +@c man begin ENVIRONMENT + +The @command{gfortran} compiler currently does not make use of any environment +variables to control its operation above and beyond those +that affect the operation of @command{gcc}. + +@xref{Environment Variables,,Environment Variables Affecting GCC, +gcc,Using the GNU Compiler Collection (GCC)}, for information on environment +variables. + +@xref{Runtime}, for environment variables that affect the +run-time behavior of programs compiled with GNU Fortran. +@c man end diff --git a/gcc/go/gccgo.texi b/gcc/go/gccgo.texi new file mode 100644 index 00000000000..66020aa7eb7 --- /dev/null +++ b/gcc/go/gccgo.texi @@ -0,0 +1,521 @@ +\input texinfo @c -*-texinfo-*- +@setfilename gccgo.info +@settitle The GNU Go Compiler + +@c Merge the standard indexes into a single one. +@syncodeindex fn cp +@syncodeindex vr cp +@syncodeindex ky cp +@syncodeindex pg cp +@syncodeindex tp cp + +@include gcc-common.texi + +@c Copyright years for this manual. +@set copyrights-go 2010-2022 + +@copying +@c man begin COPYRIGHT +Copyright @copyright{} @value{copyrights-go} Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with no +Invariant Sections, the Front-Cover Texts being (a) (see below), and +with the Back-Cover Texts being (b) (see below). +A copy of the license is included in the +@c man end +section entitled ``GNU Free Documentation License''. +@ignore +@c man begin COPYRIGHT +man page gfdl(7). +@c man end +@end ignore + +@c man begin COPYRIGHT + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@c man end +@end copying + +@ifinfo +@format +@dircategory Software development +@direntry +* Gccgo: (gccgo). A GCC-based compiler for the Go language +@end direntry +@end format + +@insertcopying +@end ifinfo + +@titlepage +@title The GNU Go Compiler +@versionsubtitle +@author Ian Lance Taylor + +@page +@vskip 0pt plus 1filll +Published by the Free Software Foundation @* +51 Franklin Street, Fifth Floor@* +Boston, MA 02110-1301, USA@* +@sp 1 +@insertcopying +@end titlepage +@contents +@page + +@node Top +@top Introduction + +This manual describes how to use @command{gccgo}, the GNU compiler for +the Go programming language. This manual is specifically about +@command{gccgo}. For more information about the Go programming +language in general, including language specifications and standard +package documentation, see @uref{https://golang.org/}. + +@menu +* Copying:: The GNU General Public License. +* GNU Free Documentation License:: + How you can share and copy this manual. +* Invoking gccgo:: How to run gccgo. +* Import and Export:: Importing and exporting package data. +* Compiler Directives:: Comments to control compilation. +* C Interoperability:: Calling C from Go and vice-versa. +* Index:: Index. +@end menu + + +@include gpl_v3.texi + +@include fdl.texi + + +@node Invoking gccgo +@chapter Invoking gccgo + +@c man title gccgo A GCC-based compiler for the Go language + +@ignore +@c man begin SYNOPSIS gccgo +gccgo [@option{-c}|@option{-S}] + [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] + [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] + [@option{-o} @var{outfile}] @var{infile}@dots{} + +Only the most useful options are listed here; see below for the +remainder. +@c man end +@c man begin SEEALSO +gpl(7), gfdl(7), fsf-funding(7), gcc(1) +and the Info entries for @file{gccgo} and @file{gcc}. +@c man end +@end ignore + +@c man begin DESCRIPTION gccgo + +The @command{gccgo} command is a frontend to @command{gcc} and +supports many of the same options. @xref{Option Summary, , Option +Summary, gcc, Using the GNU Compiler Collection (GCC)}. This manual +only documents the options specific to @command{gccgo}. + +The @command{gccgo} command may be used to compile Go source code into +an object file, link a collection of object files together, or do both +in sequence. + +Go source code is compiled as packages. A package consists of one or +more Go source files. All the files in a single package must be +compiled together, by passing all the files as arguments to +@command{gccgo}. A single invocation of @command{gccgo} may only +compile a single package. + +One Go package may @code{import} a different Go package. The imported +package must have already been compiled; @command{gccgo} will read +the import data directly from the compiled package. When this package +is later linked, the compiled form of the package must be included in +the link command. + +Go programs must generally be compiled with debugging information, and +@option{-g1} is the default as described below. Stripping a Go +program will generally cause it to misbehave or fail. + +@c man end + +@c man begin OPTIONS gccgo + +@table @gcctabopt +@item -I@var{dir} +@cindex @option{-I} +Specify a directory to use when searching for an import package at +compile time. + +@item -L@var{dir} +@cindex @option{-L} +When linking, specify a library search directory, as with +@command{gcc}. + +@item -fgo-pkgpath=@var{string} +@cindex @option{-fgo-pkgpath} +Set the package path to use. This sets the value returned by the +PkgPath method of reflect.Type objects. It is also used for the names +of globally visible symbols. The argument to this option should +normally be the string that will be used to import this package after +it has been installed; in other words, a pathname within the +directories specified by the @option{-I} option. + +@item -fgo-prefix=@var{string} +@cindex @option{-fgo-prefix} +An alternative to @option{-fgo-pkgpath}. The argument will be +combined with the package name from the source file to produce the +package path. If @option{-fgo-pkgpath} is used, @option{-fgo-prefix} +will be ignored. + +Go permits a single program to include more than one package with the +same name in the @code{package} clause in the source file, though +obviously the two packages must be imported using different pathnames. +In order for this to work with @command{gccgo}, either +@option{-fgo-pkgpath} or @option{-fgo-prefix} must be specified when +compiling a package. + +Using either @option{-fgo-pkgpath} or @option{-fgo-prefix} disables +the special treatment of the @code{main} package and permits that +package to be imported like any other. + +@item -fgo-relative-import-path=@var{dir} +@cindex @option{-fgo-relative-import-path} +A relative import is an import that starts with @file{./} or +@file{../}. If this option is used, @command{gccgo} will use +@var{dir} as a prefix for the relative import when searching for it. + +@item -frequire-return-statement +@itemx -fno-require-return-statement +@cindex @option{-frequire-return-statement} +@cindex @option{-fno-require-return-statement} +By default @command{gccgo} will warn about functions which have one or +more return parameters but lack an explicit @code{return} statement. +This warning may be disabled using +@option{-fno-require-return-statement}. + +@item -fgo-check-divide-zero +@cindex @option{-fgo-check-divide-zero} +@cindex @option{-fno-go-check-divide-zero} +Add explicit checks for division by zero. In Go a division (or +modulos) by zero causes a panic. On Unix systems this is detected in +the runtime by catching the @code{SIGFPE} signal. Some processors, +such as PowerPC, do not generate a SIGFPE on division by zero. Some +runtimes do not generate a signal that can be caught. On those +systems, this option may be used. Or the checks may be removed via +@option{-fno-go-check-divide-zero}. This option is currently on by +default, but in the future may be off by default on systems that do +not require it. + +@item -fgo-check-divide-overflow +@cindex @option{-fgo-check-divide-overflow} +@cindex @option{-fno-go-check-divide-overflow} +Add explicit checks for division overflow. For example, division +overflow occurs when computing @code{INT_MIN / -1}. In Go this should +be wrapped, to produce @code{INT_MIN}. Some processors, such as x86, +generate a trap on division overflow. On those systems, this option +may be used. Or the checks may be removed via +@option{-fno-go-check-divide-overflow}. This option is currently on +by default, but in the future may be off by default on systems that do +not require it. + +@item -fno-go-optimize-allocs +@cindex @option{-fno-go-optimize-allocs} +Disable escape analysis, which tries to allocate objects on the stack +rather than the heap. + +@item -fgo-debug-escape@var{n} +@cindex @option{-fgo-debug-escape} +Output escape analysis debugging information. Larger values of +@var{n} generate more information. + +@item -fgo-debug-escape-hash=@var{n} +@cindex @option{-fgo-debug-escape-hash} +A hash value to debug escape analysis. @var{n} is a binary string. +This runs escape analysis only on functions whose names hash to values +that match the given suffix @var{n}. This can be used to binary +search across functions to uncover escape analysis bugs. + +@item -fgo-debug-optimization +@cindex @option{-fgo-debug-optimization} +@cindex @option{-fno-go-debug-optimization} +Output optimization diagnostics. + +@item -fgo-c-header=@var{file} +@cindex @option{-fgo-c-header} +Write top-level named Go struct definitions to @var{file} as C code. +This is used when compiling the runtime package. + +@item -fgo-compiling-runtime +@cindex @option{-fgo-compiling-runtime} +Apply special rules for compiling the runtime package. Implicit +memory allocation is forbidden. Some additional compiler directives +are supported. + +@item -fgo-embedcfg=@var{file} +@cindex @option{-fgo-embedcfg} +Identify a JSON file used to map patterns used with special +@code{//go:embed} comments to the files named by the patterns. The +JSON file should have two components: @code{Patterns} maps each +pattern to a list of file names, and @code{Files} maps each file name +to a full path to the file. This option is intended for use by the +@command{go} command to implement @code{//go:embed}. + +@item -g +@cindex @option{-g for gccgo} +This is the standard @command{gcc} option (@pxref{Debugging Options, , +Debugging Options, gcc, Using the GNU Compiler Collection (GCC)}). It +is mentioned here because by default @command{gccgo} turns on +debugging information generation with the equivalent of the standard +option @option{-g1}. This is because Go programs require debugging +information to be available in order to get backtrace information. An +explicit @option{-g0} may be used to disable the generation of +debugging information, in which case certain standard library +functions, such as @code{runtime.Callers}, will not operate correctly. +@end table + +@c man end + +@node Import and Export +@chapter Import and Export + +When @command{gccgo} compiles a package which exports anything, the +export information will be stored directly in the object file. When a +package is imported, @command{gccgo} must be able to find the file. + +@cindex @file{.gox} +When Go code imports the package @file{@var{gopackage}}, @command{gccgo} +will look for the import data using the following filenames, using the +first one that it finds. + +@table @file +@item @var{gopackage}.gox +@item lib@var{gopackage}.so +@item lib@var{gopackage}.a +@item @var{gopackage}.o +@end table + +The compiler will search for these files in the directories named by +any @option{-I} options, in order in which the directories appear on +the command line. The compiler will then search several standard +system directories. Finally the compiler will search the current +directory (to search the current directory earlier, use @samp{-I.}). + +The compiler will extract the export information directly from the +compiled object file. The file @file{@var{gopackage}.gox} will +typically contain nothing but export data. This can be generated from +@file{@var{gopackage}.o} via + +@smallexample +objcopy -j .go_export @var{gopackage}.o @var{gopackage}.gox +@end smallexample + +For example, it may be desirable to extract the export information +from several different packages into their independent +@file{@var{gopackage}.gox} files, and then to combine the different +package object files together into a single shared library or archive. + +At link time you must explicitly tell @command{gccgo} which files to +link together into the executable, as is usual with @command{gcc}. +This is different from the behavior of other Go compilers. + +@node Compiler Directives +@chapter Compiler Directives + +The Go compiler supports a few compiler directives. A compiler +directive uses a @code{//} comment at the start of a line. There must +be no space between the @code{//} and the name of the directive. + +@table @code +@item //line @var{file}:@var{line} +The @code{//line} directive specifies that the source line that +follows should be recorded as having come from the given file path and +line number. Successive lines are recorded using increasing line +numbers, until the next directive. This directive typically appears +in machine-generated code, so that compilers and debuggers will show +lines in the original input to the generator. + +@item //extern @var{extern_name} +The @code{extern} directive sets the externally visible name of the +next function declaration. See @ref{Function Names}. + +@item //go:compile @var{go_name} @var{extern_name} +The @code{go:compile} directives sets the externally visible name of a +function definition or declaration. See @ref{Function Names}. + +@item //go:noescape +The @code{//go:noescape} directive specifies that the next declaration +in the file, which must be a func without a body (meaning that it has +an implementation not written in Go) does not allow any of the +pointers passed as arguments to escape into the heap or into the +values returned from the function. This information can be used during +the compiler's escape analysis of Go code calling the function. + +@item //go:nosplit +The @code{//go:nosplit} directive specifies that the next function +declared in the file must not include a stack overflow check. This is +most commonly used by low-level runtime sources invoked at times when +it is unsafe for the calling goroutine to be preempted. + +@item //go:noinline +The @code{//go:noinline} directive specifies that the next function +defined in the file may not be inlined. + +@end table + +@node C Interoperability +@chapter C Interoperability + +When using @command{gccgo} there is limited interoperability with C, +or with C++ code compiled using @code{extern "C"}. + +This information is provided largely for documentation purposes. For +ordinary use it is best to build programs with the go tool and then +use @code{import "C"}, as described at +@url{https://golang.org/cmd/cgo}. + +@menu +* C Type Interoperability:: How C and Go types match up. +* Function Names:: How Go functions are named. +@end menu + +@node C Type Interoperability +@section C Type Interoperability + +Basic types map directly: an @code{int} in Go is an @code{int} in C, +etc. Go @code{byte} is equivalent to C @code{unsigned char}. +Pointers in Go are pointers in C. A Go @code{struct} is the same as C +@code{struct} with the same field names and types. + +@cindex @code{string} in C +The Go @code{string} type is currently defined as a two-element +structure: + +@smallexample +struct __go_string @{ + const unsigned char *__data; + int __length; +@}; +@end smallexample + +You can't pass arrays between C and Go. However, a pointer to an +array in Go is equivalent to a C pointer to the equivalent of the +element type. For example, Go @code{*[10]int} is equivalent to C +@code{int*}, assuming that the C pointer does point to 10 elements. + +@cindex @code{slice} in C +A slice in Go is a structure. The current definition is: + +@smallexample +struct __go_slice @{ + void *__values; + int __count; + int __capacity; +@}; +@end smallexample + +The type of a Go function with no receiver is equivalent to a C +function whose parameter types are equivalent. When a Go function +returns more than one value, the C function returns a struct. For +example, these functions have equivalent types: + +@smallexample +func GoFunction(int) (int, float) +struct @{ int i; float f; @} CFunction(int) +@end smallexample + +A pointer to a Go function is equivalent to a pointer to a C function +when the functions have equivalent types. + +Go @code{interface}, @code{channel}, and @code{map} types have no +corresponding C type (@code{interface} is a two-element struct and +@code{channel} and @code{map} are pointers to structs in C, but the +structs are deliberately undocumented). C @code{enum} types +correspond to some integer type, but precisely which one is difficult +to predict in general; use a cast. C @code{union} types have no +corresponding Go type. C @code{struct} types containing bitfields +have no corresponding Go type. C++ @code{class} types have no +corresponding Go type. + +Memory allocation is completely different between C and Go, as Go uses +garbage collection. The exact guidelines in this area are +undetermined, but it is likely that it will be permitted to pass a +pointer to allocated memory from C to Go. The responsibility of +eventually freeing the pointer will remain with C side, and of course +if the C side frees the pointer while the Go side still has a copy the +program will fail. When passing a pointer from Go to C, the Go +function must retain a visible copy of it in some Go variable. +Otherwise the Go garbage collector may delete the pointer while the C +function is still using it. + +@node Function Names +@section Function Names + +@cindex @code{extern} +@cindex external names +Go code can call C functions directly using the @code{//extern} or +@code{//go:linkname} compiler directives. An @code{//extern} +directive must be at the beginning of the line and must start with +@code{//extern}. This must be followed by a space and then the +external name of the function. The function declaration must be on +the line immediately after the comment. For example, here is how the +C function @code{open} can be declared in Go: + +@smallexample +//extern open +func c_open(name *byte, mode int, perm int) int +@end smallexample + +You can do the same thing using the @code{//go:linkname} compiler +directive. The @code{//go:linkname} directive must be at the start of +the line. It is followed by whitespace, the name of the Go function, +more whitespace, and the external name of the function. Unlike +@code{//extern}, @code{//go:linkname} does not need to appear +immediately adjacent to the function definition or declaration. + +@smallexample +//go:linkname c_open open +func c_open(name *byte, mode int, perm int) int +@end smallexample + +The C function naturally expects a nul terminated string, which in Go +is equivalent to a pointer to an array (not a slice!) of @code{byte} +with a terminating zero byte. So a sample call from Go would look +like (after importing the @code{os} package): + +@smallexample +var name = [4]byte@{'f', 'o', 'o', 0@}; +i := c_open(&name[0], os.O_RDONLY, 0); +@end smallexample + +Note that this serves as an example only. To open a file in Go please +use Go's @code{os.Open} function instead. + +The name of Go functions accessed from C is subject to change. At +present the name of a Go function that does not have a receiver is +@code{pkgpath.Functionname}. The @var{pkgpath} is set by the +@option{-fgo-pkgpath} option used when the package is compiled; if the +option is not used, the default is @code{go.@var{packagename}}. To +call the function from C you must set the name using the @command{gcc} +@code{__asm__} extension. + +@smallexample +extern int go_function(int) __asm__ ("mypkgpath.Function"); +@end smallexample + +@node Index +@unnumbered Index + +@printindex cp + +@bye diff --git a/libgomp/libgomp.texi b/libgomp/libgomp.texi new file mode 100644 index 00000000000..10fefa97922 --- /dev/null +++ b/libgomp/libgomp.texi @@ -0,0 +1,4884 @@ +\input texinfo @c -*-texinfo-*- + +@c %**start of header +@setfilename libgomp.info +@settitle GNU libgomp +@c %**end of header + + +@copying +Copyright @copyright{} 2006-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``Funding Free Software'', the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +(a) The FSF's Front-Cover Text is: + + A GNU Manual + +(b) The FSF's Back-Cover Text is: + + You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. +@end copying + +@ifinfo +@dircategory GNU Libraries +@direntry +* libgomp: (libgomp). GNU Offloading and Multi Processing Runtime Library. +@end direntry + +This manual documents libgomp, the GNU Offloading and Multi Processing +Runtime library. This is the GNU implementation of the OpenMP and +OpenACC APIs for parallel and accelerator programming in C/C++ and +Fortran. + +Published by the Free Software Foundation +51 Franklin Street, Fifth Floor +Boston, MA 02110-1301 USA + +@insertcopying +@end ifinfo + + +@setchapternewpage odd + +@titlepage +@title GNU Offloading and Multi Processing Runtime Library +@subtitle The GNU OpenMP and OpenACC Implementation +@page +@vskip 0pt plus 1filll +@comment For the @value{version-GCC} Version* +@sp 1 +Published by the Free Software Foundation @* +51 Franklin Street, Fifth Floor@* +Boston, MA 02110-1301, USA@* +@sp 1 +@insertcopying +@end titlepage + +@summarycontents +@contents +@page + + +@node Top, Enabling OpenMP +@top Introduction +@cindex Introduction + +This manual documents the usage of libgomp, the GNU Offloading and +Multi Processing Runtime Library. This includes the GNU +implementation of the @uref{https://www.openmp.org, OpenMP} Application +Programming Interface (API) for multi-platform shared-memory parallel +programming in C/C++ and Fortran, and the GNU implementation of the +@uref{https://www.openacc.org, OpenACC} Application Programming +Interface (API) for offloading of code to accelerator devices in C/C++ +and Fortran. + +Originally, libgomp implemented the GNU OpenMP Runtime Library. Based +on this, support for OpenACC and offloading (both OpenACC and OpenMP +4's target construct) has been added later on, and the library's name +changed to GNU Offloading and Multi Processing Runtime Library. + + + +@comment +@comment When you add a new menu item, please keep the right hand +@comment aligned to the same column. Do not use tabs. This provides +@comment better formatting. +@comment +@menu +* Enabling OpenMP:: How to enable OpenMP for your applications. +* OpenMP Implementation Status:: List of implemented features by OpenMP version +* OpenMP Runtime Library Routines: Runtime Library Routines. + The OpenMP runtime application programming + interface. +* OpenMP Environment Variables: Environment Variables. + Influencing OpenMP runtime behavior with + environment variables. +* Enabling OpenACC:: How to enable OpenACC for your + applications. +* OpenACC Runtime Library Routines:: The OpenACC runtime application + programming interface. +* OpenACC Environment Variables:: Influencing OpenACC runtime behavior with + environment variables. +* CUDA Streams Usage:: Notes on the implementation of + asynchronous operations. +* OpenACC Library Interoperability:: OpenACC library interoperability with the + NVIDIA CUBLAS library. +* OpenACC Profiling Interface:: +* OpenMP-Implementation Specifics:: Notes specifics of this OpenMP + implementation +* Offload-Target Specifics:: Notes on offload-target specific internals +* The libgomp ABI:: Notes on the external ABI presented by libgomp. +* Reporting Bugs:: How to report bugs in the GNU Offloading and + Multi Processing Runtime Library. +* Copying:: GNU general public license says + how you can copy and share libgomp. +* GNU Free Documentation License:: + How you can copy and share this manual. +* Funding:: How to help assure continued work for free + software. +* Library Index:: Index of this documentation. +@end menu + + +@c --------------------------------------------------------------------- +@c Enabling OpenMP +@c --------------------------------------------------------------------- + +@node Enabling OpenMP +@chapter Enabling OpenMP + +To activate the OpenMP extensions for C/C++ and Fortran, the compile-time +flag @command{-fopenmp} must be specified. This enables the OpenMP directive +@code{#pragma omp} in C/C++ and @code{!$omp} directives in free form, +@code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form, +@code{!$} conditional compilation sentinels in free form and @code{c$}, +@code{*$} and @code{!$} sentinels in fixed form, for Fortran. The flag also +arranges for automatic linking of the OpenMP runtime library +(@ref{Runtime Library Routines}). + +A complete description of all OpenMP directives may be found in the +@uref{https://www.openmp.org, OpenMP Application Program Interface} manuals. +See also @ref{OpenMP Implementation Status}. + + +@c --------------------------------------------------------------------- +@c OpenMP Implementation Status +@c --------------------------------------------------------------------- + +@node OpenMP Implementation Status +@chapter OpenMP Implementation Status + +@menu +* OpenMP 4.5:: Feature completion status to 4.5 specification +* OpenMP 5.0:: Feature completion status to 5.0 specification +* OpenMP 5.1:: Feature completion status to 5.1 specification +* OpenMP 5.2:: Feature completion status to 5.2 specification +@end menu + +The @code{_OPENMP} preprocessor macro and Fortran's @code{openmp_version} +parameter, provided by @code{omp_lib.h} and the @code{omp_lib} module, have +the value @code{201511} (i.e. OpenMP 4.5). + +@node OpenMP 4.5 +@section OpenMP 4.5 + +The OpenMP 4.5 specification is fully supported. + +@node OpenMP 5.0 +@section OpenMP 5.0 + +@unnumberedsubsec New features listed in Appendix B of the OpenMP specification +@c This list is sorted as in OpenMP 5.1's B.3 not as in OpenMP 5.0's B.2 + +@multitable @columnfractions .60 .10 .25 +@headitem Description @tab Status @tab Comments +@item Array shaping @tab N @tab +@item Array sections with non-unit strides in C and C++ @tab N @tab +@item Iterators @tab Y @tab +@item @code{metadirective} directive @tab N @tab +@item @code{declare variant} directive + @tab P @tab @emph{simd} traits not handled correctly +@item @emph{target-offload-var} ICV and @code{OMP_TARGET_OFFLOAD} + env variable @tab Y @tab +@item Nested-parallel changes to @emph{max-active-levels-var} ICV @tab Y @tab +@item @code{requires} directive @tab P + @tab complete but no non-host devices provides @code{unified_address}, + @code{unified_shared_memory} or @code{reverse_offload} +@item @code{teams} construct outside an enclosing target region @tab Y @tab +@item Non-rectangular loop nests @tab Y @tab +@item @code{!=} as relational-op in canonical loop form for C/C++ @tab Y @tab +@item @code{nonmonotonic} as default loop schedule modifier for worksharing-loop + constructs @tab Y @tab +@item Collapse of associated loops that are imperfectly nested loops @tab N @tab +@item Clauses @code{if}, @code{nontemporal} and @code{order(concurrent)} in + @code{simd} construct @tab Y @tab +@item @code{atomic} constructs in @code{simd} @tab Y @tab +@item @code{loop} construct @tab Y @tab +@item @code{order(concurrent)} clause @tab Y @tab +@item @code{scan} directive and @code{in_scan} modifier for the + @code{reduction} clause @tab Y @tab +@item @code{in_reduction} clause on @code{task} constructs @tab Y @tab +@item @code{in_reduction} clause on @code{target} constructs @tab P + @tab @code{nowait} only stub +@item @code{task_reduction} clause with @code{taskgroup} @tab Y @tab +@item @code{task} modifier to @code{reduction} clause @tab Y @tab +@item @code{affinity} clause to @code{task} construct @tab Y @tab Stub only +@item @code{detach} clause to @code{task} construct @tab Y @tab +@item @code{omp_fulfill_event} runtime routine @tab Y @tab +@item @code{reduction} and @code{in_reduction} clauses on @code{taskloop} + and @code{taskloop simd} constructs @tab Y @tab +@item @code{taskloop} construct cancelable by @code{cancel} construct + @tab Y @tab +@item @code{mutexinoutset} @emph{dependence-type} for @code{depend} clause + @tab Y @tab +@item Predefined memory spaces, memory allocators, allocator traits + @tab Y @tab Some are only stubs +@item Memory management routines @tab Y @tab +@item @code{allocate} directive @tab N @tab +@item @code{allocate} clause @tab P @tab Initial support +@item @code{use_device_addr} clause on @code{target data} @tab Y @tab +@item @code{ancestor} modifier on @code{device} clause + @tab Y @tab See comment for @code{requires} +@item Implicit declare target directive @tab Y @tab +@item Discontiguous array section with @code{target update} construct + @tab N @tab +@item C/C++'s lvalue expressions in @code{to}, @code{from} + and @code{map} clauses @tab N @tab +@item C/C++'s lvalue expressions in @code{depend} clauses @tab Y @tab +@item Nested @code{declare target} directive @tab Y @tab +@item Combined @code{master} constructs @tab Y @tab +@item @code{depend} clause on @code{taskwait} @tab Y @tab +@item Weak memory ordering clauses on @code{atomic} and @code{flush} construct + @tab Y @tab +@item @code{hint} clause on the @code{atomic} construct @tab Y @tab Stub only +@item @code{depobj} construct and depend objects @tab Y @tab +@item Lock hints were renamed to synchronization hints @tab Y @tab +@item @code{conditional} modifier to @code{lastprivate} clause @tab Y @tab +@item Map-order clarifications @tab P @tab +@item @code{close} @emph{map-type-modifier} @tab Y @tab +@item Mapping C/C++ pointer variables and to assign the address of + device memory mapped by an array section @tab P @tab +@item Mapping of Fortran pointer and allocatable variables, including pointer + and allocatable components of variables + @tab P @tab Mapping of vars with allocatable components unsupported +@item @code{defaultmap} extensions @tab Y @tab +@item @code{declare mapper} directive @tab N @tab +@item @code{omp_get_supported_active_levels} routine @tab Y @tab +@item Runtime routines and environment variables to display runtime thread + affinity information @tab Y @tab +@item @code{omp_pause_resource} and @code{omp_pause_resource_all} runtime + routines @tab Y @tab +@item @code{omp_get_device_num} runtime routine @tab Y @tab +@item OMPT interface @tab N @tab +@item OMPD interface @tab N @tab +@end multitable + +@unnumberedsubsec Other new OpenMP 5.0 features + +@multitable @columnfractions .60 .10 .25 +@headitem Description @tab Status @tab Comments +@item Supporting C++'s range-based for loop @tab Y @tab +@end multitable + + +@node OpenMP 5.1 +@section OpenMP 5.1 + +@unnumberedsubsec New features listed in Appendix B of the OpenMP specification + +@multitable @columnfractions .60 .10 .25 +@headitem Description @tab Status @tab Comments +@item OpenMP directive as C++ attribute specifiers @tab Y @tab +@item @code{omp_all_memory} reserved locator @tab Y @tab +@item @emph{target_device trait} in OpenMP Context @tab N @tab +@item @code{target_device} selector set in context selectors @tab N @tab +@item C/C++'s @code{declare variant} directive: elision support of + preprocessed code @tab N @tab +@item @code{declare variant}: new clauses @code{adjust_args} and + @code{append_args} @tab N @tab +@item @code{dispatch} construct @tab N @tab +@item device-specific ICV settings with environment variables @tab Y @tab +@item @code{assume} directive @tab Y @tab +@item @code{nothing} directive @tab Y @tab +@item @code{error} directive @tab Y @tab +@item @code{masked} construct @tab Y @tab +@item @code{scope} directive @tab Y @tab +@item Loop transformation constructs @tab N @tab +@item @code{strict} modifier in the @code{grainsize} and @code{num_tasks} + clauses of the @code{taskloop} construct @tab Y @tab +@item @code{align} clause/modifier in @code{allocate} directive/clause + and @code{allocator} directive @tab P @tab C/C++ on clause only +@item @code{thread_limit} clause to @code{target} construct @tab Y @tab +@item @code{has_device_addr} clause to @code{target} construct @tab Y @tab +@item Iterators in @code{target update} motion clauses and @code{map} + clauses @tab N @tab +@item Indirect calls to the device version of a procedure or function in + @code{target} regions @tab N @tab +@item @code{interop} directive @tab N @tab +@item @code{omp_interop_t} object support in runtime routines @tab N @tab +@item @code{nowait} clause in @code{taskwait} directive @tab Y @tab +@item Extensions to the @code{atomic} directive @tab Y @tab +@item @code{seq_cst} clause on a @code{flush} construct @tab Y @tab +@item @code{inoutset} argument to the @code{depend} clause @tab Y @tab +@item @code{private} and @code{firstprivate} argument to @code{default} + clause in C and C++ @tab Y @tab +@item @code{present} argument to @code{defaultmap} clause @tab N @tab +@item @code{omp_set_num_teams}, @code{omp_set_teams_thread_limit}, + @code{omp_get_max_teams}, @code{omp_get_teams_thread_limit} runtime + routines @tab Y @tab +@item @code{omp_target_is_accessible} runtime routine @tab Y @tab +@item @code{omp_target_memcpy_async} and @code{omp_target_memcpy_rect_async} + runtime routines @tab Y @tab +@item @code{omp_get_mapped_ptr} runtime routine @tab Y @tab +@item @code{omp_calloc}, @code{omp_realloc}, @code{omp_aligned_alloc} and + @code{omp_aligned_calloc} runtime routines @tab Y @tab +@item @code{omp_alloctrait_key_t} enum: @code{omp_atv_serialized} added, + @code{omp_atv_default} changed @tab Y @tab +@item @code{omp_display_env} runtime routine @tab Y @tab +@item @code{ompt_scope_endpoint_t} enum: @code{ompt_scope_beginend} @tab N @tab +@item @code{ompt_sync_region_t} enum additions @tab N @tab +@item @code{ompt_state_t} enum: @code{ompt_state_wait_barrier_implementation} + and @code{ompt_state_wait_barrier_teams} @tab N @tab +@item @code{ompt_callback_target_data_op_emi_t}, + @code{ompt_callback_target_emi_t}, @code{ompt_callback_target_map_emi_t} + and @code{ompt_callback_target_submit_emi_t} @tab N @tab +@item @code{ompt_callback_error_t} type @tab N @tab +@item @code{OMP_PLACES} syntax extensions @tab Y @tab +@item @code{OMP_NUM_TEAMS} and @code{OMP_TEAMS_THREAD_LIMIT} environment + variables @tab Y @tab +@end multitable + +@unnumberedsubsec Other new OpenMP 5.1 features + +@multitable @columnfractions .60 .10 .25 +@headitem Description @tab Status @tab Comments +@item Support of strictly structured blocks in Fortran @tab Y @tab +@item Support of structured block sequences in C/C++ @tab Y @tab +@item @code{unconstrained} and @code{reproducible} modifiers on @code{order} + clause @tab Y @tab +@item Support @code{begin/end declare target} syntax in C/C++ @tab Y @tab +@item Pointer predetermined firstprivate getting initialized +to address of matching mapped list item per 5.1, Sect. 2.21.7.2 @tab N @tab +@item For Fortran, diagnose placing declarative before/between @code{USE}, + @code{IMPORT}, and @code{IMPLICIT} as invalid @tab N @tab +@end multitable + + +@node OpenMP 5.2 +@section OpenMP 5.2 + +@unnumberedsubsec New features listed in Appendix B of the OpenMP specification + +@multitable @columnfractions .60 .10 .25 +@headitem Description @tab Status @tab Comments +@item @code{omp_in_explicit_task} routine and @emph{explicit-task-var} ICV + @tab Y @tab +@item @code{omp}/@code{ompx}/@code{omx} sentinels and @code{omp_}/@code{ompx_} + namespaces @tab N/A + @tab warning for @code{ompx/omx} sentinels@footnote{The @code{ompx} + sentinel as C/C++ pragma and C++ attributes are warned for with + @code{-Wunknown-pragmas} (implied by @code{-Wall}) and @code{-Wattributes} + (enabled by default), respectively; for Fortran free-source code, there is + a warning enabled by default and, for fixed-source code, the @code{omx} + sentinel is warned for with with @code{-Wsurprising} (enabled by + @code{-Wall}). Unknown clauses are always rejected with an error.} +@item Clauses on @code{end} directive can be on directive @tab N @tab +@item Deprecation of no-argument @code{destroy} clause on @code{depobj} + @tab N @tab +@item @code{linear} clause syntax changes and @code{step} modifier @tab Y @tab +@item Deprecation of minus operator for reductions @tab N @tab +@item Deprecation of separating @code{map} modifiers without comma @tab N @tab +@item @code{declare mapper} with iterator and @code{present} modifiers + @tab N @tab +@item If a matching mapped list item is not found in the data environment, the + pointer retains its original value @tab N @tab +@item New @code{enter} clause as alias for @code{to} on declare target directive + @tab Y @tab +@item Deprecation of @code{to} clause on declare target directive @tab N @tab +@item Extended list of directives permitted in Fortran pure procedures + @tab N @tab +@item New @code{allocators} directive for Fortran @tab N @tab +@item Deprecation of @code{allocate} directive for Fortran + allocatables/pointers @tab N @tab +@item Optional paired @code{end} directive with @code{dispatch} @tab N @tab +@item New @code{memspace} and @code{traits} modifiers for @code{uses_allocators} + @tab N @tab +@item Deprecation of traits array following the allocator_handle expression in + @code{uses_allocators} @tab N @tab +@item New @code{otherwise} clause as alias for @code{default} on metadirectives + @tab N @tab +@item Deprecation of @code{default} clause on metadirectives @tab N @tab +@item Deprecation of delimited form of @code{declare target} @tab N @tab +@item Reproducible semantics changed for @code{order(concurrent)} @tab N @tab +@item @code{allocate} and @code{firstprivate} clauses on @code{scope} + @tab Y @tab +@item @code{ompt_callback_work} @tab N @tab +@item Default map-type for @code{map} clause in @code{target enter/exit data} + @tab Y @tab +@item New @code{doacross} clause as alias for @code{depend} with + @code{source}/@code{sink} modifier @tab Y @tab +@item Deprecation of @code{depend} with @code{source}/@code{sink} modifier + @tab N @tab +@item @code{omp_cur_iteration} keyword @tab Y @tab +@end multitable + +@unnumberedsubsec Other new OpenMP 5.2 features + +@multitable @columnfractions .60 .10 .25 +@headitem Description @tab Status @tab Comments +@item For Fortran, optional comma between directive and clause @tab N @tab +@item Conforming device numbers and @code{omp_initial_device} and + @code{omp_invalid_device} enum/PARAMETER @tab Y @tab +@item Initial value of @emph{default-device-var} ICV with + @code{OMP_TARGET_OFFLOAD=mandatory} @tab N @tab +@item @emph{interop_types} in any position of the modifier list for the @code{init} clause + of the @code{interop} construct @tab N @tab +@end multitable + + +@c --------------------------------------------------------------------- +@c OpenMP Runtime Library Routines +@c --------------------------------------------------------------------- + +@node Runtime Library Routines +@chapter OpenMP Runtime Library Routines + +The runtime routines described here are defined by Section 3 of the OpenMP +specification in version 4.5. The routines are structured in following +three parts: + +@menu +Control threads, processors and the parallel environment. They have C +linkage, and do not throw exceptions. + +* omp_get_active_level:: Number of active parallel regions +* omp_get_ancestor_thread_num:: Ancestor thread ID +* omp_get_cancellation:: Whether cancellation support is enabled +* omp_get_default_device:: Get the default device for target regions +* omp_get_device_num:: Get device that current thread is running on +* omp_get_dynamic:: Dynamic teams setting +* omp_get_initial_device:: Device number of host device +* omp_get_level:: Number of parallel regions +* omp_get_max_active_levels:: Current maximum number of active regions +* omp_get_max_task_priority:: Maximum task priority value that can be set +* omp_get_max_teams:: Maximum number of teams for teams region +* omp_get_max_threads:: Maximum number of threads of parallel region +* omp_get_nested:: Nested parallel regions +* omp_get_num_devices:: Number of target devices +* omp_get_num_procs:: Number of processors online +* omp_get_num_teams:: Number of teams +* omp_get_num_threads:: Size of the active team +* omp_get_proc_bind:: Whether theads may be moved between CPUs +* omp_get_schedule:: Obtain the runtime scheduling method +* omp_get_supported_active_levels:: Maximum number of active regions supported +* omp_get_team_num:: Get team number +* omp_get_team_size:: Number of threads in a team +* omp_get_teams_thread_limit:: Maximum number of threads imposed by teams +* omp_get_thread_limit:: Maximum number of threads +* omp_get_thread_num:: Current thread ID +* omp_in_parallel:: Whether a parallel region is active +* omp_in_final:: Whether in final or included task region +* omp_is_initial_device:: Whether executing on the host device +* omp_set_default_device:: Set the default device for target regions +* omp_set_dynamic:: Enable/disable dynamic teams +* omp_set_max_active_levels:: Limits the number of active parallel regions +* omp_set_nested:: Enable/disable nested parallel regions +* omp_set_num_teams:: Set upper teams limit for teams region +* omp_set_num_threads:: Set upper team size limit +* omp_set_schedule:: Set the runtime scheduling method +* omp_set_teams_thread_limit:: Set upper thread limit for teams construct + +Initialize, set, test, unset and destroy simple and nested locks. + +* omp_init_lock:: Initialize simple lock +* omp_set_lock:: Wait for and set simple lock +* omp_test_lock:: Test and set simple lock if available +* omp_unset_lock:: Unset simple lock +* omp_destroy_lock:: Destroy simple lock +* omp_init_nest_lock:: Initialize nested lock +* omp_set_nest_lock:: Wait for and set simple lock +* omp_test_nest_lock:: Test and set nested lock if available +* omp_unset_nest_lock:: Unset nested lock +* omp_destroy_nest_lock:: Destroy nested lock + +Portable, thread-based, wall clock timer. + +* omp_get_wtick:: Get timer precision. +* omp_get_wtime:: Elapsed wall clock time. + +Support for event objects. + +* omp_fulfill_event:: Fulfill and destroy an OpenMP event. +@end menu + + + +@node omp_get_active_level +@section @code{omp_get_active_level} -- Number of parallel regions +@table @asis +@item @emph{Description}: +This function returns the nesting level for the active parallel blocks, +which enclose the calling call. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_active_level(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_active_level()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_level}, @ref{omp_get_max_active_levels}, @ref{omp_set_max_active_levels} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.20. +@end table + + + +@node omp_get_ancestor_thread_num +@section @code{omp_get_ancestor_thread_num} -- Ancestor thread ID +@table @asis +@item @emph{Description}: +This function returns the thread identification number for the given +nesting level of the current thread. For values of @var{level} outside +zero to @code{omp_get_level} -1 is returned; if @var{level} is +@code{omp_get_level} the result is identical to @code{omp_get_thread_num}. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_ancestor_thread_num(int level);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_ancestor_thread_num(level)} +@item @tab @code{integer level} +@end multitable + +@item @emph{See also}: +@ref{omp_get_level}, @ref{omp_get_thread_num}, @ref{omp_get_team_size} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.18. +@end table + + + +@node omp_get_cancellation +@section @code{omp_get_cancellation} -- Whether cancellation support is enabled +@table @asis +@item @emph{Description}: +This function returns @code{true} if cancellation is activated, @code{false} +otherwise. Here, @code{true} and @code{false} represent their language-specific +counterparts. Unless @env{OMP_CANCELLATION} is set true, cancellations are +deactivated. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_cancellation(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{logical function omp_get_cancellation()} +@end multitable + +@item @emph{See also}: +@ref{OMP_CANCELLATION} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.9. +@end table + + + +@node omp_get_default_device +@section @code{omp_get_default_device} -- Get the default device for target regions +@table @asis +@item @emph{Description}: +Get the default device for target regions without device clause. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_default_device(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_default_device()} +@end multitable + +@item @emph{See also}: +@ref{OMP_DEFAULT_DEVICE}, @ref{omp_set_default_device} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.30. +@end table + + + +@node omp_get_device_num +@section @code{omp_get_device_num} -- Return device number of current device +@table @asis +@item @emph{Description}: +This function returns a device number that represents the device that the +current thread is executing on. For OpenMP 5.0, this must be equal to the +value returned by the @code{omp_get_initial_device} function when called +from the host. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_device_num(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_device_num()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_initial_device} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.0}, Section 3.2.37. +@end table + + + +@node omp_get_dynamic +@section @code{omp_get_dynamic} -- Dynamic teams setting +@table @asis +@item @emph{Description}: +This function returns @code{true} if enabled, @code{false} otherwise. +Here, @code{true} and @code{false} represent their language-specific +counterparts. + +The dynamic team setting may be initialized at startup by the +@env{OMP_DYNAMIC} environment variable or at runtime using +@code{omp_set_dynamic}. If undefined, dynamic adjustment is +disabled by default. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_dynamic(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{logical function omp_get_dynamic()} +@end multitable + +@item @emph{See also}: +@ref{omp_set_dynamic}, @ref{OMP_DYNAMIC} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.8. +@end table + + + +@node omp_get_initial_device +@section @code{omp_get_initial_device} -- Return device number of initial device +@table @asis +@item @emph{Description}: +This function returns a device number that represents the host device. +For OpenMP 5.1, this must be equal to the value returned by the +@code{omp_get_num_devices} function. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_initial_device(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_initial_device()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_num_devices} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.35. +@end table + + + +@node omp_get_level +@section @code{omp_get_level} -- Obtain the current nesting level +@table @asis +@item @emph{Description}: +This function returns the nesting level for the parallel blocks, +which enclose the calling call. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_level(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_level()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_active_level} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.17. +@end table + + + +@node omp_get_max_active_levels +@section @code{omp_get_max_active_levels} -- Current maximum number of active regions +@table @asis +@item @emph{Description}: +This function obtains the maximum allowed number of nested, active parallel regions. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_max_active_levels(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_max_active_levels()} +@end multitable + +@item @emph{See also}: +@ref{omp_set_max_active_levels}, @ref{omp_get_active_level} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.16. +@end table + + +@node omp_get_max_task_priority +@section @code{omp_get_max_task_priority} -- Maximum priority value +that can be set for tasks. +@table @asis +@item @emph{Description}: +This function obtains the maximum allowed priority number for tasks. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_max_task_priority(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_max_task_priority()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.29. +@end table + + +@node omp_get_max_teams +@section @code{omp_get_max_teams} -- Maximum number of teams of teams region +@table @asis +@item @emph{Description}: +Return the maximum number of teams used for the teams region +that does not use the clause @code{num_teams}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_max_teams(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_max_teams()} +@end multitable + +@item @emph{See also}: +@ref{omp_set_num_teams}, @ref{omp_get_num_teams} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.1}, Section 3.4.4. +@end table + + + +@node omp_get_max_threads +@section @code{omp_get_max_threads} -- Maximum number of threads of parallel region +@table @asis +@item @emph{Description}: +Return the maximum number of threads used for the current parallel region +that does not use the clause @code{num_threads}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_max_threads(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_max_threads()} +@end multitable + +@item @emph{See also}: +@ref{omp_set_num_threads}, @ref{omp_set_dynamic}, @ref{omp_get_thread_limit} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.3. +@end table + + + +@node omp_get_nested +@section @code{omp_get_nested} -- Nested parallel regions +@table @asis +@item @emph{Description}: +This function returns @code{true} if nested parallel regions are +enabled, @code{false} otherwise. Here, @code{true} and @code{false} +represent their language-specific counterparts. + +The state of nested parallel regions at startup depends on several +environment variables. If @env{OMP_MAX_ACTIVE_LEVELS} is defined +and is set to greater than one, then nested parallel regions will be +enabled. If not defined, then the value of the @env{OMP_NESTED} +environment variable will be followed if defined. If neither are +defined, then if either @env{OMP_NUM_THREADS} or @env{OMP_PROC_BIND} +are defined with a list of more than one value, then nested parallel +regions are enabled. If none of these are defined, then nested parallel +regions are disabled by default. + +Nested parallel regions can be enabled or disabled at runtime using +@code{omp_set_nested}, or by setting the maximum number of nested +regions with @code{omp_set_max_active_levels} to one to disable, or +above one to enable. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_nested(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{logical function omp_get_nested()} +@end multitable + +@item @emph{See also}: +@ref{omp_set_max_active_levels}, @ref{omp_set_nested}, +@ref{OMP_MAX_ACTIVE_LEVELS}, @ref{OMP_NESTED} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.11. +@end table + + + +@node omp_get_num_devices +@section @code{omp_get_num_devices} -- Number of target devices +@table @asis +@item @emph{Description}: +Returns the number of target devices. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_num_devices(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_num_devices()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.31. +@end table + + + +@node omp_get_num_procs +@section @code{omp_get_num_procs} -- Number of processors online +@table @asis +@item @emph{Description}: +Returns the number of processors online on that device. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_num_procs(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_num_procs()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.5. +@end table + + + +@node omp_get_num_teams +@section @code{omp_get_num_teams} -- Number of teams +@table @asis +@item @emph{Description}: +Returns the number of teams in the current team region. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_num_teams(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_num_teams()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.32. +@end table + + + +@node omp_get_num_threads +@section @code{omp_get_num_threads} -- Size of the active team +@table @asis +@item @emph{Description}: +Returns the number of threads in the current team. In a sequential section of +the program @code{omp_get_num_threads} returns 1. + +The default team size may be initialized at startup by the +@env{OMP_NUM_THREADS} environment variable. At runtime, the size +of the current team may be set either by the @code{NUM_THREADS} +clause or by @code{omp_set_num_threads}. If none of the above were +used to define a specific value and @env{OMP_DYNAMIC} is disabled, +one thread per CPU online is used. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_num_threads(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_num_threads()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_max_threads}, @ref{omp_set_num_threads}, @ref{OMP_NUM_THREADS} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.2. +@end table + + + +@node omp_get_proc_bind +@section @code{omp_get_proc_bind} -- Whether theads may be moved between CPUs +@table @asis +@item @emph{Description}: +This functions returns the currently active thread affinity policy, which is +set via @env{OMP_PROC_BIND}. Possible values are @code{omp_proc_bind_false}, +@code{omp_proc_bind_true}, @code{omp_proc_bind_primary}, +@code{omp_proc_bind_master}, @code{omp_proc_bind_close} and @code{omp_proc_bind_spread}, +where @code{omp_proc_bind_master} is an alias for @code{omp_proc_bind_primary}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{omp_proc_bind_t omp_get_proc_bind(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer(kind=omp_proc_bind_kind) function omp_get_proc_bind()} +@end multitable + +@item @emph{See also}: +@ref{OMP_PROC_BIND}, @ref{OMP_PLACES}, @ref{GOMP_CPU_AFFINITY}, + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.22. +@end table + + + +@node omp_get_schedule +@section @code{omp_get_schedule} -- Obtain the runtime scheduling method +@table @asis +@item @emph{Description}: +Obtain the runtime scheduling method. The @var{kind} argument will be +set to the value @code{omp_sched_static}, @code{omp_sched_dynamic}, +@code{omp_sched_guided} or @code{omp_sched_auto}. The second argument, +@var{chunk_size}, is set to the chunk size. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_get_schedule(omp_sched_t *kind, int *chunk_size);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_get_schedule(kind, chunk_size)} +@item @tab @code{integer(kind=omp_sched_kind) kind} +@item @tab @code{integer chunk_size} +@end multitable + +@item @emph{See also}: +@ref{omp_set_schedule}, @ref{OMP_SCHEDULE} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.13. +@end table + + +@node omp_get_supported_active_levels +@section @code{omp_get_supported_active_levels} -- Maximum number of active regions supported +@table @asis +@item @emph{Description}: +This function returns the maximum number of nested, active parallel regions +supported by this implementation. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_supported_active_levels(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_supported_active_levels()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_max_active_levels}, @ref{omp_set_max_active_levels} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.0}, Section 3.2.15. +@end table + + + +@node omp_get_team_num +@section @code{omp_get_team_num} -- Get team number +@table @asis +@item @emph{Description}: +Returns the team number of the calling thread. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_team_num(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_team_num()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.33. +@end table + + + +@node omp_get_team_size +@section @code{omp_get_team_size} -- Number of threads in a team +@table @asis +@item @emph{Description}: +This function returns the number of threads in a thread team to which +either the current thread or its ancestor belongs. For values of @var{level} +outside zero to @code{omp_get_level}, -1 is returned; if @var{level} is zero, +1 is returned, and for @code{omp_get_level}, the result is identical +to @code{omp_get_num_threads}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_team_size(int level);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_team_size(level)} +@item @tab @code{integer level} +@end multitable + +@item @emph{See also}: +@ref{omp_get_num_threads}, @ref{omp_get_level}, @ref{omp_get_ancestor_thread_num} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.19. +@end table + + + +@node omp_get_teams_thread_limit +@section @code{omp_get_teams_thread_limit} -- Maximum number of threads imposed by teams +@table @asis +@item @emph{Description}: +Return the maximum number of threads that will be able to participate in +each team created by a teams construct. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_teams_thread_limit(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_teams_thread_limit()} +@end multitable + +@item @emph{See also}: +@ref{omp_set_teams_thread_limit}, @ref{OMP_TEAMS_THREAD_LIMIT} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.1}, Section 3.4.6. +@end table + + + +@node omp_get_thread_limit +@section @code{omp_get_thread_limit} -- Maximum number of threads +@table @asis +@item @emph{Description}: +Return the maximum number of threads of the program. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_thread_limit(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_thread_limit()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_max_threads}, @ref{OMP_THREAD_LIMIT} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.14. +@end table + + + +@node omp_get_thread_num +@section @code{omp_get_thread_num} -- Current thread ID +@table @asis +@item @emph{Description}: +Returns a unique thread identification number within the current team. +In a sequential parts of the program, @code{omp_get_thread_num} +always returns 0. In parallel regions the return value varies +from 0 to @code{omp_get_num_threads}-1 inclusive. The return +value of the primary thread of a team is always 0. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_get_thread_num(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function omp_get_thread_num()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_num_threads}, @ref{omp_get_ancestor_thread_num} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.4. +@end table + + + +@node omp_in_parallel +@section @code{omp_in_parallel} -- Whether a parallel region is active +@table @asis +@item @emph{Description}: +This function returns @code{true} if currently running in parallel, +@code{false} otherwise. Here, @code{true} and @code{false} represent +their language-specific counterparts. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_in_parallel(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{logical function omp_in_parallel()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.6. +@end table + + +@node omp_in_final +@section @code{omp_in_final} -- Whether in final or included task region +@table @asis +@item @emph{Description}: +This function returns @code{true} if currently running in a final +or included task region, @code{false} otherwise. Here, @code{true} +and @code{false} represent their language-specific counterparts. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_in_final(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{logical function omp_in_final()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.21. +@end table + + + +@node omp_is_initial_device +@section @code{omp_is_initial_device} -- Whether executing on the host device +@table @asis +@item @emph{Description}: +This function returns @code{true} if currently running on the host device, +@code{false} otherwise. Here, @code{true} and @code{false} represent +their language-specific counterparts. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_is_initial_device(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{logical function omp_is_initial_device()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.34. +@end table + + + +@node omp_set_default_device +@section @code{omp_set_default_device} -- Set the default device for target regions +@table @asis +@item @emph{Description}: +Set the default device for target regions without device clause. The argument +shall be a nonnegative device number. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_default_device(int device_num);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_default_device(device_num)} +@item @tab @code{integer device_num} +@end multitable + +@item @emph{See also}: +@ref{OMP_DEFAULT_DEVICE}, @ref{omp_get_default_device} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.29. +@end table + + + +@node omp_set_dynamic +@section @code{omp_set_dynamic} -- Enable/disable dynamic teams +@table @asis +@item @emph{Description}: +Enable or disable the dynamic adjustment of the number of threads +within a team. The function takes the language-specific equivalent +of @code{true} and @code{false}, where @code{true} enables dynamic +adjustment of team sizes and @code{false} disables it. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_dynamic(int dynamic_threads);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_dynamic(dynamic_threads)} +@item @tab @code{logical, intent(in) :: dynamic_threads} +@end multitable + +@item @emph{See also}: +@ref{OMP_DYNAMIC}, @ref{omp_get_dynamic} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.7. +@end table + + + +@node omp_set_max_active_levels +@section @code{omp_set_max_active_levels} -- Limits the number of active parallel regions +@table @asis +@item @emph{Description}: +This function limits the maximum allowed number of nested, active +parallel regions. @var{max_levels} must be less or equal to +the value returned by @code{omp_get_supported_active_levels}. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_max_active_levels(int max_levels);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_max_active_levels(max_levels)} +@item @tab @code{integer max_levels} +@end multitable + +@item @emph{See also}: +@ref{omp_get_max_active_levels}, @ref{omp_get_active_level}, +@ref{omp_get_supported_active_levels} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.15. +@end table + + + +@node omp_set_nested +@section @code{omp_set_nested} -- Enable/disable nested parallel regions +@table @asis +@item @emph{Description}: +Enable or disable nested parallel regions, i.e., whether team members +are allowed to create new teams. The function takes the language-specific +equivalent of @code{true} and @code{false}, where @code{true} enables +dynamic adjustment of team sizes and @code{false} disables it. + +Enabling nested parallel regions will also set the maximum number of +active nested regions to the maximum supported. Disabling nested parallel +regions will set the maximum number of active nested regions to one. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_nested(int nested);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_nested(nested)} +@item @tab @code{logical, intent(in) :: nested} +@end multitable + +@item @emph{See also}: +@ref{omp_get_nested}, @ref{omp_set_max_active_levels}, +@ref{OMP_MAX_ACTIVE_LEVELS}, @ref{OMP_NESTED} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.10. +@end table + + + +@node omp_set_num_teams +@section @code{omp_set_num_teams} -- Set upper teams limit for teams construct +@table @asis +@item @emph{Description}: +Specifies the upper bound for number of teams created by the teams construct +which does not specify a @code{num_teams} clause. The +argument of @code{omp_set_num_teams} shall be a positive integer. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_num_teams(int num_teams);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_num_teams(num_teams)} +@item @tab @code{integer, intent(in) :: num_teams} +@end multitable + +@item @emph{See also}: +@ref{OMP_NUM_TEAMS}, @ref{omp_get_num_teams}, @ref{omp_get_max_teams} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.1}, Section 3.4.3. +@end table + + + +@node omp_set_num_threads +@section @code{omp_set_num_threads} -- Set upper team size limit +@table @asis +@item @emph{Description}: +Specifies the number of threads used by default in subsequent parallel +sections, if those do not specify a @code{num_threads} clause. The +argument of @code{omp_set_num_threads} shall be a positive integer. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_num_threads(int num_threads);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_num_threads(num_threads)} +@item @tab @code{integer, intent(in) :: num_threads} +@end multitable + +@item @emph{See also}: +@ref{OMP_NUM_THREADS}, @ref{omp_get_num_threads}, @ref{omp_get_max_threads} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.1. +@end table + + + +@node omp_set_schedule +@section @code{omp_set_schedule} -- Set the runtime scheduling method +@table @asis +@item @emph{Description}: +Sets the runtime scheduling method. The @var{kind} argument can have the +value @code{omp_sched_static}, @code{omp_sched_dynamic}, +@code{omp_sched_guided} or @code{omp_sched_auto}. Except for +@code{omp_sched_auto}, the chunk size is set to the value of +@var{chunk_size} if positive, or to the default value if zero or negative. +For @code{omp_sched_auto} the @var{chunk_size} argument is ignored. + +@item @emph{C/C++} +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_schedule(omp_sched_t kind, int chunk_size);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_schedule(kind, chunk_size)} +@item @tab @code{integer(kind=omp_sched_kind) kind} +@item @tab @code{integer chunk_size} +@end multitable + +@item @emph{See also}: +@ref{omp_get_schedule} +@ref{OMP_SCHEDULE} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.2.12. +@end table + + + +@node omp_set_teams_thread_limit +@section @code{omp_set_teams_thread_limit} -- Set upper thread limit for teams construct +@table @asis +@item @emph{Description}: +Specifies the upper bound for number of threads that will be available +for each team created by the teams construct which does not specify a +@code{thread_limit} clause. The argument of +@code{omp_set_teams_thread_limit} shall be a positive integer. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_teams_thread_limit(int thread_limit);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_teams_thread_limit(thread_limit)} +@item @tab @code{integer, intent(in) :: thread_limit} +@end multitable + +@item @emph{See also}: +@ref{OMP_TEAMS_THREAD_LIMIT}, @ref{omp_get_teams_thread_limit}, @ref{omp_get_thread_limit} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.1}, Section 3.4.5. +@end table + + + +@node omp_init_lock +@section @code{omp_init_lock} -- Initialize simple lock +@table @asis +@item @emph{Description}: +Initialize a simple lock. After initialization, the lock is in +an unlocked state. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_init_lock(omp_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_init_lock(svar)} +@item @tab @code{integer(omp_lock_kind), intent(out) :: svar} +@end multitable + +@item @emph{See also}: +@ref{omp_destroy_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.1. +@end table + + + +@node omp_set_lock +@section @code{omp_set_lock} -- Wait for and set simple lock +@table @asis +@item @emph{Description}: +Before setting a simple lock, the lock variable must be initialized by +@code{omp_init_lock}. The calling thread is blocked until the lock +is available. If the lock is already held by the current thread, +a deadlock occurs. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_lock(omp_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_lock(svar)} +@item @tab @code{integer(omp_lock_kind), intent(inout) :: svar} +@end multitable + +@item @emph{See also}: +@ref{omp_init_lock}, @ref{omp_test_lock}, @ref{omp_unset_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.4. +@end table + + + +@node omp_test_lock +@section @code{omp_test_lock} -- Test and set simple lock if available +@table @asis +@item @emph{Description}: +Before setting a simple lock, the lock variable must be initialized by +@code{omp_init_lock}. Contrary to @code{omp_set_lock}, @code{omp_test_lock} +does not block if the lock is not available. This function returns +@code{true} upon success, @code{false} otherwise. Here, @code{true} and +@code{false} represent their language-specific counterparts. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_test_lock(omp_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{logical function omp_test_lock(svar)} +@item @tab @code{integer(omp_lock_kind), intent(inout) :: svar} +@end multitable + +@item @emph{See also}: +@ref{omp_init_lock}, @ref{omp_set_lock}, @ref{omp_set_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.6. +@end table + + + +@node omp_unset_lock +@section @code{omp_unset_lock} -- Unset simple lock +@table @asis +@item @emph{Description}: +A simple lock about to be unset must have been locked by @code{omp_set_lock} +or @code{omp_test_lock} before. In addition, the lock must be held by the +thread calling @code{omp_unset_lock}. Then, the lock becomes unlocked. If one +or more threads attempted to set the lock before, one of them is chosen to, +again, set the lock to itself. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_unset_lock(omp_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_unset_lock(svar)} +@item @tab @code{integer(omp_lock_kind), intent(inout) :: svar} +@end multitable + +@item @emph{See also}: +@ref{omp_set_lock}, @ref{omp_test_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.5. +@end table + + + +@node omp_destroy_lock +@section @code{omp_destroy_lock} -- Destroy simple lock +@table @asis +@item @emph{Description}: +Destroy a simple lock. In order to be destroyed, a simple lock must be +in the unlocked state. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_destroy_lock(omp_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_destroy_lock(svar)} +@item @tab @code{integer(omp_lock_kind), intent(inout) :: svar} +@end multitable + +@item @emph{See also}: +@ref{omp_init_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.3. +@end table + + + +@node omp_init_nest_lock +@section @code{omp_init_nest_lock} -- Initialize nested lock +@table @asis +@item @emph{Description}: +Initialize a nested lock. After initialization, the lock is in +an unlocked state and the nesting count is set to zero. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_init_nest_lock(omp_nest_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_init_nest_lock(nvar)} +@item @tab @code{integer(omp_nest_lock_kind), intent(out) :: nvar} +@end multitable + +@item @emph{See also}: +@ref{omp_destroy_nest_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.1. +@end table + + +@node omp_set_nest_lock +@section @code{omp_set_nest_lock} -- Wait for and set nested lock +@table @asis +@item @emph{Description}: +Before setting a nested lock, the lock variable must be initialized by +@code{omp_init_nest_lock}. The calling thread is blocked until the lock +is available. If the lock is already held by the current thread, the +nesting count for the lock is incremented. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_set_nest_lock(omp_nest_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_set_nest_lock(nvar)} +@item @tab @code{integer(omp_nest_lock_kind), intent(inout) :: nvar} +@end multitable + +@item @emph{See also}: +@ref{omp_init_nest_lock}, @ref{omp_unset_nest_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.4. +@end table + + + +@node omp_test_nest_lock +@section @code{omp_test_nest_lock} -- Test and set nested lock if available +@table @asis +@item @emph{Description}: +Before setting a nested lock, the lock variable must be initialized by +@code{omp_init_nest_lock}. Contrary to @code{omp_set_nest_lock}, +@code{omp_test_nest_lock} does not block if the lock is not available. +If the lock is already held by the current thread, the new nesting count +is returned. Otherwise, the return value equals zero. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int omp_test_nest_lock(omp_nest_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{logical function omp_test_nest_lock(nvar)} +@item @tab @code{integer(omp_nest_lock_kind), intent(inout) :: nvar} +@end multitable + + +@item @emph{See also}: +@ref{omp_init_lock}, @ref{omp_set_lock}, @ref{omp_set_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.6. +@end table + + + +@node omp_unset_nest_lock +@section @code{omp_unset_nest_lock} -- Unset nested lock +@table @asis +@item @emph{Description}: +A nested lock about to be unset must have been locked by @code{omp_set_nested_lock} +or @code{omp_test_nested_lock} before. In addition, the lock must be held by the +thread calling @code{omp_unset_nested_lock}. If the nesting count drops to zero, the +lock becomes unlocked. If one ore more threads attempted to set the lock before, +one of them is chosen to, again, set the lock to itself. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_unset_nest_lock(omp_nest_lock_t *lock);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_unset_nest_lock(nvar)} +@item @tab @code{integer(omp_nest_lock_kind), intent(inout) :: nvar} +@end multitable + +@item @emph{See also}: +@ref{omp_set_nest_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.5. +@end table + + + +@node omp_destroy_nest_lock +@section @code{omp_destroy_nest_lock} -- Destroy nested lock +@table @asis +@item @emph{Description}: +Destroy a nested lock. In order to be destroyed, a nested lock must be +in the unlocked state and its nesting count must equal zero. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_destroy_nest_lock(omp_nest_lock_t *);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_destroy_nest_lock(nvar)} +@item @tab @code{integer(omp_nest_lock_kind), intent(inout) :: nvar} +@end multitable + +@item @emph{See also}: +@ref{omp_init_lock} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.3.3. +@end table + + + +@node omp_get_wtick +@section @code{omp_get_wtick} -- Get timer precision +@table @asis +@item @emph{Description}: +Gets the timer precision, i.e., the number of seconds between two +successive clock ticks. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{double omp_get_wtick(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{double precision function omp_get_wtick()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_wtime} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.4.2. +@end table + + + +@node omp_get_wtime +@section @code{omp_get_wtime} -- Elapsed wall clock time +@table @asis +@item @emph{Description}: +Elapsed wall clock time in seconds. The time is measured per thread, no +guarantee can be made that two distinct threads measure the same time. +Time is measured from some "time in the past", which is an arbitrary time +guaranteed not to change during the execution of the program. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{double omp_get_wtime(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{double precision function omp_get_wtime()} +@end multitable + +@item @emph{See also}: +@ref{omp_get_wtick} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 3.4.1. +@end table + + + +@node omp_fulfill_event +@section @code{omp_fulfill_event} -- Fulfill and destroy an OpenMP event +@table @asis +@item @emph{Description}: +Fulfill the event associated with the event handle argument. Currently, it +is only used to fulfill events generated by detach clauses on task +constructs - the effect of fulfilling the event is to allow the task to +complete. + +The result of calling @code{omp_fulfill_event} with an event handle other +than that generated by a detach clause is undefined. Calling it with an +event handle that has already been fulfilled is also undefined. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void omp_fulfill_event(omp_event_handle_t event);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine omp_fulfill_event(event)} +@item @tab @code{integer (kind=omp_event_handle_kind) :: event} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.0}, Section 3.5.1. +@end table + + + +@c --------------------------------------------------------------------- +@c OpenMP Environment Variables +@c --------------------------------------------------------------------- + +@node Environment Variables +@chapter OpenMP Environment Variables + +The environment variables which beginning with @env{OMP_} are defined by +section 4 of the OpenMP specification in version 4.5, while those +beginning with @env{GOMP_} are GNU extensions. + +@menu +* OMP_CANCELLATION:: Set whether cancellation is activated +* OMP_DISPLAY_ENV:: Show OpenMP version and environment variables +* OMP_DEFAULT_DEVICE:: Set the device used in target regions +* OMP_DYNAMIC:: Dynamic adjustment of threads +* OMP_MAX_ACTIVE_LEVELS:: Set the maximum number of nested parallel regions +* OMP_MAX_TASK_PRIORITY:: Set the maximum task priority value +* OMP_NESTED:: Nested parallel regions +* OMP_NUM_TEAMS:: Specifies the number of teams to use by teams region +* OMP_NUM_THREADS:: Specifies the number of threads to use +* OMP_PROC_BIND:: Whether theads may be moved between CPUs +* OMP_PLACES:: Specifies on which CPUs the theads should be placed +* OMP_STACKSIZE:: Set default thread stack size +* OMP_SCHEDULE:: How threads are scheduled +* OMP_TARGET_OFFLOAD:: Controls offloading behaviour +* OMP_TEAMS_THREAD_LIMIT:: Set the maximum number of threads imposed by teams +* OMP_THREAD_LIMIT:: Set the maximum number of threads +* OMP_WAIT_POLICY:: How waiting threads are handled +* GOMP_CPU_AFFINITY:: Bind threads to specific CPUs +* GOMP_DEBUG:: Enable debugging output +* GOMP_STACKSIZE:: Set default thread stack size +* GOMP_SPINCOUNT:: Set the busy-wait spin count +* GOMP_RTEMS_THREAD_POOLS:: Set the RTEMS specific thread pools +@end menu + + +@node OMP_CANCELLATION +@section @env{OMP_CANCELLATION} -- Set whether cancellation is activated +@cindex Environment Variable +@table @asis +@item @emph{Description}: +If set to @code{TRUE}, the cancellation is activated. If set to @code{FALSE} or +if unset, cancellation is disabled and the @code{cancel} construct is ignored. + +@item @emph{See also}: +@ref{omp_get_cancellation} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.11 +@end table + + + +@node OMP_DISPLAY_ENV +@section @env{OMP_DISPLAY_ENV} -- Show OpenMP version and environment variables +@cindex Environment Variable +@table @asis +@item @emph{Description}: +If set to @code{TRUE}, the OpenMP version number and the values +associated with the OpenMP environment variables are printed to @code{stderr}. +If set to @code{VERBOSE}, it additionally shows the value of the environment +variables which are GNU extensions. If undefined or set to @code{FALSE}, +this information will not be shown. + + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.12 +@end table + + + +@node OMP_DEFAULT_DEVICE +@section @env{OMP_DEFAULT_DEVICE} -- Set the device used in target regions +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Set to choose the device which is used in a @code{target} region, unless the +value is overridden by @code{omp_set_default_device} or by a @code{device} +clause. The value shall be the nonnegative device number. If no device with +the given device number exists, the code is executed on the host. If unset, +device number 0 will be used. + + +@item @emph{See also}: +@ref{omp_get_default_device}, @ref{omp_set_default_device}, + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.13 +@end table + + + +@node OMP_DYNAMIC +@section @env{OMP_DYNAMIC} -- Dynamic adjustment of threads +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Enable or disable the dynamic adjustment of the number of threads +within a team. The value of this environment variable shall be +@code{TRUE} or @code{FALSE}. If undefined, dynamic adjustment is +disabled by default. + +@item @emph{See also}: +@ref{omp_set_dynamic} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.3 +@end table + + + +@node OMP_MAX_ACTIVE_LEVELS +@section @env{OMP_MAX_ACTIVE_LEVELS} -- Set the maximum number of nested parallel regions +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Specifies the initial value for the maximum number of nested parallel +regions. The value of this variable shall be a positive integer. +If undefined, then if @env{OMP_NESTED} is defined and set to true, or +if @env{OMP_NUM_THREADS} or @env{OMP_PROC_BIND} are defined and set to +a list with more than one item, the maximum number of nested parallel +regions will be initialized to the largest number supported, otherwise +it will be set to one. + +@item @emph{See also}: +@ref{omp_set_max_active_levels}, @ref{OMP_NESTED} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.9 +@end table + + + +@node OMP_MAX_TASK_PRIORITY +@section @env{OMP_MAX_TASK_PRIORITY} -- Set the maximum priority +number that can be set for a task. +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Specifies the initial value for the maximum priority value that can be +set for a task. The value of this variable shall be a non-negative +integer, and zero is allowed. If undefined, the default priority is +0. + +@item @emph{See also}: +@ref{omp_get_max_task_priority} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.14 +@end table + + + +@node OMP_NESTED +@section @env{OMP_NESTED} -- Nested parallel regions +@cindex Environment Variable +@cindex Implementation specific setting +@table @asis +@item @emph{Description}: +Enable or disable nested parallel regions, i.e., whether team members +are allowed to create new teams. The value of this environment variable +shall be @code{TRUE} or @code{FALSE}. If set to @code{TRUE}, the number +of maximum active nested regions supported will by default be set to the +maximum supported, otherwise it will be set to one. If +@env{OMP_MAX_ACTIVE_LEVELS} is defined, its setting will override this +setting. If both are undefined, nested parallel regions are enabled if +@env{OMP_NUM_THREADS} or @env{OMP_PROC_BINDS} are defined to a list with +more than one item, otherwise they are disabled by default. + +@item @emph{See also}: +@ref{omp_set_max_active_levels}, @ref{omp_set_nested} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.6 +@end table + + + +@node OMP_NUM_TEAMS +@section @env{OMP_NUM_TEAMS} -- Specifies the number of teams to use by teams region +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Specifies the upper bound for number of teams to use in teams regions +without explicit @code{num_teams} clause. The value of this variable shall +be a positive integer. If undefined it defaults to 0 which means +implementation defined upper bound. + +@item @emph{See also}: +@ref{omp_set_num_teams} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.1}, Section 6.23 +@end table + + + +@node OMP_NUM_THREADS +@section @env{OMP_NUM_THREADS} -- Specifies the number of threads to use +@cindex Environment Variable +@cindex Implementation specific setting +@table @asis +@item @emph{Description}: +Specifies the default number of threads to use in parallel regions. The +value of this variable shall be a comma-separated list of positive integers; +the value specifies the number of threads to use for the corresponding nested +level. Specifying more than one item in the list will automatically enable +nesting by default. If undefined one thread per CPU is used. + +@item @emph{See also}: +@ref{omp_set_num_threads}, @ref{OMP_NESTED} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.2 +@end table + + + +@node OMP_PROC_BIND +@section @env{OMP_PROC_BIND} -- Whether theads may be moved between CPUs +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Specifies whether threads may be moved between processors. If set to +@code{TRUE}, OpenMP theads should not be moved; if set to @code{FALSE} +they may be moved. Alternatively, a comma separated list with the +values @code{PRIMARY}, @code{MASTER}, @code{CLOSE} and @code{SPREAD} can +be used to specify the thread affinity policy for the corresponding nesting +level. With @code{PRIMARY} and @code{MASTER} the worker threads are in the +same place partition as the primary thread. With @code{CLOSE} those are +kept close to the primary thread in contiguous place partitions. And +with @code{SPREAD} a sparse distribution +across the place partitions is used. Specifying more than one item in the +list will automatically enable nesting by default. + +When undefined, @env{OMP_PROC_BIND} defaults to @code{TRUE} when +@env{OMP_PLACES} or @env{GOMP_CPU_AFFINITY} is set and @code{FALSE} otherwise. + +@item @emph{See also}: +@ref{omp_get_proc_bind}, @ref{GOMP_CPU_AFFINITY}, +@ref{OMP_NESTED}, @ref{OMP_PLACES} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.4 +@end table + + + +@node OMP_PLACES +@section @env{OMP_PLACES} -- Specifies on which CPUs the theads should be placed +@cindex Environment Variable +@table @asis +@item @emph{Description}: +The thread placement can be either specified using an abstract name or by an +explicit list of the places. The abstract names @code{threads}, @code{cores}, +@code{sockets}, @code{ll_caches} and @code{numa_domains} can be optionally +followed by a positive number in parentheses, which denotes the how many places +shall be created. With @code{threads} each place corresponds to a single +hardware thread; @code{cores} to a single core with the corresponding number of +hardware threads; with @code{sockets} the place corresponds to a single +socket; with @code{ll_caches} to a set of cores that shares the last level +cache on the device; and @code{numa_domains} to a set of cores for which their +closest memory on the device is the same memory and at a similar distance from +the cores. The resulting placement can be shown by setting the +@env{OMP_DISPLAY_ENV} environment variable. + +Alternatively, the placement can be specified explicitly as comma-separated +list of places. A place is specified by set of nonnegative numbers in curly +braces, denoting the hardware threads. The curly braces can be omitted +when only a single number has been specified. The hardware threads +belonging to a place can either be specified as comma-separated list of +nonnegative thread numbers or using an interval. Multiple places can also be +either specified by a comma-separated list of places or by an interval. To +specify an interval, a colon followed by the count is placed after +the hardware thread number or the place. Optionally, the length can be +followed by a colon and the stride number -- otherwise a unit stride is +assumed. Placing an exclamation mark (@code{!}) directly before a curly +brace or numbers inside the curly braces (excluding intervals) will +exclude those hardware threads. + +For instance, the following specifies the same places list: +@code{"@{0,1,2@}, @{3,4,6@}, @{7,8,9@}, @{10,11,12@}"}; +@code{"@{0:3@}, @{3:3@}, @{7:3@}, @{10:3@}"}; and @code{"@{0:2@}:4:3"}. + +If @env{OMP_PLACES} and @env{GOMP_CPU_AFFINITY} are unset and +@env{OMP_PROC_BIND} is either unset or @code{false}, threads may be moved +between CPUs following no placement policy. + +@item @emph{See also}: +@ref{OMP_PROC_BIND}, @ref{GOMP_CPU_AFFINITY}, @ref{omp_get_proc_bind}, +@ref{OMP_DISPLAY_ENV} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.5 +@end table + + + +@node OMP_STACKSIZE +@section @env{OMP_STACKSIZE} -- Set default thread stack size +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Set the default thread stack size in kilobytes, unless the number +is suffixed by @code{B}, @code{K}, @code{M} or @code{G}, in which +case the size is, respectively, in bytes, kilobytes, megabytes +or gigabytes. This is different from @code{pthread_attr_setstacksize} +which gets the number of bytes as an argument. If the stack size cannot +be set due to system constraints, an error is reported and the initial +stack size is left unchanged. If undefined, the stack size is system +dependent. + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.7 +@end table + + + +@node OMP_SCHEDULE +@section @env{OMP_SCHEDULE} -- How threads are scheduled +@cindex Environment Variable +@cindex Implementation specific setting +@table @asis +@item @emph{Description}: +Allows to specify @code{schedule type} and @code{chunk size}. +The value of the variable shall have the form: @code{type[,chunk]} where +@code{type} is one of @code{static}, @code{dynamic}, @code{guided} or @code{auto} +The optional @code{chunk} size shall be a positive integer. If undefined, +dynamic scheduling and a chunk size of 1 is used. + +@item @emph{See also}: +@ref{omp_set_schedule} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Sections 2.7.1.1 and 4.1 +@end table + + + +@node OMP_TARGET_OFFLOAD +@section @env{OMP_TARGET_OFFLOAD} -- Controls offloading behaviour +@cindex Environment Variable +@cindex Implementation specific setting +@table @asis +@item @emph{Description}: +Specifies the behaviour with regard to offloading code to a device. This +variable can be set to one of three values - @code{MANDATORY}, @code{DISABLED} +or @code{DEFAULT}. + +If set to @code{MANDATORY}, the program will terminate with an error if +the offload device is not present or is not supported. If set to +@code{DISABLED}, then offloading is disabled and all code will run on the +host. If set to @code{DEFAULT}, the program will try offloading to the +device first, then fall back to running code on the host if it cannot. + +If undefined, then the program will behave as if @code{DEFAULT} was set. + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.0}, Section 6.17 +@end table + + + +@node OMP_TEAMS_THREAD_LIMIT +@section @env{OMP_TEAMS_THREAD_LIMIT} -- Set the maximum number of threads imposed by teams +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Specifies an upper bound for the number of threads to use by each contention +group created by a teams construct without explicit @code{thread_limit} +clause. The value of this variable shall be a positive integer. If undefined, +the value of 0 is used which stands for an implementation defined upper +limit. + +@item @emph{See also}: +@ref{OMP_THREAD_LIMIT}, @ref{omp_set_teams_thread_limit} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v5.1}, Section 6.24 +@end table + + + +@node OMP_THREAD_LIMIT +@section @env{OMP_THREAD_LIMIT} -- Set the maximum number of threads +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Specifies the number of threads to use for the whole program. The +value of this variable shall be a positive integer. If undefined, +the number of threads is not limited. + +@item @emph{See also}: +@ref{OMP_NUM_THREADS}, @ref{omp_get_thread_limit} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.10 +@end table + + + +@node OMP_WAIT_POLICY +@section @env{OMP_WAIT_POLICY} -- How waiting threads are handled +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Specifies whether waiting threads should be active or passive. If +the value is @code{PASSIVE}, waiting threads should not consume CPU +power while waiting; while the value is @code{ACTIVE} specifies that +they should. If undefined, threads wait actively for a short time +before waiting passively. + +@item @emph{See also}: +@ref{GOMP_SPINCOUNT} + +@item @emph{Reference}: +@uref{https://www.openmp.org, OpenMP specification v4.5}, Section 4.8 +@end table + + + +@node GOMP_CPU_AFFINITY +@section @env{GOMP_CPU_AFFINITY} -- Bind threads to specific CPUs +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Binds threads to specific CPUs. The variable should contain a space-separated +or comma-separated list of CPUs. This list may contain different kinds of +entries: either single CPU numbers in any order, a range of CPUs (M-N) +or a range with some stride (M-N:S). CPU numbers are zero based. For example, +@code{GOMP_CPU_AFFINITY="0 3 1-2 4-15:2"} will bind the initial thread +to CPU 0, the second to CPU 3, the third to CPU 1, the fourth to +CPU 2, the fifth to CPU 4, the sixth through tenth to CPUs 6, 8, 10, 12, +and 14 respectively and then start assigning back from the beginning of +the list. @code{GOMP_CPU_AFFINITY=0} binds all threads to CPU 0. + +There is no libgomp library routine to determine whether a CPU affinity +specification is in effect. As a workaround, language-specific library +functions, e.g., @code{getenv} in C or @code{GET_ENVIRONMENT_VARIABLE} in +Fortran, may be used to query the setting of the @code{GOMP_CPU_AFFINITY} +environment variable. A defined CPU affinity on startup cannot be changed +or disabled during the runtime of the application. + +If both @env{GOMP_CPU_AFFINITY} and @env{OMP_PROC_BIND} are set, +@env{OMP_PROC_BIND} has a higher precedence. If neither has been set and +@env{OMP_PROC_BIND} is unset, or when @env{OMP_PROC_BIND} is set to +@code{FALSE}, the host system will handle the assignment of threads to CPUs. + +@item @emph{See also}: +@ref{OMP_PLACES}, @ref{OMP_PROC_BIND} +@end table + + + +@node GOMP_DEBUG +@section @env{GOMP_DEBUG} -- Enable debugging output +@cindex Environment Variable +@table @asis +@item @emph{Description}: +Enable debugging output. The variable should be set to @code{0} +(disabled, also the default if not set), or @code{1} (enabled). + +If enabled, some debugging output will be printed during execution. +This is currently not specified in more detail, and subject to change. +@end table + + + +@node GOMP_STACKSIZE +@section @env{GOMP_STACKSIZE} -- Set default thread stack size +@cindex Environment Variable +@cindex Implementation specific setting +@table @asis +@item @emph{Description}: +Set the default thread stack size in kilobytes. This is different from +@code{pthread_attr_setstacksize} which gets the number of bytes as an +argument. If the stack size cannot be set due to system constraints, an +error is reported and the initial stack size is left unchanged. If undefined, +the stack size is system dependent. + +@item @emph{See also}: +@ref{OMP_STACKSIZE} + +@item @emph{Reference}: +@uref{https://gcc.gnu.org/ml/gcc-patches/2006-06/msg00493.html, +GCC Patches Mailinglist}, +@uref{https://gcc.gnu.org/ml/gcc-patches/2006-06/msg00496.html, +GCC Patches Mailinglist} +@end table + + + +@node GOMP_SPINCOUNT +@section @env{GOMP_SPINCOUNT} -- Set the busy-wait spin count +@cindex Environment Variable +@cindex Implementation specific setting +@table @asis +@item @emph{Description}: +Determines how long a threads waits actively with consuming CPU power +before waiting passively without consuming CPU power. The value may be +either @code{INFINITE}, @code{INFINITY} to always wait actively or an +integer which gives the number of spins of the busy-wait loop. The +integer may optionally be followed by the following suffixes acting +as multiplication factors: @code{k} (kilo, thousand), @code{M} (mega, +million), @code{G} (giga, billion), or @code{T} (tera, trillion). +If undefined, 0 is used when @env{OMP_WAIT_POLICY} is @code{PASSIVE}, +300,000 is used when @env{OMP_WAIT_POLICY} is undefined and +30 billion is used when @env{OMP_WAIT_POLICY} is @code{ACTIVE}. +If there are more OpenMP threads than available CPUs, 1000 and 100 +spins are used for @env{OMP_WAIT_POLICY} being @code{ACTIVE} or +undefined, respectively; unless the @env{GOMP_SPINCOUNT} is lower +or @env{OMP_WAIT_POLICY} is @code{PASSIVE}. + +@item @emph{See also}: +@ref{OMP_WAIT_POLICY} +@end table + + + +@node GOMP_RTEMS_THREAD_POOLS +@section @env{GOMP_RTEMS_THREAD_POOLS} -- Set the RTEMS specific thread pools +@cindex Environment Variable +@cindex Implementation specific setting +@table @asis +@item @emph{Description}: +This environment variable is only used on the RTEMS real-time operating system. +It determines the scheduler instance specific thread pools. The format for +@env{GOMP_RTEMS_THREAD_POOLS} is a list of optional +@code{[$]@@} configurations +separated by @code{:} where: +@itemize @bullet +@item @code{} is the thread pool count for this scheduler +instance. +@item @code{$} is an optional priority for the worker threads of a +thread pool according to @code{pthread_setschedparam}. In case a priority +value is omitted, then a worker thread will inherit the priority of the OpenMP +primary thread that created it. The priority of the worker thread is not +changed after creation, even if a new OpenMP primary thread using the worker has +a different priority. +@item @code{@@} is the scheduler instance name according to the +RTEMS application configuration. +@end itemize +In case no thread pool configuration is specified for a scheduler instance, +then each OpenMP primary thread of this scheduler instance will use its own +dynamically allocated thread pool. To limit the worker thread count of the +thread pools, each OpenMP primary thread must call @code{omp_set_num_threads}. +@item @emph{Example}: +Lets suppose we have three scheduler instances @code{IO}, @code{WRK0}, and +@code{WRK1} with @env{GOMP_RTEMS_THREAD_POOLS} set to +@code{"1@@WRK0:3$4@@WRK1"}. Then there are no thread pool restrictions for +scheduler instance @code{IO}. In the scheduler instance @code{WRK0} there is +one thread pool available. Since no priority is specified for this scheduler +instance, the worker thread inherits the priority of the OpenMP primary thread +that created it. In the scheduler instance @code{WRK1} there are three thread +pools available and their worker threads run at priority four. +@end table + + + +@c --------------------------------------------------------------------- +@c Enabling OpenACC +@c --------------------------------------------------------------------- + +@node Enabling OpenACC +@chapter Enabling OpenACC + +To activate the OpenACC extensions for C/C++ and Fortran, the compile-time +flag @option{-fopenacc} must be specified. This enables the OpenACC directive +@code{#pragma acc} in C/C++ and @code{!$acc} directives in free form, +@code{c$acc}, @code{*$acc} and @code{!$acc} directives in fixed form, +@code{!$} conditional compilation sentinels in free form and @code{c$}, +@code{*$} and @code{!$} sentinels in fixed form, for Fortran. The flag also +arranges for automatic linking of the OpenACC runtime library +(@ref{OpenACC Runtime Library Routines}). + +See @uref{https://gcc.gnu.org/wiki/OpenACC} for more information. + +A complete description of all OpenACC directives accepted may be found in +the @uref{https://www.openacc.org, OpenACC} Application Programming +Interface manual, version 2.6. + + + +@c --------------------------------------------------------------------- +@c OpenACC Runtime Library Routines +@c --------------------------------------------------------------------- + +@node OpenACC Runtime Library Routines +@chapter OpenACC Runtime Library Routines + +The runtime routines described here are defined by section 3 of the OpenACC +specifications in version 2.6. +They have C linkage, and do not throw exceptions. +Generally, they are available only for the host, with the exception of +@code{acc_on_device}, which is available for both the host and the +acceleration device. + +@menu +* acc_get_num_devices:: Get number of devices for the given device + type. +* acc_set_device_type:: Set type of device accelerator to use. +* acc_get_device_type:: Get type of device accelerator to be used. +* acc_set_device_num:: Set device number to use. +* acc_get_device_num:: Get device number to be used. +* acc_get_property:: Get device property. +* acc_async_test:: Tests for completion of a specific asynchronous + operation. +* acc_async_test_all:: Tests for completion of all asynchronous + operations. +* acc_wait:: Wait for completion of a specific asynchronous + operation. +* acc_wait_all:: Waits for completion of all asynchronous + operations. +* acc_wait_all_async:: Wait for completion of all asynchronous + operations. +* acc_wait_async:: Wait for completion of asynchronous operations. +* acc_init:: Initialize runtime for a specific device type. +* acc_shutdown:: Shuts down the runtime for a specific device + type. +* acc_on_device:: Whether executing on a particular device +* acc_malloc:: Allocate device memory. +* acc_free:: Free device memory. +* acc_copyin:: Allocate device memory and copy host memory to + it. +* acc_present_or_copyin:: If the data is not present on the device, + allocate device memory and copy from host + memory. +* acc_create:: Allocate device memory and map it to host + memory. +* acc_present_or_create:: If the data is not present on the device, + allocate device memory and map it to host + memory. +* acc_copyout:: Copy device memory to host memory. +* acc_delete:: Free device memory. +* acc_update_device:: Update device memory from mapped host memory. +* acc_update_self:: Update host memory from mapped device memory. +* acc_map_data:: Map previously allocated device memory to host + memory. +* acc_unmap_data:: Unmap device memory from host memory. +* acc_deviceptr:: Get device pointer associated with specific + host address. +* acc_hostptr:: Get host pointer associated with specific + device address. +* acc_is_present:: Indicate whether host variable / array is + present on device. +* acc_memcpy_to_device:: Copy host memory to device memory. +* acc_memcpy_from_device:: Copy device memory to host memory. +* acc_attach:: Let device pointer point to device-pointer target. +* acc_detach:: Let device pointer point to host-pointer target. + +API routines for target platforms. + +* acc_get_current_cuda_device:: Get CUDA device handle. +* acc_get_current_cuda_context::Get CUDA context handle. +* acc_get_cuda_stream:: Get CUDA stream handle. +* acc_set_cuda_stream:: Set CUDA stream handle. + +API routines for the OpenACC Profiling Interface. + +* acc_prof_register:: Register callbacks. +* acc_prof_unregister:: Unregister callbacks. +* acc_prof_lookup:: Obtain inquiry functions. +* acc_register_library:: Library registration. +@end menu + + + +@node acc_get_num_devices +@section @code{acc_get_num_devices} -- Get number of devices for given device type +@table @asis +@item @emph{Description} +This function returns a value indicating the number of devices available +for the device type specified in @var{devicetype}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int acc_get_num_devices(acc_device_t devicetype);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{integer function acc_get_num_devices(devicetype)} +@item @tab @code{integer(kind=acc_device_kind) devicetype} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.1. +@end table + + + +@node acc_set_device_type +@section @code{acc_set_device_type} -- Set type of device accelerator to use. +@table @asis +@item @emph{Description} +This function indicates to the runtime library which device type, specified +in @var{devicetype}, to use when executing a parallel or kernels region. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_set_device_type(acc_device_t devicetype);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_set_device_type(devicetype)} +@item @tab @code{integer(kind=acc_device_kind) devicetype} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.2. +@end table + + + +@node acc_get_device_type +@section @code{acc_get_device_type} -- Get type of device accelerator to be used. +@table @asis +@item @emph{Description} +This function returns what device type will be used when executing a +parallel or kernels region. + +This function returns @code{acc_device_none} if +@code{acc_get_device_type} is called from +@code{acc_ev_device_init_start}, @code{acc_ev_device_init_end} +callbacks of the OpenACC Profiling Interface (@ref{OpenACC Profiling +Interface}), that is, if the device is currently being initialized. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_device_t acc_get_device_type(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{function acc_get_device_type(void)} +@item @tab @code{integer(kind=acc_device_kind) acc_get_device_type} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.3. +@end table + + + +@node acc_set_device_num +@section @code{acc_set_device_num} -- Set device number to use. +@table @asis +@item @emph{Description} +This function will indicate to the runtime which device number, +specified by @var{devicenum}, associated with the specified device +type @var{devicetype}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_set_device_num(int devicenum, acc_device_t devicetype);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_set_device_num(devicenum, devicetype)} +@item @tab @code{integer devicenum} +@item @tab @code{integer(kind=acc_device_kind) devicetype} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.4. +@end table + + + +@node acc_get_device_num +@section @code{acc_get_device_num} -- Get device number to be used. +@table @asis +@item @emph{Description} +This function returns which device number associated with the specified device +type @var{devicetype}, will be used when executing a parallel or kernels +region. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int acc_get_device_num(acc_device_t devicetype);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{function acc_get_device_num(devicetype)} +@item @tab @code{integer(kind=acc_device_kind) devicetype} +@item @tab @code{integer acc_get_device_num} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.5. +@end table + + + +@node acc_get_property +@section @code{acc_get_property} -- Get device property. +@cindex acc_get_property +@cindex acc_get_property_string +@table @asis +@item @emph{Description} +These routines return the value of the specified @var{property} for the +device being queried according to @var{devicenum} and @var{devicetype}. +Integer-valued and string-valued properties are returned by +@code{acc_get_property} and @code{acc_get_property_string} respectively. +The Fortran @code{acc_get_property_string} subroutine returns the string +retrieved in its fourth argument while the remaining entry points are +functions, which pass the return value as their result. + +Note for Fortran, only: the OpenACC technical committee corrected and, hence, +modified the interface introduced in OpenACC 2.6. The kind-value parameter +@code{acc_device_property} has been renamed to @code{acc_device_property_kind} +for consistency and the return type of the @code{acc_get_property} function is +now a @code{c_size_t} integer instead of a @code{acc_device_property} integer. +The parameter @code{acc_device_property} will continue to be provided, +but might be removed in a future version of GCC. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{size_t acc_get_property(int devicenum, acc_device_t devicetype, acc_device_property_t property);} +@item @emph{Prototype}: @tab @code{const char *acc_get_property_string(int devicenum, acc_device_t devicetype, acc_device_property_t property);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{function acc_get_property(devicenum, devicetype, property)} +@item @emph{Interface}: @tab @code{subroutine acc_get_property_string(devicenum, devicetype, property, string)} +@item @tab @code{use ISO_C_Binding, only: c_size_t} +@item @tab @code{integer devicenum} +@item @tab @code{integer(kind=acc_device_kind) devicetype} +@item @tab @code{integer(kind=acc_device_property_kind) property} +@item @tab @code{integer(kind=c_size_t) acc_get_property} +@item @tab @code{character(*) string} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.6. +@end table + + + +@node acc_async_test +@section @code{acc_async_test} -- Test for completion of a specific asynchronous operation. +@table @asis +@item @emph{Description} +This function tests for completion of the asynchronous operation specified +in @var{arg}. In C/C++, a non-zero value will be returned to indicate +the specified asynchronous operation has completed. While Fortran will return +a @code{true}. If the asynchronous operation has not completed, C/C++ returns +a zero and Fortran returns a @code{false}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int acc_async_test(int arg);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{function acc_async_test(arg)} +@item @tab @code{integer(kind=acc_handle_kind) arg} +@item @tab @code{logical acc_async_test} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.9. +@end table + + + +@node acc_async_test_all +@section @code{acc_async_test_all} -- Tests for completion of all asynchronous operations. +@table @asis +@item @emph{Description} +This function tests for completion of all asynchronous operations. +In C/C++, a non-zero value will be returned to indicate all asynchronous +operations have completed. While Fortran will return a @code{true}. If +any asynchronous operation has not completed, C/C++ returns a zero and +Fortran returns a @code{false}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int acc_async_test_all(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{function acc_async_test()} +@item @tab @code{logical acc_get_device_num} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.10. +@end table + + + +@node acc_wait +@section @code{acc_wait} -- Wait for completion of a specific asynchronous operation. +@table @asis +@item @emph{Description} +This function waits for completion of the asynchronous operation +specified in @var{arg}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_wait(arg);} +@item @emph{Prototype (OpenACC 1.0 compatibility)}: @tab @code{acc_async_wait(arg);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_wait(arg)} +@item @tab @code{integer(acc_handle_kind) arg} +@item @emph{Interface (OpenACC 1.0 compatibility)}: @tab @code{subroutine acc_async_wait(arg)} +@item @tab @code{integer(acc_handle_kind) arg} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.11. +@end table + + + +@node acc_wait_all +@section @code{acc_wait_all} -- Waits for completion of all asynchronous operations. +@table @asis +@item @emph{Description} +This function waits for the completion of all asynchronous operations. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_wait_all(void);} +@item @emph{Prototype (OpenACC 1.0 compatibility)}: @tab @code{acc_async_wait_all(void);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_wait_all()} +@item @emph{Interface (OpenACC 1.0 compatibility)}: @tab @code{subroutine acc_async_wait_all()} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.13. +@end table + + + +@node acc_wait_all_async +@section @code{acc_wait_all_async} -- Wait for completion of all asynchronous operations. +@table @asis +@item @emph{Description} +This function enqueues a wait operation on the queue @var{async} for any +and all asynchronous operations that have been previously enqueued on +any queue. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_wait_all_async(int async);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_wait_all_async(async)} +@item @tab @code{integer(acc_handle_kind) async} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.14. +@end table + + + +@node acc_wait_async +@section @code{acc_wait_async} -- Wait for completion of asynchronous operations. +@table @asis +@item @emph{Description} +This function enqueues a wait operation on queue @var{async} for any and all +asynchronous operations enqueued on queue @var{arg}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_wait_async(int arg, int async);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_wait_async(arg, async)} +@item @tab @code{integer(acc_handle_kind) arg, async} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.12. +@end table + + + +@node acc_init +@section @code{acc_init} -- Initialize runtime for a specific device type. +@table @asis +@item @emph{Description} +This function initializes the runtime for the device type specified in +@var{devicetype}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_init(acc_device_t devicetype);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_init(devicetype)} +@item @tab @code{integer(acc_device_kind) devicetype} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.7. +@end table + + + +@node acc_shutdown +@section @code{acc_shutdown} -- Shuts down the runtime for a specific device type. +@table @asis +@item @emph{Description} +This function shuts down the runtime for the device type specified in +@var{devicetype}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_shutdown(acc_device_t devicetype);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_shutdown(devicetype)} +@item @tab @code{integer(acc_device_kind) devicetype} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.8. +@end table + + + +@node acc_on_device +@section @code{acc_on_device} -- Whether executing on a particular device +@table @asis +@item @emph{Description}: +This function returns whether the program is executing on a particular +device specified in @var{devicetype}. In C/C++ a non-zero value is +returned to indicate the device is executing on the specified device type. +In Fortran, @code{true} will be returned. If the program is not executing +on the specified device type C/C++ will return a zero, while Fortran will +return @code{false}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_on_device(acc_device_t devicetype);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{function acc_on_device(devicetype)} +@item @tab @code{integer(acc_device_kind) devicetype} +@item @tab @code{logical acc_on_device} +@end multitable + + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.17. +@end table + + + +@node acc_malloc +@section @code{acc_malloc} -- Allocate device memory. +@table @asis +@item @emph{Description} +This function allocates @var{len} bytes of device memory. It returns +the device address of the allocated memory. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{d_void* acc_malloc(size_t len);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.18. +@end table + + + +@node acc_free +@section @code{acc_free} -- Free device memory. +@table @asis +@item @emph{Description} +Free previously allocated device memory at the device address @code{a}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_free(d_void *a);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.19. +@end table + + + +@node acc_copyin +@section @code{acc_copyin} -- Allocate device memory and copy host memory to it. +@table @asis +@item @emph{Description} +In C/C++, this function allocates @var{len} bytes of device memory +and maps it to the specified host address in @var{a}. The device +address of the newly allocated device memory is returned. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a +variable or array element and @var{len} specifies the length in bytes. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_copyin(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{void *acc_copyin_async(h_void *a, size_t len, int async);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_copyin(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_copyin(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_copyin_async(a, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_copyin_async(a, len, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{integer(acc_handle_kind) :: async} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.20. +@end table + + + +@node acc_present_or_copyin +@section @code{acc_present_or_copyin} -- If the data is not present on the device, allocate device memory and copy from host memory. +@table @asis +@item @emph{Description} +This function tests if the host data specified by @var{a} and of length +@var{len} is present or not. If it is not present, then device memory +will be allocated and the host memory copied. The device address of +the newly allocated device memory is returned. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a variable or +array element and @var{len} specifies the length in bytes. + +Note that @code{acc_present_or_copyin} and @code{acc_pcopyin} exist for +backward compatibility with OpenACC 2.0; use @ref{acc_copyin} instead. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_present_or_copyin(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{void *acc_pcopyin(h_void *a, size_t len);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_present_or_copyin(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_present_or_copyin(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_pcopyin(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_pcopyin(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.20. +@end table + + + +@node acc_create +@section @code{acc_create} -- Allocate device memory and map it to host memory. +@table @asis +@item @emph{Description} +This function allocates device memory and maps it to host memory specified +by the host address @var{a} with a length of @var{len} bytes. In C/C++, +the function returns the device address of the allocated device memory. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a variable or +array element and @var{len} specifies the length in bytes. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_create(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{void *acc_create_async(h_void *a, size_t len, int async);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_create(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_create(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_create_async(a, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_create_async(a, len, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{integer(acc_handle_kind) :: async} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.21. +@end table + + + +@node acc_present_or_create +@section @code{acc_present_or_create} -- If the data is not present on the device, allocate device memory and map it to host memory. +@table @asis +@item @emph{Description} +This function tests if the host data specified by @var{a} and of length +@var{len} is present or not. If it is not present, then device memory +will be allocated and mapped to host memory. In C/C++, the device address +of the newly allocated device memory is returned. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a variable or +array element and @var{len} specifies the length in bytes. + +Note that @code{acc_present_or_create} and @code{acc_pcreate} exist for +backward compatibility with OpenACC 2.0; use @ref{acc_create} instead. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_present_or_create(h_void *a, size_t len)} +@item @emph{Prototype}: @tab @code{void *acc_pcreate(h_void *a, size_t len)} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_present_or_create(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_present_or_create(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_pcreate(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_pcreate(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.21. +@end table + + + +@node acc_copyout +@section @code{acc_copyout} -- Copy device memory to host memory. +@table @asis +@item @emph{Description} +This function copies mapped device memory to host memory which is specified +by host address @var{a} for a length @var{len} bytes in C/C++. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a variable or +array element and @var{len} specifies the length in bytes. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_copyout(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{acc_copyout_async(h_void *a, size_t len, int async);} +@item @emph{Prototype}: @tab @code{acc_copyout_finalize(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{acc_copyout_finalize_async(h_void *a, size_t len, int async);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_copyout(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_copyout(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_copyout_async(a, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_copyout_async(a, len, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_copyout_finalize(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_copyout_finalize(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_copyout_finalize_async(a, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_copyout_finalize_async(a, len, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{integer(acc_handle_kind) :: async} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.22. +@end table + + + +@node acc_delete +@section @code{acc_delete} -- Free device memory. +@table @asis +@item @emph{Description} +This function frees previously allocated device memory specified by +the device address @var{a} and the length of @var{len} bytes. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a variable or +array element and @var{len} specifies the length in bytes. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_delete(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{acc_delete_async(h_void *a, size_t len, int async);} +@item @emph{Prototype}: @tab @code{acc_delete_finalize(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{acc_delete_finalize_async(h_void *a, size_t len, int async);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_delete(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_delete(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_delete_async(a, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_delete_async(a, len, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_delete_finalize(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_delete_finalize(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_delete_async_finalize(a, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_delete_async_finalize(a, len, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{integer(acc_handle_kind) :: async} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.23. +@end table + + + +@node acc_update_device +@section @code{acc_update_device} -- Update device memory from mapped host memory. +@table @asis +@item @emph{Description} +This function updates the device copy from the previously mapped host memory. +The host memory is specified with the host address @var{a} and a length of +@var{len} bytes. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a variable or +array element and @var{len} specifies the length in bytes. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_update_device(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{acc_update_device(h_void *a, size_t len, async);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_update_device(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_update_device(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_update_device_async(a, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_update_device_async(a, len, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{integer(acc_handle_kind) :: async} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.24. +@end table + + + +@node acc_update_self +@section @code{acc_update_self} -- Update host memory from mapped device memory. +@table @asis +@item @emph{Description} +This function updates the host copy from the previously mapped device memory. +The host memory is specified with the host address @var{a} and a length of +@var{len} bytes. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a variable or +array element and @var{len} specifies the length in bytes. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_update_self(h_void *a, size_t len);} +@item @emph{Prototype}: @tab @code{acc_update_self_async(h_void *a, size_t len, int async);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{subroutine acc_update_self(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @emph{Interface}: @tab @code{subroutine acc_update_self(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @emph{Interface}: @tab @code{subroutine acc_update_self_async(a, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer(acc_handle_kind) :: async} +@item @emph{Interface}: @tab @code{subroutine acc_update_self_async(a, len, async)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{integer(acc_handle_kind) :: async} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.25. +@end table + + + +@node acc_map_data +@section @code{acc_map_data} -- Map previously allocated device memory to host memory. +@table @asis +@item @emph{Description} +This function maps previously allocated device and host memory. The device +memory is specified with the device address @var{d}. The host memory is +specified with the host address @var{h} and a length of @var{len}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_map_data(h_void *h, d_void *d, size_t len);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.26. +@end table + + + +@node acc_unmap_data +@section @code{acc_unmap_data} -- Unmap device memory from host memory. +@table @asis +@item @emph{Description} +This function unmaps previously mapped device and host memory. The latter +specified by @var{h}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_unmap_data(h_void *h);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.27. +@end table + + + +@node acc_deviceptr +@section @code{acc_deviceptr} -- Get device pointer associated with specific host address. +@table @asis +@item @emph{Description} +This function returns the device address that has been mapped to the +host address specified by @var{h}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_deviceptr(h_void *h);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.28. +@end table + + + +@node acc_hostptr +@section @code{acc_hostptr} -- Get host pointer associated with specific device address. +@table @asis +@item @emph{Description} +This function returns the host address that has been mapped to the +device address specified by @var{d}. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_hostptr(d_void *d);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.29. +@end table + + + +@node acc_is_present +@section @code{acc_is_present} -- Indicate whether host variable / array is present on device. +@table @asis +@item @emph{Description} +This function indicates whether the specified host address in @var{a} and a +length of @var{len} bytes is present on the device. In C/C++, a non-zero +value is returned to indicate the presence of the mapped memory on the +device. A zero is returned to indicate the memory is not mapped on the +device. + +In Fortran, two (2) forms are supported. In the first form, @var{a} specifies +a contiguous array section. The second form @var{a} specifies a variable or +array element and @var{len} specifies the length in bytes. If the host +memory is mapped to device memory, then a @code{true} is returned. Otherwise, +a @code{false} is return to indicate the mapped memory is not present. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int acc_is_present(h_void *a, size_t len);} +@end multitable + +@item @emph{Fortran}: +@multitable @columnfractions .20 .80 +@item @emph{Interface}: @tab @code{function acc_is_present(a)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{logical acc_is_present} +@item @emph{Interface}: @tab @code{function acc_is_present(a, len)} +@item @tab @code{type, dimension(:[,:]...) :: a} +@item @tab @code{integer len} +@item @tab @code{logical acc_is_present} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.30. +@end table + + + +@node acc_memcpy_to_device +@section @code{acc_memcpy_to_device} -- Copy host memory to device memory. +@table @asis +@item @emph{Description} +This function copies host memory specified by host address of @var{src} to +device memory specified by the device address @var{dest} for a length of +@var{bytes} bytes. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_memcpy_to_device(d_void *dest, h_void *src, size_t bytes);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.31. +@end table + + + +@node acc_memcpy_from_device +@section @code{acc_memcpy_from_device} -- Copy device memory to host memory. +@table @asis +@item @emph{Description} +This function copies host memory specified by host address of @var{src} from +device memory specified by the device address @var{dest} for a length of +@var{bytes} bytes. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_memcpy_from_device(d_void *dest, h_void *src, size_t bytes);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.32. +@end table + + + +@node acc_attach +@section @code{acc_attach} -- Let device pointer point to device-pointer target. +@table @asis +@item @emph{Description} +This function updates a pointer on the device from pointing to a host-pointer +address to pointing to the corresponding device data. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_attach(h_void **ptr);} +@item @emph{Prototype}: @tab @code{acc_attach_async(h_void **ptr, int async);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.34. +@end table + + + +@node acc_detach +@section @code{acc_detach} -- Let device pointer point to host-pointer target. +@table @asis +@item @emph{Description} +This function updates a pointer on the device from pointing to a device-pointer +address to pointing to the corresponding host data. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_detach(h_void **ptr);} +@item @emph{Prototype}: @tab @code{acc_detach_async(h_void **ptr, int async);} +@item @emph{Prototype}: @tab @code{acc_detach_finalize(h_void **ptr);} +@item @emph{Prototype}: @tab @code{acc_detach_finalize_async(h_void **ptr, int async);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +3.2.35. +@end table + + + +@node acc_get_current_cuda_device +@section @code{acc_get_current_cuda_device} -- Get CUDA device handle. +@table @asis +@item @emph{Description} +This function returns the CUDA device handle. This handle is the same +as used by the CUDA Runtime or Driver API's. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_get_current_cuda_device(void);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +A.2.1.1. +@end table + + + +@node acc_get_current_cuda_context +@section @code{acc_get_current_cuda_context} -- Get CUDA context handle. +@table @asis +@item @emph{Description} +This function returns the CUDA context handle. This handle is the same +as used by the CUDA Runtime or Driver API's. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_get_current_cuda_context(void);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +A.2.1.2. +@end table + + + +@node acc_get_cuda_stream +@section @code{acc_get_cuda_stream} -- Get CUDA stream handle. +@table @asis +@item @emph{Description} +This function returns the CUDA stream handle for the queue @var{async}. +This handle is the same as used by the CUDA Runtime or Driver API's. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void *acc_get_cuda_stream(int async);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +A.2.1.3. +@end table + + + +@node acc_set_cuda_stream +@section @code{acc_set_cuda_stream} -- Set CUDA stream handle. +@table @asis +@item @emph{Description} +This function associates the stream handle specified by @var{stream} with +the queue @var{async}. + +This cannot be used to change the stream handle associated with +@code{acc_async_sync}. + +The return value is not specified. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{int acc_set_cuda_stream(int async, void *stream);} +@end multitable + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +A.2.1.4. +@end table + + + +@node acc_prof_register +@section @code{acc_prof_register} -- Register callbacks. +@table @asis +@item @emph{Description}: +This function registers callbacks. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void acc_prof_register (acc_event_t, acc_prof_callback, acc_register_t);} +@end multitable + +@item @emph{See also}: +@ref{OpenACC Profiling Interface} + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +5.3. +@end table + + + +@node acc_prof_unregister +@section @code{acc_prof_unregister} -- Unregister callbacks. +@table @asis +@item @emph{Description}: +This function unregisters callbacks. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void acc_prof_unregister (acc_event_t, acc_prof_callback, acc_register_t);} +@end multitable + +@item @emph{See also}: +@ref{OpenACC Profiling Interface} + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +5.3. +@end table + + + +@node acc_prof_lookup +@section @code{acc_prof_lookup} -- Obtain inquiry functions. +@table @asis +@item @emph{Description}: +Function to obtain inquiry functions. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{acc_query_fn acc_prof_lookup (const char *);} +@end multitable + +@item @emph{See also}: +@ref{OpenACC Profiling Interface} + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +5.3. +@end table + + + +@node acc_register_library +@section @code{acc_register_library} -- Library registration. +@table @asis +@item @emph{Description}: +Function for library registration. + +@item @emph{C/C++}: +@multitable @columnfractions .20 .80 +@item @emph{Prototype}: @tab @code{void acc_register_library (acc_prof_reg, acc_prof_reg, acc_prof_lookup_func);} +@end multitable + +@item @emph{See also}: +@ref{OpenACC Profiling Interface}, @ref{ACC_PROFLIB} + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +5.3. +@end table + + + +@c --------------------------------------------------------------------- +@c OpenACC Environment Variables +@c --------------------------------------------------------------------- + +@node OpenACC Environment Variables +@chapter OpenACC Environment Variables + +The variables @env{ACC_DEVICE_TYPE} and @env{ACC_DEVICE_NUM} +are defined by section 4 of the OpenACC specification in version 2.0. +The variable @env{ACC_PROFLIB} +is defined by section 4 of the OpenACC specification in version 2.6. +The variable @env{GCC_ACC_NOTIFY} is used for diagnostic purposes. + +@menu +* ACC_DEVICE_TYPE:: +* ACC_DEVICE_NUM:: +* ACC_PROFLIB:: +* GCC_ACC_NOTIFY:: +@end menu + + + +@node ACC_DEVICE_TYPE +@section @code{ACC_DEVICE_TYPE} +@table @asis +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +4.1. +@end table + + + +@node ACC_DEVICE_NUM +@section @code{ACC_DEVICE_NUM} +@table @asis +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +4.2. +@end table + + + +@node ACC_PROFLIB +@section @code{ACC_PROFLIB} +@table @asis +@item @emph{See also}: +@ref{acc_register_library}, @ref{OpenACC Profiling Interface} + +@item @emph{Reference}: +@uref{https://www.openacc.org, OpenACC specification v2.6}, section +4.3. +@end table + + + +@node GCC_ACC_NOTIFY +@section @code{GCC_ACC_NOTIFY} +@table @asis +@item @emph{Description}: +Print debug information pertaining to the accelerator. +@end table + + + +@c --------------------------------------------------------------------- +@c CUDA Streams Usage +@c --------------------------------------------------------------------- + +@node CUDA Streams Usage +@chapter CUDA Streams Usage + +This applies to the @code{nvptx} plugin only. + +The library provides elements that perform asynchronous movement of +data and asynchronous operation of computing constructs. This +asynchronous functionality is implemented by making use of CUDA +streams@footnote{See "Stream Management" in "CUDA Driver API", +TRM-06703-001, Version 5.5, for additional information}. + +The primary means by that the asynchronous functionality is accessed +is through the use of those OpenACC directives which make use of the +@code{async} and @code{wait} clauses. When the @code{async} clause is +first used with a directive, it creates a CUDA stream. If an +@code{async-argument} is used with the @code{async} clause, then the +stream is associated with the specified @code{async-argument}. + +Following the creation of an association between a CUDA stream and the +@code{async-argument} of an @code{async} clause, both the @code{wait} +clause and the @code{wait} directive can be used. When either the +clause or directive is used after stream creation, it creates a +rendezvous point whereby execution waits until all operations +associated with the @code{async-argument}, that is, stream, have +completed. + +Normally, the management of the streams that are created as a result of +using the @code{async} clause, is done without any intervention by the +caller. This implies the association between the @code{async-argument} +and the CUDA stream will be maintained for the lifetime of the program. +However, this association can be changed through the use of the library +function @code{acc_set_cuda_stream}. When the function +@code{acc_set_cuda_stream} is called, the CUDA stream that was +originally associated with the @code{async} clause will be destroyed. +Caution should be taken when changing the association as subsequent +references to the @code{async-argument} refer to a different +CUDA stream. + + + +@c --------------------------------------------------------------------- +@c OpenACC Library Interoperability +@c --------------------------------------------------------------------- + +@node OpenACC Library Interoperability +@chapter OpenACC Library Interoperability + +@section Introduction + +The OpenACC library uses the CUDA Driver API, and may interact with +programs that use the Runtime library directly, or another library +based on the Runtime library, e.g., CUBLAS@footnote{See section 2.26, +"Interactions with the CUDA Driver API" in +"CUDA Runtime API", Version 5.5, and section 2.27, "VDPAU +Interoperability", in "CUDA Driver API", TRM-06703-001, Version 5.5, +for additional information on library interoperability.}. +This chapter describes the use cases and what changes are +required in order to use both the OpenACC library and the CUBLAS and Runtime +libraries within a program. + +@section First invocation: NVIDIA CUBLAS library API + +In this first use case (see below), a function in the CUBLAS library is called +prior to any of the functions in the OpenACC library. More specifically, the +function @code{cublasCreate()}. + +When invoked, the function initializes the library and allocates the +hardware resources on the host and the device on behalf of the caller. Once +the initialization and allocation has completed, a handle is returned to the +caller. The OpenACC library also requires initialization and allocation of +hardware resources. Since the CUBLAS library has already allocated the +hardware resources for the device, all that is left to do is to initialize +the OpenACC library and acquire the hardware resources on the host. + +Prior to calling the OpenACC function that initializes the library and +allocate the host hardware resources, you need to acquire the device number +that was allocated during the call to @code{cublasCreate()}. The invoking of the +runtime library function @code{cudaGetDevice()} accomplishes this. Once +acquired, the device number is passed along with the device type as +parameters to the OpenACC library function @code{acc_set_device_num()}. + +Once the call to @code{acc_set_device_num()} has completed, the OpenACC +library uses the context that was created during the call to +@code{cublasCreate()}. In other words, both libraries will be sharing the +same context. + +@smallexample + /* Create the handle */ + s = cublasCreate(&h); + if (s != CUBLAS_STATUS_SUCCESS) + @{ + fprintf(stderr, "cublasCreate failed %d\n", s); + exit(EXIT_FAILURE); + @} + + /* Get the device number */ + e = cudaGetDevice(&dev); + if (e != cudaSuccess) + @{ + fprintf(stderr, "cudaGetDevice failed %d\n", e); + exit(EXIT_FAILURE); + @} + + /* Initialize OpenACC library and use device 'dev' */ + acc_set_device_num(dev, acc_device_nvidia); + +@end smallexample +@center Use Case 1 + +@section First invocation: OpenACC library API + +In this second use case (see below), a function in the OpenACC library is +called prior to any of the functions in the CUBLAS library. More specificially, +the function @code{acc_set_device_num()}. + +In the use case presented here, the function @code{acc_set_device_num()} +is used to both initialize the OpenACC library and allocate the hardware +resources on the host and the device. In the call to the function, the +call parameters specify which device to use and what device +type to use, i.e., @code{acc_device_nvidia}. It should be noted that this +is but one method to initialize the OpenACC library and allocate the +appropriate hardware resources. Other methods are available through the +use of environment variables and these will be discussed in the next section. + +Once the call to @code{acc_set_device_num()} has completed, other OpenACC +functions can be called as seen with multiple calls being made to +@code{acc_copyin()}. In addition, calls can be made to functions in the +CUBLAS library. In the use case a call to @code{cublasCreate()} is made +subsequent to the calls to @code{acc_copyin()}. +As seen in the previous use case, a call to @code{cublasCreate()} +initializes the CUBLAS library and allocates the hardware resources on the +host and the device. However, since the device has already been allocated, +@code{cublasCreate()} will only initialize the CUBLAS library and allocate +the appropriate hardware resources on the host. The context that was created +as part of the OpenACC initialization is shared with the CUBLAS library, +similarly to the first use case. + +@smallexample + dev = 0; + + acc_set_device_num(dev, acc_device_nvidia); + + /* Copy the first set to the device */ + d_X = acc_copyin(&h_X[0], N * sizeof (float)); + if (d_X == NULL) + @{ + fprintf(stderr, "copyin error h_X\n"); + exit(EXIT_FAILURE); + @} + + /* Copy the second set to the device */ + d_Y = acc_copyin(&h_Y1[0], N * sizeof (float)); + if (d_Y == NULL) + @{ + fprintf(stderr, "copyin error h_Y1\n"); + exit(EXIT_FAILURE); + @} + + /* Create the handle */ + s = cublasCreate(&h); + if (s != CUBLAS_STATUS_SUCCESS) + @{ + fprintf(stderr, "cublasCreate failed %d\n", s); + exit(EXIT_FAILURE); + @} + + /* Perform saxpy using CUBLAS library function */ + s = cublasSaxpy(h, N, &alpha, d_X, 1, d_Y, 1); + if (s != CUBLAS_STATUS_SUCCESS) + @{ + fprintf(stderr, "cublasSaxpy failed %d\n", s); + exit(EXIT_FAILURE); + @} + + /* Copy the results from the device */ + acc_memcpy_from_device(&h_Y1[0], d_Y, N * sizeof (float)); + +@end smallexample +@center Use Case 2 + +@section OpenACC library and environment variables + +There are two environment variables associated with the OpenACC library +that may be used to control the device type and device number: +@env{ACC_DEVICE_TYPE} and @env{ACC_DEVICE_NUM}, respectively. These two +environment variables can be used as an alternative to calling +@code{acc_set_device_num()}. As seen in the second use case, the device +type and device number were specified using @code{acc_set_device_num()}. +If however, the aforementioned environment variables were set, then the +call to @code{acc_set_device_num()} would not be required. + + +The use of the environment variables is only relevant when an OpenACC function +is called prior to a call to @code{cudaCreate()}. If @code{cudaCreate()} +is called prior to a call to an OpenACC function, then you must call +@code{acc_set_device_num()}@footnote{More complete information +about @env{ACC_DEVICE_TYPE} and @env{ACC_DEVICE_NUM} can be found in +sections 4.1 and 4.2 of the @uref{https://www.openacc.org, OpenACC} +Application Programming Interface”, Version 2.6.} + + + +@c --------------------------------------------------------------------- +@c OpenACC Profiling Interface +@c --------------------------------------------------------------------- + +@node OpenACC Profiling Interface +@chapter OpenACC Profiling Interface + +@section Implementation Status and Implementation-Defined Behavior + +We're implementing the OpenACC Profiling Interface as defined by the +OpenACC 2.6 specification. We're clarifying some aspects here as +@emph{implementation-defined behavior}, while they're still under +discussion within the OpenACC Technical Committee. + +This implementation is tuned to keep the performance impact as low as +possible for the (very common) case that the Profiling Interface is +not enabled. This is relevant, as the Profiling Interface affects all +the @emph{hot} code paths (in the target code, not in the offloaded +code). Users of the OpenACC Profiling Interface can be expected to +understand that performance will be impacted to some degree once the +Profiling Interface has gotten enabled: for example, because of the +@emph{runtime} (libgomp) calling into a third-party @emph{library} for +every event that has been registered. + +We're not yet accounting for the fact that @cite{OpenACC events may +occur during event processing}. +We just handle one case specially, as required by CUDA 9.0 +@command{nvprof}, that @code{acc_get_device_type} +(@ref{acc_get_device_type})) may be called from +@code{acc_ev_device_init_start}, @code{acc_ev_device_init_end} +callbacks. + +We're not yet implementing initialization via a +@code{acc_register_library} function that is either statically linked +in, or dynamically via @env{LD_PRELOAD}. +Initialization via @code{acc_register_library} functions dynamically +loaded via the @env{ACC_PROFLIB} environment variable does work, as +does directly calling @code{acc_prof_register}, +@code{acc_prof_unregister}, @code{acc_prof_lookup}. + +As currently there are no inquiry functions defined, calls to +@code{acc_prof_lookup} will always return @code{NULL}. + +There aren't separate @emph{start}, @emph{stop} events defined for the +event types @code{acc_ev_create}, @code{acc_ev_delete}, +@code{acc_ev_alloc}, @code{acc_ev_free}. It's not clear if these +should be triggered before or after the actual device-specific call is +made. We trigger them after. + +Remarks about data provided to callbacks: + +@table @asis + +@item @code{acc_prof_info.event_type} +It's not clear if for @emph{nested} event callbacks (for example, +@code{acc_ev_enqueue_launch_start} as part of a parent compute +construct), this should be set for the nested event +(@code{acc_ev_enqueue_launch_start}), or if the value of the parent +construct should remain (@code{acc_ev_compute_construct_start}). In +this implementation, the value will generally correspond to the +innermost nested event type. + +@item @code{acc_prof_info.device_type} +@itemize + +@item +For @code{acc_ev_compute_construct_start}, and in presence of an +@code{if} clause with @emph{false} argument, this will still refer to +the offloading device type. +It's not clear if that's the expected behavior. + +@item +Complementary to the item before, for +@code{acc_ev_compute_construct_end}, this is set to +@code{acc_device_host} in presence of an @code{if} clause with +@emph{false} argument. +It's not clear if that's the expected behavior. + +@end itemize + +@item @code{acc_prof_info.thread_id} +Always @code{-1}; not yet implemented. + +@item @code{acc_prof_info.async} +@itemize + +@item +Not yet implemented correctly for +@code{acc_ev_compute_construct_start}. + +@item +In a compute construct, for host-fallback +execution/@code{acc_device_host} it will always be +@code{acc_async_sync}. +It's not clear if that's the expected behavior. + +@item +For @code{acc_ev_device_init_start} and @code{acc_ev_device_init_end}, +it will always be @code{acc_async_sync}. +It's not clear if that's the expected behavior. + +@end itemize + +@item @code{acc_prof_info.async_queue} +There is no @cite{limited number of asynchronous queues} in libgomp. +This will always have the same value as @code{acc_prof_info.async}. + +@item @code{acc_prof_info.src_file} +Always @code{NULL}; not yet implemented. + +@item @code{acc_prof_info.func_name} +Always @code{NULL}; not yet implemented. + +@item @code{acc_prof_info.line_no} +Always @code{-1}; not yet implemented. + +@item @code{acc_prof_info.end_line_no} +Always @code{-1}; not yet implemented. + +@item @code{acc_prof_info.func_line_no} +Always @code{-1}; not yet implemented. + +@item @code{acc_prof_info.func_end_line_no} +Always @code{-1}; not yet implemented. + +@item @code{acc_event_info.event_type}, @code{acc_event_info.*.event_type} +Relating to @code{acc_prof_info.event_type} discussed above, in this +implementation, this will always be the same value as +@code{acc_prof_info.event_type}. + +@item @code{acc_event_info.*.parent_construct} +@itemize + +@item +Will be @code{acc_construct_parallel} for all OpenACC compute +constructs as well as many OpenACC Runtime API calls; should be the +one matching the actual construct, or +@code{acc_construct_runtime_api}, respectively. + +@item +Will be @code{acc_construct_enter_data} or +@code{acc_construct_exit_data} when processing variable mappings +specified in OpenACC @emph{declare} directives; should be +@code{acc_construct_declare}. + +@item +For implicit @code{acc_ev_device_init_start}, +@code{acc_ev_device_init_end}, and explicit as well as implicit +@code{acc_ev_alloc}, @code{acc_ev_free}, +@code{acc_ev_enqueue_upload_start}, @code{acc_ev_enqueue_upload_end}, +@code{acc_ev_enqueue_download_start}, and +@code{acc_ev_enqueue_download_end}, will be +@code{acc_construct_parallel}; should reflect the real parent +construct. + +@end itemize + +@item @code{acc_event_info.*.implicit} +For @code{acc_ev_alloc}, @code{acc_ev_free}, +@code{acc_ev_enqueue_upload_start}, @code{acc_ev_enqueue_upload_end}, +@code{acc_ev_enqueue_download_start}, and +@code{acc_ev_enqueue_download_end}, this currently will be @code{1} +also for explicit usage. + +@item @code{acc_event_info.data_event.var_name} +Always @code{NULL}; not yet implemented. + +@item @code{acc_event_info.data_event.host_ptr} +For @code{acc_ev_alloc}, and @code{acc_ev_free}, this is always +@code{NULL}. + +@item @code{typedef union acc_api_info} +@dots{} as printed in @cite{5.2.3. Third Argument: API-Specific +Information}. This should obviously be @code{typedef @emph{struct} +acc_api_info}. + +@item @code{acc_api_info.device_api} +Possibly not yet implemented correctly for +@code{acc_ev_compute_construct_start}, +@code{acc_ev_device_init_start}, @code{acc_ev_device_init_end}: +will always be @code{acc_device_api_none} for these event types. +For @code{acc_ev_enter_data_start}, it will be +@code{acc_device_api_none} in some cases. + +@item @code{acc_api_info.device_type} +Always the same as @code{acc_prof_info.device_type}. + +@item @code{acc_api_info.vendor} +Always @code{-1}; not yet implemented. + +@item @code{acc_api_info.device_handle} +Always @code{NULL}; not yet implemented. + +@item @code{acc_api_info.context_handle} +Always @code{NULL}; not yet implemented. + +@item @code{acc_api_info.async_handle} +Always @code{NULL}; not yet implemented. + +@end table + +Remarks about certain event types: + +@table @asis + +@item @code{acc_ev_device_init_start}, @code{acc_ev_device_init_end} +@itemize + +@item +@c See 'DEVICE_INIT_INSIDE_COMPUTE_CONSTRUCT' in +@c 'libgomp.oacc-c-c++-common/acc_prof-kernels-1.c', +@c 'libgomp.oacc-c-c++-common/acc_prof-parallel-1.c'. +When a compute construct triggers implicit +@code{acc_ev_device_init_start} and @code{acc_ev_device_init_end} +events, they currently aren't @emph{nested within} the corresponding +@code{acc_ev_compute_construct_start} and +@code{acc_ev_compute_construct_end}, but they're currently observed +@emph{before} @code{acc_ev_compute_construct_start}. +It's not clear what to do: the standard asks us provide a lot of +details to the @code{acc_ev_compute_construct_start} callback, without +(implicitly) initializing a device before? + +@item +Callbacks for these event types will not be invoked for calls to the +@code{acc_set_device_type} and @code{acc_set_device_num} functions. +It's not clear if they should be. + +@end itemize + +@item @code{acc_ev_enter_data_start}, @code{acc_ev_enter_data_end}, @code{acc_ev_exit_data_start}, @code{acc_ev_exit_data_end} +@itemize + +@item +Callbacks for these event types will also be invoked for OpenACC +@emph{host_data} constructs. +It's not clear if they should be. + +@item +Callbacks for these event types will also be invoked when processing +variable mappings specified in OpenACC @emph{declare} directives. +It's not clear if they should be. + +@end itemize + +@end table + +Callbacks for the following event types will be invoked, but dispatch +and information provided therein has not yet been thoroughly reviewed: + +@itemize +@item @code{acc_ev_alloc} +@item @code{acc_ev_free} +@item @code{acc_ev_update_start}, @code{acc_ev_update_end} +@item @code{acc_ev_enqueue_upload_start}, @code{acc_ev_enqueue_upload_end} +@item @code{acc_ev_enqueue_download_start}, @code{acc_ev_enqueue_download_end} +@end itemize + +During device initialization, and finalization, respectively, +callbacks for the following event types will not yet be invoked: + +@itemize +@item @code{acc_ev_alloc} +@item @code{acc_ev_free} +@end itemize + +Callbacks for the following event types have not yet been implemented, +so currently won't be invoked: + +@itemize +@item @code{acc_ev_device_shutdown_start}, @code{acc_ev_device_shutdown_end} +@item @code{acc_ev_runtime_shutdown} +@item @code{acc_ev_create}, @code{acc_ev_delete} +@item @code{acc_ev_wait_start}, @code{acc_ev_wait_end} +@end itemize + +For the following runtime library functions, not all expected +callbacks will be invoked (mostly concerning implicit device +initialization): + +@itemize +@item @code{acc_get_num_devices} +@item @code{acc_set_device_type} +@item @code{acc_get_device_type} +@item @code{acc_set_device_num} +@item @code{acc_get_device_num} +@item @code{acc_init} +@item @code{acc_shutdown} +@end itemize + +Aside from implicit device initialization, for the following runtime +library functions, no callbacks will be invoked for shared-memory +offloading devices (it's not clear if they should be): + +@itemize +@item @code{acc_malloc} +@item @code{acc_free} +@item @code{acc_copyin}, @code{acc_present_or_copyin}, @code{acc_copyin_async} +@item @code{acc_create}, @code{acc_present_or_create}, @code{acc_create_async} +@item @code{acc_copyout}, @code{acc_copyout_async}, @code{acc_copyout_finalize}, @code{acc_copyout_finalize_async} +@item @code{acc_delete}, @code{acc_delete_async}, @code{acc_delete_finalize}, @code{acc_delete_finalize_async} +@item @code{acc_update_device}, @code{acc_update_device_async} +@item @code{acc_update_self}, @code{acc_update_self_async} +@item @code{acc_map_data}, @code{acc_unmap_data} +@item @code{acc_memcpy_to_device}, @code{acc_memcpy_to_device_async} +@item @code{acc_memcpy_from_device}, @code{acc_memcpy_from_device_async} +@end itemize + +@c --------------------------------------------------------------------- +@c OpenMP-Implementation Specifics +@c --------------------------------------------------------------------- + +@node OpenMP-Implementation Specifics +@chapter OpenMP-Implementation Specifics + +@menu +* OpenMP Context Selectors:: +* Memory allocation with libmemkind:: +@end menu + +@node OpenMP Context Selectors +@section OpenMP Context Selectors + +@code{vendor} is always @code{gnu}. References are to the GCC manual. + +@multitable @columnfractions .60 .10 .25 +@headitem @code{arch} @tab @code{kind} @tab @code{isa} +@item @code{x86}, @code{x86_64}, @code{i386}, @code{i486}, + @code{i586}, @code{i686}, @code{ia32} + @tab @code{host} + @tab See @code{-m...} flags in ``x86 Options'' (without @code{-m}) +@item @code{amdgcn}, @code{gcn} + @tab @code{gpu} + @tab See @code{-march=} in ``AMD GCN Options'' +@item @code{nvptx} + @tab @code{gpu} + @tab See @code{-march=} in ``Nvidia PTX Options'' +@end multitable + +@node Memory allocation with libmemkind +@section Memory allocation with libmemkind + +On Linux systems, where the @uref{https://github.com/memkind/memkind, memkind +library} (@code{libmemkind.so.0}) is available at runtime, it is used when +creating memory allocators requesting + +@itemize +@item the memory space @code{omp_high_bw_mem_space} +@item the memory space @code{omp_large_cap_mem_space} +@item the partition trait @code{omp_atv_interleaved} +@end itemize + + +@c --------------------------------------------------------------------- +@c Offload-Target Specifics +@c --------------------------------------------------------------------- + +@node Offload-Target Specifics +@chapter Offload-Target Specifics + +The following sections present notes on the offload-target specifics + +@menu +* AMD Radeon:: +* nvptx:: +@end menu + +@node AMD Radeon +@section AMD Radeon (GCN) + +On the hardware side, there is the hierarchy (fine to coarse): +@itemize +@item work item (thread) +@item wavefront +@item work group +@item compute unite (CU) +@end itemize + +All OpenMP and OpenACC levels are used, i.e. +@itemize +@item OpenMP's simd and OpenACC's vector map to work items (thread) +@item OpenMP's threads (``parallel'') and OpenACC's workers map + to wavefronts +@item OpenMP's teams and OpenACC's gang use a threadpool with the + size of the number of teams or gangs, respectively. +@end itemize + +The used sizes are +@itemize +@item Number of teams is the specified @code{num_teams} (OpenMP) or + @code{num_gangs} (OpenACC) or otherwise the number of CU +@item Number of wavefronts is 4 for gfx900 and 16 otherwise; + @code{num_threads} (OpenMP) and @code{num_workers} (OpenACC) + overrides this if smaller. +@item The wavefront has 102 scalars and 64 vectors +@item Number of workitems is always 64 +@item The hardware permits maximally 40 workgroups/CU and + 16 wavefronts/workgroup up to a limit of 40 wavefronts in total per CU. +@item 80 scalars registers and 24 vector registers in non-kernel functions + (the chosen procedure-calling API). +@item For the kernel itself: as many as register pressure demands (number of + teams and number of threads, scaled down if registers are exhausted) +@end itemize + +The implementation remark: +@itemize +@item I/O within OpenMP target regions and OpenACC parallel/kernels is supported + using the C library @code{printf} functions and the Fortran + @code{print}/@code{write} statements. +@end itemize + + + +@node nvptx +@section nvptx + +On the hardware side, there is the hierarchy (fine to coarse): +@itemize +@item thread +@item warp +@item thread block +@item streaming multiprocessor +@end itemize + +All OpenMP and OpenACC levels are used, i.e. +@itemize +@item OpenMP's simd and OpenACC's vector map to threads +@item OpenMP's threads (``parallel'') and OpenACC's workers map to warps +@item OpenMP's teams and OpenACC's gang use a threadpool with the + size of the number of teams or gangs, respectively. +@end itemize + +The used sizes are +@itemize +@item The @code{warp_size} is always 32 +@item CUDA kernel launched: @code{dim=@{#teams,1,1@}, blocks=@{#threads,warp_size,1@}}. +@end itemize + +Additional information can be obtained by setting the environment variable to +@code{GOMP_DEBUG=1} (very verbose; grep for @code{kernel.*launch} for launch +parameters). + +GCC generates generic PTX ISA code, which is just-in-time compiled by CUDA, +which caches the JIT in the user's directory (see CUDA documentation; can be +tuned by the environment variables @code{CUDA_CACHE_@{DISABLE,MAXSIZE,PATH@}}. + +Note: While PTX ISA is generic, the @code{-mptx=} and @code{-march=} commandline +options still affect the used PTX ISA code and, thus, the requirments on +CUDA version and hardware. + +The implementation remark: +@itemize +@item I/O within OpenMP target regions and OpenACC parallel/kernels is supported + using the C library @code{printf} functions. Note that the Fortran + @code{print}/@code{write} statements are not supported, yet. +@item Compilation OpenMP code that contains @code{requires reverse_offload} + requires at least @code{-march=sm_35}, compiling for @code{-march=sm_30} + is not supported. +@end itemize + + +@c --------------------------------------------------------------------- +@c The libgomp ABI +@c --------------------------------------------------------------------- + +@node The libgomp ABI +@chapter The libgomp ABI + +The following sections present notes on the external ABI as +presented by libgomp. Only maintainers should need them. + +@menu +* Implementing MASTER construct:: +* Implementing CRITICAL construct:: +* Implementing ATOMIC construct:: +* Implementing FLUSH construct:: +* Implementing BARRIER construct:: +* Implementing THREADPRIVATE construct:: +* Implementing PRIVATE clause:: +* Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses:: +* Implementing REDUCTION clause:: +* Implementing PARALLEL construct:: +* Implementing FOR construct:: +* Implementing ORDERED construct:: +* Implementing SECTIONS construct:: +* Implementing SINGLE construct:: +* Implementing OpenACC's PARALLEL construct:: +@end menu + + +@node Implementing MASTER construct +@section Implementing MASTER construct + +@smallexample +if (omp_get_thread_num () == 0) + block +@end smallexample + +Alternately, we generate two copies of the parallel subfunction +and only include this in the version run by the primary thread. +Surely this is not worthwhile though... + + + +@node Implementing CRITICAL construct +@section Implementing CRITICAL construct + +Without a specified name, + +@smallexample + void GOMP_critical_start (void); + void GOMP_critical_end (void); +@end smallexample + +so that we don't get COPY relocations from libgomp to the main +application. + +With a specified name, use omp_set_lock and omp_unset_lock with +name being transformed into a variable declared like + +@smallexample + omp_lock_t gomp_critical_user_ __attribute__((common)) +@end smallexample + +Ideally the ABI would specify that all zero is a valid unlocked +state, and so we wouldn't need to initialize this at +startup. + + + +@node Implementing ATOMIC construct +@section Implementing ATOMIC construct + +The target should implement the @code{__sync} builtins. + +Failing that we could add + +@smallexample + void GOMP_atomic_enter (void) + void GOMP_atomic_exit (void) +@end smallexample + +which reuses the regular lock code, but with yet another lock +object private to the library. + + + +@node Implementing FLUSH construct +@section Implementing FLUSH construct + +Expands to the @code{__sync_synchronize} builtin. + + + +@node Implementing BARRIER construct +@section Implementing BARRIER construct + +@smallexample + void GOMP_barrier (void) +@end smallexample + + +@node Implementing THREADPRIVATE construct +@section Implementing THREADPRIVATE construct + +In _most_ cases we can map this directly to @code{__thread}. Except +that OMP allows constructors for C++ objects. We can either +refuse to support this (how often is it used?) or we can +implement something akin to .ctors. + +Even more ideally, this ctor feature is handled by extensions +to the main pthreads library. Failing that, we can have a set +of entry points to register ctor functions to be called. + + + +@node Implementing PRIVATE clause +@section Implementing PRIVATE clause + +In association with a PARALLEL, or within the lexical extent +of a PARALLEL block, the variable becomes a local variable in +the parallel subfunction. + +In association with FOR or SECTIONS blocks, create a new +automatic variable within the current function. This preserves +the semantic of new variable creation. + + + +@node Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses +@section Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses + +This seems simple enough for PARALLEL blocks. Create a private +struct for communicating between the parent and subfunction. +In the parent, copy in values for scalar and "small" structs; +copy in addresses for others TREE_ADDRESSABLE types. In the +subfunction, copy the value into the local variable. + +It is not clear what to do with bare FOR or SECTION blocks. +The only thing I can figure is that we do something like: + +@smallexample +#pragma omp for firstprivate(x) lastprivate(y) +for (int i = 0; i < n; ++i) + body; +@end smallexample + +which becomes + +@smallexample +@{ + int x = x, y; + + // for stuff + + if (i == n) + y = y; +@} +@end smallexample + +where the "x=x" and "y=y" assignments actually have different +uids for the two variables, i.e. not something you could write +directly in C. Presumably this only makes sense if the "outer" +x and y are global variables. + +COPYPRIVATE would work the same way, except the structure +broadcast would have to happen via SINGLE machinery instead. + + + +@node Implementing REDUCTION clause +@section Implementing REDUCTION clause + +The private struct mentioned in the previous section should have +a pointer to an array of the type of the variable, indexed by the +thread's @var{team_id}. The thread stores its final value into the +array, and after the barrier, the primary thread iterates over the +array to collect the values. + + +@node Implementing PARALLEL construct +@section Implementing PARALLEL construct + +@smallexample + #pragma omp parallel + @{ + body; + @} +@end smallexample + +becomes + +@smallexample + void subfunction (void *data) + @{ + use data; + body; + @} + + setup data; + GOMP_parallel_start (subfunction, &data, num_threads); + subfunction (&data); + GOMP_parallel_end (); +@end smallexample + +@smallexample + void GOMP_parallel_start (void (*fn)(void *), void *data, unsigned num_threads) +@end smallexample + +The @var{FN} argument is the subfunction to be run in parallel. + +The @var{DATA} argument is a pointer to a structure used to +communicate data in and out of the subfunction, as discussed +above with respect to FIRSTPRIVATE et al. + +The @var{NUM_THREADS} argument is 1 if an IF clause is present +and false, or the value of the NUM_THREADS clause, if +present, or 0. + +The function needs to create the appropriate number of +threads and/or launch them from the dock. It needs to +create the team structure and assign team ids. + +@smallexample + void GOMP_parallel_end (void) +@end smallexample + +Tears down the team and returns us to the previous @code{omp_in_parallel()} state. + + + +@node Implementing FOR construct +@section Implementing FOR construct + +@smallexample + #pragma omp parallel for + for (i = lb; i <= ub; i++) + body; +@end smallexample + +becomes + +@smallexample + void subfunction (void *data) + @{ + long _s0, _e0; + while (GOMP_loop_static_next (&_s0, &_e0)) + @{ + long _e1 = _e0, i; + for (i = _s0; i < _e1; i++) + body; + @} + GOMP_loop_end_nowait (); + @} + + GOMP_parallel_loop_static (subfunction, NULL, 0, lb, ub+1, 1, 0); + subfunction (NULL); + GOMP_parallel_end (); +@end smallexample + +@smallexample + #pragma omp for schedule(runtime) + for (i = 0; i < n; i++) + body; +@end smallexample + +becomes + +@smallexample + @{ + long i, _s0, _e0; + if (GOMP_loop_runtime_start (0, n, 1, &_s0, &_e0)) + do @{ + long _e1 = _e0; + for (i = _s0, i < _e0; i++) + body; + @} while (GOMP_loop_runtime_next (&_s0, _&e0)); + GOMP_loop_end (); + @} +@end smallexample + +Note that while it looks like there is trickiness to propagating +a non-constant STEP, there isn't really. We're explicitly allowed +to evaluate it as many times as we want, and any variables involved +should automatically be handled as PRIVATE or SHARED like any other +variables. So the expression should remain evaluable in the +subfunction. We can also pull it into a local variable if we like, +but since its supposed to remain unchanged, we can also not if we like. + +If we have SCHEDULE(STATIC), and no ORDERED, then we ought to be +able to get away with no work-sharing context at all, since we can +simply perform the arithmetic directly in each thread to divide up +the iterations. Which would mean that we wouldn't need to call any +of these routines. + +There are separate routines for handling loops with an ORDERED +clause. Bookkeeping for that is non-trivial... + + + +@node Implementing ORDERED construct +@section Implementing ORDERED construct + +@smallexample + void GOMP_ordered_start (void) + void GOMP_ordered_end (void) +@end smallexample + + + +@node Implementing SECTIONS construct +@section Implementing SECTIONS construct + +A block as + +@smallexample + #pragma omp sections + @{ + #pragma omp section + stmt1; + #pragma omp section + stmt2; + #pragma omp section + stmt3; + @} +@end smallexample + +becomes + +@smallexample + for (i = GOMP_sections_start (3); i != 0; i = GOMP_sections_next ()) + switch (i) + @{ + case 1: + stmt1; + break; + case 2: + stmt2; + break; + case 3: + stmt3; + break; + @} + GOMP_barrier (); +@end smallexample + + +@node Implementing SINGLE construct +@section Implementing SINGLE construct + +A block like + +@smallexample + #pragma omp single + @{ + body; + @} +@end smallexample + +becomes + +@smallexample + if (GOMP_single_start ()) + body; + GOMP_barrier (); +@end smallexample + +while + +@smallexample + #pragma omp single copyprivate(x) + body; +@end smallexample + +becomes + +@smallexample + datap = GOMP_single_copy_start (); + if (datap == NULL) + @{ + body; + data.x = x; + GOMP_single_copy_end (&data); + @} + else + x = datap->x; + GOMP_barrier (); +@end smallexample + + + +@node Implementing OpenACC's PARALLEL construct +@section Implementing OpenACC's PARALLEL construct + +@smallexample + void GOACC_parallel () +@end smallexample + + + +@c --------------------------------------------------------------------- +@c Reporting Bugs +@c --------------------------------------------------------------------- + +@node Reporting Bugs +@chapter Reporting Bugs + +Bugs in the GNU Offloading and Multi Processing Runtime Library should +be reported via @uref{https://gcc.gnu.org/bugzilla/, Bugzilla}. Please add +"openacc", or "openmp", or both to the keywords field in the bug +report, as appropriate. + + + +@c --------------------------------------------------------------------- +@c GNU General Public License +@c --------------------------------------------------------------------- + +@include gpl_v3.texi + + + +@c --------------------------------------------------------------------- +@c GNU Free Documentation License +@c --------------------------------------------------------------------- + +@include fdl.texi + + + +@c --------------------------------------------------------------------- +@c Funding Free Software +@c --------------------------------------------------------------------- + +@include funding.texi + +@c --------------------------------------------------------------------- +@c Index +@c --------------------------------------------------------------------- + +@node Library Index +@unnumbered Library Index + +@printindex cp + +@bye diff --git a/libiberty/at-file.texi b/libiberty/at-file.texi new file mode 100644 index 00000000000..080d1951d62 --- /dev/null +++ b/libiberty/at-file.texi @@ -0,0 +1,15 @@ +@c This file is designed to be included in manuals that use +@c expandargv. + +@item @@@var{file} +Read command-line options from @var{file}. The options read are +inserted in place of the original @@@var{file} option. If @var{file} +does not exist, or cannot be read, then the option will be treated +literally, and not removed. + +Options in @var{file} are separated by whitespace. A whitespace +character may be included in an option by surrounding the entire +option in either single or double quotes. Any character (including a +backslash) may be included by prefixing the character to be included +with a backslash. 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Here is a sample; alter the names: + +@smallexample +Yoyodyne, Inc., hereby disclaims all copyright interest in the library +`Frob' (a library for tweaking knobs) written by James Random Hacker. + +@var{signature of Ty Coon}, 1 April 1990 +Ty Coon, President of Vice +@end smallexample + +That's all there is to it! diff --git a/libiberty/functions.texi b/libiberty/functions.texi new file mode 100644 index 00000000000..b56b02e0686 --- /dev/null +++ b/libiberty/functions.texi @@ -0,0 +1,2063 @@ +@c Automatically generated from *.c and others (the comments before +@c each entry tell you which file and where in that file). DO NOT EDIT! +@c Edit the *.c files, configure with --enable-maintainer-mode, +@c run 'make stamp-functions' and gather-docs will build a new copy. + +@c alloca.c:26 +@deftypefn Replacement void* alloca (size_t @var{size}) + +This function allocates memory which will be automatically reclaimed +after the procedure exits. The @libib{} implementation does not free +the memory immediately but will do so eventually during subsequent +calls to this function. Memory is allocated using @code{xmalloc} under +normal circumstances. + +The header file @file{alloca-conf.h} can be used in conjunction with the +GNU Autoconf test @code{AC_FUNC_ALLOCA} to test for and properly make +available this function. The @code{AC_FUNC_ALLOCA} test requires that +client code use a block of preprocessor code to be safe (see the Autoconf +manual for more); this header incorporates that logic and more, including +the possibility of a GCC built-in function. + +@end deftypefn + +@c asprintf.c:32 +@deftypefn Extension int asprintf (char **@var{resptr}, const char *@var{format}, ...) + +Like @code{sprintf}, but instead of passing a pointer to a buffer, you +pass a pointer to a pointer. This function will compute the size of +the buffer needed, allocate memory with @code{malloc}, and store a +pointer to the allocated memory in @code{*@var{resptr}}. The value +returned is the same as @code{sprintf} would return. If memory could +not be allocated, minus one is returned and @code{NULL} is stored in +@code{*@var{resptr}}. + +@end deftypefn + +@c atexit.c:6 +@deftypefn Supplemental int atexit (void (*@var{f})()) + +Causes function @var{f} to be called at exit. Returns 0. + +@end deftypefn + +@c basename.c:6 +@deftypefn Supplemental char* basename (const char *@var{name}) + +Returns a pointer to the last component of pathname @var{name}. +Behavior is undefined if the pathname ends in a directory separator. + +@end deftypefn + +@c bcmp.c:6 +@deftypefn Supplemental int bcmp (char *@var{x}, char *@var{y}, int @var{count}) + +Compares the first @var{count} bytes of two areas of memory. Returns +zero if they are the same, nonzero otherwise. Returns zero if +@var{count} is zero. A nonzero result only indicates a difference, +it does not indicate any sorting order (say, by having a positive +result mean @var{x} sorts before @var{y}). + +@end deftypefn + +@c bcopy.c:3 +@deftypefn Supplemental void bcopy (char *@var{in}, char *@var{out}, int @var{length}) + +Copies @var{length} bytes from memory region @var{in} to region +@var{out}. The use of @code{bcopy} is deprecated in new programs. + +@end deftypefn + +@c bsearch.c:33 +@deftypefn Supplemental void* bsearch (const void *@var{key}, @ + const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, @ + int (*@var{compar})(const void *, const void *)) + +Performs a search over an array of @var{nmemb} elements pointed to by +@var{base} for a member that matches the object pointed to by @var{key}. +The size of each member is specified by @var{size}. The array contents +should be sorted in ascending order according to the @var{compar} +comparison function. This routine should take two arguments pointing to +the @var{key} and to an array member, in that order, and should return an +integer less than, equal to, or greater than zero if the @var{key} object +is respectively less than, matching, or greater than the array member. + +@end deftypefn + +@c bsearch_r.c:33 +@deftypefn Supplemental void* bsearch_r (const void *@var{key}, @ + const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, @ + int (*@var{compar})(const void *, const void *, void *), void *@var{arg}) + +Performs a search over an array of @var{nmemb} elements pointed to by +@var{base} for a member that matches the object pointed to by @var{key}. +The size of each member is specified by @var{size}. The array contents +should be sorted in ascending order according to the @var{compar} +comparison function. This routine should take three arguments: the first +two point to the @var{key} and to an array member, and the last is passed +down unchanged from @code{bsearch_r}'s last argument. It should return an +integer less than, equal to, or greater than zero if the @var{key} object +is respectively less than, matching, or greater than the array member. + +@end deftypefn + +@c argv.c:138 +@deftypefn Extension char** buildargv (char *@var{sp}) + +Given a pointer to a string, parse the string extracting fields +separated by whitespace and optionally enclosed within either single +or double quotes (which are stripped off), and build a vector of +pointers to copies of the string for each field. The input string +remains unchanged. The last element of the vector is followed by a +@code{NULL} element. + +All of the memory for the pointer array and copies of the string +is obtained from @code{xmalloc}. All of the memory can be returned to the +system with the single function call @code{freeargv}, which takes the +returned result of @code{buildargv}, as it's argument. + +Returns a pointer to the argument vector if successful. Returns +@code{NULL} if @var{sp} is @code{NULL} or if there is insufficient +memory to complete building the argument vector. + +If the input is a null string (as opposed to a @code{NULL} pointer), +then buildarg returns an argument vector that has one arg, a null +string. + +@end deftypefn + +@c bzero.c:6 +@deftypefn Supplemental void bzero (char *@var{mem}, int @var{count}) + +Zeros @var{count} bytes starting at @var{mem}. Use of this function +is deprecated in favor of @code{memset}. + +@end deftypefn + +@c calloc.c:6 +@deftypefn Supplemental void* calloc (size_t @var{nelem}, size_t @var{elsize}) + +Uses @code{malloc} to allocate storage for @var{nelem} objects of +@var{elsize} bytes each, then zeros the memory. + +@end deftypefn + +@c filename_cmp.c:201 +@deftypefn Extension int canonical_filename_eq (const char *@var{a}, const char *@var{b}) + +Return non-zero if file names @var{a} and @var{b} are equivalent. +This function compares the canonical versions of the filenames as returned by +@code{lrealpath()}, so that so that different file names pointing to the same +underlying file are treated as being identical. + +@end deftypefn + +@c choose-temp.c:45 +@deftypefn Extension char* choose_temp_base (void) + +Return a prefix for temporary file names or @code{NULL} if unable to +find one. The current directory is chosen if all else fails so the +program is exited if a temporary directory can't be found (@code{mktemp} +fails). The buffer for the result is obtained with @code{xmalloc}. + +This function is provided for backwards compatibility only. Its use is +not recommended. + +@end deftypefn + +@c make-temp-file.c:95 +@deftypefn Replacement const char* choose_tmpdir () + +Returns a pointer to a directory path suitable for creating temporary +files in. + +@end deftypefn + +@c clock.c:27 +@deftypefn Supplemental long clock (void) + +Returns an approximation of the CPU time used by the process as a +@code{clock_t}; divide this number by @samp{CLOCKS_PER_SEC} to get the +number of seconds used. + +@end deftypefn + +@c concat.c:24 +@deftypefn Extension char* concat (const char *@var{s1}, const char *@var{s2}, @ + @dots{}, @code{NULL}) + +Concatenate zero or more of strings and return the result in freshly +@code{xmalloc}ed memory. The argument list is terminated by the first +@code{NULL} pointer encountered. Pointers to empty strings are ignored. + +@end deftypefn + +@c argv.c:495 +@deftypefn Extension int countargv (char * const *@var{argv}) + +Return the number of elements in @var{argv}. +Returns zero if @var{argv} is NULL. + +@end deftypefn + +@c crc32.c:140 +@deftypefn Extension {unsigned int} crc32 (const unsigned char *@var{buf}, @ + int @var{len}, unsigned int @var{init}) + +Compute the 32-bit CRC of @var{buf} which has length @var{len}. The +starting value is @var{init}; this may be used to compute the CRC of +data split across multiple buffers by passing the return value of each +call as the @var{init} parameter of the next. + +This is used by the @command{gdb} remote protocol for the @samp{qCRC} +command. In order to get the same results as gdb for a block of data, +you must pass the first CRC parameter as @code{0xffffffff}. + +This CRC can be specified as: + + Width : 32 + Poly : 0x04c11db7 + Init : parameter, typically 0xffffffff + RefIn : false + RefOut : false + XorOut : 0 + +This differs from the "standard" CRC-32 algorithm in that the values +are not reflected, and there is no final XOR value. These differences +make it easy to compose the values of multiple blocks. + +@end deftypefn + +@c argv.c:59 +@deftypefn Extension char** dupargv (char * const *@var{vector}) + +Duplicate an argument vector. Simply scans through @var{vector}, +duplicating each argument until the terminating @code{NULL} is found. +Returns a pointer to the argument vector if successful. Returns +@code{NULL} if there is insufficient memory to complete building the +argument vector. + +@end deftypefn + +@c strerror.c:572 +@deftypefn Extension int errno_max (void) + +Returns the maximum @code{errno} value for which a corresponding +symbolic name or message is available. Note that in the case where we +use the @code{sys_errlist} supplied by the system, it is possible for +there to be more symbolic names than messages, or vice versa. In +fact, the manual page for @code{perror(3C)} explicitly warns that one +should check the size of the table (@code{sys_nerr}) before indexing +it, since new error codes may be added to the system before they are +added to the table. Thus @code{sys_nerr} might be smaller than value +implied by the largest @code{errno} value defined in @code{}. + +We return the maximum value that can be used to obtain a meaningful +symbolic name or message. + +@end deftypefn + +@c argv.c:352 +@deftypefn Extension void expandargv (int *@var{argcp}, char ***@var{argvp}) + +The @var{argcp} and @code{argvp} arguments are pointers to the usual +@code{argc} and @code{argv} arguments to @code{main}. This function +looks for arguments that begin with the character @samp{@@}. Any such +arguments are interpreted as ``response files''. The contents of the +response file are interpreted as additional command line options. In +particular, the file is separated into whitespace-separated strings; +each such string is taken as a command-line option. The new options +are inserted in place of the option naming the response file, and +@code{*argcp} and @code{*argvp} will be updated. If the value of +@code{*argvp} is modified by this function, then the new value has +been dynamically allocated and can be deallocated by the caller with +@code{freeargv}. However, most callers will simply call +@code{expandargv} near the beginning of @code{main} and allow the +operating system to free the memory when the program exits. + +@end deftypefn + +@c fdmatch.c:23 +@deftypefn Extension int fdmatch (int @var{fd1}, int @var{fd2}) + +Check to see if two open file descriptors refer to the same file. +This is useful, for example, when we have an open file descriptor for +an unnamed file, and the name of a file that we believe to correspond +to that fd. This can happen when we are exec'd with an already open +file (@code{stdout} for example) or from the SVR4 @file{/proc} calls +that return open file descriptors for mapped address spaces. All we +have to do is open the file by name and check the two file descriptors +for a match, which is done by comparing major and minor device numbers +and inode numbers. + +@end deftypefn + +@c fopen_unlocked.c:49 +@deftypefn Extension {FILE *} fdopen_unlocked (int @var{fildes}, @ + const char * @var{mode}) + +Opens and returns a @code{FILE} pointer via @code{fdopen}. If the +operating system supports it, ensure that the stream is setup to avoid +any multi-threaded locking. Otherwise return the @code{FILE} pointer +unchanged. + +@end deftypefn + +@c ffs.c:3 +@deftypefn Supplemental int ffs (int @var{valu}) + +Find the first (least significant) bit set in @var{valu}. Bits are +numbered from right to left, starting with bit 1 (corresponding to the +value 1). If @var{valu} is zero, zero is returned. + +@end deftypefn + +@c filename_cmp.c:37 +@deftypefn Extension int filename_cmp (const char *@var{s1}, const char *@var{s2}) + +Return zero if the two file names @var{s1} and @var{s2} are equivalent. +If not equivalent, the returned value is similar to what @code{strcmp} +would return. In other words, it returns a negative value if @var{s1} +is less than @var{s2}, or a positive value if @var{s2} is greater than +@var{s2}. + +This function does not normalize file names. As a result, this function +will treat filenames that are spelled differently as different even in +the case when the two filenames point to the same underlying file. +However, it does handle the fact that on DOS-like file systems, forward +and backward slashes are equal. + +@end deftypefn + +@c filename_cmp.c:183 +@deftypefn Extension int filename_eq (const void *@var{s1}, const void *@var{s2}) + +Return non-zero if file names @var{s1} and @var{s2} are equivalent. +This function is for use with hashtab.c hash tables. + +@end deftypefn + +@c filename_cmp.c:152 +@deftypefn Extension hashval_t filename_hash (const void *@var{s}) + +Return the hash value for file name @var{s} that will be compared +using filename_cmp. +This function is for use with hashtab.c hash tables. + +@end deftypefn + +@c filename_cmp.c:94 +@deftypefn Extension int filename_ncmp (const char *@var{s1}, const char *@var{s2}, size_t @var{n}) + +Return zero if the two file names @var{s1} and @var{s2} are equivalent +in range @var{n}. +If not equivalent, the returned value is similar to what @code{strncmp} +would return. In other words, it returns a negative value if @var{s1} +is less than @var{s2}, or a positive value if @var{s2} is greater than +@var{s2}. + +This function does not normalize file names. As a result, this function +will treat filenames that are spelled differently as different even in +the case when the two filenames point to the same underlying file. +However, it does handle the fact that on DOS-like file systems, forward +and backward slashes are equal. + +@end deftypefn + +@c fnmatch.txh:1 +@deftypefn Replacement int fnmatch (const char *@var{pattern}, @ + const char *@var{string}, int @var{flags}) + +Matches @var{string} against @var{pattern}, returning zero if it +matches, @code{FNM_NOMATCH} if not. @var{pattern} may contain the +wildcards @code{?} to match any one character, @code{*} to match any +zero or more characters, or a set of alternate characters in square +brackets, like @samp{[a-gt8]}, which match one character (@code{a} +through @code{g}, or @code{t}, or @code{8}, in this example) if that one +character is in the set. A set may be inverted (i.e., match anything +except what's in the set) by giving @code{^} or @code{!} as the first +character in the set. To include those characters in the set, list them +as anything other than the first character of the set. To include a +dash in the set, list it last in the set. A backslash character makes +the following character not special, so for example you could match +against a literal asterisk with @samp{\*}. To match a literal +backslash, use @samp{\\}. + +@code{flags} controls various aspects of the matching process, and is a +boolean OR of zero or more of the following values (defined in +@code{}): + +@table @code + +@item FNM_PATHNAME +@itemx FNM_FILE_NAME +@var{string} is assumed to be a path name. No wildcard will ever match +@code{/}. + +@item FNM_NOESCAPE +Do not interpret backslashes as quoting the following special character. + +@item FNM_PERIOD +A leading period (at the beginning of @var{string}, or if +@code{FNM_PATHNAME} after a slash) is not matched by @code{*} or +@code{?} but must be matched explicitly. + +@item FNM_LEADING_DIR +Means that @var{string} also matches @var{pattern} if some initial part +of @var{string} matches, and is followed by @code{/} and zero or more +characters. For example, @samp{foo*} would match either @samp{foobar} +or @samp{foobar/grill}. + +@item FNM_CASEFOLD +Ignores case when performing the comparison. + +@end table + +@end deftypefn + +@c fopen_unlocked.c:39 +@deftypefn Extension {FILE *} fopen_unlocked (const char *@var{path}, @ + const char * @var{mode}) + +Opens and returns a @code{FILE} pointer via @code{fopen}. If the +operating system supports it, ensure that the stream is setup to avoid +any multi-threaded locking. Otherwise return the @code{FILE} pointer +unchanged. + +@end deftypefn + +@c argv.c:93 +@deftypefn Extension void freeargv (char **@var{vector}) + +Free an argument vector that was built using @code{buildargv}. Simply +scans through @var{vector}, freeing the memory for each argument until +the terminating @code{NULL} is found, and then frees @var{vector} +itself. + +@end deftypefn + +@c fopen_unlocked.c:59 +@deftypefn Extension {FILE *} freopen_unlocked (const char * @var{path}, @ + const char * @var{mode}, FILE * @var{stream}) + +Opens and returns a @code{FILE} pointer via @code{freopen}. If the +operating system supports it, ensure that the stream is setup to avoid +any multi-threaded locking. Otherwise return the @code{FILE} pointer +unchanged. + +@end deftypefn + +@c getruntime.c:86 +@deftypefn Replacement long get_run_time (void) + +Returns the time used so far, in microseconds. If possible, this is +the time used by this process, else it is the elapsed time since the +process started. + +@end deftypefn + +@c getcwd.c:6 +@deftypefn Supplemental char* getcwd (char *@var{pathname}, int @var{len}) + +Copy the absolute pathname for the current working directory into +@var{pathname}, which is assumed to point to a buffer of at least +@var{len} bytes, and return a pointer to the buffer. If the current +directory's path doesn't fit in @var{len} characters, the result is +@code{NULL} and @code{errno} is set. If @var{pathname} is a null pointer, +@code{getcwd} will obtain @var{len} bytes of space using +@code{malloc}. + +@end deftypefn + +@c getpagesize.c:5 +@deftypefn Supplemental int getpagesize (void) + +Returns the number of bytes in a page of memory. This is the +granularity of many of the system memory management routines. No +guarantee is made as to whether or not it is the same as the basic +memory management hardware page size. + +@end deftypefn + +@c getpwd.c:5 +@deftypefn Supplemental char* getpwd (void) + +Returns the current working directory. This implementation caches the +result on the assumption that the process will not call @code{chdir} +between calls to @code{getpwd}. + +@end deftypefn + +@c gettimeofday.c:12 +@deftypefn Supplemental int gettimeofday (struct timeval *@var{tp}, void *@var{tz}) + +Writes the current time to @var{tp}. This implementation requires +that @var{tz} be NULL. Returns 0 on success, -1 on failure. + +@end deftypefn + +@c hex.c:33 +@deftypefn Extension void hex_init (void) + +Initializes the array mapping the current character set to +corresponding hex values. This function must be called before any +call to @code{hex_p} or @code{hex_value}. If you fail to call it, a +default ASCII-based table will normally be used on ASCII systems. + +@end deftypefn + +@c hex.c:42 +@deftypefn Extension int hex_p (int @var{c}) + +Evaluates to non-zero if the given character is a valid hex character, +or zero if it is not. Note that the value you pass will be cast to +@code{unsigned char} within the macro. + +@end deftypefn + +@c hex.c:50 +@deftypefn Extension {unsigned int} hex_value (int @var{c}) + +Returns the numeric equivalent of the given character when interpreted +as a hexadecimal digit. The result is undefined if you pass an +invalid hex digit. Note that the value you pass will be cast to +@code{unsigned char} within the macro. + +The @code{hex_value} macro returns @code{unsigned int}, rather than +signed @code{int}, to make it easier to use in parsing addresses from +hex dump files: a signed @code{int} would be sign-extended when +converted to a wider unsigned type --- like @code{bfd_vma}, on some +systems. + +@end deftypefn + +@c safe-ctype.c:24 +@defvr Extension HOST_CHARSET +This macro indicates the basic character set and encoding used by the +host: more precisely, the encoding used for character constants in +preprocessor @samp{#if} statements (the C "execution character set"). +It is defined by @file{safe-ctype.h}, and will be an integer constant +with one of the following values: + +@ftable @code +@item HOST_CHARSET_UNKNOWN +The host character set is unknown - that is, not one of the next two +possibilities. + +@item HOST_CHARSET_ASCII +The host character set is ASCII. + +@item HOST_CHARSET_EBCDIC +The host character set is some variant of EBCDIC. (Only one of the +nineteen EBCDIC varying characters is tested; exercise caution.) +@end ftable +@end defvr + +@c hashtab.c:327 +@deftypefn Supplemental htab_t htab_create_typed_alloc (size_t @var{size}, @ +htab_hash @var{hash_f}, htab_eq @var{eq_f}, htab_del @var{del_f}, @ +htab_alloc @var{alloc_tab_f}, htab_alloc @var{alloc_f}, @ +htab_free @var{free_f}) + +This function creates a hash table that uses two different allocators +@var{alloc_tab_f} and @var{alloc_f} to use for allocating the table itself +and its entries respectively. This is useful when variables of different +types need to be allocated with different allocators. + +The created hash table is slightly larger than @var{size} and it is +initially empty (all the hash table entries are @code{HTAB_EMPTY_ENTRY}). +The function returns the created hash table, or @code{NULL} if memory +allocation fails. + +@end deftypefn + +@c index.c:5 +@deftypefn Supplemental char* index (char *@var{s}, int @var{c}) + +Returns a pointer to the first occurrence of the character @var{c} in +the string @var{s}, or @code{NULL} if not found. The use of @code{index} is +deprecated in new programs in favor of @code{strchr}. + +@end deftypefn + +@c insque.c:6 +@deftypefn Supplemental void insque (struct qelem *@var{elem}, @ + struct qelem *@var{pred}) +@deftypefnx Supplemental void remque (struct qelem *@var{elem}) + +Routines to manipulate queues built from doubly linked lists. The +@code{insque} routine inserts @var{elem} in the queue immediately +after @var{pred}. The @code{remque} routine removes @var{elem} from +its containing queue. These routines expect to be passed pointers to +structures which have as their first members a forward pointer and a +back pointer, like this prototype (although no prototype is provided): + +@example +struct qelem @{ + struct qelem *q_forw; + struct qelem *q_back; + char q_data[]; +@}; +@end example + +@end deftypefn + +@c safe-ctype.c:45 +@deffn Extension ISALPHA (@var{c}) +@deffnx Extension ISALNUM (@var{c}) +@deffnx Extension ISBLANK (@var{c}) +@deffnx Extension ISCNTRL (@var{c}) +@deffnx Extension ISDIGIT (@var{c}) +@deffnx Extension ISGRAPH (@var{c}) +@deffnx Extension ISLOWER (@var{c}) +@deffnx Extension ISPRINT (@var{c}) +@deffnx Extension ISPUNCT (@var{c}) +@deffnx Extension ISSPACE (@var{c}) +@deffnx Extension ISUPPER (@var{c}) +@deffnx Extension ISXDIGIT (@var{c}) + +These twelve macros are defined by @file{safe-ctype.h}. Each has the +same meaning as the corresponding macro (with name in lowercase) +defined by the standard header @file{ctype.h}. For example, +@code{ISALPHA} returns true for alphabetic characters and false for +others. However, there are two differences between these macros and +those provided by @file{ctype.h}: + +@itemize @bullet +@item These macros are guaranteed to have well-defined behavior for all +values representable by @code{signed char} and @code{unsigned char}, and +for @code{EOF}. + +@item These macros ignore the current locale; they are true for these +fixed sets of characters: +@multitable {@code{XDIGIT}} {yada yada yada yada yada yada yada yada} +@item @code{ALPHA} @tab @kbd{A-Za-z} +@item @code{ALNUM} @tab @kbd{A-Za-z0-9} +@item @code{BLANK} @tab @kbd{space tab} +@item @code{CNTRL} @tab @code{!PRINT} +@item @code{DIGIT} @tab @kbd{0-9} +@item @code{GRAPH} @tab @code{ALNUM || PUNCT} +@item @code{LOWER} @tab @kbd{a-z} +@item @code{PRINT} @tab @code{GRAPH ||} @kbd{space} +@item @code{PUNCT} @tab @kbd{`~!@@#$%^&*()_-=+[@{]@}\|;:'",<.>/?} +@item @code{SPACE} @tab @kbd{space tab \n \r \f \v} +@item @code{UPPER} @tab @kbd{A-Z} +@item @code{XDIGIT} @tab @kbd{0-9A-Fa-f} +@end multitable + +Note that, if the host character set is ASCII or a superset thereof, +all these macros will return false for all values of @code{char} outside +the range of 7-bit ASCII. In particular, both ISPRINT and ISCNTRL return +false for characters with numeric values from 128 to 255. +@end itemize +@end deffn + +@c safe-ctype.c:94 +@deffn Extension ISIDNUM (@var{c}) +@deffnx Extension ISIDST (@var{c}) +@deffnx Extension IS_VSPACE (@var{c}) +@deffnx Extension IS_NVSPACE (@var{c}) +@deffnx Extension IS_SPACE_OR_NUL (@var{c}) +@deffnx Extension IS_ISOBASIC (@var{c}) +These six macros are defined by @file{safe-ctype.h} and provide +additional character classes which are useful when doing lexical +analysis of C or similar languages. They are true for the following +sets of characters: + +@multitable {@code{SPACE_OR_NUL}} {yada yada yada yada yada yada yada yada} +@item @code{IDNUM} @tab @kbd{A-Za-z0-9_} +@item @code{IDST} @tab @kbd{A-Za-z_} +@item @code{VSPACE} @tab @kbd{\r \n} +@item @code{NVSPACE} @tab @kbd{space tab \f \v \0} +@item @code{SPACE_OR_NUL} @tab @code{VSPACE || NVSPACE} +@item @code{ISOBASIC} @tab @code{VSPACE || NVSPACE || PRINT} +@end multitable +@end deffn + +@c lbasename.c:23 +@deftypefn Replacement {const char*} lbasename (const char *@var{name}) + +Given a pointer to a string containing a typical pathname +(@samp{/usr/src/cmd/ls/ls.c} for example), returns a pointer to the +last component of the pathname (@samp{ls.c} in this case). The +returned pointer is guaranteed to lie within the original +string. This latter fact is not true of many vendor C +libraries, which return special strings or modify the passed +strings for particular input. + +In particular, the empty string returns the same empty string, +and a path ending in @code{/} returns the empty string after it. + +@end deftypefn + +@c lrealpath.c:25 +@deftypefn Replacement {const char*} lrealpath (const char *@var{name}) + +Given a pointer to a string containing a pathname, returns a canonical +version of the filename. Symlinks will be resolved, and ``.'' and ``..'' +components will be simplified. The returned value will be allocated using +@code{malloc}, or @code{NULL} will be returned on a memory allocation error. + +@end deftypefn + +@c make-relative-prefix.c:23 +@deftypefn Extension {const char*} make_relative_prefix (const char *@var{progname}, @ + const char *@var{bin_prefix}, const char *@var{prefix}) + +Given three paths @var{progname}, @var{bin_prefix}, @var{prefix}, +return the path that is in the same position relative to +@var{progname}'s directory as @var{prefix} is relative to +@var{bin_prefix}. That is, a string starting with the directory +portion of @var{progname}, followed by a relative pathname of the +difference between @var{bin_prefix} and @var{prefix}. + +If @var{progname} does not contain any directory separators, +@code{make_relative_prefix} will search @env{PATH} to find a program +named @var{progname}. Also, if @var{progname} is a symbolic link, +the symbolic link will be resolved. + +For example, if @var{bin_prefix} is @code{/alpha/beta/gamma/gcc/delta}, +@var{prefix} is @code{/alpha/beta/gamma/omega/}, and @var{progname} is +@code{/red/green/blue/gcc}, then this function will return +@code{/red/green/blue/../../omega/}. + +The return value is normally allocated via @code{malloc}. If no +relative prefix can be found, return @code{NULL}. + +@end deftypefn + +@c make-temp-file.c:173 +@deftypefn Replacement char* make_temp_file (const char *@var{suffix}) + +Return a temporary file name (as a string) or @code{NULL} if unable to +create one. @var{suffix} is a suffix to append to the file name. The +string is @code{malloc}ed, and the temporary file has been created. + +@end deftypefn + +@c memchr.c:3 +@deftypefn Supplemental void* memchr (const void *@var{s}, int @var{c}, @ + size_t @var{n}) + +This function searches memory starting at @code{*@var{s}} for the +character @var{c}. The search only ends with the first occurrence of +@var{c}, or after @var{length} characters; in particular, a null +character does not terminate the search. If the character @var{c} is +found within @var{length} characters of @code{*@var{s}}, a pointer +to the character is returned. If @var{c} is not found, then @code{NULL} is +returned. + +@end deftypefn + +@c memcmp.c:6 +@deftypefn Supplemental int memcmp (const void *@var{x}, const void *@var{y}, @ + size_t @var{count}) + +Compares the first @var{count} bytes of two areas of memory. Returns +zero if they are the same, a value less than zero if @var{x} is +lexically less than @var{y}, or a value greater than zero if @var{x} +is lexically greater than @var{y}. Note that lexical order is determined +as if comparing unsigned char arrays. + +@end deftypefn + +@c memcpy.c:6 +@deftypefn Supplemental void* memcpy (void *@var{out}, const void *@var{in}, @ + size_t @var{length}) + +Copies @var{length} bytes from memory region @var{in} to region +@var{out}. Returns a pointer to @var{out}. + +@end deftypefn + +@c memmem.c:20 +@deftypefn Supplemental void* memmem (const void *@var{haystack}, @ + size_t @var{haystack_len} const void *@var{needle}, size_t @var{needle_len}) + +Returns a pointer to the first occurrence of @var{needle} (length +@var{needle_len}) in @var{haystack} (length @var{haystack_len}). +Returns @code{NULL} if not found. + +@end deftypefn + +@c memmove.c:6 +@deftypefn Supplemental void* memmove (void *@var{from}, const void *@var{to}, @ + size_t @var{count}) + +Copies @var{count} bytes from memory area @var{from} to memory area +@var{to}, returning a pointer to @var{to}. + +@end deftypefn + +@c mempcpy.c:23 +@deftypefn Supplemental void* mempcpy (void *@var{out}, const void *@var{in}, @ + size_t @var{length}) + +Copies @var{length} bytes from memory region @var{in} to region +@var{out}. Returns a pointer to @var{out} + @var{length}. + +@end deftypefn + +@c memset.c:6 +@deftypefn Supplemental void* memset (void *@var{s}, int @var{c}, @ + size_t @var{count}) + +Sets the first @var{count} bytes of @var{s} to the constant byte +@var{c}, returning a pointer to @var{s}. + +@end deftypefn + +@c mkstemps.c:60 +@deftypefn Replacement int mkstemps (char *@var{pattern}, int @var{suffix_len}) + +Generate a unique temporary file name from @var{pattern}. +@var{pattern} has the form: + +@example + @var{path}/ccXXXXXX@var{suffix} +@end example + +@var{suffix_len} tells us how long @var{suffix} is (it can be zero +length). The last six characters of @var{pattern} before @var{suffix} +must be @samp{XXXXXX}; they are replaced with a string that makes the +filename unique. Returns a file descriptor open on the file for +reading and writing. + +@end deftypefn + +@c pexecute.txh:278 +@deftypefn Extension void pex_free (struct pex_obj @var{obj}) + +Clean up and free all data associated with @var{obj}. If you have not +yet called @code{pex_get_times} or @code{pex_get_status}, this will +try to kill the subprocesses. + +@end deftypefn + +@c pexecute.txh:251 +@deftypefn Extension int pex_get_status (struct pex_obj *@var{obj}, @ + int @var{count}, int *@var{vector}) + +Returns the exit status of all programs run using @var{obj}. +@var{count} is the number of results expected. The results will be +placed into @var{vector}. The results are in the order of the calls +to @code{pex_run}. Returns 0 on error, 1 on success. + +@end deftypefn + +@c pexecute.txh:261 +@deftypefn Extension int pex_get_times (struct pex_obj *@var{obj}, @ + int @var{count}, struct pex_time *@var{vector}) + +Returns the process execution times of all programs run using +@var{obj}. @var{count} is the number of results expected. The +results will be placed into @var{vector}. The results are in the +order of the calls to @code{pex_run}. Returns 0 on error, 1 on +success. + +@code{struct pex_time} has the following fields of the type +@code{unsigned long}: @code{user_seconds}, +@code{user_microseconds}, @code{system_seconds}, +@code{system_microseconds}. On systems which do not support reporting +process times, all the fields will be set to @code{0}. + +@end deftypefn + +@c pexecute.txh:2 +@deftypefn Extension {struct pex_obj *} pex_init (int @var{flags}, @ + const char *@var{pname}, const char *@var{tempbase}) + +Prepare to execute one or more programs, with standard output of each +program fed to standard input of the next. This is a system +independent interface to execute a pipeline. + +@var{flags} is a bitwise combination of the following: + +@table @code + +@vindex PEX_RECORD_TIMES +@item PEX_RECORD_TIMES +Record subprocess times if possible. + +@vindex PEX_USE_PIPES +@item PEX_USE_PIPES +Use pipes for communication between processes, if possible. + +@vindex PEX_SAVE_TEMPS +@item PEX_SAVE_TEMPS +Don't delete temporary files used for communication between +processes. + +@end table + +@var{pname} is the name of program to be executed, used in error +messages. @var{tempbase} is a base name to use for any required +temporary files; it may be @code{NULL} to use a randomly chosen name. + +@end deftypefn + +@c pexecute.txh:161 +@deftypefn Extension {FILE *} pex_input_file (struct pex_obj *@var{obj}, @ + int @var{flags}, const char *@var{in_name}) + +Return a stream for a temporary file to pass to the first program in +the pipeline as input. + +The name of the input file is chosen according to the same rules +@code{pex_run} uses to choose output file names, based on +@var{in_name}, @var{obj} and the @code{PEX_SUFFIX} bit in @var{flags}. + +Don't call @code{fclose} on the returned stream; the first call to +@code{pex_run} closes it automatically. + +If @var{flags} includes @code{PEX_BINARY_OUTPUT}, open the stream in +binary mode; otherwise, open it in the default mode. Including +@code{PEX_BINARY_OUTPUT} in @var{flags} has no effect on Unix. +@end deftypefn + +@c pexecute.txh:179 +@deftypefn Extension {FILE *} pex_input_pipe (struct pex_obj *@var{obj}, @ + int @var{binary}) + +Return a stream @var{fp} for a pipe connected to the standard input of +the first program in the pipeline; @var{fp} is opened for writing. +You must have passed @code{PEX_USE_PIPES} to the @code{pex_init} call +that returned @var{obj}. + +You must close @var{fp} using @code{fclose} yourself when you have +finished writing data to the pipeline. + +The file descriptor underlying @var{fp} is marked not to be inherited +by child processes. + +On systems that do not support pipes, this function returns +@code{NULL}, and sets @code{errno} to @code{EINVAL}. If you would +like to write code that is portable to all systems the @code{pex} +functions support, consider using @code{pex_input_file} instead. + +There are two opportunities for deadlock using +@code{pex_input_pipe}: + +@itemize @bullet +@item +Most systems' pipes can buffer only a fixed amount of data; a process +that writes to a full pipe blocks. Thus, if you write to @file{fp} +before starting the first process, you run the risk of blocking when +there is no child process yet to read the data and allow you to +continue. @code{pex_input_pipe} makes no promises about the +size of the pipe's buffer, so if you need to write any data at all +before starting the first process in the pipeline, consider using +@code{pex_input_file} instead. + +@item +Using @code{pex_input_pipe} and @code{pex_read_output} together +may also cause deadlock. If the output pipe fills up, so that each +program in the pipeline is waiting for the next to read more data, and +you fill the input pipe by writing more data to @var{fp}, then there +is no way to make progress: the only process that could read data from +the output pipe is you, but you are blocked on the input pipe. + +@end itemize + +@end deftypefn + +@c pexecute.txh:286 +@deftypefn Extension {const char *} pex_one (int @var{flags}, @ + const char *@var{executable}, char * const *@var{argv}, @ + const char *@var{pname}, const char *@var{outname}, const char *@var{errname}, @ + int *@var{status}, int *@var{err}) + +An interface to permit the easy execution of a +single program. The return value and most of the parameters are as +for a call to @code{pex_run}. @var{flags} is restricted to a +combination of @code{PEX_SEARCH}, @code{PEX_STDERR_TO_STDOUT}, and +@code{PEX_BINARY_OUTPUT}. @var{outname} is interpreted as if +@code{PEX_LAST} were set. On a successful return, @code{*@var{status}} will +be set to the exit status of the program. + +@end deftypefn + +@c pexecute.txh:237 +@deftypefn Extension {FILE *} pex_read_err (struct pex_obj *@var{obj}, @ + int @var{binary}) + +Returns a @code{FILE} pointer which may be used to read the standard +error of the last program in the pipeline. When this is used, +@code{PEX_LAST} should not be used in a call to @code{pex_run}. After +this is called, @code{pex_run} may no longer be called with the same +@var{obj}. @var{binary} should be non-zero if the file should be +opened in binary mode. Don't call @code{fclose} on the returned file; +it will be closed by @code{pex_free}. + +@end deftypefn + +@c pexecute.txh:224 +@deftypefn Extension {FILE *} pex_read_output (struct pex_obj *@var{obj}, @ + int @var{binary}) + +Returns a @code{FILE} pointer which may be used to read the standard +output of the last program in the pipeline. When this is used, +@code{PEX_LAST} should not be used in a call to @code{pex_run}. After +this is called, @code{pex_run} may no longer be called with the same +@var{obj}. @var{binary} should be non-zero if the file should be +opened in binary mode. Don't call @code{fclose} on the returned file; +it will be closed by @code{pex_free}. + +@end deftypefn + +@c pexecute.txh:34 +@deftypefn Extension {const char *} pex_run (struct pex_obj *@var{obj}, @ + int @var{flags}, const char *@var{executable}, char * const *@var{argv}, @ + const char *@var{outname}, const char *@var{errname}, int *@var{err}) + +Execute one program in a pipeline. On success this returns +@code{NULL}. On failure it returns an error message, a statically +allocated string. + +@var{obj} is returned by a previous call to @code{pex_init}. + +@var{flags} is a bitwise combination of the following: + +@table @code + +@vindex PEX_LAST +@item PEX_LAST +This must be set on the last program in the pipeline. In particular, +it should be set when executing a single program. The standard output +of the program will be sent to @var{outname}, or, if @var{outname} is +@code{NULL}, to the standard output of the calling program. Do @emph{not} +set this bit if you want to call @code{pex_read_output} +(described below). After a call to @code{pex_run} with this bit set, +@var{pex_run} may no longer be called with the same @var{obj}. + +@vindex PEX_SEARCH +@item PEX_SEARCH +Search for the program using the user's executable search path. + +@vindex PEX_SUFFIX +@item PEX_SUFFIX +@var{outname} is a suffix. See the description of @var{outname}, +below. + +@vindex PEX_STDERR_TO_STDOUT +@item PEX_STDERR_TO_STDOUT +Send the program's standard error to standard output, if possible. + +@vindex PEX_BINARY_INPUT +@vindex PEX_BINARY_OUTPUT +@vindex PEX_BINARY_ERROR +@item PEX_BINARY_INPUT +@itemx PEX_BINARY_OUTPUT +@itemx PEX_BINARY_ERROR +The standard input (output or error) of the program should be read (written) in +binary mode rather than text mode. These flags are ignored on systems +which do not distinguish binary mode and text mode, such as Unix. For +proper behavior these flags should match appropriately---a call to +@code{pex_run} using @code{PEX_BINARY_OUTPUT} should be followed by a +call using @code{PEX_BINARY_INPUT}. + +@vindex PEX_STDERR_TO_PIPE +@item PEX_STDERR_TO_PIPE +Send the program's standard error to a pipe, if possible. This flag +cannot be specified together with @code{PEX_STDERR_TO_STDOUT}. This +flag can be specified only on the last program in pipeline. + +@end table + +@var{executable} is the program to execute. @var{argv} is the set of +arguments to pass to the program; normally @code{@var{argv}[0]} will +be a copy of @var{executable}. + +@var{outname} is used to set the name of the file to use for standard +output. There are two cases in which no output file will be used: + +@enumerate +@item +if @code{PEX_LAST} is not set in @var{flags}, and @code{PEX_USE_PIPES} +was set in the call to @code{pex_init}, and the system supports pipes + +@item +if @code{PEX_LAST} is set in @var{flags}, and @var{outname} is +@code{NULL} +@end enumerate + +@noindent +Otherwise the code will use a file to hold standard +output. If @code{PEX_LAST} is not set, this file is considered to be +a temporary file, and it will be removed when no longer needed, unless +@code{PEX_SAVE_TEMPS} was set in the call to @code{pex_init}. + +There are two cases to consider when setting the name of the file to +hold standard output. + +@enumerate +@item +@code{PEX_SUFFIX} is set in @var{flags}. In this case +@var{outname} may not be @code{NULL}. If the @var{tempbase} parameter +to @code{pex_init} was not @code{NULL}, then the output file name is +the concatenation of @var{tempbase} and @var{outname}. If +@var{tempbase} was @code{NULL}, then the output file name is a random +file name ending in @var{outname}. + +@item +@code{PEX_SUFFIX} was not set in @var{flags}. In this +case, if @var{outname} is not @code{NULL}, it is used as the output +file name. If @var{outname} is @code{NULL}, and @var{tempbase} was +not NULL, the output file name is randomly chosen using +@var{tempbase}. Otherwise the output file name is chosen completely +at random. +@end enumerate + +@var{errname} is the file name to use for standard error output. If +it is @code{NULL}, standard error is the same as the caller's. +Otherwise, standard error is written to the named file. + +On an error return, the code sets @code{*@var{err}} to an @code{errno} +value, or to 0 if there is no relevant @code{errno}. + +@end deftypefn + +@c pexecute.txh:145 +@deftypefn Extension {const char *} pex_run_in_environment (struct pex_obj *@var{obj}, @ + int @var{flags}, const char *@var{executable}, char * const *@var{argv}, @ + char * const *@var{env}, int @var{env_size}, const char *@var{outname}, @ + const char *@var{errname}, int *@var{err}) + +Execute one program in a pipeline, permitting the environment for the +program to be specified. Behaviour and parameters not listed below are +as for @code{pex_run}. + +@var{env} is the environment for the child process, specified as an array of +character pointers. Each element of the array should point to a string of the +form @code{VAR=VALUE}, with the exception of the last element that must be +@code{NULL}. + +@end deftypefn + +@c pexecute.txh:301 +@deftypefn Extension int pexecute (const char *@var{program}, @ + char * const *@var{argv}, const char *@var{this_pname}, @ + const char *@var{temp_base}, char **@var{errmsg_fmt}, @ + char **@var{errmsg_arg}, int @var{flags}) + +This is the old interface to execute one or more programs. It is +still supported for compatibility purposes, but is no longer +documented. + +@end deftypefn + +@c strsignal.c:541 +@deftypefn Supplemental void psignal (int @var{signo}, char *@var{message}) + +Print @var{message} to the standard error, followed by a colon, +followed by the description of the signal specified by @var{signo}, +followed by a newline. + +@end deftypefn + +@c putenv.c:21 +@deftypefn Supplemental int putenv (const char *@var{string}) + +Uses @code{setenv} or @code{unsetenv} to put @var{string} into +the environment or remove it. If @var{string} is of the form +@samp{name=value} the string is added; if no @samp{=} is present the +name is unset/removed. + +@end deftypefn + +@c pexecute.txh:312 +@deftypefn Extension int pwait (int @var{pid}, int *@var{status}, int @var{flags}) + +Another part of the old execution interface. + +@end deftypefn + +@c random.c:39 +@deftypefn Supplement {long int} random (void) +@deftypefnx Supplement void srandom (unsigned int @var{seed}) +@deftypefnx Supplement void* initstate (unsigned int @var{seed}, @ + void *@var{arg_state}, unsigned long @var{n}) +@deftypefnx Supplement void* setstate (void *@var{arg_state}) + +Random number functions. @code{random} returns a random number in the +range 0 to @code{LONG_MAX}. @code{srandom} initializes the random +number generator to some starting point determined by @var{seed} +(else, the values returned by @code{random} are always the same for each +run of the program). @code{initstate} and @code{setstate} allow fine-grained +control over the state of the random number generator. + +@end deftypefn + +@c concat.c:160 +@deftypefn Extension char* reconcat (char *@var{optr}, const char *@var{s1}, @ + @dots{}, @code{NULL}) + +Same as @code{concat}, except that if @var{optr} is not @code{NULL} it +is freed after the string is created. This is intended to be useful +when you're extending an existing string or building up a string in a +loop: + +@example + str = reconcat (str, "pre-", str, NULL); +@end example + +@end deftypefn + +@c rename.c:6 +@deftypefn Supplemental int rename (const char *@var{old}, const char *@var{new}) + +Renames a file from @var{old} to @var{new}. If @var{new} already +exists, it is removed. + +@end deftypefn + +@c rindex.c:5 +@deftypefn Supplemental char* rindex (const char *@var{s}, int @var{c}) + +Returns a pointer to the last occurrence of the character @var{c} in +the string @var{s}, or @code{NULL} if not found. The use of @code{rindex} is +deprecated in new programs in favor of @code{strrchr}. + +@end deftypefn + +@c setenv.c:22 +@deftypefn Supplemental int setenv (const char *@var{name}, @ + const char *@var{value}, int @var{overwrite}) +@deftypefnx Supplemental void unsetenv (const char *@var{name}) + +@code{setenv} adds @var{name} to the environment with value +@var{value}. If the name was already present in the environment, +the new value will be stored only if @var{overwrite} is nonzero. +The companion @code{unsetenv} function removes @var{name} from the +environment. This implementation is not safe for multithreaded code. + +@end deftypefn + +@c setproctitle.c:31 +@deftypefn Supplemental void setproctitle (const char *@var{fmt}, ...) + +Set the title of a process to @var{fmt}. va args not supported for now, +but defined for compatibility with BSD. + +@end deftypefn + +@c strsignal.c:348 +@deftypefn Extension int signo_max (void) + +Returns the maximum signal value for which a corresponding symbolic +name or message is available. Note that in the case where we use the +@code{sys_siglist} supplied by the system, it is possible for there to +be more symbolic names than messages, or vice versa. In fact, the +manual page for @code{psignal(3b)} explicitly warns that one should +check the size of the table (@code{NSIG}) before indexing it, since +new signal codes may be added to the system before they are added to +the table. Thus @code{NSIG} might be smaller than value implied by +the largest signo value defined in @code{}. + +We return the maximum value that can be used to obtain a meaningful +symbolic name or message. + +@end deftypefn + +@c sigsetmask.c:8 +@deftypefn Supplemental int sigsetmask (int @var{set}) + +Sets the signal mask to the one provided in @var{set} and returns +the old mask (which, for libiberty's implementation, will always +be the value @code{1}). + +@end deftypefn + +@c simple-object.txh:96 +@deftypefn Extension {const char *} simple_object_attributes_compare @ + (simple_object_attributes *@var{attrs1}, simple_object_attributes *@var{attrs2}, @ + int *@var{err}) + +Compare @var{attrs1} and @var{attrs2}. If they could be linked +together without error, return @code{NULL}. Otherwise, return an +error message and set @code{*@var{err}} to an errno value or @code{0} +if there is no relevant errno. + +@end deftypefn + +@c simple-object.txh:81 +@deftypefn Extension {simple_object_attributes *} simple_object_fetch_attributes @ + (simple_object_read *@var{simple_object}, const char **@var{errmsg}, int *@var{err}) + +Fetch the attributes of @var{simple_object}. The attributes are +internal information such as the format of the object file, or the +architecture it was compiled for. This information will persist until +@code{simple_object_attributes_release} is called, even if +@var{simple_object} itself is released. + +On error this returns @code{NULL}, sets @code{*@var{errmsg}} to an +error message, and sets @code{*@var{err}} to an errno value or +@code{0} if there is no relevant errno. + +@end deftypefn + +@c simple-object.txh:49 +@deftypefn Extension {int} simple_object_find_section @ + (simple_object_read *@var{simple_object} off_t *@var{offset}, @ + off_t *@var{length}, const char **@var{errmsg}, int *@var{err}) + +Look for the section @var{name} in @var{simple_object}. This returns +information for the first section with that name. + +If found, return 1 and set @code{*@var{offset}} to the offset in the +file of the section contents and set @code{*@var{length}} to the +length of the section contents. The value in @code{*@var{offset}} +will be relative to the offset passed to +@code{simple_object_open_read}. + +If the section is not found, and no error occurs, +@code{simple_object_find_section} returns @code{0} and set +@code{*@var{errmsg}} to @code{NULL}. + +If an error occurs, @code{simple_object_find_section} returns +@code{0}, sets @code{*@var{errmsg}} to an error message, and sets +@code{*@var{err}} to an errno value or @code{0} if there is no +relevant errno. + +@end deftypefn + +@c simple-object.txh:27 +@deftypefn Extension {const char *} simple_object_find_sections @ + (simple_object_read *@var{simple_object}, int (*@var{pfn}) (void *@var{data}, @ + const char *@var{name}, off_t @var{offset}, off_t @var{length}), @ + void *@var{data}, int *@var{err}) + +This function calls @var{pfn} for each section in @var{simple_object}. +It calls @var{pfn} with the section name, the offset within the file +of the section contents, and the length of the section contents. The +offset within the file is relative to the offset passed to +@code{simple_object_open_read}. The @var{data} argument to this +function is passed along to @var{pfn}. + +If @var{pfn} returns @code{0}, the loop over the sections stops and +@code{simple_object_find_sections} returns. If @var{pfn} returns some +other value, the loop continues. + +On success @code{simple_object_find_sections} returns. On error it +returns an error string, and sets @code{*@var{err}} to an errno value +or @code{0} if there is no relevant errno. + +@end deftypefn + +@c simple-object.txh:2 +@deftypefn Extension {simple_object_read *} simple_object_open_read @ + (int @var{descriptor}, off_t @var{offset}, const char *{segment_name}, @ + const char **@var{errmsg}, int *@var{err}) + +Opens an object file for reading. Creates and returns an +@code{simple_object_read} pointer which may be passed to other +functions to extract data from the object file. + +@var{descriptor} holds a file descriptor which permits reading. + +@var{offset} is the offset into the file; this will be @code{0} in the +normal case, but may be a different value when reading an object file +in an archive file. + +@var{segment_name} is only used with the Mach-O file format used on +Darwin aka Mac OS X. It is required on that platform, and means to +only look at sections within the segment with that name. The +parameter is ignored on other systems. + +If an error occurs, this functions returns @code{NULL} and sets +@code{*@var{errmsg}} to an error string and sets @code{*@var{err}} to +an errno value or @code{0} if there is no relevant errno. + +@end deftypefn + +@c simple-object.txh:107 +@deftypefn Extension {void} simple_object_release_attributes @ + (simple_object_attributes *@var{attrs}) + +Release all resources associated with @var{attrs}. + +@end deftypefn + +@c simple-object.txh:73 +@deftypefn Extension {void} simple_object_release_read @ + (simple_object_read *@var{simple_object}) + +Release all resources associated with @var{simple_object}. This does +not close the file descriptor. + +@end deftypefn + +@c simple-object.txh:184 +@deftypefn Extension {void} simple_object_release_write @ + (simple_object_write *@var{simple_object}) + +Release all resources associated with @var{simple_object}. + +@end deftypefn + +@c simple-object.txh:114 +@deftypefn Extension {simple_object_write *} simple_object_start_write @ + (simple_object_attributes @var{attrs}, const char *@var{segment_name}, @ + const char **@var{errmsg}, int *@var{err}) + +Start creating a new object file using the object file format +described in @var{attrs}. You must fetch attribute information from +an existing object file before you can create a new one. There is +currently no support for creating an object file de novo. + +@var{segment_name} is only used with Mach-O as found on Darwin aka Mac +OS X. The parameter is required on that target. It means that all +sections are created within the named segment. It is ignored for +other object file formats. + +On error @code{simple_object_start_write} returns @code{NULL}, sets +@code{*@var{ERRMSG}} to an error message, and sets @code{*@var{err}} +to an errno value or @code{0} if there is no relevant errno. + +@end deftypefn + +@c simple-object.txh:153 +@deftypefn Extension {const char *} simple_object_write_add_data @ + (simple_object_write *@var{simple_object}, @ + simple_object_write_section *@var{section}, const void *@var{buffer}, @ + size_t @var{size}, int @var{copy}, int *@var{err}) + +Add data @var{buffer}/@var{size} to @var{section} in +@var{simple_object}. If @var{copy} is non-zero, the data will be +copied into memory if necessary. If @var{copy} is zero, @var{buffer} +must persist until @code{simple_object_write_to_file} is called. is +released. + +On success this returns @code{NULL}. On error this returns an error +message, and sets @code{*@var{err}} to an errno value or 0 if there is +no relevant erro. + +@end deftypefn + +@c simple-object.txh:134 +@deftypefn Extension {simple_object_write_section *} simple_object_write_create_section @ + (simple_object_write *@var{simple_object}, const char *@var{name}, @ + unsigned int @var{align}, const char **@var{errmsg}, int *@var{err}) + +Add a section to @var{simple_object}. @var{name} is the name of the +new section. @var{align} is the required alignment expressed as the +number of required low-order 0 bits (e.g., 2 for alignment to a 32-bit +boundary). + +The section is created as containing data, readable, not writable, not +executable, not loaded at runtime. The section is not written to the +file until @code{simple_object_write_to_file} is called. + +On error this returns @code{NULL}, sets @code{*@var{errmsg}} to an +error message, and sets @code{*@var{err}} to an errno value or +@code{0} if there is no relevant errno. + +@end deftypefn + +@c simple-object.txh:170 +@deftypefn Extension {const char *} simple_object_write_to_file @ + (simple_object_write *@var{simple_object}, int @var{descriptor}, int *@var{err}) + +Write the complete object file to @var{descriptor}, an open file +descriptor. This writes out all the data accumulated by calls to +@code{simple_object_write_create_section} and +@var{simple_object_write_add_data}. + +This returns @code{NULL} on success. On error this returns an error +message and sets @code{*@var{err}} to an errno value or @code{0} if +there is no relevant errno. + +@end deftypefn + +@c snprintf.c:28 +@deftypefn Supplemental int snprintf (char *@var{buf}, size_t @var{n}, @ + const char *@var{format}, ...) + +This function is similar to @code{sprintf}, but it will write to +@var{buf} at most @code{@var{n}-1} bytes of text, followed by a +terminating null byte, for a total of @var{n} bytes. +On error the return value is -1, otherwise it returns the number of +bytes, not including the terminating null byte, that would have been +written had @var{n} been sufficiently large, regardless of the actual +value of @var{n}. Note some pre-C99 system libraries do not implement +this correctly so users cannot generally rely on the return value if +the system version of this function is used. + +@end deftypefn + +@c spaces.c:22 +@deftypefn Extension char* spaces (int @var{count}) + +Returns a pointer to a memory region filled with the specified +number of spaces and null terminated. The returned pointer is +valid until at least the next call. + +@end deftypefn + +@c splay-tree.c:305 +@deftypefn Supplemental splay_tree splay_tree_new_with_typed_alloc @ +(splay_tree_compare_fn @var{compare_fn}, @ +splay_tree_delete_key_fn @var{delete_key_fn}, @ +splay_tree_delete_value_fn @var{delete_value_fn}, @ +splay_tree_allocate_fn @var{tree_allocate_fn}, @ +splay_tree_allocate_fn @var{node_allocate_fn}, @ +splay_tree_deallocate_fn @var{deallocate_fn}, @ +void * @var{allocate_data}) + +This function creates a splay tree that uses two different allocators +@var{tree_allocate_fn} and @var{node_allocate_fn} to use for allocating the +tree itself and its nodes respectively. This is useful when variables of +different types need to be allocated with different allocators. + +The splay tree will use @var{compare_fn} to compare nodes, +@var{delete_key_fn} to deallocate keys, and @var{delete_value_fn} to +deallocate values. Keys and values will be deallocated when the +tree is deleted using splay_tree_delete or when a node is removed +using splay_tree_remove. splay_tree_insert will release the previously +inserted key and value using @var{delete_key_fn} and @var{delete_value_fn} +if the inserted key is already found in the tree. + +@end deftypefn + +@c stack-limit.c:28 +@deftypefn Extension void stack_limit_increase (unsigned long @var{pref}) + +Attempt to increase stack size limit to @var{pref} bytes if possible. + +@end deftypefn + +@c stpcpy.c:23 +@deftypefn Supplemental char* stpcpy (char *@var{dst}, const char *@var{src}) + +Copies the string @var{src} into @var{dst}. Returns a pointer to +@var{dst} + strlen(@var{src}). + +@end deftypefn + +@c stpncpy.c:23 +@deftypefn Supplemental char* stpncpy (char *@var{dst}, const char *@var{src}, @ + size_t @var{len}) + +Copies the string @var{src} into @var{dst}, copying exactly @var{len} +and padding with zeros if necessary. If @var{len} < strlen(@var{src}) +then return @var{dst} + @var{len}, otherwise returns @var{dst} + +strlen(@var{src}). + +@end deftypefn + +@c strcasecmp.c:15 +@deftypefn Supplemental int strcasecmp (const char *@var{s1}, const char *@var{s2}) + +A case-insensitive @code{strcmp}. + +@end deftypefn + +@c strchr.c:6 +@deftypefn Supplemental char* strchr (const char *@var{s}, int @var{c}) + +Returns a pointer to the first occurrence of the character @var{c} in +the string @var{s}, or @code{NULL} if not found. If @var{c} is itself the +null character, the results are undefined. + +@end deftypefn + +@c strdup.c:3 +@deftypefn Supplemental char* strdup (const char *@var{s}) + +Returns a pointer to a copy of @var{s} in memory obtained from +@code{malloc}, or @code{NULL} if insufficient memory was available. + +@end deftypefn + +@c strerror.c:675 +@deftypefn Replacement {const char*} strerrno (int @var{errnum}) + +Given an error number returned from a system call (typically returned +in @code{errno}), returns a pointer to a string containing the +symbolic name of that error number, as found in @code{}. + +If the supplied error number is within the valid range of indices for +symbolic names, but no name is available for the particular error +number, then returns the string @samp{Error @var{num}}, where @var{num} +is the error number. + +If the supplied error number is not within the range of valid +indices, then returns @code{NULL}. + +The contents of the location pointed to are only guaranteed to be +valid until the next call to @code{strerrno}. + +@end deftypefn + +@c strerror.c:608 +@deftypefn Supplemental char* strerror (int @var{errnoval}) + +Maps an @code{errno} number to an error message string, the contents +of which are implementation defined. On systems which have the +external variables @code{sys_nerr} and @code{sys_errlist}, these +strings will be the same as the ones used by @code{perror}. + +If the supplied error number is within the valid range of indices for +the @code{sys_errlist}, but no message is available for the particular +error number, then returns the string @samp{Error @var{num}}, where +@var{num} is the error number. + +If the supplied error number is not a valid index into +@code{sys_errlist}, returns @code{NULL}. + +The returned string is only guaranteed to be valid only until the +next call to @code{strerror}. + +@end deftypefn + +@c strncasecmp.c:15 +@deftypefn Supplemental int strncasecmp (const char *@var{s1}, const char *@var{s2}) + +A case-insensitive @code{strncmp}. + +@end deftypefn + +@c strncmp.c:6 +@deftypefn Supplemental int strncmp (const char *@var{s1}, @ + const char *@var{s2}, size_t @var{n}) + +Compares the first @var{n} bytes of two strings, returning a value as +@code{strcmp}. + +@end deftypefn + +@c strndup.c:23 +@deftypefn Extension char* strndup (const char *@var{s}, size_t @var{n}) + +Returns a pointer to a copy of @var{s} with at most @var{n} characters +in memory obtained from @code{malloc}, or @code{NULL} if insufficient +memory was available. The result is always NUL terminated. + +@end deftypefn + +@c strnlen.c:6 +@deftypefn Supplemental size_t strnlen (const char *@var{s}, size_t @var{maxlen}) + +Returns the length of @var{s}, as with @code{strlen}, but never looks +past the first @var{maxlen} characters in the string. If there is no +'\0' character in the first @var{maxlen} characters, returns +@var{maxlen}. + +@end deftypefn + +@c strrchr.c:6 +@deftypefn Supplemental char* strrchr (const char *@var{s}, int @var{c}) + +Returns a pointer to the last occurrence of the character @var{c} in +the string @var{s}, or @code{NULL} if not found. If @var{c} is itself the +null character, the results are undefined. + +@end deftypefn + +@c strsignal.c:383 +@deftypefn Supplemental {const char *} strsignal (int @var{signo}) + +Maps an signal number to an signal message string, the contents of +which are implementation defined. On systems which have the external +variable @code{sys_siglist}, these strings will be the same as the +ones used by @code{psignal()}. + +If the supplied signal number is within the valid range of indices for +the @code{sys_siglist}, but no message is available for the particular +signal number, then returns the string @samp{Signal @var{num}}, where +@var{num} is the signal number. + +If the supplied signal number is not a valid index into +@code{sys_siglist}, returns @code{NULL}. + +The returned string is only guaranteed to be valid only until the next +call to @code{strsignal}. + +@end deftypefn + +@c strsignal.c:448 +@deftypefn Extension {const char*} strsigno (int @var{signo}) + +Given an signal number, returns a pointer to a string containing the +symbolic name of that signal number, as found in @code{}. + +If the supplied signal number is within the valid range of indices for +symbolic names, but no name is available for the particular signal +number, then returns the string @samp{Signal @var{num}}, where +@var{num} is the signal number. + +If the supplied signal number is not within the range of valid +indices, then returns @code{NULL}. + +The contents of the location pointed to are only guaranteed to be +valid until the next call to @code{strsigno}. + +@end deftypefn + +@c strstr.c:6 +@deftypefn Supplemental char* strstr (const char *@var{string}, const char *@var{sub}) + +This function searches for the substring @var{sub} in the string +@var{string}, not including the terminating null characters. A pointer +to the first occurrence of @var{sub} is returned, or @code{NULL} if the +substring is absent. If @var{sub} points to a string with zero +length, the function returns @var{string}. + +@end deftypefn + +@c strtod.c:27 +@deftypefn Supplemental double strtod (const char *@var{string}, @ + char **@var{endptr}) + +This ISO C function converts the initial portion of @var{string} to a +@code{double}. If @var{endptr} is not @code{NULL}, a pointer to the +character after the last character used in the conversion is stored in +the location referenced by @var{endptr}. If no conversion is +performed, zero is returned and the value of @var{string} is stored in +the location referenced by @var{endptr}. + +@end deftypefn + +@c strerror.c:734 +@deftypefn Extension int strtoerrno (const char *@var{name}) + +Given the symbolic name of a error number (e.g., @code{EACCES}), map it +to an errno value. If no translation is found, returns 0. + +@end deftypefn + +@c strtol.c:33 +@deftypefn Supplemental {long int} strtol (const char *@var{string}, @ + char **@var{endptr}, int @var{base}) +@deftypefnx Supplemental {unsigned long int} strtoul (const char *@var{string}, @ + char **@var{endptr}, int @var{base}) + +The @code{strtol} function converts the string in @var{string} to a +long integer value according to the given @var{base}, which must be +between 2 and 36 inclusive, or be the special value 0. If @var{base} +is 0, @code{strtol} will look for the prefixes @code{0} and @code{0x} +to indicate bases 8 and 16, respectively, else default to base 10. +When the base is 16 (either explicitly or implicitly), a prefix of +@code{0x} is allowed. The handling of @var{endptr} is as that of +@code{strtod} above. The @code{strtoul} function is the same, except +that the converted value is unsigned. + +@end deftypefn + +@c strtoll.c:33 +@deftypefn Supplemental {long long int} strtoll (const char *@var{string}, @ + char **@var{endptr}, int @var{base}) +@deftypefnx Supplemental {unsigned long long int} strtoull (@ + const char *@var{string}, char **@var{endptr}, int @var{base}) + +The @code{strtoll} function converts the string in @var{string} to a +long long integer value according to the given @var{base}, which must be +between 2 and 36 inclusive, or be the special value 0. If @var{base} +is 0, @code{strtoll} will look for the prefixes @code{0} and @code{0x} +to indicate bases 8 and 16, respectively, else default to base 10. +When the base is 16 (either explicitly or implicitly), a prefix of +@code{0x} is allowed. The handling of @var{endptr} is as that of +@code{strtod} above. The @code{strtoull} function is the same, except +that the converted value is unsigned. + +@end deftypefn + +@c strsignal.c:502 +@deftypefn Extension int strtosigno (const char *@var{name}) + +Given the symbolic name of a signal, map it to a signal number. If no +translation is found, returns 0. + +@end deftypefn + +@c strverscmp.c:25 +@deftypefun int strverscmp (const char *@var{s1}, const char *@var{s2}) +The @code{strverscmp} function compares the string @var{s1} against +@var{s2}, considering them as holding indices/version numbers. Return +value follows the same conventions as found in the @code{strverscmp} +function. In fact, if @var{s1} and @var{s2} contain no digits, +@code{strverscmp} behaves like @code{strcmp}. + +Basically, we compare strings normally (character by character), until +we find a digit in each string - then we enter a special comparison +mode, where each sequence of digits is taken as a whole. If we reach the +end of these two parts without noticing a difference, we return to the +standard comparison mode. There are two types of numeric parts: +"integral" and "fractional" (those begin with a '0'). The types +of the numeric parts affect the way we sort them: + +@itemize @bullet +@item +integral/integral: we compare values as you would expect. + +@item +fractional/integral: the fractional part is less than the integral one. +Again, no surprise. + +@item +fractional/fractional: the things become a bit more complex. +If the common prefix contains only leading zeroes, the longest part is less +than the other one; else the comparison behaves normally. +@end itemize + +@smallexample +strverscmp ("no digit", "no digit") + @result{} 0 // @r{same behavior as strcmp.} +strverscmp ("item#99", "item#100") + @result{} <0 // @r{same prefix, but 99 < 100.} +strverscmp ("alpha1", "alpha001") + @result{} >0 // @r{fractional part inferior to integral one.} +strverscmp ("part1_f012", "part1_f01") + @result{} >0 // @r{two fractional parts.} +strverscmp ("foo.009", "foo.0") + @result{} <0 // @r{idem, but with leading zeroes only.} +@end smallexample + +This function is especially useful when dealing with filename sorting, +because filenames frequently hold indices/version numbers. +@end deftypefun + +@c timeval-utils.c:43 +@deftypefn Extension void timeval_add (struct timeval *@var{a}, @ + struct timeval *@var{b}, struct timeval *@var{result}) + +Adds @var{a} to @var{b} and stores the result in @var{result}. + +@end deftypefn + +@c timeval-utils.c:67 +@deftypefn Extension void timeval_sub (struct timeval *@var{a}, @ + struct timeval *@var{b}, struct timeval *@var{result}) + +Subtracts @var{b} from @var{a} and stores the result in @var{result}. + +@end deftypefn + +@c tmpnam.c:3 +@deftypefn Supplemental char* tmpnam (char *@var{s}) + +This function attempts to create a name for a temporary file, which +will be a valid file name yet not exist when @code{tmpnam} checks for +it. @var{s} must point to a buffer of at least @code{L_tmpnam} bytes, +or be @code{NULL}. Use of this function creates a security risk, and it must +not be used in new projects. Use @code{mkstemp} instead. + +@end deftypefn + +@c unlink-if-ordinary.c:27 +@deftypefn Supplemental int unlink_if_ordinary (const char*) + +Unlinks the named file, unless it is special (e.g. a device file). +Returns 0 when the file was unlinked, a negative value (and errno set) when +there was an error deleting the file, and a positive value if no attempt +was made to unlink the file because it is special. + +@end deftypefn + +@c fopen_unlocked.c:31 +@deftypefn Extension void unlock_std_streams (void) + +If the OS supports it, ensure that the standard I/O streams, +@code{stdin}, @code{stdout} and @code{stderr} are setup to avoid any +multi-threaded locking. Otherwise do nothing. + +@end deftypefn + +@c fopen_unlocked.c:23 +@deftypefn Extension void unlock_stream (FILE * @var{stream}) + +If the OS supports it, ensure that the supplied stream is setup to +avoid any multi-threaded locking. Otherwise leave the @code{FILE} +pointer unchanged. If the @var{stream} is @code{NULL} do nothing. + +@end deftypefn + +@c vasprintf.c:47 +@deftypefn Extension int vasprintf (char **@var{resptr}, @ + const char *@var{format}, va_list @var{args}) + +Like @code{vsprintf}, but instead of passing a pointer to a buffer, +you pass a pointer to a pointer. This function will compute the size +of the buffer needed, allocate memory with @code{malloc}, and store a +pointer to the allocated memory in @code{*@var{resptr}}. The value +returned is the same as @code{vsprintf} would return. If memory could +not be allocated, minus one is returned and @code{NULL} is stored in +@code{*@var{resptr}}. + +@end deftypefn + +@c vfork.c:6 +@deftypefn Supplemental int vfork (void) + +Emulates @code{vfork} by calling @code{fork} and returning its value. + +@end deftypefn + +@c vprintf.c:3 +@deftypefn Supplemental int vprintf (const char *@var{format}, va_list @var{ap}) +@deftypefnx Supplemental int vfprintf (FILE *@var{stream}, @ + const char *@var{format}, va_list @var{ap}) +@deftypefnx Supplemental int vsprintf (char *@var{str}, @ + const char *@var{format}, va_list @var{ap}) + +These functions are the same as @code{printf}, @code{fprintf}, and +@code{sprintf}, respectively, except that they are called with a +@code{va_list} instead of a variable number of arguments. Note that +they do not call @code{va_end}; this is the application's +responsibility. In @libib{} they are implemented in terms of the +nonstandard but common function @code{_doprnt}. + +@end deftypefn + +@c vsnprintf.c:28 +@deftypefn Supplemental int vsnprintf (char *@var{buf}, size_t @var{n}, @ + const char *@var{format}, va_list @var{ap}) + +This function is similar to @code{vsprintf}, but it will write to +@var{buf} at most @code{@var{n}-1} bytes of text, followed by a +terminating null byte, for a total of @var{n} bytes. On error the +return value is -1, otherwise it returns the number of characters that +would have been printed had @var{n} been sufficiently large, +regardless of the actual value of @var{n}. Note some pre-C99 system +libraries do not implement this correctly so users cannot generally +rely on the return value if the system version of this function is +used. + +@end deftypefn + +@c waitpid.c:3 +@deftypefn Supplemental int waitpid (int @var{pid}, int *@var{status}, int) + +This is a wrapper around the @code{wait} function. Any ``special'' +values of @var{pid} depend on your implementation of @code{wait}, as +does the return value. The third argument is unused in @libib{}. + +@end deftypefn + +@c argv.c:289 +@deftypefn Extension int writeargv (char * const *@var{argv}, FILE *@var{file}) + +Write each member of ARGV, handling all necessary quoting, to the file +named by FILE, separated by whitespace. Return 0 on success, non-zero +if an error occurred while writing to FILE. + +@end deftypefn + +@c xasprintf.c:31 +@deftypefn Replacement char* xasprintf (const char *@var{format}, ...) + +Print to allocated string without fail. If @code{xasprintf} fails, +this will print a message to @code{stderr} (using the name set by +@code{xmalloc_set_program_name}, if any) and then call @code{xexit}. + +@end deftypefn + +@c xatexit.c:11 +@deftypefun int xatexit (void (*@var{fn}) (void)) + +Behaves as the standard @code{atexit} function, but with no limit on +the number of registered functions. Returns 0 on success, or @minus{}1 on +failure. If you use @code{xatexit} to register functions, you must use +@code{xexit} to terminate your program. + +@end deftypefun + +@c xmalloc.c:38 +@deftypefn Replacement void* xcalloc (size_t @var{nelem}, size_t @var{elsize}) + +Allocate memory without fail, and set it to zero. This routine functions +like @code{calloc}, but will behave the same as @code{xmalloc} if memory +cannot be found. + +@end deftypefn + +@c xexit.c:22 +@deftypefn Replacement void xexit (int @var{code}) + +Terminates the program. If any functions have been registered with +the @code{xatexit} replacement function, they will be called first. +Termination is handled via the system's normal @code{exit} call. + +@end deftypefn + +@c xmalloc.c:22 +@deftypefn Replacement void* xmalloc (size_t) + +Allocate memory without fail. If @code{malloc} fails, this will print +a message to @code{stderr} (using the name set by +@code{xmalloc_set_program_name}, +if any) and then call @code{xexit}. Note that it is therefore safe for +a program to contain @code{#define malloc xmalloc} in its source. + +@end deftypefn + +@c xmalloc.c:53 +@deftypefn Replacement void xmalloc_failed (size_t) + +This function is not meant to be called by client code, and is listed +here for completeness only. If any of the allocation routines fail, this +function will be called to print an error message and terminate execution. + +@end deftypefn + +@c xmalloc.c:46 +@deftypefn Replacement void xmalloc_set_program_name (const char *@var{name}) + +You can use this to set the name of the program used by +@code{xmalloc_failed} when printing a failure message. + +@end deftypefn + +@c xmemdup.c:7 +@deftypefn Replacement void* xmemdup (void *@var{input}, @ + size_t @var{copy_size}, size_t @var{alloc_size}) + +Duplicates a region of memory without fail. First, @var{alloc_size} bytes +are allocated, then @var{copy_size} bytes from @var{input} are copied into +it, and the new memory is returned. If fewer bytes are copied than were +allocated, the remaining memory is zeroed. + +@end deftypefn + +@c xmalloc.c:32 +@deftypefn Replacement void* xrealloc (void *@var{ptr}, size_t @var{size}) +Reallocate memory without fail. This routine functions like @code{realloc}, +but will behave the same as @code{xmalloc} if memory cannot be found. + +@end deftypefn + +@c xstrdup.c:7 +@deftypefn Replacement char* xstrdup (const char *@var{s}) + +Duplicates a character string without fail, using @code{xmalloc} to +obtain memory. + +@end deftypefn + +@c xstrerror.c:7 +@deftypefn Replacement char* xstrerror (int @var{errnum}) + +Behaves exactly like the standard @code{strerror} function, but +will never return a @code{NULL} pointer. + +@end deftypefn + +@c xstrndup.c:23 +@deftypefn Replacement char* xstrndup (const char *@var{s}, size_t @var{n}) + +Returns a pointer to a copy of @var{s} with at most @var{n} characters +without fail, using @code{xmalloc} to obtain memory. The result is +always NUL terminated. + +@end deftypefn + +@c xvasprintf.c:38 +@deftypefn Replacement char* xvasprintf (const char *@var{format}, va_list @var{args}) + +Print to allocated string without fail. If @code{xvasprintf} fails, +this will print a message to @code{stderr} (using the name set by +@code{xmalloc_set_program_name}, if any) and then call @code{xexit}. + +@end deftypefn + + diff --git a/libiberty/libiberty.texi b/libiberty/libiberty.texi new file mode 100644 index 00000000000..ad1f8e3d35a --- /dev/null +++ b/libiberty/libiberty.texi @@ -0,0 +1,313 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header +@setfilename libiberty.info +@settitle @sc{gnu} libiberty +@c %**end of header + +@syncodeindex fn cp +@syncodeindex vr cp +@syncodeindex pg cp + +@finalout +@c %**end of header + +@dircategory GNU libraries +@direntry +* Libiberty: (libiberty). Library of utility functions which + are missing or broken on some systems. +@end direntry + +@macro libib +@code{libiberty} +@end macro + +@ifinfo +This manual describes the GNU @libib library of utility subroutines. + +Copyright @copyright{} 2001-2022 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.3 + or any later version published by the Free Software Foundation; + with no Invariant Sections, with no Front-Cover Texts, and with no + Back-Cover Texts. A copy of the license is included in the + section entitled ``GNU Free Documentation License''. + +@ignore +Permission is granted to process this file through TeX and print the +results, provided the printed document carries a copying permission +notice identical to this one except for the removal of this paragraph +(this paragraph not being relevant to the printed manual). + +@end ignore +@end ifinfo + + +@titlepage +@title @sc{gnu} libiberty +@author Phil Edwards et al. +@page + + +@vskip 0pt plus 1filll +Copyright @copyright{} 2001-2022 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.3 + or any later version published by the Free Software Foundation; + with no Invariant Sections, with no Front-Cover Texts, and with no + Back-Cover Texts. A copy of the license is included in the + section entitled ``GNU Free Documentation License''. + +@end titlepage +@contents +@page + +@ifnottex +@node Top,Using,, +@top Introduction + +The @libib{} library is a collection of subroutines used by various +GNU programs. It is available under the Library General Public +License; for more information, see @ref{Library Copying}. + +@end ifnottex + +@menu +* Using:: How to use libiberty in your code. + +* Overview:: Overview of available function groups. + +* Functions:: Available functions, macros, and global variables. + +* Licenses:: The various licenses under which libiberty sources are + distributed. + +* Index:: Index of functions and categories. +@end menu + +@node Using +@chapter Using +@cindex using libiberty +@cindex libiberty usage +@cindex how to use + +@c THIS SECTION IS CRAP AND NEEDS REWRITING BADLY. + +To date, @libib{} is generally not installed on its own. It has evolved +over years but does not have its own version number nor release schedule. + +Possibly the easiest way to use @libib{} in your projects is to drop the +@libib{} code into your project's sources, and to build the library along +with your own sources; the library would then be linked in at the end. This +prevents any possible version mismatches with other copies of libiberty +elsewhere on the system. + +Passing @option{--enable-install-libiberty} to the @command{configure} +script when building @libib{} causes the header files and archive library +to be installed when @kbd{make install} is run. This option also takes +an (optional) argument to specify the installation location, in the same +manner as @option{--prefix}. + +For your own projects, an approach which offers stability and flexibility +is to include @libib{} with your code, but allow the end user to optionally +choose to use a previously-installed version instead. In this way the +user may choose (for example) to install @libib{} as part of GCC, and use +that version for all software built with that compiler. (This approach +has proven useful with software using the GNU @code{readline} library.) + +Making use of @libib{} code usually requires that you include one or more +header files from the @libib{} distribution. (They will be named as +necessary in the function descriptions.) At link time, you will need to +add @option{-liberty} to your link command invocation. + + +@node Overview +@chapter Overview + +Functions contained in @libib{} can be divided into three general categories. + + +@menu +* Supplemental Functions:: Providing functions which don't exist + on older operating systems. + +* Replacement Functions:: These functions are sometimes buggy or + unpredictable on some operating systems. + +* Extensions:: Functions which provide useful extensions + or safety wrappers around existing code. +@end menu + +@node Supplemental Functions +@section Supplemental Functions +@cindex supplemental functions +@cindex functions, supplemental +@cindex functions, missing + +Certain operating systems do not provide functions which have since +become standardized, or at least common. For example, the Single +Unix Specification Version 2 requires that the @code{basename} +function be provided, but an OS which predates that specification +might not have this function. This should not prevent well-written +code from running on such a system. + +Similarly, some functions exist only among a particular ``flavor'' +or ``family'' of operating systems. As an example, the @code{bzero} +function is often not present on systems outside the BSD-derived +family of systems. + +Many such functions are provided in @libib{}. They are quickly +listed here with little description, as systems which lack them +become less and less common. Each function @var{foo} is implemented +in @file{@var{foo}.c} but not declared in any @libib{} header file; more +comments and caveats for each function's implementation are often +available in the source file. Generally, the function can simply +be declared as @code{extern}. + + + +@node Replacement Functions +@section Replacement Functions +@cindex replacement functions +@cindex functions, replacement + +Some functions have extremely limited implementations on different +platforms. Other functions are tedious to use correctly; for example, +proper use of @code{malloc} calls for the return value to be checked and +appropriate action taken if memory has been exhausted. A group of +``replacement functions'' is available in @libib{} to address these issues +for some of the most commonly used subroutines. + +All of these functions are declared in the @file{libiberty.h} header +file. Many of the implementations will use preprocessor macros set by +GNU Autoconf, if you decide to make use of that program. Some of these +functions may call one another. + + +@menu +* Memory Allocation:: Testing and handling failed memory + requests automatically. +* Exit Handlers:: Calling routines on program exit. +* Error Reporting:: Mapping errno and signal numbers to + more useful string formats. +@end menu + +@node Memory Allocation +@subsection Memory Allocation +@cindex memory allocation + +The functions beginning with the letter @samp{x} are wrappers around +standard functions; the functions provided by the system environment +are called and their results checked before the results are passed back +to client code. If the standard functions fail, these wrappers will +terminate the program. Thus, these versions can be used with impunity. + + +@node Exit Handlers +@subsection Exit Handlers +@cindex exit handlers + +The existence and implementation of the @code{atexit} routine varies +amongst the flavors of Unix. @libib{} provides an unvarying dependable +implementation via @code{xatexit} and @code{xexit}. + + +@node Error Reporting +@subsection Error Reporting +@cindex error reporting + +These are a set of routines to facilitate programming with the system +@code{errno} interface. The @libib{} source file @file{strerror.c} +contains a good deal of documentation for these functions. + +@c signal stuff + + +@node Extensions +@section Extensions +@cindex extensions +@cindex functions, extension + +@libib{} includes additional functionality above and beyond standard +functions, which has proven generically useful in GNU programs, such as +obstacks and regex. These functions are often copied from other +projects as they gain popularity, and are included here to provide a +central location from which to use, maintain, and distribute them. + +@menu +* Obstacks:: Stacks of arbitrary objects. +@end menu + +@c This is generated from the glibc manual using contrib/make-obstacks-texi.pl +@include obstacks.texi + +@node Functions +@chapter Function, Variable, and Macro Listing. +@include functions.texi + +@node Licenses +@appendix Licenses + +@menu + +* Library Copying:: The GNU Library General Public License +* BSD:: Regents of the University of California + +@end menu + +@c This takes care of Library Copying. It is the copying-lib.texi from the +@c GNU web site, with its @node line altered to make makeinfo shut up. +@include copying-lib.texi + +@page +@node BSD +@appendixsec BSD + +Copyright @copyright{} 1990 Regents of the University of California. +All rights reserved. + +Redistribution and use in source and binary forms, with or without +modification, are permitted provided that the following conditions +are met: + +@enumerate + +@item +Redistributions of source code must retain the above copyright +notice, this list of conditions and the following disclaimer. + +@item +Redistributions in binary form must reproduce the above copyright +notice, this list of conditions and the following disclaimer in the +documentation and/or other materials provided with the distribution. + +@item +[rescinded 22 July 1999] + +@item +Neither the name of the University nor the names of its contributors +may be used to endorse or promote products derived from this software +without specific prior written permission. + +@end enumerate + +THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +SUCH DAMAGE. + +@node Index +@unnumbered Index + +@printindex cp + +@bye + diff --git a/libiberty/obstacks.texi b/libiberty/obstacks.texi new file mode 100644 index 00000000000..b2d2403210b --- /dev/null +++ b/libiberty/obstacks.texi @@ -0,0 +1,774 @@ +@node Obstacks +@subsection Obstacks +@cindex obstacks + +An @dfn{obstack} is a pool of memory containing a stack of objects. You +can create any number of separate obstacks, and then allocate objects in +specified obstacks. Within each obstack, the last object allocated must +always be the first one freed, but distinct obstacks are independent of +each other. + +Aside from this one constraint of order of freeing, obstacks are totally +general: an obstack can contain any number of objects of any size. They +are implemented with macros, so allocation is usually very fast as long as +the objects are usually small. And the only space overhead per object is +the padding needed to start each object on a suitable boundary. + +@menu +* Creating Obstacks:: How to declare an obstack in your program. +* Preparing for Obstacks:: Preparations needed before you can + use obstacks. +* Allocation in an Obstack:: Allocating objects in an obstack. +* Freeing Obstack Objects:: Freeing objects in an obstack. +* Obstack Functions:: The obstack functions are really macros. +* Growing Objects:: Making an object bigger by stages. +* Extra Fast Growing:: Extra-high-efficiency (though more + complicated) growing objects. +* Status of an Obstack:: Inquiries about the status of an obstack. +* Obstacks Data Alignment:: Controlling alignment of objects in obstacks. +* Obstack Chunks:: How obstacks obtain and release chunks; + efficiency considerations. +* Summary of Obstacks:: +@end menu + +@node Creating Obstacks +@subsubsection Creating Obstacks + +The utilities for manipulating obstacks are declared in the header +file @file{obstack.h}. +@pindex obstack.h + +@comment obstack.h +@comment GNU +@deftp {Data Type} {struct obstack} +An obstack is represented by a data structure of type @code{struct +obstack}. This structure has a small fixed size; it records the status +of the obstack and how to find the space in which objects are allocated. +It does not contain any of the objects themselves. You should not try +to access the contents of the structure directly; use only the macros +described in this chapter. +@end deftp + +You can declare variables of type @code{struct obstack} and use them as +obstacks, or you can allocate obstacks dynamically like any other kind +of object. Dynamic allocation of obstacks allows your program to have a +variable number of different stacks. (You can even allocate an +obstack structure in another obstack, but this is rarely useful.) + +All the macros that work with obstacks require you to specify which +obstack to use. You do this with a pointer of type @code{struct obstack +*}. In the following, we often say ``an obstack'' when strictly +speaking the object at hand is such a pointer. + +The objects in the obstack are packed into large blocks called +@dfn{chunks}. The @code{struct obstack} structure points to a chain of +the chunks currently in use. + +The obstack library obtains a new chunk whenever you allocate an object +that won't fit in the previous chunk. Since the obstack library manages +chunks automatically, you don't need to pay much attention to them, but +you do need to supply a function which the obstack library should use to +get a chunk. Usually you supply a function which uses @code{malloc} +directly or indirectly. You must also supply a function to free a chunk. +These matters are described in the following section. + +@node Preparing for Obstacks +@subsubsection Preparing for Using Obstacks + +Each source file in which you plan to use obstacks +must include the header file @file{obstack.h}, like this: + +@smallexample +#include +@end smallexample + +@findex obstack_chunk_alloc +@findex obstack_chunk_free +Also, if the source file uses the macro @code{obstack_init}, it must +declare or define two macros that will be called by the +obstack library. One, @code{obstack_chunk_alloc}, is used to allocate +the chunks of memory into which objects are packed. The other, +@code{obstack_chunk_free}, is used to return chunks when the objects in +them are freed. These macros should appear before any use of obstacks +in the source file. + +Usually these are defined to use @code{malloc} via the intermediary +@code{xmalloc} (@pxref{Unconstrained Allocation, , , libc, The GNU C Library Reference Manual}). This is done with +the following pair of macro definitions: + +@smallexample +#define obstack_chunk_alloc xmalloc +#define obstack_chunk_free free +@end smallexample + +@noindent +Though the memory you get using obstacks really comes from @code{malloc}, +using obstacks is faster because @code{malloc} is called less often, for +larger blocks of memory. @xref{Obstack Chunks}, for full details. + +At run time, before the program can use a @code{struct obstack} object +as an obstack, it must initialize the obstack by calling +@code{obstack_init} or one of its variants, @code{obstack_begin}, +@code{obstack_specify_allocation}, or +@code{obstack_specify_allocation_with_arg}. + +@comment obstack.h +@comment GNU +@deftypefun int obstack_init (struct obstack *@var{obstack-ptr}) +Initialize obstack @var{obstack-ptr} for allocation of objects. This +macro calls the obstack's @code{obstack_chunk_alloc} function. If +allocation of memory fails, the function pointed to by +@code{obstack_alloc_failed_handler} is called. The @code{obstack_init} +macro always returns 1 (Compatibility notice: Former versions of +obstack returned 0 if allocation failed). +@end deftypefun + +Here are two examples of how to allocate the space for an obstack and +initialize it. First, an obstack that is a static variable: + +@smallexample +static struct obstack myobstack; +@dots{} +obstack_init (&myobstack); +@end smallexample + +@noindent +Second, an obstack that is itself dynamically allocated: + +@smallexample +struct obstack *myobstack_ptr + = (struct obstack *) xmalloc (sizeof (struct obstack)); + +obstack_init (myobstack_ptr); +@end smallexample + +@comment obstack.h +@comment GNU +@deftypefun int obstack_begin (struct obstack *@var{obstack-ptr}, size_t chunk_size) +Like @code{obstack_init}, but specify chunks to be at least +@var{chunk_size} bytes in size. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun int obstack_specify_allocation (struct obstack *@var{obstack-ptr}, size_t chunk_size, size_t alignment, void *(*chunkfun) (size_t), void (*freefun) (void *)) +Like @code{obstack_init}, specifying chunk size, chunk +alignment, and memory allocation functions. A @var{chunk_size} or +@var{alignment} of zero results in the default size or alignment +respectively being used. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun int obstack_specify_allocation_with_arg (struct obstack *@var{obstack-ptr}, size_t chunk_size, size_t alignment, void *(*chunkfun) (void *, size_t), void (*freefun) (void *, void *), void *arg) +Like @code{obstack_specify_allocation}, but specifying memory +allocation functions that take an extra first argument, @var{arg}. +@end deftypefun + +@comment obstack.h +@comment GNU +@defvar obstack_alloc_failed_handler +The value of this variable is a pointer to a function that +@code{obstack} uses when @code{obstack_chunk_alloc} fails to allocate +memory. The default action is to print a message and abort. +You should supply a function that either calls @code{exit} +(@pxref{Program Termination, , , libc, The GNU C Library Reference Manual}) or @code{longjmp} (@pxref{Non-Local +Exits, , , libc, The GNU C Library Reference Manual}) and doesn't return. + +@smallexample +void my_obstack_alloc_failed (void) +@dots{} +obstack_alloc_failed_handler = &my_obstack_alloc_failed; +@end smallexample + +@end defvar + +@node Allocation in an Obstack +@subsubsection Allocation in an Obstack +@cindex allocation (obstacks) + +The most direct way to allocate an object in an obstack is with +@code{obstack_alloc}, which is invoked almost like @code{malloc}. + +@comment obstack.h +@comment GNU +@deftypefun {void *} obstack_alloc (struct obstack *@var{obstack-ptr}, size_t @var{size}) +This allocates an uninitialized block of @var{size} bytes in an obstack +and returns its address. Here @var{obstack-ptr} specifies which obstack +to allocate the block in; it is the address of the @code{struct obstack} +object which represents the obstack. Each obstack macro +requires you to specify an @var{obstack-ptr} as the first argument. + +This macro calls the obstack's @code{obstack_chunk_alloc} function if +it needs to allocate a new chunk of memory; it calls +@code{obstack_alloc_failed_handler} if allocation of memory by +@code{obstack_chunk_alloc} failed. +@end deftypefun + +For example, here is a function that allocates a copy of a string @var{str} +in a specific obstack, which is in the variable @code{string_obstack}: + +@smallexample +struct obstack string_obstack; + +char * +copystring (char *string) +@{ + size_t len = strlen (string) + 1; + char *s = (char *) obstack_alloc (&string_obstack, len); + memcpy (s, string, len); + return s; +@} +@end smallexample + +To allocate a block with specified contents, use the macro @code{obstack_copy}. + +@comment obstack.h +@comment GNU +@deftypefun {void *} obstack_copy (struct obstack *@var{obstack-ptr}, void *@var{address}, size_t @var{size}) +This allocates a block and initializes it by copying @var{size} +bytes of data starting at @var{address}. It calls +@code{obstack_alloc_failed_handler} if allocation of memory by +@code{obstack_chunk_alloc} failed. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun {void *} obstack_copy0 (struct obstack *@var{obstack-ptr}, void *@var{address}, size_t @var{size}) +Like @code{obstack_copy}, but appends an extra byte containing a null +character. This extra byte is not counted in the argument @var{size}. +@end deftypefun + +The @code{obstack_copy0} macro is convenient for copying a sequence +of characters into an obstack as a null-terminated string. Here is an +example of its use: + +@smallexample +char * +obstack_savestring (char *addr, size_t size) +@{ + return obstack_copy0 (&myobstack, addr, size); +@} +@end smallexample + +@noindent +Contrast this with the previous example of @code{savestring} using +@code{malloc} (@pxref{Basic Allocation, , , libc, The GNU C Library Reference Manual}). + +@node Freeing Obstack Objects +@subsubsection Freeing Objects in an Obstack +@cindex freeing (obstacks) + +To free an object allocated in an obstack, use the macro +@code{obstack_free}. Since the obstack is a stack of objects, freeing +one object automatically frees all other objects allocated more recently +in the same obstack. + +@comment obstack.h +@comment GNU +@deftypefun void obstack_free (struct obstack *@var{obstack-ptr}, void *@var{object}) +If @var{object} is a null pointer, everything allocated in the obstack +is freed. Otherwise, @var{object} must be the address of an object +allocated in the obstack. Then @var{object} is freed, along with +everything allocated in @var{obstack} since @var{object}. +@end deftypefun + +Note that if @var{object} is a null pointer, the result is an +uninitialized obstack. To free all memory in an obstack but leave it +valid for further allocation, call @code{obstack_free} with the address +of the first object allocated on the obstack: + +@smallexample +obstack_free (obstack_ptr, first_object_allocated_ptr); +@end smallexample + +Recall that the objects in an obstack are grouped into chunks. When all +the objects in a chunk become free, the obstack library automatically +frees the chunk (@pxref{Preparing for Obstacks}). Then other +obstacks, or non-obstack allocation, can reuse the space of the chunk. + +@node Obstack Functions +@subsubsection Obstack Functions and Macros +@cindex macros + +The interfaces for using obstacks are shown here as functions to +specify the return type and argument types, but they are really +defined as macros. This means that the arguments don't actually have +types, but they generally behave as if they have the types shown. +You can call these macros like functions, but you cannot use them in +any other way (for example, you cannot take their address). + +Calling the macros requires a special precaution: namely, the first +operand (the obstack pointer) may not contain any side effects, because +it may be computed more than once. For example, if you write this: + +@smallexample +obstack_alloc (get_obstack (), 4); +@end smallexample + +@noindent +you will find that @code{get_obstack} may be called several times. +If you use @code{*obstack_list_ptr++} as the obstack pointer argument, +you will get very strange results since the incrementation may occur +several times. + +If you use the GNU C compiler, this precaution is not necessary, because +various language extensions in GNU C permit defining the macros so as to +compute each argument only once. + +Note that arguments other than the first will only be evaluated once, +even when not using GNU C. + +@code{obstack.h} does declare a number of functions, +@code{_obstack_begin}, @code{_obstack_begin_1}, +@code{_obstack_newchunk}, @code{_obstack_free}, and +@code{_obstack_memory_used}. You should not call these directly. + +@node Growing Objects +@subsubsection Growing Objects +@cindex growing objects (in obstacks) +@cindex changing the size of a block (obstacks) + +Because memory in obstack chunks is used sequentially, it is possible to +build up an object step by step, adding one or more bytes at a time to the +end of the object. With this technique, you do not need to know how much +data you will put in the object until you come to the end of it. We call +this the technique of @dfn{growing objects}. The special macros +for adding data to the growing object are described in this section. + +You don't need to do anything special when you start to grow an object. +Using one of the macros to add data to the object automatically +starts it. However, it is necessary to say explicitly when the object is +finished. This is done with @code{obstack_finish}. + +The actual address of the object thus built up is not known until the +object is finished. Until then, it always remains possible that you will +add so much data that the object must be copied into a new chunk. + +While the obstack is in use for a growing object, you cannot use it for +ordinary allocation of another object. If you try to do so, the space +already added to the growing object will become part of the other object. + +@comment obstack.h +@comment GNU +@deftypefun void obstack_blank (struct obstack *@var{obstack-ptr}, size_t @var{size}) +The most basic macro for adding to a growing object is +@code{obstack_blank}, which adds space without initializing it. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun void obstack_grow (struct obstack *@var{obstack-ptr}, void *@var{data}, size_t @var{size}) +To add a block of initialized space, use @code{obstack_grow}, which is +the growing-object analogue of @code{obstack_copy}. It adds @var{size} +bytes of data to the growing object, copying the contents from +@var{data}. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun void obstack_grow0 (struct obstack *@var{obstack-ptr}, void *@var{data}, size_t @var{size}) +This is the growing-object analogue of @code{obstack_copy0}. It adds +@var{size} bytes copied from @var{data}, followed by an additional null +character. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun void obstack_1grow (struct obstack *@var{obstack-ptr}, char @var{c}) +To add one character at a time, use @code{obstack_1grow}. +It adds a single byte containing @var{c} to the growing object. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun void obstack_ptr_grow (struct obstack *@var{obstack-ptr}, void *@var{data}) +Adding the value of a pointer one can use +@code{obstack_ptr_grow}. It adds @code{sizeof (void *)} bytes +containing the value of @var{data}. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun void obstack_int_grow (struct obstack *@var{obstack-ptr}, int @var{data}) +A single value of type @code{int} can be added by using +@code{obstack_int_grow}. It adds @code{sizeof (int)} bytes to +the growing object and initializes them with the value of @var{data}. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun {void *} obstack_finish (struct obstack *@var{obstack-ptr}) +When you are finished growing the object, use +@code{obstack_finish} to close it off and return its final address. + +Once you have finished the object, the obstack is available for ordinary +allocation or for growing another object. +@end deftypefun + +When you build an object by growing it, you will probably need to know +afterward how long it became. You need not keep track of this as you grow +the object, because you can find out the length from the obstack +with @code{obstack_object_size}, before finishing the object. + +@comment obstack.h +@comment GNU +@deftypefun size_t obstack_object_size (struct obstack *@var{obstack-ptr}) +This macro returns the current size of the growing object, in bytes. +Remember to call @code{obstack_object_size} @emph{before} finishing the object. +After it is finished, @code{obstack_object_size} will return zero. +@end deftypefun + +If you have started growing an object and wish to cancel it, you should +finish it and then free it, like this: + +@smallexample +obstack_free (obstack_ptr, obstack_finish (obstack_ptr)); +@end smallexample + +@noindent +This has no effect if no object was growing. + +@node Extra Fast Growing +@subsubsection Extra Fast Growing Objects +@cindex efficiency and obstacks + +The usual macros for growing objects incur overhead for checking +whether there is room for the new growth in the current chunk. If you +are frequently constructing objects in small steps of growth, this +overhead can be significant. + +You can reduce the overhead by using special ``fast growth'' +macros that grow the object without checking. In order to have a +robust program, you must do the checking yourself. If you do this checking +in the simplest way each time you are about to add data to the object, you +have not saved anything, because that is what the ordinary growth +macros do. But if you can arrange to check less often, or check +more efficiently, then you make the program faster. + +@code{obstack_room} returns the amount of room available +in the current chunk. + +@comment obstack.h +@comment GNU +@deftypefun size_t obstack_room (struct obstack *@var{obstack-ptr}) +This returns the number of bytes that can be added safely to the current +growing object (or to an object about to be started) in obstack +@var{obstack} using the fast growth macros. +@end deftypefun + +While you know there is room, you can use these fast growth macros +for adding data to a growing object: + +@comment obstack.h +@comment GNU +@deftypefun void obstack_1grow_fast (struct obstack *@var{obstack-ptr}, char @var{c}) +@code{obstack_1grow_fast} adds one byte containing the +character @var{c} to the growing object in obstack @var{obstack-ptr}. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun void obstack_ptr_grow_fast (struct obstack *@var{obstack-ptr}, void *@var{data}) +@code{obstack_ptr_grow_fast} adds @code{sizeof (void *)} +bytes containing the value of @var{data} to the growing object in +obstack @var{obstack-ptr}. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun void obstack_int_grow_fast (struct obstack *@var{obstack-ptr}, int @var{data}) +@code{obstack_int_grow_fast} adds @code{sizeof (int)} bytes +containing the value of @var{data} to the growing object in obstack +@var{obstack-ptr}. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun void obstack_blank_fast (struct obstack *@var{obstack-ptr}, size_t @var{size}) +@code{obstack_blank_fast} adds @var{size} bytes to the +growing object in obstack @var{obstack-ptr} without initializing them. +@end deftypefun + +When you check for space using @code{obstack_room} and there is not +enough room for what you want to add, the fast growth macros +are not safe. In this case, simply use the corresponding ordinary +growth macro instead. Very soon this will copy the object to a +new chunk; then there will be lots of room available again. + +So, each time you use an ordinary growth macro, check afterward for +sufficient space using @code{obstack_room}. Once the object is copied +to a new chunk, there will be plenty of space again, so the program will +start using the fast growth macros again. + +Here is an example: + +@smallexample +@group +void +add_string (struct obstack *obstack, const char *ptr, size_t len) +@{ + while (len > 0) + @{ + size_t room = obstack_room (obstack); + if (room == 0) + @{ + /* @r{Not enough room. Add one character slowly,} + @r{which may copy to a new chunk and make room.} */ + obstack_1grow (obstack, *ptr++); + len--; + @} + else + @{ + if (room > len) + room = len; + /* @r{Add fast as much as we have room for.} */ + len -= room; + while (room-- > 0) + obstack_1grow_fast (obstack, *ptr++); + @} + @} +@} +@end group +@end smallexample + +@cindex shrinking objects +You can use @code{obstack_blank_fast} with a ``negative'' size +argument to make the current object smaller. Just don't try to shrink +it beyond zero length---there's no telling what will happen if you do +that. Earlier versions of obstacks allowed you to use +@code{obstack_blank} to shrink objects. This will no longer work. + +@node Status of an Obstack +@subsubsection Status of an Obstack +@cindex obstack status +@cindex status of obstack + +Here are macros that provide information on the current status of +allocation in an obstack. You can use them to learn about an object while +still growing it. + +@comment obstack.h +@comment GNU +@deftypefun {void *} obstack_base (struct obstack *@var{obstack-ptr}) +This macro returns the tentative address of the beginning of the +currently growing object in @var{obstack-ptr}. If you finish the object +immediately, it will have that address. If you make it larger first, it +may outgrow the current chunk---then its address will change! + +If no object is growing, this value says where the next object you +allocate will start (once again assuming it fits in the current +chunk). +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun {void *} obstack_next_free (struct obstack *@var{obstack-ptr}) +This macro returns the address of the first free byte in the current +chunk of obstack @var{obstack-ptr}. This is the end of the currently +growing object. If no object is growing, @code{obstack_next_free} +returns the same value as @code{obstack_base}. +@end deftypefun + +@comment obstack.h +@comment GNU +@deftypefun size_t obstack_object_size (struct obstack *@var{obstack-ptr}) +This macro returns the size in bytes of the currently growing object. +This is equivalent to + +@smallexample +((size_t) (obstack_next_free (@var{obstack-ptr}) - obstack_base (@var{obstack-ptr}))) +@end smallexample +@end deftypefun + +@node Obstacks Data Alignment +@subsubsection Alignment of Data in Obstacks +@cindex alignment (in obstacks) + +Each obstack has an @dfn{alignment boundary}; each object allocated in +the obstack automatically starts on an address that is a multiple of the +specified boundary. By default, this boundary is aligned so that +the object can hold any type of data. + +To access an obstack's alignment boundary, use the macro +@code{obstack_alignment_mask}. + +@comment obstack.h +@comment GNU +@deftypefn Macro size_t obstack_alignment_mask (struct obstack *@var{obstack-ptr}) +The value is a bit mask; a bit that is 1 indicates that the corresponding +bit in the address of an object should be 0. The mask value should be one +less than a power of 2; the effect is that all object addresses are +multiples of that power of 2. The default value of the mask is a value +that allows aligned objects to hold any type of data: for example, if +its value is 3, any type of data can be stored at locations whose +addresses are multiples of 4. A mask value of 0 means an object can start +on any multiple of 1 (that is, no alignment is required). + +The expansion of the macro @code{obstack_alignment_mask} is an lvalue, +so you can alter the mask by assignment. For example, this statement: + +@smallexample +obstack_alignment_mask (obstack_ptr) = 0; +@end smallexample + +@noindent +has the effect of turning off alignment processing in the specified obstack. +@end deftypefn + +Note that a change in alignment mask does not take effect until +@emph{after} the next time an object is allocated or finished in the +obstack. If you are not growing an object, you can make the new +alignment mask take effect immediately by calling @code{obstack_finish}. +This will finish a zero-length object and then do proper alignment for +the next object. + +@node Obstack Chunks +@subsubsection Obstack Chunks +@cindex efficiency of chunks +@cindex chunks + +Obstacks work by allocating space for themselves in large chunks, and +then parceling out space in the chunks to satisfy your requests. Chunks +are normally 4096 bytes long unless you specify a different chunk size. +The chunk size includes 8 bytes of overhead that are not actually used +for storing objects. Regardless of the specified size, longer chunks +will be allocated when necessary for long objects. + +The obstack library allocates chunks by calling the function +@code{obstack_chunk_alloc}, which you must define. When a chunk is no +longer needed because you have freed all the objects in it, the obstack +library frees the chunk by calling @code{obstack_chunk_free}, which you +must also define. + +These two must be defined (as macros) or declared (as functions) in each +source file that uses @code{obstack_init} (@pxref{Creating Obstacks}). +Most often they are defined as macros like this: + +@smallexample +#define obstack_chunk_alloc malloc +#define obstack_chunk_free free +@end smallexample + +Note that these are simple macros (no arguments). Macro definitions with +arguments will not work! It is necessary that @code{obstack_chunk_alloc} +or @code{obstack_chunk_free}, alone, expand into a function name if it is +not itself a function name. + +If you allocate chunks with @code{malloc}, the chunk size should be a +power of 2. The default chunk size, 4096, was chosen because it is long +enough to satisfy many typical requests on the obstack yet short enough +not to waste too much memory in the portion of the last chunk not yet used. + +@comment obstack.h +@comment GNU +@deftypefn Macro size_t obstack_chunk_size (struct obstack *@var{obstack-ptr}) +This returns the chunk size of the given obstack. +@end deftypefn + +Since this macro expands to an lvalue, you can specify a new chunk size by +assigning it a new value. Doing so does not affect the chunks already +allocated, but will change the size of chunks allocated for that particular +obstack in the future. It is unlikely to be useful to make the chunk size +smaller, but making it larger might improve efficiency if you are +allocating many objects whose size is comparable to the chunk size. Here +is how to do so cleanly: + +@smallexample +if (obstack_chunk_size (obstack_ptr) < @var{new-chunk-size}) + obstack_chunk_size (obstack_ptr) = @var{new-chunk-size}; +@end smallexample + +@node Summary of Obstacks +@subsubsection Summary of Obstack Macros + +Here is a summary of all the macros associated with obstacks. Each +takes the address of an obstack (@code{struct obstack *}) as its first +argument. + +@table @code +@item int obstack_init (struct obstack *@var{obstack-ptr}) +Initialize use of an obstack. @xref{Creating Obstacks}. + +@item int obstack_begin (struct obstack *@var{obstack-ptr}, size_t chunk_size) +Initialize use of an obstack, with an initial chunk of +@var{chunk_size} bytes. + +@item int obstack_specify_allocation (struct obstack *@var{obstack-ptr}, size_t chunk_size, size_t alignment, void *(*chunkfun) (size_t), void (*freefun) (void *)) +Initialize use of an obstack, specifying intial chunk size, chunk +alignment, and memory allocation functions. + +@item int obstack_specify_allocation_with_arg (struct obstack *@var{obstack-ptr}, size_t chunk_size, size_t alignment, void *(*chunkfun) (void *, size_t), void (*freefun) (void *, void *), void *arg) +Like @code{obstack_specify_allocation}, but specifying memory +allocation functions that take an extra first argument, @var{arg}. + +@item void *obstack_alloc (struct obstack *@var{obstack-ptr}, size_t @var{size}) +Allocate an object of @var{size} uninitialized bytes. +@xref{Allocation in an Obstack}. + +@item void *obstack_copy (struct obstack *@var{obstack-ptr}, void *@var{address}, size_t @var{size}) +Allocate an object of @var{size} bytes, with contents copied from +@var{address}. @xref{Allocation in an Obstack}. + +@item void *obstack_copy0 (struct obstack *@var{obstack-ptr}, void *@var{address}, size_t @var{size}) +Allocate an object of @var{size}+1 bytes, with @var{size} of them copied +from @var{address}, followed by a null character at the end. +@xref{Allocation in an Obstack}. + +@item void obstack_free (struct obstack *@var{obstack-ptr}, void *@var{object}) +Free @var{object} (and everything allocated in the specified obstack +more recently than @var{object}). @xref{Freeing Obstack Objects}. + +@item void obstack_blank (struct obstack *@var{obstack-ptr}, size_t @var{size}) +Add @var{size} uninitialized bytes to a growing object. +@xref{Growing Objects}. + +@item void obstack_grow (struct obstack *@var{obstack-ptr}, void *@var{address}, size_t @var{size}) +Add @var{size} bytes, copied from @var{address}, to a growing object. +@xref{Growing Objects}. + +@item void obstack_grow0 (struct obstack *@var{obstack-ptr}, void *@var{address}, size_t @var{size}) +Add @var{size} bytes, copied from @var{address}, to a growing object, +and then add another byte containing a null character. @xref{Growing +Objects}. + +@item void obstack_1grow (struct obstack *@var{obstack-ptr}, char @var{data-char}) +Add one byte containing @var{data-char} to a growing object. +@xref{Growing Objects}. + +@item void *obstack_finish (struct obstack *@var{obstack-ptr}) +Finalize the object that is growing and return its permanent address. +@xref{Growing Objects}. + +@item size_t obstack_object_size (struct obstack *@var{obstack-ptr}) +Get the current size of the currently growing object. @xref{Growing +Objects}. + +@item void obstack_blank_fast (struct obstack *@var{obstack-ptr}, size_t @var{size}) +Add @var{size} uninitialized bytes to a growing object without checking +that there is enough room. @xref{Extra Fast Growing}. + +@item void obstack_1grow_fast (struct obstack *@var{obstack-ptr}, char @var{data-char}) +Add one byte containing @var{data-char} to a growing object without +checking that there is enough room. @xref{Extra Fast Growing}. + +@item size_t obstack_room (struct obstack *@var{obstack-ptr}) +Get the amount of room now available for growing the current object. +@xref{Extra Fast Growing}. + +@item size_t obstack_alignment_mask (struct obstack *@var{obstack-ptr}) +The mask used for aligning the beginning of an object. This is an +lvalue. @xref{Obstacks Data Alignment}. + +@item size_t obstack_chunk_size (struct obstack *@var{obstack-ptr}) +The size for allocating chunks. This is an lvalue. @xref{Obstack Chunks}. + +@item void *obstack_base (struct obstack *@var{obstack-ptr}) +Tentative starting address of the currently growing object. +@xref{Status of an Obstack}. + +@item void *obstack_next_free (struct obstack *@var{obstack-ptr}) +Address just after the end of the currently growing object. +@xref{Status of an Obstack}. +@end table + diff --git a/libitm/libitm.texi b/libitm/libitm.texi new file mode 100644 index 00000000000..7dff5f8fc5c --- /dev/null +++ b/libitm/libitm.texi @@ -0,0 +1,788 @@ +\input texinfo @c -*-texinfo-*- + +@c %**start of header +@setfilename libitm.info +@settitle GNU libitm +@c %**end of header + + +@copying +Copyright @copyright{} 2011-2022 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no +Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. +A copy of the license is included in the section entitled ``GNU +Free Documentation License''. +@end copying + +@ifinfo +@dircategory GNU Libraries +@direntry +* libitm: (libitm). GNU Transactional Memory Library +@end direntry + +This manual documents the GNU Transactional Memory Library. + +@insertcopying +@end ifinfo + + +@setchapternewpage odd + +@titlepage +@title The GNU Transactional Memory Library +@page +@vskip 0pt plus 1filll +@comment For the @value{version-GCC} Version* +@sp 1 +@insertcopying +@end titlepage + +@summarycontents +@contents +@page + + +@node Top +@top Introduction +@cindex Introduction + +This manual documents the usage and internals of libitm, the GNU Transactional +Memory Library. It provides transaction support for accesses to a process' +memory, enabling easy-to-use synchronization of accesses to shared memory by +several threads. + + +@comment +@comment When you add a new menu item, please keep the right hand +@comment aligned to the same column. Do not use tabs. This provides +@comment better formatting. +@comment +@menu +* Enabling libitm:: How to enable libitm for your applications. +* C/C++ Language Constructs for TM:: + Notes on the language-level interface supported + by gcc. +* The libitm ABI:: Notes on the external ABI provided by libitm. +* Internals:: Notes on libitm's internal synchronization. +* GNU Free Documentation License:: + How you can copy and share this manual. +* Library Index:: Index of this documentation. +@end menu + + +@c --------------------------------------------------------------------- +@c Enabling libitm +@c --------------------------------------------------------------------- + +@node Enabling libitm +@chapter Enabling libitm + +To activate support for TM in C/C++, the compile-time flag @option{-fgnu-tm} +must be specified. This enables TM language-level constructs such as +transaction statements (e.g., @code{__transaction_atomic}, @pxref{C/C++ +Language Constructs for TM} for details). + +@c --------------------------------------------------------------------- +@c C/C++ Language Constructs for TM +@c --------------------------------------------------------------------- + +@node C/C++ Language Constructs for TM +@chapter C/C++ Language Constructs for TM + +Transactions are supported in C++ and C in the form of transaction statements, +transaction expressions, and function transactions. In the following example, +both @code{a} and @code{b} will be read and the difference will be written to +@code{c}, all atomically and isolated from other transactions: + +@example +__transaction_atomic @{ c = a - b; @} +@end example + +Therefore, another thread can use the following code to concurrently update +@code{b} without ever causing @code{c} to hold a negative value (and without +having to use other synchronization constructs such as locks or C++11 +atomics): + +@example +__transaction_atomic @{ if (a > b) b++; @} +@end example + +GCC follows the @uref{https://sites.google.com/site/tmforcplusplus/, Draft +Specification of Transactional Language Constructs for C++ (v1.1)} in its +implementation of transactions. + +The precise semantics of transactions are defined in terms of the C++11/C11 +memory model (see the specification). Roughly, transactions provide +synchronization guarantees that are similar to what would be guaranteed when +using a single global lock as a guard for all transactions. Note that like +other synchronization constructs in C/C++, transactions rely on a +data-race-free program (e.g., a nontransactional write that is concurrent +with a transactional read to the same memory location is a data race). + +@c --------------------------------------------------------------------- +@c The libitm ABI +@c --------------------------------------------------------------------- + +@node The libitm ABI +@chapter The libitm ABI + +The ABI provided by libitm is basically equal to the Linux variant of Intel's +current TM ABI specification document (Revision 1.1, May 6 2009) but with the +differences listed in this chapter. It would be good if these changes would +eventually be merged into a future version of this specification. To ease +look-up, the following subsections mirror the structure of this specification. + +@section [No changes] Objectives +@section [No changes] Non-objectives + +@section Library design principles +@subsection [No changes] Calling conventions +@subsection [No changes] TM library algorithms +@subsection [No changes] Optimized load and store routines +@subsection [No changes] Aligned load and store routines + +@subsection Data logging functions + +The memory locations accessed with transactional loads and stores and the +memory locations whose values are logged must not overlap. This required +separation only extends to the scope of the execution of one transaction +including all the executions of all nested transactions. + +The compiler must be consistent (within the scope of a single transaction) +about which memory locations are shared and which are not shared with other +threads (i.e., data must be accessed either transactionally or +nontransactionally). Otherwise, non-write-through TM algorithms would not work. + +For memory locations on the stack, this requirement extends to only the +lifetime of the stack frame that the memory location belongs to (or the +lifetime of the transaction, whichever is shorter). Thus, memory that is +reused for several stack frames could be target of both data logging and +transactional accesses; however, this is harmless because these stack frames' +lifetimes will end before the transaction finishes. + +@subsection [No changes] Scatter/gather calls +@subsection [No changes] Serial and irrevocable mode +@subsection [No changes] Transaction descriptor +@subsection Store allocation + +There is no @code{getTransaction} function. + +@subsection [No changes] Naming conventions + +@subsection Function pointer encryption + +Currently, this is not implemented. + + +@section Types and macros list + +@code{_ITM_codeProperties} has changed, @pxref{txn-code-properties,,Starting a +transaction}. +@code{_ITM_srcLocation} is not used. + + +@section Function list + +@subsection Initialization and finalization functions +These functions are not part of the ABI. + +@subsection [No changes] Version checking +@subsection [No changes] Error reporting +@subsection [No changes] inTransaction call + +@subsection State manipulation functions +There is no @code{getTransaction} function. Transaction identifiers for +nested transactions will be ordered but not necessarily sequential (i.e., for +a nested transaction's identifier @var{IN} and its enclosing transaction's +identifier @var{IE}, it is guaranteed that @math{IN >= IE}). + +@subsection [No changes] Source locations + +@subsection Starting a transaction + +@subsubsection Transaction code properties + +@anchor{txn-code-properties} +The bit @code{hasNoXMMUpdate} is instead called @code{hasNoVectorUpdate}. +Iff it is set, vector register save/restore is not necessary for any target +machine. + +The @code{hasNoFloatUpdate} bit (@code{0x0010}) is new. Iff it is set, floating +point register save/restore is not necessary for any target machine. + +@code{undoLogCode} is not supported and a fatal runtime error will be raised +if this bit is set. It is not properly defined in the ABI why barriers +other than undo logging are not present; Are they not necessary (e.g., a +transaction operating purely on thread-local data) or have they been omitted by +the compiler because it thinks that some kind of global synchronization +(e.g., serial mode) might perform better? The specification suggests that the +latter might be the case, but the former seems to be more useful. + +The @code{readOnly} bit (@code{0x4000}) is new. @strong{TODO} Lexical or dynamic +scope? + +@code{hasNoRetry} is not supported. If this bit is not set, but +@code{hasNoAbort} is set, the library can assume that transaction +rollback will not be requested. + +It would be useful if the absence of externally-triggered rollbacks would be +reported for the dynamic scope as well, not just for the lexical scope +(@code{hasNoAbort}). Without this, a library cannot exploit this together +with flat nesting. + +@code{exceptionBlock} is not supported because exception blocks are not used. + +@subsubsection [No changes] Windows exception state +@subsubsection [No changes] Other machine state + +@subsubsection [No changes] Results from beginTransaction + +@subsection Aborting a transaction + +@code{_ITM_rollbackTransaction} is not supported. @code{_ITM_abortTransaction} +is supported but the abort reasons @code{exceptionBlockAbort}, +@code{TMConflict}, and @code{userRetry} are not supported. There are no +exception blocks in general, so the related cases also do not have to be +considered. To encode @code{__transaction_cancel [[outer]]}, compilers must +set the new @code{outerAbort} bit (@code{0x10}) additionally to the +@code{userAbort} bit in the abort reason. + +@subsection Committing a transaction + +The exception handling (EH) scheme is different. The Intel ABI requires the +@code{_ITM_tryCommitTransaction} function that will return even when the +commit failed and will have to be matched with calls to either +@code{_ITM_abortTransaction} or @code{_ITM_commitTransaction}. In contrast, +gcc relies on transactional wrappers for the functions of the Exception +Handling ABI and on one additional commit function (shown below). This allows +the TM to keep track of EH internally and thus it does not have to embed the +cleanup of EH state into the existing EH code in the program. +@code{_ITM_tryCommitTransaction} is not supported. +@code{_ITM_commitTransactionToId} is also not supported because the +propagation of thrown exceptions will not bypass commits of nested +transactions. + +@example +void _ITM_commitTransactionEH(void *exc_ptr) ITM_REGPARM; +void *_ITM_cxa_allocate_exception (size_t); +void _ITM_cxa_free_exception (void *exc_ptr); +void _ITM_cxa_throw (void *obj, void *tinfo, void (*dest) (void *)); +void *_ITM_cxa_begin_catch (void *exc_ptr); +void _ITM_cxa_end_catch (void); +@end example + +The EH scheme changed in version 6 of GCC. Previously, the compiler +added a call to @code{_ITM_commitTransactionEH} to commit a transaction if +an exception could be in flight at this position in the code; @code{exc_ptr} is +the address of the current exception and must be non-zero. Now, the +compiler must catch all exceptions that are about to be thrown out of a +transaction and call @code{_ITM_commitTransactionEH} from the catch clause, +with @code{exc_ptr} being zero. + +Note that the old EH scheme never worked completely in GCC's implementation; +libitm currently does not try to be compatible with the old scheme. + +The @code{_ITM_cxa...} functions are transactional wrappers for the respective +@code{__cxa...} functions and must be called instead of these in transactional +code. @code{_ITM_cxa_free_exception} is new in GCC 6. + +To support this EH scheme, libstdc++ needs to provide one additional function +(@code{_cxa_tm_cleanup}), which is used by the TM to clean up the exception +handling state while rolling back a transaction: + +@example +void __cxa_tm_cleanup (void *unthrown_obj, void *cleanup_exc, + unsigned int caught_count); +@end example + +Since GCC 6, @code{unthrown_obj} is not used anymore and always null; +prior to that, @code{unthrown_obj} is non-null if the program called +@code{__cxa_allocate_exception} for this exception but did not yet called +@code{__cxa_throw} for it. @code{cleanup_exc} is non-null if the program is +currently processing a cleanup along an exception path but has not caught this +exception yet. @code{caught_count} is the nesting depth of +@code{__cxa_begin_catch} within the transaction (which can be counted by the TM +using @code{_ITM_cxa_begin_catch} and @code{_ITM_cxa_end_catch}); +@code{__cxa_tm_cleanup} then performs rollback by essentially performing +@code{__cxa_end_catch} that many times. + + + +@subsection Exception handling support + +Currently, there is no support for functionality like +@code{__transaction_cancel throw} as described in the C++ TM specification. +Supporting this should be possible with the EH scheme explained previously +because via the transactional wrappers for the EH ABI, the TM is able to +observe and intercept EH. + + +@subsection [No changes] Transition to serial--irrevocable mode +@subsection [No changes] Data transfer functions +@subsection [No changes] Transactional memory copies + +@subsection Transactional versions of memmove + +If either the source or destination memory region is to be accessed +nontransactionally, then source and destination regions must not be +overlapping. The respective @code{_ITM_memmove} functions are still +available but a fatal runtime error will be raised if such regions do overlap. +To support this functionality, the ABI would have to specify how the +intersection of the regions has to be accessed (i.e., transactionally or +nontransactionally). + +@subsection [No changes] Transactional versions of memset +@subsection [No changes] Logging functions + +@subsection User-registered commit and undo actions + +Commit actions will get executed in the same order in which the respective +calls to @code{_ITM_addUserCommitAction} happened. Only +@code{_ITM_noTransactionId} is allowed as value for the +@code{resumingTransactionId} argument. Commit actions get executed after +privatization safety has been ensured. + +Undo actions will get executed in reverse order compared to the order in which +the respective calls to @code{_ITM_addUserUndoAction} happened. The ordering of +undo actions w.r.t. the roll-back of other actions (e.g., data transfers or +memory allocations) is undefined. + +@code{_ITM_getThreadnum} is not supported currently because its only purpose +is to provide a thread ID that matches some assumed performance tuning output, +but this output is not part of the ABI nor further defined by it. + +@code{_ITM_dropReferences} is not supported currently because its semantics and +the intention behind it is not entirely clear. The +specification suggests that this function is necessary because of certain +orderings of data transfer undos and the releasing of memory regions (i.e., +privatization). However, this ordering is never defined, nor is the ordering of +dropping references w.r.t. other events. + +@subsection [New] Transactional indirect calls + +Indirect calls (i.e., calls through a function pointer) within transactions +should execute the transactional clone of the original function (i.e., a clone +of the original that has been fully instrumented to use the TM runtime), if +such a clone is available. The runtime provides two functions to +register/deregister clone tables: + +@example +struct clone_entry +@{ + void *orig, *clone; +@}; + +void _ITM_registerTMCloneTable (clone_entry *table, size_t entries); +void _ITM_deregisterTMCloneTable (clone_entry *table); +@end example + +Registered tables must be writable by the TM runtime, and must be live +throughout the life-time of the TM runtime. + +@strong{TODO} The intention was always to drop the registration functions +entirely, and create a new ELF Phdr describing the linker-sorted table. Much +like what currently happens for @code{PT_GNU_EH_FRAME}. +This work kept getting bogged down in how to represent the @var{N} different +code generation variants. We clearly needed at least two---SW and HW +transactional clones---but there was always a suggestion of more variants for +different TM assumptions/invariants. + +The compiler can then use two TM runtime functions to perform indirect calls in +transactions: +@example +void *_ITM_getTMCloneOrIrrevocable (void *function) ITM_REGPARM; +void *_ITM_getTMCloneSafe (void *function) ITM_REGPARM; +@end example + +If there is a registered clone for supplied function, both will return a +pointer to the clone. If not, the first runtime function will attempt to switch +to serial--irrevocable mode and return the original pointer, whereas the second +will raise a fatal runtime error. + +@subsection [New] Transactional dynamic memory management + +@example +void *_ITM_malloc (size_t) + __attribute__((__malloc__)) ITM_PURE; +void *_ITM_calloc (size_t, size_t) + __attribute__((__malloc__)) ITM_PURE; +void _ITM_free (void *) ITM_PURE; +@end example + +These functions are essentially transactional wrappers for @code{malloc}, +@code{calloc}, and @code{free}. Within transactions, the compiler should +replace calls to the original functions with calls to the wrapper functions. + +libitm also provides transactional clones of C++ memory management functions +such as global operator new and delete. They are part of libitm for historic +reasons but do not need to be part of this ABI. + + +@section [No changes] Future Enhancements to the ABI + +@section Sample code + +The code examples might not be correct w.r.t. the current version of the ABI, +especially everything related to exception handling. + + +@section [New] Memory model + +The ABI should define a memory model and the ordering that is guaranteed for +data transfers and commit/undo actions, or at least refer to another memory +model that needs to be preserved. Without that, the compiler cannot ensure the +memory model specified on the level of the programming language (e.g., by the +C++ TM specification). + +For example, if a transactional load is ordered before another load/store, then +the TM runtime must also ensure this ordering when accessing shared state. If +not, this might break the kind of publication safety used in the C++ TM +specification. Likewise, the TM runtime must ensure privatization safety. + + + +@c --------------------------------------------------------------------- +@c Internals +@c --------------------------------------------------------------------- + +@node Internals +@chapter Internals + +@section TM methods and method groups + +libitm supports several ways of synchronizing transactions with each other. +These TM methods (or TM algorithms) are implemented in the form of +subclasses of @code{abi_dispatch}, which provide methods for +transactional loads and stores as well as callbacks for rollback and commit. +All methods that are compatible with each other (i.e., that let concurrently +running transactions still synchronize correctly even if different methods +are used) belong to the same TM method group. Pointers to TM methods can be +obtained using the factory methods prefixed with @code{dispatch_} in +@file{libitm_i.h}. There are two special methods, @code{dispatch_serial} and +@code{dispatch_serialirr}, that are compatible with all methods because they +run transactions completely in serial mode. + +@subsection TM method life cycle + +The state of TM methods does not change after construction, but they do alter +the state of transactions that use this method. However, because +per-transaction data gets used by several methods, @code{gtm_thread} is +responsible for setting an initial state that is useful for all methods. +After that, methods are responsible for resetting/clearing this state on each +rollback or commit (of outermost transactions), so that the transaction +executed next is not affected by the previous transaction. + +There is also global state associated with each method group, which is +initialized and shut down (@code{method_group::init()} and @code{fini()}) +when switching between method groups (see @file{retry.cc}). + +@subsection Selecting the default method + +The default method that libitm uses for freshly started transactions (but +not necessarily for restarted transactions) can be set via an environment +variable (@env{ITM_DEFAULT_METHOD}), whose value should be equal to the name +of one of the factory methods returning abi_dispatch subclasses but without +the "dispatch_" prefix (e.g., "serialirr" instead of +@code{GTM::dispatch_serialirr()}). + +Note that this environment variable is only a hint for libitm and might not +be supported in the future. + + +@section Nesting: flat vs. closed + +We support two different kinds of nesting of transactions. In the case of +@emph{flat nesting}, the nesting structure is flattened and all nested +transactions are subsumed by the enclosing transaction. In contrast, +with @emph{closed nesting}, nested transactions that have not yet committed +can be rolled back separately from the enclosing transactions; when they +commit, they are subsumed by the enclosing transaction, and their effects +will be finally committed when the outermost transaction commits. +@emph{Open nesting} (where nested transactions can commit independently of the +enclosing transactions) are not supported. + +Flat nesting is the default nesting mode, but closed nesting is supported and +used when transactions contain user-controlled aborts +(@code{__transaction_cancel} statements). We assume that user-controlled +aborts are rare in typical code and used mostly in exceptional situations. +Thus, it makes more sense to use flat nesting by default to avoid the +performance overhead of the additional checkpoints required for closed +nesting. User-controlled aborts will correctly abort the innermost enclosing +transaction, whereas the whole (i.e., outermost) transaction will be restarted +otherwise (e.g., when a transaction encounters data conflicts during +optimistic execution). + + +@section Locking conventions + +This section documents the locking scheme and rules for all uses of locking +in libitm. We have to support serial(-irrevocable) mode, which is implemented +using a global lock as explained next (called the @emph{serial lock}). To +simplify the overall design, we use the same lock as catch-all locking +mechanism for other infrequent tasks such as (de)registering clone tables or +threads. Besides the serial lock, there are @emph{per-method-group locks} that +are managed by specific method groups (i.e., groups of similar TM concurrency +control algorithms), and lock-like constructs for quiescence-based operations +such as ensuring privatization safety. + +Thus, the actions that participate in the libitm-internal locking are either +@emph{active transactions} that do not run in serial mode, @emph{serial +transactions} (which (are about to) run in serial mode), and management tasks +that do not execute within a transaction but have acquired the serial mode +like a serial transaction would do (e.g., to be able to register threads with +libitm). Transactions become active as soon as they have successfully used the +serial lock to announce this globally (@pxref{serial-lock-impl,,Serial lock +implementation}). Likewise, transactions become serial transactions as soon as +they have acquired the exclusive rights provided by the serial lock (i.e., +serial mode, which also means that there are no other concurrent active or +serial transactions). Note that active transactions can become serial +transactions when they enter serial mode during the runtime of the +transaction. + +@subsection State-to-lock mapping + +Application data is protected by the serial lock if there is a serial +transaction and no concurrently running active transaction (i.e., non-serial). +Otherwise, application data is protected by the currently selected method +group, which might use per-method-group locks or other mechanisms. Also note +that application data that is about to be privatized might not be allowed to be +accessed by nontransactional code until privatization safety has been ensured; +the details of this are handled by the current method group. + +libitm-internal state is either protected by the serial lock or accessed +through custom concurrent code. The latter applies to the public/shared part +of a transaction object and most typical method-group-specific state. + +The former category (protected by the serial lock) includes: +@itemize @bullet +@item The list of active threads that have used transactions. +@item The tables that map functions to their transactional clones. +@item The current selection of which method group to use. +@item Some method-group-specific data, or invariants of this data. For example, +resetting a method group to its initial state is handled by switching to the +same method group, so the serial lock protects such resetting as well. +@end itemize +In general, such state is immutable whenever there exists an active +(non-serial) transaction. If there is no active transaction, a serial +transaction (or a thread that is not currently executing a transaction but has +acquired the serial lock) is allowed to modify this state (but must of course +be careful to not surprise the current method group's implementation with such +modifications). + +@subsection Lock acquisition order + +To prevent deadlocks, locks acquisition must happen in a globally agreed-upon +order. Note that this applies to other forms of blocking too, but does not +necessarily apply to lock acquisitions that do not block (e.g., trylock() +calls that do not get retried forever). Note that serial transactions are +never return back to active transactions until the transaction has committed. +Likewise, active transactions stay active until they have committed. +Per-method-group locks are typically also not released before commit. + +Lock acquisition / blocking rules: +@itemize @bullet + +@item Transactions must become active or serial before they are allowed to +use method-group-specific locks or blocking (i.e., the serial lock must be +acquired before those other locks, either in serial or nonserial mode). + +@item Any number of threads that do not currently run active transactions can +block while trying to get the serial lock in exclusive mode. Note that active +transactions must not block when trying to upgrade to serial mode unless there +is no other transaction that is trying that (the latter is ensured by the +serial lock implementation. + +@item Method groups must prevent deadlocks on their locks. In particular, they +must also be prepared for another active transaction that has acquired +method-group-specific locks but is blocked during an attempt to upgrade to +being a serial transaction. See below for details. + +@item Serial transactions can acquire method-group-specific locks because there +will be no other active nor serial transaction. + +@end itemize + +There is no single rule for per-method-group blocking because this depends on +when a TM method might acquire locks. If no active transaction can upgrade to +being a serial transaction after it has acquired per-method-group locks (e.g., +when those locks are only acquired during an attempt to commit), then the TM +method does not need to consider a potential deadlock due to serial mode. + +If there can be upgrades to serial mode after the acquisition of +per-method-group locks, then TM methods need to avoid those deadlocks: +@itemize @bullet +@item When upgrading to a serial transaction, after acquiring exclusive rights +to the serial lock but before waiting for concurrent active transactions to +finish (@pxref{serial-lock-impl,,Serial lock implementation} for details), +we have to wake up all active transactions waiting on the upgrader's +per-method-group locks. +@item Active transactions blocking on per-method-group locks need to check the +serial lock and abort if there is a pending serial transaction. +@item Lost wake-ups have to be prevented (e.g., by changing a bit in each +per-method-group lock before doing the wake-up, and only blocking on this lock +using a futex if this bit is not group). +@end itemize + +@strong{TODO}: Can reuse serial lock for gl-*? And if we can, does it make +sense to introduce further complexity in the serial lock? For gl-*, we can +really only avoid an abort if we do -wb and -vbv. + + +@subsection Serial lock implementation +@anchor{serial-lock-impl} + +The serial lock implementation is optimized towards assuming that serial +transactions are infrequent and not the common case. However, the performance +of entering serial mode can matter because when only few transactions are run +concurrently or if there are few threads, then it can be efficient to run +transactions serially. + +The serial lock is similar to a multi-reader-single-writer lock in that there +can be several active transactions but only one serial transaction. However, +we do want to avoid contention (in the lock implementation) between active +transactions, so we split up the reader side of the lock into per-transaction +flags that are true iff the transaction is active. The exclusive writer side +remains a shared single flag, which is acquired using a CAS, for example. +On the fast-path, the serial lock then works similar to Dekker's algorithm but +with several reader flags that a serial transaction would have to check. +A serial transaction thus requires a list of all threads with potentially +active transactions; we can use the serial lock itself to protect this list +(i.e., only threads that have acquired the serial lock can modify this list). + +We want starvation-freedom for the serial lock to allow for using it to ensure +progress for potentially starved transactions (@pxref{progress-guarantees,, +Progress Guarantees} for details). However, this is currently not enforced by +the implementation of the serial lock. + +Here is pseudo-code for the read/write fast paths of acquiring the serial +lock (read-to-write upgrade is similar to write_lock: +@example +// read_lock: +tx->shared_state |= active; +__sync_synchronize(); // or STLD membar, or C++0x seq-cst fence +while (!serial_lock.exclusive) + if (spinning_for_too_long) goto slowpath; + +// write_lock: +if (CAS(&serial_lock.exclusive, 0, this) != 0) + goto slowpath; // writer-writer contention +// need a membar here, but CAS already has full membar semantics +bool need_blocking = false; +for (t: all txns) + @{ + for (;t->shared_state & active;) + if (spinning_for_too_long) @{ need_blocking = true; break; @} + @} +if (need_blocking) goto slowpath; +@end example + +Releasing a lock in this spin-lock version then just consists of resetting +@code{tx->shared_state} to inactive or clearing @code{serial_lock.exclusive}. + +However, we can't rely on a pure spinlock because we need to get the OS +involved at some time (e.g., when there are more threads than CPUs to run on). +Therefore, the real implementation falls back to a blocking slow path, either +based on pthread mutexes or Linux futexes. + + +@subsection Reentrancy + +libitm has to consider the following cases of reentrancy: +@itemize @bullet + +@item Transaction calls unsafe code that starts a new transaction: The outer +transaction will become a serial transaction before executing unsafe code. +Therefore, nesting within serial transactions must work, even if the nested +transaction is called from within uninstrumented code. + +@item Transaction calls either a transactional wrapper or safe code, which in +turn starts a new transaction: It is not yet defined in the specification +whether this is allowed. Thus, it is undefined whether libitm supports this. + +@item Code that starts new transactions might be called from within any part +of libitm: This kind of reentrancy would likely be rather complex and can +probably be avoided. Therefore, it is not supported. + +@end itemize + +@subsection Privatization safety + +Privatization safety is ensured by libitm using a quiescence-based approach. +Basically, a privatizing transaction waits until all concurrent active +transactions will either have finished (are not active anymore) or operate on +a sufficiently recent snapshot to not access the privatized data anymore. This +happens after the privatizing transaction has stopped being an active +transaction, so waiting for quiescence does not contribute to deadlocks. + +In method groups that need to ensure publication safety explicitly, active +transactions maintain a flag or timestamp in the public/shared part of the +transaction descriptor. Before blocking, privatizers need to let the other +transactions know that they should wake up the privatizer. + +@strong{TODO} Ho to implement the waiters? Should those flags be +per-transaction or at a central place? We want to avoid one wake/wait call +per active transactions, so we might want to use either a tree or combining +to reduce the syscall overhead, or rather spin for a long amount of time +instead of doing blocking. Also, it would be good if only the last transaction +that the privatizer waits for would do the wake-up. + +@subsection Progress guarantees +@anchor{progress-guarantees} + +Transactions that do not make progress when using the current TM method will +eventually try to execute in serial mode. Thus, the serial lock's progress +guarantees determine the progress guarantees of the whole TM. Obviously, we at +least need deadlock-freedom for the serial lock, but it would also be good to +provide starvation-freedom (informally, all threads will finish executing a +transaction eventually iff they get enough cycles). + +However, the scheduling of transactions (e.g., thread scheduling by the OS) +also affects the handling of progress guarantees by the TM. First, the TM +can only guarantee deadlock-freedom if threads do not get stopped. Likewise, +low-priority threads can starve if they do not get scheduled when other +high-priority threads get those cycles instead. + +If all threads get scheduled eventually, correct lock implementations will +provide deadlock-freedom, but might not provide starvation-freedom. We can +either enforce the latter in the TM's lock implementation, or assume that +the scheduling is sufficiently random to yield a probabilistic guarantee that +no thread will starve (because eventually, a transaction will encounter a +scheduling that will allow it to run). This can indeed work well in practice +but is not necessarily guaranteed to work (e.g., simple spin locks can be +pretty efficient). + +Because enforcing stronger progress guarantees in the TM has a higher runtime +overhead, we focus on deadlock-freedom right now and assume that the threads +will get scheduled eventually by the OS (but don't consider threads with +different priorities). We should support starvation-freedom for serial +transactions in the future. Everything beyond that is highly related to proper +contention management across all of the TM (including with TM method to +choose), and is future work. + +@strong{TODO} Handling thread priorities: We want to avoid priority inversion +but it's unclear how often that actually matters in practice. Workloads that +have threads with different priorities will likely also require lower latency +or higher throughput for high-priority threads. Therefore, it probably makes +not that much sense (except for eventual progress guarantees) to use +priority inheritance until the TM has priority-aware contention management. + + +@c --------------------------------------------------------------------- +@c GNU Free Documentation License +@c --------------------------------------------------------------------- + +@include fdl.texi + +@c --------------------------------------------------------------------- +@c Index +@c --------------------------------------------------------------------- + +@node Library Index +@unnumbered Library Index + +@printindex cp + +@bye diff --git a/libquadmath/libquadmath.texi b/libquadmath/libquadmath.texi new file mode 100644 index 00000000000..fad8e62d8bc --- /dev/null +++ b/libquadmath/libquadmath.texi @@ -0,0 +1,392 @@ +\input texinfo @c -*-texinfo-*- + +@c %**start of header +@setfilename libquadmath.info +@settitle GCC libquadmath +@c %**end of header + +@copying +Copyright @copyright{} 2010-2022 Free Software Foundation, Inc. + +@quotation +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no +Invariant Sections, with the Front-Cover Texts being ``A GNU Manual,'' +and with the Back-Cover Texts as in (a) below. A copy of the +license is included in the section entitled ``GNU Free Documentation +License.'' + +(a) The FSF's Back-Cover Text is: ``You have the freedom to +copy and modify this GNU manual. +@end quotation +@end copying + +@ifinfo +@dircategory GNU Libraries +@direntry +* libquadmath: (libquadmath). GCC Quad-Precision Math Library +@end direntry + +This manual documents the GCC Quad-Precision Math Library API. + +Published by the Free Software Foundation +51 Franklin Street, Fifth Floor +Boston, MA 02110-1301 USA + +@insertcopying +@end ifinfo + + +@setchapternewpage odd + +@titlepage +@title The GCC Quad-Precision Math Library +@page +@vskip 0pt plus 1filll +@comment For the @value{version-GCC} Version* +@sp 1 +Published by the Free Software Foundation @* +51 Franklin Street, Fifth Floor@* +Boston, MA 02110-1301, USA@* +@sp 1 +@insertcopying +@end titlepage + +@summarycontents +@contents +@page + + +@node Top +@top Introduction +@cindex Introduction + +This manual documents the usage of libquadmath, the GCC Quad-Precision +Math Library Application Programming Interface (API). + + +@comment +@comment When you add a new menu item, please keep the right hand +@comment aligned to the same column. Do not use tabs. This provides +@comment better formatting. +@comment +@menu +* Typedef and constants:: Defined data types and constants +* Math Library Routines:: The Libquadmath math runtime application + programming interface. +* I/O Library Routines:: The Libquadmath I/O runtime application + programming interface. +* GNU Free Documentation License:: + How you can copy and share this manual. +* Reporting Bugs:: How to report bugs in GCC Libquadmath. +@c * Index:: Index of this documentation. +@end menu + + +@c --------------------------------------------------------------------- +@c Defined macros +@c --------------------------------------------------------------------- + +@node Typedef and constants +@chapter Typedef and constants + +The following data type has been defined via @code{typedef}. + +@table @asis +@item @code{__complex128}: @code{__float128}-based complex number +@end table + +The following macros are defined, which give the numeric limits of the +@code{__float128} data type. + +@table @asis +@item @code{FLT128_MAX}: largest finite number +@item @code{FLT128_MIN}: smallest positive number with full precision +@item @code{FLT128_EPSILON}: difference between 1 and the next larger + representable number +@item @code{FLT128_DENORM_MIN}: smallest positive denormalized number +@item @code{FLT128_MANT_DIG}: number of digits in the mantissa (bit precision) +@item @code{FLT128_MIN_EXP}: maximal negative exponent +@item @code{FLT128_MAX_EXP}: maximal positive exponent +@item @code{FLT128_DIG}: number of decimal digits in the mantissa +@item @code{FLT128_MIN_10_EXP}: maximal negative decimal exponent +@item @code{FLT128_MAX_10_EXP}: maximal positive decimal exponent +@end table + +The following mathematical constants of type @code{__float128} are defined. + +@table @asis +@item @code{M_Eq}: the constant e (Euler's number) +@item @code{M_LOG2Eq}: binary logarithm of 2 +@item @code{M_LOG10Eq}: common, decimal logarithm of 2 +@item @code{M_LN2q}: natural logarithm of 2 +@item @code{M_LN10q}: natural logarithm of 10 +@item @code{M_PIq}: pi +@item @code{M_PI_2q}: pi divided by two +@item @code{M_PI_4q}: pi divided by four +@item @code{M_1_PIq}: one over pi +@item @code{M_2_PIq}: one over two pi +@item @code{M_2_SQRTPIq}: two over square root of pi +@item @code{M_SQRT2q}: square root of 2 +@item @code{M_SQRT1_2q}: one over square root of 2 +@end table + + +@c --------------------------------------------------------------------- +@c Math routines +@c --------------------------------------------------------------------- + +@node Math Library Routines +@chapter Math Library Routines + +The following mathematical functions are available: + +@table @asis +@item @code{acosq}: arc cosine function +@item @code{acoshq}: inverse hyperbolic cosine function +@item @code{asinq}: arc sine function +@item @code{asinhq}: inverse hyperbolic sine function +@item @code{atanq}: arc tangent function +@item @code{atanhq}: inverse hyperbolic tangent function +@item @code{atan2q}: arc tangent function +@item @code{cbrtq}: cube root function +@item @code{ceilq}: ceiling value function +@item @code{copysignq}: copy sign of a number +@item @code{coshq}: hyperbolic cosine function +@item @code{cosq}: cosine function +@item @code{erfq}: error function +@item @code{erfcq}: complementary error function +@item @code{exp2q}: base 2 exponential function +@item @code{expq}: exponential function +@item @code{expm1q}: exponential minus 1 function +@need 800 +@item @code{fabsq}: absolute value function +@item @code{fdimq}: positive difference function +@item @code{finiteq}: check finiteness of value +@item @code{floorq}: floor value function +@item @code{fmaq}: fused multiply and add +@item @code{fmaxq}: determine maximum of two values +@item @code{fminq}: determine minimum of two values +@item @code{fmodq}: remainder value function +@item @code{frexpq}: extract mantissa and exponent +@item @code{hypotq}: Eucledian distance function +@item @code{ilogbq}: get exponent of the value +@item @code{isinfq}: check for infinity +@item @code{isnanq}: check for not a number +@item @code{issignalingq}: check for signaling not a number +@item @code{j0q}: Bessel function of the first kind, first order +@item @code{j1q}: Bessel function of the first kind, second order +@item @code{jnq}: Bessel function of the first kind, @var{n}-th order +@item @code{ldexpq}: load exponent of the value +@item @code{lgammaq}: logarithmic gamma function +@item @code{llrintq}: round to nearest integer value +@item @code{llroundq}: round to nearest integer value away from zero +@item @code{logbq}: get exponent of the value +@item @code{logq}: natural logarithm function +@item @code{log10q}: base 10 logarithm function +@item @code{log1pq}: compute natural logarithm of the value plus one +@item @code{log2q}: base 2 logarithm function +@need 800 +@item @code{lrintq}: round to nearest integer value +@item @code{lroundq}: round to nearest integer value away from zero +@item @code{modfq}: decompose the floating-point number +@item @code{nanq}: return quiet NaN +@item @code{nearbyintq}: round to nearest integer +@item @code{nextafterq}: next representable floating-point number +@item @code{powq}: power function +@item @code{remainderq}: remainder function +@item @code{remquoq}: remainder and part of quotient +@item @code{rintq}: round-to-nearest integral value +@item @code{roundq}: round-to-nearest integral value, return @code{__float128} +@item @code{scalblnq}: compute exponent using @code{FLT_RADIX} +@item @code{scalbnq}: compute exponent using @code{FLT_RADIX} +@item @code{signbitq}: return sign bit +@item @code{sincosq}: calculate sine and cosine simultaneously +@item @code{sinhq}: hyperbolic sine function +@item @code{sinq}: sine function +@item @code{sqrtq}: square root function +@item @code{tanq}: tangent function +@item @code{tanhq}: hyperbolic tangent function +@need 800 +@item @code{tgammaq}: true gamma function +@item @code{truncq}: round to integer, towards zero +@item @code{y0q}: Bessel function of the second kind, first order +@item @code{y1q}: Bessel function of the second kind, second order +@item @code{ynq}: Bessel function of the second kind, @var{n}-th order +@item @code{cabsq} complex absolute value function +@item @code{cargq}: calculate the argument +@item @code{cimagq} imaginary part of complex number +@item @code{crealq}: real part of complex number +@item @code{cacoshq}: complex arc hyperbolic cosine function +@item @code{cacosq}: complex arc cosine function +@item @code{casinhq}: complex arc hyperbolic sine function +@item @code{casinq}: complex arc sine function +@item @code{catanhq}: complex arc hyperbolic tangent function +@item @code{catanq}: complex arc tangent function +@item @code{ccosq} complex cosine function: +@item @code{ccoshq}: complex hyperbolic cosine function +@item @code{cexpq}: complex exponential function +@need 800 +@item @code{cexpiq}: computes the exponential function of ``i'' times a + real value +@item @code{clogq}: complex natural logarithm +@item @code{clog10q}: complex base 10 logarithm +@item @code{conjq}: complex conjugate function +@item @code{cpowq}: complex power function +@item @code{cprojq}: project into Riemann Sphere +@item @code{csinq}: complex sine function +@item @code{csinhq}: complex hyperbolic sine function +@item @code{csqrtq}: complex square root +@item @code{ctanq}: complex tangent function +@item @code{ctanhq}: complex hyperbolic tangent function +@end table + + +@c --------------------------------------------------------------------- +@c I/O routines +@c --------------------------------------------------------------------- + +@node I/O Library Routines +@chapter I/O Library Routines + +@menu +* @code{strtoflt128}: strtoflt128, Convert from string +* @code{quadmath_snprintf}: quadmath_snprintf, Convert to string +@end menu + + +@node strtoflt128 +@section @code{strtoflt128} --- Convert from string + +The function @code{strtoflt128} converts a string into a +@code{__float128} number. + +@table @asis +@item Syntax +@code{__float128 strtoflt128 (const char *s, char **sp)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{s} @tab input string +@item @var{sp} @tab the address of the next character in the string +@end multitable + +The argument @var{sp} contains, if not @code{NULL}, the address of the +next character following the parts of the string, which have been read. + +@item Example +@smallexample +#include + +int main () +@{ + __float128 r; + + r = strtoflt128 ("1.2345678", NULL); + + return 0; +@} +@end smallexample +@end table + + +@node quadmath_snprintf +@section @code{quadmath_snprintf} --- Convert to string + +The function @code{quadmath_snprintf} converts a @code{__float128} floating-point +number into a string. It is a specialized alternative to @code{snprintf}, where +the format string is restricted to a single conversion specifier with @code{Q} +modifier and conversion specifier @code{e}, @code{E}, @code{f}, @code{F}, @code{g}, +@code{G}, @code{a} or @code{A}, with no extra characters before or after the +conversion specifier. The @code{%m$} or @code{*m$} style must not be used in +the format. + +@table @asis +@item Syntax +@code{int quadmath_snprintf (char *s, size_t size, const char *format, ...)} + +@item @emph{Arguments}: +@multitable @columnfractions .15 .70 +@item @var{s} @tab output string +@item @var{size} @tab byte size of the string, including trailing NUL +@item @var{format} @tab conversion specifier string +@end multitable + +@item Note +On some targets when supported by the C library hooks are installed +for @code{printf} family of functions, so that @code{printf ("%Qe", 1.2Q);} +etc.@: works too. + +@item Example +@smallexample +#include +#include +#include + +int main () +@{ + __float128 r; + int prec = 20; + int width = 46; + char buf[128]; + + r = 2.0q; + r = sqrtq (r); + int n = quadmath_snprintf (buf, sizeof buf, "%+-#*.20Qe", width, r); + if ((size_t) n < sizeof buf) + printf ("%s\n", buf); + /* Prints: +1.41421356237309504880e+00 */ + quadmath_snprintf (buf, sizeof buf, "%Qa", r); + if ((size_t) n < sizeof buf) + printf ("%s\n", buf); + /* Prints: 0x1.6a09e667f3bcc908b2fb1366ea96p+0 */ + n = quadmath_snprintf (NULL, 0, "%+-#46.*Qe", prec, r); + if (n > -1) + @{ + char *str = malloc (n + 1); + if (str) + @{ + quadmath_snprintf (str, n + 1, "%+-#46.*Qe", prec, r); + printf ("%s\n", str); + /* Prints: +1.41421356237309504880e+00 */ + @} + free (str); + @} + return 0; +@} +@end smallexample + +@end table + + +@c --------------------------------------------------------------------- +@c GNU Free Documentation License +@c --------------------------------------------------------------------- + +@include fdl.texi + +@c --------------------------------------------------------------------- +@c Reporting Bugs +@c --------------------------------------------------------------------- + +@c For BUGURL +@include libquadmath-vers.texi + +@node Reporting Bugs +@chapter Reporting Bugs + +Bugs in the GCC Quad-Precision Math Library implementation should be +reported via @value{BUGURL}. + + +@c --------------------------------------------------------------------- +@c Index +@c --------------------------------------------------------------------- + +@c @node Index +@c @unnumbered Index +@c +@c @printindex cp + +@bye